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+publicationDate,title,abstract,id
+2022-08-09,Fractalized magnon transport on the quasicrystal with enhanced stability,"Magnonics has been receiving significant attention in magnetism and
+spintronics because of its premise for devices using spin current carried by
+magnons, quanta of spin-wave excitations of a macroscopically ordered magnetic
+media. Although magnonics has clear energy-wise advantage over conventional
+electronics due to the absence of the Joule heating, the inherent magnon-magnon
+interactions give rise to finite lifetime of the magnons which has been
+hampering the efficient realizations of magnonic devices. To promote magnonics,
+it is imperative to identify the delocalized magnon modes that are minimally
+affected by magnon-magnon interactions and thus possess a long lifetime and use
+them to achieve efficient magnon transport. Here, we suggest that quasicrystals
+may offer the solution to this problem via the critical magnon modes that are
+neither extended nor localized. We find that the critical magnon exhibits
+fractal characteristics that are absent in conventional magnon modes in regular
+solids such as a unique power-law scaling and a self-similar distribution of
+distances showing perfect magnon transmission. Moreover, the critical magnons
+have longer lifetimes compared to the extended ones in a periodic system, by
+suppressing the magnon-magnon interaction decay rate. Such enhancement of the
+magnon stability originates from the presence of the quasi-periodicity and
+intermediate localization behavior of the critical magnons. Thus, we offer the
+utility of quasicrystals and their critical spin wave functions in magnonics as
+unique fractal transport characteristics and enhanced stability.",2208.04967v1
+2023-11-30,Nanoscaled magnon transistor based on stimulated three-magnon splitting,"Magnonics is a rapidly growing field, attracting much attention for its
+potential applications in data transport and processing. Many individual
+magnonic devices have been proposed and realized in laboratories. However, an
+integrated magnonic circuit with several separate magnonic elements has yet not
+been reported due to the lack of a magnonic amplifier to compensate for
+transport and processing losses. The magnon transistor reported in [Nat.
+Commun. 5, 4700, (2014)] could only achieve a gain of 1.8, which is
+insufficient in many practical cases. Here, we use the stimulated three-magnon
+splitting phenomenon to numerically propose a concept of magnon transistor in
+which the energy of the gate magnons at 14.6 GHz is directly pumped into the
+energy of the source magnons at 4.2 GHz, thus achieving the gain of 9. The
+structure is based on the 100 nm wide YIG nano-waveguides, a directional
+coupler is used to mix the source and gate magnons, and a dual-band magnonic
+crystal is used to filter out the gate and idler magnons at 10.4 GHz frequency.
+The magnon transistor preserves the phase of the signal and the design allows
+integration into a magnon circuit.",2311.18479v1
+2023-02-03,Sub-millimeter propagation of antiferromagnetic magnons via magnon-photon coupling,"For the realization of magnon-based current-free technologies, referred to as
+magnonics, all-optical control of magnons is an important technique for
+fundamental research and application. Magnon-polariton is a coupled state of
+magnon and photon in a magnetic medium, which is expected to exhibit a
+magnon-like controllability and a photon-like high-speed propagation. Recent
+studies have observed magnon-polaritons as modulation of the incident terahertz
+wave; however, the influence of magnon-photon coupling on the magnon
+propagation property has not been explored. This study aimed to observe the
+spatiotemporal dynamics of coherent magnon-polariton through time-resolved
+imaging measurements. $\mathrm{BiFeO_3}$ was chosen as the sample, because it
+is expected to exhibit strong coupling between the magnon and photon. The
+observed dynamics suggested that antiferromagnetic magnons can propagate over
+long distances up to hundreds of micrometers through strong coupling with the
+photons. The results shed light on the understanding of the optical control of
+the magnonic systems thereby paving the way for terahertz opto-magnonics.",2302.01821v1
+2017-12-13,Anomalous magnon Nernst effect of topological magnonic materials,"The magnon transport driven by thermal gradient in a perpendicularly
+magnetized honeycomb lattice is studied. The system with the nearest-neighbor
+pseudodipolar interaction and the next-nearest-neighbor Dzyaloshinskii-Moriya
+interaction (DMI) has various topologically nontrivial phases. When an in-plane
+thermal gradient is applied, a transverse in-plane magnon current is generated.
+This phenomenon is termed as the anomalous magnon Nernst effect that closely
+resembles the anomalous Nernst effect for an electronic system. The anomalous
+magnon Nernst coefficient and its sign are determined by the magnon Berry
+curvatures distribution in the momentum space and magnon populations in the
+magnon bands. We predict a temperature-induced sign reversal in anomalous
+magnon Nernst effect under certain conditions.",1712.05027v1
+2023-08-28,Exploring wavefunction hybridization of magnon-magnon hybrid state,"We investigate magnon magnon hybrid states using a non Hermitian two band
+Hamiltonian and the concept of wavefunction hybridization. By comparing our
+model with micromagnetic simulations conducted on a synthetic antiferromagnet
+with strong magnon magnon coupling, we successfully reproduce not only the
+resonance frequencies and linewidths but also the phases and amplitudes of the
+magnon wavefunction. The hybridization effect influences the dissipation rate,
+leading to the crossing of linewidths. Additionally, we quantify the magnon
+hybridization within a magnonic Bloch sphere, which enhances the ability to
+manipulate hybrid magnons for coherent information processing.",2308.14463v1
+2015-02-13,Magnon transport through microwave pumping,"We present a microscopic theory of magnon transport in ferromagnetic
+insulators (FIs). Using magnon injection through microwave pumping, we propose
+a way to generate magnon dc currents and show how to enhance their amplitudes
+in hybrid ferromagnetic insulating junctions. To this end focusing on a single
+FI, we first revisit microwave pumping at finite (room) temperature from the
+microscopic viewpoint of magnon injection. Next, we apply it to two kinds of
+hybrid ferromagnetic insulating junctions. The first is the junction between a
+quasi-equilibrium magnon condensate and magnons being pumped by microwave,
+while the second is the junction between such pumped magnons and noncondensed
+magnons. We show that quasi-equilibrium magnon condensates generate ac and dc
+magnon currents, while noncondensed magnons produce essentially a dc magnon
+current. The ferromagnetic resonance (FMR) drastically increases the density of
+the pumped magnons and enhances such magnon currents. Lastly, using microwave
+pumping in a single FI, we discuss the possibility that a magnon current
+through an Aharonov-Casher phase flows persistently even at finite temperature.
+We show that such a magnon current arises even at finite temperature in the
+presence of magnon-magnon interactions. Due to FMR, its amplitude becomes much
+larger than the condensed magnon current.",1502.03865v2
+2021-07-07,Skyrmion Based Magnonic Crystals,"Magnonics is now an attractive field which focuses on the dynamic
+characteristics of magnons, a kind of quasiparticles in magnetic media, and
+attempt to apply magnons for functional devices. In order to construct magnon
+based devices, it is necessary to fabricate materials with specific and tunable
+magnon bands and band gaps. Skyrmion based magnonic crystals is one of the most
+suitable materials which possess periodical skyrmion structure and show
+applicative magnon bands and band gaps. In this review, we provide an overview
+over recent theoretical and experimental research on skyrmion based magnonic
+crystals. We will firstly provide an introduction of magnonic crystals and
+magnetic skyrmion. And then we will show the theoretical and experimental
+progress on skyrmion based magnonic crystals and their magnon band
+characteristics. At the end, we will give an outlook and perspectives of new
+fascinating fields on topological nontrivial magnon modes, as well as hybrid
+and quantum magnonic phenomena of skyrmion based magnonic crystals.",2107.03148v1
+2020-08-26,One- and two-magnon excitations in antiferromagnet PbFeBO4,"The linear spin-wave theory study of PbFeBO4 spin dynamics is presented. It
+is shown that the modes observed in Raman scattering experiments below Neel
+temperature are optical magnon and two-magnon excitations. Based on the magnon
+energy, two-magnon band lineshape, and Weiss temperature, the consistent set of
+the exchange coupling constants up the third neighbor is derived and compared
+with the results of ab initio calculations. The small deviation of the observed
+two-magnon band from the one-magnon density of states suggests a surprisingly
+negligible role of magnon-magnon interactions.",2008.11530v2
+2024-04-04,Interaction-induced nonlinear magnon transport in noncentrosymmetric ferromagnets,"We study the effect of the magnon-magnon interaction on the nonlinear magnon
+transport. The magnon-magnon interaction induces nonreciprocal magnon decay
+when the time-reversal symmetry is broken, and leads to nonlinear thermal
+responses of magnons. We construct a theoretical framework to study the
+nonlinear thermal responses due to the nonreciprocal magnon decay by using the
+imaginary Dyson equation and quantum kinetic theory, which is then applied to a
+model of honeycomb ferromagnets with Dzyaloshinskii-Moriya interactions. An
+order estimate shows that the nonlinear thermal response from the present
+mechanism is feasible for experimental measurement.",2404.03260v1
+2018-09-30,Magnon Valves Based on YIG/NiO/YIG All-Insulating Magnon Junctions,"As an alternative angular momentum carrier, magnons or spin waves can be
+utilized to encode information and breed magnon-based circuits with ultralow
+power consumption and non-Boolean data processing capability. In order to
+construct such a circuit, it is indispensable to design some electronic
+components with both long magnon decay and coherence length and effective
+control over magnon transport. Here we show that an all-insulating magnon
+junctions composed by a magnetic insulator (MI1)/antiferromagnetic insulator
+(AFI)/magnetic insulator (MI2) sandwich (Y3Fe5O12/NiO/Y3Fe5O12) can completely
+turn a thermogradient-induced magnon current on or off as the two Y3Fe5O12
+layers are aligned parallel or anti-parallel. The magnon decay length in NiO is
+about 3.5~4.5 nm between 100 K and 200 K for thermally activated magnons. The
+insulating magnon valve (magnon junction), as a basic building block, possibly
+shed light on the naissance of efficient magnon-based circuits, including
+non-Boolean logic, memory, diode, transistors, magnon waveguide and switches
+with sizable on-off ratios.",1810.00380v1
+2020-09-11,Magnon-magnon interaction and magnon relaxation time in ferromagnetic Cr2Ge2Te6 monolayer,"Despite the intense amount of attention and huge potential of two-dimensional
+(2D) magnets for applications in novel magnetic, magneto-optical,
+magneto-thermal and magneto-electronic devices, there has yet to be a robust
+strategy developed to systematically understand magnon-magnon (MMI)
+interactions at finite temperature. In this paper, we present a
+first-principles theoretical method to introduce the finite temperature
+magnon-magnon interaction into Heisenberg Hamiltonian through a nonlinear
+correction energy. The Wick theorem is used to decouple the four-magnon
+operators to two-magnon order. We demonstrate the capabilities of this method
+by studying the strength of MMI in Cr2Ge2Te6 (CGT) monolayer. The spin wave
+spectrum at finite temperature and the time-dependent spin autocorrelation
+function are explored. It is found that the magnon relaxation time due to
+magnon-magnon scattering increases with temperature because of the reduction in
+magnon energy, while decreases with wavevector and external magnetic field. Our
+results provide a new insight to understand the magnon damping and energy
+dissipation in two-dimensional ferromagnetic materials.",2009.05225v1
+2022-08-27,Magnon drag induced by magnon-magnon interactions characteristic of noncollinear magnets,"A noncollinear magnet consists of the magnetic moments forming a noncollinear
+spin structure. Because of this structure, the Hamiltonian of magnons acquires
+the cubic terms. Although the cubic terms are the magnon-magnon interactions
+characteristic of noncollinear magnets, their effects on magnon transport have
+not been clarified yet. Here we show that in a canted antiferromagnet the cubic
+terms cause a magnon drag that magnons drag magnon spin current and heat
+current, which can be used to enhance these currents by tuning a magnetic
+field. For a strong magnetic field, we find that the cubic terms induce
+low-temperature peaks of a spin-Seebeck coefficient, a magnon conductivity, and
+a magnon thermal conductivity, and that each value is one order of magnitude
+larger than the noninteracting value. This enhancement is mainly due to the
+magnetic field dependence of the coupling constant of the cubic terms through
+the magnetic-field dependent canting angle. Our magnon drag offers a way for
+controlling the magnon currents of noncollinear magnets via the many-body
+effect.",2208.12939v1
+2023-03-28,Tutorial: Nonlinear magnonics,"Nonlinear magnonics studies the nonlinear interaction between magnons and
+other physical platforms (phonon, photon, qubit, spin texture) to generate
+novel magnon states for information processing. In this tutorial, we first
+introduce the nonlinear interactions of magnons in pure magnetic systems and
+hybrid magnon-phonon and magnon-photon systems. Then we show how these
+nonlinear interactions can generate exotic magnonic phenomena. In the classical
+regime, we will cover the parametric excitation of magnons, bistability and
+multistability, and the magnonic frequency comb. In the quantum regime, we will
+discuss the single magnon state, Schr\""{o}dinger cat state and the entanglement
+and quantum steering among magnons, photons and phonons. The applications of
+the hybrid magnonics systems in quantum transducer and sensing will also be
+presented. Finally, we outlook the future development direction of nonlinear
+magnonics.",2303.16313v1
+2023-04-04,Full quantum theory for magnon transport in two-sublattice magnetic insulators and magnon junctions,"Magnon, as elementary excitation in magnetic systems, can carry and transfer
+angular momentum. Due to the absence of Joule heat during magnon transport,
+researches on magnon transport have gained considerable interests over the past
+decade. Recently, a full quantum theory has been employed to investigate magnon
+transport in ferromagnetic insulators (FMIs). However, the most commonly used
+magnetic insulating material in experiments, yttrium iron garnet (YIG), is a
+ferrimagnetic insulator (FIMI). Therefore, a full quantum theory for magnon
+transport in FIMI needs to be established. Here, we propose a Green's function
+formalism to compute the magnon bulk and interface current in both FIMIs and
+antiferromagnetic insulators (AFMIs). We investigate the spatial distribution
+and temperature dependence of magnon current in FIMIs and AFMIs generated by
+temperature or spin chemical potential step. In AFMIs, magnon currents
+generated by temperature step in the two sublattices cancel each other out.
+Subsequently, we numerically simulate the magnon junction effect using the
+Green's function formalism, and result shows near 100\% magnon junction ratio.
+This study demonstrates the potential for investigating magnon transport in
+specific magnonic devices using a full quantum theory.",2304.01930v1
+2020-05-27,Magnon antibunching in a nanomagnet,"We investigate the correlations of magnons inside a nanomagnet and identify a
+regime of parameters where the magnons become antibunched, i.e., where there is
+a large probability for occupation of the single-magnon state. This antibunched
+state is very different from magnons at thermal equilibrium and
+microwave-driven coherent magnons. We further obtain the steady state
+analytically and describe the magnon dynamics numerically, and ascertain the
+stability of such antibunched magnons over a large window of magnetic
+anisotropy, damping and temperature. This means that the antibunched magnon
+state is feasible in a wide class of low-damping magnetic nanoparticles. To
+detect this quantum effect, we propose to transfer the quantum information of
+magnons to photons by magnon-photon coupling and then measure the correlations
+of photons to retrieve the magnon correlations. Our findings may provide a
+promising platform to study quantum-classical transitions and for designing a
+single magnon source.",2005.13637v1
+2023-03-21,Intrinsic Magnon Orbital Hall Effect in Honeycomb Antiferromagnets,"We theoretically investigate the transport of magnon orbitals in a honeycomb
+antiferromagnet. We find that the magnon orbital Berry curvature is finite even
+without spin-orbit coupling and thus the resultant magnon orbital Hall effect
+is an intrinsic property of the honeycomb antiferromagnet rooted only in the
+exchange interaction and the lattice structure. Due to the intrinsic nature of
+the magnon orbital Hall effect, the magnon orbital Nernst conductivity is
+estimated to be orders of magnitude larger than the predicted values of the
+magnon spin Nernst conductivity that requires finite spin-orbit coupling. For
+the experimental detection of the predicted magnon orbital Hall effect, we
+invoke the magnetoelectric effect that couples the magnon orbital and the
+electric polarization, which allows us to detect the magnon orbital
+accumulation through the local voltage measurement. Our results pave a way for
+a deeper understanding of the topological transport of the magnon orbitals and
+also its utilization for low-power magnon-based orbitronics, namely magnon
+orbitronics.",2303.11687v1
+2023-04-11,Sizable suppression of magnon Hall effect by magnon damping in Cr$_2$Ge$_2$Te$_6$,"Two-dimensional (2D) Heisenberg honeycomb ferromagnets are expected to have
+interesting topological magnon effects as their magnon dispersion can have
+Dirac points. The Dirac points are gapped with finite second nearest neighbor
+Dzyaloshinskii-Moriya interaction, providing nontrivial Berry curvature with
+finite magnon Hall effect. Yet, it is unknown how the topological properties
+are affected by magnon damping. We report the thermal Hall effect in
+Cr$_2$Ge$_2$Te$_6$, an insulating 2D honeycomb ferromagnet with a large Dirac
+magnon gap and significant magnon damping. Interestingly, the thermal Hall
+conductivity in Cr$_2$Ge$_2$Te$_6$ shows the coexisting phonon and magnon
+contributions. Using an empirical two-component model, we successfully estimate
+the magnon contribution separate from the phonon part, revealing that the
+magnon Hall conductivity was 20 times smaller than the theoretical calculation.
+Finally, we suggest that such considerable suppression in the magnon Hall
+conductivity is due to the magnon damping effect in Cr$_2$Ge$_2$Te$_6$.",2304.04922v1
+2023-07-03,Cavity-Induced Strong Magnon-Magnon Coupling in Altermagnets,"Long-distance strong coupling between short-wavelength magnons remains an
+outstanding challenge in quantum magnonics, an emerging interdiscipline between
+magnonics and quantum information science. Recently, altermagnets are
+identified as the third elementary class of magnets that break the
+time-reversal symmetry without magnetization and thus combine characteristics
+of conventional collinear ferromagnets and antiferromagnets. In this work, we
+show that cavity photons can mediate the long-distance strong coupling of
+exchange magnons with opposite chiralities in altermagnets, manifesting as an
+anticrossing of the magnon-polariton spectrum in the extremely dispersive
+regime. The predicted effective magnon-magnon coupling strongly depends on the
+magnon propagation direction, and is thus highly anisotropic. Our findings are
+intimately connected to the intrinsic nature of altermagnetic magnons, i.e.,
+chirality-splitting-induced crossing of exchange magnons, which has no
+counterpart in conventional ferromagnets or antiferromagnets, and may open a
+new path way for magnon-based quantum information processing in altermagnets.",2307.00909v1
+2016-05-15,Propagation of Thermally Induced Magnonic Spin Currents,"The propagation of magnons in temperature gradients is investigated within
+the framework of an atomistic spin model with the stochastic
+Landau-Lifshitz-Gilbert equation as underlying equation of motion. We analyze
+the magnon accumulation, the magnon temperature profile as well as the
+propagation length of the excited magnons. The frequency distribution of the
+generated magnons is investigated in order to derive an expression for the
+influence of the anisotropy and the damping parameter on the magnon propagation
+length. For soft ferromagnetic insulators with low damping a propagation length
+in the range of some $\mu$m can be expected for exchange driven magnons.",1605.04543v1
+2022-01-24,Efficient Gating of Magnons by Proximity Superconductors,"Electrostatic gating confines and controls the transport of electrons in
+integrated circuits. Magnons, the quanta of spin waves of the magnetic order,
+are promising alternative information carriers, but difficult to gate. Here we
+report that superconducting strips on top of thin magnetic films can totally
+reflect magnons by its diamagnetic response to the magnon stray fields. The
+induced large frequency shifts unidirectionally blocks the magnons propagating
+normal to the magnetization. Two superconducting gates parallel to the
+magnetization create a magnonic cavity. The option to gate coherent magnons
+adds functionalities to magnonic devices, such as reprogrammable logical
+devices and increased couplings to other degrees of freedom.",2201.09532v2
+2021-08-18,Thermal squeezing and nonlinear spectral shift of magnons in antiferromagnetic insulators,"We investigate the effect of magnon-magnon interactions on the dispersion and
+polarization of magnons in collinear antiferromagnetic (AF) insulators at
+finite temperatures. In two-sublattice AF systems with either uniaxial or
+biaxial magnetocrystalline anisotropies, we implement a self-consistent
+Hartree-Fock mean-field approximation to explore the nonlinear thermal
+interactions. The resulting nonlinear magnon interactions separate into
+two-magnon intra- and interband scattering processes. Furthermore, we compute
+the temperature dependence of the magnon bandgap and AF resonance modes due to
+nonlinear magnon interactions for square and hexagonal lattices. In addition,
+we study the effect of magnon interactions on the polarization of magnon modes.
+We find that although the noninteracting eigenmodes in the uniaxial case are
+circularly polarized, but in the presence of nonlinear thermal interactions the
+local U(1) symmetry of the Hamiltonian is broken. The attractive nonlinear
+interactions squeeze the low-energy magnon modes and make them elliptical. In
+the biaxial case, on the other hand, the bare eigenmodes of low energy magnons
+are elliptically polarized but thermal nonlinear interactions squeeze them
+further. Direct measurements of the predicted temperature-dependent AF
+resonance modes and their polarization can be used as a tool to probe the
+nonlinear interactions. Our findings establish a framework for exploring the
+effect of thermal magnon interactions in technologically important magnetic
+systems, such as magnetic stability of recently discovered two-dimensional
+magnetic materials, coherent transport of magnons, Bose-Einstein condensation
+of magnons, and magnonic topological insulators.",2108.08374v4
+2022-09-07,Master equation approach to magnon relaxation and dephasing,"There has been a recent upsurge of interest in the quantum properties of
+magnons for quantum information processing. An important issue is to examine
+the stability of quantum states of magnons against various relaxation and
+dephasing channels. Since the interaction of magnons in magnetic systems may
+fall in the ultra-strong and even deep-strong coupling regimes, the relaxation
+process of magnon states is quite different from the more common quantum
+optical systems. Here we study the relaxation and dephasing of magnons based on
+the Lindblad formalism and derive a generalized master equation that describes
+the quantum dynamics of magnons. Employing this master equation, we identify
+two distinct dissipation channels for squeezed magnons, i.e., the local
+dissipation and collective dissipation, which play a role for both ferromagnets
+and antiferromagnets. The local dissipation is caused by the independent
+exchange of angular momentum between the magnonic system and the environment,
+while the collective dissipation is dressed by the parametric interactions of
+magnons and it enhances the quantumness and thermal stability of squeezed
+magnons. Further, we show how this formalism can be applied to study the pure
+dephasing of magnons caused by four-magnon scattering and magnon-phonon
+interactions. Our results provide the theoretical tools to study the
+decoherence of magnons within a full quantum-mechanical framework and further
+benefit the use of quantum states of magnons for information processing.",2209.02961v1
+2021-09-27,Numerical model for 32-bit magnonic ripple carry adder,"In CMOS-based electronics, the most straightforward way to implement a
+summation operation is to use the ripple carry adder (RCA). Magnonics, the
+field of science concerned with data processing by spin-waves and their quanta
+magnons, recently proposed a magnonic half-adder that can be considered as the
+simplest magnonic integrated circuit. Here, we develop a computation model for
+the magnonic basic blocks to enable the design and simulation of magnonic gates
+and magnonic circuits of arbitrary complexity and demonstrate its functionality
+on the example of a 32-bit integrated RCA. It is shown that the RCA requires
+the utilization of additional regenerators based on magnonic directional
+couplers with embedded amplifiers to normalize the magnon signals in-between
+the half-adders. The benchmarking of large-scale magnonic integrated circuits
+is performed. The energy consumption of 30 nm-based magnonic 32-bit adder can
+be as low as 961aJ per operation with taking into account all required
+amplifiers.",2109.12973v1
+2023-05-15,Quantum interference induced magnon blockade and antibunching in a hybrid quantum system,"In this work, we study the phenomena of quantum interference assisted magnon
+blockade and magnon antibunching in a weakly interacting hybrid
+ferromagnet-superconductor system. The magnon excitations in two yttrium iron
+garnet spheres are indirectly coupled to a superconducting qubit through
+microwave cavity modes of two mutually perpendicular cavities. We find that
+when one of the magnon mode is driven by a weak optical field, the destructive
+interference between more than two distinct transition pathways restricts
+simultaneous excitation of two magnons. We analyze the magnon correlations in
+the driven magnon mode for the case of zero detunings as well as finite
+detunings of the magnon modes and the qubit. We show that the magnon
+antibunching can be tuned by changing the magnon-qubit coupling strength ratio
+and the driving detuning. Our work proposes a possible scheme which have
+significant role in the construction of single magnon generating devices.",2305.08444v1
+2023-05-24,Topological Phases in Magnonics,"Magnonics or magnon spintronics is an emerging field focusing on generating,
+detecting, and manipulating magnons. As charge-neutral quasi-particles, magnons
+are promising information carriers because of their low energy dissipation and
+long coherence length. In the past decade, topological phases in magnonics have
+attracted intensive attention due to their fundamental importance in
+condensed-matter physics and potential applications of spintronic devices. In
+this review, we mainly focus on recent progress in topological magnonics, such
+as the Hall effect of magnons, magnon Chern insulators, topological magnon
+semimetals, etc. In addition, the evidence supporting topological phases in
+magnonics and candidate materials are also discussed and summarized. The aim of
+this review is to provide readers with a comprehensive and systematic
+understanding of the recent developments in topological magnonics.",2305.14861v2
+2023-08-11,Kerr nonlinearity induced strong spin-magnon coupling,"One pillar of quantum magnonics is the exploration of the utilization of the
+mediation role of magnons in different platforms to develop quantum
+technologies. The efficient coupling between magnons and various quantum
+entities is a prerequisite. Here, we propose a scheme to enhance the
+spin-magnon coupling by the magnonic Kerr nonlinearity in a YIG sphere. We find
+that the Kerr-enhanced spin-magnon coupling invalidates the widely used
+single-Kittel-mode approximation to magnons. It is revealed that the spin
+decoherence induced by the multimode magnons in the strong-coupling regime
+becomes not severe, but suppressed, manifesting as either population trapping
+or persistent Rabi-like oscillation. This anomalous effect is because the spin
+changes to be so hybridized with the magnons that one or two bound states are
+formed between them. Enriching the spin-magnon coupling physics, the result
+supplies a guideline to control the spin-magnon interface.",2308.05927v2
+2024-03-11,Handedness manipulation of propagating antiferromagnetic magnons,"Antiferromagnetic magnons possess a distinctive feature absent in their
+ferromagnetic counterparts: the presence of two distinct handedness modes, the
+right-handed (RH) and left-handed (LH) precession modes. The magnon handedness
+determines the sign of spin polarization carried by the propagating magnon,
+which is indispensable for harnessing the diverse functionalities. However, the
+control of coherently propagating magnon handedness in antiferromagnets has
+remained elusive so far. Here we demonstrate the manipulation and electrical
+readout of propagating magnon handedness in perpendicularly magnetized
+synthetic antiferromagnets (SAF). We find that the antiferromagnetic magnon
+handedness can be directly identified by measuring the inverse spin Hall effect
+(ISHE) voltage, which arises from the spin pumping effect caused by the
+propagating antiferromagnetic magnons in the SAF structure. The RH and LH modes
+of the magnon can be distinguishable particularly when the SAF structure is
+sandwiched by heavy metals with the same sign of spin Hall angle. Moreover, we
+succeed in controlling the handedness of propagating antiferromagnetic magnons
+by tuning the excitation microwave frequency. This work unveils promising
+avenues for harnessing magnon unique properties in antiferromagnet-based
+magnonic applications.",2403.06549v1
+2021-03-08,Anisotropic magnon-magnon coupling in synthetic antiferromagnets,"The magnon-magnon coupling in synthetic antiferromagnets advances it as
+hybrid magnonic systems to explore the quantum information technologies. To
+induce the magnon-magnon coupling, the parity symmetry between two
+magnetization needs to be broken. Here we experimentally demonstrate a
+convenient method to break the parity symmetry by the asymmetric thickness of
+two magnetic layers and thus introduce a magnon-magnon coupling in Ir-based
+synthetic antiferromagnets CoFeB(10 nm)/Ir(tIr=0.6 nm, 1.2 nm)/CoFeB(13 nm).
+Remarkably, we find that the weakly uniaxial anisotropy field (~ 20 Oe) makes
+the magnon-magnon coupling anisotropic. The coupling strength presented by a
+characteristic anticrossing gap varies in the range between 0.54 GHz and 0.90
+GHz for tIr =0.6 nm, and between nearly zero to 1.4 GHz for tIr = 1.2 nm,
+respectively. Our results demonstrate a feasible way to induce the
+magnon-magnon coupling by an asymmetric structure and tune the coupling
+strength by varying the direction of in-plane magnetic field. The magnon-magnon
+coupling in this highly tunable material system could open exciting
+perspectives for exploring quantum-mechanical coupling phenomena.",2103.04512v2
+2023-01-18,Magnon-magnon interactions induced by spin pumping-driven symmetry breaking in synthetic antiferromagnets,"The richness in both the dispersion and energy of antiferromagnetic magnons
+has spurred the magnetism community to consider antiferromagnets for future
+spintronic/magnonic applications. However, the excitation and control of
+antiferromagnetic magnons remains challenging, especially when compared to
+ferromagnetic counterparts. A middle ground is found with synthetic
+antiferromagnet metamaterials, where acoustic and optical magnons exist at GHz
+frequencies. In these materials, the magnon energy spectrum can be tuned by
+static symmetry-breaking external fields or dipolar interactions hybridizing
+optical and acoustic magnon branches. Here, we experimentally measure the
+magnon energy spectrum of synthetic antiferromagnetic tetralayers, and discover
+avoided energy level crossings in the energy spectrum that are unexplained by
+the antiferromagnetic interlayer coupling. We explain our experimental results
+using a phenomenological model incorporating both fieldlike and dampinglike
+torques generated by spin pumping in noncollinear magnetic multilayers
+separated by normal-metal spacers. We show that an asymmetry in the fieldlike
+torques acting on different magnetic layers can lift the spectral degeneracies
+of acoustic and optical magnon branches and yield symmetry-breaking induced
+magnon-magnon interactions. Our work extends the phenomenology of spin pumping
+to noncollinear magnetization configurations and significantly expands ways of
+engineering magnon-magnon interactions within antiferromagnets and quantum
+hybrid magnonic materials.",2301.07311v1
+1999-07-23,Magnon Broadening Effects in Double Layered Manganite La_1.2 Sr_1.8 Mn_2 O_7,"Magnon linewidth of La_1.2 Sr_1.8 Mn_2 O_7 near the Brillouin zone boundary
+is investigated from both theoretical and experimental points of view. Abrupt
+magnon broadening is ascribed to a strong magnon-phonon coupling. Magnon
+broadening observed in cubic perovskite manganites is also discussed.",9907362v1
+2018-02-12,Photoinduced topologically trivial magnons with finite thermal Hall effect,"In two-dimensional (2D) insulating magnets, the thermal Hall effect of
+magnons is believed to be a consequence of topological magnon insulator with
+separated magnon bands and a well-defined Chern number. Due to broken
+time-reversal symmetry the thermal Hall effect vanishes in Dirac magnons. In
+this paper, we show that periodically driven semi-Dirac magnon in 2D insulating
+honeycomb ferromagnet results in a photoinduced Dirac magnon at the topological
+phase transition between a photoinduced topological and trivial magnon
+insulator. Remarkably, the photoinduced Dirac magnon and the photoinduced
+trivial magnon insulator possess a nonzero Berry curvature and exhibit a finite
+thermal Hall effect. These intriguing properties of periodically driven 2D
+insulating magnets originate from the bosonic nature of magnons. Hence, they
+are not expected to exist in 2D electronic Floquet systems.",1802.04268v2
+2016-10-04,Resolving magnon number states in quantum magnonics,"Collective excitation modes in solid state systems play a central role in
+circuit quantum electrodynamics, cavity optomechanics, and quantum magnonics.
+In the latter, quanta of collective excitation modes in a ferromagnet, called
+magnons, interact with qubits to provide the nonlinearity necessary to access
+quantum phenomena in magnonics. A key ingredient for future quantum magnonics
+systems is the ability to probe magnon states. Here we observe individual
+magnons in a millimeter-sized ferromagnet coherently coupled to a
+superconducting qubit. Specifically, we resolve magnon number states in
+spectroscopic measurements of a transmon qubit with the hybrid system in the
+strong dispersive regime. This enables us to detect a change in the magnetic
+dipole of the ferromagnet equivalent to a single spin flipped among more than
+$10^{19}$ spins. The strong dispersive regime of quantum magnonics opens up the
+possibility of encoding superconducting qubits into non-classical magnon
+states, potentially providing a coherent interface between a superconducting
+quantum processor and optical photons.",1610.00839v1
+2018-10-01,Stabilizing Mechanism for Bose-Einstein Condensation of Interacting Magnons in Ferrimagnets and Ferromagnets,"We propose a stabilizing mechanism for the Bose-Einstein condensation (BEC)
+of interacting magnons in ferrimagnets and ferromagnets. By studying the
+effects of the magnon-magnon interaction on the stability of the magnon BEC in
+a ferrimagnet and two ferromagnets, we show that the magnon BEC remains stable
+even in the presence of the magnon-magnon interaction in the ferrimagnet and
+ferromagnet with a sublattice structure, whereas it becomes unstable in the
+ferromagnet without a sublattice structure. This indicates that the existence
+of a sublattice structure is the key to stabilizing the BEC of interacting
+magnons, and the difference between the spin alignments of a ferrimagnet and a
+ferromagnet is irrelevant. Our result can resolve a contradiction between
+experiment and theory in the magnon BEC of yttrium iron garnet. Our theoretical
+framework may provide a starting point for understanding the physics of the
+magnon BEC including the interaction effects.",1810.00584v2
+2019-10-09,Magnon Blockade in a Hybrid Ferromagnet-Superconductor Quantum System,"The implementation of a single magnon level quantum manipulation is one of
+the fundamental targets in quantum magnetism with a significant practical
+relevance for precision metrology, quantum information processing, and quantum
+simulation. Here, we demonstrate theoretically the feasibility of using a
+hybrid ferromagnet-superconductor quantum system to prepare a single magnon
+source based on magnon blockade effects. By numerically solving the quantum
+master equation, we show that the second-order correlation function of the
+magnon mode depends crucially on the relation between the qubit-magnon coupling
+strength and the driving detuning, and simultaneously signatures of the magnon
+blockade appear only under quite stringent conditions of a cryogenic
+temperature. In addition to providing perception into the quantum phenomena of
+magnon, the study of magnon blockade effects will help to develop novel
+technologies for exploring the undiscovered magnon traits at the quantum level
+and may find applications in designing single magnon emitters.",1910.03738v1
+2020-01-20,Effects of magnon-magnon interactions in a noncollinear magnet induced by combination of a symmetric and an antisymmetric exchange interaction,"We study magnon-magnon interactions and their effects in a spiral magnet
+induced by combination of an antiferromagnetic Heisenberg interaction and a
+Dzyaloshinsky-Moriya interaction. We show that the main effect of magnon-magnon
+interactions on low-energy magnons is to renormalize the coefficient of energy
+dispersion. This could explain why some experiments are consistent with the
+noninteracting theory. We also show that although the magnon-magnon
+interactions induce the pair amplitude for low-energy magnons, its effect on
+the excitation energy is negligible. This suggests that for magnons the finite
+pair amplitude does not necessarily accompany the pair condensation.",2001.06981v2
+2020-04-23,Strong coupling between magnons confined in a single magnonic cavity,"Strong coupling between magnons and cavity photons was studied extensively
+for quantum electrodynamics in the past few years. Recently, the strong
+magnon-magnon coupling between adjacent layers in magnetic multilayers has been
+reported. However, the strongly coupled magnons confined in a single nanomagnet
+remains to be revealed. Here, we report the interaction between different
+magnon modes in a single magnonic cavity. The intermodel coupling between edge
+and center magnon modes in the strong coupling regime was approached with a
+maximum coupling strength of 0.494 GHz and cooperativity of 60.1 with a damping
+of 1X10-3. Furthermore, it is found that the coupling strength is highly
+dependent on the geometric parameters of the magnonic cavity. Our findings
+could greatly enrich the still evolving field of quantum magnonics.",2004.11058v1
+2020-08-15,Magnon laser based on Brillouin light scattering,"An analogous laser action of magnons would be a subject of interest and is
+crucial for the study of nonlinear magnons spintronics. Here, we demonstrate
+the magnon laser behavior based on Brillouin light scattering in a
+ferrimagnetic insulator sphere which supports optical whispering gallery modes
+and magnon resonances. We show that the excited magnon plays what has
+traditionally been the role of the Stokes wave and is coherently amplified
+during the Brillouin scattering process, making magnon laser possible.
+Furthermore, the stimulating excited magnon number increasing exponentially
+with the input light power can be manipulated by adjusting the external
+magnetic field. In addition to providing insight into magneto-optical
+interaction, the study of magnon laser action will help to develop novel
+technologies for handling spin-wave excitations and could affect scientific
+fields beyond magnonics. Potential applications range from preparing coherent
+magnon sources to operating onchip functional magnetic devices.",2008.06628v2
+2020-10-31,Facet-dependent magnon-polarons in epitaxial ferrimagnetic Fe3O4 thin films,"Magnon-polarons are coherently mixed quasiparticles that originate from the
+strong magnetoelastic coupling of lattice vibrations and spin waves in
+magnetic-ordered materials. Recently, magnon-polarons have attracted a lot of
+attention since they provide a powerful tool to manipulate magnons, which is
+essential for magnon-based spintronic devices. In this work, we report the
+experimental observation of facet-dependent magnon-polarons in epitaxial
+ferrimagnetic Fe3O4 thin films via spin Seebeck effect measurement. The
+critical magnetic fields for the magnon-polarons in the (110)- and
+(100)-oriented Fe3O4 films are 1.5 T and 1.8 T, respectively, which arises from
+the different phonon velocities along the [110] and [100] directions. As the
+temperature decreases, the magnon-polarons-enhanced spin Seebeck voltage
+decreases in both (110)- and (100)-oriented Fe3O4 films, which could be
+attributed to the enhanced magnon-polarons scattering at elevated temperatures.
+This work demonstrates the crystal structure engineering in epitaxial magnetic
+films as a promising route to manipulate the magnon-polarons for future magnon
+spintronic applications.",2011.00195v1
+2021-06-12,Magnon-magnon entanglement and its detection in a microwave cavity,"Quantum magnonics is an emerging research field, with great potential for
+applications in magnon based hybrid systems and quantum information processing.
+Quantum correlation, such as entanglement, is a central resource in many
+quantum information protocols that naturally comes about in any study toward
+quantum technologies. This applies also to quantum magnonics. Here, we
+investigate antiferromagnets in which sublattices with ferromagnetic
+interactions can have two different magnon modes, and we show how this may lead
+to experimentally detectable bipartite continuous variable magnon-magnon
+entanglement. The entanglement can be fully characterized via a single
+squeezing parameter, or, equivalently, entanglement parameter. The clear
+relation between the entanglement parameter and the Einstein, Podolsky, and
+Rosen (EPR) function of the ground state opens up for experimental observation
+of magnon-magnon continuous variable entanglement and EPR non-locality. We
+propose a practical experimental realization to detect the EPR function of the
+ground state, in a setting that relies on magnon-photon interaction in a
+microwave cavity.",2106.06862v1
+2021-12-04,Dissipation-induced nonreciprocal magnon blockade in a magnon-based hybrid system,"We propose an experimentally realizable nonreciprocal magnonic device at the
+single-magnon level by exploiting magnon blockade in a magnon-based hybrid
+system. The coherent qubit-magnon coupling, mediated by virtual photons in a
+microwave cavity, leads to the energy-level anharmonicity of the composite
+modes. In contrast, the corresponding dissipative counterpart, induced by
+traveling microwaves in a waveguide, yields inhomogeneous broadenings of the
+energy levels. As a result, the cooperative effects of these two kinds of
+interactions give rise to the emergence of the direction-dependent magnon
+blockade. We show that this can be demonstrated by studying the equal-time
+second-order correlation function of the magnon mode. Our study opens an avenue
+to engineer nonreciprocal magnonic devices in the quantum regime involving only
+a small number of magnons.",2112.02351v1
+2022-09-09,Parity-Time Symmetry-Enhanced Simultaneous Magnon and Photon Blockade in Cavity Magnonic System,"The main challenge in the recent demonstration of conventional magnon
+blockade is to increase the nonlinearity of the system especially in comparison
+with the dissipation channels. One can consider the Kerr nonlinearity through
+which magnon blockade in a cavity magnonic system is possible provided that the
+Kerr nonlinearity is much stronger than the cavity and magnonic mode
+dissipation rates. In the present contribution, we consider a PT-symmetric
+cavity magnonic system and study the effect of PT-symmetric phase on the magnon
+statistics and hence magnon blockade. We show that the PT-symmetric phase,
+which is achievable by properly selecting the system parameters, can relax the
+requirement of large Kerr nonlinearity such that a perfect magnon blockade can
+be easily obtained even under a small value of Kerr nonlinearity. Surprisingly,
+although there is no photonic Kerr nonlinearity in the scheme, photon blockade
+can also occur simultaneously with magnon blockade. This result is arising from
+the PT-symmetric phase which can generate an effective photonic Kerr
+nonlinearity.",2209.04228v1
+2023-01-22,Magnon bundle in a strongly dissipative magnet,"Hybrid quantum systems based on magnetic platforms have witnessed the birth
+and fast development of quantum spintronics. Until now, most of the studies
+rely on magnetic excitations in low-damping magnetic insulators, particularly
+yttrium iron garnet, while a large class of magnetic systems is ruled out in
+this interdisciplinary field. Here we propose the generation of a magnon bundle
+in a hybrid magnet-qubit system, where two or more magnons are emitted
+simultaneously. By tuning the driving frequency of qubit to match the detuning
+between magnon and qubit mode, one can effectively generate a magnon bundle via
+super-Rabi oscillations. In contrast with general wisdom, magnetic dissipation
+plays an enabling role in generating the magnon bundle, where the relaxation
+time of magnons determines the typical time delay between two successive
+magnons. The maximal damping that allows an antibunched magnon bundle can reach
+the order of 0.1, which may break the monopoly of low-dissipation magnetic
+insulators in quantum spintronics and enables a large class of magnetic
+materials for quantum manipulation. Further, our finding may provide a scalable
+and generic platform to study multi-magnon physics and benefit the design of
+magnonic networks for quantum information processing.",2301.09095v1
+2023-10-13,Magnon spin capacitor,"In this work we show that a magnon spin capacitor can be realized at a
+junction between two exchange coupled ferromagnets. In this junction, the
+buildup of magnon spin over the junction is coupled to the difference in magnon
+chemical potential, realizing the magnon spin analogue of an electrical
+capacitor. The relation between magnon spin and magnon chemical potential
+difference directly follows from considering the magnon density-density
+interaction between the two ferromagnets. We analyse the junction in detail by
+considering spin injection and detection from normal metal leads, the tunneling
+current across the junction and magnon decay within the ferromagnet, showing
+that such a structure realizes a magnon spin capacitor in series with a spin
+resistor. Choosing yttrium iron garnet as the ferromagnet, we numerically
+calculate the capacitance, which ranges from picofarad to microfarad, depending
+on the area of the junction. We therefore conclude that the magnon spin
+capacitor could directly be of use in applications.",2310.09064v3
+2024-03-27,Extreme Terahertz Magnon Multiplication Induced by Resonant Magnetic Pulse Pairs,"Nonlinear interactions of spin-waves and their quanta, magnons, have emerged
+as prominent candidates for interference-based technology, ranging from quantum
+transduction to antiferromagnetic spintronics. Yet magnon multiplication in the
+terahertz (THz) spectral region represents a major challenge. Intense, resonant
+magnetic fields from THz pulse-pairs with controllable phases and amplitudes
+enable high order THz magnon multiplication, distinct from non-resonant
+nonlinearities such as the high harmonic generation by below-band gap electric
+fields. Here, we demonstrate exceptionally high-order THz nonlinear magnonics.
+It manifests as 7$^\text{th}$-order spin-wave-mixing and 6$^\text{th}$ harmonic
+magnon generation in an antiferromagnetic orthoferrite. We use THz
+multi-dimensional coherent spectroscopy to achieve high-sensitivity detection
+of nonlinear magnon interactions up to six-magnon quanta in strongly-driven
+many-magnon correlated states. The high-order magnon multiplication, supported
+by classical and quantum spin simulations, elucidates the significance of
+four-fold magnetic anisotropy and Dzyaloshinskii-Moriya symmetry breaking.
+Moreover, our results shed light on the potential quantum fluctuation
+properties inherent in nonlinear magnons.",2403.18168v1
+1999-05-11,Magnon Broadening Effect by Magnon-Phonon Interaction in Colossal Magnetoresistance Manganites,"In order to study the magnetic excitation behaviors in colossal
+magnetoresistance manganites, a magnon-phonon interacting system is
+investigated. Sudden broadening of magnon linewidth is obtained when a magnon
+branch crosses over an optical phonon branch. Onset of the broadening is
+approximately determined by the magnon density of states. Anomalous magnon
+damping at the brillouine zone boundary observed in low Curie temperature
+manganites is explained.",9905133v2
+2005-11-11,Spin wave spectrum of a magnonic crystal with an isolated defect,"Real magnonic crystals - periodic magnetic media for spin wave (magnon)
+propagation - may contain some defects. We report theoretical spin wave spectra
+of a one dimensional magnonic crystal with an isolated defect. The latter is
+modeled by insertion of an additional layer with thickness and magnetic
+anisotropy values different from those of the magnonic crystal constituent
+layers. The defect layer leads to appearance of several localized defect modes
+within the magnonic band gaps. The frequency and the number of the defect modes
+may be controlled by varying parameters of the constituent layers of the
+magnonic crystal.",0511295v1
+2007-11-10,Stability of Bose Einstein condensates of hot magnons in YIG,"We investigate the stability of the recently discovered room temperature
+Bose-Einstein condensate (BEC) of magnons in Ytrrium Iron Garnet (YIG) films.
+We show that magnon-magnon interactions depend strongly on the external field
+orientation, and that the BEC in current experiments is actually metastable -
+it only survives because of finite size effects, and because the BEC density is
+very low. On the other hand a strong field applied perpendicular to the sample
+plane leads to a repulsive magnon-magnon interaction; we predict that a
+high-density magnon BEC can then be formed in this perpendicular field
+geometry.",0711.1574v1
+2008-03-19,Magnetic field-induced one-magnon Raman scattering in the magnon Bose-Einstein condensation phase of TlCuCl$_{3}$,"We report the observation of the $A_{\rm g}$-symmetric one-magnon Raman peak
+in the magnon Bose-Einstein condensation phase of TlCuCl$_{3}$. Its Raman shift
+traces the one-magnon energy at the magnetic $\Gamma$ point, and its intensity
+is proportional to the squared transverse magnetization. The appearance of the
+one-magnon Raman scattering originates from the exchange magnon Raman process
+and reflects the change of the magnetic-state symmetry. Using the bond-operator
+representation, we theoretically clarify the Raman selection rules, being
+consistent with the experimental results.",0803.2815v1
+2021-06-23,Stimulated-Raman-Adiabatic-Passage mechanism in a magnonic environment,"We discuss the realization of a magnonic version of the
+STImulated-Raman-Adiabatic-Passage (m-STIRAP) mechanism using micromagnetic
+simulations. We consider the propagation of magnons in curved magnonic
+directional couplers. Our results demonstrate that quantum-classical analogy
+phenomena are accessible in magnonics. Specifically, the inherent advantages of
+the STIRAP mechanism, associated with dark states, can now be utilized in
+magnonics. Applications of this effect for future magnonic device
+functionalities and designs are discussed.",2106.12318v1
+2022-08-01,Calculation of magnon drag force induced by an electric current in ferromagnetic metals,"Magnon drag effect induced by an applied electric field in ferromagnetic
+metals is theoretically studied by a microscopic calculation of the force on
+magnons arising from magnon emission/absorption and scattering due to driven
+electrons. It is shown that magnon scattering contribution dominates over the
+emission/absorption one in a wide temperature regime in good metals with long
+elastic lifetime $\taue$, as the latter has a relative suppression factor of
+$(\Deltasd\taue)^{-2}$ due to the electron spin flip by the magnon, where
+$\Deltasd$ is the $sd$ exchange interaction energy. Spin-transfer efficiency is
+discussed including the magnon drag effect.",2208.00622v1
+2004-12-14,Current-induced magnetization changes in a spin valve due to incoherent emission of non-equilibrium magnons,"We describe spin transfer in a ferromagnet/normal metal/ferromagnet
+spin-valve point contact. Spin is transferred from the spin-polarized device
+current to the magnetization of the free layer by the mechanism of incoherent
+magnon emission by electrons. Our approach is based on the rate equation for
+the magnon occupation, using Fermi's golden rule for magnon emission and
+absorption and the non-equilibrium electron distribution for a biased spin
+valve. The magnon emission reduces the magnetization of the free layer. For
+anti-parallel alignment of the magnetizations of the layers and at a critical
+bias a magnon avalanche occurs, characterized by a diverging effective magnon
+temperature. This critical behavior can result in magnetization reversal and
+consequently to suppression of magnon emission. However, magnon-magnon
+scattering can lead to saturation of the magnon concentration at a large but
+finite value. The further behavior depends on the parameters of the system. In
+particular, gradual evolution of the magnon concentration followed by a
+magnetization reversal is possible. Another scenario corresponds to a step-like
+increase of the magnon concentration followed by a slow decrease. In the latter
+case a spike in the differential resistance is expected due to a contribution
+of electron-magnon scattering. A comparison of the obtained results to existing
+experimental data and theoretical approches is given.",0412348v1
+2023-12-26,Direct observation of topological magnon polarons in a multiferroic material,"Magnon polarons are novel elementary excitations possessing hybrid magnonic
+and phononic signatures, and are responsible for many exotic spintronic and
+magnonic phenomena. Despite long-term sustained experimental efforts in chasing
+for magnon polarons, direct spectroscopic evidence of their existence is hardly
+observed. Here, we report the direct observation of magnon polarons using
+neutron spectroscopy on a multiferroic Fe$_{2}$Mo$_{3}$O$_{8}$ possessing
+strong magnon-phonon coupling. Specifically, below the magnetic ordering
+temperature, a gap opens at the nominal intersection of the original magnon and
+phonon bands, leading to two separated magnon-polaron bands. Each of the bands
+undergoes mixing, interconverting and reversing between its magnonic and
+phononic components. We attribute the formation of magnon polarons to the
+strong magnon-phonon coupling induced by Dzyaloshinskii-Moriya interaction.
+Intriguingly, we find that the band-inverted magnon polarons are topologically
+nontrivial. These results uncover exotic elementary excitations arising from
+the magnon-phonon coupling, and offer a new route to topological states by
+considering hybridizations between different types of fundamental excitations.",2312.15943v1
+2014-07-12,Role of dimensionality in spontaneous magnon decay: easy-plane ferromagnet,"We calculate magnon lifetime in an easy-plane ferromagnet on a tetragonal
+lattice in transverse magnetic field. At zero temperature magnons are unstable
+with respect to spontaneous decay into two other magnons. Varying ratio of
+intrachain to interchain exchanges in this model we consider the effect of
+dimensionality on spontaneous magnon decay. The strongest magnon damping is
+found in the quasi-one-dimensional case for momenta near the Brillouin zone
+boundary. The sign of a weak interchain coupling has a little effect on the
+magnon decay rate. The obtained theoretical results suggest possibility of
+experimental observation of spontaneous magnon decay in a quasi-one-dimensional
+ferromagnet CsNiF$_3$. We also find an interesting enhancement of the magnon
+decay rate for a three-dimensional ferromagnet. The effect is present only for
+the nearest-neighbor model and is related to effective dimensionality reduction
+in the two-magnon continuum.",1407.3402v1
+2016-06-09,Integer Quantum Magnon Hall Plateau-Plateau Transition in a Spin Ice Model,"Low-energy magnon bands in a two-dimensional spin ice model become integer
+quantum magnon Hall bands. By calculating the localization length and the
+two-terminal conductance of magnon transport, we show that the magnon bands
+with disorders undergo a quantum phase transition from an integer quantum
+magnon Hall regime to a conventional magnon localized regime. Finite size
+scaling analysis as well as a critical conductance distribution shows that the
+quantum critical point belongs to the same universality class as that in the
+quantum Hall transition. We characterize thermal magnon Hall conductivity in
+disordered quantum magnon Hall system in terms of robust chiral edge magnon
+transport.",1606.02839v2
+2016-05-13,Nonlocal Drag of Magnons in a Ferromagnetic Bilayer,"Quantized spin waves, or magnons, in a magnetic insulator are assumed to
+interact weakly with the surroundings, and to flow with little dissipation or
+drag, producing exceptionally long diffusion lengths and relaxation times. In
+analogy to Coulomb drag in bilayer two dimensional electron gases, in which the
+contribution of the Coulomb interaction to the electric resistivity is studied
+by measuring the interlayer resistivity (transresistivity), we predict a
+nonlocal drag of magnons in a ferromagnetic bilayer structure based on
+semiclassical Boltzmann equations. Nonlocal magnon drag depends on magnetic
+dipolar interactions between the layers and manifests in the magnon current
+transresistivity and the magnon thermal transresistivity, whereby a magnon
+current in one layer induces a chemical potential gradient and/or a temperature
+gradient in the other layer. The largest drag effect occurs when the magnon
+current flows parallel to the magnetization, however for oblique magnon
+currents a large transverse current of magnons emerges. We examine the effect
+for practical parameters, and find that the predicted induced temperature
+gradient is readily observable.",1605.04336v1
+2020-12-22,Dirac magnons pairing via pumping,"We study pumping of magnons to the Dirac points of magnon's Brillouin zone of
+a ferromagnet on a honeycomb lattice. In particular, we consider second-order
+Suhl process, when due to interaction between magnons, a pair of magnons is
+created due to absorption of two electromagnetic wave quanta. We introduce a
+bosonic analog of the Cooper ladder for the magnon pair, which is shown to
+enhance the pairing of magnons at the Dirac points. As a result of pairing of
+the Dirac magnons, the system becomes unstable towards formation of a magnetic
+state with zero or reduced magnetization - the Dirac magnon paired state. In
+this case the resonant frequency of the pump equals to that of energy of the
+Dirac points. Our estimates suggest that the Dirac magnon paired state can be
+found in the CrBr$_{3}$ or CrCl$_{3}$ ferromagnet below in vicinity of the
+Curie temperature.",2012.12051v4
+2013-06-24,Magnon Energy Renormalization and Low-Temperature Thermodynamics of O(3) Heisenberg Ferromagnets,"We present the perturbation theory for lattice magnon fields of
+$D$-dimensional O(3) Heisenberg ferromagnet. The effective Hamiltonian for the
+lattice magnon fields is obtained starting from the effective Lagrangian, with
+two dominant contributions that describe magnon-magnon interactions identified
+as a usual gradient term for the unit vector field and a part originating in
+the Wess-Zumino-Witten term of effective Lagrangian. Feynman diagrams for
+lattice scalar fields with derivative couplings are introduced, on basis of
+which we investigate the influence of magnon-magnon interactions on magnon
+self-energy and ferromagnet free energy. We also comment appearance of spurious
+terms in the low-temperature series for the free energy by examining
+magnon-magnon interactions and internal symmetry of the effective Hamiltonian
+(Lagrangian).",1306.5584v1
+2020-01-30,Magnon-phonon interactions in magnon spintronics,"Nowadays, the interaction between phonon and magnon subsystems of a magnetic
+medium is a hot topic of research. The complexity of phonon and magnon spectra,
+the existence of both bulk and surface modes, the quantization effects, and the
+dependence of magnon properties on applied magnetic field, make this field very
+complex and intriguing. Moreover, the recent advances in the fields of
+spin-caloritronics and magnon spintronics as well as the observation of the
+spin Seebeck effect (SSE) in magnetic insulators points on the crucial role of
+magnons in spin-caloric transport processes. In this review, we collect the
+variety of different studies in which magnon-phonon interaction play important
+role. The scope of the paper covers the wide range of phenomena starting from
+the interaction of the coherent magnons with surface acoustic wave and
+finishing with the formation of magnon supercurrents in the thermal gradients.",2001.11447v1
+2021-03-11,Hybrid topological magnon-phonon modes in honeycomb and kagome lattices,"Magnons and phonons are two fundamental neutral excitations of magnetically
+ordered materials which can significantly dominate the low-energy thermal
+properties. In this work we study the interplay of magnons and phonons in
+honeycomb and Kagome lattices. When the mirror reflection with respect to the
+magnetic ordering direction is broken, the symmetry-allowed in-plane
+Dzyaloshinskii-Moriya (DM) interaction will couple the magnons to the phonons
+and the magnon-polaron states are formed. Besides, both lattice structures also
+allow for an out-of-plane DM interaction rendering the uncoupled magnons to be
+topological. Our aim is to study the interplay of such topological magnons with
+phonons. We show that the hybridization between magnons and phonons can
+significantly redistribute the Berry curvature among the bands. Especially, we
+found that the topological magnon band becomes trivial while the hybridized
+states at lower energy acquire Berry curvature strongly peaked near the avoided
+crossings. As such the thermal Hall conductivity of topological magnons shows
+significant changes due to coupling to the phonons.",2103.06959v2
+2021-06-24,Control of nonlocal magnon spin transport via magnon drift currents,"Spin transport via magnon diffusion in magnetic insulators is important for a
+broad range of spin-based phenomena and devices. However, the absence of the
+magnon equivalent of an electric force is a bottleneck. In this work, we
+demonstrate the controlled generation of magnon drift currents in yttrium iron
+garnet/platinum heterostructures. By performing electrical injection and
+detection of incoherent magnons, we find magnon drift currents that stem from
+the interfacial Dzyaloshinskii-Moriya interaction. We can further control the
+magnon drift by the orientation of the magnetic field. The drift current
+changes the magnon propagation length by up to $\pm$ 6 % relative to diffusion.
+We generalize the magnonic spin transport theory to include a finite drift
+velocity resulting from any inversion asymmetric interaction, and obtain
+results consistent with our experiments.",2106.12946v1
+2021-09-02,Enhanced magnon spin current using the bosonic Klein paradox,"Efficient manipulation of magnons for information processing is a central
+topic in spintronics and magnonics. An outstanding challenge for long-distance
+spin transport with minimal dissipation is to overcome the relaxation of
+magnons and to amplify the spin current they carry. Here, we propose to amplify
+magnon currents based on the realization of the bosonic Klein paradox in
+magnetic nanostructures. This paradox involves the magnon's antiparticle, the
+antimagnon, of which the existence is usually precluded by magnetic
+instabilities as it is an excitation at negative energy. We show that, by
+appropriately tuning the effective dissipation through spin-orbit torques, both
+magnons and antimagnons are dynamically stabilized. As a result, we find that
+the reflection coefficient of incident magnons at an interface between two
+coupled magnets can become larger than one, thereby amplifying the reflected
+magnon current. Our findings can lead to magnon amplifier devices for
+spintronic applications. Furthermore, our findings yield a solid-state platform
+to study the relativistic behavior of bosonic particles, which is an
+outstanding challenge with fundamental particles.",2109.00865v3
+2022-01-17,Pure dephasing of magnonic quantum states,"For a wide range of nonclassical magnonic states that have been proposed and
+demonstrated recently, a new time scale besides the magnon lifetime - the
+magnon dephasing time - becomes important, but this time scale is rarely
+studied. Considering exchange interaction and spin-phonon coupling, we evaluate
+the pure magnon dephasing time and find it to be smaller than the magnon
+lifetime at temperatures of a few Kelvins. By examining a magnonic cat state as
+an example, we show how pure dephasing of magnons destroys and limits the
+survival of quantum superpositions. Thus it will be critical to perform quantum
+operations within the pure dephasing time. We further derive the master
+equation for the density matrix describing such magnonic quantum states taking
+into account the role of pure dephasing, whose methodology can be generalized
+to include additional dephasing channels that experiments are likely to
+encounter in the future. Our findings enable one to design and manipulate
+robust quantum states of magnons for information processing.",2201.06637v1
+2022-03-07,Magnetoelectric Cavity Magnonics in Skyrmion Crystals,"We present a theory of magnetoelectric magnon-photon coupling in cavities
+hosting noncentrosymmetric magnets. Analogously to nonreciprocal phenomena in
+multiferroics, the magnetoelectric coupling is time-reversal and inversion
+asymmetric. This asymmetry establishes a means for exceptional tunability of
+magnon-photon coupling, which can be switched on and off by reversing the
+magnetization direction. Taking the multiferroic skyrmion-host Cu$_2$OSeO$_3$
+with ultralow magnetic damping as an example, we reveal the electrical activity
+of skyrmion eigenmodes and propose it for magnon-photon splitting of
+``magnetically dark'' elliptic modes. Furthermore, we predict a cavity-induced
+magnon-magnon coupling between magnetoelectrically active skyrmion excitations.
+We discuss applications in quantum information processing by proposing
+protocols for all-electrical magnon-mediated photon quantum gates, and a
+photon-mediated SPLIT operation of magnons. Our study highlights
+magnetoelectric cavity magnonics as a novel platform for realizing
+quantum-hybrid systems and the coherent transduction between photons and
+magnons in topological magnetic textures.",2203.03241v2
+2022-04-25,Oscillations and confluence in three-magnon scattering of ferromagnetic resonance,"We have performed a time-resolved and phase-sensitive investigation of
+three-magnon scattering of ferromagnetic resonance (FMR) over several orders of
+magnitude in excitation power. We observe a regime that hosts transient
+oscillations of the FMR magnon population, despite higher-order magnon
+interactions at large powers. Also at high powers, the scattering generates
+$180^\circ$ phase shifts of the FMR magnons. These phase shifts correspond to
+reversals in the three-magnon scattering direction, between splitting and
+confluence. These scattering reversals are most directly observed after
+removing the microwave excitation, generating coherent oscillations of the FMR
+magnon population much larger than its steady-state value during the
+excitation. Our model is in strong agreement with these findings. These
+findings reveal the transient behavior of this three-magnon scattering process,
+and the nontrivial interplay between three-magnon scattering and the magnons'
+phases.",2204.11969v4
+2022-05-06,Interband magnon drag in ferrimagnetic insulators,"We propose a new drag phenomenon, an interband magnon drag, and report on
+interaction effects and multiband effects in magnon transport of ferrimagnetic
+insulators. We study a spin-Seebeck coefficient $S_{\textrm{m}}$, a magnon
+conductivity $\sigma_{\textrm{m}}$, and a magnon thermal conductivity
+$\kappa_{\textrm{m}}$ of interacting magnons for a minimal model of
+ferrimagnetic insulators using a $1/S$ expansion of the Holstein-Primakoff
+method, the linear-response theory, and a method of Green's functions. We show
+that the interband magnon drag enhances $\sigma_{\textrm{m}}$ and reduces
+$\kappa_{\textrm{m}}$, whereas its total effects on $S_{\textrm{m}}$ are small.
+This drag results from the interband momentum transfer induced by the
+magnon-magnon interactions. We also show that the higher-energy band magnons
+contribute to $S_{\textrm{m}}$, $\sigma_{\textrm{m}}$, and
+$\kappa_{\textrm{m}}$ even for temperatures smaller than the energy difference
+between the two bands.",2205.03058v1
+2022-09-02,Tunable phonon-driven magnon-magnon entanglement at room temperature,"We report the existence of entangled steady-states in bipartite quantum
+magnonic systems at elevated temperatures. We consider dissipative dynamics of
+two magnon modes in a bipartite antiferromagnet, subjected to interaction with
+a phonon mode and an external rotating magnetic field. To quantify the
+bipartite magnon-magnon entanglement, we use entanglement negativity and
+compute its dependence on temperature and magnetic field. We provide evidence
+that the coupling between magnon and phonon modes is necessary for the
+entanglement, and that, for any given phonon frequency and magnon-phonon
+coupling rate, there are always ranges of the magnetic field amplitudes and
+frequencies for which magnon-magnon entanglement persists at room temperature.",2209.01032v2
+2023-01-27,Tunable Strong Magnon-Magnon Coupling in Two-Dimensional Array of Diamond Shaped Ferromagnetic Nanodots,"Hybrid magnonics involving coupling between magnons and different quantum
+particles have been extensively studied during past few years for varied
+interests including quantum electrodynamics. In such systems, magnons in
+magnetic materials with high spin density are utilized where the coupling
+strength is collectively enhanced by the square root of the number of spins to
+overcome the weaker coupling between individual spins and the microwave field.
+However, achievement of strong magnon-magnon coupling in a confined nanomagnets
+would be essential for on-chip integration of such hybrid systems. Here,
+through intensive study of interaction between different magnon modes in a
+Ni80Fe20 (Py) nanodot array, we demonstrate that the intermodal coupling can
+approach the strong coupling regime with coupling strength up to 0.82 GHz and
+cooperativity of 2.51. Micromagnetic simulations reveal that the intermodal
+coupling is mediated by the exchange field inside each nanodot. The coupling
+strength could be continuously tuned by varying the bias field strength and
+orientation, opening routes for external control over hybrid magnonic systems.
+These findings could greatly enrich the rapidly evolving field of quantum
+magnonics.",2301.11583v1
+2023-02-21,Adiabatic magnon spectra with and without constraining field: Benchmark against an exact magnon spectrum,"The spectrum of magnon excitations in magnetic materials can be obtained
+exactly from the transverse dynamic magnetic susceptibility, which is however
+in practice numerically expensive. Many ab initio approaches therefore consider
+instead the adiabatic magnon spectrum, which assumes a separation of time
+scales of magnons and electronic excitations. There exist two alternative
+implementations for adiabatic magnon spectra: one based on the magnetic force
+theorem (MFT) and the other with a constraining field that enforces static
+non-collinear spin configurations. We benchmark both implementations against
+the exact magnon spectrum of an exactly solvable mean-field model. While both
+adiabatic methods are equally valid in the low magnon energy and strong Stoner
+coupling limits, we find that the constraining field method performs better
+than the MFT in both the cases of strong Stoner coupling and high magnon
+energies,while the MFT performs better for combined weak coupling and low
+magnon energies.",2302.10958v1
+2023-05-05,Nonreciprocal entanglement in cavity-magnon optomechanics,"Cavity optomechanics, a promising platform to investigate macroscopic quantum
+effects, has been widely used to study nonreciprocal entanglement with Sagnec
+effect. Here we propose an alternative way to realize nonreciprocal
+entanglemment among magnons, photons, and phonons in a hybrid cavity-magnon
+optomechanics, where magnon Kerr effect is used. We show that the Kerr effect
+gives rise to a magnon frequency shift and an additional two-magnon effect.
+Both of them can be tuned from positive to negative via tuning the magectic
+field direction, leading to nonreciprocity. By tuning system parameters such as
+magnon frequency detuning or the coefficient of the two-magnon effect,
+bipartite and tripartite entanglements can be nonreciprocally enhanced. By
+further studying the defined bidirectional contrast ratio, we find that
+nonreciprocity in our system can be switch on and off, and can be engineered by
+the bath temperature. Our proposal not only provides a potential path to
+demonstrate nonreciprocal entanglement with the magnon Kerr effect, but also
+opens a direction to engineer and design diverse nonreciprocal devices in
+hybrid cavity-magnon optomechanics with nonlinear effects.",2305.03325v3
+2023-09-08,Programmable Real-Time Magnon Interference in Two Remotely Coupled Magnonic Resonators,"Magnon interference is a signature of coherent magnon interactions for
+coherent information processing. In this work, we demonstrate programmable
+real-time magnon interference, with examples of nearly perfect constructive and
+destructive interference, between two remotely coupled yttrium iron garnet
+spheres mediated by a coplanar superconducting resonator. Exciting one of the
+coupled resonators by injecting single- and double-microwave pulse leads to the
+coherent energy exchange between the remote magnonic resonators and allows us
+to realize a programmable magnon interference that can define an arbitrary
+state of coupled magnon oscillation. The demonstration of time-domain coherent
+control of remotely coupled magnon dynamics offers new avenues for advancing
+coherent information processing with circuit-integrated hybrid magnonic
+networks.",2309.04289v1
+2024-01-19,Hybridized magnonic materials for THz frequency applications,"The capability of magnons to hybridize and strongly couple with diverse
+excitations offers a promising avenue for realizing and controlling emergent
+properties that hold significant potential for applications in devices,
+circuits, and information processing. In this letter, we present recent
+theoretical and experimental developments in magnon-based hybrid systems,
+focusing on the combination of magnon excitation in an antiferromagnet with
+other excitations, namely plasmons in a topological insulator, phonons in a 2D
+AFM, and photons. The existence of THz frequency magnons, plasmons, and phonons
+makes magnon-based hybrid systems particularly appealing for
+high-operating-speed devices. In this context, we explore several directions to
+advance magnon hybrid systems, including strong coupling between a surface
+plasmon and magnon polariton in a TI/AFM bilayer, a giant spin Nernst effect
+induced by magnon phonon coupling in 2D AFMs, and control of magnon-photon
+coupling using spin torque.",2401.11010v2
+2024-03-01,Minority magnons and mode branching in monolayer Fe$_3$GeTe$_2$,"In this letter, we predict the existence of minority magnons in a monolayer
+of Fe$_3$GeTe$_2$ using first principles calculations. Minority magnons
+constitute a new type of collective magnetic excitations which increase the
+magnetic moment rather than lower it, contrary to ordinary (majority) magnons.
+The presence of such quasi-particles is made possible by the nontrivial
+ferromagnetic band structure of Fe$_3$GeTe$_2$ originating from its
+nonequivalent Fe sublattices. The result is a strong peak in the dynamic
+spin-raising susceptibility $\chi^{-+}(\omega)$ in the long wavelength limit,
+which is the hallmark of minority magnon physics. We calculate the
+susceptibility using time-dependent density functional theory and perform a
+detailed mode analysis, which allows us to separate and investigate the
+individual magnon modes as well as the Stoner excitations that constitute the
+many-body spectrum. For minority as well as majority magnons, the analysis
+reveals a plethora of magnetic excitations, which in addition to the standard
+main magnon branches include both satellite, valley and spin-inversion magnons,
+originating from the itinerancy of the ferromagnetic order. The physics
+underlying this analysis is in no way restricted to Fe$_3$GeTe$_2$, and
+minority magnons are expected to be observable in many complex ferromagnetic
+materials.",2403.00525v1
+2019-12-01,Differences in the magnon diffusion length for electrically and thermally driven magnon currents in Y$_3$Fe$_5$O$_{12}$,"Recent demonstration of efficient transport and manipulation of spin
+information by magnon currents have opened exciting prospects for processing
+information in devices. Magnon currents can be driven both electrically and
+thermally, even in magnetic insulators, by applying charge currents in an
+adjacent metal layer. Earlier reports in thin yttrium iron garnet (YIG) films
+suggested that the diffusion length of magnons is independent on the biasing
+method, but different values were obtained in thicker films. Here, we study the
+magnon diffusion length for electrically and thermally driven magnon currents
+in the linear regime in a 2-$\mu$m-thick YIG film as a function of temperature
+and magnetic field. Our results show a decrease of the magnon diffusion length
+with magnetic field for both biasing methods and at all temperatures from 5 to
+300 K, indicating that sub-thermal magnons dominate the long-range transport.
+Moreover, we demonstrate that the value of the magnon diffusion length depends
+on the driving mechanism, suggesting that different non-equilibrium magnon
+distributions are biased for each method. Finally, we demonstrate that the
+magnon diffusion length for thermally driven magnon currents is independent of
+the YIG thickness and material growth conditions, confirming that this quantity
+is an intrinsic parameter of YIG.",1912.00490v2
+2018-01-10,Floquet Weyl Magnons,"In three-dimensional (3D) quantum magnets, magnonic Weyl points (WPs)
+featuring linear band crossing of two non-degenerate magnon branches can emerge
+in certain lattice geometry when time-reversal symmetry is broken
+macroscopically. Unfortunately, there are very limited 3D quantum magnets that
+host magnonic WPs, and they are yet to be observed experimentally because the
+intrinsic perturbative interactions that break time-reversal symmetry
+macroscopically can be very negligible. Here, we present an alternative means
+via photo-irradiation, in which magnonic WPs can emerge in 3D quantum magnets
+without relying on intrinsic perturbative interactions to break time-reversal
+symmetry. By utilizing the magnonic Floquet-Bloch theory, we put forward the
+general theory of magnonic Floquet WPs in 3D quantum magnets. We show that
+periodically driven 3D magnonic Dirac nodal-line (DNL) and 3D magnonic gapped
+trivial insulators can generate 3D magnonic Floquet WPs, which can be tuned by
+the incident circularly-polarized light. We demonstrate the existence of
+magnonic Floquet WPs by combining the study of the magnon dispersions, Berry
+curvatures, and the anomalous thermal Hall effect. The general theoretical
+formalism can be applied to different magnetic insulators, and thus extending
+the concept of magnonic WPs to a broader class of 3D magnetically ordered
+systems.",1801.03499v6
+2023-01-13,Voltage-Controlled Magnon Transistor via Tunning Interfacial Exchange Coupling,"Magnon transistors that can effectively regulate magnon transport by an
+electric field are desired for magnonics which aims to provide a Joule-heating
+free alternative to the conventional electronics owing to the electric
+neutrality of magnons (the key carriers of spin-angular momenta in the
+magnonics). However, also due to their electric neutrality, magnons have no
+access to directly interact with an electric field and it is thus difficult to
+manipulate magnon transport by voltages straightforwardly. Here, we
+demonstrated a gate voltage ($V_{\rm g}$) applied on a nonmagnetic
+metal/magnetic insulator (NM/MI) interface that bended the energy band of the
+MI and then modulated the possibility for conduction electrons in the NM to
+tunnel into the MI can consequently enhance or weaken the spin-magnon
+conversion efficiency at the interface. A voltage-controlled magnon transistor
+based on the magnon-mediated electric current drag (MECD) effect in a
+Pt/Y$_{\rm 3}$Fe$_{\rm 5}$O$_{\rm 12}$ (YIG)/Pt sandwich was then
+experimentally realized with $V_{\rm g}$ modulating the magnitude of the MECD
+signal. The obtained efficiency (the change ratio between the MECD voltage at
+$\pm V_{\rm g}$) reached 10%/(MV/cm) at 300 K. This prototype of magnon
+transistor offers an effective scheme to control magnon transport by a gate
+voltage.",2301.05592v1
+2023-05-14,Cavity magnonics with easy-axis ferromagnet: Critically enhanced magnon squeezing and light-matter interaction,"Generating and probing the magnon squeezing is an important challenge in the
+field of quantum magnonics. In this work, we propose a cavity magnonics setup
+with an easy-axis ferromagnet to address this challenge. To this end, we first
+establish a mechanism for the generation of magnon squeezing in the easy-axis
+ferromagnet and show that the magnon squeezing can be critically enhanced by
+tuning an external magnetic field near the Ising phase transition point. When
+the magnet is coupled to the cavity field, the effective cavity-magnon
+interaction becomes proportional to the magnon squeezing, allowing one to
+enhance the cavity-magnon coupling strength using a static field. We
+demonstrate that the magnon squeezing can be probed by measuring the frequency
+shift of the cavity field. Moreover, a magnonic superradiant phase transition
+can be observed in our setup by tuning the static magnetic field, overcoming
+the challenge that the magnetic interaction between the cavity and the magnet
+is typically too weak to drive the superradiant transition. Our work paves the
+way to develop unique capabilities of cavity magnonics that goes beyond the
+conventional cavity QED physics by harnessing the intrinsic property of a
+magnet.",2305.08119v2
+2023-08-06,Breakdown of Chiral Edge Modes in Topological Magnon Insulators,"Topological magnon insulators (TMI) are ordered magnets supporting chiral
+edge magnon excitations. These edge states are envisioned to serve as
+topologically protected information channels in low-loss magnonic devices. The
+standard description of TMI is based on linear spin-wave theory (LSWT), which
+approximates magnons as free non-interacting particles. However, magnon
+excitations of TMI are genuinely interacting even at zero temperature, calling
+into question descriptions based on LSWT alone. Here we perform a detailed
+non-linear spin-wave analysis to investigate the stability of chiral edge
+magnons. We identify three general breakdown mechanisms: (1) The edge magnon
+couples to itself, generating a finite lifetime that can be large enough to
+lead to a spectral annihilation of the chiral state; (2) The edge magnon
+hybridizes with the extended bulk magnons and, as a consequence, delocalizes
+away from the edge; (3) Due to a bulk-magnon mediated edge-to-edge coupling,
+the chiral magnons at opposite edges hybridize. We argue that, in general,
+these breakdown mechanisms may invalidate predictions based on LSWT and violate
+the notion of topological protection. We discuss strategies how the breakdown
+of chiral edge magnons can be avoided, e.g. via the application of large
+magnetic fields. Our results highlight a challenge for the realization of
+chiral edge states in TMI and in other bosonic topological systems without
+particle number conservation.",2308.03168v1
+2024-02-29,Magnon spectrum of altermagnets: Time-dependent matrix product states vs. linearized Holstein-Primakoff calculations unravelling spontaneous magnon decay,"The energy-momentum dispersion of magnons, viewed as noninteracting and
+infinitely long-lived quasiparticles describing collective low-energy
+excitations of magnetic materials, is often presented as sharp bands obtained
+from the effective quantum spin Hamiltonian, after being simplified via
+linearized Holstein-Primakoff (HP) transformations. However, magnons are prone
+to many-body interactions with other quasiparticles which can lead to their
+spontaneous decay. The magnon-magnon interactions could affect newly classified
+altermagnets. On the other hand, sharp bands of noninteracting chiral magnons
+in RuO2, as the canonical example of altermagnets, have been very recently
+predicted. Here, we employ nonperturbative numerically (quasi)exact quantum
+many-body calculations, via time-dependent matrix product states (TDMPS), to
+obtain magnon spectral function of RuO2. These calculations produce a broadened
+magnon dispersion, which overlaps with linearized HP theory sharp bands only at
+edges/center of the Brillouin zone. Substantially deviating otherwise.
+Artificially making exchange interaction within two sublattices of RuO2 closer
+in value forces these two spectra to overlap, thereby explaining the origin of
+the failure of linearized HP theory. Such features translate into the
+difference between their respective density of states, which we also compute
+and which could be tested by Raman scattering experiments. Finally, we employ
+popular Landau-Lifshitz-Gilbert (LLG) equation-based classical atomistic spin
+dynamics (ASD) simulations to obtain dynamical structure factor and extract
+magnon spectrum from it at finite temperature. Despite including magnon-magnon
+interactions via nonlinearity of LLG equation, ASD simulations cannot fully
+match the TDMPS-computed magnon spectrum due to nonclassical effects harbored
+by altermagnets.",2402.19433v1
+1999-05-24,Soliton-Magnon Scattering in Two-Dimensional Isotropic Ferromagnets,"It is studied the scattering of magnons by the 2d topological
+Belavin-Polyakov soliton in isotropic ferromagnet. Analytical solutions of the
+scattering problem are constructed: (i) exactly for any magnon wave vectors for
+the partial wave with the azimuthal number m=1 (translational mode), and (ii)
+in the long- and short-wave limits for the rest modes. The magnon mode
+frequencies are found for the finite size magnets. An effective equation of the
+soliton motion is constructed. The magnon density of states, connected with the
+soliton-magnon interaction, is found in a long-wave approximation.",9905348v1
+2006-08-07,On the Scattering of Magnon Boundstates,"We study the scattering of magnon boundstates in the spin-chain description
+of planar N=4 SUSY Yang-Mills. Starting from the conjectured exact S-matrix for
+magnons in the SU(2) sector, we calculate the corresponding S-matrix for
+boundstates with an arbitrary number of constituent magnons. The resulting
+expression has an interesting analytic structure with both simple and double
+poles. We also calculate the semiclassical S-matrix for the scattering of the
+corresponding excitations on the string worldsheet known as Dyonic Giant
+Magnons. We find precise agreement with the magnon boundstate S-matrix in the
+limit of large 't Hooft coupling.",0608047v1
+2007-12-25,One-magnon (electromagnon) light scattering in BiFeO3 single crystals,"We observed Raman scattering from magnon in frequency range from 10 to 65
+cm-1 in BiFeO3 single crystals at cryogenic temperatures; the temperature
+dependence of the magnon frequency at 18.2 cm-1 approximates an S=5/2 Brillouin
+function up to the temperature (280 K) at which the magnon becomes overdamped.
+The diverging cross-section and the frequency-shift at 140K and 200 K implies a
+magnon-reorientation transition as in orthoferrites. Magnons in polar materials
+such as BiFeO3 are often termed electromagnons meaning that they possess an
+electric dipole moment due to magnetoelectric coupling.",0712.4040v2
+2008-09-30,Giant Magnon and Spike Solutions with Two Spins in AdS4xCP3,"In the string theory in AdS_4 \times CP^3 we construct the giant magnon and
+spike solutions with two spins in two kinds of subspaces of R_t \times CP^3 and
+derive the dispersion relations for them. For the single giant magnon solution
+in one subspace we show that its dispersion relation is associated with that of
+the big one-spin giant magnon solution in the RP^2 subspace. For the single
+giant magnon solution in the other complementary subspace its dispersion
+relation is similar to that of the one-spin giant magnon solution living in the
+S^2 subspace but has one additional spin dependence.",0809.5106v1
+2008-10-29,Finite size giant magnons and interactions,"Magnon interactions give important contributions to the wrapping interactions
+of the N=4 spin-chain. Similar effects are expected for the finite size
+corrections to the giant magnon energy in AdS_5 x S^5. In this paper I review
+the finite gap description of giant magnons and the leading order calculation
+of the finite size corrections to the giant magnon dispersion relation for
+multi-magnon states.",0810.5236v2
+2010-02-19,Strong Three-magnon Scattering in Cuprates by Resonant X-rays,"We show that Resonant Inelastic X-ray scattering (RIXS) is sensitive to
+three-magnon excitations in cuprates. Even if it requires three electrons to
+simultaneously flip their spin, the RIXS tri-magnon scattering amplitude is not
+small. At the Cu $L$-edge its intensity is generally larger than the bi-magnon
+one and at low transferred momentum even larger than the single-magnon
+intensity. At the copper $M$-edge the situation is yet more extreme: in this
+case three-magnon scattering is dominating over all other magnetic channels.",1002.3773v1
+2011-01-11,Magnon Pumping by a Time-Dependent Transverse Magnetic Field in Ferromagnetic Insulators,"The magnon pumping effect in ferromagnetic insulators under an external
+time-dependent transverse magnetic field is theoretically studied. Generation
+of a magnon current is discussed by calculating the magnon source term in the
+spin continuity equation. This term represents the non-conservation of magnons
+arising from an applied transverse magnetic field. The magnon source term has a
+resonance structure as a function of the angular frequency of the transverse
+field, and this fact is useful to enhance the pumping effect.",1101.2137v2
+2012-02-14,Magnon qubit on double Bose-Einstein condensate,"We have proposed a magnon qubit based on coupled configuration of
+Bose-Einstein condensates (BEC) in two ferromagnetic samples placed closely to
+each other. We have evaluated the magnon BEC qubit realization in the double
+BEC scheme where we found a quantum synchronism condition providing an
+effective Hamiltonian of magnon qubit. It has the form of well-known
+superconducting Josephson qubit. The possibilities for coherent magnon BEC
+qubit rotation are analyzed. Implementations of the magnon BEC qubit are
+considered for small samples and thin ferromagnetic films. Advantages of the
+proposed macroscopic qubit realization are discussed.",1202.3057v1
+2015-02-14,Energy shift of magnons in a ferromagnetic spinor-dipolar Bose-Einstein condensate,"Motivated by the recent experiment performed by the Berkeley group [G. E.
+Marti {\it et al.}, Phys. Rev. Lett. {\bf 113}, 155302 (2014)], we consider the
+dynamics of magnons in a spin-1 spinor-dipolar Bose-Einstein condensate, using
+mean-field theory. We show that the effective mass of a magnon is increased by
+the magnetic dipole-dipole interaction, as observed in the experiment. The
+magnon mass is also decreased by changing the direction of the magnetic field.
+The increase and decrease in the magnon mass manifest themselves in the
+acceleration of the magnons.",1502.04161v2
+2015-04-28,Roton minimum as fingerprint of magnon-Higgs scattering in ordered quantum antiferromagnets,"A quantitative description of magnons in long-range ordered quantum
+antiferromagnets is presented which is consistent from low to high energies. It
+is illustrated for the generic $S=1/2$ Heisenberg model on the square lattice.
+The approach is based on a continuous similarity transformation in momentum
+space using the scaling dimension as truncation criterion. Evidence is found
+for significant magnon-magnon attraction inducing a Higgs resonance. The
+high-energy roton minimum in the magnon dispersion appears to be induced by
+strong magnon-Higgs scattering.",1504.07371v2
+2008-07-01,Finite size Giant Magnons in the string dual of N=6 superconformal Chern-Simons theory,"We find the exact solution for a finite size Giant Magnon in the $SU(2)\times
+SU(2)$ sector of the string dual of the $\mathcal{N}=6$ superconformal
+Chern-Simons theory recently constructed by Aharony, Bergman, Jafferis and
+Maldacena. The finite size Giant Magnon solution consists of two magnons, one
+in each $SU(2)$. In the infinite size limit this solution corresponds to the
+Giant Magnon solution of arXiv:0806.4959. The magnon dispersion relation
+exhibits finite-size exponential corrections with respect to the infinite size
+limit solution.",0807.0205v2
+2017-06-24,Magnon cotunneling through a quantum dot,"I consider a single-level quantum dot coupled to two reservoirs of spin waves
+(magnons). Such systems have been studied recently from the point of view of
+possible coupling between electronic and magnonic spin currents. However,
+usually weakly coupled systems were investigated. When coupling between the dot
+and reservoirs is not weak, then higher order processes play a role and have to
+be included. Here I consider cotunneling of magnons through a spin-occupied
+quantum dot, which can be understood as a magnon (spin) leakage current in
+analogy to leakage currents in charge-based electronics. Particular emphasis
+has been put on investigating the effect of magnetic field and temperature
+difference between the magnonic reservoirs.",1706.07914v1
+2015-08-21,Quantum magnonics: magnon meets superconducting qubit,"The techniques of microwave quantum optics are applied to collective spin
+excitations in a macroscopic sphere of ferromagnetic insulator. We demonstrate,
+in the single-magnon limit, strong coupling between a magnetostatic mode in the
+sphere and a microwave cavity mode. Moreover, we introduce a superconducting
+qubit in the cavity and couple the qubit with the magnon excitation via the
+virtual photon excitation. We observe the magnon-vacuum-induced Rabi splitting.
+The hybrid quantum system enables generation and characterization of
+non-classical quantum states of magnons.",1508.05290v1
+2015-08-27,Guided magnonic Michelson interferometer,"Magnonics is an emerging field with potential applications in classical and
+quantum information processing. Freely propagating magnons in two-dimensional
+media suffer from dispersion, which limits their effective range and fidelity.
+We show the design of controllable magnonic circuitry, that utilise surface
+current carrying wires to create magnonic waveguides. We also show the design
+of a magnonic directional coupler and controllable Michelson interferometer to
+demonstrate its utility for information processing tasks.",1508.06722v2
+2020-09-14,Antiferromagnetic Dispersion Relations and Nature of Magnon Pressure,"We derive higher-order corrections in the magnon dispersion relations for
+two- and three-dimensional antiferromagnets exposed to magnetic and staggered
+fields that are mutually aligned. ""Dressing"" the magnons is the prerequisite to
+separate the low-temperature representation of the pressure into a piece due to
+noninteracting magnons and a piece that corresponds to the magnon-magnon
+interaction. Both in two and three spatial dimensions, the interaction in the
+pressure turns out to be attractive. While concrete figures refer to the
+spin-$\frac{1}{2}$ square-lattice and the spin-$\frac{1}{2}$ simple cubic
+lattice antiferromagnet, our results are valid for arbitrary bipartite
+geometry.",2009.06584v1
+2015-12-15,Magnon Dirac materials,"We demonstrate how a Dirac-like magnon spectrum is generated for localized
+magnetic moments forming a two-dimensional honeycomb lattice. The Dirac
+crossing point is proven to be robust against magnon-magnon interactions, as
+these only shift the spectrum. Local defects induce impurity resonances near
+the Dirac point, as well as magnon Friedel oscillations. The energy of the
+Dirac point is controlled by the exchange coupling, and thus a two-dimensional
+array of magnetic dots is an experimentally feasible realization of Dirac
+magnons with tunable dispersion.",1512.04902v2
+2020-08-31,Magnon-squeezing as a niche of quantum magnonics,"The spin excitations of ordered magnets - magnons - mediate transport in
+magnetic insulators. Their bosonic nature makes them qualitatively distinct
+from electrons. These features include quantum properties traditionally
+realized with photons. In this perspective, we present an intuitive discussion
+of one such phenomenon. Equilibrium magnon-squeezing manifests unique
+advantageous with magnons as compared to photons, including properties such as
+entanglement. Building upon the recent progress in the fields of spintronics
+and quantum optics, we outline challenges and opportunities in this emerging
+field of quantum magnonics.",2008.13536v1
+2022-07-26,Rectification of the spin Seebeck current in noncollinear antiferromagnets,"In the absence of an external magnetic field and a spin-polarized charge
+current, an antiferromagnetic system supports two degenerate magnon modes. An
+applied thermal bias activates the magnetic dynamics, leading to a magnon flow
+from the hot to the cold edge (magnonic spin Seebeck current). Both degenerate
+bands contribute to the magnon current but the orientations of the magnetic
+moments underlying the magnons are opposite in different bands. Therefore,
+while the magnon current is nonzero, the net spin current is zero.",2207.12890v1
+2022-08-30,Breaking down the magnonic Wiedemann-Franz law in the hydrodynamic regime,"Recent experiments have shown an indication of a hydrodynamic magnon behavior
+in ultrapure ferromagnetic insulators; however, its direct observation is still
+lacking. Here, we derive a set of coupled hydrodynamic equations and study the
+thermal and spin conductivities for such a magnon fluid. We reveal the drastic
+breakdown of the magnonic Wiedemann-Franz law as a hallmark of the
+hydrodynamics regime, which will become key evidence for the experimental
+realization of an emergent hydrodynamic magnon behavior. Therefore, our results
+pave the way towards the direct observation of magnon fluids.",2208.14458v3
+2023-05-11,Correlation-enhanced interaction of a Bose-Einstein condensate with parametric magnon pairs and virtual magnons,"Nonlinear interactions are crucial in science and engineering. Here, we
+investigate wave interactions in a highly nonlinear magnetic system driven by
+parametric pumping leading to Bose--Einstein condensation of spin-wave quanta
+-- magnons. Using Brillouin light scattering spectroscopy in yttrium-iron
+garnet films, we found and identified a set of nonlinear processes resulting in
+off-resonant spin-wave excitations -- virtual magnons. In particular, we
+discovered a dynamically-strong, correlation-enhanced four-wave interaction
+process of the magnon condensate with pairs of parametric magnons having
+opposite wavevectors and fully correlated phases.",2305.06896v1
+2023-06-08,Tunable magnon topology in monolayer CrI$_\mathbf{3}$ under external stimuli,"Two-dimensional (2D) honeycomb ferromagnets, such as monolayer
+chromium-trihalides, are predicted to behave as topological magnon insulators -
+characterized by an insulating bulk and topologically protected edge states,
+giving rise to a thermal magnon Hall effect. Here we report the behavior of the
+topological magnons in monolayer CrI$_3$ under external stimuli, including
+biaxial and uniaxial strain, electric gating, as well as in-plane and
+out-of-plane magnetic field, revealing that one can thereby tailor the magnetic
+states as well as the size and the topology of the magnonic bandgap. These
+findings broaden the perspective of using 2D magnetic materials to design
+topological magnonic devices.",2306.05104v1
+2023-08-11,Achieving Strong Magnon Blockade through Magnon Squeezing in a Cavity Magnetomechanical System,"We propose a scheme to achieve magnon (photon) blockade by using magnon
+squeezing within a cavity magnomechanical system under weak pump driving. Under
+ideal conditions, we observe a substantial magnon blockade effect, as well as
+simultaneous photon blockade. Moreover, both numerical and analytical results
+match perfectly, providing robust evidence of consistency. In addition to
+calculating optimal parametric gain and detuning values, we can improve the
+second-order correlation function. The proposed scheme will be a pioneering
+approach towards magnon (photon) blockade in experimental cavity
+magnomechanical systems.",2308.06367v1
+2023-12-19,Electrical Activity of Topological Chiral Edge Magnons,"Topological magnon insulators support chiral edge excitations, whose lack of
+electric charge makes them notoriously difficult to detect experimentally. We
+show that relativistic magnetoelectric coupling universally renders chiral edge
+magnons electrically active, thereby facilitating electrical probes of magnon
+topology. Considering a two-dimensional out-of-plane magnetized topological
+magnon insulator, we predict a fluctuation-activated electric polarization
+perpendicular to the sample edges. Furthermore, the chiral topological
+electromagnons give rise to a unique in-gap signal in electrical absorption
+experiments. These results suggest THz spectroscopy as a promising probe for
+topological magnons.",2312.12316v1
+2014-08-21,Magnonic band structure of domain wall magnonic crystals,"Magnonic crystals are prototype magnetic metamaterials designed for the
+control of spin wave propagation. Conventional magnonic crystals are composed
+of single domain elements. If magnetization textures, such as domain walls,
+vortices and skyrmions, are included in the building blocks of magnonic
+crystals, additional degrees of freedom over the control of the magnonic band
+structure can be achieved. We theoretically investigate the influence of domain
+walls on the spin wave propagation and the corresponding magnonic band
+structure. It is found that the rotation of magnetization inside a domain wall
+introduces a geometric vector potential for the spin wave excitation. The
+corresponding Berry phase has quantized value $4 n_w \pi$, where $n_w$ is the
+winding number of the domain wall. Due to the topological vector potential, the
+magnonic band structure of magnonic crystals with domain walls as comprising
+elements differs significantly from an identical magnonic crystal composed of
+only magnetic domains. This difference can be utilized to realize dynamic
+reconfiguration of magnonic band structure by a sole nucleation or annihilation
+of domain walls in magnonic crystals.",1408.4889v3
+2018-10-02,The Discrete Noise of Magnons,"Magnonics is a rapidly developing subfield of spintronics, which deals with
+devices and circuits that utilize spin currents carried by magnons - quanta of
+spin waves. Magnon current, i.e. spin waves, can be used for information
+processing, sensing, and other applications. A possibility of using the
+amplitude and phase of magnons for sending signals via electrical insulators
+creates conditions for avoiding Ohmic losses, and achieving ultra-low power
+dissipation. Most of the envisioned magnonic logic devices are based on spin
+wave interference, where the minimum energy per operation is limited by the
+noise level. The sensitivity and selectivity of magnonic sensors is also
+limited by the low frequency noise. However, the fundamental question ""do
+magnons make noise?"" has not been answered yet. It is not known how noisy
+magnonic devices are compared to their electronic counterparts. Here we show
+that the low-frequency noise of magnonic devices is dominated by the random
+telegraph signal noise rather than 1/f noise - a striking contrast to
+electronic devices (f is a frequency). We found that the noise level of surface
+magnons depends strongly on the power level, increasing sharply at the on-set
+of nonlinear dissipation. The presence of the random telegraph signal noise
+indicates that the current fluctuations involve random discrete macro events.
+We anticipate that our results will help in developing the next generation of
+magnonic devices for information processing and sensing.",1810.01500v1
+2021-12-07,Influence of low-energy magnons on magnon Hanle experiments in easy-plane antiferromagnets,"Antiferromagnetic materials host pairs of spin-up and spin-down magnons which
+can be described in terms of a magnonic pseudospin. The close analogy between
+this magnonic pseudospin systems and that of electronic charge carriers led to
+the prediction of fascinating phenomena in antiferromagnets. Recently, the
+associated dynamics of antiferromagnetic pseudospin has been experimentally
+demonstrated and, in particular, the first observation of the magnon Hanle
+effect has been reported. We here expand the magnonic spin transport
+description by explicitly taking into account contributions of finite-spin
+low-energy magnons. In our experiments we realize the spin injection and
+detection process by two Platinum strips and investigate the influence of the
+Pt-strips on the generation and diffusive transport of magnons in films of the
+antiferromagnetic insulator hematite. For both a 15 nm and a 100 nm thick film,
+we find a distinct signal caused by the magnon Hanle effect. However, the
+magnonic spin signal exhibits clear differences in both films. In contrast to
+the thin film, for the thicker one, we observe an oscillating behavior in the
+high magnetic field range as well as an additional offset signal in the low
+magnetic field regime. We attribute this offset signal to the presence of
+finite-spin low-energy magnons.",2112.03820v1
+2022-09-01,Magnon dynamics in parity-time-symmetric dipolarly coupled waveguides and magnonic crystals,"We consider the magnonic properties of two dipolarly coupled magnetic
+stripes, both deposited on a normal conductive substrate with strong spin-orbit
+coupling. A charge current in the substrate acts on the adjacent magnets with
+spin-orbit torques, which result in magnonic damping or antidamping of the spin
+waves, and hence a gain-loss coupling of the two magnetic stripes. The whole
+setup is demonstrated to exhibit features typical for parity-time (PT)
+symmetric systems. Phenomena are demonstrated that can be functionalized in
+magnonic devices, including reconfigurable magnonic diodes and logic devices.
+Alternative stripes designs and PT-symmetric, periodic, coupled magnonic
+textures are studied. Analytical and full numerical analysis identify the
+conditions for the appearance of exceptional points (EPs), where magnonic gain
+and loss are balanced and evidence nonreciprocal magnon propagation and
+enhanced magnon excitation around EPs. Furthermore, the dipolar coupling is
+shown to bring in a wave vector-dependent PT-symmetric behavior. Proposing and
+simulating a PT-symmetric magnonic crystal, we show how EPs and hence
+associated phenomena can be steered to a particular wave vector in a gaped
+spectrum via material design. The phenomena offer additional tools for
+magnonic-based communication and computational devices.",2209.00180v1
+2022-09-05,Nonlocal detection of interlayer three-magnon coupling,"A leading nonlinear effect in magnonics is the interaction that splits a
+high-frequency magnon into two low-frequency ones with conserved linear
+momentum. Here, we report experimental observation of nonlocal three-magnon
+scattering between spatially separated magnetic systems, viz. a CoFeB nanowire
+and an yttrium iron garnet (YIG) thin film. Above a certain threshold power of
+an applied microwave field, a CoFeB Kittel magnon splits into a pair of
+counter-propagating YIG magnons that induce voltage signals in Pt electrodes on
+each side, in excellent agreement with model calculations based on the
+interlayer dipolar interaction. The excited YIG magnon pairs reside mainly in
+the first excited (n=1) perpdendicular standing spin-wave mode. With increasing
+power, the n=1 magnons successively scatter into nodeless (n=0) magnons through
+a four-magnon process. Our results help to assess non-local scattering
+processes in magnonic circuits that may enable quantum entanglement between
+distant magnons for quantum information applications.",2209.01875v1
+2023-03-24,Magnon blockade in magnon-qubit systems,"A hybrid system established by the direct interaction between a magnon mode
+and a superconducting transmon qubit is used to realize a high-degree blockade
+for magnon. It is a fundamental way toward quantum manipulation at the level of
+a single magnon and preparation of single magnon sources. Through weakly
+driving the magnon and probing the qubit, our magnon-blockade proposal can be
+optimized when the transversal coupling strength between the magnon and qubit
+is equivalent to the detuning of the qubit and the probing field or that of the
+magnon and the driving field. Under this condition, the equal-time second-order
+correlation function $g^{(2)}(0)$ can be analytically minimized when the
+probing intensity is about three times the driving intensity. Moreover, the
+magnon blockade could be further enhanced by proper driving intensity and
+system decay rate, whose magnitudes outrange the current systems of cavity QED
+and cavity optomechanics. In particular, the correlation function achieves
+$g^{(2)}(0)\sim10^{-7}$, about two orders lower than that for the photon
+blockade in cavity optomechanics. Also, we discuss the effects on $g^{(2)}(0)$
+from thermal noise and the extra longitudinal interaction between the magnon
+and qubit. Our optimized conditions for blockade are found to persist in these
+nonideal situations.",2303.13823v2
+2023-04-21,Magnon squeezing by two-tone driving of a qubit in cavity-magnon-qubit systems,"We propose a scheme for preparing magnon squeezed states in a hybrid
+cavity-magnon-qubit system. The system consists of a microwave cavity that
+simultaneously couples to a magnon mode of a macroscopic yttrium-iron-garnet
+(YIG) sphere via the magnetic-dipole interaction and to a transmon-type
+superconducting qubit via the electric-dipole interaction. By far detuning from
+the magnon-qubit system, the microwave cavity is adiabatically eliminated. The
+magnon mode and the qubit then get effectively coupled via the mediation of
+virtual photons of the microwave cavity. We show that by driving the qubit with
+two microwave fields and by appropriately choosing the drive frequencies and
+strengths, magnonic parametric amplification can be realized, which leads to
+magnon quadrature squeezing with the noise below vacuum fluctuation. We provide
+optimal conditions for achieving magnon squeezing, and moderate squeezing can
+be obtained using currently available parameters. The generated squeezed states
+are of a magnon mode involving more than $10^{18}$ spins and thus macroscopic
+quantum states. The work may find promising applications in quantum information
+processing and high-precision measurements based on magnons and in the study of
+macroscopic quantum states.",2304.10760v4
+2024-03-20,All-magnonic repeater based on bistability,"Bistability, a universal phenomenon found in diverse fields such as biology,
+chemistry, and physics, describes a scenario in which a system has two stable
+equilibrium states and resets to one of the two states. The ability to switch
+between these two states is the basis for a wide range of applications,
+particularly in memory and logic operations. Here, we present a universal
+approach to achieve bistable switching in magnonics, the field processing data
+using spin waves. As an exemplary application, we use magnonic bistability to
+experimentally demonstrate the still missing magnonic repeater. A pronounced
+bistable window is observed in a 1um wide magnonic conduit under an external rf
+drive characterized by two magnonic stable states defined as low and high
+spin-wave amplitudes. The switching between these two states is realized by
+another propagating spin wave sent into the rf driven region. This magnonic
+bistable switching is used to design the magnonic repeater, which receives the
+original decayed and distorted spin wave and regenerates a new spin wave with
+amplified amplitude and normalized phase. Our magnonic repeater is proposed to
+be installed at the inputs of each magnonic logic gate to overcome the
+spin-wave amplitude degradation and phase distortion during previous
+propagation and achieve integrated magnonic circuits or magnonic neuromorphic
+networks.",2403.13276v1
+1999-04-17,The sublattice magnetizations of the spin-s quantum Heisenberg antiferromagnets,"We study the spin-$s$ quantum Heisenberg antiferromagnetic models in a magnon
+theory free of any unphysical magnon state. Because the unphysical magnon
+states are completely removed in the magnon Hamiltonians and during the
+approximation process, we derive spin-s (s>1/2) reliable Neel temperature $T_N$
+and reasonable sublattice magnetization unified for $T\leq T_N$.",9904243v1
+1999-07-27,The Three-Magnon Contribution to the Spin Correlation Function in Integer-Spin Antiferromagnetic Chains,"The exact form factor for the O(3) non-linear sigma model is used to predict
+the three-magnon contribution to the spin correlation function, S(q,w), near
+wavevector q=pi in an integer spin, one-dimensional antiferromagnet. The
+three-magnon contribution is extrememly broad and extremely weak; the
+integrated intensity is <2% of the single-magnon contribution.",9907431v1
+2008-03-02,Raman scattering in a Heisenberg {\boldmath $S=1/2$} antiferromagnet on the triangular lattice,"We investigate two-magnon Raman scattering from the $S=1/2$ Heisenberg
+antiferromagnet on the triangular lattice, considering both the effect of
+renormalization of the one-magnon spectrum by 1/S corrections and final-state
+magnon-magnon interactions. The bare Raman intensity displays two peaks related
+to one-magnon van-Hove singularities. We find that 1/S self-energy corrections
+to the one-magnon spectrum strongly modify this intensity profile. The central
+Raman-peak is significantly enhanced due to plateaus in the magnon dispersion,
+the high frequency peak is suppressed due to magnon damping, and the overall
+spectral support narrows considerably. Additionally we investigate final-state
+interactions by solving the Bethe-Salpeter equation to $O(1/S)$. In contrast to
+collinear antiferromagnets, the non-collinear nature of the magnetic ground
+state leads to an irreducible magnon scattering which is retarded and
+non-separable already to lowest order. We show that final-state interactions
+lead to a rather broad Raman-continuum centered around approximately twice the
+'roton'-energy. We also discuss the dependence on the scattering geometry.",0803.0130v1
+2015-02-27,Stimulated Thermalization of a Parametrically Driven Magnon Gas as a Prerequisite for Bose-Einstein Magnon Condensation,"Thermalization of a parametrically driven magnon gas leading to the formation
+of a Bose-Einstein condensate at the bottom of a spin-wave spectrum was studied
+by time- and wavevector-resolved Brillouin light scattering spectroscopy. It
+has been found that the condensation is preceded by the conversion of initially
+pumped magnons into a second group of frequency degenerated magnons, which
+appear due to parametrically stimulated scattering of the initial magnons to a
+short-wavelength spectral region. In contrast to the first magnon group, which
+wavevectors are orthogonal to the wavevectors of the magnons at the lowest
+energy states, the secondary magnons can effectively scatter to the bottom of
+the spectrum and condense there.",1502.07836v1
+2016-01-08,Microscopic origin of subthermal magnons and the spin Seebeck effect,"Recent experimental evidence points to low-energy magnons as the primary
+contributors to the spin Seebeck effect. This spectral dependence is puzzling
+since it is not observed on other thermocurrents in the same material. Here, we
+argue that the physical origin of this behavior is the magnon-magnon scattering
+mediated by phonons, in a process which conserves the number of magnons. To
+assess the importance and features of this kind of scattering, we derive the
+effective magnon-phonon interaction from a microscopic model, including band
+energy, a screened electron-electron interaction and the electron-phonon
+interaction. Unlike higher order magnon-only scattering, we find that the
+coupling with phonons induce a scattering which is very small for low-energy
+(or subthermal) magnons but increases sharply above a certain energy --
+rendering magnons above this energy poor spin-current transporters.",1601.02041v2
+2017-02-20,Temperature Dependence of Magnetic Excitations: Terahertz Magnons above the Curie Temperature,"When an ordered spin system of a given dimensionality undergoes a second
+order phase transition the dependence of the order parameter i.e. magnetization
+on temperature can be well-described by thermal excitations of elementary
+collective spin excitations (magnons). However, the behavior of magnons
+themselves, as a function of temperature and across the transition temperature
+TC, is an unknown issue. Utilizing spin-polarized high resolution electron
+energy loss spectroscopy we monitor the high-energy (terahertz) magnons,
+excited in an ultrathin ferromagnet, as a function of temperature. We show that
+the magnons' energy and lifetime decrease with temperature. The
+temperature-induced renormalization of the magnons' energy and lifetime depends
+on the wave vector. We provide quantitative results on the temperature-induced
+damping and discuss the possible mechanism e.g., multi-magnon scattering. A
+careful investigation of physical quantities determining the magnons'
+propagation indicates that terahertz magnons sustain their propagating
+character even at temperatures far above TC.",1702.06104v1
+2017-02-28,Linking Magnon-Cavity Strong Coupling to Magnon-Polaritons through Effective Permeability,"Strong coupling in cavity-magnon systems has shown great potential for use in
+spintronics and information processing technologies due to the low damping
+rates and long coherence times. Although such systems are conceptually similar
+to those coupled by magnon-polaritons (MPs), the link between magnon-cavity
+coupling and MPs has not been explicitly defined. In this work we establish
+such a connection by studying the frequency-wavevector dispersion of a strongly
+coupled magnon-cavity system, using a height-adjustable microwave cavity, and
+by modelling the observed behaviour through the system's effective
+permeability. A polariton gap between the upper and lower coupled modes of the
+magnon-cavity system is defined, and is seen to be dependent on the system's
+effective filling factor. This gap is equal to the MP polariton gap in the
+limit where filling factor = 1, corresponding to the removal of the microwave
+cavity. Thus, our work clarifies the connection between magnon-cavity and MP
+coupling, improving our understanding of magnon-photon interactions in coupled
+systems.",1703.00074v1
+2010-05-14,Finite-Size Dyonic Giant Magnons in TsT-transformed $AdS_5\times S^5$,"We investigate dyonic giant magnons propagating on $\gamma$-deformed
+$AdS_5\times S^5$ by Neumann-Rosochatius reduction method with a twisted
+boundary condition. We compute finite-size effect of the dispersion relations
+of dyonic giant magnons which generalizes the previously known case of the
+giant magnons with one angular momentum found by Bykov and Frolov.",1005.2508v1
+2017-01-24,Pumping of magnons in a Dzyaloshinskii-Moriya ferromagnet,"We formulate a microscopic linear response theory of nonequilibrium magnonic
+torques and magnon pumping applicable to multiple-magnonic-band uniform
+ferromagnets with Dzyaloshinskii-Moriya interactions. From the linear response
+theory, we identify the extrinsic and intrinsic contributions where the latter
+is expressed via the Berry curvature of magnonic bands. We observe that in the
+presence of a time-dependent magnetization Dzyaloshinskii-Moriya interactions
+can act as fictitious electric fields acting on magnons. We study various
+current responses to this fictitious field and analyze the role of Berry
+curvature. After identifying the magnon-mediated contribution to the
+equilibrium Dzyaloshinskii-Moriya interaction, we also establish the Onsager
+reciprocity between the magnon-mediated torques and heat pumping. We apply our
+theory to the magnonic heat pumping and torque responses in honeycomb and
+kagome lattice ferromagnets.",1701.06990v3
+2017-01-31,Lateral transport properties of thermally excited magnons in yttrium iron garnet films,"Spin information carried by magnons is attractive for computing technology
+and the development of magnon-based computing circuits is of great interest.
+However, magnon transport in insulators has been challenging, different from
+the clear physical picture for spin transport in conductors. Here we
+investigate the lateral transport properties of thermally excited magnons in
+yttrium iron garnet (YIG), a model magnetic insulator. Polarity reversals of
+detected spins in non-local geometry devices have been experimentally observed
+and are strongly dependent on temperature, YIG film thickness, and
+injector-detector separation distance. A competing two-channel transport model
+for thermally excited magnons is proposed, which is qualitatively consistent
+with the spin signal behavior. In addition to the fundamental significance for
+thermal magnon transport, our work furthers the development of magnonics by
+creating an easily accessible magnon source with controllable transport",1701.08932v1
+2018-05-23,Renormalization of spin excitations in hexagonal HoMnO3 by magnon-phonon coupling,"Hexagonal HoMnO3, a two-dimensional Heisenberg antiferromagnet, has been
+studied via inelastic neutron scattering. A simple Heisenberg model with a
+single-ion anisotropy describes most features of the spin-wave dispersion
+curves. However, there is shown to be a renormalization of the magnon energies
+located at around 11 meV. Since both the magnon-magnon interaction and
+magnon-phonon coupling can affect the renormalization in a noncollinear magnet,
+we have accounted for both of these couplings by using a Heisenberg XXZ model
+with 1=S expansions [1] and the Einstein site phonon model [13], respectively.
+This quantitative analysis leads to the conclusion that the renormalization
+effect primarily originates from the magnon-phonon coupling, while the
+spontaneous magnon decay due to the magnon-magnon interaction is suppressed by
+strong two-ion anisotropy.",1805.08919v1
+2014-06-26,Josephson and Persistent Spin Currents in Bose-Einstein Condensates of Magnons,"Using the Aharonov-Casher (A-C) phase, we present a microscopic theory of the
+Josephson and persistent spin currents in quasi-equilibrium Bose-Einstein
+condensates (BECs) of magnons in ferromagnetic insulators. Starting from a
+microscopic spin model that we map onto a Gross-Pitaevskii Hamiltonian, we
+derive a two-state model for the Josephson junction between the weakly coupled
+magnon-BECs. We then show how to obtain the alternating-current (ac) Josephson
+effect with magnons as well as macroscopic quantum self-trapping in a
+magnon-BEC. We next propose how to control the direct-current (dc) Josephson
+effect electrically using the A-C phase, which is the geometric phase acquired
+by magnons moving in an electric field. Finally, we introduce a magnon-BEC ring
+and show that persistent magnon-BEC currents flow due to the A-C phase.
+Focusing on the feature that the persistent magnon-BEC current is a steady flow
+of magnetic dipoles that produces an electric field, we propose a method to
+directly measure it experimentally.",1406.7004v2
+2020-12-14,Effect of magnon decays on parametrically pumped magnons,"We investigate the influence of magnon decays on the non-equilibrium dynamics
+of parametrically excited magnons in the magnetic insulator yttrium-iron garnet
+(YIG). Our investigations are motivated by a recent experiment by Noack et al.
+[Phys. Status Solidi B 256, 1900121 (2019)] where an enhancement of the spin
+pumping effect in YIG was observed near the magnetic field strength where
+magnon decays via confluence of magnons becomes kinematically possible. To
+explain the experimental findings, we have derived and solved kinetic equations
+for the non-equilibrium magnon distribution. The effect of magnon decays is
+taken into account microscopically via collision integrals derived from
+interaction vertices involving three powers of magnon operators. Our results
+agree quantitatively with the experimental data.",2012.07870v2
+2019-02-13,Magnon transport in quasi-two-dimensional van der Waals antiferromagnets,"The recent emergence of 2D van der Waals magnets down to atomic layer
+thickness provides an exciting platform for exploring quantum magnetism and
+spintronics applications. The van der Waals nature stabilizes the long-range
+ferromagnetic order as a result of magnetic anisotropy. Furthermore, giant
+tunneling magnetoresistance and electrical control of magnetism have been
+reported. However, the potential of 2D van der Waals magnets for magnonics,
+magnon-based spintronics, has not been explored yet. Here, we report the
+experimental observation of long-distance magnon transport in
+quasi-twodimensional van der Waals antiferromagnet MnPS3, which demonstrates
+the 2D magnets as promising material candidates for magnonics. As the 2D MnPS3
+thickness decreases, a shorter magnon diffusion length is observed, which could
+be attributed to the surface-impurity-induced magnon scattering. Our results
+could pave the way for exploring quantum magnonics phenomena and designing
+future magnonics devices based on 2D van der Waals magnets.",1902.04719v1
+2019-03-01,Entangling two magnon modes via magnetostrictive interaction,"We present a scheme to entangle two magnon modes in a cavity magnomechanical
+system. The two magnon modes are embodied by collective motions of a large
+number of spins in two macroscopic ferrimagnets, and couple to a single
+microwave cavity mode via magnetic dipole interaction. We show that by
+activating the nonlinear magnetostrictive interaction in one ferrimagnet,
+realized by driving the magnon mode with a strong red-detuned microwave field,
+the two magnon modes can be prepared in an entangled state. The entanglement is
+achieved by exploiting the nonlinear magnon-phonon coupling and the linear
+magnon-cavity coupling, and is in the steady state and robust against
+temperature. The entangled magnon modes in two massive ferrimagnets represent
+genuinely macroscopic quantum states, and may find applications in the study of
+macroscopic quantum mechanics and quantum information processing based on
+magnonics.",1903.00221v2
+2017-10-31,Magnonic triply-degenerate nodal points,"We generalize the concept of triply-degenerate nodal points to non-collinear
+antiferromagnets. Here, we introduce this concept to insulating quantum
+antiferromagnets on the decorated honeycomb lattice, with spin-$1$ bosonic
+quasiparticle excitations known as magnons. We demonstrate the existence of
+magnonic surface states with constant energy contours that form pairs of
+magnonic arcs connecting the surface projection of the magnonic triple nodal
+points. The quasiparticle excitations near the triple nodal points represent
+three-component bosons beyond that of magnonic Dirac, Weyl, and nodal-line
+cases. They can be regarded as a direct reflection of the intrinsic spin
+carried by magnons. Furthermore, we show that the magnonic triple nodal points
+can split into magnonic Weyl points, as the system transits from a
+non-collinear spin structure to a noncoplanar one with a nonzero scalar spin
+chirality. Our results not only apply to insulating antiferromagnets, but also
+provide a platform to seek for triple nodal points in metallic
+antiferromagnets.",1711.00007v4
+2017-11-11,Observation of the exceptional point in cavity magnon-polaritons,"Magnon-polaritons are hybrid light-matter quasiparticles originating from the
+strong coupling between magnons and photons. They have emerged as a potential
+candidate for implementing quantum transducers and memories. Owing to the
+dampings of both photons and magnons, the polaritons have limited lifetimes.
+However, stationary magnon-polariton states can be reached by a dynamical
+balance between pumping and losses, so the intrinsical nonequilibrium system
+may be described by a non-Hermitian Hamiltonian. Here we design a tunable
+cavity quantum electrodynamics system with a small ferromagnetic sphere in a
+microwave cavity and engineer the dissipations of photons and magnons to create
+cavity magnon-polaritons which have non-Hermitian spectral degeneracies. By
+tuning the magnon-photon coupling strength, we observe the polaritonic coherent
+perfect absorption and demonstrate the phase transition at the exceptional
+point. Our experiment offers a novel macroscopic quantum platform to explore
+the non-Hermitian physics of the cavity magnon-polaritons.",1711.04176v1
+2018-10-27,Microwave control of thermal magnon spin transport,"We observe that an rf microwave field strongly influences the transport of
+incoherent thermal magnons in yttrium iron garnet. Ferromagnetic resonance in
+the nonlinear regime suppresses thermal magnon transport by 95%. The transport
+is also modulated at non-resonant conditions in two cases, both related to the
+magnon band minimum. Firstly, a strong enhancement of the nonlocal signal
+appears at a static magnetic field below the resonance condition. This increase
+only occurs at one field polarity and can be as large as 800%. We attribute
+this effect to magnon kinetic processes, which give rise to band-minimum
+magnons and high-energy chiral surface modes. Secondly, the signal increases at
+a static field above the resonance condition, where the rf frequency coincides
+with the magnon band minimum. Our study gives insight into the interplay
+between coherent and incoherent spin dynamics: The rf field modifies the
+occupation of relevant magnon states and, via kinetic processes, the magnon
+spin transport.",1810.11667v1
+2019-05-11,Topological magnon insulator and quantized pumps from strongly-interacting bosons in optical superlattices,"We propose a scheme realizing topological insulators and quantized pumps for
+magnon excitations, based on strongly-interacting two-component ultracold atoms
+trapped in optical superlattices. Specifically, we show how to engineer the
+Su-Schrieffer-Heeger model for magnons using state-independent superlattices,
+and the Rice-Mele model using state-dependent superlattices. We describe
+realistic experimental protocols to detect the topological signatures of magnon
+excitations in these two models. In particular, we show that the
+non-equilibrium dynamics of a single magnon can be exploited to directly detect
+topological winding numbers and phase transitions. We also describe how
+topological (quantized) pumps can be realized with magnons, and study how this
+phenomenon depends on the initial magnon state preparation. Our study opens a
+new avenue for exploring magnonic topological phases of matter and their
+potential applications in the context of topological magnon transport.",1905.04549v1
+2021-02-22,"The role of density-dependent magnon hopping and magnon-magnon repulsion in ferrimagnetic spin-(1/2, $S$) chains in a magnetic field","We compare the ground-state features of alternating ferrimagnetic chains
+$(1/2, S)$ with $S=1,3/2,2,5/2$ in a magnetic field and the corresponding
+Holstein-Primakoff bosonic models up to order $\sqrt{s/S}$, with $s=1/2$,
+considering the fully polarized magnetization as the boson vacuum. {The
+single-particle Hamiltonian is a Rice-Mele model with uniform hopping and
+modified boundaries, while the interactions have a correlated
+(density-dependent) hopping term and magnon-magnon repulsion.} The
+magnon-magnon repulsion increases the many-magnon energy and the
+density-dependent hopping decreases the kinetic energy. We use density matrix
+renormalization group calculations to investigate the effects of these two
+interaction terms in the bosonic model{, and display the quantitative agreement
+between the results from the spin model and the full bosonic approximation. In
+particular, we verify the good accordance in the behavior of the edge states,
+associated with the ferrimagnetic plateau, from the spin and from the bosonic
+models. Furthermore, we show that the boundary magnon density strongly depends
+on the interactions and particle statistics.",2102.11143v1
+2016-09-20,Magnon nodal-line semimetals and drumhead surface states in anisotropic pyrochlore ferromagnets,"We introduce a new type of topological magnon matter: the magnonic pendant to
+electronic nodal-line semimetals. Magnon spectra of anisotropic pyrochlore
+ferromagnets feature twofold degeneracies of magnon bands along a closed loop
+in reciprocal space. These magnon nodal lines are topologically protected by
+the coexistence of inversion and time-reversal symmetry; they require the
+absence of spin-orbit interaction (no Dzyaloshinskii-Moriya interaction). We
+calculate the topological invariants of the nodal lines and show that details
+of the associated magnon drumhead surface states depend strongly on the
+termination of the surface. Magnon nodal-line semimetals complete the family of
+topological magnons in three-dimensional ferromagnetic materials.",1609.06131v1
+2016-09-26,Magnon Kerr effect in a strongly coupled cavity-magnon system,"We experimentally demonstrate magnon Kerr effect in a cavity-magnon system,
+where magnons in a small yttrium iron garnet (YIG) sphere are strongly but
+dispersively coupled to the photons in a three-dimensional cavity. When the YIG
+sphere is pumped to generate considerable magnons, the Kerr effect yields a
+perceptible shift of the cavity's central frequency and more appreciable shifts
+of the magnon modes. We derive an analytical relation between the magnon
+frequency shift and the drive power for the uniformly magnetized YIG sphere and
+find that it agrees very well with the experimental results of the Kittel mode.
+Our study paves the way to explore nonlinear effects in the cavity-magnon
+system.",1609.07891v2
+2019-07-17,Laser control of magnonic topological phases in antiferromagnets,"We study the laser control of magnon topological phases induced by the
+Aharonov-Casher effect in insulating antiferromagnets (AFs). Since the laser
+electric field can be considered as a time-periodic perturbation, we apply the
+Floquet theory and perform the inverse frequency expansion by focusing on the
+high frequency region. Using the obtained effective Floquet Hamiltonian, we
+study nonequilibrium magnon dynamics away from the adiabatic limit and its
+effect on topological phenomena. We show that a linearly polarized laser can
+generate helical edge magnon states and induce the magnonic spin Nernst effect,
+whereas a circularly polarized laser can generate chiral edge magnon states and
+induce the magnonic thermal Hall effect. In particular, in the latter, we find
+that the direction of the magnon chiral edge modes and the resulting thermal
+Hall effect can be controlled by the chirality of the circularly polarized
+laser through the change from the left-circular to the right-circular
+polarization. Our results thus provide a handle to control and design magnon
+topological properties in the insulating AF.",1907.07636v1
+2021-01-03,Magnon-polaron formation in XXZ quantum Heisenberg chains,"We study the formation of magnon-polaron excitations and the consequences of
+different time scales between the magnon and lattice dynamics. The spin-spin
+interactions along the 1D lattice are ruled by a Heisenberg Hamiltonian in the
+anisotropic form XXZ, in which each spin exhibits a vibrational degree of
+freedom around its equilibrium position. By considering a magnetoelastic
+coupling as a linear function of the relative displacement between
+nearest-neighbor spins, results provide an original framework for achieving a
+hybridized state of magnon-polaron. Such state is characterized by high
+cooperation between the underlying excitations, where the traveling or
+stationary formation of magnon-polaron depends on the effective magnetoelastic
+coupling. A systematic investigation reveals the critical amount of the
+magnon-lattice interaction ($\chi_c$) necessary to emergence of the stationary
+magnon-polaron quasi-particle. Different characteristic time scales of the
+magnon and the vibrational dynamics unveiled the threshold between the two
+regimes, as well as a limiting value of critical magnetoelastic interaction,
+above which the magnon velocity no longer interferes at the critical
+magnetoelastic coupling capable of inducing the stationary regime.",2101.00673v1
+2021-05-16,Voltage-Controlled Reconfigurable Magnonic Crystal at the Submicron Scale,"Multiferroics offer an elegant means to implement voltage-control and on the
+fly reconfigurability in microscopic, nanoscaled systems based on ferromagnetic
+materials. These properties are particularly interesting for the field of
+magnonics, where spin waves are used to perform advanced logical or analogue
+functions. Recently, the emergence of nano-magnonics {\color{black} is expected
+to} eventually lead to the large-scale integration of magnonic devices.
+However, a compact voltage-controlled, on demand reconfigurable magnonic system
+has yet to be shown. Here, we introduce the combination of multiferroics with
+ferromagnets in a fully epitaxial heterostructure to achieve such
+voltage-controlled and reconfigurable magnonic systems. Imprinting a remnant
+electrical polarization in thin multiferroic $\mathrm{BiFeO_3}$ with a
+periodicity of $500\,\mathrm{nm}$ yields a modulation of the effective magnetic
+field in the micron-scale, ferromagnetic $\mathrm{La_{2/3}Sr_{1/3}MnO_3}$
+magnonic waveguide. We evidence the magneto-electrical coupling by
+characterizing the spin wave propagation spectrum in this artificial, voltage
+induced, magnonic crystal and demonstrate the occurrence of a robust magnonic
+bandgap with $>20 \,\mathrm{dB}$ rejection.",2105.07418v1
+2022-01-06,A Perspective on Magnon Spin Nernst Effect in Antiferromagnets,"Magnon excitations in antiferromagnetic materials and their physical
+implications enable novel device concepts not available in ferromagnets,
+emerging as a new area of active research. A unique characteristic of
+antiferromagnetic magnons is the coexistence of opposite spin polarization,
+which mimics the electron spin in a variety of transport phenomena. Among them,
+the most prominent spin-contrasting phenomenon is the magnon spin Nernst effect
+(SNE), which refers to the generation of transverse pure magnon spin current
+through a longitudinal temperature gradient. We introduce selected recent
+progress in the study of magnon SNE in collinear antiferromagnets with a focus
+on its underlying physical mechanism entailing profound topological features of
+the magnon band structures. By reviewing how the magnon SNE has inspired and
+enriched the exploration of topological magnons, we offer our perspectives on
+this emerging frontier that holds potential in future spintronic
+nano-technology.",2201.01907v2
+2022-02-24,Magnon boundary states tailored by longitudinal spin-spin interactions and topology,"Since longitudinal spin-spin interaction is ubiquitous in magnetic materials,
+it is very interesting to explore the interplay between topology and
+longitudinal spin-spin interaction. Here, we examine the role of longitudinal
+spin-spin interaction on topological magnon excitations. Remarkably, even for
+single-magnon excitations, we discover topological edge states and defect edge
+states of magnon excitations in a dimerized Heisenberg XXZ chain and their
+topological properties can be distinguished via adiabatic quantum transport. We
+uncover topological phase transitions induced by longitudinal spin-spin
+interactions whose boundary is analytically obtained via the transfer matrix
+method. For multi-magnon excitations, even-magnon bound states are found to be
+always topologically trivial, but odd-magnon bound states may be topologically
+nontrivial due to the interplay between the transverse dimerization and the
+longitudinal spin-spin interaction. For two-dimensional spin systems, the
+longitudinal spin-spin interaction contributes to the coexistence of defect
+corner states, second-order topological corner states and first-order
+topological edge states. Our work opens an avenue for exploring topological
+magnon excitations and has potential applications in topological magnon
+devices.",2202.13780v2
+2022-03-25,Topological state transfers in cavity-magnon system,"We propose an experimentally feasible scheme for realizing quantum state
+transfer via the topological edge states in a one-dimensional cavity-magnon
+lattice. We find that the cavity-magnon system can be mapped analytically into
+the generalized Su-Schrieffer-Heeger model with tunable cavity-magnon coupling.
+It can be shown that the edge state can be served as a quantum channel to
+realize the photonic and magnonic state transfers by adjusting the
+cavity-cavity coupling strength. Further, our scheme can realize the quantum
+state transfer between photonic state and magnonic state by changing the
+amplitude of the intracell hopping. With a numerical simulation, we
+quantitatively show that the photonic, magnonic and magnon-to-photon state
+transfers can be achieved with high fidelity in the cavity-magnon lattice.
+Spectacularly, the three different types of quantum state transfer schemes can
+be even transformed to each other in a controllable fashion. This system
+provides a novel way of realizing quantum state transfer and can be implemented
+in quantum computing platforms.",2203.13727v1
+2022-06-16,Confinement and oscillating deconfinement crossover of two-magnon excitations in quantum spin chains quantified by spin entanglement entropy,"We introduce the spin entanglement entropy (EE) to characterize spin
+excitations. The scalings of EEs are elaborated as $\ln N$, $\ln N+D_k$ and
+$2\ln N+D$ for the single-magnon states, two-magnon bound states and two-magnon
+continuum, respectively, based on the Bethe ansatz solutions of the
+ferromagnetic spin chain with $N$ sites. The $\ln N$ divergence for the bound
+states reveals the two magnons emerge as a new quasiparticle. More importantly,
+the nonzero intercepts ($D_k,D$) embody the many-body effects of two-magnon
+states. In particular, an exact relation between the intercept of EEs and an
+observable quantity, the two-magnon distance, is established for the bound
+states. In such a case, we quantify the two-magnon confinement in a spin system
+by the increasing entanglement with the distance as a particle physics
+analogue. Moreover, the EEs can also be used to study the evolution of the
+excitations. When the bound states are immersed in the continuum in the
+alternating chain, they undergo an oscillating confinement-deconfinement
+crossover, shown by the oscillations of the EEs and two-magnon distance with
+the chain length.",2206.08018v1
+2022-09-07,Acoustic attenuation in magnetic insulator films: effects of magnon polaron formation,"A magnon and a phonon are the quanta of spin wave and lattice wave,
+respectively, and they can hybridize into a magnon polaron when their
+frequencies and wavenumbers match close enough the values at the exceptional
+point. Guided by an analytically calculated magnon polaron dispersion,
+dynamical phase-field simulations are performed to investigate the effects of
+magnon polaron formation on the attenuation of a bulk acoustic wave in a
+magnetic insulator film. It is shown that a stronger magnon-phonon coupling
+leads to a larger attenuation. The simulations also demonstrate the existence
+of a minimum magnon-phonon interaction time required for the magnon polaron
+formation, which is found to decrease with the magnetoelastic coupling
+coefficient but increase with the magnetic damping coefficient. These results
+deepen the understanding of the mechanisms of acoustic attenuation in magnetic
+crystals and provide insights into the design of new-concept spin interconnects
+that operate based on acoustically driven magnon propagation.",2209.03481v2
+2022-09-27,Radiation-free and non-Hermitian topology inertial defect states of on-chip magnons,"Radiative damping is a strong dissipation source for the quantum emitters
+hybridized with propagating photons, electrons, or phonons, which is not easily
+avoidable for on-chip magnonic emitters as well that can radiate via the
+surface acoustic waves of the substrate. Here we demonstrate in an array of
+on-chip nano-magnets coupled in a long range via exchanging the surface
+acoustic waves that a point defect in the array, which can be introduced by the
+local magnon frequency shift by a local biased magnetic field or the absence of
+a magnetic wire, strongly localizes the magnons, in contrast to the well
+spreading Bloch-like collective magnon modes in such an array setting. The
+radiation of the magnon defect states is exponentially suppressed by the
+distance of the defect to the array edges. Moreover, this defect state is
+strikingly inertial to the non-Hermitian topology that localizes all the
+extended states at one boundary. Such configuration robust magnon defect states
+towards radiation-free limit may be suitable for high-fidelity magnon quantum
+information storage in the future on-chip magnonic devices.",2209.13386v1
+2022-10-29,Antimagnonics,"Magnons are the quanta of collective spin excitations in magnetically-ordered
+systems and manipulation of magnons for computing and information processing
+has witnessed the development of ``magnonics"". A magnon corresponds to an
+excitation of the magnetic system from its ground state and the creation of a
+magnon thus increases the total energy of the system. In this perspective, we
+introduce the antiparticle of a magnon, dubbed the antimagnon, as an excitation
+that lowers the magnetic energy. We investigate the stability and thermal
+occupation of antimagnons and verify our theory by micromagnetic simulations.
+Furthermore, we show how the concept of antimagnons yields a unified picture to
+understand the magnonic analog of the Klein effect, magnonic black-hole
+horizons, and magnonic black-hole lasing. Our work may stimulate fundamental
+interest in antimagnons, as well as their applications to spintronic devices.",2210.16698v1
+2022-11-01,Ultrastrong magnon-photon coupling and entanglement in superconductor/ferromagnet nanostructures,"Ultrastrong light-matter coupling opens exciting possibilities to generate
+squeezed quantum states and entanglement. Here we propose a way to achieve this
+regime in superconducting hybrid nanostructures with ferromagnetic interlayers.
+Strong confinement of electromagnetic field between superconducting plates is
+found to result in the existence of magnon-polariton modes with ultrastrong
+magnon-photon coupling, ultra-high cooperativity and very large group
+velocities. These modes provide a numerically accurate explanation of recent
+experiments and have intriguing quantum properties. The magnon-polariton
+quantum vacuum consists of the squeezed magnon and photon states with the
+degree of squeezing controlled in wide limits by the external magnetic field.
+The ground state population of virtual photons and magnons is shown to be very
+large which can be used for generating correlated magnon and photon pairs.
+Excited states of magnon-polaritons contain bipartite entanglement between
+magnons and photons. This property can be used for transferring entanglement
+between different types of quantum systems.",2211.00462v3
+2023-01-09,Nonlinear Topological Magnon Spin Hall Effect,"When a magnon passes through two-dimensional magnetic textures, it will
+experience a fictitious magnetic field originating from the $3\times 3$
+skew-symmetric gauge fields. To date, only one of the three independent
+components of the gauge fields has been found to play a role in generating the
+fictitious magnetic field while the rest two are perfectly hidden. In this
+work, we show that they are concealed in the nonlinear magnon transport in
+magnetic textures. Without loss of generality, we theoretically study the
+nonlinear magnon-skyrmion interaction in antiferromagnets. By analyzing the
+scattering features of three-magnon processes between the circularly-polarized
+incident magnon and breathing skyrmion, we predict a giant Hall angle of both
+the confluence and splitting modes. Furthermore, we find that the Hall angle
+reverses its sign when one switches the handedness of the incident magnons. We
+dub it nonlinear topological magnon spin Hall effect. Our findings are deeply
+rooted in the bosonic nature of magnons that the particle number is not
+conserved, which has no counterpart in low-energy fermionic systems, and may
+open the door for probing gauge fields by nonlinear means.",2301.03211v1
+2023-06-24,Magnon confinement in an all-on-chip YIG cavity resonator using hybrid YIG/Py magnon barriers,"Confining magnons in cavities can introduce new functionalities to magnonic
+devices, enabling future magnonic structures to emulate established photonic
+and electronic components. As a proof-of-concept, we report magnon confinement
+in a lithographically defined all-on-chip YIG cavity created between two
+YIG/Permalloy bilayers. We take advantage of the modified magnetic properties
+of covered/uncovered YIG film to define on-chip distinct regions with
+boundaries capable of confining magnons. We confirm this by measuring multiple
+spin pumping voltage peaks in a 400 nm wide platinum strip placed along the
+center of the cavity. These peaks coincide with multiple spin-wave resonance
+modes calculated for a YIG slab with the corresponding geometry. The
+fabrication of micrometer-sized YIG cavities following this technique
+represents a new approach to control coherent magnons, while the spin pumping
+voltage in a nanometer-sized Pt strip demonstrates to be a non-invasive local
+detector of the magnon resonance intensity.",2306.14029v2
+2023-07-07,Interacting topological magnons in a checkerboard ferromagnet,"This work is devoted to studying the magnon-magnon interaction effect in a
+two-dimensional checkerboard ferromagnet with the Dzyaloshinskii-Moriya
+interaction. By means of the first-order Green function formalism, the
+influence of magnon-magnon interaction on the magnon band topology is analyzed.
+In order to verify that the gap-closing phenomenon is a signature for the
+topological phase transitions of the checkerboard ferromagnet, we display that
+the Chern numbers of renormalized magnon bands are distinct above and below the
+critical temperature. Our results show that the checkerboard ferromagnet
+possesses two topological phases and its topological phase can be controlled
+either by the temperature or applied magnetic field due to magnon-magnon
+interactions. Interestingly, we find that the topological phase transition
+occurs twice with the increase of the temperature, which is different from the
+result of the honeycomb ferromagnet.",2307.03361v1
+2023-09-17,Highly-tunable and strong nonreciprocity in coupled nonlinear cavity magnonics,"Nonreciprocity, which violates Lorentz reciprocity, plays a pivotal role in
+quantum information processing and networks. Nevertheless, achieving a desired
+and highly-tunable level of nonreciprocity has proven to be a formidable
+challenge. Here, we propose a coupled nonlinear cavity magnonic system,
+consisting of two cavities, a second-order nonlinear element, and a
+yttrium-iron-garnet sphere for supporting Kerr magnons, to realize this
+sought-after highly-tunable nonreciprocity. We first derive the critical
+condition for switching between reciprocity and nonreciprocity with undriven
+magnons, then we numerically demonstrate that a strong magnonic nonreciprocity
+can be obtained by breaking the critical condition. When magnons are driven, we
+show that a strong magnonic nonreciprocity can also be attained within the
+critical condition. Compared to previous study, the introduced nonlinear
+element not only relaxes the critical condition to both the weak and strong
+regimes, but also offers an alternative path to adjust the magnonic
+nonreciprocity. Our work provides a promising avenue to realize highly-tunable
+nonreciprocal devices with Kerr magnons.",2309.09245v2
+2023-10-12,Electrical noise spectroscopy of magnons in a quantum Hall ferromagnet,"Collective spin-wave excitations-magnons-in a quantum Hall ferromagnet are
+promising quasi-particles for next-generation spintronics devices, including
+platforms for information transfer. Detection of these charge-neutral
+excitations relies on the conversion of magnons into electrical signals in the
+form of excess electrons and holes, but if these signals are equal the magnon
+detection remains elusive. In this work, we overcome this shortcoming by
+measuring the electrical noise generated by magnons. We use the symmetry-broken
+quantum Hall ferromagnet of the zeroth Landau level in graphene to launch
+magnons. Absorption of these magnons creates excess noise above the Zeeman
+energy and remains finite even when the average electrical signal is zero.
+Moreover, we formulate a theoretical model in which the noise is generated by
+equilibration (partial or full, depending on the bias voltage) between edge
+channels and propagating magnons. Our model, which agrees with experimental
+observations, also allows us to pinpoint the regime of ballistic magnon
+transport in our device.",2310.08703v1
+2024-01-10,Electrical Non-Hermitian Control of Topological Magnon Spin Transport,"Magnonic topological phases realize chiral edge spin waves that are protected
+against backscattering, potentially enabling highly efficient spin transport.
+Here we show that the spin transport through these magnonic chiral edge states
+can be electrically manipulated by non-Hermitian control. We consider the
+paradigmatic magnon Haldane model and show that it is transformed into an
+effective non-Hermitian magnon Chern insulator by including a
+sublattice-dependent spin-orbit torque. In linear spin-wave theory, this
+electrically induced torque causes a lasing of the chiral edge magnons along
+certain edge directions, leading to an enhancement of the spin-wave amplitude.
+This prediction is confirmed by numerical simulations based on the
+Landau-Lifshitz-Gilbert equation. For a spin-wave transport setup, in which
+magnons are excited by a microwave field and detected with a normal metal
+conductor, we find that the magnon amplification is remarkably robust against
+disorder, establishing non-Hermitian control as a promising avenue for
+topological magnonics.",2401.04967v2
+2024-02-22,Impact of Magnon Interactions on Transport in Honeycomb Antiferromagnets,"The thermal transport of magnons has attracted substantial attention as an
+energy-efficient alternative to the transport of electrons. Most theoretical
+studies so far have been carried out within the frame of the linear spin-wave
+theory, which dramatically fails upon increasing the temperature and in the
+presence of competing interactions. In this work, we consider the impact of
+three- and four-magnon interactions in a honeycomb antiferromagnet, where such
+interactions are remarkably strong even at zero temperature. Using a
+combination of quantum field theory and mean-field theory, we compute the band
+structure of the interacting magnons and investigate the spin Nernst effect. We
+find that in the presence of in-plane Dzyaloshinskii-Moriya Interaction, the
+three-magnon interaction induces a non-reciprocal band splitting, even at zero
+temperature, leading to an enhancement of the spin Nernst conductivity. In
+contrast, the four-magnon interaction renormalizes the magnon spectrum at high
+temperatures, leading to a reduction of the overall magnon spin Nernst effect.
+These results suggest that interactions can massively influence the transport
+properties of magnons in antiferromagnets, even at zero temperature, and should
+be taken into account for predictive modeling.",2402.14572v1
+2024-02-25,Enhancement of Entanglement via Josephson Parametric Amplifier in a Dual Cavity-Magnon System,"In the two microwave (MW) cross-shaped cavity magnon system, we describe a
+method to produce multipartite entanglement and quantum steering. To achieve
+squeezed states of the magnons, a Josephson parametric amplifier (JPA) creates
+a squeezed vacuum field that drives the two cavities. We theoretically
+demonstrate that the cavity-cavity entanglement can be generated at the
+resonance point, however, increasing the cavity and magnon decay rates generate
+the cavity-magnon entanglement. By changing the squeezing parameter and
+increasing the decay rates, we can transfer the cavity-cavity entanglement to
+cavity-magnon entanglement. Furthermore, the cavity-cavity entanglement
+(survive up to 2.8K) not only found to be much stronger but also more robust as
+compared to cavity-magnon entanglement (survive up to 0.4K). More importantly,
+the genuine photon-magnon-photon tripartite entanglement could be achieved,
+which is robust against the thermal fluctuations and depends strongly on
+squeezing parameter. Furthermore, for current dual cavity-magnon system,
+two-way quantum steering is found when the optomagnonical couplings are equal.
+The current study offers a straightforward and practical method for achieving
+multipartite quantum correlations.",2402.16042v1
+2018-02-13,Electric control of emergent magnonic spin current and dynamic multiferroicity in magnetic insulators at finite temperatures,"Conversion of thermal energy into magnonic spin currents and/or effective
+electric polarization promises new device functionalities. A versatile approach
+is presented here for generating and controlling open circuit magnonic spin
+currents and an effective multiferroicity at a uniform temperature with the aid
+of spatially inhomogeneous, external, static electric fields. This field
+applied to a ferromagnetic insulator with a Dzyaloshinskii-Moriya type coupling
+changes locally the magnon dispersion and modifies the density of thermally
+excited magnons in a region of the scale of the field inhomogeneity. The
+resulting gradient in the magnon density can be viewed as a gradient in the
+effective magnon temperature. This effective thermal gradient together with
+local magnon dispersion result in an open-circuit, electric field controlled
+magnonic spin current. In fact, for a moderate variation in the external
+electric field the predicted magnonic spin current is on the scale of the spin
+(Seebeck) current generated by a comparable external temperature gradient.
+Analytical methods supported by full-fledge numerics confirm that both, a
+finite temperature and an inhomogeneous electric field are necessary for this
+emergent non-equilibrium phenomena. The proposal can be integrated in magnonic
+and multiferroic circuits, for instance to convert heat into electrically
+controlled pure spin current using for example nanopatterning, without the need
+to generate large thermal gradients on the nanoscale.",1802.04614v1
+2017-09-30,Tuning the diffusion of magnon in Y3Fe5O12 by light excitation,"Deliberate control of magnon transportation will lead to an energy-efficient
+technology for information transmission and processing. Y3Fe5O12(YIG),
+exhibiting extremely large magnon diffusion length due to the low magnetic
+damping constant, has been intensively investigated for decades. While most of
+the previous works focused on the determination of magnon diffusion length by
+various techniques, herein we demonstrated how to tune magnon diffusion by
+light excitation. We found that the diffusion length of thermal magnons is
+strongly dependent on light wavelength when the magnon is generated by exposing
+YIG directly to laser beam. The diffusion length, determined by a nonlocal
+geometry at room temperature, is ~30 um for the magnons produced by visible
+light (400-650 nm), and ~136-156 um for the laser between 808 nm and 980 nm.
+The diffusion distance is much longer than the reported value. In addition to
+thermal gradient, we found that light illumination affected the electron
+configuration of the Fe3+ ion in YIG. Long wavelength laser triggers a high
+spin to low spin state transition of the Fe3+ ions in FeO6 octahedron. This in
+turn causes a substantial softening of the magnon thus a dramatic increase in
+diffusion distance. The present work paves the way towards an efficient tuning
+of magnon transport behavior which is crucially important for magnon
+spintronics.",1710.00222v2
+2017-07-24,Magnonic topological insulators in antiferromagnets,"Extending the notion of symmetry protected topological phases to insulating
+antiferromagnets (AFs) described in terms of opposite magnetic dipole moments
+associated with the magnetic N$\acute{{\rm{e}}} $el order, we establish a
+bosonic counterpart of topological insulators in semiconductors. Making use of
+the Aharonov-Casher effect, induced by electric field gradients, we propose a
+magnonic analog of the quantum spin Hall effect (magnonic QSHE) for edge states
+that carry helical magnons. We show that such up and down magnons form the same
+Landau levels and perform cyclotron motion with the same frequency but
+propagate in opposite direction. The insulating AF becomes characterized by a
+topological ${\mathbb{Z}}_{2}$ number consisting of the Chern integer
+associated with each helical magnon edge state. Focusing on the topological
+Hall phase for magnons, we study bulk magnon effects such as magnonic spin,
+thermal, Nernst, and Ettinghausen effects, as well as the thermomagnetic
+properties of helical magnon transport both in topologically trivial and
+nontrivial bulk AFs and establish the magnonic Wiedemann-Franz law. We show
+that our predictions are within experimental reach with current device and
+measurement techniques.",1707.07427v2
+2018-01-15,Photoinduced Topological Phase Transitions in Topological Magnon Insulators,"Topological magnon insulators are the bosonic analogs of electronic
+topological insulators. They are manifested in magnetic materials with
+topologically nontrivial magnon bands as realized experimentally in a
+quasi-two-dimensional (quasi-2D) kagome ferromagnet Cu(1-3, bdc), and they also
+possess protected magnon edge modes. These topological magnetic materials can
+transport heat as well as spin currents, hence they can be useful for
+spintronic applications. Moreover, as magnons are charge-neutral spin-${\bf 1}$
+bosonic quasiparticles with a magnetic dipole moment, topological magnon
+materials can also interact with electromagnetic fields through the
+Aharonov-Casher effect. In this report, we study photoinduced topological phase
+transitions in intrinsic topological magnon insulators in the kagom\'e
+ferromagnets. Using magnonic Floquet-Bloch theory, we show that by varying the
+light intensity, periodically driven intrinsic topological magnetic materials
+can be manipulated into different topological phases with different sign of the
+Berry curvatures and the thermal Hall conductivity. We further show that, under
+certain conditions, periodically driven gapped topological magnon insulators
+can also be tuned to synthetic gapless topological magnon semimetals with
+Dirac-Weyl magnon cones. We envision that this work will pave the way for
+interesting new potential practical applications in topological magnetic
+materials",1801.04932v3
+2020-07-11,Magnon-bipolar carrier drag thermopower in antiferromagnetic/ferromagnetic semiconductors: theoretical formulation and experimental evidence,"Quantized spin-wave known as magnon, a bosonic quasiparticle, can drag
+electrons or holes via sd exchange interaction and boost the thermopower over
+the conventional diffusive thermopower. P-type magnon-drag thermopower has been
+observed in both ferromagnetic and antiferromagnetic metallic and degenerate
+semiconductors. However, it has been less reported for intrinsic or n-type
+magnetic semiconductors; therefore, the impact of magnon-bipolar carrier drag
+on thermopower has remained unexplored. Here, a theoretical model for
+magnon-bipolar carrier drag thermopower is derived based on the magnon-carrier
+interaction lifetimes. The model predicts that the bipolar carrier drag
+thermopower becomes independent of both the carrier and magnon relaxation
+times. A proof of concept experiment is presented that confirms this
+prediction. We also report the observation of magnon-carrier drag thermopower
+in n-type and intrinsic ferromagnetic semiconductors experimentally. The p-type
+antiferromagnetic MnTe is doped with different amounts of Cr to produce
+non-degenerate and n-type semiconductors of various carrier concentrations. Cr
+dopants have a donor nature and create ferromagnetic-antiferromagnetic clusters
+due to the Cr3+ oxidation state. Heat capacity measurements confirm the
+presence of magnons in Cr-doped MnTe. It is shown that the magnon-drag
+thermopower is significantly reduced for 3%-5% Cr-doped samples due to bipolar
+drag effects and becomes negative for 14% and 20% Cr-doped MnTe due to dominant
+magnon-electron drag thermopower.",2007.05682v1
+2021-03-01,Magnon driven skyrmion dynamics in antiferromagnets: The effect of magnon polarization,"The controllable magnetic skyrmion motion represents a highly concerned issue
+in preparing advanced skyrmion-based spintronic devices. Specifically,
+magnon-driven skyrmion motion can be easily accessible in both metallic and
+insulating magnets, and thus is highly preferred over electric current control
+further for the ultra-low energy consumption. In this work, we investigate
+extensively the dynamics of skyrmion motion driven by magnon in an
+antiferromagnet using the collective coordinate theory, focusing on the effect
+of magnon polarization. It is revealed that the skyrmion Hall motion driven by
+circularly polarized magnon becomes inevitable generally, consistent with
+earlier report. Furthermore, the elastic scattering theory and numerical
+results unveil the strong inter-dependence between the linearly polarized
+magnon and skyrmion motion, suggesting the complicated dependence of the
+skyrmion motion on the polarization nature of driving magnon. On the reversal,
+the scattering from the moving skyrmion may lead to decomposition of the
+linearly polarized magnon into two elliptically polarized magnon bands.
+Consequently, a net transverse force acting on skyrmion is generated owing to
+the broken mirror symmetry, which in turn drives a skyrmion Hall motion. The
+Hall motion can be completely suppressed only in some specific condition where
+the mirror symmetry is preserved. The present work unveils non-trivial
+skyrmion-magnon scattering behavior in antiferromagnets, advancing the
+antiferromagnetic spintronics and benefiting to high-performance devices.",2103.00898v1
+2022-01-23,Squeezed driving induced entanglement and squeezing among cavity modes and magnon mode in a magnon-cavity QED system,"We propose a scheme to generate entanglement between two cavity modes and
+squeeze magnon mode in a magnon-cavity QED system, where the two microwave
+cavity modes are coupled with a massive yttrium iron garnet (YIG) sphere
+through magnetic dipole interaction. The nonlinearity used in our system
+originates from a squeezed driving via parametric down-conversion process,
+which is the reason to cause entanglement and squeezing. By using the mean
+field approximation and employing experimentally feasible parameters, we
+demonstrate that the system shows zero entanglement and squeezing without
+squeezed driving. Meanwhile, our QED system denotes that the entanglement
+between squeezed cavity mode and magnon mode can be transferred to the other
+cavity mode and magnon mode via magnon-cavity coupling interaction, and then
+the two cavity modes get entangled. A genuinely tripartite entangled state is
+formed. We also show that magnon mode can be prepared in a squeezed state via
+magnon-cavity beam-splitter interaction, which is as a result of the squeezed
+field. Moreover, we show that it is a good way to enhance entanglement and
+squeezing by increasing the nonlinear gain coefficient of squeezed driving. Our
+results denote that magnon-cavity QED system is a powerful platform for
+studying macroscopic quantum phenomena, which illustrates a new method to
+photon-photon entanglement and magnon squeezing.",2201.09154v1
+2022-07-04,Long-distance coupling of spin qubits via topological magnons,"We consider two distant spin qubits in quantum dots, both coupled to a
+two-dimensional topological ferromagnet hosting chiral magnon edge states at
+the boundary. The chiral magnon is used to mediate entanglement between the
+spin qubits, realizing a fundamental building block of scalable quantum
+computing architectures: a long-distance two-qubit gate. Previous proposals for
+long-distance coupling with magnons involved off-resonant coupling, where the
+detuning of the spin-qubit frequency from the magnonic band edge provides
+protection against spontaneous relaxation. The topological magnon mode, on the
+other hand, lies in-between two magnonic bands far away from any bulk magnon
+resonances, facilitating strong and highly tuneable coupling between the two
+spin qubits. Even though the coupling between the qubit and the chiral magnon
+is resonant for a wide range of qubit splittings, we find that the
+magnon-induced qubit relaxation is vastly suppressed if the coupling between
+the qubit and the ferromagnet is antiferromagnetic. A fast and high-fidelity
+long-distance coupling protocol is presented capable of achieving spin-qubit
+entanglement over micrometer distances with $1\,$MHz gate speed and up to
+$99.9\%$ fidelities. The resulting spin-qubit entanglement may be used as a
+probe for the long-sought detection of topological edge magnons.",2207.01264v1
+2022-09-27,Tunable Exciton-Hybridized Magnon Interactions in a Layered Semiconductor,"The interaction between distinct excitations in solids is of both fundamental
+interest and technological importance. One example of such interactions is
+coupling between an exciton, a Coulomb bound electron-hole pair, and a magnon,
+a collective spin excitation. The recent emergence of van der Waals magnetic
+semiconductors provides a powerful platform for exploring these exciton-magnon
+interactions and their fundamental properties, such as strong correlation, as
+well as their photo-spintronic and quantum transduction applications. Here we
+demonstrate precise control of coherent exciton-magnon interactions in the
+layered magnetic semiconductor CrSBr. We show that by controlling the direction
+of applied magnetic fields relative to the crystal axes, and thus the
+rotational symmetry of the magnetic system, we can tune not only the exciton
+coupling to the bright magnon, but also to an optically dark mode via magnon
+hybridization. The exciton-magnon coupling and associated magnon dispersion
+curves can be further modulated by applying a uniaxial strain. At the critical
+strain, a dispersionless dark magnon band emerges. Our results demonstrate
+unprecedented control of the opto-mechanical-magnonic coupling, and a step
+towards the predictable and controllable implementation of hybrid quantum
+magnonics.",2209.13744v1
+2023-03-04,Controllable magnon-induced transparency in a ferromagnetic material via cross- and self-Kerr effects,"Nonlinear interactions between optical fields and magnetic modes in cavity
+magnonics constitute a rich source of various nontrivial effects in optics and
+quantum information processing. In cavity magnonics, the nonlinear cross-Kerr
+effect, which shifts the cavity's central frequency when a magnetic material is
+pumped, causes the system to exhibit both Kittle and magnetostatic modes. Here,
+we propose a new scheme for the investigation of probe fields transmission
+profiles in cavity magnonic systems composed of a microwave cavity and a
+ferromagnetic material (Yttrium iron garnet sphere). We report single-to-double
+magnon-induced transparency (MIT) dips and a sharp magnon-induced absorption
+(MIA) peak, and demonstrate how nonlinear cross- and self-Kerr interactions can
+significantly enhance or suppress these phenomena. It is observed that the
+splitting of the MIT window occurs when we incorporate magnon-magnon modes
+coupling, which helps introducing a new degree of freedom to light-matter
+interaction problems. Moreover, we investigate the propagation of group delay
+in the vicinity of transparency and demonstrate how a sharp dip allows the
+realization of slow light for a longer period of time. We found that both the
+cavity-Kittle and magnon-magnon modes coupling parameters influence the
+propagation of group delay, which demonstrates how subluminal-to-superluminal
+(and vice versa) propagation phenomena may occur and transform. These findings
+could pave the way for future research into nonlinear effects with novel
+applications in cavity magnonics devices, which might be exploited for several
+applications such as quantum computing devices and quantum memories.",2303.02332v1
+2023-05-25,Type-II Dirac points and Dirac nodal loops on the magnons of square-hexagon-octagon lattice,"We study topological magnons on an anisotropic square-hexagon-octagon (SHO)
+lattice which has been found by a two-dimensional Biphenylene network (BPN). We
+propose the concepts of type-II Dirac magnonic states where new schemes to
+achieve topological magnons are unfolded without requiring the
+Dzyaloshinsky-Moriya interactions (DMIs). In the ferromagnetic states, the
+topological distinctions at the type-II Dirac points along with one-dimensional
+(1D) closed lines of Dirac magnon nodes are characterized by the $\mathbb{Z}_2$
+invariant. We find pair annihilation of the Dirac magnons and use the Wilson
+loop method to depict the topological protection of the band-degeneracy. The
+Green's function approach is used to calculte chiral edge modes and magnon
+density of states (DOS). We introduce the DMIs to gap the type-II Dirac magnon
+points and demonstrate the Dirac nodal loops (DNLs) are robust against the DMIs
+within a certain parameter range. The topological phase diagram of magnon bands
+is given via calculating the Berry curvature and Chern number. We find that the
+anomalous thermal Hall conductivity gives connection to the magnon edge
+current. Furthermore, we derive the differential gyromagnetic ratio to exhibit
+the Einstein-de Haas effect (EdH) of magnons with topological features.",2305.16419v2
+2023-06-07,Non-Hermitian Topological Magnonics,"Dissipation in mechanics, optics, acoustics, and electronic circuits is
+nowadays recognized to be not always detrimental but can be exploited to
+achieve non-Hermitian topological phases or properties with functionalities for
+potential device applications. As elementary excitations of ordered magnetic
+moments that exist in various magnetic materials, magnons are the information
+carriers in magnonic devices with low-energy consumption for reprogrammable
+logic, non-reciprocal communication, and non-volatile memory functionalities.
+Non-Hermitian topological magnonics deals with the engineering of dissipation
+and/or gain for non-Hermitian topological phases or properties in magnets that
+are not achievable in the conventional Hermitian scenario, with associated
+functionalities cross-fertilized with their electronic, acoustic, optic, and
+mechanic counterparts, such as giant enhancement of magnonic frequency combs,
+magnon amplification, (quantum) sensing of the magnetic field with
+unprecedented sensitivity, magnon accumulation, and perfect absorption of
+microwaves. In this review article, we address the unified approach in
+constructing magnonic non-Hermitian Hamiltonian, introduce the basic
+non-Hermitian topological physics, and provide a comprehensive overview of the
+recent theoretical and experimental progress towards achieving distinct
+non-Hermitian topological phases or properties in magnonic devices, including
+exceptional points, exceptional nodal phases, non-Hermitian magnonic SSH model,
+and non-Hermitian skin effect. We emphasize the non-Hermitian Hamiltonian
+approach based on the Lindbladian or self-energy of the magnonic subsystem but
+address the physics beyond it as well, such as the crucial quantum jump effect
+in the quantum regime and non-Markovian dynamics. We provide a perspective for
+future opportunities and challenges before concluding this article.",2306.04348v2
+2023-09-26,Multiferroic Magnon Spin-Torque Based Reconfigurable Logic-In-Memory,"Magnons, bosonic quasiparticles carrying angular momentum, can flow through
+insulators for information transmission with minimal power dissipation.
+However, it remains challenging to develop a magnon-based logic due to the lack
+of efficient electrical manipulation of magnon transport. Here we present a
+magnon logic-in-memory device in a spin-source/multiferroic/ferromagnet
+structure, where multiferroic magnon modes can be electrically excited and
+controlled. In this device, magnon information is encoded to ferromagnetic bits
+by the magnon-mediated spin torque. We show that the ferroelectric polarization
+can electrically modulate the magnon spin-torque by controlling the
+non-collinear antiferromagnetic structure in multiferroic bismuth ferrite thin
+films with coupled antiferromagnetic and ferroelectric orders. By manipulating
+the two coupled non-volatile state variables (ferroelectric polarization and
+magnetization), we further demonstrate reconfigurable logic-in-memory
+operations in a single device. Our findings highlight the potential of
+multiferroics for controlling magnon information transport and offer a pathway
+towards room-temperature voltage-controlled, low-power, scalable magnonics for
+in-memory computing.",2309.14614v1
+2023-11-26,Electric Field Switching of Magnon Spin Current in a Compensated Ferrimagnet,"Manipulation of directional magnon propagation, known as magnon spin current,
+is essential for developing magnonic memory and logic devices featuring
+nonvolatile functionalities and ultralow power consumption. Magnon spin current
+can usually be modulated by magnetic field or current-induced spin torques.
+However, these approaches may lead to energy dissipation caused by Joule
+heating. Electric-field switching of magnon spin current without charge current
+is highly desired but very challenging to realize. By integrating magnonic and
+piezoelectric materials, we demonstrate manipulation of the magnon spin current
+generated by the spin Seebeck effect in the ferrimagnetic insulator Gd3Fe5O12
+(GdIG) film on a piezoelectric substrate. We observe reversible electric-field
+switching of magnon polarization without applied charge current. Through
+strain-mediated magnetoelectric coupling, the electric field induces the
+magnetic compensation transition between two magnetic states of the GdIG,
+resulting in its magnetization reversal and the simultaneous switching of
+magnon spin current. Our work establishes a prototype material platform that
+pave the way for developing magnon logic devices characterized by all electric
+field reading and writing and reveals the underlying physics principles of
+their functions.",2311.15183v1
+2024-01-03,High-degree magnon blockade with large single-excitation probability,"Optimized blockade is an efficient tool in generating a single-magnon state,
+that is fundamental to manipulate the magnonic systems at the quantum level. In
+this study, we consider a hybrid system in which a qubit is strongly coupled to
+$N$ magnons via the exchange interaction. The qubit and the magnon modes are
+subject to the probing field and driving fields, respectively. It is
+interesting to find the scalable conditions in minimizing the equal-time
+second-order correlation function $g^{(2)}(0)$ for each magnon with respect to
+$N$. In particular, the simultaneous blockade is optimized when (i) the
+detuning between the qubit (magnon) and the probing (driving field) field is
+$\sqrt{N}$ times the magnon-qubit coupling strength, (ii) the probing intensity
+is $3\sqrt{N}$ times the driving intensity, and (iii) the relative phase
+between probing and driving fields is $2/(3\sqrt{N}$) times the ratio of the
+system decay rate to the magnon-qubit coupling strength. More than a
+high-degree blockade, we can generate a significant population on the
+single-magnon state. With experimental-relevant driving intensity and decay
+rate, the correlation function can achieve about $g^{(2)}(0)\sim10^{-7}$ in
+company with a large single-magnon population $P_1\sim0.24$ when $N=1$ and
+$g^{(2)}(0)\sim10^{-7}$ with $P_1\sim0.12$ when $N=2$.",2401.01590v1
+2024-03-13,Thermal Hall effect incorporating magnon damping in localized spin systems,"We propose a theory for thermal Hall transport mediated by magnons to address
+the impact of their damping resulting from magnon-magnon interactions in
+insulating magnets. This phenomenon is anticipated to be particularly
+significant in systems characterized by strong quantum fluctuations,
+exemplified by spin-1/2 systems. Employing a nonlinear flavor-wave theory, we
+analyze a general model for localized electron systems and develop a
+formulation for thermal conductivity based on a perturbation theory, utilizing
+bosonic Green's functions with a nonzero self-energy. We derive the expression
+of the thermal Hall conductivity incorporating magnon damping. To demonstrate
+the applicability of the obtained representation, we adopt it to two $S=1/2$
+quantum spin models on a honeycomb lattice. In calculations for these systems,
+we make use of the self-consistent imaginary Dyson equation approach at finite
+temperatures for evaluating the magnon damping rate. In both systems, the
+thermal Hall conductivity is diminished due to the introduction of magnon
+damping over a wide temperature range. This effect arises due to the smearing
+of magnon spectra with nonzero Berry curvatures. We also discuss the relation
+to the damping of chiral edge modes of magnons. Our formulation can be applied
+to various localized electron systems as we begin with a general Hamiltonian
+for these systems. Our findings shed light on a new aspect of topological
+magnonics emergent from many-body effects and will stimulate further
+investigations on the impact of magnon damping on topological phenomena.",2403.08478v1
+1996-05-09,Two-magnon Raman scattering in a spin density wave antiferromagnet,"We present the results for a model calculation of resonant two-magnon Raman
+scattering in a spin density wave (SDW) antiferromagnet. The resonant
+enhancement of the two-magnon intensity is obtained from a microscopic analysis
+of the photon-magnon coupling vertex. By combining magnon-magnon interactions
+with `triple resonance` phenomena in the vertex function the resulting
+intensity line shape is found to closely resemble the measured two-magnon Raman
+signal in antiferromagnetic cuprates. Both, resonant and non-resonant Raman
+scattering are discussed for the SDW antiferromagnet and a comparison is made
+to the conventional Loudon-Fleury theory of two-magnon light scattering.",9605056v1
+2012-09-04,Microscopic Theory of Magnon-Drag Thermoelectric Transport in Ferromagnetic Metals,"A theoretical study of the magnon-drag Peltier and Seebeck effects in
+ferromagnetic metals is presented. A magnon heat current is described
+perturbatively from the microscopic viewpoint with respect to electron--magnon
+interactions and the electric field. Then, the magnon-drag Peltier coefficient
+$\Pi_\MAG$ is obtained as the ratio between the magnon heat current and the
+electric charge current. We show that $\Pi_\MAG=C_\MAG T^{5/2}$ at a low
+temperature $T$; that the coefficient $C_\MAG$ is proportional to the spin
+polarization $P$ of the electric conductivity; and that $P>0$ for $C_\MAG<0$,
+but $P<0$ for $C_\MAG>0$. From experimental results for magnon-drag Peltier
+effects, we estimate that the strength of the electron--magnon interaction is
+about 0.3 eV$\cdot\AA^{3/2}$ for permalloy.",1209.0685v2
+2013-02-24,Electron spin resonance in a dilute magnon gas as a probe of magnon scattering resonances,"We study the electron spin resonance in a dilute magnon gas that is realized
+in a ferromagnetic spin system at low temperature. A quantum cluster expansion
+is developed to show that the frequency shift of the single-magnon peak changes
+its sign and the linewidth reaches its maximum across a scattering resonance
+between magnons. Such characteristic behaviors are universal and can be used to
+experimentally locate the two-magnon resonance when an external parameter such
+as pressure is varied. Future achievement of the two-magnon resonance may have
+an impact comparable to the Feshbach resonance in ultracold atoms and will open
+up a rich variety of strongly correlated physics such as the recently proposed
+Efimov effect in quantum magnets. We also suggest how the emergence of an
+Efimov state of three magnons and its binding energy may be observed with the
+electron spin resonance.",1302.5908v2
+2013-07-05,Theory of asymmetric and negative differential magnon tunneling under temperature bias: Towards a spin Seebeck diode and transistor,"We study the nonequilibrium transport for the asymmetric and negative
+differential magnon tunneling driven by temperature bias. We demonstrate that
+the many-body magnon interaction that makes the magnonic spectrum
+temperature-dependent is the crucial factor for the emergence of rectification
+and negative differential spin Seebeck effects in magnon tunneling junctions.
+When magnonic junctions have temperature-dependent density of states, reversing
+the temperature bias is able to give asymmetric spin currents and increasing
+temperature bias could give an anomalously decreasing magnonic spin current. We
+show that these properties are relevant for building spin Seebeck diodes and
+transistors, which could play important roles in controlling information and
+energy in magnonics and spin caloritronics.",1307.1726v3
+2014-02-26,Magneto-elastic modes and lifetime of magnons in thin yttrium-iron garnet films,"We calculate the effects of the spin-lattice coupling on the magnon spectrum
+of thin ferromagnetic films consisting of the magnetic insulator yttrium-iron
+garnet. The magnon-phonon hybridisation generates a characteristic minimum in
+the spin dynamic structure factor which quantitatively agrees with recent
+Brillouin light scattering experiments. We also show that at room temperature
+the phonon contribution to the magnon damping exhibits a rather complicated
+momentum dependence: In the exchange regime the magnon damping is dominated by
+Cherenkov type scattering processes, while in the long-wavelength dipolar
+regime these processes are subdominant and the magnon damping is two orders of
+magnitude smaller. We supplement our calculations by actual measurements of the
+magnon relaxation in the dipolar regime. Our theory provides a simple
+explanation of a recent experiment probing the different temperatures of the
+magnon and phonon gases in yttrium-iron garnet.",1402.6575v2
+2014-08-06,Observation of Magnonic Band Gaps in Magnonic Crystals with Nopnreciprocal Dispersion Relation,"An effect of metallization of the magnonic crystal surface on the band gaps
+formation in the spectra of the surface spin wave (SSW) is studied both
+theoretically and experimentally. The structures under consideration are
+one-dimensional magnonic crystals based on yttrium iron garnet with an array of
+etched grooves with metal screen on the top of the corrugated surface and
+without it. Due to nonreciprocity of propagation of the SSW the shift of band
+gap to higher frequency and from the border of the Brillouin zone in presence
+of conducting overlayer was measured in transmission line experiment. Results
+of numerical calculations and model analysis are in agreement with experimental
+data and give further insight into origin of the band gap and properties of the
+nonreciprocal SSW in metallized magnonic crystals. This gives positive answer
+to the outstanding question about possibility of detection of magnonic band
+gaps in the spectra of the spin waves with nonreciprocal dispersion in magnonic
+crystals and creates potential for new applications and improvements of already
+existing prototype magnonic devices.",1408.1221v2
+2015-03-02,Supercurrent in a room temperature Bose-Einstein magnon condensate,"We report evidence for the existence of a supercurrent of magnons in a magnon
+Bose-Einstein condensate prepared in a room temperature yttrium-iron-garnet
+magnetic film and subject to a thermal gradient. The magnon condensate is
+formed in a parametrically populated magnon gas, and its temporal evolution is
+studied by time-, frequency- and wavector-resolved Brillouin light scattering
+spectroscopy. It has been found that local heating in the focal point of a
+probing laser beam enhances the temporal decrease in the density of the freely
+evolving magnon condensate after the termination of the pumping pulse, but it
+does not alter the relaxation dynamics of the gaseous magnon phase. This
+phenomenon is understood as the appearance of a magnon supercurrent within the
+condensate due to a temperature- and, consequently, magnetisation-gradient
+induced phase gradient in the condensate wave function.",1503.00482v2
+2016-06-27,Stability of a skyrmion and interaction of magnons,"The stability of a single Belavin-Polyakov (BP) skyrmion in isotropic
+Heisenberg ferromagnet is studied. Such skyrmion is higher in energy than the
+uniform ferromagnetic state and is thus metastable. Starting from the lattice
+model in two spatial dimensions and using Maleyev-Dyson representation for spin
+operators, we examine the effects of magnon-magnon interaction for two
+quantities at $T=0$. First we discuss the self-energy corrections to magnon
+energy. Second we analyze the two-particle Green's function and possible bound
+states of two magnons. The simplicity of the model makes possible full analytic
+treatment of all relevant processes. We found that the magnons remain
+well-defined quasiparticles with a finite lifetime. The bound states of two
+magnons are suppressed near the skyrmion, although they are not excluded far
+away from it. A resonance for the magnons of dilational mode in the vicinity of
+BP skyrmion is also found, which leads to a redistribution of the spectral
+weight. We conclude that the BP skyrmion as the classical topological object is
+not destroyed by quantum fluctuations.",1606.08308v2
+2016-07-06,Temperature dependence of the magnon spin diffusion length and magnon spin conductivity in the magnetic insulator yttrium iron garnet,"We present a systematic study of the temperature dependence of diffusive
+magnon spin transport, using a non-local device geometry. In our measurements,
+we detect spin signals arising from electrical and thermal magnon generation,
+and we directly extract the magnon spin diffusion length $\lambda_m$ for
+temperatures from 2 to 293 K. Values of $\lambda_m$ obtained from electrical
+and thermal generation agree within the experimental error, with
+$\lambda_m=9.6\pm0.9$ $\mu$m at room temperature to a minimum of
+$\lambda_m=5.5\pm0.7$ $\mu$m at 30 K. Using a 2D finite element model to fit
+the data obtained for electrical magnon generation we extract the magnon spin
+conductivity $\sigma_m$ as a function of temperature, which is reduced from
+$\sigma_m=5.1\pm0.2\times10^5$ S/m at room temperature to
+$\sigma_m=0.7\pm0.4\times10^5$ S/m at 5 K. Finally, we observe an enhancement
+of the signal originating from thermally generated magnons for low
+temperatures, where a maximum is observed around $T=7$ K. An explanation for
+this low temperature enhancement is however still missing and requires
+additional investigations.",1607.01506v1
+2018-11-21,Squeezed states of magnons and phonons in cavity magnomechanics,"We show how to create quantum squeezed states of magnons and phonons in a
+cavity magnomechanical system. The magnons are embodied by a collective motion
+of a large number of spins in a macroscopic ferrimagnet, and couple to cavity
+microwave photons and phonons (vibrational modes of the ferrimagnet) via the
+magnetic dipole interaction and magnetostrictive interaction, respectively. The
+cavity is driven by a weak squeezed vacuum field generated by a flux-driven
+Josephson parametric amplifier, which is essential to get squeezed states of
+the magnons and phonons. We show that the magnons can be prepared in a squeezed
+state via the cavity-magnon beamsplitter interaction, and by further driving
+the magnon mode with a strong red-detuned microwave field, the phonons are
+squeezed. We show optimal parameter regimes for obtaining large squeezing of
+the magnons and phonons, which are robust against temperature and could be
+realized with experimentally reachable parameters.",1811.09668v4
+2018-11-25,Spin current cross-correlations as a probe of magnon coherence,"Motivated by the important role of the normalized second order coherence
+function, often called $g^{(2)}$, in the field of quantum optics, we propose a
+method to determine magnon coherence in solid-state devices. Namely, we show
+that the cross-correlations of pure spin-currents injected by a ferromagnet
+into two metal leads, normalized by their dc value, replicate the behavior of
+$g^{(2)}$ when magnons are driven far from equilibrium. We consider two
+scenarios: driving by ferromagnetic resonance, which leads to the coherent
+occupation of a single mode, and driving by heating of the magnons, which leads
+to an excess of incoherent magnons. We find an enhanced normalized
+cross-correlation in the latter case, thereby demonstrating bunching of
+nonequilibrium thermal magnons due to their bosonic statistics. Our results
+contribute to the burgeoning field of quantum magnonics, which seeks to explore
+and exploit the quantum nature of magnons.",1811.10001v1
+2017-06-06,Spin Seebeck effect and magnon-magnon drag in Pt/YIG/Pt structures,"The formation of the two: injected (""coherent"") and ""thermally"" excited,
+different in energies magnon subsystems and the influence of its interaction
+with phonons and between on drag effect under spin Seebeck effect conditions in
+the magnetic insulator part of the metal/ferromagnetic insulator/metal
+structure is studied. An approximation of the effective parameters, when each
+of the interacting subsystems (""injected"", ""thermal"" magnons, and phonons) is
+characterized by its own effective temperature and drift velocities have been
+considered. The analysis of the macroscopic momentum balance equations of the
+systems of interest conducted for different ratios of the drift velocities of
+the magnon and phonon currents show that the ""injected"" magnons relaxation on
+the ""thermal"" ones is possible to be dominant over its relaxation on phonons.
+This interaction will be the defining in the forming of the temperature
+dependence of the spin-wave current under spin Seebeck effect conditions, and
+inelastic part of the magnon-magnon interaction is the dominant spin relaxation
+mechanism.",1706.02154v1
+2017-10-07,Magnon-phonon relaxation in yttrium iron garnet from first principles,"We combine the theoretical method of calculating spin wave excitation with
+the finite-temperature modeling and calculate the magnon-phonon relaxation time
+in the technologically important material Yttrium iron garnet (YIG) from first
+principles. The finite lifetime of magnon excitation is found to arise from the
+fluctuation of the exchange interaction of magnetic atoms in YIG. At room
+temperature, the magnon spectra have significant broadening that is used to
+extract the magnon-phonon relaxation time quantitatively. The latter is a
+phenomenological parameter of great importance in YIG-based spintronics
+research. We find that the magnon-phonon relaxation time for the optical magnon
+is a constant while that for the acoustic magnon is proportional to $1/k^2$ in
+the long-wavelength regime.",1710.02647v1
+2017-12-22,Chiral topological insulator of magnons,"We propose a magnon realization of 3D topological insulator in the AIII
+(chiral symmetry) topological class. The topological magnon gap opens due to
+the presence of Dzyaloshinskii-Moriya interactions. The existence of the
+topological invariant is established by calculating the bulk winding number of
+the system. Within our model, the surface magnon Dirac cone is protected by the
+sublattice chiral symmetry. By analyzing the magnon surface modes, we confirm
+that the backscattering is prohibited. By weakly breaking the chiral symmetry,
+we observe the magnon Hall response on the surface due to opening of the gap.
+Finally, we show that by changing certain parameters the system can be tuned
+between the chiral topological insulator (mcTI), three dimensional magnon
+anomalous Hall (3D-mAH), and Weyl magnon phases.",1712.08612v3
+2018-09-18,Many-body theory of spin-current driven instabilities in magnetic insulators,"We consider a magnetic insulator in contact with a normal metal. We derive a
+self-consistent Keldysh effective action for the magnon gas that contains the
+effects of magnon-magnon interactions and contact with the metal to lowest
+order. Self-consistent expressions for the dispersion relation, temperature and
+chemical potential for magnons are derived. Based on this effective action, we
+study instabilities of the magnon gas that arise due to spin-current flowing
+across the interface between the normal metal and the magnetic insulator. We
+find that the stability phase diagram is modified by an interference between
+magnon-magnon interactions and interfacial magnon-electron coupling. These
+effects persist at low temperatures and for thin magnetic insulators.",1809.06738v1
+2020-12-08,Observation of 4- and 6-magnon bound-states in the spin-anisotropic frustrated antiferromagnet FeI$_2$,"Spin-waves e.g. magnons are the conventional elementary excitations of
+ordered magnets. However, other possibilities exist. For instance, magnon
+bound-states can arise due to attractive magnon-magnon interactions and
+drastically impact the static and dynamic properties of materials. Here, we
+demonstrate a zoo of distinct multi-magnon quasiparticles in the frustrated
+spin-1 triangular antiferromagnet FeI$_2$ using time-domain terahertz
+spectroscopy. The energy-magnetic field excitation spectrum contains signatures
+of one-, two-, four- and six-magnon bound-states, which we analyze using an
+exact diagonalization approach for a dilute gas of interacting magnons. The
+two-magnon single-ion bound states occur due to strong anisotropy and the
+preponderance of even higher order excitations arises from the tendency of the
+single-ion bound states to themselves form bound states due to their very flat
+dispersion. This menagerie of tunable interacting quasiparticles provides a
+unique platform in a condensed matter setting that is reminiscent of the
+few-body quantum phenomena central to cold-atom, nuclear, and particle physics
+experiments.",2012.04205v1
+2020-12-08,Inverse-design magnonic devices,"The field of magnonics offers a new type of low-power information processing,
+in which magnons, the quanta of spin waves, carry and process data instead of
+electrons. Many magnonic devices were demonstrated recently, but the
+development of each of them requires specialized investigations and, usually,
+one device design is suitable for one function only. Here, we introduce the
+method of inverse-design magnonics, in which any functionality can be specified
+first, and a feedback-based computational algorithm is used to obtain the
+device design. Our proof-of-concept prototype is based on a rectangular
+ferromagnetic area which can be patterned using square shaped voids. To
+demonstrate the universality of this approach, we explore linear, nonlinear and
+nonreciprocal magnonic functionalities and use the same algorithm to create a
+magnonic (de-)multiplexer, a nonlinear switch and a circulator. Thus,
+inverse-design magnonics can be used to develop highly efficient rf
+applications as well as Boolean and neuromorphic computing building blocks.",2012.04544v1
+2018-12-03,Microscopic theory of magnon-drag electron flow in ferromagnetic metals,"A temperature gradient applied to a ferromagnetic metal induces not only
+independent flows of electrons and magnons but also drag currents because of
+their mutual interaction. In this paper, we present a microscopic study of the
+electron flow induced by the drag due to magnons. The analysis is based on the
+$s$-$d$ model, which describes conduction electrons and magnons coupled via the
+$s$-$d$ exchange interaction. Magnetic impurities are introduced in the
+electron subsystem as a source of spin relaxation. The obtained magnon-drag
+electron current is proportional to the entropy of magnons and to $\alpha -
+\beta$ (more precisely, to $1 - \beta/\alpha$), where $\alpha$ is the Gilbert
+damping constant and $\beta$ is the dissipative spin-transfer torque parameter.
+This result almost coincides with the previous phenomenological result based on
+the magnonic spin-motive forces, and consists of spin-transfer and
+momentum-transfer contributions, but with a slight disagreement in the former.
+The result is interpreted in terms of the nonequilibrium spin chemical
+potential generated by nonequilibrium magnons.",1812.00720v1
+2018-12-05,Controlling stability of Bose-Einstein condensation of interacting magnons in an antiferromagnet by an external magnetic field,"We propose a mechanism for destabilizing or stabilizing Bose-Einstein
+condensation (BEC) of interacting magnons in an antiferromagnet. We study how
+the interaction between magnons affects the magnon BEC in a two-sublattice
+antiferromagnet without and with an external magnetic field. We show that in
+the absence of the magnetic field the magnon BEC is destabilized by the
+attractive interband interaction, which is larger than the repulsive intraband
+interaction. We also show that in the presence of the magnetic field the magnon
+BEC is stabilized only if the magnetic field is large enough to make the
+intraband interaction larger than the interband interaction. Our results
+provide the first step for understanding the interaction effects on the magnon
+BEC in antiferromagnets and may open interaction physics of multicomponent BEC
+of magnons in magnets.",1812.01787v2
+2018-12-20,Magnon-polarons in cubic collinear Antiferromagnets,"We present a theoretical study of excitations formed by hybridization between
+magnons and phonons - magnon-polarons - in antiferromagnets. We first outline a
+general approach to determining which magnon and phonon modes can and cannot
+hybridize in a system thereby addressing the qualitative questions concerning
+magnon-polaron formation. As a specific and experimentally relevant case, we
+study Nickel Oxide quantitatively and find perfect agreement with the
+qualitative analysis, thereby highlighting the strength of the former. We find
+that there are two distinct features of antiferromagnetic magnon-polarons which
+differ from the ferromagnetic ones. First, hybridization between magnons and
+the longitudinal phonon modes is expected in many cubic antiferromagnetic
+structures. Second, we find that the very existence of certain hybridizations
+can be controlled via an external magnetic field, an effect which comes in
+addition to the ability to move the magnon modes relative to the phonons modes.",1812.09239v1
+2019-03-09,Theory of the magnon Kerr effect in cavity magnonics,"We develop a theory for the magnon Kerr effect in a cavity magnonics system,
+consisting of magnons in a small yttrium iron garnet (YIG) sphere strongly
+coupled to cavity photons, and use it to study the bistability in this hybrid
+system. To have a complete picture of the bistability phenomenon, we analyze
+two different cases in driving the cavity magnonics system, i.e., directly
+pumping the YIG sphere and the cavity, respectively. In both cases, the magnon
+frequency shifts due to the Kerr effect exhibit a similar bistable behavior but
+the corresponding critical powers are different. Moreover, we show how the
+bistability of the system can be demonstrated using the transmission spectrum
+of the cavity. Our results are valid in a wide parameter regime and generalize
+the theory of bistability in a cavity magnonics system.",1903.03754v1
+2015-08-09,Magnon-Magnon Interactions in O(3) Ferromagnets and Equations of Motion for Spin Operators,"The method of equations of motion for spin operators in the case of O(3)
+Heisenberg ferromagnet is systematically analyzed starting from the effective
+Lagrangian. It is shown that the random phase approximation and the Callen
+approximation can be understood in terms of perturbation theory for type B
+magnons. Also, the second order approximation of Kondo and Yamaji for one
+dimensional ferromagnet is reduced to the perturbation theory for type A
+magnons. An emphasis is put on the physical picture, i.e. on magnon-magnon
+interactions and symmetries of the Heisenberg model. Calculations demonstrate
+that all three approximations differ in manner in which the magnon-magnon
+interactions arising from the Wess-Zumino term are treated, from where specific
+features and limitations of each of them can be deduced.",1508.01974v1
+2020-06-17,Magnon Polarons induced by a magnetic field gradient,"In this work, we report the theoretical possibility of generating magnon
+polaron excitations through a space-varying magnetic field. The spatial
+dependence of the magnetic field in the Zeeman interaction gives rise to a
+magnon-phonon coupling when a magnetic field gradient is applied, and such a
+coupling depends directly on the strength of the gradient. It is also predicted
+that the direction of the magnetic field gradient allows control over which
+phonon polarization couples to the magnons in the material. Here we develop the
+calculations of the magnon-phonon coupling for an arbitrary (anti)ferromagnet,
+which are later used to numerically study its consequences. These results are
+compared to the ones obtained with the phenomenological magnetoelastic coupling
+in YIG, where we show that the magnon polaron bandgap seen in YIG can be also
+obtained with a magnetic field gradient of $\sim 0.1$T/m which can be achieved
+with the current experimental techniques. Our results propose a new way of
+controlling the magnetoelastic coupling in an arbitrary material and open a new
+route to exploit the magnon-phonon interaction in magnonic and spintronic
+devices.",2006.09839v1
+2020-09-26,Bose condensation and spin superfluidity of magnons in a perpendicularly magnetized film of yttrium iron garnet,"The formation of a Bose condensate of magnons in a perpendicularly magnetized
+film of yttrium iron garnet under radio-frequency pumping in a strip line is
+studied experimentally. The characteristics of nonlinear magnetic resonance and
+the spatial distribution of the Bose condensate of magnons in the magnetic
+field gradient are investigated. In these experiments, the Bosonic system of
+magnons behaves similarly to the Bose condensate of magnons in the
+antiferromagnetic superfluid 3He-B, which was studied in detail earlier.
+Magnonic BEC forms a coherently precessing state with the properties of
+magnonic superfluidity. Its stability is determined by the repulsive potential
+between excited magnons, which compensates for the inhomogeneity of the
+magnetic field.",2009.12595v1
+2021-02-04,Magnonic frequency comb through nonlinear magnon-skyrmion scattering,"An optical frequency comb consists of a set of discrete and equally spaced
+frequencies and has found wide applications in the synthesis over broad
+spectral frequencies of electromagnetic wave and precise optical frequency
+metrology. Despite the analogies between magnons and photons in many aspects,
+the analogue of optical frequency comb in magnonic system has not been
+reported. Here, we theoretically study the magnon-skyrmion interaction and find
+that magnonic frequency comb (MFC) can be generated above a threshold of
+driving amplitude, where the nonlinear scattering process involving three
+magnons prevails. The mode-spacing of the MFC is equal to the breathing-mode
+frequency of skyrmion and is thus tunable by either electric or magnetic means.
+The theoretical prediction is verified by micromagnetic simulations and the
+essential physics can be generalized to a large class of magnetic solitons. Our
+findings open a new pathway to observe the frequency comb structure in magnonic
+devices, that may inspire the study of fundamental nonlinear physics in
+spintronic platform in the future.",2102.02571v3
+2019-07-10,Mechanism for a Chemical Potential of Nonequilibrium Magnons in Parametric Parallel Pumping,"We demonstrate how a magnon chemical potential is generated in parametric
+parallel pumping. We study how a time-periodic magnetic field of this pumping
+affects magnon properties of a ferrimagnet in a nonequilibrium steady state. We
+show that the magnon distribution function of our nonequilibrium steady state
+becomes the Bose distribution function with $\mu=\omega_{\textrm{p}}/2$, where
+$\mu$ is the magnon chemical potential and $\omega_{\textrm{p}}$ is the pumping
+frequency. This result is distinct from the absence of the magnon chemical
+potential in the standard theory and can qualitatively explain its generation
+in experiments. We believe our result is a first theoretical demonstration of
+the generation of the magnon chemical potential in the parametric parallel
+pumping, providing an important step towards a thorough understanding of
+properties of nonequilibrium magnons.",1907.04552v1
+2019-10-23,Electrical manipulation of spin pumping signal through nonlocal thermal magnon transport,"We study the magnon transport in the nonlocal configuration composed of two
+Pt strips on top of yttrium iron garnet, with and without the presence of RF
+microwave generated by an on-chip antenna. We find that the spin-Hall induced
+thermal magnon heating/cooling, the Oersted field as well as the Joule heating
+generated by the a.c. current in the Pt injector can significantly influence
+the spin-pumping signal measured by the Pt detector in the presence of RF
+microwave, forcing the spin-pumping voltage to show up in the first and second
+harmonic signals in the nonlocal magnon transport measurement. These results
+indicate that nonlocal magnon transport configuration can serve as a structure
+to electrically detect and manipulate the spin-pumping signal. Furthermore,
+certain caution is needed when studying the interplay between incoherent magnon
+and coherent magnon spin transport in the nonlocal transport configuration,
+since the change in microwave-induced spin-pumping voltage can overwhelm the
+incoherent magnon transport signals.",1910.10326v2
+2019-10-23,Magnon crystallization in the kagome lattice antiferromagnet,"We present numerical evidence for the crystallization of magnons below the
+saturation field at non-zero temperatures for the highly frustrated spin-half
+kagome Heisenberg antiferromagnet. This phenomenon can be traced back to the
+existence of independent localized magnons or equivalently flat-band
+multi-magnon states. We present a loop-gas description of these localized
+magnons and a phase diagram of this transition, thus providing information for
+which magnetic fields and temperatures magnon crystallization can be observed
+experimentally. The emergence of a finite-temperature continuous transition to
+a magnon-crystal is expected to be generic for spin models in dimension $D>1$
+where flat-band multi-magnon ground states break translational symmetry.",1910.10448v3
+2020-03-25,Two-photon driven magnon-pair resonance as a signature of spin-nematic order,"We theoretically study the nonlinear magnetic resonance driven by intense
+laser or electromagnetic wave in a fully polarized frustrated magnet near a
+less-visible spin-nematic ordered phase. In general, both magnons and magnon
+pairs (two-magnon bound state) appear as the low-energy excitation in the
+saturated state of spin-nematic magnets. Their excitation energies are usually
+in terahertz (THz) or gigahertz range. Magnon pairs with angular momentum
+2$\hbar$ can be excited by the simultaneous absorption of two photons, and such
+multi-photon processes occur if the applied THz laser is strong enough. We
+compute laser-driven magnetic dynamics of a frustrated four-spin system with
+both magnon ($\hbar$) and magnon-pair (2$\hbar$) like excitations which is
+analogous to a macroscopic frustrated magnet with a spin nematic phase. We
+estimate the required strength of magnetic field of laser for the realization
+of two photon absorption, taking into account dissipation effects with the
+Lindblad equation. We show that intense THz laser with ac magnetic field of
+0.1-1.0 Tesla is enough to observe magnon-pair resonance.",2003.11240v2
+2020-04-13,Revealing ultra-strong magnon-photon coupling in a polar antiferromagnet Fe2Mo3O8 by time domain terahertz spectroscopy,"Strong coupling between magnon and electromagnetic wave can lead to the
+formation of a coupled spinphoton quasiparticle named as magnon-polariton. The
+phenomenon is well studied for ferromagnetic systems inside microwave cavities
+in recent years. However, formation of magnon-polariton is rarely seen for an
+antiferromagnet (AFM) because the strong coupling condition is not easily
+fulfilled. Here we present time-domain terahertz measurement on a multiferroic
+polar antiferromagnet Fe2Mo3O8. We find clearly beating between two modes at
+frequencies above and below the electric-active magnon frequency below TN,
+which we assign to the formation of AFM magnon-polariton. An ultra-strong
+spin-photon coupling effect is derived based on the energy level splitting.
+However, the AFM magnon-polariton is absent in the frequency domain
+measurement. Our work reveals that the coherent magnon formation driven by the
+ultrashort THz pulse provides a new way to detect polariton mode splitting.",2004.05823v2
+2020-05-25,Nonlinear losses in magnon transport due to four-magnon scattering,"We report on the impact of nonlinear four-magnon scattering on magnon
+transport in microstructured Co25Fe75 waveguides with low magnetic damping. We
+determine the magnon propagation length with microfocused Brillouin light
+scattering over a broad range of excitation powers and detect a decrease of the
+attenuation length at high powers. This is consistent with the onset of
+nonlinear four-magnon scattering. Hence, it is critical to stay in the linear
+regime, when deriving damping parameters from the magnon propagation length.
+Otherwise, the intrinsic nonlinearity of magnetization dynamics may lead to a
+misinterpretation of magnon propagation lengths and, thus, to incorrect values
+of the magnetic damping of the system.",2005.12113v2
+2020-07-17,A nonlinear magnonic nano-ring resonator,"The field of magnonics, which aims at using spin waves as carriers in data
+processing devices, has attracted increasing interest in recent years. We
+present and study micromagnetically a nonlinear nanoscale magnonic ring
+resonator device for enabling implementations of magnonic logic gates and
+neuromorphic magnonic circuits. In the linear regime, this device efficiently
+suppresses spin-wave transmission using the phenomenon of critical resonant
+coupling, thus exhibiting the behavior of a notch filter. By increasing the
+spin-wave input power, the resonance frequency is shifted leading to
+transmission curves, depending on the frequency, reminiscent of the activation
+functions of neurons or showing the characteristics of a power limiter. An
+analytical theory is developed to describe the transmission curve of magnonic
+ring resonators in the linear and nonlinear regimes and validated by a
+comprehensive micromagnetic study. The proposed magnonic ring resonator
+provides a multi-functional nonlinear building block for unconventional
+magnonic circuits.",2007.09205v2
+2020-07-27,Probing thermal magnon current mediated by coherent magnon via nitrogen-vacancy centers in diamond,"Currently, thermally excited magnons are being intensively investigated owing
+to their potential in computing devices and thermoelectric conversion
+technologies. We report the detection of thermal magnon current propagating in
+a magnetic insulator yttrium iron garnet under a temperature gradient using a
+quantum sensor: electron spins associated with nitrogen-vacancy (NV) centers in
+diamond. Thermal magnon current was observed as modified Rabi oscillation
+frequencies of NV spins hosted in a beam-shaped bulk diamond that resonantly
+coupled with coherent magnon propagating over a long distance. Additionally,
+using a nanodiamond, alteration in NV spin relaxation rates depending on the
+applied temperature gradient were observed under a non-resonant NV excitation
+condition. The demonstration of probing thermal magnon current mediated by
+coherent magnon via NV spin states serves as a basis for creating a device
+platform hybridizing spin caloritronics and spin qubits.",2007.13433v6
+2020-08-02,Observation of Antiferromagnetic Magnon Pseudospin Dynamics and the Hanle effect,"We report on experiments demonstrating coherent control of magnon spin
+transport and pseudospin dynamics in a thin film of the antiferromagnetic
+insulator hematite utilizing two Pt strips for all-electrical magnon injection
+and detection. The measured magnon spin signal at the detector reveals an
+oscillation of its polarity as a function of the externally applied magnetic
+field. We quantitatively explain our experiments in terms of diffusive magnon
+transport and a coherent precession of the magnon pseudospin caused by the
+easy-plane anisotropy and the Dzyaloshinskii-Moriya interaction. This
+experimental observation can be viewed as the magnonic analogue of the
+electronic Hanle effect and the Datta-Das transistor, unlocking the high
+potential of antiferromagnetic magnonics towards the realization of rich
+electronics-inspired phenomena.",2008.00440v2
+2020-10-18,Observation of magnon-polarons in a uniaxial antiferromagnetic insulator,"Magnon-polarons, a type of hybridized excitations between magnons and
+phonons, were first reported in yttrium iron garnet as anomalies in the spin
+Seebeck effect responses. Here we report an observation of antiferromagnetic
+(AFM) magnon-polarons in a uniaxial AFM insulator Cr2O3. Despite the relatively
+higher energy of magnon than that of the acoustic phonons, near the spin-flop
+transition of ~ 6 T, the left-handed magnon spectrum shifts downward to
+hybridize with the acoustic phonons to form AFM magnon-polarons, which can also
+be probed by the spin Seebeck effect. The spin Seebeck signal is founded to be
+enhanced due to the magnon-polarons at low temperatures.",2010.08926v1
+2020-10-20,Valley Modulation and Single-Edge Transport of Magnons in Staggered Kagome Ferromagnets,"Owing to its charge-free property, magnon is highly promising to achieve
+dissipationless transport without Joule heating and thus potentially applicable
+to energy-efficient devices. Moreover, a kagome lattice, as stacking layers of
+many magnon ferromagnets, also exhibits valley structure in quasiparticle
+spectra, which are likely to add a new dimension to magnon excitation. Here, we
+investigate valley magnon and associated valley modulation in a kagome lattice,
+with staggered exchange interaction and Dzyaloshinskii-Moriya interaction. The
+staggered exchange interaction breaks spatial inversion symmetry, leading to
+gapped degenerate valleys at $\pm K$ and consequent valley magnon Hall effect.
+When the Dzyaloshinskii-Moriya interaction is further included, the valley
+degeneracy is lifted. As a result, net magnon anomalous Hall effect and
+topological phase transition are realized. More interestingly, by tuning valley
+splitting and excitation frequency, heat currents in the kagome strip can be
+localized at one edge to achieve single-edge transport. Besides, for the kagmon
+lattice, the edge heat currents include local circulating contribution within
+triangular fine structure, together with currents flowing parallel to the
+edges. These findings give full play to spin and valley degrees of freedom and
+enrich energy-efficient magnonic device paradigms.",2010.09945v1
+2020-11-17,Local and nonlocal spin Seebeck effect in lateral Pt-$\mathrm{Cr_2O_3}$-Pt devices at low temperatures,"We have studied thermally driven magnon spin transport (spin Seebeck effect,
+SSE) in heterostructures of antiferromagnetic $\alpha$-$\mathrm{Cr_2O_3}$ and
+Pt at low temperatures. Monitoring the amplitude of the local and nonlocal SSE
+signals as a function of temperature, we found that both decrease with
+increasing temperature and disappear above 100 K and 20 K, respectively.
+Additionally, both SSE signals show a tendency to saturate at low temperatures.
+The nonlocal SSE signal decays exponentially for intermediate injector-detector
+separation, consistent with magnon spin current transport in the relaxation
+regime. We estimate the magnon relaxation length of our
+$\alpha$-$\mathrm{Cr_2O_3}$ films to be around 500 nm at 3 K. This short magnon
+relaxation length along with the strong temperature dependence of the SSE
+signal indicates that temperature-dependent inelastic magnon scattering
+processes play an important role in the intermediate range magnon transport.
+Our observation is relevant to low-dissipation antiferromagnetic magnon memory
+and logic devices involving thermal magnon generation and transport.",2011.08885v2
+2021-06-17,Cavity Magnonics,"Cavity magnonics deals with the interaction of magnons - elementary
+excitations in magnetic materials - and confined electromagnetic fields. We
+introduce the basic physics and review the experimental and theoretical
+progress of this young field that is gearing up for integration in future
+quantum technologies. Much of its appeal is derived from the strong
+magnon-photon coupling and the easily-reached nonlinear regime in microwave
+cavities. The interaction of magnons with light as detected by Brillouin light
+scattering is enhanced in magnetic optical resonators, which can be employed to
+manipulate magnon distributions. The cavity photon-mediated coupling of a
+magnon mode to a superconducting qubit enables measurements in the single
+magnon limit.",2106.09312v1
+2021-07-23,Dzyaloshinskii-Moriya Induced Topological Magnon-Phonon Hybridization in 2D Antiferromagnetic Insulators with Tunable Chern Numbers,"We theoretically study magnon-phonon hybrid excitations (magnon-polarons) in
+two-dimensional antiferromagnets on a honeycomb lattice. With an in-plane
+Dzyaloshinskii-Moriya interaction (DMI) allowed from mirror symmetry breaking
+from phonons, we find non-trivial Berry curvature around the anti-crossing
+rings among magnon and both optical and acoustic phonon bands, which gives rise
+to finite Chern numbers. We show that the Chern numbers of the magnon-polaron
+bands can be manipulated by changing the magnetic field direction or strength.
+We evaluate the thermal Hall conductivity reflecting the non-trivial Berry
+curvatures of magnon-polarons and propose a valley Hall effect resulting from
+spin-induced chiral phonons as a possible experimental signature. Our study
+complements prior work on magnon-phonon hybridized systems without optical
+phonons and suggests possible applications in spin caloritronics with
+topological magnons and chiral phonons.",2107.11484v1
+2021-11-24,A generalized model of magnon kinetics and subgap magnetic noise,"Magnetic noise spectroscopy provides a noninvasive probe of spin dynamics in
+magnetic materials. We consider two-dimensional magnetically ordered insulators
+with magnon excitations, especially those supporting long-distance magnon
+transport, where nitrogen-vacancy (NV) centers enable the access to (nearly)
+ballistic transport regime of magnons. We develop a generalized theory to
+describe the magnon transport across a wide range of length scales. The
+longitudinal dynamic spin susceptibility is derived from the Boltzmann equation
+and extended to a Lindhard form, which is modified by both the spin-conserving
+magnon collisions and spin relaxation. Our result is consistent with the
+diffusive (ballistic) model for the length scale much larger (smaller) than the
+magnon mean free path, and provides a description for the intermediate regime.
+We also give a prediction for the NV transition rate in different magnon
+transport regimes.",2111.12613v2
+2021-12-01,Strong Long-Range Spin-Spin Coupling via a Kerr Magnon Interface,"Strong long-range coupling between distant spins is crucial for spin-based
+quantum information processing. However, achieving such a strong spin-spin
+coupling remains challenging. Here we propose to realize a strong coupling
+between two distant spins via the Kerr effect of magnons in a
+yttrium-iron-garnet nanosphere. By applying a microwave field on this
+nanosphere, the Kerr effect of magnons can induce the magnon squeezing, so that
+the coupling between the spin and the squeezed magnons can be exponentially
+enhanced. This in turn allows the spin-magnon distance to increase from nano-
+to micrometer scale. By considering the virtual excitation of the squeezed
+magnons in the dispersive regime, strong spin-spin coupling mediated by the
+squeezed magnons can be achieved, and a remote quantum-state transfer, as well
+as the nonlocal two-qubit ISWAP gate with high fidelity becomes implementable.
+Our approach offers a feasible scheme to perform quantum information processing
+among distant spins.",2112.00452v3
+2021-12-21,Giant dynamical electron-magnon coupling in metal-metal-ferromagnetic insulator heterostructure,"Magnon-mediated spin transport across nonmagnetic metal (NM) and
+ferromagnetic insulator (FI) interface depends critically on electron-magnon
+coupling. We propose a novel route to enhance electron-magnon coupling
+dynamically from transport viewpoint. Using non-equilibrium Green's function a
+theoretical formalism for magnon-mediated spin current is developed. In the
+language of transport, the effective electron-magnon coupling at NM/FI
+interface is determined by self-energy of FI lead, which is proportional to
+density of states (DOS) at NM/FI interface due to nonlinear process of
+electron-magnon conversion. By modifying interfacial DOS, the spin conductance
+of 2D and 3D NM/FI systems can be increased by almost three orders of
+magnitude, setting up a new platform of manipulating dynamical electron-magnon
+coupling.",2112.11021v1
+2021-12-22,Topological magnon modes on honeycomb lattice with coupling textures,"Topological magnon modes are expected to be useful for novel applications
+such as robust information propagation, since they are immune to backscattering
+and robust against disorder. Although there are several of theoretical
+proposals for topological magnon modes and growing experimental efforts for
+realizing them by now, it is still desirable to add complementary insights on
+this important phenomenon. Here, we propose a new scheme to achieve topological
+magnon where only nearest-neighbour exchange couplings on honeycomb lattice are
+necessary. In both ferromagnets and antiferromagnets, tuning exchange couplings
+between and inside hexagonal unit cells induces a topological state accompanied
+by a band inversion between p-orbital and d-orbital like magnon modes.
+Topological magnon modes appear at the interface between a topological domain
+and a trivial domain with magnon currents, which counterpropagate depending on
+pseudospins originated from orbital angular momenta of magnon modes. This
+mimics the spin-momentum locking phenomenon in the quantum spin Hall effect.",2112.11652v1
+2021-12-29,Excitation and detection of coherent sub-terahertz magnons in ferromagnetic and antiferromagnetic heterostructures,"Excitation of coherent high-frequency magnons (quanta of spin waves) is
+critical to the development of high-speed magnonic devices. Here we
+computationally demonstrate the excitation of coherent sub-terahertz (THz)
+magnons in ferromagnetic (FM) and antiferromagnetic (AFM) thin films by a
+photoinduced picosecond acoustic pulse. Analytical calculations are also
+performed to reveal the magnon excitation mechanism. Through spin pumping and
+spin-charge conversion, these magnons can inject sub-THz charge current into an
+adjacent heavy-metal film which in turn emits electromagnetic (EM) waves. Using
+a dynamical phase-field model that considers the coupled dynamics of acoustic
+waves, spin waves, and EM waves, we show that the emitted EM wave retains the
+spectral information of all the sub-THz magnon modes and has a sufficiently
+large amplitude for near-field detection. These predictions indicate that the
+excitation and detection of sub-THz magnons can be realized in rationally
+designed FM or AFM thin-film heterostructures via ultrafast optical-pump
+THz-emission-probe spectroscopy.",2112.14749v2
+2022-05-29,Magnon squeezing enhanced entanglement in a cavity magnomechanical system,"We investigate the generation of the entanglement in a cavity magnomechanical
+system, which consists of three modes: a magnon mode, a microwave cavity mode
+and a mechanical vibration mode, the couplings of the magnon-photon and the
+magnon-phonon are achieved by the magnetic dipole interaction and the
+magnetostrictive interaction, respectively. By introducing a squeezing of the
+magnon mode, the magnon-photon and the magnon-phonon entanglements are
+significantly enhanced compared with the case without inserting the magnon
+squeezing. We find that an optimal parameter of the squeezing exists, which
+yields the maximum entanglement. This study provides a new idea for exploring
+the properties of quantum entanglement in the the cavity magnomechanical
+systems, and may have some potential applications in the quantum state
+engineering.",2205.14569v2
+2022-10-21,Tuning bulk topological magnon properties with light-induced magnons,"Although theoretical modelling and inelastic neutron scattering measurements
+have indicated the presence of topological magnon bands in multiple quantum
+magnets, experiments remain unable to detect signal of magnon thermal Hall
+effect in the quantum magnets, which is a consequence of magnons condensation
+at the bottom of the bands following Bose Einstein statistics as well as the
+concentration of Berry curvature at the higher energies. In a recent work, Malz
+et al.[Nature Communications 10, 3937 (2019)] have shown that topological
+magnons in edge states in a finite sample can be amplified using tailored
+electromagnetic fields. We extend their approach by showing that a uniform
+electromagnetic field can selectively amplify magnons with finite Berry
+curvature by breaking inversion symmetry of a lattice. Using this approach, we
+demonstrate the generation of bulk topological magnons in a Heisenberg
+ferromagnet on the breathing kagome lattice and the consequent amplification of
+thermal Hall effect.",2210.12087v2
+2022-10-31,Nonlinear spin current of photoexcited magnons in collinear antiferromagnets,"We study the nonlinear magnon spin current induced by an ac electric field
+under light irradiation in collinear antiferromagnets with broken inversion
+symmetry. For linearly polarized light, we find that a dc spin current appears
+through ``the magnon spin shift current"" mechanism, which is driven by a spin
+polarization generation in the two magnon creation process and has a close
+relationship to the geometry of magnon bands through Berry connection. For
+circularly polarized light, a dc spin current appears through ``the spin
+injection current"" mechanism, which is proportional to the relaxation time of
+magnons and can be large when the magnon lifetime is long. We demonstrate
+generation of the magnon spin shift and injection currents, based on a few toy
+models and a realistic model for a multiferroic material M$_2$Mo$_3$O$_8$.",2210.17099v3
+2022-12-12,Magnon-Plasmon Hybridization Mediated by Spin-Orbit Interaction in Magnetic Materials,"We propose a mechanism for magnon-plasmon coupling and hybridization in
+ferromagnetic (FM) and antiferromagnetic (AFM) systems. The electric field
+associated with plasmon oscillations creates a non-equilibrium spin density via
+the inverse spin galvanic effect. This plasmon-induced spin density couples to
+magnons by an exchange interaction. The strength of magnon-plasmon coupling
+depends on the magneto-electric susceptibility of the system and the wavevector
+at which the level repulsion is happened. This wavevector may be tuned by an
+applied magnetic field. In AFM systems, the degeneracy of two chiral magnons is
+broken in the presence of a magnetic field, and we find two separate hybrid
+modes for left-handed and right-handed AFM magnons. Furthermore, we show that
+magnon-plasmon coupling in AFM systems is enhanced because of strong
+intra-sublattice spin dynamics. We argue that the recently discovered
+two-dimensional magnetic systems are ideal platforms to investigate proposed
+magnon-plasmon hybrid modes.",2212.06105v1
+2023-02-14,Switchable Superradiant Phase Transition with Kerr Magnons,"The superradiant phase transition (SPT) has been widely studied in cavity
+quantum electrodynamics (CQED). However, this SPT is still subject of ongoing
+debates due to the no-go theorem induced by the so-called ${\bf A}^2$ term
+(AT). We propose a hybrid quantum system, consisting of a single-mode cavity
+simultaneously coupled to both a two-level system and yttrium-iron-garnet
+sphere supporting magnons with Kerr nonlinearity, to restore the SPT against
+the AT. The Kerr magnons here can effectively introduce an additional strong
+and tunable AT to counteract the intrinsic AT, via adiabatically eliminating
+the degrees of freedom of the magnons. We show that the Kerr magnons induced
+SPT can exist in both cases of ignoring and including the intrinsic AT. Without
+the intrinsic AT, the critical coupling strength can be dramatically reduced by
+introducing the Kerr magnons, which greatly relaxes the experimental conditions
+for observing the SPT. With the intrinsic AT, the forbidden SPT can be
+recovered with the Kerr magnons in a reversed way. Our work paves a potential
+way to manipulate the SPT against the AT in hybrid systems combining CQED and
+nonlinear magnonics.",2302.07163v2
+2023-02-17,Entangling ferrimagnetic magnons with an atomic ensemble via opto-magnomechanics,"We show how to prepare macroscopic entanglement between an atomic ensemble
+and a large number of magnons in a ferrimagnetic YIG crystal. Specifically, we
+adopt an opto-magnomechanical configuration where the magnetostriction-induced
+magnomechanical displacement couples to an optical cavity via radiation
+pressure, and the latter further couples to an ensemble of two-level atoms that
+are placed inside the cavity. We show that by properly driving the cavity and
+magnon modes, optomechanical entanglement is created which is further
+distributed to the atomic and magnonic systems, yielding stationary
+entanglement between atoms and magnons. The atom-magnon entanglement is a
+result of the combined effect of opto- and magnomechanical cooling and
+optomechanical parametric down-conversion interactions. A competition mechanism
+between two mechanical cooling channels is revealed. We further show that
+genuine tripartite entanglement of three massive subsystems, i.e., atoms,
+magnons and phonons, can also be achieved in the same system. Our results
+indicate that the hybrid opto-magnomechanical system may become a promising
+system for preparing macroscopic quantum states involving magnons, photons,
+phonons and atoms.",2302.08684v2
+2023-03-20,Meter-scale strong coupling between magnons and photons,"We experimentally realize a meter-scale strong coupling effect between
+magnons and photons at room temperature, with a coherent coupling of 20 m and a
+dissipative coupling of 7.6 m. To this end, we integrate a saturable gain into
+a microwave cavity and then couple this active cavity to a magnon mode via a
+long coaxial cable. The gain compensates for the cavity dissipation, but
+preserves the cavity radiation that mediates the indirect photon-magnon
+coupling. It thus enables the long-range strong photon-magnon coupling. With
+full access to traveling waves, we demonstrate a remote control of
+photon-magnon coupling by modulating the phase and amplitude of traveling
+waves, rather than reconfiguring subsystems themselves. Our method for
+realizing long-range strong coupling in cavity magnonics provides a general
+idea for other physical systems. Our experimental achievements may promote the
+construction of information networks based on cavity magnonics.",2303.10925v3
+2023-04-20,Magnon peak lineshape in the transverse dynamical structure factor of a magnetically polarized easy-axis $XXZ$ chain at low temperatures,"The ferromagnetically polarized gapped XXZ spin chain is studied at low
+temperatures. Utilizing only the one- and two-magnon spectrums and focusing on
+the magnon-creation contribution to the transverse dynamical susceptibility, we
+represent the latter in the form of the Dyson equation. Then, following the
+well known correspondence between the imaginary part of magnetic susceptibility
+and dynamical structure factor, we get the low-temperature formula for the
+magnon-peak lineshape. The suggested approach is effective only if the
+processes related to magnon creations and to transitions from magnons to
+coupled magnon pairs are energetically separated. As it is shown in the paper,
+such separation is inherent in the easy-axis chains with rather strong
+anisotropy. We present several plots and discuss their lineshapes. As the
+supplemental result we obtain integral representations for the
+temperature-dependent magnon resonance shift and the parameter which is usually
+associated with the decay rate. The low-temperature behavior of the resonance
+shift is studied in details. All calculations are performed up to {\it
+controllable} error $o({\rm e}^{-\beta E_{gap}})$.",2304.10645v2
+2023-06-09,Magnonic frequency comb in the magnomechanical resonator,"An optical frequency comb is a spectrum of optical radiation which consists
+of evenly spaced and phase-coherent narrow spectral lines and is initially
+invented in laser for frequency metrology purposes. A direct analogue of
+frequency combs in the magnonic systems has not been demonstrated to date. In
+our experiment, we generate a new magnonic frequency comb in the resonator with
+giant mechanical oscillation through the magnomechanical interaction. We
+observe the magnonic frequency comb contains up to 20 comb lines, which are
+separated to the mechanical frequency of the 10.08 MHz. The thermal effect
+based on the strong pump power induces the cyclic oscillation of the magnon
+frequency shift, which leads to a periodic oscillation of the magnonic
+frequency comb. Moreover, we demonstrate the stabilization and control of the
+frequency spacing of the magnonic frequency comb via injection locking. Our
+work lays the groundwork of magnonic frequency combs for sensing and metrology.",2306.07985v1
+2023-12-12,Interacting Floquet topological magnons in laser-irradiated Heisenberg honeycomb ferromagnets,"When a Heisenberg honeycomb ferromagnet is irradiated by high frequency
+circularly polarized light, the underlying uncharged magnons acquire a time
+dependent Aharonov Casher phase, which makes it a Floquet topological magnon
+insulator. In this context, we investigate the many body interaction effects of
+Floquet magnons in laser irradiated Heisenberg honeycomb ferromagnets with
+ocontaining Dzyaloshinskii Moriya interaction under the application of
+circularly polarized off resonant light. We demonstrate that the quantum
+ferromagnet systems periodically laser driven exhibits temperature driven
+topological phase transitions due to Floquet magnon magnon interactions. The
+thermal Hall effect of Floquet magnons serves as a prominent signature for
+detecting these many body effects near the critical point, enabling
+experimental investigation into this phenomenon. Our study complements the lack
+of previous theoretical works that the topological phase transition of the
+Floquet magnon under the linear spin wave approximation is only tunable by the
+light field. Our study presents a novel approach for constructing Floquet
+topological phases in periodically driven quantum magnet systems that goes
+beyond the limitations of the linear spin wave theory. We provide numerical
+results based on the well known van der Waals quantum magnet CrX3 (X=F, Cl, Br,
+and I), calling for experimental implementation.",2312.06929v1
+2023-12-14,Magnetization Reversal of 50-nm-wide Ni81Fe19 Nanostripes by Ultrashort Magnons in Yttrium Iron Garnet for Memory-Enhanced Magnonic Circuits,"Spin waves (magnons) can enable wave-based neuromorphic computing by which
+one aims at overcoming limitations inherent to conventional electronics and the
+von Neumann architecture. In this study, we explore the storage of magnon
+signals and the magnetization switching of periodic and aperiodic arrays of
+Ni81Fe19 (Py) nanostripes with widths (w) between 50 nm and 200 nm. Spin waves
+excited with low microwave power in yttrium iron garnet induce the reversal of
+the nanostripes of different w in a small opposing field. Exploiting
+microwave-to-magnon transducers for magnon modes with ultrashort wavelengths,
+we demonstrate the reversal of 50-nm-wide Py nanostripes by magnons with
+wavelength ~ 100 nm after they have propagated over 25 micrometer in YIG. The
+findings are important for designing a magnon-based in-memory computing device.",2312.09177v1
+2024-03-22,Tunable ultrastrong magnon magnon coupling and spin Hall magnetoresistance in a van der Waals antiferromagnet,"Antiferromagnetic (AFM) magnons and the manipulation of magnetisation via
+spin currents in van der Waals (vdW) materials offer substantial potential for
+applications in magnonics and spintronics. In this study, we demonstrate
+ultrastrong magnon-magnon coupling in the GHz regime within a vdW AFM,
+achieving a remarkable maximum normalised coupling strength of 0.47. Our
+investigation unveils the tunability of coupling strength through
+temperature-dependent magnetic anisotropies. Additionally, we show the prospect
+for further enhancement to the deep-strong magnon-magnon coupling regime by
+manipulating the anisotropy. Furthermore, we report spin Hall magnetoresistance
+in a vdW AFM-based device and study the field and temperature dependence. These
+findings highlight the transformative potential of vdW AFMs in advancing the
+field of spin-based technologies.",2403.15558v1
+2016-02-22,A first theoretical realization of honeycomb topological magnon insulator,"It has been recently shown that in the Heisenberg (anti)ferromagnet on the
+honeycomb lattice, the magnons (spin wave quasipacticles) realize a massless
+two-dimensional (2D) Dirac-like Hamiltonian. It was shown that the Dirac magnon
+Hamiltonian preserves time-reversal symmetry defined with the sublattice pseudo
+spins and the Dirac points are robust against magnon-magnon interactions. The
+Dirac points also occur at nonzero energy. In this paper, we propose a simple
+realization of nontrivial topology (magnon edge states) in this system. We show
+that the Dirac points are gapped when the inversion symmetry of the lattice is
+broken by introducing a next-nearest neighbour Dzyaloshinskii-Moriya (DM)
+interaction. Thus, the system realizes magnon edge states similar to Haldane
+model for quantum anomalous Hall effect in electronic systems. However, in
+contrast to electronic spin current where dissipation can be very large due to
+Ohmic heating, noninteracting topological magnons can propagate for long time
+without dissipation as magnons are uncharged particles. We observe the same
+magnon edge states for the XY model on the honeycomb lattice. Remarkably, in
+this case the model maps to interacting hardcore bosons on the honeycomb
+lattice. Quantum magnetic systems with nontrivial magnon edge states are called
+topological magnon insulators. They have been studied theoretically on the
+kagome lattice and recently observed experimentally on the kagome magnet
+Cu(1-3, bdc) with three magnon bulk bands. Our results for the honeycomb
+lattice suggests an experimental procedure to search for honeycomb topological
+magnon insulators within a class of 2D quantum magnets and ultracold atoms
+trapped in honeycomb optical lattices.",1602.06772v6
+1997-10-24,Infinite coupling magnon theory of quantum Heisenberg magnetic models of spin s,"An infinity magnon coupling term is introduced into the Holstein-Primakoff
+transformed forms of the Heisenberg ferromagnetic and antiferromagnetic models
+of any spin $s$ to rigorously remove the unphysical magnon states. This term
+makes the series expansion of the square root of the magnon operators become a
+finite series of magnon operator products. Under a simple Hubbard-like
+approximation our infinite coupling theory yields much better result than the
+existing spin wave theories, especially near transition temperatures.",9710261v1
+1999-04-26,Magnon Damping by magnon-phonon coupling in Manganese Perovskites,"Inelastic neutron scattering was used to systematically investigate the
+spin-wave excitations (magnons) in ferromagnetic manganese perovskites. In
+spite of the large differences in the Curie temperatures ($T_C$s) of different
+manganites, their low-temperature spin waves were found to have very similar
+dispersions with the zone boundary magnon softening. From the wavevector
+dependence of the magnon lifetime effects and its correlation with the
+dispersions of the optical phonon modes, we argue that a strong magneto-elastic
+coupling is responsible for the observed low temperature anomalous spin
+dynamical behavior of the manganites.",9904372v1
+2003-09-09,Magnon-Hole Scattering and Charge Order in $Sr_{14-x}Ca_xCu_{24}O_{41}$,"The magnon thermal conductivity $\kappa_{\mathrm{mag}}$ of the hole doped
+spin ladders in $\rm Sr_{14-x}Ca_xCu_{24}O_{41}$ has been investigated at low
+doping levels $x$. The analysis of $\kappa_{\mathrm{mag}}$ reveals a strong
+doping and temperature dependence of the magnon mean free path
+$l_{\mathrm{mag}}$ which is a local probe for the interaction of magnons with
+the doped holes in the ladders. In particular, this novel approach to studying
+charge degrees of freedom via spin excitations shows that charge ordering of
+the holes in the ladders leads to a freezing out of magnon-hole scattering
+processes.",0309232v2
+2005-11-14,Magnon decay in gapped quantum spin systems,"In the O(3) sigma-model description of gapped spin systems, S=1 magnons can
+only decay into three lower energy magnons. We argue that the symmetry of the
+quantum spin Hamiltonian often allows decay into two magnons, and compute this
+decay rate in model systems. Two magnon decay is present in Haldane gap S=1
+spin chains, even though it cannot be induced by any allowed term written in
+powers and gradients of the sigma-model field. We compare our results with
+recent measurements of Stone et al. (cond-mat/0511266) on a two-dimensional
+spin system.",0511353v1
+2008-10-07,Finite size giant magnons in the SU(2) x SU(2) sector of AdS_4 x CP^3,"We use the algebraic curve and Luscher's mu-term to calculate the leading
+order finite size corrections to the dispersion relation of giant magnons in
+the SU(2) x SU(2) sector of AdS_4 x CP^3. We consider a single magnon as well
+as one magnon in each SU(2). In addition the algebraic curve computation is
+generalized to give the leading order correction for an arbitrary multi-magnon
+state in the SU(2) x SU(2) sector.",0810.1246v3
+2008-10-22,Probing of a parametrically pumped magnon gas with a non-resonant packet of traveling spin waves,"The magnon gas created by spatially localized longitudinal parametric pumping
+in an yttrium-iron-garnet film is probed by a traveling packet of spin waves
+non-resonant with the pumping field. The analysis of the influence of the
+magnon gas on the amplitude and phase of the propagating spin waves allows to
+determine characteristic properties of the parametrically pumped magnon gas. A
+simple theoretical model is proposed from which the magnon density in the
+pumping region is calculated.",0810.4033v1
+2008-12-04,Bose-Einstein condensation of magnons under incoherent pumping,"Bose-Einstein condensation in a gas of magnons pumped by an incoherent
+pumping source is experimentally studied at room temperature. We demonstrate
+that the condensation can be achieved in a gas of bosons under conditions of
+incoherent pumping. Moreover, we show the critical transition point is almost
+independent of the frequency spectrum of the pumping source and is solely
+determined by the density of magnons. The electromagnetic power radiated by the
+magnon condensate was found to scale quadratically with the pumping power,
+which is in accordance with the theory of Bose-Einstein condensation in magnon
+gases.",0812.0953v1
+2008-12-15,Unbounded Multi-Magnon and Spike,"We generalize the one magnon solution in R X S^2 to unbounded M magnon and
+find the corresponding solitonic string configuration in the string sigma
+model. This configuration gives rise to the expected dispersion relation
+obtained from the spin chain model in the large 't Hooft coupling limit. After
+considering (M,M) multi-magnon or spike on R X S^2 X S^2 as a subspace of
+AdS(5)XS^5 or AdS(4)XCP^3, we investigate the dispersion relation and the
+finite size effect for (M,M) multi-magnon or spike.",0812.2727v2
+2009-01-28,Relativistic ferromagnetic magnon at the zigzag edge of graphene,"We study the spin-wave excitations near the zigzag edge of graphene. It is
+rather interesting that we obtain a single branch of relativistic ferromagnetic
+magnon due to the presence of the open boundary. Note that magnons in
+antiferomagnets appear in pairs, while the single brach magnon in ferromagnets
+does not have relativistic dispersion. Thus, the magnon near the zigzag edge of
+graphene is a hybrid of both, signaling its intrinsic property as a boundary
+excitation that must be embedded in a higher dimensional bulk system.",0901.4567v1
+2010-12-18,Raman scattering due to a one-magnon excitation process in ${\rm MnV_2O_4}$,"Unconventional peak structure in the Raman spectra due to magnon excitation
+at low temperature is observed in spinel magnet ${\rm MnV_2O_4}$, where a
+noncollinear spin state is realized by geometrical frustration. We propose a
+new mechanism to induce such a Raman scattering process due to a one-magnon
+excitation of the noncollinear spin state. Novel features of the scattering
+such as selection rules and peak position observed experimentally in ${\rm
+MnV_2O_4}$ can be explained quite naturally by considering the present
+one-magnon process. We also discuss that such one-magnon process may exist in
+various materials with noncollinear spin structures.",1012.4073v1
+2011-09-01,Light-matter interaction in antiferromagnets: the exchange-induced magnetic dipole mechanism,"We propose a novel mechanism for exchange-induced exciton-magnon absorptions
+via hopping between two antiferromagnetically coupled sites and a simultaneous
+magnetic dipole transition to an excited orbital state. The obtained selection
+rules correspond to ones for magnetic dipole transitions and are in agreement
+with the exciton-magnon transitions observed in the quasi one-dimensional
+Heisenberg antiferromagnet KCuF3. The calculated magnon density of states in
+combination with a structure dependent factor identifies the observed optical
+magnon sideband to originate from transverse magnon modes.",1109.0295v2
+2011-09-12,Spin-transfer mechanism for magnon-drag thermopower,"We point out a relation between the dissipative spin-transfer-torque
+parameter $\beta$ and the contribution of magnon drag to the thermoelectric
+power in conducting ferromagnets. Using this result we estimate $\beta$ in iron
+at low temperatures, where magnon drag is believed to be the dominant
+contribution to the thermopower. Our results may be used to determine $\beta$
+from magnon-drag-thermopower experiments, or, conversely, to infer the strength
+of magnon drag via experiments on spin transfer.",1109.2414v1
+2013-02-22,s-f(d) exchange mechanism of magnon generation by slow spinpolarons,"It is shown that in a single-axis antiferromagnetic semiconductor placed in a
+strong magnetic field, dispersionless magnons start emitting at any arbitrarily
+small velocity of an electron occurring in a spinpolaron state. If magnons are
+dispersed they are generated when the spinpolaron velocity exceeds the minimum
+phase velocity of magnons. The maximum power of magnon generation caused by the
+drift of spinpolarons is estimated.",1302.5698v1
+2013-04-07,Phenomenological model of anomalous magnon softening and damping in half-metallic manganites,"To describe anomalous zone-boundary softening and damping of magnons in
+manganites we present a phenomenological two-fluid model containing
+ferromagnetic Fermi-liquid and non-Fermi-liquid components. The Fermi-liquid
+component accounts for softening of zone-boundary magnons and for the Landau
+damping of magnons in the Stoner continuum arising at low frequencies due to
+zero-point effects. Coupling of the Fermi-liquid and non-Fermi-liquid fluids
+yields conventional long wavelength magnons damped due to their coupling with
+longitudinal spin fluctuations.",1304.1983v1
+2013-05-18,Josephson Effects in a Bose-Einstein Condensate of Magnons,"A phenomenological theory is developed, that accounts for the collective
+dynamics of a Bose-Einstein condensate of magnons. In terms of such description
+we discuss the nature of spontaneous macroscopic interference between magnon
+clouds, highlighting the close relation between such effects and the well known
+Josephson effects. Using those ideas we present a detailed calculation of the
+Josephson oscillations between two magnon clouds, spatially separated in a
+magnonic Josephson junction.",1305.4285v2
+2015-05-08,Thermal vector potential theory of magnon-driven magnetization dynamics,"Thermal vector potential formulation is applied to study thermal dynamics of
+magnetic structures in insulating ferromagnets. By separating variables of the
+magnetic structure and magnons, the equation of motion for the structure
+including spin-transfer effect due to thermal magnons is derived in the case of
+a domain wall and a vortex. The magnon current is evaluated based on a linear
+response theory with respect to the thermal vector potential representing the
+temperature gradient. It is shown that the velocity of a domain wall when
+driven by thermal magnon has a strong temperature dependence unlike the case of
+an electrically-driven domain wall in metals.",1505.01908v1
+2018-05-25,Theory of Cross-correlated Electron-Magnon Transport Phenomena: Case of Magnetic Topological Insulator,"We study transport phenomena cross-correlated among the heat and electric
+currents of magnons and Dirac electrons on the surface of ferromagnetic
+topological insulators. For a perpendicular magnetization, we calculate magnon-
+(electron-) drag anomalous Nernst/Seebeck (anomalous Ettingshausen/Peltier)
+effects and magnon-/electron-drag thermal Hall effects. The magnon-drag
+thermoelectric effects are interpreted to be caused by magnon-induced
+electromotive force. When the magnetization has in-plane components, there
+arise thermal/thermoelectric analogs of anisotropic magnetoresistance (AMR). In
+the insulating state, the thermal AMR is realized as a magnonic analog of AMR.",1805.10323v2
+2017-06-13,Signature of magnon Nernst effect in an antiferromagnetic insulator,"A magnon Nernst effect, an antiferromagnetic analogue of the magnon Hall
+effect in ferromagnetic insulators, has been studied experimentally for a
+layered antiferromagnetic insulator MnPS3 in contact with two Pt strips.
+Thermoelectric voltage in the Pt strips grown on MnPS3 single crystals exhibits
+non-monotonic temperature dependence at low temperatures, which cannot be
+explained by electronic origins in Pt but can be ascribed to the inverse spin
+Hall voltage induced by a magnon Nernst effect. Control of antiferromagnetic
+domains in the MnPS3 crystal by magnetoelectric cooling is found to modulate
+the low-temperature thermoelectric voltage in Pt, which corroborates the
+emergence of the magnon Nernst effect in Pt|MnPS3 hybrid structures.",1706.03978v1
+2018-06-04,An analog magnon adder for all-magnonic neurons,"Spin-waves are excellent data carriers with a perspective use in neuronal
+networks: Their lifetime gives the spin-wave system an intrinsic memory, they
+feature strong nonlinearity, and they can be guided and steered through
+extended magnonic networks. In this work, we present a magnon adder that
+integrates over incoming spin-wave pulses in an analog fashion. Such an adder
+is a linear prequel to a magnonic neuron, which would integrate over the
+incoming pulses until a certain nonlinearity is reached. In this work, the
+adder is realized by a resonator in combination with a parametric amplifier
+which is just compensating the resonator losses.",1806.01389v1
+2018-06-18,Relation between unidirectional spin Hall magnetoresistance and spin current-driven magnon generation,"We perform electronic measurements of unidirectional spin Hall
+magnetoresistance (USMR) in a Permalloy/Pt bilayer, in conjunction with
+magneto-optical Brillouin light spectroscopy of spin current-driven magnon
+population. We show that the current dependence of USMR closely follows the
+dipolar magnon density, and that both dependencies exhibit the same scaling
+over a large temperature range of 80-400 K. These findings demonstrate a close
+relationship between spin current-driven magnon generation and USMR, and
+indicate that the latter is likely dominated by the dipolar magnons.",1806.06581v1
+2018-12-28,Topological Magnons and Edge States in Antiferromagnetic Skyrmion Crystals,"Antiferromagnetic skyrmion crystals are magnetic phases predicted to exist in
+antiferromagnets with Dzyaloshinskii-Moriya interactions. Their spatially
+periodic noncollinear magnetic texture gives rise to topological bulk magnon
+bands characterized by nonzero Chern numbers. We find topologically-protected
+chiral magnonic edge states over a wide range of magnetic fields and
+Dzyaloshinskii-Moriya interaction values. Moreover, and of particular
+importance for experimental realizations, edge states appear at the lowest
+possible energies, namely, within the first bulk magnon gap. Thus,
+antiferromagnetic skyrmion crystals show great promise as novel platforms for
+topological magnonics.",1812.11125v1
+2019-02-11,Magnon excitations in $Cs_2CuAl_4O_8$ - a bond alternating S=1/2 spin chain with next nearest neighbor coupling,"A recent density functional theory (DFT) based analysis, complemented with
+Quantum Monte Carlo calculations revealed a highly spin-frustrating nature of
+the one-dimensional spin-$\frac{1}{2}$ compound $Cs_2CuAl_4O_8$ that comprises
+of unique bond alternations and relatively strong next nearest neighbor
+interactions. This article gives a brief account on possible magnon excitations
+that can appear in the ground state of such systems. We find that the spin
+waves obtained on top of coplanar helical reference states show multiple magnon
+modes (both acoustic and optical). However, those magnon modes turn out to be
+stable only in the absence of bond alternations.",1902.04008v1
+2019-11-12,Coherent pumping of high momentum magnons by light,"We propose to excite a large number of coherent magnons with high momentum in
+optical cavities. This is achieved by two counterpropagating optical modes that
+are detuned by the frequency of a selected magnon, similar to stimulated Raman
+scattering. In sub-mm size yttrium iron garnet spheres, a mW laser input power
+generates 10^6-10^8 coherent magnons. The large magnon population enhances
+Brillouin light scattering, a probe suitable to access their quantum
+properties.",1911.04728v1
+2019-12-25,Magnon polarons in the spin Peltier effect,"We report the observation of anomalous peak structures induced by hybridized
+magnon-phonon excitation (magnon polarons) in the magnetic field dependence of
+the spin Peltier effect (SPE) in a Lu$_{2}$Bi$_{1}$Fe$_{4}$Ga$_{1}$O$_{12}$
+(BiGa:LuIG) with Pt contact. The SPE peaks coincide with magnetic fields tuned
+to the threshold of magnon-polaron formation, consistent with the previous
+observation in the spin Seebeck effect. The enhancement of SPE is attributed to
+the lifetime increase in spin current caused by magnon-phonon hybridization in
+BiGa:LuIG.",1912.11573v1
+2019-06-03,Magnon-phonon interactions in magnetic insulators,"We address the theory of magnon-phonon interactions and compute the
+corresponding quasi-particle and transport lifetimes in magnetic insulators
+with focus on yttrium iron garnet at intermediate temperatures from anisotropy-
+and exchange-mediated magnon-phonon interactions, the latter being derived from
+the volume dependence of the Curie temperature. We find in general weak effects
+of phonon scattering on magnon transport and the Gilbert damping of the
+macrospin Kittel mode. The magnon transport lifetime differs from the
+quasi-particle lifetime at shorter wavelengths.",1906.01042v1
+2019-10-02,Direct Observation of Magnon Modes in Kagome Artificial Spin Ice with Topological Defects,"We investigate spin dynamics of artificial spin ice (ASI) where topological
+defects confine magnon modes in Ni$_{81}$Fe$_{19}$ nanomagnets arranged on an
+interconnected kagome lattice. Brillouin light scattering microscopy performed
+on magnetically disordered states exhibit a series of magnon resonances which
+depend on topological defect configurations detected by magnetic force
+microscopy. Nanomagnets on a Dirac string and between a monopole-antimonopole
+pair show pronounced modifications in magnon frequencies both in experiments
+and simulations. Our work is key for the creation and annihilation of Dirac
+strings via microwave assisted switching and reprogrammable magnonics based on
+ASIs.",1910.00874v1
+2020-10-06,A search for non-reciprocal magnons in MnPS$_3$,"Recent articles have suggested that the quasi-two dimensional antiferromagnet
+MnPS$_3$ may have non-reciprocal magnons, whereby magnons in a Brillouin zone
+corner at +q have different energies than those at $-$q. The magnons along the
+Brillouin zone boundaries were measured using neutron three-axis spectrometry,
+paying careful attention to the resolution function, to determine whether such
+non-reciprocity was present. The data show that, within the resolution, there
+are no significant differences between the magnons in opposite Brillouin zone
+corners.",2010.02898v1
+2021-06-03,Magnon spin transport around the compensation magnetic field in easy-plane antiferromagnetic insulators,"In this work, we theoretically study the magnon spin transport in easy-plane
+antiferromagnetic insulators in the presence of an in-plane magnetic field. By
+exactly calculating the magnon spectrum, we find the band splitting due to the
+magnetic anisotropy can be fully compensated by the external field at a
+particular strength, which makes its dynamics nearly equivalent to an easy-axis
+antiferromagnet. As a result, the intrinsic magnon spin Hall effect due to the
+dipole-dipole interaction, previously predicted in easy-axis antiferromagnets
+is activated in easy-plane antiferromagnets. The compensation feature also
+allows the field control of magnon spin lifetime and hence the spin diffusion
+length. The compensation feature is robust against the biaxial anisotropy.",2106.02178v1
+2021-09-19,Theory of the Magnon Parametron,"The 'magnon parametron' is a ferromagnetic particle that is parametrically
+excited by microwaves in a cavity. Above a certain threshold of the microwave
+power, a bistable steady state emerges that forms an effective Ising spin. We
+calculate the dynamics of the magnon parametron as a function of microwave
+power, applied magnetic field and temperature for the interacting magnon
+system, taking into account thermal and quantum fluctuations. We predict three
+dynamical phases, viz. a stable Ising spin, telegraph noise of thermally
+activated switching, and an intermediate regime that at lower temperatures is
+quantum correlated with significant distillible magnon entanglement. These
+three regimes of operation are attractive for alternative computing schemes.",2109.09117v1
+2021-09-20,Nonlinear magnon spin Nernst effect in antiferromagnets and strain-tunable pure spin current,"In this Letter, we study the spin Nernst effect (SNE) of magnons in the
+nonlinear response regime. We derive the formula for the nonlinear magnon spin
+Nernst current by solving the Boltzmann equation and find out that it is
+described by an extended Berry curvature dipole of magnons. The nonlinear
+magnon SNE is expected to occur in various N\'eel antiferromagnets without
+Dzyaloshinskii-Moriya interaction. In particular, the nonlinear spin Nernst
+current in the honeycomb and diamond lattice antiferromagnets can be controlled
+by strain/pressure.",2109.09464v4
+2022-06-09,Magnon-phonon interaction induced electromagnetic wave radiation in the strong coupling region,"We theoretically study the electromagnetic wave radiation of magnons driven
+by acoustic phonons in systems with strong magnon-phonon interaction. We
+evaluate the field dependence of radiation intensity spectra which exhibits the
+avoided crossing, a characteristic of strongly coupled systems. At the
+crossover where the magnon and phonon eigenstates are hybridized, we
+demonstrate the existence of two resonant radiation frequencies with circular
+polarization and the enhancement of antenna radiation efficiency by over 100
+times. Our results open up possibilities of developing ultra-compact antennas
+by using the hybridized magnon-phonon mode.",2206.04454v1
+2023-01-24,Direct observation of magnon BEC in an out-of-plane magnetized yttrium iron garnet film,"Bose-Einstain condensation occurs at an appropriate density of bosonic
+particles, depending on their mass and temperature. We were able to
+experimentally observe the transition from the spin wave regime to the magnon
+Bose-Einstein condensed state (mBEC) with increasing magnon density by a
+microwave pumping. We used optical methods to register the spatial distribution
+of the magnon density and phase. For the first time, a coherent state of
+stationary magnons was demonstrated far from the region of their excitation.",2301.10725v1
+2023-06-28,Time-dependent Schwinger boson mean-field theory of supermagnonic propagation in 2D antiferromagnets,"Understanding the speed limits for the propagation of magnons is of key
+importance for the development of ultrafast spintronics and magnonics.
+Recently, it was predicted that in 2D antiferromagnets, spin correlations can
+propagate faster than the highest magnon velocity. Here we gain deeper
+understanding of this supermagnonic effect based on time-dependent Schwinger
+boson mean-field theory. We find that the supermagnonic effect is determined by
+the competition between propagating magnons and a localized quasi-bound state,
+which is tunable by lattice coordination and quantum spin value $S$, suggesting
+a new scenario to enhance magnon propagation.",2306.16382v1
+2024-03-21,Magnonic Superconductivity,"We uncover a new superconducting state with partial spin polarization induced
+by a magnetic field. This state, which we call ""magnonic superconductor"", lacks
+a conventional pairing order parameter, but is characterized instead by a
+composite order parameter that represents the binding of electron pairs and
+magnons. We rigorously demonstrate the existence of magnonic superconductivity
+with high transition temperature in a triangular lattice Hubbard model with
+repulsive interaction. We further show that magnonic Cooper pairs can attract
+to form higher-charge bound states, which can give rise to charge-$6e$
+superconductivity.",2403.14756v1
+2012-03-26,Magnon-drag thermopile,"Thermoelectric effects in spintronics are gathering increasing attention as a
+means of managing heat in nanoscale structures and of controlling spin
+information by using heat flow. Thermal magnons (spin-wave quanta) are expected
+to play a major role, however, little is known about the underlying physical
+mechanisms involved. The reason is the lack of information about magnon
+interactions and of reliable methods to obtain it, in particular for electrical
+conductors because of the intricate influence of electrons. Here, we
+demonstrate a conceptually new device that allows us to gather information on
+magnon-electron scattering and magnon-drag effects. The device resembles a
+thermopile formed by a large number of pairs of ferromagnetic wires placed
+between a hot and a cold source and connected thermally in parallel and
+electrically in series. By controlling the relative orientation of the
+magnetization in pairs of wires, the magnon-drag can be studied independently
+of the electron and phonon-drag thermoelectric effects. Measurements as a
+function of temperature reveal the effect on magnon drag following a variation
+of magnon and phonon populations. This information is crucial to understand the
+physics of electron-magnon interactions, magnon dynamics and thermal spin
+transport.",1203.5628v1
+2017-03-11,Magnonic crystals - prospective structures for shaping spin waves in nanoscale,"We have investigated theoretically band structure of spin waves in magnonic
+crystals with periodicity in one-(1D), two- (2D) and three-dimensions (3D). We
+have solved Landau-Lifshitz equation with the use of plane wave method, finite
+element method in frequency domain and micromagnetic simulations in time domain
+to find the dynamics of spin waves and spectrum of their eigenmodes. The spin
+wave spectra were calculated in linear approximation. In this paper we show
+usefulness of these methods in calculations of various types of spin waves. We
+demonstrate the surface character of the Damon-Eshbach spin wave in 1D magnonic
+crystals and change of its surface localization with the band number and
+wavenumber in the first Brillouin zone. The surface property of the spin wave
+excitation is further exploited by covering plate of the magnonic crystal with
+conductor. The band structure in 2D magnonic crystals is complex due to
+additional spatial inhomogeneity introduced by the demagnetizing field. This
+modifies spin wave dispersion, makes the band structure of magnonic crystals
+strongly dependent on shape of the inclusions and type of the lattice. The
+inhomogeneity of the internal magnetic field becomes unimportant for magnonic
+crystals with small lattice constant, where exchange interactions dominate. For
+3D magnonic crystals, characterized by small lattice constant, wide magnonic
+band gap is found. We show that the spatial distribution of different materials
+in magnonic crystals can be explored for tailored effective damping of spin
+waves.",1703.04012v1
+2019-09-09,Klein tunneling of Weyl magnons,"Similar to Weyl semimetals, in magnetic materials, magnon bands can host Weyl
+points, around which the bosonic excitations are called Weyl magnons. Here, we
+investigate the Klein tunneling of Weyl magnons, during the process of which
+Weyl magnons tunnel through a high potential barrier. Specifically, we study
+the magnetization current carried by Weyl magnons in a quasi-one-dimensional
+magnetic wire, in the middle of which a gate magnetic field is applied to
+generate a potential barrier. The transmission probability is calculated and
+the Landauer-B\""uttiker formalism is used to find the magnetization current.
+Various types of Weyl magnons are considered, including isotropic, tilted, and
+double Weyl magnons. Unlike in Weyl semimetals where fermionic statistics is in
+charge and the current oscillates with the gate field as a result of
+Fabry-P\'erot resonances, here Bose distribution smears out the oscillations.
+We find that the tilting of the Weyl cone causes the decrease of the
+magnetization current from Klein tunneling, while for double Weyl magnons,
+Klein tunneling is absent in the direction of quadratic dispersion, but is
+enhanced in the direction of linear dispersion. Our results show that the
+behaviour of the current-voltage characteristics of magnons is rather different
+from that of electrons due to different statistics, although the
+single-particle properties, such as the transmission probabilities, are the
+same for both Weyl bosons and Weyl fermions.",1909.04109v1
+2019-02-18,Coherent control of magnon radiative damping with local photon states,"The collective excitation of ordered spins, known as spin waves or magnons,
+can in principle radiate by emitting travelling photons to an open system when
+decaying to the ground state. However, in contrast to the electric dipoles,
+magnetic dipoles contributed by magnons are more isolated from electromagnetic
+environment with negligible radiation in the vacuum, limiting their application
+in coherent communication by photons. Recently, strong interaction between
+cavity standing-wave photons and magnons has been reported, indicating the
+possible manipulation of magnon radiation via tailoring photon states. Here,
+with loading an yttrium iron garnet sphere in a one-dimensional circular
+waveguide cavity in the presence of both travelling and standing photon modes,
+we demonstrate an efficient photon emissions from magnon and a significant
+magnon radiative damping with radiation rate found to be proportional to the
+local density of states (LDOS) of photon. By modulating the LDOS including its
+magnitude and/or polarization, we can flexibly tune the photon emission and
+magnon radiative damping on demand. Our findings provide a general way in
+manipulating photon emission from magnon radiation for harnessing energy and
+angular momentum generation, transfer and storage modulated by magnon in the
+cavity and waveguide electrodynamics.",1902.06795v2
+2019-03-06,Enhancement of antiferromagnetic magnon-magnon entanglement by cavity cooling,"Magnon-photon coupling has been experimentally realized inside a cavity and
+the emerging field known as cavity spintronics has attracted significant
+attention for its potential docking with quantum information science. However,
+one seldom knows whether this coupling implies an entanglement state among
+magnons and photons or not, which is crucial for its usage in quantum
+information. Here we study the entanglement properties among magnons and
+photons in an antiferromagnet-light system and find that the entanglement
+between magnon and photon is nearly zero while the magnon-magnon entanglement
+is very strong and it can be even further enhanced through the coupling with
+the cavity photons. The maximum enhancement occurs when the antiferromagnet
+reaches resonant with the light. The essential physics can be well understood
+within the picture of cavity induced cooling of magnon-magnon state near its
+joint vacuum with stronger entanglement. Our results are significant to extend
+the cavity spintronics to quantum manipulation and further provide an alternate
+to manipulate the deep strong correlations of continuous variable entanglement
+with a generic stable condition and easy tunability.",1903.02484v2
+2018-10-05,Magnon contribution to unidirectional spin Hall magnetoresistance,"We develop a model for the magnonic contribution to the unidirectional spin
+Hall magnetoresistance (USMR) of heavy metal/ferromagnetic insulator bilayer
+films. We show that diffusive transport of Holstein-Primakoff magnons leads to
+an accumulation of spin near the bilayer interface, giving rise to a
+magnoresistance which is not invariant under inversion of the current
+direction. Unlike the electronic contribution described by Zhang and Vignale
+[Phys. Rev. B 94, 140411 (2016)], which requires an electrically conductive
+ferromagnet, the magnonic contribution can occur in ferromagnetic insulators
+such as yttrium iron garnet. We show that the magnonic USMR is, to leading
+order, cubic in the spin Hall angle of the heavy metal, as opposed to the
+linear relation found for the electronic contribution. We estimate that the
+maximal magnonic USMR in Pt|YIG bilayers is on the order of $10^{-8}$, but may
+reach values of up to $10^{-5}$ if the magnon gap is suppressed, and can thus
+become comparable to the electronic contribution in, e.g., Pt|Co. We show that
+the magnonic USMR at a finite magnon gap may be enhanced by an order of
+magnitude if the magnon diffusion length is decreased to a specific optimal
+value that depends on various system parameters.",1810.02610v2
+2020-06-29,"Hybrid magnonics: physics, circuits and applications for coherent information processing","Hybrid dynamic systems have recently gained interests with respect to both
+fundamental physics and device applications, particularly with their potential
+for coherent information processing. In this perspective, we will focus on the
+recent rapid developments of magnon-based hybrid systems, which seek to combine
+magnonic excitations with diverse excitations for transformative applications
+in devices, circuits and information processing. Key to their promising
+potentials is that magnons are highly tunable excitations and can be easily
+engineered to couple with various dynamic media and platforms. The capability
+of reaching strong coupling with many different excitations has positioned
+magnons well for studying solid-state coherent dynamics and exploiting unique
+functionality. In addition, with their gigahertz frequency bandwidth and the
+ease of fabrication and miniaturization, magnonic devices and systems can be
+conveniently integrated into microwave circuits for mimicking a broad range of
+device concepts that have been applied in microwave electronics, photonics and
+quantum information. We will discuss a few potential directions for advancing
+magnon hybrid systems, including on-chip geometry, novel coherent magnonic
+functionality, and coherent transduction between different platforms. As future
+outlook, we will discuss the opportunities and challenges of magnonic hybrid
+systems for their applications in quantum information and magnonic logic.",2006.16158v1
+2019-10-11,Chiral Magnonic Edge States in Ferromagnetic Skyrmion Crystals Controlled by Magnetic Fields,"Achieving control over magnon spin currents in insulating magnets - where
+dissipation due to Joule heating is highly suppressed - is an active area of
+research that could lead to energy-efficient spintronics applications. However,
+magnon spin currents supported by conventional systems with uniform magnetic
+order have proven hard to control. An alternative approach that relies on
+topologically protected magnonic edge states of spatially periodic magnetic
+textures has recently emerged. A prime example of such textures is the
+ferromagnetic skyrmion crystal which hosts chiral edge states providing a
+platform for magnon spin currents. Here, we show, for the first time, an
+external magnetic field can drive a topological phase transition in the spin
+wave spectrum of a ferromagnetic skyrmion crystal. The topological phase
+transition is signaled by the closing of a low-energy bulk magnon gap at a
+critical field. In the topological phase, below the critical field, two
+topologically protected chiral magnonic edge states lie within this gap, but
+they unravel in the trivial phase, above the critical field. Remarkably, the
+topological phase transition involves an inversion of two magnon bands that at
+the $\Gamma$ point correspond to the breathing and anticlockwise modes of the
+skyrmions in the crystal. Our findings suggest that an external magnetic field
+could be used as a knob to switch on and off magnon spin currents carried by
+topologically protected chiral magnonic edge states.",1910.05214v1
+2021-08-25,Quantum network with magnonic and mechanical nodes,"A quantum network consisting of magnonic and mechanical nodes connected by
+light is proposed. Recent years have witnessed a significant development in
+cavity magnonics based on collective spin excitations in ferrimagnetic
+crystals, such as yttrium iron garnet (YIG). Magnonic systems are considered to
+be a promising building block for a future quantum network. However, a major
+limitation of the system is that the coherence time of the magnon excitations
+is limited by their intrinsic loss (typically in the order of 1 $\mu$s for
+YIG). Here, we show that by coupling the magnonic system to a mechanical system
+using optical pulses, an arbitrary magnonic state (either classical or quantum)
+can be transferred to and stored in a distant long-lived mechanical resonator.
+The fidelity depends on the pulse parameters and the transmission loss. We
+further show that the magnonic and mechanical nodes can be prepared in a
+macroscopic entangled state. These demonstrate the quantum state transfer and
+entanglement distribution in such a novel quantum network of magnonic and
+mechanical nodes. Our work shows the possibility to connect two separate fields
+of optomagnonics and optomechanics, and to build a long-distance quantum
+network based on magnonic and mechanical systems.",2108.11156v3
+2021-11-11,Evidence for spin current driven Bose-Einstein condensation of magnons,"The quanta of magnetic excitations - magnons - are known for their unique
+ability to undergo Bose-Einstein condensation at room temperature. This
+fascinating phenomenon reveals itself as a spontaneous formation of a
+macroscopic coherent state under the influence of incoherent stimuli. Spin
+currents have been predicted to offer electronic control of magnon
+Bose-Einstein condensates, but this phenomenon has not been experimentally
+evidenced up to now. Here we experimentally show that current-driven
+Bose-Einstein condensation can be achieved in nanometer-thick films of magnetic
+insulators with tailored dynamic magnetic nonlinearities and minimized
+magnon-magnon interactions. We demonstrate that, above a certain threshold,
+magnons injected by the spin current overpopulate the lowest-energy level
+forming a highly coherent spatially extended state. By accessing magnons with
+essentially different energies, we quantify the chemical potential of the
+driven magnon gas and show that, at the critical current, it reaches the energy
+of the lowest magnon level. Our results pave the way for implementation of
+integrated microscopic quantum magnonic and spintronic devices.",2111.06356v1
+2022-01-14,Cavity mediated level attraction and repulsion between magnons,"We characterize some of the distinctive hallmarks of magnon-magnon
+interaction mediated by the intracavity field of a microwave cavity, along with
+their testable ramifications. In general, we foreground two widely dissimilar
+parameter domains that bring forth the contrasting possibilities of level
+splitting and level crossing. The former is observed in the regime of strong
+magnon-photon couplings, particularly when the three modes bear comparable
+relaxation rates. This character is marked by the appearance of three
+distinguishable and non-converging polariton branches in the spectral response
+to a cavity drive. However, when the bare modes are resonant and the couplings
+perfectly symmetrical, one of the spectral peaks gets wiped out. This anomalous
+extinction of polaritonic response can be traced down to the existence of a
+conspicuous dark mode alongside two frequency-shifted bright modes. In an
+alternate parameter regime, where the magnon modes are weakly coupled to the
+cavity, features of level attraction unfold, subject to a large relaxation rate
+for the cavity mode. Concurrently, for antisymmetric detunings to the magnon
+modes, a transmission window springs into existence, exhibiting transparency in
+the limit of negligible dissipation from the magnons. The emergence of level
+attraction can be reconciled with a theoretical model that embodies the
+dynamics of the magnon-magnon subsystem when the cavity field decays rapidly
+into its steady state. In this limit, we identify a purely dissipative coupling
+between the magnon modes.",2201.05685v1
+2022-06-13,An efficient material search for room temperature topological magnons,"Topologically protected magnon surface states are highly desirable as an
+ideal platform to engineer low-dissipation spintronics devices. However,
+theoretical prediction of topological magnons in strongly correlated materials
+proves to be challenging because the ab initio density functional theory
+calculations fail to reliably predict magnetic interactions in correlated
+materials. Here, we present a symmetry-based approach, which predicts
+topological magnons in magnetically ordered crystals, upon applying external
+perturbations such as magnetic/electric fields and/or mechanical strains. We
+apply this approach to carry out an efficient search for magnetic materials in
+the Bilbao Crystallographic Server, where, among 198 compounds with an over
+300-K transition temperature, we identify 12 magnetic insulators that support
+room-temperature topological magnons. They feature Weyl magnons with surface
+magnon arcs and magnon axion insulators with either chiral surface or hinge
+magnon modes, offering a route to realize energy-efficient devices based on
+protected surface magnons.",2206.06248v2
+2022-06-23,High pressure tuning of magnon-polarons in the layered antiferromagnet FePS$_3$,"Magnetic layered materials have emerged recently as promising systems to
+introduce magnetism in structures based on two-dimensional (2D) materials and
+to investigate exotic magnetic ground states in the 2D limit. In this work, we
+apply high hydrostatic pressures up to P = 8.7 GPa to the bulk layered
+antiferromagnet FePS$_3$ to tune the collective lattice excitations (phonons)
+in resonance with magnetic excitations (magnons). Close to P = 4 GPa, the
+magnon-phonon resonance is achieved and the strong coupling between these
+collective modes leads to the formation of new quasi-particles, the
+magnon-polarons, evidenced in our low temperature Raman scattering experiments
+by a particular avoided crossing behavior between the phonon and the doubly
+degenerate antiferromagnetic magnon. At the pressure-induced magnon-phonon
+resonance, three distinct coupled modes emerge. As it is mainly defined by
+intralayer properties, we show that the energy of the magnon is nearly pressure
+independent. We additionally apply high magnetic fields up to B = 30 T to fully
+identify and characterize the magnon excitations, and to explore the different
+magnon-polaron regimes for which the phonon has an energy lower-, equal to-, or
+higher- than the magnon energy. The description of our experimental data
+requires introducing a phonon-phonon coupling not taken into account in actual
+calculations.",2206.11963v1
+2022-08-29,Confinement of Bose-Einstein magnon condensates in adjustable complex magnetization landscapes,"Coherent wave states such as Bose-Einstein condensates (BECs), which
+spontaneously form in an overpopulated magnon gas even at room temperature,
+have considerable potential for wave-based computing and information processing
+at microwave frequencies. The ability to control the transport properties of
+magnon BECs plays an essential role for their practical use. Here, we
+demonstrate spatio-temporal control of the BEC density distribution through the
+excitation of magnon supercurrents in an inhomogeneously magnetized yttrium
+iron garnet film. The BEC is created by microwave parametric pumping and probed
+by Brillouin light scattering spectroscopy. The desired magnetization profile
+is prepared by heating the film with optical patterns projected onto its
+surface using a phase-based wavefront modulation technique. Specifically, we
+observe a pronounced spatially localized magnon accumulation caused by magnon
+supercurrents flowing toward each other originating in two heated regions. This
+accumulation effect increases the BEC lifetime due to the constant influx of
+condensed magnons into the confinement region. The shown approach to manipulate
+coherent waves provides an opportunity to extend the lifetime of freely
+evolving magnon BECs, create dynamic magnon textures, and study the interaction
+of magnon condensates formed in different regions of the sample.",2208.13507v1
+2022-09-08,Perspective: non-Hermitian physics in magnetic systems,"Non-Hermitian Hamiltonians provide an alternative perspective on the dynamics
+of quantum and classical systems coupled non-conservatively to an environment.
+Once primarily an interest of mathematical physicists, the theory of
+non-Hermitian Hamiltonians has solidified and expanded to describe various
+physically observable phenomena in optical, photonic, and condensed matter
+systems. Self-consistent descriptions of quantum mechanics based on
+non-Hermitian Hamiltonians have been developed and continue to be refined. In
+particular, non-Hermitian frameworks to describe magnonic and hybrid magnonic
+systems have gained popularity and utility in recent years, with new insights
+into the magnon topology, transport properties, and phase transitions coming
+into view. Magnonic systems are in many ways a natural platform in which to
+realize non-Hermitian physics because they are always coupled to a surrounding
+environment and exhibit lossy dynamics. In this perspective we review recent
+progress in non-Hermitian frameworks to describe magnonic and hybrid magnonic
+systems, such as cavity magnonic systems and magnon-qubit coupling schemes. We
+discuss progress in understanding the dynamics of inherently lossy magnetic
+systems as well as systems with gain induced by externally applied spin
+currents. We enumerate phenomena observed in both purely magnonic and hybrid
+magnonic systems which can be understood through the lens of non-Hermitian
+physics, such as PT and Anti-PT-symmetry breaking, dynamical magnetic phase
+transitions, non-Hermitian skin effect, and the realization of exceptional
+points and surfaces. Finally, we comment on some open problems in the field and
+discuss areas for further exploration.",2209.03946v2
+2022-11-15,Modification of three-magnon splitting in a flexed magnetic vortex,"We present an experimental and numerical study of three-magnon splitting in a
+micrometer-sized magnetic disk with the vortex state strongly deformed by
+static in-plane magnetic fields. Excited with a large enough power at frequency
+$f_\mathrm{RF}$, the primary radial magnon modes of a cylindrical magnetic
+vortex can decay into secondary azimuthal modes via spontaneous three-magnon
+splitting. This nonlinear process exhibits selection rules leading to
+well-defined and distinct frequencies $f_\mathrm{RF}/2\pm \Delta f$ of the
+secondary modes. Here, we demonstrate that three-magnon splitting in vortices
+can be significantly modified by deforming the magnetic vortex with in-plane
+magnetic fields, leading to a much richer three-magnon response. We find that,
+with increasing field, an additional class of secondary modes is excited which
+are localized to the highly-flexed regions adjacent to the displaced vortex
+core. While these modes satisfy the same selection rules of three-magnon
+splitting, they exhibit a much lower three-magnon threshold power compared to
+regular secondary modes of a centered vortex. The applied static magnetic
+fields are small ($\simeq$ 10 mT), providing an effective parameter to control
+the nonlinear spectral response of confined vortices. Our work expands the
+understanding of nonlinear magnon dynamics in vortices and advertises these for
+potential neuromorphic applications based on magnons.",2211.08226v2
+2023-07-12,Quantum information diode based on a magnonic crystal,"Exploiting the effect of nonreciprocal magnons in a system with no inversion
+symmetry, we propose a concept of a quantum information diode, {\it i.e.}, a
+device rectifying the amount of quantum information transmitted in the opposite
+directions. We control the asymmetric left and right quantum information
+currents through an applied external electric field and quantify it through the
+left and right out-of-time-ordered correlation (OTOC). To enhance the
+efficiency of the quantum information diode, we utilize a magnonic crystal. We
+excite magnons of different frequencies and let them propagate in opposite
+directions. Nonreciprocal magnons propagating in opposite directions have
+different dispersion relations. Magnons propagating in one direction match
+resonant conditions and scatter on gate magnons. Therefore, magnon flux in one
+direction is damped in the magnonic crystal leading to an asymmetric transport
+of quantum information in the quantum information diode. A quantum information
+diode can be fabricated from an yttrium iron garnet (YIG) film. This is an
+experimentally feasible concept and implies certain conditions: low temperature
+and small deviation from the equilibrium to exclude effects of phonons and
+magnon interactions. We show that rectification of the flaw of quantum
+information can be controlled efficiently by an external electric field and
+magnetoelectric effects.",2307.06047v1
+2023-07-26,Tunable Magnon-Photon Coupling by Magnon Band Gap in a Layered Hybrid Perovskite Antiferromagnet,"Tunability of coherent coupling between fundamental excitations is an
+important prerequisite for expanding their functionality in hybrid quantum
+systems. In hybrid magnonics, the dipolar interaction between magnon and photon
+usually persists and cannot be switched off. Here, we demonstrate this
+capability by coupling a superconducting resonator to a layered hybrid
+perovskite antiferromagnet, which exhibits a magnon band gap due to its
+intrinsic Dzyaloshinskii-Moriya interaction. The pronounced temperature
+sensitivity of the magnon band gap location allows us to set the photon mode
+within the gap and to disable magnon-photon hybridization. When the resonator
+mode falls into the magnon band gap, the resonator damping rate increases due
+to the nonzero coupling to the detuned magnon mode. This phenomena can be used
+to quantify the magnon band gap using an analytical model. Our work brings new
+opportunities in controlling coherent information processing with quantum
+properties in complex magnetic materials.",2307.14447v1
+2023-09-25,Ultrafast Demagnetization through Femtosecond Generation of Non-thermal Magnons,"Ultrafast laser excitation of ferromagnetic metals gives rise to correlated,
+highly non-equilibrium dynamics of electrons, spins and lattice, which are,
+however, poorly described by the widely-used three-temperature model (3TM).
+Here, we develop a fully ab-initio parameterized out-of-equilibrium theory
+based on a quantum kinetic approach--termed (N+2) temperature model--that
+describes magnon occupation dynamics due to electron-magnon scattering. We
+apply this model to perform quantitative simulations on the ultrafast,
+laser-induced generation of magnons in iron and demonstrate that on these
+timescales the magnon distribution is non-thermal: predominantly high-energy
+magnons are created, while the magnon occupation close to the center of the
+Brillouin zone even decreases, due to a repopulation towards higher energy
+states via a so-far-overlooked scattering term. We demonstrate that the simple
+relation between magnetization and temperature computed at equilibrium does not
+hold in the ultrafast regime and that the 3TM greatly overestimates the
+demagnetization. The ensuing Gilbert damping becomes strongly magnon wavevector
+dependent and requires a description beyond the conventional
+Landau-Lifshitz-Gilbert spin dynamics. Our ab-initio-parameterized calculations
+show that ultrafast generation of non-thermal magnons provides a sizable
+demagnetization within 200fs in excellent comparison with experimentally
+observed laser-induced demagnetizations. Our investigation emphasizes the
+importance of non-thermal magnon excitations for the ultrafast demagnetization
+process.",2309.14167v3
+2023-12-15,Magnon Bose-Einstein condensates: from time crystals and quantum chromodynamics to vortex sensing and cosmology,"Under suitable experimental conditions collective spin-wave excitations,
+magnons, form a Bose-Einstein condensate (BEC) where the spins precess with a
+globally coherent phase. Bose-Einstein condensation of magnons has been
+reported in a few systems, including superfluid phases of $^3$He, solid state
+systems such as Yttrium-iron-garnet (YIG) films, and cold atomic gases. Among
+these systems, the superfluid phases of $^3$He provide a nearly ideal test
+bench for coherent magnon physics owing to experimentally proven spin
+superfluidity, the long lifetime of the magnon condensate, and the versatility
+of the accessible phenomena. We first briefly recap the properties of the
+different magnon BEC systems, with focus on superfluid $^3$He. The main body of
+this review summarizes recent advances in application of magnon BEC as a
+laboratory to study basic physical phenomena connecting to diverse areas from
+particle physics and cosmology to new phases of condensed matter. This line of
+research complements the ongoing efforts to utilize magnon BECs as probes and
+components for potentially room-temperature quantum devices. In conclusion, we
+provide a roadmap for future directions in the field of applications of magnon
+BEC to fundamental research.",2312.10119v1
+2024-03-03,Magnonic $\varphi$ Josephson Junctions and Synchronized Precession,"There has been a growing interest in non-Hermitian physics. One of its main
+goals is to engineer dissipation and to explore ensuing functionality. In
+magnonics, the effect of dissipation due to local damping on magnon transport
+has been explored. However, the effects of non-local damping on the magnonic
+analog of the Josephson effect remain missing, despite that non-local damping
+is inevitable and has been playing a central role in magnonics. Here, we
+uncover theoretically that a surprisingly rich dynamics can emerge in magnetic
+junctions due to intrinsic non-local damping, using analytical and numerical
+methods. In particular, under microwave pumping, we show that coherent spin
+precession in the right and left insulating ferromagnet (FM) of the junction
+becomes synchronized by non-local damping and thereby a magnonic analog of the
+$\varphi$ Josephson junction emerges, where $\varphi$ stands here for the
+relative precession phase of right and left FM in the stationary limit.
+Remarkably, $\varphi$ decreases monotonically from $ \pi$ to $\pi/2$ as the
+magnon-magnon interaction, arising from spin anisotropies, increases. Moreover,
+we also find a magnonic diode effect giving rise to rectification of magnon
+currents. Our predictions are readily testable with current device and
+measurement technologies at room temperatures.",2403.01625v1
+2019-09-04,Magnon polaron formed by selectively coupled coherent magnon and phonon modes of a surface patterned ferromagnet,"Strong coupling between two quanta of different excitations leads to the
+formation of a hybridized state which paves a way for exploiting new degrees of
+freedom to control phenomena with high efficiency and precision. A magnon
+polaron is the hybridized state of a phonon and a magnon, the elementary quanta
+of lattice vibrations and spin waves in a magnetically-ordered material. A
+magnon polaron can be formed at the intersection of the magnon and phonon
+dispersions, where their frequencies coincide. The observation of magnon
+polarons in the time domain has remained extremely challenging because the weak
+interaction of magnons and phonons and their short lifetimes jeopardize the
+strong coupling required for the formation of a hybridized state. Here, we
+overcome these limitations by spatial matching of magnons and phonons in a
+metallic ferromagnet with a nanoscale periodic surface pattern. The spatial
+overlap of the selected phonon and magnon modes formed in the periodic
+ferromagnetic structure results in a high coupling strength which, in
+combination with their long lifetimes allows us to find clear evidence of an
+optically excited magnon polaron. We show that the symmetries of the localized
+magnon and phonon states play a crucial role in the magnon polaron formation
+and its manifestation in the optically excited magnetic transients.",1909.01886v4
+2022-10-15,Non-local magnon transconductance in extended magnetic insulating films.\\ Part I: spin diode effect,"This review provides a comprehensive study of the nonlinear transport
+properties of magnons, which are electrically emitted or absorbed inside
+extended YIG films by spin transfer effects via a YIG$\vert$Pt interface. Our
+purpose is to experimentally elucidate the pertinent picture behind the
+asymmetric electrical variation of the magnon transconductance analogous to an
+electric diode. The feature is rooted in the variation of the density of
+low-lying spin excitations via an electrical shift of the magnon chemical
+potential. As the intensity of the spin transfer increases in the forward
+direction (regime of magnon emission), the transport properties of low-energy
+magnon go through 3 distinct regimes: \textit{i)} at low currents, where the
+spin current is a linear function of the electrical current, the spin transport
+is ballistic and set by the film thickness; \textit{ii)} for amplitudes of the
+order of the damping compensation threshold, it switches to a highly correlated
+regime limited by magnon-magnon relaxation process and marked by a saturation
+of the magnon transconductance. Here the main bias, that controls the magnon
+density, are thermal fluctuations beneath the emitter. \textit{iii)} As the
+temperature under the emitter approaches the Curie temperature, scattering with
+high-energy magnons dominates, leading to diffusive transport. We note that
+such sequence of transport regimes bears analogy with electron hydrodynamic
+transport in ultra-pure media predicted by Radii Gurzhi. This study restricted
+to low energy part of the magnon manifold complements part II of this
+review\cite{kohno_2F}, which concentrates instead on the whole spectrum of
+propagating magnons.",2210.08304v2
+1998-02-04,Magnetic impurities in Mott-Hubbard antiferromagnets,"A formalism is developed to treat magnetic impurities in a Mott-Hubbard
+antiferromagnetic insulator within a representation involving multiple orbitals
+per site. Impurity scattering of magnons is found to be strong when the number
+of orbitals N' on impurity sites is different from the number N on host sites.
+The impurity-scattering-induced softening of magnon modes leads to enhancement
+in thermal excitation of magnons, and hence to a lowering of the Neel
+temperature in layered or three dimensional systems. Weak impurity scattering
+of magnons is obtained in the case N'=N, where the impurity is represented in
+terms of modified hopping strength, and a momentum-independent, multiplicative
+renormalization of magnon energies is obtained. Split-off magnon modes are
+obtained when the impurity-host coupling is stronger, and implications are
+discussed for two-magnon Raman scattering. The mapping between antiferromagnets
+and superconductors is utilized to contrast formation of impurity-induced
+states.",9802052v1
+2005-01-11,Ballistic magnon transport and phonon scattering in the antiferromagnet Nd$_2$CuO$_4$,"The thermal conductivity of the antiferromagnet Nd$_2$CuO$_4$ was measured
+down to 50 mK. Using the spin-flop transition to switch on and off the acoustic
+Nd magnons, we can reliably separate the magnon and phonon contributions to
+heat transport. We find that magnons travel ballistically below 0.5 K, with a
+thermal conductivity growing as $T^3$, from which we extract their velocity. We
+show that the rate of scattering of acoustic magnons by phonons grows as $T^3$,
+and the scattering of phonons by magnons peaks at twice the average Nd magnon
+frequency.",0501220v2
+2008-04-21,Giant magnons in the D1-D5 system,"We study giant magnons in the the D1-D5 system from both the boundary CFT and
+as classical solutions of the string sigma model in $AdS_3\times S^3\times
+T^4$. Re-examining earlier studies of the symmetric product conformal field
+theory we argue that giant magnons in the symmetric product are BPS states in a
+centrally extended $SU(1|1)\times SU(1|1)$ superalgebra with two more
+additional central charges. The magnons carry these additional central charges
+locally but globally they vanish. Using a spin chain description of these
+magnons and the extended superalgebra we show that these magnons obey a
+dispersion relation which is periodic in momentum. We then identify these
+states on the string theory side and show that here too they are BPS in the
+same centrally extended algebra and obey the same dispersion relation which is
+periodic in momentum. This dispersion relation arises as the BPS condition for
+the extended algebra and is similar to that of magnons in ${\cal N}=4$
+Yang-Mills",0804.3267v3
+2013-04-26,Strong magnon softening in tetragonal FeCo compounds,"Magnons play an important role in fast precessional magnetization reversal
+processes serving as a heat bath for dissipation of the Zeeman energy and thus
+being responsible for the relaxation of magnetization. Employing \emph{ab
+initio} many-body perturbation theory we studied the magnon spectra of the
+tetragonal FeCo compounds considering three different experimental $c/a$
+ratios, $c/a=$1.13, 1.18, and 1.24 corresponding to FeCo grown on Pd, Ir, and
+Rh, respectively. We find that for all three cases the short-wave-length
+magnons are strongly damped and tetragonal distortion gives rise to a
+significant magnon softening. The magnon stiffness constant $D$ decreases
+almost by a factor of two from FeCo/Pd to FeCo/Rh. The combination of soft
+magnons together with the giant magnetic anisotropy energy suggests FeCo/Rh to
+be a promising material for perpendicular magnetic recording applications.",1304.7091v1
+2014-11-26,Pattern Recognition with Magnonic Holographic Memory Device,"In this work, we present experimental data demonstrating the possibility of
+using magnonic holographic devices for pattern recognition. The prototype
+eight-terminal device consists of a magnetic matrix with micro-antennas placed
+on the periphery of the matrix to excite and detect spin waves. The principle
+of operation is based on the effect of spin wave interference, which is similar
+to the operation of optical holographic devices. Input information is encoded
+in the phases of the spin waves generated on the several edges of the magnonic
+matrix, while the output corresponds to the amplitude of the inductive voltage
+produced by the interfering spin waves on the other side of the matrix. The
+level of the output voltage depends on the combination of the input phases as
+well as on the internal structure of the magnonic matrix. Experimental data
+collected for several magnonic matrixes show the unique output signatures in
+which maxima and minima correspond to specific input phase patterns.
+Potentially, magnonic holographic devices may provide a higher storage density
+compare to the optical counterparts due to a shorter wavelength and
+compatibility with conventional electronic devices. The challenges and
+shortcoming of the magnonic holographic devices are also discussed.",1411.7082v1
+2014-12-07,Magnonic band gaps in YIG based magnonic crystals: array of grooves versus array of metallic stripes,"The magnonic band gaps of the two types of planar one-dimensional magnonic
+crystals comprised of the periodic array of the metallic stripes on yttrium
+iron garnet (YIG) film and YIG film with an array of grooves was analyzed
+experimentally and theoretically. In such periodic magnetic structures the
+propagating magnetostatic surface spin waves were excited and detected by
+microstripe transducers with vector network analyzer and by Brillouin light
+scattering spectroscopy. Properties of the magnonic band gaps were explained
+with the help of the finite element calculations. The important influence of
+the nonreciprocal properties of the spin wave dispersion induced by metallic
+stripes on the magnonic band gap width and its dependence on the external
+magnetic field has been shown. The usefulness of both types of the magnonic
+crystals for potential applications and possibility for miniaturization are
+discussed.",1412.2367v2
+2015-01-26,Dynamics of magnon fluid in Dzyaloshinskii-Moriya magnet and its manifestation in magnon-Skyrmion scattering,"We construct Holstein-Primakoff Hamiltonian for magnons in arbitrary slowly
+varying spin background, for a microscopic spin Hamiltonian consisting of
+ferromagnetic spin exchange,Dzyaloshinskii-Moriya exchange, and the Zeeman
+term. The Gross-Pitaevskii-type equation for magnon dynamics contains several
+background gauge fields pertaining to local spin chirality, inhomogeneous
+potential, and anomalous scattering that violates the boson number
+conservation. Non-trivial corrections to previous formulas derived in the
+literature are given. Subsequent mapping to hydrodynamic fields yields the
+continuity equation and the Euler equation of the magnon fluid dynamics. Magnon
+wave scattering off a localized Skyrmion is examined numerically based on our
+Gross-Pitaevskii formulation. Dependence of the effective flux experienced by
+the impinging magnon on the Skyrmion radius is pointed out, and compared with
+analysis of the same problem using the Landau-Lifshitz-Gilbert equation.",1501.06467v1
+2015-04-03,The effect of the magnon dispersion on the longitudinal spin Seebeck effect in yttrium iron garnets (YIG),"We study the temperature dependence of the longitudinal spin-Seebeck effect
+(LSSE) in a yttrium iron garnet Y3Fe5O12 (YIG) / Pt system for samples of
+different thicknesses. In this system, the thermal spin torque is
+magnon-driven. The LSSE signal peaks at a specific temperature that depends on
+the YIG sample thickness. We also observe freeze-out of the LSSE signal at high
+magnetic fields, which we attribute to the opening of an energy gap in the
+magnon dispersion. We observe partial freeze-out of the LSSE signal even at
+room temperature, where kBT is much larger than the gap. This suggests that a
+subset of the magnon population with an energy below kB x TC (TC about 40 K)
+contribute disproportionately to the LSSE; at temperatures below TC, we label
+these magnons subthermal magnons. The T-dependence of the LSSE at temperatures
+below the maximum is interpreted in terms of a new empirical model that
+ascribes most of the temperature dependence to that of the thermally driven
+magnon flux.",1504.00895v1
+2015-11-11,Cavity magnomechanics,"A dielectric body couples with electromagnetic fields through radiation
+pressure and electrostrictive forces, which mediate phonon-photon coupling in
+cavity optomechanics. In a magnetic medium, according to Korteweg-Helmholtz
+formula, magnetostrictive forces should arise and lead to phonon-magnon
+interaction. Here we report such a coupled phonon-magnon system based on
+ferrimagnetic spheres, which we term as cavity magnomechanics, by analogy to
+cavity optomechanics. Coherent phonon-magnon interactions, including
+electromagnetically induced transparency and absorption, are demonstrated.
+Excitingly, due to strong hybridization of magnon and microwave photon modes
+and their high tunability, our platform exhibits new features including
+parametric amplification of magnons and phonons, triply resonant
+photon-magnon-phonon coupling and phonon lasing. Our work demonstrates the
+fundamental principle of cavity magnomechanics and its application as a new
+information transduction platform based on coherent coupling between photons,
+phonons and magnons.",1511.03680v2
+2015-11-16,Condensing magnons in a degenerate ferromagnetic spinor Bose gas,"We observe the condensation of magnon excitations within an $F=1$ $^{87}$Rb
+spinor Bose-Einstein condensed gas. Magnons are pumped into a longitudinally
+spin-polarized gas, allowed to equilibrate to a non-degenerate distribution,
+and then cooled evaporatively at near-constant net longitudinal magnetization
+whereupon they condense. We find magnon condensation to be described
+quantitatively as the condensation of free particles in an effective potential
+that is uniform within the ferromagnetic condensate volume, evidenced by the
+number and distribution of magnons at the condensation transition. Transverse
+magnetization images reveal directly the spontaneous, inhomogeneous symmetry
+breaking by the magnon quasi-condensate, including signatures of Mermin-Ho spin
+textures that appear as phase singularities in the magnon condensate
+wavefunction.",1511.05193v1
+2016-04-07,Magnon-mediated spin current noise in ferromagnet$|$non-magnetic conductor hybrids,"The quantum excitations of the collective magnetization dynamics in a
+ferromagnet (F) - magnons - enable spin transport without an associated charge
+current. This pure spin current can be transferred to electrons in an adjacent
+non-magnetic conductor (N). We evaluate the finite temperature noise of the
+magnon-mediated spin current injected into N by an adjacent F driven by a
+coherent microwave field. We find that the dipolar interaction leads to
+squeezing of the magnon modes giving them wavevector dependent non-integral
+spin, which directly manifests itself in the shot noise. For temperatures
+higher than the magnon gap, the thermal noise is dominated by large wavevector
+magnons which exhibit negligible squeezing. The noise spectrum is white up to
+the frequency corresponding to the maximum of the temperature or the magnon
+gap. At larger frequencies, the noise is dominated by vacuum fluctuations. The
+shot noise is found to be much larger than its thermal counterpart over a broad
+temperature range, making the former easier to be measured experimentally.",1604.02079v2
+2016-04-13,Magnon spin transport driven by the magnon chemical potential in a magnetic insulator,"We develop a linear-response transport theory of diffusive spin and heat
+transport by magnons in magnetic insulators with metallic contacts. The magnons
+are described by a position dependent temperature and chemical potential that
+are governed by diffusion equations with characteristic relaxation lengths.
+Proceeding from a linearized Boltzmann equation, we derive expressions for
+length scales and transport coefficients. For yttrium iron garnet (YIG) at room
+temperature we find that long-range transport is dominated by the magnon
+chemical potential. We compare the model's results with recent experiments on
+YIG with Pt contacts [L.J. Cornelissen, et al., Nat. Phys. 11, 1022 (2015)] and
+extract a magnon spin conductivity of $\sigma_{m}=5\times10^{5}$ S/m. Our
+results for the spin Seebeck coefficient in YIG agree with published
+experiments. We conclude that the magnon chemical potential is an essential
+ingredient for energy and spin transport in magnetic insulators.",1604.03706v1
+2016-04-28,Chirality-driven Hall Transport Phenomena of Spins,"Experimental and theoretical aspects of Hall-type transport of spins in
+magnetic insulators are reviewed, with emphasis on their spin chirality origin.
+A general formalism for linear response theory of thermal Hall transport in the
+spin model is developed, which can be applied to both the magnon and the
+paramagnetic, spin-liquid regimes. Recent experiments on magnon-mediated
+thermal Hall transport in the two-dimensional kagome, and three-dimensional
+pyrochlore ferromagnetic insulators are reviewed in light of the multi-band
+magnon theory of Hall transport, and compared to the more mysterious thermal
+Hall transport found in the putative quantum spin ice material. As realizations
+of spin-chirality driven magnon transport in the real space, we review the
+general theory of emergent gauge fields governing the magnon dynamics in the
+textured magnet, and discuss its application to the magnon-Skyrmion scattering
+problem. Topological magnon Hall effect driven by the Skyrmion texture is
+discussed.",1604.08290v2
+2017-03-22,Dirac Magnon Nodal Loops in Quasi-2D Quantum Magnets,"In this report, we propose a new concept of one-dimensional (1D) closed lines
+of Dirac magnon nodes in two-dimensional (2D) momentum space of quasi-2D
+quantum magnetic systems. They are termed ""2D Dirac magnon nodal-line loops"".
+We utilize the bilayer honeycomb ferromagnets with intralayer coupling $J$ and
+interlayer coupling $J_L$, which is realizable in the honeycomb chromium
+compounds CrX$_3$ (X $\equiv$ Br, Cl, and I). However, our results can also
+exist in other layered quasi-2D quantum magnetic systems. Here, we show that
+the magnon bands of the bilayer honeycomb ferromagnets overlap for $J_L\neq 0$
+and form 1D closed lines of Dirac magnon nodes in 2D momentum space. The 2D
+Dirac magnon nodal-line loops are topologically protected by inversion and
+time-reversal symmetry. Furthermore, we show that they are robust against weak
+Dzyaloshinskii-Moriya interaction $ \Delta_{DM}< J_L$ and possess chiral magnon
+edge modes.}",1703.07783v5
+2017-08-09,Weyl magnons in pyrochlore antiferromagnets with all-in-all-out orders,"We investigate novel topological magnon band crossings of pyrochlore
+antiferromagnets with all-in-all-out (AIAO) magnetic order. By general symmetry
+analysis and spin-wave theory, we show that pyrochlore materials with AIAO
+orders can host Weyl magnons under external magnetic fields or uniaxial
+strains. Under a small magnetic field, the magnon bands of the pyrochlore with
+AIAO background can feature two opposite-charged Weyl points, which is the
+minimal number of Weyl points realizable in quantum materials and has not be
+experimentally observed so far. We further show that breathing pyrochlores with
+AIAO orders can exhibit Weyl magnons upon uniaxial strains. These findings
+apply to any pyrochlore material supporting AIAO orders, irrespective of the
+forms of interactions. Specifically, we show that the Weyl magnons are robust
+against direct (positive) Dzyaloshinskii-Moriya interactions. Because of the
+ubiquitous AIAO orders in pyrochlore magnets including R$_2$Ir$_2$O$_7$, and
+experimentally achievable external strain and magnetic field, our predictions
+provide promising arena to witness the Weyl magnons in quantum magnets.",1708.02948v2
+2018-04-12,A shortcut to gradient-corrected magnon dispersion: exchange-only case,"Ab initio calculations of the magnon dispersion in ferromagnetic materials
+typically rely on the adiabatic local density approximation (ALDA) in which the
+effective exchange-correlation field is everywhere parallel to the
+magnetization. These calculations, however, tend to overestimate the ""magnon
+stiffness"", defined as the curvature of the magnon frequency vs. wave vector
+relation evaluated at zero wave vector. Here we suggest a simple procedure to
+improve the magnon dispersion by taking into account gradient corrections to
+the ALDA at the exchange-only level. We find that this gradient correction
+always reduces the magnon stiffness. The surprisingly large size of these
+corrections ($\sim 30\%$) greatly improves the agreement between the calculated
+and the observed magnon stiffness for cobalt and nickel, which are known to be
+overestimated within the ALDA.",1804.04556v2
+2013-08-05,Magnonic momentum transfer force on domain walls confined in space,"Momentum transfer from incoming magnons to a Bloch domain wall is calculated
+using one dimensional continuum micromagnetic analysis. Due to the confinement
+of the wall in space, the dispersion relation of magnons is different from that
+of a single domain. This mismatch of dispersion relations can result in
+reflection of magnons upon incidence on the domain wall, whose direct
+consequence is a transfer of momentum between magnons and the domain wall. The
+corresponding counteraction force exerted on the wall can be used for the
+control of domain wall motion through magnonic linear momentum transfer, in
+analogy with the spin transfer torque induced by magnonic angular momentum
+transfer.",1308.0965v1
+2013-09-10,Theory of magnon-skyrmion scattering in chiral magnets,"We study theoretically the dynamics of magnons in the presence of a single
+skyrmion in chiral magnets featuring Dzyaloshinskii-Moriya interaction. We show
+by micromagnetic simulations that the scattering process of magnons by a
+skyrmion can be clearly defined although both originate in the common spins. We
+find that (i) the magnons are deflected by a skyrmion, with the angle strongly
+dependent on the magnon wavenumber due to the effective magnetic field of the
+topological texture, and (ii) the skyrmion motion is driven by magnon
+scattering through exchange of the momenta between the magnons and a skyrmion:
+the total momentum is conserved. This demonstrates that the skyrmion has a
+well-defined, though highly non-Newtonian, momentum.",1309.2361v1
+2017-06-02,Experimental investigation of the temperature-dependent magnon density and its influence on studies of spin-transfer-torque-driven systems,"We present the temperature dependence of the thermal magnon density in a thin
+ferromagnetic layer. By employing Brillouin light scattering and varying the
+temperature, an increase of the magnon density accompanied by a lowering of the
+spin-wave frequency is observed with increasing temperature. The magnon density
+follows the temperature according to the Bose-Einstein distribution function
+which leads to an approximately linear dependency. In addition, the influence
+of this effect in spin-transfer-torque-driven systems is presented. In
+particular, the increase in the magnon density with temperature sets the limit
+for a suppression of magnons in charge current-driven systems. Hence, the
+maximum possible suppression of thermal magnons occurs at a finite current.",1706.00619v1
+2018-09-04,Level Attraction Due to Dissipative Magnon-Photon Coupling,"We report dissipative magnon-photon coupling caused by cavity Lenz effect,
+where the magnons in a magnet induce a rf current in the cavity, leading to a
+cavity back action that impedes the magnetization dynamics. This effect is
+revealed in our experiment as level attraction with a coalescence of hybridized
+magnon-photon modes, which is distinctly different from level repulsion with
+mode anticrossing caused by coherent magnon-photon coupling. We develop a
+method to control the in- terpolation of coherent and dissipative magnon-photon
+coupling, and observe a matching condition where the two effects cancel. Our
+work sheds light on the so-far hidden side of magnon-photon coupling, opening a
+new avenue for controlling and utilizing light-matter interactions.",1809.01233v1
+2020-12-03,Parameter estimation and quantum entanglement in PT symmetrical cavity magnonics system,"We investigate the parameter estimation in a magnon-cavity-magnon coupled
+system. PT symmetrical two magnons system can be formed in the gain magnetic
+materials by the adiabatic elimination of the cavity field mode. We show that
+the optimal estimation will not appear at the exceptional point due to that the
+quantum fluctuations are the strongest at the exceptional point. Moreover, we
+demonstrate that the measurements at the exceptional point tend to be optimal
+with the increase of prepared time. And the direct photon detection is the
+optimal measurement for the initial state in the vacuum input state. For the
+open PT symmetrical two magnons system, the quantum fluctuations will greatly
+reduce the degree of entanglement. Finally, we show that a higher estimated
+magnetic sensitivity can be obtained by measuring the frequency of one magnon
+in the PT symmetrical two magnons system.",2012.01890v1
+2017-05-12,Floquet Topological Magnons,"We introduce the concept of Floquet topological magnons --- a mechanism by
+which a synthetic tunable Dzyaloshinskii-Moriya interaction (DMI) can be
+generated in quantum magnets using circularly polarized electric (laser) field.
+The resulting effect is that Dirac magnons and nodal magnons in two-dimensional
+(2D) and three-dimensional (3D) quantum magnets can be tuned to magnon Chern
+insulators and Weyl magnons respectively under circularly polarized laser
+field. The Floquet formalism also yields a tunable intrinsic DMI in insulating
+quantum magnets without an inversion center. We demonstrate that the Floquet
+topological magnons possess a finite thermal Hall conductivity tunable by the
+laser field.",1705.04694v5
+2018-07-05,Bridging magnonics and spin-orbitronics,"The emerging field of nano-magnonics utilizes high-frequency waves of
+magnetization - the spin waves - for the transmission and processing of
+information on the nanoscale. The advent of spin-transfer torque has spurred
+significant advances in nano-magnonics, by enabling highly efficient local
+spin-wave generation in magnonic nanodevices. Furthermore, the recent emergence
+of spin-orbitronics, which utilizes spin-orbit interaction as the source of
+spin torque, has provided a unique ability to exert spin torque over spatially
+extended areas of magnonic structures, enabling enhanced spin-wave
+transmission. Here, we experimentally demonstrate that these advances can be
+efficiently combined. We utilize the same spin-orbit torque mechanism for the
+generation of propagating spin waves, and for the long-range enhancement of
+their propagation, in a single integrated nano-magnonic device. The
+demonstrated system exhibits a controllable directional asymmetry of spin wave
+emission, which is highly beneficial for applications in non-reciprocal
+magnonic logic and neuromorphic computing.",1807.02050v1
+2018-07-24,Enhanced magnon spin transport in NiFe$_2$O$_4$ thin films on a lattice-matched substrate,"We investigate magnon spin transport in epitaxial nickel ferrite
+(NiFe$_2$O$_4$, NFO) films grown on magnesium gallate spinel (MgGa$_2$O$_4$,
+MGO) substrates, which have a lattice mismatch with NFO as small as 0.78%,
+resulting in the reduction of antiphase boundary defects and thus in improved
+magnetic properties in the NFO films. In the nonlocal transport experiments,
+enhanced signals are observed for both electrically and thermally excited
+magnons, and the magnon relaxation length ($\lambda_m$) of NFO is found to be
+around 2.5 $\mu$m at room temperature. Moreover, at both room and low
+temperatures, we present distinct features from the nonlocal spin Seebeck
+signals which arise from magnon polaron formation. Our results demonstrate
+excellent magnon transport properties (magnon spin conductivity, $\lambda_m$
+and spin mixing conductance at the interface between Pt) of NFO films grown on
+a lattice-matched substrate that are comparable with those of yttrium iron
+garnet.",1807.09013v1
+2018-12-21,Magnon heralding in cavity optomagnonics,"In the emerging field of cavity optomagnonics, photons are coupled coherently
+to magnons in solid-state systems. These new systems are promising for
+implementing hybrid quantum technologies. Being able to prepare Fock states in
+such platforms is an essential step towards the implementation of quantum
+information schemes. We propose a magnon-heralding protocol to generate a
+magnon Fock state by detecting an optical cavity photon. Due to the
+peculiarities of the optomagnonic coupling, the protocol involves two distinct
+cavity photon modes. Solving the quantum Langevin equations of the coupled
+system, we show that the temporal scale of the heralding is governed by the
+magnon-photon cooperativity and derive the requirements for generating high
+fidelity magnon Fock states. We show that the nonclassical character of the
+heralded state, which is imprinted in the autocorrelation of an optical ""read""
+mode, is only limited by the magnon lifetime for small enough temperatures. We
+address the detrimental effects of nonvacuum initial states, showing that high
+fidelity Fock states can be achieved by actively cooling the system prior to
+the protocol.",1812.09165v3
+2019-01-08,Topological magnon amplification,"Topology is quickly becoming a cornerstone in our understanding of electronic
+systems. Like their electronic counterparts, bosonic systems can exhibit a
+topological band structure, but in real materials it is difficult to ascertain
+their topological nature, as their ground state is a simple condensate or the
+vacuum, and one has to rely instead on excited states, for example a
+characteristic thermal Hall response. Here we propose driving a topological
+magnon insulator with an electromagnetic field and show that this causes edge
+mode instabilities and a large non-equilibrium steady-state magnon edge
+current. Building on this, we discuss several experimental signatures that
+unambiguously establish the presence of topological magnon edge modes.
+Furthermore, our amplification mechanism can be employed to power a topological
+travelling-wave magnon amplifier and topological magnon laser, with
+applications in magnon spintronics. This work thus represents a step toward
+functional topological magnetic materials.",1901.02282v2
+2019-02-02,Hybrid plasmon-magnon polaritons in graphene-antiferromagnet heterostructures,"We consider a hybrid structure formed by graphene and an insulating
+antiferromagnet, separated by a dielectric of thickness up to $d\simeq 500
+\,nm$. When uncoupled, both graphene and the antiferromagnetic surface host
+their own polariton modes coupling the electromagnetic field with plasmons in
+the case of graphene, and with magnons in the case of the antiferromagnet. We
+show that the hybrid structure can host two new types of hybrid polariton
+modes. First, a surface magnon-plasmon polariton whose dispersion is radically
+changed by the carrier density of the graphene layer, including a change of
+sign in the group velocity. Second, a surface plasmon-magnon polariton formed
+as a linear superposition of graphene surface plasmon and the antiferromagnetic
+bare magnon. This polariton has a dispersion with two branches, formed by the
+anticrossing between the dispersive surface plasmon and the magnon. We discuss
+the potential these new modes have for combining photons, magnons, and plasmons
+to reach new functionalities.",1902.00708v1
+2019-02-07,Integrated magnonic half-adder,"Spin waves and their quanta magnons open up a promising branch of high-speed
+and low-power information processing. Several important milestones were
+achieved recently in the realization of separate magnonic data processing units
+including logic gates, a magnon transistor and units for non-Boolean computing.
+Nevertheless, the realization of an integrated magnonic circuit consisting of
+at least two logic gates and suitable for further integration is still an
+unresolved challenge. Here we demonstrate such an integrated circuit
+numerically on the example of a magnonic half-adder. Its key element is a
+nonlinear directional coupler serving as combined XOR and AND logic gate that
+utilizes the dependence of the spin wave dispersion on its amplitude. The
+circuit constitutes of only three planar nano-waveguides and processes all
+information within the magnon domain. Benchmarking of the proposed device is
+performed showing the potential for sub-aJ energy consumption per operation.",1902.02855v2
+2019-03-07,Nonlocal Spin Transport as a Probe of Viscous Magnon Fluids,"Magnons in ferromagnets behave as a viscous fluid over a length scale, the
+momentum-relaxation length, below which momentum-conserving scattering
+processes dominate. We show theoretically that in this hydrodynamic regime
+viscous effects lead to a sign change in the magnon chemical potential, which
+can be detected as a sign change in the nonlocal resistance measured in spin
+transport experiments. This sign change is observable when the
+injector-detector distance becomes comparable to the momentum-relaxation
+length. Taking into account momentum- and spin-relaxation processes, we
+consider the quasiconservation laws for momentum and spin in a magnon fluid.
+The resulting equations are solved for nonlocal spin transport devices in which
+spin is injected and detected via metallic leads. Because of the finite
+viscosity we also find a backflow of magnons close to the injector lead. Our
+work shows that nonlocal magnon spin transport devices are an attractive
+platform to develop and study magnon-fluid dynamics.",1903.02790v2
+2019-03-11,Exchange-enhanced Ultrastrong Magnon-Magnon Coupling in a Compensated Ferrimagnet,"The ultrastrong coupling of (quasi-)particles has gained considerable
+attention due to its application potential and richness of the underlying
+physics. Coupling phenomena arising due to electromagnetic interactions are
+well explored. In magnetically ordered systems, the quantum-mechanical
+exchange-interaction should furthermore enable a fundamentally different
+coupling mechanism. Here, we report the observation of ultrastrong intralayer
+exchange-enhanced magnon-magnon coupling in a compensated ferrimagnet. We
+experimentally study the spin dynamics in a gadolinium iron garnet single
+crystal using broadband ferromagnetic resonance. Close to the ferrimagnetic
+compensation temperature, we observe ultrastrong coupling of clockwise and
+anticlockwise magnon modes. The magnon-magnon coupling strength reaches more
+than 30% of the mode frequency and can be tuned by varying the direction of the
+external magnetic field. We theoretically explain the observed phenomenon in
+terms of an exchange-enhanced mode-coupling mediated by a weak cubic
+anisotropy.",1903.04330v2
+2019-08-25,Itinerant topological magnons in Haldane Hubbard model with a nearly-flat electron band,"We elaborate the first theoretical realization of two dimensional itinerant
+topological magnons, based on the quarter filled Haldane-Hubbard model with a
+nearly-flat electron band. By using the exact diagonalization method with a
+projection onto this band, we obtain the spin wave excitations over the
+itinerant ferromagnetic ground state. In the flatband limit, the excitation
+exhibits similar dispersion to the free electron band with Dirac magnons. The
+nonflatness of the electron band opens a topological gap at Dirac points and
+leads to an acoustic magnon band with a nonzero Chern number. We further show
+that tuning the sublattice Hubbard interactions or the next-nearest-neighbor
+hopping can induce a topological transition characterized by the gap closing
+and reopening, and the existence of the in-gap magnons on magnetic domain
+walls. We find an exact set of bases for magnons in the flatband limit
+constructed from sublattice particle-hole vectors and derive an effective model
+to explore the origin of the topological magnon which is attributed to the
+``mass inversion mechanism''.",1908.09255v1
+2016-10-13,Spin wave surface states in one-dimensional planar magnonic crystals,"We have investigated surface spin wave states in one-dimensional planar
+bi-component magnonic crystals, localized on the surfaces resulting from the
+breaking of the periodic structure. The two systems have been considered: the
+magnonic crystal with periodic changes of the anisotropy field in exchange
+regime and the magnonic crystal composed of Fe and Ni stripes in dipolar regime
+with exchange interactions included. We chose the symmetric unit cell for both
+systems to implement the symmetry related criteria for existence of the surface
+states. We investigated also the surface states induced by the presence of
+perturbation of the surface areas of the magnonic crystals. We showed, that the
+system with modulated anisotropy is a direct analog of the electronic crystal.
+Therefore, the surface states in both systems have the same properties. For
+surface states existing in magnonic crystals in dipolar regime we demonstrated
+that spin waves preserve distinct differences to the electronic crystals, which
+are due to long-range dynamic dipolar interactions. We found that tuning of the
+strength of magnetization pinning resulting from the surface anisotropy or
+dipolar effect is vitally important for existence of the surface states in
+magnonic crystals.",1610.04083v1
+2017-11-13,Thermodynamic Entanglement of Magnonic Condensates,"Over the last decade, significant progresses have been achieved to create
+Bose-Einstein condensates (BEC) of magnetic excitations, i.e., magnons, at the
+room temperature, which is a novel quantum many-body system with a strong
+spin-spin correlation, and contains potential applications in magnonic
+spintronics. For quantum information science, the magnonic condensates can
+become an attractive source of quantum entanglement, which plays a central role
+in most of the quantum information processing tasks. Here we theoretically
+study the entanglement properties of a magnon gas above and below the
+condensation temperature. We show that the thermodynamic entanglement of the
+magnons is a manifestation of the off-diagonal long-range order; the
+entanglement of the condensate does not vanish, even if the spins are separated
+by an infinitely large distance, which is fundamentally distinct from the
+normal magnetic ordering below the Curie temperature. In addition, the phase
+transition point occurs when the derivative of the entanglement changes
+abruptly. Furthermore, the spin-spin entanglement can be experimentally
+accessed with the current technology. These results provide a theoretical
+foundation for a future experimental investigation of the magnon BEC in terms
+of quantum entanglement.",1711.04394v1
+2018-10-17,Conventional magnon BEC in YIG film,"The conventional magnon Bose-Einstein condensation (BEC of magnons with k =
+0) is a coherent state of excited magnons described by a common wave function.
+It was observed first in antiferromagnetic superfluid states of 3He. Here we
+report on the discovery of a very similar magnon BEC in ferrimagnetic film at
+room temperature. The experiments were performed in Yttrium Iron Garnet (YIG)
+films at a magnetic field oriented perpendicular to the film. The high-density
+quasiequilibrium state of excited magnon was formed by methods of pulse and/or
+Continuous Waves (CW) magnetic resonance. We have observed a Long Lived
+Induction Decay Signals (LLIDS), well known as a signature of spin
+superfluidity. We demonstrate that the BEC state may maintain permanently by
+continuous replenishment of magnons with a small radiofrequency (RF) field. Our
+finding opens the way for development of potential supermagnonic applications
+at an ambient conditions.",1810.08051v2
+2020-06-22,Imprinting and driving electronic orbital magnetism using magnons,"Magnons, as the most elementary excitations of magnetic materials, have
+recently emerged as a prominent tool in electrical and thermal manipulation and
+transport of spin, and magnonics as a field is considered as one of the pillars
+of modern spintronics. On the other hand, orbitronics, which exploits the
+orbital degree of freedom of electrons rather than their spin, emerges as a
+powerful platform in efficient design of currents and redistribution of angular
+momentum in structurally complex materials. Here, we uncover a way to bridge
+the worlds of magnonics and electronic orbital magnetism, which originates in
+the fundamental coupling of scalar spin chirality, inherent to magnons, to the
+orbital degree of freedom in solids. We show that this can result in efficient
+generation and transport of electronic orbital angular momentum by magnons,
+thus opening the road to combining the functionalities of magnonics and
+orbitronics to their mutual benefit in the realm of spintronics applications.",2006.13033v2
+2020-06-29,Bosonic Bott Index and Disorder-Induced Topological Transitions of Magnons,"We investigate the role of disorder on the various topological magnonic
+phases present in deformed honeycomb ferromagnets. To this end, we introduce a
+bosonic Bott index to characterize the topology of magnon spectra in finite,
+disordered systems. The consistency between the Bott index and Chern number is
+numerically established in the clean limit. We demonstrate that topologically
+protected magnon edge states are robust to moderate disorder and, as
+anticipated, localized in the strong regime. We predict a disorder-driven
+topological phase transition, a magnonic analog of the ""topological Anderson
+insulator"" in electronic systems, where the disorder is responsible for the
+emergence of the nontrivial topology. Combining the results for the Bott index
+and transport properties, we show that bulk-boundary correspondence holds for
+disordered topological magnons. Our results open the door for research on
+topological magnonics as well as other bosonic excitations in finite and
+disordered systems.",2006.16310v4
+2020-09-02,Non-local spin Seebeck effect in the bulk easy-plane antiferromagnet NiO,"We report the observation of magnon spin currents generated by the Spin
+Seebeck effect (SSE) in a bulk single crystal of the easy-plane antiferromagnet
+NiO. A magnetic field induces a non-degeneracy and thereby an imbalance in the
+population of magnon modes with opposite spin. A temperature gradient then
+gives rise to a non-zero magnon spin current. This SSE is measured both in a
+local and a non-local geometry at 5$\,$K in bulk NiO. The magnetic field
+dependence of the obtained signal is modelled by magnetic field splitting of
+the low energy magnon modes, affecting the spin Seebeck coefficient. The
+relevant magnon modes at this temperature are linked to cubic anisotropy and
+magnetic dipole-dipole interactions. The non-local signal deviates from the
+expected quadratic Joule heating by saturating at a current from around
+75$\,\mu A$ in the injector. The magnon chemical potential does not decay
+exponentially with distance and inhomogeneities may be the result of local
+magnon accumulations.",2009.01160v1
+2020-09-04,Magnonic Su-Schrieffer-Heeger Model in Honeycomb Ferromagnets,"Topological electronics has extended its richness to non-electronic systems
+where phonons and magnons can play the role of electrons. In particular,
+topological phases of magnons can be enabled by the Dzyaloshinskii-Moriya
+interaction (DMI) which acts as an effective spin-orbit coupling. We show that
+besides DMI, an alternating arrangement of Heisenberg exchange interactions
+critically determines the magnon band topology, realizing a magnonic analog of
+the Su-Schrieffer-Heeger model. On a honeycomb ferromagnet with perpendicular
+anisotropy, we calculate the topological phase diagram, the chiral edge states,
+and the associated magnon Hall effect by allowing the relative strength of
+exchange interactions on different links to be tunable. Including weak
+phonon-magnon hybridization does not change the result. Candidate materials are
+discussed.",2009.02291v1
+2015-12-04,Magnetic field dependence of the magnon spin diffusion length in the magnetic insulator yttrium iron garnet,"We investigated the effect of an external magnetic field on the diffusive
+spin transport by magnons in the magnetic insulator yttrium iron garnet (YIG),
+using a non-local magnon transport measurement geometry. We observed a decrease
+in magnon spin diffusion length $\lambda_m$ for increasing field strengths,
+where $\lambda_m$ is reduced from 9.6$\pm1.2$ $\mu$m at 10 mT to 4.2$\pm0.6$
+$\mu$m at 3.5 T at room temperature. In addition, we find that there must be at
+least one additional transport parameter that depends on the external magnetic
+field. Our results do not allow us to unambiguously determine whether this is
+the magnon equilibrium density or the magnon diffusion constant. These results
+are significant for experiments in the more conventional longitudinal spin
+Seebeck geometry, since the magnon spin diffusion length sets the length scale
+for the spin Seebeck effect as well and is relevant for its understanding.",1512.01410v1
+2017-04-18,Giant Magnons of String Theory in the Lambda Background,"The analogues of giant magnon configurations are studied on the string world
+sheet in the lambda background. This is a discrete deformation of the
+AdS(5)xS(5) background that preserves the integrability of the world sheet
+theory. Giant magnon solutions are generated using the dressing method and
+their dispersion relation is found. This reduces to the usual dyonic giant
+magnon dispersion relation in the appropriate limit and becomes relativistic in
+another limit where the lambda model becomes the generalized sine-Gordon theory
+of the Pohlmeyer reduction. The scattering of giant magnons is then shown in
+the semi-classical limit to be described by the quantum S-matrix that is a
+quantum group deformation of the conventional giant magnon S-matrix. It is
+further shown that in the small g limit, a sector of the S-matrix is related to
+the XXZ spin chain whose spectrum matches the spectrum of magnon bound states.",1704.05437v2
+2019-10-14,Direct evidence of spatial stability of Bose-Einstein condensate of magnons,"Bose-Einstein condensation of quasi-equilibrium magnons is one of few
+macroscopic quantum phenomena observed at room temperature. Since its
+discovery, it became an object of intense research, which led to the
+observation of many exciting phenomena such as quantized vortices, second
+sound, and Bogolyubov waves. However, for a long time it remained unclear, what
+physical mechanisms can be responsible for the spatial stability of the magnon
+condensate. Indeed, since magnons are believed to exhibit attractive
+interaction, it is generally expected that the magnon condensate should be
+unstable with respect to the real-space collapse, which contradicts all the
+experimental findings. Here, we provide direct experimental evidence that
+magnons in a condensate exhibit repulsive interaction resulting in the
+condensate stabilization and propose a mechanism, which is responsible for the
+interaction inversion. Our experimental conclusions are additionally supported
+by the theoretical model based on the Gross-Pitaevskii equation. Our findings
+solve a long-standing problem and provide a new insight into the physics of
+magnon Bose-Einstein condensates.",1910.06013v1
+2019-10-21,Generation of exchange magnons in thin ferromagnetic films by ultrashort acoustic pulses,"We investigate generation of exchange magnons by ultrashort, picosecond
+acoustic pulses propagating through ferromagnetic thin films. Using the
+Landau-Lifshitz-Gilbert equations we derive the dispersion relation for
+exchange magnons for an external magnetic field tilted with respect to the film
+normal. Decomposing the solution in a series of standing spin wave modes, we
+derive a system of ordinary differential equations and driven harmonic
+oscillator equations describing the dynamics of individual magnon mode. The
+external magnetoelastic driving force is given by the time-dependent spatial
+Fourier components of acoustic strain pulses inside the layer. Dependencies of
+the magnon excitation efficiencies on the duration of the acoustic pulses and
+the external magnetic field highlight the role of acoustic bandwidth and
+phonon-magnon phase matching. Our simulations for ferromagnetic nickel evidence
+the possibility of ultrafast magneto-acoustic excitation of exchange magnons
+within the bandwidth of acoustic pulses in thin samples under conditions
+readily obtained in femtosecond pump-probe experiments.",1910.09481v1
+2020-02-01,Coplanar cavity for strong coupling between photons and magnons in van der Waals antiferromagnet,"We investigate the performance of niobium nitride superconducting coplanar
+waveguide resonators towards hybrid quantum devices with magnon-photon
+coupling. We find internal quality factors ~ 20000 at 20 mK base temperature,
+in zero magnetic field. We find that by reducing film thickness below 100 nm
+internal quality factor greater than 1000 can be maintained up to parallel
+magnetic field of ~ 1 T and perpendicular magnetic field of ~ 100 mT. We
+further demonstrate strong coupling of microwave photons in these resonators,
+with magnons in chromium trichloride, a van der Waals antiferromagnet, which
+shows that these cavities serve as a good platform for studying magnon-photon
+coupling in 2D magnonics based hybrid quantum systems. We demonstrate strong
+magnon-photon coupling for both optical and acoustic magnon modes of an
+antiferromagnet.",2002.00197v2
+2020-02-03,Thermal relaxation of magnons and phonons near resonance points in magnetic insulators,"We theoretically investigate the energy relaxation rate of magnons and
+phonons near the resonance points to clarify the underlying mechanism of heat
+transport in ferromagnetic materials. We find that the simple two-temperature
+model is valid for the one-phonon/one-magnon process, as the rate of energy
+exchange between magnons and phonons is proportional to the temperature
+difference between them, and it is independent of temperature in the high
+temperature limit. We found that the magnon-phonon relaxation time due to the
+one-phonon/one-magnon interaction could be reduced to 1.48 $\mu s$ at the
+resonance point by applying an external magnetic field. It means that the
+resonance effect plays a significant role in enhancing the total magnon-phonon
+energy exchange rate, apart from the higher order interaction processes.",2002.00547v1
+2020-02-18,Ultrafast Light-driven Simultaneous Excitation of Coherent Terahertz Magnons and Phonons in Multiferroic BiFeO$_3$,"The ultrafast switching of magnetization in multiferroic materials by a
+femtosecond laser could provide various advantages in photonics and magnonics.
+An efficient approach to control the light matter interaction is the modulation
+of ultrafast coherent magnons and phonons in the high frequency range.
+Spontaneous Raman and infrared spectra reveal the excitation of magnons and
+optical phonons in multiferroic BiFeO3 in the sub few terahertz range. However,
+coherent control of such quasiparticles has not been achieved yet. In this
+study, we demonstrate that linearly polarized laser pulses simultaneously
+excite coherent magnons out of plane and in plane cyclone modes and optical
+phonon E mode in BiFeO3. Experimental results in conjugation with
+phenomenological theory, by considering three uniformly distributed magnetic
+domains reveal that impulsive stimulated Raman scattering is responsible for
+the generation of coherent magnons and phonons in BiFeO3. The observation of
+these terahertz magnon and optical phonon modes paves the way for the
+development of ultrafast magneto electro optical devices.",2002.07449v2
+2020-02-22,Bose-Einstein Condensation of Nonequilibrium Magnons in Confined Systems,"We study the formation of a room temperature magnon Bose-Einstein condensate
+(BEC) in nanoscopic systems and demonstrate that its lifetime is influenced by
+the spatial confinement. We predict how dipolar interactions and nonlinear
+magnon scattering assist in the generation of a metastable magnon BEC in
+energy-quantized nanoscopic devices. We verify our prediction by a full
+numerical simulation of the Landau-Lifshitz-Gilbert equation and demonstrate
+the generation of magnon BEC in confined insulating magnets of yttrium iron
+garnet. We directly map out the nonlinear magnon scattering processes behind
+this phase transition to show how fast quantized thermalization channels allow
+the BEC formation in confined structures. Based on our results, we discuss a
+new mechanism to manipulate the BEC lifetime in nanoscaled systems. Our study
+greatly extends the freedom to study the dynamics of magnon BEC in realistic
+systems and to design integrated circuits for BEC-based applications at room
+temperature.",2002.09777v2
+2020-02-23,"Generating lightwave-photon-and-magnon entanglement with a mechanical oscillator as a ""cold reservoir""","We present a scheme to implement a steady lightwave-photon-and-magnon
+entanglement in a hybrid photon-magnon system by adiabatically eliminating the
+auxiliary microwave cavity and effectively laser cooling a delocalized
+Bogoliubov mode. The system consists of magnons, lightwave and microwave
+photons, and phonons. The magnons are embodied by a collective motion of a
+large number of spins in a macroscopic ferrimagnet. To achieve an entangling
+interaction between magnons and lightwave photons, we drive optical cavity and
+magnon at the red and blue sideband associated with the mechanical resonator.
+In particular, optimizing the relative ratio of effect couplings, rather than
+simply increasing their magnitudes, is essential for achieving strong
+entanglement. Unlike typical dissipative entanglement schemes, our results
+cannot be described by treating the effects of the entangling reservoir via a
+Linblad master equation.",2002.10877v2
+2020-03-10,Effect of magnons on the temperature dependence and anisotropy of spin-orbit torque,"We investigate the influence of magnons on the temperature-dependence and the
+anisotropy of the spin-orbit torque (SOT). For this purpose we use 3rd order
+perturbation theory in the framework of the Keldysh formalism in order to
+derive suitable equations to compute the magnonic SOT. We find several
+contributions to the magnonic SOT, which depend differently on the spin-wave
+stiffness $\mathcal{A}$ and on the temperature $T$, with the dominating
+contribution scaling like $T^{2}/\mathcal{A}^{2}$. Based on this formalism we
+compute the magnonic SOT in the ferromagnetic Rashba model. For large Rashba
+parameters the magnonic SOT is strongly anisotropic and for small quasiparticle
+broadening it may become larger than the non-magnonic SOT.",2003.05028v3
+2020-05-26,Nonlocal stimulation of three-magnon splitting in a magnetic vortex,"We present a combined numerical, theoretical and experimental study on
+stimulated three-magnon splitting in a magnetic disk in the vortex equilibrium
+state. Our micromagnetic simulations and Brillouin-light-scattering results
+confirm that three-magnon splitting can be triggered even below threshold by
+exciting one of the secondary modes by magnons propagating in a waveguide next
+to the disk. The experiments show that stimulation is possible over an extended
+range of excitation powers and a wide range of frequencies around the
+eigenfrequencies of the secondary modes. Rate-equation calculations predict an
+instantaneous response to stimulation and the possibility to prematurely
+trigger three-magnon splitting even above threshold in a sustainable manner.
+These predictions are confirmed experimentally using time-resolved
+Brillouin-light-scattering measurements and are in a good qualitative agreement
+with the theoretical results. We believe that the controllable mechanism of
+stimulated three-magnon splitting could provide a possibility to utilize
+magnon-based nonlinear networks as hardware for reservoir or neuromorphic
+computing.",2005.12663v1
+2020-07-20,Stacking Domain Wall Magnons in Twisted van der Waals Magnets,"Using bilayer CrI$_3$ as an example, we demonstrate that stacking domain
+walls in van der Waals magnets can host one dimensional (1D) magnon channels,
+which have lower energies than bulk magnons. Interestingly, some magnon
+channels are hidden in magnetically homogeneous background and can only be
+inferred with the knowledge of stacking domain walls. Compared to 1D magnons
+confined in magnetic domain walls, 1D magnons in stacking domain walls are more
+stable against external perturbations. We show that the relaxed moir\'e
+superlattices of small-angle twisted bilayer CrI$_3$ is a natural realization
+of stacking domain walls and host interconnected moir\'e magnon network. Our
+work reveals the importance of stacking domain walls in understanding magnetic
+properties of van der Waals magnets, and extends the scope of stacking
+engineering to magnetic dynamics.",2007.10398v2
+2020-08-04,Self-hybridization and tunable magnon-magnon coupling in van der Waals synthetic magnets,"Van der Waals magnets are uniquely positioned at the intersection between
+two-dimensional materials, antiferromagnetic spintronics, and magnonics. The
+interlayer exchange interaction in these materials enables antiferromagnetic
+resonances to be accessed at GHz frequencies. Consequently, these layered
+antiferromagnets are intriguing materials out of which quantum hybrid magnonic
+devices can be fashioned. Here, we use both a modified macrospin model and
+micromagnetic simulations to demonstrate a comprehensive antiferromagnetic
+resonance spectra in van der Waals magnets near the ultrathin (monolayer)
+limit. The number of optical and acoustic magnon modes, as well as the mode
+frequencies, are found to be exquisitely sensitive to the number of layers. We
+discover a self-hybridization effect where pairs of either optical or acoustic
+magnons are found to interact and self-hybridize through the dynamic exchange
+interaction. This leads to characteristic avoided energy level crossings in the
+energy spectra. Through simulations, we show that by electrically controlling
+the damping of surface layers within heterostructures both the strength and
+number of avoided energy level crossings in the magnon spectra can be
+controlled.",2008.01298v1
+2020-08-14,"Magnonic bending, phase shifting and interferometry in a 2D reconfigurable nanodisk crystal","Strongly-interacting nanomagnetic systems are pivotal across next-generation
+technologies including reconfigurable magnonics and neuromorphic computation.
+Controlling magnetisation state and local coupling between neighbouring
+nanoelements allows vast reconfigurable functionality and a host of associated
+functionalities. However, existing designs typically suffer from an inability
+to tailor inter-element coupling post-fabrication and nanoelements restricted
+to a pair of Ising-like magnetisation states. Here, we propose a new class of
+reconfigurable magnonic crystal incorporating nanodisks as the functional
+element. Magnetic nanodisks are crucially bistable in macrospin and vortex
+states, allowing inter-element coupling to be selectively activated (macrospin)
+or deactivated (vortex). Through microstate engineering, we leverage the
+distinct coupling behaviours and magnonic band structures of bistable nanodisks
+to achieve reprogrammable magnonic waveguiding, bending, gating and
+phase-shifting across a 2D network. The potential of nanodisk-based magnonics
+for wave-based computation is demonstrated via an all-magnon interferometer
+exhibiting XNOR logic functionality. Local microstate control is achieved here
+via topological magnetic writing using a magnetic force microscope tip.",2008.06451v2
+2020-10-09,Einstein-Podolsky-Rosen entanglement and asymmetric steering between distant macroscopic mechanical and magnonic systems,"We propose a deterministic scheme for establishing hybrid
+Einstein-Podolsky-Rosen (EPR) entanglement channel between a macroscopic
+mechanical oscillator and a magnon mode in a distant yttrium-iron-garnet (YIG)
+sphere across about ten gigahertz of frequency difference. The system consists
+of a driven electromechanical cavity which is unidirectionally coupled to a
+distant electromagnonical cavity inside which a YIG sphere is placed. We find
+that far beyond the sideband-resolved regime in the electromechanical
+subsystem, stationary phonon-magnon EPR entanglement can be achieved. This is
+realized by utilizing the output field of the electromechanical cavity being an
+intermediary which distributes the electromechanical entanglement to the
+magnons, thus establishing a remote phonon-magnon entanglement. The EPR
+entanglement is strong enough such that phonon-magnon quantum steering can be
+attainable in an asymmetric manner. This long-distance macroscopic hybrid EPR
+entanglement and steering enable potential applications not only in fundamental
+tests of quantum mechanics at the macro scale, but also in quantum networking
+and one-sided device-independent quantum cryptography based on magnonics and
+electromechanics.",2010.04357v1
+2020-10-16,Insights on magnon topology and valley-polarization in 2D bilayer quantum magnets,"The rich and unconventional physics in layered 2D magnets can open new
+avenues for topological magnonics and magnon valleytronics. In particular,
+two-dimensional (2D) bilayer quantum magnets are gaining increasing attention
+due to their intriguing stacking-dependent magnetism, controllable ground
+states, and topological excitations induced by magnetic spin-orbit couplings
+(SOCs). Despite the substantial research on these materials, their topological
+features remain widely unexplored to date. The present study comprehensively
+investigates the magnon topology and magnon valley-polarization in honeycomb
+bilayers with collinear magnetic order. We elucidate the separate and combined
+effects of the SOC, magnetic ground-states, stacking order, and inversion
+symmetry breaking on the topological phases, magnon valley transport, and the
+Hall and Nernst effects. The comprehensive analysis suggests clues to determine
+the SOC's nature and predicts unconventional Hall and Nernst conductivities in
+topologically trivial phases. We further report on novel bandgap closures in
+layered antiferromagnets and detail their topological implications. We believe
+the present study provides important insights into the fundamental physics and
+technological potentials of topological 2D magnons.",2010.08621v4
+2021-01-19,Evolution of room-temperature magnon gas toward coherent Bose-Einstein condensate,"The appearance of spontaneous coherence is a fundamental feature of a
+Bose-Einstein condensate and an essential requirement for possible applications
+of the condensates for data processing and quantum computing. In the case of a
+magnon condensate in a magnetic crystal, such computing can be performed even
+at room temperature. So far, the process of coherence formation in a magnon
+condensate was inaccessible. We study the evolution of magnon radiation spectra
+by direct detection of microwave radiation emitted by magnons in a
+parametrically driven yttrium iron garnet crystal. By using specially shaped
+bulk samples, we show that the parametrically overpopulated magnon gas evolves
+to a state, whose coherence is only limited by the natural magnon relaxation
+into the crystal lattice.",2101.07890v1
+2021-03-02,Hinge Magnons from Non-collinear Magnetic Order in Honeycomb Antiferromagnet,"We propose that non-collinear magnetic order in quantum magnets can harbor a
+novel higher-order topological magnon phase with non-Hermitian topology and
+hinge magnon modes. We consider a three-dimensional system of interacting local
+moments on stacked-layers of honeycomb lattice. It initially favors a collinear
+magnetic order along an in-plane direction, which turns into a non-collinear
+order upon applying an external magnetic field perpendicular to the easy axis.
+We exploit the non-Hermitian nature of the magnon Hamiltonian to show that this
+field-induced transition corresponds to the transformation from a topological
+magnon insulator to a higher-order topological magnon state with a
+one-dimensional hinge mode. As a concrete example, we discuss the
+recently-discovered monoclinic phase of the thin chromium trihalides, which we
+propose as the first promising material candidate of the higher-order
+topological magnon phase.",2103.01919v1
+2021-05-05,Eliashberg study of superconductivity induced by interfacial coupling to antiferromagnets,"We perform Eliashberg calculations for magnon-mediated superconductivity in a
+normal metal, where the electron-magnon interaction arises from interfacial
+coupling to antiferromagnetic insulators. In agreement with previous studies,
+we find $p$-wave pairing for large doping when the antiferromagnetic interfaces
+are uncompensated, and $d$-wave pairing close to half-filling when the
+antiferromagnetic interfaces are compensated. However, for the $p$-wave phase,
+we find a considerable reduction in the critical temperature compared to
+previous weak-coupling results, as the effective frequency cutoff on the magnon
+propagator in this case is found to be much smaller than the cutoff on the
+magnon spectrum. The $d$-wave phase, on the other hand, relies less on
+long-wavelength magnons, leading to a larger effective cutoff on the magnon
+propagator. Combined with a large density of states close to half-filling, this
+might allow the $d$-wave phase to survive up to higher critical temperatures.
+Based on our findings, we provide new insight into how to realize interfacially
+induced magnon-mediated superconductivity in experiments.",2105.02235v2
+2021-07-05,Unified Treatment of Magnons and Excitons in Monolayer CrI$_3$ from Many-Body Perturbation Theory,"We present first principles calculations of the two-particle excitation
+spectrum of CrI$_3$ using many-body perturbation theory including spin-orbit
+coupling. Specifically, we solve the Bethe-Salpeter equation, which is
+equivalent to summing up all ladder diagrams with static screening and it is
+shown that excitons as well as magnons can be extracted seamlessly from the
+calculations. The resulting optical absorption spectrum as well as the magnon
+dispersion agree very well with recent measurements and we extract the
+amplitude for optical excitation of magnons resulting from spin-orbit
+interactions. Importantly, the results do not rely on any assumptions on the
+microscopic magnetic interactions such as Dzyaloshinskii-Moriya (DM), Kitaev or
+biquadratic interactions and we obtain a model independent estimate of the gap
+between acoustic and optical magnons of 0.3 meV. In addition, we resolve the
+magnon wavefunction in terms of band transitions and show that the magnon
+carries a spin that is significantly smaller than $\hbar$. This highlights the
+importance of terms that do not commute with $S^z$ in any Heisenberg model
+description.",2107.02284v1
+2021-08-24,Magnon-polarons in van der Waals antiferromagnet FePS3,"The hybridization of magnons (spin waves) with phonons, if sufficiently
+strong and comprising long wavelength excitations, may offer a new playground
+when manipulating the magnetically ordered systems with light. Applying a
+magnetic field to a quasi-2D antiferromagnet, FePS3, we tune the magnon-gap
+excitation towards coincidence with the initially lower-in-energy phonon modes.
+Hybrid magnon-phonon modes, the magnon polarons are unveiled with demonstration
+of a pronounced avoided crossing between the otherwise bare magnon and phonon
+excitations. The magnon polarons in FePS3 are primary traced with Raman
+scattering experiments, but, as we show, they also couple directly to terahertz
+photons, what evokes their further explorations in the domain of
+antiferromagnetic optospintronics.",2108.10945v3
+2021-09-16,Strong Coupling between Propagating Magnons and High-order Gyrotropic Skyrmion Modes,"Inspired by the recent achievements of the strong magnons- and spin
+textures-photons coupling via dipolar interaction, the coupling between magnons
+and the local resonances of spin textures through direct exchange interaction
+is expected but not realized yet. In this work, we demonstrated the coherent
+coupling between propagating magnons and local skyrmion resonances. Besides the
+Rabbi coupling gap (RCG) in the frequency field dispersion, a magnonic analog
+of polariton gap, polaragnonic band gap (PBG), is also observed in the
+frequency-wavenumber dispersion. The realization of coupling requires the
+gyrotropic skyrmion modes to satisfy not only their quantum number larger than
+one but also their chirality opposite to that of magnons. The observed PBG and
+RCG can be controlled to exist within different Brillouin zones (BZs) as well
+as at BZ boundaries. The coupling strength can approach the strong regime by
+selecting the wavenumber of propagating magnons. Our findings could provide a
+pure magnonic platform for investigating quantum optics phenomena in quantum
+information technology.",2109.07671v1
+2021-10-06,Optomagnonics in dispersive media: magnon-photon coupling enhancement at the epsilon-near-zero frequency,"Reaching strong light-matter coupling in solid-state systems has been long
+pursued for the implementation of scalable quantum devices. Here, we put
+forward the concept of a platform capable of achieving strong coupling between
+magnetic excitations (magnons) and optics based in an epsilon-near-zero medium,
+that's it, a medium in which the permittivity is close to zero. We adopt a
+phenomenological approach to quantize the electromagnetic field inside a
+dispersive magnetic medium and obtain a Hamiltonian describing the interaction
+between photons and magnons and the frequency-dependent coupling. We predict
+that, in the epsilon-near-zero regime, the single-magnon photon optomagnonic
+coupling can be comparable to the uniform magnon's frequency for small magnetic
+volumes. For state-of-the-art illustrative values, this would correspond to
+achieving the single-magnon strong coupling regime, where the coupling rate is
+larger than all the decay rates. Finally, we show that the non-linear energy
+spectrum intrinsic to this coupling regime regime can be probed via the
+characteristic multiple magnon sidebands in the photon power spectrum.",2110.02984v2
+2021-10-15,Functionalized high-speed magnon-polaritons resulting from the magnetic antenna effect,"Magnon-polaritons (MPs) refer to a light--magnon coupled state and can
+potentially act as information carriers, possibly enabling charge-free
+computation. However, the light--magnon coupling is inherently weak. To achieve
+sufficiently strong coupling, a large ferromagnet or coupling with a microwave
+cavity is necessary. Herein, we theoretically propose a fundamental platform
+for magnonic and magnon--optical information storage devices and discuss the
+transport properties of MP's. The proposed multi-layered structure overcomes
+the aforementioned issues. Owing to the waveguide modes, magnons placed in a
+nanometer-thin layer are strongly coupled with light, exhibiting rich
+functionalities of thick-layer MPs via the `magnetic antenna effect'. Thus, the
+thin-layer MPs are faster, and the direction is switchable. The results of this
+study will enable the integration of ferromagnetic micro and nanostructures for
+MP-based information devices without any restrictions due to cavities.",2110.08147v1
+2021-10-20,Gapless Dirac magnons in CrCl$_{3}$,"Bosonic Dirac materials are testbeds for dissipationless spin-based
+electronics. In the quasi two-dimensional honeycomb lattice of CrX$_{3}$ (X=Cl,
+Br, I), Dirac magnons have been predicted at the crossing of acoustical and
+optical spin waves, analogous to Dirac fermions in graphene. Here we show that,
+distinct from CrBr$_{3}$ and CrI$_{3}$, gapless Dirac magnons are present in
+bulk CrCl$_{3}$, with inelastic neutron scattering intensity at low
+temperatures approaching zero at the Dirac $K$ point. Upon warming,
+magnon-magnon interactions induce strong renormalization and decreased
+lifetimes, with a ~25% softening of the upper magnon branch intensity from 5 to
+50 K, though magnon features persist well above T$_{N}$. Moreover, an unusual
+negative thermal expansion (NTE) of the $a$-axis lattice constant and anomalous
+phonon behavior are observed below 50 K, indicating magnetoelastic and
+spin-phonon coupling arising from an increase in the in-plane spin correlations
+that begins tens of Kelvin above T$_{N}$.",2110.10771v1
+2021-11-01,Magnon-driven dynamics of frustrated skyrmion in synthetic antiferromagnets: Effect of skyrmion precession,"A theoretical study on the interplay of frustrated skyrmion and magnons is
+useful for revealing new physics and future experiments design. In this work,
+we investigated the magnon-driven dynamics of frustrated skyrmion in synthetic
+antiferromagnets, focusing on the effect of skyrmion precession. It is
+theoretically revealed that the scattering cross section of the injected
+magnons depends on the skyrmion precession, which in turn effectively modulates
+the skyrmion Hall motion. Specifically, the Hall angle decreases as the
+precession speed increases, which is also verified by the atomistic
+micromagnetic simulations. Moreover, the precession speed and the Hall angle of
+the frustrated skyrmion depending on the magnon intensity and damping constant
+are simulated, demonstrating the effective suppression of the Hall motion by
+the skyrmion precession. This work provides a comprehensive understanding of
+the magnon-skyrmion scattering in frustrated magnets, benefiting future
+spintronic and magnonic applications.",2111.00738v1
+2021-11-16,Optical sensing of magnons via the magnetoelastic displacement,"We show how to measure a steady-state magnon population in a magnetostatic
+mode of a ferromagnet or ferrimagnet, such as yttrium iron garnet. We adopt an
+optomechanical approach and utilize the magnetoelasticity of the ferromagnet.
+The magnetostrictive force dispersively couples magnons to the deformation
+displacement of the ferromagnet, which is proportional to the magnon
+population. By further coupling the mechanical displacement to an optical
+cavity that is resonantly driven by a weak laser, the magnetostrictively
+induced displacement can be sensed by measuring the phase quadrature of the
+optical field. The phase shows an excellent linear dependence on the magnon
+population for a not very large population, and can thus be used as a
+`magnometer' to measure the magnon population. We further study the effect of
+thermal noises, and find a high signal-to-noise ratio even at room temperature.
+At cryogenic temperatures, the resolution of magnon excitation numbers is
+essentially limited by the vacuum fluctuations of the phase, which can be
+significantly improved by using a squeezed light.",2111.08376v2
+2021-12-30,Giant magnon spin conductivity approaching the two-dimensional transport regime in ultrathin yttrium iron garnet films,"Conductivities are key material parameters that govern various types of
+transport (electronic charge, spin, heat etc.) driven by thermodynamic forces.
+Magnons, the elementary excitations of the magnetic order, flow under the
+gradient of a magnon chemical potential in proportion to a magnon (spin)
+conductivity $\sigma_{m}$. The magnetic insulator yttrium iron garnet (YIG) is
+the material of choice for efficient magnon spin transport. Here we report an
+unexpected giant $\sigma_{m}$ in record-thin YIG films with thicknesses down to
+3.7 nm when the number of occupied two-dimensional (2D) subbands is reduced
+from a large number to a few, which corresponds to a transition from 3D to 2D
+magnon transport. We extract a 2D spin conductivity ($\approx1$ S) at room
+temperature, comparable to the (electronic) spin conductivity of the
+high-mobility two-dimensional electron gas in GaAs quantum wells at millikelvin
+temperatures. Such high conductivities offer unique opportunities to develop
+low-dissipation magnon-based spintronic devices.",2112.15165v3
+2022-01-15,Physical Nature of Magnon Spin Seebeck Effect in Ferrimagnetic Insulators,"The spin Seebeck effect (SSE) in ferrimagnetic insulators (FMI) provides a
+simple method of using heat to manipulate magnons, which could be used as
+carriers of information and energy conversion. However, a theory that can
+quantitively interpret experimental results is still lacking. In this paper, we
+develop a transport theory of magnons in FMI at low temperatures by combining
+the macroscopic Boltzmann equation with microscopic quantum scattering theory.
+It is found that the scattering of magnons is dominated by phonons rather than
+magnons, and the relaxation time of magnon is inversely proportional to the
+cube of temperature. At extremely low temperature region, the magnon enters the
+ballistic transport process. In addition, we also derive the linear spatial
+distribution of the transverse SSE signal with sample position. All the
+theoretical results are in excellent agreement with the experimental data.",2201.05806v1
+2022-03-08,Topological phase transition in magnon bands in a honeycomb ferromagnet driven by sublattice symmetry breaking,"Ferromagnetic honeycomb systems are known to exhibit a magnonic topological
+phase under the existence of the next-nearest neighbor Dzyaloshinskii-Moriya
+interaction (DMI). Motivated by the recent progress in the sublattice-specific
+control of magnetic anisotropy, we study the topological phase of magnon bands
+of honeycomb ferromagnetic monolayer and bilayer with the sublattice symmetry
+breaking due to the different anisotropy energy in the presence of the DMI. We
+show that there is a topological phase transition between the topological
+magnon insulator and the topologically trivial magnon phase driven by the
+change of the relative size of the DMI and the anisotropy differences between
+the sublattices. The magnon thermal Hall conductivity is proposed as an
+experimental probe of the magnon topology.",2203.03845v1
+2022-03-30,Hybrid magnonics for short-wavelength spin waves facilitated by a magnetic heterostructure,"Recent research on hybrid magnonics has been restricted by the long magnon
+wavelengths of the ferromagnetic resonance modes. We present an experiment on
+the hybridization of 250-nm wavelength magnons with microwave photons in a
+multimode magnonic system consists of a planar cavity and a magnetic bilayer.
+The coupling between magnon modes in the two magnetic layers, i.e., the uniform
+mode in Permalloy (Py) and the perpendicular standing spin waves (PSSWs) in
+YIG, serves as an effective means for exciting short-wavelength PSSWs, which is
+further hybridized with the photon mode of the microwave resonator. The
+demonstrated magnon-photon coupling approaches the superstrong coupling regime,
+and can even be achieved near zero bias field.",2203.16310v1
+2022-04-04,Twisted Magnon Frequency Comb and Penrose Superradiance,"Quantization effects of the nonlinear magnon-vortex interaction in
+ferromagnetic nanodisks are studied. We show that the circular geometry twists
+the spin-wave fields with spiral phase dislocations carrying quantized orbital
+angular momentum (OAM). Meanwhile, the confluence and splitting scattering of
+twisted magnons off the gyrating vortex core (VC) generates a frequency comb
+consisting of discrete and equally spaced spectral lines, dubbed as twisted
+magnon frequency comb (tMFC). It is found that the mode spacing of the tMFC is
+equal to the gyration frequency of the VC and the OAM quantum numbers between
+adjacent spectral lines differ by one. By applying a magnetic field
+perpendicular to the plane of a thick nanodisk, we observe a magnonic Penrose
+superradiance inside the cone vortex state, which mimics the amplification of
+waves scattered from a rotating black hole. It is demonstrated that the
+higher-order modes of tMFC are significantly amplified while the lower-order
+ones are trapped within the VC gyrating orbit which manifests as the
+ergoregion. These results suggest a promising way to generate twisted magnons
+with large OAM and to drastically improve the flatness of the magnon comb.",2204.01582v2
+2022-06-12,Stationary optomagnonic entanglement and magnon-to-optics quantum state transfer via opto-magnomechanics,"We show how to prepare a steady-state entangled state between magnons and
+optical photons in an opto-magnomechanical configuration, where a mechanical
+vibration mode couples to a magnon mode in a ferrimagnet by the dispersive
+magnetostrictive interaction, and to an optical cavity by the radiation
+pressure. We find that, by appropriately driving the magnon mode and the cavity
+to simultaneously activate the magnomechanical Stokes and the optomechanical
+anti-Stokes scattering, a stationary optomagnonic entangled state can be
+created. We further show that, by activating the magnomechanical state-swap
+interaction and subsequently sending a weak red-detuned optical pulse to drive
+the cavity, the magnonic state can be read out in the cavity output field of
+the pulse via the mechanical transduction. The demonstrated entanglement and
+state-readout protocols in such a novel opto-magnomechanical configuration
+allow us to optically control, prepare, and read out quantum states of
+collective spin excitations in solids, and provide promising opportunities for
+the study of quantum magnonics, macroscopic quantum states, and magnonic
+quantum information processing.",2206.05688v3
+2022-07-08,Interacting topological Dirac magnons,"In this work, we study the magnon-magnon interaction effect in typical
+honeycomb ferromagnets consisting of van der Waals-bonded stacks of honeycomb
+layers, e.g., chromium trihalides CrX3 (X = F, Cl, Br, and I), that display two
+spin-wave modes (Dirac magnon). Using Green's function formalism with the
+presence of the Dzyaloshinskii-Moriya interaction, we obtain a spinor Dyson
+equation up to the second-order approximation by the cluster expansion method.
+Numerical calculations show prominent renormalizations of the single-particle
+spectrum. Furthermore, we propose a tunable renormalization effect using a
+parametric magnon amplification scheme. By amplifying the magnon population at
+different k points, the enabled renormalization effect not only reshapes the
+band structure but also modifies the Berry curvature distribution. Our work
+demonstrates the interplay between band geometry, interactions, and the
+external light field in the bosonic system and can potentially lead to new
+insights into the properties of magnon-based spintronic devices.",2207.03964v2
+2022-07-11,Direct optical probe of magnon topology in two-dimensional quantum magnets,"Controlling edge states of topological magnon insulators is a promising route
+to stable spintronics devices. However, to experimentally ascertain the
+topology of magnon bands is a challenging task. Here we derive a fundamental
+relation between the light-matter coupling and the quantum geometry of magnon
+states. This allows to establish the two-magnon Raman circular dichroism as an
+optical probe of magnon topology in honeycomb magnets, in particular of the
+Chern number and the topological gap. Our results pave the way for interfacing
+light and topological magnons in functional quantum devices.",2207.04745v1
+2022-07-20,Exact Results for the Orbital Angular Momentum of Magnons on Honeycomb Lattices,"We obtain exact results for the orbital angular momentum (OAM) of magnons at
+the high symmetry points of ferromagnetic (FM) and antiferromagnetic (AF)
+honeycomb lattices in the presence of Dzyallonshinskii-Moriya (DM)
+interactions. For the FM honeycomb lattice in the absence of DM interactions,
+the values of the OAM at the corners of the Brillouin zone (BZ) (${\bf
+k}_1^*=(0,2\sqrt{3}/9)2\pi/a $, ${\bf k}_2^*=(1/3,\sqrt{3}/9)2\pi/a ,\ldots $)
+are alternately $\pm 3\hbar /16$ for both magnon bands. The presence of DM
+interactions dramatically changes those values by breaking the degeneracy of
+the two magnon bands. The OAM values are alternately $3\hbar /8$ and 0 for the
+lower magnon band and $-3\hbar /8$ and 0 for the upper magnon band. For the AF
+honeycomb lattice, the values of the OAM at the corners of the BZ are $\mp
+(3\hbar /16)\kappa $ on one of the degenerate magnon bands and $\pm (3\hbar /8)
+(1+\kappa /2)$ on the other, where $\kappa $ measures the anisotropy and the
+result is independent of the DM interaction.",2207.09883v2
+2022-08-01,Time-dependent strain-tuning topological magnon phase transition,"Collinear magnets in honeycomb lattices under the action of time-dependent
+strains are investigated. Given the limits of high-frequency periodically
+varying deformations, we derive an effective Floquet theory for spin system
+that results in the emergence of a spin chirality. We find that the coupling
+between magnons and spin chirality depends on the details of the strain such as
+the spatial dependence and applied direction. Magnonic fluctuations about the
+ferromagnetic state are determined, and it is found that spatially homogeneous
+strains drive the magnon system into topologically protected phases. In
+particular, we show that certain uniform strain fields play the role of an
+out-of-plane next-neighbor Dzyaloshinskii-Moriya interaction. Furthermore, we
+explore the application of nonuniform strains, which lead to a confinement of
+magnon states that for uniaxial strains, propagates along the direction that
+preserves translational symmetry. Our work demonstrates a direct and novel way
+in which to manipulate the magnon spectrum based on time-dependent strain
+engineering that is relevant for exploring topological transitions in quantum
+magnonics.",2208.01170v1
+2022-09-21,Temperature-Induced Magnonic Chern Insulator in Collinear Antiferromagnets,"Thermal fluctuation in magnets will bring temperature-dependent self-energy
+corrections to the magnons, however, their effects on the topological orders of
+magnons is not well explored. Here we demonstrate that such corrections can
+induce a Chern insulating phase in two-dimensional collinear antiferromagnets
+with sublattice asymmetries by increasing temperature. We present the phase
+diagram of the system and show that the trivial magnon bands at zero
+temperature exhibit Chern insulating phase above a critical temperature before
+the paramagnetic phase transition. The self-energy corrections close and reopen
+the bandgap at {\Gamma} or K points, accompanied by a magnon chirality switch
+and nontrivial Berry curvature transition. The thermal Hall effect of magnons
+or detecting the magnon polarization can give experimentally prominent
+signatures of topological transitions. We include the numerical results based
+on van der Waals magnet MnPS3, calling for experimental implementation. Our
+work presents a new paradigm for constructing topological phase that is beyond
+the linear spin wave theory.",2209.10184v3
+2022-10-04,The spin-flop transition in the quasi two dimensional antiferromagnet MnPS3 detected via thermally generated magnon transport,"We present the detection of the spin-flop transition in the antiferromagnetic
+van der Waals material MnPS3 via thermally generated nonlocal magnon transport
+using permalloy detector strips. The inverse anomalous spin Hall effect has the
+unique power to detect an out-of-plane spin accumulation which enables us to
+detect magnons with an out-of-plane spin polarization; in contrast to strips of
+high spin-orbit material such as Pt which only possess the spin Hall effect and
+are only sensitive to an in-plane spin polarization of the spin accumulation.
+We show that nonlocal magnon transport is able to measure the spin-flop
+transition in the absence of other spurious effects. Our measurements show the
+detection of magnons generated by the spin Seebeck effect before and after the
+spin-flop transition where the signal reversal of the magnon spin accumulation
+agrees with the OOP spin polarization carried by magnon modes before and after
+the SF transition.",2210.01418v1
+2022-10-07,Composition-tunable magnon-polaron anomalies in spin Seebeck effects in epitaxial Bi$_x$Y$_{3-x}$Fe$_{5}$O$_{12}$ films,"We have investigated hybridized magnon-phonon excitation (magnon polarons) in
+spin Seebeck effects (SSEs) in Bi$_x$Y$_{3-x}$Fe$_{5}$O$_{12}$
+(Bi$_x$Y$_{3-x}$IG; $x=0$, $0.5$, and $0.9$) films with Pt contact. We observed
+sharp peak structures in the magnetic field $H$ dependence of the longitudinal
+SSE (LSSE) voltages, which appear when the phonon dispersions are tangential to
+the magnon dispersion curve in Bi$_x$Y$_{3-x}$IG. By increasing the Bi amount
+$x$, the peak fields in the LSSE shift toward lower $H$ values due to the
+reduction of the sound velocities in Bi$_x$Y$_{3-x}$IG. We also measured the
+SSE in a nonlocal configuration and found that magnon-polaron anomalies appear
+with different signs and intensities. Our result shows composition-tunability
+of magnon-polaron anomalies and provides a clue to further unravel the physics
+of magnon-polaron SSEs.",2210.03346v1
+2022-10-27,Topological magnons in one-dimensional ferromagnetic Su-Schrieffer-Heeger model with anisotropic interaction,"Topological magnons in a one-dimensional (1D) ferromagnetic (FM)
+Su-Schrieffer-Heeger (SSH) model with anisotropic exchange interactions are
+investigated. Apart from the inter-cellular isotropic Heisenberg interaction,
+the intercellular anisotropic exchange interactions, i.e. Dzyaloshinskii-Moriya
+interaction (DMI) and pseudo-dipolar interaction (PDI), also can induce the
+emergence of the non-trivial phase with two degenerate in-gap edge states
+separately localized at the two ends of the 1D chain, while the intracellular
+interactions instead unfavors the topological phase. The interplay among them
+has synergistic effects on the topological phase transition, very different
+from that in the two-dimensional (2D) ferromagnet. These results demonstrate
+that the 1D magnons possess rich topological phase diagrams distinctly
+different from the electronic version of the SSH model and even the 2D magnons.
+Due to the lower dimensional structural characteristics of this 1D topological
+magnonic system, the magnonic crystals can be constructed from bottom to top,
+which has important potential applications in the design of novel magnonic
+devices.",2210.15530v1
+2022-10-31,Magnon dynamics in a Skyrmion-textured domain wall of antiferromagnets,"We theoretically investigate the interaction between magnons and a
+Skyrmion-textured domain wall in a two-dimensional antiferromagnet and
+elucidate the resultant properties of magnon transport. Using supersymmetric
+quantum mechanics, we solve the scattering problem of magnons on top of the
+domain wall and obtain the exact solutions of propagating and bound magnon
+modes. Then, we find their properties of reflection and refraction in the
+Skyrmion-textured domain wall, where magnons experience an emergent magnetic
+field due to its non-trivial spin texture-induced effective gauge field. Based
+on the obtained scattering properties of magnons and the domain wall, we show
+that the thermal transport decreases as the domain wall's chirality increases.
+Our results suggest that the thermal transport of an antiferromagnet is tunable
+by modulating the Skyrmion charge density of the domain wall, which might be
+useful for realizing electrically tunable spin caloritronic devices.",2211.00030v1
+2022-11-10,Continuous similarity transformation for critical phenomena: easy-axis antiferromagnetic XXZ model,"We apply continuous similarity transformations (CSTs) to the easy-axis
+antiferromagnetic XXZ-model on the square lattice. The CST flow equations are
+truncated in momentum space by the scaling dimension $d$ so that all
+contributions with $d\le 2$ are taken into account. The resulting quartic
+magnon-conserving effective Hamiltonian is analyzed in the zero-, one-, and
+two-magnon sector. In this way, a quantitative description of the ground-state
+energy, the one-magnon dispersion and its gap as well as of two-magnon bound
+states is gained for anisotropies ranging from the gapped Ising model to the
+gapless Heisenberg model. We discuss the critical properties of the gap closing
+as well as the evolution of the one-magnon roton mininum. The excitation
+energies of two-magnon bound states are calculated and their decay into the
+two-magnon continuum is determined via the inverse participation ratio.",2211.05689v1
+2022-11-16,Strongly coupled magnon-plasmon polaritons in graphene- 2D ferromagnet heterostructures,"Magnons and plasmons are two very different types of collective modes, acting
+on the spin and charge degrees of freedom, respectively. At first sight, the
+formation of hybrid plasmon-magnon polaritons in heterostructures of plasmonic
+and magnetic systems would face two challenges, the small mutual interaction,
+via Zeeman coupling of the electromagnetic field of the plasmon with the spins,
+and the energy mismatch, as in most systems plasmons have energies in the eV
+range, orders of magnitude larger than magnons. Here we show that graphene
+plasmons form polaritons with the magnons of two-dimensional ferrromagnetic
+insulators, placed up to to half a micron apart, with Rabi couplings in the
+range of 100 GHz (dramatically larger than cavity QED magnonics). This strong
+coupling is facilitated both by the small energy of graphene plasmons and the
+cooperative super-radiant nature of the plasmon-magnon coupling afforded by
+phase matching. We show that the Rabi coupling can be modulated both
+electrically and mechanically and we propose a attenuated total internal
+reflection experiment to implement ferromagnetic resonance experiments on 2D
+ferromagnets driven by plasmon excitation.",2211.08949v1
+2022-12-02,Coherent magnon-induced domain wall motion in a magnetic insulator channel,"Advancing the development of spin-wave devices requires high-quality
+low-damping magnetic materials where magnon spin currents can propagate
+efficiently and interact effectively with local magnetic textures. We show that
+magnetic domain walls (DW) can modulate spin-wave transport in perpendicularly
+magnetized channels of Bi-doped yttrium-iron-garnet (BiYIG). Conversely, we
+demonstrate that the magnon spin current can drive DW motion in the BiYIG
+channel device by means of magnon spin-transfer torque. The DW can be reliably
+moved over 15 um distances at zero applied magnetic field by a magnon spin
+current excited by an RF pulse as short as 1 ns. The required energy for
+driving DW motion is orders of magnitude smaller than those reported for
+metallic systems. These results facilitate low-switching-energy magnonic
+devices and circuits where magnetic domains can be efficiently reconfigured by
+magnon spin currents flowing within magnetic channels.",2212.01408v1
+2023-01-29,Three-wave mixing of anharmonically coupled magnons,"Magnons are quantized collective spin-wave excitations in magnetically
+ordered systems. Revealing their interactions among these collective modes is
+crucial for the understanding of fundamental many-body effects in such systems
+and the development of high-speed information transport and processing devices
+based on them. Nevertheless, identifying couplings between individual magnon
+modes remains a long-standing challenge. Here, we observe unambiguous
+spectroscopic fingerprints of anharmonic coupling between distinct magnon modes
+in an antiferromagnet, as evidenced by coherent photon emission at the sum and
+difference frequencies of the two modes. This discovery is enabled by driving
+two magnon modes coherently with a pair of tailored terahertz fields and then
+disentangling a mixture of nonlinear responses with different origins,
+symmetries, and field dependences in a two-dimensional frequency-frequency
+correlation map. Our approach provides a new platform for generating nonlinear
+magnon-magnon mixings and establishes a systematic means of unveiling intricate
+couplings among distinct low-energy collective modes.",2301.12555v1
+2023-04-26,Critical Cavity-Magnon Polariton Mediated Strong Long-Distance Spin-Spin Coupling,"Strong long-distance spin-spin coupling is desperately demanded for
+solid-state quantum information processing, but it is still challenged. Here,
+we propose a hybrid quantum system, consisting of a coplanar waveguide (CPW)
+resonator weakly coupled to a single nitrogen-vacancy spin in diamond and a
+yttrium-iron-garnet (YIG) nanosphere holding Kerr magnons, to realize strong
+long-distance spin-spin coupling. With a strong driving field on magnons, the
+Kerr effect can squeeze magnons, and thus exponentially enhance the coupling
+between the CPW resonator and the squeezed magnons, which produces two
+cavity-magnon polaritons, i.e., the high-frequency polariton (HP) and
+low-frequency polariton (LP). When the enhanced cavity-magnon coupling
+approaches to the critical value, the spin is fully decoupled from the HP,
+while the coupling between the spin and the LP is significantly improved. In
+the dispersive regime, a strong spin-spin coupling is achieved with accessible
+parameters, and the coupling distance can be up to $\sim$cm. Our proposal
+provides a promising way to manipulate remote solid spins and perform quantum
+information processing in weakly coupled hybrid systems.",2304.13553v2
+2023-06-02,Chiral Anomaly Beyond Fermionic Paradigm,"Two-dimensional magnets have manifested themselves as promising candidates
+for quantum devices. We here report that the edge and strain effects during the
+device fabrication with two-dimensional honeycomb ferromagnets such as CrX$_3$
+(X=Cl, I, Br) and CrXTe$_3$ (X=Si, Ge) can be characterized by a
+(1+1)-dimensional magnon chiral anomaly beyond the fermionic paradigm. In the
+presence of zigzag edges, a pair of chiral bulk-edge magnon bands appear and
+cause an imbalance of left- and right-chirality magnons when subjected to
+nonuniform temperature or magnetic fields. In the presence of a uniaxial
+strain, the bulk Dirac magnons are broken into chiral magnon pseudo-Landau
+levels, resulting in a magnon chiral anomaly observable through a negative
+strain-resistivity of the magnetic dipole and heat. Our work demonstrates a
+chiral anomaly with (quasi)particles obeying non-fermionic statistics and will
+be instructive in understanding anomalous magnon transport.",2306.01446v2
+2023-06-26,Exciton-magnon splitting in van der Waals antiferromagnet MnPS$_3$ unveiled by second-harmonic generation,"Ultrafast and coherent generation of magnons is of great significance for
+high-speed antiferromagnetic spintronics. One possible route is by
+exciton-magnon pairwise optical excitation. To date, such exciton-magnon
+transitions have been studied mostly by linear optical means in a limited
+number of conventional three-dimensional antiferromagnets. Here we investigate
+this correlated transition in van der Waals antiferromagnet MnPS$_3$ by using
+resonant second-harmonic generation spectroscopy, a nonlinear optical probe
+sensitive to the symmetry of electronic and magnetic excitations. Two
+exciton-magnon peaks are observed, in line with the exciton-induced splitting
+of magnon density of states predicted by a Koster-Slater type theory,
+indicating significant exciton-magnon interactions. In addition, a large linear
+magnetoelectric effect of excitons is observed. These findings provide renewed
+understandings on the correlation effects in two-dimensional magnets with
+enhanced quasiparticle scattering cross-sections, and point to potential
+coherent control among charge, spin and orbital degrees of freedom in
+two-dimensional magnets by optical means.",2306.14642v1
+2023-08-02,Topological magnon-photon interaction for cavity magnonics,"The study of cavity magnonics and topological insulators has made significant
+advances over the past decade, however the possibility of combining the two
+fields is still unexplored. Here, we explore such connection by investigating
+hybrid cavity systems that incorporate both a ferromagnet and a topological
+insulator. We find that electrons in the topological surface state efficiently
+mediate the effective electric dipole coupling between the spin of the
+ferromagnet and the electric field of the cavity, in contrast with the
+conventional cavity magnonics theory based on magnetic dipole coupling. We
+refer to this coupling as topological magnon-photon interaction, estimating it
+one order of magnitude stronger than the conventional magnon-photon coupling,
+and showing that its sign can be manipulated. We discuss the potential of our
+proposed device to allow for scaling down and controlling the cavity system
+using electronics. Our results provide solid ground for exploring the
+functionalities enabled by merging cavity magnonics with topological
+insulators.",2308.01349v1
+2023-08-21,Magnon-Phonon coupling in Fe$_3$GeTe$_2$,"We study the dynamic coupling of magnons and phonons in single crystals of
+Fe3GeTe2 (FGT) using inelastic scanning tunneling spectroscopy (ISTS) with an
+ultra-low temperature scanning tunneling microscope. Inelastic scattering of
+hot carriers off phonons or magnons has been widely studied using ISTS, and we
+use it to demonstrate strong magnon-phonon coupling in FGT. We show a strong
+interaction between magnons and acoustic phonons which leads to formation of
+van Hove singularities originating in avoided level crossings and hybridization
+between the magnonic and phononic bands in this material. We identify these
+additional hybridization points in experiments and compare their energy with
+density functional theory calculations. Our findings provide a platform for
+designing the properties of dynamic magnon-phonon coupling in two-dimensional
+materials.",2308.10774v1
+2023-10-29,Magnomechanically controlled Goos-Hänchen shift in cavity QED,"Phenomena involving interactions among magnons, phonons, and photons in
+cavity magnomechanical systems have attracted considerable attention recently,
+owing to their potential applications in the microwave frequency range. One
+such important effect is the response of a probe field to such tripartite
+interaction between photon-magnon-phonon. In this paper, we study
+Goos-H\""{a}nchen shift (GHS) of a reflected probe field in a cavity
+magnomechanical system. We consider a YIG sphere positioned within a microwave
+cavity. A microwave control field directly drives the magnon mode in YIG
+sphere, whereas the cavity is driven via a weak probe field. Our results show
+that the GHS can be coherently controlled through magnon-phonon coupling via
+the control field. For instance, GHS can be tuned from positive to negative by
+tuning the magnon-phonon coupling. Similarly, the effective cavity detuning is
+another important controlling parameter for GHS. Furthermore, we observe that
+the enhancement of GHS occurs when magnon-phonon coupling is weak at resonance,
+and when the magnon-photon coupling is approximately equal to the loss of
+microwave photons. Our findings may have potential significance in applications
+related to microwave switching and sensing.",2310.19111v1
+2023-11-24,Local temperature control of magnon frequency and direction of supercurrents in a magnon Bose-Einstein condensate,"The creation of temperature variations in magnetization, and hence in the
+frequencies of the magnon spectrum in laser-heated regions of magnetic films,
+is an important method for studying Bose-Einstein condensation of magnons,
+magnon supercurrents, Bogoliubov waves, and similar phenomena. In our study, we
+demonstrate analytically, numerically, and experimentally that, in addition to
+the magnetization variations, it is necessary to consider the connected
+variations of the demagnetizing field. In case of a heat induced local minimum
+of the saturation magnetization, the combination of these two effects results
+in a local increase in the minimum frequency value of the magnon dispersion at
+which the Bose-Einstein condensate emerges. As a result, a magnon supercurrent
+directed away from the hot region is formed.",2311.14476v1
+2023-12-09,Nonreciprocal Photon-Phonon Entanglement in Kerr-Modified Spinning Cavity Magnomechanics,"Cavity magnomechanics has shown great potential in studying macroscopic
+quantum effects, especially for quantum entanglement, which is a key resource
+for quantum information science. Here we propose to realize magnons mediated
+nonreciprocal photon-phonon entanglement with both the magnon Kerr and Sagnac
+effects in cavity magnomechanics. We find that the mean magnon number can
+selectively exhibit nonreciprocal linear or nonlinear (bistable) behavior with
+the strength of the strong driving field on the cavity. Assisted by this
+driving field, the magnon-phonon coupling is greatly enhanced, leading to the
+nonreciprocal photon-phonon entanglement via the swapping interaction between
+the magnons and photons. This nonreciprocal entanglement can be significantly
+enhanced with the magnon Kerr and Sagnac effects. Given the available
+parameters, the nonreciprocal photon-phonon entanglement can be preserved at
+$\sim3$ K, showing remarkable resilience against the bath temperature. The
+result reveals that our work holds promise in developing various nonreciprocal
+devices with both the magnon Kerr and Sagnac effects in cavity magnomechanics.",2312.05561v1
+2024-01-01,Magnon Damping Minimum and Logarithmic Scaling in a Kondo-Heisenberg Model,"Recently, an anomalous temperature evolution of spin wave excitations has
+been observed in a van der Waals metallic ferromagnet Fe$_3$GeTe$_2$ (FGT) [S.
+Bao, et al., Phys. Rev. X 12, 011022 (2022)], whose theoretical understanding
+yet remains elusive. Here we study the spin dynamics of a ferromagnetic
+Kondo-Heisenberg lattice model at finite temperature, and propose a mechanism
+of magnon damping that explains the intriguing experimental results. In
+particular, we find the magnon damping rate $\gamma(T)$ firstly decreases as
+temperature lowers, due to the reduced magnon-magnon scatterings. It then
+reaches a minimum at $T_{\rm d}^*$, and rises up again following a logarithmic
+scaling $\gamma(T) \sim \ln{(T_0/T)}$ (with $T_0$ a constant) for $T < T_{\rm
+d}^*$, which can be attributed to electron-magnon scatterings of spin-flip
+type. Moreover, we obtain the phase diagram containing the ferromagnetic and
+Kondo insulator phases by varying the Kondo coupling, which may be relevant for
+experiments on pressured FGT. The presence of a magnon damping minimum and
+logarithmic scaling at low temperature indicates the emergence of the Kondo
+effect reflected in the collective excitations of local moments in a Kondo
+lattice system.",2401.00758v1
+2024-01-02,Dissipative coupling induced UWB magnonic frequency combs generation,"Magnonic frequency combs have recently attracted particular attention due to
+their potential impact on spin-wave science. Here, we demonstrate theoretically
+the generation of ultra-wideband (UWB) magnonic frequency combs induced by
+dissipative coupling in an open cavity magnomechanical system. A broadband comb
+with gigahertz repetition rates is obtained in the magnonic spectrum and a
+typical non-perturbation frequency-comb structure is also observed. The total
+width of the magnonic comb in the robust plateau region can be up to 400 comb
+lines, which is much broader and flatter than the reported in the previous
+works. Furthermore, when the dissipative coupling strength is further
+increased, the chaotic motion is predicted in the magnonic spectrum. Our
+results provide an in-depth understanding of nonlinear magnomechanic dynamics
+in open quantum systems and fundamentally broadens the research range of magnon
+in new spectral regimes.",2401.01260v1
+2024-01-04,Nonreciprocal entanglement in cavity magnomechanics exploiting chiral cavity-magnon coupling,"We show how to achieve nonreciprocal quantum entanglement in a cavity
+magnomechanical system by exploiting the chiral cavity-magnon coupling. The
+system consists of a magnon mode, a mechanical vibration mode, and two
+degenerate counter-propagating microwave cavity modes in a torus-shaped cavity.
+We show that nonreciprocal stationary microwave-magnon and -phonon bipartite
+entanglements and photon-magnon-phonon tripartite entanglement can be achieved
+by respectively driving different circulating cavity modes that hold a chiral
+coupling to the magnon mode. The nonreciprocal entanglements are shown to be
+robust against various experimental imperfections. The work may find promising
+applications of the cavity magnomechanical systems in nonreciprocal
+electromechanical quantum teleportation and chiral magnonic quantum networks.",2401.02280v2
+2024-01-25,Magnon dispersion and spin transport in CrCl$_3$ bilayers under different strain-induced magnetic states,"Atomically-thin van der Waals magnetic materials offer exceptional
+opportunities to mechanically and electrically manipulate magnetic states and
+spin textures. The possibility of efficient spin transport in these materials
+makes them promising for the development of novel nanospintronics technology.
+Using atomistic spin dynamics simulations, we investigate magnetic ground
+state, magnon dispersion, critical temperature, and magnon spin transport in
+CrCl$_3$ bilayers in the absence and presence of compressive and tensile
+strains. We show that in the presence of mechanical strain, the magnon band gap
+at the $\Gamma$ point and the critical temperature of the bilayer are
+increased. Furthermore, our simulations show that the magnon diffusion length
+is reduced in the presence of strain. Moreover, by exciting magnons through the
+spin Seebeck effect and spin Hall-induced torque, we illustrate distinctions
+between magnon spin transport in the antiferromagnetic state, under compressive
+strains, and ferromagnetic states, under tensile strains or in the unstrained
+case.",2401.13984v1
+2024-02-21,Many-body effects on superconductivity mediated by double-magnon processes in altermagnets,"Altermagnets exhibit a large electron spin splitting which can be understood
+as a result of strong coupling between itinerant electrons and localized spins.
+We consider superconductivity due to electron-magnon scattering, using
+strong-coupling Eliashberg theory to capture many-body effects that are not
+covered by a weak-coupling approach. The characteristic band structure of
+altermagnets puts significant constraints on the spin structure of electron
+scattering on the Fermi surface. We emphasize the role of spin-preserving,
+double-magnon scattering processes compared to conventional spin-flip processes
+involving a single magnon. Then, we derive the Eliashberg equations for a
+situation where double-magnon scattering mediates spin-polarized Cooper pairs,
+while both double-magnon and single-magnon scatterings contribute to many-body
+effects. These many-body effects impact superconducting properties in a way
+that differs significantly from systems where conventional spin-flip processes
+mediate superconductivity. To highlight the role of $d$-wave magnetism on
+superconductivity in altermagnets, we compare our results to those found in
+ferromagnetic half-metals and conventional antiferromagnetic metals.",2402.14061v1
+2024-03-11,Impact of spin torques and spin pumping phenomena on magnon-plasmon polaritons in antiferromagnetic insulator-semiconductor heterostructures,"We investigate the impact of spin torque and spin pumping on the surface
+magnon polariton dispersion in a antiferromagnetic insulator-semiconductor
+heterostructure. In the bilayer system, the surface magnon polaritons
+conventionally couple to the plasma-oscillations in the semiconductor via
+electromagnetic fields. Additionally, magnons in the antiferromagnetic
+insulator layer may interact with the semiconductor layer via spin torques and
+their reciprocal phenomena of spin pumping. Due to the spin-to-charge
+conversion from the spin Hall and inverse spin Hall effects in the
+semiconductor layer with a strong spin-orbit coupling, this can couple the
+magnons to the plasmons in the semiconductor layer. Our research reveals that
+modifications in the mode frequency and the hybridization gap induced by these
+phenomena depend on the thickness of the antiferromagnetic layer. In thick
+layers, the spin-pumping contribution to the frequency shift and damping is
+inversely proportional to the wavelength, while in thin layers it is inversely
+proportional to the thickness. Furthermore, hybridization of the surface magnon
+polariton and dispersive magnons in the antiferromagnet is shown to depend on
+both the thickness and wavelength of the modes.",2403.06934v1
+2014-10-14,Coherent coupling between ferromagnetic magnon and superconducting qubit,"Rigidity of an ordered phase in condensed matter results in collective
+excitation modes spatially extending in macroscopic dimensions. Magnon is a
+quantum of an elementary excitation in the ordered spin system, such as
+ferromagnet. Being low dissipative, dynamics of magnons in ferromagnetic
+insulators has been extensively studied and widely applied for decades in the
+contexts of ferromagnetic resonance, and more recently of Bose-Einstein
+condensation as well as spintronics. Moreover, towards hybrid systems for
+quantum memories and transducers, coupling of magnons and microwave photons in
+a resonator have been investigated. However, quantum-state manipulation at the
+single-magnon level has remained elusive because of the lack of anharmonic
+element in the system. Here we demonstrate coherent coupling between a magnon
+excitation in a millimetre-sized ferromagnetic sphere and a superconducting
+qubit, where the interaction is mediated by the virtual photon excitation in a
+microwave cavity. We obtain the coupling strength far exceeding the damping
+rates, thus bringing the hybrid system into the strong coupling regime.
+Furthermore, we find a tunable magnon-qubit coupling scheme utilising a
+parametric drive with a microwave. Our approach provides a versatile tool for
+quantum control and measurement of the magnon excitations and thus opens a new
+discipline of quantum magnonics.",1410.3781v1
+2015-06-23,Breakdown of long-wavelength magnons in cubic antiferromagnets with dipolar forces at small temperature,"Using $1/S$ expansion, we discuss the magnon spectrum of Heisenberg
+antiferromagnet (AF) on a simple cubic lattice with small dipolar interaction
+at small temperature $T\ll T_N$, where $T_N$ is the Neel temperature. Similar
+to 3D and 2D ferromagnets, quantum and thermal fluctuations renormalize greatly
+the bare gapless spectrum leading to a gap $\Delta\sim \omega_0$, where
+$\omega_0$ is the characteristic dipolar energy. This gap is accompanied by
+anisotropic corrections to the free energy which make the cube edges easy
+directions for the staggered magnetization (dipolar anisotropy). In accordance
+with previous results, we find that dipolar forces split the magnon spectrum
+into two branches. This splitting makes possible two types of processes which
+lead to a considerable enhance of the damping compared to the Heisenberg AF: a
+magnon decay into two other magnons and a confluence of two magnons. It is
+found that magnons are well defined quasiparticles in quantum AF. We
+demonstrate however that a small fraction of long-wavelength magnons can be
+overdamped in AFs with $S\gg1$ and in quantum AFs with a single-ion anisotropy
+competing with the dipolar anisotropy. Particular materials are pointed out
+which can be suitable for experimental observation of this long-wavelength
+magnons breakdown that contradicts expectation of the quasiparticle concept.",1506.06989v2
+2017-02-08,Magnon Spin-Momentum Locking: Various Spin Vortices and Dirac Magnons in Noncollinear Antiferromagnets,"We generalize the concept of the spin-momentum locking to magnonic systems
+and derive the formula to calculate the spin expectation value for one-magnon
+states of general two-body spin Hamiltonians. We give no-go conditions for
+magnon spin to be independent of momentum. As examples of the magnon
+spin-momentum locking, we analyze a one-dimensional antiferromagnet with the
+N\'eel order and two-dimensional kagome lattice antiferromagnets with the
+120$^\circ$ structure. We find that the magnon spin depends on its momentum
+even when the Hamiltonian has the $z$-axis spin rotational symmetry, which can
+be explained in the context of a singular band point or a $U(1)$ symmetry
+breaking. A spin vortex in momentum space generated in a kagome lattice
+antiferromagnet has the winding number $Q=-2$, while the typical one observed
+in topological insulator surface states is characterized by $Q=+1$. A magnonic
+analogue of the surface states, the Dirac magnon with $Q=+1$, is found in
+another kagome lattice antiferromagnet. We also derive the sum rule for $Q$ by
+using the Poincar\'e-Hopf index theorem.",1702.02575v4
+2018-11-08,Magnon dressing by orbital excitations in ferromagnetic planes of K$_2$CuF$_4$ and LaMnO$_3$,"We show that even when spins and orbitals disentangle in the ground state,
+spin excitations are renormalized by the local tuning of $e_g$ orbitals in
+ferromagnetic planes of K$_2$CuF$_4$ and LaMnO$_3$. As a result, dressed spin
+excitations (magnons) obtained within the electronic model propagate as
+quasiparticles and their energy renormalization depends on momentum ${\vec k}$.
+Therefore magnons in spin-orbital systems go beyond the paradigm of the
+effective Heisenberg model with nearest neighbor spin exchange derived from the
+ground state --- spin-orbital entanglement in excited states predicts large
+magnon softening at the Brillouin zone boundary, and in case of LaMnO$_3$ the
+magnon energy at the $M=(\pi,\pi)$ point may be reduced by $\sim 45$\%. In
+contrast, simultaneously the stiffness constant near the Goldstone mode is
+almost unaffected. We elucidate physics behind magnon renormalization in
+spin-orbital systems and explain why long wavelength magnons are unrenormalized
+while simultaneously energies of short wavelength magnons are reduced by
+orbital fluctuations. In fact, the ${\vec k}$-dependence of the magnon energy
+is modified mainly by dispersion which originates from spin exchange between
+second neighbors along the cubic axes $a$ and $b$.",1811.03372v1
+2014-05-07,Magnon-skyrmion scattering in chiral magnets,"Chiral magnets support topological skyrmion textures due to the
+Dzyaloshinskii-Moriya spin-orbit interaction. In the presence of a sufficiently
+large applied magnetic field, such skyrmions are large amplitude excitations of
+the field-polarized magnetic state. We investigate analytically the interaction
+between such a skyrmion excitation and its small amplitude fluctuations, i.e.,
+the magnons in a clean two-dimensional chiral magnet. The magnon spectrum is
+found to include two magnon-skyrmion bound states corresponding to a breathing
+mode and, for intermediate fields, a quadrupolar mode, which will give rise to
+subgap magnetic and electric resonances. Due to the skyrmion topology, the
+magnons scatter from a Aharonov-Bohm flux density that leads to skew and
+rainbow scattering, characterized by an asymmetric differential cross section
+with, in general, multiple peaks. As a consequence of the skew scattering, a
+finite density of skyrmions will generate a topological magnon Hall effect.
+Using the conservation law for the energy-momentum tensor, we demonstrate that
+the magnons also transfer momentum to the skyrmion. As a consequence, a magnon
+current leads to magnon pressure reflected in a momentum-transfer force in the
+Thiele equation of motion for the skyrmion. This force is reactive and governed
+by the scattering cross sections of the skyrmion; it causes not only a finite
+skyrmion velocity but also a large skyrmion Hall effect. Our results provide,
+in particular, the basis for a theory of skyrmion caloritronics for a dilute
+skyrmion gas in clean insulating chiral magnets.",1405.1568v3
+2018-09-24,Magnonic Floquet Hofstadter Butterfly,"We introduce the magnonic Floquet Hofstadter butterfly in the two-dimensional
+insulating honeycomb ferromagnet. We show that when the insulating honeycomb
+ferromagnet is irradiated by an oscillating space- and time-dependent electric
+field, the hopping magnetic dipole moment (i.e. magnon quasiparticles)
+accumulate the Aharonov-Casher phase. In the case of only space-dependent
+electric field, we realize the magnonic Hofstadter spectrum with similar
+fractal structure as graphene subject to a perpendicular magnetic field, but
+with no spin degeneracy due to broken time-reversal symmetry by the
+ferromagnetic order. In addition, the magnonic Dirac points and Landau levels
+occur at finite energy as expected in a bosonic system. Remarkably, this
+discrepancy does not affect the topological invariant of the system.
+Consequently, the magnonic Chern number assumes odd values and the magnon Hall
+conductance gets quantized by odd integers. In the case of both space- and
+time-dependent electric field, the theoretical framework is studied by the
+Floquet formalism. We show that the magnonic Floquet Hofstadter spectrum
+emerges entirely from the oscillating space- and time-dependent electric field,
+which is in stark contrast to electronic Floquet Hofstadter spectrum, where
+irradiation by circularly polarized light and a perpendicular magnetic field
+are applied independently. We study the deformation of the fractal structure at
+different laser frequencies and amplitudes, and analyze the topological phase
+transitions associated with gap openings in the magnonic Floquet Hofstadter
+butterfly.",1809.09102v1
+2017-09-22,Topological thermal Hall effect due to Weyl magnons,"We present the first theoretical evidence of zero magnetic field topological
+(anomalous) thermal Hall effect due to Weyl magnons. Here, we consider Weyl
+magnons in stacked noncoplanar frustrated kagom\'e antiferromagnets recently
+proposed by Owerre, [arXiv:1708.04240]. The Weyl magnons in this system result
+from macroscopically broken time-reversal symmetry by the scalar spin chirality
+of noncoplanar chiral spin textures. Most importantly, they come from the
+lowest excitation, therefore they can be easily observed experimentally at low
+temperatures due to the population effect. Similar to electronic Weyl nodes
+close to the Fermi energy, Weyl magnon nodes in the lowest excitation are the
+most important. Indeed, we show that the topological (anomalous) thermal Hall
+effect in this system arises from nonvanishing Berry curvature due to Weyl
+magnon nodes in the lowest excitation, and it depends on their distribution
+(distance) in momentum space. The present result paves the way to directly
+probe low excitation Weyl magnons and macroscopically broken time-reversal
+symmetry in three-dimensional frustrated magnets with the anomalous thermal
+Hall effect.",1709.07879v2
+2016-10-27,Spin Currents and Magnon Dynamics in Insulating Magnets,"Nambu-Goldstone theorem provides gapless modes to both relativistic and
+nonrelativistic systems. The Nambu-Goldstone bosons in insulating magnets are
+called magnons or spin-waves and play a key role in magnetization transport. We
+review here our past works on magnetization transport in insulating magnets and
+also add new insights, with a particular focus on magnon transport. We
+summarize in detail the magnon counterparts of electron transport, such as the
+Wiedemann-Franz law, the Onsager reciprocal relation between the Seebeck and
+Peltier coefficients, the Hall effects, the superconducting state, the
+Josephson effects, and the persistent quantized current in a ring to list a
+few. Focusing on the electromagnetism of moving magnons, i.e., magnetic
+dipoles, we theoretically propose a way to directly measure magnon currents. As
+a consequence of the Mermin-Wagner-Hohenberg theorem, spin transport is
+drastically altered in one-dimensional antiferromagnetic (AF) spin-1/2 chains;
+where the N\'eel order is destroyed by quantum fluctuations and a quasiparticle
+magnon-like picture breaks down. Instead, the low-energy collective excitations
+of the AF spin chain are described by a Tomonaga-Luttinger liquid (TLL) which
+provides the spin transport properties in such antiferromagnets some universal
+features at low enough temperature. Finally, we enumerate open issues and
+provide a platform to discuss the future directions of magnonics.",1610.08901v2
+2020-06-18,Non-Hermiticity and topological invariants of magnon Bogoliubov-de Gennes systems,"Since the theoretical prediction and experimental observation of the thermal
+Hall effect of magnons, a variety of novel phenomena that may occur in magnonic
+systems have been proposed. In this paper, we review the recent advances in the
+study of topological phases of magnon Bogoliubov-de Gennes (BdG) systems. After
+giving an overview of the previous works on electronic topological insulators
+and the thermal Hall effect of magnons, we provide the necessary background for
+bosonic BdG systems, with a particular emphasis on their non-Hermiticity
+arising from the diagonalization of the BdG Hamiltonian. After that, we
+introduce the definitions of $ \mathbb{Z}_2 $ topological invariants for
+bosonic systems with pseudo-time-reversal symmetry, which ensures the existence
+of bosonic counterparts of ""Kramers pairs"". Because of the intrinsic
+non-Hermiticity of the bosonic BdG systems, these topological invariants have
+to be defined in terms of the bosonic Berry connection and curvature. We then
+introduce theoretical models that can be thought of as magnonic analogues of
+two- and three-dimensional topological insulators in class AII. We demonstrate
+analytically and numerically that the $ \mathbb{Z}_2 $ topological invariants
+precisely characterize the presence of gapless edge/surface states. We also
+predict that bilayer CrI$_3$ with a particular stacking would be an ideal
+candidate for realization of a two-dimensional magnon system characterized by a
+nontrivial $ \mathbb{Z}_2 $ topological invariant. For three-dimensional
+topological magnon systems, the thermal Hall effect of magnons is expected to
+occur when a magnetic field is applied to the surface.",2006.10391v3
+2018-01-20,Magnon Valve Effect Between Two Magnetic Insulators,"The key physics of the spin valve involves spin-polarized conduction
+electrons propagating between two magnetic layers such that the device
+conductance is controlled by the relative magnetization orientation of two
+magnetic layers. Here, we report the effect of a magnon valve which is made of
+two ferromagnetic insulators (YIG) separated by a nonmagnetic spacer layer
+(Au). When a thermal gradient is applied perpendicular to the layers, the
+inverse spin Hall voltage output detected by a Pt bar placed on top of the
+magnon valve depends on the relative orientation of the magnetization of two
+YIG layers, indicating the magnon current induced by spin Seebeck effect at one
+layer affects the magnon current in the other layer separated by Au. We
+interpret the magnon valve effect by the angular momentum conversion and
+propagation between magnons in two YIG layers and conduction electrons in the
+Au layer. The temperature dependence of magnon valve ratio shows approximately
+a power law, supporting the above magnon-electron spin conversion mechanism.
+This work opens a new class of valve structures beyond the conventional spin
+valves.",1801.06617v2
+2021-02-26,Thermodynamics of free and bound magnons in graphene,"Symmetry-broken electronic phases support neutral collective excitations. For
+example, monolayer graphene in the quantum Hall regime hosts a nearly ideal
+ferromagnetic phase at filling factor $\nu=1$ that spontaneously breaks spin
+rotation symmetry. This ferromagnet has been shown to support spin-wave
+excitations known as magnons which can be generated and detected electrically.
+While long-distance magnon propagation has been demonstrated via transport
+measurements, important thermodynamic properties of such magnon
+populations--including the magnon chemical potential and density--have thus far
+proven out of reach of experiments. Here, we present local measurements of the
+electron compressibility under the influence of magnons, which reveal a
+reduction of the $\nu=1$ gap by up to 20%. Combining these measurements with
+estimates of the temperature, our analysis reveals that the injected magnons
+bind to electrons and holes to form skyrmions, and it enables extraction of the
+free magnon density, magnon chemical potential, and average skyrmion spin. Our
+methods furnish a novel means of probing the thermodynamic properties of
+charge-neutral excitations that is applicable to other symmetry-broken
+electronic phases.",2103.00015v1
+2021-04-01,Topological Phase Transitions of Dirac Magnons in Honeycomb Ferromagnets,"The study of the magnonic thermal Hall effect in magnets with
+Dzyaloshinskii-Moriya interaction (DMI) has recently drawn attention because of
+the underlying topology. Topological phase transitions may arise when there
+exist two or more distinct topological phases, and they are often revealed by a
+gap-closing phenomenon. In this work, we consider the magnons in honeycomb
+ferromagnets described by a Heisenberg Hamiltonian containing both an
+out-of-plane DMI and a Zeeman interaction. We demonstrate that the magnonic
+system exhibits temperature (or magnetic field) driven topological phase
+transitions due to magnon-magnon interactions. Specifically, when the
+temperature increases, the magnonic energy gap at Dirac points closes and
+reopens at a critical temperature, $T_c$. By showing that the Chern numbers of
+the magnonic bands are distinct above and below $T_c$, we confirm that the
+gap-closing phenomenon is indeed a signature for the topological phase
+transitions. Furthermore, our analysis indicates that the thermal Hall
+conductivity in the magnonic system exhibits a sign reversal at $T_c$, which
+can serve as an experimental probe of its topological nature. Our theory
+predicts that in $\rm{CrI_3}$ such a phenomenon exists and is experimentally
+accessible.",2104.00266v2
+2021-06-28,Stabilization of a nonlinear bullet coexisting with a Bose-Einstein condensate in a rapidly cooled magnonic system driven by a spin-orbit torque,"We have recently shown that injection of magnons into a magnetic dielectric
+via the spin-orbit torque (SOT) effect in the adjacent layer of a heavy metal
+subjected to the action of short (0.1 $\mu$s) current pulses allows for control
+of a magnon Bose-Einstein Condensate (BEC). Here, the BEC was formed in the
+process of rapid cooling (RC), when the electric current heating the sample is
+abruptly terminated. In the present study, we show that the application of a
+longer (1.0 $\mu$s) electric current pulse triggers the formation of a
+nonlinear localized magnonic bullet below the linear magnon spectrum. After
+pulse termination, the magnon BEC, as before, is formed at the bottom of the
+linear spectrum, but the nonlinear bullet continues to exist, stabilized for
+additional 30 ns by the same process of RC-induced magnon condensation. Our
+results suggest that a stimulated condensation of excess magnons to all highly
+populated magnonic states occurs.",2106.14710v1
+2022-01-27,Magnon transport and thermoelectric effects in ultrathin Tm3Fe5O12/Pt nonlocal devices,"The possibility of electrically exciting and detecting magnon currents in
+magnetic insulators has opened exciting perspectives for transporting spin
+information in electronic devices. However, the role of the magnetic field and
+the nonlocal thermal gradients on the magnon transport remain unclear. Here, by
+performing nonlocal harmonic voltage measurements, we investigate magnon
+transport in perpendicularly magnetized ultrathin Tm3Fe5O12 (TmIG) films
+coupled to Pt electrodes. We show that the first harmonic nonlocal voltage
+captures spin-driven magnon transport in TmIG, as expected, and the second
+harmonic is dominated by thermoelectric voltages driven by current-induced
+thermal gradients at the detector. The magnon diffusion length in TmIG is found
+to be on the order of 0.3 {\mu}m at 0.5 T and gradually decays to 0.2 {\mu}m at
+0.8 T, which we attribute to the suppression of the magnon relaxation time due
+to the increase of the Gilbert damping with field. By performing current,
+magnetic field, and distance dependent nonlocal and local measurements we
+demonstrate that the second harmonic nonlocal voltage exhibits five
+thermoelectric contributions, which originate from the nonlocal spin Seebeck
+effect and the ordinary, planar, spin, and anomalous Nernst effects. Our work
+provides a guide on how to disentangle magnon signals from diverse
+thermoelectric voltages of spin and magnetic origin in nonlocal magnon devices,
+and establish the scaling laws of the thermoelectric voltages in
+metal/insulator bilayers.",2201.11353v1
+2022-01-31,Exciton-Coupled Coherent Magnons in a 2D Semiconductor,"Two-dimensional (2D) magnetic semiconductors feature both tightly-bound
+excitons with large oscillator strength and potentially long-lived coherent
+magnons due to the presence of bandgap and spatial confinement. While magnons
+and excitons are energetically mismatched by orders of magnitude, their
+coupling can lead to efficient optical access to spin information. Here we
+report strong magnon-exciton coupling in the 2D van der Waals (vdW)
+antiferromagnetic (AFM) semiconductor CrSBr. Coherent magnons launched by
+above-gap excitation modulate the interlayer hybridization, which leads to
+dynamic modulation of excitonic energies. Time-resolved exciton sensing reveals
+magnons that can coherently travel beyond 7 micrometer, with coherence time
+above 5 ns. We observe this exciton-coupled coherent magnons in both even and
+odd number of layers, with and without compensated magnetization, down to the
+bilayer limit. Given the versatility of vdW heterostructures, these coherent 2D
+magnons may be basis for optically accessible magnonics and quantum
+interconnects.",2201.13197v2
+2022-03-09,Magnons in antiferromagnetic bcc-Cr and Cr$_2$O$_3$ from time-dependent density functional theory,"We apply time-dependent density functional theory to calculate the transverse
+magnetic susceptibility of bcc-Cr and Cr$_2$O$_3$, which constitute
+prototypical examples of antiferromagnets with itinerant and localized magnetic
+moments respectively. The exchange-correlation kernel is rescaled in order to
+enforce the Goldstone condition and the magnon dispersion relations are
+extracted based on a symmetry analysis relying on the generalized Onsager
+relation. Doing so, our calculations yield the characteristic linear magnon
+dispersion of antiferromagnets in the long wavelength limit. In the case of
+Cr$_2$O$_3$, we find that the adiabatic local density approximation yields a
+good qualitative agreement with the measured dispersion, but overestimates the
+magnon velocity and bandwidth by a factor of two. Including a Hubbard
+correction improves the magnon velocity, but at the expense of the overall
+qualitative agreement with the experimental magnon dispersion. For bcc-Cr we
+find a sharp acoustic magnon mode at low energies with a velocity in agreement
+with previously reported values. At higher energies, the acoustic magnon mode
+becomes subject to strong Landau damping and rapidly vanishes once it enters
+the Stoner continuum. In addition to the acoustic magnon mode, we also observe
+an additional collective mode along the $\Gamma\rightarrow\mathrm{R}$ direction
+with an energy of $\sim$ 1 eV, which is located inside the Stoner continuum,
+but appears to elude the effect of Landau damping.",2203.04796v2
+2022-08-27,Optomechanical-interface-induced strong spin-magnon coupling,"Strong long-distance spin-magnon coupling is essential for solid-state
+quantum information processing and single qubit manipulation. Here, we propose
+an approach to realize strong spin-magnon coupling in a hybrid optomechanical
+cavity-spin-magnon system, where the optomechanical system, consisting of two
+cavities coupled to a common high-frequency mechanical resonator, acts as
+quantum interface. By eliminating the mechanical mode, a position-position
+coupling and two-mode squeezing of two cavities are induced. In the squeezing
+presentation, the spin-photon, magnon-photon and photon-photon coupling
+strengths are exponentially amplified, thus lower- and upper-branch polaritons
+(LBP and UBP) are generated by strongly coupled squeezed modes of two cavities.
+Utilizing the critical property of the LBP, the coupling between the spin qubit
+(magnon) and LBP is greatly enhanced, while the coupling between the spin qubit
+(magnon) and UBP is fully suppressed. In the dispersive regime, strong and
+tunable spin-magnon coupling is induced by the virtual LBP, allowing quantum
+state exchange between them. Our proposal provides a promising platform to
+construct magnon-based hybrid systems and realize solid-state quantum
+information processing with optomechanical interfaces.",2208.12988v3
+2022-09-20,Electronic Manipulation of Magnon Topology by Chirality Injection from Boundaries,"Magnon bands are known to exhibit nontrivial topology in ordered magnets
+under suitable conditions, engendering topological phases referred to as
+magnonic topological insulators. Conventional methods to drive a magnonic
+topological phase transition are bulk magnetic or thermal operations such as
+changing the direction of an external magnetic field or varying the temperature
+of the system, which are undesired in device applications of magnon topology.
+In this work, we lift the limitation of the magnon topology control on the bulk
+non-electronic manipulation by proposing a scheme to manipulate magnonic
+topological phases by electronic boundary operations of spin chirality
+injection. More specifically, we consider a ferromagnetic honeycomb lattice and
+show that a finite spin chirality injected from the boundary of the system via
+the spin Hall effects introduces a tunable sublattice-symmetry-breaking mass
+term to the bosonic counterpart of the Haldane model for the Chern insulators
+and thereby allows us to electronically manipulate the bulk topology of magnons
+from the boundary. The ""shoulder"" in the thermal Hall conductivity profile is
+proposed as an experimental probe of the chirality-induced topological phase
+transition. The scheme for the boundary manipulation of the magnon topology is
+shown to work for a honeycomb antiferromagnet as well. We envisage that the
+interfacial chirality injection may offer a nonintrusive electronic means to
+tune the static and the dynamical bulk properties of general magnetic systems.",2209.09435v1
+2022-11-16,Detection sensitivity enhancement of magnon Kerr nonlinearity in cavity magnonics induced by coherent perfect absorption,"We show how to enhance the detection sensitivity of magnon Kerr nonlinearity
+(MKN) in cavity magnonics. The considered cavity-magnon system consists of a
+three-dimensional microwave cavity containing two yttrium iron garnet (YIG)
+spheres, where the two magnon modes (one has the MKN, while the other is
+linear) in YIG spheres are simultaneously coupled to microwave photons. To
+obtain the effective gain of the cavity mode, we feed two input fields into the
+cavity. By choosing appropriate parameters, the coherent perfect absorption of
+the two input fields occurs, and the cavity-magnon system can be described by
+an effective non-Hermitian Hamiltonian. Under the pseudo-Hermitian conditions,
+the effective Hamiltonian can host the third-order exceptional point (EP3),
+where the three eigenvalues of the Hamiltonian coalesce into one. When the
+magnon frequency shift $\Delta_K$ induced by the MKN is much smaller than the
+linewidths $\Gamma$ of the peaks in the transmission spectrum of the cavity
+(i.e., $\Delta_K\ll \Gamma$), the magnon frequency shift can be amplified by
+the EP3, which can be probed via the output spectrum of the cavity. The scheme
+we present provides an alternative approach to measure the MKN in the region
+$\Delta_K\ll \Gamma$ and has potential applications in designing low-power
+nonlinear devices based on the MKN.",2211.08922v2
+2022-12-08,Strong photon-magnon coupling using a lithographically defined organic ferrimagnet,"We demonstrate a hybrid quantum system composed of superconducting resonator
+photons and magnons hosted by the organic-based ferrimagnet vanadium
+tetracyanoethylene (V[TCNE]$_x$). Our work is motivated by the challenge of
+scalably integrating an arbitrarily-shaped, low-damping magnetic system with
+planar superconducting circuits, thus enabling a host of quantum magnonic
+circuit designs that were previously inaccessible. For example, by leveraging
+the inherent properties of magnons, one can enable nonreciprocal
+magnon-mediated quantum devices that use magnon propagation rather than
+electrical current. We take advantage of the properties of V[TCNE]$_x$, which
+has ultra-low intrinsic damping, can be grown at low processing temperatures on
+arbitrary substrates, and can be patterned via electron beam lithography. We
+demonstrate the scalable, lithographically integrated fabrication of hybrid
+quantum magnonic devices consisting of a thin-film superconducting resonator
+coupled to a low-damping, thin-film V[TCNE]$_x$ microstructure. Our devices
+operate in the strong coupling regime, with a cooperativity as high as 1181(44)
+at T$\sim$0.4 K, suitable for scalable quantum circuit integration. This work
+paves the way for the exploration of high-cooperativity hybrid magnonic quantum
+devices in which magnonic circuits can be designed and fabricated as easily as
+electrical wires.",2212.04423v1
+2023-02-21,Chirality selective magnon-phonon hybridization and magnon-induced chiral phonons in a layered zigzag antiferromagnet,"Two-dimensional (2D) magnetic systems possess versatile magnetic order and
+can host tunable magnons carrying spin angular momenta. Recent advances show
+angular momentum can also be carried by lattice vibrations in the form of
+chiral phonons. However, the interplay between magnons and chiral phonons as
+well as the details of chiral phonon formation in a magnetic system are yet to
+be explored. Here, we report the observation of magnon-induced chiral phonons
+and chirality selective magnon-phonon hybridization in a layered zigzag
+antiferromagnet (AFM) FePSe$_3$. With a combination of magneto-infrared and
+magneto-Raman spectroscopy, we observe chiral magnon polarons (chiMP), the new
+hybridized quasiparticles, at zero magnetic field. The hybridization gap
+reaches 0.25~meV and survives down to the quadrilayer limit. Via first
+principle calculations, we uncover a coherent coupling between AFM magnons and
+chiral phonons with parallel angular momenta, which arises from the underlying
+phonon and space group symmetries. This coupling lifts the chiral phonon
+degeneracy and gives rise to an unusual Raman circular polarization of the
+chiMP branches. The observation of coherent chiral spin-lattice excitations at
+zero magnetic field paves the way for angular momentum-based hybrid phononic
+and magnonic devices.",2302.10656v2
+2023-09-06,Strong magnon-magnon coupling in an ultralow damping all-magnetic-insulator heterostructure,"Magnetic insulators such as yttrium iron garnets (YIGs) are of paramount
+importance for spin-wave or magnonic devices as their ultralow damping enables
+ultralow power dissipation that is free of Joule heating, exotic magnon quantum
+state, and coherent coupling to other wave excitations. Magnetic insulator
+heterostructures bestow superior structural and magnetic properties and house
+immense design space thanks to the strong and engineerable exchange interaction
+between individual layers. To fully unleash their potential, realizing low
+damping and strong exchange coupling simultaneously is critical, which often
+requires high quality interface. Here, we show that such a demand is realized
+in an all-insulator thulium iron garnet (TmIG)/YIG bilayer system. The ultralow
+dissipation rates in both YIG and TmIG, along with their significant spin-spin
+interaction at the interface, enable strong and coherent magnon-magnon coupling
+with a benchmarking cooperativity value larger than the conventional
+ferromagnetic metal-based heterostructures. The coupling strength can be tuned
+by varying the magnetic insulator layer thickness and magnon modes, which is
+consistent with analytical calculations and micromagnetic simulations. Our
+results demonstrate TmIG/YIG as a novel platform for investigating hybrid
+magnonic phenomena and open opportunities in magnon devices comprising
+all-insulator heterostructures.",2309.03116v1
+2023-10-31,Dynamics of nonequilibrium magnons in gapped Heisenberg antiferromagnets,"Nonequilibrium dynamics in spin systems is a topic currently under intense
+investigation as it provides fundamental insights into thermalization,
+universality, and exotic transport phenomena. While most of the studies have
+been focused on ideal closed quantum many-body systems such as ultracold atomic
+quantum gases and one-dimensional spin chains, driven-dissipative Bose gases in
+steady states away from equilibrium in classical systems also lead to
+intriguing nonequilibrium physics. In this work, we theoretically investigate
+out-of-equilibrium dynamics of magnons in a gapped Heisenberg quantum
+antiferromagnet based on Boltzmann transport theory. We show that, by treating
+scattering terms beyond the relaxation time approximation in the Boltzmann
+transport equation, energy and particle number conservation mandate that
+nonequilibrium magnons cannot relax to equilibrium, but decay to other
+nonequilibrium stationary states, partially containing information about the
+initial states. The only decay channel for these stationary states back to
+equilibrium is through the non-conserving interactions such as boundary or
+magnon-phonon scattering. At low temperatures, these non-conserving
+interactions are much slower processes than intrinsic magnon-magnon interaction
+in a gapped spin system. Using magnon-phonon interaction as a quintessential
+type of non-conserving interaction, we then propose that nonequilibrium steady
+states of magnons can be maintained and tailored using periodic driving at
+frequencies faster than relaxation due to phonon interactions. These findings
+reveal a class of classical material systems that are suitable platforms to
+study nonequilibrium statistical physics and macroscopic phenomena such as
+classical Bose-Einstein condensation of quasiparticles and magnon supercurrents
+that are relevant for spintronic applications.",2310.20617v1
+2023-12-25,Controllable magnon frequency comb in synthetic ferrimagnets,"Magnon frequency comb provides opportunities for exploring magnon nonlinear
+effects and measuring the transmission magnon frequency in magnets, whose
+controllability becomes vital for modulating the operating frequency and
+improving the measurement accuracy. Nevertheless, such controllable frequency
+comb remains to be explored. In this work, we investigate theoretically and
+numerically the skyrmion-induced magnon frequency comb effect generated by
+interaction between the magnon excitation mode and skyrmion breathing mode in
+synthetic ferrimagnets. It is revealed that both the skyrmion breathing mode
+and the magnon frequency gap closely depend on the net angular momentum
+{\delta}s, emphasizing the pivotal role of {\delta}s as an effective control
+parameter in governing the comb teeth. With the increase of {\delta}s, the
+skyrmion size decreases, which results in the enlargement of the breathing
+frequency and the distance between the comb teeth. Moreover, the dependences of
+the magnon frequency gap on {\delta}s and the inter-layer coupling allow one to
+modulate the comb lowest coherent frequency via structural control.
+Consequently, the coherent modes generated by the comb may range from gigahertz
+to terahertz frequencies, serving as a bridge between microwave and terahertz
+waves. Thus, this work represents a substantial advance in understanding the
+magnon frequency comb effect in ferrimagnets.",2312.15584v2
+1999-04-22,Orbital Dynamics: The Origin of Anomalous Magnon Softening in Ferromagnetic Manganites,"We study the renormalization of magnons by charge and coupled orbital-lattice
+fluctuations in colossal magnetoresistance compounds. The model considered is
+an orbitally degenerate double-exchange system coupled to Jahn-Teller active
+phonons. The modulation of ferromagnetic bonds by low-energy orbital
+fluctuations is identified as the main origin of the unusual softening of the
+zone-boundary magnons observed experimentally in manganites.",9904316v2
+2006-03-14,Comment on ``Magnon wave forms in the presence of a soliton in two--dimensional antiferromagnets with a staggered field'',"Very recently Fonseca and Pires [Phys. Rev. B 73, 012403(2006)] have studied
+the soliton--magnon scattering for the isotropic antiferromagnet and calculated
+``exact'' phase shifts, which were compared with the ones obtained by the Born
+approximation. In this Comment we correct both the soliton and magnon solutions
+and point out the way how to study correctly the scattering problem.",0603395v1
+1999-03-01,Mathematical Structure of Magnons in Quantum Ferromagnets,"We provide the mathematical structure and a simple, transparent and rigorous
+derivation of the magnons as elementary quasi-particle excitations at low
+temperatures and in the infinite spin limit for a large class of Heisenberg
+ferromagnets. The magnon canonical variables are obtained as fluctuation
+operators in the infinite spin limit. Their quantum character is governed by
+the size of the magnetization.",9903004v1
+2010-02-14,The Force Between Giant Magnons,"We compute the force and torque between well-separated, slowly-moving Giant
+Magnons with arbitrary orientations on S^5. We propose an effective Hamiltonian
+for Giant Magnons in this regime.",1002.2787v1
+2012-07-24,Magnon mechanism of Josephson coupling in SFS structures,"It is shown that Josephson coupling in SFS junction due to electron-magnon
+interaction remains at a distance, when the usual proximity effect decreases
+exponentially. We obtain expression for the Josephson energy, which contain the
+parameters of the magnon spectrum and allow to estimate the value of the
+maximum superconducting current.",1207.5828v1
+2015-06-04,Three magnons in an isotropic $S=1$ ferromagnetic chain as an exactly solvable non-integrable system,"It is shown that a generalization of Bethe Ansatz based on an utilization of
+{\it degenerative discrete-diffractive} wave functions solves the three-magnon
+problem for the $S=1$ isotropic ferromagnetic infinite chain. The four-magnon
+problem is briefly discussed.",1506.01554v2
+2018-04-16,Phase modulation and amplitude modulation interconversion for magnonic circuits,"Circuit elements within magnonic computers generally operate using signals
+that are either amplitude or phase modulated (AM or PM). We propose a simple
+all-magnon circuit element capable of converting between these two types of
+encoding. We highlight the potential of our technique to augment existing
+devices and propose a novel schematic for an 'equality' gate and XNOR gate.",1804.05575v1
+2008-07-23,Issues on magnon reflection,"Two questions related to reflections of magnons in AdS/CFT are discussed:
+namely the problem of explaining the (physical) poles of the reflection
+amplitudes using Landau type diagrams and the generalization of the
+Ghoshal-Zamolodchikov boundary state formalism to magnon reflections.",0807.3646v1
+2021-10-02,Electrically Switchable van der Waals Magnon Valves,"Van der Waals magnets have emerged as a fertile ground for the exploration of
+highly tunable spin physics and spin-related technology. Two-dimensional (2D)
+magnons in van der Waals magnets are collective excitation of spins under
+strong confinement. Although considerable progress has been made in
+understanding 2D magnons, a crucial magnon device called the van der Waals
+magnon valve, in which the magnon signal can be completely and repeatedly
+turned on and off electrically, has yet to be realized. Here we demonstrate
+such magnon valves based on van der Waals antiferromagnetic insulator MnPS3. By
+applying DC electric current through the gate electrode, we show that the
+second harmonic thermal magnon (SHM) signal can be tuned from positive to
+negative. The guaranteed zero crossing during this tuning demonstrates a
+complete blocking of SHM transmission, arising from the nonlinear gate
+dependence of the non-equilibrium magnon density in the 2D spin channel. Using
+the switchable magnon valves we demonstrate a magnon-based inverter. These
+results illustrate the potential of van der Waals anti-ferromagnets for
+studying highly tunable spin-wave physics and for application in magnon-base
+circuitry in future information technology.",2110.00700v1
+2022-10-15,Non-local magnon transconductance in extended magnetic insulating films.\\Part II: two-fluid behavior,"This review presents a comprehensive study of the spatial dispersion of
+propagating magnons electrically emitted in extended yttrium-iron garnet (YIG)
+films by the spin transfer effects across a YIG$\vert$Pt interface. Our goal is
+to provide a generic framework to describe the magnon transconductance inside
+magnetic films. We experimentally elucidate the relevant spectral contributions
+by studying the lateral decay of the magnon signal. While most of the injected
+magnons do not reach the collector, the propagating magnons can be split into
+two-fluids: \textit{i)} a large fraction of high-energy magnons carrying energy
+of about $k_B T_0$, where $T_0$ is the lattice temperature, with a
+characteristic decay length in the sub-micrometer range, and \textit{ii)} a
+small fraction of low-energy magnons, which are particles carrying energy of
+about $\hbar \omega_K$, where $\omega_K/(2 \pi)$ is the Kittel frequency, with
+a characteristic decay length in the micrometer range. Taking advantage of
+their different physical properties, the low-energy magnons can become the
+dominant fluid \textit{i)} at large spin transfer rates for the bias causing
+the emission of magnons, \textit{ii)} at large distance from the emitter,
+\textit{iii)} at small film thickness, or \textit{iv)} for reduced band
+mismatch between the YIG below the emitter and the bulk due to variation of the
+magnon concentration. This broader picture complements part I \cite{kohno_SD},
+which focuses solely on the nonlinear transport properties of low-energy
+magnons.",2210.08283v2
+2023-04-21,Soft Magnons in Anisotropic Ferromagnets,"We discuss spin-wave transport in anisotropic ferromagnets with an emphasis
+on the zeroes of the band edges as a function of a magnetic field. An
+associated divergence of the magnon spin should be observable by enhanced
+magnon conductivities in non-local experiments, especially in two-dimensional
+ferromagnets.",2304.10709v1
+1999-09-28,"Finite size spectrum, magnon interactions and magnetization of S=1 Heisenberg spin chains","We report our density matrix renormalization-group and analytical work on S=1
+antiferromagnetic Heisenberg spin chains. We study the finite size behavior
+within the framework of the non-linear sigma model. We study the effect of
+magnon-magnon interactions on the finite size spectrum and on the magnetization
+curve close to the critical magnetic field, determine the magnon scattering
+length and compare it to the prediction from the non-linear $\sigma$ model.",9909388v3
+1999-12-14,Relation between the superconducting gap energy and the two-magnon Raman peak energy in Bi2Sr2Ca{1-x}YxCu2O{8+δ},"The relation between the electronic excitation and the magnetic excitation
+for the superconductivity in Bi2Sr2Ca{1-x}YxCu2O{8+\delta} was investigated by
+wide-energy Raman spectroscopy. In the underdoping region the B1g scattering
+intensity is depleted below the two-magnon peak energy due to the ""hot spots""
+effects. The depleted region decreases according to the decrease of the
+two-magnon peak energy, as the carrier concentration ncreases. This two-magnon
+peak energy also determines the B1g superconducting gap energy as $2\Delta
+\approx \alpha \hbar \omega_{\rm Two-Magnon} \approx J_{\rm effective}$
+$(\alpha=0.34-0.41)$ from under to overdoping hole concentration.",9912232v1
+2001-12-20,Zone Edge Softening and Relaxation in the Double Exchange Model,"The $J\to \infty$ double exchange model is formulated in terms of three
+auxiliary particles. A slow true bosonic magnon propagates by admixture with a
+fast fermionic pseudo-magnon. This process involves the absorption of a
+conduction electron which, for this half-metal, carries only charge degrees of
+freedom. The magnon dispersion becomes much weaker and the relaxation rate
+increases rapidly upon approaching the zone boundary. That the magnons relax
+for all wave vector values implies the existence of a low energy spin
+continuum.",0112399v1
+2003-01-10,Magnon Heat Transport in doped $\rm La_2CuO_4$,"We present results of the thermal conductivity of $\rm La_2CuO_4$ and $\rm
+La_{1.8}Eu_{0.2}CuO_4$ single-crystals which represent model systems for the
+two-dimensional spin-1/2 Heisenberg antiferromagnet on a square lattice. We
+find large anisotropies of the thermal conductivity, which are explained in
+terms of two-dimensional heat conduction by magnons within the CuO$_2$ planes.
+Non-magnetic Zn substituted for Cu gradually suppresses this magnon thermal
+conductivity $\kappa_{\mathrm{mag}}$. A semiclassical analysis of
+$\kappa_{\mathrm{mag}}$ is shown to yield a magnon mean free path which scales
+linearly with the reciprocal concentration of Zn-ions.",0301164v2
+2005-11-15,Magnon-mediated Binding between Holes in an Antiferromagnet,"The long-range forces between holes in an antiferromagnet are due to magnon
+exchange. The one-magnon exchange potential between two holes is proportional
+to cos(2\phi)/r^2 where r is the distance vector of the holes and \phi is the
+angle between r and an axis of the square crystal lattice. One-magnon exchange
+leads to bound states of holes with antiparallel spins resembling d-wave
+symmetry. The role of these bound states as potential candidates for the
+preformed Cooper pairs of high-temperature superconductivity is discussed
+qualitatively.",0511367v2
+2006-06-30,A variational coupled-cluster study of magnon-density-wave excitations in quantum antiferromagnets,"We extend recently proposed variational coupled-cluster method to describe
+excitation states of quantum antiferromagnetic bipartite lattices. We reproduce
+the spin-wave excitations (i.e., magnons with spin $\pm 1$). In addition, we
+obtain a new, spin-zero excitation (magnon-density waves) which has been
+missing in all existing spin-wave theories. Within our approximation, this
+magnon-density-wave excitation has a nonzero energy gap in a cubic lattice and
+is gapless in a square lattice, similar to those charge-density-wave
+excitations (plasmons) in quantum electron gases.",0606813v2
+2006-10-03,Three-Spin Giant Magnons in AdS_5xS^5,"From the Polyakov string action using a conformal gauge we construct a
+three-spin giant magnon solution describing a long open string in AdS_5 \times
+S^5 which rotates both in two angular directions of S^5 and in one angular
+direction of AdS_5. Through the Virasoro constraints the string motion in AdS_5
+takes an effect from the string configuration in S^5. The dispersion relation
+of the soliton solution is obtained as a superposition of two bound states of
+magnons. We show that there is a correspondence between a special giant magnon
+in AdS_2 and the sinh-Gordon soliton.",0610037v1
+2006-11-02,Dressing the Giant Magnon II,"We extend our earlier work by demonstrating how to construct classical string
+solutions describing arbitrary superpositions of scattering and bound states of
+dyonic giant magnons on S^5 using the dressing method for the SU(4)/Sp(2) coset
+model. We present a particular scattering solution which generalizes solutions
+found in hep-th/0607009 and hep-th/0607044 to the case of arbitrary magnon
+momenta. We compute the classical time delay for the scattering of two dyonic
+magnons carrying angular momenta with arbitrary relative orientation on the
+S^5.",0611033v1
+2007-03-27,Giant Magnon in NS5-brane Background,"We study the giant magnon solutions in the near horizon geometry of the
+Neveu-Schwarz (NS) 5-brane background. In conformal gauge, we find magnon
+dispersion relation in the large angular momentum (J) limit. We further show
+that the giant magnon poses uniform distribution of the angular momentum along
+the string world-sheet as in case of AdS_5\times S^5 spacetime.",0703244v2
+1995-01-19,Phonon Assisted Multimagnon Optical Absorption and Long Lived Two-Magnon States in Undoped Lamellar Copper Oxides,"We calculate the effective charge for multimagnon infrared (IR) absorption
+assisted by phonons in the parent insulating compounds of cuprate
+superconductors and the spectra for two-magnon absorption using interacting
+spin-wave theory. Recent measured bands in the mid IR [Perkins et al. Phys.
+Rev. Lett. {\bf 71} 1621 (1993)] are interpreted as involving one phonon plus a
+two-magnon virtual bound state, and one phonon plus higher multimagnon
+absorption processes. The virtual bound state consists of a narrow resonance
+occurring when the magnon pair has total momentum close to $(\pi,0)$.",9501001v1
+2007-06-10,Magnon mode truncation in a rung-dimerized asymmetric spin ladder,"An exactly solvable effective model is suggested for an asymmetric spin
+ladder with dimerized rungs. Magnon mode truncation originated from magnon
+decay (recently observed in the 1D compound ${\rm IPA-CuCl}_3$) is naturally
+described within this model. Using Bethe Ansatze we described a one-magnon
+sector and obtained relations between interaction constants of the model and
+experimentally observable quantities such as the gap and truncation energies,
+spin velocity and the truncation wave vector. It is also shown that structure
+factor turns to zero at the truncation point.",0706.1370v2
+2008-02-25,Quantum Giant Magnons,"The giant magnons are classical solitons of the O(N) sigma-model, which play
+an important role in the AdS/CFT correspondence. We study quantum giant magnons
+first at large N and then exactly using Bethe Ansatz, where giant magnons can
+be interpreted as holes in the Fermi sea. We also identify a solvable limit of
+Bethe Ansatz in which it describes a weakly-interacting Bose gas at zero
+temperature. The examples include the O(N) model at large N, weakly interacting
+non-linear Schrodinger model, and nearly isotropic XXZ spin chain in the
+magnetic field.",0802.3681v2
+2008-11-25,Theory of electric field induced one-magnon resonance in cycloidal spin magnets,"We propose a new mechanism to induce a novel one-magnon excitation by the
+electric component of light in cycloidal spin states, i.e. so called
+electromagnon process. We calculated optical spectra in the cycloidal spin
+structures as observed in multiferroic perovskite manganites RMnO3 where novel
+magnetic excitations induced by oscillating electric fields are observed. When
+symmetric spin-dependent electric polarizations are introduced, we have light
+absorptions at terahertz frequencies with one- and two-magnon excitations
+driven by the electric component of light. Our results show that some parts of
+optical spectra observed experimentally at terahertz frequencies are one-magnon
+excitation absorptions.",0811.4082v1
+2009-01-20,Role of Bound Magnon in Magnetic Domain Wall Motion,"We report on a quantum description of the domain wall (DW) motion under a
+spin current. A bound magnon, which is the zero mode of DW, is found to play a
+dominant role in DW dynamics. The bound magnon acquires its inertia by the hard
+axis anisotropy and is a free particle even under the spin current. The full
+transfer of spin angular momentum from the spin current to DW via the bound
+magnon leads to the DW motion with the adiabatic velocity, decoupling of spin
+waves from DW, and no Doppler shift in spin waves.",0901.3066v1
+2011-06-22,All-magnonic spin-transfer torque and domain wall propagation,"The spin wave transportation through a transverse magnetic domain wall (DW)
+in a magnetic nanowire is studied. It is found that spin wave passes through a
+DW without reflection. A magnon, the quantum of the spin wave, carries opposite
+spins on the two sides of the DW. As a result, there is a spin angular momentum
+transfer from the propagating magnons to the DW. This magnonic spin-transfer
+torque can efficiently drive a DW to propagate in the opposite direction to
+that of the spin wave.",1106.4382v2
+2013-02-20,"Lifetimes of antiferromagnetic magnons in two and three dimensions: experiment, theory, and numerics","A high-resolution neutron spectroscopic technique is used to measure
+momentum-resolved magnon lifetimes in the prototypical two- and
+three-dimensional antiferromagnets Rb2MnF4 and MnF2, over the full Brillouin
+zone and a wide range of temperatures. We rederived theories of the lifetime
+resulting from magnon-magnon scattering, thereby broadening their applicability
+beyond asymptotically small regions of wavevector and temperature.
+Corresponding computations, combined with a small contribution reflecting
+collisions with domain boundaries, yield excellent quantitative agreement with
+the data.",1302.4867v1
+2013-02-26,Magnon-mediated thermal transport in antiferromagnets: the link to momentum-resolved magnon lifetime data,"Transport currents in solids decay through collisions of quasiparticles with
+each other and with defects or boundaries. Since information about collisional
+lifetimes is difficult to obtain, most calculations of transport properties
+rely on parameters that are not known independently. Here, we use magnon
+lifetime data for the two-dimensional antiferromagnet Rb2MnF4 to calculate the
+magnon-mediated thermal conductivity without any adjustable parameters, thereby
+quantifying the influence of scattering from domain boundaries on transport.
+Related strategies have the potential to enhance our understanding of thermal
+transport by electronic and phononic quasiparticles greatly.",1302.6476v1
+2015-02-05,Large-Spin Expansions of Giant Magnons,"This is a talk delivered at the Workshop on Quantum Fields and Strings of the
+2014 Corfu Summer Institute. We discuss how giant magnons emerge in the context
+of the AdS5/CFT4 correspondence as the gravity duals of N = 4 super Yang-Mills
+magnon excitations. Then we present a new analytic expression for the
+dispersion relation of classical finite-size giant magnons with Lambert's
+W-function.",1502.01630v2
+2015-03-13,Upper bound of one-magnon excitation and lower bound of effective mass for ferromagnetic spinor Bose and Fermi gases,"Using a variational method, we derive an exact upper bound for one-magnon
+excitation energy in ferromagnetic spinor gases, which limits the quantum
+corrections to the effective mass of a magnon to be positive. We also derive an
+upper bound for one-magnon excitation energy in lattice systems. The results
+hold for both Bose and Fermi systems in $d$ dimensions as long as the
+interaction is local and invariant under spin rotation.",1503.03951v3
+2015-09-01,Magnon instability driven by heat current in magnetic bilayers,"We theoretically demonstrate that, in a ferromagnet/paramagnet bilayer, a
+magnon instability accompanied by a gigahertz microwave emission can be driven
+simply by means of a temperature bias. Employing many-body theory for
+investigating the effects of a phonon heat current on the magnon lifetime, we
+show that the magnon instability occurs upon the suppression of the Umklapp
+scattering at low temperatures, leading to microwave emission. The present
+finding provides crucial information about the interplay of spin current and
+heat current.",1509.00132v2
+2015-09-19,Spin torque and Nernst effects in Dzyaloshinskii-Moriya ferromagnets,"We predict that a temperature gradient can induce a magnon-mediated intrinsic
+torque and a transverse spin current in systems with non-trivial magnon Berry
+curvature. With the help of a microscopic linear response theory of
+nonequilibrium magnon-mediated torques and spin currents we identify the
+interband and intraband components that manifest in ferromagnets with
+Dzyaloshinskii-Moriya interactions and magnetic textures. To illustrate and
+assess the importance of such effects, we apply our theory to the
+magnon-mediated spin Nernst and torque responses in a kagome lattice
+ferromagnet.",1509.05847v3
+2016-06-09,Magnon spin Nernst effect in antiferromagnets,"We predict that a temperature gradient can induce a magnon-mediated spin Hall
+response in an antiferromagnet with non-trivial magnon Berry curvature. We
+develop a linear response theory which gives a general condition for a Hall
+current to be well defined, even when the thermal Hall response is forbidden by
+symmetry. We apply our theory to a honeycomb lattice antiferromagnet and
+discuss a role of magnon edge states in a finite geometry.",1606.03088v3
+2016-06-29,Damped Topological Magnons in the Kagomé-Lattice Ferromagnets,"We demonstrate that interactions can substantially undermine the
+free-particle description of magnons in ferromagnets on geometrically
+frustrated lattices. The anharmonic coupling, facilitated by the
+Dzyaloshinskii-Moriya interaction, and a highly-degenerate two-magnon continuum
+yield a strong, non-perturbative damping of the high-energy magnon modes. We
+provide a detailed account of the effect for the $S=1/2$ ferromagnet on the
+kagom\'e lattice and propose further experiments.",1606.09249v3
+2017-02-02,Magnon Condensation and Spin Superfluidity,"We consider the phenomenon of Bose-Einstein condensation of quasi-equilibrium
+magnons which leads to a spin superfluidity, the coherent quantum transfer of
+magnetization in magnetic materials. These phenomena are beyond the classical
+Landau-Lifshitz-Gilbert paradigm. The critical conditions for excited magnon
+density for ferro- and antiferromagnets, bulk and thin films are estimated and
+discussed. The BEC should occur in the antiferromagnetic hematite at much lower
+excited magnon density compared to the ferromagnetic YIG.",1702.00846v2
+2013-08-29,Exchange parameters and adiabatic magnon energies from spin-spiral calculations,"We present a method of extracting the exchange parameters of the classical
+Heisenberg model from first-principles calculations of spin-spiral total
+energies based on density functional theory. The exchange parameters of the
+transition-metal monoxides MnO and NiO are calculated and used to estimate
+magnetic properties such as transition temperatures and magnon energies.
+Furthermore we show how to relate the magnon energies directly to differences
+in spin-spiral total energies for systems containing an arbitrary number of
+magnetic sublattices. This provides a comparison between magnon energies using
+a finite number of exchange parameters and the infinite limit.",1308.6466v1
+2014-05-02,Dynamic phase diagram of dc-pumped magnon condensates,"We study the effects of nonlinear dynamics and damping by phonons on a system
+of interacting electronically pumped magnons in a ferromagnet. The nonlinear
+effects are crucial for constructing the dynamic phase diagram, which describes
+how ""swasing"" and Bose-Einstein condensation emerge out of the
+quasiequilibrated thermal cloud of magnons. We analyze the system in the
+presence of magnon damping and interactions, demonstrating the continuous onset
+of stable condensates as well as hysteretic transitions.",1405.0522v1
+2017-12-21,Topological magnons with nodal-line and triple-point degeneracies: Implications for thermal Hall effect in pyrochlore iridates,"We analyze the magnon excitations in pyrochlore iridates with all-in-all-out
+(AIAO) antiferromagnetic order, focusing on their topological features. We
+identify the magnetic point group symmetries that protect the nodal-line band
+crossings and triple-point degeneracies that dominate the Berry curvature. We
+find three distinct regimes of magnon band topology, as a function of the ratio
+of Dzyaloshinskii-Moriya (DM) interaction to the antiferromagnetic exchange. We
+show how the thermal Hall response provides a unique probe of the topological
+magnon band structure in AIAO systems.",1712.08170v2
+2017-12-27,Finite temperature magnon spectra in yttrium iron garnet from mean field approach in tight-binding model,"We study magnon spectra at finite temperature in yttrium iron garnet from
+tight-binding model with nearest neighboring exchange interaction. The spin
+reduction due to thermal magnon excitation are taken into account via the mean
+field approximation to the local spin and found to be different at two sets of
+iron atoms. The resulting temperature dependence of the spin wave gap shows
+good agreement with experiment. We find only two magnon modes are relevant to
+ferromagnetic resonance.",1712.09512v1
+2019-09-03,Magnon Accumulation in Chirally Coupled Magnets,"We report strong chiral coupling between magnons and photons in microwave
+waveguides that contain chains of small magnets on special lines. Large magnon
+accumulations at one edge of the chain emerge when exciting the magnets by a
+phased antenna array. This mechanism holds the promise of new functionalities
+in non-linear and quantum magnonics.",1909.00953v1
+2020-12-03,Dirac surface states in magnonic analogs of topological crystalline insulators,"We propose magnonic analogs of topological crystalline insulators which
+possess Dirac surface states protected by the combined symmetry of
+time-reversal and half translation. Constructing models of the topological
+magnon systems, we demonstrate that the energy current flows through the
+systems in response to an electric field, owing to the Dirac surface states
+with the spin-momentum locking. We also propose a realization of the magnonic
+analogs of topological crystalline insulators in a magnetic compound CrI$_{3}$
+with a monoclinic structure.",2012.02034v2
+2000-06-01,High-energy magnon dispersion and multi-magnon continuum in the two-dimensional Heisenberg antiferromagnet,"We use quantum Monte Carlo simulations and numerical analytic continuation to
+study high-energy spin excitations in the two-dimensional S=1/2 Heisenberg
+antiferromagnet at low temperature. We present results for both the transverse
+and longitudinal dynamic spin structure factor S(q,w) at q=(pi,0) and
+(pi/2,pi/2). Linear spin-wave theory predicts no dispersion on the line
+connecting these momenta. Our calculations show that in fact the magnon energy
+at (pi,0) is 10% lower than at (pi/2,pi/2). We also discuss the transverse and
+longitudinal multi-magnon continua and their relevance to neutron scattering
+experiments.",0006021v1
+2017-05-29,Chemical potential of quasi-equilibrium magnon gas driven by pure spin current,"We show experimentally that the spin current generated by the spin Hall
+effect drives the magnon gas in a ferromagnet into a quasi-equilibrium state
+that can be described by the Bose-Einstein statistics. The magnon population
+function is characterized either by an increased effective chemical potential
+or by a reduced effective temperature, depending on the spin current
+polarization. In the former case, the chemical potential can closely approach,
+at large driving currents, the lowest-energy magnon state, indicating the
+possibility of spin current-driven Bose-Einstein condensation.",1705.10047v1
+2016-10-07,Magnonic black holes,"We show that the interaction between spin-polarized current and magnetization
+dynamics can be used to implement black-hole and white-hole horizons for
+magnons - the quanta of oscillations in the magnetization direction in magnets.
+We consider three different systems: easy-plane ferromagnetic metals, isotropic
+antiferromagnetic metals, and easy-plane magnetic insulators. Based on
+available experimental data, we estimate that the Hawking temperature can be as
+large as 1 K. We comment on the implications of magnonic horizons for spin-wave
+scattering and transport experiments, and for magnon entanglement.",1610.02313v1
+2020-06-22,Magnon Landau Levels and Spin Responses in Antiferromagnets,"We study gauge fields produced by gradients of the Dzyaloshinskii-Moriya
+interaction and propose a model of AFM topological insulator of magnons. In the
+long wavelength limit, the Landau levels induced by the inhomogeneous
+Dzyaloshinskii-Moriya interaction exhibit relativistic physics described by the
+Klein-Gordon equation. The spin Nernst response due to the formation of
+magnonic Landau levels is compared to similar topological responses in skyrmion
+and vortex-antivortex crystal phases of AFM insulators. Our studies show that
+AFM insulators exhibit rich physics associated with topological magnon
+excitations.",2006.12423v2
+2020-02-02,Topological Valley Transport of Gapped Dirac Magnons in Bilayer Ferromagnetic Insulators,"Bilayer Heisenberg ferromagnetic insulators hold degenerate terahertz Dirac
+magnon modes associated with two opposite valleys of the hexagonal Brillouin
+zone. We show that this energy degeneracy can be removed by breaking of the
+inversion symmetry (I), leading to a topological magnon valley current. We show
+furthermore that this current leads to valley Seebeck effect for magnons and is
+thereby detectable. We perform calculations in the specific example of bilayer
+CrBr3, where I can be broken by electrostatic doping.",2002.00446v2
+2020-04-03,Twist-induced magnon Landau levels in honeycomb magnets,"Lattice deformation resulting from elastic strain is known to spatially
+modulate the wave function overlap of the atoms on the lattice and can
+drastically alter the properties of the quasiparticles. Here we elaborate that
+a twist lattice deformation in two-dimensional honeycomb quantum magnet
+nanoribbons is equivalent to an elastic gauge field giving rise to magnon
+Landau quantization. When the ground state is ferromagnetic, dispersive
+Dirac-Landau levels are induced in the center of magnon bands, while for
+antiferromagnetic nanoribbons, the twist results in dispersive equidistant
+Landau levels at the top of magnon bands. The dispersions for both types of
+Landau levels are derived in the framework of the band theory.",2004.01371v1
+2020-05-28,Nonreciprocal Magnon by Symmetric Anisotropic Exchange Interaction in Honeycomb Antiferromagnet,"We investigate a microscopic origin of nonreciprocal magnon that is distinct
+from the Dzyaloshinskii-Moriya interaction in a honeycomb antiferromagnet. The
+key ingredient is a symmetric anisotropic exchange interaction depending on the
+bond direction, which results in a valley-type nonreciprocal magnon excitations
+under the staggered antiferromagnetic ordering. Furthermore, we find this type
+of nonreciprocal magnon exhibits a peculiar magnetic-field response; the
+nonreciprocal direction can be manipulated by the in-plane rotating magnetic
+field. The obtained results can be accounted for the emergence of the magnetic
+toroidal multipoles.",2005.13729v1
+2020-07-22,Nanomagnonic cavities for strong spin-magnon coupling,"We present a theoretical approach to use ferro- or ferrimagnetic
+nanoparticles as microwave nanomagnonic cavities to concentrate microwave
+magnetic fields into deeply subwavelength volumes $\sim 10^{-13}$ mm$^3$. We
+show that the field in such nanocavities can efficiently couple to isolated
+spin emitters (spin qubits) positioned close to the nanoparticle surface
+reaching the single magnon-spin strong-coupling regime and mediate efficient
+long-range quantum state transfer between isolated spin emitters. Nanomagnonic
+cavities thus pave the way towards magnon-based quantum networks and
+magnon-mediated quantum gates.",2007.11595v1
+2020-08-16,Magnon dispersion in bilayers of two-dimensional ferromagnets,"We determine magnon spectra of an atomic bilayer magnet with ferromagnetic
+intra- and both ferro- and anti- ferromagnetic interlayer coupling. Analytic
+expressions for the full magnon band of the latter case reveal that both
+exchange interactions govern the fundamental magnon gap. The inter and
+intralayer magnetic ordering are not independent: the intralayer ferromagnetism
+stabilizes antiferromagnetic inter-layer order. The topology of these
+exchange-anisotropy spin models without spin-orbit interaction turns out to be
+trivial.",2008.06875v2
+2021-06-24,Magnonics vs. Ferronics,"Magnons are the elementary excitations of the magnetic order that carry spin,
+momentum, and energy. Here we compare the magnon with the ferron, i.e. the
+elementary excitation of the electric dipolar order that transports
+polarization and heat in ferroelectrics.",2106.12775v1
+2021-09-10,Numerical Simulation of the Coupling between Split-Ring Resonators and Antiferromagnetic Magnons,"We report on the results of simulations of the terahertz response of a split
+ring resonator (SRR) metamaterial coupled to a hypothetical antiferromagnetic
+material characterized by a magnon resonance. The simulations were done using
+finite difference time domain (FDTD) techniques. By adjusting the magnon
+frequency we find a hybridization of the resonant normal modes of the SRR and
+the magnon manifested as an avoided crossing. By varying the physical
+separation between the metamaterial and the antiferromagnet with a dielectric
+spacer, we evaluated the coupling strength between the two.",2109.05086v1
+2021-12-13,Magnon frequency renormalization by the electronic geometrical spin torque in itinerant magnets,"We investigate non-adiabatic effects on the magnon frequency in an
+interacting system of localized spins and itinerant electrons. Including the
+lowest order corrections to the adiabatic dynamics in an analytically solvable
+model, applicable to simple ferromagnets like Fe, Co and Ni, we find that the
+magnon frequency is renormalized by a geometrical torque arising from the
+electronic spin Berry curvature. Comparison to exact numerical simulations
+reveals that our analytical solution captures essential low-energy features,
+and provides a mechanism for the magnon frequency hardening observed in recent
+first principles calculations for Fe, provided the geometrical torque is taken
+into account.",2112.06547v1
+2023-01-06,Stacking-dependent topological magnons in bilayer CrI$_3$,"Motivated by the potential of atomically-thin magnets towards tunable
+high-frequency magnonics, we detail the spin-wave dispersion of bilayer
+CrI$_3$. We demonstrate that the magnonic behavior of the bilayer strongly
+depends on its stacking configuration and the interlayer magnetic ordering,
+where a topological bandgap opens in the dispersion caused by the
+Dzyaloshinskii-Moriya and Kitaev interactions, classifying bilayer CrI$_3$ as a
+topological magnon insulator. We further reveal that both size and topology of
+the bandgap in a CrI$_3$ bilayer with an antiferromagnetic interlayer ordering
+are tunable by an external magnetic field.",2301.02502v2
+2023-01-19,Interfacial Magnon-Mediated Superconductivity in Twisted Bilayer Graphene,"The interfacial coupling between electrons and magnons in adjacent layers can
+mediate an attractive electron-electron interaction and induce
+superconductivity. We consider magic-angle twisted bilayer graphene sandwiched
+between two ferromagnetic insulators to optimize this effect. As a result,
+magnons induce an interlayer superconducting state characterized by $p$-wave
+symmetry. We investigate two candidate ferromagnets. The van der Waals
+ferromagnet CrI$_3$ stands out because it allows compression to tune the
+superconducting state with an exponential sensitivity. This control adds a new
+dimension to the tunability of twisted bilayer graphene. Our results open a new
+path for exploring magnon-induced superconductivity.",2301.07909v1
+2023-06-14,Chirality Enables Thermal Magnon Transistors,"We report a theory of thermal spin pumping into proximity magnets under a
+transverse-bias-driven heat flow of magnons in magnetic films when the dipolar
+coupling to the magnetic gate is tuned to be ""chiral"". While there is no
+rectification of the magnon current in the film, we predict that chirality
+diverts a large percentage (50$\%$ for perfect chirality) of it into the gate.
+This transverse thermal spin pumping effect can be controlled by rotating the
+film magnetization and may help manage the heat flow in future magnonic
+circuits.",2306.08371v3
+2023-11-17,Magnon topological transition in skyrmion crystal,"We study the magnon spectrum in skyrmion crystal formed in thin ferromagnetic
+films with Dzyalosinskii-Moria interaction in presence of magnetic field.
+Focusing on two low-lying observable magnon modes and employing stereographic
+projection method, we develop a theory demonstrating a topological transition
+in the spectrum. Upon the increase of magnetic field, the gap between two
+magnon bands closes, with the ensuing change in the topological character of
+both bands. This phenomenon of gap closing, if confirmed in magnetic resonance
+experiments, may deserve further investigation by thermal Hall conductivity
+experiments.",2311.10622v1
+2023-12-05,Interplay between magnetism and superconductivity in a hybrid magnon-photon bilayer system,"Spin waves in magnetic films are affected by the vicinity to a
+superconductor. Here we studied a bilayer stack made of an insulating Yttrium
+Iron Garnet (YIG) film and a high-$T_c$ YBCO superconducting planar resonator.
+We investigated the hybridization of magnon and photon modes reporting the
+temperature evolution of microwave transmission spectra. Data analysis, based
+on the description of magnon modes and on the Hopfield model, shows that the
+magnon-photon coupling strength and the mode frequency shift can be ultimately
+related to the temperature dependence of the penetration depth of YBCO.",2312.02785v2
+2024-01-22,Damping-Enhanced Magnon Transmission,"The inevitable Gilbert damping in magnetization dynamics is usually regarded
+as detrimental to spin transport. Here we demonstrate in a
+ferromagnetic-insulator--normal-metal heterostructure that the strong momentum
+dependence and chirality of the eddy-current-induced damping causes also
+beneficial scattering properties. Here we show that a potential barrier that
+reflects magnon wave packets becomes transparent in the presence of a metallic
+cap layer, but only in one direction. We formulate the unidirectional
+transmission in terms of a generalized group velocity with an imaginary
+component and the magnon skin effect. This trick to turn presumably harmful
+dissipation into useful functionalities should be useful for future quantum
+magnonic devices.",2401.12022v1
+2021-11-28,Quantum magnonics: when magnon spintronics meets quantum information science,"Spintronics and quantum information science are two promising candidates for
+innovating information processing technologies. The combination of these two
+fields enables us to build solid-state platforms for studying quantum phenomena
+and for realizing multi-functional quantum tasks. For a long time, however, the
+intersection of these two fields was limited. This situation has changed
+significantly over the last few years because of the remarkable progress in
+coding and processing information using magnons. On the other hand, significant
+advances in understanding the entanglement of quasi-particles and in designing
+high-quality qubits and photonic cavities for quantum information processing
+provide physical platforms to integrate magnons with quantum systems. From
+these endeavours, the highly interdisciplinary field of quantum magnonics
+emerges, which combines spintronics, quantum optics and quantum information
+science.Here, we give an overview of the recent developments concerning the
+quantum states of magnons and their hybridization with mature quantum
+platforms. First, we review the basic concepts of magnons and quantum
+entanglement and discuss the generation and manipulation of quantum states of
+magnons, such as single-magnon states, squeezed states and quantum many-body
+states including Bose-Einstein condensation and the resulting spin
+superfluidity. We discuss how magnonic systems can be integrated and entangled
+with quantum platforms including cavity photons, superconducting qubits,
+nitrogen-vacancy centers, and phonons for coherent information transfer and
+collaborative information processing. The implications of these hybrid quantum
+systems for non-Hermitian physics and parity-time symmetry are highlighted,
+together with applications in quantum memories and high-precision measurements.
+Finally, we present an outlook on the opportunities in quantum magnonics.",2111.14241v2
+2007-01-17,Two-magnon excitations in resonant inelastic x-ray scattering from quantum Heisenberg antiferromagnets,"We study two-magnon spectra in resonant inelastic x-ray scattering (RIXS)
+from the Heisenberg antiferromanets by extending the formula of Nomura
+andIgarashi (Phys. Rev. B 71, 035110 (2005)). The core-hole potential in the
+intermediate state of RIXS gives rise to a change in the exchange coupling
+between 3d electrons, leading to an effective interaction between the core hole
+and spins of 3d electrons. We derive a formula suitable to calculate the
+two-magnon RIXS intensities, replacing the bare core-hole potential responsible
+to charge excitations by this effective interaction creating two magnons in our
+previous formula. It consists of two factors, one of which determines the
+incident-photon-energy dependence and another is the two-magnon correlation
+function. We evaluate the former factor for La_{2}CuO_{4} in terms of the
+density of states of the 4p states obtained by the band calculation. We also
+calculate the two-magnon correlation function as a function of energy loss
+\omega and momentum transfer \textbf{q} of the Heisenberg model on a square
+lattice,by summing up the ladder diagrams after transforming the magnon-magnon
+interaction into a separable form. The calculated spectra form a broad peak
+around \omega=3J for S=1/2 on the magnetic Brillouin zone boundary and vanish
+at \textbf{q}=(0,0) and (\pi,\pi). Such momentum dependence of the RIXS spectra
+could provide an excellent opportunity to study the dynamics in the Heisenberg
+model.",0701399v1
+2015-10-18,Magnetization dynamics in Fe$_x$Co$_{1-x}$ in presence of chemical disorder,"In this paper, we present a theoretical formulation of magnetization dynamics
+in disordered binary alloys based on Kubo linear response theory interfaced
+with the combination of seamlessly three approaches; density functional based
+tight-binding linear muffin-tin orbitals, generalized recursion and Augmented
+space formalism. We apply this method to study the magnetization dynamics in
+chemically disordered Fe$_x$Co$_{1-x}$ ($x$ = 0.2, 0.5, 0.8) alloys. We
+reported that the magnon energies decrease with an increase in Co
+concentration. Significant magnon softening has been observed in
+Fe$_{20}$Co$_{80}$ at the Brillouin zone boundary. The magnon-electron
+scattering increases with increasing Co content which in turn modifies the
+hybridization between the Fe and Co atoms. This reduces the exchange energy
+between the atoms and soften down the magnon energy. The lowest magnon lifetime
+in found in Fe$_{50}$Co$_{50}$, where disorder is maximum. This clearly
+indicates that the damping of magnon energies in Fe$_x$Co$_{1-x}$ is governed
+by the hybridization between Fe and Co whereas the magnon lifetime is
+controlled by disorder configuration. Our atomistic spin dynamics simulations
+show a reasonable agreement with our theoretical approach in magnon dispersion
+for different alloy compositions.",1510.05200v4
+2016-01-08,Magnons and Phonons Optically Driven Out of Local Equilibrium in a Magnetic Insulator,"Magnons are the energy quanta of fundamental spin excitations, namely spin
+waves, and they can make a considerable contribution to energy transport in
+some magnetic materials in a similar manner as lattice vibration waves or
+phonons. The coupling and possible non-equilibrium between magnons and other
+energy carriers have been used to explain several recently discovered thermally
+driven spin transport and energy conversion phenomena. Here, we report
+experiments in which local non-equilibrium between magnons and phonons in a
+single crystalline bulk magnetic insulator, Y3Fe5O12 (yttrium iron garnet, or
+YIG), has been created optically within a focused laser spot and probed
+directly with the use of micro-Brillouin light scattering (BLS). By analyzing
+the experimental results with a thermally induced magnon diffusion model, we
+obtain the magnon diffusion length of thermal magnons. By explicitly
+establishing non-equilibrium between magnons and phonons, our studies represent
+an important step toward a quantitative understanding of various spin-heat
+coupling phenomena.",1601.01982v3
+2017-01-09,Spin-Wave Modes in Transition from a Thin Film to a Full Magnonic Crystal,"Spin-wave modes are studied under the gradual transition from a flat thin
+film to a 'full' (one-dimensional) magnonic crystal. For this purpose, the
+surface of a pre-patterned 36.8 nm thin permalloy film was sequentially ion
+milled resulting in magnonic hybrid structures, referred to as
+surface-modulated magnonic crystals, with increasing modulation depth. After
+each etching step, ferromagnetic resonance measurements were performed yielding
+the spin-wave resonance modes in backward-volume and Damon-Eshbach geometry.
+The spin-wave spectra of these hybrid systems reveal an even larger variety of
+spin-wave states compared to the 'full' magnonic crystal. The measurements are
+corroborated by quasi-analytical theory and micromagnetic simulations in order
+to study the changing spin-wave mode character employing spin-wave mode
+profiles. In backward-volume geometry, a gradual transition from the uniform
+mode in the film limit to a fundamental mode in the thin part of the magnonic
+crystal was observed. Equivalently, the first and the second film modes are
+transform into a center and an edge mode of the thick part of the magnonic
+crystal. Simple transition rules from the $n^{\mathrm{th}}$ film mode to the
+$m^{\mathrm{th}}$ mode in the 'full' magnonic crystal are formulated unraveling
+the complex mode structure particularly in the backward-volume geometry. An
+analogous analysis was performed in the Damon-Eshbach geometry.",1702.05675v3
+2017-01-30,Effects of Grain Boundaries and Defects on Anisotropic Magnon Transport in Textured Sr14Cu24O41,"The strong spin-spin exchange interaction in some low-dimensional magnetic
+materials can give rise to a high group velocity and thermal conductivity
+contribution from magnons. One example is the incommensurate layered compounds
+(Sr,Ca,La)14Cu24O41. The effects of grain boundaries and defects on
+quasi-one-dimensional magnon transport in these compounds are not well
+understood. Here we report the microstructures and anisotropic thermal
+transport properties of textured Sr14Cu24O41, which are prepared by solid-state
+reaction followed by spark plasma sintering. Transmission electron microscopy
+clearly reveals nano-layered grains and the presence of dislocations and planar
+defects. The thermal conductivity contribution and mean free paths of magnons
+in the textured samples are evaluated with the use of a kinetic model for
+one-dimensional magnon transport, and found to be suppressed significantly as
+compared to single crystals at low temperatures. The experimental results can
+be explained by a one-dimensional magnon-defect scattering model, provided that
+the magnon-grain boundary scattering mean free path in the anisotropic magnetic
+structure is smaller than the average length of these nano-layers along the c
+axis. The finding suggests low transmission coefficients for magnons across
+grain boundaries.",1701.08519v1
+2016-05-07,Weak coupling of pseudoacoustic phonons and magnon dynamics in incommensurate spin ladder compound Sr14Cu24O41,"Intriguing lattice dynamics has been predicted for aperiodic crystals that
+contain incommensurate substructures. Here we report inelastic neutron
+scattering measurements of phonon and magnon dispersions in Sr14Cu24O41, which
+contains incommensurate one-dimensional (1D) chain and two-dimensional (2D)
+ladder substructures. Two distinct pseudoacoustic phonon modes, corresponding
+to the sliding motion of one sublattice against the other, are observed for
+atomic motions polarized along the incommensurate axis. In the long wavelength
+limit, it is found that the sliding mode shows a remarkably small energy gap of
+1.7-1.9 meV, indicating very weak interactions between the two incommensurate
+sublattices. The measurements also reveal a gapped and steep linear magnon
+dispersion of the ladder sublattice. The high group velocity of this magnon
+branch and weak coupling with acoustic and pseudoacoustic phonons can explain
+the large magnon thermal conductivity in Sr14Cu24O41 crystals. In addition, the
+magnon specific heat is determined from the measured total specific heat and
+phonon density of states, and exhibits a Schottky anomaly due to gapped magnon
+modes of the spin chains. These findings offer new insights into the phonon and
+magnon dynamics and thermal transport properties of incommensurate magnetic
+crystals that contain low-dimensional substructures.",1605.02133v3
+2016-08-29,Field induced spontaneous quasiparticle decay and renormalization of quasiparticle dispersion in a quantum antiferromagnet,"The notion of a quasiparticle, such as a phonon, a roton, or a magnon, is
+used in modern condensed matter physics to describe an elementary collective
+excitation. The intrinsic zero-temperature magnon damping in quantum spin
+systems can be driven by the interaction of the one-magnon states and
+multi-magnon continuum. However, detailed experimental studies on this quantum
+many-body effect induced by an applied magnetic field are rare. Here we present
+a high-resolution neutron scattering study in high fields on an S=1/2
+antiferromagnet C9H18N2CuBr4. Compared with the non-interacting linear
+spin-wave theory, our results demonstrate a variety of phenomena including
+field-induced renormalization of one-magnon dispersion, spontaneous magnon
+decay observed via intrinsic linewidth broadening, unusual non-Lorentzian
+two-peak structure in the excitation spectra, and a dramatic shift of spectral
+weight from one-magnon state to the two-magnon continuum.",1608.08172v3
+2018-12-19,Decay rates and energies of free magnons and bound states in dissipative XXZ chains,"Chains of coupled two-level atoms behave as 1D quantum spin systems,
+exhibiting free magnons and magnon bound states. While these excitations are
+well studied for closed systems, little consideration has been given to how
+they are altered by the presence of an environment. This will be especially
+important in systems that exhibit nonlocal dissipation, e.g. systems in which
+the magnons decay due to optical emission. In this work, we consider free
+magnon excitations and two-magnon bound states in an XXZ chain with nonlocal
+dissipation. We prove that whilst the energy of the bound state can lie outside
+the two-magnon continuum of energies, the decay rate of the bound state has to
+always lie within the two-magnon continuum of decay rates. We then derive
+analytically the bound state solutions for a system with nearest-neighbour and
+next-nearest-neighbour XY interaction and nonlocal dissipation, finding that
+the inclusion of nonlocal dissipation allows more freedom in engineering the
+energy and decay rate dispersions for the bound states. Finally, we numerically
+study a model of an experimental set-up that should allow the realisation of
+dissipative bound states by using Rydberg-dressed atoms coupled to a photonic
+crystal waveguide (PCW). We demonstrate that this model can exhibit many key
+features of our simpler models.",1812.07893v1
+2019-04-05,"Cluster-based Haldane phases, bound magnon crystals and quantum spin liquids of a mixed spin-1 and spin-1/2 Heisenberg octahedral chain","The mixed spin-1 and spin-1/2 Heisenberg octahedral chain with regularly
+alternating monomeric spin-1 sites and square-plaquette spin-1/2 sites is
+investigated using variational technique, localized-magnon approach, exact
+diagonalization (ED) and density-matrix renormalization group (DMRG) method.
+The investigated model has in a magnetic field an extraordinarily rich
+ground-state phase diagram, which includes the uniform and cluster-based
+Haldane phases, two ferrimagnetic phases of Lieb-Mattis type, two quantum spin
+liquids and two bound magnon crystals in addition to the fully polarized
+ferromagnetic phase. The lowest-energy eigenstates in a highly-frustrated
+parameter region belong to flat bands and hence, low-temperature thermodynamics
+above the bound magnon-crystal ground states can be satisfactorily described
+within the localized-magnon approach. The variational method provides an exact
+evidence for the magnon-crystal phase with a character of the monomer-tetramer
+ground state at zero field, while another magnon-crystal phase with a single
+bound magnon at each square plaquette is found in a high-field region. A
+diversity of quantum ground states gives rise to manifold zero-temperature
+magnetization curves, which may involve up to four wide intermediate plateaus
+at zero, one-sixth, one-third and two-thirds of the saturation magnetization,
+two quantum spin-liquid regions and two tiny plateaus at one-ninth and
+one-twelfth of the saturation magnetization corresponding to the fragmentized
+cluster-based Haldane phases.",1904.02889v2
+2019-04-29,Experimental Realization of a Passive GHz Frequency-Division Demultiplexer for Magnonic Logic Networks,"The emerging field of magnonics employs spin waves and their quanta, magnons,
+to implement wave-based computing on the micro- and nanoscale. Multi-frequency
+magnon networks would allow for parallel data processing within single logic
+elements whereas this is not the case with conventional transistor-based
+electronic logic. However, a lack of experimentally proven solutions to
+efficiently combine and separate magnons of different frequencies has impeded
+the intensive use of this concept. In this Letter, the experimental realization
+of a spin-wave demultiplexer enabling frequency-dependent separation of
+magnonic signals in the GHz range is demonstrated. The device is based on
+two-dimensional magnon transport in the form of spin-wave beams in unpatterned
+magnetic films. The intrinsic frequency-dependence of the beam direction is
+exploited to realize a passive functioning obviating an external control and
+additional power consumption. This approach paves the way to magnonic
+multiplexing circuits enabling simultaneous information transport and
+processing.",1904.12744v2
+2017-11-08,Discovery of coexisting Dirac and triply degenerate magnons in a three-dimensional antiferromagnet,"Topological magnons are emergent quantum spin excitations featured by magnon
+bands crossing linearly at the points dubbed nodes, analogous to fermions in
+topological electronic systems. Experimental realization of topological magnons
+in three dimensions has not been reported so far. Here, by measuring spin
+excitations (magnons) of a three-dimensional antiferromagnet Cu$_{3}$TeO$_{6}$
+with inelastic neutron scattering, we provide direct spectroscopic evidence for
+the coexistence of symmetry-protected Dirac and triply degenerate nodes, the
+latter involving three-component magnons beyond the Dirac-Weyl framework. Our
+theoretical calculations show that the observed topological magnon band
+structure can be well described by the linear-spin-wave theory based on a
+Hamiltonian dominated by the nearest-neighbour exchange interaction $J_1$. As
+such, we showcase Cu$_{3}$TeO$_{6}$ as an example system where Dirac and triply
+degenerate magnonic nodal excitations coexist, demonstrate an exotic
+topological state of matter, and provide a fresh ground to explore the
+topological properties in quantum materials.",1711.02960v2
+2017-11-27,Cavity Magnon Polaritons with Lithium Ferrite and 3D Microwave Resonators at milli-Kelvin Temperatures,"Single crystal Lithium Ferrite (LiFe) spheres of sub-mm dimension are
+examined at mK temperatures, microwave frequencies and variable DC magnetic
+field, for use in hybrid quantum systems and condensed matter and fundamental
+physics experiments. Strong coupling regimes of the photon-magnon interaction
+(cavity magnon polariton quasi-particles) were observed with coupling strength
+of up to 250 MHz at 9.5 GHz (2.6\%) with magnon linewidths of order 4 MHz (with
+potential improvement to sub-MHz values). We show that the photon-magnon
+coupling can be significantly improved and exceed that of the widely used
+Yttrium Iron Garnet crystal, due to the small unit cell of LiFe, allowing twice
+more spins per unit volume. Magnon mode softening was observed at low DC fields
+and combined with the normal Zeeman effect creates magnon spin wave modes that
+are insensitive to first order order magnetic field fluctuations. This effect
+is observed in the Kittel mode at 5.5 GHz (and another higher order mode at 6.5
+GHz) with a DC magnetic field close to 0.19 Tesla. We show that if the cavity
+is tuned close to this frequency, the magnon polariton particles exhibit an
+enhanced range of strong coupling and insensitivity to magnetic field
+fluctuations with both first order and second order insensitivity to magnetic
+field as a function of frequency (double magic point clock transition), which
+could potentially be exploited in cavity QED experiments.",1711.09980v2
+2019-05-29,A magnonic directional coupler for integrated magnonic half-adders,"Magnons, the quanta of spin waves, could be used to encode information in
+beyond-Moore computing applications, and magnonic device components, including
+logic gates, transistors, and units for non-Boolean computing, have already
+been developed. Magnonic directional couplers, which can function as circuit
+building blocks, have also been explored, but have been impractical because of
+their millimetre dimensions and multi-mode spectra. Here, we report a magnonic
+directional coupler based on yttrium iron garnet single-mode waveguides of 350
+nm width. We use the amplitude of a spin-wave to encode information and to
+guide it to one of the two outputs of the coupler depending on the signal
+magnitude, frequency, and the applied magnetic field. Using micromagnetic
+simulations, we also propose an integrated magnonic half-adder that consists of
+two directional couplers and processes all information within the magnon domain
+with aJ energy consumption.",1905.12353v3
+2020-06-12,Evidence for magnon-phonon coupling in the topological magnet Cu$_3$TeO$_6$,"We perform thermodynamic and inelastic neutron scattering (INS) measurements
+to study the lattice dynamics (phonons) of a cubic collinear antiferromagnet
+Cu$_3$TeO$_6$ which hosts topological spin excitations (magnons). While the
+specific heat and thermal conductivity results show that the thermal transport
+is dominated by phonons, the deviation of the thermal conductivity from a pure
+phononic model indicates that there is a strong coupling between magnons and
+phonons. In the INS measurements, we find a mode in the excitation spectra at
+4.5 K, which exhibits a slight downward dispersion around the Brillouin zone
+center. This mode disappears above the N\'{e}el temperature, and thus cannot be
+a phonon. Furthermore, the dispersion is distinct from that of a magnon.
+Instead, it can be explained by the magnon-polaron mode, which is new
+collective excitations resulting from the hybridization between magnons and
+phonons. We consider the suppression of the thermal conductivity and emergence
+of the magnon-polaron mode to be evidence for magnon-phonon coupling in
+Cu$_3$TeO$_6$.",2006.07012v2
+2021-02-03,Unveiling excitonic properties of magnons in a quantum Hall ferromagnet,"Magnons enable transferring a magnetic moment or spin over macroscopic
+distance. In quantum Hall ferromagnet, it has been predicted in the early 90s
+that spin and charges are entangled, meaning that any change of the spin
+texture modifies the charge distribution. As a direct consequence of this
+entanglement, magnons carry an electric dipole moment. Here we report the first
+evidence of the existence of this electric dipole moment in a graphene quantum
+Hall ferromagnet using a Mach-Zehnder interferometer as a quantum sensor. By
+propagating towards the interferometer through an insulating bulk, the magnon
+electric dipole moment modifies the Aharonov-Bohm flux through the
+interferometer, changing both its phase and its visibility. In particular, we
+relate the phase shift to the sign of this electric dipole moment, and the
+exponential loss of visibility to the flux of emitted magnons. Finally, we
+probe the emission energy threshold of the magnons close to filling factor v=1.
+Approaching v=0, we observe that the emission energy threshold diminishes
+towards zero, which might be linked to the existence of gapless mode in the
+canted-antiferromagnetic (CAF) phase at v=0. The detection and manipulation of
+magnons based on their electric dipole open the field for a new type of
+coherent magnon quantum circuits that will be electrostatically controlled.",2102.02068v1
+2016-11-17,Parallel pumping for magnon spintronics: Amplification and manipulation of magnon spin currents on the micron-scale,"Magnonics and magnon spintronics aim at the utilization of spin waves and
+magnons, their quanta, for the construction of wave-based logic networks via
+the generation of pure all-magnon spin currents and their interfacing with
+electrical charge transport. The promise of efficient parallel data processing
+and low power consumption renders this field one of the most promising research
+areas in spintronics. In this context, the process of parallel parametric
+amplification, i.e., the conversion of microwave photons into magnons at one
+half of the microwave frequency, has proven to be a versatile tool. Its
+beneficial and unique properties, such as frequency and mode-selectivity, the
+possibility to excite spin waves in a wide wavevector range and the creation of
+phase-correlated wave pairs, render it one of the key methods of spin-wave
+generation and amplification.
+  The application of parallel parametric amplification to micro- and
+nanostructures is an important step towards the realization of magnonic
+networks. This is motivated not only by the fact that amplifiers are an
+important tool for the construction of any extended logic network but also by
+the unique properties of parallel parametric amplification, such as a
+phase-dependent amplification. Recently, the successful application of parallel
+parametric amplification to metallic microstructures has been reported. It has
+been demonstrated that parametric amplification provides an excellent tool to
+generate and to amplify spin waves in these systems. In particular, the
+amplification greatly benefits from the discreteness of the spin-wave spectra.
+This opens up new, interesting routes of spin-wave amplification and
+manipulation. In this Review, we give an overview over the recent developments
+and achievements in this field.",1611.05893v1
+2018-01-10,Topological magnon nodal-lines and absence of magnon spin Nernst effect in layered collinear antiferromagnets,"We propose the existence of a symmetry-protected topological Dirac nodal line
+(DNL) magnonic phase in layered honeycomb collinear antiferromagnets even in
+the presence of spin-orbit Dzyaloshinskii-Moriya interaction. We show that the
+magnon spin Nernst effect, predicted to occur in strictly two-dimensional (2D)
+honeycomb collinear antiferromagnets cancels out in the layered honeycomb
+collinear antiferromagnets. In other words, the magnon spin Nernst effect in
+each 2D antiferromagnetic layer cancels out the succeeding layer. Hence, the
+Berry curvature vanish in the entire Brillouin zone due to the combination of
+time-reversal and space-inversion ($\mathcal{PT}$) symmetry. However, upon
+symmetry breaking by an external magnetic field, we show that a non-vanishing
+Berry curvature and Chern number protected topological magnon bands are induced
+in the non-collinear spin structure. This leads to an experimentally accessible
+magnon thermal Hall effect in the $\mathcal{PT}$ symmetry-broken topological
+DNL magnonic phase of layered honeycomb antiferromagnets. We propose that the
+current predicted results can be experimentally investigated in the layered
+honeycomb antiferromagnets CaMn$_2$Sb$_2$, BaNi$_2$V$_2$O$_8$, and
+Bi$_3$Mn$_4$O$_{12}$(NO$_3$).",1801.03498v6
+2019-06-13,Impact of electromagnetic fields and heat on spin transport signals in Y$_{3}$Fe$_{5}$O$_{12}$,"Exploring new strategies to perform magnon logic is a key requirement for the
+further development of magnon-based spintronics. In this work, we realize a
+three-terminal magnon transport device to study the possibility of manipulating
+magnonic spin information transfer in a magnetic insulator via localized
+magnetic fields and heat generation. The device comprises two parallel Pt wires
+as well as a Cu center wire that are deposited on the ferrimagnetic insulator
+Y$_{3}$Fe$_{5}$O$_{12}$. While the Pt wires act as spin current injector and
+detector, the Cu wire is used to create local magnetostatic fields and
+additional heat, which impact both the magnetic configuration and the magnons
+within the Y$_{3}$Fe$_{5}$O$_{12}$ below. We show that these factors can create
+a non-local signal that shows similar features as compared to an electrically
+induced magnon flow. Furthermore, a modulation of the spin transport signal
+between the Pt wires is observed, which can be partly explained by thermally
+excited spin currents of different polarization. Our results indicate a
+potential way towards the manipulation of non-local magnon signals, which could
+be useful for magnon logic.",1906.05631v2
+2019-07-01,Spin transport in an electrically-driven magnon gas near Bose-Einstein condensation: Hartree-Fock-Keldysh theory,"An easy-plane ferromagnetic insulator in a uniform external magnetic field
+and in contact with a phonon bath and a normal metal bath is studied
+theoretically in the presence of dc spin current injection via the spin Hall
+effect in the metal. The Keldysh path integral formalism is used to model the
+magnon gas driven into a nonequilibrium steady state by mismatched bath
+temperatures and/or electrical injection, and we analyze the magnon system in
+the normal (uncondensed) state, but close to the instability to Bose-Einstein
+condensation (BEC), within the self-consistent Hartree-Fock approximation. We
+find that the steady state magnon distribution function generally has a
+non-thermal form that cannot be described by a single effective chemical
+potential and effective temperature. We also show that the BEC instability in
+the electrically-driven magnon system is signaled by a sign change in the
+imaginary part of the poles for long-wavelength magnon modes and by the
+divergence of the nonequilibrium magnon distribution function. In the presence
+of two bath temperatures, we find that the correlation length of the superfluid
+order parameter fluctuations exhibits nontrivial finite temperature crossover
+behaviors that are richer than the standard crossover behaviors obtained for
+the vacuum-superfluid transition in an equilibrium dilute Bose gas. We study
+the consequences of these thermal crossovers on the magnon spin conductivity
+and obtain an inverse square-root divergence in the spin conductivity in the
+vicinity of the electrically-induced BEC instability. A spintronics device
+capable of testing our spin transport predictions is discussed.",1907.01043v2
+2019-10-16,"Thermal Hall effect, spin Nernst effect, and spin density induced by thermal gradient in collinear ferrimagnets from magnon-phonon interaction","We theoretically study the intrinsic thermal Hall and spin Nernst effect in
+collinear ferrimagnets on a honeycomb lattice with broken inversion symmetry.
+The broken inversion symmetry allows in-plane Dzyaloshinskii-Moriya interaction
+between the nearest neighbors, which does not affect the magnon spectrum in the
+linear spin wave theory. However, the Dzyaloshinskii-Moriya interaction can
+induce large Berry curvature in the magnetoelastic excitation spectrum through
+the magnon-phonon interaction to produce thermal Hall current. Furthermore, we
+find that the magnetoelastic excitations transport spin, which is inherited
+from the magnon bands. Therefore, the thermal Hall current is accompanied by
+spin Nernst current. Because the magnon-phonon interaction does not conserve
+the spin, we also study the spin density induced by thermal gradient in the
+presence of magnon-phonon interaction. We find that the intrinsic part of the
+spin density shows no asymmetric spin accumulation near the boundary of the
+system having a stripe geometry. However, because of the magnon-phonon
+interaction, we find nonzero total spin density in the system having armchair
+edges. The extrinsic part of the spin density, on the other hand, shows
+asymmetric spin accumulation near the boundary for both armchair and zigzag
+edges because of the magnon-phonon interaction. In addition, we find nonzero
+total spin density in the system having zigzag edge.",1910.07206v2
+2020-01-31,Magnon valley Hall effect in CrI3-based vdW heterostructures,"Magnonic excitations in the two-dimensional (2D) van der Waals (vdW)
+ferromagnet CrI3 are studied. We find that bulk magnons exhibit a non-trivial
+topological band structure without the need for Dzyaloshinskii-Moriya (DM)
+interaction. This is shown in vdW heterostructures, consisting of single-layer
+CrI3 on top of different 2D materials as MoTe2, HfS2 and WSe2. We find
+numerically that the proposed substrates modify substantially the out-of-plane
+magnetic anisotropy on each sublattice of the CrI3 subsystem. The induced
+staggered anisotropy, combined with a proper band inversion, leads to the
+opening of a topological gap of the magnon spectrum. Since the gap is opened
+non-symmetrically at the K+ and K- points of the Brillouin zone, an imbalance
+in the magnon population between these two valleys can be created under a
+driving force. This phenomenon is in close analogy to the so-called valley Hall
+effect (VHE), and thus termed as magnon valley Hall effect (MVHE). In linear
+response to a temperature gradient we quantify this effect by the evaluation of
+the temperature-dependence of the magnon thermal Hall effect. These findings
+open a different avenue by adding the valley degrees of freedom besides the
+spin, in the study of magnons.",2001.11934v1
+2020-02-19,Manipulation of coupling and magnon transport in magnetic metal-insulator hybrid structures,"Ferromagnetic metals and insulators are widely used for generation, control
+and detection of magnon spin signals. Most magnonic structures are based
+primarily on either magnetic insulators or ferromagnetic metals, while
+heterostructures integrating both of them are less explored. Here, by
+introducing a Pt/yttrium iron garnet (YIG)/permalloy (Py) hybrid structure
+grown on Si substrate, we studied the magnetic coupling and magnon transmission
+across the interface of the two magnetic layers. We found that within this
+structure, Py and YIG exhibit an antiferromagnetic coupling field as strong as
+150 mT, as evidenced by both the vibrating-sample magnetometry and polarized
+neutron reflectometry measurements. By controlling individual layer thicknesses
+and external fields, we realize parallel and antiparallel magnetization
+configurations, which are further utilized to control the magnon current
+transmission. We show that a magnon spin valve with an ON/OFF ratio of ~130%
+can be realized out of this multilayer structure at room temperature through
+both spin pumping and spin Seebeck effect experiments. Thanks to the efficient
+control of magnon current and the compatibility with Si technology, the
+Pt/YIG/Py hybrid structure could potentially find applications in magnon-based
+logic and memory devices.",2002.08266v1
+2020-11-11,Magnon-assisted photon-phonon conversion in the presence of the structured environments,"Quantum conversion or interface is one of the most prominent protocols in
+quantum information processing and quantum state engineering. We propose a
+photon-phonon conversion protocol in a hybrid magnomechanical system comprising
+a microwave optical mode, a driven magnon mode and a mechanical-vibrating mode.
+The microwave photons in the optical cavity are coupled to the magnons by the
+magnetic-dipole interaction, and the latter are coupled to the mechanical
+phonons by the magnetostrictive interaction. With strong photon-magnon
+interaction and strong driving on magnon, an effective Hamiltonian is
+constructed to describe the conversion between photons and phonons nearby their
+resonant point. The cavity-magnon system can then play the role of a quantum
+memory. Moreover, the faithfulness of the photon-phonon conversion is estimated
+in terms of fidelities for state evolution and state-independent transfer. The
+former is discussed in the Lindblad master equation taking account the leakages
+of photon, phonon and magnon into consideration. The latter is derived by the
+Heisenberg-Langevin equation considering the non-Markovian noise from the
+structured environments for both optical and mechanical modes. The
+state-evolution fidelity is found to be robust to the weak leakage. The
+transfer fidelity can be maintained by the Ohmic and sub-Ohmic environments of
+the photons and is insensitive to the $1/f$ noise of the phonons. Our work thus
+provides an interesting application for the magnon system as a photon-phonon
+converter in the microwave regime.",2011.05642v2
+2022-06-10,Observing high-k magnons with Mie-resonance-enhanced Brillouin light scattering,"Magnonics is a prospective beyond CMOS technology which uses magnons, the
+quanta of spin waves, for low-power information processing. Many magnonic
+concepts and devices were recently demonstrated at macro- and microscale, and
+now these concepts need to be realized at nanoscale. Brillouin light scattering
+spectroscopy and microscopy (BLS) has become a standard technique for spin wave
+visualization and characterization, and enabled many pioneering magnonic
+experiments. However, due to its fundamental limit in maximum detectable magnon
+momentum, the conventional BLS cannot be used to detect nanoscale spin waves.
+Here we show that optically induced Mie resonances in dielectric nanoparticles
+can be used to extend the range of accessible spin wave wavevectors beyond the
+BLS fundamental limit. The method is universal and can be used in many magnonic
+experiments dealing with thermally excited as well as coherently excited
+high-momentum, short-wavelength spin waves. This discovery significantly
+extends the usability and relevance of the BLS technique for nanoscale magnonic
+research.",2206.05178v3
+2023-01-18,Charged magnons on the surface of a topological insulator,"We study a system of two-dimensional Dirac electrons (as is realized on the
+surface of a 3D topological insulator) coupled to an array of localized spins.
+The spins are coupled ferromagnetically to each other, forming an ordered
+ground state with low-energy spin-wave excitations (magnons). The Dirac
+electrons couple to the spins through a spin-dependent effective Zeeman field.
+The out-of-plane effective Zeeman field therefore serves as a Dirac mass that
+gaps the electronic spectrum. Once a spin is flipped, it creates a surrounding
+domain in which the sign of the Dirac mass is opposite to that of the rest of
+the sample. Therefore, an electronic bound state appears on the domain wall, as
+predicted by Jackiw and Rebbi. However, in a quantum magnet, a localized spin
+flip does not produce an eigenstate. Instead, the eigenstates correspond to
+delocalized spin waves (magnons). As in the case of the single flipped spin,
+the delocalized magnon also binds an in-gap electronic state. We name this
+excitation a `Jackiw-Rebbi-Magnon' (JRM) and study its signature in the dynamic
+spin susceptibility. When the sample is tunnel-coupled to an electronic
+reservoir, a magnon produced in a system without any electrons hybridizes with
+a JRM (which binds a single electron), producing magnon-JRM polaritons. For
+such a system, we identify a quantum phase transition when the magnon-JRM
+polariton energy falls below that of the fully polarized ferromagnetic ground
+state.",2301.07754v2
+2023-04-15,Temperature-anisotropy conjugate magnon squeezing in antiferromagnets,"Quantum squeezing is an essential asset in the field of quantum science and
+technology. In this study, we investigate the impact of temperature and
+anisotropy on squeezing of quantum fluctuations in two-mode magnon states
+within uniaxial antiferromagnetic materials. Through our analysis, we discover
+that the inherent nonlinearity in these bipartite magnon systems gives rise to
+a conjugate magnon squeezing effect across all energy eigenbasis states, driven
+by temperature and anisotropy. We show that temperature induces amplitude
+squeezing, whereas anisotropy leads to phase squeezing. In addition, we observe
+that the two-mode squeezing characteristic of magnon eigenenergy states is
+associated with amplitude squeezing. This highlights the constructive impact of
+temperature and the destructive impact of anisotropy on two-mode magnon
+squeezing. Nonetheless, our analysis shows that the destructive effect of
+anisotropy is bounded. We demonstrate this by showing that, at a given
+temperature, the squeezing of the momentum (phase) quadrature (or equivalently,
+the stretching of the position (amplitude) quadrature) approaches a constant
+function of anisotropy after a finite value of anisotropy. Moreover, our study
+demonstrates that higher magnon squeeze factors can be achieved at higher
+temperatures, smaller levels of anisotropy, and closer to the Brillouin zone
+center. All these characteristics are specific to low-energy magnons in the
+uniaxial antiferromagnetic materials that we examine here.",2304.07602v2
+2023-04-28,Interplay of electron-magnon scattering and spin-orbit induced electronic spin-flip fcattering in a two-band Stoner model,"Magnons are one of the carriers of angular momentum that are involved in the
+ultrafast magnetization dynamics in ferromagnets, but their contribution to the
+electronic dynamics and their interplay with other scattering process that
+occur during ultrafast demagnetization has not yet been studied in the
+framework of a microscopic dynamical model. The present paper presents such an
+investigation of electronic scattering dynamics in itinerant ferromagnets at
+the level of Boltzmann scattering integrals for the magnon distributions and
+spin-dependent electron distributions. In addition to electron-magnon
+scattering, we include spin-conserving and effective Elliott-Yafet like
+spin-flip electron-electron scattering processes and the influence of phonons.
+In our model system, the creation or annihilation of magnons leads to
+transitions between two spin-split electronic bands with energy and momentum
+conservation. Due to the presence of spin-orbit coupling, Coulomb scattering
+transitions between these bands are also possible, and we describe them on an
+equal footing in terms of Boltzmann scattering integrals. For an instantaneous
+carrier excitation process we analyze the influence of both interaction
+processes on the magnon and spin-dependent electron dynamics, and show that
+their interplay gives rise to an efficient creation of magnons at higher
+energies and wave vectors accompanied by only a small increase of the
+electronic spin polarization. These results present a microscopic dynamical
+scenario that shows how non-equilibrium magnons may dominate the magnetic
+response of a ferromagnet on ultrafast timescales.",2304.14978v1
+2023-06-28,Dipolar Ultrastrong Magnon-Magnon Coupling in a 3D Multilayered Artificial Spin-Vortex Ice,"Strongly-interacting nanomagnetic arrays are ideal systems for exploring
+reconfigurable magnonics. They provide huge microstate spaces and integrated
+solutions for storage and neuromorphic computing alongside GHz functionality.
+These systems may be broadly assessed by their range of reliably accessible
+states and the strength of magnon coupling phenomena and nonlinearities.
+  Increasingly, nanomagnetic systems are expanding into three-dimensional
+architectures. This has enhanced the range of available magnetic microstates
+and functional behaviours, but engineering control over 3D states and dynamics
+remains challenging.
+  Here, we introduce a 3D magnonic metamaterial composed from multilayered
+artificial spin ice nanoarrays. Comprising two magnetic layers separated by a
+non-magnetic spacer, each nanoisland may assume four macrospin or vortex states
+per magnetic layer. This creates a system with a rich $16^N$ microstate space
+and intense static and dynamic dipolar magnetic coupling.
+  The system exhibits a broad range of emergent phenomena driven by the strong
+inter-layer dipolar interaction, including ultrastrong magnon-magnon coupling
+with normalised coupling rates of $\frac{\Delta \omega}{\gamma} = 0.57$, GHz
+mode shifts in zero applied field and chirality-selective magneto-toroidal
+microstate programming and corresponding magnonic spectral control.",2306.16159v2
+2023-11-10,Perspective on Nanoscaled Magnonic Networks,"With the rapid development of artificial intelligence in recent years,
+mankind is facing an unprecedented demand for data processing. Today, almost
+all data processing is performed using electrons in conventional complementary
+metal-oxide-semiconductor (CMOS) circuits. Over the past few decades,
+scientists have been searching for faster and more efficient ways to process
+data. Now, magnons, the quanta of spin waves, show the potential for higher
+efficiency and lower energy consumption in solving some specific problems.
+While magnonics remains predominantly in the realm of academia, significant
+efforts are being made to explore the scientific and technological challenges
+of the field. Numerous proof-of-concept prototypes have already been
+successfully developed and tested in laboratories. In this article, we review
+the developed magnonic devices and discuss the current challenges in realizing
+magnonic circuits based on these building blocks. We look at the application of
+spin waves in neuromorphic networks, stochastic and reservoir computing and
+discuss the advantages over conventional electronics in these areas. We then
+introduce a new powerful tool, inverse design magnonics, which has the
+potential to revolutionize the field by enabling the precise design and
+optimization of magnonic devices in a short time. Finally, we provide a
+theoretical prediction of energy consumption and propose benchmarks for
+universal magnonic circuits.",2311.06129v1
+2023-11-16,Quantum tomography of magnons using Brillouin light scattering,"Quantum magnonics, an emerging field focusing on the study of magnons for
+quantum applications, requires precise measurement methods capable of resolving
+single magnons. Existing techniques introduce additional dissipation channels
+and are not apt for magnets in free space. Brillouin light scattering (BLS) is
+a well-established technique for probing the magnetization known for its high
+sensitivity and temporal resolution. The coupling between magnons and photons
+is controlled by a laser input, so it can be switched off when a measurement is
+not needed. In this article, we theoretically investigate the efficacy of BLS
+for quantum tomography of magnons. We model a finite optomagnonic waveguide,
+including the optical noise added by the dielectric, to calculate the
+signal-to-noise ratio (SNR). We find that the SNR is typically low due to a
+small magneto-optical coupling; nevertheless, it can be significantly enhanced
+by injecting squeezed vacuum into the waveguide. We reconstruct the density
+matrix of the magnons from the statistics of the output photons using a maximum
+likelihood estimate. The classical component of a magnon state, defined as the
+regions of positive Wigner function, can be reconstructed with a high accuracy
+while the non-classical component necessitates either a higher SNR or a larger
+dataset. The latter requires more compact data structures and advanced
+algorithms for post-processing. The SNR is limited partially by the input laser
+power that can be increased by designing the optomagnonic cavity with a heat
+sink.",2311.10152v2
+2023-12-15,Topological magnon gap engineering in van der Waals CrI$_3$ ferromagnets,"The microscopic origin of the topological magnon band gap in CrI$_3$
+ferromagnets has been a subject of controversy for years since two main models
+with distinct characteristics, i.e., Dzyaloshinskii-Moriya (DM) and Kitaev,
+provided possible explanations with different outcome implications. Here we
+investigate the angular magnetic field dependence of the magnon gap of CrI$_3$
+by elucidating what main contributions play a major role in its generation. We
+implement stochastic atomistic spin dynamics simulations to compare the impact
+of these two spin interactions on the magnon spectra. We observe three distinct
+magnetic field dependencies between these two gap opening mechanisms. First, we
+demonstrate that the Kitaev-induced magnon gap is influenced by both the
+direction and amplitude of the applied magnetic field, while the DM-induced gap
+is solely affected by the magnetic field direction. Second, the position of the
+Dirac cones within the Kitaev-induced magnon gap shifts in response to changes
+in the magnetic field direction, whereas they remain unaffected by the magnetic
+field direction in the DM-induced gap scenario. Third, we find a
+direct-indirect magnon band-gap transition in the Kitaev model by varying the
+applied magnetic field direction. These differences may distinguish the origin
+of topological magnon gaps in CrI$_3$ and other van der Waals magnetic layers.
+Our findings pave the way for exploration and engineering topological gaps in
+van der Waals materials.",2312.09903v1
+2023-12-22,Magnon-assisted magnetization reversal of Ni81Fe19 nanostripes on Y3Fe5O12 with different interfaces,"Magnetic bit writing by short-wave magnons without conversion to the
+electrical domain is expected to be a game-changer for in-memory computing
+architectures. Recently, the reversal of nanomagnets by propagating magnons was
+demonstrated. However, experiments have not yet explored different wavelengths
+and the nonlinear excitation regime of magnons required for computational
+tasks. We report on the magnetization reversal of individual 20-nm-thick
+Ni81Fe19 (Py) nanostripes integrated onto 113-nm-thick yttrium iron garnet
+(YIG). We suppress direct interlayer exchange coupling by an intermediate layer
+such as Cu and SiO2. Exciting magnons in YIG with wavelengths {\lambda} down to
+148 nm we observe the reversal of the integrated ferromagnets in a small
+opposing field of 14 mT. Magnons with a small wavelength of {\lambda} = 195 nm,
+i.e., twice the width of the Py nanostripes, induced the reversal at an
+unprecedentedly small spin precessional power of about 1 nW after propagating
+over 15 {\mu}m in YIG. Considerations based on dynamic dipolar coupling explain
+the observed wavelength dependence of magnon-induced reversal efficiency. For
+an increased power the stripes reversed in an opposing field of only about 1
+mT. Our findings are important for the practical implementation of nonvolatile
+storage of broadband magnon signals in YIG by means of bistable nanomagnets
+without the need of an appreciable global magnetic field.",2312.15107v1
+2024-01-19,Exploration of magnon-magnon coupling in an antidot lattice: The role of non-uniform magnetization texture,"We numerically study the spin wave dynamics in an antidot lattice based on a
+Co/Pd multilayer structure with reduced perpendicular magnetic anisotropy at
+the edges of the antidots. This structure forms a magnonic crystal with a
+periodic antidot pattern and a periodic magnetization configuration consisting
+of out-of-plane magnetized bulk and in-plane magnetized rims. Our results show
+the different behavior of spin waves in the bulk and in the rims under varying
+out-of-plane external magnetic field strength, revealing complex spin-wave
+spectra and hybridizations between the modes of these two subsystems. A
+particularly strong magnon-magnon coupling, due to exchange interactions, is
+found between the fundamental bulk spin-wave mode and the second-order radial
+rim modes. However, the dynamical coupling between the spin-wave modes at low
+frequencies, involving the first-order radial rim modes, is masked by the
+changes in the static magnetization at the bulk-rim interface with magnetic
+field changes. The study expands the horizons of magnonic-crystal research by
+combining periodic structural patterning and non-collinear magnetization
+texture to achieve strong magnon-magnon coupling, highlighting the significant
+role of exchange interactions in the coupling.",2401.10540v2
+2024-02-14,Dynamic magnetic phase transition induced by parametric magnon pumping,"Uncovering pathways to optically drive magnetic order-disorder transitions on
+ultrashort timescales can lead to the realization of novel out-of-equilibrium
+quantum phenomena. A long-sought pathway is to directly excite a highly
+non-thermal energy-momentum distribution of magnons, bypassing both charge and
+lattice degrees of freedom. However, this remains elusive owing to the weak
+coupling and large momentum mismatch between photons and magnons. Here we
+demonstrate strong parametric excitation of magnons across the entire Brillouin
+zone of the antiferromagnetic insulator Sr$_2$Cu$_3$O$_4$Cl$_2$ by periodically
+modulating the superexchange interaction with the electric field of light. The
+excitation efficiency is greatly enhanced by tuning to the van Hove singularity
+in the magnon spectrum, sufficient to transiently collapse the
+antiferromagnetic state using a pulsed laser field of 10$^9$ V/m. The order
+parameter recovery timescale increases by over 1000 times as a function of
+excitation density, reflecting a crossover from high- to low-energy magnon
+dominated decay dynamics. This electric-field induced parametric magnon pumping
+mechanism is applicable to a broad range of magnetic insulators and opens up
+the possibility of dynamically engineering magnon distributions by design.",2402.09521v1
+2024-03-02,Signatures of magnon hydrodynamics in an atomically-thin ferromagnet,"Strong interactions between particles can lead to emergent collective
+excitations. These phenomena have been extensively established in electronic
+systems, but are also expected to occur for gases of neutral particles like
+spin waves, also known as magnons, in a ferromagnet. In a hydrodynamic regime
+where magnons are strongly interacting, they can form a slow collective density
+mode -- in analogy to sound waves in water -- with characteristic low-frequency
+signatures. While such a mode has been predicted in theory, its signatures have
+yet to be observed experimentally. In this work, we isolate atomically-thin
+sheets of ferromagnetic CrCl$_3$ where magnon interactions are strong, and
+develop a technique to measure its collective magnon dynamics via the quantum
+coherence of nearby Nitrogen-Vacancy (NV) centers in diamond. We find that the
+thermal magnetic fluctuations generated by CrCl$_3$ exhibit an anomalous
+temperature-dependence, whereby fluctuations increase upon decreasing
+temperature. Our analysis reveals that this anomalous trend is a consequence of
+the damping rate of a low-energy magnon sound mode which sharpens as magnon
+interactions increase with increasing temperature, providing a first glimpse of
+the magnon hydrodynamic regime.",2403.01057v1
+1996-12-11,Magnon-magnon interactions in the Spin-Peierls compound CuGeO_3,"In a magnetic substance the gap in the Raman spectrum, Delta_R, is
+approximatively twice the value of the neutron scattering gap, Delta_S, if the
+the magnetic excitations (magnons) are only weakly interacting.
+  But for CuGeO_3 the experimentally observed ratio Delta_R/Delta_S is
+approximatively 1.49-1.78, indicating attractive magnon-magnon interactions in
+the quasi-1D Spin-Peierls compound CuGe_3.
+  We present numerical estimates for Delta_R/Delta_S from exact diagonalization
+studies for finite chains and find agreement with experiment for intermediate
+values of the frustration parameter alpha.
+  An analysis of the numerical Raman intensity leads us to postulate a
+continuum of two-magnon bound states in the Spin-Peierls phase. We discuss in
+detail the numerical method used, the dependence of the results on the model
+parameters and a novel matrix-element effect due to the dimerization of the
+Raman-operator in the Spin-Peierls phase.",9612101v1
+1998-10-07,From spinons to magnons in explicit and spontaneously dimerized antiferromagnetic chains,"We reconsider the excitation spectra of a dimerized and frustrated
+antiferromagnetic Heisenberg chain. This model is taken as the simpler example
+of compiting spontaneous and explicit dimerization relevant for Spin-Peierls
+compounds. The bosonized theory is a two frequency Sine-Gordon field theory. We
+analize the excitation spectrum by semiclassical methods. The elementary
+triplet excitation corresponds to an extended magnon whose radius diverge for
+vanishing dimerization. The internal oscilations of the magnon give rise to a
+series of excited state until another magnon is emited and a two magnon
+continuum is reached. We discuss, for weak dimerization, in which way the
+magnon forms as a result of a spinon-spinon interaction potential.",9810073v1
+2003-02-24,Magnon-assisted transport and thermopower in ferromagnet-normal metal tunnel junctions,"We develop a theoretical model of magnon-assisted transport in a mesoscopic
+tunnel junction between a ferromagnetic metal and a normal (non-magnetic)
+metal. The current response to a bias voltage is dominated by the contribution
+of elastic processes rather than magnon-assisted processes and the degree of
+spin polarization of the current, parameterized by a function $P (\Pi_{\uparrow
+(\downarrow)},\Pi_{N})$, $0 \leq P \leq 1$, depends on the relative sizes of
+the majority $\Pi_{\uparrow}$ and minority $\Pi_{\downarrow}$ band Fermi
+surface in the ferromagnet and of the Fermi surface of the normal metal
+$\Pi_{N}$. On the other hand, magnon-assisted tunneling gives the dominant
+contribution to the current response to a temperature difference across the
+junction. The resulting thermopower is large, $S \sim - (k_B/e)
+(k_BT/\omega_{D})^{3/2} P (\Pi_{\uparrow (\downarrow)},\Pi_{N})$, where the
+temperature dependent factor $(k_{B}T/\omega_{D})^{3/2}$ reflects the
+fractional change in the net magnetization of the ferromagnet due to thermal
+magnons at temperature $T$ (Bloch's $T^{3/2}$ law) and $\omega_{D}$ is the
+magnon Debye energy.",0302485v1
+2003-06-24,Sound attenuation on the Bose-Einstein condensation of magnons in TlCuCl_3,"We investigated experimentally and theoretically sound attenuation in the
+quantum spin system TlCuCl_3 in magnetic fields at low temperatures. Near the
+point of Bose-Einstein condensation (BEC) of magnons a sharp peak in the sound
+attenuation is observed. The peak demonstrates a hysteresis as function of the
+magnetic field pointing to a first-order contribution to the transition. The
+sound damping has a Drude-like form arising as a result of hardcore
+magnon-magnon collisions. The strength of the coupling between lattice and
+magnons is estimated from the experimental data. The puzzling relationship
+between the transition temperature and the concentration of magnons is
+explained by their ""relativistic"" dispersion.",0306623v1
+2006-10-28,Exact one- and two-particle excitation spectra of acute-angle helimagnets above their saturation magnetic field,"The two-magnon problem for the frustrated XXZ spin-1/2 Heisenberg Hamiltonian
+and external magnetic fields exceeding the saturation field Bs is considered.
+We show that the problem can be exactly mapped onto an effective tight-binding
+impurity problem. It allows to obtain explicit exact expressions for the
+two-magnon Green's functions for arbitrary dimension and number of
+interactions. We apply this theory to a quasi-one dimensional helimagnet with
+ferromagnetic nearest neighbor J1 < 0 and antiferromagnetic next-nearest
+neighbor J2 > 0 interactions. An outstanding feature of the excitation spectrum
+is the existence of two-magnon bound states. This leads to deviations of the
+saturation field Bs from its classical value Bs(classical) which coincides with
+the one-magnon instability. For the refined frustration ratio |J2/J1|> 0.374661
+the minimum of the two-magnon spectrum occurs at the boundary of the Brillouin
+zone. Based on the two-magnon approach, we propose general analytic expressions
+for the saturation field Bs, confirming known previous results for
+one-dimensional isotropic systems, but explore also the role of interchain and
+long-ranged intrachain interactions as well as of the exchange anisotropy.",0610801v1
+2007-11-14,Magnetic-Field Induced Bose-Einstein Condensation of Magnons and Critical Behavior in Interacting Spin Dimer System TlCuCl$_3$,"Magnetization measurements were performed to investigate the critical
+behavior of the field-induced magnetic ordering in gapped spin system
+TlCuCl$_3$. The critical density of the magnons was obtained as a function of
+temperature and the magnon-magnon interaction constant was evaluated. The
+experimental phase boundary for $T < 5$ K agrees almost perfectly with the
+magnon BEC theory based on the Hartree-Fock approximation with realistic
+dispersion relations. The phase boundary can be described by the power law
+$[H_{N}(T)-H_{c}] propto T^{phi}$. With decreasing fitting temperature range,
+the critical exponent ${phi}$ decreases and converges at $phi_{BEC} =3/2$
+predicted by the magnon BEC theory.",0711.2110v1
+2008-01-14,Finite size effects for giant magnons on physical strings,"Using finite gap methods, we find the leading order finite size corrections
+for an arbitrary number of giant magnons on physical strings, where the sum of
+the momenta is a multiple of 2\pi. Our results are valid for the
+Hofman-Maldacena fundamental giant magnons as well as their dyonic
+generalizations. The energy corrections turn out to be surprisingly simple,
+especially if all the magnons are fundamental, and at leading order are
+independent of the magnon flavors. We also show how to use the Bethe ansatz to
+find finite size corrections for dyonic giant magnons with large R-charges.",0801.2064v2
+2008-10-27,N-body Dynamics of Giant Magnons in RxS2,"We pursue the question of multi-magnon dynamics, focusing on the simplest
+case of magnons moving on RxS2 and working at the semiclassical level. Through
+a Pohlmeyer reduction, the problem reduces to another well known integrable
+field theory, the sine-Gordon model, which can be exactly described through an
+N-body model of Calogero type. The two theories coincide at the level of
+equations of motion, but physical quantities like the energies (of magnons and
+solitons) and the associated phase shifts are different. We start from the
+equivalence of the two systems at the level of equations of motion and require
+that the new (string theory) model reproduces the correct magnon energies and
+the phase shift, both of which differ from the soliton case. From the
+comparison of energies we suggest a Hamiltonian, and from requiring the correct
+phase shift we are led to a nontrivial Poisson structure representing the
+magnons.",0810.4548v1
+2009-02-09,Wrapping in maximally supersymmetric and marginally deformed N=4 Yang-Mills,"In this note we give evidence for an equality of the spectra, including
+wrapping, of the SU(2)-sector spin chain for real deformations beta and
+beta+1/L, in marginally beta-deformed N=4 Yang-Mills, which appears after
+relaxing the cyclicity constraint. Evidence for the equality is given by
+evaluating the first wrapping correction to the energy of the undeformed magnon
+of momentum pi, and the beta=1/2, physical magnon, for several spin chain
+lengths L. We also show that the term of maximal transcendentality coincides
+for both magnons to all L. As a by-product we provide an expression for the
+first wrapping correction to the beta = 1/2 single-magnon operator dimension,
+valid for all even L. We then apply the symmetry to the magnon dispersion
+relation of N=4, obtaining its first wrapping correction for a discrete set of
+magnon momenta.",0902.1427v3
+2009-03-19,Dyonic Giant Magnons in CP^3: Strings and Curves at Finite J,"This paper studies giant magnons in AdS_4 x CP^3 using both the string
+sigma-model and the algebraic curve. We complete the dictionary of solutions by
+finding the dyonic generalisation of the CP^1 string solution, which matches
+the `small' giant magnon in the algebraic curve, and by pointing out that the
+solution recently constructed by the dressing method is the `big' giant magnon.
+We then use the curve to compute finite-J corrections to all cases, which for
+the non-dyonic cases always match the AFZ result. For the dyonic RP^3 magnon we
+recover the S^5 answer, but for the `small' and `big' giant magnons we obtain
+new corrections.",0903.3365v2
+2010-02-21,Vacuum entanglement governs the bosonic character of magnons,"It is well known that magnons, elementary excitations in a magnetic material,
+behave as bosons when their density is low. We study how the bosonic character
+of magnons is governed by the amount of a multipartite entanglement in the
+vacuum state on which magnons are excited. We show that if the multipartite
+entanglement is strong, magnons cease to be bosons. We also consider some
+examples, such as ground states of the Heisenberg ferromagnet and the
+transverse Ising model, the condensation of magnons, the one-way quantum
+computer, and Kitaev's toric code. Our result provides insights into the
+quantum statistics of elementary excitations in these models, and into the
+reason why a non-local transformation, such as the Jordan-Wigner
+transformation, is necessary for some many-body systems.",1002.4010v2
+2011-03-07,Theoretical prediction of rotating magnon wavepacket in ferromagnets,"We theoretically show that the magnon wavepacket has a rotational motion in
+two ways; a self-rotation and a motion along the boundary of the sample (edge
+current). They are similar to cyclotron motion of electrons, but unlike
+electrons the magnons have no charge and the rotation is not due to Lorenz
+force. These rotational motions are caused by the Berry phase in momentum space
+from magnon band structure. Furthermore, these rotational motions of the magnon
+give an additional correction term to the magnon Hall effect. We also discuss
+the Berry curvature effect in the classical limit of long-wavelength
+magnetostatic spin waves having macroscopic coherence length.",1103.1221v3
+2011-03-11,Spin pumping by parametrically excited exchange magnons,"We experimentally show that exchange magnons can be detected using a
+combination of spin pumping and inverse spin-Hall effect (iSHE) proving its
+wavelength integrating capability down to the sub-micrometer scale. The magnons
+were injected in a ferrimagnetic yttrium iron garnet film by parametric pumping
+and the iSHE-induced voltage was detected in an attached Pt layer. The role of
+the density, wavelength, and spatial localization of the magnons for the spin
+pumping efficiency is revealed. This study opens the field of the magnon-based
+information processing to magnons with nano-scale wavelengths.",1103.2229v2
+2012-09-15,Magnon-phonon coupling unmasked: a direct measurement of magnon temperature,"Thermoelectric phenomena in magnetic materials present tantalizing
+possibilities for manipulating spin-information using heat in future 'spin
+caloritronic' devices. Key to unraveling their underlying physics is to
+understand spin-lattice interactions, i.e. the coupling between magnons (the
+quanta of magnetization excitations) and phonons (the quanta of lattice
+vibrations). Here, we present the first measurements of the spatial
+distribution of magnon temperature in a magnetic system subject to a lateral
+thermal (i.e. phonon temperature) gradient and demonstrate that, contrary to
+currently accepted theory, the magnon and phonon temperatures do not differ.
+This result has profound implications. In particular, it re-opens the question
+of how the spin Seebeck effect-which allows spin currents to be produced from
+thermal gradients, and is arguably the most intriguing and technologically
+relevant thermoelectric phenomenon of all-can exist, and which physics
+underpins it. Specifically, it reveals that if the general framework of the
+current theory of the effect holds, we must adopt a new concept of spectrally
+non-uniform magnon temperature.",1209.3405v2
+2012-11-20,Bond Randomness Induced Magnon Decoherence in a Spin-1/2 Ladder Compound,"We have used a combination of neutron resonant spin-echo and triple-axis
+spectroscopies to determine the energy and linewidth of the magnon resonance in
+IPA-Cu(Cl$_{0.95}$Br$_{0.05}$)$_3$, a model spin-1/2 ladder antiferromagnet
+where Br substitution induces bond randomness. We find that the bond defects
+induce a blueshift, $\delta \Delta$, and broadening, $\delta \Gamma$, of the
+magnon gap excitation compared to the pure compound. At temperatures exceeding
+the energy scale of the inter-ladder exchange interactions, $\delta \Delta$ and
+$\delta \Gamma$ are temperature independent within the experimental error, in
+agreement with Matthiessen's rule according to which magnon-defect scattering
+yields a temperature independent contribution to the magnon mean free path.
+Upon cooling, $\delta \Delta$ and $\delta \Gamma$ become temperature dependent
+and saturate at values lower than those observed at higher temperature,
+consistent with the crossover from one-dimensional to two-dimensional spin
+correlations with decreasing temperature previously observed in pure
+IPA-CuCl$_3$. These results indicate limitations in the applicability of
+Matthiessen's rule for magnon scattering in low-dimensional magnets.",1211.4741v1
+2016-02-09,Topological magnon bound-states in periodically modulated Heisenberg XXZ chains,"Strongly interacting topological states in multi-particle quantum systems
+pose great challenges to both theory and experiment. Recently, bound states of
+elementary spin waves (magnons) in quantum magnets have been experimentally
+observed in quantum Heisenberg chains comprising ultracold Bose atoms in
+optical lattices. Here, we explore a strongly interacting topological state
+called topological magnon bound-state in the quantum Heisenberg chain under
+cotranslational symmetry. We find that the cotranslational symmetry is the key
+to the definition of a topological invariant for multi-particle quantum states,
+which enables us to characterize the topological features of multi-magnon
+excitations. We calculate energy spectra, density distributions, correlations
+and Chern numbers of the two-magnon bound-states and show the existence of
+topological protected edge bound-states. Our study not only opens a new
+prospect to pursue topological magnon bound-states, but also gives insights
+into the characterization and understanding of strongly interacting topological
+states.",1602.03217v2
+2016-02-13,Weyl magnons in breathing pyrochlore antiferromagnets,"Frustrated quantum magnets not only provide exotic ground states and unusual
+magnetic structures, but also support unconventional excitations in many cases.
+Using a physically relevant spin model for a breathing pyrochlore lattice, we
+discuss the presence of topological linear band crossings of magnons in
+antiferromagnets. These are the analogs of Weyl fermions in electronic systems,
+which we dub Weyl magnons. The bulk Weyl magnon implies the presence of chiral
+magnon surface states forming arcs at finite energy. We argue that such
+antiferromagnets present a unique example in which Weyl points can be
+manipulated in situ in the laboratory by applied fields. We discuss their
+appearance specifically in the breathing pyrochlore lattice, and give some
+general discussion of conditions to find Weyl magnons and how they may be
+probed experimentally. Our work may inspire a re-examination of the magnetic
+excitations in many magnetically ordered systems.",1602.04288v2
+2016-06-24,Tunable magnon Weyl points in ferromagnetic pyrochlores,"The dispersion relations of magnons in ferromagnetic pyrochlores with
+Dzyaloshinskii-Moriya interaction is shown to possess Weyl points, i.\,e.,
+pairs of topological nontrivial crossings of two magnon branches with opposite
+topological charge. As a consequence of their topological nature, their
+projections onto a surface are connected by magnon arcs, thereby resembling
+closely Fermi arcs of electronic Weyl semimetals. On top of this, the positions
+of the Weyl points in reciprocal space can be tuned widely by an external
+magnetic field: rotated within the surface plane, the Weyl points and magnon
+arcs are rotated as well; tilting the magnetic field out-of-plane shifts the
+Weyl points toward the center $\bar{\Gamma}$ of the surface Brillouin zone. The
+theory is valid for the class of ferromagnetic pyrochlores, i.\,e.,
+three-dimensional extensions of topological magnon insulators on kagome
+lattices. In this Letter, we focus on the $(111)$ surface, identify candidates
+of established ferromagnetic pyrochlores which apply to the considered spin
+model, and suggest experiments for the detection of the topological features.",1606.07612v1
+2017-02-14,Inelastic Light Scattering Spectroscopy of Magnons and Phonons in Nickel Oxide: Effects of Temperature,"We report results of an investigation of the temperature dependence of the
+magnon and phonon frequencies in NiO. A combination of Brillouin - Mandelstam
+and Raman spectroscopies allowed us to elucidate the evolution of the phonon
+and magnon spectral signatures from the Brillouin zone center (GHz range) to
+the second-order peaks from the zone boundary (THz range). The
+temperature-dependent behavior of the magnon and phonon bands in the NiO
+spectrum indicates the presence of antiferromagnetic (AF) order fluctuation or
+a persistent AF state at temperatures above the Neel temperature (T=523 K).
+Tuning the intensity of the excitation laser provides a method for
+disentangling the features of magnons from acoustic phonons without the
+application of a magnetic field. Our results are useful for interpretation of
+the inelastic-light scattering spectrum of NiO, and add to the knowledge of its
+magnon properties important for THz spintronic devices.",1702.04366v1
+2017-02-22,Magnonic crystals for data processing,"Magnons - the quanta of spin waves - propagating in magnetic materials with
+wavelengths at the nanometer-scale and carrying information in the form of an
+angular momentum, can be used as data carriers in next-generation, nano-sized
+low-loss information processing systems. In this respect, artificial magnetic
+materials with properties periodically varied in space, known as magnonic
+crystals, are especially promising for controlling and manipulating the magnon
+currents. In this article, different approaches for the realization of static,
+reconfigurable, and dynamic magnonic crystals are presented along with a
+variety of novel wave phenomena discovered in these crystals. Special attention
+is devoted to the utilization of magnonic crystals for processing of analog and
+digital information.",1702.06701v1
+2017-02-26,Magnon-photon coupling in antiferromagnets,"Magnon-photon coupling in antiferromagnets has many attractive features that
+do not exist in ferro- or ferrimagnets. We show quantum-mechanically that, in
+the absence of an external field, one of the two degenerated spin wave bands
+couples with photons while the other does not. The photon mode anticrosses with
+the coupled spin waves when their frequencies are close to each other. Similar
+to its ferromagnetic counterpart, the magnon-photon coupling strength is
+proportional to the square root of number of spins $\sqrt{N}$ in
+antiferromagnets. An external field removes the spin wave degeneracy and both
+spin wave bands couple to the photons, resulting in two anticrossings between
+the magnons and photons. Two transmission peaks were observed near the
+anticrossing frequency. The maximum damping that allows clear discrimination of
+the two transmission peaks is proportional to $\sqrt{N}$ and it's well below
+the damping of antiferromagnetic insulators. Therefore the strong magnon-photon
+coupling can be realized in antiferromagnets and the coherent information
+transfer between the photons and magnons is possible.",1702.07977v1
+2017-03-09,Dynamics and inertia of a skyrmion in chiral magnets and interfaces: A linear response approach based on magnon excitations,"Taking all the magnon modes into account, we derive the skyrmion dynamics in
+response to a weak external drive. A skyrmion has rotational symmetry and the
+magnon modes can be characterized by an angular momentum. For a weak distortion
+of a skyrmion, only the magnon modes with an angular momentum $|m|=1$ govern
+the dynamics of skyrmion topological center. The skyrmion inertia is determined
+by the magnon modes in the continuum spectrum. For a skyrmion driven by a
+magnetic field gradient or by a spin transfer torque generated by a current,
+the dynamical response is practically instantaneous. This justifies the rigid
+skyrmion approximation used in Thiele's collective coordinate approach. For a
+skyrmion driven by a spin Hall torque, the torque couples to the skyrmion
+motion through the magnons in the continuum and damping, therefore the skyrmion
+dynamics shows sizable inertia in this case. The trajectory of a skyrmion is an
+ellipse for an ac drive of spin Hall torque.",1703.03099v2
+2018-02-15,Electron drag in ferromagnetic structures separated by an insulating interface,"We consider electron drag in a system of two ferromagnetic layers separated
+by an insulating interface. The source of it is expected to be magnon-electron
+interactions. Namely, we assume that the external voltage is applied to the
+""active"" layer stimulating electric current through this layer. In its turn,
+the scattering of the current-carrying electrons by magnons leads to a magnon
+drag current within this layer. The 3-magnons interactions between magnons in
+the two layers (being of non-local nature) lead to magnon drag within the
+""passive"" layer which, correspondingly, produce electron drag current via
+processes of magnon-electron scattering. We estimate the drag current and
+compare it to the phonon-induced one.",1802.05485v1
+2018-02-21,Magnonic Spin-Transfer Torque in Ferromagnet/Antiferromagnet/Ferromagnet Trilayer,"In an antiferromagnet (AF) with uniaxial anisotropy, spin-up and spin-down
+magnons coexist and form an intrinsic degree of freedom resembling electrons.
+When polarized by an adjacent ferromagnet (F), a magnonic pure spin current can
+be thermally generated in an AF. We explore thermal magnon transport in an
+insulating F/AF/F trilayer where propagating magnons inside the AF spacer can
+transfer angular momenta between the two Fs. We find that a sufficiently large
+temperature gradient can switch the downstream F via magnonic spin-transfer
+torque if it is initially antiparallel with the upstream F. A reciprocal
+switching is achievable by reversing the temperature gradient. Using typical
+material parameters, we estimate the threshold to be less than 1 K/nm at room
+temperature, which can be reduced by raising temperature and enhancing the
+interfacial exchange coupling.",1802.07709v2
+2018-04-04,Anomalous nonlinearity of the magnonic edge mode,"Nonlinearity of magneto-dynamics is typically described by a single constant,
+$\mathcal{N}$, with positive and negative values indicating repulsion and
+attraction of magnons, respectively. In thin magnetic films with easy-plane
+magnetic anisotropy, magnon attraction is typically achieved for an in-plane
+magnetization. At sufficient stimulus, e.g. via application of spin transfer
+torque, the attraction can give rise to self-localized magnetic solitons, such
+as spin wave bullets, which shrink as their amplitude increases. In contrast,
+for an oblique magnetization above a certain critical angle, the repulsion of
+magnons only allows for propagating modes, which expand when pumped more
+strongly. Here we demonstrate, both analytically and using micromagnetic
+simulations, that such a dichotomic description is inadequate for magnonic edge
+modes, which naturally appear in confined magnetic systems. In particular, we
+demonstrate that the confinement potential of such modes is nonlinear in nature
+and its contribution makes $\mathcal{N}$ non-monotonically dependent on their
+amplitude. As a prominent example, edge modes show compression and expansion
+for negative and positive $\mathcal{N}$, yet remain localized. In striking
+contrast to the extended geometries, edge magnons might also repeal even for an
+in-plane magnetization.",1804.01585v1
+2018-11-22,Topological magnon bands for magnonics,"Topological excitations in magnetically ordered systems have attracted much
+attention lately. We report on topological magnon bands in ferromagnetic
+Shastry-Sutherland lattices whose edge modes can be put to use in magnonic
+devices. The synergy of Dzyaloshinskii-Moriya interactions and geometrical
+frustration is responsible for the topologically non-trivial character. Using
+exact spin wave theory we determine the finite Chern numbers of the magnon
+bands which give rise to chiral edge states. The quadratic band crossing point
+vanishes due the present anisotropies and the system enters a topological
+phase. We calculate the thermal Hall conductivity as an experimental signature
+of the topological phase. Different promising compounds are discussed as
+possible physical realizations of ferromagnetic Shastry-Sutherland lattices
+hosting the required antisymmetric Dzyaloshinskii-Moriya interactions. Routes
+to applications in magnonics are pointed out.",1811.08981v2
+2016-05-28,"Magnon Waves on Chains of YIG particles: Dispersion Relations, Faraday Rotation, and Power Transmission","We calculate the dispersion relations for magnon waves on a periodic chain of
+spherical or cylindrical Yttrium Iron Garnet (YIG) particles. We use the
+quasistatic approximation, appropriate when $kd \ll 1$, where $k$ is the wave
+number and $d$ the interparticle spacing. In this regime, because of the
+magnetic dipole-dipole interaction between the localized magnetic excitations
+on neighboring particles, dispersive magnon waves can propagate along the
+chain. The waves are analogous to plasmonic waves generated by electric
+dipole-dipole interactions between plasmons on neighboring metallic particles.
+The magnon waves can be longitudinal ($L$), transverse ($T$), or elliptically
+polarized. We find that a linearly polarized magnon wave undergoes a Faraday
+rotation as it propagates along the chain. The amount of Faraday rotation can
+be tuned by varying the off-diagonal component of the permeability tensor. We
+also discuss the possibility of wireless power transmission along the chain
+using these coupled magnon waves.",1605.08931v1
+2016-08-03,Influence of yttrium iron garnet thickness and heater opacity on the nonlocal transport of electrically and thermally excited magnons,"We studied the nonlocal transport behavior of both electrically and thermally
+excited magnons in yttrium iron garnet (YIG) as a function of its thickness.
+For electrically injected magnons, the nonlocal signals decrease monotonically
+as the YIG thickness increases. For the nonlocal behavior of the thermally
+generated magnons, or the nonlocal spin Seebeck effect (SSE), we observed a
+sign reversal which occurs at a certain heater-detector distance, and it is
+influenced by both the opacity of the YIG/heater interface and the YIG
+thickness. Our nonlocal SSE results can be qualitatively explained by the
+bulk-driven SSE mechanism together with the magnon diffusion model. Using a
+two-dimensional finite element model (2D-FEM), we estimated the bulk spin
+Seebeck coefficient of YIG at room temperature. The quantitative disagreement
+between the experimental and modeled results indicates more complex processes
+going on in addition to magnon diffusion and relaxation, especially close to
+the contacts.",1608.01178v1
+2016-08-08,Reconstruction of an effective magnon mean free path distribution from spin Seebeck measurements in thin films,"A thorough understanding of the mean-free-path (MFP) distribution of the
+energy carriers is crucial to engineer and tune the transport properties of
+materials. In this context, a significant body of work has investigated the
+phonon and electron MFP distribution, however, similar studies of the magnon
+MFP distribution have not been carried out so far. In this work, we used
+thickness-dependence measurements of the longitudinal spin Seebeck (LSSE)
+effect of yttrium iron garnet films to reconstruct the cumulative distribution
+of a SSE related effective magnon MFP. By using the experimental data reported
+by Guo et al. [Phys. Rev. X 6, 031012 (2016)], we adapted the phonon MFP
+reconstruction algorithm proposed by A.J. Minnich, [Phys. Rev. Lett. 109,
+205901 (2012)] and apply it to magnons. The reconstruction showed that magnons
+with different MFP contribute in different manner to the total LSSE and the
+effective magnon MFP distribution spreads far beyond their typical averaged
+values.",1608.02474v3
+2017-10-18,Strong Coupling of 3D Cavity Photons to Travelling Magnons At Low Temperatures,"We demonstrate strong coupling between travelling magnons in an Yttrium Iron
+Garnet film and 3D microwave cavity photons at milli-Kelvin temperatures. The
+coupling strength of $350$MHz or $7.3$\% of resonance frequency is observed.
+The magnonic subsystem is represented by the Damon-Eshbach magnetostatic
+surface wave with a distribution of wave numbers giving the linewidth of 15MHz.
+The ways to improve this parameter are discussed. The energy gap in the
+spectrum given by the Zeeman energy and the shape-anisotropy energy in the film
+geometry give rise to a significant asymmetry of the double peak structure of
+the photon-magnon avoided level crossing. A structure of two parallel YIG films
+is investigated using the same re-entrant magnetostatic surface wave transducer
+revealing a higher order magnon modes existing in both films. Combination of a
+multi-post re-entrant cavity and multiple films is a potential base for
+engineering both magnon and photon spectra.",1710.06601v1
+2017-10-27,Bulk and edge spin transport in topological magnon insulators,"We investigate the spin transport properties of a topological magnon
+insulator, a magnetic insulator characterized by topologically nontrivial bulk
+magnon bands and protected magnon edge modes located in the bulk band gaps.
+Employing the Landau-Lifshitz-Gilbert phenomenology, we calculate the spin
+current driven through a normal metal$|$topological magnon insulator$|$normal
+metal heterostructure by a spin accumulation imbalance between the metals, with
+and without random lattice defects. We show that bulk and edge transport are
+characterized by different length scales. This results in a characteristic
+system size where the magnon transport crosses over from being bulk-dominated
+for small systems to edge-dominated for larger systems. These findings are
+generic and relevant for topological transport in systems of nonconserved
+bosons.",1710.09998v2
+2017-12-25,"Magnon and Phonon Dispersion, Lifetime and Thermal Conductivity of Iron from Spin-Lattice Dynamics Simulations","In recent years, the fundamental physics of spin-thermal (i.e.,
+magnon-phonon) interaction has attracted significant experimental and
+theoretical interests given its potential paradigm-shifting impacts in areas
+like spin-thermoelectrics, spin-caloritronics and spintronics. Modelling
+studies of the transport of magnons and phonons in magnetic crystals are very
+rare. In this paper, we use spin-lattice dynamics (SLD) simulations to model
+ferromagnetic crystalline iron, where the spin and lattice systems are coupled
+through the atomic position-dependent exchange function, and thus the
+interaction between magnon and phonon is naturally considered. We then present
+a method combining SLD simulations with spectral energy analysis to calculate
+the magnon and phonon harmonic (e.g., dispersion, specific heat, group
+velocity) and anharmonic (e.g., scattering rate) properties, based on which
+their thermal conductivity values are calculated. This work represents an
+example of using SLD simulations to understand the transport properties
+involving coupled magnon and phonon dynamics.",1712.09002v1
+2018-09-13,Hybrid Architecture for Engineering Magnonic Quantum Networks,"We show theoretically that a network of superconducting loops and magnetic
+particles can be used to implement magnonic crystals with tunable magnonic band
+structures. In our approach, the loops mediate interactions between the
+particles and allow magnetic excitations to tunnel over long distances. As a
+result, different arrangements of loops and particles allow one to engineer the
+band structure for the magnonic excitations. Furthermore, we show how magnons
+in such crystals can serve as a quantum bus for long-distance magnetic coupling
+of spin qubits. The qubits are coupled to the magnets in the network by their
+local magnetic-dipole interaction and provide an integrated way to measure the
+state of the magnonic quantum network.",1809.04901v2
+2019-09-09,Modulation of magnon spin transport in a magnetic gate transistor,"We demonstrate a modulation of up to 18% in the magnon spin transport in a
+magnetic insulator (Y$_{3}$Fe$_{5}$O$_{12}$, YIG) using a common ferromagnetic
+metal (permalloy, Py) as a magnetic control gate. A Py electrode, placed
+between two Pt injector and detector electrodes, acts as a magnetic gate in our
+prototypical magnon transistor device. By manipulating the magnetization
+direction of Py with respect to that of YIG, the transmission of magnons
+through the Py|YIG interface can be controlled, resulting in a modulation of
+the non-equilibrium magnon density in the YIG channel between the Pt injector
+and detector electrodes. This study opens up the possibility of using the
+magnetic gating effect for magnon-based spin logic applications.",1909.03775v1
+2020-12-26,The interplay of Dzyaloshinskii-Moriya and Kitaev interactions for magnonic properties of Heisenberg-Kitaev honeycomb ferromagnets,"The properties of Kitaev materials are attracting ever increasing attention
+owing to their exotic properties. In realistic two-dimensional materials,
+Kitaev interaction is often accompanied by the Dzyloshinskii-Moriya
+interaction, which poses a challenge of distinguishing their magnitude
+separately. In this work, we demonstrate that it can be done by accessing
+magnonic transport properties. By studying honeycomb ferromagnets exhibiting
+Dzyaloshinskii-Moriya and Kitaev interactions simultaneously, we reveal
+non-trivial magnonic topological properties accompanied by intricate magnonic
+transport characteristics as given by thermal Hall and magnon Nernst effects.
+We also investigate the effect of a magnetic field, showing that it does not
+only break the symmetry of the system but also brings drastic modifications to
+magnonic topological transport properties, which serve as hallmarks of the
+relative strength of anisotropic exchange interactions. Based on our findings,
+we suggest strategies to estimate the importance of Kitaev interactions in real
+materials.",2012.13729v2
+2012-05-20,Brillouin light scattering spectroscopy of parametrically excited dipole-exchange magnons,"The spectral distribution of parametrically excited dipole-exchange magnons
+in an in-plane magnetized epitaxial film of yttrium-iron garnet was studied by
+means of frequency- and wavevector-resolved Brillouin light scattering
+spectroscopy. The experiment was performed in a parallel pumping geometry where
+an exciting microwave magnetic field was parallel to the magnetizing field. It
+was found that for both dipolar and exchange spectral areas parallel pumping
+excites the lowest volume magnon modes propagating in the film plane
+perpendicularly to the magnetization direction. In order to interpret the
+experimental observations, we used a microscopic Heisenberg model that includes
+exchange as well as dipole-dipole interactions to calculate the magnon spectrum
+and construct the eigenstates. As proven in our calculations, the observed
+magnons are characterized by having the highest possible ellipticity of
+precession which suggests the lowest threshold of parametric generation.
+Applying different pumping powers we observe modifications in the magnon
+spectrum that are described theoretically by a softening of the spin stiffness.",1205.4396v1
+2017-05-08,Non-local magnon transport in the compensated ferrimagnet GdIG,"We study the diffusive transport of magnons through the compensated
+ferrimagnetic insulator Gd3Fe5O12 (GdIG). The magnons are injected and detected
+electrically in a non-local measurement configuration via two parallel Pt
+strips deposited on top of the ferrimagnet. GdIG exhibits a rich magnon
+spectrum, with several thermally populated magnon bands at room temperature. We
+observe a strong temperature and field dependence of the non-local voltage in
+the detector strip. Just below the magnetization compensation temperature we
+find that the increasing magnetic field causes an unexpected enhancement of the
+non-local signal. A comparison with GdIG spin wave spectra obtained from
+atomistic modeling indicates that the thermal magnon population is important
+for understanding the non-local voltage signal.",1705.02871v1
+2017-05-11,Chiral anomaly of Weyl magnons in stacked honeycomb ferromagnets,"Chiral anomaly of Weyl magnons (WMs), featured by nontrivial band crossings
+at paired Weyl nodes (WNs) of opposite chirality, is investigated. It is shown
+that WMs can be realized in stacked honeycomb ferromagnets. Using the
+Aharonov-Casher effect that is about the interaction between magnetic moments
+and electric fields, the magnon motion in honeycomb layers can be quantized
+into magnonic Landau levels (MLLs). The zeroth MLL is chiral so that
+unidirectional WMs propagate in the perpendicular (to the layer) direction for
+a given WN under a magnetic field gradient from one WN to the other and change
+their chiralities, resulting in the magnonic chiral anomaly (MCA). A net magnon
+current carrying spin and heat through the zeroth MLL depends linearly on the
+magnetic field gradient and the electric field gradient in the ballistic
+transport.",1705.04164v1
+2017-05-17,Ballistic magnon heat conduction and possible Poiseuille flow in the helimagnetic insulator Cu$_2$OSeO$_3$,"We report on the observation of magnon thermal conductivity $\kappa_m\sim$ 70
+W/mK near 5 K in the helimagnetic insulator Cu$_2$OSeO$_3$, exceeding that
+measured in any other ferromagnet by almost two orders of magnitude. Ballistic,
+boundary-limited transport for both magnons and phonons is established below 1
+K, and Poiseuille flow of magnons is proposed to explain a magnon mean-free
+path substantially exceeding the specimen width for the least defective
+specimens in the range 2 K $<T<$ 10 K. These observations establish
+Cu$_2$OSeO$_3$ as a model system for studying long-wavelength magnon dynamics.",1705.06328v2
+2018-03-30,From Kinetic Instability to Bose-Einstein Condensation and Magnon Supercurrents,"Evolution of an overpopulated gas of magnons to a Bose-Einstein condensate
+and excitation of a magnon supercurrent, propelled by a phase gradient in the
+condensate wave function, can be observed at room-temperature by means of the
+Brillouin light scattering spectroscopy in an yttrium iron garnet material. We
+study these phenomena in a wide range of external magnetic fields in order to
+understand their properties when externally pumped magnons are transferred
+towards the condensed state via two distinct channels: A multistage
+Kolmogorov-Zakharov cascade of the weak-wave turbulence or a one-step
+kinetic-instability process. Our main result is that opening the kinetic
+instability channel leads to the formation of a much denser magnon condensate
+and to a stronger magnon supercurrent compared to the cascade mechanism alone.",1803.11548v1
+2018-06-14,Nonlinear relaxation between magnons and phonons in insulating ferromagnets,"Nonlinear relaxation between spin waves (magnons) and the crystal lattice
+(phonons) in an insulating ferromagnet is investigated theoretically. Magnons
+and phonons are described by the equilibrium Bose-Einstein distributions with
+different temperatures. The nonlinear heat current from magnons to phonons is
+calculated microscopically in terms of the Cherenkov radiation of phonons by
+magnons. The results are discussed in comparison with the well-known
+theoretical results on the nonlinear electron-phonon relaxation in metals
+[Kaganov, Lifshitz, Tanatarov, J. Exp. Theor. Phys. 31, 232 (1956)]. The
+elaborated theoretical description is relevant for spin-pumping experiments and
+thermoelectric devices in which the magnon temperature is essentially higher
+than the phonon one.",1806.05501v1
+2018-06-18,Magnonic Noise and Wiedemann-Franz Law,"We theoretically establish mutual relations among magnetic momentum, heat,
+and fluctuations of propagating magnons in a ferromagnetic insulating junction
+in terms of noise and the bosonic Wiedemann-Franz (WF) law. Using the
+Schwinger-Keldysh formalism, we calculate all transport coefficients of a noise
+spectrum for both magnonic spin and heat currents, and establish Onsager
+relations between the thermomagnetic currents and the zero-frequency noise.
+Making use of the magnonic WF law and the Seebeck coefficient in the
+low-temperature limit, we theoretically discover universal relations, i.e.
+being independent of material parameters, for both the nonequilibrium and
+equilibrium noise, and show that each noise is described solely in terms of
+thermal conductance. Finally, we introduce a magnonic spin-analog of the Fano
+factor, noise-to-current ratio, and demonstrate that the magnonic spin-Fano
+factor reduces to a universal value in the low-temperature limit and it remains
+valid even beyond a linear response regime.",1806.06965v1
+2018-07-18,Magnon-photon-phonon entanglement in cavity magnomechanics,"We show how to generate tripartite entanglement in a cavity magnomechanical
+system which consists of magnons, cavity microwave photons, and phonons. The
+magnons are embodied by a collective motion of a large number of spins in a
+macroscopic ferrimagnet, and are driven directly by an electromagnetic field.
+The cavity photons and magnons are coupled via magnetic dipole interaction, and
+the magnons and phonons are coupled via magnetostrictive (radiation
+pressure-like) interaction. We show optimal parameter regimes for achieving the
+tripartite entanglement where magnons, cavity photons, and phonons are
+entangled with each other, and we further prove that the steady state of the
+system is a genuinely tripartite entangled state. The entanglement is robust
+against temperature. Our results indicate that cavity magnomechanical systems
+could provide a promising platform for the study of macroscopic quantum
+phenomena.",1807.07158v3
+2019-01-04,Atomistic Simulation of Phonon and Magnon Thermal Transport across the Ferro-Paramagnetic Transition,"A temperature-dependent approach involving Green-Kubo equilibrium atomic and
+spin dynamics (GKEASD) is reported to assess phonon and magnon thermal
+transport processes accounting for phonon-magnon interactions. Using
+body-center cubic (BCC) iron as a case study, GKEASD successfully reproduces
+its characteristic temperature-dependent spiral and lattice thermal
+conductivities. The non-electronic thermal conductivity, i.e., the sum of
+phonon and magnon thermal conductivities, calculated using GKEASD for BCC Fe
+agrees well with experimental measurements. Spectral energy analysis reveals
+that high-frequency phonon-magnon scattering rates are one order of magnitude
+larger than those at low frequencies due to energy scattering conservation
+rules and high densities of states. Higher temperatures further accentuate this
+phenomenon. This new framework fills existing gaps in simulating thermal
+transport across the ferro- to para-magnetic transition. Future application of
+this methodology to phonon- and magnon-dominant insulators and semiconductors
+will enhance understanding of emerging thermoelectric, spin caloritronic and
+superconducting materials.",1901.00966v4
+2019-01-19,Topological Magnetoelastic Excitations in Non-Collinear Antiferromagnets,"We study the topological property of the magnetoelastic excitation in
+non-collinear antiferromagnets. As a toy model, we consider the magnon-phonon
+coupling in a triangular antiferromagnet with a $120^\circ$ N\`eel order. We
+find that in the presence of out-of-plane external magnetic field, the
+magnon-polaron bands, which arise from hybridization of magnons and phonons,
+can carry Chern number, even though the individual magnon and phonon bands are
+topologically trivial. Large Berry curvature is induced from the anti-crossing
+regions between the magnon and phonon bands, which renormalizes the thermal
+Hall conductivity of phonon bands. To compute the Berry curvature and Chern
+number of magnon-polarons, we give a simple algorithm to diagonalize
+magnetoelastic Hamiltonian without diagonalizing the phonon Hamiltonian, by
+mapping the problem to the diagonalization of bosonic Bogoliubov-de-Gennes
+(BdG) Hamiltonian. This is necessary because the contribution to the Berry
+curvature from phonon cannot be properly captured if we compute the Berry
+curvature from magnetoelastic Hamiltonian whose phonon sector has been already
+diagonalized.",1901.06500v2
+2019-02-01,Bloch oscillations of multi-magnon excitations in a Heisenberg XXZ chain,"The studies of multi-magnon excitations will extend our understandings of
+quantum magnetism and strongly correlated matters. Here, by using the
+time-evolving block decimation algorithm, we investigate the Bloch oscillations
+of two-magnon excitations under a gradient magnetic field. Through analyzing
+the symmetry of the Hamiltonian, we derive a rigorous and universal relation
+between ferromagnetic and anti-ferromagnetic systems. Under strong
+interactions, in addition to free-magnon Bloch oscillations, there appear
+fractional bounded-magnon Bloch oscillations which can be understood by an
+effective single-particle model. To extract the frequencies of Bloch
+oscillations and determine the gradient of magnetic field, we respectively
+calculate the fidelity in the time domain and the sub-standard deviation in the
+frequency domain. Our study not only explore the interaction-induced Bloch
+oscillations of multi-magnon excitations, but also provides an alternative
+approach to determine the gradient of magnetic field via ultracold atoms in
+optical lattices.",1902.00273v2
+2019-02-20,Photoinduced Floquet topological magnons in Kitaev magnets,"We study periodically driven pure Kitaev model and ferromagnetic phase of the
+Kitaev-Heisenberg model on the honeycomb lattice by off-resonant linearly and
+circularly-polarized lights at zero magnetic field. Using a combination of
+linear spin wave and Floquet theories, we show that the effective
+time-independent Hamiltonians in the off-resonant regime map onto the
+corresponding anisotropic static spin model, plus a tunable photoinduced
+magnetic field along the $[111]$ direction, which precipitates Floquet
+topological magnons and chiral magnon edge modes. They are tunable by the light
+amplitude and polarization. Similarly, we show that the thermal Hall effect
+induced by the Berry curvature of the Floquet topological magnons can also be
+tuned by the laser field. Our results pave the way for ultrafast manipulation
+of topological magnons in irradiated Kitaev magnets, and could play a pivotal
+role in the investigation of ultrafast magnon spin current generation in Kitaev
+materials.",1902.07716v2
+2019-02-22,Thermal induced monochromatic microwave generation in magnon-polariton,"We propose thermal induced generation of monochromatic microwave radiation in
+magnon-polariton. Mechanism of thermal to microwave energy transformation is
+based on intrinsic energy loss compensation of coupled magnon and microwave
+cavity oscillators by thermal induced ""negative damping"". A singularity at an
+exceptional point is achieved when at the critical value of ""negative damping""
+the damping of the system is fully compensated. At the exceptional point, the
+input energy is equally distributed between the magnon and photon subsystems of
+the magnon-polariton. The efficiency of transformation of thermal energy into
+useful microwave radiation is estimated to be as large as 17 percent due to
+magnon-photon coupling mediated direct conversation of spin current into
+microwave photons.",1902.08383v1
+2019-04-02,Universal $1/3$-suppression of magnonic shot noise in diffusive insulating magnets,"Extending a Boltzmann-Langevin theory to magnons, we show a universality of
+current-noise suppression in diffusive systems against the difference of
+quantum-statistical properties of bosons and fermions. To this end, starting
+from a quantum kinetic equation for magnons subjected to thermal gradient in
+dilute impurities, we derive a bosonic counterpart of the semiclassical
+Boltzmann-Langevin equation for electrons and evaluate a magnonic current-noise
+in the diffusive insulating magnet. We theoretically discover that compared
+with a Poissonian shot noise of magnons in an insulating ferromagnetic
+junction, the magnonic shot noise is suppressed in the diffusive insulating
+bulk magnet and noise-to-current ratio (Fano factor) at low temperatures
+exhibits a universal behavior, i.e., the same suppression $1/3$ as the one for
+electron transport in diffusive conductors, despite the difference of
+quantum-statistical properties. Finally, we show that our predictions are
+within experimental reach with current device and measurement technologies.",1904.01151v2
+2019-04-09,Antiferromagnetic magnons as highly squeezed Fock states underlying quantum correlations,"Employing the concept of two-mode squeezed states from quantum optics, we
+demonstrate a revealing physical picture for the antiferromagnetic ground state
+and excitations. Superimposed on a N{\'e}el ordered configuration, a spin-flip
+restricted to one of the sublattices is called a sublattice-magnon. We show
+that an antiferromagnetic spin-up magnon is comprised by a quantum
+superposition of states with $n+1$ spin-up and $n$ spin-down
+sublattice-magnons, and is thus an enormous excitation despite its unit net
+spin. Consequently, its large sublattice-spin can amplify its coupling to other
+excitations. Employing von Neumann entropy as a measure, we show that the
+antiferromagnetic eigenmodes manifest a high degree of entanglement between the
+two sublattices, thereby establishing antiferromagnets as reservoirs for strong
+quantum correlations. Based on these novel insights, we outline strategies for
+exploiting the strong quantum character of antiferromagetic (squeezed-)magnons
+and give an intuitive explanation for recent experimental and theoretical
+findings in antiferromagnetic magnon spintronics.",1904.04553v3
+2019-08-28,Spin functional renormalization group for quantum Heisenberg ferromagnets: Magnetization and magnon damping in two dimensions,"We use the spin functional renormalization group recently developed by two of
+us [J. Krieg and P. Kopietz, Phys. Rev. B $\bf{99}$, 060403(R) (2019)] to
+calculate the magnetization $M ( H , T )$ and the damping of magnons due to
+classical longitudinal fluctuations of quantum Heisenberg ferromagnets. In
+order to guarantee that for vanishing magnetic field $H \rightarrow 0$ the
+magnon spectrum is gapless when the spin rotational invariance is spontaneously
+broken, we use a Ward identity to express the magnon self-energy in terms of
+the magnetization. In two dimensions our approach correctly predicts the
+absence of long-range magnetic order for $H=0$ at finite temperature $T$. The
+magnon spectrum then exhibits a gap from which we obtain the transverse
+correlation length. We also calculate the wave-function renormalization factor
+of the magnons. As a mathematical by-product, we derive a recursive form of the
+generalized Wick theorem for spin operators in frequency space which
+facilitates the calculation of arbitrary time-ordered connected correlation
+functions of an isolated spin in a magnetic field.",1908.10753v2
+2019-11-16,Magnon magic angles and tunable Hall conductivity in 2D twisted ferromagnetic bilayers,"Twistronics is currently one of the most active research fields in condensed
+matter physics, following the discovery of correlated insulating and
+superconducting phases in twisted bilayer graphene (tBLG). Here, we present a
+magnonic analogue of tBLG. We study magnons in twisted ferromagnetic bilayers
+(tFBL), including exchange and Dzyaloshinskii-Moriya interactions (DMI). For
+negligible DMI, tFBL presents discrete magnon magic angles and flat moir\'e
+minibands analogous to tBLG. The DMI, however, changes the picture and renders
+the system much more exotic. The DMI in tFBL induces a rich topological magnon
+band structure for any twist angle. The twist angle turns to a control knob for
+the magnon Hall and Nernst conductivities. Gapped flat bands appear in a
+continuum of magic angles in tFBL with DMI. In the lower limit of the
+continuum, the band structure reconstructs to form bundles of topological flat
+bands. The luxury of twist-angle control over band gaps, topological
+properties, number of flat bands, Hall and Nernst conductivities renders tFBL a
+novel device from fundamental and applied perspectives.",1911.07009v5
+2015-08-04,Low-energy singlet excitations in spin- 1/2 Heisenberg antiferromagnet on square lattice,"We present an approach based on a dimer expansion which describes low-energy
+singlet excitations (singlons) in spin-$\frac12$ Heisenberg antiferromagnet on
+simple square lattice. An operator (""effective Hamiltonian"") is constructed
+whose eigenvalues give the singlon spectrum. The ""effective Hamiltonian"" looks
+like a Hamiltonian of a spin-$\frac12$ magnet in strong external magnetic field
+and it has a gapped spectrum. It is found that singlet states lie above triplet
+ones (magnons) in the whole Brillouin zone except in the vicinity of the point
+$(\pi,0)$, where their energies are slightly smaller. Based on this finding, we
+suggest that a magnon decay is possible near $(\pi,0)$ into another magnon and
+a singlon which may contribute to the dip of the magnon spectrum near $(\pi,0)$
+and reduce the magnon lifetime. It is pointed out that the singlon-magnon
+continuum may contribute to the continuum of excitations observed recently near
+$(\pi,0)$.",1508.00744v3
+2016-12-25,Magnon Planar Hall Effect and Anisotropic Magnetoresistance in a Magnetic Insulator,"Electrical resistivities can be different for charge currents travelling
+parallel or perpendicular to the magnetization in magnetically ordered
+conductors or semiconductors, resulting in the well-known planar Hall effect
+and anisotropic magnetoresistance. Here, we study the analogous anisotropic
+magnetotransport behavior for magnons in a magnetic insulator
+Y$_{3}$Fe$_{5}$O$_{12}$. Electrical and thermal magnon injection, and
+electrical detection methods are used at room temperature with transverse and
+longitudinal geometries to measure the magnon planar Hall effect and
+anisotropic magnetoresistance, respectively. We observe that the relative
+difference between magnon current conductivities parallel and perpendicular to
+the magnetization, with respect to the average magnon conductivity, i.e.
+$|(\sigma_{\parallel}^{\textrm{m}}-\sigma_{\perp}^{\textrm{m}})/\sigma_{0}^{\textrm{m}}|$
+, is approximately 5% with the majority of the measured devices showing
+$\sigma_{\perp}^{\textrm{m}}>\sigma_{\parallel}^{\textrm{m}}$.",1612.08233v1
+2017-07-20,Bistability of Cavity Magnon Polaritons,"We report the first observation of the magnon-polariton bistability in a
+cavity magnonics system consisting of cavity photons strongly interacting with
+the magnons in a small yttrium iron garnet (YIG) sphere. The bistable behaviors
+are emerged as sharp frequency switchings of the cavity magnon-polaritons
+(CMPs) and related to the transition between states with large and small number
+of polaritons. In our experiment, we align, respectively, the [100] and [110]
+crystallographic axes of the YIG sphere parallel to the static magnetic field
+and find very different bistable behaviors (e.g., clockwise and
+counter-clockwise hysteresis loops) in these two cases. The experimental
+results are well fitted and explained as being due to the Kerr nonlinearity
+with either positive or negative coefficient. Moreover, when the magnetic field
+is tuned away from the anticrossing point of CMPs, we observe simultaneous
+bistability of both magnons and cavity photons by applying a drive field on the
+lower branch.",1707.06509v2
+2017-11-02,Measurement of a Magnonic Crystal at Millikelvin Temperatures,"Hybrid systems combining magnons and superconducting quantum circuits have
+attracted increasing interest in recent years. Magnonic crystals (MCs) are one
+of the building blocks of room-temperature magnonics and can be used to create
+devices with an engineered band structure. These devices, exhibiting tunable
+frequency selectivity and the ability to store travelling excitations in the
+microwave regime, may form the basis of a set of new tools to be used in the
+context of quantum information processing. In order to ascertain the
+feasibility of such plans, MCs must be demonstrated to work at the low
+temperatures required for microwave-frequency quantum experiments. We report
+the first measurements of the transmission of microwave signals through an MC
+at 20 mK and observe a magnonic bandgap in both continuous-wave and pulsed
+excitation experiments. The spin-wave damping at low temperatures in our
+yttrium iron garnet MC is higher than expected, indicating that further work is
+necessary before the full potential of quantum experiments using magnonic
+crystals can be realised.",1711.00958v2
+2017-11-23,Elastic Gauge Fields and Hall Viscosity of Dirac Magnons,"We analyze the coupling of elastic lattice deformations to the magnon degrees
+of freedom of magnon Dirac materials. For a Honeycomb ferromagnet we find that,
+as it happens in the case of graphene, elastic gauge fields appear coupled to
+the magnon pseudospinors. For deformations that induce constant pseudomagnetic
+fields, the spectrum around the Dirac nodes splits into pseudoLandau levels. We
+show that when a Dzyaloshinskii-Moriya interaction is considered, a topological
+gap opens in the system and a Chern-Simons effective action for the elastic
+degrees of freedom is generated. Such a term encodes a phonon Hall viscosity
+response, entirely generated by fluctuations of magnons living in the vicinity
+of the Dirac points. The magnon Hall viscosity vanishes at zero temperature,
+and grows as temperature is raised and the states around the Dirac points are
+increasingly populated.",1711.08653v2
+2018-10-09,Phase-mediated magnon chaos-order transition in cavity optomagnonics,"Magnon as a quantized spin wave has attracted extensive attentions in various
+fields of physics, such as magnon spintronics, microwave photonics, and cavity
+quantum electrodynamics. Here, we explore theoretically magnon chaos-order
+transition in cavity optomagnonics, which is still remains largely unexplored
+in this emerging field. We find that the evolution of the magnon experiences
+the transition from order to period-doubling bifurcation and finally enter
+chaos by adjusting the microwave driving power. Different from the normal
+chaos, the magnon chaos-order transition proposed here is phase-mediated.
+Beyond their fundamental scientific significance, our results will contribute
+to the comprehending of nonlinear phenomena and chaos in optomagnonical system,
+and may find applications in chaos-based secure communication.",1810.04330v2
+2018-10-29,Hydrodynamic sound modes and Galilean symmetry breaking in a magnon fluid,"The non-interacting magnon gas description in ferromagnets breaks down at
+finite magnon density where momentum-conserving collisions between magnons
+become important. Observation of the collision-dominated regime, however, has
+been hampered by the lack of probes to access the energy and lengthscales
+characteristic of this regime. Here we identify a key signature of the
+collision-dominated hydrodynamic regime---a magnon sound mode---which governs
+dynamics at low frequencies and can be detected with recently-introduced spin
+qubit magnetometers. The magnon sound mode is an excitation of the longitudinal
+spin component with frequencies below the spin wave continuum in gapped
+ferromagnets. We also show that, in the presence of exchange interactions with
+SU(2) symmetry, the ferromagnet hosts an usual hydrodynamic regime that lacks
+Galilean symmetry at all energy and lengthscales. The hydrodynamic sound mode,
+if detected, can lead to a new platform to explore hydrodynamic behavior in
+quantum materials.",1810.12333v2
+2019-05-12,Optical heterodyne imaging of magnetostatic modes in one-dimensional magnonic crystals,"We demonstrate a real-space imaging of a heterodyne signal of light that is
+produced as a result of the Brillouin light scattering by coherently driven
+magnons in magnetostatic modes. With this imaging technique, we characterize
+surface magnetostatic modes (Damon-Eshbach modes) in a one-dimensional magnonic
+crystal, which is formed by patterned aluminum strips deposited on the
+ferromagnetic film. The modified band structures of the magnonic crystal are
+deduced from the Fourier transforms of the real-space images. The heterodyne
+imaging provides a simple and powerful method to probe magnons in structured
+ferromagnetic films, paving a way to investigate more complex phenomena, such
+as Anderson localization and topological transport with magnons.",1905.04683v4
+2020-06-05,Controlling the nonlinear relaxation of quantized propagating magnons in nanodevices,"Relaxation of linear magnetization dynamics is well described by the viscous
+Gilbert damping processes. However, for strong excitations, nonlinear damping
+processes such as the decay via magnon-magnon interactions emerge and trigger
+additional relaxation channels. Here, we use space- and time-resolved
+microfocused Brillouin light scattering spectroscopy and micromagnetic
+simulations to investigate the nonlinear relaxation of strongly driven
+propagating spin waves in yttrium iron garnet nanoconduits. We show that the
+nonlinear magnon relaxation in this highly quantized system possesses
+intermodal features, i.e., magnons scatter to higher-order quantized modes
+through a cascade of scattering events. We further show how to control such
+intermodal dissipation processes by quantization of the magnon band in
+single-mode devices, where this phenomenon approaches its fundamental limit.
+Our study extends the knowledge about nonlinear propagating spin waves in
+nanostructures which is essential for the construction of advanced spin-wave
+elements as well as the realization of Bose-Einstein condensates in scaled
+systems.",2006.03400v2
+2020-06-05,Hierarchy of magnon entanglement in antiferromagnets,"Continuous variable entanglement between magnon modes in Heisenberg
+antiferromagnet with Dzyaloshinskii-Moryia (DM) interaction is examined.
+Different bosonic modes are identified, which allows to establish a hierarchy
+of magnon entanglement in the ground state. We argue that entanglement between
+magnon modes is determined by a simple lattice specific factor, together with
+the ratio of the strengths of the DM and Heisenberg exchange interactions, and
+that magnon entanglement can be detected by means of quantum homodyne
+techniques. As an illustration of the relevance of our findings for possible
+entanglement experiments in the solid state, a typical antiferromagnet with the
+perovskite crystal structure is considered, and it is shown that long wave
+length magnon modes have the highest degree of entanglement.",2006.03479v1
+2020-06-14,Hypersonic heat-induced flows of magnons induced by femtosecond laser pulses,"In this work, we present evidence for the existence of a magnonic current on
+the sub-picosecond time-scale in a ferrimagnetic bilayer and its effect on
+ultrafast spin dynamics. The ferrimagnet, GdFeCo, is a material known to
+undergo ultrafast switching within 1-2ps after excitation with femtosecond
+laser pulses. Here, we show that the strong thermal gradients induced by
+applying femtosecond laser pulses and the presence of chemical inhomogeneities
+lead to local imbalances in the effective temperatures of the spins that
+produces a rapid transfer of spin angular momentum, which we interpret as an
+ultrafast spin Seebeck effect. We have quantified the typical magnon
+propagation in such a system. The results show ballistic magnon propagation
+with 30nm/ps velocities. The characteristic time scale of such magnon
+propagation indicates that this magnon transport can play an important role in
+switching, a crucial piece of understanding towards realising next generation
+data processing devices that operate at much higher frequencies.",2006.07935v1
+2013-06-12,Magnon self energy in the correlated ferromagnetic Kondo lattice model: spin-charge coupling effects on magnon excitations in manganites,"Magnon self energy due to spin-charge coupling is calculated for the
+correlated ferromagnetic Kondo lattice model using a diagrammatic expansion
+scheme. Systematically incorporating correlation effects in the form of
+self-energy and vertex corrections, the expansion scheme explicitly preserves
+the continuous spin rotation symmetry and hence the Goldstone mode. Due to a
+near cancellation of the correlation-induced quantum correction terms at
+intermediate coupling and optimal band filling relevant for ferromagnetic
+manganites, the renormalized magnon energies for the correlated FKLM are nearly
+independent of correlation term. Even at higher band fillings, despite
+exhibiting overall non-Heisenberg behavior, magnon dispersion in the \Gamma-X
+direction retains nearly Heisenberg form. Therefore, the experimentally
+observed doping dependent zone-boundary magnon softening must be ascribed to
+spin-orbital coupling effects.",1306.2769v1
+2016-09-06,Magnonic Weyl semimetal in pyrochlore ferromagnets,"Topological states of matter have been a subject of intensive studies in
+recent years because of their exotic properties such as the topologically
+protected edge and surface states. The initial studies were exclusively for
+electron systems. It is now known that topological states can also exist for
+other particles. Indeed, topologically protected edge states have already been
+found for phonons and photons. In spite of active searching for topological
+states in many fields, the studies in magnetism are relatively rare although
+topological states are apparently important and useful in magnonics. Here we
+show that the pyrochlore ferromagnets with the Dzyaloshinskii-Moriya
+interaction are intrinsic magnonic Weyl semimetals. Similar to the electronic
+Weyl semimetals, the magnon bands in a magnonic Weyl semimetal are nontrivially
+crossing in pairs at special points (called Weyl nodes) in momentum space. The
+equal energy contour around the Weyl nodes gives rise to the Fermi arcs on
+sample surfaces due to the topologically protected surface states between each
+pair of Weyl nodes. Additional Weyl nodes and Fermi arcs can be generated in
+lower energy magnon bands when an anisotropic exchange interaction is
+introduced.",1609.01500v1
+2016-11-29,Magnonic quantum Hall effect and Wiedemann-Franz law,"We present a quantum Hall effect of magnons in two-dimensional clean
+insulating magnets at finite temperature. Through the Aharonov-Casher effect, a
+magnon moving in an electric field acquires a geometric phase and forms Landau
+levels in an electric field gradient of sawtooth form. At low temperatures, the
+lowest energy band being almost flat carries a Chern number associated with a
+Berry curvature. Appropriately defining the thermal conductance for bosons, we
+find that the magnon Hall conductances get quantized and show a universal
+thermomagnetic behavior, i.e., are independent of materials, and obey a
+Wiedemann-Franz law for magnon transport. We consider magnons with quadratic
+and linear (Dirac-like) dispersions. Finally, we show that our predictions are
+within experimental reach for ferromagnets and skyrmion lattices with current
+device and measurement techniques.",1611.09752v3
+2018-01-16,Topological Magnons in a One-dimensional Itinerant Flatband Ferromagnet,"Different from previous scenarios that topological magnons emerge in local
+spin models, we propose an alternative that itinerant electron magnets can host
+topological magnons. A one-dimensional Tasaki model with a flat band is
+considered as the prototype. This model can be viewed as a quarter filled
+periodic Anderson model with impurities located in between and hybridizing with
+the nearest-neighbor conducting electrons, together with a Hubbard repulsion
+for these electrons. By increasing the Hubbard interaction, the gap between the
+acoustic and optical magnons closes and reopens while the Berry phase of the
+acoustic band changes from 0 to $\pi$, leading to the occurrence of a
+topological transition. After this transition, there always exist in-gap edge
+magnonic modes which is consistent with the bulk-edge correspondence. The
+Hubbard interaction driven transition reveals a new mechanism to realize
+non-trivial magnon bands.",1801.05255v2
+2018-08-20,Tunable Magnonic Thermal Hall Effect in Skyrmion Crystal Phases of Ferrimagnets,"We theoretically study the thermal Hall effect by magnons in skyrmion crystal
+phases of ferrimagnets in the vicinity of the angular momentum compensation
+point (CP). To this end, we start by deriving the equation of motion for
+magnons in the background of an arbitrary equilibrium spin texture, which gives
+rise to the fictitious electromagnetic field for magnons. As the net spin
+density varies, the resultant equation of motion interpolates between the
+relativistic Klein-Gordon equation at CP and the nonrelativistic
+Schr{\""o}dinger-like equation away from it. In skyrmion crystal phases, the
+right- and the left-circularly polarized magnons with respect to the order
+parameter are shown to form the Landau levels separately within the uniform
+skyrmion-density approximation. For an experimental proposal, we predict that
+the magnonic thermal Hall conductivity changes its sign when the ferrimagnet is
+tuned across CP, providing a way to control heat flux in spin-caloritronic
+devices on the one hand and a feasible way to detect CP of ferrimagnets on the
+other hand.",1808.06690v1
+2019-06-18,Reversible tuning of omnidirectional band gaps in two-dimensional magnonic crystals by magnetic field and in-plane squeezing,"By means of the plane wave method, we study nonuniform, i.e., mode- and
+k-dependent, effects in the spin-wave spectrum of a two-dimensional bicomponent
+magnonic crystal. We use the crystal based on a hexagonal lattice squeezed in
+the direction of the external magnetic field wherein the squeezing applies to
+the lattice and the shape of inclusions. The squeezing changes both the
+demagnetizing field and the spatial confinement of the excitation, which may
+lead to the occurrence of an omnidirectional magnonic band gaps. In particular,
+we study the role played by propagational effects, which allows us to explain
+the k-dependent softening of modes. The effects we found enabled us not only to
+design the width and position of magnonic band gaps, but also to plan their
+response to a change in the external magnetic field magnitude. This allows the
+reversible tuning of magnonic band gaps, and it shows that the studied
+structures are promising candidates for designing magnonic devices that are
+tunable during operation.",1906.07469v3
+2019-06-19,Introducing coherent time control to cavity-magnon-polariton modes,"By connecting light to magnetism, cavity-magnon-polaritons (CMPs) can build
+links from quantum computation to spintronics. As a consequence, CMP-based
+information processing devices have thrived over the last five years, but
+almost exclusively been investigated with single-tone spectroscopy. However,
+universal computing applications will require a dynamic control of the CMP on
+demand and within nanoseconds. In this work, we perform fast manipulations of
+the different CMP modes with independent but coherent pulses to the cavity and
+magnon system. We change the state of the CMP from the energy exchanging beat
+mode to its normal modes and further demonstrate two fundamental examples of
+coherent manipulation: First, a dynamic control over the appearance of
+magnon-Rabi oscillations, i.e., energy exchange, and second, a complete energy
+extraction by applying an anti-phase drive to the magnon. Our results show a
+promising approach to control different building blocks for a quantum internet
+and pave the way for further magnon-based quantum computing research.",1906.08103v2
+2019-06-24,Macroscopic entanglement of two magnon modes via quantum correlated microwave fields,"We present a scheme to entangle two magnon modes in two macroscopic
+yttrium-iron-garnet spheres. The two spheres are placed inside two microwave
+cavities, which are driven by a two-mode squeezed microwave field. By using the
+linear state-swap interaction between the cavity and the magnon mode in each
+cavity, the quantum correlation of the two driving fields is with high
+efficiency transferred to the two magnon modes. Considerable entanglement could
+be achieved under experimentally achievable conditions $g \gg \kappa_a \gg
+\kappa_m$, where $g$ is the cavity-magnon coupling rate and $\kappa_a$,
+$\kappa_m$ are the decay rates of the cavity and magnon modes, respectively.
+The entanglement is in the steady state and robust against temperature,
+surviving up to hundreds of milliKelvin with experimentally accessible two-mode
+squeezed source.",1906.09921v1
+2019-06-28,Control of magnons via ultrafast magnetization modulation,"We demonstrate optical control of magnons using femtosecond laser pulses by
+performing ab-initio real-time time-dependent density functional theory (TDDFT)
+simulations. We predict that the spin-wave dynamics in Fe$_{50}$Ni$_{50}$ can
+be manipulated by tailoring the applied laser pulse via three distinct
+mechanisms: (1) element selective destruction of magnon modes depending on the
+laser intensity, (2) delay dependent freezing of the magnon mode into a
+transient non-collinear state (where delay is in the pulse peak with respect to
+the start of simulations), and (3) optically induced inter sublattice transfer
+(OISTR) driven renormalization of the optical magnon frequency. Harnessing such
+processes would significantly speed up magnonic devices.",1906.12270v2
+2019-07-04,Topological Magnon-Phonon Hybrid Excitations in Two-Dimensional Ferromagnets with Tunable Chern Numbers,"We theoretically investigate magnon-phonon hybrid excitations in
+two-dimensional ferromagnets. The bulk bands of hybrid excitations, which are
+referred to as magnon-polarons, are analytically shown to be topologically
+nontrivial, possessing finite Chern numbers. We also show that the Chern
+numbers of magnon-polaron bands and the number of band-crossing lines can be
+manipulated by an external magnetic field. For experiments, we propose to use
+the thermal Hall conductivity as a probe of the finite Berry curvatures of
+magnon-polarons. Our results show that a simple ferromagnet on a square lattice
+supports topologically nontrivial magnon-polarons, generalizing topological
+excitations in conventional magnetic systems.",1907.02224v1
+2019-07-20,Magnon Bose-Einstein condensate and supercurrents over a wide temperature range,"Magnon Bose-Einstein Condensates (BECs) and supercurrents are coherent
+quantum phenomena, which appear on a macroscopic scale in parametrically
+populated solid state spinsystems. One of the most fascinating and attractive
+features of these processes is the possibility of magnon condensation and
+supercurrent excitation even at room temperature. At the same time, valuable
+information about a magnon BEC state, such as its lifetime, its formation
+threshold, and coherency, is provided by experiments at various temperatures.
+Here, we use Brillouin Light Scattering (BLS) spectroscopy for the
+investigation of the magnon BEC dynamics in a single-crystal film of yttrium
+iron garnet in a wide temperature range from 30 K to 380 K. By comparing the
+BLS results with previous microwave measurements, we re-vealed the direct
+relation between the damping of the condensed and the parametrically injected
+magnons. The enhanced supercurrent dynamics was detected at 180 K near the
+minimum of BEC damping.",1907.08805v1
+2019-10-08,Orbital Nernst Effect of Magnons,"In the past, magnons have been shown to mediate thermal transport of spin in
+various systems. Here, we reveal that the fundamental coupling of scalar spin
+chirality, inherent to magnons, to the electronic degrees of freedom in the
+system can result in the generation of sizeable orbital magnetization and
+thermal transport of orbital angular momentum. We demonstrate the emergence of
+the latter phenomenon of orbital Nernst effect by referring to the spin-wave
+Hamiltonian of kagome ferromagnets, predicting that in a wide range of systems
+the transverse current of orbital angular momentum carried by magnons in
+response to an applied temperature gradient can overshadow the accompanying
+spin current. We suggest that the discovered effect fundamentally correlates
+with the topological Hall effect of fluctuating magnets, and it can be utilized
+in magnonic devices for generating magnonic orbital torques.",1910.03317v2
+2019-10-25,Twisted magnon as a magnetic tweezer,"Wave fields with spiral phase dislocations carrying orbital angular momentum
+(OAM) have been realized in many branches of physics, such as for photons,
+sound waves, electron beams, and neutrons. However, the OAM states of magnons
+(spin waves)$-$the building block of modern magnetism$-$and particularly their
+implications have yet to be addressed. Here, we theoretically investigate the
+twisted spin-wave generation and propagation in magnetic nanocylinders. The OAM
+nature of magnons is uncovered by showing that the spin-wave eigenmode is also
+the eigenstate of the OAM operator in the confined geometry. Inspired by
+optical tweezers, we predict an exotic ""magnetic tweezer"" effect by showing
+skyrmion gyrations under twisted magnons in exchange coupled
+nanocylinder$|$nanodisk heterostructure, as a practical demonstration of
+magnonic OAM to manipulate topological spin defects. Our study paves the way
+for the emerging magnetic manipulations by harnessing the OAM degree of freedom
+of magnons.",1910.11528v2
+2020-01-03,Dissipative couplings in cavity magnonics,"Cavity Magnonics is an emerging field that studies the strong coupling
+between cavity photons and collective spin excitations such as magnons. This
+rapidly developing field connects some of the most exciting branches of modern
+physics, such as quantum information and quantum optics, with one of the oldest
+science on the earth, the magnetism. The past few years have seen a steady
+stream of exciting experiments that demonstrate novel magnon-based transducers
+and memories. Most of such cavity magnonic devices rely on coherent coupling
+that stems from direct dipole-dipole interaction. Recently, a distinct
+dissipative magnon-photon coupling was discovered. In contrast to coherent
+coupling that leads to level repulsion between hybridized modes, dissipative
+coupling results in level attraction. It opens an avenue for engineering and
+harnessing losses in hybrid systems. This article gives a brief review of this
+new frontier. Experimental observations of level attraction are reviewed.
+Different microscopic mechanisms are compared. Based on such experimental and
+theoretical reviews, we present an outlook for developing open cavity systems
+by engineering and harnessing dissipative couplings.",2001.00978v2
+2020-01-21,High order magnon bound states in the quasi-one-dimensional antiferromagnet $α$-NaMnO$_2$,"Here we report on the formation of two and three magnon bound states in the
+quasi-one-dimensional antiferromagnet $\alpha$-NaMnO$_2$, where the single-ion,
+uniaxial anisotropy inherent to the Mn$^{3+}$ ions in this material provides a
+binding mechanism capable of stabilizing higher order magnon bound states.
+While such states have long remained elusive in studies of antiferromagnetic
+chains, neutron scattering data presented here demonstrate that higher order
+$n>2$ composite magnons exist, and, specifically, that a weak three-magnon
+bound state is detected below the antiferromagnetic ordering transition of
+NaMnO$_2$. We corroborate our findings with exact numerical simulations of a
+one-dimensional Heisenberg chain with easy-axis anisotropy using matrix-product
+state techniques, finding a good quantitative agreement with the experiment.
+These results establish $\alpha$-NaMnO$_2$ as a unique platform for exploring
+the dynamics of composite magnon states inherent to a classical
+antiferromagnetic spin chain with Ising-like single ion anisotropy.",2001.07300v1
+2020-01-31,Topological magnons in CrI$_3$ monolayers: an itinerant fermion description,"Magnons dominate the magnetic response of the recently discovered insulating
+ferromagnetic two dimensional crystals such as CrI$_3$. Because of the
+arrangement of the Cr spins in a honeycomb lattice, magnons in CrI$_3$ bear a
+strong resemblance with electronic quasiparticles in graphene. Neutron
+scattering experiments carried out in bulk CrI$_3$ show the existence of a gap
+at the Dirac points, that has been conjectured to have a topological nature.
+Here we propose a theory for magnons in ferromagnetic CrI$_3$ monolayers based
+on an itinerant fermion picture, with a Hamiltonian derived from first
+principles. We obtain the magnon dispersion for 2D CrI$_3$ with a gap at the
+Dirac points with the same Berry curvature in both valleys. For CrI$_3$
+ribbons, we find chiral in-gap edge states. Analysis of the magnon wave
+functions in momentum space further confirms their topological nature.
+Importantly, our approach does not require to define a spin Hamiltonian, and
+can be applied to both insulating and conducting 2D materials with any type of
+magnetic order.",2002.00077v1
+2020-02-26,Driving a magnetized domain wall in an antiferromagnet by magnons,"We theoretically study the interaction of magnons, quanta of spin waves, and
+a domain wall in a one-dimensional easy-axis antiferromagnet in the presence of
+an external magnetic field applied along the easy axis. To this end, we begin
+by obtaining the exact solution for spin waves in the background of a domain
+wall magnetized by an external field. The finite magnetization inside the
+domain wall is shown to give rise to reflection of magnons scattering off the
+domain wall, deviating from the well-known result of reflection-free magnons in
+the absence of a magnetic field. For practical applications of the predicted
+reflection of magnons, we show that the magnon reflection contributes to the
+thermally-driven domain-wall motion. Our work leads us to envision that
+inducing a finite magnetization in antiferromagnetic solitons such as vortices
+and skyrmions can be used to engender phenomena that do not occur in the
+absence of magnetization.",2002.11777v1
+2020-03-12,Collisionless kinetic theory for parametrically pumped magnons,"We discuss collisionless kinetic equations describing the non-equilibrium
+dynamics of magnons in a ferromagnet exposed to an oscillating microwave field.
+Previously, this problem has been treated within the so-called ""S-theory"" where
+the collision integral in the kinetic equation for the magnon distribution is
+either neglected or taken into account phenomenologically via an effective
+relaxation time. However, the possibility of magnon condensation has not been
+included in S-theory. Moreover, the momentum integrations appearing in the
+magnon self-energies are usually decoupled by retaining only the term where the
+loop momentum is equal to the external momentum. In this work we critically
+examine the accuracy of these approximations and develop the proper extensions
+of S-theory. We show that these extensions can significantly modify the time
+evolution of the magnon distribution.",2003.05949v2
+2020-03-28,Valley-polarized domain wall magnons in 2D ferromagnetic bilayers,"Valleytronics is a pioneering technological field relying on the valley
+degree of freedom to achieve novel electronic functionalities. Topological
+valley-polarized electrons confined to domain walls in bilayer graphene were
+extensively studied in view of their potentials in valleytronics. Here, we
+study the magnonic version of domain wall excitations in 2D honeycomb
+ferromagnetic bilayers (FBL) with collinear order. In particular, we explore
+the implications of Dzyaloshinskii-Moriya interaction (DMI) and electrostatic
+doping (ED) on the existence and characteristics of 1D magnons confined to
+layer stacking domain walls in FBL. The coexistence of DMI and ED is found to
+enrich the topology in FBL, yet the corresponding domain wall magnons do not
+carry a well-defined valley index. On the other hand, we show that layer
+stacking domain walls in DMI-free FBL constitute 1D channels for ballistic
+transport of topological valley-polarized magnons. Our theoretical results
+raise hope towards magnon valleytronic devices based on atomically thin
+topological magnetic materials.",2003.12791v3
+2020-04-08,A formalism for magnon gravitational wave detectors,"In order to detect high frequency gravitational waves, we need a new
+detection method. In this paper, we develop a formalism for a gravitational
+wave detector using magnons in a cavity. Using Fermi normal coordinates and
+taking the non-relativistic limit, we obtain a Hamiltonian for magnons in
+gravitational wave backgrounds. Given the Hamiltonian, we show how to use the
+magnons for detecting high frequency gravitational waves. Furthermore, as a
+demonstration of the magnon gravitational wave detector, we give upper limits
+on GHz gravitational waves by utilizing known results of magnon experiments for
+an axion dark matter search.",2004.04646v3
+2020-05-08,Electrical detection of magnon-photon interaction via auxiliary spin wave mode,"We report on the electrical detection of a hybrid magnon-photon system, which
+is comprised of a magnetic sample coupled to a planar cavity. While the uniform
+Kittel mode has the largest coupling strength among all the magnon modes, it
+only generates a modest voltage signal by means of inverse spin-Hall effect. We
+have found that the generated voltage can be significantly enhanced by
+introducing a higher order magnon mode, which possesses a much higher spin
+pumping efficiency and furthermore, it is nearly degenerated with the Kittel
+mode. The experimental results can be explained by our theoretical model, and
+suggest that the use of an auxiliary magnon mode can realize the configuration
+of a magnon-photon system with both strong coupling and large spin current.",2005.04161v1
+2020-05-12,Magnonic Quadrupole Topological Insulator in Antiskyrmion Crystals,"When the crystalline symmetries that protect a higher-order topological phase
+are not preserved at the boundaries of the sample, gapless hinge modes or
+in-gap corner states cannot be stabilized. Therefore, careful engineering of
+the sample termination is required. Similarly, magnetic textures, whose quantum
+fluctuations determine the supported magnonic excitations, tend to relax to new
+configurations that may also break crystalline symmetries when boundaries are
+introduced. Here we uncover that antiskyrmion crystals provide an
+experimentally accessible platform to realize a magnonic topological quadrupole
+insulator, whose hallmark signature are robust magnonic corner states.
+Furthermore, we show that tuning an applied magnetic field can trigger the
+self-assembly of antiskyrmions carrying a fractional topological charge along
+the sample edges. Crucially, these fractional antiskyrmions restore the
+symmetries needed to enforce the emergence of the magnonic corner states. Using
+the machinery of nested Wilson loops, adapted to magnonic systems supported by
+noncollinear magnetic textures, we demonstrate the quantization of the bulk
+quadrupole moment, edge dipole moments, and corner charges.",2005.05884v2
+2020-07-29,Magnon blockade in a PT-symmetric-like cavity magnomechanical system,"We investigate the magnon blockade effect in a parity-time (PT)
+symmetric-like three-mode cavity magnomechanical system involving the
+magnon-photon and magnon-phonon interactions. In the broken and unbroken
+PT-symmetric regions, we respectively calculate the second-order correlation
+function analytically and numerically and further determine the optimal value
+of detuning. By adjusting different system parameters, we study the different
+blockade mechanisms and find that the perfect magnon blockade effect can be
+observed under the weak parameter mechanism. Our work paves a way to achieve
+the magnon blockade in experiment.",2007.14645v1
+2020-08-04,Quantitative comparison of magnon transport experiments in three-terminal YIG/Pt nanostructures acquired via dc and ac detection techniques,"All-electrical generation and detection of pure spin currents is a promising
+way towards controlling the diffusive magnon transport in magnetically ordered
+insulators. We quantitatively compare two measurement schemes, which allow to
+measure the magnon spin transport in a three-terminal device based on a yttrium
+iron garnet thin film. We demonstrate that the dc charge current method based
+on the current reversal technique and the ac charge current method utilizing
+first and second harmonic lock-in detection can both efficiently distinguish
+between electrically and thermally injected magnons. In addition, both
+measurement schemes allow to investigate the modulation of magnon transport
+induced by an additional dc charge current applied to the center modulator
+strip. However, while at low modulator charge current both schemes yield
+identical results, we find clear differences above a certain threshold current.
+This difference originates from nonlinear effects of the modulator current on
+the magnon conductance.",2008.01416v1
+2020-08-26,Direct Imaging of Resonant Phonon-Magnon Coupling,"Direct detection of phonons is important for the investigation of information
+interconversion between the resonantly coupled magnons and phonons. Here we
+report resonant coupling of magnons and phonons, which can be directly
+visualized by using micro focused Brillouin light scattering in Ni/LiNbO3
+hybrid heterostructures. The patterns of surface acoustic wave phonons,
+originating from the interference between the original wave {\psi}0(A_0,k) and
+reflected wave {\psi}1(A_1,-k), can be modulated by magnetic field due to the
+magnon-phonon coupling. By analyzing the information of phonons obtained from
+Brillouin spectroscopy, the properties of the magnon system (Ni film), e.g.,
+ferromagnetic resonance field and resonance linewidth can be determined. The
+results provide spatially resolved information about phonon manipulation and
+detection in a coupled magnon-phonon system.",2008.11391v2
+2020-08-26,Magnon bands in twisted bilayer honeycomb quantum magnets,"We study the magnon bands of twisted bilayer honeycomb quantum magnets using
+linear spin wave theory. Although the interlayer coupling can be ferromagnetic
+or antiferromagnetic, we keep the intralayer one ferromagnetic to avoid
+possible frustration. For the interlayer ferromagnetic case, we find the magnon
+bands have similar features with the corresponding electronic energy spectrums.
+Although the linear dispersions near the Dirac points are preserved in the
+magnon bands of twisted bilayer magnets, their slopes are graduately reduced
+with the decrease of the twist angles. On the other hand, the interlayer
+antiferromagnetic couplings generate quite different magnon spectra. The two
+single-layered magnon spectra are usually undecoupled due to the opposite
+orientations of the spins in the two layers. We also develop a low-energy
+continuous theory for very small twist angles, which has been verified to fit
+well with the exact tight-binding calculations. Our results may be
+experimentally observed due to the rapid progress in two-dimensional magnetic
+materials.",2008.11640v1
+2020-11-30,Spin-Wave Doppler Shift by Magnon Drag in Magnetic Insulators,"The Doppler shift of the quasiparticle dispersion by charge currents is
+responsible for the critical supercurrents in superconductors and instabilities
+of the magnetic ground state of metallic ferromagnets. Here we predict an
+analogous effect in thin films of magnetic insulators in which microwaves
+emitted by a proximity stripline generate coherent chiral spin currents that
+cause a Doppler shift in the magnon dispersion. The spin-wave instability is
+suppressed by magnon-magnon interactions that limit spin currents to values
+close to but below the threshold for the instability. The spin current
+limitations by the backaction of magnon currents on the magnetic order should
+be considered as design parameters in magnonic devices.",2011.15008v2
+2021-03-16,All-electrical Magnon Transport Experiments in Magnetically Ordered Insulators,"Angular momentum transport is one of the cornerstones of spintronics. Spin
+angular momentum is not only transported by mobile charge carriers, but also by
+the quantized excitations of the magnetic lattice in magnetically ordered
+systems. In this regard, magnetically ordered insulators provide a platform for
+magnon spin transport experiments without additional contributions from spin
+currents carried by mobile electrons. In combination with charge-to-spin
+current conversion processes in conductors with finite spin-orbit coupling it
+is possible to realize all-electrical magnon transport schemes in thin film
+heterostructures. This review provides an insight into such experiments and
+recent breakthroughs achieved. Special attention is given to charge current
+based manipulation via an adjacent normal metal of magnon transport in
+magnetically ordered insulators in terms of spin-transfer torque. Moreover, the
+influence of two magnon modes with opposite spin in antiferromagnetic
+insulators on all-electrical magnon transport experiments is discussed.",2103.08996v2
+2021-04-22,All-Optical Generation of Antiferromagnetic Magnon Currents via the Magnon Circular Photogalvanic Effect,"We introduce the magnon circular photogalvanic effect enabled by stimulated
+Raman scattering. This provides an all-optical pathway to the generation of
+directed magnon currents with circularly polarized light in honeycomb
+antiferromagnetic insulators. The effect is the leading order contribution to
+magnon photocurrent generation via optical fields. Control of the magnon
+current by the polarization and angle of incidence of the laser is
+demonstrated. Experimental detection by sizeable inverse spin Hall voltages in
+platinum contacts is proposed.",2104.10914v2
+2021-04-26,Cavity magnomechanical storage and retrieval of quantum states,"We show how a quantum state in a microwave cavity mode can be transferred to
+and stored in a phononic mode via an intermediate magnon mode in a
+magnomechanical system. For this we consider a ferrimagnetic yttrium iron
+garnet (YIG) sphere inserted in a microwave cavity, where the microwave and
+magnon modes are coupled via a magnetic-dipole interaction and the magnon and
+phonon modes in the YIG sphere are coupled via magnetostrictive forces. By
+modulating the cavity and magnon detunings and the driving of the magnon mode
+in time, a Stimulated Raman Adiabatic Passage (STIRAP)-like coherent transfer
+becomes possible between the cavity mode and the phonon mode. The phononic mode
+can be used to store the photonic quantum state for long periods as it
+possesses lower damping than the photonic and magnon modes. Thus our proposed
+scheme offers a possibility of using magnomechanical systems as quantum memory
+for photonic quantum information.",2104.12323v1
+2021-05-10,Magnon diffuse scattering in scanning transmission electron microscopy,"We present a theory and a simulation of thermal diffuse scattering due to the
+excitation of magnons in scanning transmission electron microscopy. The
+calculations indicate that magnons can present atomic contrast when detected by
+electron energy-loss spectroscopy using atomic-size electron beams. The results
+presented here indicate that the intensity of the magnon diffuse scattering in
+bcc iron at 300~K is 4 orders of magnitude weaker than the intensity of thermal
+diffuse scattering arising from atomic vibrations. In an energy range where the
+phonon and magnon dispersions do not overlap, a monochromated scanning
+transmission electron microscope equipped with direct electron detectors for
+spectroscopy is expected to resolve the magnon spectral signatures.",2105.04467v1
+2021-05-16,Anatomy of inertial magnons in ferromagnets,"We analyze dispersion relations of magnons in ferromagnetic nanostructures
+with uniaxial anisotropy taking into account inertial terms, i.e. magnetic
+nutation. Inertial effects are parametrized by damping-independent parameter
+$\beta$, which allows for an unambiguous discrimination of inertial effects
+from Gilbert damping parameter $\alpha$. The analysis of magnon dispersion
+relation shows its two branches are modified by the inertial effect, albeit in
+different ways. The upper nutation branch starts at $\omega=1/ \beta$, the
+lower branch coincides with FMR in the long-wavelength limit and deviates from
+the zero-inertia parabolic dependence $\simeq\omega_{FMR}+Dk^2$ of the exchange
+magnon. Taking a realistic experimental geometry of magnetic thin films,
+nanowires and nanodiscs, magnon eigenfrequencies, eigenvectors and $Q$-factors
+are found to depend on the shape anisotropy. The possibility of phase-matched
+magneto-elastic excitation of nutation magnons is discussed and the condition
+was found to depend on $\beta$, exchange stiffness $D$ and the acoustic
+velocity.",2105.07376v1
+2021-06-30,Confined Magnons,"Magnetic structures are known to possess magnon excitations confined to their
+surfaces and interfaces, but these spatially localized modes are often not
+resolved in spectroscopy experiments. We develop a theory to calculate the
+confined magnon spectra and its associated spin scattering function, which is
+the physical observable in neutron and electron scattering, and a proxy for
+photon spectroscopy based on X-ray, Raman and THz sources. We show that extra
+anisotropy at the surface or interface plays a key role in magnon confinement.
+We obtain analytical expressions for the confinement length scale, and show
+that it is qualitatively similar for ferromagnets and antiferromagnets in
+dimension d>=2. For d=1 we find remarkable differences between ferromagnetic
+and antiferromagnetic models. The theory indicates the presence of several
+confined magnon resonances in addition to the usual magnons thought to explain
+the excitations of magnetic nanostructures. Detecting these modes may elucidate
+the impact of the interface on spin anisotropy and magnetic order.",2106.15771v2
+2021-07-27,Nonreciprocal magnon excitations by the Dzyaloshinskii-Moriya interaction on the basis of bond magnetic toroidal multipoles,"The microscopic conditions for the emergence of nonreciprocal magnon
+excitations in noncentrosymmetric magnets are theoretically investigated. We
+show that asymmetric magnon excitations appear when a bond magnetic toroidal
+dipole becomes active, which is defined as a parallel component between the
+Dzyaloshinskii-Moriya vector and the averaged spin moments at the ends of the
+bonds. Depending on magnetic structures accompanying the bond magnetic toroidal
+dipoles, the higher-rank magnetic toroidal multipoles can also be activated in
+a magnetic cluster, which describes various angle dependences of asymmetric
+magnon excitations. We demonstrate a variety of asymmetric magnon excitations
+for two magnetic systems in the noncentrosymmetric lattice structures; a
+one-dimensional breathing chain under a uniform crystalline electric field and
+a three-dimensional layered breathing kagome structure. We show that a bottom
+shift of magnon bands occurs by the magnetic toroidal dipole and a valley
+splitting occurs by the magnetic toroidal octupole under magnetic orderings.",2107.12743v1
+2021-08-11,Remote generation of magnon Schrödinger cat state via magnon-photon entanglement,"Magnon cat state represents a macroscopic quantum superposition of collective
+magnetic excitations of large number spins that not only provides fundamental
+tests of macroscopic quantum effects but also finds applications in quantum
+metrology and quantum computation. In particular, remote generation and
+manipulation of Schr\""{o}dinger cat states are particularly interesting for the
+development of long-distance and large-scale quantum information processing.
+Here, we propose an approach to remotely prepare magnon even/odd cat states by
+performing local non-Gaussian operations on the optical mode that is entangled
+with magnon mode through pulsed optomagnonic interaction. By evaluating key
+properties of the resulting cat states, we show that for experimentally
+feasible parameters they are generated with both high fidelity and
+nonclassicality, and with a size large enough to be useful for quantum
+technologies. Furthermore, the effects of experimental imperfections such as
+the error of projective measurements and dark count when performing
+single-photon operations have been discussed, where the lifetime of the created
+magnon cat states is expected to be $t\sim1\,\mu$s.",2108.05095v1
+2021-10-13,Generation of Bell and GHZ states from a hybrid qubit-photon-magnon system,"We propose a level-resolved protocol in a hybrid architecture for connecting
+a superconducting qubit and a magnon mode contained within a microwave cavity
+(resonator) to generate the local and global entangled states, enabling a wide
+range of applications in quantum communication, quantum metrology, and quantum
+information processing. Exploiting the high-degree of controllability in such a
+hybrid qubit-photon-magnon system, we derive effective Hamiltonians at the
+second- or the third-order resonant points by virtue of the strong
+counter-rotating interactions between the resonator and the qubit and between
+the resonator and the magnon. Consequently, we can efficiently generate the
+Bell states of the photon-magnon and the qubit-magnon subsystems and the
+Greenberger-Horne-Zeilinger state of the whole hybrid system. We also check the
+robustness of our protocol against the environmental noise by the Lindblad
+master equation. Our work makes this hybrid platform of high-degree of
+controllability a high-fidelity candidate for the realization of the
+maximally-entangled multiple states.",2110.06531v1
+2021-11-23,Modeling ultrafast demagnetization and spin transport: the interplay of spin-polarized electrons and thermal magnons,"We theoretically investigate laser-induced spin transport in metallic
+magnetic heterostructures using an effective spin transport description that
+treats itinerant electrons and thermal magnons on an equal footing.
+Electron-magnon scattering is included and taken as the driving force for
+ultrafast demagnetization. We assume that in the low-fluence limit the magnon
+system remains in a quasi-equilibrium, allowing a transient nonzero magnon
+chemical potential. In combination with the diffusive transport equations for
+the itinerant electrons, the description is used to chart the full spin
+dynamics within the heterostructure. In agreement with recent experiments, we
+find that in case the spin-current-receiving material includes an efficient
+spin dissipation channel, the interfacial spin current becomes directly
+proportional to the temporal derivative of the magnetization. Based on an
+analytical calculation, we discuss that other relations between the spin
+current and magnetization may arise in case the spin-current-receiving material
+displays inefficient spin-flip scattering. Finally, we discuss the role of
+(interfacial) magnon transport and show that, a priori, it cannot be neglected.
+However, its significance strongly depends on the system parameters.",2111.11961v1
+2022-01-02,Tunable Magnonic Chern Bands and Chiral Spin Currents in Magnetic Multilayers,"Realization of novel topological phases in magnonic band structures
+represents a new opportunity for the development of spintronics and magnonics
+with low power consumption. In this work, we show that in antiparallelly
+aligned magnetic multilayers, the long-range, chiral dipolar interaction
+generates bulk bands with non-zero Chern integers and magnonic surface states
+carrying chiral spin currents. The surface states are strictly localized and
+can be easily toggled between non-trivial and trivial phases through an
+external magnetic field. The realization of chiral surface spin currents in
+this dipolarly coupled heterostructure represents a magnonic implementation of
+the coupled wire model that has been extensively explored in electronic
+systems. Our work presents an easy-to-implement system for realizing
+topological magnonic surface states and low-dissipation spin current transport
+in a tunable manner.",2201.00312v2
+2022-01-11,Parametric Excitation and Instabilities of Spin Waves driven by Surface Acoustic Waves,"The parametric excitation of spin waves by coherent surface acoustic waves is
+demonstrated experimentally in metallic magnetic thin film structures. The
+involved magnon modes are analyzed with micro-focused Brillouin light
+scattering spectroscopy and complementary micromagnetic simulations combined
+with analytical modelling are used to determine the origin of the spin-wave
+instabilities. Depending on the experimental conditions, we observe spin-wave
+instabilities originating from different phonon-magnon and magnon-magnon
+scattering processes. Our results demonstrate that an efficient excitation of
+high amplitude, strongly nonlinear magnons in metallic ferromagnets is possible
+by surface acoustic waves, which opens novel ways to create micro-scaled
+nonlinear magnonic systems for logic and data processing that can profit from
+the high excitation efficiency of phonons using piezoelectricity.",2201.04033v2
+2022-02-11,"Spin stiffness, spectral weight, and Landau damping of magnons in metallic spiral magnets","We analyze the properties of magnons in metallic electron systems with spiral
+magnetic order. Our analysis is based on the random phase approximation for the
+susceptibilities of tight binding electrons with a local Hubbard interaction in
+two or three dimensions. We identify three magnon branches from poles in the
+susceptibilities, one associated with in-plane, the other two associated with
+out-of-plane fluctuations of the spiral order parameter. We derive general
+expressions for the spin stiffnesses and the spectral weights of the magnon
+modes, from which also the magnon velocities can be obtained. Moreover, we
+determine the size of the decay rates of the magnons due to Landau damping.
+While the decay rate of the in-plane mode is of the order of its excitation
+energy, the decay rate of the out-of-plane mode is smaller so that these modes
+are asymptotically stable excitations even in the presence of Landau damping.",2202.05660v1
+2022-03-13,"Identifying, and constructing, complex magnon band topology","Magnetically ordered materials tend to support bands of coherent propagating
+spin wave, or magnon, excitations. Topologically protected surface states of
+magnons offer a new path towards coherent spin transport for spintronics
+applications. In this work we explore the variety of topological magnon band
+structures and provide insight into how to efficiently identify topological
+magnon bands in materials. We do this by adapting the topological quantum
+chemistry approach that has used constraints imposed by time reversal and
+crystalline symmetries to enumerate a large class of topological electronic
+bands. We show how to identify physically relevant models of gapped magnon band
+topology by using so-called decomposable elementary band representations, and
+in turn discuss how to use symmetry data to infer the presence of exotic
+symmetry enforced nodal topology.",2203.06678v1
+2022-03-23,Topological Hybrids of Magnons and Magnon Bound Pairs,"We consider quantum condensed matter systems without particle-number
+conservation. Since the particle number is not a good quantum number, states
+belonging to different particle-number sectors can hybridize, which causes
+topological anticrossings in the spectrum. The resulting spectral gaps support
+chiral edge excitations whose wavefunction is a superposition of states in the
+two hybridized sectors. This situation is realized in fully saturated
+spin-anisotropic quantum magnets without spin conservation, in which single
+magnons hybridize with magnon bound pairs, i.e., two-magnon bound states. The
+resulting chiral edge excitations are exotic composites that carry mixed
+spin-multipolar character, inheriting spin-dipolar and spin-quadrupolar
+character from their single-particleness and two-particleness, respectively. In
+contrast to established topological magnons, the topological effects discussed
+here are of genuine quantum mechanical origin and vanish in the classical
+limit. We discuss implications for both intrinsic anomalous Hall-type transport
+and beyond-spintronics computation paradigms. We conclude that fully polarized
+quantum magnets are a promising platform for topology caused by hybridizations
+between particle-number sectors, complementing the field of ultracold atoms
+working with a conserved number of particles.",2203.12374v1
+2022-03-31,Thermal Hall responses in frustrated honeycomb spin systems,"We study geometrical responses of magnons driven by a temperature gradient in
+frustrated spin systems. While Dzyaloshinskii-Moriya (DM) interactions are
+usually incorporated to obtain geometrically nontrivial magnon bands, here we
+investigate thermal Hall responses of magnons that do no rely on the DM
+interactions. Specifically, we focus on frustrated spin systems with sublattice
+degrees of freedom and show that a nonzero Berry curvature requires breaking of
+an effective $PT$ symmetry. According to this symmetry consideration, we study
+the $J_1$-$J_2$-$J_2^\prime$ Heisenberg models on a honeycomb lattice as a
+representative example, and demonstrate that magnons in the spiral phase
+support the thermal Hall effect once we introduce a magnetic field and
+asymmetry between the two sublattices. We also show that driving the magnons by
+a temperature gradient induces spin current generation (i.e., magnon spin
+Nernst effect) in the $J_1$-$J_2$-$J_2^\prime$ Heisenberg models.",2203.16853v1
+2022-04-04,Generation of twisted magnons via spin-to-orbital angular momentum conversion,"Twisted magnons (TMs) carrying orbital angular momentum (OAM) have attracted
+much attention from the magnonic community. The fabrication of such novel
+magnon state however is still challenging. Here we present a simple method to
+generate TMs with arbitrary radial and azimuthal quantum numbers through the
+spin-to-orbital angular momentum conversion. The conversion rate from
+plane-wave magnons to twisted ones is shown to be insensitive to the quantum
+index. The spectrum of TMs in thin nanodisks is solved analytically, showing a
+good agreement with micromagnetic simulations. Moreover, we numerically study
+the propagation of TMs in magnetic nanodisk arrays and obtain the quantitative
+dependence of the decay length on quantum indexes. Our results are helpful for
+realizing TMs with large OAMs that are indispensable for future high-capacity
+magnonic communications and computings.",2204.01629v1
+2022-04-20,Magnon drag in a metal-insulating antiferromagnet bilayer,"We study a bilayer structure consisting of an antiferromagnetic insulator and
+a normal metal. An electron current is driven in the normal metal with
+direction parallel to the interface between the materials. Due to interfacial
+exchange coupling between the localized spins in the antiferromagnet and the
+itinerant electrons in the normal metal, a magnon current can then be induced
+in the antiferromagnet. Using an uncompensated antiferromagnetic interface,
+creating an asymmetry in the interfacial coupling to the two degenerate magnon
+modes, we find that it is possible to generate a magnon spin-current. The
+magnon spin-current can be enhanced by increasing the temperature or by
+spin-splitting the magnon modes.",2204.09686v2
+2022-04-29,All-magnonic Stern-Gerlach effect in antiferromagnets,"The Stern-Gerlach (SG) effect is well known as the spin-dependent splitting
+of a beam of atoms carrying magnetic moments by a magnetic-field gradient,
+leading to the concept of electron spin. Antiferromagnets can accommodate two
+magnon modes with opposite spin polarizations, which is equivalent to the spin
+property of electrons. Here, we propose the existence of an all-magnonic SG
+effect in antiferromagnetic magnonic system, where a linearly polarized
+spin-wave beam is deflected by a straight Dzyaloshinskii-Moriya interaction
+(DMI) interface into two opposite polarized spin-wave beams propagating in two
+discrete directions. Moreover, we observe bi-focusing of antiferromagnetic spin
+waves induced by a curved DMI interface, which can also spatially separate
+thermal magnons with opposite polarizations. Our findings provide a unique
+perspective to understand the rich phenomena associated with antiferromagnetic
+magnon spin and would be helpful for polarization-dependent application of
+antiferromagnetic spintronic devices.",2204.13942v1
+2022-05-04,Magnon Nernst Effect in Magnon Spin Hall Systems,"Magnon spin Hall systems could hardly show experimentally observable particle
+and thermal transport phenomena intrinsically due to the spin cancellation.
+Here we demonstrated that the magnon spin Hall systems can exhibit magnon
+Nernst effect and thermal Hall effect under external magnetic field by
+considering two typical systems, i.e. the antiferromagnetically (AFM) coupled
+bilayer honeycomb ferromagnets and monolayer collinear honeycomb
+antiferromagnet. The both systems experience magnetic phase transitions from
+AFM phase to a field-polarized phase via a spin-flop (SF) phase or directly. In
+both systems, there exist magnon Nerst effect and also thermal Hall effect
+under a longitudinal temperature gradient, which can be regarded as the
+indicator of the magnetic phase transitions, with the Hall conductivity
+dependence on magnetic field consistent with the order of magnetic phase
+transition.",2205.01891v1
+2022-06-02,Bistability in dissipatively coupled cavity magnonics,"Dissipative coupling of resonators arising from their cooperative dampings to
+a common reservoir induces intriguingly new physics such as energy level
+attraction. In this study, we report the nonlinear properties in a
+dissipatively coupled cavity magnonic system. A magnetic material YIG (yttrium
+iron garnet) is placed at the magnetic field node of a Fabry-Perot-like
+microwave cavity such that the magnons and cavity photons are dissipatively
+coupled. Under high power excitation, a nonlinear effect is observed in the
+transmission spectra, showing bistable behaviors. The observed bistabilities
+are manifested as clockwise, counterclockwise, and butterfly-like hysteresis
+loops with different frequency detuning. The experimental results are well
+explained as a Duffing oscillator dissipatively coupled with a harmonic one and
+the required trigger condition for bistability could be determined
+quantitatively by the coupled oscillator model. Our results demonstrate that
+the magnon damping has been suppressed by the dissipative interaction, which
+thereby reduces the threshold for conventional magnon Kerr bistability. This
+work sheds light upon potential applications in developing low power
+nonlinearity devices, enhanced anharmonicity sensors and for exploring the
+non-Hermitian physics of cavity magnonics in the nonlinear regime.",2206.01231v1
+2022-06-30,Second order nonlinearity induced multipartite entanglement in a hybrid magnon cavity QED system,"We present a proposal to produce bipartite and tripartite entanglement in a
+hybrid magnon-cavity QED system. Two macroscopic yttrium iron garnet (YIG)
+spheres are coupled to a single-mode microwave cavity via magnetic dipole
+interaction, while the cavity photons are generated via the two photon process
+induced by a pump field. Using the mean field theory, we show that the second
+order nonlinearity can result in strong bipartite entanglement between cavity
+photons and magnonic modes under two conditions, i.e., $\delta_c
+\delta_{m}=2g^2$ and $\delta_c=-\delta_{m}$. For the later one, we also show
+the possibility for producing the bipartite entanglement between two magnonic
+modes and tripartite entanglement among the cavity photons and two magnonic
+modes. Combining these two conditions, we further derive a third condition,
+i.e., $\delta_m^2-\phi^2+2g^2=0$, where the tripartite entanglement can be
+achieved when two magnonic modes have different resonant frequencies.",2206.15326v1
+2022-08-05,Floquet generation of magnonic NOON state,"We propose a concise and deterministic protocol to generate NOON states in a
+hybrid system consisting of a superconducting qubit, a circuit resonator mode,
+and two magnonic modes, based on Floquet engineering. In particular, we
+construct a time-reversal-symmetry broken Hamiltonian for chiral state
+propagation of the three continuous-variable modes depending on qubit state, by
+the time modulation over qubit-resonator interaction and magnon frequency. Then
+an arbitrary magnonic NOON state can be generated by a typical
+preparing-and-measurement procedure. We analyze the robustness of our protocol
+against the systematic errors in the qubit-magnon coupling strength, the
+Floquet-driving intensity, the frequency mismatch of the magnons, and the
+counter-rotating interactions. We can obtain a high-fidelity NOON state in the
+presence of the quantum dissipation on all components.",2208.02976v2
+2022-08-05,Novel magnetic excitations beyond the single- and double-magnons,"Conventional wisdom suggests that one photon that carries one unit of angular
+momentum can change the spin angular momentum of a magnetic system with one
+unit (delta Ms = +-1) at most. This would imply that a two-photon scattering
+process can manipulate the spin angular momentum of the magnetic system with a
+maximum of two units. Here we examine the fundamental limit of the
+photon-driven transport of angular momentum by studying the magnon spectrum of
+{\alpha}-Fe2O3 using resonant inelastic x-ray scattering. We discovered a
+cascade of higher-rank magnons carrying double, triple, quadruple, and
+quintuple the spin angular momentum of a single-magnon. Guided by theoretical
+calculations, we reveal how a two-photons scattering process can create exotic
+higher-rank magnons and the relevance of these quasiparticles for magnon-based
+applications.",2208.03198v1
+2022-08-08,Temperature and Field Dependence of Ferromagnetic Magnon in Monolayer Honeycomb Spin Lattice,"Temperature and field dependence of collective spin excitations or magnon in
+monolayer honeycomb spin lattices is investigated using an anisotropic exchange
+XZ-Heisenberg model in an external field. Magnetic phase transition in the
+presence of the transverse field is the spin reorientation (SR) transition with
+magnon intensity existing above the SR temperature. The transverse field either
+decreases or sustains the spin-wave intensity in the temperature region below
+or above the SR temperature, respectively. The gap of the zero-momentum
+low-energy magnon branch closes at the SR transverse field, which is the
+critical quantum phase transition field at zero temperature. The application of
+the model to a two-dimensional CrI$_3$ explains the existence of the
+zero-momentum magnon mode above the Curie temperature and shows the suitable
+values of the exchange parameters compared with the DFT calculations. The
+estimated magnon velocity near the Dirac point in this material is about 1.74
+km/s.",2208.03913v1
+2022-09-01,\textit{Ab initio} study on spin fluctuations of itinerant kagome magnet FeSn,"Kagome antiferromagnetic metal FeSn has become an attracting platform for the
+exploration of novel electronic states, such as topological Dirac states and
+the formation of flat bands by localized electrons. Apart from the electronic
+properties, Dirac magnons and flat magnon bands have also been proposed by
+applying simplified Heisenberg models to kagome magnetic systems.Inelastic
+neutron scattering studies on FeSn found well defined magnon dispersions at low
+energies,but magnons at high energies are strongly dampled, which can not be
+explained by localized spin models. In this paper, we utilize both linear spin
+wave theory and time-dependent density functional perturbation theory to
+investigate spin fluctuations of FeSn. Through the comparison of calculated
+spin wave spectra and Stoner continuum, we explicitly show that the damping of
+magnons at high energies are due to the Landau damping, and the appearance of
+high energy optical-magnon like branches at the M and K point are resulted by
+relatively low Stoner excitation intensity at those regions.",2209.00187v1
+2022-09-07,Nonequilibrium magnons from hot electrons in antiferromagnetic systems,"We describe a \emph{nonthermal} magnon activation mechanism in
+antiferromagnetic (AFM) systems via locally equilibrated
+\emph{spin-unpolarized} hot electrons excited by an ultrafast intense laser
+pulse. We employ a quantum kinetic equation that takes into account a direct
+electron-magnon scattering channel in either bulk AFM metal or at the interface
+of the AFM/normal-metal heterostructure. The mechanism is responsible for the
+nonequilibrium population of AFM magnon modes on a subnanosecond timescale,
+which are formed shortly after the local thermalization of hot electrons by
+Coulomb interactions. Nonequilibrium magnon populations can be additionally
+manipulated by applying an external magnetic field. Our work paves the way
+toward spin dynamics control in AFM systems via the ultrafast manipulation of
+out-of-equilibrium magnon excitations.",2209.03469v2
+2022-12-11,Manifestation of the coupling phase in microwave cavity magnonics,"The interaction between microwave photons and magnons is well understood and
+originates from the Zeeman coupling between spins and a magnetic field.
+Interestingly, the magnon/photon interaction is accompanied by a phase factor
+which can usually be neglected. However, under the rotating wave approximation,
+if two magnon modes simultaneously couple with two cavity resonances, this
+phase cannot be ignored as it changes the physics of the system. We consider
+two such systems, each differing by the sign of one of the magnon/photon
+coupling strengths. This simple difference, originating from the various
+coupling phases in the system, is shown to preserve, or destroy, two potential
+applications of hybrid photon/magnon systems, namely dark mode memories and
+cavity-mediated coupling. The observable consequences of the coupling phase in
+this system is akin to the manifestation of a discrete Pancharatnam-Berry
+phase, which may be useful for quantum information processing.",2212.05389v1
+2023-01-23,Magnon-bandgap controllable artificial domain wall waveguide,"In this paper, a magnon-bandgap controllable artificial domain wall waveguide
+is proposed by means of micromagnetic simulation. By the investigation of the
+propagation behavior and dispersion relationship of spin waves in artificial
+domain wall waveguides, it is found that the nonreciprocal propagation of spin
+waves in the artificial domain walls are mainly affected by the local effective
+exchange field, and the magnon bandgap can be controlled by changing the
+maximum value of the effective exchange field. In addition, it is observed that
+the artificial domain wall waveguides are structurally more stable than the
+natural domain wall waveguides under the same spin wave injection conditions,
+and the magnon bandgap of the artificial domain wall waveguides can be adjusted
+by its width and magnetic anisotropy parameters. The bandgap controllable
+artificial domain wall scheme is beneficial to the miniaturization and
+integration of magnon devices and can be applied to future magnonic technology
+as a novel frequency filter.",2301.09291v1
+2023-02-25,Transmon probe for quantum characteristics of magnons in antiferromagnets,"The detection of magnons and their quantum properties, especially in
+antiferromagnetic (AFM) materials, is a substantial step to realize many
+ambitious advances in the study of nanomagnetism and the development of energy
+efficient quantum technologies. The recent development of hybrid systems based
+on superconducting circuits provides the possibility of engineering quantum
+sensors that exploit different degrees of freedom. Here, we examine the
+magnon-photon-transmon hybridisation based on bipartite AFM materials, which
+gives rise to an effective coupling between a transmon qubit and magnons in a
+bipartite AFM. We demonstrate how magnetically invisible magnon modes, their
+chiralities and quantum properties such as nonlocality and two-mode magnon
+entanglement in bipartite AFMs can be characterized through the Rabi frequency
+of the superconducting transmon qubit.",2302.13167v1
+2023-04-27,Conversion of chiral phonons into magnons in ferromagnets and antiferromagnets,"Chiral phonons with atomic rotations converted into electron spins result in
+a change of spin magnetizations in crystals. In this paper, we investigate a
+new conversion of chiral phonons into magnons both in ferromagnets and
+antiferromagnets by spin models with exchange and Dzyaloshinskii-Moriya
+interactions. The atomic rotations in chiral phonons are treated as slow
+phonons, which modulate spin-spin interaction and induce time-dependent magnon
+excitations due to geometric effect within adiabatic approximation. We
+demonstrate that a non-trivial change of the number of magnons requires
+breaking of the spin-rotation symmetry around the spin quantization axis. As a
+result, the clockwise and counterclockwise chiral phonons induce a change of
+the magnon number with opposite signs, which corresponds to an increasing or
+decreasing spin magnetizaton due to the chiral nature of the atomic rotations.
+In particular, in antiferromagnets, the modulation of magnons due to chiral
+phonons generates a non-zero net magnetization by the proposed effect, which is
+expect to be observed in experiments.",2304.14000v3
+2023-05-17,Spin-wave dynamics controlled by tunable ac magnonic crystal,"The magnonic crystal, which has a spatial modulation wave vector $q$, couples
+the spin wave with wave vector $k$ to the one with wave vector $k-q$. For a
+conventional magnonic crystal with direct current (dc) supply, the spin waves
+around $q/2$ are resonantly coupled to the waves near $-q/2$, and a band gap is
+opened at $k=\pm q/2$. If instead of the dc current the magnonic crystal is
+supplied with an alternating current (ac), then the band gap is \emph{shifted}
+to $k$ satisfying $|\omega_{s}(k)-\omega_{s}(k-q)|=\omega_{ac}$; here
+$\omega_{s}(k)$ is the dispersion of the spin wave, while $\omega_{ac}$ is the
+frequency of the ac modulation. The resulting gap in the case of the ac
+magnonic crystal is the half of the one caused by the dc with the same
+amplitude of modulation. The time evolution of the resonantly coupled spin
+waves controlled by properly suited ac pulses can be well interpreted as the
+motion on a Bloch sphere. The tunability of the ac magnonic crystal broadens
+the perspective of spin-wave computing.",2305.09876v1
+2023-05-18,Two-tone modulated cavity electromagnonics,"Cavity electromagnonics has increasingly emerged as a new platform for the
+fundamental study of quantum mechanics and quantum technologies. Since the
+coupling between the microwave field and magnon Kittle modes in current
+experiments is much weaker than their resonant frequencies, the anti-rotating
+terms in magnon-microwave-photon interaction can be neglected and only the
+beam-splitter-like part takes effect. In this situation, the direct generation
+of magnonic nonclassical states is impossible, unless other subsystems e.g.
+phonons, squeezed photons or superconducting qubits are incorporated. In this
+paper, we consider two-tone modulated cavity electromagnonics to keep the
+nontrivial anti-rotating terms and obtain tunable phase factors, resulting in
+an effective Hamiltonian exactly the same as that of generic linearized cavity
+optomechanics. This can therefore be exploited to directly prepare macroscopic
+magnonic quantum states, as detailedly exemplified by the generation of steady
+and strongly squeezed and entangled states, realize ultra-sensitive
+magnon-based sensing by engineering backaction-evading interaction of magnons
+and photons, and develop spintronics-related quantum information processing
+devices.",2305.10653v1
+2023-05-22,Switching of magnon parametric oscillation by magnetic field direction,"Parametric oscillation occurs when the resonance frequency of an oscillator
+is periodically modulated. Owing to time-reversal symmetry breaking in magnets,
+nonreciprocal magnons can be parametrically excited when spatial-inversion
+symmetry breaking is provided. This means that magnons with opposite
+propagation directions have different amplitudes. Here we demonstrate switching
+on and off the magnon parametric oscillation by reversing the external field
+direction applied to a Y$_3$Fe$_5$O$_{12}$ micro-structured film. The result
+originates from the nonreciprocity of surface mode magnons, leading to
+field-direction dependence of the magnon accumulation under a nonuniform
+microwave pumping. Our numerical calculation well reproduces the experimental
+result.",2305.12787v2
+2023-06-04,Topological phase transitions in a honeycomb ferromagnet with unequal Dzyaloshinskii-Moriya interactions,"This theoretical research is devoted to study topological phase transitions
+in a two-dimensional honeycomb ferromagnetic lattice with unequal
+Dzyaloshinskii-Moriya interactions for the two sublattices. With the help of a
+first-order Green function formalism, we analyze the influence of magnon-magnon
+interaction on the magnon band topology. It is found that the existence of the
+antichiral Dzyaloshinskii-Moriya interaction can led to a tilting of the
+renormalized magnon bands near the Dirac momenta. Then, the renormalized magnon
+band gaps at Dirac points have different widths. Through changing the
+temperature, we can observe the renormalized magnon band gap closing-reopening
+phenomenon, which corresponds to the topological phase transition. Our results
+show that the critical temperature of the topological phase transition is
+related to the strength of the antichiral Dzyaloshinskii-Moriya interaction.",2306.02505v2
+2023-07-04,Magnonic Hong-Ou-Mandel Effect,"We carried out numerical simulations of propagation of spin waves (magnons in
+quantum language) in a yttrium-iron garnet film. The numerical model is based
+on an original formalism. We demonstrated that a potential barrier for magnons,
+created by an Oersted field of a dc current flowing through a wire sitting on
+top of the film, is able to act as an electrically controlled partly
+transparent mirror for the magnons. We found that the mirror transparency can
+be set to 50% by properly adjusting the current strength, thus creating a
+semi-transparent mirror. A strong Hong-Ou-Mandel Effect for single magnons is
+expected in this configuration. The effect must be seen as two single magnons,
+launched simultaneously into the film from two transducers located from the
+opposite sides of the mirror, creating a two-microwave-photon state at the
+output port of one of the transducers. The probability of seeing those
+two-photon states at the output port of either transducer must be the same for
+both transducers.",2307.01547v1
+2023-07-07,Valley-Selective Phonon-Magnon Scattering in Magnetoelastic Superlattices,"Phonons and magnons are engineered by periodic potential landscapes in
+phononic and magnonic crystals, and their combined studies may enable valley
+phonon transport tunable by the magnetic field. Through nonreciprocal surface
+acoustic wave transmission, we demonstrate valley-selective phonon-magnon
+scattering in magnetoelastic superlattices. The lattice symmetry and the
+out-of-plane magnetization component control the sign of nonreciprocity. The
+phonons in the valleys play a crucial role in generating nonreciprocal
+transmission by inducing circularly polarized strains that couple with the
+magnons. The transmission spectra show a nonreciprocity peak near a
+transmission gap, matching the phononic band structure. Our results open the
+way for manipulating valley phonon transport through periodically varying
+magnon-phonon coupling.",2307.03367v2
+2023-07-19,Enhanced bipartite entanglement and Gaussian quantum steering of squeezed magnon modes,"We theoretically investigate a scheme to entangle two squeezed magnon modes
+in a double cavitymagnon system, where both cavities are driven by a two-mode
+squeezed vacuum microwave field. Each cavity contains an optical parametric
+amplifier as well as a macroscopic yttrium iron garnet (YIG) sphere placed near
+the maximum bias magnetic fields such that this leads to the excitation of the
+relevant magnon mode and its coupling with the corresponding cavity mode. We
+have obtained optimal parameter regimes for achieving the strong magnon-magnon
+entanglement and also studied the effectiveness of this scheme towards the
+mismatch of both the cavity-magnon couplings and decay parameters. We have also
+explored the entanglement transfer efficiency including Gaussian quantum
+steering in our proposed system",2307.09846v1
+2023-07-23,Spin Space Group Theory and Unconventional Magnons in Collinear Magnets,"Topological magnons have received substantial interest for their potential in
+both fundamental research and device applications due to their exotic uncharged
+yet topologically protected boundary modes. However, their understanding has
+been impeded by the lack of fundamental symmetry descriptions of magnetic
+materials, of which the spin Hamiltonians are essentially determined by the
+isotropic Heisenberg interaction. The corresponding magnon band structures
+allows for more symmetry operations with separated spin and spatial operations,
+forming spin space groups (SSGs), than the conventional magnetic space groups.
+Here we developed spin space group (SSG) theory to describe collinear magnetic
+configurations, identifying all the 1421 collinear SSGs and categorizing them
+into four types, constructing band representations for these SSGs, and
+providing a full tabulation of SSGs with exotic nodal topology. Our
+representation theory perfectly explains the band degeneracies of previous
+experiments and identifies new magnons beyond magnetic space groups with
+topological charges, including duodecuple point, octuple nodal line and
+charge-4 octuple point. With an efficient algorithm that diagnoses topological
+magnons in collinear magnets, our work offers new pathways to exploring exotic
+phenomena of magnonic systems, with the potential to advance the
+next-generation spintronic devices.",2307.12366v1
+2023-07-24,"Correlations, disorder, and multi-magnon processes in terahertz spin dynamics of magnetic nanostructures: A first-principles investigation","Understanding the profound impact of correlation effects and crystal
+imperfections is essential for an accurate description of solids. Here we study
+the role of correlation, disorder, and multi-magnon processes in THz magnons.
+Our findings reveal that a significant part of the electron self-energy, which
+goes beyond the adiabatic local spin density approximation, arises from the
+interaction between electrons and a virtual magnon gas. This interaction leads
+to a substantial modification of the exchange splitting and a renormalization
+of magnon energies, in agreement with the experimental data. We establish a
+quantitative hierarchy of magnon relaxation processes based on first
+principles.",2307.12649v3
+2023-08-20,Terahertz cavity magnon polaritons,"Hybrid light-matter coupled states, or polaritons, in magnetic materials have
+attracted significant attention due to their potential for enabling novel
+applications in spintronics and quantum information processing. However, most
+studies to date have been carried out for ferromagnetic materials with magnon
+excitations at gigahertz frequencies. Here, we have investigated strong
+resonant photon-magnon coupling at frequencies above 1 terahertz for the first
+time in a prototypical room-temperature antiferromagnetic insulator, NiO,
+inside a Fabry-P\'erot cavity. The cavity was formed by the crystal itself when
+it was thinned down to an optimized thickness. By using terahertz time-domain
+spectroscopy in high magnetic fields up to 25 T, we swept the magnon frequency
+through Fabry-P\'erot cavity modes and observed photon-magnon anticrossing
+behavior, demonstrating clear vacuum Rabi splittings exceeding the polariton
+linewidths. These results show that NiO is a promising platform for exploring
+antiferromagnetic spintronics and cavity magnonics in the terahertz frequency
+range.",2308.10159v1
+2023-08-25,Macroscopic distant magnon modes entanglement via a squeezed reservoir,"The generation of robust entanglement in quantum system arrays is a crucial
+aspect of the realization of efficient quantum information processing.
+Recently, the field of quantum magnonics has garnered significant attention as
+a promising platform for advancing in this direction. In our proposed scheme,
+we utilize a one-dimensional array of coupled cavities, with each cavity
+housing a single yttrium iron garnet (YIG) sphere coupled to the cavity mode
+through magnetic dipole interaction. To induce entanglement between YIGs, we
+employ a local squeezed reservoir, which provides the necessary nonlinearity
+for entanglement generation. Our results demonstrate the successful generation
+of bipartite and tripartite entanglement between distant magnon modes, all
+achieved through a single quantum reservoir. Furthermore, the steady-state
+entanglement between magnon modes is robust against magnon dissipation rates
+and environment temperature. Our results may lead to applications of
+cavity-magnon arrays in quantum information processing and quantum
+communication systems.",2308.13586v3
+2023-09-18,Terahertz magnon frequency comb,"Magnon frequency comb (MFC), the spin-wave spectra composing of equidistant
+coherent peaks, is attracting much attention in magnonics. A terahertz (THz)
+MFC, combining the advantages of the THz and MFC technologies, is highly
+desired because it would significantly advance the MFC applications in
+ultrafast magnonic metrology, sensing, and communications. Here, we show that
+the THz MFC can be generated by nonlinear interactions between spin waves and
+skyrmions in antiferromagnets [Z. Jin \emph{et al}.,
+\href{https://doi.org/10.48550/arXiv.2301.03211}{arXiv:2301.03211}]. It is
+found that the strength of the three-wave mixing between propagating magnons
+and breathing skyrmions follows a linear dependence on the driving frequency
+and the MFC signal can be observed over a broad driving frequency range. Our
+results extend the working frequency of MFC to the THz regime, which would have
+potential applications in ultrafast spintronic devices and promote the
+development of nonlinear magnonics in antiferromagnets.",2309.09475v1
+2023-09-28,Engineering Entangled Coherent States of Magnons and Phonons via a Transmon Qubit,"We propose a scheme for generating and controlling entangled coherent states
+(ECS) of magnons, i.e. the quanta of the collective spin excitations in
+magnetic systems, or phonons in mechanical resonators. The proposed hybrid
+circuit architecture comprises a superconducting transmon qubit coupled to a
+pair of magnonic Yttrium Iron Garnet (YIG) spherical resonators or mechanical
+beam resonators via flux-mediated interactions. Specifically, the coupling
+results from the magnetic/mechanical quantum fluctuations modulating the qubit
+inductor, formed by a superconducting quantum interference device (SQUID). We
+show that the resulting radiation-pressure interaction of the qubit with each
+mode, can be employed to generate maximally-entangled states of magnons or
+phonons. In addition, we numerically demonstrate a protocol for the preparation
+of magnonic and mechanical Bell states with high fidelity including realistic
+dissipation mechanisms. Furthermore, we have devised a scheme for reading out
+the prepared states using standard qubit control and resonator field
+displacements. Our work demonstrates an alternative platform for quantum
+information using ECS in hybrid magnonic and mechanical quantum networks.",2309.16514v1
+2023-10-09,Estimation theory of photon-magnon coupling strength in a driven-dissipative double-cavity-magnon system,"Cavity-magnon systems are emerging as a fruitful architecture for the
+integration of quantum technologies and spintronic technologies, where magnons
+are coupled to microwave photons via the magnetic-dipole interaction.
+Controllable the photon-magnon (P-M) couplings provide a powerful means of
+accessing and manipulating quantum states in such hybrid systems. Thus
+determining the relevant P-M couplings is a fundamental task. Here we address
+the quantum estimation problem for the P-M coupling strength in a
+double-cavity-magnon system with drive and dissipation. The effects of various
+physical factors on the estimation precision are investigated and the
+underlying physical mechanisms are discussed in detail. Considering that in
+practical experiments it is almost infeasible to perform measurements on the
+global quantum state of this composite system, we identify the optimal
+subsystem for performing measurements and estimations. Further, we evaluate the
+performance of different Gaussian measurements, indicating that optimal
+Gaussian measurement almost saturates the ultimate theoretical bound on the
+estimation precision given by the quantum Fisher information.",2310.05412v1
+2023-10-26,Effects of Finite Material Size On Axion-magnon Conversion,"Magnetic materials are particularly favorable targets for detecting axions
+interacting with electrons because the collective excitation of electron spins,
+the magnon, can be excited through the axion-magnon conversion process. It is
+often assumed that only the zero-momentum uniformly precessing magnetostatic
+(Kittel) mode of the magnon is excited. This is justified if the de Broglie
+wavelength of the axion is much longer than the size of the target magnetic
+material. However, if the de Broglie wavelength is shorter, finite-momentum
+magnon modes can also be excited. We systematically analyze the target material
+size dependence of the axion-magnon conversion rate. We discuss the importance
+of these effects in the detection of relativistic axions as well as in the
+detection of axion dark matter of relatively heavy mass with large material
+size.",2310.17704v2
+2023-11-10,Nonreciprocal Spin Waves in Nanoscale Domain Walls Detected by Scanning X-ray Microscopy in Perpendicular Magnetic Anisotropic Fe/Gd Multilayers,"Spin wave nonreciprocity in domain walls (DWs) allows for unidirectional
+signal processing in reconfigurable magnonic circuits. Using scanning
+transmission x-ray microscopy (STXM), we examined coherently-excited magnons
+propagating in Bloch-like DWs in amorphous Fe/Gd multilayers with perpendicular
+magnetic anisotropy (PMA). Near 1 GHz we detected magnons with short
+wavelengths down to $\lambda = 281$ nm in DWs whose minimum width amounted to
+$\delta_{\rm DW} = 52$ nm. Consistent with micromagnetic simulations, the STXM
+data reveal their nonreciprocal magnon band structures. We identified Bloch
+points which disrupted the phase evolution of magnons and induced different
+$\lambda$ adjacent to the topological defects. Our observations provide direct
+evidence of nonreciprocal spin waves within Bloch-like DWs, serving as
+programmable waveguides in magnonic devices with directed information flow.",2311.06186v1
+2023-12-12,Topological magnon-polaron transport in a bilayer van der Waals magnet,"The stacking of intrinsically magnetic van der Waals materials provides a
+fertile platform to explore tunable transport effects of magnons, presenting
+significant prospects for spintronic applications. The possibility of having
+topologically nontrivial magnons in these systems can further expand the scope
+of exploration. In this work, we consider a bilayer system with intralayer
+ferromagnetic exchange and a weak interlayer antiferromagnetic exchange, and
+study the topological magnon-polaron excitations induced by magnetoelastic
+couplings. Under an applied magnetic field, the system features a metamagnetic
+transition, where the magnetic ground state changes from antiparallel layers to
+parallel. We show that the metamagnetic transition is accompanied by a
+transition of the topological structure of the magnon polarons, which results
+in discernible changes in the topology induced transport effects. The
+magnetic-field dependence of the thermal Hall conductivity and spin Nernst
+coefficient is analyzed with linear response theories.",2312.07463v2
+2023-12-19,Macroscopic entanglement between ferrimagnetic magnons and atoms via crossed optical cavity,"We consider a two-dimensional opto-magnomechanical (OMM) system including two
+optical cavity modes, a magnon mode, a phonon mode, and a collection of
+two-level atoms. In this study, we demonstrate the methodology for generating
+stationary entanglement between two-level atoms and magnons, which are
+implemented using two optical cavities inside the setup. Additionally, we
+investigate the efficiency of transforming entanglement from atom-phonon
+entanglement to atom-magnon entanglement. The magnons are stimulated by both a
+bias magnetic field and a microwave magnetic field, and they interact with
+phonons through the mechanism of magnetostrictive interaction. This interaction
+generates magnomechanical displacement, which couples to an optical cavity via
+radiation pressure. We demonstrate that by carefully selecting the frequency
+detuning of an optical cavity, it is possible to achieve an increase in
+bipartite entanglements. Furthermore, this improvement is found to be resistant
+to changes in temperature. The entanglement between atoms and magnons plays a
+crucial role in the construction of hybrid quantum networks. Our modeling
+approach exhibits potential applications in the field of magneto-optical trap
+systems as well.",2312.11864v1
+2024-01-30,Entropy production rate and correlations of cavity magnomechanical system,"We present the irreversibility generated by a stationary cavity
+magnomechanical system composed of a yttrium iron garnet (YIG) sphere with a
+diameter of a few hundred micrometers inside a microwave cavity. In this
+system, the magnons, i.e., collective spin excitations in the sphere, are
+coupled to the cavity photon mode via magnetic dipole interaction and to the
+phonon mode via magnetostrictive force (optomechanical-like). We employ the
+quantum phase space formulation of the entropy change to evaluate the
+steady-state entropy production rate and associated quantum correlation in the
+system. We find that the behavior of the entropy flow between the cavity photon
+mode and the phonon mode is determined by the magnon-photon coupling and the
+cavity photon dissipation rate. Interestingly, the entropy production rate can
+increase/decrease depending on the strength of the magnon-photon coupling and
+the detuning parameters. We further show that the amount of correlations
+between the magnon and phonon modes is linked to the irreversibility generated
+in the system for small magnon-photon coupling. Our results demonstrate the
+possibility of exploring irreversibility in driven magnon-based hybrid quantum
+systems and open a promising route for quantum thermal applications.",2401.16857v1
+2024-02-14,Slow-Wave Hybrid Magnonics,"Cavity magnonics is an emerging research area focusing on the coupling
+between magnons and photons. Despite its great potential for coherent
+information processing, it has been long restricted by the narrow interaction
+bandwidth. In this work, we theoretically propose and experimentally
+demonstrate a novel approach to achieve broadband photon-magnon coupling by
+adopting slow waves on engineered microwave waveguides. To the best of our
+knowledge, this is the first time that slow wave is combined with hybrid
+magnonics. Its unique properties promise great potentials for both fundamental
+research and practical applications, for instance, by deepening our
+understanding of the light-matter interaction in the slow wave regime and
+providing high-efficiency spin wave transducers. The device concept can be
+extended to other systems such as optomagnonics and magnomechanics, opening up
+new directions for hybrid magnonics.",2402.08872v1
+2024-02-20,Quantum Sensing of Antiferromagnetic Magnon Two-Mode Squeezed Vacuum,"N\'eel ordered antiferromagnets exhibit two-mode squeezing such that their
+ground state is a nonclassical superposition of magnon Fock states. Here we
+theoretically demonstrate that antiferromagnets can couple to spin qubits via
+direct dispersive interaction stemming from, e.g., interfacial exchange. We
+demonstrate that this kind of coupling induces a magnon number dependent level
+splitting of the excited state resulting in multiple system excitation
+energies. This series of level splittings manifests itself as nontrivial
+excitation peaks in qubit spectroscopy thereby revealing the underlying
+nonclassical magnon composition of the antiferromagnetic quantum state. By
+appropriately choosing the drive or excitation energy, the magnonic state can
+be controlled via the qubit, suggesting that Fock states of magnon pairs can be
+generated deterministically. This enables achieving states useful for quantum
+computing and quantum information science protocols.",2402.13203v1
+2024-02-23,Magnons and fundamental magnetic interactions in a ferromagnetic monolayer: The case of Ni monolayer,"The experimental investigations of the magnetic interactions in an atomically
+thin magnetic layer are essential to understand the physics of low-dimensional
+magnets. The full spectrum of collective magnetic excitations (magnons) would
+provide an access to these fundamental interactions on the atomic scale. Here
+in order to be able to excite the magnons by means of spin-polarized electrons
+we couple a Ni monolayer to one and two atomic layers of Co and probe the full
+experimental magnon dispersion relation up to the Brillouin zone boundary.
+Comparing to the results of ab initio calculations we quantify the complex
+pattern of the magnetic exchange interaction in the Ni monolayer. We show that
+although the magnons in this system are rather stiff, the Heisenberg exchange
+coupling between the Ni spins is weak. We unravel the origin of the observed
+large magnon stiffness constant being a consequence of the small spin density
+of the Ni atoms.",2402.15251v1
+2024-03-12,Antiferromagnetic magnons on a Möbius strip: topology-induced symmetry breaking,"A M\""obius strip comprising of two antiferromagnetically coupled spin chains
+showcase exotic magnon excitations with non-trivial physical behavior, which is
+solely attributed to the real-space boundary condition even in the absence of
+local curvature effects. Counterintuitively, magnons on a M\""obius strip
+feature linear polarization of the N\'eel vector devoid of chirality even when
+the spin Hamiltonian preserves local rotational symmetry around the anisotropic
+easy axis. These linearly-polarized magnons form two non-degenerate branches
+that can neither be smoothly connected to nor be decomposed by the
+circularly-polarized magnons of opposite chirality commonly found in
+antiferromagnets. Only one branch supports standing-wave formation on the
+M\""obius strip while the other does not, owing to its spectral shift incurred
+by the boundary condition. By unraveling a hitherto unknown mechanism of
+topology-induced symmetry breaking, our findings highlight the profound impact
+of real-space topology on the physical nature of not only magnons but also
+other bosonic quasiparticles.",2403.07846v2
+2024-03-13,Thermal Hall effect in a van der Waals ferromagnet CrI3,"CrI3 is a prototypical van der Waals ferromagnet with a magnetic honeycomb
+lattice. Previous inelastic neutron scattering studies have suggested
+topological nature of its magnetic excitations with a magnon gap at the Dirac
+points, which are anticipated to give rise to magnon thermal Hall effect. Here
+we report thermal transport properties of CrI3 and show that the long-sought
+thermal Hall signal anticipated for topological magnons is fairly small. In
+contrast, we find that CrI3 exhibits an appreciable anomalous thermal Hall
+signal at lower temperature which may arise from magnon-phonon hybridization or
+magnon-phonon scattering. These findings are anticipated to stimulate further
+neutron scattering studies on CrI3 single crystal, which can shed light not
+only on the intrinsic nature of magnetic excitations but also on the
+magnon-phonon interaction.",2403.08180v1
+2024-03-17,Electrical reversal of the sign for magnon thermal Hall coefficient in van der Waals bilayer antiferromagnet,"With spin-layer locking, the manipulation of spin degree of freedom via
+perpendicular electric field can be realized in a typical antiferromagnetically
+coupled bilayer. In analogy to the electric control of the anomalous layer Hall
+effect of electron within such bilayer system, we propose here its magnon
+counterpart i.e., thermal Hall effect controlled by a perpendicular electric
+field. Unlike electrons, magnon is charged neutral and its transport in solids
+can be driven by a thermal gradient. It also exhibits Hall response due to the
+intrinsic Berry curvature of magnon, analogous to the achievement in electron
+system. Taking bilayer 2H-VSe2 with both H-type stacking interlayer
+antiferromagnetic coupling as a platform, we perform first-principles
+calculations towards the magnetic exchange coupling parameters under applied
+electric field perpendicular to the plane. Based on linear spin wave
+approximation, we then fit the magnon band structures accordingly and calculate
+the corresponding Berry curvature. The thermal Hall coefficient dependence on
+the temperature under thermal gradient can be calculated correspondingly in
+linear response regime. It is shown that electric field reversal is able to
+reverse the sign of the coefficient. These findings provide a platform for the
+realization of all-electric magnon spintronics.",2403.11119v1
+2002-09-23,Giant magnetothermopower of magnon-assisted transport in ferromagnetic tunnel junctions,"We present a theoretical description of the thermopower due to
+magnon-assisted tunneling in a mesoscopic tunnel junction between two
+ferromagnetic metals. The thermopower is generated in the course of thermal
+equilibration between two baths of magnons, mediated by electrons. For a
+junction between two ferromagnets with antiparallel polarizations, the ability
+of magnon-assisted tunneling to create thermopower $S_{AP}$ depends on the
+difference between the size $\Pi_{\uparrow, \downarrow}$ of the majority and
+minority band Fermi surfaces and it is proportional to a temperature dependent
+factor $(k_{B}T/\omega_{D})^{3/2}$ where $\omega_{D}$ is the magnon Debye
+energy. The latter factor reflects the fractional change in the net
+magnetization of the reservoirs due to thermal magnons at temperature $T$
+(Bloch's $T^{3/2}$ law). In contrast, the contribution of magnon-assisted
+tunneling to the thermopower $S_P$ of a junction with parallel polarizations is
+negligible. As the relative polarizations of ferromagnetic layers can be
+manipulated by an external magnetic field, a large difference $\Delta S =
+S_{AP} - S_P \approx S_{AP} \sim - (k_B/e) f (\Pi_{\uparrow},\Pi_{\downarrow})
+(k_BT/\omega_{D})^{3/2}$ results in a magnetothermopower effect. This
+magnetothermopower effect becomes giant in the extreme case of a junction
+between two half-metallic ferromagnets, $\Delta S \sim - k_B/e$.",0209520v1
+2003-10-15,Pions versus Magnons: From QCD to Antiferromagnets and Quantum Hall Ferromagnets,"The low-energy dynamics of pions and magnons -- the Goldstone bosons of the
+strong interactions and of magnetism -- are analogous in many ways. The
+electroweak interactions of pions result from gauging an SU(2)_L x U(1)_Y
+symmetry which then breaks to the U(1)_{em} gauge symmetry of electromagnetism.
+The electromagnetic interactions of magnons arise from gauging not only
+U(1)_{em} but also the SU(2)_s spin rotational symmetry, with the
+electromagnetic fields E and B appearing as non-Abelian vector potentials.
+Pions couple to electromagnetism through a Goldstone-Wilczek current that
+represents the baryon number of Skyrmions and gives rise to the decay \pi^0 to
+\gamma \gamma. Similarly, magnons may couple to an analogue of the
+Goldstone-Wilczek current for baby-Skyrmions which induces a magnon-two-photon
+vertex. The corresponding analogue of photon-axion conversion is photon-magnon
+conversion in an external magnetic field. The baryon number violating decay of
+Skyrmions can be catalyzed by a magnetic monopole via the Callan-Rubakov
+effect. Similarly, baby-Skyrmion decay can be catalyzed by a charged wire. For
+more than two flavors, the Wess-Zumino-Witten term enters the low-energy pion
+theory with a quantized prefactor N_c -- the number of quark colors. The magnon
+analogue of this prefactor is the anyon statistics angle \theta which need not
+be quantized.",0310353v1
+2006-07-24,Giant Magnons under NS-NS and Melvin Fields,"The giant magnon is a rotating spiky string configuration which has the same
+dispersion relation between the energy and angular momentum as that of a spin
+magnon. In this paper we investigate the effects of the NS-NS and Melvin fields
+on the giant magnon. We first analyze the energy and angular momenta of the
+two-spin spiky D-string moving on the $AdS_3\times S^1$ with the NS-NS field.
+Due to the infinite boundary of the AdS spacetime the D-string solution will
+extend to infinity and it appears the divergences. After adding the counter
+terms we obtain the dispersion relation of the corresponding giant magnon. The
+result shows that there will appear a prefactor before the angular momentum, in
+addition to some corrections in the sine function. We also see that the spiky
+profile of a rotating D-string plays an important role in mapping it to a spin
+magnon. We next investigate the energy and angular momentum of the one-spin
+spiky fundamental string moving on the $R \times S^2$ with the electric or
+magnetic Melvin field. The dispersion relation of the corresponding deformed
+giant magnon is also obtained. We discuss some properties of the correction
+terms and their relations to the spin chain with deformations.",0607161v4
+2008-04-10,Quantum Heisenberg antiferromagnets in a uniform magnetic field: nonanalytic magnetic field dependence of the magnon spectrum,"We reexamine the 1/S-correction to the self-energy of the gapless magnon of a
+D-dimensional quantum Heisenberg antiferromagnet in a uniform magnetic field h
+using a hybrid approach between 1/S-expansion and non-linear sigma model, where
+the Holstein-Primakoff bosons are expressed in terms of Hermitian field
+operators representing the uniform and the staggered components of the
+spin-operators [N. Hasselmann and P. Kopietz, Europhys. Lett. {\bf{74}}, 1067
+(2006)]. By integrating over the field associated with the uniform
+spin-fluctuations we obtain the effective action for the staggered
+spin-fluctuations on the lattice, which contains fluctuations on all length
+scales and does not have the cutoff ambiguities of the non-linear sigma model.
+We show that in dimensions D <= 3 the magnetic field dependence of the
+spin-wave velocity c(h) is non-analytic in h^2, with c(h) - c(0) proportional
+to h^2 \ln | h | in D=3, and c(h) - c(0) proportional to | h | in D=2. The
+frequency dependent magnon self-energy is found to exhibit an even more
+singular magnetic field dependence, implying a strong momentum dependence of
+the quasi-particle residue of the gapless magnon. We also discuss the problem
+of spontaneous magnon decay and show that in D > 1 dimensions the damping of
+magnons with momentum k is proportional to |k|^{2D -1} if spontaneous magnon
+decay is kinematically allowed.",0804.1704v2
+2013-05-28,Microscopic observation of magnon bound states and their dynamics,"More than eighty years ago, H. Bethe pointed out the existence of bound
+states of elementary spin waves in one-dimensional quantum magnets. To date,
+identifying signatures of such magnon bound states has remained a subject of
+intense theoretical research while their detection has proved challenging for
+experiments. Ultracold atoms offer an ideal setting to reveal such bound states
+by tracking the spin dynamics after a local quantum quench with single-spin and
+single-site resolution. Here we report on the direct observation of two-magnon
+bound states using in-situ correlation measurements in a one-dimensional
+Heisenberg spin chain realized with ultracold bosonic atoms in an optical
+lattice. We observe the quantum walk of free and bound magnon states through
+time-resolved measurements of the two spin impurities. The increased effective
+mass of the compound magnon state results in slower spin dynamics as compared
+to single magnon excitations. In our measurements, we also determine the decay
+time of bound magnons, which is most likely limited by scattering on thermal
+fluctuations in the system. Our results open a new pathway for studying
+fundamental properties of quantum magnets and, more generally, properties of
+interacting impurities in quantum many-body systems.",1305.6598v2
+2016-06-15,Topological Magnon Bands in Ferromagnetic Star Lattice,"The experimental observation of topological magnon bands and thermal Hall
+effect in a kagom\'e lattice ferromagnet Cu(1-3, bdc) has inspired the search
+for topological magnon effects in various insulating ferromagnets that lack an
+inversion center allowing a Dzyaloshinskii-Moriya (DM) spin-orbit interaction.
+The star lattice (also known as the decorated honeycomb lattice) ferromagnets
+is an ideal candidate for this purpose because it is a variant of the kagom\'e
+lattice with additional links that connect the up-pointing and down-pointing
+triangles. This gives rise to twice the unit cell of the kagom\'e lattice,
+hence a more interesting topological magnon effects. In particular, the
+triangular bridges on the star lattice can be coupled either ferromagnetically
+or antiferromagnetically which is not possible on the kagome lattice
+ferromagnets. Here, we study DM-induced topological magnon bands, chiral edge
+modes, and thermal magnon Hall effect on the star lattice ferromagnet in
+different parameter regimes. The star lattice can also be visualized as the
+parent material from which topological magnon bands can be realized for the
+kagom\'e and honeycomb lattices in some limiting cases.",1606.04904v8
+2017-03-11,Spin-wave dynamics in Permalloy/Cobalt magnonic crystals in the presence of a non-magnetic spacer,"In this paper, we theoretically study the influence of a non-magnetic spacer
+between ferromagnetic dots and ferromagnetic matrix on the frequency dispersion
+of the spin wave excitations in two-dimensional bi-component magnonic crystals.
+By means of the dynamical matrix method we investigate structures inhomogeneous
+across the thickness represented by square arrays of Cobalt or Permalloy dots
+in a Permalloy matrix. We show that the introduction of a non-magnetic spacer
+significantly modifies the total internal magnetic field especially at the
+edges of the grooves and dots. This permits the manipulation of the magnonic
+band structure of spin waves localized either at the edges of the dots or in
+matrix material at the edges of grooves. According to the micromagnetic
+simulations two types of end modes were found. The corresponding frequencies
+are significantly influenced by the end modes localization region. We also show
+that, with the use of a single ferromagnetic material, it is possible to design
+a magnonic crystal preserving properties of bi-component magnonic crystals and
+magnonic antidot lattices. Finally, the influence of the non-magnetic spacers
+on the technologically relevant parameters like group velocity and magnonic
+band width are discussed.",1703.03978v1
+2012-04-26,Thermal spin pumping mediated by magnon in the semiclassical regime,"We microscopically analyze thermal spin pumping mediated by magnons, at the
+interface between a ferromagnetic insulator and a non-magnetic metal, in the
+semiclassical regime. The generation of a spin current is discussed by
+calculating the thermal spin transfer torque, which breaks the spin
+conservation law for conduction electrons and operates the coherent magnon
+state. Inhomogeneous thermal fluctuations between conduction electrons and
+magnons induce a net spin current, which is pumped into the adjacent
+non-magnetic metal. The pumped spin current is proportional to the temperature
+difference. When the effective temperature of magnons is lower than that of
+conduction electrons, localized spins lose spin angular momentum by emitting
+magnons and conduction electrons flip from down to up by absorbing all the
+emitted momentum, and vice versa. Magnons at the zero mode cannot contribute to
+thermal spin pumping because they are eliminated by the spin-flip condition.
+Consequently thermal spin pumping does not cost any kinds of applied magnetic
+fields. We have discussed the distinction from the theory proposed by Xiao et
+al. [Phys. Rev. B, 81 (2010) 214418], Adachi et al. [Phys. Rev. B, 83 (2011)
+094410], and Bender et al. [arXiv:1111.2382].",1204.5811v2
+2014-06-23,Propulsion of a domain wall in an antiferromagnet by magnons,"We analyze the dynamics of a domain wall in an easy-axis antiferromagnet
+driven by circularly polarized magnons. Magnons pass through a stationary
+domain wall without reflection and thus exert no force on it. However, they
+reverse their spin upon transmission, thereby transferring two quanta of
+angular momentum to the domain wall and causing it to precess. A precessing
+domain wall partially reflects magnons back to the source. The reflection of
+spin waves creates a previously identified reactive force. We point out a
+second mechanism of propulsion, which we term redshift: magnons passing through
+a precessing domain wall lower their frequency by twice the angular velocity of
+the domain wall; the concomitant reduction of magnons' linear momentum
+indicates momentum transfer to the domain wall. We solve the equations of
+motion for spin waves in the background of a uniformly precessing domain wall
+with the aid of supersymmetric quantum mechanics and compute the net force and
+torque applied by magnons to the domain wall. Redshift is the dominant
+mechanism of propulsion at low spin-wave intensities; reflection dominates at
+higher intensities. We derive a set of coupled algebraic equations to determine
+the linear velocity and angular frequency of the domain wall in a steady state.
+The theory agrees well with numerical micromagnetic simulations.",1406.6051v1
+2017-06-14,Nonlocal magnon-polaron transport in yttrium iron garnet,"The spin Seebeck effect (SSE) is observed in magnetic insulator|heavy metal
+bilayers as an inverse spin Hall effect voltage under a temperature gradient.
+The SSE can be detected nonlocally as well, viz. in terms of the voltage in a
+second metallic contact (detector) on the magnetic film, spatially separated
+from the first contact that is used to apply the temperature bias (injector).
+Magnon-polarons are hybridized lattice and spin waves in magnetic materials,
+generated by the magnetoelastic interaction. Kikkawa et al. [Phys. Rev. Lett.
+\textbf{117}, 207203 (2016)] interpreted a resonant enhancement of the local
+SSE in yttrium iron garnet (YIG) as a function of the magnetic field in terms
+of magnon-polaron formation. Here we report the observation of magnon-polarons
+in \emph{nonlocal} magnon spin injection/detection devices for various
+injector-detector spacings and sample temperatures. Unexpectedly, we find that
+the magnon-polaron resonances can suppress rather than enhance the nonlocal
+SSE. Using finite element modelling we explain our observations as a
+competition between the SSE and spin diffusion in YIG. These results give
+unprecedented insights into the magnon-phonon interaction in a key magnetic
+material.",1706.04373v1
+2019-09-12,Spin Transport in Thick Insulating Antiferromagnetic Films,"Spin transport of magnonic excitations in uniaxial insulating
+antiferromagnets (AFs) is investigated. In linear response to spin biasing and
+a temperature gradient, the spin transport properties of
+normal-metal--insulating antiferromagnet--normal-metal heterostructures are
+calculated. We focus on the thick-film regime, where the AF is thicker than the
+magnon equilibration length. This regime allows the use of a drift-diffusion
+approach, which is opposed to the thin-film limit considered by Bender {\it et
+al.} 2017, where a stochastic approach is justified. We obtain the temperature-
+and thickness-dependence of the structural spin Seebeck coefficient
+$\mathcal{S}$ and magnon conductance $\mathcal{G}$. In their evaluation we
+incorporate effects from field- and temperature-dependent spin conserving
+inter-magnon scattering processes. Furthermore, the interfacial spin transport
+is studied by evaluating the contact magnon conductances in a microscopic model
+that accounts for the sub-lattice symmetry breaking at the interface. We find
+that while inter-magnon scattering does slightly suppress the spin Seebeck
+effect, transport is generally unaffected, with the relevant spin decay length
+being determined by non-magnon-conserving processes such as Gilbert damping. In
+addition, we find that while the structural spin conductance may be enhanced
+near the spin flip transition, it does not diverge due to spin impedance at the
+normal metal|magnet interfaces.",1909.05881v2
+2020-12-23,Topological Weyl magnons and thermal Hall effect in layered honeycomb ferromagnets,"In this work, we study the topological properties and magnon Hall effect of a
+three-dimensional ferromagnet in the ABC stacking honeycomb lattice, motivated
+by the recent inelastic neutron scattering study of CrI$_3$. We show that the
+magnon band structure and Chern numbers of the magnon branches are
+significantly affected by the interlayer coupling $J_c$, which moreover has a
+qualitatively different effect in the ABC stacking compared to the AA stacking
+adopted by other authors. The nontrivial Chern number of the lowest magnon band
+is stabilized by the next-nearest-neighbour Dzyaloshinsky-Moriya interaction in
+each honeycomb layer, resulting in the hopping term similar to that in the
+electronic Haldane model for graphene. However, we also find several gapless
+Weyl points, separating the non-equivalent Chern insulating phases, tuned by
+the ratio of the interlayer coupling $J_c$ and the third-neighbour Heisenberg
+interaction $J_3$. We further show that the topological character of magnon
+bands results in non-zero thermal Hall conductivity, whose sign and magnitude
+depend on $J_c$ and the intra-layer couplings. Since the interlayer coupling
+strength $J_c$ can be easily tuned by applying pressure to the quasi-2D
+material such as CrI$_3$, this provides a potential route to tuning the magnon
+thermal Hall effect in an experiment.",2012.12924v2
+2018-03-30,Nonlocal magnon spin transport in yttrium iron garnet with tantalum and platinum spin injection/detection electrodes,"We study the magnon spin transport in the magnetic insulator yttrium iron
+garnet (YIG) in a nonlocal experiment and compare the magnon spin excitation
+and detection for the heavy metal paramagnetic electrodes platinum (Pt|YIG|Pt)
+and tantalum (Ta|YIG|Ta). The electrical injection and detection processes rely
+on the (inverse) spin Hall effect in the heavy metals and the conversion
+between the electron spin and magnon spin at the heavy metal|YIG interface. Pt
+and Ta possess opposite signs of the spin Hall angle. Furthermore, their
+heterostructures with YIG have different interface properties, i.e. spin mixing
+conductances. By varying the distance between injector and detector, the magnon
+spin transport is studied. Using a circuit model based on the
+diffusion-relaxation transport theory, a similar magnon relaxation length of ~
+10 \mu m was extracted from both Pt and Ta devices. By changing the injector
+and detector material from Pt to Ta, the influence of interface properties on
+the magnon spin transport has been observed. For Ta devices on YIG the spin
+mixing conductance is reduced compared with Pt devices, which is quantitatively
+consistent when comparing the dependence of the nonlocal signal on the
+injector-detector distance with the prediction from the circuit model.",1803.11382v1
+2018-06-11,Excitation of whispering gallery magnons in a magnetic vortex,"One of the most fascinating topics in current quantum physics are hybridised
+systems, in which different quantum resonators are strongly coupled. Prominent
+examples are circular resonators with high quality factors that allow the
+coupling of optical whispering gallery modes to microwave cavities or magnon
+resonances in optomagnonics. Whispering gallery modes play a special role in
+this endeavour because of their high quality factor and strong localisation,
+which ultimately increases the overlap of the wavefunctions of quantum
+particles in hybridised systems. The hybridisation with magnons, the collective
+quantum excitations of the electron spins in a magnetically ordered material,
+is of particular interest because magnons can take over two functionalities:
+due to their collective nature they are robust and can serve as a quantum
+memory and, moreover, they can act as a wavelength converter between microwave
+and THz photons. However, the observation of whispering gallery magnons has not
+yet been achieved due to the lack of efficient excitation schemes for magnons
+with large wave vectors in a circular geometry. To tackle this problem, we
+studied nonlinear 3-magnon scattering as a means to generate whispering gallery
+magnons. This Letter discusses the basics of this nonlinear mechanism in a
+confined, circular geometry from experimental and theoretical point of view.",1806.03910v1
+2018-12-03,Symmetry and localization properties of defect modes in magnonic superlattices,"Symmetry and localization properties of defect modes of a one-dimensional
+bi-component magnonic superlattice are theoretically studied. The magnonic
+superlattice can be seen as a periodic array of nanostripes, where stripes with
+different width, termed as defect stripes, are periodically introduced. By
+controlling the geometry of the defect stripes, a transition from dispersive to
+practically flat spin-wave defect modes can be observed inside the magnonic
+band gaps. It is shown that the spin-wave profile of the defect modes can be
+either symmetric or antisymmetric, depending on the geometry of the defect. Due
+to the localized character of the defect modes, a particular magnonic
+superlattice is proposed, wherein the excitation of either symmetric or
+antisymmetric flat magnonic modes is enabled at the same time. Also, it is
+demonstrated that the relative frequency position of the antisymmetric mode
+inside the band gap does not significantly change with the application of an
+external field, while the symmetric modes move to the edges of the frequency
+band gaps. The results are complemented by numerical simulations, where an
+excellent agreement is observed between both methods. The proposed theory
+allows exploring different ways to control the dynamic properties of the defect
+modes in metamaterial magnonic superlattices, which can be useful for
+applications on multifunctional microwave devices operating over a broad
+frequency range.",1812.00897v1
+2019-01-24,Fundamentals of magnon-based computing,"A disturbance in the local magnetic order of a solid body can propagate
+across a material just like a wave. This wave is named spin wave, and its
+quanta are known as magnons. Recently, physicists proposed the usage of magnons
+to carry and process information instead of electrons as it is the case of
+electronics. This technology opens access to a new generation of computers in
+which data are processed without motion of any real particles like electrons.
+This leads to a sizable decrease in the accompanying heating losses and,
+consequently, to lower energy consumption, which is crucial due to the ever
+increasing demand for computing devices. Moreover, unique properties of spin
+waves allow for the utilisation of unconventional computing concepts, giving
+the vision of a significantly faster and more powerful next-generation of
+information processing systems.
+  The current review addresses a selection of fundamental topics that form the
+basis of the magnon-based computing and are of primary importance for the
+further development of this concept. First, the transport of spin-wave-carried
+information in one and two dimensions that is required for the realization of
+logic elements and integrated magnon circuits is covered. Second, the
+convertors between spin waves and electron (charge and spin) currents are
+discussed. These convertors are necessary for the compatibility of magnonic
+devices with modern CMOS technology. The paper starts with basics on spin waves
+and the related methodology. In addition, the general ideas behind magnon-based
+computing are presented. The review finishes with conclusions and an outlook on
+the perspective use of spin waves.",1901.08934v1
+2019-03-10,Magnons at low excitations: Observation of incoherent coupling to a bath of two-level-systems,"Collective magnetic excitation modes, magnons, can be coherently coupled to
+microwave photons in the single excitation limit. This allows for access to
+quantum properties of magnons and opens up a range of applications in quantum
+information processing, with the intrinsic magnon linewidth representing the
+coherence time of a quantum resonator. Our measurement system consists of a
+yttrium iron garnet (YIG) sphere and a three-dimensional (3D) microwave cavity
+at temperatures and excitation powers typical for superconducting quantum
+circuit experiments. We perform spectroscopic measurements to determine the
+limiting factor of magnon coherence at these experimental conditions. Using the
+input-output formalism, we extract the magnon linewidth $\kappa_\mathrm{m}$. We
+attribute the limitations of the coherence time at lowest temperatures and
+excitation powers to incoherent losses into a bath of near-resonance two-level
+systems (TLSs), a generic loss mechanism known from superconducting circuits
+under these experimental conditions. We find that the TLSs saturate when
+increasing the excitation power from quantum excitation to multi-photon
+excitation and their contribution to the linewidth vanishes. At higher
+temperatures, the TLSs saturate thermally and the magnon linewidth decreases as
+well.",1903.03981v3
+2019-11-03,Ferromagnetic dynamics detected via one- and two-magnon NV relaxometry,"The NV center in diamond has proven to be a powerful tool for locally
+characterizing the magnetic response of microwave excited ferromagnets. To
+date, this has been limited by the requirement that the FMR excitation
+frequency be less than the NV spin resonance frequency. Here we report NV
+relaxometry based on a two-magnon Raman-like process, enabling detection of FMR
+at frequencies higher than the NV frequency. For high microwave drive powers,
+we observe an unexpected field-shift of the NV response relative to a
+simultaneous microwave absorption signal from a low damping ferrite film. We
+show that the field-shifted NV response is due to a second order Suhl
+instability. The instability creates a large population of non-equilibrium
+magnons which relax the NV spin, even when the uniform mode FMR frequency
+exceeds that of the NV spin resonance frequency, hence ruling out the
+possibility that the NV is relaxed by a single NV-resonant magnon. We argue
+that at high frequencies the NV response is due to a two-magnon relaxation
+process in which the difference frequency of two magnons matches the NV
+frequency, and at low frequencies we evaluate the lineshape of the one-magnon
+NV relaxometry response using spinwave instability theory.",1911.00829v1
+2019-12-05,Steering magnonic dynamics and permeability at exceptional points in a parity-time symmetric waveguide,"Tuning the low-energy magnetic dynamics is a key element in designing novel
+magnetic metamaterials, spintronic devices and magnonic logic circuits. This
+study uncovers a new, highly effective way of controlling the magnetic
+permeability via shaping the magnonic properties in coupled magnetic waveguides
+separated by current carrying spacer with strong spin-orbit coupling. The
+spin-orbit torques exerted on the waveguides leads to an externally tunable
+enhancement of magnetic damping in one waveguide and a decreased damping in the
+other, constituting so a magnetic parity-time (PT) symmetric system with
+emergent magnetic properties at the verge of the exceptional point where
+magnetic gains/losses are balanced. In addition to controlling the magnetic
+permeability, phenomena inherent to PT-symmetric systems are identified,
+including the control on magnon power oscillations, nonreciprocal magnon
+propagation, magnon trapping and enhancement as well as the increased
+sensitivity to magnetic perturbation and abrupt spin reversal. These
+predictions are demonstrated analytically and confirmed by full numerical
+simulations under experimentally feasible conditions. The position of the
+exceptional points and the strength of the spontaneous PT symmetry breaking can
+be tuned by external electric and/or magnetic fields. The roles of the
+intrinsic magnetic damping, and the possibility of an electric control via
+Dzyaloshinskii-Moriya interaction are exposed and utilized for mode dispersion
+shaping and magnon amplification and trapping. The results point to a new route
+to designing optomagnonic waveguides, traps, sensors, and circuits.",1912.02500v1
+2016-03-11,"Magnon-drag thermopower and Nernst coefficient in Fe, Co, and Ni","Magnon-drag is shown to dominate the thermopower of elemental Fe from 2 to 80
+K and of elemental Co from 150 to 600 K; it is also shown to contribute to the
+thermopower of elemental Ni from 50 to 500 K. Two theoretical models are
+presented for magnon-drag thermopower. One is a hydrodynamic theory based
+purely on non-relativistic, Galilean, spin-preserving electron-magnon
+scattering. The second is based on spin-motive forces, where the thermopower
+results from the electric current pumped by the dynamic magnetization
+associated with a magnon heat flux. In spite of their very different
+microscopic origins, the two give similar predictions for pure metals at low
+temperature, allowing us to semi-quantitatively explain the observed
+thermopower of elemental Fe and Co without adjustable parameters. We also find
+that magnon-drag may contribute to the thermopower of Ni. A spin-mixing model
+is presented that describes the magnon-drag contribution to the Anomalous
+Nernst Effect in Fe, again enabling a semi-quantitative match to the
+experimental data without fitting parameters. Our work suggests that particle
+non-conserving processes may play an important role in other types of drag
+phenomena, and also gives a predicative theory for improving metals as
+thermoelectric materials.",1603.03736v3
+2017-07-27,Electron spin resonance for the detection of long-range spin nematic order,"In this paper we propose that electron spin resonance (ESR) measurements
+enable us to detect the long-range spin nematic order. We show that the
+frequency of the paramagnetic resonance peak in the ESR spectrum is shifted by
+the ferroquadrupolar order parameter together with other quantities. The
+ferroquadrupolar order parameter is extractable from the angular dependence of
+the frequency shift. In contrast, the antiferroquadrupolar order parameter is
+usually invisible in the frequency shift. Instead, the long-range
+antiferroquadrupolar order yields a characteristic resonance peak in the ESR
+spectrum, which we call a magnon-pair resonance peak. This resonance
+corresponds to the excitation of the bound magnon pair at the wave vector $\bm
+k={\bm 0}$. Reflecting the condensation of bound magnon pairs, the field
+dependence of the magnon-pair resonance frequency shows a singular upturn at
+the saturation field. Moreover, the intensity of the magnon-pair resonance peak
+shows a characteristic angular dependence and it vanishes when the magnetic
+field is parallel to one of the axes that diagonalize the weak anisotropic
+interactions. We confirm these general properties of the magnon-pair resonance
+peak in the spin nematic phase by studying an $S=1$ bilinear-biquadratic model
+on the square lattice in the linear flavor-wave approximation. In addition, we
+argue applications to the $S=1/2$ frustrated ferromagnets and also the $S=1/2$
+orthogonal dimer spin system SrCu$_2$(BO$_3$)$_2$, both of which are candidate
+materials of spin nematics. Our theory for the antiferroquadrupolar ordered
+phase is consistent with many features of the magnon-pair resonance peak
+experimentally observed in the low-magnetization regime of
+SrCu$_2$(BO$_3$)$_2$.",1707.08784v2
+2017-11-20,Temperature dependent relaxation of dipole-exchange magnons in yttrium iron garnet films,"Low energy consumption enabled by charge-free information transport, which is
+free from ohmic heating, and the ability to process phase-encoded data by
+nanometer-sized interference devices at GHz and THz frequencies are just a few
+benefits of spin-wave-based technologies. Moreover, when approaching cryogenic
+temperatures, quantum phenomena in spin-wave systems pave the path towards
+quantum information processing. In view of these applications, the lifetime of
+magnons$-$spin-wave quanta$-$is of high relevance for the fields of magnonics,
+magnon spintronics and quantum computing. Here, the relaxation behavior of
+parametrically excited magnons having wavenumbers from zero up to $6\cdot 10^5
+\mathrm{rad~cm}^{-1}$ was experimentally investigated in the temperature range
+from 20 K to 340 K in single crystal yttrium iron garnet (YIG) films
+epitaxially grown on gallium gadolinium garnet (GGG) substrates as well as in a
+bulk YIG crystal$-$the magnonic materials featuring the lowest magnetic damping
+known so far. As opposed to the bulk YIG crystal in YIG films we have found a
+significant increase in the magnon relaxation rate below 150 K$-$up to 10.5
+times the reference value at 340 K$-$in the entire range of probed wavenumbers.
+This increase is associated with rare-earth impurities contaminating the YIG
+samples with a slight contribution caused by coupling of spin waves to the spin
+system of the paramagnetic GGG substrate at the lowest temperatures.",1711.07517v1
+2018-10-10,Magnonic Floquet Quantum Spin Hall Insulator in Bilayer Collinear Antiferromagnets,"We study irradiated two-dimensional insulating bilayer honeycomb ferromagnets
+and antiferromagnets coupled antiferromagnetically with a zero net
+magnetization. The former is realized in the recently synthesized bilayer
+honeycomb chromium triiodide CrI$_{\bf 3}$. In both systems, we show that
+circularly-polarized electric field breaks time-reversal symmetry and induces a
+dynamical Dzyaloshinskii-Moriya interaction in each honeycomb layer. However,
+the resulting bilayer antiferromagnetic system still preserves a combination of
+time-reversal and space-inversion ($\mathcal{PT}$) symmetry. We show that the
+magnon topology of the bilayer antiferromagnetic system is characterized by a
+$\pmb{\mathbb{Z}_2}$ Floquet topological invariant. Therefore, the system
+realizes a magnonic Floquet quantum spin Hall insulator with spin filtered
+magnon edge states. This leads to a non-vanishing Floquet magnon spin Nernst
+effect, whereas the Floquet magnon thermal Hall effect vanishes due to
+$\mathcal{PT}$ symmetry. We study the rich $\pmb{\mathbb{Z}_2}$ Floquet
+topological magnon phase diagram of the system as a function of the light
+amplitudes and polarizations. We further discuss the great impact of the
+results on future experimental realizations.",1810.04677v4
+2018-10-11,"Magnons in a Quasicrystal: Propagation, Localization and Extinction of Spin Waves in Fibonacci Structures","Magnonic quasicrystals exceed the possibilities of spin wave (SW)
+manipulation offered by regular magnonic crystals, because of their more
+complex SW spectra with fractal characteristics. Here, we report the direct
+x-ray microscopic observation of propagating SWs in a magnonic quasicrystal,
+consisting of dipolarly coupled permalloy nanowires arranged in a
+one-dimensional Fibonacci sequence. SWs from the first and second band as well
+as evanescent waves from the band gap between them are imaged. Moreover,
+additional mini-band gaps in the spectrum are demonstrated, directly indicating
+an influence of the quasiperiodicity of the system. The experimental results
+are interpreted using numerical calculations and we deduce a simple model to
+estimate the frequency position of the magnonic gaps in quasiperiodic
+structures. The demonstrated features of SW spectra in one-dimensional magnonic
+quasicrystals allows utilizing this class of metamaterials for magnonics and
+makes them an ideal basis for future applications.",1810.04931v2
+2020-01-20,Direct observation of 2D magnons in atomically thin CrI$_3$,"Exfoliated chromium triiodide (CrI$_3$) is a layered van der Waals (vdW)
+magnetic insulator that consists of ferromagnetic layers coupled through
+antiferromagnetic interlayer exchange. The resulting permutations of magnetic
+configurations combined with the underlying crystal symmetry produces tunable
+magneto-optical phenomena that is unique to the two-dimensional (2D) limit.
+Here, we report the direct observation of 2D magnons through magneto-Raman
+spectroscopy with optical selection rules that are strictly determined by the
+honeycomb lattice and magnetic states of atomically thin CrI$_3$. In
+monolayers, we observe an acoustic magnon mode of ~0.3 meV with
+cross-circularly polarized selection rules locked to the magnetization
+direction. These unique selection rules arise from the discrete conservation of
+angular momentum of photons and magnons dictated by threefold rotational
+symmetry in a rotational analogue to Umklapp scattering. In bilayers, by tuning
+between the layered antiferromagnetic and ferromagnetic-like states, we observe
+the switching of two magnon modes. The bilayer structure also enables Raman
+activity from the optical magnon mode at ~17 meV (~4.2 THz) that is otherwise
+Raman-silent in the monolayer. From these measurements, we quantitatively
+extract the spin wave gap, magnetic anisotropy, intralayer and interlayer
+exchange constants, and establish 2D magnets as a new system for exploring
+magnon physics.",2001.07025v1
+2020-03-27,Spatial separation of degenerate components of magnon Bose-Einstein condensate by using a local acceleration potential,"Bose-Einstein condensation (BEC) of magnons is one of few macroscopic quantum
+phenomena observable at room temperature. Due to competition of the exchange
+and the magnetic dipole interactions the minimum-energy magnon state is doubly
+degenerate and corresponds to two antiparallel non-zero wavevectors.
+Correspondingly, magnon BEC differs essentially from other condensates, since
+it takes place simultaneously at +/-k_min. The degeneracy of BEC and
+interaction between its two components have significant impact on the
+condensate properties. Phase locking of the two condensates causes formation of
+a standing wave of the condensate density and quantized vortices. Additionally,
+interaction between the two components is believed to be important for
+stabilization of the condensate with respect to the real-space collapse. Thus,
+the possibility to create a non-degenerate, single-component condensate is
+decisive for understanding of underlying physics of magnon BEC. Here, we
+experimentally demonstrate an approach, which allows one to accomplish this
+challenging task. We show that this can be achieved by using a separation of
+the two components of the degenerate condensate in the real space by applying a
+local pulsed magnetic field, which causes their motion in the opposite
+directions. Thus, after a certain delay, the two clouds corresponding to
+different components become well separated in the real space. We find that the
+motion of the clouds can be described well based on the peculiarities of the
+magnon dispersion characteristics. Additionally, we show that, during the
+motion, the condensate cloud harvests non-condensed magnons, which results in a
+partial compensation of the condensate depletion.",2003.12436v1
+2020-08-03,Symmetry-resolved two-magnon excitations in a strong spin-orbit-coupled bilayer antiferromagnet,"We used a combination of polarized Raman spectroscopy and spin wave
+calculations to study magnetic excitations in the strong spin-orbit-coupled
+(SOC) bilayer perovskite antiferromagnet $Sr_3Ir_2O_7$. We observed two broad
+Raman features at ~ 800 $cm^{-1}$ and ~ 1400 $cm^{-1}$ arising from magnetic
+excitations. Unconventionally, the ~ 800 $cm^{-1}$ feature is fully symmetric
+($A_{1g}$) with respect to the underlying tetragonal ($D_{4h}$) crystal lattice
+which, together with its broad line shape, definitively rules out the
+possibility of a single magnon excitation as its origin. In contrast, the ~
+1400 $cm^{-1}$ feature shows up in both the $A_{1g}$ and $B_{2g}$ channels.
+From spin wave and two-magnon scattering cross-section calculations of a
+tetragonal bilayer antiferromagnet, we identified the ~ 800 $cm^{-1}$ (~ 1400
+$cm^{-1}$) feature as two-magnon excitations with pairs of magnons from the
+zone-center $\Gamma$ point (zone-boundary van Hove singularity X point). We
+further found that this zone-center two-magnon scattering is unique to bilayer
+perovskite magnets which host an optical branch in addition to the acoustic
+branch, as compared to their single layer counterparts. This zone-center
+two-magnon mode is distinct in symmetry from the time-reversal symmetry broken
+spin wave gap and phase mode proposed to explain the ~ 92 meV (742 $cm^{-1}$)
+gap in RIXS magnetic excitation spectra of $Sr_3Ir_2O_7$.",2008.01052v1
+2020-10-26,Ultra-strong photon-to-magnon coupling in multilayered heterostructures involving superconducting coherence via ferromagnetic layers,"The critical step for future quantum industry demands realization of
+efficient information exchange between different-platform hybrid systems,
+including photonic and magnonic systems, that can harvest advantages of
+distinct platforms. The major restraining factor for the progress in certain
+hybrid systems is the fundamentally weak coupling parameter between the
+elemental particles. This restriction impedes the entire field of hybrid
+magnonics by making realization of scalable on-chip hybrid magnonic systems
+unattainable. In this work, we propose a general flexible approach for
+realization of on-chip hybrid magnonic systems with unprecedentedly strong
+coupling parameters. The approach is based on multilayered micro-structures
+containing superconducting, insulating and ferromagnetic layers with modified
+both photon phase velocities and magnon eigen-frequencies. Phenomenologically,
+the enhanced coupling strength is provided by the radically reduced photon mode
+volume. The microscopic mechanism of the phonon-to-magnon coupling in studied
+systems evidences formation of the long-range superconducting coherence via
+thick strong ferromagnetic layers. This coherence is manifested by coherent
+superconducting screening of microwave fields by the
+superconductor/ferromagnet/superconductor three-layers in presence of
+magnetization precession. This discovery offers new opportunities in microwave
+superconducting spintronics for quantum technologies.",2010.13553v1
+2020-11-12,Interaction-stabilized topological magnon insulator in ferromagnets,"Condensed matter systems admit topological collective excitations above a
+trivial ground state, an example being Chern insulators formed by Dirac bosons
+with a gap at finite energies. However, in contrast to electrons, there is no
+particle-number conservation law for collective excitations. This gives rise to
+particle number-nonconserving many-body interactions whose influence on
+single-particle topology is an open issue of fundamental interest in the field
+of topological quantum materials. Taking magnons in ferromagnets as an example,
+we uncover topological magnon insulators that are stabilized by interactions
+through opening Chern-insulating gaps in the magnon spectrum. This can be
+traced back to the fact that the particle-number nonconserving interactions
+break the effective time-reversal symmetry of the harmonic theory. Hence,
+magnon-magnon interactions are a source of topology that can introduce chiral
+edge states, whose chirality depends on the magnetization direction.
+Importantly, interactions do not necessarily cause detrimental damping but can
+give rise to topological magnons with exceptionally long lifetimes. We identify
+two mechanisms of interaction-induced topological phase transitions---one
+driven by an external field, the other by temperature---and show that they
+cause unconventional sign reversals of transverse transport signals, in
+particular of the thermal Hall conductivity. We identify candidate materials
+where this many-body mechanism is expected to occur, such as the metal-organic
+kagome-lattice magnet Cu(1,3-benzenedicarboxylate), the van der Waals
+honeycomb-lattice magnet CrI$_3$, and the multiferroic kamiokite
+(Fe$_2$Mo$_3$O$_8$). Our results demonstrate that interactions can play an
+important role in generating nontrivial topology.",2011.06543v1
+2021-05-12,Coherent spin-wave transport in an antiferromagnet,"Magnonics is a research field complementary to spintronics, in which the
+quanta of spin waves (magnons) replace electrons as information carriers,
+promising less energy dissipation. The development of ultrafast nanoscale
+magnonic logic circuits calls for new tools and materials to generate coherent
+spin waves with frequencies as high, and wavelengths as short, as possible.
+Antiferromagnets can host spin waves at THz frequencies and are therefore seen
+as a future platform for the fastest and the least dissipative transfer of
+information. However, the generation of short-wavelength coherent propagating
+magnons in antiferromagnets has so far remained elusive. Here we report the
+efficient emission and detection of a nanometer-scale wavepacket of coherent
+propagating magnons in antiferromagnetic DyFeO3 using ultrashort pulses of
+light. The subwavelength nanoscale confinement of the laser field due to large
+absorption creates a strongly non-uniform spin excitation profile, thereby
+enabling the propagation of a broadband continuum of coherent THz spin waves.
+The wavepacket features magnons with detected wavelengths down to 125 nm and
+supersonic velocities up to 13 km/s that propagate over macroscopic distances.
+The long-sought source of coherent short-wavelength spin carriers demonstrated
+here opens up new prospects for THz antiferromagnetic magnonics and coherence
+mediated logic devices at THz frequencies.",2105.05886v1
+2021-08-26,Coherent strong-coupling of terahertz magnons and phonons in a Van der Waals antiferromagnetic insulator,"Emergent cooperative motions of individual degrees of freedom, i.e.
+collective excitations, govern the low-energy response of system ground states
+under external stimulations and play essential roles for understanding
+many-body phenomena in low-dimensional materials. The hybridization of distinct
+collective modes provides a route towards coherent manipulation of coupled
+degrees of freedom and quantum phases. In magnets, strong coupling between
+collective spin and lattice excitations, i.e., magnons and phonons, can lead to
+coherent quasi-particle magnon polarons. Here, we report the direct observation
+of a series of terahertz magnon polarons in a layered zigzag antiferromagnet
+FePS3 via far-infrared (FIR) transmission measurements. The characteristic
+avoided-crossing behavior is clearly seen as the magnon-phonon detuning is
+continuously changed via Zeeman shift of the magnon mode. The coupling strength
+g is giant, achieving 120 GHz (0.5 meV), the largest value reported so far.
+Such a strong coupling leads to a large ratio of g to the resonance frequency
+(g/{\omega}) of 4.5%, and a value of 29 in cooperativity
+(g^2/{\gamma}_{ph}{\gamma}_{mag}). Experimental results are well reproduced by
+first-principle calculations, where the strong coupling is identified to arise
+from phonon-modulated anisotropic magnetic interactions due to spin-orbit
+coupling. These findings establish FePS3 as an ideal testbed for exploring
+hybridization-induced topological magnonics in two dimensions and the coherent
+control of spin and lattice degrees of freedom in the terahertz regime.",2108.11619v1
+2021-11-01,Magnon-phonon coupling from a crossing symmetric screened interaction,"The magnon-phonon coupling has received growing attention in recent years due
+to its central role in spin caloritronics and the emerging field of acoustic
+spintronics. At resonance, this magnetoelastic interaction drives the formation
+of magnon polarons, which underpin exotic phenomena such as magnonic heat
+currents and phononic spin, but has with a few recent exceptions only been
+investigated using mesoscopic spin-lattice models. Motivated to integrate the
+magnon-phonon coupling into first-principle many-body electronic structure
+theory, we set up to derive the non-relativistic exchange-contribution, which
+is more subtle than the spin-orbit contribution, using Schwinger's method of
+functional derivatives. To avoid having to solve the famous Hedin-Baym
+equations self-consistently, the phonons are treated as a perturbation to the
+electronic structure. A formalism is developed around the idea of imposing
+crossing symmetry on the interaction, in order to treat charge and spin on
+equal footing. By an iterative scheme, we find that the spin-flip component of
+the ${\mathit collective}$ four-point interaction, $\mathcal{V}$, which is used
+to calculate the magnon spectrum, contains a first-order ""screened T matrix""
+part and an arguably more important second-order part, which in the limit of
+local spins describes the same processes of phonon emission and absorption as
+obtained from phenomenological magnetoelastic models. Here, the ""order"" refers
+to the ${\mathit screened}$ ${\mathit collective}$ four-point interaction,
+$\mathcal{W}$ - the crossing-symmetric analog of Hedin's $W$.
+Proof-of-principle model calculations are performed at varying temperatures for
+the isotropic magnon spectrum in three dimensions in the presence of a flat
+optical phonon branch.",2111.00908v1
+2022-02-25,Direct probing of strong magnon-photon coupling in a planar geometry,"We demonstrate direct probing of strong magnon-photon coupling using
+Brillouin light scattering spectroscopy in a planar geometry. The magnonic
+hybrid system comprises a split-ring resonator loaded with epitaxial yttrium
+iron garnet thin films of 200 nm and 2.46 $\mu$m thickness. The Brillouin light
+scattering measurements are combined with microwave spectroscopy measurements
+where both biasing magnetic field and microwave excitation frequency are
+varied. The cooperativity for the 200 nm-thick YIG films is 4.5, and larger
+cooperativity of 137.4 is found for the 2.46 $\mu$m-thick YIG film. We show
+that Brillouin light scattering is advantageous for probing the magnonic
+character of magnon-photon polaritons, while microwave absorption is more
+sensitive to the photonic character of the hybrid excitation. A miniaturized,
+planar device design is imperative for the potential integration of magnonic
+hybrid systems in future coherent information technologies, and our results are
+a first stepping stone in this regard. Furthermore, successfully detecting the
+magnonic hybrid excitation by Brillouin light scattering is an essential step
+for the up-conversion of quantum signals from the optical to the microwave
+regime in hybrid quantum systems.",2202.12696v1
+2022-04-07,Gaps in Topological Magnon Spectra: Intrinsic vs. Extrinsic Effects,"For topological magnon spectra, determining and explaining the presence of a
+gap at a magnon crossing point is a key to characterize the topological
+properties of the system. An inelastic neutron scattering study of a single
+crystal is a powerful experimental technique that is widely employed to probe
+the magnetic excitation spectra of topological materials. Here, we show that
+when the scattering intensity rapidly disperses in the vicinity of a crossing
+point, such as a Dirac point, the apparent topological gap size is extremely
+sensitive to experimental conditions including sample mosaic, resolution, and
+momentum integration range. We demonstrate these effects using comprehensive
+neutron-scattering measurements of CrCl$_3$. Our measurements confirm the
+gapless nature of the Dirac magnon in CrCl$_3$, but also reveal an artificial,
+i.e. extrinsic, magnon gap unless the momentum integration range is carefully
+controlled. Our study provides an explanation of the apparent discrepancies
+between spectroscopic and first-principles estimates of Dirac magnon gap sizes,
+and provides guidelines for accurate spectroscopic measurement of topological
+magnon gaps.",2204.03720v1
+2022-08-18,Nonlinear magnon control of atomic spin defects in scalable quantum devices,"Ongoing efforts in quantum engineering have recently focused on integrating
+magnonics into hybrid quantum architectures for novel functionalities. While
+hybrid magnon-quantum spin systems have been demonstrated with nitrogen-vacancy
+(NV) centers in diamond, they have remained elusive on the technologically
+promising silicon carbide (SiC) platform mainly due to difficulties in finding
+a resonance overlap between the magnonic system and the spin centers. Here we
+circumvent this challenge by harnessing nonlinear magnon scattering processes
+in a magnetic vortex to access magnon modes that overlap in frequency with
+silicon-vacancy ($\textrm{V}_{\mathrm{Si}}$) spin transitions in SiC. Our
+results offer a route to develop hybrid systems that benefit from marrying the
+rich nonlinear dynamics of magnons with the advantageous properties of SiC for
+scalable quantum technologies.",2208.09036v1
+2022-11-24,Chiral magnons in altermagnetic RuO2,"Magnons in ferromagnets have one chirality, and typically are in the GHz
+range and have a quadratic dispersion near the zero wavevector. In contrast,
+magnons in antiferromagnets are commonly considered to have bands with both
+chiralities that are degenerate across the entire Brillouin zone, and to be in
+the THz range and to have a linear dispersion near the center of the Brillouin
+zone. Here we theoretically demonstrate a new class of magnons on a
+prototypical $d$-wave altermagnet RuO$_2$ with the compensated antiparallel
+magnetic order in the ground state. Based on density-functional-theory
+calculations we observe that the THz-range magnon bands in RuO$_2$ have an
+alternating chirality splitting, similar to the alternating spin splitting of
+the electronic bands, and a linear magnon dispersion near the zero wavevector.
+We also show that, overall, the Landau damping of this metallic altermagnet is
+suppressed due to the spin-split electronic structure, as compared to an
+artificial antiferromagnetic phase of the same RuO$_2$ crystal with
+spin-degenerate electronic bands and chirality-degenerate magnon bands.",2211.13806v1
+2023-02-10,Laser-induced magnonic band gap formation and control in YIG/GaAs heterostructure,"We demonstrate the laser-induced control over spin-wave (SW) transport in the
+magnonic crystal (MC) waveguide formed from the semiconductor slab placed on
+the ferrite film. We considered bilayer MC with periodical grooves performed on
+the top of the n-type gallium arsenide slab side that oriented to the yttrium
+iron garnet film. To observe the appearance of magnonic gap induced by laser
+radiation, the fabricated structure was studied by the use of microwave
+spectroscopy and Brillouin light-scattering. We perform detailed numerical
+studies of this structure. We showed that the optical control of the magnonic
+gaps (frequency width and position) is related to the variation of the charge
+carriers' concentration in GaAs. We attribute these to nonreciprocity of SW
+transport in the layered structure. Nonreciprocity was induced by the laser
+exposure of the GaAs slab due to SWs' induced electromagnetic field screening
+by the optically-generated charge carriers. We showed that SW dispersion,
+nonreciprocity, and magnonic band gap position and width in the
+ferrite-semiconductor magnonic crystal can be modified in a controlled manner
+by laser radiation. Our results show the possibility of the integration of
+magnonics and semiconductor electronics on the base of YIG/GaAs structures.",2302.05310v1
+2023-02-13,Raman scattering study of multimagnon (bi- and tri-magnon) excitations and rotonlike points in the distorted triangular lattice antiferromagnet,"We investigate the experimental signatures of Raman spectroscopy of bi- and
+tri-magnon excitations in the distorted triangular lattice antiferromagnets
+alpha-LCr2O4 (L=Sr, Ca). We utilize spin wave theory to analyze the nearly 120
+degree spin-3/2 spiral ordered antiferromagnetic ground state to compute the
+single-magnon density of states, single-magnon dispersion, and bimagnon and
+trimagnon Raman spectra (polarized and unpolarized). It is found that Raman
+scattering is capable of capturing the effect of the rotonlike M and M' points
+on the bimagnon Raman spectrum. Our calculation confirms the connection between
+single-magnon rotonlike excitation energy and bimagnon Raman excitation
+spectrum observed experimentally. The roton energy minimum in momentum space is
+half of the energy of a bimagnon excitation signal. The experimental magnetic
+Raman scattering result displays two peaks which have a Raman shift of 15 meV
+and 40 meV, respectively. Theoretical modeling and analysis of the experimental
+spectrum of alpha-SrCr2O4 within our distorted Heisenberg Hamiltonian lattice
+suggests that the low-energy peak at 15 meV is associated with the bimagnon
+excitation, whereas the high-energy peak around 40 meV is primarily a trimagnon
+excitation. Based on our fitting procedure we propose a new set of magnetic
+interaction parameters for alpha-SrCr2O4. These parameters reproduce not only
+the experimental Raman spectrum, but also the inelastic neutron scattering
+response (including capturing high energy magnon branches). We also compute the
+unpolarized bimagnon and trimagnon Raman spectra for alpha-CaCr2O4.
+Furhtermore, we found that the polarization sensitivity of Raman spectrum can
+be utilized to distinguish the bi- and tri-magnon excitation channels.",2302.06642v1
+2023-03-08,True amplification of spin waves in magnonic nano-waveguides,"Magnonic nano-devices exploit magnons -- quanta of spin waves -- to transmit
+and process information within a single integrated platform that has the
+potential to outperform traditional semiconductor-based electronics for low
+power applications. The main missing cornerstone of this information
+nanotechnology is an efficient scheme for the direct amplification of
+propagating spin waves. The recent discovery of spin-orbit torque provided an
+elegant mechanism for propagation losses compensation. While partial
+compensation of the spin-wave damping has allowed for spin-wave signal
+modulation, true amplification - the exponential increase in the spin-wave
+intensity during propagation - has so far remained elusive. Here we evidence
+the operating conditions to achieve unambiguous amplification using clocked
+nanoseconds-long spin-orbit torque pulses in sub-micrometer wide magnonic
+waveguides, where the effective magnetization has been engineered to be close
+to zero to suppress the detrimental magnon-magnon scattering. As a result, we
+achieve an exponential increase in the intensity of propagating spin waves up
+to 500 % at a propagation distance of several micrometers. These results pave
+the way towards the implementation of energy efficient, cascadable magnonic
+architectures for wave-based information processing and complex on-chip
+computation.",2303.04695v2
+2023-04-03,Observation of spin-wave moiré edge and cavity modes in twisted magnetic lattices,"We report the experimental observation of the spin-wave moir\'e edge and
+cavity modes using Brillouin light scattering spectro-microscopy in a
+nanostructured magnetic moir\'e lattice consisting of two twisted triangle
+antidot lattices based on an yttrium iron garnet thin film. Spin-wave moir\'e
+edge modes are detected at an optimal twist angle and with a selective
+excitation frequency. At a given twist angle, the magnetic field acts as an
+additional degree of freedom for tuning the chiral behavior of the magnon edge
+modes. Micromagnetic simulations indicate that the edge modes emerge within the
+original magnonic band gap and at the intersection between a mini-flatband and
+a propagation magnon branch. Our theoretical estimate for the Berry curvature
+of the magnon-magnon coupling suggests a non-trivial topology for the chiral
+edge modes and confirms the key role played by the dipolar interaction. Our
+findings shed light on the topological nature of the magnon edge mode for
+emergent moir\'e magnonics.",2304.01001v1
+2023-04-19,Magnon-magnon interaction in monolayer MnBi$_2$Te$_4$,"MnBi$_2$Te$_4$, the first confirmed intrinsic antiferromagnetic topological
+insulator, has garnered increasing attention in recent years. Here we
+investigate the energy correction and lifetime of magnons in MnBi$_2$Te$_4$
+caused by magnon-magnon interaction. First, a calculation based on the density
+functional theory was performed to get the parameters of the magnetic
+Hamiltonian of MnBi$_2$Te$_4$. Subsequently, the perturbation method of
+many-body Green's function was employed and the first-order self-energy
+[$\Sigma^{(1)}(\bm k)$] and second-order self-energy [$\Sigma^{(2)}(\bm
+k,\varepsilon_{\bm k})$] of magnon were obtained. Numerical computations reveal
+that the corrections from both $\Sigma^{(1)}(\bm k)$ and $\Sigma^{(2)}(\bm
+k,\varepsilon_{\bm k})$ strongly rely on momentum and temperature, with the
+energy renormalization near the Brillouin zone (BZ) boundary being
+significantly more pronounced than that near the BZ center. Furthermore, our
+findings indicate the occurrence of dip structures in the renormalized magnon
+spectrum near the $\rm K$ and $\rm M$ points. These dip structures are
+determined to be attributed to the influence of $\Sigma^{(2)}(\bm
+k,\varepsilon_{\bm k})$.",2304.09637v3
+2023-07-20,The challenges of measuring spin Seebeck noise,"Just as electronic shot noise in driven conductors results from the
+granularity of charge and the statistical variation in the arrival times of
+charge carriers, there are predictions for fundamental noise in magnon currents
+due to angular momentum being carried by discrete excitations. The inverse spin
+Hall effect as a transduction mechanism to convert spin current into charge
+current raises the prospect of experimental investigations of such magnon shot
+noise. Spin Seebeck effect measurements have demonstrated the electrical
+detection of thermally driven magnon currents and have been suggested as an
+avenue for accessing spin current fluctuations. Using spin Seebeck structures
+made from yttrium iron garnet on gadolinium gallium garnet, we demonstrate the
+technical challenges inherent in such noise measurements. While there is a
+small increase in voltage noise in the inverse spin Hall detector at low
+temperatures associated with adding a magnetic field, the dependence on field
+orientation implies that this is not due to magnon shot noise. We describe
+theoretical predictions for the expected magnitude of magnon shot noise,
+highlighting ambiguities that exist. Further, we show that magnon shot noise
+detection through the standard inverse spin Hall approach is likely impossible
+due to geometric factors. Implications for future attempts to measure magnon
+shot noise are discussed.",2307.11218v2
+2023-08-02,Impulsive Fermi magnon-phonon resonance in antiferromagnetic $CoF_{2}$,"Understanding spin-lattice interactions in antiferromagnets is one of the
+most fundamental issues at the core of the recently emerging and booming fields
+of antiferromagnetic spintronics and magnonics. Recently, coherent nonlinear
+spin-lattice coupling was discovered in an antiferromagnet which opened the
+possibility to control the nonlinear coupling strength and thus showing a novel
+pathway to coherently control magnon-phonon dynamics. Here, utilizing intense
+narrow band terahertz (THz) pulses and tunable magnetic fields up to 7 T, we
+experimentally realize the conditions of the Fermi magnon-phonon resonance in
+antiferromagnetic $CoF_{2}$. These conditions imply that both the spin and the
+lattice anharmonicities harvest energy transfer between the subsystems, if the
+magnon eigenfrequency $f_{m}$ is twice lower than the frequency of the phonon
+$2f_{m}=f_{ph}$. Performing THz pump-infrared probe spectroscopy in conjunction
+with simulations, we explore the coupled magnon-phonon dynamics in the vicinity
+of the Fermi-resonance and reveal the corresponding fingerprints of an
+impulsive THz-induced response. This study focuses on the role of nonlinearity
+in spin-lattice interactions, providing insights into the control of coherent
+magnon-phonon energy exchange.",2308.01052v1
+2023-12-12,Spatiotemporal visualization of a surface acoustic wave coupled to magnons across a submillimeter-long sample by pulsed laser interferometry,"Surface acoustic waves (SAWs) coupled to magnons have attracted much
+attention because they allow for the long-range transport of magnetic
+information which cannot be achieved by magnon alone. We employed pulsed laser
+interferometry to visualize the entire spatiotemporal dynamics of a SAW that
+travels on a nickel (Ni) thin film and is coupled to magnons. It was possible
+to trace the coupling-induced amplitude reduction and phase shift that occurs
+as the SAW propagates over a distance of 0.4 mm. The observed changes are
+consistent with results obtained from conventional radio-frequency transmission
+measurements, which probe the total SAW absorption due to magnon--phonon
+coupling. This result verifies that our method can accurately capture the
+spatiotemporal dynamics of a SAW coupled to magnons across the entire length of
+the sample. Additionally, we validated our time-resolved profiles by comparing
+them with theoretical results that take the echo wave due to reflection into
+account. The impact of the echo wave is significant even when it has propagated
+over a distance on the order of millimeters. Our imaging results highlight the
+visualization of the long-range propagation of the SAW coupled to magnons and
+offer more information about the surface vibration profiles in such devices.",2312.07029v1
+2023-12-12,Confined magnon dispersion in ferromagnetic and antiferromagnetic thin films in a second quantization approach: the case of Fe and NiO,"We present a methodology based on the calculation of the inelastic scattering
+from magnons via the spin scattering function in confined geometries such as
+thin films using a second quantization formalism, for both ferromagnetic and
+antiferromagnetic materials. The case studies are chosen with an aim to
+demonstrate the effects of film thickness and crystal orientation on magnon
+modes, using bcc Fe(100) and NiO with (100) and (111) crystallographic
+orientations as prototypical systems. Due to the quantization of the
+quasi-momentum we observe a granularity in the inelastic spectra in the
+reciprocal space path reflecting the orientation of the thin film. This
+approach also allows to capture softer modes that appear due to the partial
+interaction of magnetic moments close to the surface in a thin film geometry,
+in addition to bulk modes. The softer modes are also affected by
+crystallographic orientations as illustrated by the different surface-related
+peaks of NiO magnon density of states at approximately ~ 65 meV for (100) and ~
+42 meV for (111). Additionally, we explore the role of anisotropy on magnon
+modes, revealing that introducing anisotropy to both Fe and NiO films increases
+the overall hardness of the magnon modes. The introduction of a surface
+anisotropy produces a shift of the surface-related magnon DOS peak to higher
+energies with increased surface anisotropy, and in some cases leading to
+surface confined mode.",2312.07715v1
+2024-03-13,Hybrid magnon-phonon cavity for large-amplitude terahertz spin-wave excitation,"Terahertz (THz) spin waves or their quanta, magnons, can be efficiently
+excited by acoustic phonons because these excitations have similar wavevectors
+in the THz regime. THz acoustic phonons can be produced using photoacoustic
+phenomena but typically have a low population and thus a relatively low
+displacement amplitude. The magnetization amplitude and population of the
+acoustically excited THz magnons are thus usually small. Using analytical
+calculations and dynamical phase-field simulations, we show that a freestanding
+metal/magnetic-insulator (MI)/dielectric multilayer can be designed to produce
+large-amplitude THz spin wave via cavity-enhanced magnon-phonon interaction.
+The amplitude of the acoustically excited THz spin wave in the freestanding
+multilayer is predicted to be more than ten times larger than in a
+substrate-supported multilayer. Acoustically excited nonlinear magnon-magnon
+interaction is demonstrated in the freestanding multilayer. The simulations
+also indicate that the magnon modes can be detected by probing the charge
+current in the metal layer generated via spin-charge conversion across the
+MI/metal interface and the resulting THz radiation. Applications of the
+freestanding multilayer in THz optoelectronic transduction are computationally
+demonstrated.",2403.08186v1
+2017-08-06,Thermally Driven Long Range Magnon Spin Currents in Yttrium Iron Garnet due to Intrinsic Spin Seebeck Effect,"The longitudinal spin Seebeck effect refers to the generation of a spin
+current when heat flows across a normal metal/magnetic insulator interface.
+Until recently, most explanations of the spin Seebeck effect use the
+interfacial temperature difference as the conversion mechanism between heat and
+spin fluxes. However, recent theoretical and experimental works claim that a
+magnon spin current is generated in the bulk of a magnetic insulator even in
+the absence of an interface. This is the so-called intrinsic spin Seebeck
+effect. Here, by utilizing a non-local spin Seebeck geometry, we provide
+additional evidence that the total magnon spin current in the ferrimagnetic
+insulator yttrium iron garnet (YIG) actually contains two distinct terms: one
+proportional to the gradient in the magnon chemical potential (pure magnon spin
+diffusion), and a second proportional to the gradient in magnon temperature
+($\nabla T_m$). We observe two characteristic decay lengths for magnon spin
+currents in YIG with distinct temperature dependences: a temperature
+independent decay length of ~ 10 ${\mu}$m consistent with earlier measurements
+of pure ($\nabla T_m = 0$) magnon spin diffusion, and a longer decay length
+ranging from about 20 ${\mu}$m around 250 K and exceeding 80 ${\mu}$m at 10 K.
+The coupled spin-heat transport processes are modeled using a finite element
+method revealing that the longer range magnon spin current is attributable to
+the intrinsic spin Seebeck effect ($\nabla T_m \neq 0$), whose length scale
+increases at lower temperatures in agreement with our experimental data.",1708.01941v3
+2018-02-27,Strain-Induced Topological Magnon Phase Transitions: Applications to Kagome-Lattice Ferromagnets,"A common feature of topological insulators is that they are characterized by
+topologically invariant quantity such as the Chern number and the
+$\mathbb{Z}_2$ index. This quantity distinguishes a nontrivial topological
+system from a trivial one. A topological phase transition may occur when there
+are two topologically distinct phases, and it is usually defined by a gap
+closing point where the topologically invariant quantity is ill-defined. In
+this paper, we show that the magnon bands in the strained (distorted)
+kagome-lattice ferromagnets realize an example of a topological magnon phase
+transition in the realistic parameter regime of the system. When spin-orbit
+coupling (SOC) is neglected (i.e. no Dzyaloshinskii-Moriya interaction), we
+show that all three magnon branches are dispersive with no flat band, and there
+exists a critical point where tilted Dirac and semi-Dirac point coexist in the
+magnon spectra. The critical point separates two gapless magnon phases as
+opposed to the usual phase transition. Upon the inclusion of SOC, we realize a
+topological magnon phase transition point at the critical strain
+$\delta_c=\frac{1}{2}\big[ 1-(D/J)^2\big]$, where $D$ and $J$ denote the
+perturbative SOC and the Heisenberg spin exchange interaction respectively. It
+separates two distinct topological magnon phases with different Chern numbers
+for $\delta<\delta_c$ and for $\delta>\delta_c$. The associated anomalous
+thermal Hall conductivity develops an abrupt change at $\delta_c$, due to the
+divergence of the Berry curvature in momentum space. The proposed topological
+magnon phase transition is experimentally feasible by applying external
+perturbations such as uniaxial strain or pressure.",1802.10095v3
+2021-02-05,Quantum engineering with hybrid magnonics systems and materials,"Quantum technology has made tremendous strides over the past two decades with
+remarkable advances in materials engineering, circuit design and dynamic
+operation. In particular, the integration of different quantum modules has
+benefited from hybrid quantum systems, which provide an important pathway for
+harnessing the different natural advantages of complementary quantum systems
+and for engineering new functionalities. This review focuses on the current
+frontiers with respect to utilizing magnetic excitatons or magnons for novel
+quantum functionality. Magnons are the fundamental excitations of magnetically
+ordered solid-state materials and provide great tunability and flexibility for
+interacting with various quantum modules for integration in diverse quantum
+systems. The concomitant rich variety of physics and material selections enable
+exploration of novel quantum phenomena in materials science and engineering. In
+addition, the relative ease of generating strong coupling and forming hybrid
+dynamic systems with other excitations makes hybrid magnonics a unique platform
+for quantum engineering. We start our discussion with circuit-based hybrid
+magnonic systems, which are coupled with microwave photons and acoustic
+phonons. Subsequently, we are focusing on the recent progress of magnon-magnon
+coupling within confined magnetic systems. Next we highlight new opportunities
+for understanding the interactions between magnons and nitrogen-vacancy centers
+for quantum sensing and implementing quantum interconnects. Lastly, we focus on
+the spin excitations and magnon spectra of novel quantum materials investigated
+with advanced optical characterization.",2102.03222v1
+2023-06-01,Impact of magnetic anisotropy on the magnon Hanle effect in $α$-Fe$_2$O$_3$,"In easy-plane antiferromagnets, the nature of the elementary excitations of
+the spin system is captured by the precession of the magnon pseudospin around
+its equilibrium pseudofield, manifesting itself in the magnon Hanle effect.
+Here, we investigate the impact of growth-induced changes in the magnetic
+anisotropy on this effect in the antiferromagnetic insulator
+$\alpha$-Fe$_2$O$_3$ (hematite). To this end, we compare the structural,
+magnetic, and magnon-based spin transport properties of $\alpha$-Fe$_2$O$_3$
+films with different thicknesses grown by pulsed laser deposition in molecular
+and atomic oxygen atmospheres. While in films grown with molecular oxygen a
+spin-reorientation transition (Morin transition) is absent down to $10\,$K, we
+observe a Morin transition for those grown by atomic-oxygen-assisted
+deposition, indicating a change in magnetic anisotropy. Interestingly, even for
+a $19\,$nm thin $\alpha$-Fe$_2$O$_3$ film grown with atomic oxygen we still
+detect a Morin transition at $125\,$K. We characterize the magnon Hanle effect
+in these $\alpha$-Fe$_2$O$_3$ films via all-electrical magnon transport
+measurements. The films grown with atomic oxygen show a markedly different
+magnon spin signal from those grown in molecular oxygen atmospheres. Most
+importantly, the maximum magnon Hanle signal is significantly enhanced and the
+Hanle peak is shifted to lower magnetic field values for films grown with
+atomic oxygen. These observations suggest a change of magnetic anisotropy for
+$\alpha$-Fe$_2$O$_3$ films fabricated by atomic-oxygen-assisted deposition
+resulting in an increased oxygen content in these films. Our findings provide
+new insights into the possibility to fine-tune the magnetic anisotropy in
+$\alpha$-Fe$_2$O$_3$ and thereby to engineer the magnon Hanle effect.",2306.00375v1
+2023-10-30,Dynamical renormalisation of a spin Hamiltonian via high-order nonlinear magnonics,"The macroscopic magnetic order in the ground state of solids is determined by
+the spin-dependent Hamiltonian of the system. In the absence of external
+magnetic fields, this Hamiltonian contains the exchange interaction, which is
+of electrostatic origin, and the spin-orbit coupling, whose magnitude depends
+on the atomic charge. Spin-wave theory provides a representation of the entire
+spectrum of collective magnetic excitations, called magnons, assuming the
+interactions to be constant and the number of magnons in the system negligible.
+However, the electric field component of light is able to perturb electrostatic
+interactions, charge distributions and, at the same time, can create a magnon
+population. A fundamental open question therefore concerns the possibility to
+optically renormalise the spin Hamiltonian. Here, we test this hypothesis by
+using femtosecond laser pulses to resonantly pump electric-dipole-active pairs
+of high-energy magnons near the edges of the Brillouin zone. The transient spin
+dynamics reveals the activation and a surprising amplification of coherent
+low-energy zone-centre magnons, which are not directly driven. Strikingly, the
+spectrum of these low-energy magnons differs from the one observed in thermal
+equilibrium, the latter being consistent with spin-wave theory. The light-spin
+interaction thus results in a room-temperature renormalisation of the magnetic
+Hamiltonian, with an estimated modification of the magnetic interactions by 10%
+of their ground-state values. We rationalise the observation in terms of a
+novel resonant scattering mechanism, in which zone-edge magnons couple
+nonlinearly to the zone-centre modes. In a quantum mechanical model, we
+analytically derive the corrections to the spectrum due to the photo-induced
+magnon population, which are consistent with our experiments. Our results
+present a milestone for an all-optical engineering of Hamiltonians.",2310.19667v1
+1997-02-18,The NMR relaxation rate of O in undoped Sr_2CuO_2Cl_2: Probing two-dimensional magnons at short distances,"We calculate the nuclear relaxation rate of oxygen in the undoped quasi
+two-dimensional quantum Heisenberg antiferromagnet Sr_2CuO_2Cl_2 above the Neel
+temperature. The calculation is performed at two-loop order with the help of
+the Dyson-Maleev formulation of the spin-wave expansion, taking all scattering
+processes involving two and three magnons into account. At low temperatures T
+we find 1 / T_1 = c_1 T^3 + c_2 T^4 + O (T^5), and give explicit expressions
+for the coefficients c_1 (two-magnon scattering) and c_2 (three magnon
+scattering). We compare our result with a recent experiment by Thurber et al.
+and show that this experiment directly probes the existence of short-wavelength
+magnons in a two-dimensional antiferromagnet.",9702160v2
+1997-11-11,Accurate mapping of quantum Heisenberg magnetic models of spin $s$ on strong-coupling magnon systems,"An infinite-$U$ term is introduced into the Holstein-Primakoff-transformed
+magnon hamiltonian of quantum Heisenberg magnetic models of spin $s$. This term
+removes the unphysical spin wave states on every site and truncates
+automatically the expansion in powers of the magnon occupation operator. The
+resultant strong-coupling magnon hamiltonians are accurately equivalent to the
+original spin hamiltonians. The on-site $U$ levels and their implications are
+studied. Within a simple decoupling approximation for our strong-coupling
+magnon models we can easily reproduce the results for the (sublattice)
+magnetizations obtained previously for the original spin model. But our bosonic
+hamiltonians without any unphysical states allow for substantially improved
+values for the spectral weight in the ground state and for lower ground-state
+energies than those obtained within previous approximations.",9711086v1
+1998-05-14,Magnon modes and magnon-vortex scattering in two-dimensional easy-plane ferromagnets,"We calculate the magnon modes in the presence of a vortex in a circular
+system, combining analytical calculations in the continuum limit with a
+numerical diagonalization of the discrete system. The magnon modes are
+expressed by the S-matrix for magnon-vortex scattering, as a function of the
+parameters and the size of the system and for different boundary conditions.
+Certain quasi-local translational modes are identified with the frequencies
+which appear in the trajectory X(t) of the vortex center in recent Molecular
+Dynamics simulations of the full many-spin model. Using these quasi-local modes
+we calculate the two parameters of a 3rd-order quation of motion for X(t). This
+equation was recently derived by a collective variable theory and describes
+very well the trajectories observed in the simulations. Both parameters, the
+vortex mass and a factor on the third time derivative of X(t), depend strongly
+on the boundary conditions.",9805177v1
+1998-09-18,Hopping-disorder-induced effects upon the two-Magnon Raman Scattering spectrum in an Antiferromagnet,"Two-magnon Raman scattering intensity is obtained for two-dimensional
+spin-1/2 antiferromagnets in presence of hopping disorder. A consistent mode
+assignment scheme is prescribed which essentially establishes a correspondence
+between the hopping-disordered and the pure system. It is seen that a minute
+amount of disorder in hopping leads to a good agreement of the Raman lineshape
+experimentally obtained for the copper-oxide insulators such as ${\rm
+{La_{2}CuO_{4}}}$. Also it is observed that a considerable asymmetry with
+respect to the two-magnon peak appears and the spectral intensity persisting
+much beyond $4J$ (where the joint magnon density of states peaks). This has
+been argued earlier by us [S. Basu and A. Singh, Phys. Rev. B, {\bf {53}}, 6406
+(1996)] to be arising due to highly asymmetric magnon-energy renormalization
+because of a cooperative effect arising from local correlation in hopping
+disorder.",9809251v1
+2001-05-21,"Magnon Heat Transport in (Sr,La)_14Cu_24O_41","We have measured the thermal heat conductivity kappa of the compounds
+Sr_14Cu_24O_41 and Ca_9La_5Cu_24O_41 containing doped and undoped spin ladders,
+respectively. We find a huge anisotropy of both, the size and the temperature
+dependence of kappa which we interpret in terms of a very large heat
+conductivity due to the magnetic excitations of the one-dimensional spin
+ladders. This magnon heat conductivity decreases with increasing hole doping of
+the ladders. The magnon heat transport is analyzed theoretically using a simple
+kinetic model. From this analysis we determine the spin gap and the temperature
+dependent mean free path of the magnons which ranges by several thousand
+angstroms at low temperature. The relevance of several scattering channels for
+the magnon transport is discussed.",0105407v1
+2001-06-08,Subgap transport in ferromagnet-superconductor junctions due to magnon-assisted Andreev reflection,"We propose a new process of magnon-assisted Andreev reflection at a
+ferromagnetic metal - superconductor interface, which consists of the
+simultaneous injection of a Cooper pair from the superconductor and the
+emission of a magnon inside the ferromagnet. At low temperature this process
+represents an additional channel for sub-gap transport across an FS interface,
+which lifts restrictions on the current resulting from the necessity to match
+spin-polarized current in the ferromagnet with spin-less current in the
+superconductor. For a junction between a superconductor and a ferromagnet with
+an arbitrary degree of polarization, the inelastic magnon-assisted Andreev
+reflection process would manifest itself as a nonlinear addition to the $I(V)$
+characteristics which is asymmetric with respect to the sign of the bias
+voltage and is related to the density of states of magnons in the ferromagnet.
+Expressions for the subgap $I(V)$ characteristics are given for arbitrary
+interfacial quality whilst the limiting cases of uniformly transparent and
+disordered interfaces are discussed in detail.",0106161v1
+2001-12-14,Magnon delocalization in ferromagnetic chains with long-range correlated disorder,"We study one-magnon excitations in a random ferromagnetic Heisenberg chain
+with long-range correlations in the coupling constant distribution. By
+employing an exact diagonalization procedure, we compute the localization
+length of all one-magnon states within the band of allowed energies $E$. The
+random distribution of coupling constants was assumed to have a power spectrum
+decaying as $S(k)\propto 1/k^{\alpha}$. We found that for $\alpha < 1$,
+one-magnon excitations remain exponentially localized with the localization
+length $\xi$ diverging as 1/E. For $\alpha = 1$ a faster divergence of $\xi$ is
+obtained. For any $\alpha > 1$, a phase of delocalized magnons emerges at the
+bottom of the band. We characterize the scaling behavior of the localization
+length on all regimes and relate it with the scaling properties of the
+long-range correlated exchange coupling distribution.",0112274v1
+2003-09-08,Dynamical structure factors of S=1 bond-alternating Heisenberg chains,"We calculate the dynamical structural factor of the S=1 bond-alternating
+Heisenberg chain. In the Haldane phase, the lowest excited states form the
+lower edge of the multimagnon continuum in $0 \leq q \leq q_c$ and the
+one-magnon mode in $q_c \leq q \leq \pi$. As the system approaches the gapless
+point, $q_c$ shifts towards $q=\pi$ and the largest integrated intensity of the
+one-magnon mode is decreased. In the singlet-dimer phase, the one-magnon mode
+appears in $0 \leq q \leq q_c$. As the bond-alternation becomes strong, $q_c$
+shifts towards $q=\pi$. In the antiferromagnetic-ferromagnetic bond-alternation
+region with a strong ferromagnetic coupling, the lowest excited states form the
+lower edge of the multimagnon continuum in $0 \leq q \leq 0.2\pi$ and $0.8\pi
+\leq q \leq \pi$, and the one-magnon mode appears in $0.2\pi<q<0.8\pi$. The
+largest integrated intensity of the one-magnon mode is 93%, which is slightly
+smaller than that in the S=1 Haldane-gap system. We further discuss the
+dynamical structural factor in connection with the inelastic neutron-scattering
+experiments.",0309178v1
+2003-09-19,Exact eigenstates and macroscopic magnetization jumps in strongly frustrated spin lattices,"For a class of frustrated spin lattices including e.g. the 1D sawtooth chain,
+the 2D kagom\'e and checkerboard, as well as the 3D pyrochlore lattices we
+construct exact product eigenstates consisting of several independent,
+localized one-magnon states in a ferromagnetic background. Important
+geometrical elements of the relevant lattices are triangles being attached to
+polygons or lines. Then the magnons can be trapped on these polygons/lines. If
+the concentration of localized magnons is small they can be distributed
+randomly over the lattice. Increasing the number of localized magnons their
+distribution over the lattice becomes more and more regular and finally the
+magnons condensate in a crystal-like state. The physical relevance of these
+eigenstates emerges in high magnetic fields where they become groundstates of
+the system. As a result a macroscopic magnetization jump appears in the
+zero-temperature magnetization curve just below the saturation field. The
+height of the jump decreases with increasing spin quantum number and vanishes
+in the classical limit. Thus it is a true macroscopic quantum effect.",0309455v1
+2003-09-25,Magnon Localization in Mattis Glass,"We study the spectral and transport properties of magnons in a model of a
+disordered magnet called Mattis glass, at vanishing average magnetization. We
+find that in two dimensional space, the magnons are localized with the
+localization length which diverges as a power of frequency at small
+frequencies. In three dimensional space, the long wavelength magnons are
+delocalized. In the delocalized regime in 3d (and also in 2d in a box whose
+size is smaller than the relevant localization length scale) the magnons move
+diffusively. The diffusion constant diverges at small frequencies. However, the
+divergence is slow enough so that the thermal conductivity of a Mattis glass is
+finite, and we evaluate it in this paper. This situation can be contrasted with
+that of phonons in structural glasses whose contribution to thermal
+conductivity is known to diverge (when inelastic scattering is neglected).",0309594v1
+2005-03-01,Berry phase of magnons in textured ferromagnets,"We study the energy spectrum of magnons in a ferromagnet with topologically
+nontrivial magnetization profile. In the case of inhomogeneous magnetization
+corresponding to a metastable state of ferromagnet, the spin-wave equation of
+motion acquires a gauge potential leading to a Berry phase for the magnons
+propagating along a closed contour. The effect of magnetic anisotropy is
+crucial for the Berry phase: we show that the anisotropy suppresses its
+magnitude, which makes the Berry phase observable in some cases, similar to the
+Aharonov-Bohm effect for electrons. For example, it can be observed in the
+interference of spin waves propagating in mesoscopic rings. We discuss the
+effect of domain walls on the interference in ferromagnetic rings, and propose
+some experiments with a certain geometry of magnetization. We also show that
+the nonvanishing average topological field acts on the magnons like a uniform
+magnetic field on electrons. It leads to the quantization of the magnon
+spectrum in the topological field.",0503013v1
+2005-03-10,Localized-magnon states in strongly frustrated quantum spin lattices,"Recent developments concerning localized-magnon eigenstates in strongly
+frustrated spin lattices and their effect on the low-temperature physics of
+these systems in high magnetic fields are reviewed. After illustrating the
+construction and the properties of localized-magnon states we describe the
+plateau and the jump in the magnetization process caused by these states.
+Considering appropriate lattice deformations fitting to the localized magnons
+we discuss a spin-Peierls instability in high magnetic fields related to these
+states. Last but not least we consider the degeneracy of the localized-magnon
+eigenstates and the related thermodynamics in high magnetic fields. In
+particular, we discuss the low-temperature maximum in the isothermal entropy
+versus field curve and the resulting enhanced magnetocaloric effect, which
+allows efficient magnetic cooling from quite large temperatures down to very
+low ones.",0503243v2
+2005-09-21,Bose-Einstein condensation of magnons in Cs$_{2}$CuCl$_{4}$: a dilute gas limit near the saturation magnetic field,"Based on a realistic spin Hamiltonian for a frustrated quasi-two dimensional
+spin-1/2 antiferromagnet Cs$_{2}$CuCl$_{4}$, a three-dimensional spin ordering
+in the applied magnetic field $B$ near the saturation value $B_{c}$ is studied
+within the magnon Bose-Einstein condensation (BEC) scenario. With the use of a
+hard-core boson formulation of the spin model, a strongly anysotropic magnon
+dispersion in Cs$_{2}$CuCl$_{4}$ is calculated. In the dilute magnon limit near
+$B_{c}$, the hard-core boson constraint is resulted in an effective magnon
+interaction which is treated in the Hartree-Fock approximation. The critical
+temperature $T_{c}$ is calculated as a function of a magnetic field $B$ and
+compared with the phase boundary $T_{c}(B) $ experimentally determined in
+Cs$_{2}$CuCl$_{4}$ [Phys. Rev. Lett. \textbf{95}, 127202 (2005)].",0509552v1
+2005-12-12,Hardcore Magnons in the S=1/2 Heisenberg Model on the Square Lattice,"We propose a versatile approach to treat commonly arising constraints. It is
+illustrated for interacting magnons of the Heisenberg antiferromagnet on a
+square lattice. For systems of $L\times L$ sites a non-perturbative continuous
+unitary transformation (CUT) is used to derive an effective Hamiltonian
+conserving the number of magnons. They are bosonic particles with a hardcore
+constraint which is captured by a local, repulsive interaction U. The limits
+$U\to\infty$ and $L\to\infty$ are achieved by extrapolation. The residual spin
+gap $\Delta_1$ is smaller than 0.01J reflecting the gapless nature of the
+magnons. The one-magnon dispersion displays all known characteristics.",0512244v2
+2006-04-28,Linear independence of localized magnon states,"At the magnetic saturation field, certain frustrated lattices have a class of
+states known as ""localized multi-magnon states"" as exact ground states. The
+number of these states scales exponentially with the number $N$ of spins and
+hence they have a finite entropy also in the thermodynamic limit $N\to \infty$
+provided they are sufficiently linearly independent. In this article we present
+rigorous results concerning the linear dependence or independence of localized
+magnon states and investigate special examples. For large classes of spin
+lattices including what we called the orthogonal type and the isolated type as
+well as the kagom\'{e}, the checkerboard and the star lattice we have proven
+linear independence of all localized multi-magnon states. On the other hand the
+pyrochlore lattice provides an example of a spin lattice having localized
+multi-magnon states with considerable linear dependence.",0604649v1
+2006-04-24,Magnon Bound States and the AdS/CFT Correspondence,"We study the spectrum of asymptotic states in the spin-chain description of
+planar N=4 SUSY Yang-Mills. In addition to elementary magnons, the asymptotic
+spectrum includes an infinite tower of multi-magnon bound states with exact
+dispersion relation, Delta-J_{1} = sqrt{Q^{2}+(lambda/pi^2)sin^2(p/2)}, where
+the positive integer Q is the number of constituent magnons. These states
+account precisely for the known poles in the exact S-matrix. Like the
+elementary magnon, they transform in small representations of supersymmetry and
+are present for all values of the 't Hooft coupling. At strong coupling we
+identify the dual states in semiclassical string theory.",0604175v2
+2006-07-04,Multispin Giant Magnons,"We investigate giant magnons from classical rotating strings in two different
+backgrounds. First we generalize the solution of Hofman and Maldacena and
+investigate new magnon excitations of a spin chain which are dual to a string
+on $R\times S^5$ with two non-vanishing angular momenta. Alowing string
+dynamics along the third angle in the five sphere, we find a dispersion
+relation that reproduces the Hofman and Maldacena and the one found by Dorey
+for the two spin case. In the second part of the paper we generalize the two
+""spin"" giant magnon to the case of $\b$-deformed $\axs$ background. We find
+agreement between the dispersion relation of the rotating string and the
+proposed dispersion relation of the magnon bound state on the spin chain.",0607018v3
+2006-08-03,The magnon kinematics of the AdS/CFT correspondence,"The planar dilatation operator of N=4 supersymmetric Yang-Mills is the
+hamiltonian of an integrable spin chain whose length is allowed to fluctuate.
+We will identify the dynamics of length fluctuations of planar N=4 Yang-Mills
+with the existence of an abelian Hopf algebra Z symmetry with non-trivial
+co-multiplication and antipode. The intertwiner conditions for this Hopf
+algebra will restrict the allowed magnon irreps to those leading to the magnon
+dispersion relation. We will discuss magnon kinematics and crossing symmetry on
+the spectrum of Z. We also consider general features of the underlying Hopf
+algebra with Z as central Hopf subalgebra, and discuss the giant magnon
+semiclassical regime.",0608029v2
+2006-10-02,Fat Magnon,"We consider a D-brane type state which shares the characteristic of the
+recently found giant magnon of Hofman and Maldacena. More specifically we find
+a bound state of giant graviton (D3-brane) and giant magnon (F-string), which
+has exactly the same anomalous dimension as that of the giant magnon. It is
+described by the D3-brane with electric flux which is topologically a $S^3$
+elongated by the electric flux. The angular momentum and energy are infinite,
+but split sensibly into two parts -- the infinite part precisely the same as
+that of the giant magnon and the finite part which can be identified as the
+contribution from the giant graviton. We discuss that the corresponding dual
+gauge theory operator is not a simple chain type but rather admixture of the
+(sub-)determinant and chain types.",0610027v4
+2008-04-04,"Spin-charge coupling in a band ferromagnet: magnon-energy reduction, anomalous softening, and damping","The effects of correlation-induced coupling between spin and charge
+fluctuations on spin-wave excitations in a band ferromagnet are investigated by
+including self-energy and vertex corrections within a systematic
+inverse-degeneracy expansion scheme which explicitly preserves the Goldstone
+mode. Arising from the scattering of a magnon into intermediate spin-excitation
+states (including both magnon and Stoner excitations) accompanied with charge
+fluctuations in the majority spin band, this spin-charge coupling results not
+only in a substantial reduction of magnon energies but also in anomalous
+softening and significant magnon damping for zone-boundary modes lying within
+the Stoner gap. Our results are in good qualitative agreement with recent
+spin-wave excitation measurements in colossal magneto-resistive manganites and
+ferromagnetic ultrathin films of transition metals.",0804.0680v1
+2008-11-17,"Giant Magnons in AdS4 x CP3: Embeddings, Charges and a Hamiltonian","This paper studies giant magnons in CP3, which in all known cases are old
+solutions from S5 placed into two- and three-dimensional subspaces of CP3,
+namely CP1, RP2 and RP3. We clarify some points about these subspaces, and
+other potentially interesting three- and four-dimensional subspaces. After
+confirming that E-(J1-J4)/2 is a Hamiltonian for small fluctuations of the
+relevant 'vacuum' point particle solution, we use it to calculate the
+dispersion relation of each of the inequivalent giant magnons. We comment on
+the embedding of finite-J solutions, and use these to compare string solutions
+to giant magnons in the algebraic curve.",0811.2423v2
+2009-02-18,Theory of coherence in Bose-Einstein condensation phenomena in a microwave driven interacting magnon gas,"Strong experimental evidences of the formation of quasi-equilibrium
+Bose-Einstein condensation (BEC) of magnons at room temperature in a film of
+yttrium iron garnet (YIG) excited by microwave radiation have been recently
+reported. Here we present a theory for the magnon gas driven by a microwave
+field far out of equilibrium showing that the nonlinear magnetic interactions
+create cooperative mechanisms for the onset of a phase transition leading to
+the spontaneous generation of quantum coherence and magnetic dynamic order in a
+macroscopic scale. The theory provides rigorous support for the formation of a
+BEC of magnons in a YIG film magnetized in the plane. We show that the system
+develops coherence only when the microwave driving power exceeds a threshold
+value and that the theoretical result for the intensity of the Brillouin light
+scattering from the BEC as a function of power agrees with the experimental
+data. The theory also explains quantitatively experimental measurements of
+microwave emission from the uniform mode generated by the confluence of BEC
+magnon pairs in a YIG film when the driving power exceeds a critical value.",0902.3138v1
+2009-02-18,Dressed Giant Magnons on CP^3,"A new example of AdS/CFT duality relating IIA string theory on AdS_4 x CP^3
+to N=6 superconformal Chern-Simons theory has recently been provided by ABJM.
+By now a number of papers have considered particular giant magnon classical
+string solutions in the CP^3 background, corresponding to excitations in the
+spin chain picture of the dual field theory. In this paper we apply the CP^3 =
+SU(4)/S(U(3) x U(1)) dressing method to the problem of constructing general
+classical string solutions describing various configurations of giant magnons.
+As a particular application we present a new giant magnon solution on CP^3.
+Interestingly the dressed solution carries only a single SO(6) charge, in
+contrast with the dyonic magnons found in previous applications of the dressing
+method.",0902.3179v3
+2009-03-11,Low-Temperature Heat Transport in the Low-Dimensional Quantum Magnet NiCl_{2}-4SC(NH_{2})_{2},"We report a study of the low-temperature thermal conductivity of
+NiCl_{2}-4SC(NH_{2})_{2}, which is a spin-1 chain system exhibiting the magnon
+Bose-Einstein condensation (BEC) in magnetic field. It is found that the low-T
+thermal conductivity along the spin-chain direction shows strong anomalies at
+the lower and upper critical fields of the magnon BEC state. In this state,
+magnons act mainly as phonon scatterers at relatively high temperature, but
+change their role to heat carriers upon temperature approaching zero. The
+result demonstrates a large thermal conductivity in the magnon BEC state and
+points to a direct analog between the magnon BEC and the conventional one.",0903.1912v2
+2010-03-22,Magnon pairing in quantum spin nematic,"Competing ferro- and antiferromagnetic exchange interactions may lead to the
+formation of bound magnon pairs in the high-field phase of a frustrated quantum
+magnet. With decreasing field, magnon pairs undergo a Bose-condensation prior
+to the onset of a conventional one-magnon instability. We develop an analytical
+approach to study the zero-temperature properties of the magnon-pair
+condensate, which is a bosonic analog of the BCS superconductors.
+Representation of the condensate wave-function in terms of the coherent bosonic
+states reveals the spin-nematic symmetry of the ground-state and allows one to
+calculate various static properties. Sharp quasiparticle excitations are found
+in the nematic state with a small finite gap. We also predict the existence of
+a long-range ordered spin-nematic phase in the frustrated chain material
+LiCuVO4 at high fields.",1003.4096v3
+2010-07-12,Variable damping and coherence in a high-density magnon gas,"We report on the fast relaxation behavior of a high-density magnon gas
+created by a parametric amplification process. The magnon gas is probed using
+the technique of spin-wave packet recovery by parallel parametric pumping.
+Experimental results show a damping behavior which is in disagreement with both
+the standard model of exponential decay and with earlier observations of
+non-linear damping. In particular, the inherent magnon damping is found to
+depend upon the presence of the parametric pumping field. A phenomenological
+model which accounts for the dephasing of the earlier injected magnons is in
+good agreement with the experimental data.",1007.1895v3
+2011-03-09,Magnetization and magnon excitation energies of the magnetic semiconductors EuTe and EuO on the basis of the renormalized spin wave theory,"We present analytic expressions for the temperature dependent magnetization
+and magnon dispersion relation of the antiferromagnetic (AFM) EuTe and the
+ferromagnetic (FM) EuO. These bulk semiconductors represent concentrated spin
+systems for which the interaction between magnons has to be taken into account.
+We do this using the renormalized spin wave theory. A higher order Green's
+function according to Tjablikov is used for their description. As a result, we
+obtain a modified Bloch- T3/2 law, for low temperatures and high magnetic
+fields. A full analytic expression is given for the sublattice magnetization of
+the AFM EuTe (B0=0), with a N\'eel temperature of TN = 9.81 K. The
+magnetization curves {\sigma}N(T) of EuO (for 0 \leq T \leq 0.68TC) and
+{\sigma}R(T) (for 0.82TC < T < TC) agree well with experiment. The spin wave
+excitation energy perfectly matches experimental data from inelastic neutron
+scattering. In the case of EuTe the magnon excitation energies exhibit a
+characteristic maximum. For q = 0, an energy gap Eg occurs in the spin wave
+spectrum, a consequence of the AFM exchange interaction J2(T). Such energy gaps
+exist in the spectrum of magnon excitation energies only in systems with AFM
+interactions.",1103.1831v1
+2011-03-16,The Semi-Classical Spectrum of Solitons and Giant Magnons,"In this note, we summarize recent progress in constructing and then
+semi-classically quantizing solitons, or non-abelian Q-balls, in the symmetric
+space sine-Gordon theories. We then consider the images of these solitons in
+the related constrained sigma model, which are the dyonic giant magnons on the
+string theory world-sheet. Focussing on the case of the symmetric space S^5, we
+perform a semi-classical quantization of the solitons and magnons and show that
+both lead to Chern-Simons quantum mechanics on the internal moduli space which
+is a real Grassmannian SO(4)/SO(2)xSO(2) but---importantly---with a different
+coupling constant. Quantizing this system shows that both the Q-balls and
+magnons come in a tower of states transforming in symmetric representations of
+the SO(4) symmetry group; however, the former come in a finite tower whereas
+the latter come in the well-known infinite tower of dyonic giant magnons.",1103.3148v2
+2011-05-27,"Magnonic spin-transfer torque MRAM with low power, high speed, and error-free switching","A new class of spin-transfer torque magnetic random access memory (STT-MRAM)
+is discussed, in which writing is achieved using thermally initiated magnonic
+current pulses as an alternative to conventional electric current pulses. The
+magnonic pulses are used to destabilize the magnetic free layer from its
+initial direction, and are followed immediately by a bipolar electric current
+exerting conventional spin-transfer torque on the free layer. The combination
+of thermal and electric currents greatly reduces switching errors, and
+simultaneously reduces the electric switching current density by more than an
+order of magnitude as compared to conventional STT-MRAM. The energy efficiency
+of several possible electro-thermal circuit designs have been analyzed
+numerically. As compared to STT-MRAM with perpendicular magnetic anisotropy,
+magnonic STT-MRAM reduces the overall switching energy by almost 80%.
+Furthermore, the lower electric current density allows the use of thicker
+tunnel barriers, which should result in higher tunneling magneto-resistance and
+improved tunnel barrier reliability. The combination of lower power, improved
+reliability, higher integration density, and larger read margin make magnonic
+STT-MRAM a promising choice for future non-volatile storage.",1105.5473v1
+2011-07-06,Edge magnetism of Heisenberg model on honeycomb lattice,"In our previous study, a single-branch of ferromagnetic magnon with linear
+dispersion is shown to exist near the (uncompensated) zigzag edge for
+Heisenberg model on honeycomb lattice. Here we develop a field-theory
+description for the edge magnon and find its dynamics is captured by the
+one-dimensional relativistic Klein-Gordon equation. It is intriguing that the
+boundary field theory for the edge magnon is tied up with its bulk counterpart,
+described by the two-dimensional Klein-Gordon equation. Furthermore, we also
+reveal how the parity symmetry relates evanescent modes on opposite edges in a
+honeycomb nanoribbon. By employing alternative methods, including Schwinger
+bosons and density-matrix renormalization group, we also demonstrate that the
+relativistic edge magnon is robust even when the Neel order in the bulk is
+destroyed by quantum fluctuations. The edge magnon is a direct consequence of
+uncompensated edge and may be verified in realistic materials by experimental
+probes.",1107.1102v2
+2012-03-07,Magnonic band gap design by the edge modulation of micro-sized waveguides,"The potential to control the number of the spin-wave band gaps of a magnonic
+crystal (MC) by variation of its geometry is investigated by numerical
+simulations. The magnonic crystal is represented by a micro-sized planar
+ferromagnetic waveguide with periodically variable width. By choosing a
+step-like or sinusoidal variation of the width, the magnonic crystal reveals
+multiple or single band gaps, respectively. This allows for additional degrees
+of freedom in the design of MC based microwave filters and phase shifters with
+desired characteristics. The MCs band gaps have been studied in the space and
+frequency domains exploring the spin-wave spectrum dependence on the probing
+position inside the magnonic crystal.",1203.1469v1
+2012-06-28,Thermalization of magnons in yttrium-iron garnet: nonequilibrium functional renormalization group approach,"Using a nonequilibrium functional renormalization group (FRG) approach we
+calculate the time evolution of the momentum distribution of a magnon gas in
+contact with a thermal phonon bath. As a cutoff for the FRG procedure we use a
+hybridization parameter {\Lambda} giving rise to an artificial damping of the
+phonons. Within our truncation of the FRG flow equations the time evolution of
+the magnon distribution is obtained from a rate equation involving
+cutoff-dependent nonequilibrium self-energies, which in turn satisfy FRG flow
+equations depending on cutoff-dependent transition rates. Our approach goes
+beyond the Born collision approximation and takes the feedback of the magnons
+on the phonons into account. We use our method to calculate the thermalization
+of a quasi two-dimensional magnon gas in the magnetic insulator yttrium-iron
+garnet after a highly excited initial state has been generated by an external
+microwave field. We obtain good agreement with recent experiments.",1206.6689v3
+2012-08-03,Field-dependence of magnon decay in yttrium iron garnet thin films,"We discuss threshold field-dependence of the decay rate of the uniform magnon
+mode in yttrium iron garnet (YIG) thin films. We demonstrate that decays must
+cease to exist in YIG films of thickness less than 1 \mu m, the lengthscale
+defined by the exchange length. We show that due to the symmetry of the
+three-magnon coupling the decay rate is linear in \Delta H=(Hc-H) in the
+vicinity of the threshold field Hc instead of the step-like \Gamma
+\Theta(\Delta H) expected from the two-dimensional character of magnon
+excitations in such films. For thicker films, the decay rate should exhibit
+multiple steps due to thresholds for decays into a sequence of the
+two-dimensional magnon bands. For yet thicker films, such thresholds merge and
+crossover to the three-dimensional single-mode behavior: \Gamma |\Delta
+H|^{3/2}.",1208.0831v1
+2012-10-12,Topological Magnon Insulator in Insulating Ferromagnet,"In the ferromagnetic insulator with Dzyaloshinskii-Moriya interaction, we
+theoretically predict and numerically verify a topological magnon insulator,
+where the charge-free magnon is topologically protected to transport along the
+edge while it is insulating in the bulk. Within the bulk band gaps, edge states
+form a connected loop as a $4\pi$- or $8\pi$-period M\""{o}bius strip in the
+wave vector space. As a consequence, the chiral energy current traveling along
+the corresponding edge is topologically protected from defects or disorders.
+Using the nonequilibrium Green's function method, we demonstrate that the
+energy current carried by magnons with energy in the bulk gap localizes at
+edges and prefers to travel along one edge in only one direction at
+nonequilibrium steady state. Our prediction about topological magnon insulator
+could be observed at a wide energy range in the thin film of the insulating
+ferromagnet, such as Lu$_2$V$_2$O$_7$.",1210.3487v2
+2013-02-07,Dynamics of a Bose-Einstein Condensate of Excited Magnons,"The emergence of a non-equilibrium Bose-Einstein-like condensation of magnons
+in rf-pumped magnetic thin films has recently been experimentally observed. We
+present here a complete theoretical description of the non-equilibrium
+processes involved. It it demonstrated that the phenomenon is another example
+of the presence of a Bose-Einstein-like condensation in non-equilibrium
+many-boson systems embedded in a thermal bath, better referred-to as
+Fr\""{o}hlich-Bose-Einstein condensation. The complex behavior emerges after a
+threshold of the exciting intensity is attained. It is inhibited at higher
+intensities when the magnon-magnon interaction drives the magnons to internal
+thermalization. The observed behavior of the relaxation to equilibrium after
+the end of the pumping pulse is also accounted for and the different processes
+fully described.",1302.1765v1
+2013-12-05,Signature of Electron-magnon Umklapp Scattering in L10 FePt probed by Thermoelectric Measurements,"We report unconventional thermoelectric power (Seebeck coefficient, S) in L10
+structured FePt films. The temperature dependence of S can be well fitted by a
+phenomenological expression consisting of electron diffusion and magnon-drag
+contributions. Interestingly, the magnon drag coefficient carries an opposite
+sign to that of electron diffusion, revealing a dominant contribution from the
+elusive electron-magnon Umklapp scattering. DFT calculations identify several
+bands crossing the Brillouin zone boundaries, facilitating the Umklapp process.
+The large spin-orbit coupling in FePt results in strong mixing of majority and
+minority spins among some of those bands, greatly enhancing the electron-magnon
+scattering.",1312.1634v4
+2014-01-13,Microkelvin thermometry with Bose-Einstein condensates of magnons and applications to studies of the AB interface in superfluid $^3$He,"Coherent precession of trapped Bose-Einstein condensates of magnons is a
+sensitive probe for magnetic relaxation processes in superfluid 3He-B down to
+the lowest achievable temperatures. We use the dependence of the relaxation
+rate on the density of thermal quasiparticles to implement thermometry in 3He-B
+at temperatures below 300 $\mu$K. Unlike popular vibrating wire or quartz
+tuning fork based thermometers, magnon condensates allow for contactless
+temperature measurement and make possible an independent in situ determination
+of the residual zero-temperature relaxation provided by the radiation damping.
+We use this magnon-condensate-based thermometry to study the thermal impedance
+of the interface between A and B phases of superfluid 3He. The magnon
+condensate is also a sensitive probe of the orbital order-parameter texture.
+This has allowed us to observe for the first time the non-thermal signature of
+the annihilation of two AB interfaces.",1401.2953v2
+2014-01-16,A thermodynamic theory for thermal-gradient-driven domain wall motion,"Spin waves (or magnons) interact with magnetic domain walls (DWs) in a
+complicated way that a DW can propagate either along or against magnon flow.
+However, thermally activated magnons always drive a DW to the hotter region of
+a nanowire of magnetic insulators under a temperature gradient. We
+theoretically illustrate why it is surely so by showing that DW entropy is
+always larger than that of a domain as long as material parameters do not
+depend on spin textures. Equivalently, the total free energy of the wire can be
+lowered when the DW moves to the hotter region. The larger DW entropy is
+related to the increase of magnon density of states at low energy originated
+from the gapless magnon bound states.",1401.4021v2
+2014-04-22,Coherent magnon optics in a ferromagnetic spinor Bose-Einstein condensate,"We measure the mass, gap, and magnetic moment of a magnon in the
+ferromagnetic $F=1$ spinor Bose-Einstein condensate of $^{87}$Rb. We find an
+unusually heavy magnon mass of $1.038(2)_\mathrm{stat}(8)_\mathrm{sys}$ times
+the atomic mass, as determined by interfering standing and running coherent
+magnon waves within the dense and trapped condensed gas. This measurement is
+shifted significantly from theoretical estimates. The magnon energy gap of
+$h\times 2.5(1)_\mathrm{stat}(2)_\mathrm{sys}\;\mathrm{Hz}$ and the effective
+magnetic moment of $-1.04(2)_\mathrm{stat}(8)\,\mu_\textrm{bare}$ times the
+atomic magnetic moment are consistent with mean-field predictions. The nonzero
+energy gap arises from magnetic dipole-dipole interactions.",1404.5631v1
+2014-12-25,Normal-mode splitting in the coupled system of hybridized nuclear magnons and microwave photons,"In the weak ferromagnetic MnCO$_3$ system, a low-frequency collective spin
+excitation (magnon) is the hybridized oscillation of nuclear and electron spins
+coupled through the hyperfine interaction. By using a split-ring resonator, we
+performed transmission spectroscopy measurements of MnCO$_3$ system and
+observed, for the first time, avoiding crossing between the hybridized
+nuclear-electron magnon mode and the resonator mode in the NMR-frequency range.
+The splitting strength is quite large due to the large spin density of
+$^{55}$Mn, and the cooperativity value $C=0.2$ (magnon-photon coupling
+parameter) is close to the conditions of strong coupling. The results reveal a
+new class of spin systems, in which the coupling between nuclear spins and
+photons is mediated by electron spins via the hyperfine interaction, and in
+which the similar normal-mode splitting of the hybridized nuclear magnon mode
+and the resonator mode can be observed.",1412.7799v3
+2015-02-13,Bose-Einstein condensation of magnons in atomic hydrogen gas,"We report on experimental observation of BEC-like behaviour of quantized
+electron spin waves (magnons) in a dense gas of spin polarized atomic hydrogen.
+The magnons are trapped and controlled with inhomogeneous magnetic fields, and
+described by a Schr\""odinger-like wave equation, in analogy to the BEC
+experiments with neutral atoms. We have observed the appearance of a sharp
+feature in the ESR spectrum displaced from the normal spin wave spectrum. We
+believe that this observation corresponds to a sudden growth of the ground
+state population of the magnons and emergence of their spontaneous coherence
+for hydrogen gas densities exceeding a critical value, dependent on the
+trapping potential. We interpret the results as a BEC of non-equilibrium
+magnons which were formed by applying the rf power.",1502.03963v1
+2015-02-27,Collective dynamical skyrmions excitations in magnonic crystal,"We investigate theoretically skyrmion magnonic crystal, i.e., the dynamics of
+the magnetization in a chain of the ferromagnetic nanodots being in skyrmion
+magnetic configuration. We show that collective excitations are possible to be
+observed in the structure. We present the dispersion relation of the coupled
+skyrmions. It exhibit a periodical property in dependence on wave vector,
+characteristic feature of the band structure in magnonic crystals. Spatial
+analysis of the magnetization amplitude associated with the magnonic bands
+confirms type of the excited modes, as breathing and clockwise gyrotropic
+dynamical skyrmions. These high and low frequency excitations, propagate with
+negative and positive group velocity, respectively, and can be explored for
+study fundamental properties and technological applications in spintronics and
+magnonics.",1502.08024v1
+2015-03-19,Critical suppression of spin Seebeck effect by magnetic fields,"The longitudinal spin Seebeck effect (LSSE) in Pt/Y$_3$Fe$_5$O$_{12}$ (YIG)
+junction systems has been investigated at various magnetic fields and
+temperatures. We found that the LSSE voltage in a Pt/YIG-slab system is
+suppressed by applying high magnetic fields and this suppression is critically
+enhanced at low temperatures. The field-induced suppression of the LSSE in the
+Pt/YIG-slab system is too large at around room temperature to be explained
+simply by considering the effect of the Zeeman gap in magnon excitation. This
+result requires us to introduce magnon-frequency-dependent mechanism into the
+scenario of LSSE; low-frequency magnons dominantly contribute to the LSSE. The
+magnetic field dependence of the LSSE voltage was observed to change by
+changing the thickness of YIG, suggesting that the thermo-spin conversion by
+the low-frequency magnons is suppressed in thin YIG films due to the long
+characteristic lengths of such magnons.",1503.05764v2
+2015-04-08,Scattering of high-energy magnons off a magnetic skyrmion,"We discuss the scattering of high-energy magnons off a single magnetic
+skyrmion within the field-polarized ground state of a two-dimensional chiral
+magnet. For wavevectors larger than the inverse skyrmion radius, $k r_s \gg 1$,
+the magnon scattering is dominated by an emerging magnetic field whose flux
+density is essentially determined by the topological charge density of the
+skyrmion texture. This leads to skew and rainbow scattering characterized by an
+asymmetric and oscillating differential cross section. We demonstrate that the
+transversal momentum transfer to the skyrmion is universal due to the
+quantization of the total emerging flux while the longitudinal momentum
+transfer is negligible in the high-energy limit. This results in a
+magnon-driven skyrmion motion approximately antiparallel to the incoming magnon
+current and a universal relation between current and skyrmion-velocity.",1504.02108v2
+2015-05-08,Nonreciprocal magnon propagation in a noncentrosymmetric ferromagnet,"Relativistic spin-orbit interaction drastically modifies electronic band and
+endows emergent functionalities. One of the example is the Rashba effect. In
+noncentrosymmetric systems such as interface and polar materials, the
+electronic band is spin-splitted depending on the momentum direction owing to
+the spin-orbit interaction, which is useful for the electric manipulation of
+spin current. Similar relativistic band-modification is also emergent for spin
+wave (magnon) in magnetic materials. The asymmetric magnon band dispersion
+induced by the Dzyaloshinskii-Moriya interaction, which is antisymmetric
+exchange interaction originating from the spin-orbit interaction, is
+theoretically expected, and experimentally observed recently in
+noncentrosymmetric ferromagnets. Here, we demonstrate that the nonreciprocal
+microwave response can be induced by the asymmetric magnon band in a
+noncentrosymmetric ferrimagnet LiFe$_5$O$_8$. This result may pave a new path
+to designing magnonic device based on the relativistic band engineering.",1505.01942v1
+2015-05-23,Long distance transport of magnon spin information in a magnetic insulator at room temperature,"The transport of spin information has been studied in various materials, such
+as metals, semiconductors and graphene. In these materials, spin is transported
+by diffusion of conduction electrons. Here we study the diffusion and
+relaxation of spin in a magnetic insulator, where the large bandgap prohibits
+the motion of electrons. Spin can still be transported, however, through the
+diffusion of non-equilibrium magnons, the quanta of spin wave excitations in
+magnetically ordered materials. Here we show experimentally that these magnons
+can be excited and detected fully electrically in linear response, and can
+transport spin angular momentum through the magnetic insulator yttrium iron
+garnet (YIG) over distances as large as 40 micrometer. We identify two
+transport regimes: the diffusion limited regime for distances shorter than the
+magnon relaxation length, and the relaxation limited regime for larger
+distances. With a model similar to the diffusion-relaxation model for electron
+spin transport in (semi)conducting materials, we extract the magnon relaxation
+length lambda = 9.4 micrometer in a 200 nm thin YIG film at room temperature.",1505.06325v1
+2016-04-24,Optomagnonics in Magnetic Solids,"Coherent conversion of photons to magnons, and back, provides a natural
+mechanism for rapid control of interactions between stationary spins with long
+coherence times and high-speed photons. Despite the large frequency difference
+between optical photons and magnons, coherent conversion can be achieved
+through a three-particle interaction between one magnon and two photons whose
+frequency difference is resonant with the magnon frequency, as in optomechanics
+with two photons and a phonon. The large spin density of a transparent
+ferromagnetic insulator (such as the ferrite yttrium iron garnet) in an optical
+cavity provides an intrinsic photon-magnon coupling strength that we calculate
+to exceed reported optomechanical couplings. A large cavity photon number and
+properly selected cavity detuning produce a predicted effective coupling
+strength sufficient for observing electromagnetically induced transparency and
+the Purcell effect, and even to reach the ultra-strong coupling regime.",1604.07052v2
+2016-06-09,Spin dynamical phase and anti-resonance in a strongly coupled magnon-photon system,"We experimentally studied a strongly coupled magnon-photon system via
+microwave transmission measurements. An anti-resonance, i.e. the suppression of
+the microwave transmission, is observed, indicating a relative phase change
+between the magnon response and the driving microwave field. We show that this
+anti-resonance feature can be used to interpret the phase evolution of the
+coupled magnon-microwave system and apply this technique to reveal the phase
+evolution of magnon dark modes. Our work provides a standard procedure for the
+phase analysis of strongly coupled systems, enabling the phase characterization
+of each subsystem, and can be generally applied to other strongly coupled
+systems.",1606.03056v1
+2017-03-13,Quasiparticle Breakdown and Spin Hamiltonian of the Frustrated Quantum Pyrochlore Yb$_2$Ti$_2$O$_7$ in Magnetic Field,"The frustrated pyrochlore magnet Yb$_2$Ti$_2$O$_7$ has the remarkable
+property that it orders magnetically, but has no propagating magnons over wide
+regions of the Brillouin zone. Here we use inelastic neutron scattering to
+follow how the spectrum evolves in cubic-axis magnetic fields. At high fields
+we observe in addition to dispersive magnons also a two-magnon continuum, which
+grows in intensity upon reducing the field and overlaps with the one-magnon
+states at intermediate fields leading to strong renormalization of the
+dispersion relations, and magnon decays. Using heat capacity measurements we
+find that the low and high field regions are smoothly connected with no sharp
+phase transition, with the spin gap increasing monotonically in field. Through
+fits to an extensive data set we re-evaluate the spin Hamiltonian finding
+dominant quantum exchange terms, which we propose are responsible for the
+anomalously strong fluctuations and quasiparticle breakdown effects observed at
+low fields.",1703.04506v1
+2018-02-22,Interlayer Couplings Mediated by Antiferromagnetic Magnons,"Collinear antiferromagnets (AFs) support two degenerate magnon excitations
+carrying opposite spin polarizations, by which magnons can function as
+electrons in various spin-related phenomena. In an insulating
+ferromagnet(F)/AF/F trilayer, we explore the magnon-mediated interlayer
+coupling by calculating the magnon thermal energy in the AF as a function of
+the orientations of the Fs. The effect manifests as an interlayer exchange
+interaction and a perpendicular magnetic anisotropy; they both depend on
+temperature and the AF thickness. In particular, the exchange interaction turns
+out to be antiferromagnetic at low temperatures and ferromagnetic at high
+temperatures, whose magnitude can be $10-100$ $\mu$eV for nanoscale
+separations, allowing experimental verification.",1802.07867v2
+2018-02-28,The effects of thermal and correlated noise on magnons in a quantum ferromagnet,"The dynamics and thermal equilibrium of spin waves (magnons) in a quantum
+ferromagnet as well as the macroscopic magnetisation are investigated. Thermal
+noise due to an interaction with lattice phonons and the effects of spatial
+correlations in the noise are considered. We first present a Markovian master
+equation approach with analytical solutions for any homogeneous spatial
+correlation function of the noise. We find that spatially correlated noise
+increases the decay rate of magnons with low wave vectors to their thermal
+equilibrium, which also leads to a faster decay of the ferromagnet's
+magnetisation to its steady-state value. For long correlation lengths and
+higher temperature we find that additionally there is a component of the
+magnetisation which decays very slowly, due to a reduced decay rate of fast
+magnons. This effect could be useful for fast and noise-protected quantum or
+classical information transfer and magnonics. We further compare ferromagnetic
+and antiferromagnetic behaviour in noisy environments and find qualitatively
+similar behaviour in Ohmic but fundamentally different behaviour in super-Ohmic
+environments.",1802.10258v2
+2018-04-25,Magnon thermal Hall effect in kagome antiferromagnets with Dzyaloshinskii-Moriya interactions,"We theoretically study magnetic and topological properties of
+antiferromagnetic kagome spin systems in the presence of both in- and
+out-of-plane Dzyaloshinskii-Moriya interactions. In materials such as the iron
+jarosites, the in-plane interactions stabilize a canted noncollinear ""umbrella""
+magnetic configuration with finite scalar spin chirality. We derive expressions
+for the canting angle, and use the resulting order as a starting point for a
+spin-wave analysis. We find topological magnon bands, characterized by non-zero
+Chern numbers. We calculate the magnon thermal Hall conductivity, and propose
+the iron jarosites as a promising candidate system for observing the magnon
+thermal Hall effect in a noncollinear spin configuration. We also show that the
+thermal conductivity can be tuned by varying an applied magnetic field, or the
+in-plane Dzyaloshinskii-Moriya strength. In contrast with previous studies of
+topological magnon bands, the effect is found to be large even in the limit of
+small canting.",1804.09783v2
+2018-11-01,Non-Hermitian magnon-photon interference in an atomic ensemble,"The beam-splitter (BS) is one of the most common and important components in
+modern optics, and lossless BS which features unitary transformation induces
+Hermitian evolution of light. However, the practical BS based on the conversion
+between different degree of freedoms are naturally non-Hermitian, as a result
+of essentially open quantum dynamics. In this work, we experimentally
+demonstrate a non-Hermitian BS for the interference between traveling photonic
+and localized magnonic modes. The non-Hermitian magnon-photon BS is achieved by
+the coherent and incoherent interaction mediated by the excited levels of
+atoms, which is reconfigurable by adjusting the detuning of excitation.
+Unconventional correlated interference pattern is observed at the photon and
+magnon output ports. Our work is potential for extending to single-quantum
+level to realize interference between a single photon and magnon, which
+provides an efficient and simple platform for future tests of non-Hermitian
+quantum physics.",1811.00307v1
+2018-11-05,Topological transitions of spin-excitations in insulating chiral antiferromagnets,"We present a comprehensive study of strain-induced topological magnon phase
+transitions in insulating three-dimensional (3D) topological chiral
+antiferromagnets on the kagome-lattice. We show that by applying (100) uniaxial
+strain, 3D insulating antiferromagnetic Weyl magnons (WMs) manifest as an
+intermediate phase between a strain-induced 3D magnon Chern insulator (MCI)
+with integer Chern numbers and a 3D trivial magnon insulator with zero Chern
+number. In addition, we show that strain suppresses the topological thermal
+Hall conductivity of magnons in these systems. Due to the similarity between 3D
+insulating and metallic kagome chiral antiferromagnets, we envision that the
+current results could also manifest in the 3D antiferromagnetic topological
+Weyl semimetals Mn$_3$Sn\slash Ge.",1811.01946v6
+2010-05-06,"Giant Magnons in Symmetric Spaces: Explicit N-soliton solutions for CP^n, SU(n) and S^n","Giant magnons are one of the main manifestations of integrability on the
+string theory side of the AdS/CFT correspondence. Motivated by the recent
+advances in their study, especially in the context of the string theory dual of
+ABJM theory, we present and prove explicit N-soliton solutions for the relevant
+CP^n, SU(n) and S^n sigma models. The proof is based on solving the dressing
+method recursion with the help of determinant operations, and our solutions
+hold for any choice of vacuum and soliton parameters. We further specialize our
+results for the choices that lead to giant magnons, and as an application, we
+calculate the classical time delay due to the scattering of an arbitrary number
+of CP^2 elementary dyonic magnons. The determinant expressions for our
+N-soliton solutions could possibly be used for the derivation of an effective
+particle description of magnon scattering.",1005.1066v2
+2017-01-08,Nonlocal magnon spin transport in NiFe$_2$O$_4$ thin films,"We report magnon spin transport in nickel ferrite (NiFe$_2$O$_4$, NFO)/
+platinum (Pt) bilayer systems at room temperature. A nonlocal geometry is
+employed, where the magnons are excited by the spin Hall effect or by the Joule
+heating induced spin Seebeck effect at the Pt injector, and detected at a
+certain distance away by the inverse spin Hall effect at the Pt detector. The
+dependence of the nonlocal magnon spin signals as a function of the magnetic
+field is closely related to the NFO magnetization behavior. In contrast, we
+observe that the magnetoresistance measured locally at the Pt injector does not
+show a clear relation with the average NFO magnetization. We estimate the
+magnon spin relaxation length to be 3.1 $\pm$ 0.2 $\mu$m in the investigated
+NFO samples.",1701.02041v2
+2017-01-18,Conversion of electronic to magnonic spin current at heavy-metal magnetic-insulator interface,"Electronic spin current is convertible to magnonic spin current via the
+creation or annihilation of thermal magnons at the interface of a magnetic
+insulator and a metal with a strong spin-orbital coupling. So far this
+phenomenon was evidenced in the linear regime. Based on analytical and
+fulledged numerical results for the non-linear regime we demonstrate that the
+generated thermal magnons or magnonic spin current in the insulator is
+asymmetric with respect to the charge current direction in the metal and
+exhibits a nonlinear dependence on the charge current density, which is
+explained by the tuning effect of the spin Hall torque and the magnetization
+damping. The results are also discussed in light of and are in line with recent
+experiments pointing to a new way of non-linear manipulation of spin with
+electrical means.",1701.05148v1
+2017-01-20,Two-magnon excitations in resonant inelastic x-ray scattering studied by spin-density-wave formalism,"We study two-magnon excitations in resonant inelastic x-ray scattering (RIXS)
+at the transition-metal $K$-edge. Instead of working with effective Heisenberg
+spin models, we work with a Hubbard-type model ($d$-$p$ model) for a typical
+insulating cuprate La$_2$CuO$_4$. For the antiferromagnetic ground state within
+the spin-density-wave (SDW) mean-field formalism, we calculate the dynamical
+correlation function within the random-phase approximation (RPA), and then
+obtain two-magnon excitation spectra by calculating the convolution of it.
+Coupling between the $K$-shell hole and the magnons in the intermediate state
+is calculated by means of diagrammatic perturbation expansion in the Coulomb
+interaction. Calculated momentum dependence of RIXS spectra agrees well with
+that of experiments. A notable difference from previous calculations based on
+the Heisenberg spin models is that RIXS spectra have a large two-magnon weight
+near the zone center, which may be confirmed by further careful high-resolution
+experiments.",1701.05684v2
+2017-01-28,Magnetic Domain Walls as Hosts of Spin Superfluids and Generators of Skyrmions,"A domain wall in a magnet with easy-axis anisotropy is shown to harbor spin
+superfluid associated with its spontaneous breaking of the U(1) spin-rotational
+symmetry. The spin superfluid is shown to have several topological properties,
+which are absent in conventional superfluids. First, the associated phase slips
+create and destroy skyrmions to obey the conservation of the total skyrmion
+charge, which allows us to use a domain wall as a generator and detector of
+skyrmions. Secondly, the domain wall engenders the emergent magnetic flux for
+magnons along its length, which are proportional to the spin supercurrent
+flowing through it, and thereby provides a way to manipulate magnons. Thirdly,
+the spin supercurrent can be driven by the magnon current traveling across it
+owing to the spin transfer between the domain wall and magnons, leading to the
+magnonic manipulation of the spin superfluid. The theory for superfluid spin
+transport within the domain wall is confirmed by numerical simulations.",1701.08273v2
+2018-05-30,Magnonic band gap and mode hybridization in continuous Permalloy film induced by vertical coupling with an array of Permalloy ellipses,"We investigate magnonic band structure in thin homogeneous permalloy film
+decorated with periodic array of elliptically shaped permalloy dots and
+separated by non-magnetic Pt spacer. We demonstrated experimentally formation
+of the magnonic band structure for Damon-Eshbach wave propagating in permalloy
+film with the band gap opened at the Brillouin zone border and band splitting
+at smaller wavenumbers, due to the Bragg interference and interaction of
+propagating wave of the continuous film with a standing resonant mode of the
+nano-ellipses, respectively. The shape anisotropy of the permalloy nanodots
+allows to control the spin wave dynamics through the switch between two states
+of the magnetization with respect to the underneath film magnetization, thus
+enabling magnonic band structure reprogrammability. With numerical analysis we
+show, that predominant role in formation of the magnonic band structure is
+played by a vertical dynamic coupling between propagating wave in the film and
+magnetization oscillations in the nanodots.",1805.12178v2
+2008-07-07,Finite-Size Effects for Multi-Magnon States,"We propose the generalized Luscher formula for multi-magnon states by which
+one can compute the finite-size correction to the energy of multi giant magnons
+at classical and one-loop levels. It is shown that the F-term of our formula is
+consistent with the exact finite-size spectrum of the sinh-Gordon model, and
+the mu-term agrees with the finite-size energy of magnon boundstate of the
+asymptotic Bethe Ansatz in the su(2) sector at strong coupling. In an appendix,
+we evaluate our formula at weak coupling under some approximations, and find
+that the transcendental terms arise from a sum over an infinite tower of BPS
+boundstates.",0807.0643v4
+2008-07-15,Magnons and BFKL,"We extract from the double logarithmic contributions to DGLAP anomalous
+dimensions for twist-two operators up to three-loops the magnon dispersion
+relation for planar N=4 supersymmetric Yang-Mills. Perturbatively the magnon
+dispersion relation agrees with the expansion of the anomalous dimension for
+spin-one as well as with the non-collinear double logarithmic contributions to
+the BFKL anomalous dimensions analytically extended to negative spin. The
+all-loop expression for the magnon dispersion relation is determined by the
+double logarithmic resummation of the corresponding Bethe-Salpeter equation. A
+potential map relating the spin chain magnon to BFKL eigenfunctions in the
+double logarithm approximation is suggested.",0807.2339v2
+2009-12-16,Parametric pumping and kinetics of magnons in dipolar ferromagnets,"The time evolution of magnons subject to a time-dependent microwave field is
+usually described within the so-called ""S-theory"", where kinetic equations for
+the distribution function are obtained within the time-dependent Hartree-Fock
+approximation. To explain the recent observation of ""Bose-Einstein condensation
+of magnons"" in an external microwave field [Demokritov et al., Nature 443, 430
+(2006)], we extend the ""S-theory"" to include the Gross-Pitaevskii equation for
+the time-dependent expectation values of the magnon creation and annihilation
+operators. We explicitly solve the resulting coupled equations within a simple
+approximation where only a single condensed mode is retained. We also
+re-examine the usual derivation of an effective boson model from a realistic
+spin model for yttrium-iron garnet films and argue that in the parallel pumping
+geometry (where both the static and the time-dependent magnetic field are
+parallel to the macroscopic magnetization) the time-dependent Zeemann energy
+cannot give rise to magnon condensation.",0912.3254v2
+2009-12-23,The Ginzburg-Landau model of Bose-Einstein condensation of magnons,"We introduce a system of phenomenological equations for Bose-Einstein
+condensates of magnons in the one-dimensional setting. The nonlinearly coupled
+equations, written for amplitudes of the right-and left-traveling waves,
+combine basic features of the Gross-Pitaevskii and complex Ginzburg-Landau
+models. They include localized source terms, to represent the microwave
+magnon-pumping field. With the source represented by the $\delta $-functions,
+we find analytical solutions for symmetric localized states of the magnon
+condensates. We also predict the existence of asymmetric states with unequal
+amplitudes of the two components. Numerical simulations demonstrate that all
+analytically found solutions are stable. With the $\delta $-function terms
+replaced by broader sources, the simulations reveal a transition from the
+single-peak stationary symmetric states to multi-peak ones, generated by the
+modulational instability of extended nonlinear-wave patterns. In the
+simulations, symmetric initial conditions always converge to symmetric
+stationary patterns. On the other hand, asymmetric inputs may generate
+nonstationary asymmetric localized solutions, in the form of traveling or
+standing waves. Comparison with experimental results demonstrates that the
+phenomenological equations provide for a reasonably good model for the
+description of the spatiotemporal dynamics of magnon condensates.",0912.4663v1
+2012-04-16,Topological chiral magnonic edge mode in a magnonic crystal,"Topological phases have been explored in various fields in physics such as
+spintronics, photonics, liquid helium, correlated electron system and
+cold-atomic system. This leads to the recent foundation of emerging materials
+such as topological band insulators, topological photonic crystals and
+topological superconductors/superfluid. In this paper, we propose a topological
+magnonic crystal which provides protected chiral edge modes for magnetostatic
+spin waves. Based on a linearized Landau-Lifshitz equation, we show that a
+magnonic crystal with the dipolar interaction acquires spin-wave volume-mode
+band with non-zero Chern integer. We argue that such magnonic systems are
+accompanied by the same integer numbers of chiral spin-wave edge modes within a
+band gap for the volume-mode bands. In these edge modes, the spin wave
+propagates in a unidirectional manner without being scattered backward, which
+implements novel fault-tolerant spintronic devices.",1204.3349v3
+2016-08-01,Noncollinear Antiferromagnetic Haldane Magnon Insulator,"In this Letter we present a comprehensive study of topological magnon bands
+and thermal Hall effect in non-collinear antiferromagnetic systems on the
+honeycomb lattice with an intrinsic Dzyaloshinskii-Moriya interaction. We
+theoretically show that the system possesses topological magnon bands with
+Chern number protected edge modes accompanied by a nonzero thermal magnon Hall
+effect. These features result from non-collinearity of the magnetic moments due
+to an applied out-of-plane magnetic field. Our results provide an experimental
+clue towards the realization of topological magnon transports in honeycomb
+antiferromagnetic compounds such as XPS$_3$ (X=Mn,Fe) and
+$\alpha$-Cu$_2$V$_2$O$_7$.",1608.00545v12
+2016-08-05,On supercurrents in Bose-Einstein magnon condensates in YIG ferrimagnet,"Recently E. Sonin commented [1] on our preprint ""Supercurrent in a room
+temperature Bose-Einstein magnon condensate"" [2,3], arguing that our ""claim of
+detection of spin supercurrent is premature and has not been sufficiently
+supported by presented experimental results and their theoretical
+interpretation."" We consider the appearance of this Comment as a sign of
+significant interest into the problem of supercurrents in Bose-Einstein magnon
+condensates. Here, we explicitly address E. Sonin's comments and show that our
+interpretation of our experimental results as a detection of a magnon
+supercurrent is fully supported not only by the experimental results
+themselves, but also by independent theoretical analysis [4].",1608.01813v2
+2016-08-30,Magnon Hall Effect without Dzyaloshinskii-Moriya Interaction,"Topological magnon bands and magnon Hall effect in insulating collinear
+ferromagnets are induced by the Dzyaloshinskii-Moriya interaction (DMI) even at
+zero magnetic field. In the geometrically frustrated star lattice, a
+coplanar/noncollinear $\mathbf q=0$ magnetic ordering may be present due to
+spin frustration. This magnetic structure, however, does not exhibit
+topological magnon effects even with DMI in contrast to collinear ferromagnets.
+We show that a magnetic field applied perpendicular to the star plane induces a
+non-coplanar spin configuration with nonzero spin scalar chirality, which
+provides topological effects without the need of DMI. The non-coplanar spin
+texture originates from the topology of the spin configurations and does not
+need the presence of DMI or magnetic ordering, which suggests that this
+phenomenon may be present in the chiral spin liquid phases of frustrated
+magnetic systems. We propose that these anomalous topological magnon effects
+can be accessible in Polymeric Iron (III) Acetate --- a star-lattice
+antiferromagnet with both spin frustration and long-range magnetic ordering.",1608.08605v6
+2017-06-13,Light scattering by magnons in whispering gallery mode cavities,"Brillouin light scattering is an established technique to study magnons, the
+elementary excitations of a magnet. Its efficiency can be enhanced by cavities
+that concentrate the light intensity. Here, we theoretically study inelastic
+scattering of photons by a magnetic sphere that supports optical whispering
+gallery modes in a plane normal to the magnetization. Magnons with low angular
+momenta scatter the light in the forward direction with a pronounced asymmetry
+in the Stokes and the anti-Stokes scattering strength, consistent with earlier
+studies. Magnons with large angular momenta constitute Damon Eschbach modes are
+shown to inelastically reflect light. The reflection spectrum contains either a
+Stokes or anti-Stokes peak, depending on the direction of the magnetization, a
+selection rule that can be explained by the chirality of the Damon Eshbach
+magnons. The controllable energy transfer can be used to manage the
+thermodynamics of the magnet by light.",1706.04106v1
+2017-10-10,Weak localization of magnons in a disordered two-dimensional antiferromagnet,"We propose the weak localization of magnons in a disordered two-dimensional
+antiferromagnet. We derive the longitudinal thermal conductivity $\kappa_{xx}$
+for magnons of a disordered Heisenberg antiferromagnet in the linear-response
+theory with the linear-spin-wave approximation. We show that the back
+scattering of magnons is enhanced critically by the particle-particle-type
+multiple impurity scattering. This back scattering causes a logarithmic
+suppression of $\kappa_{xx}$ with the length scale in two dimensions. We also
+argue a possible effect of inelastic scattering on the temperature dependence
+of $\kappa_{xx}$. This weak localization is useful to control turning the
+magnon thermal current on and off.",1710.03445v2
+2017-10-10,Negative magneto-thermal-resistance in a disordered two-dimensional antiferromagnet,"We demonstrate that a weak external magnetic field can induce negative
+magneto-thermal-resistance for magnons in a disordered two-dimensional
+antiferromagnet. We study the main effect of a weak external magnetic field on
+the longitudinal thermal conductivity, $\kappa_{xx}$, for a disordered
+antiferromagnet using the weak-localization theory for magnons. We show that
+the weak-localization correction term of $\kappa_{xx}$ positively increases
+with increasing the magnetic field parallel to the ordered spins. Since this
+increase corresponds to a decrease of the thermal resistivity, this phenomenon
+is negative magneto-thermal-resistance for magnons. This negative
+magneto-thermal-resistance and the weak localization of magnons will be used to
+control the magnon thermal current in antiferromagnetic spintronics devices. We
+also discuss several implications for further experimental and theoretical
+studies for disordered magnets.",1710.03446v2
+2017-12-22,Neutron Scattering Signatures of Magnon Weyl Points,"We study the inelastic neutron scattering cross section in the vicinity of
+touching points in magnon bands. Among the possible touching points are magnon
+Weyl points in three dimensional ordered magnets with significant spin-orbit
+coupling that are characterized by a linear dispersion in their vicinity. A
+Weyl point is topologically protected by its net chirality and here we show
+that this leads to a characteristic form for the dynamical structure factor. To
+address this question, we show that scattering intensities in the vicinity of
+arbitrary magnon two-band touching points are identical to expectation values
+of the pseudospin polarization along some direction $\hat{\boldsymbol{n}}$ in
+momentum space fixed by the magnetic Hamiltonian. This approach applied to Weyl
+points shows that they are singular points in the intensity of the form
+$\hat{\boldsymbol{n}}\cdot \delta\hat{\boldsymbol{k}}$ regardless of the
+magnetic ground state. We make specific predictions for the experimental
+signatures of such intensity singularities in several spin models hosting Weyl
+magnons applicable to candidate materials.",1712.08535v1
+2017-12-28,Topological magnon bands in the zigzag and stripy phases of antiferromagnetic honeycomb lattice,"We investigated the topological property of magnon bands in the collinear
+magnetic orders of zigzag and stripy phases for the antiferromagnetic honeycomb
+lattice and identified Berry curvature and symmetry constraints on the magnon
+band structure. Different symmetries of both zigzag and stripy phases lead to
+different topological properties, in particular, the magnon bands of the stripy
+phase being disentangled with a finite Dzyaloshinskii-Moriya (DM) term with
+non-zero spin Chern number. This is corroborated by calculating the spin Nernst
+effect. Our study establishes the existence of the non-trivial magnon band
+topology for all observed collinear antiferromagnetic honeycomb lattice in the
+presence of the DM term.",1712.09801v1
+2018-09-17,Unraveling the influence of electronic and magnonic spin current injection near the magnetic ordering transition of IrMn metallic antiferromagnets,"Although spin injection at room temperature in an IrMn metallic
+antiferromagnet strongly depends on the transport regime, and is more efficient
+in the case of magnonic transport, in this article, we present experimental
+data demonstrating that the enhanced efficiency of spin injection caused by
+spin fluctuations near the ordering temperature can be as efficient for the
+electronic and magnonic transport regimes. By selecting representative
+interacting environments, we also demonstrated that the amplification of spin
+injection near the ordering temperature of the IrMn antiferromagnet is
+independent of exchange coupling with an adjacent NiFe ferromagnet. In
+addition, our findings confirm that the spin current carried by magnons
+penetrates deeper than that transported by conduction electrons in IrMn.
+Finally, our data indicates that the value of the ordering temperature for the
+IrMn antiferromagnet is not significantly affected by either the electronic or
+magnonic nature of the spin current probe, or by exchange coupling.",1809.06174v1
+2020-12-02,Electric field control of interaction between magnons and quantum spin defects,"Hybrid systems coupling quantum spin defects (QSD) and magnons can enable
+unique spintronic device functionalities and probes for magnetism. Here, we add
+electric field control of magnon-QSD coupling to such systems by integrating
+ferromagnet-ferroelectric multiferroic with nitrogen-vacancy (NV) center spins.
+Combining quantum relaxometry with ferromagnetic resonance measurements and
+analytical modeling, we reveal that the observed electric-field tuning results
+from ferroelectric polarization control of the magnon-generated fields at the
+NV. Exploiting the demonstrated control, we also propose magnon-enhanced hybrid
+electric field sensors with improved sensitivity.",2012.01497v2
+2020-12-29,Twist-induced Near-field Thermal Switch Using Nonreciprocal Surface Magnon-Polaritons,"We explore that two ferromagnetic insulator slabs host a strong twist-induced
+near-field radiative heat transfer in the presence of twisted magnetic fields.
+Using the formalism of fluctuational electrodynamics, we find the existence of
+large twist-induced thermal switch ratio in large damping condition and
+nonmonotonic twist manipulation for heat transfer in small damping condition,
+associated with the different twist-induced effects of nonreciprocal elliptic
+surface magnon-polaritons, hyperbolic surface magnon-polaritons, and
+twist-non-resonant surface magnon-polaritons. Moreover, the near-field
+radiative heat transfer can be significantly enhanced by the twist-non-resonant
+surface magnon-polaritons in the ultra-small damping condition. Such
+twist-induced effect is applicable for other kinds of anisotropic slabs with
+timereversal symmetry breaking. Our findings provide a way to twisted and
+magnetic control in nanoscale thermal management and improve it with
+twistronics concepts.",2012.14733v1
+2012-05-23,Spontaneous Magnon Decays,"A theoretical overview of the phenomenon of spontaneous magnon decays in
+quantum antiferromagnets is presented. The intrinsic zero-temperature damping
+of magnons in quantum spin systems is a fascinating many-body effect, which has
+recently attracted significant attention in view of its possible observation in
+neutron-scattering experiments. An introduction to the theory of magnon
+interactions and a discussion of necessary symmetry and kinematic conditions
+for spontaneous decays are provided. Various parallels with the decays of
+anharmonic phonons and excitations in superfluid 4He are extensively used.
+Three principal cases of spontaneous magnon decays are considered:
+field-induced decays in Heisenberg antiferromagnets, zero-field decays in
+spiral antiferromagnets, and triplon decays in quantum-disordered magnets.
+Analytical results are compared with available numerical data and prospective
+materials for experimental observation of the decay-related effects are briefly
+discussed.",1205.5278v3
+2012-05-24,Giant Magnon Gap in Bilayer Iridate Sr3Ir2O7: Enhanced Pseudo-dipolar Interactions Near the Mott Transition,"Using resonant inelastic x-ray scattering, we observe in the bilayer iridate
+Sr3Ir2O7, a spin-orbit coupling driven magnetic insulator with a small charge
+gap, a magnon gap of ~92 meV for both acoustic and optical branches. This
+exceptionally large magnon gap exceeds the total magnon bandwidth of ~70 meV
+and implies a marked departure from the Heisenberg model, in stark contrast to
+the case of the single-layer iridate Sr2IrO4. Analyzing the origin of these
+observations, we find that the giant magnon gap results from bond-directional
+pseudo-dipolar interactions that are strongly enhanced near the metal-insulator
+transition boundary. This suggests that novel magnetism, such as that inspired
+by the Kitaev model built on the pseudo-dipolar interactions, may emerge in
+small charge-gap iridates.",1205.5337v1
+2017-05-05,Nano-patterned magnonic crystals based on ultrathin YIG films,"We demonstrate a microscopic magnonic-crystal waveguide produced by
+nano-patterning of a 20 nm thick film of Yttrium Iron Garnet. By using the
+phase-resolved micro-focus Brillouin light scattering spectroscopy, we map the
+intensity and the phase of spin waves propagating in such a periodic magnetic
+structure. Based on these maps, we obtain the dispersion and the attenuation
+characteristics of spin waves providing detailed information about the physics
+of spin-wave propagation in the magnonic crystal. We show that, in contrast to
+the simplified physical picture, the maximum attenuation of spin waves is
+achieved close to the edge of the magnonic band gap, which is associated with
+non-trivial reflection characteristics of spin waves in non-uniform field
+potentials.",1705.02267v1
+2017-05-24,Topological Magnon Bands and Unconventional Thermal Hall Effect on the Frustrated Honeycomb and Bilayer Triangular Lattice,"In the conventional ferromagnetic systems, topological magnon bands and
+thermal Hall effect are due to the Dzyaloshinskii-Moriya interaction (DMI). In
+principle, however, the DMI is either negligible or it is not allowed by
+symmetry in some quantum magnets. Therefore, we expect that topological magnon
+features will not be present in those systems. In addition, quantum magnets on
+the triangular-lattice are not expected to possess topological features as the
+DMI or spin-chirality cancels out due to equal and opposite contributions from
+adjacent triangles. Here, however, we predict that the isomorphic frustrated
+honeycomb-lattice and bilayer triangular-lattice antiferromagnetic system will
+exhibit topological magnon bands and topological thermal Hall effect in the
+absence of an intrinsic DMI. These unconventional topological magnon features
+are present as a result of magnetic-field-induced non-coplanar spin
+configurations with nonzero scalar spin chirality. The relevance of the results
+to realistic bilayer triangular antiferromagnetic materials are discussed.",1705.08892v5
+2017-09-12,Direct observation of magnon-phonon coupling in yttrium iron garnet,"The magnetic insulator yttrium iron garnet (YIG) with a ferrimagnetic
+transition temperature of $\sim$560 K has been widely used in microwave and
+spintronic devices. Anomalous features in the spin Seeback effect (SSE)
+voltages have been observed in Pt/YIG and attributed to the magnon-phonon
+coupling. Here we use inelastic neutron scattering to map out low-energy spin
+waves and acoustic phonons of YIG at 100 K as a function of increasing magnetic
+field. By comparing the zero and 9.1 T data, we find that instead of splitting
+and opening up gaps at the spin wave and acoustic phonon dispersion
+intersecting points, magnon-phonon coupling in YIG enhances the hybridized
+scattering intensity. These results are different from expectations of
+conventional spin-lattice coupling, calling for new paradigms to understand the
+scattering process of magnon-phonon interactions and the resulting
+magnon-polarons.",1709.03940v1
+2018-07-13,Magnon band topology in spin-orbital coupled magnets: classification and application to $α$-RuCl$_3$,"In spite of flourishing studies on the topology of spin waves, a generic
+framework to classify and compute magnon band topology in non-collinear magnets
+is still missing. In this work we provide such a theory framework, by mapping
+an arbitrary linear spin wave into a local free-fermion Hamiltonian with
+exactly the same spectrum, symmetry implementation and band topology, which
+allows for a full classification and calculation on any topological properties
+of magnon bands. We apply this fermionization approach to honeycomb Kitaev
+magnet $\alpha$-RuCl$_3$, and show the existence of topologically protected
+magnon band crossings, and field-induced magnon Chern bands under small
+magnetic fields.",1807.05232v2
+2018-07-25,Strong microwave photon-magnon coupling in multiresonant dielectric antennas (Perspective),"Achieving quantum-level control over electromagnetic waves, magnetisation
+dynamics, vibrations and heat is invaluable for many practical application and
+possible by exploiting the strong radiation-matter coupling. Most of the modern
+strong microwave photon-magnon coupling developments rely on the integration of
+metal-based microwave resonators with a magnetic material. However, it has
+recently been realised that all-dielectric resonators made of or containing
+magneto-insulating materials can operate as a standalone strongly-coupled
+system characterised by low dissipation losses and strong local microwave field
+enhancement. Here, after a brief overview of recent developments in the field,
+I discuss examples of such dielectric resonant systems and demonstrate their
+ability to operate as multiresonant antennas for light, microwaves, magnons,
+sound, vibrations and heat. This multiphysics behaviour opens up novel
+opportunities for the realisation of multiresonant coupling such as, for
+example, photon-magnon-phonon coupling. I also propose several novel systems in
+which strong photon-magnon coupling in dielectric antennas and similar
+structures is expected to extend the capability of existing devices or may
+provide an entirely new functionality. Examples of such systems include novel
+magnetofluidic devices, high-power microwave power generators, and hybrid
+devices exploiting the unique properties of electrical solitons.",1807.09827v1
+2018-12-26,Magnonic Band Structure Established by Chiral Spin-Density Waves in Thin Film Ferromagnets,"Recent theoretical studies have demonstrated the possibility to excite and
+sustain noncollinear magnetization states in ferromagnetic nanowires. The
+resulting state is referred to as a spin-density wave (SDW). SDWs can be
+interpreted as hydrodynamic states with a constant fluid density and fluid
+velocity in systems with easy-plane anisotropy. Here, we consider the effect of
+the nonlocal dipole field arising from the finite thickness of magnetic thin
+films on the spatial profile of the SDW and on the associated magnon
+dispersion. Utilizing a hydrodynamic formulation of the Larmor torque equation,
+it is found that the nonlocal dipole field modulates the fluid velocity. Such a
+modulation induces a magnonic band structure unlike the typical dispersion
+relation for magnons on uniform magnetization. The analytical results are
+validated by micromagnetic simulations. Band gaps on the order of GHz are
+numerically observed to depend on the SDW fluid velocity and film thickness for
+realistic material parameters. The presented results suggest that SDWs can find
+applications as reconfigurable magnonic crystals.",1812.10571v1
+2019-01-12,Kelvin modes of a skyrmion line in chiral magnets and the associated magnon transport,"Magnetic skyrmions in bulk crystals are line-like topologically protected
+spin textures. They allow for the propagation of magnons along the skyrmion
+line but are localized inside the skyrmion line. Analogous to the vortex line,
+these propagating modes are the Kelvin modes of a skyrmion line. In crystals
+without an inversion center, it is known that the magnon dispersion in the
+ferromagnetic state is asymmetric in the wavevector. It is natural to expect
+that the dispersion of the Kelvin modes is also asymmetric with respect to the
+wavevector. We study the Kelvin modes of a skyrmion line in the ferromagnetic
+background. In contrast, we find that the lowest Kelvin mode is symmetric in
+the wavevector in the low energy region despite the inversion symmetry
+breaking. Other Kelvin modes below the magnon continuum are asymmetric, and
+most of them have a positive group velocity. Our results suggest that a
+skyrmion line can function as a one-way waveguide for magnons.",1901.03812v2
+2019-01-17,Topological pumping of a single magnon in a one-dimensional spin-dependent optical superlattice,"Topological pumping of ultracold atomic gases has recently been demonstrated
+in two experiments (Nat. Phys. 12, 296; 12, 350 (2016)). Here we study the
+topological pumping of a single magnon in a dynamically controlled
+spin-dependent optical superlattice. When the interaction between atoms is
+strong, this system supports a dynamical version of topological magnon
+insulator phase. By initially putting a single magnon in the superlattice and
+slowly varying the dynamical controlled parameter over one period, the shift of
+the magnon density center is quantized and equal to the topological Chern
+number. Moreover, we also find that the direction of this quantized shift is
+entanglement-dependent. Our result provides a route for realizing topological
+pumping of quasiparticles in strongly correlated ultracold atomic system and
+for studying the interplay between topological pumping and quantum
+entanglement.",1901.05614v1
+2019-02-08,Hybrid quantum systems based on magnonics,"Engineered quantum systems enabling novel capabilities for communication,
+computation, and sensing have blossomed in the last decade. Architectures
+benefiting from combining distinct and complementary physical quantum systems
+have emerged as promising platforms for developing quantum technologies. A new
+class of hybrid quantum systems based on collective spin excitations in
+ferromagnetic materials has led to the diverse set of experimental platforms
+which are outlined in this review article. The coherent interaction between
+microwave cavity modes and collective spin-wave modes is presented as the
+backbone of the development of more complex hybrid quantum systems. Indeed,
+quanta of excitation of the spin-wave modes, called magnons, can also interact
+coherently with optical photons, phonons, and superconducting qubits in the
+fields of cavity optomagnonics, cavity magnomechanics, and quantum magnonics,
+respectively. Notably, quantum magnonics provides a promising platform for
+performing quantum optics experiments in magnetically-ordered solid-state
+systems. Applications of hybrid quantum systems based on magnonics for quantum
+information processing and quantum sensing are also outlined briefly.",1902.03024v2
+2019-02-11,Interplay of electronic and spin degrees in ferromagnetic SrRuO$_3$: anomalous softening of magnon gap and stiffness,"The magnon dispersion of ferromagnetic SrRuO$_3$ was studied by inelastic
+neutron scattering experiments on single crystals as function of temperature.
+Even at low temperature the magnon modes exhibit substantial broadening
+pointing to strong interaction with charge carriers. We find an anomalous
+temperature dependence of both the magnon gap and the magnon stiffness, which
+soften upon cooling in the ferromagnetic phase. Both effects trace the
+temperature dependence of the anomalous Hall effect. We argue that these
+results show that Weyl points and the anomalous Hall effect can directly
+influence the spin dynamics in metallic ferromagnets.",1902.04036v1
+2019-03-01,Indirect observation of phase conjugate magnons from non-degenerate four-wave mixing,"A phase conjugate mirror utilising four-wave mixing in a magnetic system is
+experimentally realised for the first time. Indirect evidence of
+continuous-wave phase conjugation has been observed experimentally and is
+supported by simulations. The experiment utilizes a pump-probe method to excite
+a four-wave mixing process. Two antennae are used to pump a region of a
+thin-film yttrium iron garnet waveguide with magnons of frequency $f_{1}$ to
+create a spatio-temporally periodic potential. As the probe magnons of
+$f_{\mathrm{p}}$ impinge on the pumped region, a signal with frequency
+$f_{\mathrm{c}} = 2f_{1}-f_{\mathrm{p}}$ is observed. The amplitude of the
+nonlinear signal was highly dependent on the applied magnetic field $H$. Width
+modes of the probe magnons and standing wave modes of the pump magnons were
+shown to affect the amplitude of the signal at $f_{\mathrm{c}}$. Experimental
+data is compared with simulations and theory to suggest that $f_{\mathrm{c}}$
+is a phase conjugate of $f_{\mathrm{p}}$.",1903.00400v1
+2019-03-06,Symmetry-protected topological magnons in three dimensional Kitaev materials,"Topological phases in magnetic materials offer novel tunability of
+topological properties via varying the underlying magnetism. We show that three
+dimensional Kitaev materials can provide a great opportunity for controlling
+symmetry-protected topological nodal magnons. These materials are originally
+considered as strong candidates for the Kitaev quantum spin liquid due to the
+bond-dependent frustrating spin exchange interactions. As a concrete example,
+we consider the symmetry and topology of the magnons in the canted zig-zag
+ordered state in the hyperhoneycomb $\beta\text{-}\mathrm{Li_2IrO_3}$, which
+can be obtained by applying a magnetic field in the counter-rotating spiral
+state at zero field. It is shown that the magnetic glide symmetries and the
+non-Hermitian nature of the bosonic magnons lead to unique topological
+protection that is different from the case of the fermionic counterparts. We
+investigate how such topological magnons can be controlled by changing the
+symmetry of the underlying spin exchange interactions.",1903.02559v1
+2019-03-08,Magnon quantum anomalies in Weyl ferromagnets,"When subjected to parallel electric field $\mathbf E$ and magnetic field
+$\mathbf B$, Weyl semimetals exhibit the exotic transport property known as the
+chiral anomaly due to the pumping of electrons between Weyl cones of opposite
+chiralities. When one or both electromagnetic (EM) fields are replaced by
+strain-induced chiral pseudo-electromagnetic (pseudo-EM) fields, other types of
+quantum anomalies occur. In the present paper, we will show that such quantum
+anomalies can be reproduced in a completely different system -- a Weyl
+ferromagnet whose magnonic structure remarkably encodes Weyl physics. By
+analytical and numerical calculations, we will show that the magnon bands can
+be Landau-quantized by either an inhomogeneous electric field $\mathbf E$ or a
+chiral pseudo-electric field $\mathbf e$ induced by a torsional strain, and
+magnons can be pumped along bands by either an inhomogeneous magnetic field
+$\mathbf B$ or a chiral pseudo-magnetic field $\mathbf b$ due to a dynamic
+uniaxial strain. We list the magnon quantum anomalies and the associated
+anomalous spin and heat currents in the Weyl ferromagnet, and show they are
+distinct from their Weyl semimetal counterparts.",1903.03664v1
+2019-03-12,Probing GHz Gravitational Waves with Graviton-magnon Resonance,"A novel method for extending frequency frontier in gravitational wave
+observations is proposed. It is shown that gravitational waves can excite a
+magnon. Thus, gravitational waves can be probed by a graviton-magnon detector
+which measures resonance fluorescence of magnons. Searching for gravitational
+waves with a wave length $\lambda$ by using a ferromagnetic sample with a
+dimension $l$, the sensitivity of the graviton-magnon detector reaches spectral
+densities, around $5.4 \times 10^{-22} \times (\frac{l}{\lambda /2\pi})^{-2} \
+[{\rm Hz}^{-1/2}]$ at 14 GHz and $8.6 \times 10^{-21} \times (\frac{l}{\lambda
+/2\pi})^{-2} \ [{\rm Hz}^{-1/2}]$ at 8.2 GHz, respectively.",1903.04843v4
+2019-03-26,Asymmetric quantum shot noise in magnon transport,"We study a frequency-dependent noise-to-current ratio for asymmetric,
+symmetric, and noncommutative current-noise in a ferromagnetic insulating
+junction, and extract quantum-mechanical properties of magnon transport at low
+temperatures. We demonstrate that the noncommutative noise, vanished in the
+dc-limit (i.e., a classical regime), increases monotonically as a function of
+frequency, and show that the noncommutative noise associated directly with
+quantum fluctuations of magnon currents breaks through the classical upper
+limit determined by the symmetric noise and realizes asymmetric quantum shot
+noise. Finally, we show that our theoretical predictions are within
+experimental reach with current device and measurement scheme while exploiting
+low temperatures. Our work provides a platform toward experimental access to
+quantum fluctuations of magnon currents.",1903.10639v1
+2019-04-03,Non-Hermitian topology of spontaneous magnon decay,"Spontaneous magnon decay is a generic feature of the magnetic excitations of
+anisotropic magnets and isotropic magnets with non-collinear order. In this
+paper, we argue that the effect of interactions on one-magnon states can, under
+many circumstances, be treated in terms of an effective, energy independent,
+non-Hermitian Hamiltonian for the magnons. In the vicinity of Dirac or Weyl
+touching points, we show that the spectral function has a characteristic
+anisotropy arising from topologically protected exceptional points or lines in
+the non-Hermitian spectrum. Such features can, in principle, be detected using
+inelastic neutron scattering or other spectroscopic probes. We illustrate this
+physics through a concrete example: a honeycomb ferromagnet with
+Dzyaloshinskii-Moriya exchange. We perform interacting spin wave calculations
+of the structure factor and spectral function of this model, showing good
+agreement with results from a simple effective non-Hermitian model for the
+splitting of the Dirac point. Finally, we argue that the zoo of known
+topological protected magnon band structures may serve as a nearly ideal
+platform for realizing and exploring non-Hermitian physics in solid-state
+systems.",1904.02160v1
+2019-04-11,Thermalization of hot electrons via interfacial electron-magnon interaction,"Recent work on layered structures of superconductors (S) or normal metals (N)
+in contact with ferromagnetic insulators (FI) has shown how the properties of
+the previous can be strongly affected by the magnetic proximity effect due to
+the static FI magnetization. Here we show that such structures can also exhibit
+a new electron thermalization mechanism due to the coupling of electrons with
+the dynamic magnetization, i.e., magnons in FI. We here study the heat flow
+between the two systems and find that in thin films the heat conductance due to
+the interfacial electron-magnon collisions can dominate over the well-known
+electron-phonon coupling below a certain characteristic temperature that can be
+straightforwardly reached with present-day experiments. We also study the role
+of the magnon band gap and the induced spin-splitting field induced in S on the
+resulting heat conductance and show that heat balance experiments can reveal
+information about such quantities in a way quite different from typical magnon
+spectroscopy experiments.",1904.05696v2
+2019-04-12,Magnetic excitations in hole-doped Sr2IrO4: A comparison with electron-doped cuprates,"We have studied the evolution of magnetic and orbital excitations as a
+function of hole-doping in single crystal samples of Sr2Ir(1-x)Rh(x)O4 (0.07 <
+x < 0.42) using high resolution Ir L3-edge resonant inelastic x-ray scattering
+(RIXS). Within the antiferromagnetically ordered region of the phase diagram (x
+< 0.17) we observe highly dispersive magnon and spin-orbit exciton modes.
+Interestingly, both the magnon gap energy and the magnon bandwidth appear to
+increase as a function of doping, resulting in a hardening of the magnon mode
+with increasing hole doping. As a result, the observed spin dynamics of
+hole-doped iridates more closely resemble those of the electron-doped, rather
+than hole-doped, cuprates. Within the paramagnetic region of the phase diagram
+(0.17 < x < 0.42) the low-lying magnon mode disappears, and we find no evidence
+of spin fluctuations in this regime. In addition, we observe that the orbital
+excitations become essentially dispersionless in the paramagnetic phase,
+indicating that magnetic order plays a crucial role in the propagation of the
+spin-orbit exciton.",1904.06402v1
+2019-11-27,Ellipticity and Dissipation Effects in Magnon Spin Valves,"We consider alignment-dependent spin and heat transport across a magnon spin
+valve in the tunneling regime, i.e., a junction consisting of two weakly
+coupled ferromagnetic insulators. We determine the difference in spin and heat
+conductance between the parallel and antiparallel configuration of the
+magnetization direction. The dependence of these conductances on both the
+Gilbert damping and ellipticity is studied. We find that both magnon
+ellipticity and dissipation open channels for magnons to tunnel through in the
+antiparallel configuration. Our results highlight an important difference
+between electronic and magnon spin transport in spin-valve structures and may
+be important for the development of devices based on magnetic insulators.",1911.12017v2
+2019-12-31,Probing magnon-magnon coupling in exchange coupled Y$_3$Fe$_5$O$_{12}$/Permalloy bilayers with magneto-optical effects,"We demonstrate the magnetically-induced transparency (MIT) effect in
+Y$_3$Fe$_5$O$_{12}$(YIG)/Permalloy(Py) coupled bilayers. The measurement is
+achieved via a heterodyne detection of the coupled magnetization dynamics using
+a single wavelength that probes the magneto-optical Kerr and Faraday effects of
+Py and YIG, respectively. Clear features of the MIT effect are evident from the
+deeply modulated ferromagnetic resonance of Py due to the
+perpendicular-standing-spin-wave of YIG. We develop a phenomenological model
+that nicely reproduces the experimental results including the induced amplitude
+and phase evolution caused by the magnon-magnon coupling. Our work offers a new
+route towards studying phase-resolved spin dynamics and hybrid magnonic
+systems.",1912.13407v2
+2015-08-23,Asymmetric Magnon Excitation by Spontaneous Toroidal Ordering,"Effects of spontaneous toroidal ordering on magnetic excitation are
+theoretically investigated for a localized spin model that includes a staggered
+Dzyaloshinsky-Moriya interaction and anisotropic exchange interactions, which
+arise from the antisymmetric spin-orbit coupling and the multi-orbital
+correlation effect. We show that the model exhibits a Neel-type
+antiferromagnetic order, which simultaneously accompanies a ferroic toroidal
+order. We find that the occurrence of toroidal order modulates the magnon
+dispersion in an asymmetric way with respect to the wave number: a toroidal
+dipole order on the zigzag chain leads to a band-bottom shift, while a toroidal
+octupole order on the honeycomb lattice gives rise to a valley splitting. These
+asymmetric magnon excitations could be a source of unusual magnetic responses,
+such as nonreciprocal magnon transport. A variety of modulations are discussed
+while changing the lattice and magnetic symmetries. Implications of candidate
+materials for asymmetric magnon excitations are presented.",1508.05627v2
+2016-03-02,"Magnetic transitions in the topological magnon insulator Cu(1,3-bdc)","Topological magnon insulators are a new class of magnetic materials that
+possess topologically nontrivial magnon bands. As a result, magnons in these
+materials display properties analogous to those of electrons in topological
+insulators. Here, we present magnetization, specific heat, and neutron
+scattering measurements of the ferromagnetic kagome magnet Cu(1,3-bdc). Our
+measurements provide a detailed description of the magnetic structure and
+interactions in this material, and confirm that it is an ideal prototype for
+topological magnon physics in a system with a simple spin Hamiltonian.",1603.00901v2
+2016-10-12,Microscopic derivation of magnon spin current in a topological insulator/ferromagnet heterostructure,"We investigate a spin-electricity conversion effect in a topological
+insulator/ferromagnet heterostructure. In the spin-momentum-locked surface
+state, an electric current generates nonequilibrium spin accumulation, which
+causes a spin-orbit torque that acts on the ferromagnet. When spins in the
+ferromagnet are completely parallel to the accumulated spin, this spin-orbit
+torque is zero. In the presence of spin excitations, however, a coupling
+between magnons and electrons enables us to obtain a nonvanishing torque. In
+this paper, we consider a model of the heterostructure in which a
+three-dimensional magnon gas is coupled with a two-dimensional massless Dirac
+electron system at the interface. We calculate the torque induced by an
+electric field, which can be interpreted as a magnon spin current, up to the
+lowest order of the electron-magnon interaction. We derive the expressions for
+high and low temperatures and estimate the order of magnitude of the induced
+spin current for realistic materials at room temperature.",1610.03636v3
+2016-12-18,Bottleneck accumulation of hybrid magneto-elastic bosons,"It is known that an ensemble of magnons, quanta of spin waves, can be
+prepared as a Bose gas of weakly interacting quasiparticles with conservation
+of the particle number. Furthermore, the thermalization of the overpopulated
+magnon gas can lead to the formation of a Bose-Einstein condensate at the
+bottom of a spin-wave spectrum. However, magnon-phonon scattering processes can
+significantly modify this scenario and new quasiparticles are formed -
+magneto-elastic bosons. Our observations of a parametrically populated magnon
+gas in a single-crystal film of Yttrium Iron Garnet by means of
+wavevector-resolved Brillouin light scattering spectroscopy including
+magneto-elastic coupling resulted in the discovery of a novel condensation
+phenomenon: A spontaneous accumulation of hybrid magneto-elastic bosonic
+quasiparticles at the intersection of the lowest magnon mode and a transversal
+acoustic wave.",1612.05925v1
+2017-07-03,Tunneling between chiral magnets: Spin current generation without external fields,"Magnons can generate a spin current, and the standard generating mechanism
+requires at least one external field. Since this mechanism is often applied to
+a multilayer system including a magnet and a paramagnetic metal, the system can
+possess not only the charge current induced by the spin current but also the
+charge current induced by the external field. The latter is an unnecessary
+accompaniment. Here we show that the tunneling of a magnon pair between chiral
+magnets can generate a spin current even without external fields. This
+phenomenon originates from a phase difference between magnon pairs of separate,
+weakly coupled chiral magnets, and is essentially different from the mechanism
+using the angle degree of freedom of the magnon Bose-Einstein condensates. The
+pair's tunneling is possible in chiral magnets due to lack of the
+Goldstone-type gapless excitations. This phenomenon opens the door to
+spintronics not requiring any external field and using the magnon pair
+tunneling.",1707.00382v1
+2018-10-19,Magnon properties of random alloys,"We study magnon properties in terms of spin stiffness, Curie temperatures and
+magnon spectrum of Fe-Ni, Co-Ni and Fe-Co random alloys using a combination of
+electronic structure calculations and atomistic spin dynamics simulations.
+Influence of the disorder are studied in detail by use of large supercells with
+random atomic arrangement. It is found that disorder affects the magnon
+spectrum in vastly different ways depending on the system. Specifically, it is
+more pronounced in Fe-Ni alloys compared to Fe-Co alloys. In particular, the
+magnon spectrum at room temperature in Permalloy (Fe$_{20}$Ni$_{80}$) is found
+to be rather diffuse in a large energy interval while in Fe$_{75}$Co$_{25}$ it
+forms sharp branches. Fe-Co alloys are very interesting from a technological
+point of view due to the combination of large Curie temperatures and very low
+calculated Gilbert damping of $\sim$0.0007 at room temperature for Co
+concentrations around 20--30\%.",1810.08487v1
+2019-05-10,Helicity-Changing Brillouin Light Scattering by Magnons in a Ferromagnetic Crystal,"Brillouin light scattering in ferromagnetic materials usually involves one
+magnon and two photons and their total angular momentum is conserved. Here, we
+experimentally demonstrate the presence of a helicity-changing two-magnon
+Brillouin light scattering in a ferromagetic crystal, which can be viewed as a
+four-wave mixing process involving two magnons and two photons. Moreover, we
+observe an unconventional helicity-changing one-magnon Brillouin light
+scattering, which apparently infringes the conservation law of the angular
+momentum. We show that the crystal angular momentum intervenes to compensate
+the missing angular momentum in the latter scattering process.",1905.04018v5
+2019-05-27,Steady Bell state generation via magnon-photon coupling,"We show that parity-time ($\mathcal{PT}$) symmetry can be spontaneously
+broken in the recently reported energy level attraction of magnons and cavity
+photons. In the $\mathcal{PT}$-broken phase, magnon and photon form a
+high-fidelity Bell state with maximum entanglement. This entanglement is steady
+and robust against the perturbation of environment, in contrast to the general
+wisdom that expects instability of the hybridized state when the symmetry is
+broken. This anomaly is further understood by the compete of non-Hermitian
+evolution and particle number conservation of the hybridized system. As a
+comparison, neither $\mathcal{PT}$-symmetry broken nor steady magnon-photon
+entanglement is observed inside the normal level repulsion case. Our results
+may open a novel window to utilize magnon-photon entanglement as a resource for
+quantum technologies.",1905.11117v1
+2020-06-25,Magnon-exciton proximity coupling at a van der Waals heterointerface,"Spin and photonic systems are at the heart of modern information devices and
+emerging quantum technologies. An interplay between electron-hole pairs
+(excitons) in semiconductors and collective spin excitations (magnons) in
+magnetic crystals would bridge these heterogeneous systems, leveraging their
+individual assets in novel interconnected devices. Here, we report the
+magnon-exciton coupling at the interface between a magnetic thin film and an
+atomically-thin semiconductor. Our approach allies the long-lived magnons
+hosted in a film of yttrium iron garnet (YIG) to strongly-bound excitons in a
+flake of a transition metal dichalcogenide, MoSe$_2$. The magnons induce on the
+excitons a dynamical valley Zeeman effect ruled by interfacial exchange
+interactions. This nascent class of hybrid system suggests new opportunities
+for information transduction between microwave and optical regions.",2006.14257v2
+2020-09-17,Investigation of entanglement measures across the magnetization process of a highly frustrated spin-1/2 Heisenberg octahedral chain as a new paradigm of the localized-magnon approach,"The bipartite entanglement across the magnetization process of a highly
+frustrated spin-1/2 Heisenberg octahedral chain is examined within the concept
+of localized magnons, which enables a simple calculation of the concurrence
+measuring a strength of the pairwise entanglement between nearest-neighbor and
+next-nearest-neighbor spins from square plaquettes. A full exact
+diagonalization of the finite-size Heisenberg octahedral chain with up to 4
+unit cells (20 spins) evidences an extraordinary high precision of the
+localized-magnon theory in predicting measures of the bipartite entanglement at
+sufficiently low temperatures. While the monomer-tetramer phase emergent at low
+enough magnetic fields exhibits presence (absence) of the bipartite
+entanglement between the nearest-neighbor (next-nearest-neighbor) spins, the
+magnon-crystal phase emergent below the saturation field contrarily displays
+identical bipartite entanglement between the nearest-neighbor and
+next-nearest-neighbor spins. The presented results verify a new paradigm of the
+localized-magnon approach concerned with a simple calculation of entanglement
+measures.",2009.08504v1
+2020-09-21,"Simultaneous blockade of a photon phonon, and magnon induced by a two-level atom","The hybrid microwave optomechanical-magnetic system has recently emerged as a
+promising candidate for coherent information processing because of the
+ultrastrong microwave photon-magnon coupling and the longlife of the magnon and
+phonon. As a quantum information processing device, the realization of a single
+excitation holds special meaning for the hybrid system. In this paper, we
+introduce a single two-level atom into the optomechanical-magnetic system and
+show that an unconventional blockade due to destructive interference cannot
+offer a blockade of both the photon and magnon. Meanwhile, under the condition
+of single excitation resonance, the blockade of the photon, phonon, and magnon
+can be achieved simultaneously even in a weak optomechanical region, but the
+phonon blockade still requires the cryogenic temperature condition.",2009.09871v1
+2020-09-22,Magnon Thermal Edelstein Effect Detected by Inverse Spin Hall Effect,"In an easy-plane antiferromagnet with the Dzyaloshinskii-Moriya interaction
+(DMI), magnons are subject to an effective spin-momentum locking. An in-plane
+temperature gradient can generate interfacial accumulation of magnons with a
+specified polarization, realizing the magnon thermal Edelstein effect. We
+theoretically investigate the injection and detection of this thermally-driven
+spin polarization in an adjacent heavy metal with strong spin Hall effect. We
+find that the inverse spin Hall voltage depends monotonically on both
+temperature and the DMI but non-monotonically on the hard-axis anisotropy.
+Counterintuitively, the magnon thermal Edelstein effect is an even function of
+a magnetic field applied along the N\'eel vector.",2009.10703v2
+2021-02-12,Topological Thermal Hall Effect of Magnons in Magnetic Skyrmion Lattice,"Topological transports of fermions are governed by the Chern numbers of the
+energy bands lying below the Fermi energy. For bosons, e.g. phonons and magnons
+in a crystal, topological transport is dominated by the Chern number of the
+lowest energy band when the band gap is comparable to the thermal energy. Here,
+we demonstrate the presence of topological transport by bosonic magnons in a
+lattice of magnetic skyrmions - topological defects formed by a vortex-like
+texture of spins. We find a distinct thermal Hall signal in the magnetic
+skyrmion phase of an insulating polar magnet GaV4Se8, identified as the
+topological thermal Hall effect of magnons governed by the Chern number of the
+lowest energy band of the magnons in a triangular lattice of magnetic
+skyrmions. Our findings lay a foundation for studying topological phenomena of
+other bosonic excitations through thermal Hall probe.",2102.06430v3
+2015-07-10,Magnon dark modes and gradient memory,"Extensive efforts have been expended in developing hybrid quantum systems to
+overcome the short coherence time of superconducting circuits by introducing
+the naturally long-lived spin degree of freedom. Among all the possible
+materials, single-crystal yttrium iron garnet has shown up very recently as a
+promising candidate for hybrid systems, and various highly coherent
+interactions, including strong and even ultra-strong coupling, have been
+demonstrated. One distinct advantage of these systems is that the spins are in
+the form of well-defined magnon modes, which allows flexible and precise
+tuning. Here we demonstrate that by dissipation engineering, a non-Markovian
+interaction dynamics between the magnon and the microwave cavity photon can be
+achieved. Such a process enables us to build a magnon gradient memory to store
+information in the magnon dark modes, which decouple from the microwave cavity
+and thus preserve a long life-time. Our findings provide a promising approach
+for developing long-lifetime, multimode quantum memories.",1507.02791v1
+2015-12-02,Bose-Einstein Condensation of Magnons Pumped by the Bulk Spin Seebeck Effect,"We propose inducing Bose-Einstein condensation of magnons in a magnetic
+insulator by a heat flow oriented toward its boundary. At a critical heat flux,
+the oversaturated thermal gas of magnons accumulated at the boundary
+precipitates the condensate, which then grows gradually as the thermal bias is
+dialed up further. The thermal magnons thus pumped by the magnonic bulk (spin)
+Seebeck effect must generally overcome both the local Gilbert damping
+associated with the coherent magnetic dynamics as well as the radiative
+spin-wave losses toward the magnetic bulk, in order to achieve the threshold of
+condensation. We quantitatively estimate the requisite bias in the case of the
+ferrimagnetic yttrium iron garnet, discuss different physical regimes of
+condensation, and contrast it with the competing (so-called Doppler-shift) bulk
+instability.",1512.00557v1
+2016-09-03,Magnon-phonon coupling and two-magnon continuum in two-dimensional triangular antiferromagnet CuCrO2,"CuCrO2 is a manifestation of a two-dimensional triangular antiferromagnet
+which exhibits an incommensurate noncollinear magnetic structure similar to a
+classical 120 degree ordering. Using the inelastic neutron scattering
+technique, direct evidence of a magnon-phonon coupling in CuCrO2 is revealed
+via the mixed magnon-phonon character of the excitation mode at 12.5 meV as
+well as a minimum at the zone boundary. A simple model Hamiltonian that
+incorporates an exchange striction type magnon-phonon coupling reproduces the
+observed features accurately. Also, continuum excitations originating from the
+interaction between quasiparticles are observed with strong intensity at the
+zone boundary. These features of the magnetic excitations are key to an
+understanding of the emergent excitations in noncollinear antiferromagnetic
+compounds.",1609.00785v1
+2016-09-13,Formation of new phase inclusions in the system of quasi-equilibrium magnons of high density,"The paper studies the spatial variation of the magnetization in a
+nonconducting magnetic sample with an excess number of magnons in comparison to
+the equilibrium. The phenomenon is considered using the Landau-Lifshits
+equation with additional terms describing the longitudinal relaxation of the
+magnetization, the magnon diffusion and the magnon creation by external
+pumping. The free energy of the system is presented in the mean field
+approximation. It is shown that, if the pumping exceeds some critical value,
+regions of the new phase arise where the magnetic moments are oriented opposite
+to the magnetization of the magnetic sample. The phenomenon is similar to the
+appearance of droplets of the condensed phase in the supersaturated vapor. The
+appearance of the new phase either in the form of a single domain or a
+periodical lattice is demonstrated. The studied process is a competitor to the
+process of the Bose-Einstein condensation of magnons.",1609.04768v1
+2018-01-19,Nonabelian magnonics in antiferromagnets,"We present a semiclassical formalism for antiferromagnetic (AFM) magnonics
+which promotes the central ingredient of spin wave chirality, encoded in a
+quantity called magnonic isospin, to a first-class citizen of the theory. We
+use this formalism to unify results of interest from the field under a single
+chirality-centric formulation. Our main result is that the isospin is governed
+by unitary time evolution, through a Hamiltonian projected down from the full
+spin wave dynamics. Because isospin is SU(2)-valued, its dynamics on the Bloch
+sphere are precisely rotations - which, in general, do not commute.
+Consequently, the induced group of operations on AFM spin waves is nonabelian.
+This is a paradigmatic departure from ferromagnetic magnonics, which operates
+purely within the abelian group generated by spin wave phase and amplitude. Our
+investigation of this nonabelian magnonics in AFM insulators focuses on
+studying several simple gate operations, and offering in broad strokes a
+program of study for interesting new logic families in antiferromagnetic spin
+wave systems",1801.06535v3
+2019-06-10,Low-energy dynamics of the Affleck-Kennedy-Lieb-Tasaki model in the one- and two-triplon basis,"The elementary excitation in the antiferromagnetic spin-1 model known as the
+Affleck-Kennedy-Lieb-Tasaki (AKLT) Hamiltonian has been described alternatively
+as magnons or kink-like solitons (triplons). The latter, which we call the
+triplon throughout this paper, has been proven equivalent descriptions of the
+same magnon excitation and not an independent branch of excited states. On the
+other hand, no careful examination of multi-magnon and multi-triplon
+equivalence was made in the past. In this paper we prove that two-magnon and
+two-triplon states are also identical descriptions of the same excited states,
+and furthermore that their energies break down as the sum of one-triplon
+energies exactly for the AKLT Hamiltonian. The statement holds despite the fact
+that the model is non-integrable. Such magnon/triplon dichotomy is conjectured
+to hold for arbitrary n-magnon and n-triplon states. The one- and two-triplon
+states form orthogonal sets that can be used to span the low-energy Hilbert
+space. We construct an effective version of the AKLT Hamiltonian within such
+subspace, and work out the correction to the one-triplon energy gap that finds
+excellent agreement with the known exact value.",1906.03758v1
+2019-07-02,Bias-free reconfigurable magnonic phase shifter based on a spin-current controlled ferromagnetic resonator,"Controllable phase modulation plays a pivotal role in the researches of
+magnonic logic gates. Here we propose a reconfigurable spin-current controlled
+magnonic phase shifter based on a ferromagnetic resonator. The proposed phase
+shifter requires no magnetic bias field during operation. The device is
+directly configured over the waveguide while keeping the original structure of
+the waveguide unaffected. Numerical micromagnetic simulations show that the
+phase shifter could yield either a {\pi}-phase or no shift depending on the
+magnetization status of the resonator, which can be controlled by a current
+pulse. Moreover, the phase-shifting operation could be affected by spin
+current. At different input current density, the device could be either used as
+a dynamic controlled phase shifter or a spin-wave valve. Finally, a XNOR
+magnonic logic gate is demonstrated using the proposed phase shifter. Our work
+can be a beneficial step to enhance the functionality and compatibility of the
+magnonic logic circuits.",1907.01303v1
+2019-10-24,Resources of nonlinear cavity magnonics for quantum information,"We theoretically explore nonlinearities of ferromagnets in microwave cavities
+in the classical and quantum regimes, and assess the resources for quantum
+information, i.e. fluctuation squeezing and bipartite entanglement. The
+(semi-)classical analysis of the anharmonic oscillator (Duffing) model for the
+Kittel mode when including all other magnon modes, reveals chaotic and
+limit-cycle phases that do not survive in quantum calculations. However,
+magnons with nonzero wavenumbers that are driven by the Suhl instability of the
+Kittel mode, form a genuine limit cycle. We subsequently compute bounds for the
+distillable entanglement, as well as entanglement of formation for the
+bipartite configurations of the mixed magnon modes. The distillable
+entanglement of bipartite states accessible from a covariance matrix vanishes,
+but can be recovered by injection locking. The predicted magnon entanglement
+can be experimentally tested with yttrium iron garnet samples under realistic
+conditions.",1910.11130v1
+2020-01-20,The topological magnon bands in the Flux state in Sashtry-Sutherland lattice,"We investigate low energy magnon excitations above the non-collinear flux
+state and non-coplanar canted flux state in a Heisenberg anti-ferromagnet with
+Dzyaloshinskii-Moriya interaction~(DMI) on a Sashtry-Sutherland lattice.While
+previous studies have shown the presence of topological magnetic excitation in
+the dimer and ferromagnetic phases on the Shastry-Sutherland lattice, our
+results establish the non-trivial topology of magnons in the anti-ferromagnetic
+flux and canted flux states. Our results uncover the existence of a multitude
+of topological phase transitions in the magnon sector -- evidenced by the
+changing Chern numbers of the single magnon bands -- as the Hamiltonian
+parameters are varied, even when the ground state remains unchanged. The
+thermal Hall conductivity is calculated and its derivative is shown to exhibit
+a logarithmic divergence at the phase transitions, independent of the type of
+band touching involved. This may provide a useful means to identify the energy
+at which the transition occurs. Finally, we propose the way to realize the
+studied model in a practical material.",2001.07008v1
+2020-02-28,Spin Hall magnetoresistance in Pt/YIG bilayers via varying magnon excitation,"Spin Hall magnetoresistance (SMR) and magnon excitation magnetoresistance
+(MMR) that all generate via the spin Hall effect and inverse spin Hall effect
+in a nonmagnetic material are always related to each other. However, the
+influence of magnon excitation for SMR is often overlooked due to the
+negligible MMR. Here, we investigate the SMR in Pt/Y3Fe5O12 (YIG) bilayers from
+5 to 300K, in which the YIG are treated after Ar+-ion milling. The SMR in the
+treated device is smaller than in the non-treated. According to theoretical
+simulation, we attribute this phenomenon to the reduction of the interfacial
+spin-mixing conductance at the treated Pt/YIG interface induced by the magnon
+suppression. Our experimental results point out that the SMR and the MMR are
+inter-connected, and the former could be modulated via magnon excitation. Our
+findings provide a new approach for separating and clarifying the underlying
+mechanisms.",2002.12550v1
+2020-02-29,Nonreciprocal Emergence of Hybridized Magnons in magnetic thin Films,"We investigate the transfer and control of nonreciprocity through magnons
+themselves in permalloy thin films deposited on surface oxide silicon
+substrate. Evidences of nonreciprocal emergence of hybridized dipole exchange
+magnons (spin waves) at two permalloy surfaces are provided by studying magnon
+transmission and asymmetry, via Brillouin light scattering measurements. The
+dipole dominated spin wave and exchange dominated spin wave are found to be
+localized near the top and bottom surfaces, respectively, and traveling along
+opposite directions. The nonreciprocity and the localization are intertwined
+and ca n be tuned by an in plane magnetic field. The effects are well explained
+by the magnetostatic theory and can be quantitatively reproduced by the
+micromagnetic simulations. Our findings provide a simple and flexible approach
+to nonreciprocal all magnon logi c devices with highly compatible with silicon
+based integrated circuit technology.",2003.00230v4
+2020-03-12,"Tunable multiwindow magnomechanically induced transparency, Fano resonances, and slow-to-fast light conversion","We investigate the absorption and transmission properties of a weak probe
+field under the influence of a strong control field in a hybrid cavity
+magnomechanical system in the microwave regime. This hybrid system consists of
+two ferromagnetic material yttrium iron garnet (YIG) spheres strongly coupled
+to a single cavity mode. In addition to two magnon-induced transparency (MIT)
+that arise due to strong photon-magnon interactions, we observe a
+magnomechanically induced transparency (MMIT) due to the presence of nonlinear
+phonon-magnon interaction. In addition, we discuss the emergence and tunability
+of the multiple Fano resonances in our system. We find that due to strong
+photon-magnon coupling the group delay of the probe field can be enhanced
+significantly. The subluminal or superluminal propagation depends on the
+frequency of the magnons, which can be easily tuned by an external bias
+magnetic field. Besides, the group delay of the transmitted field can also be
+controlled with the control field power.",2003.13760v4
+2020-04-07,Optomagnonic Barnett effect,"Combining the technologies of quantum optics and magnonics, we find that the
+circularly polarized laser can dynamically realize the quasiequilibrium magnon
+Bose-Einstein condensates (BEC). The Zeeman coupling between the laser and
+spins generates the optical Barnett field, and its direction is controllable by
+switching the laser chirality. We show that the optical Barnett field develops
+the total magnetization in insulating ferrimagnets with reversing the local
+magnetization, which leads to the quasiequilibrium magnon BEC. This
+laser-induced magnon BEC transition through optical Barnett effect, dubbed the
+optomagnonic Barnett effect, provides an access to coherent magnons in the high
+frequency regime of the order of terahertz. We also propose a realistic
+experimental setup to observe the optomagnonic Barnett effect using current
+device and measurement technologies as well as the laser chirping. The
+optomagnonic Barnett effect is a key ingredient for the application to
+ultrafast spin transport.",2004.03353v2
+2020-04-15,Topological magnon bands in a room temperature Kagome magnet,"Topological magnon is a vibrant research field gaining more and more
+attention in the past few years. Among many theoretical proposals and limited
+experimental studies, ferromagnetic Kagome lattice emerges as one of the most
+elucidating systems. Here we report neutron scattering studies of YMn6Sn6, a
+metallic system consisting of ferromagnetic Kagome planes. This system
+undergoes a commensurate-to-incommensurate antiferromagnetic phase transition
+upon cooling with the incommensurability along the out-of-plane direction. We
+observe magnon band gap opening at the symmetry-protected K points and ascribe
+this feature to the antisymmetric Dzyaloshinskii-Moriya (DM) interactions. Our
+observation supports the existence of topological Dirac magnons in both the
+commensurate collinear and incommensurate coplanar magnetic orders, which is
+further corroborated by symmetry analysis. This finding places YMn6Sn6 as a
+promising candidate for room-temperature magnon spintronics applications.",2004.07121v1
+2020-04-23,Nanoscale Detection of Magnon Excitations with Variable Wavevectors Through a Quantum Spin Sensor,"We report the optical detection of magnons with a broad range of wavevectors
+in magnetic insulator Y3Fe5O12 thin films by proximate nitrogen-vacancy (NV)
+single-spin sensors. Through multi-magnon scattering processes, the excited
+magnons generate fluctuating magnetic fields at the NV electron spin resonance
+frequencies, which accelerate the relaxation of NV spins. By measuring the
+variation of the emitted spin-dependent photoluminescence of the NV centers,
+magnons with variable wavevectors up to ~ 5 x 10^7 m-1 can be optically
+accessed, providing an alternative perspective to reveal the underlying spin
+behaviors in magnetic systems. Our results highlight the significant
+opportunities offered by NV single-spin quantum sensors in exploring nanoscale
+spin dynamics of emergent spintronic materials.",2004.11067v1
+2020-05-03,Berry curvature for coupled waves of magnons and electromagnetic waves,"In this paper, we introduce Berry curvature, topological Chern number and
+topological chiral edge mode, that emerge from a hybridization between magnon
+and electromagnetic wave in a ferromagnet insulator. By focusing on the energy
+conservation, we first reformulate the Landau-Lifshitz-Maxwell equation into a
+Hermitian eigenvalue equation. From the eigenvalue equation, we define the
+Berry curvature of the magnon-photon coupled waves. We show that the Berry
+curvature thus introduced shows a prominent peak around a hybridization point
+between magnon mode and photon mode, and a massive hybrid mode takes a non-zero
+Chern number ($\pm 1$) due to the magnon-photon coupling. In accordance with
+the non-zero Chern number, the topological edge modes emerge inside the
+hybridization gap at a domain wall between two ferromagnetic insulators with
+opposite magnetizations.",2005.01105v1
+2020-05-10,Stationary entanglement between light and microwave via ferromagnetic magnons,"We show how to generate stationary entanglement between light and microwave
+in a hybrid opto-electro-magnonical system which mainly consists of a microwave
+cavity, a yttrium iron garnet (YIG) sphere and a nanofiber. The optical modes
+in nanofiber can evanescently coupled to whispering gallery modes, that are
+able to interact with magnon mode via spin-orbit interaction, in YIG sphere,
+while the microwave cavity photons and magnons are coupled through magnetic
+dipole interaction simultaneously. Under reasonable parameter regimes, pretty
+amount of entanglement can be generated, and it also shows persistence against
+temperature. Our work is expected to provide a new perspective for building
+more advanced and comprehensive quantum networks along with magnons for
+fast-developing quantum technology and for studying the macroscopic quantum
+phenomena.",2005.04581v3
+2020-05-20,Detectability of Axion Dark Matter with Phonon Polaritons and Magnons,"Collective excitations in condensed matter systems, such as phonons and
+magnons, have recently been proposed as novel detection channels for light dark
+matter. We show that excitation of i) optical phonon polaritons in polar
+materials in an ${\mathcal O}$(1 T) magnetic field (via the axion-photon
+coupling), and ii) gapped magnons in magnetically ordered materials (via the
+axion wind coupling to the electron spin), can cover the difficult-to-reach
+${\mathcal O}$(1-100) meV mass window of QCD axion dark matter with less than a
+kilogram-year exposure. Finding materials with a large number of optical phonon
+or magnon modes that can couple to the axion field is crucial, suggesting a
+program to search for a range of materials with different resonant energies and
+excitation selection rules; we outline the rules and discuss a few candidate
+targets, leaving a more exhaustive search for future work. Ongoing development
+of single photon, phonon and magnon detectors will provide the key for
+experimentally realizing the ideas presented here.",2005.10256v1
+2020-05-28,Moiré magnons in twisted bilayer magnets with collinear order,"We explore the moir\'e magnon bands in twisted bilayer magnets with
+next-nearest neighboring Dzyaloshinskii-Moriya interactions, assuming that the
+out-of-plane collinear magnetic order is preserved under weak interlayer
+coupling. By calculating the magnonic band structures and the topological Chern
+numbers for four representative cases, we find that (i) the valley moir\'e
+bands are extremely flat over a wide range of continuous twist angles; (ii) the
+topological Chern numbers of the lowest few flat bands vary significantly with
+the twist angle; and (iii) the lowest few topological flat bands in bilayer
+antiferromagnets entail nontrivial thermal spin transport in the transverse
+direction; These properties make twisted bilayer magnets an ideal platform to
+study the magnonic counterparts of moir\'e electrons, where the statistical
+distinction between magnons and electrons leads to fundamentally new physical
+behavior.",2005.14096v2
+2020-07-22,Theoretical realization of rich magnon topology by symmetry-breaking in honeycomb bilayer ferromagnets,"We reveal the rich magnon topology in honeycomb bilayer ferromagnets (HBF)
+induced by the combined effect of interlayer exchange, Dzyaloshinskii-Moriya
+interaction (DMI), and electrostatic doping (ED). In particular, we present a
+systematic study of the Hamiltonian non-adiabatic evolution in the HBF
+parametric space, spanned by the symmetry-breaking terms (DMI and ED) and
+interlayer exchange. We determine the band closure manifolds which are found to
+divide the parametric space into six distinct regions, matched with five
+distinct topological phases and one topologically trivial phase. The
+characteristic Chern numbers and thermal Hall conductivities are calculated for
+the topological phases. Edge spectra, dictated by the bulk-edge correspondence,
+are also analyzed in the nanoribbon version of the model. Both bulk and edge
+spectra are found to be nonreciprocal as a consequence of ED and edge magnons
+are observed to counter propagate on opposite edges. The predicted results
+offer new insights on the manipulation of magnonic Chern numbers and magnon
+topological transport via experimentally tunable parameters.",2007.11692v2
+2020-07-27,Magnonic Superradiant Phase Transition,"We show that the low-temperature phase transition in ErFeO3 that occurs at a
+critical temperature of ~ 4 K can be described as a magnonic version of the
+superradiant phase transition (SRPT). The role of photons in the
+quantum-optical SRPT is played by Fe magnons, while that of two-level atoms is
+played by Er spins. Our spin model, which is reduced to an extended Dicke
+model, takes into account the short-range, direct exchange interactions between
+Er spins in addition to the long-range Er-Er interactions mediated by Fe
+magnons. By using realistic parameters determined by recent terahertz
+magnetospectroscopy and magnetization experiments, we demonstrate that it is
+the cooperative, ultrastrong coupling between Er spins and Fe magnons that
+causes the phase transition. This work thus proves ErFeO3 to be a unique system
+that exhibits a SRPT in thermal equilibrium, in contrast to previous
+observations of laser-driven non-equilibrium SRPTs.",2007.13263v1
+2020-07-30,Electron-magnon spin conversion and magnonic spin pumping in antiferromagnet/heavy metal heterostructure,"We study the exchange between electron and magnon spins at the interface of
+an antiferromagnet and a heavy metal at finite temperatures. The underlying
+physical mechanism is based on spin torque associated with the
+creation/annihilation of thermal magnons with right-hand and left-hand
+polarization. The creation/annihilation process depends strongly on the
+relative orientation between the polarization of the electron and the magnon
+spins. For a sufficiently strong spin transfer torque (STT), the conversion
+process becomes nonlinear, generating a nonzero net spin pumping current in the
+AFM that can detected in the neighboring metal layer. Applying an external
+magnetic field renders possible the manipulation of the STT driving thermal
+spin pumping. Our theoretical results are experimentally feasible and are of a
+direct relevance to antiferromagnet-based spintronic devices.",2007.15512v1
+2020-08-07,Cavity magnon polariton based precision magnetometry,"A photon-magnon hybrid system can be realised by coupling the electron spin
+resonance of a magnetic material to a microwave cavity mode. The quasiparticles
+associated with the system dynamics are the cavity magnon polaritons, which
+arise from the mixing of strongly coupled magnons and photons. We illustrate
+how these particles can be used to probe the magnetisation of a sample with a
+remarkable sensitivity, devising suitable spin-magnetometers which ultimately
+can be used to directly assess oscillating magnetic fields. Specifically, the
+capability of cavity magnon polaritons of converting magnetic excitations to
+electromagnetic ones, allows for translating to magnetism the quantum-limited
+sensitivity reached by state-of-the-art electronics. Here we employ hybrid
+systems composed of microwave cavities and ferrimagnetic spheres, to
+experimentally implement two types of novel spin-magnetometers.",2008.03062v2
+2020-08-08,Two-magnon frequency-pulling effect in ferromagnetic resonance,"We report the experimental observation in thin films of the hybridization of
+the uniform ferromagnetic resonance mode with nonuniform magnons as a result of
+the two-magnon scattering mechanism, leading to a frequency-pulling effect on
+the ferromagnetic resonance. This effect, when not properly accounted for,
+leads to a discrepancy in the dependence of the ferromagnetic resonance field
+on frequency for different field orientations. The frequency-pulling effect is
+the complement of the broadening of the ferromagnetic resonance lineshape by
+two-magnon scattering and can be calculated using the same parameters. By
+accounting for the two-magnon frequency shifts through these means, consistency
+is achieved in fitting data from in-plane and perpendicular-to-plane resonance
+conditions.",2008.03423v2
+2020-08-17,Scattering of magnons at graphene quantum-Hall-magnet junctions,"Motivated by recent non-local transport studies of quantum-Hall-magnet (QHM)
+states formed in monolayer graphene's $N=0$ Landau level, we study the
+scattering of QHM magnons by gate-controlled junctions between states with
+different integer filling factors $\nu$. For the $\nu=1|-1|1$ geometry we find
+magnons are weakly scattered by electric potential variation in the junction
+region, and that the scattering is chiral when the junction lacks a mirror
+symmetry. For the $\nu=1|0|1$ geometry, %in which the scattering region
+contains a $\nu=0$ canted antiferromagnet, we find that kinematic constraints
+completely block magnon transmission if the incident angle exceeds a critical
+value. Our results explain the suppressed non-local-voltage signals observed in
+the $\nu=1|0|1$ case. We use our theory to propose that valley-waves generated
+at $\nu=-1|1$ junctions and magnons can be used in combination to probe the
+spin/valley flavor structure of QHM states at integer and fractional filling
+factors.",2008.07583v1
+2020-10-08,Chiral Hinge Magnons in Second-Order Topological Magnon Insulators,"When interacting spins in condensed matter order ferromagnetically, their
+ground state wave function is topologically trivial. Nonetheless, in two
+dimensions, the ferromagnetic state can support spin excitations with
+nontrivial topology, an exotic state known as topological magnon insulator
+(TMI). Here, we theoretically unveil and numerically confirm a novel
+ferromagnetic state in three dimensions dubbed second-order TMI, whose
+hallmarks are excitations at its hinges, where facets intersect. Since
+ferromagnetism naturally comes with broken time-reversal symmetry, the hinge
+magnons are chiral, rendering backscattering impossible. Hence, they trace out
+a three-dimensional path about the sample unimpeded by defects and are
+topologically protected by the spectral gap. They are remarkably robust against
+disorder and simultaneously highly tunable by atomic-level engineering of the
+sample termination. Our findings empower magnonics with the tools of
+higher-order topology, a promising route to combine low-energy information
+transfer free of Joule heating with three-dimensional vertical integration.",2010.04142v1
+2020-10-19,Magnetic texture based magnonics,"The spontaneous magnetic orders arising in ferro-, ferri- and
+antiferromagnets stem from various magnetic interactions. Depending on the
+interplay and competition among the Heisenberg exchange interaction,
+Dzyaloshinskii-Moriya exchange interaction, magnetic dipolar interaction and
+crystal anisotropies, a great variety of magnetic textures may be stabilized,
+such as magnetic domain walls, vortices, Skyrmions and spiral helical
+structures. While each of these spin textures responds to external forces in a
+specific manner with characteristic resonance frequencies, they also interact
+with magnons, the fundamental collective excitation of the magnetic order,
+which can propagate in magnetic materials free of charge transport and
+therefore with low energy dissipation. Recent theories and experiments found
+that the interplay between spin waves and magnetic textures is particularly
+interesting and rich in physics. In this review, we introduce and discuss the
+theoretical framework of magnons living on a magnetic texture background, as
+well as recent experimental progress in the manipulation of magnons via
+magnetic textures. The flexibility and reconfigurability of magnetic textures
+are discussed regarding the potential for applications in information
+processing schemes based on magnons.",2010.09180v1
+2020-10-28,Floquet Cavity Electromagnonics,"Hybrid magnonics has recently attracted intensive attentions as a promising
+platform for coherent information processing. In spite of its rapid
+development, on-demand control over the interaction of magnons with other
+information carriers, in particular microwave photons in electromagnonic
+systems, has been long missing, significantly limiting the broad applications
+of hybrid magnonics. Here, we show that by introducing Floquet engineering into
+cavity electromagnonics, coherent control on the magnon-microwave photon
+coupling can be realized. Leveraging the periodic temporal modulation from a
+Floquet drive, our first-of-its-kind Floquet cavity electromagnonic system can
+manipulate the interaction between hybridized cavity electromagnonic modes on
+demand. Moreover, we demonstrate a new coupling regime in such systems: the
+Floquet ultrastrong coupling, where the Floquet splitting is comparable with or
+even larger than the level spacing of the two interacting modes, resulting in
+the breakdown of the rotating wave approximation. Our findings open up new
+directions for magnon-based coherent signal processing.",2010.14727v1
+2020-11-25,Antiferromagnetic magnon pseudospin: Dynamics and diffusive transport,"We formulate a theoretical description of antiferromagnetic magnons and their
+transport in terms of an associated pseudospin. The need and strength of this
+formulation emerges from the antiferromagnetic eigenmodes being formed from
+superpositions of spin-up and -down magnons, depending on the material
+anisotropies. Consequently, a description analogous to that of spin-1/2
+electrons is demonstrated while accounting for the bosonic nature of the
+antiferromagnetic eigenmodes. Introducing the concepts of a pseudospin chemical
+potential together with a pseudofield and relating magnon spin to pseudospin
+allows a consistent description of diffusive spin transport in
+antiferromagnetic insulators with any given anisotropies and interactions.
+Employing the formalism developed, we elucidate the general features of recent
+non-local spin transport experiments in antiferromagnetic insulators hosting
+magnons with different polarisations. The pseudospin formalism developed herein
+is valid for any pair of coupled bosons and is likely to be useful in other
+systems comprising interacting bosonic modes.",2011.12927v1
+2021-01-22,Opportunities for long-range magnon-mediated entanglement of spin qubits via on- and off-resonant coupling,"The ability to manipulate entanglement between multiple spatially-separated
+qubits is essential for quantum information processing. Although
+nitrogen-vacancy (NV) centers in diamond provide a promising qubit platform,
+developing scalable two-qubit gates remains a well-known challenge. To this
+end, magnon-mediated entanglement proposals have attracted attention due to
+their long-range spin-coherent propagation. Optimal device geometries and gate
+protocols of such schemes, however, have yet to be determined. Here we predict
+strong long-distance ($>\mu$m) NV-NV coupling via magnon modes with
+cooperativities exceeding unity in ferromagnetic bar and waveguide structures.
+Moreover, we explore and compare on-resonant transduction and off-resonant
+virtual-magnon exchange protocols, and discuss their suitability for generating
+or manipulating entangled states at low temperatures ($T\lesssim 150$ mK) under
+realistic experimental conditions. This work will guide future experiments that
+aim to entangle spin qubits in solids with magnon excitations.",2101.09220v2
+2021-03-09,Strong Magnon-Magnon Coupling in Synthetic Antiferromagnets,"Synthetic antiferromagnet, comprised of two ferromagnetic layers separated by
+a non-magnetic layer, possesses two uniform precession resonance modes:
+in-phase acoustic mode and out-of-phase optic mode. In this work, we
+theoretically and numerically demonstrated the strong coupling between acoustic
+and optic magnon modes. The strong coupling is attributed to the symmetry
+breaking of the system, which can be realized by tilting the bias field or
+constructing an asymmetrical synthetic antiferromagnet. It is found that the
+coupling strength can be highly adjusted by tuning the tilting angle of bias
+field, the magnitude of antiferromagnetic interlayer exchange coupling, and the
+thicknesses of ferromagnetic layers. Furthermore, the coupling between acoustic
+and optic magnon modes can even reach the ultrastrong coupling regime. Our
+findings show high promise for investigating quantum phenomenon with a magnonic
+platform.",2103.05153v1
+2021-03-19,Remote magnon entanglement between two massive ferrimagnetic spheres via cavity optomagnonics,"Recent studies show that hybrid quantum systems based on magnonics provide a
+new and promising platform for generating macroscopic quantum states involving
+a large number of spins. Here we show how to entangle two magnon modes in two
+massive yttrium-iron-garnet (YIG) spheres using cavity optomagnonics, where
+magnons couple to high-quality optical whispering gallery modes supported by
+the YIG sphere. The spheres can be as large as 1 mm in diameter and each sphere
+contains more than $10^{18}$ spins. The proposal is based on the asymmetry of
+the Stokes and anti-Stokes sidebands generated by the magnon-induced Brillouin
+light scattering in cavity optomagnonics. This allows one to utilize the Stokes
+and anti-Stokes scattering process, respectively, for generating and verifying
+the entanglement. Our work indicates that cavity optomagnonics could be a
+promising system for preparing macroscopic quantum states.",2103.10595v2
+2021-03-20,Ultrafast amplification and non-linear magneto-elastic coupling of coherent magnon modes in an antiferromagnet,"We investigate the role of domain walls in the ultrafast magnon dynamics of
+an antiferromagnetic NiO single crystal in a pump-probe experiment with
+variable pump photon energy. Analysing the amplitude of the energy-dependent
+photo-induced ultrafast spin dynamics, we detect a yet unreported coupling
+between the material's characteristic THz- and a GHz-magnon modes. We explain
+this unexpected coupling between two orthogonal eigenstates of the
+corresponding Hamiltonian by modelling the magneto-elastic interaction between
+spins in different domains. We find that such interaction, in the non-linear
+regime, couples the two different magnon modes via the domain walls and it can
+be optically exploited via the exciton-magnon resonance.",2103.11203v2
+2021-03-26,Switching magnon chirality in artificial antiferromagnet,"Magnons in antiferromagnets can support both right-handed and left-handed
+chiralities, which shed a light on the chirality-based spintronics. Here we
+demonstrate the switching and reading of magnon chirality in an artificial
+antiferromagnet. The coexisting antiferromagnetic and ferromagnetic
+characteristic resonance modes are discovered, which permits a high tunability
+in the modulation of magnon chirality. The reading of the chirality is
+accomplished via the chirality-dependent spin pumping as well as spin
+rectification effect. Our result illustrates an ideal antiferromagnetic
+platform for handling magnon chirality and paves the way for chirality-based
+spintronics.",2103.14483v2
+2021-04-07,Strain engineering of topological magnons in chromium trihalides from first-principles,"Recent experiments evidence the direct observation of spin waves in chromium
+trihalides and a gap at the Dirac points of the magnon dispersion in bulk
+CrI$_3$. However, the topological origin of this feature remains unclear and
+its emergence at the 2D limit has not yet been proven experimentally. Herein,
+we perform a fully self-consistent ab initio analysis that supports the
+presence of topological magnons in chromium trihalides monolayers. Our results
+confirm the existence of a gap around the K high-symmetry point in the linear
+magnon dispersion of CrI$_3$, which originates as a direct consequence of
+intralayer Dzyaloshinskii-Moriya (DM) interaction. In addition, our orbital
+resolved analysis reveals the microscopic mechanisms that can be exploited
+using strain engineering to increase the strength of the DM interaction and
+thus control the gap size in CrI$_3$. This paves the way to the further
+development of this family of materials as building-blocks for topological
+magnonics at the limit of miniaturization.",2104.03023v2
+2021-05-18,Parity-symmetry-breaking quantum phase transition via parametric drive in a cavity magnonic system,"We study the parity-symmetry-breaking quantum phase transition (QPT) in a
+cavity magnonic system driven by a parametric field, where the magnons in a
+ferrimagnetic yttrium-iron-garnet sphere strongly couple to a microwave cavity.
+With appropriate parameters, this cavity magnonic system can exhibit a rich
+phase diagram, including the parity-symmetric phase, parity-symmetry-broken
+phase, and bistable phase. When increasing the drive strength beyond a critical
+threshold, the cavity magnonic system undergoes either a first- or second-order
+nonequilibrium QPT from the parity-symmetric phase with microscopic excitations
+to the parity-symmetry-broken phase with macroscopic excitations, depending on
+the parameters of the system. Our work provides an alternate way to engineer
+the QPT in a hybrid quantum system containing the spin ensemble in a ferri- or
+ferromagnetic material with strong exchange interactions.",2105.08371v3
+2021-05-24,Phase-resolved electrical detection of coherently coupled magnonic devices,"We demonstrate the electrical detection of magnon-magnon hybrid dynamics in
+yttrium iron garnet/permalloy (YIG/Py) thin film bilayer devices. Direct
+microwave current injection through the conductive Py layer excites the hybrid
+dynamics consisting of the uniform mode of Py and the first standing spin wave
+($n=1$) mode of YIG, which are coupled via interfacial exchange. Both the two
+hybrid modes, with Py or YIG dominated excitations, can be detected via the
+spin rectification signals from the conductive Py layer, providing phase
+resolution of the coupled dynamics. The phase characterization is also applied
+to a nonlocally excited Py device, revealing the additional phase shift due to
+the perpendicular Oersted field. Our results provide a device platform for
+exploring hybrid magnonic dynamics and probing their phases, which are crucial
+for implementing coherent information processing with magnon excitations",2105.11057v1
+2021-06-10,Photoinduced Floquet topological magnons in a ferromagnetic checkerboard lattice,"This theoretical work is devoted to investigating laser-irradiated Floquet
+topological magnon insulators on a two-dimensional checkerboard ferromagnet and
+corresponding topological phase transitions. It is shown that the checkerboard
+Floquet topological magnon insulator is able to be transformed from a
+topological magnon insulator into another one possessing various Berry
+curvatures and Chern numbers by changing the light intensity. Especially, we
+also show that both Tamm-like and topologically protected Floquet magnon edge
+states can exist when a nontrivial gap opens. In addition, our results display
+that the sign of the Floquet thermal Hall conductivity is also tunable via
+varying the light intensity of the laser field.",2106.05936v3
+2021-07-20,Intrinsic Magnon Nernst Effects in Pyrochlore Iridate Thin Films,"We theoretically study the magnon spin thermal transport using a strong
+coupling approach in pyrochlore iridate trilayer thin films grown along the
+[111] direction. As a result of the Dzyaloshinskii-Moriya interaction (DMI),
+the spin configuration of the ground state is an all-in/all-out ordering on
+neighboring tetrahedra of the pyrochlore lattice. In such a state, the system
+has an inversion symmetry and a Nernst-type thermal spin current response is
+well defined. We calculate the temperature dependence of the magnon Nernst
+response with respect to the magnon band topology controlled by the spin-orbit
+coupling parameters and observe topologically protected chiral edge modes over
+a range of parameters. Our study complements prior work on the magnon thermal
+Hall effect in thin-film pyrochlore iridates and suggests that the [111] grown
+thin-film pyrochlore iridates are a promising candidate for thermal spin
+transport and spin caloritronic devices.",2107.09613v1
+2021-07-22,Driven-dissipative Quantum Dynamics in Cavity Magnon-Polariton System,"The dynamics of arbitrary-order quantum correlations in a cavity
+magnon-polariton system are investigated based on the quantum master equation
+in the coherent state representation. The phenomena of Rabi-like oscillation
+and level repulsion of the average cavity-photon number agree remarkably well
+with existing experimental observations. The competing nature of coherent and
+incoherent components in these two cases is further revealed by the
+second-order quantum coherence of the cavity photons and magnons, which can be
+systematically tuned by the driving microwave and thermal bath. Our results
+demonstrate the rich higher-order quantum dynamics induced by magnetic
+light-matter interaction, and serve as an indispensable step toward exploring
+nonclassical states for cavity photons and magnons in quantum cavity magnonics.",2107.10444v2
+2021-08-09,Conductivity Enhancement in a Diffusive Fermi Liquid due to Bose-Einstein Condensation of Magnons,"We theoretically study the conductivity of a disordered 2D metal when it is
+coupled to ferromagnetic magnons with a quadratic spectrum and a gap $\Delta$.
+In the diffusive limit, a combination of disorder and magnon-mediated electron
+interaction leads to a sharp metallic correction to the Drude conductivity as
+the magnons approach criticality, i.e., $\Delta \to 0$. The correction is
+non-singular and is distinctively weaker than, for example, the logsquared
+correction obtained when disordered electrons couple to diffusive spin
+fluctuations near a Hertz-Millis transition. The possibility of verifying this
+prediction in an S = 1/2 easy-plane ferromagnetic insulator K$_2$CuF$_4$ under
+an external magnetic field is proposed. Our results show that the onset of a
+magnon BEC in an insulator can be detected via electrical transport
+measurements on the proximate metal.",2108.04277v4
+2021-09-09,Magnonic spin Joule heating and rectification effects,"Nonlinear devices, such as transistors, enable contemporary computing
+technologies. We theoretically investigate nonlinear effects, bearing a high
+fundamental scientific and technical relevance, in magnonics with emphasis on
+superconductor-ferromagnet hybrids. Accounting for finite magnon chemical
+potential, we theoretically demonstrate magnonic spin-Joule heating, the spin
+analogue of conventional electronic Joule heating. Besides suggesting a key
+contribution to magnonic heat transport in a broad range of devices, it
+provides insights into the thermal physics of non-conserved bosonic
+excitations. Considering a spin-split superconductor self-consistently, we
+demonstrate its interface with a ferromagnetic insulator to harbor large
+tunability of spin and thermal conductances. We further demonstrate hysteretic
+rectification I-V characteristics in this hybrid, where the hysteresis results
+from the superconducting state bistability.",2109.04329v2
+2021-11-02,Chiral Magnonic Resonators: Rediscovering the Basic Magnetic Chirality in Magnonics,"The outlook for producing useful practical devices within the paradigm of
+magnonics rests on our ability to emit, control and detect coherent exchange
+spin waves on the nanoscale. Here, we argue that all these key functionalities
+can be delivered by chiral magnonic resonators - soft magnetic elements
+chirally coupled, via magneto-dipole interaction, to magnonic media nearby.
+Starting from the basic principles of chiral coupling, we outline how they
+could be used to construct devices and explore underpinning physics, ranging
+from basic logic gates to field programmable gate arrays, in-memory computing,
+and artificial neural networks, and extending from one- to two- and
+three-dimensional architectures.",2111.01508v1
+2021-11-29,Tailoring High-Frequency Magnonics in Monolayer Chromium Trihalides,"Monolayer chromium trihalides, the archetypal two dimensional (2D) magnetic
+materials, are readily suggested as a promising platform for high frequency
+magnonics. Here we detail the spin wave properties of monolayer CrBr$_3$ and
+CrI$_3$, using spin dynamics simulations parametrized from the first
+principles. We reveal that spin wave dispersion can be tuned in a broad range
+of frequencies by strain, paving the way towards flexo magnonic applications.
+We further show that ever present halide vacancies in these monolayers host
+sufficiently strong Dzyaloshinskii Moriya interaction to scatter spin waves,
+which promotes design of spin-wave guides by defect engineering. Finally we
+discuss the spectra of spin-waves propagating across a moir\'e periodic
+modulation of magnetic parameters in a van der Waals heterobilayer, and show
+that the nanoscale moir\'e periodicities in such samples are ideal for
+realization of a magnonic crystal in the terahertz frequency range. Recalling
+the additional tunability of magnetic 2D materials by electronic gating, our
+results situate these systems among the front-runners for prospective high
+frequency magnonic applications.",2111.14305v1
+2021-12-08,Role of Magnon-Magnon Scattering in Magnon Polaron Spin Seebeck Effect,"The spin Seebeck effect (SSE) signal of magnon polarons in bulk-Y3Fe5O12
+(YIG)/Pt heterostructures is found to drastically change as a function of
+temperature. It appears as a dip in the total SSE signal at low temperatures,
+but as the temperature increases, the dip gradually decreases before turning to
+a peak. We attribute the observed dip-to-peak transition to the rapid rise of
+the four-magnon scattering rate. Our analysis provides important insights into
+the microscopic origin of the hybridized excitations and the overall
+temperature dependence of the SSE anomalies.",2112.04621v1
+2021-12-09,Tuneable electron-magnon coupling of ferromagnetic surface states in PdCoO$_2$,"Controlling spin wave excitations in magnetic materials underpins the
+burgeoning field of magnonics. Yet, little is known about how magnons interact
+with the conduction electrons of itinerant magnets, or how this interplay can
+be controlled. Via a surface-sensitive spectroscopic approach, we demonstrate a
+strong and highly-tuneable electron-magnon coupling at the Pd-terminated
+surface of the delafossite oxide PdCoO$_2$, where a polar surface charge
+mediates a Stoner transition to itinerant surface ferromagnetism. We show how
+the coupling can be enhanced 7-fold with increasing surface disorder, and
+concomitant charge carrier doping, becoming sufficiently strong to drive the
+system into a polaronic regime, accompanied by a significant quasiparticle mass
+enhancement. Our study thus sheds new light on electron-magnon interactions in
+solid-state materials, and the ways in which these can be controlled.",2112.04869v1
+2021-12-20,Theory of drift-enabled control in nonlocal magnon transport,"Electrically injected and detected nonlocal magnon transport has emerged as a
+versatile method for transporting spin as well as probing the spin excitations
+in a magnetic insulator. We examine the role of drift currents in this
+phenomenon as a method for controlling the magnon propagation length.
+Formulating a phenomenological description, we identify the essential
+requirements for existence of magnon drift. Guided by this insight, we examine
+magnetic field gradient, asymmetric contribution to dispersion, and temperature
+gradient as three representative mechanisms underlying a finite magnon drift
+velocity, finding temperature gradient to be particularly effective.",2112.10819v2
+2021-12-27,Observation of magnon cross-Kerr effect in cavity magnonics,"When there is a certain amount of field inhomogeneity, the biased
+ferrimagnetic crystal will exhibit the higher-order magnetostatic (HMS) mode in
+addition to the uniform-precession Kittel mode. In cavity magnonics, we show
+both experimentally and theoretically the cross-Kerr-type interaction between
+the Kittel mode and HMS mode. When the Kittel mode is driven to generate a
+certain number of excitations, the HMS mode displays a corresponding frequency
+shift and vice versa. The cross-Kerr effect is caused by an exchange
+interaction between these two spin-wave modes. Utilizing the cross-Kerr effect,
+we realize and integrate a multi-mode cavity magnonic system with only one
+yttrium iron garnet (YIG) sphere. Our results will bring new methods to
+magnetization dynamics studies and pave a way for novel cavity magnonic devices
+by including the magnetostatic mode-mode interaction as an operational degree
+of freedom.",2112.13807v1
+2022-01-16,Coherent coupling of two remote magnonic resonators mediated by superconducting circuits,"We demonstrate microwave-mediated distant magnon-magnon coupling on a
+superconducting circuit platform, incorporating chip-mounted single-crystal
+Y$_3$Fe$_5$O$_{12}$ (YIG) spheres. Coherent level repulsion and dissipative
+level attraction between the magnon modes of the two YIG spheres are
+demonstrated. The former is mediated by cavity photons of a superconducting
+resonator, and the latter is mediated by propagating photons of a coplanar
+waveguide. Our results open new avenues towards exploring integrated hybrid
+magnonic networks for coherent information processing on a quantum-compatible
+superconducting platform.",2201.05937v1
+2022-01-18,Magnon Spectrum of the Amorphous Ferromagnet Co$_4$P from Atomistic Spin Dynamics,"An anomaly in the magnon dispersion of the amorphous ferromagnet Co$_{4}$P,
+often referred to as a `roton-like' excitation, attracted much attention half a
+century ago. With the current interest in heat and spin currents in amorphous
+magnets, we apply modern simulation methods, combining reverse Monte Carlo to
+build the atomic structure and the stochastic Landau-Lifshitz equation for spin
+dynamics, to re-investigate the magnetic excitation spectrum. We find two
+magnon valleys, one at the origin and another at a finite wavenumber close to
+the observations, but without a magnon gap. We conclude that the second dip is
+due to Umklapp scattering caused by residual long-range order, which may be an
+alternative explanation of the putative roton excitation. Our study paves the
+way to study magnon transport in amorphous magnets and related spintronic
+applications.",2201.06986v1
+2022-01-26,Nonlinear magnon polaritons,"We experimentally and theoretically demonstrate that nonlinear spin-wave
+interactions suppress the hybrid magnon-photon quasiparticle or ""magnon
+polariton"" in microwave spectra of an yttrium iron garnet film detected by an
+on-chip split-ring resonator. We observe a strong coupling between the Kittel
+and microwave cavity modes in terms of an avoided crossing as a function of
+magnetic fields at low microwave input powers, but a complete closing of the
+gap at high powers. The experimental results are well explained by a
+theoretical model including the three-magnon decay of the Kittel magnon into
+spin waves. The gap closure originates from the saturation of the ferromagnetic
+resonance above the Suhl instability threshold by a coherent back reaction from
+the spin waves.",2201.10889v2
+2022-01-26,Spin Wave Electromagnetic Nano-Antenna Enabled by Tripartite Phonon-Magnon-Photon Coupling,"We investigate tripartite coupling between phonons, magnons and photons in a
+periodic array of elliptical magnetostrictive nanomagnets delineated on a
+piezoelectric substrate to form a two-dimensional two-phase multiferroic
+crystal. A surface acoustic wave (phonons) of 5 - 35 GHz frequency launched
+into the substrate causes the magnetizations of the nanomagnets to precess at
+the frequency of the wave, giving rise to spin waves (magnons). The spin waves,
+in turn, radiate electromagnetic waves (photons) into the surrounding space at
+the surface acoustic wave frequency. Here, the phonons couple into magnons,
+which then couple into photons. This tripartite phonon-magnon-photon coupling
+is exploited to implement an extreme sub-wavelength electromagnetic antenna
+whose measured radiation efficiency and antenna gain exceed the theoretical
+limits for traditional antennas by more than two orders of magnitude at some
+frequencies. Micro-magnetic simulations are in excellent agreement with
+experimental observations and provide insight into the spin wave modes that
+couple into radiating electromagnetic modes to implement the antenna.",2201.11110v1
+2022-02-09,Electric field control of magnons in magnetic thin films: ab initio predictions for 2D metallic heterostructures,"We explore possibilities for control of magnons in two-dimensional
+heterostructures by an external electric field acting across a dielectric
+barrier. By performing ab-initio calculations for a Fe monolayer and a Fe
+bilayer, both suspended in vacuum and deposited on Cu(001), we demonstrate that
+external electric field can significantly modify magnon lifetimes and that
+these changes can be related to field-induced changes in the layer-resolved
+Bloch spectral functions. For systems with more magnon dispersion branches, the
+gap between high- and low-energy eigenmodes varies with the external field.
+These effects are strongly influenced by the substrate. Considerable
+variability in how the magnon spectra are sensitive to the external electric
+field can be expected, depending on the substrate and on the thickness of the
+magnetic layer.",2202.04525v1
+2022-03-10,Magnon-Cooparons in magnet-superconductor hybrids,"Generation and detection of spinful Cooper pairs in conventional
+superconductors has been intensely pursued by designing increasingly complex
+magnet-superconductor hybrids. Here, we demonstrate theoretically that magnons
+with nonzero wavenumbers universally induce a cloud of spinful triplet Cooper
+pairs around them in an adjacent conventional superconductor. The resulting
+composite quasiparticle, termed magnon-cooparon, consists of a spin flip in the
+magnet screened by a cloud of the spinful superfluid condensate. Thus, it
+inherits a large effective mass, which can be measured experimentally.
+Furthermore, we demonstrate that two magnetic wires deposited on a
+superconductor serve as a controllable magnonic directional coupler mediated by
+the nonlocal and composite nature of magnon-cooparons. Our analysis predicts a
+quasiparticle that enables generation, control, and use of spinful triplet
+Cooper pairs in the simplest magnet-superconductor heterostructures.",2203.05336v2
+2022-03-22,Analog quantum control of magnonic cat states on-a-chip by a superconducting qubit,"We propose to directly and quantum-coherently couple a superconducting
+transmon qubit to magnons - the quanta of the collective spin excitations, in a
+nearby magnetic particle. The magnet's stray field couples to the qubit via a
+superconducting quantum interference device (SQUID). We predict a resonant
+qubit-magnon exchange and a nonlinear radiation-pressure interaction that are
+both stronger than dissipation rates and tunable by an external flux bias. We
+additionally demonstrate a quantum control scheme that generates qubit-magnon
+entanglement and magnonic Schr\""{o}dinger cat states with high fidelity.",2203.11893v2
+2022-03-30,Excitation and transport of bound magnon clusters in frustrated ferromagnetic chain,"We investigate magnetic excitations and spin transport properties of a
+frustrated spin chain with ferromagnetic nearest-neighbor and antiferromagnetic
+next-nearest-neighbor exchange couplings in a magnetic field by density-matrix
+renormalization group methods. In the field-induced quadrupole and octupole
+regimes, the low-energy excitation is governed by two- and three-magnon bound
+states, respectively, so that bound magnon clusters would contribute to the
+spin transport. We show that spin current correlations decrease when the system
+goes from the quadrupole regime into the octupole regime. This indicates that
+the spin transport is suppressed in the octupole regime, although bound
+three-magnon clusters carry a larger amount of angular momentum than bound
+two-magnon clusters.",2203.16321v1
+2022-04-24,Thermal Evolution of Dirac Magnons in the Honeycomb Ferromagnet CrBr$_3$,"CrBr$_3$ is an excellent realization of the two-dimensional honeycomb
+ferromagnet, which offers a bosonic equivalent of graphene with Dirac magnons
+and topological character. We perform inelastic neutron scattering (INS)
+measurements using state-of-the-art instrumentation to update 50-year-old data,
+thereby enabling a definitive comparison both with recent experimental claims
+of a significant gap at the Dirac point and with theoretical predictions for
+thermal magnon renormalization. We demonstrate that CrBr$_3$ has next-neighbor
+$J_2$ and $J_3$ interactions approximately 5\% of $J_1$, an ideal Dirac magnon
+dispersion at the K point, and the associated signature of isospin winding. The
+magnon lifetime and the thermal band renormalization show the universal $T^2$
+evolution expected from an interacting spin-wave treatment, but the measured
+dispersion lacks the predicted van Hove features, highlighting the need for a
+deeper theoretical analysis.",2204.11355v1
+2022-05-05,Spin-wave localization on phasonic defects in one-dimensional magnonic quasicrystal,"We report on the evolution of the spin-wave spectrum under structural
+disorder introduced intentionally into one-dimensional magnonic quasicrystal.
+We study theoretically a system composed of ferromagnetic strips arranged in a
+Fibonacci sequence. We considered several stages of disorder in the form of
+phasonic defects, where different rearrangements of strips are introduced. By
+transition from the quasiperiodic order towards disorder, we show a gradual
+degradation of spin-waves fractal spectra and closing of the frequency gaps. In
+particular, the phasonic defects lead to the disappearance of the van Hove
+singularities at the frequency gap edges by moving modes into the frequency
+gaps and appearing new modes inside the frequency gaps. These modes disperse
+and eventually can close the gap, with increasing disorder levels. The work
+reveals how the the presence of disorder modifies the intrinsic spin wave
+localization existing in undefected magnonic quasicrystals. The paper
+contributes to the knowledge of magnonic Fibonacci quasicrystals and opens the
+way to study of the phasonic defects in two-dimensional magnonic quasicrystals.",2205.02702v2
+2022-05-09,Direct and alternating magnon spin currents across a junction interface irradiated by linearly polarized laser,"The developments in the field of quantum optics raise expectations that
+laser-matter coupling is a promising building block for magnonics. Here, we
+propose a method for the generation of direct and alternating spin currents of
+magnons across the junction interface irradiated by linearly polarized laser.
+In a junction of ferromagnetic insulators with a large electronic gap, the spin
+angular momentum is exchanged during the tunneling process of magnons across
+the junction interface. The advanced technology in the field of plasmonics and
+metamaterials realizes that spins irradiated by the laser field interact only
+with the magnetic component of the laser through the Zeeman coupling. Using an
+analytic perturbation theory, we provide a general formula for magnon transport
+induced by the inversion symmetry breaking across the junction interface. Then,
+we show that those spin currents are enhanced by the ferromagnetic resonance,
+and the period of the ac spin current is one-half of that of the laser magnetic
+field. Finally, we estimate the magnitude of the spin current, and find that it
+will be within experimental reach.",2205.04572v1
+2022-06-18,Magnon straintronics in the 2D van der Waals ferromagnet CrSBr from first-principles,"The recent isolation of two-dimensional (2D) magnets offers tantalizing
+opportunities for spintronics and magnonics at the limit of miniaturization.
+One of the key advantages of atomically-thin materials is their outstanding
+deformation capacity, which provides an exciting avenue to control their
+properties by strain engineering. Herein, we investigate the magnetic
+properties, magnon dispersion and spin dynamics of the air-stable 2D magnetic
+semiconductor CrSBr ($T_C$ = 146 K) under mechanical strain using
+first-principles calculations. Our results provide a deep microscopic analysis
+of the competing interactions that stabilize the long-range ferromagnetic order
+in the monolayer. We showcase that the magnon dynamics of CrSBr can be modified
+selectively along the two main crystallographic directions as a function of
+applied strain, probing the potential of this quasi-1D electronic system for
+magnon straintronics applications. Moreover, we predict a strain-driven
+enhancement of $T_C$ considering environmental screening by ~30%, allowing the
+propagation of spin waves at higher temperatures.",2206.09277v1
+2022-06-20,Chiral current in Floquet cavity-magnonics,"Floquet engineering can induce complex collective behaviour and interesting
+synthetic gauge-field in quantum systems through temporal modulation of system
+parameters by periodic drives. Using a Floquet drive on frequencies of the
+magnon modes, we realize a chiral state-transfer in a cavity-magnonic system.
+The time-reversal symmetry is broken in such a promising platform for coherent
+information processing. In particular, the photon mode is adiabatically
+eliminated in the large-detuning regime and the magnon modes under conditional
+longitudinal drives can be indirectly coupled to each other with a
+phase-modulated interaction. The effective Hamiltonian is then used to generate
+chiral currents in a circular loop, whose dynamics is evaluated to measure the
+symmetry of the system Hamiltonian. Beyond the dynamics limited in the manifold
+with a fixed number of excitations, our protocol applies to the
+continuous-variable systems with arbitrary states. Also it is found to be
+robust against the systematic errors in the photon-magnon coupling strength and
+Kerr nonlinearity.",2206.09540v2
+2022-06-23,Anisotropic magnon damping by zero-temperature quantum fluctuations in ferromagnetic CrGeTe$_3$,"Spin and lattice are two fundamental degrees of freedom in a solid, and their
+fluctuations about the equilibrium values in a magnetic ordered crystalline
+lattice form quasiparticles termed magnons (spin waves) and phonons (lattice
+waves), respectively. In most materials with strong spin-lattice coupling
+(SLC), the interaction of spin and lattice induces energy gaps in the spin wave
+dispersion at the nominal intersections of magnon and phonon modes. Here we use
+neutron scattering to show that in the two-dimensional (2D) van der Waals
+honeycomb lattice ferromagnetic CrGeTe3, spin waves propagating within the 2D
+plane exhibit an anomalous dispersion, damping, and break-down of quasiparticle
+conservation, while magnons along the c axis behave as expected for a local
+moment ferromagnet. These results indicate the presence of dynamical SLC
+arising from the zero-temperature quantum fluctuations in CrGeTe3, suggesting
+that the observed in-plane spin waves are mixed spin and lattice quasiparticles
+fundamentally different from pure magnons and phonons.",2206.11962v1
+2022-07-07,Exciton-assisted low-energy magnetic excitations in a photoexcited Mott insulator on a square lattice,"The photoexcitation of a Mott insulator on a square lattice weakens the
+intensity of both single- and two-magnon excitations as observed in
+time-resolved resonant-inelastic X-ray scattering and time-resolved Raman
+scattering, respectively. However, the spectral changes in the low-energy
+regions below the magnons have not yet been clearly understood. To uncover the
+nature of the photoinduced low-energy magnetic excitations of the Mott
+insulator, we numerically investigate the transient magnetic dynamics in a
+photoexcited half-filled Hubbard model on a square lattice. After turning off a
+pump pulse tuned for an absorption edge, new magnetic signals clearly emerge
+well below the magnon energy in both single- and two-magnon excitations. We
+find that the low-energy excitations are predominantly created via excitonic
+states at the absorption edge. These exciton-assisted magnetic excitations may
+provide a possible explanation for the low-energy spectral weight in a recent
+time-resolved two-magnon Raman scattering experiment for insulating
+YBa$_2$Cu$_3$O$_{6.1}$.",2207.03141v2
+2022-08-19,Phononic-crystal cavity magnomechanics,"Establishing a way to control magnetic dynamics and elementary excitations
+(magnons) is crucial to fundamental physics and the search for novel phenomena
+and functions in magnetic solid-state systems. Electromagnetic waves have been
+developed as means of driving and sensing in magnonic and spintronics devices
+used in magnetic spectroscopy, non-volatile memory, and information processors.
+However, their millimeter-scale wavelengths and undesired cross-talk have
+limited operation efficiency and made individual control of densely integrated
+magnetic systems difficult. Here, we utilize acoustic waves (phonons) to
+control magnetic dynamics in a miniaturized phononic crystal micro-cavity and
+waveguide architecture. We demonstrate acoustic pumping of localized
+ferromagnetic magnons, where their back-action allows dynamic and
+mode-dependent modulation of phononic cavity resonances. The phononic crystal
+platform enables spatial driving, control and read-out of tiny magnetic states
+and provides a means of tuning acoustic vibrations with magnons. This
+alternative technology enhances the usefulness of magnons and phonons for
+advanced sensing, communications and computation architectures that perform
+transduction, processing, and storage of classical and quantum information.",2208.09105v1
+2022-08-23,Visualization of moiré magnons in monolayer ferromagnet,"Two-dimensional magnetic materials provide an ideal platform to explore
+collective many-body excitations associated with spin fluctuations. In
+particular, it should be feasible to explore, manipulate and ultimately design
+magnonic excitations in two-dimensional van der Waals magnets in a controllable
+way. Here we demonstrate the emergence of moir\'e magnon excitations, stemming
+from the interplay of spin-excitations in monolayer CrBr$_3$ and the moir\'e
+pattern stemming from the lattice mismatch with the underlying substrate. The
+existence of moir\'e magnons is further confirmed via inelastic quasiparticle
+interference, showing the appearance of a dispersion pattern correlated with
+the moir\'e length scale. Our results provide a direct visualization in
+real-space of the dispersion of moir\'e magnons, demonstrating the versatility
+of moir\'e patterns in creating emerging many-body excitations.",2208.10991v2
+2022-08-24,Stimulated amplification of propagating spin waves,"Spin-wave amplification techniques are key to the realization of magnon-based
+computing concepts. We introduce a novel mechanism to amplify spin waves in
+magnonic nanostructures. Using the technique of rapid cooling, we create a
+non-equilibrium state in excess of high-energy magnons and demonstrate the
+stimulated amplification of an externally seeded, propagating spin wave. Using
+an extended kinetic model, we qualitatively show that the amplification is
+mediated by an effective energy flux of high energy magnons into the low energy
+propagating mode, driven by a non-equilibrium magnon distribution.",2208.11455v2
+2022-09-08,Dominance of Electron-Magnon Scattering in Itinerant Ferromagnet Fe3GeTe2,"Fe3GeTe2 is a 2-dimensional van der Waals material exhibiting itinerant
+ferromagnetism upto 230 K. Here, we study aspects of scattering mechanism in
+Fe3Ge2Te2 single crystals via resistivity, magneto-transport and Hall effect
+measurements. The quadratic temperature dependence of electrical resistivity
+below the Curie temperature hints towards the dominance of electron-magnon
+scattering. A non-saturating positive magnetoresistance (MR) is observed at low
+temperatures when the magnetic field is applied parallel to the sample plane.
+The linear negative MR at high fields for T < TC corroborates to the
+suppression in magnon population due to the damping of spin waves. In the high
+temperature regime T > TC,MR can be described by the scattering from spin
+fluctuations using the model described by Khosla and Fischer. Isothermal Hall
+resistivity curves unveil the presence of anomalous Hall resistivity.
+Correlation between MR and side jump mechanism further reveals that the
+electron-magnon scattering is responsible for the side jump contribution to the
+anomalous Hall effect. Our results provide a clear understanding of the role of
+electron-magnon scattering on anomalous Hall effect that rules out its origin
+to be the topological band structure.",2209.03555v1
+2022-10-12,Quantum amplification of spin currents in cavity magnonics by a parametric drive induced long-lived mode,"Cavity-mediated magnon-magnon coupling can lead to a transfer of spin-wave
+excitations between two spatially separated magnetic samples. We enunciate how
+the application of a two-photon parametric drive to the cavity can lead to
+stark amplification in this transfer efficiency. The recurrent multiphoton
+absorption by the cavity opens up an infinite ladder of accessible energy
+levels, which can induce higher-order transitions within the magnon Fock space.
+This is reflected in a heightened spin-current response from one of the
+magnetic samples when the neighboring sample is coherently pumped. The
+enhancement induced by the parametric drive can be considerably high within the
+stable dynamical region. Specifically, near the periphery of the stability
+boundary, the spin current is amplified by several orders of magnitude. Such
+striking enhancement factors are attributed to the emergence of parametrically
+induced strong coherences precipitated by a long-lived mode. While
+contextualized in magnonics, the generality of the principle would allow
+applications to energy transfer between systems contained in parametric
+cavities.",2210.05898v1
+2022-10-13,Nonlocal drag by topological surface magnons in a pyrochlore ferromagnet,"The nontrivial topology of quasiparticle wavefunctions can manifest
+themselves in the form of observable surface states. This is now well
+established in electronic systems, with Dirac and Weyl semimetals bringing to
+fore the exotic nature of these topologically protected entities. Magnons -
+which refer to collective excitations of localized spins - offer another sector
+where many of these concepts could be realized. Here, we report magneto-thermal
+measurements on a pyrochlore ferromagnet which is theoretically predicted to
+host such topological magnons. It is demonstrated that the thermoelectric
+potential across a metal layer deposited on single crystalline specimens of
+Y$_2$V$_2$O$_7$ can be used to measure the magnon Hall effect. Moreover, a
+direct manifestation of topologically protected magnon surface states is
+observed - via the interfacial drag which these surface spin currents impose on
+the conduction electrons of the adjacent metallic layer.",2210.07058v1
+2022-11-24,Influence of non-local damping on magnon properties of ferromagnets,"We study the influence of non-local damping on magnon properties of Fe, Co,
+Ni and Fe$_{1-x}$Co$_{x}$ ($x=30\%,50\%$) alloys. The Gilbert damping parameter
+is typically considered as a local scalar both in experiment and in theoretical
+modelling. However, recent works have revealed that Gilbert damping is a
+non-local quantity that allows for energy dissipation between atomic sites.
+With the Gilbert damping parameters calculated from a state-of-the-art
+real-space electronic structure method, magnon lifetimes are evaluated from
+spin dynamics and linear response, where a good agreement is found between
+these two methods. It is found that non-local damping affects the magnon
+lifetimes in different ways depending on the system. Specifically, we find that
+in Fe, Co, and Ni the non-local damping decreases the magnon lifetimes, while
+in $\rm Fe_{70}Co_{30}$ and Fe$_{50}$Co$_{50}$ an opposite, non-local damping
+effect is observed, and our data show that it is much stronger in the former.",2211.13486v1
+2022-11-28,Spurious Symmetry Enhancement and Interaction-Induced Topology in Magnons,"Linear spin wave theory (LSWT) is the standard technique to compute the
+spectra of magnetic excitations in quantum materials. In this paper, we show
+that LSWT, even under ordinary circumstances, may fail to implement the
+symmetries of the underlying ordered magnetic Hamiltonian leading to spurious
+degeneracies. In common with pseudo-Goldstone modes in cases of quantum
+order-by-disorder these degeneracies tend to be lifted by magnon-magnon
+interactions. We show how, instead, the correct symmetries may be restored at
+the level of LSWT. In the process we give examples, supported by
+nonperturbative matrix product based time evolution calculations, where
+symmetries dictate that there should be a topological magnon gap but where LSWT
+fails to open up this gap. We also comment on possible spin split magnons in
+MnF$_2$ and similar rutiles by analogy to recently proposed altermagnets.",2211.15157v1
+2022-11-29,Ground states and magnonics in orthogonally-coupled symmetric all-antiferromagnetic junctions,"In this work, the rich ground-state structure of orthogonally-coupled
+symmetric all-antiferromagnetic junctions with easy-plane anisotropy is
+reported. Spin reorientation process rather than the traditional spin flop (SF)
+occurs, resulting in a novel phase in which N\'{e}el vectors preserve the
+mirror-reflection symmetry (termed as ``MRS phase""). The phase transitions
+between SF and MRS phases can be either the first- or second-order. After
+disturbed by external stimuli, magnons with different parities emerge. For
+in-plane dc fields, no couplings between magnons occur. When dc fields become
+oblique, coherent couplings between magnons with opposite parity emerge,
+leading to anticrossings in resonance frequencies. However, self-hybridization
+among magnons with the same parity never happens. More interestingly, spin
+waves based on MRS phase are linearly polarized and their polarization
+directions can be fine controlled.",2211.16063v1
+2022-12-04,Renormalization of antiferromagnetic magnons by superconducting condensate and quasiparticles,"The ability to modify and tune the spin-wave dispersion is one of the most
+important requirements for engineering of magnonic networks. In this study we
+demonstrate the promise of synthetic thin-film hybrids composed of an
+antiferromagnetic insulator (AF) and a normal (N) or superconducting (S) metal
+for tuning and modifying the spin-wave dispersion in antiferromagnetic
+insulators. The key ingredient is the uncompensated magnetic moment at the
+AF/S(N) interface, which induces an effective exchange field in the adjacent
+metal via the interface exchange interaction. The exchange field spin polarizes
+quasiparticles in the metal and induces spinful triplet Cooper pairs screening
+the magnon. The quasiparticle and Cooper pair polarization renormalizes the
+magnon dispersion. The renormalization results in the splitting of the
+otherwise degenerate AF magnon modes with no need to apply a magnetic field. It
+is also proposed that measurements of the renormalized dispersion relations can
+provide the amplitude of the effective exchange field induced by the AF in the
+adjacent metal.",2212.01831v2
+2022-12-07,"Observation of magnon bound states in the long-range, anisotropic Heisenberg model","Over the recent years coherent, time-periodic modulation has been established
+as a versatile tool for realizing novel Hamiltonians. Using this approach,
+known as Floquet engineering, we experimentally realize a long-ranged,
+anisotropic Heisenberg model with tunable interactions in a trapped ion quantum
+simulator. We demonstrate that the spectrum of the model contains not only
+single magnon excitations but also composite magnon bound states. For the
+long-range interactions with the experimentally realized power-law exponent,
+the group velocity of magnons is unbounded. Nonetheless, for sufficiently
+strong interactions we observe bound states of these unconventional magnons
+which possess a non-diverging group velocity. By measuring the configurational
+mutual information between two disjoint intervals, we demonstrate the
+implications of the bound state formation on the entanglement dynamics of the
+system. Our observations provide key insights into the peculiar role of
+composite excitations in the non-equilibrium dynamics of quantum many-body
+systems.",2212.03899v1
+2022-12-12,Slow inter-minima relaxation and its consequence for BEC of magnons,"Two recent articles of the Munster University experimental team led by S.O.
+Demokritov displayed several important facts related to the Bose-Einstein
+condensation of magnons (BECM) under permanent pumping first discovered in
+2006. They contradicted existing theories of this phenomenon, which predict the
+attractive interaction between magnons and strong spontaneous violation of the
+reflection symmetry. In this article, we show that these theories implicitly
+assumed all relaxation processes to be fast compared with the lifetime of the
+magnons, whereas one of them -- relaxation between two minima of energy -- is
+slow. We classify processes responsible for the inter-minima relaxation and
+present their analytic theory. We analyze how the slow inter-minima relaxation
+modifies the anticipated properties of a ferromagnet with the magnon
+condensate.",2212.06085v2
+2023-02-13,Zero-frequency chiral magnonic edge states protected by non-equilibrium topology,"Topological bosonic excitations must, in contrast to their fermionic
+counterparts, appear at finite energies. This is a key challenge for magnons,
+as it prevents straightforward excitation and detection of
+topologically-protected magnonic edge states and their use in magnonic devices.
+In this work, we show that in a non-equilibrium state, in which the
+magnetization is pointing against the external magnetic field, the
+topologically-protected chiral edge states in a magnon Chern insulator can be
+lowered to zero frequency, making them directly accessible by existing
+experimental techniques. We discuss the spin-orbit torque required to stabilize
+this non-equilibrium state, and show explicitly using numerical
+Landau-Lifshitz-Gilbert simulations that the edge states can be excited with a
+microwave field. Finally, we consider a propagating spin wave spectroscopy
+experiment, and demonstrate that the edge states can be directly detected.",2302.06597v3
+2023-02-16,Coherent feedback control of quantum correlations in cavity magnomechanical system with magnon squeezing,"We address a scheme to enhance the quantum correlations in cavity
+opto-magnomechanical system by using the coherent feedback loop in the presence
+of magnon squeezing. The proposed coherent feedback-control allows a
+significant enhancement of the entanglement of three bipartite subsystems,
+i.e., photon-phonon, photon-magnon and phonon-magnon. We also study the
+Einstein-Podolsky-Rosen steering and one-way steering in the presence of
+thermal effects without imposing additional conditions of asymmetric losses or
+noises in the subsystems. Furthermore, we investigate the sensitiveness of the
+scheme to the magnon squeezing, and its performance in non-ideal situations in
+which losses and noises are taken into account.",2302.08567v2
+2023-03-02,Unidirectional Microwave Transduction with Chirality Selected Short-Wavelength Magnon Excitations,"Nonreciprocal magnon propagation has recently become a highly potential
+approach of developing chip-embedded microwave isolators for advanced
+information processing. However, it is challenging to achieve large
+nonreciprocity in miniaturized magnetic thin-film devices because of the
+difficulty of distinguishing propagating surface spin waves along the opposite
+directions when the film thickness is small. In this work, we experimentally
+realize unidirectional microwave transduction with sub-micron-wavelength
+propagating magnons in a yttrium iron garnet (YIG) thin film delay line. We
+achieve a non-decaying isolation of 30 dB with a broad field-tunable band-pass
+frequency range up to 14 GHz. The large isolation is due to the selection of
+chiral magnetostatic surface spin waves with the Oersted field generated from
+the coplanar waveguide antenna. Increasing the geometry ratio between the
+antenna width and YIG thickness drastically reduces the nonreciprocity and
+introduces additional magnon transmission bands. Our results pave the way for
+on-chip microwave isolation and tunable delay line with short-wavelength
+magnonic excitations.",2303.00936v1
+2023-03-13,Anti-helical edge magnons in patterned antiferromagnetic thin film,"Helical edge states in topological insulators give counterpropagating spin
+current on the two parallel edges. We here propose anti-helical edge states of
+magnons in patterned antiferromagnetic thin films, which host copropagating
+spin current on the two parallel edges, where the two magnon modes with
+opposite chirality act like the spin. The embedded heavy metal dot array in the
+thin film induces interfacial Dzyaloshinskii-Moriya interactions (iDMIs),
+drives the magnon bands into nontrivial topological phases, characterized by
+spin Chern number. The resulting helical edge modes lead to spin current with
+the direction dependent on the sign of iDMI parameter. In a strip geometry, we
+combine two subsystems with two embedded metal dot arrays, which give opposite
+iDMI parameters. Anti-helical edge states emerge, compensated by the
+counterpropagating bulk confined states. Helical and anti-helical edge states
+are verified by the micromagnetic simulations. Our work is quite helpful in the
+field of magnon spintronics based on antiferromagnets.",2303.06830v1
+2023-03-27,Entangling cavity-magnon polaritons by interacting with phonons,"We show how to entangle two cavity-magnon polaritons (CMPs) formed by two
+strongly coupled microwave cavity and magnon modes. This is realized by
+introducing vibration phonons, via magnetostriction, into the system that are
+dispersively coupled to the magnon mode. Stationary entanglement between two
+CMPs can be achieved when they are respectively resonant with the two sidebands
+of the drive field scattered by the phonons, and when the proportions of the
+cavity and magnon modes in the two polaritons are appropriately chosen. The
+entangled CMPs can improve the detection sensitivity in the dark matter search
+experiments using CMPs, and can also lead to the emission of
+frequency-entangled microwave photons.",2303.15217v5
+2023-04-18,Linear scaling relationship of Néel temperature and dominant magnons in pyrochlore ruthenates,"We present a systematic Raman spectroscopy study on a series of pyrochlore
+ruthenates, a system which is not yet clearly settled on its magnetic origin
+and structure. Apart from the Raman-active phonon modes, new peaks that appear
+in the energy range of 15 - 35 meV below the N\'{e}el temperature are assigned
+as one-magnon modes. The temperature evolution of one-magnon modes displays no
+significant thermal dependence in mode frequencies while the intensities
+decrease monotonically. Remarkably, one-magnons from all compounds show similar
+characteristics with a single dominant peak at lower energy and weaker side
+peaks at a couple of meV higher energy. Most importantly, we uncover a striking
+proportionality between the dominant magnon mode energies and the N\'{e}el
+temperature values. Our results suggest the Ru ions may have similar or the
+same magnetic phase in all pyrochlore ruthenates of our study. We have thus
+found an avenue for directly tuning the magnetic exchange interaction by the
+selection of the $A$-site ion.",2304.08815v2
+2023-04-19,Cavity magnomechanical coupling with coupled magnon modes in a synthetic antiferromagnet,"On-chip cavity magnomechanics is an emerging field exploring acoustic and
+magnonic functionalities of various ferromagnetic materials and structures
+using strongly confined phonons. It is expected that such cavity magnomechanics
+can be extended to multilayer ferromagnets, especially synthetic
+antiferromagnets (SAFs) that exhibit zero net magnetization through interlayer
+exchange coupling. However, the conventional theoretical framework for a single
+ferromagnet cannot be used directly because of the antiferromagnetic
+magnetization dynamics associated with the interlayer exchange coupling. In
+this paper, we theoretically investigate phonon-magnon coupling with a
+three-layer SAF. Our formulation of the phonon-magnon coupling constants
+reveals that the acoustic (optical) magnon mode dominantly couples to the
+cavity phonon when the magnetization angles in the two ferromagnetic layers are
+antiparallel (orthogonal). Moreover, numerical calculations including the
+effects of dipole-dipole interactions and in-plane uniaxial magnetic anisotropy
+allow us to predict phonon frequency shifts and linewidth broadening that can
+be detected in experiments. These theoretical insights would greatly help us to
+make a strategy for bringing the system into the strong coupling regime and to
+devise novel control protocols in analogy to cavity quantum electrodynamics and
+cavity optomechanics.",2304.09458v2
+2023-05-01,Theoretical analysis of multi-magnon excitations in resonant inelastic x-ray scattering spectra of two-dimensional antiferromagnets,"Resonant inelastic x-ray spectroscopy (RIXS) has emerged as an important tool
+to explore magnetism in two-dimensional (2D) antiferromagnet realized in
+strongly correlated materials. Here we consider the Heisenberg model with
+nearest and next nearest neighbor hopping relevant to the study of magnetic
+excitations of the cuprate family. We compute the RIXS cross-section within the
+ultra-short core-hole lifetime (UCL) expansion of the Kramers-Heisenberg
+scattering amplitude that allows perturbative solution within linear spin wave
+theory (LSWT). We report detailed results for both spin-conserving and
+non-conserving channels. Apart from the widely discussed single magnon and
+bimagnon contributions, we show that three-magnon contributions in the spin
+non-conserving channel are useful to explain certain features of the RIXS data
+for two-dimensional cuprates. We confirm the qualitative correctness of the
+LSWT conclusions for the three-magnon excitation with exact diagonalization.
+Our work puts constraints on the dispersion of the three-magnon in the
+Brillouin zone, opening new avenues for realizing higher modes of
+quasiparticles using RIXS.",2305.00802v1
+2023-05-01,Coherent and incoherent magnons induced by strong ultrafast demagnetization in thin permalloy films,"Understanding spin dynamics on femto- and picosecond timescales offers new
+opportunities for faster and more efficient spintronic devices. Here, we
+experimentally investigate the coherent spin dynamics after ultrashort laser
+excitation by time-resolved magneto optical Kerr effect (TR-MOKE) in thin
+Ni80Fe20 films. We provide a detailed study of the magnetic field and pump
+fluence dependence of the coherent precessional dynamics. We show that the
+coherent precession lifetime increases with the applied external magnetic field
+which cannot be understood by viscous Gilbert damping of the coherent magnons.
+Instead, it can be explained by nonlinear magnon interactions and by the change
+in the fraction of incoherent magnons. This interpretation is in agreement with
+the observed trends of the coherent magnon amplitude and lifetime as a function
+of the exciting laser fluence. Our results provide a new insight into the
+magnetization relaxation processes in ferromagnetic thin films, which is of
+great importance for further spintronic applications.",2305.00814v2
+2023-05-19,Quantum transduction of superconducting qubit in electro-optomechanical and electro-optomagnonical system,"We study the quantum transduction of a superconducting qubit to an optical
+photon in electro-optomechanical and electro-optomagnonical systems. The
+electro-optomechanical system comprises a flux-tunable transmon qubit coupled
+to a suspended mechanical beam, which then couples to an optical cavity.
+Similarly, in an electro-optomagnonical system, a flux-tunable transmon qubit
+is coupled to an optical whispering gallery mode via a magnon excitation in a
+YIG ferromagnetic sphere. In both systems, the transduction process is done in
+sequence. In the first sequence, the qubit states are encoded in coherent
+excitations of phonon/magnon modes through the phonon/magnon-qubit interaction,
+which is non-demolition in the qubit part. We then measure the phonon/magnon
+excitations, which reveal the qubit states, by counting the average number of
+photons in the optical cavities. The measurement of the phonon/magnon
+excitations can be performed at a regular intervals of time.",2305.11629v1
+2023-05-19,Antiferromagnetic-ferromagnetic homostructures with Dirac magnons in van der Waals magnet CrI$_3$,"Van der Waals (vdW) Dirac magnon system CrI$_3$, a potential host of
+topological edge magnons, orders ferromagnetically (FM) (T$_C=61$ K) in the
+bulk, but antiferromagnetic (AFM) order has been observed in nanometer thick
+flakes, attributed to monoclinic (M) type stacking. We report neutron
+scattering measurements on a powder sample where the usual transition to the
+rhombohedral (R) phase was inhibited for a majority of the structure. Elastic
+measurements (and the opening of a hysteresis in magnetization data on a
+pressed pellet) showed that an AFM transition is clearly present below $\sim$50
+K, coexisting with the R-type FM order. Inelastic measurements showed a
+decrease in magnon energy compared to the R phase, consistent with a smaller
+interlayer magnetic coupling in M-type stacking. A gap remains at the Dirac
+point, suggesting that the same nontrivial magnon topology reported for the R
+phase may be present in the M phase as well.",2305.11750v1
+2023-06-08,Resolving nonclassical magnon composition of a magnetic ground state via a qubit,"Recently gained insights into equilibrium squeezing and entanglement harbored
+by magnets point towards exciting opportunities for quantum science and
+technology, while concrete protocols for exploiting these are needed. Here, we
+theoretically demonstrate that a direct dispersive coupling between a qubit and
+a noneigenmode magnon enables detecting the magnonic number states' quantum
+superposition that forms the ground state of the actual eigenmode -
+squeezed-magnon - via qubit excitation spectroscopy. Furthermore, this unique
+coupling is found to enable control over the equilibrium magnon squeezing and a
+deterministic generation of squeezed even Fock states via the qubit state and
+its excitation. Our work demonstrates direct dispersive coupling to
+noneigenmodes, realizable in spin systems, as a general pathway to exploiting
+the equilibrium squeezing and related quantum properties thereby motivating a
+search for similar realizations in other platforms.",2306.05065v2
+2023-07-10,Realization of an extremely anisotropic Heisenberg magnet in Rydberg atom arrays,"Strong mutual interactions correlate elementary excitations of quantum matter
+and plays a key role in a range of emergent phenomena, from binding and
+condensation to quantum thermalization and many-body localization. Here, we
+employ a Rydberg quantum simulator to experimentally demonstrate strongly
+correlated spin transport in anisotropic Heisenberg magnets, where the
+magnon-magnon interaction can be tuned two orders of magnitude larger than the
+magnon hopping strength. In our approach, the motion of magnons is controlled
+by an induced spin-exchange interaction through Rydberg dressing, which enables
+coherent transport of a single Rydberg excitation across a chain of
+ground-state atoms. As the most prominent signature of a giant anisotropy, we
+show that nearby Rydberg excitations form distinct types of magnon bound
+states, where a tightly bound pair exhibits frozen dynamics in a fragmented
+Hilbert space, while a loosely bound pair propagates and establishes
+correlations beyond a single lattice site. Our scheme complements studies using
+resonant dipole-dipole interactions between Rydberg states, and opens the door
+to exploring quantum thermodynamics with ultrastrong interactions and kinetic
+constraints.",2307.04342v1
+2023-07-20,Magnon Spin Photogalvanic Effect in Collinear Ferromagnets,"We propose a spin photogalvanic effect of magnons with broken inversion
+symmetry. The dc spin photocurrent is generated via the Aharonov-Casher effect,
+which includes the Drude, Berry curvature dipole, shift, injection, and
+rectification components with distinct quantum geometric origin. Based on a
+symmetry classification, we uncover that there exist linearly polarized (LP)
+magnon spin photocurrent responses in the breathing kagome-lattice ferromagnet
+with Dzyaloshinskii-Moriya interaction, and the circularly polarized (CP)
+responses due to the symmetry breaking by applying a uniaxial strain. We
+address that the topological phase transitions can be characterized by the spin
+photocurrents. This study presents a deeper insight into the nonlinear
+responses of light-magnon interactions, and suggests a possible way to generate
+and control the magnon spin current in real materials.",2307.10882v1
+2023-08-30,Chiral cavity-magnonic system for the unidirectional emission of a tunable squeezed microwave field,"Unidirectional photon emission is crucial for constructing quantum networks
+and realizing scalable quantum information processing. In the present work an
+efficient scheme is developed for the unidirectional emission of a tunable
+squeezed microwave field. Our scheme is based on a chiral cavity magnonic
+system, where a magnon mode in a single-crystalline yttrium iron garnet (YIG)
+sphere is selectively coupled to one of the two degenerate rotating microwave
+modes in a torus-shaped cavity with the same chirality. With the YIG sphere
+driven by a two-color Floquet field to induce sidebands in the magnon-photon
+coupling, we show that the unidirectional emission of a tunable squeezed
+microwave field can be generated via the assistance of the dissipative magnon
+mode and a waveguide. Moreover, the direction of the proposed one-way emitter
+can be controlled on demand by reversing the biased magnetic field. Our work
+opens up an avenue to create and manipulate one-way nonclassical microwave
+radiation field and could find potential quantum technological applications.",2308.15826v1
+2023-09-12,Anisotropy-assisted magnon condensation in ferromagnetic thin films,"We theoretically demonstrate that adding an easy-axis magnetic anisotropy
+facilitates magnon condensation in thin yttrium iron garnet (YIG) films.
+Dipolar interactions in a quasi-equilibrium state stabilize room-temperature
+magnon condensation in YIG. Even though the out-of-plane easy-axis anisotropy
+generally competes with the dipolar interactions, we show that adding such
+magnetic anisotropy may even assist the generation of the magnon condensate
+electrically via the spin transfer torque mechanism. We use analytical
+calculations and micromagnetic simulations to illustrate this effect. Our
+results may explain the recent experiment on Bi-doped YIG and open a pathway
+toward applying current-driven magnon condensation in quantum spintronics.",2309.05982v3
+2023-11-09,Magnon-phonon coupling of synthetic antiferromagnets in a surface acoustic wave cavity resonator,"We use a surface acoustic wave (SAW) cavity resonator to study the coupling
+of acoustic magnons in a synthetic antiferromagnet (SAF) and the phonons
+carried by SAWs. The SAF is composed of a CoFeB/Ru/CoFeB trilayer and the
+scattering matrix of the SAW resonator is studied to assess the coupling. We
+find that the spectral linewidth of the SAW resonator is modulated when the
+frequency of the excited magnons approaches the SAW resonance frequency.
+Moreover, the linewidth modulation varies with the magnitude and orientation of
+the external magnetic field. Such change in the spectral linewidth can be well
+reproduced using macrospin-like model calculations. From the model analyses, we
+estimate the magnon-phonon coupling strength to be $\sim$15.6 MHz at a SAW
+resonance frequency of 1.8 GHz: the corresponding magnomechanical cooperativity
+is $\sim$0.66. As the spectral shape hardly changes in a CoFeB single layer
+reference sample under the same experimental condition, these results show that
+SAF provides an ideal platform to study magnon-phonon coupling in a SAW cavity
+resonator.",2311.05275v1
+2024-02-02,Entanglement enhancement of two different magnon modes via nonlinear effect in cavity magnomechanics,"We present a scheme to enhance two different magnon modes entanglement in
+cavity magnomechanics via nonlinear effect. The scheme demonstrated that
+nonlinear effects enhance entanglement of the two magnon modes. Moreover, the
+entanglement of the two magnon modes is also significantly enhanced by
+microwave parametric amplification (PA) and magnon self-Kerr nonlinearity. Not
+only dose nonlinear effect enhances the strength of entanglement, but it also
+increases the robustness of entanglement against temperature. Our proposed
+scheme plays an important role in the research of fundamental theories of
+quantum physics and quantum information processing theory.",2402.01150v1
+2024-02-05,Controlling magnon-photon coupling in a planar geometry,"The tunability of magnons enables their interaction with various other
+quantum excitations, including photons, paving the route for novel hybrid
+quantum systems. Here, we study magnon-photon coupling using a high-quality
+factor split-ring resonator and single-crystal yttrium iron garnet (YIG)
+spheres at room temperature. We investigate the dependence of the coupling
+strength on the size of the sphere and find that the coupling is stronger for
+spheres with a larger diameter as predicted by theory. Furthermore, we
+demonstrate strong magnon-photon coupling by varying the position of the YIG
+sphere within the resonator. Our experimental results reveal the expected
+correlation between the coupling strength and the rf magnetic field. These
+findings demonstrate the control of coherent magnon-photon coupling through the
+theoretically predicted square-root dependence on the spin density in the
+ferromagnetic medium and the magnetic dipolar interaction in a planar
+resonator.",2402.03071v1
+2024-03-05,Magnon kinetic theory of the antiferromagnetic Hanle effect,"Motivated by the recently discovered magnonic Hanle effect in an insulating
+antiferromagnet [Wimmer et al., Phys. Rev. Lett. 125, 247204 (2020)], we
+develop a spin transport theory based on low-energy waves of antiferromagnetic
+N\'eel order. These waves have two polarizations, which we describe in analogy
+to optics using the Stokes vector on the Poincar\'e sphere. We find that the
+polarization, which encodes the magnon spin angular momentum, changes
+periodically with a frequency that is nonlinear in the magnetic field. This
+explains the observed asymmetry in the Hanle signal as a function of the
+magnetic field, along with other salient experimental features. By providing an
+energy-resolved description of the spin injection, our theory combines the
+kinetic transport of magnons with the coherent dynamics of their polarization
+in an intuitive way. This opens a general perspective on a coherent control of
+magnonic spin density in collinear antiferromagnets.",2403.03358v1
+2024-03-11,Magnon bands and transverse transport in a proposed two-dimensional $Cu_2F_5$ ferrimagnet,"The copper fluoride $Cu_2F_5$ is a proposed stable compound that can be seen
+as a layered magnetic lattice of $S=1$ and $S=1/2$ sites, corresponding to
+copper ions. Intending to cast light on the transport properties of
+ferrimagnetic magnons, we use the linear spin wave approach to study the magnon
+band structure of the 2D lattice in a ferrimagnetic off-plane order, as well as
+the transverse transport of magnons in the crystal bulk. That transverse
+(Hall-like) transport can be induced by a magnetic field or temperature
+gradient, and within the linear response theory is generated by the Berry
+curvature of the eigenstates. As in most of the cases for magnons, the Berry
+curvature here is related to Dzyaloshinskii-Moriya interactions between
+next-near-neighbors. The band structure of the system is non-degenerate and the
+transport coefficients are non-null. We also determine the condition for two
+transport coefficients to change sign in response to temperature.",2403.07169v1
+2024-04-02,Understanding spin currents from magnon dispersion and polarization: Spin-Seebeck effect and neutron scattering study on Tb3Fe5O12,"Magnon spin currents in the ferrimagnetic garnet Tb3Fe5O12 with 4f electrons
+were examined through the spin-Seebeck effect and neutron scattering
+measurements. The compound shows a magnetic compensation, where the
+spin-Seebeck signal reverses above and below Tcomp = 249.5(4) K. Unpolarized
+neutron scattering unveils two major magnon branches with finite energy gaps,
+which are well-explained in the framework of spin-wave theory. Their
+temperature dependencies and the direction of the precession motion of magnetic
+moments, i.e. magnon polarization, defined using polarized neutrons, explain
+the reversal at Tcomp and decay of the spin-Seebeck signals at low
+temperatures. We illustrate an example that momentum- and energy-resolved
+microscopic information is a prerequisite to understanding the magnon spin
+current.",2404.01603v1
+1995-11-15,Resonant Two-Magnon Raman Scattering in Cuprate Antiferromagnetic Insulators,"We present results of low-temperature two-magnon resonance Raman excitation
+profile measurements for single layer Sr_2CuO_2Cl_2 and bilayer YBa_2Cu_3O_{6 +
+\delta} antiferromagnets over the excitation region from 1.65 to 3.05 eV. These
+data reveal composite structure of the two-magnon line shape and strong
+nonmonotic dependence of the scattering intensity on excitation energy. We
+analyze these data using the triple resonance theory of Chubukov and Frenkel
+(Phys. Rev. Lett., 74, 3057 (1995)) and deduce information about magnetic
+interaction and band parameters in these materials.",9511080v1
+1997-10-15,Softening and Broadening of the Zone Boundary Magnons in Pr0.63Sr0.37MnO3,"We have studied the spin dynamics in Pr$_{0.63}$Sr$_{0.37}$MnO$_3$ above and
+below the Curie temperature $T_C=301$ K. Three distinct new features have been
+observed: a softening of the magnon dispersion at the zone boundary for
+$T<T_C$, significant broadening of the zone boundary magnons as $T\to T_C$, and
+no evidence for residual spin-wave like excitations just above $T_C$. The
+results are inconsistent with double exchange models that have been
+successfully applied to higher $T_C$ samples, indicating an evolution of the
+spin system with decreasing $T_C$.",9710157v1
+1998-06-06,Magnons and skyrmions in fractional Hall ferromagnets,"Recent experiments have established a qualitative difference between the
+magnetization temperature-dependences $M(T)$ of quantum Hall ferromagnets at
+integer and fractional filling factors. We explain this difference in terms of
+the relative energies of collective magnon and particle-hole excitations in the
+two cases. Analytic calculations for hard-core model systems are used to
+demonstrate that, in the fractional case, interactions suppress the
+magnetization at finite temperatures and that particle-hole excitations rather
+than long-wavelength magnons control $M(T)$ at low $T$.",9806087v1
+1998-07-13,Magnetic Properties of (VO)_2P_2O_7 from Frustrated Interchain Coupling,"Neutron-scattering experiments on (VO)_2P_2O_7 reveal both a gapped magnon
+dispersion and an unexpected, low-lying second mode. The proximity and
+intensity of these modes suggest a frustrated coupling between the alternating
+spin chains. We deduce the minimal model containing such a frustration, and
+show that it gives an excellent account of the magnon dispersion, static
+susceptibility and electron spin resonance absorption. We consider two-magnon
+states which bind due to frustration, and demonstrate that these may provide a
+consistent explanation for the second mode.",9807186v2
+1998-08-10,Instability of antiferromagnetic magnons in strong fields,"We predict that spin-waves in an ordered quantum antiferromagnet (AFM) in a
+strong magnetic field become unstable with respect to spontaneous two-magnon
+decays. At zero temperature, the instability occurs between the threshold field
+$H^*$ and the saturation field $H_c$. As an example, we investigate the
+high-field dynamics of a Heisenberg antiferromagnet on a square lattice and
+show that the single-magnon branch of the spectrum disappears in the most part
+of the Brillouin zone.",9808100v2
+1998-08-31,Magnon Wave-function and Impurity Effects in S=1 Antiferromagnetic Chains: A Large-n Approach,"A large-n approximation to the S=1 antiferromagnetic chain, using the
+symmetric tensor representation and its conjugate, is developed to order 1/n in
+order to calculate the magnon wave-function and to study the effect of
+modifying the exchange coupling from J to J' on a single link. It is shown that
+a magnon boundstate exists below the Haldane gap for arbitrarily small negative
+J'-J but only above a certain critical value of J'-J for positive values. In
+the former case the binding energy vanishes as the square of (J-J').",9808345v1
+1999-05-04,Quantum spin ladder with dynamic phonons. Bound states of magnons and phonons,"We consider the two-chain Heisenberg ladder with antiferromagnetic
+interactions. Our approach is based on the description of spin excitations as
+triplets above a strong-coupling singlet ground state. It is shown that
+interaction with dynamic phonons drastically changes the dispersion of the
+elementary triplet excitation (magnon) and the spin structure factor. It is
+also shown that a new triplet excitation appears in the spectrum: the bound
+state of a magnon and a phonon.",9905030v1
+2000-01-31,Magnon dispersions in quantum Heisenberg ferrimagnetic chains at zero temperature,"Within the Dyson-Maleev boson formalism, we study the zero-temperature magnon
+dispersions in a family of one-dimensional quantum Heisenberg ferrimagnets
+composed of two different spins $(S_1,S_2)$ in the elementary cell. It is shown
+that the spin-wave theory can produce precise quantitative results for the
+low-energy excitations. The spin-stiffness constant $\rho_s$ and the optical
+magnon gap $\Delta$ of different $(S_1,S_2)$ ferrimagnetic systems are
+calculated, respectively, to second and third order in the quasiparticle
+interaction. The spin-wave results are compared with available numerical
+estimates.",0001441v1
+2000-10-26,Magnon-assisted Andreev reflection in a ferromagnet-superconductor junction,"We study subgap transport in a ferromagnet-superconductor junction at low
+temperature due to Andreev reflection. The mismatch of spin polarized current
+in the ferromagnet and spinless current in the superconductor results in an
+additional contact resistance which can be reduced by magnon emission in the
+ferromagnet. Using the s-f model and focusing on half-metallic ferromagnets, we
+calculate the corresponding nonlinear contribution to the current which is
+asymmetric with respect to the sign of the bias voltage and is related to the
+density of states of magnons in the ferromagnet.",0010421v1
+2001-08-01,Order from disorder: Quantum spin gap in magnon spectra of LaTiO_3,"A theory of the anisotropic superexchange and low energy spin excitations in
+a Mott insulator with t_{2g} orbital degeneracy is presented. We observe that
+the spin-orbit coupling induces frustrating Ising-like anisotropy terms in the
+spin Hamiltonian, which invalidate noninteracting spin wave theory. The
+frustration of classical states is resolved by an order from disorder
+mechanism, which selects a particular direction of the staggered moment and
+generates a quantum spin gap. The theory explains well the observed magnon gaps
+in LaTiO_3. As a test case, a specific prediction is made on the splitting of
+magnon branches at certain momentum directions.",0108016v2
+2001-12-13,Magnon softening and damping in the ferromagnetic manganites due to orbital correlations,"We present a theory for spin excitations in ferromagnetic metallic manganites
+and demonstrate that orbital fluctuations have strong effects on the magnon
+dynamics in the case these compounds are close to a transition to an orbital
+ordered state. In particular we show that the scattering of the spin
+excitations by low-lying orbital modes with cubic symmetry causes both the
+magnon softening and damping observed experimentally.",0112252v2
+2002-02-26,Magnetothermopower and magnon-assisted transport in ferromagnetic tunnel junctions,"We present a model of the thermopower in a mesoscopic tunnel junction between
+two ferromagnetic metals based upon magnon-assisted tunneling processes. In our
+model, the thermopower is generated in the course of thermal equilibration
+between two baths of magnons, mediated by electrons. We predict a particularly
+large thermopower effect in the case of a junction between two half-metallic
+ferromagnets with antiparallel polarizations, $S_{AP} \sim - (k_B/e)$, in
+contrast to $S_{P} \approx 0$ for a parallel configuration.",0202475v1
+2002-04-17,Inelastic neutron scattering signal from deconfined spinons in a fractionalized antiferromagnet,"We calculate the contribution of deconfined spinons to inelastic neutron
+scattering (INS) in the fractionalized antiferromagnet (AF*), introduced
+elsewhere. We find that the presence of free spin-1/2 charge-less excitations
+leads to a continuum INS signal above the Neel gap. This signal is found above
+and in addition to the usual spin-1 magnon signal, which to lowest order is the
+same as in the more conventional confined antiferromagnet. We calculate the
+relative weights of these two signals and find that the spinons contribute to
+the longitudinal response, where the magnon signal is absent to lowest order.
+Possible higher-order effects of interactions between magnons and spinons in
+the AF* phase are also discussed.",0204382v1
+2002-05-02,Magnon Dispersion in the Field-Induced Magnetically Ordered Phase of TlCuCl3,"The magnetic properties of the interacting dimer system TlCuCl3 are
+investigated within a bond-operator formulation. The observed field-induced
+staggered magnetic order perpendicular to the field is described as a Bose
+condensation of magnons which are linear combinations of dimer singlet and
+triplet modes. This technique accounts for the magnetization curve and for the
+field dependence of the magnon dispersion curves observed by high-field neutron
+scattering measurements.",0205052v2
+2002-05-06,High-energy magnon dispersion in the half-filled Hubbard model: A comparison with La$_2$CuO$_4$,"We use quantum Monte Carlo methods and single-mode approximation to study the
+magnon dispersion in the 2D half-filled Hubbard and phonon-coupled Heisenberg
+models. We find that in the Hubbard model with $U/t< 8$, high-energy magnon
+dispersion is similar to those observed in inelastic neutron scattering
+experiments in ${La}_2{CuO}_4$. On the other hand, our studies of a 2D
+Heisenberg model coupled to dynamic optical bond phonons, fails to reproduce
+the experimental dispersion. These results can be interpreted as evidence for
+intermediate $U/t$ and charge fluctuations in the cuprate materials.",0205107v1
+2003-10-07,One dimensional gapless magnons in a single anisotropic ferromagnetic nanolayer,"Gapless magnons in a plane ferromagnet with normal axis anisotropy are shown
+to exist besides the usual gapped modes that affect spin dependent transport
+properties only above a finite temperature. These magnons are one dimensional
+objects, in the sense that they are localized inside the domain walls that form
+in the film. They may play an essential role in the spin dependent scattering
+processes even down to very low temperatures.",0310159v1
+2004-04-10,Nuclear Spin-Lattice Relaxation in One-Dimensional Heisenberg Ferrimagnets: Three-Magnon versus Raman Processes,"Nuclear spin-lattice relaxation in one-dimensional Heisenberg ferrimagnets is
+studied by means of a modified spin-wave theory. We consider the second-order
+process, where a nuclear spin flip induces virtual spin waves which are then
+scattered thermally via the four-magnon exchange interaction, as well as the
+first-order process, where a nuclear spin directly interacts with spin waves
+via the hyperfine interaction. We point out a possibility of the three-magnon
+relaxation process predominating over the Raman one and suggest model
+experiments.",0404243v2
+2004-10-08,Quasiparticle excitations in frustrated antiferromagnets,"We have computed the quasiparticle wave function corresponding to a hole
+injected in a triangular antiferromagnet. We have taken into account
+multi-magnon contributions within the self consistent Born approximation. We
+have found qualitative differences, under sign reversal of the integral
+transfer t, regarding the multi-magnon components and the own existence of the
+quasiparticle excitations. Such differences are due to the subtle interplay
+between magnon-assisted and free hopping mechanisms. We conclude that the
+conventional quasiparticle picture can be broken by geometrical frustration
+without invoking spin liquid phases.",0410209v1
+2005-04-26,Two-magnon excitations observed by neutron scattering in the two-dimensional spin-5/2 Heisenberg antiferromagnet Rb2MnF4,"The low-temperature magnetic excitations of the two-dimensional spin-5/2
+square-lattice Heisenberg antiferromagnet Rb2MnF4 have been probed using pulsed
+inelastic neutron scattering. In addition to dominant sharp peaks identified
+with one-magnon excitations, a relatively weak continuum scattering is also
+observed at higher energies. This is attributed to neutron scattering by pairs
+of magnons and the observed intensities are consistent with predictions of spin
+wave theory.",0504684v1
+2005-08-17,Magnonic Crystal Theory of the Spin-Wave Frequency Gap in Low-Doped $La_{1-x}Ca_{x}MnO_{3}$ Manganites,"A theory of three-dimensional (3D) hypothetical magnonic crystal (conceived
+as the magnetic counterpart of the well-known photonic crystal) is developed
+and applied to explain the existence of a spin-wave frequency gap recently
+revealed in low-doped manganites $La_{1-x}Ca_{x}MnO_{3}$ by neutron scattering.
+A successful confrontation with the experimental results allows us to formulate
+a working hypothesis that certain manganites could be regarded as 3D magnonic
+crystals existing in nature.",0508389v1
+2005-08-17,Magnetic Composites: Magnonic Excitations vs. Three-Dimensional Structural Periodicity,"This study deals with the spin wave spectrum in magnetic macrostructure
+(composed of two ferromagnetic materials) showing a 3D periodicity: spherical
+ferromagnetic grains disposed in the nodes of a simple cubic crystal lattice
+are embedded in a matrix with different ferromagnetic properties. It is shown
+that the \textit{magnonic spectrum} of this composite structure exhibits
+frequency regions \textit{forbidden} for magnon propagation, and the energy
+gaps are found to be sensitive to the exchange contrast between the constituent
+materials as well as to the magnetization contrast. The widths of the
+respective magnonic gaps are studied as functions of parameters characterizing
+the magnetic structure.",0508390v1
+2005-12-24,Modified spin-wave theory of nuclear magnetic relaxation in one-dimensional quantum ferrimagnets: Three-magnon versus Raman processes,"Nuclear spin-lattice relaxation in one-dimensional Heisenberg ferrimagnets is
+studied by means of a modified spin-wave theory. Calculating beyond the
+first-order mechanism, where a nuclear spin directly interacts with spin waves
+through the hyperfine coupling, we demonstrate that the
+exchange-scattering-enhanced three-magnon nuclear relaxation may generally
+predominate over the Raman one with increasing temperature and decreasing
+field. Recent proton spin-lattice relaxation-time (T_1_) measurements on the
+ferrimagnetic chain compound NiCu(C_7_H_6_N_2_O_6_)(H_2_O)_3_2H_2_O suggest
+that the major contribution to 1/T_1_ be made by the three-magnon scattering.",0512629v1
+2006-06-07,Ferromagnetic relaxation by magnon-induced currents,"A theory for calculating spin wave relaxation times based on the
+magnon-electron interaction is developed. The theory incorporates a thin film
+geometry and is valid for a large range of magnon frequencies and wave vectors.
+For high conductivity metals such as permalloy, the wave vector dependent
+damping constant approaches values as high as 0.2, showing the large magnitude
+of the effect, and can dominate experimentally observed relaxation.",0606197v1
+2006-06-30,Spin-Wave Lifetimes Throughout the Brillouin Zone,"We use a neutron spin-echo method with $\mu$eV resolution to determine the
+lifetimes of spin waves in the prototypical antiferromagnet MnF$_2$ over the
+entire Brillouin zone. A theory based on the interaction of magnons with
+longitudinal spin fluctuations provides an excellent, parameter-free
+description of the data, except at the lowest momenta and temperatures. This is
+surprising, given the prominence of alternative theories based on magnon-magnon
+interactions in the literature. The results and technique open up a new avenue
+for the investigation of fundamental concepts in magnetism. The technique also
+allows measurement of the lifetimes of other elementary excitations (such as
+lattice vibrations) throughout the Brillouin zone.",0606814v1
+2006-10-25,Domain-Wall Waves (2D Magnons) in Superconducting Ferromagnets,"Propagation of the magnetization waves along domain walls (2D magnons) in a
+superconducting ferromagnet has been studied theoretically. The magnetostatic
+fields (long-range dipole-dipole interaction) have a crucial effect on the
+spectrum of 2D magnons. But this effect is essentially affected by the
+superconducting Meissner currents, which screen the magnetostatic fields and
+modify the long-wavelength spectrum from square-root to linear. The excitation
+of the domain wall waves by an electromagnetic wave incident on a
+superconducting-ferromagnet sample has been considered. This suggests using
+measurements of the surface impedance for studying the domain wall waves, and
+eventually for effective probing of superconductivity-ferromagnetism
+coexistence.",0610699v1
+2007-01-12,Spectroscopy of the parametric magnons excited by 4-wave process,"Using a Magnetic Resonace Force Microscope, we have performed ferromagnetic
+resonance (FMR) spectroscopy on parametric magnons created by 4-wave process.
+This is achieved by measuring the differential response to a small source
+modulation superimposed to a constant excitation power that drives the dynamics
+in the saturation regime of the transverse component. By sweeping the applied
+field, we observe abrupt readjustement of the total number of magnons each time
+the excitation coincides with a parametric mode. This gives rise to
+ultra-narrow peaks whose linewith is lower than $5~10^{-6}$ of the applied
+field.",0701287v1
+2006-05-16,Dyonic Giant Magnons,"We study the classical spectrum of string theory on AdS_5 X S^5 in the
+Hofman-Maldacena limit. We find a family of classical solutions corresponding
+to Giant Magnons with two independent angular momenta on S^5. These solutions
+are related via Pohlmeyer's reduction procedure to the charged solitons of the
+Complex sine-Gordon equation. The corresponding string states are dual to BPS
+boundstates of many magnons in the spin-chain description of planar N=4 SUSY
+Yang-Mills. The exact dispersion relation for these states is obtained from a
+purely classical calculation in string theory.",0605155v2
+2007-03-20,Giant Magnons and Singular Curves,"We obtain the giant magnon of Hofman-Maldacena and its dyonic generalisation
+on R x S^3 < AdS_5 x S^5 from the general elliptic finite-gap solution by
+degenerating its elliptic spectral curve into a singular curve. This alternate
+description of giant magnons as finite-gap solutions associated to singular
+curves is related through a symplectic transformation to their already
+established description in terms of condensate cuts developed in
+hep-th/0606145.",0703180v2
+1996-12-20,On the two-magnon bound states for the quantum Heisenberg chain with variable range exchange,"The spectrum of finite-difference two-magnon operator is investigated for
+quantum S=1/2 chain with variable range exchange of the form $h(j-k)\propto
+\sinh^{-2}a(j-k)$. It is found that usual bound state appears for some values
+of the total pseudomomentum of two magnons as for the Heisenberg chain with
+nearest-neighbor spin interaction. Besides this state, a new type of bound
+state with oscillating wave function appears at larger values of the total
+pseudomomentum.",9612008v1
+2007-04-18,Semiclassical Quantization of the Giant Magnon,"Solitons in field theory provide a window into regimes not directly
+accessible by the fundamental perturbative degrees of freedom. Motivated by
+interest in the worldsheet S-matrix of string theory in AdS_5 x S^5 in the
+limit of infinite worldsheet volume we consider the semiclassical quantization
+of a particular soliton of this theory: the Hofman-Maldacena `giant magnon'
+spinning string. We obtain explicit formulas for the complete spectrum of
+bosonic and fermionic fluctuations around the giant magnon. As an application
+of these results we confirm that the one-loop correction to the classical
+energy vanishes as expected.",0704.2389v2
+2007-08-06,Multi-magnon bound states in the frustrated ferromagnetic 1D chain,"We study a one-dimensional Heisenberg chain with competing ferromagnetic
+nearest-neighbor and antiferromagnetic next-nearest neighbor interactions in
+magnetic field. Starting from the fully polarized high-field state, we
+calculate the dispersions of the lowest-lying $n$-magnon excitations and the
+saturation field (n=2,3,4). We show that the lowest-lying excitations are
+always bound multi-magnon states with a total momentum of $\pi$ except for a
+small parameter range. We argue that bose condensation of the bound $n$ magnons
+leads to novel Tomonaga-Luttinger liquids with multi-polar correlations;
+nematic and triatic ordered liquids correspond to n=2 and n=3.",0708.0701v1
+2007-10-18,Spin Vortex in Magnon BEC of Superfluid 3He-B,"The phenomenon of the spontaneous phase-coherent precession of magnetization
+in superfluid 3He and the related effects of spin superfluidity are based on
+the true Bose-Einstein condensation of magnons. Several different magnon BEC
+states have been observed: homogeneously precessing domain (HPD); BEC
+condensation in the spin-orbit potential trap (Q-balls); coherent precession
+with fractional magnetization; and two modes of the coherent precession in
+squeezed aerogel. The spin superfluidity effects, like spin Josephson
+phenomena, spin current vortices, spin phase slippage, long distance
+magnetization transport by spin supercurrents have been observed.",0710.3448v1
+2008-01-19,Electrical control of magnon propagation in multiferroic BiFeO3 films,"The spin wave spectra of multiferroic BiFeO3 films is calculated using a
+phenomenological Landau theory that includes magnetostatic effects. The lowest
+frequency magnon dispersion is shown to be quite sensitive to the angle between
+spin wave propagation vector and the Neel moment. Since electrical switching of
+the Neel moment has recently been demonstrated in this material, the
+sensitivity of the magnon dispersion permits direct electrical switching of
+spin wave propagation. This effect can be used to construct spin wave logical
+gates without current pulses, potentially allowing reduced power dissipation
+per logical operation.",0801.3012v1
+2008-04-23,Phonons in magnon superfluid and symmetry breaking field,"Recent experiments [1],[2] which measured the spectrum of the Goldstone
+collective mode of coherently precessing state in 3He-B are discussed using the
+presentation of the coherent spin precession in terms of the Bose-Einstein
+condensation of magnons. The mass in the spectrum of the Goldstone boson --
+phonon in the superfluid magnon liquid -- is induced by the symmetry breaking
+field, which is played by the RF magnetic field",0804.3709v3
+2008-06-16,Exact solutions for N-magnon scattering,"Giant magnon solutions play an important role in various aspects of the
+AdS/CFT correspondence. We apply the dressing method to construct an explicit
+formula for scattering states of an arbitrary number N of magnons on R x S^3.
+The solution can be written in Hirota form and in terms of determinants of N x
+N matrices. Such a representation may prove useful for the construction of an
+effective particle Hamiltonian describing magnon dynamics.",0806.2466v1
+2008-08-04,Dynamics of a one-dimensional spinor Bose liquid: a phenomenological approach,"The ground state of a spinor Bose liquid is ferromagnetic, while the softest
+excitation above the ground state is the magnon mode. The dispersion relation
+of the magnon in a one-dimensional liquid is periodic in the wavenumber q with
+the period 2\pi n, determined by the density n of the liquid. Dynamic
+correlation functions, such as e.g. spin-spin correlation function, exhibit
+power-law singularities at the magnon spectrum, $\omega\to\omega_m(q,n)$.
+Without using any specific model of the inter-particle interactions, we relate
+the corresponding exponents to independently measurable quantities
+$\partial\omega_m/\partial q$ and $\partial\omega_m/\partial n$.",0808.0479v2
+2008-09-18,Giant Magnons and Spiky Strings on S^3 with B-field,"We study solutions for a rotating string on S^3 with a background NS-NS
+B-field and show the existence of spiky string and giant magnon as two limiting
+solutions. We make a connection to the sine-Gordon model via the Polyakov
+worldsheet action and study the effect of B-field. In particular, we find the
+magnon solution can be mapped to the excitation of a fractional spin chain. We
+conjecture a B-deformed SYM to be the gauge theory dual to this background.",0809.3269v2
+2008-12-08,Multi-magnon bound states in easy-axis ferromagnetic zigzag spin chain,"The frustrated spin-1/2 chain with weakly anisotropic ferromagnetic
+nearest-neighbor and antiferromagnetic next-nearest-neighbor exchanges is
+studied. We focus on the excitation spectrum and the low-temperature
+thermodynamics in the ferromagnetic region of the ground state phase diagram.
+It is shown that the excitation spectrum of the model is characterized by the
+existence of the multi-magnon bound states. These excitations determine the
+low-temperature magnetic susceptibility. The energy of the bound magnon
+complexes is found using the scaling estimates of the perturbation theory and
+numerical calculations. The relation of the considered model to the
+edge-sharing cuprate $Li_2CuO_4$ is discussed.",0812.1425v1
+2009-02-28,Magnon BEC in superfluid 3He-A,"The new mode of magnetization precession in superfluid 3He-A in a squeezed
+aerogel has been recently reported. We consider this mode in terms of the
+Bose-Einstein condensation (BEC) of magnons. The difference between magnon BEC
+states in 3He-A and in 3He-B is discussed.",0903.0016v2
+2009-11-04,Theory of Resonant Inelastic X-ray Scattering by Collective Magnetic Excitations,"I present a tractable theory for the Resonant Inelastic X-ray Scattering
+(RIXS) spectral function of magnons. The low-energy transition operator is
+written as a product of local spin operators times fundamental x-ray absorption
+spectra. This leads to simple selection rules for the magnetic cross section.
+The scattering cross section linear (quadratic) in spin operators is
+proportional to the magnetic circular (linear) dichroic absorption. RIXS is a
+novel tool to measure magnetic quasi particles (magnons) and the incoherent
+spectral weight, as well as multiple magnons up to very high energy losses, in
+small samples, thin films and multilayers, complementary to Neutron scattering.",0911.0706v2
+2009-11-16,Electron-Magnon Scattering in Anomalous Hall Effect,"We study the role played by electron-magnon scattering in the anomalous Hall
+effect. We find that it has important contributions distinct from other
+scattering processes like impurities scattering and phonon scattering. As a
+demonstration, we calculate the Hall conductivity for a two dimensional Dirac
+model. The result indicates that as system control parameter varies, the
+competition between magnon scattering and other types of scattering changes the
+Hall conductivity drastically. In particular, the side jump contribution could
+acquire a strong temperature dependence.",0911.3134v1
+2010-04-08,Spin-charge and spin-orbital coupling effects on spin dynamics in ferromagnetic manganites,"Correlation-induced spin-charge and spin-orbital coupling effects on spin
+dynamics in ferromagnetic manganites are calculated with realistic parameters
+in order to provide a quantitative comparison with experimental results for
+spin stiffness, magnon dispersion, magnon damping, anomalous zone-boundary
+magnon softening, and Curie temperature. The role of orbital degeneracy,
+orbital ordering, and orbital correlations on spin dynamics in different doping
+regimes is highlighted.",1004.1352v2
+2010-07-09,Boundary Giant Magnons and Giant Gravitons,"We construct the full set of boundary giant magnons on $\mathbb{R}\times
+S^{2}$ attached to the maximal $Z=0$ giant graviton by mapping from the general
+solution to static sine-Gordon theory on the interval and compute the values of
+$\Delta-J$ at finite $J$, including the leading order corrections when $J$ is
+large. We then consider the Born-Infeld theory of the giant graviton itself to
+construct BIon spike solutions that correspond to the world volume description
+of the boundary giant magnons at finite $J$.",1007.1674v2
+2010-11-05,Giant magnons and non-maximal giant gravitons,"We produce the open strings on $\mathbb{R}\times S^{2}$ that correspond to
+the solutions of integrable boundary sine-Gordon theory by making use of the
+$N$-magnon solutions provided in \cite{KPV} together with explicit moduli.
+Relating the two boundary parameters in a special way we describe the
+scattering of giant magnons with non-maximal $Y=0$ giant gravitons and
+calculate the leading contribution to the associated magnon scattering phase.",1011.1440v1
+2011-05-16,Three-point Correlation functions of Giant magnons with finite size,"We compute holographic three-point correlation functions or structure
+constants of a zero-momentum dilaton operator and two (dyonic) giant magnon
+string states with a finite-size length in the semiclassical approximation. We
+show that the semiclassical structure constants match exactly with the
+three-point functions between two su(2) magnon single trace operators with
+finite size and the Lagrangian in the large 't Hooft coupling constant limit. A
+special limit J>>sqrt(lambda) of our result is compared with the relevant
+result based on the L\""uscher corrections.",1105.3084v2
+2011-06-10,Rotational motion of magnon and thermal Hall effect,"Due to the Berry curvature in momentum space, the magnon wavepacket undergoes
+two types of orbital motions in analogy with the electron system: the
+self-rotation motion and a motion along the boundary of the sample (edge
+current). The magnon edge current causes the thermal Hall effect, and these
+orbital motions give corrections to the thermal transport coefficients. We also
+apply our theory to the magnetostatic spin wave in a thin-film ferromagnet, and
+derive expression for the Berry curvature.",1106.1987v1
+2012-08-27,Spin-wave modes and band structure of rectangular CoFeB antidot lattices,"We present an investigation of rectangular antidot lattices in a CoFeB film.
+Magnonic band structures are numerically calculated, and band gaps are
+predicted which shift in frequency by 0.9 GHz when rotating the external field
+from the long to the short axis of the unit cell. We demonstrate by
+time-resolved experiments that magnonic dipolar surface modes are split in
+frequency by 0.6 GHz which agrees well with the theoretical prediction. These
+findings provide the basis for directional spin-wave filtering with magnonic
+devices.",1208.5339v1
+2012-08-28,Magnon Mediated Electric Current Drag Across a Ferromagnetic Insulator Layer,"In a semiconductor hererostructure, the Coulomb interaction is responsible
+for the electric current drag between two 2D electron gases across an electron
+impenetrable insulator. For two metallic layers separated by a ferromagnetic
+insulator (FI) layer, the electric current drag can be mediated by a
+nonequilibrium magnon current of the FI. We determine the drag current by using
+the semiclassical Boltzmann approach with proper boundary conditions of
+electrons and magnons at the metal-FI interface.",1208.5812v1
+2012-10-09,Spin convertance at magnetic interfaces,"The exchange interaction between the conduction electrons and magnetic
+moments at magnetic interface leads to mutual conversion between electron spin
+current and magnon current. We introduce a concept of spin convertance which
+quantitatively measures the magnon current induced by electron spin
+accumulation and the spin current created by magnon accumulation at the
+interface. We predict the phenomena on charge and spin drag across a magnetic
+insulator spacer for several layered structures.",1210.2735v3
+2012-10-22,Excitations in a quantum spin liquid with random bonds,"We present results of inelastic neutron scattering study on two bond
+disordered quasi twodimensional quantum magnets
+(C$_4$H$_12$N$_2$)Cu$_2$(Cl$_{1-x}$Br$_x$)$_6$ with x=0.035 and 0.075. We
+observe the increase of spin gap, reduction of magnon bandwidth and a decrease
+of magnon lifetimes compared to x=0 sample. Additional magnon damping is
+observed at higher energies away from zone center which is found to follow the
+density of single particle states.",1210.5899v1
+2012-11-14,Ultrafast charge recombination in photoexcited Mott-Hubbard insulator,"We present a calculation of the recombination rate of the excited
+holon-doublon pairs based on the two-dimensional model relevant for undoped
+cuprates which shows that fast processes, observed in pump-probe experiments on
+Mott-Hubbard insulators in picosecond range, can be explained even
+quantitatively with the multi-magnon emission. The precondition is the
+existence of the Mott-Hubbard bound exciton of the s-type. We find that its
+decay is exponentially dependent on the Mott-Hubbard gap and on the magnon
+energy, with a small prefactor which can be traced back to strong correlations
+and consequently large exciton-magnon coupling.",1211.3236v1
+2013-02-19,The temperature dependence of quantum spin pumping generated using electron spin resonance with three-magnon splittings,"On the basis of the Schwinger-Keldysh formalism, we have closely investigated
+the temperature dependence of quantum spin pumping by electron spin resonance.
+We have clarified that three-magnon splittings excite non-zero modes of magnons
+and characterize the temperature dependence of quantum spin pumping. Our
+theoretical result qualitatively agrees with the experiment by Czeschka et al.
+that the mixing conductance is little influenced by temperature [F. D. Czeschka
+et al., Phys. Rev. Lett., 107, 046601 (2011)].",1302.4777v1
+2013-02-24,Bose-Einstein condensation of magnons in spin pumping systems,"We clarify the condition for the occurrence of magnon Bose-Einstein
+condensation (BEC) in spin pumping systems without using external pumping
+magnetic fields. The Goldstone model is generalized and the stability of the
+vacuum is closely investigated. By applying the generalized Goldstone model to
+spin pumping systems, the condition for the experimental realization of the
+stable magnon BEC in spin pumping systems is theoretically proposed.",1302.5858v1
+2014-07-31,Universal critical behavior of the two-magnon-bound-state mass gap for the (2+1)-dimensional Ising model,"The two-magnon-bound-state mass gap m_2 for the two-dimensional quantum Ising
+model was investigated by means of the numerical diagonalization method; the
+low-lying spectrum is directly accessible via the numerical diagonalization
+method. It has been claimed that the ratio m_2/m_1 (m_1: one-magnon mass gap)
+is a universal constant in the vicinity of the critical point. Aiming to
+suppress corrections to scaling (lattice artifact), we consider the spin-S=1
+Ising model with finely-adjusted extended interactions. The simulation result
+for the finite-size cluster with N \le 20 spins indicates the mass-gap ratio
+m_2/m_1=1.84(1).",1407.8243v1
+2014-09-25,Interfacial Spin and Heat Transfer between Metals and Magnetic Insulators,"We study the role of thermal magnons in the spin and heat transport across a
+normal-metal/insulating-ferromagnet interface, which is beyond an elastic
+electronic spin transfer. Using an interfacial exchange Hamiltonian, which
+couples spins of itinerant and localized orbitals, we calculate spin and energy
+currents for an arbitrary interfacial temperature difference and misalignment
+of spin accumulation in the normal metal relative to the ferromagnetic order.
+The magnonic contribution to spin current leads to a temperature-dependent
+torque on the magnetic order parameter; reciprocally, the coherent precession
+of the magnetization pumps spin current into the normal metal, the magnitude of
+which is affected by the presence of thermal magnons.",1409.7128v1
+2014-12-19,Spin waves in one-dimensional bi-component quasicrystals,"We studied finite Fibonacci sequence of Co and Py stripes aligned
+side-by-side and in direct contact with each other. Calculations based on
+continuous model including exchange and dipole interactions were performed for
+structures feasible for fabrication and characterization of main properties of
+magnonic quasicrystals. We have shown the fractal structure of the magnonic
+spectrum with a number of magnonics gaps of different width. Also localization
+of spin waves in quasicrystals and existence of surface spin waves in finite
+quaiscrystal structure is demonstrated.",1412.6301v4
+2015-01-13,Spin effects induced by thermal perturbation in a normal metal/magnetic insulator system,"Using one of the methods of quantum nonequilibrium statistical physics we
+have investigated the spin transport transverse to the normal
+metal/ferromagnetic insulator interface in hybrid nanostructures. An
+approximation of the effective parameters, when each of the interacting
+subsystems (electron spin, magnon, and phonon) is characterized by its own
+effective temperature have been considered. The generalized Bloch equations
+which describe the spin-wave current propagation in the dielectric have been
+derived. Finally, two sides of the spin transport ""coin"" have been revealed:
+the diffusive nature of the magnon motion and magnon relaxation processes,
+responsible for the spin pumping and the spin-torque effect.",1501.02983v1
+2015-05-06,Spintronics and Magnon Bose-Einstein Condensation,"Spintronics is the science and technology of electric control over spin
+currents in solid-state-based devices. Recent advances have demonstrated a
+coupling between electronic spin currents in non-magnetic metals and magnons in
+magnetic insulators. The coupling is due to spin transfer and spin pumping at
+interfaces between the normal metals and magnetic insulators. In this Chapter,
+we review these developments and the prospects they raise for electric control
+of quasi-equilibrium magnon Bose-Einstein condensates and spin superfluidity.",1505.01329v1
+2016-01-16,Measurements of anisotropic mass of magnons confined in a harmonic trap in superfluid $^3$He-B,"We can pump magnons to a nearly harmonic magneto-textural trap in superfluid
+$^3$He-B. Using the NMR spectroscopy of levels in the trap we have measured the
+anisotropic magnon mass and related values of the spin-wave velocities. Based
+on our measurements we provide values of the Fermi-liquid parameter $F^a_1$.",1601.04192v1
+2016-02-22,Exchange magnon induced resistance asymmetry in permalloy spin-Hall oscillators,"We investigate magnetization dynamics in a spin-Hall oscillator using a
+direct current measurement as well as conventional microwave spectrum analysis.
+When the current applies an anti-damping spin-transfer torque, we observe a
+change in resistance which we ascribe to the excitation of incoherent exchange
+magnons. A simple model is developed based on the reduction of the effective
+saturation magnetization, quantitatively explaining the data. The observed
+phenomena highlight the importance of exchange magnons on the operation of
+spin-Hall oscillators.",1602.06710v1
+2017-02-14,Cavity mediated effective interaction between phonon and magnon,"Optomagnonics and optomechanics have various applications ranging from
+tunable light sources to optical manipulation for quantum information science.
+Here, we propose a hybrid system with the interaction between phonon and magnon
+which could be tuned by the electromagnetic field based on the radiation
+pressure and magneto-optical effect. The self energy of the magnon and phonon
+induced by the electromagnetic field and the influence of the thermal noise are
+studied. Moreover, the topological features of the hybrid system is illustrated
+with resort to the dynamical encircling with the exceptional points, and the
+chiral characteristics under these encirclements are found.",1702.04030v1
+2018-11-25,Self-localization of magnons and magnetoroton in a binary Bose-Einstein condensate,"We consider a two-component Bose-condensed mixture characterized by positive
+s-wave scattering lengths. We assume equal densities and intra-species
+interactions. By doing the Bogoliubov transformation of an effective
+Hamiltonian we obtain the lower energy magnon dispersion incorporating the
+superfluid entrainment between the components. We argue that p-wave pairing of
+distinct bosons should be accompanied by self-localization of magnons and
+formation of a magnetoroton. We demonstrate the effect on a model system of
+particles interacting via step potentials.",1811.10099v2
+2014-05-20,Giant Magnon on Deformed AdS(3)xS(3),"We study giant magnon solutions for strings moving on a deformed AdS(3)xS(3)
+background. We impose a conformal gauge on the Polyakov action and proceed with
+solving the Virasoro constraints. The expressions of the conserved charge J and
+the energy of a single magnon excitation are then computed. Then we determine
+the dispersion relation in the infinite J limit configuration and we find that
+it reduces to celebrated Hofman-Maldacena dispersion relation when the
+deformation parameter goes to zero.",1405.5017v2
+2014-06-03,Finite-size giant magnons on η-deformed AdS_5 x S^5,"We consider strings moving in the R_t x S^3_\eta subspace of the
+\eta-deformed AdS_5 x S^5 and obtain a class of solutions depending on several
+parameters. They are characterized by the string energy and two angular
+momenta. Finite-size dyonic giant magnon belongs to this class of solutions.
+Further on, we restrict ourselves to the case of giant magnon with one nonzero
+angular momentum, and obtain the leading finite-size correction to the
+dispersion relation.",1406.0628v1
+2016-05-05,Theory of magnon motive force in chiral ferromagnets,"We predict that magnon motive force can lead to temperature dependent,
+nonlinear chiral damping in both conducting and insulating ferromagnets. We
+estimate that this damping can significantly influence the motion of skyrmions
+and domain walls at finite temperatures. We also find that in systems with low
+Gilbert damping moving chiral magnetic textures and resulting magnon motive
+forces can induce large spin and energy currents in the transverse direction.",1605.01694v2
+2016-07-30,Magnon-bound-state hierarchy for the two-dimensional transverse-field Ising model in the ordered phase,"In the ordered phase for an Ising ferromagnet, the magnons are attractive to
+form a series of bound states with the mass gaps, $m_2<m_3 < \dots$. Each ratio
+$m_{2,3,\dots}/m_1$ ($m_1$: the single-magnon mass) is expected to be a
+universal constant in the vicinity of the critical point. In this paper, we
+devote ourselves to the $(2+1)$-dimensional counterpart, for which the
+universal hierarchical character remains unclear. We employed the exact
+diagonalization method, which enables us to calculate the dynamical
+susceptibility via the continued-fraction expansion. Thereby, we observe a
+variety of signals including $m_{2,3,4}$, and the spectrum is analyzed with the
+finite-size-scaling method to estimate the universal mass-gap ratios.",1608.00083v1
+2018-03-09,Non-local coupling between antiferromagnets and ferromagnets in cavities,"Microwaves couple to magnetic moments in both ferromagnets and
+antiferromagnets. Although the magnons in ferromagnets and antiferromagnets
+radically differ, they can become entangled via strong coupling to the same
+microwave mode in a cavity. The equilibrium configuration of the magnetic
+moments crucially governs the coupling between the different magnons because
+the antiferromagnetic and ferromagnetic magnons have the opposite spins when
+their dispersion relations cross. We derive analytical expressions for the
+coupling strengths and find that the coupling between antiferromagnets and
+ferromagnets is comparable to the coupling between two ferromagnets. Our
+findings reveal a robust link between cavity spintronics with ferromagnets and
+antiferromagnets.",1803.03486v1
+2018-07-26,Emission of coherent propagating magnons by insulator-based spin-orbit torque oscillators,"We experimentally demonstrate generation of coherent propagating magnons in
+ultra-thin magnetic-insulator films by spin-orbit torque induced by dc electric
+current. We show that this challenging task can be accomplished by utilizing
+magnetic-insulator films with large perpendicular magnetic anisotropy. We
+demonstrate simple and flexible spin-orbit torque devices, which can be used as
+highly efficient nanoscale sources of coherent propagating magnons for
+insulator-based spintronic applications.",1807.09976v1
+2019-01-29,Evaluation protocol for revealing magnonic contrast in STXM-FMR measurements,"We present a statistically motivated method to extract magnonic contrast from
+STXM-FMR measurement with microwave frequencies of the order of \unit[10]{GHz}.
+With this method it is possible to generate phase and amplitude profiles with a
+spatial resolution of about \unit[30]{nm} given by the STXM resolution,
+furthermore this method allows fo a rigoros transformation to reciprocal
+\vec{k}-space, revealing \vec{k}-dependent magnon properties.",1901.10595v1
+2019-02-24,Half-Metallic Ferromagnets and Spin Gapless Semiconductors,"A brief review of experimental and theoretical studies of half-metallic
+ferromagnets (HMF) and spin gapless semiconductors (SGS) is given. The data on
+resistivity and magnetoresistivity are presented. An important role of
+non-quasiparticle states owing to electron-magnon scattering in transport
+properties is discussed. The problem of low-temperature resistivity in HMF is
+treated in terms of one-magnon and two-magnon scattering processes.",1902.08972v1
+2019-03-18,Theory of spin transport through antiferromagnetic insulator,"A theoretical formulation for spin transport through an antiferromagnetic
+(AF) insulator is presented in the case driven/detected by direct/inverse spin
+Hall effect in two heavy metal contacts. The spin signal is shown to be
+transferred by the ferromagnetic correlation function of the antiferromagnet,
+which is calculated based on a magnon representation. To cover high temperature
+regimes, we include an auxiliary field representing short AF correlations and a
+temperature-dependent damping due to magnon scattering. The diffusion length
+for spin is long close to the degeneracy of the two AF magnons, and has a
+maximum as function of temperature near the N\'eel transition.",1903.07223v1
+2019-03-30,Superconductivity at metal-antiferromagnetic insulator interfaces,"Magnons in antiferromagnetic insulators couple strongly to conduction
+electrons in adjacent metals. We show that this interfacial tie can lead to
+superconductivity in a tri-layer consisting of a metal sandwiched between two
+antiferromagnetic insulators. The critical temperature is closely related to
+the magnon gap, which can be in the THz range. We estimate the critical
+temperature in MnF$_2$-Au-MnF$_2$ to be on the order of 1 K. The Umklapp
+scattering at metal-antiferromagnet interfaces leads to a d-wave
+superconductive pairing, in contrast to the p-wave superconductivity mediated
+by magnons in ferromagnets.",1904.00233v1
+2015-08-19,Antiferromagnetic Magnonic Crystals,"We describe the features of magnonic crystals based upon antiferromagnetic
+elements. Our main results are that with a periodic modulation of either
+magnetic fields or system characteristics, such as the anisotropy, it is
+possible to tailor the spin wave spectra of antiferromagnetic systems into a
+band-like organization that displays a segregation of allowed and forbidden
+bands. The main features of the band structure, such as bandwidths and
+bandgaps, can be readily manipulated. Our results provide a natural link
+between two steadily growing fields of spintronics: antiferromagnetic
+spintronics and magnonics.",1508.04497v1
+2017-07-12,Superconductivity Induced by Interfacial Coupling to Magnons,"We consider a thin normal metal sandwiched between two ferromagnetic
+insulators. At the interfaces, the exchange coupling causes electrons within
+the metal to interact with magnons in the insulators. This electron-magnon
+interaction induces electron-electron interactions, which, in turn, can result
+in p-wave superconductivity. In the weak-coupling limit, we solve the gap
+equation numerically and estimate the critical temperature. In YIG-Au-YIG
+trilayers, superconductivity sets in at temperatures somewhere in the interval
+between 1 and 10 K. EuO-Au-EuO trilayers require a lower temperature, in the
+range from 0.01 to 1 K.",1707.03754v1
+2017-11-25,Giant magnon-like solution in Sch_5 x S^5,"In this paper we have found a classical giant magnon-like solution with both
+infinite and finite angular momentum moving in Sch_5 x S^5 with B-field, which
+is believed to be dual to dipole-deformed N=4 super Yang-Mills theory. This
+string state propagates as a point particle in non-trivial subspace of the
+Sch_5 space but shows a giant magnon-like property in the S^2 subspace. We
+derive the energy-momentum dispersion relations and their finite-size
+correction for the case of finite but large angular momentum.",1711.09252v3
+2019-05-19,Curvature induced magnonic crystal in nanowires,"A new type of magnonic crystals, curvature induced ones, is realized in
+ferromagnetic nanowires with periodically deformed shape. A magnon band
+structure of such crystal is fully determined by its curvature: the developed
+theory is well confirmed by simulations. An application to nanoscale spintronic
+devises with the geometrically tunable parameters is proposed, namely, to
+filter elements.",1905.07795v4
+2020-06-22,Semiclassical quantization of the mixed-flux AdS$_3$ giant magnon,"We obtain explicit formulas for the eight bosonic and eight fermionic
+fluctuations around the mixed-flux generalization of the Hofman-Maldacena giant
+magnon on AdS$_3 \times$S$^3 \times$T$^4$ and AdS$_3 \times$S$^3 \times$S$^3
+\times$S$^1$. As a check of our results, we confirm that the semiclassical
+quantization of these fluctuations leads to a vanishing one-loop correction to
+the magnon energy, as expected from symmetry based arguments.",2006.12080v2
+2015-07-24,On-chip artificial magnon-polariton device for voltage control of electromagnetically induced transparency,"We demonstrate an on-chip device utilizing the concept of artificial cavity
+magnon-polariton (CMP) coupling between the microwave cavity mode and the
+dynamics of the artificial magnetism in a split ring resonator. This on-chip
+device allows the easy tuning of the artificial CMP gap by using a DC voltage
+signal, which enables tuneable electrodynamically induced transparency. The
+high tunability of the artificial magnon-polariton system not only enables the
+study of the characteristic phenomena associated with distinct coupling
+regimes, but also may open up avenues for designing novel microwave devices and
+ultra-sensitive sensors.",1507.06940v1
+2016-11-28,Berry curvature in magnon-phonon hybrid systems,"We theoretically study the Berry curvature of the magnon induced by the
+hybridization with the acoustic phonons via the spin-orbit and dipolar
+interactions. We first discuss the magnon-phonon hybridization via the dipolar
+interaction, and show that the dispersions have gapless points in momentum
+space, some of which form a loop. Next, when both spin-orbit and dipolar
+interactions are considered, we show anisotropic texture of the Berry curvature
+and its divergence with and without gap-closing. Realistic evaluation of the
+consequent anomalous velocity is given for yttrium iron garnet.",1611.08993v1
+2017-04-17,Weyl and nodal ring magnons in three-dimensional honeycomb lattices,"We study the topological properties of magnon excitations in a wide class of
+three dimensional (3D) honeycomb lattices with ferromagnetic ground states. It
+is found that they host nodal ring magnon excitations. These rings locate on
+the same plane in the momentum space. The rings can be gapped by
+Dzyaloshinskii-Moriya (DM) interactions to form two Weyl points with opposite
+charges. We explicitly discuss these physics in the simplest 3D honeycomb
+lattice, the hyperhoneycomb lattice and show drumhead and arc surface states in
+the nodal ring and Weyl phases, respectively, due to the bulk-boundary
+correspondence.",1704.04898v1
+2020-01-04,Nonrelativistic giant magnons from Newton Cartan strings,"We show nonrelativistic (NR) giant magnon dispersion relations by probing the
+torsional Newton Cartan (TNC) geometry with (semi)classical nonrelativistic
+rigidly rotating strings. We construct NR sigma models over $ R \times S^2 $
+and consider two specific limiting cases those are of particular interest. Both
+of these limiting conditions give rise to what we identify as the \emph{small}
+momentum limit of the giant magnon dispersion relation in the dual SMT at
+\emph{strong} coupling. We further generalize our results in the presence of
+background NS-NS fluxes. Our analysis reveals that unlike its relativistic
+counterpart, the NR string theory lacks of single spike solutions.",2001.01061v2
+2020-04-30,Magnon Current Generation by Dynamical Distortion,"The interaction between spin and nanomechanical degrees of freedom attracts
+interest from the viewpoint of basic science and device applications. We study
+the magnon current induced by the torsional oscillation of ferromagnetic
+nanomechanical cantilever. We find that a finite Dzyaloshinskii-Moriya (DM)
+interaction emerges by the torsional oscillation, which is described by the
+spin gauge field, and the DM interaction leads to the detectably-large magnon
+current with frequency same as that of the torsional oscillation. Our theory
+paves the way for studying torsional spin-nanomechanical phenomena by using the
+spin gauge field.",2004.14707v1
+2020-10-11,Multispin magnons from Spin-Matrix strings on $ AdS_5 \times S^5 $,"The present Letter derives multispin nonrelativistic magnon spectrum
+considering various near BPS corners within $ SU(1,2|3) $ Spin-Matrix theory
+(SMT) limit of strings on $ AdS_5 \times S^5 $. In particular, we focus on some
+typical rotating string solutions those correspond to two spin as well as three
+spin configurations in the bulk and identify the associated nonrelativistic
+magnon like excitations in these models.",2010.05179v2
+2020-10-21,Thermal gating of magnon exchange in magnetic multilayers with antiferromagnetic spacers,"We observe a strong thermally-controlled magnon-mediated interlayer coupling
+of two ferromagnetic layers via an antiferromagnetic spacer in spin-valve type
+trilayers. The effect manifests itself as a field-induced coherent switching of
+the two ferromagnets, which can be controlled by varying temperature and the
+spacer thickness. We explain the observed behavior as due to a strong
+hybridization of the ferro- and antiferro-magnetic magnon modes in the trilayer
+at temperatures just below the N\'eel temperature of the antiferromagnetic
+spacer.",2010.11134v1
+2021-04-30,Micromagnetic modeling of magnon coherent states in a nonuniform magnetic field,"The study of the dynamics of magnetically ordered states in strong excitation
+through micromagnetic modeling has become relevant due to the observation of
+magnon Bose condensation. In particular, the question has arisen about the
+possibility of describing the coherent quantum state by the quasi-classical
+Landau-Lifshitz-Gilbert equations. We performed micromagnetic simulations of
+magnetization precession with a high angle of deviation in an out-of-plane
+nonuniform dc field. Our results confirm the formation of coherent magnon state
+under conditions of high excitation. This coherent state extends over long
+distances and described by a spatially inhomogeneous amplitude and a
+homogeneous precession phase.",2104.14804v1
+2022-06-19,Low-temperature asymptotics for transverse autocorrelator of the magnetically polarized Ising chain studied by ordinary and nested Dyson equations,"Suggesting two versions for the Plakida-Tserkovnikov algorithm breakdown in
+the low-temperature regime, we derive ordinary and nested Dyson equations for
+the transverse autocorrelator of the magnetically polarized Ising chain. Using
+them we get the corresponding low-temperature asymptotics for the
+autocorrelator. We show that the ordinary Dyson equation results in a correct
+$o({\rm e}^{-\beta E_{gap}})$ account of the magnon creation process, while the
+nested Dyson equation additionally gives the correct $o({\rm e}^{-\beta
+E_{gap}})$ contribution associated with transitions from magnons to bound
+two-magnon states. The obtained result may be useful for the extension of the
+suggested approach on the polarized $XXZ$-chain.",2206.09301v1
+2023-01-14,Quantum entanglement generation on magnons assisted with microwave cavities coupled to a superconducting qubit,"We present protocols to generate quantum entanglement on nonlocal magnons in
+hybrid systems composed of yttrium iron garnet (YIG) spheres, microwave
+cavities and a superconducting (SC) qubit. In the schemes, the YIGs are coupled
+to respective microwave cavities in resonant way, and the SC qubit is placed at
+the center of the cavities, which interacts with the cavities simultaneously.
+By exchanging the virtual photon, the cavities can indirectly interact in the
+far-detuning regime. Detailed protocols are presented to establish entanglement
+for two, three and arbitrary $N$ magnons with reasonable fidelities.",2301.05820v1
+2023-02-08,Dielectric relaxation by quantum critical magnons,"We report the experimental observation of dielectric relaxation by quantum
+critical magnons. Complex capacitance measurements reveal a dissipative feature
+with a temperature-dependent amplitude due to low-energy lattice excitations
+and an activation behavior of the relaxation time. The activation energy
+softens close to a field-tuned magnetic quantum critical point at $H=H_c$ and
+follows single-magnon energy for $H>H_c$, showing its magnetic origin. Our
+study demonstrates the electrical activity of coupled low-energy spin and
+lattice excitations, an example of quantum multiferroic behavior.",2302.04234v1
+2023-02-17,Control of magnon-photon coupling by spin torque,"We demonstrate the influence of damping and field-like torques in the
+magnon-photon coupling process by classically integrating the generalized
+Landau-Lifshitz-Gilbert equation with RLC equation in which a phase correlation
+between dynamic magnetization and microwave current through combined Amp\`ere
+and Faraday effects are considered. We show that the gap between two hybridized
+modes can be controlled in samples with damping parameter in the order of
+$10^{-3}$ by changing the direction of the dc current density $J$ if a certain
+threshold is reached. Our results suggest that an experimental realization of
+the proposed magnon-photon coupling control mechanism is feasible in yttrium
+iron garnet/Pt hybrid structures.",2302.08910v1
+2023-03-15,Non-ergodic one-magnon magnetization dynamics of the antiferromagnetic delta chain,"We investigate the one-magnon dynamics of the antiferromagnetic delta chain
+as a paradigmatic example of tunable equilibration. Depending on the ratio of
+nearest and next-nearest exchange interactions the spin system exhibits a flat
+band in one-magnon space - in this case equilibration happens only partially,
+whereas it appears to be complete with dispersive bands as generally expected
+for generic Hamiltonians. We provide analytical as well as numerical insight
+into the phenomenon.",2303.08638v1
+2023-04-13,Magnon squeezing in conical spin spirals,"We investigate squeezing of magnons in a conical spin spiral configuration.
+We find that while the energy of magnons propagating along the $\boldsymbol{k}$
+and the $-\boldsymbol{k}$ directions can be different due to the non-reciprocal
+dispersion, these two modes are connected by the squeezing, hence can be
+described by the same squeezing parameter. The squeezing parameter diverges at
+the center of the Brillouin zone due to the translational Goldstone mode of the
+system, but the squeezing also vanishes for certain wave vectors. We discuss
+possible ways of detecting the squeezing.",2304.06338v2
+2023-10-01,Exact Entanglement Propagation Dynamics in Integrable Heisenberg Chains,"The exact single-magnon entanglement evolution in Heisenberg chains is
+obtained using the Quantum Correlation Transfer Function (QCTF) formulation.
+The individual spins' entanglement is given by a hypergeometric function, and
+its transient behavior is described via a Bessel function of the first kind.
+The presented characterization through the lens of QCTF allowed for calculating
+the ballistic single-magnon entanglement edge velocity in Heisenberg chains,
+which has not been achieved before. Our results can be extended to the
+multi-magnon regime, therefore opening up the means to explain equilibration
+dynamics and thermodynamics in Heisenberg chains.",2310.00717v2
+2023-12-07,Thermomagnetic Anomalies by Magnonic Criticality in Ultracold Atomic Transport,"We investigate thermomagnetic transport in an ultracold atomic system with
+two ferromagnets linked via a magnetic quantum point contact. Using
+nonequilibrium Green's function approach, we show a divergence in spin
+conductance and a slowing down of spin relaxation that manifest in the weak
+effective-Zeeman-field limit. These anomalous spin dynamics result from the
+magnonic critical point at which magnons become gapless due to spontaneous
+magnetization. Our findings unveil untapped dynamics in ultracold atomic
+systems, opening new avenues in thermomagnetism.",2312.04280v1
+2024-01-02,Efficient Magnon Injection and Detection via the Orbital Rashba Edelstein Effect,"Orbital currents and accumulation provide a new avenue to boost spintronic
+effects in nanodevices. Here we use interconversion effects between charge
+current and orbital angular momentum to demonstrate a dramatic increase in the
+magnon spin injection and detection efficiencies in nanodevices consisting of a
+magnetic insulator contacted by Pt/CuOx electrodes. Moreover, we note distinct
+variations in efficiency for magnon spin injection and detection, indicating a
+disparity in the direct and inverse orbital Rashba Edelstein effect
+efficiencies.",2401.01090v1
+2024-03-13,Are Magnons just the van der Waals interaction in Disguise?,"The MBD model of the van der Waals interaction is extended to also consider
+magnetic interactions, and it is demonstrated how this can be made to reproduce
+the Heisenberg Hamiltonian. It is found that this leads to a weak coupling
+between the charge dipole waves that are the basis for the electric-only van
+der Waals interaction and the spin-dipole waves (magnons) of the Heisenberg
+model. By applying the same level of theory to both simultaneously we
+demonstrate that magnons and charge-dipole waves may both be considered to be a
+basis for the fluctuating part of the many-body electron density.",2403.08676v1
+2024-04-08,Lattice-Assisted Molecular Excitations in Frustrated Pyrochlores,"Resonance-like molecular excitations have been discovered in a series of
+pyrochlore antiferromagnets, yet their origins and relationships with the
+coexisting magnon excitations remain a puzzle. Here, by incorporating the
+spin-lattice coupling and the consequent four-spin interactions through the
+site-phonon model, we accomplish a unified description of the molecular and
+magnon excitations, revealing the molecular modes as statistical approximations
+of the dispersive magnon excitations. Our work demonstrates a general approach
+to understand exotic spin dynamics in magnetoelastic systems.",2404.05523v1
+2024-04-09,Magnon transmission across $ν=1|-1|1$ mono-layer graphene junction as a probe of electronic structure,"We study magnon transmission across gate-controlled junctions in the $n=0$
+manifold of Landau levels in monolayer graphene, allowing for both spin and
+valley Zeeman fields. We show that by tuning the external perpendicular
+magnetic field, the phase in the intermediate region of a $1|\nu_m|1$ sandwich
+geometry can be changed, due to which the magnon transmission can be switched
+between fully transmitting and fully blocked. Our analysis, along with the
+experimental measurements, can be used to determine the anisotropic couplings
+in the sample.",2404.06355v1
+1995-03-02,Resonant two-magnon Raman scattering in parent compounds of high-T$_c$ superconductors.,"We propose a theory of two-magnon Raman scattering from the insulating parent
+compounds of high-T$_c$ superconductors, which contains information not only on
+magnetism, but also on the electronic properties in these materials. We use
+spin density wave formalism for the Hubbard model, and study diagrammatically
+the profile of the two-magnon scattering and its intensity dependence on the
+incoming photon frequency $\omega_i$ both for $\omega_i \ll U$ and in the
+resonant regime, in which the energy of the incident photon is close to the gap
+between conduction and valence bands. In the nonresonant case, we identify the
+diagrams which contribute to the conventional Loudon-Fleury Hamiltonian. In the
+resonant regime, where most of the experiments have been done, we find that the
+dominant contribution to Raman intensity comes from a different diagram, one
+which allows for a simultaneous vanishing of all three of its denominators
+(i.e., a triple resonance). We study this diagram in detail and show that the
+triple resonance, combined with the spin-density-wave dispersion relation for
+the carriers, explains the unusual features found in the two-magnon profile and
+in the two-magnon peak intensity dependence on the incoming photon frequency.
+In particular, our theory predicts a maximum of the two-magnon peak intensity
+right at the upper edge of the features in the optical data, which has been one
+of the key experimental puzzles.",9503010v1
+2007-12-26,Reflecting Magnon Bound States,"In N=4 super Yang-Mills spin chain, we compute reflection amplitudes of
+magnon bound-state off giant graviton. We first compute the reflection
+amplitude off Y=0 brane boundary and compare it with the scattering amplitude
+between two magnon bound-states in the bulk. We find that analytic structure of
+the two amplitudes are intimately related each other: the boundary reflection
+amplitude is a square-root of the bulk scattering amplitude. Using such
+relation as a guide and taking known results at weak and strong coupling limits
+as inputs, we find the reflection amplitude of an elementary magnon off Z=0
+giant graviton boundary. The reflection phase factor is shown to solve crossing
+and unitarity relations. We then compute the reflection amplitude of magnon
+bound-state off the Z=0 brane boundary and observe that its analytic structures
+are again intimately related to the bulk scattering and the Y=0 boundary
+reflection amplitudes. We also take dyonic giant magnon limit of these
+reflection amplitudes and confirm that their phase-shifts agree completely with
+string worldsheet computations based on complex sine-Gordon soliton scattering.",0712.4144v3
+2012-10-15,"Exciton-magnon transitions in the frustrated chromium antiferromagnets CuCrO2, alpha-CaCr2O4, CdCr2O4, and ZnCr2O4","We report on optical transmission spectroscopy of the Cr-based frustrated
+triangular antiferromagnets CuCrO2 and alpha-CaCr2O4, and the spinels CdCr2O4
+and ZnCr2O4 in the near-infrared to visible-light frequency range. We explore
+the possibility to search for spin correlations far above the magnetic ordering
+temperature and for anomalies in the magnon lifetime in the magnetically
+ordered state by probing exciton-magnon sidebands of the spin-forbidden
+crystal-field transitions of the Cr3+ ions (spin S = 3/2). In CuCrO2 and
+alpha-CaCr2O4 the appearance of fine structures below T_N is assigned to magnon
+sidebands by comparison with neutron scattering results. The temperature
+dependence of the line width of the most intense sidebands in both compounds
+can be described by an Arrhenius law. For CuCrO2 the sideband associated with
+the 4A2 -> 2T2 transition can be observed even above T_N. Its line width does
+not show a kink at the magnetic ordering temperature and can alternatively be
+described by a Z2 vortex scenario proposed previously for similar materials.
+The exciton-magnon features in alpha-CaCr2O4 are more complex due to the
+orthorhombic distortion. While for CdCr2O4 magnon sidebands are identified
+below T_N and one sideband excitation is found to persist across the magnetic
+ordering transition, only a weak fine structure related to magnetic ordering
+has been observed in ZnCr2O4.",1210.3938v2
+2014-08-13,High Cooperativity Cavity QED with Magnons at Microwave Frequencies,"Using a sub-millimetre sized YIG (Yttrium Iron Garnet) sphere mounted in a
+magnetic field-focusing cavity, we demonstrate an ultra-high cooperativity of
+$10^5$ between magnon and photon modes at millikelvin temperatures and
+microwave frequencies. The cavity is designed to act as a magnetic dipole by
+using a novel multiple-post approach, effectively focusing the cavity magnetic
+field within the YIG crystal with a filling factor of 3%. Coupling strength
+(normal-mode splitting) of 2 GHz, (equivalent to 76 cavity linewidths or $0.3$
+Hz per spin), is achieved for a bright cavity mode that constitutes about 10%
+of the photon energy and shows that ultra-strong coupling is possible in spin
+systems at microwave frequencies. With straight forward optimisations we
+demonstrate that with that this system has the potential to reach
+cooperativities of $10^7$, corresponding to a normal mode splitting of 5.2 GHz
+and a coupling per spin approaching 1 Hz. We also observe a three-mode strong
+coupling regime between a dark cavity mode and a magnon mode doublet pair,
+where the photon-magnon and magnon-magnon couplings (normal-mode splittings)
+are 143 MHz and 12.5 MHz respectively, with HWHM bandwidth of about 0.5 MHz.",1408.2905v3
+2014-10-14,Low frequency noise peak near magnon emission energy in magnetic tunnel junctions,"We report on the low frequency (LF) noise measurements in magnetic tunnel
+junctions (MTJs) below 4 K and at low bias, where the transport is strongly
+affected by scattering with magnons emitted by hot tunnelling electrons, as
+thermal activation of magnons from the environment is suppressed. For both
+CoFeB/MgO/CoFeB and CoFeB/AlO$_{x}$/CoFeB MTJs, enhanced LF noise is observed
+at bias voltage around magnon emission energy, forming a peak in the bias
+dependence of noise power spectra density, independent of magnetic
+configurations. The noise peak is much higher and broader for unannealed
+AlO$_{x}$-based MTJ, and besides Lorentzian shape noise spectra in the
+frequency domain, random telegraph noise (RTN) is visible in the time traces.
+During repeated measurements the noise peak reduces and the RTN becomes
+difficult to resolve, suggesting defects being annealed. The Lorentzian shape
+noise spectra can be fitted with bias-dependent activation of RTN, with the
+attempt frequency in the MHz range, consistent with magnon dynamics. These
+findings suggest magnon-assisted activation of defects as the origin of the
+enhanced LF noise.",1410.3586v2
+2015-02-06,Higgs Mode and Magnon Interactions in 2D Quantum Antiferromagnets from Raman Scattering,"We present a theory for Raman scattering on 2D quantum antiferromagnets. The
+microscopic Fleury-Loudon Hamiltonian is expressed in terms of an effective
+$O(3)$ - model. Well within the N\'eel ordered phase, the Raman spectrum
+contains a two-magnon and a two-Higgs contribution, which are calculated
+diagramatically. The vertex functions for both the Higgs and magnon
+contributions are determined from a numerical solution of the corresponding
+Bethe-Salpeter equation. Due to the momentum dependence of the Raman vertex in
+the relevant $B_{1g}+E_{2g}$ symmetry, the contribution from the Higgs mode is
+strongly suppressed. Except for intermediate values of the Higgs mass, it does
+not show up as separate peak in the spectrum but gives rise to a broad
+continuum above the dominant contribution from two-magnon excitations. The
+latter give rise to a broad, asymmetric peak at $\omega\simeq 2.44\, J$, which
+is a result of magnon-magnon interactions mediated by the Higgs mode. The full
+Raman spectrum is determined completely by the antiferromagnetic exchange
+coupling $J$ and a dimensionless Higgs mass. Experimental Raman spectra of
+undoped cuprates turn out to be in very good agreement with the theory only
+with inclusion of the Higgs contribution. They thus provide a clear signature
+of the presence of a Higgs mode in spin one-half 2D quantum antiferromagnets.",1502.01857v4
+2015-03-25,Rigorous numerical study of strong microwave photon-magnon coupling in all-dielectric magnetic multilayers,"We demonstrate theoretically a strong local enhancement of the intensity of
+the in-plane microwave magnetic field in multilayered structures made from a
+magneto-insulating yttrium iron garnet (YIG) layer sandwiched between two
+non-magnetic layers with a high dielectric constant matching that of YIG. The
+enhancement is predicted for the excitation regime when the microwave magnetic
+field is induced inside the multilayer by the transducer of a stripline
+Broadband Ferromagnetic Resonance (BFMR) setup. By means of a rigorous
+numerical solution of the Landau-Lifshitz-Gilbert equation consistently with
+the Maxwell's equations, we investigate the magnetisation dynamics in the
+multilayer. We reveal a strong photon-magnon coupling, which manifests itself
+as anti-crossing of the ferromagnetic resonance (FMR) magnon mode supported by
+the YIG layer and the electromagnetic resonance mode supported by the whole
+multilayered structure. The frequency of the magnon mode depends on the
+external static magnetic field, which in our case is applied tangentially to
+the multilayer in the direction perpendicular to the microwave magnetic field
+induced by the stripline of the BFMR setup. The frequency of the
+electromagnetic mode is independent of the static magnetic field. Consequently,
+the predicted photon-magnon coupling is sensitive to the applied magnetic field
+and thus can be used in magnetically tuneable metamaterials based on
+simultaneously negative permittivity and permeability achievable thanks to the
+YIG layer. We also suggest that the predicted photon-magnon coupling may find
+applications in microwave quantum information systems.",1503.07282v1
+2016-04-18,Magnon Hall effect in AB-stacked bilayer honeycomb quantum magnets,"Motivated by the fact that many bilayer quantum magnets occur in nature, we
+generalize the study of thermal Hall transports of spin excitations to bilayer
+magnetic systems. It is shown that bilayer magnetic systems can be coupled
+either ferromagnetically or antiferromagnetically. We study both scenarios on
+the honeycomb lattice and show that the system realizes topologically
+nontrivial magnon bands induced by alternating next-nearest-neighbour
+Dzyaloshinsky-Moriya interaction (DMI). As a result, the bilayer system
+realizes both magnon Hall effect and magnon spin Nernst effect. We show that
+antiferromagnetically coupled layers differ from ferromagnetically coupled
+layers by a sign change in the conductivities as the magnetic field is
+reversed. Furthermore, Chern number protected magnon edge states are observed
+and propagate in the same direction on the top and bottom layers in
+ferromagnetically coupled layers, whereas the magnon edge states propagate in
+opposite directions for antiferromagnetically coupled layers.",1604.05292v9
+2017-08-14,Weyl magnons in noncoplanar stacked kagome antiferromagnets,"Weyl nodes have been experimentally realized in photonic, electronic, and
+phononic crystals. However, magnonic Weyl nodes are yet to be seen
+experimentally. In this paper, we propose Weyl magnon nodes in noncoplanar
+stacked frustrated kagome antiferromagnets, naturally available in various real
+materials. Most crucially, the Weyl nodes in the current system occur at the
+lowest excitation and possess a topological (anomalous) thermal Hall effect,
+therefore they are experimentally accessible at low temperatures due to the
+population effect of bosonic quasiparticles. In stark contrast to other
+magnetic systems, the current Weyl nodes do not rely on time-reversal symmetry
+breaking by the magnetic order. Rather, they result from explicit
+macroscopically broken time reversal symmetry by the scalar spin chirality of
+noncoplanar spin textures, and can be generalized to chiral spin liquid states.
+Moreover, the scalar spin chirality gives a real space Berry curvature which is
+not available in previously studied magnetic Weyl systems. We show the
+existence of magnon arc surface states connecting projected Weyl magnon nodes
+on the surface Brillouin zone. We also uncover the first realization of
+triply-degenerate nodal magnon point in the non-collinear regime with zero
+scalar spin chirality.",1708.04240v6
+2018-04-19,Effect of magnons on interfacial phonon drag in YIG/metal systems,"We examine substrate-to-film interfacial phonon drag on typical spin Seebeck
+heterostructures, in particular studying the effect of ferromagnetic magnons on
+the phonon-electron drag dynamics at the interface. We investigate with high
+precision the effect of magnons in the Pt|YIG heterostructure by designing a
+magnon drag thermocouple; a hybrid sample with both a Pt|YIG film and Pt|GGG
+interface accessible isothermally via a 6 nm Pt film patterned in a rectangular
+U shape with one arm on the 250 nm YIG film and the other on GGG. We measure
+the voltage between the isothermal ends of the U, while applying a temperature
+gradient parallel to the arms and perpendicular to the bottom connection. With
+a uniform applied temperature gradient, the Pt acts as a differential
+thermocouple. We conduct temperature-dependent longitudinal thermopower
+measurements on this sample. Results show that the YIG interface actually
+decreases the thermopower of the film, implying that magnons impede phonon
+drag. We repeat the experiment using metals with low spin Hall angles, Ag and
+Al, in place of Pt. We find that the phonon drag peak in thermopower is killed
+in samples where the metallic interface is with YIG. We also investigate
+magneto-thermopower and YIG film thickness dependence. These measurements
+confirm our findings that magnons impede the phonon-electron drag interaction
+at the metallic interface in these heterostructures.",1804.07023v1
+2017-12-18,Magnon-induced non-Markovian friction of a domain wall in a ferromagnet,"Motivated by the recent study on the quasiparticle-induced friction of
+solitons in superfluids, we theoretically study magnon-induced intrinsic
+friction of a domain wall in a one-dimensional ferromagnet. To this end, we
+start by obtaining the hitherto overlooked dissipative interaction of a domain
+wall and its quantum magnon bath to linear order in the domain-wall velocity
+and to quadratic order in magnon fields. An exact expression for the pertinent
+scattering matrix is obtained with the aid of supersymmetric quantum mechanics.
+We then derive the magnon-induced frictional force on a domain wall in two
+different frameworks: time-dependent perturbation theory in quantum mechanics
+and the Keldysh formalism, which yield identical results. The latter, in
+particular, allows us to verify the fluctuation-dissipation theorem explicitly
+by providing both the frictional force and the correlator of the associated
+stochastic Langevin force. The potential for magnons induced by a domain wall
+is reflectionless, and thus the resultant frictional force is non-Markovian
+similarly to the case of solitons in superfluids. They share an intriguing
+connection to the Abraham-Lorentz force that is well-known for its causality
+paradox. The dynamical responses of a domain wall are studied under a few
+simple circumstances, where the non-Markovian nature of the frictional force
+can be probed experimentally. Our work, in conjunction with the previous study
+on solitons in superfluids, shows that the macroscopic frictional force on
+solitons can serve as an effective probe of the microscopic degrees of freedom
+of the system.",1712.06578v1
+2018-09-19,"From ""Weak"" to ""Strong"" Hole Confinement in a Mott Insulator","We study the problem of a single hole in an Ising antiferromagnet and, using
+the magnon expansion and analytical methods, determine the expansion
+coefficients of its wave function in the magnon basis. In the 1D case, the hole
+is ""weakly"" confined in a potential well and the magnon coefficients decay
+exponentially in the absence of a string potential. This behavior is in sharp
+contrast to the 2D square plane where the hole is ""strongly"" confined by a
+string potential and the magnon coefficients decay superexponentially. The
+latter is identified here to be a fingerprint of the strings in doped
+antiferromagnets that can be recognized in the numerical or cold atom
+simulations of the 2D doped Hubbard model. Finally, we attribute the
+differences between the 1D and 2D cases to the magnon-magnon interactions being
+crucially important in a 1D spin system.",1809.07120v6
+2019-11-28,Magnon damping in the zigzag phase of the Kitaev-Heisenberg-$Γ$ model on a honeycomb lattice,"We calculate magnon dispersions and damping in the Kitaev-Heisenberg model
+with an off-diagonal exchange $\Gamma$ and isotropic third-nearest-neighbor
+interaction $J_3$ on a honeycomb lattice. This model is relevant to a
+description of the magnetic properties of iridium oxides $\alpha$-Li$_2$IrO$_3$
+and Na$_2$IrO$_3$, and Ru-based materials such as $\alpha$-RuCl$_3$. We use an
+unconventional parametrization of the spin-wave expansion, in which each
+Holstein-Primakoff boson is represented by two conjugate hermitian operators.
+This approach gives us an advantage over the conventional one in identifying
+parameter regimes where calculations can be performed analytically. Focusing on
+the parameter regime with the zigzag spin pattern in the ground state that is
+consistent with experiments, we demonstrate that one such region is $\Gamma =
+K>0$, where $K$ is the Kitaev coupling. Within our approach we are able to
+obtain explicit analytical expressions for magnon energies and eigenstates and
+go beyond the standard linear spin-wave theory approximation by calculating
+magnon damping and demonstrating its role in the dynamical structure factor. We
+show that the magnon damping effects in both Born and self-consistent
+approximations are very significant, underscoring the importance of non-linear
+magnon coupling in interpreting broad features in the neutron-scattering
+spectra.",1911.12829v2
+2019-12-22,First-principles study of magnon-phonon interactions in gadolinium iron garnet,"We obtained the spin-wave spectrum based on a first-principles method of
+exchange constants, calculated the phonon spectrum by the first-principles
+phonon calculation method, and extracted the broadening of the magnon spectrum,
+$\Delta \omega$, induced by magnon-phonon interactions in gadolinium iron
+garnet (GdIG). Using the obtained exchange constants, we reproduce the
+experimental Curie temperature and the compensation temperature from spin
+models using Metropolis Monte Carlo (MC) simulations. In the lower-frequency
+regime, the fitted positions of the magnon-phonon dispersion crossing points
+are consistent with the inelastic neutron scattering experiment. We found that
+the $\Delta \omega$ and magnon wave vector $k$ have a similar relationship in
+YIG. The broadening of the acoustic spin-wave branch is proportional to
+$k^{2}$, while that of the YIG-like acoustic branch and the optical branch are
+a constant. At a specific $k$, the magnon-phonon thermalization time of
+$\tau_{mp}$ are approximately $10^{-9}$~s, $10^{-13}$~s, and $10^{-14}$~s for
+acoustic branch, YIG-like acoustic branch, and optical branch, respectively.
+This research provides specific and effective information for developing a
+clear understanding of the spin-wave mediated spin Seebeck effect and
+complements the lack of lattice dynamics calculations of GdIG.",1912.10432v1
+2019-05-12,Elementary excitations in the ordered phase of spin-1/2 J1-J2 model on square lattice,"We use recently proposed four-spin bond-operator technique (BOT) to discuss
+spectral properties of frustrated spin-$\frac12$ $J_1$--$J_2$ Heisenberg
+antiferromagnet on square lattice at $J_2<0.4J_1$ (i.e., in the N\'eel ordered
+phase). This formalism is convenient for the consideration of low-lying
+excitations which appear in conventional approaches as multi-magnon bound
+states (e.g., the Higgs excitation) because separate bosons describe them in
+BOT. At $J_2=0$, the obtained magnon spectrum describes accurately available
+experimental data. However, calculated one-magnon spectral weights and the
+transverse dynamical structure factor (DSF) do not reproduce experimental
+findings quantitatively around the momentum ${\bf k}=(\pi,0)$. Then, we do not
+support the conjecture that the continuum of excitations observed
+experimentally and numerically near ${\bf k}=(\pi,0)$ is of the Higgs-magnon
+origin. Upon $J_2$ increasing, one-magnon spectral weights decrease and spectra
+of high-energy spin-0 and spin-1 excitations move down. One of spin-0
+quasiparticles becomes long-lived and its spectrum merges with the magnon
+spectrum in the most part of the Brillouin zone at $J_2\approx0.3J_1$. We
+predict that the Higgs excitation and another spin-0 quasiparticle become
+long-lived around ${\bf k}=(\pi/2,\pi/2)$ at $J_2\agt0.3J_1$ and produce sharp
+anomalies in the longitudinal DSF.",1905.04710v2
+2020-09-10,Spin waves in alloys at finite temperatures: application for FeCo magnonic crystal,"We study theoretically the influence of the temperature and disorder on the
+spin wave spectrum of the magnonic crystal Fe$_{1-c}$Co$_{c}$. Our formalism is
+based on the analysis of a Heisenberg Hamiltonian by means of the wave vector
+and frequency dependent transverse magnetic susceptibility. The exchange
+integrals entering the model are obtained from the \emph{ab initio} magnetic
+force theorem. The coherent potential approximation is employed to treat the
+disorder and random phase approximation in order to account for the softening
+of the magnon spectrum at finite temperatures. The alloy turns out to exhibit
+many advantageous properties for spintronic applications. Apart from high Curie
+temperature, its magnonic bandgap remains stable at elevated temperatures and
+is largely unaffected by the disorder. We pay particular attention to the
+attenuation of magnons introduced by the alloying. The damping turns out to be
+a non-monotonic function of the impurity concentration due to the non-trivial
+evolution of the value of exchange integrals with the Co concentration. The
+disorder induced damping of magnons is estimated to be much smaller than their
+Landau damping.",2009.04712v6
+2021-02-26,Control of the Bose-Einstein Condensation of Magnons by the Spin-Hall Effect,"Previously, it has been shown that rapid cooling of yttrium-iron-garnet
+(YIG)/platinum (Pt) nano structures, preheated by an electric current sent
+through the Pt layer, leads to overpopulation of a magnon gas and to subsequent
+formation of a Bose-Einstein condensate (BEC) of magnons. The spin Hall effect
+(SHE), which creates a spin-polarized current in the Pt layer, can inject or
+annihilate magnons depending on the electric current and applied field
+orientations. Here we demonstrate that the injection or annihilation of magnons
+via the SHE can prevent or promote the formation of a rapid cooling induced
+magnon BEC. Depending on the current polarity, a change in the BEC threshold of
+-8% and +6% was detected. These findings demonstrate a new method to control
+macroscopic quantum states, paving the way for their application in spintronic
+devices.",2102.13481v2
+2015-07-14,Wiedemann-Franz Law for Magnon Transport,"One of the main goals of spintronics is to improve transport of information
+carriers and to achieve new functionalities with ultra-low dissipation. A most
+promising strategy for this holy grail is to use pure magnon currents created
+and transported in insulating magnets, in the complete absence of any
+conducting metallic elements. Here we propose a realistic solution to this
+fundamental challenge by analyzing magnon and heat transport in insulating
+ferromagnetic junctions. We calculate all transport coefficients for magnon
+transport and establish Onsager relations between them. We theoretically
+discover that magnon transport in junctions has a universal behavior, i.e. is
+independent of material parameters, and establish a magnon analog of the
+celebrated Wiedemann-Franz law which governs charge transport at low
+temperatures. We calculate the Seebeck and Peltier coefficients which are
+crucial quantities for spin caloritronics and demonstrate that they assume
+universal values in the low temperature limit. Finally, we show that our
+predictions are within experimental reach with current device and measurement
+technologies.",1507.03807v5
+2018-08-22,Role of magnons and the size effect in heat transport through an insulating ferromagnet/insulator interface,"While recent experiments on the spin Seebeck effect have revealed the
+decisive role of the magnon contribution to the heat current $Q$ in hybrid
+systems containing thin ferromagnetic layers, the available acoustic mismatch
+theory does not account for their magnetic properties. Here, we analyze
+theoretically the heat transfer through an insulating ferromagnet (F)
+sandwiched between two insulators (I). Depending on the relation between the F
+thickness, $d$, and the mean free path of phonons generated by magnons,
+$l_{ls}$, we reveal two qualitatively different regimes in the nonlinear heat
+transport through the F/I interfaces. Namely, in thick F layers the regime of
+conventional ""Joule"" heating with $Q \propto T_s^4$ is realized, in which the
+detailed structure of the F/I interfaces is inessential. Here $T_s$ is the
+magnon temperature. By contrast, in thin F layers with $d\ll l_{ls}$, most of
+phonons emitted by magnons can leave F without being absorbed in its interior,
+giving rise to the \emph{magnon overheating} regime with $Q \propto T_s^m$ and
+$m\gtrsim7$. Conditions for the examination of both regimes and the
+determination of $T_s$ from experiments are discussed. The reported results are
+relevant for the theoretical analysis of the spin Seebeck effect and the
+development of magnon-based spin caloritronic devices.",1808.07294v1
+2019-07-17,Neutron Scattering Study of Magnetic Anisotropy in a Tetragonal Antiferromagnet Bi$_2$CuO$_4$,"We present a comprehensive study of magnon excitations in the tetragonal
+easy-plane anti-ferromagnet Bi$_2$CuO$_4$ using inelastic neutron scattering
+and spin wave analyses. The nature of low energy magnons, and hence the
+anisotropy in this material, has been controversial. We show unambiguously that
+the low energy magnon spectrum consists of a gapped and a gapless mode, which
+we attribute to out-of-plane and in-plane spin fluctuations, respectively. We
+modelled the observed magnon spectrum using linear spin wave analysis of a
+minimal anisotropic spin model motivated by the lattice symmetry. By studying
+the magnetic field dependence of the (1, 0, 0) Bragg peak intensity and the
+in-plane magnon intensity, we observed a spin-flop transition in the $ab$ plane
+at $\sim0.4$~T which directly indicates the existence of a small in-plane
+anisotropy that is classically forbidden. It is only by taking into account
+magnon zero-point fluctuations beyond the linear spin wave approximation, we
+could explain this in-plane anisotropy and its magnitude, the latter of which
+is deduced from critical field of the spin-flop transition. The microscopic
+origins of the observed anisotropic interactions are also discussed. We found
+that our data is inconsistent with a large Dzyaloshinskii-Moriya interaction,
+which suggests a potential departure of Bi$_2$CuO$_4$ from the conventional
+theories of magnetic anisotropy for other cuprates.",1907.07784v2
+2020-03-09,Predicted strong coupling of solid-state spins via a single magnon mode,"We propose an approach to realize a hybrid quantum system composed of a
+diamond nitrogen-vacancy (NV) center spin coupled to a magnon mode of the
+low-damping, low-moment organic ferrimagnet vanadium tetracyanoethylene. We
+derive an analytical expression for the spin-magnon cooperativity as a function
+of NV position under a micron-scale perpendicularly magnetized disk, and show
+that, surprisingly, the cooperativity will be higher using this magnetic
+material than in more conventional materials with larger magnetic moments, due
+to in part to the reduced demagnetization field. For reasonable experimental
+parameters, we predict that the spin-magnon-mode coupling strength is $g\sim
+10$ kHz. For isotopically pure $^{12}$C diamond we predict strong coupling of
+an NV spin to the unoccupied magnon mode, with cooperativity $\mathcal C=6$ for
+a wide range of NV spin locations within the diamond, well within the spatial
+precision of NV center implantation. Thus our proposal describes a practical
+pathway for single-spin-state-to-single-magnon-occupancy transduction and for
+entangling NV centers over micron length scales.",2003.04341v2
+2020-04-20,Giant transition-state enhancement of quasiparticle spin-Hall effect in an exchange-spin-split superconductor detected by non-local magnon spin-transport,"Although recent experiments and theories have shown a variety of exotic
+transport properties of non-equilibrium quasiparticles (QPs) in superconductor
+(SC)-based devices with either Zeeman or exchange spin-splitting, how QP
+interplays with magnon spin currents remains elusive. Here, using non-local
+magnon spin-transport devices where a singlet SC (Nb) on top of a ferrimagnetic
+insulator (Y3Fe5O12) serves as a magnon spin detector, we demonstrate that the
+conversion efficiency of magnon spin to QP charge via inverse spin-Hall effect
+(iSHE) in such an exchange-spin-split SC can be greatly enhanced by up to 3
+orders of magnitude compared with that in the normal state, particularly when
+its interface superconducting gap matches the magnon spin accumulation. Through
+systematic measurements with varying the current density and SC thickness, we
+identify that superconducting coherence peaks and exchange spin-splitting of
+the QP density-of-states, yielding a larger spin excitation while retaining a
+modest QP charge-imbalance relaxation, are responsible for the giant QP iSHE.
+The latter exchange-field-modified QP relaxation is experimentally proved by
+spatially resolved measurements with varying the separation of electrical
+contacts on the spin-split Nb.",2004.09467v2
+2020-07-03,Light-induced topological magnons in two-dimensional van der Waals magnets,"Driving a two-dimensional Mott insulator with circularly polarized light
+breaks time-reversal and inversion symmetry, which induces an optically-tunable
+synthetic scalar spin chirality interaction in the effective low-energy spin
+Hamiltonian. Here, we show that this mechanism can stabilize topological magnon
+excitations in honeycomb ferromagnets and in optical lattices. We find that the
+irradiated quantum magnet is described by a Haldane model for magnons that
+hosts topologically-protected edge modes. We study the evolution of the magnon
+spectrum in the Floquet regime and via time propagation of the magnon
+Hamiltonian for a slowly varying pulse envelope. Compared to similar but
+conceptually distinct driving schemes based on the Aharanov-Casher effect, the
+dimensionless light-matter coupling parameter $\lambda = eEa/\hbar\omega$ at
+fixed electric field strength is enhanced by a factor $\sim 10^5$. This
+increase of the coupling parameter allows to induce a topological gap of the
+order of $\Delta \approx 2$ meV with realistic laser pulses, bringing an
+experimental realization of light-induced topological magnon edge states within
+reach.",2007.01714v4
+2020-08-24,Loop-gas description of the localized-magnon states on the kagome lattice with open boundary conditions,"The high-field regime of the spin-s XXZ antiferromagnet on the kagome lattice
+gives rise to macroscopically degenerate ground states thanks to a completely
+flat lowest single-magnon band. The corresponding excitations can be localized
+on loops in real space and have been coined ""localized magnons"". Thus, the
+description of the many-body ground states amounts to characterizing the
+allowed classical loop configurations and eliminating the quantum mechanical
+linear relations between them. Here, we investigate this loop-gas description
+on finite kagome lattices with open boundary conditions and compare the results
+with exact diagonalization for the spin-1/2 XY model on the same lattice. We
+find that the loop gas provides an exact account of the degenerate ground-state
+manifold while a hard-hexagon description misses contributions from nested loop
+configurations. The densest packing of the loops corresponds to a magnon
+crystal that according to the zero-temperature magnetization curve is a stable
+ground state of the spin-1/2 XY model in a window of magnetic fields of about
+4% of the saturation field just below this saturation field. We also present
+numerical results for the specific heat obtained by the related methods of
+thermal pure quantum (TPQ) states and the finite-temperature Lanczos method
+(FTLM). For a field in the stability range of the magnon crystal, one finds a
+low-temperature maximum of the specific heat that corresponds to a
+finite-temperature phase transition into the magnon crystal at low
+temperatures.",2008.10614v2
+2020-11-19,Topological insulators and semimetals in classical magnetic systems,"Pursuing topological phases in natural and artificial materials is one of the
+central topics in modern physical science and engineering. In classical
+magnetic systems, spin waves (or magnons) and magnetic solitons (such as domain
+wall, vortex, skyrmion, etc) represent two important excitations. Recently, the
+topological insulator and semimetal states in magnon- and soliton-based
+crystals (or metamaterials) have attracted growing attention owing to their
+interesting dynamics and promising applications for designing robust spintronic
+devices. Here, we give an overview of current progress of topological phases in
+structured classical magnetism. We first provide a brief introduction to spin
+wave, and discuss its topological properties including magnon Hall effects,
+topological magnon insulators, and Dirac (Weyl) magnon semimetals. Appealing
+proposal of topological magnonic devices is also highlighted. We then review
+the collective-coordinate approach for describing the dynamics of magnetic
+soliton lattice. Pedagogical topological models such as the
+Su-Schrieffer-Heeger model and the Haldane model and their manifestation in
+magnetic soliton crystals are elaborated. Then we focus on the topological
+properties of magnetic solitons, by theoretically analyzing the first-order
+topological insulating phases in low dimensional systems and higher-order
+topological states in breathing crystals. Finally, we discuss the experimental
+realization and detection of the edge states in both the magnonic and solitonic
+crystals. We remark the challenges and future prospects before concluding this
+article.",2011.09751v1
+2021-01-21,Magnon-mediated interlayer coupling in an all-antiferromagnetic junction,"The interlayer coupling mediated by fermions in ferromagnets brings about
+parallel and anti-parallel magnetization orientations of two magnetic layers,
+resulting in the giant magnetoresistance, which forms the foundation in
+spintronics and accelerates the development of information technology. However,
+the interlayer coupling mediated by another kind of quasi-particle, boson, is
+still lacking. Here we demonstrate such a static interlayer coupling at room
+temperature in an antiferromagnetic junction Fe2O3/Cr2O3/Fe2O3, where the two
+antiferromagnetic Fe2O3 layers are functional materials and the
+antiferromagnetic Cr2O3 layer serves as a spacer. The N\'eel vectors in the top
+and bottom Fe2O3 are strongly orthogonally coupled, which is bridged by a
+typical bosonic excitation (magnon) in the Cr2O3 spacer. Such an orthogonally
+coupling exceeds the category of traditional collinear interlayer coupling via
+fermions in ground state, reflecting the fluctuating nature of the magnons, as
+supported by our magnon quantum well model. Besides the fundamental
+significance on the quasi-particle-mediated interaction, the strong coupling in
+an antiferromagnetic magnon junction makes it a realistic candidate for
+practical antiferromagnetic spintronics and magnonics with ultrahigh-density
+integration.",2101.08665v1
+2021-07-06,Topological magnon insulator spin excitations in the two-dimensional ferromagnet CrBr$_3$,"Topological magnons are bosonic analogues of topological fermions in
+electronic systems. They have been studied extensively by theory but rarely
+realized by experiment. Here, by performing inelastic neutron scattering
+measurements on single crystals of a two-dimensional ferromagnet CrBr$_3$,
+which was classified as Dirac magnon semimetal featured by the linear bands
+crossing at the Dirac points, we fully map out the magnetic excitation spectra,
+and reveal that there is an apparent gap of $\sim$3.5~meV between the acoustic
+and optical branches of the magnons at the K point. By collaborative efforts
+between experiment and theoretical calculations using a five-orbital Hubbard
+model obtained from first-principles calculations to derive the exchange
+parameters, we find that a Hamiltonian with Heisenberg exchange interactions,
+next-nearest-neighbor Dzyaloshinskii-Moriya (DM) interaction, and single-ion
+anisotropy is more appropriate to describe the system. Calculations using the
+model show that the lower and upper magnon bands separated by the gap exhibit
+Chern numbers of $\pm1$. These results indicate that CrBr$_3$ is a topological
+magnon insulator, where the nontrivial gap is a result of the DM interaction.",2107.02486v1
+2021-08-01,Directional excitation of a high-density magnon gas using coherently driven spin waves,"Controlling magnon densities in magnetic materials enables driving spin
+transport in magnonic devices. We demonstrate the creation of large,
+out-of-equilibrium magnon densities in a thin-film magnetic insulator via
+microwave excitation of coherent spin waves and subsequent multi-magnon
+scattering. We image both the coherent spin waves and the resulting incoherent
+magnon gas using scanning-probe magnetometry based on electron spins in
+diamond. We find that the gas extends unidirectionally over hundreds of
+micrometers from the excitation stripline. Surprisingly, the gas density far
+exceeds that expected for a boson system following a Bose-Einstein distribution
+with a maximum value of the chemical potential. We characterize the momentum
+distribution of the gas by measuring the nanoscale spatial decay of the
+magnetic stray fields. Our results show that driving coherent spin waves leads
+to a strong out-of-equilibrium occupation of the spin-wave band, opening new
+possibilities for controlling spin transport and magnetic dynamics in target
+directions.",2108.00467v1
+2021-12-09,From the spin eigenmodes of isolated Néel skyrmions to the magnonic bands of a skyrmionic crystal: a micromagnetic study as a function of the strength of both the interfacial Dzyaloshinskii-Moriya and the exchange constants,"The presence of interfacial Dzyaloshinskii-Moriya interaction (DMI) may lead
+to the appearance of N\'eel skyrmions in ferromagnetic films. These
+topologically protected structures, whose diameter is as small as a few
+nanometers, can be nowadays stabilized at room temperature and have been
+proposed for the realization of artificial magnonic crystals and new spintronic
+devices, such as racetrack memories. In this perspective, it is of utmost
+importance to analyze their dynamical properties in the GHz range, i.e. in the
+operation range of current communication devices. Here we exploited the
+software MuMax3 to calculate the dynamics of N\'eel skyrmions in the range
+between 1 and 30 GHz, considering first the eigenmodes of an isolated skyrmion,
+then the case of two interacting skyrmions and finally a linear chain,
+representing a one-dimensional magnonic crystal, whose magnonic band structure
+has been calculated as a function of the strength of both the DMI- and the
+exchange-constants, namely D and A. The magnonic bands can be interpreted as
+derived from the eigenmodes of isolated skyrmions, even if hybridization and
+anti-crossing phenomena occur for specific ranges of values of D and A.
+Therefore, varying the latter parameters, for instance by a proper choice of
+the materials and thicknesses, may enable one to fine-tune the permitted and
+forbidden frequency interval of the corresponding magnonic crystal.",2112.04967v2
+2022-03-21,Magnon squeezing enhanced ground-state cooling in cavity magnomechanics,"Cavity magnomechanics has recently become a new platform for studying
+macroscopic quantum phenomena. The magnetostriction induced vibration mode of a
+large-size ferromagnet or ferrimagnet reaching its ground state represents a
+genuine macroscopic quantum state. Here we study the ground-state cooling of
+the mechanical vibration mode in a cavity magnomechanical system, and focus on
+the role of magnon squeezing in improving the cooling efficiency. The magnon
+squeezing is obtained by exploiting the magnon self-Kerr nonlinearity. We find
+that the magnon squeezing can significantly and even completely suppress the
+magnomechanical Stokes scattering. It thus becomes particularly useful in
+realizing ground-state cooling in the unresolved-sideband regime, where the
+conventional sideband cooling protocols become inefficient. We also find that
+the coupling to the microwave cavity plays only an adverse effect in mechanical
+cooling. This makes essentially the two-mode magnomechanical system (without
+involving the microwave cavity) a preferred system for cooling the mechanical
+motion, in which the magnon mode is established by a uniform bias magnetic
+field and a microwave drive field.",2203.10767v4
+2022-03-30,Tunable magnetically induced transparency spectra in magnon-magnon coupled Y3Fe5O12/permalloy bilayers,"Hybrid magnonic systems host a variety of characteristic quantum phenomena
+such as the magnetically-induced transparency (MIT) and Purcell effect, which
+are considered useful for future coherent quantum information processing. In
+this work, we experimentally demonstrate a tunable MIT effect in the
+Y3Fe5O12(YIG)/Permalloy(Py) magnon-magnon coupled system via changing the
+magnetic field orientations. By probing the magneto-optic effects of Py and
+YIG, we identify clear features of MIT spectra induced by the mode
+hybridization between the uniform mode of Py and the perpendicular standing
+spin-wave modes of YIG. By changing the external magnetic field orientations,
+we observe a tunable coupling strength between the YIG's spin-wave modes and
+the Py's uniform mode, upon the application of an out-of-plane magnetic field.
+This observation is theoretically interpreted by a geometrical consideration of
+the Py and YIG magnetization under the oblique magnetic field even at a
+constant interfacial exchange coupling. Our findings show high promise for
+investigating tunable coherent phenomena with hybrid magnonic platforms.",2203.16303v1
+2022-04-29,Entangling mechanical vibrations of two massive ferrimagnets by fully exploiting the nonlinearity of magnetostriction,"Quantum entanglement in the motion of macroscopic objects is of significance
+to both fundamental studies and quantum technologies. Here we show how to
+entangle the mechanical vibration modes of two massive ferrimagnets that are
+placed in the same microwave cavity. Each ferrimagnet supports a magnon mode
+and a low-frequency vibration mode coupled by the magnetostrictive force. The
+two magnon modes are, respectively, coupled to the microwave cavity by the
+magnetic dipole interaction. We first generate a stationary nonlocal entangled
+state between the vibration mode of the ferrimagnet-1 and the magnon mode of
+the ferrimagnet-2. This is realized by continuously driving the ferrimagnet-1
+with a strong red-detuned microwave field and the entanglement is achieved by
+exploiting the magnomechanical parametric down-conversion and the cavity-magnon
+state-swap interaction. We then switch off the pump on the ferrimagnet-1 and,
+simultaneously, turn on a red-detuned pulsed drive on the ferrimagnet-2. The
+latter drive is used to activate the magnomechanical beamsplitter interaction,
+which swaps the magnonic and mechanical states of the ferrimagnet-2.
+Consequently, the previously generated phonon-magnon entanglement is
+transferred to the mechanical modes of two ferrimagnets. The work provides a
+scheme to prepare entangled states of mechanical motion of two massive objects,
+which may find applications in various studies exploiting macroscopic entangled
+states.",2204.14010v4
+2022-05-27,Magnonic Casimir Effect in Ferrimagnets,"Quantum fluctuations are the key concepts of quantum mechanics. Quantum
+fluctuations of quantum fields induce a zero-point energy shift under spatial
+boundary conditions. This quantum phenomenon, called the Casimir effect, has
+been attracting much attention beyond the hierarchy of energy scales, ranging
+from elementary particle physics to condensed matter physics together with
+photonics. However, the application of the Casimir effect to spintronics has
+not yet been investigated enough, particularly to ferrimagnetic thin films,
+although yttrium iron garnet (YIG) is one of the best platforms for
+spintronics. Here we fill this gap. Using the lattice field theory, we
+investigate the Casimir effect induced by quantum fields for magnons in
+insulating magnets and find that the magnonic Casimir effect can arise not only
+in antiferromagnets but also in ferrimagnets including YIG thin films. Our
+result suggests that YIG, the key ingredient of magnon-based spintronics, can
+serve also as a promising platform for manipulating and utilizing Casimir
+effects, called Casimir engineering. Microfabrication technology can control
+the thickness of thin films and realize the manipulation of the magnonic
+Casimir effect. Thus, we pave the way for magnonic Casimir engineering.",2205.13802v3
+2022-07-14,Terahertz field-driven magnon upconversion in an antiferromagnet,"Tailored light excitation and nonlinear control of lattice vibrations have
+emerged as powerful strategies to manipulate the properties of quantum
+materials out of equilibrium. Generalizing the use of coherent phonon-phonon
+interactions to nonlinear couplings among other types of collective modes would
+open unprecedented opportunities in the design of novel dynamic functionalities
+in solids. For example, the collective excitations of magnetic order -- magnons
+-- can carry information with little energy dissipation, and their coherent and
+nonlinear control would provide an attractive route to achieve
+collective-mode-based information processing and storage in forthcoming
+spintronics and magnonics. Here, we discover that intense terahertz (THz)
+fields can initiate processes of magnon upconversion mediated by an
+intermediate magnetic resonance. By using a suite of advanced spectroscopic
+tools, including a newly demonstrated two-dimensional (2D) THz polarimetry
+technique enabled by single-shot detection, we unveil the unidirectional nature
+of coupling between distinct magnon modes of a canted antiferromagnet.
+Calculations of spin dynamics further suggest that this coupling is a universal
+feature of antiferromagnets with canted magnetic moments. These results
+demonstrate a route to inducing desirable energy transfer pathways and
+THz-induced coupling between coherent magnons in solids and pave the way for a
+new era in the development of ultrafast control of magnetism.",2207.07103v2
+2022-09-18,Theory of magnon-polaritons in quantum Ising materials,"We present a theory of magnon-polaritons in quantum Ising materials, and
+develop a formalism describing the coupling between light and matter as an
+Ising system is tuned through its quantum critical point. The theory is applied
+to Ising materials having multilevel single-site Hamiltonians, in which
+multiple magnon modes are present, such as the insulating Ising magnet
+LiHoF$_4$ . We find that the magnon-photon coupling strengths may be tuned by
+the applied transverse field, with the coupling between the soft mode present
+in the quantum Ising material and a photonic resonator mode diverging at the
+quantum critical point of the material. A fixed system of spins will not
+exhibit the diamagnetic response expected when light is coupled to mobile spins
+or atoms. Without the diamagnetic response, one expects a divergent
+magnon-photon coupling strength to lead to a superradiant quantum phase
+transition. However, this neglects the effects of damping and decoherence
+present in any real system. We show that damping and decoherence may block the
+superradiant quantum phase transition, and lead to weak coupling between the
+soft magnon mode and the resonator mode. The results of the theory are applied
+to experimental data on the model system LiHoF$_4$ in a microwave resonator.",2209.08674v1
+2022-09-19,Observation of nonreciprocal magnon Hanle effect,"The precession of magnon pseudospin about the equilibrium pseudofield, the
+latter capturing the nature of magnonic eigen-excitations in an
+antiferromagnet, gives rise to the magnon Hanle effect. Its realization via
+electrically injected and detected spin transport in an antiferromagnetic
+insulator demonstrates its high potential for devices and as a convenient probe
+for magnon eigenmodes and the underlying spin interactions in the
+antiferromagnet. Here, we observe a nonreciprocity in the Hanle signal measured
+in hematite using two spatially separated platinum electrodes as spin
+injector/detector. Interchanging their roles was found to alter the detected
+magnon spin signal. The recorded difference depends on the applied magnetic
+field and reverses sign when the signal passes its nominal maximum at the
+so-called compensation field. We explain these observations in terms of a spin
+transport direction-dependent pseudofield. The latter leads to a
+nonreciprocity, which is found to be controllable via the applied magnetic
+field. The observed nonreciprocal response in the readily available hematite
+films opens interesting opportunities for realizing exotic physics predicted so
+far only for antiferromagnets with special crystal structures.",2209.09040v1
+2022-09-29,Spin Dynamics in Patterned Magnetic Multilayers with Perpendicular Magnetic Anisotropy,"The magnetization dynamics in nanostructures has been extensively studied in
+the last decades, and nanomagnetism has evolved significantly over that time,
+discovering new effects, developing numerous applications, and identifying
+promising new directions. This includes magnonics, an emerging research field
+oriented on the study of spin-wave dynamics and their applications. In this
+context, thin ferromagnetic films with perpendicular magnetic anisotropy (PMA)
+offer interesting opportunities to study spin waves, in particular, due to
+out-of-plane magnetization in remanence or at relatively weak external magnetic
+fields. This is the only magnetization configuration offering isotropic
+in-plane spin-wave propagation within the sample plane, the forward volume
+magnetostatic spin-wave geometry. The isotropic dispersion relation is highly
+important in designing signal-processing devices, offering superior prospects
+for direct replicating various concepts from photonics into magnonics.
+Analogous to photonic or phononic crystals, which are the building blocks of
+optoelectronics and phononics, magnonic crystals are considered as key
+components in magnonics applications. Arrays of nanodots and structured
+ferromagnetic thin films with a periodic array of holes, popularly known as
+antidot lattices based on PMA multilayers have been recently studied. Novel
+magnonic properties related to propagating spin-wave modes, exploitation of the
+band gaps, and confined modes, were demonstrated. Also, the existence of
+nontrivial magnonic band topologies has been shown. Moreover, the combination
+of PMA and Dzyaloshinskii-Moriya interaction leads to the formation of chiral
+magnetization states, including N\'eel domain walls, skyrmions, and skyrmionium
+states.",2209.14824v2
+2022-11-30,Topological magnons driven by the Dzyaloshinskii-Moriya interaction in the centrosymmetric ferromagnet Mn$_5$Ge$_3$,"The phase of the quantum-mechanical wave function can encode a topological
+structure with wide-ranging physical consequences, such as anomalous transport
+effects and the existence of edge states robust against perturbations. While
+this has been exhaustively demonstrated for electrons, properties associated
+with the elementary quasiparticles in magnetic materials are still
+underexplored. Here, we show theoretically and via inelastic neutron scattering
+experiments that the bulk ferromagnet Mn$_5$Ge$_3$ hosts gapped topological
+Dirac magnons. Although inversion symmetry prohibits a net
+Dzyaloshinskii-Moriya interaction in the unit cell, it is locally allowed and
+is responsible for the gap opening in the magnon spectrum. This gap is
+predicted and experimentally verified to close by rotating the magnetization
+away from the $c$-axis with an applied magnetic field. Hence, Mn$_5$Ge$_3$
+realizes a gapped Dirac magnon material in three dimensions. Its tunability by
+chemical doping or by thin film nanostructuring defines an exciting new
+platform to explore and design topological magnons. More generally, our
+experimental route to verify and control the topological character of the
+magnons is applicable to bulk centrosymmetric hexagonal materials, which calls
+for systematic investigation.",2211.16925v2
+2023-03-07,Magnon currents excited by the spin Seebeck effect in ferromagnetic EuS thin films,"A magnetic insulator is an ideal platform to propagate spin information by
+exploiting magnon currents. However, until now, most studies have focused on
+Y$_3$Fe$_5$O$_{12}$ (YIG) and a few other ferri- and antiferromagnetic
+insulators, but not on pure ferromagnets. In this study, we demonstrate for the
+first time that magnon currents can propagate in ferromagnetic insulating thin
+films of EuS. By performing both local and non-local transport measurements in
+18-nm-thick films of EuS using Pt electrodes, we detect magnon currents arising
+from thermal generation by the spin Seebeck effect. By comparing the dependence
+of the local and non-local signals with the temperature (< 30 K) and magnetic
+field (< 9 T), we confirm the magnon transport origin of the non-local signal.
+Finally, we extract the magnon diffusion length in the EuS film (~140 nm), a
+short value in good correspondence with the large Gilbert damping measured in
+the same film.",2303.03833v2
+2023-07-21,Observation of strong coupling between a mechanical oscillator and a cavity-magnon polariton,"Cavity magnomechanics (CMM) is an emerging field and has received much
+attention in the past decade. It deals with coherent couplings among microwave
+cavity photons, magnons and vibration phonons. So far, all previous CMM
+experiments have been operated in the weak-coupling regime. This considerably
+limits prospective various applications of the system. Here, we demonstrate the
+CMM system in the strong-coupling regime and observe the associated normal-mode
+splitting. In this regime, the mechanical oscillator is strongly coupled to a
+cavity-magnon polariton that is formed by strongly coupled cavity photons and
+magnons, and the polariton-mechanics cooperativity reaches $4\times10^3$, which
+is improved by three orders of magnitude than previous CMM experiments. The
+system is then in the triple-strong-coupling regime and the normal modes of the
+system are the hybridization of microwave photons, magnons and phonons. This is
+achieved by significantly reducing the decay rate of the polariton mode using
+coherent perfect absorption and the decay rate is reduced by four orders of
+magnitude. The work paves the way towards coherent control and measurement of
+the quantum states of phonons, photons and magnons, and provides a new platform
+for the study of rich strong-coupling effects in multipartite hybrid systems.",2307.11328v2
+2023-07-22,Quantum parametric amplifiation of phonon-mediated magnon-spin interaction,"The recently developed hybrid magnonics provides new opportunities for
+advances in both the study of magnetism and the development of quantum
+information processing. However, engineering coherent quantum state transfer
+between magnons and specific information carriers, in particular, mechanical
+oscillators and solid-state spins, remains challenging due to the intrinsically
+weak interactions and the frequency mismatch between diffrent components. Here,
+we show how to strongly couple the magnon modes in a nanomagnet to the
+quantized mechanical motion (phonons) of a micromechanical cantilever in a
+hybrid tripartite system. The coherent and enhanced magnon-phonon coupling is
+engineered by introducing the quantum parametric amplifiation of the mechanical
+motion. With experimentally feasible parameters, we show that the mechanical
+parametric drive can be adjusted to drive the system into the strong-coupling
+regime and even the ultrastrong-coupling regime. Furthermore, we show the
+coherent state transfer between the nanomagnet and a nitrogen-vacancy center in
+the dispersive-coupling regime, with the magnon-spin interaction mediated by
+the virtually-excited squeezed phonons. The amplifid mechanical noise can
+hardly interrupt the coherent dynamics of the system even for low mechanical
+quality factors, which removes the requirement of applying additional
+engineered-reservoir techniques. Our work opens up prospects for developing
+novel quantum transducers, quantum memories and high-precision measurements.",2307.11961v1
+2023-08-22,Magnon-mediated qubit coupling determined via dissipation measurements,"Controlled interaction between localized and delocalized solid-state spin
+systems offers a compelling platform for on-chip quantum information processing
+with quantum spintronics. Hybrid quantum systems (HQSs) of localized
+nitrogen-vacancy (NV) centers in diamond and delocalized magnon modes in
+ferrimagnets-systems with naturally commensurate energies-have recently
+attracted significant attention, especially for interconnecting isolated spin
+qubits at length-scales far beyond those set by the dipolar coupling. However,
+despite extensive theoretical efforts, there is a lack of experimental
+characterization of the magnon-mediated interaction between NV centers, which
+is necessary to develop such hybrid quantum architectures. Here, we
+experimentally determine the magnon-mediated NV-NV coupling from the
+magnon-induced self-energy of NV centers. Our results are quantitatively
+consistent with a model in which the NV center is coupled to magnons by dipolar
+interactions. This work provides a versatile tool to characterize HQSs in the
+absence of strong coupling, informing future efforts to engineer entangled
+solid-state systems.",2308.11710v1
+2023-10-29,Higher-order topological corner and bond-localized modes in magnonic insulators,"We theoretically investigate a two-dimensional decorated honeycomb lattice
+framework to realize a second-order topological magnon insulator (SOTMI) phase
+featuring distinct corner-localized modes. Our study emphasizes the pivotal
+role of spin-magnon mapping in characterizing bosonic topological properties,
+which exhibit differences from their fermionic counterparts. We employ a
+symmetry indicator topological invariant to identify and characterize this
+SOTMI phase, particularly for systems respecting time-reversal and ${\sf{C}}_6$
+rotational symmetry. Using a spin model defined on a honeycomb lattice
+geometry, we demonstrate that introducing ``\textit{kekul\'e}'' type
+distortions yields a topological phase. In contrast, ``\textit{anti-kekul\'e}''
+distortions result in a non-topological magnonic phase. The presence of
+kekul\'e distortions manifests in two distinct topologically protected bosonic
+corner modes - an \textit{intrinsic} and a \textit{pseudo}, based on the
+specific edge terminations. On the other hand, anti-kekul\'e distortions give
+rise to \SW{\textit{Tamm/Shockley}} type bond-localized boundary modes, which
+are non-topological and reliant on particular edge termination. We further
+investigate the effects of random out-of-plane exchange anisotropy disorder on
+the robustness of these bosonic corner modes. The distinction between SOTMIs
+and their fermionic counterparts arises due to the system-specific magnonic
+onsite energies, a crucial feature often overlooked in prior literature. Our
+study unveils exciting prospects for engineering higher-order topological
+phases in magnon systems and enhances our understanding of their unique
+behavior within decorated honeycomb lattices.",2310.19010v2
+2023-10-30,Cavity magnomechanics: from classical to quantum,"Hybrid quantum systems based on magnons in magnetic materials have made
+significant progress in the past decade. They are built based on the couplings
+of magnons with microwave photons, optical photons, vibration phonons, and
+superconducting qubits. In particular, the interactions among magnons,
+microwave cavity photons, and vibration phonons form the system of cavity
+magnomechanics (CMM), which lies in the interdisciplinary field of cavity QED,
+magnonics, quantum optics, and quantum information. Here, we review the
+experimental and theoretical progress of this emerging field. We first
+introduce the underlying theories of the magnomechanical coupling, and then
+some representative classical phenomena that have been experimentally observed,
+including magnomechanically induced transparency, magnomechanical dynamical
+backaction, magnon-phonon cross-Kerr nonlinearity, etc. We also discuss a
+number of theoretical proposals, which show the potential of the CMM system for
+preparing different kinds of quantum states of magnons, phonons, and photons,
+and hybrid systems combining magnomechanics and optomechanics and relevant
+quantum protocols based on them. Finally, we summarize this review and provide
+an outlook for the future research directions in this field.",2310.19237v3
+2023-11-09,Electrically induced angular momentum flow between separated ferromagnets,"Converting angular momentum between different degrees of freedom within a
+magnetic material results from a dynamic interplay between electrons, magnons
+and phonons. This interplay is pivotal to implementing spintronic device
+concepts that rely on spin angular momentum transport. We establish a new
+concept for long-range angular momentum transport that further allows to
+address and isolate the magnonic contribution to angular momentum transport in
+a nanostructured metallic ferromagnet. To this end, we electrically excite and
+detect spin transport between two parallel and electrically insulated
+ferromagnetic metal strips on top of a diamagnetic substrate. Charge-to-spin
+current conversion within the ferromagnetic strip generates electronic spin
+angular momentum that is transferred to magnons via electron-magnon coupling.
+We observe a finite angular momentum flow to the second ferromagnetic strip
+across a diamagnetic substrate over micron distances, which is electrically
+detected in the second strip by the inverse charge-to-spin current conversion
+process. We discuss phononic and dipolar interactions as the likely cause to
+transfer angular momentum between the two strips. Moreover, our work provides
+the experimental basis to separate the electronic and magnonic spin transport
+and thereby paves the way towards magnonic device concepts that do not rely on
+magnetic insulators.",2311.05290v1
+2023-11-22,Controlling selection rules for magnon scattering in nanomagnets by spatial symmetry breaking,"Nanomagnets are the building blocks of many existing and emergent spintronic
+technologies. Magnetization dynamics of nanomagnets is often dominated by
+nonlinear processes, which have been recently shown to have many surprising
+features and far-reaching implications for applications. Here we develop a
+theoretical framework uncovering the selection rules for multimagnon processes
+and discuss their underlying mechanisms. For its technological relevance, we
+focus on the degenerate three-magnon process in thin elliptical nanodisks to
+illustrate our findings. We parameterize the selection rules through a set of
+magnon interaction coefficients which we calculate using micromagnetic
+simulations. We postulate the selection rules and investigate how they are
+altered by perturbations, that break the symmetry of static magnetization
+configuration and spatial spin-wave profiles and that can be realized by
+applying off-symmetry-axis or nonuniform magnetic fields. Our work provides the
+phenomenological understanding into the mechanics of magnon interaction as well
+as the formalism for determining the interaction coefficients from simulations
+and experimental data. Our results serve as a guide to analyze magnon processes
+inherently present in spin-torque devices for boosting their performance or to
+engineer a specific nonlinear response of a nanomagnet used in neuromorphic or
+quantum magnonic application.",2311.13726v1
+2023-12-31,"Magnon, doublon and quarton excitations in 2D trimerized Heisenberg models","We investigate the magnetic excitations of the trimerized Heisenberg models
+with intra-trimer interaction $J_1$ and inter-trimer interaction $J_2$ on four
+different two-dimensional lattices using a combination of stochastic series
+expansion quantum Monte Carlo (SSE QMC) and stochastic analytic continuation
+methods (SAC), complemented by cluster perturbation theory (CPT). These models
+exhibit quasi-particle-like excitations when $g=J_2/J_1$ is small,
+characterized by low-energy magnons, intermediate-energy doublons, and
+high-energy quartons. The low-energy magnons are associated with the magnetic
+ground states. They can be described by the linear spin wave theory (LSWT) of
+the effective block spin model and the original spin model. Doublons and
+quartons emerge from the corresponding internal excitations of the trimers with
+distinct energy levels, which can be effectively analyzed using perturbation
+theory when the ratio of exchange interactions $g$ is small. In this small $g$
+regime, we observe a clear separation between the magnon and higher-energy
+spectra. However, as $g$ increases, these three spectra gradually merge into
+the magnon modes or continua. Nevertheless, the LSWT fails to provide
+quantitative descriptions of the higher-energy excitation bands due to
+significant quantum fluctuations. Notably, in the Collinear II and trimerized
+hexagon lattice, a broad continuum emerges above the single-magnon spectrum,
+originating from the quasi-1D physics due to the dilute connections between
+chains. Our numerical analysis of these 2D trimers yields valuable theoretical
+predictions and explanations for the inelastic neutron scattering (INS) spectra
+of 2D magnetic materials featuring trimerized lattices.",2401.00376v1
+2024-01-04,Nonreciprocal photon blockade with Kerr magnons,"Nonreciprocal devices, allowing to manipulate one-way signals, are crucial to
+quantum information processing and quantum network. Here we propose a nonlinear
+cavity-magnon system, consisting of a microwave cavity coupled to one or two
+yttrium-iron-garnet (YIG) spheres supporting magnons with Kerr nonlinearity, to
+investigate nonreciprocal photon blockade. The nonreciprocity originates from
+the direction-dependent Kerr effect, distinctly different from previous
+proposals with spinning cavities and dissipative couplings. For a single sphere
+case, nonreciprocal photon blockade can be realized by manipulating the
+nonreciprocal destructive interference between two active paths, via vary the
+Kerr coefficient from positive to negative, or vice versa. By optimizing the
+system parameters, the perfect and well tuned nonreciprocal photon blockade can
+be predicted. For the case of two spheres with opposite Kerr effects, only
+reciprocal photon blockade can be observed when two cavity-magnon coupling
+strengths Kerr strengths are symmetric. However, when coupling strengths or
+Kerr strengths become asymmetric, nonreciprocal photon blockade appears. This
+implies that two-sphere nonlinear cavity-magnon systems can be used to switch
+the transition between reciprocal and nonreciprocal photon blockades. Our study
+offers a potential platform for investigating nonreciprocal photon blockade
+effect in nonlinear cavity magnonics.",2401.02251v1
+2024-02-08,Assessing the atomic moment picture of spin dynamics: the perspective of \textit{ab initio} magnon wavefunction,"Our understanding of collective spin fluctuation in materials relies largely
+on Heisenberg-type spin Hamiltonians. Implicit in these spin models is the
+atomic moment picture that in transverse spin dynamics the magnetization around
+an atom undergoes precessional motion as a rigid moment, which has been
+challenged by emerging theoretical and experimental advances. To assess the
+validity of the atomic moment picture in spin dynamics, however, necessitates
+magnon wavefunctions from \textit{ab initio} methods without \textit{a priori}
+spin models. To this end, we develop an efficient model-free {\it ab initio}
+method for computing magnon spectrum and wavefunctions. Niu-Kleinman's
+adiabatic spin-wave dynamics is reformulated using linear perturbation theory
+into a generalized eigenvalue problem, which can be solved to produce magnon
+spectrum and wavefunctions without assuming atomic moments. We have implemented
+this method in the framework of density functional perturbation theory (DFPT).
+A dynamical extension of Niu-Kleinman equation of motion is proposed to improve
+inaccurate predicted magnon energies due to imperfect adiabaticity at higher
+energies. Based on so-obtained {\it ab initio} magnon wavefunctions, we find
+the atomic moment picture to be valid in typical ferromagnets and
+antiferromagnets, but fails in the molecular orbital crystal Na$_2$IrO$_3$. Our
+results suggest that the usual spin Hamiltonian approach should be taken with a
+grain of salt, and possible experimental ramification on the issue is
+discussed.",2402.05473v2
+2024-02-22,Combinatorial split-ring and spiral meta-resonator for efficient magnon-photon coupling,"Developing hybrid materials and structures for electromagnetic wave
+engineering has been a promising route towards novel functionalities and
+tunabilities in many modern applications and perspectives in new quantum
+technologies. Despite its established success in engineering optical light and
+terahertz waves, the implementation of meta-resonators operating at the
+microwave band is still emerging, especially those that allow for on-chip
+integration and size miniaturization, which has turned out crucial to
+developing hybrid quantum systems at the microwave band. In this work, we
+present a microwave meta-resonator consisting of split-ring and and spiral
+resonators, and implement it to the investigation of photon-magnon coupling for
+hybrid magnonic applications. We observe broadened bandwidth to the split ring
+modes augmented by the additional spiral resonator, and, by coupling the modes
+to a magnetic sample, the resultant photon-magnon coupling can be significantly
+enhanced to more than ten-fold. Our work suggests that combinatorial, hybrid
+microwave resonators may be a promising approach towards future development and
+implementation of photon-magnon coupling in hybrid magnonic systems.",2402.15535v2
+2024-03-07,Nonequilibrium magnonic thermal transport engineering,"Thermal conductivity, a fundamental parameter characterizing thermal
+transport in solids, is typically determined by electron and phonon transport.
+Although other transport properties including electrical conductivity and
+thermoelectric conversion coefficients have material-specific values, it is
+known that thermal conductivity can be modulated artificially via phonon
+engineering techniques. Here, we demonstrate another way of artificially
+modulating the heat conduction in solids: magnonic thermal transport
+engineering. The time-domain thermoreflectance measurements using ferromagnetic
+metal/insulator junction systems reveal that the thermal conductivity of the
+ferromagnetic metals and interfacial thermal conductance vary significantly
+depending on the spatial distribution of nonequilibrium spin currents.
+Systematic measurements of the thermal transport properties with changing the
+boundary conditions for spin currents show that the observed thermal transport
+modulation stems from magnon origin. This observation unveils that magnons
+significantly contribute to the heat conduction even in ferromagnetic metals at
+room temperature, upsetting the conventional wisdom that the thermal
+conductivity mediated by magnons is very small in metals except at low
+temperatures. The magnonic thermal transport engineering offers a new principle
+and method for active thermal management.",2403.04166v1
+1997-10-06,Multi-Magnon Scattering in the Ferromagnetic XXX-Model with Inhomogeneities,"We determine the transition amplitude for multi-magnon scattering induced
+through an inhomogeneous distribution of the coupling constant in the
+ferromagnetic XXX-model. The two and three particle amplitudes are explicitely
+calculated at small momenta. This suggests a rather plausible conjecture also
+for a formula of the general n-particle amplitude.",9710055v1
+1998-09-10,Introduction to the Bethe ansatz I,"The Bethe ansatz for the one-dimensional s=1/2 Heisenberg ferromagnet is
+introduced at an elementary level. The presentation follows Bethe's original
+work very closely. A detailed description and a complete classification of all
+two-magnon scattering states and two-magnon bound states are given for finite
+and infinite chains. The paper is designed as a tutorial for beginning graduate
+students. It includes 10 problems for further study.",9809162v1
+1999-10-21,Optical absorption of spin ladders,"We present a theory of phonon-assisted optical two-magnon absorption in
+two-leg spin-ladders. Based on the strong intra-rung-coupling limit we show
+that collective excitations of total spin S=0, 1 and 2 exist outside of the
+two-magnon continuum. It is demonstrated that the singlet collective state has
+a clear signature in the optical spectrum.",9910322v1
+2004-12-15,Nuclear Magnetic Relaxation in the Ferrimagnetic Chain Compound NiCu(C_7_H_6_N_2_O_6_)(H_2_O)_3_2H_2_O: Three-Magnon Scattering?,"Recent proton spin-lattice relaxation-time (T_1_) measurements on the
+ferrimagnetic chain compound NiCu(C_7_H_6_N_2_O_6_)(H_2_O)_3_2H_2_O are
+explained by an elaborately modified spin-wave theory. We give a strong
+evidence of the major contribution to 1/T_1_ being made by the three-magnon
+scattering rather than the Raman one.",0412389v1
+1998-07-14,A New Look at the Ashtekar-Magnon Energy Condition,"In 1975, Ashtekar and Magnon showed that an energy condition selects a unique
+quantization procedure for certain observers in general, curved spacetimes. We
+generalize this result in two important ways, by eliminating the need to assume
+a particular form for the (quantum) Hamiltonian, and by considering the
+surprisingly nontrivial extension to nonminimal coupling.",9807028v1
+1998-06-26,Cherenkov radiation of magnon and phonon by the slow magnetic monopole,"The Cherenkov radiation of magnons at passage of the heavy slow magnetic
+monopole through an ordered magnetic matter is considered. Also the Cherenkov
+radiation of phonons at monopole movement in medium is discussed.",9806495v1
+2006-07-03,Dressing the Giant Magnon,"We apply the dressing method to construct new classical string solutions
+describing various scattering and bound states of magnons. These solutions
+carry one, two or three SO(6) charges and correspond to multi-soliton
+configurations in the generalized sine-Gordon models.",0607009v3
+2006-12-16,A note on two-spin magnon-like energy-charge relations from M-theory viewpoint,"We show that for each M-theory background, having subspaces with metrics of
+given type, there exist M2-brane configurations, which in appropriate limit
+lead to two-spin magnon-like energy-charge relations, established for strings
+on AdS_5 x S^5, its beta-deformation, and for membrane in AdS_4 x S^7.",0612175v2
+2008-03-27,Finite Size Giant Magnon,"The quantization of the giant magnon away from the infinite size limit is
+discussed. We argue that this quantization inevitably leads to string theory on
+a Z_M-orbifold of S^5. This is shown explicitly and examined in detail in the
+near plane-wave limit.",0803.4028v2
+2009-01-29,"Spin-waves in triangular lattice antiferromagnet: decays, spectrum renormalization, and singularities","We present a comprehensive study of the dynamical properties of the quantum
+Heisenberg antiferromagnet on a triangular lattice within the framework of
+spin-wave theory. The distinct features of spin-wave excitations in the
+triangular-lattice antiferromagnet are (i) finite lifetime at zero temperature
+due to spontaneous two-magnon decays, (ii) strong renormalization of magnon
+energies with respect to the harmonic result, and (iii) logarithmic
+singularities in the decay rate Gamma_k. Quantum corrections to the magnon
+spectrum are obtained using both the on-shell and off-shell solutions of the
+Dyson equation with the lowest-order magnon self-energy. At low-energies magnon
+excitations remain well-defined albeit with the anomalous decay rate Gamma_k ~
+k^2 at k->0 and Gamma_k ~ |k-Q_AF|^7/2 at k->Q_AF. At high energies, magnons
+are heavily damped with the decay rate reaching (2 Gamma_k/E_k) ~ 0.3 for the
+case S=1/2. The on-shell solution shows logarithmic singularities in Gamma_k
+with the concomitant jump-like discontinuities in E_k along certain contours in
+the momentum space. Such singularities are even more prominent in the magnon
+spectral function A(k,w). Although the off-shell solution removes such
+log-singularities, the decay rates remain strongly enhanced. We also discuss
+the role of higher-order corrections and show that such singularities may lead
+to complete disappearance of the spectrum in the vicinity of certain k-points.
+The kinematic conditions for two-magnon decays are analyzed for various
+generalizations of the triangular-lattice antiferromagnet as well as for the
+XXZ model on a kagome lattice. Our results suggest that decays and
+singularities in the spin-wave spectra must be ubiquitous in all these systems.",0901.4803v3
+2009-04-27,The Fate of the Two-Magnon Bound State in the Heisenberg Antiferromagnet,"The energy spectrum of the two-magnon bound states in the Heisenberg-Ising
+antiferromagnet on the square lattice are calculated using series expansion
+methods. The results confirm an earlier spin-wave prediction of Oguchi and
+Ishikawa, that the bound states vanish into the continuum before the isotropic
+Heisenberg limit is reached.",0904.4085v1
+2010-12-09,Twisted Magnons,"We study spin chains for superconformal quiver gauge theories in the moduli
+space of N=2 orbifolds. Independent of integrability, which is generally
+broken, we use the centrally extended SU(2|2) symmetry of the magnons to fix
+their dispersion relations and two-body S-matrices, as functions of the exactly
+marginal couplings.",1012.2097v2
+2011-05-17,Finite size effect on the magnon's correlation functions,"We calculate the finite size correction on the three-point correlation
+function between two giant magnons and one marginal operator. We also check
+that the structure constant in the string set-up is exactly the same as one of
+the RG analysis in the gauge theory.",1105.3279v2
+2011-06-18,Finite-size Giant Magnons on AdS_4 x CP^3_γ,"We investigate finite-size giant magnons propagating on \gamma-deformed AdS_4
+x CP^3_{\gamma} type IIA string theory background, dual to one parameter
+deformation of the N=6 super Chern-Simoms-matter theory. Analyzing the
+finite-size effect on the dispersion relation, we find that it is modified
+compared to the undeformed case, acquiring \gamma dependence.",1106.3686v1
+2012-08-03,"On finite size corrections to the dispersion relations of giant magnon and single spike on γ-deformed T^{1,1}","In this paper we consider the finite size effects for the strings in \beta
+-deformed AdS_{5}\times T^{1,1} background. We analyze the finite size
+corrections for the cases of giant magnon and single spike string solution. The
+finite size corrections for the undeformed case are straightforwardly obtained
+sending the deformation parameter to zero.",1208.0698v1
+2012-08-30,Free from spurious solutions integral equation for three-magnon bound states in 1D XXZ ferromagnet,"A new integral equation for three-magnon bound states in XXZ spin chain is
+suggested. Unlike the one presented by C. K. Majumdar about 40 years ago this
+equation does not have spurious solutions. Such an advantage is a result of
+decomposition of the wave function in the Bloch basis rather than in the basis
+of flat waves.",1208.6177v1
+2016-01-19,Classification of magnons in Rotated Ferromagnetic Heisenberg model and their competing responses in transverse fields,"Competing orders is a general concept to describe various quantum phases and
+transitions in various materials. One efficient way to investigate competing
+orders is to first classify different class of excitations in a given quantum
+phase, then study their competing responses under various external probes. This
+strategy may not only lead to deep understanding of the quantum phase itself,
+but also its deep connections to various other quantum phases nearby. We
+implement this approach by studying the Rotated Ferromagnetic Heisenberg model
+(RFHM) in two different transverse fields $h_x$ and $h_z$ which can be
+intuitively visualized as studying spin-orbit couplings (SOC) effects in 2d
+Ising or anisotropic XY model in a transverse field. At a special SOC class, it
+was known that the RFHM at a zero field owns an exact ground state called Y-x
+state. It supports non only the commensurate C-C$_0$ and C-C$_{\pi} $ magnons,
+but also the in-commensurate C-IC magnons. These magnons are non-relativistic,
+not contained in the exact ground state, so need to be thermally excited. Their
+dramatic response under the longitudinal $ h_y $ field was recently worked out
+by the authors. Here we find they respond very differently under the two
+transverse fields. Any $h_x$ ($h_z$) changes the collinear Y-x state to a
+canted co-planar YX-x (YZ-x) state which suffers quantum fluctuations. The
+C-C$_0$, C-C$_{\pi} $ and C-IC magnons sneak into the quantum ground state,
+become relativistic and play leading roles even at $ T=0 $. We map out the
+boundaries among the C-C$_0$, C-C$_{\pi} $ and C-IC magnons, especially the
+detailed evolution of the C-IC magnons inside the canted phases. As $h_x$
+($h_z$) increases further, the C-C$_0$ magnons always win the competition and
+emerge as the seeds to drive a transition from the YX-x (YZ-x) to the X-FM (
+Z-FM ) which is shown to be in the 3d Ising universality class.",1601.05067v1
+2018-11-03,Tunable Spin Seebeck Diode with Magnonic Spin Tunneling Junction,"We theoretically investigate the spin--wave spin current induced by the spin
+Seebeck effect in magnonic spin tunneling junctions (MSTJs) for arbitrary
+magnetization directions. We show that the MSTJ functions as a \textit{tunable}
+spin Seebeck diode in which the tunneling spin current can be turned on and off
+with high efficiency by controlling the magnetization direction.",1811.01141v1
+2008-07-11,Numerical evidence for unstable magnons at high fields in the Heisenberg antiferromagnet on the square lattice,"We find evidence for decaying magnons at strong magnetic field in the square
+lattice spin-1/2 Heisenberg antiferromagnet. The results are obtained using
+Quantum Monte Carlo simulations combined with a Bayesian inference technique to
+obtain dynamics and are consistent with predictions from spin wave theory.",0807.1837v2
+2016-08-22,"Thermally induced magnonic spin current, thermomagnonic torques and domain wall dynamics in the presence of Dzyaloshinskii-Moriya interaction","Thermally activated domain wall (DW) motion in magnetic insulators has been
+considered theoretically, with a particular focus on the role of
+Dzyaloshinskii-Moriya Interaction (DMI) and thermomagnonic torques. The
+thermally assisted DW motion is a consequence of the magnonic spin current due
+to the applied thermal bias. In addition to the exchange magnonic spin current
+and the exchange adiabatic and the entropic spin transfer torques, we also
+consider the DMI-induced magnonic spin current, thermomagnonic DMI field-like
+torque and the DMI entropic torque. Analytical estimations are supported by
+numerical calculations. We found that the DMI has a substantial influence on
+the size and the geometry of DWs, and that the DWs become oriented parallel to
+the long axis of the nanostrip. Increasing the temperature smoothes the DWs.
+Moreover, the thermallyinduced magnonic current generates a torque on the DWs,
+which is responsible for their motion. From our analysis it follows that for a
+large enough DMI the influence of DMI-induced field-like torque is much
+stronger than that of the DMI and the exchange entropic torques. By
+manipulating the strength of the DMI constant, one can control the speed of the
+DW motion, and the direction of the DW motion can be switched, as well. We also
+found that DMI not only contributes to the total magnonic current, but also it
+modifies the exchange magnonic spin current, and this modification depends on
+the orientation of the steady state magnetization. The observed phenomenon can
+be utilized in spin caloritronics devices, for example in the DMI based thermal
+diodes. By switching the magnetization direction, one can rectify the total
+magnonic spin current.",1608.06179v1
+2017-10-15,Long-wave magnons in a ferromagnetic film,"An asymptotically exact theory of spectrum and transverse distribution of
+magnetization in long-wave magnons is presented. It is based on exact
+analytical solution of linearized Landau-Lifshitz equation in a film. The
+quantization of the transverse wave parameters and wave vectors is studied.",1710.05362v1
+2018-03-02,Long lifetime of thermally-excited magnons in bulk yttrium iron garnet,"Spin currents are generated within the bulk of magnetic materials due to heat
+flow, an effect called intrinsic spin-Seebeck. This bulk bosonic spin current
+consists of a diffusing thermal magnon cloud, parametrized by the magnon
+chemical potential ($\mu_{m}$), with a diffusion length of several microns in
+yttrium iron garnet (YIG). Transient opto-thermal measurements of the
+spin-Seebeck effect (SSE) as a function of temperature reveal the time
+evolution of $\mu_{m}$ due to intrinsic SSE in YIG. The interface SSE develops
+at times < 2 ns while the intrinsic SSE signal continues to evolve at times >
+500 $\mu$s, dominating the temperature dependence of SSE in bulk YIG.
+Time-dependent SSE data are fit to a multi-temperature model of coupled
+spin/heat transport using finite element method (FEM), where the magnon spin
+lifetime ($\tau$) and magnon-phonon thermalization time ($\tau_{mp}$) are used
+as fit parameters. From 300 K to 4 K, $\tau_{mp}$ varies from 1 to 10 ns,
+whereas $\tau$ varies from 2 to 60 $\mu$s with the spin lifetime peaking at 90
+K. At low temperature, a reduction in $\tau$ is observed consistent with
+impurity relaxation reported in ferromagnetic resonance measurements. These
+results demonstrate that the thermal magnon cloud in YIG contains extremely low
+frequency magnons (~10 GHz) providing spectral insight to the microscopic
+scattering processes involved in magnon spin/heat diffusion.",1803.01054v3
+2015-08-11,Transport between metals and magnetic insulators,"We derive the Onsager response matrix of fluctuation-mediated spin-collinear
+transport through a ferromagnetic insulator and normal metal interface driven
+by a temperature difference, spin accumulation, or magnetic field. We predict
+magnon-squeezing spin currents, magnetic field-induced cooling (magnon Peltier
+effect), temperature induced magnetization (thermal magnetic field) as well as
+universal spin Seebeck/Peltier coefficients.",1508.02486v2
+2016-09-26,Bethe Ansatz approach to the three-magnon problem in an infinite $XX$ spin chain with Izing next neighboring ferromagnetic interaction,"Using the traditional and degenerative discrete-diffractive versions of Bethe
+Ansatz we construct a rude set of three-magnon states in the infinite $XX$ spin
+chain with Izing next neighboring ferromagnetic term.",1609.07941v1
+2019-10-02,Magnonics and Supermagnonics,"The magnetic community continues to discuss the possibility to observe the
+magnetic superfluidity, despite the fact that it has been discovered long time
+ago. It was observed in antiferromagnetic states of superfluid $^3$He in 1984.
+In this article we reminds the main principles of spin superfluidity and
+related Bose-Einstain magnon condensation. We discuss applications of this
+phenomenon in supermagnonic devises.",1910.02841v1
+2022-06-10,Theory of Moire Magnets and Topological Magnons: Applications to Twisted Bilayer CrI3,"We develop a comprehensive theory of twisted bilayer magnetism. Starting from
+the first-principles calculations of two-dimensional honeycomb magnet CrI3, we
+construct the generic spin models that represent a broad class of twisted
+bilayer magnetic systems. Using Monte-Carlo method, we discover a variety of
+non-collinear magnetic orders and topological magnons that have been overlooked
+in the previous theoretical and experimental studies. As a function of the
+twist angle, the collinear magnetic order undergoes the phase transitions to
+the non-collinear order and the magnetic domain phase. In the magnetic domain
+phase, we find that the spatially varying interlayer coupling produces the
+magnetic skyrmions even in the absence of the Dzyaloshinskii-Moriya
+interactions. In addition, we describe the critical phenomena of the magnetic
+phase transitions by constructing the field theoretical model of the moire
+magnet. Our continuum model well-explains the nature of the phase transitions
+observed in the numerical simulations. Finally, we classify the topological
+properties of the magnon excitations. The magnons in each phases are
+characterized by the distinct mass gaps with different physical origins. In the
+collinear ferromagnetic order, the higher-order topological magnonic insulator
+phase occurs. It serves as a unique example of the higher-order topological
+phase in magnonic system, since it does not require non-collinear order or
+asymmetric form of the interactions. In the magnetic domain phases, the magnons
+are localized along the domain wall and form one-dimensional topological edge
+mode. As the closed domain walls deform to a open network, the confined edge
+mode extends to form a network model of the topological magnons.",2206.05264v1
+2023-11-28,Temperature dependence of the magnon-phonon interaction in high overtone bulk acoustic resonator-ferromagnetic thin film hybrids,"Tailored magnon-phonon hybrid systems, where high overtone bulk acoustic
+resonators couple resonantly to the magnonic mode of a ferromagnetic thin film,
+are considered optimal for the creation of acoustic phonons with a defined
+circular polarization. This class of devices is therefore ideal for the
+investigation of phonon propagation properties and assessing their capacity to
+transport angular momentum in the classical and potentially even in the quantum
+regime. Here, we study the coupling between the magnons in a ferromagnetic
+\ch{Co25Fe75} thin film and the transverse acoustic phonons in a bulk acoustic
+wave resonators formed by the sapphire substrate onto which the film is
+deposited. Using broadband ferromagnetic resonance experiments as a function of
+temperature, we investigate the strength of the coherent magnon-phonon
+interaction and the individual damping rates of the magnons and phonons
+participating in the process. This demonstrates that this coupled magnon-phonon
+system can reach a cooperativity $C\approx 1$ at cryogenic temperatures. Our
+experiments also showcase the potential of strongly coupled magnon-phonon
+systems for strain sensing applications.",2311.16725v1
+1994-09-27,Resonant two-magnon Raman scattering in antiferromagnetic insulators,"We propose a theory of two-magnon {\it resonant\/} Raman scattering from
+antiferromagnetic insulators, which contains information both on the magnetism
+and the carrier properties in the lighly doped phases. We argue that the
+conventional theory does not work in the resonant regime, in which the energy
+of the incident photon is close to the gap between the conduction and valence
+bands. We identify the diagram which gives the dominant contribution to Raman
+intensity in this regime and show that it can explain the unusual features in
+the two-magnon profile and in the two-magnon peak intensity dependence on the
+incoming photon frequency.",9409114v1
+1995-11-01,Theory of Phonon-Assisted Multimagnon Optical Absorption and Bimagnon States in Quantum Antiferromagnets,"We calculate the effective charge for multimagnon infrared (IR) absorption
+assisted by phonons in a perovskite like antiferromagnet and we compute the
+spectra for two magnon absorption using interacting spin-wave theory. The full
+set of equations for the interacting two magnon problem is presented in the
+random phase approximation for arbitrary total momentum of the magnon pair. The
+spin wave theory results fit very well the primary peak of recent measured
+bands in the parent insulating compounds of cuprate superconductors. The line
+shape is explained as being due to the absorption of one phonon plus a new
+quasiparticle excitation of the Heisenberg Hamiltonian that consists off a long
+lived virtual bound state of two magnons (bimagnon). The bimagnon states have
+well defined energy and momentum in a substantial portion of the Brillouin
+zone. The higher energy bands are explained as one phonon plus higher
+multimagnon absorption processes. Other possible experiments for observing
+bimagnons are proposed. In addition we predict the line shape for the spin one
+system La$_2$NiO$_4$.",9511005v1
+1998-09-10,Magnon splitting induced by charge ordering in NaV_2O_5,"We consider the effects of charge ordering in NaV_2O_5 (below T_SP) on the
+exchange constants and on the magnon dispersion. We show that the
+experimentally observed splitting of the magnon branches along the a direction
+is induced by charge ordering. We find that one can distinguish between the
+proposed 'zig-zag' and 'in-line' patterns of charge ordering. Only the zig-zag
+ordering is consistent with the experimental results regarding (i) the unusual
+intensity modulation observed in magnetic neutron scattering, (ii) the
+reduction in the intra-ladder exchange constant below T_SP, and (iii) the
+magnon dispersion along a. We estimate the inter-ladder exchange constant to be
+1.01meV=11.7K for T>T_SP.",9809154v2
+1998-12-02,Observation of magnetic order in La_{1.9}Sr_{0.1}CuO_{4} from two-magnon Raman scattering,"We reported two-magnon Raman scattering from La_{1.9}Sr_{0.1}CuO_4, which has
+a suppressed Tc=12 K, as the temperature is lowered below 37 K and an ordered
+spin phase is formed. The two-magnon Raman intensity increases with decreasing
+temperature. The magnetic scattering in La_{1.9}Sr_{0.1}CuO_4 is totally
+different from that reported in the parent compound La_2CuO_4. We analyze the
+line shape of the two-magnon scattering within the traditional Loudon-Fleury
+theory and find the superexchange constant J=1052 cm^{-1}. The calculation of
+the frequency moment suggests that the quantum fluctuations are very weak in
+the system. The room temperature Raman scattering from La_2CuO_4 is also
+measured. Strong features appear in the one-phonon spectrum at the frequencies
+of the longitudinal optical (LO) infrared modes which we suggest become Raman
+active through a Fr\""{o}hlich-interaction.",9812027v1
+1999-04-27,Spin-wave contributions to nuclear magnetic relaxation in magnetic metals,"The longitudinal and transverse nuclear magnetic relaxation rates $1/T_1(T)$
+and $1/T_2(T)$ are calculated for three- and two-dimensional (3D and 2D)
+metallic ferro- and antiferromagnets (FM and AFM) with localized magnetic
+moments in the spin-wave temperature region. The contribution of the one-magnon
+decay processes is strongly enhanced in comparison with the standard $T$-linear
+Korringa term, especially for the FM case. For the 3D AFM case this
+contribution diverges logarithmically, the divergence being cut at the magnon
+gap $\omega_0$ due to magnetic anisotropy, and for the 2D AFM case as
+$\omega_0^{-1}$. The electron-magnon scattering processes yield $T^2\ln
+(T/\omega_0)$ and $T^2/\omega_0^{1/2}$-terms in $1/T_1$ for the 3D AFM and 2D
+FM cases, respectively. The two-magnon (``Raman'') contributions are
+investigated and demonstrated to be large in the 2D FM case. Peculiarities of
+the isotropic 2D limit (where the correlation length is very large) are
+analyzed.",9904384v3
+2000-01-12,Raman Scattering from Magnetic Excitations in the Spin Ladder Compounds CaV2O5 and MgV2O5,"We present the Raman-scattering spectra of CaV2O5 and MgV2O5. The magnetic
+contribution in the Raman spectra of CaV2O5 is found in the form of a strong
+asymmetric line, centered at 2Delta, with a tail on the high-energy side. Our
+analysis of its spectral shape shows that the magnetic ordering in CaV2O5 can
+be described using a S=1/2 two-leg ladder Heisenberg antiferromagnetic model
+with Jparallel/Jperp = 0.1, and a small interladder exchange. The spin gap and
+exchange constant are estimated to be Delta = 400 cm-1 (570 K) and Jperp = 640
+K. No magnon bound states are found. In contrast to CaV2O5 the existence of the
+spin-gap is not confirmed in MgV2O5, since we found no feature in the spectra
+which could be associated with the onset of the two-magnon continuum. Instead,
+we observe two-magnon excitation at 340 cm-1, presumably related to the top of
+the two-magnon brunch.",0001168v2
+2000-04-21,Thermal conductivity of Mg-doped CuGeO_3 at very low temperatures: Heat conduction by antiferromagnetic magnons,"Thermal conductivity \kappa is measured at very low temperatures down to 0.28
+K for pure and Mg-doped CuGeO_3 single crystals. The doped samples carry larger
+amount of heat than the pure sample at the lowest temperature. This is because
+antiferromagnetic magnons appear in the doped samples and are responsible for
+the additional heat conductivity, while \kappa of the pure sample represents
+phonon conductivity at such low temperatures. The maximum energy of the magnon
+is estimated to be much lower than the spin-Peierls-gap energy. The result
+presents the first example that \kappa at very low temperatures probes the
+magnon transport in disorder-induced antiferromagnetic phase of spin-gap
+systems.",0004367v1
+2000-05-12,Two-magnon states in Cu(NO3)2*2.5D2O using inelastic neutron scattering,"We report measurements of the two-magnon states in a dimerized
+antiferromagnetic chain material, copper nitrate
+(\QTR{group}{Cu(NO$_{3}$)$_{2}\cdot 2.5$D$_{2}$O}). Using inelastic neutron
+scattering, we have studied the one- and two-magnon excitation spectra in a
+large single crystal of this material. We compare this new data with
+perturbative expansions of the alternating Heisenberg chain and find good
+agreement with these calculations. The data may also show evidence for the
+recently proposed S=1 two-magnon bound state (Phys. Rev. B54, R9624 (1996)).",0005222v1
+2000-07-11,Spin-1 Antiferromagnetic Heisenberg Chains in an External Staggered Field,"We present in this paper a nonlinear sigma-model analysis of a spin-1
+antiferromagnetic Heisenberg chain in an external commensurate staggered
+magnetic field. After rediscussing briefly and extending previous results for
+the staggered magnetization curve, the core of the paper is a novel
+calculation, at the tree level, of the Green functions of the model. We obtain
+precise results for the elementary excitation spectrum and in particular for
+the spin gaps in the transverse and longitudinal channels. It is shown that,
+while the spectral weight in the transverse channel is exhausted by a single
+magnon pole, in the longitudinal one, besides a magnon pole a two-magnon
+continuum appears as well whose weight is a stedily increasing function of the
+applied field, while the weight of the magnon decreases correspondingly. The
+balance between the two is governed by a sum rule that is derived and
+discussed. A detailed comparison with the present experimental and numerical
+(DMRG) status of the art as well as with previous analytical approaches is also
+made.",0007188v1
+2000-11-29,Magnon dispersion and thermodynamics in CsNiF_3,"We present an accurate transfer matrix renormalization group calculation of
+the thermodynamics in a quantum spin-1 planar ferromagnetic chain. We also
+calculate the field dependence of the magnon gap and confirm the accuracy of
+the magnon dispersion derived earlier through an 1/n expansion. We are thus
+able to examine the validity of a number of previous calculations and further
+analyze a wide range of experiments on CsNiF_3 concerning the magnon
+dispersion, magnetization, susceptibility, and specific heat. Although it is
+not possible to account for all data with a single set of parameters, the
+overall qualitative agreement is good and the remaining discrepancies may
+reflect departure from ideal quasi-one-dimensional model behavior. Finally, we
+present some indirect evidence to the effect that the popular interpretation of
+the excess specific heat in terms of sine-Gordon solitons may not be
+appropriate.",0011496v1
+2002-07-02,"Magnon Exchange Mechanism of Superconductivity: ZrZn_2, URhGe","The magnon exchange mechanism of superconductivity was developed to explain
+in a natural way the fact that the superconductivity in $UGe_2$, $ZrZn_2$ and
+$URhGe$ is confined to the ferromagnetic phase.The order parameter is a spin
+anti-parallel component of a spin-1 triplet with zero spin projection. The
+transverse spin fluctuations are pair forming and the longitudinal ones are
+pair breaking. In the present paper, a superconducting solution, based on the
+magnon exchange mechanism, is obtained which closely matches the experiments
+with $ZrZn_2$ and $URhGe$. The onset of superconductivity leads to the
+appearance of complicated Fermi surfaces in the spin up and spin down momentum
+distribution functions. Each of them consist of two pieces, but they are
+simple-connected and can be made very small by varying the microscopic
+parameters. As a result, it is obtained that the specific heat depends on the
+temperature linearly, at low temperature, and the coefficient $\gamma=\frac
+{C}{T}$ is smaller in the superconducting phase than in the ferromagnetic one.
+The absence of a quantum transition from ferromagnetism to ferromagnetic
+superconductivity in a weak ferromagnets $ZrZn_2$ and $URhGe$ is explained
+accounting for the contribution of magnon self-interaction to the spin
+fluctuations' parameters. It is shown that in the presence of an external
+magnetic field the system undergoes a first order quantum phase transition.",0207078v1
+2002-07-29,A neutron scattering study of two-magnon states in the quantum magnet copper nitrate,"We report measurements of the two-magnon states in a dimerized
+antiferromagnetic chain material, copper nitrate (Cu(NO3)2*2.5D2O). Using
+inelastic neutron scattering we have measured the one and two magnon excitation
+spectra in a large single crystal. The data are in excellent agreement with a
+perturbative expansion of the alternating Heisenberg Hamiltonian from the
+strongly dimerized limit. The expansion predicts a two-magnon bound state for q
+~ (2n+1)pi*d which is consistent with the neutron scattering data.",0207678v1
+2002-12-01,Theoretical analysis of magnetic Raman scattering in La2CuO4: two-magnon intensity with the inclusion of ring exchange,"We evaluate the Raman light scattering intensity for the square lattice
+Heisenberg antiferromagnet with plaquette ring exchange J_\Box. With the
+exchange couplings as fixed before from an accurate fit to the spin-wave
+dispersion in La2CuO4, leading in particular to J_\Box=0.24J, we demonstrate in
+a parameter free calculation that the inclusion of the plaquette exchange
+contribution to the dispersion and the magnon-magnon interaction vertex gives a
+peak position in $B_{1g}$ scattering geometry E_max = 2.71J which is in
+excellent agreement with the experimental data. Yet, the intrinsic width and
+the lineshape of the two-magnon remain beyond a descriptions in terms of a
+spin-only Hamiltonian.",0212014v1
+2003-09-27,Amplitudes for magnon scattering by vortices in two-dimensional weakly easy-plane ferromagnets,"We study magnon modes in the presence of a vortex in a circular easy-plane
+ferromagnet. The problem of vortex-magnon scattering is investigated for
+partial modes with different values of the azimuthal quantum number m over a
+wide range of wave numbers. The analysis was done by combining analytical and
+numerical calculations in the continuum limit with numerical diagonalization of
+adequately large discrete systems. The general laws governing vortex-magnon
+interactions are established. We give simple physical explanations of the
+scattering results: the splitting of doublets for the modes with opposite signs
+of $m$, which takes place for the long wavelength limit, is an analogue of the
+Zeeman splitting in the effective magnetic field of the vortex. A singular
+behavior for the scattering amplitude, $\sigma_m\propto k$, takes place as $k$
+diverges; it corresponds to the generalized Levinson theorem and can be
+explained by the singular behavior of the effective magnetic field at the
+origin.",0309640v1
+2004-01-23,Nonmonotonic inelastic tunneling spectra due to surface spin excitations in ferromagnetic junctions,"The paper addresses inelastic spin-flip tunneling accompanied by surface spin
+excitations (magnons) in ferromagnetic junctions. The inelastic tunneling
+current is proportional to the magnon density of states which is
+energy-independent for the surface waves and, for this reason, cannot account
+for the bias-voltage dependence of the observed inelastic tunneling spectra.
+This paper shows that the bias-voltage dependence of the tunneling spectra can
+arise from the tunneling matrix elements of the electron-magnon interaction.
+These matrix elements are derived from the Coulomb exchange interaction using
+the itinerant-electron model of magnon-assisted tunneling. The results for the
+inelastic tunneling spectra, based on the nonequilibrium Green's function
+calculations, are presented for both parallel and antiparallel magnetizations
+in the ferromagnetic leads.",0401460v6
+2005-07-26,One-magnon states and electron spin resonance in spin-ladders with singlet-rung ground statein a staggered magnetic field,"One-magnon problem for spin-ladders with exact singlet-rung ground state in
+arbitrary oriented constant and staggered magnetic fields is studied. For two
+special configurations when the both fields are parallel or perpendicular to
+each other the exact formulas for eigenstates and eigenvectors are presented.
+In the parallel case the one-magnon contribution to the ESR absorption line
+shape is obtained. The latter is non-Lorentzian, has finite range and a gap
+around resonance. For low fields both the range of the spectrum and the width
+of the gap are controlled by the width of the one-magnon zone in zero magnetic
+field. Some other interactions usually contributing to the ESR line shape are
+also briefly discussed.",0507619v1
+2006-01-26,Spin dynamics characterization in magnetic dots,"The spin structure in a magnetic dot, which is an example of a quantum
+few-body system, is studied as a function of exchange coupling strength and dot
+size with in the semiclassical approximation on a discrete lattice. As the
+exchange coupli ng is decreased or the size is increased, the ground state
+undergoes a phase cha nge from a single domain ferromagnet to a spin vortex.
+The line separating these two phases has been calculated numerically for small
+system sizes. %, and analytically for larger dots. The dipolar interaction has
+been fully included in our calculations. Magnon frequencies in such a dot have
+also been calculated in both phases by the linearized equation of motion
+method. These results have also been reproduced f rom the Fourier transform of
+the spin autocorrelation function. From the magnon Density Of States (DOS), it
+is possible to identify the magnetic phase of the dot. Furthermore, the magnon
+modes have been characterized for both the ferromagnetic and the vortex phase,
+and the magnon instability mechanism leading to the vortex-ferro transition has
+also been identified. The results can also be used to compute finite
+temperature magnetization or vort icity of magnetic dots.",0601624v1
+2006-06-26,From the Hubbard Model to a Systematic Low-Energy Effective Field Theory for Magnons and Holes in an Antiferromagnet,"The low-energy physics of antiferromagnets is governed by their Goldstone
+bosons -- the magnons -- and it is described by a low-energy effective field
+theory. In analogy to baryon chiral perturbation theory, we construct the
+effective field theory for magnons and holes in an antiferromagnet. It is a
+systematic low-energy expansion based on symmetry considerations and on the
+fact that the holes are located in pockets centered at k=(pi/2a,\pm pi/2a).
+Even though the symmetries are extracted from the Hubbard model, the effective
+theory is universal and makes model-independent predictions about the dynamical
+mechanisms in the antiferromagnetic phase. The low-energy effective theory has
+been used to investigate one-magnon exchange which leads to a d-wave-shaped
+bound state of holes.",0606662v1
+2006-06-22,"Magnons, Classical Strings and beta-Deformations","Motivated by the recent work of Hofman and Maldacena we construct a classical
+string solution on the beta-deformed AdS_5 \times \tilde{S}^5 background. This
+string solution is identified with a magnon state of the integrable spin chain
+description of the N=1 supersymmetric beta-deformed gauge theory. The string
+solution carries two angular momenta, an infinite J_1 and a finite J_2 which
+classically can take arbitrary values. It corresponds to the magnon of charge
+J_2 propagating on an infinite spin chain. We derive an exact dispersion
+relation for this magnon from string theory.",0606220v2
+2006-07-06,Spiky strings and giant magnons on S5,"Recently, classical solutions for strings moving in AdS5 x S5 have played an
+important role in understanding the AdS/CFT correspondence. A large set of them
+were shown to follow from an ansatz that reduces the solution of the string
+equations of motion to the study of a well-known integrable 1-d system known as
+the Neumann-Rosochatius (NR) system. However, other simple solutions such as
+spiky strings or giant magnons in S5 were not included in the NR ansatz. We
+show that, when considered in the conformal gauge, these solutions can be also
+accomodated by a version of the NR-system. This allows us to describe in detail
+a giant magnon solution with two additional angular momenta and show that it
+can be interpreted as a superposition of two magnons moving with the same
+speed. In addition, we consider the spin chain side and describe the
+corresponding state as that of two bound states in the infinite SU(3) spin
+chain. We construct the Bethe ansatz wave function for such bound state.",0607044v3
+2007-03-11,On the Singularities of the Magnon S-matrix,"We investigate the analytic structure of the magnon S-matrix in the
+spin-chain description of planar ${\cal N}=4$ SUSY Yang-Mills/$AdS_{5}\times
+S^{5}$ strings. Semiclassical analysis suggests that the exact S-matrix must
+have a large family of poles near the real axis in momentum space. In this
+article we show that these are double poles corresponding to the exchange of
+pairs of BPS magnons. Their locations in the complex plane are uniquely fixed
+by the known dispersion relation for the BPS particles. The locations precisely
+agree with the recent conjecture for the $S$ matrix by Beisert, Hernandez,
+Lopez, Eden and Staudacher (hep-th/0609044 and hep-th/0610251). These poles do
+not signal the presence of new bound states. In fact, a certain non-BPS
+localized classical solution, which was thought to give rise to new bound
+states, can actually decay into a pair of BPS magnons.",0703104v2
+2007-05-09,Dynamics of quantum spin liquid and spin solid phases in IPA-CuCl3 under field,"Inelastic and elastic neutron scattering is used to study spin correlations
+in the quasi-one dimensional quantum antiferromagnet IPA-CuCl3 in strong
+applied magnetic fields. A condensation of magnons and commensurate transverse
+long-range ordering is observe at a critical filed $H_c=9.5$ T. The field
+dependencies of the energies and polarizations of all magnon branches are
+investigated both below and above the transition point. Their dispersion is
+measured across the entire 1D Brillouin zone in magnetic fields up to 14 T. The
+critical wave vector of magnon spectrum truncation [Masuda et al., Phys. Rev.
+Lett. 96, 047210 (2006)] is found to shift from h_c 0.35 at H>H_c. A drastic
+reduction of magnon bandwidths in the ordered phase [Garlea et al., Phys. Rev.
+Lett. 98, 167202 (2007)] is observed and studied in detail. New features of the
+spectrum, presumably related to this bandwidth collapse, are observed just
+above the transition field.",0705.1360v1
+2007-08-02,On the multi-spin magnon and spike solutions from membranes,"Recently important classes of solitonic string solutions were obtained -
+giant magnons and single spikes. In previous study we showed the existence of
+giant magnon-like membrane solutions and studied their properties. In this
+paper we investigate classical rotating membranes representing analog of a
+specific class of string spiky solutions. Using the reduction to the
+Neumann-Rosochatius integrable system we find analog of the string single spike
+solutions. In contrast to the magnon-like solutions, this case is characterized
+with finite difference of energy and ``winding number'' and finite spins as
+well.",0708.0325v3
+2007-08-05,Bose-Einstein condensation of magnons in superfluid 3He,"The possibility of Bose-Einstein condensation of excitations has been
+discussed for a long time. The phenomenon of the phase-coherent precession of
+magnetization in superfluid 3He and the related effects of spin superfluidity
+are based on the true Bose-Einstein condensation of magnons. Several different
+states of coherent precession has been observed in 3He-B: homogeneously
+precessing domain (HPD); persistent signal formed by Q-balls at very low
+temperatures; coherent precession with fractional magnetization; and two new
+modes of the coherent precession in compressed aerogel. In compressed aerogel
+the coherent precession has been also found in 3He-A. Here we demonstrate that
+all these cases are examples of a Bose-Einstein condensation of magnons, with
+the magnon interaction term in the Gross-Pitaevskii equation being provided by
+different types of spin-orbit coupling in the background of the coherent
+precession.",0708.0663v1
+2007-08-21,Magnons in Ferromagnetic Metallic Manganites,"Ferromagnetic (FM) manganites, a group of likely half-metallic oxides, are of
+special interest not only because they are a testing ground of the classical
+doubleexchange interaction mechanism for the colossal magnetoresistance, but
+also because they exhibit an extraordinary arena of emergent phenomena. These
+emergent phenomena are related to the complexity associated with strong
+interplay between charge, spin, orbital, and lattice. In this review, we focus
+on the use of inelastic neutron scattering to study the spin dynamics, mainly
+the magnon excitations in this class of FM metallic materials. In particular,
+we discussed the unusual magnon softening and damping near the Brillouin zone
+boundary in relatively narrow band compounds with strong Jahn-Teller lattice
+distortion and charge/orbital correlations. The anomalous behaviors of magnons
+in these compounds indicate the likelihood of cooperative excitations involving
+spin, lattice, as well as orbital degrees of freedom.",0708.2891v1
+2007-10-15,Fermionic representation for the ferromagnetic Kondo lattice model -- diagrammatic study of spin-charge coupling effects on magnon excitations,"A purely fermionic representation is introduced for the ferromagnetic Kondo
+lattice model which allows conventional diagrammatic tools to be employed to
+study correlation effects. Quantum 1/S corrections to magnon excitations are
+investigated using a systematic inverse-degeneracy expansion scheme which
+incorporates correlation effects in the form of self-energy and vertex
+corrections, while explicitly preserving the continuous spin-rotation symmetry.
+Magnon self-energy is studied in the full range of interaction strength, and
+shown to result in strong magnon damping and anomalous softening for zone
+boundary modes, which accounts for several zone-boundary anomalies observed in
+recent spin-wave measurements of ferromagnetic manganites.",0710.2828v1
+2008-03-17,Interacting finite-size magnons,"We explicitly construct a large class of finite-volume two-magnon string
+solutions moving on R x S^2. In particular, by making use of the relationship
+between the O(3) sigma model and sine-Gordon theory we are able to find
+solutions corresponding to the periodic analogues of magnon scattering and
+breather-like solutions. After semi-classically quantizing these solutions we
+invert the implicit expressions for the excitation energies in certain limits
+and find the corrections for the multi-magnon states. For the breather-like
+solutions we express the energies directly in terms of the action variable
+whereas for the scattering solution we express the result as a combination of
+corrections to the dispersion relation and to the scattering phase.",0803.2324v2
+2008-05-08,Giant magnons in TsT-transformed AdS_5 x S^5,"We consider giant magnons propagating in a \gamma-deformed AdS_5 x S^5
+background obtained from AdS_5 x S^5 by means of a chain of TsT
+transformations. We point out that in the light-cone gauge and in the infinite
+J limit the deformed and undeformed string models share the same magnon
+dispersion relation, the \su(2|2)\oplus \su(2|2)-invariant world-sheet S-matrix
+and the dressing factor. The \gamma-dependence in the limit is only due to
+different level-matching conditions. We consider the reduction of the deformed
+model to R x S^3 and determine the leading \gamma-dependence of the dispersion
+relation for a finite J giant magnon.",0805.1070v2
+2008-12-24,Design and optimization of one-dimensional ferrite-film based magnonic crystals,"One-dimensional magnonic crystals have been implemented as gratings of
+shallow grooves chemically etched into the surface of yttrium-iron garnet
+films. Scattering of backward volume magnetostatic spin waves from such
+structures is investigated experimentally and theoretically. Well-defined
+rejection frequency bands are observed in transmission characteristics of the
+magnonic crystals. The loss inserted by the gratings and the rejections bands
+bandwidths are studied as a function of the film thickness, the groove depth,
+the number of grooves, and the groove width. The experimental data are well
+described by a theoretical model based on the analogy of a spin-wave
+film-waveguide with a microwave transmission line. Our study shows that
+magnonic crystals with required operational characteristics can be engineered
+by adjusting these geometrical parameters.",0812.4553v1
+2009-04-02,S-duality and the giant magnon dispersion relation,"We use S-duality and planarity to propose an argument for the
+non-renormalization of the dispersion relation of giant magnon solutions in
+type IIB string theory on AdS_5 x S^5. We compute the spectrum of giant magnons
+for (p,q)-strings from field theory at strong coupling by using the central
+charge properties of electrically and magnetically charged supersymmetric
+states in the Coulomb branch of N=4 super Yang-Mills. We argue that the
+coupling dependence of the giant magnon dispersion relation conjectured in the
+literature using integrability assumptions is in fact the only functional
+dependence compatible with S-duality.",0904.0444v3
+2009-04-09,Evaluating the locality of intrinsic precession damping in transition metals,"The Landau-Lifshitz-Gilbert damping parameter is typically assumed to be a
+local quantity, independent of magnetic configuration. To test the validity of
+this assumption we calculate the precession damping rate of small amplitude
+non-uniform mode magnons in iron, cobalt, and nickel. At scattering rates
+expected near and above room temperature, little change in the damping rate is
+found as the magnon wavelength is decreased from infinity to a length shorter
+than features probed in recent experiments. This result indicates that
+non-local effects due to the presence of weakly non-uniform modes, expected in
+real devices, should not appreciably affect the dynamic response of the element
+at typical operating temperatures. Conversely, at scattering rates expected in
+very pure samples around cryogenic temperatures, non-local effects result in an
+order of magnitude decrease in damping rates for magnons with wavelengths
+commensurate with domain wall widths. While this low temperature result is
+likely of little practical importance, it provides an experimentally testable
+prediction of the non-local contribution of the spin-orbit torque-correlation
+model of precession damping. None of these results exhibit strong dependence on
+the magnon propagation direction.",0904.1455v1
+2009-04-24,Magnon BEC and Spin Superfluidity: a 3He primer,"Bose-Einstein condensation (BEC) is a quantum phenomenon of formation of the
+collective quantum state, in which the macroscopic number of particles occupies
+the lowest energy state and thus is governed by a single wave function. Here we
+highlight the BEC in a magnetic subsystem -- the BEC of magnons, elementary
+magnetic excitations. Magnon BEC is manifested as the spontaneously emerging
+state of the precessing spins, in which all spins precess with the same
+frequency and phase even in the inhomogeneous magnetic field. We consider this
+phenomenon on example of spin precession in superfluid phases of $^3$He. The
+magnon BEC in these phases has all the properties of spin superfluidity. The
+states of the phase-coherent precession belong to the class of the coherent
+quantum states, which manifest themselves by superfluidity, superconductivity,
+quantum Hall effect, Josephson effect and many other macroscopic quantum
+phenomena.",0904.3889v1
+2009-05-15,A New and Elementary CP^n Dyonic Magnon,"We show that the dressing transformation method produces a new type of dyonic
+CP^n magnon in terms of which all the other known solutions are either
+composites or arise as special limits. In particular, this includes the
+embedding of Dorey's dyonic magnon via an RP^3 subspace of CP^n. We also show
+how to generate Dorey's dyonic magnon directly in the S^n sigma model via the
+dressing method without resorting to the isomorphism with the SU(2) principle
+chiral model when n=3. The new dyon is shown to be either a charged dyon or
+topological kink of the related symmetric-space sine-Gordon theories associated
+to CP^n and in this sense is a direct generalization of the soliton of the
+complex sine-Gordon theory.",0905.2534v2
+2009-10-28,"Orbital fluctuations, spin-orbital coupling, and anomalous magnon softening in an orbitally degenerate ferromagnet","The correlated motion of electrons in the presence of strong orbital
+fluctuations and correlations is investigated with respect to magnetic
+couplings and excitations in an orbitally degenerate ferromagnet. Introduction
+of the orbital degree of freedom results in a class of diagrams representing
+spin-orbital coupling which become particularly important near the orbital
+ordering instability. Low-energy staggered orbital fluctuation modes,
+particularly with momentum near (\pi/2,\pi/2,0) (corresponding to CE-type
+orbital correlations), are shown to generically yield strong intrinsically
+non-Heisenberg (1-\cos q)^2 magnon self energy correction, resulting in no spin
+stiffness reduction, but strongly suppressed zone-boundary magnon energies in
+the Gamma-X direction. The zone-boundary magnon softening is found to be
+strongly enhanced with increasing hole doping and for narrow-band materials,
+which provides insight into the origin of zone-boundary anomalies observed in
+ferromagnetic manganites.",0910.5321v2
+2009-11-09,Giant Spinons,"We study the spectrum around the ""antiferromagnetic"" states of the planar
+AdS_5/CFT_4 duality. In contrast to the familiar large-spin limit J \to \infty
+where each magnon momentum scales as p \sim 1/J << 1, we consider a novel
+""large-winding"" limit in which the total momentum becomes infinitely large,
+\sum_j p_j \to \infty. Upon taking the limit we identify ""spinon"" excitations
+of both gauge and string theories. In particular, a (classical) string spinon
+turns out to be an infinite set of spiky strings, which are closely related to
+well-known infinite-spin strings: giant magnons. Furthermore, we show that the
+curious agreement of scattering phase-shifts of two spikes and that of two
+giant magnons can be accounted for by regarding the spinon scattering as
+factorised scatterings of infinitely many magnons.",0911.1528v2
+2010-02-08,Self-localization of magnon Bose-Einstein condensates in the ground state and on excited levels: from harmonic to box-like trapping potential,"Long-lived coherent spin precession of 3He-B at low temperatures around 0.2
+Tc is a manifestation of Bose-Einstein condensation of spin-wave excitations or
+magnons in a magnetic trap which is formed by the order-parameter texture and
+can be manipulated experimentally. When the number of magnons increases, the
+orbital texture reorients under the influence of the spin-orbit interaction and
+the profile of the trap gradually changes from harmonic to a square well, with
+walls almost impenetrable to magnons. This is the first experimental example of
+Bose condensation in a box. By selective rf pumping the trap can be populated
+with a ground-state condensate or one at any of the excited energy levels. In
+the latter case the ground state is simultaneously populated by relaxation from
+the exited level, forming a system of two coexisting condensates.",1002.1674v3
+2011-02-01,Low Temperature Dynamics of Magnons in a Spin-1/2 Ladder Compound,"We have used a combination of neutron resonant spin-echo and triple-axis
+spectroscopies to determine the energy, fine structure, and linewidth of the
+magnon resonance in the model spin-1/2 ladder antiferromagnet IPA-CuCl_3 at
+temperatures T << Delta_0 /k_B, where Delta_0 is the spin gap at T=0. In this
+low-temperature regime we find that the results deviate substantially from the
+predictions of the non-linear sigma model proposed as a description of magnon
+excitations in one-dimensional quantum magnets and attribute these deviations
+to real-space and spin-space anisotropies in the spin Hamiltonian as well as
+scattering of magnon excitations from a dilute density of impurities. These
+effects are generic to experimental realizations of one-dimensional quantum
+magnets.",1102.0214v1
+2011-04-08,Low-temperature heat transport of Nd_2CuO_4: Roles of Nd magnons and spin-structure transitions,"We report the magnetic-field dependence of thermal conductivity (\kappa) of
+an insulating cuprate Nd_2CuO_4 at very low temperatures down to 0.3 K. It is
+found that apart from the paramagnetic moments scattering on phonons, the
+Nd^{3+} magnons can act as either heat carriers or phonon scatterers, which
+strongly depends on the long-range antiferromagnetic transition and the
+field-induced transitions of spin structure. In particular, the Nd^{3+} magnons
+can effectively transport heat in the spin-flopped state of the Nd^{3+}
+sublattice. However, both the magnon transport and the magnetic scattering are
+quenched at very high fields. The spin re-orientations under the in-plane field
+can be conjectured from the detailed field dependence of \kappa.",1104.1514v1
+2011-06-14,Two-magnon Raman scattering in A$_{0.8}$Fe$_{1.6}$Se$_2$ systems: competition between superconductivity and antiferromagnetic order,"We have performed Raman-scattering measurements on high-quality single
+crystals of A$_{0.8}$Fe$_{1.6}$Se$_2$ superconductors of several compositions.
+We find a broad, asymmetric peak around 1600 cm$^{-1}$ (200 meV), which we
+identify as a two-magnon process involving optical magnons. The intensity of
+the two-magnon peak falls sharply on entering the superconducting phase. This
+effect, which is entirely absent in the non-superconducting system
+KFe$_{1.5}$Se$_2$, requires a strong mutual exclusion between
+antiferromagnetism and superconductivity arising from proximity effects within
+regions of microscale phase separation.",1106.2706v2
+2011-08-11,Thermoelectric Spin-Transfer Torque MRAM with Sub-Nanosecond Bi-Directional Writing using Magnonic Current,"A new genre of Spin-Transfer Torque (STT) MRAM is proposed, in which
+bi-directional writing is achieved using thermoelectrically controlled magnonic
+current as an alternative to conventional electric current. The device uses a
+magnetic tunnel junction (MTJ), which is adjacent to a non-magnetic metallic
+and a ferrite film. This film stack is heated or cooled by a Peltier element
+which creates a bi-directional magnonic pulse in the ferrite film. Conversion
+of magnons to spin current occurs at the ferrite-metal interface, and the
+resulting spin-transfer torque is used to achieve sub-nanosecond precessional
+switching of the ferromagnetic free layer in the MTJ. Compared to electric
+current driven STT-MRAM with perpendicular magnetic anisotropy (PMA),
+thermoelectric STT-MRAM reduces the overall magnetization switching energy by
+more than 40% for nano-second switching, combined with a write error rate (WER)
+of less than 10-9 and a lifetime of 10 years or higher. The combination of
+higher thermal activation energy, sub-nanosecond read/write speed, improved
+tunneling magneto-resistance (TMR) and tunnel barrier reliability make
+thermoelectric STT-MRAM a promising choice for future non-volatile memory
+applications.",1108.2386v1
+2011-12-24,Frustrated spin chains in strong magnetic field: dilute two-component Bose gas regime,"We study the ground state of frustrated spin-S chains in a strong magnetic
+field in the immediate vicinity of saturation. In strongly frustrated chains,
+the magnon dispersion has two degenerate minima at inequivalent momenta $\pm
+Q$, and just below the saturation field the system can be effectively
+represented as a dilute one-dimensional lattice gas of two species of bosons
+that correspond to magnons with momenta around $\pm Q$. We present a theory of
+effective interactions in such a dilute magnon gas that allows us to make
+quantitative predictions for arbitrary values of the spin. With the help of
+this method, we are able to establish the magnetic phase diagram of frustrated
+chains close to saturation and study phase transitions between several
+nontrivial states, including a two-component Luttinger liquid, a vector chiral
+phase, and phases with bound magnons. We study those phase transitions
+numerically and find a good agreement with our analytical predictions.",1112.5720v2
+2012-02-26,"Magnons and crystal field transitions in hexagonal REMnO3 (RE = Er, Tm, Yb, Lu) single crystals","Far-infrared optical transmission spectra of the antiferromagnetic
+resonances, or magnons, and crystal field transitions have been studied in
+hexagonal REMnO3 (RE = Er, Tm, Yb, Lu) single crystals. The magnon and CF
+frequencies, their oscillator strengths, and effective g-factors have been
+measured using external magnetic fields up to 9 T in the temperature range
+between 1.5 K and 100 K. The magnon frequency increases systematically with a
+decrease of the RE ion radius. The magnetic ordering of RE ions (RE=Er, Tm, Yb)
+was observed at low temperatures T<3.5 K and in strong external magnetic
+fields. The observed effects are analyzed taking into account main magnetic
+interactions in the system including exchange of the Mn3+ spins with RE3+
+paramagnetic moments.",1202.5803v1
+2012-06-20,Lifetime of Gapped Excitations in a Collinear Quantum Antiferromagnet,"We demonstrate that local modulations of magnetic couplings have a profound
+effect on the temperature dependence of the relaxation rate of optical magnons
+in a wide class of antiferromagnets in which gapped excitations coexist with
+acoustic spin waves. In a two-dimensional collinear antiferromagnet with an
+easy-plane anisotropy, the disorder-induced relaxation rate of the gapped mode,
+Gamma_imp=Gamma_0+A(TlnT)^2, greatly exceeds the magnon-magnon damping,
+Gamma_m-m=BT^5, negligible at low temperatures. We measure the lifetime of
+gapped magnons in a prototype XY antiferromagnet BaNi2(PO4)2 using a
+high-resolution neutron-resonance spin-echo technique and find experimental
+data in close accord with the theoretical prediction. Similarly strong effects
+of disorder in the three-dimensional case and in noncollinear antiferromagnets
+are discussed.",1206.4690v2
+2012-08-30,Efimov effect in quantum magnets,"Physics is said to be universal when it emerges regardless of the underlying
+microscopic details. A prominent example is the Efimov effect, which predicts
+the emergence of an infinite tower of three-body bound states obeying discrete
+scale invariance when the particles interact resonantly. Because of its
+universality and peculiarity, the Efimov effect has been the subject of
+extensive research in chemical, atomic, nuclear and particle physics for
+decades. Here we employ an anisotropic Heisenberg model to show that collective
+excitations in quantum magnets (magnons) also exhibit the Efimov effect. We
+locate anisotropy-induced two-magnon resonances, compute binding energies of
+three magnons and find that they fit into the universal scaling law. We propose
+several approaches to experimentally realize the Efimov effect in quantum
+magnets, where the emergent Efimov states of magnons can be observed with
+commonly used spectroscopic measurements. Our study thus opens up new avenues
+for universal few-body physics in condensed matter systems.",1208.6214v2
+2012-09-25,Ultrafast magnon-transistor at room temperature,"We study sequential tunneling of magnetic excitations in nonitinerant systems
+(either magnons or spinons) through triangular molecular magnets. It is known
+that the quantum state of such molecular magnets can be controlled by
+application of an electric- or a magnetic field. Here, we use this fact to
+control the flow of a spin current through the molecular magnet by electric- or
+magnetic means. This allows us to design a system that behaves as a
+magnon-transistor. We show how to combine three magnon-transistors to form a
+NAND-gate, and give several possible realizations of the latter, one of which
+could function at room temperature using transistors with a 11 ns switching
+time.",1209.5594v2
+2013-02-25,Phase Diagram for Magnon Condensate in Yttrium Iron Garnet Film,"Recently, magnons, which are quasiparticles describing the collective motion
+of spins, were found to undergo Bose-Einstein condensation (BEC) at room
+temperature in films of Yttrium Iron Garnet (YIG). Unlike other quasiparticle
+BEC systems, this system has a spectrum with two degenerate minima, which makes
+it possible for the system to have two condensates in momentum space. Recent
+Brillouin Light scattering studies for a microwave-pumped YIG film of thickness
+d=5 $\mu$m and field H=1 kOe find a low-contrast interference pattern at the
+characteristic wavevector $Q$ of the magnon energy minimum. In this report, we
+show that this modulation pattern can be quantitatively explained as due to
+non-symmetric but coherent Bose-Einstein condensation of magnons into the two
+energy minima. Our theory predicts a transition from a high-contrast symmetric
+phase to a low-contrast non-symmetric phase on varying the $d$ and $H$, and a
+new type of collective oscillations.",1302.6128v1
+2013-02-27,Specific heat and thermal conductivity of ferromagnetic magnons in Yttrium Iron Garnet,"The specific heat and thermal conductivity of the insulating ferrimagnet
+Y$_3$Fe$_5$O$_{12}$ (Yttrium Iron Garnet, YIG) single crystal were measured
+down to 50 mK. The ferromagnetic magnon specific heat $C$$_m$ shows a
+characteristic $T^{1.5}$ dependence down to 0.77 K. Below 0.77 K, a downward
+deviation is observed, which is attributed to the magnetic dipole-dipole
+interaction with typical magnitude of 10$^{-4}$ eV. The ferromagnetic magnon
+thermal conductivity $\kappa_m$ does not show the characteristic $T^2$
+dependence below 0.8 K. To fit the $\kappa_m$ data, both magnetic defect
+scattering effect and dipole-dipole interaction are taken into account. These
+results complete our understanding of the thermodynamic and thermal transport
+properties of the low-lying ferromagnetic magnons.",1302.6739v1
+2013-04-26,A micro-structured ion-implanted magnonic crystal,"We investigate spin-wave propagation in a microstructured magnonic-crystal
+waveguide fabricated by localized ion implantation. The irradiation caused a
+periodic variation in the saturation magnetization along the waveguide. As a
+consequence, the spin-wave transmission spectrum exhibits a set of frequency
+bands, where spin-wave propagation is suppressed. A weak modification of the
+saturation magnetization by 7% is sufficient to decrease the spin-wave
+transmission in the band gaps by a factor of 10. These results evidence the
+applicability of localized ion implantation for the fabrication of efficient
+micron- and nano-sized magnonic crystals for magnon spintronic applications.",1304.7122v1
+2013-05-21,Effect of Hole Shape on Spin-Wave Band Structure in One-Dimensional Magnonic Antidot Waveguide,"We present the possibility of tuning the spin-wave band structure,
+particularly the bandgaps in a nanoscale magnonic antidot waveguide by varying
+the shape of the antidots. The effects of changing the shape of the antidots on
+the spin-wave dispersion relation in a waveguide have been carefully monitored.
+We interpret the observed variations by analysing the equilibrium magnetic
+configuration and the magnonic power and phase distribution profiles during
+spin-wave dynamics. The inhomogeneity in the exchange fields at the antidot
+boundaries within the waveguide is found to play a crucial role in controlling
+the band structure at the discussed length scales. The observations recorded
+here will be important for future developments of magnetic antidot based
+magnonic crystals and waveguides.",1305.4812v2
+2013-11-26,Magnon breakdown in a two dimensional triangular lattice Heisenberg antiferromagnet of multiferroic LuMnO$_3$,"The breakdown of magnons, the quasiparticles of magnetic systems, has rarely
+been seen. By using an inelastic neutron scattering technique we report the
+observation of spontaneous magnon decay in multiferroic LuMnO$_3$, a simple
+two-dimensional Heisenberg triangular lattice antiferromagnet, with large spin,
+S = 2. The origin of this rare phenomenon lies in the non-vanishing cubic
+interaction between magnons in the spin Hamiltonian arising from the
+noncollinear 120$^o$ spin structure. We observed all three key features of the
+nonlinear effects as theoretically predicted: a roton-like minimum, a flat
+mode, and a linewidth broadening, in our inelastic neutron scattering
+measurements of single crystal LuMnO$_3$. Our results show that quasiparticles
+in a system hitherto thought of as ""classical"" can indeed break down.",1311.6652v1
+2014-01-05,Magnon-Mediated Dzyaloshinskii-Moriya Torque in Homogeneous Ferromagnets,"In thin magnetic layers with structural inversion asymmetry and spin-orbit
+coupling, a Dzyaloshinskii-Moriya interaction arises at the interface. When a
+spin wave current ${\bf j}_m$ flows in a system with a homogeneous
+magnetization {\bf m}, this interaction produces an effective field-like torque
+on the form ${\bf T}_{\rm FL}\propto{\bf m}\times({\bf z}\times{\bf j}_m)$ as
+well as a damping-like torque, ${\bf T}_{\rm DL}\propto{\bf m}\times[({\bf
+z}\times{\bf j}_m)\times{\bf m}]$ in the presence of spin-wave relaxation
+(${\bf z}$ is normal to the interface). These torques mediated by the magnon
+flow can reorient the time-averaged magnetization direction and display a
+number of similarities with the torques arising from the electron flow in a
+magnetic two dimensional electron gas with Rashba spin-orbit coupling. This
+magnon-mediated spin-orbit torque can be efficient in the case of magnons
+driven by a thermal gradient.",1401.0883v2
+2014-09-30,Direct observation of the Dzyaloshinskii-Moriya interaction in a Pt/Co/Ni film,"The interfacial Dzyaloshinskii-Moriya interaction (DMI) in an in-plane
+anisotropic Pt(4nm)/Co(1.6nm)/Ni(1.6nm) film has been directly observed by
+Brillouin spectroscopy. It is manifested in the asymmetry of the measured
+magnon dispersion relation, from which the DMI constant has been evaluated.
+Linewidth measurements reveal that the lifetime of the magnons is asymmetric
+with respect to their counter-propagating directions. The lifetime asymmetry is
+dependent on the magnon frequency, being more pronounced the higher the
+frequency. Analytical calculations of the magnon dispersion relation and
+linewidth agree well with experiments.",1409.8570v2
+2014-11-14,Lifetimes of Magnons in Two-Dimensional Diluted Ferromagnetic Systems,"Spin dynamics in low dimensional magnetic systems has been of fundamental
+importance for a long time and has currently received an impetus owing to the
+emerging field of nanoelectronics. Knowledge of the spin wave lifetimes, in
+particular, can be favorable for future potential applications. We investigate
+the low-temperature spin wave excitations in two-dimensional disordered
+ferromagnetic systems, with a particular focus on the long wavelength magnon
+lifetimes. A semi-analytical Green's functions based approach is used to
+determine the dynamical spectral functions, for different magnetic impurity
+concentrations, from which the intrinsic linewidth is extracted. We obtain an
+unambiguous $q^4$ scaling of the magnon linewidth which is ascribed to the
+disorder induced damping of the spin waves, thereby settling a longstanding
+unresolved issue on the wave-vector dependence. Our findings are also in good
+agreement with previous theoretical studies on Heisenberg ferromagnets.
+Additionally, we demonstrate the futility of using the low moments associated
+with the spectral densities to evaluate the magnon dispersions and lifetimes.",1411.3876v2
+2014-12-15,String theory in AdS_3 x S^3 x T^4 with mixed flux: semiclassical and 1-loop phase in the S-matrix,"We present a semiclassical derivation of the tree-level and 1-loop dressing
+phases in the massive sector of string theory on AdS_3 x S^3 x T^4 supplemented
+by R-R and NS-NS 3-form fluxes. In analogy with the AdS_5 x S^5 case, we use
+the dressing method to obtain scattering solutions for dyonic giant magnons
+which allows us to determine the semiclassical bound-state S-matrix and its
+1-loop correction. We also find that the 1-loop correction to the dyonic giant
+magnon energy vanishes. Looking at the relation between the bound-state picture
+and elementary magnons in terms of the fusion procedure we deduce the
+elementary dressing phases. In both the semiclassical and 1-loop cases we find
+agreement with recent proposals from finite-gap equations and unitarity cut
+methods. Further, we find consistency with the finite-gap picture by
+determining the resolvent for the dyonic giant magnon from the semiclassical
+bosonic scattering data.",1412.4764v3
+2015-01-14,A spin-wave logic gate based on a width-modulated dynamic magnonic crystal,"An electric current controlled spin-wave logic gate based on a
+width-modulated dynamic magnonic crystal is realized. The device utilizes a
+spin-wave waveguide fabricated from a single-crystal Yttrium Iron Garnet film
+and two conducting wires attached to the film surface. Application of electric
+currents to the wires provides a means for dynamic control of the effective
+geometry of the waveguide and results in a suppression of the magnonic band
+gap. The performance of the magnonic crystal as an AND logic gate is
+demonstrated.",1501.03486v2
+2015-01-17,Kondo dynamics in one-dimensional doped ferromagnetic insulators,"Some well-established examples of itinerant-electron ferromagnetism in one
+dimension occur in a Mott-insulating phase. We examine the consequences of
+doping a ferromagnetic insulator and cou- pling magnons to gapless charge
+fluctuations. Using a bosonization scheme for strongly interacting electrons,
+we derive an effective field theory for the magnon-holon interaction. When the
+magnon momentum matches the Fermi momentum of the holons, the backscattering of
+the magnon at low energies gives rise to a Kondo effect of a pseudospin defined
+from the chirality degree of freedom (right- or left-moving particles). The
+crossover between weak-coupling and strong-coupling fixed points of the
+effective mobile-impurity model is then investigated using a numerical
+renormalization group approach.",1501.04220v1
+2015-02-03,Probing single magnon excitations in Sr$_2$IrO$_4$ using O $K$-edge resonant inelastic X-ray scattering,"Resonant inelastic X-ray scattering (RIXS) at the $L$-edge of transition
+metal elements is now commonly used to probe single magnon excitations. Here we
+show that single magnon excitations can also be measured with RIXS at the
+$K$-edge of the surrounding ligand atoms when the center heavy metal elements
+have strong spin-orbit coupling. This is demonstrated with oxygen $K$-edge RIXS
+experiments on the perovskite Sr$_2$IrO$_4$, where low energy peaks from single
+magnon excitations were observed. This new application of RIXS has excellent
+potential to be applied to a wide range of magnetic systems based on heavy
+elements, for which the $L$-edge RIXS energy resolutions in the hard X-ray
+region is usually poor.",1502.00752v1
+2015-02-22,Excitation and detection of propagating spin waves at the single magnon level,"Ferro- and ferrimagnets play host to small-signal, microwave-frequency
+magnetic excitations called spin waves, the quanta of which are known as
+magnons. Over the last decade, the field of spin-wave dynamics has contributed
+much to our understanding of fundamental magnetism. To date, experiments have
+focussed overwhelmingly on the study of room-temperature systems within
+classical limits. Here we demonstrate, for the first time, the excitation and
+detection of propagating spin waves at the single magnon level. Our results
+allow us to project that coupling of propagating spin-wave excitations to
+quantum circuits is achievable, enabling fundamental quantum-level studies of
+magnon systems and potentially opening doors to novel hybrid quantum
+measurement and information processing devices.",1502.06263v1
+2015-03-25,Effect of broken symmetry on resonant inelastic x-ray scattering from undoped cuprates,"We study the magnetic excitation spectra of resonant inelastic x-ray
+scattering (RIXS) at the $L$-edge from undoped cuprates beyond the fast
+collision approximation. We analyse the effect of the symmetry breaking ground
+state on the RIXS process of the Heisenberg model by using a projection
+procedure. We derive the expressions of the scattering amplitude in both
+one-magnon and two-magnon excitation channels. Each of them consists of the
+isotropic and anisotropic contributions. The latter is a new finding and
+attributed to the long range order of the ground state. The presence of
+anisotropic terms is supported by numerical calculations on a two-dimensional
+spin cluster. We express the RIXS spectra in the form of spin-correlation
+functions with the coefficients evaluated on the cluster, and calculate the
+function in a two dimensional system within the $1/S$ expansion. Due to the
+anisotropic terms, the spectral intensities are considerably enhanced around
+momentum transfer $\textbf{q}=0$ in both one-magnon and two-magnon excitation
+channels. This finding may be experimentally confirmed by examining carefully
+the $\textbf{q}$-dependence of the spectra.",1503.07264v1
+2015-04-06,Spin Pumping in Electrodynamically Coupled Magnon-Photon Systems,"We use electrical detection, in combination with microwave transmission, to
+investigate both resonant and non-resonant magnon-photon coupling at room
+temperature. Spin pumping in a dynamically coupled magnon-photon system is
+found to be distinctly different from previous experiments. Characteristic
+coupling features such as modes anti-crossing, line width evolution, peculiar
+line shape, and resonance broadening are systematically measured and
+consistently analyzed by a theoretical model set on the foundation of classical
+electrodynamic coupling. Our experimental and theoretical approach pave the way
+for pursuing microwave coherent manipulation of pure spin current via the
+combination of spin pumping and magnon-photon coupling.",1504.01335v1
+2015-05-05,Spin pumping from a ferromagnet into a hopping insulator: the role of resonant absorption of magnons,"Motivated by recent experiments on spin pumping from a ferromagnet into
+organic materials in which the charge transport is due to hopping, we study
+theoretically the generation and propagation of spin current in a hopping
+insulator. Unlike metals, the spin polarization at the boundary with
+ferromagnet is created as a result of magnon absorption within pairs of
+localized states and it spreads following the current-currying resistor network
+(although the charge current is absent). We consider a classic resonant
+mechanism of the ac absorption in insulators and adapt it to the absorption of
+magnons. A strong enhancement of pumping efficiency is predicted when the
+Zeeman splitting of the localized states in external magnetic field is equal to
+the frequency of ferromagnetic resonance. Under this condition the absorption
+of a magnon takes place within individual sites.",1505.01211v1
+2015-06-17,Anomalous Dimensions of Heavy Operators from Magnon Energies,"We study spin chains with boundaries that are dual to open strings suspended
+between systems of giant gravitons and dual giant gravitons. The anomalous
+dimensions computed in the gauge theory are in complete quantitative agreement
+with energies computed in the dual string theory. The comparison makes use of a
+description in terms of magnons, generalizing results for a single maximal
+giant graviton. The symmetries of the problem determine the structure of the
+magnon boundary reflection/scattering matrix up to a phase. We compute a
+reflection/scattering matrix element at weak coupling and verify that it is
+consistent with the answer determined by symmetry. We find the
+reflection/scattering matrix does not satisfy the boundary Yang-Baxter equation
+so that the boundary condition on the open spin chain spoils integrability. We
+also explain the interpretation of the double coset ansatz in the magnon
+language.",1506.05224v2
+2015-06-17,Magnetic field control of the spin Seebeck effect,"The origin of the suppression of the longitudinal spin Seebeck effect by
+applied magnetic fields is studied. We perform numerical simulations of the
+stochastic Landau-Lifshitz-Gilbert equation of motion for an atomistic spin
+model and calculate the magnon accumulation in linear temperature gradients for
+different strengths of applied magnetic fields and different length scales of
+the temperature gradient. We observe a decrease of the magnon accumulation with
+increasing magnetic field and we reveal that the origin of this effect is a
+field dependent change of the frequency distribution of the propagating
+magnons. With increasing field the magnonic spin currents are reduced due to a
+suppression of parts of the frequency spectrum. By comparison with measurements
+of the magnetic field dependent longitudinal spin Seebeck effect in YIG thin
+films with various thicknesses, we find that our model describes the
+experimental data very well, demonstrating the importance of this effect for
+experimental systems.",1506.05290v1
+2015-10-12,Spin wave approach to the two-magnon Raman scattering in an J1x-J1y-J2-Jc antiferromagnetic Heisenberg model,"We study the two-magnon non-resonant Raman scattering in the (pi,pi) and
+(pi,0) ordered antiferromagnetic phases of a J1x-J1y-J2-Jc Heisenberg model on
+the tetragonal lattice within the framework of the spin-wave theory. We discuss
+the effects of various tuning factors to the two-magnon Raman spectra. We find
+that both the magnetic frustration J2/J1 and the interlayer exchange coupling
+Jc may significantly affect the spectra in both the B1g and A1g' channels in
+the (pi,pi) Neel ordered phase. Moreover, we find a splitting of the two-magnon
+peak in the (pi,0) antiferromagnetic phase. We further discuss the implications
+of our results to the BaMnBi2 and iron pnictide systems.",1510.03359v1
+2016-05-31,Electric field control of magnon-induced magnetization dynamics in multiferroics,"We consider theoretically the effect of an inhomogeneous magnetoelectric
+coupling on the magnon-induced dynamics of a ferromagnet. The magnon-mediated
+magnetoelectric torque affects both the homogeneous magnetization and
+magnon-driven domain wall motion. In the domains, we predict a reorientation of
+the magnetization, controllable by the applied electric field, which is almost
+an order of magnitude larger than that observed in other physical systems via
+the same mechanism. The applied electric field can also be used to tune the
+domain wall speed and direction of motion in a linear fashion, producing domain
+wall velocities several times the zero field velocity. These results show that
+multiferroic systems offer a promising arena to achieve low-dissipation
+magnetization rotation and domain wall motion by exciting spin-waves.",1606.00007v2
+2016-06-23,Electromagnon dispersion probed by inelastic x-ray scattering,"Inelastic x-ray scattering with meV energy resolution (IXS) is an ideal tool
+to measure collective excitations in solids and liquids. In non-resonant
+scattering condition, the cross section is strongly dominated by lattice
+vibrations (phonons). However, it is possible to probe additional degrees of
+freedom such as magnetic fluctuations that are strongly coupled to the phonons.
+The IXS spectrum of the coupled system will contain not only the phonon
+dispersion (majority component) but also the so far undetected magnetic
+correlation function (minority component). Here we report the discovery of
+strong magnon-phonon coupling in LiCrO$_2$ that enables the measurement of
+magnetic correlations throughout the Brillouin-zone via IXS. We found
+electromagnon excitations and electric dipole active two-magnon excitations in
+the magnetically ordered phase and paraelectromagnons in the paramagnetic phase
+of LiCrO$_2$. We predict that the numerous group of (frustrated) magnets with
+dominant direct exchange and non-collinear magnetism shows similarly strong
+coupling and surprisingly large and measurable IXS cross section for magnons
+and multi-magnon processes.",1606.07321v1
+2016-07-27,Voltage-Controlled Nano-Scale Reconfigurable Magnonic Crystal,"A nano-scale reconfigurable magnonic crystal is designed using
+voltage-controlled perpendicular magnetic anisotropy (PMA) in
+ferromagnetic-dielectric hetero-structures. A periodic array of gate metallic
+stripes is placed on top of a MgO/Co structure in order to apply a periodic
+electric field and to modify the PMA in Co. It is numerically demonstrated that
+the application of the voltage to the gate stripes modifies the spin-wave
+propagation and leads to the formation of band gaps in the spin-wave spectrum.
+The band gaps are dynamically controllable, i.e. it is possible to switch band
+gaps on and off within a few nanoseconds. The width and the center frequency of
+the band gaps is defined by the applied voltage. At last, it is shown that the
+application of the voltage to selected, rather than to all gate stripes allows
+for a pre-defined modification of the band gap spectra. The proposed
+voltage-controlled reconfigurable magnonic crystal opens a new way to low power
+consumption magnonic applications.",1607.07975v1
+2017-02-08,Magnon-polaron transport in magnetic insulators,"We theoretically study the effects of strong magnetoelastic coupling on the
+transport properties of magnetic insulators. We develop a Boltzmann transport
+theory for the mixed magnon-phonon modes (magnon polarons) and determine
+transport coefficients and spin diffusion length. Magnon-polaron formation
+causes anomalous features in the magnetic field and temperature dependence of
+the spin Seebeck effect when the disorder scattering in the magnetic and
+elastic subsystems is sufficiently different. Experimental data by Kikkawa et
+al. [PRL 117, 207203 (2016)] on yttrium iron garnet films can be explained by
+an acoustic quality that is much better than the magnetic quality of the
+material. We predict similar anomalous features in the spin and heat
+conductivity and non-local spin transport experiments.",1702.02270v1
+2017-01-30,Ultrafast optical excitation of coherent magnons in antiferromagnetic NiO,"In experiment and theory, we resolve the mechanism of ultrafast optical
+magnon excitation in antiferromagnetic NiO. We employ time-resolved optical
+two-color pump-probe measurements to study the coherent non-thermal spin
+dynamics. Optical pumping and probing with linearly and circularly polarized
+light along the optic axis of the NiO crystal scrutinizes the mechanism behind
+the ultrafast optical magnon excitation. A phenomenological symmetry-based
+theory links these experimental results to expressions for the optically
+induced magnetization via the inverse Faraday effect and the inverse
+Cotton-Mouton effect. We obtain striking agreement between experiment and
+theory that, furthermore, allows us to extract information about the spin
+domain distribution. We also find that in NiO the energy transfer into the
+magnon mode via the inverse Cotton-Mouton effect is about three orders of
+magnitude more efficient than via the inverse Faraday effect.",1702.05666v1
+2017-03-18,Entanglement of condensed magnons via momentum-space fragmentation,"A scheme is presented for engineering momentum-space entanglement of
+fragmented magnon condensates. We consider easy plane frustrated
+antiferromagnets in which the magnon dispersion has degenerate minima that
+represent umbrella chiral spin textures. With an applied magnetic field, we
+tune the Hamiltonian near a quantum critical point that is is signaled by a
+singularity in the entanglement entropy. The ground state develops
+momentum-space entanglement of the chiral spin textures. The size of the
+entangled superposition is accessible experimentally through the magnetic
+structure factor. Our model is motivated by equilibrium magnon condensates in
+frustrated antiferromagnets such as CsCuCl3, and it can also be simulated in
+spin-orbit coupled Mott insulators in atomic optical lattices and circuit
+quantum electrodynamics.",1703.06232v1
+2017-03-23,Magnon activation by hot electrons via non-quasiparticle states,"We consider the situation when a femtosecond laser pulse creates a hot
+electron state in half-metallic ferromagnet (e. g. ferromagnetic semiconductor)
+on a picosecond timescale but do not act directly on localized spin system. We
+show that the energy and magnetic moment transfer from hot itinerant electrons
+to localized spins is facilitated by the so-called non-quasiparticle states,
+which are the scattering states of a magnon and spin-majority electron. The
+magnon distribution is described by a quantum kinetic equation that we derive
+using the Keldysh diagram technique. In a typical ferromagnetic semiconductor
+such as EuO magnons remain essentially in non-equilibrium on a scale of the
+order of microsecond after the laser pulse.",1703.08106v1
+2017-03-24,Dirac and nodal line magnons in three-dimensional antiferromagnets,"We study the topological properties of magnon excitations in
+three-dimensional antiferromagnets, where the ground state configuration is
+invariant under time-reversal followed by space-inversion ($PT$-symmetry). We
+prove that Dirac points and nodal lines, the former being the limiting case of
+the latter, are the generic forms of symmetry-protected band crossings between
+magnon branches. As a concrete example, we study a Heisenberg spin model for a
+""spin-web"" compound, Cu$_3$TeO$_6$, and show the presence of the magnon Dirac
+points assuming a collinear magnetic structure. Upon turning on
+symmetry-allowed Dzyaloshinsky-Moriya interactions, which introduce a small
+non-collinearity in the ground state configuration, we find that the Dirac
+points expand into nodal lines with nontrivial $Z_2$-topological charge, a new
+type of nodal lines unpredicted in any materials so far.",1703.08545v3
+2018-02-03,Magnon scattering in the transport coefficients of CoFe alloys,"Resistivity $\rho$, thermopower ${\cal S}$, and thermal conductivity $\kappa$
+were measured simultaneously on a set of CoFe alloy films. Variation of the
+Co-content $x_\mathrm{Co}$ allows for a systematic tuning of the Fermi level
+through the band structure, and the study of the interplay between electronic
+and magnetic contributions to the transport coefficients. While band structure
+and magnon effects in $\rho$ and $\kappa$ are rather weak, they turn out to be
+very significant in ${\cal S}$. The evolution of Mott and magnon drag
+contributions to ${\cal S}$ is traced between the two limiting cases of pure Fe
+and pure Co. In addition, we find an interesting sign change of the magnon
+drag.",1802.01038v1
+2018-02-12,Topological Magnons in Kitaev Magnets at High Fields,"We study the Kitaev-Heisenberg-$\Gamma$-$\Gamma'$ model that describes the
+magnetism in strong spin-orbit coupled honeycomb lattice Mott insulators. In
+strong $[111]$ magnetic fields that bring the system into the fully polarized
+paramagnetic phase, we find that the spin wave bands carry nontrivial Chern
+numbers over large regions of the phase diagram implying the presence of chiral
+magnon edge states. In contrast to other topological magnon systems, the
+topological nontriviality of these systems results from the presence of magnon
+number non-conserving terms in the Hamiltonian. Since the effects of
+interactions are suppressed by $J/h$, the validity of the single particle
+picture is tunable making paramagnetic phases particularly suitable for the
+exploration of this physics. Using time dependent DMRG and interacting spin
+wave theory, we demonstrate the presence of the chiral edge mode and its
+evolution with field.",1802.04283v1
+2018-04-06,Magnons versus electrons in thermal spin transport through metallic interfaces,"We develop a theory for spin transport in magnetic metals that treats the
+contribution of magnons and electrons on equal footing. As an application we
+consider thermally-driven spin injection across an interface between a magnetic
+metal and a normal metal, i.e., the spin-dependent Seebeck effect. We show that
+the ratio between magnonic and electronic contribution scales as
+$\sqrt{T/T_C}T_F/T_C$, with the Fermi temperature $T_F$ and the Curie
+temperature $T_C$. Since, typically, $T_C \ll T_F$, the magnonic contribution
+may dominate the thermal spin injection, even though the interface is more
+transparent for electronic spin current.",1804.02172v1
+2018-04-06,Thermoelastic enhancement of the magnonic spin Seebeck effect in thin films and bulk samples,"A non-uniform temperature profile may generate a pure spin current in
+magnetic films, as observed for instance in the spin Seebeck effect. In
+addition, thermally induced elastic deformations may set in that could affect
+the spin current. A self-consistent theory of the magnonic spin Seebeck effect
+including thermally activated magneto-elastic effects is presented and
+analytical expressions for the thermally activated deformation tensor and
+dispersion relations for coupled magneto-elastic modes are obtained. We derived
+analytical results for bulk (3D) systems and thin magnetic (2D) films.
+  We observed that the displacement vector and the deformation tensor in bulk
+systems decay asymptotically as $u\sim1/R^{2}$ and $\varepsilon\sim1/R^{3}$,
+respectively, while the decays in thin magnetic films proceed slower following
+$u\sim1/R$ and $\varepsilon\sim1/R^{2}$. The dispersion relations evidence a
+strong anisotropy in the magnetic excitations. We observed that a thermoelastic
+steady state deformation may lead to both an enchantment or a reduction of the
+gap in the magnonic spectrum. The reduction of the gap increases the number of
+magnons contributing to the spin Seebeck effect and offers new possibilities
+for the thermoelastic control of the Spin Seebeck effect.",1804.02185v1
+2018-04-08,Optical cooling of magnons,"Inelastic scattering of light by spin waves generates an energy flow between
+the light and magnetization fields, a process that can be enhanced and
+controlled by concentrating the light in magneto-optical resonators. Here, we
+model the cooling of a sphere made of a magnetic insulator, such as yttrium
+iron garnet (YIG), using a monochromatic laser source. When the magnon
+lifetimes are much larger than the optical ones, we can treat the latter as a
+Markovian bath for magnons. The steady-state magnons are canonically
+distributed with a temperature that is controlled by the light intensity. We
+predict that such a cooling process can significantly reduce the temperature of
+the magnetic order within current technology.",1804.02683v1
+2018-11-14,Microscopic Theory of Ultrafast Out-of-Equilibrium Dynamics in Magnetic Insulators. Unraveling the Magnon-Phonon Coupling,"The interaction between lattice and spins is at the heart of an extremely
+intriguing ultrafast dynamics in magnetic materials. In this work we formulate
+a general non-equilibrium theory that disentangles the complex interplay
+between them in a THz laser-excited antiferromagnetic insulator. The theory
+provides a quantitative description of the transient energy flow between the
+spin and lattice sub-systems, subject to magnon-phonon and phonon-phonon
+scatterings, giving rise to finite life-times of the quasiparticles and to the
+equilibration time of the system. We predict a novel kind of scattering process
+where two magnons of opposite polarizations decay into a phonon, previously
+omitted in the literature. The theory is combined with first-principle
+calculations and then applied to simulate a realistic dynamics of NiO. The main
+relaxation channels and hot spots in the reciprocal space, giving the strongest
+contribution to the energy transfer between phonons and magnons are identified.
+The diverse interaction strengths lead to distinct coupled dynamics of the
+lattice and spin systems and subsequently to different equilibration
+timescales.",1811.05841v1
+2013-08-09,Relativistic and thermal effects on the magnon spectrum of a ferromagnetic monolayer,"A spin model including magnetic anisotropy terms and Dzyaloshinsky-Moriya
+interactions is studied for the case of a ferromagnetic monolayer with C2v
+symmetry like Fe/W(110). Using the quasiclassical stochastic
+Landau-Lifshitz-Gilbert equations, the magnon spectrum of the system is derived
+using linear response theory. The Dzyaloshinsky-Moriya interaction leads to
+asymmetry in the spectrum, while the anisotropy terms induce a gap. It is shown
+that in the presence of lattice defects, both the Dzyaloshinsky-Moriya
+interactions and the two-site anisotropy lead to a softening of the magnon
+energies. Two methods are developed to investigate the magnon spectrum at
+finite temperatures. The theoretical results are compared to atomistic spin
+dynamics simulations and a good agreement is found between them.",1308.2082v2
+2014-03-02,Generalized two-temperature model for coupled phonon-magnon diffusion,"We generalize the two-temperature model [Sanders and Walton, Phys. Rev. B,
+15, 1489 (1977)] for coupled phonon-magnon diffusion to include the effect of
+the concurrent magnetization flow. Working within the framework of Boltzmann
+transport equation, we derive the constitutive equations for coupled
+phonon-magnon transport driven by gradients of both temperature and external
+magnetic fields, and the corresponding conservation laws. Our equations reduce
+to the original Sanders-Walton two-temperature model under a uniform external
+field, but predict a new magnon cooling effect driven by a non-uniform magnetic
+field in a homogeneous single-domain ferromagnet. We estimate the magnitude of
+the cooling effect in yttrium iron garnet, and show it is within current
+experimental reach. With properly optimized materials, the predicted cooling
+effect can potentially supplement the conventional magnetocaloric effect in
+cryogenic applications in the future.",1403.0279v1
+2018-05-02,RIXS studies of magnons and bimagnons in the lightly doped cuprate La2-xSrxCuO4,"We investigated the doping dependence of magnetic excitations in the lightly
+doped cuprate La2-xSrxCuO4 via combined studies of resonant inelastic x-ray
+scattering (RIXS) at the Cu L3-edge and theoretical calculations. With
+increasing doping, the magnon dispersion is found to be essentially unchanged,
+but the spectral width broadens and the spectral weight varies differently at
+different momenta. Near the Brillouin zone center, we directly observe bimagnon
+excitations which possess the same energy scale and doping dependence as
+previously observed by Raman spectroscopy. They disperse weakly in
+energy-momentum space, and are consistent with a bimagnon dispersion that is
+renormalized by the magnon-magnon interaction at the zone center.",1805.00701v1
+2018-05-10,Designing Rashba-Dresselhaus effect in magnetic insulators,"One of the major strategies to control magnetism in spintronics is to utilize
+the coupling between electron spin and its orbital motion. The Rashba and
+Dresselhaus spin-orbit couplings induce magnetic textures of band electrons
+called spin momentum locking, which produces a spin torque by the injection of
+electric current. However, joule heating had been a bottleneck for device
+applications. Here, we propose a theory to generate further rich spin textures
+in insulating antiferromagnets with broken spatial inversion symmetry (SIS),
+which is easily controlled by a small magnetic field. In antiferromagnets, the
+ordered moments host two species of magnons that serve as internal degrees of
+freedom in analogy with electron spins. The Dzyaloshinskii-Moriya interaction
+introduced by the SIS breaking couples the two-magnon-degrees of freedom with
+the magnon momentum. We present a systematic way to design such texture and to
+detect it via magnonic spin current for the realization of antiferromagnetic
+memory.",1805.03925v2
+2012-01-10,Quantum spin pumping mediated by magnon,"We theoretically propose quantum spin pumping mediated by magnons, under a
+time-dependent transverse magnetic field, at the interface between a
+ferromagnetic insulator and a non-magnetic metal. The generation of a spin
+current under a thermal equilibrium condition is discussed by calculating the
+spin transfer torque, which breaks the spin conservation law for conduction
+electrons and operates the coherent magnon state. Localized spins lose spin
+angular momentum by emitting magnons and conduction electrons flip from down to
+up by absorbing the momentum. The spin transfer torque has a resonance
+structure as a function of the angular frequency of the applied transverse
+field. This fact is useful to enhance the spin pumping effect induced by
+quantum fluctuations. We also discuss the distinction between our quantum spin
+pumping theory and the one proposed by Tserkovnyak et al.",1201.1947v3
+2012-04-16,Bose analogs of MIT bag model of hadrons in coherent precession,"Recently it was demonstrated that magnon condensation in the trap exhibits
+the phenomenon of self-localization. When the number of magnons in the textural
+trap increases, they drastically modify the profile of the gap and highly
+increase its size. The trap gradually transforms from the initial harmonic one
+to the box with walls almost impenetrable for magnons. The resulting
+texture-free ""cavity"" filled by the magnon condensate wave function becomes the
+bosonic analog of the MIT bag, in which hadron is seen as a cavity surrounded
+by the QCD vacuum, in which the free quarks are confined in the ground or
+excited state. Here we consider the bosonic analog of the MIT bag with quarks
+on the ground and excited levels.",1204.3423v2
+2013-09-12,One-Dimensional Dispersive Magnon Excitation in the Frustrated Spin-2 Chain System Ca3Co2O6,"Using inelastic neutron scattering, we have observed a quasi-one-dimensional
+dispersive magnetic excitation in the frustrated triangular-lattice spin-2
+chain oxide Ca3Co2O6. At the lowest temperature (T = 1.5 K), this magnon is
+characterized by a large zone-center spin gap of ~27 meV, which we attribute to
+the large single-ion anisotropy, and disperses along the chain direction with a
+bandwidth of ~3.5 meV. In the directions orthogonal to the chains, no
+measurable dispersion was found. With increasing temperature, the magnon
+dispersion shifts towards lower energies, yet persists up to at least 150 K,
+indicating that the ferromagnetic intrachain correlations survive up to 6 times
+higher temperatures than the long-range interchain antiferromagnetic order. The
+magnon dispersion can be well described within the predictions of linear
+spin-wave theory for a system of weakly coupled ferromagnetic chains with large
+single-ion anisotropy, enabling the direct quantitative determination of the
+magnetic exchange and anisotropy parameters.",1309.3222v2
+2013-09-19,Exact spectral function for hole-magnon coupling in the ferromagnetic CuO$_3$-like chain,"We present the exact spectral function for a single oxygen hole with spin
+opposite to ferromagnetic order within a one-dimensional CuO$_{3}$-like spin
+chain. We find that local Kondo-like exchange interaction generates five
+different states in the strong coupling regime. It stabilizes a spin polaron
+which is a bound state of a moving charge dressed by magnon excitations, with
+essentially the same dispersion as predicted by mean field theory. We then
+examine in detail the evolution of the spectral function for increasing
+strength of the hole-magnon interaction. We also demonstrate that the $s$ and
+$p$ symmetry of orbital states in the conduction band are essentially
+equivalent to each other and find that the simplified models do not suffice to
+reproduce subtle aspects of hole-magnon coupling in the charge-transfer model.",1309.5054v1
+2014-06-03,Large-Spin and Large-Winding Expansions of Giant Magnons and Single Spikes,"We generalize the method of our recent paper on the large-spin expansions of
+Gubser-Klebanov-Polyakov (GKP) strings to the large-spin and large-winding
+expansions of finite-size giant magnons and finite-size single spikes. By
+expressing the energies of long open strings in RxS2 in terms of Lambert's
+W-function, we compute the leading, subleading and next-to-subleading series of
+classical exponential corrections to the dispersion relations of
+Hofman-Maldacena giant magnons and infinite-winding single spikes. We also
+compute the corresponding expansions in the doubled regions of giant magnons
+and single spikes that are respectively obtained when their angular and linear
+velocities become smaller or greater than unity.",1406.0796v4
+2014-06-30,Magnons and continua in a magnetized and dimerized spin-1/2 chain,"We examine the magnetic field dependent excitations of the dimerized spin-1/2
+chain, copper nitrate, with antiferromagnetic intra-dimer exchange $J_1=0.44$
+meV and exchange alternation $\alpha=J_2/J_1=0.24$. Magnetic excitations in
+three distinct regimes of magnetization are probed through inelastic neutron
+scattering at low temperatures. At low and high fields there are three and two
+long-lived magnon-like modes, respectively. The number of modes and the
+anti-phase relationship between the wave-vector dependent energy and intensity
+of magnon scattering reflect the distinct ground states: A singlet ground state
+at low fields $\mu_0H < \mu_0H_{c1} = 2.8$~T and an $S_z=1/2$ product state at
+high fields $\mu_0H > \mu_0H_{c2} = 4.2$~T. In the intermediate field regime, a
+continuum of scattering for $\hbar\omega\approx J_1$ is indicative of a
+strongly correlated gapless quantum state without coherent magnons.",1406.7596v1
+2016-05-21,Landau-Lifshitz theory of the magnon-drag thermopower,"Metallic ferromagnets subjected to a temperature gradient exhibit a magnonic
+drag of the electric current. We address this problem by solving a stochastic
+Landau-Lifshitz equation to calculate the magnon-drag thermopower. The
+long-wavelength magnetic dynamics result in two contributions to the
+electromotive force acting on electrons: (1) An adiabatic Berry-phase force
+related to the solid angle subtended by the magnetic precession and (2) a
+dissipative correction thereof, which is rooted microscopically in the
+spin-dephasing scattering. The first contribution results in a net force
+pushing the electrons towards the hot side, while the second contribution drags
+electrons towards the cold side, i.e., in the direction of the magnonic drift.
+The ratio between the two forces is proportional to the ratio between the
+Gilbert damping coefficient $\alpha$ and the coefficient $\beta$ parametrizing
+the dissipative contribution to the electromotive force.",1605.06578v1
+2016-05-27,Combined Brillouin light scattering and microwave absorption study of magnon-photon coupling in a split-ring resonator/YIG film system,"Microfocused Brillouin light scattering (BLS) and microwave absorption (MA)
+are used to study magnon-photon coupling in a system consisting of a split-ring
+microwave resonator and a yttrium iron garnet (YIG) film. The split-ring
+resonantor is defined by optical lithography and loaded with a 1 $\mu$m-thick
+YIG film grown by liquid phase epitaxy. BLS and MA spectra of the hybrid system
+are simultaneously recorded as a function of the applied magnetic field
+magnitude and microwave excitation frequency. Strong coupling of the magnon and
+photon modes is found with a coupling strength of $g_\text{eff}/2 \pi = 63$
+MHz. The combined BLS and MA data allows to study the continuous transition of
+the hybridized modes from a purely magnonic to a purely photonic mode by
+varying the applied magnetic field and microwave frequency. Furthermore, the
+BLS data represent an up-conversion of the microwave frequency coupling to
+optical frequencies.",1605.08531v1
+2017-06-10,Spin wave nonreciprocity and magnonic band structure in thin permalloy film induced by dynamical coupling with an array of Ni stripes,"An efficient way for the control of spin wave propagation in a magnetic
+medium is the use of periodic patterns known as magnonic crystals (MCs).
+However, the fabrication of MCs especially bi-components, with periodicity on
+nanoscale, is a challenging task due to the requirement for sharp interfaces.
+An alternative method to circumvent this problem is to use homogeneous
+ferromagnetic film with modified periodically surrounding. The structure is
+also suitable for exploiting nonreciprocal properties of the surface spin
+waves. In this work, we demonstrate that the magnonic band structure forms in
+thin permalloy film due to dynamical magnetostatic coupling with Ni stripes
+near its surface. We show, that the band gap width can be systematically tuned
+by the changing interlayer thickness between film and stripes. We show also the
+effect of nonreciprocity, which is seen at the band gap edge shifted from the
+Brillouin zone boundary and also in nonreciprocal interaction of propagating
+spin waves in Py film with the standing spin waves in Ni stripes. Our findings
+open possibility for further investigation and exploitation of the
+nonreciprocity and band structure in magnonic devices.",1706.03202v1
+2017-06-15,Squeezed Dirac and Topological Magnons in a Bosonic Honeycomb Optical Lattice,"Quantum information storage using charge-neutral quasiparticles are expected
+to play a crucial role in the future of quantum computers. In this regard,
+magnons or collective spin-wave excitations in solid-state materials are
+promising candidates in the future of quantum computing. Here, we study the
+quantum squeezing of Dirac and topological magnons in a bosonic honeycomb
+optical lattice with spin-orbit interaction by utilizing the mapping to quantum
+spin-$1/2$ XYZ Heisenberg model on the honeycomb lattice with discrete Z$_2$
+symmetry and a Dzyaloshinskii-Moriya interaction. We show that the squeezed
+magnons can be controlled by the Z$_2$ anisotropy and demonstrate how the noise
+in the system is periodically modified in the ferromagnetic and
+antiferromagnetic phases of the model. Our results also apply to solid-state
+honeycomb (anti)ferromagnetic insulators.",1706.04974v2
+2017-06-19,Magnon transport through a quantum dot: Conversion to electronic spin and charge currents,"We consider a single-level quantum dot coupled to magnetic insulators
+(magnonic reservoirs) and magnetic metals (electronic reservoirs). The whole
+system is in an external magnetic field. In a general case, the system includes
+two magnonic and two electronic reservoirs, but we also present results for
+some specific situations, where only two or three reservoirs are effectively
+connected to the dot. The main objective is the analysis of the conversion of
+magnon current to electronic spin and charge currents, and {\it vice versa}. We
+consider the limiting case of large Coulomb energy in the dot (Coulomb
+blockade), as well as the case when the Coulomb energy is finite and double
+occupancy is allowed.",1706.05991v1
+2017-10-05,Spin Hall and Nernst effects of Weyl magnons,"In this paper, we present a simple model of a three-dimensional insulating
+magnetic structure which represents a magnonic analog of the layered electronic
+system described in [Phys. Rev. Lett. {\bf 107}, 127205 (2011)]. In particular,
+our model realizes Weyl magnons as well as surface states with a Dirac
+spectrum. In this model, the Dzyaloshinskii-Moriya interaction is responsible
+for the separation of opposite Weyl points in momentum space. We calculate the
+intrinsic (due to the Berry curvature) transport properties of Weyl and
+so-called anomalous Hall effect (AHE) magnons. The results are compared with
+fermionic analogs.",1710.02115v2
+2017-10-17,One dimensional Cherenkov processes in ferromagnetic insulator,"One dimensional Cherenkov processes in ferromagnetic isolators are studied
+with perturbation theory under the constraint condition of conservation of
+energy and momentum. It is shown that the magnon-phonon interaction channels
+are limited and wave number dependent, which result in respectively $1/k^{2}$
+and $1/k^{4}$ dependence of the lifetime and the relaxation time of long
+wavelength magnons. The reciprocal of relaxation time between magnons and
+phonons, $1/\tau_{mp}$, is found to be a linearly increasing function of the
+temperature as $T>$ 70 K. Based on the Sanders-Walton model, we further show
+that when a thermal (phonon) gradient is applied along the system, the
+temperature difference between the phonon bath and the magnons with wave-vector
+$k$ becomes more pronounced as $k$ decreasing.",1710.06155v2
+2018-09-04,Topological Magnon Insulator with a Kekule Bond Modulation,"We examine the combined effects of a Kekule coupling texture (KC) and a
+Dzyaloshinskii-Moriya interaction (DMI) in a two-dimensional ferromagnetic
+honeycomb lattice. By analyzing the gap closing conditions and the inversions
+of the bulk bands, we identify the parameter range in which the system behaves
+as a trivial or a nontrivial topological magnon insulator. We find four
+topological phases in terms of the KC parameter and the DMI strength. We
+present the bulk-edge correspondence for the magnons in a honeycomb lattice
+with an armchair or a zigzag boundary. Furthermore, we find Tamm-like edge
+states due to the intrinsic on-site interactions along the boundary sites. Our
+results may have significant implications to magnon transport properties in the
+2D magnets at low temperatures.",1809.01073v2
+2019-08-30,Amplitude and Phase Noise of Magnons,"The low-frequency amplitude and phase noise spectra of magnetization waves,
+i.e. magnons, was measured in the yttrium iron garnet (YIG) waveguides. This
+type of noise, which originates from the fluctuations of the physical
+properties of the YIG crystals, has to be taken into account in the design of
+YIG-based RF generators and magnonic devices for data processing, sensing and
+imaging applications. It was found that the amplitude noise level of magnons
+depends strongly on the power level, increasing sharply at the on-set of
+nonlinear dissipation. The noise spectra of both the amplitude and phase noise
+have the Lorentzian shape with the characteristic frequencies below 100 Hz.",1909.00085v1
+2019-09-04,Chiral coupling of magnons in waveguides,"We theoretically investigate the collective excitation of multiple
+(sub)millimeter-sized ferromagnets mediated by waveguide photons. By the
+position of the magnets in the waveguide, the magnon-photon coupling can be
+tuned to be chiral, i.e., magnons only couple with photons propagating in one
+direction, leading to asymmetric transfer of angular momentum and energy
+between the magnets. A large imbalance in the magnon number distribution over
+the magnets can be achieved with a long chain of magnets, which concentrate at
+one edge. The chain also supports standing waves with low radiation efficiency
+that is inert to the chirality.",1909.01817v1
+2020-12-01,Magnon hybridization in ferrimagnetic heterostructures,"We study magnon hybridization in a ferrimagnetic heterostructure consisting
+of ultrathin gadolinium iron garnet and yttrium iron garnet layers and show the
+localized and extended spatial profiles of the magnon modes with different
+polarizations. These modes are expected to have distinct thermal excitation
+properties in the presence of a temperature gradient across the
+heterostructure. From a quantitative analysis of their consequences on
+longitudinal spin Seebeck effect, we predict an observable shift of the
+sign-changing temperature with respect to the one previously observed in
+gadolinium iron garnet. Moreover, the sign-changing point of spin Seebeck
+signal is found to be tunable by YIG thickness. Our results suggest the
+necessity of taking into account the temperature difference between the magnon
+modes in ferrimagnetic heterostructures.",2012.00576v1
+2020-12-01,Design of an optomagnonic crystal: towards optimal magnon-photon mode matching at the microscale,"We put forward the concept of an optomagnonic crystal: a periodically
+patterned structure at the microscale based on a magnetic dielectric, which can
+co-localize magnon and photon modes. The co-localization in small volumes can
+result in large values of the photon-magnon coupling at the single quanta
+level, which opens perspectives for quantum information processing and quantum
+conversion schemes with these systems. We study theoretically a simple geometry
+consisting of a one-dimensional array of holes with an abrupt defect,
+considering the ferrimagnet Yttrium Iron Garnet (YIG) as the basis material. We
+show that both magnon and photon modes can be localized at the defect, and use
+symmetry arguments to select an optimal pair of modes in order to maximize the
+coupling. We show that an optomagnonic coupling in the kHz range is achievable
+in this geometry, and discuss possible optimization routes in order to improve
+both coupling strengths and optical losses.",2012.00760v2
+2020-12-22,Crystalline symmetry-dependent magnon formation in itinerant ferromagnet SrRuO3,"SrRuO3 (SRO) is an itinerant ferromagnet with strong coupling between the
+charge, spin, and lattice degrees of freedom. This strong coupling suggests
+that the electronic and magnetic behaviors of SRO are highly susceptible to
+changes in the lattice distortion. Here we show how the spin interaction and
+resultant magnon formation change with the modification in the crystallographic
+orientation. We fabricated SRO epitaxial thin films with (100), (110), and
+(111) surface orientations, to systematically modulate the spin interaction and
+spin dimensionality. The reduced spin dimensionality and enhanced exchange
+interaction in the (111)-oriented SRO thin film significantly suppresses magnon
+formation. Our study comprehensively demonstrates the facile tunability of
+magnon formation and spin interaction in correlated oxide thin films.",2012.11865v1
+2020-12-29,Nonreciprocal Multi-mode and Indirect Couplings in Cavity Magnonics,"We investigate the magnon-photon couplings by employing a small magnet within
+an irregular resonant cavity, which leads to a desirable nonreciprocity with a
+big isolation ratio. Moreover, the higher-order couplings between the spin wave
+modes with the polarized photon modes also exhibit the nonreciprocity. These
+couplings between polarized photon and spin waves could be regarded as an
+indirect multi-modes coupling between the ferromagnetic resonance (FMR) mode
+and spin wave mode magnons mediated by the cavity mode photons. We also derive
+a coupling matrix to predict the characteristics of this kind of indirect
+coupling. The existence of the indirect couplings broaden the field range of
+the nonreciprocity of the system. The achieved nonreciprocal multi-mode
+magnon-photon couplings in a single system offer a feasible method to improve
+the signal transmission quality.",2012.14765v2
+2000-06-06,Spectral function of transverse spin fluctuations in an antiferromagnet,"The spectral function of transverse spin fluctuations, including the
+contributions from both the single-particle and the collective (magnon)
+excitations in an antiferromagnet, is evaluated for the Hubbard model with NN
+and NNN hoppings in the full U-range from weak coupling to strong coupling. For
+the NN hopping model, the magnon excitations are dominant for U > 2.5 (d=2), so
+that an effective spin description of the AF state holds down to a surprisingly
+low U value. In the weak coupling limit the spectral function is suppressed at
+low energies, as if due to an effective gap. NNN hopping t' leads to magnon
+softening and also a significant increase in the low-energy spectral function
+due to single-particle excitations. Evolution of the magnon spectrum with t' is
+studied in the strong coupling limit, and the quantum spin- fluctuation
+correction to sublattice magnetization in d=2 and the Neel temperature in d=3
+are also evaluated.",0006079v1
+2017-04-29,Magnon spectrum in two- and three- dimensional skyrmion crystals,"We study the low-energy magnon spectrum of the skyrmion crystal (SkX) ground
+state, appearing in two-dimensional ferromagnet with Dzyaloshinskii-Moriya
+interaction and magnetic field. We approximate SkX hexagonal superlattice by a
+set of overlapping disks, and find the lattice period by minimizing the
+classical energy density. The determined spectrum of magnons on the disc of
+optimal radius is stable and only two lowest energy levels can be considered as
+localized. The subsequent hybridization of these levels in the SkX lattice
+leads to tight-binding spectrum. The localized character of the lowest magnon
+states is lost at small and at high fields, which is interpreted as melting of
+SkX. The classical energy of SkX is slightly above the energy of a single
+conical spiral, and a consideration of quantum corrections can favor the
+skyrmion ground state. Extending our analysis to three-dimensional case, we
+argue that these quantum corrections become more important at finite
+temperatures, when the average spin value is decreased.",1705.00196v1
+2017-05-08,Helimagnon resonances in an intrinsic chiral magnonic crystal,"We experimentally study magnetic resonances in the helical and conical
+magnetic phases of the chiral magnetic insulator Cu$_2$OSeO$_3$ at the
+temperature $T$=5 K. Using a broadband microwave spectroscopy technique based
+on vector network analysis, we identify three distinct sets of helimagnon
+resonances in the frequency range 2 GHz $\leq f \leq$ 20 GHz. The extracted
+resonance frequencies are in accordance with calculations of the helimagnon
+bandstructure found in an intrinsic chiral magnonic crystal. The periodic
+modulation of the equilibrium spin direction that leads to the formation of the
+magnonic crystal is a direct consequence of the chiral magnetic ordering caused
+by the Dzyaloshinskii-Moriya interaction. The opening of magnon band-gaps
+allows for excitation of helimagnons with wave vectors that are multiples of
+the spiral wave vector.",1705.02874v2
+2017-05-18,The Final Chapter In The Saga Of YIG,"The magnetic insulator Yttrium Iron Garnet can be grown with exceptional
+quality, has a ferrimagnetic transition temperature of nearly 600 K, and is
+used in microwave and spintronic devices that can operate at room temperature.
+The most accurate prior measurements of the magnon spectrum date back nearly 40
+years, but cover only 3 of the lowest energy modes out of 20 distinct magnon
+branches. Here we have used time-of-flight inelastic neutron scattering to
+measure the full magnon spectrum throughout the Brillouin zone. We find that
+the existing model of the excitation spectrum, well known from an earlier work
+titled ""The Saga of YIG"", fails to describe the optical magnon modes. Using a
+very general spin Hamiltonian, we show that the magnetic interactions are both
+longer-ranged and more complex than was previously understood. The results
+provide the basis for accurate microscopic models of the finite temperature
+magnetic properties of Yttrium Iron Garnet, necessary for next-generation
+electronic devices.",1705.06594v1
+2018-03-06,Combined Molecular and Spin Dynamics Simulation of BCC Iron with Vacancy Defects,"Utilizing an atomistic computational model which handles both translational
+and spin degrees of freedom, combined molecular and spin dynamics simulations
+have been performed to investigate the effect of vacancy defects on spin wave
+excitations in ferromagnetic iron. Fourier transforms of space and
+time-displaced correlation functions yield the dynamic structure factor,
+providing characteristic frequencies and lifetimes of the spin wave modes.
+Comparison of the system with a 5% vacancy concentration with pure lattice data
+shows a decrease in frequency as well as a decrease in lifetime for all
+transverse spin wave excitations observed. Additionally, a rugged spin wave
+line shape for low-q spin waves indicates the presence of multiple localized
+excitations near defect sites resulting in reduced excitation lifetimes due to
+increased magnon-magnon scattering. We observe further evidence of increased
+magnon-magnon scattering as the peaks in the longitudinal spin wave spectrum
+become less distinct.",1803.02468v1
+2018-03-21,Spin caloric effects in antiferromagnets assisted by an external spin current,"Searching for novel spin caloric effects in antiferromagnets we study the
+properties of thermally activated magnons in the presence of an external spin
+current and temperature gradient. We predict the spin Peltier effect --
+generation of a heat flux by spin accumulation -- in an antiferromagnetic
+insulator with cubic or uniaxial magnetic symmetry. This effect is related with
+spin-current induced splitting of the relaxation times of the magnons with
+opposite spin direction. We show that the Peltier effect can trigger
+antiferromagnetic domain wall motion with a force whose value grows with the
+temperature of a sample. At a temperature, larger than the energy of the
+low-frequency magnons, this force is much larger than the force caused by
+direct spin transfer between the spin current and the domain wall. We also
+demonstrate that the external spin current can induce the magnon spin Seebeck
+effect. The corresponding Seebeck coefficient is controlled by the current
+density. These spin-current assisted caloric effects open new ways for the
+manipulation of the magnetic states in antiferromagnets.",1803.07949v1
+2018-06-21,Magnon-induced high-order sideband generation,"Magnon Kerr nonlinearity plays crucial roles in the study of cavity
+optomagnonics system and may bring many novel physical phenomena and important
+applications. In this work, we report the investigation of high- order sideband
+generation induced by magnon Kerr nonlinearity in a cavity-magnon system, which
+is critically lacking in this emerging research field. We uncover that the
+driving field plays a significant role in controlling the generation and
+amplification of the higher-order sidebands and the sideband spacing can be
+adjusted by regulating the beat frequency between the pump laser and the probe
+laser, which is extremely eventful for the spacing modulation of the sideband
+spectrum. Based on the recent experimental progress, our results deepen our
+cognition into optomagnonics nonlinearity and may find interesting applications
+in optical frequency metrology and optical communications.",1806.08289v2
+2018-06-27,Boltzmann approach to the longitudinal spin Seebeck effect,"We develop a Boltzmann transport theory of coupled magnon-phonon transport in
+ferromagnetic insulators. The explicit treatment of the magnon-phonon coupling
+within the Boltzmann approach allows us to calculate the low-temperature
+magnetic-field dependence of the spin-Seebeck voltage. Within the Boltzmann
+theory we find that this magnetic field dependence shows similar features as
+found by Flebus et al. [Phys. Rev. B 95, 144420 (2017)] for a strongly coupled
+magnon phonon system that forms magnon-polarons, and consistent with
+experimental findings in yttrium iron garnet by Kikkawa et al. [Phys. Rev.
+Lett. 117, 207203 (2016)]. In addition to the anomalous magnetic-field
+dependence of the spin Seebeck effect, we also predict a dependence on the
+system size.",1806.10445v1
+2018-12-10,Topologically nontrivial magnonic solitons,"The intrinsic non-linearities of the spin dynamics in condensed matter
+systems give rise to a rich phenomenology that can be strongly affected by
+topology. Here we study formation of magnonic solitons in the topologically
+nontrivial bandgap of a spin lattice realization of the Haldane model, in both
+static and dynamic (Floquet) regimes. We consider nonlinearities caused by
+magnetic crystalline anisotropy and magnon-magnon interactions. We find soliton
+formation power thresholds as a function of anisotropy coefficient and
+interaction strength. We predict different classes of topological solitons for
+the same topological class of the underlying lattice and explain it in terms of
+a transition from a topologically nontrivial mass to a trivial one. Our
+findings imply that a soliton can phase-separate, containing boundaries between
+topologically trivial and non-trivial phases, which is associated with a
+vanishing spin wave gap.",1812.03738v2
+2018-12-11,Uniform Perpendicular and Parallel Staggered Susceptibility of Antiferromagnetic Films,"We investigate the thermodynamic behavior of antiferromagnetic films in
+external magnetic fields oriented perpendicular to the staggered magnetization.
+Within the systematic effective Lagrangian framework we first calculate the
+two-point function and the dispersion relation for the two types of magnons up
+to one-loop order. This allows us to split the two-loop free energy density
+into a piece that originates from noninteracting dressed magnons, and a second
+piece that corresponds to the genuine magnon-magnon interaction. We then
+discuss the low-temperature series for various thermodynamic quantities,
+including the parallel staggered and uniform perpendicular susceptibilities,
+and analyze the role of the spin-wave interaction at finite temperature.",1812.04392v2
+2019-01-04,Spin phases of the helimagnetic insulator Cu$_2$OSeO$_3$ probed by magnon heat conduction,"We report studies of thermal conductivity as functions of magnetic field and
+temperature in the helimagnetic insulator Cu$_2$OSeO$_3$ that reveal novel
+features of the spin-phase transitions as probed by magnon heat conduction. The
+tilted conical spiral and low-temperature skyrmion phases, recently identified
+in small-angle neutron scattering studies, are clearly identified by sharp
+signatures in the magnon thermal conductivity. Magnon scattering associated
+with the presence of domain boundaries in the tilted conical phase and regions
+of skyrmion and conical-phase coexistence are identified.",1901.01242v1
+2019-01-17,Magnon Condensation in a Dense Nitrogen-Vacancy Spin Ensemble,"The feasibility of creating a Bose-Einstein condensate of magnons using a
+dense ensemble of nitrogen-vacancy spin defects in diamond is investigated.
+Through assessing a density-dependent spin exchange interaction strength and
+the magnetic phase transition temperature ($T_c$) using the
+Sherrington-Kirkpatrick model, the minimum temperature-dependent concentration
+for magnetic self-ordering is estimated. For a randomly dispersed spin
+ensemble, the calculated average exchange constant exceeds the average dipole
+interaction strengths for concentrations approximately greater than 70 ppm,
+while $T_c$ is estimated to exceed 10 mK beyond 90 ppm, reaching 300 K at a
+concentration of approximately 450 ppm. On this basis, the existence of
+dipole-exchange spin waves and their plane-wave dispersion is postulated and
+estimated using a semiclassical magnetostatic description. This is discussed
+along with a $T_c$-based estimate of the four-magnon scattering rate, which
+indicates magnons and their condensation may be detectable in thin films for
+concentrations greater than 90 ppm.",1901.05818v1
+2019-01-18,Magnon-Fluxon interaction in a ferromagnet/superconductor heterostructure,"Ferromagnetism and superconductivity are most fundamental phenomena in
+condensed matter physics. Entailing opposite spin orders, they share an
+important conceptual similarity: Disturbances in magnetic ordering in magnetic
+materials can propagate in the form of spin waves (magnons) while magnetic
+fields penetrate superconductors as a lattice of magnetic flux quanta
+(fluxons). Despite a rich choice of wave and quantum phenomena predicted,
+magnon-fluxon coupling has not been observed experimentally so far. Here, we
+clearly evidence the interaction of spin waves with a flux lattice in
+ferromagnet/superconductor Py/Nb bilayers. We demonstrate that, in this system,
+the magnon frequency spectrum exhibits a Bloch-like band structure which can be
+tuned by the biasing magnetic field. Furthermore, we observe Doppler shifts in
+the frequency spectra of spin waves scattered on a flux lattice moving under
+the action of a transport current in the superconductor.",1901.06156v1
+2019-02-15,Gigahertz frequency antiferromagnetic resonance and strong magnon-magnon coupling in the layered crystal CrCl3,"We report broadband microwave absorption spectroscopy of the layered
+antiferromagnet CrCl3. We observe a rich structure of resonances arising from
+quasi-two-dimensional antiferromagnetic dynamics. Due to the weak interlayer
+magnetic coupling in this material, we are able to observe both optical and
+acoustic branches of antiferromagnetic resonance in the GHz frequency range and
+a symmetry-protected crossing between them. By breaking rotational symmetry, we
+further show that strong magnon-magnon coupling with large tunable gaps can be
+induced between the two resonant modes.",1902.05669v2
+2019-02-26,Strong magnon-photon coupling in ferromagnet-superconducting resonator thin-film devices,"We demonstrate strong magnon-photon coupling of a thin-film permalloy device
+fabricated on a coplanar superconducting resonator. A coupling strength of
+0.152 GHz and a cooperativity of 68 are found for a 30-nm-thick permalloy
+stripe. The coupling strength is tunable by rotating the biasing magnetic field
+or changing the volume of permalloy. We also observe an enhancement of
+magnon-photon coupling in the nonlinear regime of the superconducting
+resonator, which is mediated by the nucleation of dynamic flux vortices. Our
+results demonstrate a critical step towards future integrated hybrid systems
+for quantum magnonics and on-chip coherent information transfer.",1902.09715v1
+2019-03-06,Microwave magnon damping in YIG films at millikelvin temperatures,"Magnon systems used in quantum devices require low damping if coherence is to
+be maintained. The ferrimagnetic electrical insulator yttrium iron garnet (YIG)
+has low magnon damping at room temperature and is a strong candidate to host
+microwave magnon excitations in future quantum devices. Monocrystalline YIG
+films are typically grown on gadolinium gallium garnet (GGG) substrates. In
+this work, comparative experiments made on YIG waveguides with and without GGG
+substrates indicate that the material plays a significant role in increasing
+the damping at low temperatures. Measurements reveal that damping due to
+temperature-peak processes is dominant above 1 K. Damping behaviour that we
+show can be attributed to coupling to two-level fluctuators (TLFs) is observed
+below 1 K. Upon saturating the TLFs in the substrate-free YIG at 20 mK,
+linewidths of 1.4 MHz are achievable: lower than those measured at room
+temperature.",1903.02527v3
+2019-03-11,Spin waves in thin films and magnonic crystals with Dzyaloshinskii-Moriya interactions,"The influence of the Dzyaloshinskii-Moriya interaction in ultra-thin
+ferromagnetic films and chiral magnonic crystals on the behavior of spin waves
+is reviewed. During the last decade, it has been shown, both theoretically and
+experimentally, that this anisotropic exchange interaction produces
+non-reciprocal features on the spin-wave spectrum of a magnetic system, a
+phenomenon that occurs both for bulk and interfacial Dzyaloshinskii-Moriya
+coupling. More recently, the concept of a chiral magnonic crystal has been
+introduced, where the interfacial Dzyaloshinskii-Moriya interaction is
+periodic. The effect of this periodicity include additional features such as
+flat bands, indirect gaps, and an unusual spin-wave evolution.",1903.04288v2
+2019-03-12,Magnon Landau levels and emergent supersymmetry in strained antiferromagnets,"Inhomogeneous strain applied to lattice systems can induce artificial gauge
+fields for particles moving on this lattice. Here we demonstrate how to
+engineer a novel state of matter, namely an antiferromagnet with a Landau-level
+excitation spectrum of magnons. We consider a honeycomb-lattice Heisenberg
+model and show that triaxial strain leads to equally spaced pseudo-Landau
+levels at the upper end of the magnon spectrum, with degeneracies
+characteristic of emergent supersymmetry. We also present a particular strain
+protocol which induces perfectly quantized magnon Landau levels over the whole
+bandwidth. We discuss experimental realizations and generalizations.",1903.05097v2
+2019-03-18,A series of magnon crystals appearing under ultrahigh magnetic fields in a kagomé antiferromagnet,"Search for a new quantum state of matter emerging in a crystal is one of
+recent trends in condensed matter physics. For magnetic materials, geometrical
+frustration and high magnetic field are two key ingredients to realize it: a
+conventional magnetic order is possibly destroyed by competing interactions
+(frustration) and is replaced by an exotic state that is characterized in terms
+of quasiparticles, that are magnons, and the magnetic field can control the
+density and chemical potential of the magnons. Here we show that a synthetic
+copper mineral, Cd-kapellasite, comprising a kagome lattice made of
+corner-sharing triangles of Cu2+ ions carrying spin-1/2 exhibits an
+unprecedented series of fractional magnetization plateaux in ultrahigh magnetic
+fields up to 160 T, which may be interpreted as crystallizations of emergent
+magnons localized on the hexagon of the kagome lattice. Our observation reveals
+a novel type of particle physics realized in a highly frustrated magnet.",1903.07283v1
+2019-03-18,Thermal Hall Effect Induced by Magnon-Phonon Interactions,"We propose a new mechanism for the thermal Hall effect in exchange spin-wave
+systems, which is induced by the magnon-phonon interaction. Using symmetry
+arguments, we first show that this effect is quite general, and exists whenever
+the mirror symmetry in the direction of the magnetization is broken. We then
+demonstrate our result in a collinear ferromagnet on a square lattice, with
+perpendicular easy-axis anisotropy and Dzyaloshinskii-Moriya interaction from
+mirror symmetry breaking. We show that the thermal Hall conductivity is
+controlled by the resonant contribution from the anti-crossing points between
+the magnon and phonon branches, and estimate its size to be comparable to that
+of the magnon mediated thermal Hall effect.",1903.07702v2
+2019-04-25,Microscopic origin of level attraction for a coupled magnon-photon system in a microwave cavity,"We discuss various microscopic mechanisms for level attraction in a
+hybridized magnon-photon system of a ferromagnet in a microwave cavity. The
+discussion is based upon the electromagnetic theory of continuous media where
+the effects of the internal magnetization dynamics of the ferromagnet are
+described using dynamical response functions. This approach is in agreement
+with quantized multi-oscillator models of coupled photon-magnon dynamics. We
+demonstrate that to provide the attractive interaction between the modes, the
+effective response functions should be diamagnetic. Magneto-optical coupling is
+found to be one mechanism for the effective diamagnetic response, which is
+proportional to photon number. A dual mechanism based on the Aharonov-Casher
+effect is also highlighted, which is instead dependent on magnon number.",1904.11570v2
+2019-08-01,Universal prethermal dynamics in Heisenberg ferromagnets,"We study the universal far from equilibrium dynamics of magnons in Heisenberg
+ferromagnets. We show that such systems exhibit universal scaling in momentum
+and time of the quasiparticle distribution function, with the universal
+exponents distinct from those recently observed in Bose-Einstein condensates.
+This new universality class originates from the SU(2) symmetry of the
+Hamiltonian, which leads to a strong momentum-dependent magnon-magnon
+scattering amplitude. We compute the universal exponents using the Boltzmann
+kinetic equation and incoherent initial conditions that can be realized with
+microwave pumping of magnons. We compare our numerical results with analytic
+estimates of the scaling exponents and demonstrate the robustness of the
+scaling to variations in the initial conditions. Our predictions can be tested
+in quench experiments of spin systems in optical lattices and pump-probe
+experiments in ferromagnetic insulators such as yttrium iron garnet.",1908.00554v2
+2019-08-09,Observation of anti-PT symmetry phase transition in the magnon-cavity-magnon coupled system,"As the counterpart of PT symmetry, abundant phenomena and potential
+applications of anti-PT symmetry have been predicted or demonstrated
+theoretically. However, experimental realization of the coupling required in
+the anti-PT symmetry is difficult. Here, by coupling two YIG spheres to a
+microwave cavity, the large cavity dissipation rate makes the magnons coupled
+dissipatively with each other, thereby obeying a two-dimensional anti-PT
+Hamiltonian. In terms of the magnon-readout method, a new method adopted here,
+we demonstrate the validity of our method in constructing an anti-PT system and
+present the counterintuitive level attraction process. Our work provides a new
+platform to explore the anti-PT symmetry properties and paves the way to study
+multi-magnoncavity-polariton systems.",1908.03358v1
+2019-08-21,Nonreciprocity and Unidirectional Invisibility in Cavity Magnonics,"We reveal the cooperative effect of coherent and dissipative magnon-photon
+couplings in an open cavity magnonic system, which leads to nonreciprocity with
+a considerably large isolation ratio and flexible controllability. Furthermore,
+we discover unidirectional invisibility for microwave propagation, which
+appears at the zero-damping condition for hybrid magnon-photon modes. A simple
+model is developed to capture the generic physics of the interference between
+coherent and dissipative couplings, which accurately reproduces the
+observations over a broad range of parameters. This general scheme could
+inspire methods to achieve nonreciprocity in other systems.",1908.07907v1
+2019-08-28,Two-Magnon Bound States in the Kitaev Model in a $[111]$-Field,"It is now well established that the Kitaev honeycomb model in a magnetic
+field along the $[111]$-direction harbors an intermediate gapless quantum spin
+liquid (QSL) phase sandwiched between a gapped non-abelian QSL at low fields
+$H< H_{c1}$ and a partially polarized phase at high fields $H> H_{c2}$. Here,
+we analyze the low field and high field phases and phase transitions in terms
+of single- and two-magnon excitations using exact diagonalization (ED) and
+density matrix renormalization group (DMRG) methods. We find that the energy to
+create a bound state of two-magnons $\Delta_p$ becomes lower than the energy to
+create a single spin flip $\Delta_s$ near $H_{c2}$. In the entire Kitaev spin
+liquid $\Delta_p<\Delta_s$ and both gaps vanish at $H_{c2}$. We make testable
+predictions for magnon pairing that could be observable in Raman scattering
+measurements on Kitaev QSL candidate materials.",1908.10877v1
+2019-11-05,Exceptional points in dissipatively coupled spin dynamics,"We theoretically investigate dynamics of classical spins exchange-coupled
+through an isotropic medium. The coupling is treated at the adiabatic level of
+the medium's response, which mediates a first-order in frequency dissipative
+interaction along with an instantaneous Heisenberg exchange. The resultant
+damped spin precession yields exceptional points (EPs) in the coupled spin
+dynamics, which should be experimentally accessible with the existing magnetic
+heterostructures. In particular, we show that an EP is naturally approached in
+an antiferromagnetic dimer by controlling local damping, while the same is
+achieved by tuning the dissipative coupling between spins in the ferromagnetic
+case. Extending our treatment to one-dimensional spin chains, we show how EPs
+can emerge within the magnonic Brillouin zone by tuning the dissipative
+properties. The critical point, at which an EP pair emerges out of the
+Brillouin zone center, realizes a gapless Weyl point in the magnon spectrum.
+Tuning damping beyond this critical point produces synchronization (level
+attraction) of magnon modes over a finite range of momenta, both in ferro- and
+antiferromagnetic cases. We thus establish that damped magnons can generically
+yield singular points in their band structure, close to which their kinematic
+properties, such as group velocity, become extremely sensitive to the control
+parameters.",1911.01619v2
+2019-11-13,Tailoring spin wave channels in a reconfigurable artificial spin ice,"Artificial spin ices are ensembles of geometrically-arranged, interacting
+nanomagnets which have shown promising potential for the realization of
+reconfigurable magnonic crystals. Such systems allow for the manipulation of
+spin waves on the nanoscale and their potential use as information carriers.
+However, there are presently two general obstacles to the realization of
+artificial spin ice-based magnonic crystals: the magnetic state of artificial
+spin ices is difficult to reconfigure and the magnetostatic interactions
+between the nanoislands are often weak, preventing mode coupling. We
+demonstrate, using micromagnetic modeling, that coupling a reconfigurable
+artificial spin ice geometry made of weakly interacting nanomagnets to a soft
+magnetic underlayer creates a complex system exhibiting dynamically coupled
+modes. These give rise to spin wave channels in the underlayer at well-defined
+frequencies, based on the artificial spin ice magnetic state, which can be
+reconfigured. These findings open the door to the realization of reconfigurable
+magnonic crystals with potential applications for data transport and processing
+in magnonic-based logic architectures.",1911.05354v4
+2019-11-26,Ultrastrong coupling between a microwave resonator and antiferromagnetic resonances of rare earth ion spins,"Quantum magnonics is a new and active research field, leveraging the strong
+collective coupling between microwaves and magnetically ordered spin systems.
+To date work in quantum magnonics has focused on transition metals and almost
+entirely on ferromagnetic resonances in yttrium iron garnet (YIG).
+Antiferromagnetic systems have gained interest as they produce no stray field,
+and are therefore robust to magnetic perturbations and have narrow, shape
+independent resonant linewidths. Here we show the first experimental evidence
+of ultrastrong-coupling between a microwave cavity and collective
+antiferromagnetic resonances (magnons) in a rare earth crystal. The combination
+of the unique optical and spin properties of the rare earths and collective
+antiferromagnetic order paves the way for novel quantum magnonic applications.",1911.11311v1
+2019-11-27,Observation of the Magnon Polarization,"We measure the mode-resolved direction of the precessional motion of the
+magnetic order, i.e., magnon polarization, via the chiral term of inelastic
+polarized neutron scattering spectra. The magnon polarisation is important in
+spintronics, affecting thermodynamic properties such as the magnitude and sign
+of the spin Seebeck effect. The observation of both signs of magnon
+polarization in Y3Fe5O12 also gives direct proof of its ferrimagnetic nature.
+The experiments agree very well with atomistic simulations of the scattering
+cross section.",1911.11968v1
+2019-12-23,Ultrafast dynamics of entanglement in Heisenberg antiferromagnets,"We investigate entanglement dynamics in the antiferromagnetic Heisenberg
+model in two dimensions following a spatially anisotropic quench of the
+exchange interactions. Opposed to established results in one dimension, the
+magnon quasiparticles show an initial growth of entanglement dynamics that does
+not depend on the system size and is governed by the oscillation period of the
+exchange interaction. We ascribe this to the dominance of the intrinsic
+entanglement of short wavelength non-propagating magnon-pairs, which also leads
+to a competition between area-law and volume-law contribution in the
+entanglement dynamics. Furthermore, by adopting the neural-network quantum
+states, we provide numerical evidence that this behavior survives even in the
+presence of strong magnon-magnon interactions, suggesting new avenues for
+manipulating entanglement dynamics in quantum materials.",1912.10845v3
+2016-03-03,Thermal spin current and spin accumulation at ferromagnetic insulator/nonmagnetic metal interface,"Spin current injection and spin accumulation near a ferromagnetic insulator
+(FI)/nonmagnetic metal (NM) bilayer film under a thermal gradient is
+investigated theoretically. Using the Fermi golden rule and the Boltzmann
+equations, we find that FI and NM can exchange spins via interfacial
+electron-magnon scattering because of the imbalance between magnon emission and
+absorption caused by either non-equilibrium distribution of magnons or
+non-equilibrium between magnons and electrons. A temperature gradient in FI
+and/or a temperature difference across the FI/NM interface generates a spin
+current which carries angular momenta parallel to the magnetization of FI from
+the hotter side to the colder one. Interestingly, the spin current induced by a
+temperature gradient in NM is negligibly small due to the nonmagnetic nature of
+the non-equilibrium electron distributions. The results agree well with all
+existing experiments.",1603.00942v1
+2016-03-03,Cloaking the magnons,"We propose two approaches to cloak the spin waves (magnons) by investigating
+magnetization dynamics. One approach is based on a spatially inhomogeneous
+anisotropic magnetic moment tensor. The other mechanism is using a spatially
+inhomogeneous anisotropic gyromagnetic factor tensor and an inhomogeneous
+external magnetic field. For both approaches, the damping tensor is also
+inhomogeneous and anisotropic. The magnetic characteristic functions of the
+magnetic materials have been theoretically derived for both mechanisms. A
+non-magnetic core, which prevents magnons from entering and consequently
+distorts the spin wave propagation, can be cloaked by a structured magnetic
+shell to redirect the spin wave around the core using the above design
+mechanisms. We discuss the feasibility of the proposed mechanisms in an
+ensemble of quantum dot molecules and magnetic semiconductors. The proposed
+approaches shed light on transformation magnonics, and can be utilized for
+future spin-wave lenses, concentrators, low back-scattering waveguides, and
+ultimately quantum computing.",1603.01000v1
+2016-10-14,Edge Magnon Excitation in Spin Dimer Systems,"Magnetic excitation in a spin dimer system on a bilayer honeycomb lattice is
+investigated in the presence of a zigzag edge, where disordered and ordered
+phases can be controlled by a quantum phase transition. In analogy with the
+case of graphene with a zigzag edge, a flat edge magnon mode appears in the
+disordered phase. In an ordered phase, a finite magnetic moment generates a
+mean-field potential to the magnon. Since the potential is nonuniform on the
+edge and bulk sites, it affects the excitation, and the dispersion of the edge
+mode deviates from the flat shape. We investigate how the edge magnon mode
+evolves when the phase changes through the quantum phase transition and discuss
+the similarities to ordered spin systems on a monolayer honeycomb lattice.",1610.04333v1
+2016-12-01,Electrically Driven Bose-Einstein Condensation of Magnons in Antiferromagnets,"We explore routes to realize electrically driven Bose-Einstein condensation
+of magnons in insulating antiferromagnets. Even in insulating antiferromagnets,
+the localized spins can strongly couple to itinerant spins in adjacent metals
+via spin-transfer torque and spin pumping. We describe the formation of
+steady-state magnon condensates controlled by a spin accumulation polarized
+along the staggered field in an adjacent normal metal. Two types of magnons
+exist in antiferromagnets, which carry opposite magnetic moments. Consequently,
+and in contrast to ferromagnets, Bose-Einstein condensation can occur for
+either sign of the spin accumulation. This condensation may occur even at room
+temperature when the interaction with the normal metal is fast compared to the
+relaxation processes within the antiferromagnet. In antiferromagnets, the
+operating frequencies of the condensate are orders of magnitude faster than in
+ferromagnets.",1612.00366v1
+2016-12-14,Finite-size Effect for Dyonic Giant Magnons in $CP^3_β$,"We studied the finite-size giant magnons in
+$\text{AdS}_4\times\text{CP}^3_{\beta}$ background using the classical spectral
+curve constructed in this paper. We computed the finite-size corrections to the
+dispersion relations for the $RP^3$ giant magnons using our twisted algebraic
+curve based on the method proposed in arXiv:0810.1246, in which the authors
+computed the finite-size corrections of giant magnons in
+$\text{AdS}_4\times\text{CP}^3$ by introducing a finite-size resolvent
+$G_{\text{finite}}(x)$. We obtained exactly the same result as in
+arXiv:1106.3686, where a totally different approach was used.",1612.04613v5
+2016-12-21,Topologically non-trivial magnon bands in artificial square spin ices subject to Dzyaloshinskii-Moriya interaction,"Systems that exhibit topologically protected edge states are interesting both
+from a fundamental point of view as well as for potential applications, the
+latter because of the absence of back-scattering and robustness to
+perturbations. It is desirable to be able to control and manipulate such edge
+states. Here, we show that artificial square ices can incorporate both
+features: an interfacial Dzyaloshinksii-Moriya gives rise to topologically
+non-trivial magnon bands, and the equilibrium state of the spin ice is
+reconfigurable with different configurations having different magnon
+dispersions and topology. The topology is found to develop as odd-symmetry bulk
+and edge magnon bands approach each other, so that constructive band inversion
+occurs in reciprocal space. Our results show that topologically protected bands
+are supported in square spin ices.",1612.07203v5
+2017-07-12,THz-frequency cavity magnon-phonon-polaritons in the strong coupling regime,"We demonstrate the strong coupling of both magnons and phonons to terahertz
+(THz) frequency electromagnetic (EM) waves confined to a photonic crystal (PhC)
+cavity. Our cavity consists of a two-dimensional array of air-holes cut into a
+hybrid slab of ferroelectric lithium niobate (LiNbO$_3$) and erbium
+orthoferrite (ErFeO$_3$), a canted antiferromagnetic crystal. The phonons in
+LiNbO$_3$ and the magnons in ErFeO$_3$ are strongly coupled to the electric and
+magnetic field components of the confined EM wave, respectively. This leads to
+the formation of new cavity magnon-phonon-polariton modes, which we
+experimentally observe as a normal-mode splitting in the frequency spectrum and
+an avoided crossing in the temperature-frequency plot. The cavity also has a
+mode volume of $V=3.4\times10^{-3}\lambda^3\simeq0.5(\lambda/n)^3$ $\mu$m$^3$
+and can achieve a Q-factor as high as 1000. These factors facilitate the
+pursuit of the fields of THz cavity spintronics and quantum electrodynamics.",1707.03503v1
+2018-10-09,Non-uniform spin wave softening in 2D magnonic crystals as a tool for opening omnidirectional magnonic band gaps,"By means of the plane wave method we study spin wave dynamics in
+two-dimensional bi-component magnonic crystals based on a squeezed hexagonal
+lattice and consist of a permalloy thin film with cobalt inclusions. We explore
+the dependence of a spin wave frequency on the external magnetic field,
+especially in weak fields where the mode softening takes place. For considered
+structures, the mode softening proves to be highly non-uniform on both the mode
+number and the wave vector. We found this effect to be responsible for the
+omnidirectional band gap opening. Moreover, we show that the enhancement of the
+demagnetizing field caused by the squeezing of the structure is of crucial
+importance for the non-uniform mode softening. This allows us to employ this
+mechanism to design magnonic gaps with different sensitivity for the tiny
+change of the external field. The effects we have found should be useful in
+designing and optimization of spin wave filters highly tunable by a small
+external magnetic field.",1810.04005v3
+2020-06-11,Nonlocal magnon entanglement generation in coupled hybrid cavity systems,"We investigate dynamical generation of macroscopic nonlocal entanglements
+between two remote massive magnon-superconducting-circuit hybrid systems. Two
+fiber-coupled microwave cavities are employed to serve as an interaction
+channel connecting two sets of macroscopic hybrid units each containing a
+magnon (hosted by a Yttrium-Iron-Garnet sphere) and a superconducting-circuit
+qubit. Surprisingly, it is found that stronger coupling does not necessarily
+mean faster entanglement generation. The proposed hybrid system allows the
+existence of an optimal fiber coupling strength that requests the shortest
+amount of time to generate a systematic maximal entanglement. Our theoretical
+results are shown to be within the scope of specific parameters that can be
+achieved with current technology. The noise effects on the implementation of
+systems are also treated in a general environment suggesting the robustness of
+entanglement generation. Our discrete-variable qubit-like entanglement theory
+of magnons may lead to direct applications in various quantum information
+tasks.",2006.06132v3
+2020-06-19,Coexistence and interaction of spinons and magnons in an antiferromagnet with alternating antiferromagnetic and ferromagnetic quantum spin chains,"In conventional quasi-one-dimensional antiferromagnets with quantum spins,
+magnetic excitations are carried by either magnons or spinons in different
+energy regimes: they do not coexist independently, nor could they interact with
+each other. In this Letter, by combining inelastic neutron scattering, quantum
+Monte Carlo simulations and Random Phase Approximation calculations, we report
+the discovery and discuss the physics of the coexistence of magnons and spinons
+and their interactions in Botallackite-Cu2(OH)3Br. This is a unique quantum
+antiferromagnet consisting of alternating ferromagnetic and antiferromagnetic
+Spin-1/2 chains with weak inter-chain couplings. Our study presents a new
+paradigm where one can study the interaction between two different types of
+magnetic quasiparticles, magnons and spinons.",2006.10922v2
+2020-06-19,Orbital Magnetic Moment of Magnons,"In experiments and applications usually the spin magnetic moment of magnons
+is considered. In this Paper we identify an additional degree of freedom of
+magnons: an \emph{orbital} magnetic moment brought about by spin-orbit
+coupling.Our microscopic theory uncovers that spin magnetization
+$\vec{M}^\mathrm{S}$ and orbital magnetization $\vec{M}^\mathrm{O}$ are
+independent quantities. They are not necessarily collinear; thus, even when the
+total spin moment is compensated due to antiferromagnetism ($\vec{M}^\mathrm{S}
+= \vec{0}$), $\vec{M}^\mathrm{O}$ may be nonzero. This scenario of orbital weak
+ferromagnetism is realized in paradigmatic kagome antiferromagnets with
+Dzyaloshinskii-Moriya interaction. We demonstrate that magnets exhibiting a
+magnonic orbital moment are omnipresent and propose transport experiments for
+probing it.",2006.11107v1
+2020-06-20,Tunable magnon-magnon coupling in synthetic antiferromagnets,"In this work, we study magnon-magnon coupling in synthetic antiferromagnets
+(SyAFs) using microwave spectroscopy at room temperature. Two distinct
+spin-wave modes are clearly observed and are hybridised at degeneracy points.
+We provide a phenomenological model that captures the coupling phenomena and
+experimentally demonstrate that the coupling strength is controlled by the
+out-of-plane tilt angle as well as the interlayer exchange field. We
+numerically show that a spin-current mediated damping in SyAFs plays a role in
+influencing the coupling strength.",2006.11633v2
+2020-09-04,Magnon-induced Giant Anomalous Nernst Effect in Single Crystal MnBi,"Thermoelectric modules are a promising approach to energy harvesting and
+efficient cooling. In addition to the longitudinal Seebeck effect, recently
+transverse devices utilizing the anomalous Nernst effect (ANE) have attracted
+interest. For high conversion efficiency, it is required that the material
+should have a large ANE thermoelectric power and low electrical resistance, the
+product of which is the ANE conductivity. ANE is usually explained in terms of
+intrinsic contributions from Berry curvature. Our observations suggest that
+extrinsic contributions also matter. Studying single-crystal MnBi, we find a
+very high ANE thermopower (~10 $\mu$V/K) under 0.6 T at 80 K, and a transverse
+thermoelectric conductivity of over 40 A/Km. With insight from theoretical
+calculations, we attribute this large ANE predominantly to a new advective
+magnon contribution arising from magnon-electron spin-angular momentum
+transfer. We propose that introducing large spin-orbit coupling into
+ferromagnetic materials may enhance the ANE through the extrinsic contribution
+of magnons.",2009.02211v3
+2020-09-08,Unconventional Singularity in Anti-Parity-Time Symmetric Cavity Magnonics,"By engineering an anti-parity-time (anti-PT) symmetric cavity magnonics
+system with precise eigenspace controllability, we observe two different
+singularities in the same system. One type of singularity, the exceptional
+point (EP), is produced by tuning the magnon damping. Between two EPs, the
+maximal coherent superposition of photon and magnon states is robustly
+sustained by the preserved anti-PT symmetry. The other type of singularity,
+arising from the dissipative coupling of two anti-resonances, is an
+unconventional bound state in the continuum (BIC). At the settings of BICs, the
+coupled system exhibits infinite discontinuities in the group delay. We find
+that both singularities co-exist at the equator of the Bloch sphere, which
+reveals a unique hybrid state that simultaneously exhibits the maximal coherent
+superposition and slow light capability.",2009.03950v1
+2020-09-28,Spin-orbit coupling and linear crossings of dipolar magnons in van der Waals antiferromagnets,"A magnon spin-orbit coupling, induced by the dipole-dipole interaction, is
+derived in monoclinic-stacked bilayer honeycomb spin lattice with perpendicular
+magnetic anisotropy and antiferromagnetic interlayer coupling. Linear crossings
+are predicted in the magnon spectrum around the band minimum in G valley, as
+well as in the high frequency range around the zone boundary. The linear
+crossings in K and K' valleys, which connect the acoustic and optical bands,
+can be gapped when the intralayer dipole-dipole or Kitaev interactions exceed
+the interlayer dipole-dipole interaction, resulting in a phase transition from
+semimetal to insulator. Our results are useful for analyzing the magnon spin
+dynamics and transport properties in van der Waals antiferromagnet.",2009.13660v1
+2021-01-31,Vortex-mediated relaxation of magnon BEC into light Higgs quasiparticles,"A magnon Bose-Einstein condensate in superfluid $^3$He is a fine instrument
+for studying the surrounding macroscopic quantum system. At zero temperature,
+the BEC is subject to a few, distinct forms of decay into other collective
+excitations, owing to momentum and energy conservation in a quantum vacuum. We
+study the vortex-Higgs mechanism: the vortices relax the requirement for
+momentum conservation, allowing the optical magnons of the BEC to transform
+into light Higgs quasiparticles. This observation expands the spectrum of
+possible interactions between magnetic quasiparticles in $^3$He-B, opens
+pathways for hunting down elusive phenomena such as the Kelvin wave cascade or
+bound Majorana fermions, and lays groundwork for building magnon-based quantum
+devices.",2102.00419v2
+2021-02-15,Magnetodynamic properties of dipole-coupled 1D magnonic crystals,"Magnonic crystals are magnetic metamaterials, that provide a promising way to
+manipulate magnetodynamic properties by controlling the geometry of the
+patterned structures. Here, we study the magnetodynamic properties of 1D
+magnonic crystals consisting of parallel NiFe strips with different strip
+widths and separations. The strips couple via dipole-dipole interactions. As an
+alternative to experiments and/or micromagnetic simulations, we investigate the
+accuracy of a simple macrospin model. For the case of simple strips, a model
+with a single free parameter to account for an overestimation of the
+out-of-plane demagnetization of the magnonic lattice is described. By adjusting
+this parameter a good fit with experimental as well as micromagnetic results is
+obtained. Moreover, the Gilbert damping is found independent of the lattice
+constant however the inhomogeneous linewidth broadening found to increase with
+decreasing stripe separation.",2102.07712v2
+2013-06-07,Theory of carrier-mediated magnonic superlattices,"We present a minimal one-dimensional model of collective spin excitations in
+itinerant ferromagnetic superlattices within the regime of parabolic
+spin-carrier dispersion. We discuss the cases of weakly and strongly modulated
+magnetic profiles finding evidences of antiferromagnetic correlations for
+long-wave magnons (especially significant in layered systems), with an insight
+into the ground state properties. In addition, the presence of local minima in
+the magnonic dispersion suggests the possibility of (thermal) excitation of
+spin waves with a relatively well controlled wave length. Some of these
+features could be experimentally tested in DMS superlattices based on thin
+doped magnetic layers, acting as natural interfaces between (spin)electronic
+and magnonic degrees of freedom.",1306.1658v2
+2015-07-07,Rayleigh-Jeans condensation of pumped magnons in thin film ferromagnets,"We show that the formation of a magnon condensate in thin ferromagnetic films
+can be explained within the framework of a classical stochastic non-Markovian
+Landau-Lifshitz-Gilbert equation where the properties of the random magnetic
+field and the dissipation are determined by the underlying phonon dynamics. We
+have numerically solved this equation for a tangentially magnetized
+yttrium-iron garnet film in the presence of a parallel parametric pumping
+field. We obtain a complete description of all stages of the nonequilibrium
+time evolution of the magnon gas which is in excellent agreement with
+experiments. Our calculation proves that the experimentally observed
+condensation of magnons in yttrium-iron garnet at room temperature is a purely
+classical phenomenon which should be called Rayleigh-Jeans rather than
+Bose-Einstein condensation.",1507.01717v2
+2016-09-30,Magnon dispersion shift in the induced-ferromagnetic phase of the noncentrosymmetric MnSi,"Small angle neutron inelastic scattering measurement has been performed to
+study the magnon dispersion relation in the field-induced-ferromagnetic phase
+of the noncentrosymmetric binary compound MnSi. For the magnons propagating
+parallel or anti-parallel to the external magnetic field, we experimentally
+confirmed that the dispersion relation is asymmetrically shifted along the
+magnetic field direction. This magnon dispersion shift is attributed to the
+relativistic Dzyaloshinskii-Moriya interaction, which is finite in
+noncentrosymmetric magnets, such as MnSi. The shift direction is found to be
+switchable by reversing the external magnetic field direction.",1609.09583v1
+2018-08-16,Chiral Phonon Transport Induced by Topological Magnons,"The plethora of recent discoveries in the field of topological electronic
+insulators has inspired a search for boson systems with similar properties.
+There are predictions that ferromagnets on a two-dimensional honeycomb lattice
+may host chiral edge magnons. In such systems, we theoretically study how
+magnons and phonons couple. We find topological magneto-polarons around the
+avoided crossings between phonons and topological magnons. Exploiting this
+feature along with our finding of Rayleigh edge phonons in armchair ribbons, we
+demonstrate the existence of chiral edge modes with a phononic character. We
+predict that these modes mediate a chirality in the coherent phonon response
+and suggest to measure this effect via elastic transducers. These findings
+reveal a possible approach towards heat management in future devices.",1808.05493v2
+2018-08-28,${\mathbb Z}_2$ Topological Invariant for Magnon Spin Hall Systems,"We propose a definition of a ${\mathbb Z}_2$ topological invariant for magnon
+spin Hall systems which are the bosonic analog of two-dimensional topological
+insulators in class AII. The existence of ""Kramers pairs"" in these systems is
+guaranteed by pseudo-time-reversal symmetry which is the same as time-reversal
+symmetry up to some unitary transformation. The ${\mathbb Z}_2$ index of each
+Kramers pair of bands is expressed in terms of the bosonic counterparts of the
+Berry connection and curvature. We construct explicit examples of magnon spin
+Hall systems and demonstrate that our ${\mathbb Z}_2$ index precisely
+characterizes the presence or absence of helical edge states. The proposed
+${\mathbb Z}_2$ index and the formalism developed can be applied not only to
+magnonic systems but also to other non-interacting bosonic systems.",1808.09149v4
+2019-05-31,Experimental observation of exceptional surface in synthetic dimensions with magnon polaritons,"Exceptional points (EPs) are singularities of energy levels in non-Hermitian
+systems. In this Letter, we demonstrate the surface of EPs on a magnon
+polariton platform composed of coupled magnons and microwave photons. Our
+experiments show that EPs form a three-dimensional exceptional surface (ES)
+when the system is tuned in a four-dimensional synthetic space. We demonstrated
+that there exists an exceptional saddle point (ESP) in the ES which originates
+from the unique couplings between magnons and microwave photons. Such an ESP
+exhibits unique anisotropic behaviors in both the real and imaginary part of
+the eigenfrequencies. To the best of our knowledge, this is the first
+experimental observation of ES, opening up new opportunities for
+high-dimensional control of non-Hermitian systems.",1906.00044v1
+2019-06-14,Short-range antiferromagnetic correlation effect on conduction electrons in two-dimensional strongly correlated electron systems,"We investigate magnetic polarons in two-dimensional strongly correlated
+electron systems, where conduction electrons interact with
+antiferromagnetically interacting localized spins. Starting from a basic model,
+we derive a simplified model with the help of spin Green's function and a
+perturbation analysis. A strong coupling analysis is applied to the model,
+where the sum of the scattering wave vectors is approximated to be $(\pi,\pi)$
+or zero, using the equation of motion for the conduction electron Green's
+function, and we discuss the pseudogap like behavior associated with the
+suppression of the quasiparticle weights and the transition from the large
+magnetic polaron to the small magnetic polaron. In the antiferromagnetic
+long-range ordered state, the spectral weight of the conduction electrons has a
+form of broad humps due to Franck-Condon broadening associated with the
+multi-magnon scattering. The band folding feature due to the $(\pi,\pi)$
+scattering disappears as we increase the number of the magnons involved in the
+multi-magnon scattering. It is crucial to include long-range antiferromagnetic
+correlations as well as dumping of magnons.",1906.06031v2
+2019-06-28,Magnon gravitomagnetoelectric effect in noncentrosymmetric antiferromagnetic insulators,"We study the magnon contribution to the gravitomagnetoelectric (gravito-ME)
+effect, in which the magnetization is induced by a temperature gradient, in
+noncentrosymmetric antiferromagnetic insulators. This phenomenon is totally
+different from the ME effect, because the temperature gradient is coupled to
+magnons but an electric field is not. We derive a general formula of the
+gravito-ME susceptibility in terms of magnon wave functions and find that a
+difference in $g$ factors of magnetic ions is crucial. We also apply our
+formula to a specific model. Although the obtained gravito-ME susceptibility is
+small, we discuss several ways to enhance this phenomenon.",1906.12031v3
+2019-06-28,Microscopic mechanism of level attraction,"The emerging level attraction from dissipative light-matter coupling
+converges the typical Rabi-splitting feature from coherent coupling and
+exhibits potentials in topological information processing. However, the
+underlying microscopic quantum mechanism of dissipative coupling still remains
+unclear, which brings difficulties in quantifying and manipulating
+coherence-dissipation competition and thereby the flexible control of level
+attraction. Here, by coupling magnon to a cavity supporting both standing and
+travelling waves, we identify the travelling-wave state to be responsible for
+magnon-photon dissipative coupling. By characterizing radiative broadening of
+magnon linewidth, we quantify the coherent and dissipative coupling strengths
+and their competition. The effective magnon-photon coupling strength, as a net
+result of competition, is analytically presented in quantum theory to show good
+agreement with measurements. In this manner, we extend the control dimension of
+level attraction by tuning field torque on magnetization or global cavity
+geometry. Our finding opens new routines to engineer coupled harmonic
+oscillator system.",1906.12142v2
+2019-07-01,Magnon decay theory of Gilbert damping in metallic antiferromagnets,"Gilbert damping is a key property governing magnetization dynamics in ordered
+magnets. We present a theoretical study of intrinsic Gilbert damping induced by
+magnon decay in antiferromagnetic metals through $s$-$d$ exchange interaction.
+Our theory delineates the qualitative features of damping in metallic
+antiferromagnets owing to their bipartite nature, in addition to providing
+analytic expressions for the damping parameters. Magnon-induced intraband
+electron scattering is found to predominantly cause magnetization damping,
+whereas the N\'eel field is found to be damped via disorder. Depending on the
+conduction electron band structure, we predict that magnon-induced interband
+electron scattering around band crossings may be exploited to engineer a strong
+N\'eel field damping.",1907.01045v1
+2019-07-15,Probing magnon dynamics and interactions in a ferromagnetic spin-1 chain,"NiNb$_{2}$O$_{6}$ is an almost ideal realization of a 1D spin-1 ferromagnetic
+Heisenberg chain compound with weak unidirectional anisotropy. Using
+time-domain THz spectroscopy, we measure the low-energy electrodynamic response
+of NiNb$_{2}$O$_{6}$ as a function of temperature and external magnetic field.
+At low temperatures, we find a magnon-like spin-excitation, which corresponds
+to the lowest energy excitation at $q\sim0$. At higher temperatures, we
+unexpectedly observe a temperature-dependent renormalization of the
+spin-excitation energy, which has a strong dependence on field direction. Using
+theoretical arguments, exact diagonalizations and finite temperature dynamical
+Lanczos calculations, we construct a picture of magnon-magnon interactions that
+naturally explains the observed renormalization. This unique scenario is a
+consequence of the spin-1 nature and has no analog in the more widely studied
+spin-1/2 systems.",1907.06542v1
+2019-07-15,Cavity mediated dissipative coupling of distant magnetic moments: theory and experiment,"We investigate long-range coherent and dissipative coupling between two
+spatially separated magnets while both are coupled to a microwave cavity. A
+careful examination of the system shows that the indirect interaction between
+two magnon modes is dependent on their individual mechanisms of direct coupling
+to the cavity. If both magnon modes share the same form of coupling to the
+cavity (either coherent or dissipative), then the indirect coupling between
+them will produce level repulsion. Conversely, if the magnon modes have
+different forms of coupling to the cavity (one coherent and one dissipative),
+then their indirect coupling will produce level attraction. We further
+demonstrate the cavity-mediate nature of the indirect interaction through
+investigating the dependence of the indirect coupling strength on the frequency
+detuning between the magnon and cavity modes. Our work theoretically and
+experimentally explores indirect cavity mediate interactions in systems
+exhibiting both coherent and dissipative coupling, which opens a new avenue for
+controlling and utilizing light-matter interactions.",1907.06783v1
+2019-07-24,Intrinsic spin Nernst effect of magnons in a noncollinear antiferromagnet,"We investigate the intrinsic magnon spin current in a noncollinear
+antiferromagnetic insulator. We introduce a definition of the magnon spin
+current in a noncollinear antiferromagnet and find that it is in general
+non-conserved, but for certain symmetries and spin polarizations the averaged
+effect of non-conserving terms can vanish. We formulate a general linear
+response theory for magnons in noncollinear antiferromagnets subject to a
+temperature gradient and analyze the effect of symmetries on the response
+tensor. We apply this theory to single-layer potassium iron jarosite
+KFe$_3$(OH)$_6$(SO$_4$)$_2$ and predict a measurable spin current response.",1907.10567v3
+2019-10-11,Hannay Angles in Magnetic Dynamics,"We consider, within the framework developed by Hannay for classical
+integrable systems [Journal of Physics A: Mathematical and General {\bf 18},
+221 (1985)], the geometric phases that occur in semi-classical magnetic
+dynamics. Such geometric phases are generically referred to as Hannay angles,
+and, in the context of magnetic dynamics, may arise as a result of both
+adiabatically-varying ellipticity and axis of magnetization precession. We
+elucidate both effects and their interplay for single-domain magnetic dynamics
+within a simple model with time-dependent anisotropies and external field.
+Subsequently, we consider spin waves and rederive, from our classical approach,
+some known results on what is commonly referred to as the magnon Berry phase.
+As an aside, these results are used to give an interpretation for geometric
+phases that occur in superfluids. Finally, we develop a Green's function
+formalism for elliptical magnons. Within this formalism, we consider magnon
+transport in a mesoscopic ring and show how it is influenced by interference
+effects that are tuned by the Hannay angle that results from a varying
+ellipticity. Our results may inform the field of magnonics that seeks to
+utilize spin waves in applications.",1910.05099v2
+2019-10-21,Entanglement-based single-shot detection of a single magnon with a superconducting qubit,"The recent development of hybrid systems based on superconducting circuits
+has opened up the possibility of engineering sensors of quanta of different
+degrees of freedom. Quantum magnonics, which aims to control and read out
+quanta of collective spin excitations in magnetically-ordered systems,
+furthermore provides unique opportunities for advances in both the study of
+magnetism and the development of quantum technologies. Using a superconducting
+qubit as a quantum sensor, we report the detection of a single magnon in a
+millimeter-sized ferromagnetic crystal with a quantum efficiency of up
+to~$0.71$. The detection is based on the entanglement between a magnetostatic
+mode and the qubit, followed by a single-shot measurement of the qubit state.
+This proof-of-principle experiment establishes the single-photon detector
+counterpart for magnonics.",1910.09096v1
+2019-10-31,Coherent spin pumping in a strongly coupled magnon-magnon hybrid system,"We experimentally identify coherent spin pumping in the magnon-magnon hybrid
+modes of permalloy/yttrium iron garnet (Py/YIG) bilayers. Using broadband
+ferromagnetic resonance, an ""avoided crossing"" is observed between the uniform
+mode of Py and the spin wave mode of YIG due to the fieldlike interfacial
+exchange coupling. We also identify additional linewidth suppression and
+enhancement for the in-phase and out-of-phase hybrid modes, respectively,
+\textcolor{black}{which can be interpreted as concerted dampinglike torque from
+spin pumping}. Our analysis predicts inverse proportionality of both fieldlike
+and dampinglike torques to the square root of the Py thickness, which
+quantitatively agrees with experiments.",1910.14470v2
+2020-01-11,Spin Seebeck effect and magnon diffusion length in $\rm{\mathbf{Fe}}_{\mathbf{3}}\rm{\mathbf{O}}_{\mathbf{4}}$,"The determination of the magnon diffusion length (MDL) is important for
+increasing the efficiency of spin Seebeck effect (SSE) based devices utilising
+non-metallic magnets. We extract the MDL at $50$ and $300\,\rm{K}$ in an
+$\rm{Fe}_{3}\rm{O}_{4}$ single crystal from the magnon dispersion obtained
+using inelastic neutron scattering (INS) and find them to be equal within
+error. We then measure the heat flux normalised SSE responses and in-plane
+magnetization of $\rm{Fe}_{3}\rm{O}_{4}$ thin films and normalise by the static
+magnetization contribution to the SSE before determining the MDLs from a fit of
+the thickness dependence. We find that the MDLs determined in this way are
+smaller than that measured from INS which maybe due to differences in magnon
+propagation between bulk and thin film $\rm{Fe}_{3}\rm{O}_{4}$.",2001.03738v1
+2020-02-12,Topological magnonics in the two-dimensional van der Waals magnet CrI3,"In this article, we calculate the magnon spectrum of Kitaev-Heisenberg
+magnets. This model has been recently proposed as a spin Hamiltonian to model
+$\text{CrI}_3$ and other two-dimensional magnets. It is a minimal spin
+Hamiltonian that includes a contribution stemming from a Heisenberg, isotropic
+exchange, and a contribution arising from a Kitaev interaction, anisotropic and
+frustrated exchange. Our calculations reveal the topological nature of the
+magnons and a gap that opens at the $K$ and $K^\prime$ points. These
+topological properties give rise to effects such as thermal Hall effect. In
+addition to the bulk properties, we calculate the magnon spectrum of
+nanoribbons illustrating the corresponding edge states.",2002.05266v1
+2020-04-01,Gradual pressure-induced enhancement of magnon excitations in CeCoSi,"CeCoSi is an intermetallic antiferromagnet with a very unusual
+temperature-pressure phase diagram: at ambient pressure it orders below
+$T_{\mathrm{N}} = 8.8$ K, while application of hydrostatic pressure induces a
+new magnetically ordered phase with exceptionally high transition temperature
+of $\sim40$ K at 1.5 GPa. We studied the magnetic properties and the
+pressure-induced magnetic phase of CeCoSi by means of elastic and inelastic
+neutron scattering (INS) and heat capacity measurements. At ambient pressure
+CeCoSi orders into a simple commensurate AFM structure with a reduced ordered
+moment of only $m_{\mathrm{Ce}} = 0.37(6)$ $\mu_{\mathrm{B}}$. Specific heat
+and low-energy INS indicate a significant gap in the low-energy magnon
+excitation spectrum in the antiferromagnetic phase, with the CEF excitations
+located above 10 meV. Hydrostatic pressure gradually shifts the energy of the
+magnon band towards higher energies, and the temperature dependence of the
+magnons measured at 1.5 GPa is consistent with the phase diagram. Moreover, the
+CEF excitations are also drastically modified under pressure.",2004.00442v2
+2020-04-29,Non-reciprocal magnons in a two dimensional crystal with off-plane magnetization,"Non reciprocal spin waves have a chiral asymmetry so that their energy is
+different for two opposite wave vectors. They are found in atomically thin
+ferromagnetic overlayers with in plane magnetization and are linked to the
+anti-symmetric Dzyaloshinskii-Moriya surface exchange. We use an itinerant
+fermion theory based on first principles calculations to predict that
+non-reciprocal magnons can occur in Fe$_3$GeTe$_2$, the first stand alone
+metallic two dimensional crystal with off-plane magnetization. We find that
+both the energy and lifetime of magnons are non-reciprocal and we predict that
+acoustic magnons can have lifetimes up to hundreds of picoseconds, orders of
+magnitude larger than in other conducting magnets.",2004.14179v2
+2020-05-19,Dissipation-based Quantum Sensing of Magnons with a Superconducting Qubit,"Hybrid quantum devices expand the tools and techniques available for quantum
+sensing in various fields. Here, we experimentally demonstrate quantum sensing
+of the steady-state magnon population in a magnetostatic mode of a
+ferrimagnetic crystal. Dispersively coupling the magnetostatic mode to a
+superconducting qubit allows the detection of magnons using Ramsey
+interferometry with a sensitivity on the order of $10^{-3}$
+$\text{magnons}/\sqrt{\text{Hz}}$. The protocol is based on dissipation as
+dephasing via fluctuations in the magnetostatic mode reduces the qubit
+coherence proportionally to the number of magnons.",2005.09250v1
+2020-05-21,Non-Hermitian coherent coupling of nanomagnets by exchange spin waves,"Non-Hermitian physics has recently attracted much attention in optics and
+photonics. Less explored is non-Hermitian magnonics that provides opportunities
+to take advantage of the inevitable dissipation of magnons or spin waves in
+magnetic systems. Here we demonstrate non-Hermitian coherent coupling of two
+distant nanomagnets by fast spin waves with sub-50 nm wavelengths. Magnons in
+two nanomagnets are unidirectionally phase-locked with phase shifts controlled
+by magnon spin torque and spin-wave propagation. Our results are attractive for
+analog neuromorphic computing that requires unidirectional information
+transmission.",2005.10452v1
+2020-07-06,Possible odd-frequency Amperean magnon-mediated superconductivity in topological insulator -- ferromagnetic insulator bilayer,"We study the magnon-mediated pairing between fermions on the surface of a
+topological insulator (TI) coupled to a ferromagnetic insulator with a tilted
+mean field magnetization. Tilting the magnetization towards the interfacial
+plane reduces the magnetic band gap and leads to a shift in the effective TI
+dispersions. We derive and solve the self-consistency equation for the
+superconducting gap in two different situations, where we neglect or include
+the frequency dependence of the magnon propagator. Neglecting the frequency
+dependence results in p-wave Amperean solutions. We also find that tilting the
+magnetization into the interface plane favors Cooper pairs with center of mass
+momenta parallel to the magnetization vector, increasing $T_c$ compared to the
+out-of-plane case. Including the frequency dependence of the magnon propagator,
+and solving for a low number of Matsubara frequencies, we find that the
+eigenvectors of the Amperean solutions at the critical temperature are
+dominantly odd in frequency and even in momentum, thus opening the possibility
+for odd-frequency Amperean pairing.",2007.02953v2
+2020-07-17,Entangling the vibrational modes of two massive ferromagnetic spheres using cavity magnomechanics,"We present a scheme to entangle the vibrational phonon modes of two massive
+ferromagnetic spheres in a dual-cavity magnomechanical system. In each cavity,
+a microwave cavity mode couples to a magnon mode (spin wave) via the magnetic
+dipole interaction, and the latter further couples to a deformation phonon mode
+of the ferromagnetic sphere via a nonlinear magnetostrictive interaction. We
+show that by directly driving the magnon mode with a red-detuned microwave
+field to activate the magnomechanical anti-Stokes process a
+cavity-magnon-phonon state-swap interaction can be realized. Therefore, if the
+two cavities are further driven by a two-mode squeezed vacuum field, the
+quantum correlation of the driving fields is successively transferred to the
+two magnon modes and subsequently to the two phonon modes, i.e., the two
+ferromagnetic spheres become remotely entangled. Our work demonstrates that
+cavity magnomechanical systems allow to prepare quantum entangled states at a
+more massive scale than currently possible with other schemes.",2007.09083v3
+2020-07-28,Pair emission from a relativistic domain wall in antiferromagnets,"Magnon emission and excitation by a relativistic domain wall at a constant
+velocity in antiferromagnet is theoretically studied. A pair emission due to a
+quadratic magnon coupling is shown to be dominant. The emission corresponds in
+the comoving frame to a vacuum polarization induced by a zero-energy
+instability of the Lorentz-boosted anomalous response function. The emission
+rate is sensitive to the magnon dispersion and wall profile, and is
+significantly enhanced for a thin wall with velocity close to the effective
+light velocity. The Ohmic damping constant due to magnon excitation at low
+velocity is calculated.",2007.13939v1
+2020-08-12,Topological properties of multilayer magnon insulators,"Two-dimensional magnetic insulators can be promising hosts for topological
+magnons. In this study, we show that ABC-stacked honeycomb lattice multilayers
+with alternating Dzyaloshinskii-Moriya interaction (DMI) reveal a rich
+topological magnon phase diagram. Based on our bandstructure and Berry
+curvature calculations, we demonstrate jumps in the thermal Hall behavior that
+corroborate with topological phase transitions triggered by adjusting the DMI
+and interlayer coupling. We connect the phase diagram of generic multilayers to
+a bilayer and a trilayer system. We find an even-odd effect amongst the
+multilayers where the even layers show no jump in thermal Hall conductivity,
+but the odd layers do. We also observe the presence of topological proximity
+effect in our trilayer. Our results offer new schemes to manipulate Chern
+numbers and their measurable effects in topological magnonic systems.",2008.05487v2
+2020-11-03,Symmetry breaking induced magnon-magnon coupling in synthetic antiferromagnets,"We propose a general theory of microwave absorption spectroscopy for
+symmetry-breaking synthetic antiferromagnets (SAFs). Generally, inhomogeneity
+or different thickness of the two ferromagnetic sublayers of a SAF results in
+the intrinsic symmetry breaking, while out-of-plane components of dc magnetic
+fields lead to the extrinsic one. The broken symmetry of SAFs excludes the
+original symmetry-protected crossing between pure in-phase and out-of-phase
+resonance modes with opposite parity. Alternatively, new frequency branches
+become hybridization of original bare modes in terms of
+symmetry-breaking-induced magnon-magnon coupling, which results in an indirect
+gap in ferromagnetic resonance frequencies. Also, the dependence of gap width
+on the degree of symmetry breaking for several typical cases are presented and
+compared with existing experiments. Our theory provides a simple but physical
+understanding on the rich structure of ferromagnetic resonance spectra for
+asymmetric SAFs.",2011.01583v1
+2020-11-12,"Experimental parameters, combined dynamics, and nonlinearity of a Magnonic-Opto-Electronic Oscillator (MOEO)","We report the construction and characterization of a comprehensive
+magnonic-opto-electronic oscillator (MOEO) system based on 1550-nm photonics
+and yttirum iron garnet (YIG) magnonics. The system exhibits a rich and
+synergistic parameter space because of the ability to control individual
+photonic, electronic, and magnonic components. Taking advantage of the spin
+wave dispersion of YIG, the frequency self-generation as well as the related
+nonlinear processes become sensitive to the external magnetic field. Besides
+being known as a narrowband filter and a delay element, the YIG delayline
+possesses spin wave modes that can be controlled to mix with the optoelectronic
+modes to generate higher-order harmonic beating modes. With the high
+sensitivity and external tunability, the MOEO system may find usefulness in
+sensing applications in magnetism and spintronics beyond optoelectronics and
+photonics.",2011.06155v1
+2020-11-16,Electrically induced strong modulation of magnons transport in ultrathin magnetic insulator films,"Magnon transport through a magnetic insulator can be controlled by
+current-biased heavy-metal gates that modulate the magnon conductivity via the
+magnon density. Here, we report nonlinear modulation effects in 10$\,$nm thick
+yttrium iron garnet (YIG) films. The modulation efficiency is larger than
+40\%/mA. The spin transport signal at high DC current density (2.2$\times
+10^{11}\,$A/m$^{2}$) saturates for a 400$\,$nm wide Pt gate, which indicates
+that even at high current levels a magnetic instability cannot be reached in
+spite of the high magnetic quality of the films.",2011.07800v1
+2020-11-17,Sum-frequency excitation of coherent magnons,"Coherent excitation of magnons is conventionally achieved through Raman
+scattering processes, in which the difference-frequency components of the
+driving field are resonant with the magnon energy. Here, we describe mechanisms
+by which the sum-frequency components of the driving field can be used to
+coherently excite magnons through two-particle absorption processes. We use the
+Landau-Lifshitz-Gilbert formalism to compare the spin-precession amplitudes
+that different types of impulsive stimulated and ionic Raman scattering
+processes and their sum-frequency counterparts induce in an antiferromagnetic
+model system. We show that sum-frequency mechanisms enabled by linearly
+polarized driving fields yield excitation efficiencies comparable or larger
+than established Raman techniques, while elliptical polarizations produce only
+weak and circularly polarizations no sum-frequency components at all. The
+mechanisms presented here complete the map for dynamical spin control by the
+means of Raman-type processes.",2011.08730v1
+2020-11-25,Magnon-phonon hybridization in quasi-2D antiferromagnet MnPSe$_3$,"Magnetic excitations in van der Waals (vdW) materials, especially in the
+two-dimensional (2D) limit, are an exciting research topic from both the
+fundamental and applied perspectives. Using temperature-dependent,
+magneto-Raman spectroscopy, we identify the hybridization of two-magnon
+excitations with two separate E$_\mathrm{g}$ phonons in MnPSe$_3$, a magnetic
+vdW material that could potentially host 2D antiferromagnetism. Results from
+first principles calculations of the phonon and magnon spectra further support
+our identification. The Raman spectra's rich temperature dependence through the
+magnetic transition displays an avoided-crossing behavior in the phonons'
+frequency and a concurrent decrease in their lifetimes. We construct a model
+based on the interaction between a discrete level and a continuum that
+reproduces these observations. The strong magnon-phonon hybridization reported
+here highlights the need to understand its effects on spin transport
+experiments in magnetic vdW materials.",2011.12557v2
+2021-01-26,Supermagnonic propagation in two-dimensional antiferromagnets,"We investigate the propagation of magnons after ultrashort perturbations of
+the exchange interaction in the prototype two-dimensional Heisenberg
+antiferromagnet. Using the recently proposed neural quantum states, we predict
+highly anisotropic spreading in space constrained by the symmetry of the
+perturbation. Interestingly, the propagation speed at the shortest length and
+time scale is up to 40% higher than the highest magnon velocity. We argue that
+the enhancement stems from extraordinary strong magnon-magnon interactions,
+suggesting new avenues for manipulating information transfer on ultrashort
+length and time scales.",2101.10945v2
+2021-03-09,"Dynamic transverse magnetic susceptibility in the projector augmented-wave method. Application to Fe, Ni, and Co","We present a first principles implementation of the dynamic transverse
+magnetic susceptibility in the framework of linear response time-dependent
+density functional theory. The dynamic susceptibility allows one to obtain the
+magnon dispersion as well as magnon lifetimes for a particular material, which
+strongly facilitates the interpretation of inelastic neutron scattering
+experiments as well as other spectroscopic techniques. We apply the method to
+Fe, Ni, and Co and perform a thorough convergence analysis with respect the
+basis set size, $k$-point sampling, spectral smearing and unoccupied bands. In
+particular, it is shown that while the gap error (acoustic magnon energy at
+$\mathbf{q}=\mathbf{0}$) is highly challenging to converge, the spin-wave
+stiffness and the dispersion relation itself are much less sensitive to
+convergence parameters. Our final results agrees well with experimentally
+extracted magnon dispersion relations except for Ni, where it is well-known
+that the exchange splitting energy is poorly represented in the local density
+approximation. We also find good agreement with previous first principles
+calculations and explain how differences in the calculated dispersion relations
+can arise from subtle differences in computational approaches.",2103.05409v2
+2021-03-11,Proposal for a Bell test in cavity optomagnonics,"We present a proposal to test Bell inequality in the emerging field of cavity
+optomagnonics, where a sphere of ferromagnetic crystal supports two optical
+whispering gallery modes and one magnon mode. The two optical modes are driven
+by two laser pulses, respectively. Entanglement between magnon mode and one of
+the two optical modes will be generated by the first pulse, and the state of
+magnon mode is subsequently mapped into another optical mode via the second
+pulse. Hence correlated photon-photon pairs is created out of the cavity. A
+Bell test can be implemented using these pairs, which enables us to test local
+hidden-variable models at macroscopic optomagnonical system. Our results show
+that a significant violation of Bell inequality can be obtained in the
+experimentally relevant weak-coupling regime. The violation of Bell inequality
+not only verifies the entanglement between magnons and photons, but also
+implies that cavity optomagnonics is a promising platform for quantum
+information processing tasks.",2103.06429v2
+2021-03-12,Double accumulation and anisotropic transport of magneto-elastic bosons in yttrium iron garnet films,"Interaction between quasiparticles of a different nature, such as magnons and
+phonons in a magnetic medium, leads to the mixing of their properties and the
+formation of hybrid states in the areas of intersection of individual spectral
+branches. We recently reported the discovery of a new phenomenon mediated by
+the magnon-phonon interaction: the spontaneous bottleneck accumulation of
+magneto-elastic bosons under electromagnetic pumping of pure magnons into a
+ferrimagnetic yttrium iron garnet film. Here, by studying the transport
+properties of the accumulated magneto-elastic bosons, we reveal that such
+accumulation occurs in two frequency-distant groups of quasiparticles:
+quasi-phonons and quasi-magnons. They propagate with different speeds in
+different directions relative to the magnetization field. The theoretical model
+we propose qualitatively describes the double accumulation effect, and the
+analysis of the two-dimensional spectrum of quasiparticles in the hybridization
+region allows us to determine the wavevectors and frequencies of each of the
+groups.",2103.07338v1
+2021-03-12,Superconductivity provides a giant enhancement to the spin battery effect,"We develop a theory of the spin battery effect in
+superconductor/ferromagnetic insulator (SC/FI) systems taking into account the
+magnetic proximity effect. We demonstrate that the spin-energy mixing enabled
+by the superconductivity leads to the enhancement of spin accumulation by
+several orders of magnitude relative to the normal state. This finding can
+explain the recently observed giant inverse spin Hall effect generated by
+thermal magnons in the SC/FI system. We suggest a non-local electrical
+detection scheme which can directly probe the spin accumulation driven by the
+magnetization dynamics. We predict a giant Seebeck effect converting the magnon
+temperature bias into the non-local voltage signal. We also show how this can
+be used to enhance the sensitivity of magnon detection even up to the
+single-magnon level.",2103.07412v1
+2021-04-20,Magnetic dipolar modes in magnon-polariton condensates,"For dipole-carrying excitations observed in a high-quality resonator,
+strong-coupling modes can appear as composite bosons with the spontaneous
+formation of quantized vortices in the condensed phase of a polariton fluid. In
+exciton-polaritons, in particular, it leads to sustained trapping of the
+emitted photon. In this paper, we show that magnon-polaritons can be realized
+due to magnon condensation caused by magnetic dipole-dipole interaction. In a
+quasi-2D ferrite disk placed in a microwave cavity, one observes quantum
+confinement effects of magnetic-dipolar-mode (MDM) oscillations. These modes,
+characterized by energy eigenstates with rotational superflows and quantized
+vortices, are exhibited as spinor condensates. Along with the condensation of
+MDM magnons in the quasi-2D disk of the magnetic insulator, electric dipole
+condensation is also observed. At the MDM resonances, transfer between angular
+momenta in the magnetic insulator and in the vacuum cavity, demonstrates
+generation of vortex flows with fixed handedness. This indicates unique
+topological properties of polariton wavefronts. One observes curved wavefronts
+and effects of supperradiance in microwave structures. In an environment of
+scattering states of microwave waveguide, EM waves can carry the topological
+phases of MDM resonances.",2104.10048v1
+2021-05-04,Non-local magnon transport in a magnetic domain wall wave guide,"Magnetic domain walls function as a wave guide for low energy magnons. In
+this paper we develop the theory for the non-local transport of these bound
+magnons through a ferromagnetic insulator that are injected and detected
+electrically in adjacent normal metal leads by spin-flip scatting processes and
+the (inverse) spin-Hall effect. Our set-up requires a twofold degeneracy of the
+magnetic ground state, which we realize by an easy axis and hard axis
+anisotropy, in the ferromagnetic insulator. This is readily provided by a broad
+range of materials. The domain wall is a a topologically protected feature of
+the system and we obtain the non-local spin transport through it. Thereby we
+provide a framework for reconfigureable magnonic devices.",2105.01694v1
+2021-05-18,Magnon-mediated quantum battery under systematic errors,"Quantum battery is one of the most prominent micro-devices in the
+rapid-developing quantum thermodynamics. We propose a quantum charging protocol
+in which both battery and charger are consisted of a many-spin system. The
+battery and charger are connected via the Kittle mode of the magnon system,
+that serves as a charging wire and then enables a long-range charging protocol.
+Counter-intuitively, we find that the spin-spin couplings insider both battery
+and charger can be used to promote the charging performance in comparison to
+the noninteracting condition. And a remarkable promotion is realized at a
+""sweet"" spot in terms of the average coupling strength. Moreover, we apply the
+quantum-state-diffusion equation to test the robustness of our magnon-mediated
+charging protocol to the systematic errors about the magnon frequency.",2105.08387v2
+2021-05-21,Coherent and Dissipative Cavity Magnonics,"Strong interactions between magnetic materials and electrodynamic cavities
+mix together spin and photon properties, producing unique hybridized behaviour.
+The study of such coupled spin-photon systems, known as cavity magnonics, is
+motivated by the flexibility and controllability of these hybridized states for
+spintronic and quantum information technologies. In this tutorial we examine
+and compare both coherent and dissipative interactions in cavity magnonics. We
+begin with a familiar case study, the coupled harmonic oscillator, which
+provides insight into the unique characteristics of coherent and dissipative
+coupling. We then examine several canonical cavity magnonic systems,
+highlighting the requirements for different coupling mechanisms, and conclude
+with recent applications of spin-photon hybridization, for example, the
+development of quantum transducers, memory architectures, isolators and
+enhanced sensing.",2105.10491v2
+2021-05-24,Advances in coherent coupling between magnons and acoustic phonons,"The interaction between magnetic and acoustic excitations have recently
+inspired many interdisciplinary studies ranging from fundamental physics to
+circuit implementation. Specifically, the exploration of their coherent
+interconversion enabled via the magnetoelastic coupling opens a new playground
+combining straintronics and spintronics, and provides a unique platform for
+building up on-chip coherent information processing networks with miniaturized
+magnonic and acoustic devices. In this Perspective, we will focus on the recent
+progress of magnon-phonon coupled dynamic systems, including materials,
+circuits, imaging and new physics. In particular, we highlight the unique
+features such as nonreciprocal acoustic wave propagation and strong coupling
+between magnons and phonons in magnetic thin-film systems, which provides a
+unique platform for their coherent manipulation and transduction. We will also
+review the frontier of surface acoustic wave resonators in coherent quantum
+transduction and discuss how the novel acoustic circuit design can be applied
+in microwave spintronics.",2105.11051v1
+2021-05-28,Exceptional sign changes of the non-local spin Seebeck effect in antiferromagnetic hematite,"Low power spintronic devices based on the propagation of pure magnonic spin
+currents in antiferromagnetic insulator materials offer several distinct
+advantages over ferromagnetic components including higher frequency magnons and
+a stability against disturbing external magnetic fields. In this work, we make
+use of the insulating antiferromagnetic phase of iron oxide, the mineral
+hematite $\alpha$-Fe$_2$O$_3$ to investigate the long distance transport of
+thermally generated magnonic spin currents. We report on the excitation of
+magnons generated by the spin Seebeck effect, transported both parallel and
+perpendicular to the antiferromagnetic easy-axis under an applied magnetic
+field. Making use of an atomistic hematite toy model, we calculate the
+transport characteristics from the deviation of the antiferromagnetic ordering
+from equilibrium under an applied field. We resolve the role of the magnetic
+order parameters in the transport, and experimentally we find significant
+thermal spin transport without the need for a net magnetization.",2105.13653v1
+2021-06-02,Topological Magnons: A Review,"At sufficiently low temperatures magnetic materials often enter a correlated
+phase hosting collective, coherent magnetic excitations such as magnons or
+triplons. Drawing on the enormous progress on topological materials of the last
+few years, recent research has led to new insights into the geometry and
+topology of these magnetic excitations. Berry phases associated to magnetic
+dynamics can lead to observable consequences in heat and spin transport while
+analogues of topological insulators and semimetals can arise within magnon band
+structures from natural magnetic couplings. Magnetic excitations offer a
+platform to explore the interplay of magnetic symmetries and topology, to drive
+topological transitions using magnetic fields. examine the effects of
+interactions on topological bands and to generate topologically protected spin
+currents at interfaces. In this review, we survey progress on all these topics,
+highlighting aspects of topological matter that are unique to magnon systems
+and the avenues yet to be fully investigated.",2106.01430v1
+2021-06-03,Mass-energy equivalence for terahertz magnon excitation in antiferromagnetic domain walls,"The theory of special relativity is one of the most significant achievements
+in modern physics, with several important predictions such as time dilation,
+size contraction for a moving object and mass-energy equivalence. Recent
+studies have demonstrated size contraction for an antiferromagnetic (AFM)
+domain wall (DW). Here, we show the mass-energy equivalence by numerically
+investigating the excitation of terahertz (THz) magnons from a moving AFM DW
+under the magnetic anisotropy energy gradient. The energy of magnons comes from
+the loss of DW mass, accompanied with a DW width broadening, overcoming the
+Lorentz contraction effect. Our results pave the way to study relativistic
+physics in AFM textures and to efficiently generate THz magnons by electric
+means.",2106.01631v2
+2021-06-15,Nonreciprocal high-order sidebands induced by magnon Kerr nonlinearity,"We propose an effective approach for creating robust nonreciprocity of
+high-order sidebands, including the first-, second- and third-order sidebands,
+at microwave frequencies. This approach relies on magnon Kerr nonlinearity in a
+cavity magnonics system composed of two microwave cavities and one yttrium iron
+garnet (YIG) sphere. By manipulating the driving power applied on YIG and the
+frequency detuning between the magnon mode in YIG and the driving field, the
+effective Kerr nonlinearity can be strengthened, thereby inducing strong
+transmission non-reciprocity. More interestingly, we find the higher the
+sideband order, the stronger the transmission nonreciprocity marked by the
+higher isolation ratio in the optimal detuning regime. Such a series of
+equally-spaced high-order sidebands have potential applications in frequency
+comb-like precision measurement, besides structuring high-performance on-chip
+nonreciprocal devices.",2106.09542v1
+2021-07-08,Nonreciprocal magnon fluxonics upon ferromagnet/superconductor hybrids,"Ferromagnet/superconductor heterostructures allow for the combination of
+unique physical phenomena offered by the both fields of magnetism and
+superconductivity. It was shown recently that spin waves can be efficiently
+scattered in such structures by a lattice of static or moving magnetic flux
+quanta (Abrikosov vortices), resulting in bandgaps in the spin-wave spectra.
+Here, we realize a nonreciprocal motion of a vortex lattice in nanoengineered
+symmetric and asymmetric pinning landscapes and investigate the non-reciprocal
+scattering of magnons on fluxons. We demonstrate that the magnon bandgap
+frequencies can be tuned by the application of a low-dissipative transport
+current and by its polarity reversal. Furthermore, we exploit the rectifying
+(vortex diode or ratchet) effect by the application of a 100 MHz-frequency ac
+current to deliberately realize bandgap up- or downshifts during one ac
+halfwave while keeping the bandgap frequency constant during the other ac
+halfwave. The investigated phenomena allow for the realization of
+energy-efficient hybrid magnonic devices, such as microwave filters with an
+ultra-high bandgap tunability of 10 GHz/mA and a fast modulation of the
+transmission characteristics on the 10 ns time scale.",2107.04095v1
+2021-07-23,Green's function formalism for nonlocal elliptical magnon transport,"We develop a non-equilibrium Green's function formalism to study magnonic
+spin transport through a strongly anisotropic ferromagnetic insulator contacted
+by metallic leads. We model the ferromagnetic insulator as a finite-sized
+one-dimensional spin chain, with metallic contacts at the first and last sites
+that inject and detect spin in the form of magnons. In the presence of
+anisotropy, these ferromagnetic magnons become elliptically polarized, and spin
+conservation is broken. We show that this gives rise to a novel parasitic spin
+conductance, which becomes dominant at high anisotropy. Moreover, the spin
+state of the ferromagnet becomes squeezed in the high-anisotropy regime. We
+show that the squeezing may be globally reduced by the application of a local
+spin bias.",2107.11072v2
+2021-08-04,Theory of Huge Thermoelectric Effect Based on Magnon Drag Mechanism: Application to Thin-Film Heusler Alloy,"To understand the unexpectedly high thermoelectric performance observed in
+the thin-film Heusler alloy Fe$_2$V$_{0.8}$W$_{0.2}$Al, we study the magnon
+drag effect, generated by the tungsten based impurity band, as a possible
+source of this enhancement, in analogy to the phonon drag observed in FeSb$_2$.
+Assuming that the thin-film Heusler alloy has a conduction band integrating
+with the impurity band, originated by the tungsten substitution, we derive the
+electrical conductivity $L_{11}$ based on the self-consistent t-matrix
+approximation and the thermoelectric conductivity $L_{12}$ due to magnon drag,
+based on the linear response theory, and estimate the temperature dependent
+electrical resistivity, Seebeck coefficient and power factor. Finally, we
+compare the theoretical results with the experimental results of the thin-film
+Heusler alloy to show that the origin of the exceptional thermoelectric
+properties is likely to be due to the magnon drag related with the
+tungsten-based impurity band.",2108.01880v1
+2021-08-04,Spin interactions and topological magnonics in chromium trihalide CrClBrI,"The discovery of spontaneous magnetism in van der Waal (vdW) magnetic
+monolayers has opened up an unprecedented platform for investigating magnetism
+in purely two-dimensional systems. Recently, it has been shown that the
+magnetic properties of vdW magnets can be easily tuned by adjusting the
+relative composition of halides. Motivated by these experimental advances, here
+we derive a model for a trihalide CrClBrI monolayer from symmetry principles
+and we find that, in contrast to its single-halide counterparts, it can display
+highly anisotropic nearest- and next-to-nearest neighbor Dzyaloshinskii-Moriya
+and Heisenberg interactions. Depending on the parameters, the DM interactions
+are responsible for the formation of exotic chiral spin states, such as
+skyrmions and spin cycloids, as shown by our Monte Carlo simulations. Focusing
+on a ground state with a two-sublattice unit cell, we find spin-wave bands with
+nonvanishing Chern numbers. The resulting magnon edge states yield a magnon
+thermal Hall conductivity that changes sign as function of temperature and
+magnetic field, suggesting chromium trihalides as a candidate for testing
+topological magnon transport in two-dimensional noncollinear spin systems.",2108.02165v4
+2021-08-06,Magnon transport in $\mathrm{\mathbf{Y_3Fe_5O_{12}}}$/Pt nanostructures with reduced effective magnetization,"For applications making use of magnonic spin currents damping effects, which
+decrease the spin conductivity, have to be minimized. We here investigate the
+magnon transport in an yttrium iron garnet thin film with strongly reduced
+effective magnetization. We show that in a three-terminal device the effective
+magnon conductivity can be increased by a factor of up to six by a current
+applied to a modulator electrode, which generates damping compensation above a
+threshold current. Moreover, we find a linear dependence of this threshold
+current on the applied magnetic field. We can explain this behavior by the
+reduced effective magnetization and the associated nearly circular
+magnetization precession.",2108.03263v1
+2021-08-18,Magnetoelastic coupling enabled tunability of magnon spin current generation in 2D antiferromagnets,"We theoretically investigate the magnetoelastic coupling (MEC) and its effect
+on magnon transport in two-dimensional antiferromagnets with a honeycomb
+lattice. MEC coeffcient along with magnetic exchange parameters and spring
+constants are computed for monolayers of transition metal trichalcogenides with
+N\'eel order ($\text{MnPS}_3$ and $\text{VPS}_3$) and zigzag order
+($\text{CrSiTe}_3$, $\text{NiPS}_3$ and $\text{NiPSe}_3$) by $ab$ $initio$
+calculations. Using these parameters, we predict that the spin-Nernst
+coefficient is significantly enhanced due to magnetoelastic coupling. Our study
+shows that although Dzyaloshinskii-Moriya interaction can produce spin Nernst
+effect in these materials, other mechanisms such as magnon-phonon coupling
+should be taken into account. We also demonstrate that the magnetic anisotropy
+is an important factor for control of magnon-phonon hybridization and
+enhancement of the Berry curvature and thus the spin-Nernst coefficient. Our
+results pave the way towards gate tunable spin current generation in 2D magnets
+by SNE via electric field modulation of MEC and anisotropy.",2108.07999v1
+2021-08-19,Perturbations of giant magnons and single spikes in $\mathbb R \times S^2$,"Perturbations of giant magnons and single spikes in a $2+1$ dimensional
+$\mathbb R \times S^2$ background spacetime are analysed. Using the form of the
+giant magnon solution in the Jevicki-Jin gauge,the well-known Jacobi equation
+for small normal deformations of an embedded time-like surface are written
+down. Surprisingly, this equation reduces to a simple wave equation in a
+Minkowski background. The finiteness of perturbations and the ensuing stability
+of such giant magnons under small deformations are then discussed. It turns out
+that only the zero mode has finite deformations and is stable. Thereafter, we
+move on to explore the single spike solution in the Jevicki-Jin gauge. We
+obtain and solve the perturbation equation numerically and address stability
+issues.",2108.08622v1
+2021-09-01,Thermal Hall effect of magnons in collinear antiferromagnetic insulators: signatures of magnetic and topological phase transitions,"We demonstrate theoretically that the thermal Hall effect of magnons in
+collinear antiferromagnetic insulators is an indicator of magnetic and
+topological phase transitions in the magnon spectrum. The transversal heat
+current of magnons caused by a thermal gradient is calculated for an
+antiferromagnet on a honeycomb lattice. An applied magnetic field drives the
+system from the antiferromagnetic phase via a spin-flop phase into the
+field-polarized phase. Besides these magnetic phase transitions we find
+topological phase transitions within the spin-flop phase. Both types of
+transitions manifest themselves in prominent and distinguishing features in the
+thermal conductivities; depending on the temperature, the conductivity changes
+by several orders of magnitude, providing a tool to discern experimentally the
+two types of phase transitions. We include numerical results for the van der
+Waals magnet MnPS$_3$.",2109.00278v1
+2021-09-14,Magnon Condensation in Dimerized Antiferromagnets with Spin-Orbit Coupling,"Bose-Einstein condensation (BEC) of triplet excitations triggered by a
+magnetic field, sometimes called magnon BEC, in dimerized antiferromagnets
+gives rise to a long-range antiferromagnetic order in the plane perpendicular
+to the applied magnetic field. To explore the effects of spin-orbit coupling on
+magnon condensation, we study a spin model on a distorted honeycomb lattice
+with dimerized Heisenberg exchange ($J$ terms) and uniform off-diagonal
+exchange ($\Gamma'$ terms) interactions. Via variational Monte Carlo
+calculations and spin-wave theory, we find that an out-of-plane magnetic field
+can induce different types of long-range magnetic orders, no matter if the
+ground state is a non-magnetic dimerized state or an ordered N\'{e}el state.
+Furthermore, the critical properties of field-driven phase transitions in the
+presence of spin-orbit couplings, as illustrated from spin-wave spectrum and
+interpreted by effective field theory, can be different from the conventional
+magnon BEC. Our study is helpful to understand the rich phases of spin-orbit
+coupled antiferromagnets induced by magnetic fields.",2109.06518v2
+2021-09-30,Interaction of magnons with plasmons in a system of antiferromagnetic insulators coupled to a superconductor microwave cavity through the interfacial exchange interaction,"A superconductor can interact with magnets through the magnetic field which
+is induced by the supercurrent. However, this interaction is rather weak and
+requires relatively large magnets to reach a sizable hybridization of microwave
+electromagnetic modes with magnons. The size of the device can be drastically
+reduced by means of the large interfacial exchange interaction between spins in
+a magnet and a superconductor. In the spin-orbit coupled superconductor this
+interaction can be transmitted to the s-wave condensate through a mixing of
+triplet and singlet Cooper pairs. In this paper we theoretically consider thin
+antiferromagnetic films, which make a spin compensated contact to a
+superconducting wire, which forms a cavity for Mooij-Sch\""{o}n plasma waves.
+The effective Lagrangian is derived where the interaction of these waves with
+magnons is taken into account. Frequencies of hybrid magnon-plasmon modes are
+calculated. A system of two micromagnets placed far apart are also considered
+and their mutual coupling through the cavity mode is calculated.",2109.14973v1
+2021-09-30,Optomagnonic Josephson effect in antiferromagnets,"Combining advanced technologies of optics and antiferromagnetic spintronics,
+we present a method to realize ultrafast spin transport. The optical Barnett
+effect provokes quasiequilibrium Bose-Einstein condensates (BECs) of magnons
+associated with the fully spin-polarized state in insulating antiferromagnets
+(AFs). This optomagnonic Barnett effect enables us to exploit coherent magnons
+of high frequency over the conventional ones of (sub-) terahertz associated
+with the N\'eel magnetic order. We show that the macroscopic coherence of those
+optical magnon BECs induces a spin current across the junction interface of
+weakly coupled two insulating AFs, and this optomagnonic Josephson effect
+realizes ultrafast spin transport. The period of the optomagnonic Josephson
+oscillation is much shorter than the conventional one of the order of
+picoseconds. Thus we propose a way to realize ultrafast spin transport in AFs
+by means of the macroscopic coherence of optical magnon BECs.",2109.15202v1
+2021-10-21,Multi-magnon quantum many-body scars from tensor operators,"We construct a family of three-body spin-1/2 Hamiltonians with a
+super-extensive set of infinitely long-lived multi-magnon states. A magnon in
+each such state carries either quasi-momentum zero or fixed $p_0\neq$ 0, and
+energy $\Omega$ . These multi-magnon states provide an archetypal example of
+quantum many-body scars: they are eigenstates at finite energy density that
+violate the eigenstate thermalization hypothesis, and lead to persistent
+oscillations in local observables in certain quench experiments. On the
+technical side, we demonstrate the systematic derivation of scarred
+Hamiltonians that satisfy a restricted spectrum generating algebra using an
+operator basis built out of irreducible tensor operators. This operator basis
+can be constructed for any spin, spatial dimension or continuous non-Abelian
+symmetry that generates the scarred subspace.",2110.11448v3
+2021-10-27,Interface modes in planar one-dimensional magnonic crystals,"We present the concept of Zak phase for spin waves in planar magnonic
+crystals and discuss the conditions for the existence of interface modes
+localized on the boundary between two magnonic crystals with centrosymmetric
+unit cells. Using the symmetry criterion and the calculated logarithmic
+derivative of the Bloch function we study the interface modes to demonstrate
+the bulk-edge correspondence. Our theoretical results are verified numerically
+for structures in the exchange and exchange-dipolar regimes and extended to the
+case in which one of the magnonic crystals has an arbitrary unit cell.
+Moreover, we show that by shifting the unit cell the interface modes can be
+caused to traverse the bandgap edges.",2110.14726v4
+2021-11-01,Long-Time Memory and Ternary Logic Gate Using a Multistable Cavity Magnonic System,"Multistability is an extraordinary nonlinear property of dynamical systems
+and can be explored to implement memory and switches. Here we experimentally
+realize the tristability in a three-mode cavity magnonic system with Kerr
+nonlinearity. The three stable states in the tristable region correspond to the
+stable solutions of the frequency shift of the cavity magnon polariton under
+specific driving conditions. We find that the system staying in which stable
+state depends on the history experienced by the system, and this state can be
+harnessed to store the history information. In our experiment, the memory time
+can reach as long as 5.11 s. Moreover, we demonstrate the ternary logic gate
+with good on-off characteristics using this multistable hybrid system. Our new
+findings pave a way towards cavity magnonics-based information storage and
+processing.",2111.01558v1
+2021-11-10,Light propagation and magnon-photon coupling in optically dispersive magnetic media,"Achieving strong coupling between light and matter excitations in hybrid
+systems is a benchmark for the implementation of quantum technologies. We
+recently proposed [arXiv:2110.02984] that strong single-particle coupling
+between magnons and light can be realized in a magnetized epsilon-near-zero
+(ENZ) medium, in which magneto-optical effects are enhanced. Here we present a
+detailed derivation of the magnon-photon coupling Hamiltonian in dispersive
+media both for degenerate and non-degenerate optical modes, and show the
+enhancement of the coupling near the ENZ frequency. Moreover, we show that the
+coupling of magnons to plane-wave non-degenerate Voigt modes vanishes at
+specific frequencies due to polarization selection rules tuned by dispersion.
+Finally, we present specific results using a Lorentz dispersion model. Our
+results pave the way for the design of dispersive optomagnonic systems,
+providing a general theoretical framework for describing engineering ENZ-based
+optomagnonic systems.",2111.05851v1
+2021-11-11,Anomalous Thermal Hall Effect in an Insulating van der Waals Magnet VI3,"Two-dimensional (2D) van der Waals (vdW) magnets have been a fertile
+playground for the discovery and exploration of physical phenomena and new
+physics. In this Letter, we report the observation of an anomalous thermal Hall
+effect (THE) with \k{appa}_xy ~ 1x10^(-2) W K^(-1) m^(-1) in an insulating van
+der Waals ferromagnet VI3. The thermal Hall signal persists in the absence of
+an external magnetic field and flips sign upon the switching of the
+magnetization. In combination with theoretical calculations, we show that VI3
+exhibits a dual nature of the THE, i.e., dominated by topological magnons
+hosted by the ferromagnetic honeycomb lattice at higher temperatures and by
+phonons induced by the magnon-phonon coupling at lower temperatures. Our
+results not only position VI3 as the first ferromagnetic system to investigate
+both anomalous magnon and phonon THEs, but also render it as a potential
+platform for spintronics/magnonics applications.",2111.06039v1
+2021-11-12,Classical analog of qubit logic based on a magnon Bose-Einstein condensate,"We present a classical version of several quantum bit (qubit) functionalities
+using a two-component magnon Bose-Einstein condensate formed at opposite
+wavevectors in a room-temperature yttrium-iron-garnet ferrimagnetic film. The
+macroscopic wavefunctions of these two condensates serve as orthonormal basis
+states that form a system being a classical counterpart of a single qubit.
+Solving the Gross-Pitaevskii equation and employing micromagnetic numerical
+simulations, we first show how to initialize the system in one of the basis
+states: the application of wavevector-selective parallel parametric pumping
+allows us to form only a single condensate in one of the two lowest energy
+states of the magnon gas. Next, by translating the concept of Rabi-oscillations
+into the wavevector domain, we demonstrate how to manipulate the magnon-BEC
+system along the polar axis in the Bloch sphere representation. We also discuss
+the manipulation regarding the azimuthal angle.",2111.06798v2
+2021-12-06,Accumulation of magnetoelastic bosons in yttrium iron garnet: kinetic theory and wave vector resolved Brillouin light scattering,"We derive and solve quantum kinetic equations describing the accumulation of
+magnetoelastic bosons in an overpopulated magnon gas realized in a thin film of
+the magnetic insulator yttrium iron garnet. We show that in the presence of a
+magnon condensate, there is a non-equilibrium steady state in which incoherent
+magnetoelastic bosons accumulate in a narrow region in momentum space for
+energies slightly below the bottom of the magnon spectrum. The results of our
+calculations agree quite well with Brillouin light scattering measurements of
+the stationary non-equilibrium state of magnons and magnetoelastic bosons in
+yttrium iron garnet.",2112.03310v2
+2021-12-14,Essential model parameters for nonreciprocal magnons in multisublattice systems,"We theoretically investigate the microscopic conditions for emergent
+nonreciprocal magnons toward unified understanding on the basis of a
+microscopic model analysis. We show that the products of the Bogoliubov
+Hamiltonian obtained within the linear spin wave approximation is enough to
+obtain the momentum-space functional form and the key ingredients in the
+nonreciprocal magnon dispersions in an analytical way even without solving the
+eigenvalue problems. We find that the odd order of an effective antisymmetric
+Dzyaloshinskii-Moriya interaction and/or the even order of an effective
+symmetric anisotropic interaction in the spin rotated frame can be a source of
+the antisymmetric dispersions. We present possible kinetic paths of magnons
+contributing to the antisymmetric dispersions in the one- to four-sublattice
+systems with the general exchange interactions. We also test the formula for
+both ferromagnetic and antiferromagnetic orderings in the absence of spatial
+inversion symmetry.",2112.07071v1
+2022-01-25,Protocol for generating an arbitrary quantum state of the magnetization in cavity magnonics,"We propose and numerically evaluate a protocol to generate an arbitrary
+quantum state of the magnetization in a magnet. The protocol involves
+repeatedly exciting a frequency-tunable superconducting transmon and
+transferring the excitations to the magnet via a microwave cavity. To avoid
+decay, the protocol must be much shorter than magnon lifetime. Speeding up the
+protocol by simply shortening the pulses leads to non-resonant leakage of
+excitations to higher levels of the transmon accompanied by higher decoherence.
+We discuss how to correct for such leakages by applying counter pulses to
+de-excite these higher levels. In our protocol, states with a maximum magnon
+occupation of up to $\sim9$ and average magnon number up to $\sim4$ can be
+generated with fidelity $>0.75$.",2201.10170v1
+2022-02-06,Coexistence of coupling-induced transparency and absorption of transmission signals in magnon-mediated photon-photon coupling,"Coexistence of coupling-induced transparency (CIT) and absorption (CIA) of
+signals in magnon-mediated photon-photon coupling was experimentally determined
+in a planar hybrid structure consisting of a yttrium iron garnet (YIG) film and
+three concentric inverted-split-ring resonators (ISRRs). The experimental
+observation of simultaneous CIT and CIA phenomena was ascribed to
+magnon-mediated photon-photon coupling between the individually decoupled
+ISRRs. In order to capture the generic physics of the observed interactions, we
+constructed an appropriate analytical model based on the balance between the
+coherent and dissipative multiple-paths interactions, which model precisely
+reproduced both the CIT and CIA experimentally observed from a single hybrid
+system. This work, promisingly, can provide guidance for design of efficient,
+flexible, and well-controllable photon-magnonic devices that are highly in
+demand for applications to quantum technologies currently under development.",2202.02667v1
+2022-02-17,Higher-order Topological Phases of Magnons in van der Waals Honeycomb Ferromagnets,"We theoretically propose a second-order topological magnon insulator by
+stacking the van der Waals honeycomb ferromagnets with antiferromagnetic
+interlayer coupling. The system exhibits Z$_{2}$ topological phase, protected
+by pseudo-time-reversal symmetry (PTRS). An easy-plane anisotropy term breaks
+PTRS and destroys the topological phase. Nevertheless, it respects a magnetic
+two-fold rotational symmetry which protects a second-order topological phase
+with corner modes in bilayer and hinge modes along stacking direction.
+Moreover, an introduced staggered interlayer coupling establishes a
+Z$_{2}$$\times$Z topology, giving rise to gapped topological surface modes
+carrying non-zero Chern numbers. Consequently, chiral hinge modes propagate
+along the horizontal hinges in a cuboid geometry and are robust against
+disorders. Our work bridges the higher-order topology and magnons in van der
+Waals platforms, and could be used for constructing topological magnonic
+devices.",2202.08424v1
+2022-03-11,Laser induced enhanced coupling between photons and squeezed magnons in antiferromagnets,"In this paper we consider a honeycomb antiferromagnet subject to an external
+laser field. Obtaining a time-independent effective Hamiltonian, we find that
+the external laser renormalizes the exchange interaction between the in-plane
+components of the spin-operators, and induces a synthetic Dzyaloshinskii-Moria
+interaction (DMI) between second neighbors. The former allows the control of
+the magnon dispersion's bandwidth and the latter breaks time-reversal symmetry
+inducing non-reciprocity in momentum space. The eigen-excitations of the system
+correspond to squeezed magnons whose squeezing parameters depend on the
+properties of the laser. When studying how these spin excitations couple with
+cavity photons, we obtain a coupling strength which can be enhanced by an order
+of magnitude via careful tuning of the laser's intensity, when compared to the
+case where the laser is absent. The transmission plots through the cavity are
+presented, allowing the mapping of the magnons' dispersion relation.",2203.05809v1
+2022-03-15,Topological magnon band structure of emergent Landau levels in a skyrmion lattice,"The motion of a spin excitation across topologically non-trivial magnetic
+order exhibits a deflection that is analogous to the effect of the Lorentz
+force on an electrically charged particle in an orbital magnetic field. We used
+polarized inelastic neutron scattering to investigate the propagation of
+magnons (i.e., bosonic collective spin excitations) in a lattice of skyrmion
+tubes in manganese silicide. For wave vectors perpendicular to the skyrmion
+tubes, the magnon spectra are consistent with the formation of finely spaced
+emergent Landau levels that are characteristic of the fictitious magnetic field
+used to account for the nontrivial topological winding of the skyrmion lattice.
+This provides evidence of a topological magnon band structure in reciprocal
+space, which is borne out of the nontrivial real-space topology of a magnetic
+order.",2203.08159v1
+2022-03-21,Antiferromagnetic cavity magnon polaritons in collinear and canted phases of hematite,"Cavity spintronics explores light matter interactions at the interface
+between spintronic and quantum phenomena. Until now, studies have focused on
+the hybridization between ferromagnets and cavity photons.In this article, we
+realize antiferromagnetic cavity-magnon polaritons. The collective spin motion
+in single hematite crystals ({\alpha}-Fe2O3) hybridizes with 18 - 45 GHz
+microwave cavity photons with required specific symmetries. We show
+theoretically and experimentally that the photon-magnon coupling in the
+collinear phase is mediated by the dynamical Neel vector and the weak magnetic
+moment in the canted phase by measuring across the Morin transition. The
+coupling strength g is shown to scale with the anisotropy field in the
+collinear phase and with the Dzyaloshinskii-Moriya field in the canted phase.
+We achieve a strong coupling regime both in canted (C > 25 at 300 K) and
+noncolinear phases (C > 4 at 150 K) and thus coherent information exchange with
+antiferromagnets These results evidence a generic strategy to achieve
+cavity-magnon polaritons in antiferromagnets for different symmetries, opening
+the field of cavity spintronics to antiferromagnetic materials.",2203.10924v1
+2022-03-29,Orbital Angular Momentum of Magnons in Collinear Magnets,"We study the orbital angular momentum of magnons for collinear ferromagnet
+(FM) and antiferromagnetic (AF) systems with nontrivial networks of exchange
+interactions. The orbital angular momentum of magnons for AF and FM zig-zag and
+honeycomb lattices becomes nonzero when the lattice contains two inequivalent
+sites and is largest at the avoided-crossing points or extremum of the
+frequency bands. Hence, the arrangement of exchange interactions may play a
+more important role at producing the orbital angular momentum of magnons than
+the spin-orbit coupling energy and the resulting non-collinear arrangement of
+spins.",2203.15677v3
+2022-04-06,Magnon mediated spin entanglement in the strong coupling regime,"We present that two spin defects (SDs) can be entangled through a magnon
+polariton mode, within the strong coupling regime. The magnonic modes are
+provided by an antiferromagnetic (AF) MnF$_{2}$ layer and their dispersion is
+characterized by the layer's thickness. The macroscopic quantum electrodynamics
+theory is used to describe the light-matter interactions, where the Green's
+functions are its core element. The individual SD relaxes by exciting the
+magnon polariton modes, exhibiting high enhancement values of the Purcell
+factor. When two SDs are considered, an oscillatory population exchange is
+observed between them, a sign of strong light-matter coupling, where the
+concurrence value is used to quantify the level of entanglement. The thinner AF
+layers can potentially be used to promote interactions between multiple spins
+through long range coupling, this is a desired feature to fabricate high demand
+applications in the fields of quantum measurement and computation.",2204.02533v1
+2022-04-26,Spin waves and magnetic exchange Hamiltonian in CrSBr,"CrSBr is an air-stable 2D van der Waals semiconducting magnet with great
+technological promise, but its atomic-scale magnetic interactions -- crucial
+information for high-frequency switching -- are poorly understood. We present
+an experimental study to determine the CrSBr magnetic exchange Hamiltonian and
+bulk magnon spectrum. We confirm the $A$-type antiferromagnetic order using
+single crystal neutron diffraction. We also measure the magnon dispersions
+using inelastic neutron scattering and rigorously fit the excitation modes to a
+spin wave model. The magnon spectrum is well described by an intra-plane
+ferromagnetic Heisenberg exchange model with seven nearest in-plane exchanges.
+This fitted exchange Hamiltonian enables theoretical predictions of CrSBr
+behavior: as one example, we use the fitted Hamiltonian to predict the presence
+of chiral magnon edge modes with a spin-orbit enhanced CrSBr heterostructure.",2204.12461v2
+2022-04-27,Beating Fabry-Pérot interference pattern in a magnonic scattering junction in the graphene quantum Hall ferromagnet,"At filling factor $\nu=0,\pm1$, the ground state of graphene is a particular
+SU(4) ferromagnet which hosts a rich phase diagram along with several spin,
+pseudospin or ""entanglement"" magnon modes. Motivated by recent experiments, we
+study a $\nu=-1|0|-1$ Fabry-P\'erot magnonic junction. If the ground state at
+$\nu=0$ is spin polarized, there exist two spin modes which interfere and
+create a beating pattern, while pseudospin modes are reflected. The same
+scenario occurs for pseudospin magnon if the $\nu=0$ ground state is pseudospin
+polarized. The observation of such an interference pattern would provide
+information on the low-energy anisotropies and thus on the ground state.",2204.12795v2
+2022-04-29,Electrically Active Domain Wall Magnons in Layered van der Waals Antiferromagnets,"We study theoretically domain wall (DW) magnons-elementary collective
+excitations of magnetic DWs -- in easy-axis layered van der Waals (vdW)
+antiferromagnets, where they behave as normal modes of coupled spin
+superfluids. We uncover that, due to spin-charge coupling in vdW magnets, such
+DW magnons can be activated by voltage-induced torques, thereby providing a
+path for their low-dissipation and nanoscale excitation. Moreover, the
+electrical activation and the number of DW magnons at a frequency can be
+controlled by applying symmetry-breaking static magnetic field, adding
+tunability of signal transmission by them. Our results highlight that domain
+walls in vdW magnets provide a promising platform to route coherent spin
+information for a broad range of explorations in spintronics and magnetism.",2204.13909v1
+2022-05-12,Violation of the magnonic Wiedemann-Franz law in the strong nonlinear regime,"The celebrated Wiedemann-Franz (WF) law which governs the relation between
+charge and heat transport traces back to the experimental discovery in 1853 by
+Wiedemann and Franz. Despite the fundamental difference of the
+quantum-statistical properties between fermions and bosons, the linear-in-$T$
+behavior of the WF law at low temperatures has recently been found to be the
+universal property by the discovery of the WF law for magnon transport.
+However, the WF law is for the linear response, and whether or not the
+universal law is valid even in the nonlinear regime of Bose systems remains an
+open issue. Here we provide a solution to this fundamental challenge. We show
+that the ratio of the thermal to spin transport coefficient of magnons in
+topologically trivial insulating magnets exhibits a different behavior from the
+linear response and the universal law breaks down in the strong nonlinear
+regime. This finding is within experimental reach with current device and
+measurement technologies. Our discovery is the key ingredient in magnon-based
+spintronics, in the evaluation of the figure of merit for thermomagnetic
+conversion elements of spintronics devices.",2205.06366v1
+2022-06-16,Defect-induced edge ferromagnetism and fractional spin excitations of the SU(4) $π$-flux Hubbard model on honeycomb lattice,"Recently, a SU(4) $\pi$-flux Hubbard model on the honeycomb lattice has been
+proposed to study the spin-orbit excitations of $\alpha$-ZrCl$_3$
+[Phys.~Rev.~Lett. 121.097201~(2017)]. Based on this model with a zigzag edge,
+we show the edge defects can induce edge flat bands that result in a SU(4) edge
+ferromagnetism. We develop an effective one-dimensional interaction Hamiltonian
+to study the corresponding SU(4) spin excitations. Remarkably, SU(4) spin
+excitations of the edge ferromagnet appear as a continuum covering the entire
+energy region rather than usual magnons. Through further entanglement entropy
+analysis, we suggest that the continuum consists of fractionalized spin
+excitations from the disappeared magnons, except for that from the
+particle-hole Stoner excitations. Moreover, in ribbon systems with finite
+widths, the disappeared magnons can be restored in the gap formed by the
+finite-size effect and the optical branch of the restored magnons are found to
+be topological nontrivial.",2206.08036v1
+2022-06-24,Ground state selection by magnon interactions in the fcc antiferromagnet,"We study the nearest-neighbor Heisenberg antiferromagnet on a face-centered
+cubic lattice with arbitrary spin S. The model exhibits degenerate classical
+ground states including two collinear structures AF1 and AF3 described by
+different propagation vectors that are prime candidates for the quantum ground
+state. We compute the energy for each of the two states as a function of S
+using the spin-wave theory that includes magnon-magnon interaction in a
+self-consistent way and the numerical coupled cluster method. Our results
+unambiguously demonstrate that quantum fluctuations stabilize the AF1 state for
+realistic values of spin. Transition to the harmonic spin-wave result, which
+predicts the AF3 state, takes place only for S > 10. We also study quantum
+renormalization of the magnon spectra for both states as a function of spin.",2206.12102v1
+2022-06-29,Mechanical Bistability in Kerr-modified Cavity Magnomechanics,"Bistable mechanical vibration is observed in a cavity magnomechanical system,
+which consists of a microwave cavity mode, a magnon mode, and a mechanical
+vibration mode of a ferrimagnetic yttrium-iron-garnet (YIG) sphere. The
+bistability manifests itself in both the mechanical frequency and linewidth
+under a strong microwave drive field, which simultaneously activates three
+different kinds of nonlinearities, namely, magnetostriction, magnon self-Kerr,
+and magnon-phonon cross-Kerr nonlinearities. The magnon-phonon cross-Kerr
+nonlinearity is first predicted and measured in magnomechanics. The system
+enters a regime where Kerr-type nonlinearities strongly modify the conventional
+cavity magnomechanics that possesses only a radiation-pressure-like
+magnomechanical coupling. Three different kinds of nonlinearities are
+identified and distinguished in the experiment. Our work demonstrates a new
+mechanism for achieving mechanical bistability by combining magnetostriction
+and Kerr-type nonlinearities, and indicates that such Kerr-modified cavity
+magnomechanics provides a unique platform for studying many distinct
+nonlinearities in a single experiment.",2206.14588v2
+2022-06-29,Spin-Wave Optics in YIG by Ion-Beam Irradiation,"We demonstrate direct focused ion beam (FIB) writing as an enabling
+technology for realizing spin-wave-optics devices. It is shown that ion-beam
+irradiation changes the characteristics of YIG films on a submicron scale in a
+highly controlled way, allowing to engineer the magnonic index of refraction
+adapted to desired applications. This technique does not physically remove
+material, and allows rapid fabrication of high-quality architectures of
+modified magnetization in magnonic media with minimal edge damage (compared to
+more common techniques such as etching or milling). By experimentally showing
+magnonic versions of a number of optical devices (lenses, gratings,
+Fourier-domain processors) we envision this technology as the gateway to
+building magnonic computing devices that rival their optical counterparts in
+their complexity and computational power.",2206.14696v1
+2022-07-06,Topological magnons on the triangular kagome lattice,"We present the topology of magnons on the triangular kagome lattice (TKL) by
+calculating its Berry curvature, Chern number and edge states. In addition to
+the ferromagnetic state, the TKL hosts ferrimagnetic ground state as its two
+sublattices can couple with each other either ferromagnetically or
+antiferromagnetically. Using Holstein-Primakoff (HP) boson theory and Green's
+function approach, we find that the TKL has a rich topological band structure
+with added high Chern numbers compared with the kagome and honeycomb lattices.
+The magnon edge current allows a convenient calculation of thermal Hall
+coefficients and the orbital angular momentum gives correlation to the
+Einstein-de Haas effect. We apply the calculations to the TKL and derive the
+topological gyromagnetic ratio showing a nonzero Einstein-de Haas effect in the
+zero temperature limit. Our results render the TKL as a potential platform for
+quantum magnonics applications including high-precision mechanical sensors and
+information transmission.",2207.02886v2
+2022-07-26,Anderson-Higgs mass of magnons in superconductor/ferromagnet/superconductor systems,"Anderson-Higgs mechanism of mass generation is a generic concept in
+high-energy and condensed matter physics. It shows up through the Meissner
+effect providing the expulsion of static and low-frequency magnetic fields from
+superconductors. However, it does not affect propagating electromagnetic waves
+with a spectrum gap determined by the plasma frequency, which is too large to
+be sensitive to the superconducting transition. Here we demonstrate the
+spectroscopic manifestation of the Anderson-Higgs mass, showing that it
+determines the spectrum gap of magnons in
+superconductor/ferromagnet/superconductor multilayers. Moreover, we show that
+this effect has been observed in recent experiments as a spontaneous
+ferromagnetic resonance frequency shift in such systems. Our theory explains
+many unusual experimental features and suggests effective controls over the
+magnon spectrum with tunable spectral gap and group-velocity reversal. These
+findings pave the way to a wide range of advanced functionalities for possible
+applications in magnonics.",2207.13201v2
+2022-08-22,Magnetically Tuned Continuous Transition from Weak to Strong Coupling in Terahertz Magnon Polaritons,"Depending on the relative rates of coupling and dissipation, a light-matter
+coupled system is either in the weak- or strong-coupling regime. Here, we
+present a unique system where the coupling rate continuously increases with an
+externally applied magnetic field while the dissipation rate remains constant,
+allowing us to monitor a weak-to-strong coupling transition as a function of
+magnetic field. We observed a Rabi splitting of a terahertz magnon mode in
+yttrium orthoferrite above a threshold magnetic field of ~14 T. Based on a
+microscopic theoretical model, we show that with increasing magnetic field the
+magnons transition into magnon polaritons through an exceptional point, which
+will open up new opportunities for in situ control of non-Hermitian systems.",2208.10030v1
+2022-08-23,Reversal of nanomagnets by propagating magnons in ferrimagnetic yttrium iron garnet enabling nonvolatile magnon memory,"Despite the unprecedented downscaling of CMOS integrated circuits,
+memory-intensive machine learning and artificial intelligence applications are
+limited by data conversion between memory and processor. There is a challenging
+quest for novel approaches to overcome this so-called von Neumann bottleneck.
+Magnons are the quanta of spin waves and transport angular momenta through
+magnets. They enable power-efficient computation without charge flow and would
+solve the conversion problem if spin wave amplitudes could be stored directly
+in a magnetic memory cell. Here, we report the reversal of ferromagnetic
+nanostripes by spin waves which propagate through an underlying spin-wave bus
+made from yttrium iron garnet. Thereby, the charge-free angular momentum flow
+is stored after transmission over a macroscopic distance. We show that spin
+waves can reverse large arrays of ferromagnetic stripes at a strikingly small
+power level of nW. Combined with the already existing wave logic, our discovery
+is path-breaking for the new era of magnonics-based in-memory computation and
+beyond von Neumann computer architectures.",2208.10923v1
+2022-08-23,Field-induced spin nematic Tomonaga-Luttinger liquid of the $S=1/2$ spin ladder system with the anisotropic ferromagnetic rung interaction,"The $S=1/2$ quantum spin ladder system with the anisotropic ferromagnetic
+exchange interaction on the rung under magnetic field is investigated using the
+numerical diagonalization and the density matrix renormalization group (DMRG)
+analyses. It is found that the nematic-spin-correlation-dominant
+Tomonaga-Luttinger liquid (TLL) appears in some high magnetic field. It is
+included in the TLL phase where the two-magnon bound state is realized. For
+some suitable parameters, after the field-induced phase transition from this
+two-magnon-bound TLL phase to the single-magnon TLL one, the re-entrant
+transition to the two-magnon-bound TLL phase occurs, which is confirmed by the
+magnetization curves by the DMRG. Several phase diagrams on the plane of the
+coupling anisotropy versus the magnetization and the magnetic field are
+presented. The present result is a proposal of the candidate system which
+exhibits the spin nematic phase without the biquadratic interaction or the
+frustration.",2208.10994v1
+2022-09-14,Generation of Spin-Wave Pulses by Inverse Design,"The development of fast magnonic information processing nanodevices requires
+operating with short spin-wave pulses, but, the shorter the pulses, the more
+affected they are by information loss due to broadening and dispersion. The
+capability of engineering spin-wave pulses and controlling their propagation
+could solve this problem. Here, we provide a method to generate linear
+spin-wave pulses with a desired spatial-temporal profile in magnonic waveguides
+based on inverse design. As relevant examples, we theoretically predict that
+both rectangular and self-compressing spin-wave pulses can be generated in
+state-of-the-art waveguides with fidelities >96% using narrow stripline
+antennas. The method requires minimal computational overhead and is universal,
+i.e., it applies to arbitrary targeted pulse shapes, type of waves (exchange or
+dipolar), waveguide materials, and waveguide geometries. It can also be
+extended to more complex magnonic structures. Our results could lead to the
+utilization of large-scale magnonic circuits for classical and quantum
+information processing.",2209.06608v1
+2022-10-14,Transversal transport of magnons in a modified Lieb lattice,"We studied a two-band magnon insulating model whose geometry is that of a
+modified Lieb lattice in which one of the sites was removed. Anisotropic
+ferromagnetic exchange interactions exist between the three nearest neighbors,
+and the anisotropy opens a gap in the magnon energy band structure. A
+non-vanishing Berry curvature is induced by a Dzyaloshinskii-Moriya interaction
+(DMI). The topology of the bands is trivial (in the sense of a null Chern
+number), but the finite Berry curvature induces Hall-like transport effects
+whose coefficients were calculated. Their dependence on temperature was studied
+and shows a resemblance with other magnon insulating systems found in the
+literature. The dependence on exchange couplings, DMI parameter, and external
+magnetic field was also investigated.",2210.07757v2
+2022-10-21,Easy-plane antiferromagnet in tilted field: gap in magnon spectrum and susceptibility,"Motivated by recent experimental data on dichloro-tetrakis thiourea-nickel
+(DTN) [T.A. Soldatov $\textit{et al}$, Phys. Rev. B ${\bf 101}$, 104410
+(2020)], a model of antiferromagnet on a tetragonal lattice with single-ion
+easy-plane anisotropy in the tilted external magnetic field is considered.
+Using the smallness of the in-plane field component, we analytically address
+field dependence of the energy gap in ``acoustic'' magnon mode and transverse
+uniform magnetic susceptibility in the ordered phase. It is shown that the
+former is non-monotonic due to quantum fluctuations, which was indeed observed
+experimentally. The latter is essentially dependent on the ``optical'' magnon
+rate of decay on two magnons. At magnetic fields close to the one which
+corresponds to the center of the ordered phase, it leads to experimentally
+observed dynamical diamagnetism phenomenon.",2210.12058v1
+2022-10-27,Quantum-state engineering in cavity magnomechanics formed by two-dimensional magnetic materials,"Cavity magnomechanics has become an ideal platform to explore macroscopic
+quantum effects. Bringing together magnons, phonons, and photons in a system,
+it opens many opportunities for quantum technologies. It was conventionally
+realized by an yttrium iron garnet, which exhibits a parametric magnon-phonon
+coupling $\hat{m}^\dag\hat{m}(\hat{b}^\dag+\hat{b})$, with $\hat{m}$ and
+$\hat{b}$ being the magnon and phonon modes. Inspired by the recent realization
+of two-dimensional (2D) magnets, we propose a cavity magnomechanical system
+using a 2D magnetic material with both optical and magnetic drivings. It
+features the coexisting photon-phonon radiation-pressure coupling and quadratic
+magnon-phonon coupling $\hat{m}^\dag\hat{m}(\hat{b}^\dag+\hat{b})^2$ induced by
+the magnetostrictive interaction. A stable squeezing of the phonon and bi- and
+tri-partite entanglements among the three modes are generated in the regimes
+with a suppressed phonon number. Compared with previous schemes, ours does not
+require any extra nonlinear interaction and reservoir engineering and is robust
+against the thermal fluctuation. Enriching the realization of cavity
+magnomechanics, our system exhibits its superiority in quantum-state
+engineering due to the versatile interactions enabled by its 2D feature.",2210.15519v2
+2022-11-04,Pattern recognition with a magnon-scattering reservoir,"Magnons are elementary excitations in magnetic materials and undergo
+nonlinear multimode scattering processes at large input powers. In experiments
+and simulations, we show that the interaction between magnon modes of a
+confined magnetic vortex can be harnessed for pattern recognition. We study the
+magnetic response to signals comprising sine wave pulses with frequencies
+corresponding to radial mode excitations. Three-magnon scattering results in
+the excitation of different azimuthal modes, whose amplitudes depend strongly
+on the input sequences. We show that recognition rates above 95\% can be
+attained for four-symbol sequences using the scattered modes, with strong
+performance maintained with the presence of amplitude noise in the inputs.",2211.02328v1
+2022-11-07,Interaction of gapless spin waves and a domain wall in an easy-cone ferromagnet,"We theoretically study the interaction of spin waves and a domain wall in a
+quasi-one-dimensional easy-cone ferromagnet. The gapless spin waves on top of a
+domain wall are found to exhibit finite reflection in contrast to the
+well-known perfect transmission of gapful spin waves in easy-axis magnets.
+Based on the obtained scattering properties, we study the thermal-magnon-driven
+dynamics of a domain wall subjected to a thermal bias within the
+Landau-B\""uttiker formalism, where transmitted magnons are shown to exert the
+magnonic torque on the domain wall and thereby drive it with the velocity
+linear to the applied thermal bias. The peculiar gapless nature of spin waves
+in easy-cone magnets enables the thermally-driven domain-wall motion even at
+low temperatures, differing from the easy-axis case where the domain-wall
+velocity is exponentially suppressed at low temperatures. Our work suggests
+that easy-cone magnets can serve as a useful platform to study the interaction
+of gapless spin waves and nonlinear excitations and thereby realize
+low-temperature magnon-related phenomena.",2211.03331v1
+2022-11-10,Chiral coupling between a ferromagnetic magnon and a superconducting qubit,"Chiral coupling at the single-quantum level promises to be a remarkable
+potential for quantum information processing. Here we propose to achieve a
+chiral interaction between a magnon mode in a ferromagnetic sphere and a
+superconducting qubit mediated by a one-dimensional coupled-cavity array. When
+the qubit is coupled to two lattice sites of the array and each one is encoded
+with a tunable phase, we can acquire a directional qubit-magnon interaction via
+the quantum interference effect. This work opens up a new route to construct
+chiral devices, which are expected to become a building block in quantum
+magnonic networks.",2211.05285v2
+2022-12-03,Strong On-Chip Microwave Photon-Magnon Coupling Using Ultra-low Damping Epitaxial Y3Fe5O12 Films at 2 Kelvin,"Y3Fe5O12 is arguably the best magnetic material for magnonic quantum
+information science (QIS) because of its extremely low damping. We report
+ultralow damping at 2 K in epitaxial Y3Fe5O12 thin films grown on a diamagnetic
+Y3Sc2Ga3O12 substrate that contains no rare-earth elements. Using these
+ultralow damping YIG films, we demonstrate for the first time strong coupling
+between magnons in patterned YIG thin films and microwave photons in a
+superconducting Nb resonator. This result paves the road towards scalable
+hybrid quantum systems that integrate superconducting microwave resonators, YIG
+film magnon conduits, and superconducting qubits into on-chip QIS devices.",2212.01708v1
+2023-01-12,Towards Magnonic Logic and Neuromorphic Computing: Controlling Spin-Waves by Spin-Polarized Current,"Spin-waves (magnons) are among the prime candidates for building fast yet
+energy-efficient platforms for information transport and computing. We here
+demonstrate theoretically and in state-of-the-art micromagnetic simulation the
+effects that strategically-injected spin-polarized current can have on
+controlling magnonic transport. We reveal analytically that the Zhang-Li
+spin-transfer-torque induced by applied current is analogous to the
+Dzyaloshinskii-Moriya interaction for scattering the magnons in the linear
+regime, to then provide a generalized Snell's law that describes the spin-wave
+propagation across regions with different current densities. We validate the
+latter in numerical simulations of realistic systems, and exemplify how these
+findings may help advance the design of spin-wave logic and neuromorphic
+computing devices.",2301.04922v1
+2023-02-17,Control of the magnon-polariton hybridization with a microwave pump,"Pump-induced magnon modes (PIMs) are recently discovered elementary
+excitations in ferrimagnets that offer significant tunability to spin dynamics.
+Here, we investigate the coupling between a PIM and cavity magnon polaritons
+(CMPs) by driving a cavity magnonic system away from equilibrium with a
+microwave pump. In our experiment, the Walker mode simultaneously couples with
+the PIM and cavity photons and thus combines two strongly coherent coupling
+processes in a single cavity structure. Such a PIM-CMP hybridization system
+acquires complementary properties from both the PIM and CMPs, allowing it to be
+freely manipulated by the magnetic field, the pump power and the pump
+frequency. These coherent manipulations exhibit unique behaviors beyond the
+intrinsic properties limited by the material nature and electromagnetic
+boundary conditions, thereby creating opportunities for extending the control
+of hybrid devices.",2302.08665v2
+2023-02-23,Giant supermagnonic Bloch point velocities by jet propulsion effect in cylindrical ferromagnetic nanowires,"Achieving high velocities of magnetic domain walls is a crucial factor for
+their use as information carriers in modern nanoelectronic applications. In
+nanomagnetism and spintronics, these velocities are often limited either by
+internal domain wall instabilities, known as the Walker breakdown phenomenon,
+or by spin wave emission, known as the magnonic regime. In the rigid domain
+wall model, the maximum magnon velocity acts as an effective ""speed of light"",
+providing a relativistic analogy for the domain wall speed limitation.
+Cylindrical magnetic nanowires are an example of systems with the absence of
+the Walker breakdown phenomenon. Here we demonstrate that in cylindrical
+nanowires with high magnetization such as Iron, also the magnonic limit could
+be outstandingly surpassed. Our numerical modelling shows the Bloch point
+domain wall velocities as high as 14 km/s, well above the magnonic limit
+estimated in the interval 1.7-2.0 km/s. The key ingredient is the conical shape
+of the domain wall which elongates and breaks during the dynamics, leading to
+domain wall acceleration due to the jet propulsion effect. This effect will be
+very important for three-dimensional spintronic networks based on cylindrical
+magnetic nanowires.",2302.12329v1
+2023-03-20,Secondary Excitation of Spin-Waves: How Electromagnetic Cross-Talk Impacts on Magnonic Devices,"This work examines the impact of electromagnetic cross-talk in magnonic
+devices when using inductive spin-wave (SW) transducers. We present detailed
+electrical SW spectroscopy measurements showing the signal contributions to be
+considered in magnonic device design. We further provide a rule of thumb
+estimation for the cross-talk that is responsible for the secondary SW
+excitation at the output transducer. Simulations and calibrated electrical
+characterizations underpin this method. Additionally, we visualize the
+secondary SW excitation via time-resolved MOKE imaging in the forward-volume
+configuration in a 100nm Yttrium-Iron-Garnet (YIG) system. Our work is a step
+towards fast yet robust joint electromagentic-micromagnetic magnonic device
+design.",2303.11303v2
+2023-03-27,Refined Spin Wave Model and Multi-magnon Bound States in $Li_{2}CuO_{2}$,"Here we report a study of the spin dynamics in the ferromagnetic chain
+compound $Li_{2}CuO_{2}$. Inelastic neutron scattering measurements allow for
+the spin Hamiltonian to be determined using a $J_{1}-J_{2}$ $XXZ$-Heisenberg
+spin chain model with weak interchain interactions. The primary exchange
+parameters determined from our data are qualitatively consistent with those of
+Lorenz $et$ $al.$ [Europhys. Lett. 88, 37002 (2009)], and our data allow for
+the resolution of additional interchain exchange interactions. We also observe
+the formation of two- and, potentially, three-magnon bound states. The
+two-magnon bound state exists only in the magnetically ordered phase of this
+material, consistent with stabilization by the weak, Ising-like exchange
+anisotropy of the nearest-neighbor intrachain interaction. In contrast, the
+potential three-magnon state persists in a finite temperature regime above
+$T_{N}$, indicating an unconventional character. Our results establish
+$Li_{2}CuO_{2}$ as an experimental platform for the study of exchange
+anisotropy-stabilized bound states in a ferromagnetic chain.",2303.15639v2
+2023-03-28,Topological phase diagrams of in-plane field polarized Kitaev magnets,"While the existence of a magnetic field induced quantum spin liquid in Kitaev
+magnets remains under debate, its topological properties often extend to
+proximal phases where they can lead to unusual behaviors of both fundamental
+and applied interests. Subjecting a generic nearest neighbor spin model of
+Kitaev magnets to a sufficiently strong in-plane magnetic field, we study the
+resulting polarized phase and the associated magnon excitations. In contrast to
+the case of an out-of-plane magnetic field where the magnon band topology is
+enforced by a three-fold symmetry, we find that it is possible for
+topologically trivial and nontrivial parameter regimes to coexist under
+in-plane magnetic fields. We map out the topological phase diagrams of the
+magnon bands, revealing a rich pattern of variation of the Chern number over
+the parameter space and the field angle. We further compute the magnon thermal
+Hall conductivity as a weighted summation of Berry curvatures, and discuss
+experimental implications of our results to planar thermal Hall effects in
+Kitaev magnets.",2303.16222v1
+2023-04-01,Controllable Fano-type optical response and four-wave mixing via magnetoelastic coupling in a opto-magnomechanical system,"We analytically investigate the Fano-type optical response and four-wave
+mixing (FWM) process by exploiting the magnetoelasticity of a ferromagnetic
+material. The deformation of the ferromagnetic material plays the role of
+mechanical displacement, which is simultaneously coupled to both optical and
+magnon modes. We report that the magnetostrictively induced displacement
+demonstrates Fano profiles, in the output field, which is well-tuned by
+adjusting the system parameters, like effective magnomechanical coupling,
+magnon detuning, and cavity detuning. It is found that the magnetoelastic
+interaction also gives rise to the FWM phenomenon. The number of the FWM
+signals mainly depends upon the effective magnomechanical coupling and the
+magnon detuning. Moreover, the FWM spectrum exhibits suppressive behavior upon
+increasing (decreasing) the magnon (cavity) decay rate. The present scheme will
+open new perspectives in highly sensitive detection and quantum information
+processing.",2304.00237v1
+2023-04-17,Geometric similarities and topological phases in surface magnon polaritons,"Highly spatially-squeezed polaritons, with propagation momentum significantly
+larger than free-space modes at the same frequency, enable varied and extreme
+control over light-matter interaction. Compared to other polaritons, surface
+magnon polaritons, the magnetic counterpart of surface phonon polaritons, have
+received relatively little attention. Here, we investigate the dispersion and
+properties of surface-magnon polaritons, highlighting the impact of geometric
+similarities and applying them to various surface-magnon polariton devices in
+both conventional and topological settings. Our theory predicts a method for
+strongly localizing and significantly enhancing magnetic fields in the
+microwave range and developing compact and lossless connectors capable of
+interconnecting waveguides with vastly different input and output impedances.
+Our work opens new avenues for manipulating magnetic fields in the microwave
+regime and for exploring topological phases in polariton platforms.",2304.09763v1
+2023-05-09,Magnon dispersion in ferromagnetic SrRuO$_3$,"The magnetic excitations in ferromagnetic SrRuO$_3$ were studied by inelastic
+neutron scattering combining experiments on triple-axis and time-of-flight
+spectrometers with and without polarization analysis. A quadratic spin-wave
+dispersion with an anisotropy gap describes the low-energy low-temperature
+response. The magnon dispersion extends to at least 35 meV and there is no
+direct evidence for a continuum of Stoner excitations below this energy.
+However, the magnon response is weakened at higher energy. In addition to the
+anomalous softening of the spin-wave stiffness and of the gap, which is induced
+by the topology of the Bloch states, the magnon excitations are broadened in
+energy and this effect increases upon heating.",2305.05497v1
+2023-05-10,Proposal for optomagnonic teleportation and entanglement swapping,"A protocol for realizing discrete-variable quantum teleportation in an
+optomagnonic system is provided. Using optical pulses, an arbitrary photonic
+qubit state encoded in orthogonal polarizations is transferred onto the joint
+state of a pair of magnonic oscillators in two macroscopic yttrium-iron-garnet
+(YIG) spheres that are placed in an optical interferometer. We further show
+that optomagnonic entanglement swapping can be realized in an extended
+dual-interferometer configuration with a joint Bell-state detection.
+Consequently, magnon Bell states are prepared. We analyze the effect of the
+residual thermal occupation of the magnon modes on the fidelity in both the
+teleportation and entanglement swapping protocols.",2305.05889v1
+2023-06-03,Giant Enhancement of Magnonic Frequency Combs by Exceptional Points,"With their incomparable time-frequency accuracy, frequency combs have
+significantly advanced precision spectroscopy, ultra-sensitive detection, and
+atomic clocks. Traditional methods to create photonic, phononic, and magnonic
+frequency combs hinge on material nonlinearities which are often weak,
+necessitating high power densities to surpass their initiation thresholds,
+which subsequently limits their applications. Here, we introduce a novel
+nonlinear process to efficiently generate magnonic frequency combs (MFCs) by
+exploiting exceptional points (EPs) in a coupled system comprising a
+pump-induced magnon mode and a Kittel mode. Even without any cavity, our method
+greatly improves the efficiency of nonlinear frequency conversion and achieves
+optimal MFCs at low pump power. Additionally, our novel nonlinear process
+enables excellent tunability of EPs using the polarization and power of the
+pump, simplifying MFC generation and manipulation. Our work establishes a
+synergistic relationship between non-Hermitian physics and MFCs, which is
+advantages for coherent/quantum information processing and ultra-sensitive
+detection.",2306.02120v1
+2023-06-04,Topological magnets and magnons in twisted bilayer MoTe$_2$ and WSe$_2$,"Twisted homobilayer transition metal dichalcogenide (TMD) offers a versatile
+platform for exploring band topology, interaction-driven phases, and magnetic
+orders. We study the interaction-driven phases in twisted TMD homobilayers and
+their low-energy collective excitations, focusing on the effect of band
+topology on magnetism and its thermal stability. From Hartree-Fock theory of
+the continuum model, we identify several magnetic and topological phases. By
+tuning the displacement field, we find two phase transitions involving a change
+in topology and magnetism respectively. We analyze the magnon spectrum,
+revealing the crucial role of band topology in stabilizing 2D ferromagnetism by
+amplifying easy-axis magnetic anisotropy, resulting in a large magnon gap of up
+to 7 meV. As the magnon gap is directly tied to the stability of the magnetic
+phase to thermal fluctuations, our findings have several important experimental
+implications.",2306.02501v2
+2023-06-26,Repulsively bound magnon excitations of a spin-1/2 XXZ chain in a staggered transverse field,"We study the excitation spectrum of the one-dimensional spin-1/2 XXZ chain
+with antiferromagnetic Ising anisotropy across a magnetic quantum phase
+transition induced by the application of a site-dependent transverse magnetic
+field. Motivated by the chain antiferromagnet BaCo$_2$V$_2$O$_8$, we consider a
+situation where the transverse magnetic field has a strong uniform component
+and a weaker staggered part. To determine the nature of the excitations giving
+rise to the spin dynamical structure factor, we use a combination of analytical
+approaches and the numerically exact time-dependent matrix product state
+method. We identify below the quantum phase transition high-energy many-body
+two-magnon and three-magnon repulsively bound states which are clearly visible
+due to the staggered component of the magnetic field. At high magnetic fields
+and low temperature, single magnons dominate the dynamics. Our theory results
+are in very good agreement with terahertz spectroscopy experimental results
+presented in [Wang et al., in preparation].",2306.14742v2
+2023-06-30,Spin Swapping for an Exchange Magnon Spin Current,"We propose the spin swapping effect for an exchange magnon spin current in a
+perpendicularly magnetized ferromagnetic medium with in plane anisotropy on the
+surface. The excitation of a magnon current flowing along an in-plane direction
+with an out-of-plane spin polarization leads to the generation of a secondary
+exchange spin current propagating along the out-of-plane direction,
+characterized by an in-plane spin polarization. The resulting exchange magnon
+spin current can induce an inverse spin Hall voltage of micro-volts. The
+exchange coupling at the interface between regions with different magnetic
+anisotropies plays a crucial role in generating the spin swapping effect. This
+is in contrast to the recently reported spin swapping for an exchange spin
+current in a canted antiferromagnet due to the Dzyaloshiskii-Moriya
+interaction.",2306.17383v1
+2023-07-06,Realization of the unidirectional amplification in a cavity magnonic system,"We experimentally demonstrate the nonreciprocal microwave amplification using
+a cavity magnonic system, consisting of a passive cavity (i.e., the split-ring
+resonator), an active feedback circuit integrated with an amplifier, and a
+ferromagnetic spin ensemble (i.e., a yttrium-iron-garnet sphere). Combining the
+amplification provided by the active circuit and the nonreciprocity supported
+by the cavity magnonics, we implement a nonreciprocal amplifier with the
+functions of both unidirectional amplification and reverse isolation. The
+microwave signal is amplified by 11.5 dB in the forward propagating direction
+and attenuated in the reverse direction by -34.7 dB, giving an isolation ratio
+of 46.2 dB. Such a unidirectional amplifier can be readily employed in quantum
+technologies, where the device can simultaneously amplify the weak signal
+output by the quantum system and isolate the sensitive quantum system from the
+backscattered external noise. Also, it is promising to explore more functions
+and applications using a cavity magnonic system with real gain.",2307.02826v2
+2023-07-24,In-plane magnetocrystalline anisotropy in the van der Waals antiferromagnet FePSe$_3$ probed by magneto-Raman scattering,"Magnon gap excitations selectively coupled to phonon modes have been studied
+in FePSe$_3$ layered antiferromagnet with magneto-Raman scattering experiments
+performed at different temperatures. The bare magnon excitation in this
+material has been found to be split (by $\approx~1.2$ cm$^{-1}$) into two
+components each being selectively coupled to one of the two degenerated, nearby
+phonon modes. Lifting the degeneracy of the fundamental magnon mode points out
+toward the biaxial character of the FePS$_3$ antiferromagnet, with an
+additional in-plane anisotropy complementing much stronger, out-of-plane
+anisotropy. Moreover, the tunability, with temperature, of the phonon- versus
+the magnon-like character of the observed coupled modes has been demonstrated.",2307.12692v1
+2023-08-04,Strong squeezing of microwave output fields via reservoir-engineered cavity magnomechanics,"We show how to achieve strong squeezing of a microwave output field by
+reservoir engineering a cavity magnomechanical system, consisting of a
+microwave cavity, a magnon mode, and a mechanical vibration mode. The magnon
+mode is simultaneously driven by two microwave fields at the blue and red
+sidebands associated with the vibration mode. The two-tone drive induces a
+squeezed magnonic reservoir for the intracavity field, leading to a squeezed
+cavity mode due to the cavity-magnon state swapping, which further yields a
+squeezed cavity output field. The squeezing of the output field is stationary
+and substantial using currently available parameters in cavity magnomechanics.
+The work indicates the potential of the cavity magnomechanical system in
+preparing squeezed microwave fields, and may find promising applications in
+quantum information science and quantum metrology.",2308.02222v3
+2023-08-15,Tunable topological magnon-polaron states and anomalous Hall phenomena in two-dimensional ferromagnetic insulators,"We study magnon-polaron hybrid states, mediated by Dzyaloshinskii-Moriya and
+magnetoelastic interactions, in a two-dimensional ferromagnetic insulator. The
+magnetic system consists of both in-plane and flexural acoustic and optical
+phonon bands, as well as acoustic and optical magnon bands. Through
+manipulation of the ground-state magnetization direction using a magnetic
+field, we demonstrate the tunability of Chern numbers and (spin) Berry
+curvatures of magnon-polaron hybrid bands. This adjustment subsequently
+modifies two anomalous Hall responses of the system, namely, thermal Hall and
+spin Nernset signals. Notably, we find that by changing the magnetic field
+direction in particular directions, it is possible to completely suppress the
+thermal Hall signal while maintaining a finite spin Nernst signal. Our finding
+reveals the intricate interplay between topological and quantum geometrical
+phenomena and magnetic ordering, offering compelling avenues for on-demand
+control over emergent quantum states in condensed matter systems.",2308.08048v2
+2023-08-18,Spin-wave dispersion and magnon chirality in multiferroic TbMnO3,"Inelastic neutron scattering experiments combining time-of-flight and
+polarized techniques yield a comprehensive picture of the magnon dispersion in
+multiferroic TbMnO3 including the dynamic chirality. Taking into account only
+Mn3+ moments, spin-wave calculations including nearest-neighbor interactions,
+frustrating next-nearest neighbor exchange as well as single-ion anisotropy and
+antisymmetric terms describe the energy dispersion and the distribution of
+neutron scattering intensity in the multiferroic state very well. Polarized
+neutron scattering reveals strong dynamic chirality of both signs that may be
+controlled by external electric fields in the multiferroic phase. Also above
+the onset of long-range multiferroic order in zero electric field, a small
+inelastic chiral component can be inverted by an electric field. The
+microscopic spin-wave calculations fully explain also the dynamic chirality of
+magnetic excitations, which is imprinted by the static chirality of the
+multiferroic phase. The ordering of Tb3+ moments at lower temperature reduces
+the broadening of magnons but also renders the magnon dispersion more complex.",2308.09407v1
+2023-08-28,Spin wave mode conversion in an in-plane magnetized microscale T-shaped YIG magnonic splitter,"As one of the fundamental magnonic devices, a magnonic splitter device has
+been proposed and spin wave propagation in this device has been studied
+numerically and experimentally. In the present work, we fabricated a T-shaped
+magnonic splitter with 6 $\mu$m-wide three arms using a 100 nm-thick yttrium
+iron garnet film and, using time-resolved magneto-optic Kerr microscopy,
+observed that spin waves split into both, the vertical and the horizontal
+direction at the junction. Analyzing the results, we found that spin wave modes
+are converted into another during the splitting process and the splitting
+efficiency is dominantly dependent on the 1st order of incoming spin waves.",2308.14327v1
+2023-09-13,Magnon gap excitations in van der Waals antiferromagnet MnPSe$_3$,"Magneto-spectroscopy methods have been employed to study the zero-wavevector
+magnon excitations in MnPSe$_3$. Experiments carried out as a function of
+temperature and the applied magnetic field show that two low-energy magnon
+branches of MnPSe$_3$ in its antiferromagnetic phase are gapped. The
+observation of two low-energy magnon gaps (at 14 and 0.7 cm$^{-1}$) implies
+that MnPSe$_3$ is a biaxial antiferromagnet. A relatively strong out-of-plane
+anisotropy imposes the spin alignment to be in-plane whereas the spin
+directionality within the plane is governed by a factor of 2.5 $\times$
+10$^{-3}$ weaker in-plane anisotropy.",2309.06866v1
+2023-09-13,Topological superconductivity mediated by magnons of helical magnetic states,"We recently showed that spin fluctuations of noncoplanar magnetic states can
+induce topological superconductivity in an adjacent normal metal [M{\ae}land et
+al., Phys. Rev. Lett. 130, 156002 (2023)]. The noncolinear nature of the spins
+was found to be essential for this result, while the necessity of noncoplanar
+spins was unclear. In this paper we show that magnons in coplanar, noncolinear
+magnetic states can mediate topological superconductivity in a normal metal.
+Two models of the Dzyaloshinskii-Moriya interaction are studied to illustrate
+the need for a sufficiently complicated Hamiltonian describing the magnetic
+insulator. The Hamiltonian, in particular the specific form of the
+Dzyaloshinskii-Moriya interaction, affects the magnons and by extension the
+effective electron-electron interaction in the normal metal. Symmetry arguments
+are applied to complement this discussion. We solve a linearized gap equation
+in the case of weak-coupling superconductivity. The result is a
+time-reversal-symmetric topological superconductor, as confirmed by calculating
+the topological invariant. In analogy with magnon-mediated superconductivity
+from antiferromagnets, Umklapp scattering enhances the critical temperature of
+superconductivity for certain Fermi momenta.",2309.07211v2
+2023-09-26,Kinetic Ferromagnetism and Topological Magnons of the Hole-Doped Kitaev Spin Liquid,"We study the effect of hole doping on the Kitaev spin liquid (KSL) and find
+that for ferromagnetic (FM) Kitaev exchange $K$ the system is very susceptible
+to the formation of a FM spin polarization. Through density matrix
+renormalization group (DMRG) simulations on finite systems, we uncover that the
+introduction of a single hole with a hopping strength of just $t\sim{}0.28K$ is
+enough to disrupt fractionalization and polarize the spins in the [001]
+direction due to an order-by-disorder mechanism. Taking into account a material
+relevant FM anisotropic spin exchange $\varGamma$ drives the polarization
+towards the [111] direction via a reorientation transition into a topological
+FM state with chiral magnon excitations. We develop a parton mean-field theory
+incorporating fermionic holons and bosonic spinons/magnons, which accounts for
+the doping induced FM phases and topological magnon excitations. We discuss
+experimental signatures and implications for Kitaev candidate materials.",2309.15153v1
+2023-10-23,Spin pumping in an altermagnet/normal metal bilayer,"Altermagnetism is a subclass of antiferromagnetism that features
+spin-polarized electron bands of a non-relativistic origin despite the absence
+of a net magnetiation in the material. We here theoretically study spin pumping
+from an altermagnetic insulator into a normal metal. The symmetry properties of
+the lattice and spin order of the altermagnet alters the magnon dispersion
+compared to a conventional square lattice antiferromagnet. Nevertheless, the
+pumped spin current turns out to be equal to the current which is pumped from a
+conventional antiferromagnet. This occurs so long that the magnetic field which
+sets the altermagnetic spins into precessional motion is spatially homogeneous.
+These results show that while spin pumping is possible using altermagnets, the
+altermagnetic spin order does not readily leave unique fingerprints in the
+pumped spin current. Our model provides a suitable starting point for
+investigating more complex models where finite momentum magnons contribute to
+spin pumping due to magnon-magnon interactions or where the magnetic field
+inducing spin pumping is spatially inhomogeneous.",2310.15220v1
+2023-11-15,Broad-Wavevector Spin Pumping of Flat-Band Magnons,"We report the experimental observation of large spin pumping signals in
+YIG/Pt system driven by broad-wavevector spin-wave spin current. 280 nm-wide
+microwave inductive antennas offer broad-wavevector excitation which, in
+combination with quasi-flatband of YIG, allows a large number of magnons to
+participate in spin pumping at a given frequency. Through comparison with
+ferromagnetic resonance spin pumping, we attribute the enhancement of the spin
+current to the multichromatic magnons. The high efficiency of spin current
+generation enables us to uncover nontrivial propagating properties in ultra-low
+power regions. Additionally, our study achieves the spatially separated
+detection of magnons, allowing the direct extraction of the decay length. The
+synergistic combination of the capability of broad-wavevector excitation,
+enhanced voltage signals, and nonlocal detection provides a new avenue for the
+electrical exploration of spin waves dynamics.",2311.09098v1
+2023-11-23,Exciting high-frequency short-wavelength spin waves using high harmonics of a magnonic cavity mode,"Confined spin-wave modes are a promising object for studying nonlinear
+effects and future quantum technologies. Here, using micromagnetic simulations,
+we use a microwave magnetic field from a coplanar waveguide (CPW) to pump a
+standing spin-wave confined in the cavity of magnonic crystal. We find that the
+frequency of the fundamental cavity mode is equal to the ferromagnetic
+resonance frequency of the plane film and overlaps with the magnonic bandgap,
+allowing high magnetic field tunability. Multi-frequency harmonics of the
+cavity mode are generated once the microwave amplitude surpasses a certain
+threshold. Specifically, the second and third harmonics at 0.5 T equate to 48.6
+and 72.9 GHz with wavelengths of 44 and 22 nm respectively, which propagate
+into the crystal. This effect reaches saturation when the CPW covers the entire
+cavity, making the system feasible for realization. These processes show
+potential for the advancement of magnonics at high-frequencies and very
+short-wavelengths.",2311.14143v1
+2023-11-27,Zero-field spin wave turns,"Spin-wave computing, a potential successor to CMOS-based technologies, relies
+on the efficient manipulation of spin waves for information processing. While
+basic logic devices like magnon transistors, gates, and adders have been
+experimentally demonstrated, the challenge for complex magnonic circuits lies
+in steering spin waves through sharp turns. In this study we demonstrate with
+micromagnetic simulations and Brillouin light scattering microscopy
+experiments, that dipolar spin waves can propagate through 90-degree turns
+without distortion. The key lies in carefully designed in-plane magnetization
+landscapes, addressing challenges posed by anisotropic dispersion. The
+experimental realization of the required magnetization landscape is enabled by
+spatial manipulation of the uniaxial anisotropy using corrugated magnonic
+waveguides. The findings presented in this work should be considered in any
+magnonic circuit design dealing with anisotropic dispersion and spin wave
+turns.",2311.16335v1
+2023-11-28,Coherent phonon-magnon interactions detected by micro-focused Brillouin light scattering spectroscopy,"We investigated the interaction of surface acoustic waves and spin waves with
+spatial resolution by micro-focused Brillouin light scattering spectroscopy in
+a Co$_{40}$Fe$_{40}$B$_{20}$ ferromagnetic layer on a LiNbO$_{3}$-piezoelectric
+substrate. We experimentally demonstrate that the magnetoelastic excitation of
+magnons by phonons is coherent by studying the interfering BLS-signals of the
+phonons and magnons during their conversion process.We find a pronounced
+spatial dependence of the phonon annihilation and magnon excitation which we
+map as a function of the magnetic field. The coupling efficiency of the surface
+acoustic waves (SAWs) and the spin waves (SWs) is characterized by a magnetic
+field dependent decay of the SAWs amplitude.",2311.16688v1
+2023-12-14,"Tripartite Phonon-Magnon-Plasmon Coupling, Parametric Amplification, and Formation of a Phonon-Magnon-Plasmon Polariton in a Two-Dimensional Periodic Array of Magnetostrictive/Plasmonic Bilayered Nanodots","Coupling between spin waves (SWs) and other types of waves in nanostructured
+magnetic media has garnered increased attention in recent years because of the
+rich physics and the potential to produce disruptive technologies. Among this
+family of intriguing phenomena, we recently reported a new one: coupling
+between SWs and hybridized phonon-plasmon waves, resulting in tripartite
+coupling of magnons, phonons, and plasmons. Here, this acousto-plasmo-magnonic
+phenomenon is studied in a two-dimensional periodic array of bilayered [Co/Al]
+nanodots on a silicon substrate, where the Co is a magnetostrictive constituent
+responsive to magneto-elastic coupling and the Al acts as a source of surface
+plasmons. Time-resolved magneto-optical-Kerr-effect microscopy revealed
+parametric amplification and strong coupling between two spin wave modes
+mediated by a hybrid phonon-plasmon wave. The strong coupling forms a new
+quasi-particle: the phonon-plasmonmagnon polariton.",2312.09343v1
+2023-12-17,Cryogenic hybrid magnonic circuits based on spalled YIG thin films,"Yttrium iron garnet (YIG) magnonics has sparked extensive research interests
+toward harnessing magnons (quasiparticles of collective spin excitation) for
+signal processing. In particular, YIG magnonics-based hybrid systems exhibit
+great potentials for quantum information science because of their wide
+frequency tunability and excellent compatibility with other platforms. However,
+the broad application and scalability of thin-film YIG devices in the quantum
+regime has been severely limited due to the substantial microwave loss in the
+host substrate for YIG, gadolinium gallium garnet (GGG), at cryogenic
+temperatures. In this study, we demonstrate that substrate-free YIG thin films
+can be obtained by introducing the controlled spalling and layer transfer
+technology to YIG/GGG samples. Our approach is validated by measuring a hybrid
+device consisting of a superconducting resonator and a spalled YIG film, which
+gives a strong coupling feature indicating the good coherence of our system.
+This advancement paves the way for enhanced on-chip integration and the
+scalability of YIG-based quantum devices.",2312.10660v2
+2024-01-06,Cavity magnonics with domain walls in insulating ferromagnetic wires,"Magnetic domain walls (DWs) are topological defects that exhibit robust
+low-energy modes that can be harnessed for classical and neuromorphic
+computing. However, the quantum nature of these modes has been elusive thus
+far. Using the language of cavity optomechanics, we show how to exploit a
+geometric Berry-phase interaction between the localized DWs and the extended
+magnons in short ferromagnetic insulating wires to efficiently cool the DW to
+its quantum ground state or to prepare nonclassical states exhibiting a
+negative Wigner function that can be extracted from the power spectrum of the
+emitted magnons. Moreover, we demonstrate that magnons can mediate long-range
+entangling interactions between qubits stored in distant DWs, which could
+facilitate the implementation of a universal set of quantum gates. Our proposal
+relies only on the intrinsic degrees of freedom of the ferromagnet, and can be
+naturally extended to explore the quantum dynamics of DWs in ferrimagnets and
+antiferromagnets, as well as quantum vortices or skyrmions confined in
+insulating magnetic nanodisks.",2401.03164v1
+2024-01-09,Signatures of novel magnon-phonon coupling in frustrated double perovskite square lattices,"Low-dimensional frustrated magnetic square networks feature a variety of
+unconventional phases with novel emergent excitations. Often these excitations
+are intertwined and manifest into intriguing phenomena, an area that has
+remained largely unexplored in square-lattice systems, especially, double
+perovskites (A2BB'O6). In this study, we explore these interactions between the
+fundamental excitations such as phonons and magnons in square-lattice
+Sr2CuTeO6, Sr2CuWO6, and Ba2CuWO6 isostructural double perovskites that exhibit
+both short-ranged (TS) as well as long-ranged Neel antiferromagnetic (TN)
+transitions. Our Raman measurements at variable temperatures reveal an
+intriguing broad peak (identified as 2-magnon (2M)) surviving beyond TS for
+W-based compositions contrary to the Te-based system, suggesting a key role of
+diamagnetic B'-site cation on their magnetism. The thermal response of 2M
+intriguingly shows signatures of correlation with phonons and control over
+their anharmonicity, depicting magnon-phonon interaction. Further, a few
+phonons exhibit anomalies across the magnetic transitions implying the presence
+of spin-phonon coupling. In particular, the phonon modes at ~ 194 cm-1 of
+Sr2CuTeO6 and ~ 168 cm-1 of Sr2CuWO6, that show a strong correlation with the
+2M, exhibit the strongest spin-phonon coupling suggesting their roles in
+mediating magnon-phonon interactions in these systems.",2401.04624v1
+2024-01-11,Room-temperature Magnetic Thermal Switching by Suppressing Phonon-Magnon Scattering,"Thermal switching materials, whose thermal conductivity can be controlled
+externally, show great potential in contemporary thermal management.
+Manipulating thermal transport properties through magnetic fields has been
+accomplished in materials that exhibit a high magnetoresistance. However, it is
+generally understood that the lattice thermal conductivity attributed to
+phonons is not significantly impacted by the magnetic fields. In this study, we
+experimentally demonstrate the significant impact of phonon-magnon scattering
+on the thermal conductivity of the rare-earth metal gadolinium near room
+temperature, which can be controlled by a magnetic field to realize thermal
+switching. Using first-principles lattice dynamics and spin-lattice dynamics
+simulations, we attribute the observed change in phononic thermal conductivity
+to field-suppressed phonon-magnon scattering. This research suggests that
+phonon-magnon scattering in ferromagnetic materials is crucial for determining
+their thermal conductivity, opening the door to innovative
+magnetic-field-controlled thermal switching materials.",2401.05607v1
+2024-01-20,Finite-Temperature Hole-Magnon Dynamics in an Antiferromagnet,"Employing the numerically accurate multiple Davydov Ansatz in combination
+with the thermo-field dynamics approach, we delve into interplay of the
+finite-temperature dynamics of holes and magnons in an antiferromagnet, which
+allows for scrutinizing previous predictions from self-consistent Born
+approximation while offering, for the first time, accurate finite-temperature
+computation of detailed magnon dynamics as a response and a facilitator to the
+hole motion. The study also uncovers pronounced temperature dependence of the
+magnon and hole populations, pointing to the feasibility of potential thermal
+manipulation and control of hole dynamics. Our methodology can be applied not
+only to the calculation of steady-state angular-resolved photoemission spectra,
+but also to the simulation of femtosecond terahertz pump-probe and other
+nonlinear signals for the characterization of antiferromagnetic materials.",2401.11184v1
+2024-01-31,Keldysh Theory of Thermal Transport in Multiband Hamiltonians,"We establish a comprehensive theoretical framework for systems subjected to a
+static uniform temperature gradient, employing the non-equilibrium
+Keldysh-Dyson formalism. This framework interprets the statistical force due to
+the temperature gradient as a mechanical force, utilizing both Luttinger's
+scalar and Moreno-Coleman-Tatara's vector potentials, which collectively
+emulate the gauge invariance stemming from the conservation of energy. Our
+approach has the ability to treat heat current and heat magnetization on an
+equal footing, thereby extending and generalizing previous formalisms. The
+derived result for the thermal conductivity is applied to investigate the
+thermal characteristics of Weyl magnons in a stacked honeycomb ferromagnet
+featuring a trivial insulator phase, a magnon Chern insulator phase, and three
+Weyl magnon phases. Against the expectation from the Berry curvature, the
+magnon Chern insulator phase exhibits the highest transverse thermal
+conductivity.",2401.17652v1
+2024-02-10,Magnons and spikes for $\mathcal{N}=2$ linear quivers and their non-Abelian T-duals,"We compute the spectra associated with various semiclassical string states
+that propagate over $\mathcal{N}=2$ Gaiotto-Maldacena backgrounds. As an
+interesting special case, for the Abelian T- dual solution, we discover giant
+magnon and single spike configurations while imposing appropriate boundary
+conditions. However, for Sfetsos-Thompson backgrounds, one has to adopt a
+different string embedding which reveals ``modified'' dispersion relations both
+for magnons and spikes. These results boil down into the standard dispersion
+relations in the limit when the rank of the associated $SU(N_c)$ color gauge
+group becomes large enough. We further generalize our analysis in the presence
+of flavor D6 branes. Our analysis reveals a new set of dispersion relations,
+which shows that both magnons and spikes are ceased to exist in the presence of
+flavor excitations.",2402.06897v1
+2024-03-18,SU(3) gauge field of magnons in antiferromagnetic skyrmion crystals,"Quasiparticle excitations in material solids often experience a fictitious
+gauge field, which can be a potential source of intriguing transport phenomena.
+Here, we show that low-energy excitations in insulating antiferromagnetic
+skyrmion crystals on the triangular lattice are effectively described by
+magnons with an SU(3) gauge field. The three-sublattice structure in the
+antiferromagnetic skyrmion crystals is inherited as three internal degrees of
+freedom for the magnons, which are coupled with their kinetic motion via the
+SU(3) gauge field that arises from the topologically nontrivial spin texture in
+real space. We also demonstrate that the non-commutativity of the SU(3) gauge
+field breaks an effective time-reversal symmetry and contributes to a magnon
+thermal Hall effect.",2403.11655v2
+2024-04-04,Spin dynamics and possible topological magnons in non-stoichiometric pyrochlore iridate Tb$_2$Ir$_2$O$_7$ studied by RIXS,"We report a resonant inelastic X-ray scattering study on a single crystal of
+a non-stoichiometric pyrochlore iridate Tb$_{2+x}$Ir$_{2-x}$O$_{7-y}$ ($x
+\simeq 0.25$) that magnetically orders at $T_{\rm{N}}\simeq 50$ K. We find that
+the strength of the spin-orbit coupling and the trigonal distortion of the
+IrO$_6$ octahedra are comparable with the ones obtained in other pyrochlore
+iridates. We observe a propagating gapped magnon mode at low energy, and model
+it using a Hamiltonian consisting of a Heisenberg exchange [$J = 16.2(9)$ meV]
+and Dzyaloshinskii-Moriya interactions [$D = 5.2(3)$ meV], which shows the
+robustness of interactions despite Tb-stuffing at the Ir-site. Strikingly, the
+ratio $D/J = 0.32(3)$ supports possible non-trivial topological magnon band
+crossing. This material may thus host coexisting fermionic and bosonic
+topology, with potential for manipulating electronic and magnonic topological
+bands thanks to the $d-f$ interaction.",2404.03829v1
+2013-10-31,Signatures of electron-magnon interaction in charge and spin currents in magnetic tunnel junctions: A nonequilibrium many-body perturbation theory approach,"We develop a numerically exact scheme for resumming certain classes of
+Feynman diagrams in the self-consistent perturbation expansion for the electron
+and magnon self-energies in the nonequilibrium Green function formalism applied
+to a coupled electron-magnon (\mbox{e-m}) system which is driven out of
+equilibrium by the applied finite bias voltage. Our scheme operates with the
+electronic and magnonic GFs and the corresponding self-energies viewed as
+matrices in the Keldysh space, rather than conventionally extracting their
+retarded and lesser components. This is employed to understand the effect of
+inelastic \mbox{e-m} scattering on charge and spin current vs. bias voltage
+$V_b$ in F/I/F magnetic tunnel junctions (MTJs), which are modeled on a
+one-dimensional (1D) tight-binding lattice for the electronic subsystem and 1D
+Heisenberg model for the magnonic subsystem. For this purpose, we evaluate Fock
+diagram for the electronic self-energy and the electron-hole polarization
+bubble diagram for the magnonic self-energy. The respective electronic and
+magnonic GF lines within these diagrams are the fully interacting ones, thereby
+requiring to solve the ensuing coupled system of nonlinear integral equations
+self-consistently. Despite using the 1D model and treating \mbox{e-m}
+interaction in many-body fashion only within a small active region consisting
+of few lattice sites around the F/I interface, our analysis captures essential
+features of the so-called zero-bias anomaly observed in both MgO- and
+AlO$_x$-based realistic 3D MTJs where the second derivative $d^2 I/dV_b^2$
+(i.e., inelastic electron tunneling spectrum) of charge current exhibits sharp
+peaks of opposite sign on either side of the zero bias voltage.",1310.8551v4
+2017-08-10,Nearly deconfined spinon excitations in the square-lattice spin-1/2 Heisenberg antiferromagnet,"We study the dynamic spin structure factor of the spin-$1/2$ square-lattice
+Heisenberg antiferromagnet and of the $J$-$Q$ model (with 4-spin interactions
+$Q$ and Heisenberg exchange $J$). Using an improved method for stochastic
+analytic continuation of imaginary-time correlation functions computed with QMC
+simulations, we can treat the sharp ($\delta$-function) contribution from
+spinwaves (magnons) and a continuum at higher energy. The results for the
+Heisenberg model agree with neutron scattering experiments on
+Cu(DCOO)$_2$$\cdot$4D$_2$O, where a broad spectral-weight continuum at
+$q=(\pi,0)$ was interpreted as deconfined spinons. Our results at $(\pi,0)$
+show a similar reduction of the magnon weight and a large continuum, while the
+continuum is much smaller at $q=(\pi/2,\pi/2)$ (as also seen experimentally).
+Turning on $Q$, we observe a rapid reduction of the $(\pi,0)$ magnon weight to
+zero, well before the deconfined quantum phase transition into a spontaneously
+dimerized state. We re-interpret the picture of deconfined spinons at $(\pi,0)$
+in the experiments as nearly deconfined spinons---a precursor to deconfined
+quantum criticality. To further elucidate the picture of a fragile
+$(\pi,0)$-magnon in the Heisenberg model and its depletion in the $J$-$Q$
+model, we introduce an effective model in which a magnon can split into two
+spinons that do not separate but fluctuate in and out of the magnon space (in
+analogy with the resonance between a photon and a particle-hole pair in the
+exciton-polariton problem). The model reproduces the $(\pi,0)$ and
+$(\pi/2,\pi/2)$ features of the Heisenberg model. It can also account for the
+rapid loss of the $(\pi,0)$ magnon with increasing $Q$ and a remarkable
+persistence of a large magnon pole at $q=(\pi/2,\pi/2)$ even at the deconfined
+critical point.",1708.03232v3
+2017-11-21,Eavesdropping on spin waves inside the domain-wall nanochannel via three-magnon processes,"One recent breakthrough in the field of magnonics is the experimental
+realization of reconfigurable spin-wave nanochannels formed by magnetic domain
+wall with a width of $10-100$ nm [Wagner \emph{et al}., Nat. Nano. \textbf{11},
+432 (2016)]. This remarkable progress enables an energy-efficient spin-wave
+propagation with a well-defined wave vector along its propagating path inside
+the wall. In the mentioned experiment, a micro-focus Brillouin light scattering
+spectroscopy was taken in a line-scans manner to measure the frequency of the
+bounded spin wave. Due to their localization nature, the confined spin waves
+can hardly be detected from outside the wall channel, which guarantees the
+information security to some extent. In this work, we theoretically propose a
+scheme to detect/eavesdrop on the spin waves inside the domain-wall nanochannel
+via nonlinear three-magnon processes. We send a spin wave in one magnetic
+domain to interact with the bounded mode in the wall. Two kinds of three-magnon
+processes, i.e., confluence and splitting, are expected to occur. The
+confluence process is conventional. We predict a stimulated three-magnon
+splitting (or ""magnon laser"") effect: the presence of a bound magnon
+propagating along the domain wall channel assists the splitting of the incident
+wave into two modes, one of which is identical to the bound mode in the
+channel. Micromagnetic simulations confirm our theoretical analysis. These
+results demonstrate that one is able to uniquely infer the spectrum of the
+spin-wave in the domain-wall nanochannel once we know both the injection and
+the transmitted waves.",1711.07615v2
+2020-09-21,Thermal Hall effect from two-dimensional Schwinger-boson gas with Rashba spin-orbit interaction: application to ferromagnets with in-plane Dzyaloshinskii-Moriya interaction,"Recently, uncovering the sources of thermal Hall effect in insulators has
+become an important issue. In the case of ferromagnetic insulators, it is well
+known that Dzyaloshinskii-Moriya (DM) interaction can induce magnon thermal
+Hall effect. Specifically, the DM vector parallel to the magnetization
+direction induces complex magnon hopping amplitudes, so that magnons act as if
+they feel Lorentz force. However, the DM vector which is orthogonal to the
+magnetization direction has hitherto been neglected as a possible source of
+magnon thermal Hall effect. This is because they play no role in the linear
+spin wave theory, an often invoked approximation when computing the magnon
+thermal Hall effect. Here, we challenge this expectation by presenting the
+self-consistent Schwinger-boson mean field study of two-dimensional magnets
+with ferromagnetic Heisenberg interaction and in-plane DM interaction. We find
+that the relevant Schwinger-boson mean field Hamiltonian takes the form of
+two-dimensional electron gas with Rashba spin-orbit interaction, which is known
+to show anomalous Hall effect, spin Hall effect, and Rashba-Edelstein effect,
+whose thermal counterparts also appear in our system. Importantly, the thermal
+Hall effect can be induced when out-of-plane magnetic field is applied, and
+persists even when the magnetic field is large, so that the spins are
+significantly polarized, and the linear spin wave theory is expected to be a
+reasonable approximation. Since the linear spin wave theory predicts vanishing
+thermal Hall effect, our result implies that linear spin wave is not a
+sufficient approximation, and that magnon-magnon interaction must be taken into
+account to predict the correct thermal Hall conductivity.",2009.09621v1
+2020-07-30,Magnon and Spin Transition Contribution in Heat Capacity of Ferromagnetic Cr-doped MnTe: Experimental Evidence for a Paramagnetic Spin-Caloritronic Effect,"We present experimental evidence for the simultaneous existence of the
+magnons and spin-state transition contributions to the heat capacity in
+ferromagnetic (FM) Cr-doped MnTe (Tc~280K), where the magnon heat capacity is
+attributed to the observed magnon-bipolar carrier-drag thermopower. The
+pristine antiferromagnetic (AFM) MnTe shows only a magnon-induced peak in the
+heat capacity near the Neel temperature, TN~307K. However, Cr-doped MnTe shows
+a magnon-contributed heat capacity peak at ~293K with an additional peak in the
+deep paramagnetic domain near 780K. Temperature-dependent magnetic
+susceptibility reveals that Cr-doping initially creates low-spin (LS) states
+Mn2+ ions into MnTe near and below TN due to a higher crystal field induced by
+Cr ions. Above 400K, LS Mn2+ ions start converting into high-spin (HS) Mn2+
+ions. The LS-to-HS transition of Mn2+ leads to an excess entropy and hence
+excess heat capacity contribution in the system. Temperature-dependent X-ray
+diffraction (XRD) and magnetic field-dependent susceptibility (M-H) confirmed
+no presence of any structural changes and magnetic polaron, respectively. Both
+XRD and M-H ensure that the peak of the heat capacity in the paramagnetic
+domain is originated solely by the spin-state transition. The heat capacity
+versus temperature was calculated to explain the contribution of each
+component, including the ones due to the phonons, magnons, spin-transition,
+Schottky anomaly, and lattice dilation. With the recent advances in
+spin-caloritronics extending the spin-based effects from magnetic to
+paramagnetic materials, the data from the heat capacity can play a crucial role
+to probe the presence of different phenomena such as paramagnon-carrier-drag
+and spin-entropy thermopowers.",2007.15232v1
+2022-10-07,Magnon bands in pyrochlore slabs with Heisenberg exchange and anisotropies,"The pyrochlore lattice is a versatile venue to probe the properties of
+magnetically ordered states induced or perturbed by anisotropic terms like the
+Dzyaloshinskii-Moriya interactions or single-ion anisotropy. Several such
+ordered states have been investigated recently as precursors of topological
+magnons and the associated surface states. In parallel, there has been recent
+progress in growing thin films of magnetic materials with this lattice
+structure along high symmetry directions of the lattice. In both cases, an
+account of the magnetic excitations of relevant Hamiltonians for finite slabs
+is a necessary step in the analysis of the physics of these systems. We study
+here magnon bands in the slab geometry for a class of spin models on the
+pyrochlore lattice with Heisenberg exchange, Dzyaloshinskii-Moriya interaction
+and spin-ice anisotropy. For a range of model parameters, for both
+ferromagnetic and antiferromagnetic exchange, we compute the classical ground
+states for different slab orientations and determine the spin wave excitations
+above them. We analyze the ferromagnetic splay phase, the all-in-all-out phase
+and a coplanar phase and evaluate magnon dispersions for slabs oriented
+perpendicular to the $[111]$, $[100]$ and $[110]$ directions. For all the
+phases considered, depending on the slab orientation, magnon band structures
+can be non-reciprocal and we highlight the differences in the three
+orientations from this point-of-view. Finally, we present details of the
+surface localized magnons for all the three slab orientations in the phases we
+study. For the ferromagnetic splay phase and the all-in-all-out phase we
+analyze surface states associated with point degeneracies or nodal lines in the
+bulk spectrum by computing the magnonic Berry curvature and Weyl charges or
+Chern numbers associated with it.",2210.03548v3
+2023-08-18,"Magnon Diffusion Length and Longitudinal Spin Seebeck Effect in Vanadium Tetracyanoethylene (V[TCNE]$_x$, $x \sim 2$)","Spintronic, spin caloritronic, and magnonic phenomena arise from complex
+interactions between charge, spin, and structural degrees of freedom that are
+challenging to model and even more difficult to predict. This situation is
+compounded by the relative scarcity of magnetically-ordered materials with
+relevant functionality, leaving the field strongly constrained to work with a
+handful of well-studied systems that do not encompass the full phase space of
+phenomenology predicted by fundamental theory. Here we present an important
+advance in this coupled theory-experiment challenge, wherein we extend existing
+theories of the spin Seebeck effect (SSE) to explicitly include the
+temperature-dependence of magnon non-conserving processes. This expanded theory
+quantitatively describes the low-temperature behavior of SSE signals previously
+measured in the mainstay material yttrium iron garnet (YIG) and predicts a new
+regime for magnonic and spintronic materials that have low saturation
+magnetization, $M_S$, and ultra-low damping. Finally, we validate this
+prediction by directly observing the spin Seebeck resistance (SSR) in the
+molecule-based ferrimagnetic semiconductor vanadium tetracyanoethylene
+(V[TCNE]$_x$, $x \sim 2$). These results validate the expanded theory, yielding
+SSR signals comparable in magnitude to YIG and extracted magnon diffusion
+length ($\lambda_m>1$ $\mu$ m) and magnon lifetime for V[TCNE]$_x$
+($\tau_{th}\approx 1-10$ $\mu$ s) exceeding YIG ($\tau_{th}\sim 10$ ns).
+Surprisingly, these properties persist to room temperature despite relatively
+low spin wave stiffness (exchange). This identification of a new regime for
+highly efficient SSE-active materials opens the door to a new class of magnetic
+materials for spintronic and magnonic applications.",2308.09752v1
+2023-10-08,Floquet-engineering the exceptional points in parity-time-symmetric magnonics,"Magnons serve as a testing ground for fundamental aspects of Hermitian and
+non-Hermitian wave mechanics and are of high relevance for information
+technology. This study presents setups for realizing spatio-temporally driven
+parity-time (PT) symmetric magnonics based on coupled magnetic waveguides and
+magnonic crystals. A charge current in a metal layer with strong spin-orbit
+coupling sandwiched between two insulating magnetic waveguides leads to gain or
+loss in the magnon amplitude depending on the directions of the magnetization
+and the charge currents. When gain in one waveguide is balanced by loss in the
+other waveguide a PT-symmetric system hosting non-Hermitian degeneracies (or
+exceptional points (EPs)) is realized. For AC current multiple EPs appear for a
+certain gain/loss strength and mark the boundaries between the preserved
+PT-symmetry and the broken PT-symmetry phases. The number of islands of broken
+PT-symmetry phases and their extensions is tunable by the frequency and the
+strength of the spacer current. At EP and beyond, the induced and amplified
+magnetization oscillations are strong and self-sustained. In particular, these
+magnetization auto-oscillations in broken PT-symmetry phase occur at low
+current densities and do not require further adjustments such as tilt angle
+between electric polarization and equilibrium magnetization direction in
+spin-torque oscillators, pointing to a new design of these oscillators and
+their utilization in computing and sensoric. It is also shown how the periodic
+gain/loss mechanism allows for the generation of high-frequency spin waves with
+low-frequency currents. For spatially-periodic gain/loss acting on a magnonic
+crystal, magnon modes approaching each other at the Brillouin-zone boundaries
+are highly susceptible to PT-symmetry, allowing for a wave-vector-resolved
+experimental realization at very low currents.",2310.09300v1
+2023-10-30,Schwinger mechanism of magnon-antimagnon pair production on magnetic field inhomogeneities and the bosonic Klein effect,"Effective field theory of low-energy exitations-magnons that describes
+antiferromagnets is mapped into scalar electrodynamics of a charged scalar
+field interacting with an external electromagnetic potential. In the presence
+of a constant inhomogeneous external magnetic field the latter problem is
+technically reduced to the problem of charged-particle creation from the vacuum
+by an electric potential step (x-step). Magnetic moment plays here the role of
+the electric charge, and magnons and antimagnons differ from each other in the
+sign of the magnetic moment. In the framework of such a consideration, it is
+important to take into account the vacuum instability (the Schwinger effect)
+under the magnon-antimagnon production on magnetic field inhomogeneities (an
+analog of pair creation from the vacuum by electric-like fields). We
+demonstrate how to use the strong field QED with x-steps developed by the
+authors (SPG and DMG) to study the magnon-antimagnon pair production on
+magnetic field inhomogeneities. Characteristics of the vacuum instability
+obtained for some magnetic steps that allows exact solving the Klein-Gordon
+equation are presented. In particular, we consider examples of magnetic steps
+with very sharp field derivatives that correspond to a regularization of the
+Klein step. In the case of smooth-gradient steps, we describe an universal
+behavior of the flux density of created magnon pairs. We also note that since
+the low-energy magnons are bosons with small effective mass, then for the first
+time maybe the opportunity will arise to observe the Schwinger effect in the
+case of the Bose statistics, in particular, the bosonic Klein effect in
+laboratory conditions. Moreover, it turns out that in the case of the Bose
+statistics appears a new mechanism for amplifying the effect of the pair
+creation, which we call statistically-assisted Schwinger effect.",2310.20035v1
+2024-01-25,Few-magnon excitations in a frustrated spin-$S$ ferromagnetic chain with single-ion anisotropy,"We study few-magnon excitations in a finite-size spin-$S$ chain with
+ferromagnetic nearest-neighbor (NN) interaction $J>0$ and antiferromagnetic
+next-nearest-neighbor (NNN) interaction $J'<0$, in the presence of the
+single-ion (SI) anisotropy $D$. We first reveal the condition for the emergence
+of zero-excitation-energy states. In the isotropic case with $\Delta=\Delta'=1$
+($\Delta$ and $\Delta'$ are the corresponding anisotropy parameters), a
+threshold of $J/|J'|$ above which the ground state is ferromagnetic is
+determined by exact diagonalization for short chains up to $12$ sites. Using a
+set of exact two-magnon Bloch states, we then map the two-magnon problem to a
+single-particle one on an effective open chain with both NN and NNN hoppings.
+The whole two-magnon excitation spectrum is calculated for large systems and
+the commensurate-incommensurate transition in the lowest-lying mode is found to
+exhibit different behaviors between $S=1/2$ and higher spins due to the
+interplay of the SI anisotropy and the NNN interaction. For the commensurate
+momentum $k=-\pi$, the effective lattice is decoupled into two NN open chains
+that can be exactly solved via a plane-wave ansatz. Based on this, we
+analytically identify in the $\Delta'-D/|J'|$ plane the regions supporting the
+SI or NNN exchange two-magnon bound states near the edge of the band. In
+particular, we prove that there always exists a lower-lying NN exchange
+two-magnon bound state near the band edge for arbitrary $S\geq 1/2$. Finally,
+we numerically calculate the $n$-magnon spectra for $S=1/2$ with $n\leq5$ by
+using a spin-operator matrix element method. The corresponding $n$-magnon
+commensurate instability regions are determined for finite chains and
+consistent results with prior literature are observed.",2401.14101v2
+1994-05-14,Dynamical T=0 correlations of the S=1/2 1D Heisenberg Anti-Ferromagnet with 1/r^2 exchange in a magnetic field,"We present a new selection rule for matrix elements of local spin operators
+in the $S=1/2$ ``Haldane-Shastry'' model. Based on this rule we extend a recent
+exact calculation \cite{H93} of the ground-state dynamical spin correlation
+function $S^{ab}(n,t)$ = $\langle 0 | S^a(n,t)S^b(0,0)| 0 \rangle$ and its
+Fourier-transform $S^{ab}(Q,E)$ of this model to a finite magnetic field. In
+zero field, only {\it two-spinon} excitations contribute to the spectral
+function; in the (positively) partially-spin-polarized case, there are two
+types of elementary excitations: {\it spinons} ($\Delta S^z = \pm 1/2$) and
+{\it magnons} ($\Delta S^z = -1 $). The magnons are divided into left- or
+right-moving branches. The only classes of excited states contributing to the
+spectral functions are: (I) two spinons, (II) two spinons + one magnon, (IIIa)
+two spinons + two magnons (moving in opposite directions), (IIIb) one magnon.
+The contributions to the various correlations are: $S^{-+}$: (I); $S^{zz}$:
+(I)+(II); $S^{+-}$: (I)+(II)+(III). In the zero-field limit there are no
+magnons, while in the fully-polarized case, there are no spinons. We discuss
+the relation of the spectral functions to correlations of the
+Calogero-Sutherland model at coupling $\lambda = 2$.",9405043v1
+2006-04-19,Giant Magnons,"Studies of ${\cal N}=4$ super Yang Mills operators with large R-charge have
+shown that, in the planar limit, the problem of computing their dimensions can
+be viewed as a certain spin chain. These spin chains have fundamental
+``magnon'' excitations which obey a dispersion relation that is periodic in the
+momentum of the magnons. This result for the dispersion relation was also shown
+to hold at arbitrary 't Hooft coupling. Here we identify these magnons on the
+string theory side and we show how to reconcile a periodic dispersion relation
+with the continuum worldsheet description. The crucial idea is that the
+momentum is interpreted in the string theory side as a certain geometrical
+angle. We use these results to compute the energy of a spinning string. We also
+show that the symmetries that determine the dispersion relation and that
+constrain the S-matrix are the same in the gauge theory and the string theory.
+We compute the overall S-matrix at large 't Hooft coupling using the string
+description and we find that it agrees with an earlier conjecture. We also find
+an infinite number of two magnon bound states at strong coupling, while at weak
+coupling this number is finite.",0604135v2
+2006-06-14,Finite-size Effects from Giant Magnons,"In order to analyze finite-size effects for the gauge-fixed string sigma
+model on AdS_5 x S^5, we construct one-soliton solutions carrying finite
+angular momentum J. In the infinite J limit the solutions reduce to the
+recently constructed one-magnon configuration of Hofman and Maldacena. The
+solutions do not satisfy the level-matching condition and hence exhibit a
+dependence on the gauge choice, which however disappears as the size J is taken
+to infinity. Interestingly, the solutions do not conserve all the global
+charges of the psu(2,2|4) algebra of the sigma model, implying that the
+symmetry algebra of the gauge-fixed string sigma model is different from
+psu(2,2|4) for finite J, once one gives up the level-matching condition. The
+magnon dispersion relation exhibits exponential corrections with respect to the
+infinite J solution. We also find a generalisation of our one-magnon
+configuration to a solution carrying two charges on the sphere. We comment on
+the possible implications of our findings for the existence of the Bethe ansatz
+describing the spectrum of strings carrying finite charges.",0606126v2
+2009-06-25,Intermediate-statistics spin waves,"In this paper, we show that spin waves, the elementary excitation of the
+Heisenberg magnetic system, obey a kind of intermediate statistics with a
+finite maximum occupation number n. We construct an operator realization for
+the intermediate statistics obeyed by magnons, the quantized spin waves, and
+then construct a corresponding intermediate-statistics realization for the
+angular momentum algebra in terms of the creation and annihilation operators of
+the magnons. In other words, instead of the Holstein-Primakoff representation,
+a bosonic representation subject to a constraint on the occupation number, we
+present an intermediate-statistics representation with no constraints. In this
+realization, the maximum occupation number is naturally embodied in the
+commutation relation of creation and annihilation operators, while the
+Holstein-Primakoff representation is a bosonic operator relation with an
+additional putting-in-by-hand restriction on the occupation number. We deduce
+the intermediate-statistics distribution function for magnons. On the basis of
+these results, we calculate the dispersion relations for ferromagnetic and
+antiferromagnetic spin waves. The relations between the intermediate statistics
+that magnons obey and the other two important kinds of intermediate statistics,
+Haldane-Wu statistics and the fractional statistics of anyons, are discussed.
+We also compare the spectrum of the intermediate-statistics spin wave with the
+exact solution of the one-dimensional s = 1/2 Heisenberg model, which is
+obtained by the Bethe ansatz method. For ferromagnets, we take the
+contributions from the interaction between magnons (the quartic contribution),
+the next-to-nearest neighbor interaction, and the dipolar interaction into
+account for comparison with the experiment.",0906.4818v1
+2010-03-25,Spin superfluidity and magnon BEC,"The spin superfluidity -- superfluidity in the magnetic subsystem of a
+condensed matter - is manifested as the spontaneous phase-coherent precession
+of spins first discovered in 1984 in 3He-B. This superfluid current of spins -
+spin supercurrent - is one more representative of superfluid currents known or
+discussed in other systems, such as the superfluid current of mass and atoms in
+superfluid 4He; superfluid current of electric charge in superconductors;
+superfluid current of hypercharge in Standard Model of particle physics;
+superfluid baryonic current and current of chiral charge in quark matter; etc.
+Spin superfluidity can be described in terms of the Bose condensation of spin
+waves - magnons. We discuss different phases of magnon superfluidity, including
+those in magnetic trap; and signatures of magnons superfluidity: (i) spin
+supercurrent, which transports the magnetization on a macroscopic distance more
+than 1 cm long; (ii) spin current Josephson effect which shows interference
+between two condensates; (iii) spin current vortex - a topological defect which
+is an analog of a quantized vortex in superfluids, of an Abrikosov vortex in
+superconductors, and cosmic strings in relativistic theories; (iv) Goldstone
+modes related to the broken U(1) symmetry - phonons in the spin-superfluid
+magnon gas; etc. We also touch the topic of spin supercurrent in general
+including spin Hall and intrinsic quantum spin Hall effects.",1003.4889v3
+2013-12-11,"Magnonic Band Structure, Complete Bandgap and Collective Spin Wave Excitation in Nanoscale Two--Dimensional Magnonic Crystals","We present the observation of a complete bandgap and collective spin wave
+excitation in two-dimensional magnonic crystals comprised of arrays of
+nanoscale antidots and nanodots, respectively. Considering that the frequencies
+dealt with here fall in the microwave band, these findings can be used for the
+development of suitable magnonic metamaterials and spin wave based signal
+processing. We also present the application of a numerical procedure, to
+compute the dispersion relations of spin waves for any high symmetry direction
+in the first Brillouin zone. The results obtained from this procedure has been
+reproduced and verified by the well established plane wave method for an
+antidot lattice, when magnetization dynamics at antidot boundaries is pinned.
+The micromagnetic simulation based method can also be used to obtain
+iso--frequency countours of spin waves. Iso--frequency contours are analougous
+of the Fermi surfaces and hence, they have the potential to radicalize our
+understanding of spin wave dynamics. The physical origin of bands, partial and
+full magnonic bandgaps has been explained by plotting the spatial distribution
+of spin wave energy spectral density. Although, unfettered by rigid assumptions
+and approximations, which afflict most analytical methods used in the study of
+spin wave dynamics, micromagnetic simulations tend to be computationally
+demanding. Thus, the observation of collective spin wave excitation in the case
+of nanodot arrays, which can obviate the need to perform simulations may also
+prove to be valuable.",1312.3044v1
+2013-12-20,Magnon condensation with finite degeneracy on the triangular lattice,"We study the spin 1/2 triangular-lattice $J_1$-$J_2$-$J_3$ antiferromagnet
+close to the saturation field using the dilute Bose gas theory, where the
+magnetic structure is determined by the condensation of magnons. We focus on
+the case of ferromagnetic $J_1$ and antiferromagnetic $J_2,J_3$, that is
+particularly rich because frustration effects allow the single-magnon energy
+dispersion to have six-fold degenerate minima at incommensurate momenta. Our
+calculation also includes an interlayer coupling $J_0$, which covers both
+antiferromagnetic and ferromagnetic cases including negligibly small regime
+(two-dimensional case). Besides the spiral and fan phases, we find a new
+double-$q$ phase (superposition of two modes), dubbed ""${\bf Q}_0$-${\bf Q}_1$""
+(or simply ""01"") phase, that enjoys a new type of multiferroic character.
+Certain phase boundaries have a singular $J_0$ dependence for $J_0\to 0$,
+implying that even a very small interlayer coupling drastically changes the
+ground state. A mechanism for this singularity is presented. Moreover, in some
+regions of the parameter space, we show that a dilute gas of magnons can not be
+stable, and phase separation (corresponding to a magnetization jump) is
+expected. In the $J_1$-$J_2$ model ($J_3=0$), formation of two-magnon bound
+states is observed, which can lead to a quadrupolar (spin-nematic) ordered
+phase. Exact diagonalization analysis is also applied to the search of bound
+states.",1312.5935v2
+2014-11-12,Magnonic Holographic Memory: from Proposal to Device,"In this work, we present recent developments in magnonic holographic memory
+devices exploiting spin waves for information transfer. The devices comprise a
+magnetic matrix and spin wave generating/detecting elements placed on the edges
+of the waveguides. The matrix consists of a grid of magnetic waveguides
+connected via cross junctions. Magnetic memory elements are incorporated within
+the junction while the read-in and read-out is accomplished by the spin waves
+propagating through the waveguides. We present experimental data on spin wave
+propagation through NiFe and YIG magnetic crosses. The obtained experimental
+data show prominent spin wave signal modulation (up to 20 dB for NiFe and 35 dB
+for YIG) by the external magnetic field, where both the strength and the
+direction of the magnetic field define the transport between the cross arms. We
+also present experimental data on the 2-bit magnonic holographic memory built
+on the double cross YIG structure with micro-magnets placed on the top of each
+cross. It appears possible to recognize the state of each magnet via the
+interference pattern produced by the spin waves with all experiments done at
+room temperature. Magnonic holographic devices aim to combine the advantages of
+magnetic data storage with wave-based information transfer. We present
+estimates on the spin wave holographic devices performance, including power
+consumption and functional throughput. According to the estimates, magnonic
+holographic devices may provide data processing rates higher than 10^18
+bits/cm2/s while consuming 0.15uW. Technological challenges and fundamental
+physical limits of this approach are also discussed.",1411.3388v1
+2015-01-27,"Magnon spectra and strong spin-lattice coupling in magnetically frustrated MnB2O4 (B = Mn,V): Inelastic light scattering studies","The ferrimagnetic spinels MnB2O4 (B = Mn,V) exhibit a similar series of
+closely spaced magnetic and structural phase transitions at low temperatures,
+reflecting both magnetic frustration and a strong coupling between the spin and
+lattice degrees of freedom. Careful studies of excitations in MnB2O4 (B =
+Mn,V), and the evolution of these excitations with temperature, are important
+for obtaining a microscopic description of the role that magnetic excitations
+and spin-lattice coupling play in the low temperature phase transitions of
+these materials. We report an inelastic light (Raman) scattering study of the
+temperature and magnetic field dependences of one- and two-magnon excitations
+in MnV2O4 and Mn3O4. We observe a pair of q=0 one-magnon modes at 74 cm^{-1}
+and 81 cm^{-1} in MnV2O4, which is in contrast with the single 80 cm^{-1} q=0
+magnon that has been reported for MnV2O4 based on previous neutron scattering
+measurements and spin wave calculations. Additionally, we find that the
+two-magnon energy of MnV2O4 decreases (""softens"") with decreasing temperature
+below T_{N}, which we attribute to strong coupling between magnetic and
+vibrational excitations near the zone boundary.",1501.06897v1
+2015-10-14,Field-induced dynamical properties of the $XXZ$ model on a honeycomb lattice,"We present a comprehensive $1/S$ study of the field-induced dynamical
+properties of the nearest-neighbor $XXZ$ antiferromagnet on a honeycomb lattice
+using the formalism of the nonlinear spin-wave theory developed for this model.
+The external magnetic field controls spin frustration in the system and induces
+non-collinearity of the spin structure, which is essential for the two-magnon
+decay processes. Our results include an intriguing field-evolution of the
+regions of the Brillouin zone wherein decays of spin excitations are prominent,
+a detailed classification of the decay channels involving magnons from both
+excitation branches, and a thorough analysis of the singularities in the magnon
+spectra due to coupling to the two magnon continuum, all of which are
+illustrated for several field and anisotropy values. We highlight a number of
+features related to either the non-Bravais nature of the lattice, or the
+existence of the Dirac-like points in the spectrum. In addition, the asymptotic
+behavior of the decay rates near high-symmetry points is analyzed in detail.
+The inelastic neutron-scattering spin-spin structure factor is obtained in the
+leading $1/S$ order and is shown to exhibit qualitatively distinct fingerprints
+of the decay-induced magnon dynamics such as quasiparticle peaks broadened by
+decays and strong spectral weight redistribution.",1510.04275v2
+2017-02-16,Nonreciprocal magnons and symmetry-breaking in the noncentrosymmetric antiferromagnet,"Magnons, the spin-wave quanta, are disturbances that embody a wave
+propagating through a background medium formed by ordered magnetic moments. In
+an isotropic Heisenberg system, these disturbances vary in a continuous manner
+around an ordered spin structure, thus requiring infinitesimal energy as a
+wavevector approaches a magnetic zone centre. However, competing anisotropic
+interactions arising from broken symmetry can favour a distinct static and
+dynamic spin state causing a shift of the minimum point of the magnon
+dispersion to a nonreciprocal wavevector. Here we report the first direct
+evidence of these nonreciprocal magnons in an antiferromagnet. In the
+antiferromagnet we investigated, namely, noncentrosymmetric
+$\alpha$-Cu$_2$V$_2$O$_7$, they are caused by the incompatibility between
+anisotropic exchange and antisymmetric Dzyaloshinskii-Moriya interactions
+resulting in competing collinear and helical spin structures, respectively. The
+nonreciprocity introduces the difference in the phase velocity of the
+counter-rotating modes, causing the opposite spontaneous magnonic Faraday
+rotation of the left- and right-propagating spin-waves. The breaking of spatial
+inversion and time reversal symmetry is revealed as a magnetic-field-induced
+asymmetric energy shift, which provides a test for the detailed balance
+relation.",1702.04889v1
+2017-02-17,Spin conductance of YIG thin films driven from thermal to subthermal magnons regime by large spin-orbit torque,"We report a study on spin conductance in ultra-thin films of Yttrium Iron
+Garnet (YIG), where spin transport is provided by propagating spin waves, that
+are generated and detected by direct and inverse spin Hall effects in two Pt
+wires deposited on top. While at low current the spin conductance is dominated
+by transport of thermal magnons, at high current, the spin conductance is
+dominated by low-damping non-equilibrium magnons thermalized near the spectral
+bottom by magnon-magnon interaction, with consequent a sensitivity to the
+applied magnetic field and a longer decay length. This picture is supported by
+microfocus Brillouin Light Scattering spectroscopy.",1702.05226v3
+2017-08-18,Magnon Dispersion and Specific Heat of Chiral Magnets on the Pyrochlore Lattice,"Chiral magnets are magnetically ordered insulators having spin scalar
+chirality, and magnons of chiral magnets have been poorly understood. We study
+the magnon dispersion and specific heat for four chiral magnets with Q=0 on the
+pyrochlore lattice. This study is based on the linear-spin-wave approximation
+for the S=1/2 effective Hamiltonian consisting of two kinds of Heisenberg
+interaction and two kinds of Dzyaloshinsky-Moriya interaction. We show that the
+three-in-one-out type chiral magnets possess an optical branch of the magnon
+dispersion near q=0, in addition to three quasiacoustic branches. This differs
+from the all-in/all-out type chiral magnets, which possess four quasiacoustic
+branches. We also show that all four chiral magnets have a gapped magnon energy
+at q=0, indicating the absence of the Goldstone type gapless excitation. These
+results are useful for experimentally identifying the three-in-one-out or
+all-in/all-out type chiral order. Then, we show that there is no qualitative
+difference in the specific heat among the four magnets. This indicates that the
+specific heat is not useful for distinguishing the kinds of chiral orders. We
+finally compare our results with experiments and provide a proposal for the
+three-in-one-out type chiral magnets.",1708.05532v1
+2018-02-26,Spin Seebeck effect and ballistic transport of quasi-acoustic magnons in room-temperature yttrium iron garnet films,"We studied the transient behavior of the spin current generated by the
+longitudinal spin Seebeck effect (LSSE) in a set of platinum-coated yttrium
+iron garnet (YIG) films of different thicknesses. The LSSE was induced by means
+of pulsed microwave heating of the Pt layer and the spin currents were measured
+electrically using the inverse spin Hall effect in the same layer. We
+demonstrate that the time evolution of the LSSE is determined by the evolution
+of the thermal gradient triggering the flux of thermal magnons in the vicinity
+of the YIG/Pt interface. These magnons move ballistically within the YIG film
+with a constant group velocity, while their number decays exponentially within
+an effective propagation length. The ballistic flight of the magnons with
+energies above 20K is a result of their almost linear dispersion law, similar
+to that of acoustic phonons. By fitting the time-dependent LSSE signal for
+different film thicknesses varying by almost an order of magnitude, we found
+that the effective propagation length is practically independent of the YIG
+film thickness. We consider this fact as strong support of a ballistic
+transport scenario - the ballistic propagation of quasi-acoustic magnons in
+room temperature YIG.",1802.09593v1
+2017-01-18,Excitation of magnon accumulation by laser clocking as a source of long-range spin waves in transparent magnetic films,"Optical tools are of great promise for generation of spin waves due to the
+possibility to manipulate on ultrashort time scales and to provide local
+excitation. However, a single laser pulse can inject spin waves only with a
+broad frequency spectrum, resulting in a short propagation distance and low
+amplitude. Here we excite a magnetic garnet film by a train of fs-laser pulses
+with 1 GHz repetition rate so that pulse separation is smaller than decay time
+of the magnetic modes which allows to achieve collective photonic impact on
+magnetization. It establishes a quasi-stationary source of SWs, namely a
+coherent magnon accumulation (""magnon cloud""). This approach has several
+appealing features: (i) the source is tunable; (ii) the SW amplitude can be
+significantly enhanced; (iii) the spectrum of the generated SWs is quite narrow
+that provides longer propagation distance; (iv) the periodic pumping results in
+almost constant in time SW amplitude up to 100 um away from the source; and (v)
+the SW emission shows a pronounced directionality. These results expand the
+capabilities of ultrafast coherent optical control of magnetization and pave a
+way for applications in data processing, including the quantum regime. The
+quasi-stationary magnon accumulation might be also of interest for the problem
+of magnon Bose-Einstein condensate.",1701.05109v1
+2011-11-11,Real and Virtual Bound States in Lüscher Corrections for CP3 Magnons,"We study classical and quantum finite-size corrections to giant magnons in
+AdS_4 x CP^3 using generalised L\""uscher formulae. L\""uscher F-terms are
+organised in powers of the exponential suppression factor exp(-Delta/2h)^m, and
+we calculate all terms in this series, matching one-loop algebraic curve
+results from our previous paper arXiv:1006.2174. Starting with the second term,
+the structure of these terms is different to those in AdS_5 x S^5 thanks to the
+appearance of heavy modes in the loop, which can here be interpreted as
+two-particle bound states in the mirror theory. By contrast, physical bound
+states can represent dyonic giant magnons, and we also calculate F-terms for
+these solutions. L\""uscher mu-terms, suppressed by exp(-Delta/E), instead give
+at leading order the classical finite-size correction. For an elementary dyonic
+giant magnon, we recover the correction given by arXiv:0903.3365. We then
+extend this to calculate the next term in 1/h, giving a one-loop prediction.
+Finally we also calculate F-terms for the various composite giant magnons, RP^3
+and `big', again finding agreement to all orders.",1111.2839v3
+2012-01-14,Effect of lattice geometry on magnon Hall effect in ferromagnetic insulators,"We have investigated the thermal Hall effect of magnons for various
+ferromagnetic insulators. For pyrochlore ferromagnetic insulators
+Lu$_2$V$_2$O$_7$, Ho$_2$V$_2$O$_7$, and In$_2$Mn$_2$O$_7$, finite thermal Hall
+conductivities have been observed below the Curie temperature $T_C$ . From the
+temperature and magnetic field dependences, it is concluded that magnons are
+responsible for the thermal Hall effect. The Hall effect of magnons can be well
+explained by the theory based on the Berry curvature in momentum space induced
+by the Dzyaloshinskii-Moriya (DM) interaction. The analysis has been extended
+to the transition metal (TM) oxides with perovskite structure. The thermal Hall
+signal was absent or far smaller in La$_2$NiMnO$_6$ and YTiO$_3$, which have
+the distorted perovskite structure with four TM ions in the unit cell. On the
+other hand, a finite thermal Hall response is discernible below $T_C$ in
+another ferromagentic perovskite oxide BiMnO$_3$, which shows orbital ordering
+with a larger unit cell. The presence or absence of the thermal Hall effect in
+insulating pyrochlore and perovskite systems reflect the geometric and
+topological aspect of DM-induced magnon Hall effect.",1201.3002v2
+2017-06-11,Dirac magnons in honeycomb ferromagnets,"The discovery of the Dirac electron dispersion in graphene led to the
+question of the Dirac cone stability with respect to interactions. Coulomb
+interactions between electrons were shown to induce a logarithmic
+renormalization of the Dirac dispersion. With a rapid expansion of the list of
+compounds and quasiparticle bands with linear band touching, the concept of
+bosonic Dirac materials has emerged. We consider a specific case of
+ferromagnets consisting of the Van der Waals-bonded stacks of honeycomb layers,
+e.g chromium trihalides CrX3 (X = F, Cl, Br and I), that display two spin wave
+modes with energy dispersion similar to that for the electrons in graphene. At
+the single particle level, these materials resemble their fermionic
+counterparts. However, how different particle statistics and interactions
+affect the stability of Dirac cones has yet to be determined. To address the
+role of interacting Dirac magnons, we expand the theory of ferromagnets beyond
+the standard Dyson theory to a case of non-Bravais honeycomb layers. We
+demonstrate that magnon-magnon interactions lead to a significant
+momentum-dependent renormalization of the bare band structure in addition to
+strongly momentum-dependent magnon lifetimes. We show that our theory
+qualitatively accounts for hitherto unexplained anomalies in a nearly half
+century old magnetic neutron scattering data for CrBr3. We also show that
+honeycomb ferromagnets display dispersive surface and edge states, unlike their
+electronic analogs.",1706.03384v1
+2017-10-09,Laser-driven quantum magnonics and THz dynamics of the order parameter in antiferromagnets,"The impulsive generation of two-magnon modes in antiferromagnets by
+femtosecond optical pulses, so-called femto-nanomagnons, leads to coherent
+longitudinal oscillations of the antiferromagnetic order parameter that cannot
+be described by a thermodynamic Landau-Lifshitz approach. We argue that this
+dynamics is triggered as a result of a laser-induced modification of the
+exchange interaction. In order to describe the oscillations we have formulated
+a quantum mechanical description in terms of magnon pair operators and coherent
+states. Such an approach allowed us to} derive an effective macroscopic
+equation of motion for the temporal evolution of the antiferromagnetic order
+parameter. An implication of the latter is that the photo-induced spin dynamics
+represents a macroscopic entanglement of pairs of magnons with femtosecond
+period and nanometer wavelength. By performing magneto-optical pump-probe
+experiments with 10 femtosecond resolution in the cubic KNiF$_3$ and the
+uniaxial K$_2$NiF$_4$ collinear Heisenberg antiferromagnets, we observed
+coherent oscillations at the frequency of 22 THz and 16 THz, respectively. The
+detected frequencies as a function of the temperature ideally fit the
+two-magnon excitation up to the N\'eel point. The experimental signals are
+described as dynamics of magnetic linear dichroism due to longitudinal
+oscillations of the antiferromagnetic vector.",1710.03143v3
+2017-12-12,Microwave to optical photon conversion by means of travelling-wave magnons in YIG films,"In this work we study theoretically the efficiency of a travelling magnon
+based microwave to optical photon converter for applications in Quantum
+Information (QI). The converter employs an epitaxially grown yttrium iron
+garnet (YIG) film as the medium for propagation of travelling magnons (spin
+waves). The conversion is achieved through coupling of magnons to guided
+optical modes of the film. The total microwave to optical photon conversion
+efficiency is found to be larger than in a similar process employing a YIG
+sphere by at least 4 orders of magnitude. By creating an optical resonator of a
+large length from the film (such that the traveling magnon decays before
+forming a standing wave over the resonator length) one will be able to further
+increase the efficiency by several orders of magnitude, potentially reaching a
+value similar to achieved with opto-mechanical resonators. Also, as a spin-off
+result, it is shown that isolation of more that 20 dB with direct insertion
+losses about 5 dBm can be achieved with YIG film based microwave isolators for
+applications in Quantum Information.
+  An important advantage of the suggested concept of the QI devices based on
+travelling spin waves is a perfectly planar geometry and a possibility of
+implementing a the device as a hybrid opto-microwave chip.",1712.04304v2
+2017-09-19,Criteria for accurate determination of the magnon relaxation length from the nonlocal spin Seebeck effect,"The nonlocal transport of thermally generated magnons not only unveils the
+underlying mechanism of the spin Seebeck effect, but also allows for the
+extraction of the magnon relaxation length ($\lambda_m$) in a magnetic
+material, the average distance over which thermal magnons can propagate. In
+this study, we experimentally explore in yttrium iron garnet (YIG)/platinum
+systems much further ranges compared with previous investigations. We observe
+that the nonlocal SSE signals at long distances ($d$) clearly deviate from a
+typical exponential decay. Instead, they can be dominated by the nonlocal
+generation of magnon accumulation as a result of the temperature gradient
+present away from the heater, and decay geometrically as $1/d^2$. We emphasize
+the importance of looking only into the exponential regime (i.e., the
+intermediate distance regime) to extract $\lambda_m$. With this principle, we
+study $\lambda_m$ as a function of temperature in two YIG films which are 2.7
+and 50 $\mu$m in thickness, respectively. We find $\lambda_m$ to be around 15
+$\mu$m at room temperature and it increases to 40 $\mu$m at $T=$ 3.5 K. Finite
+element modeling results agree with experimental studies qualitatively, showing
+also a geometrical decay beyond the exponential regime. Based on both
+experimental and modeling results we put forward a general guideline for
+extracting $\lambda_m$ from the nonlocal spin Seebeck effect.",1709.06321v1
+2018-03-22,Field induced magnon excitation and in gap absorption of Kitaev candidate RuCl3,"We use time-domain terahertz spectroscopy to measure the low energy
+conductivity and magnons in RuCl$_3$ under external magnetic field. At zero
+field, an oscillation with a frequency of 0.62 THz is clearly observed in
+time-domain spectrum below T$_N$, which is identified as a magnon excitation in
+the magnetic order state. The magnon excitation is not affected by the external
+magnetic field $\textbf{H}_{DC}$ when it is applied along the c-axis, but is
+clearly suppressed when $\textbf{H}_{DC}$ is applied within ab plane. More
+interestingly, when the magnetic component of THz wave $\textbf{h}(t)$ is
+perpendicular to the applied in-plane magnetic field, we observe another
+coherent oscillation at slightly higher energy scale at the field above 2 T,
+which is eventually suppressed for $H_{DC}>$5 T. The measurement seems to
+indicate that the in-plane magnetic field can lift the degeneracy of two
+branches of low energy magnons at $\Gamma$ point. The low energy optical
+conductivity calculated from the measured transmission spectrum is dominated by
+a broad continuum contribution, which is not affected by changing either
+temperature or external magnetic field. The continuum is likely to be related
+to the fractional spin excitation due to dominated Kitaev interaction in the
+material.",1803.08398v1
+2019-01-02,Skyrmion Tubes as Magnonic Waveguides,"Various latest experiments have proven the theoretical prediction that domain
+walls in planar magnetic structures can channel spin waves as outstanding
+magnonic waveguides, establishing a superb platform for building magnonic
+devices. Recently, three-dimensional nanomagnetism has been boosted up and
+become a significant branch of magnetism, because three-dimensional magnetic
+structures expose a lot of emerging physics hidden behind planar ones and will
+inevitably provide broader room for device engineering. Skyrmions and
+antiSkyrmions, as natural three-dimensional magnetic configurations, are not
+considered yet in the context of spin-wave channeling and steering. Here, we
+show that skyrmion tubes can act as nonplanar magnonic waveguides if excited
+suitably. An isolated skyrmion tube in a magnetic nanoprism induces spatially
+separate internal and edge channels of spin waves; the internal channel has a
+narrower energy gap, compared to the edge channel, and accordingly can transmit
+signals at lower frequencies. Additionally, we verify that those spin-wave
+beams along magnetic nanoprism are restricted to the regions of potential
+wells. Transmission of spin-wave signals in such waveguides results from the
+coherent propagation of locally driven eigenmodes of skyrmions, i.e., the
+breathing and rotational modes. Finally, we find that spin waves along the
+internal channels are less susceptible to magnetic field than those along the
+edge channels. Our work will open a new arena for spin-wave manipulation and
+help bridge skyrmionics and magnonics.",1901.00253v1
+2019-01-07,Abnormal anti-crossing effect in photon-magnon coupling,"We report the experimental demonstration of an abnormal, opposite
+anti-crossing effect in a photon-magnon-coupled system that consists of an
+Yttrium Iron Garnet film and an inverted pattern of split-ring resonator
+structure (noted as ISRR) in a planar geometry. It is found that the normal
+shape of anti-crossing dispersion typically observed in photon-magnon coupling
+is changed to its opposite anti-crossing shape just by changing the
+position/orientation of the ISRR's split gap with respect to the microstrip
+line axis along which ac microwave currents are applied. Characteristic
+features of the opposite anti-crossing dispersion and its linewidth evolution
+are analyzed with the help of analytical derivations based on electromagnetic
+interactions. The observed opposite anti-crossing dispersion is ascribed to the
+compensation of both intrinsic damping and coupling-induced damping in the
+magnon modes. This compensation is achievable by controlling the relative
+strength and phase of oscillating magnetic fields generated from the ISRR's
+split gap and the microstrip feeding line. The position/orientation of an
+ISRR's split gap provides a robust means of controlling the dispersion shape of
+anti-crossing and its damping in a photon-magnon coupling, thereby offering
+more opportunity for advanced designs of microwave devices.",1901.01729v2
+2019-01-10,Spin-wave Confinement and Coupling in Organic-Based Magnetic Nanostructures,"Vanadium tetracyanoethylene (V[TCNE]$_\text{x}$) is an organic-based
+ferrimagnet that exhibits robust magnetic ordering (T$_\text{C}$ of over 600
+K), high quality-factor (high-Q) microwave resonance (Q up to 3,500), and
+compatibility with a wide variety of substrates and encapsulation technologies.
+Here, we substantially expand the potential scope and impact of this emerging
+material by demonstrating the ability to produce engineered nanostructures with
+tailored magnetic anisotropy that serve as a platform for the exploration of
+cavity magnonics, revealing strongly coupled quantum confined standing wave
+modes that can be tuned into and out of resonance with an applied magnetic
+field. Specifically, time-domain micromagnetic simulations of these
+nanostructures faithfully reproduce the experimentally measured spectra,
+including the quasi-uniform mode and higher-order spin-wave (magnon) modes.
+Finally, when the two dominant magnon modes present in the spectra are brought
+into resonance by varying the orientation of the in-plane magnetic field, we
+observe anti-crossing behavior indicating strong coherent coupling between
+these two magnon modes at room temperature. These results position
+V[TCNE]$_\text{x}$ as a leading candidate for the development of coherent
+magnonics, with potential applications ranging from microwave electronics to
+quantum information.",1901.03286v2
+2019-08-16,Antiferromagnetic cavity optomagnonics,"Currently, there is a growing interest in studying the coherent interaction
+between magnetic systems and electromagnetic radiation in a cavity, prompted
+partly by possible applications in hybrid quantum systems. We propose a
+multimode cavity optomagnonic system based on antiferromagnetic insulators,
+where optical photons couple coherently to the two homogeneous magnon modes of
+the antiferromagnet. These have frequencies typically in the THz range, a
+regime so far mostly unexplored in the realm of coherent interactions, and
+which makes antiferromagnets attractive for quantum transduction from THz to
+optical frequencies. We derive the theoretical model for the coupled system,
+and show that it presents unique characteristics. In particular, if the
+antiferromagnet presents hard-axis magnetic anisotropy, the optomagnonic
+coupling can be tuned by a magnetic field applied along the easy axis. This
+allows to bring a selected magnon mode into and out of a dark mode, providing
+an alternative for a quantum memory protocol. The dynamical features of the
+driven system present unusual behavior due to optically induced magnon-magnon
+interactions, including regions of magnon heating for a red detuned driving
+laser. The multimode character of the system is evident in a substructure of
+the optomagnonically induced transparency window.",1908.06110v2
+2019-11-18,Experimental observation of Josephson oscillations in a room-temperature Bose-Einstein magnon condensate,"The alternating current (ac) Josephson effect in a time-independent
+spatially-inhomogeneous setting is manifested by the occurrence of Josephson
+oscillations - periodic macroscopic phase-induced collective motions of the
+quantum condensate. So far, this phenomenon was observed at cryogenic
+temperatures in superconductors, in superfluid helium, and in Bose-Einstein
+condensates (BECs) of trapped atoms. Here, we report on the discovery of the ac
+Josephson effect in a magnon BEC carried by a room-temperature ferrimagnetic
+film. The BEC is formed in a parametrically populated magnon gas in the spatial
+vicinity of a magnetic trench created by a dc electric current. The appearance
+of the Josephson effect is manifested by oscillations of the magnon BEC density
+in the trench, caused by a coherent phase shift between this BEC and the BEC in
+the nearby regions. Our findings advance the physics of room-temperature
+macroscopic quantum phenomena and will allow for their application for data
+processing in magnon spintronics devices.",1911.07802v3
+2019-11-21,Modulation-induced long-range magnon bound states in one-dimensional optical lattices,"Ultracold two-level atoms in optical lattices offer an excellent experimental
+platform to explore magnon excitations [Fukuhara et al 2013 Nat. Phys. 9, 235;
+Fukuhara et al 2013 Nature 502, 76]. Here, we investigate how gradient magnetic
+field and periodically modulated tunneling strength affect the two-magnon
+excitations in these ultracold atomic systems. In the resonant condition where
+the driving frequency matches and smooths the potential bias, the system gains
+translational invariance in both space and time in the rotating frame, and thus
+we can develop a Floquet-Bloch band theory for two magnons. We find a new kind
+of bound states with relative distance no less than two sites, apart from the
+conventional bound states with relative distance at one site, which indicates
+the modulation-induced long-range interaction. We analytically derive an
+effective Hamiltonian via the many-body perturbation theory for a deeper
+understanding of such novel bound states and explore the interplay between
+these two types of bound states. Moreover, we propose to probe
+modulation-induced bound states via quantum walks. Our study not only provides
+a scheme to form long-range magnon bound states, but also lays a cornerstone
+for engineering exotic quantum states in multi-particle Floquet systems.",1911.09369v2
+2019-12-11,Travelling photons mediated interactions between a magnon mode and a cavity photon mode,"We systematically study the indirect interaction between a magnon mode and a
+cavity photon mode mediated by travelling photons of a waveguide. From a
+general Hamiltonian, we derive the effective coupling strength between two
+separated modes, and obtain the theoretical expression of system's
+transmission. Accordingly, we design an experimental set-up consisting of a
+shield cavity photon mode, microstrip line and a magnon system to test our
+theoretical predictions. From measured transmission spectra, indirect
+interaction, as well as mode hybridization, between two modes can be observed.
+All experimental observations support our theoretical predictions. In this
+work, we clarify the mechanism of travelling photon mediated interactions
+between two separate modes. Even without spatial mode overlap, two separated
+modes can still couple with each other through their correlated dissipations
+into a mutual travelling photon bus. This conclusion may help us understand the
+recently discovered dissipative coupling effect in cavity magnonics systems.
+Additionally, the physics and technique developed in this work may benefit us
+in designing new hybrid systems based on the waveguide magnonics.",1912.05478v1
+2016-03-14,Topological honeycomb magnon Hall effect: A calculation of thermal Hall conductivity of magnetic spin excitations,"Quite recently, magnon Hall effect of spin excitations has been observed
+experimentally on the kagome and pyrochlore lattices. Thermal Hall conductivity
+$\kappa^{xy}$, changes sign as a function of magnetic field or temperature on
+the kagome lattice, and $\kappa^{xy}$ changes sign upon reversing the sign of
+the magnetic field on the pyrochlore lattice. Motivated by these recent
+exciting experimental observations, we theoretically propose a simple
+realization of magnon Hall effect in a two-band model on the honeycomb lattice.
+The magnon Hall effect of spin excitations arises in the usual way via the
+breaking of inversion symmetry of the lattice, however, by a
+next-nearest-neighbour Dzyaloshinsky-Moriya (DM) interaction. We find that
+$\kappa^{xy}$ has a fixed sign for all parameter regimes considered. These
+results are in contrast to the Lieb, kagome and pyrochlore lattices. We further
+show that the low-temperature dependence on the magnon Hall conductivity
+follows a $T^{2}$ law, as opposed to the kagome and pyrochlore lattices. These
+results suggest an experimental procedure to measure thermal Hall conductivity
+within a class of 2D honeycomb quantum magnets and ultracold atoms trapped in
+honeycomb optical lattice.",1603.04331v6
+2016-03-21,Inelastic Magnon Scattering,"We study the worldsheet S-matrix of a string attached to a D-brane in
+AdS$_5\times$S$^5$. The D-brane is either a giant graviton or a dual giant
+graviton. In the gauge theory, the operators we consider belong to the
+$su(2|3)$ sector of the theory. Magnon excitations of open strings can exhibit
+both elastic (when magnons in the bulk of the string scatter) and inelastic
+(when magnons at the endpoint of an open string participate) scattering. Both
+of these $S$-matrices are determined (up to an overall phase) by the
+$su(2|2)^2$ global symmetry of the theory. In this note we study the $S$-matrix
+for inelastic scattering. We show that it exhibits poles corresponding to
+boundstates of bulk and boundary magnons. A crossing equation is derived for
+the overall phase. It reproduces the crossing equation for maximal giant
+gravitons, in the appropriate limit. Finally, scattering in the $su(2)$ sector
+is computed to two loops. This two loop result, which determines the overall
+phase to two loops, will be useful when a unique solution to the crossing
+equation is to be selected.",1603.06414v2
+2016-10-27,Magnonic Analogs of Topological Dirac Semimetals,"In electronic topological Dirac semimetals the conduction and valence bands
+touch at discrete points in the Brillouin zone and form Dirac cones. They are
+robust against spin-orbit interaction (SOI) and protected by crystal
+symmetries. They can be driven to different topological phases by breaking the
+symmetries. In the low-temperature quantum magnetic systems the magnon
+dispersions have similar band structures as the electron dispersions, but with
+positive definite energies. In these magnetic systems SOI manifests in the form
+of the Dzyaloshinskii-Moriya interaction (DMI). In this Communication, we
+identify two types of {\it magnonic Dirac semimetals} in quasi-two-dimensional
+quantum magnets. The first type is a consequence of topological phase
+transition between trivial and topological magnon insulators and the second
+type is intrinsic and protected by crystal symmetries. They are robust against
+DMI and can be driven to a topological magnon phase by breaking the symmetries.
+They can be manipulated by an external magnetic field and accessible by the
+bulk sensitive inelastic neutron scattering experiments.",1610.08869v14
+2017-07-08,Magnetic ground state and magnon-phonon interaction in multiferroic h-YMnO$_3$,"Inelastic neutron scattering has been used to study the magneto-elastic
+excitations in the multiferroic manganite hexagonal YMnO$_3$. An avoided
+crossing is found between magnon and phonon modes close to the Brillouin zone
+boundary in the $(a,b)$-plane. Neutron polarization analysis reveals that this
+mode has mixed magnon-phonon character. An external magnetic field along the
+$c$-axis is observed to cause a linear field-induced splitting of one of the
+spin wave branches. A theoretical description is performed, using a Heisenberg
+model of localized spins, acoustic phonon modes and a magneto-elastic coupling
+via the single-ion magnetostriction. The model quantitatively reproduces the
+dispersion and intensities of all modes in the full Brillouin zone, describes
+the observed magnon-phonon hybridized modes, and quantifies the magneto-elastic
+coupling. The combined information, including the field-induced magnon
+splitting, allows us to exclude several of the earlier proposed models and
+point to the correct magnetic ground state symmetry, and provides an effective
+dynamic model relevant for the multiferroic hexagonal manganites.",1707.02468v2
+2020-06-20,Momentum-dependent magnon lifetime in the metallic non-collinear triangular antiferromagnet CrB2,"Non-collinear magnetic order arises for various reasons in several magnetic
+systems and exhibits interesting spin dynamics. Despite its ubiquitous
+presence, little is known of how magnons, otherwise stable quasiparticles,
+decay in these systems, particularly in metallic magnets. Using inelastic
+neutron scattering, we examine the magnetic excitation spectra in a metallic
+non-collinear antiferromagnet CrB$_{2}$, in which Cr atoms form a triangular
+lattice and display incommensurate magnetic order. Our data show intrinsic
+magnon damping and continuum-like excitations that cannot be explained by
+linear spin wave theory. The intrinsic magnon linewidth $\Gamma(q,E_{q})$ shows
+very unusual momentum dependence, which our analysis shows to originate from
+the combination of two-magnon decay and the Stoner continuum. By comparing the
+theoretical predictions with the experiments, we identify where in the momentum
+and energy space one of the two factors becomes more dominant. Our work
+constitutes a rare comprehensive study of the spin dynamics in metallic
+non-collinear antiferromagnets. It reveals, for the first time, definite
+experimental evidence of the higher-order effects in metallic antiferromagnets.",2006.11530v2
+2015-12-24,Ultra-High Cooperativity Interactions between Magnons and Resonant Photons in a YIG sphere,"Resonant photon modes of a 5mm diameter YIG sphere loaded in a cylindrical
+cavity in the 10-30GHz frequency range are characterised as a function of
+applied DC magnetic field at millikelvin temperatures. The photon modes are
+confined mainly to the sphere, and exhibited large mode filling factors in
+comparison to previous experiments, allowing ultrastrong coupling with the
+magnon spin wave resonances. The largest observed coupling between photons and
+magnons is $2g/2\pi=7.11$ GHz for a 15.5 GHz mode, corresponding to a
+cooperativity of $C=1.51\pm0.47\times10^7$. Complex modifications beyond a
+simple multi-oscillator model, of the photon mode frequencies were observed
+between 0 and 0.1 Tesla. Between 0.4 to 1 Tesla, degenerate resonant photon
+modes were observed to interact with magnon spin wave resonances with different
+couplings strengths, indicating time reversal symmetry breaking due to the
+gyrotropic permeability of YIG. Bare dielectric resonator mode frequencies were
+determined by detuning magnon modes to significantly higher frequencies with
+strong magnetic fields. By comparing measured mode frequencies at 7 Tesla with
+Finite Element modelling, a bare dielectric permittivity of $15.96\pm0.02$ of
+the YIG crystal has been determined at about $20$ mK.",1512.07773v5
+2016-09-01,The role of the internal demagnetizing field in a surface-modulated magnonic crystal,"Magnonic crystals with locally alternating properties and specific
+periodicities exhibit interesting effects, such as a multitude of different
+spin-wave states and large band gaps. This work aims for demonstrating and
+understanding the key role of local demagnetizing fields in such systems. To
+achieve this, hybrid structures are investigated consisting of a continuous
+thin film with a stripe modulation on top favorable due to the adjustability of
+the magnonic effects with the modulation size. For a direct access to the spin
+dynamics, a magnonic crystal was reconstructed from `bottom-up', i.e., the
+structural shape as well as the internal field landscape of the structure were
+experimentally obtained on the nanoscale using electron holography.
+Subsequently, both properties were utilized to perform dynamic response
+calculations. The simulations yield the frequency-field dependence as well as
+the angular dependence of spin waves in a magnonic crystal and reveal the
+governing role of the internal field landscape around the backward-volume
+geometry. The complex angle-dependent spin-wave behavior is described for a 360
+degree in-plane rotation of an external field by connecting the internal field
+landscape with the individual spin-wave localization.",1609.00342v3
+2016-09-12,Topological Magnon Insulator in NonCoplanar Kagomé Antiferromagnets: Supplemental Material of arXiv:1608.04561,"Topological magnon insulators in insulating Kagom\'e ferromagnets have been
+extensively studied in a series of papers. It has been established that
+Dzyaloshinskii-Moriya interaction (DMI) is the key ingredient to observe a
+nontrivial topological magnon with edge modes. However, insulating
+antiferromagnets on the Kagom\'e lattice are frustrated systems considered as a
+playground for studying quantum spin liquid physics. In these systems the DMI
+can induce a coplanar but noncollinear magnetic orders with a $\mathbf{q}=0$
+propagating wavevector. We show that topological magnon bands are absent in
+this coplanar spin texture in sharp contrast to collinear ferromagnets with
+DMI. Hence, geometrically frustrated Kagom\'e antiferromagnets can be deemed
+topologically trivial. The presence of an out-of-plane magnetic field in these
+frustrated magnets induces noncoplanar spin textures exhibiting a nonzero spin
+scalar chirality. We show that the field-induced spin chirality provides
+topological magnon bands in Kagom\'e antiferromagnets without the need of DMI
+and survives in the chiral spin liquid phase of frustrated magnets. Possible
+experimentally material includes iron jarosite KFe$_3$(OH)$_{6}$(SO$_{4}$)$_2$.",1609.03563v5
+2018-08-22,Long-distance supercurrent transport in a room-temperature Bose-Einstein magnon condensate,"The term supercurrent relates to a macroscopic dissipation-free collective
+motion of a quantum condensate and is commonly associated with such famous
+low-temperature phenomena as superconductivity and superfluidity. Another type
+of motion of quantum condensates is second sound - a wave of the density of a
+condensate. Recently, we reported on an enhanced decay of a parametrically
+induced Bose-Einstein condensate (BEC) of magnons caused by a supercurrent
+outflow of the BEC phase from the locally heated area of a room temperature
+magnetic film. Here, we present the direct experimental observation of a
+long-distance spin transport in such a system. The condensed magnons being
+pushed out from the potential well within the heated area form a density wave,
+which propagates through the BEC many hundreds of micrometers in the form of a
+specific second sound pulse - Bogoliubov waves - and is reflected from the
+sample edge. The discovery of the long distance supercurrent transport in the
+magnon BEC further advances the frontier of the physics of quasiparticles and
+allows for the application of related transport phenomena for low-loss data
+transfer in perspective magnon spintronics devices.",1808.07407v1
+2019-06-12,Frequency-Division Multiplexing in Magnonic Logic Networks Based on Caustic-Like Spin-Wave Beams,"Wave-based data processing by spin waves and their quanta, magnons, is a
+promising technique to overcome the challenges which CMOS-based logic networks
+are facing nowadays. The advantage of these quasi-particles lies in their
+potential for the realization of energy efficient devices on the micro- to
+nanometer scale due to their charge-less propagation in magnetic materials. In
+this paper, the frequency dependence of the propagation direction of
+caustic-like spin-wave beams in microstructured ferromagnets is studied by
+micromagnetic simulations. Based on the observed alteration of the propagation
+angle, an approach to spatially combine and separate spin-wave signals of
+different frequencies is demonstrated. The presented magnetic structure
+constitutes a prototype design of a passive circuit enabling frequency-division
+multiplexing in magnonic logic networks. It is verified that spin-wave signals
+of different frequencies can be transmitted through the device simultaneously
+without any interaction or creation of spurious signals. Due to the wave-based
+approach of computing in magnonic networks, the technique of frequency-division
+multiplexing can be the basis for parallel data processing in single magnonic
+devices, enabling the multiplication of the data throughput.",1906.04993v2
+2019-07-05,Tunability of domain structure and magnonic spectra in antidot arrays of Heusler alloy,"Materials suitable for magnonic crystals demand low magnetic damping and long
+spin wave (SW) propagation distance. In this context Co based Heusler compounds
+are ideal candidates for magnonic based applications. In this work, antidot
+arrays (with different shapes) of epitaxial
+$\mathrm{Co}_2\mathrm{Fe}_{0.4}\mathrm{Mn}_{0.6}\mathrm{Si}$ (CFMS) Heusler
+alloy thin films have been prepared using e-beam lithography and sputtering
+technique. Magneto-optic Kerr effect and ferromagnetic resonance analysis have
+confirmed the presence of dominant cubic and moderate uniaxial magnetic
+anisotropies in the thin films. Domain imaging via x-ray photoemission electron
+microscopy on the antidot arrays reveals chain like switching or correlated
+bigger domains for different shape of the antidots. Time-resolved MOKE
+microscopy has been performed to study the precessional dynamics and magnonic
+modes of the antidots with different shapes. We show that the optically induced
+spin-wave spectra in such antidot arrays can be tuned by changing the shape of
+the holes. The variation in internal field profiles, pinning energy barrier,
+and anisotropy modifies the spin-wave spectra dramatically within the antidot
+arrays with different shapes. We further show that by combining the
+magnetocrystalline anisotropy with the shape anisotropy, an extra degree of
+freedom can be achieved to control the magnonic modes in such antidot lattices.",1907.02746v1
+2019-10-19,Propagation of spin-waves packets in individual nano-sized yttrium iron garnet magnonic conduits,"Modern-days CMOS-based computation technology is reaching its fundamental
+limitations. The emerging field of magnonics, which utilizes spin waves for
+data transport and processing, proposes a promising path to overcome these
+limitations. Different devices have been demonstrated recently on the macro-
+and microscale, but the feasibility of the magnonics approach essentially
+relies on the scalability of the structure feature size down to an extent of a
+few 10 nm, which are typical sizes for the established CMOS technology. Here,
+we present a study of propagating spin-wave packets in individual yttrium iron
+garnet (YIG) conduits with lateral dimensions down to 50 nm. Space and time
+resolved micro-focused Brillouin-Light-Scattering (BLS) spectroscopy is used to
+characterize the YIG nanostructures and measure the spin-wave decay length and
+group velocity directly. The revealed magnon transport at the scale comparable
+to the scale of CMOS proves the general feasibility of a magnon-based data
+processing.",1910.08801v2
+2019-10-21,High-frequency magnon excitation due to femtosecond spin-transfer torques,"Femtosecond laser pulses can induce ultrafast demagnetization as well as
+generate bursts of hot electron spin currents. In trilayer spin valves
+consisting of two metallic ferromagnetic layers separated by a nonmagnetic one,
+hot electron spin currents excited by an ultrashort laser pulse propagate from
+the first ferromagnetic layer through the spacer reaching the second magnetic
+layer. When the magnetizations of the two magnetic layers are noncollinear,
+this spin current exerts a torque on magnetic moments in the second
+ferromagnet. Since this torque is acting only within the sub-ps timescale, it
+excites coherent high-frequency magnons as recently demonstrated in
+experiments. Here, we calculate the temporal shape of the hot electron spin
+currents using the superdiffusive transport model and simulate the response of
+the magnetic system to the resulting ultrashort spin-transfer torque pulse by
+means of atomistic spin-dynamics simulations. Our results confirm that the
+acting spin-current pulse is short enough to excite magnons with frequencies
+beyond 1 THz, a frequency range out of reach for current induced spin-transfer
+torques. We demonstrate the formation of thickness dependent standing spin
+waves during the first picoseconds after laser excitation. In addition, we vary
+the penetration depth of the spin-transfer torque to reveal its influence on
+the excited magnons. Our simulations clearly show a suppression effect of
+magnons with short wavelengths already for penetration depths in the range of 1
+nm confirming experimental findings reporting penetration depths below $2\,
+{\rm nm}$.",1910.09412v1
+2020-01-27,Resonant thermal energy transfer to magnons in a ferromagnetic nanolayer,"Energy harvesting is a modern concept which makes dissipated heat useful by
+transferring thermal energy to other excitations. Most of the existing
+principles for energy harvesting are realized in systems which are heated
+continuously, for example generating DC voltage in thermoelectric devices. Here
+we present the concept of high-frequency energy harvesting where the dissipated
+heat in a sample excites resonant magnons in a 5-nm thick ferromagnetic metal
+layer. The sample is excited by femtosecond laser pulses with a repetition rate
+of 10 GHz which results in temperature modulation at the same frequency with
+amplitude ~0.1 K. The alternating temperature excites magnons in the
+ferromagnetic nanolayer which are detected by measuring the net magnetization
+precession. When the magnon frequency is brought onto resonance with the
+optical excitation, a 12-fold increase of the amplitude of precession indicates
+efficient resonant heat transfer from the lattice to coherent magnons. The
+demonstrated principle may be used for energy harvesting in various nanodevices
+operating at GHz and sub-THz frequency ranges.",2001.09732v2
+2020-04-22,Excitation of high-frequency magnon modes in magnetoelastic films by short strain pulses,"Development of energy efficient techniques for generation of spin waves
+(magnons) is important for implementation of low-dissipation spin-wave-based
+logic circuits and memory elements. A promising approach to achieve this goal
+is based on the injection of short strain pulses into ferromagnetic films with
+a strong magnetoelastic coupling between spins and strains. Here we report
+micromagnetoelastic simulations of the magnetization and strain dynamics
+excited in Fe$_{81}$Ga$_{19}$ films by picosecond and nanosecond acoustic
+pulses created in a GaAs substrate by a transducer subjected to an optical or
+electrical impulse. The simulations performed via the numerical solution of the
+coupled Landau-Lifshitz-Gilbert and elastodynamic equations show that the
+injected strain pulse induces an inhomogeneous magnetization precession in the
+ferromagnetic film. The precession lasts up to 1 ns and can be treated as a
+superposition of magnon modes having the form of standing spin waves. For
+Fe$_{81}$Ga$_{19}$ films with nanoscale thickness, up to seven (six) distinct
+modes have been revealed under free-surface (pinning) magnetic boundary
+conditions. Remarkably, magnon modes with frequencies over 1 THz can be excited
+by acoustic pulses with an appropriate shape and duration in the films
+subjected to a moderate external magnetic field. This finding shows that short
+strain pulses represent a promising tool for the generation of THz spin waves
+necessary for the implementation of high-speed magnonic devices.",2004.10838v1
+2020-04-30,Current-Controlled Nanomagnetic Writing for Reconfigurable Magnonic Crystals,"Strongly-interacting nanomagnetic arrays are crucial across an ever-growing
+suite of technologies. Spanning neuromorphic computing, control over
+superconducting vortices and reconfigurable magnonics, the utility and appeal
+of these arrays lies in their vast range of distinct, stable magnetisation
+states. Different states exhibit different functional behaviours, making
+precise, reconfigurable state control an essential cornerstone of such systems.
+However, few existing methodologies may reverse an arbitrary array element, and
+even fewer may do so under electrical control, vital for device integration.
+  We demonstrate selective, reconfigurable magnetic reversal of ferromagnetic
+nanoislands via current-driven motion of a transverse domain wall in an
+adjacent nanowire. The reversal technique operates under all-electrical control
+with no reliance on external magnetic fields, rendering it highly suitable for
+device integration across a host of magnonic, spintronic and neuromorphic logic
+architectures. Here, the reversal technique is leveraged to realise two fully
+solid-state reconfigurable magnonic crystals, offering magnonic gating,
+filtering, transistor-like switching and peak-shifting without reliance on
+global magnetic fields.",2004.14709v1
+2020-05-23,Enhanced entanglement and asymmetric EPR steering between magnons,"The generation and manipulation of strong entanglement and
+Einstein-Podolsky-Rosen (EPR) steering in macroscopic systems are outstanding
+challenges in modern physics. Especially, the observation of asymmetric EPR
+steering is important for both its fundamental role in interpreting the nature
+of quantum mechanics and its application as resource for the tasks where the
+levels of trust at different parties are highly asymmetric. Here, we study the
+entanglement and EPR steering between two macroscopic magnons in a hybrid
+ferrimagnet-light system. In the absence of light, the two types of magnons on
+the two sublattices can be entangled, but no quantum steering occurs when they
+are damped with the same rates. In the presence of the cavity field, the
+entanglement can be significantly enhanced, and strong two-way asymmetric
+quantum steering appears between two magnons with equal dispassion. This is
+very different from the conventional protocols to produce asymmetric steering
+by imposing additional unbalanced losses or noises on the two parties at the
+cost of reducing steerability. The essential physics is well understood by the
+unbalanced population of acoustic and optical magnons under the cooling effect
+of cavity photons. Our finding may provide a novel platform to manipulate the
+quantum steering and the detection of bi-party steering provides a knob to
+probe the magnetic damping on each sublattice of a magnet.",2005.11471v1
+2020-05-28,Spin-Pumping-Induced Non-Linear Electric Current on the Surface of a Ferromagnetic Topological Insulator,"We investigate the spin-pumping-induced electric current on the surface of a
+three-dimensional topological insulator hybridized with a ferromagnet, namely,
+ferromagnetic topological insulator. In order to do this, we establish the
+microscopic formalism and construct the perturbation theory using a Keldysh
+Green's function approach. We analyze how this electric current is generated by
+an exchange interaction and an external ac magnetic field, which is the driving
+force of ferromagnetic resonance as well as the spin pumping. The mechanism is
+as follows. First, the ferromagnetic resonance is driven and a zero-momentum
+magnon emerges. It is the fluctuation from the saturation magnetization
+pointing parallel to the precession axis of the ferromagnetic resonance. After
+then, the spin pumping is generated with the zero-momentum magnon being the
+carrier of spin. The zero-momentum magnon and the topological insulator surface
+state couples through the exchange interaction and the spin carried by the
+magnon is transferred to it. Owing to the spin-momentum locking, the
+transferred spin is converted into the momentum of topological insulator
+surface state leading to the generation of electric current flowing
+perpendicular to the precession axis of the ferromagnetic resonance. It is
+quadratic in the amplitude of external ac magnetic field whereas it is linear
+to the strength of the exchange interaction. The associated electric voltage is
+described by the spectrum of zero-momentum magnon. The non-linearity of
+spin-pumping-induced electric current in the ac magnetic field as well as the
+linearity in the exchange-interaction strength reflects that the surface of
+ferromagnetic topological insulator has a high-performing functionality of
+generating the electric charge current by magnetic controlling.",2005.13850v1
+2020-07-06,Stable Higgs mode in anisotropic quantum magnets,"Low-energy excitations associated with the amplitude fluctuation of an order
+parameter in condensed matter systems can mimic the Higgs boson, an elementary
+particle in the standard model, and are dubbed as Higgs modes. Identifying the
+condensed-matter Higgs mode is challenging because it is known in many cases to
+decay rapidly into other low-energy bosonic modes, which renders the Higgs mode
+invisible. Therefore, it is desirable to find a way to stabilize the Higgs
+mode, which can offer an insight into the stabilization mechanism of the Higgs
+mode in condensed matter physics. In quantum magnets, magnetic order caused by
+spontaneous symmetry breaking supports transverse (magnons) and longitudinal
+(Higgs modes) fluctuations. When a continuous symmetry is broken, the Goldstone
+magnon mode generally has a lower excitation energy than the Higgs mode,
+causing a rapid decay of the latter. In this work, we show that a stable Higgs
+mode exists in anisotropic quantum magnets near the quantum critical point
+between the dimerized and magnetically ordered phases. We find that an easy
+axis anisotropy increases the magnon gap such that the magnon mode is above the
+Higgs mode near the quantum critical point, and the decay of the Higgs mode
+into the magnon mode is forbidden kinematically. Our results suggest that the
+anisotropic quantum magnets provide ideal platforms to explore the Higgs
+physics in condensed matter systems.",2007.02498v1
+2020-08-13,Magnetization Dynamics of Nanoscale Magnetic Materials: A Perspective,"Nanomagnets form the building blocks for a gamut of miniaturized
+energy-efficient devices including data storage, memory, wave-based computing,
+sensors and biomedical devices. They also offer a span of exotic phenomena and
+stern challenges. The progress in the magnetization dynamics of single
+nanomagnets and one- and two-dimensional arrays of nanostructures in the form
+of dots, antidots, nanoparticles, binary and bicomponent structures and
+patterned multilayers have been presented. Progress in unconventional and new
+structures like artificial spin ice and three-dimensional nanomagnets and spin
+textures like domain walls, vortex and skyrmions have been presented.
+Furthermore, a huge variety of new topics in the magnetization dynamics of
+magnetic nanostructures are rapidly emerging. An overview of the steadily
+evolving topics like spatio-temporal imaging of fast dynamics of
+nanostructures, dynamics of spin textures, artificial spin ice have been
+discussed. In addition, dynamics of contemporary and newly transpired magnetic
+architectures such as nanomagnet arrays with complex basis and symmetry,
+magnonic quasicrystals, fractals, defect structures, novel three-dimensional
+structures have been introduced. Effects of various spin-orbit coupling and
+ensuing spin textures as well as quantum hybrid systems comprising of
+magnon-photon, magnon-phonon and magnon-magnon coupling, antiferromagnetic
+nanostructures are rapidly growing and are expected to dominate this research
+field in the coming years. Finally, associated topics like nutation dynamics
+and nanomagnet antenna are briefly discussed. Despite showing a great progress,
+only a small fraction of nanomagnetism and its ancillary topics have been
+explored so far and huge efforts are envisaged in this evergrowing research
+area in the generations to come.",2008.05819v1
+2020-11-17,Non-local magnon-based transport in yttrium iron garnet/platinum heterostructures at high temperatures,"The spin Hall effect in a heavy metal thin film allows to probe the magnetic
+properties of an adjacent magnetic insulator via magnetotransport measurements.
+Here, we investigate the magnetoresistive response of yttrium iron
+garnet/platinum heterostructures from room temperature to beyond the Curie
+temperature $T_\mathrm{C, YIG} \approx 560\,\mathrm{K}$ of the ferrimagnetic
+insulator. We find that the amplitude of the (local) spin Hall
+magnetoresistance decreases monotonically from $300\,\mathrm{K}$ towards
+$T_\mathrm{C}$, mimicking the evolution of the saturation magnetization of
+yttrium iron garnet. Interestingly, the spin Hall magnetoresistance vanishes
+around $500\,\mathrm{K}$, well below $T_\mathrm{C}$, which we attribute to the
+formation of a parasitic interface layer by interdiffusion. Around room
+temperature the non-local magnon-mediated magnetoresistance exhibits a power
+law scaling $T^{\alpha}$ with $\alpha = 3/2$, as already reported. The exponent
+decreases gradually to $\alpha \sim 1/2$ at around $420\,\mathrm{K}$, before
+the non-local magnetoresistance vanishes rapidly at a similar temperature as
+the spin Hall magnetoresistance. We attribute the reduced $\alpha$ at high
+temperatures to the increasing thermal magnon population which leads to
+enhanced scattering of the non-equilibrium magnon population and a reduced
+magnon diffusion length. Finally, we find a magnetic field independent offset
+voltage in the non-local signal for $T > 470\,\mathrm{K}$ which we associate
+with electronic leakage currents through the normally insulating yttrium iron
+garnet film. Indeed, this non-local offset voltage is thermally activated with
+an energy close to the band gap.",2011.08589v1
+2021-06-15,Cavity magnon-polaritons in cuprate parent compounds,"Cavity control of quantum matter may offer new ways to study and manipulate
+many-body systems. A particularly appealing idea is to use cavities to enhance
+superconductivity, especially in unconventional or high-$T_c$ systems.
+Motivated by this, we propose a scheme for coupling Terahertz resonators to the
+antiferromagnetic fluctuations in a cuprate parent compound, which are believed
+to provide the glue for Cooper pairs in the superconducting phase. First, we
+derive the interaction between magnon excitations of the Ne\'el-order and polar
+phonons associated with the planar oxygens. This mode also couples to the
+cavity electric field, and in the presence of spin-orbit interactions mediates
+a linear coupling between the cavity and magnons, forming hybridized
+magnon-polaritons. This hybridization vanishes linearly with photon momentum,
+implying the need for near-field optical methods, which we analyze within a
+simple model. We then derive a higher-order coupling between the cavity and
+magnons which is only present in bilayer systems, but does not rely on
+spin-orbit coupling. This interaction is found to be large, but only couples to
+the bimagnon operator. As a result we find a strong, but heavily damped,
+bimagnon-cavity interaction which produces highly asymmetric cavity line-shapes
+in the strong-coupling regime. To conclude, we outline several interesting
+extensions of our theory, including applications to carrier-doped cuprates and
+other strongly-correlated systems with Terahertz-scale magnetic excitations.",2106.07828v1
+2021-06-17,Attraction from frustration in ladder systems,"We analyze the formation of multi-particle bound states in ladders with
+frustrated kinetic energy in two component bosonic and two component fermionic
+systems. We focus on the regime of light doping relative to insulating states
+at half-filling, spin polarization close to 100 percent, and strong repulsive
+interactions. A special feature of these systems is that the binding energy
+scales with single particle tunneling $t$ rather than exchange interactions,
+since effective attraction arises from alleviating kinetic frustration. For two
+component Fermi systems on a zigzag ladder we find a bound state between a hole
+and a flipped spin (magnon) with a binding energy that can be as large as
+$0.6t$. We demonstrate that magnon-hole attraction leads to formation of
+clusters comprised of several holes and magnons and expound on
+antiferromagentic correlations for the transverse spin components inside the
+clusters. We identify several many-body states that result from
+self-organization of multi-particle bound states, including a Luttinger liquid
+of hole-magnon pairs and a density wave state of two hole - three magnon
+composites. We establish a symmetry between the spectra of Bose and Fermi
+systems and use it to establish the existence of antibound states in two
+component Bose mixtures with SU(2) symmetric repulsion on a zigzag ladder. We
+also consider Bose and Fermi systems on a square ladder with flux and
+demonstrate that both systems support bound states. We discuss experimental
+signatures of multi-particle bound states in both equilibrium and dynamical
+experiments. We point out intriguing connections between these systems and the
+quark bag model in QCD.",2106.09600v1
+2021-06-20,Parametric generation of spin waves in nano-scaled magnonic conduits,"The research feld of magnonics proposes a low-energy wave-logic computation
+technology based on spin waves to complement the established CMOS technology
+and provide a basis for emerging unconventional computation architectures.
+However, magnetic damping is a limiting factor for all-magnonic logic circuits
+and multi-device networks, ultimately rendering mechanisms to effciently
+manipulate and amplify spin waves a necessity. In this regard, parallel pumping
+is a versatile tool since it allows to selectively generate and amplify spin
+waves. While extensively studied in microscopic systems, nano-scaled systems
+are lacking investigation to assess the feasibility and potential future use of
+parallel pumping in magnonics. Here, we investigate a longitudinally magnetized
+100 nm-wide magnonic nano-conduit using space and time-resolved micro-focused
+Brillouin-light-scattering spectroscopy. Employing parallel pumping to generate
+spin waves, we observe that the non-resonant excitation of dipolar spin waves
+is favored over the resonant excitation of short wavelength exchange spin
+waves. In addition, we utilize this technique to access the effective spin-wave
+relaxation time of an individual nano-conduit, observing a large relaxation
+time up to (115.0 +- 7.6) ns. Despite the significant decrease of the pumping
+effciency in the investigated nano-conduit, a reasonably small threshold is
+found rendering parallel pumping feasible on the nano-scale.",2106.10727v2
+2021-06-28,Exact solutions of few-magnon problems in the spin-$S$ periodic XXZ chain,"We solve few-magnon problems for a finite-size spin-$S$ periodic Heisenberg
+XXZ chain with single-ion anisotropy through constructing sets of exact Bloch
+states achieving block diagonalization of the system. Concretely, the
+two-magnon (three-magnon) problem is converted to a single-particle one on a
+one-dimensional (two-dimensional) effective lattice whose size depends linearly
+(quadratically) on the total number of sites. For parameters lying within
+certain ranges, various types of multimagnon bound states are manifested and
+shown to correspond to edge states on the effective lattices. In the absence of
+the single-ion anisotropy, we reveal the condition under which exact
+zero-energy states emerge. As applications of the formalism, we calculate the
+transverse dynamic structure factor for a higher-spin chain near saturation
+magnetization and find signatures of the multimagnon bound states. We also
+calculate the real-time three-magnon dynamics from certain localized states,
+which are relevant to cold-atom quantum simulations, by simulating
+single-particle quantum walks on the effective lattices. This provides a
+physically transparent interpretation of the observed dynamics in terms of
+propagation of bound state excitations. Our method can be directly applied to
+more general spin or itinerant particle systems possessing translational
+symmetry.",2106.14809v4
+2021-06-30,Electron-magnon coupling and quasiparticle lifetimes on the surface of a topological insulator,"The fermionic self-energy on the surface of a topological insulator proximity
+coupled to ferro- and antiferromagnetic insulators is studied. An enhanced
+electron-magnon coupling is achieved by allowing the electrons on the surface
+of the topological insulator to have a different exchange coupling to the two
+sublattices of the antiferromagnet. Such a system is therefore seen as superior
+to a ferromagnetic interface for the realization of magnon-mediated
+superconductivity. The increased electron-magnon-coupling simultaneously
+increases the self-energy effects. In this paper we show how the inverse
+quasiparticle lifetime and energy renormalization on the surface of the
+topological insulator can be kept low close to the Fermi level by using a
+magnetic insulator with a sufficient easy-axis anisotropy. We find that the
+antiferromagnetic case is most interesting from both a theoretical and an
+experimental standpoint due to the increased electron-magnon coupling, combined
+with a reduced need for easy-axis anisotropy compared to the ferromagnetic
+case. We also consider a set of material and instrumental parameters where
+these self-energies should be measurable in angle-resolved photoemission
+spectroscopy experiments, paving the way for a measurement of the interfacial
+exchange coupling strength.",2107.00028v2
+2021-07-08,Topological magnon insulators in two-dimensional van der Waals ferromagnets CrSiTe$_3$ and CrGeTe$_3$: towards intrinsic gap-tunability,"The bosonic analogues of topological insulators have been proposed in
+numerous theoretical works, but their experimental realization is still very
+rare, especially for spin systems. Recently, two-dimensional (2D) honeycomb van
+der Waals (vdW) ferromagnets have emerged as a new platform for topological
+spin excitations. Here, via a comprehensive inelastic neutron scattering study
+and theoretical analysis of the spin-wave excitations, we report the
+realization of topological magnon insulators in CrXTe$_3$ (X=Si, Ge) compounds.
+The nontrivial nature and intrinsic tunability of the gap opening at the magnon
+band-crossing Dirac points are confirmed, while the emergence of the
+corresponding in-gap topological edge states is demonstrated theoretically. The
+realization of topological magnon insulators with intrinsic gap-tunability in
+this class of remarkable 2D materials will undoubtedly lead to new and
+fascinating technological applications in the domain of magnonics and
+topological spintronics.",2107.03835v1
+2022-01-27,Magnon-Polaron Driven Thermal Hall Effect in a Heisenberg-Kitaev Antiferromagnet,"The thermal Hall effect, defined as a heat current response transversal to an
+applied temperature gradient, is a central experimental probe of exotic
+electrically insulating phases of matter. A key question is how the interplay
+between magnetic and structural degrees of freedom gives rise to a nonzero
+thermal Hall conductivity (THC). Here, we present evidence for an intrinsic
+thermal Hall effect in the Heisenberg-Kitaev antiferromagnet and spin-liquid
+candidate Na$_2$Co$_2$TeO$_6$ brought about by the quantum-geometric Berry
+curvature of so-called magnon polarons, resulting from magnon-phonon
+hybridization. At low temperatures, our field- and temperature-dependent
+measurements show a negative THC for magnetic fields below 10 T and a sign
+change to positive THC above. Theoretically, the sign and the order of
+magnitude of the THC cannot be solely explained with magnetic excitations. We
+demonstrate that, by incorporating spin-lattice coupling into our theoretical
+calculations, the Berry curvature of magnon polarons counteracts the purely
+magnonic contribution, reverses the overall sign of the THC, and increases its
+magnitude, which significantly improves agreement with experimental data. Our
+work highlights the crucial role of spin-lattice coupling in the thermal Hall
+effect.",2201.11396v2
+2022-05-19,Resonant phonon-magnon interactions in free-standing metal-ferromagnet multilayer structures,"We analyze resonant magneto-elastic interactions between standing
+perpendicular spin wave modes (exchange magnons) and longitudinal acoustic
+phonon modes in free-standing hybrid metal-ferromagnet bilayer and trilayer
+structures. Whereas the ferromagnetic layer acts as a magnetic cavity, all
+metal layers control the frequencies and eigenmodes of acoustic vibrations. The
+here proposed design allows for achieving and tuning the spectral and spatial
+modes overlap between phonons and magnons that results in their strong resonant
+interaction. Realistic simulations for gold-nickel multilayers show that
+sweeping the external magnetic field should allow for observing resonantly
+enhanced interactions between individual magnon and phonon modes in a broad
+range of frequencies spanning from tens of GHz up to several hundreds of GHz,
+which can be finely tuned through the multilayer design. Our results would
+enable the systematic study and the deep understanding of resonantly enhanced
+magneto-elastic coupling between individual phonon and magnon modes up to
+frequencies of great contemporary fundamental and applied interest.",2205.09805v1
+2022-10-05,Particle zoo in a doped spin chain: Correlated states of mesons and magnons,"It is a widely accepted view that the interplay of spin- and charge-degrees
+of freedom in doped antiferromagnets (AFMs) gives rise to the rich physics of
+high-temperature superconductors. Nevertheless, it remains unclear how
+effective low-energy degrees of freedom and the corresponding field theories
+emerge from microscopic models, including the $t-J$ and Hubbard Hamiltonians. A
+promising view comprises that the charge carriers have a rich internal parton
+structure on intermediate scales, but the interplay of the emergent partons
+with collective magnon excitations of the surrounding AFM remains unexplored.
+Here we study a doped one-dimensional spin chain in a staggered magnetic field
+and demonstrate that it supports a zoo of various long-lived excitations. These
+include magnons; mesonic pairs of spinons and chargons, along with their
+ro-vibrational excitations; and tetra-parton bound states of mesons and
+magnons. We identify these types of quasiparticles in various spectra using
+DMRG simulations. Moreover, we introduce a strong-coupling theory describing
+the polaronic dressing and molecular binding of mesons to collective magnon
+excitations. The effective theory can be solved by standard tools developed for
+polaronic problems, and can be extended to study similar physics in
+two-dimensional doped AFMs in the future. Experimentally, the doped spin-chain
+in a staggered field can be directly realized in quantum gas microscopes.",2210.02320v1
+2022-11-12,Quantum control of a single magnon in a macroscopic spin system,"Non-classical quantum states are the pivotal features of a quantum system
+that differs from its classical counterpart. However, the generation and
+coherent control of quantum states in a macroscopic spin system remain an
+outstanding challenge. Here we experimentally demonstrate the quantum control
+of a single magnon in a macroscopic spin system (i.e., 1~mm-diameter
+yttrium-iron-garnet sphere) coupled to a superconducting qubit via a microwave
+cavity. By tuning the qubit frequency {\it in situ} via the Autler-Townes
+effect, we manipulate this single magnon to generate its non-classical quantum
+states, including the single-magnon state and the superposition state of a
+single magnon and vacuum. Moreover, we confirm the deterministic generation of
+these non-classical states by Wigner tomography. Our experiment offers the
+first reported deterministic generation of the non-classical quantum states in
+a macroscopic spin system and paves a way to explore its promising applications
+in quantum engineering.",2211.06644v3
+2022-12-22,Spin wave dispersion of ultra-low damping hematite ($α\text{-Fe}_2\text{O}_3$) at GHz frequencies,"Low magnetic damping and high group velocity of spin waves (SWs) or magnons
+are two crucial parameters for functional magnonic devices. Magnonics research
+on signal processing and wave-based computation at GHz frequencies focussed on
+the artificial ferrimagnetic garnet Y$_3$Fe$_5$O$_{12}$ (YIG) so far. We report
+on spin-wave spectroscopy studies performed on the natural mineral hematite
+($\alpha\text{-Fe}_2\text{O}_3$) which is a canted antiferromagnet. By means of
+broadband GHz spectroscopy and inelastic light scattering, we determine a
+damping coefficient of $1.1\times10^{-5}$ and magnon group velocities of a few
+10 km/s, respectively, at room temperature. Covering a large regime of wave
+vectors up to $k\approx 24~{\rm rad}/\mu$m, we find the exchange stiffness
+length to be relatively short and only about 1 \r{A}. In a small magnetic field
+of 30 mT, the decay length of SWs is estimated to be 1.1 cm similar to the best
+YIG. Still, inelastic light scattering provides surprisingly broad and partly
+asymmetric resonance peaks. Their characteristic shape is induced by the large
+group velocities, low damping and distribution of incident angles inside the
+laser beam. Our results promote hematite as an alternative and sustainable
+basis for magnonic devices with fast speeds and low losses based on a stable
+natural mineral.",2212.11887v2
+2023-01-25,Enhanced tripartite interactions in spin-magnon-mechanical hybrid systems,"Coherent tripartite interactions among degrees of freedom of completely
+different nature are instrumental for quantum information and simulation
+technologies, but they are generally difficult to realize and remain largely
+unexplored. Here, we predict a tripartite coupling mechanism in a hybrid setup
+comprising a single NV center and a micromagnet. We propose to realize direct
+and strong tripartite interactions among single NV spins, magnons and phonons
+via modulating the relative motion between the NV center and the micromagnet.
+Specifically, by introducing a parametric drive (two-phonon drive) to modulate
+the mechanical motion (such as the center-of-mass motion of a NV spin in
+diamond trapped in an electrical trap or a levitated micromagnet in a magnetic
+trap), we can obtain a tunable and strong spin-magnon-phonon coupling at the
+single quantum level, with up to two orders of magnitude enhancement for the
+tripartite coupling strength. This enables, for example, tripartite
+entanglement among solid-state spins, magnons, and mechanical motions in
+quantum spin-magnonics-mechanics with realistic experimental parameters. This
+protocol can be readily implemented with the well-developed techniques in ion
+traps or magnetic traps, and could pave the way for general applications in
+quantum simulations and information processing based on directly and strongly
+coupled tripartite systems.",2301.10424v1
+2023-05-10,Giant spin Nernst effect in a two-dimensional antiferromagnet due to magnetoelastic coupling-induced gaps and interband transitions between magnon-like bands,"We analyze theoretically the origin of the spin Nernst and thermal Hall
+effects in FePS3 as a realization of two-dimensional antiferromagnet (2D AFM).
+We find that a strong magnetoelastic coupling, hybridizing magnetic excitation
+(magnon) and elastic excitation (phonon), combined with
+time-reversal-symmetry-breaking, results in a Berry curvature hotspots in the
+region of anticrossing between the two distinct hybridized bands. Furthermore,
+large spin Berry curvature emerges due to interband transitions between two
+magnon-like bands, where a small energy gap is induced by magnetoelastic
+coupling between such bands that are energetically distant from anticrossing of
+hybridized bands. These nonzero Berry curvatures generate topological
+transverse transport (i.e., the thermal Hall effect) of hybrid excitations,
+dubbed magnon-polaron, as well as of spin (i.e., the spin Nernst effect)
+carried by them, in response to applied longitudinal temperature gradient. We
+investigate the dependence of the spin Nernst and thermal Hall conductivities
+on the applied magnetic field and temperature, unveiling very large spin Nernst
+conductivity even at zero magnetic field. Our results suggest FePS3 AFM, which
+is already available in 2D form experimentally, as a promising platform to
+explore the topological transport of the magnon-polaron quasiparticles at THz
+frequencies.",2305.06020v2
+2023-06-23,Phonon Frequency and its Modification by Magnon-Phonon Coupling from All-Temperature Theory of Magnon,"The all-temperature magnon (ATM) theory [J. Phys. Condens. Matter 21,
+336003/1-14, 2009] has been used to analyze the temperature dependence of
+magnetization as well as the internal energy components of a mono-domain
+ferromagnetic solid. The critical exponents have been in better agreement with
+experiment than their mean-field theory and critical phenomenon theory
+counterparts, and unlike in the latter theories, vary from one ferromagnet to
+another. Expressions have been derived for the thermally averaged spin-center
+force constants and their break-up in terms of the base-line related (solid)
+and exchange-cum-field mediated (magnetic) components. These components give
+rise to expressions for phonon frequencies and their modifications by
+magnon-phonon coupling. The derived expressions are suitable for a correct
+quantum chemical evaluation of the involved properties. A detailed numerical
+calculation using spin configurations at varying crystal geometries is hardly
+possible even today and beyond the scope of the present work. The focus here is
+on the correctness and explaining the trends of properties. It has been shown
+that the frequency modification by magnon-phonon interaction can be negative
+for certain phonon branches near the ferromagnetic transition temperature.
+Also, the ratio of frequency modification and phonon frequency is approximately
+proportional to the ratio of curvatures of the involved energy surfaces.",2306.13346v2
+2023-07-12,Electrical detectability of magnon-mediated spin current shot noise,"A magnonic spin current crossing a ferromagnet-metal interface is accompanied
+by spin current shot noise arising from the discrete quanta of spin carried by
+magnons. In thin films, e.g., the spin of so-called squeezed magnons have been
+shown to deviate from the common value $\hbar$, with corresponding changes in
+the spin noise. In experiments, spin currents are typically converted to charge
+currents via the inverse spin Hall effect. We here analyze the magnitude of the
+spin current shot noise in the charge channel for a typical electrically
+detected spin pumping experiment, and find that the voltage noise originating
+from the spin current shot noise is much smaller than the inevitable
+Johnson-Nyquist noise. Furthermore, we find that due to the local nature of the
+spin-charge conversion, the ratio of spin current shot noise and
+Johnson-Nyquist noise cannot be systematically enhanced by tuning the sample
+geometry, in contrast to the linear increase in dc spin pumping voltage with
+sample length. Instead, the ratio depends sensitively on material-specific
+transport properties. Our analysis thus provides guidance for the experimental
+detection of squeezed magnons through spin pumping shot noise.",2307.06103v2
+2023-08-31,Magnon Orbital Angular Momentum of Ferromagnetic Honeycomb and Zig-Zag Lattices,"By expanding the gauge $\lambda_n(k)$ for magnon band $n$ in harmonics of
+momentum ${\bf k} =(k,\phi )$, we demonstrate that the only observable
+component of the magnon orbital angular momentum $O_n({\bf k})$ is its angular
+average over all angles $\phi$, denoted by $F_n(k)$. For both the FM honeycomb
+and zig-zag lattices, we show that $F_n(k)$ is nonzero in the presence of a
+Dzyalloshinzkii-Moriya (DM) interaction. The FM zig-zag lattice model with
+exchange interactions $0<J_1< J_2$ provides a new system where the effects of
+orbital angular momentum are observable. For the zig-zag model with equal
+exchange interactions $J_{1x}$ and $J_{1y}$ along the $x$ and $y$ axis, the
+magnon bands are degenerate along the boundaries of the Brillouin zone with
+$k_x-k_y =\pm \pi/a$ and the Chern numbers $C_n$ are not well defined. However,
+a revised model with $J_{1y}\ne J_{1x}$ lifts those degeneracy and produces
+well-defined Chern numbers of $C_n=\pm 1$ for the two magnon bands. When
+$J_{1y}=J_{1x}$, the thermal conductivity $\kappa^{xy}(T)$ of the FM zig-zag
+lattice is largest for $J_2/J_1>6$ but is still about four times smaller than
+that of the FM honeycomb lattice at high temperatures. Due to the removal of
+band degeneracies, $\kappa^{xy}(T)$ is slightly enhanced when $J_{1y}\ne
+J_{1x}$.",2308.16832v2
+2023-09-21,A Series Expansion Study for Large Negative Quantum Renormalization of Magnon Spectra in the $S=1/2$ Kagome-Lattice Heisenberg Antiferromagnet Cs$_{2}$Cu$_{3}$SnF$_{12}$,"The series expansion method is used to study magnon spectra of the kagome
+system with nearest-neighbor exchange interaction $J$ and out-of-plane
+Dzyaloshinskii-Moriya (DM) interaction $D^{\parallel}$, which is a minimal
+model for Cs$_{2}$Cu$_{3}$SnF$_{12}$. Compared to the magnon spectra by the
+linear spin wave (LSW) theory, we find that dispersions at high energy part
+suffer downward deformation, which is similar to the triangle lattice case, in
+addition to the reduction of the energy scale of about 40\% as pointed out in a
+neutron-scattering study by Ono {\it et al.} Using a reliable estimation
+$J=20.7$ meV in a previous study on the magnetic susceptibility of
+Cs$_{2}$Cu$_{3}$SnF$_{12}$, we use $D^{\parallel}$ as the fitting parameter to
+reproduce the experimental magnon spectra and obtain $D^{\parallel}=0.12J$. We
+also report that a roton-like minimum occurs at the M point and a maximum at
+points somewhat away from the $\Gamma$ point. Compression of the LSW magnon
+band is commonly seen in the kagome and triangular-lattice systems, which may
+be viewed as being pushed from above by the spinon continuum.",2309.11778v1
+2023-10-24,Spin wave excitations in low dimensional systems with large magnetic anisotropy,"The low energy excitation spectrum of a two-dimensional ferromagnetic
+material is dominated by single-magnon excitations that show a gapless
+parabolic dispersion relation with the spin wave vector. This occurs as long as
+magnetic anisotropy and anisotropic exchange are negligible compared to
+isotropic exchange. However, to maintain magnetic order at finite temperatures,
+it is necessary to have sizable anisotropy to open a gap in the spin wave
+excitation spectrum. We consider four real two-dimensional systems for which
+ferromagnetic order at finite temperature has been observed or predicted.
+Density functional theory calculations of the total energy differences for
+different spin configurations permit us to extract the relevant parameters and
+connect them with a spin Hamiltonian. The corresponding values of the Curie
+temperature are estimated using a simple model and found to be mostly
+determined by the value of the isotropic exchange. The exchange and anisotropy
+parameters are used in a toy model of finite-size periodic chains to study the
+low-energy excitation spectrum, including single-magnon and two-magnon
+excitations. At low energies we find that single-magnon excitations appear in
+the spectrum together with two-magnon excitations. These excitations present a
+gap that grows particularly for large values of the magnetic anisotropy or
+anisotropic exchange, relative to the isotropic exchange.",2310.15942v1
+2023-12-07,Magnon-Photon Coupling in an Opto-Electro-Magnonic Oscillator,"The opto-electronic oscillators (OEOs) hosting self-sustained oscillations by
+a time delayed mechanism are of particular interest in long-haul signal
+transmission and processing. On the other hand, owing to their unique
+tunability and compatibility, magnons - as elementary excitations of spin waves
+- are advantageous carriers for coherent signal transduction across different
+platforms. In this work, we integrated an opto-electronic oscillator with a
+magnonic oscillator consisting of a microwave waveguide and a yttrium iron
+garnet sphere. We find that, in the presence of the magnetic sphere, the
+oscillator power spectrum exhibits sidebands flanking the fundamental OEO
+modes. The measured waveguide transmission reveals anti-crossing gaps, a
+hallmark of the coupling between the opto-electronic oscillator modes and the
+Walker modes of the sphere. Experimental results are well reproduced by a
+coupled-mode theory that accounts for nonlinear magnetostrictive interactions
+mediated by the magnetic sphere. Leveraging the advanced fiber-optic
+technologies in opto-electronics, this work lays out a new, hybrid platform for
+investigating long distance coupling and nonlinearity in coherent magnonic
+phenomena.",2312.04676v2
+2023-12-08,Engineering synthetic gauge fields through the coupling phases in cavity magnonics,"Cavity magnonics, which studies the interaction of light with magnetic
+systems in a cavity, is a promising platform for quantum transducers, quantum
+memories, and devices with non-reciprocal behaviour. At microwave frequencies,
+the coupling between a cavity photon and a magnon, the quasi-particle of a spin
+wave excitation, is a consequence of the Zeeman interaction between the
+cavity's magnetic field and the magnet's macroscopic spin. For each
+photon/magnon interaction, a coupling phase factor exists, but is often
+neglected in simple systems. However, in ""loop-coupled"" systems, where there
+are at least as many couplings as modes, the coupling phases become relevant
+for the physics and lead to synthetic gauge fields. We present experimental
+evidence of the existence of such coupling phases by considering two spheres
+made of Yttrium-Iron-Garnet and two different re-entrant cavities. We predict
+numerically the values of the coupling phases, and we find good agreement
+between theory and the experimental data. Theses results show that in cavity
+magnonics, one can engineer synthetic gauge fields, which can be useful for
+cavity-mediated coupling, dark mode memories, and building nonreciprocal
+devices.",2312.04915v3
+2023-12-29,In-Plane Magnon Valve Effect in Magnetic Insulator/Heavy Metal/ Magnetic Insulator Device,"We propose an in-plane magnon valve (MV), a sandwich structure composed of
+ferromagnetic insulator/heavy metal/ferromagnetic insulator (MI/HM/MI). When
+the magnetizations of the two MI layers are parallel, the longitudinal
+conductance in the HM layer is greater than that in the antiparallel state
+according to the magnetic proximity effect, termed as the in-plane magnon valve
+effect. We investigate the dependence of MV ratio (MVR), which is the relative
+change in longitudinal conductance between the parallel and antiparallel MV
+states, on the difference in electronic structure between magnetized and
+non-magnetized metal atoms, revealing that MVR can reach 100%. Additionally,
+the dependence of MVR on the thickness of metal layer is analyzed, revealing an
+exponential decrease with increasing thickness. Then we investigate the
+dependence of HM layer conductance on the relative angle between the
+magnetizations of two MI layers, illustrating the potential of MV as a
+magneto-sensitive magnonic sensor. We also investigate the effect of Joule
+heating on the measurement signal based on the spin Seebeck effect. Two
+designed configurations are proposed according to whether the electron current
+is parallel or perpendicular to the magnetization of the MI layer. In the
+parallel configuration, the transverse voltage differs between the parallel and
+antiparallel MV states. While in the perpendicular configuration, the
+longitudinal resistance differs. Quantitative numerical results indicate the
+feasibility of detecting a voltage signal using the first configuration in
+experiments. Our work contributes valuable insights for the design, development
+and integration of magnon devices",2312.17413v1
+2024-03-01,Microwave-to-optics conversion using magnetostatic modes and a tunable optical cavity,"Quantum computing, quantum communication and quantum networks rely on hybrid
+quantum systems operating in different frequency ranges. For instance, the
+superconducting qubits work in the gigahertz range, while the optical photons
+used in communication are in the range of hundreds of terahertz. Due to the
+large frequency mismatch, achieving the direct coupling and information
+exchange between different information carriers is generally difficult.
+Accordingly, a quantum interface is demanded, which serves as a bridge to
+establish information linkage between different quantum systems operating at
+distinct frequencies. Recently, the magnon mode in ferromagnetic spin systems
+has received significant attention. While the inherent weak optomagnonic
+coupling strength restricts the microwave-to-optical photon conversion
+efficiency using magnons, the versatility of the magnon modes, together with
+their readily achievable strong coupling with other quantum systems, endow them
+with many distinct advantages. Here, we realize the magnon-based
+microwave-light interface by adopting an optical cavity with adjustable free
+spectrum range and different kinds of magnetostatic modes in two microwave
+cavity configurations. By optimizing the parameters, an internal conversion
+efficiency of $1.28 \times 10^{-7}$ is achieved. We analyze the impact of
+various parameters on the microwave-to-optics conversion. The study provides
+useful guidance and insights to further enhancing the microwave-to-optics
+conversion efficiency using magnons.",2403.00345v2
+2011-04-25,Magnetic excitations in L-edge resonant inelastic x-ray scattering from cuprate compounds,"We study the magnetic excitation spectra in L-edge resonant inelastic x-ray
+scattering (RIXS) from undoped cuprates. We analyze the second-order dipole
+allowed process that the strong perturbation works through the intermediate
+state in which the spin degree of freedom is lost at the core-hole site. Within
+the approximation neglecting the perturbation on the neighboring sites, we
+derive the spin-flip final state in the scattering channel with changing the
+polarization, which leads to the RIXS spectra expressed as the dynamical
+structure factor of the transverse spin components. We assume a spherical form
+of the spin-conserving final state in the channel without changing the
+polarization, which leads to the RIXS spectra expressed as the 'exchange'-type
+multi-spin correlation function. Evaluating numerically the transition
+amplitudes to these final states on a finite-size cluster, we obtain a sizable
+amount of the transition amplitude to the spin-conserving final state in
+comparison with that to the spin-flip final state. We treat the itinerant
+magnetic excitations in the final state by means of the 1/S-expansion method.
+Evaluating the higher-order correction with 1/S, we find that the peak arising
+from the one-magnon excitation is reduced with its weight, and the continuous
+spectra arising from the three-magnon excitations come out. The interaction
+between two magnons is treated by summing up the ladder diagrams. On the basis
+of these results, we analyze the L_3-edge RIXS spectra in Sr_2CuO_2Cl_2 in
+comparison with the experiment. It is shown that the three-magnon excitations
+as well as the two-magnon excitations give rise to the intensity in the high
+energy side of the one-magnon peak, making the spectral shape asymmetric with
+wide width, in good agreement with the experiment.",1104.4683v2
+2014-08-14,Quantum magnetism of spinor bosons in optical lattices with synthetic non-Abelian gauge fields,"We study quantum magnetism of interacting spinor bosons at integer fillings
+hopping in a square lattice in the presence of non-Abelian gauge fields. In the
+strong coupling limit, it leads to the Rotated ferromagnetic Heisenberg model
+(RFHM) which is a new class of quantum spin model. We introduce Wilson loops to
+characterize frustrations and gauge equivalent classes. For a special
+equivalent class, we identify a new spin-orbital entangled commensurate ground
+state. It supports not only commensurate magnons, but also a new gapped
+elementary excitation: in-commensurate magnons with two gap minima continuously
+tuned by the SOC strength. At low temperatures, these magnons lead to dramatic
+effects in many physical quantities such as density of states, specific heat,
+magnetization, uniform susceptibility, staggered susceptibility and various
+spin correlation functions. The commensurate magnons lead to a pinned central
+peak in the angle resolved light or atom Bragg spectroscopy. However, the
+in-commensurate magnons split it into two located at their two gap minima. At
+high temperatures, the transverse spin structure factors depend on the SOC
+strength explicitly. The whole set of Wilson loops can be mapped out by
+measuring the specific heat at the corresponding orders in the high temperature
+expansion. We argue that one gauge may be realized in current experiments and
+other gauges may also be realized in near future experiments. The results
+achieved along the exact solvable line sets up the stage to investigate
+dramatic effects when tuning away from it by various means. We sketch the
+crucial roles to be played by these magnons at other equivalent classes, with
+spin anisotropic interactions and in the presence of finite magnetic fields.
+Various experimental detections of these new phenomena are discussed. Rotated
+Anti-ferromagnetic Heisenberg model are also briefly mentioned.",1408.3399v3
+2016-07-22,Magnon-induced long-range correlations and their neutron-scattering signature in quantum magnets,"We consider the coupling of the magnons in both quantum ferromagnets and
+antiferromagnets to the longitudinal order-parameter fluctuations, and the
+resulting nonanalytic behavior of the longitudinal susceptibility. In classical
+magnets it is well known that long-range correlations induced by the magnons
+lead to a singular wave-number dependence of the form $1/k^{4-d}$ in all
+dimensions 2<d<4, for both ferromagnets and antiferromagnets. At zero
+temperature we find a profound difference between the two cases. Consistent
+with naive power counting, the longitudinal susceptibility in a quantum
+antiferromagnet scales as $k^{d-3}$ for 1<d<3, whereas in a quantum ferromagnet
+the analogous result, $k^{d-2}$, is absent due to a zero scaling function. This
+absence of a nonanalyticity in the longitudinal susceptibility is due to the
+lack of magnon number fluctuations in the ground state of a quantum
+ferromagnet; correlation functions that are sensitive to other fluctuations do
+exhibit the behavior predicted by simple power counting. Also of interest is
+the dynamical behavior as expressed in the longitudinal part of the dynamical
+structure factor, which is directly measurable via neutron scattering. For both
+ferromagnets and antiferromagnets there is a logarithmic singularity at the
+magnon frequency with a prefactor that vanishes as $T\to 0$. In the
+antiferromagnetic case there also is a nonzero contribution at T=0 that is
+missing for ferromagnets. Magnon damping due to quenched disorder restores the
+expected scaling behavior of the longitudinal susceptibility in the
+ferromagnetic case; it scales as $k^{d-2}$ if the order parameter is not
+conserved, or as $k^d$ if it is. Detailed predictions are made for both two-
+and three-dimensional systems at both T=0 and in the limit of low temperatures,
+and the physics behind the various nonanalytic behaviors is discussed.",1607.06790v1
+2017-06-17,Magnon-phonon coupling effects on the indirect K-edge resonant inelastic X-ray scattering spectrum of a 2D Heisenberg antiferromagnet,"We compute the effects of magnon-phonon coupling on the indirect K-edge
+bimagnon resonant inelastic x-ray scattering (RIXS) intensity spectrum of a
+square lattice Heisenberg antiferromagnet. We analyze the effects of competing
+nearest and next--nearest magnetic and magnon-phonon coupling interaction in
+the RIXS spectrum, for both the antiferromagnetic (AF) and the collinear
+antiferromagnetic (CAF) phases of the model. Utilizing the Dyson-Maleev
+representation of spin operators, the Bethe-Salpeter ladder approximation
+scheme for the bimagnon interacting channel, and considering the lowest order
+magnon-phonon-magnon scattering interaction we highlight distinct features in
+the X-ray spectrum. Considering damping effects, arising due to the presence of
+phonons, we find that in the AF phase the RIXS intensity spectrum attains a
+maximum value primarily localized around the K $\left(\pm\frac{\pi}{2}, \pm
+\frac{\pi}{2}\right)$ - point. For the CAF phase the intensity is broadly
+distributed with a significant scattering intensity located around the Y
+$\left(\pm\frac{\pi}{2}, 0\right)$ - point. Furthermore, in the CAF phase for
+suitable anisotropy, nearest-, and next-nearest neighbor interaction parameters
+the phonon effects can manifest itself as a distinct peak both below and above
+the bimagnon peak. Such a feature is in contrast to the antiferromagnetic
+spectrum where the effect due to the phonon peak was located consistently
+beyond the bimagnon peak in the high energy end of the spectrum. Additionally,
+in the CAF phase we find the RIXS bimagnon-phonon spectrum to be more sensitive
+to anisotropy compared to its antiferromagnetic counterpart. We conclude that
+the ultimate effect of magnon-phonon effects in the indirect K-edge RIXS
+spectrum, in both the antiferromagnetic and the collinear antiferromagnetic
+phase, is an observable effect.",1706.05478v2
+2016-12-15,Magnons and Magnetodielectric Effects in CoCr$_2$O$_4$: Raman Scattering Studies,"Magnetoelectric materials have generated wide technological and scientific
+interest because of the rich phenomena these materials exhibit, including the
+coexistence of magnetic and ferroelectric orders, magnetodielectric behavior,
+and exotic hybrid excitations such as electromagnons. The multiferroic spinel
+material, CoCr$_2$O$_4$, is a particularly interesting example of a
+multiferroic material, because evidence for magnetoelectric behavior in the
+ferrimagnetic phase seems to conflict with traditional noncollinear-spin-driven
+mechanisms for inducing a macroscopic polarization. This paper reports an
+inelastic light scattering study of the magnon and phonon spectrum of
+CoCr$_2$O$_4$ as simultaneous functions of temperature, pressure, and magnetic
+field. Below the Curie temperature ($T_C \sim 94$ K) of CoCr$_2$O$_4$ we
+observe a $\omega \sim 16 \,\text{cm}^{-1}$ $\boldsymbol q=0$ magnon having
+T$_{1g}$-symmetry, which has the transformation properties of an axial vector.
+The anomalously large Raman intensity of the T$_{1g}$-symmetry magnon is
+characteristic of materials with a large magneto-optical response and likely
+arises from large magnetic fluctuations that strongly modulate the dielectric
+response in CoCr$_2$O$_4$. The Raman susceptibility of the T$_{1g}$-symmetry
+magnon exhibits a strong magnetic-field dependence that is consistent with the
+magnetodielectric response observed in CoCr$_2$O$_4$, suggesting that
+magnetodielectric behavior in CoCr$_2$O$_4$ primarily arises from the
+field-dependent suppression of magnetic fluctuations that are strongly coupled
+to long-wavelength phonons. Increasing the magnetic anisotropy in CoCr$_2$O$_4$
+with applied pressure decreases the magnetic field-dependence of the
+T$_{1g}$-symmetry magnon Raman susceptibility in CoCr$_2$O$_4$, suggesting that
+strain can be used to control the magnetodielectric response in CoCr$_2$O$_4$.",1612.05283v1
+2020-06-28,Avoided quasiparticle decay and enhanced excitation continuum in the spin-1/2 near-Heisenberg triangular antiferromagnet Ba3CoSb2O9,"We explore the magnetic excitations of the spin-1/2 triangular
+antiferromagnet Ba3CoSb2O9 in its 120 degree ordered phase using single-crystal
+high-resolution inelastic neutron scattering. Sharp magnons with no decay are
+observed throughout reciprocal space, with a strongly renormalized dispersion
+and multiple soft modes compared to linear spin wave theory. We propose an
+empirical parametrization that can quantitatively capture the complete
+dispersions in the three-dimensional Brillouin zone and explicitly show that
+the dispersion renormalizations have the direct consequence that one to two
+magnon decays are avoided throughout reciprocal space, whereas such decays
+would be allowed for the unrenormalized dispersions. At higher energies, we
+observe a very strong continuum of excitations with highly-structured intensity
+modulations extending up at least 4x the maximum one-magnon energy. The
+one-magnon intensities decrease much faster upon increasing energy than
+predicted by linear spin wave theory and the higher-energy continuum contains
+much more intensity than can be accounted for by a two-magnon cross-section,
+suggesting a significant transfer of spectral weight from the high-energy
+magnons into the higher-energy continuum states. We attribute the strong
+dispersion renormalizations and substantial transfer of spectral weight to
+continuum states to the effect of quantum fluctuations and interactions beyond
+the spin wave approximation, and make connections to theoretical approaches
+that might capture such effects. Finally, through measurements in a strong
+applied magnetic field, we find evidence for magnetic domains with opposite
+senses for the spin rotation in the 120 degree ordered ground state, as
+expected in the absence of Dzyaloshinskii-Moriya interactions, when the sense
+of spin rotation is selected via spontaneous symmetry breaking.",2006.15554v1
+2021-05-02,Steady state entanglement of distant nitrogen-vacancy centers in a coherent thermal magnon bath,"We investigate steady-state entanglement (SSE) between two nitrogen-vacancy
+(NV) centers in distant nanodiamonds on an ultrathin Yttrium Iron Garnet (YIG)
+strip. We determine the dephasing and dissipative interactions of the qubits
+with the quanta of spin waves (magnon bath) in the YIG depending on the qubit
+positions on the strip. We show that the magnon's dephasing effect can be
+eliminated, and we can transform the bath into a multimode displaced thermal
+state using external magnetic fields. Entanglement dynamics of the qubits in
+such a displaced thermal bath have been analyzed by deriving and solving the
+master equation. An additional electric field is considered to engineer the
+magnon dispersion relation at the band edge to control the Markovian character
+of the open system dynamics. We determine the optimum geometrical parameters of
+the system of distant qubits and the YIG strip to get SSE. Furthermore,
+parameter regimes for which the shared displaced magnon bath can sustain
+significant SSE against the local dephasing and decoherence of NV centers to
+their nuclear spin environments have been determined. Along with SSE, we
+investigate the steady-state coherence (SSC) and explain the physical mechanism
+of how delayed SSE appears following a rapid generation and sudden death of
+entanglement using the interplay of decoherence-free subspace states, system
+geometry, displacement of the thermal bath, and enhancement of the qubit
+dissipation near the magnon band edge. A non-monotonic relation between bath
+coherence and SSE is found, and critical coherence for maximum SSE is
+determined. Our results illuminate the efficient use of system geometry, band
+edge in bath spectrum, and reservoir coherence to engineer system-reservoir
+interactions for robust SSE and SSC.",2105.00519v2
+2022-12-10,Ring-Exchange Interaction Effects on Magnons in Dirac Magnet CoTiO$_3$,"In magnetically ordered materials with localized electrons, the fundamental
+magnetic interactions are due to exchange of electrons [1-3]. Typically, only
+the interaction between pairs of electrons' spins is considered to explain the
+nature of the ground state and its excitations, whereas three-, four-, and
+six-spin interactions are ignored. When these higher order processes occur in a
+loop they are called cyclic or ring exchange. The ring-exchange interaction is
+required to explain low temperature behavior in bulk and thin films of solid
+$^3$He [4-8]. It also plays a crucial role in the quantum magnet La$_2$CuO$_4$
+[9,10]. Here, we use a combination of time domain THz (TDTS) and magneto-Raman
+spectroscopies to measure the low energy magnetic excitations in CoTiO$_3$, a
+proposed Dirac topological magnon material [11,12] where the origin of the
+energy gap in the magnon spectrum at the Brillouin zone center remains unclear.
+We measured the magnetic field dependence of the energies of the two lowest
+energy magnons and determine that the gap opens due to the ring-exchange
+interaction between the six spins in a hexagon. This interaction also explains
+the selection rules of the THz magnon absorption. Finally, we clarify that
+topological surface magnons are not expected in CoTiO$_3$. Our study
+demonstrates the power of combining TDTS and Raman spectroscopies with theory
+to identify the microscopic origins of the magnetic excitations in quantum
+magnets.",2212.05278v1
+2023-02-22,Unveiling the impact of temperature on magnon diffuse scattering detection in the transmission electron microscope,"Magnon diffuse scattering (MDS) signals could be studied with high spatial
+resolution in scanning transmission electron microscopy (STEM), thanks to
+recent technological progress in electron energy loss spectroscopy. However,
+detecting MDS signals in STEM is challenging due to their overlap with stronger
+thermal diffuse scattering (TDS) signals. In bcc Fe at 300 K, MDS signals
+greater than or comparable to TDS signals occur under the central Bragg disk,
+into a currently inaccesible energy-loss region. Therefore, to detect MDS in
+STEM, it is necessary to find conditions in which TDS and MDS signals can be
+separated. Temperature may be a key factor due to the distinct thermal
+signatures of magnon and phonon signals. In this work, we present a study on
+the effects of temperature on MDS and TDS in bcc Fe -- considering a detector
+outside the central Bragg disk and a fixed convergent electron probe -- using
+the frozen phonon and frozen magnon multislice methods. Our study reveals that
+neglecting the effects of atomic vibrations causes the MDS signal to grow
+approximately linearly up to the Curie temperature of Fe, after which it
+exhibits less variation. The MDS signal displays an alternating behavior due to
+dynamical diffraction, instead of increasing monotonically as a function of
+thickness. Including the effects of atomic vibrations through a complex atomic
+electrostatic potential causes the linear growth of the MDS signal to change to
+a non-linear behavior that exhibits a predominant peak for a sample of
+thickness 16.072 nm at 1100 K. In contrast, the TDS signal grows more linearly
+than the MDS signal but still exhibits appreciable dynamical diffraction
+effects. An analysis of the signal-to-noise ratio (SNR) shows that the MDS
+signal can be a statistically significant contribution to the total scattering
+intensity under realizable measurement conditions and acquisition times.",2302.11462v2
+2023-08-14,Investigation of Phonon Lifetimes and Magnon-Phonon Coupling in YIG/GGG Hybrid Magnonic Systems in the Diffraction Limited Regime,"Quantum memories facilitate the storage and retrieval of quantum information
+for on-chip and long-distance quantum communications. Thus, they play a
+critical role in quantum information processing and have diverse applications
+ranging from aerospace to medical imaging fields. Bulk acoustic wave (BAW)
+phonons are one of the most attractive candidates for quantum memories because
+of their long lifetime and high operating frequency. In this work, we establish
+a modeling approach that can be broadly used to design hybrid magnonic
+high-overtone bulk acoustic wave resonator (HBAR) structures for high-density,
+long-lasting quantum memories and efficient quantum transduction devices. We
+illustrate the approach by investigating a hybrid magnonic system, where BAW
+phonons are excited in a gadolinium iron garnet (GGG) thick film via coupling
+with magnons in a patterned yttrium iron garnet (YIG) thin film. We present
+theoretical and numerical analyses of the diffraction-limited BAW phonon
+lifetimes, modeshapes, and their coupling strengths to magnons in planar and
+confocal YIG/GGG HBAR structures. We utilize Fourier beam propagation and
+Hankel transform eigenvalue problem methods and discuss the effectiveness of
+the two methods to predict the HBAR phonons. We discuss strategies to improve
+the phonon lifetimes, since increased lifetimes have direct implications on the
+storage times of quantum states for quantum memory applications. We find that
+ultra-high, diffraction-limited, cooperativities and phonon lifetimes on the
+order of ~10^5 and ~10 milliseconds, respectively, could be achieved using a
+CHBAR structure with 10mum lateral YIG dimension. Additionally, the confocal
+HBAR structure will offer more than 100-fold improvement of integration
+density. A high integration density of on-chip memory or transduction centers
+is naturally desired for high-density memory or transduction devices.",2308.06896v2
+2023-12-26,Observation of Magnon Damping Minimum Induced by Kondo Coupling in a van der Waals Ferromagnet Fe$_{3-x}$GeTe$_{2}$,"In heavy-fermion systems with $f$ electrons, there is an intricate interplay
+between Kondo screening and magnetic correlations, which can give rise to
+various exotic phases. Recently, similar interplay appears to also occur in
+$d$-electron systems, but the underlying mechanism remains elusive. Here, using
+inelastic neutron scattering, we investigate the temperature evolution of the
+low-energy spin waves in a metallic van der Waals ferromagnet
+Fe$_{3-x}$GeTe$_{2}$ (Curie temperature $T_{\rm C}\sim160$ K), where the
+Kondo-lattice behavior emerges in the ferromagnetic phase below a
+characteristic temperature $T^*\sim90$ K. We observe that the magnon damping
+constant diverges at both low and high temperatures, exhibiting a minimum
+coincidentally around $T^*$. Such an observation is analogous to the
+resistivity minimum as due to the single-impurity Kondo effect. This unusual
+behavior is described by a formula that combines logarithmic and power terms,
+representing the dominant contributions from Kondo screening and thermal
+fluctuations, respectively. Furthermore, we find that the magnon damping
+increases with momentum below $T_{\rm C}$. These findings can be explained by
+considering spin-flip electron-magnon scattering, which serves as a magnonic
+analog of the Kondo-impurity scattering, and thus provides a measure of the
+Kondo coupling through magnons. Our results provide critical insights into how
+Kondo coupling manifests itself in a system with magnetic ordering and shed
+light on the coexistence of and interplay between magnetic order and Kondo
+effect in itinerant 3$d$-electron systems.",2312.15961v1
+1993-11-09,S(k) for Haldane Gap Antiferromagnets: Large-scale Numerical Results vs. Field Theory and Experiment,"The structure function, S(k), for the s=1, Haldane gap antiferromagnetic
+chain, is measured accurately using the recent density matrix renormalization
+group method, with chain-length 100. Excellent agreement with the nonlinear
+$\sigma$ model prediction is obtained, both at $k\approx \pi$ where a single
+magnon process dominates and at $k\approx 0$ where a two magnon process
+dominates. We repeat our calculation with crystal field anisotropy chosen to
+model NENP, obtaining good agreement with both field theory predictions and
+recent experiments. Correlation lengths, gaps and velocities are determined for
+both polarizations.",9311021v2
+1995-09-13,Spin-wave excitation spectra and spectral weights in square lattice antiferromagnets,"Using a recently developed method for calculating series expansions of the
+excitation spectra of quantum lattice models, we obtain the spin-wave spectra
+for square lattice, $S=1/2$ Heisenberg-Ising antiferromagnets. The calculated
+spin-wave spectrum for the Heisenberg model is close to but noticeably
+different from a uniformly renormalized classical (large-$S$) spectrum with the
+renormalization for the spin-wave velocity of approximately $1.18$. The
+relative weights of the single-magnon and multi-magnon contributions to neutron
+scattering spectra are obtained for wavevectors throughout the Brillouin zone.",9509077v1
+1995-10-12,"Spinons, Solitons and Magnons in One-dimensional Heisenberg-Ising Antiferromagnets","We calculate the excitation spectra for the one-$d$ Heisenberg-Ising
+antiferromagnets by expansions around the Ising limit. For $S=1/2$, the
+calculated expansion coefficients for the spinon-spectra agree term by term
+with the solution of Johnson and McCoy. For $S=1$, the solitons become gapless
+before the Heisenberg limit is reached, signalling a transition to the Haldane
+phase. By applying a staggered field we calculate the one-magnon spectra for
+the $S=1$ Heisenberg chain. For $S=3/2$ the quantum renormalization of the
+spin-wave spectra is calculated to be approximately $1.16$.",9510064v1
+1996-12-02,One-dimensional spin-liquid without magnon excitations,"It is shown that a sufficiently strong four-spin interaction in the spin-1/2
+spin ladder can cause dimerization. Such interaction can be generated either by
+phonons or (in the doped state) by the conventional Coulomb repulsion between
+the holes. The dimerized phases are thermodynamically undistinguishable from
+the Haldane phase, but have dramatically different correlation functions: the
+dynamical magnetic susceptibility, instead of displaying a sharp single magnon
+peak near $q = \pi$, shows only a two-particle threshold separated from the
+ground state by a gap.",9612014v2
+1997-04-10,Magnetic Excitations in the S=1/2 Alternating Chain Compound (VO)_2P_2O_7,"Magnetic excitations in an array of (VO)_2P_2O_7 single crystals have been
+measured using inelastic neutron scattering. Until now, (VO)_2P_2O_7 has been
+thought of as a two-leg antiferromagnetic Heisenberg spin ladder with chains
+running in the a-direction. The present results show unequivocally that
+(VO)_2P_2O_7 is best described as an alternating spin-chain directed along the
+crystallographic b-direction. In addition to the expected magnon with magnetic
+zone-center energy gap \Delta = 3.1 meV, a second excitation is observed at an
+energy just below 2\Delta. The higher mode may be a triplet two-magnon bound
+state.",9704092v1
+1997-12-05,Spin flip scattering in magnetic junctions,"Processes which flip the spin of an electron tunneling in a junction made up
+of magnetic electrodes are studied. It is found that: i) Magnetic impurities
+give a contribution which increases the resistance and lowers the
+magnetoresistance, which saturates at low temperatures. The conductance
+increases at high fields. ii) Magnon assisted tunneling reduces the
+magnetoresistance as $T^{3/2}$, and leads to a non ohmic contribution to the
+resistance which goes as $V^{3/2}$, iii) Surface antiferromagnetic magnons,
+which may appear if the interface has different magnetic properties from the
+bulk, gives rise to $T^2$ and $V^2$ contributions to the magnetoresistance and
+resistance, respectively, and, iv) Coulomb blockade effects may enhance the
+magnetoresistance, when transport is dominated by cotunneling processes.",9712075v1
+1999-01-21,Interplay between Mesoscopic and Microscopic Fluctuations in Ferromagnets,"A model of a ferromagnet is considered, in which there arise mesoscopic
+fluctuations of paramagnetic phase. The presence of these fluctuations
+diminishes the magnetization of the ferromagnet, softens the spin-wave
+spectrum, increases the spin-wave attenuation, shortens the magnon free path,
+lowers the critical point, and can change the order of phase transition. A
+special attention is paid to the interplay between these mesoscopic
+paramagnetic fluctuations and microscopic fluctuations due to magnons. One of
+the main results of this interplay is an essential extension of the region of
+parameters where the ferromagnet-paramagnet phase transition is of first order.",9901213v1
+1999-01-30,The correlation length of the Heisenberg antiferromagnet with arbitrary spin S,"Experiments and numerical data on the correlation length for large S disagree
+strongly with the theoretical prediction based on the effective field theory
+prescription of the magnon physics. The reason is that for large S, at any
+accessible correlation lengths, the cut-off effects from the non-magnon scales
+become large and can not be treated by an effective field theory. We study
+these effects in a spin-wave expansion. The corrected prediction connects the
+renormalized classical and the classical scaling regions smoothly and comes
+close to the data.",9901355v1
+1999-08-09,Realization of Bose-Einstein condensation of dilute magnons in TlCuCl$_3$,"The recent observation [Oosawa et al. J. Phys. : Condens. Matter {\bf 11},
+265 (1999)] of the field-induced N\'{e}el ordering in a spin-gap magnetic
+compound TlCuCl$_3$ is interpreted as a Bose-Einstein Condensation of magnons.
+A mean-field calculation based on this picture is shown to describe well the
+temperature dependence of the magnetization. The present system opens a new
+area for studying Bose-Einstein condensation of thermodynamically large number
+of particles in a grand-canonical ensemble.",9908118v1
+1999-10-07,Theory of anomalous magnon softening in ferromagnetic manganites,"In metallic manganites with low Curie temperatures, a peculiar softening of
+the magnon spectrum close to the magnetic zone boundary has experimentally been
+observed. Here we present a theory of the renormalization of the magnetic
+excitation spectrum in colossal magnetoresistance compounds. The theory is
+based on the modulation of magnetic exchange bonds by the orbital degree of
+freedom of double-degenerate e_g electrons. The model considered is an
+orbitally degenerate double-exchange system coupled to Jahn-Teller active
+phonons which we treat in the limit of strong onsite repulsions. Charge and
+coupled orbital-lattice fluctuations are identified as the main origin of the
+unusual softening of the magnetic spectrum.",9910106v1
+2000-05-24,Evolution of the Spin Gap Upon Doping a 2-Leg Ladder,"The evolution of the spin gap of a 2-leg ladder upon doping depends upon the
+nature of the lowest triplet excitations in a ladder with two holes. Here we
+study this evolution using various numerical techniques for a t-t'-J ladder as
+the next-near-neighbor hopping t' is varied. We find that depending on the
+value of t', the spin gap can evolve continuously or discontinuously and the
+lowest triplet state can correspond to a magnon, a bound magnon-hole-pair, or
+two separate quasi-particles. Previous experimental results on the
+superconducting two-leg ladder Sr12Ca2Cu24O41 are discussed.",0005403v1
+2000-09-04,Observation of anomalous single-magnon scattering in half-metallic ferromagnets by chemical pressure control,"Temperature variation of resistivity and specific heat have been measured for
+prototypical half-metallic ferromagnets,
+  R_0.6Sr_0.4MnO_3, with controlling the one-electron bandwidth W. We have
+found variation of the temperature scalings in the resistivity from
+  T^2 (R = La, and Nd) to T^3 (R = Sm), and have interpreted the $T^3-law in
+terms of the anomalous single-magnon scattering (AMS) process in the
+half-metallic system.",0009035v1
+2000-09-04,Magnon scattering processes and low temperature resistivity in CMR manganites,"Low temperature resistivity of CMR manganites is investigated. At the ground
+state, conduction electrons are perfectly spin polarized, which is called
+half-metallic. From one-magnon scattering processes, it is discussed that the
+resistivity of a half metal as a function of temperature scales as rho(T) -
+rho(0) propto T^3. We take (Nd,Tb,Sr)MnO_3 as an example to compare theory and
+experiments. The result is in a good agreement.",0009036v1
+2000-10-30,Anisotropic charge transfer mechanism in La$_{2-x}$Sr$_x$CuO$_4$ and Bi$_2$Sr$_2$Ca$_{1-x}$Y$_x$Cu$_2$O$_{8+δ}$,"Raman spectra of La$_{2-x}$Sr$_x$CuO$_4$ are similar to those of
+Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ except for the split two-magnon peaks at the
+stripe phase and the stronger step-like decrease in the low energy $B_{\rm 2g}$
+spectra. The suppressed $B_{\rm 1g}$ spectral region below the two-magnon peak
+decreases as the carrier density increases, whereas the energy of the step-like
+suppression is little dependent on the carrier density. It suggests the
+anisotropic charge transfer mechanism coupled with magnetic excitations along
+the nearest neighbor Cu sites and the phononic excitations along the diagonal
+direction.",0010472v1
+2000-12-06,Magnons in the ferromagnetic Kondo-lattice model,"The magnetic properties of the ferromagnetic Kondo-lattice model (FKLM) are
+investigated. Starting from an analysis of the magnon spectrum in the spin-wave
+regime, we examine the ferromagnetic stability as a function of the occupation
+of the conduction band $n$ and the strength $J$ of the coupling between the
+localised moments and the conduction electrons. From the properties of the
+spin-wave stiffness $D$ the ferromagnetic phase at zero temperature is derived.
+Using an approximate formula the critical temperature $T_c$ is calculated as a
+function of $J$ and $n$.",0012086v1
+2000-12-19,Significance of the direct relaxation process in the low-energy spin dynamics of a one-dimensional ferrimagnet NiCu(C_7H_6N_2O_6)(H_2O)_3 2H_2O,"In response to recent nuclear-magnetic-resonance measurements on a
+ferrimagnetic chain compound NiCu(C_7H_6N_2O_6)(H_2O)_3 2H_2O [Solid State
+Commun. {\bf 113} (2000) 433], we calculate the nuclear spin-lattice relaxation
+rate 1/T_1 in terms of a modified spin-wave theory. Emphasizing that the
+dominant relaxation mechanism arises from the direct (single-magnon) process
+rather than the Raman (two-magnon) one, we explain the observed temperature and
+applied-field dependences of 1/T_1. Ferrimagnetic relaxation phenomena are
+generally discussed and novel ferrimagnets with extremely slow dynamics are
+predicted.",0012342v1
+2002-01-04,Magnon modes for thin circular vortex state magnetic dot,"The magnetization in a magnetic microdot made from soft magnetic materials
+can have a vortex-like ground state structure resulting from competition
+between the exchange and dipolar interactions. Normal mode magnon frequencies
+for such dots are calculated taking into account both exchange and
+magnetostatic effects. The presence of a low-lying mode as well as doublet
+structure with small splitting is demonstrated. Estimates of the mode
+frequencies for permalloy dots are obtained, and the possibility of
+experimental detection of such modes is discussed.",0201050v1
+2002-09-17,Magnetic Order and Dynamics in an Orbitally Degenerate Ferromagnetic Insulator,"Neutron scattering was used to determine the spin structure and the magnon
+spectrum of the Mott--Hubbard insulator YTiO$_3$. The magnetic structure is
+complex, comprising substantial G-type and A-type antiferromagnetic components
+in addition to the predominant ferromagnetic component. The magnon spectrum, on
+the other hand, is gapless and nearly isotropic. We show that these findings
+are inconsistent with the orbitally ordered states thus far proposed for
+YTiO$_3$ and discuss general implications for a theoretical description of
+exchange interactions in orbitally degenerate systems.",0209400v1
+2002-11-22,Nonlinear microscopic relaxation of uniform magnetization precession,"Dynamic relaxation for nonlinear magnetization excitation is analyzed. For
+direct processes, such as magnon-electron scattering and two-magnon scattering,
+the relaxation rate is determined from the linear case simply by utilizing the
+magnetization oscillation frequency for nonlinear excitation. For an indirect
+process, such as slow-relaxing impurities, the analysis gives an additional
+relaxation term proportional to the excitation level. In all cases the
+effective magnetization damping is increased compared to
+Landau-Lifshitz-Gilbert damping.",0211499v1
+2003-01-28,Longitudinal magnon in the tetrahedral spin system Cu2Te2O5Br2 near quantum criticality,"We present a comprehensive study of the coupled tetrahedra-compound
+Cu2Te2O5Br2 by theory and experiments in external magnetic fields. We report
+the observation of a longitudinal magnon in Raman scattering in the ordered
+state close to quantum criticality. We show that the excited
+tetrahedral-singlet sets the energy scale for the magnetic ordering temperature
+T_N. This energy is determined experimentally. The ordering temperature T_N has
+an inverse-log dependence on the coupling parameters near quantum criticality.",0301546v1
+2004-02-24,Dynamical model of the dielectric screening of conjugated polymers,"A dynamical model of the dielectric screening of conjugated polymers is
+introduced and solved using the density matrix renormalization group method.
+The model consists of a line of quantized dipoles interacting with a polymer
+chain. The polymer is modelled by the Pariser-Parr-Pople (P-P-P) model. It is
+found that: (1) Compared to isolated, unscreened single chains, the screened
+1Bu- exciton binding energy is typically reduced by ca. 1 eV to just over 1 eV;
+(2) Covalent (magnon and bi-magnon) states are very weakly screened compared to
+ionic (exciton) states; (3) Screening of the 1Bu- exciton is closer to the
+dispersion than solvation limit.",0402569v1
+2004-05-26,Bose-Einstein condensation of magnons,"We use the Renormalization Group method to study the Bose-Einstein
+condensation of the interacting dilute magnons which appears in three
+dimensional spin systems in magnetic field. The obtained temperature dependence
+of the critical field $H_c(T)-H_c(0) \sim T^{2}$ is different from the recent
+self-consistent Hartree-Fock-Popov calculations (cond-mat/0405422) in which a
+$T^{3/2}$ dependence was reported . The origin of this difference is discussed
+in the framework of quantum critical phenomena.",0405619v1
+2004-06-11,Bose-Einstein condensation of magnons in TlCuCl$_3$,"A quantitative study of the field-induced magnetic ordering in TlCuCl$_3$ in
+terms of a Bose-Einstein condensation (BEC) of magnons is presented. It is
+shown that the hitherto proposed simple BEC scenario is in quantitative and
+qualitative disagreement with experiment. It is further shown that even very
+small Dzyaloshinsky-Moriya interactions or a staggered $g$ tensor component of
+a certain type can change the BEC picture qualitatively. Such terms lead to a
+nonzero condensate density for all temperatures and a gapped quasiparticle
+spectrum. Including this type of interaction allows us to obtain good agreement
+with experimental data.",0406262v1
+2004-12-08,Further Series Studies of the Spin-1/2 Heisenberg Antiferromagnet at T=0: Magnon Dispersion and Structure Factors,"We have extended our previous series studies of quantum antiferromagnets at
+zero temperature by computing the one-magnon dispersion curves and various
+structure factors for the linear chain, square and simple cubic lattices. Many
+of these results are new; others are a substantial extension of previous work.
+These results are directly comparable with neutron scattering experiments and
+we make such comparisons where possible.",0412184v2
+2005-03-17,Raman resonance in spin S two-leg ladder systems,"We argue that the Raman intensity in a spin S two-leg spin-ladder has a
+pseudo-resonance peak, whose width is very small at large S. The
+pseudo-resonance originates from the existence of a local minimum in the magnon
+excitation spectrum, and is located slightly below twice the magnon energy at
+the minimum. The physics behind the peak is similar to the excitonic scenario
+for the neutron and Raman resonances in a d-wave superconductor.",0503453v1
+2005-06-30,Magnon transport and spin current switching through quantum dots,"We study the nonequilibrium spin current through a quantum dot consisting of
+two localized spin-1/2 coupled to two ferromagnetic insulators. The influence
+of an intra-dot magnetic field and exchange coupling, different dot-reservoir
+coupling configurations, and the influence of magnon chemical potential
+differences vs. magnetic field gradients onto the spin current are examined. We
+discuss various spin switching mechanisms and find that, in contrast to
+electronic transport, the spin current is very sensitive to the specific
+coupling configuration and band edges. In particular, we identify 1- and
+2-magnon transport processes which can lead to resonances and antiresonances
+for the spin current.",0506806v1
+2005-10-21,Structural distortions of frustrated quantum spin lattices in high magnetic fields,"We study the stability of some strongly frustrated antiferromagnetic spin
+lattices in high magnetic fields against lattice distortions. In particular, we
+consider a spin-s anisotropic Heisenberg antiferromagnet on the
+square-kagom\'{e} and kagom\'{e} lattices. The independent localized magnons
+embedded in a ferromagnetic environment, which are the ground state at the
+saturation field, imply lattice instabilities for appropriate lattice
+distortions fitting to the structure of the localized magnons. We discuss in
+detail the scenario of this spin-Peierls instability in high magnetic fields
+which essentially depends on the values of the exchange interaction anisotropy
+\Delta and spin s.",0510582v1
+2005-11-11,Magnonics: Experiment to Prove the Concept,"An experimental scheme for studying spin wave propagation across thin film
+samples is proposed. An experiment upon a periodically layered nanowire is
+numerically simulated, while the sample might equally well be a continuous film
+or an array of elements (e.g. nanowires) that either have uniform composition
+or are periodically layered as in a magnonic crystal. The experiments could be
+extended to study domain wall induced spin wave phase shifts, and used for
+creation of the spin wave magnetic logic devices.",0511290v1
+2006-01-18,Decay of quasiparticles in quantum spin liquids,"Magnetic excitations are studied in gapped quantum spin systems, for which
+spontaneous two-magnon decays are allowed by symmetry. Interaction between one-
+and two-particle states acquires nonanalytic frequency and momentum dependence
+near the boundary of two-magnon continuum. This leads to a termination point of
+single-particle branch for one-dimensional systems and to strong suppression of
+quasiparticle weight in two dimensions. The momentum dependence of the decay
+rate is calculated in arbitrary dimensions and effect of external magnetic
+field is discussed.",0601405v1
+2006-08-22,Clustering induced suppression of ferromagnetism in diluted magnets,"Ferromagnetism in diluted magnets in the compensated regime p << x is shown
+to be suppressed by the formation of impurity spin clusters. The majority bulk
+spin couplings are shown to be considerably weakened by the preferential
+accumulation of holes in spin clusters, resulting in low-energy magnon
+softening and enhanced low-temperature decay of magnetic order. A locally
+self-consistent magnon renormalization analysis of spin dynamics shows that
+although strong intra-cluster correlations tend to prolong global order, T_c is
+still reduced compared to the ordered case.",0608474v2
+2006-09-08,Peak resistance temperature and low temperature resistivity in thin film $La_{1-x} Ca_x Mn O_3$ mixtures for x <= 1/3,"The electrical resistivity of La$_{1-x}$Ca$_{x}$MnO$_{3}$ thin films grown on
+(001) NdGaO$_{3}$ and (100) SrTiO$_{3}$ substrates by off-axis sputtering has
+been studied as a function of the Calcium doping level. The samples have very
+narrow rocking curves and excellent in plane registry with the substrate. A
+strong correlation between the peak resistance temperature and the polaronic
+hopping energy is seen which is not simply linear. The low temperature
+resistivity is seen to be fit better by a model of single magnon scattering,
+and a near linear correlation between the resistivity due to magnon scattering
+and static impurities is observed.",0609206v1
+2006-12-22,Magnon Dispersion and Anisotropies in SrCu$_2$(BO$_3$)$_2$,"We study the dispersion of the magnons (triplet states) in
+SrCu$_2$(BO$_3$)$_2$ including all symmetry-allowed Dzyaloshinskii-Moriya
+interactions. We can reduce the complexity of the general Hamiltonian to a new
+simpler form by appropriate rotations of the spin operators. The resulting
+Hamiltonian is studied by both perturbation theory and exact numerical
+diagonalization on a 32-site cluster. We argue that the dispersion is dominated
+by Dzyaloshinskii-Moriya interactions. We point out which combinations of these
+anisotropies affect the dispersion to linear-order, and extract their
+magnitudes.",0612598v2
+2007-01-12,Momentum dependent light scattering in insulating cuprates,"We investigate the problem of inelastic x-ray scattering in the spin$-{1/2}$
+Heisenberg model on the square lattice. We first derive a momentum dependent
+scattering operator for the $A_{1g}$ and $B_{1g}$ polarization geometries. On
+the basis of a spin-wave analysis, including magnon-magnon interactions and
+exact-diagonalizations, we determine the qualitative shape of the spectra. We
+argue that our results may be relevant to help interpret inelastic x-ray
+scattering experiments in the antiferromagnetic phase of the cuprates.",0701289v1
+2007-01-19,Excited states of quantum many-body interacting systems: A variational coupled-cluster description,"We extend recently proposed variational coupled-cluster method to describe
+excitation states of quantum many-body interacting systems. We discuss, in
+general terms, both quasiparticle excitations and quasiparticle-density-wave
+excitations (collective modes). In application to quantum antiferromagnets, we
+reproduce the well-known spin-wave excitations, i.e. quasiparticle magnons of
+spin $\pm 1$. In addition, we obtain new, spin-zero magnon-density-wave
+excitations which has been missing in Anserson's spin-wave theory. Implications
+of these new collective modes are discussed.",0701482v1
+1992-03-18,Quantum Galilei Group as Symmetry of Magnons,"Inhomogeneous quantum groups are shown to be an effective algebraic tool in
+the study of integrable systems and to provide solutions equivalent to the
+Bethe ansatz. The method is illustrated on the 1D Heisenberg ferromagnet whose
+symmetry is shown to be the quantum Galilei group Gamma_q(1) here introduced.
+Both the single magnon and the s=1/2 bound states of n-magnons are completely
+described by the algebra.",9203048v1
+2006-07-18,Magnon-Like Dispersion Relation from M-Theory,"We investigate classical rotating membranes in two different backgrounds.
+First, we obtain membrane solution in $AdS_4\times S^7$ background, analogous
+to the solution obtained by Hofman and Maldacena in the case of string theory.
+We find a magnon type dispersion relation similar to that of Hofman and
+Maldacena and to the one found by Dorey for the two spin case. In the appendix
+of the paper, we consider membrane solutions in $AdS_7\times S^4$, which give
+new relations between the conserved charges.",0607116v3
+2006-09-29,A T-duality interpretation of the relationship between massive and massless magnonic TBA systems,"We propose an alternative understanding of the relationship between massive
+and massless magnonic TBA systems, using the T-duality symmetries of the
+Homogeneous sine-Gordon models. This is shown to be in agreement with a
+previous treatment by Dorey, Dunning and Tateo, based on the properties of
+Y-systems.",0609224v3
+2006-10-27,The Asymptotic Spectrum of the N=4 Super Yang-Mills Spin Chain,"In this paper we discuss the asymptotic spectrum of the spin chain
+description of planar N=4 SUSY Yang-Mills. The states appearing in the spectrum
+belong to irreducible representations of the unbroken supersymmetry SU(2|2) x
+SU(2|2) with non-trivial extra central extensions. The elementary magnon
+corresponds to the bifundamental representation while boundstates of Q magnons
+form a certain short representation of dimension 16Q^{2}. Generalising the
+Beisert's analysis of the Q=1 case, we derive the exact dispersion relation for
+these states by purely group theoretic means.",0610295v1
+2006-12-30,Zero modes for the giant magnon,"We explicitly construct the eight fermion zero mode solutions for the
+Hofman-Maldacena giant magnon. The solutions are naturally gauge fixed under
+the \kappa-symmetry. Substituting the solutions back into the Lagrangian leads
+to a simple expression that can be quantized directly. We also show how to
+construct the SU(2|2)\times SU(2|2) superalgebra from these zero modes. For
+completeness we also find the four bosonic zero mode solutions.",0701005v3
+2004-06-02,Ultra-cold Neutron Production in Anti-ferromagnetic Oxygen Solid,"Spin waves, or magnons, in the anti-ferromagnetic $\alpha$ phase of solid
+oxygen provide a novel mechanism for ultra-cold neutron (UCN) production.
+Magnons dominate the energy exchange mechanisms for cold neutrons and UCN in
+solid $\alpha$-oxygen, much in the same way as do phonons in solid deuterium
+superthermal UCN sources. We present calculations of UCN production and
+upscattering rates in S-O$_2$. The results indicate that S-O$_2$ is potentially
+a much more efficient UCN source material than solid deuterium.",0406004v1
+2000-04-11,Theory of acoustic analog of magneto-optic Kerr effect under magnon-phonon resonance,"Theory of the acoustic analog of the polar Kerr effect is developed for an
+inclined incidence of the p-type wave on the interface between isotropic
+non-magnetic medium and ferromagnetic cubic crystal. Magnetic field dependences
+of ellipticity and rotation of the polarization plane of the reflected wave
+under magnon-phonon resonance are analysed in a weak-coupling approximation for
+interaction of magnetic and elastic subsystems.",0004017v1
+2007-06-04,"Spiky Strings, Giant Magnons and beta-deformations","We study rigid string solutions rotating on the S^3 subspace of the
+beta-deformed AdS_5xS^5 background found by Lunin and Maldacena. For particular
+values of the parameters of the solutions we find the known giant magnon and
+single spike strings. We present a single spike string solution on the deformed
+S^3 and find how the deformation affects the dispersion relation. The possible
+relation of this string solution to spin chains and the connection of the
+solutions on the undeformed S^3 to the sine-Gordon model are briefly discussed.",0706.0442v2
+2007-07-04,Quantum Scattering of Giant Magnons,"We perform a first-principles semi-classical computation of the one-loop
+corrections to the dispersion relation and S-matrix of Giant Magnons in AdS_5 x
+S^5 string theory. The results agree exactly with expectations based on the
+strong coupling expansion of the exact Asymptotic Bethe Ansatz equations. In
+particular we reproduce the Hernandez-Lopez term in the dressing phase.",0707.0668v2
+2007-07-31,Giant magnon bound states from strongly coupled N=4 SYM,"We calculate in a very simple way the spectrum of giant magnon bound states
+at strong coupling in N=4 SYM, by utilizing the description of the field theory
+vacuum in terms of a condensate of eigenvalues of commuting matrices. We
+further show that these calculations can be understood in terms of the central
+charge extension that permits the calculation of BPS masses in the Coulomb
+branch of N=4 SYM. This paper shows further evidence that the strong coupling
+expansion of the maximally supersymmetric Yang-Mills theory in four dimensions
+can be done systematically from first principles, without the assumption of
+integrability.",0707.4669v1
+2007-08-16,Wrapping interactions at strong coupling -- the giant magnon,"We derive generalized Luscher formulas for finite size corrections in a
+theory with a general dispersion relation. For the AdS_5xS^5 superstring these
+formulas encode leading wrapping interaction effects. We apply the generalized
+mu-term formula to calculate finite size corrections to the dispersion relation
+of the giant magnon at strong coupling. The result exactly agrees with the
+classical string computation of Arutyunov, Frolov and Zamaklar. The agreement
+involved a Borel resummation of all even loop-orders of the BES/BHL dressing
+factor thus providing a strong consistency check for the choice of the dressing
+factor.",0708.2208v2
+2007-12-13,Bose-Einstein Condensation in Magnetic Insulators,"The elementary excitations in antiferromagnets are magnons, quasiparticles
+with integer spin and Bose statistics. In an experiment their density is
+controlled efficiently by an applied magnetic field and can be made finite to
+cause the formation of a Bose-Einstein condensate (BEC). Studies of magnon
+condensation in a growing number of magnetic materials provide a unique window
+into an exciting world of quantum phase transitions (QPT) and exotic quantum
+states.",0712.2250v1
+2007-12-25,Singularities of the Magnon Boundstate S-Matrix,"We study the conjectured exact S-matrix for the scattering of BPS magnon
+boundstates in the spin-chain description of planar N=4 SUSY Yang-Mills. The
+conjectured S-matrix exhibits both simple and double poles at complex momenta.
+Some of these poles lie parametrically close to the real axis in momentum space
+on the branch where particle energies are positive. We show that all such poles
+are precisely accounted for by physical processes involving one or more
+on-shell intermediate particles belonging to the known BPS spectrum.",0712.4068v1
+2008-01-08,Magnetic excitations in SrCu2O3: a Raman scattering study,"We investigated temperature dependent Raman spectra of the one-dimensional
+spin-ladder compound SrCu2O3. At low temperatures a two-magnon peak is
+identified at 3160+/-10 cm^(-1) and its temperature dependence analyzed in
+terms of a thermal expansion model. We find that the two-magnon peak position
+must include a cyclic ring exchange of J_cycl/J_perp=0.09-0.25 with a coupling
+constant along the rungs of J_perp approx. 1215 cm^(-1) (1750 K) in order to be
+consistent with other experiments and theoretical results.",0801.1303v1
+2008-01-29,A new derivation of Luscher F-term and fluctuations around the giant magnon,"In this paper we give a new derivation of the generalized Luscher F-term
+formula from a summation over quadratic fluctuations around a given soliton.
+The result is very general providing that S-matrix is diagonal and is valid for
+arbitrary dispersion relation. We then apply this formalism to compute the
+leading finite size corrections to the giant magnon dispersion relation coming
+from quantum fluctuations.",0801.4463v3
+2008-05-15,Dynamical Casimir effect for magnons in a spinor Bose-Einstein condensate,"Magnon excitation in a spinor Bose-Einstein condensate by a driven magnetic
+field is shown to have a close analogy with the dynamical Casimir effect. A
+time-dependent external magnetic field amplifies quantum fluctuations in the
+magnetic ground state of the condensate, leading to magnetization of the
+system. The magnetization occurs in a direction perpendicular to the magnetic
+field breaking the rotation symmetry. This phenomenon is numerically
+demonstrated and the excited quantum field is shown to be squeezed.",0805.2210v1
+2008-05-27,Scattering of backward spin waves in a one-dimensional magnonic crystal,"Scattering of backward volume magnetostatic spin waves from a one-dimensional
+magnonic crystal, realized by a grating of shallow grooves etched into the
+surface of an yttrium-iron garnet film, was experimentally studied. Rejection
+frequency bands were clearly observed. The rejection efficiency and the
+frequency width of the rejection bands increase with increasing groove depth. A
+theoretical model based on the analogy of a spin-wave film-waveguide with a
+microwave transmission line was used to interpret the obtained experimental
+results.",0805.4142v1
+2008-06-24,Magnon like solutions for strings in I-brane background,"We study the solutions for fundamental string rotating in a background
+generated by a 1+1 dimensional intersection of two orthogonal stacks of
+fivebranes in type IIB string theory. We show the existence of magnon like
+solutions for the string moving simultaneously in the two spheres in this
+background and find the relevant dispersion relation among the various
+conserved charges.",0806.3879v2
+2008-08-27,Heralded single-magnon quantum memory for photon polarization states,"We demonstrate a heralded quantum memory based on mapping of a photon
+polarization state onto a single collective-spin excitation (magnon) shared
+between two spatially overlapped atomic ensembles. The polarization fidelity is
+measured by quantum state tomography to be above 90(2)% for any input
+polarization, which far exceeds the classical limit of 2/3. The process also
+constitutes a quantum non-destructive probe that detects and regenerates a
+photon without touching its - potentially undetermined - polarization.",0808.3603v1
+2008-10-03,Finite-Size Corrections of the $\mathbb{CP}^3$ Giant Magnons: the Lüscher terms,"We compute classical and first quantum finite-size corrections to the
+recently found giant magnon solutions in two different subspaces of
+$\mathbb{CP}^3$. We use the L\""{u}scher approach on the recently proposed exact
+S-matrix for $\mathcal{N}=6$ superconformal Chern-Simons theory. We compare our
+results with the string and algebraic curve computations and find agreement,
+thus providing a non-trivial test for the new $AdS_4/CFT_3$ correspondence
+within an integrability framework.",0810.0704v2
+2008-10-13,Finite-size Effect of the Dyonic Giant Magnons in N=6 super Chern-Simons Theory,"We consider finite-size effects for the dyonic giant magnon of the type IIA
+string theory on AdS_4 x CP^3 by applying Luscher mu-term formula which is
+derived from a recently proposed S-matrix for the N=6 super Chern-Simons
+theory. We compute explicitly the effect for the case of a symmetric
+configuration where the two external bound states, each of A and B particles,
+have the same momentum p and spin J_2. We compare this with the classical
+string theory result which we computed by reducing it to the
+Neumann-Rosochatius system. The two results match perfectly.",0810.2079v2
+2008-10-20,Spiky Strings in AdS(4) X CP**3 with Neveu-Schwarz Flux,"We study general rotating string solution in the AdS(4) X CP**3 background
+with a B_NS holonomy turned on over ${\bf CP}^1$ $\subset $ $ {\bf CP}^3$. We
+find the giant magnon and single spike solutions for the string moving in this
+background corresponding to open spin chain. We calculate the corresponding
+dispersion relation among various conserved charges for both the cases. We
+further study the finite size effect on both the giant magnon and single spike
+solutions.",0810.3516v3
+2008-11-03,Giant magnons and spiky strings on the conifold,"We find explicit solutions for giant magnons and spiky strings on the
+squashed three dimensional sphere. For a special value of the squashing
+parameter the solutions describe strings moving in a sector of the conifold,
+while for another value of the squashing parameter we recover the known results
+on the round three dimensional sphere. A new feature is that the energy and the
+momenta enter in the dispersion relation of the conifold in a transcendental
+way.",0811.0145v1
+2008-12-15,Zero Modes for the Boundary Giant Magnons,"We study the fermion zero-mode dynamics for open strings ending on the giant
+graviton branes. For the open string ending on the Z=0 brane, the quantization
+of the fermion zero-modes of boundary giant magnons reproduces the 256 states
+of the boundary degrees with the precise realization of the SU(2|2) X SU(2|2)
+symmetry algebra. Also for the open string ending on the Y=0 brane, we
+reproduce the unique vacuum state from the fermion zero-modes.",0812.2645v2
+2009-02-19,Giant Magnons on CP^3 by Dressing Method,"We consider classical string spectrum of R x CP^3, and construct a family of
+solutions with residual SU(2) symmetry by the dressing method on SU(4)/U(3)
+sigma model. All of them obey the square-root type dispersion relation, as is
+expected from the su(2|2) symmetry. A single dyonic giant magnon is not found
+in this approach.",0902.3368v3
+2009-05-08,Multipartite entangled magnon states as quantum communication channels,"We explicate conditions under which, the two magnon state becomes highly
+entangled and is useful for several quantum communication protocols. This
+state, which is experimentally realizable in quantum dots using Heisenberg
+exchange interaction, is found to be suitable for carrying out deterministic
+teleportation of an arbitrary two qubit composite system. Further, conditions
+for which the channel capacity reaches ""Holevo bound"", allowing maximal amount
+of classical information to be encoded, are derived. Later, an explicit
+protocol for the splitting and sharing of a two qubit entangled state among two
+parties, using this state as an entangled resource, is demonstrated.",0905.1233v2
+2009-05-17,Physics of $π$-Meson Condensation and High Temperature Cuprate Superconductors,"The idea of condensation of the Goldstone $\pi$-meson field in nuclear matter
+had been put forward a long time ago. However, it was established that the
+normal nuclear density is too low, it is not sufficient to condensate
+$\pi$-mesons. This is why the $\pi$-condensation has never been observed.
+Recent experimental and theoretical studies of high temperature cuprate
+superconductors have revealed condensation of Goldstone magnons, the effect
+fully analogous to the $\pi$-condensation. The magnon condensation has been
+observed. It is clear now that quantum fluctuations play a crucial role in the
+condensation, in particular they drive a quantum phase transition that destroys
+the condensate at some density of fermions.",0905.2717v1
+2009-08-16,A note on strings in deformed AdS_4 x CP3: giant magnon and single spike solutions,"In this paper we study the solitonic string solutions of magnon and single
+spike type in the beta-deformed AdS_4 x CP3 background. We find the dispersion
+relations which are supposed to give the anomalous dimension of the gauge
+theory operators.",0908.2246v3
+2009-08-21,"Strings on the deformed T^{1,1}: giant magnon and single spike solutions","In this paper we find giant magnon and single spike string solutions in a
+sector of the gamma-deformed conifold. We examine the dispersion relations and
+find a behavior analogous to the undeformed case. The transcendental functional
+relations between the conserved charges are shifted by certain gamma-dependent
+term. The latter is proportional to the total momentum and thus qualitatively
+different from known cases.",0908.3065v1
+2009-10-28,Interacting spin waves in the ferromagnetic Kondo lattice model,"We present an new approach for the ferromagnetic, three-dimensional,
+translational-symmetric Kondo lattice model which allows us to derive both
+magnon energies and linewidths (lifetimes) and to study the properties of the
+ferromagnetic phase at finite temperatures. Both ""anomalous softening"" and
+""anomalous damping"" are obtained and discussed. Our method consists of mapping
+the Kondo lattice model onto an effective Heisenberg model by means of the
+""modified RKKY interaction"" and the ""interpolating self-energy approach"". The
+Heisenberg model is approximatively solved by applying the Dyson-Maleev
+transformation and using the ""spectral density approach"" with a broadened
+magnon spectral density.",0910.5478v2
+2009-11-23,Production of Ultra-Cold-Neutrons in Solid α-Oxygen,"Our recent neutron scattering measurements of phonons and magnons in solid
+\alpha-oxygen have led us to a new understanding of the production mechanismen
+of ultra-cold-neutrons (UCN) in this super-thermal converter. The UCN
+production in solid \alpha-oxygen is dominated by the excitation of phonons.
+The contribution of magnons to UCN production becomes only slightly important
+above E >10 meV and at E >4 meV. Solid \alpha-oxygen is in comparison to solid
+deuterium less effcient in the down-scattering of thermal or cold neutrons into
+the UCN energy regime.",0911.4398v2
+2010-03-17,Three-magnon bound states in exactly rung-dimerized spin ladders,"Three magnon bound states in all total spin sectors of general nonintegrable
+exactly rung-dimerized spin ladder are obtained by Bethe Ansatz. Basing on this
+result a dispersion law for $m$-magnon ($m>3$) bound states is conjectured. It
+is suggested that (depending on correlations between coupling constants) a
+behavior of the gas parameter (density of rung-triplets) on the boundary of the
+rung-dimerized phase may either be smooth or have a leap.",1003.3472v2
+2010-06-21,Magnonic spin-wave modes in CoFeB antidot lattices,"In this manuscript time-resolved magneto-optical Kerr effect experiments on
+structured CoFeB films are presented. The geometries considered are two
+dimensional square lattices of micrometer-sized antidots, fabricated by a
+focused ion beam. The spin-wave spectra of these magnonic crystals show a novel
+precessional mode, which can be related to a Bloch state at the zone boundary.
+Additionally, another magnetic mode of different nature appears, whose
+frequency displays no dependence on the externally applied magnetic field.
+These findings are interpreted as delocalized and localized modes,
+respectively.",1006.4038v1
+2010-08-06,Ferromagnetic phases in spin-Fermion systems,"Spin-Fermion systems which obtain their magnetic properties from a system of
+localized magnetic moments being coupled to conducting electrons are
+considered. The dynamical degrees of freedom are spin-$s$ operators of
+localized spins and spin-1/2 Fermi operators of itinerant electrons.
+Renormalized spin-wave theory, which accounts for the magnon-magnon
+interaction, and its extension are developed to describe the two ferrimagnetic
+phases in the system: low temperature phase $0<T<T^{*}$, where all electrons
+contribute the ordered ferromagnetic moment, and high temperature phase
+$T^{*}<T<T_C$, where only localized spins form magnetic moment. The
+magnetization as a function of temperature is calculated. The theoretical
+predictions are utilize to interpret the experimentally measured
+magnetization-temperature curves of $UGe_2$..",1008.1148v1
+2010-10-12,"Phonon, Two-Magnon and Electronic Raman Scattering of Fe1+yTe1-xSex","We have measured Raman scattering spectra of single-crystalline FeTe0.6Se0.4
+(T_c ~ 14.5 K) and its parent compound Fe1.074Te at various temperatures. In
+the parent compound Fe1.074Te, A1g and B1g modes have been observed at 157.5
+and 202.3 cm-1, respectively, at 5 K. These frequencies qualitatively agree
+with the calculated results. Two-magnon excitation has been observed around
+2300 cm-1 for both compounds. Temperature dependence between the electronic
+Raman spectra below and above T_c has been observed and 2\Delta and
+2\Delta/k_BT_C have been estimated as 5.0 meV and 4.0, respectively.",1010.2374v2
+2010-10-26,Close to the Giant Magnons,"We consider the most general string configurations on the R_t x S^3 subspace
+of AdS_5 xS^5, described by the Neumann-Rosochatius integrable system. Under
+some restrictions on the parameters of the solution and in an appropriate
+limit, they correspond to small deviation from the known finite-size giant
+magnon solutions with one and two angular momenta. Analyzing the finite-size
+effect on the dispersion relation, we find that the leading correction is
+modified in a way similar to the gamma-deformed case R_t x S^3_gamma. The
+subleading correction for a string with one angular momentum is also found. It
+depends on the same parameter, which describes the generalization of the
+leading correction.",1010.5465v1
+2010-10-29,Magnetic and Electronic Raman Scattering at the Nodal Spin-Density-Wave Transition in BaFe2As2,"Two magnon excitations and the nodal spin density wave (SDW) gap were
+observed in BaFe2As2 by Raman scattering. Below the SDW transition temperature
+(TSDW) nodal SDW gap opens together with new excitations in reconstructed
+electronic states. The two-magnon peak remains above TSDW and moreover the
+energy increases a little. The change from the long-range ordered state to the
+short-range correlated state is compared to the cuprate superconductors.",1010.6151v1
+2010-12-15,Correlation functions of magnon and spike,"After considering a solitonic string moving in the Poincare $AdS$ and
+two-dimensional sphere, we calculate the two-point correlation function of
+magnon and spike in the semi-classical limit without any explicit solution. We
+also calculate the three-point correlation functions between two heavy and one
+light operators. We find that the coupling between two heavy and one light
+operators in the string side is the exactly same as one obtained from the gauge
+theory by using the RG analysis.",1012.3293v2
+2011-01-14,Antiferromagnets at low Temperatures,"The low-temperature properties of the Heisenberg antiferromagnet in 2+1
+space-time dimensions are analyzed within the framework of effective
+Lagrangians. It is shown that the magnon-magnon interaction is very weak and
+repulsive, manifesting itself through a term proportional to five powers of the
+temperature in the pressure. The structure of the low-temperature series for
+antiferromagnets in 2+1 dimensions is compared with the structure of the
+analogous series for antiferromagnets in 3+1 dimensions. The model-independent
+and systematic effective field theory approach clearly proves to be superior to
+conventional condensed matter methods such as spin-wave theory.",1101.2919v1
+2011-04-06,Three-point correlators for giant magnons,"Three-point correlation functions in the strong-coupling regime of the
+AdS/CFT correspondence can be analyzed within a semiclassical approximation
+when two of the vertex operators correspond to heavy string states having large
+quantum numbers while the third vertex corresponds to a light state with fixed
+charges. We consider the case where the heavy string states are chosen to be
+giant magnon solitons with either a single or two different angular momenta,
+for various different choices of light string states.",1104.1160v2
+2011-04-11,Correlation function of dyonic strings,"We investigate the two- and three-point correlation functions of the dyonic
+magnon and spike, which correspond to the solitonic string moving in the
+Poincare AdS and three-dimensional sphere. We show that the coupling between
+two dyonic magnons or spikes together with a marginal scalar operator in the
+string theory is exactly the same as one obtained by the RG analysis in the
+gauge theory.",1104.1896v1
+2011-05-24,Long-lived magnons throughout the Brillouin zone of the strong-leg spin ladder (C$_7$H$_{10}$N)$_2$CuBr$_4$,"Inelastic neutron scattering is used to measure spin excitations in fully
+deuterated single crystal samples of the strong-leg antiferromagnetic S=1/2
+spin ladder compound (C$_7$H$_{10}$N)$_2$CuBr$_4$. Sharp resolution-limited
+magnons are observed across the entire one-dimensional Brillouin zone. The
+results validate the previously proposed {\it symmetric} spin ladder model and
+provide a reliable estimate of the relevant exchange interactions.",1105.4832v1
+2011-06-16,Thermomagnonic spin transfer and Peltier effects in insulating magnets,"We study the coupled magnon energy transport and collective magnetization
+dynamics in ferromagnets with magnetic textures. By constructing a
+phenomenological theory based on irreversible thermodynamics, we describe
+motion of domain walls by thermal gradients and generation of heat flows by
+magnetization dynamics. From microscopic description based on magnon kinetics,
+we estimate the transport coefficients and analyze the feasibility of
+energy-related applications in insulating ferromagnets, such as yttrium iron
+garnet and europium oxide.",1106.3135v2
+2011-06-28,Three-point Correlation Function of Giant Magnons in the Lunin-Maldacena background,"We compute semiclassical three-point correlation function, or structure
+constant, of two finite-size (dyonic) giant magnon string states and a light
+dilaton mode in the Lunin-Maldacena background, which is the \gamma-deformed,
+or TsT-transformed AdS_5 x S_{\gamma}^5, dual to N = 1 super Yang-Mills theory.
+We also prove that an important relation between the structure constant and the
+conformal dimension, checked for the N = 4 super Yang-Mills case, still holds
+for the \gamma-deformed string background.",1106.5656v1
+2011-07-05,Storage-recovery phenomenon in magnonic crystal,"The phenomenon of wave trapping in an artificial crystal with limited number
+of periods is demonstrated experimentally using spin waves in a magnonic
+crystal. The information stored in the crystal is recovered afterwards by
+parametric amplification of the trapped wave. The storage process is based on
+the excitation of standing internal crystal modes and differs principally from
+the well-known phenomenon of deceleration of light in photonic crystals.",1107.0984v1
+2011-07-29,Temperature dependence of spin currents in one- and three-dimensional insulators,"The temperature dependence of spin currents in insulators at the finite
+temperature near zero Kelvin is theoretically studied. The spin currents are
+carried by Jordan-Wigner fermions and magnons in one- and three- dimensional
+insulators. The quasiparticle description of one-dimensional spin systems is
+valid only in the finite temperature near zero Kelvin. These spin currents are
+generated by the external magnetic field gradient along the quantization axis
+and also by the two-particle interaction gradient. In one-dimensional
+insulators, quantum fluctuations are strong and the spin current carried by
+Jordan-Wigner fermions shows the stronger dependence on temperatures than the
+one by magnons.",1107.5867v1
+2011-09-22,Intrinsic coupling of orbital excitations to spin fluctuations in Mott insulators,"We show how the general and basic asymmetry between two fundamental degrees
+of freedom present in strongly correlated oxides, spin and orbital, has very
+profound repercussions on the elementary spin and orbital excitations. Whereas
+the magnons remain largely unaffected, orbitons become inherently coupled with
+spin fluctuations in spin-orbital models with antiferromagnetic and
+ferroorbital ordered ground states. The composite orbiton-magnon modes that
+emerge fractionalize again in one dimension, giving rise to spin-orbital
+separation in the peculiar regime where spinons are faster than orbitons.",1109.4745v1
+2011-10-18,Life times and chirality of spin-waves in antiferromagnetic and ferromagnetic FeRh: time depedent density functional theory perspective,"The study of the spin excitations in antiferromagnetic (AFM) and
+ferromagnetic (FM) phases of FeRh is reported. We demonstrate that although the
+Fe atomic moments are well defined there is a number of important phenomena
+absent in the Heisenberg description: Landau damping of spin waves, large Rh
+moments induced by the AFM magnons, the formation of the optical magnons
+terminated by Stoner excitations. We relate the properties of the spin-wave
+damping to the features of the Stoner continuum and compare the chirality of
+the spin excitations in AFM, FM and paramagnetic (PM) systems.",1110.3913v1
+2012-05-31,Bose-Einstein Condensation of Magnons in NiCl2-4SC(NH2)2,"A Bose-Einstein condensation (BEC) has been observed in magnetic insulators
+in the last decade. The bosons that condensed are magnons, associated with an
+ordered magnetic phase induced by a magnetic field. We review the experiments
+in the spin-gap compound NiCl2-4SC(NH2)2, in which the formation of BEC occurs
+by applying a magnetic field at low temperatures. This is a contribution to the
+celebration for the 50th anniversary of the Solid State and Low Temperature
+Laboratory of the University of S\~ao Paulo, where this compound was first
+magnetically characterized.",1206.0035v1
+2012-11-22,Observation of Phonon-Assisted Magnon Absorption in Spin-Orbit Coupling Induced Mott Insulator Sr$_{2}$IrO$_{4}$,"The infrared transmission measurement was performed for a two-dimensional
+spin-orbit coupling induced Mott insulator Sr$_{2}$IrO$_{4}$ with a
+layered-perovskite structure. A phonon-assisted magnon mode was observed at
+around 1870 cm$^{-1}$ in the absorption spectrum below 180 K. The
+nearest-neighbor superexchange interaction $J$ was estimated to be 57 meV,
+which is about a half of the $J$ value of a copper oxide La$_{2}$CuO$_{4}$. Our
+results indicate the possibility that nontrivial properties such as
+superconductivity are realized at rather high temperature in iridium oxides.",1211.5241v2
+2013-01-24,Phonon-Magnon coupling in CoF$_2$ investigated by time-of-flight neutron spectroscopy,"We report the results of inelastic neutron scattering investigation on the
+model antiferromagnet CoF$_2$ by time-of-flight neutron spectroscopy. We
+measured the details of the scattering function $S(Q,\omega)$ as a function of
+temperature with two different incident neutron wavelengths. The temperature
+and Q dependence of the measured scattering function suggests the presence of
+magnon-phonon coupling in almost all branches. The present results are in
+agreement with the strong magnetoelastic effects observed previously.",1301.5788v1
+2013-02-04,Gravity waves on the surface of topological superfluid 3He-B,"We have observed waves on the free surface of 3He-B sample at temperatures
+below 0.2mK. The waves are excited by vibrations of the cryostat and detected
+by coupling the surface to the Bose-Einstein condensate of magnon
+quasiparticles in the superfluid. The two lowest gravity-wave modes in our
+cylindrical container are identified. Damping of the waves increases with
+temperature linearly with the density of thermal quasiparticles, as expected.
+Additionally finite damping of the waves in the zero-temperature limit and
+enhancement of magnetic relaxation of magnon condensates by the surface waves
+are observed. We discuss whether the latter effects may be related to Majorana
+fermions bound to the surface of the topological superfluid.",1302.0764v1
+2013-12-24,S matrix from matrix product states,"We use the matrix product state formalism to construct stationary scattering
+states of elementary excitations in generic one-dimensional quantum lattice
+systems. Our method is applied to the spin-1 Heisenberg antiferromagnet, for
+which we calculate the full magnon-magnon S matrix for arbitrary momenta and
+spin, the two-particle contribution to the spectral function and the
+magnetization curve. As our method provides an accurate microscopic
+representation of the interaction between elementary excitations, we envisage
+the description of low-energy dynamics of one-dimensional spin chains in terms
+of these particlelike excitations.",1312.6793v2
+2014-08-14,Design of a spin-wave majority gate employing mode selection,"The design of a microstructured, fully functional spin-wave majority gate is
+presented and studied using micromagnetic simulations. This all-magnon logic
+gate consists of three-input waveguides, a spin-wave combiner and an output
+waveguide. In order to ensure the functionality of the device, the output
+waveguide is designed to perform spin-wave mode selection. We demonstrate that
+the gate evaluates the majority of the input signals coded into the spin-wave
+phase. Moreover, the all-magnon data processing device is used to perform logic
+AND-, OR-, NAND- and NOR- operations.",1408.3235v1
+2014-09-24,Dissipationless Multiferroic Magnonics,"We propose that the magnetoelectric effect in multiferroic insulators with
+coplanar antiferromagnetic spiral order, such as BiFeO$_{3}$, enables
+electrically controlled dissipationless magnonics. Applying an oscillating
+electric field in these materials with frequency as low as household frequency
+can activate Goldstone modes that manifests fast planar rotations of spins,
+whose motion is not obstructed by crystalline anisotropy. Combining with spin
+ejection mechanisms, such a fast planar rotation can deliver electricity at
+room temperature over a distance of the magnetic domain, which is free from the
+energy loss due to Gilbert damping.",1409.6900v2
+2014-11-10,Magnon spectrum in ferromagnets with a skyrmion,"The analysis of the spin wave excitations in two-dimensional isotropic
+Heisenberg ferromagnet is performed with a single skyrmion in the ground state.
+We employ the ideas of semiclassical quantization method, duly modified for the
+use of the lattice model and Maleyev-Dyson boson representation of spin
+operators. The resulting Schr\""odinger equation for magnons describes the
+dispersion and wave functions of spin-wave excitations with strictly
+non-negative spectrum. In contrast to usual ferromagnet, we demonstrate the
+existence of three zero modes, corresponding to conformal symmetries
+spontaneously violated by the skyrmion configuration.",1411.2452v2
+2014-12-20,A HHL 3-point correlation function in the η-deformed AdS_5 x S^5,"We derive the 3-point correlation function between two giant magnons heavy
+string states and the light dilaton operator with zero momentum in the
+\eta-deformed AdS_5 x S^5 valid for any J_1 and \eta in the semiclassical
+limit. We show that this result satisfies a consistency relation between the
+3-point correlation function and the conformal dimension of the giant magnon.
+We also provide a leading finite J_1 correction explicitly.",1412.6668v1
+2015-01-09,Creation and Amplification of Electro-Magnon Solitons by Electric Field in Nanostructured Multiferroics,"We develop a theoretical description of electro-magnon solitons in a coupled
+ferroelectric-ferromagnetic heterostructure. The solitons are considered in the
+weakly nonlinear limit as a modulation of plane waves corresponding to two,
+electric- and magnetic-like branches in the spectrum. Emphasis is put on
+magnetic-like envelope solitons that can be created by an alternating electric
+field. It is shown also that the magnetic pulses can be amplified by an
+electric field with a frequency close to the band edge of the magnetic branch.",1501.02064v1
+2015-01-30,The open Heisenberg chain under boundary fields: a magnonic logic gate,"We study the spin transport in the quantum Heisenberg spin chain subject to
+boundary magnetic fields and driven out of equilibrium by Lindblad dissipators.
+An exact solution is given in terms of matrix product states, which allows us
+to calculate exactly the spin current for any chain size. It is found that the
+system undergoes a discontinuous spin-valve-like quantum phase transition from
+ballistic to sub-diffusive spin current, depending on the value of the boundary
+fields. Thus, the chain behaves as an extremely sensitive magnonic logic gate
+operating with the boundary fields as the base element.",1501.07732v2
+2015-06-18,Dispersive read-out of ferromagnetic resonance for strongly coupled magnons and microwave photons,"We demonstrate the dispersive measurement of ferromagnetic resonance in a
+yttrium iron garnet sphere embedded within a microwave cavity. The reduction in
+the longitudinal magnetization at resonance is measured as a frequency shift in
+the cavity mode coupled to the sphere. This measurement is a result of the
+intrinsic non-linearity in magnetization dynamics, indicating a promising route
+towards experiments in magnon cavity quantum electro-dynamics.",1506.05631v1
+2015-06-30,Spin-wave localization in disordered magnets,"The effect of disorder on magnonic transport in low-dimensional magnetic
+materials is studied in the framework of a classical spin model. Numerical
+investigations give insight into scattering properties of the systems and show
+the existence of Anderson localization in 1D and weak localization in 2D,
+potentially affecting the functionality of magnonic devices.",1506.09045v2
+2015-09-09,Spin wave vortex from the scattering on Bloch point solitons,"The interaction of a spin wave with a stationary Bloch point is studied. The
+topological non-trivial structure of the Bloch point manifests in the
+propagation of spin waves endowing them with a gauge potential that resembles
+the one associated with the interaction of a magnetic monopole and an electron.
+By pursuing this analogy, we are led to the conclusion that the scattering of
+spin waves and Bloch points is accompanied by the creation of a magnon vortex.
+Interference between such a vortex and a plane wave leads to dislocations in
+the interference pattern that can be measurable by means of magnon holography.",1509.02891v1
+2015-10-08,Nematic ordering in pyrochlore antiferromagnets: high-field phase of chromium spinel oxides,"Motivated by recent observation of a new high field phase near saturation in
+chromium spinels $A$Cr$_2$O$_4$ ($A=$ Zn, Cd, Hg), we study the $S = 3/2$
+pyrochlore Heisenberg antiferromagnet with biquadratic interactions. Magnon
+instability analysis at the saturation field reveals that a very small
+biquadratic interaction can induce magnon pairing in pyrochlore
+antiferromagnets, which leads to the emergence of a ferro-quadrupolar phase, or
+equivalently a spin nematic phase, below the saturation field. We present the
+magnetic phase diagram in an applied field, studying both $S=3/2$ and $S=1$
+spin systems. The relevance of our result to chromium spinels is discussed.",1510.02373v1
+2016-04-25,Bias-free spin-wave phase shifter for magnonic logic,"A design of a magnonic phase shifter operating without an external bias
+magnetic field is proposed. The phase shifter uses a localized collective spin
+wave mode propagating along a domain wall ""waveguide"" in a dipolarly-coupled
+magnetic dot array existing in a chessboard antiferromagnetic (CAFM) ground
+state. It is demonstrated numerically that remagnetization of a single magnetic
+dot adjacent to the domain wall waveguide introduces a controllable phase shift
+in the propagating spin wave mode without significant change of the mode
+amplitude. It is also demonstrated that a logic XOR gate can be realized in the
+same system.",1604.07337v1
+2016-07-16,"Comment on ""Supercurrent in a room temperature Bose-Einstein magnon condensate""","The comment explains that the preprint arXiv:1503.0042 has not presented
+persuasive theoretical or experimental arguments of existence of spin
+supercurrents in a magnon condensate prepared in a room temperature
+yttrium-iron-garnet magnetic film because the authors did not check known
+criteria for existence of spin supercurrents in magnetically ordered materials.
+Also they did not compare their supercurrent interpretation with a competing
+and more realistic scenario of transport by spin diffusion.",1607.04720v2
+2018-04-09,Microwave non-reciprocity of magnon excitations in a non-centrosymmetric antiferromagnet Ba$_2$MnGe$_2$O$_7$,"We have investigated the microwave non-reciprocity for a non-centrosymmetric
+antiferromagnet Ba$_2$MnGe$_2$O$_7$. The magnon modes expected by the
+conventional spin wave theory for staggered antiferromagnets are certainly
+observed. The magnitudes of exchange interaction and magnetic anisotropy are
+obtained by the comparison with the theory. The microwave non-reciprocity is
+identified for one of these mode. The relative magnitude of microwave
+non-reciprocity can be explained with use of spin wave theory and Kubo formula.",1804.03250v1
+2013-08-16,Influence of ferromagnetic ordering on Raman scattering in CoS$_2$,"The effects of phonon anharmonicity, phonon-magnon and electron-phonon
+interactions on the temperature dependence of Raman optical phonon modes are
+theoretically investigated. Besides of the Klemens result for the phonon width
+due to anharmonicity, the corresponding lineshift is derived. We argue that the
+phonon decay into two magnons has very low intensity in ferromagnets with low
+Curie temperatures. Therefore, the electron interband transitions accompanied
+with the ferromagnetic ordering are included in considerations to get a good
+quantitative agreement with experiments.",1308.3571v1
+2017-01-16,Hierarchy of the low-lying excitations for the $(2+1)$-dimensional $q=3$ Potts model in the ordered phase,"The $(2+1)$-dimensional $q=3$ Potts model was simulated with the exact
+diagonalization method. In the ordered phase, the elementary excitations
+(magnons) are attractive, forming a series of bound states in the low-energy
+spectrum. We investigate the low-lying spectrum through a dynamical
+susceptibility, which is readily tractable with the exact diagonalization
+method via the continued-fraction expansion. As a result, we estimate the
+series of (scaled) mass gaps, $m_{2,3,4}/m_1$ ($m_1$: single-magnon mass), in
+proximity to the transition point.",1701.04232v1
+2008-07-16,Spiky Strings on AdS(4) X CP**3,"We study a giant magnon and a spike solution for the string rotating on
+AdS(4) X CP**3 geometry. We consider rigid rotating fundamental string in the
+SU(2) X SU(2) sector inside the CP**3 and find out the general form of all the
+conserved charges. We find out the dispersion relation corresponding to both
+the known giant magnon and the new spike solutions. We further study the finite
+size correction in both cases.",0807.2559v3
+2008-07-17,"Giant magnons in AdS_4/CFT_3: dispersion, quantization and finite--size corrections","We study giant magnon solutions in AdS4 \times CP3. We compute quantum
+corrections to their dispersion relation. We find out that the one--loop
+correction vanishes in infinite volume. This implies that the interpolating
+function h(\lambda) between strong and weak coupling regimes does not have a
+constant term \lambda^0 at strong coupling. We also compute first nonvanishing
+finite volume correction to the one--loop expression. When compared to the
+L\""{u}sher formula, our results could provide a nontrivial check of the AdS4
+\times CP3 S--matrix proposed recently in arXiv:0807.1924.",0807.2861v3
+2008-07-21,Neumann-Rosochatius integrable system for strings on AdS_4 x CP^3,"We use the reduction of the string dynamics on AdS_4 x CP^3 to the
+Neumann-Rosochatius integrable system. All constraints can be expressed simply
+in terms of a few parameters. We analyze the giant magnon and single spike
+solutions on R_t x CP^3 with two angular momenta in detail and find the
+energy-charge relations. The finite-size effects of the giant magnon and single
+spike solutions are analyzed.",0807.3134v2
+2011-11-10,Magnonic band structure of a two-dimensional magnetic superlattice,"The frequencies and linewidths of spin waves in a two-dimensional periodic
+superlattice of magnetic materials are found, using the Landau-Lifshitz-Gilbert
+equations. The form of the exchange field from a surface-torque-free boundary
+between magnetic materials is derived, and magnetic-material combinations are
+identified which produce gaps in the magnonic spectrum across the entire
+superlattice Brillouin zone for hexagonal and square-symmetry superlattices.",1111.2506v1
+2012-01-12,Finite-size effects of beta-deformed AdS_5/CFT_4 at strong coupling,"We compute both classical and quantum finite-size corrections at leading
+order in the strong coupling limit for the (dyonic) giant magnon in the
+Lunin-Maldacena background. Based on the exact S-martix conjectured for the
+deformed theory, we generalize the Luscher formula to include twisted boundary
+conditions and show that the results match with those derived both by
+finite-size classical solutions of the giant magnon and by algebraic curve
+analysis.",1201.2635v1
+2014-05-14,Generation of magnonic spin wave traps,"Spatially resolved measurements of the magnetization dynamics induced by an
+intense laser pump-pulse reveal that the frequencies of resulting spin wave
+modes depend strongly on the distance to the pump center. This can be
+attributed to a laser generated temperature profile. On a CoFeB thin film
+magnonic crystal, Damon-Eshbach modes are expected to propagate away from the
+point of excitation. The experiments show that this propagation is frustrated
+by the strong temperature gradient",1405.3470v1
+2014-05-27,Strongly coupled magnons and cavity microwave photons,"We realize a cavity magnon-microwave photon system in which magnetic dipole
+interaction mediates strong coupling between collective motion of large number
+of spins in a ferrimagnet and the microwave field in a three-dimensional
+cavity. By scaling down the cavity size and increasing number of spins, an
+ultrastrong coupling regime is achieved with a cooperativity reaching 12600.
+Interesting dynamic features including classical Rabi oscillation, magnetically
+induced transparency, and Purcell effect are demonstrated in this highly
+versatile platform, highlighting its great potential for coherent information
+processing.",1405.7062v1
+2014-06-10,Spontaneous chiral symmetry breaking on a fully polarized frustrated magnet at finite temperature,"Frustration can introduce more-than-two minima in a spin dispersion relation
+even in a fully polarized magnet under high magnetic field. We generally
+discuss, on the fully polarized phase, the possibility of the chiral symmetry
+breaking where the number of magnons pumped by finite temperature deviates to
+one side of minima. We study this phase by constructing the Ginzburg-Landau
+energy which is controlled by the external magnetic field and interactions
+between magnons near the dispersion minima. This chirality breaking phase
+accompanies, not a magnetization perpendicular to the external field, but the
+vector chirality $S_m \times S_n$. We also discuss the possibility of the
+chirality breaking phase on LiCuVO4 slightly above the saturation field.",1406.2617v1
+2017-10-24,Indirect coupling of magnons by cavity photons,"The interaction between two magnetic spheres in microwave cavities is studied
+by Mie scattering theory beyond the magnetostatic and rotating wave
+approximations. We demonstrate that two spatially separated dielectric and
+magnetic spheres can be strongly coupled over a long distance by standing
+cavity modes. The interactions splits acoustical (dark) and optical (bright)
+modes in a way that can be mapped on a molecular orbital theory of the hydrogen
+molecule. Breaking the symmetry by assigning different radii to the two spheres
+introduces ""ionic"" character to the magnonic bonds. These results illustrate
+the coherent and controlled energy exchange between objects in microwave
+cavities.",1710.08907v1
+2017-12-08,Giant magnons and spiky strings in the Schrodinger/dipole-deformed CFT correspondence,"We construct semi-classical string solutions of the Schr\""odinger $Sch_5
+\times S^5$ spacetime, which is conjectured to be the gravity dual of a
+non-local dipole-deformed CFT. They are the counterparts of the giant magnon
+and spiky string solutions of the undeformed $AdS_5 \times S^5$ to which they
+flow when the deformation parameter is turned off. They live in an $S^3$
+subspace of the five-sphere along the directions of which the $B$-field has
+non-zero components having also extent in the $Sch_5$ part of the metric.
+Finally, we speculate on the form of the dual field theory operators.",1712.03091v2
+2018-09-03,Loschmidt-amplitude wave function spectroscopy and the physics of dynamically driven phase transitions,"We introduce the Loschmidt amplitude as a powerful tool to perform
+spectroscopy of generic many-body wave functions and use it to interrogate the
+wave function obtained after ramping the transverse field quantum Ising model
+through its quantum critical point. Previous results are confirmed and a more
+complete understanding of the population of defects and of the effects of
+magnon-magnon interaction or finite-size corrections is obtained. The influence
+of quantum coherence is clarified.",1809.00733v2
+2018-09-23,The antiferromagnetic phase of the Floquet-driven Hubbard model,"A saddle point plus fluctuations analysis of the periodically driven
+half-filled two-dimensional Hubbard model is performed. For drive frequencies
+below the equilibrium gap, we find discontinuous transitions to time-dependent
+solutions. A highly excited, generically non-thermal distribution of magnons
+occurs even for drive frequencies far above the gap. Above a critical drive
+amplitude, the low-energy magnon distribution diverges as the frequency tends
+to zero and antiferromagnetism is destroyed, revealing the generic importance
+of collective mode excitations arising from a non-equilibrium drive.",1809.08607v2
+2019-09-12,Quantum computation of magnon spectra,"We demonstrate quantum computation of two-point correlation functions for a
+Heisenberg spin chain. Using the IBM Q 20 quantum machines, we find that for
+two sites the correlation functions produce the exact results reliably. For
+four sites, results from the IBM Q 20 Tokyo quantum computer are noisy due to
+read out errors and decoherence. Nevertheless, the correlation functions retain
+the correct spectral information. This is illustrated in the frequency domain
+by accurately extracting the magnon energies from peaks in the spectral
+function.",1909.05701v2
+2017-05-03,Controlling Chiral Domain Walls in Antiferromagnets Using Spin-Wave Helicity,"In antiferromagnets, the Dzyaloshinskii-Moriya interaction lifts the
+degeneracy of left- and right-circularly polarized spin waves. This
+relativistic coupling increases the efficiency of spin-wave-induced domain wall
+motion and leads to higher drift velocities. We show that in biaxial
+antiferromagnets, the spin-wave helicity controls both the direction and
+magnitude of the magnonic force on chiral domain walls. By contrast, in
+uniaxial antiferromagnets, the magnonic force is propulsive with a helicity
+dependent strength.",1705.01572v2
+2017-05-11,Bethe Ansatz for two-magnon scattering states in 2D and 3D Heisenberg-Ising ferromagnets,"Various versions of the Bethe ansatz are suggested for evaluation of
+scattering two-magnon states in 2D and 3D Heisenberg-Ising ferromagnets. It is
+shown that for 2D square (3D qubic) finite-periodic or infinite lattices about
+a half (3/4) of states have a correctly 2D- (3D-) generalized Bethe form. The
+remaining scattering states are treated (on the infinite lattices only) within
+the degenerative discrete-diffractive modification of the Bethe ansatz
+previously suggested by the author.",1705.04117v2
+2017-05-25,Prediction of ultra-narrow Higgs resonance in magnon Bose-condensates,"Higgs resonance modes in condensed matter systems are generally broad;
+meaning large decay widths or short relaxation times. This common feature has
+obscured and limited their observation to a select few systems. Contrary to
+this, the present work predicts that Higgs resonances in magnetic field
+induced, three-dimensional magnon Bose-condensates have vanishingly small decay
+widths. Specifically for parameters relating to TlCuCl$_3$, we find an energy
+($\Delta_H$) to width ($\Gamma_H$) ratio $\Delta_H/\Gamma_H\sim500$, making
+this the narrowest predicted Higgs mode in a condensed matter system, some two
+orders of magnitude `narrower' than the sharpest condensed matter Higgs
+observed so far.",1705.09007v1
+2019-01-02,Fermion zero modes for the mixed-flux AdS$_3$ giant magnon,"We explicitly construct the four and two fermion zero modes for the
+mixed-flux generalization of the Hofman-Maldacena giant magnon on two of the
+AdS$_3$ backgrounds with maximal amount of supersymmetry, AdS$_3 \times$S$^3
+\times$T$^4$ and AdS$_3 \times$S$^3 \times$S$^3 \times$S$^1$. We also show how
+to get the $\mathfrak{psu}(1|1)^4$ and $\mathfrak{su}(1|1)^2$ superalgebras
+from the semiclassically quantized fermion zero modes.",1901.00530v2
+2019-02-07,Intrinsic Spin Decay Length in Antiferromagnetic Insulator,"We report intrinsic spin decay length of an antiferromagnetic insulator. We
+found that at an antiferromagnetic/ferromagnetic interface, a spin current
+generated by spin pumping is strongly suppressed by two-magnon scattering. By
+eliminating the two-magnon contribution, we discovered that the characteristic
+length of spin decay in NiO changes by two-orders of magnitude through the
+paramagnetic to antiferromagnetic transition. The spin decay length in the
+antiferromagnetic state is longer than 100 nm, which is an order of magnitude
+longer than previously believed. These results provide a crucial piece of
+information for the fundamental understanding of the physics of spin transport.",1902.02462v1
+2019-02-08,Magnetic excitations and transport properties in frustrated ferromagnetic chain,"To clarify the transport property mediated by bound magnons in a spin nematic
+state, we investigate the spin Drude weight of a spin-1/2 $J_{1}$-$J_{2}$
+Heisenberg chain with ferromagnetic $J_{1}$ and antiferromagnetic $J_{2}$ in a
+magnetic field by numerical diagonalization. At zero magnetic field, numerical
+results with up to 24 sites suggest that the spin Drude weight would be zero in
+the thermodynamic limit, indicating diffusive spin transport. With increasing
+the magnetic field, the spin Drude weight is enhanced at low temperatures,
+indicating that bound magnons would contribute to the spin transport.",1902.02932v1
+2019-03-28,Spin Seebeck and Spin Nernst Effects of Magnons in Noncollinear Antiferromagnetic Insulators,"Our joint theoretical and computer experimental study of heat-to-spin
+conversion reveals that noncollinear antiferromagnetic insulators are promising
+materials for generating magnon spin currents upon application of a temperature
+gradient: they exhibit spin Seebeck and spin Nernst effects. Using Kubo theory
+and spin dynamics simulations, we explicitly evaluate these effects in a single
+kagome sheet of potassium iron jarosite, KFe$_3$(OH)$_6$(SO$_4$)$_2$, and
+predict a spin Seebeck conversion factor of $0.2 \mu\mathrm{V}/\mathrm{K}$ at a
+temperature of $20 \mathrm{K}$.",1903.11896v1
+2019-04-03,Frustrated quantum Heisenberg double-tetrahedral and octahedral chains at high magnetic fields,"We consider the spin-1/2 antiferromagnetic Heisenberg model on two
+one-dimensional frustrated lattices, double-tetrahedral chain and octahedral
+chain, with almost dispersionless (flat) lowest magnon band in a strong
+magnetic field. Using the localized magnons picture, we construct an effective
+description of the one-dimensional chains with triangle and square traps within
+the strong coupling approximation. We perform extensive exact diagonalization
+and density matrix renormalization group calculations to check the validity of
+the obtained effective Hamiltonians by comparison with the initial models with
+special focus on the magnetization and specific heat at high magnetic fields.",1904.02240v2
+2019-04-24,Layered optomagnonic structures: Time Floquet scattering-matrix approach,"A fully dynamic theoretical approach to layered optomagnonic structures,
+based on a time Floquet scattering-matrix method, is developed. Its
+applicability is demonstrated on a simple design of a dual photonic-magnonic
+cavity, formed by sandwiching a magnetic garnet thin film between two
+dielectric Bragg mirrors, subject to continuous excitation of a perpendicular
+standing spin wave. Some remarkable phenomena, including nonlinear
+photon-magnon interaction effects and enhanced inelastic light scattering in
+the strong-coupling regime, fulfilling a triple-resonance condition, are
+analyzed and the limitations of the quasistatic adiabatic approximation are
+established.",1904.10714v1
+2019-08-03,On the Regge limit of Fishnet correlators,"We study the Regge trajectories of the Mellin amplitudes of the $0-,1-$ and
+$2-$ magnon correlators of the Fishnet theory. Since fishnet theory is both
+integrable and conformal, the correlation functions are known exactly. We find
+that while for $0$ and $1$ magnon correlators, the Regge poles can be exactly
+determined as a function of coupling, $2$-magnon correlators can only be dealt
+with perturbatively. We evaluate the resulting Mellin amplitudes at weak
+coupling, while for strong coupling we do an order of magnitude calculation.",1908.01123v3
+2019-08-28,Effect of inhomogeneous Dzyaloshinskii-Moriya interaction on antiferromagnetic spin-wave propagation,"We investigate the effect of inhomogeneous Dzyaloshinskii-Moriya interaction
+(DMI) on antiferromagnetic spin-wave propagation theoretically and numerically.
+We find that antiferromagnetic spin waves can be amplified at a boundary where
+the DMI varies. The inhomogeneous DMI also provides a way to construct a
+magnonic crystal with forbidden and allowed antiferromagnetic spin-wave bands
+in terahertz frequency ranges. In contrast to ferromagnetic spin waves,
+antiferromagnetic spin waves experience a polarization-dependent phase shift
+when passing through the inhomogeneous DMI, offering a magnonic crystal that
+also serves as a spin-wave polarizer.",1908.10650v1
+2016-10-13,Electronic control of magnonic and spintronic devices,"Nanometric magnonic and spintronic devices need magnetic field control in
+addition to conventional electronic control. In this work we review ways to
+replace magnetic field control by an electronic one in order to circumvent
+appearance of stray magnetic fields or the difficulty of creating large
+magnetic fields over nanometric distances. Voltage control is compared to
+current control and corresponding devices are compared from their energetic
+efficiency point of view.",1610.04011v1
+2017-07-03,Theory of magnon-mediated tunnel magneto-Seebeck effect,"The tunnel magneto-Seebeck effect is the dependence of the thermopower of
+magnetic tunnel junctions on the magnetic configuration. It is conventionally
+interpreted in terms of a thermoelectric generalization of the tunnel
+magnetoresistance. Here, we investigate the heat-driven electron transport in
+these junctions associated with electron-magnon scattering, using stochastic
+Landau-Lifshitz phenomenology and quantum kinetic theory. Our findings
+challenge the widely accepted single-electron picture of the tunneling
+thermopower in magnetic junctions.",1707.00674v1
+2020-06-03,Circulating cavity magnon polaritons,"We predict magnon polariton states circulating unidirectionally in a
+microwave cavity when loaded by a number of magnets on special lines. Realistic
+finite-element numerical simulations, including dielectric, time-dependent and
+non-linear effects, confirm the validity of the approximations of a fully
+analytical input-output model. We find that a phased antenna array can focus
+all power into a coherent microwave beam with controlled direction and an
+intensity that scales with the number of magnets.",2006.02203v1
+2020-06-15,Open giant magnons suspended between dual giant gravitons in ${\cal N}=4$ SYM,"We study classical solutions to the Nambu-Goto string on $AdS_2 \times S^1$
+and $AdS_3 \times S^1$ corresponding to strings stretched between wrapped
+branes extending in $AdS$. The solutions are obtained by analytic continuation
+of giant magnon solutions, cut at the position of the branes.
+  These solutions carry one or two $SO(2,4)$ charges and a single $SO(6)$
+charge. We compute their energies and show their relation to $\frac{1}{2}$-BPS
+geometries. Their relevance to the $SL(2)$ sector of $\mathcal{N}=4$ SYM is
+also discussed.",2006.08649v1
+2021-02-12,Impossibility of Increasing N$\acute{\textrm{e}}$el Temperature in Zigzag Graphene Nanoribbon by Electric Field and Carrier Doping,"We investigated the dependence of N$\acute{\textrm{e}}$el temperature as a
+critical temperature on the electric field and hole-electron doping in the
+antiferromagnetically ordered zigzag graphene nanoribbon. The temperature was
+calculated by averaging the magnon energy in the Brillouin zone within the
+mean-field approximation. We employed the generalized Bloch theorem instead of
+the supercell approach to reduce the computational cost significantly to obtain
+the magnon spectrum. We showed that the N$\acute{\textrm{e}}$el temperature
+reduces when increasing both the electric field and the hole-electron doping,
+thus these treatments will never enhance the N$\acute{\textrm{e}}$el
+temperature.",2102.06508v1
+2015-12-14,Gauge and emergent electromagnetic fields for moving magnetic topological solitons,"We apply the general conception of non-Abelian gauge fields for description
+of magnetic soliton excitations. We show that the component of the gauge field
+along the soliton local magnetization (Abelian part of the gauge potential)
+determines dynamics of spin fluctuations over the soliton background in a
+ferromagnet. Assumption that the gauge field is a pure gauge allows calculating
+the gauge field components and finding simple expressions for the emergent
+electromagnet fields related to the soliton motion. The gauge field results in
+soliton-magnon interaction leading to renormalization of the soliton and magnon
+dynamics. The presented approach allows reaching more deep understanding of a
+relationship of the field theory and condensed matter magnetism.",1512.04396v1
+2016-09-07,Thermally induced magnon accumulation in two-sublattice magnets,"We present a temperature dependent study of the thermal excitation of
+magnonic spin currents in two-sublattice magnetic materials. Using atomistic
+spin model simulations, we study the local magnetization profiles in the
+vicinity of a temperature step in antiferromagnets, as well as in ferrimagnets.
+It is shown that the strength of the excitation of the spin currents in these
+systems scales with the derivative of the magnetization with respect to the
+temperature.",1609.02161v1
+2016-09-15,Route toward high-speed nano-magnonics,"We study experimentally the possibility to utilize pulses of pure spin
+current, produced via the nonlocal spin injection mechanism, to generate short
+packets of spin waves propagating in nanoscale magnetic waveguides. The
+spatially and time-resolved micro-focus Brillouin light scattering spectroscopy
+measurements demonstrate that the excitation by spin current results in
+extremely fast transient response, enabling efficient generation of short
+spin-wave packets with duration down to a few nanoseconds. The proposed method
+opens a route for the implementation of high-speed magnonic systems for
+transmission and processing of information on the nanoscale.",1609.04526v1
+2016-11-05,Magnonic analog of relativistic Zitterbewegung in an antiferromagnetic spin chain,"We theoretically investigate the spin wave (magnon) excitations in a
+classical antiferromagnetic spin chain with easy-axis anisotropy. We obtain a
+Dirac-like equation by linearizing the Landau- Lifshitz-Gilbert equation in
+this antiferromagnetic system, in contrast to the ferromagnetic system in which
+a Schr\""{o}dinger equation is derived. The Hamiltonian operator in the
+Dirac-like equation is a pseudo-Hermitian. We compute and demonstrate the
+relativistic Zitterbewegung (trembling motion) in the antiferromagnetic spin
+chain by measuring the expectation values of the wave packet position.",1611.01512v2
+2019-10-25,Voltage-Controlled Magnonic Spin Tunneling Junction,"We theoretically investigate the effective exchange interaction,
+$J_\mathrm{eff}$, mediated by conductive electrons within a nonmagnetic metal
+spacer, in the presence of a bias voltage, sandwiched by two ferromagnetic
+insulators. On the basis of the tight-binding model, we show the voltage and
+spacer thickness dependences of $J_\mathrm{eff}$, and its contorollability is
+demonstrated. We also propose a new magnonic device with the functions of both
+field effect transistor and non-volatile memory.",1910.11549v2
+2020-02-07,Order Parameter and Magnetization of Antiferromagnets in Mutually Parallel Staggered and Magnetic Fields,"We explore the behavior of the order parameter and the magnetization of
+antiferromagnetic solids subjected to mutually parallel staggered and magnetic
+fields. The effective field theory analysis of the partition function is taken
+up to the two-loop level, where the magnon-magnon interaction comes into play.
+These interaction effects, however, are small. A phenomenon that comes rather
+unexpectedly is that the finite-temperature magnetization increases with
+temperature when the strengths of the staggered and magnetic field are held
+constant.",2002.02958v1
+2020-03-21,Low-temperature asymptotic of the transverse dynamical structure factor for a magnetically polarized XX chain,"Dyson equation for the real two-time commutator retarded one-magnon Green
+function of the ferromagnetically polarized XX chain is suggested following the
+Plakida-Tserkovnikov algorithm. Starting from this result a low-temperature
+integral representation for the corresponding magnon self energy is obtained by
+the truncated form factor expansion however without any resummations. Within
+the suggested approach the low-temperature asymptotics of the transverse
+dynamical structure factor may be readily studied. Some obtained line shapes
+are presented.",2003.09743v3
+2020-03-28,Magnon binding in BaCdVO(PO$_4$)$_2$,"The bond-nematic state has both long-range ordering of magnetic quadrupoles
+and the high entanglement typical of spin liquids, and as such can be thought
+of as a spin liquid crystal. One of the most promising materials in which to
+find such a state is BaCdVO(PO$_4$)$_2$, in which a magnetically silent phase
+has been found between a magnetically ordered low-field phase and the
+high-field polarised phase. Here I study the magnetic Hamiltonian of
+BaCdVO(PO$_4$)$_2$, and, for the Hamiltonian-parameters determined by fits to
+inelastic neutron scattering experiments, show that magnons condense out of the
+polarised state as bound pairs. This is direct theoretical support for the
+existence of a bond-nematic state just below the saturation field.",2003.12747v1
+2020-07-23,Magnetic characteristics of epitaxial NiO films studied by Raman spectroscopy,"Raman spectroscopy is utilized to study the magnetic characteristics of
+heteroepitaxial NiO thin films grown by plasma-assisted molecular beam epitaxy
+on MgO(100) substrates. For the determination of the N\'eel temperature, we
+demonstrate a reliable approach by analyzing the temperature dependence of the
+Raman peak originating from second-order scattering by magnons. The
+antiferromagnetic coupling strength is found to be strongly influenced by the
+growth conditions. The low-temperature magnon frequency and the N\'eel
+temperature are demonstrated to depend on the biaxial lattice strain and the
+degree of structural disorder which is dominated by point defects.",2007.11982v1
+2020-10-04,Bethe ansatz on a quantum computer?,"We consider the feasibility of studying the anisotropic Heisenberg quantum
+spin chain with the Variational Quantum Eigensolver (VQE) algorithm, by
+treating Bethe states as variational states, and Bethe roots as variational
+parameters. For short chains, we construct exact one-magnon trial states that
+are functions of the variational parameter, and implement the VQE calculations
+in Qiskit. However, exact multi-magnon trial states appear to be out out of
+reach.",2010.01609v2
+2020-10-16,Zero-magnon sound in quantum Heisenberg ferromagnets,"Using a functional renormalization group approach we show that at low
+temperatures and in a certain range of magnetic fields the longitudinal dynamic
+structure factor of quantum Heisenberg ferromagnets in dimensions $D\leq 2$
+exhibits a well-defined quasi-particle peak with linear dispersion that we
+identify as zero-magnon sound. In $D>2$ the larger phase space available for
+the decay into transverse spin waves leads only to a broad hump centered at
+zero frequency whose width scales linearly in momentum.",2010.08425v3
+2021-04-05,Two-magnon Raman scattering in antiferromagnetic phases of frustrated spin models on the honeycomb lattice,"We calculate the two-magnon Raman scattering spectra in antiferromagnetic
+phases of several frustrated spin models defined on the honeycomb lattice.
+These include the N\'{e}el antiferromagnetic phase of a $J_1$-$J_2$-$J_3$ model
+and the stripe phase of the Heisenberg-Kitaev model. We show that both the
+magnetic frustration and the anisotropy of interactions may significantly
+affect the Raman spectra. We further discuss the implications of our results to
+the magnetic excitations of the iron-based compound BaFe$_2$Se$_2$O and show
+how the magnetic interactions can be extracted from fit to the Raman spectrum.",2104.01903v1
+2021-11-05,Multiple optical gaps and laser with magnonic pumping in 2D Ising superconductors,"Ising superconductivity has been recently discovered in 2D transition metal
+dichalcogenides. We report that such superconductors have unusual optical
+properties controlled by the in-plane Zeeman field. First, we find several
+optical gaps visible as peaks of the conductivity and the Raman susceptibility.
+Moreover, we find that the Ising spin splitting in the spectrum of Bogolubov
+quasiparticles enables strong population inversion generated by the
+time-dependent Zeeman field. Ultimately this leads to the possibility of the
+superconducting laser with magnonic pumping which can be realized in the van
+der Waals structures consisting of the Ising superconductor and the
+ferromagnetic insulator layers.",2111.03623v1
+2022-06-30,Single magnon excited states of a Heisenberg spin-chain using a quantum computer,"Excited states of spin-chains play an important role in condensed matter
+physics. We present a method of calculating the single magnon excited states of
+the Heisenberg spin-chain that can be efficiently implemented on a quantum
+processor for small spin chains. Our method involves finding the stationary
+points of the energy vs wavenumber curve. We implement our method for 4-site
+and 8-site Heisenberg Hamiltonians using numerical techniques as well as using
+an IBM quantum processor. Finally, we give an insight into the circuit
+complexity and scaling of our proposed method.",2206.15300v1
+2022-08-29,Experimental generation of circulating cavity magnon polaritons,"We experimentally realize circularly polarised unidirectional cavity magnon
+polaritons in a torus-shaped microwave cavity loaded by a small magnetic
+sphere. At special positions the clockwise and counterclockwise modes are
+circularly polarized, such that only one of them couples to the magnet, which
+breaks the mode degeneracy. We reveal the chiral nature of the spectral energy
+and angular momentum flow by observing and modelling non-reciprocities of the
+microwave scattering matrix.",2208.13408v3
+2022-12-02,Interplay between spin wave and magnetic vortex,"In this paper, the interplay between spin wave and magnetic vortex is
+studied. We find three types of magnon scatterings: skew scattering, symmetric
+side deflection and back reflection, which associate with respectively magnetic
+topology, energy density distribution and linear momentum transfer torque
+within vortex. The vortex core exhibits two translational modes: the intrinsic
+circular mode and a coercive elliptical mode, which can be excited based on
+permanent and periodic magnon spin-transfer torque effects of spin wave.
+Lastly, we propose a vortex-based spin wave valve in which via inhomogeneity
+modulation we access arbitrary control of the phase shift.",2212.01172v1
+2023-01-03,Amplitude representation of Landau-Lifshitz equation and its application to ferromagnetic films,"The purpose of this article is to develop a systematic approach to the
+solution of the Landau-Lifshitz equation in terms of the magnon wave function
+{\psi} (r) and apply it to physical phenomena in a thin ferromagnetic film.
+This article has also a purpose to represent the modern state of art for the
+properties of ferromagnetic films and the pumping-induced Bose-Einstein
+condensation of magnons in them at room temperature. Thus, it can be considered
+as a review on basic principles and the recent advances in the field.",2301.01391v1
+2023-02-15,Coherent Microwave Emission of a Gain-Driven Polariton,"By developing a gain-embedded cavity magnonics platform, we create
+gain-driven polariton (GDP) that is activated by an amplified electromagnetic
+field. Distinct effects of gain-driven light-matter interaction, such as
+polariton auto-oscillations, polariton phase singularity, self-selection of a
+polariton bright mode, and gain-induced magnon-photon synchronization, are
+theoretically studied and experimentally manifested. Utilizing the
+gain-sustained photon coherence of the GDP, we demonstrate polariton-based
+coherent microwave amplication (~ 40 dB) and achieve high-quality coherent
+microwave emission (Q > 10^9).",2302.08904v1
+2023-02-22,Magnons in the fan phase of anisotropic frustrated antiferromagnets,"Elementary excitations spectrum of the fan phase of anisotropic frustrated
+antiferromagnets is discussed analytically. In the linear spin-wave
+approximation, the spectrum is determined by the Hamiltonian, including normal,
+anomalous, and umklapp terms. The latter mix states with momenta which differ
+by two modulation vectors of the fan structure. This mixing leads to essential
+rearrangement of the low-energy part of the spectrum, which is shown to consist
+of a gapless phason branch with linear dispersion and a gapped ``optical''
+branch, which corresponds to the fan structure amplitude oscillations. In the
+high-energy part of the spectrum, the effect of the umklapps is negligible, and
+the excitations are similar to the magnons of the fully polarized phase.",2302.11235v1
+2023-05-22,Acousto-magnonic Hall effect in honeycomb antiferromagnets,"The recently discovered van der Waals antiferromagnets have suffered from the
+lack of a comprehensive method to study their magnetic properties. Here, we
+propose a dissipationless magnon spin Hall current driven by surface acoustic
+waves as a novel probe for such antiferromagnets. Our results pave the way
+towards mechanical detection and manipulation of the magnetic order in
+two-dimensional antiferromagnets. Furthermore, they will overcome the
+difficulties with weak magnetic responses inherent in the use of
+antiferromagnets and hence provide a building block for future
+antiferromagnetic spintronics.",2305.13375v1
+2023-07-10,Surface magnon spectra of nodal loop semimetals,"In this paper we establish a connection between the bulk topological
+structure and the magnetic properties of drumhead surface states of nodal loop
+semimetals. We identify the magnetic characteristics of the surface states and
+compute the system's magnon spectrum by treating electron-electron interactions
+on a mean-field level. We draw attention to a subtle connection between a
+Lifshitz-like transition of the surface states driven by mechanical distortions
+and the magnetic characteristics of the system. Our findings may be
+experimentally verified e.g. by spin polarized electron energy loss
+spectroscopy of nodal semimetal surfaces.",2307.04620v2
+2023-08-16,Two-dimensional altermagnets: Superconductivity in a minimal microscopic model,"We propose a minimal toy model for a two-dimensional altermagnet. The model
+unravels altermagnetic properties at a microscopic level. We find spin-split
+electron- and non-degenerate magnon bands with a $d$-wave symmetry. We use the
+model to explore magnon-mediated superconductivity in altermagnets. The
+dominant superconducting state is spin-polarized with a $p$-wave symmetry. The
+state adopts its characteristics from the spin-split electron bands.
+Furthermore, we find that the superconducting critical temperature of
+altermagnets can be significantly enhanced by tuning the chemical potential.",2308.08606v2
+2023-09-07,Electric Analog of Magnons in Order-Disorder Ferroelectrics,"We analyze the ``ferron"" excitations in order-disorder ferroelectrics by a
+microscopic pseudo-spin model. We demonstrate that analogous to magnons, the
+quanta of spin waves in magnetic materials, ferrons carry both static and
+oscillating electric dipole moments, exhibit a Stark effect, and may be
+parametrically excited by THz radiation. The anti-crossing gap of the
+ferron-photon hybrid depends strongly on propagation direction and an applied
+static electric field. We predict ferron diffusion lengths that can reach
+centimeters, which implies efficient transport of electric polarization by
+temperature gradients. These properties suggest that ferroelectric materials
+may be useful for information technology beyond data storage applications.",2309.03691v1
+2023-10-06,A Physical Theory of Two-stage Thermalization,"One indication of thermalization time is subsystem entanglement reaching
+thermal values. Recent studies on local quantum circuits reveal two exponential
+stages with decay rates $r_1$ and $r_2$ of the purity before and after
+thermalization. We provide an entanglement membrane theory interpretation, with
+$r_1$ corresponding to the domain wall free energy. Circuit geometry can lead
+to $r_1 < r_2$, producing a ``phantom eigenvalue"". Competition between the
+domain wall and magnon leads to $r_2 < r_1$ when the magnon prevails. However,
+when the domain wall wins, this mechanism provides a practical approach for
+measuring entanglement growth through local correlation functions.",2310.04491v1
+2023-11-16,Unidirectional propagation of zero-momentum magnons,"We report on experimental observation of unidirectional propagation of
+zero-momentum magnons in synthetic antiferromagnet consisting of strained
+CoFeB/Ru/CoFeB trilayer. Inherent non-reciprocity of spin waves in synthetic
+antiferromagnets with uniaxial anisotropy results in smooth and monotonous
+dispersion relation around Gamma point, where the direction of the phase
+velocity is reversed, while the group velocity direction is conserved. The
+experimental observation of this phenomenon by intensity-, phase-, and
+time-resolved Brillouin light scattering microscopy is corroborated by
+analytical models and micromagnetic simulations.",2311.10044v1
+2023-11-21,Magnonic spin current shot noise in an itinerant Fermi gas,"Spin transport phenomena at strongly-correlated interfaces play central roles
+in fundamental physics as well as spintronic applications. To anatomize
+spin-transport carriers, we propose the detection of the spin current noise in
+interacting itinerant fermions. The Fano factor given by the ratio between the
+spin current and its noise reflects elementary carriers of spin transport at
+the interface of spin-polarized Fermi gases realized in ultracold atoms. The
+change of the Fano factor microscopically evinces a crossover from the
+quasiparticle transport to magnon transport in itinerant fermionic systems.",2311.12383v2
+2023-12-05,Topological superconductivity in quantum wires mediated by helical magnons,"Triplet superconductivity arises in systems where the effective electronic
+attraction favors Cooper pairs with a symmetric spin structure, as may occur in
+non-collinear magnetic systems. Here we show that topological triplet
+superconductivity can be realized in a one-dimensional quantum wire through the
+interaction with magnetic fluctuations of a helical magnet. The magnon-mediated
+attraction favors triplet superconductivity over a large sector of magnetic
+parameters, and stabilizes a topological phase with a superconducting gap of
+the order of 1 meV over an extended region of chemical potentials.",2312.02655v1
+2024-01-28,Dynamical theory of angle-resolved electron energy loss and gain spectroscopies of phonons and magnons including multiple scattering effects,"We present a method for computing angle-resolved electron-energy-loss and
+gain spectroscopies for phonon and magnon excitations in transmission electron
+microscopy. Fractional scattering intensities are derived from the
+temperature-dependent time auto-correlation of the electron beam wave function.
+This method captures both single and multiple scattering processes, as well as
+dynamical diffraction effects. Our method remains computationally efficient,
+and it is easy to parallelize.",2401.15599v2
+2024-01-29,Topological magnon-polarons in honeycomb antiferromagnets with spin-flop transition,"We theoretically investigate the thermal Hall transport of magnon-polarons in
+a two-dimensional honeycomb antiferromagnetic insulator under the influence of
+a perpendicular magnetic field, varying in strength. The application of a
+perpendicular magnetic field induces a magnetic phase transition from the
+collinear antiferromagnetic phase to the spin-flop phase, leading to a
+significant alteration in Hall transport across the transition point. In this
+paper, our focus is on the intrinsic contribution to thermal Hall transport
+arising from the magnetoelastic interaction. To facilitate experimental
+verification of our theoretical results, we present the dependence of thermal
+Hall conductivity on magnetic field strength and temperature.",2401.15888v1
+2024-02-16,Parametric instability in a magnomechanical system,"We study parametric instability in a magnomechanical system, specifically
+examining magnon tunneling between moving ferromagnetic insulators. Our
+analysis reveals that quantum fluctuations generate spin currents above a
+critical velocity threshold, while no spin currents occur below this threshold
+at low temperatures. The critical velocity depends on magnon stiffness and
+Zeeman energy. Approaching the threshold, the spin current becomes divergent,
+linked to the PT-symmetry-breaking transition. This enhanced behavior could
+offer sensitive measurements and signal amplification in quantum technology.",2402.10796v1
+2024-03-18,Current-induced magnon trapping in spin torque oscillation,"Spin torque nano-oscillators realized by magnetization dynamics trapped in a
+current-induced potential are reported. We fabricated Ni$_{81}$Fe$_{19}$/Pt
+nanostructures and measured current-induced microwave emission from the
+structures. The result shows an increase in the magnitude and spectral
+narrowing of the microwave emission. We demonstrate that the current-induced
+magnetic field suppresses magnon radiation loss and significantly reduces the
+linewidth and the threshold current required for the spin torque oscillation.",2403.11618v1
+1997-12-15,Spin Tunneling in Conducting Oxides,"Direct tunneling in ferromagnetic junctions is compared with
+impurity-assisted, surface state assisted, and inelastic contributions to a
+tunneling magnetoresistance (TMR). Theoretically calculated direct tunneling in
+iron group systems leads to about a 30% change in resistance, which is close to
+experimentally observed values. It is shown that the larger observed values of
+the TMR might be a result of tunneling involving surface polarized states. We
+find that tunneling via resonant defect states in the barrier radically
+decreases the TMR (down to 4% with Fe-based electrodes), and a resonant tunnel
+diode structure would give a TMR of about 8%. With regards to inelastic
+tunneling, magnons and phonons exhibit opposite effects: one-magnon emission
+generally results in spin mixing and, consequently, reduces the TMR, whereas
+phonons are shown to enhance the TMR. The inclusion of both magnons and phonons
+reasonably explains an unusual bias dependence of the TMR.
+  The model presented here is applied qualitatively to half-metallics with 100%
+spin polarization, where one-magnon processes are suppressed and the change in
+resistance in the absence of spin-mixing on impurities may be arbitrarily
+large. Even in the case of imperfect magnetic configurations, the resistance
+change can be a few 1000 percent. Examples of half-metallic systems are
+CrO$_2$/TiO$_2$ and CrO$_2$/RuO$_2$, and an account of their peculiar band
+structures is presented. The implications and relation of these systems to CMR
+materials which are nearly half-metallic, are discussed.",9712170v2
+1998-03-12,Static and dynamic structure factors in the Haldane phase of the bilinear-biquadratic spin-1,"The excitation spectra of the T=0 dynamic structure factors for the spin,
+dimer, and trimer fluctuation operators as well as for the newly defined center
+fluctuation operator in the one-dimensional S=1 Heisenberg model wi th
+isotropic bilinear $(J\cos\theta)$ and biquadratic $(J\sin\theta)$ exchange are
+investigated via the recursion method for systems with up to N=18 site s over
+the predicted range, $-\pi/4<\theta\lesssim\pi/4$, of the topologically ordered
+Haldane phase. The four static and dynamic structure factors probe t he
+ordering tendencies in the various coupling regimes and the elementary and
+composite excitations which dominate the T=0 dynamics. At $\theta =
+\arctan{1/3}$ (VBS point), the dynamically relevant spectra in the invariant
+subspaces with total spin $S_T = 0,1,2$ are dominated by a branch of magnon
+states $(S_T = 1)$, by continua of two-magnon scattering states $(S_T =
+0,1,2)$, and by discrete branches of two-magnon bound states with positive
+interaction energy $(S_T = 0,2)$. The dimer and trimer spectra at $q=\pi$ ar e
+found to consist of single modes with $N$-independent excitation energies
+$\omega_\lambda^D/|e_0|=5$ and $\omega_\lambda^T/|e_0|=6$, where $e_0=E_0/N$ is
+the ground-state energy per site. The basic structure of the dynamically
+relevant excitation spectrum remains the same over a substantial parameter
+range within the Haldane phase. At the transition to the dimerized phase
+($\theta=-\pi/4$), the two-magnon excitations turn into two-spinon excitations.",9803147v1
+2002-12-20,Magnon Exchange Mechanism of Ferromagnetic Superconductivity,"The magnon exchange mechanism of ferromagnetic superconductivity
+(FM-superconductivity) was developed to explain in a natural way the fact that
+the superconductivity in $UGe_2$, $ZrZn_2$ and $URhGe$ is confined to the
+ferromagnetic phase.The order parameter is a spin anti-parallel component of a
+spin-1 triplet with zero spin projection. The transverse spin fluctuations are
+pair forming and the longitudinal ones are pair breaking. In the present paper,
+a superconducting solution, based on the magnon exchange mechanism, is obtained
+which closely matches the experiments with $ZrZn_2$ and $URhGe$. The onset of
+superconductivity leads to the appearance of complicated Fermi surfaces in the
+spin up and spin down momentum distribution functions. Each of them consist of
+two pieces, but they are simple-connected and can be made very small by varying
+the microscopic parameters. As a result, it is obtained that the specific heat
+depends on the temperature linearly, at low temperature, and the coefficient
+$\gamma=\frac {C}{T}$ is smaller in the superconducting phase than in the
+ferromagnetic one. The absence of a quantum transition from ferromagnetism to
+ferromagnetic superconductivity in a weak ferromagnets $ZrZn_2$ and $URhGe$ is
+explained accounting for the contribution of magnon self-interaction to the
+spin fluctuations' parameters. It is shown that in the presence of an external
+magnetic field the system undergoes a first order quantum phase transition.",0212520v1
+2003-11-13,Magnon squeezing in an antiferromagnet: reducing the spin noise below the standard quantum limit,"At absolute zero temperature, thermal noise vanishes when a physical system
+is in its ground state, but quantum noise remains as a fundamental limit to the
+accuracy of experimental measurements. Such a limitation, however, can be
+mitigated by the formation of squeezed states. Quantum mechanically, a squeezed
+state is a time-varying superposition of states for which the noise of a
+particular observable is reduced below that of the ground state at certain
+times. Quantum squeezing has been achieved for a variety of systems, including
+the electromagnetic field, atomic vibrations in solids and molecules, and
+atomic spins, but not so far for magnetic systems. Here we report on an
+experimental demonstration of spin wave (i.e., magnon) squeezing. Our method
+uses femtosecond optical pulses to generate correlations involving pairs of
+magnons in an antiferromagnetic insulator, MnF2. These correlations lead to
+quantum squeezing in which the fluctuations of the magnetization of a
+crystallographic unit cell vary periodically in time and are reduced below that
+of the ground state quantum noise. The mechanism responsible for this squeezing
+is stimulated second order Raman scattering by magnon pairs. Such squeezed
+states have important ramifications in the emerging fields of spintronics and
+quantum computing involving magnetic spin states or the spin-orbit coupling
+mechanism.",0311329v1
+2004-02-19,Self-energy corrections in an antiferromagnet -- interplay of classical and quantum effects on quasiparticle dispersion,"Self-energy corrections due to fermion-magnon interaction are studied in the
+antiferromagnetic state of the $t-t'-t''$ Hubbard model within the rainbow
+(noncrossing) approximation in the full $U$ range from weak to strong coupling.
+The role of classical (mean-field) features of fermion and magnon dispersion,
+associated with finite $U,t',t''$, are examined on quantum corrections to
+quasiparticle energy, weight, one-particle density of states etc. A finite-$U$
+induced classical dispersion term, absent in the $t-J$ model, is found to play
+an important role in suppressing the quasiparticle weight for states near ${\bf
+k}=(0,0)$, as seen in cuprates. For intermediate $U$, the renormalized AF band
+gap is found to be nearly half of the classical value, and the weak coupling
+limit is quite non-trivial due to strongly suppressed magnon amplitude. For
+finite $t'$, the renormalized AF band gap is shown to vanish at a critical
+interaction strength $U_c$, yielding a spin fluctuation driven first-order AF
+insulator - PM metal transition. Quasiparticle dispersion evaluated with the
+same set of Hubbard model cuprate parameters, as obtained from a recent magnon
+spectrum fit, provides excellent agreement with ARPES data for $\rm Sr_2 Cu O_2
+Cl_2 $.",0402487v3
+2006-02-14,Electron-phonon coupling in the self-consistent Born approximation of the t-J model,"We study an undoped t-J model with electron-phonon interaction using the
+self-consistent Born approximation (SCBA). By neglecting vertex corrections,
+the SCBA solves a boson-holon model, where a holon couples to phonons and
+magnons. Comparison with exact diagonalization results for the t-J model
+suggests that the SCBA describes the electron-phonon interaction fairly
+accurately over a substantial range of J/t values. Exact diagonalization of the
+boson-holon model shows that the deviations are mainly due to the neglect of
+vertex corrections for small J/t and due to the replacement of the t-J model by
+the boson-holon model for large J/t. For typical values of J/t, the
+electron-phonon part Sigma_ep of the electron self-energy has comparable
+contributions from the second order diagram in the electron-phonon interaction
+and a phonon induced change of magnon diagrams. A very simple approximation to
+Sigma_ep gives a rather accurate effective mass. Using this approximation, we
+study the factors influencing the electron-phonon interaction. Typically, we
+find that the magnons nominally have a stronger coupling to the holon than the
+phonons. The phonons, nevertheless, drive the formation of small polarons
+(self-localization) due to important differences between the character of the
+phonon and magnon couplings.",0602327v1
+2006-02-24,Magnetization dynamics in dysprosium orthoferrites via inverse Faraday effect,"The ultrafast non-thermal control of magnetization has recently become
+feasible in canted antiferromagnets through photomagnetic instantaneous pulses
+[A.V. Kimel {\it et al.}, Nature {\bf 435}, 655 (2005)]. In this experiment
+circularly polarized femtosecond laser pulses set up a strong magnetic field
+along the wave vector of the radiation through the inverse Faraday effect,
+thereby exciting non-thermally the spin dynamics of dysprosium orthoferrites. A
+theoretical study is performed by using a model for orthoferrites based on a
+general form of free energy whose parameters are extracted from experimental
+measurements. The magnetization dynamics is described by solving coupled
+sublattice Landau-Lifshitz-Gilbert equations whose damping term is associated
+with the scattering rate due to magnon-magnon interaction. Due to the inverse
+Faraday effect and the non-thermal excitation, the effect of the laser is
+simulated by magnetic field Gaussian pulses with temporal width of the order of
+hundred femtoseconds. When the field is along the z-axis, a single resonance
+mode of the magnetization is excited. The amplitude of the magnetization and
+out-of-phase behavior of the oscillations for fields in z and -z directions are
+in good agreement with the cited experiment. The analysis of the effect of the
+temperature shows that magnon-magnon scattering mechanism affects the decay of
+the oscillations on the picosecond scale. Finally, when the field pulse is
+along the x-axis, another mode is excited, as observed in experiments. In this
+case the comparison between theoretical and experimental results shows some
+discrepancies whose origin is related to the role played by anisotropies in
+orthoferrites.",0602593v1
+2006-06-29,Two-Hole Bound States from a Systematic Low-Energy Effective Field Theory for Magnons and Holes in an Antiferromagnet,"Identifying the correct low-energy effective theory for magnons and holes in
+an antiferromagnet has remained an open problem for a long time. In analogy to
+the effective theory for pions and nucleons in QCD, based on a symmetry
+analysis of Hubbard and t-J-type models, we construct a systematic low-energy
+effective field theory for magnons and holes located inside pockets centered at
+lattice momenta (\pm pi/2a,\pm pi/2a). The effective theory is based on a
+nonlinear realization of the spontaneously broken spin symmetry and makes
+model-independent universal predictions for the entire class of lightly doped
+antiferromagnetic precursors of high-temperature superconductors. The
+predictions of the effective theory are exact, order by order in a systematic
+low-energy expansion. We derive the one-magnon exchange potentials between two
+holes in an otherwise undoped system. Remarkably, in some cases the
+corresponding two-hole Schr\""odinger equations can even be solved analytically.
+The resulting bound states have d-wave characteristics. The ground state wave
+function of two holes residing in different hole pockets has a d_{x^2-y^2}-like
+symmetry, while for two holes in the same pocket the symmetry resembles d_{xy}.",0606766v1
+2006-08-07,Magnon Bound-state Scattering in Gauge and String Theory,"It has been shown that, in the infinite length limit, the magnons of the
+gauge theory spin chain can form bound states carrying one finite and one
+strictly infinite R-charge. These bound states have been argued to be
+associated to simple poles of the multi-particle scattering matrix and to world
+sheet solitons carrying the same charges. Classically, they can be mapped to
+the solitons of the complex sine-Gordon theory.
+  Under relatively general assumptions we derive the condition that simple
+poles of the two-particle scattering matrix correspond to physical bound states
+and construct higher bound states ``one magnon at a time''. We construct the
+scattering matrix of the bound states of the BDS and the AFS S-matrices. The
+bound state S-matrix exhibits simple and double poles and thus its analytic
+structure is much richer than that of the elementary magnon S-matrix. We also
+discuss the bound states appearing in larger sectors and their S-matrices. The
+large 't Hooft coupling limit of the scattering phase of the bound states in
+the SU(2) sector is found to agree with the semiclassical scattering of world
+sheet solitons. Intriguingly, the contribution of the dressing phase has an
+independent world sheet interpretation as the soliton-antisoliton scattering
+phase shift. The small momentum limit provides independent tests of these
+identifications.",0608049v3
+2009-05-10,Incoherent bound states in an infinite $XXZ$ chain at $Δ=-1/2$,"For an infinite $XXZ$ chain with $\Delta=-1/2$ we have obtained a family of
+translationary invariant three-magnon states which do not satisfy the string
+conjecture. All of them have the same energy.",0905.1494v1
+2010-10-13,Electric-field control of spin waves at room temperature in multiferroic BiFeO3,"To face the challenges lying beyond current CMOS-based technology, new
+paradigms for information processing are required. Magnonics proposes to use
+spin waves to carry and process information, in analogy with photonics that
+relies on light waves, with several advantageous features such as potential
+operation in the THz range and excellent coupling to spintronics. Several
+magnonic analog and digital logic devices have been proposed, and some
+demonstrated. Just as for spintronics, a key issue for magnonics is the large
+power required to control/write information (conventionally achieved through
+magnetic fields applied by strip lines, or by spin transfer from large
+spin-polarized currents). Here we show that in BiFeO3, a room-temperature
+magnetoelectric material, the spin wave frequency (>600 GHz) can be tuned
+electrically by over 30%, in a non-volatile way and with virtually no power
+dissipation. Theoretical calculations indicate that this effect originates from
+a linear magnetoelectric effect related to spin-orbit coupling induced by the
+applied electric field. We argue that these properties make BiFeO3 a promising
+medium for spin wave generation, conversion and control in future magnonics
+architectures.",1010.2678v1
+2011-01-03,The building blocks of magnonics,"Novel material properties can be realized by designing waves' dispersion
+relations in artificial crystals. The crystal's structural length scales may
+range from nano- (light) up to centimeters (sound waves). Because of their
+emergent properties these materials are called metamaterials. Different to
+photonics, where the dielectric constant dominantly determines the index of
+refraction, in a ferromagnet the spin-wave index of refraction can be
+dramatically changed already by the magnetization direction. This allows a
+different flexibility in realizing dynamic wave guides or spin-wave switches.
+The present review will give an introduction into the novel functionalities of
+spin-wave devices, concepts for spin-wave based computing and magnonic
+crystals. The parameters of the magnetic metamaterials are adjusted to the
+spin-wave k-vector such that the magnonic band structure is designed. However,
+already the elementary building block of an antidot lattice, the singular hole,
+owns a strongly varying internal potential determined by its magnetic dipole
+field and a localization of spin-wave modes. Photo-magnonics reveal a way to
+investigate the control over the interplay between localization and
+delocalization of the spin-wave modes using femtosecond lasers, which is a
+major focus of this review. We will discuss the crucial parameters to realize
+free Bloch states and how, by contrast, a controlled localization might allow
+to gradually turn on and manipulate spin-wave interactions in spin-wave based
+devices in the future.",1101.0479v2
+2011-02-01,Yangian symmetry of boundary scattering in AdS/CFT and the explicit form of bound state reflection matrices,"The reflection matrices of multi magnon bound states are obtained explicitely
+by exploiting the Yangian symmetry of boundary scattering on the Y=0 maximal
+giant graviton brane.",1102.0122v1
+2012-02-21,Quantum critical behavior in three-dimensional one-band Hubbard model at half filling,"One-band Hubbard model with hopping parameter $t$ and Coulomb repulsion $U$
+is considered at half filling. By means of the Schwinger bosons and slave
+Fermions representation of the electron operators and integrating out the
+spin-singlet Fermi fields an effective Heisenberg model with antiferromagnetic
+exchange constant is obtained for vectors which identifies the local
+orientation of the spin of the itinerant electrons. The amplitude of the spin
+vectors is an effective spin of the itinerant electrons accounting for the fact
+that some sites, in the ground state, are doubly occupied or empty. Accounting
+adequately for the magnon-magnon interaction the N\'{e}el temperature is
+calculated. When the ratio $\frac tU$ is small enough ($\frac tU\leq 0.09$) the
+effective model describes a system of localized electrons. Increasing the ratio
+increases the density of doubly occupied states which in turn decreases the
+effective spin and N\'{e}el temperature. The phase diagram in plane of
+temperature $\frac {T_N}{U}$ and parameter $\frac tU$ is presented. The quantum
+critical point ($T_N=0$) is reached at $\frac tU=0.9$. The magnons in the
+paramagnetic phase are studied and the contribution of the magnons'
+fluctuations to the heat capacity is calculated. At N\'{e}el temperature the
+heat capacity has a peak which is suppressed when the system approaches quantum
+critical point.",1202.4627v2
+2013-07-25,Relaxation of Bose-Einstein Condensates of Magnons in Magneto-Textural Traps in Superfluid $^3$He-B,"In superfluid $^3$He-B externally pumped quantized spin-wave excitations or
+magnons spontaneously form a Bose-Einstein condensate in a 3-dimensional trap
+created with the order-parameter texture and a shallow minimum in the
+polarizing field. The condensation is manifested by coherent precession of the
+magnetization with a common frequency in a large volume. The trap shape is
+controlled by the profile of the applied magnetic field and by the condensate
+itself via the spin-orbit interaction. The trapping potential can be
+experimentally determined with the spectroscopy of the magnon levels in the
+trap. We have measured the decay of the ground state condensates after
+switching off the pumping in the temperature range $(0.14\div
+0.2)T_{\mathrm{c}}$. Two contributions to the relaxation are identified: (1)
+spin-diffusion with the diffusion coefficient proportional to the density of
+thermal quasiparticles and (2) the approximately temperature-independent
+radiation damping caused by the losses in the NMR pick-up circuit. The measured
+dependence of the relaxation on the shape of the trapping potential is in a
+good agreement with our calculations based on the magnetic field profile and
+the magnon-modified texture. Our values for the spin diffusion coefficient at
+low temperatures agree with the theoretical prediction and earlier measurements
+at temperatures above $0.5T_{\mathrm{c}}$.",1307.6782v2
+2013-11-07,Giant magnon solution and dispersion relation in string theory in AdS_3 x S^3 x T^4 with mixed flux,"We address the question about the exact form of the dispersion relation for
+light-cone string excitations in string theory in AdS3 x S3 x T4 with mixed R-R
+and NS-NS 3-form fluxes. The analogy with string theory in AdS5 x S5 suggests
+that in addition to the data provided by the perturbative near-BMN expansion
+and the symmetry algebra considerations there is also another source of
+information about the dispersion relation -- the semiclassical giant magnon
+solution. In earlier work in arXiv:1303.1037 and arXiv:1304.4099 it was found
+that the symmetry algebra constraints consistent with perturbative expansion do
+not completely determine the form of the dispersion relation. The aim of the
+present paper is to fix it by constructing a generalization of the known dyonic
+giant magnon soliton on S3 to the presence of a non-zero NS-NS flux described
+by a WZ term in the string action. We find that the angular momentum of this
+soliton gets shifted by a term linear in world-sheet momentum. We also discuss
+the symmetry algebra of the string light-cone S-matrix and show that the exact
+dispersion relation, which should have the correct perturbative BMN and
+semiclassical giant magnon limits, should also contain such a linear momentum
+term. The simplicity of the resulting bound-state picture provides a strong
+argument in favour of this dispersion relation.",1311.1794v2
+2013-11-29,Magnon radiation by moving Abrikosov vortices in ferromagnetic superconductors and superconductor-ferromagnet multilayers,"In systems combining type-II superconductivity and magnetism the
+non-stationary magnetic field of moving Abrikosov vortices may excite spin
+waves, or magnons. This effect leads to the appearance of an additional damping
+force acting on the vortices. By solving the London and Landau-Lifshitz-Gilbert
+equations we calculate the magnetic moment induced force acting on vortices in
+ferromagnetic superconductors and superconductor/ferromagnet superlattices. If
+the vortices are driven by a dc force, magnon generation due to the Cherenkov
+resonance starts as the vortex velocity exceeds some threshold value. For an
+ideal vortex lattice this leads to an anisotropic contribution to the
+resistivity and to the appearance of resonance peaks on the current voltage
+characteristics. For a disordered vortex array the current will exhibit a
+step-like increase at some critical voltage. If the vortices are driven by an
+ac force with a frequency \omega, the interaction with magnetic moments will
+lead to a frequency-dependent magnetic contribution \eta_M to the vortex
+viscosity. If \omega is below the ferromagnetic resonance frequency \omega_F,
+vortices acquire additional inertia. For \omega > \omega_F dissipation is
+enhanced due to magnon generation. The viscosity \eta_M can be extracted from
+the surface impedance of the ferromagnetic superconductor. Estimates of the
+magnetic force acting on vortices for the U-based ferromagnetic superconductors
+and cuprate/manganite superlattices are given.",1311.7620v1
+2014-09-19,Study of strong photon-magnon coupling in a YIG-film split-ring resonant system,"By using the stripline Microwave Vector Network Analyzer Ferromagnetic
+Resonance and Pulsed Inductive Microwave Magnetometry spectroscopy techniques,
+we study a strong coupling regime of magnons to microwave photons in the planar
+geometry of a lithographically formed split-ring resonator (SRR) loaded by a
+single-crystal epitaxial yttrium-iron garnet (YIG) film. Strong anti-crossing
+of the photon modes of SRR and of the magnon modes of the YIG film is observed
+in the applied-magnetic-field resolved measurements. The coupling strength
+extracted from the experimental data reaches 9 percent at 3 GHz.
+  Theoretically, we propose an equivalent circuit model of an SRR loaded by a
+magnetic film. This model follows from the results of our numerical simulations
+of the microwave field structure of the SRR and of the magnetization dynamics
+in the YIG film driven by the microwave currents in the SRR. The equivalent
+circuit model is in good agreement with the experiment. It provides a simple
+physical explanation of the process of mode anti-crossing.
+  Our findings are important for future applications in microwave quantum
+photonic devices as well as in magnetically tunable metamaterials exploiting
+the strong coupling of magnons to microwave photons.",1409.5499v1
+2014-11-14,Light Higgs channel of the resonant decay of magnon condensate in superfluid $^3$He-B,"In superfluids the order parameter, which describes spontaneous symmetry
+breaking, is an analogue of the Higgs field in the Standard Model of particle
+physics. Oscillations of the field amplitude are massive Higgs bosons, while
+oscillations of the orientation are massless Nambu-Goldstone bosons. The
+125~GeV Higgs boson, discovered at Large Hadron Collider, is light compared to
+electroweak energy scale, which led to a suggestion of the ``little Higgs''
+extension of the Standard Model, in which the light Higgs appears as a NG mode
+acquiring mass due to violation of a hidden symmetry. Here we show that such
+light Higgs exists in superfluid $^3$He-B, where one of three Nambu-Goldstone
+spin-wave modes acquires small mass due to the spin-orbit interaction. Other
+modes become optical and acoustic magnons. We observe parametric decay of
+Bose-Einstein condensate of optical magnons to light Higgs modes and decay of
+optical to acoustic magnons. Formation of a light Higgs from a Nambu-Goldstone
+mode observed in $^3$He-B opens a possibility that such scenario can be
+realized in other systems, where violation of some hidden symmetry is possible,
+including the Standard Model.",1411.3983v4
+2015-04-10,Long range pure magnon spin diffusion observed in a non-local spin-Seebeck geometry,"The spin diffusion length for thermally excited magnon spins is measured by
+utilizing a non-local spin-Seebeck effect measurement. In a bulk single crystal
+of yttrium iron garnet (YIG) a focused laser thermally excites magnon spins.
+The spins diffuse laterally and are sampled using a Pt inverse spin Hall effect
+detector. Thermal transport modeling and temperature dependent measurements
+demonstrate the absence of spurious temperature gradients beneath the Pt
+detector and confirm the non-local nature of the experimental geometry.
+Remarkably, we find that thermally excited magnon spins in YIG travel over 120
+$\mu$m at 23 K, indicating that they are robust against inelastic scattering.
+The spin diffusion length is found to be at least 47 $\mu$m and as high as 73
+$\mu$m at 23 K in YIG, while at room temperature it drops to less than 10
+$\mu$m. Based on this long spin diffusion length, we envision the development
+of thermally powered spintronic devices based on electrically insulating, but
+spin conducting materials.",1504.02808v2
+2015-06-19,Origin of the thickness-dependent low-temperature enhancement of spin Seebeck effect in YIG films,"The temperature dependent longitudinal spin Seebeck effect (SSE) in heavy
+metal (HM)/ Y3Fe5O12 (YIG) bilayers is investigated as a function of different
+magnetic field strength, different HM detection material, and YIG thickness
+ranging from nm to mm. A large enhancement of the SSE signal is observed at low
+temperatures leading to a peak of the signal amplitude. We demonstrate that
+this enhancement shows a clear dependence on the film thickness, being more
+pronounced for thicker films and vanishing for films thinner than 600 nm. The
+peak temperature depends on the applied magnetic field strength as well as on
+the detection material and interface, revealing a more complex behavior beyond
+the currently discussed phonon-magnon coupling mechanism that considers only
+bulk effects. While the thickness dependence and magnetic field dependence can
+be well explained in the framework of the magnon-driven SSE by taking into
+account the frequency dependent propagation length of thermally excited magnons
+in the bulk material, the temperature dependence of the SSE is significantly
+influenced by the interface coupling to an adjacent detection layer. This
+indicates that previously neglected interface effects play a key role and that
+the spin current traversing the interface and being detected in the HM depends
+differently on the magnon frequency for different HMs.",1506.06037v1
+2016-04-14,"Longitudinal magnon, inversion breaking and magnetic instabilities in the pseudo-Kagome francisites Cu3Bi(SeO3)2O2X with X=Br, Cl","We performed Raman studies and a dielectric characterization of the
+pseudo-kagome Cu3Bi(SeO3)2O2X (X = Cl, Br). These compounds share competing
+nearest-neighbour ferromagnetic exchange and frustrating next-nearest-neighbour
+antiferromagnetic exchange as well as highly noncollinear magnetic ground
+state. However, at low temperature they differ with respect to the existence of
+inversion symmetry. For both compounds there exists a pronounced interplay of
+polar phonon modes with quantum magnetic fluctuations. A novel Raman mode
+appears for temperatures below the Neel temperature with a Fano lineshape and
+an enormous intensity that exceeds most of the phonon lines. We discuss a
+possible contribution of longitudinal magnons to this signal. In contrast, one
+magnon scattering based on linear transvers magnons is excluded based on a
+symmetry analysis of spin wave representations and Raman tensor calculations.
+There exists evidence that in these pseudo-kagome compounds magnetic quantum
+fluctuations carry an electric dipole moment. Our data as well as a comparison
+with previous far-infrared spectra allow us to conclude that Cu3Bi(SeO3)2O2Cl
+changes its symmetry most likely from Pmmn to P21mn with a second order
+structural phase transition at T*=120 K and becomes multiferroic.
+Cu3Bi(SeO3)2O2Br represents an interesting counter part as it does not show
+this instability and stays inversion symmetric down to lowest temperatures,
+investigated.",1604.04249v1
+2017-03-02,Diversity of quantum ground states and quantum phase transitions of a spin-1/2 Heisenberg octahedral chain,"The spin-1/2 Heisenberg octahedral chain with regularly alternating monomeric
+and square-plaquette sites is investigated using various analytical and
+numerical methods: variational technique, localized-magnon approach, exact
+diagonalization (ED) and density-matrix renormalization group (DMRG) method.
+The model belongs to the class of flat-band systems and it has a rich
+ground-state phase diagram including phases with spontaneously broken
+translational symmetry. Moreover, it exhibits an anomalous low-temperature
+thermodynamics close to continuous or discontinuous field-driven quantum phase
+transitions between three quantum ferrimagnetic phases, tetramer-hexamer phase,
+monomer-tetramer phase, localized-magnon phase and two different spin-liquid
+phases. If the intra-plaquette coupling is at least twice as strong as the
+monomer-plaquette coupling, the variational method furnishes a rigorous proof
+of the monomer-tetramer ground state in a low-field region and the
+localized-magnon approach provides an exact evidence of a single magnon trapped
+at each square plaquette in a high-field region. In the rest of parameter space
+we have numerically studied the ground-state phase diagram and magnetization
+process using DMRG and ED methods. It is shown that the zero-temperature
+magnetization curve may involve up to four intermediate plateaus at zero,
+one-fifth, two-fifth and three-fifth of the saturation magnetization, while the
+specific heat exhibits a striking low-temperature peak in a vicinity of
+discontinuous quantum phase transitions.",1703.00715v2
+2017-03-09,Magnon mode selective spin transport in compensated ferrimagnets,"We investigate the generation of magnonic thermal spin currents and their
+mode selective spin transport across interfaces in insulating, compensated
+ferrimagnet/normal metal bilayer systems. The spin Seebeck effect signal
+exhibits a non-monotonic temperature dependence with two sign changes of the
+detected voltage signals. Using different ferrimagnetic garnets, we demonstrate
+the universality of the observed complex temperature dependence of the spin
+Seebeck effect. To understand its origin, we systematically vary the interface
+between the ferrimagnetic garnet and the metallic layer, and by using different
+metal layers we establish that interface effects play a dominating role. They
+do not only modify the magnitude of the spin Seebeck effect signal but in
+particular also alter its temperature dependence. By varying the temperature,
+we can select the dominating magnon mode and we analyze our results to reveal
+the mode selective interface transmission probabilities for different magnon
+modes and interfaces. The comparison of selected systems reveals
+semi-quantitative details of the interfacial coupling depending on the
+materials involved, supported by the obtained field dependence of the signal.",1703.03218v2
+2017-08-07,Field dependence of non-reciprocal magnons in chiral MnSi,"Spin waves in chiral magnetic materials are strongly influenced by the
+Dzyaloshinskii-Moriya interaction resulting in intriguing phenomena like
+non-reciprocal magnon propagation and magnetochiral dichroism. Here, we study
+the non-reciprocal magnon spectrum of the archetypical chiral magnet MnSi and
+its evolution as a function of magnetic field covering the field-polarized and
+conical helix phase. Using inelastic neutron scattering, the magnon energies
+and their spectral weights are determined quantitatively after deconvolution
+with the instrumental resolution. In the field-polarized phase the imaginary
+part of the dynamical susceptibility $\chi''(\varepsilon, {\bf q})$ is shown to
+be asymmetric with respect to wavevectors ${\bf q}$ longitudinal to the applied
+magnetic field ${\bf H}$, which is a hallmark of chiral magnetism. In the
+helimagnetic phase, $\chi''(\varepsilon, {\bf q})$ becomes increasingly
+symmetric with decreasing ${\bf H}$ due to the formation of helimagnon bands
+and the activation of additional spinflip and non-spinflip scattering channels.
+The neutron spectra are in excellent quantitative agreement with the low-energy
+theory of cubic chiral magnets with a single fitting parameter being the
+damping rate of spin waves.",1708.02098v2
+2017-08-09,Chiral liquid phase of simple quantum magnets,"We study a $T=0$ quantum phase transition between a quantum paramagnetic
+state and a magnetically ordered state for a spin $S=1$ XXZ Heisenberg
+antiferromagnet on a two-dimensional triangular lattice. The transition is
+induced by an easy plane single-ion anisotropy $D$. At the mean-field level,
+the system undergoes a direct transition at a critical $D = D_c$ between a
+paramagnetic state at $D > D_c$ and an ordered state with broken U(1) symmetry
+at $D < D_c$. We show that beyond mean field the phase diagram is very
+different and includes an intermediate, partially ordered chiral liquid phase.
+Specifically, we find that inside the paramagnetic phase the Ising ($J_z$)
+component of the Heisenberg exchange binds magnons into a two-particle bound
+state with zero total momentum and spin. This bound state condenses at $D >
+D_c$, before single-particle excitations become unstable, and gives rise to a
+chiral liquid phase, which spontaneously breaks spatial inversion symmetry, but
+leaves the spin-rotational U(1) and time-reversal symmetries intact. This
+chiral liquid phase is characterized by a finite vector chirality without long
+range dipolar magnetic order. In our analytical treatment, the chiral phase
+appears for arbitrarily small $J_z$ because the magnon-magnon attraction
+becomes singular near the single-magnon condensation transition. This phase
+exists in a finite range of $D$ and transforms into the magnetically ordered
+state at some $D<D_c$. We corroborate our analytic treatment with numerical
+density matrix renormalization group calculations.",1708.02980v2
+2018-11-27,Magnon topology and thermal Hall effect in trimerized triangular lattice antiferromagnet,"The non-trivial magnon band topology and its consequent responses have been
+extensively studied in two-dimensional magnetisms. However, the triangular
+lattice antiferromagnet (TLAF), the best-known frustrated two-dimensional
+magnet, has received less attention than the closely related Kagome system,
+because of the spin-chirality cancellation in the umbrella ground state of the
+undistorted TLAF. In this work, we study the band topology and the thermal Hall
+effect (THE) of the TLAF with (anti-)trimerization distortion under the
+external perpendicular magnetic field using the linearized spin wave theory. We
+show that the spin-chirality cancellation is removed in such case, giving rise
+to the non-trivial magnon band topology and the finite THE. Moreover, the
+magnon bands exhibit band topology transitions tuned by the magnetic field. We
+demonstrate that such transitions are accompanied by the logarithmic divergence
+of the first derivative of the thermal Hall conductivity. Finally, we examine
+the above consequences by calculating the THE in the hexagonal manganite
+YMnO$_3$, well known to have anti-trimerization.",1811.11201v2
+2018-05-15,Thermal Hall effect and topological edge states in a square lattice antiferromagnet,"We show that the two dimensional spatial inversion-symmetry (SIS) broken
+square lattice antiferromagnet with easy-plane spin anisotropy exhibits a
+thermal Hall effect and the edge modes characterized by the Z 2 topological
+invariant. These topological properties require a nonzero Berry curvature, and
+its origin is ascribed to the Dzyaloshinskii-Moriya (DM) interactions or the
+noncoplanar magnetic ordering generating a U(1) gauge field that couples to the
+kinetic motion of magnons. Although this picture is established in ferromagnets
+on the kagome and pyrochlore lattices, it does not apply to our square lattice
+model since such gauge field cancels out in an edge shared geometry. Instead,
+our case has an analogy with the anomalous Hall effect of Rashba electronic
+system where the spin orbit coupling generates an SU(2) gauge field. The two
+species of magnons defined on antiferromagnetic sublattices can be regarded as
+the pseudo-spin degrees of freedom of magnons. The DM interactions that emerge
+due to the SIS breaking serve as a pseudo-spin orbit coupling of magnons and
+generate a Berry curvature, when the direction of the magnetic moments is
+properly controlled by the magnetic field. The thermal Hall conductivity of our
+antiferromagnet shows rapid growth in temperature T beyond the power-law,
+reflecting the almost gapless low energy branch of the antiferromagnet, which
+distinctively differs from the T^7/2 -dependence in the pyrochlore
+ferromagnets. The present system serves as a standard model for the
+noncentrosymmetric crystals Ba2MnGe2O7 and Ba2CoGe2O7.",1805.05872v3
+2011-11-13,Thermal spin pumping and magnon-phonon-mediated spin-Seebeck effect,"The spin-Seebeck effect (SSE) in ferromagnetic metals and insulators has been
+investigated systematically by means of the inverse spin-Hall effect (ISHE) in
+paramagnetic metals. The SSE generates a spin voltage as a result of a
+temperature gradient in a ferromagnet, which injects a spin current into an
+attached paramagnetic metal. In the paramagnet, this spin current is converted
+into an electric field due to the ISHE, enabling the electric detection of the
+SSE. The observation of the SSE is performed in longitudinal and transverse
+configurations consisting of a ferromagnet/paramagnet hybrid structure, where
+thermally generated spin currents flowing parallel and perpendicular to the
+temperature gradient are detected, respectively. Our results explain the SSE in
+terms of a two-step process: (1) the temperature gradient creates a
+non-equilibrium state in the ferromagnet governed by both magnon and phonon
+propagations and (2) the non-equilibrium between magnons in the ferromagnet and
+electrons in the paramagnet at the contact interface leads to ""thermal spin
+pumping"" and the ISHE signal. The non-equilibrium state of metallic magnets
+(e.g. Ni81Fe19) under a temperature gradient is governed mainly by the phonons
+in the sample and the substrate, while in insulating magnets (e.g. Y3Fe5O12)
+both magnon and phonon propagations appear to be important. The phonon-mediated
+non-equilibrium that drives the thermal spin pumping is confirmed also by
+temperature-dependent measurements, giving rise to a giant enhancement of the
+SSE signals at low temperatures.",1111.3036v2
+2014-06-13,Low Energy Electrodynamics of Novel Spin Excitations in the Quantum Spin Ice Yb$_2$Ti$_2$O$_7$,"In condensed matter systems, the formation of long range order (LRO) with
+broken symmetry is often accompanied by new types of excitations. However, in
+many magnetic pyrochlore oxides, geometrical frustration suppresses
+conventional LRO while at the same time non-trivial spin correlations are
+observed. For such materials, a natural question to ask then is what is the
+nature of the excitations in this highly correlated state without broken
+symmetry? Frequently the application of a symmetry breaking field can stabilize
+excitations whose properties still reflect certain aspects of the anomalous
+state without long-range order. Here we report evidence of novel magnetic
+excitations in the quantum spin ice material Yb$_2$Ti$_2$O$_7$, obtained from
+time-domain terahertz spectroscopy (TDTS). At large fields, both magnon and
+two-magnon-like excitations are observed in a $<$001$>$ directed magnetic field
+illustrating the stabilization of a field induced LRO state. The unique ability
+of TDTS to measure complex response functions allows a direct study of magnetic
+responses in different polarization channels, revealing the existence of an
+unusual left-hand polarized magnon. The g-factors of these excitations are
+dramatically enhanced in the low-field limit, showing a cross-over of these
+one- and two-magnon states into features consistent with quantum string-like
+excitations proposed to exist in quantum spin ice in a small $<$001$>$ applied
+field.",1406.3576v1
+2018-09-07,Electron-magnon scattering in elementary ferromagnets from first principles: lifetime broadening and band anomalies,"We study the electron-magnon scattering in bulk Fe, Co, and Ni within the
+framework of many-body perturbation theory implemented in the full-potential
+linearized augmented-plane-wave method. To this end, a $\mathbf{k}$-dependent
+self-energy ($GT$ self-energy) describing the scattering of electrons and
+magnons is constructed from the solution of a Bethe-Salpeter equation for the
+two-particle (electron-hole) Green function, in which single-particle Stoner
+and collective spin-wave excitations (magnons) are treated on the same footing.
+Partial self-consistency is achieved by the alignment of the chemical
+potentials. The resulting renormalized electronic band structures exhibit
+strong spin-dependent lifetime effects close to the Fermi energy, which are
+strongest in Fe. The renormalization can give rise to a loss of quasiparticle
+character close to the Fermi energy, which we attribute to electron scattering
+with spatially extended spin waves. This scattering is also responsible for
+dispersion anomalies in conduction bands of iron and for the formation of
+satellite bands in nickel. Furthermore, we find a band anomaly at a binding
+energy of 1.5~eV in iron, which results from a coupling of the quasihole with
+single-particle excitations that form a peak in the Stoner continuum. This band
+anomaly was recently observed in photoemission experiments. On the theory side,
+we show that the contribution of the Goldstone mode to the $GT$ self-energy is
+expected to (nearly) vanish in the long-wavelength limit. We also present an
+in-depth discussion about the possible violation of causality when an
+incomplete subset of self-energy diagrams is chosen.",1809.02395v2
+2020-12-23,Hot electron relaxation in normal state of iron pnictides: memory function approach,"This study leads to the investigation of the non-equilibrium electron
+relaxation in the normal state of iron pnictides. Here we consider the
+relaxation of electrons due to their coupling with magnons and phonons in the
+metallic state of iron pnictides using the memory function approach. In the
+present model, electrons live at a higher temperature than that of the phonon
+and magnon baths, mimicking a non-equilibrium steady state situation. Further
+we analyze theoretically the generalized Drude scattering rate within the
+framework of Two Temperature Model and study the full frequency and temperature
+behavior for it. In zero frequency regime, the rate of electron-magnon
+scattering and electron-phonon scattering shows a linear temperature dependence
+at higher temperature values greater than Bloch-Gr\""{u}neisen temperature.
+Whereas at lower temperature values, $T\ll\Theta_{BG}$, corresponding
+scattering rates follow the temperature behavior as ($1/\tau_{e-p} \varpropto
+T^3$) and ($1/\tau_{e-m} \varpropto T^{3/2}$), respectively. In the AC regime,
+we compute that $1/\tau \propto \omega^2$ for $\omega\ll\omega_{BG}$ and for
+the values greater than the Bloch-Gr\""{u}neisen frequency, it is
+$\omega$-independent. Also, in lower frequency and zero temperature limit, we
+have observed the different frequency scale of electron-magnon and
+electron-phonon scattering i.e ($1/\tau \propto \omega^{3/2}$) and
+($1/\tau\propto \omega^{3}$). These results can be viewed with the pump-probe
+experimental setting for the normal state of iron pnictides.",2012.12650v1
+2017-05-05,Neutron-scattering study of yttrium iron garnet,"The nuclear and magnetic structure and full magnon dispersions of yttrium
+iron garnet Y$_3$Fe$_5$O$_{12}$ have been studied by neutron scattering. The
+refined nuclear structure is distorted to a trigonal space group of $R\bar{3}$.
+The highest-energy dispersion extends up to 86 meV. The observed dispersions
+are reproduced by a simple model with three nearest-neighbor-exchange integrals
+between 16$a$ (octahedral) and 24$d$ (tetrahedral) sites, $J_{aa}$, $J_{ad}$,
+and $J_{dd}$, which are estimated to be 0.00$\pm$0.05, $-$2.90$\pm$0.07, and
+$-$0.35$\pm$0.08 meV, respectively. The lowest-energy dispersion below 14 meV
+exhibits a quadratic dispersion as expected from ferromagnetic magnons. The
+imaginary part of $q$-integrated dynamical spin susceptibility $\chi$""($E$)
+exhibits a square-root energy-dependence in the low energies. The magnon
+density of state is estimated from the $\chi$""($E$) obtained on an absolute
+scale. The value is consistent with a single polarization mode for the magnon
+branch expected theoretically.",1705.02167v5
+2017-05-12,Pseudo-Goldstone magnons in the frustrated S=3/2 Heisenberg helimagnet ZnCr2Se4 with a pyrochlore magnetic sublattice,"Low-energy spin excitations in any long-range ordered magnetic system in the
+absence of magnetocrystalline anisotropy are gapless Goldstone modes emanating
+from the ordering wave vectors. In helimagnets, these modes hybridize into the
+so-called helimagnon excitations. Here we employ neutron spectroscopy supported
+by theoretical calculations to investigate the magnetic excitation spectrum of
+the isotropic Heisenberg helimagnet ZnCr2Se4 with a cubic spinel structure, in
+which spin-3/2 magnetic Cr3+ ions are arranged in a geometrically frustrated
+pyrochlore sublattice. Apart from the conventional Goldstone mode emanating
+from the (0 0 q) ordering vector, low-energy magnetic excitations in the
+single-domain proper-screw spiral phase show soft helimagnon modes with a small
+energy gap of ~0.17 meV, emerging from two orthogonal wave vectors (q 0 0) and
+(0 q 0) where no magnetic Bragg peaks are present. We term them
+pseudo-Goldstone magnons, as they appear gapless within linear spin-wave theory
+and only acquire a finite gap due to higher-order quantum-fluctuation
+corrections. Our results are likely universal for a broad class of symmetric
+helimagnets, opening up a new way of studying weak magnon-magnon interactions
+with accessible spectroscopic methods.",1705.04642v3
+2019-01-17,Observation of topological magnon insulator states in a superconducting circuit,"Searching topological states in artificial systems has recently become a
+rapidly growing field of research. Meanwhile, significant experimental
+progresses on observing topological phenomena have been made in superconducting
+circuits. However, topological insulator states have not yet been reported in
+this system. Here, for the first time, we experimentally realize a tunable
+dimerized spin chain model and observe the topological magnon insulator states
+in a superconducting qubit chain. Via parametric modulations of the qubit
+frequencies, we show that the qubit chain can be flexibly tuned into
+topologically trivial or nontrivial magnon insulator states. Based on
+monitoring the quantum dynamics of a single-qubit excitation in the chain, we
+not only measure the topological winding numbers, but also observe the
+topological magnon edge and defect states. Our experiment exhibits the great
+potential of tunable superconducting qubit chain as a versatile platform for
+exploring non-interacting and interacting symmetry-protected topological
+states.",1901.05683v2
+2019-01-27,Observation of band narrowing and mode conversion in two-dimensional binary magnonic crystal,"We introduce a new type of binary magnonic crystal, where Ni$_{80}$Fe$_{20}$
+nanodots of two different sizes are diagonally connected forming a unit and
+those units are arranged in a square lattice. The magnetization dynamics of the
+sample is measured by using time-resolved magneto-optical Kerr effect
+microscope with varying magnitude and in-plane orientation ($\phi$) of the bias
+magnetic field. Interestingly, at $\phi=0^{\circ}$, the spin-wave mode profiles
+show frequency selective spatial localization of spin-wave power within the
+array. With the variation of $\phi$ in the range $0^{\circ}<\phi\leq
+45^{\circ}$, we observe band narrowing due to localized to extended spin-wave
+mode conversion. Upon further increase of $\phi$, the spin-wave modes slowly
+lose the extended nature and become fully localized again at 90$^{\circ}$. We
+have extensively demonstrated the role of magnetostatic stray field
+distribution on the rotational symmetries obtained for the spin-wave modes.
+From micromagnetic simulations, we find that the dipole-exchange coupling
+between the nano-dots leads to remarkable modifications of the spin-wave mode
+profiles when compared with arrays of individual small and large dots.
+Numerically, we also show that the physical connection between the nano-dots
+provides more control points over the spin-wave propagation in the lattice at
+different orientations of bias magnetic field. This new type of binary magnonic
+crystal may find potential applications in magnonic devices such as spin-wave
+waveguide, filter, coupler, and other on-chip microwave communication devices.",1901.09325v1
+2019-02-11,Spin-wave phase inverter upon a single nanodefect,"Local modification of magnetic properties of nanoelements is a key to design
+future-generation magnonic devices, in which information is carried and
+processed via spin waves. One of the biggest challenges here is to fabricate
+simple and miniature phase-controlling elements with broad tunability. Here, we
+successfully realize such spin-wave phase shifter upon a single nanogroove
+milled by focused ion beam in a Co-Fe microsized magnonic waveguide. By varying
+the groove depth and the in-plane bias magnetic field we continuously tune the
+spin-wave phase and experimentally evidence a complete phase inversion. The
+microscopic mechanism of the phase shift is based on the combined action of the
+nanogroove as a geometrical defect and the lower spin-wave group velocity in
+the waveguide under the groove where the magnetization is reduced due to the
+incorporation of Ga ions during the ion-beam milling. The proposed phase
+shifter can easily be on-chip integrated with spin-wave logic gates and other
+magnonic devices. Our findings are crucial for designing nano-magnonic circuits
+and for the development of spin-wave nano-optics.",1902.03758v1
+2019-03-04,Consideration of Thermal Hall Effect in Undoped Cuprates,"A recent observation of thermal Hall effect of magnetic origin in underdoped
+cuprates calls for critical re-examination of low-energy magnetic dynamics in
+undoped antiferromagnetic compound on square lattice, where traditional,
+renormalized spin-wave theory was believed to work well. Using
+Holstein-Primakoff boson formalism, we find that magnon-based theories can lead
+to finite Berry curvature in the magnon band once the Dzyaloshinskii-Moriya
+spin interaction is taken into account explicitly, but fail to produce non-zero
+thermal Hall conductivity. Assuming accidental doping by impurities and magnon
+scattering off of such impurity sites fails to predict skew scattering at the
+level of Born approximation. Local formation of skyrmion defects is also found
+incapable of generating magnon thermal Hall effect. Turning to spinon-based
+scenario, we write down a simple model by adding spin-dependent diagonal
+hopping to the well-known {\pi}-flux model of spinons. The resulting two-band
+model has Chern number in the band structure, and generates thermal Hall
+conductivity whose magnetic field and temperature dependences mimic closely the
+observed thermal Hall signals. In disclaimer, there is no firm microscopic
+basis of this model and we do not claim to have found an explanation of the
+data, but given the unexpected nature of the experimental observation, it is
+hoped this work could serve as a first step towards reaching some level of
+understanding.",1903.01125v3
+2019-03-31,Control of the Coupling Strength and the Linewidth of a Cavity-Magnon Polariton,"The full coherent control of hybridized systems such as strongly coupled
+cavity photon-magnon states is a crucial step to enable future information
+processing technologies. Thus, it is particularly interesting to engineer
+deliberate control mechanisms such as the full control of the coupling strength
+as a measure for coherent information exchange. In this work, we employ cavity
+resonator spectroscopy to demonstrate the complete control of the coupling
+strength of hybridized cavity photon-magnon states. For this, we use two
+driving microwave inputs which can be tuned at will. Here, only the first input
+couples directly to the cavity resonator photons, whilst the second tone
+exclusively acts as a direct input for the magnons. For these inputs, both the
+relative phase $\phi$ and amplitude $\delta_0$ can be independently controlled.
+We demonstrate that for specific quadratures between both tones, we can
+increase the coupling strength, close the anticrossing gap, and enter a regime
+of level merging. At the transition, the total amplitude is enhanced by a
+factor of 1000 and we observe an additional linewidth decrease of $13\%$ at
+resonance due to level merging. Such control of the coupling, and hence
+linewidth, open up an avenue to enable or suppress an exchange of information
+and bridging the gap between quantum information and spintronics applications.",1904.00393v1
+2019-04-25,Skyrmion solids in monolayer graphene,"Partially filled Landau levels host competing orders, with electron solids
+prevailing close to integer fillings before giving way to fractional quantum
+Hall liquids as the Landau level fills. Here, we report the observation of an
+electron solid with noncolinear spin texture in monolayer graphene, consistent
+with solidification of skyrmions---topological spin textures characterized by
+quantized electrical charge. In electrical transport, electron solids reveal
+themselves through a rapid metal-insulator transition in the bulk electrical
+conductivity as the temperature is lowered, accompanied by the emergence of
+strongly nonlinear dependence on the applied bias voltage. We probe the spin
+texture of the solids using a modified Corbino geometry that allows
+ferromagnetic magnons to be launched and detected. We find that magnon
+transport is highly efficient when one Landau level is filled ($\nu=1$),
+consistent with quantum Hall ferromagnetic spin polarization; however, even
+minimal doping immediately quenches the the magnon signal while leaving the
+vanishing low-temperature charge conductivity unchanged. Our results can be
+understood by the formation of a solid of charged skyrmions near $\nu=1$, whose
+noncolinear spin texture leads to rapid magnon decay. Data near fractional
+fillings further shows evidence for several fractional skyrmion crystals,
+suggesting that graphene hosts a vast and highly tunable landscape of coupled
+spin and charge orders.",1904.11485v1
+2019-04-29,Magnon-Mediated Indirect Exciton Condensation through Antiferromagnetic Insulators,"Electrons and holes residing on the opposing sides of an insulating barrier
+and experiencing an attractive Coulomb interaction can spontaneously form a
+coherent state known as an indirect exciton condensate. We study a trilayer
+system where the barrier is an antiferromagnetic insulator. The electrons and
+holes here additionally interact via interfacial coupling to the
+antiferromagnetic magnons. We show that by employing magnetically uncompensated
+interfaces, we can design the magnon-mediated interaction to be attractive or
+repulsive by varying the thickness of the antiferromagnetic insulator by a
+single atomic layer. We derive an analytical expression for the critical
+temperature $T_c$ of the indirect exciton condensation. Within our model,
+anisotropy is found to be crucial for achieving a finite $T_c$, which increases
+with the strength of the exchange interaction in the antiferromagnetic bulk.
+For realistic material parameters, we estimate $T_c$ to be around 7 K, the same
+order of magnitude as the current experimentally achievable exciton
+condensation where the attraction is solely due to the Coulomb interaction. The
+magnon-mediated interaction is expected to cooperate with the Coulomb
+interaction for condensation of indirect excitons, thereby providing a means to
+significantly increase the exciton condensation temperature range.",1904.12699v3
+2019-08-01,Quasi-Two-Dimensional Magnon Identification in Antiferromagnetic FePS3 via Magneto-Raman Spectroscopy,"Recently it was discovered that van der Waals-bonded magnetic materials
+retain long range magnetic ordering down to a single layer, opening many
+avenues in fundamental physics and potential applications of these fascinating
+materials. One such material is FePS3, a large spin (S=2) Mott insulator where
+the Fe atoms form a honeycomb lattice. In the bulk, FePS3 has been shown to be
+a quasi-two-dimensional-Ising antiferromagnet, with additional features in the
+Raman spectra emerging below the Neel temperature of approximately 120 K. Using
+magneto-Raman spectroscopy as an optical probe of magnetic structure, we show
+that one of these Raman-active modes in the magnetically ordered state is
+actually a magnon with a frequency of of approximately 3.7 THz (122 cm-1).
+Contrary to previous work, which interpreted this feature as a phonon, our
+Raman data shows the expected frequency shifting and splitting of the magnon as
+a function of temperature and magnetic field, respectively, where we determine
+the g-factor to be approximately 2. In addition, the symmetry behavior of the
+magnon is studied by polarization-dependent Raman spectroscopy and explained
+using the magnetic point group of FePS3.",1908.00608v1
+2019-11-29,Real space observation of magnon interaction with driven space-time crystals,"The concept of Space-Time Crystals (STC), i.e. translational symmetry
+breaking in time and space, was recently proposed and experimentally
+demonstrated for quantum systems. Here, we transfer this concept to magnons and
+experimentally demonstrate a driven STC at room temperature. The STC is
+realized by strong homogeneous micro-wave pumping of a micron-sized permalloy
+(Py) stripe and is directly imaged by Scanning Transmission X-ray Microscopy
+(STXM). For a fundamental understanding of the formation of the STC,
+micromagnetic simulations are carefully adapted to model the experimental
+findings. Beyond the mere generation of a STC, we observe the formation of a
+magnonic band structure due to back folding of modes at the STC's Brillouin
+zone boundaries. We show interactions of magnons with the STC that appear as
+lattice scattering. This results in the generation of ultra short spin waves
+down to 100 nm wavelength that cannot be described by classical dispersion
+relations for linear spin wave excitations. We expect that room temperature
+STCs will be a useful tool to investigate non-linear wave physics, as they can
+be easily generated and manipulated to control their spatial and temporal band
+structure.",1911.13192v1
+2019-12-16,Dynamics of reconfigurable artificial spin ice: towards magnonic functional materials,"Over the past few years, the study of magnetization dynamics in artificial
+spin ices has become a vibrant field of study. Artificial spin ices are
+ensembles of geometrically arranged, interacting magnetic nanoislands, which
+display frustration by design. These were initially created to mimic the
+behavior in rare earth pyrochlore materials and to study emergent behavior and
+frustration using two-dimensional magnetic measurement techniques. Recently, it
+has become clear that it is possible to create artificial spin ices, which can
+potentially be used as functional materials. In this Perspective, we review the
+resonant behavior of spin ices (which is in the GHz frequency range), focusing
+on their potential application as magnonic crystals. In magnonic crystals, spin
+waves are functionalized for logic applications by means of band structure
+engineering. While it has been established that artificial spin ices can
+possess rich mode spectra, the applicability of spin ices to create magnonic
+crystals hinges upon their reconfigurability. Consequently, we describe recent
+work aiming to develop techniques and create geometries allowing full
+reconfigurability of the spin ice magnetic state. We also discuss experimental,
+theoretical, and numerical methods for determining the spectral response of
+artificial spin ices, and give an outlook on new directions for reconfigurable
+spin ices.",1912.07280v2
+2016-03-18,Magnons in Sr$_2$CuO$_3$: possible evidence for Goldstone-Higgs interaction in a weakly ordered spin-1/2 chain antiferromagnet,"The Goldstone theorem mandates that a spontaneous symmetry breaking entails
+the emergence of gap(mass)less excitations. In the case where a rotational
+invariance of a system of spin magnetic moments is broken by an
+antiferromagnetic order, these are well-known transverse spin waves. The
+interaction of such Goldstone magnons with the Higgs amplitude mode of the
+order parameter is usually discarded, even though glimpses of Higgs physics
+have recently been reported in a quantum magnet, a topological insulator, and
+ferroelectric and disordered superconductor systems. The Goldstone-Higgs
+interactions could be expected to grow in importance near a quantum critical
+point (QCP), where the symmetry-breaking order is weak, and its amplitude
+fluctuations are significant. Here we report an electron spin resonance (ESR)
+study of a nearly one-dimensional spin-1/2 chain system, Sr$_2$CuO$_3$, which
+presents exactly such a case. The ESR spectra at $T > T_N$, in the disordered
+Luttinger-spin-liquid phase with unconfined spinons reveal ideal
+Heisenberg-chain behavior with only very small, field-independent linewidth,
+$\sim 1/T$. In the ordered state, below $T_N$, we identify antiferromagnetic
+resonance (AFMR) modes, which are well described by pseudo-Goldstone magnons in
+the model of a collinear biaxial antiferromagnet with two gaps, $\Delta_1 =
+23.0$ GHz and $\Delta_2 = 13.3$ GHz. Additionally, we observe a major resonant
+response of special nature, which we attribute to magnon interaction with the
+Higgs amplitude mode in a weakly ordered antiferromagnet. Its unusual field
+dependence indicates the presence of a quantum phase transition at $\mu_0 H
+\simeq 9.4$ T.",1603.05869v2
+2016-12-06,Thermal conductivity of local moment models with strong spin-orbit coupling,"We study the magnetic and lattice contributions to the thermal conductivity
+of electrically insulating strongly spin-orbit coupled magnetically ordered
+phases on a two-dimensional honeycomb lattice using the Kitaev-Heisenberg
+model. Depending on model parameters, such as the relative strength of the
+spin-orbit induced anisotropic coupling, a number of magnetically ordered
+phases are possible. In this work, we study two distinct regimes of thermal
+transport depending on whether the characteristic energy of the phonons or the
+magnons dominates, and focus on two different relaxation mechanisms, boundary
+scattering and magnon-phonon scattering. For spatially anisotropic magnetic
+phases, the thermal conductivity tensor can be highly anisotropic when the
+magnetic energy scale dominates, since the magnetic degrees of freedom dominate
+the thermal transport for temperatures well below the magnetic transition
+temperature. In the opposite limit in which the phonon energy scale dominates,
+the thermal conductivity will be nearly isotropic, reflecting the isotropic (at
+low temperatures) phonon dispersion assumed for the honeycomb lattice. We
+further discuss the extent to which thermal transport properties are influenced
+by strong spin-orbit induced anisotropic coupling in the local moment regime of
+insulating magnetic phases. The developed methodology can be applied to any 2D
+magnon-phonon system, and more importantly to systems where an analytical
+Bogoliubov transformation cannot be found and magnon bands are not necessarily
+isotropic.",1612.01658v1
+2018-10-10,Photo-induced Floquet Weyl magnons in noncollinear antiferromagnets,"We study periodically driven insulating noncollinear stacked kagome
+antiferromagnets with a conventional symmetry-protected three-dimensional (3D)
+in-plane $120^\circ$ spin structure, with either positive or negative vector
+chirality. We show that the symmetry protection of the in-plane $120^\circ$
+spin structure can be broken in the presence of an off-resonant circularly or
+linearly polarized electric field propagating parallel to the in-plane
+$120^\circ$ spin structure (say along the $x$ direction). Consequently,
+topological Floquet Weyl magnon nodes with opposite chirality are photoinduced
+along the $k_x$ momentum direction. They manifest as the monopoles of the
+photoinduced Berry curvature. We also show that the system exhibits a
+photoinduced magnon thermal Hall effect for circularly polarized electric
+field. Furthermore, we show that the photoinduced chiral spin structure is a
+canted 3D in-plane $120^\circ$ spin structure, which was recently observed in
+the equilibrium noncollinear antiferromagnetic Weyl semimetals Mn$_3$Sn\slash
+Ge. Our result not only paves the way towards the experimental realization of
+Weyl magnons and photoinduced thermal Hall effects, but also provides a
+powerful mechanism for manipulating the intrinsic properties of 3D topological
+antiferromagnets.",1810.04675v5
+2019-05-03,Optical excitation of magnons in an easy-plane antiferromagnet: Application to Sr$_2$IrO$_4$,"We study the interaction of a (classical) light field with the magnetic
+degrees of freedom in the two-dimensional antiferromagnet Sr$_2$IrO$_4$. The
+reduced space group symmetry of the crystal allows for several channels for
+spin-operator bilinears to couple to the electric field. Integrating out
+high-energy degrees of freedom in a Keldysh framework, we derive induced
+effective fields which enter the equations of motion of the low-energy mode of
+in-plane rotations which couple to the out-of-plane magnetization. Considering
+a pump-probe protocol, these induced fields excite magnetization oscillations
+which can subsequently probed, e.g. using Kerr rotation. We discuss how the
+induced fields depend on polarization and frequency of the driving light, and
+our study applies to both resonant and non-resonant regimes. Crucially, the
+induced fields depend on the two-magnon density of states, thus allowing for
+further insight into properties of the magnetic excitation spectrum.
+Furthermore, these effects rely upon (weak) magnon-interactions, and so are
+beyond a ""Floquet magnon"" description.",1905.01313v3
+2019-05-27,Influence of nonmagnetic dielectric spacers on the spin wave response of one-dimensional planar magnonic crystals,"The one-dimensional planar magnonic crystals are usually fabricated as a
+sequence of stripes intentionally or accidentally separated by non-magnetic
+spacers. The influence of spacers on shaping the spin wave spectra is complex
+and still not completely clarified. We performed the detailed numerical studies
+of the one-dimensional single- and bi-component magnonic crystals comprised of
+a periodic array of thin ferromagnetic stripes separated by non-magnetic
+spacers. We showed that the dynamic dipolar interactions between the stripes
+mediated by non-magnetic spacer, even ultra-narrow, significantly shift up the
+frequency of the ferromagnetic resonance and simultaneously reduce the spin
+wave group velocity, which is manifested by the flattening of the magnonic
+band. We attributed these changes in the spectra to the modifications of
+dipolar pinning and shape anisotropy both dependent on the width of the spacers
+and the thickness of the stripes, as well as to the dynamical magnetic volume
+charges formed due to inhomogeneous spin wave amplitude.",1905.11016v4
+2019-07-31,Ferromagnetism and its stability from the one-magnon spectrum in twisted bilayer graphene,"We study ferromagnetism and its stability in twisted bilayer graphene. We
+work with a Hubbard-like interaction that corresponds to the screened Coulomb
+interaction in a well-defined limit where the Thomas-Fermi screening length
+$l_\text{TF}$ is much larger than monolayer graphene's lattice spacing $l_g \ll
+l_\text{TF}$ and much smaller than the Moir\'e super lattice's spacing $
+l_\text{TF} \ll l_{\text{Moir\'e}}$. We show that in the perfectly flat band
+""chiral"" limit and at filling fractions $\pm 3/4$, the saturated ferromagnetic
+(spin and valley polarized) states are ideal ground states candidates in the
+large band-gap limit. By assuming a large enough substrate (hBN) induced
+sub-lattice potential, the same argument can be applied to filling fractions
+$\pm 1/4$. We estimate the regime of stability of the ferromagnetic phase
+around the chiral limit by studying the exactly calculated spectrum of
+one-magnon excitations. The instability of the ferromagnetic state is signaled
+by a negative magnon excitation energy. This approach allows us to deform the
+results of the idealized chiral model (by increasing the bandwidth and/or
+modified interactions) towards more realistic systems. Furthermore, we use the
+low energy part of the exact one-magnon spectrum to calculate the
+spin-stiffness of the Goldstone modes throughout the ferromagnetic phase. The
+calculated value of spin-stiffness can determine the excitation energy of
+charged skyrmions.",1907.13633v1
+2020-01-15,Nonreciprocal surface acoustic wave propagation via magneto-rotation coupling,"One of the most fundamental forms of magnon-phonon interaction is an
+intrinsic property of magnetic materials, the ""magnetoelastic coupling"". This
+particular form of interaction has been the basis for describing magnetic
+materials and their strain related applications, where strain induces changes
+of internal magnetic fields. Different from the magnetoelastic coupling, more
+than 40 years ago, it was proposed that surface acoustic waves may induce
+surface magnons via rotational motion of the lattice in anisotropic magnets.
+However, a signature of this magnon-phonon coupling mechanism, termed
+magneto-rotation coupling, has been elusive. Here, we report the first
+observation and theoretical framework of the magneto-rotation coupling in a
+perpendicularly anisotropic ultra-thin film Ta/CoFeB(1.6 nm)/MgO, which
+consequently induces nonreciprocal acoustic wave attenuation with a
+unprecedented ratio up to 100$\%$ rectification at the theoretically predicted
+optimized condition. Our work not only experimentally demonstrates a
+fundamentally new path for investigating magnon-phonon coupling, but also
+justify the feasibility of the magneto-rotation coupling based application.",2001.05135v3
+2020-03-03,Van Hove singularity in the magnon spectrum of the antiferromagnetic quantum honeycomb lattice,"The magnetic excitation spectrum of the quantum magnet YbCl$_3$ is studied
+with inelastic neutron scattering. The spectrum exhibits an unusually sharp
+feature within a broad continuum, as well as conventional spin waves. By
+including both transverse and longitudinal channels of the neutron response,
+linear spin wave theory with a single Heisenberg interaction on the honeycomb
+lattice reproduces all of the key features in the spectrum. In particular, the
+broad continuum corresponds to a two-magnon contribution from the longitudinal
+channel, while the sharp feature within this continuum is identified as a Van
+Hove singularity in the joint density of states, which indicates the
+two-dimensional nature of the two-magnon continuum. We term these singularities
+magneto-caustic features in analogy with caustic features in ray optics where
+focused envelopes of light are generated when light passes through or reflects
+from curved or distorted surfaces. The experimental demonstration of a sharp
+Van Hove singularity in a two-magnon continuum is important because analogous
+features in potential two-spinon continua could distinguish quantum spin
+liquids from merely disordered systems. These results establish YbCl$_3$ as a
+nearly ideal two-dimensional honeycomb lattice material hosting strong quantum
+effects in the unfrustrated limit.",2003.01754v1
+2020-03-15,Magnetic-field-induced tunability of spin Hamiltonians: Resonances and Efimov states in Yb$_2$Ti$_2$O$_7$,"Universality is a powerful concept that arises from the divergence of a
+characteristic length scale. For condensed matter systems, this length scale is
+typically the correlation length, which diverges at critical points separating
+two different phases. Few-particle systems exhibit a simpler form of
+universality when the $s$-wave scattering length diverges. A prominent example
+of universal phenomena is the emergence of an infinite tower of three-body
+bound states obeying discrete scale invariance, known as the Efimov effect,
+which has been subject to extensive research in chemical, atomic, nuclear and
+particle physics. In principle, these universal phenomena can also emerge in
+the excitation spectrum of condensed matter systems, such as quantum
+magnets~[Y. Nishida, Y. Kato, and C. Batista, Nat. Phys. 9, 93 (2013)].
+However, the limited tunability of the effective inter-particle interaction
+relative to the kinetic energy has precluded so far their observation. Here we
+demonstrate that a high degree of magnetic-field-induced tunability can also be
+achieved in quantum magnets with strong spin-orbit coupling: a two-magnon
+resonance condition can be achieved in Yb$_2$Ti$_2$O$_7$ with a field of $\sim$
+13~T along the [110] direction, which leads to the formation of Efimov states
+in the three-magnon spectrum of this material. Raman scattering experiments can
+reveal the field-induced two-magnon resonance, as well as the Efimov
+three-magnon bound states that emerge near the resonance condition.",2003.06738v2
+2020-04-16,A Magnon Scattering Platform,"Scattering experiments have revolutionized our understanding of nature.
+Examples include the discovery of the nucleus, crystallography, and the
+discovery of the double helix structure of DNA. Scattering techniques differ by
+the type of the particles used, the interaction these particles have with
+target materials and the range of wavelengths used. Here, we demonstrate a new
+2-dimensional table-top scattering platform for exploring magnetic properties
+of materials on mesoscopic length scales. Long lived, coherent magnonic
+excitations are generated in a thin film of YIG and scattered off a magnetic
+target deposited on its surface. The scattered waves are then recorded using a
+scanning NV center magnetometer that allows sub-wavelength imaging and
+operation under conditions ranging from cryogenic to ambient environment. While
+most scattering platforms measure only the intensity of the scattered waves,
+our imaging method allows for spatial determination of both amplitude and phase
+of the scattered waves thereby allowing for a systematic reconstruction of the
+target scattering potential. Our experimental results are consistent with
+theoretical predictions for such a geometry and reveal several unusual features
+of the magnetic response of the target, including suppression near the target
+edges and gradient in the direction perpendicular to the direction of surface
+wave propagation. Our results establish magnon scattering experiments as a new
+platform for studying correlated many-body systems.",2004.07763v1
+2020-08-12,Strongly two-dimensional exchange interactions in the in-plane metallic antiferromagnet Fe$_2$As probed by inelastic neutron scattering,"To understand spin interactions in materials of the Cu$_2$Sb structure type,
+inelastic neutron scattering of Fe$_2$As single crystals was examined at
+different temperatures and incident neutron energies. The experimental phonon
+spectra match well with the simulated phonon spectra obtained from density
+functional theory (DFT) calculations. The measured magnon spectra were compared
+to the simulated magnon spectra obtained via linear spin wave theory with the
+exchange coupling constants calculated using the spin polarized, relativistic
+Korringa-Kohn-Rostoker method in Zhang et al. (2013). The simulated magnon
+spectra broadly agree with the experimental data although, the energy values
+are underestimated along the $K$ direction. Exchange coupling constants between
+Fe atoms were refined by fits to the experimental magnon spectra, revealing
+stronger nearest neighbor Fe1-Fe1 exchange coupling than previously reported.
+The strength of this exchange coupling is almost an order of magnitude higher
+than other exchange interactions despite the three-dimensional nature of the
+phonon interactions. The lack of scattering intensity at energies above 60 meV
+makes unconstrained determination of the full set of exchange interactions
+difficult, which may be a fundamental challenge in metallic antiferromagnets.",2008.05050v2
+2020-08-21,Magnons Parametric Pumping in Bulk Acoustic Waves Resonator,"We report on the experimental observation of excitation and detection of
+parametric spin waves and spin currents in the bulk acoustic wave resonator.
+The hybrid resonator consists of ZnO piezoelectric film, yttrium iron garnet
+(YIG) films on gallium gadolinium garnet substrate, and a heavy metal Pt layer.
+Shear bulk acoustic waves are electrically excited in the ZnO layer due to
+piezoeffect at the resonant frequencies of the resonator. The magnetoelastic
+interaction in the YIG film emerges magnons (spin waves) excitation by acoustic
+waves either on resonator's eigenfrequencies or the half-value frequencies at
+supercritical power. We investigate acoustic pumping of magnons at the
+half-value frequencies and acoustic spin pumping from parametric magnons, using
+the inverse spin Hall effect in the Pt layer. The constant electric voltage in
+the Pt layer, depending on the frequency, the magnetic field, and the pump
+power, was systematically studied. We explain the low threshold obtained (~0.4
+mW) by the high efficiency of electric power transmission into the acoustic
+wave in the resonator.",2008.09520v1
+2020-08-24,Ultrastrong Magnon-Magnon Coupling Dominated by Antiresonant Interactions,"Exotic quantum vacuum phenomena are predicted in cavity quantum
+electrodynamics (QED) systems with ultrastrong light-matter interactions. Their
+ground states are predicted to be vacuum squeezed states with suppressed
+quantum fluctuations. The source of such phenomena are antiresonant terms in
+the Hamiltonian, yet antiresonant interactions are typically negligible
+compared to resonant interactions in light-matter systems. We report an unusual
+coupled matter-matter system of magnons that can simulate a unique cavity QED
+Hamiltonian with coupling strengths that are easily tunable into the
+ultrastrong coupling regime and with dominant antiresonant terms. We found a
+novel regime where vacuum Bloch-Siegert shifts, the hallmark of antiresonant
+interactions, greatly exceed analogous frequency shifts from resonant
+interactions. Further, we theoretically explored the system's ground state and
+calculated up to 5.9 dB of quantum fluctuation suppression. These observations
+demonstrate that magnonic systems provide an ideal platform for simulating
+exotic quantum vacuum phenomena predicted in ultrastrongly coupled light-matter
+systems.",2008.10721v2
+2020-11-19,An insulating doped antiferromagnet with low magnetic symmetry as a room temperature spin conduit,"We report room temperature long-distance spin transport of magnons in
+antiferromagnetic thin film hematite doped with Zn. The additional dopants
+significantly alter the magnetic anisotropies, resulting in a complex
+equilibrium spin structure that is capable of efficiently transporting spin
+angular momentum at room temperature without the need for a well-defined, pure
+easy-axis or easy-plane anisotropy. We find intrinsic magnon spin-diffusion
+lengths of up to 1.5 {\mu}m, and magnetic domain governed decay lengths of 175
+nm for the low frequency magnons, through electrical transport measurements
+demonstrating that the introduction of non-magnetic dopants does not strongly
+reduce the transport length scale showing that the magnetic damping of hematite
+is not significantly increased. We observe a complex field dependence of the
+non-local signal independent of the magnetic state visible in the local
+magnetoresistance and direct magnetic imaging of the antiferromagnetic domain
+structure. We explain our results in terms of a varying and
+applied-field-dependent ellipticity of the magnon modes reaching the detector
+electrode allowing us to tune the spin transport.",2011.09755v1
+2021-01-29,Comparison of Spin-Wave Modes in Connected and Disconnected Artificial Spin Ice Nanostructures Using Brillouin Light Scattering Spectroscopy,"Artificial spin ice systems have seen burgeoning interest due to their
+intriguing physics and potential applications in reprogrammable memory, logic
+and magnonics. Integration of artificial spin ice with functional magnonics is
+a relatively recent research direction, with a host of promising results. As
+the field progresses, direct in-depth comparisons of distinct artificial spin
+systems are crucial to advancing the field. While studies have investigated the
+effects of different lattice geometries, little comparison exists between
+systems comprising continuously connected nanostructures, where spin-waves
+propagate via dipole-exchange interaction, and systems with nanobars
+disconnected at vertices where spin-wave propagation occurs via stray
+dipolar-field. Gaining understanding of how these very different coupling
+methods affect both spin-wave dynamics and magnetic reversal is key for the
+field to progress and provides crucial system-design information including for
+future systems containing combinations of connected and disconnected elements.
+Here, we study the magnonic response of two kagome spin ices via Brillouin
+light scattering, a continuously connected system and a disconnected system
+with vertex gaps. We observe distinct high-frequency dynamics and magnetization
+reversal regimes between the systems, with key distinctions in spin-wave
+localization and mode quantization, microstate-trajectory during reversal and
+internal field-profiles. These observations are pertinent for the fundamental
+understanding of artificial spin systems and broader design and engineering of
+reconfigurable functional magnonic crystals.",2101.12619v2
+2021-03-10,Eigenmodes of a disordered FeCo magnonic crystal at finite temperatures,"In this report we present a systematic study of the magnonic modes in the
+disordered Fe$_{0.5}$Co$_{0.5}$ alloy based on the Heisenberg Hamiltonian using
+two complementary approaches. In order to account for substitutional disorder,
+on the one hand we directly average the transverse magnetic susceptibility in
+real space over different disorder configurations and on the other hand we use
+the coherent potential approximation (CPA). While the method of direct
+averaging is numerically exact, it is computationally expensive and limited by
+the maximal size of the supercell which can be simulated on a computer. On the
+contrary the CPA does not suffer from this drawback and yields a cheap
+numerical scheme. Therefore, we additionally compare the results of these two
+approaches and show that the CPA gives very good results for most of the
+magnetic properties, including the magnon energies and the spatial shape of the
+eigenmodes. However, it turns out that while reproducing the general trend, the
+CPA systematically underestimates the disorder induced damping of the magnons.
+This provides evidence that the physics of impurity scattering in this system
+is governed by non-local effects missing in the CPA. Finally, we study the real
+space eigenmodes of the system, including their spatial shapes, and analyze
+their temperature dependence within the random phase approximation.",2103.05967v2
+2021-03-29,Electrically switchable entanglement channel in van der Waals magnets,"Two dimensional layered van der Waals (vdW) magnets have demonstrated their
+potential to study both fundamental and applied physics due to their remarkable
+electronic properties. However, the connection of vdW magnets to spintronics as
+well as quantum information science is not clear. In particular, it remains
+elusive whether there are novel magnetic phenomena only belonging to vdW
+magnets, but absent in the widely studied crystalline magnets. Here we consider
+the quantum correlations of magnons in a layered vdW magnet and identify an
+entanglement channel of magnons across the magnetic layers, which can be
+effectively tuned and even deterministically switched on and off by both
+magnetic and electric means. This is a unique feature of vdW magnets in which
+the underlying physics is well understood in terms of the competing roles of
+exchange and anisotropy fields that contribute to the magnon excitation.
+Furthermore, we show that such a tunable entanglement channel can mediate the
+electrically controllable entanglement of two distant qubits, which also
+provides a protocol to indirectly measure the entanglement of magnons. Our
+findings provide a novel avenue to electrically manipulate the qubits and
+further open up new opportunities to utilize vdW magnets for quantum
+information science.",2103.15899v1
+2021-06-29,Neutron Scattering Study on Yttrium Iron Garnet for Spintronics,"Spin current -- a flow of the spin degree of freedom in matter -- has vital
+importance in spintronics. Propagation of the spin current ranges over a whole
+momentum space; however, generated spin currents are mainly detected in the
+long-wavelength limit. To facilitate practical uses of spintronics and
+magnonics, microscopic understanding of the spin current is necessary. We here
+address yttrium iron garnet, which is a well-employed ferrimagnet for
+spintronics, and review {\it in re} the momentum- and energy-resolved
+characteristics of its magnetism. Using {\it unpolarized} neutrons, we refined
+its detailed crystal and magnetic structure, and examined magnetic excitations
+through four decades (10~$\mu$eV-100~meV) using chopper spectrometers in
+J-PARC, Japan. We also measured mode-resolved directions of the precessional
+motion of the magnetic moment, i.e., magnon polarization, which carries the
+spin current in insulators through {\it polarized} neutron scattering, using a
+triple-axis spectrometer in ILL, France. The magnon polarization is a hitherto
+untested fundamental property of magnets, affecting the thermodynamic
+properties of the spin current. Our momentum- and energy-resolved experimental
+findings provide an intuitive understanding of the spin current and demonstrate
+the importance of neutron scattering techniques for spintronics and magnonics.",2106.15752v1
+2021-06-30,Origin of Nonlinear Damping due to Mode Coupling in Auto-Oscillatory Modes Strongly Driven by Spin-Orbit Torque,"We investigate the physical origin of nonlinear damping due to mode coupling
+between several auto-oscillatory modes driven by spin-orbit torque in
+constricted Py/Pt heterostructures by examining the dependence of
+auto-oscillation on temperature and applied field orientation. We observe a
+transition in the nonlinear damping of the auto-oscillation modes extracted
+from the total oscillation power as a function of drive current, which
+coincides with the onset of power redistribution amongst several modes and the
+crossover from linewidth narrowing to linewidth broadening in all individual
+modes. This indicates the activation of another relaxation process by nonlinear
+magnon-magnon scattering within the modes. We also find that both nonlinear
+damping and threshold current in the mode-interaction damping regime at high
+drive current after transition are temperature independent, suggesting that the
+mode coupling occurs dominantly through a non-thermal magnon scattering process
+via a dipole or exchange interaction rather than thermally excited
+magnon-mediated scattering. This finding presents a promising pathway to
+overcome the current limitations of efficiently controlling the interaction
+between two highly nonlinear magnetic oscillators to prevent mode crosstalk or
+inter-mode energy transfer and deepens understanding of complex nonlinear spin
+dynamics in multimode spin wave systems.",2107.00150v2
+2021-07-14,Frequency fluctuations of ferromagnetic resonances at milliKelvin temperatures,"Unwanted fluctuations over time, in short, noise, are detrimental to device
+performance, especially for quantum coherent circuits. Recent efforts have
+demonstrated routes to utilizing magnon systems for quantum technologies, which
+are based on interfacing single magnons to superconducting qubits. However, the
+coupling of several components often introduces additional noise to the system,
+degrading its coherence. Researching the temporal behavior can help to identify
+the underlying noise sources, which is a vital step in increasing coherence
+times and the hybrid device performance. Yet, the frequency noise of the
+ferromagnetic resonance (FMR) has so far been unexplored. Here, we investigate
+such FMR frequency fluctuations of a YIG sphere down to mK-temperatures, and
+find them independent of temperature and drive power. This suggests that the
+measured frequency noise in YIG is dominated by so far undetermined noise
+sources, which properties are not consistent with the conventional model of
+two-level systems, despite their effect on the sample linewidth. Moreover, the
+functional form of the FMR frequency noise power spectral density (PSD) cannot
+be described by a simple power law. By employing time-series analysis, we find
+a closed function for the PSD that fits our observations. Our results underline
+the necessity of coherence improvements to magnon systems for useful
+applications in quantum magnonics.",2107.06531v1
+2021-08-04,Theory of quantum entanglement and the structure of two-mode squeezed antiferromagnetic magnon vacuum,"Recent investigations of the quantum properties of an antiferromagnet in the
+spin wave approximation have identified the eigenstates as two-mode squeezed
+sublattice states. The uniform squeezed vacuum and one-magnon states were shown
+to display a massive sublattice entanglement. Here we expand this investigation
+and study the squeezing properties of all sublattice Fock states throughout the
+magnetic Brillouin zone. We derive the full statistics of the sublattice magnon
+number with wave number $\vec k$ in the ground state and show that magnons are
+created in pairs with opposite wavevectors, hence, resulting in entanglement of
+both modes. To quantify the degree of entanglement we apply the
+Duan-Giedke-Cirac-Zoller inequality and show that it can be violated for all
+modes. The degree of entanglement decrease towards the corners of the Brillouin
+zone. We relate the entanglement to measurable correlations of components of
+the N\'eel and the magnetization vectors, thus, allowing to experimentally test
+the quantum nature of the squeezed vacuum. The distinct $\vec k$-space
+structure of the probabilites shows that the squeezed vacuum has a nonuniform
+shape that is revealed through the $\vec k$-dependent correlators for the
+magnetization and the N\'eel vectors.",2108.01942v3
+2021-08-23,Dzyaloshinskii-Moriya anisotropy effect on field-induced magnon condensation in kagome antiferromagnet $α-Cu_3Mg(OH)_6Br_2$,"We performed a comprehensive electron spin resonance, magnetization and heat
+capacity study on the field-induced magnetic phase transitions in the kagome
+antiferromagnet $\alpha-Cu_3Mg(OH)_6Br_2$. With the successful preparation of
+single crystals, we mapped out the magnetic phase diagrams under the $c$-axis
+and $ab$-plane directional magnetic fields $B$. For $B\|c$, the
+three-dimensional (3D) magnon Bose-Einstein condensation (BEC) is evidenced by
+the power law scaling of the transition temperature, $T_c\propto
+(B_c-B)^{2/3}$. For $B\|ab$, the transition from the canted antiferromagetic
+(CAFM) state to the fully polarized (FP) state is a crossover rather than phase
+transition, and the characteristic temperature has a significant deviation from
+the 3D BEC scaling. The different behaviors of the field-induced magnetic
+transitions for $B\|c$ and $B\|ab$ could result from the Dzyaloshinkii-Moriya
+(DM) interaction with the DM vector along the $c$-axis, which preserves the
+$c$-axis directional spin rotation symmetry and breaks the spin rotation
+symmetry when $B\|ab$. The 3D magnon BEC scaling for $B\|c$ is immune to the
+off-stoichiometric disorder in our sample
+$\alpha-Cu_{3.26}Mg_{0.74}(OH)_6Br_2$. Our findings have the potential to shed
+light on the investigations of the magnetic anisotropy and disorder effects on
+the field-induced magnon BEC in the quantum antiferromagnet.",2108.10020v1
+2021-10-29,4D visualization of the photoexcited coherent magnon by an X-ray free electron laser,"X-ray free electron lasers (XFEL) create femtosecond X-ray pulses with high
+brightness and high longitudinal coherence allowing to extend X-ray
+spectroscopy and scattering techniques into the ultrafast time-domain. These
+X-rays are a powerful probe for studying coherent quasiparticle excitations in
+condensed matter triggered by an impulsive optical laser pump. However, unlike
+coherent phonons, other quasiparticles have been rarely observed due to small
+signal changes and lack of standards for the identification. Here, we exploit
+resonant magnetic X-ray diffraction using an XFEL to visualize a photoexcited
+coherent magnon in space and time. Large intensity oscillations in
+antiferromagnetic and ferromagnetic Bragg reflections from precessing moment
+are observed in a multiferroic Y-type hexaferrite. The precession trajectory
+reveals that a large, long-lived, photoinduced magnetic-field changes the net
+magnetization substantially through the large-amplitude of the magnon. This
+work demonstrates an efficient XFEL probe for the coherent magnon in the
+spotlight for opto-spintronics application.",2110.15626v1
+2022-01-26,Multi-band Bose-Einstein condensate at four-particle scattering resonance,"Superfluidity and superconductivity are macroscopic manifestations of quantum
+mechanics, which have fascinated scientists since their discoveries roughly a
+century ago. Ever since the initial theories of such quantum fluids were
+formulated, there has been speculation as to the possibility of multi-component
+quantum order. A particularly simple multi-component condensate is built from
+particles occupying different quantum states, or bands, prior to condensation.
+The particles in one or both bands may undergo condensation, as seen for
+certain solids and anticipated for certain cold atom systems. For bulk solids,
+the different bands always order simultaneously, with conventional pairing
+characterized by complex order parameters describing the condensates in each
+band. Another type of condensate, notably occurring at room temperature, has
+been identified for magnons, the magnetic analogue of lattice vibrations,
+injected by microwaves into yttrium iron garnet. Here we show that magnon
+quantization for thin samples results in a new multi-band magnon condensate. We
+establish a phase diagram, as a function of microwave drive power and frequency
+relative to the magnon bands, revealing both single and multi-band
+condensation. The most stable multi-band condensate is found in a narrow regime
+favoured on account of a resonance in the scattering between two bands. Our
+discovery introduces a flexible non-equilibrium platform operating at room
+temperature for a well-characterised material, exploiting a Feshbach-like
+resonance, for examining multi-band phenomena. It points to qualitatively new
+ways to engineer and control condensates and superconducting states in
+multiband systems and potential devices containing multiple interacting
+condensates.",2201.11043v1
+2022-03-24,Writable spin wave nanochannels in an artificial-spin-ice-mediated ferromagnetic thin film,"Magnonics, which employs spin-waves to transmit and process information, is a
+promising venue for low-power data processing. One of the major challenges is
+the local control of the spin-wave propagation path. Here, we introduce the
+concept of writable magnonics by taking advantage of the highly flexible
+reconfigurability and rewritability of artificial spin ice systems. Using
+micromagnetic simulations, we show that globally switchable spin-wave
+propagation and the locally writable spin-wave nanochannels can be realized in
+a ferromagnetic thin film underlying an artificial pinwheel spin ice. The
+rewritable magnonics enabled by reconfigurable spin wave nanochannels provides
+a unique setting to design programmable magnonic circuits and logic devices for
+ultra-low power applications.",2203.12812v2
+2022-04-26,A puzzling insensitivity of magnon spin diffusion to the presence of 180$^\circ$ domain walls in a ferrimagnetic insulator,"We present room-temperature measurements of magnon spin diffusion in
+epitaxial ferrimagnetic insulator MgAl$_{0.5}$Fe$_{1.5}$O$_{4}$ (MAFO) thin
+films near zero applied magnetic field where the sample forms a multi-domain
+state. Due to a weak uniaxial magnetic anisotropy, the domains are separated
+primarily by 180$^\circ$ domain walls. We find, surprisingly, that the presence
+of the domain walls has very little effect on the spin diffusion -- nonlocal
+spin transport signals in the multi-domain state retain at least 95% of the
+maximum signal strength measured for the spatially-uniform magnetic state, over
+distances at least five times the typical domain size. This result is in
+conflict with simple models of interactions between magnons and static domain
+walls, which predict that the spin polarization carried by the magnons reverses
+upon passage through a 180$^\circ$ domain wall.",2204.12377v1
+2022-09-21,Dynamics of photo-induced ferromagnetism in oxides with orbital degeneracy,"By using intense coherent electromagnetic radiation, it may be possible to
+manipulate the properties of quantum materials very quickly, or even induce new
+and potentially useful phases that are absent in equilibrium. For instance,
+ultrafast control of magnetic dynamics is crucial for a number of proposed
+spintronic devices and can also shed light on the possible dynamics of
+correlated phases out of equilibrium. Inspired by recent experiments on
+spin-orbital ferromagnet YTiO$_3$ we consider the nonequilibrium dynamics of
+Heisenberg ferromagnetic insulator with low-lying orbital excitations. We model
+the dynamics of the magnon excitations in this system following an optical
+pulse which resonantly excites infrared-active phonon modes. As the phonons
+ring down they can dynamically couple the orbitals with the low-lying magnons,
+leading to a dramatically modified effective bath for the magnons. We show this
+transient coupling can lead to a dynamical acceleration of the magnetization
+dynamics, which is otherwise bottlenecked by small anisotropy. Exploring the
+parameter space more we find that the magnon dynamics can also even completely
+reverse, leading to a negative relaxation rate when the pump is blue-detuned
+with respect to the orbital bath resonance. We therefore show that by using
+specially targeted optical pulses, one can exert a much greater degree of
+control over the magnetization dynamics, allowing one to optically steer
+magnetic order in this system. We conclude by discussing interesting parallels
+between the magnetization dynamics we find here and recent experiments on
+photo-induced superconductivity, where it is similarly observed that depending
+on the initial pump frequency, an apparent metastable superconducting phase
+emerges.",2209.10567v1
+2022-11-21,Magnetic monopole induced polarons in atomic superlattices,"Magnetic monopoles have been realized as emergent quasiparticles in both
+condensed matter and ultracold atomic platforms, with growing interests in the
+coupling effects between the monopole and different magnetic quasiparticles. In
+this work, interaction effects between monopoles and magnons are investigated
+for an atomic pseudospin chain. We reveal that the monopole can excite a
+virtual magnon cloud in the paramagnetic chain, thereby giving rise to a new
+type of polaron, the monopole-cored polaron (McP). The McP is composed of the
+monopole as the impurity core and the virtual magnon excitation as the dressing
+cloud. The magnon dressing facilitates the Dirac string excitation and impacts
+the monopole hopping. This induces an anti-trapping effect of the McP, which
+refers to the fact that the dressing enhances the mobility of the McP, in
+contrast to the self-trapping of the common polarons. Moreover, heterogeneous
+bipolarons are shown to exist under the simultaneous doping of a north and a
+south monopole. The heterogeneous bipolaron possesses an inner degree of
+freedom composed of two identical impurities. Our investigation sheds light on
+the understanding of how the coupling between the impurity core and the
+dressing cloud can engineer the property of the polaron",2211.11481v1
+2023-01-16,Antiferromagnetic magnon spintronic based on non-reciprocal and non-degenerated ultra-fast spin-waves in the canted antiferromagnet α-Fe2O3,"Spin-waves in antiferromagnets hold the prospects for the development of
+faster, less power-hungry electronics, as well as promising physics based on
+spin-superfluids and coherent magnon-condensates. For both these perspectives,
+addressing electrically coherent antiferromagnetic spin-waves is of importance,
+a prerequisite that has so far been elusive, because unlike
+ferromagnets,antiferromagnets couple weakly to radiofrequency fields. Here, we
+demonstrate the detection of ultra-fast non-reciprocal spin-waves in the
+dipolar-exchange regime of a canted antiferromagnet using both inductive and
+spintronic transducers. Using time-of-flight spin-wave spectroscopy on hematite
+({\alpha}-Fe2O3), we find that the magnon wave packets can propagate as fast as
+20 km/s for reciprocal bulk spin-wave modes and up to 6 km/s for surface-spin
+waves propagating parallel to the antiferromagnetic Neel vector. We finally
+achieve efficient electrical detection of non-reciprocal spin-wave transport
+using non-local inverse spin-Hall effects. The electrical detection of coherent
+non-reciprocal antiferromagnetic spin waves paves the way for the development
+of antiferromagnetic and altermagnet-based magnonic devices.",2301.06329v2
+2023-01-27,Magnomechanical backaction corrections due to coupling to higher order Walker modes and Kerr nonlinearities,"The radiation pressure-like coupling between magnons and phonons in magnets
+can modify the phonon frequency (magnomechanical spring effect) and decay rate
+(magnomechanical decay) via dynamical backaction. Such effects have been
+recently observed by coupling the uniform magnon mode of a magnetic sphere (the
+Kittel mode) to a microwave cavity. In particular, the ability to evade
+backaction effects was demonstrated [C.A. Potts et al., arXiv:2211.13766
+[quant-ph] (2022)], a requisite for applications such as magnomechanical based
+thermometry. However, deviations were observed from the predicted
+magnomechanical decay rate within the standard theoretical model. In this work,
+we account for these deviations by considering corrections due to (i) magnetic
+Kerr nonlinearities and (ii) the coupling of phonons to additional magnon
+modes. Provided that such additional modes couple weakly to the driven cavity,
+our model yields a correction proportional to the average Kittel magnon mode
+occupation. We focus our results on magnetic spheres, where we show that the
+magnetostatic Walker modes couple to the relevant mechanical modes as
+efficiently as the Kittel mode. Our model yields excellent agreement with the
+experimental data.",2301.11920v4
+2023-04-17,Emergent SU(3) magnons and thermal Hall effect in the antiferromagnetic skyrmion lattice,"Complexity of quantum phases of matter is often understood by the underlying
+gauge structures, as was recognized by the $\mathbb{Z}_2$ and U(1) gauge theory
+description of spin liquid in frustrated magnets. Anomalous Hall effect of
+conducting electrons can intrisically arise from U(1) gauges expressing the
+spatial modulation of ferromagnetic moments or from SU(2) gauges representing
+the spin-orbit coupling effect. Similarly, in insulating ferro and
+antiferromagnets, the magnon excitations can contribute to anomalous transports
+by feeling the U(1) and SU(2) gauges arising from the features of ordered
+moments or interactions. In this work, we report the emergent higher rank SU(3)
+gauge structure in the magnon transport based on the thermal conductivity
+measurements of MnSc$_2$S$_4$ in an applied field up to 14\,T. The thermal Hall
+coefficient takes a substantial value when the material enters a
+three-sublattice antiferromagnetic skyrmion phase, which is confirmed by the
+large-scale spin wave theory. The excited magnons are dressed with SU(3) gauge
+field, which is a mixture of three species of U(1) gauge fields originating
+from the slowly varying magnetic moments on these sublattices.",2304.08029v1
+2023-04-19,Real-time observation of magnetization and magnon dynamics in a two-dimensional topological antiferromagnet MnBi2Te4,"Atomically thin van der Waals magnetic materials have not only provided a
+fertile playground to explore basic physics in the two-dimensional (2D) limit
+but also created vast opportunities for novel ultrafast functional devices.
+Here we systematically investigate ultrafast magnetization dynamics and spin
+wave dynamics in few-layer topological antiferromagnetic MnBi2Te4 crystals as a
+function of layer number, temperature, and magnetic field. We find
+laser-induced (de)magnetization processes can be used to accurately track the
+distinct magnetic states in different magnetic field regimes, including showing
+clear odd-even layer number effects. In addition, strongly field-dependent
+antiferromagnetic magnon modes with tens of gigahertz frequencies are optically
+generated and directly observed in the time domain. Remarkably, we find that
+magnetization and magnon dynamics can be observed in not only the time-resolved
+magneto-optical Kerr effect but also the time resolved reflectivity, indicating
+strong correlation between the magnetic state and electronic structure. These
+measurements present the first comprehensive overview of ultrafast spin
+dynamics in this novel 2D antiferromagnet, paving the way for potential
+applications in 2D antiferromagnetic spintronics and magnonics as well as
+further studies of ultrafast control of both magnetization and topological
+quantum states.",2304.09390v2
+2023-05-16,Magnon Hall effect in antiferromagnetic lattices,"Topology applied to condensed matter is an important area of research and
+technology, and topological magnetic excitations have recently become an active
+field of study. This paper presents a general discussion of magnon Hall
+transport in two-dimensional antiferromagnets. Although the Chern number is
+zero for a collinear antiferromagnet, we offer a general discussion that can be
+used in the more general case. First, we study the Union Jack lattice, where an
+effective time-reversal symmetry is broken, making the system display the
+magnon Hall effect. Then, we investigate the brick-wall lattice where such
+symmetry is present. Consequently, we have a phenomenon similar to the quantum
+spin Hall effect in electronic systems. Both lattices have not yet been studied
+from the topological point of view. The coexistence of opposite spin
+polarization in an antiferromagnet resembles the electron spin in various
+transport phenomena. We study magnon transport in the lattices mentioned above
+with Dzyaloshinskii-Moriya interaction and easy-axis single-ion anisotropy. We
+calculate the Berry curvature from the eigenvalues of the Hamiltonian. From
+that, we plot the spin Hall and thermal Hall conductivities, as well as the
+spin Nernst coefficient, as functions of the temperature. In the Union Jack
+lattice, we treat the effect of anharmonic interactions using a mean-field spin
+wave theory where the Hamiltonian becomes implicitly temperature-dependent. We
+determine self-consistently the renormalized dispersion and the staggered
+magnetization as a function of temperature. Our calculations can be applied to
+other antiferromagnetic lattices.",2305.09077v2
+2023-05-16,Non-Hermitian Casimir Effect of Magnons,"There has been a growing interest in non-Hermitian quantum mechanics. The key
+concepts of quantum mechanics are quantum fluctuations. Quantum fluctuations of
+quantum fields confined in a finite-size system induce the zero-point energy
+shift. This quantum phenomenon, the Casimir effect, is one of the most striking
+phenomena of quantum mechanics in the sense that there are no classical analogs
+and has been attracting much attention beyond the hierarchy of energy scales,
+ranging from elementary particle physics to condensed matter physics, together
+with photonics. However, the non-Hermitian extension of the Casimir effect and
+the application to spintronics have not yet been investigated enough, although
+exploring energy sources and developing energy-efficient nanodevices are its
+central issues. Here we fill this gap. By developing a magnonic analog of the
+Casimir effect into non-Hermitian systems, we show that this non-Hermitian
+Casimir effect of magnons is enhanced as the Gilbert damping constant (i.e.,
+the energy dissipation rate) increases. When the damping constant exceeds a
+critical value, the non-Hermitian Casimir effect of magnons exhibits an
+oscillating behavior, including a beating one, as a function of the film
+thickness and is characterized by the exceptional point. Our result suggests
+that energy dissipation serves as a key ingredient of Casimir engineering.",2305.09231v1
+2023-06-03,Manipulating chiral-spin transport with ferroelectric polarization,"A collective excitation of the spin structure in a magnetic insulator can
+transmit spin-angular momentum with negligible dissipation. This quantum of a
+spin wave, introduced more than nine decades ago, has always been manipulated
+through magnetic dipoles, (i.e., timereversal symmetry). Here, we report the
+experimental observation of chiral-spin transport in multiferroic BiFeO3, where
+the spin transport is controlled by reversing the ferroelectric polarization
+(i.e., spatial inversion symmetry). The ferroelectrically controlled magnons
+produce an unprecedented ratio of up to 18% rectification at room temperature.
+The spin torque that the magnons in BiFeO3 carry can be used to efficiently
+switch the magnetization of adja-cent magnets, with a spin-torque efficiency
+being comparable to the spin Hall effect in heavy metals. Utilizing such a
+controllable magnon generation and transmission in BiFeO3, an alloxide,
+energy-scalable logic is demonstrated composed of spin-orbit injection,
+detection, and magnetoelectric control. This observation opens a new chapter of
+multiferroic magnons and paves an alternative pathway towards low-dissipation
+nanoelectronics.",2306.02185v1
+2023-11-06,Effects of dilution in a 2D topological magnon insulator,"We study the effect of diluting a two-dimensional ferromagnetic insulator
+hosting a topological phase in the clean limit. By considering the
+ferromagnetic Heisenberg model in the honeycomb lattice with second
+nearest-neighbor Dzyanshikii-Moriya interaction, and working in the linear
+spin-wave approximation, we establish the topological phase diagram as a
+function of the fraction $p$ of diluted magnetic atoms. The topological phase
+with Chern number $C=1$ is robust up to a moderate dilution $p_{1}^{*}$, while
+above a higher dilution $p_{2}^{*}>p_{1}^{*}$ the system becomes trivial.
+Interestingly, both $p_{1}^{*}$ and $p_{2}^{*}$ are below the classical
+percolation threshold $p_{c}$ for the honeycomb lattice, which gives physical
+significance to the obtained phases. In the topological phase for
+$p<p_{1}^{*}$, the magnon spectrum is gapless but the states filling the
+topological, clean-limit gap region are spatially localized. For energies above
+and below the region of localized states, there are windows composed of
+extended states. This is at odds with standard Chern insulators, where extended
+states occur only at single energies. For dilutions $p_{1}^{*}<p<p_{2}^{*}$,
+the two regions of extended states merge and a continuum of delocalized states
+appears around the middle of the magnon spectrum. For this range of dilutions
+the Chern number seems to be ill defined in the thermodynamic limit, and only
+for $p>p_{2}^{*}$, when all states become localized, the system shows $C=0$ as
+expected for a trivial phase. Replacing magnetic with non-magnetic atoms in a
+systems hosting a magnon Chern insulator in the clean limit puts all the three
+phases within experimental reach.",2311.03457v1
+2023-12-26,All solution grown epitaxial magnonic crystal of thulium iron garnet thin film,"Magnonics has shown the immense potential of compatibility with CMOS devices
+and the ability to be utilized in futuristic quantum computing. Therefore, the
+magnonic crystals, both metallic and insulating, are under extensive
+exploration. The presence of high spin-orbit interaction induced by the
+presence of rare-earth elements in thulium iron garnet (TmIG) increases its
+potential in magnonic applications. Previously, TmIG thin films were grown
+using ultra-high vacuum-based techniques. Here, we present a cost-effective
+solution-based approach that enables the excellent quality interface and
+surface roughness of the epitaxial TmIG/GGG. The deposited TmIG (12.2 nm) thin
+film's physical and spin dynamic properties are investigated in detail. The
+confirmation of the epitaxy using X-ray diffraction in $\phi$-scan geometry
+along with the X-ray reflectivity and atomic force for the thickness and
+roughness analysis and topography, respectively. The epitaxial TmIG/GGG have
+confirmed the perpendicular magnetic anisotropy utilizing the
+polar-magneto-optic Kerr effect. Analyzing the ferromagnetic resonance study of
+TmIG/GGG thin films provides the anisotropy constant K$_U$ = 20.6$\times$10$^3$
+$\pm$ 0.2$\times$10$^3$ N/m$^2$ and the Gilbert damping parameter $\alpha$ =
+0.0216 $\pm$ 0.0028. The experimental findings suggest that the
+solution-processed TmIG/GGG thin films have the potential to be utilized in
+device applications.",2312.15973v1
+2024-01-03,Observation of the Magnonic Dicke Superradiant Phase Transition,"Two-level atoms coupled with single-mode cavity photons are predicted to
+exhibit a quantum phase transition when the coupling strength exceeds a
+critical value, entering a phase in which atomic polarization and photonic
+field are finite even at zero temperature and without external driving.
+However, this phenomenon, the superradiant phase transition (SRPT), is
+forbidden by a no-go theorem due to the existence of the diamagnetic term in
+the Hamiltonian. Here, we present spectroscopic evidence for a magnonic SRPT in
+ErFeO$_3$, where the role of the photonic mode (two-level atoms) in the
+photonic SRPT is played by an Fe$^{3+}$ magnon mode (Er$^{3+}$ spins). The
+absence of the diamagnetic term in the Fe$^{3+}$-Er$^{3+}$ exchange coupling
+ensures that the no-go theorem does not apply. Terahertz and gigahertz
+magnetospectroscopy experiments revealed the signatures of the SRPT -- a kink
+and a softening, respectively, of two spin-magnon hybridized modes at the
+critical point.",2401.01873v1
+2023-12-01,Large enhancement of spin-orbit torques under a MHz modulation due to phonon-magnon coupling,"The discovery of spin-orbit torques (SOTs) generated through the spin Hall or
+Rashba effects provides an alternative write approach for magnetic
+random-access memory (MRAM), igniting the development of spin-orbitronics in
+recent years. Quantitative characterization of SOTs highly relies on the
+SOT-driven ferromagnetic resonance (ST-FMR), where a modulated microwave
+current is used to generate ac SOTs and the modulation-frequency is usually
+less than 100 kHz (the limit of conventional lock-in amplifiers). Here we have
+investigated the SOT of typical SOT material/ferromagnet bilayers in an
+extended modulation-frequency range, up to MHz, by developing the ST-FMR
+measurement. Remarkably, we found that the measured SOTs are enhanced about
+three times in the MHz range, which cannot be explained according to present
+SOT theory. We attribute the enhancement of SOT to additional magnon
+excitations due to phonon-magnon coupling, which is also reflected in the
+slight changes of resonant field and linewidth in the acquired ST-FMR spectra,
+corresponding to the modifications of effective magnetization and damping
+constant, respectively. Our results indicate that the write current of SOT-MRAM
+may be reduced with the assistant of phonon-magnon coupling.",2401.02967v1
+2024-01-10,Transverse and longitudinal magnons in strongly anisotropic antiferromagnet FePSe3,"FePSe3 is a collinear honeycomb antiferromagnet with an easy-axis anisotropy
+and large spins S=2. It belongs to a family of magnetic van der Waals
+materials, which recently attracted a considerable attention. In this work we
+present an experimental magneto-optical study of the low-energy excitation
+spectrum in FePSe3, together with its theoretical description. The observed
+response contains several types of magnon excitations. Two of them are
+conventional transverse magnons described by a classical theory of
+antiferromagnetic resonance. Two other modes are identified as multimagnon
+hexadecapole excitations with an anomalous g factor approximately equal to four
+times the g factor of a single Fe^2+ ion. These quasiparticles correspond to
+full reversals of iron spins that coherently propagate in the up-down
+antiferromagnetic structure. They constitute a novel type of collective
+excitations in anisotropic magnetic solids, called longitudinal magnons.
+Comparison between theory and experiment allows us to estimate the microscopic
+parameters of FePSe3 including exchange coupling constants and the single-ion
+anisotropy.",2401.05557v2
+2024-01-11,"Two-dimensional altermagnets from high throughput computational screening: symmetry requirements, chiral magnons and spin-orbit effects","We present a high throughput computational search for altermagnetism in
+two-dimensional (2D) materials based on the Computational 2D Materials Database
+(C2DB). We start by showing that the symmetry requirements for altermagnetism
+in 2D are somewhat more strict compared to bulk materials and applying these
+yields a total of 7 altermagnets in the C2DB. The collinear ground state in
+these monolayers are verified by spin spiral calculations using the generalized
+Bloch theorem. We focus on four $d$-wave altermagnetic materials belonging to
+the $P2_1'/c'$ magnetic space group - RuF$_4$, VF$_4$, AgF$_2$ and OsF$_4$. The
+first three of these are known experimentally as van der Waals bonded bulk
+materials and are likely to be exfoliable from their bulk parent compounds. We
+perform a detailed analysis of the electronic structure and non-relativistic
+spin splitting in $k$-space exemplified by RuF$_4$. The magnon spectrum of
+RuF$_4$ is calculated from the magnetic force theorem and it is shown that the
+symmetries that enforce degenerate magnon bands in anti-ferromagnets are absent
+in altermagnets and give rise to the obtained non-degenerate magnon spectrum.
+We then include spin-orbit effects and show that these will dominate the
+splitting ofmagnons in RuF$_4$. Finally, we provide an example of $i$-wave
+altermagnetism in the 2H phase of FeBr$_3$.",2401.05992v1
+2024-02-06,Magnon mediated spin pumping by coupled ferrimagnetic garnets heterostructure,"Spin pumping has significant implications for spintronics, providing a
+mechanism to manipulate and transport spins for information processing.
+Understanding and harnessing spin currents through spin pumping is critical for
+the development of efficient spintronic devices. The use of a magnetic
+insulator with low damping, enhances the signal-to-noise ratio in crucial
+experiments such as spin-torque ferromagnetic resonance (FMR) and spin pumping.
+A magnetic insulator coupled with a heavy metal or quantum material offers a
+more straight forward model system, especially when investigating spin-charge
+interconversion processes to greater accuracy. This simplicity arises from the
+absence of unwanted effects caused by conduction electrons unlike in
+ferromagnetic metals. Here, we investigate the spin pumping in coupled
+ferrimagnetic (FiM) Y3Fe5O12 (YIG)/Tm3Fe5O12 (TmIG) bilayers combined with
+heavy-metal (Pt) using the inverse spin Hall effect (ISHE). It is observed that
+magnon transmission occurs at both of the FiMs FMR positions. The enhancement
+of spin pumping voltage (Vsp) in the FiM garnet heterostructures is attributed
+to the strong interfacial exchange coupling between FiMs. The modulation of Vsp
+is achieved by tuning the bilayer structure. Further, the spin mixing
+conductance for these coupled systems is found to be 10^18 m^-2. Our findings
+describe a novel coupled FiM system for the investigation of magnon coupling
+providing new prospects for magnonic devices.",2402.03734v1
+2024-02-19,Designed spin-texture-lattice to control anisotropic magnon transport in antiferromagnets,"Spin waves in magnetic materials are promising information carriers for
+future computing technologies due to their ultra-low energy dissipation and
+long coherence length. Antiferromagnets are strong candidate materials due, in
+part, to their stability to external fields and larger group velocities.
+Multiferroic aniferromagnets, such as BiFeO$_3$ (BFO), have an additional
+degree of freedom stemming from magnetoelectric coupling, allowing for control
+of the magnetic structure, and thus spin waves, with electric field.
+Unfortunately, spin-wave propagation in BFO is not well understood due to the
+complexity of the magnetic structure. In this work, we explore long-range spin
+transport within an epitaxially engineered, electrically tunable,
+one-dimensional (1D) magnonic crystal. We discover a striking anisotropy in the
+spin transport parallel and perpendicular to the 1D crystal axis. Multiscale
+theory and simulation suggests that this preferential magnon conduction emerges
+from a combination of a population imbalance in its dispersion, as well as
+anisotropic structural scattering. This work provides a pathway to
+electrically-reconfigurable magnonic crystals in antiferromagnets.",2402.12341v1
+2024-04-05,Field-dependent Magnons in a Honeycomb Antiferromagnet CoTiO$_3$,"We report field-dependent high-resolution inelastic neutron scattering (INS)
+measurements on the honeycomb lattice magnet, CoTiO$_3$, to study the evolution
+of its magnon excitations across a spin reorientation transition driven by an
+in-plane magnetic field. By carrying out elastic neutron scattering in a
+magnetic field, we show that the sample transitions from a collinear
+antiferromagnetic state with multiple magnetic domains at a low field to a
+mono-domain state with a canted magnetic structure at a high field. Concurrent
+with this transition, we observed significant changes in both the energy and
+the width of the zone center magnon peak. The observed width change is argued
+to be consistent with an unusual zero-field state with extended domain walls.
+On the other hand, the magnon spectra near the $\mathbf{K}$ point of the
+Brillouin zone boundary are found to be largely insensitive to the changes in
+the ordered moment directions and the domain configuration. We argue that this
+observation is difficult to explain within the framework of the bond-dependent
+model proposed in a recent INS study [Elliot \textit{et\,al}, Nat. Commun.,
+\textbf{12}, 3936 (2021)]. Our study therefore calls for alternative
+explanations for the observed $\mathbf{K}$-point gap in CoTiO$_3$.",2404.04390v1
+1995-01-16,Spin-Waves in the Mid-Infrared Spectrum of Antiferromagnetic YBa$_2$Cu$_3$O$_{6.0}$,"The mid-infrared spin-wave spectrum of antiferromagnetic
+YBa$_2$Cu$_3$O$_{6.0}$\ was determined by infrared transmission and reflection
+measurements ($\bbox{k} \!\! \parallel $c) at $T\!=\!10\!$~K.\@ Excitation of
+single magnons of the optical branch was observed at
+$E_{\text{op}}\!=\!178.0\!$~meV.\@ Two further peaks at $346\!$~meV
+($\approx\!1.94\,E_{\text{op}}$) and $470\!$~meV
+($\approx\!2.6\,E_{\text{op}}$) both belong to the two-magnon spectrum. Linear
+spin wave theory is in good agreement with the measured two-magnon spectrum,
+and allows to determine the exchange constant $J$ to be about $120\!$~meV,
+whereas the intrabilayer coupling $J_{12}$ is approximately $0.55\,J$.",9501065v1
+1995-08-23,Spin-ordering and magnon collective modes for two-dimensional electron lattices in strong magnetic fields,"We study the spin-ordering and the magnon collective modes of the
+two-dimensional Wigner crystal state at strong magnetic fields. Our work is
+based on the Hartree-Fock approximation for the ground state and the
+time-dependent Hartree-Fock approximation for the collective modes. We find
+that the ground state is ferromagnetic, i.e that all spins are aligned at T=0
+even when the electronic g-factor is negligibly small. The magnon calculations
+show that the spin-stiffness is much smaller in the crystal state than in fluid
+states which occur at nearby Landau level filling factors.",9508100v1
+1996-06-03,Magnetic excitation spectrum of dimerized antiferromagnetic chains,"Motivated by recent measurements on CuGeO$_3$ the spectrum of magnetic
+excitations of an antiferromagnetic $S=\frac{1}{2}$ chain with alternating
+coupling strength is investigated. Wave vector dependent magnons and a
+continuum with square root behavior at the band edges are found. The spectral
+density of the continua is calculated. Spin rotation symmetry fixes the gap of
+the continuum to be twice the elementary magnon gap. This is in excellent
+agreement with experimental results. In addition, the existence of bound states
+of two magnons is predicted: below the continuum a singlet and a triplet, above
+the continuum an ``anti-bound'' quintuplet. The results are based on field
+theoretic arguments, RPA calculations, and consideration of the limit of strong
+alternation.",9606001v1
+1996-07-08,A Neutron Scattering Study of Magnetic Excitations in the Spin Ladder (VO)2P2O7,"In this letter we report results from inelastic neutron scattering
+experiments on powder samples of vanadyl pyrophosphate, (VO)2P2O7. We see
+evidence for three magnetic excitations, at 3.5 meV, 6.0 meV and 14 meV. The
+intensity of the 3.5 meV mode is strong near Q=0.8 A-1, consistent with the
+one-magnon gap mode reported previously and predicted by the spin-ladder model.
+The magnetic scattering at 14 meV may be due to the top of the one-magnon band
+or the two-magnon continuum predicted in the ladder model. The 6.0 meV mode
+also peaks in intensity at Q=0.8 A-1. This mode has not been reported
+previously and was not anticipated by existing theoretical treatments of the
+spin ladder.",9607059v1
+1998-01-21,A Study of the S=1/2 Alternating Chain using Multiprecision Methods,"In this paper we present results for the ground state and low-lying
+excitations of the $S=1/2$ alternating Heisenberg antiferromagnetic chain. Our
+more conventional techniques include perturbation theory about the dimer limit
+and numerical diagonalization of systems of up to 28 spins. A novel application
+of multiple precision numerical diagonalization allows us to determine
+analytical perturbation series to high order; the results found using this
+approach include ninth-order perturbation series for the ground state energy
+and one magnon gap, which were previously known only to third order. We also
+give the fifth-order dispersion relation and third-order exclusive neutron
+scattering structure factor for one-magnon modes and numerical and analytical
+binding energies of S=0 and S=1 two-magnon bound states.",9801224v1
+1998-03-09,Disorder-enhanced delocalization and local-moment quenching in a disordered antiferromagnet,"The interplay of disorder and spin-fluctuation effects in a disordered
+antiferromagnet is studied. In the weak-disorder regime (W \le U), while the
+energy gap decreases rapidly with disorder, the sublattice magnetization,
+including quantum corrections, is found to remain essentially unchanged in the
+strong correlation limit. Magnon energies and Neel temperature are enhanced by
+disorder in this limit. A single paradigm of disorder-enhanced delocalization
+qualitatively accounts for all these weak disorder effects. Vertex corrections
+and magnon damping, which appear only at order (W/U)^4, are also studied. With
+increasing disorder a crossover is found at W \sim U, characterized by a rapid
+decrease in sublattice magnetization due to quenching of local moments, and
+formation of spin vacancies. The latter suggests a spin-dilution behavior,
+which is indeed observed in softened magnon modes, lowering of Neel
+temperature, and enhanced transverse spin fluctuations.",9803094v3
+1998-05-10,Assisted Tunneling in Ferromagnetic Junctions and Half-Metallic Oxides,"Different mechanisms of spin-dependent tunneling are analyzed with respect to
+their role in tunnel magnetoresistance (TMR). Microscopic calculation within a
+realistic model shows that direct tunneling in iron group systems leads to
+about a 30% change in resistance, which is close but lower than experimentally
+observed values. The larger observed values of the tunnel magnetoresistance
+(TMR) might be a result of tunneling involving surface polarized states. It is
+found that tunneling via resonant defect states in the barrier radically
+decreases the TMR by order of magnitude. One-magnon emission is shown to reduce
+the TMR, whereas phonons increase the effect. The inclusion of both magnons and
+phonons reasonably explains an unusual bias dependence of the TMR. The model
+presented here is applied qualitatively to half-metallics with 100% spin
+polarization, where one-magnon processes are suppressed and the change in
+resistance in the absence of spin-mixing on impurities may be arbitrarily
+large. Even in the case of imperfect magnetic configurations, the resistance
+change can be a few 1000 percent. Examples of half-metallic systems are
+CrO2/TiO2 and CrO2/RuO2.",9805114v1
+1998-07-16,Low temperature resistivity in a nearly half-metallic ferromagnet,"We consider electron transport in a nearly half-metallic ferromagnet, in
+which the minority spin electrons close to the band edge at the Fermi energy
+are Anderson-localized due to disorder. For the case of spin-flip scattering of
+the conduction electrons due to the absorption and emission of magnons, the
+Boltzmann equation is exactly soluble to the linear order. From this solution
+we calculate the temperature dependence of the resistivity due to single magnon
+processes at sufficiently low temperature, namely $k_BT\ll D/L^2$, where $L$ is
+the Anderson localization length and $D$ is the magnon stiffness. And depending
+on the details of the minority spin density of states at the Fermi level, we
+find a $T^{1.5}$ or $T^{2}$ scaling behavior for resistivity. Relevance to the
+doped perovskite manganite systems is discussed.",9807244v1
+1999-07-23,Unconventional one-magnon scattering resistivity in half metals,"Low-temperature resistivity of half-metals is investigated. To date it has
+been discussed that the one-magnon scattering process in half-metals is
+irrelevant for low-temperature resistivity, due to the fully spin-polarized
+electronic structure at the ground state. If one takes into account the
+non-rigid-band behavior of the minority band due to spin fluctuations at finite
+temperatures, however, the unconventional one-magnon scattering process is
+shown to be most relevant and gives T^3 dependence in resistivity. This
+behavior may be used as a crucial test in the search for half-metallic
+materials which are potentially important for applications. Comparison with
+resistivity data of
+  La_1-x Sr_x MnO_3 as candidates for half-metals shows good agreement.",9907363v2
+1999-08-02,Magnon-Paramagnon Effective Theory of Itinerant Ferromagnets,"The present work is devoted to the derivation of an effective
+magnon-paramagnon theory starting from a microscopic lattice model of
+ferromagnetic metals. For some values of the microscopic parameters it
+reproduces the Heisenberg theory of localized spins. For small magnetization
+the effective model describes the physics of weak ferromagnets in accordance
+with the experimental results. It is written in a way which keeps O(3) symmetry
+manifest,and describes both the order and disordered phases of the system.
+  Analytical expression for the Curie temperature,which takes the magnon
+fluctuations into account exactly, is obtained. For weak ferromagnets $T_c$ is
+well below the Stoner's critical temperature and the critical temperature
+obtained within Moriya's theory.",9908024v3
+2000-03-14,Two-magnon Raman scattering in insulating cuprates: Modifications of the effective Raman operator,"Calculations of Raman scattering intensities in spin 1/2 square-lattice
+Heisenberg model, using the Fleury-Loudon-Elliott theory, have so far been
+unable to describe the broad line shape and asymmetry of the two magnon peak
+found experimentally in the cuprate materials. Even more notably, the
+polarization selection rules are violated with respect to the
+Fleury-Loudon-Elliott theory. There is comparable scattering in $B_{1g}$ and
+$A_{1g}$ geometries, whereas the theory would predict scattering in only
+$B_{1g}$ geometry. We review various suggestions for this discrepency and
+suggest that at least part of the problem can be addressed by modifying the
+effective Raman Hamiltonian, allowing for two-magnon states with arbitrary
+total momentum. Such an approach based on the Sawatzsky-Lorenzana theory of
+optical absorption assumes an important role of phonons as momentum sinks. It
+leaves the low energy physics of the Heisenberg model unchanged but
+substantially alters the Raman line-shape and selection rules, bringing the
+results closer to experiments.",0003248v2
+2001-01-11,Internal Modes and Magnon Scattering on Topological Solitons in 2d Easy-Axis Ferromagnets,"We study the magnon modes in the presence of a topological soliton in a 2d
+Heisenberg easy-axis ferromagnet. The problem of magnon scattering on the
+soliton with arbitrary relation between the soliton radius R and the ""magnetic
+length"" Delta_0 is investigated for partial modes with different values of the
+azimuthal quantum numbers m. Truly local modes are shown to be present for all
+values of m, when the soliton radius is enough large. The eigenfrequencies of
+such internal modes are calculated analytically on limiting case of a large
+soliton radius and numerically for arbitrary soliton radius. It is demonstrated
+that the model of an isotropic magnet, which admits an exact analytical
+investigation, is not adequate even for the limit of small radius solitons,
+R<<Delta_0: there exists a local mode with nonzero frequency. We use the data
+about local modes to derive the effective equation of soliton motion; this
+equation has the usual Newtonian form in contrast to the case of the easy-plane
+ferromagnet. The effective mass of the soliton is found.",0101150v1
+2001-01-31,Bulk and Edge excitations in a $ν=1$ quantum Hall ferromagnet,"In this article, we shall focus on the collective dynamics of the fermions in
+a $\nu = 1$ quantum Hall droplet. Specifically, we propose to look at the
+quantum Hall ferromagnet. In this system, the electron spins are ordered in the
+ground state due to the exchange part of the Coulomb interaction and the Pauli
+exclusion principle. The low energy excitations are ferromagnetic magnons. To
+provide a means for describing these magnons, we shall discuss a method of
+introducing collective coordinates in the Hilbert space of many-fermion
+systems. These collective coordinates are bosonic in nature. They map a part of
+the fermionic Hilbert space into a bosonic Hilbert space. Using this technique,
+we shall interpret the magnons as bosonic collective ex citations in the
+Hilbert space of the many-electron Hall system. By considering a Hall droplet
+of finite extent, we shall also obtain the effective Lagrangian governing the
+spin collective excitations at the edge of the sample.",0101475v1
+2001-05-31,Bulk and edge excitations of a $ν=1$ Hall ferromagnet,"In this article, we shall focus on the collective dynamics of the fermions in
+a $\nu = 1$ quantum Hall droplet. Specifically, we propose to look at the
+quantum Hall ferromagnet. In this system, the electron spins are ordered in the
+ground state due to the exchange part of the Coulomb interaction and the Pauli
+exclusion principle. The low energy excitations are ferromagnetic magnons. In
+order to obtain an effective Lagrangian for these magnons, we shall introduce
+bosonic collective coordinates in the Hilbert space of many-fermion systems.
+These collective coordinates describe a part of the fermionic Hilbert space.
+Using this technique, we shall interpret the magnons as bosonic collective
+excitations in the Hilbert space of the many-electron Hall system. Furthermore,
+by considering a Hall droplet of finite extent, we shall also obtain the
+effective Lagrangian governing the spin collective excitations at the edge of
+the sample.",0105626v1
+2001-08-29,Macroscopic magnetization jumps due to independent magnons in frustrated quantum spin lattices,"For a class of frustrated spin lattices including the kagome lattice we
+construct exact eigenstates consisting of several independent, localized
+one-magnon states and argue that they are ground states for high magnetic
+fields. If the maximal number of local magnons scales with the number of spins
+in the system, which is the case for the kagome lattice, the effect persists in
+the thermodynamic limit and gives rise to a macroscopic jump in the
+zero-temperature magnetization curve just below the saturation field. The
+effect decreases with increasing spin quantum number and vanishes in the
+classical limit. Thus it is a true macroscopic quantum effect.",0108498v2
+2001-11-06,Direct Measurement of the Spin Hamiltonian and Observation of Condensation of Magnons in the 2D Frustrated Quantum Magnet Cs2CuCl4,"We propose a method for measuring spin Hamiltonians and apply it to the
+spin-1/2 Heisenberg antiferromagnet Cs2CuCl4, which shows a 2D fractionalized
+RVB state at low fields. By applying strong fields we fully align the spin
+moment of Cs2CuCl4 transforming it into an effective ferromagnet. In this phase
+the excitations are conventional magnons and their dispersion relation measured
+using neutron scattering give the exchange couplings directly, which are found
+to form an anisotropic triangular lattice with small Dzyaloshinskii-Moriya
+terms. Using the field to control the excitations we observe Bose condensation
+of magnons into an ordered ground state.",0111079v1
+2002-06-27,Magnon-Mediated Superconductivity in Itinerant Ferromagnets,"The present paper discusses magnon-mediated superconductivity in
+ferromagnetic metals. The mechanism explains in a natural way the fact that the
+superconductivity in UGe_2, ZrZn_2 and URhGe is apparently confined to the
+ferromagnetic phase.The order parameter is a spin anti-parallel component ofa
+spin-1 triplet with zero spin projection. The transverse spinfluctuations are
+pair forming and the longitudinal ones are pair breaking.The competition
+between magnons and paramagnons explains the existence of two successive
+quantum phase transitions in UGe_2, from ferromagnetism to ferromagnetic
+superconductivity, and at higher pressure to paramagnetism. The maximum T_{SC}
+results from the suppression of the paramagnon contribution. To form a Cooper
+pair an electron transfers from one Fermi surface to the other. As a result,
+the onset of superconductivity leads to the appearance of two Fermi surfaces in
+each of the spin up and spin down momentum distribution functions. This fact
+explains the linear temperaturedependence at low temperature of the specific
+heat, and the experimental results for UGe_2.",0206534v2
+2003-02-11,Magnon and phonon assisted tunneling in a high-magnetoresistance tunnel junction using Co$_{75}$Fe$_{25}$ ferromagnetic electrodes,"Magnetoelectric properties of the spin-valve-type tunnel junction of Ta(5\
+nm)/Ni$_{79}$Fe$_{21}$ (25 nm)/Ir$_{22}$Mn$_{78}$ (10 nm)/Co$_{75}$Fe$_{25}$ (4
+nm)/Al (0.8 nm)-oxide/Co$_{75}$Fe$_{25}$ (4 nm)/Ni$_{79}$Fe$_{21}$ (20 nm)/Ta
+(5 nm) are investigated both experimentally and theoretically. It is shown that
+both magnon and phonon excitations contribute to the tunneling process.
+Moreover, we show that there are two branches of magnon with spin $S=1/2$ and
+3/2 respectively. The theoretical results are in good agreement with the
+experimental data.",0302210v2
+2003-09-29,Magnons in CMR pyrochlore Tl2Mn2O7,"Well defined spin waves were observed when the spin dynamics of Tl2Mn2O7, the
+first pyrochlore compound found to exhibit colossal magnetoresistance, was
+measured [J.W.Lynn et al., Phys.Rev.Lett. 80,4582(1998)], in stark contrast
+with the experimental results on the larger family of magnetoresistive
+manganites with perovskite structure. In this work, we present our calculation
+for the spin waves in Tl2Mn2O7, which we described using the microscopic
+generic model proposed recently for this compound [C.I.Ventura and M.A.Gusmao,
+Phys.Rev.B 65, 14422(2002)]. We have employed a canonical transformation to
+determine perturbatively the effective spin-wave Hamiltonian, obtaining
+therefrom the renormalization of the ferromagnetic spin waves related to the
+localized Mn$^{4+}$ spins, due to their coupling with the conduction electrons
+present. We have calculated the magnon dispersion relations along different
+paths in the first Brillouin zone, comparing them with those which are obtained
+for an ideal isotropic ferromagnet. This comparison evidences an agreement
+between the ferromagnetic magnons obtained from the generic model and the bare
+spin waves, such as had been found in neutron scattering experiments.",0309684v1
+2003-12-02,Drastic enhancement of magnon thermal conductivity in the Bose-Einstein condensed state of TlCuCl$_3$,"We have measured the thermal conductivity of a TlCuCl$_3$ single crystal in
+magnetic fields up to 14 T. It has been found that the temperature dependence
+of the thermal conductivity exhibits a sharp peak at 4 K in zero field, which
+is suppressed by the application of magnetic fields up to 7 T. The peak is
+concluded to be attributable to the enhancement of the thermal conductivity due
+to phonons because of the formation of a spin-gap state. In high magnetic
+fields above 7 T, on the other hand, another sharp peak appears around 4 K and
+this is enhanced with increasing magnetic field. This peak is regarded as being
+attributable to the enhancement of the thermal conductivity due to magnons
+and/or phonons because of the drastic extension of the mean free path of
+magnons and/or phonons in the Bose-Einstein condensed state.",0312063v2
+2004-01-09,Thermal Spin Valves,"The ability of an insulating solid to conduct heat is rarely effected by the
+application of a magnetic field. We have found, however, that the low
+temperature heat conduction of some solids increases by more than a factor of
+two with the application of a modest magnetic field. The effect occurs in
+low-dimensional magnetically ordered materials when a small gap, \delta, in the
+acoustic magnon (spin wave) spectra is closed using a magnetic field H >
+\delta/g\mu_B. Since all magnetically ordered materials must have a gap in the
+magnon spectra for magnons with k = 0, this may be a very general effect. Extra
+heat is carried through the solid only when the magentic field exceeds the
+critical value (H > \delta/g\mu_B). At this critical field the tiny atomic
+magnets in the solid abruptly change the direction they point which results in
+more heat flowing through the material. The magnetic field thus acts as a heat
+switch. We have observed this effect in three quite different magnetically
+ordered materials: K_2V_3O_8, Nd_2CuO_4 and Pr_2CuO_4. Several possible
+explanations for these effects will be discussed.",0401154v1
+2004-09-08,Multi-Triplet Magnons in SrCu$_2$(BO$_3$)$_2$ Studied by Thermal Conductivity Measurements in Magnetic Fields,"We have measured the thermal conductivity parallel to the a-axis of the
+Zn-free and 1% Zn-substituted SrCu$_{2-x}$Zn$_x$(BO$_3$)$_2$ in magnetic fields
+up to 14 T, in order to examine the thermal conductivity due to the
+multi-triplet magnons. It has been found that the thermal conductivity peak
+observed in the spin gap state is suppressed by the substitution of Zn for Cu
+in high magnetic fields above 6 T, while it is not changed in low magnetic
+fields below 6 T. The results suggest that the thermal conductivity peak in the
+spin-gap state of SrCu$_2$(BO$_3$)$_2$ is composed of not only thermal
+conductivity due to phonons but also that due to the multi-triplet magnons in
+high fields above 6 T.",0409178v2
+2005-04-04,Theory of Spin-Wave Frequency Gaps in 3D Magnonic Crystals. Application to Manganites,"his study is an investigation of spin wave spectrum in macrostructures
+composed of two ferromagnetic materials and showing a 3D periodicity: spherical
+ferromagnetic grains disposed in the nodes of a 3D crystal lattice are embedded
+in a matrix with different ferromagnetic properties. Frequency ranges forbidden
+to spin wave propagation are found in the calculated magnonic spectra. Both the
+position and the width of the gaps are found to depend on the magnetic
+(exchange and magnetization) contrasts in the composite material, as well as on
+its structural parameters (filling fraction, crystal lattice type). Having
+applied our theory to interpretation of the existence of a spin wave gap in
+doped manganites, recently revealed in neutron scattering experiments by S.
+Hennion {\em et al.}, we obtained a good (though approximate) quantitative
+agreement with the experimental results. A working hypothesis is proposed on
+this basis, supposing that certain manganites can be treated as natural 3D
+magnonic crystals.",0504073v1
+2005-05-03,Bose-Einstein Condensation of Magnons in Cs2CuCl4,"We report on results of specific heat measurements on single crystals of the
+frustrated quasi-2D spin-1/2 antiferromagnet Cs_2CuCl_4 (T_N=0.595 K) in
+external magnetic fields B<12 T and for temperatures T>30 mK. Decreasing B from
+high fields leads to the closure of the field-induced gap in the magnon
+spectrum at a critical field B_c = 8.51 T and a magnetic phase transition is
+clearly seen below B_c. In the vicinity to B_c, the phase transition boundary
+is well described by the power-law T_c(B)\propto (B_c-B)^{1/\phi} with the
+measured critical exponent \phi\simeq 1.5. These findings are interpreted as a
+Bose-Einstein condensation of magnons.",0505058v1
+2005-06-14,Systematic Low-Energy Effective Theory for Magnons and Charge Carriers in an Antiferromagnet,"By electron or hole doping quantum antiferromagnets may turn into
+high-temperature superconductors. The low-energy dynamics of antiferromagnets
+are governed by their Nambu-Goldstone bosons -- the magnons -- and are
+described by an effective field theory analogous to chiral perturbation theory
+for the pions in strong interaction physics. In analogy to baryon chiral
+perturbation theory -- the effective theory for pions and nucleons -- we
+construct a systematic low-energy effective theory for magnons and electrons or
+holes in an antiferromagnet. The effective theory is universal and makes
+model-independent predictions for the entire class of antiferromagnetic
+cuprates. We present a detailed analysis of the symmetries of the Hubbard model
+and discuss how these symmetries manifest themselves in the effective theory. A
+complete set of linearly independent leading contributions to the effective
+action is constructed. The coupling to external electromagnetic fields is also
+investigated.",0506324v2
+2005-06-20,Hole and electron dynamics in the triangular-lattice antiferromagnet -- interplay of frustration and spin fluctuations,"Single-particle dynamics in the 120$^{\circ}$ ordered antiferromagnetic state
+of the triangular-lattice Hubbard model is studied using a physically
+transparent fluctuation approach in terms of multiple magnon emission and
+absorption processes within the noncrossing approximation. Hole and electron
+spectral features are evaluated at intermediate $U$, and analyzed in terms of a
+competition between the frustration-induced direct hopping and the virtual
+hopping terms. Finite $U$-induced competing interactions and frustration
+effects contributing through the magnon dispersion are also discussed. Finite
+contribution to self-energy correction from long-wavelength (Goldstone) modes,
+together with the high density of electron scattering states in the narrow,
+sharp peak in the upper band, result in strong fermion-magnon scattering
+leading to pronounced incoherent behaviour in the electron dynamics. The
+fluctuation-induced first-order metal-insulator transition due to vanishing
+band gap is also discussed.",0506488v2
+2005-07-05,One-magnon Raman scattering in La(2)CuO(4): the origin of the field-induced mode,"We investigate the one-magnon Raman scattering in the layered
+antiferromagnetic La(2)CuO(4) compound. We find that the Raman signal is
+composed by two one-magnon peaks: one in the B1g channel, corresponding to the
+Dzyaloshinskii-Moryia (DM) mode, and another in the B3g channel, corresponding
+to the XY mode. Furthermore, we show that a peak corresponding to the XY mode
+can be induced in the planar (RR) geometry when a magnetic field is applied
+along the easy axis for the sublattice magnetization. The appearance of such
+field-induced mode (FIM) signals the existence of a new magnetic state above
+the Neel temperature T_N, where the direction of the weak-ferromagnetic moment
+(WFM) lies within the CuO(2) planes.",0507103v2
+2005-11-04,Magnetic excitations and phonons in the spin-chain compound NaCu2O2,"We report an inelastic light scattering study of single-crystalline
+NaCu$_2$O$_2$, a spin-chain compound known to exhibit a phase with helical
+magnetic order at low temperatures. Phonon excitations were studied as a
+function of temperature and light polarization, and the phonon frequencies are
+compared to the results of ab-initio lattice dynamical calculations, which are
+also reported here. The good agreement between the observed and calculated
+modes allows an assignment of the phonon eigenvectors. Two distinct high-energy
+two-magnon features as well as a sharp low-energy one-magnon peak were also
+observed. These features are discussed in terms of the magnon modes expected in
+a helically ordered state. Their polarization dependence provides evidence of
+substantial exchange interactions between two closely spaced spin chains within
+a unit cell. At high temperatures, the spectral features attributable to
+magnetic excitations are replaced by a broad, quasielastic mode due to
+overdamped spin excitations.",0511116v1
+2006-02-16,Finite Temperature Dynamics of the Spin 1/2 Bond Alternating Heisenberg Antiferromagnetic Chain,"We present results for the dynamic structure factor of the S=1/2 bond
+alternating Heisenberg chain over a large range of frequencies and
+temperatures. Data are obtained from a numerical evaluation of thermal averages
+based on the calculation of all eigenvalues and eigenfunctions for chains of up
+to 20 spins. Interpretation is guided by the exact temperature dependence in
+the noninteracting dimer limit which remains qualitatively valid up to an
+interdimer exchange $\lambda \approx 0.5$. The temperature induced central peak
+around zero frequency is clearly identified and aspects of the crossover to
+spin diffusion in its variation from low to high temperatures are discussed.
+The one-magnon peak acquires an asymmetric shape with increasing temperature.
+The two-magnon peak is dominated by the S=1 bound state which remains well
+defined up to temperatures of the order of J. The variation with temperature
+and wavevector of the integrated intensity for one and two magnon scattering
+and of the central peak are discussed.",0602387v2
+2006-07-19,Multiple Magnon Modes and Consequences for the Bose-Einstein Condensed Phase in BaCuSi2O6,"The compound BaCuSi2O6 is a quantum magnet with antiferromagnetic dimers of S
+= 1/2 moments on a quasi-2D square lattice. We have investigated its spin
+dynamics by inelastic neutron scattering experiments on single crystals with an
+energy resolution considerably higher than in an earlier study. We observe
+multiple magnon modes, indicating clearly the presence of magnetically
+inequivalent dimer sites. This more complex spin Hamiltonian leads to a
+distinct form of magnon Bose-Einstein condensate (BEC) phase with a spatially
+modulated condensate amplitude.",0607465v2
+2006-08-25,Excitations from a Bose-Einstein condensate of magnons in coupled spin ladders,"The weakly coupled quasi-one-dimensional spin ladder compound
+(CH$_3$)$_2$CHNH$_3$CuCl$_3$ is studied by neutron scattering in magnetic
+fields exceeding the critical field of Bose-Einstein condensation of magnons.
+Commensurate long-range order and the associated Goldstone mode are detected
+and found to be similar to those in a reference 3D quantum magnet. However, for
+the upper two massive magnon branches the observed behavior is totally
+different, culminating in a drastic collapse of excitation bandwidth beyond the
+transition point.",0608566v3
+2006-10-19,Bose-Einstein condensation of magnons in magnets with predominant ferromagnetic interaction,"We discuss Bose-Einstein condensation of magnons (BEC) in magnets with
+predominant ferromagnetic (FM) interaction in magnetic field $H$ near
+saturation ($H_c$). Because $H_c$ is independent of FM couplings, magnetic
+materials of this type can have small $H_c$ that makes them promising
+candidates for experimental investigation of BEC. Ferromagnets with easy-plane
+anisotropy and antiferromagnets (AFs) containing weakly coupled FM planes or
+chains are discussed in detail. We observe small effective interaction between
+magnons near the QCP in such magnets, in contrast to AFs with strong AF
+coupling previously discussed. In particular, this smallness allows us to find
+crossovers in the critical temperature $T_c(H)\propto (H_c-H)^{1/\phi}$ from
+$\phi=3/2$ to $\phi=1$ in quasi-1D magnets, and from $\phi=3/2$ to
+$\phi\approx1$ ($T_c\ln T_c\propto H_c-H$) in quasi-2D ones.",0610536v4
+2006-12-14,Systematic Low-Energy Effective Field Theory for Electron-Doped Antiferromagnets,"In contrast to hole-doped systems which have hole pockets centered at $(\pm
+\frac{\pi}{2a},\pm \frac{\pi}{2a})$, in lightly electron-doped antiferromagnets
+the charged quasiparticles reside in momentum space pockets centered at
+$(\frac{\pi}{a},0)$ or $(0,\frac{\pi}{a})$. This has important consequences for
+the corresponding low-energy effective field theory of magnons and electrons
+which is constructed in this paper. In particular, in contrast to the
+hole-doped case, the magnon-mediated forces between two electrons depend on the
+total momentum $\vec P$ of the pair. For $\vec P = 0$ the one-magnon exchange
+potential between two electrons at distance $r$ is proportional to $1/r^4$,
+while in the hole case it has a $1/r^2$ dependence. The effective theory
+predicts that spiral phases are absent in electron-doped antiferromagnets.",0612363v1
+2006-12-31,Excitation spectra and ground state properties of the layered spin-1/2 frustrated antiferromagnets Cs_2CuCl_4 and Cs_2CuBr_4,"We use series expansion methods to study ground- and excited-state properties
+in the helically ordered phase of spin-1/2 frustrated antiferromagnets on an
+anisotropic triangular lattice. We calculate the ground state energy, ordering
+wavevector, sublattice magnetization and one-magnon excitation spectrum for
+parameters relevant to Cs_2CuCl_4 and Cs_2CuBr_4. Both materials are modeled in
+terms of a Heisenberg model with spatially anisotropic exchange constants; for
+Cs_2CuCl_4 we also take into account the additional Dzyaloshinskii-Moriya (DM)
+interaction. We compare our results for Cs_2CuCl_4 with unpolarized neutron
+scattering experiments and find good agreement. In particular, the large
+quantum renormalizations of the one-magnon dispersion are well accounted for in
+our analysis, and inclusion of the DM interaction brings the theoretical
+predictions for the ordering wavevector and the magnon dispersion closer to the
+experimental results.",0701014v1
+2007-01-18,On the theory of Bose-Einstein condensation of quasiparticles: on the possibility of condensation of magnons at high temperatures,"Bose condensation of quasiparticles in physical systems of finite size iz
+considered for the case of ferromagnetic thin films. It is shown that in
+accordance with present-day experimental capabilities which permit one to
+achieve densities of long-wave spin excitation of 1018-1019 cm-3, in such films
+the formation of condensate of such quasiparticles begins at temperatures T~100
+K (room one including). It is found that Bose condensation is accompanied by
+scaling phenomenon according to which the main thermodynamic variable is not
+the number N of particles but the ratio N/T. This indicates that condensation
+of magnons can be observed at relatively low magnon densities. The roles played
+by the shape of the spectrum and film thickness are analyzed.",0701437v1
+2006-12-11,Connecting giant magnons to the pp-wave: An interpolating limit of $AdS_5 \times S^5$,"We consider a particular large-radius limit of the worldsheet $S$-matrix for
+strings propagating on $AdS_5 \times S^5$. This limiting theory interpolates
+smoothly between the so-called plane-wave and giant-magnon regimes of the
+theory. The sigma model in this region simplifies; it stands as a toy model of
+the full theory, and may be easier to solve directly. The $S$ matrix of the
+limiting theory is non-trivial, and receives contributions to all orders in the
+$\alpha'$ expansion. We analyze a guess for the full worldsheet $S$ matrix that
+was formulated recently by Beisert, Hernandez and Lopez, and Beisert, Eden, and
+Staudacher, and take the corresponding limit. After doing a Borel resummation
+we find that the proposed $S$ matrix reproduces the expected results in the
+giant-magnon region. In addition, we rely on general considerations to draw
+some basic conclusions about the analytic structure of the $S$ matrix.",0612079v4
+2007-02-06,Gauge invariant finite size spectrum of the giant magnon,"It is shown that the finite size corrections to the spectrum of the giant
+magnon solution of classical string theory, computed using the uniform
+light-cone gauge, are gauge invariant and have physical meaning. This is seen
+in two ways: from a general argument where the single magnon is made gauge
+invariant by putting it on an orbifold as a wrapped state obeying the level
+matching condition as well as all other constraints, and by an explicit
+calculation where it is shown that physical quantum numbers do not depend on
+the uniform light-cone gauge parameter. The resulting finite size effects are
+exponentially small in the $R$-charge and the exponent (but not the prefactor)
+agrees with gauge theory computations using the integrable Hubbard model.",0702043v3
+2007-04-17,q-Deformed Supersymmetry and Dynamic Magnon Representations,"It was recently noted that the dispersion relation for the magnons of planar
+N=4 SYM can be identified with the Casimir of a certain deformation of the
+Poincare algebra, in which the energy and momentum operators are supplemented
+by a boost generator J. By considering the relationship between J and su(2|2) x
+R^2, we derive a q-deformed super-Poincare symmetry algebra of the kinematics.
+Using this, we show that the dynamic magnon representations may be obtained by
+boosting from a fixed rest-frame representation. We comment on aspects of the
+coalgebra structure and some implications for the question of boost-covariance
+of the S-matrix.",0704.2069v2
+2007-04-26,Colossal magnon-phonon coupling in multiferroic Eu$_{0.75}$Y$_{0.25}$MnO$_3$,"We report the spectra of magnetically induced electric dipole absorption in
+Eu$_{0.75}$Y$_{0.25}$MnO$_3$ from temperature dependent far infrared
+spectroscopy (10-250 cm$^{-1}$). These spectra, which occur only in the $e||a$
+polarization, consist of two relatively narrow electromagnon features that
+onset at $T_{FE}=30$ K and a broad absorption band that persists to
+temperatures well above $T_N=47$ K. The observed excitations account for the
+step up of the static dielectric constant in the ferroelectric phase. The
+electromagnon at 80 cm$^{-1}$ is observed to be strongly coupled to the nearby
+lowest optical phonon which transfers more than 1/2 of its spectral weight to
+the magnon. We attribute the origin of the broad background absorption to the
+two magnon emission decay process of the phonon.",0704.3632v4
+2007-06-08,Optical coupling to spin waves in the cycloidal multiferroic BiFeO3,"The magnon and optical phonon spectrum of an incommensurate multiferroic such
+as BiFeO3 is considered in the framework of a phenomenological Landau theory.
+The resulting spin wave spectrum is quite distinct from commensurate substances
+due to soft mode anisotropy and magnon zone folding. The former allows
+electrical control of spin wave propagation via reorientation of the
+spontaneous ferroelectric moment. The latter gives rise to multiple
+magneto-dielectric resonances due to the coupling of optical phonons at zero
+wavevector to magnons at integer multiples of the cycloid wavevector. These
+results show that the optical response of a multiferroic reveals much more
+about its magnetic excitations than previously anticipated on the basis of
+simpler models.",0706.1260v3
+2007-06-11,"Spiral phases and two-particle bound states from a systematic low-energy effective theory for magnons, electrons, and holes in an antiferromagnet","We have constructed a systematic low-energy effective theory for hole- and
+electron-doped antiferromagnets, where holes reside in momentum space pockets
+centered at $(\pm\frac{\pi}{2a},\pm\frac{\pi}{2a})$ and where electrons live in
+pockets centered at $(\frac{\pi}{a},0)$ or $(0,\frac{\pi}{a})$. The effective
+theory is used to investigate the magnon-mediated binding between two holes or
+two electrons in an otherwise undoped system. We derive the one-magnon exchange
+potential from the effective theory and then solve the corresponding
+two-quasiparticle Schr\""odinger equation. As a result, we find bound state wave
+functions that resemble $d_{x^2-y^2}$-like or $d_{xy}$-like symmetry. We also
+study possible ground states of lightly doped antiferromagnets.",0706.1423v1
+2007-11-21,The Ising model and planar N=4 Yang-Mills,"The scattering-matrix for planar Yang-Mills with N=4 supersymmetry relies on
+the assumption that integrability holds to all orders in perturbation theory.
+In this note we define a map from the spectral variables x^{\pm},
+parameterizing the long-range magnon momenta, to couplings in a two-dimensional
+Ising model. Under this map integrability of planar N=4 Yang-Mills becomes
+equivalent to the Yang-Baxter equation for the two-dimensional Ising model, and
+the long-range variables x^{\pm} translate into the entries of the Ising
+transfer matrices. We explore the Ising correlation length which equals the
+inverse magnon momentum in the small momentum limit. The critical regime is
+thus reached for vanishing magnon momentum. We also discuss the meaning of the
+Kramers-Wannier duality transformation on the gauge theory, together with that
+of the Ising model critical points.",0711.3404v2
+2008-01-06,Finite-Size Effects for Dyonic Giant Magnons,"We compute finite-size corrections to dyonic giant magnons in two ways. One
+is by examining the asymptotic behavior of helical strings of hep-th/0609026 as
+elliptic modulus k goes to unity, and the other is by applying the generalized
+Luscher formula for mu-term of arXiv:0708.2208 to the situation in which
+incoming particles are boundstates. By careful choice of poles in the
+su(2|2)^2-invariant S-matrix, we find agreement of the two results, which makes
+possible to predict the (leading) finite-size correction for dyonic giant
+magnons to all orders in the 't Hooft coupling.",0801.0747v5
+2008-01-24,Quantum Wrapped Giant Magnon,"Understanding the finite-size corrections to the fundamental excitations of a
+theory is the first step towards completely solving for the spectrum in finite
+volume. We compute the leading exponential correction to the quantum energy of
+the fundamental excitation of the light-cone gauged string in AdS(5) x S(5),
+which is the giant magnon solution. We present two independent ways to obtain
+this correction: the first approach makes use of the algebraic curve
+description of the giant magnon. The second relies on the purely
+field-theoretical Luscher formulas, which depend on the world-sheet S-matrix.
+We demonstrate the agreement to all orders in g/Delta of these approaches,
+which in particular presents a further test of the S-matrix. We comment on
+generalizations of this method of computation to other string configurations.",0801.3671v1
+2008-03-24,Spin-Charge-Lattice Coupling through Resonant Multi-Magnon Excitations in Multiferroic BiFeO3,"Spin-charge-lattice coupling mediated by multi-magnon processes is
+demonstrated in multiferroic BiFeO3. Experimental evidence of two and three
+magnons excitations as well as multimagnon coupling at electronic energy scales
+and high temperatures are reported. Temperature dependent Raman experiments
+show up to five resonant enhancements of the 2-magnon excitation below the Neel
+temperature. These are shown to be collective interactions between on-site Fe
+d-d electronic resonance, phonons and multimagnons",0803.3473v2
+2008-03-31,Vibrating giant spikes and the large-winding sector,"The single spike is a rigidly rotating classical string configuration closely
+related to the giant magnon. We calculate bosonic and fermionic modes of this
+solution, from which we see that it is not supersymmetric. It can be viewed as
+an excitation above a hoop of string wound around the equator, in the same
+sense that the magnon is an excitation above an orbiting point particle. We
+find the operator which plays the role of the Hamiltonian for this sector,
+which compared to the magnon's E-J has the angular momentum replaced by a
+winding charge. The single spike solution is unstable, and we use the modes to
+attempt a semi-classical computation of its lifetime.",0803.4222v2
+2008-06-10,Ferrimagnetism of MnV_2O_4 spinel,"The spinel MnV_2O_4 is a two-sublattice ferrimagnet, with site A occupied by
+the Mn^{2+} ion and site B by the V^{3+} ion. The magnon of the system, the
+transversal fluctuation of the total magnetization, is a complicated mixture of
+the sublattice A and B transversal magnetic fluctuations. As a result, the
+magnons' fluctuations suppress in a different way the manganese and vanadium
+magnetic orders and one obtains two phases. At low temperature (0,T^*) the
+magnetic orders of the Mn and V ions contribute to the magnetization of the
+system, while at the high temperature (T^*,T_N), the vanadium magnetic order is
+suppressed by magnon fluctuations, and only the manganese ions have non-zero
+spontaneous magnetization. A modified spin-wave theory is developed to describe
+the two phases and to calculate the magnetization as a function of temperature.
+The anomalous $M(T)$ curve reproduces the experimentally obtained ZFC
+magnetization.",0806.1641v1
+2008-06-27,Observation of Spin Fluctuations in a High-Tc Parent Compound Using Resonant Inelastic X-ray Scattering,"We report the first observation of soft-x-ray scattering from spin
+fluctuations in a high-Tc parent compound. An antiferromagnetic charge transfer
+insulator, CaCuO2, was irradiated by Cu M-edge soft x-rays. Ultra-high
+resolution measurements of scattered intensity revealed magnon-magnon
+excitations, due to spin exchange scattering, as low-energy loss features. The
+process is analogous to optical Raman scattering. The spectra provide the first
+measurement of the two-magnon excitation energy and the antiferromagnetic
+exchange parameter in infinite-layer CaCuO2. The results reveal resonant
+inelastic soft x-ray scattering as a novel probe of the spin dynamics in
+cuprates.",0806.4432v1
+2008-06-30,The SU(2) x SU(2) sector in the string dual of N=6 superconformal Chern-Simons theory,"We examine the string dual of the recently constructed $\mathcal{N}=6$
+superconformal Chern-Simons theory of Aharony, Bergman, Jafferis and Maldacena
+(ABJM theory). We focus in particular on the $SU(2)\times SU(2)$ sector. We
+find a sigma-model limit in which the resulting sigma-model is two
+Landau-Lifshitz models added together. We consider a Penrose limit for which we
+can approach the $SU(2)\times SU(2)$ sector. Finally, we find a new Giant
+Magnon solution in the $SU(2)\times SU(2)$ sector corresponding to one magnon
+in each $SU(2)$. We put these results together to find the full magnon
+dispersion relation and we compare this to recently found results for ABJM
+theory at weak coupling.",0806.4959v4
+2008-10-02,Doubly excited ferromagnetic spin-chain as a pair of coupled kicked rotors,"We show that the dynamics of a doubly-excited 1D Heisenberg ferromagnetic
+chain, subject to short pulses from a parabolic magnetic field may be analyzed
+as a pair of quantum kicked rotors. By focusing on the two-magnon dynamics in
+the kicked XXZ model we investigate how the anisotropy parameter - which
+controls the strength of the magnon-magnon interaction - changes the nature of
+the coupling between the two ""image"" coupled Kicked Rotors. We investigate
+quantum state transfer possibilities and show that one may control whether the
+spin excitations are transmitted together, or separate from each other.",0810.0454v3
+2008-11-04,Physical Origin and Generic Control of Magnonic Band Gaps of Dipole-Exchange Spin Waves in Width-Modulated-Nanostrip Waveguides,"We report, for the first time, on a novel planar structure of
+magnonic-crystal waveguides, made of a single magnetic material, in which the
+allowed and forbidden bands of propagating dipole-exchange spin-waves can be
+manipulated by the periodic modulation of different widths in thin-film
+nanostrips. The origin of the presence of several magnonic wide band gaps and
+the crucial parameters for controlling those band gaps of the order of ~10 GHz
+are found by micromagnetic numerical and analytical calculations. This work can
+offer a route to the potential application to broad-band spin-wave filters in
+the GHz frequency range.",0811.0411v3
+2008-12-17,The antiferromagnetic spin-1/2 Heisenberg model on the square lattice in a magnetic field,"We study the field dependence of the antiferromagnetic spin-1/2 Heisenberg
+model on the square lattice by means of exact diagonalizations. In a first
+part, we calculate the spin-wave velocity, the spin-stiffness, and the magnetic
+susceptibility and thus determine the microscopic parameters of the low-energy
+long-wavelength description. In a second part, we present a comprehensive study
+of dynamical spin correlation functions for magnetic fields ranging from zero
+up to saturation. We find that at low fields, magnons are well defined in the
+whole Brillouin zone, but the dispersion is substantially modified by quantum
+fluctuations compared to the classical spectrum. At higher fields, decay
+channels open and magnons become unstable with respect to multi-magnon
+scattering. Our results directly apply to inelastic neutron scattering
+experiments.",0812.3420v3
+2008-12-19,Direct Observation of Magnon Fractionalization in the Quantum Spin Ladder,"We measure by inelastic neutron scattering the spin excitation spectra as a
+function of applied magnetic field in the quantum spin-ladder material
+(C5H12N)2CuBr4. Discrete magnon modes at low fields in the quantum disordered
+phase and at high fields in the saturated phase contrast sharply with a spinon
+continuum at intermediate fields characteristic of the Luttinger-liquid phase.
+By tuning the magnetic field, we drive the fractionalization of magnons into
+spinons and, in this deconfined regime, observe both commensurate and
+incommensurate continua.",0812.3880v1
+2009-02-13,"Magnons, their Solitonic Avatars and the Pohlmeyer Reduction","We study the solitons of the symmetric space sine-Gordon theories that arise
+once the Pohlmeyer reduction has been imposed on a sigma model with the
+symmetric space as target. Under this map the solitons arise as giant magnons
+that are relevant to string theory in the context of the AdS/CFT
+correspondence. In particular, we consider the cases S^n, CP^n and SU(n) in
+some detail. We clarify the construction of the charges carried by the solitons
+and also address the possible Lagrangian formulations of the symmetric space
+sine-Gordon theories. We show that the dressing, or Backlund, transformation
+naturally produces solitons directly in both the sigma model and the symmetric
+space sine-Gordon equations without the need to explicitly map from one to the
+other. In particular, we obtain a new magnon solution in CP^3. We show that the
+dressing method does not produce the more general ""dyonic"" solutions which
+involve non-trivial motion of the collective coordinates carried by the
+solitons.",0902.2405v1
+2009-04-02,Current-controlled dynamic magnonic crystal,"We demonstrate a current-controlled, dynamic magnonic crystal. It consists of
+a ferrite film whose internal magnetic field exhibits a periodic, cosine-like
+variation. The field modulation is created by a direct current flowing through
+an array of parallel wires placed on top of a spin-wave waveguide. A single,
+pronounced rejection band in the spin-wave transmission characteristics is
+formed due to spin-wave scattering from the inhomogeneous magnetic field. With
+increasing current the rejection band depth and its width increase strongly.
+The magnonic crystal allows a fast control of its operational characteristics
+via the applied direct current. Simulations confirm the experimental results.",0904.0332v1
+2009-05-04,Magnon BEC and various phases of 3D quantum helimagnets under high magnetic field,"We study high-field phase diagram and low-energy excitations of
+three-dimensional quantum helimagnets. Slightly below the saturation field, the
+emergence of magnetic order may be viewed as Bose-Einstein condensation (BEC)
+of magnons. The method of dilute Bose gas enables a quantitative analysis of
+quantum effects in these helimagnets and thereby three phases are found: cone,
+coplanar fan and a phase-separated one. As an application, we map out the phase
+diagram of a 3D helimagnet which consists of frustrated J1-J2 chains as a
+function of frustration and an interchain coupling. Moreover, we also calculate
+the stability of the 2-magnon bound state to investigate the possibility of the
+bound-magnon BEC.",0905.0249v2
+2009-05-04,Direct current control of three magnon scattering processes in spin-valve nanocontacts,"We have investigated the generation of spin waves in the free layer of an
+extended spin-valve structure with a nano-scaled point contact driven by both
+microwave and direct electric current using Brillouin light scattering
+microscopy. Simultaneously with the directly excited spin waves, strong
+nonlinear effects are observed, namely the generation of eigenmodes with
+integer multiple frequencies (2 \emph{f}, 3 \emph{f}, 4 \emph{f}) and modes
+with non-integer factors (0.5 \emph{f}, 1.5 \emph{f}) with respect to the
+excitation frequency \emph{f}. The origin of these nonlinear modes is traced
+back to three magnon scattering processes. The direct current influence on the
+generation of the fundamental mode at frequency \emph{f} can be related to the
+spin-transfer torque, while the efficiency of three-magnon-scattering processes
+is controlled by the Oersted field as an additional effect of the direct
+current.",0905.0323v1
+2009-10-28,Scattering of Giant Magnons in CP^3,"We study classical scattering phase of CP^2 dyonic giant magnons in R_t x
+CP^3. We construct two-soliton solutions explicitly by the dressing method.
+Using these solutions, we compute the classical time delays for the scattering
+of giant magnons, and compare them to boundstate S-matrix elements derived from
+the conjectured AdS_4/CFT_3 S-matrix by Ahn and Nepomechie in the strong
+coupling limit. Our result is consistent with the conjectured S-matrix. The
+dyonic solutions play an essential role in revealing the polarization
+dependence of scattering phase.",0910.5315v5
+2010-03-10,Dynamical properties of a three-dimensional diluted Heisenberg model,"We study the magnetic excitation spectrum in three-dimensional diluted
+ferromagnetic nearest-neighbor systems down to the percolation threshold. The
+disorder effects resulting from the dilution are handled accurately within
+self-consistent local random phase approximation approach. The calculations are
+performed using relatively large systems containing typically 20 000 localized
+spins, a systematic average over many configurations of disorder is performed.
+We analyze in details the change in the magnon spectrum and magnon density of
+states as we increase the dilution. The zone of stability of the well-defined
+magnon modes is shown to shrink drastically as we approach the percolation
+threshold. We also calculate the spin stiffness which appears to vanish at the
+percolation threshold exactly. A comparison with available data, based on a
+different theoretical approach, is also provided. We hope that this study will
+motivate new experimental studies based on inelastic neutron-scattering
+measurements.",1003.2077v2
+2010-04-12,Brillouin light scattering studies of planar metallic magnonic crystals,"The application of Brillouin light scattering to the study of the spin-wave
+spectrum of one- and two-dimensional planar magnonic crystals consisting of
+arrays of interacting stripes, dots and antidots is reviewed. It is shown that
+the discrete set of allowed frequencies of an isolated nanoelement becomes a
+finite-width frequency band for an array of identical interacting elements. It
+is possible to tune the permitted and forbidden frequency bands, modifying the
+geometrical or the material magnetic parameters, as well as the external
+magnetic field. From a technological point of view, the accurate fabrication of
+planar magnonic crystals and a proper understanding of their magnetic
+excitation spectrum in the GHz range is oriented to the design of filters and
+waveguides for microwave communication systems.",1004.1881v1
+2010-06-03,Bose Glass-BEC Transition of Magnons in Tl$_{1-x}$K$_x$CuCl$_3$,"We report the magnetic-field induced Bose glass$-$BEC transition of magnons
+in Tl$_{1-x}$K$_x$CuCl$_3$ and its critical behavior investigated through
+specific heat and ESR measurements. The field dependence of the BEC transition
+temperature $T_{\rm N}$ can be described by the power law $\left[H\,{-}\,H_{\rm
+c}\right]\,{\propto}\,T_{\rm N}^{\phi}$ near the quantum critical point $H_{\rm
+c}\,{\sim}\,3.5$ T. The critical exponent ${\phi}$ tends to reach a value
+smaller than 1/2 with decreasing fitting window in contrast with
+${\phi}\rightarrow 3/2$ for the standard BEC in pure system. At sufficiently
+low temperatures, the ESR line shape for $H\,{\simeq}\,H_{\rm c}$ is
+intermediate between Gaussian and Lorentzian. This indicates the localization
+of magnons for $H\,{<}H_{\rm c}$ at T=0.",1006.0584v1
+2010-08-05,Influence of spin waves on transport through a quantum-dot spin valve,"We study the influence of spin waves on transport through a single-level
+quantum dot weakly coupled to ferromagnetic electrodes with noncollinear
+magnetizations. Side peaks appear in the differential conductance due to
+emission and absorption of spin waves. We, furthermore, investigate the
+nonequilibrium magnon distributions generated in the source and drain lead. In
+addition, we show how magnon-assisted tunneling can generate a fullly
+spin-polarized current without an applied transport voltage. We discuss the
+influence of spin waves on the current noise. Finally, we show how the magnonic
+contributions to the exchange field can be detected in the finite-frequency
+Fano factor.",1008.0948v2
+2010-12-15,Theory of two magnon Raman scattering in antiferromagnetic iron pnictides,"Although the parent iron-based pnictides and chalcogenides are itinerant
+antiferromagnets, the use of local moment picture to understand their magnetic
+properties is still widespread. We study magnetic Raman scattering from a local
+moment perspective for various quantum spin models proposed for this new class
+of superconductors. These models vary greatly in the level of magnetic
+frustration and show a vastly different two-magnon Raman response. Light
+scattering by two-magnon excitations thus provides a robust and independent
+measure of the underlying spin interactions. In accord with other recent
+experiments, our results indicate that the amount of magnetic frustration in
+these systems may be small.",1012.3254v2
+2011-02-01,One-dimentional magnonic crystal as a medium with magnetically tunable disorder on a periodical lattice,"We show that periodic magnetic nanostructures (magnonic crystals) represent
+an ideal system for studying excitations on disordered periodical lattices
+because of the possibility of controlled variation of the degree of disorder by
+varying the applied magnetic field. Ferromagnetic resonance (FMR) data
+collected inside minor hysteresis loops for a periodic array of Permalloy
+nanowires of alternating width and magnetic force microscopy images of the
+array taken after running each of these loops were used to establish convincing
+evidence that there is a strong correlation between the type of FMR response
+and the degree of disorder of the magnetic ground state. We found two types of
+dynamic responses: anti-ferromagnetic (AFM) and ferromagnetic (FM), which
+represent collective spin wave modes or collective magnonic states. Depending
+on the history of sample magnetization either AFM or FM state is either the
+fundamental FMR mode or represents a state of a magnetic defect on the
+artificial crystal. A fundamental state can be transformed into a defect one
+and vice versa by controlled magnetization of the sample.",1102.0069v1
+2011-04-07,Width of the longitudinal magnon in the vicinity of the O(3) quantum critical point,"We consider a three-dimensional quantum antiferromagnet in the vicinity of a
+quantum critical point separating the magnetically ordered and the magnetically
+disordered phases. A specific example is TlCuCl$_3$ where the quantum phase
+transition can be driven by hydrostatic pressure and/or by external magnetic
+field. As expected two transverse and one longitudinal magnetic excitation have
+been observed in the pressure driven magnetically ordered phase. According to
+the experimental data, the longitudinal magnon has a substantial width, which
+has not been understood and has remained a puzzle. In the present work, we
+explain the mechanism for the width, calculate the width and relate value of
+the width with parameters of the Bose condensate of magnons observed in the
+same compound. The method of an effective quantum field theory is employed in
+the work.",1104.1245v1
+2011-04-07,Consequences of current conservation in systems with partial magnetic order,"We discuss the consequences of spin current conservation in systems with
+SU(2) spin symmetry that is spontaneously broken by partial magnetic order,
+using a momentum-space approach. The long-distance interaction is mediated by
+Goldstone magnons, whose interaction is expressed in terms of the electron
+Green's functions. There is also a Higgs mode, whose excitation energy can be
+calculated. The case of fast magnons obeying linear dispersion relation in
+three spatial dimensions admits nonperturbative treatment using the Gribov
+equation, and the solution exhibits singular behaviour which has an
+interpretation as a tower of spin-1 electronic excitations. This occurs near
+the Mott insulator state. The electrons are more free in the case of slow
+magnons, where the perturbative corrections are less singular at the
+thresholds. We then turn our attention to the problem of high-Tc
+superconductivity, through the discussion of the stability of the
+antiferromagnetic ground state in two spatial dimensions. We argue that this is
+caused by an effective mixing of the Goldstone and Higgs modes, which in turn
+is caused by an effective Goldstone-boson condensation. The instability of the
+antiferromagnetic system is analyzed by studying the non-perturbative behaviour
+of the Higgs boson self-energy using the Dyson-Schwinger equations.",1104.1247v1
+2011-04-19,"Determination of Boundary Scattering, Intermagnon Scattering, and the Haldane Gap in Heisenberg Chains","Low-lying magnon dispersion in a S=1 Heisenberg antiferromagnetic (AF) chain
+is analyzed using the non-Abelian DMRG method. The scattering length $a_{\rm
+b}$ of the boundary coupling and the inter-magnon scattering length $a$ are
+determined. The scattering length $a_{\rm b}$ is found to exhibit a
+characteristic diverging behavior at the crossover point. In contrast, the
+Haldane gap $\Delta$, the magnon velocity $v$, and $a$ remain constant at the
+crossover. Our method allowed estimation of the gap of the S=2 AF chain to be
+$\Delta = 0.0891623(9)$ using a chain length longer than the correlation length
+$\xi$.",1104.3633v2
+2011-05-05,Antiferromagnet with two coupled antiferromagnetic sublattices in a magnetic field,"We discuss the magnon spectrum of an antiferromagnet (AF) in a magnetic field
+$h$ consisting of two interpenetrating AF sublattices coupled by the exchange
+interaction at T=0. One-ion easy-plane anisotropy is also taken into account.
+We calculate using the 1/S expansion the gap in the spectrum which is a
+manifestation of the order-by-disorder effect in this system and the optical
+magnon mode splitting. Both of these phenomena originate from the
+inter-sublattice interaction. We calculate also the gap value at $h\approx h_c$
+in the leading order of the small parameter $(h_c-h)/h_c$ using the magnon
+Bose-Einstein condensation treatment, where $h_c$ is the saturation field. By
+comparing results obtained within these two approaches we conclude that the 1/S
+expansion gives a qualitatively correct result at $h\sim h_c$ even at large
+one-ion anisotropy but it overestimates the gap value. The application is
+discussed of these results to the actively studied AF of the considered type
+$\rm NiCl_2$-$\rm 4SC(NH_2)_2$ (DTN).",1105.1044v1
+2011-05-10,Spontaneous magnon decays in planar ferromagnet,"We predict that spin-waves in an easy-plane ferromagnet have a finite
+lifetime at zero temperature due to spontaneous decays. In zero field the
+damping is determined by three-magnon decay processes, whereas decays in the
+two-particle channel dominate in a transverse magnetic field. Explicit
+calculations of the magnon damping are performed in the framework of the
+spin-wave theory for the $XXZ$ square-lattice ferromagnet with an anisotropy
+parameter $\lambda<1$. In zero magnetic field the decays occur for
+$\lambda^*<\lambda<1$ with $\lambda^*\approx 1/7$. We also discuss possibility
+of experimental observation of the predicted effect in a number of
+ferromagnetic insulators.",1105.1893v1
+2011-05-24,Multi-Frequency Magnonic Logic Circuits for Parallel Data Processing,"We describe and analyze magnonic logic circuits enabling parallel data
+processing on multiple frequencies. The circuits combine bi-stable (digital)
+input/output elements and an analog core. The data transmission and processing
+within the analog part is accomplished by the spin waves, where logic 0 and 1
+are encoded into the phase of the propagating wave. The latter makes it
+possible to utilize a number of bit carrying frequencies as independent
+information channels. The operation of the magnonic logic circuits is
+illustrated by numerical modeling. We also present the estimates on the
+potential functional throughput enhancement and compare it with scaled CMOS.
+The described multi-frequency approach offers a fundamental advantage over the
+transistor-based circuitry and may provide an extra dimension for the Moor's
+law continuation. The shortcoming and potentials issues are also discussed.",1105.4671v1
+2011-09-07,Systematic Low-Energy Effective Field Theory for Magnons and Holes in an Antiferromagnet on the Honeycomb Lattice,"Based on a symmetry analysis of the microscopic Hubbard and t-J models, a
+systematic low-energy effective field theory is constructed for hole-doped
+antiferromagnets on the honeycomb lattice. In the antiferromagnetic phase,
+doped holes are massive due to the spontaneous breakdown of the $SU(2)_s$
+symmetry, just as nucleons in QCD pick up their mass from spontaneous chiral
+symmetry breaking. In the broken phase the effective action contains a
+single-derivative term, similar to the Shraiman-Siggia term in the square
+lattice case. Interestingly, an accidental continuous spatial rotation symmetry
+arises at leading order. As an application of the effective field theory we
+consider one-magnon exchange between two holes and the formation of two-hole
+bound states. As an unambiguous prediction of the effective theory, the wave
+function for the ground state of two holes bound by magnon exchange exhibits
+$f$-wave symmetry.",1109.1419v2
+2011-10-04,Disorder instability of the magnon condensate in a frustrated spin ladder,"The effect of disorder is studied on the field-induced quantum phase
+transition in the frustrated spin-ladder compound H8C4SO2Cu2(Cl[1-x]Brx)4 using
+bulk magnetic and thermodynamic measurements. The parent material (x=0) is a
+quantum spin liquid, which in applied fields is known to form a magnon
+condensate with long-range helimagnetic order. We show that bond randomness
+introduced by a chemical substitution on the non-magnetic halogene site
+destroys this phase transition at very low concentrations, already for x=0.01.
+The extreme fragility of the magnon condensate is attributed to random
+frustration in the incommensurate state.",1110.0806v3
+2011-12-21,Direct detection of magnon spin transport by the inverse spin Hall effect,"Conversion of traveling magnons into an electron carried spin current is
+demonstrated in a time resolved experiment using a spatially separated
+inductive spin-wave source and an inverse spin Hall effect (ISHE) detector. A
+short spin-wave packet is excited in a yttrium-iron garnet (YIG) waveguide by a
+microwave signal and is detected at a distance of 3 mm by an attached Pt layer
+as a delayed ISHE voltage pulse. The delay in the detection appears due to the
+finite spin-wave group velocity and proves the magnon spin transport. The
+experiment suggests utilization of spin waves for the information transfer over
+macroscopic distances in spintronic devices and circuits.",1112.4969v1
+2012-03-07,Dynamical structure factor of quasi-2D antiferromagnet in high fields,"We study high-field magnon dynamics and examine the dynamical structure
+factor in the quasi-2D tetragonal Heisenberg antiferromagnet with interlayer
+coupling corresponding to realistic materials. Within spin-wave theory, we show
+that a non-zero interlayer coupling mitigates singular corrections to the
+excitation spectrum occurring in the high-field regime that would otherwise
+require a self-consistent approach beyond the 1/S approximation. For the fields
+between the threshold for decays and saturation field we observe widening of
+the two-magnon sidebands with significant shifting of the spectral weight away
+from the quasiparticle peak. We find spectrum broadening throughout large
+regions of the Brillouin zone, dramatic redistributions of spectral weight to
+the two-magnon continuum, two-peak structures and other features clearly unlike
+conventional single-particle peaks.",1203.1621v2
+2012-07-27,"Half-Metallic Ferromagnetism in the Heusler Compound Co$_2$FeSi revealed by Resistivity, Magnetoresistance, and Anomalous Hall Effect measurements","We present electrical transport data for single-crystalline Co$_2$FeSi which
+provide clear-cut evidence that this Heusler compound is truly a half-metallic
+ferromagnet, i.e. it possesses perfect spin-polarization. More specifically,
+the temperature dependence of $\rho$ is governed by electron scattering off
+magnons which are thermally excited over a sizeable gap $\Delta\approx 100 K$
+($\sim 9 meV$) separating the electronic majority states at the Fermi level
+from the unoccupied minority states. As a consequence, electron-magnon
+scattering is only relevant at $T\gtrsim\Delta$ but freezes out at lower
+temperatures, i.e., the spin-polarization of the electrons at the Fermi level
+remains practically perfect for $T\lesssim\Delta$. The gapped magnon population
+has a decisive influence on the magnetoresistance and the anomalous Hall effect
+(AHE): i) The magnetoresistance changes its sign at $T\sim 100 K$, ii) the
+anomalous Hall coefficient is strongly temperature dependent at $T\gtrsim 100
+K$ and compatible with Berry phase related and/or side-jump electronic
+deflection, whereas it is practically temperature-independent at lower
+temperatures.",1207.6611v1
+2012-08-20,Reversal and Termination of Current-Induced Domain Wall Motion via Magnonic Spin-Transfer Torque,"We investigate the domain wall dynamics of a ferromagnetic wire under the
+combined influence of a spin-polarized current and magnonic spin-transfer
+torque generated by an external field, taking also into account Rashba
+spin-orbit coupling interactions. It is demonstrated that current-induced
+motion of the domain wall may be completely reversed in an oscillatory fashion
+by applying a magnonic spin-transfer torque as long as the spin-wave velocity
+is sufficiently high. Moreover, we show that the motion of the domain wall may
+be fully terminated by means of the generation of spin-waves, suggesting the
+possibility to pin the domain-walls to predetermined locations. We also discuss
+how strong spin-orbit interactions modify these results.",1208.4108v1
+2012-08-27,Photo-magnonics,"In the framework of magnonics all-optical femtosecond laser experiments are
+used to study spin waves and their relaxation paths. Magnonic crystal
+structures based on antidots allow the control over the spin-wave modes. In
+these two-dimensional magnetic metamaterials with periodicities in the
+wave-length range of dipolar spin waves the spin-wave bands and dispersion are
+modified. Hence, a specific selection of spin-wave modes excited by laser
+pulses is possible. Different to photonics, the modes depend strongly on the
+strength of the magneto-static potential at around each antidot site - the
+dipolar field. While this may lead to a mode localization, also for filling
+fractions around or below 10%, Bloch states are found in low damping
+ferromagnetic metals. In this chapter, an overview of these mechanisms is given
+and the connection to spin-wave band spectra calculated from an analytical
+model is established. Namely, the plane-wave method yields flattened bands as
+well as band gaps at the antidot lattice Brillouin zone boundary.",1208.5383v1
+2012-08-29,Electron spin resonance shifts in S=1 antiferromagnetic chains,"We discuss electron spin resonance (ESR) shifts in spin-1 Heisenberg
+antiferromagnetic chains with a weak single-ion anisotropy based on several
+effective field theories, the O(3) nonlinear sigma model (NLSM) in the Haldane
+phase, free fermion theories around the lower and the upper critical fields. In
+the O(3) NLSM, the single-ion anisotropy corresponds to a composite operator
+which creates two magnons at the same time and position. Therefore, even inside
+a parameter range where free magnon approximation is valid, we have to take
+interactions among magnons into account. Though the O(3) NLSM is only valid in
+the Haldane phase, an appropriate translation of Faddeev-Zamolodchikov
+operators of the O(3) NLSM to fermion operators enables one to treat ESR shifts
+near the lower critical field in a similar manner to discussions in Haldane
+phase. We present that our theory gives quantitative agreements with recent ESR
+experimental results on an spin-1 chain compounds NDMAP.",1208.6017v2
+2012-10-12,"Spin superfluidity, coherent spin precession, and magnon BEC","Spin superfluidity, coherent spin precession, and magnon BEC are intensively
+investigated theoretically and experimentally nowadays. Meanwhile, clear
+definition and differentiation between these related phenomena is needed. It is
+argued that spin stiffness, which leads to existence of coherent spin
+precession and dissipationless spin supercurrents, is a necessary but not
+sufficient condition for spin superfluidity. The latter is defined as a
+possibility of spin transport on macroscopical distances with sufficiently
+large spin supercurrents. This possibility is realized at special topology of
+the magnetic-order-parameter space, such as, e.g., that in easy-plane
+antiferromagnets. It is argued that an arbitrarily chosen formal criterion for
+the existence of magnon BEC has no connection with conditions for observation
+of macroscopic dissipationless spin transport.",1210.3451v1
+2012-11-26,Magnon Supersolid and Anomalous Hysteresis in Spin Dimers on a Triangular Lattice,"We study the magnetic phase diagram and hysteresis behavior of weakly coupled
+spin dimers on a triangular lattice using the cluster mean-field method with
+cluster-size scaling. We find that the magnetization curve has plateaus at 1/3
+and 2/3 of the total magnetization, in which local singlet and triplet states
+form a superlattice pattern. Moreover, if increasing (decreasing) the magnetic
+field from the 1/3 (2/3) plateau, the Bose-Einstein condensation (BEC) of
+triplons occurs on the superlattice background, leading to the transition into
+magnon supersolid phase. We also find that the first-order transition between
+these solid states and the standard magnon BEC state exhibits an anomalous
+hysteresis upon cycling the magnetic field; the transition can occur only from
+solid to BEC, and the system cannot return to the initial solid state in the
+reverse process.",1211.5880v2
+2012-12-07,Brillouin Light Scattering Spectra as local Temperature Sensors for Thermal Magnons and Acoustic Phonons,"We demonstrate the use of the micro-Brillouin light scattering (micro-BLS)
+technique as a local temperature sensor for magnons in a Permalloy thin film
+and phonons in the glass substrate. A systematic shift in the frequencies of
+two thermally excited perpendicular standing spin wave modes as the film is
+uniformly heated allows us to achieve a temperature resolution better than 2.5
+K. We demonstrate that the micro-BLS spectra can be used to measure the local
+temperatures of phonons and magnons across a thermal gradient. Such local
+temperature sensors are useful for investigating spin caloritronic and thermal
+transport phenomena in general.",1212.1520v2
+2012-12-11,Raman scattering in a Heisenberg S=1/2 antiferromagnet on the anisotropic triangular lattice,"We investigate the two-magnon Raman scattering from an anisotropic S=1/2
+triangular Heisenberg antiferromagnet Cs2CuCl4. We find that the Raman response
+is very sensitive to magnon-magnon interactions and to scattering geometries, a
+feature that is in remarkable contrast with the polarization-independent Raman
+signal from the isotropic triangular Heisenberg antiferromagnet. Since a
+spin-liquid ground state gives rise to a similar rotationally invariant Raman
+response, our results on the polarization dependence of the scattering spectrum
+suggest that Raman spectroscopy provides a useful probe, complementary to
+neutron scattering, of the ground-state properties of Cs2CuCl4, particularly
+whether the time-reversal symmetry is broken in the ground state.",1212.2286v2
+2013-01-10,"Comment on ""Physical Origin and Generic Control of Magnonic Band Gaps of Dipole-Exchange Spin Waves in Width-Modulated Nanostrip Waveguides"" [K.-S. Lee, D.-S. Han, and S.-K. Kim, PRL 102, 127202 (2009), arXiv:0811.0411]","In Ref. [PRL 102, 127202 (2009)] Lee et al. reported the existence of large
+magnonic bandgaps in one-dimensional width-modulated Permalloy nanostripe
+waveguides based on OOMMF simulations. However, as the symmetry of the magnetic
+field pulse they applied to excite the spin waves (SWs) was not general, the
+entire set of SW branches with A symmetry was omitted from the magnonic band
+structures (see below). This omission has unfortunately led to misleading
+conclusions of, for instance, the number, width and position of the bandgaps.
+We present here the full band structure based on three different theoretical
+approaches that gave consistent predictions, thus corroborating the methods
+employed, namely, a microscopic approach, OOMMF simulations, and a method based
+on the linearized Landau-Lifshitz equation. Further, we provide a physical
+interpretation using group theory.",1301.2036v1
+2013-02-25,Varied Perturbation Theory for the Dispersion Dip in the Two-Dimensional Heisenberg Quantum Antiferromagnet,"We study the roton-like dip in the magnon dispersion at the boundary of the
+Brillouin zone in the isotropic S=1/2 Heisenberg quantum antiferromagnet. This
+high-energy feature is sometimes seen as indication of a fractionalization of
+the magnons to spinons. In this article, we provide evidence that the
+description of the dip in terms of magnons can be improved significantly by
+applying more advanced evaluation schemes. In particular, we illustrate the
+usefulness of the application of the principle of minimal sensitivity in varied
+perturbation theory. Thereby, we provide an example for the application of this
+approach to an extended condensed matter problem governed by correlations which
+can trigger analogous investigations for many other systems.",1302.6201v2
+2013-03-05,Dynamics and relaxation in spin nematics,"We study dynamics and relaxation of elementary excitations (magnons) in the
+spin nematic (quadrupole ordered) phase of S=1 magnets. We develop a general
+phenomenological theory of spin dynamics and relaxation for spin-1 systems.
+Results of the phenomenological approach are compared to those obtained by
+microscopic calculations for the specific S=1 model with isotropic bilinear and
+biquadratic exchange interactions. This model exhibits a rich behavior
+depending on the ratio of bilinear and biquadratic exchange constants,
+including several points with an enhanced symmetry. It is shown that symmetry
+plays an important role in relaxation. Particularly, at the SU(3) ferromagnetic
+point the magnon damping $\Gamma$ depends on its wavevector k as $\Gamma\propto
+k^{4}$, while a deviation from the high-symmetry point changes the behavior of
+the leading term to $\Gamma\propto k^{2}$. We point out a similarity between
+the behavior of magnon relaxation in spin nematics to that in an isotropic
+ferromagnet.",1303.1194v2
+2013-03-14,Spin-current order in anisotropic triangular antiferromagnets,"We analyze instabilities of the collinear up-up-down state of a
+two-dimensional quantum spin-S spatially anisotropic triangular lattice
+antiferromagnet in a magnetic field. We find, within large-S approximation,
+that near the end point of the plateau, the collinear state becomes unstable
+due to condensation of two-magnon bound pairs rather than single magnons. The
+two-magnon instability leads to a novel 2D vector chiral phase with alternating
+spin currents but no magnetic order in the direction transverse to the field.
+This phase breaks a discrete Z_2 symmetry but preserves a continuous U(1) one
+of rotations about the field axis. It possesses orbital antiferromagnetism and
+displays a magnetoelectric effect.",1303.3519v2
+2013-03-26,Double zigzag spin chain in strong magnetic field close to saturation,"We study the ground state phase diagram of a frustrated spin tube in a strong
+external magnetic field. This model can be viewed as two coupled zigzag spin
+chains, or as a two-leg spin ladder with frustrating next-nearest-neighbor
+couplings along the legs, and its study is motivated by the physics of such
+materials as Sulfolane-Cu_{2}Cl_{4} and BiCu_{2}PO_{6}. In magnetic fields
+right below the saturation, the system can be effectively represented as a
+dilute gas of two species of bosonic quasiparticles that correspond to magnons
+with inequivalent incommensurate momenta at two degenerate minima of the magnon
+dispersion. Using the method previously proposed and tested for frustrated spin
+chains, we calculate effective interactions in this two-component Bose gas. On
+this basis, we establish the phase diagram of nearly-saturated frustrated spin
+tube, which is shown to include the two-component Luttinger liquid, two types
+of vector chiral phases, and phases whose physics is determined by the presence
+of bound magnons. We study the phase diagram of the model numerically by means
+of the density matrix renormalization group technique, and find a good
+agreement with our analytical predictions.",1303.6662v1
+2013-04-08,Intrinsic and extrinsic mirror symmetry breaking in anti-dot spin-wave waveguides,"We theoretically study the spin-wave spectra in magnonic waveguides
+periodically patterned with square anti-dots in nanoscale with pinned
+magnetization at the edges. We show that the breaking of the mirror symmetry of
+the waveguide by the structural changes can result in a magnonic band gap
+closing. These intrinsic symmetry breaking can be compensated by properly
+chosen asymmetric external bias magnetic field, i.e. in an extrinsic way. As a
+result the magnonic gaps existing in the ideal symmetric structure can be
+recovered. The model used for the explanation also suggests that this idea
+could be generic both for exchange and dipolar interaction regimes of
+spin-waves and also for other types of waves, e.g., electrons in the graphene
+ribbons.",1304.1799v1
+2013-05-22,Spin-wave nonreciprocity based on interband magnonic transitions,"We theoretically demonstrate linear spin-wave nonreciprocity in a Ni80Fe20
+nanostripe waveguide, based on interband magnonic transitions induced by a
+time-reversal and spatialinversion symmetry breaking magnetic field. An
+analytical coupled-mode theory of spin waves, developed to describe the
+transitions which are accompanied by simultaneous frequency and wavevector
+shifts of the coupled spin waves, is well corroborated by numerical
+simulations. Our findings could pave the way for the realization of spin-wave
+isolation and the dynamic control of spin-wave propagation in nanoscale
+magnonic integrated circuits via an applied magnetic field.",1305.5018v3
+2013-07-18,Gutzwiller Approach for Elementary Excitations in $S=1$ Antiferromagnetic Chains,"In a previous paper [Phys. Rev. B 85,195144 (2012)], variational Monte Carlo
+method (based on Gutzwiller projected states) was generalized to $S=1$ systems.
+This method provided very good trial ground states for the gapped phases of
+$S=1$ bilinear-biquadratic (BLBQ) Heisenberg chain. In the present paper, we
+extend the approach to study the low-lying elementary excitations in $S=1$
+chains. We calculate the one-magnon and two-magnon excitation spectra of the
+BLBQ Heisenberg chain and the results agree very well with recent data in
+literature. In our approach, the difference of the excitation spectrum between
+the Haldane phase and the dimer phase (such as the even/odd size effect) can be
+understood from their different topology of corresponding mean field theory. We
+especially study the Takhtajan-Babujian critical point. Despite the fact that
+the `elementary excitations' are spin-1 magnons which are different from the
+spin-1/2 spinons in Bethe solution, we show that the excitation spectrum,
+critical exponent ($\eta=0.74$) and central charge ($c=1.45$) calculated from
+our theory agree well with Bethe ansatz solution and conformal field theory
+predictions.",1307.4958v2
+2013-11-13,Fokker-Planck approach to the theory of magnon-driven spin Seebeck effect,"Following the theoretical approach by Xiao et al [Phys. Rev. B 81, 214418
+(2010)] to the spin Seebeck effect, we calculate the mean value of the total
+spin current flowing through a normalmetal/ ferromagnet interface. The spin
+current emitted from the ferromagnet to the normal metal is evaluated in the
+framework of the Fokker-Planck approach for the stochastic
+Landau-Lifshitz-Gilbert equation. We show that the total spin current depends
+not only on the temperature difference between the electron and the magnon
+baths, but also on the external magnetic field and magnetic anisotropy. Apart
+from this, the spin current is shown to saturate with increasing magnon
+temperature, and the saturation temperature increases with increasing magnetic
+field and/or magnetic anisotropy.",1311.3117v1
+2013-11-19,Observation of the spin Peltier effect,"We report the observation of the spin Peltier effect (SPE) in the
+ferrimagnetic insulator Yttrium Iron Garnet (YIG), i.e. a heat current
+generated by a spin current flowing through a Platinum (Pt)|YIG interface. The
+effect can be explained by the spin torque that transforms the spin current in
+the Pt into a magnon current in the YIG. Via magnon-phonon interactions the
+magnetic fluctuations modulate the phonon temperature that is detected by a
+thermopile close to the interface. By finite-element modelling we verify the
+reciprocity between the spin Peltier and spin Seebeck effect. The observed
+strong coupling between thermal magnons and phonons in YIG is attractive for
+nanoscale cooling techniques.",1311.4772v1
+2013-12-04,Transient Carrier Dynamics in a Mott Insulator with Antiferromagnetic Order,"We study transient dynamics of hole carriers injected at a certain time into
+a Mott insulator with antiferromagnetic long range order. This is termed
+``dynamical hole doping"" as contrast with chemical hole doping. Theoretical
+framework for the transient carrier dynamics are presented based on the two
+dimensional $t-J$ model. Time dependences of the optical conductivity spectra
+as well as the one-particle excitation spectra are calculated based on the
+Keldysh Green's function formalism at zero temperature combined with the
+self-consistent Born approximation. At early stage after dynamical hole doping,
+the Drude component appears, and then incoherent components originating from
+hole-magnon scatterings start to grow. Fast oscillatory behavior due to
+coherent magnon, and slow relaxation dynamics are confirmed in the spectra.
+Time profiles are interpreted as that doped bare holes are dressed by magnon
+clouds, and are relaxed into spin polaron quasi-particle states. Characteristic
+relaxation times for Drude and incoherent peaks strongly depend on momentum of
+a dynamically doped hole, and the exchange constant. Implications to the recent
+pump-probe experiments are discussed.",1312.1077v1
+2014-01-20,On the theory of inhomogeneous Bose-Einstein condensation of magnons in yttrium garnet,"The Bose-Einstein condensation (BEC) of magnons created by a strong pumping
+in ferromagnetic thin films of yttrium iron garnet used as systems of finite
+size is considered analytically. Such a peculiarity, typical for this magnetic
+material, as the presence of a minimum in the spectrum of spin waves at a
+finite value of the wave vector is taken into account. The definition of
+hightemperature BEC is introduced and its characteristics are discussed. A role
+of boundary conditions for spin variables is analyzed, and it is shown that in
+the case of free spins on the boundary the magnon lattice can form in the
+system. The factors responsible for its appearance are discussed.",1401.4854v1
+2014-02-27,Magneto- to electro-active transmutation of spin waves in ErMnO3,"The low energy dynamical properties of the multiferroic hexagonal perovskite
+ErMnO3 have been studied by inelastic neutron scattering as well as terahertz
+and far infrared spectroscopies on synchrotron source. From these complementary
+techniques, we have determined the magnon and crystal field spectra and
+identified a zone center magnon only excitable by the electric field of an
+electromagnetic wave. Using comparison with the isostructural YMnO3 compound
+and crystal field calculations, we propose that this dynamical magnetoelectric
+process is due to the hybridization of a magnon with an electro-active crystal
+field transition.",1402.7018v1
+2014-04-01,Raman study of magnetic excitations and magneto-elastic coupling in alpha-SrCr2O4,"Using Raman spectroscopy, we investigate the lattice phonons, magnetic
+excitations, and magneto-elastic coupling in the distorted triangular-lattice
+Heisenberg antiferromagnet alpha-SrCr2O4, which develops helical magnetic order
+below 43 K. Temperature dependent phonon spectra are compared to predictions
+from density functional theory calculations which allows us to assign the
+observed modes and identify weak effects arising from coupled lattice and
+magnetic degrees of freedom. Raman scattering associated with two-magnon
+excitations is observed at 20 meV and 40 meV. These energies are in general
+agreement with our ab-initio calculations of exchange interactions and earlier
+theoretical predictions of the two-magnon Raman response of triangular-lattice
+antiferromagnets. The temperature dependence of the two-magnon excitations
+indicates that spin correlations persist well above the N\'eel temperature.",1404.0355v2
+2014-09-09,Magnetization pumping and dynamics in a Dzyaloshinskii-Moriya magnet,"We formulate a phenomenological description of thin ferromagnetic layers with
+inversion asymmetry where the single-domain magnetic dynamics experiences
+magnon current-induced torques and leads to magnon-motive forces. We first
+construct a phenomenological theory based on irreversible thermodynamics,
+taking into account the symmetries of the system. Furthermore, we confirm that
+these effects originate from Dzyaloshinskii-Moriya interactions from the
+analysis based on the stochastic Landau-Lifshitz-Gilbert equation. Our
+phenomenological results generalize to a general form of Dzyaloshinskii-Moriya
+interactions and to other systems, such as pyrochlore crystals and chiral
+magnets. Possible applications include spin current generation, magnetization
+reversal and magnonic cooling.",1409.2846v3
+2014-09-25,Tuning the Band Structures of a 1D Width-Modulated Magnonic Crystal by a Transverse Magnetic Field,"Theoretical studies, based on three independent techniques, of the band
+structure of a one-dimensional width-modulated magnonic crystal under a
+transverse magnetic field are reported. The band diagram is found to display
+distinct behaviors when the transverse field is either larger or smaller than a
+critical value. The widths and center positions of bandgaps exhibit unusual
+non-monotonic and large field-tunability through tilting the direction of
+magnetization. Some bandgaps can be dynamically switched on and off by simply
+tuning the strength of such a static field. Finally, the impact of the lowered
+symmetry of the magnetic ground state on the spin-wave excitation efficiency of
+an oscillating magnetic field is discussed. Our finding reveals that the
+magnetization direction plays an important role in tailoring magnonic band
+structures and hence in the design of dynamic spin-wave switches.",1409.7183v1
+2014-12-11,Magnon Hall effect and anisotropic thermal transport in NiFe and YIG ferromagnets,"The Righi-Leduc effect refers to the thermal analogue of the Hall effect, for
+which the electric current is replaced by the heat current and the electric
+field by the temperature gradient. In both cases, the magnetic field generates
+a transverse force that deviates the carriers (electron, phonon, magnon) in the
+direction perpendicular to the current. In a ferromagnet, the magnetization
+plays the role of the magnetic field, and the corresponding effect is called
+anomalous Hall effect. Furthermore, a second transverse contribution due to the
+anisotropy, the planar Hall effect, is superimposed to the anomalous Hall
+effect. We report experimental evidence of the thermal counterpart of the Hall
+effects in ferromagnets, namely the magnon Hall effect (or equivalently the
+anomalous Righi-Leduc effect) and the planar Righi-Leduc effect, measured on
+ferromagnets that are either electrical conductor (NiFe) or insulator (YIG).
+The study shows the universal character of these new thermokinetic effects,
+related to the intrinsic chirality of the anisotropic ferromagnetic degrees of
+freedom.",1412.3723v1
+2015-01-06,Sensing magnetic nanoparticles using nano-confined ferromagnetic resonances in a magnonic crystal,"We demonstrate the use of the magnetic-field-dependence of highly spatially
+confined, GHz-frequency ferromagnetic resonances in a ferromagnetic
+nanostructure for the detection of adsorbed magnetic nanoparticles. This is
+achieved in a large area magnonic crystal consisting of a thin ferromagnetic
+film containing a periodic array of closely spaced, nano-scale anti-dots. Stray
+fields from nanoparticles within the anti-dots modify resonant dynamic
+magnetisation modes in the surrounding magnonic crystal, generating easily
+measurable resonance peak shifts. The shifts are comparable to the resonance
+linewidths for high anti-dot filling fractions with their signs and magnitudes
+dependent upon the modes' localisations (in agreement with micromagnetic
+simulation results). This is a highly encouraging result for the development of
+frequency-based nanoparticle detectors for high speed nano-scale biosensing.",1501.01171v1
+2015-02-06,Thermal Hall conductivity in the frustrated pyrochlore magnet Tb2Ti2O7,"In a ferromagnet, the spin excitations are the well-studied magnons. In
+frustrated quantum magnets, long-range magnetic order fails to develop despite
+a large exchange coupling between the spins. In contrast to the magnons in
+conventional magnets, their spin excitations are poorly understood. Are they
+itinerant or localized? Here we show that the thermal Hall conductivity
+$\kappa_{xy}$ provides a powerful probe of spin excitations in the ""quantum
+spin ice"" pyrochlore Tb$_2$Ti$_2$O$_7$. The thermal Hall response is large even
+though the material is transparent. The Hall response arises from spin
+excitations with specific characteristics that distinguish them from magnons.
+At low temperature ($T<$ 1 K), the thermal conductivity imitates that of a
+dirty metal. Using the Hall angle, we construct a phase diagram showing how the
+excitations are suppressed by a magnetic field.",1502.02006v1
+2015-03-05,Analytical soliton solution for the Landau-Lifshitz equation of one dimensional magnonic crystal,"Nonlinear localized magnetic excitations in one dimensional magnonic crystal
+is investigated under periodic magntic field. The governing Landau-Lifshitz
+equation is transformed into variable coefficient nonlinear Schrodinger
+equation(VCNLS) using sterographic projection. The VCNLS equation is in general
+nonintegrable, by using painleve analysis necessary conditions for the VCNLS
+equation to pass Weiss-Tabor-Carnevale (WTC) Painleve test are obtained. A
+sufficient integrability condition is obtained by further exploring a
+transformation, which can map the VCNLS equation into the well-known standard
+nonlinear Schrodinger equation. The transformation built a systematic
+connection between the solution of the standard nonlinear Schrodinger equation
+and VC-NLS equation. The results shows the excitation of magnetization in the
+form of soliton has spatialperiod exists on the background of spin Bloch waves.
+Such solution exisits only certain constrain conditions on the coefficient of
+the VCNLS equation are satisfied. The analytical results suggest a way to
+control the dynamics of magnetization in the form of solitons by an appropriate
+spatial modulation of the nonlinearity coefficient in the governing VCNLS
+equation which is determined by the ferromagnetic materials which forms the
+magnonic crystal.",1503.01559v1
+2015-03-30,Magnon contribution to the magnetoresistance of iron nanowires deposited using pulsed electrodeposition,"Iron nanowires with a square cross section are grown by pulsed
+electrodeposition within a newly developed nanochannel template that allows for
+easy characterization. Measurements of the magnetoresistance as a function of
+magnetic field and temperature are performed within a large parameter window
+allowing for the investigation of the magnonic contribution to the
+magnetoresistance of electrodeposited iron nanowires. Values for the
+temperature dependent magnon stiffness D(T) are extracted.",1503.08595v1
+2015-06-03,In-plane angular dependence of the spin-wave nonreciprocity of an ultrathin film with Dzyaloshinskii-Moriya interaction,"The nonreciprocal propagation of spin waves in an ultrathin Pt/Co/Ni film has
+been measured by Brillouin light scattering. The frequency nonreciprocity, due
+to the interfacial Dzyaloshinskii-Moriya interaction (DMI), has a sinusoidal
+dependence on the in-plane angle between the magnon wavevector and the applied
+magnetic field. The results, which are in good agreement with analytical
+predictions reported earlier, yield a value of the DMI constant which is the
+same as that obtained previously from a study of the magnon dispersion
+relations. We have demonstrated that our magnon-dynamics based method can
+experimentally ascertain the DMI constant of multilayer thin films.",1506.01134v1
+2015-09-14,Spectral characteristics of time resolved magnonic spin Seebeck effect,"Spin Seebeck effect (SSE) holds promise for new spintronic devices with
+low-energy consumption. The underlying physics, essential for a further
+progress, is yet to be fully clarified. This study of the time resolved
+longitudinal SSE in the magnetic insulator yttrium iron garnet (YIG) concludes
+that a substantial contribution to the spin current stems from small
+wave-vector subthermal exchange magnons. Our finding is in line with the recent
+experiment by S. R. Boona and J. P. Heremans, Phys. Rev. B 90, 064421 (2014).
+Technically, the spin-current dynamics is treated based on the
+Landau-Lifshitz-Gilbert (LLG) equation also including magnons back-action on
+thermal bath, while the formation of the time dependent thermal gradient is
+described self-consistently via the heat equation coupled to the magnetization
+dynamics",1509.04018v1
+2015-09-18,Theory and experiment on cavity magnon polariton in the 1D configuration,"We have theoretically and experimentally investigated the dispersion of the
+cavity-magnon-polariton (CMP) in a 1D configuration, created by inserting a low
+damping magnetic insulator into a high-quality 1D microwave cavity. By
+simplifying the full-wave simulation based on the transfer matrix approach in
+the long wavelength limit, an analytic approximation of the CMP dispersion has
+been obtained. The resultant coupling strength of the CMP shows different
+dependence on the sample thickness as well as the permittivity of the sample,
+determined by the parity of the cavity modes. These scaling effects of the
+cavity and material parameters are confirmed by experimental data. Our work
+provide a detailed understanding of the 1D CMP, which could help to engineer
+coupled magnon-photon system.",1509.05804v1
+2015-10-07,Cavity optomagnonics with spin-orbit coupled photons,"We experimentally implement a system of cavity optomagnonics, where a sphere
+of ferromagnetic material supports whispering gallery modes (WGMs) for photons
+and the magnetostatic mode for magnons. We observe pronounced nonreciprocity
+and asymmetry in the sideband signals generated by the magnon-induced Brillouin
+scattering of light. The spin-orbit coupled nature of the WGM photons, their
+geometric birefringence and the time-reversal symmetry breaking in the magnon
+dynamics impose the angular-momentum selection rules in the scattering process
+and account for the observed phenomena. The unique features of the system may
+find interesting applications at the crossroad between quantum optics and
+spintronics.",1510.01837v4
+2015-10-13,Optomagnonic whispering gallery microresonators,"Magnons in ferrimagnetic insulators such as yttrium iron garnet (YIG) have
+recently emerged as promising candidates for coherent information processing in
+microwave circuits. Here we demonstrate optical whispering gallery modes of a
+YIG sphere interrogated by a silicon nitride photonic waveguide, with quality
+factors approaching $10^6$ in the telecom c-band after surface treatments.
+Moreover, in contrast to conventional Faraday setup, this implementation allows
+input photon polarized colinearly to the magnetization to be scattered to a
+sideband mode of orthogonal polarization. This Brillouin scattering process is
+enhanced through triply resonant magnon, pump and signal photon modes - all of
+whispering gallery nature - within an ""optomagnonic cavity"". Our results show
+the potential use of magnons for mediating microwave-to-optical carrier
+conversion.",1510.03545v1
+2015-11-12,Thermally-driven spin torques in layered magnetic insulators,"Thermally-driven spin-transfer torques have recently been reported in
+electrically insulating ferromagnet$|$normal-metal heterostructures. In this
+paper, we propose two physically distinct mechanisms for such torques. The
+first is a local effect: out-of-equilibrium, thermally-activated magnons in the
+ferromagnet, driven by a spin Seebeck effect, exert a torque on the
+magnetization via magnon-magnon scattering with coherent dynamics. The second
+is a nonlocal effect which requires an additional magnetic layer to provide the
+symmetry breaking necessary to realize a thermal torque. The simplest structure
+in which to induce a nonlocal thermal torque is a spin valve composed of two
+insulating magnets separated by a normal metal spacer; there, a thermal flux
+generates a pure spin current through the spin valve, which results in a torque
+when the magnetizations of the layers are misaligned.",1511.04104v1
+2016-01-04,Unidirectional terahertz light absorption in the pyroelectric ferrimagnet CaBaCo4O7,"Spin excitations were studied by absorption spectroscopy in CaBaCo4O7 which
+is a type-I multiferroic compound with the largest magnetic-order induced
+ferroelectric polarization ({\Delta}P=17mC/m2) reported, so far. We observed
+two optical magnon branches: a solely electric dipole allowed one and a mixed
+magnetoelectric resonance. The entangled magnetization and polarization
+dynamics of the magnetoelectric resonance gives rise to unidirectional light
+absorption, i.e. that magnon mode absorbs the electromagnetic radiation for one
+propagation direction but not for the opposite direction. Our systematic study
+of the magnetic field and temperature dependence of magnon modes provides
+information about the energies and symmetries of spin excitations, which is
+required to develop a microscopic spin model of CaBaCo4O7.",1601.00444v1
+2016-01-21,Spin pumping in strongly coupled magnon-photon systems,"We experimentally investigate magnon-polaritons, arising in ferrimagnetic
+resonance experiments in a microwave cavity with a tuneable quality factor. To
+his end, we simultaneously measure the electrically detected spin pumping
+signal and microwave reflection (the ferrimagnetic resonance signal) of a
+yttrium iron garnet (YIG) / platinum (Pt) bilayer in the microwave cavity. The
+coupling strength of the fundamental magnetic resonance mode and the cavity is
+determined from the microwave reflection data. All features of the magnetic
+resonance spectra predicted by first principle calculations and an input-output
+formalism agree with our experimental observations. By changing the decay rate
+of the cavity at constant magnon-photon coupling rate, we experimentally tune
+in and out of the strong coupling regime and successfully model the
+corresponding change of the spin pumping signal. Furthermore, we observe the
+coupling and spin pumping of several spin wave modes and provide a quantitative
+analysis of their coupling rates to the cavity.",1601.05681v1
+2016-01-26,LLM Magnons,"We consider excitations of LLM geometries described by coloring the LLM plane
+with concentric black rings. Certain closed string excitations are localized at
+the edges of these rings. The string theory predictions for the energies of
+magnon excitations of these strings depends on the radii of the edges of the
+rings. In this article we construct the operators dual to these closed string
+excitations and show how to reproduce the string theory predictions for magnon
+energies by computing one loop anomalous dimensions. These operators are linear
+combinations of restricted Schur polynomials. The distinction between what is
+the background and what is the excitation is accomplished in the choice of the
+subgroup and the representations used to construct the operator.",1601.06914v1
+2016-01-27,Observation of magnon-mediated current drag in Pt/yttrium iron garnet/Pt(Ta) trilayers,"Pure spin current, a flow of spin angular momentum without flow of any
+companying net charge, is generated in two common ways. One makes use of the
+spin Hall effect in normal metals (NM) with strong spin-orbit coupling, such as
+Pt or Ta. The other utilizes the collective motion of magnetic moments or spin
+waves with the quasi-particle excitations called magnons. A popular material
+for the latter is yttrium iron garnet, a magnetic insulator (MI). Here we
+demonstrate in NM/MI/NM trilayers that these two types of spin currents are
+interconvertible across the interfaces, predicated as the magnon-mediated
+current drag phenomenon. The transmitted signal scales linearly with the
+driving current without a threshold and follows the power-law with n ranging
+from 1.5 to 2.5. Our results indicate that the NM/MI/NM trilayer structure can
+serve as a scalable pure spin current valve device which is an essential
+ingredient in spintronics.",1601.07429v1
+2016-02-11,Probing ultrafast spin dynamics in the antiferromagnetic multiferroic HoMnO$_3$ through a magnon resonance,"We demonstrate a new approach for directly measuring the ultrafast energy
+transfer between elec- trons and magnons, enabling us to track spin dynamics in
+an antiferromagnet (AFM). In multiferroic HoMnO3, optical photoexcitation
+creates hot electrons, after which changes in the spin order are probed with a
+THz pulse tuned to a magnon resonance. This reveals a photoinduced
+transparency, which builds up over several picoseconds as the spins heat up due
+to energy transfer from hot elec- trons via phonons. This spin-lattice
+thermalization time is ?10 times faster than that of typical ferromagnetic (FM)
+manganites. We qualitatively explain the fundamental differences in
+spin-lattice thermalization between FM and AFM systems and apply a Boltzmann
+equation model for treating AFMs. Our work gives new insight into spin-lattice
+thermalization in AFMs and demonstrates a new approach for directly monitoring
+the ultrafast dynamics of spin order in these systems.",1602.03872v2
+2016-04-25,Magnon based logic in a multi-terminal YIG/Pt nanostructure,"Boolean logic is the foundation of modern digital information processing.
+Recently, there has been a growing interest in phenomena based on pure spin
+currents, which allow to move from charge to spin based logic gates. We study a
+proof-of-principle logic device based on the ferrimagnetic insulator Yttrium
+Iron Garnet (YIG), with Pt strips acting as injectors and detectors for
+nonequilibrium magnons. We experimentally observe incoherent superposition of
+magnons generated by different injectors. This allows to implement a fully
+functional majority gate, enabling multiple logic operations (AND and OR) in
+one and the same device. Clocking frequencies of the order of several GHz and
+straightforward down-scaling make our device promising for applications.",1604.07262v1
+2016-06-06,Spin Nernst Effect of Magnons in Collinear Antiferromagnets,"In a collinear antiferromagnet with easy-axis anisotropy, symmetry guarantees
+that the spin wave modes are doubly degenerate. The two modes carry opposite
+spin angular momentum and exhibit opposite chirality. Using a honeycomb
+antiferromagnet in the presence of the Dzyaloshinskii-Moriya interaction, we
+show that a longitudinal temperature gradient can drive the two modes to
+opposite transverse directions, realizing a spin Nernst effect of magnons with
+vanishing thermal Hall current. We find that magnons around the {\Gamma}-point
+and the K-point contribute oppositely to the transverse spin transport, and
+their competition leads to a sign change of the spin Nernst coefficient at
+finite temperature. Possible material candidates are discussed.",1606.01952v3
+2016-06-09,"Competing effects at Pt/YIG interfaces: spin Hall magnetoresistance, magnon excitations and magnetic frustration","We study the spin Hall magnetoresistance (SMR) and the magnon spin transport
+(MST) in Pt/Y3Fe5O12(YIG)-based devices with intentionally modified interfaces.
+Our measurements show that the surface treatment of the YIG film results in a
+slight enhancement of the spin-mixing conductance and an extraordinary increase
+in the efficiency of the spin-to-magnon excitations at room temperature. The
+surface of the YIG film develops a surface magnetic frustration at low
+temperatures, causing a sign change of the SMR and a dramatic suppression of
+the MST. Our results evidence that SMR and MST could be used to explore
+magnetic properties of surfaces, including those with complex magnetic
+textures, and stress the critical importance of the non-magnetic/ferromagnetic
+interface properties in the performance of the resulting spintronic devices.",1606.02968v2
+2016-07-08,Magnon Polarons in the Spin Seebeck Effect,"Sharp structures in magnetic field-dependent spin Seebeck effect (SSE)
+voltages of Pt/Y$_{3}$Fe$_{5}$O$_{12}$ (YIG) at low temperatures are attributed
+to the magnon-phonon interaction. Experimental results are well reproduced by a
+Boltzmann theory that includes the magnetoelastic coupling (MEC). The SSE
+anomalies coincide with magnetic fields tuned to the threshold of
+magnon-polaron formation. The effect gives insight into the relative quality of
+the lattice and magnetization dynamics.",1607.02312v2
+2016-07-25,Damping of parametrically excited magnons in the presence of the longitudinal spin Seebeck effect,"The impact of the longitudinal spin Seebeck effect (LSSE) on the magnon
+damping in magnetic-insulator/nonmagnetic-metal bilayers was recently discussed
+in several reports. However, results of those experiments can be blurred by
+multimode excitation within the measured linewidth. In order to avoid possible
+intermodal interference, we investigated the damping of a single magnon group
+in a platinum covered Yttrium Iron Garnet (YIG) film by measurement of the
+threshold of its parametric excitation. Both dipolar and exchange spin-wave
+branches were probed. It turned out that the LSSE-related modification of
+spin-wave damping in a micrometer-thick YIG film is too weak to be observed in
+the entire range of experimentally accessible wavevectors. At the same time,
+the change in the mean temperature of the YIG layer, which can appear by
+applying a temperature gradient, strongly modifies the damping value.",1607.07274v1
+2016-07-27,Field-induced decays in $XXZ$ triangular-lattice antiferromagnets,"We investigate field-induced transformations in the dynamical response of the
+$XXZ$ model on the triangular lattice that are associated with the anharmonic
+magnon coupling and decay phenomena. A set of concrete theoretical predictions
+is made for a close physical realization of the spin-1/2 $XXZ$ model,
+Ba$_3$CoSb$_2$O$_9$. We demonstrate that dramatic modifications in magnon
+spectrum must occur in low out-of-plane fields that are easily achievable for
+this material. The hallmark of the effect is a coexistence of the clearly
+distinct well-defined magnon excitations with significantly broadened ones in
+different regions of the ${\bf k}-\omega$ space. The field-induced decays are
+generic for this class of models and become more prominent at larger
+anisotropies and in higher fields.",1607.08238v2
+2017-02-13,Collective spin excitations of helices and magnetic skyrmions: review and perspectives of magnonics in non-centrosymmetric magnets,"Magnetic materials hosting correlated electrons play an important role for
+information technology and signal processing. The currently used ferro-, ferri-
+and antiferromagnetic materials provide microscopic moments (spins) that are
+mainly collinear. Recently more complex spin structures such as spin helices
+and cycloids have regained a lot of interest. The interest has been initiated
+by the discovery of the skyrmion lattice phase in non-centrosymmetric helical
+magnets. In this review we address how spin helices and skyrmion lattices
+enrich the microwave characteristics of magnetic materials. When discussing
+perspectives for microwave electronics and magnonics we focus particularly on
+insulating materials as they avoid eddy current losses, offer low spin-wave
+damping, and might allow for electric field control of collective spin
+excitations. Thereby, they further fuel the vision of magnonics operated at low
+energy consumption.",1702.03668v1
+2017-02-22,Domain wall motion by localized temperature gradients,"Magnetic domain wall (DW) motion induced by a localized Gaussian temperature
+profile is studied in a Permalloy nanostrip within the framework of the
+stochastic Landau-Lifshitz-Bloch equation. The different contributions to
+thermally induced DW motion, entropic torque and magnonic spin transfer torque,
+are isolated and compared. The analysis of magnonic spin transfer torque
+includes a description of thermally excited magnons in the sample. A third
+driving force due to a thermally induced dipolar field is found and described.
+Finally, thermally induced DW motion is studied under realistic conditions by
+taking into account the edge roughness. The results give quantitative insights
+into the different mechanisms responsible for domain wall motion in temperature
+gradients and allow for comparison with experimental results.",1702.06725v1
+2017-02-22,Is spin superfluidity possible in YIG films?,"Recently it was suggested that stationary spin supercurrents (spin
+superfluidity) are possible in the magnon condensate observed in
+yttrium-iron-garnet (YIG) magnetic films under strong external pumping. Here we
+analyze this suggestion. From topology of the equilibrium order parameter in
+YIG one must not expect energetic barriers making spin supercurrents
+metastable. However some small barriers of dynamical origin are possible
+nevertheless. The critical phase gradient (analog of the Landau critical
+velocity in superfluids) is proportional to intensity of the coherent spin wave
+(number of condensed magnons). The conclusion is that although spin
+superfluidity in YIG films is possible in principle, the published claim of its
+observation is not justified.
+  The analysis revealed that the widely accepted spin-wave spectrum in YIG
+films with magnetostatic and exchange interaction required revision. This led
+to revision of non-linear corrections, which determine stability of the magnon
+condensate with and without spin supercurrents.",1702.06994v2
+2017-02-27,Breakdown of Magnons in a Strongly Spin-Orbital Coupled Magnet,"The description of quantized collective excitations stands as a landmark in
+the quantum theory of condensed matter. A prominent example occurs in
+conventional magnets, which support bosonic magnons - quantized harmonic
+fluctuations of the ordered spins. In striking contrast is the recent discovery
+that strongly spin-orbital coupled magnets, such as $\alpha$-RuCl$_3$, may
+display a broad excitation continuum inconsistent with conventional magnons.
+Due to incomplete knowledge of the underlying interactions unraveling the
+nature of this continuum remains challenging. The most discussed explanation
+refers to a coherent continuum of fractional excitations analogous to the
+celebrated Kitaev spin liquid. Here we present a more general scenario. We
+propose that the observed continuum represents incoherent excitations
+originating from strong magnetic anharmoniticity that naturally occurs in such
+materials. This scenario fully explains the observed inelastic magnetic
+response of $\alpha$-RuCl$_3$ and reveals the presence of nontrivial
+excitations in such materials extending well beyond the Kitaev state.",1702.08466v3
+2017-03-09,Overcoming thermal noise in non-volatile spin wave logic,"Spin waves are propagating disturbances in magnetically ordered materials,
+analogous to lattice waves in solid systems and are often described from a
+quasiparticle point of view as magnons. The attractive advantages of
+Joule-heat-free transmission of information, utilization of the phase of the
+wave as an additional degree of freedom and lower footprint area compared to
+conventional charge-based devices have made spin waves or magnon spintronics a
+promising candidate for beyond-CMOS wave-based computation. However, any
+practical realization of an all-magnon based computing system must undergo the
+essential steps of a careful selection of materials and demonstrate robustness
+with respect to thermal noise or variability. Here, we aim at identifying
+suitable materials and theoretically demonstrate the possibility of achieving
+error-free clocked non-volatile spin wave logic device, even in the presence of
+thermal noise and clock jitter or clock skew.",1703.03460v2
+2017-03-13,Influence of the Dzyaloshinskii-Moriya interaction on the FMR spectrum of magnonic crystals and confined structures,"We study the effect of surface-induced Dzyaloshinskii-Moriya interaction
+(DMI) on the ferromagnetic resonance (FMR) spectrum of thickness-modulated
+one-dimensional magnonic crystals and isolated stripes. The DMI is found to
+substantially increases the intensity of absorption peaks and shifts the
+frequencies of the laterally quantized modes. The role of the DMI is determined
+by analyzing the amplitude and phase distributions of dynamic magnetic
+excitations calculated with frequency- and time-domain calculation methods. We
+propose experimentally realizable magnonic crystals and confined structures
+with multiple FMR absorption peaks. The frequency or magnetic field separation
+between FMR lines is exploited to propose a method for estimation of the DMI
+strength.",1703.04463v1
+2017-03-29,Magnon dispersion in Ca2RuO4: impact of spin-orbit coupling and oxygen moments,"The magnon dispersion of Ca$_2$RuO$_4$ has been studied by polarized and
+unpolarized neutron scattering experiments on crystals containing 0, 1 and 10 %
+of Ti. The entire dispersion of transverse magnons can be well described by a
+conventional spin-wave model with interaction and anisotropy parameters that
+agree with density functional theory calculations. Spin-orbit coupling strongly
+influences the magnetic excitations, which is most visible in large energies of
+the magnetic zone-center modes arising from magnetic anisotropy. We find
+evidence for a low-lying additional mode that exhibits strongest scattering
+intensity near the antiferromagnetic zone center. This extra signal can be
+explained by a sizable magnetic moment of 0.11 Bohr magnetons on the apical
+oxygens parallel to the Ru moment, which is found in the density functional
+theory calculations. The energy and the signal strength of the additional
+branch are well described by taking into account this oxygen moment with weak
+ferromagnetic coupling between Ru and O moments.",1703.10017v1
+2018-04-17,Reprogrammable magnonic band structure of layered Permalloy/Cu/Permalloy nanowires,"Reprogrammability of magnonic band structure in layered
+Permalloy/Cu/Permalloy nanowires is demonstrated to depend on the relative
+orientation of the two layers magnetization. By using Brillouin light
+spectroscopy, we show that when the layers are aligned parallel two dispersive
+modes, with positive and negative group velocity, are observed while when the
+magnetic layers are aligned anti-parallel, only one dispersive mode, with
+positive group velocity, is detected. Our findings are successfully compared
+and interpreted in terms of a microscopic (Hamiltonian-based) method. An
+explanation for the observed behavior can be attributed to mode-mixing (or
+hybridization) effect when the two magnetic layers are aligned anti-parallel.
+This work opens the path to magnetic field-controlled reconfigurable magnonic
+crystals with multi-modal frequency transmission characteristics.",1804.06217v1
+2018-11-08,Calculated magnetic exchange interactions in Dirac magnon material Cu3TeO6,"Recently topological aspects of magnon band structure have attracted much
+interest, and especially, the Dirac magnons in Cu3TeO6 have been observed
+experimentally. In this work, we calculate the magnetic exchange interactions
+J's using the first-principles linear-response approach and find that these J's
+are short-range and negligible for the Cu-Cu atomic pair apart by longer than 7
+Angstrom. Moreover there are only 5 sizable magnetic exchange interactions, and
+according to their signs and strengths, modest magnetic frustration is
+expected. Based on the obtained magnetic exchange couplings, we successfully
+reproduce the experimental spin-wave dispersions. The calculated neutron
+scattering cross section also agrees very well with the experiments. We also
+calculate Dzyaloshinskii-Moriya interactions (DMIs) and estimate the canting
+angle (about 1.3{\deg}) of the magnetic non-collinearity based on the
+competition between DMIs and J's, which is consistent with the experiment. The
+small canting angle agrees with that the current experiments cannot distinguish
+the DMI induced nodal line from a Dirac point in the spin-wave spectrum.
+Finally we analytically prove that the ""sum rule"" conjectured in [Nat. Phys.
+14, 1011 (2018)] holds but only up to the 11th nearest neighbour.",1811.03603v1
+2018-11-14,Tunable space-time crystal in room-temperature magnetodielectrics,"We report the experimental realization of a space-time crystal with tunable
+periodicity in time and space in the magnon Bose-Einstein Condensate (BEC),
+formed in a room-temperature Yttrium Iron Garnet (YIG) film by radio-frequency
+space-homogeneous magnetic field. The magnon BEC is prepared to have a well
+defined frequency and non-zero wavevector. We demonstrate how the crystalline
+""density"" as well as the time and space textures of the resulting crystal may
+be tuned by varying the experimental parameters: external static magnetic
+field, temperature, thickness of the YIG film and power of the radio-frequency
+field. The proposed space-time crystals provide a new dimension for exploring
+dynamical phases of matter and can serve as a model nonlinear Floquet system,
+that brings in touch the rich fields of classical nonlinear waves, magnonics
+and periodically driven systems.",1811.05801v1
+2018-11-15,Criticality of the magnon-bound-state hierarchy for the quantum Ising chain with the long-range interactions,"The quantum Ising chain with the interaction decaying as a power law
+$1/r^{1+\sigma}$ of the distance between spins $r$ was investigated
+numerically. A particular attention was paid to the low-energy spectrum,
+namely, the single-magnon and two-magnon-bound-state masses, $m_{1,2}$,
+respectively, in the ordered phase. It is anticipated that for each $\sigma$,
+the scaled bound-state mass $m_2/m_1$ should take a universal constant
+(critical amplitude ratio) in the vicinity of the critical point. In this
+paper, we calculated the amplitude ratio $m_2/m_1$ with the exact
+diagonalization method, which yields the spectral information such as $m_{1,2}$
+directly. As a result, we found that the scaled mass $m_2/m_1$ exhibits a
+non-monotonic dependence on $\sigma$; that is, the bound state is stabilized by
+an intermediate value of $\sigma$. Such a feature is accordant with a recent
+observation based on the non-perturbative-renormalization-group method.",1811.06241v1
+2018-11-18,Topological thermal Hall effect driven by fluctuation of spin chirality in frustrated antiferromagnets,"By revealing an underlying relation between the Dzyaloshinskii-Moriya
+interaction (DMI) and the scalar spin chirality, we develop the theory of
+magnon thermal Hall effects in antiferromagnetic systems. The dynamic
+fluctuation of the scalar chirality is shown to directly respond to the
+nontrivial topology of magnon bands. In materials such as the jarosites
+compounds KFe$_3$(OH)$_6$(SO$_4$)$_2$ and veseignite BaCu$_3$V$_2$O$_8$(OH)$_2$
+in the presence of in-plane DMI, the time-reversal symmetry can be broken by
+the fluctuations of scalar chirality even in the case of coplanar
+$\mathbf{q}=0$ magnetic configuration. The spin-wave Hamiltonian is influenced
+by a fictitious magnetic flux determined by the in-plane DMI. Topological
+magnon bands and corresponding nonzero Chern numbers are presented without the
+need of a canted non-coplanar magnetic ordering. The canting angle dependence
+of thermal Hall conductivity is discussed in detail as well. These results
+offer a clear principle of chirality-driven topological effects in
+antiferromagnetically coupled systems.",1811.07319v3
+2010-05-04,S-matrix for magnons in the D1-D5 system,"We show that integrability and symmetries of the near horizon geometry of the
+D1-D5 system determine the S-matrix for the scattering of magnons with
+polarizations in AdS3 $\times$ S3 completely up to a phase. Using
+semi-classical methods we evaluate the phase to the leading and to the one-loop
+approximation in the strong coupling expansion. We then show that the phase
+obeys the unitarity constraint implied by the crossing relations to the
+one-loop order. We also verify that the dispersion relation obeyed by these
+magnons is one-loop exact at strong coupling which is consistent with their BPS
+nature.",1005.0501v4
+2014-03-11,Overcoming damping in spin wave propagation: A continuous excitation approach to determine time-dependent dispersion diagrams in 2D magnonic crystals,"We propose an alternative micromagnetic approach to determine the spin wave
+dispersion relations in magnonic structures. Characteristic of the method is
+that a limited area of the system is continuously excited with a spatially
+uniform oscillating field, tuned at a given frequency. After a transitory time,
+the regime magnetization dynamics is collected and a spatial Fourier analysis
+on it determines the frequency vs wave vector relation. Combining several
+simulations in any predetermined range of frequencies, at any resolution, we
+investigate the dispersion relations for different kinds of magnonic crystals:
+a dot array, an antidot array, and a bicomponent film. Especially compared to
+traditional pulse-excitation methods this technique has many advantages. First,
+the excitation power is concentrated at a single frequency, allowing the
+corresponding spin waves to propagate with very low attenuation, resulting in a
+higher k-space resolution. Second, the model allows to include very large wave
+vector components, necessary to describe the high-frequency response of
+non-quantized spin waves in quasi-continuous systems. Finally, we address some
+possible experimental opportunities with respect to excitation/detection
+techniques over large distances and the observation of the odd/even symmetry of
+spin waves using Brillouin light scattering.",1403.2549v1
+2017-01-10,Temperature dependence of the non-local spin Seebeck effect in YIG/Pt nanostructures,"We study the transport of thermally excited non-equilibrium magnons through
+the ferrimagnetic insulator YIG using two electrically isolated Pt strips as
+injector and detector. The diffusing magnons induce a non- local inverse spin
+Hall voltage in the detector corresponding to the so-called non-local spin
+Seebeck effect (SSE). We measure the non-local SSE as a function of temperature
+and strip separation. In experiments at room temperature we observe a sign
+change of the non-local SSE voltage at a characteristic strip separation d0, in
+agreement with previous investigations. At lower temperatures however, we find
+a strong temperature dependence of d0. This suggests that both the angular
+momentum transfer across the YIG/Pt interface as well as the transport
+mechanism of the magnons in YIG as a function of temperature must be taken into
+account to describe the non-local spin Seebeck effect.",1701.02635v1
+2017-01-14,Paving Spin-Wave Fibers in Magnonic Nanocircuits Using Spin-Orbit Torque,"Recent studies have revealed that domain walls in magnetic nanostructures can
+serve as compact, energy-efficient spin-wave waveguides for building magnonic
+devices that are considered promising candidates for overcoming the challenges
+and bottlenecks of today's CMOS technologies. However, imprinting long
+strip-domain walls into magnetic nanowires remains a challenge, especially in
+curved geometries. Here, through micromagnetic simulations, we present a method
+for writing strip-domain walls into curved magnetic nanowires using spin-orbit
+torque. We employ Y-shaped magnetic nanostructures as well as an S-shaped
+magnetic nanowire to demonstrate the injection process. In addition, we verify
+that the Y-shaped nanostructures that incorporate strip-domain walls can
+function as superior spin-wave multiplexers, and that spin-wave propagation
+along each conduit can be controllably manipulated. This spin-wave multiplexer
+based on strip-domain walls is expected to become a key signal-processing
+component in magnon spintronics.",1701.03886v1
+2017-01-31,Tunable magnon-photon coupling in a compensating ferrimagnet - from weak to strong coupling,"We experimentally study the magnon-photon coupling in a system consitsing of
+the compensating ferrimagnet gadolinium iron garnet (GdIG) and a
+three-dimensional microwave cavity. The temperature is varied in order to tune
+the GdIG magnetization and to observe the transition from the weak coupling
+regime to the strong coupling regime. By measuring and modelling the complex
+reflection parameter of the system the effective coupling rate g eff and the
+magnetization M eff of the sample are extracted. Comparing g eff with the
+magnon and the cavity decay rate we conclude that the strong coupling regime is
+easily accessible using GdIG. We show that the effective coupling strength
+follows the predicted square root dependence on the magnetization.",1701.08969v3
+2018-05-04,Effective damping enhancement in noncollinear spin structures,"Damping mechanisms in magnetic systems determine the lifetime, diffusion and
+transport properties of magnons, domain walls, magnetic vortices, and
+skyrmions. Based on the phenomenological Landau-Lifshitz-Gilbert equation, here
+the effective damping parameter in noncollinear magnetic systems is determined
+describing the linewidth in resonance experiments or the decay parameter in
+time-resolved measurements. It is shown how the effective damping can be
+calculated from the elliptic polarization of magnons, arising due to the
+noncollinear spin arrangement. It is concluded that the effective damping is
+larger than the Gilbert damping, and it may significantly differ between
+excitation modes. Numerical results for the effective damping are presented for
+the localized magnons in isolated skyrmions, with parameters based on the
+Pd/Fe/Ir(111) model-type system.",1805.01815v2
+2018-05-21,Inverse Edelstein effect induced by magnon - phonon coupling,"We demonstrate a spin to charge current conversion via magnon-phonon coupling
+and inverse Edelstein effect on the hybrid device Ni/Cu(Ag)/Bi$_{2}$O$_{3}$.
+The generation of spin current ($J_{s}\approx 10^{8}A/m^{2}$) due to magnon -
+phonon coupling reveals the viability of acoustic spin pumping as mechanism for
+the development of spintronic devices. A full in-plane magnetic field angle
+dependence of the power absorption and a combination of longitudinal and
+transverse voltage detection reveals the symmetric and asymmetric components of
+the inverse Edelstein effect voltage induced by Rayleigh type surface acoustic
+waves. While the symmetric components are well studied, asymmetric components
+are widely unexplored. We assign the asymmetric contributions to the
+interference between longitudinal and shear waves and an anisotropic charge
+distribution in our hybrid device.",1805.07900v1
+2018-05-27,Dynamical structure factors in the nematic phase of frustrated ferromagnetic spin chains,"Frustrated spin systems can show phases with spontaneous breaking of
+spin-rotational symmetry without the formation of local magnetic order. We
+study the dynamic response of the spin-nematic phase of one-dimensional
+spin-1/2 systems, characterized by slow large-distance decay of quadrupolar
+correlations, by numerically computing one-spin and two-spin dynamical
+structure factors at zero temperature using time-dependent density matrix
+renormalization group methods. We interpret the results in terms of an
+effective theory of gapped magnon excitations interacting with a
+quasi-condensate of bound magnon pairs. This employs an extension of the
+well-known Tomonaga-Luttinger liquid theory which includes the magnon states as
+a mobile impurity. A good qualitative understanding of the characteristic
+thresholds and their intensity in the structure factors is obtained this way.
+Our results are useful in the interpretation of inelastic neutron scattering
+and resonant inelastic x-ray scattering experiments.",1805.10612v2
+2008-07-25,Frustration-induced quantum phase transitions in a quasi-one-dimensional ferrimagnet: Hard-core boson map and the Ton ks-Girardeau limit,"We provide evidence of a superfluid-insulator transition (SIT) of magnons in
+a quasi-one-dimensional quantum ferrimagnet with {\it isotropic} competing
+antiferromagnetic spin interactions. This SIT occurs between two distinct
+ferrimagnetic phases due to the frustration-induced closing of the gap to a
+magnon excitation. It thus causes a coherent superposition of singlet and
+triplet states at lattice unit cells and a power-law decay on the staggered
+spin correlation function along the transverse direction to the spontaneous
+magnetization. A hard-core boson map suggests that asymptotically close to the
+SIT the magnons attain the Tonks-Girardeau limit. The quantized nature of the
+condensed singlets is observed before a first-order transition to a singlet
+magnetic spiral phase accompanied by critical antiferromagnetic ordering. In
+the limit of strong frustration, the system undergoes a decoupling transition
+to an isolated gapped two-leg ladder and a critical single linear chain.",0807.4153v1
+2011-11-10,Electronic Pumping of Quasiequilibrium Bose-Einstein Condensed Magnons,"We theoretically investigate spin transfer between a system of
+quasiequilibrated Bose-Einstein condensed magnons in an insulator in direct
+contact with a conductor. While charge transfer is prohibited across the
+interface, spin transport arises from the exchange coupling between insulator
+and conductor spins. In normal insulator phase, spin transport is governed
+solely by the presence of thermal and spin-diffusive gradients; the presence of
+Bose-Einstein condensation (BEC), meanwhile, gives rise to a
+temperature-independent condensate spin current. Depending on the thermodynamic
+bias of the system, spin may flow in either direction across the interface,
+engendering the possibility of a dynamical phase transition of magnons. We
+discuss experimental feasibility of observing a BEC steady state (fomented by a
+spin Seebeck effect), which is contrasted to the more familiar spin-transfer
+induced classical instabilities.",1111.2382v2
+2013-09-09,Sub-microsecond fast temporal evolution of the spin Seebeck effect,"We present temporal evolution of the spin Seebeck effect in a YIG|Pt bilayer
+system. Our findings reveal that this effect is a sub-microseconds fast
+phenomenon governed by the temperature gradient and the thermal magnons
+diffusion in the magnetic materials. A comparison of experimental results with
+the thermal-driven magnon-diffusion model shows that the temporal behavior of
+this effect depends on the time development of the temperature gradient in the
+vicinity of the YIG|Pt interface. The effective thermal-magnon diffusion length
+for YIG|Pt systems is estimated to be around 700nm.",1309.2164v1
+2014-06-28,Magnetic excitation spectrum of LuFe2O4 measured with inelastic neutron scattering,"We report neutron inelastic scattering measurements and analysis of the
+spectrum of magnons propagating within the Fe2O4 bilayers of LuFe2O4. The
+observed spectrum is consistent with six magnetic modes and a single prominent
+gap, which is compatible with a single bilayer magnetic unit cell containing
+six spins. We model the magnon dispersion by linear spin-wave theory and find
+very good agreement with the domain-averaged spectrum of a spin-charge bilayer
+superstructure comprising one Fe3+ -rich monolayer and one Fe2+ -rich
+monolayer. These findings indicate the existence of polar bilayers in LuFe2O4,
+contrary to recent studies that advocate a charge-segregated non-polar bilayer
+model. Weak scattering observed below the magnon gap suggests that a fraction
+of the bilayers contain other combinations of charged monolayers not included
+in the model. Refined values for the dominant exchange interactions are
+reported.",1406.7418v1
+2016-05-25,Chirality-induced magnon transport in AA-stacked bilayer honeycomb chiral magnets,"In this Letter, we study the magnetic transport in AA-stacked bilayer
+honeycomb chiral magnets coupled either ferromagnetically or
+antiferromagnetically. For both couplings, we observe chirality-induced gaps,
+chiral protected edge states, magnon Hall and magnon spin Nernst effects of
+magnetic spin excitations. For ferromagnetically coupled layers, thermal Hall
+and spin Nernst conductivities do not change sign as function of magnetic field
+or temperature similar to single-layer honeycomb ferromagnetic insulator. In
+contrast, for antiferromagnetically coupled layers, we observe a sign change in
+the thermal Hall and spin Nernst conductivities as the magnetic field is
+reversed. We discuss possible experimental accessible honeycomb bilayer quantum
+materials in which these effects can be observed.",1605.07971v5
+2017-06-05,Terahertz-driven magnetism dynamics in the orthoferrite DyFeO3,"Terahertz driven magnetization dynamics are explored in the orthoferrite
+DyFeO3. A high-field, single cycle THz pulse is used to excite magnon modes in
+the crystal together with other resonances. Both quasi-ferromagnetic and
+quasi-antiferromagnetic magnon modes are excited and appear in time-resolved
+measurements of the Faraday rotation. Other modes are also observed in the
+measurements of the time-resolved linear birefringence. Analysis of the
+excitation process reveals that despite larger than expected electro-optical
+susceptibility it is mainly the THz magnetic field that couples to the
+quasi-ferromagnetic and quasi-antiferromagnetic magnon branches.",1706.01545v1
+2017-06-06,Antiferromagnetic Domain Wall as Spin Wave Polarizer and Retarder,"As a collective quasiparticle excitation of the magnetic order in magnetic
+materials, spin wave, or magnon when quantized, can propagate in both
+conducting and insulating materials. Like the manipulation of its optical
+counterpart, the ability to manipulate spin wave polarization is not only
+important but also fundamental for magnonics. With only one type of magnetic
+lattice, ferromagnets can only accommodate the right-handed circularly
+polarized spin wave modes, which leaves no freedom for polarization
+manipulation. In contrast, antiferromagnets, with two opposite magnetic
+sublattices, have both left and right circular polarizations, and all linear
+and elliptical polarizations. Here we demonstrate theoretically and confirm by
+micromagnetic simulations that, in the presence of Dzyaloshinskii-Moriya
+interaction, an antiferromagnetic domain wall acts naturally as a spin wave
+polarizer or a spin wave retarder (waveplate). Our findings provide extremely
+simple yet flexible routes toward magnonic information processing by harnessing
+the polarization degree of freedom of spin wave.",1706.01617v1
+2017-06-10,Mapping the magnonic landscape in patterned magnetic structures,"We report the development of a hybrid numerical / analytical model capable of
+mapping the spatially-varying distributions of the local ferromagnetic
+resonance (FMR) frequency and dynamic magnetic susceptibility in a wide class
+of patterned and compositionally modulated magnetic structures. Starting from
+the numerically simulated static micromagnetic state, the magnetization is
+deliberately deflected orthogonally to its equilibrium orientation, and the
+magnetic fields generated in response to this deflection are evaluated using
+micromagnetic software. This allows us to calculate the elements of the
+effective demagnetizing tensor, which are then used within a linear analytical
+formalism to map the local FMR frequency and dynamic magnetic susceptibility.
+To illustrate the typical results that one can obtain using this model, we
+analyze three micromagnetic systems boasting non-uniformity in either one or
+two dimensions, and successfully explain the spin-wave emission observed in
+each case, demonstrating the ubiquitous nature of the Schl\""omann excitation
+mechanism underpinning the observations. Finally, the developed model of local
+FMR frequency could be used to explain how spin waves could be confined and
+steered using magnetic non-uniformities of various origins, rendering it a
+powerful tool for the mapping of the graded magnonic index in magnonics.",1706.03212v1
+2017-06-19,Orbiton-magnon interplay in the spin-orbital polarons of KCuF3 and LaMnO3,"We present a quasi-analytical solution of a spin-orbital model of KCuF$_{3}$,
+using the variational method for Green's functions. By analyzing the spectra
+for different partial bosonic compositions as well as the full solution, we
+show that hole propagation needs both orbiton and magnon excitations to
+develop, but the orbitons dominate the picture. We further elucidate the role
+of the different bosons by analyzing the self-energies for simplified models,
+establishing that because of the nature of the spin-orbital ground state,
+magnons alone do not produce a full quasiparticle band, in contrast to
+orbitons. Finally, using the electron-hole transformation between the $e_g$
+states of KCuF$_3$ and LaMnO$_3$ we suggest the qualitative scenario for
+photoemission experiments in LaMnO$_3$.",1706.06071v1
+2017-06-27,Evidence for the role of the magnon energy relaxation length in the Spin Seebeck Effect,"Temperature-dependent spin-Seebeck effect data on Pt|YIG
+(Y$_3$Fe$_5$O$_{12}$)|GGG (Gd$_3$Ga$_5$O$_{12}$) are reported for YIG films of
+various thicknesses. The effect is reported as a spin-Seebeck resistivity
+(SSR), the inverse spin-Hall field divided by the heat flux, to circumvent
+uncertainties about temperature gradients inside the films. The SSR is a
+non-monotonic function of YIG thickness. A diffusive model for magnon transport
+demonstrates how these data give evidence for the existence of two distinct
+length scales in thermal spin transport, a spin diffusion length and a magnon
+energy relaxation length.",1706.09021v2
+2017-06-30,Spin-wave propagation in cubic anisotropic materials,"The information carrier of modern technologies is the electron charge whose
+transport inevitably generates Joule heating. Spin-waves, the collective
+precessional motion of electron spins, do not involve moving charges and thus
+avoid Joule heating. In this respect, magnonic devices in which the information
+is carried by spin-waves attract interest for low-power computing. However
+implementation of magnonic devices for practical use suffers from low spin-wave
+signal and on/off ratio. Here we demonstrate that cubic anisotropic materials
+can enhance spin-wave signals by improving spin-wave amplitude as well as group
+velocity and attenuation length. Furthermore, cubic anisotropic material shows
+an enhanced on/off ratio through a laterally localized edge mode, which closely
+mimics the gate-controlled conducting channel in traditional field-effect
+transistors. These attractive features of cubic anisotropic materials will
+invigorate magnonics research towards wave-based functional devices.",1706.10057v1
+2017-10-06,Spectral Weight of Resonant Inelastic X-Ray Scattering in Doped Cuprates: Effect of Core-Hole Lifetime,"We examine the effect of core-hole lifetime on the spectral weight of
+resonant inelastic x-ray scattering (RIXS) in hole-doped cuprates. We calculate
+the spectral weight by using exact diagonalization technique for a 4x4 doped
+Hubbard lattice and find that spin-flip channel detecting single-magnon
+excitation is less sensitive to the core-hole lifetime while in non-spin-flip
+channel the spectral weight is strongly dependent on the lifetime. In the
+latter, charge and two-magnon excitations predominately contribute to RIXS for
+short and long core-hole lifetimes, respectively. For a realistic value of the
+core-hole lifetime in cuprates, both the charge and two-magnon excitations are
+expected to contribute to non-spin-flip channel in RIXS when the
+incident-photon energy is tuned to the main peak of x-ray absorption spectrum.",1710.02250v1
+2017-10-12,Magnon spin Hall magnetoresistance of a gapped quantum paramagnet,"Motivated by recent experimental work, we consider spin transport between a
+normal metal and a gapped quantum paramagnet. We model the latter as the
+magnonic Mott-insulating phase of an easy-plane ferromagnetic insulator. We
+evaluate the spin current mediated by the interface exchange coupling between
+the ferromagnet and the adjacent normal metal. For the strongly interacting
+magnons that we consider, this spin current gives rise to a spin Hall
+magnetoresistance that strongly depends on the magnitude of the magnetic field,
+rather than its direction. This Letter may motivate electrical detection of the
+phases of quantum magnets and the incorporation of such materials into
+spintronic devices.",1710.04431v2
+2017-12-15,Inplane anisotropy of longitudinal thermal conductivities and weak localization of magnons in a disordered spiral magnet,"We demonstrate the inplane anisotropy of longitudinal thermal conductivities
+and the weak localization of magnons in a disordered screw-type spiral magnet
+on a square lattice. We consider a disordered spin system, described by a spin
+Hamiltonian for the antiferromagnetic Heisenberg interaction and the
+Dzyaloshinsky-Moriya interaction with the mean-field type potential of
+impurities. We derive longitudinal thermal conductivities for the disordered
+screw-type spiral magnet in the weak-localization regime by using the
+linear-response theory with the linear-spin-wave approximation and performing
+perturbation calculations. We show that the inplane longitudinal thermal
+conductivities are anisotropic due to the Dzyaloshinsky-Moriya interaction.
+This anisotropy may be useful for experimentally estimating the magnitude of a
+ratio of the Dzyaloshinsky-Moriya interaction to the Heisenberg interaction. We
+also show that the main correction term gives a logarithmic suppression with
+the length scale due to the critical back scattering. This suggests that the
+weak localization of magnons is ubiquitous for the disordered two-dimensional
+magnets having global time-reversal symmetry. We finally discuss several
+implications for further research.",1712.05575v2
+2018-09-04,Separation of the two-magnon scattering contribution to damping for the determination of the spin mixing conductance,"We present angle dependent measurements of the damping properties of
+epitaxial Fe layers with MgO, Al and Pt capping layers. Based on the
+preferential distribution of lattice defects following the crystal symmetry, we
+make use of a model of the defect density to separate the contribution of
+two-magnon scattering to the damping from the isotropic contribution
+originating in the spin pumping effect, the viscous Gilbert damping and the
+magnetic proximity effect. The separation of the two-magnon contribution, which
+depends strongly on the defect density, allows for the measurement of a value
+of the effective spin mixing conductance which is closer to the value
+exclusively due to spin pumping. The influence of the defect density for
+bilayers systems due to the different capping layers and to the unavoidable
+spread in defect density from sample to sample is thus removed. This shows the
+potential of studying spin pumping phenomena in fully ordered systems in which
+this separation is possible, contrary to polycrystalline or amorphous metallic
+thin films.",1809.01042v1
+2018-09-17,On the speed of domain walls in thin nanotubes: the transition from the linear to the magnonic regime,"Numerical simulations of domain wall propagation in thin nanotubes when an
+external magnetic field is applied along the nanotube axis have shown an
+unexpected behavior described as a transition from a linear to a magnonic
+regime. As the applied magnetic field increases, the initial regime of linear
+growth of the speed with the field is followed by a sudden change in slope
+accompanied by the emission of spin waves. In this work an analytical formula
+for the speed of the domain wall that explains this behavior is derived by
+means of an asymptotic study of the Landau Lifshitz Gilbert equation for thin
+nanotubes. We show that the dynamics can be reduced to a one dimensional
+hyperbolic reaction diffusion equation, namely, the damped double Sine Gordon
+equation, which shows the transition to the magnonic regime as the domain wall
+speed approaches the speed of spin waves. This equation has been previously
+found to describe domain wall propagation in weak ferromagnets with the
+mobility proportional to the Dzyaloshinskii-Moriya interaction constant, for
+Permalloy nanotubes the mobility is proportional to the nanotube radius.",1809.06278v3
+2019-08-31,High-fidelity magnonic gates for surface spin waves,"We study the propagation of surface spin waves in two wave guides coupled
+through the dipole-dipole interaction. Essential for the observations made here
+is the magneto-electric coupling between the spin waves and the effective
+ferroelectric polarization. This allows an external electric field to act on
+spin waves and to modify the band gaps of magnonic excitations in individual
+layers. By an on/off switching of the electric field and/or varying its
+strength or direction with respect to the equilibrium magnetization, it is
+possible to permit or ban the propagation of the spin waves in selected
+waveguide. We propose experimentally feasible nanoscale device operating as a
+high fidelity surface wave magnonic gate.",1909.00162v1
+2019-09-01,Magnetic field-dependent low-energy magnon dynamics in $α$-RuCl3,"Revealing the spin excitations of complex quantum magnets is key to
+developing a minimal model that explains the underlying magnetic correlations
+in the ground state. We investigate the low-energy magnons in $\alpha$-RuCl$_3$
+by combining time-domain terahertz spectroscopy under an external magnetic
+field and model Hamiltonian calculations. We observe two absorption peaks
+around 2.0 and 2.4 meV, which we attribute to zone-center spin waves. Using
+linear spin-wave theory with only nearest-neighbor terms of the exchange
+couplings, we calculate the antiferromagnetic resonance frequencies and reveal
+their dependence on an external field applied parallel to the nearest-neighbor
+Ru-Ru bonds. We find that the magnon behavior in an applied magnetic field can
+be understood only by including an off-diagonal $\Gamma$ exchange term to the
+minimal Heisenberg-Kitaev model. Such an anisotropic exchange interaction that
+manifests itself as a result of strong spin-orbit coupling can naturally
+account for the observed mixing of the modes at higher fields strengths.",1909.00462v1
+2019-09-06,The interplay of large two-magnon ferromagnetic resonance linewidths and low Gilbert damping in Heusler thin films,"We report on broadband ferromagnetic resonance linewidth measurements
+performed on epitaxial Heusler thin films. A large and anisotropic two-magnon
+scattering linewidth broadening is observed for measurements with the
+magnetization lying in the film plane, while linewidth measurements with the
+magnetization saturated perpendicular to the sample plane reveal low Gilbert
+damping constants of $(1.5\pm0.1)\times 10^{-3}$, $(1.8\pm0.2)\times 10^{-3}$,
+and $<8\times 10^{-4}$ for Co$_2$MnSi/MgO, Co$_2$MnAl/MgO, and Co$_2$FeAl/MgO,
+respectively. The in-plane measurements are fit to a model combining Gilbert
+and two-magnon scattering contributions to the linewidth, revealing a
+characteristic disorder lengthscale of 10-100 nm.",1909.02738v2
+2019-09-12,Magnetostrictively induced stationary entanglement between two microwave fields,"We present a scheme to entangle two microwave fields by using the nonlinear
+magnetostrictive interaction in a ferrimagnet. The magnetostrictive interaction
+enables the coupling between a magnon mode (spin wave) and a mechanical mode in
+the ferrimagnet, and the magnon mode simultaneously couples to two microwave
+cavity fields via the magnetic dipole interaction. The magnon-phonon coupling
+is enhanced by directly driving the ferrimagnet with a strong red-detuned
+microwave field, and the driving photons are scattered onto two sidebands
+induced by the mechanical motion. We show that two cavity fields can be
+prepared in a stationary entangled state if they are respectively resonant with
+two mechanical sidebands. The present scheme illustrates a new mechanism for
+creating entangled states of optical fields, and enables potential applications
+in quantum information science and quantum tasks that require entangled
+microwave fields.",1909.05936v3
+2019-09-17,SU(3) Topology of Magnon-Phonon Hybridization in 2D Antiferromagnets,"Magnon-phonon hybrid excitations are studied theoretically in a
+two-dimensional antiferromagnet with an easy axis normal to the plane. We show
+that two magnon bands and one phonon band are intertwined by the magnetoelastic
+coupling through a nontrivial SU(3) topology, which can be intuitively
+perceived by identifying a skyrmion structure in the momentum space. We develop
+a continuum theory as the long-wavelength approximation to the tight-binding
+model, showing our results are insensitive to lattice details and generally
+applicable to two-dimensional antiferromagnets. The theoretical results can be
+probed by measuring the thermal Hall conductance as a function of the
+temperature and the magnetic field. We envision that the magnetoelastic
+coupling in antiferromagnets can be a promising venue in search of various
+topological excitations, which cannot be found in magnetic or elastic models
+alone.",1909.08031v2
+2020-12-21,Inverse Faraday Effect in an Optomagnonic Waveguide,"Single-mode high-index-contrast waveguides have been ubiquitously exploited
+in optical, microwave, and phononic structures for achieving enhanced
+wave-matter interactions. Although micro-scale optomechanical and
+electro-optical devices have been widely studied, optomagnonic devices remain a
+grand challenge at the microscale. Here, we introduce a planar optomagnonic
+waveguide platform based on a ferrimagnetic insulator that simultaneously
+supports single transverse mode of spin waves (magnons) and highly confined
+optical modes. The co-localization of spin and light waves gives rise to
+enhanced inverse Faraday effect, and as a result, magnons are excited by an
+effective magnetic field generated by interacting optical photons. Moreover,
+the strongly enhanced optomagnonic interaction allows us to observe such effect
+using low-power (milliwatt level) light signals in the continuous-wave form, as
+opposed to high-intensity (megawatt peak power) light pulses that are typically
+required in magnetic bulk materials or thin films. The optically-driven magnons
+are detected electrically with preserved phase coherence, showing the
+feasibility for launching spin waves with low-power continuous optical fields.",2012.11119v2
+2020-12-31,Soft magnon contributions to dielectric constant in spiral magnets with domain walls,"Competing magnetic exchange interactions often result in non-collinear
+magnetic states, such as spin spirals, which break the inversion symmetry and
+induce ferroelectric polarization. The resulting strong interactions between
+magnetic and dielectric degrees of freedom lead to a technologically important
+possibility to control magnetic order by electric fields and to electromagnons,
+magnetic excitations that can be excited by an electric dipole of the
+electromagnetic field. Here we study the effects of chiral domain walls on
+magnetoelectric properties of spiral magnets. We use a quasi-1D model
+Hamiltonian with competing Heisenberg exchange interactions, leading to a spin
+spiral, and Dzyaloshinskii-Moriya interactions, that couple spins and electric
+dipoles and mix magnon and phonon excitations. The results suggest that low
+frequency dielectric anomalies in spiral magnets, such as TbMnO3 and MnWO4, may
+originate from hybrid magnon - polar phonon excitations associated with domain
+walls.",2012.15383v1
+2012-05-03,Beliaev theory of spinor Bose-Einstein condensates,"By generalizing the Green's function approach proposed by Beliaev [1, 2], we
+investigate the effect of quantum depletion on the energy spectra of elementary
+excitations in an F = 1 spinor Bose-Einstein condensate, in particular, of 87Rb
+atoms in an external magnetic field. We find that quantum depletion increases
+the effective mass of magnons in the spin-wave excitations with quadratic
+dispersion relations. The enhancement factor turns out to be the same for both
+ferromagnetic and polar phases, and also independent of the magnitude of the
+external magnetic field. The lifetime of these magnons in a 87Rb spinor BEC is
+shown to be much longer than that of phonons. We propose an experimental setup
+to measure the effective mass of these magnons in a spinor Bose gas by
+exploiting the effect of a nonlinear dispersion relation on the spatial
+expansion of a wave packet of transverse magnetization. This type of
+measurement has practical applications, for example, in precision magnetometry.",1205.0657v1
+2017-09-12,Green's function formalism for spin transport in metal-insulator-metal heterostructures,"We develop a Green's function formalism for spin transport through
+heterostructures that contain metallic leads and insulating ferromagnets. While
+this formalism in principle allows for the inclusion of various magnonic
+interactions, we focus on Gilbert damping. As an application, we consider
+ballistic spin transport by exchange magnons in a metal-insulator-metal
+heterostructure with and without disorder. For the former case, we show that
+the interplay between disorder and Gilbert damping leads to spin current
+fluctuations. For the case without disorder, we obtain the dependence of the
+transmitted spin current on the thickness of the ferromagnet. Moreover, we show
+that the results of the Green's function formalism agree in the clean and
+continuum limit with those obtained from the linearized stochastic
+Landau-Lifshitz-Gilbert equation. The developed Green's function formalism is a
+natural starting point for numerical studies of magnon transport in
+heterostructures that contain normal metals and magnetic insulators.",1709.03775v1
+2017-09-29,Thermodynamic properties of Ba$_2$CoSi$_2$O$_6$Cl$_2$ in strong magnetic field: Realization of flat-band physics in a highly frustrated quantum magnet,"The search for flat-band solid-state realizations is a crucial issue to
+verify or to challenge theoretical predictions for quantum many-body flat-band
+systems. For frustrated quantum magnets flat bands lead to various
+unconventional properties related to the existence of localized many-magnon
+states. The recently synthesized magnetic compound Ba$_2$CoSi$_2$O$_6$Cl$_2$
+seems to be an almost perfect candidate to observe these features in
+experiments. We develop a theory for Ba$_2$CoSi$_2$O$_6$Cl$_2$ by adapting the
+localized-magnon concept to this compound. We first show that our theory
+describes the known experimental facts and then we propose new experimental
+studies to detect a field-driven phase transition related to a
+Wigner-crystal-like ordering of localized magnons at low temperatures.",1709.10356v2
+2018-03-06,Evolution of Magnetic Excitations Across the Metal-Insulator Transition in a Pyrochlore Iridate Eu$_{2}$Ir$_{2}$O$_{7}$,"We report Resonant Inelastic X-ray Scattering (RIXS) study of the magnetic
+excitation spectrum in a highly insulating Eu$_{2}$Ir$_{2}$O$_{7}$ single
+crystal that exhibits a metal-insulator transition at $T_{MI}$ = 111(7) K. A
+propagating magnon mode with 20 meV bandwidth and 28 meV magnon gap is found in
+the excitation spectrum at 7 K, which is expected in the all-in-all-out (AIAO)
+magnetically ordered state. This magnetic excitation exhibits substantial
+softening as temperature is raised towards $T_{MI}$, and turns into highly
+damped excitation in the paramagnetic phase. Remarkably, the softening occurs
+throughout the whole Brillouin zone including the zone boundary. This
+observation is inconsistent with magnon renormalization expected in a local
+moment system, and indicates that the strength of electron correlation in
+Eu$_{2}$Ir$_{2}$O$_{7}$ is only moderate, so that electron itinerancy should be
+taken into account in describing its magnetism.",1803.02248v1
+2018-03-09,Spin transport across antiferromagnets induced by the spin Seebeck effect,"For prospective spintronics devices based on the propagation of pure spin
+currents, antiferromagnets are an interesting class of materials that
+potentially entail a number of advantages as compared to ferromagnets. Here, we
+present a detailed theoretical study of magnonic spin current transport in
+ferromagnetic-antiferromagnetic multilayers by using atomistic spin dynamics
+simulations. The relevant length scales of magnonic spin transport in
+antiferromagnets are determined. We demonstrate the transfer of angular
+momentum from a ferromagnet into an antiferromagnet due to the excitation of
+only one magnon branch in the antiferromagnet. As an experimental system, we
+ascertain the transport across an antiferromagnet in
+YIG$|$Ir$_{20}$Mn$_{80}|$Pt heterostructures. We determine the spin transport
+signals for spin currents generated in the YIG by the spin Seebeck effect and
+compare to measurements of the spin Hall magnetoresistance in the
+heterostructure stack. By means of temperature-dependent and
+thickness-dependent measurements, we deduce conclusions on the spin transport
+mechanism across IrMn and furthermore correlate it to its
+paramagnetic-antiferromagnetic phase transition.",1803.03416v1
+2018-03-11,Skyrmions Driven by Intrinsic Magnons,"We study the dynamics of a skyrmion in a magnetic insulating nanowire in the
+presence of time-dependent oscillating magnetic field gradients. These ac
+fields act as a net driving force on the skyrmion via its own intrinsic
+magnetic excitations. In a microscopic quantum field theory approach we include
+the unavoidable coupling of the external field to the magnons, which gives rise
+to time-dependent dissipation for the skyrmion. We demonstrate that the
+magnetic ac field induces a super-Ohmic to Ohmic crossover behavior for the
+skyrmion dissipation kernels with time-dependent Ohmic terms. The ac driving of
+the magnon bath at resonance results in a unidirectional helical propagation of
+the skyrmion in addition to the otherwise periodic bounded motion.",1803.04001v2
+2018-03-13,Spin wave localization and guiding by magnon band structure engineering in yttrium iron garnet,"In spintronics the propagation of spin-wave excitations in magnetically
+ordered materials can also be used to transport and process information. One of
+the most popular materials in this regard is the ferrimagnetic insulator
+yttrium-iron-garnet due its exceptionally small spin-wave damping parameter.
+While the small relaxation rate allows for large propagation length of magnetic
+excitations, it also leads to non-locality of the magnetic properties. By
+imaging spin waves their band structure is mapped. In doing so wave vector
+selection is shown to suppress dispersion effects to a large extent allowing
+for local measurements of spin relaxation. Moreover we demonstrate even higher
+control of magnon propagation by employing the wave vector selectivity near an
+avoided crossing of different spin-wave modes where the group velocity
+approaches zero. Here local engineering of the dispersion allows constructing
+magnonic waveguides and at the same time reveals the local relaxation
+properties.",1803.04943v3
+2018-03-16,Two-dimensional Dirac nodal loop magnons in collinear antiferromagnets,"We study the nontrivial linear magnon band crossings in the collinear
+antiferromagnets on the two-dimensional (2D) CaVO lattice, also realized in
+some iron-based superconductors such as AFe$_{1.6+x}$Se$_2$ (A = K, Rb, Cs). It
+is shown that the combination of space-inversion and time-reversal symmetry
+($\mathcal{PT}$-symmetry) leads to doubly-degenerate eight magnon branches,
+which cross each other linearly along a one-dimensional loop in the 2D
+Brillouin zone. We show that the Dirac nodal loops (DNLs) are not present in
+the collinear ferromagnet on this lattice. Thus, the current 2D
+antiferromagnetic DNLs are symmetry-protected and they provide a novel platform
+to search for their analogs in 2D electronic antiferromagnetic systems.",1803.06349v3
+2018-03-28,Unidirectional Magnon-Driven Domain Wall Motion Due to the Interfacial Dzyaloshinskii-Moriya Interaction,"We demonstrate a unidirectional motion of a quasiparticle without an explicit
+symmetry breaking along the space-time coordinate of the particle motion. This
+counterintuitive behavior originates from a combined action of two intrinsic
+asymmetries in the other two directions. We realize this idea with the
+magnon-driven motion of a magnetic domain wall in thin films with interfacial
+asymmetry. Contrary to previous studies, the domain wall moves along the same
+direction regardless of the magnon-flow direction. Our general symmetry
+analysis and numerical simulation reveal that the odd order contributions from
+the interfacial asymmetry is unidirectional, which is dominant over
+bidirectional contributions in the realistic regime. We develop a simple
+analytic theory on the unidirectional motion, which provides an insightful
+description of this counterintuitive phenomenon.",1803.10776v3
+2018-06-06,Excitation of magnon spin photocurrents in antiferromagnetic insulators,"In the circular photogalvanic effect, circularly polarized light can produce
+a direct electron photocurrent in metals and the direction of the current
+depends on the polarization. We suggest that an analogous nonlinear effect
+exists for antiferromagnetic insulators wherein the total spin of light and
+spin waves is conserved. In consequence, a spin angular momentum is expected to
+be transfered from photons to magnons so that a circularly polarized
+electromagnetic field will generate a direct magnon spin current. The direction
+of the current is determined by the helicity of the light. We show that this
+resonant effect appears as a second order light-matter interaction. We find
+also a geometric contribution to the spin photocurrent, which appears for
+materials with complex lattice structures and Dzyaloshinskii-Moriya
+interactions.",1806.02442v2
+2018-12-04,Spin transport in a magnetic insulator with zero effective damping,"Applications based on spin currents strongly profit from the control and
+reduction of their effective damping and their transport properties. We here
+experimentally observe magnon mediated transport of spin (angular) momentum
+through a 13.4 nm thin yttrium iron garnet film with full control of the
+magnetic damping via spin-orbit torque. Above a critical spin-orbit torque, the
+fully compensated damping manifests itself as an increase of magnon
+conductivity by almost two orders of magnitude. We compare our results to
+theoretical expectations based on recently predicted current induced magnon
+condensates and discuss other possible origins of the observed critical
+behaviour.",1812.01334v3
+2018-12-12,Laser-Irradiated CrI$_3$: When Chiral Photons Meet Topological Magnons,"Insulating honeycomb ferromagnet CrI$_3$ has recently attracted considerable
+attention due to its potential use for dissipationless spintronics
+applications. Recently, topological spin excitations have been observed
+experimentally in bulk CrI$_3$ by L. Chen, et al. [Phys. Rev. X ${\bf 8}$,
+041028 (2018)] using inelastic neutron scattering. This suggest that bulk
+CrI$_3$ has strong spin-orbit coupling and its spin Hamiltonian should include
+a next-nearest neighbour Dzyaloshinskii-Moriya (DM) interaction. Inspired by
+this experiment, we study non-equilibrium emergent photon-dressed topological
+spin and thermal Hall transports in laser-irradiated CrI$_3$ with and without
+the DM interaction. We show that the spin excitations can be manipulated into
+different topological phases with different Chern numbers. Most importantly, we
+show that the emergent photon-dressed spin and thermal Hall response can be
+switched to different signs. Hence, the generated magnon spin photocurrents can
+be manipulated by the laser field, which is of great interest in ultrafast spin
+current generation and could pave the way for future applications of CrI$_3$ to
+topological opto-spintronics and opto-magnonics.",1812.05101v2
+2019-01-18,Magnonic Weyl states in Cu2OSeO3,"The multiferroic ferrimagnet Cu$_2$OSeO$_3$ with a chiral crystal structure
+attracted a lot of recent attention due to the emergence of magnetic skyrmion
+order in this material. Here, the topological properties of its magnon
+excitations are systematically investigated by linear spin-wave theory and
+inelastic neutron scattering. When considering Heisenberg exchange interactions
+only, two degenerate Weyl magnon nodes with topological charges $\pm$2 are
+observed at high-symmetry points. Each Weyl point splits into two as the
+symmetry of the system is further reduced by including into consideration the
+nearest-neighbor Dzyaloshinsky-Moriya interaction, crucial for obtaining an
+accurate fit to the experimental spin-wave spectrum. The predicted topological
+properties are verified by surface state and Chern number analysis.
+Additionally, we predict that a measurable thermal Hall conductivity can be
+associated with the emergence of the Weyl points, the position of which can be
+tuned by changing the crystal symmetry of the material.",1901.06192v1
+2019-01-22,Control of the magnon-photon level attraction in a planar cavity,"A resistive coupling circuit is used to model the recently discovered
+dissipative coupling in a hybridized cavity photon-magnon system. With this
+model as a basis we have designed a planar cavity in which a controllable
+transition between level attraction and level repulsion can be achieved. This
+behaviour can be quantitatively understood using an LCR circuit model with a
+complex coupling strength. Our work therefore develops and verifies a circuit
+method to model level repulsion and level attraction and confirms the
+universality of dissipative coupling in the cavity photon-magnon system. The
+realization of both coherent and dissipative couplings in a planar cavity may
+provide new avenues for the design and adaptation of dissipatively coupled
+systems for practical applications in information processing.",1901.07633v2
+2019-01-26,Unconventional Thermal Magnon Hall Effect in a Ferromagnetic Topological Insulator,"We present theoretically the thermal Hall effect of magnons in a
+ferromagnetic lattice with a Kekul\'e-O coupling (KOC) modulation and a
+Dzyaloshinskii-Moriya interaction (DMI). Through a strain-based mechanism for
+inducing the KOC modulation, we identify four topological phases in terms of
+the KOC parameter and DMI strength. We calculate the thermal magnon Hall
+conductivity ${\kappa^{xy}}$ at low temperature in each of these phases. We
+predict an unconventional conductivity due to a non-zero Berry curvature
+emerging from band proximity effects in the topologically trivial phase. We
+find sign changes of ${\kappa^{xy}}$ as a function of the model parameters,
+associated with the local Berry curvature and occupation probability of the
+bulk bands. Throughout, ${\kappa^{xy}}$ can be easily tuned with external
+parameters such as the magnetic field and temperature.",1901.09213v2
+2019-01-29,The effects of three magnons interactions in the magnon-density waves of triangular spin lattices,"We investigate the magnon-density waves proposed as the longitudinal
+excitations in triangular lattice antiferromagnets by including the cubic and
+quartic corrections in the large-s expansion. The longitudinal excitation
+spectra for the two-dimensional (2D) triangular antiferromagnetic model and
+quasi-one dimensional (quasi-1D) antiferromagnetic materials have been obtained
+for a general quantum spin number $s$. For the 2D triangular lattice model, we
+find a significant reduction (about 40 %) in the energy spectra at the zone
+boundaries due to both the cubic and quartic corrections. For the quasi-1D
+antiferromagnets, since the cubic term comes from the very weak couplings on
+the hexagonal planes, they make very little correction to the energy spectra,
+whereas the major correction contribution comes from the quartic terms in the
+couplings along the chains with the numerical values for the energy gaps in
+good agreement with the experimental results as reported earlier (Ref.~41).",1901.11007v2
+2019-01-30,Surface dynamics of rough magnetic films,"The chirality of Damon-Eshbach (DE) magnons affects the transport of energy
+and angular momentum at the surface of magnetic films and spheres. We calculate
+the surface-disorder-limited dephasing and transport lifetimes of surface modes
+of sufficiently thick high-quality magnetic films such as yttrium iron garnet.
+In spite of their chirality surface magnons are not protected, but interact
+strongly with smooth surface roughness. Nevertheless, for long-range disorder
+the transport is much less affected by the suppressed back scattering (vertex
+correction). Moreover, in the presence of roughness ferromagnetic resonance
+under a \textit{uniform} microwave field can gennerate a considerable amount of
+surface magnons.",1901.11046v2
+2019-02-25,Topological spin Hall effects and tunable skyrmion Hall effects in uniaxial antiferromagnetic insulators,"Recent advances in the physics of current-driven antiferromagnetic skyrmions
+have observed the absence of a Magnus force. We outline the symmetry reasons
+for this phenomenon, and show that this cancellation will fail in the case of
+spin polarized currents. Pairing micromagnetic simulations with semiclassical
+spin wave transport theory, we demonstrate that skyrmions produce a
+spin-polarized transverse magnon current, and that spin-polarized magnon
+currents can in turn produce transverse motion of antiferromagnetic skyrmions.
+We examine qualitative differences in the frequency dependence of the skyrmion
+Hall angle between ferromagnetic and antiferromagnetic cases, and close by
+proposing a simple skyrmion-based magnonic device for demultiplexing of spin
+channels.",1902.09382v2
+2019-03-04,Enhancement of superconductivity mediated by antiferromagnetic squeezed magnons,"We investigate theoretically magnon-mediated superconductivity in a
+heterostructure consisting of a normal metal and a two-sublattice
+antiferromagnetic insulator. The attractive electron-electron pairing
+interaction is caused by an interfacial exchange coupling with magnons residing
+in the antiferromagnet, resulting in p-wave, spin-triplet superconductivity in
+the normal metal. Our main finding is that one may significantly enhance the
+superconducting critical temperature by coupling the normal metal to only one
+of the two antiferromagnetic sublattices employing, for example, an
+uncompensated interface. Employing realistic material parameters, the critical
+temperature increases from vanishingly small values to values significantly
+larger than 1 K as the interfacial coupling becomes strongly
+sublattice-asymmetric. We provide a general physical picture of this
+enhancement mechanism based on the notion of squeezed bosonic eigenmodes.",1903.01470v3
+2019-03-05,Optimal mode matching in cavity optomagnonics,"Inelastic scattering of photons is a promising technique to manipulate
+magnons but it suffers from weak intrinsic coupling. We theoretically discuss
+an idea to increase optomagnonic coupling in optical whispering gallery mode
+cavities, by generalizing previous analysis to include the exchange
+interaction. We predict that the optomagnonic coupling constant to surface
+magnons in yttrium iron garnet (YIG) spheres with radius $300\,\mathrm{\mu}$m
+can be up to $40$ times larger than that to the macrospin Kittel mode. Whereas
+this enhancement falls short of the requirements for magnon manipulation in
+YIG, nanostructuring and/or materials with larger magneto-optical constants can
+bridge this gap.",1903.01718v2
+2019-03-05,Strong Coupling between Microwave Photons and Nanomagnet Magnons,"Coupled microwave photon-magnon hybrid systems offer promising applications
+by harnessing various magnon physics. At present, in order to realize high
+coupling strength between the two subsystems, bulky ferromagnets with large
+spin numbers are utilized, which limits their potential applications for
+scalable quantum information processing. In this paper, by enhancing single
+spin coupling strength using lithographically defined superconducting
+resonators, we report high cooperativities between a resonator mode and a
+Kittel mode in nanometer thick Permalloy wires. The on-chip, lithographically
+scalable, and superconducting quantum circuit compatible design provides a
+direct route towards realizing hybrid quantum systems with nanomagnets, whose
+coupling strength can be precisely engineered and dynamic properties can be
+controlled by various mechanisms derived from spintronic studies.",1903.01887v3
+2019-03-07,Interplay between intra- and inter-nanowires dynamic dipolar interactions in the spin wave band structure of Py/Cu/Py nanowires,"We have studied both experimentally and theoretically the reprogrammable spin
+wave band structure in Permalloy(10nm)/Cu(5nm)/Permalloy(30nm) nanowire arrays
+of width w=280 nm and inter-wire separation in the range from 80 to 280 nm. We
+found that, depending on the inter-wire separation, the anti-parallel
+configuration, where the magnetizations of the two Permalloy layers point in
+opposite directions, is stabilized over specific magnetic field ranges thus
+enabling us to directly compare the band structure with that of the parallel
+alignment. We show that collective spin waves of the Bloch type propagate
+through the arrays with different magnonic bandwidths as a consequence of the
+interplay between the intra- and inter-nanowire dynamic dipolar interactions. A
+detailed understanding, e.g. whether they have a stationary or propagating
+character, is achieved by considering the phase relation (in-phase or
+out-of-phase) between the dynamic magnetizations in the two ferromagnetic
+layers and their average value. This work opens the path to magnetic
+field-controlled reconfigurable layered magnonic crystals that can be used for
+future nanoscale magnon spintronic devices.",1903.02935v1
+2019-03-21,Room temperature and low-field resonant enhancement of spin Seebeck effect in partially compensated magnets,"Resonant enhancement of spin Seebeck effect (SSE) due to phonons was recently
+discovered in Y3Fe5O12 (YIG). This effect is explained by hybridization between
+the magnon and phonon dispersions. However, this effect was observed at low
+temperatures and high magnetic fields, limiting the scope for applications.
+Here we report observation of phonon-resonant enhancement of SSE at room
+temperature and low magnetic field. We observed in Lu2BiFe4GaO12 and
+enhancement 700 % greater than that in a YIG film and at very low magnetic
+fields around 10-1 T, almost one order of magnitude lower than that of YIG. The
+result can be explained by the change in the magnon dispersion induced by
+magnetic compensation due to the presence of non-magnetic ion substitutions.
+Our study provides a way to tune the magnon response in a crystal by chemical
+doping with potential applications for spintronic devices.",1903.09007v1
+2019-03-29,Quantum Simulation of the Fermion-Boson Composite Quasi-Particles with a Driven Qubit-Magnon Hybrid Quantum System,"We experimentally demonstrate strong coupling between the ferromagnetic
+magnons in a small yttrium-iron-garnet (YIG) sphere and the drive-field-induced
+dressed states of a superconducting qubit, which gives rise to the double
+dressing of the superconducting qubit. The YIG sphere and the superconducting
+qubit are embedded in a microwave cavity and the effective coupling between
+them is mediated by the virtual cavity photons. The theoretical results fit the
+experimental observations well in a wide region of the drive-field power
+resonantly applied to the superconducting qubit and reveal that the driven
+qubit-magnon hybrid quantum system can be harnessed to emulate a
+particle-hole-symmetric pair coupled to a bosonic mode. This hybrid quantum
+system offers a novel platform for quantum simulation of the composite
+quasi-particles consisting of fermions and bosons.",1903.12498v1
+2019-04-01,Inelastic spin-wave scattering by Bloch domain wall flexure oscillations,"The calculations of the inelastic spin wave scattering by flexure vibrations
+of the Bloch domain wall (Winters magnons) in thin magnetic films are
+presented. The approach is based on the interaction of the propagating spin
+waves with the dynamical emergent electromagnetic field generated by the moving
+inhomogeneous magnetization texture (domain wall). The probability of the spin
+wave scattering for the Winters magnon emission and absorption processes
+essentially rises with the spin wave scattering angle increase up to 900. The
+angular dependence of the scattering probability is essentially stronger for
+the magnon absorption processes that allow distinguishing these elementary
+emission/absorption processes experimentally.",1904.00596v1
+2019-04-12,Spin excitations of magnetoelectric LiNiPO$_4$ in multiple magnetic phases,"Spin excitations of magnetoelectric LiNiPO$_4$ are studied by infrared
+absorption spectroscopy in the THz spectral range as a function of magnetic
+field through various commensurate and incommensurate magnetically ordered
+phases up to 33\,T. Six spin resonances and a strong two-magnon continuum are
+observed in zero magnetic field. Our systematic polarization study reveals that
+some of the excitations are usual magnetic-dipole active magnon modes, while
+others are either electromagnons, electric-dipole active, or magnetoelectric,
+both electric- and magnetic-dipole active spin excitations. Field-induced
+shifts of the modes for all three orientations of the field along the
+orthorhombic axes allow us to refine the values of the relevant exchange
+couplings, single-ion anisotropies, and the Dzyaloshinskii-Moriya interaction
+on the level of a four-sublattice mean-field spin model. This model also
+reproduces the spectral shape of the two-magnon absorption continuum, found to
+be electric-dipole active in the experiment.",1904.06106v1
+2019-04-18,Magnonic Analogue Black/White Hole Horizon in Superfluid $^3$He-B: experiment,"We provide experimental details of the first experiment made in zero
+temperature limit ($\sim$ 600\,$\mu$K) studying the magnonic black/white hole
+horizon analogue using absolutely pure physical system based on the spin
+superfluidity in superfluid $^3$He-B. We show that spin precession waves
+propagating on the background of the spin super-currents in a channel between
+two Bose-Einstein condensates of magnons in form of homogeneously precessing
+domains mimic the properties of the black/white horizon. Once the white hole
+horizon is formed and blocks the propagation of the spin-precession waves
+between two domains, we observed an amplification effect, i.e. when the energy
+of the spin precession waves reflected from the horizon is higher than the
+energy of the excited spin precession waves before horizon was formed.
+Moreover, the estimated temperature of the spontaneous Hawking radiation in
+this model system is about four orders of magnitude lower than the system's
+background temperature what makes it a promising tool to study the effect of
+spontaneous Hawking radiation.",1904.09183v1
+2019-08-09,Sustained coherent spin wave emission using frequency combs,"We demonstrate sustained coherent emission of spin waves in NiFe films using
+rapid demagnetization from high repetition rate femtosecond laser pulse trains.
+As the pulse separation is shorter than the magnon decay time, magnons having a
+frequency equal to a multiple of the 1 GHz repetition-rate are coherently
+amplified. Using scanning micro-Brillouin Light Scattering (BLS) we observe
+this coherent amplification as strong peaks spaced 1 GHz apart. The BLS counts
+vs. laser power exhibit a stronger than parabolic dependence consistent with
+counts being proportional to the square of the magnetodynamic amplitude, and
+the demagnetization pulse strength being described by a Bloch law. Spatial spin
+wave mapping demonstrates how both localized and propagating spin waves can be
+excited, and how the propagation direction can be directly controlled. Our
+results demonstrate the versatility of BLS spectroscopy for rapid
+demagnetization studies and enable a new platform for photo-magnonics where
+sustained coherent spin waves can be utilized.",1908.03388v2
+2019-08-13,Anti-chiral edge states in Heisenberg ferromagnet on a honeycomb lattice,"We demonstrate the emergence of anti-chiral edge states in a Heisenberg
+ferromagnet with Dzyaloshinskii-Moriya interaction(DMI) on a honeycomb lattice
+with in-equivalent sub-lattices. The DMI, which acts between atoms of the same
+species, differs in magnitude for the two sub-lattices, resulting in a shifting
+of the energy of the magnon bands in opposite directions at the two Dirac
+points. The chiral symmetry is broken and for sufficiently strong asymmetry,
+the band shifting leads to anti-chiral edge states (in addition to the normal
+chiral edge states) in a rectangular strip where the magnon current propagates
+in the same direction along the two edges. This is compensated by a
+counter-propagating bulk current that is enabled by the broken chiral symmetry.
+We analyze the resulting magnon current profile across the width of the system
+in details and suggest realistic experimental probes to detect them. Finally,
+we propose a material that can potentially exhibit such anti-chiral edge
+states.",1908.04580v2
+2019-08-23,Magnon Pairs and Spin-Nematic Correlation in the Spin-Seebeck Effect,"Investigating exotic magnetic materials with spintronic techniques is
+effective at advancing magnetism as well as spintronics. In this work, we
+report unusual field-induced suppression of the spin-Seebeck effect (SSE) in a
+quasi one-dimensional frustrated spin-$\frac{1}{2}$ magnet LiCuVO$_4$, known to
+exhibit spin-nematic correlation in a wide range of external magnetic field
+$B$. The suppression takes place above $|B| > 2$ T in spite of the $B$-linear
+isothermal magnetization curves in the same $B$ range. The result can be
+attributed to the growth of the spin-nematic correlation while increasing $B$.
+The correlation stabilizes magnon pairs carrying spin-2, thereby suppressing
+the interfacial spin injection of SSE by preventing the spin-1 exchange between
+single magnons and conduction electrons at the interface. This interpretation
+is supported by integrating thermodynamic measurements and theoretical analysis
+on the SSE.",1908.08701v1
+2019-08-26,Disentangle magnon magnetoresistance from anisotropic and spin Hall magnetoresistance in NiFe/Pt bilayers,"We conducted a systematic angular dependence study of nonlinear
+magnetoresistance in NiFe/Pt bilayers at variable temperature and field using
+the Wheatstone bridge method. We successfully disentangled magnon
+magnetoresistance from other types of magnetoresistances based on their
+different temperature and field dependences. Both the spin Hall/anisotropic and
+magnon magnetoresistances contain sine phi and sine 3 phi components with phi
+the angle between current and magnetization, but they exhibit different field
+and temperature dependence. The competition between different types of
+magnetoresistances leads to a sign reversal of sine 3 phi component at a
+specific magnetic field, which was not reported previously. The
+phenomenological model developed is able to account for the experimental
+results for both NiFe/Pt and NiFe/Ta samples with different layer thicknesses.
+Our results demonstrate the importance of disentangling different types of
+magnetoresistances when characterizing the charge-spin interconversion process
+in magnetic heterostructures.",1908.09571v2
+2019-08-29,Magnon crystals and magnetic phases in a Kagomé-stripe antiferromagnet,"In this work we analyze the magnetization properties of an antiferromagnetic
+Kagom\'e stripe lattice, motivated by the recent synthesis of materials
+exhibiting this structure. By employing a variety of techniques that include
+numerical methods as Density Matrix Renormalization Group and Monte Carlo
+simulations, as well as analytical techniques, as perturbative low energy
+effective models and exact solutions, we characterize the magnetization process
+and magnetic phase diagram of a Kagom\'e stripe lattice. The model captures a
+variety of behaviors present in the two dimensional Kagom\'e lattice, which are
+described here by analytical models and numerically corroborated. In addition
+to the characterization of semiclassical intermediate plateaus, it is worth
+noting the determination of an exact magnon crystal phase which breaks the
+underlying symmetry of the lattice. This magnon crystal phase generalizes
+previous findings and according to our knowledge is reported here for the first
+time.",1908.11269v2
+2019-11-22,Thermodynamic Bethe Ansatz for Fishnet CFT,"We present the TBA equations and the Y-system for the exact spectrum of
+general multi-magnon local operators in the $D$-dimensional anisotropic version
+of the bi-scalar fishnet CFT. The mixing matrix of such operators is given in
+terms of fishnet planar graphs of multi-wheel and multi-spiral type. These
+graphs probe the two main building blocks of the TBA approach that are the
+magnon dispersion relation and the magnon scattering matrix and which we both
+obtain by diagonalising suitable graph-building operators. We also obtain the
+dual version of the TBA equations, which relates, in the continuum limit,
+$D$-dimensional graphs to two dimensional sigma models in $AdS_{D+1}$. It
+allows us to verify a general formula obtained by A.~Zamolodchikov for the
+critical coupling.",1911.10213v1
+2019-12-15,Magnon-photon strong coupling for tunable microwave circulators,"We present a generic theoretical framework to describe non-reciprocal
+microwave circulation in a multimode cavity magnonic system and assess the
+optimal performance of practical circulator devices. We show that high
+isolation (> 56 dB), extremely low insertion loss (< 0.05 dB), and flexible
+bandwidth control can be potentially realized in high-quality-factor
+superconducting cavity based magnonic platforms. These circulation
+characteristics are analyzed with materials of different spin densities. For
+high-spin-density materials such as yttrium iron garnet, strong coupling
+operation regime can be harnessed to obtain a broader circulation bandwidth. We
+also provide practical design principles for a highly integratible
+low-spin-density material (vanadium tetracyanoethylene) for narrow-band
+circulator operation, which could benefit noise-sensitive quantum microwave
+measurements. This theory can be extended to other coupled systems and provide
+design guidelines for achieving tunable microwave non-reciprocity for both
+classical and quantum applications.",1912.07128v2
+2019-12-16,Magnon-mediated superconductivity on the surface of a topological insulator,"We study superconductivity on the surface of a topological insulator,
+mediated by magnetic fluctuations in an adjacent ferromagnetic or
+antiferromagnetic insulator. Superconductivity can arise from effective
+interactions between helical fermions induced by interfacial fermion-magnon
+interactions. For both ferromagnetic and antiferromagnetic insulators, these
+fermion-fermion interactions have the correct structure to facilitate pairing
+between particles located on the same side of the Fermi surface, also known as
+Amperean pairing. In antiferromagnets, the strength of the induced interactions
+can be enhanced by coupling the topological insulator asymmetrically to the two
+sublattices of the antiferromagnet. This effect is further amplified by next
+nearest neighbor frustration in the antiferromagnetic insulator. The
+enhancement makes the induced interactions significantly stronger in the
+antiferromagnetic case, as compared to the ferromagnetic case. These results
+indicate that an uncompensated antiferromagnetic interface might be a better
+candidate than a ferromagnetic interface for proximity-induced magnon-mediated
+superconductivity on the surface of a topological insulator.",1912.07607v2
+2019-12-17,Topological magnons in ferromagnetic Kitaev-Heisenberg model on CaVO lattice,"A number of topological phases are found to emerge in the ferromagnetic
+Kitaev-Heisenberg model on CaVO lattice in the presence of
+Dzyaloshinskii-Moriya interaction. Heisenberg and Kitaev terms have been
+considered on nearest and next-nearest neighbor bonds in a variety of ways.
+Both isotropic and anisotropic couplings are taken into account. Topological
+phases are characterized by Chern numbers for the distinct magnon bands as well
+as the number of modes for topologically protected gapless magnon edge states.
+Band structure, dispersion relation along the high-symmetric points of first
+Brillouin zone, density of states and thermal Hall conductance have been
+evaluated for every phase. An extensive Phase diagram has been constructed.
+Topological phase transition in the parameter space is also studied.",1912.07877v2
+2019-12-18,Theory of Quantum Acoustomagnonics and Acoustomechanics with a Micromagnet,"Recently [1], we proposed a new way to engineer a flexible acoustomechanical
+coupling between the center-of-mass motion of an isolated micromagnet and one
+of its internal acoustic phonons by using a magnon as a passive mediator. In
+our approach, the coupling is enabled by the strong magnetoelastic interaction
+between magnons and acoustic phonons which originates from the small particle
+size. Here, we substantially extend our previous work. First, we provide the
+full theory of the quantum acoustomagnonic interaction in small micromagnets
+and analytically calculate the magnon-phonon coupling rates. Second, we fully
+derive the acoustomechanical Hamiltonian presented in Ref. [1]. Finally, we
+extend our previous results for the fundamental acoustic mode to higher order
+modes. Specifically, we show the cooling of the center-of-mass motion with a
+range of internal acoustic modes. Additionally, we derive the power spectral
+densities of the center-of-mass motion which allow to probe the same acoustic
+modes.",1912.08745v2
+2015-08-05,Thermal conductivity in large-$J$ two-dimensional antiferromagnets: Role of phonon scattering,"Motivated by the recent heat transport experiments in 2D antiferromagnets,
+such as La$_2$CuO$_4$, where the exchange coupling $J$ is larger than the Debye
+energy $\Theta_{\rm D}$, we discuss different types of relaxation processes for
+magnon heat current with a particular focus on coupling to 3D phonons. We study
+thermal conductivity by these in-plane magnetic excitations using two distinct
+techniques, Boltzmann formalism within the relaxation-time approximation and
+memory-function approach. Within these approaches, a close consideration is
+given to the scattering of magnons by both acoustic and optical branches of
+phonons. A remarkable accord between the two methods with regards to the
+asymptotic behavior of the effective relaxation rates is demonstrated.
+Additional scattering mechanisms, due to grain boundaries, impurities, and
+finite correlation length in the paramagnetic phase, are discussed and included
+in the calculations of the thermal conductivity $\kappa(T)$. Again, we
+demonstrate a close similarity of the results from the two techniques of
+calculating $\kappa(T)$. Our complementary approach strongly suggests that
+scattering from optical or zone-boundary phonons is important for magnon heat
+current relaxation in a high temperature window of $\Theta_D\lesssim T \ll J$.",1508.01221v1
+2015-08-20,Superstrong Coupling of a Microwave Cavity to YIG Magnons,"Multiple-post reentrant 3D lumped cavity modes have been realized to design
+the concept of discrete Whispering Gallery and Fabry-Perot-like Modes for
+multimode microwave Quantum Electrodynamics experiments. Using a magnon
+spin-wave resonance of a submillimeter-sized Yttrium-Iron-Garnet sphere at
+milliKelvin temperatures and a four-post cavity, we demonstrate the
+ultra-strong coupling regime between discrete Whispering Gallery Modes and a
+magnon resonance with strength of 1.84 GHz. By increasing the number of posts
+to eight and arranging them in a D$_4$ symmetry pattern, we expand the mode
+structure to that of a discrete Fabry-Perot cavity and modify the Free Spectral
+Range (FSR). We reach the superstrong coupling regime, where spin-photon
+coupling strength is larger than FSR, with coupling strength in the 1.1 to 1.5
+GHz range.",1508.04967v3
+2016-03-31,Enhanced spin Seebeck effect signal due to spin-momentum locked topological surface states,"Spin-momentum locking in protected surface states enables efficient
+electrical detection of magnon decay at a
+magnetic-insulator/topological-insulator heterojunction. Here we demonstrate
+this property using the spin Seebeck effect, i.e. measuring the transverse
+thermoelectric response to a temperature gradient across a thin film of yttrium
+iron garnet, an insulating ferrimagnet, and forming a heterojunction with
+(BixSb1-x)2Te3, a topological insulator. The non-equilibrium magnon population
+established at the interface can decay in part by interactions of magnons with
+electrons near the Fermi energy of the topological insulator. When this decay
+channel is made active by tuning (BixSb1-x)2Te3 to a bulk insulator, a large
+electromotive force emerges in the direction perpendicular to the in-plane
+magnetization of yttrium iron garnet. The enhanced, tunable spin Seebeck effect
+which occurs when the Fermi level lies in the bulk gap offers unique advantages
+over the usual spin Seebeck effect in metals and therefore opens up exciting
+possibilities in spintronics.",1603.09427v1
+2016-10-26,Time-resolved measurements of surface spin-wave pulses at millikelvin temperatures,"In this work, we experimentally investigate the propagation of pulsed
+magnetostatic surface spin-wave (magnon) signals in an yttrium iron garnet
+(YIG) waveguide at millikelvin temperatures. Our measurements are performed in
+a dilution refrigerator at microwave frequencies. The excellent signal-to-noise
+ratio afforded by the low-temperature environment allows the propagation of the
+pulses to be observed in detail. The work gives insight both into
+low-temperature magnon dynamics in YIG and the potential application of systems
+of propagating magnons to solid-state quantum information processing.",1610.08402v2
+2016-10-31,Strong coupling of magnons in a YIG sphere to photons in a planar superconducting resonator in the quantum limit,"We report measurements of a superconducting coplanar waveguide resonator
+(CPWR) coupled to a sphere of yttrium-iron garnet. The non-uniform CPWR field
+allows us to excite various magnon modes in the sphere. Mode frequencies and
+relative coupling strengths are consistent with theory. Strong coupling is
+observed to several modes even with, on average, less than one excitation
+present in the CPWR. The time response to square pulses shows oscillations at
+the mode splitting frequency. These results indicate the feasibility of
+combining magnonic and planar superconducting quantum devices.",1610.09963v2
+2016-12-13,Noninteger-spin magnonic excitations in untextured magnets,"Interactions are responsible for intriguing physics, e.g. emergence of exotic
+ground states and excitations, in a wide range of systems. Here we
+theoretically demonstrate that dipole-dipole interaction leads to bosonic
+eigen-excitations with average spin ranging from zero to above $\hbar$ in
+magnets with uniformly magnetized ground states. These exotic excitations can
+be interpreted as quantum coherent conglomerates of spin $\hbar$ magnons, the
+eigen-excitations when the dipolar interactions are disregarded. We further
+find that the eigenmodes in an easy-axis antiferromagnet are spin-zero
+quasiparticles instead of the widely believed spin $\pm \hbar$ magnons. The
+latter re-emerge when the symmetry is broken by a sufficiently large applied
+magnetic field. The average spin greater than $\hbar$ is accompanied by vacuum
+fluctuations and may be considered to be a weak form of frustration.",1612.04163v2
+2017-07-04,Effective Minkowski to Euclidean signature change of the magnon BEC pseudo-Goldstone mode in polar 3He,"We discuss the effective metric experienced by the Nambu-Goldstone mode
+propagating in the broken symmetry spin-superfluid state of coherent precession
+of magnetization. This collective mode represents the phonon in the RF driven
+or pulsed out-of-equilibrium Bose-Einstein condensate (BEC) of optical magnons.
+We derive the effective BEC free energy and consider the phonon spectrum when
+the spin superfluid BEC is formed in the anisotropic polar phase of superfluid
+3He, experimentally observed in uniaxial aerogel 3He-samples. The coherent
+precession of magnetization experiences an instability at a critical value of
+the tilting angle of external magnetic field with respect to the anisotropy
+axis. From the action of quadratic deviations around equilibrium, this
+instability is interpreted as a Minkowski-to-Euclidean signature change of the
+effective phonon metric. We also note the similarity between the magnon BEC in
+the unstable region and an effective vacuum scalar ""ghost"" condensate.",1707.00905v4
+2017-11-08,Bose-Einstein condensation of magnons and spin superfluidity in the polar phase of $^3$He,"The polar phase of $^3$He, which is topological spin-triplet superfluid with
+the Dirac nodal line in the spectrum of Bogolubov quasiparticles, has been
+recently stabilized in a nanoconfined geometry. We pump magnetic excitations
+(magnons) into the sample of polar phase and observe how they form a
+Bose-Einstein condensate, revealed by coherent precession of the magnetization
+of the sample. Spin superfluidity, which supports this coherence, is associated
+with the spontaneous breaking of U(1) symmetry by the phase of precession. We
+observe the corresponding Nambu-Goldstone boson and measure its mass emerging
+when applied rf field violates the U(1) symmetry explicitly. We suggest that
+the magnon BEC in the polar phase is a powerful probe for topological objects
+such as vortices and solitons and topological nodes in the fermionic spectrum.",1711.02915v1
+2018-10-02,Spin-dependent (inverse) spin Hall effect in Co$_{60}$Fe$_{20}$B$_{20}$,"In ferromagnetic metals, the interconversion of spin and charge currents via
+the spin Hall effect and its inverse can depend on the angle between the
+ferromagnets magnetization and the spin current polarization direction. Here,
+such a spin-dependent (inverse) spin Hall effect is found in the ferromagnetic
+alloy Co$_{60}$Fe$_{20}$B$_{20}$. In a nonlocal magnon transport experiment,
+Co$_{60}$Fe$_{20}$B$_{20}$ is used to both excite and detect magnonic spin
+currents flowing in the ferrimagnetic insulator Y$_{3}$Fe$_{5}$O$_{12}$. We
+find that the signal amplitude is significantly modulated by tuning the
+direction of the Co$_{60}$Fe$_{20}$B$_{20}$ magnetization. We design a sample
+structure that completely prevents direct magnonic coupling between the
+ferromagnets. Thus, we can identify unambiguously an intrinsic electronic
+origin of the observed effect.",1810.01227v3
+2018-10-23,Magnonic Analogue of Black/White Hole Horizon in Superfluid $^3$He-B,"We report on theoretical model and experimental results of the experiment
+made in a limit of absolute zero temperature ($\sim$ 600\,$\mu$K) studying the
+spin wave analogue of black/white hole horizon using spin (magnonic)
+superfluidity in superfluid $^3$He-B. As an experimental tool simulating the
+properties of the black/white horizon we used the spin-precession waves
+propagating on the background of the spin super-currents between two
+Bose-Einstein condensates of magnons in form of homogeneously precessing
+domains. We provide experimental evidence of the white hole formation for spin
+precession waves in this system, together with observation of an amplification
+effect. Moreover, the estimated temperature of the spontaneous Hawking
+radiation in this system is about four orders of magnitude lower than the
+system's background temperature what makes it a promising tool to study the
+effect of spontaneous Hawking radiation.",1810.09890v2
+2019-05-11,Spin Seebeck effect from antiferromagnetic magnons and critical spin fluctuations in epitaxial FeF2 films,"We report a longitudinal spin Seebeck effect (SSE) study in epitaxially grown
+FeF2(110) antiferromagnetic (AFM) thin films with strong uniaxial anisotropy
+over the temperature range of 3.8 - 250 K. Both the magnetic field- and
+temperature-dependent SSE signals below the N\'eel temperature (TN=70 K) of the
+FeF2 films are consistent with a theoretical model based on the excitations of
+AFM magnons without any net induced static magnetic moment. In addition to the
+characteristic low-temperature SSE peak associated with the AFM magnons, there
+is another SSE peak at TN which extends well into the paramagnetic phase. All
+the SSE data taken at different magnetic fields up to 12 T near and above the
+critical point TN follow the critical scaling law very well with the critical
+exponents for magnetic susceptibility of 3D Ising systems, which suggests that
+the AFM spin correlation is responsible for the observed SSE near TN.",1905.04408v1
+2019-05-16,Three-dimensional topological magnon systems,"We propose a class of models for a magnonic analog of topological insulators
+in three dimensions. The models have pseudo-time-reversal symmetry which
+ensures the existence of bosonic Kramers pairs. We define a set of
+$\mathbb{Z}_2$ topological invariants that characterizes different topological
+phases and determines the presence or absence of surface Dirac cones. This is
+demonstrated by considering a bosonic counterpart of the Fu-Kane-Mele model on
+a diamond lattice. The model is found to exhibit three distinct phases
+analogous to strong topological, weak topological, and trivial insulator phases
+of the original fermionic model. We also discuss a possible realization of the
+thermal Hall effect of surface magnons in the presence of a magnetic field in
+proximity to a normal ferromagnet.",1905.06748v3
+2019-05-31,Detecting Light Dark Matter with Magnons,"Scattering of light dark matter with sub-eV energy deposition can be detected
+with collective excitations in condensed matter systems. When dark matter has
+spin-independent couplings to atoms or ions, it has been shown to efficiently
+excite phonons. Here we show that, if dark matter couples to the electron spin,
+magnon excitations in materials with magnetic dipole order offer a promising
+detection path. We derive general formulae for single magnon excitation rates
+from dark matter scattering, and demonstrate as a proof of principle the
+projected reach of a yttrium iron garnet target for several dark matter models
+with spin-dependent interactions. This highlights the complementarity of
+various collective excitations in probing different dark matter interactions.",1905.13744v2
+2020-06-12,Symmetry Approach to Chiral Optomagnonics in Antiferromagnetic Insulators,"We discuss several aspects of chiral optomagnonics in antiferromagnetic
+insulators by considering common symmetries between the electromagnetic field
+and spin excitations. This approach allows us to look at optical and magnetic
+materials from similar perspectives, and discuss useful analogies between them.
+We show that spin waves in collinear antiferromagnets and the electromagnetic
+field in vacuum are both invariant under the same eight-dimensional algebra of
+symmetry transformations. By such analogy, we can extend the concept of optical
+chirality to antiferromagnetic insulators, and demonstrate that the spin-wave
+dynamics in these materials in the presence of a spin current is similar to
+that of the light inside chiral metamaterials. Photo-excitation of magnonic
+spin currents is also discussed from the symmetry point of view. It is
+demonstrated that a direct magnonic spin photocurrent can be exited by
+circularly polarized light, which can be considered as a magnonic analogue of
+the photogalvanic effect. We also note that the Zitterbewegung process should
+appear and may play a role in photo-excitation processes.",2006.07399v1
+2020-06-20,Stratonovich-Ito integration scheme in ultrafast spin caloritronics,"The magnonic spin Seebeck effect is a key element of spin caloritronic, a
+field that exploits thermal effects for spintronic applications. Early studies
+were focused on investigating the steady-state nonequilibrium magnonic spin
+Seebeck current, and the underlying physics of the magnonic spin Seebeck effect
+is now relatively well established. However, the initial steps of the formation
+of the spin Seebeck current are in the scope of recent interest. To address
+this dynamical aspect theoretically we propose here a new approach to the
+time-resolved spin Seebeck effect. Our method exploits the supersymmetric
+theory of stochastics and Ito - Stratonovich integration scheme. We found that
+in the early step the spin Seebeck current has both nonzero transversal and
+longitudinal components. As the magnetization dynamics approaches the
+steady-state, the transversal components decay through dephasing over the
+dipole-dipole reservoir. The time scale for this process is typically in the
+sub-nanoseconds pointing thus to the potential of an ultrafast control of the
+dynamical spin Seebeck during its buildup.",2006.11471v1
+2020-06-25,Transition magnon modes in thin ferromagnetic nanogratings,"This work presents micromagnetic simulations in ferromagnetic nanogratings
+for the full range of directions of an applied in-plane external magnetic
+field. We focus on the modification of the magnon mode characteristics when the
+magnetic field orientation is gradually changed between the classical
+Damon-Eshbach (DE) and backward-volume (BV) geometries. We found that in a
+specific range of field directions, the magnon mode parameters differ
+significantly from the parameters in the classical cases, namely, the modes are
+characterized by complex spatial distributions and have low group velocities.
+The center of this range corresponds to the direction of the external magnetic
+field, which gives the maximal nonuniform distribution of the static
+magnetization in the nanogratings.",2006.14394v2
+2020-09-09,Sub-pico-liter magneto-optical cavities,"Microwave-to-optical conversion via ferromagnetic magnons has so-far been
+limited by the optical coupling rates achieved in mm-scale whispering gallery
+mode resonators. Towards overcoming this limitation, we propose and demonstrate
+an open magneto-optical cavity containing a thin-film of yttrium iron garnet
+(YIG). We achieve a 0.1 pL (100 $\mu$m$^{3}$) optical mode volume, $\sim$50
+times smaller than previous devices. From this, we estimate the magnon
+single-photon coupling rate is $G\approx50$ Hz. This open cavity design offers
+the prospect of wavelength scale mode volumes, small polarization splittings,
+and good magneto-optical mode overlap. With achievable further improvements and
+optimization, efficient microwave-optical conversion and magnon cooling devices
+become a realistic possibility.",2009.04162v1
+2020-09-09,Effect of dipolar interactions on cavity magnon-polaritons,"The strong photon-magnon coupling between an electromagnetic cavity and two
+yttrium iron garnet (YIG) spheres has been investigated in the context of a
+strong mutual dipolar interaction between the spheres. A decrease in the
+coupling strength between the YIG spheres and the electromagnetic cavity is
+observed, along with an increase of the total magnetic losses, as the distance
+between the spheres is decreased. A model of inhomogeneous broadening of the
+ferromagnetic resonance linewidth, partly mitigated by the dipolar narrowing
+effect, reproduces the reduction in the coupling strength observed
+experimentally. These findings have important implications for the
+understanding of strongly coupled photon-magnon system involving densely packed
+magnetic objects, such as ferromagnetic nanowires arrays, in which the total
+coupling strength with an electromagnetic cavity might become limited due to
+mutual dipolar interactions.",2009.04557v1
+2020-09-10,Sensing chiral magnetic noise via quantum impurity relaxometry,"We present a theory for quantum impurity relaxometry of magnons in thin
+films, exhibiting quantitative agreement with recent experiments without
+needing arbitrary scale factors used in theoretical models thus far. Our theory
+reveals that chiral coupling between prototypical spin>1/2 quantum impurities
+and magnons plays a central role in determining impurity relaxation, which is
+further corroborated by our experiments on nickel films interfaced with
+nitrogen-vacancy centers. Along with advancing magnonics and understanding
+decoherence in hybrid quantum platforms with magnets, the ability of a quantum
+impurity spin to sense chiral magnetic noise presents an opportunity to probe
+chiral phenomena in condensed matter.",2009.05060v1
+2020-09-16,Dynamical mass generation for ferromagnetic skyrmions in two dimensions,"Magnetic skyrmions are topological magnetization textures that are
+characterized by the homotopy group of two dimensional spheres. Despite years
+of intensive research on skyrmions, the fundamental problem of the inertia of a
+skyrmion in driven motion remains unresolved. By properly taking into account a
+direct coupling between skyrmion motion and the correspondingly excited
+magnons, we identify a dynamical mass for the skyrmion in motion. The direct
+coupling between skyrmion motion and magnons can be employed to engineer
+skyrmion dynamics with magnons through ingenious material and geometry design.",2009.07486v4
+2020-09-17,Spin-wave focusing induced skyrmion generation,"We propose a new method to generate magnetic skyrmions through spin-wave
+focusing in chiral ferromagnets.A lens is constructed to focus spin waves by a
+curved interface between two ferromagnetic thin films with different
+perpendicular magnetic anisotropies. Based on the principle of identical
+magnonic path length, we derive the lens contour that can be either elliptical
+or hyperbolical depending on the magnon refractive index. Micromagnetic
+simulations are performed to verify the theoretical design. It is found that
+under proper condition magnetic skyrmions emerge near the focus point of the
+lens where the spin-wave intensity has been significantly enhanced. A close
+investigation shows that a magnetic droplet first forms and then converts to
+the skyrmion accompanying with a change of topological charge. Phase diagram
+about the amplitude and duration-time of the exciting field for skyrmion
+generation is obtained. Our findings would be helpful for designing novel
+spintronic devices combining the advantages of skyrmionics and magnonics.",2009.08091v1
+2021-02-09,Nonlinear Decay of Quantum Confined Magnons in Itinerant Ferromagnets,"Quantum confinement leads to the emergence of several magnon modes in
+ultrathin layered magnetic structures. We probe the lifetime of these quantum
+confined modes in a model system composed of three atomic layers of Co grown on
+different surfaces. We demonstrate that the quantum confined magnons exhibit
+nonlinear decay rates, which strongly depend on the mode number, in sharp
+contrast to what is assumed in the classical dynamics. Combining the
+experimental results with those of linear-response density functional
+calculations we provide a quantitative explanation for this nonlinear damping
+effect. The results provide new insights into the decay mechanism of spin
+excitations in ultrathin films and multilayers and pave the way for tuning the
+dynamical properties of such structures.",2102.04956v1
+2021-02-11,Magnonics in collinear magnetic insulating systems,"In the last decades, collinear magnetic insulating systems have emerged as
+promising energy-saving information carriers. Their elementary collective spin
+excitations, i.e., magnons, can propagate for long distances bypassing the
+Joule heating effects that arise from electron scattering in metal-based
+devices. This tutorial article provides an introduction to theoretical and
+experimental advances in the study of magnonics in collinear magnetic
+insulating systems. We start by outlining the quantum theory of spin waves in
+ferromagnetic and antiferromagnetic systems and we discuss their quantum
+statistics. We review the phenomenology of spin and heat transport of the
+coupled coherent and incoherent spin dynamics and the interplay between
+magnetic excitations and lattice degrees of freedom. Finally, we introduce the
+reader to the key ingredients of two experimental probes of magnetization
+dynamics, spin transport and NV-center relaxometry setups, and discuss
+experimental findings relevant to the outlined theory.",2102.08829v1
+2021-02-24,Phase-controlled pathway interferences and switchable fast-slow light in a cavity-magnon polariton system,"We study the phase controlled transmission properties in a compound system
+consisting of a 3D copper cavity and an yttrium iron garnet (YIG) sphere. By
+tuning the relative phase of the magnon pumping and cavity probe tones,
+constructive and destructive interferences occur periodically, which strongly
+modify both the cavity field transmission spectra and the group delay of light.
+Moreover, the tunable amplitude ratio between pump-probe tones allows us to
+further improve the signal absorption or amplification, accompanied by either
+significantly enhanced optical advance or delay. Both the phase and
+amplitude-ratio can be used to realize in-situ tunable and switchable fast-slow
+light. The tunable phase and amplitude-ratio lead to the zero reflection of the
+transmitted light and an abrupt fast-slow light transition. Our results confirm
+that direct magnon pumping through the coupling loops provides a versatile
+route to achieve controllable signal transmission, storage, and communication,
+which can be further expanded to the quantum regime, realizing coherent-state
+processing or quantum-limited precise measurements.",2102.12181v1
+2013-06-05,Dynamical structure factor of triangular-lattice antiferromagnet,"We elucidate the role of magnon interaction and spontaneous decays in the
+spin dynamics of the triangular-lattice Heisenberg antiferromagnet by
+calculating its dynamical structure factor within the spin-wave theory.
+Explicit theoretical results for neutron-scattering intensity are provided for
+spins S=1/2 and S=3/2. The dynamical structure factor exhibits unconventional
+features such as quasiparticle peaks broadened by decays, non-Lorentzian
+lineshapes, and significant spectral weight redistribution to the two-magnon
+continuum. This rich excitation spectrum illustrates the complexity of the
+triangular-lattice antiferromagnet and provides distinctive qualitative and
+quantitative fingerprints for experimental observation of decay-induced magnon
+dynamics.",1306.1231v3
+2013-06-18,"Magnon, phonon and electron temperature profiles and the spin Seebeck effect in magnetic insulator/normal metal hybrid structures","We calculate the phonon, electron and magnon temperature profiles in yttrium
+iron garnet/platinum bilayers by diffusive theory with appropriate boundary
+conditions, in particular taking into account interfacial thermal resistances.
+Our calculations show that in thin film hybrids, the interface magnetic heat
+conductance qualitatively affects the magnon temperature. Based on published
+material parameters we assess the degree of non-equilibrium at the yttrium iron
+garnet/platinum interface. The magnitude of the spin Seebeck effect derived
+from this approach compares well with experimental results for the longitudinal
+spin Seebeck effect. Additionally we address the temperature profiles in the
+transverse spin Seebeck effect.",1306.4292v2
+2015-07-22,Spin-current emission governed by nonlinear spin dynamics,"Coupling between conduction electrons and localized magnetization is
+responsible for a variety of phenomena in spintronic devices. This coupling
+enables to generate spin currents from dynamical magnetization. Due to the
+nonlinearity of magnetization dynamics, the spin-current emission through the
+dynamical spin-exchange coupling offers a route for nonlinear generation of
+spin currents. Here, we demonstrate spin-current emission governed by nonlinear
+magnetization dynamics in a metal/magnetic insulator bilayer. The spin-current
+emission from the magnetic insulator is probed by the inverse spin Hall effect,
+which demonstrates nontrivial temperature and excitation power dependences of
+the voltage generation. The experimental results reveal that nonlinear
+magnetization dynamics and enhanced spin-current emission due to magnon
+scatterings are triggered by decreasing temperature. This result illustrates
+the crucial role of the nonlinear magnon interactions in the spin-current
+emission driven by dynamical magnetization, or nonequilibrium magnons, from
+magnetic insulators.",1507.06081v1
+2015-07-30,Quasi-soliton scattering in quantum spin chains,"The quantum scattering of magnon bound states in the anisotropic Heisenberg
+spin chain is shown to display features similar to the scattering of solitons
+in classical exactly solvable models. Localized colliding Gaussian wave packets
+of bound magnons are constructed from string solutions of the Bethe equations
+and subsequently evolved in time, relying on an algebraic Bethe ansatz based
+framework for the computation of local expectation values in real space-time.
+The local magnetization profile shows the trajectories of colliding wave
+packets of bound magnons, which obtain a spatial displacement upon scattering.
+Analytic predictions on the displacements for various values of anisotropy and
+string lengths are derived from scattering theory and Bethe ansatz phase
+shifts, matching time evolution fits on the displacements. The time evolved
+block decimation (TEBD) algorithm allows for the study of scattering
+displacements from spin-block states, showing similar scattering displacement
+features.",1507.08624v2
+2015-12-16,Interacting Double Coset Magnons,"We consider the anomalous dimensions of restricted Schur polynomials
+constructed using n~O(N) complex adjoint scalars Z and m complex adjoint
+scalars Y. We fix m<<n so that our operators are almost half BPS. At leading
+order in m/n this system corresponds to a dilute gas of m free magnons. Adding
+the first correction of order m/n to the anomalous dimension, which arises at
+two loops, we find non-zero magnon interactions. The form of this new operator
+mixing is studied in detail for a system of two giant gravitons with four
+strings attached.",1512.05019v1
+2016-11-01,Topological invariant and cotranslational symmetry in strongly interacting multi-magnon systems,"It is still an outstanding challenge to characterize and understand the
+topological features of strongly interacting states such as bound-states in
+interacting quantum systems. Here, by introducing a cotranslational symmetry in
+an interacting multi-particle quantum system, we systematically develop a
+method to define a Chern invariant, which is a generalization of the well-known
+Thouless-Kohmoto-Nightingale-den Nijs invariant, for identifying strongly
+interacting topological states. As an example, we study the topological
+multi-magnon states in a generalized Heisenberg XXZ model, which can be
+realized by the currently available experiment techniques of cold atoms [Phys.
+Rev. Lett. \textbf{111}, 185301 (2013); Phys. Rev. Lett. \textbf{111}, 185302
+(2013)]. Through calculating the two-magnon excitation spectrum and the defined
+Chern number, we explore the emergence of topological edge bound-states and
+give their topological phase diagram. We also analytically derive an effective
+single-particle Hofstadter superlattice model for a better understanding of the
+topological bound-states. Our results not only provide a new approach to
+defining a topological invariant for interacting multi-particle systems, but
+also give insights into the characterization and understanding of strongly
+interacting topological states.",1611.00205v2
+2016-11-06,Terahertz-frequency magnon-phonon-polaritons in the strong coupling regime,"Strong coupling between light and matter occurs when the two interact
+strongly enough to form new hybrid modes called polaritons. Here we report on
+the strong coupling of both the electric and magnetic degrees of freedom to an
+ultrafast terahertz (THz) frequency electromagnetic wave. In our system,
+optical phonons in a slab of ferroelectric lithium niobate (LiNbO$_3$) are
+strongly coupled to a THz electric field to form phonon-polaritons, which are
+simultaneously strongly coupled to magnons in an adjacent slab of canted
+antiferromagnetic erbium orthoferrite (ErFeO$_3$) via the THz magnetic field.
+The strong coupling leads to the formation of new magnon-phonon-polariton
+modes, which we experimentally observe in the wavevector-frequency dispersion
+curve as an avoided crossing and in the time-domain as a normal-mode beating.
+Our simple yet versatile on-chip waveguide platform provides a promising avenue
+by which to explore both ultrafast THz spintronics applications and the quantum
+nature of the interaction.",1611.01814v3
+2016-11-22,Control and Local Measurement of the Spin Chemical Potential in a Magnetic Insulator,"The spin chemical potential characterizes the tendency of spins to diffuse.
+Probing the spin chemical potential could provide insight into materials such
+as magnetic insulators and spin liquids and aid optimization of spintronic
+devices. Here, we introduce single-spin magnetometry as a generic platform for
+non-perturbative, nanoscale characterization of spin chemical potentials. We
+use this platform to investigate magnons in a magnetic insulator, surprisingly
+finding that the magnon chemical potential can be efficiently controlled by
+driving the system's ferromagnetic resonance. We introduce a symmetry-based
+two-fluid theory describing the underlying magnon processes, realize the first
+experimental determination of the local thermomagnonic torque, and illustrate
+the detection sensitivity using electrically controlled spin injection. Our
+results open the way for nanoscale control and imaging of spin transport in
+mesoscopic spin systems.",1611.07408v1
+2016-11-26,Specific Heat of Spin Excitations Measured by FerromagneticResonance,"Using ferromagnetic-resonance spectroscopy (FMR), we investigate the
+anisotropic properties of epitaxial 3 nmPt/2 nmAg/10 nmFe/10 nmAg/GaAs(001)
+films in fully saturated meta-stable states at temperatures ranging from 70 K
+to 280 K. By comparison to spin-wave theory calculations, we identify the role
+of thermal fluctuation of magnons in overcoming the energy barrier associated
+with these meta-stable states. We show that the energy associated with the size
+of the barrier that bounds the meta-stable regime is proportional to the heat
+stored in the magnonic bath. Our findings offer the possibility to measure the
+magnonic contribution to the heat capacity by FMR, independent of other
+contributions at temperatures ranging from 0 K to ambient temperature and
+above. The only requirement being that the selected sample exhibits magnetic
+anisotropy, here, magnetocrystalline anisotropy.",1611.08713v2
+2017-04-17,Raman scattering from Higgs mode oscillations in the two-dimensional antiferromagnet Ca$_2$RuO$_4$,"We present and analyze Raman spectra of the Mott insulator Ca$_2$RuO$_4$,
+whose quasi-two-dimensional antiferromagnetic order has been described as a
+condensate of low-lying spin-orbit excitons with angular momentum $J_{eff}=1$.
+In the $A_g$ polarization geometry, the amplitude (Higgs) mode of the
+spin-orbit condensate is directly probed in the scalar channel, thus avoiding
+infrared-singular magnon contributions. In the $B_{1g}$ geometry, we observe a
+single-magnon peak as well as two-magnon and two-Higgs excitations. Model
+calculations using exact diagonalization quantitatively agree with the
+observations. Together with recent neutron scattering data, our study provides
+strong evidence for excitonic magnetism in Ca$_2$RuO$_4$ and points out new
+perspectives for research on the Higgs mode in two dimensions.",1704.04991v2
+2017-04-25,Probing length-scale separation of thermal and spin currents by nanostructuring YIG,"We have fabricated bulk nanostructured ferrimagnetic materials with different
+grain sizes by sintering ball-milled Y3Fe5O12 (YIG) nanoparticles and measured
+the grain-size dependence of the thermal conductivity and spin Seebeck
+thermopower. The nanostructuring reduces both thermal conductivity and
+thermopower, but the reduction of the latter was found to be considerably
+stronger despite the moderate difference in magnetization, which suggests that
+the length scales of transport of magnons and phonons contributing to the spin
+Seebeck effect are significantly larger than that of phonons carrying thermal
+current. This is consistent with the measurements of high-magnetic-field
+response of the spin Seebeck thermopower and low-temperature thermal
+conductivity, where the quenching of magnons seen in single-crystalline YIG was
+not observed in nanostructured YIG due to scattering of long-range low
+frequency magnons.",1704.07568v1
+2018-01-30,Edge on-site potential effects in a honeycomb topological magnon insulator,"The difference between the edge on-site potential and the bulk values in a
+magnonic topological honeycomb lattice leads to the formation of edge states in
+a bearded boundary, and the same difference is found to be the responsible for
+the absence of edge states in a zig-zag termination. In a finite lattice, the
+intrinsic on-site interactions along the boundary sites generate an effective
+defect and Tamm-like edge states appear for both zig-zag and bearded
+terminations. If a non-trivial gap is induced, Tamm-like and topologically
+protected edge states appear in the band structure. The effective defect can be
+strengthened by an external on-site potential and the dispersion relation,
+velocity and magnon-density of the edge states become tunable.",1801.09945v1
+2018-08-02,Quantum kinetic theory of spin-transfer torque and magnon-assisted transport in nanostructures,"We theoretically investigate the role of spin fluctuations in charge
+transport through a magnetic junction. Motivated by recent experiments that
+measure a nonlinear dependence of the current on electrical bias, we develop a
+systematic understanding of the interplay of charge and spin dynamics in
+nanoscale magnetic junctions. Our model captures two distinct features arising
+from these fluctuations: magnon-assisted transport and the effect of
+spin-transfer torque on the magnetoconductance. The latter stems from magnetic
+misalignment in the junction induced by spin-current fluctuations. As the
+temperature is lowered, inelastic quantum scattering takes over thermal
+fluctuations, exhibiting signatures that make it readily distinguishable from
+magnon-assisted transport.",1808.00777v2
+2018-08-19,Quantized excitation spectra by magnon confinement in quasi-one-dimensional S=1 spin systems,"We apply the infinite time-evolving-block-decimation algorithm to calculate
+the dynamical spin-structure factors of the quasi-one-dimensional (q1D) S=1
+antiferromagnetic spin system with the single-ion anisotropy and the bond
+alternation. We find that excitation continuum originating from magnons is
+quantized, when the staggered field induced by the weak inter-chain interaction
+is taken into account. The excitation energies of the quantized excitation
+spectra are well explained by negative zeros of the Airy functions, when the
+easy-axis anisotropy is strong and the ground state is located deep in the
+N\'eel phase. This quantization of the magnon continuum is a counterpart of the
+spinon confinement, which has been recently discussed in q1D S=1/2
+antiferromagnets. We further show that, when the staggered field exists, the
+quantized excitation spectra appear the phase boundary between the Haldane
+phase and the N\'eel phase of the phase diagram without the staggered field.
+However, the quantized excitation spectra disappear in the singlet dimer phase.",1808.06270v2
+2019-06-05,Phonon laser in a cavity magnomechanical system,"The phonon analog of an optical laser has become the focus of research. We
+theoretically study phonon laser in a cavity magnomechanical system, which
+consist of a microwave cavity, a small ferromagnetic sphere and an uniform
+external bias magnetic field. This system can realize the phonon-magnon
+coupling and the cavity photon-magnon coupling via magnetostrictive interaction
+and magnetic dipole interaction respectively, the magnons are driven directly
+by a strong microwave field simultaneously. Frist, the intensity of driving
+magnetic field which can reach the threshold condition of phonon laser is
+given. Then, we demonstrate that the phonon laser can be well controlled by an
+adjustable external magnetic field without changing other parameters, which
+provides an additional degree of freedom compared to the phonon laser in
+optomechanical systems. Finally, with the experimentally feasible parameters,
+threshold power in our scheme is close to the case of optomechanical systems.
+Our results provide a theoretical basis for the realization of phonon lasers in
+magnomechanical systems.",1906.01871v3
+2019-06-18,Magnon-polaron excitations in the noncollinear antiferromagnet Mn$_3$Ge,"We present the detailed inelastic neutron scattering measurements of the
+noncollinear antiferromagnet Mn$_3$Ge. Time-of-flight and triple-axis
+spectroscopy experiments were conducted at the temperature of 6~K, well below
+the high magnetic ordering temperature of 370~K. The magnetic excitations have
+a 5-meV gap and display an anisotropic dispersive mode reaching $\simeq 90$~meV
+at the boundaries of the magnetic Brillouin zone. The spectrum at the zone
+center shows two additional excitations that demonstrate characteristics of
+both magnons and phonons. The \textit{ab initio} lattice-dynamics calculations
+show that these can be associated with the magnon-polaron modes resulting from
+the hybridization of the spin fluctuations and the low-energy optical phonons.
+The observed magnetoelastic coupling agrees with the previously found negative
+thermal expansion in this compound and resembles the features reported in the
+spectroscopic studies of other antiferromagnets with the similar noncollinear
+spin structures.",1906.07640v1
+2019-06-28,Ground-state cooling of an magnomechanical resonator induced by magnetic damping,"Quantum manipulation of mechanical resonators has been widely applied in
+fundamental physics and quantum information processing. Among them, cooling the
+mechanical system to its quantum ground state is regarded as a key step. In
+this work, we propose a scheme which one can realize ground-state cooling of
+resonator in a cavity magnomechanical system. The system consists of a
+microwave cavity and a small ferromagnetic sphere, in which phonon-magnon
+coupling and cavity photon-magnon coupling can be achieved via magnetostrictive
+interaction and magnetic dipole interaction, respectively. After adiabatically
+eliminating the cavity mode, an effective Hamiltonian which consists of magnon
+and mechanical modes is obtained. Within experimentally feasible parameters, we
+demonstrate that the ground-state cooling of the magnomechanical resonator can
+be achieved by extra magnetic damping. Unlike optomechanical cooling,
+magnomechanical interaction is utilized to realize the cooling of resonators.
+We further illustrate the ground-state cooling can be effectively controlled by
+the external magnetic field.",1906.12081v1
+2019-07-01,Chemical potential of an antiferromagnetic magnon gas,"Understanding the statistics of quasi-particle excitations in magnetic
+systems is essential for exploring new magnetic phases and collective quantum
+phenomena. While the chemical potential of a ferromagnetic gas has been
+extensively investigated both theoretically and experimentally, its
+antiferromagnetic counterpart remains uncharted. Here, we derive the statistics
+of a two-component U(1)-symmetric Bose gas and apply our results to an
+axially-symmetric antiferromagnetic insulator. We find that the two magnon
+eigenmodes of the system are described by an equal and opposite chemical
+potential, in analogy with a particle-antiparticle pair. Furthermore, we derive
+the thermomagnonic torques describing the interaction between the coherent and
+incoherent antiferromagnetic spin dynamics. Our results show that the magnitude
+and sign of the chemical potential can be tuned via an AC magnetic field
+driving resonantly one of the magnon modes. Finally, we propose NV-center
+relaxometry as a method to experimentally test our predictions.",1907.00931v1
+2019-07-05,Theory for shift current of bosons: Photogalvanic spin current in ferrimagnetic and antiferromagnetic insulators,"We theoretically study the optical generation of dc spin current (i.e., a
+spin-current solar cell) in ordered antiferromagnetic and ferrimagnetic
+insulators, motivated by a recent study on the laser-driven spinon spin current
+in noncentrosymmetric quantum spin chains [H. Ishizuka and M. Sato, Phys. Rev.
+Lett. 122, 197702 (2019)]. Using a non-linear response theory for magnons, we
+analyze the dc spin current generated by a linearly-polarized electromagnetic
+wave (typically, terahertz or gigahertz waves). Considering noncentrosymmetric
+two-sublattice magnets as an example, we find a finite dc spin current
+conductivity at $T=0$, where no thermally-excited magnons exist; this is in
+contrast to the case of the spinon spin current, in which the optical
+transition of the Fermi degenerate spinons plays an essential role. We find
+that the dc spin-current conductivity is insensitive to the Gilbert damping,
+i.e., it may be viewed as a shift current carried by bosonic particles
+(magnons). Our estimate shows that an electric-field intensity of
+$E\sim10^4-10^6$ V/cm is sufficient for an observable spin current. Our theory
+indicates that the linearly-polarized electromagnetic wave generally produces a
+dc spin current in noncentrosymmetric magnetic insulators.",1907.02734v1
+2019-07-14,Realization of Attractive Level Crossing via a Dissipative Mode,"The new field of spin cavitronics focuses on the interaction between the
+magnon excitation of a magnetic element and the electromagnetic wave in a
+microwave cavity. In strong interaction regime, such interaction usually gives
+rise to the level anti-crossing for the magnonic and the electromagnetic mode.
+Recently, the attractive level crossing has been observed, and is explained by
+a non-Hermitian model Hamiltonian. However, the mechanism of the such
+attractive coupling is still unclear. Here we reveal the secret by using a
+simple model with two harmonic oscillators coupled to a third oscillator with
+large dissipation. We further identify this dissipative third-party as the
+invisible cavity mode with large leakage in the cavity-magnon experiments. This
+understanding enables designing dissipative coupling in all sorts of coupled
+systems.",1907.06222v2
+2019-10-09,Magnetic field dependence of the nonlocal spin Seebeck effect in Pt/YIG/Pt systems at low temperatures,"We report the nonlocal spin Seebeck effect (nlSSE) in a lateral configuration
+of Pt/Y$_3$Fe$_5$O$_{12}$(YIG)/Pt systems as a function of the magnetic field
+$B$ (up to 10 T) at various temperatures $T$ (3 K < $T$ < 300 K). The nlSSE
+voltage decreases with increasing $B$ in a linear regime with respect to the
+input power (the applied charge-current squared $I^2$). The reduction of the
+nlSSE becomes substantial when the Zeeman energy exceeds thermal energy at low
+temperatures, which can be interpreted as freeze-out of magnons relevant for
+the nlSSE. Furthermore, we found the non-linear power dependence of the nlSSE
+with increasing $I$ at low temperatures ($T$ < 20 K), at which the $B$-induced
+signal reduction becomes less visible. Our experimental results suggest that in
+the non-linear regime high-energy magnons are over populated than those
+expected from the thermal energy. We also estimate the magnon spin diffusion
+length as functions of $B$ and $T$.",1910.04046v1
+2019-10-17,Phonon Transport Controlled by Ferromagnetic Resonance,"The resonant coupling of phonons and magnons is important for the
+interconversion of phononic and spin degrees of freedom. We studied the phonon
+transmission in LiNbO3 manipulated by the dynamic magnetization in a Ni thin
+film. It was observed that the phonons could be absorbed strongly through
+resonant magnon-phonon coupling, which was realized by optimizing the
+interfacial coupling between Ni and LiNbO3. The line shapes of phonon
+transmission were further investigated considering the magnon-phonon
+interconversion in the elastically driven ferromagnetic resonance process. The
+results promote unique routes for phonon manipulation and detection in the
+presence of magnetization dynamics.",1910.08148v1
+2019-10-18,Magnetic field control of topological magnon-polaron bands in two-dimensional ferromagnets,"We theoretically study magnon-phonon hybrid excitations in a square lattice
+ferromagnet subjected to a magnetic field by varying the field direction. The
+bulk bands of hybrid excitations, which are referred to as magnon-polarons, are
+investigated by considering all three phonon modes: vertical phonon, transverse
+phonon, and longitudinal phonon. We show that the topological proprieties of
+three hybridizations are different in terms of the Berry curvature and the
+Chern numbers. We also find that the topological properties of the bands can be
+controlled by changing the direction of the magnetic field, exhibiting one or
+more topological phase transitions. The dependence of thermal Hall conductivity
+as a function of magnetic field direction is proposed as an experiment probe of
+our theoretical results.",1910.08603v1
+2019-10-30,The magnon-mediated attraction between two holes doped in a CuO$_2$ layer,"Using a realistic multi-band model for two holes doped into a CuO$_2$ layer,
+we devise a method to turn off the magnon-mediated interaction between the
+holes. This allows us to verify that this interaction is attractive, and
+therefore could indeed be (part of) the superconducting glue. We derive its
+analytical expression and show that it consists of a novel kind of
+pair-hopping+spin-exchange terms. Its coupling constant is fitted from the
+ground state energy obtained with variational exact diagonalization, and it
+faithfully reproduces the effect of the magnon-mediated attraction in the
+entire Brillouin zone. For realistic parameter values, this effective
+interaction is borderline strong enough to bind the holes into preformed pairs.",1910.14069v1
+2020-01-02,Origin of Strong Two-Magnon Scattering in Heavy Metal/Ferromagnet/Oxide Heterostructures,"We experimentally investigate the origin of the two-magnon scattering (TMS)
+in heavy-metal (HM)/ferromagnet (FM)/oxide heterostructures (FM = Co, Ni81Fe19,
+or Fe60Co20B20) by varying the materials located above and below the FM layers.
+We show that strong TMS in HM/FM/oxide systems arises primarily at the HM/FM
+interface and increases with the strength of interfacial spin-orbit coupling
+and magnetic roughness at this interface. TMS at the FM/oxide interface is
+relatively weak, even in systems where spin-orbit coupling at this interface
+generates strong interfacial magnetic anisotropy. We also suggest that the
+spin-current-induced excitation of non-uniform short-wavelength magnon at the
+HM/FM interface may function as a mechanism of spin memory loss for the
+spin-orbit torque exerted on the uniform mode.",2001.00300v1
+2020-01-29,Detecting Light Boson Dark Matter through Conversion into Magnon,"Light boson dark matter such as axion or hidden photon can be resonantly
+converted into a magnon in a magnetic insulator under the magnetic field, which
+can be detected experimentally. We provide a quantum mechanical formulation for
+the magnon event rate and show that the result is consistent with that obtained
+by a classical calculation. Besides, it is pointed out that the experimental
+setup of the QUAX proposal for the axion detection also works as a detector of
+hidden photon dark matter. It has good sensitivity in the mass range around 1
+meV, which is beyond astrophysical constraints.",2001.10666v3
+2020-03-10,Dynamics of a two-dimensional quantum spin-orbital liquid: spectroscopic signatures of fermionic magnons,"We provide an exact study of dynamical correlations for the quantum
+spin-orbital liquid phases of an SU(2)-symmetric Kitaev honeycomb lattice
+model. We show that the spin dynamics in this Kugel-Khomskii type model is
+exactly the density-density correlation function of S=1 fermionic magnons,
+which could be probed in resonant inelastic x-ray scattering experiments. We
+predict the characteristic signatures of spin-orbital fractionalization in
+inelastic scattering experiments and compare them to the ones of the
+spin-anisotropic Kitaev honeycomb spin liquid. In particular, the resonant
+inelastic x-ray scattering response shows a characteristic momentum dependence
+directly related to the dispersion of fermionic excitations. The neutron
+scattering cross section displays a mixed response of fermionic magnons as well
+as spin-orbital excitations. The latter has a bandwidth of broad excitations
+and a vison gap that is three times larger than that of the spin-1/2 Kitaev
+model.",2003.04835v3
+2020-03-25,Asymmetric scattering behaviors of spin wave dependent on magnetic vortex chirality,"In this letter, an asymmetric spin wave scattering behaviors caused by vortex
+chirality are investigated in cross-shaped ferromagnetic system. In the system,
+four scattering behaviors are found, 1) asymmetric skew scattering, depending
+on the polarity of vortex core, 2) back scattering (reflection), depending on
+the vortex core stiffness, 3) side deflection scattering, depending on
+structural symmetry of the vortex circulation, and 4) geometrical scattering,
+depending on waveguide structure. The first and second scattering behaviors are
+attributed to nonlinear topological magnon spin Hall effect related to magnon
+spin-transfer torque effect, which has value for magnonic exploration and
+application.",2003.11193v2
+2020-04-05,Magnon spectrum and electron spin resonance in antiferromagnet with large single-ion easy plane anisotropy,"Motivated by recent experiments on quantum magnet
+NiCl$_{2}$-4SC(NH$_{2}$)$_{2}$ (DTN) and its Br-doped counterpart DTNX we
+propose a theoretical description of optical magnon branch in the
+antiferromagnet with large single-ion anisotropy in the magnetically ordered
+phase. In the framework of the 1/S expansion we derive analytical expressions
+for optical magnon with $\mathbf{k}=0$ energy magnetic field dependence
+$\Delta(h)$. It is shown that in the linear spin wave approximation $\Delta(h)$
+is monotonic without extrema whereas first order in 1/S corrections makes it
+drastically different function with a minimum near the center of magnetically
+ordered phase. The latter behaviour was observed in ESR experiments. Moreover,
+we show that $\Delta(h)$ has nontrivial dependence on the system parameters. It
+solves the discrepancy between inelastic neutron scattering data where the
+growth of interaction constants in DTNX with small Br concentration was
+observed and ESR experiments showing almost unchanged $\Delta(h)$ in comparison
+with pure DTN.",2004.02170v2
+2020-04-06,Resonant inelastic x-ray scattering study of vector chiral ordered kagome antiferromagnet,"We study the resonant inelastic x-ray scattering (RIXS) features of vector
+chiral ordered kagome antiferromagnets. Utilizing a group theoretical formalism
+that respects lattice site symmetry, we calculated the $L$ -edge magnon
+contribution for the vesignieite compound BaCu$_{3}$V$_{2}$O$_{8}$(OH)$_{2}$.
+We show that polarization dependence of the $L$ -edge RIXS spectrum can be used
+to track magnon branches. We predict a non-zero $L$ -edge signal in the
+non-cross $\pi-\pi$ polarization channel. At the $K$ -edge, we derived the
+two-site effective RIXS and Raman scattering operator for two-magnon excitation
+in vesignieite using the Shastry-Shraiman formalism. Our derivation considers
+spin-orbit coupling effects in virtual hopping processes. We find vector chiral
+correlation (four-spin) contribution that is proportional to the RIXS spectrum.
+Our scattering operator formalism can be applied to a host of non-collinear
+non-coplanar magnetic materials at both the $L$ and $K$ -edge. We demonstrate
+that vector chiral correlations can be accessed by RIXS experiments.",2004.02871v2
+2020-04-21,Optical observation of quasiperiodic Heisenberg antiferromagnets in two dimensions,"We calculate magnetic Raman spectra of Heisenberg antiferromagnets on the
+two-dimensional Penrose lattice. We follow the Shastry-Shraiman formulation of
+Raman scattering in a strongly correlated Hubbard system and obtain the second-
+and fourth-order effective Raman operators. The second-order Raman intensity
+comes from the E2 mode, and it is invariant under an arbitrary rotation of
+polarization vectors. The fourth-order Raman intensities consist of A1 and A2,
+as well as E2, modes and therefore yield strong polarization dependence. In
+particular, the A2 mode intensity directly detects the dynamical spin-chirality
+fluctuations. Employing linearly and circularly polarized lights, we can
+separately extract every irreducible representation from the observations. We
+further discuss effects of magnon-magnon interactions on the magnetic Raman
+scattering. Our theory provides a reasonable explanation for the two-magnon
+scattering process.",2004.09850v1
+2020-05-04,Spin-orbit-torque magnonics,"The field of magnonics, which utilizes propagating spin waves for nano-scale
+transmission and processing of information, has been significantly advanced by
+the advent of the spin-orbit torque. The latter phenomenon can allow one to
+overcome two main drawbacks of magnonic devices - low energy efficiency of
+conversion of electrical signals into spin wave signals, and fast spatial decay
+of spin waves in thin-film waveguiding structures. At first glance, the
+excitation and amplification of spin waves by spin-orbit torques can seem to be
+straightforward. Recent research indicates, however, that the lack of the
+mode-selectivity in the interaction of spin currents with dynamic magnetic
+modes and the onset of dynamic nonlinear phenomena represent significant
+obstacles. Here, we discuss the possible route to overcoming these limitations,
+based on the suppression of nonlinear spin-wave interactions in magnetic
+systems with perpendicular magnetic anisotropy. We show that this approach
+enables efficient excitation of coherent magnetization dynamics and propagating
+spin waves in extended spatial regions, and is expected to enable practical
+implementation of complete compensation of spin-wave propagation losses.",2005.01391v1
+2020-05-08,Observation of terahertz magnon of Kaplan-Kittel exchange resonance in yttrium-iron garnet by Raman spectroscopy,"Backscattering Raman spectroscopic investigations were performed on an
+yttrium-iron garnet single crystal using linearly and circularly polarized
+light. A terahertz (THz) magnon of the Kaplan-Kittel (KK) exchange resonance
+was discovered, which had been regarded as unobservable via optical methods.
+The KK exchange resonance had a 7.8-THz frequency at 80 K, and the polarization
+selection rule led to an antisymmetric Raman tensor of the $A_{2}$ mode.
+Moreover, the assignment of all the Raman-active phonon modes, $3A_{1g}$,
+$8E_{g}$, and $14T_{2g}$, was proposed. This study will stimulate further
+investigation of the coupling of THz magnons and phonons and pave the way
+toward THz optomagnonics.",2005.03852v2
+2020-05-20,Einstein-de Haas Effect of Topological Magnons,"We predict the existence of Einstein-de Haas effect in topological magnon
+insulators. Temperature variation of angular momentum in the topological state
+shows a sign change behavior, akin to the low temperature thermal Hall
+conductance response. This manifests itself as a macroscopic mechanical
+rotation of the material hosting topological magnons. We show that an
+experimentally observable Einstein-de Haas effect can be measured in the
+square-octagon, the kagome, and the honeycomb lattices. Albeit, the effect is
+the strongest in the square-octagon lattice. We treat both the low and the high
+temperature phases using spin wave and Schwinger boson theory, respectively. We
+propose an experimental set up to detect our theoretical predictions. We
+suggest candidate square-octagon materials where our theory can be tested.",2005.10273v2
+2020-05-22,Dipolar spin waves in uniaxial easy-axis antiferromagnets: A natural topological nodal-line semimetal,"The existence of the magnetostatic surface spin waves in ferromagnets, known
+as Damon-Eshbach mode, was recently demonstrated to originate from the topology
+of the dipole-dipole interaction. In this work, we study the topological
+characteristics of magnons in easy-axis antiferromagnets with uniaxial
+anisotropy. The dipolar spin waves are found to be, driven by the dipole-dipole
+interaction, in a topological nodal-line semimetal phase, which hosts
+Damon-Eshbach-type surface modes due to the bulk-edge correspondence. The long
+wavelength character of dipolar spin waves makes our proposal valid for any
+natural uniaxial easy-axis antiferromagnet, and thus enriches the candidates of
+topological magnonic materials. In contrast to the nonreciprocal property in
+ferromagnetic case, the surface modes with opposite momentum coexist at each
+surface, but with different chiralities. Such a chirality-momentum or
+spin-momentum locking, similar to that of electronic surface states in
+topological insulators, offers the opportunity to design novel chirality-based
+magnonic devices in antiferromagnets.",2005.10971v1
+2020-07-06,Hippopede curves for modelling radial spin waves in an azimuthal graded magnonic landscape,"We propose a mathematical model for describing radially propagating spin
+waves emitted from the core region in a magnetic patch with n vertices in a
+magnetic vortex state. The azimuthal anisotropic propagation of surface spin
+waves (SSW) into the domain, and confined spin waves (or Winter's Magnons, WM)
+in domain walls increases the complexity of the magnonic landscape. In order to
+understand the spin wave propagation in these systems, we first use an approach
+based on geometrical curves called 'hippopedes', however it provides no insight
+into the underlying physics. Analytical models rely on generalized expressions
+from the dispersion relation of SSW with an arbitrary angle between
+magnetization M and wavenumber k. The derived algebraic expression for the
+azimuthal dispersion is found to be equivalent to that of the 'hippopede'
+curves. The fitting curves from the model yield a spin wave wavelength for any
+given azimuthal direction, number of patch vertices and excitation frequency,
+showing a connection with fundamental physics of exchange dominated surface
+spin waves. Analytical results show good agreement with micromagnetic
+simulations and can be easily extrapolated to any n-corner patch geometry.",2007.02646v2
+2020-07-23,Density Wave Mediated Dzyaloshinskii-Moriya Interactions,"We investigate the effect that density wave states have on the localized
+spins of a square lattice. We find that topologically nontrivial density wave
+states can induce stable Dzyaloshinskii-Moriya (DM) interactions among the
+localized spins of the lattice in the presence of an external magnetic field,
+and we study the resulting spin models for both antiferromagnetic and
+ferromagnetic backgrounds. While the density wave state itself can contribute
+to the the thermal Hall effect, as shown by Li & Lee (arXiv:1905.04248v3),
+symmetry considerations preclude the resulting spin excitations from inducing a
+further thermal Hall effect. We utilize a Holstein-Primakoff (HP) substitution
+about the classical mean-field ground state to calculate the magnon dispersion
+for LSCO and find that the density wave induces a weak $d_{x^2-y^2}$
+anisotropy; upon calculating the non-Abelian Berry curvature for this magnon
+branch we show explicitly that the magnon contribution to $\kappa_{xy}$ is
+zero. Finally, we calculate corrections to the magnetic ground state energy,
+spin canting angles, and the spin-wave dispersion due to the topological
+density wave for ferromagnetic backgrounds. We find that terms linear in the HP
+bosons can affect the critical behavior, a point previously overlooked in the
+literature.",2007.11719v1
+2020-07-26,Fractionalized Spin Excitations in the Edge Ferromagnetic State of Graphene: Signature of the Ferromagnetic Luttinger Liquid,"The elementary excitations from the conventional magnetic ordered states,
+such as ferromagnets and antiferromagnets, are magnons. Here, we elaborate a
+case where the well-defined magnons are absent completely and the spin
+excitation spectra exhibit an entire continuum in the itinerant edge
+ferromagnetic state of graphene arising from the flatband edge electronic
+states. Based on the further studies of the entanglement entropy and
+finite-size analysis, we show that the continuum other than the Stoner part
+results from the spin-1/2 spinons deconfined from magnons. The spinon continuum
+in a magnetically ordered state is ascribed to a ferromagnetic Luttinger liquid
+in this edge ferromagnet. The investigation is carried out by using the
+numerical exact diagonalization method with a projection of the interacting
+Hamiltonian onto the flat band.",2007.13142v1
+2020-07-30,Resonant subwavelength control of the phase of spin waves reflected from a ferromagnetic film edge,"Using frequency-domain finite element calculations cross-checked with
+micromagnetic simulations, we demonstrate that the phase of spin waves
+reflected from an interface between a permalloy film and a bilayer can be
+controlled by changing dimensions of the bilayer. Treating the bilayer formed
+by the permalloy film and a ferromagnetic stripe as a segment of a multi-mode
+waveguide, we show that spin-wave Fabry-Perot resonances of one of its modes
+are responsible for the high sensitivity of the phase of reflected waves to
+stripe width and the stripe-film separation. Thus, the system is a unique
+realization of a fully magnonic Gires-Tournois interferometer based on a
+two-modes resonator, which can be treated as a magnonic counterpart of a
+metasurface, since it enables manipulation of the phase of spin waves at
+subwavelength distances. Knowledge gained from these calculations might be used
+to design magnonic devices such as flat lenses or magnetic particle detectors.",2007.15226v5
+2020-07-30,Coherent multi-mode conversion from microwave to optical wave via a magnon-cavity hybrid system,"Coherent conversion from microwave to optical wave opens new research avenues
+towards long distant quantum network covering quantum communication, computing,
+and sensing out of the laboratory. Especially multi-mode enabled system is
+essential for practical applications. Here we experimentally demonstrate
+coherent multi-mode conversion from the microwave to optical wave via
+collective spin excitation in a single crystal yttrium iron garnet (YIG,
+Y3Fe5O12) which is strongly coupled to a microwave cavity mode in a
+three-dimensional rectangular cavity. Expanding collective spin excitation mode
+of our magnon-cavity hybrid system from Kittel to multi magnetostatic modes, we
+verify that the size of YIG sphere predominantly plays a crucial role for the
+microwave-to-optical multi-mode conversion efficiency at resonant conditions.
+We also find that the coupling strength between multi magnetostatic modes and a
+cavity mode is manipulated by the position of a YIG inside the cavity. It is
+expected to be valuable for designing a magnon hybrid system that can be used
+for coherent conversion between microwave and optical photons.",2007.15299v1
+2020-08-04,Bose-Einstein condensate of Dirac magnons: Pumping and collective modes,"We explore the formation and collective modes of Bose-Einstein condensate of
+Dirac magnons (Dirac BEC). While we focus on two-dimensional Dirac magnons, an
+employed approach is general and could be used to describe Bose-Einstein
+condensates with linear quasiparticle spectrum in various systems. By using a
+phenomenological multicomponent model of pumped boson population together with
+bosons residing at Dirac nodes, the formation and time evolution of condensates
+of Dirac bosons is investigated. The condensate coherence and its
+multicomponent nature are manifested in the Rabi oscillations whose period is
+determined by the gap in the spin-wave spectrum. A Dirac nature of the
+condensates could be also probed by the spectrum of collective modes. It is
+shown that the Haldane gap provides an efficient means to tune between the
+gapped and gapless collective modes as well as controls their stability.",2008.01328v2
+2020-08-05,Magnon-driven dynamics of a hybrid system excited with ultrafast optical pulses,"The potential of photon-magnon hybrid systems as building blocks for quantum
+information science has been widely demonstrated, and it is still the focus of
+much research. We leverage the strengths of this unique heterogeneous physical
+system in the field of precision physics beyond the standard model, where the
+sensitivity to the so-called ""invisibles"" is currently being boosted by quantum
+technologies. Here, we demonstrate that quanta of spin waves, driven by
+tiniest, effective magnetic field, can be detected in a large frequency band
+using a hybrid system as transducer. This result can be applied to the search
+of cosmological signals related, for example, to cold Dark Matter, which may
+directly interact with magnons. Our model of the transducer is based on a
+second-quantisation two-oscillators hybrid system, it matches the observations,
+and can be easily extended to thoroughly describe future large-scale
+ferromagnetic haloscopes.",2008.02317v1
+2020-08-13,Concurrence of topological electrons and magnons in the Kagome ferromagnet CoCu3(OH)6Cl2,"Spin and charge are two interrelated properties of electrons. However, most
+of previous works on topological matter study the electronic and magnonic
+excitations separately. In this paper, by combining density functional theory
+calculations with the Schwinger boson method, we determine the topological
+electronic band structures and topological magnon spectrum simultaneously in
+the ferromagnetic ground state of the narrow-band-gap CoCu3(OH)6Cl2, which is
+an ABC stacking Kagome lattice material with fractional occupancy on Cu sites.
+This material provides an ideal platform to study the interplay of different
+types of topological excitations. Our work also proposes a useful method to
+deal with correlated topological magnetic systems with narrow band gaps.",2008.05692v1
+2020-08-21,Spin waves in skyrmionic structures with various topological charges,"Equilibrium properties and localised magnon excitations are investigated in
+topologically distinct skyrmionic textures. The observed shape of the
+structures and their orientation on the lattice is explained based on their
+vorticities and the symmetry of the crystal. The transformation between
+different textures and their annihilation as a function of magnetic field is
+understood based on the energy differences between them. The angular momentum
+spin-wave eigenmodes characteristic of cylindrically symmetric structures are
+combined in the distorted spin configurations, leading to avoided crossings in
+the magnon spectrum. The susceptibility of the skyrmionic textures to
+homogeneous external fields is calculated, revealing that a high number of
+modes become detectable due to the hybridization between the angular momentum
+eigenmodes. These findings should contribute to the observation of spin waves
+in distorted skyrmionic structures via experiments and numerical simulations,
+widening the range of their possible applications in magnonic devices.",2008.09392v2
+2020-08-21,Quantum sensing of a coherent single spin excitation in a nuclear ensemble,"The measurement of single quanta in a collection of coherently interacting
+objects is transformative in the investigations of emergent quantum phenomena.
+An isolated nuclear-spin ensemble is a remarkable platform owing to its
+coherence, but detecting its single spin excitations has remained elusive.
+Here, we use an electron spin qubit in a semiconductor quantum dot to sense a
+single nuclear-spin excitation (a nuclear magnon) with 1.9-ppm precision via
+the 200-kHz hyperfine shift on the 28-GHz qubit frequency. We demonstrate this
+single-magnon precision across multiple modes identified by nuclear species and
+polarity. Finally, we monitor the coherent dynamics of a nuclear magnon and the
+emergence of quantum correlations competing against decoherence. A direct
+extension of this work is to probe engineered quantum states of the ensemble
+including long-lived memory states.",2008.09541v1
+2020-08-25,Short-range Thermal Magnon Diffusion in Magnetic Garnet,"Using the spin Seebeck effect (SSE), we study the propagation distance of
+thermal spin currents inside a magnetic insulator thin film in the short-range
+regime. We disambiguate spin currents driven by temperature and chemical
+potential gradients by comparing the SSE signal before and after adding a
+thermalization capping layer on the same device. We report that the measured
+spin decay behavior near the heat source is well accounted for by a diffusion
+model where the magnon diffusion length is in submicron range, \textit{i.e.}
+two orders of magnitude smaller than previous estimates inferred from the
+long-range behavior. Our results highlight the caveat in applying a diffusive
+theory to describe thermal magnon transport, where a single decay length may
+not capture the behavior on all length scales.",2008.10942v1
+2020-10-21,Determination of magnon mass of neodymium magnet by temperature dependence of spontaneous magnetization,"The effective mass of a magnon in a neodymium magnet is evaluated using Bloch
+temperature dependence of spontaneous magnetization. We used the Hall effect
+magnetometer and thermo-couple thermometer for measuring of the temperature of
+the water in which the encapsulated commercial magnet is immersed. The
+experiment can be repeated in every school and methodological remarks for
+experimental data processing are given with great detail and attention. The
+purpose of the paper is to illustrate the simple relation between the quantum
+spectrum of magnons and the easily measured magnetic field of a permanent
+magnet.",2010.11229v2
+2020-11-09,Microwave Quantum Illumination via Cavity Magnonics,"Quantum illumination (QI) is a quantum sensing protocol mainly for target
+detection which uses entangled signal-idler photon pairs to enhance the
+detection efficiency of low-reflectivity objects immersed in thermal noisy
+environments. Especially, due to the naturally occurring background radiation,
+the photon emitted toward potential targets more appropriately lies in the
+microwave region. Here, we propose a hybrid quantum source based on cavity
+magnonics for microwave QI, where the medium that bridges the optical and the
+microwave modes is magnon, the quanta of spin wave. Within experimentally
+accessible parameters, significant microwave-optical quantum resources of
+interest can be generated, leading to orders of magnitude lower detecting error
+probability compared with the electro-optomechanical prototype quantum radar
+and any classical microwave radar with equal transmitted energy.",2011.04301v2
+2020-11-29,Cross-sublattice Spin Pumping and Magnon Level Attraction in van der Waals Antiferromagnets,"We theoretically study spin pumping from a layered van der Waals
+antiferromagnet in its canted ground state into an adjacent normal metal. We
+find that the resulting dc spin pumping current bears contributions along all
+spin directions. Our analysis allows for detecting intra- and cross-sublattice
+spin-mixing conductances via measuring the two in-plane spin current
+components. We further show that sublattice symmetry-breaking Gilbert damping
+can be realized via interface engineering and induces a dissipative coupling
+between the optical and acoustic magnon modes. This realizes magnon level
+attraction and exceptional points in the system. Furthermore, the dissipative
+coupling and cross-sublattice spin pumping contrive to produce an
+unconventional spin current in the out-of-plane direction. Our findings provide
+a route to extract the spin mixing conductance matrix and uncovers the unique
+opportunities, such as level attraction, offered by van der Waals
+antiferromagnet-normal metal hybrids.",2011.14314v1
+2021-01-12,Temperature dependence of the mean magnon collision time in a spin Seebeck device,"Based on the relaxation time approximation, the mean collision time for
+magnon scattering $\tau_c(T)$ is computed from the experimental spin Seebeck
+coefficient of a bulk YIG / Pt bilayer. The scattering results to be composed
+by two processes: the low temperature one, with a $T^{-1/2}$ dependence, is
+attributed to the scattering by defects and provides a mean free path around 10
+$\mu$m; the high temperature one, depending on $T^{-4}$, is associated to the
+scattering by other magnons. The results are employed to predict the thickness
+dependence of the spin Seebeck coefficient for thin films.",2101.04405v1
+2021-03-09,Spin-Space Groups and Magnon Band Topology,"Band topology is both constrained and enriched by the presence of symmetry.
+The importance of anti-unitary symmetries such as time reversal was recognized
+early on leading to the classification of topological band structures based on
+the ten-fold way. Since then, lattice point group and non-symmorphic symmetries
+have been seen to lead to a vast range of possible topologically nontrivial
+band structures many of which are realized in materials. In this paper we show
+that band topology is further enriched in many physically realizable instances
+where magnetic and lattice degrees of freedom are wholly or partially
+decoupled. The appropriate symmetry groups to describe general magnetic systems
+are the spin-space groups. Here we describe cases where spin-space groups are
+essential to understand the band topology in magnetic materials. We then focus
+on magnon band topology where the theory of spin-space groups has its simplest
+realization. We consider magnetic Hamiltonians with various types of coupling
+including Heisenberg and Kitaev couplings revealing a hierarchy of enhanced
+magnetic symmetry groups depending on the nature of the lattice and the
+couplings. We describe, in detail, the associated representation theory and
+compatibility relations thus characterizing symmetry-enforced constraints on
+the magnon bands revealing a proliferation of nodal points, lines, planes and
+volumes.",2103.05656v1
+2021-03-11,Spin Nernst Effect of Antiferromagnetic Magnons in the Presence of Spin Diffusion,"Magnon spin Nernst effect was recently proposed as an intrinsic effect in
+antiferromagnets, where spin diffusion and boundary spin transmission have been
+ignored. However, diffusion processes are essential to convert a bulk spin
+current into boundary spin accumulation, which determines the spin injection
+rate into detectors through imperfect transmission. We formulate a diffusive
+theory to describe the detection of magnon spin Nernst effect with boundary
+conditions reflecting real device geometry. Thanks to the spin diffusion
+effect, the output signals in both electronic and optical detection grow
+rapidly with an increasing system size in the transverse dimension, which
+eventually saturate. Counterintuitively, the measurable signals are even
+functions of magnetic field, yielding optical detection more favorable than
+electronic detection.",2103.06870v3
+2021-03-18,Cherenkov radiation of spin waves by ultra-fast moving magnetic flux quanta,"Despite theoretical predictions for a Cherenkov-type radiation of spin waves
+(magnons) by various propagating magnetic perturbations, fast-enough moving
+magnetic field stimuli have not been available so far. Here, we experimentally
+realize the Cherenkov radiation of spin waves in a Co-Fe magnonic conduit by
+fast-moving (>1 km/s) magnetic flux quanta (Abrikosov vortices) in an adjacent
+Nb-C superconducting strip. The radiation is evidenced by the microwave
+detection of spin waves propagating a distance of 2 micrometers from the
+superconductor and it is accompanied by a magnon Shapiro step in its
+current-voltage curve. The spin-wave excitation is unidirectional and
+monochromatic, with sub-40 nm wavelengths determined by the period of the
+vortex lattice. The phase-locking of the vortex lattice with the excited spin
+wave limits the vortex velocity and reduces the dissipation in the
+superconductor.",2103.10156v2
+2021-04-22,Dynamical Backaction Magnomechanics,"Dynamical backaction resulting from radiation pressure forces in
+optomechanical systems has proven to be a versatile tool for manipulating
+mechanical vibrations. Notably, dynamical backaction has resulted in the
+cooling of a mechanical resonator to its ground-state, driving phonon lasing,
+the generation of entangled states, and observation of the optical-spring
+effect. In certain magnetic materials, mechanical vibrations can interact with
+magnetic excitations (magnons) via the magnetostrictive interaction, resulting
+in an analogous magnon-induced dynamical backaction. In this article, we
+directly observe the impact of magnon-induced dynamical backaction on a
+spherical magnetic sample's mechanical vibrations. Moreover, dynamical
+backaction effects play a crucial role in many recent theoretical proposals;
+thus, our work provides the foundation for future experimental work pursuing
+many of these theoretical proposals.",2104.11218v2
+2021-04-22,Theory for electrical detection of the magnon Hall effect induced by dipolar interactions,"We derive the anomalous Hall contributions arising from dipolar interactions
+to diffusive spin transport in magnetic insulators. Magnons, the carriers of
+angular momentum in these systems, are shown to have a non-zero Berry
+curvature, resulting in a measurable Hall effect. For yttrium iron garnet (YIG)
+thin films we calculate both the anomalous and magnon spin conductivities. We
+show that for a magnetic field perpendicular to the film the anomalous Hall
+conductivity is finite. This results in a non-zero Hall signal, which can be
+measured experimentally using Permalloy strips arranged like a Hall bar on top
+of the YIG thin film. We show that electrical detection and injection of spin
+is possible, by solving the resulting diffusion-relaxation equation for a Hall
+bar. We predict the experimentally measurable Hall coefficient for a range of
+temperatures and magnetic field strengths. Most strikingly, we show that there
+is a sign change of the Hall coefficient associated with increasing the
+thickness of the film.",2104.11304v1
+2021-04-27,Magnon modes as a joint effect of surface ferromagnetism and spin-orbite coupling in CoSi chiral topological semimetal,"CoSi single crystal is a known realization of a chiral topological semimetal
+with simultaneously broken mirror and inversion symmetries. In addition to the
+symmetry-induced spin-orbit coupling, surface ferromagnetism is known in
+nominally diamagnetic CoSi structures, which appears due to the distorted bonds
+and ordered vacancies near the surface. We experimentally investigate electron
+transport through a thin CoSi flake at high current density. Surprisingly, we
+demonstrate $dV/dI(I)$ curves which are qualitatively similar to ones for
+ferromagnetic multilayers with characteristic $dV/dI$ magnon peaks and
+unconventional magnetic field evolution of the peaks' positions. We understand
+these observations as a result of current-induced spin polarization due to the
+significant spin-orbit coupling in CoSi. Scattering of non-equilibrium
+spin-polarized carriers within the surface ferromagnetic layer is responsible
+for the precessing spin-wave excitations, so the observed magnon modes are the
+joint effect of surface ferromagnetism and spin-orbit coupling in a CoSi chiral
+topological semimetal. Thus, thin CoSi flakes behave as magnetic conductors
+with broken inversion symmetry, which is important for different spintronic
+phenomena.",2104.13252v1
+2021-05-12,Magnon spin current induced by triplet Cooper pair supercurrents,"At the interface between a ferromagnetic insulator and a superconductor there
+is a coupling between the spins of the two materials. We show that when a
+supercurrent carried by triplet Cooper pairs flows through the superconductor,
+the coupling induces a magnon spin current in the adjacent ferromagnetic
+insulator. The effect is dominated by Cooper pairs polarized in the same
+direction as the ferromagnetic insulator, so that charge and spin supercurrents
+produce similar results. Our findings demonstrate a way of converting Cooper
+pair supercurrents to magnon spin currents.",2105.05861v2
+2021-05-16,Tunable anisotropic quantum Rabi model via a magnon--spin-qubit ensemble,"The ongoing rapid progress towards quantum technologies relies on new hybrid
+platforms optimized for specific quantum computation and communication tasks,
+and researchers are striving to achieve such platforms. We study theoretically
+a spin qubit exchange-coupled to an anisotropic ferromagnet that hosts magnons
+with a controllable degree of intrinsic squeezing. We find this system to
+physically realize the quantum Rabi model from the isotropic to the
+Jaynes-Cummings limit with coupling strengths that can reach the deep-strong
+regime. We demonstrate that the composite nature of the squeezed magnon enables
+concurrent excitation of three spin qubits coupled to the same magnet. Thus,
+three-qubit Greenberger-Horne-Zeilinger and related states needed for
+implementing Shor's quantum error-correction code can be robustly generated.
+Our analysis highlights some unique advantages offered by this hybrid platform,
+and we hope that it will motivate corresponding experimental efforts.",2105.07430v2
+2021-05-24,Cavity magnomechanics with surface acoustic waves,"Magnons, namely spin waves, are collective spin excitations in ferromagnets,
+and their control through coupling with other excitations is a key technology
+for future hybrid spintronic devices. Although strong coupling has been
+demonstrated with microwave photonic structures, an alternative approach
+permitting high density integration and minimized electromagnetic crosstalk is
+required. Here we report a planar cavity magnomechanical system, where the
+cavity of surface acoustic waves enhances the spatial and spectral power
+density to thus implement magnon-phonon coupling at room temperature.
+Excitation of spin-wave resonance involves significant acoustic power
+absorption, whereas the collective spin motion reversely exerts a back-action
+force on the cavity dynamics. The cavity frequency and quality-factor are
+significantly modified by the back-action effect, and the resultant
+cooperativity exceeds unity, suggesting coherent interaction between magnons
+and phonons. The demonstration of a chip-scale magnomechanical system paves the
+way to the development of novel spin-acoustic technologies for classical and
+quantum applications.",2105.11127v1
+2021-05-28,Implementation and enhancement of nonreciprocal quantum synchronization with strong isolation in antiferromagnet-cavity systems,"Sensitive signal detection and processing in classical world, especially in
+quantum regime, require nonreciprocal manipulation. In this paper we show how
+to achieve nonreciprocal quantum synchronization for two magnon modes in a
+two-sublattice antiferromagnet with strong isolation.The antiferromagnet is
+trapped in a cavity with two posts so that the two magnon modes not only couple
+to each other through a parametric-type interaction, but also interact with a
+same cavity respectively in a beam splitter-type and parametric-type ways.
+Under the condition of system's stability, we show that nonreciprocal quantum
+synchronization between two magnon modes is mainly dependent on resonance
+frequency of the cavity caused by direction of input currents. In
+addition,quantum synchronization is enhanced by the increase of interaction
+strength between two Bogoliubov modes and cavity mode. Moreover, numerical
+simulation results with parameters commonly used in current experiments show
+that the present scheme may be feasible.",2105.13525v1
+2021-06-15,Two-dimensional spin models with macroscopic degeneracy,"We consider a class of anisotropic spin-$\frac{1}{2}$ models with competing
+ferro- and antiferromagnetic interactions on two-dimensional Tasaki and kagome
+lattices consisting of corner sharing triangles. For certain values of the
+interactions the ground state is macroscopically degenerated in zero magnetic
+field. In this case the ground state manifold consists of isolated magnons as
+well as the bound magnon complexes. The ground state degeneracy is estimated
+using a special form of exact wave function which admits arrow configuration
+representation on two-dimensional lattice. The comparison of this estimate with
+the result for some special exactly solved models shows that the used approach
+determines the number of the ground states with exponential accuracy. It is
+shown that the main contribution to the ground state degeneracy and the
+residual entropy is given by the bound magnon complexes.",2106.07965v1
+2021-06-19,Approaching to the deep-strong photon-to-magnon coupling,"In this work, the ultra-strong photon-to-magnon coupling is demonstrated for
+on-chip multilayered superconductor/ferromagnet/insulator hybrid thin film
+structures reaching the coupling strength above 6 GHz, the coupling ratio about
+0.6, the single-spin coupling strength about 350 Hz, and cooperativity about
+10^4. High characteristics of coupling are achieved owing to a radical
+suppression of the photon phase velocity in electromagnetic resonator. With
+achieved coupling the spectrum reveals inapplicability of the Dicke model, and
+evidences contribution of the diamagnetic A^2 interaction term in the
+Hamiltonian of the system, which satisfies the Thomas-Reiche-Kuhn sum rule. The
+contribution of the A^2 term denotes validity of the Hopfield quantum model and
+manifests observation of a different hybrid polariton quasi-particle, namely,
+the plasmon-magnon polariton.",2106.10450v1
+2021-07-07,Polarization dependent scattering in cavity optomagnonics,"The polarization dependence of magnon-photon scattering in an optical
+microcavity is reported. Due to the short cavity length, the mode-matching
+conditions found in previously explored, large path-length whispering gallery
+resonators are absent. Nonetheless, for cross-polarized scattering a strong and
+broadband suppression of one side-band is observed. This arises due to an
+interference between the Faraday and second-order Cotton-Mouton effects. To
+fully account for the suppression of the cross-polarized scattering, it is
+necessary to consider the squeezing of magnon modes intrinsic to thin-film
+geometry. A co-polarized scattering due to Cotton-Mouton effect is also
+observed. In addition, the magnon modes involved are identified as
+Damon-Eshbach surface modes, whose non-reciprocal propagation could be
+exploited in devices applications. This work experimentally demonstrates the
+important role of second order Cotton-Mouton effect for optomagnonic devices.",2107.03214v1
+2021-07-12,Instabilities of heavy magnons in an anisotropic magnet,"The search for new elementary particles is one of the most basic pursuits in
+physics, spanning from subatomic physics to quantum materials. Magnons are the
+ubiquitous elementary quasiparticle to describe the excitations of
+fully-ordered magnetic systems. But other possibilities exist, including
+fractional and multipolar excitations. Here, we demonstrate that strong quantum
+interactions exist between three flavors of elementary quasiparticles in the
+uniaxial spin-one magnet FeI2. Using neutron scattering in an applied magnetic
+field, we observe spontaneous decay between conventional and heavy magnons and
+the recombination of these quasiparticles into a super-heavy bound-state. Akin
+to other contemporary problems in quantum materials, the microscopic origin for
+new physics in FeI2 is the quasi-flat nature of excitation bands and the
+presence of Kitaev anisotropic magnetic exchange interactions.",2107.05694v3
+2021-07-23,"Dirac magnons, nodal lines, and nodal plane in elemental gadolinium","We investigate the magnetic excitations of elemental gadolinium (Gd) using
+inelastic neutron scattering, showing that Gd is a Dirac magnon material with
+nodal lines at $K$ and nodal planes at half integer $\ell$. We find an
+anisotropic intensity winding around the $K$-point Dirac magnon cone, which is
+interpreted to indicate Berry phase physics. Using linear spin wave theory
+calculations, we show the nodal lines have non-trivial Berry phases, and
+topological surface modes. We also discuss the origin of the nodal plane in
+terms of a screw-axis symmetry, and introduce a topological invariant
+characterizing its presence and effect on the scattering intensity. Together,
+these results indicate a highly nontrivial topology, which is generic to
+hexagonal close packed ferromagnets. We discuss potential implications for
+other such systems.",2107.11372v3
+2021-08-07,Strong Momentum-Dependent Electron-Magnon Renormalization of a Surface Resonance on Iron,"The coupling of fermionic quasiparticles to magnons is essential for a wide
+range of processes, from ultrafast magnetization dynamics in ferromagnets to
+Cooper pairing in superconductors. Although magnon energies are generally much
+larger than phonon energies, up to now their electronic band renormalization
+effect in ferromagnetic metals suggests a significantly weaker quasiparticle
+interaction. Here, using spin- and angle-resolved photoemission, we show an
+extraordinarily strong renormalization leading to replica-band formation of an
+iron surface resonance at ~200 meV. Its strong magnetic linear dichroism
+unveils the magnetic nature and momentum dependence of the energy
+renormalization. By determining the frequency- and momentum-dependent
+self-energy due to generic electron-boson interaction to compute the resultant
+electron spectral function, we show that the surface-state replica formation is
+consistent with strong coupling to an optical spin wave in a Fe thin film.",2108.03421v1
+2021-08-10,Fragmentation and emergent integrable transport in the weakly tilted Ising chain,"We investigate emergent quantum dynamics of the tilted Ising chain in the
+regime of a weak transverse field. Within the leading order perturbation
+theory, the Hilbert space is fragmented into exponentially many decoupled
+sectors. We find that the sector made of isolated magnons is integrable with
+dynamics being governed by a constrained version of the XXZ spin Hamiltonian.
+As a consequence, when initiated in this sector, the Ising chain exhibits
+ballistic transport on unexpectedly long times scales. We quantitatively
+describe its rich phenomenology employing exact integrable techniques such as
+Generalized Hydrodynamics. Finally, we initiate studies of
+integrability-breaking magnon clusters whose leading-order transport is
+activated by scattering with surrounding isolated magnons.",2108.04845v2
+2021-08-12,Magnetic interactions and spin excitations in van der Waals ferromagnet VI$_3$,"Using a combination of density functional theory (DFT) and spin-wave theory
+methods, we investigate the magnetic interactions and spin excitations in
+semiconducting VI$_3$. Exchange parameters of monolayer, bilayer, and bulk
+forms are evaluated by mapping the magnetic energies of various spin
+configurations, calculated using DFT+$U$, onto the Heisenberg model. The
+intralayer couplings remain largely unchanged in three forms of VI$_3$, while
+the interlayer couplings show stronger dependence on the dimensionality of the
+materials. We calculate the spin-wave spectra within a linear spin-wave theory
+and discuss how various exchange parameters affect the magnon bands. The
+magnon-magnon interaction is further incorporated, and the Curie temperature is
+estimated using a self-consistently renormalized spin-wave theory. To
+understand the roles of constituent atoms on magnetocrystalline anisotropy
+energy (MAE), we resolve MAE into sublattices and find that a strong negative
+V-I inter-sublattice contribution is responsible for the relatively small
+easy-axis MAE in VI$_3$.",2108.05528v1
+2021-08-19,Intrinsic topological magnons in arrays of magnetic dipoles,"We study a simple magnetic system composed of periodically modulated magnetic
+dipoles with an easy axis. Upon adjusting the modulation amplitude alone,
+chains and two-dimensional stacked chains exhibit a rich magnon spectrum where
+frequency gaps and magnon speeds are easily manipulable. The blend of
+anisotropy due to dipolar interactions between magnets and geometrical
+modulation induces a magnetic phase with fractional Zak number in infinite
+chains and end states in open one-dimensional systems. In two dimensions it
+gives rise to topological modes at the edges of stripes. Tuning the amplitude
+in two-dimensional lattices causes a band touching, which triggers the exchange
+of the Chern numbers of the volume bands and switches the sign of the thermal
+conductivity.",2108.08459v2
+2021-09-01,Magnonic Proximity Effect in Insulating Ferro- and Antiferromagnetic Trilayers,"The design of spin-transport based devices such as magnon transistors or spin
+valves will require multilayer systems composed of different magnetic materials
+with different physical properties. Such layered structures can show various
+interface effects, one class of which being proximity effects, where a certain
+physical phenomenon that occurs in the one layers leaks into another one. In
+this work a magnetic proximity effect is studied in trilayers of different
+ferro- and antiferromagnetic materials within an atomistic spin model. We find
+the magnetic order in the central layer - with lower critical temperature -
+enhanced, even for the case of an antiferromagnet surrounded by ferromagnets.
+We further characterize this proximity effect via the magnon spectra which are
+specifically altered, especially for the case of the antiferromagnet in the
+central layer.",2109.00286v1
+2021-09-23,Quantum Interference between Photons and Single Quanta of Stored Atomic Coherence,"Essential for building quantum networks over remote independent nodes, the
+indistinguishability of photons has been extensively studied by observing the
+coincidence dip in the Hong-Ou-Mandel interferometer. However,
+indistinguishability is not limited to the same type of bosons. For the first
+time, we hereby observe quantum interference between flying photons and a
+single quantum of stored atomic coherence (magnon) in an atom-light beam
+splitter interface. We demonstrate that the Hermiticity of this interface
+determines the type of quantum interference between photons and magnons.
+Consequently, not only the bunching behavior that characterizes bosons is
+observed, but counterintuitively, fermionlike antibunching as well. The hybrid
+nature of the demonstrated magnon-photon quantum interface can be applied to
+versatile quantum memory platforms, and can lead to fundamentally different
+photon distributions from those occurring in boson sampling.",2109.11148v2
+2021-09-27,Entanglement of magnon excitations in spin chains,"We calculate exactly the entanglement content of magnon excited states in the
+integrable spin-1/2 XXX and XXZ chains in the scaling limit. In particular, we
+show that as far as the number of excited magnons with respect to the size of
+the system is small one can decompose the entanglement content, in the scaling
+limit, to the sum of the entanglement of particular excited states of free
+fermionic or bosonic theories. In addition we conjecture that the entanglement
+content of the generic translational invariant free fermionic and bosonic
+Hamiltonians can be also classified, in the scaling limit, with respect to the
+entanglement content of the fermionic and bosonic chains with the number
+operator as the Hamiltonian in certain circumstances. Our results effectively
+classify the entanglement content of wide range of integrable spin chains in
+the scaling limit.",2109.12826v2
+2021-10-05,The impact of defects on excitations in two-dimensional bipartite uniaxial antiferromagnet insulators,"We address scatterings of spin waves off uncorrelated defects in
+two-dimensional (2D) easy-axis antiferromagnet (AFM) insulators. Although an
+onsite magnetic anisotropy leads gapped Goldstone modes, such that a long range
+(AFM) order can be established in 2D, lattice imperfections tend to weaken, and
+eventually destroy the magnetic ordering. Here, the impact of defects is
+considered within two limits, single and multiple defects. Using Green's
+function, we perform self consistent simulations to study magnon properties
+such as density of states and lifetime of induced resonances. Our findings show
+that repulsive defects decrease the magnon density of states while attractive
+ones may enhance it. We provide a comprehensive analysis of how defects can
+result in a reduction and even closing, the anisotropy induced gap, which
+weakens the long range (AFM) order parameter in the 2D state. We conclude that
+a small concentration of random defects can fill the gap of magnon spectrum.",2110.02045v3
+2021-10-06,Magnon Interference Tunneling Spectroscopy as a Probe of 2D Magnetism,"Probing two-dimensional single-layer quantum magnets remains a significant
+challenge. In this letter, we propose exploiting tunneling spectroscopy in the
+presence of magnetic impurities to obtain information about the magnon
+dispersion relations in analogy to quasiparticle interference in non-magnetic
+materials. We show this technique can be used to establish the dispersion
+relations even for frustrated magnets, where the presence of an impurity
+generally leads to a nontrivial spin texture. Finally, we consider the problem
+of establishing Chern magnon bands in 2D magnets showing how tuneable
+impurities allow probing the nature of the surface states.",2110.02662v1
+2021-10-13,Fractional spin excitations in the infinite-layer cuprate CaCuO$_2$,"We use resonant inelastic x-ray scattering (RIXS) to investigate the magnetic
+dynamics of the infinite-layer cuprate CaCuO2. We find that close to the
+(1/2,0) point the single magnon decays into a broad continuum of excitations
+accounting for 80% of the total magnetic spectral weight. Polarization resolved
+RIXS spectra reveal the overwhelming dominance of spin-flip ($\Delta S = 1$)
+characterof this continuum with respect to the $\Delta S= 0$ multimagnon
+contributions. Moreover, its incident energy dependence is identical to that of
+the magnon, supporting a common physical origin. We propose that the continuum
+originates from the decay of the magnon into spinon pairs, and we relate it to
+the exceptionally high ring exchange $J_\mathrm{c} \sim J_1$ of CaCuO2. In the
+infinite layer cuprates long-range and multi-site hopping integrals are pivotal
+and amplify the 2D quantum magnetism effects in spite the 3D antiferromagnetic
+N\'eel order.",2110.06666v1
+2021-10-14,Influence of static correlation on the magnon dynamics of an itinerant ferromagnet with competing exchange interactions -- a first principles study of MnBi,"We present first principles calculations of the dynamic susceptibility in
+strained and doped ferromagnetic MnBi using time-dependent density functional
+theory. In spite of being a metal, MnBi exhibits signatures of strong
+correlation and a proper description in the framework of density functional
+theory requires Hubbard corrections to the Mn $d$-orbitals. To permit
+calculations of the dynamic susceptibility with Hubbard corrections applied to
+the ground state electronic structure, we use a consistent rescaling of the
+exchange-correlation kernel maintaining the delicate balance between the magnon
+dispersion and the Stoner continuum. We find excellent agreement with the
+experimentally observed magnon dispersion for pristine MnBi and show that the
+material undergoes a phase transition to helical order under application of
+either doping or strain. The presented methodology paves the way for future
+LR-TDDFT studies of magnetic phase transitions, also for the wide range of
+materials with pronounced static correlation effects that are not accounted for
+at the LDA level.",2110.07282v3
+2021-10-21,Massless Dirac magnons in the two dimensional van der Waals honeycomb magnet CrCl3,"Two dimensional van der Waals ferromagnets with honeycomb structures are
+expected to host the bosonic version of Dirac particles in their magnon
+excitation spectra. Using inelastic neutron scattering, we study spin wave
+excitations in polycrystalline CrCl$_3$, which exhibits ferromagnetic honeycomb
+layers with antiferromagnetic stackings along the $c$-axis. For comparison,
+polycrystal samples of CrI$_3$ with different grain sizes are also studied. We
+find that the powder-averaged spin wave spectrum of CrCl$_3$ at $T$ = 2 K can
+be adequately explained by the two dimensional spin Hamiltonian including
+in-plane Heisenberg exchanges only. The observed excitation does not exhibit
+noticeable broadening in energy, which is in remarkable contrast to the
+substantial broadening observed in CrI$_3$. Based on these results, we conclude
+that the ferromagnetic phase of CrCl$_3$ hosts massless Dirac magnons and is
+thus not topological.",2110.10894v1
+2021-11-04,Control of the phase of reflected spin-waves from magnonic Gires-Tournois interferometer of subwavelength width,"The phase is one of the fundamental properties of a wave that allows to
+control interference effects and can be used to efficiently encode information.
+We examine numerically a magnonic resonator of the Gires-Tournois
+interferometer type, which enables the control of the phase of spin waves
+reflected from the edges of the ferromagnetic film. The considered
+interferometer consists of a Py thin film and a thin, narrow Py stripe placed
+above its edge, both coupled magnetostatically. We show that the resonances and
+the phase of the reflected spin waves are sensitive for a variation of the
+geometrical parameters of this bi-layerd part of the system. The high
+sensitivity to film, stripe, and non-magnetic spacer thicknesses, offers a
+prospect for developing magnonic metasurfaces and sensors.",2111.02678v1
+2021-11-14,Single-sideband microwave-to-optical conversion in high-Q ferrimagnetic microspheres,"Coherent conversion of microwave and optical photons can significantly expand
+the ability to control the information processing and communication systems.
+Here, we experimentally demonstrate the microwave-to-optical frequency
+conversion in a magneto-optical whispering gallery mode microcavity. By
+applying a magnetic field parallel to the microsphere equator, the intra-cavity
+optical field will be modulated when the magnon is excited by the microwave
+drive, leading to microwave-to-optical conversion via the magnetic Stokes and
+anti-Stokes scattering processes. The observed single sideband conversion
+phenomenon indicates a non-trivial optical photon-magnon interaction mechanism,
+which is derived from the magnon induced both the frequency shift and modulated
+coupling rate of optical modes. In addition, we demonstrate the single-sideband
+frequency conversion with an ultrawide tuning range up to 2.5GHz, showing its
+great potential in microwave-to-optical conversion.",2111.07325v1
+2021-12-06,Unified formulation of interfacial magnonic pumping from non-collinear magnets,"We establish a general formulation for spin current pumped by magnons at the
+interface between a normal metal and a magnetic insulator, valid for any
+non-collinear magnetic configuration in the linear spin wave regime. This
+current is generated by driving the system in a non-equilibrium state, covering
+setups such as thermal spin injection (spin Seebeck effect) or spin voltage by
+irradiation of the insulator (spin pumping). We illustrate the formula in the
+special case of a honeycomb topological ferromagnet, for simplicity, and cover
+both the spin Seebeck and spin-pumping setups. We show how the topological
+parameters influence the spin current and propose a way to obtain a
+contribution mainly from the topological edge magnons in the spin pumping case.",2112.02946v1
+2021-12-23,Electric-field-induced parametric excitation of exchange magnons in a CoFeB/MgO junction,"Electric-field controlled magnetization dynamics is an important integrant in
+low power spintronic devices. In this letter, we demonstrate electric-field
+induced parametric excitation for CoFeB/MgO junctions by using interfacial
+in-plane magnetic anisotropy. When the in-plane magnetic anisotropy and the
+external magnetic field are parallel to each other, magnons are efficiently
+excited by using electric-field induced parametric excitation. Its wavelength
+and wavenumber are tuned by changing input power and frequency of the applied
+voltage. A generalized phenomenological model is developed to explain the
+underlying role of the electric-field torque. Electrical excitation with no
+Joule heating offers a good opportunity for developing magnonic devices and
+exploring various nonlinear dynamics in magnetic systems.",2112.12308v2
+2022-01-12,The angular dependence of magnetization dynamics induced by a GHz range strain pulse,"The dynamics of magnetization is important in spintronics, where the coupling
+between phonon and magnon attracts much attention. In this work, we study the
+angular dependence of the coupling between longitudinal-wave phonon and magnon.
+We investigated the magnetization dynamics using the time-resolved
+magneto-optical Kerr effect, which allows measuring spin-wave resonances and
+the magnetic echo signal. The frequency, mode number, and amplitude of the
+spin-wave resonance change with the out-of-plane angle of the external magnetic
+field. The amplitude of the magnetic echo signal caused by the strain pulse
+also changes with the angle. We calculate these angular dependences based on
+the Landau-Lifshitz-Gilbert equation and find that the angles of the external
+field and magnetic moment are important factors for the phonon-magnon coupling
+when phonon propagates in the thickness direction under the out-of-plane
+magnetic field.",2201.04396v1
+2022-01-29,Accelerated adiabatic passage in cavity magnomechanics,"Cavity magnomechanics provides a readily-controllable hybrid system, that
+consisted of cavity mode, magnon mode, and phonon mode, for quantum state
+manipulation. To implement a fast-and-robust state transfer between the hybrid
+photon-magnon mode and the phonon mode, we propose two accelerated
+adiabatic-passage protocols individually based on the counterdiabatic
+Hamiltonian for transitionless quantum driving and the Levis-Riesenfeld
+invariant for inverse engineering. Both the counterdiabatic Hamiltonian and the
+Levis-Riesenfeld invariant generally apply to the continuous-variable systems
+with arbitrary target states. It is interesting to find that our
+counterdiabatic Hamiltonian can be constructed in terms of the creation and
+annihilation operators rather than the system-eigenstates and their
+time-derivatives. Our protocol can be optimized with respect to the stability
+against the systematic errors of coupling strength and frequency detuning. It
+contributes to a quantum memory for photonic and magnonic quantum information.
+We also discuss the effects from dissipation and the counter-rotating
+interactions.",2201.12536v1
+2022-02-07,Spin-transfer-assisted parametric pumping of magnons in yttrium iron garnet,"The combination of parametric pumping and spin-transfer torque is a powerful
+approach that enables high-level control over magnetic excitations in thin-film
+ferromagnets. The excitation parameters, such as pumping power and external
+field strength, affect the instabilities of individual magnon modes. We
+theoretically explore how the simultaneous effects of parametric pumping and
+spin transfer torque influence these magnetic instabilities in a thin-film
+ferromagnet. Within the Landau-Lifshitz-Gilbert framework, we perform
+micromagnetic simulations of magnon excitations in yttrium iron garnet by
+pumping, spin transfer torque, and a combination of the two. We find that
+consistent with experimental results, the magnitude and direction of the
+spin-transfer torque tune the parametric instability thresholds.",2202.03247v2
+2022-02-07,Magnetization dynamics affected by phonon pumping,"""Pumping"" of phonons by a dynamic magnetization promises to extend the range
+and functionality of magnonic devices. We explore the impact of phonon pumping
+on room-temperature ferromagnetic resonance (FMR) spectra of bilayers of thin
+yttrium iron garnet (YIG) films on thick gadolinium gallium garnet substrates
+over a wide frequency range. At low frequencies the Kittel mode hybridizes
+coherently with standing ultrasound waves of a bulk acoustic resonator to form
+magnon polarons that induce rapid oscillations of the magnetic susceptibility,
+as reported before. At higher frequencies, the phonon resonances overlap,
+merging into a conventional FMR line, but with an increased line width. The
+frequency dependence of the increased line broadening follows the predictions
+from phonon pumping theory in the thick substrate limit. In addition, we find
+substantial magnon-phonon coupling of a perpendicular standing spin wave (PSSW)
+mode. This evidences the importance of the mode overlap between the acoustic
+and magnetic modes, and provides a route towards engineering the magnetoelastic
+mode coupling.",2202.03331v1
+2022-02-10,Amplifying spin waves along Néel domain wall by spin-orbit torque,"Traveling spin waves in magnonic waveguides undergo severe attenuation, which
+tends to result in a finite propagation length of spin waves, even in magnetic
+materials with the accessible lowest damping constant, heavily restricting the
+development of magnonic devices. Compared with the spin waves in traditional
+waveguides, propagating spin waves along strip domain wall are expected to
+exhibit enhanced transmission. Here, we demonstrate, theoretically and through
+micromagnetic simulations, that spin-orbit torque associated with a
+ferromagnet/heavy metal bilayer can efficiently control the attenuation of spin
+waves along a N\'eel-type strip domain wall, despite the complexity in the
+ground-state magnetization configuration. The direction of the electric current
+applied to the heavy-metal layer determines whether these spin waves are
+amplified or further attenuated otherwise. Remarkably, our simulations reveal
+that the effective current densities required to efficiently tune the decay of
+such spin waves are just ~10^10 Am-2, roughly an order smaller than those
+required in conventional spin waveguides. Our results will enrich the toolset
+for magnonic technologies.",2202.05181v1
+2022-02-23,Spin canting in nonlinear terahertz magnon dynamics revealed by magnetorefractive probing in orthoferrite,"We excite the spin precession in rare-earth orthoferrite YFeO3 by the
+magnetic field of intense terahertz pulse and probe its dynamics by transient
+absorption change in the near infrared. The observed waveforms contain
+quasi-ferromagnetic-mode magnon oscillation and its second harmonics with a
+comparably strong amplitude. The result can be explained by dielectric function
+derived from magnetorefractive Hamiltonian. We reveal that the strong second
+harmonic signal microscopically originates from novel dynamics of the
+quasi-ferromagnetic mode magnon at nonlinear regime, wherein spin canting angle
+periodically oscillates.",2202.11365v1
+2022-02-24,Magnon corner states in twisted bilayer honeycomb magnets,"Search for higher-order topological insulators, characterized by
+topologically protected gapless boundary states of codimension higher than one,
+in bosonic systems has attracted growing interest. Here, we establish twisted
+bilayer honeycomb magnets as a new platform for hosting second-order
+topological magnon insulators (SOTMIs) without fine-tuning. We employ a simple,
+minimal Heisenberg spin model to describe misaligned bilayer sheets of
+honeycomb ferromagnetic magnets with a large commensurate twist angle. We found
+that the higher-order topology in this bilayer system shows a significant
+dependence on the interlayer exchange coupling. The SOTMI, featuring
+topologically protected magnon corner states, appears for ferromagnetic
+interlayer couplings, while the twisted bilayer exhibits a nodal phase in the
+case of antiferromagnetic interlayer coupling.",2202.12151v2
+2022-03-03,The fate of the spin polaron in the 1D antiferromagnets,"The stability of the spin polaron quasiparticle, well established in studies
+of a single hole in the 2D antiferromagnets, is investigated in the 1D
+antiferromagnets using a $t$-$J$ model. We perform an exact slave fermion
+transformation to the holon-magnon basis, and diagonalize numerically the
+resulting model in the presence of a single hole. We prove that the spin
+polaron is stable for any strength of the magnon-magnon interaction except for
+the unique value of the SU(2)-symmetric 1D $t$-$J$ model. Fine-tuning to this
+unique value is extremely unlikely to occur in quasi-1D antiferromagnets,
+therefore the spin polaron is the stable quasiparticle of real 1D materials.
+Our results lead to a new interpretation of the ARPES spectra of quasi-1D
+antiferromagnets in the spin polaron language.",2203.01846v4
+2022-03-07,Switchable selective interactions in a Dicke Model with Driven Biased term,"In this work, we propose a method to investigate controllable qubit-resonator
+interactions in a Dicke model with driven biased term. The nonlinearity of
+spectrum, which can be induced by qubit-resonator interactions, plays an
+important role in such controllable interactions. To gain insight into
+mechanism of the nonlinearity, we perform a unitary transformation to the
+Hamiltonian. The results show that the nonlinearity of the transformed
+Hamiltonian depends on the qubit-resonator coupling strength. The general forms
+of the effective Hamiltonians are discussed in detail based on the frequency
+modulation approach. The dynamical evolution can be switched on and off by
+adjusting the modulation parameters. By utilizing such controllable
+interactions, we discuss the creation of Dicke states and arbitrary
+superposition of Dicke states. We also consider the nonlinearity of energy
+level for the limit of large qubit numbers. In the thermodynamics limit, the
+kerr type nonlinearity is induced from ""magnon""-resonator coupling, and the
+selective preparation of ""magnon"" Fock states can be studied under ""magnon""
+scenario.",2203.03301v1
+2022-03-08,Multi-Center Magnon Excitations Open the Entire Brillouin Zone to Terahertz Magnetometry of Quantum Magnets,"Due to the small photon momentum, optical spectroscopy commonly probes
+magnetic excitations only at the center of the Brillouin zone; however, there
+are ways to override this restriction. In the case of the distorted kagome
+quantum magnet Y-kapellasite, Y$_3$Cu$_9$(OH)$_{19}$Cl$_8$, under scrutiny
+here, the magnon density of states can be accessed over the entire Brillouin
+zone through three-center magnon excitations. This mechanism is aided by the
+three different magnetic sublattices and strong short-range correlations in the
+distorted kagome lattice. The results of THz time-domain experiments agree
+remarkably well with linear spin-wave theory. Relaxing the conventional
+zone-center constraint of photons gives a new aspect to probe magnetism in
+matter.",2203.04343v1
+2022-03-30,Nonvolatile Electric Field Control of Thermal Magnons in the Absence of an Applied Magnetic Field,"Spin transport through magnetic insulators has been demonstrated in a variety
+of materials and is an emerging pathway for next-generation spin-based
+computing. To modulate spin transport in these systems, one typically applies a
+sufficiently strong magnetic field to allow for deterministic control of
+magnetic order. Here, we make use of the well-known multiferroic
+magnetoelectric, BiFeO3, to demonstrate non-volatile, hysteretic,
+electric-field control of thermally excited magnon current in the absence of an
+applied magnetic field. These findings are an important step toward
+magnon-based devices, where electric-field-only control is highly desirable.",2203.16519v2
+2022-04-10,Unveiling a Pump-Induced Magnon Mode via its Strong Interaction with Walker Modes,"We observe a power-dependent anticrossing of Walker spin-wave modes under
+microwave pumping when a ferrimagnet is placed in a microwave waveguide that
+does not support any discrete photon mode. We interpret this unexpected
+anticrossing as the generation of a pump-induced magnon mode that couples
+strongly to the Walker modes of the ferrimagnet. This anticrossing inherits an
+excellent tunability from the pump, which allows us to control the anticrossing
+via the pump power, frequency, and waveform. Further, we realize a remarkable
+functionality of this anticrossing, namely, a microwave frequency comb, in
+terms of the nonlinear interaction that mixes the pump and probe frequencies.
+Such a frequency comb originates from the magnetic dynamics and thereby does
+not suffer from the charge noise. The unveiled hybrid magnonics driven away
+from its equilibrium enriches the utilization of anticrossing for coherent
+information processing.",2204.04590v2
+2022-04-12,Loschmidt echo and Momentum Distribution in a Kitaev Spin Chain,"We investigate the Loschmidt echo in a one-dimensional spin chain having
+Kitaev-type interaction in constant and kicked magnetic fields. The Loschmidt
+echo for the initial states having different magnon excitations shows long-time
+revivals for smaller chains and has short-time revival peaks for the longer
+chains. The system near the critical point shows peculiarly long-time revival
+peaks of the Loschmidt echo for relatively larger chains. The presence of a
+magnon in the initial state affects the Loschmidt echo revival peaks. The
+momentum distribution function exhibits maxima for a few momenta that are
+associated with the momentum of the magnon excitation present in the initial
+states. The probability maxima decay as O(1/N ) with the system size. For the
+Hamiltonian with kicked magnetic fields, the Loschmidt echo depends on the kick
+period. For a special kick period, the Loschmidt echo shows no evolution at all
+irrespective of the system size.",2204.05564v1
+2022-05-16,Twisting the near-field radiative heat switch in hyperbolic antiferromagnets,"We study the twisted control of the near-field radiative heat transfer
+between two hyperbolic antiferromagnetic insulators under external magnetic
+fields. We show that the near-field heat flux can be affected by both the twist
+angle $\theta$ and the magnitude of the applied magnetic field with different
+broken symmetries. Irrespective of twist angle, the external magnetic field
+causes the radiative heat flux to change nonmonotonically, and the minimum heat
+flux can be found with the magnetic fields of about 1.5 T. Such nonmonotonic
+behavior is due to the fact that the magnetic field can radically change the
+nature of the magnon polaritons with time reversal symmetry breaking. The field
+not only affects the topological structure of surface magnon polaritons, but
+also induces the volume magnon polaritons that progressively dominate the heat
+transfer as the field increases. We further propose a twist-induced thermal
+switch device with inversion symmetry breaking, which can severely regulate
+radiative heat flux through different magnetic fields. Our findings account for
+a characteristic modulation of radiative heat transfer with implications for
+applications in dynamic thermal management.",2205.07648v1
+2022-05-20,Tunable large spin Nernst effect in a two-dimensional magnetic bilayer,"We theoretically investigate topological spin transport of the
+magnon-polarons in bilayer magnet with two-dimensional square lattices. Our
+theory is motivated by recent reports on the van der Waals magnets which show
+the reversible electrical switching of the interlayer magnetic order between
+antiferromagnetic and ferromagnetic orders. The magnetoelastic interaction
+opens band gaps and allows the interband transition between different
+excitation states. In the layered antiferromagnet, due to the interband
+transition between the magnon-polaron states, the spin Berry curvature which
+allows the topological spin transport occurs even if the time-reversal symmetry
+is preserved. We find that the spin Berry curvature in the layered
+antiferromagnet is very large due to the small energy spacing between two
+magnon-like states. As a result, the spin Nernst conductivity shows sudden
+increase (or decrease) at the phase transition point between ferromagnetic and
+antiferromagnetic phases. Our result suggest that the ubiquity of tunable
+topological spin transports in two dimensional magnetic systems.",2205.09970v1
+2022-05-25,Quantum topological phase transitions in skyrmion crystals,"Topological order is important in many aspects of condensed matter physics,
+and has been extended to bosonic systems. In this Letter we report on the
+nontrivial topology of the magnon bands in two distinct quantum skyrmion
+crystals appearing in zero external magnetic field. This is revealed by nonzero
+Chern numbers for some of the bands. As a bosonic analog of the quantum
+anomalous Hall effect, we show that topological magnons can appear in skyrmion
+crystals without explicitly breaking time-reversal symmetry with an external
+magnetic field. By tuning the value of the easy-axis anisotropy at zero
+temperature, we find eight quantum topological phase transitions signaled by
+discontinuous jumps in certain Chern numbers. We connect these quantum
+topological phase transitions to gaps closing and reopening between magnon
+bands.",2205.12965v2
+2022-06-02,Diagonal and off-diagonal thermal conduction with resonant phonon scattering in $Ni_3TeO_6$,"The coupling between phonon and magnon is ubiquitous in magnetic materials
+and plays a crucial role in many aspects of magnetic properties, most notably
+in spintronics. Yet, this academically and technologically interesting problem
+still poses a severe challenge to a general understanding of the issue in
+certain materials. We report that Ni3TeO6 exhibits clear evidence of
+significant magnon-phonon coupling in both longitudinal thermal conductivity
+($\kappa_{xx}$) and thermal Hall coefficient ($\kappa_{xy}$). The
+Debye-Callaway model, a phenomenological description for phonon heat
+conduction, can explain the measured magnetic field dependence of
+$\kappa_{xx}(H)$: phonon scattering from spin fluctuation in the paramagnetic
+phase and additional scattering due to magnon-phonon coupling in the collinear
+antiferromagnetic phase. We further suggest that a similar approach could be
+applied to understand the finite $\kappa_{xy}$ values in $Ni_3TeO_6$.",2206.00837v2
+2022-06-05,Evidence of Magnon-Mediated Orbital Magnetism in a Quasi-2D Topological Magnon Insulator,"We explore spin dynamics in Cu(1,3-bdc), a quasi-2D topological magnon
+insulator. The results show that the thermal evolution of Land\'e $g$-factor
+($g$) is anisotropic: $g_\textrm{in-plane}$ reduces while
+$g_\textrm{out-plane}$ increases with increasing temperature $T$. Moreover, the
+anisotropy of the $g$-factor ($\Delta g$) and the anisotropy of saturation
+magnetization ($\Delta M_\textrm{s}$) are correlated below 4 K, but they
+diverge above 4 K. We show that the electronic orbital moment contributes to
+the $g$ anisotropy at lower $T$, while the topological orbital moment induced
+by thermally excited spin chirality dictates the $g$ anisotropy at higher $T$.
+Our work suggests an interplay among topology, spin chirality, and orbital
+magnetism in Cu(1,3-bdc).",2206.02191v1
+2022-06-21,Dipolar spin-waves and tunable band gap at the Dirac points in the 2D magnet ErBr3,"Topological magnon insulators constitute a growing field of research for
+their potential use as information carriers without heat dissipation. We report
+an experimental and theoretical study of the magnetic ground-state and
+excitations in the van der Waals two-dimensional honeycomb magnet ErBr3. We
+show that the magnetic properties of this compound are entirely governed by the
+dipolar interactions which generate a continuously degenerate non-collinear
+ground-state on the honeycomb lattice with spins confined in the plane. We find
+that the magnon dispersion exhibits Dirac-like cones when the magnetic moments
+in the ground-state are related by time-reversal and inversion symmetries
+associated with a Berry phase \pi as in single-layer graphene. A magnon band
+gap opens when the dipoles are rotated away from this state, entailing a finite
+Berry curvature in the vicinity of the K and K' Dirac points. Our results
+illustrate that the spin-wave dispersion of dipoles on the honeycomb lattice
+can be reversibly controlled from a magnetic phase with Dirac cones to a
+topological antiferromagnetic insulator with non-trivial valley Chern number.",2206.10168v1
+2022-06-26,Tripartite high-dimensional magnon-photon entanglement in PT -symmetry broken phases of a non-Hermitian hybrid system,"Hybrid systems that combine spin ensembles and superconducting circuits
+provide a promising platform for implementing quantum information processing.
+We propose a non-Hermitian magnoncircuit-QED hybrid model consisting of two
+cavities and an yttrium iron garnet (YIG) sphere placed in one of the cavities.
+Abundant exceptional points (EPs), parity-time (PT )-symmetry phases and PT
+-symmetry broken phases are investigated in the parameter space. Tripartite
+highdimensional entangled states can be generated steadily among modes of the
+magnon and photons in PT -symmetry broken phases, corresponding to which the
+stable quantum coherence exists. Results show that the tripartite
+high-dimensional entangled state is robust against the dissipation of hybrid
+system, independent of a certain initial state, and insensitive to the
+fluctuation of magnonphoton coupling. Further, we propose to simulate the
+hybrid model with an equivalent LCR circuit. This work may provide prospects
+for realizing multipartite high-dimensional entangled states in the
+magnon-circuit-QED hybrid system.",2206.12769v1
+2022-06-29,Reservoir engineering strong quantum entanglement in cavity magnomechanical systems,"We construct a hybrid cavity magnomechanical system to transfer the bipartite
+entanglements and achieve the strong microwave photon-phonon entanglement based
+on the reservoir engineering approach. The magnon mode is coupled to the
+microwave cavity mode via magnetic dipole interaction, and to the phonon mode
+via magnetostrictive force (optomechanical-like). It is shown that the initial
+magnon-phonon entanglement can be transferred to the photon-phonon subspace in
+the case of these two interactions cooperating. In reservoir-engineering
+parameter regime, the initial entanglement is directionally transferred to the
+photon-phonon subsystem, so we obtain a strong bipartite entanglement in which
+the magnon mode acts as the cold reservoir to effectively cooling the
+Bogoliubov mode delocalized over the cavity and the mechanical deformation
+mode. Moreover, as the dissipation ratio between the cold reservoir mode and
+the target mode increases, we can achieve greater quantum entanglement and
+better cooling effect. Our results indicate that the steady-state entanglement
+is robust against temperature. The scheme may provides potential applications
+for quantum information processing, and is expected to be extended to other
+three-mode systems.",2206.14365v2
+2022-07-21,Unidirectional Spin Hall Magnetoresistance in Antiferromagnetic Heterostructures,"Unidirectional spin Hall magnetoresistance (USMR) has been widely reported in
+the heavy metal / ferromagnet (HM/FM) bilayer systems. We observe the USMR in
+the Pt/{\alpha}-Fe2O3 bilayers where the {\alpha}-Fe2O3 is an antiferromagnetic
+(AFM) insulator. Systematic field and temperature dependent measurements
+confirm the magnonic origin of the USMR. The appearance of AFM-USMR is driven
+by the imbalance of creation and annihilation of AFM magnons by spin orbit
+torque due to thermal random field. However, unlike its ferromagnetic
+counterpart, theoretical modeling reveals that the USMR in Pt/{\alpha}-Fe2O3 is
+determined by the antiferromagtic magnon number, and with a non-monotonic field
+dependence. Our findings extend the generality of the USMR which pave the ways
+for the highly sensitive detection of AF spin state.",2207.10346v1
+2022-08-05,Frequency-dependent Phonon-mediated Unidirectional Magnetoresistance in a Metal on an Insulator with Highly Nonequilibrium Magnons,"Heavy metal (HM)/magnet bilayers host many magnetoresistances (MR) and spin
+caloritronic effects. Here we show that the spin Peltier effect and
+electron-phonon scattering produce much larger unidirectional MR of an HM on a
+magnetic insulator than existing theories that neglect the interplay between MR
+and spin caloritronic effects. By accounting for local nonequilibrium in both
+the magnon chemical potential and temperature, our analytical model attributes
+the observed frequency dependence of the spin Peltier MR and the spin Seebeck
+effect to the reduction of the thermal penetration depth, which approaches the
+1 micron scale magnon spin diffusion length at high frequencies.",2208.03388v1
+2022-09-13,Topological magnons in Kitaev magnets with finite Dzyaloshinskii-Moriya interaction at high field,"There have been intensive studies on Kitaev materials for the sake of the
+realization of exotic states such as quantum spin liquid and topological
+orders. In realistic materials, the Kitaev interaction may coexist with the
+Dzyaloshinskii-Moriya interaction (DMI), and it is a challenge to distinguish
+their magnitudes separately. Here, we study the topological magnon excitations
+and related thermal Hall conductivity of kagome magnet exhibiting Heisenberg,
+Kitaev and DM interactions exposed to a magnetic field. In a strong magnetic
+field perpendicular to the plane of the lattice ([111] direction) that bring
+the system into the fully polarized paramagnetic phase, we find that the magnon
+bands carry nontrivial Chern numbers in the full region of the phase diagram.
+Furthermore, there are phase transitions relate two topological phases with
+opposite Chern numbers, which lead to the sign changes of the thermal Hall
+conductivity. In the phase with negative thermal conductivity, the Kitaev
+interaction is relatively large and the width of the phase increases with the
+strength of DMI. Hence the study here will contribute to the understanding of
+related compounds.",2209.05813v1
+2022-09-19,Unidirectional orbital magnetoresistance in light metal/ferromagnet bilayers,"We report the observation of a unidirectional magnetoresistance (UMR) that
+originates from the nonequilibrium orbital momentum induced by an electric
+current in a naturally oxidized Cu/Co bilayer. The orbital-UMR scales with the
+torque efficiency due to the orbital Rashba-Edelstein effect upon changing the
+Co thickness and temperature, reflecting their common origin. We attribute the
+UMR to orbital-dependent electron scattering and orbital-to-spin conversion in
+the ferromagnetic layer. In contrast to the spin-current induced UMR, the
+magnon contribution to the orbital-UMR is absent in thin Co layers, which we
+ascribe to the lack of coupling between low energy magnons and orbital current.
+The magnon contribution to the UMR emerges in Co layers thicker than about 5
+nm, which is comparable to the orbital-to-spin conversion length. Our results
+provide insight into orbital-to-spin momentum transfer processes relevant for
+the optimization of spintronic devices based on light metals and orbital
+transport.",2209.09355v1
+2022-09-21,Tailoring spin waves in 2D transition metal phosphorus trichalcogenides via atomic-layer substitution,"The family of two-dimensional (2D) van der Waals transition metal phosphorus
+trichalcogenides has received a renewed interest due to their intrinsic 2D
+antiferromagnetism, which proves them as unprecedented and highly tunable
+building blocks for spintronics and magnonics at the single-layer limit.
+Herein, motivated by the exciting potential of atomic-substitution demonstrated
+in Janus transition metal dichalcogenides, we investigate the crystal,
+electronic and magnetic structure of selenized Janus monolayers based on
+MnPS$_3$ and NiPS$_3$ from first-principles. In addition, we calculate the
+magnon dispersion and perform real-time real-space atomistic dynamic
+simulations to explore the propagation of spin waves in MnPS$_3$, NiPS$_3$,
+MnPS$_{1.5}$Se$_{1.5}$ and NiPS$_{1.5}$Se$_{1.5}$. Our calculations predict a
+drastic enhancement of magnetic anisotropy and the emergence of large
+Dzyaloshinskii-Moriya interactions, which arises from the induced broken
+inversion symmetry in the 2D Janus layers. These results pave the way to the
+development of Janus 2D transition metal phosphorus trichalcogenides and
+highlight their potential for magnonic applications.",2209.10356v1
+2022-10-18,Simultaneous multitone microwave emission by DC-driven spintronic nano-element,"Current-induced self-sustained magnetization oscillations in spin-torque
+nano-oscillators (STNOs) are promising candidates for ultra-agile microwave
+sources or detectors. While usually STNOs behave as a monochrome source, we
+report here clear bimodal simultaneous emission of incommensurate microwave
+oscillations, where the two tones correspond to two parametrically coupled
+eigenmodes with tunable splitting. The emission range is crucially sensitive to
+the change in hybridization of the eigenmodes of free and fixed layers, for
+instance, through a slight tilt of the applied magnetic field from the normal
+of the nano-pillar. Our experimental findings are supported both analytically
+and by micromagnetic simulations, which ascribe the process to four-magnon
+scattering between a pair of radially symmetric magnon modes and a pair of
+magnon modes with opposite azimuthal index. Our findings open up new
+possibilities for cognitive telecommunications and neuromorphic systems that
+use frequency multiplexing to improve communication performance.",2210.09752v1
+2022-10-24,Optimal anti-ferromagnets for light dark matter detection,"We propose anti-ferromagnets as optimal targets to hunt for sub-MeV dark
+matter with spin-dependent interactions. These materials allow for multi-magnon
+emission even for very small momentum transfers, and are therefore sensitive to
+dark matter particles as light as the keV. We use an effective theory to
+compute the event rates in a simple way. Among the materials studied here, we
+identify nickel oxide (a well-assessed anti-ferromagnet) as an ideal candidate
+target. Indeed, the propagation speed of its gapless magnons is very close to
+the typical dark matter velocity, allowing the absorption of all its kinetic
+energy, even through the emission of just a single magnon.",2210.13516v2
+2022-11-07,Dynamic self-organisation and pattern formation by magnon-polarons,"Nonlinear dynamics can give rise, via the processes of self-organisation and
+pattern formation, to the spontaneous manifestation of order in open and
+complex systems far from equilibrium. Self-organising systems, transforming the
+inflow of energy into information, are ubiquitously found in current topical
+areas of science ranging from brainwave entrainment and neuromorphic computing
+to energy-efficient data storage technologies. In the latter, magnetic
+materials play a pivotal role combining very fast switching with permanent
+retention of information. However, it has been shown that, at very short time
+scales, magnetisation dynamics become chaotic due to internal instabilities,
+resulting in incoherent spin-wave excitations that ultimately destroy magnetic
+ordering. Here, contrary to all expectations, we show that such chaos gives
+rise to a periodic pattern of reversed magnetic domains, with a feature size
+far smaller than the spatial extent of the excitation. We explain this pattern
+as a result of phase-synchronisation of magnon-polaron waves, driven by strong
+coupling of magnetic and elastic modes. Our results reveal not only the
+peculiar formation and evolution of magnon-polarons at short time-scales, but
+also present a novel mechanism of magnetization reversal driven by coherent
+packets of short-wavelength quasiparticles.",2211.03723v1
+2022-11-23,Anatomy of spin wave driven magnetic texture motion via magnonic torques,"The interplay between spin wave and magnetic texture represents the
+information exchange between the fast and slow dynamical parts of magnetic
+systems. Here we formulate a set of magnonic torques acting on background
+magnetic texture, by extracting time-invariant information from the fast
+precessing spin waves. Under the frame of magnonic torques, we use theoretical
+formulations and micromagnetic simulations to investigate the spin wave driven
+domain wall motion in two typical symmetry-breaking situations: the rotational
+symmetry broken by the Dzyaloshinkii-Moriya interaction, and the translational
+symmetry broken by magnetic damping. The torque-based microscopic analyses
+provide compact yet quantitative tools to reinterpret the magnetic texture
+dynamics induced by spin wave, beyond the conventional framework of global
+momentum conservation.",2211.12958v1
+2022-11-27,Entangled atomic ensemble and YIG sphere in coupled microwave cavities,"We present a scheme to generate distant bipartite and tripartite entanglement
+between an atomic ensemble and a yttrium iron garnet (YIG) sphere in coupled
+microwave cavities. The system we consider has five excitation modes namely
+cavity-1 photons, atomic ensemble, cavity-2 photons, magnon and phonon modes in
+YIG sphere. We show that significant bipartite entanglement exists between
+indirectly coupled subsystems in the cavities, which is robust against
+temperature. Moreover, we present suitable detuning parameters for a
+significant tripartite entanglement of ensemble, magnon, and phonon modes. We
+also demonstrate the existence of tripartite entanglement between magnon and
+phonon modes of YIG sphere with indirectly coupled cavity photons. Further, we
+show that cavity-cavity coupling strength affects both the degree and transfer
+of quantum entanglement between various subsystems. It follows that an
+appropriate cavity-cavity coupling optimizes the distant entanglement by
+increasing the entanglement strength and critical temperature for its
+existence.",2211.14914v1
+2022-12-01,Nonreciprocal Phonon Propagation in a Metallic Chiral Magnet,"The phonon magnetochiral effect (MChE) is the nonreciprocal acoustic and
+thermal transports of phonons caused by the simultaneous breaking of the mirror
+and time-reversal symmetries. So far, the phonon MChE has been observed only in
+a ferrimagnetic insulator Cu2OSeO3, where the nonreciprocal response disappears
+above the Curie temperature of 58 K. Here, we study the nonreciprocal acoustic
+properties of a room-temperature ferromagnet Co9Zn9Mn2 for unveiling the phonon
+MChE close to the room temperature. Surprisingly, the nonreciprocity in this
+metallic compound is enhanced at higher temperatures and observed up to 250 K.
+This clear contrast between insulating Cu2OSeO3 and metallic Co9Zn9Mn2 suggests
+that metallic magnets have a mechanism to enhance the nonreciprocity at higher
+temperatures. From the ultrasound and microwave-spectroscopy experiments, we
+conclude that the magnitude of the phonon MChE of Co9Zn9Mn2 mostly depends on
+the magnon bandwidth, which increases at low temperatures and hinders the
+magnon-phonon hybridization. Our results suggest that the phonon nonreciprocity
+could be further enhanced by engineering the magnon band of materials.",2212.00225v2
+2022-12-18,Micromagnetic study of spin transport in easy-plane antiferromagnetic insulators,"Magnon eigenmodes in easy-plane antiferromagnetic insulators are linearly
+polarized and are not expected to carry any net spin angular momentum.
+Motivated by recent nonlocal spin transport experiments in the easy-plane phase
+of hematite, we perform a series of micromagnetic simulations in a nonlocal
+geometry at finite temperatures. We show that by tuning an external magnetic
+field, we can control the magnon eigenmodes and the polarization of the spin
+transport signal in these systems. We argue that a coherent beating oscillation
+between two orthogonal linearly polarized magnon eigenmodes is the mechanism
+responsible for finite spin transport in easy-plane antiferromagnetic
+insulators. The sign of the detected spin signal is also naturally explained by
+the proposed coherent beating mechanism. Our finding opens a path for on-demand
+control of the spin signal in a large class of easy-plane antiferromagnetic
+insulators.",2212.09024v3
+2022-12-22,Hybrid Magnonic-Oscillator System,"We propose a hybrid magnonic-oscillator system based on the combination of a
+spin transfer auto-oscillator and a magnonic waveguide to open new perspectives
+for spin-wave based circuits. The system is composed of a spin transfer
+oscillator based on a vortex state which is dipolarly coupled to a nanoscale
+spin-wave waveguide with longitudinal magnetization. In its auto-oscillating
+regime, the oscillator emits coherent spin waves with tunable and controllable
+frequencies, directions and amplitudes into the waveguide. We demonstrate the
+principle of this method using micromagnetic simulations and show that
+reconfiguration of the system is possible by changing the chirality and
+polarity of the magnetic vortex. Spin waves are emitted into the waveguide with
+high non-reciprocity and the preferred direction depends on the core polarity
+of the vortex. In contrast, different vortex chiralities lead to different
+amplitudes of the emitted waves. Our findings open up a novel way to design an
+agile spintronic device for the coherent and tunable generation of propagating
+spin waves.",2212.11532v1
+2023-01-05,Ultrafast spontaneous spin switching in an antiferromagnet,"Owing to their high magnon frequencies, antiferromagnets are key materials
+for future high-speed spintronics. Picosecond switching of antiferromagnetic
+order has been viewed a milestone for decades and pursued only by using
+ultrafast external perturbations. Here, we show that picosecond spin switching
+occurs spontaneously due to thermal fluctuations in the antiferromagnetic
+orthoferrite Sm0.7Er0.3FeO3. By analysing the correlation between the
+pulse-to-pulse polarisation fluctuations of two femtosecond optical probes, we
+extract the autocorrelation of incoherent magnon fluctuations. We observe a
+strong enhancement of the magnon fluctuation amplitude and the coherence time
+around the critical temperature of the spin reorientation transition. The
+spectrum shows two distinct modes, one corresponding to the quasi-ferromagnetic
+mode and another one which has not been previously reported in pump-probe
+experiments. Comparison to a stochastic spin dynamics simulation reveals this
+new mode as smoking gun of ultrafast spontaneous spin switching within the
+double-well anisotropy potential.",2301.02006v1
+2023-01-09,Long distance magnon transport in the van der Waals antiferromagnet CrPS$_4$,"We demonstrate the potential of van der Waals magnets for spintronic
+applications by reporting long-distance magnon spin transport in the
+electrically insulating antiferromagnet chromium thiophosphate (CrPS$_4$) with
+perpendicular magnetic anisotropy. We inject and detect magnon spins
+non-locally by Pt contacts and monitor the non-local resistance as a function
+of an in-plane magnetic field up to 7 Tesla. We observe a non-local resistance
+over distances up to at least a micron below the Neel temperature (T$_{\rm N}$
+= 38 Kelvin) close to magnetic field strengths that saturate the sublattice
+magnetizations.",2301.03268v1
+2023-02-19,Laser Cooling of Nuclear Magnons,"The initialization of nuclear spin to its ground state is challenging due to
+its small energy scale compared with thermal energy, even at cryogenic
+temperature. In this Letter, we propose an opto-nuclear quadrupolar effect,
+whereby two-color optical photons can efficiently interact with nuclear spins.
+Leveraging such an optical interface, we demonstrate that nuclear magnons, the
+collective excitations of nuclear spin ensemble, can be cooled down optically.
+Under feasible experimental conditions, laser cooling can suppress the
+population and entropy of nuclear magnons by more than two orders of magnitude,
+which could facilitate the application of nuclear spins in quantum information
+science.",2302.09615v2
+2023-02-22,Advanced magnon-optic effects with spin-wave leaky modes,"We numerically demonstrate the excitation of leaky spin waves (SWs) guided
+along a ferromagnetic stripe by an obliquely incident SW beam on the thin film
+edge placed below the stripe. During propagation, leaky waves emit energy back
+to the layer in the form of plane waves and several laterally shifted parallel
+SW beams. This resonance excitation, combined with interference effects of the
+reflected and re-emitted waves, results in the magnonic Woods anomaly and
+significant increase of the Goos-Hanchen shift magnitude. Hence, we provide a
+unique platform to control SW reflection and to transfer SWs from a 2D platform
+into the 1D guiding mode that can be used to form a transdimensional magnonic
+router.",2302.11507v3
+2023-02-25,Magnonic Hall Effect and Magnonic Holography of Hopfions,"Hopfions are localized and topologically non-trivial magnetic configurations
+that have received considerable attention in recent years. Through a
+micromagnetic approach, we analyze the scattering of spin waves by magnetic
+hopfions. We show that the spin waves experience an emergent electromagnetic
+field related to the topological properties of the hopfion. We find that spin
+waves propagating along the hopfion symmetry axis are deflected by the magnetic
+texture, which acts as a convergent or divergent lens, depending on the spin
+wave propagation direction. The effect differs for spin waves propagating along
+the plane perpendicular to the symmetry axis. In the last case, they respond
+with a skew scattering and a closely related Aharonov-Bohm effect. This allows
+probing the existence of a magnetic hopfion by magnonic holography.",2302.13190v1
+2023-03-08,Nonreciprocity in Cavity Magnonics at Milikelvin Temperature,"Incorporating cavity magnonics has opened up a new avenue in controlling
+non-reciprocity. This work examines a yttrium iron garnet sphere coupled to a
+planar microwave cavity at milli-Kelvin temperature. Non-reciprocal device
+behavior results from the cooperation of coherent and dissipative coupling
+between the Kittel mode and a microwave cavity mode. The device's
+bi-directional transmission was measured and compared to the theory derived
+previously in the room temperature experiment. Investigations are also
+conducted into key performance metrics such as isolation, bandwidth, and
+insertion loss. The findings point to the coexistence of coherent and
+dissipative interactions at cryogenic conditions, and one can leverage their
+cooperation to achieve directional isolation. This work foreshadows the
+application of a cavity magnonic isolator for on-chip readout and signal
+processing in superconducting circuitry.",2303.04358v1
+2023-03-22,Phonon and magnon jets above the critical current in nanowires with planar domain walls,"We show through non-equilibrium non-adiabatic electron-spin-lattice
+simulations that above a critical current in magnetic atomic wires with a
+narrow domain wall (DW), a couple of atomic spaces in width, the electron flow
+triggers violent stimulated emission of phonons and magnons with an almost
+complete conversion of the incident electron momentum flux into a phonon and
+magnon flux. Just below the critical levels of the current flow, the DW
+achieves maximal velocity of about $3\times 10^{4}$ m/s, entering a strongly
+non-adiabatic regime of DW propagation, followed by a breakdown at higher
+biases. Above this threshold a further increase of the current with the applied
+bias is impossible -- the electronic current suffers a heavy suppression and
+the DW stops. This poses a fundamental limit to the current densities
+attainable in atomic wires. At the same time it opens up an exciting way of
+generating the alternative quasi-particle currents, described above, once the
+requisite electronic-structure properties are met.",2303.12879v2
+2023-03-23,Majorana-magnon interactions in topological Shiba chains,"A chain of magnetic impurities deposited on the surface of a superconductor
+can form a topological Shiba band that supports Majorana zero modes and holds a
+promise for topological quantum computing. Yet, most experiments scrutinizing
+these zero modes rely on transport measurements, which only capture local
+properties. Here we propose to leverage the intrinsic dynamics of the magnetic
+impurities to access their non-local character. We use linear response theory
+to determine the dynamics of the uniform magnonic mode in the presence of
+external $ac$ magnetic fields and coupling the Shiba electrons. We demonstrate
+that this mode, which spreads over the entire chain of atoms, becomes imprinted
+with the parity of the ground state and, moreover, can discriminate between
+Majorana and trivial zero modes located at the ends of the chain. Our approach
+offers a non-invasive alternative to the scanning tunneling microscopy
+techniques used to probe Majorana zero modes. Conversely, the magnons could
+facilitate the manipulation of Majorana zero modes in topological Shiba chains.",2303.13513v2
+2023-03-26,Compact localised states in magnonic Lieb lattices,"Lieb lattice is one of the simplest bipartite lattices where compact
+localized states (CLS) are observed. This type of localisation is induced by
+the peculiar topology of the unit cell, where the modes are localized only on
+one sublattice due to the destructive interference of partial waves. The CLS
+exist in the absence of defects and are associated with the flat bands in the
+dispersion relation. The Lieb lattices were successfully implemented as optical
+lattices or photonic crystals. This work demonstrates the possibility of
+magnonic Lieb lattice realization where the flat bands and CLS can be observed
+in the planar structure of sub-micron in-plane sizes. Using forward volume
+configuration, we investigated numerically (using the finite element method)
+the Ga-dopped YIG layer with cylindrical inclusions (without Ga content)
+arranged in a Lieb lattice of the period 250 nm. We tailored the structure to
+observe, for the few lowest magnonic bands, the oscillatory and evanescent spin
+waves in inclusions and matrix, respectively. Such a design reproduces the Lieb
+lattice of nodes (inclusions) coupled to each other by the matrix with the CLS
+in flat bands.",2303.14843v1
+2023-04-14,Gauge-Invariant Measure of the Magnon Orbital Angular Momentum,"Unlike the Berry phase, the orbital angular momentum (OAM) of magnons with
+two-dimensional wavevector k in band n is not gauge invariant for arbitrary
+phase lambda_n(k). However, by integrating the OAM over the orientation $\phi $
+of wavevector k, we construct a gauge-invariant function F_n(k). Like F_n(k),
+the average OAM for magnon band n in a circle of radius k is also gauge
+invariant. We demonstrate these results for a ferromagnet on a honeycomb
+lattice with Dzyalloshinskii-Moriya interactions between next-nearest neighbor
+spins. With wavevectors k restricted to the first Brillouin zone, the angular
+averaged OAM F_n(k) then has opposite signs for lower and upper bands n=1 and 2
+for all k.",2304.07379v2
+2023-04-19,Nonreciprocal ultrastrong magnon-photon coupling in the bandgap of photonic crystals,"We observe a nonreciprocal ultrastrong magnon-photon coupling in the bandgap
+of photonic crystals by introducing a single crystal YIG cylinder into copper
+photonic crystals cavity as a point defect. The coupling strength reaches up to
+1.18 GHz, which constitutes about 10.9% of the photon energy compared to the
+photon frequency around 10.8 GHz. It is fascinating that the coupling achieves
+unidirectional signal transmission in the whole bandgap. This study
+demonstrates the possibility of controlling nonreciprocal magnon-photon
+coupling by manipulating the structure of photonic crystals, providing new
+methods to investigate the influence of magnetic point defects on microwave
+signal transmission.",2304.09627v1
+2023-05-14,Quantum-Enhanced Metrology in Cavity Magnomechanics,"Magnons, as fundamental quasiparticles emerged in elementary spin
+excitations, hold a big promise for innovating quantum technologies in
+information coding and processing. Here we discover subtle roles of
+entanglement in a metrological scheme based on an experimentally feasible
+cavity magnomechanical system, where the magnons are responsible for sensing a
+weak magnetic field whereas the cavity field carries out a precision
+measurement of the weak field. By establishing exact relations between the
+Fisher information and entanglement, we show that for the weak coupling case
+the measurement precision can reach the Heisenberg limit, whereas quantum
+criticality enables us to enhance measurement precision for the strong coupling
+case. In particular, we also find that the entanglement between magnons and
+photons is of crucial importance during the dynamical encoding process, but the
+presence of such an entanglement in the measurement process dramatically
+reduces the final measurement precision.",2305.08045v2
+2023-05-29,Intrinsic nonlinear thermal Hall transport of magnons: A Quantum kinetic theory approach,"We present a systematic study of the nonlinear thermal Hall responses in
+bosonic systems using the quantum kinetic theory framework. We demonstrate the
+existence of an intrinsic nonlinear boson thermal current, arising from the
+quantum metric which is a wavefunction dependent band geometric quantity. In
+contrast to the nonlinear Drude and nonlinear anomalous Hall contributions, the
+intrinsic nonlinear thermal conductivity is independent of the scattering
+timescale. We demonstrate the dominance of this intrinsic thermal Hall response
+in topological magnons in a two-dimensional ferromagnetic honeycomb lattice
+without Dzyaloshinskii-Moriya interaction. Our findings highlight the
+significance of band geometry induced nonlinear thermal transport and motivate
+experimental probe of the intrinsic nonlinear thermal Hall response with
+implications for quantum magnonics.",2305.18127v2
+2023-05-29,Light-induced weak ferromagnetism through nonlinear magnonic rectification,"Rectification describes the generation of a quasistatic component from an
+oscillating field, such as an electric polarization in optical rectification,
+or a structural distortion in nonlinear phononic rectification. Here, we
+present a third fundamental process for magnetization, in which spin precession
+is rectified along the coordinates of a nonlinearly driven magnon mode in an
+antiferromagnet. We demonstrate theoretically that a quasistatic magnetization
+can be induced by transient spin canting in response to the coherent excitation
+of a chiral phonon mode that produces an effective magnetic field for the
+spins. This mechanism, which we call nonlinear magnonic rectification, is
+generally applicable to magnetic systems that exhibit infrared-active chiral
+phonon modes. Our results serve as an example of light-induced weak
+ferromagnetism and open a promising avenue towards creating dynamical spin
+configurations that are not accessible in equilibrium.",2305.18656v2
+2023-06-13,Magnon gap excitations and spin-entangled optical transition in van der Waals antiferromagnet NiPS3,"Optical magneto-spectroscopy methods (Raman scattering, far-infrared
+transmission, and photoluminescence) have been applied to investigate the
+properties of the NiPS3 semiconducting antiferromagnet. The fundamental magnon
+gap excitation in this van der Waals material has been found to be split into
+two components, in support of the biaxial character of the NiPS3
+antiferromagnet. Photoluminescence measurements in the near-infrared spectral
+range show that the intriguing 1.475 eV-excitation unique to the NiPS3
+antiferromagnetic phase splits upon the application of the in-plane magnetic
+field. The observed splitting patterns are correlated with properties of magnon
+excitations and reproduced with the simple model proposed. Possible routes
+toward a firm identification of the spin-entangled 1.475 eV-optical excitation
+in NiPS3, which can hardly be recognized as a coherent Zhang-Rice exciton, are
+discussed.",2306.07660v1
+2023-07-01,Edge and corner skin effects of chirally coupled magnons characterized by a topological winding tuple,"We investigate a long-ranged coupled and non-Hermitian two-dimensional array
+of nanomagnets, fabricated on a thin magnetic substrate and subjected to an
+in-plane magnetic field. We predict topology-driven edge and corner skin
+effects of magnetic eigenmodes with the localization position at boundaries
+precisely characterized by a topological winding tuple $({\cal W}_1,{\cal
+W}_2)$. By varying the direction of the in-plane field, all magnon states pile
+up either at different edges of the array with $({\cal W}_1=\pm 1,{\cal
+W}_2=0)$ or $({\cal W}_1=0,{\cal W}_2=\pm 1)$, or at different corners
+characterized by $({\cal W}_1=\pm 1,{\cal W}_2=\pm 1)$. Exploiting the
+non-Hermitian topology is potentially helpful for designing useful magnonic
+metasurface in the future.",2307.00353v2
+2023-07-08,Magnon influence on the superconducting density of states in superconductor$-$ferromagnetic-insulator bilayers,"Superconductor$-$ferromagnetic-insulator heterostructures are paradigmatic
+systems for studying the mutual influence of superconductivity and magnetism
+via proximity effects. In particular, spin-split superconductivity is realized
+in such structures. Recent experiments and theories demonstrate a rich variety
+of transport phenomena occurring in devices based on such heterostructures that
+suggest direct applications in thermoelectricity, low-dissipative spintronics,
+radiation detection, and sensing. In this work we investigate the influence of
+the electron-magnon interaction at the superconductor$-$ferromagnetic-insulator
+interface on the spin-split superconductivity. It is predicted that due to the
+magnon-mediated electron spin-flip processes the spin-split quasiparticle
+branches are partially mixed and reconstructed, and the BCS-like spin-split
+shape of the superconducting density of states, which is typical for
+superconductors in the effective exchange field, is strongly modified. An
+odd-frequency superconducting order parameter admixture to the leading singlet
+order parameter is also found. These findings expand the physical picture of
+spin-split superconductivity beyond the mean-field description of the
+ferromagnet exchange field.",2307.03954v2
+2023-07-14,Achieving unidirectional propagation of twisted magnons in a magnetic nanodisk array,"Twisted magnons (TMs) have great potential applications in communication and
+computing owing to the orbital angular momentum (OAM) degree of freedom.
+Realizing the unidirectional propagation of TMs is the key to design functional
+magnonics devices. Here we theoretically study the propagation of TMs in
+one-dimensional magnetic nanodisk arrays. By performing micromagnetic
+simulations, we find that the one-dimensional nanodisk array exhibits a few
+bands due to the collective excitations of TMs. A simple model by considering
+the exchange interaction is proposed to explain the emerging multiband
+structure and theoretical results agree well with micromagnetic simulations.
+Interestingly, for a zigzag structure, the dispersion curves and propagation
+images of TMs show obvious nonreciprocity for specific azimuthal quantum number
+($l$), which originates from a geometric effect depending on the phase
+difference of TMs and the relative angle between two adjacent nanodisks.
+Utilizing this feature, one can conveniently realize the unidirectional
+propagation of TMs with arbitrary nonzero $l$. Our work provides important
+theoretical references for controlling the propagation of TMs.",2307.07347v1
+2023-07-18,Distant entanglement via photon hopping in a coupled magnomechanical system,"We theoretically propose a scheme to generate distant bipartite entanglement
+between various subsystems in coupled magnomechanical systems where both the
+microwave cavities are coupled through single photon hopping parameter. Each
+cavity also contains a magnon mode and phonon mode and this gives five
+excitation modes in our model Hamiltonian which are cavity-1 photons, cavity-2
+photons, magnon, and phonon modes in both YIG spheres. We found that
+significant bipartite entanglement exists between indirectly coupled subsystems
+in coupled microwave cavities for an appropriate set of parameters regime.
+Moreover, we also obtain suitable cavity and magnon detuning parameters for a
+significant distant bipartite entanglement in different bipartitions. In
+addition, it can be seen that a single photon hopping parameter significantly
+affects both the degree as well as the transfer of quantum entanglement between
+various bipartitions. Hence, our present study related to coupled microwave
+cavity magnomechanical configuration will open new perspectives in coherent
+control of various quantum correlations including quantum state transfer among
+macroscopic quantum systems",2307.09424v1
+2023-08-16,Nontrivial Aharonov-Bohm effect and alternating dispersion of magnons in cone-state ferromagnetic rings,"Soft magnetic dots in the form of thin rings have unique topological
+properties. They can be in a vortex state with no vortex core. Here, we study
+the magnon modes of such systems both analytically and numerically. In an
+external magnetic field, magnetic rings are characterized by easy-cone
+magnetization and shows a giant splitting of doublets for modes with the
+opposite value of the azimuthal mode quantum number. The effect of the
+splitting can be refereed as a magnon analog of the topology-induced
+Aharonov-Bohm effect. For this we develop an analytical theory to describe the
+non-monotonic dependence of the mode frequencies on the azimuthal mode number,
+influenced by the balance between the local exchange and non-local dipole
+interactions.",2308.08486v3
+2023-09-07,Gænice: a general model for magnon band structure of artificial spin ices,"Arrays of artificial spin ices exhibit reconfigurable ferromagnetic resonance
+frequencies that can be leveraged and designed for potential
+applications.However, analytical and numerical studies of the frequency
+response of artificial spin ices have remained somewhat limited due to the need
+of take into account nonlocal dipole fields in theoretical calculations or by
+long computation times in micromagnetic simulations. Here, we introduce
+Gaenice, a framework to compute magnon dispersion relations of arbitrary
+artificial spin ice configurations. Gaenice makes use of a tight-binding
+approach to compute the magnon bands. It also provides the user complete
+control of the interaction terms included, e.g., external field, anisotropy,
+exchange, and dipole, making it useful also to compute ferromagnetic resonances
+for a variety of structures, such as multilayers and ensembles of weakly or
+non-interacting nanoparticles. Because it relies on a semi-analytical model,
+Gaenice is computationally inexpensive and efficient, making it an attractive
+tool for the exploration of large parameter spaces.",2309.03826v2
+2023-09-10,Cavity-Magnon-Polariton spectroscopy of strongly hybridized electro-nuclear spin excitations in LiHoF4,"We first present a formalism that incorporates the input-output formalism and
+the linear response theory to employ cavity-magnon-polariton coupling as a
+spectroscopic tool for investigating strongly hybridized electro-nuclear spin
+excitations. A microscopic relation between the generalized susceptibility and
+the scattering parameter |S11| in strongly hybridized cavity-magnon-polariton
+systems has been derived without resorting to semi-classical approximations.
+The formalism is then applied to both analyze and simulate a specific systems
+comprising a model quantum Ising magnet (LiHoF4) and a high-finesse 3D
+re-entrant cavity resonator. Quantitative information on the electro-nuclear
+spin states in LiHoF4 is extracted, and the experimental observations across a
+broad parameter range were numerically reproduced, including an external
+magnetic field titraversing a quantum critical point. The method potentially
+opens a new avenue not only for further studies on the quantum phase transition
+in LiHoF4 but also for a wide range of complex magnetic systems.",2309.05051v1
+2023-09-14,Phase control of magnons in the van der Waals antiferromagnet NiPS$_3$,"We demonstrate phase control of magnons in the van der Waals antiferromagnet
+NiPS$_3$ using optical excitation by polarized light. The sign of the coherent
+precession of spin amplitude changes upon (1) reversing the helicity of a
+circularly polarized pump beam, or (2) rotating the polarization of a linearly
+polarized pump by $\pi/2$. Because these two excitation pathways have
+comparable generation efficiency, the phase of spin precession can be
+continuously tuned from 0 to $2\pi$ by controlling the polarization state of
+the pump pulse. The ability to excite magnons with a desired phase has
+potential applications in the design of a spin-wave phased array and ultrafast
+spin information processing.",2309.07451v1
+2023-09-22,Strongly Coupled Spin Waves and Surface Acoustic Waves at Room Temperature,"Here, we report the observation of strong coupling between magnons and
+surface acoustic wave (SAW) phonons in a thin CoFeB film constructed in an
+on-chip SAW resonator by analyzing SAW phonon dispersion anticrossings. Our
+device design provides the tunability of the film thickness with a fixed phonon
+wavelength, which is a departure from the conventional approach in strong
+magnon--phonon coupling research. We detect a monotonic increase in the
+coupling strength by expanding the film thickness, which agrees with our
+theoretical model. Our work offers a significant way to advance fundamental
+research and the development of devices based on magnon--phonon hybrid
+quasiparticles.",2309.12690v1
+2023-12-05,Giant natural optical rotation from chiral electromagnons in a collinear antiferromagnet,"In NiTe$_3$O$_6$ with a chiral crystal structure, we report on a giant
+natural optical rotation of the lowest-energy magnon. This polarization
+rotation, as large as 140 deg/mm, corresponds to a path difference between
+right and left circular polarizations that is comparable to the sample
+thickness. Natural optical rotation, being a measure of structural chirality,
+is highly unusual for long-wavelength magnons. The collinear antiferromagnetic
+order of NiTe$_3$O$_6$ makes this giant effect even more peculiar: Chirality of
+the crystal structure does not affect the magnetic ground state but is strongly
+manifested in the lowest excited state. We show that the dynamic
+magnetoelectric effect, turning this magnon to a magnetic- and electric-dipole
+active hybrid mode, generates the giant natural optical rotation. In finite
+magnetic fields, it also leads to a strong optical magnetochiral effect.",2312.02733v1
+2023-12-06,Magnon interactions in the quantum paramagnetic phase of CoNb$_2$O$_6$,"In this work, we study effects of magnon interactions in the excitation
+spectrum of CoNb$_2$O$_6$ in the quantum paramagnetic phase in transverse
+field, where the $1/S$ spin-wave theory exhibits unphysical divergences at the
+critical field. We propose a self-consistent Hartree-Fock approach that
+eliminates such unphysical singularities while preserving the integrity of the
+singular threshold phenomena of magnon decay and spectrum renormalization that
+are present in both theory and experiment. With the microscopic parameters
+adopted from previous studies, this method yields a close quantitative
+agreement with the available experimental data for CoNb$_2$O$_6$ in the
+relevant regime. Insights into the general structure of the spin-anisotropic
+model of CoNb$_2$O$_6$ and related zigzag chain materials are also provided and
+a discussion of the effects of additional longitudinal field on the spectrum is
+given.",2312.03829v3
+2023-12-08,Towards an experimental proof of the magnonic Aharonov$-$Casher effect,"Controlling the phase and amplitude of spin waves in magnetic insulators with
+an electric field opens the way to fast logic circuits with ultra-low power
+consumption. One way to achieve such control is to manipulate the magnetization
+of the medium via magnetoelectric effects. In experiments with magnetostatic
+spin waves in an yttrium iron garnet film, we have obtained the first evidence
+of a theoretically predicted phenomenon: The change of the spin-wave phase due
+to the magnonic Aharonov$-$Casher effect$-$the geometric accumulation of the
+magnon phase as these quasiparticles propagate through an electric field
+region.",2312.05113v1
+2023-12-13,Defect-sensitive High-frequency Modes in a Three-Dimensional Artificial Magnetic Crystal,"Modern three-dimensional nanofabrication methods make it possible to generate
+arbitrarily shaped nanomagnets, including periodic networks of interconnected
+magnetic nanowires. Structurally similar to optical or acoustic metamaterials,
+these arrays could represent magnetic variants of such artificial materials.
+Using micromagnetic simulations, we investigate a three-dimensional array of
+interconnected magnetic nanowires with intersection points corresponding to
+atomic positions of a diamond lattice. The high-frequency excitation spectrum
+of this artificial magnetic crystal (AMC) is governed by its microstructure
+and, to a lesser extent, by the magnetic configuration. The magnetic system
+displays characteristics of three-dimensional artificial spin ice. It can
+contain Dirac-type magnetic defect structures, which modify the magnonic
+spectrum of the AMC similarly as defect sites in a natural diamond crystal
+influence optical absorption spectra. Our study opens new perspectives for
+applying such materials in high-density magnonic devices and shows that AMCs
+represent a promising category of magnonic materials with tunable properties.",2312.08415v1
+2023-12-23,Pulse-driven depinning of magnetic gap modes in ferromagnetic films,"Manipulation of magnons in artificial magnonic crystals (MCs) leads to
+fascinating nonlinear wave phenomena such as the generation of gap solitons,
+which has been mostly limited to one-dimensional systems. Here, we propose a
+model system for the magnetization in two-dimensional MCs subjected to a
+periodic external magnetic field, describing the dynamics of magnetic gap
+solitons (MGSs) formed by nonlinear self-trapping. We show the formation,
+stability, and dynamics for various two-dimensional gap modes, including gap
+solitons and vortical ones. Their existence regions depend on the anisotropic
+axis orientation of the ferromagnetic film. The Bloch oscillation and depinning
+propagation of MGSs under constant spin-current injections are discovered and
+characterized. We design a scheme of pulse current injection to achieve
+distortionless propagation of MGSs. These findings show that the 2D magnonic
+crystals can be viewed as a building block for MGSs-based storage and
+transmission, where the propagation and localization are variously controlled
+and reconfigurable.",2312.15200v1
+2024-01-15,Transient Magnetoelastic Coupling in CrSBr,"Recent research has revealed remarkable properties of the two-dimensional
+(2D) van der Waals layered crystal CrSBr, which is both a semiconductor and an
+A-type antiferromagnet. Here we show the role of strong magnetoelastic coupling
+in the generation and propagation of coherent magnons in CrSBr. Time and
+spatially resolved magneto-optical Kerr effect (tr-MOKE) microscopy reveals two
+time-varying transient strain fields induced by out-of-plane transverse and
+in-plane longitudinal lattice displacements. These transient strain fields
+launch coherent wavepackets of magnons, optical and acoustic at 24.6 GHz and
+33.4 GHz, respectively. These findings suggest mechanisms for controlling and
+manipulating coherent magnons from distinct magnetoelastic couplings in this 2D
+van der Waals magnetic semiconductor.",2401.07828v1
+2024-01-19,Excess heat capacity in magnetically ordered Ce heavy fermion metals,"We study the magnetic heat capacity of a series of magnetically ordered
+Ce-based heavy fermion materials, which show an anomalous $T^3$ heat capacity
+in excess of the phonon contribution in many materials. For compounds for which
+magnon models have been worked out, we show that the local-moment magnon heat
+capacity derived from the measured magnon spectra underestimates the
+experimental specific heat. The excess heat capacity reveals increasing density
+of states with increasing energy, akin to a pseudogap. We show that this
+anomalous temperature-dependent term is not associated with proximity to a
+quantum critical point (QCP), but is strongly correlated with $T_N$, indicating
+the anomalous excitations are governed by the magnetic exchange interaction.
+This insight may hold key information for understanding magnetically ordered
+heavy fermions.",2401.10718v1
+2024-01-22,Generating magnon Bell states via parity measurement,"We propose a scheme to entangle two magnon modes based on parity measurement.
+In particular, we consider a system that two yttrium-iron-garnet spheres are
+coupled to a $V$-type superconducting qutrit through the indirect interactions
+mediated by cavity modes. An effective parity-measurement operator that can
+project the two macroscopic spin systems to the desired subspace emerges when
+the ancillary qutrit is projected to the ground state. Consequently,
+conventional and multi-excitation magnon Bell states can be generated from any
+separable states with a nonvanishing population in the desired subspace. The
+target state can be distilled with a near-to-unit fidelity only by several
+rounds of measurements and can be stabilized in the presence of decoherence. In
+addition, a single-shot version of our scheme is obtained by shaping the
+detuning in the time domain. Our scheme that does not rely on any nonlinear
+effect brings insight to the entangled-state generation in massive
+ferrimagnetic materials via quantum measurement.",2401.11684v1
+2024-01-23,Topological magnons in a non-coplanar magnetic order on the triangular lattice,"The bond-dependent Kitaev interaction $K$ is familiar in the effective spin
+model of transition metal compounds with octahedral ligands. In this work, we
+find a peculiar non-coplanar magnetic order can be formed with the help of $K$
+and next nearest neighbor Heisenberg coupling $J_2$ on triangular lattice. It
+can be seen as a miniature version of skyrmion lattice, since it has nine spins
+and integer topological number in a magnetic unit cell. The magnon excitations
+in such an order is studied by the linear spin-wave theory. Of note is that the
+change in the relative size of $J_2$ and $K$ will produce topological magnon
+phase transitions although the topological number remains unchanged. We also
+calculated the experimentally observable thermal Hall conductivity, and found
+that the signs of thermal Hall conductivity will change with topological phase
+transitions or temperature changes in certain regions.",2401.12505v2
+2024-02-26,Distinct Optical Excitation Mechanisms of a Coherent Magnon in a van der Waals Antiferromagnet,"The control of antiferromagnets with ultrashort optical pulses has emerged as
+a prominent field of research. Tailored laser excitation can launch coherent
+spin waves at terahertz frequencies, yet a comprehensive description of their
+generation mechanisms is still lacking despite extensive efforts. Using
+terahertz emission spectroscopy, we investigate the generation of a coherent
+magnon mode in the van der Waals antiferromagnet NiPS$_3$ under a range of
+photoexcitation conditions. By tuning the pump photon energy from transparency
+to resonant with a $d$-$d$ transition, we reveal a striking change in the
+coherent magnon's dependence on the pump polarization, indicating two distinct
+excitation mechanisms. Our findings provide a strategy for the manipulation of
+magnetic modes via photoexcitation around sub-gap electronic states.",2402.17041v2
+2024-02-27,Semiclassical approach to spin dynamics of a ferromagnetic S=1 chain,"Motivated by recent experimental progress in the quasi-one-dimensional
+quantum magnet NiNb$_2$O$_6$, we study the spin dynamics of an S=1
+ferromagnetic Heisenberg chain with single-ion anisotropy by using a
+semiclassical molecular dynamics approach. This system undergoes a quantum
+phase transition from a ferromagnetic to a paramagnetic state under a
+transverse magnetic field, and the magnetic responses reflecting this
+transition is well described by our semiclassical method. We show that at
+low-temperature the transverse component of the dynamical structure factor
+depicts clearly the magnon dispersion, and the longitudinal component exhibits
+two continua associated with single- and two-magnon excitations, respectively.
+These spin excitation spectra show interesting temperature dependence as
+effects of magnon interactions.Our findings shed light on experimental
+detection of spin excitations in a large class of quasi-one-dimensional
+magnets.",2402.17416v1
+2024-03-20,Thermal Hall effect driven by phonon-magnon hybridization in a honeycomb antiferromagnet,"The underlying mechanism of the thermal Hall effect (THE) generated by
+phonons in a variety of insulators is yet to be identified. Here, we report on
+a sizeable thermal Hall conductivity in NiPS$_3$, a van de Waals stack of
+honeycomb layers with a zigzag antiferromagnetic order below $T_N$ = 155 K. The
+longitudinal ($\kappa_{aa}$) and the transverse ($\kappa_{ab}$) thermal
+conductivities peak at the same temperature and the thermal Hall angle
+($\kappa_{ab}/\kappa_{aa}/B$) respects a previously identified bound. The
+amplitude of $\kappa_{ab}$ is extremely sensitive to the amplitude of
+magnetization along the $b$-axis, in contrast to the phonon mean free path,
+which is not at all. We show that the magnon and acoustic phonon bands cross
+each other along the $b^\ast$ orientation in the momentum space. The
+exponential temperature dependence of $\kappa_{ab}$ above its peak reveals an
+energy scale on the order of magnitude of the gap expected to be opened by
+magnon-phonon hybridization. This points to an intrinsic scenario for THE with
+possible relevance to other magnetic insulators.",2403.13306v1
+2024-03-25,Magnon-microwave backaction noise evasion in cavity magnomechanics,"In cavity magnomechanical systems, magnetic excitations couple simultaneously
+with mechanical vibrations and microwaves, combining the tunability of the
+magnetization, the long lifetimes of mechanical modes and the whole measurement
+toolbox of microwave systems. Such hybrid systems have been proposed for
+applications ranging from thermometry to entanglement generation. However,
+backaction noise can hinder the measurement of the mechanical vibrations,
+potentially rendering such applications infeasible. In this paper, we
+investigate the noise introduced in a mechanical mode of a cavity
+magnomechanical system in a one-tone drive scheme and propose a scheme for
+realizing backaction evasion measurements of the mechanical vibrations. Our
+proposal consists of driving the microwave cavity with two tones separated by
+twice the phonon frequency and with amplitudes balanced to generate equal
+numbers of coherent magnons. We demonstrate that different configurations of
+such a scheme are possible and show that drives centered around the lower
+frequency magnon-microwave polariton in a triple resonance scheme add the
+minimum imprecision noise in the measurement, even though such configuration is
+not the most robust to imperfections.",2403.17185v1
+2024-03-31,Quantum Weak Force Sensing with Squeezed Magnomechanics,"Cavity magnomechanics, exhibiting remarkable experimental tunability, rich
+magnonic nonlinearities, and compatibility with various quantum systems, has
+witnessed considerable advances in recent years. However, the potential
+benefits of using cavity magnomechanical (CMM) systems in further improving the
+performance of quantum-enhanced sensing for weak forces remain largely
+unexplored. Here we show that the performance of a quantum CMM sensor can be
+significantly enhanced beyond the standard quantum limit (SQL), by squeezing
+the magnons. We find that, for comparable parameters, two orders of enhancement
+in force sensitivity can be achieved in comparison with the case without the
+magnon squeezing. Moreover, we show optimal parameter regimes of homodyne angle
+for minimizing added quantum noise. Our findings provide a promising approach
+for highly tunable and compatible quantum force sensing using hybrid CMM
+devices, with potential applications ranging from quantum precision
+measurements to quantum information processing.",2404.00723v1
+2024-04-03,Enhancement of Magnon Transport by Superconductor Meissner Screening,"Recent experiments observe the spin-wave-Meissner-current modes in
+ferromagnetic insulator-superconductor heterostructures, in which the
+coherently excited spin waves seemingly do not decay as usual beneath the
+superconductor strip [Borst et al., Science 382, 430 (2023)]. We interpret this
+phenomenon by demonstrating that the stray magnetic field emitted by the
+magnetization dynamics is reflected, focused, and enhanced inside the
+ferromagnet by the supercurrent induced in the superconductor, such that the
+group velocity of spin waves is strongly enhanced. Analytical and numerical
+calculations based on this model predict that the coherent transport of magnons
+is enhanced by close to 500% for yttrium iron garnet capped by superconducting
+NbN with a decay length exceeding millimeters. Our finding may augment the
+performance of magnons in quantum information and quantum transport processing.",2404.02598v1
+2024-04-05,Magnetoroton in a two-dimensional Bose-Bose mixture,"We extend our theory of slow magnons in a two-component Bose-Einstein
+condensate to the case of two spatial dimensions (2D). We provide a detailed
+discussion of polaronic corrections to the magnon branch of the elementary
+excitation spectrum in a weakly- and strongly-interacting regimes. In a dilute
+system, the latter may be achieved by adjusting inter-species attraction such
+as to obtain a resonance in the $p$-wave scattering channel. Resonantly
+enhanced $p$-wave attraction results in the self-localization of magnons and
+formation of a magnetoroton. The nature of a ground state beyond the
+magnetoroton instability remains to be explored. We suggest a dilute p-wave
+crystal of alternating polarization as a possible candidate. In contrast to
+three dimensions (3D), the required strength of the attractive potential in the
+$s$-wave channel here corresponds to tight binding, and we suggest a potential
+realization of our model with excitons in 2D semiconductors.",2404.04440v1
+2024-04-09,Robustness of topological magnons in disordered arrays of skyrmions,"The effects of disorder on the robustness of topological magnon states of
+two-dimensional ferromagnetic skyrmions is investigated. It is diagnosed by
+evaluating a real space topological invariant, the bosonic Bott index (BI). The
+disorder simultaneously breaks the axially symmetric shape and the crystalline
+ordering of the skyrmions array. The corresponding magnonic fluctuations and
+band spectrum are determined in terms of magnetic field and strength of
+disorder. We observe the closing of the existing band gaps as the individual
+skyrmions start to occupy random positions. The analysis reveals that
+topological states (TSs) persist beyond the perturbative limit when skyrmions
+reach the glassy phase. In addition, the localization of topologically
+protected edge states is weakened by the disordered skyrmion structure with
+increasing localization length. Our findings shed light on the physical
+understanding of the coexistence of disordered magnetic textures and their
+topological spin fluctuations.",2404.06541v1
+2006-02-28,Field dependence of the magnetic spectrum in anisotropic and Dzyaloshinskii-Moriya antiferromagnets: II. Raman spectroscopy,"We compare the theoretical predictions of the previous article [L. Benfatto
+and M. B. Silva Neto, cond-mat/0602419], with Raman spectroscopy experiments in
+Sr(2)CuO(2)Cl(2) and untwinned La(2)CuO(4) single crystals. We construct the
+magnetic point group for the magnetically ordered phase of the two compounds,
+Sr(2)CuO(2)Cl(2) and La(2)CuO(4), and we classify all the Raman active
+one-magnon excitations according to the irreducible co-representations for the
+associated magnetic point group. We then measure the evolution of the
+one-magnon Raman energies and intensities for low and moderate magnetic fields
+along the three crystallographic directions. In the case of La(2)CuO(4), we
+demonstrate that from the jump of the Dzyaloshinskii-Moriya gap at the critical
+magnetic field H_c ~ 6.6 T for the weak-ferromagnetic transition one can
+determine the value of the interlayer coupling J_\perp/J ~ 3.2 x 10^-5. We
+furthermore determine the components of the anisotropic gyromagnetic tensor as
+g_s^a=2.0, g_s^b=2.08, and the upper bound g_s^c=2.65. For the case of
+Sr(2)CuO(2)Cl(2), we compare the Raman data obtained in an in-plane magnetic
+field with previous magnon-gap measurements done by ESR. Using the very low
+magnon gap estimated by ESR (~ 0.05 meV), the data for the one-magnon Raman
+energies agree reasonably well with the theoretical predictions for the case of
+a transverse field (only hardening of the gap).",0602664v2
+2010-09-21,Twisting the Mirror TBA,"We study finite-size corrections to the magnon dispersion relation in three
+models which differ from string theory on AdS5 x S5 in their boundary
+conditions. Asymptotically, this is accomplished by twisting the transfer
+matrix in a way which manifestly preserves integrability. In model I all
+world-sheet fields are periodic, whereas model II represents a particular
+orbifold of AdS5 x S5 and model III is a beta-deformed theory. For models I and
+II we construct the one-particle TBA equations and use them to determine the
+leading finite-size correction to the asymptotic Bethe equation. We also make
+some interesting observations concerning the quantization conditions for the
+momentum. For the same models we compute the leading and for model II the
+next-to-leading order finite-size corrections to the asymptotic magnon
+dispersion relation. Furthermore, we apply L\""uscher's formulae to compute the
+leading finite-size corrections in beta-deformed theory. In addition to
+reproducing known results, we provide new predictions for two-particle states
+from the sl(2) sector, to be confronted with explicit field-theoretic
+calculations in the dual gauge theory. Finally, we prove that the leading
+finite-size correction to the energy of an sl(2) magnon in orbifold theory is
+the same as the one for an su(2) magnon in beta-deformed theory for special
+values of beta. We also speculate that for these values of beta our result for
+the next-to-leading order correction in the orbifold model might coincide with
+the corresponding correction to the energy of su(2) magnon in beta-deformed
+theory.",1009.4118v3
+2012-04-23,Spin nematic phase in (quasi-)one-dimensional frustrated magnet in strong magnetic field,"We discuss spin-1/2 one-dimensional (1D) and quasi-1D magnets with competing
+ferromagnetic nearest-neighbor $J_1$ and antiferromagnetic
+next-nearest-neighbor $J$ exchange interactions in strong magnetic field $H$.
+It is well known that due to attraction between magnons quantum phase
+transitions (QPTs) take place at $H=H_s$ from the fully polarized phase to
+nematic ones if $J>|J_1|/4$. Such a transition at $J>0.368|J_1|$ is
+characterized by softening of the two-magnon bound-state spectrum. Using a bond
+operator formalism we propose a bosonic representation of the spin Hamiltonian
+containing, aside from bosons describing one-magnon spin-1 excitations, a boson
+describing spin-2 excitations which spectrum coincides at $H\ge H_s$ with the
+two-magnon bound-state spectrum obtained before. The presence of the bosonic
+mode in the theory that softens at $H=H_s$ makes substantially standard the QPT
+consideration. In 1D case at $H<H_s$, we find an expression for the
+magnetization which describes well existing numerical data. Expressions for
+spin correlators are obtained which coincide with those derived before either
+in the limiting case of $J\gg|J_1|$ or using a phenomenological theory. In
+quasi-1D magnets, we find that the boundary in the $H$--$T$ plane between the
+fully polarized and the nematic phases is given by $H_s(0)-H_s(T)\propto
+T^{3/2}$. Simple expressions are obtained in the nematic phase for static spin
+correlators, spectra of magnons and the soft mode, magnetization and the
+nematic order parameter. All static two-spin correlation functions are short
+ranged with the correlation length proportional to $1/\ln(1+|J_1|/J)$.
+Dynamical spin susceptibilities are discussed and it is shown that the soft
+mode can be observed experimentally in the longitudinal channel.",1204.4983v3
+2019-03-12,Magnon interactions in the frustrated pyrochlore ferromagnet Yb$_2$Ti$_2$O$_7$,"The frustrated rare-earth pyrochlore Yb$_2$Ti$_2$O$_7$ is remarkable among
+magnetic materials: despite a ferromagnetically ordered ground state it
+exhibits a broad, nearly gapless, continuum of excitations. This broad
+continuum connects smoothly to the sharp one-magnon excitations expected, and
+indeed observed, at high magnetic fields, raising the question: how does this
+picture of sharp magnons break down as the field is lowered? In this paper, we
+consider the effects of magnon interactions in Yb$_2$Ti$_2$O$_7$, showing that
+their inclusion greatly extends the reach of spin-wave theory. First, we show
+that magnon interactions shift the phase boundary between the (splayed)
+ferromagnet (SFM) and the antiferromagnetic $\Gamma_5$ phase so that
+Yb$_2$Ti$_2$O$_7$ lies very close to it. Next, we show how the high-field limit
+connects to lower fields; this includes corrections to the critical fields for
+the $[111]$ and $[1\bar{1}0]$ directions, bringing them closer to the observed
+experimental values, as well as accounting for the departures from linear spin
+wave theory that appear in $[001]$ applied fields below 3 T [Thompson et al.,
+Phys. Rev. Lett. 119, 057203 (2017)]. Turning to low-fields, though the extent
+of the experimentally observed broadening is not quite reproduced, we find a
+rough correspondence between non-linear spin-wave theory and inelastic neutron
+scattering data on both a single-crystal sample, as well as on a powder sample
+[Pe\c{c}anha-Antonio et al., Phys. Rev. B, 96, 214415 (2017)]. We conclude with
+an outlook on implications for future experimental and theoretical work on
+Yb$_2$Ti$_2$O$_7$ and related materials, highlighting the importance of
+proximity to the splayed ferromagnet-$\Gamma_5$ phase boundary and its
+potential role in intrinsic or extrinsic explanations of the low-field physics
+of Yb$_2$Ti$_2$O$_7$.",1903.05098v1
+2016-12-21,Bose-Einstein Condensation of Quasi-Particles by Rapid Cooling,"The fundamental phenomenon of Bose-Einstein Condensation (BEC) has been
+observed in different systems of real and quasi-particles. The condensation of
+real particles is achieved through a major reduction in temperature while for
+quasi-particles a mechanism of external injection of bosons by irradiation is
+required. Here, we present a novel and universal approach to enable BEC of
+quasi-particles and to corroborate it experimentally by using magnons as the
+Bose-particle model system. The critical point to this approach is the
+introduction of a disequilibrium of magnons with the phonon bath. After heating
+to an elevated temperature, a sudden decrease in the temperature of the
+phonons, which is approximately instant on the time scales of the magnon
+system, results in a large excess of incoherent magnons. The consequent
+spectral redistribution of these magnons triggers the Bose-Einstein
+condensation.",1612.07305v3
+2017-11-02,Topological spin excitations observed in a three-dimensional antiferromagnet,"Band topology, or global wave-function structure that enforces novel
+properties in the bulk and on the surface of crystalline materials, is
+currently under intense investigations for both fundamental interest and its
+technological promises. While band crossing of non-trivial topological nature
+was first studied in three dimensions for electrons, the underlying physical
+idea is not restricted to fermionic excitations. In fact, experiments have
+confirmed the possibility to have topological band crossing of electromagnetic
+waves in artificial structures. Fundamental bosonic excitations in real
+crystals, however, have not been observed to exhibit the counterpart under
+ambient pressure and magnetic field, where the difficulty is in part because
+natural materials cannot be precisely engineered like artificial structures.
+Here, we use inelastic neutron scattering to reveal the presence of topological
+spin excitations (magnons) in a three-dimensional antiferromagnet, Cu3TeO6,
+which features a unique lattice of magnetic spin-1/2 Cu2+ ions. Beyond previous
+understanding, we find that the material's spin lattice possesses a variety of
+exchange interactions, with the interaction between the ninth-nearest
+neighbours being as strong as that between the nearest neighbours. Although
+theoretical analysis indicates that the presence of topological magnon band
+crossing is independent of model details, Cu3TeO6 turns out to be highly
+favourable for the experimental observation, as its optical magnons are
+spectrally sharp and intense due to the highly interconnected spin network and
+the large magnetic cell. The observed magnon band crossing generally has the
+form of a special type of Z2-topological nodal lines that are yet to be found
+in fermion systems, rendering magnon systems a fertile ground for exploring
+novel band topology.",1711.00632v1
+2018-10-25,Inhomogeneous magnon scattering during ultrafast demagnetization,"Ni$_{0.8}$Fe$_{0.2}$ (Py) and Py alloyed with Cu exhibit intriguing ultrafast
+demagnetization behavior, where the Ni magnetic moment shows a delayed response
+relative to the Fe, an effect which is strongly enhanced by Cu alloying. We
+have studied a broad range of Cu concentrations to elucidate the effects of Cu
+alloying in Py. The orbital/spin magnetic moment ratios are largely unaffected
+by Cu alloying, signifying that Cu-induced changes in the ultrafast
+demagnetization are not related to spin-orbit interactions. We show that magnon
+diffusion can explain the delayed Ni response, which we attribute to an
+enhanced magnon generation rate in the Fe sublattice relative to the Ni
+sublattice. Furthermore, Py exhibits prominent RKKY-like exchange interactions,
+which are strongly enhanced between Fe atoms and diminished between Ni atoms by
+Cu alloying. An increased Fe magnon scattering rate is expected to occur
+concurrently with this increased Fe-Fe exchange interaction, supporting the
+results obtained from the magnon diffusion model.",1810.10994v1
+2021-02-01,Strong-Magnetic-Field Magnon Transport in Monolayer Graphene,"At high magnetic fields, monolayer graphene hosts competing phases
+distinguished by their breaking of the approximate SU(4) isospin symmetry.
+Recent experiments have observed an even denominator fractional quantum Hall
+state thought to be associated with a transition in the underlying isospin
+order from a spin-singlet charge density wave at low magnetic fields to an
+antiferromagnet at high magnetic fields, implying that a similar transition
+must occur at charge neutrality. However, this transition does not generate
+contrast in typical electrical transport or thermodynamic measurements and no
+direct evidence for it has been reported, despite theoretical interest arising
+from its potentially unconventional nature. Here, we measure the transmission
+of ferromagnetic magnons through the two dimensional bulk of clean monolayer
+graphene. Using spin polarized fractional quantum Hall states as a benchmark,
+we find that magnon transmission is controlled by the detailed properties of
+the low-momentum spin waves in the intervening Hall fluid, which is highly
+density dependent. Remarkably, as the system is driven into the
+antiferromagnetic regime, robust magnon transmission is restored across a wide
+range of filling factors consistent with Pauli blocking of fractional quantum
+hall spin-wave excitations and their replacement by conventional ferromagnetic
+magnons confined to the minority graphene sublattice. Finally, using devices in
+which spin waves are launched directly into the insulating charge-neutral bulk,
+we directly detect the hidden phase transition between bulk insulating charge
+density wave and a canted antiferromagnetic phases at charge neutrality,
+completing the experimental map of broken-symmetry phases in monolayer
+graphene.",2102.01061v1
+2018-01-04,Complex temperature dependence of coupling and dissipation of cavity-magnon polaritons from milliKelvin to room temperature,"Hybridized magnonic-photonic systems are key components for future
+information processing technologies such as storage, manipulation or conversion
+of data both in the classical (mostly at room temperature) and quantum
+(cryogenic) regime. In this work, we investigate a YIG sphere coupled strongly
+to a microwave cavity over the full temperature range from $290\,\mathrm{K}$
+down to $30\,\mathrm{mK}$. The cavity-magnon polaritons are studied from the
+classical to the quantum regime where the thermal energy is less than one
+resonant microwave quanta, i.e. at temperatures below $1\,\mathrm{K}$. We
+compare the temperature dependence of the coupling strength $g_{\rm{eff}}(T)$,
+describing the strength of coherent energy exchange between spin ensemble and
+cavity photon, to the temperature behavior of the saturation magnetization
+evolution $M_{\rm{s}}(T)$ and find strong deviations at low temperatures. The
+temperature dependence of magnonic disspation is governed at intermediate
+temperatures by rare earth impurity scattering leading to a strong peak at
+$40\,$K. The linewidth $\kappa_{\rm{m}}$ decreases to $1.2\,$MHz at $30\,$mK,
+making this system suitable as a building block for quantum electrodynamics
+experiments. We achieve an electromagnonic cooperativity in excess of $20$ over
+the entire temperature range, with values beyond $100$ in the milliKelvin
+regime as well as at room temperature. With our measurements, spectroscopy on
+strongly coupled magnon-photon systems is demonstrated as versatile tool for
+spin material studies over large temperature ranges. Key parameters are
+provided in a single measurement, thus simplifying investigations
+significantly.",1801.01439v1
+2018-08-03,Decoupled spin dynamics in the rare-earth orthoferrite YbFeO$_3$: Evolution of magnetic excitations through the spin-reorientation transition,"In this paper we present a comprehensive study of magnetic dynamics in the
+rare-earth orthoferrite YbFeO$_3$ at temperatures below and above the
+spin-reorientation (SR) transition $T_{\mathrm{SR}}=7.6$ K, in magnetic fields
+applied along the $a, b$ and $c$ axes. Using single-crystal inelastic neutron
+scattering, we observed that the spectrum of magnetic excitations consists of
+two collective modes well separated in energy: 3D gapped magnons with a
+bandwidth of $\sim$60 meV, associated with the antiferromagnetically (AFM)
+ordered Fe subsystem, and quasi-1D AFM fluctuations of $\sim$1 meV within the
+Yb subsystem, with no hybridization of those modes. The spin dynamics of the Fe
+subsystem changes very little through the SR transition and could be well
+described in the frame of semiclassical linear spin-wave theory. On the other
+hand, the rotation of the net moment of the Fe subsystem at $T_{\mathrm{SR}}$
+drastically changes the excitation spectrum of the Yb subsystem, inducing the
+transition between two regimes with magnon and spinon-like fluctuations. At $T
+< T_{\mathrm{SR}}$, the Yb spin chains have a well defined field-induced
+ferromagnetic (FM) ground state, and the spectrum consists of a sharp
+single-magnon mode, a two-magnon bound state, and a two-magnon continuum,
+whereas at $T > T_{\mathrm{SR}}$ only a gapped broad spinon-like continuum
+dominates the spectrum. In this work we show that a weak quasi-1D coupling
+within the Yb subsystem $J_\text{Yb-Yb}$, mainly neglected in previous studies,
+creates unusual quantum spin dynamics on the low energy scales. The results of
+our work may stimulate further experimental search for similar compounds with
+several magnetic subsystems and energy scales, where low-energy fluctuations
+and underlying physics could be ""hidden"" by a dominating interaction.",1808.01269v2
+2020-03-28,Theory of the anomalous spin dynamics of spin-$\frac{1}{2}$ triangular lattice Heisenberg antiferromagnet and its application to Ba$_3$CoSb$_2$O$_9$,"Although it is well accepted that the spin-$\frac{1}{2}$ triangular lattice
+Heisenberg antiferromagnet(TLHAF) has a long range ordered ground state, a
+thorough understanding of its spin dynamics is still missing. While the linear
+spin wave theory(LSWT) predicts three branches of magnon mode in the magnetic
+Brillouin zone(MBZ), the 1/S expansion at the next order is found to break down
+in a large portion of the MBZ centered around the M point, leaving the fate of
+the magnon modes there undecided. Recent neutron scattering measurement on
+Ba$_3$CoSb$_2$O$_9$, an ideal realization of the spin-$\frac{1}{2}$ TLHAF,
+provides a surprising answer to this issue. Two, rather than three branches of
+magnon mode are observed around the M point, whose dispersion are strongly
+renormalized with respect to the LSWT prediction and exhibit pronounced
+roton-like minimum at the M point. This is accompanied by a strong spin
+fluctuation continuum at higher energy, inside which two strong and broad
+spectral peaks of unknown origin are observed. In this work, we propose a
+simple picture for these spectral anomalies by invoking the resonating valence
+bond(RVB) physics in the description of the ground state of the system. We find
+that the roton-like minimum in the magnon dispersion can be explained by the
+coupling between the collective spin fluctuation and the continuum of Dirac
+spinon excitation moving in a $\pi$-flux background. We also propose that the
+two broad peaks in the continuum can be understood respectively as the Landau
+damped third magnon mode and the Landau damped longitudinal mode. Such a
+picture can be verified by studying the polarization character of the various
+spectral features.",2003.12688v1
+2020-08-06,Magnon versus electron mediated spin-transfer torque exerted by spin currents across antiferromagnetic insulator to switch magnetization of adjacent ferromagnetic metal,"The recent experiment [Y. Wang et al., Science 366, 1125 (2019)] on
+magnon-mediated spin-transfer torque (MSTT) was interpreted in terms of a
+picture where magnons are excited within an antiferromagnetic insulator (AFI),
+by applying nonequilibrium electronic spin density at one of its surfaces, so
+that their propagation across AFI deprived of conduction electrons eventually
+leads to reversal of magnetization of a ferromagnetic metal (FM) attached to
+the opposite surface of AFI. We employ a recently developed time-dependent
+nonequilibrium Green functions combined with the Landau-Lifshitz-Gilbert
+equation (TDNEGF+LLG) formalism to evolve conduction electrons
+quantum-mechanically while they interact via self-consistent back-action with
+localized magnetic moments described classically by atomistic spin dynamics
+solving a system of LLG equations. Upon injection of square current pulse as
+the initial condition, TDNEGF+LLG simulations of FM-polarizer/AFI/FM-analyzer
+junctions show that reversal of localized magnetic moments within FM-analyzer
+is less efficient, in the sense of requiring larger pulse height and its longer
+duration, than conventional electron-mediated STT (ESTT) driving magnetization
+switching in standard FM-polarizer/normal-metal/FM-analyzer spin valve. Since
+both electronic, generated by spin pumping from AFI, and magnonic, generated by
+direct transmission from AFI, spin currents are injected into the FM-analyzer,
+its localized magnetic moments will experience combined MSTT and ESTT.
+Nevertheless, by artificially turning off ESTT we demonstrate that MSTT plays a
+dominant role whose understanding, therefore, paves the way for
+all-magnon-driven magnetization switching devices with no electronic parts.",2008.02794v3
+2021-07-19,Multimagnon dynamics and thermalization in the $S=1$ easy-axis ferromagnetic chain,"Quasiparticles are physically motivated mathematical constructs for
+simplifying the seemingly complicated many-body description of solids. A
+complete understanding of their dynamics and the nature of the effective
+interactions between them provides rich information on real material properties
+at the microscopic level. In this work, we explore the dynamics and
+interactions of magnon quasiparticles in a ferromagnetic spin-1 Heisenberg
+chain with easy-axis onsite anisotropy, a model relevant for the explanation of
+recent terahertz optics experiments on NiNb$_2$O$_6$ [P. Chauhan et al., Phys.
+Rev. Lett. 124, 037203 (2020)],and nonequilibrium dynamics in ultracold atomic
+settings [W.C. Chung et al., Phys. Rev. Lett. 126, 163203 (2021)]. We build a
+picture for the properties of clouds of a few magnons with the help of exact
+diagonalization and density matrix renormalization group calculations supported
+by physically motivated Jastrow wavefunctions. We show how the binding energy
+of magnons effectively reduces with their number and explain how this energy
+scale is of direct relevance for dynamical magnetic susceptibility
+measurements. This understanding is used to make predictions for
+ultracold-atomic platforms which are ideally suited to study the thermalization
+of multimagnon states. We simulate the nonequilibrium dynamics of these chains
+using the matrix product state based time-evolution block decimation algorithm
+and explore the dependence of revivals and thermalization on magnon density and
+easy-axis onsite anisotropy (which controls the strength of effective magnon
+interactions). We observe behaviors akin to those reported for many-body
+quantum scars which we explain with an analytic approximation that is accurate
+in the limit of small anisotropy.",2107.09105v2
+2022-02-04,Unusual dynamics of spin-1/2 antiferromagnets on the triangular lattice in magnetic field,"We theoretically discuss dynamical properties of spin-1/2 Heisenberg
+antiferromagnet on the triangular lattice in magnetic field $\bf H$. We use the
+recently proposed bond-operator theory which operates with quantum states of
+the whole magnetic unit cell containing three spins. This technique describes
+accurately short-range spin correlations and provides a quantitative
+description of elementary excitations which appear in other approaches as bound
+states of conventional low-energy quasiparticles (e.g., magnons). In
+quantitative agreement with previous numerical and analytical findings, we
+observe four phases with coplanar spin arrangements upon the field increasing:
+the three-sublattice Y-phase, the collinear ""up-up-down"" (UUD) state, the
+non-collinear V-phase, and the collinear fully polarized (FP) state. We
+demonstrate that apart from magnons there are spin-0 elementary excitations in
+the UUD state one of which is long lived and its spectrum lies below magnon
+branches. This mode originates from a high-energy quasiparticle at $H=0$ and it
+produces anomalies only in the longitudinal spin correlator. In the V-phase, we
+obtain multiple short-wavelength spin excitations which have no counterparts in
+the semiclassical spin-wave theory. We demonstrate a highly nontrivial field
+evolution of quasiparticles spectra on the way from one collinear state (UUD)
+to another one (FP) via the non-collinear V-phase (in which the longitudinal
+and the transverse channels are mixed). In particular, some parts of the spin-0
+branch in the UUD state become parts of the spin-1 (magnon) branch in the FP
+phase whereas some parts of one magnon branch turn into parts of spin-2 branch.
+Such evolution would be very difficult to find by any conventional analytical
+approach. Our results are in good agreement with neutron experimental data
+obtained recently in $\rm Ba_3CoSb_2O_9$, $\rm KYbSe_2$, and $\rm CsYbSe_2$.",2202.02120v3
+2022-10-13,Single- and Multimagnon Dynamics in Antiferromagnetic $α$-Fe$_2$O$_3$ Thin Films,"Understanding the spin dynamics in antiferromagnetic (AFM) thin films is
+fundamental for designing novel devices based on AFM magnon transport. Here, we
+study the magnon dynamics in thin films of AFM $S=5/2$ $\alpha$-Fe$_2$O$_3$ by
+combining resonant inelastic x-ray scattering, Anderson impurity model plus
+dynamical mean-field theory, and Heisenberg spin model. Below 100 meV, we
+observe the thickness-independent (down to 15 nm) acoustic single-magnon mode.
+At higher energies (100-500 meV), an unexpected sequence of equally spaced,
+optical modes is resolved and ascribed to $\Delta S_z = 1$, 2, 3, 4, and 5
+magnetic excitations corresponding to multiple, noninteracting magnons. Our
+study unveils the energy, character, and momentum-dependence of single and
+multimagnons in $\alpha$-Fe$_2$O$_3$ thin films, with impact on AFM magnon
+transport and its related phenomena. From a broader perspective, we generalize
+the use of L-edge resonant inelastic x-ray scattering as a multispin-excitation
+probe up to $\Delta S_z = 2S$. Our analysis identifies the spin-orbital mixing
+in the valence shell as the key element for accessing excitations beyond
+$\Delta S_z = 1$, and up to, e.g., $\Delta S_z = 5$. At the same time, we
+elucidate the novel origin of the spin excitations beyond the $\Delta S_z = 2$,
+emphasizing the key role played by the crystal lattice as a reservoir of
+angular momentum that complements the quanta carried by the absorbed and
+emitted photons.",2210.06911v4
+2022-12-05,Phonon-mediated strong coupling between a three-dimensional topological insulator and a two-dimensional antiferromagnetic material,"Van der Waals antiferromagnetic and topological insulator materials provide
+powerful platforms for modern optical, electronic, and spintronic devices
+applications. The interaction between an antiferromagnet (AFM) and a
+topological insulator (TI), if sufficiently strong, could offer emergent hybrid
+material properties that enable new functionality exceeding what is possible in
+any individual material constituent. In this work, we study strong coupling
+between THz excitations in a three dimensional (3D) topological insulator and a
+quasi-two dimensional (2D) antiferromagnetic material resulting in a new
+hybridized mode, namely a surface Dirac plasmon-phonon-magnon polariton. We
+find that the interaction between a surface Dirac plasmon polariton in the 3D
+TI and a magnon polariton in the 2D AFM is mediated by the phonon coupling in
+the 3D TI material. The coupling of phonons with an electromagnetic wave
+propagating in the 3D TI enhances the permittivity of the TI thin film in a way
+that results in a strong correlation between the dispersion of Dirac plasmon
+polaritons on the surfaces of the TI with the thickness of the TI. As a result,
+the dispersion of surface Dirac plasmon polaritons in the TI can be tuned
+toward resonance with the magnon polariton in the AFM material by varying the
+TI's thickness, thereby enhancing the strength of the coupling between the
+excitations in the two materials. The strength of this coupling, which results
+in the surface Dirac plasmon-phonon-magnon polariton, can be parameterized by
+the amplitude of the avoided-crossing splitting between the two polariton
+branches at the magnon resonance frequency...",2212.02656v1
+2023-04-25,Riemann meets Goldstone: magnon scattering off quantum Hall skyrmion crystals probes interplay of symmetry breaking and topology,"We introduce a model to study magnon scattering in skyrmion crystals,
+sandwiched between ferromagnets which act as the source of magnons. Skyrmions
+are topological objects while skyrmion crystals break internal and
+translational symmetries, thus our setup allows us to study the interplay of
+topology and symmetry breaking. Starting from a basis of holomorphic theta
+functions, we construct an analytical ansatz for such a junction with finite
+spatially modulating topological charge density in the central region and
+vanishing in the leads. We then construct a suitably defined energy functional
+for the junction and derive the resulting equations of motion, which resemble a
+Bogoliubov-de Gennes-like equation. Using analytical techniques, field theory,
+heuristic models and microscopic recursive transfer-matrix numerics, we
+calculate the spectra and magnon transmission properties of the skyrmion
+crystal. We find that magnon transmission can be understood via a combination
+of low-energy Goldstone modes and effective emergent Landau levels at higher
+energies. The former manifests in discrete low-energy peaks in the transmission
+spectrum which reflect the nature of the Goldstone modes arising from symmetry
+breaking. The latter, which reflect the topology, lead to band-like
+transmission features, from the structure of which further details of the
+excitation spectrum of the skyrmion crystal can be inferred. Such
+characteristic transmission features are absent in competing phases of the
+quantum Hall phase diagram, and hence provide direct signatures of skyrmion
+crystal phases and their spectra. Our results directly apply to quantum Hall
+heterojunction experiments in monolayer graphene with the central region doped
+slightly away from unit filling, a $\nu = 1:1 \pm \delta \nu: 1$ junction and
+are also relevant to junctions formed by metallic magnets or in junctions with
+artificial gauge fields.",2304.13049v1
+2023-06-12,Field-induced bound-state condensation and spin-nematic phase in SrCu$_2$(BO$_3$)$_2$ revealed by neutron scattering up to 25.9 T,"Bose-Einstein condensation (BEC) underpins exotic forms of order ranging from
+superconductivity to superfluid 4 He. In quantum magnetic materials, ordered
+phases induced by an applied magnetic field can be described as the BEC of
+magnon excitations. With sufficiently strong magnetic frustration, exemplified
+by the system SrCu$_2$(BO$_3$)$_2$ , no clear magnon BEC is observed and the
+complex spectrum of multi-magnon bound states may allow a different type of
+condensation, but the high fields required to probe this physics have remained
+a barrier to detailed investigation. Here we exploit the first purpose-built
+high-field neutron scattering facility to measure the spin excitations of
+SrCu$_2$(BO$_3$)$_2$ up to 25.9 T and use cylinder matrix-product-states (MPS)
+calculations to reproduce the experimental spectra with high accuracy. Multiple
+unconventional features point to a condensation of $S = 2$ bound states into a
+spin-nematic phase, including the gradients of the one-magnon branches, the
+presence of many novel composite two- and three-triplon excitations and the
+persistence of a one-magnon spin gap. This gap reflects a direct analogy with
+superconductivity, suggesting that the spin-nematic phase in
+SrCu$_2$(BO$_3$)$_2$ is best understood as a condensate of bosonic Cooper
+pairs. Our results underline the wealth of unconventional states yet to be
+found in frustrated quantum magnetic materials under extreme conditions.",2306.07389v1
+2023-12-01,Exploring kinetically induced bound states in triangular lattices with ultracold atoms: spectroscopic approach,"Quantum simulations with ultracold fermions in triangular optical lattices
+have recently emerged as a new platform for studying magnetism in frustrated
+systems. Experimental realizations of the Fermi Hubbard model revealed striking
+contrast between magnetism in bipartite and triangular lattices. In bipartite
+lattices magnetism peaks at half filling, and doped charge carriers tend to
+suppress magnetic correlations. In triangular lattices for large $U/t$,
+magnetism is enhanced by doping away from $n=1$ because kinetic energy of
+dopants can be lowered through developing magnetic correlations. This
+corresponds to formation of magnetic polarons, with hole and doublon doping
+resulting in antiferro- and ferromagnetic polarons respectively. Snapshots
+obtained with quantum gas microscopes revealed formation of magnetic polarons
+around dopants at temperatures exceeding the superexchange energy scale. In
+this work we discuss theoretically that additional insight into properties of
+magnetic polarons can be achieved using spectroscopic experiments with
+ultracold atoms. We consider starting from a spin polarized state with small
+hole doping and applying a two-photon Raman photoexcitation, which transfers
+atoms into a different spin state. We show that such magnon injection spectra
+exhibit a separate peak corresponding to formation of a bound state between a
+hole and a magnon. This polaron peak is separated from the simple magnon
+spectrum by energy proportional to single particle tunneling and can be easily
+resolved with currently available experimental techniques. For some momentum
+transfer there is an additional peak corresponding to photoexciting a bound
+state between two holes and a magnon. We point out that in two component Bose
+mixtures in triangular lattices one can also create dynamical magnetic
+polarons, with one hole and one magnon forming a repulsive bound state.",2312.00768v1
+2024-02-19,Magnetic anisotropy and GGG substrate stray field in YIG films down to millikelvin temperatures,"Quantum magnonics investigates the quantum-mechanical properties of magnons
+such as quantum coherence or entanglement for solid-state quantum information
+technologies at the nanoscale. The most promising material for quantum
+magnonics is the ferrimagnetic yttrium iron garnet (YIG), which hosts magnons
+with the longest lifetimes. YIG films of the highest quality are grown on a
+paramagnetic gadolinium gallium garnet (GGG) substrate. The literature has
+reported that ferromagnetic resonance (FMR) frequencies of YIG/GGG decrease at
+temperatures below 50 K despite the increase in YIG magnetization. We
+investigated a 97 nm-thick YIG film grown on 500 $\mathrm{\mu}$m-thick GGG
+substrate through a series of experiments conducted at temperatures as low as
+30 mK, and using both analytical and numerical methods. Our findings suggest
+that the primary factor contributing to the FMR frequency shift is the stray
+magnetic field created by the partially magnetized GGG substrate. This stray
+field is antiparallel to the applied external field and is highly
+inhomogeneous, reaching up to 40 mT in the center of the sample. At
+temperatures below 500 mK, the GGG field exhibits a saturation that cannot be
+described by the standard Brillouin function for a paramagnet. Including the
+calculated GGG field in the analysis of the FMR frequency versus temperature
+dependence allowed the determination of the cubic and uniaxial anisotropies. We
+find that the total anisotropy increases more than three times with the
+decrease in temperature down to 2 K. Our findings enable accurate predictions
+of the YIG/GGG magnetic systems behavior at low and ultra-low millikelvin
+temperatures, crucial for developing quantum magnonic devices.",2402.12112v1
+1997-09-21,The dispersion of a single hole in an antiferromagnet,"We revisit the problem of the dispersion of a single hole injected into a
+quantum antiferromagnet. We applied a spin-density-wave formalism extended to a
+large number of orbitals and obtained an integral equation for the full
+quasiparticle Green's function in the self-consistent ""non-crossing"" Born
+approximation. We found that for $t/J \gg 1$, the bare fermionic dispersion is
+completely overshadowed by the self-energy corrections. We obtain a broad
+incoherent continuum which extends over a frequency range of $\sim 6t$ and a
+narrow region of width $O(JS)$ below the top of the valence band, where the
+excitations are mostly coherent, though with a small quasiparticle residue $Z
+\sim J/t$. Furthermore, we argue in this paper that two-magnon Raman scattering
+as well as neutron scattering experiments strongly suggest that the zone
+boundary magnons are not free particles since a substantial portion of their
+spectral weight is transferred into an incoherent background. We modeled this
+effect by introducing a cutoff $q_c$ in the integration over magnon momenta. We
+found analytically that for small $q_c$, the strong coupling solution for the
+Green's function is universal, and both effective masses are equal to
+$(4JS)^{-1}$. We further computed the full fermionic dispersion for $J/t =0.4$
+relevant for $Sr_2CuO_2Cl_2$, and $t^\prime=-0.4J$ and found not only that the
+masses are both equal to $(2J)^{-1}$, but also that the energies at $(0,0)$ and
+$(0,\pi)$ are equal, the energy at $(0,\pi/2)$ is about half of that at
+$(0,0)$, and the bandwidth for the coherent excitations is around $3J$. All of
+these results are in full agreement with the experimental data.",9709235v1
+2000-03-06,Modeling of the Magnetic Susceptibilities of the Ambient- and High-Pressure Phases of (VO)_{2}P_{2}O_{7},"The magnetic susceptibilities chi versus temperature T of powders and single
+crystals of the ambient-pressure (AP) and high-pressure (HP) phases of
+(VO)_{2}P_{2}O_{7} are analyzed using an accurate theoretical prediction of
+chi(T, J1, J2) for the spin-1/2 antiferromagnetic alternating-exchange (J1, J2)
+Heisenberg chain. The results are consistent with recent models with two
+distinct types of alternating-exchange chains in the AP phase and a single type
+in the HP phase. The spin gap for each type of chain is derived from the
+respective set of two fitted alternating exchange constants and the one-magnon
+dispersion relation for each of the two types of chains in the AP phase is
+predicted. The influences of interchain coupling on the derived intrachain
+exchange constants, spin gaps, and dispersion relations are estimated using a
+mean-field approximation for the interchain coupling. The accuracies of the
+spin gaps obtained using fits to the low-T chi(T) data by theoretical low-T
+approximations are determined. The results of these studies are compared with
+previously reported estimates of the exchange couplings and spin gaps in the AP
+and HP phases and with the magnon dispersion relations in the AP phase measured
+previously using inelastic neutron scattering.",0003065v2
+2002-09-14,"Magnon-polaron and Spin-polaron Signatures in the Specific Heat and Electrical Resistivity of $La_{0.6}Y_{0.1}Ca_{0.3}MnO_3$ in Zero Magnetic Field, and the Effect of $Mn-O-Mn$ Bond Environment","$La_{0.6}Y_{0.1}Ca_{0.3}MnO_{3}$, an $ABO_{3}$ perovskite manganite oxide,
+exhibits a non trivial behavior in the vicinity of the sharp peak found in the
+resistivity $\rho$ as a function of temperature $T$ in zero magnetic field. The
+various features seen on $d\rho/dT$ are discussed in terms of competing phase
+transitions. They are related to the $Mn-O-Mn$ bond environment depending on
+the content of the $A$ crystallographic site. A Ginzburg-Landau type theory is
+presented for incorporating concurrent phase transitions. The specific heat $C$
+of such a compound is also examined from 50 till 200 K. A log-log analysis
+indicates different regimes. In the low temperature conducting ferromagnetic
+phase, a collective magnon signature ($C \simeq T^{3/2}$) is found as for what
+are called magnon-polaron excitations. A $C \simeq T^{2/3}$ law is found at
+high temperature and discussed in terms of the fractal dimension of the
+conducting network of the weakly conducting (so-called insulating) phase and
+Orbach estimate of the excitation spectral behaviors. The need of considering
+both independent spin scattering and collective spin scattering is thus
+emphasized. The report indicates a remarkable agreement for the Fisher-Langer
+formula, i.e. $C$ $\sim$ $d\rho/dT$ at second order phase transitions. Within
+the Attfield model, we find an inverse square root relationship between the
+critical temperature(s) and the total local $Mn-O-Mn$ strain.",0209340v1
+2003-03-28,Magnons in the half-doped manganites,"Recently, based on the refined crystal structure of Pr0.6Ca0.4MnO3 from
+neutron diffraction, Daoud-Aladine et al.[PRL89,97205(2002)] have proposed a
+new ground state structure for the half-doped manganites R0.5Ca0.5MnO3, where R
+is a trivalent ion like Bi,La,Pr,Sm or Y. Their proposal describes the CE
+magnetic structure attributed to these materials as an arrangement of dimers
+along the ferromagnetic Mn zig-zag chains that form it. However, the dimers'
+proposal is in conflict with the Goodenough-Kanamori-Anderson rules, which give
+a coherent description of many transition metal insulating compounds and
+predict the coexistence of Mn3+ and Mn4+ ions in equal parts in the half-doped
+manganites. On the other hand, Rivadulla et al.[PRB 66, 174432 (2002)] have
+studied several single crystal samples of half-doped manganites and propose a
+phase diagram in terms of the tolerance factor which contains both types of
+structures. In the present work we have calculated the magnon dispersion
+relations for the CE magnetic structure, arising for each type of proposal: the
+charge ordered and the dimer phases, respectively. We consider a
+three-dimensional unit cell containing 16 spins, and compare the magnetic
+excitations along different paths in the first Brillouin zone. We conclude that
+measurement of the magnon dispersion relations should allow a clear distinction
+between the two proposals, predicting qualitative differences arising along
+specific directions of propagation in the first Brillouin zone.",0303613v1
+2003-07-01,Observation of extended scattering continua characteristic of spin fractionalization in the 2D frustrated quantum magnet Cs2CuCl4 by neutron scattering,"The magnetic excitations of the quasi-2D spin-1/2 Heisenberg antiferromagnet
+on an anisotropic triangular lattice Cs2CuCl4 are explored throughout the 2D
+Brillouin zone using inelastic neutron scattering. In the spin liquid phase
+above the transition to magnetic order extended excitation continua are
+observed, characteristic of fractionalization of S=1 spin waves into pairs of
+deconfined S=1/2 spinons and the hallmark of a resonating-valence-bond (RVB)
+state. The weak inter-layer couplings stabilize incommensurate spiral order at
+low temperatures and in this phase sharp magnons carrying a small part of the
+total scattering weight are observed at low energies below the continuum lower
+boundary. Linear spin-wave theory including one- and two-magnon processes can
+describe the sharp magnon excitation, but not the dominant continuum
+scattering, which instead is well described by a parameterized two-spinon
+cross-section. Those results suggest a cross-over in the nature of excitations
+from S=1 spin waves at low energies to S=1/2 spinons at medium to high
+energies, which could be understood if Cs2CuCl4 was in the close proximity of a
+transition between a fractional spin liquid and a magnetically-ordered phase.",0307025v1
+2003-09-18,Field- and pressure-induced magnetic quantum phase transitions in TlCuCl_3,"Thallium copper chloride is a quantum spin liquid of S = 1/2 Cu^2+ dimers.
+Interdimer superexchange interactions give a three-dimensional magnon
+dispersion and a spin gap significantly smaller than the dimer coupling. This
+gap is closed by an applied hydrostatic pressure of approximately 2kbar or by a
+magnetic field of 5.6T, offering a unique opportunity to explore the both types
+of quantum phase transition and their associated critical phenomena. We use a
+bond-operator formulation to obtain a continuous description of all disordered
+and ordered phases, and thus of the transitions separating these. Both
+pressure- and field-induced transitions may be considered as the Bose-Einstein
+condensation of triplet magnon excitations, and the respective phases of
+staggered magnetic order as linear combinations of dimer singlet and triplet
+modes. We focus on the evolution with applied pressure and field of the
+magnetic excitations in each phase, and in particular on the gapless
+(Goldstone) modes in the ordered regimes which correspond to phase fluctuations
+of the ordered moment. The bond-operator description yields a good account of
+the magnetization curves and of magnon dispersion relations observed by
+inelastic neutron scattering under applied fields, and a variety of
+experimental predictions for pressure-dependent measurements.",0309440v1
+2005-03-22,Anisotropy effects on the magnetic excitations of a ferromagnetic monolayer below and above the Curie temperature,"The field-driven reorientation transition of an anisotropic ferromagnetic
+monolayer is studied within the context of a finite-temperature Green's
+function theory. The equilibrium state and the field dependence of the magnon
+energy gap $E_0$ are calculated for static magnetic field $H$ applied in plane
+along an easy or a hard axis. In the latter case, the in-plane reorientation of
+the magnetization is shown to be continuous at T=0, in agreement with free spin
+wave theory, and discontinuous at finite temperature $T>0$, in contrast with
+the prediction of mean field theory. The discontinuity in the orientation angle
+creates a jump in the magnon energy gap, and it is the reason why, for $T>0$,
+the energy does not go to zero at the reorientation field. Above the Curie
+temperature $T_C$, the magnon energy gap $E_0(H)$ vanishes for H=0 both in the
+easy and in the hard case. As $H$ is increased, the gap is found to increase
+almost linearly with $H$, but with different slopes depending on the field
+orientation. In particular, the slope is smaller when $H$ is along the hard
+axis. Such a magnetic anisotropy of the spin-wave energies is shown to persist
+well above $T_C$ ($T \approx 1.2 T_C$).",0503538v4
+2005-10-16,Magnetic vortex dynamics in a 2D easy plane ferromagnet,"In this thesis, we consider the dynamics of vortices in the easy plane
+insulating ferromagnet in two dimensions. In addition to the quasiparticle
+excitations, here spin waves or magnons, this magnetic system admits a family
+of vortex solutions carrying two topological invariants, the winding number or
+vorticity, and the polarization. A vortex is approximately described as a
+particle moving about the system, endowed with an effective mass and acted upon
+by a variety of forces. Classically, the vortex has an inter-vortex potential
+energy giving a Coulomb-like force (attractive or repulsive depending on the
+relative vortex vorticity), and a gyrotropic force, behaving as a self-induced
+Lorentz force, whose direction depends on both topological indices. Expanding
+semiclassically about a many-vortex solution, the vortices are quantized by
+considering the scattered magnon states, giving a zero point energy correction
+and a many-vortex mass tensor. The vortices cannot be described as independent
+particles--that is, there are off-diagonal mass terms, such as 1/2 Mij vi vj,
+that are non-negligible. This thesis examines the full vortex dynamics in
+further detail by evaluating the Feynman-Vernon influence functional, which
+describes the evolution of the vortex density matrix after the magnon modes
+have been traced out. In addition to the set of forces already known, we find
+new damping forces acting both longitudinally and transversely to the vortex
+motion. The vortex motion within a collective cannot be entirely separated:
+there are damping forces acting on one vortex due to the motion of another. The
+effective damping forces have memory effects: they depend not only on the
+current motion of the vortex collection but also on the motion history.",0510414v1
+2006-06-10,Topological solitons in highly anisotropic two dimensional ferromagnets,"e study the solitons, stabilized by spin precession in a classical
+two--dimensional lattice model of Heisenberg ferromagnets with non-small
+easy--axis anisotropy. The properties of such solitons are treated both
+analytically using the continuous model including higher then second powers of
+magnetization gradients, and numerically for a discrete set of the spins on a
+square lattice. The dependence of the soliton energy $E$ on the number of spin
+deviations (bound magnons) $N$ is calculated. We have shown that the
+topological solitons are stable if the number $N$ exceeds some critical value
+$N_{\rm{cr}}$. For $N < N_{\rm{cr}}$ and the intermediate values of anisotropy
+constant $K_{\mathrm{eff}} <0.35J$ ($J$ is an exchange constant), the soliton
+properties are similar to those for continuous model; for example, soliton
+energy is increasing and the precession frequency $ \omega (N)$ is decreasing
+monotonously with $N$ growth. For high enough anisotropy $K_{\mathrm{eff}} >
+0.6 J$ we found some fundamentally new soliton features absent for continuous
+models incorporating even the higher powers of magnetization gradients. For
+high anisotropy, the dependence of soliton energy E(N) on the number of bound
+magnons become non-monotonic, with the minima at some ""magic"" numbers of bound
+magnons. Soliton frequency $\omega (N)$ have quite irregular behavior with
+step-like jumps and negative values of $\omega $ for some regions of $N$. Near
+these regions, stable static soliton states, stabilized by the lattice effects,
+exist.",0606263v1
+2006-08-18,Effects of dilution and disorder on magnetism in diluted spin systems,"The influence of configurational disorder on the magnetic properties of
+diluted Heisenberg spin systems is studied with regard to the ferromagnetic
+stability of diluted magnetic semiconductors. The equation of motion of the
+magnon Green's function is decoupled by Tyablikov approximation. With supercell
+approach, the concentrations of magnetic ions are determined by the size of the
+supercell in which there is only one magnetic ion per supercell in our method.
+In order to distinguish the influence of dilution and disorder, there are two
+kinds of supercells being used: the \textit{diluted and ordered} case and the
+\textit{diluted and disordered} case. The configurational averaging of magnon
+Green function due to disorder is treated in the augmented space formalism. The
+random exchange integrals between two supercells are treated as a matrix. The
+obtained magnon spectral densities are used to calculate the temperature
+dependence of magnetization and Curie temperature. The results are shown as
+following: (i) dilution leads to increasing the averaged distance of two
+magnetic ions, further decreases the effective exchange integrals and is main
+reason to reduce Curie temperature; (ii) spatial position disorder of magnetic
+ions results in the dispersions of the exchange integrals between two
+supercells and slightly changes ferromagnetic transition temperature; (iii) the
+exponential damping of distance dependence obviously reduces Curie temperature
+and should be set carefully in any phenomenological model.",0608418v2
+2007-05-02,Magnetic Excitations in La2CuO4 probed by Indirect Resonant Inelastic X-ray Scattering,"Recent experiments on La$_2$CuO$_4$ suggest that indirect resonant inelastic
+X-ray scattering (RIXS) might provide a probe for transversal spin dynamics. We
+present in detail a systematic expansion of the relevant magnetic RIXS cross
+section by using the ultrashort core-hole lifetime (UCL) approximation. We
+compute the scattering intensity and its momentum dependence in leading order
+of the UCL expansion. The scattering is due to two-magnon processes and is
+calculated within a linear spin-wave expansion of the Heisenberg spin model for
+this compound, including longer range and cyclic spin interactions. We observe
+that the latter terms in the Hamiltonian enhance the first moment of the
+spectrum if they strengthen the antiferromagnetic ordering. The theoretical
+spectra agree very well with experimental data, including the observation that
+scattering intensity vanishes for the transferred momenta ${\bf q} = (0,0)$ and
+${\bf q} = (\pi,\pi)$. We show that at finite temperature there is an
+additional single-magnon contribution to the scattering with a spectral weight
+proportional to $T^3$. We also compute the leading corrections to the UCL
+approximation and find them to be small, putting the UCL results on a solid
+basis. All this univocally points to the conclusion that the observed low
+temperature RIXS intensity in La$_2$CuO$_4$ is due to two-magnon scattering.",0705.0263v4
+2008-01-17,Towards the theory of ferrimagnetism,"Two-sublattice ferrimagnet, with spin-$s_1$ operators $\bf{S_{1i}}$ at the
+sublattice $A$ site and spin-$s_2$ operators $\bf{S_{2i}}$ at the sublattice
+$B$ site, is considered. The magnon of the system, the transversal fluctuation
+of the total magnetization, is a complicate mixture of the transversal
+fluctuations of the sublattice $A$ and $B$ spins. As a result, the magnons'
+fluctuations suppress in a different way the magnetic orders of the $A$ and $B$
+sublattices and one obtains two phases. At low temperature $(0,T^*)$ the
+magnetic orders of the $A$ and $B$ spins contribute to the magnetization of the
+system, while at the high temperature $(T^*,T_N)$, the magnetic order of the
+spins with a weaker intra-sublattice exchange is suppressed by magnon
+fluctuations, and only the spins with stronger intra-sublattice exchange has
+non-zero spontaneous magnetization. The $T^*$ transition is a transition
+between two spin-ordered phases in contrast to the transition from spin-ordered
+state to disordered state ($T_N$-transition). There is no additional symmetry
+breaking, and the Goldstone boson has a ferromagnetic dispersion in both
+phases. A modified spin-wave theory is developed to describe the two phases.
+All known Neel's anomalous $M(T)$ curves are reproduced, in particular that
+with ""compensation point"". The theoretical curves are compared with
+experimental ones for sulpho-spinel $MnCr2S_{4-x}Se_{x}$ and rare earth iron
+garnets.",0801.2651v1
+2008-03-27,Aspects of Integrability in AdS/CFT Duality,"In this dissertation, we discuss how our understanding of the large-N
+spectrum of AdS/CFT has been deepened by integrability-based approaches. We
+begin with a comprehensive review of the integrability of the gauge theory
+spin-chain and that of the string sigma model. In the light of the AdS/CFT
+duality, they should be just two ways of describing the same underlying
+integrability, and it is believed that the unified integrability can be
+characterised by a set of Bethe ansatz equations which is valid for all values
+of the 't Hooft coupling. By studying the asymptotic spectrum of the AdS/CFT in
+the infinite spin/R-charge limit, we first identify the corresponding solitonic
+counterparts in the context of the AdS/CFT, which are the so-called dyonic
+giant magnons and the SYM magnon boundstates. Then we show that the S-matrix
+computed directly from the string solitons scattering precisely reproduces the
+prediction from the conjecture. We further perform an analyticity test by
+studying the singularities of the conjectured magnon boundstate S-matrix and
+checking the physicality conditions. These tests give strong positive supports
+for the integrability of large-N AdS/CFT as well as the specific form of the
+conjectured Bethe ansatz equations. Concerning the string theory integrability,
+we also provide a detailed study of certain classical string solutions on AdS_5
+x S^5. These are constructed in such a way they correspond to generic soliton
+solutions of (Complex) sine/sinh-Gordon equations via the so-called Pohlmeyer
+reduction procedure. Furthermore, we describe them in terms of
+algebro-geometric data as finite-gap solutions, giving a complete map of the
+elliptic string solutions.",0803.3999v2
+2010-02-07,Magnetic nature of the 500 meV peak in $\rm La_{2-x}Sr_{x}CuO_4$ observed with resonant inelastic x-ray scattering at the Cu $K$-edge,"We present a comprehensive study of the temperature and doping dependence of
+the 500 meV peak observed at ${\bf q}=(\pi,0)$ in resonant inelastic x-ray
+scattering (RIXS) experiments on $\rm La_2CuO_4$. The intensity of this peak
+persists above the N\'eel temperature (T$_{N}$=320 K), but decreases gradually
+with increasing temperature, reaching zero at around T=500 K. The peak energy
+decreases with temperature in close quantitative accord with the behavior of
+the two-magnon $\rm B_{1g}$ Raman peak in $\rm La_2CuO_4$, and with suitable
+rescaling, agrees with the Raman peak shifts in $\rm EuBa_2Cu_3O_6$ and $\rm
+K_2NiF_4$. The overall dispersion of this excitation in the Brillouin zone is
+found to be in agreement with theoretical calculations for a two-magnon
+excitation. Upon doping, the peak intensity decreases analogous to the Raman
+mode intensity and appears to track the doping dependence of the spin
+correlation length. Taken together, these observations strongly suggest that
+the 500 meV mode is magnetic in character and is likely a two-magnon
+excitation.",1002.1440v1
+2010-06-18,The Relativistic Avatars of Giant Magnons and their S-Matrix,"The motion of strings on symmetric space target spaces underlies the
+integrability of the AdS/CFT correspondence. Although these theories, whose
+excitations are giant magnons, are non-relativistic they are classically
+equivalent, via the Polhmeyer reduction, to a relativistic integrable field
+theory known as a symmetric space sine-Gordon theory. These theories can be
+formulated as integrable deformations of gauged WZW models. In this work we
+consider the class of symmetric spaces CP^{n+1} and solve the corresponding
+generalized sine-Gordon theories at the quantum level by finding the exact
+spectrum of topological solitons, or kinks, and their S-matrix. The latter
+involves a trignometric solution of the Yang-Baxer equation which exhibits a
+quantum group symmetry with a tower of states that is bounded, unlike for
+magnons, as a result of the quantum group deformation parameter q being a root
+of unity. We test the S-matrix by taking the semi-classical limit and comparing
+with the time delays for the scattering of classical solitons. We argue that
+the internal CP^{n-1} moduli space of collective coordinates of the solitons in
+the classical theory can be interpreted as a q-deformed fuzzy space in the
+quantum theory. We analyse the n=1 case separately and provide a further test
+of the S-matrix conjecture in this case by calculating the central charge of
+the UV CFT using the thermodynamic Bethe Ansatz.",1006.3667v2
+2011-02-25,Elastic constants and ultrasonic attenuation in the cone state of the frustrated antiferromagnet Cs_2CuCl_4,"In an external magnetic field perpendicular to the plane of the layers, the
+quasi two-dimensional frustrated antiferromagnet Cs_2CuCl_4 exhibits a
+magnetically ordered ""cone state"" at low temperatures. In this state the
+component of the magnetic moments in field direction is finite, while their
+projection onto the plane of the layers forms a spiral. We present both
+theoretical and experimental results for the magnetic field dependence of the
+elastic constants and the ultrasonic attenuation rate in the cone state. Our
+theoretical analysis is based on the usual spin-wave expansion around the
+classical ground state of a Heisenberg model on an anisotropic triangular
+lattice with Dzyaloshinskii-Moriya interactions. Magnon-phonon interactions are
+modeled by expanding the exchange interactions up to second order in powers of
+the phonon coordinates. As long as the external magnetic field is not too close
+to the critical field where the cone state becomes unstable, we obtain
+reasonable agreement between theory and experiment, suggesting that at least in
+this regime magnons behave as well-defined quasiparticles. We also show that
+the assumption of well-defined magnons implies that at long wavelengths the
+ultrasonic attenuation rate in the cone state of Cs_2CuCl_4 is proportional to
+the fourth power of the phonon momentum.",1102.5342v2
+2011-07-04,A Relativistic Relative of the Magnon S-Matrix,"We construct a relativistic scattering theory based on a q deformation and
+large string tension limit of the magnon S-matrix of the string world sheet
+theory in AdS_5 x S^5. The S-matrix falls naturally into a previously studied
+class associated to affine quantum groups, in this case for a twisted affine
+loop superalgebra associated to an outer automorphism of sl(2|2). This infinite
+algebra includes the celebrated triply extended psl(2|2) x R^3 algebra, but
+only two of the centres, the lightcone components of the 2-momentum, are
+non-vanishing. The algebra has the interpretation as an extended supersymmetry
+algebra including a non-trivial R-symmetry. The representation theory of this
+algebra has some complications in that tensor products are reducible but
+indecomposable, however, we find that structure meshes perfectly with the
+bootstrap, or fusion, equations of S-matrix theory. The bootstrap equations can
+then be used inductively to generate the complete S-matrix. Unlike the magnon
+theory, the relativistic theory only has a finite set of states and we find
+that - at least when the deformation parameter q is a root of unity - the
+spectrum matches precisely the soliton spectrum of the relativistic theory
+underlying the Pohlmeyer reduction of the string world sheet theory known as
+the semi-symmetric space sine-Gordon theory.",1107.0628v2
+2011-08-05,Magnons and electromagnons in a spin-lattice-coupled frustrated magnet CuFeO2 as seen via inelastic neutron scattering,"We have investigated spin-wave excitations in a four-sublattice (4SL)
+magnetic ground state of a frustrated magnet CuFeO2, in which `electromagnon'
+(electric-field-active magnon) excitation has been discovered by recent
+terahertz time-domain spectroscopy [Seki et al. Phys. Rev. Lett. 105 097207
+(2010)]. In previous study, we have identified two spin-wave branches in the
+4SL phase by means of inelastic neutron scattering measurements under applied
+uniaxial pressure. [T. Nakajima et al. J. Phys. Soc. Jpn. 80 014714 (2011) ] In
+the present study, we have performed high-energy-resolution inelastic neutron
+scattering measurements in the 4SL phase, resolving fine structures of the
+lower-energy spin-wave branch near the zone center. Taking account of the
+spin-driven lattice distortions in the 4SL phase, we have developed a model
+Hamiltonian to describe the spin-wave excitations. The determined Hamiltonian
+parameters have successfully reproduced the spin-wave dispersion relations and
+intensity maps obtained in the inelastic neutron scattering measurements. The
+results of the spin-wave analysis have also revealed physical pictures of the
+magnon and electromagnon modes in the 4SL phase, suggesting that collinear and
+noncollinear characters of the two spin-wave modes are the keys to understand
+the dynamical coupling between the spins and electric dipole moments in this
+system.",1108.1297v1
+2012-07-31,Spin excitations in a single La$_2$CuO$_4$ layer,"The dynamics of S=1/2 quantum spins on a 2D square lattice lie at the heart
+of the mystery of the cuprates
+\cite{Hayden2004,Vignolle2007,Li2010,LeTacon2011,Coldea2001,Headings2010,Braicovich2010}.
+In bulk cuprates such as \LCO{}, the presence of a weak interlayer coupling
+stabilizes 3D N\'{e}el order up to high temperatures. In a truly 2D system
+however, thermal spin fluctuations melt long range order at any finite
+temperature \cite{Mermin1966}. Further, quantum spin fluctuations transfer
+magnetic spectral weight out of a well-defined magnon excitation into a
+magnetic continuum, the nature of which remains controversial
+\cite{Sandvik2001,Ho2001,Christensen2007,Headings2010}. Here, we measure the
+spin response of \emph{isolated one-unit-cell thick layers} of \LCO{}. We show
+that coherent magnons persist even in a single layer of \LCO{} despite the loss
+of magnetic order, with no evidence for resonating valence bond (RVB)-like spin
+correlations \cite{Anderson1987,Hsu1990,Christensen2007}. Thus these
+excitations are well described by linear spin wave theory (LSWT). We also
+observe a high-energy magnetic continuum in the isotropic magnetic response.
+This high-energy continuum is not well described by 2 magnon LSWT, or indeed
+any existing theories.",1208.0018v1
+2013-10-01,Linear Spin Wave Analysis for General Magnetic Orders in the Kondo Lattice Model,"We extend the formulation of the spin wave theory for the Kondo lattice
+model, which was mainly used for the ferromagnetic metallic state, to general
+magnetic orders including complex noncollinear and noncoplanar orders. The 1/S
+expansion is reformulated in the matrix form depending on the size of the
+magnetic unit cell. The noncollinearity and noncoplanarity of the localized
+moments are properly taken into account by the matrix elements of the
+para-unitary matrix used in the diagonalization of the Bogoliubov-de Gennes
+type Hamiltonian for magnons. We apply the formulation within the linear spin
+wave approximation to a typical noncollinear case, the $120^{\circ}$ N{\'e}el
+order on a triangular lattice at half filling. We calculate the magnon
+excitation spectrum and the quantum correction to the magnitude of ordered
+moments as functions of the strength of the Hund's-rule coupling, $J_{\rm
+H}/t$. We find that the magnon excitation shows softening at $J_{\rm H}/t
+\simeq 2.9$, which indicates that the $120^{\circ}$ order is destabilized for
+smaller $J_{\rm H}/t$. On the other hand, we show that the $120^{\circ}$ order
+is stable in the entire range of $J_{\rm H}/t \gtrsim 2.9$, and, in the limit
+of $J_{\rm H}/t \to \infty$, the form of the spin wave spectrum approaches that
+for the antiferromagnetic Heisenberg model, while the bandwidth is proportional
+to $t^2/J_{\rm H}$. The reduction of the ordered moment is smaller than that
+for the spin-only model, except in the vicinity of the softening.",1310.0176v1
+2014-01-19,Topological excitations in a Kagomé magnet,"It is shown here that a Kagom\'e magnet, with Heisenberg and
+Dzyaloshinskii-Moriya interactions causes non trivial topological and chiral
+magnetic properties. Chirality---that is, left or right handedness---is a very
+important concept in a broad range of scientific areas, and particularly, in
+condensed matter physics. Inversion symmetry breaking relates chirality with
+skyrmions, that are protected field configurations with particle-like and
+topological properties. Here, the reported numerical simulations and
+theoretical considerations reveal that the magnetic excitations of the Kagom\'e
+magnet can both be of regular bulk magnon character, as well as, having a
+non-trivial topological nature. We also find that under special circumstances,
+skyrmions emerge as excitations, having stability even at room temperature.
+Chiral magnonic edge states of a Kagom\'e magnet offer, in addition, a
+promising way to create, control and manipulate skyrmions. This has potential
+for applications in spintronics, magnonics and skyrmionics, i.e., for
+information storage or as logic devices based on the transportation and control
+of these particles. Collisions between these particle-like excitations are
+found to be elastic in the skyrmion-skyrmion channel, albeit without
+mass-conservation for an individual skyrmion. Skyrmion-antiskyrmion collisions
+are found to be more complex, where annihilation and creation of these objects
+have a distinct non-local nature.",1401.4757v2
+2014-10-22,The connection between vortex-like topological excitations and conventional excitations in quantum ferromagnetic spin systems on two dimensional lattice and their stability,"We present a scheme for the construction of quantum states of vortex like
+topological excitations corresponding to spin- 1/2 strongly XY anisotropic
+nearest neighbor Heisenberg Ferromagnet on two dimensional lattice. The
+procedure involving Pauli spin basis states is carried out corresponding to
+both infinite dilute limit and finite density limit of vortex/anti-vortex. It
+is found that the corresponding quantum mechanical states representing charge 1
+quantum vortices/ anti-vortices can be expressed as linear combinations of
+single magnon states, composite multi-magnon states and the ground state.
+Detailed calculations show that these states are quantum mechanically stable
+states of the Hamiltonian only when the system size exceeds certain threshold
+value. Our analysis indicates that the interactions between different magnon
+modes can very well generate these topological excitations. Possible
+applications of our calculations to real magnetic systems are also discussed.
+Magnetic measurements probing spin dynamics may be undertaken to verify the
+existence of the threshold size for the stability of vortices.",1410.5921v3
+2014-10-24,Macroscopic quantum superposition of spin ensembles with ultra-long coherence times via superradiant masing,"Macroscopic quantum phenomena such as lasers, Bose-Einstein condensates,
+superfluids, and superconductors are of great importance in foundations and
+applications of quantum mechanics. In particular, quantum superposition of a
+large number of spins in solids is highly desirable for both quantum
+information processing and ultrasensitive magnetometry. Spin ensembles in
+solids, however, have rather short collective coherence time (typically less
+than microseconds). Here we demonstrate that under realistic conditions it is
+possible to maintain macroscopic quantum superposition of a large spin ensemble
+(such as about ~10^{14} nitrogen-vacancy center electron spins in diamond) with
+an extremely long coherence time ~10^8 sec under readily accessible conditions.
+The scheme, following the mechanism of superradiant lasers, is based on
+superradiant masing due to coherent coupling between collective spin
+excitations (magnons) and microwave cavity photons. The coherence time of the
+macroscopic quantum superposition is the sum of the magnon life time and the
+cavity lifetime, further elongated by the total number of coherent magnons and
+photons, which have macroscopic values when masing occurs. The macroscopic
+quantum coherence of spin ensembles can be exploited for magnetometry with
+sensitivity ~10 fT/(Hz)^{1/2}. The long-living collective states of spin
+ensembles in solids will provide a new platform for studying macroscopic
+quantum phenomena and are useful for quantum technologies.",1410.6565v1
+2014-11-19,Magnons and Excitation Continuum in XXZ triangular antiferromagnetic model: Application to $Ba_3CoSb_2O_9$,"We investigate the excitation spectrum of the triangular-lattice
+antiferromagnetic $XXZ$ model using series expansions and mean field Schwinger
+bosons approaches. The single-magnon spectrum computed with series expansions
+exhibits rotonic minima at the middle points of the edges of the Brillouin
+zone, for all values of the anisotropy parameter in the range $0\leq
+J^z/J\leq1$. Based on the good agreement with series expansions for the
+single-magnon spectrum, we compute the full dynamical magnetic structure factor
+within the mean field Schwinger boson approach to investigate the relevance of
+the $XXZ$ model for the description of the unusual spectrum found recently in
+$Ba_3CoSb_2O_9$. In particular, we obtain an extended continuum above the spin
+wave excitations, which is further enhanced and brought closer to those
+observed in $Ba_3CoSb_2O_9$ with the addition of a second neighbor exchange
+interaction approximately 15% of the nearest-neighbor value. Our results
+support the idea that excitation continuum with substantial spectral-weight are
+generically present in two-dimensional frustrated spin systems and
+fractionalization in terms of {\it bosonic} spinons presents an efficient way
+to describe them.",1411.5298v2
+2015-04-22,Thermally Driven Ratchet Motion of Skyrmion Microcrystal and Topological Magnon Hall Effect,"Spontaneously emergent chirality is an issue of fundamental importance across
+the natural sciences. It has been argued that a unidirectional (chiral)
+rotation of a mechanical ratchet is forbidden in thermal equilibrium, but
+becomes possible in systems out of equilibrium. Here we report our finding that
+a topologically nontrivial spin texture known as a skyrmion - a particle-like
+object in which spins point in all directions to wrap a sphere - constitutes
+such a ratchet. By means of Lorentz transmission electron microscopy we show
+that micron-sized crystals of skyrmions in thin films of Cu2OSeO3 and MnSi
+display a unidirectional rotation motion. Our numerical simulations based on a
+stochastic Landau-Lifshitz-Gilbert equation suggest that this rotation is
+driven solely by thermal fluctuations in the presence of a temperature
+gradient, whereas in thermal equilibrium it is forbidden by the Bohr-van
+Leeuwen theorem. We show that the rotational flow of magnons driven by the
+effective magnetic field of skyrmions gives rise to the skyrmion rotation,
+therefore suggesting that magnons can be used to control the motion of these
+spin textures.",1504.05860v1
+2015-09-01,Magnon-driven longitudinal spin Seebeck effect in F|N and N|F|N structures: role of asymmetric in-plane magnetic anisotropy,"The influence of an asymmetric in-plane magnetic anisotropy on the thermally
+activated spin current is studied theoretically for two different systems; (i)
+the system consisting of a ferromagnetic insulator in a direct contact with a
+nonmagnetic metal, and the sandwich structure consisting of a ferromagnetic
+insulating part sandwiched between two nonmagnetic metals. It is shown that
+when the difference between the temperatures of the two nonmagnetic metals in a
+structure is not large, the spin pumping currents from the magnetic part to the
+nonmagnetic ones are equal in amplitude and have opposite directions, so only
+the spin torque current contributes to the total spin current. The spin current
+flows then from the nonmagnetic metal with the higher temperature to the
+nonmagnetic metal having a lower temperature. Its amplitude varies linearly
+with the difference in temperatures. In addition, we have found that if the
+magnetic anisotropy is in the layer plane, then the spin current increases with
+the magnon temperature, while in the case of an out-of-plane magnetic
+anisotropy the spin current decreases when the magnon temperature enhances.
+Enlarging the difference between the temperatures of the nonmagnetic metals,
+the linear response becomes important, as confirmed by analytical expressions
+inferred from the Fokker-Planck approach and by the results obtained upon a
+full numerical integration of the stochastic Landau-Lifshitz-Gilbert equation.",1509.00376v1
+2016-01-07,Hubbard model with Rashba or Dresselhaus spin-orbit coupling and Rotated Anti-ferromagnetic Heisenberg Model,"In this work, we investigate the possible dramatic effects of Rashba or
+Dresselhaus spin-orbit coupling (SOC) on fermionic Hubbard model in a 2d square
+lattice. In the strong coupling limit, it leads to the Rotated
+Anti-ferromagnetic Heisenberg model which is a new class of quantum spin model.
+For a special equivalent class, we identify a new spin-orbital entangled
+commensurate ground ( Y-y ) state subject to strong quantum fluctuations at
+$T=0$. We evaluate the quantum fluctuations by the spin wave expansion up to
+order $ 1/S^2 $. In some SOC parameter regime, the Y-y state supports a massive
+relativistic in-commensurate magnon ( C-IC ) with its two gap minima positions
+continuously tuned by the SOC parameters. The C-IC magnons dominate all the low
+temperature thermodynamic quantities and also lead to the separation of the
+peak positions between the longitudinal and the transverse spin structure
+factors. In the weak coupling limit, any weak repulsive interaction also leads
+to a weak Y-y state. There is only a crossover from the weak to the strong
+coupling. High temperature expansions of the specific heats in both weak and
+strong coupling are presented. The dramatic roles to be played by these C-IC
+magnons at generic SOC parameters or under various external probes are hinted.
+Experimental applications to both layered noncentrosymmetric materials and cold
+atom are discussed.",1601.01642v2
+2017-03-14,Finite-Temperature Dynamics and Thermal Intraband Magnon Scattering in Haldane Spin-One Chains,"The antiferromagnetic spin-one chain is considerably one of the most
+fundamental quantum many-body systems, with symmetry protected topological
+order in the ground state. Here, we present results for its dynamical spin
+structure factor at finite temperatures, based on a combination of exact
+numerical diagonalization, matrix-product-state calculations and quantum Monte
+Carlo simulations. Open finite chains exhibit a sub-gap band in the thermal
+spectral functions, indicative of localized edge-states. Moreover, we observe
+the thermal activation of a distinct low-energy continuum contribution to the
+spin spectral function with an enhanced spectral weight at low momenta and its
+upper threshold. This emerging thermal spectral feature of the Haldane spin-one
+chain is shown to result from intra-band magnon scattering due to the thermal
+population of the single-magnon branch, which features a large bandwidth-to-gap
+ratio. These findings are discussed with respect to possible future studies on
+spin-one chain compounds based on inelastic neutron scattering.",1703.04652v2
+2018-02-05,Integrable Subsectors from Holography,"We consider operators in ${\cal N}=4$ super Yang-Mills theory dual to closed
+string states propagating on a class of LLM geometries. The LLM geometries we
+consider are specified by a boundary condition that is a set of black rings on
+the LLM plane. When projected to the LLM plane, the closed strings are polygons
+with all corners lying on the outer edge of a single ring. The large $N$ limit
+of correlators of these operators receives contributions from non-planar
+diagrams even for the leading large $N$ dynamics. Our interest in these
+fluctuations is because a previous weak coupling analysis argues that the net
+effect of summing the huge set of non-planar diagrams, is a simple rescaling of
+the 't Hooft coupling. We carry out some nontrivial checks of this proposal.
+Using the $su(2|2)^2$ symmetry we determine the two magnon $S$-matrix and
+demonstrate that it agrees, up to two loops, with a weak coupling computation
+performed in the CFT. We also compute the first finite size corrections to both
+the magnon and the dyonic magnon by constructing solutions to the Nambu-Goto
+action that carry finite angular momentum. These finite size computations
+constitute a strong coupling confirmation of the proposal.",1802.01367v2
+2018-02-09,Monocrystalline free standing 3D yttrium iron garnet magnon nano resonators,"Nano resonators in which mechanical vibrations and spin waves can be coupled
+are an intriguing concept that can be used in quantum information processing to
+transfer information between different states of excitation. Until now, the
+fabrication of free standing magnetic nanostructures which host long lived spin
+wave excitatons and may be suitable as mechanical resonators seemed elusive. We
+demonstrate the fabrication of free standing monocrystalline yttrium iron
+garnet (YIG) 3D nanoresonators with nearly ideal magnetic properties. The
+freestanding 3D structures are obtained using a complex lithography process
+including room temperature deposition and lift-off of amorphous YIG and
+subsequent crystallization by annealing. The crystallization nucleates from the
+substrate and propagates across the structure even around bends over distances
+of several micrometers to form e.g. monocrystalline resonators as shown by
+transmission electron microscopy. Spin wave excitations in individual
+nanostructures are imaged by time resolved scanning Kerr microscopy. The narrow
+linewidth of the magnetic excitations indicates a Gilbert damping constant of
+only $\alpha = 2.6 \times 10^{-4}$ rivalling the best values obtained for
+epitaxial YIG thin film material. The new fabrication process represents a leap
+forward in magnonics and magnon mechanics as it provides 3D YIG structures of
+unprecedented quality. At the same time it demonstrates a completely new route
+towards the fabrication of free standing crystalline nano structures which may
+be applicable also to other material systems.",1802.03176v2
+2018-02-20,Magnon-photon coupling in a non-collinear magnetic insulator Cu$_2$OSeO$_3$,"Anticrossing behavior between magnons in a non-collinear chiral magnet
+Cu$_2$OSeO$_3$ and a two-mode X-band microwave resonator was studied in the
+temperature range 5-100K. In the field-induced ferrimagnetic phase, we observed
+a strong coupling regime between magnons and two microwave cavity modes with a
+cooperativity reaching 3600. In the conical phase, cavity modes are
+dispersively coupled to a fundamental helimagnon mode, and we demonstrate that
+the magnetic phase diagram of Cu$_2$OSeO$_3$ can be reconstructed from the
+measurements of the cavity resonance frequency. In the helical phase, a
+hybridized state of a higher-order helimagnon mode and a cavity mode - a
+helimagnon polariton - was found. Our results reveal a new class of magnetic
+systems where strong coupling of microwave photons to non-trivial spin textures
+can be observed.",1802.07113v3
+2018-02-26,Magnon-induced superconductivity in a topological insulator coupled to ferro- and antiferromagnetic insulators,"We study the effective interactions between Dirac fermions on the surface of
+a three-dimensional topological insulator due to the proximity coupling to the
+magnetic fluctuations in a ferromagnetic or antiferromagnetic insulator. Our
+results show that the magnetic fluctuations can mediate attractive interactions
+between Dirac fermions of both Amperean and BCS type. In the ferromagnetic
+case, we find pairing between fermions with parallel momenta, so-called
+Amperean pairing, whenever the effective Lagrangian for the magnetic
+fluctuations does not contain a quadratic term. The pairing interaction also
+increases with increasing Fermi momentum, and is in agreement with previous
+studies in the limit of high chemical potential. If a quadratic term is
+present, the pairing is instead of BCS type above a certain chemical potential.
+In the antiferromagnetic case, BCS pairing occurs when the ferromagnetic
+coupling between magnons on the same sublattice exceeds the antiferromagnetic
+coupling between magnons on different sublattices. Outside this region in
+parameter space, we again find that Amperean pairing is realized.",1802.09524v4
+2018-11-23,Broadening Frequency Range of a Ferromagnetic Axion Haloscope with Strongly Coupled Cavity-Magnon Polaritons,"With the axion being a prime candidate for dark matter, there has been some
+recent interest in direct detection through a so called `Ferromagnetic
+haloscope.' Such devices exploit the coupling between axions and electrons in
+the form of collective spin excitations of magnetic materials with the readout
+through a microwave cavity. Here, we present a new, general, theoretical
+treatment of such experiments in a Hamiltonian formulation for strongly coupled
+magnons and photons, which hybridise as cavity-magnon polaritons. Such strongly
+coupled systems have an extended measurable dispersive regime. Thus, we extend
+the analysis and operation of such experiments into the dispersive regime,
+which allows any ferromagnetic haloscope to achieve improved bandwidth with
+respect to the axion mass parameter space. This experiment was implemented in a
+cryogenic setup, and initial search results are presented setting laboratory
+limits on the axion-electron coupling strength of $g_{aee}>3.7\times10^{-9}$ in
+the range $33.79~\mu$eV$< m_a<33.94~\mu$eV with $95\%$ confidence. The
+potential bandwidth of the Ferromagnetic haloscope was calculated to be in two
+bands, the first of about $1$GHz around $8.24$GHz (or $4.1~\mu$eV mass range
+around $34.1~\mu$eV) and the second of about $1.6$GHz around $10$GHz
+($6.6~\mu$eV mass range around $41.4~\mu$eV). Frequency tuning may also be
+easily achieved via an external magnetic field which changes the ferromagnetic
+resonant frequency with respect to the cavity frequency. The requirements
+necessary for future improvements to reach the DFSZ axion model band are
+discussed in the paper.",1811.09348v3
+2014-03-04,Spin excitations of half-doped bilayer manganites: intermediate phase,"The ground state of half-doped manganites involves intricate spin, charge and
+orbital orderings, which are difficult to discern experimentally. In this work,
+we resort to the theoretical analysis of the spin fluctuation spectrum of the
+half-doped bilayer Pr(Ca$_{0.9}$Sr$_{0.1}$)$_2$ Mn$_2$O$_7$ in order to get an
+insight of its electronic ground state. By means of the linear spin wave
+approximation, we compute the magnon dispersion for a family of localized spin
+models, which can describe several phases proposed for the ground state of
+half-doped manganites, like the intermediate one proposed by Efremov et al.
+[Nat.Mats. 3, 853, (2004)] along with its particular cases corresponding to
+Goodenough's CE phase [Phys. Rev. 100, 564, (1955)] and Zener polaron or dimer
+phases. We obtain an excellent agreement between theory and experiment when the
+ground state is assumed to be a generalized Goodenough's CE phase, with a
+Mn-charge disproportionation inside the experimentally expected range. As
+essential ingredients for our improved fit of the upper and lower magnon
+branches measured around the gap, we identified two next-nearest neighbour
+exchange interactions between the planar Mn zig-zag chains, one for each type
+of Mn ion present. In connection with this finding, we revisited the magnetic
+excitations of the laminar related compounds, focusing on the upper magnon
+branches. Here we prove that their measurement would provide the key to
+identify unambiguously the ground state present in the layered half-doped
+manganites.",1403.0971v2
+2017-01-10,Motion of skyrmions in nanowires driven by magnonic momentum-transfer forces,"We study the motion of magnetic skyrmions in a nanowire induced by a
+spin-wave current $J$ flowing out of a driving layer close to the edge of the
+wire. By applying micromagnetic simulation and an analysis of the effective
+Thiele equation, we find that the skyrmion trajectory is governed by an
+interplay of both forces due to the magnon current and the wire boundary. The
+skyrmion is attracted to the driving layer and is accelerated by the repulsive
+force due to the wire boundary. We consider both cases of a driving
+longitudinal and transverse to the nanowire, but a steady-state motion of the
+skyrmion is only obtained for a transverse magnon current. For the latter case,
+we find in the limit of low current densities $J$ the velocity-current relation
+$v \sim J/\alpha$ where $v$ is the skyrmion velocity and $\alpha$ is the
+Gilbert damping. For large $J$ in case of strong driving, the skyrmion is
+pushed into the driving layer resulting in a drop of the skyrmion velocity and,
+eventually, the destruction of the skyrmion.",1701.02430v2
+2016-05-20,Two-dimensional terahertz magnetic resonance spectroscopy of collective spin waves,"Nonlinear manipulation of nuclear and electron spins is the basis for all
+advanced methods in magnetic resonance including multidimensional nuclear
+magnetic and electron spin resonance spectroscopies, magnetic resonance
+imaging, and in recent years, quantum control over individual spins. The
+methodology is facilitated by the ease with which the regime of strong coupling
+can be reached between radiofrequency or microwave magnetic fields and nuclear
+or electron spins respectively, typified by sequences of magnetic pulses that
+control the magnetic moment directions. The capabilities meet a bottleneck,
+however, for far-infrared magnetic resonances characteristic of correlated
+electron materials, molecular magnets, and proteins that contain high-spin
+transition metal ions. Here we report the development of two-dimensional
+terahertz magnetic resonance spectroscopy and its use for direct observation of
+the nonlinear responses of collective spin waves (magnons). The spectra show
+magnon spin echoes and 2-quantum signals that reveal pairwise correlations
+between magnons at the Brillouin zone center. They also show resonance-enhanced
+second-harmonic and difference-frequency signals. Our methods are readily
+generalizable to multidimensional magnetic resonance spectroscopy and nonlinear
+coherent control of terahertz-frequency spin systems in molecular complexes,
+biomolecules, and materials.",1605.06476v3
+2016-05-29,Heisenberg Necklace Model in Magnetic Field,"Motivated by the experimental realizations of nearly one-dimensional spin-1/2
+Heisenberg model found in chain cuprates SrCuO$_2$ and Sr$_2$CuO$_3$, which
+remain in a quantum-critical Luttinger liquid state down to temperatures that
+are much lower than in-chain exchange coupling, we consider the perturbation to
+this state caused by interactions with nuclear spins on the same sites. We
+study the low-energy sector of the Heisenberg Necklace model and estimate the
+effect of the coupling between the nuclear and the electronic spins on the
+overall spins dynamics and its dependence on the magnetic field. We find that
+the Necklace model has a characteristic energy scale, $\Lambda \sim
+J^{1/3}(\gamma I)^{2/3}$, at which the coupling between spins of the necklace
+and the spins of the Heisenberg chain becomes strong. In the strong magnetic
+field $\mu_B B > \Lambda$ the low energy spectrum is gapless, but two gapless
+bosonic modes have different velocities whose ratio at strong fields approaches
+a universal number, $\sqrt 2 +1$. In the case of Sr$_2$CuO$_3$ the energy scale
+$\Lambda $ is sizable and comparable to the Neel ordering temperature induced
+by the inter-chain coupling, and thus could noticeably modify the low
+temperature magnon dynamics. We further find that the above energy scale is
+insensitive to strong magnetic field, $\mu_B B \gg \Lambda \sim J^{1/3}(\gamma
+I)^{2/3}$, and therefore the interaction with nuclear spins cannot lead to
+unusually strong magnetic field dependence of the magnon spectrum observed by
+ESR in Sr$_2$CuO$_3$, which has been attributed to the magnon interaction with
+the Higgs mode.",1605.09014v2
+2017-06-23,Ferroic collinear multilayer magnon spin valve,"Information transport and processing by pure magnonic spin currents in
+insulators is a promising alternative to conventional charge-current driven
+spintronic devices. The absence of Joule heating as well as the reduced spin
+wave damping in insulating ferromagnets has been suggested to enable the
+implementation of efficient logic devices. After the proof of concept for a
+logic majority gate based on the superposition of spin waves has been
+successfully demonstrated, further components are required to perform complex
+logic operations. A key component is a switch that corresponds to a
+conventional magnetoresistive spin valve. Here, we report on magnetization
+orientation dependent spin signal detection in collinear magnetic multilayers
+with spin transport by magnonic spin currents. We find in Y3Fe5O12|CoO|Co
+tri-layers that the detected spin signal depends on the relative alignment of
+Y3Fe5O12 and Co. This demonstrates a spin valve behavior with an effect
+amplitude of 120% in our systems. We demonstrate the reliability of the effect
+and investigate the origin by both temperature and power dependent
+measurements, showing that spin rectification effects and a magnetic layer
+alignment dependent spin transport effect result in the measured signal.",1706.07592v1
+2017-11-30,Effective interactions in a quantum Bose-Bose mixture,"We generalize the Beliaev diagrammatic theory of an interacting spinless
+Bose-Einstein condensate to the case of a binary mixture. We derive a set of
+coupled Dyson equations and find analytically the Green's functions of the
+system. The elementary excitation spectrum consists of two branches, one of
+which takes the characteristic parabolic form in the limit of a
+spin-independent interaction. We observe renormalization of the magnon mass and
+the spin-wave velocity due to the Andreev-Bashkin entrainment effect. For a 3D
+weakly-interacting gas the spectrum can be obtained by applying the Bogoliubov
+transformation to the second-quantized Hamiltonian in which the microscopic
+two-body potentials in each channel are replaced by the corresponding off-shell
+scattering amplitudes. The superfluid drag density can be calculated by
+considering a mixture of phonons and magnons interacting via the effective
+potentials. We show that this problem is identical to the second-order
+perturbative treatment of a Bose polaron. In 2D the drag contributes to the
+magnon dispersion already in the first approximation. Our consideration
+provides a basis for systematic study of emergent phases in quantum degenerate
+Bose-Bose mixtures.",1712.00039v3
+2019-09-11,Discovering momentum-dependent magnon spin texture in insulating antiferromagnets: Role of the Kitaev interaction,"We theoretically show that the Kitaev interaction generates a novel class of
+spin texture in the excitation spectrum of the antiferromagnetic insulator
+found in the Kitaev-Heisenberg-$\Gamma$ model. In conducting electronic
+systems, there is a series of vortex type of spin texture along the Fermi
+surface induced by Rashba and Dresselhaus spin-orbit coupling. Such spin
+textures are rarely found in magnetic insulators, since there had been no
+systematic ways to control the kinetics of its quasi-particle called magnon
+using a magnetic field or spacially asymmetric exchange couplings. Here, we
+propose a general framework to explore such spin textures in arbitrary
+insulating antiferromagnets. We introduce an analytical method to transform any
+complicated Hamiltonian to the simple representation based on pseudo-spin
+degrees of freedom. The direction of the pseudo-spin on a Bloch sphere
+describes the degree of contributions from the two magnetic sublattices to the
+spin moment carried by the magnon. The momentum dependent fictitious ""Zeeman
+field"" determines the direction of the pseudo-spin and thus becomes the control
+parameter of the spin texture, which is explicitly described by the original
+model parameters. The framework enabled us to clarify the uncovered aspect of
+the Kitaev interaction, and further provides a tool to easily design or explore
+materials with intriguing magnetic properties. Since these spin textures can be
+a source of a pure spin current, the Kitaev materials $A_{2}$PrO$_{3}$ ($A$
+=Li, Na) shall become a potential platform of power-saving spintronics devices.",1909.05174v2
+2017-05-08,Experimental Verification of the Universality of Magnetic-Field-Induced Bose-Einstein Condensation of Magnons,"CsFeBr$_3$ is an $S\,{=}\,1$ hexagonal antiferromagnet that has a singlet
+ground state owing to its large easy-plane single-ion anisotropy. The critical
+behavior of the magnetic-field-induced phase transition for a magnetic field
+parallel to the $c$ axis, which can be described by the Bose-Einstein
+condensation (BEC) of magnons under the $U(1)$ symmetry, was investigated via
+magnetization and specific heat measurements down to 0.1$\,$K. For the specific
+heat measurement, we have developed a method of effectively suppressing the
+torque acting on a sample with strong anisotropy that uses the spin dimer
+compound Ba$_2$CoSi$_2$O$_6$Cl$_2$ with large and anisotropic Van Vleck
+paramagnetism. The temperature dependence of the transition field $H_{\rm
+c}(T)$ was found to follow the power-law $H_{\rm c}(T)\,{-}\,H_{\rm
+c}\,{\propto}\,T^{\phi}$ with a critical exponent of
+${\phi}\,{=}\,1.50\,{\pm}\,0.02$ and critical field of $H_{\rm c}\,{=}\,2.60$
+T. This result verifies the universality of the three-dimensional BEC of
+magnons described by ${\phi}_{\rm BEC}\,{=}\,3/2$.",1705.02739v2
+2017-08-31,Antiferromagnetic magnons from fractionalized excitations,"We develop an approach to describe antiferromagnetic magnons on a bipartite
+lattice supporting the N\'{e}el state using fractionalized degrees of freedom
+typically inherent to quantum spin liquids. In particular we consider a
+long-range magnetically ordered state of interacting two-dimensional quantum
+spin$-1/2$ models using the Chern-Simons (CS) fermion representation of
+interacting spins. The interaction leads to Cooper instability and pairing of
+CS fermions, and to CS superconductivity which spontaneously violates the
+continuous $\mathrm{U}(1)$ symmetry generating a linearly-dispersing gapless
+Nambu-Goldstone mode due to phase fluctuations. We evaluate this mode and show
+that it is in high-precision agreement with magnons of the corresponding
+N\'{e}el antiferromagnet irrespective to the lattice symmetry. Using the
+fermion formulation of a system with competing interactions, we show that the
+frustration gives raise to nontrivial long-range four, six, and higher-leg
+interaction vertices mediated by the CS gauge field, which are responsible for
+restoring of the continuous symmetry at sufficiently strong frustration. We
+identify these new interaction vertices and discuss their implications to
+unconventional phase transitions. We also apply the proposed theory to a model
+of anyons that can be tuned continuously from fermions to bosons.",1709.00060v2
+2018-03-06,Magnon-assisted tunnelling in van der Waals heterostructures based on CrBr3,"The growing family of two-dimensional (2D) materials that are now available
+can be used to assemble van der Waals heterostructures with a wide range of
+properties. Of particular interest are tunnelling heterostructures, which have
+been used to study the electronic states both in the tunnelling barrier and in
+the emitter and collector contacts. Recently, 2D ferromagnets have been studied
+theoretically and experimentally. Here we investigate electron tunnelling
+through a thin (2-6 layers) ferromagnetic CrBr3 barrier. For devices with
+non-magnetic barriers, conservation of momentum can be relaxed by
+phonon-assisted tunnelling or by tunnelling through localised states. In the
+case of our ferromagnetic barrier the dominant tunnelling mechanisms are the
+emission of magnons at low temperatures or scattering of electrons on localised
+magnetic excitations above the Curie temperature. Tunnelling with magnon
+emission offers the possibility of injecting spin into the collector electrode.",1803.02120v2
+2018-06-03,Field evolution of magnons in $α$-RuCl$_3$ by high-resolution polarized terahertz spectroscopy,"The Kitaev quantum spin liquid (KSL) is a theoretically predicted state of
+matter whose fractionalized quasiparticles are distinct from bosonic magnons,
+the fundamental excitation in ordered magnets. The layered honeycomb
+antiferromagnet $\alpha$-RuCl$_3$ is a KSL candidate material, as it can be
+driven to a magnetically disordered phase by application of an in-plane
+magnetic field, with $H_c \sim 7$ T. Here we report a detailed characterization
+of the magnetic excitation spectrum of this material by high-resolution
+time-domain terahertz (THz) spectroscopy. We observe two sharp magnon
+resonances whose frequencies and amplitudes exhibit a discontinuity as a
+function of applied magnetic field, as well as two broader peaks at higher
+energy. Below the N\'eel temperature, we find that linear spin wave theory can
+account for all of these essential features of the spectra when a
+$C_3$-breaking distortion of the honeycomb lattice and the presence of
+structural domains are taken into account.",1806.00855v2
+2019-01-22,High-harmonic generation in quantum spin systems,"We theoretically study the high-harmonic generation (HHG) in one-dimensional
+spin systems. While in electronic systems the driving by AC electric fields
+produces radiation from the dynamics of excited charges, we consider here the
+situation where spin systems excited by a magnetic field pulse generate
+radiation via a time-dependent magnetization. Specifically, we study the
+magnetic dipole radiation in two types of ferromagnetic spin chain models, the
+Ising model with static longitudinal field and the XXZ model, and reveal the
+structure of the spin HHG and its relation to spin excitations. For weak laser
+amplitude, a peak structure appears which can be explained by time-dependent
+perturbation theory. With increasing amplitude, plateaus with well-defined
+cutoff energies emerge. In the Ising model with longitudinal field, the
+thresholds of the multiple plateaus in the radiation spectra can be explained
+by the annihilation of multiple magnons. In the XXZ model, which retains the
+$\mathbf{Z}_{2}$ symmetry, the laser magnetic field can induce a phase
+transition of the ground state when it exceeds a critical value, which results
+in a drastic change of the spin excitation character. As a consequence, the
+first cutoff energy in the HHG spectrum changes from a single-magnon to a
+two-magnon energy at this transition. Our results demonstrate the possibility
+of generating high-harmonic radiation from magnetically ordered materials and
+the usefulness of high-harmonic signals for extracting information on the spin
+excitation spectrum.",1901.07588v2
+2019-01-31,Triplet superconductivity in ferromagnets due to magnon exchange,"We consider the superconducting pairing induced by spin waves exchange in a
+ferromagnet with both conduction and localized electrons, the latter being
+described as spins. We use the microscopic Eliashberg theory to describe the
+pairing of conducting electrons and the RPA approach to treat the localized
+spins assuming an exchange coupling between the conducting electrons and spins.
+In the framework of non relativistic Hamiltonian twe found that he spin wave
+exchange results in equal spin electron pairing described by the two components
+of the order parameter, $\Delta^{\uparrow}$ (both spins up) and
+$\Delta^{\downarrow}$ (both spins down). Due to the conservation of total spin
+projection on the axis of the spontaneous ferromagnetic moment, the spin wave
+exchange at low temperatures includes an emission of magnons and an absorption
+of thermal magnons by the conduction electrons. The absorption and emission
+processes depend differently on the temperature, with the absorption being
+progressively suppressed as the temperature drops. As a result, the
+superconducting pairing exists only if the electron-spin wave exchange
+parameter $g$ exceeds some critical value $g_c$. At $g>g_c$ pairing vanishes if
+the temperature drops below the lowest point $T_{cl}$ or increases above the
+upper critical point $T_{ch} \approx T_m$ (the Curie temperature) where the
+spin waves cease to exist. This behavior inherent to the spin carrying glue is
+in an obvious disagreement with the results of conventional BCS approach which
+assumes that the effective electron-electron attraction is simply proportional
+to the static magnetic susceptibility.",1901.11248v1
+2019-02-28,Finite field regime for a quantum spin liquid in $α$-RuCl$_3$,"An external magnetic field can induce a transition in $\alpha$-RuCl$_3$ from
+an ordered zigzag state to a disordered state that is possibly related to the
+Kitaev quantum spin liquid. Here we present new field dependent inelastic
+neutron scattering and magnetocaloric effect measurements implying the
+existence of an additional transition out of the quantum spin liquid phase at
+an upper field limit $B_u$. The neutron scattering shows three distinct regimes
+of magnetic response. In the low field ordered state the response shows magnon
+peaks; the intermediate field regime shows only continuum scattering, and above
+$B_u$ the response shows sharp magnon peaks at the lower bound of a strong
+continuum. Measurable dispersion of magnon modes along the $(0,0,L)$ direction
+implies non-negligible inter-plane interactions. Combining the magnetocaloric
+effect measurements with other data a $T-B$ phase diagram is constructed. The
+results constrain the range where one might expect to observe quantum spin
+liquid behavior in $\alpha$-RuCl$_3$.",1903.00056v3
+2019-03-02,Excitation of unidirectional exchange spin waves by a nanoscale magnetic grating,"Magnon spintronics is a prosperous field that promises beyond-CMOS technology
+based on elementary excitations of the magnetic order that act as information
+carriers for future computational architectures. Unidirectional propagation of
+spin waves is key to the realization of magnonic logic devices. However,
+previous efforts to enhance the Damon-Eshbach-type nonreciprocity did not
+realize (let alone control) purely unidirectional propagation. Here we
+experimentally demonstrate excitations of unidirectional exchange spin waves by
+a nanoscale magnetic grating consisting of Co nanowires fabricated on an
+ultrathin yttrium iron garnet film. We explain and model the nearly perfect
+unidirectional excitation by the chirality of the magneto-dipolar interactions
+between the Kittel mode of the nanowires and the exchange spin waves of the
+film. Reversal of the magnetic configurations of film and nanowire array from
+parallel to antiparallel changes the direction of the excited spin waves. Our
+results raise the prospect of a chiral magnonic logic without the need for
+fragile surface states.",1903.00638v1
+2019-03-15,The Krein-Schrödinger Formalism of Bosonic BdG and Certain Classical Systems and Their Topological Classification,"To understand recent works on classical and quantum spin equations and their
+topological classification, we develop a unified mathematical framework for
+bosonic BdG systems and associated classical wave equations; it applies not
+just to equations that describe quantized spin excitations in magnonic crystals
+but more broadly to other systems that are described by a BdG hamiltonian.
+Because here the generator of dynamics, the analog of the hamiltonian, is
+para-, aka Krein-, hermitian but not hermitian, the theory of Krein spaces
+plays a crucial role. For systems which are thermodynamically stable, the
+classical equations can be expressed as a Schr\""odinger equation with a
+hermitian hamiltonian. We then proceed to apply the Cartan-Altland-Zirnbauer
+classification scheme: to properly understand what topological class these
+equations belong to, we need to conceptually distinguish between symmetries and
+constraints. Complex conjugation enters as a particle-hole constraint (as
+opposed to a symmetry), since classical waves are necessarily real-valued.
+Because of this distinction only commuting symmetries enter in the topological
+classification. Our arguments show that the equations for spin waves in
+magnonic crystals are a system of class A, the same topological class as
+quantum hamiltonians describing the Integer Quantum Hall Effect. Consequently,
+the magnonic edge modes first predicted by Shindou et al. are indeed analogs of
+the Quantum Hall Effect, and their net number is topologically protected.",1903.06354v1
+2019-04-04,Resonant inelastic x-ray scattering study of bond order and spin excitations in nickelate thin-film structures,"We used high-resolution resonant inelastic x-ray scattering (RIXS) at the Ni
+$L_3$ edge to simultaneously investigate high-energy interband transitions
+characteristic of Ni-O bond ordering and low-energy collective excitations of
+the Ni spins in the rare-earth nickelates $R$NiO$_3$ ($R$ = Nd, Pr, La) with
+pseudocubic perovskite structure. With the support of calculations based on a
+double-cluster model we quantify bond order (BO) amplitudes for different thin
+films and heterostructures and discriminate short-range BO fluctuations from
+long-range static order. Moreover we investigate magnetic order and exchange
+interactions in spatially confined $R$NiO$_3$ slabs by probing dispersive
+magnon excitations. While our study of superlattices (SLs) grown in the (001)
+direction of the perovskite structure reveals a robust non-collinear spin
+spiral magnetic order with dispersive magnon excitations that are essentially
+unperturbed by BO modulations and spatial confinement, we find magnons with
+flat dispersions and strongly reduced energies in SLs grown in the
+$(111)_{\text{pc}}$ direction that exhibit collinear magnetic order. These
+results give insight into the interplay of different collective ordering
+phenomena in a prototypical 3$d$ transition metal oxide and establish RIXS as a
+powerful tool to quantitatively study several order parameters and the
+corresponding collective excitations within one experiment.",1904.02782v2
+2019-04-19,Quantum Brownian Motion of a Magnetic Skyrmion,"Within a microscopic theory, we study the quantum Brownian motion of a
+skyrmion in a magnetic insulator coupled to a bath of magnon-like quantum
+excitations. The intrinsic skyrmion-bath coupling gives rise to damping terms
+for the skyrmion center-of-mass, which remain finite down to zero temperature
+due to the quantum nature of the magnon bath. We show that the quantum version
+of the fluctuation-dissipation theorem acquires a non-trivial temperature
+dependence. As a consequence, the skyrmion mean square displacement is finite
+at zero temperature and has a fast thermal activation that scales quadratically
+with temperature, contrary to the linear increase predicted by the classical
+phenomenological theory. The effects of an external oscillating drive which
+couples directly on the magnon bath are investigated. We generalize the
+standard quantum theory of dissipation and we show explicitly that additional
+time-dependent dissipation terms are generated by the external drive. From
+these we emphasize a friction and a topological charge renormalization term,
+which are absent in the static limit. The skyrmion response function inherits
+the time periodicity of the driving field and it is thus enhanced and lowered
+over a driving cycle. Finally, we provide a generalized version of the
+nonequilibrium fluctuation-dissipation theorem valid for weakly driven baths.",1904.09215v1
+2019-08-15,Steering between Level Repulsion and Attraction: Broad tunability of Two-Port Driven Cavity Magnon-Polaritons,"Cavity-magnon polaritons (CMPs) are the associated quasiparticles of the
+hybridization between cavity photons and magnons in a magnetic sample placed in
+a microwave resonator. In the strong coupling regime, where the macroscopic
+coupling strength exceeds the individual dissipation, there is a coherent
+exchange of information. This renders CMPs as promising candidates for future
+applications such as in information processing. Recent advances on the study of
+the CMP now allow not only for creation of CMPs on demand, but also for tuning
+of the coupling strength - this can be thought of as enhancing or suppressing
+of information exchange. Here, we go beyond standard single-port driven CMPs
+and employ a two-port driven CMP. We control the coupling strength by the
+relative phase $\phi$ and amplitude field ratio $\delta_0$ between both ports.
+Specifically, we derive a new expression from Input-Output theory for the study
+of the two-port driven CMP and discuss the implications on the coupling
+strength. Furthermore, we examine intermediate cases where the relative phase
+is tuned between its maximal and minimal value and, in particular, the high
+$\delta_0$ regime, which has not been yet explored.",1908.05439v2
+2019-12-18,Gravitational realization of magnons in a ferromagnetic spin chain,"A gravitational model of magnons in thermal equilibrium with a ferromagnetic
+spin chain is developed in a phenomenological bottom-up approach. A large
+Schwarzschild-AdS black hole background is used as the thermal reservoir and
+the magnon dynamics is obtained by scalar fields and branes in the bulk. The
+key feature of this model is that the coupling of the spin chain is related
+with the radial position in which the brane is located. We further study a
+ferromagnetic spin chain with a competing interaction and find that the
+couplings are related by the difference of positions of the branes. We show how
+to obtain the model from a weak limit of a dynamical gravitational system. This
+allows us to embed the model into a holographic system. The couplings can be
+related to entanglement entropy at finite temperature of the CFT since the
+turning point of minimal surfaces coincides with the position of the branes.
+The difference of entropy is used to define a notion of distance between the
+chain couplings.",1912.08761v2
+2019-12-20,Slow-wave based magnonic diode,"Spin waves, the collective excitations of the magnetic order parameter, and
+magnons, the associated quasiparticles, are envisioned as possible data
+carriers in future wave-based computing architectures. On the road towards
+spin-wave computing, the development of a diode-like device capable of
+transmitting spin waves in only one direction, thus allowing controlled signal
+routing, is an essential step. Here, we report on the design and experimental
+realization of a microstructured magnonic diode in a ferromagnetic bilayer
+system. Effective unidirectional propagation of spin waves is achieved by
+taking advantage of nonreciprocities produced by dynamic dipolar interactions
+in transversally magnetized media, which lack symmetry about their horizontal
+midplane. More specifically, dipolar-induced nonreciprocities are used to
+engineer the spin-wave dispersion relation of the bilayer system so that the
+group velocity is reduced to very low values for one direction of propagation,
+and not for the other, thus producing unidirectional slow spin waves. Brillouin
+light scattering and propagating spin-wave spectroscopy are used to demonstrate
+the diode-like behavior of the device, the composition of which was previously
+optimized through micromagnetic simulations. simulations.",1912.09735v1
+2016-03-24,Persistent paramagnons deep in the metallic phase of Sr$_{2-x}$La$_x$IrO$_4$,"We have studied the magnetic excitations of electron-doped
+Sr$_{2-x}$La$_x$IrO$_4$ ($0 \leq x \leq 0.10$) using resonant inelastic x-ray
+scattering (RIXS) at the Ir L$_3$-edge. The long range magnetic order is
+rapidly lost with increasing $x$, but two-dimensional short-range order (SRO)
+and dispersive magnon excitations with nearly undiminished spectral weight
+persist well into the metallic part of the phase diagram. The magnons in the
+SRO phase are heavily damped and exhibit anisotropic softening. Their
+dispersions are well described by a pseudospin-1/2 Heisenberg model with
+exchange interactions whose spatial range increases with doping. We also find a
+doping-independent high-energy magnetic continuum, which is not described by
+this model. The spin-orbit excitons arising from the pseudospin-3/2 manifold of
+the Ir ions broaden substantially in the SRO phase, but remain largely
+separated from the low-energy magnons. Pseudospin-1/2 models are therefore a
+good starting point for the theoretical description of the low-energy magnetic
+dynamics of doped iridates.",1603.07547v2
+2016-12-20,Magnons in a two dimensional transverse field XXZ model,"The XXZ model on a square lattice in the presence of a transverse magnetic
+field is studied within the spin wave theory to investigate the resulting
+canted antiferromagnet. The small and large field regimes are probed separately
+both for easy-axis and easy-plane scenarios which reveal an unentangled
+factorized ground state at an intermediate value of the field. Goldstone modes
+are obtained for the field-free $XY$ antiferromagnet as well as for the
+isotropic antiferromagnet with field up to its saturation value. Moreover, for
+an easy-plane anisotropy, we find that there exists a non-zero field, where
+magnon degeneracy appears as a result of restoration of an U(1) sublattice
+symmetry and that, across that field, there occurs a magnon band crossing. For
+completeness, we then obtain the system phase diagram for $S=1/2$ via large
+scale quantum Monte Carlo simulations using the stochastic series expansion
+technique. Our numerical method is based on a quantization of spin along the
+direction of the applied magnetic field and does not suffer from a
+sign-problem, unlike comparable algorithms based on a spin quantization along
+the axis of anisotropy. With this formalism, we are also able to obtain powder
+averages of the transverse and longitudinal magnetizations, which may be useful
+for understanding experimental measurements on polycrystalline samples.",1612.06608v3
+2017-11-20,Continuum of quantum fluctuations in a three-dimensional $S\!=\!1$ Heisenberg magnet,"Conventional crystalline magnets are characterized by symmetry breaking and
+normal modes of excitation called magnons with quantized angular momentum
+$\hbar$. Neutron scattering correspondingly features extra magnetic Bragg
+diffraction at low temperatures and dispersive inelastic scattering associated
+with single magnon creation and annihilation. Exceptions are anticipated in
+so-called quantum spin liquids as exemplified by the one-dimensional spin-1/2
+chain which has no magnetic order and where magnons accordingly fractionalize
+into spinons with angular momentum $\hbar/2$. This is spectacularly revealed by
+a continuum of inelastic neutron scattering associated with two-spinon
+processes and the absence of magnetic Bragg diffraction. Here, we report
+evidence for these same key features of a quantum spin liquid in the
+three-dimensional Heisenberg antiferromagnet NaCaNi$_2$F$_7$. Through specific
+heat and neutron scattering measurements, Monte Carlo simulations, and analytic
+approximations to the equal time correlations, we show that NaCaNi$_2$F$_7$ is
+an almost ideal realization of the spin-1 antiferromagnetic Heisenberg model on
+a pyrochlore lattice with weak connectivity and frustrated interactions.
+Magnetic Bragg diffraction is absent and 90\% of the spectral weight forms a
+continuum of magnetic scattering not dissimilar to that of the spin-1/2 chain
+but with low energy pinch points indicating NaCaNi$_2$F$_7$ is in a Coulomb
+phase. The residual entropy and diffuse elastic scattering points to an exotic
+state of matter driven by frustration, quantum fluctuations and weak exchange
+disorder.",1711.07509v1
+2020-09-14,Effective field theory of magnon: Dynamics in chiral magnets and Schwinger mechanism,"We develop the effective field theoretical descriptions of spin systems in
+the presence of symmetry-breaking effects: the magnetic field, single-ion
+anisotropy, and Dzyaloshinskii-Moriya interaction. Starting from the lattice
+description of spin systems, we show that the symmetry-breaking terms
+corresponding to the above effects can be incorporated into the effective field
+theory as a combination of a background (or spurious) $\SO(3)$ gauge field and
+a scalar field in the symmetric tensor representation, which are eventually
+fixed at their physical values. We use the effective field theory to
+investigate mode spectra of inhomogeneous ground states, with focusing on
+one-dimensionally inhomogeneous states, such as helical and spiral states.
+Although the helical and spiral ground states share a common feature of
+supporting the gapless Nambu-Goldstone modes associated with the translational
+symmetry breaking, they have qualitatively different dispersion relations:
+isotropic in the helical phase while anisotropic in the spiral phase. We also
+discuss the magnon production induced by an inhomogeneous magnetic field, and
+find a formula akin to the Schwinger formula. Our formula for the magnon
+production gives a finite rate for antiferromagnets, and a vanishing rate for
+ferromagnets, whereas that for ferrimagnets interpolates between the two cases.",2009.06694v1
+2020-09-16,Unconventional magnon excitation by off-resonant microwaves,"It is widely recognized that a physical system can only respond to a periodic
+driving significantly when the driving frequency matches the normal mode
+frequency of the system, which leads to resonance. Off-resonant phenomena are
+rarely considered because of the difficulty to realize strong coupling between
+physical systems and off-resonant waves. Here we examine the response of a
+magnetic system to squeezed light and surprisingly find that the magnons are
+maximally excited when the effective driving frequency is several orders of
+magnitude larger than the resonant frequency. The generated magnons are
+squeezed which brings the advantage of tunable squeezing through an external
+magnetic field. Furthermore, we demonstrate that such off-resonant
+quasi-particle excitation is universal in all the hybrid systems in which the
+coherent and parametric interaction of bosons exists and that it is purely a
+quantum effect, which is rooted in the quantum fluctuations of particles in the
+squeezed vacuum. Our findings may provide an unconventional route to study
+off-resonant phenomena and may further benefit the use of hybrid matter-light
+systems in continuous variable quantum information.",2009.07948v2
+2020-09-22,Magnon-mediated spin currents in Tm3Fe5O12/Pt with perpendicular magnetic anisotropy,"The control of pure spin currents carried by magnons in magnetic insulator
+(MI) garnet films with a robust perpendicular magnetic anisotropy (PMA) is of
+great interest to spintronic technology as they can be used to carry, transport
+and process information. Garnet films with PMA present labyrinth domain
+magnetic structures that enrich the magnetization dynamics, and could be
+employed in more efficient wave-based logic and memory computing devices. In
+MI/NM bilayers, where NM being a normal metal providing a strong spin-orbit
+coupling, the PMA benefits the spin-orbit torque (SOT) driven magnetization's
+switching by lowering the needed current and rendering the process faster,
+crucial for developing magnetic random-access memories (SOT-MRAM). In this
+work, we investigated the magnetic anisotropies in thulium iron garnet (TIG)
+films with PMA via ferromagnetic resonance measurements, followed by the
+excitation and detection of magnon-mediated pure spin currents in TIG/Pt driven
+by microwaves and heat currents. TIG films presented a Gilbert damping constant
+{\alpha}~0.01, with resonance fields above 3.5 kOe and half linewidths broader
+than 60 Oe, at 300 K and 9.5 GHz. The spin-to-charge current conversion through
+TIG/Pt was observed as a micro-voltage generated at the edges of the Pt film.
+The obtained spin Seebeck coefficient was 0.54 {\mu}V/K, confirming also the
+high interfacial spin transparency.",2009.10299v1
+2021-02-13,Accumulation and control of spin waves in magnonic dielectric microresonators by a comb of ultrashort laser pulses,"Spin waves in magnetic microresonators are at the core of modern magnonics.
+Here we demonstrate a new method of tunable excitation of different spin wave
+modes in magnetic microdisks by using a train of laser pulses coming at a
+repetition rate higher than the decay rate of spin precession. The microdisks
+are etched in a transparent bismuth iron garnet film and the light pulses
+influence the spins nonthermally through the inverse Faraday effect. The high
+repetition rate of the laser stimulus of 10 GHz establishes an interplay
+between the spin wave resonances in the frequency and momentum domains. As a
+result, scanning of the focused laser spot near the disk boarder changes
+interference pattern of the magnons and leads to a resonant dependence of the
+spin wave amplitude on the external magnetic field. Apart from that, we
+achieved a switching between volume and surface spin waves by a small variation
+of the external magnetic field.",2102.07021v4
+2021-02-16,Magnonic band structure in CoFeB/Ta/NiFe meander-shaped magnetic bilayers,"In this work, we investigate the spin-wave propagation in three-dimensional
+nanoscale CoFeB/Ta/NiFe meander structures fabricated on a structured SiO2/Si
+substrate. The magnonic band structure has been experimentally determined by
+wavevector-resolved Brillouin light scattering (BLS) spectroscopy and a set of
+stationary modes interposed by two dispersive modes of Bloch type have been
+identified. The results could be understood by micromagnetic and finite element
+simulations of the mode distributions in both real space and the frequency
+domain. The dispersive modes periodically oscillate in frequency over the
+Brillouin zones and correspond to modes, whose spatial distributions extend
+over the entire sample and are either localized exclusively in the CoFeB layer
+or the entire CoFeB/Ta/NiFe magnetic bilayer. Stationary modes are mainly
+concentrated in the vertical segments of the CoFeB and NiFe layers and show
+negligible amplitudes in the horizon-tal segments. The findings are compared
+with those of single-layer CoFeB meander structures with the same geometry
+parameters, which reveals the influence of the dipolar coupling between the two
+ferromagnetic layers on the magnonic band structure.",2102.08223v2
+2013-06-04,Determination of the origin of the spin Seebeck effect - bulk vs. interface effects,"The observation of the spin Seebeck effect in insulators has meant a
+breakthrough for spin caloritronics due to the unique ability to generate pure
+spin currents by thermal excitations in insulating systems without moving
+charge carriers. Since the recent first observation, the underlying mechanism
+and the origin of the observed signals have been discussed highly
+controversially. Here we present a characteristic dependence of the
+longitudinal spin Seebeck effect amplitude on the thickness of the insulating
+ferromagnet (YIG). Our measurements show that the observed behavior cannot be
+explained by any effects originating from the interface, such as magnetic
+proximity effects in the spin detector (Pt). Comparison to theoretical
+calculations of thermal magnonic spin currents yields qualitative agreement for
+the thickness dependence resulting from the finite effective magnon propagation
+length so that the origin of the effect can be traced to genuine bulk magnonic
+spin currents ruling out parasitic interface effects.",1306.0784v1
+2015-07-10,Theoretical Study of $L$-edge Resonant Inelastic X-ray Scattering in La$_2$CuO$_4$ on the Basis of Detailed Electronic Band Structure,"We study theoretically resonant inelastic x-ray scattering (RIXS) at the Cu
+$L_3$-edge in a typical parent compound of high-$T_c$ cuprate superconductors
+La$_2$CuO$_4$ on the basis of a detailed electronic band structure. We
+construct a realistic and precise tight-binding model by employing the
+maximally-localized Wannier functions derived from a first-principles
+electronic structure calculation, and then take account of the Coulomb
+repulsion between d electrons at each Cu site. The antiferromagnetic ground
+state is described within the Hartree-Fock approximation, and take account of
+electron correlations in the intermediate states of RIXS within the
+random-phase approximation (RPA). Calculated RIXS spectra agree well with the
+experimentally observed features including low-energy magnon excitation,
+$d$-$d$ excitations, and charge-transfer excitations, over a wide
+excitation-energy range. In particular, we stress the importance of photon
+polarization dependence: the intensity of magnon excitation and the spectral
+structure of $d$-$d$ excitations depend significantly not only on the
+polarization direction of incident incoming photons but also that of outgoing
+photons. It is demonstrated that the single-magnon excitation intensity is
+maximized when the polarization directions of incoming and outgoing photons are
+perpendicular to each other.",1507.02795v2
+2016-09-07,Magnonic Interferometric Switch for Multi-Valued Logic Circuits,"We investigated a possible use of the magnonic interferometric switches in
+multi-valued logic circuits. The switch is a three-terminal device consisting
+of two spin channels where input, control, and output signals are spin waves.
+Signal modulation is achieved via the interference between the source and gate
+spin waves. We report experimental data on a micrometer scale prototype based
+on Y3Fe2(FeO4)3 structure. The output characteristics are measured at different
+angles of the bias magnetic field. The On/Off ratio of the prototype exceeds 36
+dB at room temperature. Experimental data is complemented by the theoretical
+analysis and the results of micro magnetic simulations showing spin wave
+propagation in a micrometer size magnetic junction. We also present the results
+of numerical modeling illustrating the operation of a nanometer-size switch
+consisting of just 20 spins in the source-drain channel. The utilization of
+spin wave interference as a switching mechanism makes it possible to build
+nanometer-scale logic gates, and minimize energy per operation, which is
+limited only by the noise margin. The utilization of phase in addition to
+amplitude for information encoding offers an innovative route towards
+multi-state logic circuits. We describe possible implementation of the
+three-value logic circuits based on the magnonic interferometric switches. The
+advantages and shortcomings inherent in interferometric switches are also
+discussed.",1609.02217v1
+2016-09-12,"Spontaneous decays of magneto-elastic excitations in noncollinear antiferromagnet (Y,Lu)MnO3","When magnons and phonons, the fundamental quasiparticles of the solid, are
+coupled to one another, they form a new hybrid quasi-particle, leading to novel
+phenomena and interesting applications. Despite its wide-ranging importance,
+however, detailed experimental studies on the underlying Hamiltonian is rare
+for actual materials. Moreover, the anharmonicity of such magnetoelastic
+excitations remains largely unexplored although it is essential for a proper
+understanding of their diverse thermodynamic behaviour as well as intrinsic
+zero-temperature decay. Here we show that in noncollinear antiferromagnets, a
+strong magnon-phonon coupling can significantly enhance the anharmonicity,
+resulting in the creation of magnetoelastic excitations and their spontaneous
+decay. By measuring the spin waves over the full Brillouin zone and carrying
+out anharmonic spin wave calculations using a Hamiltonian with an explicit
+magnon-phonon coupling, we have identified a hybrid magnetoelastic mode in
+(Y,Lu)MnO3 and quantified its decay rate and the exchange-striction coupling
+term required to produce it. Our work has wide implications for understanding
+of the spin-phonon coupling and the resulting excitations of the broad classes
+of noncollinear magnets.",1609.03262v1
+2016-09-12,Topological Magnon Bands and Unconventional Superconductivity in Pyrochlore Iridate Thin Films,"We theoretically study the magnetic properties of pyrochlore iridate bilayer
+and trilayer thin films grown along the $[111]$ direction using a strong
+coupling approach. We find the ground state magnetic configurations on a mean
+field level and carry out a spin-wave analysis about them. In the trilayer case
+the ground state is found to be the all-in-all-out (AIAO) state, whereas the
+bilayer has a deformed AIAO state. For all parameters of the spin-orbit coupled
+Hamiltonian we study, the lowest magnon band in the trilayer case has a nonzero
+Chern number. In the bilayer case we also find a parameter range with nonzero
+Chern numbers. We calculate the magnon Hall response for both geometries,
+finding a striking sign change as function of temperature. Using a slave-boson
+mean-field theory we study the doping of the trilayer system and discover an
+unconventional time-reversal symmetry broken $d+id$ superconducting state. Our
+study complements prior work in the weak coupling limit and suggests that the
+$[111]$ grown thin film pyrochlore iridates are a promising candidate for
+topological properties and unconventional orders.",1609.03612v3
+2018-08-08,Kink far below the Fermi level reveals new electron-magnon scattering channel in Fe,"Many properties of real materials can be modeled using ab initio methods
+within a single-particle picture. However, for an accurate theoretical
+treatment of excited states, it is necessary to describe electron-electron
+correlations including interactions with bosons: phonons, plasmons, or magnons.
+In this work, by comparing spin- and momentum-resolved photoemission
+spectroscopy measurements to many-body calculations carried out with a newly
+developed first-principles method, we show that a kink in the electronic band
+dispersion of a ferromagnetic material can occur at much deeper binding
+energies than expected (E_b=1.5 eV). We demonstrate that the observed spectral
+signature reflects the formation of a many-body state that includes a photohole
+bound to a coherent superposition of renormalized spin-flip excitations. The
+existence of such a many-body state sheds new light on the physics of the
+electron-magnon interaction which is essential in fields such as spintronics
+and Fe-based superconductivity.",1808.02682v2
+2018-08-20,Calculating critical temperatures for ferromagnetic order in two-dimensional materials,"Magnetic order in two-dimensional (2D) materials is intimately coupled to
+magnetic anisotropy (MA) since the Mermin-Wagner theorem implies that
+rotational symmetry cannot be spontaneously broken at finite temperatures in
+2D. Large MA thus comprises a key ingredient in the search for magnetic 2D
+materials that retains the magnetic order above room temperature. Magnetic
+interactions are typically modeled in terms of Heisenberg models and the
+temperature dependence on magnetic properties can be obtained with the Random
+Phase Approximation (RPA), which treats magnon interactions at the mean-field
+level. In the present work we show that large MA gives rise to strong
+magnon-magnon interactions that leads to a drastic failure of the RPA. We then
+demonstrate that classical Monte Carlo (MC) simulations correctly describe the
+critical temperatures in the large MA limit and agree with RPA when the MA
+becomes small. A fit of the MC results leads to a simple expression for the
+critical temperatures as a function of MA and exchange coupling constants,
+which significantly simplifies the theoretical search for new 2D magnetic
+materials with high critical temperatures. The expression is tested on a
+monolayer of CrI$_3$, which were recently observed to exhibit ferromagnetic
+order below 45 K and we find excellent agreement with the experimental value.",1808.06400v3
+2019-07-03,Dirac magnons in a honeycomb lattice quantum XY magnet CoTiO3,"The discovery of massless Dirac electrons in graphene and topological
+Dirac-Weyl materials has prompted a broad search for bosonic analogues of such
+Dirac particles. Recent experiments have found evidence for Dirac magnons above
+an Ising-like ferromagnetic ground state in a two-dimensional (2D) kagome
+lattice magnet and in the van der Waals layered honeycomb crystal CrI$_3$, and
+in a 3D Heisenberg magnet Cu$_3$TeO$_6$. Here we report on our inelastic
+neutron scattering investigation on large single crystals of a stacked
+honeycomb lattice magnet CoTiO$_3$, which is part of a broad family of ilmenite
+materials. The magnetically ordered ground state of CoTiO$_3$ features
+ferromagnetic layers of Co$^{2+}$, stacked antiferromagnetically along the
+$c$-axis. We discover that the magnon dispersion relation exhibits strong
+easy-plane exchange anisotropy and hosts a clear gapless Dirac cone along the
+edge of the 3D Brillouin zone. Our results establish CoTiO$_3$ as a model
+pseudospin-$1/2$ material to study interacting Dirac bosons in a 3D quantum XY
+magnet.",1907.02061v1
+2019-10-08,Magnon Bose-Einstein Condensation and Superconductivity in a Frustrated Kondo Lattice,"Motivated by recent experiments on magnetically frustrated heavy fermion
+metals, we theoretically study the phase diagram of the Kondo lattice model
+with a nonmagnetic valence bond solid ground state on a ladder. A similar
+physical setting may be naturally occurring in YbAl$_3$C$_3$, CeAgBi$_2$, and
+TmB$_4$ compounds. In the insulating limit, the application of a magnetic field
+drives a quantum phase transition to an easy-plane antiferromagnet, which is
+described by a Bose-Einstein condensation of magnons. Using a combination of
+field theoretical techniques and density matrix renormalization group
+calculations we demonstrate that in one dimension this transition is stable in
+the presence of a metallic Fermi sea and its universality class in the local
+magnetic response is unaffected by the itinerant gapless fermions. Moreover, we
+find that fluctuations about the valence bond solid ground state can mediate an
+attractive interaction that drives unconventional superconducting correlations.
+We discuss the extensions of our findings to higher dimensions and argue that,
+depending on the filling of conduction electrons, the magnon Bose-Einstein
+condensation transition can remain stable in a metal also in dimensions two and
+three.",1910.03589v2
+2020-01-31,Temperature dependence of spin pinning and spin-wave dispersion in nanoscopic ferromagnetic waveguides,"The field of magnonics attracts significant attention due to the possibility
+of utilizing information coded into the spin-wave phase or amplitude to perform
+computation operations on the nanoscale. Recently, spin waves were investigated
+in Yttrium Iron Garnet (YIG) waveguides with widths ranging down to 50 nm and
+aspect ratios thickness over width approaching unity. A critical width was
+found, below which the exchange interaction suppresses the dipolar pinning
+phenomenon and the system becomes unpinned. Here we continue these
+investigations and analyse the pinning phenomenon and spin-wave dispersions as
+a function of temperature, thickness and material of choice. Higher order
+modes, the influence of a finite wavevector along the waveguide and the impact
+of the pinning phenomenon on the spin-wave lifetime are discussed as well as
+the influence of a trapezoidal cross section and edge roughness of the
+waveguides. The presented results are of particular interest for potential
+applications in magnonic devices and the incipient field of quantum magnonics
+at cryogenic temperatures.",2002.00003v1
+2020-02-05,Phonon angular momentum Hall effect,"Spin Hall effect is the transverse flow of the electron spin in conductors
+under external electric field. Similarly, thermal gradient in magnetic
+insulators can drive a transverse flow of the spin angular momentum of magnons,
+which provides a thermal alternative for spin manipulation. Recently, the
+phonon angular momentum (PAM), which is the angular momentum of atoms as a
+result of their orbital motion around their equilibrium positions, has garnered
+attention as a quantity analogous to the magnon spin. However, can we
+manipulate PAM like magnon spin? Here, we show that temperature gradient
+generally induces a transverse flow of PAM, which we term the phonon angular
+momentum Hall effect (PAMHE). The PAMHE relies only on the presence of
+transverse and longitudinal acoustic phonons, and it is therefore ubiquitous in
+condensed matter systems. As a consequence of the PAMHE, PAM accumulates at the
+edges of a crystal. When the atoms in the crystal carry nonzero Born effective
+charge, the edge PAM induces edge magnetization, which may be observed through
+optical measurement. We believe that PAMHE provides a new principle for the
+manipulation of angular momenta in insulators and opens up an avenue for
+developing functional materials based on phonon engineering.",2002.01659v2
+2020-04-05,Spin wave based tunable switch between superconducting flux qubits,"Quantum computing hardware has received world-wide attention and made
+considerable progress recently. YIG thin film have spin wave (magnon) modes
+with low dissipation and reliable control for quantum information processing.
+However, the coherent coupling between a quantum device and YIG thin film has
+yet been demonstrated. Here, we propose a scheme to achieve strong coupling
+between superconducting flux qubits and magnon modes in YIG thin film. Unlike
+the direct $\sqrt{N}$ enhancement factor in coupling to the Kittel mode or
+other spin ensembles, with N the total number of spins, an additional spatial
+dependent phase factor needs to be considered when the qubits are magnetically
+coupled with the magnon modes of finite wavelength. To avoid undesirable
+cancelation of coupling caused by the symmetrical boundary condition, a CoFeB
+thin layer is added to one side of the YIG thin film to break the symmetry. Our
+numerical simulation demonstrates avoided crossing and coherent transfer of
+quantum information between the flux qubits and the standing spin waves in YIG
+thin films. We show that the YIG thin film can be used as a tunable switch
+between two flux qubits, which have modified shape with small direct inductive
+coupling between them. Our results manifest that it is possible to couple flux
+qubits while suppressing undesirable cross-talk.",2004.02156v1
+2020-05-20,Spin excitations in the frustrated triangular lattice antiferromagnet NaYbO$_2$,"Here we present a neutron scattering-based study of magnetic excitations and
+magnetic order in NaYbO$_2$ under the application of an external magnetic
+field. The crystal electric field-split $J = 7/2$ multiplet structure is
+determined, revealing a mixed $|m_z>$ ground state doublet and is consistent
+with a recent report Ding et al. [1]. Our measurements further suggest
+signatures of exchange effects in the crystal field spectrum, manifested by a
+small splitting in energy of the transition into the first excited doublet. The
+field-dependence of the low-energy magnetic excitations across the transition
+from the quantum disordered ground state into the fluctuation-driven ordered
+regime is analyzed. Signs of a first-order phase transition into a noncollinear
+ordered state are revealed at the upper-field phase boundary of the ordered
+regime, and higher order magnon scattering, suggestive of strong magnon-magnon
+interactions, is resolved within the previously reported $up-up-down$ phase.
+Our results reveal a complex phase diagram of field-induced order and spin
+excitations within NaYbO$_2$ and demonstrate the dominant role of quantum
+fluctuations cross a broad range of fields within its interlayer frustrated
+triangular lattice.",2005.10375v1
+2020-05-29,Long-distance spin-transport across the Morin phase transition up to room temperature in ultra-low damping single crystals of the antiferromagnet α-Fe2O3,"Antiferromagnetic materials can host spin-waves with polarizations ranging
+from circular to linear depending on their magnetic anisotropies. Until now,
+only easy-axis anisotropy antiferromagnets with circularly polarized spin-waves
+were reported to carry spin-information over long distances of micrometers. In
+this article, we report long-distance spin-transport in the easy-plane canted
+antiferromagnetic phase of hematite and at room temperature, where the linearly
+polarized magnons are not intuitively expected to carry spin. We demonstrate
+that the spin-transport signal decreases continuously through the easy-axis to
+easy-plane Morin transition, and persists in the easy-plane phase through
+current induced pairs of linearly polarized magnons with dephasing lengths in
+the micrometer range. We explain the long transport distance as a result of the
+low magnetic damping, which we measure to be below 0.0001 as in the best
+ferromagnets. All of this together demonstrates that long-distance transport
+can be achieved across a range of anisotropies and temperatures, up to room
+temperature, highlighting the promising potential of this insulating
+antiferromagnet for magnon-based devices.",2005.14414v5
+2021-01-10,Optical magnons with dominant bond-directional exchange interactions in a honeycomb lattice iridate $α$-Li$_{2}$IrO$_{3}$,"We have used resonant inelastic x-ray scattering to reveal optical magnons in
+a honeycomb lattice iridate $\alpha$-Li$_{2}$IrO$_{3}$. The spectrum in the
+energy region 20-25 meV exhibits momentum dependence, of which energy is
+highest at the location of the magnetic Bragg peak, ($\textit{h}, \textit{k}$)
+= ($\pm$0.32, 0), and lowered toward (0, 0) and ($\pm$1, 0). We compare our
+data with a linear spin-wave theory based on a generic nearest-neighbor spin
+model. We find that a dominant bond-directional Kitaev interaction of order 20
+meV is required to explain the energy scale observed in our study. The observed
+excitations are understood as stemming from optical magnon modes whose
+intensity is modulated by a structure factor, resulting in the apparent
+momentum dependence. We also observed diffuse magnetic scattering arising from
+the short-range magnetic correlation well above $\textit{T}_{N}$. In contrast
+to Na$_{2}$IrO$_{3}$, this diffuse scattering lacks the $C_3$ rotational
+symmetry of the honeycomb lattice, suggesting that the bond anisotropy is far
+from negligible in $\alpha$-Li$_{2}$IrO$_{3}$.",2101.03471v1
+2021-01-19,Reconfigurable magnonic mode-hybridisation and spectral control in a bicomponent artificial spin ice,"Strongly-interacting nanomagnetic arrays are finding increasing use as model
+host systems for reconfigurable magnonics. The strong inter-element coupling
+allows for stark spectral differences across a broad microstate space due to
+shifts in the dipolar field landscape. While these systems have yielded
+impressive initial results, developing rapid, scaleable means to access abroad
+range of spectrally-distinct microstates is an open research problem.We present
+a scheme whereby square artificial spin ice is modified by widening a
+'staircase' subset of bars relative to the rest of the array, allowing
+preparation of any ordered vertex state via simple global-field protocols.
+Available microstates range from the system ground-state to high-energy
+'monopole' states, with rich and distinct microstate-specific magnon spectra
+observed. Microstate-dependent mode-hybridisation and anticrossings are
+observed at both remanence and in-field with dynamic coupling strength tunable
+via microstate-selection. Experimental coupling strengths are found up to g /
+2$\pi$ = 0.15 GHz. Microstate control allows fine mode-frequency shifting, gap
+creation and closing, and active mode number selection.",2101.07767v3
+2021-01-23,Antiferromagnets with random vacancies and substitutional spins on the triangular lattice,"We discuss theoretically static and dynamical properties of $XY$ and
+Heisenberg antiferromagnets on triangular lattice with random vacancies and
+substitutional spins. It is shown that the distortion of $120^\circ$ magnetic
+order produced by a single defect is described by electrostatic equations for a
+field of an electrically neutral complex of six charges located around the
+impurity. The first finite term in the multipole expansion of this field is the
+octupole moment which decays as $1/r^3$ with the distance $r$. The linearity of
+equations allows to describe analytically the distortion of the long-range
+magnetic order at a small concentration $c$ of defects. We obtain analytically
+renormalization of the elastic neutron scattering cross section and the magnon
+spectrum $\epsilon_{\bf k}$ in the leading order in $c$. We find that the
+scattering on impurities renormalizes weakly the bare spectrum $\epsilon_{\bf
+k}\propto k$ at $k\gg\sqrt c$. However the renormalization is substantial of
+the long-wavelength magnon spectrum at $k\ll\sqrt c$: $\epsilon_{\bf k}\propto
+\sqrt{c /\ln(1/k)}$ at $k\to0$ and there is a parametrically large region in
+which magnons with not too small momenta are overdamped and localized. This
+strong modification of the long-wavelength spectrum leads to the stabilization
+of the slightly distorted magnetic long-range order at $T<T_N\sim
+S^2J/\ln(1/c)$ and to the considerable change in the density of states and in
+the specific heat. The overdamped modes arise also in quasi-2D spin systems on
+a stacked triangular lattice.",2101.09511v3
+2021-02-28,Topological excitations in quasi two-dimensional quantum magnets with weak interlayer interactions,"The study of topological magnetic excitations has attracted widespread
+attention in the past few years. In this thesis, I have studied some examples
+of novel topological magnonic phases/phenomena in low-dimensional quantum
+magnets. The first chapter motivates the research based on the research gap in
+this field of study. The second chapter is written to make the thesis
+self-sufficient and the concepts are explained through examples. In the second
+chapter, the following formalisms and physical observables are described:
+Holstein-Primakoff, bond operator, Schwinger boson, Bogoliubov-Valatin, Group
+theory, Berry-phase, Berry-curvature, Chern number, thermal Hall conductance,
+Nernst conductivity, dynamical spin structure factor, edge-current. The main
+results of the thesis are shown in the third, fourth, and fifth chapters. In
+the third chapter, I have shown that anti-chiral edge states (co-propagating
+edge states) arise in the ferromagnetic Heisenberg model on the honeycomb
+lattice with Dzyaloshinskii-Moriya (DM) interactions. My results suggest that
+such anti-chiral edge states may be induced in certain realistic models of
+quantum magnets. In the fourth chapter, I have found the emergence of many
+magnon band-topological phases in the flux state of the Shastry-Sutherland
+model. I have derived a simple analytical form of the temperature dependence of
+derivative of thermal Hall conductivity near the band topological transition
+point which I propose to be experimentally useful. In the fifth chapter, I have
+investigated the emergence of Weyl triplons due to inter-layer DM-interaction
+in a microscopic model of SrCu2(BO3)2, a widely studied frustrated quantum
+magnet. I have shown that the thermal magnon Hall conductivity has a
+quasi-linear dependence as a function of the magnetic field in a Weyl-triplon
+region.",2103.00401v1
+2021-03-15,Determining the range of magnetic interactions from the relations between magnon eigenvalues at high-symmetry k points,"Magnetic exchange interactions (MEIs) define networks of coupled magnetic
+moments and lead to a surprisingly rich variety of their magnetic properties.
+Typically MEIs can be estimated by fitting experimental results. But how many
+MEIs need to be included in the fitting process for a material is not clear a
+priori, which limits the quality of results obtained by these conventional
+methods. In this paper, based on linear spin-wave theory but without performing
+matrix diagonalization, we show that for a general quadratic spin Hamiltonian,
+there is a simple relation between the Fourier transform of MEIs and the sum of
+square of magnon energies (SSME). We further show that according to the
+real-space distance range within which MEIs are considered relevant, one can
+obtain the corresponding relationships between SSME in momentum space. We also
+develop a theoretical tool for tabulating the rule about SSME. By directly
+utilizing these characteristics and the experimental magnon energies at only a
+few high-symmetry k points in the Brillouin zone, one can obtain strong
+constraints about the range of exchange path beyond which MEIs can be safely
+neglected. Our methodology is also general applicable for other Hamiltonian
+with quadratic Fermi or Boson operators.",2103.08486v1
+2021-04-14,Finite-element dynamic-matrix approach for spin-wave dispersions in magnonic waveguides with arbitrary cross section,"We present a numerical approach to efficiently calculate spin-wave
+dispersions and spatial mode profiles in magnetic waveguides of arbitrarily
+shaped cross section with any non-collinear equilibrium magnetization which is
+translationally invariant along the waveguide. Our method is based on the
+propagating-wave dynamic-matrix approach by Henry et al. and extends it to
+arbitrary cross sections using a finite-element method. We solve the linearized
+equation of motion of the magnetization only in a single waveguide cross
+section which drastically reduces computational effort compared to common
+three-dimensional micromagnetic simulations. In order to numerically obtain the
+dipolar potential of individual spin-wave modes, we present a plane-wave
+version of the hybrid finite-element/boundary-element method by Frekdin and
+Koehler which, for the first time, we extend to a modified version of the
+Poisson equation. Our method is applied to several important examples of
+magnonic waveguides including systems with surface curvature, such as magnetic
+nanotubes, where the curvature leads to an asymmetric spin-wave dispersion. In
+all cases, the validity of our approach is confirmed by other methods. Our
+method is of particular interest for the study of curvature-induced or
+magnetochiral effects on spin-wave transport but also serves as an efficient
+tool to investigate standard magnonic problems.",2104.06943v1
+2021-04-19,Magnetic coupling in Y$_3$Fe$_5$O$_{12}$/Gd$_3$Fe$_5$O$_{12}$ heterostructures,"Ferrimagnetic Y$_3$Fe$_5$O$_{12}$ (YIG) is the prototypical material for
+studying magnonic properties due to its exceptionally low damping. By
+substituting the yttrium with other rare earth elements that have a net
+magnetic moment, we can introduce an additional spin degree of freedom. Here,
+we study the magnetic coupling in epitaxial
+Y$_3$Fe$_5$O$_{12}$/Gd$_3$Fe$_5$O$_{12}$ (YIG/GIG) heterostructures grown by
+pulsed laser deposition. From bulk sensitive magnetometry and surface sensitive
+spin Seebeck effect (SSE) and spin Hall magnetoresistance (SMR) measurements,
+we determine the alignment of the heterostructure magnetization through
+temperature and external magnetic field. The ferromagnetic coupling between the
+Fe sublattices of YIG and GIG dominates the overall behavior of the
+heterostructures. Due to the temperature dependent gadolinium moment, a
+magnetic compensation point of the total bilayer system can be identified. This
+compensation point shifts to lower temperatures with increasing thickness of
+YIG due the parallel alignment of the iron moments. We show that we can control
+the magnetic properties of the heterostructures by tuning the thickness of the
+individual layers, opening up a large playground for magnonic devices based on
+coupled magnetic insulators. These devices could potentially control the magnon
+transport analogously to electron transport in giant magnetoresistive devices.",2104.09592v1
+2021-06-18,Inelastic spin-wave beam scattering by edge-localized spin waves in ferromagnetic thin film,"Spin waves are promising chargeless information carriers for the future,
+energetically efficient beyond-CMOS systems. Among many advantages there are
+the ease of achieving nonlinearity, the variety of possible interactions, and
+excitation types. Although the rapidly developing magnonic research has already
+yielded impressive realizations, multi-mode nonlinear effects, particularly
+with the propagating waves and their nanoscale realizations, are still an open
+research problem. We study theoretically the dynamic interactions of the spin
+waves confined to the edge of a thin ferromagnetic film with the spin-wave beam
+incident at this edge. We found the inelastically scattered spin-wave beams at
+frequencies increased and decreased by the frequency of the edge spin-wave
+relative to the specularly reflected beam. We observed a strong dependence of
+the angular shift of the inelastic scattered spin-wave beam on the edge-mode
+frequency, which allowed us to propose a magnonic demultiplexing of the signal
+encoded in spin waves propagating along the edge. Since dynamic magnetostatic
+interactions, which are ubiquitous in the spin-wave dynamics, are decisive in
+this process, this indicates the possibility of implementing the presented
+effects, also in other configurations and their use in magnonic systems.",2106.09954v3
+2021-06-24,Magnetic excitations of the field induced states in BaCo2(AsO4)2 probed by time-domain terahertz spectroscopy,"Searching for Kitaev quantum spin liquid (QSL) is a fascinating and
+challenging problem. Much effort has been devoted to honeycomb lattice
+candidates with strong spin-orbit coupling in 5d-electron iridates and
+4delectron RuCl3. Recently, theoretical studies suggested that the 3d7 Co-based
+honeycomb materials with high spin state S=3/2 and effective orbital angular
+momentum L=1 could also be promising candidates of Kitaev QSL. One of the
+candidates, BaCo2(AsO4)2, was revisited recently. The long range magnetic order
+in BaCo2(AsO4)2 can be suppressed by very weak in-plane magnetic field,
+suggesting its proximity to Kitaev QSL. Here we perform time domain terahertz
+spectroscopy measurement to study the magnetic excitations on BaCo2(AsO4)2. We
+observe different magnon excitations upon increasing external magnetic field.
+In particular, the system is easily driven to a field-polarized paramagnetic
+phase, after the long range magnetic order is suppressed by a weak field Hc 2.
+The spectra beyond Hc2 are dominated by single magnon and two magnon
+excitations without showing signature of QSL. We discuss the similarity and
+difference of the excitation spectra between BaCo2(AsO4)2 and the widely
+studied Kitaev QSL candidate RuCl3.",2106.13100v1
+2021-09-02,Magnon heat transport in a two-dimensional Mott insulator,"Whether or not anomalies in the thermal conductivity in insulating cuprates
+can be attributed to antiferromagnetic order and magnons in a 2D Mott insulator
+remains an intriguing open question. To shed light on this issue, we
+investigate the thermal conductivity $\kappa$ and its relationship with the
+specific heat $c_v$ in the half-filled 2D single-band Hubbard model, using the
+numerically exact determinant quantum Monte Carlo algorithm and maximum entropy
+analytic continuation. At low temperatures where the charge degrees of freedom
+are gapped-out and $c_v$ exhibits a clear magnon peak, we observe that thermal
+conductivity $\kappa$ also tends to form a peak at similar temperatures.
+Reducing temperature further produces a sharp upturn in $\kappa$, associated
+with an increasing mean-free path. We identify this as the high-temperature
+side of the anomalous peak in insulating cuprates, where the mean-free path
+eventually is cut-off by other scattering effects, including phonons, disorder,
+and physical size. Different scattering effects in our model are identified and
+analyzed in the thermal diffusivity.",2109.01119v2
+2021-12-10,"Observation and control of collective spin-wave mode-hybridisation in chevron arrays and square, staircase and brickwork artificial spin ices","Dipolar magnon-magnon coupling has long been predicted in nano-patterned
+artificial spin systems. However, observation of such phenomena and related
+collective spin-wave signatures have until recently proved elusive or limited
+to low-power edge-modes which are difficult to measure experimentally. Here we
+describe the requisite conditions for dipolar mode-hybridisation, how it may be
+controlled, why it was not observed earlier and how strong coupling may occur
+between nanomagnet bulk-modes. We experimentally investigate four
+nano-patterned artificial spin system geometries: `chevron' arrays, `square',
+`staircase' and `brickwork' artificial spin ices. We observe significant
+dynamic dipolar-coupling in all systems with relative coupling strengths and
+avoided-crossing gaps supported by micromagnetic-simulation results. We
+demonstrate reconfigurable mode-hybridisation regimes in each system via
+microstate control, and in doing so elucidate the underlying dynamics governing
+dynamic dipolar-coupling with implications across reconfigurable magnonics. We
+demonstrate that confinement of the bulk-modes via edge effects play a critical
+role in dipolar hybridised-modes, and treating nanoislands as a coherently
+precessing macro-spins or standing spin-waves are insufficient to capture
+experimentally-observed coupling phenomena. Finally, we present a
+parameter-space search detailing how coupling strength may be tuned via
+nanofabrication-dimensions and material properties.",2112.05354v1
+2021-12-10,Impact of the interfacial Dzyaloshinskii-Moriya interaction on the band structure of one-dimensional artificial magnonic crystals: a micromagnetic study,"We present the results of a systematic micromagnetic study of the effect of
+the Dzyaloshinskii-Moriya interaction (DMI) on the spin wave band structure of
+two one-dimensional magnonic crystals (MCs), both with the same periodicity
+p=300 nm, but different implementation of the DMI modulation. In the first
+system the artificial periodicity was achieved by modulating the interfacial
+DMI constant D, while in the second system also the sample morphology was
+modulated. Due to the folding property of the band structure in the dispersion
+relations of the magnonic crystals it is possible to extend the sensitivity of
+Brillouin light scattering towards weak DMI strength (D in the range from 0 to
+0.5 mJ/m2), by measuring the frequency splitting of folded modes in high-order
+artificial Brillouin zones, since the splitting increases almost linearly with
+the band index. For relatively large values of the DMI (D in the range from 1.0
+to 2.0 mJ/m2) the spin waves dispersion relations present flat modes for
+positive wavevectors, separated by forbidden frequency gaps whose amplitude
+depend on the value of D. These frequency gaps are more pronounced for the
+sample with morphology modulation. The non-reciprocal, localised, spatial
+profiles of these modes in both MCs are discussed with reference to spin waves
+in plain films and in isolated stripes of the same thickness.",2112.05360v1
+2021-12-11,Anisotropic long-range spin transport in canted antiferromagnetic orthoferrite YFeO$_3$,"In antiferromagnets, the efficient propagation of spin-waves has until now
+only been observed in the insulating antiferromagnet hematite, where circularly
+(or a superposition of pairs of linearly) polarized spin-waves propagate over
+long distances. Here, we report long-distance spin-transport in the
+antiferromagnetic orthoferrite YFeO$_3$, where a different transport mechanism
+is enabled by the combined presence of the Dzyaloshinskii-Moriya interaction
+and externally applied fields. The magnon decay length is shown to exceed
+hundreds of nano-meters, in line with resonance measurements that highlight the
+low magnetic damping. We observe a strong anisotropy in the magnon decay
+lengths that we can attribute to the role of the magnon group velocity in the
+propagation of spin-waves in antiferromagnets. This unique mode of transport
+identified in YFeO$_3$ opens up the possibility of a large and technologically
+relevant class of materials, i.e., canted antiferromagnets, for long-distance
+spin transport.",2112.05947v1
+2021-12-15,Decoupling of static and dynamic criticality in a driven Mott insulator,"Dynamically driven interacting quantum many-body systems have the potential
+to exhibit properties that defy the laws of equilibrium statistical mechanics.
+A widely studied model is the impulsively driven antiferromagnetic Mott
+insulator, which is predicted to realize exotic transient phenomena including
+dynamical phase transitions into thermally forbidden states and highly
+non-thermal magnon distributions. However such far-from-equilibrium regimes,
+where conventional time-dependent Ginzburg-Landau descriptions fail, are
+experimentally challenging to prepare and to probe especially in solid state
+systems. Here we use a combination of time-resolved second harmonic optical
+polarimetry and coherent magnon spectroscopy to interrogate $n$-type
+photo-doping induced ultrafast magnetic order parameter dynamics in the Mott
+insulator Sr$_2$IrO$_4$. We uncover an unusual far-from-equilibrium critical
+regime in which the divergences of the magnetic correlation length and
+relaxation time are decoupled. This violation of conventional thermal critical
+behavior arises from the interplay of photo-doping and non-thermal magnon
+population induced demagnetization effects. Our findings, embodied in a
+non-equilibrium ""phase diagram"", provide a blueprint for engineering the
+out-of-equilibrium properties of quantum matter, with potential applications to
+terahertz spintronics technologies.",2112.08397v1
+2021-12-28,"Phonon, Electron, and Magnon Excitations in Antiferromagnetic L1$_{0}$-type MnPt","Antiferromagnetic L1$_{0}$-type MnPt is a material with relatively simple
+crystal and magnetic structure, recently attracting interest due to its high
+N{\'{e}}el temperature and wide usage as a pinning layer in magnetic devices.
+While it is experimentally well characterized, the theoretical understanding is
+much less developed, in part due to the challenging accuracy requirements
+dictated by the small underlying energy scales that govern magnetic ordering in
+antiferromagnetic metals. In this work, we use density functional theory, the
+Korringa-Kohn-Rostoker formalism, and a Heisenberg model to establish a
+comprehensive theoretical description of antiferromagnetic L1$_{0}$-type MnPt,
+along with accuracy limits, by thoroughly comparing to available literature
+data. Our simulations show that the contribution of the magnetic dipole
+interaction to the magnetocrystalline anisotropy energy of $K_{1}$=1.07$\times
+10^{6}$\,J/m$^3$ is comparable in magnitude to the spin-orbit contribution.
+Using our result for the magnetic susceptibility of $5.25\times10^{-4}$, a
+lowest magnon frequency of about 2.02\,THz is predicted, confirming THz spin
+dynamics in this material. From our data for electron, phonon, and magnon
+dispersion we compute the individual contributions to the total heat capacity
+and show that the dominant term at or above 2\,K arises from phonons. From the
+Landau-Lifshitz-Gilbert equation, we compute a N\'{e}el temperature of
+990--1070 K. Finally, we quantify the magnitude of the magneto-optical Kerr
+effect generated by applying an external magnetic field. Our results provide
+insight into the underlying physics, which is critical for a deep understanding
+of fundamental limits of the time scale of spin dynamics, stability of the
+magnetic ordering, and the possibility of magneto-optical detection of
+collective spin motion.",2112.13954v1
+2022-03-22,"Towards lattice-gas description of low-temperature properties above the Haldane and cluster-based Haldane ground states of a mixed spin-(1,1/2) Heisenberg octahedral chain","The rich ground-state phase diagram of the mixed spin-(1,1/2) Heisenberg
+octahedral chain was previously elaborated from effective mixed-spin Heisenberg
+chains, which were derived by employing a local conservation of a total spin on
+square plaquettes of an octahedral chain. Here we present a comprehensive
+analysis of the thermodynamic properties of this model. In the highly
+frustrated parameter region the lowest-energy eigenstates of the mixed-spin
+Heisenberg octahedral chain belong to flat bands, which allow a precise
+description of low-temperature magnetic properties within the localized-magnon
+approach exploiting a classical lattice-gas model of hard-core monomers. The
+present article provides a more comprehensive version of the localized-magnon
+approach, which extends the range of its validity down to a less frustrated
+parameter region involving the Haldane and cluster-based Haldane ground states.
+A comparison between results of the developed localized-magnon theory and
+accurate numerical methods such as full exact diagonalization and
+finite-temperature Lanczos technique convincingly evidence that the
+low-temperature magnetic properties above the Haldane and the cluster-based
+Haldane ground states can be extracted from a classical lattice-gas model of
+hard-core monomers and dimers, which is additionally supplemented by a
+hard-core particle spanned over the whole lattice representing the gapped
+Haldane phase.",2203.11569v1
+2022-04-04,Measuring a population of spin waves from the electrical noise of an inductively coupled antenna,"We study how a population of spin waves can be characterized from the
+analysis of the electrical microwave noise delivered by an inductive antenna
+placed in its vicinity. The measurements are conducted on a synthetic
+antiferromagnetic thin stripe covered by a micron-sized antenna that feeds a
+spectrum analyser after amplification. The antenna noise contains two
+contributions. The population of incoherent spin waves generates a fluctuating
+field that is sensed by the antenna: this is the ""magnon noise"". The antenna
+noise also contains the contribution of the electronic fluctuations: the
+Johnson-Nyquist noise. The latter depends on all impedances within the
+measurement circuit, which includes the antenna self-inductance. As a result,
+the electronic noise contains information about the magnetic susceptibility of
+the stripe, though it does not inform on the absolute amplitude of the magnetic
+fluctuations. For micrometer-sized systems at thermal equilibrium, the
+electronic noise dominates and the pure magnon noise cannot be determined. If
+in contrast the spinwave bath is not at thermal equilibrium with the
+measurement circuit, and if the spin wave population can be changed then one
+could measure a mode-resolved effective magnon temperature provided specific
+precautions are implemented.",2204.01427v2
+2022-05-24,Emission of coherent THz magnons in an antiferromagnetic insulator triggered by ultrafast spin-phonon interactions,"Antiferromagnetic materials have been proposed as new types of narrowband THz
+spintronic devices owing to their ultrafast spin dynamics. Manipulating
+coherently their spin dynamics, however, remains a key challenge that is
+envisioned to be accomplished by spin-orbit torques or direct optical
+excitations. Here, we demonstrate the combined generation of broadband THz
+(incoherent) magnons and narrowband (coherent) magnons at 1 THz in low damping
+thin films of NiO/Pt. We evidence, experimentally and through modelling, two
+excitation processes of magnetization dynamics in NiO, an off-resonant
+instantaneous optical spin torque and a strain-wave-induced THz torque induced
+by ultrafast Pt excitation. Both phenomena lead to the emission of a THz signal
+through the inverse spin Hall effect in the adjacent heavy metal layer. We
+unravel the characteristic timescales of the two excitation processes found to
+be < 50 fs and > 300 fs, respectively, and thus open new routes towards the
+development of fast opto-spintronic devices based on antiferromagnetic
+materials.",2205.11965v1
+2022-07-08,Measuring the magnon-photon coupling in shaped ferromagnets: tuning of the resonance frequency,"Cavity photons and ferromagnetic spins excitations can exchange information
+coherently in hybrid architectures, at speeds set by their mutual coupling
+strength. Speed enhancement is usually achieved by optimizing the geometry of
+the electromagnetic cavity. Here we show that the geometry of the ferromagnet
+plays also an important role, by setting the fundamental frequency of the
+magnonic resonator. Using focused ion beam patterning, we vary the aspect ratio
+of different Permalloy samples reaching operation frequencies above 10 GHz
+while working at low external magnetic fields. Additionally, we perform broad
+band ferromagnetic resonance measurements and cavity experiments that
+demonstrate that the magnon-photon coupling strength can be estimated using
+either open transmission lines or resonant cavities, yielding very good
+agreement. Finally, we describe a simple theoretical framework based on
+electromagnetic and micromagnetic simulations that successfully accounts for
+the experimental results. This approach can be used to design hybrid quantum
+systems exploiting whatsoever magnetostatic mode excited in ferromagnets of
+arbitrary size and shape and to tune their operation conditions.",2207.03829v3
+2022-09-09,Thermal Hall conductivity with sign change in the Heisenberg-Kitaev kagome magnet,"The Heisenberg-Kitaev (HK) model on various lattices have attracted a lot of
+attention because they may lead to exotic states such as quantum spin liquid
+and topological orders. The rare-earth-based kagome lattice (KL) compounds
+$\rm{Mg_2RE_3Sb_3O_{14}}$ $\rm{(RE=Gd, Er)}$ and $\rm{(RE=Nd)}$ have ${\bf
+q=0}$, $120^\circ$ order and canted ferromagnetic (CFM) order, respectively.
+Interestingly, the HK model on the KL has the same ground state long-range
+orders. In the theoretical phase diagram, the CFM phase resides in a continuous
+parameter region and there is no phase change across special parameter points,
+such as the Kitaev ferromagnetic (KFM) point, the ferromagnetic (FM) point and
+its dual FM point. However, a ground state property cannot distinguish a system
+with or without topological nontrivial excitations and related phase
+transitions. Here, we study the topological magnon excitations and related
+thermal Hall conductivity in the HK model on the KL with CFM order. The CFM
+phase can be divided into two regions related by the Klein duality, with the
+self dual KFM point as their boundary. We find that the scalar spin chirality
+which is intrinsic in the CFM order changes sign across the KFM point. This
+leads to the opposite Chern numbers of corresponding magnon bands in the two
+regions, and also the sign change of the magnon thermal Hall conductivity.",2209.04133v1
+2022-09-12,Unidirectional propagation of spin waves excited by femtosecond laser pulses in a planar waveguide,"Low-energy magnonic logic circuits are an actively developing field of modern
+magnetism. The potential benefits of magnonics for data processing are vitally
+dependent on units based on non-reciprocal propagation of spin waves in analogy
+to semiconductor diodes and transistors in electronics. In this article, we
+suggest the approach to realize non-reciprocal propagation of spin waves in a
+ferromagnetic metallic waveguide by exciting them with femtosecond laser pulse.
+Using micromagnetic modeling, we show that the combination of an external
+magnetic field and the position of the excitation laser spot across the
+waveguide leads to unidirectional propagation of the excited spin-wave packet.
+The results are crucial for the design of hybrid magnonic-photonic circuits in
+future generations of data processing devices.",2209.05611v3
+2022-11-21,Excitonic instability towards a Potts-nematic quantum paramagnet,"Magnetic frustration can lead to peculiar magnetic orderings that break a
+discrete symmetry of the lattice in addition to the fundamental magnetic
+symmetries (i.e., spin rotation invariance and time-reversal symmetry). In this
+work, we focus on frustrated quantum magnets and study the nature of the
+quantum phase transition between a paramagnet and a magnetically ordered state
+with broken threefold ($Z_3$) crystal rotation symmetry. We predict the
+transition to happen in two stages, giving rise to an intermediate nematic
+phase in which rotation symmetry is broken but the system remains magnetically
+disordered. The nematic transition is described by the three-state Potts model.
+This prediction is based on an analysis of bound states formed from two-magnon
+excitations in the paramagnet, which become gapless while single-magnon
+excitations remain gapped. By considering three different lattice models, we
+demonstrate a generic instability towards two-magnon bound state formation in
+the Potts-nematic nematic channel. We present both numerical results and a
+general analytical perturbative formula for the bound state binding energy
+similar to BCS theory. We further discuss a number of different materials that
+realize key features of the model considered, and thus provide promising venues
+for possible experimental observation.",2211.11739v1
+2023-01-07,High-efficiency entanglement of microwave fields in cavity opto-magnomechanical systems,"We demonstrate a scheme to realize high-efficiency entanglement of two
+microwave fields in a dual opto-magnomechanical system. The magnon mode
+simultaneously couples with the microwave cavity mode and phonon mode via
+magnetic dipole interaction and magnetostrictive interaction, respectively.
+Meanwhile, the phonon mode couples with the optical cavity mode via radiation
+pressure. Each magnon mode and optical cavity mode adopts a strong red detuning
+driving field to activate the beam splitter interaction. Therefore, the
+entangled state generated by the injected two-mode squeezed light in optical
+cavities can be eventually transferred into two microwave cavities. A
+stationary entanglement E_{a_{1}a_{2}}=0.54 is obtained when the input two-mode
+squeezed optical field has a squeezing parameter r=1. The entanglement
+E_{a_{1}a_{2}} increases as the squeezing parameter r increases, and it shows
+the flexible tunability of the system. Meanwhile, the entanglement survives up
+to an environmental temperature about 385 mK, which shows high robustness of
+the scheme. The proposed scheme provides a new mechanism to generate entangled
+microwave fields via magnons, which enables the degree of the prepared
+microwave entanglement to a more massive scale. Our result is useful for
+applications which require high entanglement of microwave fields like quantum
+radar, quantum navigation, quantum teleportation, quantum wireless fidelity
+(Wi-Fi) network, etc.",2301.02808v2
+2023-01-18,"Magnons, Phonons, and Thermal Hall Effect in Candidate Kitaev Magnet $α$-RuCl$_3$","We study the nature of the debated thermal Hall effect in the candidate
+Kitaev material $\alpha$-RuCl$_3$. Without assuming the existence of a gapped
+spin liquid, we show that a realistic minimal spin model in the canted zigzag
+phase suffices, at the level of linear spin-wave theory, to qualitatively
+explain the observed temperature and magnetic field dependence of the
+non-quantized thermal Hall conductivity $\kappa_{xy}$, with its origin lying in
+the Berry curvature of the magnon bands. The magnitude of the effect is however
+too small compared to the measurement by Czajka et al. [Nat. Mater. 22, 36-41
+(2023)], even after scanning a broad range of model parameters so as to
+maximize $\kappa_{xy}/T$. Recent experiments suggest that phonons play an
+important role, which we show couple to the spins, endowing phonons with
+chirality. The resulting intrinsic contribution, from both magnons and phonons,
+is however still insufficient to explain the observed magnitude of the Hall
+signal. After careful analysis of the extrinsic phonon mechanisms, we use the
+recent experimental data on thermal transport in $\alpha$-RuCl$_3$ by
+Lefran\c{c}ois et al. [Phys. Rev. X 12, 021025 (2022)] to determine the
+phenomenological ratio of the extrinsic and intrinsic contributions $\eta\equiv
+\kappa_{xy}^{E}/\kappa_{xy}^{I}$. We find $\eta=1.2\pm 0.5$, which when
+combined with our computed intrinsic value, explains quantitavely both the
+magnitude and detailed temperature dependence of the experimental thermal Hall
+effect in $\alpha$-RuCl$_3$.",2301.07401v2
+2023-02-02,Ultrastrong Magnon-Photon Coupling Achieved by Magnetic Films in Contact with Superconducting Resonators,"Coherent coupling between spin wave excitations (magnons) and microwave
+photons in a cavity may disclose new paths to unconventional phenomena as well
+as for novel applications. Here, we present a systematic investigation on YIG
+(Yttrium Iron Garnet) films on top of coplanar waveguide resonators made of
+superconducting YBCO. We first show that spin wave excitations with frequency
+higher than the Kittel mode can be excited by putting in direct contact a
+5~$\mu$m thick YIG film with the YBCO coplanar resonator (cavity frequency
+$\omega_c/2 \pi = 8.65$~GHz). With this configuration, we obtain very large
+values of the collective coupling strength $\lambda/2 \pi \approx 2$~GHz and
+cooperativity $C=5 \times 10^4$. Transmission spectra are analyzed by a
+modified Hopfield model for which we provide an exact solution that allows us
+to well reproduce spectra by introducing a limited number of free parameters.
+It turns out that the coupling of the dominant magnon mode with photons exceeds
+0.2 times the cavity frequency, thus demonstrating the achievement of the
+ultrastrong coupling regime with this architecture. Our analysis also shows a
+vanishing contribution of the diamagnetic term which is a peculiarity of pure
+spin systems.",2302.00804v2
+2023-04-25,Bose-Einstein condensations of magnons in quantum magnets with spin-orbit coupling in a Zeeman field,"We study the response of a quantum magnet with spin-orbit coupling (SOC) to a
+Zeeman field by constructing effective actions and performing Renormalization
+Group (RG) analysis. There are several novel classes of quantum phase
+transitions at a low $ h_{c1} $ and an upper critical field $ h_{c2} $ driven
+by magnon condensations at commensurate (C-) or in-commensurate (IC-) momenta $
+0 < k_0 < \pi $. The intermediate IC- Skyrmion crystal (IC-SkX) phase is
+controlled by a line of fixed points in the RG flows labeled by $ k_0 $. We
+derive the relations between the quantum spin and the order parameters of the
+effective actions which determine the spin-orbital structures of the IC-SkX
+phase. We also analyze the operator contents near $ h_{c1} $ and $ h_{c2} $
+which determine the exotic excitation spectra inside the IC-SkX. The intrinsic
+differences between the magnon condensations at the C- and IC- momenta are
+explored. The two critical fields $ h_{c1} < h_{c2} $ and the intermediate
+IC-SkX phase could be a generic feature to any quantum magnets with SOC in a
+Zeeman field. Experimental implications to some materials or cold atom systems
+with SOC in a Zeeman field are presented.",2304.12612v1
+2023-04-26,Bond-dependent anisotropy and magnon decay in cobalt-based Kitaev triangular antiferromagnet,"The Kitaev model, a honeycomb network of spins with bond-dependent
+anisotropic interactions, is a rare example of having a quantum spin liquid
+ground state. Although most Kitaev model candidate materials eventually order
+magnetically due to inevitable non-Kitaev terms, their bond-dependent
+anisotropy manifests in unusual spin dynamics. It has recently been suggested
+that bond-dependent anisotropy can stabilise novel magnetic phases and exotic
+spin dynamics on the geometrically frustrated triangular lattice. However, few
+materials have been identified with simultaneous geometric frustration and
+bond-dependent anisotropy. Here, we report a frustrated triangular lattice with
+bond-dependent anisotropy in the cobalt-based triangular van der Waals
+antiferromagnet CoI2. Its momentum and energy-resolved spin dynamics exhibit
+substantial magnon breakdown and complex level repulsion, as measured by
+inelastic neutron scattering. A thorough examination of excitations in both the
+paramagnetic and magnetically ordered states reveals that the bond-dependent
+anisotropy is the origin of the spiral order and the magnon breakdown found in
+CoI2. Our result paves the way toward a new research direction for the Kitaev
+model with geometrical frustration.",2304.13236v3
+2023-04-29,Observation of linear magnetoelectric effect in a Dirac magnon antiferromagnet Cu$_3$TeO$_6$,"Cu$_3$TeO$_6$, a three-dimensional antiferromagnet forming a unique spin-web
+lattice of spin-1/2 Cu2+ ions below the Neel temperature T$_N$ = 62 K, has
+recently been found to exhibit topological Dirac or nodal magnon dispersion. In
+this study, we report the discovery of the linear magnetoelectric (ME) effects
+in Cu$_3$TeO$_6$ below TN. Our pyroelectric current measurements at a constant
+magnetic field (H) reveal a linear increase of electric polarization (P) with H
+for both P // H and P $\perp$ H configurations; a maximum P // [110] = 20
+$\mu$C/m$^2$ is obtained at u0H // [1-10] = 14 T, corresponding to a linear ME
+coefficient 1.8 ps/m. Magnetic point group analysis and Monte-Carlo simulations
+confirm that finite linear ME coefficients are allowed in the off-diagonal and
+diagonal ME tensor components, consistent with the magnetic point group of
+$\bar{3}'$. As the parity-time symmetry can be broken in the presence of H or
+electric field E in the linear ME materials, we envisage that Cu$_3$TeO$_6$
+should exhibit a H- or E-induced transformation in the topological magnon
+dispersion from a Dirac point/nodal line type into two Weyl point types.",2305.00215v1
+2023-08-10,Ferromagnetic monolayer with interfacial Dzyaloshinskii-Moriya interaction: magnon spectrum and effect of quenched disorder,"We discuss theoretically a ferromagnetic monolayer with an interfacial
+Dzyaloshinskii-Moriya interaction (iDMI) and a small axial anisotropy. It is
+shown that the system has a long-period cycloid magnetic order slightly
+distorted by the anisotropy whose modulation vector $\bf k$ can have several
+orientations. We find that due to iDMI-induced umklapp terms in the
+Hamiltonian, the spectrum of long-wavelength magnons is essentially
+anisotropic: it is linear and quadratic for momenta directed along and
+perpendicular to $\bf k$, respectively. Due to such a quasi-1D spectrum, the
+temperature correction to the mean spin value has a power-law singularity
+hampering the magnetic ordering at $T\ne0$. We demonstrate that the umklapps
+lead to a peculiar band structure of the magnon spectrum similar to electronic
+bands in solids. We discuss also the effect of vacancies and defect bonds on
+system properties at $T=0$. Owing to the quasi-1D character of the spectrum,
+the distortion of the cycloid structure by a single defect bond is described by
+the field of 1D electric dipole. As a result, even infinitesimal concentrations
+of defects $c$ destroy the long-range order and establish a short-range order
+whose correlation length shows a power-law dependence on $1/c$. Our findings
+should also be applicable to ultra-thin films with strong enough iDMI.",2308.05283v1
+2023-08-24,Dynamics of quantum spin-nematics: Comparisons with canted antiferromagnets,"The identification of spin-nematic states is challenging due to the absence
+of Bragg peaks. However, the study of dynamical physical quantities provides a
+promising avenue for characterizing these states. In this study, we investigate
+the dynamical properties of spin-nematic states in three-dimensional quantum
+spin systems in a magnetic field, using a two-component boson theory that
+incorporates magnons and bi-magnons. Our particular focus lies on the dynamical
+spin structure factor at zero temperature and the nuclear magnetic resonance
+(NMR) relaxation rate at finite temperatures. Our findings reveal that the
+dynamical structure factor does not exhibit any diverging singularity across
+momentum and frequency while providing valuable information about the form
+factor of bi-magnon states and the underlying structure of spin-nematic order.
+Furthermore, we find a temperature dependence in the NMR relaxation rate
+proportional to $T^3$ at low temperatures, similar to canted antiferromagnets.
+A clear distinction arises as there is no critical divergence of the NMR
+relaxation rate at the spin-nematic transition temperature. Our theoretical
+framework provides a comprehensive understanding of the excitation spectrum and
+the dynamical properties of spin-nematic states, covering arbitrary spin values
+$S$ and encompassing site and bond nematic orders. Additionally, we apply the
+same methodology to analyze these dynamical quantities in a canted
+antiferromagnetic state and compare the results with those in the spin-nematic
+states.",2308.12569v2
+2023-09-06,Universal spin wavepacket transport in van der Waals antiferromagnets,"Antiferromagnets (AFMs) are promising platforms for the transmission of
+quantum information via magnons (the quanta of spin waves), offering advantages
+over ferromagnets with regard to dissipation, speed of response, and immunity
+to external fields. Recently, it was shown that in the insulating van der Waals
+(vdW) semiconductor, CrSBr, strong spin-exciton coupling enables readout of
+magnon density and propagation using photons of visible light. This exciting
+observation came with a puzzle: photogenerated magnons were observed to
+propagate 10$^3$ times faster than the velocity inferred from neutron
+scattering, leading to a conjecture that spin wavepackets are carried along by
+coupling to much faster elastic modes. Here we show, through a combination of
+theory and experiment, that the propagation mechanism is, instead, coupling
+within the magnetic degrees of freedom through long range dipole-dipole
+coupling. This mechanism is an inevitable consequence of Maxwell's equations,
+and as such, will dominate the propagation of spin at long wavelengths in the
+entire class of vdW magnets currently under intense investigation. Moreover,
+identifying the mechanism of spin propagation provides a set of optimization
+rules, as well as caveats, that are essential for any future applications of
+these promising systems.",2309.03278v1
+2023-10-06,Antiferromagnetic magnonic charge current generation via ultrafast optical excitation,"N\'eel spin-orbit torque allows a charge current pulse to efficiently
+manipulate the N\'eel vector in antiferromagnets, which offers a unique
+opportunity for ultrahigh density information storage with high speed. However,
+the reciprocal process of N\'eel spin-orbit torque, the generation of ultrafast
+charge current in antiferromagnets has not been demonstrated. Here, we report
+the experimental observation of charge current generation in antiferromagnetic
+metallic Mn2Au thin films using ultrafast optical excitation. The ultrafast
+laser pulse excites antiferromagnetic magnons, resulting in instantaneous
+non-equilibrium spin polarization at the antiferromagnetic spin sublattices
+with broken spatial symmetry. Then the charge current is generated directly via
+spin-orbit fields at the two sublattices, which is termed as the reciprocal
+phenomenon of N\'eel spin-orbit torque, and the associated THz emission can be
+detected at room temperature. Besides the fundamental significance on the
+Onsager reciprocity, the observed magnonic charge current generation in
+antiferromagnet would advance the development of antiferromagnetic THz emitter.",2310.03987v1
+2023-10-09,Mapping of Spin-Wave Transport in Thulium Iron Garnet Thin Films Using Diamond Quantum Microscopy,"Spin waves, collective dynamic magnetic excitations, offer crucial insights
+into magnetic material properties. Rare-earth iron garnets offer an ideal
+spin-wave (SW) platform with long propagation length, short wavelength,
+gigahertz frequency, and applicability to magnon spintronic platforms. Of
+particular interest, thulium iron garnet (TmIG) has attracted a huge interest
+recently due to its successful growth down to a few nanometers, observed
+topological Hall effect and spin orbit torque-induced switching effects.
+However, there is no direct spatial measurement of its SW properties. This work
+uses diamond nitrogen vacancy (NV) magnetometry in combination with SW
+electrical transmission spectroscopy to study SW transport properties in TmIG
+thin films. NV magnetometry allows probing spin waves at the sub-micrometer
+scale, seen by the amplification of the local microwave magnetic field due to
+the coupling of NV spin qubits with the stray magnetic field produced by the
+microwave-excited spin waves. By monitoring the NV spin resonances, the SW
+properties in TmIG thin films are measured as function of the applied magnetic
+field, including their amplitude, decay length (~ 50 um), and wavelength (0.8 -
+2 um). These results pave the way for studying spin qubit-magnon interactions
+in rare-earth magnetic insulators, relevant to quantum magnonics applications.",2310.06188v4
+2023-10-23,Microscopic theory of spin Seebeck effect in antiferromagnets,"We develop a microscopic theory for the spin Seebeck effect (SSE) in N\'eel
+and canted phases of antiferromagnetic insulators. We calculate the DC spin
+current tunneling from the antiferromagnet to an attached metal, incorporating
+the spin-wave theory and the non-equilibrium Green's function approach. Our
+result shows a sign change of the spin current at the spin-flop phase
+transition between N\'eel and canted phases, which is in agreement with a
+recent experiment for the SSE of $\rm Cr_2O_3$ in a semi-quantitative level.
+The sign change can be interpreted from the argument based on the density of
+states of up- and down-spin magnons, which is related to the polarized-neutron
+scattering spectra. The theory also demonstrates that the spin current in the
+N\'eel phase is governed by the magnon correlation, while that in the canted
+phase consists of two parts: Contributions from not only the magnon dynamics
+but also the static transverse magnetization. This result leads to a prediction
+that at sufficiently low temperatures, the spin current non-monotonically
+changes as a function of magnetic field in the canted phase. Towards a more
+unified understanding of the SSE in antiferromagnets, we further discuss some
+missing links of theories of SSE: Interface properties, effects of the
+transverse spin moment in the canted phase, the spin-orbit coupling in the
+metal, etc. Finally, we compare the SSE of antiferromagnets with those of
+different magnetic phases such as ferromagnets, ferrimagnets, an
+one-dimensional spin liquid, a spin-nematic liquid, and a spin-Peierls
+(dimerized) phase.",2310.15292v2
+2023-11-22,Quantum spin dynamics due to strong Kitaev interactions in the triangular-lattice antiferromagnet CsCeSe$_2$,"The extraordinary properties of the Kitaev model have motivated an intense
+search for new physics in materials that combine geometrical and bond
+frustration. In this work, we employ inelastic neutron scattering, spin wave
+theory, and exact diagonalization to study the spin dynamics in the perfect
+triangular-lattice antiferromagnet (TLAF) CsCeSe$_2$. This material orders into
+a stripe phase, which is demonstrated to arise as a consequence of the
+off-diagonal bond-dependent terms in the spin Hamiltonian. By studying the spin
+dynamics at intermediate fields, we identify an interaction between the
+single-magnon state and the two-magnon continuum that causes decay of coherent
+magnon excitations, level repulsion, and transfer of spectral weight to the
+continuum that are controlled by the strength of the magnetic field. Our
+results provide a microscopic mechanism for the stabilization of the stripe
+phase in TLAF and show how complex many-body physics can be present in the spin
+dynamics in a magnet with strong Kitaev coupling even in an ordered ground
+state.",2311.13146v2
+2023-11-28,Quantum Fluctuations in a Weakly Correlated Mott Insulator,"Quantum fluctuations in low-dimensional systems and near quantum phase
+transitions have significant influences on material properties. Yet, it is
+difficult to experimentally gauge the strength and importance of quantum
+fluctuations. Here we provide a resonant inelastic x-ray scattering study of
+magnon excitations in Mott insulating cuprates. From the thin film of
+SrCuO$_2$, single- and bi-magnon dispersions are derived. Using an effective
+Heisenberg Hamiltonian generated from the Hubbard model, we show that the
+single magnon dispersion is only described satisfactorily when including
+significant renormalization stemming from quantum fluctuations. Comparative
+results on La$_2$CuO$_4$ indicate that quantum fluctuations are much stronger
+in SrCuO$_2$ suggesting closer proximity to a magnetic quantum critical point.
+Monte Carlo calculations suggest an exotic incommensurate magnetic order as the
+ground state that competes with the antiferromagnetic N\'eel order. Our results
+indicate that SrCuO$_2$ -- due to strong quantum fluctuations -- is a unique
+starting point for the exploration of novel magnetic ground states.",2311.16553v1
+2023-11-29,Nonlinear erasing of propagating spin-wave pulses in thin-film Ga:YIG,"Nonlinear phenomena are key for magnon-based information processing, but the
+nonlinear interaction between two spin-wave signals requires their
+spatio-temporal overlap which can be challenging for directional processing
+devices. Our study focuses on a gallium-substituted yttrium iron garnet film,
+which exhibits an exchange-dominated dispersion relation and thus provides a
+particularly broad range of group velocities compared to pure YIG. Using time-
+and space-resolved Brillouin light scattering spectroscopy, we demonstrate the
+excitation of time-separated spin-wave pulses at different frequencies from the
+same source, where the delayed pulse catches up with the previously excited
+pulse and outruns it due to its higher group velocity. By varying the
+excitation power of the faster pulse, the outcome can be finely tuned from a
+linear superposition to a nonlinear interaction of both pulses, resulting in a
+full attenuation of the slower pulse. Therefore, our findings demonstrate the
+all-magnonic erasing process of a propagating magnonic signal, which enables
+the realization of complex temporal logic operations with potential
+application, e.g., in inhibitory neuromorphic functionalities.",2311.17821v2
+2024-02-24,Steerable current-driven emission of spin waves in magnetic vortex pairs,"The efficient excitation of spin waves is a key challenge in the realization
+of magnonic devices. We demonstrate the current-driven generation of spin waves
+in antiferromagnetically coupled magnetic vortices. We employ time-resolved
+scanning transmission X-ray microscopy (TR-STXM) to directly image the emission
+of spin waves upon the application of an alternating current flowing directly
+through the magnetic stack. Micromagnetic simulations allow us to identify the
+origin of the excitation to be the current-driven Oersted field, which in the
+present system proves to be orders of magnitude more efficient than the
+commonly used excitation via stripline antennas. Our numerical studies also
+reveal that the spin-transfer torque can lead to the emission of spin waves as
+well, yet only at much higher current amplitudes. By using magnetostrictive
+materials, we futhermore demonstrate that the direction of the magnon
+propagation can be steered by increasing the excitation amplitude, which
+modifies the underlying magnetization profile through an additional anisotropy
+in the magnetic layers. The demonstrated methods allow for the efficient and
+tunable excitation of spin waves, marking a significant advance in the
+generation and control of spin waves in magnonic devices.",2402.15831v1
+2024-03-14,"Stoner ferromagnetism, correlated metal and thermoelectricity in partially flat-band materials","Recent discovery of correlated electronic phases in twisted heterostructures
+raised a surge of interests in studying models and materials with flat bands
+where the electronic excitations are nearly dispersionless in momentum space.
+As such, the kinetic energy is quenched and the correlations are enhanced,
+giving rise to a plethora of unusual magnetic, superconducting and transport
+behaviors. Finding materials whose energy bands are completely flat is rather
+challenging, yet those whose dispersion is flat only in a portion of the
+momentum space might be more accessible in material search. In this work, we
+propose a partially flat-band system on a square lattice. Using the Hubbard
+model, it is demonstrated that the suppression of the electronic kinetic energy
+in the flat portion of the band dispersion drives the system to Stoner
+ferromagnetism even at very weak interactions, i.e., much smaller than the
+bandwidth, with significantly enhanced Curie temperature. While the low-energy
+magnon modes are well defined collective excitations, flat magnon bands can be
+observed at high energies. We show that the strong interaction leads to
+reduction of the flat portion of the magnon band. However, tuning the chemical
+potential at a strong interaction regime may lead to spin density wave at
+finite wave vectors. Then, focusing on the non-magnetic correlated phase and
+using dynamical mean-field theory, we demonstrate the appearance of a flat-band
+induced sharp peak in the density of states in addition to the
+correlation-induced Mott bands. Furthermore, the large seebeck coefficient and
+the figure of merit of the proposed partially flat-band model, compared to
+symmetric regular band models, put them in the category of efficient
+thermoelectric materials.",2403.09147v1
+1993-06-16,Large-Scale Numerical Evidence for Bose Condensation in the S=1 Antiferromagnetic Chain in a Strong Field,"Using the recently proposed density matrix renormalization group technique we
+show that the magnons in the S=1 antiferromagnetic Heisenberg chain effectively
+behaves as bosons that condense at a critical field h_c.",9306036v1
+1997-11-10,Numerical Calculations of the B1g Raman Spectrum of the Two-Dimensional Heisenberg Model,"The B1g Raman spectrum of the two-dimensional S=1/2 Heisenberg model is
+discussed within Loudon-Fleury theory at both zero and finite temperature. The
+exact T=0 spectrum for lattices with up to 6*6 sites is computed using Lanczos
+exact diagonalization. A quantum Monte Carlo (QMC) method is used to calculate
+the corresponding imaginary-time correlation function and its first two
+derivatives for lattices with up to 16*16 spins. The imaginary-time data is
+continued to real frequency using the maximum-entropy method, as well as a fit
+based on spinwave theory. The numerical results are compared with spinwave
+calculations for finite lattices. There is a surprisingly large change in the
+exact spectrum going from 4*4 to 6*6 sites. In the former case there is a
+single dominant two-magnon peak at frequency w/J appr. 3.0, whereas in the
+latter case there are two approximately equal-sized peaks at w/J appr. 2.7 and
+3.9. This is in good qualitative agreement with the spinwave calculations
+including two-magnon processes on the same lattices. Both the Lanczos and the
+QMC results indicate that the actual infinite-size two-magnon profile is
+broader than the narrow peak obtained in spinwave theory, but the positions of
+the maxima agree to within a few percent. The higher-order contributions
+present in the numerical results are merged with the two-magnon profile and
+extend up to frequencies w/J appr. 7. The first three frequency cumulants of
+the spectrum are in excellent agreement with results previously obtained from a
+series expansion around the Ising limit. Typical experimental B1g$ spectra for
+La2CuO4 are only slightly broader than what we obtain here. The exchange
+constant extracted from the peak position is J appr. 1400K, in good agreement
+with values obtained from neutron scattering and NMR experiments.",9711083v1
+1998-04-01,The two-leg t-J ladder: a spin liquid generated by Gutzwiller projection of magnetic bands,"The ground state of the two-leg Heisenberg ladder is identified as an RVB
+type spin liquid, which is generated by Gutzwiller projection of tight-binding
+bands with flux pi per plaquet. Explicit trial wave functions for the magnon
+and hole excitations are formulated in terms of spinons and holons.",9804002v3
+1999-03-09,Skyrmion dynamics in quantum Hall ferromagnets,"Exploring a classical solution of the non-linear sigma model for a quantum
+Hall ferromagnet, a skyrmion-magnon effective hamiltonian is obtained via the
+collective coordinates method. Using the Feynman-Vernon functional integral
+formalism for this model we find the temperature dependent transport
+coefficients which characterize a single skyrmion dynamics.",9903143v1
+1999-08-26,Spin-1/2 periodic nonuniform XX chains and the spin-Peierls instability,"Using continued fractions we obtained the exact result for the density of
+magnon states of the regularly alternating spin-1/2 XX chain with
+Dzyaloshinskii-Moriya interaction. We examined the stability of the magnetic
+chain with respect to the spin-Peierls dimerization.",9908385v1
+2000-01-03,Spin-Peierls instability in the spin-1/2 transverse XX chain with Dzyaloshinskii-Moriya interaction,"We calculate exactly the density of magnon states of the regularly
+alternating spin-1/2 XX chain with Dzyaloshinskii-Moriya interaction. The
+obtained results permit us to examine the stability of the chain with respect
+to spin-Peierls dimerization. We found that depending on the dependences of
+Dzyaloshinskii-Moriya interaction on distortion amplitude it may act either in
+favour of the dimerization or against the dimerization.",0001014v1
+2002-03-13,Linear energy bounds for Heisenberg spin systems,"Recently obtained results on linear energy bounds are generalized to
+arbitrary spin quantum numbers and coupling schemes. Thereby the class of
+so-called independent magnon states, for which the relative ground-state
+property can be rigorously established, is considerably enlarged. We still
+require that the matrix of exchange parameters has constant row sums, but this
+can be achieved by means of a suitable gauge and need not be considered as a
+physical restriction.",0203270v1
+2005-06-02,N-leg integer-spin ladders and tubes in commensurate external fields -Nonlinear sigma model approach-,"We investigate the low-energy properties of N-leg integer-spin ladders and
+tubes with an antiferromagnetic (AF) intrachain coupling. In the odd-leg tubes,
+the AF rung coupling causes the frustration. To treat all ladders and tubes
+systematically, we apply S\'en\'echal's method [Phys. Rev. B 52, 15319 (1995)],
+based on the nonlinear sigma model. This strategy is valid in the weak
+interchain (rung) coupling regime. We show that all frustrated tubes possess
+six-fold degenerate spin-1 magnon bands, as the lowest excitations, while other
+ladders and tubes have a standard triply degenerate bands. We also consider
+effects of four kinds of Zeeman terms: uniform, staggered only along the rung,
+only along the chain, or both directions. The above prediction of the no-field
+case implies that a sufficiently strong uniform field yields a two-component
+Tomonaga-Luttinger liquid (TLL) due to the condensation of doubly degenerate
+lowest magnons in frustrated tubes. In contrast, the field induces a standard
+one-component TLL in all other systems. This is supported by symmetry and
+bosonization arguments based on the Ginzburg-Landau theory. The bosonization
+also suggests that the two-component TLL vanishes and a one-component TLL
+appears, when the uniform field becomes larger for the second lowest magnon
+bands to touch the zero-energy line. This transition could be observed as a
+cusp singularity in the magnetization process. All the analyses for the systems
+with a staggered Zeeman term suggest that the emergence of the doubly
+degenerate transverse magnons and the single longitudinal one is universal for
+the one-dimensional AF spin systems with weak staggered field.",0506049v3
+2007-01-24,Critical properties and Bose Einstein Condensation in dimer spin systems,"We analyze the spin relaxation time $1/T_1$ for a system made of weakly
+coupled one dimensional ladders.This system allows to probe the dimensional
+crossover between a Luttinger liquid and a Bose-Einstein condensateof magnons.
+We obtain the temperature dependence of $1/T_1$ in the various dimensional
+regimes, and discuss the experimental consequences.",0701590v1
+1999-03-02,Remarks on Goldstone bosons and hard thermal loops,"The hard thermal loop effective action for Goldstone bosons is deduced by
+symmetry arguments from the corresponding result for gauge bosons. Pseudoscalar
+mesons in Chromodynamics and magnons in an antiferromagnet are discussed as
+special cases, including the hard thermal loop contribution to their
+scattering.",9903232v1
+2002-01-15,Magnon-mediated NMR quantum gates in a 1-D antiferromagnet,"We propose a method of controlling a quantum logic gate in a solid-state NMR
+quantum computer. A switchable inter-qubit coupling can be generated by using
+the longitudinal component of the Suhl-Nakamura interaction induced by a local
+singlet-triplet excitation in a 1-D antiferromagnet with a spin gap.",0201060v1
+2005-05-17,Qubit entanglement in multimagnon states,"The qubit entanglement induced by quasiparticle excitations in the Heisenberg
+spin chain and its relationship to the Bethe Ansatz structure of the eigenmodes
+is studied. A phenomenon called entanglement quenching, which suppresses
+eigenstate entanglement, is described and shown to be mediated by Goldstone
+magnons. Scattering states are characterized by short-range entanglement, and
+never exhibit entanglement at the longest range. In contrast, bound states have
+complex long-range entanglement structures.",0505124v1
+2010-07-30,Energy relaxation in the Gross-Pitaevskii equation,"We introduce a dissipation term in the Gross-Pitaevskii equation that
+describes the stimulated relaxation of condensed bosons due to scattering with
+a different type of particles. This situation applies to Bose-Einstein
+condensates of quasi-particles in the solid state, such as magnons and
+excitons. Our model is compatible with the phenomenology of superfluidity:
+supercurrents are stable up to a critical speed and decay when they are faster.",1007.5453v1
+2010-08-02,Entanglement perturbation theory for the elementary excitation in one dimension,"The entanglement perturbation theory is developed to calculate the excitation
+spectrum in one dimension. Applied to the spin-$\frac{1}{2}$ antiferromagnetic
+Heisenberg model, it reproduces the des Cloiseaux-Pearson Bethe ansatz result.
+As for spin-1, the spin-triplet magnon spectrum has been determined for the
+first time for the entire Brillouin zone, including the Haldane gap at $k=\pi$.",1008.0346v1
+2011-06-28,Classical strings in $AdS_4\times\mathbb{CP}^3$ with three angular momenta,"In this paper, rotating strings in three directions of $AdS_4 \times
+\mathbb{CP}^3$ geometry are studied; its divergent energy limit, and conserved
+charges are also determined. An interpretation of these configurations as
+either giant magnons or spiky strings are discussed.",1106.5684v2
+2011-10-17,Divergent energy strings in $AdS_5\times S^5$ with three angular momenta,"In this paper, novel solutions for strings with three angular momenta in
+$AdS_5 \times S^5$ geometry are presented; the divergent energy limit and the
+corresponding conserved charges, as well as dispersion relation are also
+determined. Interpretations of these configurations as either a giant magnon
+(GM) or a spiky string (SS) are discussed.",1110.3682v2
+2013-04-02,Entanglement of one-magnon Schur-Weyl states,"We investigate the entanglement properties of symmetry states of the
+Schur-Weyl duality. Our approach based on reduced two-qubit density matrices,
+and concurrence as the measure of entanglement. We show that all kinds of
+entangled graphs, which describe the entanglement structure in Schur-Weyl
+states are completely coded in the corresponding Young tableau.",1304.0590v1
+2013-10-27,Fundamental limitations of half-metallicicity in spintronic materials,"Zero-point spin fluctuations are shown to strongly influence the ground state
+of ferromagnetic metals and to impose limitations for the fully spin polarized
+state assumed in half-metallic ferromagnets, which may influence their
+applications in spintronics. This phenomenon leads to the low-frequency Stoner
+excitations and cause strong damping and softening of magnons in
+magnetoresistive manganites observed experimentally.",1310.7174v1
+2014-02-25,Transverse magneto-optical Kerr effect in subwavelength dielectric gratings,"We demonstrate theoretically a large transverse magneto-optical Kerr effect
+(TMOKE) in subwavelength gratings consisting of alternating magneto-insulating
+and nonmagnetic dielectric nanostripes. The reflectivity of the grating reaches
+$96\%$ at the frequencies corresponding to the maximum of the TMOKE response.
+The combination of a large TMOKE response and high reflectivity is important
+for applications in $3$D imaging, magneto-optical data storage, and magnonics.",1402.6075v1
+2015-04-24,Signatures of indirect K-edge resonant inelastic x-ray scattering on magnetic excitations in triangular lattice antiferromagnet,"We compute the K-edge indirect resonant inelastic x-ray scattering (RIXS)
+spectrum of a triangular lattice antiferromagnet in its ordered coplanar 3-
+sublattice 120 degree magnetic state. By considering the first order
+self$-$energy corrections to the spin wave spectrum, magnon decay rate,
+bimagnon interactions within the ladder approximation Bethe-Salpeter scheme,
+and the effect of three-magnon contributions up to 1/S- order we find that the
+RIXS spectra is non-trivially affected. For a purely isotropic triangular
+lattice model, the peak splitting mechanism and the appearance of a multipeak
+RIXS structure is primarily dictated by the damping of magnon modes. At a
+scattering wavevector corresponding to the zone center \Gamma point and at the
+roton point q=M, where the magnon decay rate is zero, a stable single peak
+forms. At the $\Gamma$ point, the contribution is purely trimagnon at the 1/S
+level and occurs approximately at the trimagnon energy of 6JS. The roton peak
+occurs at a lower energy of 4JS. The K-edge single peak RIXS spectra at the
+roton momentum can be utilized as an experimental signature to detect the
+presence of roton excitations. A unique feature of the triangular lattice
+K-edge RIXS spectra is the nonvanishing RIXS intensity at both the zone center
+$\Gamma$ point and the antiferromagnetic wavevector K point. This result is in
+sharp contrast to the vanishing K-edge RIXS intensity of the collinear magnetic
+phases on the square lattice. We find that including XXZ anisotropy leads to
+additional peak splitting, including at the roton scattering wavevector where
+the single peak destabilizes towards a two-peak structure. The observed
+splitting is consistent with our earlier theoretical prediction of the effects
+of spatial anisotropy on the RIXS spectra of a frustrated quantum magnet [Luo,
+Datta, and Yao, Phys. Rev. B 89, 165103 (2014)].",1504.06609v1
+2012-01-25,Spin-Density-Wave Gap with Dirac Nodes and Two-Magnon Raman Scattering in BaFe2As2,"Raman selection rules for electronic and magnetic excitations in BaFe2As2
+were theoretically investigated and applied them to the separate detection of
+the nodal and anti-nodal gap excitations at the spin density wave (SDW)
+transition and the separate detection of the nearest and the next nearest
+neighbor exchange interaction energies. The SDW gap has Dirac nodes, because
+many orbitals participate in the electronic states near the Fermi energy. Using
+a two-orbital band model the electronic excitations near the Dirac node and the
+anti-node are found to have different symmetries. Applying the symmetry
+difference to Raman scattering the nodal and anti-nodal electronic excitations
+are separately obtained. The low-energy spectra from the anti-nodal region have
+critical fluctuation just above TSDW and change into the gap structure by the
+first order transition at TSDW, while those from the nodal region gradually
+change into the SDW state. The selection rule for two-magnon scattering from
+the stripe spin structure was obtained. Applying it to the two-magnon Raman
+spectra it is found that the magnetic exchange interaction energies are not
+presented by the short-range superexchange model, but the second derivative of
+the total energy of the stripe spin structure with respect to the moment
+directions. The selection rule and the peak energy are expressed by the
+two-magnon scattering process in an insulator, but the large spectral weight
+above twice the maximum spin wave energy is difficult to explain by the decayed
+spin wave. It may be explained by the electronic scattering of itinerant
+carriers with the magnetic self-energy in the localized spin picture or the
+particle-hole excitation model in the itinerant spin picture. The magnetic
+scattering spectra are compared to the insulating and metallic cuprate
+superconductors whose spins are believed to be localized.",1201.5207v1
+2019-02-01,Quantum thermodynamics of complex ferrimagnets,"High-quality magnets such as yttrium iron garnet (YIG) are electrically
+insulating and very complex. By implementing a quantum thermostat into
+atomistic spin dynamics we compute YIG's key thermodynamic properties, viz. the
+magnon power spectrum and specific heat, for a large temperature range. The
+results differ (sometimes spectacularly) from simple models and classical
+statistics, but agree with available experimental data.",1902.00449v1
+2019-03-13,"Dynamical structure factor of the $J_1-J_2$ Heisenberg model on the triangular lattice: magnons, spinons, and gauge fields","Understanding the nature of the excitation spectrum in quantum spin liquids
+is of fundamental importance, in particular for the experimental detection of
+candidate materials. However, current theoretical and numerical techniques have
+limited capabilities, especially in obtaining the dynamical structure factor,
+which gives a crucial characterization of the ultimate nature of the quantum
+state and may be directly assessed by inelastic neutron scattering. In this
+work, we investigate the low-energy properties of the $S=1/2$ Heisenberg model
+on the triangular lattice, including both nearest-neighbor $J_1$ and
+next-nearest-neighbor $J_2$ super-exchanges, by a dynamical variational Monte
+Carlo approach that allows accurate results on spin models. For $J_2=0$, our
+calculations are compatible with the existence of a well-defined magnon in the
+whole Brillouin zone, with gapless excitations at $K$ points (i.e., at the
+corners of the Brillouin zone). The strong renormalization of the magnon branch
+(also including roton-like minima around the $M$ points, i.e., midpoints of the
+border zone) is described by our Gutzwiller-projected state, where Abrikosov
+fermions are subject to a non-trivial magnetic $\pi$-flux threading half of the
+triangular plaquettes. When increasing the frustrating ratio $J_2/J_1$, we
+detect a progessive softening of the magnon branch at $M$, which eventually
+becomes gapless within the spin-liquid phase. This feature is captured by the
+band structure of the unprojected wave function (with $2$ Dirac points for each
+spin component). In addition, we observe an intense signal at low energies
+around the $K$ points, which cannot be understood within the unprojected
+picture and emerges only when the Gutzwiller projection is considered,
+suggesting the relevance of gauge fields for the low-energy physics of spin
+liquids.",1903.05691v3
+2016-10-20,Magnetic excitations in quasi-one dimensional helimagnets: Magnon decays and in uence of the inter-chain interactions,"We present a comprehensive study of the magnetic properties of the long-range
+ordered quasi-one dimensional $J_{1}$-$J_{2}$ systems with a newly developed
+torque equilibrium spin-wave expansion approach, which can describe the spin
+Casimir and magnon decay effects in a unified framework. While the framework
+does not lose the generality, our discussion will be restricted to two
+representative types of inter-chain coupling systems: $J_{3}$- or
+$J_{4}$-system respectively. In spite of the long-range spiral order, the
+dynamical properties of these systems turn out to be highly nontrivial due to
+the incommensurate noncollinear spin configuration and the strong quantum
+fluctuation effects enhanced by the frustration and low-dimensionality. Both
+the systems show prominent spin Casimir effects induced by the vacuum
+fluctuation of the spin waves and related modification of the ordering vector,
+Lifshitz point's position and sublattice magnetization. Significant and
+spontaneous magnon decay effects are manifested in the quantum corrections to
+the excitation spectrum. By adjusting the strength of magnetic anisotropy and
+varying the approximation scheme, it is revealed that these striking distinct
+features are quite robust and have deep connection with both the spin Casimir
+and the magnon decay effects. Thus these special consequences of the
+inter-chain coupling on the spin wave dynamics may be served as a set of probes
+for different types of inter-chain couplings in experiments. At last, to guide
+experimental measurements such as inelastic neutron scattering in realistic
+materials and complement our theoretical framework, we develop the analytical
+theory of the dynamical structure factor within the torque equilibrium
+formulism and provide the explicit results of the quasi-one dimensional
+$J_{1}$-$J_{2}$ systems.",1610.06365v2
+2019-05-10,Experimental Implementations of Cavity-Magnon Systems: from Ultra Strong Coupling to Applications in Precision Measurement,"Several experimental implementations of cavity-magnon systems are presented.
+First an Yttrium Iron Garnet (YIG) block is placed inside a re-entrant cavity
+where the resulting hybrid mode is measured to be in the ultra strong coupling
+regime. When fully hybridised the ratio between the coupling rate and uncoupled
+mode frequencies is determined to be $g/\omega=0.46$. Next a thin YIG cylinder
+is placed inside a loop gap cavity. The bright mode of this cavity couples to
+the YIG sample and is similarly measured to be in the ultra strong coupling
+regime with ratio of coupling rate to uncoupled mode frequencies as
+$g/\omega=0.34$. A larger spin density medium such as lithium ferrite (LiFe) is
+expected to improve couplings by a factor of 1.46 in both systems as coupling
+strength is shown to be proportional to the square root of spin density and
+magnetic moment. Such strongly coupled systems are potentially useful for
+cavity QED, hybrid quantum systems and precision dark matter detection
+experiments. The YIG disc in the loop gap cavity, is, in particular, shown to
+be a strong candidate for dark matter detection. Finally, a LiFe sphere inside
+a two post re-entrant cavity is considered. In past work it was shown that the
+magnon mode in the sample has a turnover point in frequency. Additionally, it
+was predicted that if the system was engineered such that it fully hybridised
+at this turnover point the cavity-magnon polariton (CMP) transition frequency
+would become insensitive to both first and second order magnetic bias field
+fluctuations, a result useful for precision frequency applications. This work
+implements such a system by engineering the cavity mode frequency to near this
+turnover point, with suppression in sensitivity to second order bias magnetic
+field fluctuations shown.",1905.04002v2
+2021-01-29,Topological magnons for thermal Hall transport in frustrated magnets with bond-dependent interactions,"Thermal transport in topologically-ordered phases of matter provides valuable
+insights as it can detect the charge-neutral quasiparticles that would not
+directly couple to electromagnetic probes. An important example is edge heat
+transport of Majorana fermions in a chiral spin liquid, which leads to a
+half-quantized thermal Hall conductivity. This signature is precisely what has
+recently been measured in $\alpha$-RuCl$_3$ under external magnetic fields. The
+plateau-like behavior of the half-quantized thermal Hall conductivity as a
+function of external magnetic field, and the peculiar sign change depending on
+the magnetic field orientation, has been proposed as strong evidence for the
+non-Abelian Kitaev spin liquid. Alternatively, for in-plane magnetic fields, it
+was theoretically shown that such a sign structure can also arise from
+topological magnons in the field-polarized state. In this work, we investigate
+the full implications of topological magnons as heat carriers on thermal
+transport measurements. We first prove analytically that for any commensurate
+order with a finite magnetic unit cell, reversing the field direction leads to
+a sign change in the magnon thermal Hall conductivity in two-dimensional
+systems. We verify this proof numerically with nontrivial magnetic orders as
+well as the field-polarized state in Kitaev magnets subjected to an in-plane
+field. In the case of a tilted magnetic field, whereby there exist both finite
+in-plane and out-of-plane field components, we find that the plateau-like
+behavior of the thermal Hall conductivity and the sign change upon reversing
+the in-plane component of the magnetic field arise in the partially-polarized
+state, as long as the in-plane field contribution to the Zeeman energy is
+significant. While these results are consistent with the experimental
+observations, we comment on other aspects requiring investigation in future
+studies.",2102.00014v2
+2018-08-17,Collective excitations in spin-1/2 magnets through bond-operator formalism designed both for paramagnetic and ordered phases,"We present a bond-operator theory (BOT) suitable for description both
+magnetically ordered phases and paramagnetic phases with singlet ground states
+in spin-1/2 magnets. Proposed BOT provides a regular expansion of physical
+quantities in powers of 1/n, where n is the maximum number of bosons which can
+occupy a unit cell (physical results correspond to n=1). Two variants of BOT
+are suggested: for two and for four spins in the unit cell (two-spin and
+four-spin BOTs, respectively). We consider spin-1/2 Heisenberg antiferromagnet
+(HAF) on simple square lattice bilayer by the two-spin BOT. Ground-state energy
+E, staggered magnetization M, and quasiparticles spectra found within the first
+order in 1/n are in good quantitative agreement with previous results both in
+paramagnetic and in ordered phases not very close to the quantum critical point
+between the phases. By doubling the unit cell in two directions, we discuss
+spin-1/2 HAF on square lattice using the suggested four-spin BOT. Magnon
+spectrum, E, and M found in the first order in 1/n are in good quantitative
+agreement with previous numerical and experimental results. We observe a
+special moderately damped spin-0 quasiparticle (""singlon"" for short) whose
+energy is smaller than the energy of the Higgs mode in the most part of the
+Brillouin zone. By considering HAF with Izing-type anisotropy, we find that
+both Higgs and ""singlon"" modes stem from two-magnon bound states which merge
+with two-magnon continuum not far from the isotropic limit. We demonstrate that
+""singlons"" appear explicitly in ""scalar"" correlators one of which describes the
+Raman intensity in $B_{1g}$ symmetry. The latter is expressed in the leading
+order in 1/n via the ""singlon"" Green's function at zero momentum which shows an
+asymmetric peak. The position of this peak coincides with the position of
+""two-magnon"" peak observed experimentally in, e.g., layered cuprates.",1808.05841v2
+2020-01-17,Thermal spin transport and spin in thermoelectrics,"This article reviews the principles that govern the combined transport of
+spin, heat, and charge. The extensive thermodynamic quantity associated with
+spin transport is the magnetization; its Onsager-conjugate force is in general
+the derivative of the free energy with respect to the magnetization. Spins are
+carried in one of two ways: (1) by spin-polarized free electrons in magnetic
+metals and doped semiconductors, or (2) by spin waves (magnons) that reside on
+localized electrons on unfilled d- or f-shells of transition metal or
+rare-earth elements. The paper covers both cases in separate chapters. In both
+cases, it is possible to define a spin chemical potential whose gradient is the
+more practical conjugate force to spin transport. The paper further describes
+the anomalous Hall, spin Hall, and inverse spin Hall effects in magnetic and
+non-magnetic solids with strong spin-orbit coupling because these effects are
+used to generate and measure spin fluxes. Spin transport across interfaces is
+described next, and includes spin pumping and spin transfer torque. The final
+chapter then puts all these concepts together to describe the spin-Seebeck,
+spin-Peltier, and magnon-drag effects, which exist in ferromagnetic,
+antiferromagnetic, and even paramagnetic solids. Magnon-drag, in particular, is
+a high-temperature effect that boosts the thermopower of metals by an order of
+magnitude and that of semiconductors by a factor of 2 or 3 above the electronic
+diffusion thermopower. This is the only example where a spin-driven effect is
+larger than a charge-driven effect. Magnon drag leads a simple binary
+paramagnetic semiconductor, MnTe, to have zT > 1 without optimization. This
+shows how adding spin as an additional design parameter in thermoelectrics
+research is a new and promising approach toward the quest for high-zT
+materials.",2001.06366v1
+2020-04-12,Spin vortex lattice in the Landau vortex-free state of rotating superfluids,"We show that the Landau vortex-free state in rotating container may give rise
+to the lattice of spin vortices. We consider this effect on example of spin
+vortices in magnon Bose-Einstein condensate (the phase coherent spin
+precession) in the B-phase of superfluid $^3$He, and on example of spin
+vortices in the polar phase of $^3$He.",2004.05583v1
+2020-07-15,"Relativistic exchange interactions in CrX$_3$ (X=Cl, Br, I) monolayers","It has been predicted theoretically and indirectly confirmed experimentally
+that single-layer CrX$_3$ (X=Cl, Br, I) might be the prototypes of topological
+magnetic insulators (TMI). In this work, by using first-principles calculations
+combined with atomistic spin dynamics we provide a complete picture of the
+magnetic interactions and magnetic excitations in CrX$_3$. The focus is here on
+the two most important aspects for the actual realization of TMI, namely the
+relativistic magnetic interactions and the finite-size (edge) effects. We
+compute the full interaction tensor, which includes both Kitaev and
+Dzyaloshinskii-Moriya terms, which are considered as the most likely mechanisms
+for stabilizing topological magnons. First, we instigate the properties of bulk
+CrI$_3$ and compare the simulated magnon spectrum with the experimental data
+[Phys. Rev. X 8, 041028 (2018)]. Our results suggest that a large size of
+topological gap, seen in experiment ($\approx$ 4 meV), can not be explained by
+considering pair-wise spin interactions only. We identify several possible
+reasons for this disagreement and suggest that a pronounced magneto-elastic
+coupling should be expected in this class of materials. The magnetic
+interactions in the monolayers of CrX$_3$ are also investigated. The strength
+of the anisotropic interactions is shown to scale with the position of halide
+atom in the Periodic Table, the heavier the element the larger is the
+anisotropy. Comparing the magnons for the bulk and single-layer CrI$_3$, we
+find that the size of the topological gap becomes smaller in the latter case.
+Finally, we investigate finite-size effects in monolayers and demonstrate that
+the anisotropic couplings between Cr atoms close to the edges are much stronger
+than those in ideal periodic structure. This should have impact on the dynamics
+of the magnon edge modes in this class of materials.",2007.07611v2
+2021-05-10,Magnon-phonon interactions enhance the gap at the Dirac point in the spin-wave spectra of CrI$_3$ two-dimensional magnets,"Recent neutron-diffraction experiments in honeycomb CrI$_3$ quasi-2D
+ferromagnets have evinced the existence of a gap at the Dirac point in their
+spin-wave spectra. The existence of this gap has been attributed to strong
+in-plane Dzyaloshinskii-Moriya or Kitaev (DM/K) interactions and suggested to
+set the stage for topologically protected edge states to sustain
+non-dissipative spin transport. We perform state-of-the-art simulations of the
+spin-wave spectra in monolayer CrI$_3$, based on time-dependent
+density-functional perturbation theory (TDDFpT) and fully accounting for
+spin-orbit couplings (SOC) from which DM/K interactions ultimately stem. While
+our results are in qualitative agreement with experiments, the computed TDDFpT
+magnon gap at the Dirac point is found to be 0.47~meV, roughly 6 times smaller
+than the most recent experimental estimates, so questioning that intralayer
+anisotropies alone can explain the observed gap. Lattice-dynamical
+calculations, performed within density-functional perturbation theory (DFpT),
+indicate that a substantial degeneracy and a strong coupling between
+vibrational and magnetic excitations exist in this system, providing a possible
+additional gap-opening mechanism in the spin-wave spectra. In order to pursue
+this path, we introduce an interacting magnon-phonon Hamiltonian featuring a
+linear coupling between lattice and spin fluctuations, enabled by the magnetic
+anisotropy induced by SOC. Upon determination of the relevant interaction
+constants by DFpT and supercell calculations, this model allows us to propose
+magnon-phonon interactions as an important microscopic mechanism responsible
+for the enhancement of the gap in the range of $\approx 4$~meV around the Dirac
+point of the CrI$_3$ monolayer.",2105.04531v4
+2022-05-15,Surface plasmon-phonon-magnon polariton in a topological insulator-antiferromagnetic bilayer structure,"We present a robust technique for computationally studying surface polariton
+modes in hybrid materials. We use a semi-classical model that allows us to
+understand the physics behind the interactions between collective excitations
+of the hybrid system and develop a scattering and transfer matrix method that
+imposes the proper boundary conditions to solve Maxwell equations and derive a
+general equation describing the surface polariton in a heterostructure
+consisting of N constituent materials. We apply this method to a test structure
+composed of a topological insulator (TI) and an antiferromagnetic material
+(AFM) to study the resulting surface Dirac plasmon-phonon-magnon polariton
+(DPPMP). We find that interactions between the excitations of the two
+constituents result in the formation of hybridized modes and the emergence of
+avoided-crossing points in the dispersion relations for the DPPMP. For the
+specific case of a Bi2Se3 TI material, the polariton branch with low frequency
+below 2 THz redshifts upon increasing the thickness of TI thin film, which
+leads to an upper bound on the thickness of the TI layer that will allow an
+observable signature of strong coupling and the emergence of hybridized states.
+We also find that the strength of the coupling between the TI and the AFM,
+which is parameterized by the amplitude of the avoided-crossing splitting
+between the two polariton branches at the magnon resonance frequency, depends
+on the magnitude of the magnetic dipole and the line width of the magnon in the
+AFM material as well as on the Fermi energy of Dirac plasmon in the TI.
+Finally, we predict that materials with extremely high quality, i.e. low
+scattering loss rate, are essential to achieve an experimentally-observable
+strong coupling between a TI and AFM.",2205.07367v1
+2022-08-14,Spin-wave theory in a randomly disordered lattice: A Heisenberg ferromagnet,"Starting from the hamiltonian for the Heisenberg ferromagnet which comprise
+randomly distributed nonmagnetic ions as impurities in a Bravais lattice, we
+express the spin operators by means of the Dyson-Maleev transformation in terms
+of the Bose operators of the second quantization. Then by using methods of
+quantum statistical field theory, we derive the partition function and the free
+energy for the system. We adopt the Matsubara thermal perturbation method to a
+portion of the hamiltonian which describes the interaction between magnons and
+the stationary field of nonmagnetic ions. Upon averaging over all possible
+distributions of impurities, we express the free energy of the system as a
+function of the mean impurity concentration. Subsequently, we set up the
+double-time single particle Green function at temperature T in the momentum
+space in terms of magnon operators and derive the equation of motion for the
+Green function through the Heisenberg equation of motion and then solve the
+resulting equation. From this, we calculate the self-energy and then the
+spectral density for the system. We apply the formalism to the case of the
+simple cubic lattice and compute the density of states, the spectral density
+function and the lifetime of the magnons as a function of energy for several
+values of the mean concentration of nonmagnetic ions in the lattice. We
+calculate magnon energy spectrum as a function of average impurity
+concentration fraction c, which shows that for low lying states, the excitation
+energy increases continuously with c in the studied range 0.1 < c < 0.7. We use
+the spectral density function to compute some thermal quantities. We have
+obtained closed form expressions for the configurationally averaged physical
+quantities of interest in a unified fashion as functions of c to any order of c
+applicable below a critical percolation concentration.",2208.06910v1
+2022-12-05,Spin excitation continuum to topological magnon crossover and thermal Hall conductivity in Kitaev magnets,"There has been great interest in identifying a Kitaev quantum spin liquid
+state in frustrated magnets with bond-dependent interactions. In particular,
+the experimental report of a half-quantized thermal Hall conductivity in
+$\alpha$-RuCl$_3$ in the presence of a magnetic field has generated excitement
+as it could be strong evidence for a field-induced chiral spin liquid. More
+recent experiments, however, provide a conflicting interpretation advocating
+for topological magnons in the field-polarized state as the origin of the
+non-quantized thermal Hall conductivity observed in their experiments. An
+inherent difficulty in distinguishing between the two scenarios is the phase
+transition between a putative two-dimensional spin liquid and the
+field-polarized state exists only at zero temperature, while the behaviour at
+finite temperature is mostly crossover phenomena. In this work, we provide
+insights into the finite temperature crossover behavior between the spin
+excitation continuum in a quantum spin liquid and topological magnons in the
+field-polarized state in three different theoretical models with large Kitaev
+interactions. These models allow for a field-induced phase transition from a
+spin liquid (or an intermediate field-induced spin liquid) to the
+field-polarized state in the quantum model. We obtain the dynamical spin
+structure factor as a function of magnetic field using molecular dynamics
+simulations and compute thermal Hall conductivity in the field-polarized
+regime. We demonstrate the gradual evolution of the dynamical spin structure
+factor exhibiting crossover behaviour near magnetic fields where
+zero-temperature phase transitions occur in the quantum model. We also examine
+nonlinear effects on topological magnons and the validity of thermal Hall
+conductivity computed using linear spin wave theory. We discuss the
+implications of our results to existing and future experiments.",2212.02516v1
+2023-01-09,Thermal Hall conductivity of $α$-RuCl$_3$,"Thermal Hall conductivity originating from topological magnons is observed in
+the Kitaev candidate $\alpha$-RuCl$_3$ in broad intervals of temperature and
+in-plane magnetic field, raising questions on the role of the Majorana mode in
+heat conduction.",2301.03526v1
+2023-04-24,Perspective on non-Hermitian physics in magnetic systems,"A perspective on non-Hermitian physics in magnetic systems is addressed in
+this short article, including exceptional points, exceptional nodal phases, the
+non-Hermitian SSH model, and the non-Hermitian skin effect.",2304.11948v2
+2023-06-16,Bose-Einstein condensation of a two-magnon bound state in a spin-one triangular lattice,"Interactions of collective excitations often lead to rich emergent phenomena
+in many-particle quantum systems. In ordered magnets, the elementary
+excitations are spin waves (magnons), which obey Bose-Einstein statistics.
+Similar to the Cooper pairs in superconductors, magnons can be paired into
+bound states under attractive interactions. Even more interestingly, the Zeeman
+coupling to a magnetic field acts as a chemical potential that can tune the
+particle density through a quantum critical point (QCP), beyond which a
+``hidden order'' is predicted to exist. However, experimental confirmation of
+this QCP and the associated new state of matter remain elusive. Here we report
+direct observation of the Bose-Einstein condensation (BEC) of the two-magnon
+bound state in Na$_2$BaNi(PO$_4$)$_2$. Comprehensive thermodynamic measurements
+confirmed the existence of a two-dimensional BEC-QCP at the saturation field.
+Inelastic neutron scattering experiments were performed to accurately establish
+the magnetic exchange model. An exact solution of the model found stable
+2-magnon bound states that were further confirmed by an electron spin resonance
+(ESR) experiment, demonstrating that the QCP is due to the pair condensation
+and the phase below saturation field is the long-sought-after spin nematic (SN)
+phase.",2306.09695v1
+2024-02-22,Laser patterning of magnonic structure via local crystallization of Yittrium Iron Garnet,"The fabrication and integration of high-quality structures of Yttrium Iron
+Garnet (YIG) is critical for magnonics.Films with excellent properties are
+obtained only on single crystal Gadolinium Gallium Garnet (GGG) substrates
+using high-temperature processes. The subsequent realization of magnonic
+structures via lithography and etching is not straightforward as it requires a
+tight control of the edge roughness, to avoid magnon scattering, and
+planarization in case of multilayer devices. In this work we describe a
+different approach based on local laser annealing of amorphous YIG films,
+avoiding the need for subjecting the entire sample to high thermal budgets and
+for physical etching. Starting from amorphous and paramagnetic YIG films grown
+by pulsed laser deposition at room temperature on GGG, a 405 nm laser is used
+for patterning arbitrary shaped ferrimagnetic structures by local
+crystallization. In thick films (160 nm) the laser induced surface corrugation
+prevents the propagation of spin-wave modes in patterned conduits. For thinner
+films (80 nm) coherent propagation is observed in 1.2 micron wide conduits
+displaying an attenuation length of 5 micron which is compatible with a damping
+coefficient of about 5e-3. Possible routes to achieve damping coefficients
+compatible with state-of-the art epitaxial YIG films are discussed.",2402.14444v1
+1995-05-03,Magnetic Raman Scattering in Two-Dimensional Spin-1/2 Heisenberg Antiferromagnets: Spectral Shape Anomaly and Magnetostrictive Effects,"We calculate the Raman spectrum of the two-dimensional (2D) spin-1/2
+Heisenberg antiferromagnet by exact diagonalization and quantum Monte Carlo
+techniques on clusters of up to 144 sites and, on a 16-site cluster, by
+considering the phonon-magnon interaction which leads to random fluctuations of
+the exchange integral. Results are in good agreement with experiments on
+various high-T_c precursors, such as La_2CuO_4 and YBa_2Cu_3O_{6.2}. In
+particular, our calculations reproduce the broad lineshape of the two-magnon
+peak, the asymmetry about its maximum, the existence of spectral weight at high
+energies, and the observation of nominally forbidden A_{1g} scattering.",9505012v1
+1995-10-26,Properties of lightly doped t-J two-leg ladders,"We have numerically investigated the doped t-J ladder using exact
+diagonalization. We have studied both the limit of strong inter-chain coupling
+and isotropic coupling. The ladder scales to the Luther-Emery liquid regime in
+the strong inter-chain coupling limit. In this strong coupling limit there is a
+simple picture of the excitation spectrum that can be continued to explain the
+behavior at isotropic coupling. At J=0 we have indications of a ferromagnetic
+ground state. At a large $J/t$ the ladder is phase separated into holes and a
+Heisenberg ladder. At intermediate coupling the ground state shows hole pairing
+with a modified d-wave symmetry. The excitation spectrum separates into a
+limited number of quasiparticles which carry charge $+|e|$ and spin ${1\over
+2}$ and a triplet magnon mode. At half-filling the former vanish but the latter
+evolves continuously into the magnon band of the spin liquid. At low doping the
+quasiparticles form a dilute Fermi gas with a strong attraction but
+simultaneously the Fermi wave vector, as would be measured in photoemission, is
+large. The dynamical structure factors are calculated and are found to be very
+similar to calculations on 2D clusters.",9510150v1
+1996-11-14,Heisenberg model with Dzyaloshinskii-Moriya interaction: A Schwinger boson study,"We present a Schwinger-boson approach to the Heisenberg model with
+Dzyaloshinskii-Moriya interaction. We write the anisotropic interactions in
+terms of Schwinger bosons keeping the correct symmetries present in the spin
+representation, which allows us to perform a conserving mean-field
+approximation. Unlike previous studies of this model by linear spin-wave
+theory, our approach takes into account magnon-magnon interactions and includes
+the effects of three-boson terms characteristic of noncollinear phases. The
+results reproduce the linear spin-wave predictions in the semiclassical large-S
+limit, and show a small renormalization in the strong quantum limit S=1/2. For
+the sake of definiteness, we specialize the calculations for the pattern of
+Moriya vectors corresponding to the orthorhombic phase in La_2CuO_4, and give a
+fairly detailed account of the behavior of ground-state energy, anisotropy gap,
+and net ferromagnetic moment. In the last part of this work we generalize our
+approach to describe the geometry of the intermediate phase in
+La_{2-x}Nd_xCuO_4, and discuss the effects of including nondegenerate 2p_z
+oxygen orbitals in the calculations.",9611116v1
+1997-08-11,Excitations and Possible Bound States in the S=1/2 Alternating Chain Compound (VO)2P2O7,"Magnetic excitations in an array of (VO)2P2O7 single crystals have been
+measured using inelastic neutron scattering. Until now, (VO)2P2O7 has been
+thought of as a two-leg antiferromagnetic Heisenberg spin ladder with chains
+running in the a-direction. The present results show unequivocally that
+(VO)2P2O7 is best described as an alternating spin-chain directed along the
+crystallographic b-direction. In addition to the expected magnon with magnetic
+zone-center energy gap DE = 3.1$ meV, a second excitation is observed at an
+energy just below 2DE. The higher mode may be a triplet two-magnon bound state.
+Numerical results in support of bound modes are presented.",9708078v1
+1997-11-06,Observation of three-magnon light scattering in CuGeO_3,"Temperature and magnetic field dependent polarized Brillouin spectra of
+CuGeO_3 are reported. In addition to a bound singlet state at 30 cm^{-1}, a new
+feature has been observed at 18 cm^{-1}. This feature is interpreted in terms
+of a novel three-magnon light scattering process between excited triplet
+states.",9711047v1
+1998-02-13,Spin and orbital excitations in magnetic insulators with Jahn-Teller ions,"The elementary excitations of a model Hamiltonian that captures the low
+energy behavior of a simple two-fold degenerate Hubbard Hamiltonian with Hund's
+rule coupling, is studied. The phase diagram in the mean-field limit and in a
+two-site approach reveals a rich variety of phases where both the orbital and
+the spin degrees of freedom are ordered. We show that besides usual spin waves
+(magnons) there exist also orbital waves (orbitons) and, most interestingly, in
+a completely ferromagnetically coupled system, a combined spin-orbital
+excitation which can be visualized as a bound state of magnons and orbitons.
+For a completely degenerate system the bound states are found to be the lowest
+lying elementary excitations, both in one- and two-dimensions. Finally we
+extend our treatment to almost-degenerate systems. This can serve as an example
+that the elementary excitations in orbitally degenerate strongly correlated
+electron systems in general carry both spin and orbital character.",9802146v1
+1998-04-09,Charged Magnons in NaV2O5,"We investigated the temperature-dependent optical conductivity of NaV2O5 in
+the energy range 4 meV-4 eV. The intensities and the polarization dependence of
+the detected electronic excitations give a direct indication for a
+broken-parity electronic ground-state and for a non-centrosymmetric crystal
+structure of the system in the high-temperature phase. A direct two-magnon
+optical absorption process, proposed in this Letter, is in quantitative
+agreement with the optical data. By analyzing the optically allowed phonons at
+various temperatures above and below the phase transition, we conclude that a
+second-order change to a larger unit cell takes place below 34 K.",9804110v3
+1999-04-06,Non-Fermi-liquid behavior in the Kondo lattices induced by peculiarities of magnetic ordering and spin dynamics,"A scaling consideration of the Kondo lattices is performed with account of
+singularities in the spin excitation spectral function. It is shown that a
+non-Fermi-liquid (NFL) behavior between two critical values of the bare $s-f$
+coupling constant occurs naturally for complicated magnetic structures with
+several magnon branches. This may explain the fact that a NFL behavior takes
+place often in the heavy-fermion systems with peculiar spin dynamics. Another
+kind of a NFL-like state (with different critical exponents) can occur for
+simple antiferromagnets with account of magnon damping, and for paramagnets,
+especially with two-dimensional character of spin fluctuations. The mechanisms
+proposed lead to some predictions about behavior of specific heat, resistivity,
+magnetic susceptibility, and anisotropy parameter, which can be verified
+experimentally.",9904072v3
+1999-08-13,Spin Wave Theory of Double Exchange Ferromagnets,"We construct the 1/S spin-wave expansion for double exchange ferromagnets at
+T=0. It is assumed that the value of Hund's rule coupling, J_H, is sufficiently
+large, resulting in a fully saturated, ferromagnetic half-metallic ground
+state. We evaluate corrections to the magnon dispersion law, and we also find
+that, in contrast to earlier statements in the literature, magnon-electron
+scattering does give rise to spin wave damping. We analyse the momentum
+dependence of these quantities and discuss the experimental implications for
+colossal magnetoresistance compounds.",9908202v3
+1999-09-06,Excitation Spectra of Structurally Dimerized and Spin-Peierls Chains in a Magnetic Field,"The dynamical spin structure factor and the Raman response are calculated for
+structurally dimerized and spin-Peierls chains in a magnetic field, using exact
+diagonalization techniques. In both cases there is a spin liquid phase composed
+of interacting singlet dimers at small fields h < h_c1, an incommensurate
+regime (h_c1 < h < h_c2) in which the modulation of the triplet excitation
+spectra adapts to the applied field, and a fully spin polarized phase above an
+upper critical field h_c2. For structurally dimerized chains, the spin gap
+closes in the incommensurate phase, whereas spin-Peierls chains remain gapped.
+In the spin liquid regimes, the dominant feature of the triplet spectra is a
+one-magnon bound state, separated from a continuum of states at higher
+energies. There are also indications of a singlet bound state above the
+one-magnon triplet.",9909093v1
+2000-04-25,Can a frustrated spin-cluster model describe the low-temperature physics of NaV_2O_5 ?,"Recent experimental evidence suggest the existence of three distinct
+V-valence states (V^{+4}, V^{+4.5} and V^{+5}) in the low-temperature phase of
+NaV_2O_5 in apparent discrepancy with the observed spin-gap. We investigate a
+novel spin cluster model, consisting of weakly coupled, frustrated four-spin
+clusters aligned along the crystallographic b-axis that was recently proposed
+to reconcile these experimental observations. We have studied the phase diagram
+and the magnon dispersion relation of this model using DMRG, exact
+diagonalization and a novel cluster-operator theory. We find a spin-gap for all
+parameter values and two distinct phases, a cluster phase and a Haldane phase.
+We evaluate the size of the gap and the magnon dispersion and find no parameter
+regime which would reproduce the experimental results. We conclude that this
+model is inappropriate for the low-temperature regime of NaV_2O_5.",0004404v1
+2000-04-27,Two-magnon Raman scattering in spin-ladder geometries and the ratio of rung and leg exchange constants,"We discuss ways in which the ratio of exchange constants along the rungs and
+legs of a spin-ladder material influences the two-magnon Raman scattering
+spectra and hence can be determined from it. We show that within the
+Fleury-Loudon-Elliott approach, the Raman line-shape does not change with
+polarization geometries. This lineshape is well known to be difficult to
+calculate accurately from theory. However, the Raman scattering intensities do
+vary with polarization geometries, which are easy to calculate. With some
+assumptions about the Raman scattering Hamiltonian, the latter can be used to
+estimate the ratio of exchange constants. We apply these results to Sugai's
+recent measurements of Raman scattering from spin-ladder materials such as
+La$_6$Ca$_8$Cu$_{24}$O$_{41}$ and Sr$_{14}$Cu$_{24}$O$_{41}$.",0004477v3
+2001-01-19,Nature of Spin Excitations in Two-dimensional Mott Insulators: Undoped Cuprates and Other Materials,"We investigate the excitation spectrum of a two-dimensional resonating
+valence bond (RVB) state. Treating the $pi$-flux phase with antiferromagnetic
+correlations as a variational ground state, we recover the long wavelength
+magnon as an ""RVB exciton"". However, we find that this excitation does NOT
+exhaust the entire spectral weight and the high energy spectrum is dominated by
+fermionic excitations. The latter can be observed directly by inelastic neutron
+scattering and we predict their characteristic energy scales along different
+high symmetry directions in the magnetic Brillouin zone. We also interpret
+experimental results on two magnon Raman scattering and mid-infrared absorption
+within this scenario.",0101298v2
+2001-06-22,A Spin-Resolved Photoemission Study of Photohole Lifetimes in Ferromagnetic Gadolinium,"High resolution spin-resolved photoemission is used to probe the properties
+of a Gd(0001) surface state. The state shows both a spin-mixing behavior
+reflecting the exchange of magnons with the local moments and a reduction of
+the exchange splitting with increasing temperature. The surface state
+polarization at low T suggests that the surface layer has an enhanced Tc of
+365K or greater. Measurements of the photoemission linewidths show that at low
+temperatures, the lifetime of a majority spin photohole is predominantly
+limited by electron-phonon scattering and that of a minority spin photohole by
+electron-magnon scattering. Since similar behavior may be expected for bulk
+states close to the Fermi level, the transport properties of this material will
+also be determined by different decay mechanisms in the two channels.",0106453v1
+2001-06-24,Spontaneous Magnetization of the O(3) Ferromagnet at Low Temperatures,"We investigate the low-temperature behavior of ferromagnets with a
+spontaneously broken symmetry O(3) $\to$ O(2). The analysis is performed within
+the perspective of nonrelativistic effective Lagrangians, where the dynamics of
+the system is formulated in terms of Goldstone bosons. Unlike in a
+Lorentz-invariant framework (chiral perturbation theory), where loop graphs are
+suppressed by two powers of momentum, loops involving ferromagnetic spin waves
+are suppressed by three momentum powers. The leading coefficients of the
+low-temperature expansion for the partition function are calculated up to order
+$p^{10}$. In agreement with Dyson's pioneering microscopic analysis of the
+cubic ferromagnet, we find that, in the spontaneous magnetization, the
+magnon-magnon interaction starts manifesting itself only at order $T^4$. The
+striking difference with respect to the low-temperature properties of the O(3)
+antiferromagnet is discussed from a unified point of view, relying on the
+effective Lagrangian technique.",0106492v1
+2001-08-06,Plaquette Boson-Fermion Model of Cuprates,"The strongly interacting Hubbard model on the square lattice is reduced to
+the low energy Plaquette Boson Fermion Model (PBFM). The four bosons (an
+antiferromagnon triplet and a d-wave hole pair), and the fermions are defined
+by the lowest plaquette eigenstates. We apply the Contractor Renormalization
+method of Morningstar and Weinstein to compute the boson effective
+interactions. The range-3 truncation error is found to be very small, signaling
+short hole-pair and magnon coherence lengths. The pair-hopping and magnon
+interactions are comparable, which explains the rapid destruction of
+antiferromagnetic order with emergence of superconductivity, and validates a
+key assumption of the projected SO(5) theory. A vacuum crossing at larger
+doping marks a transition into the overdoped regime. With hole fermions
+occupying small Fermi pockets and Andreev coupled to hole pair bosons, the PBFM
+yields several testable predictions for photoemmission, tunneling asymmetry and
+entropy measurements.",0108087v2
+2001-12-24,Stability of the doped antiferromagnetic state of the t-t'-Hubbard model,"The next-nearest-neighbour hopping term t' is shown to stabilize the AF state
+of the doped Hubbard model with respect to transverse perturbations in the
+order- parameter by strongly suppressing the intraband particle-hole processes.
+For a fixed sign of t', this stabilization is found to be significantly
+different for electron and hole doping, which qualitatively explains the
+observed difference in the degree of robustness of the AF state in the
+electron-doped (Nd_{2-x}Ce_{x}CuO_{4}) and hole-doped (La_{2-x}Sr_{x}CuO_{4})
+cuprates. The t'-U phase diagram is obtained for both signs of the t' term,
+showing the different regions of stability and instability of the doped
+antiferromagnet. Doping is shown to suppress the t'-induced frustration due to
+the competing interaction J'. A study of transverse spin fluctuations in the
+metallic AF state reveals that the decay of magnons into particle-hole
+excitations yields an interesting low-energy result \Gamma \sim \omega for
+magnon damping.",0112438v1
+2002-05-18,Resonant Two-Magnon Raman Scattering and Photoexcited States in Two-Dimensional Mott Insulators,"We investigate the resonant two-magnon Raman scattering in two-dimensional
+(2D) Mott insulators by using a half-filled 2D Hubbard model in the strong
+coupling limit. By performing numerical diagonalization calculations for small
+clusters, we find that the Raman intensity is enhanced when the incoming photon
+energy is not near the optical absorption edge but well above it, being
+consistent with experimental data. The absence of resonance near the gap edge
+is associated with the presence of background spins, while photoexcited states
+for resonance are found to be characterized by the charge degree of freedom.
+The resonance mechanism is different from those proposed previously.",0205388v2
+2002-07-01,Spin fluctuations in a metallic antiferromagnet,"The magnon energy and amplitude renormalization due to intraband
+particle-hole excitations are studied in a metallic antiferromagnet. The change
+in sign of the intraband contribution with $\omega$ results in significant
+differences between static and dynamical behaviours. For electron doping, while
+the coherent magnon peak looses spectral weight and is shifted to higher energy
+with doping, the low-energy incoherent part becomes increasingly prominent as
+it narrows in width and shifts to lower energy. Implications for spin dynamics
+in the electron-doped cuprate $\rm Nd_{2-x} Ce_x Cu O_4$ are discussed. Due to
+an exact cancellation of two logarithmically divergent spin-fluctuation
+processes, the AF order parameter is unaffected to leading order. For hole
+doping, short wavelength transverse perturbations ($q > q^* \sim \sqrt{x}$) are
+found to be stable, implying short-range AF order with a spin correlation
+length $\xi/a \sim 1/\sqrt{x}$.",0207032v1
+2002-11-25,Resonant two-magnon Raman scattering in two-dimensional and ladder-type Mott insulators,"We investigate the resonant two-magnon Raman scattering in the
+two-dimensional (2D) and ladder-type Mott insulators by using a half-filled
+Hubbard model in the strong coupling limit. By performing numerical
+diagonalization calculations for small clusters, we find that the model can
+reproduce the experimental features in the 2D that the Raman intensity is
+enhanced when the incoming photon energy is not near the absorption edge but
+well above it. In the ladder-type Mott insulators, the Raman intensity is found
+to resonate with absorption spectrum in contrast to the 2D system. The
+difference between 2D and the ladder systems is explained by taking into
+account the fact that the ground state in 2D is a spin-ordered state while that
+in ladder is a spin-gapped one.",0211552v1
+2003-02-26,Field-induced structural evolution in the spin-Peierls compound CuGeO$_3$: high-field ESR study,"The dimerized-incommensurate phase transition in the spin-Peierls compound
+CuGeO$_3$ is probed using multifrequency high-resolution electron spin
+resonance (ESR) technique, in magnetic fields up to 17 T. A field-induced
+development of the soliton-like incommensurate superstructure is clearly
+indicated as a pronounced increase of the ESR linewidth $\Delta B$ (magnon
+excitations), with a $\Delta B_{max}$ at $B_{c}\sim$ 13.8 T. The anomaly is
+explained in terms of the magnon-soliton scattering, and suggests that the
+soliton-like phase exists close to the boundary of the dimerized-incommensurate
+phase transition. In addition, magnetic excitation spectra in 0.8% Si-doped
+CuGeO$_3$ are studied. Suppression of the $\Delta B$ anomaly observed in the
+doped samples suggests a collapse of the long-range-ordered soliton states upon
+doping, that is consistent with high-field neutron scattering experiments.",0302542v2
+2003-09-10,Spectrum and transition rates of the XX chain analyzed via Bethe ansatz,"As part of a study that investigates the dynamics of the s=1/2 XXZ model in
+the planar regime |Delta|<1, we discuss the singular nature of the Bethe ansatz
+equations for the case Delta=0 (XX model). We identify the general structure of
+the Bethe ansatz solutions for the entire XX spectrum, which include states
+with real and complex magnon momenta. We discuss the relation between the
+spinon or magnon quasiparticles (Bethe ansatz) and the lattice fermions
+(Jordan-Wigner representation). We present determinantal expressions for
+transition rates of spin fluctuation operators between Bethe wave functions and
+reduce them to product expressions. We apply the new formulas to two-spinon
+transition rates for chains with up to N=4096 sites.",0309247v1
+2003-12-09,Magnetic-field induced spin-Peierls instability in strongly frustrated quantum spin lattices,"For a class of frustrated antiferromagnetic spin lattices (in particular, the
+square-kagom\'{e} and kagom\'{e} lattices) we discuss the impact of recently
+discovered exact eigenstates on the stability of the lattice against
+distortions. These eigenstates consist of independent localized magnons
+embedded in a ferromagnetic environment and become ground states in high
+magnetic fields. For appropriate lattice distortions fitting to the structure
+of the localized magnons the lowering of magnetic energy can be calculated
+exactly and is proportional to the displacement of atoms leading to a
+spin-Peierls lattice instability. Since these localized states are present only
+for high magnetic fields, this instability might be driven by magnetic field.
+The hysteresis of the spin-Peierls transition is also discussed.",0312216v2
+2004-02-26,Unifying Magnons and Triplons in Stripe-Ordered Cuprate Superconductors,"Based on a two-dimensional model of coupled two-leg spin ladders, we derive a
+unified picture of recent neutron scattering data of stripe-ordered
+La_(15/8)Ba_(1/8)CuO_4, namely of the low-energy magnons around the
+superstructure satellites and of the triplon excitations at higher energies.
+The resonance peak at the antiferromagnetic wave vector Q_AF in the
+stripe-ordered phase corresponds to a saddle point in the dispersion of the
+magnetic excitations. Quantitative agreement with the neutron data is obtained
+for J= 130-160 meV and J_cyc/J = 0.2-0.25.",0402659v2
+2004-03-12,Consequences of spin-orbit coupling for the Bose-Einstein condensation of magnons,"In the first part we discuss how the BEC picture for magnons is modified by
+anisotropies induced by spin-orbit coupling. In particular we focus on the
+effects of antisymmetric spin interactions and/or a staggered component of the
+$g$ (gyromagnetic) tensor. Such terms lead to a gapped quasiparticle spectrum
+and a nonzero condensate density for all temperatures so that no phase
+transition occurs. We contrast this to the effect of crystal field anisotropies
+which are also induced by spin-orbit coupling. In the second part we study the
+field-induced magnetic ordering in TlCuCl$_3$ on a quantitative level. We show
+that the usual BEC picture does not allow for a good description of the
+experimental magnetisation data and argue that antisymmetric spin interactions
+and/or a staggered $g$ tensor component are still crucial, although both are
+expected to be tiny in this compound due to crystal symmetries. Including this
+type of interaction we obtain excellent agreement with experimental data.",0403311v2
+2004-05-18,Bose-Einstein Condensation of Magnons in TlCuCl3: Phase diagram and specific heat from a self-consistent Hartee-Fock calculation with a realistic dispersion relation,"We extend the self-consistent Hartree-Fock-Popov calculations by Nikuni et
+al. [Phys. Rev. Lett. 84, 5868 (2000)] concerning the Bose-Eistein condensation
+of magnons in TlCuCl3 to include a realistic dispersion of the excitations. The
+result for the critical field as a function of temperature behaves as
+Hc(T)-Hc(0) T^{3/2} below 2K but deviates from this simple power-law at higher
+temperature and is in very good agreement with the experimental results. The
+specific heat is computed as a function of temperature for different values of
+the magnetic field. It shows a lambda-like shape at the transition and is in
+good qualitative agreement with the results of Oosawa et al. [Phys. Rev. B 63,
+134416 (2001)].",0405422v2
+2004-06-21,Nonquasiparticle states in half-metallic ferromagnets,"Anomalous magnetic and electronic properties of the half-metallic
+ferromagnets (HMF) have been discussed. The general conception of the HMF
+electronic structure which take into account the most important correlation
+effects from electron-magnon interactions, in particular, the spin-polaron
+effects, is presented. Special attention is paid to the so called
+non-quasiparticle (NQP) or incoherent states which are present in the gap near
+the Fermi level and can give considerable contributions to thermodynamic and
+transport properties. Prospects of experimental observation of the NQP states
+in core-level spectroscopy is discussed. Special features of transport
+properties of the HMF which are connected with the absence of one-magnon
+spin-flip scattering processes are investigated. The temperature and magnetic
+field dependences of resistivity in various regimes are calculated. It is shown
+that the NQP states can give a dominate contribution to the temperature
+dependence of the impurity-induced resistivity and in the tunnel junction
+conductivity. First principle calculations of the NQP-states for the prototype
+half-metallic material NiMnSb within the local-density approximation plus
+dynamical mean field theory (LDA+DMFT) are presented.",0406487v1
+2004-07-08,Study of Field-Induced Magnetic Order in Singlet-Ground-State Magnet CsFeCl$_3$,"The field-induced magnetic order in the singlet-ground-state system
+CsFeCl$_3$ has been studied by measuring magnetization and neutron diffraction.
+The field dependence of intensity for the neutron magnetic reflection has
+clearly demonstrated that the field-induced ordered phase is described by the
+order parameter $<S_x>$. A condensate growth of magnons is investigated through
+the temperature dependence of $M_z$ and $M_{\perp}$, and this ordering is
+discussed in the context of a magnon Bose-Einstein condensation. Development of
+the coherent state and the static correlation length has been observed in the
+incommensurate phase in the field region of $5 < H < 6$ T at 1.8 K. At $H >
+H_{\rm c}$, a satellite peak was found in coexistence with the commensurate
+peak at the phase boundary around 10 T, which indicates that the tilt of the
+c-axis would be less than $\sim 0.5^{\circ}$ in the whole experiments.",0407196v2
+2004-07-09,Magnetically Stabilized Nematic Order I: Three-Dimensional Bipartite Optical Lattices,"We study magnetically stabilized nematic order for spin-one bosons in optical
+lattices. We show that the Zeeman field-driven quantum transitions between
+non-nematic Mott states and quantum spin nematic states in the weak hopping
+limit are in the universality class of the ferromagnetic XXZ (S=1/2) spin
+model. We further discuss these transitions as condensation of interacting
+magnons. The development of O(2) nematic order when external fields are applied
+corresponds to condensation of magnons, which breaks a U(1) symmetry.
+Microscopically, this results from a coherent superposition of two non-nematic
+states at each individual site. Nematic order and spin wave excitations around
+critical points are studied and critical behaviors are obtained in a dilute gas
+approximation. We also find that spin singlet states are unstable with respect
+to quadratic Zeeman effects and Ising nematic order appears in the presence of
+any finite quadratic Zeeman coupling. All discussions are carried out for
+states in three dimensional bipartite lattices.",0407259v1
+2004-10-16,Low-lying magnon excitations in integer-spin ladders and tubes,"We consider low-energy excitation structures of N-leg integer-spin ladder and
+tube systems with an antiferromagnetic (AF) intrachain coupling and a uniform
+external field. The tube means the ladder with the periodic boundary condition
+along the interchain (rung) direction. Odd-leg AF-rung tubes have the
+frustration. In order to analyze all systems including frustrated tubes, we
+apply a field-theoretical method based on the nonlinear sigma model. We mainly
+focus on the systems without any external fields. In this case, it is shown
+that the lowest bands of frustrated tubes always consist of six-fold degenerate
+magnon excitations, while those of all other systems are triply degenerate.
+This result implies that the ground states of frustrated tubes (all
+non-frustrated systems) become a two (one)-component Tomonaga-Luttinger liquid,
+when a sufficiently strong uniform field is applied.",0410419v3
+2005-05-16,Spin Waves in a Periodically Layered Magnetic Nanowire,"We report a simple theoretical derivation of the spectrum and damping of spin
+waves in a cylindrical periodically structured magnetic nanowire (cylindrical
+magnonic crystal) in the ""effective medium"" approximation. The dependence of
+the ""effective"" magnetic parameters upon the individual layer parameters is
+shown to be different from the arithmetic average over the volume of the
+superlattice. The formulae that are obtained can be applied firstly in the
+description of spin wave dispersion in the first allowed band of the structure;
+and secondly in the design of a magnonic crystal with band-gaps in an arbitrary
+part of the spin wave spectrum.",0505382v1
+2005-06-23,Magnon Heat Conductivity and Mean Free Paths in Two-Leg Spin Ladders: A Model-Independent Determination,"The magnon thermal conductivity $\kappa_{\mathrm{mag}}$ of the spin ladders
+in $\rm Sr_{14}Cu_{24-x}Zn_xO_{41}$ has been investigated at low doping levels
+$x=0$, 0.125, 0.25, 0.5 and 0.75. The Zn-impurities generate nonmagnetic
+defects which define an upper limit for $l_{\mathrm{mag}}$ and therefore allow
+a clear-cut relation between $l_{\mathrm{mag}}$ and $\kappa_{\mathrm{mag}}$ to
+be established independently of any model. Over a large temperature range we
+observe a progressive suppression of $\kappa_{\mathrm{mag}}$ with increasing
+Zn-content and find in particular that with respect to pure $\rm
+Sr_{14}Cu_{24}O_{41}$ $\kappa_{\mathrm{mag}}$ is strongly suppressed even in
+the case of tiny impurity densities where $l_{\mathrm{mag}}\lesssim 374$~{\AA}.
+This shows unambiguously that large $l_{\mathrm{mag}}\approx 3000$~{\AA} which
+have been reported for $\rm Sr_{14}Cu_{24}O_{41}$ and $\rm
+La_{5}Ca_9Cu_{24}O_{41}$ on basis of a kinetic model are in the correct order
+of magnitude.",0506595v2
+2005-07-22,Neutron Scattering Study of Quantum Phase Transitions in Integral Spin Chains,"Quite a few low-dimensional magnets are quantum-disordered ``spin liquids''
+with a characteristic gap in the magnetic excitation spectrum. Among these are
+antiferromagnetic chains of integer quantum spins. Their generic feature are
+long-lived massive (gapped) excitations (magnons) that are subject to Zeeman
+splitting in external magnetic fields. The gap in one of the magnon branches
+decreases with field, driving a soft-mode quantum phase transition. The system
+then enters a qualitatively new high-field phase. The actual properties at high
+fields, particularly the spin dynamics, critically depend on the system under
+consideration. Recent neutron scattering studies of organometallic polymer
+crystals NDMAP (Haldane spin chains with anisotropy) and NTENP (dimerized S=1
+chains) revealed rich and unique physics.",0507534v1
+2005-10-06,New light on magnetic excitations: indirect resonant inelastic X-ray scattering on magnons,"Recent experiments show that indirect resonant inelastic X-ray scattering
+(RIXS) is a new probe of spin dynamics. Here I derive the cross-section for
+magnetic RIXS and determine the momentum dependent four-spin correlation
+function that it measures. These results show that this technique offers
+information on spin dynamics that is complementary to e.g. neutron scattering.
+The RIXS spectrum of Heisenberg antiferromagnets is calculated. It turns out
+that only scattering processes that involve at least two magnons are allowed.
+Other selection rules imply that the scattering intensity vanishes for specific
+transferred momenta ${\bf q}$, in particular for ${\bf q}=0$. The calculated
+spectra agree very well with the experimental data.",0510140v3
+2005-11-01,Possibility of a Two-Component Tomonaga-Luttinger Liquid in Frustrated Integer-Spin Tubes,"Uniform-field effects for frustrated odd-leg integer-spin tubes (cylinder
+type spin systems) are investigated in the weak interchain-coupling regime. We
+predict that, as the field exceeds the spin gap, a two-component
+Tomonaga-Luttinger liquid (TLL) appears due to the condensation of the doubly
+degenerate lowest magnons. Furthermore, it is argued that when the uniform
+field is so strong that the second lowest magnons are also condensed, the
+two-component TLL is destroyed and a new one-component TLL emerges. This
+quantum phase transition may be detected as a magnetization cusp.",0511024v2
+2005-11-16,Field-induced Bose-Einstein condensation of interacting dilute magnons in three-dimensional spin systems: A renormalization-group study,"We use the Renormalization Group method to study the magnetic field influence
+on the Bose-Einstein condensation of interacting dilute magnons in three
+dimensional spin systems. We first considered a model with SU(2) symmetry
+(universality class $z=1$) and we obtain for the critical magnetic field a
+power law dependence on the critical temperature, $[H_c(T)-H_c(0)]\sim T^2$. In
+the case of U(1) symmetry (universality class $z=2$) the dependence is
+different, and the magnetic critical field depends linearly on the critical
+temperature, $[H_c(T)-H_c(0)]\sim T$. By considering a more relevant model,
+which includes also the system's anisotropy, we obtain for the same symmetry
+class a $T^{3/2}$ dependence of the magnetic critical field on the critical
+temperature. We discuss these theoretical predictions of the renormalization
+group in connection with experimental results reported in the literature.",0511388v1
+2005-12-09,On the Bose-Einstein Condensation of Magnons in Cs2CuCl4,"In a recent paper \cite{Radu}, Radu \textit{et al.} report experimental
+results they claim to support Bose-Einstein condensation (BEC) of magnons in
+Cs$_2$CuCl$_4$. It is true that an experimentally measured critical power law
+scaling exponent in agreement with the BEC universality class would support the
+realization of a BEC in magnetic systems that order as a canted
+antiferromagnet. It can be shown, however, that the claim of Radu {\it et al.}
+is overstated in this instance, because their determination of the critical
+exponent $\phi$ relies on a model-dependent theoretical approximation to the
+critical field $H_{\textrm{c1}}$ for which the associated errors are neglected.
+We show that when these errors are included, the uncertainty in the obtained
+exponent is so large that the available experimental data cannot be used to
+differentiate between contending universality classes.",0512193v1
+2006-01-02,Three--body Correlation Effects on the Spin Dynamics of Double--Exchange Ferromagnets,"We present a variational calculation of the spin wave excitation spectrum of
+double--exchange ferromagnets in different dimensions. Our theory recovers the
+Random Phase approximation and 1/S expansion results as limiting cases and can
+be used to study the intermediate exchange coupling and electron concentration
+regime relevant to the manganites. In particular, we treat exactly the long
+range three--body correlations between a Fermi sea electron--hole pair and a
+magnon excitation and show that they strongly affect the spin dynamics in the
+parameter range relevant to experiments in the manganites. The manifestations
+of these correlations are many-fold. We demonstrate that they significantly
+change the ferromagnetic phase boundary. In addition to a decrease in the
+magnon stiffness, we obtain an instability of the ferromagnetic state against
+spin wave excitations close to the Brillouin zone boundary.Within a range of
+intermediate concentrations, we find a strong softening of the spin wave
+dispersion as compared to the Heisenberg ferromagnet with the same stiffness,
+which changes into hardening for other concentrations. We discuss the relevance
+of these results to experiments in colossal magnetoresistance ferromagnets.",0601025v2
+2006-04-02,Universal low-temperature behavior of frustrated quantum antiferromagnets in the vicinity of the saturation field,"We study the low-temperature thermodynamic properties of a number of
+frustrated quantum antiferromagnets which support localized magnon states in
+the vicinity of the saturation field. For this purpose we use 1) a mapping of
+the low-energy degrees of freedom of spin systems onto the hard-core object
+lattice gases and 2) an exact diagonalization of finite spin systems of up to
+N=30 sites. The considered spin systems exhibit universal behavior which is
+determined by a specific hard-core object lattice gas representing the
+independent localized magnon states. We test the lattice gas description by
+comparing its predictions with the numerical results for low-lying energy
+states of finite spin systems. For all frustrated spin systems considered we
+find a strong variation of the low-temperature specific heat passing the
+saturation field and a maximum in the isothermal entropy at saturation field
+resulting in an enhanced magnetocaloric effect.",0604023v1
+2006-04-03,Canted Ferromagnetism in Double Exchange Model with on-site Coulomb Repulsion,"The double exchange model with on-site Coulomb repulsion is considered.
+Schwinger-bosons representation of the localized spins is used and two
+spin-singlet Fermion operators are introduced. In terms of the new Fermi fields
+the on-site Hund's interaction is in a diagonal form and the true magnons of
+the system are identified. The singlet fermions can be understood as electrons
+dressed by a cloud of repeatedly emitted and reabsorbed magnons. Rewritten in
+terms of Schwinger-bosons and spin-singlet fermions the theory is U(1) gauge
+invariant. We show that spontaneous breakdown of the gauge symmetry leads to
+\emph{\textbf{canted ferromagnetism with on-site spins of localized and
+delocalized electrons misaligned}}. On-site canted phase emerges in double
+exchange model when Coulomb repulsion is large enough. The quantum phase
+transition between ferromagnetism and canted phase is studied varying the
+Coulomb repulsion for different values of parameters in the theory such as
+Hund's coupling and chemical potential.",0604047v1
+2006-04-27,Raman scattering from phonons and magnons in RFe3)BO3)4,"Inelastic light scattering spectra of several members of the RFe3(BO3)4
+family reveal a cascade of phase transitions as a function of temperature,
+starting with a structural, weakly first order, phase transition followed by
+two magnetic phase transitions. Those consist of the ordering of the Fe-spin
+sublattice revealed by all the compound, and a subsequent spin-reorientational
+transition for GdFe3(BO3)4. The Raman data evidence a strong coupling between
+the lattice and magnetic degrees of freedom in these borates. The Fe-sublattice
+ordering leads to a strong suppression of the low energy magnetic scattering,
+and a multiple peaked two-magnon scattering continuum is observed. Evidence for
+short-range correlations is found in the `paramagnetic' phase by the
+observation of a broad magnetic continuum in the Raman data, which persists up
+to surprisingly high temperatures.",0604615v1
+2006-05-25,Magnon bands of N-leg integer-spin antiferromagnetic systems in the weak interchain-coupling regime,"Using the exact results of the O(3) nonlinear sigma model (NLSM) and a few
+quantitative numerical data for integer-spin antiferromagnetic (AF) chains, we
+systematically estimate all magnon excitation energies of N-leg integer-spin AF
+ladders and tubes in the weak-interchain-coupling regime. Our method is based
+on a first-order perturbation theory for the strength of the interchain
+coupling. It can deal with any kind of interchain interactions, in principle.
+We confirm that results of the perturbation theory are in good agreement with
+those of a quantum Monte Carlo simulation and with our recent study based on a
+saddle-point approximation of the NLSM [Phys. Rev. B 72, 104438 (2005)]. Our
+theory further supports the existence of a Haldane (gapped) phase even in a
+d-dimensional (d\geq 2) spatially anisotropic integer-spin AF model, if the
+exchange coupling in one direction is sufficiently strong compared with those
+in all the other directions. The strategy in this paper is applicable to other
+N-leg systems consisting of gapped chains which low-energy physics is exactly
+or quantitatively known.",0605635v2
+2006-07-27,Magnon Bose condensation in symmetry breaking magnetic field,"Magnon Bose condensation (BC)in the symmetry breaking magnetic field is a
+result of unusual form of the Zeeman energy, which has terms linear in the
+spin-wave operators and terms mixing excitations differ in the Wave-vector of
+the magnetic structure. The following examples are considered: simple
+easy-plane tetragonal antiferromagnets (AF), frustrated AF family$R_2Cu O_4$
+where $R=Pr,Nd$ etc. and cubic magnets with the Dzyaloshinskii-Moriya
+interaction ($Mn Si$ etc.). In all cases the BC becomes important when the
+magnetic field becomes comparable with the spin-wave gap. The theory is
+illustrated by existing experimental results.",0607711v2
+2006-08-01,Magnon Decay in Noncollinear Quantum Antiferromagnets,"Instability of the excitation spectrum of an ordered noncollinear Heisenberg
+antiferromagnet (AF) with respect to spontaneous two-magnon decays is
+investigated. We use a spin-1/2 AF on a triangular lattice as an example and
+examine the characteristic long- and short wave-length features of its
+zero-temperature spectrum within the 1/S-approximation. The kinematic
+conditions are shown to be crucial for the existence of decays and for overall
+properties of the spectrum. The XXZ and the J-J' generalizations of the model,
+as well as the role of higher-order corrections are discussed.",0608035v4
+2006-08-31,Momentum-dependent light scattering in a 2D Heisenberg antiferromagnet,"Motivated by the achievements of the $X$-ray scattering technique, we
+analyzed the profile of the light scattering intensity $R(q, \omega)$ at a
+finite $q$ in a 2D Heisenberg antiferromagnet. Previous Raman scattering
+studies at $q=0$ identified the two-magnon peak in $B_{1g}$ scattering
+geometry. We found that the $B_{1g}$ peak disperses downwards at a finite $q$,
+and its intensity increases, reaching its maximum at $q= q_0 = (0, \pi)$ and
+symmetry related points. In addition, the intensity in the $A_{1g}$ geometry
+becomes non-zero at a finite $q$, and also displays a two-magnon peak which
+gains strength and disperses to larger frequencies with increasing $q$, and
+reaches its highest intensity at $q_0$. We found that the profile of $R(q_0,
+\omega)$ is equivalent in $A_{1g}$ and $B_{1g}$ geometries.",0609002v1
+2006-10-20,Probing Anomalous Longitudinal Fluctuations of the Interacting Bose Gas via Bose-Einstein Condensation of Magnons,"The emergence of a finite staggered magnetization in quantum Heisenberg
+antiferromagnets subject to a uniform magnetic field can be viewed as
+Bose-Einstein condensation of magnons. Using non-perturbative results for the
+infrared behavior of the interacting Bose gas, we present exact results for the
+staggered spin-spin correlation functions of quantum antiferromagnets in a
+magnetic field at zero temperature. In particular, we show that in dimensions 1
+< D <= 3 the longitudinal dynamic structure factor S_parallel(q,omega)
+describing staggered spin fluctuations in the direction of the staggered
+magnetization exhibits a critical continuum whose weight can be controlled
+experimentally by varying the magnetic field.",0610575v3
+2006-10-23,Magnetic excitations in multiferroic TbMnO3,"The magnetic excitations in multiferroic TbMnO3 have been studied by
+inelastic neutron scattering in the spiral and sinusoidally ordered phases. At
+the incommensurate magnetic zone center of the spiral phase, we find three
+low-lying magnons whose character has been fully determined using
+neutron-polarization analysis. The excitation at the lowest energy is the
+sliding mode of the spiral, and two modes at 1.1 and 2.5meV correspond to
+rotations of the spiral rotation plane. These latter modes are expected to
+couple to the electric polarization. The 2.5meV-mode is in perfect agreement
+with recent infra-red-spectroscopy data giving strong support to its
+interpretation as an hybridized phonon-magnon excitation.",0610620v1
+2006-12-12,Universal properties of highly frustrated quantum magnets in strong magnetic fields,"The purpose of the present paper is two-fold. On the one hand, we review some
+recent studies on the low-temperature strong-field thermodynamic properties of
+frustrated quantum spin antiferromagnets which admit the so-called
+localized-magnon eigenstates. One the other hand, we provide some complementary
+new results. We focus on the linear independence of the localized-magnon
+states, the estimation of their degeneracy with the help of auxiliary classical
+lattice-gas models and the analysis of the contribution of these states to
+thermodynamics.",0612281v2
+2007-01-09,Twenty years of magnon Bose condensation and spin current superfluidity in 3He-B,"20 years ago a new quantum state of matter was discovered and identified. The
+observed dynamic quantum state of spin precession in superfluid 3He-B bears the
+properties of spin current superfluidity, Bose condensation of spin waves --
+magnons, off-diagonal long-range order and related phenomena of quantum
+coherence",0701180v13
+2007-01-30,Magnetic Excitations in the Spin-1 Anisotropic Heisenberg Antiferromagnetic Chain System NiCl$_2$-4SC(NH$_2$)$_2$,"NiCl$_2$-4SC(NH$_2$)$_2$ (DTN) is a quantum S=1 chain system with strong
+easy-pane anisotropy and a new candidate for the Bose-Einstein condensation of
+the spin degrees of freedom. ESR studies of magnetic excitations in DTN in
+fields up to 25 T are presented. Based on analysis of the single-magnon
+excitation mode in the high-field spin-polarized phase and previous
+experimental results [Phys. Rev. Lett. 96, 077204 (2006)], a revised set of
+spin-Hamiltonian parameters is obtained. Our results yield $D=8.9$ K, $J_c=2.2$
+K, and $J_{a,b}=0.18$ K for the anisotropy, intrachain, and interchain exchange
+interactions, respectively. These values are used to calculate the
+antiferromagnetic phase boundary, magnetization and the frequency-field
+dependence of two-magnon bound-state excitations predicted by theory and
+observed in DTN for the first time. Excellent quantitative agreement with
+experimental data is obtained.",0701750v1
+2007-03-07,Magnon condensation into Q-ball in 3He-B,"The theoretical prediction of Q-balls in relativistic quantum fields is
+realized here experimentally in superfluid 3He-B. The condensed-matter analogs
+of relativistic Q-balls are responsible for an extremely long lived signal of
+magnetic induction -- the so-called Persistent Signal -- observed in NMR at the
+lowest temperatures. This Q-ball is another representative of a state with
+phase coherent precession of nuclear spins in 3He-B, similar to the well known
+Homogeneously Precessing Domain which we interpret as Bose condensation of spin
+waves -- magnons. At large Q the effect of self-localization is observed. In
+the language of relativistic quantum fields it is caused by interaction between
+the charged and neutral fields, where the neutral field provides the potential
+for the charged one. In the process of self-localization the charged field
+modifies locally the neutral field so that the potential well is formed in
+which the charge is condensed.",0703183v3
+2006-04-13,Higher Loop Bethe Ansatz for Open Spin-Chains in AdS/CFT,"We propose a perturbative asymptotic Bethe ansatz (PABA) for open spin-chain
+systems whose Hamiltonians are given by matrices of anomalous dimension for
+composite operators, and apply it to two types of composite operators related
+to two different brane configurations. One is an AdS_4 \times S^2-brane in the
+bulk AdS_5 \times S^5 which gives rise to a defect conformal field theory
+(dCFT) in the dual field theory, and the other is a giant graviton system with
+an open string excitation. In both cases, excitations on open strings attaching
+to D-branes (a D5-brane for the dCFT case, and a spherical D3-brane for the
+giant graviton case) can be represented by magnon states in the spin-chains
+with appropriate boundary conditions, in which informations of the D-branes are
+encoded. We concentrate on single-magnon problems, and explain how to calculate
+boundary S-matrices via the PABA technique. We also discuss the energy spectrum
+in the BMN limit.",0604100v3
+2006-12-27,Emergent Classical Strings from Matrix Model,"Generalizing the idea of hep-th/0509015 by Berenstein, Correa, and Vazquez,
+we study many-magnon states in an SU(2) sector of a reduced matrix quantum
+mechanics obtained from N=4 SU(N) super Yang-Mills on R x S^3. Generic Q-magnon
+states are described as a chain of ``string-bits'' joining Q+1 eigenvalues of
+background matrices which form a 1/2 BPS circular droplet in the large N limit.
+We will concentrate on infinitely long states whose first and last eigenvalues
+localize at the edge of the droplet. Each constituent string-bit has a complex
+quasi-momentum in general, while the total quasi-momentum P of the state is
+real. For given Q and P, the minimum energy of the chain of string-bits is
+realized when the Q+1 eigenvalues are equally spaced on one and the same line
+segment joining the two outmost eigenvalues localized on the edge with angular
+difference P. Such configuration of bound string-bits precisely reproduces the
+dispersion relation for dyonic giant magnons in classical string theory. We
+also show the emergence of two-spin folded/circular strings in special infinite
+spin limit as particular configurations of closed chains of string-bits.",0612269v1
+2007-07-09,"Evidence for strong 5d electron correlations and electron-magnon coupling in a pyrochlore, Y2Ir2O7","We report the observation of an unusual behavior of highly extended 5d
+electrons in Y2Ir2O7 belonging to pyrochlore family of great current interest
+using high resolution photoemission spectroscopy. The experimental bulk spectra
+reveal an intense lower Hubbard band in addition to weak intensities in the
+vicinity of the Fermi level, e_F. This provides a direct evidence for strong
+electron correlation among the 5d electrons, despite their highly extended
+nature. The high resolution spectrum at room temperature exhibits a pseudogap
+at e_F and |e - e_F|^2 dependence demonstrating the importance of electron
+correlation in this system. Remarkably, in the magnetically ordered phase (T <
+150 K), the spectral lineshape evolves to a |e - e_F|^1.5 dependence
+emphasizing the dominant role of electron-magnon coupling.",0707.1179v1
+2007-07-24,Strong orientational effect of stretched aerogel on the 3He order parameter,"Deformation of aerogel strongly modifies the orientation of the order
+parameter of superfluid 3He confined in aerogel. We used a radial squeezing of
+aerogel to keep the orbital angular momentum of the 3He Cooper pairs in the
+plane perpendicular to the magnetic field. We did not find strong evidence for
+a ""polar"" phase, with a nodal line along the equator of the Fermi surface,
+predicted to occur at large radial squeezing. Instead we observed 3He-A with a
+clear experimental evidence of the destruction of the long-range order by
+random anisotropy -- the Larkin-Imry-Ma effect. In 3He-B we observed and
+identified new modes of NMR, which are impossible to obtain in bulk 3He-B. One
+of these modes is characterized by a repulsive interaction between magnons,
+which is suitable for the magnon Bose-Einstein condensation (BEC).",0707.3544v3
+2007-07-26,Curie temperature of the two band double exchange model for manganites,"We consider two-band double exchange model and calculate the critical
+temperature in ferromagnetic regime (Curie temperature). The localized spins
+are represented in terms of the Schwinger-bosons, and two spin-singlet Fermion
+operators are introduced. In terms of the new Fermi fields the on-site Hund's
+interactions are in a diagonal form and one accounts for them exactly.
+Integrating out the spin-singlet fermions we derive an effective Heisenberg
+type model for a vector which describes the local orientations of the total
+magnetization. The transversal fluctuations of the vector are the true magnons
+in the theory, which is a base for Curie temperature calculation. The critical
+temperature is calculated employing the Schwinger-bosons mean-field theory.
+While approximate, this technic of calculation captures the essentials of the
+magnon fluctuations in the theory, and for 2D systems one obtains zero Curie
+temperature, in accordance with Mermin-Wagner theorem.",0707.3891v1
+2007-08-17,Magnetic Phase Diagram of Spin-1/2 Two-Leg Ladder with Four-Spin Ring Exchange,"We study the spin-1/2 two-leg Heisenberg ladder with four-spin ring exchanges
+under a magnetic field. We introduce an exact duality transformation which is
+an extension of the spin-chirality duality developed previously and yields a
+new self-dual surface in the parameter space. We then determine the magnetic
+phase diagram using the numerical approaches of the density-matrix
+renormalization-group and exact diagonalization methods. We demonstrate the
+appearance of a magnetization plateau and the Tomonaga-Luttinger liquid with
+dominant vector-chirality quasi-long-range order for a wide parameter regime of
+strong ring exchange. A ""nematic"" phase, in which magnons form bound pairs and
+the magnon-pairing correlation functions dominate, is also identified.",0708.2338v1
+2007-09-26,On the anatomy of multi-spin magnon and single spike string solutions,"We study rigid string solutions rotating in $AdS_5\times S^5$ background. For
+particular values of the parameters of the solutions we find multispin
+solutions corresponding to giant magnons and single spike strings. We present
+an analysis of the dispersion relations in the case of three spin solutions
+distributed only in $S^5$ and the case of one spin in $AdS_5$ and two spins in
+$S^5$. The possible relation of these string solutions to gauge theory
+operators and spin chains are briefly discussed.",0709.4231v3
+2007-10-11,Scattering of single spikes,"We apply the dressing method to a string solution given by a static string
+wrapped around the equator of a three-sphere and find that the result is the
+single spike solution recently discussed in the literature. Further application
+of the method allows the construction of solutions with multiple spikes. In
+particular we construct the solution describing the scattering of two single
+spikes and compute the scattering phase shift. As a function of the dressing
+parameters, the result is exactly the same as the one for the giant magnon, up
+to non-logarithmic terms. This suggests that the single spikes should be
+described by an integrable spin chain closely related to the one associated to
+the giant magnons. The field theory interpretation of such spin chain however
+is still unclear.",0710.2300v2
+2007-11-22,A note on the Near Flat Limit for strings in the Maldacena-Nunez background,"Recently Maldacena and Swanson suggested a new limit of string theory on the
+$AdS_5\times S^5$ background, the so called near flat space limit. The
+resulting reduced theory interpolates between the pp-wave limit and giant
+magnon type string solutions. It was shown that the reduced model possess many
+features of the original theory. On the other hand, theories with less
+supersymmetry are of great importance for the string/gauge theory
+correspondence. In this paper we study the near flat limit reduction of string
+theory on the Maldacena-Nunez background, which is dual to $\N=1$ Yang-Mills
+theory. The reduced model interpolates between the pp-wave limit and a certain
+magnon type subsector of the theory. The similarity of the structures of the
+reduced model obtained here and that by Maldacena and Swanson indicates the
+possibility of existence of integrable subsectors of strings on the
+Maldacena-Nunez background.",0711.3600v4
+2008-01-11,Melting of magnetic correlations in charge-orbital ordered La(0.5)Sr(1.5)MnO(4) : competition of ferro and antiferromagnetic states,"The magnetic correlations in the charge- and orbital-ordered manganite
+La(0.5)Sr(1.5)MnO(4) have been studied by elastic and inelastic neutron
+scattering techniques. Out of the well-defined CE-type magnetic structure with
+the corresponding magnons a competition between CE-type and ferromagnetic
+fluctuations develops. Whereas ferromagnetic correlations are fully suppressed
+by the static CE-type order at low temperature, elastic and inelastic CE-type
+correlations disappear with the melting of the charge-orbital order at high
+temperature. In its charge-orbital disordered phase, La(0.5)Sr(1.5)MnO(4)
+exhibits a dispersion of ferromagnetic correlations which remarkably resembles
+the magnon dispersion in ferromagnetically ordered metallic perovskite
+manganites.",0801.1787v1
+2008-04-10,Magneto-elastic interaction in cubic helimagnets with B20 structure,"The magneto-elastic interaction in cubic helimagnets with B20 symmetry is
+considered. It is shown that this interaction is responsible for negative
+contribution to the square of the spin-wave gap $\Delta$ which is alone has to
+disrupt assumed helical structure. It is suggested that competition between
+positive part of $\Delta^2_I$ which stems from magnon-magnon interaction and
+its negative magneto-elastic part leads to the quantum phase transition
+observed at high pressure in $Mn Si$ and $Fe Ge$. This transition has to occur
+when $\Delta^2=0$. For $Mn Si$ from rough estimations at ambient pressure both
+parts $\Delta_I$ and $|\Delta_{ME}|$ are comparable with the experimentally
+observed gap. The magneto-elastic interaction is responsible also for $2\m k$
+modulation of the lattice where $\m k$ is the helix wave-vector and
+contribution to the magnetic anisotropy.
+  Experimental observation by $x$-ray and neutron scattering the lattice
+modulation allows determine the strength of anisotropic part of the
+magneto-elastic interaction responsible for above phenomena and the lattice
+helicity.",0804.1678v1
+2008-04-11,"Two-magnon Raman scattering from the Cu3O4 layers in (Sr,Ba)2Cu3O4Cl2","(Sr$_{2}$,Ba$_{2}$)Cu$_{3}$O$_{4}$Cl$_{2}$ are antiferromagnetic insulators
+which are akin to the parent compounds of the cuprate superconductors but with
+two distinct magnetic ordering temperatures related to two magnetic Cu$_{I}$
+and Cu$_{II}$ spin sublattices. Here we present a study of these materials by
+means of Raman spectroscopy. Following the temperature and polarization
+dependence of the data we readily identify two distinct features at around 3000
+cm$^{-1}$ and 300 cm$^{-1}$ that are related to two-magnon scattering from the
+two sublattices. The estimated spin-exchange coupling constants for the
+Cu$_{I}$ and Cu$_{II}$ sublattices are found to be J$_{I}\sim$139-143(132-136)
+meV and J$_{II}\sim$14(11) meV for Sr(Ba) compounds. Moreover, we observe modes
+at around 480 and 445 cm$^{-1}$ for the Sr and Ba containing samples
+respectively, that disappears at the ordering temperature of the Cu$_{II}$. We
+argue that this modes may also be of magnetic origin and possibly related to
+interband transitions between the Cu$_{I}$-Cu$_{II}$ sublattices.",0804.1859v2
+2008-04-18,On the giant magnon and spike solutions for strings on AdS$_3\times$ S$^3$,"We study solutions for the rotating strings on the sphere with a background
+NS-NS field and on the Anti-de-Sitter spacetime. We show the existence of
+magnon and single spike solutions on R$\times$S$^2$ in the presence of constant
+magnetic field as two limiting cases. We also study the solution for strings on
+AdS$_3\times$ S$^3$ with Melvin deformation. The dispersion relations among
+various conserved charges are shown to receive finite corrections due to the
+deformation parameter. We further study the rotating string on AdS$_3 \times$
+S$^3$ geometry with two conserved angular momenta on S$^3$ and one spin along
+the AdS$_3$. We show that there exists two kinds of solutions: a circular
+string solution and a helical string. We find out the dispersion relation among
+various charges and give physical interpretation of these solutions.",0804.2923v3
+2008-06-01,Anomalous frequency and intensity scaling of collective and local modes in a coupled spin tetrahedron system,"We report on the magnetic excitation spectrum of the coupled spin tetrahedral
+system Cu$_{2}$Te$_{2}$O$_{5}$Cl$_{2}$ using Raman scattering on single
+crystals. The transition to an ordered state at T$_{N}^{Cl}$=18.2 K evidenced
+from thermodynamic data leads to the evolution of distinct low-energy magnetic
+excitations superimposed by a broad maximum. These modes are ascribed to
+magnons with different degree of localization and a two-magnon continuum. Two
+of the modes develop a substantial energy shift with decreasing temperature
+similar to the order parameter of other Neel ordered systems. The other two
+modes show only a negligible temperature dependence and dissolve above the
+ordering temperature in a continuum of excitations at finite energies. These
+observations point to a delicate interplay of magnetic inter- and
+intra-tetrahedra degrees of freedom and an importance of singlet fluctuations
+in describing a spin dynamics.",0806.0147v1
+2008-08-04,Reflecting magnons from D7 and D5 branes,"We obtain the reflection matrices for the scattering of elementary magnons
+from certain open boundaries, corresponding to open strings ending on D7 and D5
+branes in $AdS_5\times S^5$. In each case we consider two possible orientations
+for the vacuum state. We show that symmetry arguments are sufficient to
+determine the reflection matrices up to at most two unknown functions. The D7
+reflection matrices obey the boundary Yang Baxter-Equation. This is automatic
+for one vacuum orientation, and requires a natural choice of ratio between two
+unknowns for the other. In contrast, the D5 reflection matrices do not obey the
+boundary Yang Baxter-Equation. In both cases we show consistency with the
+existent weak and strong coupling results.",0808.0452v3
+2008-08-15,Collective excitations in two-dimensional antiferromagnet in strong magnetic field,"We discuss spin-$\frac12$ two-dimensional (2D) Heisenberg antiferromagnet
+(AF) on a square lattice at T=0 in strong magnetic field H near its saturation
+value $H_c$. A perturbation approach is proposed to obtain spectrum of magnons
+with momenta not very close to AF vector in the leading order in small
+parameter $(H_c-H)/H_c$. We find that magnons are well-defined quasi-particles
+at $H>0.9H_c$ although the damping is quite large near the zone boundary. A
+characteristic rotonlike local minimum in the spectrum is observed at ${\bf
+k}=(\pi,0)$ accompanied by decrease of the damping near $(\pi,0)$. The
+suggested approach can be used in discussion of short-wavelength excitations in
+other 2D Bose gases of particles or quasi-particles.",0808.2127v3
+2008-11-25,Electric-dipole active two-magnon excitation in {\textit{ab}} spiral spin phase of a ferroelectric magnet Gd$_{\textbf{0.7}}$Tb$_{\textbf{0.3}}$MnO$_{\textbf 3}$,"A broad continuum-like spin excitation (1--10 meV) with a peak structure
+around 2.4 meV has been observed in the ferroelectric $ab$ spiral spin phase of
+Gd$_{0.7}$Tb$_{0.3}$MnO$_3$ by using terahertz (THz) time-domain spectroscopy.
+Based on a complete set of light-polarization measurements, we identify the
+spin excitation active for the light $E$ vector only along the a-axis, which
+grows in intensity with lowering temperature even from above the magnetic
+ordering temperature but disappears upon the transition to the $A$-type
+antiferromagnetic phase. Such an electric-dipole active spin excitation as
+observed at THz frequencies can be ascribed to the two-magnon excitation in
+terms of the unique polarization selection rule in a variety of the
+magnetically ordered phases.",0811.4098v1
+2009-01-18,Stable topological textures in a classical 2D Heisenberg model,"We show that stable localized topological soliton textures (skyrmions) with
+$\pi_2$ topological charge $\nu \geq 1$ exist in a classical 2D Heisenberg
+model of a ferromagnet with uniaxial anisotropy. For this model the soliton
+exist only if the number of bound magnons exceeds some threshold value $N_{\rm
+cr}$ depending on $\nu $ and the effective anisotropy constant $K_{\rm eff}$.
+We define soliton phase diagram as the dependence of threshold energies and
+bound magnons number on anisotropy constant. The phase boundary lines are
+monotonous for both $\nu=1$ and $\nu >2$, while the solitons with $\nu=2$
+reveal peculiar nonmonotonous behavior, determining the transition regime from
+low to high topological charges. In particular, the soliton energy per
+topological charge (topological energy density) achieves a minimum neither for
+$\nu=1$ nor high charges, but rather for intermediate values $\nu=2$ or
+$\nu=3$.",0901.2707v1
+2009-01-22,Magnon-Mediated Pairing and Isotope Effect in Iron-based Superconductors,"Within a minimal model for the iron-based superconductors in which itinerant
+electrons interact with a band of local moments, we derive a a general
+conclusion for multi-band superconductivity. In a multi-band superconductor,
+due to the Adler theorem, the inter-band scattering dominates the intra-band
+scattering at the long wave length limit as long as both interactions are
+induced by Goldstone boson (which is magnon in our case) and the transfered
+momentum is nonzero. Such kind of interaction leads to a well-known
+sigh-reversing superconductivity even if the inter-band and intra-band
+interaction are repulsive. This effect can be modeled as arising from an
+internal Josephson link between the Fermi surface sheets. Our model is also
+consistent with the recently discovered coexistence of superconductivity and
+magnetic order in iron-pnictides. Although the experimentally observed isotope
+effect is large, $\alpha=0.4$, we show that it is consistent with a
+non-phononic mechanism in which it is the isotope effects result in a change in
+the lattice constant and as a consequence the zero-point motion of the Fe
+atoms.",0901.3538v2
+2009-01-28,A phason disordered two dimensional quantum antiferromagnet,"We examine a novel type of disorder in quantum antiferromagnets. Our model
+consists of localized spins with antiferromagnetic exchanges on a bipartite
+quasiperiodic structure, which is geometrically disordered in such a way that
+no frustration is introduced. In the limit of zero disorder, the structure is
+the perfect Penrose rhombus tiling. This tiling is progressively disordered by
+augmenting the number of random ""phason flips"" or local tile-reshuffling
+operations. The ground state remains N\'eel ordered, and we have studied its
+properties as a function of increasing disorder using linear spin wave theory
+and quantum Monte Carlo. We find that the ground state energy decreases,
+indicating enhanced quantum fluctuations with increasing disorder. The magnon
+spectrum is progressively smoothed, and the effective spin wave velocity of low
+energy magnons increases with disorder. For large disorder, the ground state
+energy as well as the average staggered magnetization tend towards limiting
+values characteristic of this type of randomized tilings.",0901.4441v1
+2009-02-08,Three-magnon problem for exactly rung-dimerized spin ladders: from general outlook to Bethe Ansatze,"Three-magnon problem for exactly rung-dimerized spin ladder is brought up
+separately at all total spin sectors. At first a special duality transformation
+of the $\rm Schr\ddot odinger$ equation is found within general outlook. Then
+the problem is treated within Coordinate Bethe Ansatze. A straightforward
+approach is developed to obtain pure scattering states. At values S=0 and S=3
+of total spin the $\rm Schr\ddot odinger$ equation has the form inherent in the
+$XXZ$ chain. For $S=1,2$ solvability holds only in five previously found {\it
+completely integrable} cases. Nevertheless a partial S=1 Bethe solution always
+exists even for general non integrable model. Pure scattering states for all
+total spin sectors are presented explicitly.",0902.1335v1
+2009-03-21,Scattering of surface and volume spin waves in a magnonic crystal,"The operational characteristics of a magnonic crystal, which was fabricated
+as an array of shallow grooves etched on a surface of a magnetic film, were
+compared for magnetostatic surface spin waves and backward volume magnetostatic
+spin waves. In both cases the formation of rejection frequency bands was
+studied as a function of the grooves depth. It has been found that the
+rejection of the volume wave is considerably larger than of the surface one.
+The influences of the nonreciprocity of the surface spin waves as well as of
+the scattering of the lowest volume spin-wave mode into higher thickness volume
+modes on the rejection efficiency are discussed.",0903.3686v1
+2009-04-17,Control of bound-pair transport by periodic driving,"We investigate the effect of periodic driving by an external field on systems
+with attractive pairing interactions. These include spin systems (like the
+ferromagnetic XXZ model) as well as ultracold fermionic atoms described by the
+attractive Hubbard model. We show that a well-known phenomenon seen in
+periodically driven systems--the renormalization of the exchange coupling
+strength--acts selectively on bound-pairs of spins/atoms, relative to
+magnon/bare atom states. Thus one can control the direction and speed of
+transport of bound-pair relative to magnon/unpaired atom states, and thus
+coherently achieve spatial separation of these components. Applications to
+recent experiments on transport with fermionic atoms in optical lattices which
+consist of mixtures of bound-pairs and bare atoms are discussed.",0904.2614v6
+2009-04-22,Theory of Thermal Hall Effect in Quantum Magnets,"We present a theory of the thermal Hall effect in insulating quantum magnets,
+where the heat current is totally carried by charge-neutral objects such as
+magnons and spinons. Two distinct types of thermal Hall responses are
+identified. For ordered magnets, the intrinsic thermal Hall effect for magnons
+arises when certain conditions are satisfied for the lattice geometry and the
+underlying magnetic order. The other type is allowed in a spin liquid which is
+a novel quantum state since there is no order even at zero temperature. For
+this case, the deconfined spinons contribute to the thermal Hall response due
+to Lorentz force. These results offer a clear experimental method to prove the
+existence of the deconfined spinons via a thermal transport phenomenon.",0904.3427v3
+2009-05-07,Towards the theory of ferrimagnetism II,"The present paper is a sequel to the paper by Karchev (2008
+J.Phys.:Condens.Matter {\bf 20} 325219). A two-sublattice ferrimagnet, with
+spin-$s_1$ operators $\bf{S_{1i}}$ at the sublattice $A$ site and spin-$s_2$
+operators $\bf{S_{2i}}$ at the sublattice $B$ site, is considered. Renormalized
+spin-wave theory, which accounts for the magnon-magnon interaction, and its
+extension are developed to describe the two ferrimagnetic phases $(0,T^*)$ and
+$(T^*,T_N)$ in the system, and to calculate the magnetization as a function of
+temperature.
+  The influence of the parameters in the theory on the characteristic
+temperatures $T_N$ and $T^*$ is studied. It is shown that, increasing the
+inter-sublattice exchange interaction, the ratio $T_N/T^*>1$ decreases
+approaching one, and above some critical value of the exchange constant there
+is only one phase $T_N = T^*$, and the magnetization-temperature curve has the
+typical Curie-Weiss profile. When the intra-exchange constant of sublattice
+with stronger intra-exchange interaction increases the $Ne\grave{e}l$
+temperature increases while $T^*$ remains unchanged. Finally, when the magnetic
+order of the sublattice with smaller magnetic order decreases, $T^*$ decreases.
+The theoretical predictions are utilize to interpret the experimentally
+measured magnetization-temperature curves.",0905.1036v1
+2009-08-17,Magnon dispersion to four loops in the ABJM and ABJ models,"The ABJM model is a superconformal Chern-Simons theory with N=6 supersymmetry
+which is believed to be integrable in the planar limit. However, there is a
+coupling dependent function that appears in the magnon dispersion relation and
+the asymptotic Bethe ansatz that is only known to leading order at strong and
+weak coupling. We compute this function to four loops in perturbation theory by
+an explicit Feynman diagram calculation for both the ABJM model and the ABJ
+extension. We find that all coefficients have maximal transcendentality. We
+then compute the four-loop wrapping correction for a scalar operator in the 20
+of SU(4) and find that it agrees with a recent prediction from the ABJM
+Y-system of Gromov, Kazakov and Vieira. We also propose a limit of the ABJ
+model that might be perturbatively integrable at all loop orders but has a
+short range Hamiltonian.",0908.2463v3
+2009-09-19,Cooperative order and excitation spectra in the bicomponent spin networks,"A ferrimagnetic spin model composed of $S=1/2$ spin-dimers and $S=5/2$
+spin-chains is studied by combining the bond-operator representation (for
+$S=1/2$ spin-dimers) and Holstein-Primakoff transformation (for $S=5/2$ spins).
+A finite interaction $J_{\rm DF}$ between the spin-dimer and the spin chain
+makes the spin chains ordered antiferromagnetically and the spin dimers
+polarized. The effective interaction between the spin chains, mediated by the
+spin dimers, is calculated up to the third order. The staggered magnetization
+in the spin dimer is shown proportional to $J_{\rm DF}$. It presents an
+effective staggered field reacting on the spin chains. The degeneracy of the
+triplons is lifted due to the chain magnetization and a mode with longitudinal
+polarization is identified. Due to the triplon-magnon interaction, the
+hybridized triplon-like excitations show different behaviors near the vanishing
+$J_{\rm DF}$. On the other hand, the hybridized magnon-like excitations open a
+gap $\Delta_A\sim J_{\rm DF}$. These results consist well with the experiments
+on Cu$_{2}$Fe$_{2}$Ge$_{4}$O$_{13}$.",0909.3576v2
+2009-11-10,Spin-wave propagation in a microstructured magnonic crystal,"Transmission of microwave spin waves through a microstructured magnonic
+crystal in the form of a permalloy waveguide of a periodically varying width
+was studied experimentally and theoretically. The spin wave characteristics
+were measured by spatially-resolved Brillouin light scattering microscopy. A
+rejection frequency band was clearly observed. The band gap frequency was
+controlled by the applied magnetic field. The measured spin-wave intensity as a
+function of frequency and propagation distance is in good agreement with a
+model calculation.",0911.1920v1
+2010-01-11,Magnon softening in a ferromagnetic monolayer: a first-principles spin dynamics study,"We study the Fe/W(110) monolayer system through a combination of first
+principles calculations and atomistic spin dynamics simulations. We focus on
+the dispersion of the spin waves parallel to the [001] direction. Our results
+compare favorably with the experimental data of Prokop et al. [Phys. Rev. Lett.
+102, 177206], and correctly capture a drastic softening of the magnon spectrum,
+with respect to bulk bcc Fe. The suggested shortcoming of the itinerant
+electron model, in particular that given by density functional theory, is
+refuted. We also demonstrate that finite temperature effects are significant,
+and that atomistic spin dynamics simulations represent a powerful tool with
+which to include these.",1001.1669v2
+2010-01-22,Theory of electromagnon in the multiferroic Mn perovskites: Vital role of higher harmonic components of the spiral spin order,"We study theoretically the electromagnon and its optical spectrum (OS) of the
+terahertz-frequency regime in the magnetic-spiral-induced multiferroic phases
+of the rare-earth (R) Mn perovskites, RMnO3, taking into account the elliptical
+deformation or the higher harmonics of the spiral spin configuration, which has
+been missed so far. A realistic spin Hamiltonian, which gives phase diagrams in
+agreement with experiments, resolves a long standing puzzle, i.e., the
+double-peak structure of the OS with a larger low-energy peak originating from
+magnon modes hybridized with the zone-edge state. We also predict the magnon
+branches associated with the electromagnon, which can be tested by
+neutron-scattering experiment.",1001.3905v1
+2010-02-12,Instability of Magnons in Two-dimensional Antiferromagnet at High Magnetic Fields,"Spin dynamics of the square lattice Heisenberg antiferromagnet, \BaMnGeO, is
+studied by a combination of bulk measurements, neutron diffraction, and
+inelastic neutron scattering techniques. Easy plane type antiferromagnetic
+order is identified at $T \le 4.0$ K. The exchange interactions are estimated
+as $J_1$ = 27.8(3)${\mu}$eV and $J_2$ = 1.0(1) ${\mu}$eV, and the saturation
+field $H_{\rm C}$ is 9.75 T. Magnetic excitation measurements with high
+experimental resolution setup by triple axis neutron spectrometer reveals the
+instability of one magnon excitation in the field range of $0.7H_{\rm C}
+\lesssim H \lesssim 0.85H_{\rm C}$.",1002.2470v1
+2010-02-19,Electromagnons in the multiferroic state of perovskite manganites with symmetric-exchange striction,"We have investigated electrically-active magnetic excitations
+(electromagnons) in perovskite manganites with the $E$-type (up-up-down-down)
+spin structure by terahertz spectroscopy. Eu$_{1-x}$Y$_x$MnO$_3$ (0.1$\le
+x\le$1) and Y$_{1-y}$Lu$_y$MnO$_3$ (0$\le y\le$1) without magnetic $f$-moments,
+which host collinear sinusoidal, $A$-type, cycloidal, and $E$-type spin orders,
+are used to examine the systematics of possible electromagnons. Three-peak
+structures (23, 35, 45 cm$^{-1}$) of magnetic origin show up in the $E$-type
+phase with little composition ($y$) dependence of frequencies, making a
+contrast with the electromagnons observed in the cycloidal-spin ($x\le0.8$)
+phases. One of these electromagnon is ascribed to the zone-edge magnon mode
+based on the calculated magnon dispersions.",1002.3676v1
+2010-06-27,Spin wave resonances in antiferromagnets,"Spin wave resonances with enormously large wave numbers corresponding to wave
+vectors 10^5-10^6 cm^{-1} are observed in thin plates of FeBO3. The study of
+spin wave resonances allows one to obtain information about the spin wave
+spectrum. The temperature dependence of a non-uniform exchange constant is
+determined for FeBO3. Considerable softening of the magnon spectrum resulting
+from the interaction of magnons, is observed at temperatures above 1/3 of the
+Neel temperature. The excitation level of spin wave resonances is found to
+depend significantly on the inhomogeneous elastic distortions artificially
+created in the sample. A theoretical model to describe the observed effects is
+proposed.",1006.5192v1
+2010-07-09,Quantum finite-size effects for dyonic magnons in the AdS_4 x CP^3,"We compute quantum corrections to finite-size effects for various dyonic
+giant magnons in the AdS_4 x CP^3 in two different approaches. The off-shell
+algebraic curve method is used to quantize the classical string configurations
+in semi-classical way and to compute the corrections to the string energies.
+These results are compared with the F-term L\""uscher formula based on the
+S-matrix of the AdS_4 / CFT_3. The fact that the two results match exactly
+provides another stringent test for the all-loop integrability conjecture and
+the exact S-matrix based on it.",1007.1598v2
+2010-07-19,Anomalously large damping of long-wavelength quasiparticles caused by long-range interaction,"We demonstrate that long-range interaction in a system can lead to a very
+strong interaction between long-wavelength quasiparticles and make them heavily
+damped. In particular, we discuss magnon spectrum using 1/S expansion in 3D
+Heisenberg ferromagnet (FM) with arbitrary small dipolar forces at T<<T_C. We
+obtain that a fraction of long-wavelength magnons with energies e_k<T has
+anomalously large damping G_k (ratio G_k/e_k reaches 0.3 for certain k). This
+effect is observed both in quantum and classical FMs. Remarkably, this result
+contradicts expectation of the quasiparticle concept according which a weakly
+excited state of a many-body system can be represented as a collection of
+weakly interacting elementary excitations. Particular materials are pointed out
+which are suitable for corresponding experiments.",1007.3081v2
+2010-07-19,Bose-Einstein condensation at finite momentum and magnon condensation in thin film ferromagnets,"We use the Gross-Pitaevskii equation to determine the spatial structure of
+the condensate density of interacting bosons whose energy dispersion epsilon_k
+has two degenerate minima at finite wave-vectors q. We show that in general the
+Fourier transform of the condensate density has finite amplitudes for all
+integer multiples of q. If the interaction is such that many Fourier components
+contribute, the Bose condensate is localized at the sites of a one-dimensional
+lattice with spacing 2pi/q; in this case Bose-Einstein condensation resembles
+the transition from a liquid to a crystalline solid. We use our results to
+investigate the spatial structure of the Bose condensate formed by magnons in
+thin films of ferromagnets with dipole-dipole interactions.",1007.3200v3
+2010-08-09,Observation of the Magnon Hall Effect,"The Hall effect usually occurs when the Lorentz force acts on a charge
+current in a conductor in the presence of perpendicular magnetic field. On the
+other hand, neutral quasi-particles such as phonons and spins can carry heat
+current and potentially show the Hall effect without resorting to the Lorentz
+force. We report experimental evidence for the anomalous thermal Hall effect
+caused by spin excitations (magnons) in an insulating ferromagnet with a
+pyrochlore lattice structure. Our theoretical analysis indicates that the
+propagation of the spin wave is influenced by the Dzyaloshinskii-Moriya
+spin-orbit interaction, which plays the role of the vector potential as in the
+intrinsic anomalous Hall effect in metallic ferromagnets.",1008.1564v1
+2010-08-31,Magnetic excitations in the low-temperature ferroelectric phase of multiferroic YMn2O5 using inelastic neutron scattering,"We studied magnetic excitations in a low-temperature ferroelectric phase of
+the multiferroic YMn2O5 using inelastic neutron scattering (INS). We identify
+low-energy magnon modes and establish a correspondence between the magnon peaks
+observed by INS and electromagnon peaks observed in optical absorption [1].
+Furthermore, we explain the microscopic mechanism, which results in the
+lowest-energy electromagnon peak, by comparing the inelastic neutron spectral
+weight with the polarization in the commensurate ferroelectric phase.",1008.5354v2
+2010-09-02,Theory of magnon-driven spin Seebeck effect,"The spin Seebeck effect is a spin-motive force generated by a temperature
+gradient in a ferromagnet that can be detected via normal metal contacts
+through the inverse spin Hall effect [K. Uchida {\it et al.}, Nature {\bf 455},
+778-781 (2008)]. We explain this effect by spin pumping at the contact that is
+proportional to the spin-mixing conductance of the interface, the inverse of a
+temperature-dependent magnetic coherence volume, and the difference between the
+magnon temperature in the ferromagnet and the electron temperature in the
+normal metal [D. J. Sanders and D. Walton, Phys. Rev. B {\bf 15}, 1489 (1977)].",1009.0318v2
+2010-10-27,Magnetic spin excitations in Mn doped GaAs : A model study,"We provide a quantitative theoretical model study of the dynamical magnetic
+properties of optimally annealed Ga$_{1-x}$Mn$_x$As. This model has already
+been shown to reproduce accurately the Curie temperatures for
+Ga$_{1-x}$Mn$_x$As. Here we show that the calculated spin stiffness are in
+excellent agreement with those which were obtained from ab-initio based
+studies. In addition, an overall good agreement is also found with available
+experimental data. We have also evaluated the magnon density of states and the
+typical density of states from which the ""mobility edge"", separating the
+extended from localized magnon states, was determined. The power of the model
+lies in its ability to be generalized for a broad class of diluted magnetic
+semiconductor materials, thus it bridges the gap between first principle
+calculations and model based studies.",1010.5763v2
+2010-11-30,Phonons and their Coupling to Magnons in n=2 Ruddlesden-Popper Compounds,"The number of absorption and Raman optical modes for each Wyckoff orbit in
+the high-temperature tetragonal (I4/mmm) parent lattice of the
+Ruddlesden-Popper compounds Ca$_3$X$_2$O$_7$, with X=Mn or X=Ti is given. We
+analyze the effect of sequential perturbations which lower the symmetry to Cmcm
+and Cmc2$_1$ and finally include magnetic ordering. We determine the power law
+behavior (within mean field theory) for the cross section for photon absorption
+and Raman scattering of modes which appear as the symmetry is successively
+lowered. In the Cmc2$_1$ phase we give a symmetry analysis to discuss the
+magnon-phonon coupling which in other systems gives rise to ""electromagnons.""
+From our results we suggest several experiments to clarify the phase diagram
+and other properties of these systems.",1011.6672v2
+2010-12-21,Non-Volatile Magnonic Logic Circuits Engineering,"We propose a concept of magnetic logic circuits engineering, which takes an
+advantage of magnetization as a computational state variable and exploits spin
+waves for information transmission. The circuits consist of magneto-electric
+cells connected via spin wave buses. We present the result of numerical
+modeling showing the magneto-electric cell switching as a function of the
+amplitude as well as the phase of the spin wave. The phase-dependent switching
+makes it possible to engineer logic gates by exploiting spin wave buses as
+passive logic elements providing a certain phase-shift to the propagating spin
+waves. We present a library of logic gates consisting of magneto-electric cells
+and spin wave buses providing 0 or p phase shifts. The utilization of phases in
+addition to amplitudes is a powerful tool which let us construct logic circuits
+with a fewer number of elements than required for CMOS technology. As an
+example, we present the design of the magnonic Full Adder Circuit comprising
+only 5 magneto-electric cells. The proposed concept may provide a route to more
+functional wave-based logic circuitry with capabilities far beyond the limits
+of the traditional transistor-based approach.",1012.4768v1
+2011-02-14,Thermal conductivity of pure and Zn-doped LiCu_2O_2 single crystals,"We report a study of the low-temperature thermal conductivity (\kappa) of
+pure and Zn-doped LiCu_2O_2 single crystals. The \kappa(T) of pure LiCu_2O_2
+single crystal shows a double-peak behavior, with two peaks locating at 48 K
+and 14 K, respectively. The different dependences of the peaks on the Zn
+concentration indicate that the high-T peak is likely due to the phonon
+transport while the low-T one is attributed to the magnon transport in the spin
+spiral ordering state. In addition, the magnetic field can gradually suppress
+the low-T peak but does not affect the high-T one; this further confirms that
+the low-T peak is originated from the magnon heat transport.",1102.2788v1
+2011-05-27,Resonances in a dilute gas of magnons and metamagnetism of isotropic frustrated ferromagnetic spin chains,"We show that spin-S chains with SU(2)-symmetric, ferromagnetic
+nearest-neighbor and frustrating antiferromagnetic next-nearest-neighbor
+exchange interactions exhibit metamagnetic behavior under the influence of an
+external magnetic field for small S, in the form of a first-order transition to
+the fully polarized state. The corresponding magnetization jump increases
+gradually starting from an S-dependent critical value of exchange couplings and
+takes a maximum in the vicinity of a ferromagnetic Lifshitz point. The
+metamagnetism results from resonances in the dilute magnon gas caused by an
+interplay between quantum fluctuations and frustration.",1105.5626v2
+2011-06-22,Tunable Magnonic Frequency and Damping in [Co/Pd]8 Multilayers with Variable Co Layer Thickness,"We report the experimental observation of collective picosecond magnetization
+dynamics in [Co/Pd]8 multilayers with perpendicular magnetic anisotropy. The
+precession frequency shows large and systematic variation from about 5 GHz to
+about 90 GHz with the decrease in the Co layer thickness from 1.0 nm to 0.22 nm
+due to the linear increase in the perpendicular magnetic anisotropy. The
+damping coefficient 'alpha' is found to be inversely proportional to the Co
+layer thickness and a linear relation between the perpendicular magnetic
+anisotropy and 'alpha' is established. We discuss the possible reasons behind
+the enhanced damping as the d-d hybridization at the interface and spin
+pumping. These observations are significant for the applications of these
+materials in spintronics and magnonic crystals.",1106.4491v1
+2011-07-13,More three-point correlators of giant magnons with finite size,"In the framework of the semiclassical approach, we compute the normalized
+structure constants in three-point correlation functions, when two of the
+vertex operators correspond to heavy string states, while the third vertex
+corresponds to a light state. This is done for the case when the heavy string
+states are finite-size giant magnons with one or two angular momenta, and for
+two different choices of the light state, corresponding to dilaton operator and
+primary scalar operator. The relevant operators in the dual gauge theory are
+Tr(F_{\mu\nu}^2 Z^j+...) and Tr(Z^j). We first consider the case of AdS_5 x S^5
+and N = 4 super Yang-Mills. Then we extend the obtained results to the
+gamma-deformed AdS_5 x S^5_\gamma, dual to N = 1 super Yang-Mills theory,
+arising as an exactly marginal deformation of N = 4 super Yang-Mills.",1107.2645v1
+2011-08-16,Magnetic rogue wave in a perpendicular anisotropic ferromagnetic nanowire with spin-transfer torque,"We present the current controlled motion of dynamic soliton embedded in spin
+wave background in ferromagnetic nanowire. With the stronger breather character
+we get the novel magnetic rogue wave and clarify its formation mechanism. The
+generation of magnetic rogue wave is mainly arose from the accumulation of
+energy and magnons toward to its central part. We also observe that the
+spin-polarized current can control the exchange rate of magnons between
+envelope soliton and background, and the critical current condition is obtained
+analytically. Even more interesting is that the spin-transfer torque plays the
+completely opposite role for the cases of below and above the critical value.",1108.3252v2
+2011-08-18,Three-point correlators: finite-size giant magnons and singlet scalar operators on higher string levels,"In the framework of the semiclassical approach, we compute the normalized
+structure constants in three-point correlation functions, when two of the
+vertex operators correspond to ""heavy"" string states, while the third vertex
+corresponds to a ""light"" state. This is done for the case when the ""heavy""
+string states are finite-size giant magnons, carrying one or two angular
+momenta. The ""light"" states are taken to be singlet scalar operators on higher
+string levels. We first consider the case of string theory on AdS_5xS^5 dual to
+N = 4 super Yang-Mills. Then we extend the obtained results to the
+gamma-deformed AdS_5x S^5, corresponding to N = 1 super Yang-Mills theory,
+appearing as an exactly marginal deformation of N=4 super Yang-Mills.",1108.3812v1
+2011-09-03,Low-temperature heat transport of the layered spin-dimer compound Ba_3Mn_2O_8,"We report the study on the low-temperature heat transport of Ba_3Mn_2O_8
+single crystal, a layered spin-dimer compound exhibiting the
+magnetic-field-induced magnetic order or the magnon Bose-Einstein condensation.
+The thermal conductivities (\kappa) along both the ab plane and the c axis show
+nearly isotropic dependence on magnetic field, that is, \kappa is strongly
+suppressed with increasing field, particularly at the critical fields of
+magnetic phase transitions. These results indicate that the magnetic
+excitations play a role of scattering phonons and the scattering effect is
+enhanced when the magnetic field closes the gap in the spin spectrum. In
+addition, the magnons in the BEC state of this materials do not show notable
+ability of carrying heat.",1109.0587v1
+2011-09-12,Single-ion anisotropy in Haldane chains and form factor of the O(3) nonlinear sigma model,"We consider spin-1 Haldane chains with single-ion anisotropy, which exists in
+known Haldane chain materials. We develop a perturbation theory in terms of
+anisotropy, where magnon-magnon interaction is important even in the low
+temperature limit. The exact two-particle form factor in the O(3) nonlinear
+sigma model leads to quantitative predictions on several dynamical properties
+including dynamical structure factor and electron spin resonance frequency
+shift. These agree very well with numerical results, and with experimental data
+on the Haldane chain material Ni(C$_5$H$_{14}$N$_2$)$_2$N$_3$(PF$_6$).",1109.2607v2
+2011-10-04,Isospin Dynamics in Sr2IrO4 : Forging Links to Cuprate Superconductivity,"We used resonant inelastic x-ray scattering to reveal the nature of magnetic
+interactions in Sr2IrO4, a 5d transition-metal oxide with a spin-orbit
+entangled ground state and Jeff=1/2 magnetic momemts, referred to as
+'isospins'. The magnon dispersion in Sr2IrO4 is well described by an
+antiferromagnetic Heisenberg model with isospin one-half moments on a square
+lattice, which renders the low-energy effective physics of Sr2IrO4 much akin to
+that in superconducting cuprates. This is further supported by the observation
+of exciton modes in Sr2IrO4 whose dispersion is strongly renormalized by
+magnons, which can be understood by analogy to the hole propagation in the
+background of antiferromagnetically ordered spins in the cuprates.",1110.0759v1
+2011-12-15,"Selective spin wave excitation in ferromagnetic (Ga,Mn)As layers by picosecond strain pulses","We demonstrate selective excitation of a spin wave mode in a ferromagnetic
+(Ga,Mn)As film by picosecond strain pulses. For a certain range of magnetic
+fields applied in the layer plane only a single frequency is detected for the
+magnetization precession. We explain this selectivity of spin mode excitation
+by the necessity of spatial matching of magnon and phonon eigenfunctions, which
+represents a selection rule analogous to momentum conservation for
+magnon-phonon interaction in bulk ferromagnetic materials.",1112.3394v1
+2012-06-07,Semiquantitative theory for high-field low-temperature properties of a distorted diamond spin chain,"We consider the antiferromagnetic Heisenberg model on a distorted diamond
+chain and use the localized-magnon picture adapted to a distorted geometry to
+discuss some of its high-field low-temperature properties. More specifically,
+in our study we assume that the partition function for a slightly distorted
+geometry has the same form as for ideal geometry, though with slightly
+dispersive one-magnon energies. We also discuss the relevance of such a
+description to azurite.",1206.1441v2
+2012-08-25,Magnon-mediated interactions between fermions depend strongly on the lattice structure,"We propose two new methods to calculate exactly the spectrum of two
+spin-${1\over 2}$ charge carriers moving in a ferromagnetic background, at zero
+temperature. We find that if the spins are located on a different sublattice
+than that on which the fermions move, magnon-mediated effective interactions
+are very strong and can bind the fermions into low-energy bipolarons with
+triplet character. This never happens in models where spins and charge carriers
+share the same lattice, whether they are in the same band or in different
+bands. This proves that effective one-lattice models do not describe correctly
+the low-energy part of the two-carrier spectrum of a two-sublattice model, even
+though they may describe the low-energy single-carrier spectrum appropriately.",1208.5144v1
+2012-08-25,The role of the lattice structure in determining the magnon-mediated interactions between charge carriers doped into a magnetically ordered background,"We use two recently proposed methods to calculate exactly the spectrum of two
+spin-${1\over 2}$ charge carriers moving in a ferromagnetic background, at zero
+temperature, for three types of models. By comparing the low-energy states in
+both the one-carrier and the two-carrier sectors, we analyze whether complex
+models with multiple sublattices can be accurately described by simpler
+Hamiltonians, such as one-band models. We find that while this is possible in
+the one-particle sector, the magnon-mediated interactions which are key to
+properly describe the two-carrier states of the complex model are not
+reproduced by the simpler models. We argue that this is true not just for
+ferromagnetic, but also for antiferromagnetic backgrounds. Our results question
+the ability of simple one-band models to accurately describe the low-energy
+physics of cuprate layers.",1208.5146v1
+2012-11-23,Comment on Strings in AdS3 x S3 x S3 x S1 at One Loop,"This paper studies semiclassical strings in AdS3 x S3 x S3 x S1 using the
+algebraic curve. Calculating one-loop corrections to the energy of the giant
+magnon fixes the constant term c in the expansion of the coupling h(\lambda).
+Comparing these to similar corrections for long spinning strings gives a
+prediction for the one-loop term f_1 in the expansion of the cusp anomalous
+dimension f(h), for all \alpha (where \alpha --> 1 is the AdS3 x S3 x T4
+limit). For these semiclassical mode sums there is a similar choice of
+regularisation prescriptions to that encountered in AdS4 x CP3. However at
+\alpha \neq 1/2 they lead to different values of f_1 and are therefore not
+related by a simple change of the coupling. The algebraic curve is also used to
+calculate various finite-size corrections for giant magnons, which are
+well-behaved as \alpha --> 1, and can be compared to the recently published
+S-matrices.",1211.5587v3
+2012-12-12,Highly Dispersive Scattering From Defects In Non-Collinear Magnets,"We demonstrate that point-like defects in non-collinear magnets give rise to
+a highly dispersive structure in the magnon scattering, violating a standard
+paradigm of its momentum independence. For a single impurity spin coupled to a
+prototypical non-collinear antiferromagnet we find that the resolvent is
+dominated by a distinct dispersive structure with its momentum-dependence set
+by the magnon dispersion and shifted by the ordering vector. This feature is a
+consequence of umklapp scattering off the impurity-induced spin texture, which
+arises due to the non-collinear ground state of the host system. Detailed
+results for the staggered and uniform magnetization of this texture as well as
+the T-matrix from numerical linear spin-wave theory are presented.",1212.2972v1
+2012-12-24,Excited states of the quasi-one-dimensional hexagonal quantum antiferromagnets,"We investigate the excited states of the quasi-one-dimensional quantum
+antiferromagnets on hexagonal lattices, including the longitudinal modes based
+on the magnon-density waves. A model Hamiltonian with a uniaxial single-ion
+anisotropy is first studied by a spin-wave theory based on the one-boson
+method; the ground state thus obtained is employed for the study of the
+longitudinal modes. The full energy spectra of both the transverse modes (i.e.,
+magnons) and the longitudinal modes are obtained as functions of the
+nearest-neighbor coupling and the anisotropy constants. We have found two
+longitudinal modes due to the non-collinear nature of the triangular
+antiferromagnetic order, similar to that of the phenomenological field theory
+approach by Affleck. The excitation energy gaps due to the anisotropy and the
+energy gaps of the longitudinal modes without anisotropy are then investigated.
+We then compare our results for the longitudinal energy gaps at the magnetic
+wavevectors with the experimental results for several antiferromagnetic
+compounds with both integer and non-integer spin quantum numbers, and we find
+good agreement after the higher-order contributions are included in our
+calculations.",1212.5924v3
+2013-01-10,Magnetic structure and magnon dispersion in LaSrFeO$_4$,"We present elastic and inelastic neutron scattering data on LaSrFeO$_4$. We
+confirm the known magnetic structure with the magnetic moments lying in the
+tetragonal basal plane, but contrarily to previous reports our macroscopic and
+neutron diffraction data do not reveal any additional magnetic phase transition
+connected to a spin reorientation or to a redistribution of two irreducible
+presentations. Our inelastic neutron scattering data reveals the magnon
+dispersion along the main-symmetry directions [0 $\xi$ 0] and [$\xi$ -$\xi$ 0].
+The dispersion can be explained within linear spin-wave theory yielding an
+antiferromagnetic nearest-neighbour interaction parameter $J_{1}=7.4(1)$ meV
+and a next-nearest neighbour interaction parameter $J_{2}=0.4(1)$ meV. The
+dispersion is gapped with the out-of-plane anisotropy gap found at
+$\Delta_{out}=5.26(2)$ meV, while evidence is present that the in-plane
+anisotropy gap lies at lower energies, where it cannot be determined due to
+limited instrument resolution.",1301.2106v1
+2013-02-15,A novel magnetic phase prior to a saturation moment in frustrated spinel oxides in ultra-high magnetic fields,"We have investigated the magnetic-field induced phases of a typical
+three-dimensional frustrated magnet, CdCr$_2$O$_4$, in magnetic fields of up to
+120 T that is generated by the single-turn coil techniques. We focused on
+magnetic phase transitions in proximity of a saturated magnetization moment. We
+utilized both the electromagnetic induction method using magnetic pick-up coils
+and magneto-optical spectroscopies of the $d$-$d$ transitions and the
+exciton-magnon-phonon transitions to study the magnetic properties subjected to
+ultra-high magnetic fields. Anomalies were observed in magneto-optical
+absorption intensity as well as differential magnetization prior to a fully
+polarized magnetic phase (a vacuum state in the magnon picture), revealing a
+novel magnetic phase associated with changes in both crystal and magnetic
+structures accompanied by the first order phase transition. Magnetic superfluid
+state such as an umbrella-like magnetic structure or a spin nematic state, is
+proposed as a candidate for the novel magnetic phase, which is found universal
+in the series of chromium spinel oxides, $A$Cr$_2$O$_4$ ($A$ = Zn, Cd, Hg).",1302.3664v1
+2013-03-07,Theory of atomistic simulation of spin-transfer torque in nanomagnets,"In spin-transfer torque (STT) for technological applications, the
+miniaturization of the magnet may reach the stage of requiring a fully
+quantum-mechanical treatment. We present an STT theory which uses the quantum
+macrospin ground and excited (magnon) states of the nanomagnet. This allows for
+energy and angular momentum exchanges between the current electron and the
+nano-magnet. We develop a method of magnetization dynamics simulation which
+captures the heating effect on the magnet by the spin-polarized current and the
+temperature-dependence in STT. We also discuss the magnetostatics effect on
+magnon scattering for ferromagnetic relaxation in a thin film. Our work
+demonstrates a realistic step towards simulation of quantum spin-transfer
+torque physics in nano-scale magnets.",1303.1775v1
+2013-03-12,Worldsheet one-loop energy correction to IIA Giant Magnon,"We compute one-loop corrections to the energy of a IIA giant magnon solution
+in the $AdS_4 \times CP^3$ background by using the standard quantum field
+theory (QFT) techniques. The string action is expanded around the solution to
+the quadratic order in the fluctuation fields. The resulting action has 2D
+coordinate dependent-coefficients, a feature that complicates the analysis. The
+solution contains a worldsheet velocity parameter $v$, and is expanded in terms
+of the parameter. A perturbative analysis is carried out by treating the
+$v$-dependent parts as vertices. The energy is computed by first putting the
+system in a box of length $L$ and Fourier-transforming the fields into the
+discrete momentum modes. We compare our result with the results obtained by the
+algebraic curve method.",1303.2743v3
+2013-03-18,Wave modes of collective vortex gyration in dipolar-coupled-dot-array magnonic crystals,"Lattice vibration modes are collective excitations in periodic arrays of
+atoms or molecules. These modes determine novel transport properties in solid
+crystals. Analogously, in periodical arrangements of magnetic vortex-state
+disks, collective vortex motions have been predicted. Here, we experimentally
+observe wave modes of collective vortex gyration in one-dimensional (1D) chains
+of periodic disks using time-resolved scanning transmission x-ray microscopy.
+The observed modes are interpreted based on micromagnetic simulation and
+numerical calculation of coupled Thiele equations. Dispersion of the modes is
+found to be strongly affected by both vortex polarization and chirality
+ordering, as revealed by the explicit analytical form of 1D infinite chains. A
+thorough understanding thereof is fundamental both for lattice vibrations and
+vortex dynamics, which we demonstrate for 1D magnonic crystals. Such magnetic
+disk arrays with vortex-state ordering, referred to as magnetic metastructure,
+offer potential implementation into information processing devices.",1303.4170v1
+2013-04-10,"Lee, Han, and Kim Reply","In Letter [1], we reported our finding on the physical origin of wide
+band-gap opening in planar nanostrips, as derived by application of periodic
+width modulations in the magnetic waveguides. K. Di et al. in their Comment[2],
+however, argued that the band gap can be reduced remarkably by applying a
+linear combination of symmetric and antisymmetric fields (see 'A+B' in the
+inset of Fig. 1(a)). They also insisted that they could find a complete set of
+magnonic bands based on all of the mode symmetries. However, their work does
+not constitute grounds for judging our method ""wrong"" and our conclusions
+""erroneous"". Moreover, the excitation field alluded to in the Comment is not
+sufficiently general to obtain the complete set of magnonic band structures,
+but rather remains specific. The grounds of these conclusions, drawn from our
+further work, are the following.",1304.2859v1
+2013-04-24,Observation of an inter-sublattice exchange magnon in CoCr$_2$O$_4$ and analysis of magnetic ordering,"We report on an investigation of optical properties of multiferroic
+CoCr$_{2}$O$_{4}$ at terahertz frequencies in magnetic fields up to 30 T. Below
+the ferrimagnetic transition (94 K), the terahertz response of
+CoCr$_{2}$O$_{4}$ is dominated by a magnon mode, which shows a steep
+magnetic-field dependence. We ascribe this mode to an exchange resonance
+between two magnetic sublattices with different $g$-factors. In the framework
+of a simple two-sublattice model (the sublattices are formed by Co$^{2+}$ and
+Cr$^{3+}$ ions), we find the inter-sublattice coupling constant, $\lambda = -
+(18 \pm 1)$ K, and trace the magnetization for each sublattice as a function of
+field. We show that the Curie temperature of the Cr$^{3+}$ sublattice,
+$\Theta_{2}$ = $(49 \pm 2)$ K, coincides with the temperature range, where
+anomalies of the dielectric and magnetic properties of CoCr$_{2}$O$_{4}$ have
+been reported in literature.",1304.6525v1
+2013-04-26,Landau-Lifshitz theory of the longitudinal spin Seebeck effect,"Thermal-bias-induced spin angular momentum transfer between a paramagnetic
+metal and ferromagnetic insulator is studied theoretically based on the
+stochastic Landau-Lifshitz-Gilbert (LLG) phenomenology. Magnons in the
+ferromagnet establish a nonequilibrium steady state by equilibrating with
+phonons via bulk Gilbert damping and electrons in the paramagnet via spin
+pumping, according to the fluctuation-dissipation theorem. Subthermal magnons
+and the associated spin currents are treated classically, while the appropriate
+quantum crossover is imposed on high-frequency magnetic fluctuations. We
+identify several length scales in the ferromagnet, which govern qualitative
+changes in the dependence of the thermally-induced spin current on the magnetic
+film thickness.",1304.7295v2
+2013-05-07,Micromagnetic modelling of anisotropic damping in ferromagnet,"We report a numerical implementation of the Landau-Lifshitz-Baryakhtar
+theory, which dictates that the micromagnetic relaxation term obeys the
+symmetry of the magnetic crystal, i. e. replacing the single intrinsic damping
+constant with a tensor of corresponding symmetry. The effect of anisotropic
+relaxation is studied in thin saturated ferromagnetic disk and ellipse with and
+without uniaxial magneto-crystalline anisotropy. We investigate the angular
+dependency of the linewidth of magnonic resonances with respect to the given
+structure of the relaxation tensor. The simulations suggest that the anisotropy
+of the magnonic linewidth is determined by only two factors: the projection of
+the relaxation tensor onto the plane of precession and the ellipticity of the
+later.",1305.1641v2
+2013-05-20,The 'Higgs' amplitude mode in weak ferromagnetic metals,"Using Ferromagnetic Fermi liquid theory, Bedell and Blagoev derived the
+collective low-energy excitations of a weak ferromagnet. They obtained the
+well-known magnon (Nambu-Goldstone) mode and found a new gapped mode that was
+never studied in weak ferromagnetic metals. In this article we have identified
+this mode as the Higgs boson (amplitude mode) of a ferromagnetic metal. This is
+identified as the Higgs since it can be show that it corresponds to a
+fluctuation of the amplitude of the order parameter. We use this model to
+describe the itinerant-electron ferromagnetic material MnSi. By fitting the
+model with the existing experimental results, we calculate the dynamical
+structure function and see well-defined peaks contributed from the magnon and
+the Higgs. Our estimates of the relative intensity of the Higgs amplitude mode
+suggest that it can be seen in neutron scattering experiments on MnSi.",1305.4674v2
+2013-05-28,Magnonic band gaps in waveguides with a periodic variation of the saturation magnetization,"We present a micromagnetic analysis of spin-wave propagation in a magnonic
+crystal realized as a permalloy spin-wave waveguide with a spatial periodical
+variation of its saturation magnetization. Frequency band gaps were clearly
+observed in the spin-wave transmission spectra and their origin is traced back
+to an overlap of individual band gaps of the fundamental and the higher order
+spin-wave width modes. The control of the depth, width and the position in
+frequency and space of the rejection band gaps by the width areas with a
+reduced magnetization and by the modulation level, are discussed in this study.",1305.6619v1
+2013-07-14,Controlling frustrated liquids and solids with an applied field in a kagome Heisenberg antiferromagnet,"Quantum spin-1/2 kagome Heisenberg antiferromagnet is the representative
+frustrated system possibly hosting a spin liquid. Clarifying the nature of this
+elusive topological phase is a key challenge in condensed matter, however, even
+identifying it still remains unsettled. Here, we apply a magnetic field and
+discover a series of spin gapped phases appearing at five different fractions
+of magnetization by means of grand canonical density matrix renormalization
+group, an unbiased state-of-art numerical technique. The magnetic field dopes
+magnons and first gives rise to a possible Z3 spin liquid plateau at
+1/9-magnetization. Higher field induces a self-organized super-lattice-unit, a
+six-membered ring of quantum spins, resembling an atomic orbital structure.
+Putting magnons into this unit one by one yields three quantum solid plateaus.
+We thus find that the magnetic field could control the transition between
+various emergent phases by continuously releasing the frustration.",1307.3710v2
+2013-10-24,Spin Excitations in Half-Doped Manganites,"We investigate magnetic excitations in half-doped colossal magnetoresistance
+manganites. In particular, we focus on spin excitations in the CE phase
+originally proposed by Goodenough (Phys. Rev. 100, 564 (1955)). Using a
+localized spin model we calculated magnons for 3D-perovskite compounds such as
+La$_{1-x}$M$_x$MnO$_3$, where M=Ca,Sr,Ba, and for their 2D-laminar
+counterparts. We compared them with predictions for the spin excitations
+corresponding to other phases proposed. For the laminar half-doped manganite
+La$_{0.5}$Sr$_{1.5}$MnO$_4$, for which magnon measurements by inelastic neutron
+scattering exist, as well as an estimation of the magnetic couplings, our
+calculations agree well with the experimental data.",1310.6714v1
+2013-11-12,Leggett's Modes in Magnetic Systems with Jahn-Teller distortion,"Leggett's mode is a collective excitation corresponding to the oscillation of
+the relative phase of the order parameters in a two band superconductor, with
+frequency proportional to interband coupling. We report on the existence of
+modes, similar to Leggett's mode, in magnetic systems with Jahn-Teller
+distortion. The minimal Kugel-Khomskii model, which describes simultaneously
+both the spin and the orbital order, is studied. The dynamical degrees of
+freedom are spin-$s$ operators of localized spins and pseudospin-$\tau$
+operators, which respond to the orbital degeneracy and satisfy the similar
+commutation relation with those of the spin operators. In the case of
+""antiferro"" spin and pseudospin order the system possesses two
+antiferromagnetic magnons with equal spin-wave velocities and two Leggett's
+modes with equal gaps proportional to the square root of the spin-pseudospin
+interaction constant. In the case of ""ferro"" spin and pseudospin order the
+system possesses one ferromagnetic magnon and one Leggett's mode with gap
+proportional to the spin-pseudospin interaction constant.",1311.2733v3
+2013-11-12,On the Possibility of Reversible Magnonic Logic Gates,"We propose and develop a concept of magnonic logic gates enabling reversible
+computing. The gates consist of passive elements: waveguides, cross-junctions
+and phase shifters. Logical 0 and 1 are encoded in the relative phase of the
+propagating spin wave packets (0 or {\pi}). The gates contain several possible
+trajectories for each packet to propagate from the input to the output.
+Re-direction of the spin wave packets among the possible trajectories is due to
+the interference in the magnetic cross-junctions. Two wave packets coming to
+the cross-junction in-phase propagate through the junction without reflection.
+Two packets coming out-of-phase to the junction are completely reflected back.
+The operation of the cross-junction is illustrated by numerical modeling. We
+estimate the power dissipation in the proposed circuits and the feasibility of
+cascading such magnetic devices in large circuits. The proposed gates may
+potentially provide a route to magnetic reversible logic circuitry with power
+dissipation less than kT per operation.",1311.2918v1
+2013-12-04,The square-kagome quantum Heisenberg antiferromagnet at high magnetic fields: The localized-magnon paradigm and beyond,"We consider the spin-1/2 antiferromagnetic Heisenberg model on the
+two-dimensional square-kagome lattice with almost dispersionless lowest magnon
+band. For a general exchange coupling geometry we elaborate low-energy
+effective Hamiltonians which emerge at high magnetic fields. The effective
+model to describe the low-energy degrees of freedom of the initial frustrated
+quantum spin model is the (unfrustrated) square-lattice spin-1/2 $XXZ$ model in
+a $z$-aligned magnetic field. For the effective model we perform quantum Monte
+Carlo simulations to discuss the low-temperature properties of the
+square-kagome quantum Heisenberg antiferromagnet at high magnetic fields. We
+pay special attention to a magnetic-field driven
+Berezinskii-Kosterlitz-Thouless phase transition which occurs at low
+temperatures.",1312.1111v1
+2013-12-17,Real-Space Visualization of Remnant Mott Gap and Magnon Excitations,"We demonstrate the ability to visualize real-space dynamics of charge gap and
+magnon excitations in the Mott phase of the single-band Hubbard model and the
+remnants of these excitations with hole or electron doping. At short times, the
+character of magnetic and charge excitations is maintained even for large
+doping away from the Mott and antiferromagnetic phases. Doping influences both
+the real-space patterns and long timescales of these excitations with a clear
+carrier asymmetry attributable to particle-hole symmetry breaking in the
+underlying model. Further, a rapidly-oscillating charge density wave-like
+pattern weakens, but persists as a visible demonstration of a sub-leading
+instability at half-filling which remains upon doping. The results offer an
+approach to analyzing the behavior of systems where momentum-space is either
+inaccessible or poorly defined.",1312.5312v2
+2014-01-21,Magnonic Holographic Memory,"Holography is a technique based on the wave nature of light which allows us
+to utilize wave interference between the object beam and the coherent
+background. Holography is usually associated with images being made from light,
+however, this is only a narrow field of holography. The first holograms were
+designed for use with electron microscopes and it was not until a decade later
+with the advent of the laser that optical holographic images were popularized.
+Multiple other fields have had major contributions made by using wave
+interference to produce holograms, including acoustic holograms used in seismic
+applications, and microwave holography used in radar systems. Holography has
+been also recognized as a future data storing technology with unprecedented
+data storage capacity and ability to write and read a large number of data in a
+highly parallel manner. Here, we present a magnonic holographic memory device
+exploiting spin wave interference.",1401.5133v1
+2014-02-13,High-Energy Continuum of Magnetic Excitations in the Two-Dimensional Quantum Antiferromagnet Sr2CuO2Cl2,"We have measured the magnetic excitation spectrum of the model square-lattice
+spin-1/2 antiferromagnet $\rm Sr_2CuO_2Cl_2$ over a broad range of energy and
+momentum using high-resolution inelastic neutron scattering (INS). The magnon
+dispersion along the zone boundary was accurately measured to be a 43 meV
+between (1/2,0) and (3/4,1/4) indicating the importance of coupling beyond
+nearest neighbors in the spin Hamiltonian. We observe a strong momentum
+dependent damping of the zone-boundary magnons at (1/2,0) revealing a high
+energy continuum of magnetic excitations. A direct comparison between our INS
+measurements and resonant inelastic X-ray scattering (RIXS) measurements shows
+that the RIXS spectrum contains significant contributions from higher energy
+excitations not previously considered. Our observations demonstrate that this
+high-energy continuum of magnetic fluctuations is a ubiquitous feature of
+insulating monolayer cuprates, apparent in both inelastic neutron and light
+scattering measurements.",1402.3282v1
+2014-02-25,Delta chain with ferromagnetic and antiferromagnetic interactions at the critical point,"We investigate the spin-1/2 Heisenberg model on the delta chain (sawtooth
+chain) with ferromagnetic nearest-neighbor and antiferromagnetic next-neighbor
+interactions. For a special ratio between these interactions there is a class
+of exact ground states formed by localized magnons and the ground state is
+macroscopically degenerate with a large residual entropy per spin
+$s_0=\frac{1}{2}\ln 2$. An important feature of this model is a sharp decrease
+of the gaps for excited states with an increase of the number of magnons. These
+excitations give an essential contribution to the low-temperature
+thermodynamics. The behavior of the considered model is compared with that of
+the delta chain with both antiferromagnetic interactions.",1402.6087v1
+2014-02-26,Improved Domain Wall Dynamics and Magnonic Torques using Topological Insulators,"We investigate the magnetization dynamics that arise when a thin-film
+ferromagnet is deposited on a topological insulator (TI), focusing in
+particular on domain-wall motion via current and the possibility of a spin-wave
+torque acting on the magnetization. We show analytically that the coupling
+between the magnetic domain wall and the TI removes the degeneracy of the wall
+profile with respect to its chirality and topological charge. Moreover, we find
+that the threshold for Walker breakdown of domain wall motion is substantially
+increased and determined by the interaction with the TI, allowing for higher
+attainable wall velocities than in the conventional case where the hard axis
+anisotropy determines the Walker threshold. Finally, we show that the allowed
+modes of spin-wave excitations and the ensuing magnetization dynamics in the
+presence of a TI coupling enable a magnonic torque acting even on homogeneous
+magnetization textures. Our results indicate that the TI-ferromagnet
+interaction has a similar effect on the magnetization dynamics as an intrinsic
+Dzyaloshinskii-Moriya interaction in ferromagnets.",1402.6701v2
+2014-02-27,On the longitudinal spin current induced by a temperature gradient in a ferromagnetic insulator,"Based on the solution of the stochastic Landau-Lifshitz-Gilbert equation
+discretized for a ferromagnetic chain subject to a uniform temperature
+gradient, we present a detailed numerical study of the spin dynamics with a
+focus particularly on finite-size effects. We calculate and analyze the net
+longitudinal spin current for various temperature gradients, chain lengths, and
+external static magnetic fields. In addition, we model an interface formed by a
+nonuniformly magnetized finite-size ferromagnetic insulator and a normal metal
+and inspect the effects of enhanced Gilbert damping on the formation of the
+space-dependent spin current within the chain. A particular aim of this study
+is the inspection of the spin Seebeck effect beyond the linear response regime.
+We find that within our model the microscopic mechanism of the spin Seebeck
+current is the magnon accumulation effect quantified in terms of the exchange
+spin torque. According to our results, this effect drives the spin Seebeck
+current even in the absence of a deviation between the magnon and phonon
+temperature profiles. Our theoretical findings are in line with the recently
+observed experimental results by M. Agrawal et al., Phys. Rev. Lett. 111,
+107204 (2013).",1402.6899v1
+2014-02-28,Lattice and spin excitations in multiferroic h-YMnO3,"We used Raman and terahertz spectroscopies to investigate lattice and
+magnetic excitations and their cross-coupling in the hexagonal YMnO3
+multiferroic. Two phonon modes are strongly affected by the magnetic order.
+Magnon excitations have been identified thanks to comparison with neutron
+measurements and spin wave calculations but no electromagnon has been observed.
+In addition, we evidenced two additional Raman active peaks. We have compared
+this observation with the anti-crossing between magnon and acoustic phonon
+branches measured by neutron. These optical measurements underly the unusual
+strong spin-phonon coupling.",1402.7239v1
+2014-04-01,Semi-classical scalar products in the generalised SU(2) model,"In these notes we review the field-theoretical approach to the computation of
+the scalar product of multi-magnon states in the Sutherland limit where the
+magnon rapidities condense into one or several macroscopic arrays. We formulate
+a systematic procedure for computing the 1/M expansion of the
+on-shell/off-shell scalar product of M-magnon states in the generalised
+integrable model with SU(2)-invariant rational R-matrix. The coefficients of
+the expansion are obtained as multiple contour integrals in the rapidity plane.",1404.0235v3
+2014-04-08,Resonant inelastic x-ray scattering on single-magnons at oxygen $K$-edges,"The recent discovery that resonant inelastic x-ray scattering can probe
+single-magnon (SM) dispersions in transition metal (TM) oxides when the x-ray
+energy is tuned to the TM $L$-edge, has put this technique on a par with
+inelastic neutron scattering. It is generally presumed that selection rules
+forbid SM-scattering at oxygen (O) $K$-edges. However, based on a symmetry
+analysis and exact diagonalization study, we show that SM-scattering at O
+K-edges becomes allowed when (i) spin-orbit coupling is present in the TM
+d-shell and (ii) inversion symmetry at the O-site is broken. For cuprates the
+resulting SM-amplitude is very weak but in iridates both prerequisites can
+amply be fulfilled.",1404.2040v1
+2014-07-25,Analysis of resonant inelastic x-ray scattering from Sr$_2$IrO$_4$ in an itinerant-electron approach,"We analyze the resonant x-ray scattering (RIXS) spectra from Sr$_2$IrO$_4$ in
+an itinerant electron approach. Employing a multi-orbital tight-binding model
+on the square lattice, we calculate the one-electron energy band within the
+Hartree-Fock approximation, which leads to an antiferromagnetic ground state.
+We then evaluate the two-particle Green's functions for the particle-hole pair
+excitations within the random phase approximation, which are connected to the
+RIXS spectra within the fast collision approximation. The calculated RIXS
+spectra exhibit two-peak structure with slightly different energies in the
+low-energy region, which are originated from the bound states in the
+two-particle Green's function. They may be interpreted as the split modes of
+magnon. We also obtain several $\delta$-function peaks, which arise from the
+bound states around the bottom of energy continuum. They may be called as the
+exciton modes. These characteristics are in qualitative agreement with the RIXS
+experiment, demonstrating that the weak coupling theory could explain both the
+magnon and the exciton peaks in the RIXS spectra on an equal footing.",1407.6766v1
+2014-07-28,Magneto Seebeck effect in REFeAsO (RE=rare earth) compounds: probing the magnon drag scenario,"We investigate Seebeck effect in REFeAsO (RE=rare earth)compounds as a
+function of temperature and magnetic field up to 30T. The Seebeck curves are
+characterized by a broad negative bump around 50K, which is sample dependent
+and strongly enhanced by the application of a magnetic field. A model for the
+temperature and field dependence of the magnon drag contribution to the Seebeck
+effect by antiferromagnetic (AFM) spin fluctuation is developed. It accounts
+for the magnitude and scaling properties of such bump feature in our
+experimental data. This analysis allows to extract precious information on the
+coupling between electrons and AFM spin fluctuations in these parent compound
+systems, with implications on the pairing mechanism of the related
+superconducting compounds.",1407.7358v1
+2014-08-13,Temperature-Dependent Interplay of Dzyaloshinskii-Moriya Interaction and Single-Ion Anisotropy in Multiferroic BiFeO$_3$,"Low-energy magnon excitations in multiferroic BiFeO$_3$ were measured in
+detail as a function of temperature around several Brillouin zone centers by
+inelastic neutron scattering experiments on single crystals. Unique features
+around 1 meV are directly associated with the interplay of the
+Dzyaloshinskii-Moriya interaction and a small single-ion anisotropy. The
+temperature dependence of these and the exchange interactions were determined
+by fitting the measured magnon dispersion with spin-wave calculations. The
+spectra best fits an easy-axis type magnetic anisotropy and the deduced
+exchange and anisotropy parameters enable us to determine the anharmonicity of
+the magnetic cycloid. We then draw a direct connection between the changes in
+the parameters of spin Hamiltonian with temperature and the physical properties
+and structural deformations of BiFeO$_3$.",1408.2942v2
+2014-10-01,Holes Localized on a Skyrmion in a Doped Antiferromagnet on the Honeycomb Lattice: Symmetry Analysis,"Using the low-energy effective field theory for hole-doped antiferromagnets
+on the honeycomb lattice, we study the localization of holes on Skyrmions, as a
+potential mechanism for the preformation of Cooper pairs. In contrast to the
+square lattice case, for the standard radial profile of the Skyrmion on the
+honeycomb lattice, only holes residing in one of the two hole pockets can get
+localized. This differs qualitatively from hole pairs bound by magnon exchange,
+which is most attractive between holes residing in different momentum space
+pockets. On the honeycomb lattice, magnon exchange unambiguously leads to
+$f$-wave pairing, which is also observed experimentally. Using the
+collective-mode quantization of the Skyrmion, we determine the quantum numbers
+of the localized hole pairs. Again, $f$-wave symmetry is possible, but other
+competing pairing symmetries cannot be ruled out.",1410.0218v1
+2014-10-06,Possible coupling between magnons and phonons in multiferroic CaMn7O12,"Spin and lattice dynamics of CaMn7O12 ceramics were investigated using
+infrared, THz and inelastic neutron scattering (INS) spectroscopies in the
+temperature range 2 to 590 K, and, at low temperatures, in applied magnetic
+fields of up to 12 T. On cooling, we observed phonon splitting accompanying the
+structural phase transition at Tc = 450K as well as the onset of the
+incommensurately modulated structure at 250 K. In the two antiferromagnetic
+phases below T_N1 = 90K and T_N2 = 48 K, several infrared-active excitations
+emerge in the meV range; their frequencies correspond to the maxima in the
+magnon density of states obtained by INS. At the magnetic phase transitions,
+these modes display strong anomalies and for some of them, a transfer of
+dielectric strength from the higher-frequency phonons is observed. We propose
+that these modes are electromagnons. Remarkably, at least two of these modes
+remain active also in the paramagnetic phase; for this reason, we call them
+paraelectromagnons. In accordance with this observation, quasielastic neutron
+scattering revealed short-range magnetic correlations persisting within
+temperatures up to 500K above T_N1.",1410.1394v1
+2014-10-30,Quantum versus classical polarons in a ferromagnetic CuO$_3$-like chain,"We present an exact solution for an itinerant hole added into the oxygen
+orbitals of a CuO$_{3}$-like ferromagnetic chain. Using the Green's function
+method, the quantum polarons obtained for the Heisenberg SU(2) interaction
+between localized Cu spins are compared with the polarons in the Ising chain.
+We find that magnons with large energy are favorable towards quasiparticle
+existence, even in the case of relatively modest electron-magnon coupling. We
+observe two quasiparticle states with dispersion $\sim 2t$ each, which emerge
+from the incoherent continuum when the exchange coupling $J$ increases. Quantum
+fluctuations in the spin system modify the incoherent part of the spectrum and
+change the spectral function qualitatively, beyond the bands derived from the
+perturbation theory.",1410.8481v1
+2014-11-14,Modelling Dynamical Fluorescent Micro Thermal Imaging of the Heat Diffusion in the La5Ca9Cu24O41 Spin Ladder Compound,"The dynamical fluorescent microthermal imaging (FMI) experiment has been used
+to investigate the phonon-magnon interaction in the 1D Heisenberg
+antiferromagnet La5Ca9Cu24O41. This material shows highly anisotropic heat
+conductivity due to the efficient magnetic heat transport along the spin
+ladders in the compound. To extract information on the phonon-magnon
+interaction we modelled the dynamic heat transport experiment using a two
+temperature model approach, taking both the crystal as well as the PMMA/EuTTA
+fluorescent heat imaging layer into account. The simulations are carried out by
+the finite element method using COMSOL Multiphysics Heat Transfer Module. The
+results of the numerical calculations are expected to be used for the data
+analysis of the experimental studies.",1411.3872v2
+2014-12-05,Magnetic order and electromagnon excitations in DyMnO3 studied by neutron scattering experiments,"Magnetic order and excitations in multiferroic DyMnO3 were studied by neutron
+scattering experiments using a single crystal prepared with enriched 162Dy
+isotope. The ordering of Mn moments exhibits pronounced hysteresis arising from
+the interplay between Mn and Dy magnetism which possesses a strong impact on
+the ferroelectric polarization. The magnon dispersion resembles that reported
+for TbMnO3. We identify the excitations at the magnetic zone center and near
+the zone boundary in the b direction, which can possess electromagnon
+character. The lowest frequency of the zone-center magnons is in good agreement
+with a signal in a recent optical measurement so that this mode can be
+identified as the electromagnon coupled by the same Dzyaloshinski-Moriya
+interaction as the static multiferroic phase.",1412.1938v1
+2014-12-11,High-field magnetic resonance of spinons and magnons in a triangular lattice S=1/2 antiferromagnet Cs2CuCl4,"The electron spin resonance doublet indicating the width of the two spinon
+continuum in a spin-1/2 triangular-lattice Heisenberg antiferromagnet Cs2CuCl4
+was studied in high magnetic field. The doublet was found to collapse in a
+magnetic field of a half of the saturation field. The collapse of the doublet
+occurs via vanishing of the high frequency component in a qualitative agreement
+with the theoretical prediction for the S=1/2 chain. The field of the collapse
+is, however, much lower than expected for the S=1/2 chain. This is proposed to
+be due to the destruction of frustration of interchain exchange bonds in a
+magnetic field, which restores the 2D character of this spin system. In the
+saturated phase the mode with the Larmor frequency and a much weaker mode
+downshifted for 119~GHz are observed. The weak mode is of exchange origin, it
+demonstrates a positive frequency shift at heating corresponding to the
+repulsion of magnons in the saturated phase.",1412.3776v1
+2015-01-23,Giant gap in the magnon excitations of the quasi-1D chain compound Sr3NiIrO6,"Inelastic neutron scattering on the spin-chain compound Sr$_3$NiIrO$_6$
+reveals gapped quasi-1D magnetic excitations. The observed one-magnon band
+between 29.5 and 39 meV consists of two dispersive modes. The spin wave
+spectrum could be well fitted with an antiferromagnetic anisotropic exchange
+model and single ion anisotropy on the Ni site. The extracted dominant
+anisotropic antiferromagnetic intra-chain exchange interaction between Ir and
+Ni ions are $J_z=19.5$ meV and $J_{xy}=12.1$ meV. These values justify previous
+electronic structure calculations, showing the importance of Ir spin orbit
+coupling on the electron correlations. The magnetic excitations survive up to
+200 K well above the magnetic ordering temperature of $T_N \sim 70$ K, also
+indicating a quasi-1D nature of the magnetic interactions in Sr$_3$NiIrO$_6$.
+Our results not only support the idea of the existence of a new temperature
+scale well above $T_N$, but also emphasize the need to consider new exchange
+paths complicated by the SOC, resulting in additional characteristic
+temperatures in such spin-chain systems.",1501.05735v1
+2015-02-18,Where are the roots of the Bethe Ansatz equations?,"Changing the variables in the Bethe Ansatz Equations (BAE) for the XXZ
+six-vertex model we had obtained a coupled system of polynomial equations. This
+provided a direct link between the BAE deduced from the Algebraic Bethe Ansatz
+(ABA) and the BAE arising from the Coordinate Bethe Ansatz (CBA). For two
+magnon states this polynomial system could be decoupled and the solutions given
+in terms of the roots of some self-inversive polynomials. From theorems
+concerning the distribution of the roots of self-inversive polynomials we made
+a thorough analysis of the two magnon states, which allowed us to find the
+location and multiplicity of the Bethe roots in the complex plane, to discuss
+the completeness and singularities of Bethe's equations, the ill-founded
+string-hypothesis concerning the location of their roots, as well as to find an
+interesting connection between the BAE with Salem's polynomials.",1502.05316v2
+2015-04-02,Electron-Magnon Scattering in Magnetic Heterostructures Far Out-of-Equilibrium,"We present a theory of out-of-equilibrium ultrafast spin dynamics in magnetic
+heterostructures based on the s-d model of ferromagnetism. Both in the bulk and
+across interfaces, the exchange processes between the itinerant s and the
+localized d electrons are described by kinetic rate equations for
+electron-magnon spin-flop scattering. The principal channel for dissipation of
+angular momentum is provided by spin relaxation of the itinerant electrons. Our
+theory extends interfacial spin phenomena such as torques, pumping, and the
+Peltier and Seebeck effects to address laser-induced rapid spin dynamics, in
+which the effective electron temperature may approach or even exceed the Curie
+temperature.",1504.00511v1
+2015-04-02,Thermodynamic Magnon Recoil for Domain Wall Motion,"We predict a thermodynamic magnon recoil effect for domain wall motions in
+the presence of temperature gradients. All current thermodynamic theories
+assert that a magnetic domain wall must move toward the hotter side, based on
+equilibrium thermodynamic arguments. Microscopic calculations on the other hand
+show that a domain wall can move either along or against the direction of heat
+currents, depending on how strong the heat currents are reflected by the domain
+wall. We have resolved the inconsistency between these two approaches by
+augmenting the theory in the presence of thermal gradients by incorporating in
+the free energy of domain walls by a heat current term present in
+nonequilibrium steady states. The condition to observe a domain wall
+propagation toward the colder regime is derived analytically and can be tested
+by future experiments.",1504.00651v2
+2015-04-07,Thermal conductivity of IPA-CuCl_3: Evidences of ballistic magnon transport and limited applicability of the Bose-Einstein condensation model,"The heat transport of the spin-gapped material (CH_3)_2CHNH_3CuCl_3
+(IPA-CuCl_3), a candidate quantum magnet with Bose-Einstein condensation (BEC),
+is studied at ultra-low temperatures and in high magnetic fields. Due to the
+presence of the spin gap, the zero-field thermal conductivity (\kappa) is
+purely phononic and shows a ballistic behavior at T < 1 K. When the gap is
+closed by magnetic field at H = H_{c1}, where a long-range antiferromanetic
+(AF) order of Cu^{2+} moments is developed, the magnons contribute
+significantly to heat transport and exhibit a ballistic T^3 behavior at T < 600
+mK. In addition, the low-T \kappa(H) isotherms show sharp peaks at H_{c1},
+which indicates a gap re-opening in the AF state (H > H_{c1}) and demonstrates
+limited applicability of the BEC model to IPA-CuCl_3.",1504.01465v1
+2015-05-22,Thermometry and cooling of a Bose-Einstein condensate to 0.02 times the critical temperature,"Ultracold gases promise access to many-body quantum phenomena at convenient
+length and time scales. However, it is unclear whether the entropy of these
+gases is low enough to realize many phenomena relevant to condensed matter
+physics, such as quantum magnetism. Here we report reliable single-shot
+temperature measurements of a degenerate $^{87}$Rb gas by imaging the momentum
+distribution of thermalized magnons, which are spin excitations of the atomic
+gas. We record average temperatures as low as
+$0.022(1)_\text{stat}(2)_\text{sys}$ times the Bose-Einstein condensation
+temperature, indicating an entropy per particle, $S/N\approx0.001\, k_B$ at
+equilibrium, that is well below the critical entropy for antiferromagnetic
+ordering of a Bose-Hubbard system. The magnons themselves can reduce the
+temperature of the system by absorbing energy during thermalization and by
+enhancing evaporative cooling, allowing low-entropy gases to be produced within
+deep traps.",1505.06196v1
+2015-06-02,Scattering particles in quantum spin chains,"A variational approach for constructing an effective particle description of
+the low-energy physics of one-dimensional quantum spin chains is presented.
+Based on the matrix product state formalism, we compute the one- and
+two-particle excitations as eigenstates of the full microscopic Hamiltonian. We
+interpret the excitations as particles on a strongly-correlated background with
+non-trivial dispersion relations, spectral weights and two-particle S matrices.
+Based on this information, we show how to describe a finite density of
+excitations as an interacting gas of bosons, using its approximate
+integrability at low densities. We apply our framework to the Heisenberg
+antiferromagnetic ladder: we compute the elementary excitation spectrum and the
+magnon-magnon S matrix, study the formation of bound states and determine both
+static and dynamic properties of the magnetized ladder.",1506.01008v2
+2015-06-03,Magnetization reversal using excitation of collective modes in nanodot matrices,"The large arrays of magnetic dots are the building blocks of magnonic
+crystals and the emerging bit patterned media for future recording technology.
+In order to fully utilize the functionalities of high density magnetic
+nanodots, a method for the selective reversal of a single nanodot in a matrix
+of dots is desired. We have proposed a method for magnetization reversal of a
+single nanodot with microwave excitation in a matrix of magneto-statically
+interacting dots. The method is based on the excitation of collective modes and
+the spatial anomaly in the microwave power absorption. We perform numerical
+simulations to demonstrate the possibility of switching a single dot from any
+initial state of a 3 by 3 matrix of dots, and develop a theoretical model for
+the phenomena. We discuss the applicability of the proposed method for
+introducing defect modes in magnonic crystals as well as for future magnetic
+recording.",1506.01359v1
+2015-06-23,Chirality-dependent transmission of spin waves through domain walls,"Spin-wave technology (magnonics) has the potential to further reduce the size
+and energy consumption of information processing devices. In the submicrometer
+regime (exchange spin waves), topological defects such as domain walls may
+constitute active elements to manipulate spin waves and perform logic
+operations. We predict that spin waves that pass through a domain wall in an
+ultrathin perpendicular-anisotropy film experience a phase shift that depends
+on the orientation of the domain wall (chirality). The effect, which is absent
+in bulk materials, originates from the interfacial Dzyaloshinskii-Moriya
+interaction and can be interpreted as a geometric phase. We demonstrate
+analytically and by means of micromagnetic simulations that the phase shift is
+strong enough to switch between constructive and destructive interference. The
+two chirality states of the domain wall may serve as a memory bit or spin-wave
+switch in magnonic devices.",1506.07038v2
+2015-09-01,Spin dynamics of antiferromagnetically coupled bilayers - the case of Cr_2TeO_6,"Understanding the dynamics of interacting quantum spins has been one of the
+active areas of condensed matter physics research. Recently, extensive
+inelastic neutron scattering measurements have been carried out in an
+interesting class of systems, Cr_2(W, Te, Mo)O_6. These systems consist of
+bilayers of Cr^{3+} spins (S=3/2) with strong antiferromagnetic inter-bilayer
+coupling (J) and tuneable intra-bilayer coupling (j) from ferro (for W and Mo)
+to antiferro (for Te). In the limit when J>|j|, the system reduces to weakly
+interacting quantum spin-3/2 dimers. In this paper we discuss the
+low-temperature magnetic properties of Cr_2TeO_6 systems where both intra-layer
+and inter-layer exchange couplings are antiferromagnetic, i.e. J,j>0. Using
+linear spin-wave theory we obtain the magnon dispersion, sublattice
+magnetization, two-magnon density of states, and longitudinal spin-spin
+correlation function.",1509.00101v3
+2015-09-11,Two-magnon Raman scattering and pseudospin-lattice interactions in Sr2IrO4 and Sr3Ir2O7,"We have used Raman scattering to investigate the magnetic excitations and
+lattice dynamics in the prototypical spin-orbit Mott insulators Sr2IrO4 and
+Sr3Ir2O7. Both compounds exhibit pronounced two-magnon Raman scattering
+features with different energies, lineshapes, and temperature dependencies,
+which in part reflect the different influence of long-range frustrating
+exchange interactions. Additionally, we find strong Fano asymmetries in the
+lineshapes of low-energy phonon modes in both compounds, which disappear upon
+cooling below the antiferromagnetic ordering temperatures. These unusual phonon
+anomalies indicate that the spin-orbit coupling in Mott-insulating iridates is
+not sufficiently strong to quench the orbital dynamics in the paramagnetic
+state.",1509.03396v1
+2015-09-14,Highly anisotropic magnon dispersion in Ca2RuO4: evidence for strong spin orbit coupling,"The magnon disp ersion in Ca2RuO4 has been determined by inelastic neutron
+scattering on single crytals containing 1% of Ti. The dispersion is well
+described by a conventional Heisenberg model suggesting a local moment model
+with nearest neighbor interaction of J=8 meV. Nearest and next-nearest neighbor
+interaction as well as inter-layer coupling parameters are required to properly
+describe the entire dispersion. Spin-orbit coupling induces a very large
+anisotropy gap in the magnetic excitations in apparent contrast with a simple
+planar magnetic model. Orbital ordering breaking tetragonal symmetry, and
+strong spin-orbit coupling can thus be identified as important factors in this
+system.",1509.03999v2
+2015-11-29,Ultrafast electron-phonon-magnon interactions at noble metal-ferromagnet interfaces,"Ultrafast optical excitation of gold-cobalt bilayers triggers the nontrivial
+interplay between the electronic, acoustic, and magnetic degrees of freedom.
+Laser-heated electrons generated at the gold-air interface diffuse through the
+layer of gold and strongly overheat the lattice in cobalt resulting in the
+emission of ultrashort acoustic pulses and generation of exchange-coupled
+magnons. Time-resolved optical measurements allow for extracting the thermal
+boundary (Kapitza) resistances at metal/metal interfaces and the hot electron
+diffusion length in ferromagnetic materials. Both the experimental data and the
+analytical treatment of the two-temperature model reveal the role of the
+Kapitza resistance in transient lattice overheating.",1511.09060v3
+2016-01-26,Edge instabilities and skyrmion creation in magnetic layers,"We study both analytically and numerically the edge of two-dimensional
+ferromagnets with Dzyaloshinskii-Moriya (DM) interactions, considering both
+chiral magnets and magnets with interface-induced DM interactions. We show that
+in the field-polarized ferromagnetic phase magnon states exist which are bound
+to the edge, and we calculate their spectra within a continuum field theory.
+Upon lowering an external magnetic field, these bound magnons condense at a
+finite momentum and the edge becomes locally unstable. Micromagnetic
+simulations demonstrate that this edge instability triggers the creation of a
+helical phase which penetrates the field-polarized state within the bulk. A
+subsequent increase of the magnetic field allows to create skyrmions close to
+the edge in a controlled manner.",1601.06922v2
+2016-02-12,Spin dynamics in the high-field phases of volborthite,"We report single-crystal 51V NMR studies on volborthite Cu3V2O7(OH)2 2H2O,
+which is regarded as a quasi-two-dimensional frustrated magnet with competing
+ferromagnetic and antiferromagnetic interactions. In the 1/3 magnetization
+plateau above 28 T, the nuclear spin-lattice relaxation rate 1/T1 indicates an
+excitation gap with a large effective g factor in the range of 4.6-5.9,
+pointing to magnon bound states. Below 26 T where the gap has closed, the NMR
+spectra indicate small internal fields with a Gaussian-like distribution,
+whereas 1/T1 shows a power-law-like temperature dependence in the paramagnetic
+state, which resembles a slowing down of spin fluctuations associated with
+magnetic order. We discuss the possibility of an exotic spin state caused by
+the condensation of magnon bound states below the magnetization plateau.",1602.04028v2
+2016-04-08,Spin-Superfluidity and Spin-Current Mediated Non-Local Transport,"Some strategies for reducing energy consumption in information processing
+devices involve the use of spin rather than charge to carry information. This
+idea is especially attractive when the spin current is a collective one carried
+by the condensate of a magnetically ordered state, rather than a quasiparticle
+current carried by electrons or magnons. In this Chapter we explain how
+easy-plane magnets can be viewed as Bose-Einstein condensates of magnons,
+defined in terms of quanta of the spin-component perpendicular to the easy
+plane, and how they can carry dissipationless spin-currents that induce
+non-local interactions between electrically isolated conducting channels. We
+comment specifically on important differences between superconductivity in
+normal/superconducting/normal circuits and spin-superfluidity in
+normal/magnetic/normal circuits.",1604.02429v1
+2016-04-22,Frustrated Ising chains on the triangular lattice in Sr$_3$NiIrO$_6$,"Inelastic neutron scattering study on the spin-chain compound Sr$_3$NiIrO$_6$
+reveals gapped quasi-1D magnetic excitations. The observed one-magnon band
+between 29.5 and 39 meV consists of magnon modes of the Ni$^{2+}$ ions. The
+fitting of the spin wave spectrum reveals strongly coupled Ising-like chains
+along the $c$-axis that are weakly coupled into a frustrated triangular lattice
+in the $ab$-plane. The magnetic excitations survive up to 200 K well above the
+magnetic ordering temperature of $T_N \sim 75$ K, also indicating a quasi-1D
+nature of the magnetic interactions in Sr$_3$NiIrO$_6$. Our microscopic model
+is in good agreement with ab initio electronic structure calculations and
+explains the giant spin flip field observed in bulk magnetization measurements.",1604.06569v1
+2016-04-28,"Magnetization Saturation Process in the Magnonic Anti-dot Structures Based on (Ga,Mn)As: A Magnetometric Study","Applicability of dilute magnetic semiconductors (DMS) in electronic devices
+relies upon the understanding and control of their magnetic anisotropy. This
+paper explores one of the ways in engineering magnetic anisotropy in epitaxial
+layers of DMS by forming them into magnonic structures. For this purpose the
+canonical ferromagnetic DMS, namely (Ga,Mn)As, is employed. The anti-dot
+systems based on (Ga,Mn)As layers of various thicknesses are fabricated with
+focused ion beam apparatus and studied by means of microscopy as well as
+magnetometry. The magnetometric data - collected along two nonequivalent
+in-plane crystallographic directions of (Ga,Mn)As: [110] and [1-10] - shows the
+effect of structuring on high-field magnetization process, whereas no
+significant change of the width of hysteresis loop in anti-dot samples is
+observed.",1604.08607v1
+2016-06-23,Spin-Hall nano-oscillator with oblique magnetization and Dzyaloshinskii-Moriya interaction as generator of skyrmions and nonreciprocal spin-waves,"Spin-Hall oscillators are promising sources of spin-wave signals for
+magnonics applications, and can serve as building blocks for magnonic logic in
+ultralow power computation devices. Here, we analytically and micromagnetically
+study magnetization dynamics excited in a Spin-Hall oscillator with oblique
+magnetization when the spin-Hall effect and interfacial Dzyaloshinskii-Moriya
+interaction act simultaneously. Our key results are (i) excitation of
+nonreciprocal spin-waves propagating perpendicularly to the in-plane projection
+of the static magnetization, (ii) skyrmions generation by pure spin-current,
+(iii) excitation of a new spin-wave mode with a spiral spatial profile
+originating from a gyrotropic rotation of a dynamical skyrmion. These results
+demonstrate that Spin-Hall oscillators can be used as generators of magnetic
+skyrmions and different types of propagating spin-waves for magnetic data
+storage and signal processing applications.",1606.07280v1
+2016-07-08,Control of magnon-photon coupling strength in a planar resonator/YIG thin film configuration,"A systematic study of the coupling at room temperature between ferromagnetic
+resonance (FMR) and a planar resonator is presented. The chosen magnetic
+material is a ferrimagnetic insulator (Yttrium Iron Garnet: YIG) which is
+positioned on top of a stop band (notch) filter based on a stub line
+capacitively coupled to a 50 $\Omega$ microstrip line resonating at 4.731 GHz.
+Control of the magnon-photon coupling strength is discussed in terms of the
+microwave excitation configuration and the YIG thickness from 0.2 to 41 $\mu$m.
+From the latter dependence, we extract a single spin-photon coupling of
+g$_{0}$/2$\pi$=162$\pm$6 mHz and a maximum of an effective coupling of 290 MHz.",1607.02358v3
+2017-02-16,"Magnetization dynamics in magnonic structures with different geometries: interfaces, notches and waveguides","The discovery of the ultrafast magnetization dynamics twenty years ago has
+led to a broad variety of experimental techniques to explore phenomena in
+magnetic materials with high temporal resolution. In the present article we
+present a study dealing with broadband excitation of spin-wave packets at
+different magnonic crystal continuous magnetic film interfaces. Similar to
+protected conducting states on the surfaces of topological band insulators,
+these interfaces exhibit surface spin-wave modes that propagate out of the
+crystal into the continuous film. The propagation distance depends on the
+direction of the applied magnetic field as well as the surface geometry of the
+crystal.",1702.05041v1
+2017-02-27,Dynamics of Bound Magnon Pairs in the Quasi-One-Dimensional Frustrated Magnet LiCuVO_4,"We report on the dynamics of the spin-1/2 quasi-one-dimensional frustrated
+magnet LiCuVO$\mathrm{_4}$ measured by nuclear spin relaxation in high magnetic
+fields 10--34 T, in which the ground state has spin-density-wave order. The
+spin fluctuations in the paramagnetic phase exhibit striking anisotropy with
+respect to the magnetic field. The transverse excitation spectrum probed by
+$^{51}$V nuclei has an excitation gap, which increases with field. On the other
+hand, the gapless longitudinal fluctuations sensed by $^7$Li nuclei grow with
+lowering temperature, but tend to be suppressed with increasing field. Such
+anisotropic spin dynamics and its field dependence agree with the theoretical
+predictions and are ascribed to the formation of bound magnon pairs, a
+remarkable consequence of the frustration between ferromagnetic nearest
+neighbor and antiferromagnetic next-nearest-neighbor interactions.",1702.08573v2
+2017-03-11,Confined states in photonic-magnonic crystals with complex unit cell,"We have investigated multifunctional periodic structures in which
+electromagnetic waves and spin waves can be confined in the same areas. Such
+simultaneous localization of both sorts of excitations can potentially enhance
+the interaction between electromagnetic waves and spin waves. The system we
+considered has a form of one dimensional photonic-magnonic crystal with two
+types of magnetic layers (thicker and thinner ones) separated by sections of
+the dielectric photonic crystals. We focused on the electromagnetic defect
+modes localized in the magnetic layers (areas where spin waves can be exited)
+and decaying in the sections of conventional (nonmagnetic) photonic crystals.
+We showed how the change of relative thickness of two types of the magnetic
+layers can influence on the spectrum of spin waves and electromagnetic defect
+modes, both localized in magnetic parts of the system.",1703.04013v1
+2017-08-19,Current induced multi-mode propagating spin waves in a spin transfer torque nano-contact with strong perpendicular magnetic anisotropy,"Current induced spin wave excitations in spin transfer torque nano-contacts
+are known as a promising way to generate exchange-dominated spin waves at the
+nano-scale. It has been shown that when these systems are magnetized in the
+film plane, broken spatial symmetry of the field around the nano-contact
+induced by the Oersted field opens the possibility for spin wave mode
+co-existence including a non-linear self-localized spin-wave bullet and a
+propagating mode. By means of micromagnetic simulations, here we show that in
+systems with strong perpendicular magnetic anisotropy (PMA) in the free layer,
+two propagating spin wave modes with different frequency and spatial
+distribution can be excited simultaneously. Our results indicate that in-plane
+magnetized spin transfer nano-contacts in PMA materials do not host a solitonic
+self-localized spin-wave bullet, which is different from previous studies for
+systems with in plane magnetic anisotropy. This feature renders them
+interesting for nano-scale magnonic waveguides and crystals since magnon
+transport can be configured by tuning the applied current.",1708.05886v1
+2017-08-30,Propagation of self-localised Q-ball solitons in the $^3$He universe,"In relativistic quantum field theories, compact objects of interacting bosons
+can become stable owing to conservation of an additive quantum number $Q$.
+Discovering such $Q$-balls propagating in the Universe would confirm
+supersymmetric extensions of the standard model and may shed light on the
+mysteries of dark matter, but no unambiguous experimental evidence exists. We
+report observation of a propagating long-lived $Q$-ball in superfluid $^3$He,
+where the role of $Q$-ball is played by a Bose-Einstein condensate of magnon
+quasiparticles. We achieve accurate representation of the $Q$-ball Hamiltonian
+using the influence of the number of magnons, corresponding to the charge $Q$,
+on the orbital structure of the superfluid $^3$He order parameter. This
+realisation supports multiple coexisting $Q$-balls which in future allows
+studies of $Q$-ball dynamics, interactions, and collisions.",1708.09224v1
+2018-02-05,Micromagnetic view on ultrafast magnon generation by femtosecond spin current pulses,"In this Article we discuss a micromagnetic modelling approach to describe the
+ultrafast spin-transfer torque excitation of coherent and incoherent magnons on
+the nanoscale. Implementing the action of a femtosecond spin current pulse
+entering an orthogonally magnetized thin ferromagnetic film, we reproduce
+recent experimental results and reveal the factors responsible for the unequal
+excitation efficiency of various spin waves. Our findings are in an excellent
+agreement with the results of an analytical description of spin-wave excitation
+based on classical kinetic equations. Furthermore, we suggest an experimental
+design allowing for the excitation of laterally propagating spin waves beyond
+the optical diffraction limit. Our findings demonstrate that the classical
+micromagnetic picture retains its predictive and interpretative power on
+femtosecond temporal and nanometer spatial scales.",1802.01305v1
+2018-04-18,Spin dynamics from time-dependent density functional perturbation theory,"We present a new method to model spin-wave excitations in magnetic solids,
+based on the Liouville-Lanczos approach to time-dependent density functional
+perturbation theory. This method avoids computationally expensive sums over
+empty states and naturally deals with the coupling between spin and charge
+fluctuations, without ever explicitly computing charge-density
+susceptibilities. Spin-wave excitations are obtained with one Lanczos chain per
+magnon wave-number and polarization, avoiding the solution of the
+linear-response problem for every individual value of frequency, as other
+state-of-the-art approaches do. Our method is validated by computing magnon
+dispersions in bulk Fe and Ni, resulting in agreement with previous theoretical
+studies in both cases, and with experiment in the case of Fe. The disagreement
+in the case of Ni is also comparable with that of previous computations.",1804.06573v2
+2018-11-08,Quasistatic oscillations in subwavelength particles: Can one observe energy eigenstates?,"In increasing the capabilities of the optical and microwave techniques
+further into the subwavelength regime, quasistatic resonant structures has
+attracted considerable interest. Electromagnetic responses of electrostatic
+(ES) plasmon resonances in optics and magnetostatic (MS) magnon resonances in
+microwaves give rise to a strong enhancement of local fields near the surfaces
+of subwavelength particles. In the near-field regions of subwavelength
+particles one can only measure the electric or the magnetic field with
+accuracy. Such uncertainty in definition of the electric or magnetic field
+components raises the question of energy eigenstates of quasistatic
+oscillations. The energy eigenstate problem can be properly formulated when
+potential functions, used in the quasistatic-resonance problems, are introduced
+as scalar wave functions. In this case, one should observe quasistatic-wave
+retardation effects still staying in frames of the quasistatic description of
+oscillations in a subwavelength particle. In this paper, we analyze the problem
+of energy quantization of ES resonances in subwavelength optical metallic
+structures with plasmon oscillations and MS resonances in subwavelength
+microwave ferrite particles with magnon oscillations. We show that in a case of
+MS-potential scalar wave function one can observe quasistatic retardation
+effects and obtain a proper formulation of the energy eigenstate problem.",1811.03314v1
+2018-11-24,Goos-Hänchen effect in light transmission through biperiodic photonic-magnonic crystals,"We present a theoretical investigation of the Goos-H\""anchen effect, i.e.,
+the lateral shift of the light beam transmitted through one-dimensional
+biperiodic multilayered photonic systems consisting of equidistantmagnetic
+layers separated by finite size dielectric photonic crystals. We show that the
+increase of the number of periods in the photonic-magnonic structure leads to
+increase of the Goos-H\""anchen shift in the vicinity of the frequencies of
+defect modes located inside the photonic band gaps. Presence of the linear
+magnetoelectric coupling in the magnetic layers can result in a vanishing of
+the positive maxima of the cross-polarized contribution to the Goos-H\""anchen
+shift.",1811.09865v1
+2018-11-24,Faraday effect in bi-periodic photonic-magnonic crystals,"We present a theoretical investigation of the polarization plane rotation at
+light transmission - Faraday effect, through one-dimensional multilayered
+magneto-photonic systems consisting of periodically distributed magnetic and
+dielectric layers. We calculate Faraday rotation spectra of photonic-magnonic
+crystals, where cell (or supercell) is composed of magnetic layer and
+dielectric layer (or section of dielectric photonic crystal). We found that the
+Faraday rotation of p-polarized incident light is increasing in the
+transmission band with the number of magnetic supercells. The increase of
+Faraday rotation is observed also in vicinity of the band-gap modes localized
+in magnetic layers but the maximal polarization plane rotation angles are
+reached at minimal transmittivity. We show that presence of linear
+magneto-electric interaction in the magnetic layers leads to significant
+increase of the Faraday rotation angles of s-polarized incident light in the
+vicinity of the fine-structured modes inside the photonic-band-gap.",1811.09866v1
+2010-05-10,Spectrum of short-wavelength magnons in two-dimensional quantum Heisenberg antiferromagnet on a square lattice: third order expansion in 1/S,"The spectrum of short-wavelength magnons in two-dimensional quantum
+Heisenberg antiferromagnet on a square lattice is calculated in the third order
+in $1/S$ expansion. It is shown that $1/S$ series for $S=1/2$ converges fast in
+the whole Brillouin zone except for the neighborhood of the point ${\bf
+k}=(\pi,0)$, at which absolute values of the third and the second order
+$1/S$-corrections are approximately equal to each other. It is shown that the
+third order corrections make deeper the roton-like local minimum at ${\bf
+k}=(\pi,0)$ improving the agreement with the recent experiments and numerical
+results in the neighborhood of this point. It is suggested that $1/S$ series
+converges slowly near ${\bf k}=(\pi,0)$ also for $S=1$ although the spectrum
+renormalization would be small in this case due to very small values of
+high-order $1/S$ corrections.",1005.1568v1
+2010-05-12,Ferromagnetism of $UGe_2$,"Magnetism of $UGe_2$ is due to the magnetic ordered moments of $5f$ uranium
+electrons. The strong spin-orbit coupling splits them into two groups. The
+magnetization is investigated in terms of two vector fields ${\bf M}_{1i}$ and
+${\bf M}_{2i}$ which identify the local orientation of the magnetization of the
+two groups of $f$ electrons. Renormalized spin-wave theory, which accounts for
+the magnon-magnon interaction, and its extension are developed to describe two
+ferromagnetic phases in the system: low temperature large moment phase
+$0<T<T^{*}$ (FM2), where all $5f$ electrons contribute the ordered
+ferromagnetic moment, and high temperature low-moment phase $T^{*}<T<T_C$
+(FM1), where $f$ electrons are partially ordered. Both phases are strictly
+ferromagnetic in accordance with experiment. The magnetization as a function of
+temperature is calculated. The anomalous temperature dependence of the ordered
+moment, known from the experiments with $UGe_2$, is very well reproduced
+theoretically. Below $T_x$ ($T^*$ in the present paper) the ferromagnetic
+moment increases in an anomalous way. The new understanding of the anomalous
+$FM2\to FM1$ transition, as a result of the magnetic order of two well
+separated groups of $f$ electrons, yields the key to an understanding of the
+ferromagnetism and transport properties in these compounds.",1005.2032v1
+2010-05-15,Coupling between magnon and ligand-field excitations in magnetoelectric Tb3Fe5O12 garnet,"The spectra of far-infrared transmission in Tb3Fe5O12 magnetoelectric single
+crystals have been studied in the range between 15 and 100 cm-1, in magnetic
+fields up to 10 T, and for temperatures between 5 and 150 K. We attribute some
+of the observed infrared-active excitations to electric-dipole transitions
+between ligand-field split states of Tb3+ ions. Anticrossing between the
+magnetic exchange excitation and the ligand-field transition occurs at the
+temperature between 60 and 80 K. The corresponding coupling energy for this
+interaction is 6 cm-1. Temperature-induced softening of the hybrid IR
+excitation correlates with the increase of the static dielectric constant. We
+discuss the possibility for hybrid excitations of magnons and ligand-field
+states and their possible connection to the magnetoelectric effect in
+Tb3Fe5O12.",1005.2705v1
+2013-08-06,Two magnon bound state causes ultrafast thermally induced magnetisation switching,"There has been much interest recently in the discovery of thermally induced
+magnetisation switching, where a ferrimagnetic system can be switched
+deterministically without and applied magnetic field. Experimental results
+suggest that the reversal occurs due to intrinsic material properties, but so
+far the microscopic mechanism responsible for reversal has not been identified.
+Using computational and analytic methods we show that the switching is caused
+by the excitation of two magnon bound states, the properties of which are
+dependent on material factors. This discovery allows us to accurately predict
+the switching behaviour and the identification of this mechanism will allow new
+classes of materials to be identified or designed to use this switching in
+memory devices in the THz regime.",1308.1314v1
+2013-08-12,AC current generation in chiral magnetic insulators and skyrmion motion induced by the spin Seebeck effect,"We show that a temperature gradient induces an ac electric current in
+multiferroic insulators when the sample is embedded in a circuit. We also show
+that a thermal gradient can be used to move magnetic skyrmions in insulating
+chiral magnets: the induced magnon flow from the hot to the cold region drives
+the skyrmions in the opposite direction via a magnonic spin transfer torque.
+Both results are combined to compute the effect of skyrmion motion on the ac
+current generation and demonstrate that skyrmions in insulators are a promising
+route for spin caloritronics applications.",1308.2634v3
+2013-08-30,Spin-motive force and orbital-motive force: from magnon BEC to chiral Weyl superfluids,"Spin-motive geometric force acting on electrons in metallic ferromagnets is
+extended to spin-motive force in magnon BEC, which is represented by
+phase-coherent precession of magnetization, and to the orbital-motive force in
+superfluid 3He-A. In 3He-A there are two contributions to the orbital-motive
+force. One of them comes from the chiral nature of this liquid. Another one
+originates from chiral Weyl fermions living in the vicinity of the
+topologically protected Weyl points, and is related to the phenomenon of chiral
+anomaly.",1308.6700v3
+2014-03-23,Magnon dispersion and Single hole motion in 2D frustrated antiferromagnets with four-sublattice structures,"We study a two dimensional spin-$\frac{1}{2}$ $J_1-J_2$ antiferromagnet in a
+square lattice using the linearized spin wave theory recognizing the
+4-sublattice nature of the underlying magnetic lattice. Multiple magnon modes
+with optical and acoustic branches about the stable Neel ordered and double
+acoustic branches about the columnar reference states are obtained for small
+and large values of $\lambda(=J_2/J_1)$ respectively. An additional uniaxial
+anisotropy, for large $\lambda$, can lead to distinct spin gaps in such
+systems, as also witnessed experimentally. The single hole spectral behavior in
+a 2D $t-J_1-J_2$ model, for small frustration, is then calculated within the
+non-crossing approximation. Our results match fairly well with exact
+diagonalization results from a $4\times4$ cluster. Hole spectral features and
+their evolution with $\lambda$ resulting in ""water-fall""-like smooth spectral
+weight transfer are discussed. Hole energy bands are identified and the
+corresponding energy-shift and reduction in width with spin-frustration are
+indicated.",1403.5742v3
+2017-01-05,Excitation and detection of short-waved spin waves in ultrathin Ta/CoFeB/MgO-layer system suitable for spin-orbit-torque magnonics,"We report on the excitation and detection of short-waved spin waves with wave
+vectors up to about $40\,\mathrm{rad}\,\mu\mathrm{m}^{-1}$ in spin-wave
+waveguides made from ultrathin, in-plane magnetized Co$_{8}$Fe$_{72}$B$_{20}$
+(CoFeB). The CoFeB is incorporated in a layer stack of Ta/CoFeB/Mgo, a layer
+system featuring large spin orbit torques and a large perpendicular magnetic
+anisotropy constant. The short-waved spin waves are excited by nanometric
+coplanar waveguides and are detected via spin rectification and microfocussed
+Brillouin light scattering spectroscopy. We show that the large perpendicular
+magnetic anisotropy benefits the spin-wave lifetime greatly, resulting in a
+lifetime comparable to bulk systems without interfacial damping. The presented
+results pave the way for the successful extension of magnonics to ultrathin
+asymmetric layer stacks featuring large spin orbit torques.",1701.01399v1
+2017-01-16,Four-Point Functions with a Twist,"We study the OPE of correlation functions of local operators in planar N=4
+super Yang-Mills theory. The considered operators have an explicit spacetime
+dependence that is defined by twisting the translation generators with certain
+R-symmetry generators. We restrict to operators that carry a small number of
+excitations above the twisted BMN vacuum. The OPE limit of the four-point
+correlator is dominated by internal states with few magnons on top of the
+vacuum. The twisting directly couples all spacetime dependence of the
+correlator to these magnons. We analyze the OPE in detail, and single out the
+extremal states that have to cancel all double-trace contributions.",1701.04424v3
+2017-01-17,Mutually attracting spin waves in the square-lattice quantum antiferromagnet,"The Heisenberg model for S=1/2 describes the interacting spins of electrons
+localized on lattice sites due to strong repulsion. It is the simplest
+strong-coupling model in condensed matter physics with wide-spread
+applications. Its relevance has been boosted further by the discovery of curate
+high-temperature superconductors. In leading order, their undoped parent
+compounds realize the Heisenberg model on square-lattices. Much is known about
+the model, but mostly at small wave vectors, i.e., for long-range processes,
+where the physics is governed by spin waves (magnons), the Goldstone bosons of
+the long-range ordered antiferromagnetic phase. Much less, however, is known
+for short-range processes, i.e., at large wave vectors. Yet these processes are
+decisive for understanding high-temperature superconductivity. Recent reports
+suggest that one has to resort to qualitatively different fractional
+excitations, spinons. By contrast, we present a comprehensive picture in terms
+of dressed magnons with strong mutual attraction on short length scales. The
+resulting spectral signatures agree strikingly with experimental data",1701.04730v2
+2017-01-27,Collective dynamics in atomistic models with coupled translational and spin degrees of freedom,"Using an atomistic model that simultaneously treats the dynamics of
+translational and spin degrees of freedom, we perform combined molecular and
+spin dynamics simulations to investigate the mutual influence of the phonons
+and magnons on their respective frequency spectra and lifetimes in
+ferromagnetic bcc iron. By calculating the Fourier transforms of the space- and
+time-displaced correlation functions, the characteristic frequencies and the
+linewidths of the vibrational and magnetic excitation modes were determined.
+Comparison of the results with that of the stand-alone molecular dynamics and
+spin dynamics simulations reveals that the dynamic interplay between the
+phonons and magnons leads to a shift in the respective frequency spectra and a
+decrease in the lifetimes. Moreover, in the presence of lattice vibrations,
+additional longitudinal magnetic excitations were observed with the same
+frequencies as the longitudinal phonons.",1701.07906v1
+2017-01-31,Spin waves in planar quasicrystal of Penrose tiling,"We investigated two-dimensional magnonic structures which are the
+counterparts of photonic quasicrystals forming Penrose tiling. We considered
+the slab composed of Ni (or Py) disks embedded in Fe (or Co) matrix. The disks
+were arranged in quasiperiodic Pernose-like structure. The infinite
+quasicrystal was approximated by its rectangular section with periodic boundary
+conditions applied. This approach allowed us to use the plane wave method to
+find the frequency spectrum of eigenmodes for spin waves and their spatial
+profiles. The calculated integrated density of states shows more distictive
+magnonic gaps for the structure composed of materials of high magnetic contrast
+(Ni and Fe) and relatively high filling fraction. This proves the impact of
+quasiperiodic long-range order on the spectrum of spin waves. We also
+investigated the localization of SW eingenmodes resulting from the
+quasipeiodicity of the structure.",1701.09125v1
+2018-05-01,Spontaneous Exact Spin-Wave Fractals in Magnonic Crystals,"Exact fractals of nonlinear waves that rely on strong dispersion and
+nonlinearity and arise spontaneously out of magnetic media were observed for
+the first time. The experiments make use of a microwave to excite a spin wave
+in a quasi-one-dimensional magnonic crystal. When the power of the input
+microwave (Pin) is low, the output signal has a power-frequency spectrum that
+consists of a single peak. When Pin is increased to a certain level, the new
+side modes are generated through modulational instability (MI), resulting in a
+comb-like frequency spectrum. With a further increase in Pin, each peak in the
+frequency comb can evolve into its own, finer comb through the MI. As Pin is
+increased further, one can observe yet another set of finer frequency combs.
+Such a frequency-domain fractal manifests itself as multiple layers of
+amplitude modulation in the time-domain signal.",1805.00517v2
+2018-05-03,Sculpting the Spin-Wave Response of Artificial Spin Ice via Microstate Selection,"The spin-wave dynamics of the ferromagnetic nanoarrays termed artificial spin
+ice (ASI) are known to vary depending on their magnetic microstate. However,
+little work has been done to characterise this relationship. Recent advances in
+control over the magnetic configuration of ASI bring designs harnessing the
+interplay between spin-wave eigenmodes and the microstate within reach,
+offering diverse applications including reconfigurable magnonic crystals,
+microwave filters and microstate read-out probes. These designs hinge on a
+strong understanding of the underlying spin wave-microstate correspondence.
+  Here, we analyse the effects of the magnetic microstate on spin-wave spectra
+of honeycomb ASI systems via micromagnetic simulation. We find the spin-wave
+spectrum to be highly-tunable via the microstate to an enhanced degree relative
+to existing magnonic crystals, with mode shifting and (de)activation realised
+by reversing individual nanoislands. Symmetries of ASI systems and the
+chirality of magnetic defects are found to play important roles in determining
+the high-frequency response.",1805.01397v3
+2018-05-09,Programmable control of spin-wave transmission in a domain-wall spin valve,"Active manipulation of spin waves is essential for the development of
+magnon-based technologies. Here, we demonstrate programmable spin-wave
+filtering by resetting the spin structure of a pinned 90$^\circ$ N\'{e}el
+domain wall in a continuous CoFeB film with abrupt rotations of uniaxial
+magnetic anisotropy. Using phase-resolved micro-focused Brillouin light
+scattering and micromagnetic simulations, we show that broad 90$^\circ$
+head-to-head or tail-to-tail magnetic domain walls are transparent to spin
+waves over a broad frequency range. In contrast, magnetic switching to a
+90$^\circ$ head-to-tail configuration produces much narrower domain walls at
+the same pinning locations. Spin waves are strongly reflected by a resonance
+mode in these magnetic domain walls. Based on these results, we propose a
+magnetic spin-wave valve with two parallel domain walls. Switching the
+spin-wave valve from an open to a close state changes the transmission of spin
+waves from nearly 100% to 0% at the resonance frequency. This active control
+over spin-wave transport could be utilized in magnonic logic devices or
+non-volatile memory elements.",1805.03470v1
+2018-05-21,Nonreciprocal superposition state in antiferromagnetic optospintronics,"The absence of net magnetization, which forbids any stray magnetic fields, is
+one of the greatest advantages of antiferromagnets in device applications. In
+conventional antiferromagnets, however, spin current cannot be extracted
+without the aid of a static magnetic field. Here, we develop a theory of
+antiferromagnetic opto-spintronics to resolve this fundamental dilemma. By
+coupling a linearly polarized photon and nonreciprocal magnon bands, we
+construct a superposition state of left- and right-handed magnon states with
+opposite group velocities. We numerically demonstrate that by using this
+superposition state, an antiferromagnetic spin current can be efficiently
+generated without a net magnetic field including net magnetization. We also
+find that the breakdown of the superposition state induces the stripe
+superfluid phase of a two-component Bose-Einstein condensate. Our results lay
+the foundation for manipulating the superposition states of emergent particles
+in devices.",1805.08226v3
+2018-05-22,Non-reciprocal magnons in non-centrosymmetric MnSi,"Using two cold-neutron triple-axis spectrometers we have succeeded in fully
+mapping out the field-dependent evolution of the non-reciprocal magnon
+dispersion relations in all magnetic phases of MnSi. The non-reciprocal nature
+of the dispersion manifests itself in a full asymmetry (non-reciprocity) of the
+dynamical structure factor $S(q, E, \mu_0 H_{int})$ with respect to flipping
+either the direction of the applied magnetic field $\mu_0 H_{int}$, the reduced
+momentum transfer $q$, or the energy transfer $E$.",1805.08750v2
+2018-05-23,Spectral signatures of fractionalization in the frustrated Heisenberg model on the square lattice,"We employ a variational Monte Carlo approach to efficiently obtain the
+dynamical structure factor for the spin-1/2 $J_1-J_2$ Heisenberg model on the
+square lattice. Upon increasing the frustrating ratio $J_2/J_1$, the ground
+state undergoes a continuous transition from a N\'eel antiferromagnet to a
+$\mathbb{Z}_{2}$ gapless spin liquid. We identify the characteristic spectral
+features in both phases and highlight the existence of a broad continuum of
+excitations in the proximity of the spin-liquid phase. The magnon branch, which
+dominates the spectrum of the unfrustrated Heisenberg model, gradually loses
+its spectral weight, thus releasing nearly-deconfined spinons, whose signatures
+are visible even in the magnetically ordered state. Our results show how free
+spinons emerge across a quantum critical point, providing evidence for the
+fractionalization of magnons into deconfined spinons.",1805.09287v2
+2009-12-10,Magnonic crystal based forced dominant wavenumber selection in a spin-wave active ring,"Spontaneous excitation of the dominant mode in a spin-wave active ring -- a
+self-exciting positive-feedback system incorporating a spin-wave transmission
+structure -- occurs at a certain threshold value of external gain. In general,
+the wavenumber of the dominant mode is extremely sensitive to the properties
+and environment of the spin-wave transmission medium, and is almost impossible
+to predict. In this letter, we report on a backward volume magnetostatic
+spin-wave active ring system incorporating a magnonic crystal. When mode
+enhancement conditions -- readily predicted by a theoretical model -- are
+satisfied, the ring geometry permits highly robust and consistent forced
+dominant wavenumber selection.",0912.2029v3
+2009-12-11,"Orbital order, stacking defects and spin-fluctuations in the $p$-electron molecular solid RbO$_2$","We examine magnon and orbiton behavior in localized O$_2$ anti-bonding
+molecular $\pi^*$ orbitals using an effective Kugel-Khomskii Hamiltonian
+derived from a two band Hubbard model with hopping parameters taken from {\em
+ab initio} density functional calculations. The considerable difference between
+intraband and interband hoppings leads to a strong coupling between the spin
+wave dispersion and the orbital ground state, providing a straightforward way
+of experimentally determining the orbital ground state from the measured magnon
+dispersion. The near degeneracy of different orbital ordered states leads to
+stacking defects which further modulate spin-fluctuation spectra. Proliferation
+of orbital domains disrupts long-range magnetic order, thus causing a
+significant reduction in the observed N\'eel temperature.",0912.2334v2
+2011-11-14,Nematic phase and phase separation near saturation field in frustrated ferromagnets,"We study the effects of quantum fluctuations in magnetic properties of
+quantum frustrated ferromagnets in a magnetic field. It is shown that a
+non-classical phase or a phase separation appears due to quantum fluctuations
+below the saturation field in a parameter range close to the classical
+zero-field phase boundary between ferromagnetic and antiferromagnetic phases,
+for the case that the classical antiferromagnetic state is not an eigenstate of
+the quantum model. As an example to which this argument is applicable, we study
+the S=1/2 J1-J2 Heisenberg model with ferromagnetic J1 (J1<0) on the bcc
+lattice using a dilute Bose gas approach. For -1.50097 < J1/J2 < -1.389,
+magnons form f-wave two-magnon bound states, leading to a spin nematic phase,
+and for -1.389 < J1/J2 < -0.48 a canted coplanar antiferromagnetic phase
+appears accompanied with a phase separation below the saturation field.",1111.3184v3
+2011-11-14,Superatom Representation of High-TC Superconductivity Revisited,"A ""super-atom"" conceptual interface between chemistry and physics is proposed
+in order to assist in the search for higher TC superconductors. High-TC
+superconductivity HTSC is articulated as the entanglement of two disjoint
+electronic manifolds in the vicinity of a common Fermi energy. The resulting
+HTSC ground state couples near-degenerate protected local ""super-atom"" states
+to virtual magnons in an antiferromagnetic AFM embedding. The composite Cooper
+pairs emerge as the interaction particles for virtual magnons mediated
+""self-coherent entanglement"" of super-atom states. A H\""uckel type resonating
+valence bond RVB formalism is employed in order to illustrate the real-space
+Cooper pairs as well as their delocalization and Bose Einstein condensation BEC
+on a ring of super-atoms. The chemical potential \mu(BEC) for Cooper pairs
+joining the condensate is formulated in terms of the super-exchange
+interaction, and consequently the TC in terms of the Ne\'el temperature. A
+rationale for the robustness of the HTSC ground state is proposed: achieving
+local maximum ""electron correlation entropy"" at the expense of non-local phase
+rigidity.",1111.3190v1
+2011-11-21,Magnetic excitations in the spin-1 anisotropic antiferromagnet $NiCl_2-4SC(NH_2)_2$,"The spin-1 anisotropic antiferromagnet NiCl_2-4SC(NH2)_2 exhibits a
+field-induced quantum phase transition that is formally analogous to
+Bose-Einstein condensation. Here we present results of systematic high-field
+electron spin resonance (ESR) experimental and theoretical studies of this
+compound with a special emphasis on single-ion two-magnon bound states. In
+order to clarify some remaining discrepancies between theory and experiment,
+the frequency-field dependence of magnetic excitations in this material is
+reanalyzed. In particular, a more comprehensive interpretation of the
+experimental signature of single-ion two-magnon bound states is shown to be
+fully consistent with theoretical results. We also clarify the structure of the
+ESR spectrum in the so-called intermediate phase.",1111.5017v2
+2012-04-05,The Magnon Spectrum in the Domain Ferromagnetic State of Antisite Disordered Double Perovskites,"In their ideal structure, double perovskites like Sr_2FeMoO_6 have
+alternating Fe and Mo along each cubic axes, and a homogeneous ferromagnetic
+metallic ground state. Imperfect annealing leads to the formation of structural
+domains. The moments on mislocated Fe atoms that adjoin each other across the
+domain boundary have an antiferromagnetic coupling between them. This leads to
+a peculiar magnetic state, with ferromagnetic domains coupled
+antiferromagnetically. At short distance the system exhibits ferromagnetic
+correlation while at large lengthscales the net moment is strongly suppressed
+due to inter-domain cancellation. We provide a detailed description of the spin
+wave excitations of this complex magnetic state, obtained within a 1/S
+expansion, for progressively higher degree of mislocation, i.e., antisite
+disorder. At a given wavevector the magnons propagate at multiple energies,
+related, crudely, to `domain confined' modes with which they have large
+overlap. We provide a qualitative understanding of the trend observed with
+growing antisite disorder, and contrast these results to the much broader
+spectrum that one obtains for uncorrelated antisites.",1204.1194v1
+2012-04-11,A short note on spin pumping theory with Landau-Lifshitz-Gilbert equation under quantum fluctuation; necessity for quantization of localized spin,"We would like to point out the blind spots of the approach combining the spin
+pumping theory proposed by Tserkovnyak et al. with the Landau-Lifshitz-Gilbert
+equation; this method has been widely used for interpreting vast experimental
+results. The essence of the spin pumping effect is the quantum fluctuation.
+Thus, localized spin degrees of freedom should be quantized, i.e. be treated as
+magnons not as classical variables. Consequently, the precessing ferromagnet
+can be regarded as a magnon battery. This point of view will be useful for
+further progress of spintronics.",1204.2339v1
+2013-08-30,Superconducting instability of a non-magnetic metallic band in an antiferromagnetic background,"It is shown that a non-magnetic metallic band in the presence of an
+antiferromagnetic background coupled only by the exchange interaction develops
+a superconducting instability similar to the one described by BCS theory plus
+additional terms that strongly renormalize the spin excitation spectra. A
+Bardeen-Pines-like hole-hole interaction Hamiltonian, mediated by magnetic
+excitations, is deduced from a microscopic model of a fermion band and a spin
+band that interact with each other only via the exchange interaction. The
+theory shows the appearance of an attractive interaction when the Fermi
+velocity in the non-magnetic band is larger than the magnon velocity in the
+magnetic band. The electron-magnon scattering is suppressed by the appearance
+of a spin gap simultaneously with the superconducting state. Although this
+model may well describe a general class of materials to be discovered, the
+possibility that this theory could describe superconducting cuprates is
+discussed.",1309.0032v1
+2013-09-12,Cluster Functional Renormalization Group,"Functional renormalization group (FRG) has become a diverse and powerful tool
+to derive effective low-energy scattering vertices of interacting many-body
+systems. Starting from a non-interacting expansion point of the action, the
+flow of the RG parameter Lambda allows to trace the evolution of the effective
+one-particle and two-particle vertices towards low energies by taking into
+account the vertex corrections between all parquet channels in an unbiased
+fashion. In this work, we generalize the expansion point at which the
+diagrammatic resummation procedure is initiated from a free UV limit to a
+cluster product state. We formulate a cluster FRG scheme where the
+non-interacting building blocks (i.e., decoupled spin clusters) are treated
+exactly, and the inter-cluster couplings are addressed via RG. As a benchmark
+study, we apply our cluster FRG scheme to the spin-1/2 bilayer Heisenberg model
+(BHM) on a square lattice where the neighboring sites in the two layers form
+the individual 2-site clusters. Comparing with existing numerical evidence for
+the BHM, we obtain reasonable findings for the spin susceptibility, magnon
+dispersion, and magnon quasiparticle weight even in coupling regimes close to
+antiferromagnetic order. The concept of cluster FRG promises applications to a
+large class of interacting electron systems.",1309.3262v1
+2013-09-26,Magnetic frustration in BaCuSi2O6 released,"Han Purple (BaCuSi2O6) is not only an ancient pigment, but also a valuable
+model material for studying Bose-Einstein condensation (BEC) of magnons in high
+magnetic fields. Using precise low-temperature structural data and extensive
+density-functional calculations, we elucidate magnetic couplings in this
+compound. The resulting magnetic model comprises two types of nonequivalent
+spin dimers, in excellent agreement with the (63,65)Cu nuclear magnetic
+resonance data. We further argue that leading interdimer couplings connect the
+upper site of one dimer to the bottom site of the contiguous dimer, and not the
+upper-to-upper and bottom-to-bottom sites, as assumed previously. This finding
+is verified by inelastic neutron scattering data and implies the lack of
+magnetic frustration in BaCuSi2O6, thus challenging existing theories of the
+magnon BEC in this compound.",1309.6762v1
+2014-05-02,Weyl fermions induced Magnon electrodynamics in Weyl semimetal,"Weyl fermions, which are fermions with definite chiralities, can give rise to
+anomalous breaking of the symmetry of the physical system which they are a part
+of. In their (3+1)-dimensional realizations in condensed matter systems, i.e.,
+the so-called Weyl semimetals, this anomaly gives rise to topological
+electromagnetic response of magnetic fluctuations, which takes the form of
+non-local interaction between magnetic fluctuations and electromagnetic fields.
+We study the physical consequences of this non-local interaction, including
+electric field assisted magnetization dynamics, an extra gapless magnon
+dispersion, and polariton behaviors that feature ""sibling"" bands in small
+magnetic fields.",1405.0491v2
+2014-05-06,Hybridizing ferromagnetic magnons and microwave photons in the quantum limit,"We demonstrate large normal-mode splitting between a magnetostatic mode (the
+Kittel mode) in a ferromagnetic sphere of yttrium iron garnet and a microwave
+cavity mode. Strong coupling is achieved in the quantum regime where the
+average number of thermally or externally excited magnons and photons is less
+than one. We also confirm that the coupling strength is proportional to the
+square root of the number of spins. A nonmonotonic temperature dependence of
+the Kittel-mode linewidth is observed below 1 K and is attributed to the
+dissipation due to the coupling with a bath of two-level systems.",1405.1913v2
+2014-05-20,Triplet excitations in graphene-based systems,"In this article we investigate the excitations in a single graphene layer and
+in a single-walled carbon nanotube, i.e. the spectrum of magnetic excitations
+is calculated. In the absence of interactions in these systems there is a
+unique gap in the electron-hole continuum. We show that in the presence of
+Coulomb correlations new states, magnons, appear in this forbidden region.
+Coulomb interaction is examined in the context of Pariser-Parr-Pople (PPP)
+model which takes into account long range nature of interaction. The energy of
+new bound states depends on the strength of Coulomb forces. The calculations
+are performed for arbitrary electron-hole ($e-h$) momentum $\textbf{q}$ what
+allows to find the magnons dispersion law $\varepsilon(\textbf{q})$, effective
+mass $m^*$ and velocity $v_{gr}$. Finally, we determine the critical values of
+system parameters when this type of excitations can exist.",1405.5150v2
+2014-06-08,Stability and magnetization curve of spin-nematic phase slightly below saturation field,"We discuss the magnetization process slightly below the saturation field in
+frustrated magnets. A condensation of bound magnons on the spin-polarized state
+induces either a spin nematic phase or a state with phase separation. The
+(effective) interaction between the bound magnon pairs not only is crucial to
+the stability of the nematic phase, but also determines the slope of the
+magnetization curve near saturation. We generally derive the expression of this
+interaction by using the perturbative scattering theory. By applying the method
+to coupled zigzag chains LiCuVO4, we find the positive pair-pair interaction
+implying the stability of the spin nematic phase. We also point out that the
+magnetization curve of LiCuVO4 is almost vertical (i.e. very large dM/dH) near
+the saturation exhibiting one-dimensional feature despite non-negligible
+interchain couplings.",1406.1960v1
+2014-06-14,Electric-field coupling to spin waves in a centrosymmetric ferrite,"We experimentally demonstrate that the spin-orbit interaction can be utilized
+for direct electric-field tuning of the propagation of spin waves in a
+single-crystal yttrium iron garnet magnonic waveguide. Magnetoelectric coupling
+not due to the spin-orbit interaction, and hence an order of magnitude weaker,
+leads to electric-field modification of the spin-wave velocity for waveguide
+geometries where the spin-orbit interaction will not contribute. A theory of
+the phase shift, validated by the experiment data, shows that, in the exchange
+spin wave regime, this electric tuning can have high efficiency. Our findings
+point to an important avenue for manipulating spin waves and developing
+electrically tunable magnonic devices.",1406.3675v1
+2014-06-19,Band structure of magnonic crystals with defects: Brillouin spectroscopy and micromagnetic simulations,"Using Brillouin spectroscopy, the first observation has been made of the band
+structures of nanostructured defect magnonic crystals. The samples are
+otherwise one-dimensional periodic arrays of equal-width Ni80Fe20 and cobalt
+nanostripes, where the defects are stripes of a different width. A
+dispersionless defect branch emerges within the bandgap with a frequency
+tunable by varying the defect stripe width, while the other branches observed
+are similar to those of a defect-free crystal. Micromagnetic and finite-element
+simulations performed unveil additional tiny bandgaps and the
+frequency-dependent localization of the defect mode in the vicinity of the
+defects.",1406.4981v2
+2014-06-23,Magnon-Driven Domain-Wall Motion with the Dzyaloshinskii-Moriya Interaction,"We study domain wall (DW) motion induced by spin waves (magnons) in the
+presence of Dzyaloshinskii-Moriya interaction (DMI). The DMI exerts a torque on
+the DW when spin waves pass through the DW, and this torque represents a linear
+momentum exchange between the spin wave and the DW. Unlike angular momentum
+exchange between the DW and spin waves, linear momentum exchange leads to a
+rotation of the DW plane rather than a linear motion. In the presence of an
+effective easy plane anisotropy, this DMI induced linear momentum transfer
+mechanism is significantly more efficient than angular momentum transfer in
+moving the DW.",1406.5997v2
+2016-08-02,Magnetic Domain Wall Floating on a Spin Superfluid,"We theoretically investigate the transfer of angular momentum between a spin
+superfluid and a domain wall in an exchange coupled easy-axis and easy-plane
+magnetic insulator system. A domain wall in the easy-axis magnet absorbs spin
+angular momentum via disrupting the flow of a superfluid spin current in the
+easy-plane magnet. Focusing on an open geometry, where the spin current is
+injected electrically via a nonequilibrium spin accumulation, we derive
+analytical expressions for the resultant superfluid-mediated motion of the
+domain wall. The analytical results are supported by micromagnetic simulations.
+The proposed phenomenon extends the regime of magnon-driven domain-wall motion
+to the case when the magnons are condensed and exhibit superfluidity.
+Furthermore, by controlling the pinning of the domain wall, we propose a
+realization of a reconfigurable spin transistor. The long-distance
+dissipationless character of spin superfluids can thus be exploited for
+manipulating soliton-based memory and logic devices.",1608.00683v1
+2016-08-17,Quenched Magnon excitations by oxygen sublattice reconstruction in (SrCuO$_2$)$_n$/(SrTiO$_3$)$_2$ superlattices,"The recently discovered structural reconstruction in the cuprate superlattice
+(SrCuO$_2$)$_n$/(SrTiO$_3$)$_2$ has been investigated across the critical value
+of $n=5$ using resonant inelastic x-ray scattering (RIXS). We find that at the
+critical value of $n$, the cuprate layer remains largely in the bulk-like
+two-dimensional structure with a minority of Cu plaquettes being reconstructed.
+The partial reconstruction leads to quenching of the magnons starting at the
+$\Gamma$-point due to the minority plaquettes acting as scattering points.
+Although comparable in relative abundance, the doped charge impurities in
+electron-doped cuprate superconductors do not show this quenching of magnetic
+excitations.",1608.05092v1
+2017-06-07,Making the Dzyaloshinskii-Moriya interaction visible,"Brillouin light spectroscopy is a powerful and robust technique for measuring
+the interfacial Dzyaloshinskii-Moriya interaction in thin films with broken
+inversion symmetry. Here we show that the magnon visibility, i.e. the intensity
+of the inelastically scattered light, strongly depends on the thickness of the
+dielectric seed material - SiO$_2$. By using both, analytical thin-film optics
+and numerical calculations, we reproduce the experimental data. We therefore
+provide a guideline for the maximization of the signal by adapting the
+substrate properties to the geometry of the measurement. Such a boost-up of the
+signal eases the magnon visualization in ultrathin magnetic films, speeds-up
+the measurement and increases the reliability of the data.",1706.02258v1
+2017-06-08,Equations of Motion and Frequency Dependence of Magnon-Induced Domain Wall Motion,"Spin waves can induce domain wall motion in ferromagnets. We derive the
+equations of motion for a transverse domain wall driven by spin waves. Our
+calculations show that the magnonic spin-transfer torque does not cause
+rotation-induced Walker breakdown. The amplitude of spin waves that are excited
+by a localized microwave field depends on the spatial profile of the field and
+the excitation frequency. By taking this frequency dependence into account, we
+show that a simple one-dimensional model may reproduce much of the puzzling
+frequency dependence observed in early numerical studies.",1706.02709v2
+2017-06-27,Noise in tunneling spin current across coupled quantum spin chains,"We theoretically study the spin current and its dc noise generated between
+two spin-1/2 spin chains weakly coupled at a single site in the presence of an
+over-population of spin excitations and a temperature elevation in one
+subsystem relative to the other, and compare the corresponding transport
+quantities across two weakly coupled magnetic insulators hosting magnons. In
+the spin chain scenario, we find that applying a temperature bias exclusively
+leads to a vanishing spin current and a concomitant divergence in the spin Fano
+factor, defined as the spin current noise-to-signal ratio. This divergence is
+shown to have an exact analogy to the physics of electron scattering between
+fractional quantum Hall edge states and not to arise in the magnon scenario. We
+also reveal a suppression in the spin current noise that exclusively arises in
+the spin chain scenario due to the fermion nature of the spin-1/2 operators. We
+discuss how the spin Fano factor may be extracted experimentally via the
+inverse spin Hall effect used extensively in spintronics.",1706.09030v2
+2017-06-30,Raman scattering study of vibrational and magnetic excitations in Sr$_{2-x}$La$_x$IrO$_4$,"We have measured the doping and temperature dependence of lattice vibrations
+and magnetic excitations in the prototypical doped spin-orbit Mott insulator
+Sr$_{2-x}$La$_x$IrO$_4$ (x=0, 0.015, and 0.10). Our findings show that the
+pseudospin-lattice coupling -- responsible for the renormalization of several
+low energy phonon modes -- is preserved even when long-range magnetic order is
+suppressed by doping. In our most highly doped sample, the single magnon
+(Gamma-point) excitation disappears while the two-magnon mode softens and
+becomes heavily damped. Doping induced electron-phonon coupling is also
+observed in a higher energy phonon mode. We observe two different
+electron-phonon interaction channels, which provide evidence of the coexistence
+of fluctuating magnetic moments and mobile carriers in doped iridates.",1706.10103v2
+2017-10-25,Co- and contra-directional vertical coupling between ferromagnetic layers with grating for short-wavelength spin wave generation,"The possibility to generate short spin waves is of great interest in the
+field of magnonics nowadays. We present an effective and technically affordable
+way of conversion of long spin waves, which may be generated by conventional
+microwave antenna, to the short, sub-micrometer waves. It is achieved by
+grating-assisted resonant dynamic dipolar interaction between two ferromagnetic
+layers separated by some distance. We analyze criteria for the optimal
+conversion giving a semi-analytical approach for the coupling coefficient. We
+show by the numerical calculations the efficient energy transfer between layers
+which may be either of co-directional or contra-directional type. Such a system
+may operate either as a short spin wave generator or a frequency filter, moving
+foreward possible application of magnonics.",1710.09138v1
+2017-10-25,Collective spin waves in arrays of Permalloy nanowires with single-side periodically modulated width,"We have experimentally and numerically investigated the dispersion of
+collective spin waves prop-agating through arrays of longitudinally magnetized
+nanowires with periodically modulated width. Two nanowire arrays with
+single-side modulation and different periodicity of modulation were studied and
+compared to the nanowires with homogeneous width. The spin-wave dispersion,
+meas-ured up to the third Brillouin zone of the reciprocal space, revealed the
+presence of two dispersive modes for the width-modulated NWs, whose amplitude
+of magnonic band depends on the modula-tion periodicity, and a set of
+nondispersive modes at higher frequency. These findings are different from
+those observed in homogeneous width NWs where only the lowest mode exhibits
+sizeable dis-persion. The measured spin-wave dispersion has been satisfactorily
+reproduced by means of dynam-ical matrix method. Results presented in this work
+are important in view of the possible realization of frequency tunable magnonic
+device.",1710.09163v1
+2017-12-04,"Faster, farther, stronger: spin transfer torque driven high order propagating spin waves in nano-contact magnetic tunnel junctions","Short wave-length exchange-dominated propagating spin waves will enable
+magnonic devices to operate at higher frequencies and higher data transmission
+rates.1 While GMR based magnetic nano-contacts are highly efficient injectors
+of propagating spin waves2,3, the generated wave lengths are 2.6 times the
+nano-contact diameter4, and the electrical signal strength remains much too
+weak for practical applications. Here we demonstrate nano-contact based spin
+wave generation in magnetic tunnel junction stacks, and observe large discrete
+frequency steps consistent with the hitherto ignored possibility of second and
+third order propagating spin waves with wave lengths of 120 and 74 nm, i.e.
+much smaller than the 150 nm nano-contact. These higher-order propagating spin
+waves will not only enable magnonic devices to operate at much higher
+frequencies, but also greatly increase their transmission rates and spin wave
+propagating lengths, both proportional to the much higher group velocity.",1712.00954v2
+2017-12-08,Magnon-induced superconductivity in field-cooled spin-1/2 antiferromagnets,"If, during the preparation, an external magnetic field is applied upon
+cooling we say it has been field cooled. A novel mechanism for insulator-metal
+transition and superconductivity in field-cooled spin-$1/2$ antiferromagnets on
+bcc lattice is discussed. Applying a magnetic field along the sublattice B
+magnetization, we change the magnetic and transport properties of the material.
+There is a critical value $H_{cr1}$. When the magnetic field is below the
+critical one $H<H_{cr1}$ the prepared material is a spin$-1/2$
+antiferromagnetic insulator. When $H>H_{cr1}$ the sublattice A electrons are
+delocalized and the material is metal. There is a second critical value
+$H_{cr2}>H_{cr1}$. When $H=H_{cr2}$, it is shown that the Zeeman splitting of
+the sublattice A electrons is zero and they do not contribute to the
+magnetization of the system. At this quantum partial order point (QPOP) the
+sublattice B transversal spin fluctuations (magnons) interact with sublattice A
+electrons inducing spin anti-parallel \emph{p}-wave superconductivity which
+coexists with magnetism. At zero temperature the magnetic moment of sublattice
+B electrons is maximal. Below the N\'{e}el temperature $(T_N)$ the gap is
+approximately constant with a small increase when the system approaches $T_N$.
+It abruptly falls down to zero at temperatures above $T_N$.",1712.02983v1
+2017-12-09,Magnonic waveguide based on exchange-spring magnetic structure,"We propose to use a soft/hard exchange-spring coupling bilayer magnetic
+structure to introduce a narrow channel for spin-wave propagation. We show by
+micromagnetic simulations that broad-band Damon-Eshbach geometry spin waves can
+be strongly localized into the channel and propagate effectively with a proper
+high group velocity. The beamwidth of the bound mode spin waves is almost
+independent from the frequency and is smaller than 24nm. For a low-frequency
+excitation, we further investigate the appearance of two other spin beams in
+the lateral of the channel. In contrast to a domain wall, the channel formed by
+exchange-spring coupling can be easier to realize in experimental scenarios and
+holds stronger immunity to surroundings. This work is expected to open new
+possibilities for energy-efficient spin-wave guiding as well as to help shape
+the field of beam magnonics.",1712.03392v1
+2017-12-13,Mobile bound states of Rydberg excitations in a lattice,"Spin lattice models play central role in the studies of quantum magnetism and
+non-equilibrium dynamics of spin excitations -- magnons. We show that a spin
+lattice with strong nearest-neighbor interactions and tunable long-range
+hopping of excitations can be realized by a regular array of laser driven
+atoms, with an excited Rydberg state representing the spin-up state and a
+Rydberg-dressed ground state corresponding to the spin-down state. We find
+exotic interaction-bound states of magnons that propagate in the lattice via
+the combination of resonant two-site hopping and non-resonant second-order
+hopping processes. Arrays of trapped Rydberg-dressed atoms can thus serve as a
+flexible platform to simulate and study fundamental few-body dynamics in spin
+lattices.",1712.04713v1
+2017-12-19,Observation of time quasicrystal and its transition to superfluid time crystal,"We report experimental realization of a quantum time quasicrystal, and its
+transformation to a quantum time crystal. We study Bose-Einstein condensation
+of magnons, associated with coherent spin precession, created in a flexible
+trap in superfluid $^3$He-B. Under a periodic drive with an oscillating
+magnetic field, the coherent spin precession is stabilized at a frequency
+smaller than that of the drive, demonstrating spontaneous breaking of discrete
+time translation symmetry. The induced precession frequency is incommensurate
+with the drive, and hence the obtained state is a time quasicrystal. When the
+drive is turned off, the self-sustained coherent precession lives a
+macroscopically-long time, now representing a time crystal with broken symmetry
+with respect to continuous time translations. Additionally, the magnon
+condensate manifests spin superfluidity, justifying calling the obtained state
+a time supersolid or a time super-crystal.",1712.06877v5
+2017-12-22,Nanomagnonic waveguides based on reconfigurable spin-textures for spin computing,"Magnonics is gaining momentum as an emerging technology for information
+processing. The wave character and Joule heating-free propagation of spin-waves
+hold promises for highly efficient analog computing platforms, based on
+integrated magnonic circuits. Miniaturization is a key issue but, so far, only
+few examples of manipulation of spin-waves in nanostructures have been
+demonstrated, due to the difficulty of tailoring the nanoscopic magnetic
+properties with conventional fabrication techniques. In this Letter, we
+demonstrate an unprecedented degree of control in the manipulation of
+spin-waves at the nanoscale by using patterned reconfigurable spin-textures. By
+space and time-resolved scanning transmission X-ray microscopy imaging, we
+provide direct evidence for the channeling and steering of propagating
+spin-waves in arbitrarily shaped nanomagnonic waveguides based on patterned
+domain walls, with no need for external magnetic fields or currents.
+Furthermore, we demonstrate a prototypic nanomagnonic circuit based on two
+converging waveguides, allowing for the tunable spatial superposition and
+interaction of confined spin-waves modes.",1712.08293v1
+2018-09-06,Statistical Thermodynamics of the Fröhlich-Bose-Einstein Condensation of Magnons out of Equilibrium,"A non-equilibrium statistical-thermodynamic approach to the study of a
+Fr\""ohlich-Bose-Einstein condensation of magnons under radio-frequency
+radiation pumping is presented. Such a system displays a complex behavior
+consisting in steady-state conditions to the emergence of a synergetic
+dissipative structure resembling the Bose-Einstein condensation of systems in
+equilibium. A kind of ""two fluid model"" arises: the ""normal"" non-equilibrium
+structure and Fr\""ohlich condensate or ""non-equilibrium"" one, which is shown to
+be an attractor to the system. We analyze some aspects of the irreversible
+thermodynamics of this dissipative complex system, namely, its informational
+entropy, expressions for the fluctuations in non-equilibrium conditions, the
+associated Maxwell relations and the formulation of a generalized
+$\mathscr{H}$-theorem. We also study the informational entropy production of
+the system, an order parameter is introduced and Glansdorff-Prigogine criteria
+for evolution and (in)stability are verified.",1809.03335v1
+2018-09-19,Photocontrol of magnetic structure in an itinerant magnet,"We study the photoinduced magnetic transition in an itinerant magnet
+described by the double-exchange model, in which conduction electrons couple
+with localized spins through the ferromagnetic (FM) Hund coupling. It is shown
+that intense light applied to the FM ground state induces an antiferromagnetic
+(AFM) order, in contrast to the AFM-to-FM transition due to the photocarrier
+injection. In particular, we focus on the mechanism for instability of the FM
+structure by the light irradiation. The magnon spectrum in the Floquet state is
+formulated on the basis of the pertrubative expansion of the Floquet Green
+function. The magnon dispersion shows softening at momentum $(\pi,\pi)$ in the
+square lattice with increasing the light amplitude, implying photoinduced AFM
+instability. This result is mainly attributed to a nonequilibrium electron
+distribution, which promotes low-energy Stoner excitations. The transient
+optical conductivity spectra characterized by interband excitations and Floquet
+sidepeaks are available to identify the photoinduced AFM state.",1809.07132v1
+2019-09-20,Effects of Dzyaloshinskii-Moriya interactions in volborthite: Magnetic orders and thermal Hall effect,"Volborthite offers an interesting example of a highly frustrated quantum
+magnet in which ferromagnetic and antiferromagnetic interactions compete on
+anisotropic kagome lattices. A recent density functional theory calculation has
+provided a magnetic model based on coupled trimers, which is consistent with a
+broad 1/3-magnetization plateau observed experimentally. Here we study the
+effects of Dzyaloshinskii-Moriya (DM) interactions in volborthite. We derive an
+effective model in which pseudospin-1/2 moments emerging on trimers form a
+network of an anisotropic triangular lattice. Using the effective model, we
+show that for a magnetic field perpendicular to the kagome layer, magnon
+excitations from the 1/3-plateau feel a Berry curvature due to the DM
+interactions, giving rise to a thermal Hall effect. Our magnon Bose gas theory
+can explain qualitative features of the magnetization and the thermal Hall
+conductivity measured experimentally. A further quantitative comparison with
+experiment poses constraints on the coupling constants in the effective model,
+promoting a quasi-one-dimensional picture. Based on this picture, we analyze
+low-temperature magnetic phase diagrams using effective field theory, and point
+out their crucial dependence on the field direction.",1909.09425v2
+2019-09-20,Tuning entanglement by squeezing magnons in anisotropic magnets,"We theoretically study the entanglement between two arbitrary spins in a
+magnetic material, where magnons naturally form a general squeezed coherent
+state, in the presence of an applied magnetic field and axial anisotropies.
+Employing concurrence as a measure of entanglement, we demonstrate that spins
+are generally entangled in thermodynamic equilibrium, with the amount of
+entanglement controlled by the external fields and anisotropies. As a result,
+the magnetic medium can serve as a resource to store and process quantum
+information. We, furthermore, show that the entanglement can jump
+discontinuously when decreasing the applied magnetic field. This tunable
+entanglement can be potentially used as an efficient switch in
+quantum-information processing tasks.",1909.09653v2
+2020-12-03,Total Moment Sum Rule for Magnets in the Vicinity of Quantum Critical Point,"It is known that the longitudinal and transverse excitation modes can exist
+in the vicinity of a quantum critical point in the ordered phase of quantum
+magnetic systems. The total moment sum rule for such systems is derived on the
+basis of the extended spin-wave theory, where both longitudinal and transverse
+magnetic excitations are taken into account. The sum rule is resolved into
+elastic, one-magnon, and two-magnon components. The formulation is applicable
+to spin systems with the longitudinal mode, such as $S=1$ systems with
+single-ion anisotropy of easy-plane type and spin dimer systems. The result
+helps us analyze and understand measured data of inelastic neutron scattering.",2012.01669v1
+2000-06-20,Microscopic Theory of Dipole-Exchange Spin Waves in Ferromagnetic Films: Linear and Nonlinear Processes,"The linear and nonlinear processes in ferromagnetic films at low temperatures
+T<< Tc are studied in a microscopic theory. Both the long-range magnetic
+dipole-dipole and the Heisenberg exchange interactions to nearest and
+next-nearest neighbors are included. The results obtained for the linearized
+spin-wave spectrum are compared with previous macroscopic theories. For
+ultrathin films (or for large wave vectors) the microscopic theory provides
+important corrections. The nonlinear dynamics of the spin waves are studied
+through a finite-temperature perturbation theory based on Feynman diagrams. We
+obtain explicit results for the energy shift and damping (or reciprocal
+lifetime) of the dipole-exchange spin waves due to all possible three-magnon
+and four-magnon processes involving combinations of the surface and quantized
+bulk spin waves at low temperatures. To investigate different dipole
+interaction strengths (relative to the exchange) numerical results are
+presented using parameters for Fe, EuO, and GdCl3.",0006308v1
+2017-05-26,"Low-energy spin dynamics of orthoferrites AFeO$_3$ (A = Y, La, Bi)","YFeO$_3$ and LaFeO$_3$ are members of the rare-earth orthoferrites family
+with \textit{Pbnm} space group. Using inelastic neutron scattering, the
+low-energy spin excitations have been measured around magnetic Brillouin zone
+center. Splitting of magnon branches and non-zero magnon gap is observed for
+both compounds, which is similar to the behavior observed in multiferroic
+BiFeO$_3$. Spin wave calculations which include both Dzyaloshinsky-Moriya
+interactions and single-ion anisotropy in the spin-Hamiltonian comprehensively
+accounts for all the experimentally observed features. Our results offer
+insight into the unifying physics underlying the Fe$^{3+}$-based perovskites as
+well as their distinguishing characteristics.",1705.09441v3
+2017-09-19,Spin Seebeck effect in a polar antiferromagnet $α$-Cu$_{2}$V$_{2}$O$_{7}$,"We have studied the longitudinal spin Seebeck effect in a polar
+antiferromagnet $\alpha$-Cu$_{2}$V$_{2}$O$_{7}$ in contact with a Pt film.
+Below the antiferromagnetic transition temperature of
+$\alpha$-Cu$_{2}$V$_{2}$O$_{7}$, spin Seebeck voltages whose magnetic field
+dependence is similar to that reported in antiferromagnetic MnF$_{2}$$\mid$Pt
+bilayers are observed. Though a small weak-ferromagnetic moment appears owing
+to the Dzyaloshinskii-Moriya interaction in $\alpha$-Cu$_{2}$V$_{2}$O$_{7}$,
+the magnetic field dependence of spin Seebeck voltages is found to be
+irrelevant to the weak ferromagnetic moments. The dependences of the spin
+Seebeck voltages on magnetic fields and temperature are analyzed by a magnon
+spin current theory. The numerical calculation of spin Seebeck voltages using
+magnetic parameters of $\alpha$-Cu$_{2}$V$_{2}$O$_{7}$ determined by previous
+neutron scattering studies reveals that the magnetic-field and temperature
+dependences of the spin Seebeck voltages for
+$\alpha$-Cu$_{2}$V$_{2}$O$_{7}$$\mid$Pt are governed by the changes in magnon
+lifetimes with magnetic fields and temperature.",1709.06330v1
+2018-03-08,Quantum Interactions of Topological Solitons from Electrodynamics,"The Casimir energy for the classically stable configurations of the
+topological solitons in 2D quantum antiferromagnets is studied by performing
+the path-integral over quantum fluctuations. The magnon fluctuation around the
+solitons saturating the Bogomol'nyi inequality may be viewed as a charged
+scalar field coupled with an effective magnetic field induced by the solitons.
+The magnon-soliton couping is closely related to the Pauli Hamiltonian, with
+which the effective action is calculated by adapting the worldline formulation
+of the derivative expansion for the 2+1d quantum electrodynamics in an external
+field. The resulting framework is more flexible than the conventional
+scattering analysis based on the Dashen-Hasslacher-Neveu formula. We obtain a
+short-range attractive well and a universal long-range $1/r$-type repulsive
+potential between two solitons.",1803.03181v5
+2018-03-12,Probing ultrafast spin-relaxation and precession dynamics in a cuprate Mott insulator with 7-fs optical pulses,"A charge excitation in a two-dimensional Mott insulator is strongly coupled
+with the surrounding spins, which is observed as magnetic-polaron formations of
+doped carriers and a magnon sideband in the Mott-gap transition spectrum.
+However, the dynamics related to the spin sector are difficult to measure.
+Here, we show that pump-probe reflection spectroscopy with 7-fs laser pulses
+can detect the optically induced spin dynamics in Nd$_2$CuO$_4$, a cuprate Mott
+insulator. The bleaching signal at the Mott-gap transition is enhanced at
+$\sim$18 fs, which corresponds to the spin-relaxation time in magnetic-polaron
+formations and is characterized by the exchange interaction. More importantly,
+ultrafast coherent oscillations appear in the time evolutions of the
+reflectivity changes, and their frequencies (1400-2700 cm$^{-1}$) are equal to
+the probe energy measured from the Mott-gap transition peak. These oscillations
+originate from interferences between charge excitations with two magnons and
+provide direct evidence for charge-spin coupling.",1803.04158v1
+2018-03-20,Polarization-dependent resonant inelastic X-ray scattering study at the Cu L and O K-edge of YBa$_2$Cu$_3$O$_{7-x}$,"We present a study on the high-Tc superconductor (HTSC) YBa2Cu3O7-x (YBCO)
+using polarization-dependent X-ray absorption and resonant inelastic X-ray
+scattering. High-resolution measurements using synchrotron-radiation are
+compared with calculations using a quasi-atomic multiplet approach performed at
+the Cu 2p3/2-edge of YBCO. We use a multiplet approach within the single
+impurity Anderson model to reproduce and understand the character of the
+localized low-energy excitations in YBCO. We observe a distinct peak at about
+0.5 eV in O K RIXS. This peak shows dependence on doping, incident energy, and
+momentum transfer that suggests that it has a different origin than the
+previously discussed cuprate bi-magnons. Therefore, we assign it to
+multi-magnon excitations between the Zhang Rice bands and/or the Upper Hubbard
+bands, respectively.",1803.07507v1
+2018-03-26,Tunable Snell's law for spin waves in heterochiral magnetic films,"Thin ferromagnetic films with an interfacially induced DMI exhibit nontrivial
+asymmetric dispersion relations that lead to unique and useful magnonic
+properties. Here we derive an analytical expression for the magnon propagation
+angle within the micromagnetic framework and show how the dispersion relation
+can be approximated with a comprehensible geometrical interpretation in the
+k-space of the propagation of spin waves. We further explore the refraction of
+spin waves at DMI interfaces in heterochiral magnetic films, after deriving a
+generalized Snell's law tunable by an in-plane magnetic field, that yields
+analytical expressions for critical incident angles. The found asymmetric
+Brewster angles at interfaces of regions with different DMI strengths,
+adjustable by magnetic field, support the conclusion that heterochiral
+ferromagnetic structures are an ideal platform for versatile spin-wave guides.",1803.09648v1
+2018-03-29,Giant resonant nonlinear damping in nanoscale ferromagnets,"Magnetic damping is a key metric for emerging technologies based on magnetic
+nanoparticles, such as spin torque memory and high-resolution biomagnetic
+imaging. Despite its importance, understanding of magnetic dissipation in
+nanoscale ferromagnets remains elusive, and the damping is often treated as a
+phenomenological constant. Here we report the discovery of a giant
+frequency-dependent nonlinear damping that strongly alters the response of a
+nanoscale ferromagnet to spin torque and microwave magnetic field. This novel
+damping mechanism originates from three-magnon scattering that is strongly
+enhanced by geometric confinement of magnons in the nanomagnet. We show that
+the giant nonlinear damping can invert the effect of spin torque on a
+nanomagnet leading to a surprising current-induced enhancement of damping by an
+antidamping torque. Our work advances understanding of magnetic dynamics in
+nanoscale ferromagnets and spin torque devices.",1803.10925v1
+2018-06-01,Optical determination of the exchange stiffness constant in an iron garnet,"Brillouin light scattering measurements were performed in the backscattering
+geometry on a Bi-substituted rare earth iron garnet. We observed two different
+peaks, one attributed to a surface spin wave in the dipole-exchange regime. The
+other is referred to as a backscattering magnon mode, because the incident
+light in this case is scattered backward by exchange-dominated spin wave inside
+the material. We propose a method to estimate the exchange stiffness constant
+from the frequency of the backscattering magnon mode. The obtained value is
+comparable with the previously reported values for Y$ _3 $Fe$ _5 $O$ _{12} $.",1806.00228v2
+2018-06-13,Origins of the unidirectional spin Hall magnetoresistance in metallic bilayers,"Recent studies evidence the emergence of asymmetric electron transport in
+layered conductors owing to the interplay between electrical conductivity,
+magnetization, and the spin Hall or Rashba- Edelstein effects. Here, we
+investigate the unidirectional magnetoresistance (UMR) caused by the
+current-induced spin accumulation in Co/Pt and CoCr/Pt bilayers. We identify
+three competing mechanisms underpinning the resistance asymmetry, namely
+interface and bulk spin-dependent electron scattering and electron-magnon
+scattering. Our measurements provide a consistent description of the current,
+magnetic field, and temperature dependence of the UMR and show that both
+positive and negative UMR can be obtained by tuning the interface and bulk
+spin-dependent scattering terms relative to the magnon population.",1806.05305v1
+2018-06-23,Magnetic and magnetoresistive behavior of the ferromagnetic heavy fermion YbNi$_2$,"We present a study on the magnetic susceptibility $\chi(T)$ and electrical
+resistance, as a function of temperature and magnetic field $R(T,H)$, of the
+ferromagnetic heavy fermion YbNi$_2$. The X-ray diffraction analysis shows that
+the synthesized polycrystalline samples crystallizes in the cubic Laves phase
+structure C15, with a spatial group $Fd\overline{3}m$. The magnetic
+measurements indicate a ferromagnetic behavior with transition temperature at 9
+K. The electrical resistance is metallic-like at high temperatures and no
+signature of Kondo effect was observed. In the ferromagnetic state, the
+electrical resistance can be justified by electron-magnon scattering
+considering the existence of an energy gap in the magnonic spectrum. The energy
+gap was determined for various applied magnetic fields. Magnetoresistance as a
+function of applied magnetic field, subtracted from the $R(T,H)$ curves at
+several temperatures, is negative from 2 K until about 40 K for all applied
+magnetic fields. The negative magnetoresistance originates from the suppression
+of magnetic disorder by the magnetic field.",1806.08881v1
+2018-06-27,Site-selective Probe of Magnetic Excitations in Rare-earth Nickelates using Resonant Inelastic X-ray Scattering,"We have used high-resolution resonant inelastic x-ray scattering (RIXS) to
+study a thin film of NdNiO$_3$, a compound whose unusual spin- and bond-ordered
+electronic ground state has been of long-standing interest. Below the magnetic
+ordering temperature, we observe well-defined collective magnon excitations
+along different high-symmetry directions in momentum space. The magnetic
+spectra depend strongly on the incident photon energy, which we attribute to
+RIXS coupling to different local electronic configurations of the expanded and
+compressed NiO$_6$ octahedra in the bond-ordered state. Both the noncollinear
+magnetic ground state and the observed site-dependent magnon excitations are
+well described by a model that assumes strong competition between the
+antiferromagnetic superexchange and ferromagnetic double-exchange interactions.
+Our study provides direct insight into the magnetic dynamics and exchange
+interactions of the rare-earth nickelates, and demonstrates that RIXS can serve
+as a site-selective probe of magnetism in these and other materials.",1806.10499v1
+2018-07-06,Quantum Dynamics of the Square-Lattice Heisenberg Model,"Despite nearly a century of study of the $S=1/2$ Heisenberg model on the
+square lattice, there is still disagreement on the nature of its high-energy
+excitations. By tuning toward the Heisenberg model from the exactly soluble
+Ising limit, we find that the strongly attractive magnon interactions of the
+latter naturally account for a number of spectral features of the Heisenberg
+model. This claim is backed up both numerically and analytically. Using the
+density matrix renormalization group method, we obtain the dynamical structure
+factor for a cylindrical geometry, allowing us to continuously connect both
+limits. Remarkably, a semi-quantitative description of certain observed
+features arises already at the lowest non-trivial order in perturbation theory
+around the Ising limit. Moreover, our analysis uncovers that high-energy
+magnons are localized on a single sublattice, which is related to the
+entanglement properties of the ground state.",1807.02399v2
+2018-07-09,Spin wave dynamics in artificial anti spin-ice systems: experimental and theoretical investigations,"Reversed structures of artificial spin-ice systems, where elongated holes
+with elliptical shape (antidots) are arranged into a square array with two
+orthogonal sublattices, are referred to as anti-squared spin-ice. Using
+Brillouin light scattering spectroscopy and plane wave method calculations, we
+investigate the spin wave propagation perpendicular to the applied field
+direction for two 20 nm thick Permalloy nanostructures which differ by the
+presence of single and double elliptical antidots. For the spin waves
+propagation along the principal antidot lattice axis, the spectrum consists of
+flat bands separated by several frequency gaps which are the effect of spin
+wave amplitude confinement in the regions between antidots. Contrarily, for
+propagation direction at 45 degrees with respect to the antidot symmetry axis,
+straight and narrow channels of propagation are formed, leading to broadening
+of bands and closing of the magnonics gaps. Interestingly, in this case, extra
+magnonic band gaps occur due to the additional periodicity along this
+direction. The width and the position of these gaps depend on the presence of
+single or double antidots. In this context, we discuss possibilities for the
+tuning of spin wave spectra in anti-squared spin ice structures.",1807.03016v1
+2018-07-10,Spin Wave Analysis of Low-Temperature Thermal Hall Effect in the Candidate Kitaev Spin Liquid $α$-RuCl${}_3$,"Proposed effective Hamiltonians from the literature for the material
+$\alpha$-RuCl${}_3$ are used to compute the magnon thermal Hall conductivity,
+$\kappa_{xy}$, using linear spin wave theory for the magnetically ordered
+state. No model previously proposed that was tested explains published
+experimental data. Models with Kitaev interaction $K>0$ are seen to predict
+$\kappa_{xy}\gtrsim 0$, which is inconsistent with the data. Fluctuations
+toward a Kitaev-type spin liquid would have the wrong sign to explain the data.
+However, a slight variant of a previously proposed model predicts a large
+$\kappa_{xy}$, demonstrating that the low-temperature thermal Hall effect could
+be generated exclusively by the Berry curvature of the magnon bands. The
+experimental data of $\kappa_{xy}$ can therefore serve as another method to
+constrain a proposed effective Hamiltonian.",1807.03857v1
+2018-07-11,Electron-phonon coupling in undoped cuprate $YBa_2Cu_3O_6$ estimated from Raman and optical conductivity spectra,"We study experimentally the Raman response of the undoped high-Tc parent
+compound $YBa_2Cu_3O_6$, and give a unified theory of the two-magnon Raman peak
+and optical conductivity based on the Hubbard-Holstein model with
+electron-phonon coupling (EPC). The Hubbard model without EPC can qualitatively
+account for the experimentally observed resonance of the Raman response, but
+only the Hubbard-Holstein model (i) reproduces asymmetry of the Raman spectrum,
+(ii) validates experimental visibility of the two-magnon peak, and (iii)
+predicts the correct shape and energy of the lower edge of the charge transfer
+gap in optical conductivity. Comparison of experiments with the theory gives
+the EPC strength $\lambda$ = 0.6. This result convincingly indicates the vital
+role of EPC in high-Tc cuprates providing a clue to the mechanism of high-Tc.",1807.04256v1
+2018-07-17,Magnon-phonon conversion experiment and phonon spin,"Recent experiment demonstrates magnon to phonon conversion in a YIG film
+under the application of a non-uniform magnetic field. Light scattered from
+phonons is observed to change its polarization state interpreted by the authors
+signifying phonon spin. In this note we argue that the experimental data merely
+shows the exchange of angular momentum $\pm \hbar$ per photon. We suggest that
+it has physical origin in the orbital angular momentum of phonons. The
+distinction between spin and orbital parts of the total angular momentum, and
+between phonons and photons with added emphasis on their polarizations is
+explained. The main conclusion of the present note is that phonon spin
+hypothesis is unphysical.",1807.08614v2
+2018-07-25,Anharmonic magnon excitations in noncollinear and charge-ordered RbFe$^{2+}$Fe$^{3+}$F$_6$,"RbFe$^{2+}$Fe$^{3+}$F$_6$ is an example of a charge ordered antiferromagnet
+where iron sites, with differing valences, are structurally separated into two
+interpenetrating sublattices. The low temperature magnetically ordered
+Fe$^{2+}$ ($S$=2) and Fe$^{3+}$ ($S$=5/2) moments form a noncollinear
+orthogonal structure with the Fe$^{3+}$ site displaying a reduced static
+ordered moment. Neutron spectroscopy on single crystals finds two distinct spin
+wave branches with a dominant coupling along the Fe$^{3+}$ chain axis
+($b$-axis). High resolution spectroscopic measurements find an intense energy
+and momentum broadened magnetic band of scattering bracketing a momentum-energy
+region where two magnon processes are kinematically allowed. These anharmonic
+excitations are enhanced in this non collinear magnet owing to the orthogonal
+spin arrangement.",1807.09605v1
+2018-12-15,Novel magnetic field tuning of quantum spin excitations in a weakly coupled $S=$1/2 Heisenberg spin chain as seen from NMR,"We report our NMR study of the spin excitations in the quasi-one dimensional
+(1D) $S=1/2$ quantum magnet CH$_3$NH$_3$Cu(HCOO)$_3$ lying in the 1D-3D
+dimensional crossover regime with Dzyaloshinskii-Moriya(DM) interactions. Above
+$T_N$, the spinon excitation is observed from the constant $1/T_1$ at low
+temperatures contributed from the staggered spin susceptibility. At low
+temperatures well below $T_N$, the $1/T_1$ begins to flatten out under weak
+magnetic fields. With the increasing field intensity, $1/T_1$ tends to show a
+power-law temperature dependence gradually, with the index increasing from zero
+to $\sim3$, and finally $\sim5$, which are the respective typical
+characteristic for the dominating two-magnon Raman process and three-magnon
+scattering contributions to the nuclear relaxation in a conventional 3D magnet.
+A possible physical mechanism for this novel magnetic field tuning of quantum
+spin excitations related with the enhanced effective staggered field created by
+the DM interactions under magnetic field is discussed.",1812.06261v2
+2019-01-17,Magnonic band structure in a Co/Pd stripe domain system investigated by Brillouin light scattering and micromagnetic simulations,"By combining Brillouin Light Scattering and micromagnetic simulations we
+studied the spin-wave dynamics of a Co/Pd thin film multilayer, features a
+stripe domain structure at remanence. The periodic up and down domains are
+separated by cork-screw type domain walls. The existence of these domains
+causes a scattering of the otherwise bulk and surface spin-wave modes, which
+form mode families, similar to a one dimensional magnonic crystal. The
+dispersion relation and mode profiles of spin waves are measured for
+transferred wave vector parallel and perpendicular to the domain axis.",1901.05985v1
+2019-01-21,"Magnonics: Spin Waves Connecting Charges, Spins and Photons","Spin waves (SW) are the excitation of the spin system in a ferromagnetic
+condensed matter body. They are collective excitations of the electron system
+and, from a quasi-classical point of view, can be understood as a coherent
+precession of the electrons' spins. Analogous to photons, they are also
+referred to as magnons indicating their quasi-particle character. The
+collective nature of SWs is established by the short-range exchange interaction
+as well as the non-local magnetic dipolar interaction, resulting in coherence
+of SWs from mesoscopic to even macroscopic length scales. As one consequence of
+this collective interaction, SWs are ""charge current free"" and, therefore, less
+subject to dissipation caused by scattering with impurities on the atomic
+level. This is a clear advantage over diffusive transport in spintronics that
+not only uses the charge of an electron but also its spin degree of freedom.
+Any (spin) current naturally involves motion and, thus, scattering of electrons
+leading to excessive heating as well as losses. This renders SWs a promising
+alternative to electric (spin) currents for the transport of spin information -
+one of the grand challenges of condensed matter physics.",1901.07021v1
+2019-01-25,Focused ion beam modification of non-local magnon-based transport in yttrium iron garnet/platinum heterostructures,"We study the impact of Ga ion exposure on the local and non-local
+magnetotransport response in heterostructures of the ferrimagnetic insulator
+yttrium iron garnet and platinum. In particular, we cut the yttrium iron garnet
+layer in between two electrically separated wires of platinum using a Ga ion
+beam, and study the ensuing changes in the magnetoresistive response. We find
+that the non-local magnetoresistance signal vanishes when the yttrium iron
+garnet film between the Pt wires is fully cut, although the local spin Hall
+magnetoresistance signal remains finite. This observation corroborates the
+notion that pure spin currents carried by magnons are crucial for the non-local
+magnetotransport effects observed in magnetic insulator/metal nanostructures.",1901.08894v1
+2019-01-28,Flat-band spin dynamics and phonon anomalies of the saw-tooth spin-chain system Fe$_2$O(SeO$_3$)$_2$,"Fe$^{3+}$ $S = 5/2$ ions form saw-tooth like chains along the $a$ axis of the
+oxo-selenite Fe$_2$O(SeO$_3$)$_2$ and an onset of long-range magnetic order is
+observed for temperatures below $T_C = 105$ K. This order leads to distinct
+fingerprints in phonon mode linewidths and energies as resolved by Raman
+scattering. In addition, new excitations with small linewidths emerge below $T
+= 150$ K, and are assigned to two-magnon scattering processes with the
+participation of flat-band and high energy magnon branches. From this a set of
+exchange coupling constants is estimated. The specific ratio of the saw-tooth
+spine-spine and spine-vertex interactions may explain the instability of the
+dimer quantum ground state against an incommensurate 3D magnetic order.",1901.09617v1
+2019-01-30,Exceptional magnetic sensitivity of PT-symmetric cavity magnon polaritons,"Achieving magnetometers with ultrahigh sensitivity at room temperature is an
+outstanding problem in physical sciences and engineering. Recently developed
+non-Hermitian cavity spintronics offers new possibilities. In this work we
+predict an exceptional magnetic sensitivity of cavity magnon polaritons with
+the peculiar parity-time (PT) symmetry. Based on the input-output formalism, we
+demonstrate a ""Z""-shape spectrum including two sideband modes and a dark-state
+branch with an ultranarrow linewidth in the exact PT phase. The spectrum
+evolves to a step function when the polariton touches the third-order
+exceptional point, accompanied by an ultrahigh sensitivity with respect to the
+detuning. The estimated magnetic sensitivity can approach 10^{-15}T Hz^{-1/2}
+in the strong coupling region, which is two orders of magnitude higher than
+that of the state-of-the-art magnetoelectric sensor. We derive the condition
+for the noiseless sensing performance. Purcell-like effect is observed when the
+PT symmetry is broken. A possible experimental scheme to realize our proposal
+is also discussed.",1901.10685v2
+2019-02-25,Driving magnetization dynamics in an on-demand magnonic crystal by magneto-elastic interaction,"Using spatial light interference of ultrafast laser pulses, we generate a
+lateral modulation in the magnetization profile of an otherwise uniformly
+magnetized film, whose magnetic excitation spectrum is monitored via the
+coherent and resonant interaction with elastic waves. We find an unusual
+dependence of the magnetoelastic coupling as the externally applied magnetic
+field is angle- and field-tuned relative to the wave vector of the
+magnetization modulation, which can be explained by the emergence of spatially
+inhomogeneous spin-wave modes. In this regard, the spatial light interference
+methodology can be seen as a user-configurable, temporally windowed, on-demand
+magnonic crystal, potentially of arbitrary two-dimensional shape, which allows
+control and selectivity of the spatial distribution of spin waves. Calculations
+of spin waves using a variety of methods, demonstrated here using the
+plane-wave method and micromagnetic simulation, can identify the spatial
+distribution and associated energy scales of each excitation, which opens the
+door to a number of excitation methodologies beyond our chosen elastic wave
+excitation.",1902.09186v1
+2019-02-26,A new class of nonreciprocal spin waves on the edges of 2D antiferromagnetic honeycomb nanoribbons,"Antiferromagnetic two-dimensional (2D) materials are currently under
+intensive theoretical and experimental investigations in view of their
+potential applications in antiferromagnet-based magnonic and spintronic
+devices. Recent experimental studies revealed the importance of magnetic
+anisotropy and Dzyaloshinskii-Moriya interactions (DMI) on the ordered ground
+state and the magnetic excitations in these materials. Here we present a robust
+classical field theory approach to analyze the effect of magnetic anisotropy
+and Dzyaloshinskii-Moriya interactions (DMI) on the edge and bulk spin waves in
+2D antiferromagnetic nanoribbons. We predict the existence of a new class of
+nonreciprocal edge spin waves characterized by opposite polarizations in
+opposite directions. These novel edge spin waves are induced by the DMI and are
+fundamentally different from conventional nonreciprocal spin waves for which
+the polarization is independent of the propagation direction. Aside this
+breakthrough in the field of antiferromagnetic spin waves, the study further
+analysis the effect of the edges structure on the magnetic excitations. In
+particular, we show that anisotropic bearded edges nanoribbons act as magnetic
+topological insulators with exceptionally interesting potentials for
+applications in magnonics.",1902.09704v3
+2019-03-02,Enhanced thermal Hall conductivity below 1 Kelvin in the pyrochlore magnet Yb$_2$Ti$_2$O$_7$,"In this letter, we report the gigantic thermal Hall effect $\kappa_{xy}$ in
+the low-field correlated-paramagnetic state of the frustrated pyrochlore
+Yb$_2$Ti$_2$O$_7$. We observed a record magnitude for the thermal Hall angle in
+an insulator, $\left|\kappa_{xy}\right|/\kappa_{xx}\sim 2\,\%$. The signal
+onsets at $T\sim 3\,$K and is severely weakened around the transition to canted
+ferromagnetic order at $T_\text{CFM}=0.275\,$K. Besides the large
+$\kappa_{xy}>0$ of the fluctuating regime, a sign change towards negative
+$\kappa_{xy}$ occurs at the lowest temperatures and in moderate field, where
+sharp magnon excitations appear in the inelastic neutron scattering spectra. We
+analyze the magnon-Hall signal and its suppression with field
+semi-quantitatively. A contribution of phonon skew scattering to $\kappa_{xy}$
+is ruled out by a comparison of $\kappa_{xx}$ for Tb-, Yb-, and Y-based rare
+earth pyrochlore titanates. These results represent the first report of
+non-vanishing $\kappa_{xy}$ measured in a dilution refrigerator ($T <
+0.29\,$K).",1903.00595v2
+2019-03-03,Goos-Hanchen Shift of a Spin-Wave Beam at the Interface Between Two Ferromagnets,"Spin waves are promising information carriers which can be used in modern
+magnonic devices, characterized by higher performance and lower energy
+consumption than presently used electronic circuits. However, before practical
+application of spin waves, the efficient control over spin wave amplitude and
+phase needs to be developed. We analyze analytically reflection and refraction
+of the spin waves at the interface between two ferromagnetic materials. In the
+model we consider the system consisting of two semi-infinite ferromagnetic
+media, separated by the ultra-narrow interface region with the magnetic
+anisotropy. We have found the Goos-Hanchen shift for spin waves in transmission
+and reflection, and performed detailed investigations of its dependence on the
+anisotropy at the interface and materials surrounding the interface. We have
+demonstrated possibility of obtaining Goos-Hanchen shift of several wavelengths
+in reflection for realistic material parameters. That proves the possibility
+for change of the spin waves phase in ferromagnetic materials at subwavelength
+distances, which can be regarded as a metasurface for magnonics.",1903.00861v1
+2019-03-20,Spin dynamics of antiferromagnetically coupled ferromagnetic bilayers -- the case of Cr$_2$WO$_6$ and Cr$_2$MoO$_6$,"Recent inelastic neutron diffraction measurements on Cr$_2$(Te, W, Mo)O$_6$
+have revealed that these systems consist of bilayers of spin-3/2 Cr$^{3+}$ ions
+with strong antiferromagnetic inter-bilayer coupling and tuneable intra-bilayer
+coupling from ferro (for W and Mo) to antiferro (for Te). These measurements
+have determined the ground state spin structure and the values of sublattice
+magnetization, which shows significant reduction of sublattice magnetization
+from the atomic spin value of 3.0$\mu_B$ for Cr$^{3+}$ atoms. In an earlier
+paper we theoretically investigated the low temperature spin dynamics of
+Cr$_2$TeO$_6$ bilayer system where both the intra and inter-bilayer couplings
+are antiferromagnetic. In this paper we investigate Cr$_2$WO$_6$ and
+Cr$_2$MoO$_6$ systems where intra-bilayer exchange couplings are ferromagnetic
+but the inter-bilayer exchange couplings are antiferromagnetic. We obtain the
+magnon dispersion, sublattice magnetization, two-magnon density of states,
+longitudinal spin-spin correlation function, and its powder average and compare
+the results for these systems with results for Cr$_2$TeO$_6$.",1903.08512v1
+2019-03-28,Topological phases of higher Chern numbers in Kitaev-Heisenberg ferromagnet with further-neighbor interactions,"Emergence of multiple topological phases with a series of Chern numbers, $\pm
+1$, $\mp 1$, $\pm 2$, $\mp 2$, $\pm 3$ and $\mp 4$, are observed in a
+ferromagnetic Kitaev-Heisenberg-spin-anisotropic model on honeycomb lattice
+with further neighbor interactions in the presence of an external magnetic
+field. Magnon Chern insulating dispersions of this two-band model are studied
+by using linear spin-wave theory formulated on the exact ferromagnetic ground
+state. Magnon edge states are obtained for the respective topological phases
+along with density of states. A topological phase diagram of this model is
+presented. Behavior of thermal Hall conductivity for those phases is studied.
+Sharp jumps of thermal hall conductivity is noted near the vicinity of phase
+transition points. Topological phases of the Kitaev spin-liquid compounds,
+$\alpha$-RuCl$_3$, X$_2$IrO$_3$, X = (Na, Li) and CrY$_3$, Y = (Cl, Br, I) are
+characterized based on this theoretical findings.",1903.11882v2
+2019-04-08,Quantum entanglement between two magnon modes via Kerr nonlinearity,"We propose a scheme to entangle two magnon modes via Kerr nonlinear effect
+when driving the systems far-from-equilibrium. We consider two macroscopic
+yttrium iron garnets (YIGs) interacting with a single-mode microcavity through
+the magnetic dipole coupling. The Kittel mode describing the collective
+excitations of large number of spins are excited through driving cavity with a
+strong microwave field. We demonstrate how the Kerr nonlineraity creates the
+entangled quantum states between the two macroscopic ferromagnetic samples,
+when the microcavity is strongly driven by a blue-detuned microwave field. Such
+quantum entanglement survives at the steady state. Our work offers new insights
+and guidance to designate the experiments for observing the entanglement in
+massive ferromagnetic materials. It can also find broad applications in
+macroscopic quantum effects and magnetic spintronics.",1904.04167v1
+2019-04-12,Bosonic Dirac Materials on a honeycomb antiferromagnetic Ising model,"Motivated by the recent proposal of Bosonic Dirac materials (BDM), we
+revisited the Ising model on a honeycomb lattice in the presence of the
+longitudinal and transverse fields. We apply linear spin-wave theory to obtain
+the magnon dispersion and its degenerated points. These special degenerated
+points emerge on the excitation spectrum as a function of the external fields
+and can be identified as Bosonic Dirac Points (BDP). Since that, in the
+vicinity of these points the Magnons becomes massless with a linear energy
+spectrum as well as insensible in relation to weak impurity, exactly as it
+occurs with a Fermionic Dirac point. We also have calculated the quantum and
+thermal fluctuations over the ground state of the system using Effective Field
+Theory. Our results point out that this simple model can host Bosonic Dirac
+points and therefore is a suitable prototype to build a Bosonic Dirac material
+only controlled by external field.",1904.06323v1
+2019-04-16,Multiple magnon modes in the Co$_3$Sn$_2$S$_2$ Weyl semimetal candidate,"We experimentally investigate electron transport in kagome-lattice
+ferromagnet Co$_3$Sn$_2$S$_2$, which is regarded as a time-reversal symmetry
+broken Weyl semimetal candidate. We demonstrate $dV/dI(I)$ curves with
+pronounced asymmetric $dV/dI$ spikes, similar to those attributed to
+current-induced spin-wave excitations in ferromagnetic multilayers. In contrast
+to multilayers, we observe several $dV/dI$ spikes' sequences at low,
+$\approx$10$^4$ A/cm$^2$, current densities for a thick single-crystal
+Co$_3$Sn$_2$S$_2$ flake in the regime of fully spin-polarized bulk. The spikes
+at low current densities can be attributed to novel magnon branches in magnetic
+Weyl semimetals, which are predicted due to the coupling between two magnetic
+moments mediated by Weyl fermions. Presence of spin-transfer effects at low
+current densities in Co$_3$Sn$_2$S$_2$ makes the material attractive for
+applications in spintronics.",1904.07762v2
+2019-04-18,Transient Response of the Cavity-Magnon-Polariton,"The Rabi oscillations of a coupled spin-photon system are experimentally
+studied using time domain microwave transmission measurements. An external
+magnetic bias field is applied to control the amplitude and frequency of Rabi
+oscillations, which are a measure of the coherent spin-photon energy exchange
+and coupling strength respectively. The amplitude and frequency control is
+described in the time domain as the transient response of a two-level
+spin-photon system. This approach reveals the link between steady state and
+transient behaviour of the cavity-magnon-polariton, which is necessary to
+interpret time domain cavity-spintronic experiments. This transient model also
+allows us to understand and quantify the polariton mode composition, which can
+be controlled by the bias field.",1904.08591v1
+2019-08-07,Compressive-strain induced enhancement of exchange interactions and short-range magnetic order in Sr$_2$IrO$_4$ investigated by Raman spectroscopy,"We have carried out Raman spectroscopy experiments to investigate two-magnon
+excitations in epitaxial thin films of the quasi-two-dimensional
+antiferromagnetic Mott insulator Sr$_2$IrO$_4$ under in-plane misfit strain.
+With in-plane biaxial compression, the energy of the two-magnon peak increases,
+and the peak remains observable over a wider temperature range above the N\'eel
+temperature, indicating strain-induced enhancement of the superexchange
+interactions between $\it{J}_{eff}$ = 1/2 pseudospins. From density functional
+theory calculations, we have found an increase of the nearest-neighbor hopping
+parameter and exchange interaction with increasing biaxial compressive strain,
+in agreement with the experimental observations. Our experimental and
+theoretical results provide perspectives for systematic, theory-guided strain
+control of the primary exchange interactions in 5$\it{d}$ transition metal
+oxides.",1908.02716v1
+2019-08-13,Magnetic structure and excitations of the topological semimetal YbMnBi$_2$,"We investigated the magnetic structure and dynamics of YbMnBi$_2$, with
+elastic and inelastic neutron scattering, to shed light on the topological
+nature of the charge carriers in the antiferromagnetic phase. We confirm C-type
+antiferromagnetic ordering of the Mn spins below $T_{\rm N} = 290$ K, and
+determine that the spins point along the $c$-axis to within about $3^\circ$.
+The observed magnon spectrum can be described very well by the same effective
+spin Hamiltonian as was used previously to model the magnon spectrum of
+CaMnBi$_2$. Our results show conclusively that the creation of Weyl nodes in
+YbMnBi$_2$ by the time-reversal-symmetry breaking mechanism can be excluded in
+the bulk.",1908.04872v1
+2019-08-15,Collective Excitations of Quantum Anomalous Hall Ferromagnets in Twisted Bilayer Graphene,"We present a microscopic theory for collective excitations of quantum
+anomalous Hall ferromagnets (QAHF) in twisted bilayer graphene. We calculate
+the spin magnon and valley magnon spectra by solving Bethe-Salpeter equations,
+and verify the stability of QAHF. We extract the spin stiffness from the
+gapless spin wave dispersion, and estimate the energy cost of a
+skyrmion-antiskyrmion pair, which is found to be comparable in energy with the
+Hartree-Fock gap. The valley wave mode is gapped, implying that the valley
+polarized state is more favorable compared to the valley coherent state. Using
+a nonlinear sigma model, we estimate the valley ordering temperature, which is
+considerably reduced from the mean-field transition temperature due to thermal
+excitations of valley waves.",1908.05417v2
+2019-08-16,Scaling Analysis of Anomalous Hall Resistivity in the Co$_{2}$TiAl Heusler Alloy,"A comprehensive magnetotransport study including resistivity ($\rho_{xx}$) at
+various fields, isothermal magnetoresistance and Hall resistivity ($\rho_{xy}$)
+has been carried out at different temperatures on the Co$_{2}$TiAl Heusler
+alloy. Co$_{2}$TiAl alloy shows a paramagnetic (PM) to ferromagnetic (FM)
+transition below the curie temperature (T$_{C}$) $\sim$ 125 K. In the FM
+region, resistivity and magnetoresistance reveals a spin flip electron-magnon
+scattering and the Hall resistivity unveils the anomalous Hall resistivity
+($\rho_{xy}^{AH}$). Scaling of anomalous Hall resistivity with resistivity
+establishes the extrinsic scattering process responsible for the anomalous hall
+resistivity; however Skew scattering is the dominant mechanism compared to the
+side-jump contribution. A one to one correspondence between magnetoresistance
+and side-jump contribution to anomalous Hall resistivity verifies the
+electron-magnon scattering being the source of side-jump contribution to the
+anomalous hall resistivity.",1908.05974v1
+2019-08-24,Magnetic order and anisotropic interactions induced by mixing between the $J=1/2$ and $3/2$ sectors in spin-orbit coupled honeycomb-lattice compounds,"Novel magnetic ordering on the honeycomb lattice due to emergent weak
+anisotropic interactions generated by the mixing between the $J=1/2$ sector and
+the magnetically inactive 3/2 sector is investigated in a three-orbital
+interacting electron model in the absence of Hund's coupling. Self-consistent
+determination of magnetic order yields anisotropic N\'{e}el and zigzag orders
+for different parameter regimes, highlighting the effect of the emergent
+single-ion anisotropy. Study of magnon excitations shows extremely small magnon
+energy scale compared to the hopping energy scale, and enhancement of
+anisotropy effects for smaller spin-orbit coupling. These results account for
+several features of the honeycomb lattice compounds such as $\rm Na_2 Ir O_3$
+and $\rm Ru Cl_3$, where the leading order anisotropic interactions within the
+magnetically active $J=1/2$ sector are completely quenched due to the
+edge-sharing octahedra.",1908.09130v1
+2019-11-01,Giant unidirectional magnetoresistance in topological insulator -- ferromagnetic semiconductor heterostructures,"The unidirectional magnetoresistance (UMR) is one of the most complex
+spin-dependent transport phenomena in ferromagnet/non-magnet bilayers, which
+involves spin injection and accumulation due to the spin Hall effect (SHE) or
+Rashba-Edelstein effect (REE), spin-dependent scattering, and magnon scattering
+at the interface or in the bulk of the ferromagnet. While UMR in metallic
+bilayers has been studied extensively in very recent years, its magnitude is as
+small as 10$^-$$^5$, which is too small for practical applications. Here, we
+demonstrate a giant UMR effect in a heterostructure of BiSb topological
+insulator -- GaMnAs ferromagnetic semiconductor. We obtained a large UMR ratio
+of 1.1%, and found that this giant UMR is governed not by the giant
+magnetoresistance (GMR)-like spin-dependent scattering, but by magnon
+emission/absorption and strong spin-disorder scattering in the GaMnAs layer.
+Our results provide new insight into the complex physics of UMR, as well as a
+strategy for enhancing its magnitude for device applications.",1911.00247v1
+2019-11-09,The magnonic superfluid droplet at room temperature,"We declare the observation of spin superfluid state in Yttrium Iron Garnet
+(YIG) at room temperature. It is similar to a Homogeneous Precessing State
+(HPD), observed earlier in antiferromagnetic superfluid $^3$He-B. The formation
+of this state explains by the repulsive interaction between magnons, which is
+required as a prior condition for the spin superfluidity. It establishes an
+energy gap, which stabilizes the long range superfluid transport of
+magnetization and determines the Ginzburg-Landau coherence length. This
+discovery paves a way to many quantum applications of supermagnonics at room
+temperature, such as magnetic Josephson effect, long distance spin transport,
+Q-bit, quantum logics, magnetic sensors and others.",1911.03708v1
+2019-11-30,Microwave dynamics of pure and doped anisotropic S=1 chain antiferromagnet NiCl2-4SC(NH2)2,"We studied electron spin resonance in a quantum magnet NiCl2-4SC(NH2)2,
+demonstrating a field-induced quantum phase transition from a
+quantum-disordered phase to an antiferromagnet. We observe two branches of the
+antiferromagnetic resonance of the ordered phase, one of them has a gap and the
+other is a Goldstone mode with zero frequency at a magnetic field along the
+four-fold axis. This zero frequency mode acquires a gap at a small tilting of
+the magnetic field with respect to this direction. The upper gap was found to
+be reduced in the doped compound Ni(Cl(1-x)Br(x))2-4SC(NH2)2 with $x=0.21$.
+This reduction is unexpected because of the previously reported rise of the
+main exchange constant in a doped compound. Further, a nonresonant diamagnetic
+susceptibility $\chi^{\prime}$ was found for the ordered phase in a wide
+frequency range above the quasi-Goldstone mode. This dynamic diamagnetism is as
+large as the dynamic susceptibility of the paramagnetic resonance. We speculate
+that it originates from a two-magnon absorption band of low-frequency
+dispersive magnon branch.",1912.00172v1
+2019-12-27,Multi-particle finite-volume effects for hexagon tessellations,"Correlation functions of gauge-invariant composite operators in N=4 super
+Yang-Mills theory can be computed by integrability using triangulations. The
+elementary tile in this process is the hexagon, which should be glued by
+appropriately inserting resolutions of the identity involving virtual
+(""mirror"") magnons. We consider this problem for five-point functions of
+protected operators. At one-loop in the 't Hooft coupling, it is necessary to
+glue three adjacent tiles which involves two virtual magnons scattering among
+each other. We show that the result can be simplified by using an adapted
+mirror rotation and employing appropriate summation techniques. The
+mirror-particle contributions then yield hyperlogarithms of weight two.
+Finally, we use these results to investigate braiding prescriptions introduced
+in earlier work on the problem.",1912.12231v1
+2015-08-06,"Phenomenological description of the nonlocal magnetization relaxation in magnonics, spintronics, and domain-wall dynamics","A phenomenological equation called Landau-Lifshitz-Baryakhtar (LLBar)
+equation, which could be viewed as the combination of Landau-Lifshitz (LL)
+equation and an extra ""exchange damping"" term, was derived by Baryakhtar using
+Onsager's relations. We interpret the origin of this ""exchange damping"" as
+nonlocal damping by linking it to the spin current pumping. The LLBar equation
+is investigated numerically and analytically for the spin wave decay and domain
+wall motion. Our results show that the lifetime and propagation length of
+short-wavelength magnons in the presence of nonlocal damping could be much
+smaller than those given by LL equation. Furthermore, we find that both the
+domain wall mobility and the Walker breakdown field are strongly influenced by
+the nonlocal damping.",1508.01478v1
+2016-03-15,A Realization of the Haldane-Kane-Mele Model in a System of Localized Spins,"We theoretically study a spin Hamiltonian for spin-orbit-coupled ferromagnets
+on the honeycomb lattice. We find that the effective Hamiltonian for magnons, a
+quanta of spin-wave excitations from ordered states, is equivalent to the
+Haldane model for electrons in the honeycomb lattice, which indicates the
+nontrivial topology of the magnon bands and the existence of the associated
+edge state. We also take the Schwinger boson (or bosonic spinon)
+representations of spins that are applicable both to ordered and disordered
+phases. We show that the spinon bands within the mean-field treatment are
+topologically nontrivial, which causes a spin Nernst effect, by adopting the
+properties of the Kane-Mele model. A feasible experimental realization of the
+spin Hamiltonian is proposed.",1603.04827v2
+2016-03-17,Spin-Wave Fiber,"Spin waves are collective excitations propagating in the magnetic medium with
+ordered magnetizations. Magnonics, utilizing the spin wave (magnon) as
+information carrier, is a promising candidate for low-dissipation computation
+and communication technologies. We discover that, due to the
+Dzyaloshinskii-Moriya interaction, the scattering behavior of spin wave at a
+magnetic domain wall follows a generalized Snell's law, where two magnetic
+domains work as two different mediums. Similar to optical total reflection that
+occurs at the water-air interfaces, spin waves may experience total reflection
+at magnetic domain walls when their incident angle larger than a critical
+value. We design a spin wave fiber using a magnetic domain structure with two
+domain walls, and demonstrate that such a spin wave fiber can transmit spin
+waves over long distance by total internal reflections, in analogy to an
+optical fiber. Our design of spin wave fiber opens up new possibilities in pure
+magnetic information processing.",1603.05325v1
+2016-03-18,Entanglement Entropy of the N=4 SYM spin chain,"We present a detailed study of the Entanglement Entropy (EE) of excited
+states in all closed rank one subsectors of N=4 SYM, namely SU(2), SU(1|1) and
+SL(2). Exploiting the techniques of the Coordinate and the Algebraic Bethe
+Ansatz we obtain the EE for spin chains with up to seven magnons, at leading
+order in the coupling expansion but exact in the length of the spin chain and
+of the part of it that we cut. Focusing on the superconformal primary operator
+with two magnons in the BMN limit, we derive analytic and exact, in the
+coupling $\lambda'$, expressions for the Renyi and the EE. The interpolating
+functions for the Renyi and the EE monotonically increase as the coupling
+increases from the weak coupling $\lambda' \rightarrow 0$ regime to the strong
+coupling $\lambda' \rightarrow \infty$ regime. This results to a violation of a
+certain bound for the EE that is present at weak coupling and confirms the
+physical intuition that entanglement increases when the coupling increases.",1603.05929v2
+2016-03-21,Topological hard-core bosons on the honeycomb lattice,"This paper presents a connection between the topological properties of
+hardcore bosons and that of magnons in quantum spin magnets. We utilize the
+Haldane-like hardcore bosons on the honeycomb lattice as an example. We show
+that this system maps to a spin-$1/2$ quantum XY model with a
+next-nearest-neighbour Dzyaloshinsky-Moriya interaction. We obtain the magnon
+excitations of the quantum spin model and compute the edge states, Berry
+curvature, thermal and spin Nernst conductivities. Due to the mapping from spin
+variables to bosons, the hardcore bosons possess the same nontrivial
+topological properties as those in quantum spin system. These results are
+important in the study of magnetic excitations in quantum magnets and they are
+also useful for understanding the control of ultracold bosonic quantum gases in
+honeycomb optical lattices, which is experimentally accessible.",1603.06495v4
+2016-03-25,Magnon edge states in hardcore-Bose-Hubbard model,"Quantum Monte Carlo (QMC) simulation has uncovered nonzero Berry curvature
+and bosonic edge states in hardcore-Bose-Hubbard model on the gapped honeycomb
+lattice. The competition between the chemical potential and staggered onsite
+potential leads to an interesting quantum phase diagram comprising superfluid
+phase, Mott insulator, and charge density wave insulator. In this paper, we
+present a semiclassical perspective of this system by mapping to a spin-$1/2$
+quantum XY model. We give an explicit analytical origin of the quantum phase
+diagram, the Berry curvatures, and the edge states using semiclassical
+approximations. We find very good agreements between the semiclassical analyses
+and the QMC results. Our results show that the topological properties of
+hardcore-Bose-Hubbard model are the same as those of magnon in the
+corresponding quantum spin system. Our results are applicable to systems of
+ultracold bosonic atoms trapped in honeycomb optical lattices.",1603.07989v4
+2016-03-29,Current-induced asymmetric magnetoresistance due to energy transfer via quantum spin-flip process,"Current-induced magnetization excitation is a core phenomenon for
+next-generation magnetic nanodevices, and has been attributed to the
+spin-transfer torque (STT) that originates from the transfer of the spin
+angular momentum between a conduction electron and a local magnetic moment
+through the exchange coupling. However, the same coupling can transfer not only
+spin but also energy, though the latter transfer mechanism has been largely
+ignored. Here we report on experimental evidence concerning the energy transfer
+in ferromagnet/heavy metal bilayers. The magnetoresistance (MR) is found to
+depend significantly on the current direction down to low in-plane currents,
+for which STT cannot play any significant role. Instead we find that the
+observed MR is consistent with the energy transfer mechanism through the
+quantum spin-flip process, which predicts short wavelength,
+current-direction-dependent magnon excitations in the THz frequency range. Our
+results unveil another aspect of current-induced magnetic excitation, and open
+a channel for the dc-current-induced generation of THz magnons.",1603.08746v1
+2016-10-07,Local thermomagnonic torques in two-fluid spin dynamics,"We develop a general phenomenology describing the interplay between coherent
+and incoherent dynamics in ferromagnetic insulators. Using the Onsager
+reciprocity and Neumann's principle, we derive expressions for the local
+thermomagnonic torques exerted by thermal magnons on the order-parameter
+dynamics and the reciprocal pumping processes, which are in close analogy to
+the spin-transfer torque and spin pumping at metallic interfaces. Our formalism
+is applicable to general long-wavelength dynamics and, although here we
+explicitly focus on ferromagnetic insulators possessing U(1) symmetry, our
+approach can be easily extended to other classes of magnetic materials. As an
+illustrative example, we apply our theory to investigate a domain wall floating
+over a spin superfluid, whose dynamics is triggered thermally at the system's
+edge. Our results demonstrate that the local pumping of coherent spin dynamics
+by a thermal magnon gas offers an alternative route - with no need for
+conducting components and thus devoid of Ohmic losses - for the control and
+manipulation of topological solitons.",1610.02224v1
+2016-12-20,Spin liquid mediated RKKY interaction,"We propose an RKKY-type interaction that is mediated by a spin liquid. If a
+spin liquid ground state exists such an interaction could leave a fingerprint
+by ordering underlying localized moments such as nuclear spins. This
+interaction has a unique phenomenology that is distinct from the RKKY
+interaction found in fermionic systems; most notably the lack of a Fermi
+surface and absence of the requirement for itinerant electrons, since most spin
+liquids are insulators. As a working example we investigate the two-dimensional
+spin-1/2 kagome antiferromagnet (KAFM), although the treatment remains general
+and can be extended to other spin liquids and dimensions. We find that several
+different nuclear spin orderings minimize the RKKY-type energy induced by the
+KAFM but are unstable due to a zero-energy flat magnon band. Despite this we
+show that a small magnetic field is able to gap out this magnon spectrum for
+some of the orderings resulting in an intricate nuclear magnetism.",1612.06868v2
+2017-11-01,Spin current noise of the spin Seebeck effect and spin pumping,"We theoretically investigate the fluctuation of a pure spin current induced
+by the spin Seebeck effect and spin pumping in a normal metal (NM)/ferromagnet
+(FM) bilayer system. Starting with a simple FI--NM interface model with both
+spin-conserving and spin-non-conserving processes, we derive general
+expressions of the spin current and the spin-current noise at the interface
+within second-order perturbation of the FI--NM coupling strength, and estimate
+them for an yttrium iron garnet (YIG) --platinum interface. We show that the
+spin-current noise can be used to determine the effective spin carried by a
+magnon, modified by the spin-non-conserving process at the interface. In
+addition, we show that it provides information on the effective spin of a
+magnon, heating at the interface under spin pumping, and spin Hall angle of the
+NM.",1711.00237v2
+2017-11-09,Pairing from strong repulsion in triangular lattice Hubbard model,"We propose a paring mechanism between holes in the dilute limit of doped
+frustrated Mott insulators. Hole pairing arises from a hole-hole-magnon
+three-body bound state. This pairing mechanism has its roots on single-hole
+kinetic energy frustration, which favors antiferromagnetic (AFM) correlations
+around the hole. We demonstrate that the AFM polaron (hole-magnon bound state)
+produced by a single-hole propagating on a field-induced polarized background
+is strong enough to bind a a second hole. The effective interaction between
+these three-body bound states is repulsive, implying that this pairing
+mechanism is relevant for superconductivity.",1711.03233v2
+2017-11-27,Characterization of Spin-Transfer-Torque effect induced magnetization dynamics driven by short current pulses,"We present a time-resolved study of the magnetization dynamics in a
+microstructured Cr$|$Heusler$|$Pt waveguide driven by the Spin-Hall-Effect and
+the Spin-Transfer-Torque effect via short current pulses. In particular, we
+focus on the determination of the threshold current at which the spin-wave
+damping is compensated. We have developed a novel method based on the temporal
+evolution of the magnon density at the beginning of an applied current pulse at
+which the magnon density deviates from the thermal level. Since this method
+does not depend on the signal-to-noise ratio, it allows for a robust and
+reliable determination of the threshold current which is important for the
+characterization of any future application based on the Spin-Transfer-Torque
+effect.",1711.09647v1
+2017-11-28,Spin eigen-excitations of the magnetic skyrmion and problem of the effective mass,"Properties of magnon modes localized on a ferromagnetic skyrmion are studied.
+Three types of possible asymptotic behavior of the modes eigenfrequencies are
+found for the case of large skyrmion radius $R_s$, namely $\omega_0\sim
+R_s^{-2}$ for the breathing mode, $\omega_{-|\mu|}\sim R_s^{-1}$ and
+$\omega_{|\mu|}\sim R_s^{-3}$ for modes with negative and positive azimuthal
+quantum numbers, respectively. A number of properties of the magnon
+eigenfunctions are determined. This enables us to demonstrate that the skyrmion
+dynamics based on the traveling wave model is described by the massless Thiele
+equation.",1711.10461v1
+2018-10-23,Higher-order exceptional point in a cavity magnonics system,"We propose to realize the pseudo-Hermiticity in a cavity magnonics system
+consisting of the Kittel modes in two small yttrium-iron-garnet spheres coupled
+to a microwave cavity mode. The effective gain of the cavity can be achieved
+using the coherent perfect absorption of the two input fields fed into the
+cavity. With certain constraints of the parameters, the Hamiltonian of the
+system has the pseudo-Hermiticity and its eigenvalues can be either all real or
+one real and other two constituting a complex-conjugate pair. By varying the
+coupling strengths between the two Kittel modes and the cavity mode, we find
+the existence of the third-order exceptional point in the parameter space, in
+addition to the usual second-order exceptional point existing in the system
+with parity-time symmetry. Also, we show that these exceptional points can be
+demonstrated by measuring the output spectrum of the cavity.",1810.09689v3
+2019-05-04,Identification and time-resolved study of YIG spin wave modes in a MW cavity in strong coupling regime,"Recently, the hybridization of microwave-frequency cavity modes with
+collective spin excitations attracted large interest for the implementation of
+quantum computation protocols, which exploit the transfer of information among
+these two physical systems. Here, we investigate the interaction among the
+magnetization precession modes of a small YIG sphere and the MW electromagnetic
+modes, resonating in a tridimensional aluminum cavity. In the strong coupling
+regime, anti-crossing features were observed in correspondence of various
+magnetostatic modes, which were excited in a magnetically saturated sample.
+Time-resolved studies show evidence of Rabi oscillations, demonstrating
+coherent exchange of energy among photons and magnons modes. To facilitate the
+analysis of the standing spin-wave patterns, we propose here a new procedure,
+based on the introduction of a novel functional variable. The resulting easier
+identification of magnetostatic modes can be exploited to investigate, control
+and compare many-levels hybrid systems in cavity- and opto-magnonics research.",1905.01522v2
+2019-05-09,Bidirectional spin-wave-driven domain wall motion in antiferromagnetically coupled ferrimagnets,"We investigate ferrimagnetic domain wall dynamics induced by circularly
+polarized spin waves theoretically and numerically. We find that the direction
+of domain wall motion depends on both the circular polarization of spin waves
+and the sign of net spin density of ferrimagnet. Below the angular momentum
+compensation point, left- (right-) circularly polarized spin waves push a
+domain wall towards (away from) the spin-wave source. Above the angular
+momentum compensation point, on the other hand, the direction of domain wall
+motion is reversed. This bidirectional motion originates from the fact that the
+sign of spin-wave-induced magnonic torque depends on the circular polarization
+and the subsequent response of the domain wall to the magnonic torque is
+governed by the net spin density. Our finding provides a way to utilize a spin
+wave as a versatile driving force for bidirectional domain wall motion.",1905.03521v1
+2019-05-20,Quantum drives produce strong entanglement between YIG samples without using intrinsic nonlinearities,"We show how to generate an entangled pair of yttrium iron garnet (YIG)
+samples in a cavity-magnon system without using any nonlinearities which are
+typically very weak. This is against the conventional wisdom which necessarily
+requires strong Kerr like nonlinearity. Our key idea, which leads to
+entanglement, is to drive the cavity by a weak squeezed vacuum field generated
+by a flux-driven Josephson parametric amplifier (JPA). The two YIG samples
+interact via the cavity. For modest values of the squeezing of the pump, we
+obtain significant entanglement. This is the principal feature of our scheme.
+We discuss entanglement between macroscopic spheres using several different
+quantitative criteria. We show the optimal parameter regimes for obtaining
+entanglement which is robust against temperature. We also discuss squeezing of
+the collective magnon variables.",1905.07884v2
+2019-05-21,High-Field Expansion Approach to Kagome Antiferromagnets with Dzyaloshinskii-Moriya Interactions,"We apply linked cluster expansion techniques to study the polarized
+high-field phase of a spin-half antiferromagnet on the Kagome lattice with
+Heisenberg and Dzyaloshinskii-Moriya interactions (DMI). We find that the Dirac
+points of the single-magnon spectrum without DMI are robust against arbitrary
+DMI when the magnetic field lies in the Kagome plane. Unlike the typical case
+where DMI gaps the spectrum, here we find that varying the DMI merely shifts
+the location of the Dirac points. In contrast, a magnetic field with a
+component out of the Kagome plane gaps the spectrum, leading to topological
+magnon bands. We map out a topological phase diagram as the couplings are
+varied by computing the band Chern numbers. A pair of phase transitions are
+observed and we find an enhanced thermal Hall conductivity near the phase
+boundary.",1905.08805v2
+2020-06-01,Strong magnon-photon coupling within a tunable cryogenic microwave cavity,"The ability to achieve strong-coupling has made cavity-magnon systems an
+exciting platform for the development of hybrid quantum systems and the
+investigation of fundamental problems in physics. Unfortunately, current
+experimental realizations are constrained to operate at a single frequency,
+defined by the geometry of the microwave cavity. In this article we realize a
+highly-tunable, cryogenic, microwave cavity strongly coupled to magnetic spins.
+The cavity can be tuned in situ by up to 1.5 GHz, approximately 15% of its
+original 10 GHz resonance frequency. Moreover, this system remains within the
+strong-coupling regime at all frequencies with a cooperativity of approximately
+800.",2006.01223v2
+2020-06-15,Femtosecond laser pulse driven caustic spin wave beams,"Controlling the directionality of spin waves is a key ingredient in
+wave-based computing methods such as magnonics. In this paper, we demonstrate
+this particular aspect by using an all-optical point-like source of continuous
+spin waves based on frequency comb rapid demagnetization. The emitted spin
+waves contain a range of k-vectors and by detuning the applied magnetic field
+slightly off the ferromagnetic resonance (FMR), we observe X-shaped caustic
+spin-wave patterns at $70^{\circ}$ propagation angles as predicted by theory.
+When the harmonic of the light source approaches theFMR, the caustic pattern
+gives way to uniaxial spin-wave propagation perpendicular to the in-plane
+component of the applied field. This field-controlled propagation pattern and
+directionality of optically emitted short-wavelength spin waves provide
+additional degrees of freedom when designing magnonic devices.",2006.08219v1
+2020-06-27,A Comprehensible Review: Magnonic Magnetoelectric Coupling in Ferroelectric/ Ferromagnetic Composites,"Composite materials consisting of coupled magnetic and ferroelectric layers
+hold the promise for new emergent properties such as controlling magnetism with
+electric fields. Obviously, the interfacial coupling mechanism plays a crucial
+role and its understanding is the key for exploiting this material class for
+technological applications. This short review is focused on the magnonic-based
+magnetoelectric coupling that forms at the interface of a metallic ferromagnet
+with a ferroelectric insulator. After analyzing the physics behind this
+coupling, the implication for the magnetic, transport, and optical properties
+of these composite materials is discussed. Furthermore, examples for the
+functionality of such interfaces are illustrated by the electric field
+controlled transport through ferroelectric/ferromagnetic tunnel junctions, the
+electrically and magnetically controlled optical properties, and the generation
+of electromagnon solitons for the use as reliable information carriers.",2006.15290v2
+2020-09-10,Current jumps in flat band ladders with Dzyaloshinskii-Moriya interactions,"Localized magnons states, due to flat bands in the spectrum, is an intensely
+studied phenomenon and can be found in many frustrated magnets of different
+spatial dimensionality. The presence of Dzyaloshinskii-Moriya (DM) interactions
+may change radically the behavior in such systems. In this context, we study a
+paradigmatic example of a one-dimensional frustrated antiferromagnet, the
+sawtooth chain in the presence of DM interactions. Using both path integrals
+methods and numerical Density Matrix Renormalization Group, we revisit the
+physics of localized magnons and determine the consequences of the DM
+interaction on the ground state. We have studied the spin current behavior,
+finding three different regimes. First, a Luttinger-liquid regime where the
+spin current shows a step behavior as a function of parameter $D$, at a low
+magnetic field. Increasing the magnetic field, the system is in the Meissner
+phase at the $m = 1/2$ plateau, where the spin current is proportional to the
+DM parameter. Finally, further increasing the magnetic field and for finite $D$
+there is a small stiffness regime where the spin current shows, at fixed
+magnetization, a jump to large values at $D = 0$, a phenomenon also due to the
+flat band.",2009.04970v2
+2020-09-30,Electronic structure and finite temperature magnetism of yttrium iron garnet,"Yttrium iron garnet is a complex ferrimagnetic insulator with 20 magnon modes
+which is used extensively in fundamental experimental studies of magnetisation
+dynamics. As a transition metal oxide with moderate gap (2.8 eV), yttrium iron
+garnet requires a careful treatment of electronic correlation. We have applied
+quasiparticle self-consistent GW to provide a fully ab initio description of
+the electronic structure and resulting magnetic properties, including the
+parameterisation of a Heisenberg model for magnetic exchange interactions.
+Subsequent spin dynamical modelling with quantum statistics extends our
+description to the magnon spectrum and thermodynamic properties such as the
+Curie temperature, finding favourable agreement with experimental measurements.
+This work provides a snapshot of the state-of-the art in modelling of complex
+magnetic insulators.",2009.14601v1
+2021-02-01,Magnon-assisted dynamics of a hole doped in a cuprate superconductor,"We calculate the quasiparticle dispersion and spectral weight of the
+quasiparticle that results when a hole is added to an antiferromagnetically
+ordered CuO$_2$ plane of a cuprate superconductor. We also calculate the magnon
+contribution to the quasiparticle spectral function. We start from a multiband
+model for the cuprates considered previously [Nat. Phys. \textbf{10}, 951
+(2014)]. We map this model and the operator for creation of an O hole to an
+effective one-band generalized $t-J$ model, without free parameters. The
+effective model is solved using the state of the art self-consistent Born
+approximation. Our results reproduce all the main features of experiments. They
+also reproduce qualitatively the dispersion of the multiband model, giving
+better results for the intensity near wave vector $(\pi,\pi)$, in comparison
+with the experiments. In contrast to what was claimed in [Nat. Phys.
+\textbf{10}, 951 (2014)], we find that spin fluctuations play an essential role
+in the dynamics of the quasiparticle, and hence in both its weight and
+dispersion.",2102.01177v1
+2021-02-02,"Coupled spin-orbital fluctuations in a three orbital model for $4d$ and $5d$ oxides with electron fillings $n=3,4,5$ -- Application to $\rm NaOsO_3$, $\rm Ca_2RuO_4$, and $\rm Sr_2IrO_4$","A unified approach is presented for investigating coupled spin-orbital
+fluctuations within a realistic three-orbital model for strongly spin-orbit
+coupled systems with electron fillings $n=3,4,5$ in the $t_{2g}$ sector of
+$d_{yz},d_{xz},d_{xy}$ orbitals. A generalized fluctuation propagator is
+constructed which is consistent with the generalized self-consistent
+Hartree-Fock approximation where all Coulomb interaction contributions
+involving orbital diagonal and off-diagonal spin and charge condensates are
+included. Besides the low-energy magnon, intermediate-energy orbiton and
+spin-orbiton, and high-energy spin-orbit exciton modes, the generalized
+spectral function also shows other high-energy excitations such as the Hund's
+coupling induced gapped magnon modes. We relate the characteristic features of
+the coupled spin-orbital excitations to the complex magnetic behavior resulting
+from the interplay between electronic bands, spin-orbit coupling, Coulomb
+interactions, and structural distortion effects, as realized in the compounds
+$\rm NaOsO_3$, $\rm Ca_2RuO_4$, and $\rm Sr_2IrO_4$.",2102.01400v2
+2021-02-02,Topological Aspects of Antiferromagnets,"The long fascination antiferromagnetic materials have exerted on the
+scientific community over about a century has been entirely renewed recently
+with the discovery of several unexpected phenomena including various classes of
+anomalous spin and charge Hall effects and unconventional magnonic transport,
+but also homochiral magnetic entities such as skyrmions. With these
+breakthroughs, antiferromagnets standout as a rich playground for the
+investigation of novel topological behaviors, and as promising candidate
+materials for disruptive low-power microelectronic applications. Remarkably,
+the newly discovered phenomena are all related to the topology of the magnetic,
+electronic or magnonic ground state of the antiferromagnets. This review
+exposes how non-trivial topology emerges at different levels in
+antiferromagnets and explores the novel mechanisms that have been discovered
+recently. We also discuss how novel classes of quantum magnets could enrich the
+currently expanding field of antiferromagnetic spintronics and how spin
+transport can in turn favor a better understanding of exotic quantum
+excitations.",2102.01632v3
+2021-02-05,Symmetry-Driven Spin-Wave Gap Modulation in Nanolayered SrRuO3/SrTiO3 Heterostructures: Implications for Spintronic Applications,"A strong correlation between magnetic interaction and topological symmetries
+leads to unconventional magneto-transport behavior. Weyl fermions induce
+topologically protected spin-momentum locking, which is closely related to
+spin-wave gap formation in magnetic crystals. Ferromagnetic SrRuO3, regarded as
+a strong candidate for Weyl semimetal, inherently possesses a nonzero spin-wave
+gap owing to its strong magnetic anisotropy. In this paper, we propose a method
+to control the spin-wave dynamics by nanolayer designing of the SrRuO3/SrTiO3
+superlattices. In particular, the six-unit-cell-thick SrRuO3 layers within the
+superlattices undergo a phase transition in crystalline symmetry from
+orthorhombic to tetragonal, as the thickness of the SrTiO3 layers is modulated
+with atomic-scale precision. Consequently, the magnetic anisotropy, anomalous
+Hall conductivity, and spin-wave gap could be systematically manipulated. Such
+customization of magnetic anisotropy via nanoscale heterostructuring offers a
+novel control knob to tailor the magnon excitation energy for future spintronic
+applications, including magnon waveguides and filters. Our nanolayer approach
+unveils the important correlation between the tunable lattice degrees of
+freedom and spin dynamics in topologically non-trivial magnetic materials.",2102.03008v1
+2021-02-08,Multiple-magnon excitations shape the spin spectrum of cuprate parent compounds,"Thanks to high resolution and polarization analysis, resonant inelastic x-ray
+scattering (RIXS) magnetic spectra of La2CuO4, Sr2CuO2Cl2 and CaCuO2 reveal a
+rich set of properties of the spin 1/2 antiferromagnetic square lattice of
+cuprates. The leading single-magnon peak energy dispersion is in excellent
+agreement with the corresponding inelastic neutron scattering measurements.
+However, the RIXS data unveil an asymmetric lineshape possibly due to odd
+higher order terms. Moreover, a sharp bimagnon feature emerges from the
+continuum at (1/2,0), coincident in energy with the bimagnon peak detected in
+optical spectroscopy. These findings show that the inherently complex spin
+spectra of cuprates, an exquisite manifestation of quantum magnetism, can be
+effectively explored by exploiting the richness of RIXS cross sections.",2102.04078v1
+2021-02-23,Tunable Cooperativity in Coupled Spin--Cavity Systems,"We experimentally study the tunability of the cooperativity in coupled
+spin--cavity systems by changing the magnetic state of the spin system via an
+external control parameter. As model system, we use the skyrmion host material
+Cu$_2$OSeO$_3$ coupled to a microwave cavity resonator. In the different
+magnetic phases we measure a dispersive coupling between the resonator and the
+magnon modes and model our results by using the input--output formalism. Our
+results show a strong tunability of the normalized coupling rate by magnetic
+field, allowing us to change the magnon--photon cooperativity from 1 to 60 at
+the phase boundaries of the skyrmion lattice state.",2102.11713v1
+2013-06-05,Dynamical mean-field theory for quantum spin systems: Test of solutions for magnetically ordered states,"A spin version of dynamical mean-field theory is extended for magnetically
+ordered states in the Heisenberg model. The self-consistency equations are
+solved with high numerical accuracy by means of the continuous-time quantum
+Monte Carlo with bosonic baths coupled to the spin. The resultant solution is
+critically tested by known physical properties. In contrast with the mean-field
+theory, soft paramagnons appear near the transition temperature. Moreover, the
+Nambu-Goldstone mode (magnon) in the ferromagnetic phase is reproduced
+reasonably well. However, antiferromagnetic magnons have an energy gap in
+contradiction to the Nambu-Goldstone theorem. The origin of this failure is
+discussed in connection with an artificial first-order nature of the
+transition.",1306.1186v2
+2016-09-23,Electromagnon resonance in a collinear spin state of a polar antiferromagnet Fe2Mo3O8,"Magnetic excitations are investigated for a hexagonal polar magnet Fe2Mo3O8
+by terahertz spectroscopy. We observed magnon modes including an electric-field
+active magnon, electromagnon, in the collinear antiferromagnetic phase with
+spins parallel to the c axis. We unravel the nature of these excitations by
+investigating the correlation between the evolution of the mode profile and the
+magnetic transition from antiferromagnetic to ferrimagnetic order induced by
+magnetic field or Zn-doping. We propose that the observed electromagnon mode
+involves the collective precession of the spins with oscillating in-plane
+electric polarization through the mechanism of the linear magnetoelectric
+effect.",1609.07230v2
+2016-09-26,Observables in the Guarino-Jafferis-Varela/CS-SYM duality,"We study various semiclassical observables in the duality proposed by
+Guarino, Jafferis and Varela, between a warped $AdS_4\times$ squashed $S^6$
+gravitational solution and a 3 dimensional ${\cal N}=2$ SYM-CS$_k$ conformal
+gauge theory, deformed from the maximal $SU(N)$ ${\cal N}=8$ SYM. Baryon
+vertices corresponding to particle-like branes have unusual behaviour with $N$
+and $k$ and present strong evidence for a certain level-rank duality. Wilson
+loops and the anomalous dimensions of operators of high spin scale like
+$(N/k)^{3/2}$. The entanglement entropy behaves like in a usual CFT. Giant
+magnon operators obey the same law as in 4 dimensional ${\cal N}=4$ SYM, and
+giant gravitons are also sub-determinant operators.",1609.08008v2
+2016-09-24,Optical manipulation of a magnon-photon hybrid system,"We demonstrate an all-optical method for manipulating the magnetization in a
+1-mm YIG (yttrium-iron-garnet) sphere placed in a $\sim0.17\,$T uniform
+magnetic field. An harmonic of the frequency comb delivered by a multi-GHz
+infrared laser source is tuned to the Larmor frequency of the YIG sphere to
+drive magnetization oscillations, which in turn give rise to a radiation field
+used to thoroughly investigate the phenomenon. The radiation damping issue that
+occurs at high frequency and in the presence of highly magnetizated materials,
+has been overcome by exploiting magnon-photon strong coupling regime in
+microwave cavities. Our findings demonstrate an effective technique for
+ultrafast control of the magnetization vector in optomagnetic materials via
+polarization rotation and intensity modulation of an incident laser beam. We
+eventually get a second-order susceptibility value of $\sim10^{-7}$ cm$^2$/MW
+for single crystal YIG.",1609.08147v1
+2017-04-07,Reconfigurable nano-scale spin-wave directional coupler,"A spin-wave (SW) directional coupler comprised of two laterally parallel
+nano-scale dipolarly-coupled SW waveguides is proposed and studied using
+micromagnetic simulations and analytical theory. The energy of a SW excited in
+one of the waveguides in the course of propagation is periodically transferred
+to the other waveguide and back, and the spatial half-period of this transfer
+is defined as the coupling length. The coupling length is determined by the
+dipolar coupling between the waveguides, and the fraction of the SW energy
+transferred to the other waveguide at the device output can be varied with the
+SW frequency, bias magnetic field, and relative orientation of the waveguide's
+static magnetizations. The proposed design of a directional coupler can be used
+in digital computing-oriented magnonics as a connector (multiplexer) of
+magnonic conduits without a direct contact, or in the analog microwave signal
+processing as a reconfigurable nano-scale power divider and/or frequency
+separator.",1704.02255v1
+2017-04-28,Thermal Control of the Magnon-Photon Coupling in a Notch Filter coupled to a Yttrium-Iron-Garnet/Platinum System,"We report thermal control of mode hybridization between the ferromagnetic
+resonance (FMR) and a planar resonator (notch filter) working at 4.74 GHz. The
+chosen magnetic material is a ferrimagnetic insulator (Yttrium Iron Garnet:
+YIG) covered by 6 nm of platinum (Pt). A current induced heating method has
+been used in order to enhance the temperature of the YIG/Pt system. The device
+permits us to control the transmission spectra and the magnon-photon coupling
+strength at room temperature. These experimental findings reveal potentially
+applicable tunable microwave filtering function.",1704.08896v3
+2018-01-22,Localization of magnon modes in a curved magnetic nanowire,"Spin waves in magnetic nanowires can be bound by a local bending of the wire.
+The eigenfrequency of a truly local magnon mode is determined by the curvature:
+a general analytical expression is established for any infinitesimally weak
+localized curvature of the wire. The interaction of the local mode with spin
+waves, propagating through the bend, results in scattering features, which is
+well confirmed by spin-lattice simulations.",1801.06945v3
+2018-01-31,Finite-temperature dynamic structure factor of the spin-1 XXZ chain with single-ion anisotropy,"Improving matrix-product state techniques based on the purification of the
+density matrix, we are able to accurately calculate the finite-temperature
+dynamic response of the infinite spin-1 XXZ chain with single-ion anisotropy in
+the Haldane, large-$D$ and antiferromagnetic phases. Distinct thermally
+activated scattering processes make a significant contribution to the spectral
+weight in all cases. In the Haldane phase intraband magnon scattering is
+prominent, and the onsite anisotropy causes the magnon to split into singlet
+and doublet branches. In the large-$D$ phase response, the intraband signal is
+separated from an exciton-antiexciton continuum. In the antiferromagnetic
+phase, holons are the lowest-lying excitations, with a gap that closes at the
+transition to the Haldane state. At finite temperatures, scattering between
+domain-wall excitations becomes especially important and strongly enhances the
+spectral weight for momentum transfer $\pi$.",1801.10572v2
+2018-08-08,Exact Correlation Functions in Conformal Fishnet Theory,"We compute exactly various 4-point correlation functions of shortest scalar
+operators in bi-scalar planar four-dimensional ""fishnet"" CFT. We apply the OPE
+to extract from these functions the exact expressions for the scaling
+dimensions and the structure constants of all exchanged operators with an
+arbitrary Lorentz spin. In particular, we determine the conformal data of the
+simplest unprotected two-magnon operator analogous to the Konishi operator, as
+well as of the one-magnon operator. We show that at weak coupling 4-point
+correlation functions can be systematically expanded in terms of harmonic
+polylogarithm functions and verify our results by explicit calculation of
+Feynman graphs at a few orders in the coupling. At strong coupling we obtain
+that the correlation functions exhibit the scaling behaviour typical for
+semiclassical description hinting at the existence of the holographic dual.",1808.02688v1
+2018-08-20,Gilbert damping of [Co/Pd]n/Py multilayer thin films,"Understanding the Gilbert damping in exchange-coupled multilayer materials is
+particularly important to develop future fast switching spintronics devices.
+Here, we report an experimental investigation of temperature-dependent Gilbert
+damping in [Co/Pd]n/Py multilayer films of varying the number of Co/Pd
+repetitions by ferromagnetic resonance. The results demonstrate that three
+independent contributions to the Gilbert damping are identified, namely the
+intrinsic Gilbert damping, the inhomogeneous linewidth broadening and the
+two-magnon scattering contribution. Of particular interest, the two-magnon
+scattering intensity increases as the enlargement of number repetitions of
+Co/Pd due to the larger pinning effect at the interface between Py and the
+Co/Pd layers. The Gilbert damping increases monotonically as the temperature
+decreases from 300K to 50K. Our findings open the door to comprehend the
+physical origin of the Gilbert damping in ultrathin exchange-coupled multilayer
+films.",1808.06515v2
+2018-08-30,Coexisting spinons and magnons in frustrated zigzag spin-1/2 chain compound $β$-TeVO$_4$,"We investigate magnetic excitations in the frustrated zigzag spin-1/2 chain
+compound $\beta$-TeVO$_4$ by inelastic neutron scattering. In the magnetically
+ordered ground state, the excitation spectrum exhibits coexisting magnon
+dispersion, characteristic of long-range magnetic order, and a spinon-like
+continuum that prevails above 2 meV, indicating the dominance of intrachain
+interactions. Combining linear-spin-wave-theory and pre-calculated
+spinon-continuum results, we reproduce the experimental spectrum. Our analysis
+offers a minimal exchange-network model which determines dominant intrachain
+interactions, their anisotropies and weak interchain interactions. The obtained
+parameters explain the magnetic ordering vector and spin excitations in the
+magnetic ground state.",1808.10174v1
+2019-06-01,Coherent ac spin current transmission across an antiferromagnetic CoO insulator,"The recent discovery of spin-current transmission through antiferromagnetic
+(AFM) insulating materials opens up unprecedented opportunities for fundamental
+physics and spintronics applications. The great mystery currently surrounding
+this topic is: how could THz AFM magnons mediate a GHz spin current? This
+mis-match of frequencies becomes particularly critical for the case of coherent
+ac spin-current, raising the fundamental question of whether a GHz ac
+spin-current can ever keep its coherence inside an AFM insulator and so drive
+the spin precession of another FM layer coherently? Utilizing element- and
+time-resolved x-ray pump-probe measurements on Py/Ag/CoO/Ag/Fe75Co25/MgO(001)
+heterostructures, we demonstrate that a coherent GHz ac spin current pumped by
+the permalloy (Py) ferromagnetic resonance (FMR) can transmit coherently across
+an antiferromagnetic CoO insulating layer to drive a coherent spin precession
+of the FM Fe75Co25 layer. Further measurement results favor thermal magnons
+rather than evanescent spin waves as the mediator of the coherent ac spin
+current in CoO.",1906.00155v1
+2019-06-04,Thickness dependence of spin Peltier effect visualized by thermal imaging technique,"Magnon propagation length in a ferrimagnetic insulator yttrium iron garnet
+(YIG) has been investigated by measuring and analyzing the YIG-thickness t_YIG
+dependence of the spin Peltier effect (SPE) in a Pt/YIG junction system. By
+means of the lock-in thermography technique, we measured the spatial
+distribution of the SPE-induced temperature modulation in the Pt/YIG system
+with the t_YIG gradation, allowing us to obtain the accurate t_YIG dependence
+of SPE with high t_YIG resolution. Based on the t_YIG dependence of SPE, we
+verified the applicability of several phenomenological models to estimate the
+magnon diffusion length in YIG.",1906.01560v3
+2019-06-13,Magnetoelasticity of $\mathrm{Co_{25}}\mathrm{Fe_{75}}$ thin films,"We investigate the magnetoelastic properties of
+$\mathrm{Co_{25}}\mathrm{Fe_{75}}$ and $\mathrm{Co_{10}}\mathrm{Fe_{90}}$ thin
+films by measuring the mechanical properties of a doubly clamped string
+resonator covered with multi-layer stacks containing these films. For the
+magnetostrictive constants we find
+$\lambda_{\mathrm{Co_{25}}\mathrm{Fe_{75}}}=(-20.68\pm0.25)\times10^{-6}$ and
+$\lambda_{\mathrm{Co_{10}}\mathrm{Fe_{90}}}=(-9.80\pm0.12)\times10^{-6}$ at
+room temperature. In stark contrast to the positive magnetostriction previously
+found in bulk CoFe crystals. $\mathrm{Co_{25}}\mathrm{Fe_{75}}$ thin films
+unite low damping and sizable magnetostriction and are thus a prime candidate
+for micromechanical magnonic applications, such as sensors and hybrid
+phonon-magnon systems.",1906.05543v1
+2019-06-17,Ferromagnetism and superconductivity in twisted double bilayer graphene,"We present a theory of competing ferromagnetic and superconducting orders in
+twisted double bilayer graphene (TDBG). In our theory, ferromagnetism is
+induced by Coulomb repulsion, while superconductivity with intervalley
+equal-spin pairing can be mediated by electron-acoustic phonon interactions. We
+calculate the transition temperatures for ferromagnetism and superconductivity
+as a function of moir\'e band filling factor, and find that superconducting
+domes can appear on both the electron and hole sides of the ferromagnetic
+insulator at half filling. We show that the ferromagnetic insulating gap has a
+dome shape dependence on the layer potential difference, which provides an
+explanation to the experimental observation that the ferromagnetic insulator
+only develops over a finite range of external displacement field. We also
+verify the stability of the half-filled ferromagnetic insulator against two
+types of collective excitations, i.e., spin magnons and valley magnons.",1906.07302v2
+2019-06-19,String theory on the Schrodinger pp-wave background,"We study string theory on the pp-wave geometry obtained by taking the Penrose
+limit around a certain null geodesic of the non-supersymmetric Schrodinger
+background. We solve for the spectrum of bosonic excitations and find
+compelling agreement with the dispersion relation of the giant magnons in the
+Schrodinger background obtained previously in arXiv:1712.03091. Inspired by the
+pp-wave spectrum we conjecture an exact in the t'Hooft coupling dispersion
+relation for the magnons in the original Schrodinger background. We show that
+the pp-wave background admits exactly 16 Killing spinors. We use the explicit
+form of the latter in order to derive the supersymmetry algebra of the
+background which explicitly depends on the deformation parameter. Its bosonic
+subalgebra is of the Newton-Hooke type.",1906.08269v2
+2019-07-09,Quantum Acoustomechanics with a Micromagnet,"We theoretically show how to strongly couple the center-of-mass motion of a
+micromagnet in a harmonic potential to one of its acoustic phononic modes. The
+coupling is induced by a combination of an oscillating magnetic field gradient
+and a static homogeneous magnetic field. The former parametrically couples the
+center-of-mass motion to a magnonic mode while the latter tunes the magnonic
+mode in resonance with a given acoustic phononic mode. The magnetic fields can
+be adjusted to either cool the center-of-mass motion to the ground state, or to
+enter into the strong quantum coupling regime. The center-of-mass can thus be
+used to probe and manipulate an acoustic mode, thereby opening new
+possibilities for out-of-equilibrium quantum nanophysics. Our results hold for
+experimentally feasible parameters and apply to levitated micromagnets as well
+as micromagnets deposited on a clamped nanomechanical oscillator.",1907.04039v2
+2019-07-17,Majorana-Magnon Crossover by a Magnetic Field in the Kitaev Model: Continuous-Time Quantum Monte Carlo Study,"Kitaev quantum spin liquids host Majorana fermions via the fractionalization
+of spins. In a magnetic field, the Majorana fermions were predicted to comprise
+a topological state, which has attracted great attention by the discovery of
+the half-quantized thermal Hall conductivity. Nevertheless, a reliable theory
+remains elusive for the field effect, especially at finite temperature. Here we
+present unbiased large-scale numerical results for the Kitaev model in a wide
+range of magnetic field and temperature. We find that the unconventional
+paramagnetic region showing fractional spin dynamics extends at finite
+temperature, far beyond the field range where the topological state is expected
+at zero temperature. Our results show the confinement-deconfinement behavior
+between the fractional Majorana excitations and the conventional magnons.",1907.07299v2
+2019-09-30,Magnonic Analogue of Edelstein Effect in Antiferromagnetic Insulators,"We investigate the nonequilibrium spin polarization due to a temperature
+gradient in antiferromagnetic insulators, which is the magnonic analogue of the
+inverse spin-galvanic effect of electrons. We derive a linear response theory
+of a temperature-gradient-induced spin polarization for collinear and
+noncollinear antiferromagnets, which comprises both extrinsic and intrinsic
+contributions. We apply our theory to several noncentrosymmetric
+antiferromagnetic insulators, i.e., to a one-dimensional antiferromagnetic spin
+chain, a single layer of kagome noncollinear antiferromagnet, e.g.,
+$\text{KFe}_3(\text{OH})_6(\text{SO}_4)_2$, and a noncollinear breathing
+pyrochlore antiferromagnet, e.g., LiGaCr$_4$O$_8$. The shapes of our
+numerically evaluated response tensors agree with those implied by the magnetic
+symmetry. Assuming a realistic temperature gradient of $10 \text{K}/\text{mm}$,
+we find two-dimensional spin densities of up to $\sim 10^6\hbar/\text{cm}^2$
+and three-dimensional bulk spin densities of up to $\sim
+10^{14}\hbar/\text{cm}^3$, encouraging an experimental detection.",1910.00143v1
+2019-10-16,Spin-Wave frequency division multiplexing in an yttrium iron garnet microstripe magnetized by inhomogeneous field,"Spin waves are promising candidates for information processing and
+transmission in a broad frequency range. In the realization of magnonic
+devices, the frequency depended division of the spin wave frequencies is a
+critical function for parallel information processing. In this work, we
+demonstrate a proof-of-concept spin-wave frequency division multiplexing method
+by magnetizing a homogenous magnetic microstripe with an inhomogeneous field.
+The symmetry breaking additional field is introduced by a permalloy stripe
+simply placed in lateral proximity to the waveguide. Spin waves with different
+frequencies can propagate independently, simultaneously and separately in space
+along the shared waveguide. This work brings new potentials for parallel
+information transmission and processing in magnonics.",1910.07136v1
+2019-10-18,Universal Characterisation of Cavity--Magnon Polariton Coupling Strength Verified in Modifiable Microwave Cavity,"A comprehensive study of the frequency dependence of the photon-magnon
+coupling for different magnetic samples is made possible with a tuneable
+3D--printed re--entrant cavity. Strong coupling is achieved, with values
+ranging between 20--140 MHz. The reworked theory, experimentally verified for
+the first time here, enables coupling values to be calculated from simulations
+alone, enabling future experiments with exotic cavity designs to be precisely
+engineered, with no limitations on sample and cavity geometry. Finally, the
+requirements of the deep strong coupling regime are shown to be achievable in
+such experiments.",1910.08333v3
+2019-10-31,Ultrafast magnetic dynamics in insulating YBa$_2$Cu$_3$O$_{6+x}$ revealed by time resolved two-magnon Raman Scattering,"Measurement and control of magnetic order and correlations in real time is a
+rapidly developing scientific area relevant for magnetic memory and spintronics
+[1,15]. In these experiments an ultra-short laser pulse (pump) is first
+absorbed by excitations carrying electric dipole moment. These then give their
+energy to the magnetic subsystem monitored by a time-resolved probe. A lot of
+progress has been made in investigations of ferromagnets but antiferromagnets
+are more challenging. Here we introduce time-resolved two-magnon Raman
+scattering as a novel real time probe of magnetic correlations especially
+well-suited for antiferromagnets. Its application to the antiferromagnetic
+charge transfer insulator YBa$_2$Cu$_3$O$_{6+x}$ revealed rapid demagnetization
+within 90fs of photoexcitation. The relaxation back to thermal equilibrium is
+characterized by much slower timescales. We interpret these results in terms of
+slow relaxation of the charge sector and rapid equilibration of the magnetic
+sector to a prethermal state characterized by parameters that change slowly as
+the charge sector relaxes.",1910.14585v3
+2020-01-16,Evidence of standing spin-waves in a van der Waals magnetic material,"Spin-waves have been studied for data storage, communication and logic
+circuits in the field of spintronics based on their potential to substitute
+electrons. Recent discovery of magnetism in two-dimensional (2D) systems such
+as monolayer CrI$_3$ and Cr$_2$Ge$_2$Te$_6$ has led to a renewed interest in
+such applications of magnetism in the 2D limit. Here we present direct evidence
+of standing spin-waves along with the uniform precessional resonance modes in
+van der Waals magnetic material, CrCl$_3$. Our experiment is the first direct
+observation of standing spin-wave modes, set up across a thickness of 20
+$\mu$m, in a van der Waals material. We detect standing spin-waves in the
+vicinity of both, optical and acoustic, branches of the antiferromagnetic
+resonance. We also observe magnon-magnon coupling, softening of resonance modes
+with temperature and extract the evolution of interlayer exchange field as a
+function of temperature.",2001.05981v1
+2020-01-24,Propagating magnetic droplet solitons as moveable nanoscale spin-wave sources with tunable direction of emission,"Magnetic droplets are strongly nonlinear and localized spin-wave solitons
+that can be formed in current-driven nanocontacts. Here, we propose a simple
+way to launch droplets in an inhomogeneous nanoscopic waveguide. We use the
+drift motion of a droplet and show that in a system with broken translational
+symmetry, the droplet acquires a linear momentum and propagates. We find that
+the droplet velocity can be tuned via the strength of the break in symmetry and
+the size of the nanocontact. In addition, we demonstrate that the launched
+droplet can propagate up to several micrometers in a realistic system with
+reasonable damping. Finally, we demonstrate how an annihilating droplet
+delivers its momentum to a highly nonreciprocal spin-wave burst with a tunable
+wave vector with nanometer wavelengths. Such a propagating droplet can be used
+as a moveable spin-wave source in nanoscale magnonic networks. The presented
+method enables full control of the spin-wave emission direction, which can
+largely extend the freedom to design integrated magnonic circuits with a single
+spin-wave source.",2001.08967v1
+2020-01-29,Magnon-Phonon Quantum Correlation Thermometry,"A large fraction of quantum science and technology requires low-temperature
+environments such as those afforded by dilution refrigerators. In these
+cryogenic environments, accurate thermometry can be difficult to implement,
+expensive, and often requires calibration to an external reference. Here, we
+theoretically propose a primary thermometer based on measurement of a hybrid
+system consisting of phonons coupled via a magnetostrictive interaction to
+magnons. Thermometry is based on a cross-correlation measurement in which the
+spectrum of back-action driven motion is used to scale the thermomechanical
+motion, providing a direct measurement of the phonon temperature independent of
+experimental parameters. Combined with a simple low-temperature compatible
+microwave cavity read-out, this primary thermometer is expected to become a
+popular thermometer for experiments below 1 K.",2001.11124v1
+2020-01-30,An anomalous refraction of spin waves as a way to guide signals in curved magnonic multimode waveguides,"We present a method for efficient spin wave guiding within the magnonic
+nanostructures. Our technique is based on the anomalous refraction in the
+metamaterial flat slab. The gradual change of the material parameters
+(saturation magnetization or magnetic anisotropy) across the slab allows
+tilting the wavefronts of the transmitted spin waves and controlling the
+refraction. Numerical studies of the spin wave refraction are preceded by the
+analytical calculations of the phase shift acquired by the spin wave due to the
+change of material parameters in a confined area. We demonstrate that our
+findings can be used to guide the spin waves smoothly in curved waveguides,
+even through sharp bends, without reflection and scattering between different
+waveguide's modes, preserving the phase -- the quantity essential for wave
+computing.",2001.11356v1
+2020-02-03,Quantum walk versus classical wave: Distinguishing ground states of quantum magnets by spacetime dynamics,"We investigate the wavepacket spreading after a single spin flip in
+prototypical two-dimensional ferromagnetic and antiferromagnetic quantum spin
+systems. We find characteristic spatial magnon density profiles: While the
+ferromagnet shows a square-shaped pattern reflecting the underlying lattice
+structure, as exhibited by quantum walkers, the antiferromagnet shows a
+circular-shaped pattern which hides the lattice structure and instead resembles
+a classical wave pattern. We trace these fundamentally different behaviors back
+to the distinctly different magnon energy-momentum dispersion relations and
+also provide a real-space interpretation. Our findings point to new
+opportunities for real-time, real-space imaging of quantum magnets both in
+materials science and in quantum simulators.",2002.00812v3
+2020-02-08,Higher-order exceptional points in all-magnetic structures,"Magnetometers with exceptional sensitivity are highly demanded in solving a
+variety of physical and engineering problems, such as measuring Earth's weak
+magnetic fields and prospecting mineral deposits and geological structures. It
+has been shown that the non-Hermitian degeneracy at exceptional points (EPs)
+can provide a new route for that purpose, because of the nonlinear response to
+external perturbations. One recent work [H. Yang et al., Phys. Rev. Lett. 121,
+197201 (2018)] has made the first step to realize the second-order magnonic EP
+in ferromangetic bilayers respecting the parity-time symmetry. In this paper,
+we generalize the idea to higher-order cases by considering ferromagnetic
+trilayers consisting of a gain, a neutral, and a (balanced-)loss layer. We
+observe both second- and third-order magnonic EPs by tuning the interlayer
+coupling strength, the external magnetic field, and the gain-loss parameter. We
+show that the magnetic sensitivity can be enhanced by $3$ orders of magnitude
+comparing to the conventional magnetic tunneling junction based sensors. Our
+results pave the way for studying high-order EPs in purely magnetic system and
+for designing magnetic sensors with ultrahigh sensitivity.",2002.03085v1
+2020-02-14,Spin-wave diode and circulator based on unidirectional coupling,"In magnonics, an emerging branch of wave physics characterized by low-energy
+consumption, it is highly desirable to realize circuit elements within the
+scope of spin-wave computing. Here, based on numerical simulations, we
+demonstrate the functionality of the spin-wave diode and the circulator to
+steer and manipulate spin waves over a wide range of frequency in the GHz
+regime. They take advantage of the unidirectional coupling induced by the
+interfacial Dzyaloshinskii-Moriya interaction to transfer the spin wave between
+thin ferromagnetic layers in only one direction of propagation. Using the
+multilayered structure consisting of Py and Co in direct contact with Pt, we
+obtain sub-micrometer-size devices of high efficiency. In the diode, the power
+loss ratio between forward and reverse direction reaches 22 dB, while in the
+four-port circulator, the efficiency exceeds 13 dB. Thus, our work contributes
+to the emerging branch of energy-efficient magnonic logic devices, where,
+thanks to short wavelength of spin waves, it is possible to realize nanoscale
+devices.",2002.06096v1
+2020-02-26,Control of spin dynamics in artificial honeycomb spin-ice-based nanodisks,"We report the experimental and theoretical characterization of the
+angular-dependent spin dynamics in arrays of ferromagnetic nanodisks arranged
+on a honeycomb lattice. The magnetic field and microwave frequency dependence,
+measured by broadband ferromagnetic resonance, reveal a rich spectrum of modes
+that is strongly affected by the microstate of the network. Based on symmetry
+arguments with respect to the external field, we show that certain parts of the
+ferromagnetic network contribute to the detected signal. A comparison of the
+experimental data with micromagnetic simulations reveals that different
+subsections of the lattice predominantly contribute to the high-frequency
+response of the array. This is confirmed by optical characterizations using
+microfocused Brillouin light scattering. Furthermore, we find indications that
+nucleation and annihilation of vortex-like magnetization configurations in the
+low-field range affect the dynamics, which is different from clusters of
+ferromagnetic nanoellipses. Our work opens up new perspectives for designing
+magnonic devices that combine geometric frustration in gyrotropic vortex
+crystals at low frequencies with magnonic crystals at high frequencies.",2002.11694v1
+2020-03-06,Spin-accumulation induced magnetic texture in a metal-insulator bilayer,"We consider the influence of a spin accumulation in a normal metal on the
+magnetic statics and dynamics in an adjacent magnetic insulator. In particular,
+we focus on arbitary angles between the spin accumulation and the easy-axis of
+the magnetic insulator. Based on Landau-Lifshitz-Gilbert phenomenology
+supplemented with magnetoelectronic circuit theory, we find that the magnetic
+texture twists into a stable configuration that turns out to be described by a
+virtual, or image, domain wall configuration, i.e., a domain wall outside the
+ferromagnet. We show that even when the spin accumulation is perpendicular to
+the anisotropy axis, the magnetic texture develops a component parallel to the
+spin accumulation for sufficiently large spin bias. The emergence of this
+parallel component gives rise to threshold behavior in the spin Hall
+magnetoresistance and nonlocal magnon transport. This threshold can be used to
+design novel spintronic and magnonic devices that can be operated without
+external magnetic fields.",2003.03226v1
+2020-03-12,Double Yang-Baxter deformation of spinning strings,"We study the reduction of classical strings rotating in the deformed
+three-sphere truncation of the double Yang-Baxter deformation of the
+$\hbox{AdS}_3 \times \hbox{S}^3 \times \hbox{T}^4$ background to an integrable
+mechanical model. The use of the generalized spinning-string ansatz leads to an
+integrable deformation of the Neumann-Rosochatius system. Integrability of this
+system follows from the fact that the usual constraints for the Uhlenbeck
+constants apply to any deformation that respects the isometric coordinates of
+the three-sphere. We construct solutions to the system in terms of the
+underlying ellipsoidal coordinate. The solutions depend on the domain of the
+deformation parameters and the reality conditions of the roots of a fourth
+order polynomial. We obtain constant-radii, giant-magnon and trigonometric
+solutions when the roots degenerate, and analyze the possible solutions in the
+undeformed limit. In the case where the deformation parameters are purely
+imaginary and the polynomial involves two complex-conjugated roots, we find a
+new class of solutions. The new class is connected with twofold giant-magnon
+solutions in the degenerate limit of infinite period.",2003.05724v2
+2020-03-13,AC Josephson effect between two superfluid time crystals,"Quantum time crystals are systems characterised by spontaneously emerging
+periodic order in the time domain. A range of such phases has been reported.
+The concept has even been discussed in popular literature, and deservedly so:
+while the first speculation on a phase of broken time translation symmetry did
+not use the name ""time crystal"", it was later adopted from 1980's popular
+culture. For the physics community, however, the ultimate qualification of a
+new concept is its ability to provide predictions and insight. Confirming that
+time crystals manifest the basic dynamics of quantum mechanics is a necessary
+step in that direction. We study two adjacent quantum time crystals
+experimentally. The time crystals, realised by two magnon condensates in
+superfluid $^3$He-B, exchange magnons leading to opposite-phase oscillations in
+their populations -- AC Josephson effect -- while the defining periodic motion
+remains phase coherent throughout the experiment.",2003.06313v1
+2020-03-25,Magnon Trap by Chiral Spin Pumping,"Chiral spin pumping is the generation of a unidirectional spin current in
+half of ferromagnetic films or conductors by dynamic dipolar stray fields from
+close-by nanomagnets. We formulate a general theory of long-range chiral
+interactions between magnets mediated by unidirectional traveling waves, e.g.,
+spin waves in a magnetic film or microwaves in a waveguide. The traveling waves
+emitted by an excited magnet can be perfectly trapped by a second, initially
+passive, magnet by a dynamical interference effect. When both magnets are
+excited by a uniform microwave, the chiral interaction between them creates a
+large imbalance in their magnon numbers.",2003.11581v2
+2020-04-13,Impact of the surface phase transition on magnon and phonon excitations in BiFeO3 nanoparticles,"We have performed Raman scattering measurements on BiFeO3 nanoparticles and
+studied both magnetic and lattice modes. We reveal strong anomalies between 140
+K and 200 K in the frequency of magnon and E(LO1), E(TO1) and A1(LO1) phonon
+modes. These anomalies are related to a surface expansion and are enhanced for
+nanoparticle sizes approaching the spin cycloidal length. These observations
+point out the strong interplay between the surface, the lattice, and the
+magnetism for sizes of BiFeO3 nanoparticles close to the cycloid periodicity.",2004.06028v1
+2020-04-20,Ultra Thin Films of Yttrium Iron Garnet with Very Low Damping: A Review,"Thin Yttrium Iron Garnet (YIG) is a promising material for integrated
+magnonics. In order to introduce YIG into nanofabrication processes it is
+necessary to fabricate very thin YIG films with a thickness well below 100 nm
+while retaining the extraordinary magnetic properties of the material,
+especially its long magnon lifetime and spin wave propagation length. Here, we
+give a brief introduction into the topic and we review and discuss the various
+results published over the last decade in this area. Especially for ultrathin
+films it turns out that pulsed layer deposition and sputtering are the most
+promising candidates. In addition, we discuss the application of room
+temperature deposition and annealing for lift-off based nanopatterning and the
+properties of nanostructures obtained by this method over the past years.",2004.09094v1
+2020-05-13,Waveguide cavity optomagnonics for broadband multimode microwave-to-optics conversion,"Cavity optomagnonics has emerged as a promising platform for studying
+coherent photon-spin interactions as well as tunable microwave-to-optical
+conversion. However, current implementation of cavity optomagnonics in
+ferrimagnetic crystals remains orders of magnitude larger in volume than
+state-of-the-art cavity optomechanical devices, resulting in very limited
+magneto-optical interaction strength. Here, we demonstrate a cavity
+optomagnonic device based on integrated waveguides and its application for
+microwave-to-optical conversion. By designing a ferrimagnetic rib waveguide to
+support multiple magnon modes with maximal mode overlap to the optical field,
+we realize a high magneto-optical cooperativity which is three orders of
+magnitude higher compared to previous records obtained on polished YIG spheres.
+Furthermore, we achieve tunable conversion of microwave photons at around 8.45
+GHz to 1550 nm light with a broad conversion bandwidth as large as 16.1 MHz.
+The unique features of the system point to novel applications at the crossroad
+between quantum optics and magnonics.",2005.06429v1
+2020-05-15,Multiple magnon modes in spin-1/2 Heisenberg antiferromagnet on simple square lattice in strong magnetic field,"We discuss spin-$\frac12$ Heisenberg antiferromagnet on simple square lattice
+in magnetic field $H$ using recently proposed bond-operator technique. It is
+well known that magnetically ordered phases of quantum magnets are well
+described at least qualitatively by the conventional spin-wave theory that only
+introduces quantum corrections into the classical solution of the problem. We
+observe that quantum fluctuations change drastically dynamical properties of
+the considered model at $H$ close to its saturation value: the dynamical
+structure factor shows anomalies corresponding to Green's function poles which
+have no counterparts in the spin-wave theory. That is, quantum fluctuations
+produce multiple short-wavelength magnon modes not changing qualitatively the
+long-wavelength spin dynamics. Our results are in agreement with previous
+quantum Monte-Carlo simulations and exact diagonalization of finite clusters.",2005.07537v3
+2020-05-18,From deconfined spinons to coherent magnons in an antiferromagnetic Heisenberg chain with long range interactions,"We study the spectrum and the nature of the excitations of an
+antiferromagnetic (AFM) Heisenberg chain with staggered long range
+interactions, both numerically using the time-dependent density matrix
+renormalization group (tDMRG) method and by means of a multi-spinon
+approximation that qualitatively explains its main features. The unfrustrated
+long-range nature of the exchange effectively increases the dimensionality of
+the system and the chain is able to undergo true symmetry breaking and develop
+long range order, transitioning from a gapless spin liquid to a gapless ordered
+AFM phase. We calculated the momentum resolved spin dynamical structure factor
+and found that for weakly decaying interactions the emergence of N\'eel order
+can be associated to the formation of bound states of spinons that become
+coherent magnons. The quasiparticle band leaks out from the two-spinon
+continuum that is pushed up to higher energies. Our physical picture is also
+supported by an analysis of the behavior of the excitations in real-time.",2005.09086v2
+2020-05-20,Quantum Geometry and Stability of Moiré Flatband Ferromagnetism,"Several moir\'e systems created by various twisted bilayers have manifested
+magnetism under flatband conditions leading to enhanced interaction effects. We
+theoretically study stability of moir\'e flatband ferromagnetism against
+collective excitations, with a focus on the effects of Bloch band quantum
+geometry. The spin magnon spectrum is calculated using different approaches,
+including Bethe-Salpeter equation, single mode approximation, and an analytical
+theory. One of our main results is an analytical expression for the spin
+stiffness in terms of the Coulomb interaction potential, the Berry curvatures,
+and the quantum metric tensor, where the last two quantities characterize the
+quantum geometry of moir\'e bands. This analytical theory shows that Berry
+curvatures play an important role in stiffening the spin magnons. Furthermore,
+we construct an effective field theory for the magnetization fluctuations, and
+show explicitly that skyrmion excitations bind an integer number of electrons
+that is proportional to the Bloch band Chern number and the skyrmion winding
+number.",2005.10254v2
+2020-07-06,"Triplons, Magnons, and Spinons in a Single Quantum Spin System: SeCuO3","Quantum spin systems exhibit an enormous range of collective excitations, but
+their spin waves, gapped triplons, fractional spinons, or yet other modes are
+generally held to be mutually exclusive. Here we show by neutron spectroscopy
+on SeCuO$_3$ that magnons, triplons, and spinons are present simultaneously. We
+demonstrate that this is a consequence of a structure consisting of two coupled
+subsystems and identify all the interactions of a minimal magnetic model. Our
+results serve qualitatively to open the field of multi-excitation spin systems
+and quantitatively to constrain the complete theoretical description of one
+member of this class of materials.",2007.02972v2
+2020-07-15,Local Probes for Charge-Neutral Edge States in Two-Dimensional Quantum Magnets,"The bulk-boundary correspondence is a defining feature of topological states
+of matter. However, for quantum magnets such as spin liquids or topological
+magnon insulators a direct observation of topological surface states has proven
+challenging because of the charge-neutral character of the excitations. Here we
+propose spin-polarized scanning tunneling microscopy as a spin-sensitive local
+probe to provide direct information about charge neutral topological edge
+states. We show how their signatures, imprinted in the local structure factor,
+can be extracted by specifically employing the strengths of existing
+technologies. As our main example, we determine the dynamical spin correlations
+of the Kitaev honeycomb model with open boundaries. We show that by contrasting
+conductance measurements of bulk and edge locations, one can extract direct
+signatures of the existence of fractionalized excitations and non-trivial
+topology. The broad applicability of this approach is corroborated by a second
+example of a kagome topological magnon insulator.",2007.07912v1
+2020-07-20,"Topology of many-body edge and extended quantum states in an open spin chain: 1/3--plateau, Kosterlitz-Thouless transition, and Luttinger liquid","Quantum many-body edge and extended magnon excitations from the 1/3 --
+plateau of the anisotropic Heisenberg model on an open AB$_2$ chain in a
+magnetic field $h$ are unveiled using the density matrix renormalization group
+and exact diagonalization. By tuning both the anisotropy and $h$ in the rich
+phase diagram, the edge states penetrate in the bulk, whose gap closes in a
+symmetry-protected topological Kosterlitz-Thouless transition. Also, we witness
+the squeezed chain effect, the breaking of the edge states degeneracy, and a
+topological change of the excitations from gapped magnons with quadratic
+long-wavelength dispersion to a linear spinon dispersion in the Luttinger
+liquid gapless phase as the anisotropy $\lambda$ approaches the critical point
+from the $\lambda>0$ side of the phase diagram.",2007.10414v1
+2020-07-22,Nuclear Magnetic Relaxation Time near Compensation Temperature in Ferrimagnetic Insulator,"The nuclear magnetic relaxation time $T_1$ in ferrimagnetic insulators is
+calculated by a Raman process of hyperfine interaction with a meanfield
+approximation. It is found that the 1/$T_1$ on one site rapidly increases near
+the compensation temperature $T_0$, whereas that on another site does not
+increase up to Curie temperature $T_c$. This is due to that the band width of
+soft magnon becomes comparable to $T_0$. The increasing behavior of 1/$T_1$
+below $T_c$ is found also in another type ferrimagnet, which shows hump
+structure in the temperature dependence of magnetization instead of
+compensation. Also in this case, we find the rapid increase of 1/$T_1$ below
+$T_c$, even though the magnetization does not show the compensation. Such a
+coexistence of soft and hard magnons will lead to remarkable properties of
+ferrimagnet.",2007.11214v3
+2020-08-05,Torque equilibrium spin wave theory of Raman scattering in an anisotropic triangular lattice antiferromagnet with Dzyaloshinskii-Moriya interaction,"We apply torque equilibrium spin wave theory (TESWT) to investigate an
+anisotropic XXZ antiferromagnetic model with Dzyaloshinskii-Moriya (DM)
+interaction in a triangular lattice. Considering the quasiparticle vacuum as
+our reference, we provide an accurate analysis of the non-collinear ground
+state of a frustrated triangular lattice magnet using the TESWT formalism. We
+elucidate the effects of quantum fluctuations on the ordering wave vector based
+on model system parameters. We study the single magnon dispersion, the
+two-magnon continuum using the spectral function, and the Raman spectrum of
+bimagnon and trimagnon excitations. We present our results for the $HH, VV$,
+and the $HV$ polarization Raman geometry dependence of the bimagnon and the
+trimagnon excitation spectrum where $H (V)$ represents horizontal (vertical)
+polarization. Our calculations show that both the $HH$ and the $HV$
+polarization spectrum can be used to determine the degree of anisotropy of our
+system. We calculate the Raman spectra of Ba$_3$CoSb$_2$O$_9$ and
+Cs$_2$CuCl$_4$.",2008.02287v2
+2020-08-10,Entanglement enhanced and one-way steering in PT -symmetric cavity magnomechanics,"We study creation of entanglement and quantum steering in a parity-time- (PT
+-) symmetric cavity magnomechanical system. There is magnetic dipole
+interaction between the cavity and photon-magnon, and there is also
+magnetostrictive interaction which is induced by the phononmagnon coupling in
+this system. By introducing blue-detuned driving microwave field to the system,
+the bipartite entanglement of the system with PT -symmetry is significantly
+enhanced versus the case in the conventional cavity magnomechanical systems
+(loss-loss systems). Moreover, the one-way quantum steering between
+magnon-phonon and photon-phonon modes can be obtained in the unbroken-PT
+-symmetric regime. The boundary of stability is demonstrated and this show that
+the steady-state solutions are more stable in the gain and loss systems. This
+work opens up a route to explore the characteristics of quantum entanglement
+and steering in magnomechanical systems, which might have potential
+applications in quantum state engineering and quantum information.",2008.03870v1
+2020-09-30,Phase-modulated cavity magnon polaritons as a precise magnetic field probe,"We describe and operate a novel spin-magnetometer based on the phase
+modulation of cavity magnon polaritons. In this scheme a rf magnetic field is
+detected through the sidebands it induces on a pump, and the experimental
+configuration allows for a negligible pump noise and a high frequency readout.
+The demonstrator setup, based on a copper cavity coupled to an yttrium iron
+garnet sphere hybrid system, reached a sensitivity of
+$2.0\,\mathrm{pT/\sqrt{Hz}}$, evading the pump noise and matching the
+theoretical previsions. An optimized setup can attain a rf magnetic field
+sensitivity of about $8\,\mathrm{fT/\sqrt{Hz}}$ at room temperature. An orders
+of magnitude improvement is expected at lower temperatures, making this
+instrument one of the few magnetometers accessing the sub-fT limit. Due to its
+natural applications, miniaturization and multiplexing are eventually
+discussed.",2010.00093v3
+2020-10-13,Antiphase Oscillations in the Time-Resolved Spin Structure Factor of a Photoexcited Mott Insulator,"Motivated by the recent development of time-resolved resonant-inelastic x-ray
+scattering (TRRIXS) in photoexcited antiferromagnetic Mott insulators, we
+numerically investigate momentum-dependent transient spin dynamics in a
+half-filled Hubbard model on a square lattice. After turning off a pumping
+photon pulse, the intensity of a dynamical spin structure factor temporally
+oscillates with frequencies determined by the energy of two magnons in the
+antiferromagnetic Mott insulator. We find an antiphase behavior in the
+oscillations between two orthogonal momentum directions, parallel and
+perpendicular to the electric field of a pump pulse. The phase difference comes
+from the $B_{1g}$ channel of the two-magnon excitation. Observing the antiphase
+oscillations will be a big challenge for TRRIXS experiments when their time
+resolution will be improved by more than an order of magnitude.",2010.06151v2
+2020-10-19,Controllable optical response and tunable sensing based on self interference in waveguide QED systems,"We study the self interference effect of a resonator coupled with a bent
+waveguide at two separated ports. Such interference effects are shown to be
+similar for the cases of standing-wave and traveling-wave resonators, while in
+the system of two separated resonators indirectly coupled via a waveguide, the
+coupling forms and the related interference effects depend on which kind of
+resonators is chosen. Due to the self interference, controllable optical
+responses including tunable linewidth and frequency shift, and optical dark
+state can be achieved. Moreover, we consider a self-interference photon-magnon
+hybrid model and show phase-dependent Fano-like line shapes which have
+potential applications in frequency sensing. The photon-magnon hybridization
+can not only enhance the sensitivity and provide tunable working region, but
+also enables optical readout of the magnetic field strength in turn. The
+results in this paper provide a deeper insight into the self interference
+effect and its potential applications.",2010.09319v2
+2020-10-19,Theory of the low-temperature longitudinal spin Seebeck effect,"Using a simplified microscopic model of coupled spin and lattice excitations
+in a ferromagnetic insulator we evaluate the magnetic-field dependence of the
+spin Seebeck effect at low temperatures. The model includes Heisenberg exchange
+coupling, a harmonic lattice potential, and a pseudo-dipolar exchange
+interaction. Our approach goes beyond previous work [Phys. Rev. B 98, 134421
+(2018)] in that it does not rely on the a priori assumption of a fast
+equilibration of the magnon and phonon distributions. Our theory shows that
+singular features in the magnetic-field dependence of the spin Seebeck effect
+at low temperatures observed by Kikkawa et al. [Phys. Rev. Lett. 117, 207203
+(2016)] are independent of the relative strength of magnon-impurity and
+phonon-impurity scattering.",2010.09571v2
+2020-10-28,Strong coupling of quantized spin waves in ferromagnetic bilayers,"We formulate a strong-coupling theory for perpendicular standing spin waves
+(PSSWs) in ferromagnetic bilayers with the interlayer exchange coupling (IEC).
+Employing the Hoffmann boundary condition and the energy-flow continuity across
+the interface, we show that the PSSWs are still quantized but with non-integral
+quantum numbers, in sharp contrast to that of a single layer. The magnon-magnon
+coupling is characterized by the spectrum splitting which is linear with the
+IEC in the weak-coupling region, but getting saturated in the strong-coupling
+limit. Analytical predictions are verified by full micromagnetic simulations
+with good agreement.",2010.14981v2
+2020-11-09,The effect of confinement on thermally induced fluctuations in nanomagnets,"We study the magnetization dynamics in nanomagnets excited by stochastic
+magnetic fields to mimic temperature in a micromagnetic framework. The effect
+of confinement arising from the finite size of the structures is investigated,
+and we visualise the spatial extension of the internal magnon modes.
+Furthermore, we determine the temperature dependence of the magnon modes, and
+focus specifically on the low frequency edge modes, which are found to display
+fluctuations associated with switching between C- and S-states, thus posing an
+energy barrier. We classify this fluctuating behaviour in three different
+regimes, and calculate the associated energy barriers using the Arrhenius law.",2011.04494v3
+2020-11-09,Spin-wave dynamics and symmetry breaking in an artificial spin ice,"Artificial spin ices are periodic arrangements of interacting nanomagnets
+successfully used to investigate emergent phenomena in the presence of
+geometric frustration. Recently, it has been shown that artificial spin ices
+can be used as building blocks for creating functional materials, such as
+magnonic crystals, and support a large number of programmable magnetic states.
+We investigate the magnetization dynamics in a system exhibiting anisotropic
+magnetostatic interactions owing to locally broken structural inversion
+symmetry. We find a rich spin-wave spectrum and investigate its evolution in an
+external magnetic field. We determine the evolution of individual modes, from
+building blocks up to larger arrays, highlighting the role of symmetry breaking
+in defining the mode profiles. Moreover, we demonstrate that the mode spectra
+exhibit signatures of long-range interactions in the system. These results
+contribute to the understanding of magnetization dynamics in spin ices beyond
+the kagome and square ice geometries and are relevant for the realization of
+reconfigurable magnonic crystals based on spin ices.",2011.04505v2
+2020-11-12,"Edge states in quantum spin chains: the interplay among interaction, gradient magnetic field and Floquet engineering","We explore the edge defects induced by spin-spin interaction in a finite
+paradigmatic Heisenberg spin chain. By introducing a gradient magnetic field
+and a periodically-modulated spin-exchange strength, the resonance between
+modulation frequency and magnetic field gradient can also induce asymmetric
+defects at the edges, dubbed as Floquet-Wannier-Zeeman edge defects. The
+interplay between these two types of edge defects allows us to manipulate the
+magnon edge states from an isolated band into a continuum one. In the
+high-frequency regime, we analytically derive effective models to interpret the
+formation mechanisms for edge states by employing the multiscale perturbation
+analysis. Our study offers new insights to understand and control the magnon
+edge states governed by the interplay between edge defects induced by the
+spin-spin interaction and the Floquet-Wannier-Zeeman manipulation.",2011.06164v4
+2020-11-16,Magnonic Goos-Hanchen effect induced by one dimensional solitons,"The magnon spectral problem is solved in terms of the spectrum of a
+diagonalizable operator for a generic class of magnetic states that includes
+several types of domain walls and the chiral solitons of monoaxial helimagnets.
+Focusing on the isolated solitons of monoaxial helimagnets, it is shown that
+the spin waves scattered (reflected and transmitted) by the soliton suffer a
+lateral displacement analogous to the Goos-Hanchen effect of optics. The
+displacement is a fraction of the wavelength, but can be greatly enhanced by
+using an array of well separated solitons. Contrarily to the Goos-Hanchen
+effect recently studied in some magnetic systems, which takes place at
+interfaces between different magnetic systems, the effect predicted here takes
+place at the soliton position, what it is interesting from the point of view of
+applications since solitons can be created at different places and moved across
+the material. This kind of Goos-Hanchen effect is not particular of monoaxial
+helimagnets, but it is generic of a class of magnetic states, including domain
+walls in systems with interfacial Dzyaloshinskii-Moriya interaction.",2011.07886v1
+2020-11-17,Brillouin-Mandelstam Light Scattering Spectroscopy: Applications in Phononics and Spintronics,"Recent years witnessed much broader use of Brillouin inelastic light
+scattering spectroscopy for the investigation of phonons and magnons in novel
+materials, nanostructures, and devices. Driven by developments in
+instrumentation and the strong need for accurate knowledge of energies of
+elemental excitations, the Brillouin - Mandelstam spectroscopy is rapidly
+becoming an essential technique, complementary to the Raman inelastic light
+scattering spectroscopy. We provide an overview of recent progress in the
+Brillouin light scattering technique, focusing on the use of this photonic
+method for the investigation of confined acoustic phonons, phononic
+metamaterials, magnon propagation and scattering. The Review emphasizes
+emerging applications of the Brillouin - Mandelstam spectroscopy for phonon
+engineered structures and spintronic devices and concludes with a perspective
+for future directions.",2011.08352v1
+2021-01-13,Fast and robust magnon transport in a spin chain,"A protocol for fast and robust magnon transport in a one-dimensional spin
+chain is devised. Employing an approximate mapping between the chain and a
+single harmonically trapped particle, we exploit the known analytic control
+protocols for the latter and adopt them to achieve fast, high-fidelity
+transport in the chain. We compare the performance with finite time adiabatic
+protocols, establishing that the designed scheme allows for significantly
+faster and more stable transport. Furthermore, we show that a sharp transition
+exists between regions in which the protocol is effective and when it breaks
+down, giving rise to a heuristic speed limit for the process.",2101.04995v2
+2021-01-25,Nonreciprocal Transmission and Entanglement in a cavity-magnomechanical system,"Quantum entanglement, a key element for quantum information is generated with
+a cavity-magnomechanical system. It comprises of two microwave cavities, a
+magnon mode and a vibrational mode, and the last two elements come from a YIG
+sphere trapped in the second cavity. The two microwave cavities are connected
+by a superconducting transmission line, resulting in a linear coupling between
+them. The magnon mode is driven by a strong microwave field and coupled to
+cavity photons via magnetic dipole interaction, and at the same time interacts
+with phonons via magnetostrictive interaction. By breaking symmetry of the
+configuration, we realize nonreciprocal photon transmission and one-way
+bipartite quantum entanglement. By using current experimental parameters for
+numerical simulation, it is hoped that our results may reveal a new strategy to
+built quantum resources for the realization of noise-tolerant quantum
+processors, chiral networks, and so on.",2101.09931v1
+2021-03-23,Ultralow threshold bistability and generation of long-lived mode in a dissipatively coupled nonlinear system: application to magnonics,"The prospect of a system possessing two or more stable states for a given
+excitation condition is of topical interest with applications in information
+processing networks. In this work, we establish the remote transfer of
+bistability from a nonlinear resource in a dissipatively coupled two-mode
+system. As a clear advantage over coherently coupled settings, the dissipative
+nature of interaction is found to support a lower pumping threshold for
+bistable signals. For comparable parameters, the bistability threshold for
+dissipatively coupled systems is lower by a factor of about five. The resulting
+hysteresis can be studied spectroscopically by applying a probe field through
+the waveguide and examining the polariton character of the transmitted field.
+Our model is generic, apropos of an extensive set of quantum systems, and we
+demonstrate our results in the context of magnonics where experimental interest
+has flourished of late. As a consequence of dissipative coupling and the
+nonlinearity, a long-lived mode emerges, which is responsible for heightened
+transmission levels and pronounced sensitivity in signal propagation through
+the fiber.",2103.12861v1
+2021-04-11,Ultrafast Measurements of the Interfacial Spin Seebeck Effect in Au and Rare-Earth Iron Garnet Bilayers,"We investigate picosecond spin-currents across Au/iron-garnet interfaces in
+response to ultrafast laser heating of the electrons in the Au film. In the
+picoseconds after optical heating, interfacial spin currents occur due to an
+interfacial temperature difference between electrons in the metal and magnons
+in the insulator. We report measurements of this interfacial longitudinal spin
+Seebeck effect between Au and rare-earth iron-garnet insulators, i.e. RE$_3$
+Fe$_5$O$_{12}$, where RE is Y, Eu, Tb, Tm. We use time domain thermoreflectance
+(TDTR) measurements to characterize the thermal response of the bilayer to
+ultrafast optical heating. We use time-resolved magneto-optic Kerr effect
+(TR-MOKE) measurements of the Au layer to measure the time-evolution of spin
+accumulation in the Au film. We observe a spin Seebeck effect between Au/TmIG
+that is three times larger than for an Au/YIG bilayer. The interfacial thermal
+conductance between electrons in the Au and magnons in the TmIG layer is ~ 3
+$\frac{MW}{m^2 K}$.",2104.05075v2
+2021-04-13,Theory of spin-Hall magnetoresistance in the AC (terahertz) regime,"In bilayers consisting of a normal metal (N) with spin-orbit coupling and a
+ferromagnet (F), the combination of the spin-Hall effect, the spin-transfer
+torque, and the inverse spin-Hall effect gives a small correction to the
+in-plane conductivity of N, which is referred to as spin-Hall magnetoresistance
+(SMR). We here present a theory of the SMR and the associated off-diagonal
+conductivity corrections for frequencies up to the terahertz regime. We show
+that the SMR signal has pronounced singularities at the spin-wave frequencies
+of F, which identifies it as a potential tool for all-electric spectroscopy of
+magnon modes. A systematic change of the magnitude of the SMR at lower
+frequencies is associated with the onset of a longitudinal magnonic
+contribution to spin transport across the F-N interface.",2104.06518v2
+2021-04-23,Electric polarization and nonlinear optical effects in noncentrosymmetric magnets,"We study electric polarization and nonlinear optical effects in spin systems
+with broken inversion symmetry. We apply strong coupling expansion to the
+underlying electronic Hamiltonians, and systematically derive expressions for
+electric polarization in spin systems that are represented in terms of spin
+operators. The magnon representation of the obtained electric polarization
+operator allows us to compute linear and nonlinear optical responses by the
+standard diagrammatic method. We apply our formalism to Heisenberg model with
+alternating coupling constants and $J_1$-$J_2$ model with inversion symmetry
+breaking. We demonstrate that these inversion broken spin systems support dc
+current flow upon magnon excitations which arises from the shift current
+mechanism.",2104.11418v2
+2021-04-23,Spin-wave frequency combs,"We experimentally demonstrate the generation of spin-wave frequency combs
+based on the nonlinear interaction of propagating spin waves in a
+microstructured waveguide. By means of time and space-resolved Brillouin light
+scattering spectroscopy, we show that the simultaneous excitation of spin waves
+with different frequencies leads to a cascade of four-magnon scattering events
+which ultimately results in well-defined frequency combs. Their spectral weight
+can be tuned by the choice of amplitude and frequency of the input signals.
+Furthermore, we introduce a model for stimulated four-magnon scattering which
+describes the formation of spin-wave frequency combs in the frequency and time
+domain.",2104.11491v2
+2021-04-27,Exceptional field dependence of antiferromagnetic magnons in LiFePO$_4$,"Low-energy magnon excitations in magnetoelectric LiFePO$_4$ have been
+investigated by high-frequency high-field electron spin resonance spectroscopy
+in magnetic fields up to B = 58 T and frequencies up to f = 745 GHz. For
+magnetic fields applied along the easy magnetic axis, the excitation gap
+softens and vanishes at the spin-flop field of BSF = 32 T before hardening
+again at higher fields. In addition, for B smaller than BSF we observe a
+resonance mode assigned to excitations due to Dzyaloshinskii-Moriya
+(DM)-interactions, thereby evidencing sizable DM interaction of approx 150
+micro eV in LiFePO4. Both the magnetisation and the excitations up to high
+magnetic fields are described in terms of a mean-field theory model which
+extends recent zero field inelastic neutron scattering results. Our results
+imply that magnetic interactions as well as magnetic anisotropy have a sizable
+quadratic field dependence which we attribute to significant magnetostriction.",2104.13275v1
+2021-05-06,Short spin waves detection by means of the magneto-optical intensity effect,"It is proposed a novel method of the spectrally selective detection of the
+short spin waves (or magnons) by means of the transverse magneto-optical (MO)
+intensity effect in transmission in the magnetoplasmonic nanostructure. The
+method is based on the analysis of the MO effect spectrum versus the modulation
+of the sample magnetization (i.e. spin wave) and related spatial symmetry
+breaking in the magnetic layer. The spatial symmetry breaking leads to the
+appearance of MO effect modulation at the normal incidence of light in the
+spectral range of the optical states (SPP and waveguide modes) and the breaking
+of the antisymmetry of the effect with respect to the sign of the incidence
+angle of light. Besides it is revealed that the magnitude of the MO effect
+varies with respect to the phase shift between the spin wave and the plasmonic
+grating as a harmonic function with a period equal to the magnon wavelength.
+All these facts allow to detect the spin waves of the certain wavelength
+propagating in the nanostructure by measuring of the MO effect in the
+nanostructure.",2105.02539v1
+2021-05-07,Field-angle dependence of thermal Hall conductivity in magnetically ordered Kitaev-Heisenberg system,"We study magnetic excitations and thermal Hall effect on the
+Kitaev-Heisenberg model under magnetic fields. By employing the spin-wave
+theory for the magnetic orders realized in this model, we examine the
+topological nature of the spin-wave dispersions and calculate the thermal Hall
+conductivity. The comprehensive investigations on the field-angle dependence
+clarify that the thermal Hall conductivity is sensitive to the spin ordered
+pattern and excitation spectra of magnons; this quantity is enhanced by the
+noncoplanar spin configurations and small magnon gap in the excitation
+spectrum. On the other hand, we also find a common feature in the field-angle
+dependence of the thermal Hall conductivity. It vanishes when the magnetic
+field is on the planes spanned by the spin axes. We reveal that the behavior is
+intrinsic to the Kitaev -Heisenberg model in an applied field and demonstrate
+that the introduction of the off-diagonal spin interaction causes the
+disappearance of the feature in the thermal Hall conductivity.",2105.03113v1
+2021-05-26,Antiferromagnetic magnons and local anisotropy: dynamical mean-field study,"We present a dynamical mean-field study of antiferromagnetic magnons in one-,
+two- and three-orbital Hubbard model of square and bcc cubic lattice at
+intermediate coupling strength. Weinvestigate the effect of anisotropy
+introduced by an external magnetic field or single-ion anisotropy.For the
+latter we tune continuously between the easy-axis and easy-plane models. We
+also analyzea model with spin-orbit coupling in cubic site-symmetry setting.
+The ordered states as well as themagnetic excitations are sensitive to even a
+small breaking ofSU(2)symmetry of the model andfollow the expectations of
+spin-wave theory as well as general symmetry considerations.",2105.12468v2
+2021-05-28,Anisotropic Magnon Spin Transport in Ultra-thin Spinel Ferrite Thin Films -- Evidence for Anisotropy in Exchange Stiffness,"We report measurements of magnon spin transport in a spinel ferrite,
+magnesium aluminum ferrite $\mathrm{MgAl_{0.5}Fe_{1.5}O_4}$ (MAFO), which has a
+substantial in-plane four-fold magnetic anisotropy. We observe spin diffusion
+lengths $> 0.8$ $\mathrm{\mu m}$ at room temperature in 6 nm films, with spin
+diffusion length 30% longer along the easy axes compared to the hard axes. The
+sign of this difference is opposite to the effects just of anisotropy in the
+magnetic energy for a uniform magnetic state. We suggest instead that
+accounting for anisotropy in exchange stiffness is necessary to explain these
+results.",2105.13943v1
+2021-06-04,Neutron diffraction of field-induced magnon condensation in the spin-dimerized antiferromagnet Sr$_{3}$Cr$_{2}$O$_{8}$,"In this work, we investigate the evolution and settling of magnon
+condensation in the spin-1/2 dimer system Sr$_{3}$Cr$_{2}$O$_{8}$ using a
+combination of magnetostriction in pulsed fields and inelastic neutron
+scattering in a continuous magnetic field. The magnetic structure in the
+Bose-Einstein condensation (BEC) phase was probed by neutron diffraction in
+pulsed magnetic fields up to 39~T. The magnetic structure in this phase was
+confirmed to be an XY-antiferromagnetic structure validated by irreducible
+representational analysis. The magnetic phase diagram as a function of an
+applied magnetic field for this system is presented. Furthermore, zero-field
+neutron diffraction results indicate that dimerization plays an important role
+in stabilizing the low-temperature crystal structure.",2106.02360v1
+2021-06-07,Voltage-control of damping constant in magnetic-insulator/topological-insulator bilayers,"The magnetic damping constant is a critical parameter for magnetization
+dynamics and the efficiency of memory devices and magnon transport. Therefore,
+its manipulation by electric fields is crucial in spintronics. Here, we
+theoretically demonstrate the voltage-control of magnetic damping in ferro- and
+ferrimagnetic-insulator (FI)/topological-insulator (TI) bilayers. Assuming a
+capacitor-like setup, we formulate an effective dissipation torque induced by
+spin-charge pumping at the FI/TI interface as a function of an applied voltage.
+By using realistic material parameters, we find that the effective damping for
+a FI with 10nm thickness can be tuned by one order of magnitude under the
+voltage with 0.25V. Also, we provide perspectives on the voltage-induced
+modulation of the magnon spin transport on proximity-coupled FIs.",2106.03332v1
+2021-06-08,Spectral-fingerprinting: Microstate readout via remanence ferromagnetic resonance in artificial spin systems,"Artificial spin ices are magnetic metamaterials comprising
+geometrically-tiled interacting nanomagnets. There is significant interest in
+these systems for reconfigurable magnonics due to their vast microstate
+landscape. Studies to-date have focused on the in-field GHz spin-wave response,
+convoluting effects from applied field, nanofabrication-imperfections
+('quenched disorder') and microstate-dependent dipolar field landscapes. Here,
+we study artificial spin ices in pure and disordered microstates and evaluate
+their zero-field spectra. Removing the applied field allows us to deconvolute
+contributions to reversal dynamics and spin-wave spectra, directly measuring
+the dipolar field landscape and quenched disorder. Mode-amplitude provides
+population readout of nanomagnet magnetisation direction, and hence net
+magnetisation as well as local vertex populations. We demonstrate
+microstate-fingerprinting via distinct spectral-readout of three microstates
+with identical (zero) magnetisation, supported by simulation. These results
+establish remanence 'spectral-fingerprinting' as a rapid, scalable on-chip
+readout of both magnetic state and nanoscale dipolar field texture, a critical
+step in realising next-generation functional magnonic devices.",2106.04406v2
+2021-06-24,Magnon Transport in the Presence of Antisymmetric Exchange in a Weak Antiferromagnet,"The Dzyaloshinskii-Moriya interaction (DMI) is at the heart of many modern
+developments in the research field of spintronics. DMI is known to generate
+noncollinear magnetic textures, and can take two forms in antiferromagnets:
+homogeneous or inter-sublattice, leading to small, canted moments and
+inhomogeneous or intra-sublattice, leading to formation of chiral structures.
+In this work, we first determine the strength of the effective field created by
+the DMI, using SQUID based magnetometry and transport measurements, in thin
+films of the antiferromagnetic iron oxide hematite, $\alpha$-Fe$_2$O$_3$. We
+demonstrate that DMI additionally introduces reconfigurability in the long
+distance magnon transport in these films under different orientations of a
+magnetic field. This arises as a hysteresis centred around the easy-axis
+direction for an external field rotated in opposing directions whose width
+decreases with increasing magnetic field as the Zeeman energy competes with the
+effective field created by the DMI.",2106.12853v2
+2021-06-24,Magnetic skyrmion generation by reflective spin-wave focusing,"We propose a method to generate magnetic skyrmions by focusing spin waves
+totally reflected by a curved film edge. Based on the principle of identical
+magnonic path length, we derive the edge contour that is parabolic and
+frequency-independent. Micromagnetic simulations are performed to verify our
+theoretical design. It is found that under proper conditions, magnetic droplet
+first emerges near the focal point where the spin-wave intensity has been
+significantly enhanced, and then converts to magnetic skyrmion accompanied by a
+change of the topological charge. The phase diagram about the amplitude and
+frequency of the driving field for skyrmion generation is obtained. Our finding
+would be helpful for the designment of spintronic devices combing the advantage
+of skyrmionics and magnonics.",2106.12876v1
+2021-07-01,Novel elementary excitations in spin-1/2 antiferromagnets on the triangular lattice,"We discuss spin-$\frac12$ Heisenberg antiferromagnet on the triangular
+lattice using the recently proposed bond-operator technique (BOT). We use the
+variant of the BOT which takes into account all spin degrees of freedom in the
+magnetic unit cell containing three spins. Apart from conventional magnons
+known from the spin-wave theory (SWT), there are novel high-energy collective
+excitations in the BOT which are built from high-energy excitations of the
+magnetic unit cell. We obtain also another novel high-energy quasiparticle
+which has no counterpart not only in the SWT but also in the harmonic
+approximation of the BOT. All observed elementary excitations produce visible
+anomalies in dynamical spin correlators. We show that quantum fluctuations
+considerably change properties of conventional magnons predicted by the SWT.
+The effect of a small easy-plane anisotropy is discussed. The anomalous spin
+dynamics with multiple peaks in the dynamical structure factor is explained
+that was observed recently experimentally in $\rm Ba_3CoSb_2O_9$ and which the
+SWT could not describe even qualitatively.",2107.00256v5
+2021-07-08,Nonequilibrium phase transition in a driven-dissipative quantum antiferromagnet,"A deeper theoretical understanding of driven-dissipative interacting systems
+and their nonequilibrium phase transitions is essential both to advance our
+fundamental physics understanding and to harness technological opportunities
+arising from optically controlled quantum many-body states. This paper provides
+a numerical study of dynamical phases and the transitions between them in the
+nonequilibrium steady state of the prototypical two-dimensional Heisenberg
+antiferromagnet with drive and dissipation. We demonstrate a nonthermal
+transition that is characterized by a qualitative change in the magnon
+distribution, from subthermal at low drive to a generalized Bose-Einstein form
+including a nonvanishing condensate fraction at high drive. A finite-size
+analysis reveals static and dynamical critical scaling at the transition, with
+a discontinuous slope of the magnon number versus driving field strength and
+critical slowing down at the transition point. Implications for experiments on
+quantum materials and polariton condensates are discussed.",2107.03841v3
+2021-07-10,The field-angle anisotropy of proximate Kitaev systems under an in-plane magnetic field,"We have investigated the field-angle behaviors of magnetic excitations under
+an in-plane magnetic field for proximate Kitaev systems. By employing the exact
+diagonalization method in conjunction with the linear spin wave theory, we have
+demonstrated that the magnetic excitation gap in the polarized phase is
+determined by the magnon excitation at $M$ points and has a strong anisotropy
+with respect to the field direction in the vicinity of the critical field
+limit. The specific heat from this magnon excitation bears qualitatively the
+same anisotropic behaviors as expected one for the non-Abelian spin liquid
+phase in the Kitaev model and experimentally observed one of the intermediate
+phases in $\alpha$-RuCl$_3$.",2107.04785v2
+2021-07-12,Nonlinear two-level dynamics of quantum time crystals,"A time crystal is a macroscopic quantum system in periodic motion in its
+ground state, stable only if isolated from energy exchange with the
+environment. For this reason, coupling separate time crystals is challenging,
+and time crystals in a dynamic environment have yet not been studied. In our
+experiments, two coupled time crystals made of spin-wave quasiparticles
+(magnons) form a macroscopic two-level system. The two levels evolve in time as
+determined intrinsically by a nonlinear feedback. Magnons move from the ground
+level to the excited level driven by the Landau-Zener effect, combined with
+Rabi population oscillations. We thus demonstrate how to arrange spontaneous
+dynamics between interacting time crystals. Our experiments allow access to
+every aspect and detail of the interaction in a single run of the experiment,
+inviting technological exploitation-- potentially even at room temperature.",2107.05236v1
+2021-07-19,Damped Dirac magnon in a metallic kagome antiferromagnet FeSn,"The kagome lattice is a fertile platform to explore topological excitations
+with both Fermi-Dirac and Bose-Einstein statistics. While relativistic Dirac
+Fermions and flat-bands have been discovered in the electronic structure of
+kagome metals, the spin excitations have received less attention. Here we
+report inelastic neutron scattering studies of the prototypical kagome magnetic
+metal FeSn. The spectra display well-defined spin waves extending up to 120
+meV. Above this energy, the spin waves become progressively broadened,
+reflecting interactions with the Stoner continuum. Using linear spin wave
+theory, we determine an effective spin Hamiltonian that reproduces the measured
+dispersion. This analysis indicates that the Dirac magnon at the K-point
+remarkably occurs on the brink of a region where well-defined spin waves become
+unobservable. Our results emphasize the influential role of itinerant carriers
+on the topological spin excitations of metallic kagome magnets.",2107.08915v1
+2021-07-20,Quantitative Determination of the Confinement and Deconfinement of spinons in the anomalous spectra of Antiferromagnets via the Entanglement Entropy,"We introduce an entanglement entropy analysis to quantitatively identify the
+confinement and deconfinement of the spinons in the spin excitations of quantum
+magnets. Our proposal is implemented by the parton construction of a
+honeycomb-lattice antiferromagnet exhibiting high-energy anomalous spectra. To
+obtain the quasiparticles of spin excitations for entanglement entropy
+calculations, we develop an effective Hamiltonian using the random phase
+approximation. We elaborate quantitatively the deconfinement-to-confinement
+transition of spinons in the anomalous spectra with the increase of the Hubbard
+interaction, indicating the avoided fractionalization of magnons in the strong
+interaction regime. Meanwhile, the Higgs mode at the {\Gamma}0 point is
+fractionalized into four degenerate spinon pairs, although it appears as a
+sharp well-defined peak in the spectra. Our work extends our understanding of
+the deconfinement of the spinon and its coexistence with the magnon in quantum
+magnets.",2107.09241v1
+2021-07-29,Magnon band structure of skyrmion crystals and stereographic projection approach,"Using semiclassical method combined with stereographic projection approach,
+we investigate the magnetic dynamics of the skyrmion crystal (SkX), formed in
+planar ferromagnet with both Dzyaloshinskii-Moriya interaction and uniform
+magnetic field. The topologically non-trivial ground state of SkX is described
+in stereographic projection by the complex valued function with simple poles at
+skyrmions' positions. We use the earlier proposed ansatz for this ground state
+function in the form of the sum of individual skyrmions. The dynamics follows
+from the second variation of the classical action. Numerical analysis yields
+the magnon band structure of tight-binding form in accordance with previously
+known results. There are two sets of bands, one set with a flat dispersion,
+topologically trivial and rapidly evolving with magnetic field. Another set is
+robust to magnetic field, characterized by pronounced dispersion and with the
+Berry curvature which may be sign-reversal in the Brillouin zone. The developed
+theory can be straightforwardly generalized for the analysis of magnetic
+dynamics in topological spin structures of other types.",2107.14335v1
+2021-08-03,Unusual spin pseudogap behavior in the spin web lattice Cu$_3$TeO$_6$ probed by $^{125}$Te nuclear magnetic resonance,"We present a $^{125}$Te nuclear magnetic resonance (NMR) study in the
+three-dimensional spin web lattice Cu$_3$TeO$_6$, which harbors topological
+magnons. The $^{125}$Te NMR spectra and the Knight shift $\mathcal{K}$ as a
+function of temperature show a drastic change at $T_\text{S}\sim 40$ K much
+lower than the N\'eel ordering temperature $T_\text{N}\sim 61$ K, providing
+evidence for the first-order structural phase transition within the
+magnetically ordered state. Most remarkably, the temperature dependence of the
+spin-lattice relaxation rate $T_1^{-1}$ unravels spin-gap-like magnetic
+excitations, which sharply sets in at $T^*\sim 75$ K, the temperature well
+above $T_\text{N}$. The spin gap behavior may be understood by weakly
+dispersive optical magnon branches of high-energy spin excitations originating
+from the unique corner-sharing Cu hexagon spin-1/2 network with low
+coordination number.",2108.01288v1
+2021-08-05,Magnonic thermal transport using the quantum Boltzmann equation,"We present a formula for thermal transport in the bulk of Bose systems based
+on the quantum Boltzmann equation (QBE). First, starting from the quantum
+kinetic equation and using the Born approximation for impurity scattering, we
+derive the QBE of Bose systems and provide a formula for thermal transport
+subjected to a temperature gradient. Next, we apply the formula to magnons.
+Assuming a relaxation time approximation and focusing on the linear response
+regime, we show that the longitudinal thermal conductivity of the QBE exhibits
+the different behavior from the conventional. The thermal conductivity of the
+QBE reduces to the Drude-type in the limit of the quasiparticle approximation,
+while not in the absence of the approximation. Finally, applying the
+quasiparticle approximation to the QBE, we find that the correction to the
+conventional Boltzmann equation is integrated as the self-energy into the
+spectral function of the QBE, and this enhances the thermal conductivity. Thus
+we shed light on the thermal transport property of the QBE beyond the
+conventional.",2108.02875v1
+2021-08-14,Laser-controlled real- and reciprocal-space topology in multiferroic insulators,"Magnetic materials in which it is possible to control the topology of their
+magnetic order in real space or the topology of their magnetic excitations in
+reciprocal space are highly sought-after as platforms for alternative data
+storage and computing architectures. Here we show that multiferroic insulators,
+owing to their magneto-electric coupling, offer a natural and advantageous way
+to address these two different topologies using laser fields. We demonstrate
+that via a delicate balance between the energy injection from a high-frequency
+laser and dissipation, single skyrmions -- archetypical topological magnetic
+textures -- can be set into motion with a velocity and propagation direction
+that can be tuned by the laser field amplitude and polarization, respectively.
+Moreover, we uncover an ultrafast Floquet magnonic topological phase transition
+in a laser-driven skyrmion crystal and we propose a new diagnostic tool to
+reveal it using the magnonic thermal Hall conductivity.",2108.06535v2
+2021-08-16,Lattice-driven femtosecond magnon dynamics in $α$-MnTe,"The light-induced femtosecond dynamics of the sublattice magnetizations in
+the antiferromagnetically ordered phase of the semiconductor $\alpha$-MnTe is
+investigated theoretically as function of an external driving field. The
+electromagnetic field is coupled to optical modes and the concomitant atomic
+displacements modulate the Heisenberg exchange couplings. We derive the
+equations of motion for the time-dependent sublattice magnetization in spin
+wave theory and analyze the contributions from the driven magnon modes. The
+antiferromagnetic order parameter exhibits coherent longitudinal oscillations
+determined by the external driving frequency which decay due to dephasing.
+Including a phenomenological dissipative term to mimic spin-lattice relaxation
+processes leads to relaxation back to thermal equilibrium. We provide
+approximate analytic solutions of the resulting differential equations which
+allow us to understand the effect of the driving light pulse on the amplitude,
+frequency, and lifetime of the coherent spin dynamics.",2108.07079v2
+2021-09-13,Model of the low temperature magnetic phases of gadolinium gallium garnet,"The magnetic behaviour of gadolinium gallium garnet in an external magnetic
+field at zero temperature is considered. For high fields a classical spin model
+of the gadolinium ions predicts a spin configuration that is periodic at the
+level of the smallest repeating unit cell. The quantum version of the model is
+treated via a truncated Holstein-Primakoff transformation with axes defined by
+the classical spin configuration, and the magnon excitation bands are
+calculated. The model predicts a transition in the field range of $1.9$ --
+$2.1\mathrm{T}$, sensitive to the direction of the applied field, which is
+caused by one or more magnon modes becoming soft as the field is decreased. In
+general the soft modes occur at incommensurate wavevectors and therefore break
+the periodicity of the spin configuration below the transition. One exception
+occurs when the field aligns with one of the principle crystal axes, in which
+case periodicity of the spin configuration is found to be maintained on a
+larger crystallographic cubic cell even below the transition. This simple case
+is studied in more detail. Comparisons are drawn with existing experimental
+data, and further experimental tests of the model are suggested.",2109.05827v1
+2021-09-15,Type-II Weyl Excitation in Vortex Arrays,"Weyl-like magnon excitations in ordered magnets have attracted significant
+recent attention. Despite of the tantalizing physics and application prospects,
+the experimental observation of Weyl magnons is still challenging owing to
+their extraordinarily high frequency that is not accessible to the microstrip
+antenna technique. Here we predict gigahertz Weyl excitations in the collective
+dynamics of dipolar-coupled magnetic vortices arranged in a three-dimensional
+stacked honeycomb lattice. It is found that the inversion symmetry breaking
+leads to the emergence of the type-II Weyl semimetal (WSM) state with tilted
+dispersion. We derive the full phase diagram of the vortex arrays that support
+WSMs with both single and double pairs of Weyl nodes, and the topological
+insulator phase. We observe robust arc surface states in a dual-segment fashion
+due to the tilted nature of type-II WSMs. Our findings uncover the
+low-frequency WSM phase in magnetic texture based crystals that are
+indispensable for future Weyltronic applications.",2109.07083v1
+2021-09-23,Magnon Landau levels in the strained antiferromagnetic honeycomb nanoribbons,"The pseudo-magnetic field created by a non-uniform unaxial strain is
+introduced into the antiferromagnetic honeycomb nanoribbons. The formation of
+magnon pseudo-Landau levels, which appear from the upper end of the spectrum
+and whose level spacings are proportional to the square root of the level
+index, is revealed by the linear spin-wave theory. The antiferromagnetic order
+is gradually weakened along the $y$-direction by the strain. At large enough
+strength, the system is decoupled into isolated zigzag chains near the upper
+boundary, and demonstrates one-dimensional magnetic property there. While the
+quantum Monte Carlo simulations also predict such a transition, this exact
+method gives a critical point deeper in the bulk. We also investigate the $XY$
+antiferromagnetic honeycomb nanoribbons, and find similar pseudo-Landau levels
+and antiferromagnetic evolution. Our results unveil the effect of a non-uniform
+unaxial strain on the spin excitaions, and may be realized experimentally based
+on two-dimensional quantum magnetic materials.",2109.11189v2
+2021-09-28,"Spin wave propagation in uniform waveguide: effects, modulation and its application","With the advent of the post-Moore era, researches on beyond-Complementary
+Metal Oxide Semiconductor (CMOS) approaches have been attracted more and more
+attention. Magnonics, or spin wave is one of the most promising technology
+beyond CMOS, which magnons-quanta for spin waves-process the information
+analogous to electronic charges in electronics. Information transmission by
+spin waves, which uses the frequency, amplitude and (or) phase to encode
+information, has a great many of advantages such as extremely low energy loss
+and wide-band frequency. Moreover, using the nonlinear characteristics of spin
+waves for information transmission can increase the extra degree of freedom of
+information. This review provides a tutorial overview over the effects of spin
+wave propagation and recent research progress in uniform spin wave waveguide.
+The propagation characteristics of spin waves in uniform waveguides and some
+special propagation phenomena such as spin wave beam splitting and
+self-focusing are described by combining experimental phenomena and theoretical
+formulas. Furthermore, we summarize methods for modulating propagation of spin
+wave in uniform waveguide, and comment on the advantages and limitations of
+these methods. The review may promote the development of information
+transmission technology based on spin waves.",2109.13464v1
+2021-10-15,Frustrated magnetism of spin-1/2 Heisenberg diamond and octahedral chains as a statistical-mechanical monomer-dimer problem,"It is evidenced that effective lattice-gas models of hard-core monomers and
+dimers afford a proper description of low-temperature features of spin-1/2
+Heisenberg diamond and octahedral chains. Besides monomeric particles assigned
+within the localized-magnon theory to bound one- and two-magnon eigenstates,
+the effective monomer-dimer lattice-gas model additionally includes dimeric
+particles assigned to a singlet-tetramer (singlet-hexamer) state as a
+cornerstone of dimer-tetramer (tetramer-hexamer) ground state of a spin-1/2
+Heisenberg diamond (octahedral) chain. A feasibility of the effective
+description is confirmed through the exact diagonalization and
+finite-temperature Lanczos methods. Both quantum spin chains display rich
+ground-state phase diagrams including discontinuous as well as continuous
+field-driven phase transitions, whereby the specific heat shows in vicinity of
+the former phase transitions an extraordinary low-temperature peak coming from
+a highly-degenerate manifold of low-lying excitations.",2110.07958v3
+2021-11-18,Magnons and Spinons in $\mathrm{Ba}_2\mathrm{CoTeO}_6 $: A Composite System of Isolated Spin-$1/2$ Triangular Heisenberg-like and Frustrated Honeycomb Ising-like Antiferromagnets,"We report the neutron scattering results on magnetic orderings and
+excitations in $\mathrm{Ba}_2\mathrm{CoTeO}_6$ composed of two almost isolated
+subsystems A and B, which are described as an $S\,{=}\,1/2$ triangular
+Heisenberg-like antiferromagnet and a frustrated honeycomb Ising-like
+antiferromagnet, respectively. Stripy ordering of subsystem B was confirmed
+below $T_{\rm N1}\,{=}\,12.0$ K, whereas sharp streaks were observed along
+$(1/3, 1/3, L)$ and $(2/3, 2/3, L)$ at 0.3 K (${\ll}\,T_{\rm N2}\,{=}\,3.0$ K).
+This indicates the two-dimensional nature of ordering in subsystem A. It was
+found that the excitation spectra of both subsystems are well separated and
+independent of each other. The excitation spectrum of subsystem A is composed
+of two single-magnon branches with roton-like minima at the M point and a
+clearly structured intense continuum, as similarly observed in
+$\mathrm{Ba}_3\mathrm{CoSb}_2\mathrm{O}_9$, which is strongly indicative of
+spinon excitations. Dispersion curves for subsystem B can be described by
+linear spin wave theory within the third-neighbor exchange interaction.",2111.09558v1
+2021-11-19,Terahertz-Light Driven Coupling of Antiferromagnetic Spins to Lattice,"Understanding spin-lattice coupling represents a key challenge in modern
+condensed matter physics, with crucial importance and implications for
+ultrafast and 2D-magnetism. The efficiency of angular momentum and energy
+transfer between spins and the lattice imposes fundamental speed limits on the
+ability to control spins in spintronics, magnonics and magnetic data storage.
+We report on an efficient nonlinear mechanism of spin-lattice coupling driven
+by THz light pulses. A nearly single-cycle THz pulse resonantly interacts with
+a coherent magnonic state in the antiferromagnet CoF2 and excites the
+Raman-active THz phonon. The results reveal the unique functionality of
+antiferromagnets allowing ultrafast spin-lattice coupling using light.",2111.10186v3
+2021-11-26,A modal approach to modelling spin wave scattering,"Efficient numerical methods are required for the design of optimised devices.
+In magnonics, the primary computational tool is micromagnetic simulations,
+which solve the Landau-Lifshitz equation discretised in time and space.
+However, their computational cost is high, and the complexity of their output
+hinders insight into the physics of the simulated system, especially in the
+case of multimode propagating wave-based devices. We propose a finite-element
+modal method allowing an efficient solution of the scattering problem for
+dipole-exchange spin waves propagating perpendicularly to the magnetisation
+direction. The method gives direct access to the scattering matrix of the whole
+system and its components. We extend the formula for the power carried by a
+magnetostatic mode in the Damon-Eshbach configuration to the case with
+exchange, allowing the scattering coefficients to be normalised to represent
+the fraction of the input power transferred to each output channel. We apply
+the method to the analysis of spin-wave scattering on a basic functional block
+of magnonic circuits, consisting of a resonator dynamically coupled to a thin
+film. The results and the method are validated by comparison with micromagnetic
+simulations.",2111.13448v2
+2021-12-03,Quasiparticle metamorphosis in the random t-J model,"Motivated by the pseudogap-Fermi liquid transition in doped Mott insulators,
+we examine the excitations of a $t$-$J$ model with random and all-to-all
+hopping and exchange. The stability of quasiparticles such as spin-1/2
+fermions, spin-1 magnons, and emergent Jordan-Wigner (JW) spinless fermions is
+cast as a problem of localization in the many-body Hilbert space, which is
+studied by the FEAST eigensolver algorithm. At low dopings, magnons and JW
+fermions are better defined than spin-1/2 fermions, which are unstable. Upon
+crossing a critical value of doping around $p_c$ = 1/3, their stabilities are
+interchanged. Near the critical doping, these quasiparticles are all found to
+be ill-defined. The critical point is thus associated with a localization
+transition in the many-body Hilbert space",2112.01760v2
+2021-12-08,Intertwining of lasing and superradiance under spintronic pumping,"We introduce a quantum optics platform featuring the minimal ingredients for
+the description of a spintronically pumped magnon condensate, which we use to
+promote driven-dissipative phase transitions in the context of spintronics. We
+consider a Dicke model weakly coupled to an out-of-equilibrium bath with a
+tunable spin accumulation. The latter is pumped incoherently in a fashion
+reminiscent of experiments with magnet-metal heterostructures. The core of our
+analysis is the emergence of a hybrid lasing-superradiant regime that does not
+take place in an ordinary pumped Dicke spin ensemble, and which can be traced
+back to the spintronics pumping scheme. We interpret the resultant
+non-equilibrium phase diagram from both a quantum optics and a spintronics
+standpoint, supplying a conceptual bridge between the two fields. The outreach
+of our results concern dynamical control in magnon condensates and
+frequency-dependent gain media in quantum optics.",2112.04509v2
+2021-12-15,Spin Waves and Dirac Magnons in a Honeycomb Lattice Zig-zag Antiferromagnet BaNi2(AsO4)2,"The topological properties of massive and massless fermionic quasiparticles
+have been intensively investigated over the past decade in topological
+materials without magnetism. Recently, the bosonic analogs of such
+quasiparticles arising from spin waves have been reported in the
+two-dimensional (2D) honeycomb lattice ferromagnet/antiferromagnet and the 3D
+antiferromagnet. Here we use time-of-flight inelastic neutron scattering to
+study spin waves of the S = 1 honeycomb lattice antiferromagnet BaNi2(AsO4)2,
+which has a zig-zag antiferromagnetic (AF) ground state identical to that of
+the Kitaev quantum spin liquid candidate alpha-RuCl3. We determine the magnetic
+exchange interactions in the zig-zag AF ordered phase, and show that spin waves
+in BaNi2(AsO4)2 have symmetry-protected Dirac points inside the Brillouin zone
+boundary. These results provide a microscopic understanding of the zig-zag AF
+order and associated Dirac magnons in honeycomb lattice magnets, and are also
+important for establishing the magnetic interactions in Kitaev quantum spin
+liquid candidates.",2112.07915v1
+2021-12-27,An Effective Field Theory of Magneto-Elasticity,"We utilize the coset construction to derive the effective field theory of
+magnon-phonon interactions in (anti)-ferromagnetic and ferrimagnetic insulating
+materials. The action is used to calculate the equations of motion which
+generalize the Landau-Lifshitz and stress equations to allow for
+magneto-acoustic couplings to all orders in the fields at lowest order in the
+derivative expansion. We also include the symmetry breaking effects due to
+Zeeman, and Dzyaloshinsky-Moriya interactions. This effective theory is a
+toolbox for the study of magneto-elastic phenomena from first principles. As an
+example we use this theory to calculate the leading order contribution to the
+magnon decay width due to its the decay into phonons.",2112.13873v3
+2022-01-17,Mode attraction in Floquet systems with memory: application to magnonics,"Level attraction is a type of mode hybridization in open systems where
+instead of forming a hybridization gap, the energy spectrum of two modes
+coalesce in a region bounded by exceptional points. We demonstrate that this
+phenomenon can be realized in a Floquet system with memory, which appears in
+describing linear excitations in a nonlinear driven system with a limit cycle.
+Linear response of the system in this state is different from its response near
+thermodynamic equilibrium. We develop a general formalism and provide an
+example in the context of cavity magnonics, where we show that magnetic
+excitations in systems driven far from the equilibrium may show level
+attraction with cavity photons. Our approach works equally well for quantum and
+semiclassical magnetic dynamics. The theory is formulated so that it can be
+used in combination with micromagnetic simulations to explore a wide range of
+experimentally interesting systems.",2201.06547v2
+2022-01-20,Superfluid-Mott insulator quantum phase transition in a cavity optomagnonic system,"The emerging hybrid cavity optomagnonic system is a very promising quantum
+information processing platform for its strong or ultrastrong photon-magnon
+interaction on the scale of micrometers in the experiment. In this paper, the
+superfluid-Mott insulator quantum phase transition in a two-dimensional cavity
+optomagnonic array system has been studied based on this characteristic. The
+analytical solution of the critical hopping rate is obtained by the mean field
+approach, second perturbation theory and Landau second order phase transition
+theory. The numerical results show that the increasing coupling strength and
+the positive detunings of the photon and the magnon favor the coherence and
+then the stable areas of Mott lobes are compressed correspondingly. Moreover,
+the analytical results agree with the numerical ones when the total excitation
+number is lower. Finally, an effective repulsive potential is constructed to
+exhibit the corresponding mechanism. The results obtained here provide an
+experimentally feasible scheme for characterizing the quantum phase transitions
+in a cavity optomagnonic array system, which will offer valuable insight for
+quantum simulations.",2201.08086v1
+2022-01-22,Dissipative generation of significant amount of photon-phonon asymmetric steering in magnomechanical interfaces,"We propose an effective approach for generating significant amount of
+entanglement and asymmetric steering between photon and phonon in a cavity
+magnomechanical system which consists of a microwave cavity and a yttrium iron
+garnet sphere. By driving the magnon mode of the yttrium iron garnet sphere
+with blue-detuned microwave field, the magnon mode can be acted as an
+engineered resevoir cools the Bogoliubov modes of microwave cavity mode and
+mechanical mode via beam-splitter-like interaction. In this way, the microwave
+cavity mode and mechanical mode are driven to two-mode squeezed states in the
+stationary limit. In particular, strong two-way and one-way asymmetric quantum
+steering between the photon and phonon modes can be obtained with even equal
+dissipation. It is very different from the conventional proposal of asymmetric
+quantum steering, where additional unbalanced losses or noises on the two
+subsystems has been imposed. Our finding may be significant to expand our
+understanding of the essential physics of asymmetric steering and extend the
+potential application of the cavity spintronics to device-independent quantum
+key distribution.",2201.08965v1
+2022-01-27,Effect of vertex corrections on the enhancement of Gilbert damping in spin pumping into a two-dimensional electron gas,"We theoretically consider the effect of vertex correction on spin pumping
+from a ferromagnetic insulator (FI) into a two-dimensional electron gas (2DEG)
+in which the Rashba and Dresselhaus spin-orbit interactions coexist. The
+Gilbert damping in the FI is enhanced by elastic spin-flipping or magnon
+absorption. We show that the Gilbert damping due to elastic spin-flipping is
+strongly enhanced by the vertex correction when the ratio of the two spin-orbit
+interactions is near a special value at which the spin relaxation time diverges
+while that due to magnon absorption shows only small modification. We also show
+that the shift in the resonant frequency due to elastic spin-flipping is
+strongly enhanced in a similar way as the Gilbert damping.",2201.11498v3
+2022-01-30,Nonreciprocal Spin Waves Driven by Left-Hand Microwaves,"It is a conventional wisdom that a left-hand microwave cannot efficiently
+excite the spin wave (SW) in ferromagnets, due to the constraint of angular
+momentum conservation. In this work, we show that the left-hand microwave can
+drive nonreciprocal SWs in the presence of a strong ellipticity-mismatch
+between the microwave and precessing magnetization. A critical frequency is
+predicted, at which the left-hand microwave cannot excite SWs. Away from it the
+SW amplitude sensitively depends on the ellipticity of left-hand microwaves, in
+sharp contrast to the case driven by right-hand ones. By tuning the microwave
+frequency, we observe a switchable SW non-reciprocity in a ferromagnetic single
+layer. A mode-dependent mutual demagnetizing factor is proposed to explain this
+finding. Our work advances the understanding of the photon-magnon conversion,
+and paves the way to designing diode-like functionalities in nano-scaled
+magnonics.",2202.00780v3
+2022-03-06,Elongated Skyrmion as Spin Torque Nano-Oscillator and Magnonic Waveguide,"Spin torque nano-oscillator has been extensively studied both theoretically
+and experimentally in recent decades due to its potential applications in
+future microwave communication technology and neuromorphic computing. In this
+work, we present a skyrmion-based spin torque nano-oscillator driven by a
+spatially uniform direct current, where the skyrmion is confined by two pinning
+sites. Different from other skyrmion-based oscillators that arise from the
+circular motion or the breathing mode of a skyrmion, the steady-state
+oscillatory motions are produced by the periodic deformation of an elongated
+skyrmion. Through micromagnetic simulations, we find that the oscillation
+frequency depends on the driving current, the damping constant as well as the
+characteristics of pinning sites. This nonlinear response to direct current
+turns out to be universal and can also appear in the case of antiskyrmions,
+skyrmioniums and domain walls. Furthermore, the elongated skyrmion possesses a
+rectangle-like domain wall, which could also serve as a magnonic waveguide.
+Utilizing the propagation of spin waves in this waveguide, we propose a device
+design of logic gate and demonstrate its performance.",2203.02969v2
+2022-03-15,Magnetic field-controlled lattice thermal conductivity in MnBi2Te4,"Phonon properties and the lattice thermal conductivity are not generally
+understood to be sensitive to magnetic fields. Using an applied field to change
+MnBi2Te4 between antiferromagnetic (AFM), canted (CAFM) and ferromagnetic (FM)
+phases we discovered a new way to control the lattice thermal conductivity,
+generating both a positive and a negative magnetic field dependence. We report
+the field dependence of the thermal conductivity, k, in the in-plane direction
+under an applied magnetic field along the cross-plane direction in MnBi2Te4
+from 2K to 30K. k decreases with field in the AFM phase, saturates in the CAFM
+phase, and increases with field in the FM phase. We explain this in terms of
+the field-induced changes of the magnon gap which modifies which magnon-phonon
+scattering processes are allowed by energy conservation. We also report
+magneto-Seebeck coefficient, Nernst coefficient and thermal Hall data measured
+in the same configuration. This finding may open a way to design magnetically
+controlled heat switches.",2203.08032v2
+2022-04-12,Stabilization and application of asymmetric Néel skyrmions in hybrid nanostructures,"Increasing amounts of information force the continuous improvement of
+information storage and processing technologies, further device
+miniaturization, and their efficiency increase. Magnetic skyrmions, topological
+quasiparticles, and the smallest stable magnetic textures possess intriguing
+properties and potential for data storage applications. Hybrid nanostructures
+with elements of different magnetization orientations can offer additional
+advantages for developing skyrmion-based spintronic and magnonic devices. We
+show that an N\'eel-type skyrmion confined within a nanodot placed on top of a
+ferromagnetic stripe produces a unique and compelling platform for exploring
+mutual coupling between magnetization textures. The skyrmion induces an imprint
+upon the stripe, which, in turn, asymmetrically squeezes the skyrmion in the
+dot, increasing their size and the range of skyrmion stability for small values
+of DMI, as well as introducing skyrmion bi-stability. At the end, we present a
+proof-of-concept technique for unconstrained transport of a skyrmion along a
+racetrack based on proposed hybrid systems. Our results demonstrate a hybrid
+structure that is promising for applications in magnonics and spintronics.",2204.05620v1
+2022-04-16,Accelerated Magnonic Motional Cooling with Deep Reinforcement Learning,"Achieving fast cooling of motional modes is a prerequisite for leveraging
+such bosonic quanta for high-speed quantum information processing. In this
+work, we address the aspect of reducing the time limit for cooling below that
+constrained by the conventional sideband cooling techniques; and propose a
+scheme to apply deep reinforcement learning (DRL) to achieve this. In
+particular, we have shown how the scheme can be used effectively to accelerate
+the dynamic motional cooling of a macroscopic magnonic sphere, and how it can
+be uniformly extended for more complex systems, for example, a tripartite
+opto-magno-mechanical system to obtain cooling of the motional mode below the
+time bound of coherent cooling. While conventional sideband cooling methods do
+not work beyond the well-known rotating wave approximation (RWA) regimes, our
+proposed DRL scheme can be applied uniformly to regimes operating within and
+beyond the RWA, and thus this offers a new and complete toolkit for rapid
+control and generation of macroscopic quantum states for application in quantum
+technologies.",2204.07710v1
+2022-04-19,Role of shape anisotropy on thermal gradient-driven domain wall dynamics in magnetic nanowires,"We investigate the magnetic domain wall (DW) dynamics in uniaxial/biaxial
+nanowires under a thermal gradient (TG). The findings reveal that the DW
+propagates toward the hotter region in both nanowires. The main physics of such
+observations is the magnonic angular momentum transfer to the DW. The hard
+(shape) anisotropy exists in biaxial nanowire, which contributes an additional
+torque, hence DW speed is larger than that in uniaxial nanowire. With lower
+damping, the DW velocity is smaller and DW velocity increases with damping
+which is opposite to usual expectation. To explain this, it is predicted that
+there is a probability to form the standing spin-waves (which do not carry net
+energy/momentum) together with travelling spin-waves if the propagation length
+of thermally-generated spin-waves is larger than the nanowire length. For
+larger-damping, DW decreases with damping since the magnon propagation length
+decreases. Therefore, the above findings might be useful in realizing the
+spintronic (racetrack memory) devices.",2204.09101v2
+2022-05-02,Switching of the information backflow between a helical spin system and non-Markovian bath,"The dissipative dynamics of the spin chain coupled to the non-Markovian
+magnonic reservoir was studied. The chirality of the chain is formed due to the
+magnetoelectric coupling. We explored the sign of the trace distance derivative
+and found the alternating positive/negative periods in system's time evolution.
+The negative sign is associated with the flow of information from the system to
+the bath and decrease in states distinguishability, while the positive sign is
+related to the flow of the information in the opposite direction and increase
+in distinguishability. We found the distinct effect of the applied electric and
+magnetic fields. While the Dzyaloshinskii-Moriya interaction and external
+electric field lead to reshuffling of the periods, the applied magnetic field
+leads to the swift positive-negative transitions. Thus, in the helical quantum
+rings coupled to the non-Markovian magnonic baths, it is possible to control
+the directions of information flow through the external fields.",2205.00985v1
+2022-05-17,"Spin Dynamics, Loop Formation and Cooperative Reversal in Artificial Quasicrystals with Tailored Exchange Coupling","Aperiodicity and un-conventional rotational symmetries allow quasicrystalline
+structures to exhibit unprecedented physical and functional properties. In
+magnetism, artificial ferromagnetic quasicrystals exhibited knee anomalies
+suggesting reprogrammable magnetic properties via nonstochastic switching.
+However, the decisive roles of short-range exchange and long-range dipolar
+interactions have not yet been clarified for optimized reconfigurable
+functionality. We report broadband spin-wave spectroscopy and X-ray
+photoemission electron microscopy on different quasicrystal lattices consisting
+of ferromagnetic Ni81Fe19 nanobars arranged on aperiodic Penrose and Ammann
+tilings with different exchange and dipolar interactions. We imaged the
+magnetic states of partially reversed quasicrystals and analyzed their
+configurations in terms of the charge model, geometrical frustration and the
+formation of flux-closure loops. Only the exchange-coupled lattices are found
+to show aperiodicity-specific collective phenomena and non-stochastic
+switching. Both, exchange and dipolarly coupled quasicrystals show magnonic
+excitations with narrow linewidths in minor loop measurements. Thereby
+reconfigurable functionalities in spintronics and magnonics become realistic.",2205.08224v1
+2022-07-19,Discrete time crystal made of topological edge magnons,"We report the emergence of time-crystalline behavior in the \pi-Berry phase
+protected edge states of a Heisenberg ferromagnet in the presence of an
+external driving field. The magnon amplification due to the external field
+spontaneously breaks the discrete time-translational symmetry, resulting in a
+discrete time crystal with a period that is twice that of the applied EM field.
+We discuss the nature and symmetry protection of the time crystalline edge
+states and their stability against various perturbations that are expected in
+real quantum magnets. We propose an experimental signature to unambiguously
+detect the time crystalline behavior and identify two recently discovered
+quasi-2D magnets as potential hosts. We present a first-of-its-kind realization
+of time crystals at topological edge states, which can be generalized and
+extrapolated to other bosonic quasi-particle systems that exhibit parametric
+pumping and topological edge states.",2207.09077v2
+2022-08-02,Finite-frequency spin conductance of a ferro-/ferrimagnetic-insulator|normal-metal interface,"The interface between a ferro-/ferrimagnetic insulator and a normal metal can
+support spin currents polarized collinear with and perpendicular to the
+magnetization direction. The flow of angular momentum perpendicular to the
+magnetization direction (""transverse"" spin current) takes place via spin torque
+and spin pumping. The flow of angular momentum collinear with the magnetization
+(""longitudinal"" spin current) requires the excitation of magnons. In this
+article we extend the existing theory of longitudinal spin transport [Bender
+and Tserkovnyak, Phys. Rev. B 91, 140402(R) (2015)] in the zero-frequency
+weak-coupling limit in two directions: We calculate the longitudinal spin
+conductance non-perturbatively (but in the low-frequency limit) and at finite
+frequency (but in the limit of low interface transparency). For the
+paradigmatic spintronic material system YIG|Pt, we find that non-perturbative
+effects lead to a longitudinal spin conductance that is ca. 40% smaller than
+the perturbative limit, whereas finite-frequency corrections are relevant at
+low temperatures < 100 K only, when only few magnon modes are thermally
+occupied.",2208.01420v1
+2022-08-15,Entanglement enhancement in cavity magnomechanics by an optical parametric amplifier,"We propose a method to enhance bipartite and tripartite entanglement in
+cavity magnomechanics using an optical parametric amplifier (OPA). We analyze
+this system and identified parametric regimes where different types of
+entanglement are enhanced. We show that a proper choice of the phase of the
+parametric amplifier leads to the enhancement of the bipartite entanglements.
+Moreover, the tripartite entanglement is also significantly enhanced in the
+presence of OPA. The OPA not only enhances the strength of entanglement but
+also increases the domain of entanglement over a wider space of detunings as
+compared to the system when no OPA is present. Similarly, the robustness of
+entanglement against temperature is also enhanced. Another important
+consequence of OPA is the fact that it relaxes the requirement of strong
+magnon-phonon coupling to generate cavity-magnon entanglement which is
+necessary for the case when OPA is not present. We believe that the presented
+scheme is a step forward to realize robust quantum entanglement using current
+technology.",2208.07207v1
+2022-08-17,Competing Incommensurate Spin Fluctuations and Magnetic Excitations in Infinite-Layer Nickelate Superconductors,"The recently discovered infinite-layer nickelates show great promise in
+helping to disentangle the various cooperative mechanisms responsible for
+high-temperature superconductivity. However, lack of antiferromagnetic order in
+the pristine nickelates presents a challenge for connecting the physics of the
+cuprates and nickelates. Here, by using a quantum many-body Green's
+function-based approach to treat the electronic and magnetic structures, we
+unveil the presence of many two- and three-dimensional magnetic stripe
+instabilities that are shown to persist across the phase diagram of LaNiO$_2$.
+Our analysis indicates that the magnetic properties of the infinite-layer
+nickelates are closer to those of the doped cuprates which host inhomogeneous
+ground states rather than the undoped cuprates. The computed magnon spectrum in
+LaNiO$_2$ is found to contain an admixture of contributions from localized and
+itinerant carriers. The theoretically obtained magnon dispersion is in accord
+with the results of the corresponding RIXS experiments. Our study gives insight
+into the origin of inhomogeneity in the infinite-layer nickelates and their
+relationship with the cuprates.",2208.08375v1
+2022-08-23,Microwave-optics Entanglement via Cavity Optomagnomechanics,"Microwave-optics entanglement is a vital component for building hybrid
+quantum networks. Here, a new mechanism for preparing stationary entanglement
+between microwave and optical cavity fields in a cavity optomagnomechanical
+system is proposed. It consists of a magnon mode in a ferrimagnetic crystal
+that couples directly to a microwave cavity mode via the magnetic dipole
+interaction, and indirectly to an optical cavity through the deformation
+displacement of the crystal. The mechanical displacement is induced by the
+magnetostrictive force and coupled to the optical cavity via radiation
+pressure. Both the opto- and magnomechanical couplings are dispersive.
+Magnon-phonon entanglement is created via magnomechanical parametric
+down-conversion, which is further distributed to optical and microwave photons
+via simultaneous optomechanical beamsplitter interaction and electromagnonic
+state-swap interaction, yielding stationary microwave-optics entanglement. The
+microwave-optics entanglement is robust against thermal noise, which will find
+broad potential applications in quantum networks and quantum information
+processing with hybrid quantum systems.",2208.10703v2
+2022-09-05,Topological edge states in dipolar zig-zag stripes,"We study the magnon spectrum of stacked zig-zag chains of point magnetic
+dipoles with an easy axis. The anisotropy due to the dipolar interactions and
+the two-point basis of the zig-zag chain unit cell combine to give rise to
+topologically non-trivial magnon bands in 2D zig-zag lattices. Adjusting the
+distance between the two sublattice sites in the unit cell causes a band
+touching, which triggers the exchange of the Chern numbers of volume bands
+switching the sign of the thermal conductivity and the sense of motion of edges
+modes in zig-zag stripes. We show that these topological features survive when
+the range of the dipolar interactions is truncated up to the second nearest
+neighbors.",2209.02019v1
+2022-09-08,Terahertz Magnetic and Lattice Excitations in van der Waals Ferromagnet VI3,"We use the synergy of infrared, terahertz, and Raman spectroscopies with DFT
+calculations to shed light on the magnetic and lattice properties of VI3. The
+structural transition at TS1 = 79 K is accompanied by a large splitting of
+polar phonon modes. Below TS1, strong ferromagnetic fluctuations are observed.
+The variations of phonon frequencies at 55 K induced by magnetoelastic coupling
+enhanced by spin-orbit interaction indicate the proximity of long-range
+ferromagnetic order. Below TC = 50 K, two Raman modes simultaneously appear and
+show dramatic softening in the narrow interval around the temperature TS2 of
+the second structural transition associated with the order-order magnetic phase
+transition. Below TS2, a magnon in the THz range appears in Raman spectra. The
+THz magnon observed in VI3 indicates the application potential of 2D van der
+Waals ferromagnets in ultrafast THz spintronics, which has previously been
+considered an exclusive domain of antiferromagnets.",2209.03725v2
+2022-09-28,Spin triangle chain with ferromagnetic and antiferromagnetic interactions on the transition line,"We investigate spin-$\frac{1}{2}$ anisotropic model of a linear chain of
+triangles with competing ferro- and antiferromagnetic interactions and
+ferromagneic Heisenberg interactions between triangles. For a certain ratio
+between interactions the one-magnon excitation band is dispersionless leading
+to an existence of localized-magnon states which form macroscopically
+degenerated ground states. The spectrum of excitations has a specific structure
+depending on the value of the triangle-triangle interaction. Such specific
+structure determines the low-temperature thermodynamics and, in particular, the
+temperature dependence of a specific heat. In the limit of strong anisotropy of
+interactions the spectrum has a multi-scale structure which consists of subsets
+rank-ordered on small parameter. Each subset is responsible for the appearance
+of the peak in the temperature dependence of the specific heat.",2209.14459v1
+2022-10-03,Chirality-induced one-way quantum steering between two waveguide-mediated ferrimagnetic microspheres,"One-way quantum steering is of importance for quantum technologies, such as
+secure quantum teleportation. In this paper, we study the generation of one-way
+quantum steering between two distant yttrium iron garnet (YIG) microspheres in
+chiral waveguide electromagonics. We consider that the magnon mode with the
+Kerr nonlinearity in each YIG sphere is chirally coupled to left- and
+right-propagating guided photons in the waveguide. We find that quantum
+steering between the magnon modes is absent with non-chirality but is present
+merely in the form of one way (i.e., one-way steering) when the chirality
+occurs. The maximal achievable steering is obviously improved as the chirality
+degree increases. We further find that when the waveguide's outputs are
+subjected to continuous homodyne detection, the steering can be considerably
+enhanced and asymmetric steering with strong entanglement can also be achieved
+by tuning the chirality. Our study shows that chirality can be explored to
+effectively realize one-way quantum steering. Compared to other studies on
+achieving asymmetric steering via controlling intrinsic dissipation, e.g.
+cavity loss rates, our scheme merely depends on the chirality enabled via
+positioning the micromagnets in the waveguide and is continuously adjustable
+and experimentally more feasible.",2210.00710v1
+2022-10-12,Electrical Seebeck-Contrast Observation of Magnon Hall Effect in Topological Ferromagnet Lu$_2$V$_2$O$_7$/Heavy Metal Heterostructures,"The observation of the magnon Hall effect (MHE) has relied solely on the
+challenging measurement of the thermal Hall conductivity. Here, we report a
+highly sensitive electrical Seebeck-contrast method for the observation of MHE
+in Lu$_2$V$_2$O$_7$/heavy metal heterostructures, that is highly desirable for
+the exploration of new MHE materials and their applications. Using measuring
+wires with very different Seebeck coefficients, we established a general method
+that can separate contributions (e.g., MHE) that generates a lateral
+temperature drop, from those [e.g., anomalous Nernst effect (ANE) and spin
+Seebeck effect (SSE)] that generate a lateral electric field. We show that a
+suitable heavy metal overlayer can eliminate the inherent ANE and SSE signals
+from the semiconducting Lu$_2$V$_2$O$_7$. The MHE in Lu$_2$V$_2$O$_7$ is
+quasi-isotropic among crystals with different orientations. In addition to the
+previously reported transverse MHE under an in-plane temperature gradient, we
+have uncovered longitudinal MHE under an out-of-plane temperature gradient.",2210.06606v2
+2022-10-26,Nonreciprocal collective magnetostatic wave modes in geometrically asymmetric bilayer structure with nonmagnetic spacer,"Nonreciprocity, i.e. inequivalence in amplitudes and frequencies of spin
+waves propagating in opposite directions, is a key property underlying
+functionality in prospective magnonic devices. Here we demonstrate
+experimentally and theoretically a simple approach to induce frequency
+nonreciprocity in a magnetostatically coupled ferromagnetic bilayer structure
+with a nonmagnetic spacer by its geometrical asymmetry. Using Brillouin light
+scattering, we show the formation of two collective spin wave modes in
+Fe$_{81}$Ga$_{19}$/Cu/Fe$_{81}$Ga$_{19}$ structure with different thicknesses
+of ferromagnetic layers. Experimental reconstruction and theoretical modeling
+of the dispersions of acoustic and optical collective spin wave modes reveal
+that both possess nonreciprocity reaching several percent at the wavenumber of
+$22~\cdot~10^4$ rad cm$^{-1}$. The analysis demonstrates that the shift of the
+amplitudes of counter-propagating coupled modes towards either of the layers is
+responsible for the nonreciprocity because of the pronounced dependence of spin
+wave frequency on the layers thickness. The proposed approach enables the
+design of multilayered ferromagnetic structures with a given spin wave
+dispersion for magnonic logic gates.",2210.14882v2
+2022-10-27,Spin-current driven Dzyaloshinskii-Moriya interaction in the multiferroic BiFeO3 from first-principles,"The electrical control of magnons opens up new ways to transport and process
+information for logic devices. In magnetoelectrical multiferroics, the
+Dzyaloshinskii-Moriya (DM) interaction directly allow for such a control and,
+hence, is of major importance. We determine the origin and the strength of the
+(converse) spin current DM interaction in the R3c bulk phase of the
+multiferroic BiFeO3 based on density functional theory. Our data supports only
+the existence of one DM interaction contribution originating from the spin
+current model. By exploring then magnon dispersion in the full Brillouin Zone,
+we show that the exchange is isotropic, but the DM interaction and anisotropy
+prefer any propagation and any magnetization direction within the full (111)
+plane. Our work emphasizes the significance of the asymmetric potential induced
+by the spin current over the structural asymmetry induced by the anionic
+octahedron in multiferroics such as BiFeO3.",2210.15591v1
+2022-11-02,Disentangling Electron-Boson Interactions on the Surface of a Familiar Ferromagnet,"We report energy renormalizations from electron-phonon and electron-magnon
+interactions in spin minority surface resonances on Ni(111). The different
+interactions are identified, disentangled, and quantified from the
+characteristic signatures they provide to the complex self-energy and the
+largely different binding energies at which they occur. The observed
+electron-magnon interactions exhibit a strong dependence on momentum and energy
+band position in the bulk Brillouin zone. In contrast, electron-phonon
+interactions from the same bands appear to be relatively momentum- and
+symmetry-independent. Additionally, a moderately strong ($\lambda>0.5$)
+electron-phonon interaction is distinguished from a near-parabolic spin
+majority band not crossing the Fermi level.",2211.01431v2
+2022-11-07,"Magnetic excitations, phase diagram and order-by-disorder in the extended triangular-lattice Hubbard model","The dynamical structure factor is an important observable of quantum magnets
+but due to numerical and theoretical limitations, it remains a challenge to
+make predictions for Hubbard-like models beyond one dimension. In this work, we
+study the magnetic excitations of the triangular lattice Hubbard model
+including next-nearest neighbor hopping. Starting from the 120$^{\circ}$ and
+stripe magnetic orders we compute the magnon spectra within a self-consistent
+random phase approximation. In the stripe phase, we generically find accidental
+zero modes related to a classical degeneracy known from the corresponding
+$J_1$-$J_2$ Heisenberg model. We extend the order-by-disorder mechanism to
+Hubbard systems and show how quantum fluctuations stabilize the stripe order.
+In addition, the frustration-induced condensation of magnon modes allows us to
+map out the entire phase diagram which is in remarkable agreement with recent
+numerical works. We discuss connections to experiments on triangular lattice
+compounds and the relation of our results to the proposed chiral spin liquid
+phase.",2211.03654v2
+2022-11-17,Optically-mediated remote entanglement generation in magnon-cavity systems,"We study the remote entanglement generation between macroscopic microwave
+magnon modes in a coupled cavity system. The cavities are connected via an
+optical fiber, which necessitates the use of a frequency conversion inside the
+cavity. The converter may be implemented via a rare-earth doped crystal acting
+like an effective three-level system. The entanglement dynamics of the system
+is analytically studied, and an active optimal control method is also proposed
+where one may generate maximally entangled Bell states on demand with a given
+evolution time. The system dynamics and its control have also been studied in a
+generic non-Markovian open system framework, and the generated entanglement is
+found to be robust against environmental noises.",2211.09315v1
+2022-11-20,Plasmon-magnon interactions in two-dimensional honeycomb magnets,"Two-dimensional honeycomb ferromagnets offer the unprecedented opportunity to
+study interactions between collective modes that in standard bulk ferromagnets
+do not cross paths. Indeed, they harbor an optical spin-wave branch, i.e. a
+spin wave which disperses weakly near the Brillouin zone center. When doped
+with free carriers, they also host the typical gapless plasmonic mode of 2D
+itinerant electron/hole systems. When the plasmon branch meets the optical
+spin-wave branch, energy and momentum matching occurs, paving the way for
+interactions between the charge and spin sector. In this Letter we present a
+microscopic theory of such plasmon-magnon interactions, which is based on a
+double random phase approximation. We comment on the possibility to unveil this
+physics in recently isolated 2D honeycomb magnets such as ${\rm Cr}_2{\rm
+Ge}_2{\rm Te}_6$.",2211.11098v1
+2022-11-24,Dynamical Backaction Evading Magnomechanics,"The interaction between magnons and mechanical vibrations dynamically modify
+the properties of the mechanical oscillator, such as its frequency and decay
+rate. Known as dynamical backaction, this effect is the basis for many
+theoretical protocols, such as entanglement generation or mechanical
+ground-state cooling. However, dynamical backaction is also detrimental for
+specific applications. Here, we demonstrate the implementation of a cavity
+magnomechanical measurement that fully evades dynamical backaction effects.
+Through careful engineering, the magnomechanical scattering rate into the
+hybrid magnon-photon modes can be precisely matched, eliminating dynamical
+backaction damping. Backaction evasion is confirmed via the measurement of a
+drive-power-independent mechanical linewidth.",2211.13766v3
+2022-11-30,Enhancement of magnon-photon-phonon entanglement in a cavity magnomechanics with coherent feedback loop,"We propose a scheme to improve magnon-photon-phonon entanglement in cavity
+magnomechanics using coherent feedback loop. In addition, we prove that the
+steady state and dynamical state of the system is a genuine tripartite
+entanglement state. We use the logarithmic negativity as the witness of quantum
+correlations to quantify the entanglement of all bipartite subsystem, and
+genuine tripartite entanglement via the nonzero minimum residual contangle, in
+steady and dynamical regime. We consider the feasible experiment parameters to
+realize the tripartite entanglement. We show that the entanglement can be
+significantly improved with coherent feedback using a suitable tuning of the
+reflective parameter of the beam splitter. The entanglement is robust against
+the thermal effects. Our proposal scheme to improve the entanglement can be of
+interest to applications in quantum information.",2211.17052v1
+2022-12-02,Surface Ferron Excitations in Ferroelectrics and Their Directional Routing,"The duality between the electric and magnetic dipoles inspires recent
+comparisons between ferronics and magnonics. Here we predict surface
+polarization waves or ``ferrons"" in ferroelectric insulators, taking the
+long-range dipolar interaction into account. We predict properties that are
+strikingly different from the magnetic counterpart, \textit{i.e.} the surface
+``Damon-Eshbach"" magnons in ferromagnets. The dipolar interaction pushes the
+ferron branch with locked circular polarization and momentum to the ionic
+plasma frequency. The low-frequency modes are on the other hand in-plane
+polarized normal to their wave vectors. The strong anisotropy of the lower
+branch renders directional emissions of electric polarization and chiral near
+fields when activated by a focused laser beam, allowing optical routing in
+ferroelectric devices.",2212.01047v2
+2022-12-08,Exploring High Frequency Gravitational Waves with Magnons,"Detecting gravitational waves with frequencies higher than 10 kHz requires
+new strategies. In previous papers, we proposed magnon gravitational wave
+detectors and gave the first limit on GHz gravitational waves by reinterpreting
+the existing data from axion dark matter experiments. In this paper, we show
+that the sensitivity can be improved by constructing the detector specific to
+gravitational waves. In particular, we employ an infinite sum of terms in the
+expansion of Fermi normal coordinates to probe gravitational waves with a
+wavelength comparable to the detector size. As a consequence, we obtain
+sensitivity of around $h_c \sim 10^{-20}$.",2212.04094v2
+2022-12-14,High-angular momentum excitations in collinear antiferromagnet FePS$_3$,"We report on magneto-optical studies of the quasi-two-dimensional van der
+Waals antiferromagnet FePS$_3$. Our measurements reveal an excitation that
+closely resembles the antiferromagnetic resonance mode typical of easy-axis
+antiferromagnets, nevertheless, it displays an unusual, four-times larger
+Zeeman splitting in an applied magnetic field. We identify this excitation with
+an $|S_z|=4$ multipolar magnon -- a single-ion 4-magnon bound state -- that
+corresponds to a full reversal of a single magnetic moment of the Fe$^{2+}$
+ion. We argue that condensation of multipolar magnons in large-spin materials
+with a strong magnetic anisotropy can produce new exotic states.",2212.07221v1
+2022-12-18,Ground-state cooling of a massive mechanical oscillator by feedback in cavity magnomechanics,"Cooling the motion of a massive mechanical oscillator into its quantum ground
+state plays an essential role in observing macroscopic quantum effects in
+mechanical systems. Here we propose a measurement-based feedback cooling
+protocol in cavity magnomechanics that is able to cool the mechanical vibration
+mode of a macroscopic ferromagnet into its ground state. The mechanical mode
+couples to a magnon mode via a dispersive magnetostrictive interaction, and the
+latter further couples to a microwave cavity mode via the magnetic-dipole
+interaction. A feedback loop is introduced by measuring the amplitude of the
+microwave cavity output field and applying a force onto the mechanical
+oscillator that is proportional to the amplitude fluctuation of the output
+field. We show that by properly designing the feedback gain, the mechanical
+damping rate can be significantly enhanced while the mechanical frequency
+remains unaffected. Consequently, the vibration mode can be cooled into its
+quantum ground state in the unresolved-sideband regime at cryogenic
+temperatures. The protocol is designed for cavity magnomechanical systems using
+ferromagnetic materials which possess strong magnetostriction along with large
+magnon dissipation.",2212.09002v1
+2023-02-06,Thermal Hall effect in a van der Waals triangular magnet FeCl2,"Thermal transport is a pivotal probe for studying low-energy, charge-neutral
+quasi-particles in insulating magnets. In this Letter, we report an observation
+of large magneto-thermal conductivity and thermal Hall effect (THE) in a van
+der Waals antiferromagnet FeCl2. The magneto-thermal conductivity reaches over
+~700%, indicating strong magnon-phonon coupling. Furthermore, we find an
+appreciable thermal Hall signal which changes sign concurrently with the
+spin-flip transition from the antiferromagnetic state to the polarized
+ferromagnetic state. Our theoretical calculations suggest that, in addition to
+the Berry curvature induced at the anticrossing points of the hybridized magnon
+and acoustic phonon modes of FeCl2, other mechanisms are needed to account for
+the magnitude of the observed THE.",2302.02855v1
+2023-02-15,Superradiant phase transition induced by the indirect Rabi interaction,"We theoretically study the superradiant phase transition (SPT) in an indirect
+Rabi model, where both a two-level system and a single mode bosonic field
+couple to an auxiliary bosonic field. We find that the indirect spin-field
+coupling induced by the virtual excitation of the auxiliary field can allow the
+occurrence of a SPT at a critical point, and the influence of the so-called
+$A^2$ term in the normal Rabi model is naturally avoided. In the large detuning
+regime, we present the analytical expression of quantum critical point in terms
+of the original system parameters. The critical atom-field coupling strength is
+tunable, which will loosen the conditions on realizing the SPT. Considering a
+hybrid magnon-cavity-qubit system, we predict the squeezed cat state of magnon
+generated with feasible experimental parameters, which has potential
+applications in quantum metrology and quantum information processing.",2302.07506v1
+2023-02-20,Optimizing the magnon-phonon cooperativity in planar geometries,"Optimizing the cooperativity between two distinct particles is an important
+feature of quantum information processing. Of particular interest is the
+coupling between spin and phonon, which allows for integrated long range
+communication between gates operating at GHz frequency. Using local light
+scattering, we show that, in magnetic planar geometries, this attribute can be
+tuned by adjusting the orientation and strength of an external magnetic field.
+The coupling strength is enhanced by about a factor of 2 for the out-of-plane
+magnetized geometry where the Kittel mode is coupled to circularly polarized
+phonons, compared to the in-plane one where it couples to linearly polarized
+phonons. We also show that the overlap between magnon and phonon is maximized
+by matching the Kittel frequency with an acoustic resonance that satisfies the
+half-wave plate condition across the magnetic film thickness. Taking the
+frequency dependence of the damping into account, a maximum cooperativity of
+about 6 is reached in garnets for the normal configuration near 5.5 GHz.",2302.09936v2
+2023-02-21,Aluminium substituted yttrium iron garnet thin films with reduced Curie temperature,"Magnetic garnets such as yttrium iron garnet (Y$_3$Fe$_5$O$_{12}$, YIG) are
+widely used in spintronic and magnonic devices. Their magnetic and
+magneto-optical properties can be modified over a wide range by tailoring their
+chemical composition. Here, we report the successful growth of Al-substituted
+yttrium iron garnet (YAlIG) thin films via radio frequency sputtering in
+combination with an ex situ annealing step. Upon selecting appropriate process
+parameters, we obtain highly crystalline YAlIG films with different Al$^{3+}$
+substitution levels on both, single crystalline Y$_3$Al$_5$O$_{12}$ (YAG) and
+Gd$_3$Ga$_5$O$_{12}$ (GGG) substrates. With increasing Al$^{3+}$ substitution
+levels, we observe a reduction of the saturation magnetisation as well as a
+systematic decrease of the magnetic ordering temperature to values well below
+room temperature. YAlIG thin films thus provide an interesting material
+platform for spintronic and magnonic experiments in different magnetic phases.",2302.10517v2
+2023-03-15,Acoustically driven magnon-phonon coupling in a layered antiferromagnet,"Harnessing the causal relationships between mechanical and magnetic
+properties of van der Waals materials presents a wealth of untapped opportunity
+for scientific and technological advancement, from precision sensing to novel
+memories. This can, however, only be exploited if the means exist to
+efficiently interface with the magnetoelastic interaction. Here, we demonstrate
+acoustically-driven spin-wave resonance in a crystalline antiferromagnet,
+chromium trichloride, via surface acoustic wave irradiation. The resulting
+magnon-phonon coupling is found to depend strongly on sample temperature and
+external magnetic field orientation, and displays a high sensitivity to
+extremely weak magnetic anisotropy fields in the few~mT range. Our work
+demonstrates a natural pairing between power-efficient strain-wave technology
+and the excellent mechanical properties of van der Waals materials,
+representing a foothold towards widespread future adoption of dynamic
+magneto-acoustics.",2303.08305v1
+2023-03-27,Non-linear magnon transport in a bilayer van der Waals antiferromagnets,"In this paper, we study the Berry curvature induced linear and nonlinear
+magnon transport in bilayer van der Waals antiferromagnets, where we deduce
+forms for the spin and energy currents within the semiclassical Boltzmann
+formalism under the relaxation time approximation. Even in the absence of the
+Dzyaloshinskii-Moriya interaction, if we turn on the layer-dependent
+electrostatic doping (ED) potential and anisotropy in the Heisenberg
+interactions, the linear response remains zero, whereas, we obtain a nonzero
+nonlinear thermal Hall response resulting from higher moments of the Berry
+curvature. We show that, there is a sign reversal of nonlinear thermal Hall
+conductivity with varying strength of ED potential, which can be potentially
+useful in spin-based technologies. We also comment on the momentum and
+temperature dependence of the relaxation time which can influence the transport
+properties.",2303.15426v1
+2023-04-05,Pinch points and half moons encode Berry curvature,"""Half moons"", distinctive crescent patterns in the dynamical structure
+factor, have been identified in inelastic neutron scattering experiments for a
+wide range of frustrated magnets. In an earlier paper [H. Yan et al., Phys.
+Rev. B 98, 140402(R) (2018)] we have shown how these features are linked to the
+local constraints realized in classical spin liquids. Here we explore their
+implication for the topology of magnon bands. The presence of half moons
+indicates a separation of magnetic degrees of freedom into irrotational and
+incompressible components. Where bands satisfying these constraints meet, it is
+at a singular point encoding Berry curvature of $\pm 2\pi$. Interactions which
+mix the bands open a gap, resolving the singularity, and leading to bands with
+finite Berry curvature, accompanied by characteristic changes to half--moon
+motifs. These results imply that inelastic neutron scattering can, in some
+cases, be used to make rigorous inference about the topological nature of
+magnon bands.",2304.02203v2
+2023-04-05,Control of 4-magnon-scattering in a magnonic waveguide by pure spin current,"We use a pure spin current originating from the spin Hall effect to generate
+a spin-orbit torque (SOT) strongly reducing the effective damping in an
+adjacent ferromagnet. Due to additional microwave excitation, large spin-wave
+amplitudes are achieved exceeding the threshold for 4-magnon scattering, thus
+resulting in additional spin-wave signals at discrete frequencies. Two or more
+modes are generated below and above the directly pumped mode with equal
+frequency spacing. It is shown how this nonlinear process can be controlled in
+magnonic waveguides by the applied dc current and the microwave pumping power.
+The sudden onset of the nonlinear effect after exceeding the thresholds can be
+interpreted as spiking phenomenom which makes the effect potentially
+interesting for neuromorphic computing applications. Moreover, we investigated
+this effect under microwave frequency and external field variation. The
+appearance of the additional modes was investigated in the time-domain
+revealing a time delay between the directly excited and the simultaneously
+generated nonlinear modes. Furthermore, spatially resolved measurements show
+different spatial decay lengths of the directly pumped mode and nonlinear
+modes.",2304.02708v1
+2023-05-04,Integrating Magnons for Quantum Information,"Magnons, the quanta of collective spin excitations in magnetically ordered
+materials, have distinct properties that make them uniquely appealing for
+quantum information applications. They can have ultra-small wavelengths down to
+the nanometer scale even at microwave frequencies. They can provide coupling to
+a diverse set of other quantum excitations, and their inherently gyrotropic
+dynamics forms the basis for pronounced non-reciprocities. In this article we
+discuss what the current research challenges are for integrating magnetic
+materials into quantum information systems and provide a perspective on how to
+address them.",2305.03164v1
+2023-05-05,Coexistence of Dirac Fermions and Magnons in a Layered Two-Dimensional Semiquinoid Metal-Organic Framework,"We predict the magnetic and electronic properties of a novel metal-organic
+framework. By combining density functional theory and density matrix
+renormalization group approaches, we find the diatomic Kagome crystal structure
+of the metal-semiquinoid framework (H$_2$NMe$_2$)$_2$M$_2$(Cl$_2$dhbq)$_3$ (M =
+Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) to host a rich variety of
+antiferromagnetic (AFM) and ferromagnetic (FM) Dirac semimetallic,
+spin-polarized Dirac fermions, and flat band magnetic insulators and metallic
+phases. Concomitantly, the spin excitation spectrum of the various magnetic
+systems display multiple Dirac-like and nodal-ring crossings. This suggests
+that the metal-semiquinoid system is an ideal platform for examining the
+intertwining of Dirac fermions and magnons.",2305.03867v2
+2023-05-07,Lectures on spintronics and magnonincs,"In this series of lectures, we discuss the basic theoretical concepts of
+magnonics and spintronics. We first briefly recall the relevant topics from
+quantum mechanics, electrodynamics of continuous media, and basic theory of
+magnetism. We then discuss the classical theory of magnetic dynamics:
+ferromagnetic and antiferromagnetic resonance, dynamic susceptibilities, and
+spin waves. We open the main discussion with phenomena of spin and exchange
+spin currents, spin torques, the spin Hall effect, and the spin Hall and Hanle
+magnetoresistance. Special emphasis is given to the effects of spin transfer
+torque and spin pumping, where we follow the celebrated derivation utilizing
+Landauer quantum multi-channel scattering matrix approach. Finally, we outline
+the most important features distinguishing antiferromagnetic dynamics from
+ferromagnetic one, which make antiferromagnets particularly promising material
+candidates for spintronics and magnonics.",2305.04385v1
+2023-05-10,Investigation of Spin-Wave Dynamics in Gyroid Nanostructures,"A new concept in magnonics studies the dynamics of spin waves (SWs) in
+three-dimensional nanosystems. It is a natural evolution from conventionally
+used planar systems to explore magnetization configurations and dynamics in 3D
+nanostructures with lengths near intrinsic magnetic scales. In this work, we
+perform broadband ferromagnetic resonance (BBFMR) measurements and
+micromagnetic simulations of nanoscale magnetic gyroids - a periodic chiral
+structure consisting entirely of chiral triple junctions. Our results show
+unique properties of the network, such as the localization of the SW modes,
+evoking their topological properties, and the substantial sensitivity to the
+direction of the static magnetic field. The presented results open a wide range
+of applications in the emerging field of 3D magnonic crystals and spintronics.",2305.06319v2
+2023-05-31,Magnetization dynamics in a three-dimensional interconnected nanowire array,"Three-dimensional magnetic nanostructures have recently emerged as artificial
+magnetic material types with unique properties bearing potential for
+applications, including magnonic devices. Interconnected magnetic nanowires are
+a sub-category within this class of materials that is attracting particular
+interest. We investigate the high-frequency magnetization dynamics in a cubic
+array of cylindrical magnetic nanowires through micromagnetic simulations based
+on a frequency-domain formulation of the linearized Landau-Lifshitz-Gilbert
+equation. The small-angle high-frequency magnetization dynamics excited by an
+external oscillatory field displays clear resonances at distinct frequencies.
+These resonances are identified as oscillations connected to specific geometric
+features and micromagnetic configurations. The geometry- and
+configuration-dependence of the nanowire array's absorption spectrum
+demonstrates the potential of such magnetic systems for tuneable and
+reprogrammable magnonic applications.",2306.00174v1
+2023-06-15,Efficient Spin Seebeck and Spin Nernst Effects of Magnons in Altermagnets,"We report two non-degenerate magnon modes with opposite spins or chiralities
+in collinearly antiferromagnetic insulators driven by symmetry-governed
+anisotropic exchange couplings. The consequent giant spin splitting contributes
+to spin Seebeck and spin Nernst effects generating longitudinal and transverse
+spin currents when the temperature gradient applies along and away from the
+main crystal axis, without requiring any external magnetic field and spin-orbit
+coupling. Based on first-principle calculations, we predict feasible material
+candidates holding robust altermagnetic spin configurations and
+room-temperature structural stability to efficiently transport spin. The spin
+Seebeck conductivity is comparable to the records of antiferromagnets that
+require the magnetic field, and the spin Nernst conductivity is two orders in
+magnitude larger than that in antiferromagnetic monolayers that need Berry
+curvature.",2306.08976v2
+2023-06-23,Spin transport between polarized Fermi gases near the ferromagnetic phase transition,"We theoretically study the spin current between two polarized Fermi gases
+with repulsive interactions near the itinerant ferromagnetic phase transition.
+We consider a two-terminal model where the left reservoir is fixed to be fully
+polarized while the polarization of the right reservoir is tuned through a
+fictitious magnetic field defined by the chemical-potential difference between
+different atomic hyperfine states. We calculate the spectra of the spin-flip
+susceptibility function, which displays a magnon dispersion emerging from the
+Stoner continuum at low momentum in the ferromagnetic phase. Based on the
+spin-flip susceptibility and using Keldysh Green's function formalism, we
+investigate the spin current induced by quasiparticle and spin-flip tunneling
+processes, respectively, and show their dependence on the polarization bias
+between two reservoirs. The one-body (quasiparticle) tunneling demonstrates a
+linear dependence with respect to the polarization bias. In contrast, the
+spin-flip process manifests a predominantly cubic dependence on the bias. While
+indicating an enhanced magnon tunneling in the strong-coupling regime, our
+results also demonstrate a characteristic behavior around the critical
+repulsive strength for ferromagnetic phase transition at low temperatures.",2306.13536v2
+2023-07-13,Magnon-magnon coupling in synthetic ferrimagnets,"Magnetic multilayers with interlayer exchange coupling have been widely
+studied for both static and dynamic regimes. Their dynamical responses depend
+on the exchange coupling strength and magnetic properties of individual layers.
+Magnetic resonance spectra in such systems are conveniently discussed in terms
+of coupling of acoustic and optical modes. At a certain value of applied
+magnetic field, the two modes come close to being degenerate and the spectral
+gap indicates the strength of mode hybridisation. In this work, we
+theoretically and experimentally study the mode hybridisation of
+interlayer-exchange-coupled moments with dissimilar magnetisation and thickness
+of two ferromagnetic layers. In agreement with symmetry analysis for
+eigenmodes, our low-symmetry multilayers exhibit sizable spectral gaps for all
+experimental conditions. The spectra agree well with the predictions from the
+Landau-Lifshitz-Gilbert equation at the macrospin limit whose parameters are
+independently fixed by static measurements.",2307.06888v2
+2023-08-22,Observation of Current-induced Nonlinear Spin Polarization in Pt-Py Bilayers,"We experimentally observe nonlinear spin polarization in metallic bilayers of
+platinum and permalloy by means of spin-torque ferromagnetic resonance (ST-FMR)
+with the spin-Hall effects. The ST-FMR results under massive dc current
+injection contain striking features, which are not caused by extrinsic Joule
+heating, but by intrinsic nonlinear spin polarization. The emergence of
+nonlinear spin polarization is consistent with observation of unidirectional
+spin-Hall magnetoresistance due to magnon generation/annihilation. Moreover,
+the magnon generation (annihilation) leads to effective magnetization shrinkage
+(expansion) revealed by the ST-FMR measurements. The present study paves a way
+to spin-Hall effect based nonlinear spintronic devices as well as
+6th-generation mobile communication light sources.",2308.11156v2
+2023-08-28,Spin-wave spectral analysis in crescent-shaped ferromagnetic nanorods,"The research on the properties of spin waves (SWs) in three-dimensional
+nanosystems is an innovative idea in the field of magnonics. Mastering and
+understanding the nature of magnetization dynamics and binding of SWs at
+surfaces, edges, and in-volume parts of three-dimensional magnetic systems
+enables the discovery of new phenomena and suggests new possibilities for their
+use in magnonic and spintronic devices. In this work, we use numerical methods
+to study the effect of geometry and external magnetic field manipulations on
+the localization and dynamics of SWs in crescent-shaped (CS) waveguides. It is
+shown that changing the magnetic field direction in these waveguides breaks the
+symmetry and affects the localization of eigenmodes with respect to the static
+demagnetizing field. This in turn has a direct effect on their frequency.
+Furthermore, CS structures were found to be characterized by significant
+saturation at certain field orientations, resulting in a cylindrical
+magnetization distribution. Thus, we present chirality-based nonreciprocal
+dispersion relations for high-frequency SWs, which can be controlled by the
+field direction (shape symmetry) and its amplitude (saturation).",2308.14678v1
+2023-09-13,Looking at the magnetic properties of half metal from the paramagnetic phase: DFT+DMFT study of exchange interactions in CrO$_2$,"We study magnetic properties of CrO$_2$ within the density functional theory
+plus dynamical mean-field theory (DFT+DMFT) approach in the paramagnetic phase.
+We consider the 3-orbital (per Cr site) model, containing only $t_{2g}$ states,
+the $5$-orbital model, including all $d$-states, as well as the model including
+also the oxygen $p$-states. Using the recently proposed approach of calculation
+of exchange interactions in paramagnetic phase, we extract exchange interaction
+parameters and magnon dispersions for these models. While the magnon dispersion
+in the 3-orbital model possesses negative branches in accordance with previous
+studies in ferromagnetic phase, this drawback is removed in the $5$-orbital
+model. The model containing oxygen states overestimates the exchange
+interactions and spin stiffness. Therefore, the $5$-orbital model appears as
+most adequate for describing magnetic properties of CrO$_2$, in accordance with
+the recent experimental data of fixed valence of chromium in this compound. The
+possibility of describing magnetic properties of this material starting from
+paramagnetic phase points to the correspondence of magnetic properties in this
+phase and ferromagnetic phase and possible important contributions of RKKY
+exchange interactions in paramagnetic phase of CrO$_2$.",2309.06892v1
+2023-10-19,Micromagnetic Simulation of Three-dimensional Nanoarchitectures,"The thesis discusses micromagnetic simulation studies on high-frequency
+magnetic dynamics in three-dimensional ferromagnetic nanoarchitectures made of
+interconnected magnetic nanowire networks. Such artificial magnetic materials
+with nanoscale features have recently emerged as a vivid topic of research, as
+their geometry has a decisive impact on their magnetic properties. By studying
+their static magnetization structure, we find that these systems display a
+behavior analogous to that of 3D artificial spin ice lattices, with frustrated
+interactions and the emergence of monopole-like defect structures at the wires'
+intersection points. Our simulations reveal a high activity of these defect
+sites in the magnonic high-frequency spectrum. We study various 3D
+nanoarchitectures and show that their geometry and magnetization state results
+in characteristic high-frequency signatures. Controlling these features could
+open new pathways for magnonics research and reprogrammable magnetic
+metamaterials.",2310.12839v1
+2023-11-03,Cryogenic spin Peltier effect detected by a RuO$_2$-AlO$_x$ on-chip microthermometer,"We report electric detection of the spin Peltier effect (SPE) in a bilayer
+consisting of a Pt film and a Y$_{3}$Fe$_5$O$_{12}$ (YIG) single crystal at the
+cryogenic temperature $T$ as low as 2 K based on a RuO$_2$$-$AlO$_x$ on-chip
+thermometer film. By means of a reactive co-sputtering technique, we
+successfully fabricated RuO$_2$$-$AlO$_x$ films having a large temperature
+coefficient of resistance (TCR) of $\sim 100\% ~\textrm{K}^{-1}$ at around
+$2~\textrm{K}$. By using the RuO$_2$$-$AlO$_x$ film as an on-chip temperature
+sensor for a Pt/YIG device, we observe a SPE-induced temperature change on the
+order of sub-$\mu \textrm{K}$, the sign of which is reversed with respect to
+the external magnetic field $B$ direction. We found that the SPE signal
+gradually decreases and converges to zero by increasing $B$ up to
+$10~\textrm{T}$. The result is attributed to the suppression of magnon
+excitations due to the Zeeman-gap opening in the magnon dispersion of YIG,
+whose energy much exceeds the thermal energy at 2 K.",2311.01711v1
+2023-11-13,Microwave-to-Optical Quantum Transduction Utilizing the Topological Faraday Effect of Topological Insulator Heterostructures,"The quantum transduction between microwave and optical photons is essential
+for realizing scalable quantum computers with superconducting qubits. Due to
+the large frequency difference between microwave and optical ranges, the
+transduction needs to be done via intermediate bosonic modes or nonlinear
+processes. So far, the transduction efficiency $\eta$ via the magneto-optic
+Faraday effect (i.e., the light-magnon interaction) in the ferromagnet YIG has
+been demonstrated to be small as $\eta\sim 10^{-8} \mathrm{-} 10^{-15}$ due to
+the sample size limitation inside the cavity. Here, we take advantage of the
+fact that three-dimensional topological insulator thin films exhibit a
+topological Faraday effect that is independent of the sample thickness. This
+leads to a large Faraday rotation angle and therefore enhanced light-magnon
+interaction in the thin film limit. We show theoretically that the transduction
+efficiency can be greatly improved to $\eta\sim10^{-4}$ by utilizing the
+heterostructures consisting of topological insulator thin films such as
+Bi$_2$Se$_3$ and ferromagnetic insulator thin films such as YIG.",2311.07293v1
+2023-12-13,Detection of Geometric Phases in Spin Waves using Nitrogen-Vacancy Centers,"Due to their robustness, the implementation of geometric phases provides a
+reliable and controllable way to manipulate the phase of a spin wave, thereby
+paving the way towards functional magnonics-based data processing devices.
+Moreover, geometric phases in spin waves are interesting from a fundamental
+perspective as they contain information about spin wave band structures and
+play an important role in magnon Hall effects. In this paper we propose to
+directly measure geometric phases in spin wave systems using the magnetic field
+sensing capabilities of nitrogen-vacancy (NV) centers. We demonstrate the
+general principles of this method on two systems in which spin waves acquire a
+geometric phase, namely a wire with a magnetic domain wall and a system with
+position-dependent anisotropy axes, and explicitly show how this phase can be
+deduced from the NV center signal.",2312.08137v1
+2023-12-18,Fractional Topological Charges in 2D Magnets,"Magnetic skyrmions and antiskyrmions are characterised by an integer
+topological charge $\mathcal Q =\mp 1$, describing the winding of the magnetic
+orientation. Half-integer winding numbers, $\mathcal Q=\pm \frac{1}{2}$, can be
+obtained for magnetic vortices (merons). Here, we discuss the physics of
+magnets with fractional topological charge which is neither integer nor
+half-integer. We argue that in ferromagnetic films with cubic anisotropy,
+textures with $\mathcal Q=\pm\frac{1}{6} $ or $\pm\frac{1}{8}$ arise naturally
+when three or more magnetic domains meet. We also show that a single magnetic
+skyrmion with $\mathcal Q =-1$ can explode into four fractional defects, each
+carrying charge $\mathcal Q=-\frac{1}{4}$. Additionally, we investigate a point
+defect with a non-quantised fractional charge ($\mathcal Q\neq \frac{n}{m},
+n,m\in\mathbb{Z}$) which can move parallel to a magnetic domain wall. Only
+defects with fractional charge lead to an Aharonov-Bohm effect for magnons. We
+investigate the resulting forces on a fractional defect due to magnon currents.",2312.11435v1
+2023-12-20,Beyond the Tensionless Limit: Integrability in the Symmetric Orbifold,"The symmetric orbifold of $\mathbb{T}^4$ is exactly dual to string theory on
+$\mathrm{AdS}_3\times \mathrm{S}^3 \times \mathbb{T}^4$ with minimal ($k=1$)
+NS-NS flux. In this paper we study the perturbation of the symmetric orbifold
+that is dual to switching on R-R flux, and hence to deforming the theory away
+from the tensionless point. More specifically, we determine systematically the
+action of a centrally extended supersymmetry algebra on the CFT states, and
+deduce from it the anomalous conformal dimensions. In the $w$-twisted sector
+with large $w$ the structure is similar to what was found for $\mathcal{N}=4$
+SYM: the basic excitations are multi-magnons whose individual dispersion
+relation is fixed by symmetry, and the comparison with the BMN answer suggests
+that the result is true to all orders in perturbation theory. Finally we show
+that the multi-magnon states interact via an integrable $S$-matrix and possess
+a natural family of bound states.",2312.13288v2
+2023-12-25,Entangling two Dicke states in a periodic modulated quantum system,"We propose a theoretical approach for entangling two Dicke states in a
+periodic modulated quantum system. By considering two qubit ensembles that are
+nonuniformly coupled to a common resonator, we can derive an effective
+Hamiltonian whose energy levels depend nonlinearly on the excitation number of
+each qubit ensemble. More simplified effective Hamiltonian can be obtained by
+selecting appropriate driving parameters and initial state. Based on the
+dynamic evolution of the effective Hamiltonian, we can selectively achieve
+Dicke state transitions and generate entangled Dicke states controllably. For a
+special case, we can obtain ensemble-ensemble entangled states by performing a
+projective even-odd cat measurement. By implementing Gaussian soft temporal
+modulation, we can effectively suppress off-resonant contributions in the
+interaction and enhance the fidelity of target states. Furthermore, by
+utilizing the Holstein-Primakoff transformation, we study the
+resonator-ensemble coupling system in the thermodynamic limit and investigate
+the generation of entangled magnon states. Additionally, we propose a scheme of
+creating magnon NOON states through frequency modulation and study the
+influence of decoherence on the fidelity of target states.",2312.15568v1
+2024-01-16,"Influence of temperature, doping, and amorphization on the electronic structure and magnetic damping of iron","Hybrid magnonic quantum systems have drawn increased attention in recent
+years for coherent quantum information processing, but too large magnetic
+damping is a persistent concern when metallic magnets are used. Their intrinsic
+damping is largely determined by electron-magnon scattering induced by
+spin-orbit interactions. In the low scattering limit, damping is dominated by
+intra-band electronic transitions, which has been theoretically shown to be
+proportional to the electronic density of states at the Fermi level. In this
+work, we focus on body-centered-cubic iron as a paradigmatic ferromagnetic
+material. We comprehensively study its electronic structure using
+first-principles density functional theory simulations and account for finite
+lattice temperature, boron (B) doping, and structure amorphization. Our results
+indicate that temperature induced atomic disorder and amorphous atomic
+geometries only have a minor influence. Instead, boron doping noticeably
+decreases the density of states near the Fermi level with an optimal doping
+level of 6.25%. In addition, we show that this reduction varies significantly
+for different atomic geometries and report that the highest reduction
+correlates with a large magnetization of the material. This may suggest
+materials growth under external magnetic fields as a route to explore in
+experiment.",2401.08076v1
+2024-01-25,Enhancing Weak magnetic field sensing of cavity-magnon system with dual frequency modulation,"The crucial limitation of improving the sensitivity of the detection of weak
+magnetic fields is the unavoidable measurement noise. In this paper, we propose
+a scheme to achieve precise sensing robust against additional noise by
+employing a dual-frequency bias field modulation within a cavity magnon system.
+We find that the anti-rotating wave term can amplify the signal of the detected
+magnetic field, but this amplification effect must coexist with the rotating
+wave term. In particular, by the bias field modulation, we find the robustness
+against cavity field thermal noise is substantially enhanced, quantum noise and
+cavity field thermal noise is greatly reduced, and the external magnetic field
+signal is amplified, thereby improving the weak magnetic field sensing system's
+sensitivity. Compared with the previous scheme, our scheme requires neither an
+ultra- or deep-strong coupling mechanism nor the suppression of the additional
+noise by increasing the electromagnetic cooperativity. Our scheme could provide
+a valuable candidate for weak magnetic field sensing.",2401.13879v1
+2024-02-07,Broadband squeezed light field by magnetostriction in an opto-magnomechanical,"We present a novel mechanism for generating a wide bandwidth squeezed optical
+output field in an opto-magnomechanical system. In this system, the magnon
+(mechanical) mode in the yttrium-iron-garnet crystal is coupled to the
+microwave field (optical field) through magnetic dipole (radiation pressure)
+interaction. The magnetostrictive force induced by the yttrium-iron-garnet
+crystal causes a mechanical displacement and creates a quadrature squeezed
+magnon mode. Eventually, this quadrature squeezed mechanical mode is
+transferred to the output optical field through state-swap interaction. Our
+results demonstrate the optimal parameter range for obtaining a stable squeezed
+optical output field with a wide bandwidth. Moreover, the squeezed light field
+exhibits strong robustness to environmental temperature. The new scheme we
+propose has potential applications in quantum precision measurements, quantum
+wireless networks, quantum radar, etc.",2402.04983v1
+2024-02-12,Continuum of spin excitations in an ordered magnet,"Continuum of spin excitations observed in inelastic neutron scattering
+experiments are often considered as a strong evidence of quantum spin liquid
+formation. When quantum spin liquid is indeed the ground state of a
+disorder-free magnetic compound, the elementary excitation is no longer the
+conventional spin waves (magnons). Instead, the magnons fractionalize into
+spinons, leaving only a two-spinon continuum detectable in inelastic neutron
+scattering experiments. For a clean ordered antiferromagnet, it was unclear if
+we can observe a continuous spectrum similar to the ones in a quantum spin
+liquid state. Here we show that the magnetically ordered state in
+Na$_2$BaCo(PO$_4$)$_2$ is able to host a spin excitation continuum induced by
+strong quantum fluctuations. Thus, a second thought is necessary when
+concluding such continuum as signature of quantum spin liquid in new material
+explorations.",2402.07730v1
+2024-02-12,Photoinduced Topological Phase Transitions in a Kitaev kagome magnet,"Based on the magnetic Floquet-Bloch theory, we investigate topological
+natures of Floquet magnons in a laser-irradiated kagome magnet exhibiting
+Heisenberg, Kitaev and Dzyaloshinskii Moriya interactions in the presence of an
+external magnetic field applied along directions of [111]. In a strong magnetic
+field perpendicular to the lattice plane [111] direction, the system is in the
+fully polarized paramagnetic phase and the magnon band carries an asymmetric
+Chern number throughout the region of the phase diagram. Our results show that
+periodically driven intrinsic topological magnetic materials can be manipulated
+into different topological phases with different thermal conductivities and
+Berry curvature signatures by adjusting the light intensity throughout the
+phase diagram region.",2402.07731v1
+2024-02-28,"SU(3) altermagnetism: Lattice models, chiral magnons, and flavor-split bands","Altermagnetism, a type of magnetic order that combines properties of
+ferromagnets and antiferromagnets, has generated significant interest recently,
+in particular due to its potential spintronics applications. Here, we show that
+altermagnetic states, which typically involve collinear magnetic order of SU(2)
+spins, can be generalized to higher SU($N$) symmetry groups. We construct a
+two-dimensional Heisenberg model for a three-sublattice SU(3) altermagnet and
+analyze its excitation spectrum via flavor-wave theory. By deriving a general
+formula for the chirality of the excitations, we show that the SU(3)
+altermagnet harbors chiral magnons that are split in energy. We also compute
+the electronic band structure for a metallic system of the same symmetry and
+map out the polarization of the resulting flavor-split bands. We conclude by
+discussing further generalizations.",2402.18629v1
+2024-03-09,Hybrid Spin-Orbit Exciton-Magnon Excitations in FePS$_3$,"FePS$_3$ is a layered van der Waals (vdW) Ising antiferromagnet that has
+recently been studied in the context of true 2D magnetism, and emerged as an
+ideal material platform for investigating strong spin-phonon coupling, and
+non-linear magneto-optical phenomena. In this work, we demonstrate an important
+unresolved role of spin-orbit coupling (SOC) in the ground state and
+excitations of this compound. Combining first principles calculations with
+Linear Flavor Wave Theory (LFWT), we find strong mixing and spectral overlap of
+different spin-orbital single-ion states. As such, the low-lying excitations
+form complex mixtures of local degrees of freedom most accurately viewed as
+hybrid spin-orbit exciton-magnon modes. Complete parameterization of the
+resulting low-energy model including all such degrees of freedom requires
+nearly half a million coupling constants. Despite this complexity, we show that
+such a model can be inexpensively derived using local many-body-based
+approaches, which yield quantitative agreement with recent experiments. The
+results highlight the importance of SOC even in first row transition metals,
+and provide essential insight into the properties of 2D magnets with unquenched
+orbital moments.",2403.05958v1
+2024-03-19,Acoustoelectric non-local spin wave power detector for studying magnon-phonon coupling,"We have developed a simple detection scheme to study spin waves excited by
+surface acoustic wave (SAW) in ferromagnetic thin films. Metallic antennas made
+of Ta and a ferromagnetic element are placed along the SAW propagation path.
+The SAW excites spin waves in the ferromagnetic element and induces
+acoustoelectric current in the antennas, which are detected as a DC voltage.
+The DC voltage takes an extremum at the spin wave resonance condition, which
+demonstrates that the antenna acts as a non-local spin wave detector. The
+antennas placed before and after the ferromagnetic element along the SAW
+propagation path can probe spin wave excitation from reflected and transmitted
+SAWs, respectively. Interestingly, we find characteristics of spin wave
+excitations that are different for the reflected and transmitted SAWs: the
+former excites spin waves with larger frequency with broader linewidth compared
+to the latter. The results show that the antennas act as a non-local spin wave
+power detector and can be used to map out the spin wave spectra in a unique
+way, providing insights into the magnon-phonon coupling in magnetic
+nanostructures fabricated on phononic SAW devices.",2403.12745v1
+2024-03-20,Dipole-dipole-interaction-induced entanglement between two-dimensional ferromagnets,"We investigate the viability of dipole-dipole interaction as a means of
+entangling two distant ferromagnets. To this end we make use of the Bogoliubov
+transformation as a symplectic transformation. We show that the coupling of the
+uniform magnon modes can be expressed using four squeezing parameters which we
+interpret in terms of hybridization, one-mode and two-mode squeezing. We
+utilize the expansion in terms of the squeezing parameters to obtain an
+analytic formula for the entanglement in the magnon ground state using the
+logarithmic negativity as entanglement measure. Our investigation predicts that
+for infinitely large two-dimensional ferromagnets, the dipole-dipole
+interaction does not lead to significant long-range entanglement. However, in
+the case of finite ferromagnets, finite entanglement can be expected",2403.13354v1
+2024-03-26,Magnonic inverse-design processor,"Artificial Intelligence (AI) technology has revolutionized our everyday lives
+and research. The concept of inverse design, which involves defining a
+functionality by a human and then using an algorithm to search for the device's
+design, opened new perspectives for information processing. A specialized
+AI-driven processor capable of solving an inverse problem in real-time offers a
+compelling alternative to the time and energy-intensive CMOS computations.
+Here, we report on a magnon-based processor that uses a complex reconfigurable
+medium to process data in the gigahertz range, catering to the demands of 5G
+and 6G telecommunication. Demonstrating its versatility, the processor solves
+inverse problems using two algorithms to realize RF notch filters and
+demultiplexers. The processor also exhibits potential for binary, reservoir,
+and neuromorphic computing paradigms.",2403.17724v1
+2024-03-27,Collective excitations in competing phases in two and three dimensions,"We investigate the superconducting (SC), charge-density wave (CDW), and
+antiferromagnetic (AFM) phases in the extended Hubbard model at zero
+temperature and half-filling. We employ the iterated equations of motion
+approach to compute the two-particle Green's functions and their spectral
+densities. This renders a comprehensive analysis of the behavior of collective
+excitations possible as the model's parameters are tuned across phase
+transitions. We identify the well-known amplitude (Higgs) and phase
+(Anderson-Bogoliubov) modes within the superconducting phase and observe a
+similar excitation (cooperon) in the CDW phase which shifts towards zero energy
+as the system approaches the phase transition to the SC phase. In the CDW
+phase, close to the phase transition to the AFM phase, we find a collective
+mode, an exciton, that does not change significantly and another mode, a
+longitudinal magnon, that emerges from the two-particle continuum as the system
+approaches the phase transition to the AFM phase. It becomes identical with the
+former at the transition. In the AFM phase, their roles are reversed.
+Additionally, we find a transversal Goldstone magnon located at zero energy.",2403.18701v1
+2024-03-28,Influence of disorder at Insulator-Metal interface on spin transport,"Motivated by experimental work showing enhancement of spin transport between
+Yttrium Iron Garnet and Platinum by a thin antiferromagnetic insulator between
+them, we consider spin transport through the interface of a non-magnetic metal
+and compensated antiferromagnetically ordered insulator and focus on the
+significance of the interface itself. The spin transport is carried by
+spin-polarized electrons in the metal and by magnons in the insulator. We
+compute the spin current in the presence of a spin accumulation in the metal,
+cause by the spin Hall effect, and a thermal gradient using Fermi's Golden Rule
+in the presence of interfacial disorder. For a perfectly clean interface, the
+in-plane momentum is conserved by the electron-magnon scattering events that
+govern the spin transport through the interface. We calculate how
+disorder-induced broadening of scattering matrix elements with respect to the
+in-plane momentum influences the spin current. As a general result, we observe
+that for many experimental setups, specifically for high temperatures, one
+should expect a rather small effect of interface disorder on the measured spin
+current, while for small temperatures there is a significant reduction of a
+spin current with increasing disorder.",2403.19277v1
+2004-05-28,Macroscopic entanglement of many-magnon states,"We study macroscopic entanglement of various pure states of a one-dimensional
+N-spin system with N>>1. Here, a quantum state is said to be macroscopically
+entangled if it is a superposition of macroscopically distinct states. To judge
+whether such superposition is hidden in a general state, we use an essentially
+unique index p: A pure state is macroscopically entangled if p=2, whereas it
+may be entangled but not macroscopically if p<2. This index is directly related
+to the stability of the state. We calculate the index p for various states in
+which magnons are excited with various densities and wavenumbers. We find
+macroscopically entangled states (p=2) as well as states with p=1. The former
+states are unstable in the sense that they are unstable against some local
+measurements. On the other hand, the latter states are stable in the senses
+that they are stable against local measurements and that their decoherence
+rates never exceed O(N) in any weak classical noises. For comparison, we also
+calculate the von Neumann entropy S(N) of a subsystem composed of N/2 spins as
+a measure of bipartite entanglement. We find that S(N) of some states with p=1
+is of the same order of magnitude as the maximum value N/2. On the other hand,
+S(N) of the macroscopically entangled states with p=2 is as small as O(log N)<<
+N/2. Therefore, larger S(N) does not mean more instability. We also point out
+that these results are analogous to those for interacting many bosons.
+Furthermore, the origin of the huge entanglement, as measured either by p or
+S(N), is discussed to be due to the spatial propagation of magnons.",0405173v2
+2010-09-30,A New Method of Calculating the Spin-Wave Velocity $c$ of Spin-1/2 Antiferromagnets With $O(N)$ Symmetry in a Monte Carlo Simulation,"Motivated by the so-called cubical regime in magnon chiral perturbation
+theory, we propose a new method to calculate the low-energy constant, namely
+the spin-wave velocity $c$ of spin-1/2 antiferromagnets with $O(N)$ symmetry in
+a Monte Carlo simulation. Specifically we suggest that $c$ can be determined by
+$c = L/\beta$ when the squares of the spatial and temporal winding numbers are
+tuned to be the same in the Monte Carlo calculations. Here $\beta$ and $L$ are
+the inverse temperature and the box size used in the simulations when this
+condition is met. We verify the validity of this idea by simulating the quantum
+spin-1/2 XY model. The $c$ obtained by using the squares of winding numbers is
+given by $c = 1.1348(5)Ja$ which is consistent with the known values of $c$ in
+the literature. Unlike other conventional approaches, our new idea provides a
+direct method to measure $c$. Further, by simultaneously fitting our Monte
+Carlo data of susceptibilities $\chi_{11}$ and spin susceptibilities $\chi$ to
+their theoretical predictions from magnon chiral perturbation theory, we find
+$c$ is given by $c = 1.1347(2)Ja$ which agrees with the one we obtain by the
+new method of using the squares of winding numbers. The low-energy constants
+magnetization density ${\cal M}$ and spin stiffenss $\rho$ of quantum spin-1/2
+XY model are determined as well and are given by ${\cal M} = 0.43561(1)/a^2$
+and $\rho = 0.26974(5)J$, respectively. Thanks to the prediction power of
+magnon chiral perturbation theory which puts a very restricted constraint among
+the low-energy constants for the model considered here, the accuracy of ${\cal
+M}$ we present in this study is much precise than previous Monte Carlo result.",1009.6122v1
+2014-11-11,Magnonic Charge Pumping via Spin-Orbit Coupling,"The interplay between spin, charge, and orbital degrees of freedom has led to
+the development of spintronic devices like spin-torque oscillators, spin-logic
+devices, and spin-transfer torque magnetic random-access memories. In this
+development spin pumping, the process where pure spin-currents are generated
+from magnetisation precession, has proved to be a powerful method for probing
+spin physics and magnetisation dynamics. The effect originates from direct
+conversion of low energy quantised spin-waves in the magnet, known as magnons,
+into a flow of spins from the precessing magnet to adjacent normal metal leads.
+The spin-pumping phenomenon represents a convenient way to electrically detect
+magnetisation dynamics, however, precessing magnets have been limited so far to
+pump pure spin currents, which require a secondary spin-charge conversion
+element such as heavy metals with large spin Hall angle or multi-layer layouts
+to be detectable. Here, we report the experimental observation of charge
+pumping in which a precessing ferromagnet pumps a charge current, demonstrating
+direct conversion of magnons into high-frequency currents via the relativistic
+spin-orbit interaction. The generated electric current, differently from spin
+currents generated by spin-pumping, can be directly detected without the need
+of any additional spin to charge conversion mechanism and amplitude and phase
+information about the relativistic current-driven magnetisation dynamics. The
+charge-pumping phenomenon is generic and gives a deeper understanding of the
+recently observed spin-orbit torques, of which it is the reciprocal effect and
+which currently attract interest for their potential in manipulating magnetic
+information. Furthermore, charge pumping provides a novel link between
+magnetism and electricity and may find application in sourcing alternating
+electric currents.",1411.2779v1
+2016-04-27,Collective spin excitations in bi-component magnonic crystals consisting of bi-layer Permalloy/Fe nanowires,"In the developing field of magnonics,it is very important to achieve
+tailoring of spin wave propagation by both a proper combination of materials
+with different magnetic properties and their nanostructuring on the
+submicrometric scale. We have exploited deep ultra-violet lithography, in
+combination with tilted shadow deposition technique, to fabricate arrays of
+closely spaced bi-layer nanowires (NWs), with separation d=100 nm and
+periodicity a=440 nm, having bottom and top layers made of Permalloy and Iron,
+respectively. The NWs have either rectangular cross section (bottom and upper
+layers of equal width) or L-shaped cross section (upper layer of half width).
+The frequency dispersion of collective spin wave excitations in the above
+bi-layered NWs arrays has been measured by the Brillouin light scattering
+technique while sweeping the wave vector perpendicularly to the wire length
+over three Brillouin zones of the reciprocal space. For the rectangular NWs,
+the lowest frequency fundamental mode, characterized by a quasi- uniform
+profile of the amplitude of the dynamic magnetization across the NW width,
+exhibits a sizeable and periodic frequency dispersion. A similar dispersive
+mode is also present in L-shaped NWs, but the mode amplitude is concentrated in
+the thin side of the NWs. The width and the center frequency of the magnonic
+band associated with the above fundamental modes has been analyzed, showing
+that both can be tuned by varying the external applied field. Moreover, for the
+L-shaped NWs it is shown that there is also a second dispersive mode,at higher
+frequency,characterized by an amplitude concentrated in the thick side of the
+NW. These experimental results have been quantitatively reproduced by an
+original numerical model that includes two-dimensional Green's function of the
+dipole field of the dynamic magnetization and interlayer exchange coupling
+between the layers.",1604.07950v1
+2018-02-19,Dynamical structure factor of the triangular antiferromagnet: the Schwinger boson theory beyond the mean field approach,"We compute the zero temperature dynamical structure factor $S({\bf
+q},\omega)$ of the triangular lattice Heisenberg model (TLHM) using a Schwinger
+boson approach that includes the Gaussian fluctuations ($1/N$ corrections) of
+the saddle point solution. While the ground state of this model exhibits a
+well-known 120$^{\circ}$ magnetic ordering, experimental observations have
+revealed a strong quantum character of the excitation spectrum. We conjecture
+that this phenomenon arises from the proximity of the ground state of the TLHM
+to the quantum melting point separating the magnetically ordered and spin
+liquid states. Within this scenario, magnons are described as collective modes
+(two spinon-bound states) of a spinon condensate (Higgs phase) that
+spontaneously breaks the SU(2) symmetry of the TLHM. Crucial to our results is
+the proper account of this spontaneous symmetry breaking. The main qualitative
+difference relative to semi-classical treatments ($1/S$ expansion) is the
+presence of a high-energy spinon continuum extending up to about three times
+the single-magnon bandwidth. In addition, the magnitude of the ordered moment
+($m=0.224$) agrees very well with numerical results and the low energy part of
+the single-magnon dispersion is in very good agreement with series expansions.
+Our results indicate that the Schwinger boson approach is an adequate starting
+point for describing the excitation spectrum of some magnetically ordered
+compounds that are near the quantum melting point separating this Higgs phase
+from the {\it deconfined} spin liquid state.",1802.06878v4
+2018-04-06,Magnon excitations and quantum critical behavior of the ferromagnet U$_4$Ru$_7$Ge$_6$,"We present an extensive study of the ferromagnetic heavy fermion compound
+U$_4$Ru$_7$Ge$_6$. Measurements of electrical resistivity, specific heat and
+magnetic properties show that U$_4$Ru$_7$Ge$_6$ orders ferromagnetically at
+ambient pressure with a Curie temperature $T_{C} = 6.8 \pm 0.3$ K. The low
+temperature magnetic behavior of this soft ferromagnet is dominated by the
+excitation of gapless spin-wave modes. Our results on the transport properties
+of U$_4$Ru$_7$Ge$_6$ under pressures up to $2.49$ GPa suggest that
+U$_4$Ru$_7$Ge$_6$ has a putative ferromagnetic quantum critical point (QCP) at
+$P_c \approx 1.7 \pm 0.02$ GPa. In the ordered phase, ferromagnetic magnons
+scatter the conduction electrons and give rise to a well defined power law
+temperature dependence in the resistivity. The coefficient of this term is
+related to the spin-wave stiffness and measurements of the very low temperature
+resistivity allow to accompany the behavior of this quantity as the the
+ferromagnetic QCP is approached. We find that the spin-wave stiffness decreases
+with increasing pressure implying that the transition to the non-magnetic Fermi
+liquid state is driven by the softening of the magnons. The observed quantum
+critical behavior of the magnetic stiffness is consistent with the influence of
+disorder in our system. At quantum criticality ($P = P_c \approx 1.7 \pm 0.02$
+GPa), the resistivity shows the behavior expected for an itinerant metallic
+system near a ferromagnetic QCP.",1804.02420v1
+2018-11-26,Cavity Spintronics: An Early Review of Recent Progress in the Study of Magnon-Photon Level Repulsion,"Light-matter interactions lie at the heart of condensed matter physics,
+providing physical insight into material behaviour while enabling the design of
+new devices. Perhaps this is most evident in the push to develop quantum
+information and spintronic technologies. On the side of quantum information,
+engineered light-matter interactions offer a powerful means to access and
+control quantum states, while at the same time new insights into spin-photon
+manipulation will benefit the development of spintronic technologies. In this
+context the recent discovery of hybridization between ferromagnets and cavity
+photons has ushered in a new era of light-matter exploration at the crossroads
+of quantum information and spintronics. The key player in this rapidly
+developing field of cavity spintronics is a quasiparticle, the
+cavity-magnon-polariton. In this early review of recent work, the fundamental
+behaviour of the cavity-magnon-polariton is summarized and related to the
+development of new spintronic applications. In the last few years a
+comprehensive theoretical framework of spin-photon hybridization has been
+developed. On an intuitive level many features can be described by a model of
+coupled oscillators, however the origin of hybridization is only revealed by
+considering a comprehensive electrodynamic framework. Here both approaches are
+summarized and a quantum description using the input-output formalism is
+outlined. Based on this foundation, in depth experimental investigations of the
+coupled spin-photon system have been performed. For example, the influence of
+hybridization on spin current generation has been revealed and several in-situ
+coupling control mechanisms have been developed. The many recent developments
+within this field represent only the first steps in what appears to be a bright
+future for cavity spintronics.",1811.10659v1
+2018-09-11,Neutron Scattering Investigation of Rhenium Orbital Ordering in $3d-5d$ Double Perovskite Ca$_2$FeReO$_6$,"We have carried out inelastic neutron scattering experiments to study
+magnetic excitations in ordered double perovskite Ca$_2$FeReO$_6$. We found a
+well-defined magnon mode with a bandwidth of $\sim$50meV below the
+ferri-magnetic ordering temperature ($T_c\sim$520K), similar to previously
+studied Ba$_2$FeReO$_6$. The spin excitation is gapless for most temperatures
+within the magnetically ordered phase. However, a spin gap of $\sim$10meV opens
+up below $\sim$150K, which is well below the magnetic ordering temperature but
+coincides with a previously reported metal-insulator transition and onset of
+structural distortion. The observed temperature dependence of spin gap provides
+strong evidence for ordering of Re orbitals at $\sim$150~K, in accordance with
+earlier proposal put forward by Oikawa $\it{et.\,al}$ based on neutron
+diffraction [J. Phys. Soc. Jpn., $\bf{72}$, 1411 (2003)] as well as recent
+theoretical work by Lee and Marianetti [Phys. Rev. B, $\bf{97}$, 045102
+(2018)]. The presence of separate orbital and magnetic ordering in
+Ca$_2$FeReO$_6$ suggests weak coupling between spin and orbital degrees of
+freedom and hints towards a sub-dominant role played by spin orbit coupling in
+describing its magnetism. In addition, we observed only one well-defined magnon
+band near magnetic zone boundary, which is incompatible with simple
+ferrimagnetic spin waves arising from Fe and Re local moments, but suggests a
+strong damping of Re magnon mode.",1809.03647v2
+2019-08-07,Analysis of the linear relationship between asymmetry and magnetic moment at the M-edge of 3d transition metals,"The magneto-optical response of Fe and Ni during ultrafast demagnetization is
+studied experimentally and theoretically. We have performed pump-probe
+experiments in the transverse magneto-optical Kerr effect (T-MOKE) geometry
+using photon energies that cover the M-absorption edges of Fe and Ni between 40
+to 72 eV. The asymmetry was detected by measuring the reflection of light for
+two different orientations of the sample magnetization. Density functional
+theory (DFT) wasused to calculate the magneto-optical response of different
+magnetic configurations, representing different types of excitations:
+long-wavelength magnons, short wavelength magnons, and Stoner excitations. In
+the case of Fe, we find that the calculated asymmetry is strongly dependent on
+the specific type of magnetic excitation. Our modelling also reveals that
+during remagnetization Fe is, to a reasonable approximation, described by
+magnons, even though small non-linear contributions could indicate some degree
+of Stoner excitations as well. In contrast, we find that the calculated
+asymmetry in Ni is rather insensitive to the type of magnetic excitations.
+However, there is a weak non-linearity in the relation between asymmetry and
+the off-diagonal component of the dielectric tensor, which does not originate
+from the modifications of the electronic structure. Our experimental and
+theoretical results thus emphasize the need of considering a coupling between
+asymmetry and magnetization that may be more complex that a simple linear
+relationship. This insight is crucial for the microscopic interpretation of
+ultrafast magnetization experiments.",1908.02872v1
+2019-11-13,Unveiling domain wall dynamics of ferrimagnets in thermal magnon currents: competition of angular momentum transfer and entropic torque,"Control of magnetic domain wall motion holds promise for efficient
+manipulation and transfer of magnetically stored information. Thermal magnon
+currents, generated by temperature gradients, can be used to move magnetic
+textures, from domain walls, to magnetic vortices and skyrmions. In the last
+years, theoretical studies have centered in ferro- and antiferromagnetic spin
+structures, where domain walls always move towards the hotter end of the
+thermal gradient. Here we perform numerical studies using atomistic spin
+dynamics simulations and complementary analytical calculations to derive an
+equation of motion for the domain wall velocity. We demonstrate that in
+ferrimagnets, domain wall motion under thermal magnon currents shows a much
+richer dynamics. Below the Walker breakdown, we find that the temperature
+gradient always pulls the domain wall towards the hot end by minimizating its
+free energy, in agreement with the observations for ferro- and antiferromagnets
+in the same regime. Above Walker breakdown, the ferrimagnetic domain wall can
+show the opposite, counterintuitive behavior of moving towards the cold end. We
+show that in this case, the motion to the hotter or the colder ends is driven
+by angular momentum transfer and therefore strongly related to the angular
+momentum compensation temperature, a unique property of ferrimagnets where the
+intrinsic angular momentum of the ferrimagnet is zero while the sublattice
+angular momentum remains finite. In particular, we find that below the
+compensation temperature the wall moves towards the cold end, whereas above it,
+towards the hot end. Moreover, we find that for ferrimagnets, there is a torque
+compensation temperature at which the domain wall dynamics shows similar
+characteristics to antiferromagnets, that is, quasi-inertia-free motion and the
+absence of Walker breakdown.",1911.05393v1
+2019-12-19,Magnon-driven chiral charge and spin pumping and electron-magnon scattering from time-dependent quantum transport combined with atomistic spin dynamics theory,"Using newly developed quantum-classical hybrid framework, we investigate
+interaction between spin-polarized conduction electrons and a single spin wave
+(SW) coherently excited within a metallic ferromagnetic nanowire. When the
+nanowire hosting SW is attached to two normal metal (NM) leads, with no dc bias
+voltage applied between them, the SW pumps chiral electronic charge and spin
+currents into the leads---their direction is tied to the direction of SW
+propagation and they scale linearly with the frequency of the precession. This
+is in contrast to: standard pumping by the uniform precession mode with
+identical spin currents flowing in both directions and no accompanying charge
+current; or experimentally observed [C.~Ciccarelli et al., Nat. Nanotech. 10,
+50 (2014); M.~Evelt et al., Phys. Rev. B 95, 024408 (2017)] magnonic charge
+pumping which requires spin-orbit coupling spin-orbit coupling. The mechanism
+behind our prediction is nonadiabaticity due to time-retardation
+effects---motion of localized magnetic moment affects conduction electron spin
+in a retarded way, so that it takes a finite time until the electron spin
+reacts to the motion of the classical vector. Upon injecting dc spin-polarized
+charge current from the left NM lead, electrons interact with SW where
+outflowing charge and spin current into the right NM lead are changed due to
+both scattering off time-dependent potential generated by the SW and
+superposition with the currents pumped by the SW itself. Using Lorentzian
+voltage pulse to excite leviton out of the Fermi sea, which carries one
+electron charge with no accompanying electron-hole pairs and behaves as
+soliton-like quasiparticle, we describe how a single electron interacts with a
+single SW.",1912.09452v2
+2017-11-30,Topological magnons in a kagome lattice spin system with $XXZ$ and Dzyaloshinskii-Moriya interactions,"We study the phases of a spin system on the Kagome lattice with
+nearest-neighbor $XXZ$ interactions with anisotropy ratio $\Delta$ and
+Dzyaloshinsky-Moriya interactions with strength $D$. In the classical limit
+where the spin $S$ at each site is very large, we find a rich phase diagram of
+the ground state as a function of $\Delta$ and $D$. There are five distinct
+phases which correspond to different ground state spin configurations in the
+classical limit. We use spin wave theory to find the bulk energy bands of the
+magnons in some of these phases. We also study a strip of the system which has
+infinite length and finite width; we find modes which are localized on one of
+the edges of the strip with energies which lie in the gaps of the bulk modes.
+In the ferromagnetic phase in which all the spins point along the $+ \hat z$ or
+$- \hat z$ direction, the bulk bands are separated from each other by finite
+energy gaps. This makes it possible to calculate the Berry curvature at all
+momenta, and hence the Chern numbers for every band; the number of edge states
+is related to the Chern numbers. Interestingly, we find that there are four
+different regions in this phase where the Chern numbers are different. Hence
+there are four distinct topological phases even though the ground state spin
+configuration is identical in all these phases. We calculate the thermal Hall
+conductivity of the magnons as a function of the temperature in the above
+ferromagnetic phase; we find that this can distinguish between the various
+topological phases. These results are valid for all values of $S$.In the other
+phases, there are no gaps between the different bands; hence the edge states
+are not topologically protected.",1711.11232v3
+2020-09-28,"Magnetic-field dependence of low-energy magnons, anisotropic heat conduction, and spontaneous relaxation of magnetic domains in the cubic helimagnet ZnCr2Se4","Anisotropic low-temperature properties of the cubic spinel helimagnet
+ZnCr2Se4 in the single-domain spin-spiral state are investigated by a
+combination of neutron scattering, thermal conductivity, ultrasound velocity,
+and dilatometry measurements. In an applied magnetic field, neutron
+spectroscopy shows a complex and nonmonotonic evolution of the spin-wave
+spectrum across the quantum-critical point that separates the spin-spiral phase
+from the field-polarized ferromagnetic phase at high fields. A tiny spin gap of
+the pseudo-Goldstone magnon mode, observed at wave vectors that are
+structurally equivalent but orthogonal to the propagation vector of the spin
+helix, vanishes at this quantum critical point, restoring the cubic symmetry in
+the magnetic subsystem. The anisotropy imposed by the spin helix has only a
+minor influence on the lattice structure and sound velocity but has a much
+stronger effect on the heat conductivities measured parallel and perpendicular
+to the magnetic propagation vector. The thermal transport is anisotropic at T <
+2 K, highly sensitive to an external magnetic field, and likely results
+directly from magnonic heat conduction. We also report long-time thermal
+relaxation phenomena, revealed by capacitive dilatometry, which are due to
+magnetic domain motion related to the destruction of the single-domain magnetic
+state, initially stabilized in the sample by the application and removal of
+magnetic field. Our results can be generalized to a broad class of helimagnetic
+materials in which a discrete lattice symmetry is spontaneously broken by the
+magnetic order.",2009.13424v1
+2020-09-28,Effective Field Theory of Dark Matter Direct Detection With Collective Excitations,"We develop a framework for computing light dark matter direct detection rates
+through single phonon and magnon excitations via general effective operators.
+Our work generalizes previous calculations focused on spin-independent
+interactions involving the total nucleon and electron numbers $N$ (the usual
+route to excite phonons) and spin-dependent interactions involving the total
+electron spin $S$ (the usual route to excite magnons), leading us to identify
+new responses involving the orbital angular momenta $L$, as well as spin-orbit
+couplings $L\otimes S$ in the target. All four types of responses can excite
+phonons, while couplings to electron's $S$ and $L$ can also excite magnons. We
+apply the effective field theory approach to a set of well-motivated
+relativistic benchmark models, including (pseudo-)scalar mediated interactions,
+and models where dark matter interacts via a multipole moment, such as a dark
+electric dipole, magnetic dipole or anapole moment. We find that couplings to
+point-like degrees of freedom $N$ and $S$ often dominate dark matter detection
+rates, implying that exotic materials with orbital $L$ order or large
+spin-orbit couplings $L\otimes S$ are not necessary to have strong reach to a
+broad class of DM models. We highlight that phonon based crystal experiments in
+active R&D (such as SPICE) will probe light dark matter models well beyond
+those having a simple spin-independent interaction, including e.g. models with
+dipole and anapole interactions. Lastly, we make publicly available a code,
+PhonoDark, which computes single phonon production rates in a wide variety of
+materials with the effective field theory framework.",2009.13534v2
+2019-10-08,Highly dispersive magnons with spin-gap like features in the frustrated ferromagnetic S=1/2 chain compound Ca2Y2Cu5O10 detected by inelastic neutron scattering,"We report inelastic neutron scattering experiments in Ca2Y2Cu5O10 and map out
+the full one magnon dispersion which extends up to a record value of 53 meV for
+frustrated ferromagnetic (FM) edge-sharing CuO2 chain (FFESC) cuprates. A
+homogeneous spin-1/2 chain model with a FM nearest-neighbor (NN), an
+antiferromagnetic (AFM) next-nearest-neighbor (NNN) inchain, and two diagonal
+AFM interchain couplings (ICs) analyzed within linear spin-wave theory (LSWT)
+reproduces well the observed strong dispersion along the chains and a weak one
+perpendicularly. The ratio R=|J_{a2}/J_{a1}| of the FM NN and the AFM NNN
+couplings is found as ~0.23, close to the critical point Rc=1/4 which separates
+ferromagnetically and antiferromagnetically correlated spiral magnetic ground
+states in single chains, whereas Rc>0.25 for coupled chains is considerably
+upshifted even for relatively weak IC. Although the measured dispersion can be
+described by homogeneous LSWT, the scattering intensity appears to be
+considerably reduced at ~11.5 and ~28 meV. The gap-like feature at 11.5 meV is
+attributed to magnon-phonon coupling whereas based on DMRG simulations of the
+dynamical structure factor the gap at 28 meV is considered to stem partly from
+quantum effects due to the AFM IC. Another contribution is ascribed to the
+intrinsic superstructure from the distorting incommensurate pattern of CaY
+cationic chains adjacent to the CuO2 ones. It gives rise to non-equivalent CuO4
+units and Cu-O-Cu bond angles Phi and a resulting distribution of all exchange
+integrals. The J's fitted by homogeneous LSWT are regarded as average values.
+The record value of the FM NN integral J1=24 meV among FFESC cuprates can be
+explained by a non-universal Phi (not 90 deg.) and Cu-O bond length dependent
+anisotropic mean direct FM Cu-O exchange K_{pd}~120 meV. Enhanced K_{pd} values
+are also needed to compensate a significant AFM J_{dd} > ~6 meV.",1910.03209v1
+2020-01-08,Dirac Hamiltonians for bosonic spectra,"Dirac materials are of great interest as condensed matter realizations of the
+Dirac and Weyl equations. In particular, they serve as a starting point for the
+study of topological phases. This physics has been extensively studied in
+electronic systems such as graphene, Weyl- and Dirac semi-metals. In contrast,
+recent studies have highlighted several examples of Dirac-like cones in
+collective excitation spectra, viz. in phonon, magnon and triplon bands. These
+cannot be directly related to the Dirac or Weyl equations as they are bosonic
+in nature with pseudo-unitary band bases. In this article, we show that any
+Dirac-like equation can be smoothly deformed into a form that is applicable to
+bosonic bands. The resulting bosonic spectra bear a two-to-one relation to that
+of the parent Dirac system. Their dispersions inherit several interesting
+properties including conical band touching points and a gap-opening-role for
+`mass' terms. The relationship also extends to the band eigenvectors with the
+bosonic states carrying the same Berry connections as the parent fermionic
+states. The bosonic bands thus inherit topological character as well. If the
+parent fermionic system has non-trivial topology that leads to mid-gap surface
+states, the bosonic analogue also hosts surface states that lie within the
+corresponding band gap. The proposed bosonic Dirac structure appears in several
+known models. In materials, it is realized in Ba$_2$CuSi$_2$O$_6$Cl$_2$ and
+possibly in CoTiO$_3$ as well as in paramagnetic honeycomb ruthenates. Our
+results allow for a rigorous understanding of Dirac phononic and magnonic
+systems and enable concrete predictions, e.g., of surface states in magnonic
+topological insulators and Weyl semi-metals.",2001.02694v2
+2020-04-08,Spin dynamics of a magnetic Weyl semimetal Sr$_{1-x}$Mn$_{1-y}$Sb$_2$,"Dirac matters provide a platform for exploring the interplay of their
+carriers with other quantum phenomena. Sr$_{1-x}$Mn$_{1-y}$Sb$_2$ has been
+proposed to be a magnetic Weyl semimetal and provides an excellent platform to
+study the coupling between Weyl fermions and magnons. Here, we report
+comprehensive inelastic neutron scattering (INS) measurements on single
+crystals of Sr$_{1-x}$Mn$_{1-y}$Sb$_2$, which have been well characterized by
+magnetization and magnetotransport measurements, both of which demonstrate that
+the material is a topologically nontrivial semimetal. The INS spectra clearly
+show a spin gap of $\sim6$ meV. The dispersion in the magnetic Mn layer extends
+up to about 76 meV, while that between the layers has a narrow band width of 6
+meV. We find that the linear spin-wave theory using a Heisenberg spin
+Hamiltonian can reproduce the experimental spectra with the following
+parameters: a nearest-neighbor ($SJ_1\sim28.0$ meV) and next-nearest-neighbor
+in-plane exchange interaction ($SJ_2\sim9.3$ meV) , interlayer exchange
+coupling ($SJ_c\sim-0.1$ meV), and spin anisotropy constant ($SD\sim-0.07$
+meV). Despite the coexistence of Weyl fermions and magnons, we find no clear
+evidence that the magnetic dynamics are influenced by the Weyl fermions in
+Sr$_{1-x}$Mn$_{1-y}$Sb$_2$, possibly because that the Weyl fermions and magnons
+reside in the Sb and Mn layers separately, and the interlayer coupling is weak
+due to the quasi-two-dimensional nature of the material, as also evident from
+the small $SJ_c$ of -0.1 meV.",2004.03893v1
+2021-01-25,Long-range spin-wave propagation in transversely magnetized nano-scaled conduits,"Magnonics attracts increasing attention in the view of novel low-energy
+computation technologies based on spin waves. Recently, spin-wave propagation
+in longitudinally magnetized nano-scaled spin-wave conduits was demonstrated,
+proving the fundamental feasibility of magnonics at the sub-100 nm scale.
+Transversely magnetized nano-conduits, which are of great interest in this
+regard as they offer a large group velocity and a potentially chirality-based
+protected transport of energy, have not yet been investigated due to their
+complex internal magnetic field distribution. Here, we present a study of
+propagating spin waves in a transversely magnetized nanoscopic yttrium iron
+garnet conduit of 50 nm width. Space and time-resolved micro-focused
+Brillouin-light-scattering spectroscopy is employed to measure the spin-wave
+group velocity and decay length. A long-range spin-wave propagation is observed
+with a decay length of up to (8.0+-1.5) {\mu}m and a large spin-wave lifetime
+of up to (44.7+-9.1) ns. The results are supported with micromagnetic
+simulations, revealing a single-mode dispersion relation in contrast to the
+common formation of localized edge modes for microscopic systems. Furthermore,
+a frequency non-reciprocity for counter-propagating spin waves is observed in
+the simulations and the experiment, caused by the trapezoidal cross-section of
+the structure. The revealed long-distance spin-wave propagation on the
+nanoscale is particularly interesting for an application in spin-wave devices,
+allowing for long-distance transport of information in magnonic circuits, as
+well as novel low-energy device architectures.",2101.10192v1
+2022-06-17,Quantum Dynamics of Magnetic Skyrmions: Consistent Path Integral Formulation,"We present a path integral formalism for the intrinsic quantum dynamics of
+magnetic skyrmions coupled to a thermal background of magnetic fluctuations.
+Upon promoting the skyrmion's collective coordinate $\boldsymbol{R}$ to a
+dynamic variable and integrating out the magnonic heat bath, we derive the
+generalized equation of motion for $\boldsymbol{R}$ with a non-local damping
+term that describes a steady-state skyrmion dynamics at finite temperatures.
+Being essentially temperature dependent, the intrinsic damping is shown to
+originate from the coupling of thermally activated magnon modes to the
+adiabatic potential driven by a rigid skyrmion motion, which can be regarded as
+another manifestation of emergent electrodynamics inherent to topological
+magnetic textures. We further argue that the diagonal components of the damping
+term act as the source of dissipation and inertia, while its off-diagonal
+components modify the gyrotropic motion of a magnetic skyrmion. By means of
+numerical calculations for the lattice spin model of chiral ferromagnets, we
+study the temperature behavior of the intrinsic damping as a function of
+magnetic field in periodic and confined geometries. The intrinsic damping is
+demonstrated to be highly non-local, revealing its quantum-mechanical nature,
+that becomes more pronounced with increasing temperature. At high temperatures
+when the magnon occupation factors are large, the intrinsic damping is shown to
+yield a modified Thiele's equation with the additional non-local dissipative
+and mass terms that exhibit an almost linear temperature behavior. Our results
+provide a microscopic background for semiclassical magnetization dynamics and
+establish a framework for understanding spin caloritronics effects in
+topological magnetic textures.",2206.08532v2
+2022-08-11,Universal behavior of magnon-mediated spin transport in disordered NM/NM/FI heterostructure,"We numerically investigate the magnon-mediated spin transport and scaling
+behaviors of a nonmagnetic metal/nonmagnetic metal/ferromagnetic insulator
+(NM/NM/FI) heterostructure in the presence of Anderson disorders. For the
+two-dimensional (2D) NM/NM/FI system, an enhancement of spin conductance in the
+weak disorder regime is found due to the increasing of the interfacial density
+of states (DOS) at NM/FI interface. As a result, a new scaling regime is
+uncovered in the metallic regime where the spin conductance fluctuation rms(G)
+scales linearly with the average spin conductance <G>, independent of system
+parameters such as Fermi energies and temperatures. The competition between the
+disorder-enhanced interfacial DOS and disorder-suppressed spin transport
+results in a non-monotonic dependence of average spin conductance on disorder
+strength. In the localized regime, the variance of lnG for different system
+parameters follows a universal function that depends linearly on the average of
+logarithm of spin conductance <lnG>.The distribution of lnG in the localized
+regime is non-Gaussian whose deviation from Gaussian can be characterized by
+the third and fourth order cumulants of lnG, denoted as k3 and k4,
+respectively. We find that k3~<-lnG>^3/2 and k4~<lnG>^2. This suggests that the
+spin conductance mediated by magnon in NM/NM/FI hybrid systems belongs to a
+different universality class. For fixed <lnG>, the lnG distribution in the
+localized regime for different system parameters is found to collapse onto a
+single curve, suggesting the distribution P(lnG;<lnG>) is a universal function
+that depends only on <lnG>. Furthermore, spin thermopower S in the presence of
+disorder is studied and the variance of lnS is found to scale linearly with
+<lnS> for different system parameters in the localized regime. Spin conductance
+and spin thermopower for 1D NM/NM/FI are also studied.",2208.05759v2
+2023-02-01,Ramification of complex magnetism in Nd$_2$Ir$_2$O$_7$ observed by Raman scattering spectroscopy,"Using Raman scattering spectroscopy, we uncover a complex magnetic behavior
+of Nd$_2$Ir$_2$O$_7$, which stands out among magnetic pyrochlores by the lowest
+temperature of the all-in-all-out (AIAO) Ir moments ordering
+($T^\mathrm{N}_{\small\rm{Ir}}=33$~K) and the highest temperature at which AIAO
+order of rare-earth Nd ions is detected ($T^\mathrm{*}_{\small\rm{Nd}}$=15~K).
+Our work suggests that in the temperature range between 15~K and 33~K, Nd
+magnetic moments exhibit characteristic spin ice fluctuations, which indicate a
+strong enhancement of magnetic interactions between Nd ions. This complex
+behavior emerges from the interplay of strong spin-orbit coupling, electronic
+correlations, and geometric frustration on two magnetic pyrochlore sublattices
+of Nd and Ir ions. The ordering of Ir magnetic moments is accompanied by an
+appearance of one-magnon Raman modes at 26.3 and 29.6 meV compatible with the
+AIAO order and of a broad mode at 14 meV, characteristic of the spinon
+continuum originated from Nd spin ice fluctuations. While two one-magnon
+excitations show minimal temperature evolution with decreasing temperature, the
+14 meV mode shifts to higher frequencies as the temperature approaches a
+crossover to Nd AIAO order, broadens, and disappears below 15~K. An additional
+two-magnon excitation of the AIAO Nd order at around 33 meV appears in the
+spectra at low temperatures. These rather high energies of magnetic excitations
+of Nd moments make Nd$_2$Ir$_2$O$_7$ a particularly attractive playground to
+study the rare-earth magnetism on the pyrochlore lattice.",2302.00579v2
+2023-06-28,Degenerate and non-degenerate parametric excitation in YIG nanostructures,"We study experimentally the processes of parametric excitation in microscopic
+magnetically saturated disks of nanometer-thick Yttrium Iron Garnet. We show
+that, depending on the relative orientation between the parametric pumping
+field and the static magnetization, excitation of either degenerate or
+non-degenerate magnon pairs is possible. In the latter case, which is
+particularly important for applications associated with the realization of
+computation in the reciprocal space, a single-frequency pumping can generate
+pairs of magnons whose frequencies correspond to different eigenmodes of the
+disk. We show that, depending on the size of the disk and the modes involved,
+the frequency difference in a pair can vary in the range 0.1-0.8 GHz. We
+demonstrate that in this system, one can easily realize a practically important
+situation where several magnon pairs share the same mode. We also observe the
+simultaneous generation of up to six different modes using a fixed-frequency
+monochromatic pumping. Our experimental findings are supported by numerical
+calculations that allow us to unambiguously identify the excited modes. Our
+results open new possibilities for the implementation of reciprocal-space
+computing making use of low damping magnetic insulators.",2306.16094v1
+2024-03-05,Anomalous continuum scattering and higher-order van Hove singularity in the strongly anisotropic S = 1/2 triangular lattice antiferromagnet,"The S = 1/2 triangular lattice antiferromagnet (TLAF) stands out as a
+paradigmatic example of frustrated quantum magnetism. An ongoing challenge
+involves understanding the influence of exchange anisotropy on the collective
+behavior within such systems. Using inelastic neutron scattering (INS) and
+advanced calculation techniques, we have studied the low and high temperature
+spin dynamics of Ba2La2CoTe2O12 (BLCTO): a Co2+-based Jeff = 1/2 TLAF that
+exhibits 120 deg order below TN = 3.26 K. The spin Hamiltonian was determined
+by fitting the energy-resolved paramagnetic excitations measured at T > TN,
+revealing an exceptionally strong easy-plane XXZ exchange anisotropy. Below TN,
+the excitation spectrum exhibits a high energy continuum having a larger
+spectral weight than the single-magnon modes. Combined with advanced
+theoretical calculations of magnetic excitations based on magnons and spinons,
+this observation suggests a scenario characterized by a spinon confinement
+length that markedly exceeds the lattice spacing. We conjecture that this
+phenomenon arises due to the proximity to a quantum melting point, which
+persists even in the presence of strong easy-plane XXZ anisotropy. Finally, we
+highlight characteristic flat features in the excitation spectrum, which are
+connected to higher-order van Hove singularities in the magnon dispersion and
+are directly induced by easy-plane XXZ anisotropy. Our results provide a rare
+experimental insight into the nature of highly anisotropic S = 1/2 TLAFs
+between the Heisenberg and XY limits.",2403.03210v1
+1993-11-09,Spin Excitations and Sum Rules in the Heisenberg Antiferromagnet,"Various bounds for the energy of collective excitations in the Heisenberg
+antiferromagnet are presented and discussed using the formalism of sum rules.
+We show that the Feynman approximation significantly overestimates (by about
+30\% in the $S={1\over2}$ square lattice) the spin velocity due to the non
+negligible contribution of multi magnons to the energy weighted sum rule. We
+also discuss a different, Goldstone type bound depending explicitly on the
+order parameter (staggered magnetization). This bound is shown to be
+proportional to the dispersion of classical spin wave theory with a
+q-independent normalization factor. Rigorous bounds for the excitation energies
+in the anisotropic Heisenberg model are also presented.",9311020v1
+1993-11-16,Quantum Phases of the Shraiman-Siggia Model,"We examine phases of the Shraiman-Siggia model of lightly-doped, square
+lattice quantum antiferromagnets in a self-consistent, two-loop, interacting
+magnon analysis. We find magnetically-ordered and quantum-disordered phases
+both with and without incommensurate spin correlations. The quantum disordered
+phases have a pseudo-gap in the spin excitation spectrum. The quantum
+transition between the magnetically ordered and commensurate quantum-disordered
+phases is argued to have the dynamic critical exponent $z=1$ and the same
+leading critical behavior as the disordering transition in the pure $O(3)$
+sigma model. The relationship to experiments on the doped cuprates is
+discussed.",9311037v1
+1994-08-02,Composite-Fermion Picture for the Spin-Wave Excitation in the fractional quantum Hall system,"Spin-wave excitation mode from the spin-polarized ground state in the
+fractional quantum Hall liquid with odd fractions ($\nu=1/3,1/5$) numerically
+obtained by the exact diagonalization of finite systems is shown to be
+accurately described, for wavelengths exceeding the magnetic length, in terms
+of the composite-fermion mean-field approximation for the spin-wave (magnon)
+theory formulated in the spherical geometry. This indicates that the composite
+picture extends to excited states, and also provides the spin stiffness in
+terms of peculiar exchange interactions.",9408004v1
+1995-08-21,Two--magnon scattering and the spin--phonon interaction beyond the adiabatic approximation,"We consider a model of Raman scattering for a two--dimensional $S=1/2$
+Heisenberg Anti-Ferromagnet which includes a {\it dynamical} spin--phonon
+interaction. We observe a broadening of the line shape due to increased
+coupling with excited high--energy spin states. Our results are close to a
+model of random static exchange interactions, first introduced in this context
+by Haas {\it et al.} [J. Appl. Phys. {\bf 75}, 6340, (1994)], which, when
+extended to large numbers of spins, explains experiments in the parent
+insulating compounds of high-$T_c$ superconductors.",9508089v1
+1995-10-18,Zero field muon spin lattice relaxation rate in a Heisenberg ferromagnet at low temperature,"We provide a theoretical framework to compute the zero field muon spin
+relaxation rate of a Heisenberg ferromagnet at low temperature. We use the
+linear spin wave approximation. The rate, which is a measure of the spin
+lattice relaxation induced by the magnetic fluctuations along the easy axis,
+allows one to estimate the magnon stiffness constant.",9510096v1
+1995-11-23,Sharp Photoemission Spactra in the Quantum Antiferromagnet,"The low energy photoemission spectra in quantum antiferromagnets are studied
+by using several approximation-free calculations and rigorous theorems. The
+important and measurable property found is that the hole eigenstates with
+momenta differing by the antiferromagnetic wavevector $Q$ are equivalent and
+degenerate in energy. However the corresponding eigenstates differs by the
+presence or the absence of a well defined quasiparticle corresponding to a
+singular -zero energy- magnon, carrying spin one and momentum $Q$. This
+difference between the two eigenstates affects dramatically the spectral weight
+as a function of the scattered momentum, since a sharp effect at the surface of
+the magnetic Brillouin zone is predicted, in apparent agreement with recent
+experimental data.",9511114v1
+1995-12-22,Theory of Nuclear Magnetic Relaxation in Haldane Gap Materials: An Illustration of the Use of (1+1)-Dimensional Field Theory Techniques,"A comprehensive theory of nuclear magnetic relaxation is developed for
+Haldane Gap materials using nonlinear sigma, boson and fermion models. We
+include a thorough discussion of of the effects of interchain couplings,
+nearest neighbour hyperfine couplings and crystal structure. We also introduce
+a new theory of impurities corresponding to broken chain ends weakly coupled to
+bulk magnons. The work is compared to recent experiments on NENP.",9512161v2
+1996-01-29,Raman Response in Doped Antiferromagnets,"The resonant part of the $B_{1g}$ electronic Raman scattering response is
+calculated within the $t-J$ model on a planar lattice as a function of
+temperature and hole doping, using a finite-temperature diagonalization method
+for small systems. Results, directly applicable to experiments on cuprates,
+reveal on doping a very pronounced increase of the width of the two-magnon
+Raman peak, accompanied by a decrease of the total intensity. At the same time
+the peak position does not shift substantially in the underdoped regime.",9601136v2
+1996-07-30,An extension of the characteristic angle method to the easy-plane spin-3/2 ferromagnet,"The Characteristic Angle (CA) method [Lei Zhou and Ruibao Tao, J. Phys. A,
+{\bf 27} 5599] developed previously for the easy-plane spin-1 magnetic systems
+has been successfully extended to the spin-3/2 case. A compact form of the CA
+spin-3/2 operator transformation is given, then the ground state energy, the
+magnon dispersion relation and the spontaneous magnetization are discussed for
+an easy-plane spin-3/2 ferromagnet by using the CA method. Comparisons with the
+old theoretical methods are made in the end.",9607218v1
+1997-03-04,Magnetic and thermodynamic properties of Sr_{2}LaFe_{3}O_{9},"Using a Dirac-Heisenberg Hamiltonian with biquadratic exchange interactions,
+we study the effect of iron disproportionation on the magnetic ordering, and
+describe the first-order magnetic transition occurring in the perovskite
+Sr_{2}LaFe_{3}O_{9}. Upon fitting the experimental data, we give an estimate of
+the exchange integrals for the antiferromagntic and ferromagnetic interactions,
+in agreement with previous works on kindered compounds. Spin-wave theory yields
+a magnon spectrum with a gapless antiferromagnetic mode together with two
+gapped ferromagnetic ones.",9703044v1
+1997-05-26,Symmetry and dimension of the magnon dispersion of inorganic spin-Peierls systems,"The data on the dispersion of the magnetic excitations of CuGeO_3 in the
+spin-Peierls dimerized phase are analyzed. On the basis of the lattice
+structure it is shown that even along the chains the $d=2$ character cannot be
+neglected. The symmetry of the dispersion differs from the one assumed so far.
+The magnetic resonance data is reinterpreted. The possibility of interchain
+rather than intrachain frustration is discussed.",9705258v1
+1997-11-13,An SO(5) Symmetric Ladder,"We construct an SO(5) symmetric electron model on a two-chain ladder with
+purely local interactions on a rung. The ground state phase diagram of this
+model is determined in the strong-coupling limit. The relationship between the
+spin-gap magnon mode of the spin-gap insulator and the $\pi$ resonance mode of
+the d-wave pairing phase is discussed. We also present the exact ground state
+for an SO(5) superspin model.",9711117v1
+1997-12-08,Non-Haldane Spin Liquid Models with Exact Ground States,"We present a family of spin ladder models which admit exact solution for the
+ground state and exhibit non-Haldane spin liquid properties as predicted
+recently by Nersesyan and Tsvelik [Phys. Rev. Lett. v.78, 3939 (1997)], and
+study their excitation spectrum using a simple variational ansatz. The
+elementary excitation is neither a magnon nor a spinon, but a pair of
+propagating triplet or singlet solitons connecting two spontaneously dimerized
+ground states. Second-order phase transitions separate this phase from the
+Haldane phase and the rung-dimer phase.",9712087v3
+1998-02-04,Dynamical effects of phonons on soliton binding in spin-Peierls systems,"The role of dynamical magneto-elastic coupling in spin-Peierls chains is
+investigated by numerical and analytical techniques. We show that a Heisenberg
+spin chain coupled to dynamical optical phonons exhibits a transition towards a
+spontaneously dimerized state in a wide range of parameter space. The low
+energy excitations are characterized as solitons. No binding between solitons
+occurs in the isolated spin-phonon chain and the dynamical spin structure
+factor shows a broad magnon dispersion. However, elastic interchain coupling
+can lead to the formation of bound states.",9802053v2
+1998-03-14,Bound states of magnons in the S=1/2 quantum spin ladder,"We study the excitation spectrum of the two-leg antiferromagnetic S=1/2
+Heisenberg ladder. Our approach is based on the description of the excitations
+as triplets above a strong-coupling singlet ground state. The quasiparticle
+spectrum is calculated by treating the excitations as a dilute Bose gas with
+infinite on-site repulsion. We find singlet (S=0) and triplet (S=1)
+two-particle bound states of the elementary triplets. We argue that bound
+states generally exist in any dimerized quantum spin model.",9803180v1
+1998-06-18,The symmetry problem in NaV2O5,"We discuss the symmetry of NaV2O5 in the high temperature phase on the basis
+of optical conductivity data. Conclusive information cannot be obtained by
+studying the optically allowed lattice vibrations. However, intensity and
+polarization of the electronic excitations give a direct indication for a
+broken-parity electronic ground-state. This is responsible for the detection of
+charged bi-magnons in the optical spectrum.",9806222v1
+1998-07-09,Magnitoelastic interaction and long-range magnetic ordering in two-dimesional ferromagnetics,"The influence of magnitoelastic (ME) interaction on the stabilization of
+long-range magnetic order (LMO) in the two-dimensional easy-plane ferromagnetic
+is investigated in this work. The account of ME exchange results in the root
+dispersion law of magnons and appearance of ME gap in the spectra of elementary
+excitations. Such a behavior of the spectra testifies to the stabilization of
+LMO and finite Curie's temperature.",9807129v1
+1998-08-24,Theory of magnetic excitations in the Kondo lattice,"We present a theory for the spin excitations of the Kondo lattice. We derive
+an effective Hamiltonian, which describes Fermionic spin 1/2 charge
+fluctuations interacting with Bosonic triplet spin fluctuations. We show that
+already the simplest approximation possible, i.e. replacing the magnon
+self-energy by the free polarization bubble for the charge excitation Greens
+function, gives a quantitative description of the `spin gap' and `charge gap'
+as obtained in numerical calculations for the Kondo insulator.",9808261v1
+1998-12-09,Thermodynamics of the t-J Ladder: A Stable Finite Temperature Density Matrix Renormalization Group Calculation,"Accurate numerical simulations of a doped t-J model on a two-leg ladder are
+presented for the particle number, chemical potential, magnetic susceptibility
+and entropy in the limit of large exchange coupling on the rung using a finite
+temperature density matrix renormalization group (TDMRG) method. This required
+an improved algorithm to achieve numerical stability down to low temperatures.
+The thermal dissociation of hole pairs and of the rung singlets are separately
+observed and the evolution of the hole pair binding energy and magnon spin gap
+with hole doping is determined.",9812144v1
+1999-05-24,Temperature behavior of the magnon modes of the square lattice antiferromagnet,"A spin-wave theory of short-range order in the square lattice Heisenberg
+antiferromagnet is formulated. With growing temperature from T=0 a gapless mode
+is shown to arise simultaneously with opening a gap in the conventional
+spin-wave mode. The spectral intensity is redistributed from the latter mode to
+the former. For low temperatures the theory reproduces results of the modified
+spin-wave theory by M.Takahashi, J.E.Hirsch et al. and without fitting
+parameters gives values of observables in good agreement with Monte Carlo
+results in the temperature range 0 <= T < 0.8J where J is the exchange
+constant.",9905340v1
+1999-06-16,Perturbation Theory by Flow Equations: Dimerized and Frustrated S=1/2 Chain,"The flow equation method (Wegner 1994) is used as continuous unitary
+transformation to construct perturbatively effective Hamiltonians. The method
+is illustrated in detail for dimerized and frustrated antiferromagnetic S=1/2
+chains. The effective Hamiltonians conserve the number of elementary
+excitations which are S=1 magnons for the dimerized chains. The sectors of
+different number of excitations are clearly separated. Easy-to-use results for
+the gap, the dispersion and the ground state energies of the chains are
+provided.",9906243v1
+1999-06-25,Structure and relevant dimension of the Heisenberg model and applications to spin rings,"For the diagonalization of the Hamilton matrix in the Heisenberg model
+relevant dimensions are determined depending on the applicable symmetries.
+Results are presented, both, by general formulae in closed form and by the
+respective numbers for a variety of special systems. In the case of cyclic
+symmetry, diagonalizations for Heisenberg spin rings are performed with the use
+of so-called magnon states. Analytically solvable cases of small spin rings are
+singled out and evaluated.",9906382v1
+1999-08-26,Magnons in real materials from density-functional theory,"We present an implementation of the adiabatic spin-wave dynamics of Niu and
+Kleinman. This technique allows to decouple the spin and charge excitations of
+a many-electron system using a generalization of the adiabatic approximation.
+The only input for the spin-wave equations of motion are the energies and Berry
+curvatures of many-electron states describing frozen spin spirals. The latter
+are computed using a newly developed technique based on constrained
+density-functional theory, within the local spin density approximation and the
+pseudo-potential plane-wave method. Calculations for iron show an excellent
+agreement with experiments.",9908386v1
+2000-02-04,Robust half-metallicity and metamagnetism in Fe_{x}Co_{1-x}S_{2},"The Fe_{x}Co_{1-x}S_{2} system is predicted, on the basis of density
+functional calculations, to be a half metal for a large range of
+concentrations. Unlike most known half metals, the half metallicity in this
+system should be very stable with respect to crystallographic disorder and
+other types of defects. The endmember of the series, CoS_{2}, is not a half
+metal, but exhibits interesting and unusual magnetic properties which can,
+however, be reasonably well understood within the density functional theory,
+particularly with the help of the extended Stoner model. Calculations suggest
+strong electron-phonon and electron-magnon coupling in the system, and probably
+a bad metal behavior at high temperatures.",0002069v1
+2000-03-21,Quantum renormalization of high energy excitations in the 2D Heisenberg antiferromagnet,"We find using Monte Carlo simulations of the spin-1/2 2D square lattice
+nearest neighbour quantum Heisenberg antiferromagnet that the high energy peak
+locations at (pi,0) and (pi/2,pi/2) differ by about 6%, (pi/2,pi/2) being the
+highest. This is a deviation from linear spin wave theory which predicts equal
+magnon energies at these points.",0003350v2
+2000-05-09,Spin-Waves in itinerant ferromagnets,"We introduce a novel approach for the investigation of spin-wave excitations
+in itinerant ferromagnets. Our theory is based on a variational treatment of
+general multi-band Hubbard models which describe elements and compounds of
+transition metals. The magnon dispersion is derived approximately as the energy
+of a variational spin-wave state in the limit of large spatial dimensions. A
+numerical evaluation of our results is feasible for general multi-band models.
+As a first application we consider a model with two degenerate orbitals per
+lattice site. From our results we can conclude that spin-wave excitations in
+strong itinerant ferromagnets are very similar to those in ferromagnetic spin
+systems.",0005154v1
+2000-05-24,Andreev Peaks and Massive Magnons in Cuprate SNS junctions,"The projected SO(5) theory (pSO(5)) is used to resolve the puzzle of two
+distinct energy gaps in high T$_c$ Superconductor-Normal-Superconductor
+junctions. Counter to conventional theory of multiple Andreev reflections
+(MAR), the differential resistance peaks are associated with the
+antiferromagnetic resonance observed in neutron scattering, and not with Cooper
+pair breaking. The pSO(5) and MAR theories differ by the expected tunneling
+charges at the peaks. We propose that shot noise experiments could discriminate
+against the conventional interpretation.",0005420v2
+2000-08-01,Introduction to the Bethe Ansatz III,"Having introduced the magnon in part I and the spinon in part II as the
+relevant quasi-particles for the interpretation of the spectrum of low-lying
+excitations in the one-dimensional (1D) s=1/2 Heisenberg ferromagnet and
+antiferromagnet, respectively, we now study the low-lying excitations of the
+Heisenberg antiferromagnet in a magnetic field and interpret these collective
+states as composites of quasi-particles from a different species. We employ the
+Bethe ansatz to calculate matrix elements and show how the results of such a
+calculation can be used to predict lineshapes for neutron scattering
+experiments on quasi-1D antiferromagnetic compounds. The paper is designed as a
+tutorial for beginning graduate students. It includes 11 problems for further
+study.",0008018v1
+2000-08-09,Bulk experimental evidence of half-metallic ferromagnetism in doped manganites,"We report precise measurements and quantitative data analysis on the
+low-temperature resistivity of several ferromagnetic manganite films. We
+clearly show that there exists a T^{4.5} term in low-temperature resistivity,
+and that this term is in quantitative agreement with the quantum theory of
+two-magnon scattering for half metallic ferromagnets. Our present results
+provide the first bulk experimental evidence of half-metallic ferromagnetism in
+doped manganites.",0008151v1
+2000-08-10,Discussion of a spin-cluster model for the low temperature phase of NaV_2O_5,"We discuss magnetic excitations of a spin-cluster model which has been
+suggested to describe the low temperature phase of alpha'-NaV_2O_5. This model
+fulfills all symmetry criteria proposed by recent x-ray investigations. We find
+that this model is not able to describe the occurence of two well separated
+magnon lines perpendicular to the ladder direction as observed in INS
+experiments. We suggest further experimental analysis to generally distinguish
+between models with double reflection or inversion symmetry.",0008172v2
+2000-10-19,Magnetic Collective Mode Dispersion in High Temperature Superconductors,"Recent neutron scattering experiments in the superconducting state of YBCO
+have been interpreted in terms of a magnetic collective mode whose dispersion
+relative to the commensurate wavevector has a curvature opposite in sign to a
+conventional magnon dispersion. The purpose of this article is to demonstrate
+that simple linear response calculations are in support of a collective mode
+interpretation, and to explain why the dispersion has the curvature it does.",0010298v1
+2000-10-20,Dynamical stripe structure in La$_{2-x}$Sr$_x$CuO$_4$ observed by Raman scattering,"The dynamical stripe structure relating to the ""1/8 problem"" was investigated
+in La$_{2-x}$Sr$_x$CuO$_4$ utilizing the high frequency response of Raman
+scattering. The split of the two-magnon peak due to the formation of the stripe
+structure was observed at whole Sr concentration region from $x=0.035$ to 0.25
+at low temperatures. Especially clear split was observed at low carrier
+concentration region $x=0.035 - 0.06$ and at $x \sim 1/8$. The onset
+temperatures of these stripe structures are as high as 300-350 K, which are
+much higher than the temperatures measured by slow response probes.",0010305v1
+2000-11-07,Electron Spin Flip Relaxation by One Magnon Processes: Application to the Gadolinium surface band,"The ""s-f model"", also known as the ferromagnetic Kondo lattice, contains a
+description of band electrons coupled to localized spins which is an
+appropriate description of the magnetic part of the low-energy physics of Gd
+metal. Here the model is used to estimate the lifetime broadening of the
+minority spin component of the surface electron band in ferromagnetic
+gadolinium metal at temperatures below the Curie temperature. The low
+temperature result 0.10 eV agrees nicely with a measurement by Fedorov et al.",0011121v2
+2000-12-06,Dispersion of the neutron resonance in cuprate superconductors,"We argue that recently measured downward dispersion of the neutron resonance
+peak in cuprate superconductors is naturally explained if the resonance is
+viewed as a spin-1 collective mode in a d-wave superconductor. The reduction of
+the resonant frequency away from the antiferromagnetic wave vector is a direct
+consequence of the momentum dependence of the d-wave superconducting gap. When
+the magnetic correlation length becomes large, the dispersion should become
+magnon-like, i.e., curve upwards from (pi,pi).",0012065v2
+2001-04-05,Nonlinear dynamics of the classical isotropic Heisenberg antiferromagnetic chain: the sigma model sector and the kink sector,"We identify two distinct low-energy sectors in the classical isotropic
+antiferromagnetic Heisenberg spin-S chain. In the continuum limit, we show that
+two types of rotation generators arise for the field in each sector. Using
+these, the Lagrangian for sector I is shown to be that of the nonlinear sigma
+model. Sector II has a null Lagrangian; Its Hamiltonian density is just the
+Pontryagin term. Exact solutions are found in the form of magnons and
+precessing pulses in I and moving kinks in II. The kink has `spin' S. Sector I
+has a higher minimum energy than II.",0104093v1
+2001-05-23,Field-Induced Magnetic Order in Quantum Spin Liquids,"We study magnetic field-induced three-dimensional ordering transitions in
+low-dimensional quantum spin liquids, such as weakly coupled, antiferromagnetic
+spin-1/2 Heisenberg dimers and ladders. Using stochastic series expansion
+quantum Monte Carlo simulations, thermodynamic response functions are obtained
+down to ultra-low temperatures. We extract the critical scaling exponents which
+dictate the power-law dependence of the transition temperature on the applied
+magnetic field. These are compared with recent experiments on candidate
+materials and with predictions for the Bose-Einstein condensation of magnons
+obtained in mean-field theory.",0105464v1
+2001-05-31,Strong Enhancement of Superconducting T_c in Ferromagnetic Phases,"It is shown that the critical temperature for spin-triplet, p-wave
+superconductivity mediated by spin fluctuations is generically much higher in a
+Heisenberg ferromagnetic phase than in a paramagnetic one, due to the coupling
+of the magnons to the longitudinal magnetic susceptibility. Together with the
+tendency of the low-temperature ferromagnetic transition in very clean
+Heisenberg magnets to be of first order, this qualitatively explains the phase
+diagram recently observed in UGe_2.",0105627v2
+2001-06-04,An analytical strong coupling approach in dynamical mean-field theory,"In the limit of infinite spatial dimensions a thermodynamically consistent
+theory of the strongly correlated electron systems, which is valid for
+arbitrary value of the Coulombic interaction ($U<\infty$), is built. For the
+Hubbard model the total auxiliary single-site problem exactly splits into four
+subspaces, which describe Fermi and non-Fermi liquid components. Such
+analytical approach allows to construct different thermodynamically consistent
+approximations: alloy-analogy approximation, Hartree-Fock approximation and
+further, that describes the self-consistent renormalization of the bosonic
+excitations (magnons and doublons).",0106044v2
+2001-06-06,Low Voltage I-V Characteristics in Magnetic Tunnel Junctions,"We show that elastic currents that take into account variations of the tunnel
+transmitivity with voltage and a large ratio of majority to minority spin
+densities of states of the $s$ band, can account for the low voltage current
+anomalies observed in magnet-oxide-magnet junctions. The anomalies can be
+positive, negative or have a mixed form, depending of the position of the Fermi
+level in the $s$ band, in agreement with observations. Magnon contribution is
+negligible small to account for the sharp drop of the magnetoresistance with
+the voltage bias.",0106123v1
+2001-07-16,Continuous canonical transformation for the double exchange model,"The method of continuous canonical transformation is applied to the double
+exchange model with a purpose to eliminate the interaction term responsible for
+non conservation of magnon number. Set of differential equations for the
+effective Hamiltonian parameters is derived. Within the lowest order
+(approximate) solution we reproduce results of the standard (single step)
+canonical transformation. Results of the selfconsistent numerical treatment are
+compared with the other known studies for this model.",0107331v1
+2001-08-06,Li Induced Spin and Charge Excitations in a Spin Ladder,"A lithium dopant in a cuprate spin ladder acts as a vacant (non-magnetic)
+site accompanied by an extra hole bound by a Coulomb potential. We find that,
+although the undoped ladder spin gap is not essentially altered by Li doping, a
+dopant-magnon bound state appears within the gap. Contrary to the case of
+Zn-doped ladders, we predict that, in the Li-doped ladder, the spin liquid
+character is very robust against antiferromagnetism. We also predict the
+spatial dependence of the density of states in the vicinity of the dopant which
+could be measured by local spectroscopic probes.",0108099v1
+2001-08-27,Independent magnon states on magnetic polytopes,"For many spin systems with constant isotropic antiferromagnetic
+next-neighbour Heisenberg coupling the minimal energies E_{min}(S) form a
+rotational band, i.e. depend approximately quadratically on the total spin
+quantum number S, a property which is also known as Lande interval rule.
+However, we find that for certain coupling topologies, including recently
+synthesised icosidodecahedral structures this rule is violated for high total
+spins. Instead the minimal energies are a linear function of total spin. This
+anomaly results in a corresponding jump of the magnetisation curve which
+otherwise would be a regular staircase.",0108432v1
+2001-08-29,Order by distortion and string modes in pyrochlore antiferromagnet,"We study the effects of magnetoelastic couplings on pyrochlore
+antiferromagnets. We employ Landau theory, extending an investigation begun by
+Yamashita and Ueda for the case of S=1, and semiclassical analyses to argue
+that such couplings generate bond order via a spin--Peierls transition. This is
+followed by, or concurrent with, a transition into one of several possible
+low-temperature Neel phases, with most simply collinear, but also coplanar or
+mixed spin patterns. In a collinear Neel phase, a dispersionless string-like
+magnon mode dominates the resulting excitation spectrum, providing a
+distinctive signature of the parent geometrically frustrated state. We comment
+on the experimental situation.",0108505v1
+2001-10-16,"Spin Waves, Phase Separation, and Interphase Boundaries in Double Exchange Magnets","We study a classical double exchange magnet with direct antiferromagnetic
+superexchange coupling, J, between the localized spins. It is shown that the
+de-stabilization of the ferromagnetic ground state with increasing J leads to
+phase separation; the latter always preempts the spin-wave instability
+(softening of the magnon spectrum). It is also found that the boundaries
+separating the ferromagnetic and antiferromagnetic areas of the sample tend to
+be abrupt.",0110322v2
+2001-12-24,Magnetic phase diagram of the half-filled t-t'-Hubbard model -- finite-U effects on competing interactions and frustration,"The magnon propagator is evaluated in the AF (\pi,\pi,\pi) and the F-AF
+(0,\pi,\pi) states at the RPA level, and the spin-fluctuation corrections are
+compared. Transverse spin fluctuations are sharply enhanced by the frustration-
+inducing NNN hopping t', reducing the zero-temperature AF order in two
+dimensions, and the Neel temperature in three dimensions. The phase boundary
+between the insulating AF and F-AF states is obtained in the full range of
+interaction strength, indicating that the AF state is interestingly stabilized
+with decreasing U.",0112442v1
+2002-04-04,"Boundaries, Cusps and Caustics in the Multimagnon Continua of 1D Quantum Spin Systems","The multimagnon continua of 1D quantum spin systems possess several
+interesting singular features that may soon be accessible experimentally
+through inelastic neutron scattering. These include cusps and composition
+discontinuities in the boundary envelopes of two-magnon continuum states and
+discontinuities in the density of states, ""caustics"", on and within the
+continuum, which will appear as discontinuities in scattering intensity. In
+this note we discuss the general origins of these continuum features, and
+illustrate our results using the alternating Heisenberg antiferromagnetic chain
+and two-leg ladder as examples.",0204115v1
+2002-04-14,Raman scattering through surfaces having biaxial symmetry,"Magnetic Raman scattering in two-leg spin ladder materials and the
+relationship between the anisotropic exchange integrals are analyzed by P. J.
+Freitas and R. R. P. Singh in Phys. Rev. B, {\bf 62}, 14113 (2000). The angular
+dependence of the two-magnon scattering is shown to provide information for the
+magnetic anisotropy in the Sr_14Cu_24O_41 and La_6Ca_8Cu_24O_41 compounds. We
+point out that the experimental results of polarized Raman measurements at
+arbitrary angles with respect to the crystal axes have to be corrected for the
+light ellipticity induced inside the optically anisotropic crystals. We refer
+quantitatively to the case of Sr_14Cu_24O_41 and discuss potential implications
+for spectroscopic studies in other materials with strong anisotropy.",0204312v1
+2002-06-15,Effect of a Staggered Magnetic Field on the S=1 Haldane Chain with Single-ion Anisotropy,"We analyze the gaps in the excitation spectrum of a Haldane chain with
+single-ion anisotropy in a staggered field. We show that the gap along the
+direction of the field increases at a faster rate than the others, while its
+spectral weight decreases, being transferred to a two-magnon continuum.",0206288v1
+2002-07-04,Large N behavior of string solutions in the Heisenberg model,"We investigate the large $N$ behavior of the complex solutions for the two
+magnon system in the S=1/2 Heisenberg XXZ model. The Bethe ansatz equations are
+numerically solved for the string solutions with new iteration method. A clear
+evidence of the violation of the string configurations is found at
+$N=22,62,121,200,299,417$, but the broken states are still Bethe states. The
+number of the Bethe states is consistent with the exact diagonalization, except
+one singular state.",0207117v1
+2002-07-04,Quantum spin liquid in antiferromagnetic chain S=1/2 with Acoustic Phonons,"A spin and phonon excitations spectrum are studied using quantum Monte Carlo
+method in antiferromagnetic chain with spins $S=1/2$ coupled nonadiabaticity
+with acoustic phonons . It is found the critical coupling exists to open gap in
+the triplet excitation spectrum for any phonon velocity. The phase boundaries
+of delocalized phonons and propagated the bound states of magnon and a phonon
+are calculated. It is shown that the spherical symmetry of the spin-spin
+correlation functions is broken . The magnetic and optical properties $CuGeO_3$
+are explained without using spin-Peierls transition.",0207118v1
+2002-10-15,Spin-wave Hamiltonian in double-exchange systems,"A simple derivation of the effective spin-wave Hamiltonian for a
+double-exchange system with infinitely large Hund's-rule coupling is
+demonstrated. The formalism can be applied to models with arbitrary range of
+hopping as well as those with randomness. The result shows that, within the
+leading order of the 1/S expansion, one magnon excitation spectrum can be
+described by the Heisenberg model.",0210333v1
+2003-01-23,Excitations of anisotropic spin-1 chains with matrix product ground state,"We investigate a large class of antiferromagnetic spin-1 chains with nearest
+neighbour interaction and exactly known matrix product ground state. The
+spectrum of low-lying excitations is calculated numerically by DMRG and exact
+diagonalisation. Spin liquid behaviour with an excitation gap is observed
+meeting the Haldane scenario. Further, we compare properties of the anisotropic
+model with the well-known isotropic AKLT model and use the analytical single
+mode approximation to obtain a quantitative understanding of the excitation
+gap. The low-lying excited states can be interpreted in terms of a magnon-like
+elementary excitation.",0301435v1
+2003-03-20,About possible Phonon to Magnon alignment in 2 dimensions and theory of superconductivity in Copper-Oxide planes,"We suggest that the phonon dispersion in cuprates becomes strongly
+anisotropic due to interaction with spin waves; moreover the phonon dispersion
+becomes singular along $|k_x|=|k_y|$ directions. This would allow more
+electrons to form Cooper pairs and increase temperature of the superconducting
+transition. The interaction of phonons with spin waves is more important than
+the interaction of phonons with free electrons, because spin waves do not have
+the Fermi surface constrain.",0303402v5
+2003-04-25,Peculiar roles of spins in the thermal conductivity of pure and doped La_{2}CuO_{4}: Comparison with CuGeO_{3},"In-plane and out-of-plane thermal conductivities (\kappa_{ab} and \kappa_{c})
+are measured on single crystals of pure, 1%-hole-doped, and 1%-Zn-doped
+La_{2}CuO_{4}. The roles of magnons and the spin stripes in the heat transport
+in these samples are discussed. Comparison with the heat transport in
+CuGeO_{3}, which shows similar \kappa(T) behavior as that of La_{2}CuO_{4},
+gives us a lesson of how the heat transport can probe the difference in the
+spin ground state.",0304569v1
+2003-05-19,"Raman scattering studies of spin, charge, and lattice dynamics in Ca_{2-x}Sr_{x}RuO_{4} (0 =< x < 0.2)","We use Raman scattering to study spin, charge, and lattice dynamics in
+various phases of Ca_{2-x}Sr_{x}RuO_{4}. With increasing substitution of Ca by
+Sr in the range 0 =< x < 0.2, we observe (1) evidence for an increase of the
+electron-phonon interaction strength, (2) an increased temperature-dependence
+of the two-magnon energy and linewidth in the antiferromagnetic insulating
+phase, and (3) evidence for charge gap development, and hysteresis associated
+with the structural phase change, both of which are indicative of a first-order
+metal-insulator transition (T_{MI}) and a coexistence of metallic and
+insulating components for T < T_{MI}.",0305427v1
+2003-06-25,Dimerization versus Orbital Moment Ordering in the Mott insulator YVO$_3$,"We use exact diagonalization combined with mean-field theory to investigate
+the phase diagram of the spin-orbital model for cubic vanadates. The spin-orbit
+coupling competes with Hund's exchange and triggers a novel phase, with the
+ordering of $t_{2g}$ orbital magnetic moments stabilized by the tilting of
+VO$_6$ octahedra. It explains qualitatively spin canting and reduction of
+magnetization observed in YVO$_3$. At finite temperature an orbital Peierls
+instability in the $C$-type antiferromagnetic phase induces modulation of
+magnetic exchange constants even in absence of lattice distortions. The
+calculated spin structure factor shows a magnon splitting due to the orbital
+Peierls dimerization.",0306637v1
+2003-07-07,Universal scaling at field-induced magnetic phase transitions,"We study field-induced magnetic order in cubic lattices of dimers with
+antiferromagnetic Heisenberg interactions. The thermal critical exponents at
+the quantum phase transition from a spin liquid to a magnetically ordered phase
+are determined from Stochastic Series Expansion Quantum Monte Carlo
+simulations. These exponents are independent of the interdimer coupling ratios,
+and converge to the value obtained by considering the transition as a
+Bose-Einstein condensation of magnons, alpha_(BEC) = 1.5. The scaling results
+are of direct relevance to the spin-dimer systems TlCuCl_3 and KCuCl_3, and
+explain the broad range of exponents reported for field-induced ordering
+transitions.",0307126v1
+2003-07-15,Signatures of pairing mechanisms and order parameters in ferromagnetic superconductors,"Two predictions are made for properties of the ferromagnetic superconductors
+discovered recently. The first one is that spin-triplet, p-wave pairing in such
+materials will give the magnons a mass inversely proportional to the square of
+the magnetization. The second one is based on a specific mechanism for p-wave
+pairing, and predicts that the observed broad anomaly in the specific heat of
+URhGe will be resolved into a split transition with increasing sample quality.
+These predictions will help discriminate between different possible mechanisms
+for ferromagnetic superconductivity.",0307348v1
+2003-11-03,Current-driven domain wall motion in thin ferromagnetic wires,"The coupling between a current and a Bloch wall is examined in the half-metal
+limit of the double exchange model. The conduction electrons transfer angular
+momentum to the Bloch wall with 100% efficiency in the absence of pinning. The
+wall is displaced without distortion with velocity proportional to the current.
+In the presence of a pinning potential either the angular momentum is destroyed
+by the perpendicular component of the anisotropy field or is converted to
+coherent magnons. A moving wall has its velocity reduced by pinning. The
+expression for the velocity agrees surprisingly well with experiment.",0311039v2
+2004-01-20,The spin excitation spectrum in striped bilayer compounds,"The spin dynamics of bilayer cuprate compounds are studied in a basic model.
+The magnetic spectral properties are calculated in linear spin-wave theory for
+several stripe configurations which differ by the relative location of the
+stripes in the layers. We focus on the bilayer splitting of the magnon bands
+near the incommensurate low energy peaks as well as near the $\pi$ resonance,
+distinguishing between the odd and even channel. We find that a x-shaped
+dispersion near the $\pi$ resonance is generic for stripes. By comparison of
+our results to neutron scattering data for $\mathrm{YBa_2Cu_3O_{6+x}}$ we
+conclude that the stripe model is consistent with characteristic features of
+bilayer high-$T_c$ compounds.",0401354v1
+2004-01-24,Normal metal to ferromagnetic superconductor tunneling,"We study the point-contact tunneling between normal metal and ferromagnetic
+superconductor. In the case of magnon-induced pairing the tunneling conductance
+is continuous and smooth function of the applied voltage. For small values of
+the applied voltage the Ohm law holds. We show that one can obtain the
+magnetization and the superconducting order parameter from the tunneling
+conduc- tance. In the case of paramagnon-induced superconductivity the
+tunneling does not depend on the magnetization. We argue that tunneling
+experiment can unambiguously determine the correct pairing mechanism in the
+ferromagnetic superconductors.",0401480v2
+2004-01-31,Resonant magnetic mode in superconducting 2-leg ladders,"The spin dynamics of a doped 2-leg spin ladder is investigated by numerical
+techniques. We show that a hole pair-magnon boundstate evolves at finite hole
+doping into a sharp magnetic excitation below the two-particle continuum. This
+is supported by a field theory argument based on a SO(6)-symmetric ladder.
+Similarities and differences with the resonant mode of the high-T$_c$ cuprates
+are discussed.",0402011v1
+2004-02-20,Low-frequency incommensurate magnetic response in strongly correlated systems,"It is shown that in the t-J model of Cu-O planes at low frequencies the
+dynamic spin structure factor is peaked at incommensurate wave vectors
+(1/2+-delta,1/2)$, (1/2,1/2+-delta). The incommensurability is connected with
+the momentum dependencies of the magnon frequency and damping near the
+antiferromagnetic wave vector. The behavior of the incommensurate peaks is
+similar to that observed in La_{2-x}(Ba,Sr)_xCuO_{4+y} and YBa_2Cu_3O_{7-y}:
+for hole concentrations 0.02<x<=0.12 we find that delta is nearly proportional
+to x, while for x>0.12 it tends to saturation. The incommensurability
+disappears with increasing temperature. Generally the incommensurate magnetic
+response is not accompanied by an inhomogeneity of the carrier density.",0402512v1
+2004-02-25,Spin-polaron model: transport properties of EuB$_6$,"To understand anomalous transport properties of EuB$_6$, we have studied the
+spin-polaron Hamiltonian incorporating the electron-phonon interaction.
+Assuming a strong exchange interaction between the carriers and the localized
+spins, the electrical conductivity is calculated. The temperature and magnetic
+field dependence of the resistivity of EuB$_6$ are well explained. At low
+temperature, magnons dominate the conduction process, whereas the lattice
+contribution becomes significant at very high temperature due to the scattering
+with the phonons. Large negative magnetoresistance near the ferromagnetic
+transition is also reproduced as observed in EuB$_6$.",0402608v1
+2004-04-15,Magnetic groundstate and Fermi surface of bcc Eu,"Using spin-spiral technique within the full potential linearized
+augmented-plane-waves (LAPW) electronic structure method we investigate the
+magnon spectrum and N\'eel temperature of bcc Eu. Ground state corresponding to
+an incommensurate spin-spiral is obtained in agreement with experiment and
+previous calculations. We demonstrate that the magnetic coupling is primarily
+through the intra-atomic $f-s$ and $f-d$ exchange and
+Ruderman-Kittel-Kasuya-Yosida mechanism. We show that the existence of this
+spin-spiral is closely connected to a nesting feature of the Fermi surface
+which was not noticed before.",0404369v1
+2004-05-25,Exact low-temperature behavior of kagome antiferromagnet at high fields,"Low-energy degrees of freedom of a spin-1/2 kagome antiferromagnet in the
+vicinity of the saturation field are mapped to a hard-hexagon model on a
+triangular lattice. The latter model is exactly solvable. The presented mapping
+allows to obtain quantitative description of the magnetothermodynamics of a
+quantum kagome antiferromagnet up to exponentially small corrections as well as
+predict the critical behavior for the transition into a magnon crystal state.
+Analogous mapping is presented for the sawtooth chain, which is mapped onto a
+model of classical hard dimers on a chain.",0405578v2
+2004-06-21,"Magnetic susceptibility, exchange interactions and spin-wave spectra in the local spin density approximation","Starting from exact expression for the dynamical spin susceptibility in the
+time-dependent density functional theory a controversial issue about exchange
+interaction parameters and spin-wave excitation spectra of itinerant electron
+ferromagnets is reconsidered. It is shown that the original expressions for
+exchange integrals based on the magnetic force theorem (J. Phys. F14 L125
+(1984)) are optimal for the calculations of the magnon spectrum whereas static
+response function is better described by the ``renormalized'' magnetic force
+theorem by P. Bruno (Phys. Rev. Lett. 90, 087205 (2003)). This conclusion is
+confirmed by the {\it ab initio} calculations for Fe and Ni.",0406488v1
+2004-07-09,Stability of the spiral phase in the 2D extended t-J model,"We analyze the t-t'-t''-J model at low doping by chiral perturbation theory
+and show that the (1,0) spiral state is stabilized by the presence of t',t''
+above critical values around 0.2J, assuming t/J=3.1. We find that the (magnon
+mediated) hole-hole interactions have an important effect on the region of
+charge stability in the space of parameters t',t'', generally increasing
+stability, while the stability in the magnetic sector is guaranteed by the
+presence of spin quantum fluctuations (order from disorder effect). These
+conclusions are based on perturbative analysis performed up to two loops, with
+very good convergence.",0407242v1
+2004-08-18,Hole dynamics in spin and orbital ordered vanadium perovskites,"Hole dynamics in spin and orbital ordered vanadates with perovskite structure
+is investigated. A mobile hole coupled to the spin excitation (magnon) in the
+spin G-type and orbital C-type (SG/OC) ordered phase, and that to the orbital
+excitation (orbiton) in the spin C-type and orbital G-type (SC/OG) one are
+formulated on an equal footing. The observed fragile character of the (SG/OC)
+order is attributed to the orbiton softening caused by a reduction of the
+taggered magnetic order parameter. It is proposed that the qualitatively
+different hole dynamics in the two spin-orbital ordered phases in vanadates can
+be probed by the optical spectra.",0408395v1
+2004-10-19,Haldane-gap chains in a magnetic field,"We consider quasi one dimensional spin-1 Heisenberg chains with crystal field
+anisotropy in a uniform magnetic field. We determine the dynamical structure
+factor in various limits and obtain a fairly complete qualitative picture of
+how it changes with the applied field. In particular, we discuss how the width
+of the higher energy single magnon modes depends on the field. We consider the
+effects of a weak interchain coupling. We discuss the relevance of our results
+for recent neutron scattering experiments on the quasi-1D Haldane-gap compound
+NDMAP.",0410487v1
+2004-10-20,Spin-Transfer Torque and Electron-Magnon Scattering,"According to the spin-torque model, current-driven magnetic dynamics in
+ferromagnetic multilayers is determined by the transfer of electron spin
+perpendicular to the layers' magnetizations. By separating the largest
+contributions to the magnetic dynamics, we demonstrate that the dominant effect
+of spin-torque is rather due to the electron spin parallel to the field. We
+show that this effect can be equivalently described as stimulated
+current-driven excitation of spin-waves, and discuss four specifically
+quantum-mechanical aspects of spin-transfer, not described by the spin-torque.",0410520v1
+2004-11-13,Existence of the Spin-Wave Gap in a Deformed Flat-Band Hubbard Model,"We consider a deformed flat-band Hubbard model under a periodic boundary
+condition in arbitrary dimensions. We show that the ground state is only
+all-spin-up or -down state. We obtain upper and lower bounds of the one-magnon
+spin-wave energy with an arbitrary momentum. This dispersion relation is the
+same as that in the XXZ model in the certain parameter region. Therefore the
+spin wave has a finite energy gap. These results suggests the our model and the
+XXZ model.",0411362v1
+2004-11-28,Two-magnon Raman scattering in spin-ladders with exact singlet-rung ground state,"We suggest a family of spin-ladder models with exact singlet-rung vacuum. In
+addition to the terms describing interactions along legs and rungs the
+Hamiltonian has frustration and cyclic terms. Using coordinate Bethe ansatze
+all one- and two-dimensional states are constructed. The explicit formula for
+zero-temperature Raman scattering cross section is derived. The corresponding
+line-shapes are strongly asymmetric and have no more than one van-Hove
+singularity. The results are in good agreement with experimental data.",0411700v2
+2004-12-08,"The Gap Function Phi(k,w) for a Two-leg t-J Ladder and the Pairing Interaction","The gap function phi(k,omega), determined from a Lanczos calculation for a
+doped 2-leg t-J ladder, is used to provide insight into the spatial and
+temporal structure of the pairing interaction. It implies that this interaction
+is a local near-neighbor coupling which is retarded. The onset frequency of the
+interaction is set by the energy of an S=1 magnon-hole-pair and it is spread
+out over a frequency region of order the bandwith.",0412186v1
+2004-12-09,Modified Spin-Wave Theory for Nanomagnets : Application to the Keplerate Molecule Mo(72)Fe(30),"We adapt Takahashi's modified spin-wave theory to the context of
+nano-magnets, and apply it to the molecular compound based on the giant
+magnetic molecule Mo(72)Fe(30). This involves solving numerically the
+mean-field equations and then forcing the sublattice magnetizations to zero by
+means of local chemical potentials for the magnons. We have thus constructed a
+quantum state with no local magnetization at all temperatures, appropriate to a
+finite-size system, but with strong correlations. We compare theoretical
+results to specific heat and ESR measurements.",0412244v1
+2005-01-20,Quantum Heisenberg antiferromagnets: a survey of the activity in Firenze,"Over the years the research group in Firenze has produced a number of
+theoretical results concerning the statistical mechanics of quantum
+antiferromagnetic models, which range from the theory of two-magnon Raman
+scattering to the characterization of the phase transitions in quantum
+low-dimensional antiferromagnetic models. Our research activity was steadily
+aimed to the understanding of experimental observations.",0501496v1
+2005-02-22,Large magnetic field-induced spectral weight enhancement of high-energy spin excitations in $La_{1.88}Sr_{0.12}CuO_{4}$,"We report electronic Raman scattering experiments on a superconducting ${\rm
+La_{1.88}Sr_{0.12}CuO_{4}}$ single crystal in a magnetic field. At low
+temperatures, the spectral weight of the high-energy two-magnon peak increases
+linearly with field and is amplified by a factor of more than two at 14 T. The
+effect disappears at elevated temperatures and is not present in undoped ${\rm
+La_{2}CuO_{4}}$. This observation is discussed in terms of an electronically
+inhomogeneous state in which the field enhances the volume fraction of a phase
+with local antiferromagnetic order at the expense of the superconducting phase.",0502524v1
+2005-02-24,Lifetime Widths of Surface States on Magnetic Lanthanide Metals,"Low-temperature scanning tunneling spectroscopy is used to study electronic
+structure and dynamics of d-like surface states of trivalent lanthanide metals
+from La to Lu. The magnetic exchange splitting of these states is found to
+scale with the 4f spin multiplied by an effective exchange-coupling constant
+that increases with 4f occupancy in an approximately linear way. The dynamics
+of the surfaces states, as revealed by the lifetime width, is dominated by
+electron-phonon scattering in the occupied region and by electron-magnon
+scattering in the unoccupied region, respectively.",0502581v1
+2005-04-01,Doped two-leg ladder with ring exchange,"The effect of a ring exchange on doped two-leg ladders is investigated
+combining exact diagonalization (ED) and density matrix renormalization group
+(DMRG) computations. We focus on the nature and weights of the low energy
+magnetic excitations and on superconducting pairing. The stability with respect
+to this cyclic term of a remarkable resonant mode originating from a hole
+pair-magnon bound state is examined. We also find that, near the zero-doping
+critical point separating rung-singlet and dimerized phases, doping reopens a
+spin gap.",0504027v2
+2005-04-26,"Magnetic exchange coupling and Curie temperature of Ni(1+x)MnSb (x=0, 0.25, 0.5, 0.75, 1) from first principles","We study the dependence of magnetic interactions and Curie temperature in
+Ni(1+x)MnSb system on the Ni concentration within the framework of the
+density-functional theory. The calculation of the exchange parameters is based
+on the super-cell and frozen-magnon approaches. The Curie temperatures, Tc, are
+calculated within the random-phase approximation. In agreement with experiment
+we obtain decrease of the Curie temperature with increasing Ni content.",0504685v1
+2005-05-31,Dynamical properties of S=1 bond-alternating Heisenberg chains at finite temperatures,"Dynamical structure factors of the S=1 bond-alternating spin chains in the
+dimer phase are calculated at finite temperature, using the pair dynamical
+correlated-effective-field approximation. At T=0, the delta-function-type peak
+of the one-magnon mode appears. When temperature is increased, such a sharp
+peak is broadened and the additional weak peak caused by the excitation from
+the triplet state to the quintet state emerges in the higher energy region. The
+results are discussed in comparison with those obtained by the exact
+diagonalization method.",0505735v3
+2005-06-29,Nonanalytic Corrections to Fermi-Liquid Behavior in Helimagnets,"The Goldstone mode in the ordered phase of itinerant helimagnets, such as
+MnSi or FeGe, is determined and shown to have a strongly anisotropic dispersion
+relation. The softness of this mode is, in a well-defined sense, in between
+that of ferromagnetic and antiferromagnetic magnons, respectively. It is shown
+that this soft mode leads to nonanalytic corrections to Fermi-liquid behavior,
+with a T-contribution to the specific heat coefficient, and a
+T^{5/2}-contribution to the resistivity. The quasi-particle inelastic lifetime
+shows anisotropic behavior in momentum space.",0506770v1
+2005-07-20,Persistent spin current in mesoscopic ferrimagnetic spin ring,"Using a semiclassical approach, we study the persistent magnetization current
+of a mesoscopic ferrimagnetic ring in a nonuniform magnetic field. At zero
+temperature, there exists persistent spin current because of the quantum
+fluctuation of magnons, similar to the case of an antiferromagnetic spin ring.
+At low temperature, the current shows activation behavior because of the
+field-induced gap. At higher temperature, the magnitude of the spin current is
+proportional to temperature T, similar to the reported result of a
+ferromagnetic spin ring.",0507467v2
+2005-11-06,Dynamics of composite Haldane spin chains in IPA-CuCl3,"Magnetic excitations in the quasi-one-dimensional antiferromagnet IPA-CuCl3
+are studied by cold neutron inelastic scattering. Strongly dispersive gap
+excitations are observed. Contrary to previously proposed models, the system is
+best described as an asymmetric quantum spin ladder. The observed spectrum is
+interpreted in terms of ``composite'' Haldane spin chains. The key difference
+from actual S=1 chains is a sharp cutoff of the single-magnon spectrum at a
+certain critical wave vector.",0511143v1
+2006-03-05,Dynamical vertex approximation - a step beyond dynamical mean field theory,"We develop a diagrammatic approach with local and nonlocal self-energy
+diagrams, constructed from the local irreducible vertex. This approach includes
+the local correlations of dynamical mean field theory and long-range
+correlations beyond. It allows for example to describe (para-)magnons and weak
+localization effects in strongly correlated systems. As a first application, we
+study the interplay between nonlocal antiferromagnetic correlations and the
+strong local correlations emerging in the vicinity of a Mott-Hubbard
+transition.",0603100v2
+2006-03-14,Fingerprints of the Magnetic Polaron in Nonequilibrium Electron Transport through a Quantum Wire Coupled to a Ferromagnetic Spin Chain,"We study nonequilibrium quantum transport through a mesoscopic wire coupled
+via local exchange to a ferromagnetic spin chain. Using the Keldysh formalism
+in the self-consistent Born approximation, we identify fingerprints of the
+magnetic polaron state formed by hybridization of electronic and magnon states.
+Because of its low decoherence rate, we find coherent transport signals. Both
+elastic and inelastic peaks of the differential conductance are discussed as a
+function of external magnetic fields, the polarization of the leads and the
+electronic level spacing of the wire.",0603374v2
+2006-05-06,Evidence for multimagnon-mediated nuclear spin relaxation in the intertwining double-cain ferrimagnet $Ca_3 Cu_3 (PO_4)_4$,"The nuclear spin-lattice relaxation time $T_1$ of $^{31}P$ nuclei in the
+title compound is measured for the first time and interpreted in terms of a
+modified spin-wave theory. We establish a novel scenario for one-dimensional
+ferrimagnetic spin dynamics -- it is three-magnon processes enhanced by
+exchange scattering, rather than Raman processes, that make the major
+contribution to $1/T_1$.",0605157v2
+2006-05-22,Coupling of phonons and electromagnons in GdMnO_3,"The infrared and Terahertz properties of GdMnO_3 have been investigated as
+function of temperature and magnetic field, with special emphasis on the phase
+boundary between the incommensurate and the canted antiferromagnetic
+structures. The heterogeneous incommensurate phase reveals strong
+magnetodielectric effects, characterized by significant magnetoelectric
+contributions to the static dielectric permittivity and by the existence of
+electrically excited magnons (electromagnons). In the commensurate canted
+antiferromagnetic phase the magnetoelectric contributions to the dielectric
+constant and electromagnons are suppressed. The corresponding spectral weight
+is transferred to the lowest lattice vibration demonstrating the strong
+coupling of phonons with electromagnons.",0605523v1
+2006-07-07,Broken axisymmetry phase of a spin-1 ferromagnetic Bose-Einstein condensate,"A spin-1 ferromagnetic Bose-Einstein condensate subject to a certain magnetic
+field exhibits a broken-axisymmetry phase in which the magnetization tilts
+against the applied magnetic field due to the competition between
+ferromagnetism and linear and quadratic Zeeman effects. The Bogoliubov analysis
+shows that in this phase two Goldstone modes associated with U(1) and SO(2)
+symmetry breakings exist, in which phonons and magnons are coupled to restore
+the two broken symmetries.",0607184v1
+2006-09-17,Universal conductance fluctuations in epitaxial GaMnAs ferromagnets: structural and spin disorder,"Mesoscopic transport measurements reveal a large effective phase coherence
+length in epitaxial GaMnAs ferromagnets, contrary to usual 3d-metal
+ferromagnets. Universal conductance fluctuations of single nanowires are
+compared for epilayers with a tailored anisotropy. At large magnetic fields,
+quantum interferences are due to structural disorder only, and an unusual
+behavior related to hole-induced ferromagnetism is evidenced, for both quantum
+interferences and decoherence. At small fields, phase coherence is shown to
+persist down to zero field, even in presence of magnons, and an additional spin
+disorder contribution to quantum interferences is observed under domain walls
+nucleation.",0609410v1
+2006-09-25,"Light-Induced Magnetic Precession in (Ga,Mn)As Slabs: Hybrid Standing-Wave Damon-Eshbach Modes","Coherent oscillations associated with spin precessions were observed in
+ultrafast optical experiments on ferromagnetic (Ga,Mn)As films. Using a
+complete theoretical description of the processes by which light couples to the
+magnetization, values for the exchange and anisotropy constants were obtained
+from the field-dependence of the magnon frequencies and the
+oscillation-amplitude ratios. Results reveal a relatively large negative
+contribution to the energy due to surface anisotropy leading to excitations
+that are a mixture of bulk waves and surface modes.",0609646v1
+2006-10-23,Mechanism of temperature dependence of the magnetic anisotropy energy in ultrathin Cobalt and Nickel films,"Temperature dependent FMR-measurements of Ni and Co films are analysed using
+a microscopic theory for ultrathin metallic systems. The mechanism governing
+the temperature dependence of the magnetic anisotropy energy is identified and
+discussed. It is reduced with increasing temperature. This behavior is found to
+be solely caused by magnon excitations.",0610649v1
+2006-10-27,Local moment fluctuations in an optimally-doped high Tc superconductor,"We present results of neutron scattering experiments on YBa2Cu3O6.95
+(Tc=93K). Our results indicate that magnetic collective modes due to correlated
+local moments are present both above and below Tc in optimally doped YBCO. The
+magnon-like modes are robust and not overdamped by itinerant particle-hole
+excitations, which may point at a substantial static or slowly fluctuating
+charge inhomogeneity. We compare the experimental results to predictions of the
+Fermi liquid (FL) theory in the Random Phase Approximation (RPA).",0610755v2
+2006-12-12,Lattice gas description of pyrochlore and checkerboard antiferromagnets in a strong magnetic field,"Quantum Heisenberg antiferromagnets on pyrochlore and checkerboard lattices
+in a strong external magnetic field are mapped onto hard-core lattice gases
+with an extended exclusion region. The effective models are studied by the
+exchange Monte Carlo simulations and by the transfer matrix method. The
+transition point and the critical exponents are obtained numerically for a
+square-lattice gas of particles with the second-neighbor exclusion, which
+describes a checkerboard antiferromagnet. The exact structure of the magnon
+crystal state is determined for a pyrochlore antiferromagnet.",0612283v2
+2006-12-21,Spin wave excitations: The main source of the temperature dependence of Interlayer exchange coupling in nanostructures,"Quantum mechanical calculations based on an extended Heisenberg model are
+compared with ferromagnetic resonance (FMR) experiments on prototype trilayer
+systems Ni_7/Cu_n/Co_2/Cu(001) in order to determine and separate for the first
+time quantitatively the sources of the temperature dependence of interlayer
+exchange coupling. Magnon excitations are responsible for about 75% of the
+reduction of the coupling strength from zero to room temperature. The remaining
+25% are due to temperature effects in the effective quantum well and the
+spacer/magnet interfaces.",0612568v1
+2007-03-05,Non--Heisenberg Spin Dynamics of Double-Exchange Ferromagnets with Coulomb Repulsion,"With a variational three--body calculation we study the role of the interplay
+between the onsite Coulomb, Hund's rule, and superexchange interactions on the
+spinwave excitation spectrum of itinerant ferromagnets. We show that
+correlations between a Fermi sea electron--hole pair and a magnon result in a
+very pronounced zone boundary softening and strong deviations from the
+Heisenberg spinwave dispersion. We show that this spin dynamics depends
+sensitively on the Coulomb and exchange interactions and discuss its possible
+relevance to experiments in the manganites.",0703099v2
+2007-03-12,Effect of Polarized Current on the Magnetic State of Antiferromagnet,"We provide evidence for the effects of spin polarized current on a
+nanofabricated antiferromagnet incorporated into a spin-valve structure.
+Signatures of current-induced effects include bipolar steps in differential
+resistance, current-induced changes of exchange bias correlated with these
+steps, and deviations from the statistics expected for thermally activated
+switching of spin valves. We explain our observations by a combination of spin
+torque exerted on the interfacial antiferromagnetic moments, and
+electron-magnon scattering in antiferromagnet.",0703281v2
+2007-03-30,Field-induced paramagnons at the metamagnetic transition in Ca1.8Sr0.2RuO4,"The magnetic excitations in Ca1.8Sr0.2RuO4 were studied across the
+metamagnetic transition and as a function of temperature using inelastic
+neutron scattering. At low temperature and low magnetic field the magnetic
+response is dominated by a complex superposition of incommensurate
+antiferromagnetic fluctuations. Upon increasing the magnetic field across the
+metamagnetic ransition, paramagnon and finally well-defined magnon scattering
+is induced, partially suppressing the incommensurate signals. The high-field
+phase in Ca1.8Sr0.2RuO4 has, therefore, to be considered as an intrinsically
+ferromagnetic state stabilized by the magnetic field.",0703806v1
+1992-12-18,Finite size and temperature effects in the AF Heisenberg model,"The low temperature and large volume effects in the d=2+1 antiferromagnetic
+quantum Heisenberg model are dominated by magnon excitations. The leading and
+next-to-leading corrections are fully controlled by three physical constants,
+the spin stiffness, the spin wave velocity and the staggered magnetization.
+Among others, the free energy, the ground state energy, the low lying
+excitations, staggered magnetization, staggered and uniform susceptibilities
+are studied here. The special limits of very low temperature and infinite
+volume are considered also.",9212022v1
+1993-11-10,Nonrelativistic effective Lagrangians,"Chiral perturbation theory is extended to nonrelativistic systems with
+spontaneously broken symmetry. In the effective Lagrangian, order parameters
+associated with the generators of the group manifest themselves as effective
+coupling constants of a topological term, which is gauge invariant only up to a
+total derivative. In the case of the ferromagnet, a term connected with the
+Brouwer degree dominates the derivative expansion. The general analysis
+includes antiferromagnetic magnons and phonons, while the effective field
+theory of fluids or gases is beyond the scope of the method.",9311264v1
+1999-07-26,The Casimir energy of skyrmions in the 2+1-dimensional O(3)-model,"One-loop quantum corrections to the classical vortices in 2+1 dimensional
+O(3)-models are evaluated. Skyrme and Zeeman potential terms are used to
+stabilize the size of topological solitons. Contributions from zero modes,
+bound-states and scattering phase-shifts are calculated for vortices with
+winding index n=1 and n=2. For both cases the S-matrix shows a pronounced
+series of resonances for magnon-vortex scattering in analogy to the
+well-established baryon resonances in hadron physics, while vortices with n>2
+are already classically unstable against decay. The quantum corrections
+destabilize the classically bound n=2 configuration. Approximate independence
+of the results with respect to changes in the renormalization scale is
+demonstrated.",9907492v1
+1992-04-17,Heisenberg XXZ Model and Quantum Galilei Group,"The 1D Heisenberg spin chain with anisotropy of the XXZ type is analyzed in
+terms of the symmetry given by the quantum Galilei group Gamma_q(1). We show
+that the magnon excitations and the s=1/2, n-magnon bound states are determined
+by the algebra. Thus the Gamma_q(1) symmetry provides a description that
+naturally induces the Bethe Ansatz. The recurrence relations determined by
+Gamma_q(1) permit to express the energy of the n-magnon bound states in a
+closed form in terms of Tchebischeff polynomials.",9204054v1
+1998-08-28,"Goldstone and Pseudo-Goldstone Bosons in Nuclear, Particle and Condensed-Matter Physics","These notes review the effective lagrangian treatment of Goldstone and
+pseudo-Goldstone bosons, taking examples from high-energy/nuclear and
+condensed-matter physics. The contents are:
+  1. Goldstone Bosons
+  2. Pions: A Relativistic Application
+  3. Magnons: Nonrelativistic Applications
+  4. SO(5) Invariance and Superconductors
+  5. Bibliography",9808176v3
+2005-04-19,"Notes on non-extremal, charged, rotating black holes in minimal D=5 gauged supergravity","We consider the non-extremal, charged, rotating black hole solution of five
+dimensional minimal gauged supergravity of Cvetic, Lu and Pope [Phys.Lett. B
+598 (2004) 273]. We compute the Ashtekar-Magnon-Das mass and show it agrees
+with the thermodynamic mass. We find a reducible Killing tensor and integrate
+the geodesic equation explicitly. We also compute the Euclidean action of the
+black hole and show it satisfies the quantum statistical relation. Further we
+present a Smarr relation. We end with a discussion of applications to string
+theory.",0504158v1
+2005-11-28,Controlling quantum state transfer in spin chain with the confined field,"As a demonstration of the spectrum-parity matching condition (SPMC) for
+quantum state transfer, we investigate the propagation of single-magnon state
+in the Heisenberg chain in the confined external tangent magnetic field
+analytically and numerically. It shows that the initial Gaussian wave packet
+can be retrieved at the counterpart location near-perfectly over a longer
+distance if the dispersion relation of the system meets the SPMC approximately.",0511246v1
+2006-03-14,Levinson theorem for Aharonov-Bohm scattering in two dimensions,"We apply the recently generalized Levinson theorem for potentials with
+inverse square singularities [Sheka et al, Phys.Rev.A, v.68, 012707 (2003)] to
+Aharonov-Bohm systems in two-dimensions. By this theorem, the number of bound
+states in a given m-th partial wave is related to the phase shift and the
+magnetic flux. The results are applied to 2D soliton-magnon scattering.",0603123v3
+2007-04-26,Coupling of phonons and spin waves in triangular antiferromagnet,"We investigate the influence of the spin-phonon coupling in the triangular
+antiferromagnet where the coupling is of the exchange-striction type. The
+magnon dispersion is shown to be modified significantly at wave vector (2pi,0)
+and its symmetry-related points, exhibiting a roton-like minimum and an
+eventual instability in the dispersion. Various correlation functions such as
+equal-time phonon correlation, spin-spin correlation, and local magnetization
+are calculated in the presence of the coupling.",0704.3510v2
+2007-05-22,Two interacting GL-equations in High-T$_c$ superconductivity and quantum chromodynamics,"The possible connection between High-T$_c$ superconductivity and quantum
+chromodynamics is considered that is based on two interacting Ginzburg-Landau
+equations. For High-T$_c$ superconductivity these two equations describe Cooper
+electrons interacting with different kind of quasi particles (phonons, magnons,
+excitons and so on). The interaction term describes a possible interaction
+between different kind of quasi particles. For quantum chromodynamics the
+equations describe two kinds of gauge condensates. The condensates describe a
+gauge potential from a subalgebra of the SU(3) gauge group and the
+corresponding coset. Regular solutions are found which describe the situation
+where one field, $\psi_1$, is pushed out by another, $\psi_2$.",0705.3170v1
+2007-06-14,Spin-waves in a complex magnetic system: nonextensive approach,"In this paper we analyze the spin-wave excitations (magnons) of an
+inhomogeneous spin system within the Boltzmann-Gibbs framework and then connect
+the results with the nonextensive approach (in the sense of Tsallis
+statistics). Considering an equivalence between those two frameworks, we could
+connect the entropic parameter q with moments of the distribution of exchange
+integrals of the inhomogenous system. It ratifies the idea that the entropic
+parameter is connected to the microscopic properties of the system.",0706.2201v2
+2007-11-15,The QCD spin chain S matrix,"Beisert et al. have identified an integrable SU(2,2) quantum spin chain which
+gives the one-loop anomalous dimensions of certain operators in large N QCD. We
+derive a set of nonlinear integral equations (NLIEs) for this model, and
+compute the scattering matrix of the various (in particular, magnon)
+excitations.",0711.2415v3
+2007-12-15,Dynamic and Static Excitations of a Classical Discrete Anisotropic Heisenberg Ferromagnetic Spin Chain,"Using Jacobi elliptic function addition formulas and summation identities we
+obtain several static and moving periodic soliton solutions of a classical
+anisotropic, discrete Heisenberg spin chain with and without an external
+magnetic field. We predict the dispersion relations of these nonlinear
+excitations and contrast them with that of magnons and relate these findings to
+the materials realized by a discrete spin chain. As limiting cases, we discuss
+different forms of domain wall structures and their properties.",0712.2503v1
+2008-03-20,Interplay between magnetic and lattice excitations in BiFeO$_3$,"We have performed Raman scattering investigations on the high energy magnetic
+excitations in a BiFeO$_3$ single crystal as a function of both temperature and
+laser excitation energy. A strong feature observed at 1250 cm$^{-1}$ in the
+Raman spectra has been previously assigned to two phonon overtone. We show here
+that its unusual frequency shift with the excitation energy and its asymmetric
+temperature dependent Fano lineshape reveal a strong coupling to magnetic
+excitations. In the same energy range, we have also identified the two-magnon
+excitation with a temperature dependence very similar to $\alpha$-Fe$_2$O$_3$
+hematite.",0803.3015v1
+2008-04-14,Dissipation characteristics of quantized spin waves in nano-scaled magnetic ring structures,"The spatial profiles and the dissipation characteristics of spin-wave
+quasi-eigenmodes are investigated in small magnetic Ni$_{81}$Fe$_{19}$ ring
+structures using Brillouin light scattering microscopy. It is found, that the
+decay constant of a mode decreases with increasing mode frequency. Indications
+for a contribution of three-magnon processes to the dissipation of higher-order
+spin-wave quasi-eigenmodes are found.",0804.2200v1
+2008-04-14,On the observation of the spin resonance in superconducting CeCoIn_5,"Recent observation of a resonance spin excitation at (1/2,1/2,1/2) in the
+superconducting state of CeCoIn_5 [C. Stock et al., Phys. Rev. Lett. {\bf 100}
+087001 (2008)] was interpreted as an evidence for d_{x^2-y^2} gap symmetry, by
+analogy with the cuprates. This is true if the resonance is a spin exciton. We
+argue that such description is undermined by the three-dimensionality of
+CeCoIn_5. We show that in 3D systems the excitonic resonance only emerges at
+strong coupling, and is weak. We argue in favor of the alternative, magnon
+scenario, which does not require a d_{x^2-y^2} gap.",0804.2217v1
+2008-05-11,Evolution of Spin-Orbital-Lattice Coupling in the $R$VO$_3$ Perovskites,"We introduce a microscopic model which unravels the physical mechanisms
+responsible for the observed phase diagram of the $R$VO$_3$ perovskites. It
+reveals a nontrivial interplay between superexchange, the orbital-lattice
+coupling due to the GdFeO$_3$-like rotations of the VO$_6$ octahedra, and
+orthorhombic lattice distortions. We find that the lattice strain affects the
+onset of the magnetic and orbital order by partial suppression of orbital
+fluctuations. The present approach provides also a natural explanation of the
+observed reduction of magnon energies from LaVO$_3$ to YVO$_3$.",0805.1545v1
+2008-05-20,The Exchange Parameters in Lanthanum Manganites,"The spin-wave spectrum in the metallic ferromagnetic lantha-num cubic
+manganites was investigated. The interactions with four coordination spheres
+(32 neighbors) were taken into ac-count. The Heisenberg superexchange between
+all manganese ions as well as double exchange between the manganese ions with
+different valence were under consideration. The obtained magnon spectrum
+permits to investigate dispersion relations along an any crystallographic
+directions. This possibility was used for the numerical evaluation of the
+exchange parameters in the compounds La0.75Ca0.25MnO3 and La0.70Ca0.30MnO3 from
+the inelastic neutron scattering data.",0805.3006v1
+2008-06-12,Finite-size effects in the superconformal beta-deformed N=4 SYM,"We study finite size effects for composite operators in the SU(2) sector of
+the superconformal beta-deformed N=4 SYM theory. In particular we concentrate
+on the spectrum of one single magnon. Since in this theory one-impurity states
+are non BPS we compute their anomalous dimensions including wrapping
+contributions up to four loops and discuss higher order effects.",0806.2103v2
+2008-06-13,Negative differential conductivity in far-from-equilibrium quantum spin chains,"We show that, when a finite anisotropic Heisenberg spin-1/2 chain in the
+gapped regime is driven far from equilibrium, oppositely polarized
+ferromagnetic domains build up at the edges of the chain, thus suppressing
+quantum spin transport. As a consequence, a negative differential conductivity
+regime arises, where increasing the driving decreases the current. The above
+results are explained in terms of magnon localization and are shown to be
+structurally stable against breaking of integrability.",0806.2236v2
+2008-06-24,Spin dynamics in point contacts to single ferromagnetic films,"Excitation of magnons or spin-waves driven by nominally unpolarized transport
+currents in point contacts of normal and ferromagnetic metals is probed by
+irradiating the contacts with microwaves. Two characteristic dynamic effects
+are observed: a rectification of off-resonance microwave current by spin-wave
+nonlinearities in the point contact conductance, and a resonant stimulation of
+spin-wave modes in the nano-contact core by the microwave field. These
+observations provide a direct evidence that the magnetoconductance effects
+observed are due to GHz spin dynamics at the ferromagnetic interface driven by
+the spin transfer torque effect of the transport current.",0806.3805v1
+2008-09-03,Detection of coherent magnons via ultrafast pump-probe reflectance spectroscopy in multiferroic Ba0.6Sr1.4Zn2Fe12O22,"We report the detection of a magnetic resonance mode in multiferroic
+Ba0.6Sr1.4Zn2Fe12O22 using time domain pump-probe reflectance spectroscopy.
+Magnetic sublattice precession is coherently excited via picosecond thermal
+modification of the exchange energy. Importantly, this precession is recorded
+as a change in reflectance caused by the dynamic magnetoelectric effect. Thus,
+transient reflectance provides a sensitive probe of magnetization dynamics in
+materials with strong magnetoelectric coupling, such as multiferroics,
+revealing new possibilities for application in spintronics and ultrafast
+manipulation of magnetic moments.",0809.0672v1
+2008-09-28,Coherent terahertz needle radiation emission mechanism from nanostructured ferromagnetic metal films excited by femtosecond laser pulses,"A coherent terahertz needle radiation emission mechanism is proposed. This
+mechanism can be realized in the experiments on femtosecond laser pulses
+interacting with surface of nanostructured ferromagnetic metal film. The
+proposed mechanism is based on exciting of coupled coherent phonon-magnon modes
+on a nanostructured metal surface by laser femtosecond pulse. The value of the
+Poynting vector for the terahertz radiation is estimated.",0809.4868v1
+2008-11-27,Single impurity operators at critical wrapping order in the beta-deformed N=4 SYM,"We study the spectrum of one single magnon in the superconformal
+beta-deformed N=4 SYM theory in the planar limit. We compute the anomalous
+dimensions of one-impurity operators O_{1,L}= tr(phi Z^{L-1}), including
+wrapping contributions at their critical order L.",0811.4594v2
+2008-12-30,BPS ansatzes as electric form-factors,"We argue that BPS ansatzes, entering manifestly vacuum BPS monopole solutions
+to equations of motion in the (Minkowskian) non-Abelian Higgs model play the
+role of some electric form-factors and that this implies (soft) violating the
+CP-invariance of the mentioned model, similar to taking place in the Euclidian
+Yang-Mills (YM) theory with instantons, generating the $\theta$-term in the
+appropriate effective Hamiltonian.",0812.5080v5
+2009-01-11,Magnetic soliton transport over topological spin texture in chiral helimagnet with strong easy-plane anisotropy,"We show the existence of an isolated soliton excitation over the topological
+ground state configuration in chiral helimagnet with the Dzyaloshinskii-Moryia
+exchange and the strong easy-plane anisotropy. The magnetic field perpendicular
+to the helical axis stabilizes the kink crystal state which plays a role of
+""topological protectorate"" for the traveling soliton with a definite
+handedness. To find new soliton solution, we use the B\""{a}cklund
+transformation technique. It is pointed out that the traveling soliton carries
+the magnon density and a magnetic solition transport may be realized.",0901.1423v1
+2009-01-25,Sketching the Theory of Copper Oxide High Temperature Superconductivity,"The role of the anti-bonding state in the electron correlations in Copper
+Oxide HTSC is analyzed. Then the t-J Hamiltonian is used to establish the
+formation of the charge stripes in underdoped oxides. It is proposed that these
+stripes make up the boundaries between the two degenerate anti-ferromagnetic
+(AFM) states, and that they are a key factor in switching between these states.
+We also provide a theoretical expression for the charge driven AFM magnons that
+have been observed by Neutron scattering experiments. Finally, the double
+correlation theory is applied to the stripe phase of holes to result in the
+superconductive gap and in the ""pseudogap"".",0901.3896v2
+2009-02-10,Low-temperature thermodynamics of one class of flat-band models,"We consider the antiferromagnetic Heisenberg model and the repulsive Hubbard
+model for a class of frustrated lattices with a completely dispersionless
+(flat) lowest one-particle (either one-magnon or one-electron) band. We
+construct exact many-particle ground states for a wide range of particle
+densities, calculate their degeneracy, and, as a result, obtain closed-form
+expressions for the low-temperature thermodynamic quantities around a
+particular value of the magnetic field $h_{\rm{sat}}$ or the chemical potential
+$\mu_0$. We confirm our analytic findings by numerical data for finite
+lattices.",0902.1627v1
+2009-02-10,The Bethe Ansatz Equations for Reflecting Magnons,"We derive the Bethe Ansatz Equations on the half line for particles
+interacting through factorized $S$-matrices invariant relative to the centrally
+extended $su(2|2)$ Lie superalgebra and $su(1|2)$ open boundaries. These
+equations may be of relevance for the study of the spectrum of open strings on
+$AdS_{5} \times S^5$ background attached to Y=0 giant graviton branes. An
+one-dimensional spin chain hamiltonian associated to this system is also
+derived.",0902.1681v2
+2009-02-25,Hydrodynamic relation in 2D Heisenberg antiferromagnet in a field,"The spin-stiffness \rho_s of a 2D Heisenberg antiferromagnet depends
+non-analytically on external magnetic field. We demonstrate that the
+hydrodynamic relation between \rho_s, the uniform susceptibility \chi, and the
+spin-wave velocity $c$ is not violated by such a behavior because similar
+non-analytic terms from all three quantities mutually cancel out. In this work,
+explicit expressions for the field-dependent spin stiffness and for the magnon
+velocity of the 2D square lattice antiferromagnet are obtained by direct
+calculation to order 1/S and in the whole range of magnetic fields.",0902.4455v1
+2009-03-04,On the wrapping correction to single magnon energy in twisted N=4 SYM,"We apply Zeilberger summation to derive a closed formula for the wrapping
+correction to one-impurity states in the su(2) sector of the beta-deformed N=4
+SYM theory at beta=1/2. As an application depending heavily on the result, we
+compute the large volume expansion of the wrapping correction.",0903.0778v2
+2009-04-02,Emergent geometry in N=6 Chern-Simons-matter theory,"We investigate a strong coupling expansion of N=6 superconformal Chern-Simons
+theory obtained from the semiclassical analysis of low energy, effective
+degrees of freedom given by the eigenvalues of a certain matrix model. We show
+how the orbifolded sphere S^7/Z_k of the dual geometry emerges dynamically from
+the distribution of the eigenvalues. As a test of this approach we compute the
+energy of off-diagonal excitations, finding perfect agreement with the
+dispersion relation of giant magnons.",0904.0449v2
+2009-05-05,Edge exponent in the dynamic spin structure factor of the Yang-Gaudin model,"The dynamic spin structure factor $\mathcal{S}(k,\omega)$ of a system of
+spin-1/2 bosons is investigated at arbitrary strength of interparticle
+repulsion. As a function of $\omega$ it is shown to exhibit a power-law
+singularity at the threshold frequency defined by the energy of a magnon at
+given $k.$ The power-law exponent is found exactly using a combination of the
+Bethe Ansatz solution and an effective field theory approach.",0905.0598v1
+2009-05-12,Polar phonons and spin excitations coupling in multiferroic BiFeO3 crystals,"Raman scattering measurements on BiFeO3 single crystals show an important
+coupling between the magnetic order and lattice vibrations. The temperature
+evolution of phonons shows that the lowest energy E and A1 phonon modes are
+coupled to the spin order up to the Neel temperature. Furthermore, low
+temperature anomalies associated with the spin re-orientation are observed
+simultaneously in both the E phonon and the magnon. These results suggest that
+magnetostriction plays an important role in BiFeO3.",0905.1891v1
+2009-08-18,Spectral collapse in ensembles of meta-molecules,"We report on a new collective phenomenon in metamaterials: spectral line
+collapse with increasing number of the unit cell resonators (meta-molecules).
+Resembling the behaviour of exotic states of matter, such as Bose-Einstein
+condensates of excitons and magnons, this new effect is linked to the
+suppression of radiation losses in periodic arrays. We demonstrate
+experimentally spectral line collapse at microwave, terahertz and optical
+frequencies. It emerges as a universal and truly scalable effect underpinned by
+classical electromagnetic interactions between the excited meta-molecules.",0908.2533v1
+2009-10-10,Spin Order and Excitations in Triangular Antiferromagnet La2Ca2MnO7,"We report a spin S = 3/2 triangular antiferromagnet with nearest-neighbor
+coupling J = 0.29 meV in La2Ca2MnO7. A genuinely two-dimensional,
+three-sublattice order develops below 2.80 K << the Weiss constant (25 K). The
+spin excitations deviate substantially from linear spin-wave theory, suggesting
+that magnon breakdown occurs in the material. Such a breakdown has been
+anticipated in recent theoretical studies, although the excitation spectrum
+remains to be accounted for.",0910.1904v1
+2009-11-26,Bose-Einstein condensation of semi-hard bosons in S=1 dimerized organic compound F2PNNNO,"An analysis of the energy spectrum and the magnetization curve of
+two-dimensional organic antiferromagnet F2PNNNO with a spin-one dimerized
+structure shows that a behavior of the compound in an external magnetic field
+can be explained within a lattice boson model with an extended Pauli's
+exclusion principle, i.e. no more than two bosons per a dimer. The unusual
+magnetization curve observed experimentally in the compound reflects a sequence
+of phase transitions intrinsic for a lattice boson system with strong on-site
+and inter-site repulsions due to a tuning of magnon density by the applied
+magnetic field.",0911.5039v1
+2010-01-25,Evidence for effective thermal boundary resistance from magnon/phonon disequilibrium,"We use the time-resolved magneto-optical Kerr effect (TRMOKE) to measure the
+local temperature and heat flow dynamics in ferromagnetic SrRuO3 thin films.
+After heating by a pump pulse, the film temperature decays exponentially,
+indicating that the heat flow out of the film is limited by the film/substrate
+interface. We show that this behavior is consistent with an effective boundary
+resistance resulting from disequilibrium between the spin and phonon
+temperatures in the film.",1001.4557v1
+2010-03-04,Quantum critical surface of the zigzag spin chain under magnetic field: Application to superconducting quantum dots,"We analyze the exact ground state of XXZ zigzag spin chain with applied
+magnetic field and find the quantum critical surface. Using the theorem of
+positive semi-definite matrix, we can prove that the ground states for a
+specific region, are fully polarized state and one magnon states. With Bethe
+ansatz, we argue that this is the quantum critical surface in all cases. A
+first in the literature, we derive the analytical expression of quantum
+critical surface for superconducting quantum dots array in the presence of gate
+voltage.",1003.0954v1
+2010-04-01,Phenomenological Model of Longitudinal Spin Fluctuations in Itinerant Antiferromagnets,"We present the phenomenological analysis of the spectrum of longitudinal spin
+fluctuations in isotropic itinerant electron antiferromagnets with account of
+spin anharmonicity giving rise to coupling of transverse and longitudinal
+normal modes. The spectrum consists of a quasielastic part forming a central
+peak or a dip, depending on temperature and the Landau relaxation rate. Effects
+of spin fluctuation coupling also give rise to an inelastic part of the
+spectrum which has a form of resonances or antiresonances near the magnon
+frequencies related to non-propagating longitudinal excitations.",1004.0136v1
+2010-06-07,The t-J model on a semi-infinite lattice,"The hole spectral function of the t-J model on a two-dimensional
+semi-infinite lattice is calculated using the spin-wave and noncrossing
+approximations. In the case of small hole concentration and strong
+correlations, $t\gg J$, several near-boundary site rows appear to be depleted
+of holes. The reason for this depletion is a deformation of the magnon cloud,
+which surrounds the hole, near the boundary. The hole depletion in the boundary
+region leads to a more complicated spectral function in the boundary row in
+comparison with its bulk shape.",1006.1215v1
+2010-06-21,On the reflection of magnon bound states,"We investigate the reflection of two-particle bound states of a free open
+string in the light-cone AdS_5 x S^5 string sigma model, for large angular
+momentum J=J_56 and ending on a D7 brane which wraps the entire AdS_5 and a
+maximal S^3 of S^5. We use the superspace formalism to analyse fundamental and
+two-particle bound states in the cases of supersymmetry-preserving and
+broken-supersymmetry boundaries. We find the boundary S-matrices corresponding
+to bound states both in the bulk and on the boundary.",1006.4102v2
+2010-06-22,Complete bond-operator theory of the two-chain spin ladder,"The discovery of the almost ideal, two-chain spin-ladder material
+(C_5H_12N)_2CuBr_4 has once again focused attention on this most fundamental
+problem in low-dimensional quantum magnetism. Within the bond-operator
+framework, three qualitative advances are introduced which extend the theory to
+all finite temperatures and magnetic fields in the gapped regime. This
+systematic description permits quantitative and parameter-free experimental
+comparisons, which are presented for the specific heat, and predictions for
+thermal renormalization of the triplet magnon excitations.",1006.4196v1
+2010-06-24,Field-induced decay dynamics in square-lattice antiferromagnet,"Dynamical properties of the square-lattice Heisenberg antiferromagnet in
+applied magnetic field are studied for arbitrary value S of the spin. Above the
+threshold field for two-particle decays, the standard spin-wave theory yields
+singular corrections to the excitation spectrum with logarithmic divergences
+for certain momenta. We develop a self-consistent approximation applicable for
+S >= 1, which avoids such singularities and provides regularized magnon decay
+rates. Results for the dynamical structure factor obtained in this approach are
+presented for S = 1 and S = 5/2.",1006.4838v2
+2010-07-23,Super-Atom Representation of High-TC Superconductivity,"A resonating valence bond RVB approach is taken to demonstrate formation of
+real-space Cooper pairs and High-TC superconductivity HTS. Non-adiabatic
+coupling between holes aggregates (super-atoms) and undoped anti-ferromagnet
+cause virtual excitations in either system due to inter-system coupling. HTS is
+said to reflect cooperative co-existence of two Bose-Einstein condensates in
+terms of one real-space Cooper pair condensate, and a second magnon condensate,
+which form at the same critical temperature. TC is formulated in terms of the
+super-exchange interaction. Connection is made to an equivalent real-space BCS
+formulation of HTS. Novel perspectives on the HTS in the electron-doped
+Sr1-xLaxCuO2 and Nd2-xCexCuO4 emerge.",1007.4115v1
+2010-08-02,Tunneling spectroscopy probing magnetic and nonmagnetic electrodes in tunnel junctions,"Tunneling spectroscopy is applied to tunnel junctions with only one or no
+ferromagnetic electrode to study the excitation of quasi particles in magnetic
+tunnel junctions. The bias dependence is investigated with high accuracy by
+inelastic electron tunneling spectroscopy. Both types of junctions show a zero
+bias anomaly that is different in size and sign compared to magnetic tunnel
+junctions, i.e. junctions with two ferromagnetic electrodes. A pronounced
+difference is also found depending on the material that is probed by the
+tunneling electrons, which might be attributed to the excitation of magnons.",1008.0326v1
+2010-08-27,Electromagnons in the spin collinear state of a triangular lattice antiferromagnet,"Terahertz time-domain spectroscopy was performed to directly probe the
+low-energy (1-5 meV) electrodynamics of triangular lattice antiferromagnets
+CuFe1-xGaxO2 (x = 0.00, 0.01, and 0.035). We discovered an electromagnon
+(electric-field-active magnon) excitation at 2.3 meV in the paraelectric
+up-up-down-down collinear magnetic phase, while this electromagnon vanishes in
+the ferroelectric helimagnetic phase. Anti-correlation with noncollinear
+magnetism excludes the exchange-striction mechanism as the origin of dynamical
+magnetoelectric coupling, and hence evidences the observation of spin-orbit
+coupling mediated electromagnon in the present compound.",1008.4709v1
+2010-09-15,Anomalous High-Energy Spin Excitations in La2CuO4,"Inelastic neutron scattering is used to investigate the collective magnetic
+excitations of the high-temperature superconductor parent antiferromagnet
+La2CuO4. We find that while the lower energy excitations are well described by
+spin-wave theory, including one- and two-magnon scattering processes, the
+high-energy spin waves are strongly damped near the (1/2,0) position in
+reciprocal space and merge into a momentum dependent continuum. This anomalous
+damping indicates the decay of spin waves into other excitations, possibly
+unbound spinon pairs.",1009.2915v1
+2010-10-12,Linear-response theory of spin Seebeck effect in ferromagnetic insulators,"We formulate a linear response theory of the spin Seebeck effect, i.e., a
+spin voltage generation from heat current flowing in a ferromagnet. Our
+approach focuses on the collective magnetic excitation of spins, i.e., magnons.
+We show that the linear-response formulation provides us with a qualitative as
+well as quantitative understanding of the spin Seebeck effect observed in a
+prototypical magnet, yttrium iron garnet.",1010.2325v2
+2010-10-12,Coherent spin-current oscillations in transverse magnetic fields,"We address the coherence of the dynamics of spin-currents with components
+transverse to an external magnetic field for the spin-1/2 Heisenberg chain. We
+study current autocorrelations at finite temperatures and the real-time
+dynamics of currents at zero temperature. Besides a coherent Larmor
+oscillation, we find an additional collective oscillation at higher
+frequencies, emerging as a coherent many-magnon effect at low temperatures.
+Using numerical and analytical methods, we analyze the oscillation frequency
+and decay time of this coherent current-mode versus temperature and magnetic
+field.",1010.2351v2
+2010-10-19,Yangian symmetry of the Y=0 maximal giant graviton,"We study the remnants of Yangian symmetry of AdS/CFT magnons reflecting from
+boundaries with no degrees of freedom. We present the generalized twisted
+boundary Yangian of open strings ending on boundaries which preserve only a
+subalgebra h of the bulk algebra g, where (g,h) is a symmetric pair. This is
+realized by open strings ending on the D3 brane known as the Y=0 maximal giant
+graviton in AdS_5 x S^5. We also consider the Yangian symmetry of the boundary
+which preserves an su(1|2) subalgebra only.",1010.3761v2
+2011-01-22,Brief Note on AMD Conserved Quantities in Quadratic Curvature Theories,"Motivated by the recent work on critical gravity theories in dimensions D>3,
+we reexamine the results in [arXiv:hep-th/0501044], where the conformal mass
+definition of Ashtekar, Magnon and Das (AMD) for asymptotically AdS space-times
+was generalized to incorporate curvature squared terms. The results in
+[arXiv:hep-th/0501044] appear to contradict the findings in critical gravity,
+where, using the methods of Deser and Tekin, black holes were shown to have
+zero mass. We show that after correcting an error in [arXiv:hep-th/0501044],
+the AMD approach actually produces results in complete agreement with those
+obtained by using the methods of Deser and Tekin.",1101.4267v2
+2011-02-04,Phonon driven spin distribution due to the spin-Seebeck effect,"Here we report on measurements of the spin-Seebeck effect of GaMnAs over an
+extended temperature range alongside the thermal conductivity, specific heat,
+magnetization, and thermoelectric power. The amplitude of the spin-Seebeck
+effect in GaMnAs scales with the thermal conductivity of the GaAs substrate and
+the phonon-drag contribution to the thermoelectric power of the GaMnAs,
+demonstrating that phonons drive the spin redistribution. A phenomenological
+model involving phonon-magnon drag explains the spatial and temperature
+dependence of the measured spin distribution.",1102.1024v1
+2011-03-31,Spiky Strings on NS5-branes,"We study rigidly rotating strings in the near horizon geometry of a stack of
+Neveu-Schwarz (NS) 5-branes. We solve the Nambu-Goto action of the fundamental
+string in the presence of a NS-NS two form $(B_{\mu\nu})$ and find out limiting
+cases corresponding to magnon and spike like solutions.",1103.6153v3
+2011-04-28,Spin and Orbital Characters of Excitations in Iron Arsenide Superconductors Revealed by Simulated Fe L-Edge RIXS,"We theoretically examine the orbital excitations coupled to the spin degree
+of freedom in the parent state of the iron-arsenide superconductor, based on
+the calculation in a five-band itinerant model. The calculated Fe $L_3$-edge
+resonant inelastic x-ray scattering (RIXS) spectra disclose the presence of
+spin-flip excitations involving several specific orbitals. Magnon excitations
+predominantly composed of a single orbital component can be seen in
+experiments, although its spectral weight is smaller than spin-flipped
+interorbital high-energy excitations. The detailed polarization and momentum
+dependence is also discussed with predictions for the experiments.",1104.5424v2
+2011-05-30,Dynamical spin-flip susceptibility for a strongly interacting ultracold Fermi gas,"The Stoner model predicts that a two-component Fermi gas at increasing
+repulsive interactions undergoes a ferromagnetic transition. Using the
+random-phase approximation we study the dynamical properties of the interacting
+Fermi gas. For an atomic Fermi gas under harmonic confinement we show that the
+transverse (spin-flip) dynamical susceptibility displays a clear signature of
+the ferromagnetic phase in a magnon peak emerging from the Stoner particle-hole
+continuum. The dynamical spin susceptibilities could be experimentally explored
+via spin-dependent Bragg spectroscopy.",1105.5997v1
+2011-08-09,"Magnetic phases of a highly frustrated magnet, ZnCr2O4, up to an ultra-high magnetic field of 600 T","The Faraday rotation and magneto-optical absorption spectral measurements
+were conducted to reveal the full-magnetization process and map out a magnetic
+phase diagram of a typical geometrical frustrated magnet, ZnCr2O4, by using the
+electromagnetic flux compression method in ultra-magnetic fields up to 600 T. A
+fully polarized ferromagnetic phase is observed in which the absorption spectra
+associated with an exciton-magnon-phonon transition disappears. Furthermore,
+prior to the fully polarized ferromagnetic phase above 410 T, we found a novel
+magnetic phase above 350 T followed by a canted 3:1 phase.",1108.1932v1
+2011-09-12,Rotating Strings in AdS(4) X CP(3) with B-NS holonomy,"We study solutions for rigidly rotating strings on AdS$_4 \times$ CP$^3$ in
+the presence of $B_{\rm NS}$ holonomy turned on over $CP^1 \subset CP^3$. We
+construct general solutions for rotating strings with two and three angular
+momenta in $CP^3$ and discuss various limits corresponding to giant magnon and
+spike like solutions.",1109.2458v2
+2011-12-14,Dynamics of Thermal Effects in the Spin-Wave Theory of Quantum Antiferromagnets,"We derive a master equation that allows us to study non-equilibrium dynamics
+of a quantum antiferromagnet. By resorting to spin-wave theory, we obtain a
+closed analytic form for the magnon decay rates. These turn out to be closely
+related to form factors, which are experimentally accessible by means of
+neutron and Raman scattering. Furthermore, we compute the time evolution of the
+staggered magnetization showing that, for moderate temperatures, the magnetic
+order is not spoiled even if the coupling is fully isotropic.",1112.3158v3
+2012-06-06,Magnon-driven quantum-dot heat engine,"We investigate a heat- to charge-current converter consisting of a
+single-level quantum dot coupled to two ferromagnetic metals and one
+ferromagnetic insulator held at different temperatures. We demonstrate that
+this nano engine can act as an optimal heat to spin-polarized charge current
+converter in an antiparallel geometry, while it acts as a heat to pure spin
+current converter in the parallel case. We discuss the maximal output power of
+the device and its efficiency.",1206.1259v2
+2012-06-12,Spiky Strings on I-brane,"We study rigidly rotating strings in the near horizon geometry of the 1+1
+dimensional intersection of two orthogonal stacks of NS5-branes, the so called
+I-brane background. We solve the equations of motion of the fundamental string
+action in the presence of two form NS-NS fluxes that the I-brane background
+supports and write down general form of conserved quantities. We further find
+out two limiting cases corresponding to giant magnon and single spike like
+strings in various parameter space of solutions.",1206.2539v2
+2012-06-21,On Rotating and Oscillating Four-Spin Strings in AdS5 X S5,"We study rigidly rotating strings in AdS5 X S5 background with one spin along
+AdS5 and three angular momenta along S5. We find dispersion relations among
+various charges and interpret them as giant magnon and spiky string solutions
+in various limits. Further we present an example of oscillating string which
+oscillates in the radial direction of the AdS5 and at the same time rotates in
+S5.",1206.4920v2
+2012-07-13,Magnetic relaxation in bilayers of yttrium iron garnet/platinum due to the dynamic coupling at the interface,"We show that in ferromagnetic (FM)/normal metal (NM) bilayers the dynamic
+coupling at the interface transfers an additional magnetic relaxation from the
+heavily damped motion of the conduction electron spins in the NM layer to the
+FM spins. While the FM relaxation rates due to two-magnon scattering and spin
+pumping decrease rapidly with increasing FM film thickness, the damping due to
+the dynamic coupling does not depend on the FM film thickness. The proposed
+mechanism explains the very large broadening of ferromagnetic resonance lines
+in thick films of yttrium iron garnet after deposition of a Pt layer.",1207.3330v1
+2012-07-28,Excitations and spin correlations near the interface of two three-dimensional Heisenberg antiferromagnets,"Magnetic excitations and spin correlations near the interface of two
+spin-$\frac12$ Heisenberg antiferromagnets are considered using the spin-wave
+approximation. When the interaction between boundary spins differs essentially
+from exchange constants inside the antiferromagnets, quasi-two-dimensional spin
+waves appear in the near-boundary region. They eject bulk magnons from this
+region, thereby dividing the antiferromagnets into areas with different
+magnetic excitations. The decreased dimensionality of the near-boundary modes
+leads to amplified nearest-neighbor spin correlations in the interface area.",1207.6688v1
+2012-08-05,Quantum bath refrigeration towards absolute zero: unattainability principle challenged,"A minimal model of a quantum refrigerator (QR), i.e. a periodically
+phase-flipped two-level system permanently coupled to a finite-capacity bath
+(cold bath) and an infinite heat dump (hot bath), is introduced and used to
+investigate the cooling of the cold bath towards the absolute zero (T=0).
+Remarkably, the temperature scaling of the cold-bath cooling rate reveals that
+it does not vanish as T->0 for certain realistic quantized baths, e.g. phonons
+in strongly disordered media (fractons) or quantized spin-waves in ferromagnets
+(magnons). This result challenges Nernst's third-law formulation known as the
+unattainability principle.",1208.1015v1
+2012-09-03,Longitudinal magnetic excitation in KCuCl3 studied by Raman scattering under hydrostatic pressures,"We measure Raman scattering in an interacting spin-dimer system KCuCl3 under
+hydrostatic pressures up to 5 GPa mediated by He gas. In the pressure-induced
+quantum phase, we observe a one-magnon Raman peak, which originates from the
+longitudinal magnetic excitationand is observable through the second-order
+exchange interaction Raman process. We report the pressure dependence of the
+frequency, halfwidth and Raman intensity of this mode.",1209.0235v1
+2012-09-25,Hydrodynamic Description of Spin-1 Bose-Einstein Condensates,"We establish a complete set of hydrodynamic equations for a spin-1
+Bose-Einstein condensate (BEC), which are equivalent to the multi-component
+Gross-Pitaevskii equations and expressed in terms of only observable physical
+quantities: the spin density and the nematic (or quadrupolar) tensor in
+addition to the density and the mass current that appear in the hydrodynamic
+description of a scalar BEC. The obtained hydrodynamic equations involve a
+generalized Mermin-Ho relation that is valid regardless of the spatiotemporal
+dependence of the spin polarization. Low-lying collec- tive modes for phonons
+and magnons are reproduced by linearizing the hydrodynamic equations. We also
+apply the single-mode approximation to the hydrodynamic equations and find a
+complete set of analytic solutions.",1209.5509v1
+2012-11-01,Spin Seebeck effect in antiferromagnets and compensated ferrimagnets,"We theoretically investigate the spin Seebeck effect (SSE) in
+antiferromagnets and ferrimagnets, and show that the SSE vanishes in
+antiferromagnets but survives in ferrimagnets even at the magnetization
+compensation point despite the absence of its saturation magnetization. The
+non-vanishing SSE in ferrimagnets stems from two non-degenerate magnons. We
+demonstrate that the magnitude of the SSE in ferrimagnets is unchanged across
+the magnetization compensation point.",1211.0123v1
+2012-12-14,Leading finite-size effects on some three-point correlators in AdS_5 x S^5,"In the framework of the semiclassical approach, we find the leading
+finite-size effects on the normalized structure constants in some three-point
+correlation functions in AdS_5 x S^5, expressed in terms of the conserved
+string angular momenta J_1, J_2, and the worldsheet momentum p_w, identified
+with the momentum p of the magnon excitations in the dual spin-chain arising in
+N=4 SYM in four dimensions.",1212.3485v4
+2013-02-06,p-wave superconductivity near a transverse saturation field,"We investigate reentrant superconductivity in an Ising ferromagnetic
+superconductor URhGe under a transverse magnetic field h_x. The superconducting
+transition temperature for p-wave order parameters T_{sc} is calculated and
+shows two domes as a function of h_x. We find strong enhancement of T_{sc} in
+the high-field dome near a saturation field h_s where the spins align in the
+transverse direction. Soft magnons generate strong attractive interactions
+there. Spin components of the pairing show a significant change between h_x<h_s
+and h_x>h_s. We also discuss the appearance of superconductivity with zero-spin
+pair due to cancellation between external and exchange fields.",1302.1364v1
+2013-03-07,Thickness dependence of the degree of spin polarization of the electrical current in permalloy thin films,"Spin-polarized electrical transport is investigated in $
+Al_{2}O_{3}/Ni_{80}Fe_{20}/Al_{2}O_{3}$ thin films for permalloy thickness
+between 6 and 20nm. The degree of spin-polarization of the current flowing in
+the plane of the film is measured through the current induced spin wave Doppler
+shift. We find that it decreases as the film thickness decreases, from 0.72 at
+20nm to 0.46 at 6nm. This decrease is attributed to a spin depolarization
+induced by the film surfaces. A model is proposed which takes into account the
+contributions of the different sources of electron scattering (alloy disorder,
+phonons, thermal magnons, grain boundaries, film surfaces) to the measured
+spin-dependent resistivities.",1303.1692v1
+2013-04-08,Leading finite-size effects on some three-point correlators in TsT-deformed AdS_5 x S^5,"We compute the leading finite-size effects on the normalized structure
+constants in semiclassical three-point correlation functions of two finite-size
+giant magnon string states and three different types of ""light"" states -
+primary scalar operators, dilaton operator with nonzero momentum and singlet
+scalar operators on higher string levels. This is done for the case of
+TsT-transformed, or gamma-deformed, AdS_5 x S^5 string theory background, dual
+to N = 1 super Yang-Mills theory in four dimensions, arising as an exactly
+marginal deformation of N = 4 super Yang-Mills.",1304.2139v2
+2013-05-09,Spin Conductivity in Two-Dimensional Non-Collinear Antiferromagnets,"We propose a method to derive the spin current operator for non-collinear
+Heisenberg antiferromagnets. We show that the spin conductivity calculated by
+the spectral representation with the spin current satisfies the f-sum rule. We
+also study the spin conductivity at T=0 within spin wave theory. We show how
+the spin conductivity depends on the external magnetic field with changing
+magnon spectrum. We also find that the spin Drude weight vanishes for any
+external magnetic field at T=0.",1305.2072v3
+2013-07-03,Numerical study of magnetization plateaux in the spin-1/2 kagome Heisenberg antiferromagnet,"We clarify the existence of several magnetization plateaux for the kagome
+$S=1/2$ antiferromagnetic Heisenberg model in a magnetic field. Using
+approximate or exact localized magnon eigenstates, we are able to describe in a
+similar manner the plateau states that occur for magnetization per site
+$m=1/3$, $5/9$, and $7/9$ of the saturation value. These results are confirmed
+using large-scale Exact Diagonalization on lattices up to 63 sites.",1307.0975v2
+2013-07-18,Semiclassical Strings on Curved Branes,"We study semiclassical strings in the near horizon geometry of certain curved
+branes. We investigate the rigidly rotating strings in the near horizon
+geometry of NS5-branes wrapped on AdS3 x S3 and in the presence of background
+NS-NS flux. We study several string solutions corresponding to giant magnon,
+single spike and more general folded strings for the fundamental string in this
+background. We comment that in the S-dual background the situation changes
+drastically.",1307.4926v1
+2013-10-25,Goldstone-mode Instability leading to Fragmentation in a Spinor Bose-Einstein Condensate,"We apply the number-conserving Bogoliubov theory to spinor Bose-Einstein
+condensates and show that the Goldstone magnon leads instability leading to
+fragmentation. Unlike the dynamical instability, where modes with complex
+eigenfrequencies grow exponentially, here the zero-energy mode exhibits
+algebraic growth. We also point out that a small fraction of thermally excited
+atoms enhances the fragmentation dynamics.",1310.6989v3
+2013-11-01,Thermo-magnonic diode: rectification of energy and magnetization currents,"We investigate the dynamics of two coupled macrospins connected to thermal
+baths at different temperatures. The system behaves like a diode which allows
+the propagation of energy and mag- netization currents in one direction only.
+This effect is described by a simple model of two coupled nonlinear oscillators
+interacting with two independent reservoirs. It is shown that the rectification
+phenomenon can be interpreted as a a stochastic phase synchronization of the
+two spin-oscillators. A brief comparison with realistic micromagnetic
+simulations is presented. This new effect yields promising opportunities in
+spin-caloritronics devices.",1311.0123v2
+2014-01-27,Spin chains and classical strings in rotating Rindler-AdS space,"In this paper, we study the spin chain and string excitation in the rotating
+Rindler-$AdS_3$ proposed in [12]. We obtain a one-parameter deformed $SL(2)$
+spin chain at the fast spin limit. Two-spin GKP-like solutions are studied at
+short and long string limits. General ansatz for the giant magnons and the
+spiky strings are analyzed in detail for various $\beta$. At last, we explore
+its counterpart in analytic continuation and pp-wave limit.",1401.6915v1
+2014-02-20,Transverse ultrasonic anomaly in La1/3Sr2/3MnO3,"The charge ordering (CO) transition in polycrystalline La1/3Sr2/3MnO3 has
+been studied by measuring the resistivity, magnetization and transverse
+ultrasonic velocity. At about 235K, a conspicuous increase in resistivity was
+observed, while the magnetization shows a cusp structure, corresponding to an
+antiferromagnetic charge ordering transition. Around this transition
+temperature, dramatic anomaly in transverse sound velocity was observed. The
+simultaneous occurrence of electron, magnon and phonon anomalous features
+implies strong spin-phonon coupling and electron-phonon in La1/3Sr2/3MnO3. The
+analysis suggests that the spin-phonon interaction is due to single-ion
+magnetostriction, and electron-phonon coupling originates from the Jahn-Teller
+effect of Mn3+.",1402.4857v2
+2014-04-04,Conformal Mass in AdS gravity,"We show that the Ashtekar-Magnon-Das (AMD) mass and other conserved
+quantities are equivalent to the Kounterterm charges in the asymptotically AdS
+spacetimes that satisfy the Einstein equations, if we assume the same
+asymptotic fall-off behavior of the Weyl tensor as considered by AMD. This
+therefore implies that, in all dimensions, the conformal mass can be directly
+derived from the bulk action and the boundary terms, which are written in terms
+of the extrinsic curvature.",1404.1411v2
+2014-04-18,Validity of spin wave theory for the quantum Heisenberg model,"Spin wave theory is a key ingredient in our comprehension of quantum spin
+systems, and is used successfully for understanding a wide range of magnetic
+phenomena, including magnon condensation and stability of patterns in dipolar
+systems. Nevertheless, several decades of research failed to establish the
+validity of spin wave theory rigorously, even for the simplest models of
+quantum spins. A rigorous justification of the method for the three-dimensional
+quantum Heisenberg ferromagnet at low temperatures is presented here. We derive
+sharp bounds on its free energy by combining a bosonic formulation of the model
+introduced by Holstein and Primakoff with probabilistic estimates and operator
+inequalities.",1404.4717v1
+2014-04-30,String solutions in AdS_3 x S^3 x T^4 with NS-NS B-field,"We develop an approach for solving the string equations of motion and
+Virasoro constraints in any background which has some (unfixed) number of
+commuting Killing vector fields. It is based on a specific ansatz for the
+string embedding. We apply the above mentioned approach for strings moving
+inAdS_3 x S^3 x T^4 with 2-form NS-NS B-field. We succeeded to find solutions
+for a large class of string configurations on this background. In particular,
+we derive dyonic giant magnon solutions in the R_t x S^3 subspace, and obtain
+the leading finite-size correction to the dispersion relation.",1404.7644v1
+2014-07-18,Microwave-induced spin currents in ferromagnetic-insulator|normal-metal bilayer system,"A microwave technique is employed to simultaneously examine the spin pumping
+and the spin Seebeck effect processes in a YIG|Pt bilayer system. The
+experimental results show that for these two processes, the spin current flows
+in opposite directions. The temporal dynamics of the longitudinal spin Seebeck
+effect exhibits that the effect depends on the diffusion of bulk
+thermal-magnons in the thermal gradient in the
+ferromagnetic-insulator|normal-metal system.",1407.4957v2
+2014-07-29,Spin-Hall Nano-oscillator: a micromagnetic study,"This letter studies the dynamical behavior of spin-Hall nanoscillators from a
+micromagnetic point of view. The model parameters have been identified by
+reproducing recent experimental data quantitatively. Our results indicate that
+a strongly localized mode is observed for in-plane bias fields such as in the
+experiments, while predict the excitation of an asymmetric propagating mode for
+large enough out-of plane bias field similarly to what observed in spin-torque
+nanocontact oscillators. Our findings show that spin-Hall nanoscillators can
+find application as spin-wave emitters for magnonic applications where spin
+waves are used for transmission and processing information on nanoscale.",1407.7655v1
+2014-08-20,Second cluster integral from the spectrum of an infinite XXZ spin chain,"First and second terms of the low-temperature cluster expansion for the free
+energy density of a magnetically polarized $XXZ$ spin chain is obtained within
+the propagator approach suggested by E. W. Montroll and J. C. Ward. All the
+calculations employ only one- and two-magnon infinite-chain spectrums. In the
+$XXX$-point the result reproduces the well known S. Katsura's formula obtained
+50 years ago by finite-chain calculations.",1408.4586v2
+2014-11-17,Curved magnonic waveguides based on domain walls,"The channeling of spin waves with domain walls in ultrathin ferromagnetic
+films is demonstrated theoretically and through micromagnetics simulations. It
+is shown that propagating excitations localized to the wall, which appear in
+the frequency gap of bulk spin wave modes, can be guided effectively in curved
+geometries and can propagate in close proximity to other channels with no
+perceptible scattering or loss in coherence. For N\'eel-type walls arising from
+an interfacial Dzyaloshinskii-Moriya interaction, the channeling is strongly
+nonreciprocal and group velocities can exceed 1 km/s in the long wavelength
+limit for certain propagation directions.",1411.4525v1
+2014-11-28,Guided magnon transport in spin chains: transport speed and correcting for disorder,"High fidelity quantum information transport is necessary for most practical
+models of quantum computation. By analogy with optical wave guides, a
+spatio-temporally varying magnetic potential on a one dimensional spin chain
+can achieve high fidelity transport of spin excitations. By comparing different
+potential shapes, we establish the effects of potential shape on the fidelity
+and transport speed. We incorporate disorder into our model and show methods to
+minimise its effect on transport. Finally, we discuss implementations of our
+scheme in several accessible systems based on hydrogenic approximations.",1411.7749v1
+2014-12-22,Rotating and Orbiting Strings in Dp-brane background,"We probe the open fundamental strings in Dp-brane (p=1, 3, 5) backgrounds and
+find new classes of rotating and orbiting string solutions. We show that for
+various worldsheet embedding ansatz we get solutions of the string equations of
+motion that correspond to the well known giant magnon and single spikes, in
+addition to few new solutions corresponding to the orbiting strings. We make a
+systematic study of both rigidly rotating and orbiting strings in D1, D3 and
+D5-brane backgrounds.",1412.6941v1
+2015-03-27,Giant dielectric nonlinearities at a magnetic Bose-Einstein condensation,"We experimentally investigate the dielectric response of the low-dimensional
+gapped quantum magnet Cu$_2$Cl$_{4}\cdot$H$_8$C$_4$SO$_2$ near a magnetic
+field-induced quantum critical point, which separates the quantum-disordered
+and helimagnetic ground states. The observed magnetocapacitive effect
+originates from an improper ferroelectric nature of the transition, which
+itself is perhaps one of the best known realizations of Bose--Einstein
+condensation of magnons. Despite that, we find that the magnetocapacitive
+effect associated with the transition exhibits huge and very unusual
+anharmonicities.",1503.08173v2
+2015-05-13,Optical detection of magnetic orders in HgCr$_2$O$_4$ frustrated spin magnet under pulsed high magnetic fields,"A magneto-optical survey was conducted for HgCr$_2$O$_4$ powder samples under
+pulsed high magnetic fields of up to 55 T. Intensity changes in magnetic fields
+observed for the exciton-magnon-phonon optical transition spectra coincide well
+with those of magnetization, lattice distortion from X-ray diffraction, and
+electron-magnetic resonances. The last-ordered phase was detected prior to the
+fully polarized magnetic phase, similarly to the other chromium spinel oxide,
+ZnCr$_2$O$_4$ and CdCr$_2$O$_4$.",1505.03216v1
+2015-06-23,Effects of magnetic anisotropy on spin dynamics of ferromagnetic frustrated chain,"By exploiting density-matrix renormalization group techniques, we investigate
+the spin dynamics of a spin-1/2 one-dimensional J1-J2 XXZ model with competing
+ferromagnetic J1 and antiferromagnetic J2 exchange couplings under applied
+magnetic fields. Numerical results of spin excitation spectra show that in the
+field-induced spin quadrupole regime, the longitudinal component has a gapless
+mode and the transverse component has a gapped mode irrespective of the
+exchange anisotropy. The excitation gap of the transverse spin excitation
+increases as the exchange anisotropy increases over the XY-like and Ising-like
+regions, demonstrating that two-magnon bound states are stabilized due to the
+easy-axis anisotropy.",1506.06883v1
+2015-09-08,Anomalous Hall effect driven by dipolar spin waves in uniform ferromagnets,"A new type of anomalous Hall effect is shown to arise from the interaction of
+conduction electrons with dipolar spin waves in ferromagnets. This effect
+exists even in homogeneous ferromagnets without relativistic spin-orbit
+coupling. The leading contribution to the Hall conductivity is proportional to
+the chiral spin correlation of dynamical spin textures and is physically
+understood in terms of the skew scattering by dipolar magnons.",1509.02284v1
+2015-10-18,Two-Fluid Theory for Spin Superfluidity in Magnetic Insulators,"We investigate coupled spin and heat transport in easy-plane magnetic
+insulators. These materials display a continuous phase transition between
+normal and condensate states that is controlled by an external magnetic field.
+Using hydrodynamic equations supplemented by Gross-Pitaevski phenomenology and
+magnetoelectric circuit theory, we derive a two-fluid model to describe the
+dynamics of thermal and condensed magnons, and the appropriate boundary
+conditions in a hybrid normal-metal|magnetic-insulator|normal-metal
+heterostructure. We discuss how the emergent spin superfluidity can be
+experimentally probed via a spin Seebeck effect measurement.",1510.05316v2
+2015-11-25,Topological spin waves in the atomic-scale magnetic skyrmion crystal,"We study the spin waves of the triangular skyrmion crystal that emerges in a
+two dimensional spin lattice model as a result of the competition between
+Heisenberg exchange, Dzyalonshinkii-Moriya interactions, Zeeman coupling and
+uniaxial anisotropy. The calculated spin wave bands have a finite Berry
+curvature that, in some cases, leads to non-zero Chern numbers, making this
+system topologically distinct from conventional magnonic systems. We compute
+the edge spin-waves, expected from the bulk-boundary correspondence principle,
+and show that they are chiral, which makes them immune to elastic
+backscattering. Our results illustrate how topological phases can occur in
+self-generated emergent superlattices at the mesoscale.",1511.08244v1
+2016-01-02,Semiclassical structure constants in the eta-deformed AdS_5 x S^5: Leading finite-size corrections,"We consider the leading finite-size effects on some structure constants for
+the $\eta$ - deformed $AdS_5\times S^5$ background in the framework of the
+semiclassical approach. The leading finite-size corrections are derived for the
+cases when we have two heavy string states represented by giant magnons and for
+two different choices of the light states corresponding to dilaton operator
+with nonzero momentum and primary scalar operators. Since the dual field theory
+is still unknown, the results obtained here must be considered as conjectures
+or as predictions from the string theory side.",1601.00127v2
+2016-02-02,Magnetization Dynamics of Topological Defects and the Spin Solid in Kagome Artificial Spin Ice,"We report broadband spin-wave spectroscopy on kagome artificial spin ice
+(ASI) made of large arrays of interconnected Ni$_{80}$Fe$_{20}$ nanobars.
+Spectra taken in saturated and disordered states exhibit a series of resonances
+with characteristic magnetic field dependencies. Making use of micromagnetic
+simulations, we identify resonances that reflect the spin-solid-state and
+monopole-antimonopole pairs on Dirac strings. The latter resonances allow for
+the generation of highly-charged vertices in ASIs via microwave assisted
+switching. Our findings open further perspectives for fundamental studies on
+ASIs and their usage in reprogrammable magnonics.",1602.00918v1
+2016-04-22,Swift thermal steering of domain walls in ferromagnetic MnBi stripes,"We predict a fast domain wall (DW) motion induced by a thermal gradient
+across a nanoscopic ferromagnetic stripe of MnBi. The driving mechanism is an
+exchange torque fueled by magnon accumulation at the DWs. Depending on the
+thickness of the sample, both hot-to-cold and cold-to-hot DW motion directions
+are possible. The finding unveils an energy efficient way to manipulate DWs as
+an essential element in magnetic information processing such as racetrack
+memory.",1604.06575v1
+2016-04-28,Energy repartition in the nonequilibrium steady state,"The concept of temperature in nonequilibrium thermodynamics is an outstanding
+theoretical issue. We propose an energy repartition principle that leads to a
+spectral (mode-dependent) temperature in steady-state nonequilibrium systems.
+The general concepts are illustrated by analytic solutions of the classical
+Heisenberg spin chain connected to Langevin heat reservoirs with arbitrary
+temperature profiles. Gradients of external magnetic fields are shown to
+localize spin waves in a Wannier-Zeemann fashion, while magnon interactions
+renormalize the spectral temperature. Our generic results are applicable to
+other thermodynamic systems such as Newtonian liquids, elastic solids, and
+Josephson junctions.",1604.08369v2
+2016-07-21,Spin wave and spin flip in hexagonal LuMnO3 single crystal,"Manipulate and control of spin wave and spin flip are crucial for future
+developments of magnonic and spintronic devices. We present that the spin wave
+in hexagonal LuMnO3 single crystal can be selectively excited with laser
+polarization perpendicular to the c-axis of hexagonal LuMnO3 and photon energy
+~ 1.8 eV. The selective excitation of spin wave also suggests that the spin
+flip can be selectively controlled in hexagonal manganites. In addition, the
+physical origin of spin wave correlated with spin flip in hexagonal manganites
+is discussed.",1607.06212v1
+2018-04-27,Angular Dependent Magnetization Dynamics with Mirror-symmetric Excitations in Artificial Quasicrystalline Nanomagnet Lattices,"We report angle-dependent spin-wave spectroscopy on aperiodic
+quasicrystalline magnetic lattices, i.e., Ammann, Penrose P2 and P3 lattices
+made of large arrays of interconnected Ni$_{80}$Fe$_{20}$ nanobars. Spin-wave
+spectra obtained in the nearly saturated state contain distinct sets of
+resonances with characteristic angular dependencies for applied in-plane
+magnetic fields. Micromagnetic simulations allow us to attribute detected
+resonances to mode profiles with specific mirror symmetries. Spectra in the
+reversal regime show systematic emergence and disappearance of spin wave modes
+indicating reprogrammable magnonic characteristics.",1804.10630v1
+2018-11-02,New magnetic states in nanorings created by anisotropy gradients,"Magnetic nanorings have been widely studied due to their potential
+applications in spintronic and magnonic devices. In this work, by means of
+analytical calculations and micromagnetic simulations we have analyzed the
+magnetic energy of nanorings with variable anisotropy along their radius. Four
+magnetic states, including two new magnetic configurations, here called meron
+and knot-like states, are considered, looking to the relative lower energy
+states as a function of anisotropy. Phase diagrams with this states are
+presented.",1811.01069v1
+2018-11-06,Parametrically squeezed states of microwave magnons in yttrium iron garnet films,"We demonstrate theoretically, and confirm experimentally, that nonlinear spin
+waves excited in thin yttrium iron garnet films are good candidates for
+squeezing vacuum quantum noise. The experimental demonstration is in the form
+of a measurement of spin-wave induced modulation instability (IMI) conducted in
+the classical regime. The experiment evidences strong phase locking of an idler
+wave parametrically generated in the film with a deterministic small-signal
+wave launched into the film from an external source. The theory predicts that
+the same behaviour will be observed for vacuum quantum noise, resulting in
+squeezing of the noise.",1811.02104v1
+2010-05-24,Application of entanglement conditions to spin systems,"There have been numerous studies of entanglement in spin systems. These have
+usually focussed on examining the entanglement between individual spins or
+determining whether the state of the system is completely separable. Here we
+present conditions that allow us to determine whether blocks of spins are
+entangled. We show that sometimes these conditions can detect entanglement
+better than conditions involving individual spins. We apply these conditions to
+study entanglement in spin wave states, both when there are only a few magnons
+present and also at finite temperature.",1005.4448v1
+2014-03-24,Skyrmionic spin Seebeck effect via dissipative thermomagnonic torques,"We derive thermomagnonic torque and its ""$\beta$-type"" dissipative correction
+from the stochastic Landau-Lifshitz-Gilbert equation. The ""$\beta$-type""
+dissipative correction describes viscous coupling between magnetic dynamics and
+magnonic current and it stems from spin mistracking of the magnetic order. We
+show that thermomagnonic torque is important for describing temperature
+gradient induced motion of skyrmions in helical magnets while dissipative
+correction plays an essential role in generating transverse Magnus force. We
+propose to detect such skyrmionic motion by employing the transverse spin
+Seebeck effect geometry.",1403.6160v2
+2017-01-13,Magnetic ground states for bent nanotubes,"Magnetic nanotubes have been widely studied because they are promising
+candidates to be part in devices based on spintronic and magnonic technologies.
+However, the experimental techniques used to prepare these elements could not
+guarantee to have perfect nanostructures. Therefore, some geometric
+imperfections can appear. In this direction, the bent of a nanotube could play
+an essential role in the magnetic properties of a device. In this work, we
+analyze the influence of curvature on the magnetic properties of a bent
+nanotube, a topic scarcely studied, and that can have a strong impact on
+applications.",1701.03656v2
+2017-01-13,Delocalized charge carriers in strongly disordered t-J model,"We study the influence of the electron-magnon interaction on the particle
+transport in strongly disordered systems. The analysis is based on results
+obtained for a single hole in the one-dimensional t-J model. Unless there
+exists a mechanism that localizes spin excitations, the charge carrier remains
+delocalized even for a very strong disorder and shows subdiffusive motion up to
+the longest accessible times. However, upon inspection of the propagation times
+between neighboring sites as well as a careful finite-size scaling we
+conjecture that the anomalous subdiffusive transport may be transient and
+should eventually evolve into a normal diffusive motion.",1701.03659v1
+2017-01-20,Probing of the interfacial Heisenberg and Dzyaloshinskii--Moriya exchange interaction by magnon spectroscopy,"This Topical Review presents an overview of the recent experimental results
+on the quantitative determination of the magnetic exchange parameters in
+ultrathin magnetic films and multilayers, grown on different substrates. The
+experimental approaches to probe both the symmetric Heisenberg as well as the
+antisymmetric Dzyaloshinskii--Moriya exchange interaction in ultrathin magnetic
+films and at interfaces are discussed in detail. It is explained how the
+experimental spectrum of magnetic excitations can be used to quantify the
+strength of these interactions.",1701.05850v1
+2011-11-23,Dispersion of orbital excitations in 2D quantum antiferromagnets,"We map the problem of the orbital excitation (orbiton) in a 2D
+antiferromagnetic and ferroorbital ground state onto a problem of a hole in 2D
+antiferromagnet. The orbiton turns out to be coupled to magnons and can only be
+mobile on a strongly renormalized scale by dressing with magnetic excitations.
+We show that this leads to a dispersion relation reflecting the two-site unit
+cell of the antiferromagnetic background, in contrast to the predictions based
+on a mean-field approximation and linear orbital-wave theory.",1111.5522v1
+2011-11-28,Quasi-one-dimensional magnons in an intermetallic marcasite,"We present inelastic neutron scattering measurements and first principles
+calculations examining the intermetallic marcasite CrSb2. The observed spin
+wave dispersion implies that the magnetic interactions are strongly
+one-dimensional with antiferromagnetic chains parallel to the crystalline
+c-axis. Such low-dimensional excitations are unexpected in a semiconducting
+intermetallic system. Moreover this material may be further interesting in that
+the magnetic anisotropy may enhance thermoelectric properties along particular
+crystallographic directions.",1111.6499v1
+2012-01-11,Local magnetic anisotropy in BaFe$_2$As$_2$: a polarized inelastic neutron scattering study,"The anisotropy of the magnetic excitations in BaFe$_2$As$_2$ was studied by
+polarized inelastic neutron scattering which allows one to separate the
+components of the magnetic response. Despite the in-plane orientation of the
+static ordered moment we find the in-plane polarized magnons to exhibit a
+larger gap than the out-of-plane polarized ones indicating very strong
+single-ion anisotropy within the layers. It costs more energy to rotate a spin
+within the orthorhombic {\it a-b} plane than rotating it perpendicular to the
+FeAs layers.",1201.2332v1
+2012-04-09,Ising model: secondary phase transition,"Lttice-spin phonons are considered, which make the heat capacity at the
+critical temperature satisfy experimental observations better. There is a BEC
+phase transition in an Ising model attributable to the lattice-spin phonons. We
+proved that the spin-wave theory only is available after BEC transition, and
+the magnons have the same characteristics as the lattice-spin phonons',
+resulting from quantum effect. Energy-level overlap effect at ultralow
+temperature is found. A prediction of BEC phase transition in a crystal is put
+forward as our theory generalization.",1204.1807v1
+2014-05-21,Spiky strings on AdS3 x S3 with NS-NS flux,"We study rigidly rotating strings in the background of AdS3 x S3 with
+Neveu-Schwarz (NS) fluxes. We find two interesting limiting cases corresponding
+to the known giant magnon and the new single spike solution of strings in the
+above background and write down the dispersion relations among various
+conserved charges. We use proper regularization to find the correct relations
+among them. We further study the circular and infinite spiky strings on AdS and
+study their properties.",1405.5497v3
+2014-06-13,On the Rotating and Oscillating strings in $(AdS_3\times S^3)_{\varkappa}$,"We study rigidly rotating strings in the $\varkappa$-deformed $AdS_3 \times
+S^3$ background. We find out two classes of solutions corresponding to the
+giant magnon and single spike solutions of the string rotating in two
+$S^2_{\varkappa}$ subspace of rotations reduced along two different isometries.
+We verify that the dispersion relations reduce to the well known relation in
+the $\varkappa\rightarrow 0$ limit. We further study some oscillating string
+solutions in the $S^3_{\varkappa}$ subspace.",1406.3642v4
+2014-06-20,Thermoelectric energy harvesting with quantum dots,"We review recent theoretical work on thermoelectric energy harvesting in
+multi-terminal quantum-dot setups. We first discuss several examples of
+nanoscale heat engines based on Coulomb-coupled conductors. In particular, we
+focus on quantum dots in the Coulomb-blockade regime, chaotic cavities and
+resonant tunneling through quantum dots and wells. We then turn towards
+quantum-dot heat engines that are driven by bosonic degrees of freedom such as
+phonons, magnons and microwave photons. These systems provide interesting
+connections to spin caloritronics and circuit quantum electrodynamics.",1406.5329v2
+2016-05-12,Transmission of spin waves in ordered FeRh epitaxial thin films,"We report on B2-ordering dependence of magnetostatic surface spin waves in
+ferromagnetic FeRh at room temperature. Spin waves transmit over a distance
+longer than 21 {\mu}m in highly ordered FeRh alloys even with relatively large
+spin-orbit interaction. The long-range transmission likely arises from the
+induced Rh moments of the ordered FeRh due to ferromagnetic exchange
+interaction between Fe and Rh. The results indicate a potential of using FeRh
+in spintronic and magnonic applications by integrating with other fascinating
+magnetic characteristics of FeRh such as electric field induced magnetic phase
+transition.",1605.03798v1
+2016-08-22,Spin transport in half-metallic ferromagnets,"We theoretically investigate spin transport in half-metallic ferromagnets at
+finite temperatures. The side-jump and skew-scattering contributions to spin
+Hall conductivity are derived using the Kubo formula. The electron-magnon
+interaction causes a finite density of states in the energy gap of the
+minority-spin band and induces spin Hall conductivity. We show that spin Hall
+conductivity is proportional to $T^{3/2}$, with $T$ being temperature and is
+sensitive to $T$. We propose that spin Hall conductivity may be a tool to study
+the minority-spin state.",1608.06333v2
+2017-06-01,Cavity mediated manipulation of distant spin currents using cavity-magnon-polariton,"Using electrical detection of a strongly coupled spin-photon system comprised
+of a microwave cavity mode and two magnetic samples, we demonstrate the long
+distance manipulation of spin currents. This distant control is not limited by
+the spin diffusion length, instead depending on the interplay between the local
+and global properties of the coupled system, enabling systematic spin current
+control over large distance scales (several centimeters in this work). This
+flexibility opens the door to improved spin current generation and manipulation
+for cavity spintronic devices.",1706.00347v1
+2017-12-13,Some semiclassical structure constants for AdS_4 x CP^3,"We compute structure constants in three-point functions of three string
+states in AdS_4 x CP^3 in the framework of the semiclassical approach. We
+consider HHL correlation functions where two of the states are ""heavy"" string
+states of finite-size giant magnons carrying one or two angular momenta and the
+other one corresponds to such ""light"" states as dilaton operators with non-zero
+momentum, primary scalar operators, and singlet scalar operators with higher
+string levels.",1712.04816v2
+2018-09-24,Phonon Magnetochiral Effect,"Magnetochiral effect (MChE) of phonons, a nonreciprocal acoustic property
+arising due to the symmetry principles, is demonstrated in a chiral-lattice
+ferrimagnet Cu$_2$OSeO$_3$. Our high-resolution ultrasound experiments reveal
+that the sound velocity differs for parallel and antiparallel propagation with
+respect to the external magnetic field.The sign of the nonreciprocity depends
+on the chirality of the crystal in accordance with the selection rule of the
+MChE. The nonreciprocity is enhanced below the magnetic ordering temperature
+and at higher ultrasound frequencies, which is quantitatively explained by a
+proposed magnon-phonon hybridization mechanism.",1809.08775v1
+2018-09-26,Resonant magnetic induction tomography of a magnetized sphere,"We demonstrate the structural imaging of magnetostatic spin-wave modes hosted
+in a millimeter-sized ferromagnetic sphere. Unlike for low-dimensional magnetic
+materials, there is no prior technique to image these modes in bulk magnetized
+solid of revolution. Based on resonant magnetic induction tomography in the
+microwave range, our approach ensures the robust identification of these
+non-trivial spin-wave modes by establishing their azimuthal and polar
+dependences, starting point of magnonic fundamental studies and hybrid systems
+with complex spin textures well beyond the uniform precession mode.",1809.09785v2
+2019-09-01,Electric-field control of collective spin excitations in Neel-type skyrmions,"We demonstrate that an electric field could activate the three low-energy
+eigenmodes of the Neel-type skyrmion lattice via the electrically induced
+Dzyaloshinskii-Moriya interaction. In particular, we predict that the relative
+intensity of the clockwise rotation mode against the counter-clockwise rotation
+mode is significantly enhanced for the electrical activation in comparison with
+the magnetic activation. We also discover that the electrically and
+magnetically active modes obey unique selection rules. These findings promise a
+fresh pathway towards energy-efficient electrical manipulation of skyrmion
+excitations for future skyrmion-based magnonics.",1909.00348v1
+2019-09-26,Magnetic Doublon Bound States in the Kondo Lattice Model,"We present a novel pairing mechanism for electrons, mediated by magnons.
+These paired bound states are termed ""magnetic doublons"". Applying numerically
+exact techniques (full diagonalization and the density-matrix renormalization
+group, DMRG) to the Kondo lattice model at strong exchange coupling $J$ for
+different fillings and magnetic configurations, we demonstrate that magnetic
+doublon excitations exist as composite objects with very weak dispersion. They
+are highly stable, support a novel ""inverse"" colossal magnetoresistance and
+potentially other effects.",1909.11896v2
+2020-12-23,Analytic description of spin waves in dipolar/octupolar pyrochlore magnets,"We derive analytic forms for spin waves in pyrochlore magnets with
+dipolar-octupolar interactions, such as ${\rm Nd}_2{\rm Zr}_2{\rm O}_7$. We
+obtain full knowledge of the diagonalized magnonic Hamiltonian within the
+linear spin wave approximation. We also consider the effect of a ""breathing
+mode"" as a perturbation of this system. The breathing mode lifts the degeneracy
+of the upper band of the spin wave dispersion along the direction $X\to W$ in
+$k$-space.",2012.12500v1
+2000-06-02,Dzyaloshinskii-Moriya interaction in NaV$_2$O$_5$: a microscopic study,"We present a unified account of magnetic exchange and Raman scattering in the
+quasi-one-dimensional transition-metal oxide NaV$_2$O$_5$. Based on a
+cluster-model approach explicit expressions for the exchange integral and the
+Raman-operator are given. It is demonstrated that a combination of the
+electronic-structure and the Dzyaloshinskii-Moriya interaction, allowed by
+symmetry in this material, are responsible for the finite Raman cross-section
+giving rise to both, one- and two-magnon scattering amplitudes.",0006036v1
+2000-06-13,Coherent dipolar correlations in the ground-state of Kagome frustrated antiferromagnets,"We propose a new model for the nature of the low temperature phase of a
+geometrically frustrated antiferromgnet (AFM) with a Kagome lattice,
+SrCr$_{8-x}$Ga$_{4+x}$O$_{19}$. We propose that the long-range dipolar
+interaction between the magnetic Cr$^{3+}$ ions introduces correlations in
+their dynamics. The dipolar ground-state has the spins performing correlated
+zero-point oscillations in a coherent state with a well defined global phase
+and a complex order-parameter (i.e. Off-Diagonal Long Range Order). We
+calculate the magnon excitations of such a dipolar array and we find good
+agreement with the spin-wave velocities infered from measurements of the
+specific-heat. Various experimental properties of these materials are naturally
+explained by such a model.",0006215v1
+2012-05-30,Exceptional Operators in N=4 super Yang-Mills,"We consider one particularly interesting class of composite gauge-invariant
+operators in N=4 super Yang-Mills theory. An exceptional feature of these
+operators is that in the Thermodynamic Bethe Ansatz approach the one-loop
+rapidities of the constituent magnons are shown to be exact in the 't Hooft
+coupling constant. This is used to propose the mirror TBA description for these
+operators. The proposal is shown to pass several non-trivial checks.",1205.6660v1
+2017-05-29,Rectifying full-counting statistics in a spin Seebeck engine,"We investigate the rectification and negative differential effects of
+full-counting statistics of conjugate thermal spin transport in a spin Seebeck
+engine. The engine is made by an electron/magnon interface diode driven by a
+temperature bias, of which the scaled cumulant generating function is
+formulated in the framework of nonequilibrium Green's function. The strongly
+fluctuating interfacial electron density of states induced by quantum dot is
+responsible for these intriguing properties. This work is relevant for
+designing efficient spin caloritronic engine and can broaden our view in
+nonequilibrium thermodynamics and the nonlinear phenomenon in quantum transport
+system.",1705.10025v2
+2017-09-05,Gate-controlled magnonic-assisted switching of magnetization in ferroelectric/ferromagnetic junctions,"Interfacing a ferromagnet with a polarized ferroelectric gate generates a
+non-uniform, interfacial spin density coupled to the ferroelectric polarization
+allowing so for an electric field control of effective transversal field to
+magnetization. Here we study the dynamic magnetization switching behavior of
+such a multilayer system based on the Landau-Lifshitz-Baryakhtar equation,
+demonstrating that interfacial magnetoelectric coupling is utilizable as a
+highly localized and efficient tool for manipulating magnetism.",1709.01286v1
+2017-09-06,Edge states in a ferromagnetic honeycomb lattice with armchair boundaries,"We investigate the properties of magnon edge states in a ferromagnetic
+honeycomb lattice with armchair boundaries. In contrast with fermionic
+graphene, we find novel edge states due to the missing bonds along the boundary
+sites. After introducing an external on-site potential at the outermost sites
+we find that the energy spectra of the edge states are tunable. Additionally,
+when a non-trivial gap is induced, we find that some of the edge states are
+topologically protected and also tunable. Our results may explain the origin of
+the novel edge states recently observed in photonic lattices. We also discuss
+the behavior of these edge states for further experimental confirmations",1709.01855v1
+2018-07-12,Finite Size Effect from Classical Strings in deformed AdS$_3\times$ S$^3$,"We study the finite size effect of rigidly rotating and spinning folded
+strings in $(AdS_3\times S^3)_{\varkappa}$ background. We calculate the leading
+order exponential corrections to the infinite size dispersion relation of the
+giant magnon, and single spike solutions. For the spinning folded strings we
+write the finite size effect in terms of the known Lambert $W$-function.",1807.04601v3
+2019-01-10,Finite size effect from classical strings in $AdS_3 \times S^3$ with NS-NS flux,"We study the finite size effect of rigidly rotating strings and closed folded
+strings in $AdS_3\times S^3$ geometry with NS-NS B-field. We calculate the
+classical exponential corrections to the dispersion relation of infinite size
+giant magnon and single spike in terms of Lambert $\mathbf{W}-$function. We
+also write the analytic expression for the dispersion relation of finite size
+Gubser-Klebanov-Polyakov (GKP) string in the form of Lambert
+$\mathbf{W}-$function.",1901.03026v2
+2019-01-14,Physics Beyond Colliders: QCD Working Group Report,"This report summarises the main findings of the QCD Working Group in the CERN
+Physics Beyond Colliders Study.",1901.04482v1
+2019-01-15,On soliton solutions of the time-discrete generalized lattice Heisenberg magnet model,"Generalized lattice Heisenberg magnet model is an integrable model exhibiting
+soliton solutions. The model is physically important for describing the magnon
+bound states (or soliton excitations) with arbitrary spin, in magnetic
+materials. In this paper, a time-discrete generalized lattice Heisenberg magnet
+(GLHM) model is investigated. By writing down the Lax pair representation of
+the time-discrete GLHM model, we present explicitly the underlying integrable
+structure like, the Darboux transformation and soliton solutions.",1901.04671v1
+2019-03-22,Spin-wave coupling to electromagnetic cavity fields in dysposium ferrite,"Coupling of spin-waves with electromagnetic cavity field is demonstrated in
+an antiferromagnet, dysprosium ferrite (DyFeO3). By measuring transmission at
+0.2-0.35 THz and sweeping sample temperature, magnon-photon coupling signatures
+were found at crossings of spin-wave resonances with Fabry-Perot cavity modes
+formed in samples. The obtained spectra are explained in terms of classical
+electrodynamics and a microscopic model.",1903.09590v2
+2019-08-24,Chiral Pumping of Spin Waves,"We report a theory for the coherent and incoherent chiral pumping of spin
+waves into thin magnetic films through the dipolar coupling with a local
+magnetic transducer, such as a nanowire. The ferromagnetic resonance of the
+nanowire is broadened by the injection of unidirectional spin waves that
+generate a non-equilibrium magnetization in only half of the film. A
+temperature gradient between the local magnet and film leads to a
+unidirectional flow of incoherent magnons, i.e., a chiral spin Seebeck effect.",1908.09141v2
+2019-11-05,Spin chains and classical strings in two parameters $q$-deformed AdS$_3\times$S$^3$,"In this paper, we study the spin chain and string excitation in the
+two-parameters $q$-deformed AdS$_3\times$S$^3$ proposed by Hoare. We obtain the
+deformed spin chain model at the fast spin limit for choices of deformed
+parameters. General ansatz for giant magnons are studied in great detail and
+complicated dispersion relation is treated perturbatively. We also study
+several types of hanging string solutions and their charges and spins are
+analyzed numerically. At last, we explore its pp-wave limit and find its
+solution only depends on the difference of deformed parameters.",1911.01567v1
+2019-11-07,Magnetic monopoles and toroidal moments in LuFeO$_3$ and related compounds,"Magnetic monopoles and toroidal order are compelling features that have long
+been theorized but remain elusive in real materials. Multiferroic hexagonal
+ferrites are an interesting realization of frustrated triangular lattice, where
+magnetic order is coupled to ferroelectricity and trimerization. Here we
+propose a mechanism, through which magnetic monopolar and toroidal orders
+emerge from the combination of 120$^\circ$ antiferromagnetism and
+trimerization, present in hexagonal manganites and ferrites. The experimentally
+observable signatures of magnetic monopolar and toroidal orders are identified
+in the inelastic neutron scattering cross section, simulated from a microscopic
+model of LuFeO3. The non-reciprocal magnon propagation is demonstrated.",1911.02704v1
+2019-11-25,Cavity Optomagnonics,"In the recent years a series of experimental and theoretical efforts have
+centered around a new topic: the coherent, cavity-enhanced interaction between
+optical photons and solid state magnons. The resulting emerging field of Cavity
+Optomagnonics is of interest both at a fundamental level, providing a new
+platform to study light-matter interaction in confined structures, as well as
+for its possible relevance for hybrid quantum technologies. In this chapter I
+introduce the basic concepts of Cavity Optomagnonics and review some
+theoretical developments.",1911.11104v1
+2019-12-04,Free energy asymptotics of the quantum Heisenberg spin chain,"We consider the ferromagnetic quantum Heisenberg model in one dimension, for
+any spin $S\geq 1/2$. We give upper and lower bounds on the free energy,
+proving that at low temperature it is asymptotically equal to the one of an
+ideal Bose gas of magnons, as predicted by the spin-wave approximation. The
+trial state used in the upper bound yields an analogous estimate also in the
+case of two spatial dimensions, which is believed to be sharp at low
+temperature.",1912.01967v2
+2019-12-09,On the singularities of the R-R AdS_3 x S^3 x T^4 S matrix,"We investigate the analytic properties of the exact magnon S matrix of string
+theory on AdS_3 x S^3 x T^4 with R-R flux. We show that the previously proposed
+dressing factors have the exact double-pole/zero structure expected from Landau
+box diagrams. This constitutes a strong consistency check of our dressing
+factors, much as the Dorey-Hofman-Maldacena poles do for the all-loop dressing
+factor in AdS_5 x S^5.",1912.04320v2
+2019-12-13,Angular Momentum Conservation and Phonon Spin in Magnetic Insulators,"We develop a microscopic theory of spin-lattice interactions in magnetic
+insulators, separating rigid-body rotations and the internal angular momentum,
+or spin, of the phonons, while conserving the total angular momentum. In the
+low-energy limit, the microscopic couplings are mapped onto experimentally
+accessible magnetoelastic constants. We show that the transient phonon spin
+contribution of the excited system can dominate over the magnon spin, leading
+to nontrivial Einstein-de Haas physics.",1912.06616v2
+2016-03-10,Resonant excitation of the spin-wave current in hybrid nanostructures,"Using the non-equilibrium statistical operator method (NSO), we have
+investigated the spin transport through the interface in a
+semiconductor/ferromagnetic insulator hybrid structure. We have analyzed the
+approximation of effective parameters, when each of the considered subsystems
+(conduction electrons, magnons, and phonons) is characterized by its effective
+temperature. We have constructed the macroscopic equations, describing the
+spin-wave current caused by both resonantly excited spin system of conduction
+electrons and by an inhomogeneous thermal field in the ferromagnetic insulator.",1603.03207v1
+2016-12-13,Theory of magnons in spin systems with Dzyaloshinskii-Moriya interaction,"We study in this paper magnetic properties of a system of quantum Heisenberg
+spins interacting with each other via a ferromagnetic exchange interaction J
+and an in-plane Dzyaloshinskii-Moriya interaction D. The non-collinear ground
+state due to the competition between J and D is determined. We employ a
+self-consistent Green'function theory to calculate the spin-wave spectrum and
+the layer magnetizations at finite T in two and three dimensions as well as in
+a thin film with surface effects. Analytical details and the validity of the
+method are shown and discussed.",1612.04147v1
+2017-07-27,Ultrafast nanoscale magnetic switching via intense picosecond electron bunches,"The magnetic field associated with a picosecond intense electron pulse is
+shown to switch locally the magnetization of extended films and nanostructures
+and to ignite locally spin waves excitations. Also, topologically protected
+magnetic textures such as skyrmions can be imprinted swiftly in a sample with a
+residual Dzyaloshinskii-Moriya spin-orbital coupling. Characteristics of the
+created excitations such as the topological charge or the width of the magnon
+spectrum can be steered via the duration and the strength of the electron
+pulses. The study points to a possible way for a spatiotemporally controlled
+generation of magnetic and skyrmionic excitations.",1707.08838v1
+2017-11-07,Dzyaloshinskii-Moriya interaction induced extrinsic linewidth broadening of ferromagnetic resonance,"For a thin ferromagnetic film with the Dzyaloshinskii-Moriya interaction
+(DMI), we derive an expression of the extrinsic ferromagnetic resonance (FMR)
+linewidth in a quantum mechanical way, taking into account scatterings from
+structural inhomogeneity. In the presence of the DMI, the magnon dispersion
+exhibits rich resonant states, especially in small external magnetic fields and
+strong DMI strength. It is found that the FMR linewidth shows several
+characteristic features such as a finite linewidth at zero frequency and peaks
+in the low frequency range.",1711.02263v1
+2019-05-21,Collective spin dynamics of Z2 vortex crystals in triangular Kitaev-Heisenberg antiferromagnets,"We show that the mesoscopic incommensurate $\mathbb{Z}_2$ vortex crystals
+proposed for layered triangular anisotropic magnets can be most saliently
+identified by two distinctive signatures in dynamical spin response
+experiments: The presence of pseudo-Goldstone `phonon' modes at low frequencies
+$\omega$, associated with the collective vibrations of the vortex cores, and a
+characteristic multi-scattered intensity profile at higher $\omega$, arising
+from a large number of Bragg reflections and magnon bandgaps. These are direct
+fingerprints of the large vortex sizes and magnetic unit cells and the
+solitonic spin profile around the vortex cores.",1905.08694v2
+2020-06-03,Finite size effects in classical string solutions of the Schrodinger geometry,"We study finite size corrections to the semiclassical string solutions of the
+Schrodinger spacetime. We compute the leading order exponential corrections to
+the infinite size dispersion relation of the single spin giant magnon and of
+the single spin single spike solutions. The solutions live in a $S^3$ subspace
+of the five-sphere and extent in the Schrodinger part of the metric. In the
+limit of zero deformation the finite size dispersion relations flow to the
+undeformed $AdS_5 \times S^5$ counterparts and in the infinite size limit the
+correction term vanishes and the known infinite size dispersion relations are
+obtained.",2006.02285v1
+2020-06-22,Magnetic excitations of Sr$_3$Ir$_2$O$_7$ observed by inelastic neutron scattering measurement,"In this short note, we report on the first inelastic neutron scattering (INS)
+study on high-energy magnetic excitations in Sr$_3$Ir$_2$O$_7$. We observed
+excitations between $\sim$80 meV and $\sim$180 meV. The peak position of the
+excitations is consistent with the dispersion of a single magnon determined by
+resonant inelastic X-ray scattering (RIXS) measurement. Thus, our results
+demonstrate that INS and RIXS observe identical excitations in iridate oxides,
+as in La$_2$CuO$_4$.",2006.12074v2
+2020-06-22,Macroscale non-local transfer of superconducting signatures to a ferromagnet in a cavity,"Cavity spintronics recently heralded non-local magnonic signal transfer
+between magnetic samples. Here we show that by including superconductors in the
+cavity, we can make use of these principles to bring composite
+superconductor--ferromagnet systems to the macroscale. We analyze how a
+superconductor's a.c. conductivity influences the spin dynamics of a spatially
+separated magnet, and we discuss the potential impact on spintronic
+applications.",2006.12516v2
+2020-09-04,Detection of Ferromagnetic Resonance from 1 nm-thick Co,"To explore the further possibilities of nanometer-thick ferromagnetic films
+(ultrathin ferromagnetic films), we investigated the ferromagnetic resonance
+(FMR) of 1 nm-thick Co film. Whilst an FMR signal was not observed for the Co
+film grown on a SiO2 substrate, the insertion of a 3 nm-thick amorphous Ta
+buffer layer beneath the Co enabled the detection of a salient FMR signal,
+which was attributed to the smooth surface of the amorphous Ta. This result
+implies the excitation of FMR in an ultrathin ferromagnetic film, which can
+pave the way to controlling magnons in ultrathin ferromagnetic films.",2009.01977v1
+2021-02-23,Fast acquisition of spin-wave dispersion by compressed sensing,"For the realization of magnonic devices, spin-wave dispersions need to be
+identified. Recently, the time-resolved pump-probe imaging method combined with
+the Fourier transform was demonstrated for obtaining the dispersions in the
+lower-wavenumber regime. However, the measurement takes a long time when the
+sampling rate is sufficiently high. Here, we demonstrated the fast acquisition
+of spin-wave dispersions by using the compressed sensing technique. Further, we
+quantitatively evaluated the consistency of the results. Our results can be
+applied to other various pump-probe measurements, such as observations based on
+the electro-optical effects.",2102.11626v1
+2013-06-07,Symmetric and asymmetric excitations of a strong-leg quantum spin ladder,"The zero-field excitation spectrum of the strong-leg spin ladder
+(C$_7$H$_10$N)$_2$CuBr$_4$ (DIMPY) is studied with a neutron time-of-flight
+technique. The spectrum is decomposed into its symmetric and asymmetric parts
+with respect to the rung momentum and compared with theoretical results
+obtained by the density matrix renormalization group method. Additionally, the
+calculated dynamical correlations are shown for a wide range of rung and leg
+coupling ratios in order to point out the evolution of arising excitations, as
+e.g. of the two-magnon bound state from the strong to the weak coupling limit.",1306.1671v1
+2016-09-15,Spin Transport through the metallic antiferromagnet FeMn,"We investigate spin transport through metallic antiferromagnets using
+measurements based on spin pumping combined with inverse spin Hall effects in
+Ni80Fe20/FeMn/W trilayers. The relatively large magnitude and opposite sign of
+spin Hall effects in W compared to FeMn enable an unambiguous detection of spin
+currents transmitted through the entire FeMn layer thickness. Using this
+approach we can detect two distinctively different spin transport regimes,
+which we associate with electronic and magnonic spin currents respectively. The
+latter can extend to relatively large distances (up to 9 nm) and is enhanced
+when the antiferromagnetic ordering temperature is close to the measurement
+temperature.",1609.04834v1
+2016-09-19,Large Unidirectional Magnetoresistance in a Magnetic Topological Insulator,"We report current-direction dependent or unidirectional magnetoresistance
+(UMR) in magnetic/nonmagnetic topological insulator (TI) heterostructures,
+Cr$_x$(Bi$_{1-y}$Sb$_y$)$_{2-x}$Te$_3$/(Bi$_{1-y}$Sb$_y$)$_2$Te$_3$, that is
+several orders of magnitude larger than in other reported systems. From the
+magnetic field and temperature dependence, the UMR is identified to originate
+from the asymmetric scattering of electrons by magnons. In particular, the
+large magnitude of UMR is an outcome of spin-momentum locking and a small Fermi
+wavenumber at the surface of TI. In fact, the UMR is maximized around the Dirac
+point with the minimal Fermi wavenumber.",1609.05906v1
+2016-11-01,Spin-Mechanical Inertia in Antiferromagnet,"Angular momentum conservation has served as a guiding principle in the
+interplay between spin dynamics and mechanical rotations. However, in an
+antiferromagnet with vanishing magnetization, new fundamental rules are
+required to properly describe spin-mechanical phenomena. Here we show that the
+N\'eel order dynamics affects the mechanical motion of a rigid body by
+modifying its inertia tensor in the presence of strong magnetocrystalline
+anisotropy. This effect depends on temperature when magnon excitations are
+considered. Such a spin-mechanical inertia can produce measurable consequences
+at small scales.",1611.00100v3
+2016-11-14,Low-temperature evolution of the spectral weight of a spin-up carrier moving in a ferromagnetic background,"We derive the lowest-temperature correction to the self-energy of a spin-up
+particle injected in a ferromagnetic background. The background is modeled with
+both Heisenberg and Ising Hamiltonians so that differences due to gapless vs.
+gapped magnons can be understood. Beside the expected thermal broadening of the
+quasiparticle peak as it becomes a resonance inside a continuum, we also find
+that spectral weight is transferred to regions lying outside this continuum. We
+explain the origin of this spectral weight transfer and its low-temperature
+evolution.",1611.04575v1
+2016-11-25,Electrical Detection of Spin Backflow from an Antiferromagnetic Insulator/Y3Fe5O12 Interface,"Spin Hall magnetoresistance (SMR) has been observed in Pt/NiO/Y3Fe5O12 (YIG)
+heterostructures with characteristics very different from those in Pt/YIG. We
+show that the SMR in Pt/NiO/YIG strongly correlates with spin conductance, both
+sharing very strong temperature dependence due to antiferromagnetic magnons and
+spin fluctuation. This phenomenon indicates that spin current generated by spin
+Hall effect in the Pt transmits through the insulating NiO and is reflected
+from the NiO/YIG interface. Inverted SMR has been observed below a temperature
+which increases with the NiO thickness, suggesting spin-flip reflection from
+the antiferromagnetic NiO exchange coupled with the YIG.",1611.08593v1
+2016-11-30,Finite-size effect of η-deformed AdS_5 x S^5 at strong coupling,"We compute Luscher corrections for a giant magnon in the \eta-deformed
+(AdS_5\times S^5)_{\eta} using the su(2|2)_q-invariant S-matrix at strong
+coupling and compare with the finite-size effect of the corresponding string
+state, derived previously. We find that these two results match and confirm
+that the su(2|2)_q-invariant S-matrix is describing world-sheet excitations of
+the \eta-deformed background.",1611.09992v2
+2017-04-19,"Crystal field excitations and magnons: their roles in oxyselenides Pr2O2M2OSe2 (M = Mn, Fe)","We present the results of neutron scattering experiments to study the crystal
+and magnetic structures of the Mott-insulating transition metal oxyselenides
+Pr2O2M2OSe2 (M = Mn, Fe). The structural role of the non-Kramers Pr3+ ion is
+investigated and analysis of Pr3+ crystal field excitations performed.
+Long-range order of Pr3+ moments in Pr2O2Fe2OSe2 can be induced by an applied
+magnetic field.",1704.05750v1
+2018-01-14,Polar phase of superfluid $^3$He: Dirac lines in the parameter and momentum spaces,"The time reversal symmetric polar phase of the spin-triplet superfluid $^3$He
+has two types of Dirac nodal lines. In addition to the Dirac loop in the
+spectrum of the fermionic Bogoliubov quasiparticles in the momentum space
+$(p_x,p_y,p_z)$, the spectrum of bosons (magnons) has Dirac loop in the 3D
+space of parameters -- the components of magnetic field $(H_x,H_y,H_z)$. The
+bosonic Dirac system lives on the border between the type-I and type-II.",1801.04576v2
+2019-07-26,Thermodynamics of Antiferromagnetic Solids in Magnetic Fields,"We analyze the thermodynamic properties of antiferromagnetic solids subjected
+to a combination of mutually orthogonal uniform magnetic and staggered fields.
+Low-temperature series for the pressure, order parameter and magnetization up
+to two-loop order in the effective expansion are established. We evaluate the
+self-energy and the dispersion relation of the dressed magnons in order to
+discuss the impact of spin-wave interactions on thermodynamic observables.",1907.11480v1
+2019-10-02,Continuous Aharonov--Bohm effect,"The Aharonov--Bohm effect in a model system described by the generalized
+Schr\""{o}dinger equation is considered. The scattering cross section is
+calculated in the standard formulation: an electron beam impinges on a long
+impenetrable solenoid encompassing a magnetic field. It is shown that the
+incident wave is scattered regardless of whether the magnetic flux through the
+solenoid is an integer of flux quanta whereby the scattering cross section
+becomes a continuously nonzero function of the total magnetic flux. The problem
+may find its application in investigations of the soliton-magnon interaction in
+the low-dimensional magnetism.",1910.00890v1
+2019-10-09,Scattering of exchange spin waves from regions of modulated magnetization,"We investigate the reflection coefficient of spin waves propagating in an
+ultra-thin ferromagnetic film with regions where saturation magnetization is
+modulated. We find analytically and using micromagnetic simulations that there
+are transmission resonances that depend on the width of the regions and on the
+energy of excitation. Our results resemble the quantum mechanical
+Ramsauer-Townsend effect in which an electron with certain energies can
+propagate above a potential field without scattering. Our findings are useful
+for reconfigurable magnonic devices where the saturation magnetization can be
+dynamically controlled via a thermal landscape.",1910.04303v1
+2019-10-09,Thermally controlled confinement of spin wave field in a magnonic YIG waveguide,"Methods for detecting spin waves rely on electrodynamical coupling between
+the spin wave dipolar field and an inductive probe. While this coupling is
+usually treated as constant, in this work, we experimentally and theoretically
+show that it is indeed temperature dependent. By measuring the spin wave
+magnetic field as a function of temperature of, and distance to the sample, we
+demonstrate that there is both a longitudinal and transversal confinement of
+the field near the YIG-Air interface. Our results are relevant for spin wave
+detection, in particular in the field of spin wave caloritronics",1910.04304v1
+2020-01-10,Long-Range Phonon Spin Transport in Ferromagnet-Nonmagnetic Insulator Heterostructures,"We investigate phonon spin transport in an insulating
+ferromagnet-nonmagnet-ferromagnet heterostructure. We show that the
+magnetoelastic interaction between the spins and the phonons leads to nonlocal
+spin transfer between the magnets. This transfer is mediated by a local phonon
+spin current and accompanied by a phonon spin accumulation. The spin
+conductance depends nontrivially on the system size, and decays over millimeter
+length scales for realistic material parameters, far exceeding the decay
+lengths of magnonic spin currents.",2001.03462v2
+2020-01-19,Chiral Coupling to Magnetodipolar Radiation,"We review and extend the theory of chiral pumping of spin waves by
+magnetodipolar stray fields that generate unidirectional spin currents and
+asymmetric magnon densities. We illustrate the physical principles by two kinds
+of chiral excitations of magnetic films, i.e., by the evanescent Oersted field
+of a narrow metallic stripline with an AC current bias and a magnetic nanowire
+under ferromagnetic resonance.",2001.06821v2
+2020-02-28,Quantum Damping of Skyrmion Crystal Eigenmodes due to Spontaneous Quasiparticle Decay,"The elementary excitations of skyrmion crystals experience both emergent
+magnetic fields and anharmonic interactions brought about by the topologically
+nontrivial noncollinear texture. The resulting flat bands cause strong
+spontaneous quasiparticle decay, dressing the eigenmodes of skyrmion crystals
+with a finite zero-temperature quantum lifetime. Sweeping the flat bands
+through the spectrum by changing the magnetic field leads to an externally
+controllable energy-selective magnon breakdown. In particular, we uncover that
+the three fundamental modes, i.e., the anticlockwise, breathing, and clockwise
+mode, exhibit distinct decay behavior, with the clockwise (anticlockwise) mode
+being the least (most) stable mode out of the three.",2002.12676v1
+2020-04-28,More on Schrödinger holography,"We find explicit solutions for giant magnons and spiky strings living on the
+Schr\""odinger $Schr_5 \times T^{1,1}$ and compute dispersion relations. The
+holographic dual field theory is conjectured to be a non-local dipole-deformed
+CFT at strong coupling. We find that the dependence between conserved charges
+in the dispersion relations is transcendental, which is quite different from
+the most symmetric case of spherical internal space. Keeping the squashing
+parameter $b$ general allows us to take some limits and to compare our results
+to known cases.",2004.13802v1
+2020-10-29,Difference between angular momentum and pseudoangular momentum,"In condensed matter systems it is necessary to distinguish between the
+momentum of the constituents of the system and the pseudomomentum of
+quasiparticles. The same distinction is also valid for angular momentum and
+pseudoangular momentum. Based on Noether's theorem, we demonstrate that the
+recently discussed orbital angular momenta of phonons and magnons are
+pseudoangular momenta. This conceptual difference is important for a proper
+understanding of the transfer of angular momentum in condensed matter systems,
+especially in spintronics applications.",2010.15616v2
+2021-03-03,The studies on phonons and magnons in (Ni80Fe20/Au/Co/Au) multilayers of different number of repetitions,"In Ni80Fe20/Au/Co/Au deposited on silicon substrate the interaction between
+spin waves and surface acoustic waves is observed by Brillion light scattering
+spectroscopy. We show that by changing the number of receptions in the
+multilayer we can tune the dispersion of surface acoustic waves (SAWs) not
+affecting significantly fundamentals spin wave (SW) mode. As a result, we can
+control (activate or deactivate) the magnetoelastic interaction between
+fundamental SW mode and SAWs by the thickness of the magnetostrictive
+multilayer.",2103.02686v2
+2021-03-15,Magnetically switchable spin wave retarder with $90^\circ$ antiferromagnetic domain wall,"Polarization, denoting the precession direction with respect to the
+background magnetization, is an intrinsic degree of freedom of spin wave. Using
+magnetic textures to control the spin wave polarization is fundamental and
+indispensable toward reprogrammable polarization-based magnonics. Here, we show
+that due to the intrinsic cubic anisotropy, a $90^\circ$ antiferromagnetic
+domain wall naturally acts as a spin wave retarder (wave-plate). Moreover, for
+a $90^\circ$ domain wall pair developed by introducing a second domain in a
+homogenous antiferromagnetic wire, the sign of retarding effect can be flipped
+by simply switching the direction of the intermediate domain.",2103.08342v2
+2021-03-15,Ferromagnetic Resonance in Permalloy Metasurfaces,"Permalloy films with one-dimensional (1D) profile modulation of submicron
+periodicity are fabricated based on commercially available DVD-R discs and
+studied using ferromagnetic resonance (FMR) method and micromagnetic numerical
+simulations. The main resonance position shows in-plane angular dependence
+which is strongly reminiscent of that in ferromagnetic films with uniaxial
+magnetic anisotropy. The main signal and additional low field lines are
+attributed to multiple standing spin wave resonances defined by the grating
+period. The results may present interest in magnetic metamaterials and
+magnonics applications.",2103.08704v1
+2021-04-05,Thermal Hall Effect of Chiral Spin Fluctuations,"Using a two-dimensional square lattice Heisenberg model with a Rashba-type
+Dzyaloshinskii-Moriya interaction, we demonstrate that chiral spin fluctuations
+can give rise to a thermal Hall effect in the absence of any static spin
+texture or momentum space topology. It is shown by means of Monte Carlo and
+stochastic spin dynamics simulations that the thermal Hall response is finite
+at elevated temperature outside of the linear spin wave regime and consistent
+with the presence of thermal fluctuation-induced nontrivial topology. Our
+result suggests that the high-fluctuation phases outside of the conventional
+regime of magnonics may yet be a promising area of exploration for spin-based
+electronics.",2104.02168v1
+2021-04-06,Quantum States of a Skyrmion in a 2D Antiferromagnet,"Quantum states of a skyrmion in a 2D antiferromagnetic lattice are obtained
+by quantizing the scaling parameter of Belavin-Polyakov model. Skyrmion
+classical collapse due to violation of the translational invariance of the
+continuous spin-field model by the lattice is replaced in quantum mechanics by
+transitions between discrete energy levels of the skyrmion. Rates of
+transitions due to the emission of magnons are computed. Ways of detecting
+quantization of skyrmion states are discussed.",2104.02212v1
+2021-08-13,Coupling the Higgs mode and ferromagnetic resonance in spin-split superconductors with Rashba spin-orbit coupling,"We consider the Higgs mode at nonzero momentum in superconductors and
+demonstrate that in the presence of Rashba spin-orbit coupling, it couples
+linearly with an external exchange field. The Higgs-spin coupling dramatically
+modifies the spin susceptibility near the superconducting critical temperature
+and consequently enhances the spin pumping effect in a ferromagnetic
+insulator/superconductor bilayer system. We show that this effect can be
+detected by measuring the magnon-induced voltage generated by the inverse spin
+Hall effect.",2108.06202v2
+2021-10-23,Optical interface for a hybrid magnon-photon resonator,"We study optical detection of magnetic resonance of a ferrimagnetic sphere
+resonator, which is strongly coupled to a microwave loop gap resonator. Optical
+fibers are employed for coupling the sphere resonator with light in the telecom
+band. We find that magnetic resonance can be optically detected in the region
+of anti-crossing between the loop gap and the ferrimagnetic resonances. By
+measuring the response time of the optical detection we rule out the
+possibility that microwave induced heating is responsible for the optical
+detectability.",2110.13644v1
+2021-11-04,Sequence of superconducting states in field cooled $FeCr_2S_4$,"In the present article we discuss theoretically the emergence of
+superconductivity in field cooled $FeCr_2S_4$. The chromium electrons form a
+triplet $t_{2g}$ states and due to antiferromagnetic exchange with the iron
+spins have Zeeman splitting. Applied, during preparation, magnetic field along
+the moment of iron ions, successively compensates the Zeeman splittings. The
+chromium electrons with zero Zeeman energy form Cooper pairs induced by iron
+magnons. In that way, we predict theoretically the existence of sequence of
+superconducting states in field cooled $FeCr_2S_4$. Actually there are three
+different superconductors prepared applying, during preparation, different
+magnetic fields. In these compounds superconductivity coexist with the
+saturated magnetism of iron ions.",2111.02765v1
+2021-11-18,Antiferromagnetic Resonance Revisited: Dissipative Coupling without Dissipation,"The antiferromagnet is a closed Hermitian system, we find that its
+excitations, even in the absence of dissipation, can be viewed as a
+non-Hermitian system with dissipative coupling. Consequently, the
+antiferromagnetic resonance spectrum does not show the typical level repulsion,
+but shows the level attraction -- a characteristic behavior often observed in
+non-Hermitian systems. Such behavior is because the antiferromagnetic ground
+state is $\mathcal{PT}$-symmetric. This new understanding on antiferromagnetic
+resonance also explains the mysterious enhancement of antiferromagnetic damping
+rate. Being effectively non-Hermitian, antiferromagnetic magnons can be used
+for quantum entanglement generation without introducing a third party like
+external pumping.",2111.09682v1
+2021-12-07,Curvilinear manipulation of polarized spin wave,"Polarization, the precession direction with respect to the background
+magnetization, is an intrinsic degree of freedom of spin wave. Introducing
+symmetry breaking mechanisms lies in the heart of lifting the degeneracy
+between polarized spin wave modes, and is essential in constructing
+polarization-based magnonic devices. Here we show that polarized spin waves can
+be naturally harnessed in a curved antiferromagnetic wire via tuning its
+curvature and torsion. Specifically, we investigate evolution of polarized spin
+wave in a spin wave rotator and a spin wave interferometer based on magnetic
+circular helices, and correlate these curvilinear effects to the Berry phase
+accumulated along wires.",2112.03748v1
+2022-03-12,Excitations of the ferroelectric order,"We identify the bosonic excitations in ferroelectrics that carry electric
+dipoles from the phenomenological Landau-Ginzburg-Devonshire theory. The
+""ferron"" quasi-particles emerge from the concerted action of anharmonicity and
+broken inversion symmetry. In contrast to magnons, the transverse excitations
+of the magnetic order, the ferrons in displacive ferroelectrics are
+longitudinal with respect to the ferroelectric order. Based on the ferron
+spectrum, we predict temperature dependent pyroelectric and electrocaloric
+properties, electric-field-tunable heat and polarization transport, and
+ferron-photon hybridization.",2203.06367v1
+2022-06-01,Dynamic Fingerprints of Synthetic Antiferromagnet Nanostructures with Interfacial Dzyaloshinskii-Moriya Interaction,"Synthetic antiferromagnet (SAF) nanostructures with interfacial
+Dzyaloshinskii-Moriya interaction can host topologically distinct spin textures
+such as skyrmions and thus are regarded as promising candidates for both
+spintronics and magnonics applications. Here, we present comprehensive
+micromagnetic simulations of such material systems and discuss the rich phase
+diagrams that contain various types of magnetic configurations. Aside from the
+static properties, we further discuss the resonant excitations of the
+calculated magnetic states which include individual skyrmions and skyrmioniums.
+Finally, the internal modes of SAF skyrmion clusters are studied and discussed
+in the context of magnetic sensing applications based on the dynamic
+fingerprint in broadband ferromagnetic resonance measurements.",2206.00554v2
+2023-02-25,A Perspective on Ferrons,"The duality between electric and magnetic dipoles in electromagnetism only
+partly applies to condensed matter. In particular, the elementary excitations
+of the magnetic and ferroelectric orders, namely magnons and ferrons,
+respectively, have received asymmetric attention from the condensed matter
+community in the past. In this perspective, we introduce and summarize the
+current state of the budding field of ""ferronics"" and speculate about its
+potential applications in thermal, information, and communication technology.",2302.12985v1
+2023-03-22,Even-odd effect for spin current through thin antiferromagnetic insulator,"Magnon spin transport in a metal-antiferromagnetic insulator-ferromagnetic
+insulator heterostructure is considered. The spin current is generated via the
+spin Seebeck effect and in the limit of clean sample where the effects of
+interface imperfections and lattice defects are excluded. For NiO as an
+antiferromagnetic insulator we have a magnetic order of antiferromagnetically
+combined planes which are internally in ferromagnetic order. We find that the
+sign of the spin current depends on the magnetization direction of the plane
+next to the metal resulting in an even-odd effect for the spin current.
+Moreover, as long as damping is excluded, this even-odd effect is the only
+remaining dependence on the NiO thickness for high temperatures.",2303.12282v1
+2023-04-19,Thermoelectric effect of skyrmion crystal confined in a magnetic disk,"We theoretically propose that an electric voltage can be generated by thermal
+gradient with a rotating skyrmion crystal confined in a magnetic disk. We find
+that the rotation of skyrmion crystal induced by diffusive thermal magnon
+currents in the presence of temperature gradient gives rise to spinmotive
+forces in the radial direction through coupling to conduction-electron spins.
+The amplitude of generated spinmotive force is larger for a larger temperature
+gradient at a lower temperature. The proposed phenomenon can be exploited as
+spintronics-based thermoelectric devices to realize the conversion of heat to
+electricity.",2304.09503v1
+2023-05-22,Stoner ferromagnetism in a momentum-confined interacting 2D electron gas,"In this work we investigate the ground state of a momentum-confined
+interacting 2D electron gas, a momentum-space analog of an infinite quantum
+well. The study is performed by combining analytical results with a numerical
+exact diagonalization procedure. We find a ferromagnetic ground state near a
+particular electron density and for a range of effective electron (or hole)
+masses. We argue that this observation may be relevant to the generalized
+Stoner ferromagnetism recently observed in multilayer graphene systems. The
+collective magnon excitations exhibit a linear dispersion, which originates
+from a diverging spin stiffness.",2305.13373v1
+2023-05-30,Quantum spin fluctuations and the stability of atomically-sized Bloch points,"We reveal the role of the spin variables' zero-point fluctuations (ZPFs) on
+the stability of Bloch point (BP) singularities. As topological solitons, BPs
+are important in topological transitions in nanomagnets. BPs present a
+singularity at their core, where the long-length-scale approximation fails. We
+found that ZPFs bloom nearby this core, reducing the effective magnetic moment
+and increasing the BP's stability. As suggested by classical models, the
+magnonic eigenmodes found by our methods fit with the bound state of an
+electron surrounding a dyon, with a magnetic and an electric charge.",2305.18704v1
+2023-08-01,Overview of superconductivity in field-cooled magnetic materials,"Considerable experimental skills have been accumulated in the preparation of
+field-cooled (FC) magnetic materials. This stimulates the search for FC
+magnetic materials that are superconductors.
+  The article overviews the recent proposed mechanism of superconductivity in
+field-cooled magnetic materials.
+  It is based on previously published results for magnon-induced
+superconductivity in field-cooled spin-1/2 antiferromagnets $[PRB96,214409]$
+(arXiv:1712.02983), Sequence of superconducting states in field cooled
+$FeCr_2S_4$ $[JPCM33,495604]$
+  (arXiv:2111.02765) and Partial order induced superconductivity in $Fe^{2+}$
+iron. $[EPL126,47001]$ (arXiv:1902.02290).",2308.00470v1
+2023-11-11,Emergence and enhancement of feedback control induced quantum entanglement,"We present a scheme for controlling quantum correlations by applying feedback
+to the cavity mode that exits a cavity while interacting with a mechanical
+oscillator and magnons. In a hybrid cavity magnomechanical system with a
+movable mirror, the proposed coherent feedback scheme allows for the
+enhancement of both bipartite and tripartite quantum correlations. Moreover, we
+demonstrate that the resulting entanglement remains robust with respect to
+ambient temperatures in the presence of coherent feedback control.",2311.06578v3
+2023-12-15,Nonlinear enhancement of coherent magnetization dynamics,"Magnets are interesting materials for classical and quantum information
+technologies. However, the short decoherence and dephasing times that determine
+the scale and speed of information networks, severely limit the appeal of
+employing the ferromagnetic resonance. Here we show that the lifetime and
+coherence of the uniform Kittel mode can be enhanced by 3-magnon
+interaction-induced mixing with the long-lived magnons at the minima of the
+dispersion relation. Analytical and numerical calculations based on this model
+explain recent experimental results and predict experimental signatures of
+quantum coherence.",2312.09856v1
+2024-01-30,Coherent and dissipative coupling in a magneto-mechanical system,"Hybrid elastic and spin waves hold promises for energy-efficient and
+versatile generation and detection of magnetic signals, with potentially long
+coherence times. Here we report on the combined elastic and magnetic dynamics
+in a one-dimensional magneto-mechanical crystal composed of an array of
+magnetic nanowires. Phononic and magnonic modes are impulsively excited by an
+optical ultrafast trigger and their decay is monitored by time resolved Magneto
+Optical Kerr Effect, with complementary Brillouin Light Scattering measurements
+and micromagnetic simulations. The strength and degree of mixing of coherent
+and dissipative coupling of the quasi-particles is determined quantitatively.",2401.16994v1
+2024-02-05,Modelling nanomagnet vertex dynamics through Coulomb charges,"We investigate the magnetization dynamics in nanomagnet vertices often found
+in artificial spin ices. Our analysis involves creating a simplified model that
+depicts edge magnetization using magnetic charges. We utilize the model to
+explore the energy landscape, its associated curvatures, and the fundamental
+modes. Our study uncovers specific magnonic regimes and transitions between
+magnetization states, marked by zero-modes, which can be understood within the
+framework of Landau theory. To verify our model, we compare it with
+micromagnetic simulations, demonstrating a noteworthy agreement.",2402.03036v1
+1999-09-23,The Pseudogap in La(2-x)Sr(x)CuO(4): A Raman Viewpoint,"We report the results of Raman scattering experiments on single crystals of
+La(2-x)Sr(x)CuO(4) [La214] as a function of temperature and doping. In
+underdoped compounds low-energy B1g spectral weight is depleted in association
+with the opening of a pseudogap on regions of the Fermi surface located near
+(pi, 0) and (0, pi). The magnitude of the depletion increases with decreasing
+doping, and in the most underdoped samples, with decreasing temperature. The
+spectral weight that is lost at low-energies (omega < 800 cm-1) is transferred
+to the higher energy region normally occupied by multi-magnon scattering. From
+the normal state B2g spectra we have determined the scattering rate
+Gamma(omega, T) of qausiparticles located near the diagonal directions in
+k-space, (pi/2, pi/2) regions. In underdoped compounds, Gamma(omega, T) is
+suppressed at low temperatures for energies less than Eg(x) ~ 800 cm-1. The
+observed doping dependence of the two-magnon scattering and the scattering rate
+suppression thus suggest that the pseudogap is characterized by an energy scale
+Eg ~ J, where J is the antiferromagnetic super-exchange energy. Comparison with
+the results from other techniques provides a consistent picture of the
+pseudogap in La214.",9909342v3
+2002-03-08,Low-temperature electrical transport in bilayer manganite La$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$,"The temperature $T$ and magnetic field $H$ dependence of anisotropic in-plane
+$\rho_{ab}$ and out-of-plane $\rho_{c}$ resistivities have been investigated in
+single crystals of the bilayer manganite La$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$.
+Below the Curie transition temperature $T_c=$ 125 K, $\rho_{ab}$ and $\rho_{c}$
+display almost the same temperature dependence with an up-turn around 50 K. In
+the metallic regime (50 K $\leq T \leq$ 110 K), both $\rho_{ab}(T)$ and
+$\rho_{c}(T)$ follow a $T^{9/2}$ dependence, consistent with the two-magnon
+scattering. We found that the value of the proportionality coefficient
+$B_{ab}^{fit}$ and the ratio of the exchange interaction $J_{ab}/J_c$ obtained
+by fitting the data are in excellent agreement with the calculated $B_{ab}$
+based on the two-magnon model and $J_{ab}/J_c$ deduced from neutron scattering,
+respectively. This provides further support for this scattering mechanism. At
+even lower $T$, in the non-metallic regime ($T<$ 50 K), {\it both} the in-plane
+$\sigma_{ab}$ and out-of-plane $\sigma_{c}$ conductivities obey a $T^{1/2}$
+dependence, consistent with weak localization effects. Hence, this demonstrates
+the three-dimensional metallic nature of the bilayer manganite
+La$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$ at $T<T_c$.",0203197v1
+2002-05-08,Quasiparticles governing the zero-temperature dynamics of the 1D spin-1/2 Heisenberg antiferromagnet in a magnetic field,"The T=0 dynamical properties of the one-dimensional (1D) $s=1/2$
+  Heisenberg antiferromagnet in a uniform magnetic field are studied via Bethe
+ansatz for cyclic chains of $N$ sites. The ground state at magnetization
+$0<M_z<N/2$, which can be interpreted as a state with $2M_z$ spinons or as a
+state of $M_z$ magnons, is reconfigured here as the vacuum for a different
+species of quasiparticles, the {\em psinons} and {\em antipsinons}. We
+investigate three kinds of quantum fluctuations, namely the spin fluctuations
+parallel and perpendicular to the direction of the applied magnetic field and
+the dimer fluctuations. The dynamically dominant excitation spectra are found
+to be sets of collective excitations composed of two quasiparticles excited
+from the psinon vacuum in different configurations. The Bethe ansatz provides a
+framework for (i) the characterization of the new quasiparticles in relation to
+the more familiar spinons and magnons, (ii) the calculation of spectral
+boundaries and densities of states for each continuum, (iii) the calculation of
+transition rates between the ground state and the dynamically dominant
+collective excitations, (iv) the prediction of lineshapes for dynamic structure
+factors relevant for experiments performed on a variety of quasi-1D
+antiferromagnetic compounds, including KCuF$_3$,
+  Cu(C$_4$H$_4$N$_2)(NO_3)_2$, and CuGeO$_3$.",0205142v1
+2002-11-28,Low energy spin wave excitations in bilayered magnetic manganite La$_{2-2x}$Sr$_{1+2x}$Mn$_{2}$O$_{7}$ ($0.30\leq{x}\leq{0.50}$),"We have studied the low-temperature behavior of the magnetization and the
+specific heat of the bilayered perovskite system $%
+La_{2-2x}Sr_{1+2x}Mn_{2}O_{7}$, for $0.30\leq x\leq 0.50$. Our analysis reveals
+that below 30 K the temperature dependence of the magnetization of the
+ferromagnetic samples, $x=0.30$, 0.32, and 0.36, in a field of 1T can be
+interpreted in terms of the thermal excitations of a two-dimensional gas of
+ferromagnetic magnons. The specific heat in zero field for these samples as for
+the $x=0.50$ antiferromagnetic one, is linear with temperature between the
+range of 1.8K $\leq $ T $\leq $ 10K. This behavior can be also explained by the
+magnon gas model. By comparing specific heat measurements in zero field with
+those taken in a field of 9T we are able to extract the lattice and electronic
+contributions and determine the in-plane exchange interactions. That are found
+to be in reasonable agreement with the values inferred from the analysis of the
+magnetization data and also with the values reported by inelastic neutron
+scattering studies. In addition, we found that the electronic density of states
+obtained for the $x=0.50$ sample is in agreement with previous band structure
+calculations.",0211677v3
+2004-07-30,Central peak in the pseudogap of high T_c superconductors,"We study the effect of antiferromagnetic (AF) correlations in the three-band
+Emery model, with respect to the experimental situation in weakly underdoped
+and optimally doped BSCCO. In the vicinity of the vH singularity of the
+conduction band there appears a central peak in the middle of a pseudogap,
+which is in an antiadiabatic regime, insensitive to the time scale of the
+mechanism responsible for the pseudogap. We find a quantum low-temperature
+regime corresponding to experiment, in which the pseudogap is created by
+zero-point motion of the magnons, as opposed to the usual semiclassical
+derivation, where it is due to a divergence of the magnon occupation number.
+Detailed analysis of the spectral functions along the (pi,0)-(pi,pi) line show
+significant agreement with experiment, both qualitative and, in the principal
+scales, quantitative. The observed slight approaching-then-receding of both the
+wide and narrow peaks with respect to the Fermi energy is also reproduced. We
+conclude that optimally doped BSCCO has a well-developed pseudogap of the order
+of 1000 K. This is only masked by the narrow antiadiabatic peak, which provides
+a small energy scale, unrelated to the AF scale, and primarily controlled by
+the position of the chemical potential.",0407800v3
+2004-10-28,Transport properties in manganite thin films,"The resistivity of thin $La_{0.7}A_{0.3}MnO_{3}$ films ($A=Ca, Sr$) is
+investigated in a wide temperature range. The comparison of the resistivities
+is made among films grown by different techniques and on several substrates
+allowing to analyze samples with different amounts of disorder. In the
+low-temperature nearly half-metallic ferromagnetic state the prominent
+contribution to the resistivity scales as $T^{\alpha}$ with $\alpha \simeq 2.5$
+for intermediate strengths of disorder supporting the theoretical proposal of
+single magnon scattering in presence of minority spin states localized by the
+disorder. For large values of disorder the low-temperature behavior of the
+resistivity is well described by the law $T^{3}$ characteristic of anomalous
+single magnon scattering processes, while in the regime of low disorder the
+$\alpha$ exponent tends to a value near 2. In the high temperature insulating
+paramagnetic phase the resistivity shows the activated behavior characteristic
+of polaronic carriers. Finally in the whole range of temperatures the
+experimental data are found to be consistent with a phase separation scenario
+also in films doped with strontium ($A=Sr$).",0410743v1
+2005-06-14,High field properties of geometrically frustrated magnets,"Above the saturation field, geometrically frustrated quantum antiferromagnets
+have dispersionless low-energy branches of excitations corresponding to
+localized spin-flip modes. Transition into a partially magnetized state occurs
+via condensation of an infinite number of degrees of freedom. The ground state
+below the phase transition is a magnon crystal, which breaks only translational
+symmetry and preserves spin-rotations about the field direction. We give a
+detailed review of recent works on physics of such phase transitions and
+present further theoretical developments. Specifically, the low-energy degrees
+of freedom of a spin-1/2 kagom\'e antiferromagnet are mapped to a hard hexagon
+gas on a triangular lattice. Such a mapping allows to obtain a quantitative
+description of the magnetothermodynamics of a quantum kagom\'e antiferromagnet
+from the exact solution for a hard hexagon gas. In particular, we find the
+exact critical behavior at the transition into a magnon crystal state, the
+universal value of the entropy at the saturation field, and the position of
+peaks in temperature- and field-dependence of the specific heat. Analogous
+mapping is presented for the sawtooth chain, which is mapped onto a model of
+classical hard dimers on a chain. The finite macroscopic entropies of
+geometrically frustrated magnets at the saturation field lead to a large
+magnetocaloric effect.",0506327v2
+2006-02-17,Field dependence of the magnetic spectrum in anisotropic and Dzyaloshinskii-Moriya antiferromagnets: I. Theory,"We consider theoretically the effects of an applied uniform magnetic field on
+the magnetic spectrum of anisotropic two-dimensional and Dzyaloshinskii-Moriya
+layered quantum Heisenberg antiferromagnets. The first case is relevant for
+systems such as the two-dimensional square lattice antiferromagnet
+Sr(2)CuO(2)Cl(2), while the later is known to be relevant to the physics of the
+layered orthorhombic antiferromagnet La(2)CuO(4). We first establish the
+correspondence betwenn the low-energy spectrum obtained within the anisotropic
+non-linear sigma model and by means of the spin-wave approximation for a
+standard easy-axis antiferromagent. Then, we focus on the field-theory approach
+to calculate the magnetic field dependence of the magnon gaps and spectral
+intensities for magnetic fields applied along the three possible
+crystallographic directions. We discuss the various possible ground states and
+their evolution with temperature for the different field orientations, and the
+occurrence of spin-flop transitions for fields perpendicular to the layers
+(transverse fields) as well as for fields along the easy axis (longitudinal
+fields). Measurements of the one-magnon Raman spectrum in Sr(2)CuO(2)Cl(2) and
+La(2)CuO(4) and a comparison between the experimental results and the
+predictions of the present theory will be reported in part II of this research
+work [L. Benfatto et al., cond-mat/0602664].",0602419v3
+2006-06-15,Exact eigenstates of highly frustrated spin lattices probed in high fields,"Strongly frustrated antiferromagnets such as the magnetic molecule
+{Mo72Fe30}, the kagome, or the pyrochlore lattice exhibit a variety of
+fascinating properties like low-lying singlets, magnetization plateaus as well
+as magnetization jumps. During recent years exact many-body eigenstates could
+be constructed for several of these spin systems. These states become ground
+states in high magnetic fields, and they also lead to exotic behavior. A key
+concept to an understanding of these properties is provided by independent
+localized magnons. The energy eigenvalue of these n-magnon states scales
+linearly with the number n of independent magnons and thus with the total
+magnetic quantum number M=Ns-n. In an applied field this results in a giant
+magnetization jump which constitutes a new macroscopic quantum effect. It will
+be demonstrated that this behavior is accompanied by a massive degeneracy, an
+extensive (T=0)-entropy, and thus a large magnetocaloric effect at the
+saturation field. The connection to flat band ferromagnetism will be outlined.",0606401v2
+2006-07-25,Spin dynamics in the diluted ferromagnetic Kondo lattice model,"The interplay of disorder and competing interactions is investigated in the
+carrier-induced ferromagnetic state of the Kondo lattice model within a
+numerical finite-size study in which disorder is treated exactly. Competition
+between impurity spin couplings, stability of the ferromagnetic state, and
+magnetic transition temperature are quantitatively investigated in terms of
+magnon properties for different models including dilution, disorder, and
+weakly-coupled spins. A strong optimization is obtained for T_c at hole doping
+p << x, highlighting the importance of compensation in diluted magnetic
+semiconductors. The estimated T_c is in good agreement with experimental
+results for Ga_{1-x}Mn_x As for corresponding impurity concentration, hole
+bandwidth, and compensation. Finite-temperature spin dynamics is quantitatively
+studied within a locally self-consistent magnon renormalization scheme, which
+yields a substantial enhancement in T_c due to spin clustering, and highlights
+the nearly-paramagnetic spin dynamics of weakly-coupled spins. The large
+enhancement in density of low-energy magnetic excitations due to disorder and
+competing interactions results in a strong thermal decay of magnetization,
+which fits well with the Bloch form M_0(1-BT^{3/2}) at low temperature, with B
+of same order of magnitude as obtained in recent squid magnetization
+measurements on Ga_{1-x}Mn_x As samples.",0607633v1
+2006-08-29,Collective modes for an array of magnetic dots in the vortex state,"The dispersion relations for collective magnon modes for square-planar arrays
+of vortex-state magnetic dots, having closure magnetic flux are calculated. The
+array dots have no direct contact between each other, and the sole source of
+their interaction is the magnetic dipolar interaction. The magnon formalism
+using Bose operators along with translational symmetry of the lattice, with the
+knowledge of mode structure for the isolated dot, allows the diagonalization of
+the system Hamiltonian giving the dispersion relation. Arrays of vortex-state
+dots show a large variety of collective mode properties, such as positive or
+negative dispersion for different modes. For their description, not only
+dipolar interaction of effective magnetic dipoles, but non-dipolar terms common
+to higher multipole interaction in classical electrodynamics can be important.
+The dispersion relation is shown to be non-analytic as the value of the
+wavevector approaches zero for all dipolar active modes of the single dot. For
+vortex-state dots the interdot interaction is not weak, because, the dynamical
+part (in contrast to the static magnetization of the vortex state) dot does not
+contain the small parameter, the ratio of vortex core size to the dot radius.
+This interaction can lead to qualitative effects like the formation of modes of
+angular standing waves instead of modes with definite azimuthal number known
+for the insolated vortex state dot.",0608638v1
+2006-11-09,"Ferromagnetism in the t-t' Hubbard model: interplay of lattice, band dispersion, and interaction effects studied within a Goldstone-mode preserving scheme","Ferromagnetism in the Hubbard model is investigated on sc, bcc, and fcc
+lattices using a systematic inverse-degeneracy ($1/{\cal N}$) expansion which
+incorporates self-energy and vertex corrections such that spin-rotation
+symmetry and the Goldstone mode are explicitly preserved. First-order quantum
+corrections to magnon energies are evaluated for several cases, providing a
+comprehensive picture of the interplay of lattice, band dispersion, and
+interaction effects on the stability of the ferromagnetic state with respect to
+both long- and short-wavelength fluctuations. Our results support the belief
+that ferromagnetism is a generic feature of the Hubbard model at intermediate
+and strong coupling provided the DOS is sufficiently asymmetric and strongly
+peaked near band edge, as for fcc lattice with finite $t'$. For
+short-wavelength modes, behavior of a characteristic energy scale $\omega^*
+\sim T_c$ (magnon-DOS-peak energy) is in excellent agreement with the $T_c$ vs.
+$n$ behavior within DMFT, both with respect to the stable range of densities
+($0.20 < n < 0.85$) as well as the optimal density $n=0.65$. However, our
+finding of vanishing spin stiffness near optimal density highlights the role of
+long-wavelength fluctuations in further reducing the stable range of densities.",0611238v1
+2006-11-17,Field-driven phase transitions in a quasi-two-dimensional quantum antiferromagnet,"We report magnetic susceptibility, specific heat, and neutron scattering
+measurements as a function of applied magnetic field and temperature to
+characterize the $S=1/2$ quasi-two-dimensional frustrated magnet piperazinium
+hexachlorodicuprate (PHCC). The experiments reveal four distinct phases. At low
+temperatures and fields the material forms a quantum paramagnet with a 1 meV
+singlet triplet gap and a magnon bandwidth of 1.7 meV. The singlet state
+involves multiple spin pairs some of which have negative ground state bond
+energies. Increasing the field at low temperatures induces three dimensional
+long range antiferromagnetic order at 7.5 Tesla through a continuous phase
+transition that can be described as magnon Bose-Einstein condensation. The
+phase transition to a fully polarized ferromagnetic state occurs at 37 Tesla.
+The ordered antiferromagnetic phase is surrounded by a renormalized classical
+regime. The crossover to this phase from the quantum paramagnet is marked by a
+distinct anomaly in the magnetic susceptibility which coincides with closure of
+the finite temperature singlet-triplet pseudo gap. The phase boundary between
+the quantum paramagnet and the Bose-Einstein condensate features a finite
+temperature minimum at $T=0.2$ K, which may be associated with coupling to
+nuclear spin or lattice degrees of freedom close to quantum criticality.",0611463v1
+2007-02-27,Low temperature specific heat and possible gap to magnetic excitations in the Heisenberg pyrochlore antiferromagnet Gd2Sn207,"The Gd2Sn2O7 pyrochlore Heisenberg antiferromagnet displays a phase
+transition to a four sublattice Neel ordered state at a temperature near 1 K.
+Despite the seemingly conventional nature of the ordered state, the specific
+heat has been found to be described in the temperature range 350-800 mK by an
+anomalous T-squared power law. A similar temperature dependence has also been
+reported for Gd2Ti2O7, another pyrochlore Heisenberg material. Such anomalous
+T-squared behavior in Cv has been argued to be correlated to an unusual
+energy-dependence of the density of states which also seemingly manifests
+itself in low-temperature spin fluctuations found in muon spin relaxation
+experiments. In this paper, we report calculations of Cv that consider spin
+wave like excitations out of the Neel order observed in Gd2Sn2O7 and argue that
+the parametric T-squared behavior does not reflect the true low-energy
+excitations of Gd2Sn2O7. Rather, we find that the low-energy excitations of
+this material are antiferromagnetic magnons gapped by single-ion and dipolar
+anisotropy effects, and that the lowest temperature of 350 mK considered in
+previous specific heat measurements accidentally happens to coincide with a
+crossover temperature below which magnons become thermally activated and Cv
+takes an exponential form. We argue that further specific heat measurements
+that extend down to at least 100 mK are required in order to ascribe an
+unconventional description of magnetic excitations out of the ground state of
+Gd2Sn2O7 or to invalidate the standard picture of gapped excitations proposed
+herein.",0702661v2
+2004-02-19,Static black holes with a negative cosmological constant: Deformed horizon and anti-de Sitter boundaries,"Using perturbative techniques, we investigate the existence and properties of
+a new static solution for the Einstein equation with a negative cosmological
+constant, which we call the deformed black hole. We derive a solution for a
+static and axisymmetric perturbation of the Schwarzschild-anti-de Sitter black
+hole that is regular in the range from the horizon to spacelike infinity. The
+key result is that this perturbation simultaneously deforms the two boundary
+surfaces--i.e., both the horizon and spacelike two-surface at infinity. Then we
+discuss the Abbott-Deser mass and the Ashtekar-Magnon one for the deformed
+black hole, and according to the Ashtekar-Magnon definition, we construct the
+thermodynamic first law of the deformed black hole. The first law has a
+correction term which can be interpreted as the work term that is necessary for
+the deformation of the boundary surfaces. Because the work term is negative,
+the horizon area of the deformed black hole becomes larger than that of the
+Schwarzschild-anti-de Sitter black hole, if compared under the same mass,
+indicating that the quasistatic deformation of the Schwarzschild-anti-de Sitter
+black hole may be compatible with the thermodynamic second law (i.e., the area
+theorem).",0402082v2
+2007-07-31,Renormalized spin wave excitations in the antiferromagnetic Heisenberg-Kondo model for heavy fermions,"Recent inelastic neutron scattering experiments in CeIn3 and CePd2Si2 single
+crystals, measured spin wave excitations at low temperatures. These two heavy
+fermion compounds exhibit antiferromagnetic long-range order, but a strong
+competition between the Ruderman-Kittel-Kasuya-Yosida(RKKY) interaction and
+Kondo effect is evidenced by their nearly equal Neel and Kondo temperatures.
+Our aim is to show how magnons such as measured in the antiferromagnetic phase
+of these Ce compounds, can be described with a microscopic Heisenberg-Kondo
+model as introduced by J.R.Iglesias, C.Lacroix and B.Coqblin, used before for
+studies of the non-magnetic phase. The model includes the correlated Ce-4f
+electrons hybridized with the conduction band, and we consider competing RKKY
+(Heisenberg-like J_{H}) and Kondo (J_{K}) antiferromagnetic couplings. Carrying
+on a series of unitary transformations, we perturbatively derive a second-order
+effective Hamiltonian which, projected onto the antiferromagnetic electron
+ground state, describes the spin wave excitations, renormalized by their
+interaction with correlated itinerant electrons. We numerically study how the
+different parameters of the model influence the renormalization of the magnons,
+yielding useful information for the analysis of inelastic neutron scattering
+experiments in antiferromagnetic heavy fermion compounds. We also compare our
+results with available experimental data, finding good agreement with the spin
+wave measurements in cubic CeIn3.",0708.0023v1
+2008-08-19,Three-dimensional N=6 SCFT's and their membrane dynamics,"We analyze several aspects of the recent construction of three-dimensional
+conformal gauge theories by Aharony et al. in various regimes. We pay special
+attention to understanding how the M-theory geometry and interpretation can be
+extracted from the analysis of the field theory. We revisit the calculations of
+the moduli space of vacua and the complete characterization of chiral ring
+operators by analyzing the field theory compactified on a 2-sphere. We show
+that many of the states dual to these operators can be interpreted as D-brane
+states in the weak coupling limit. Also, various features of the dual AdS
+geometry can be obtained by performing a strong coupling expansion around
+moduli space configurations, even though one is not taking the planar
+expansion. In particular, we show that at strong coupling the corresponding
+weak coupling D-brane states of the chiral ring localize on particular
+submanifolds of the dual geometry that match the M-theory interpretation. We
+also study the massive spectrum of fields in the moduli space. We use this to
+investigate the dispersion relation of giant magnons from the field theory
+point of view. Our analysis predicts the exact functional form of the
+dispersion relation as a function of the world-sheet momentum, independently of
+integrability assumptions, but not the exact form with respect to the 't Hooft
+coupling. We also get the dispersion relation of bound states of giant magnons
+from first principles, providing evidence for the full integrability of the
+corresponding spin chain model at strong 't Hooft coupling.",0808.2503v2
+2009-09-28,Thermodynamics of O(N) Antiferromagnets in 2+1 Dimensions,"Within the framework of effective Lagrangians we calculate the free energy
+density for an O($N$) antiferromagnet in 2+1 dimensions up to three-loop order
+in the perturbative expansion and derive the low-temperature series for various
+thermodynamic quantities. In particular, we show that the magnon-magnon
+interaction in the O(3) antiferromagnet in $d$=2+1 -- the O(3)-invariant
+quantum Heisenberg antiferromagnet on a square or a honeycomb lattice -- is
+very weak and repulsive and manifests itself through a term proportional to
+five powers of the temperature in the free energy density. Remarkably, the
+corresponding coefficient is fully determined by the leading-order effective
+Lagrangian ${\cal L}^2_{eff}$ and does not involve any higher order effective
+constants from ${\cal L}^4_{eff}$ related to the anisotropies of the lattice --
+the symmetries are thus very restrictive in $d$=2+1. We also compare our
+results that apply to O($N$) antiferromagnets in 2+1 dimensions with the those
+for O($N$) antiferromagnets in 3+1 dimensions. The present work demonstrates
+the efficiency of the fully systematic effective Lagrangian method in the
+condensed matter domain, which clearly proves to be superior to spin-wave
+theory. We would like to emphasize that the structure of the low-temperature
+series derived in the present work is model-independent and universal as it
+only relies on symmetry considerations.",0909.5239v1
+2010-05-31,Spin Chains in N=2 Superconformal Theories: from the Z_2 Quiver to Superconformal QCD,"In this paper we find preliminary evidence that N=2 superconformal QCD, the
+SU(N_c) SYM theory with N_f= 2 N_c fundamental hypermultiplets, might be
+integrable in the large N Veneziano limit. We evaluate the one-loop dilation
+operator in the scalar sector of the N=2 superconformal quiver with SU(N_c) X
+SU(N_{\check c}) gauge group, for N_c = N_{\check c}. Both gauge couplings g
+and \check g are exactly marginal. This theory interpolates between the Z_2
+orbifold of N=4 SYM, which corresponds to \check g=g, and N=2 superconformal
+QCD, which is obtained for \check g -> 0. The planar one-loop dilation operator
+takes the form of a nearest-neighbor spin-chain Hamiltonian. For superconformal
+QCD the spin chain is of novel form: besides the color-adjoint fields
+\phi^a_{b}, which occupy individual sites of the chain, there are ""dimers""
+Q^a_{i} \bar Q^i_{b} of flavor-contracted fundamental fields, which occupy two
+neighboring sites. We solve the two-body scattering problem of magnon
+excitations and study the spectrum of bound states, for general \check g/g. The
+dimeric excitations of superconformal QCD are seen to arise smoothly for \check
+g -> 0 as the limit of bound wavefunctions of the interpolating theory. Finally
+we check the Yang-Baxter equation for the two-magnon S-matrix. It holds as
+expected at the orbifold point \check g = g. While violated for general \check
+g \neq g, it holds again in the limit \check g -> 0, hinting at one-loop
+integrability of planar N=2 superconformal QCD.",1006.0015v2
+2010-08-10,Numerical study of the spin-1/2 Heisenberg antiferromagnet on a 48-site triangular lattice,"We numerically study the magnetization and the dispersion relation of a
+frustrated quantum spin system. Our method, which is named the stochastic state
+selection method, is a kind of Monte Carlo method to give eigenstates of the
+system through statistical averaging processes.
+  Using the stochastic state selection method with some constraints, we make a
+successful study of the spin-1/2 Heisenberg antiferromagnet on a 48-site
+triangular lattice. We calculate the sublattice magnetization and the static
+structure function in the ground state. Our result on the sublattice
+magnetization is consistent with the value given by the linear spin wave
+theory. This adds an evidence for the analysis based on the spontaneous
+symmetry breaking of the semi-classical Neel order in the ground state.
+  We also evaluate the low-lying one magnon spectra of the model with all wave
+vectors available on a 48-site triangular lattice. We find that at the ordering
+wave vector there is a Goldstone mode, which is in good agreement with the
+result from the spin wave analysis. The magnon spectra with other wave vectors,
+however, are quite different from results obtained by the linear spin wave
+theory. We observe a flat dispersion relation with a strong downward
+renormalization. Our results are compatible with those recently reported in the
+series expansion study and in the order 1/S calculation of the spin wave
+analysis.",1008.1612v1
+2010-11-25,Calculation of the Expected Zero Field Muon Relaxation Rate in the Geometrically Frustrated Rare Earth Pyrochlore Gd2Sn2O7 Antiferromagnet,"The magnetic insulator Gd2Sn2O7 is one of many geometrically frustrated
+magnetic materials known to exhibit a nonzero muon spin polarization relaxation
+rate, $\lambda(T)$, down to the lowest temperature (T) studied. Such behaviour
+is typically interpreted as a significant level of persisting spin dynamics
+(PSD) of the host material. In the case of Gd2Sn2O7, such PSD comes as a
+surprise since magnetic specific heat measurements suggest conventional gapped
+magnons, which would naively lead to an exponentially vanishing $\lambda(T)$ as
+$T \rightarrow 0$. In contrast to most materials that display PSD, the ordered
+phase of Gd2Sn2O7 is well characterized and both the nature and the magnitude
+of the interactions have been inferred from the magnetic structure and the
+temperature dependence of the magnetic specific heat. Based on this
+understanding, the temperature dependence of the muon spin polarization
+relaxation through the scattering of spin waves (magnons) is calculated. The
+result explicitly shows that, despite the unusual extensive number of weakly
+dispersive (gapped)excitations characterizing Gd2Sn2O7, a remnant of the zero
+modes of the parent frustrated pyrochlore Heisenberg antiferromagnet, the
+temperature dependence of the calculated $\lambda(T)$ differs dramatically from
+the experimental one. Indeed, the calculation conforms to the naive expectation
+of an exponential collapse of $\lambda(T)$ at temperatures below ~ 0.7K. This
+result, for the first time, illustrates crisply and quantitatively the paradox
+that presents itself with the pervasive occurrence of PSD in highly frustrated
+magnetic systems as evinced by muon spin relaxation measurements.",1011.5689v1
+2010-12-29,Finite-size corrections for quantum strings on AdS_4 x CP^3,"We revisit the calculation of curvature corrections to the pp-wave energy of
+type IIA string states on AdS_4 x CP^3 initiated in arXiv:0807.1527. Using the
+near pp-wave Hamiltonian found in arXiv:0912.2257, we compute the first
+non-vanishing correction to the energy of a set of bosonic string states at
+order 1/R^2, where R is the curvature radius of the background. The leading
+curvature corrections give rise to cubic, order 1/R, and quartic, order 1/R^2,
+terms in the Hamiltonian, for which we implement the appropriate normal
+ordering prescription. Including the contributions from all possible fermionic
+and bosonic string states, we find that there exist logarithmic divergences in
+the sums over mode numbers which cancel between the cubic and quartic
+Hamiltonian. We show that the cubic Hamiltonian naturally requires that the
+cutoff for summing over heavy modes must be twice the one for light modes. With
+this prescription the strong-weak coupling interpolating function h(\lambda),
+entering the magnon dispersion relation, does not receive a one-loop
+correction, in agreement with the algebraic curve spectrum. However, the single
+magnon dispersion relation exhibits finite-size exponential corrections.",1101.0004v2
+2011-03-01,Inelastic Neutron and X-ray Scattering from Incommensurate Magnetic Systems,"Neutrons and X-rays are powerful probes for studying magnetic and lattice
+excitations in strongly correlated materials over very wide ranges of momentum
+and energy transfers. In the focus of the present work are the incommensurate
+magnetic systems MnSi and Cr. Under application of a magnetic field, helically
+ordered MnSi transforms into a weak itinerant ferromagnet. Using polarized
+neutrons we demonstrate that the Stoner excitations are spin flip excitations.
+The amplitude (longitudinal) fluctuations associated with the magnon modes are
+already strong far away from T_C. Interestingly, even the non spin flip
+excitations associated with the Stoner modes are observable. In Cr, we have
+observed Kohn anomalies in the phonon spectrum at those incommensurate
+positions in reciprocal space, where the spin density wave is observed. The
+corresponding phonon and magnon modes are not coupled. In addition, an
+anomalous softening of a transverse phonon branch along the N-H zone boundary
+line is observed that is caused by strong electron phonon coupling. High
+resolution neutron scattering indicate that the low energy Fincher-Burke
+excitations may rather correspond to localized modes in momentum and energy and
+not to propagating collective modes. Finally, we demonstrate that in the near
+future it may become feasible to investigate excitations in very small samples
+thus allowing to measure the dynamics of strongly correlated materials under
+extreme conditions and in the vicinity of quantum phase transitions.",1103.0161v1
+2011-08-04,Luescher formula for GKP string,"We investigate finite-size corrections to anomalous dimensions of large-spin
+twist-two operators in the planar maximally supersymmetric Yang-Mills theory.
+We develop a framework for analysis of these corrections, that is complementary
+to the conventional spin-chain approach, by making use of the hole rather than
+the magnon picture. From the dual string theory perspective where the
+large-spin operator is identified with the Gubser-Klebanov-Polyakov (GKP)
+string, our approach is equivalent to constructing the first Luescher
+correction to the energy of the GKP string by incorporating the contribution of
+virtual excitations propagating on it. It allows us to propose a formula that
+controls a particular class of large-spin corrections to the twist-two
+anomalous dimension and holds at any value of the coupling constant. Compared
+to wrapping corrections computed with magnons propagating on the spin chain,
+the finite-size corrections that are encoded in our formalism start at a lower
+loop level. Our formalism thus calls for modification of the asymptotic
+contributions which are conventionally incorporated within the Asymptotic Bethe
+Ansatz. An educated guess allows us to remedy this pitfall and successfully
+confront our predictions with known results up to five loop accuracy at weak
+coupling. Finally, our formula sheds light on the weak-to-strong coupling
+transition for the subleading large-spin corrections under study and confirms
+stringy expectations at strong coupling where they are found to be identical to
+the first Luescher correction to the vacuum energy of the O(6) sigma model.",1108.0999v1
+2011-09-15,Uncovering selective excitations using the resonant profile of indirect inelastic x-ray scattering in correlated materials: Observing two-magnon scattering and relation to the dynamical structure factor,"Resonant inelastic x-ray scattering (RIXS) is a spectroscopic technique which
+has been widely used to study various elementary excitations in correlated and
+other condensed matter systems. For strongly correlated materials, besides
+boosting the overall signal the dependence of the resonant profile on incident
+photon energy is still not fully understood. Previous endeavors in connecting
+indirect RIXS, such as Cu K-edge for example where scattering takes place only
+via the core-hole created as an intermediate state, with the charge dynamical
+structure factor S(q,\omega) neglected complicated dependence on the
+intermediate state configuration. To resolve this issue, we performed an exact
+diagonalization study of the RIXS cross-section using the single-band Hubbard
+model by fully addressing the intermediate state contribution. Our results are
+relevant to indirect RIXS in correlated materials, such as high Tc cuprates. We
+demonstrate that RIXS spectra can be reduced to S(q,\omega) when there is no
+screening channel for the core-hole potential in the intermediate state. We
+also show that two-magnon excitations are highlighted at the resonant photon
+energy when the core-hole potential in the corresponding intermediate state is
+poorly screened. Our results demonstrate that different elementary excitations
+can be emphasized at different intermediate states, such that selecting the
+exact incident energy is critical when trying to capture a particular
+elementary excitation.",1109.3446v2
+2011-09-28,"Different dimensionality trends in the Landau damping of magnons in iron, cobalt and nickel: time dependent density functional study","We study the Landau damping of ferromagnetic magnons in Fe, Co, and Ni as the
+dimensionality of the system is reduced from three to two. We resort to the
+\textit{ab initio} linear response time dependent density functional theory in
+the adiabatic local spin density approximation. The numerical scheme is based
+on the Korringa-Kohn-Rostoker Green's function method. The key points of the
+theoretical approach and the implementation are discussed. We investigate the
+transition metals in three different forms: bulk phases, free-standing thin
+films and thin films supported on a nonmagnetic substrate. We demonstrate that
+the dimensionality trends in Fe and Ni are opposite: in Fe the transition from
+bulk bcc crystal to Fe/Cu(100) film reduces the damping whereas in Ni/Cu(100)
+film the attenuation increases compared to bulk fcc Ni. In Co, the strength of
+the damping depends relatively weakly on the sample dimensionality. We explain
+the difference in the trends on the basis of the underlying electronic
+structure. The influence of the substrate on the spin-wave damping is analyzed
+by employing Landau maps representing wave-vector resolved spectral density of
+the Stoner excitations.",1109.6217v2
+2012-03-27,High frequency permeability of magnonic metamaterials with magnetic inclusions of complex shape,"We present a method of calculation of the effective magnetic permeability of
+magnonic metamaterials containing periodically arranged magnetic inclusions of
+arbitrary shapes. The spectrum of spin wave modes confined in the inclusions is
+fully taken into account. Within the scope of the proposed method, we compare
+two approaches. The first approach is based on a simple semi-analytical theory
+that uses the numerically calculated susceptibility tensor of an isolated
+inclusion as input data. Within the second approach, micromagnetic packages
+with periodic boundary conditions (PBC) are used to calculate the
+susceptibility of a single 2D periodic array of such inclusions, with the whole
+3D metamaterial consisting of a stack of such arrays. To calculate the
+susceptibility tensor of an isolated inclusion, we have implemented and
+compared two different methods: (a) a micromagnetic method, in which we have
+employed three different micromagnetic packages: the finite element package
+NMAG and the two finite differences packages OOMMF and MicroMagus; and (b) the
+modified dynamical matrix method. To illustrate the methodology, we have
+calculated the effective permeability of a metamaterial consisting of a stack
+of hexagonal arrays of magnetic nanodisks in a non-magnetic matrix. The range
+of geometrical parameters for which such a metamaterial is characterized by the
+negative permeability has been identified. The critical comparison of the
+different micromagnetic packages and the dynamical matrix method (based on the
+calculation of the susceptibility tensor of an isolated inclusion) has
+demonstrated that their results agree to within 3 %.",1203.6116v1
+2012-07-19,Difference in Bose-Einstein condensation of conserved and unconserved particles,"The peculiarities in the Bose-Einstein condensation of particles and
+quasiparticles are discussed. The difference between the condensation of
+conserved and unconserved particles is analyzed. A classification of
+quasiparticles is given. The emphasis is made on the ability of particles and
+quasiparticles to condense. Illustrations include: general Bose-condensed
+atomic systems, such as ensembles of trapped atoms, Bose gases with conserved
+and unconserved number of atoms, vibrating atoms in double-well lattices,
+Holstein-Primakoff magnons, Schwinger bosons, slave bosons, and the
+condensation of singletons and triplons. The basic difference is that the
+system of particles, whose total number is conserved, can form equilibrium as
+well as nonequilibrium condensates, while unconserved particles can condense
+only in a nonequilibrium system subject to external pumping supporting the
+density of these particles sufficient for their condensation. The examples of
+such a nonequilibrium condensation of unconserved particles are the
+Bose-Einstein condensation of excitons, polaritons, and photons. Elementary
+collective excitations, such as bogolons and phonons, being self-consistently
+defined, do not condense. Magnons cannot condense in equilibrium systems.
+Controversies, existing in literature with regard to the Bose-Einstein
+condensation of some quasiparticles, are explained. Pushing a system out of
+equilibrium may favor the condensation of unconserved quasiparticles, but
+suppresses the condensate fraction of conserved particles.",1207.4621v1
+2013-01-07,Persistent high-energy spin excitations in iron pnictide superconductors,"Motivated by the premise that superconductivity in iron-based superconductors
+is unconventional and mediated by spin fluctuations, an intense research effort
+has been focused on characterizing the spin excitation spectrum in the
+magnetically ordered parent phases of the Fe-pnictides2,3 and - chalcogenides4.
+For these undoped materials it is well-established that the spin excitation
+spectrum consists of a sharp, highly dispersive magnon spanning an energy range
+of up to 200 meV (ref. 3). The fate of these high-energy magnetic modes upon
+sizable doping is hitherto unresolved. Using resonant inelastic x-ray
+scattering we show that optimally doped superconducting Ba0.6K0.4Fe2As2 retains
+well defined, dispersive high-energy modes of magnetic origin. These paramagnon
+modes are softer than, though as intense as, the magnon of undoped
+antiferromagnetic BaFe2As2. The persistence of spin excitations well into the
+superconducting phase suggests that, if spin fluctuations are responsible for
+superconducting pairing, they originate from a distinctly correlated
+spin-state. This connects Fe-pnictide superconductors to the high-Tc cuprates,
+for which in spite of fundamental differences in the electronic structure,
+similar paramagnon modes are present5.",1301.1289v1
+2013-01-17,Spin-wave excitations in presence of nanoclusters of magnetic impurities,"Nanoscale inhomogeneities and impurity clustering are often found to
+drastically affect the magnetic and transport properties in disordered/diluted
+systems, giving rise to rich and complex phenomena. However, the physics of
+these systems still remains to be explored in more details as can be seen from
+the scarce literature available. We present a detailed theoretical analysis of
+the effects of nanoscale inhomogeneities on the spin excitation spectrum in
+diluted magnetic systems. The calculations are performed on relatively large
+systems (up to $N$=$66^3$). It is found that even low concentrations of
+inhomogeneities have drastic effects on both the magnon density of states and
+magnon excitations. These effects become even more pronounced in the case of
+short ranged magnetic interactions between the impurities. In contrast to the
+increase of critical temperatures $T_C$, reported in previous studies, the
+spin-stiffness $D$ is systematically suppressed in the presence of nanoscale
+inhomogeneities. Moreover $D$ is found to strongly depend on the
+inhomogeneities' concentration, the cluster size, as well as the range of the
+magnetic interactions. The findings are discussed in the prospect of potential
+spintronics applications. We believe that this detailed numerical work could
+initiate future experimental studies to probe this rich physics with the most
+appropriate tool, Inelastic Neutron Scattering (INS).",1301.4111v2
+2013-03-21,Persistence of magnetic excitations in La2-xSrxCuO4 from the undoped insulator to the heavily overdoped non-superconducting metal,"One of the most intensely studied scenarios of high-temperature
+superconductivity (HTS) postulates pairing by exchange of magnetic excitations
+[1]. Indeed, such excitations have been observed up to around optimal doping in
+the cuprates [2-7]. In the heavily overdoped regime neutron scattering
+measurements indicate that magnetic excitations have effectively disappeared
+[8-10], and this was argued to cause the demise of HTS with overdoping [1, 8,
+10]. Here we use resonant inelastic x-ray scattering (RIXS), which is sensitive
+to complementary parts of reciprocal space, to measure the evolution of the
+magnetic excitations in La2-xSrxCuO4 across the entire phase diagram, from a
+strongly correlated insulator (x = 0) to a non-superconducting metal (x =
+0.40). For x = 0, well-defined magnon excitations are observed [11]. These
+magnons broaden with doping, but they persist with a similar dispersion and
+comparable intensity all the way to the non-superconducting, heavily overdoped
+metallic phase. The destruction of HTS with overdoping is therefore caused
+neither by the general disappearance nor by the overall softening of magnetic
+excitations; other factor(s), such as the redistribution of spectral weight,
+must be considered.",1303.5359v3
+2013-04-15,Frustrated quantum Heisenberg antiferromagnets at high magnetic fields: Beyond the flat-band scenario,"We consider the spin-1/2 antiferromagnetic Heisenberg model on three
+frustrated lattices (the diamond chain, the dimer-plaquette chain and the
+two-dimensional square-kagome lattice) with almost dispersionless lowest magnon
+band. Eliminating high-energy degrees of freedom at high magnetic fields, we
+construct low-energy effective Hamiltonians which are much simpler than the
+initial ones. These effective Hamiltonians allow a more extended analytical and
+numerical analysis. In addition to the standard strong-coupling perturbation
+theory we also use a localized-magnon based approach leading to a substantial
+improvement of the strong-coupling approximation. We perform extensive exact
+diagonalization calculations to check the quality of different effective
+Hamiltonians by comparison with the initial models. Based on the
+effective-model description we examine the low-temperature properties of the
+considered frustrated quantum Heisenberg antiferromagnets in the high-field
+regime. We also apply our approach to explore thermodynamic properties for a
+generalized diamond spin chain model suitable to describe azurite at high
+magnetic fields. Interesting features of these highly frustrated spin models
+consist in a steep increase of the entropy at very small temperatures and a
+characteristic extra low-temperature peak in the specific heat. The most
+prominent effect is the existence of a magnetic-field driven
+Berezinskii-Kosterlitz-Thouless phase transition occurring in the
+two-dimensional model.",1304.4136v1
+2013-12-17,Longitudinal Excitations in Bipartite and Hexagonal Antiferromagnetic Spin Lattices,"Based on our recently proposed magnon-density-waves using the microscopic
+many-body approach, we investigate the longitudinal excitations in quantum
+antiferromagnets by including the second order corrections in the large-$s$
+expansion. The longitudinal excitation spectra for a general spin quantum
+number using the antiferromagnetic Heisenberg Hamiltonian are obtained for
+various spin lattice models. For bipartite lattice models, we find that the
+numerical results for the energy gaps for the longitudinal modes at $q\to0$ and
+the magnetic ordering wavevector $\bf Q$ are reduced by about $40-50\%$ after
+including the second order corrections. Thus, our estimate of the energy gaps
+for the quasi-one-dimensional (quasi-1D) antiferromagnetic compound KCuF$_3$ is
+in better agreement with the experimental result. For the quasi-1D
+antiferromagnets on hexagonal lattices, the full excitation spectra of both the
+transverse modes (i.e., magnons) and the longitudinal modes are obtained as
+functions of the nearest-neighbor coupling and the anisotropy constants. We
+find two longitudinal modes due to the non-collinear nature of the triangular
+antiferromagnetic order, similar to that of the phenomenological field theory
+approach by Affleck. We compare our results for the longitudinal energy gaps at
+the magnetic wavevectors with the experimental results for several
+antiferromagnetic compounds with both integer and non-integer spin quantum
+numbers, and also find good agreement after the higher-order contributions are
+included in our calculations.",1312.4929v1
+2013-12-24,Phonon and magnetic dimer excitations in Fe-based S=2 spin ladder compound BaFe$_2$Se$_2$O,"Raman scattering spectra of new Fe-based S=2 spin ladder compound
+BaFe$_2$Se$_2$O are measured in a temperature range between 15 K and 623 K. All
+six A$_{1g}$ and two B$_{1g}$ Raman active modes of BaFe$_2$Se$_2$O, predicted
+by the factor-group analysis, have been experimentally observed at energies
+that are in a rather good agreement with the lattice dynamics calculation. The
+antiferromagnetic long-range spin ordering in BaFe$_2$Se$_2$O below $T_N$=240 K
+leaves a fingerprint both in the A$_{1g}$ and B$_{1g}$ phonon mode linewidth
+and energy. In the energy range between 400 and 650 cm$^{-1}$ we have observed
+magnetic excitation related structure in the form of magnon continuum, with the
+peaks corresponding to the singularities in the one dimensional density of
+magnon states. The onset value of magnetic continuum (2$\Delta_{S}$) is found
+at about 437 cm$^{-1}$ at 15 K. The magnetic continuum disappears at about 623
+K, which lead us to conclude that the short-range magnetic ordering in
+BaFe$_2$Se$_2$O exists apparently up to 2.6$T_N$.",1312.6844v1
+2014-12-01,Coexistence of superconductivity and magnetism in spin-fermion model of ferrimagnetic spinel in an external magnetic field,"A two-sublattice spin-fermion model of ferrimagnetic spinel, with spin-$1/2$
+itinerant electrons at the sublattice $A$ site and spin-$s$ localized electrons
+at the sublattice $B$ site is considered. The exchange between itinerant and
+localized electrons is antiferromanetic. As a result the external magnetic
+field, applied along the magnetization of the localized electrons, compensates
+the Zeeman splitting due to the spin-fermion exchange and magnon-fermion
+interaction induces spin anti-parallel p-wave superconductivity which coexists
+with magnetism. We have obtained five characteristic values of the applied
+field (in units of energy) $H_{cr1}<H_3<H_0<H_4<H_{cr2}$. At $H_0$ the external
+magnetic field compensates the Zeeman splitting. When $H_{cr1}<H<H_{cr2}$ the
+spin antiparallel p-wave superconductivity with $T_{1u}$ configuration coexists
+with magnetism. The superconductor to normal magnet transition at finite
+temperature is second order when $H$ runs the interval $(H_3,H_4)$. It is an
+abrupt transition when $H_{cr1}<H<H_3$ or $H_4<H<H_{cr2}$. This is proved
+calculating the temperature dependence of the gap for three different values of
+the external magnetic field $H_{cr1}<H<H_3$, $H_4<H<H_{cr2}$ and $H=H_0$. In
+the first two cases the abrupt fall to zero of the gap at superconducting
+critical temperature shows that the superconductor to normal magnet transition
+is first order. The Hubbard term (Coulomb repulsion), in a weak coupling
+regime, does not affect significantly the magnon induced superconductivity.
+Relying on the above results one can formulate a recipe for preparing a
+superconductor from ferrimagnetic spinel: i) hydrostatic pressure above the
+critical value of insulator-metal transition. ii) external magnetic field along
+the sublattice magnetization with higher amplitude.",1412.0450v1
+2015-05-13,Interpolating relativistic and non-relativistic Nambu-Goldstone and Higgs modes,"When a continuous symmetry is spontaneously broken in non-relativistic
+theories, there appear Nambu-Goldstone (NG) modes, whose dispersion relations
+are either linear (type-I) or quadratic (type-II). We give a general framework
+to interpolate between relativistic and non-relativistic NG modes, revealing a
+nature of type-I and II NG modes in non-relativistic theories. The
+interpolating Lagrangians have the nonlinear Lorentz invariance which reduces
+to the Galilei or Schrodinger invariance in the non-relativistic limit. We find
+that type-I and type-II NG modes in the interpolating region are accompanied
+with a Higgs mode and a chiral NG partner, respectively, both of which are
+gapful. In the ultra-relativistic limit, a set of a type-I NG mode and its
+Higgs partner remains, while a set of type-II NG mode and gapful NG partner
+turns to a set of two type-I NG modes. In the non-relativistic limit, the both
+types of accompanied gapful modes become infinitely massive, disappearing from
+the spectrum. The examples contain a phonon in Bose-Einstein condensates, a
+magnon in ferromagnets, and a Kelvon and dilaton-magnon localized around a
+skyrmion line in ferromagnets.",1505.03299v3
+2015-09-08,Magnon spectrum of the helimagnetic insulator Cu2OSeO3,"Complex low-temperature ordered states in chiral magnets are typically
+governed by a competition between multiple magnetic interactions. The
+chiral-lattice multiferroic Cu2OSeO3 became the first insulating helimagnetic
+material in which a long-range order of topologically stable spin vortices
+known as skyrmions was established. Here we employ state-of-the-art inelastic
+neutron scattering (INS) to comprehend the full three-dimensional spin
+excitation spectrum of Cu2OSeO3 over a broad range of energies. Distinct types
+of high- and low-energy dispersive magnon modes separated by an extensive
+energy gap are observed in excellent agreement with the previously suggested
+microscopic theory based on a model of entangled Cu4 tetrahedra. The comparison
+of our INS data with model spin-dynamical calculations based on these
+theoretical proposals enables an accurate quantitative verification of the
+fundamental magnetic interactions in Cu2OSeO3 that are essential for
+understanding its abundant low-temperature magnetically ordered phases.",1509.02432v2
+2016-01-15,Bidirectional conversion between microwave and light via ferromagnetic magnons,"Coherent conversion of microwave and optical photons in the single-quantum
+level can significantly expand our ability to process signals in various
+fields. Efficient up-conversion of a feeble signal in the microwave domain to
+the optical domain will lead to quantum-noise-limited microwave amplifiers.
+Coherent exchange between optical photons and microwave photons will also be a
+stepping stone to realize long-distance quantum communication. Here we
+demonstrate bidirectional and coherent conversion between microwave and light
+using collective spin excitations in a ferromagnet. The converter consists of
+two harmonic oscillator modes, a microwave cavity mode and a magnetostatic mode
+called Kittel mode, where microwave photons and magnons in the respective modes
+are strongly coupled and hybridized. An itinerant microwave field and a
+travelling optical field can be coupled through the hybrid system, where the
+microwave field is coupled to the hybrid system through the cavity mode, while
+the optical field addresses the hybrid system through the Kittel mode via
+Faraday and inverse Faraday effects. The conversion efficiency is theoretically
+analyzed and experimentally evaluated. The possible schemes for improving the
+efficiency are also discussed.",1601.03908v3
+2016-01-22,Study of the cavity-magnon-polariton transmission line shape,"We experimentally and theoretically investigate the microwave transmission
+line shape of the cavity-magnon-polariton (CMP) created by inserting a low
+damping magnetic insulator into a high quality 3D microwave cavity. While fixed
+field measurements are found to have the expected Lorentzian characteristic, at
+fixed frequencies the field swept line shape is in general asymmetric. Such
+fixed frequency measurements demonstrate that microwave transmission can be
+used to access magnetic characteristics of the CMP, such as the field line
+width $\Delta H$. By developing an effective oscillator model of the microwave
+transmission we show that these line shape features are general characteristics
+of harmonic coupling. At the same time, at the classical level the underlying
+physical mechanism of the CMP is electrodynamic phase correlation and a second
+model based on this principle also accurately reproduces the experimental line
+shape features. In order to understand the microscopic origin of the effective
+coupled oscillator model and to allow for future studies of CMP phenomena to
+extend into the quantum regime, we develop a third, microscopic description,
+based on a Green's function formalism. Using this method we calculate the
+transmission spectra and find good agreement with the experimental results.",1601.06049v2
+2016-06-14,Solitary magnons in the $S={5\over2}$ antiferromagnet CaFe$_{2}$O$_{4}$,"CaFe$_{2}$O$_{4}$ is a $S={5\over 2}$ anisotropic antiferromagnet based upon
+zig-zag chains having two competing magnetic structures, denoted as the A
+($\uparrow \uparrow \downarrow \downarrow$) and B ($\uparrow \downarrow
+\uparrow \downarrow$) phases, which differ by the $c$-axis stacking of
+ferromagnetic stripes. We apply neutron scattering to demonstrate that the
+competing A and B phase order parameters results in magnetic antiphase
+boundaries along $c$ which freeze on the timescale of $\sim$ 1 ns at the onset
+of magnetic order at 200 K. Using high resolution neutron spectroscopy, we find
+quantized spin wave levels and measure 9 such excitations localized in regions
+$\sim$ 1-2 $c$-axis lattice constants in size. We discuss these in the context
+of solitary magnons predicted to exist in anisotropic systems. The magnetic
+anisotropy affords both competing A+B orders as well as localization of spin
+excitations in a classical magnet.",1606.04243v1
+2016-07-19,Kitaev materials beyond iridates: order by quantum disorder and Weyl magnons in rare-earth double perovskites,"Motivated by the experiments on the rare-earth double perovskites, we propose
+a generalized Kitaev-Heisenberg model to describe the generic interaction
+between the spin-orbit-entangled Kramers' doublets of the rare-earth moments.
+We carry out a systematic analysis of the mean-field phase diagram of this new
+model. In the phase diagram, there exist large regions with a continuous U(1)
+or O(3) degeneracy. Since no symmetry of the model protects such a continuous
+degeneracy, we predict that the quantum fluctuation lifts the continuous
+degeneracy and favors various magnetic orders in the phase diagram. From this
+order by quantum disorder mechanism, we further predict that the magnetic
+excitations of the resulting ordered phases are characterized by nearly gapless
+pseudo-Goldstone modes. We find that there exist Weyl magnon excitations for
+certain magnetic orders. We expect our prediction to inspire further study of
+Kitaev physics, the order by quantum disorder phenomenon and topological spin
+wave modes in the rare-earth magnets and the systems alike.",1607.05618v3
+2017-02-15,Spin waves in periodic antidot waveguide of complex base,"We consider the planar magnonic waveguide with a periodic sequence of
+antidots forming zig-zag pattern, where two neighboring antidots are shifted
+towards the opposite edges of the waveguide. This system has a complex base
+with two antidots in one unit cell. The Brillouin zone is here two-times
+narrower than the Brillouin zone for the waveguide without displacement of
+antidots. We have shown that for dispersion relation folded into narrower
+Brillouin zone, new frequency gap can be opened and their width can be
+controlled by the shift of the antidots. We found that, the different strength
+of spin wave pinning at the edges of the periodic waveguide (and their
+antidots)determines the dependence of the width of gap on the shift of
+antidots. For the systems with completely free or ideally pinned magnetization,
+these dependencies are qualitatively different. We have found an optimum shift
+of antidot for maximzing the width of the gap for the system with pinned
+magnetization. More interestingly, we notice that for this kind of geometry of
+the structure, majority of the modes are doubly degenerate at the edge of
+Brillouin zone and have a finite group velocity at the very close vicinity of
+the edge of Brillouin zone, for larger values of antidot shift. This empowers
+us to design magnonic waveguide to steer the spin waves.",1702.04667v2
+2017-02-16,Mobile Spin Impurity in an Optical Lattice,"We investigate the Fermi polaron problem in a spin-1/2 Fermi gas in an
+optical lattice for the limit of both strong repulsive contact interactions and
+one dimension. In this limit, a polaronic-like behaviour is not expected, and
+the physics is that of a magnon or impurity. While the charge degrees of
+freedom of the system are frozen, the resulting tight-binding Hamiltonian for
+the impurity's spin exhibits an intriguing structure that strongly depends on
+the filling factor of the lattice potential. This filling dependency also
+transfers to the nature of the interactions for the case of two magnons and the
+important spin balanced case. At low filling, and up until near unit filling,
+the single impurity Hamiltonian faithfully reproduces a single-band,
+quasi-homogeneous tight-binding problem. As the filling is increased and the
+second band of the single particle spectrum of the periodic potential is
+progressively filled, the impurity Hamiltonian, at low energies, describes a
+single particle trapped in a multi-well potential. Interestingly, once the
+first two bands are fully filled, the impurity Hamiltonian is a near-perfect
+realisation of the Su-Schrieffer-Heeger model. Our studies, which go well
+beyond the single-band approximation, that is, the Hubbard model, pave the way
+for the realisation of interacting one-dimensional models of condensed matter
+physics.",1702.05097v2
+2018-01-23,Super Scatterers Based on Artificial Localized Magnon Resonances,"The interaction between electromagnetic waves and objects is strongly
+affected by the shape and material composition of the latter. Artificially
+created materials, formed by a subwavelength structuring of their unit cells,
+namely metamaterials, can exhibit peculiar responses to electromagnetic
+radiation and provide additional powerful degrees of freedom to the scatterer
+design. In particular, negative material susceptibilities give rise to strong
+resonant interactions with deeply subwavelength particles. While the negative
+electrical permittivity of natural noble metals manifests itself in localized
+plasmon resonant oscillations, negative magnetic permeability is virtually
+non-existent in nature. Here the concept of artificial magnon resonance in
+subwavelength objects with effective negative permeability, designed based on
+the metamaterial approach, is demonstrated. Strong localized oscillations of
+the magnetic fields within an array of split ring resonators, forming a sphere,
+hybridize in a collective mode of the structure. As a result, extremely high
+scattering cross section, exceeding that of a steel sphere with the same radius
+by four orders of magnitude, was demonstrated. Furthermore, the scattering
+cross section of subwavelength metamaterial-based sphere was shown to be
+comparable to the low frequency (MHz) radar signature of a big military
+aircraft. Super scatterers, based on tunable resonances within artificially
+created materials, can find use in a broad range of electromagnetic
+applications, including wireless communications, radars, RFID, internet of
+things hardware and many others.",1802.01663v1
+2018-02-06,Spin transport in multilayer systems with fully epitaxial NiO thin films,"We report on the generation and transport of thermal spin currents in fully
+epitaxial {\gamma}-Fe$_2$O$_3$/NiO(001)/Pt and Fe$_3$O$_4$/NiO(001)/Pt
+trilayers. A thermal gradient, perpendicular to the plane of the sample,
+generates a magnonic spin current in the ferrimagnetic maghemite
+({\gamma}-Fe$_2$O$_3$) and magnetite (Fe$_3$O$_4$) thin films by means of the
+spin Seebeck effect. The spin current propagates across the epitaxial,
+antiferromagnetic insulating NiO layer, before being detected in the Pt layer
+by the inverse spin Hall effect. The transport of the spin signal is studied as
+a function of the NiO thickness, temperature and ferrimagnetic material where
+the spin current is generated. In epitaxial NiO grown on maghemite, the spin
+Seebeck signal decays exponentially as a function of the NiO thickness, with a
+spin-diffusion length for thermally-generated magnons of {\lambda}$_{MSDL}$ =
+$1.6 \pm 0.2$ nm, largely independent on temperature. We see no enhancement of
+the spin current signal as previously reported for certain temperatures and
+thicknesses of the NiO. In epitaxial NiO grown on magnetite, the
+temperature-averaged spin diffusion length is {\lambda}$_{MSDL}$ = $3.8 \pm
+0.3$ nm, and we observe an enhancement of the spin signal when the NiO
+thickness is 0.8 nm, demonstrating that the growth conditions dramatically
+affect the spin transport properties of the NiO even for full epitaxial growth.
+In contrast to theoretical predictions for coherent spin transport, we do not
+see vastly different spin diffusion lengths between epitaxial and
+polycrystalline NiO layers.",1802.01844v1
+2018-04-14,Interplay of Wave Localization and Turbulence in Spin Seebeck Effect,"One of the most important discoveries in spintronics is the spin Seebeck
+effect (SSE) recently observed in both insulating and (semi-)conducting
+magnets. However, the very existence of the effect in transverse configuration
+is still a subject of current debates, due to conflicting results reported in
+different experiments. Present understanding of the SSE is mainly based on a
+particle-like picture with the local equilibrium approximation (LEA), i.e.,
+spatially resolved temperature-field assumed to describe the system. In this
+work, we abandon the LEA to some extent and develop a wave theory to explain
+the SSE, by highlighting the interplay between wave localization and
+turbulence. We show that the emerging SSE with a sign change in the
+high/low-temperature regions is closely related to the extendedness of the spin
+wave that senses an average temperature of the system. On the one hand,
+ubiquitous disorders (or magnetic field gradients) can strongly suppress the
+transverse spin Seebeck effect (TSSE) due to Anderson (or Wannier-Zeeman)
+spin-wave localization. On the other hand, the competing wave turbulence of
+interacting magnons tends to delocalize the wave, and thus remarkably revives
+the TSSE before the magnon self-trapping. Our theory provides a promising route
+to resolve the heated debate on TSSE with a clear experiment scheme to test it
+in future spin caloritronic devices.",1804.05157v1
+2014-03-03,Semi-classical analysis of the inner product of Bethe states,"We study the inner product of two Bethe states, one of which is taken
+on-shell, in an inhomogeneous XXX chain in the Sutherland limit, where the
+number of magnons is comparable with the length L of the chain and the magnon
+rapidities arrange in a small number of macroscopically large Bethe strings.
+The leading order in the large L limit is known to be expressed through a
+contour integral of a dilogarithm. Here we derive the subleading term. Our
+analysis is based on a new contour-integral representation of the inner product
+in terms of a Fredholm determinant. We give two derivations of the sub-leading
+term. Besides a direct derivation by solving a Riemann-Hilbert problem, we give
+a less rigorous, but more intuitive derivation by field-theoretical methods.
+For that we represent the Fredholm determinant as an expectation value in a
+Fock space of chiral fermions and then bosonize. We construct a collective
+field for the bosonized theory, the short wave-length part of which may be
+evaluated exactly, while the long wave-length part is amenable to a $1/L$
+expansion. Our treatment thus results in a systematic 1/L expansion of
+structure factors within the Sutherland limit.",1403.0358v2
+2016-12-30,Magnetization jump in one dimensional $J-Q_{2}$ model with anisotropic exchange,"We investigate the adiabatic magnetization process of the one-dimensional
+$J-Q_{2}$ model with XXZ anisotropy $g$ in an external magnetic field $h$ by
+using density matrix renormalization group (DMRG) method. According to the
+characteristic of the magnetization curves, we draw a magnetization phase
+diagram consisting of four phases. For a fixed nonzero pair coupling $Q$, i)
+when $g<-1$, the ground state is always ferromagnetic in spite of $h$; ii) when
+$g>-1$ but still small, the whole magnetization curve is continuous and smooth;
+iii) if further increasing $g$, there is a macroscopic magnetization jump from
+partially- to fully-polarized state; iv) for a sufficiently large $g$, the
+magnetization jump is from non- to fully-polarized state. By examining the
+energy per magnon and the correlation function, we find that the origin of the
+magnetization jump is the condensation of magnons and the formation of magnetic
+domains. We also demonstrate that while the experienced states are
+Heisenberg-like without long-range order, all the \textit{jumped-over} states
+have antiferromagnetic or N\'eel long-range orders, or their mixing.",1701.00013v3
+2008-07-05,Vector chiral and multipolar orders in the spin-1/2 frustrated ferromagnetic chain in magnetic field,"We study the one-dimensional spin-1/2 Heisenberg chain with competing
+ferromagnetic nearest-neighbor J_1 and antiferromagnetic next-nearest-neighbor
+J_2 exchange couplings in the presence of magnetic field. We use both numerical
+approaches (the density matrix renormalization group method and exact
+diagonalization) and effective field-theory approach, and obtain the
+ground-state phase diagram for wide parameter range of the coupling ratio
+J_1/J_2. The phase diagram is rich and has a variety of phases, including the
+vector chiral phase, the nematic phase, and other multipolar phases. In the
+vector chiral phase, which appears in relatively weak magnetic field, the
+ground state exhibits long-range order (LRO) of vector chirality which
+spontaneously breaks a parity symmetry. The nematic phase shows a quasi-LRO of
+antiferro-nematic spin correlation, and arises as a result of formation of
+two-magnon bound states in high magnetic fields. Similarly, the higher
+multipolar phases, such as triatic (p=3) and quartic (p=4) phases, are formed
+through binding of p magnons near the saturation fields, showing quasi-LRO of
+antiferro-multipolar spin correlations. The multipolar phases cross over to
+spin density wave phases as the magnetic field is decreased, before
+encountering a phase transition to the vector chiral phase at a lower field.
+The implications of our results to quasi-one-dimensional frustrated magnets
+(e.g., LiCuVO_4) are discussed.",0807.0858v2
+2008-07-03,Spin wave excitations in the antiferromagnetic Heisenberg-Kondo model for heavy fermions,"Recent inelastic neutron scattering experiments in CeIn$_{3}$ and
+CePd$_{2}$Si$_{2}$ single crystals measured spin wave excitations at low
+temperatures. These two heavy fermion compounds exhibit antiferromagnetic
+long-range order, but a strong competition between the
+Ruderman-Kittel-Kasuya-Yosida(RKKY) interaction and Kondo effect is evidenced
+by their nearly equal N\'eel and Kondo temperatures. Our aim is to show how
+magnons such as measured in the antiferromagnetic phase of these Ce compounds,
+can be described with a microscopic Heisenberg-Kondo model introduced by
+J.R.Iglesias, C.Lacroix and B.Coqblin, used before for studies of the
+non-magnetic phase. The model includes the correlated Ce-$4 f$ electrons
+hybridized with the conduction band, where we also allow for correlations, and
+we consider competing
+  RKKY (Heisenberg-like $J_{H} $) and Kondo ($J_{K}$) antiferromagnetic
+couplings. Carrying on a series of unitary transformations, we perturbatively
+derive a second-order effective Hamiltonian which, projected onto the
+antiferromagnetic electron ground state, describes the spin wave excitations,
+renormalized by their interaction with correlated itinerant electrons. We
+numerically study how the different parameters of the model influence the
+renormalization of the magnons, yielding useful information for the analysis of
+inelastic neutron scattering experiments in antiferromagnetic heavy fermion
+compounds. We also compare our results with the available experimental data,
+finding good agreement with the spin wave measurements in cubic CeIn$_3$.",0807.1246v1
+2011-11-01,Phase diagrams of $\rm La_{1-x}Ca_xMnO_3$ in Double Exchange Model with added antiferromagnetic and Jahn-Teller interaction,"The phase diagram of the multivalent manganites $\rm La_{1-x}Ca_xMnO_3$, in
+space of temperature and doping $x$, is a challenge for the theoretical
+physics. It is an important test for the model used to study these compounds
+and the method of calculation. To obtain theoretically this diagram for
+$x<0.5$, we consider the two-band Double Exchange Model for manganites with
+added Jahn-Teller coupling and antiferromagnetic Heisenberg term. In order to
+calculate Curie and N\'{e}el temperatures we derive an effective Heisenberg
+model for a vector which describes the local orientation of the total
+magnetization of the system. The exchange constants of this model are different
+for different space directions and depend on the density of $e_g$ electrons,
+antiferromagnetic constants and the Jahn-Teller energy. To reproduce the well
+known phase transitions from A-type antiferromagnetism to ferromagnetism at low
+$x$ and C-type antiferromagnetism to G-type antiferromagnetism at large $x$, we
+argue that the antiferromagnetic exchange constants should depend on the
+lattice direction. We show that ferromagnetic to A-type antiferromagnetic
+transition results from the Jahn-Teller distortion. Accounting adequately for
+the magnon-magnon interaction, Curie and N\'{e}el temperatures are calculated.
+The results are in very good agreement with the experiment and provide values
+for the model parameters, which best describe the behavior of the critical
+temperature for $x<0.5$.",1111.0267v1
+2011-11-09,Terahertz and infrared spectroscopic evidence of phonon-paramagnon coupling in hexagonal piezomagnetic YMnO3,"Terahertz and far-infrared electric and magnetic responses of hexagonal
+piezomagnetic YMnO3 single crystals are investigated. Antiferromagnetic
+resonance is observed in the spectra of magnetic permeability mu_a [H(omega)
+oriented within the hexagonal plane] below the Neel temperature T_N. This
+excitation softens from 41 to 32 cm-1 on heating and finally disappears above
+T_N. An additional weak and heavily-damped excitation is seen in the spectra of
+complex dielectric permittivity epsilon_c within the same frequency range. This
+excitation contributes to the dielectric spectra in both antiferromagnetic and
+paramagnetic phases. Its oscillator strength significantly increases on heating
+towards room temperature thus providing evidence of piezomagnetic or
+higher-order couplings to polar phonons. Other heavily-damped dielectric
+excitations are detected near 100 cm-1 in the paramagnetic phase in both
+epsilon_c and epsilon_a spectra and they exhibit similar temperature behavior.
+These excitations appearing in the frequency range of magnon branches well
+below polar phonons could remind electromagnons; however, their temperature
+dependence is quite different. We have used density functional theory for
+calculating phonon dispersion branches in the whole Brillouin zone. A detailed
+analysis of these results and of previously published magnon dispersion
+branches brought us to the conclusion that the observed absorption bands stem
+from phonon-phonon and phonon- paramagnon differential absorption processes.
+The latter is enabled by a strong short-range in-plane spin correlations in the
+paramagnetic phase.",1111.2161v1
+2011-11-28,Strings in AdS_4 x CP^3: finite size spectrum vs. Bethe Ansatz,"We compute the first curvature corrections to the spectrum of light-cone
+gauge type IIA string theory that arise in the expansion of $AdS_4\times
+\mathbb{CP}^3$ about a plane-wave limit. The resulting spectrum is shown to
+match precisely, both in magnitude and degeneration that of the corresponding
+solutions of the all-loop Gromov--Vieira Bethe Ansatz. The one-loop dispersion
+relation correction is calculated for all the single oscillator states of the
+theory, with the level matching condition lifted. It is shown to have all
+logarithmic divergences cancelled and to leave only a finite exponentially
+suppressed contribution, as shown earlier for light bosons. We argue that there
+is no ambiguity in the choice of the regularization for the self-energy sum,
+since the regularization applied is the only one preserving unitarity.
+Interaction matrices in the full degenerate two-oscillator sector are
+calculated and the spectrum of all two light magnon oscillators is completely
+determined. The same finite-size corrections, at the order 1/J, where $J$ is
+the length of the chain, in the two-magnon sector are calculated from the all
+loop Bethe Ansatz. The corrections obtained by the two completely different
+methods coincide up to the fourth order in $\lambda' =\lambda/J^2$. We
+conjecture that the equivalence extends to all orders in $\lambda$ and to
+higher orders in 1/J.",1111.6628v3
+2012-01-05,Longitudinal and transverse static spin fluctuations in layered ferro- and antiferromagnets,"We analyse the momentum dependence of static non-uniform susceptibilities of
+layered local-moment systems below Curie (Neel) temperature within the
+1/S-expansion, the renormalization-group approach, and first order of
+1/N-expansion. We argue that the previously known results of the spin-wave
+theory and renormalization-group approach for the transverse spin
+susceptibility acquire strong corrections already at sufficiently low
+temperatures, which appear due to the interaction of the incomping magnon
+having momentum q with magnons with momenta k<q. Such corrections can not be
+treated in the standard renormalization-group approach, but can be described by
+both, 1/S and 1/N expansions. The results of these expansions can be
+successfully extrapolated to the magnetic transition temperature T=T_M yielding
+the correct weight of static spin fluctuations, determined by the O(3)
+symmetry. For the longitudinal susceptibility, the summation of leading terms
+of 1/S expansion within the parquet approach allows to fulfill the sumrule for
+the weights of transverse and longitudinal fluctuations in a broad temperature
+region below T_M outside the critical regime. We also discuss the effect of
+longitudinal spin fluctuations on the (sublattice) magnetization of layered
+systems.",1201.1148v4
+2016-05-07,Prime Factorization Using Magnonic Holographic Device,"Determining the prime factors of a given number N is a problem, which
+requires super-polynomial time for conventional digital computers. A
+polynomial-time algorithm was invented by P. Shor for quantum computers.
+However, the realization of quantum computers is associated with significant
+technological challenges in achieving and preserving quantum entanglement.
+Prime factorization can be also solved by using classical wave interference
+without quantum entanglement. In this work, we present experimental data
+showing prime factorization by utilizing spin wave interference. The prime
+factorization includes three major steps. First, general type computer
+calculates the sequence of numbers mkmod(N), where N is the number to be
+factorized, m is a randomly chosen positive integer, and k=0,1,2,3,4,5,6 .. .
+Next, the period of calculated sequence r is determined by exploiting spin wave
+interference. Finally, the general type computer finds the primes based on the
+obtained r. The experiment on the period finding was accomplished on the
+6-terminal Y3Fe2(FeO4)3 device. We chose number 15 for a test and found its
+primes in a sequence of measurements. The obtained data demonstrate an example
+of solving a prime factorization problem using classical wave interference. We
+discuss the physical and technological limitations of this approach, which
+define the maximum size of N and the computational speed. Though this classical
+approach cannot compete with the quantum algorithm in efficiency, magnonic
+holographic devices can be potentially utilized as complementary logic units
+aimed to speed up prime factorization with classical computers.",1605.02127v1
+2017-06-16,Long-distance spin transport in a disordered magnetic insulator,"Spin transport through magnetic insulators via magnons has recently been
+explored for a growing variety of magnetic systems with long-range order and
+well-understood spin excitation spectra. Here we show dramatic effects of spin
+transport through an amorphous magnetic insulator, which is both magnetically
+and structurally disordered. We generate and detect spin flow though amorphous
+yttrium-iron-garnet ($a$-YIG) thin films in a non-local geometry by use of the
+spin Hall and inverse spin Hall effects in platinum strips separated by 10 or
+more microns. By comparing non-local spin transport in $a$-YIG on suspended
+micromachined thermal isolation platforms to the same experiment performed on a
+bulk substrate, we show strong effects of in-plane thermal gradients on spin
+transport in the disordered magnetic insulator. The resulting non-local voltage
+signals are orders of magnitude larger than those seen in crystalline magnetic
+insulators, with easily measurable spin signals seen even at distances in
+excess of $100$ microns. In analogy to heat transport, where disordered
+materials support a range of vibrational excitations that can allow large
+thermal conductivities, we suggest that efficient spin transport in disordered
+magnetic systems can occur via a similar spectrum of excitations that relies on
+strong local exchange interactions and does not require long-range order. This
+work not only opens a new area for fundamental experimental and theoretical
+studies of spin transport, but also sets a new direction in materials science
+for magnonic and spintronic devices.",1706.05196v1
+2017-12-25,Effects of nuclear spins on the transport properties of the edge of two-dimensional topological insulators,"The electrons in the edge channels of two-dimensional topological insulators
+can be described as a helical Tomonaga-Luttinger liquid. They couple to nuclear
+spins embedded in the host materials through the hyperfine interaction, and are
+therefore subject to elastic spin-flip backscattering on the nuclear spins. We
+investigate the nuclear-spin-induced edge resistance due to such backscattering
+by performing a renormalization-group analysis. Remarkably, the effect of this
+backscattering mechanism is stronger in a helical edge than in nonhelical
+channels, which are believed to be present in the trivial regime of InAs/GaSb
+quantum wells. In a system with sufficiently long edges, the disordered nuclear
+spins lead to an edge resistance which grows exponentially upon lowering the
+temperature. On the other hand, electrons from the edge states mediate an
+anisotropic Ruderman-Kittel-Kasuya-Yosida nuclear spin-spin interaction, which
+induces a spiral nuclear spin order below the transition temperature. We
+discuss the features of the spiral order, as well as its experimental
+signatures. In the ordered phase, we identify two backscattering mechanisms,
+due to charge impurities and magnons. The backscattering on charge impurities
+is allowed by the internally generated magnetic field, and leads to an
+Anderson-type localization of the edge states. The magnon-mediated
+backscattering results in a power-law resistance, which is suppressed at zero
+temperature. Overall, we find that in a sufficiently long edge the nuclear
+spins, whether ordered or not, suppress the edge conductance to zero as the
+temperature approaches zero.",1712.09040v2
+2018-09-27,Low-temperature Atomistic Spin Relaxation and Non-equilibrium Intensive Properties Using Steepest-Entropy-Ascent Quantum-Inspired Thermodynamics Modeling,"The magnetization of body-centered cubic iron at low temperatures is
+calculated with the steepest-entropy-ascent quantum thermodynamics (SEAQT)
+framework. This framework assumes that a thermodynamic property in an isolated
+system traces the path through state space with the greatest entropy
+production. Magnetization is calculated from the expected value of a
+thermodynamic ensemble of quantized spin waves based on the Heisenberg spin
+model applied to an ensemble of coupled harmonic oscillators. A realistic
+energy landscape is obtained from a magnon dispersion relation calculated using
+spin-density-functional-theory. The equilibrium magnetization as well as the
+evolution of magnetization from a non-equilibrium state to equilibrium are
+calculated from the path of steepest entropy ascent determined from the SEAQT
+equation of motion in state space. The framework makes it possible to model the
+temperature- and time-dependence of magnetization without a detailed
+description of magnetic damping. The approach is also used to define intensive
+properties (temperature and magnetic field strength) that are fundamentally,
+i.e., canonically or grand canonically, valid for any non-equilibrium state.
+Given the assumed magnon dispersion relation, the SEAQT framework is used to
+calculate the equilibrium magnetization at different temperatures and external
+magnetic fields and the results are shown to closely agree with experiment for
+temperatures less than 500 K. The time-dependent evolution of magnetization
+from different initial states and interactions with a reservoir is also
+predicted.",1809.10619v2
+2020-12-02,"Synthesis, structure and magnetic properties of honeycomb-layered Li3Co2SbO6 with new data on its sodium precursor, Na3Co2SbO6","Li3Co2SbO6 is prepared by molten salt ion exchange and its structure refined
+by the Rietveld method confirming the honeycomb-type Co/Sb ordering of its Na
+precursor. Monoclinic rather than trigonal symmetry of Na3Co2SbO6 is directly
+demonstrated for the first time by peak splitting in the high-resolution
+synchrotron XRD pattern. The long-range antiferromagnetic order is established
+at TN about 6.7 K and 9.9 K in Na3Co2SbO6 and Li3Co2SbO6, respectively,
+confirmed by both the magnetic susceptibility and specific heat. Spin-wave
+analysis of specific heat data indicates the presence of 3D AFM magnons in
+Na3Co2SbO6 and 2D AFM magnons in Li3Co2SbO6. The field dependence of the
+magnetization almost reaches saturation in moderate magnetic fields up to 9 T
+and demonstrates characteristic features of magnetic field induced
+spin-reorientation transitions for both A3Co2SbO6 (A = Na, Li). Overall
+thermodynamic studies show that the magnetic properties of both compounds are
+very sensitive to an external magnetic field, thus predicting a non-trivial
+ground state with a rich magnetic phase diagram. The ground state spin
+configuration of Li3Co2SbO6 has been determined by low-temperature neutron
+powder diffraction. It represents a ferromagnetic arrangement of moments in the
+honeycomb layers with antiferromagnetic coupling between adjacent layers.",2012.01093v1
+2020-12-02,Engineered magnetization and exchange stiffness in direct-write Co-Fe nanoelements,"Media with engineered magnetization are essential building blocks in
+superconductivity, magnetism and magnon spintronics. However, the established
+thin-film and lithographic techniques insufficiently suit the realization of
+planar components with on-demand-tailored magnetization in the lateral
+dimension. Here, we demonstrate the engineering of the magnetic properties of
+CoFe-based nanodisks fabricated by the mask-less technique of focused electron
+beam induced deposition (FEBID). The material composition in the nanodisks is
+tuned \emph{in-situ} via the e-beam waiting time in the FEBID process and their
+post-growth irradiation with Ga ions. The magnetization $M_s$ and exchange
+stiffness $A$ of the disks are deduced from perpendicular ferromagnetic
+resonance measurements. The achieved $M_s$ variation in the broad range from
+$720$ emu/cm$^3$ to $1430$ emu/cm$^3$ continuously bridges the gap between the
+$M_s$ values of such widely used magnonic materials as permalloy and CoFeB. The
+presented approach paves a way towards nanoscale 2D and 3D systems with
+controllable and space-varied magnetic properties.",2012.01481v1
+2018-03-07,"Voltage driven, local, and efficient excitation of nitrogen-vacancy centers in diamond","Magnetic sensing technology has found widespread application in industries as
+diverse as transportation, medicine, and resource exploration. Such use cases
+often require highly sensitive instruments to measure the extremely small
+magnetic fields involved, relying on difficult to integrate Superconducting
+Quantum Interference Device (SQUID) and Spin-Exchange Relaxation Free (SERF)
+magnetometers. A potential alternative, nitrogen vacancy (NV) centers in
+diamond, has shown great potential as a high sensitivity and high resolution
+magnetic sensor capable of operating in an unshielded, room-temperature
+environment. Transitioning NV center based sensors into practical devices,
+however, is impeded by the need for high power RF excitation to manipulate
+them. Here we report an advance that combines two different physical phenomena
+to enable a highly efficient excitation of the NV centers: magnetoelastic drive
+of ferromagnetic resonance (FMR) and NV-magnon coupling. Our work demonstrates
+a new pathway to combine acoustics and magnonics that enables highly energy
+efficient and local excitation of NV centers without the need for any external
+RF excitation, and thus could lead to completely integrated, on-chip, atomic
+sensors.",1803.02863v2
+2018-03-27,Generation and annihilation time of magnetic droplet solitons,"Magnetic droplet solitons were first predicted to occur in materials with
+uniaxial magnetic anisotropy due to a long-range attractive interaction between
+elementary magnetic excitations, magnons. A non-equilibrium magnon population
+provided by a spin-polarized current in nanocontacts enables their creation and
+there is now clear experimental evidence for their formation, including direct
+images obtained with scanning x-ray transmission microscopy. Interest in
+magnetic droplets is associated with their unique magnetic dynamics that can
+lead to new types of high frequency nanometer scale oscillators of interest for
+information processing, including in neuromorphic computing. However, there are
+no direct measurements of the time required to nucleate droplet solitons or
+their lifetime---experiments to date only probe their steady-state
+characteristics, their response to dc spin currents. Here we determine the
+timescales for droplet annihilation and generation using current pulses.
+Annihilation occurs in a few nanoseconds while generation can take several
+nanoseconds to a microsecond depending on the pulse amplitude. Micromagnetic
+simulations show that there is an incubation time for droplet generation that
+depends sensitively on the initial magnetic state of the nanocontact. An
+understanding of these processes is essential to utilizing the unique
+characteristics of magnetic droplet solitons oscillators, including their high
+frequency, tunable and hysteretic response.",1803.10334v1
+2018-06-04,Magnetic Order with Fractionalized Excitations: Applications to $\mathrm{Yb}_2 \mathrm{Ti}_2 \mathrm{O}_7$,"A recent inelastic neutron scattering experiment on $\mathrm{Yb}_2
+\mathrm{Ti}_2 \mathrm{O}_7$ uncovers an unusual scattering continuum in the
+spin excitation spectrum despite the splayed ferromagnetic order in the ground
+state. While there exist well defined spin wave excitations at high magnetic
+fields, the one magnon modes and the two magnon continuum start to strongly
+overlap upon decreasing the field, and eventually they become the scattering
+continuum at zero field. Motivated by these observations, we investigate the
+possible emergence of a magnetically ordered ground state with fractionalized
+excitations in the spin model with the exchange parameters determined from two
+previous experiments. Using the fermionic parton mean field theory, we show
+that the magnetically ordered state with fractionalized excitations can arise
+as a stable mean field ground state in the presence of sufficiently strong
+quantum fluctuations. The spin excitation spectrum in such a ground state is
+computed and shown to have the scattering continuum. Upon increasing the
+magnetic field, the fractionalized magnetically ordered state is suppressed,
+and is eventually replaced by the conventional magnetically ordered phase at
+high fields, which is consistent with the experimental data. We discuss further
+implications of these results to the experiments and possible improvements on
+the theoretical analysis.",1806.01276v1
+2018-06-06,Photo-induced Entanglement in a Magnonic Floquet Topological Insulator,"When irradiated via high frequency circularly polarized light, the
+stroboscopic dynamics in a Heisenberg spin system on a honeycomb lattice
+develops a next nearest neighbor (NNN) Dzyaloshinskii-Moriya (DM) type
+term\cite{owerre}, making it a magnonic Floquet topological insulator. We
+investigate the entanglement generation and its evolution on such systems -
+particularly an irradiated ferromagnetic XXZ spin-$\frac{1}{2}$ model in a
+honeycomb lattice as the system parameters are optically tuned. In the high
+frequency limit, we compute the lowest quasi-energy state entanglement in terms
+of the concurrence between nearest neighbor (NN) and NNN pair of spins and
+witness the entanglement transitions occurring there. For the easy axis
+scenario, the unirradiated system forms a product state but entanglement grows
+between the NNN spin pairs beyond some cut-off DM strength. Contrarily in easy
+planar case, NN and NNN spins remain already entangled in the unirradiated
+limit. It then goes through an entanglement transition which causes decrease
+(increase) of the NN (NNN) concurrences down to zero (up to some higher value)
+at some critical finite DM interaction strength. For a high frequency of
+irradiation and a suitably chosen anisotropy parameter, we can vary the field
+strength to witness sudden death and revival of entanglement in the Floquet
+system. Both exact diagonalization and modified Lanczos techniques are used to
+obtain the results upto 24 site lattice. We also calculate the thermal
+entanglement and obtain estimates for the threshold temperatures below which
+non-zero concurrence can be expected in the system.",1806.02125v3
+2018-06-21,"Flat Bands, Indirect Gaps, and Unconventional Spin-Wave Behavior Induced by a Periodic Dzyaloshinskii-Moriya Interaction","Periodically patterned metamaterials are known for exhibiting wave properties
+similar to the ones observed in electronic band structures in crystal lattices.
+In particular, periodic ferromagnetic materials are characterized by the
+presence of bands and bandgaps in their spin-wave spectrum at tunable GHz
+frequencies. Recently, the fabrication of magnets hosting Dzyaloshinskii-Moriya
+interactions has been pursued with high interest since properties such as the
+stabilization of chiral spin textures and nonreciprocal spin-wave propagation
+emerge from this antisymmetric exchange coupling. In this context, to further
+engineer the magnon band structure, we propose the implementation of magnonic
+crystals with periodic Dzyaloshinskii-Moriya interactions, which can be
+obtained, for instance, via patterning of periodic arrays of heavy-metals wires
+on top of an ultrathin magnetic film. We demonstrate through theoretical
+calculations and micromagnetic simulations that such systems show an unusual
+evolution of the standing spin waves around the gaps in areas of the film that
+are in contact with the heavy-metal wires. We also predict the emergence of
+indirect gaps and flat bands and, effects that depend on the strength of the
+Dzyaloshinskii-Moriya interaction. This study opens new routes towards
+engineered metamaterials for spin-wave-based devices.",1806.08333v2
+2018-07-02,Emission and Propagation of Multi-Dimensional Spin Waves with nanoscale wavelengths in Anisotropic Spin Textures,"Spin waves offer intriguing novel perspectives for computing and signal
+processing, since their damping can be lower than the Ohmic losses in
+conventional CMOS circuits. For controlling the spatial extent and propagation
+of spin waves on the actual chip, magnetic domain walls show considerable
+potential as magnonic waveguides. However, low-loss guidance of spin waves with
+nanoscale wavelengths, in particular around angled tracks, remains to be shown.
+Here we experimentally demonstrate that such advanced control of propagating
+spin waves can be obtained using natural features of magnetic order in an
+interlayer exchange-coupled, anisotropic ferromagnetic bilayer. Using Scanning
+Transmission X-Ray Microscopy, we image generation of spin waves and their
+propagation across distances exceeding multiple times the wavelength, in
+extended planar geometries as well as along one-dimensional domain walls, which
+can be straight and curved. The observed range of wavelengths is between 1
+{\mu}m and 150 nm, at corresponding excitation frequencies from 250 MHz to 3
+GHz. Our results show routes towards practical implementation of magnonic
+waveguides employing domain walls in future spin wave logic and computational
+circuits.",1807.00897v2
+2018-07-11,Strong coupling of a single photon to a magnetic vortex,"Strong light-matter coupling is a necessary condition for exchanging
+information in quantum information protocols. It is used to couple different
+qubits (matter) via a quantum bus (photons) or to communicate different type of
+excitations, e.g. transducing between light and phonons or magnons. An
+unexplored, so far, interface is the coupling between light and topologically
+protected particle like excitations as magnetic domain walls, skyrmions or
+vortices. Here, we show theoretically that a single photon living in a
+superconducting cavity can be coupled strongly to the gyrotropic mode of a
+magnetic vortex in a nanodisc. We combine numerical and analytical calculations
+for a superconducting coplanar waveguide resonator and different realizations
+of the nanodisc (materials and sizes). We show that, for enhancing the
+coupling, constrictions fabricated in the resonator are beneficial, allowing to
+reach the strong coupling in CoFe discs of radius $200-400$ nm having resonance
+frequencies of few GHz. The strong coupling regime permits to exchange
+coherently a single photon and quanta of vortex excitations. Thus, our
+calculations show that the device proposed here serves as a transducer between
+photons and gyrating vortices, opening the way to complement superconducting
+qubits with topologically protected spin-excitations like vortices or
+skyrmions. We finish by discussing potential applications in quantum data
+processing based on the exploitation of the vortex as a short-wavelength magnon
+emitter.",1807.04075v2
+2019-03-21,Non-reciprocity of spin waves in magnetic nanotubes with helical equilibrium magnetization,"Spin waves (SWs) in magnetic nanotubes have shown interesting nonreciprocal
+properties in their dispersion relation, group velocity, frequency linewidth
+and attenuation lengths. The reported chiral effects are similar to those
+induced by the Dzyaloshinskii-Moriya interaction, but originating from the
+dipole-dipole interaction. Here we show, that the isotropic-exchange
+interaction can also induce chiral effects in the SW transport; the so-called
+Berry phase of SWs. We demonstrate that with the application of magnetic
+fields, the nonreciprocity of the different SW modes can be tuned between the
+fully dipolar governed and the fully exchange governed cases, as they are
+directly related to the underlaying equilibrium state. In the helical state,
+due to the combined action of the two effects every single sign combination of
+the azimuthal and axial wave vectors leads to different dispersion, allowing
+for a very sophisticated tuning of the SW transport. A disentanglement of the
+dipole-dipole and exchange contributions so far was not reported for the SW
+transport in nanotubes. Furthermore, we propose a device based on coplanar
+waveguides that would allow to selectively measure the exchange or dipole
+induced SW nonreciprocities. In the context of magnonic applications, our
+results might encourage further developments in the emerging field of 3D
+magnonic devices using curved magnetic membranes.",1903.09062v2
+2019-03-25,Quantum Many-Body Scars and Space-Time Crystalline Order from Magnon Condensation,"We study the eigenstate properties of a nonintegrable spin chain that was
+recently realized experimentally in a Rydberg-atom quantum simulator. In the
+experiment, long-lived coherent many-body oscillations were observed only when
+the system was initialized in a particular product state. This pronounced
+coherence has been attributed to the presence of special ""scarred"" eigenstates
+with nearly equally-spaced energies and putative nonergodic properties despite
+their finite energy density. In this paper we uncover a surprising connection
+between these scarred eigenstates and low-lying quasiparticle excitations of
+the spin chain. In particular, we show that these eigenstates can be accurately
+captured by a set of variational states containing a macroscopic number of
+magnons with momentum $\pi$. This leads to an interpretation of the scarred
+eigenstates as finite-energy-density condensates of weakly interacting
+$\pi$-magnons. One natural consequence of this interpretation is that the
+scarred eigenstates possess long-range order in both space and time, providing
+a rare example of the spontaneous breaking of continuous time-translation
+symmetry. We verify numerically the presence of this space-time crystalline
+order and explain how it is consistent with established no-go theorems
+precluding its existence in ground states and at thermal equilibrium.",1903.10517v2
+2019-03-31,Magnetic skyrmion spectrum under voltage excitation and its linear modulation,"Magnetic skyrmions are topological quasiparticles with great potential for
+applications in future information storage and processing devices because of
+their nanoscale size, high stability, and large velocity. Recently, the
+high-frequency properties of skyrmions have been explored for magnon
+nanodevices. Here we systematically study the dynamics of an isolated skyrmion
+under voltage excitation through the voltage-controlled magnetic anisotropy
+effect in a circular thin film. A theoretical model considering the
+demagnetization energy, which has often been neglected or treated superficially
+in previous skyrmion research but is demonstrated to have importance in
+determining the skyrmion dynamic state, is developed. With our model, the
+periodic oscillation of the skyrmion radius can be solved numerically with
+similar precision compared to micromgnetic simulations, and the characteristic
+frequency of the skyrmion breathing can be determined analytically with greater
+precision than previous studies. Furthermore, we find that the breathing
+skyrmion can be analogized as a modulator by investigating its linear
+modulation functionality under sinusoidal-form voltage excitation. Different
+from the conventional modulation system with complex CMOS circuits, this
+skyrmion modulator device integrates with both the modulation and carrier wave
+generation functionality, thus showing greater convenience and efficiency in
+applications. Our findings can provide useful guidance for both theoretical and
+experimental skyrmions research as well as the development of skyrmion-based
+magnonic devices with significant potential applicability in future
+communication system.",1904.00404v2
+2019-04-21,Brillouin-Mandelstam Spectroscopy of Stress-Modulated Spatially Confined Spin Waves in Ni Thin Films on Piezoelectric Heterostructures,"We report results of micro-Brillouin-Mandelstam light scattering spectroscopy
+of thermal magnons in the two-phase synthetic multiferroic structure consisting
+of a piezoelectric (PMN-PT) substrate and a Ni thin film with the thickness of
+64 nm. The experimental data reveal the first two modes of the perpendicular
+standing spin waves (PSSW) spatially confined across the Ni thin film. A
+theoretical analysis of the frequency dependence of the PSSW peaks on the
+external magnetic field reveals the asymmetric boundary condition, i.e.
+pinning, for variable magnetization at different surfaces of the Ni thin film.
+The strain field induced by applying DC voltage to PMN-PT substrate leads to a
+down shift of PSSW mode frequency owing to the magneto-elastic effect in Ni,
+and corresponding changes in the spin wave resonance conditions. The observed
+non-monotonic dependence of the PSSW frequency on DC voltage is related to an
+abrupt change of the pinning parameter at certain values of the voltage. The
+obtained results are important for understanding the thermal magnon spectrum in
+ferromagnetic films and development of the low-power spin-wave devices.",1904.09553v1
+2019-08-29,High-temperature spin dynamics in the Heisenberg chain: Magnon propagation and emerging KPZ-scaling in the zero-magnetization limit,"The large-scale dynamics of quantum integrable systems is often dominated by
+ballistic modes due to the existence of stable quasi-particles. We here
+consider as an archetypical example for such a system the spin-$\frac{1}{2}$
+XXX Heisenberg chain that features magnons and their bound states. An
+interesting question, which we here investigate numerically, arises with
+respect to the fate of ballistic modes at finite temperatures in the limit of
+zero magnetization $m{=}0$. At a finite magnetization density $m$, the spin
+autocorrelation function $\Pi(x,t)$ (at high temperatures) typically exhibits a
+trimodal behavior with left- and right-moving quasi-particle modes and a broad
+center peak with slower dynamics. The broadening of the fastest propagating
+modes exhibits a sub-diffusive $t^{1/3}$ scaling at large magnetization
+densities, $m {\rightarrow} \frac{1}{2}$, familiar from non-interacting models;
+it crosses over into a diffusive scaling $t^{1/2}$ upon decreasing the
+magnetization to smaller values. The behavior of the center peak appears to
+exhibit a crossover from transient super-diffusion to ballistic relaxation at
+long times. In the limit $m{\to}0$, the weight carried by the propagating peaks
+tends to zero; the residual dynamics is carried only by the central peak; it is
+sub-ballistic and characterized by a dynamical exponent $z$ close to the value
+$\frac{3}{2}$ familiar from Kardar-Parisi-Zhang (KPZ) scaling. We confirm,
+employing elaborate finite-time extrapolations, that the spatial scaling of the
+correlator $\Pi$ is in excellent agreement with KPZ-type behavior and analyze
+the corresponding corrections.",1908.11432v2
+2019-11-01,Role of spin mixing conductance in determining thermal spin pumping near the ferromagnetic phase transition in EuO_{1-x} and La2NiMnO6,"We present a comprehensive study of the temperature (T) dependence of the
+longitudinal spin Seebeck effect (LSSE) in Pt/EuO_{1-x} and Pt/La2NiMnO6 (LNMO)
+hybrid structures across their Curie temperatures (Tc). Both systems host
+ferromagnetic interaction below Tc, hence present optimal conditions for
+testing magnon spin current based theories against ferrimagnetic YIG. Notably,
+we observe an anomalous Nernst effect (ANE) generated voltage in bare
+EuO_{1-x}, however, we find LSSE predominates the thermal signals in the
+bilayers with Pt. The T-dependence of the LSSE in small T-range near Tc could
+be fitted to a power law of the form (Tc-T)^P. The derived critical exponent,
+P, was verified for different methods of LSSE representation and sample
+crystallinity. The results are explained based on the magnon-driven thermal
+spin pumping mechanism that relate the T-dependence of LSSE to the spin mixing
+conductance (Gmix) at the heavy metal/ferromagnet (HM/FM) interface, which in
+turn is known to vary in accordance with the square of the spontaneous
+magnetization (Ms). Additionally, the T-dependence of the real part of Gmix
+derived from spin Hall magnetoresistance measurements at different temperatures
+for the Pt/LNMO structure, further establish the interdependence.",1911.00211v1
+2019-11-21,Low damping and microstructural perfection of sub-40nm-thin yttrium iron garnet films grown by liquid phase epitaxy,"The field of magnon spintronics is experiencing an increasing interest in the
+development of solutions for spin-wave-based data transport and processing
+technologies that are complementary or alternative to modern CMOS
+architectures. Nanometer-thin yttrium iron garnet (YIG) films have been the
+gold standard for insulator-based spintronics to date, but a potential process
+technology that can deliver perfect, homogeneous large-diameter films is still
+lacking. We report that liquid phase epitaxy (LPE) enables the deposition of
+nanometer-thin YIG films with low ferromagnetic resonance losses and
+consistently high magnetic quality down to a thickness of 20 nm. The obtained
+epitaxial films are characterized by an ideal stoichiometry and perfect film
+lattices, which show neither significant compositional strain nor geometric
+mosaicity, but sharp interfaces. Their magneto-static and dynamic behavior is
+similar to that of single crystalline bulk YIG. We found, that the Gilbert
+damping coefficient alpha is independent of the film thickness and close to 1 x
+10-4, and that together with an inhomogeneous peak-to-peak linewidth broadening
+of delta H0|| = 0.4 G, these values are among the lowest ever reported for YIG
+films with a thickness smaller than 40 nm. These results suggest, that
+nanometer-thin LPE films can be used to fabricate nano- and micro-scaled
+circuits with the required quality for magnonic devices. The LPE technique is
+easily scalable to YIG sample diameters of several inches.",1911.09400v1
+2019-12-16,Spin-current manipulation of photoinduced magnetization dynamics in heavy metal / ferromagnet double layer based nanostructures,"Spin currents offer a way to control static and dynamic magnetic properties,
+and therefore they are crucial for next-generation MRAM devices or spin-torque
+oscillators. Manipulating the dynamics is especially interesting within the
+context of photo-magnonics. In typical $3d$ transition metal ferromagnets like
+CoFeB, the lifetime of light-induced magnetization dynamics is restricted to
+about 1 ns, which e.g. strongly limits the opportunities to exploit the wave
+nature in a magnonic crystal filtering device. Here, we investigate the
+potential of spin-currents to increase the spin wave lifetime in a functional
+bilayer system, consisting of a heavy metal (8 nm of $\beta$-Tantalum
+(Platinum)) and 5 nm CoFeB. Due to the spin Hall effect, the heavy metal layer
+generates a transverse spin current when a lateral charge current passes
+through the strip. Using time-resolved all-optical pump-probe spectroscopy, we
+investigate how this spin current affects the magnetization dynamics in the
+adjacent CoFeB layer. We observed a linear spin current manipulation of the
+effective Gilbert damping parameter for the Kittel mode from which we were able
+to determine the system's spin Hall angles. Furthermore, we measured a strong
+influence of the spin current on a high-frequency mode. We interpret this mode
+an an exchange dominated higher order spin-wave resonance. Thus we infer a
+strong dependence of the exchange constant on the spin current.",1912.07728v1
+2019-12-17,Antiferromagnetic CuMnAs: Ab initio description of finite temperature magnetism and resistivity,"Noncollinear magnetic moments in antiferromagnets (AFM) lead to a complex
+behavior of electrical transport, even to a decreasing resistivity due to an
+increasing temperature. Proper treatment of such phenomena is required for
+understanding AFM systems at finite temperatures; however first-principles
+description of these effects is complicated. With ab initio techniques, we
+investigate three models of spin fluctuations (magnons) influencing the
+transport in AFM CuMnAs; the models are numerically feasible and easily
+implementable to other studies. We numerically justified a fully relativistic
+collinear disordered local moment approach and we present its uncompensated
+generalization. A saturation or a decrease of resistivity caused by magnons,
+phonons, and their combination (above approx. 400 K) was observed and explained
+by changes in electronic structure. Within the coherent potential
+approximation, our finite-temperature approaches may be applied also to systems
+with impurities, which are found to have a large impact not only on residual
+resistivity, but also on canting of magnetic moments from the AFM to the
+ferromagnetic (FM) state.",1912.08025v4
+2016-03-07,Superfluidity and spin superfluidity in spinor Bose gases,"We show that spinor Bose gases subject to a quadratic Zeeman effect exhibit
+coexisting superfluidity and spin superfluidity, and study the interplay
+between these two distinct types of superfluidity. To illustrate that the basic
+principles governing these two types of superfluidity are the same, we describe
+the magnetization and particle-density dynamics in a single hydrodynamic
+framework. In this description spin and mass supercurrents are driven by their
+respective chemical potential gradients. As an application, we propose an
+experimentally accessible stationary state, where the two types of
+supercurrents counterflow and cancel each other, thus resulting in no mass
+transport. Furthermore, we propose a straightforward setup to probe spin
+superfluidity by measuring the in-plane magnetization angle of the whole cloud
+of atoms. We verify the robustness of these findings by evaluating the
+four-magnon collision time, and find that the time scale for coherent
+(superfluid) dynamics is separated from that of the slower incoherent dynamics
+by one order of magnitude. Comparing the atom and magnon kinetics reveals that
+while the former can be hydrodynamic, the latter is typically collisionless
+under most experimental conditions. This implies that, while our
+zero-temperature hydrodynamic equations are a valid description of spin
+transport in Bose gases, a hydrodynamic description that treats both mass and
+spin transport at finite temperatures may not be readily feasible.",1603.01996v2
+2016-12-20,Current-nonlinear Hall effect and spin-orbit torque magnetization switching in a magnetic topological insulator,"Precise estimation of spin Hall angle as well as successful maximization of
+spin-orbit torque (SOT) form a basis of electronic control of magnetic
+properties with spintronic functionality. Until now, current-nonlinear Hall
+effect, or second harmonic Hall voltage has been utilized as one of the methods
+for estimating spin Hall angle, which is attributed to the magnetization
+oscillation by SOT. Here, we argue the second harmonic Hall voltage in
+magnetic/nonmagnetic topological insulator (TI) heterostructures,
+Cr$_x$(Bi$_{1-y}$Sb$_y$)$_{2-x}$Te$_3$/(Bi$_{1-y}$Sb$_y$)$_2$Te$_3$. From the
+angular, temperature and magnetic field dependence, it is unambiguously shown
+that the large second harmonic Hall voltage in TI heterostructures is governed
+not by SOT but mainly by asymmetric magnon scattering mechanism without
+magnetization oscillation. Thus, this method does not allow an accurate
+estimation of spin Hall angle when magnons largely contribute to electron
+scattering. Instead, the SOT contribution in a TI heterostructure is
+exemplified by current pulse induced non-volatile magnetization switching,
+which is realized with a current density of $\sim 2.5 \times 10^{10}
+\mathrm{A/m}^2$, showing its potential as spintronic materials.",1612.06862v2
+2017-07-12,X-Ray Microscopy of Spin Wave Focusing using a Fresnel Zone Plate,"Magnonics, i.e. the artificial manipulation of spin waves, is a flourishing
+field of research with many potential uses in data processing within reach.
+Apart from the technological applications the possibility to directly influence
+and observe these types of waves is of great interest for fundamental research.
+Guidance and steering of spin waves has been previously shown and lateral spin
+wave confinement has been achieved. However, true spin wave focusing with both
+lateral confinement and increase in amplitude has not been shown before. Here,
+we show for the first time spin wave focusing by realizing a Fresnel zone plate
+type lens. Using x-ray microscopy we are able to directly image the propagation
+of spin waves into the nanometer sized focal spot. Furthermore, we observe that
+the focal spot can be freely moved in a large area by small variations of the
+bias field. Thus, this type of lens provides a steerable intense nanometer
+sized spin wave source. Potentially, this could be used to selectively
+illuminate magnonic devices like nano oscillators with a steerable spin wave
+beam.",1707.03664v1
+2017-11-14,Magnon Splitting Induced by Charge Transfer in the Three-Orbital Hubbard Model,"Understanding spin excitations and their connection to unconventional
+superconductivity have remained a central issue since the discovery of the
+cuprates. Direct measurement of the dynamical spin structure factor in the
+parent compounds can provide key information on important interactions relevant
+in the doped regime, and variations in the magnon dispersion have been linked
+closely to differences in crystal structure between families of cuprate
+compounds. Here, we elucidate the relationship between spin excitations and
+various controlling factors thought to be significant in high-$T_c$ materials
+by systematically evaluating the dynamical spin structure factor for the
+three-orbital Hubbard model, revealing differences in the spin dispersion along
+the Brillouin zone axis and the diagonal. Generally, we find that the absolute
+energy scale and momentum dependence of the excitations primarily are sensitive
+to the effective charge-transfer energy, while changes in the on-site Coulomb
+interactions have little effect on the details of the dispersion. In
+particular, our result highlights the splitting between spin excitations along
+the axial and diagonal directions in the Brillouin zone. This splitting
+decreases with increasing charge-transfer energy and correlates with changes in
+the apical oxygen position, and general structural variations, for different
+cuprate families.",1711.04931v2
+2018-10-02,Strong quantum interactions prevent quasiparticle decay,"Quantum states of matter---such as solids, magnets and topological
+phases---typically exhibit collective excitations---phonons, magnons, anyons.
+These involve the motion of many particles in the system, yet, remarkably, act
+like a single emergent entity---a quasiparticle. Known to be long-lived at the
+lowest energies, common wisdom says that quasiparticles become unstable when
+they encounter the inevitable continuum of many-particle excited states at high
+energies. Whilst correct for weak interactions, we show that this is far from
+the whole story: strong interactions generically stabilise quasiparticles by
+pushing them out of the continuum. This general mechanism is straightforwardly
+illustrated in an exactly solvable model. Using state-of-the-art numerics, we
+find it at work also in the spin-$\frac{1}{2}$ triangular lattice Heisenberg
+antiferromagnet (TLHAF) near the isotropic point---this is surprising given the
+common expectation of magnon decay in this paradigmatic frustrated magnet.
+Turning to existing experimental data, we identify the detailed phenomenology
+of avoided decay in the TLHAF material Ba$_3$CoSb$_2$O$_9$, and even in liquid
+helium---one of the earliest instances of quasiparticle decay. Our work unifies
+various phenomena above the universal low-energy regime in a comprehensive
+description. This broadens our window of understanding of many-body
+excitations, and provides a new perspective for controlling and stabilising
+quantum matter in the strongly-interacting regime.",1810.01422v1
+2018-10-16,Extreme enhancement of spin relaxation mediated by surface magnon polaritons,"Polaritons in metals, semimetals, semiconductors, and polar insulators, with
+their extreme confinement of electromagnetic energy, provide many promising
+opportunities for enhancing typically weak light-matter interactions such as
+multipolar radiation, multiphoton spontaneous emission, Raman scattering, and
+material nonlinearities. These highly confined polaritons are
+quasi-electrostatic in nature, with most of their energy residing in the
+electric field. As a result, these ""electric"" polaritons are far from optimized
+for enhancing emission of a magnetic nature, such as spin relaxation, which is
+typically many orders of magnitude slower than corresponding electric decays.
+Here, we propose using surface magnon polaritons in negative magnetic
+permeability materials such as MnF$_2$ and FeF$_2$ to strongly enhance
+spin-relaxation in nearby emitters in the THz spectral range. We find that
+these magnetic polaritons in 100 nm thin-films can be confined to lengths over
+10,000 times smaller than the wavelength of a photon at the same frequency,
+allowing for a surprising twelve orders of magnitude enhancement in magnetic
+dipole transitions. This takes THz spin-flip transitions, which normally occur
+at timescales on the order of a year, and forces them to occur at sub-ms
+timescales. Our results suggest an interesting platform for polaritonics at THz
+frequencies, and more broadly, a new way to use polaritons to control
+light-matter interactions.",1810.06761v1
+2018-10-16,Superfluid spin transport in ferro- and antiferromagnets,"This paper focuses on spin superfluid transport, observation of which was
+recently reported in antiferromagnet Cr$_2$O$_3$ [Yuan et al., Sci. Adv. 4,
+eaat1098 (2018)]. This paper analyzes the role of dissipation in transformation
+of spin current injected with incoherent magnons to a superfluid spin current
+near the interface where spin is injected. The Gilbert damping parameter in the
+Landau-Lifshitz-Gilbert theory does not describe dissipation properly, and the
+dissipation parameters are calculated from the Boltzmann equation for magnons
+scattered by defects. The two-fluid theory is developed similar to the
+two-fluid theory for superfluids. This theory shows that the influence of
+temperature variation in bulk on the superfluid spin transport (bulk Seebeck
+effect) is weak at low temperatures. The scenario that the results of Yuan et
+al. are connected with the Seebeck effect at the interface between the spin
+detector and the sample is also discussed.
+  The Landau criterion for an antiferromagnet put in a magnetic field is
+derived from the spectrum of collective spin modes. The Landau instability
+starts in the gapped mode earlier than in the Goldstone gapless mode, in
+contrast to easy-plane ferromagnets where the Goldstone mode becomes unstable.
+The structure of the magnetic vortex in the geometry of the experiment is
+determined. The vortex core has the skyrmion structure with finite
+magnetization component normal to the magnetic field. This magnetization
+creates stray magnetic fields around the exit point of the vortex line from the
+sample, which can be used for experimental detection of vortices.",1810.07020v4
+2018-10-25,Exchange dependent ultrafast magnetization dynamics in Fe$_{1-x}$Ni$_{x}$ alloys,"Element specific ultrafast demagnetization was studied in Fe$_{1-x}$Ni$_{x}$
+alloys, covering the concentration range between $0.1<x<0.9$. For all
+compositions, we observe a delay in the onset of Ni demagnetization relative to
+the Fe demagnetization. We find that the delay is correlated to the Curie
+temperature and hence also the exchange interaction. The temporal evolution of
+demagnetization is fitted to a magnon diffusion model based on the
+presupposition of enhanced ultrafast magnon generation in the Fe sublattice.
+The spin wave stiffness extracted from this model correspond well to known
+experimental values.",1810.11001v1
+2019-05-25,Large-$S$ limit of the large-$N$ theory for the triangular antiferromagnet,"Large-$S$ and large-$N$ theories (spin value $S$ and spinor component number
+$N$) are complementary, and sometimes conflicting, approaches to quantum
+magnetism. While large-$S$ spin-wave theory captures the correct semiclassical
+behavior, large-$N$ theories, on the other hand, emphasize the quantumness of
+spin fluctuations. In order to evaluate the possibility of the non-trivial
+recovery of the semiclassical magnetic excitations within a large-$N$ approach,
+we compute the large-$S$ limit of the dynamic spin structure of the triangular
+lattice Heisenberg antiferromagnet within a Schwinger boson spin
+representation. We demonstrate that, only after the incorporation of Gaussian
+($1/N$) corrections to the saddle-point ($N=\infty$) approximation, we are able
+to exactly reproduce the linear spin wave theory results in the large-$S$
+limit. The key observation is that the effect of $1/N$ corrections is to cancel
+out exactly the main contribution of the saddle-point solution; while the
+collective modes (magnons) consist of two spinon bound states arising from the
+poles of the RPA propagator. This result implies that it is essential to
+consider the interaction of the spinons with the emergent gauge fields and that
+the magnon dispersion relation should not be identified with that of the
+saddle-point spinons.",1905.10689v3
+2020-06-23,Imaging non-collinear antiferromagnetic textures via single spin relaxometry,"Antiferromagnetic materials are promising platforms for next-generation
+spintronics owing to their fast dynamics and high robustness against parasitic
+magnetic fields. However, nanoscale imaging of the magnetic order in such
+materials with zero net magnetization remains a major experimental challenge.
+Here we show that non-collinear antiferromagnetic spin textures can be imaged
+by probing the magnetic noise they locally produce via thermal populations of
+magnons. To this end, we perform nanoscale, all-optical relaxometry with a
+scanning quantum sensor based on a single nitrogen-vacancy (NV) defect in
+diamond. Magnetic noise is detected through an increase of the spin relaxation
+rate of the NV defect, which results in an overall reduction of its
+photoluminescence signal under continuous laser illumination. As a
+proof-of-concept, the efficiency of the method is demonstrated by imaging
+various spin textures in synthetic antiferromagnets, including domain walls,
+spin spirals and antiferromagnetic skyrmions. This imaging procedure could be
+extended to a large class of intrinsic antiferromagnets and opens up new
+opportunities for studying the physics of localized spin wave modes for
+magnonics.",2006.13130v1
+2020-09-08,Chiral phase transition and thermal Hall effect in an anisotropic spin model on the kagome lattice,"We present a study of the thermal Hall effect in the extended Heisenberg
+model with $XXZ$ anisotropy in the kagome lattice. This model has the
+particularity that, in the classical case, and for a broad region in parameter
+space, an external magnetic field induces a chiral symmetry breaking: the
+ground state is a doubly degenerate $q=0$ order with either positive or
+negative net chirality. Here, we focus on the effect of this chiral phase
+transition in the thermal Hall conductivity using Linear-Spin-Waves theory. We
+explore the topology and calculate the Chern numbers of the magnonic bands,
+obtaining a variety of topological phase transitions. We also compute the
+magnonic effect to the critical temperature associated with the chiral phase
+transition ($T_c^{SW}$). Our main result is that, the thermal Hall
+conductivity, which is null for $T>T_c^{SW}$, becomes non-zero as a consequence
+of the spontaneous chiral symmetry breaking at low temperatures. Therefore, we
+present a simple model where it is possible to ""switch"" on/off the thermal
+transport properties introducing a magnetic field and heating or cooling the
+system.",2009.03941v2
+2021-02-17,Axion search with quantum nondemolition detection of magnons,"The axion provides a solution for the strong CP problem and is one of the
+leading candidates for dark matter. This paper proposes an axion detection
+scheme based on quantum nondemolition detection of magnon, i.e., quanta of
+collective spin excitations in solid, which is expected to be excited by the
+axion-electron interaction predicted by the Dine-Fischer-Srednicki-Zhitnitsky
+(DFSZ) model. The prototype detector is composed of a ferrimagnetic sphere as
+an electronic spin target and a superconducting qubit. Both of these are
+embedded inside a microwave cavity, which leads to a coherent effective
+interaction between the uniform magnetostatic mode in the ferrimagnetic crystal
+and the qubit. An upper limit for the coupling constant between an axion and an
+electron is obtained as $g_{aee}<2.6\times10^{-6}$ at the 95% confidence level
+for the axion mass of $33.117$$\mu$eV $<m_{a}<33.130$$\mu$eV.",2102.08764v4
+2021-02-26,Beyond magnons in Nd2ScNbO7: An Ising pyrochlore antiferromagnet with all in all out order and random fields,"We report the low temperature magnetic properties of Nd$^{3+}$ pyrochlore
+$\rm Nd_2ScNbO_7$. Susceptibility and magnetization show an easy-axis moment,
+and heat capacity reveals a phase transition to long range order at
+$T_N=371(2)$ mK with a fully recovered $\Delta S = R \ln(2)$, 53\% of it
+recovered for $T>T_N$. Elastic neutron scattering shows a long-range
+all-in-all-out magnetic order with low-$Q$ diffuse elastic scattering.
+Inelastic neutron scattering shows a low-energy flat-band, indicating a
+magnetic Hamiltonian similar to $\rm Nd_2Zr_2O_7$. Nuclear hyperfine
+excitations measured by ultra-high-resolution neutron backscattering indicates
+a distribution of static electronic moments below $T_N$, which may be due to
+B-site disorder influencing Nd crystal electric fields. Analysis of heat
+capacity data shows an unexpected $T$-linear or $T^{3/2}$ term which is
+inconsistent with conventional magnon quasiparticles, but is consistent with
+fractionalized spinons or gapless local spin excitations. We use legacy data to
+show similar behavior in $\rm Nd_2Zr_2O_7$. Comparing local static moments also
+reveals a suppression of the nuclear Schottky anomaly in temperature,
+evidencing a fraction of Nd sites with nearly zero static moment, consistent
+with exchange-disorder-induced random singlet formation. Taken together, these
+measurements suggest an unusual fluctuating magnetic ground state which mimics
+a spin-liquid -- but may not actually be one.",2102.13656v1
+2015-12-03,Cavity quantum electrodynamics with ferromagnetic magnons in a small yttrium-iron-garnet sphere,"Hybridizing collective spin excitations and a cavity with high cooperativity
+provides a new research subject in the field of cavity quantum electrodynamics
+and can also have potential applications to quantum information. Here we report
+an experimental study of cavity quantum electrodynamics with ferromagnetic
+magnons in a small yttrium-iron-garnet (YIG) sphere at both cryogenic and room
+temperatures. We observe for the first time a strong coupling of the same
+cavity mode to both a ferromagnetic-resonance (FMR) mode and a magnetostatic
+(MS) mode near FMR in the quantum limit. This is achieved at a temperature ~ 22
+mK, where the average microwave photon number in the cavity is less than one.
+At room temperature, we also observe strong coupling of the cavity mode to the
+FMR mode in the same YIG sphere and find a slight increase of the damping rate
+of the FMR mode. These observations reveal the extraordinary robustness of the
+FMR mode against temperature. However, the MS mode becomes unobservable at room
+temperature in the measured transmission spectrum of the microwave cavity
+containing the YIG sphere. Our numerical simulations show that this is due to a
+drastic increase of the damping rate of the MS mode.",1512.00983v1
+2016-09-19,Geometrical complexity of the antidots unit cell effect on the spin wave excitations spectra,"We have investigated theoretically (with micromagnetic simulations and plane
+wave method) and experimentally (with ferromagnetic resonance and Brillouin
+light scattering) three types of antidot lattices (ADLs) based on permalloy
+thin films with increased complexity of the unit cell: simple square,
+bi-component square and wave-like ADL. We have found that placing a small
+additional antidot in the center of the unit cell of the square ADL modify
+significantly the spin wave spectrum and its dependence on the orientation of
+the in-plane magnetic field. We also check the further changes of spin wave
+spectrum resulting from the introduction of air-gaps connecting small and large
+antidots. In particular, the presence of small antidots change the dependence
+of the frequency of the fundamental mode on the angle of the in-plane applied
+magnetic field. The air-gaps strongly discriminates the propagation of spin
+waves in two principal direction of ADL lattice, orthogonal to each other. In
+spite of these spectral changes, the spatial distribution of the spin wave
+amplitude generally preserves some similarities for all three structures. We
+also highlighted out the role of defects in the ADL in the observed spectra.
+The obtained results can be interesting for the magnonics applications of the
+magnonic crystals.",1609.05663v1
+2016-09-27,Identical Spin Rotation Effect and Electron Spin Waves in Quantum Gas of Atomic Hydrogen,"We present an experimental study of electron spin waves in atomic hydrogen
+gas compressed to high densities of $\sim 5 \times 10^{18}$ cm$^{-3}$ at
+temperatures ranging from 0.26 to 0.6 K in strong magnetic field of 4.6 T.
+Hydrogen gas is in a quantum regime when the thermal de Broglie wavelength is
+much larger than the s-wave scattering length. In this regime the identical
+particle effects play major role in atomic collisions and lead to the Identical
+Spin Rotation effect (ISR). We observed a variety of spin wave modes caused by
+this effect with strong dependence on the magnetic potential caused by
+variations of the polarizing magnetic field. We demonstrate confinement of the
+ISR modes in the magnetic potential and manipulate their properties by changing
+the spatial profile of magnetic field. We have found that at a high enough
+density of H gas the magnons accumulate in their ground state in the magnetic
+trap and exhibit long coherence, which has a profound effect on the electron
+spin resonance spectra. Such macroscopic accumulation of the ground state
+occurs at a certain critical density of hydrogen gas, where the chemical
+potential of the magnons becomes equal to the energy of their ground state in
+the trapping potential.",1609.08432v2
+2016-11-17,Low-temperature heat transport of spin-gapped quantum magnets,"This article reviews low-temperature heat transport studies of spin-gapped
+quantum magnets in the last few decades. Quantum magnets with small spins and
+low dimensionality exhibit a variety of novel phenomena. Among them, some
+systems are char-acteristic of having quantum-mechanism spin gap in their
+magnetic excitation spectra, including spin-Peierls systems, S = 1 Haldane
+chains, S = 1/2 spin ladders, and spin dimmers. In some particular spin-gapped
+systems, the XY-type antiferromagnetic state induced by magnetic field that
+closes the spin gap can be described as a magnon Bose-Einstein condensation
+(BEC). Heat transport is effective in probing the magnetic excitations and
+magnetic phase transitions, and has been extensively studied for the
+spin-gapped systems. A large and ballistic spin thermal conductivity was
+observed in the two-leg Heisenberg S = 1/2 ladder compounds. The characteristic
+of magnetic thermal transport of the Haldane chain systems is quite
+controversial on both the theoretical and experimental results. For the
+spin-Peierls system, the spin excitations can also act as heat carriers. In
+spin-dimer compounds, the magnetic excitations mainly play a role of scattering
+phonons. The magnetic excitations in the magnon BEC systems displayed dual
+roles, carrying heat or scattering phonons, in different materials.",1611.05578v1
+2019-07-02,Three-point functions at strong coupling in the BMN limit,"We consider structure constants of single-trace operators at strong coupling
+in planar $\mathcal{N}=4$ SYM theory using the hexagon formalism. We
+concentrate on heavy-heavy-light correlators where the heavy operators are BMN
+operators, with large R-charges and finite anomalous dimensions, and the light
+one is a finite-charge chiral primary operator. They describe the couplings
+between two highly boosted strings and a supergravity mode in the bulk dual. In
+the hexagon framework, two sums over virtual magnons are needed to bind the
+hexagons together around the light operator. We evaluate these sums explicitly
+at strong coupling, for a certain choice of BMN operators, and show that they
+factorise into a ratio of Gamma functions and a simple stringy prefactor. The
+former originates from giant mirror magnons scanning the AdS geometry while the
+latter stems from small fluctuations around the BMN vacuum. The resulting
+structure constants have poles at positions where an enhanced mixing with
+double-trace operators is expected and zeros whenever the process is forbidden
+by supersymmetry. We also discuss the transition to the classical regime, when
+the length of the light operator scales like the string tension, where we
+observe similitudes with the Neumann coefficients of the pp-wave String Field
+Theory vertex.",1907.01534v1
+2019-10-02,Distinct magneto-Raman signatures of spin-flip phase transitions in CrI3,"The discovery of 2-dimensional (2D) materials, such as CrI3, that retain
+magnetic ordering at monolayer thickness has resulted in a surge of research in
+2D magnetism from both pure and applied perspectives. Here, we report a
+magneto-Raman spectroscopy study on multilayered CrI3, focusing on two new
+features in the spectra which appear at temperatures below the magnetic
+ordering temperature and were previously assigned to high frequency magnons. We
+observe a striking evolution of the Raman spectra with increasing magnetic
+field in which clear, sudden changes in intensities of the modes are attributed
+to the interlayer ordering changing from antiferromagnetic to ferromagnetic at
+a critical magnetic field. Our work highlights the sensitivity of the Raman
+modes to weak interlayer spin ordering in CrI3. In addition, we theoretically
+examine potential origins for the new modes, which we deduce are unlikely
+single magnons.",1910.01237v3
+2019-10-08,Field evolution of low-energy excitations in the hyperhoneycomb magnet $β$-Li$_2$IrO$_3$,"$^7$Li nuclear magnetic resonance (NMR) and terahertz (THz) spectroscopies
+are used to probe magnetic excitations and their field dependence in the
+hyperhoneycomb Kitaev magnet $\beta$-Li$_2$IrO$_3$. Spin-lattice relaxation
+rate ($1/T_1$) measured down to 100\,mK indicates gapless nature of the
+excitations at low fields (below $H_c\simeq 2.8$\,T), in contrast to the gapped
+magnon excitations found in the honeycomb Kitaev magnet $\alpha$-RuCl$_3$ at
+zero applied magnetic field. At higher temperatures in $\beta$-Li$_2$IrO$_3$,
+$1/T_1$ passes through a broad maximum without any clear anomaly at the N\'eel
+temperature $T_N\simeq 38$\,K, suggesting the abundance of low-energy
+excitations that are indeed observed as two peaks in the THz spectra, both
+correspond to zone-center magnon excitations. At higher fields (above $H_c$),
+an excitation gap opens, and a re-distribution of the THz spectral weight is
+observed without any indication of an excitation continuum, in contrast to
+$\alpha$-RuCl$_3$ where an excitation continuum was reported.",1910.03251v2
+2019-10-30,Magnon spectrum of the Weyl semimetal half-Heusler compound GdPtBi,"The compound GdPtBi is known as a material where the non-trivial topology of
+electronic bands interplays with an antiferromagnetic order, which leads to the
+emergence of many interesting magnetotransport phenomena. Although the magnetic
+structure of the compound has previously been reliably determined, the magnetic
+interactions responsible for this type of order remained controversial. In the
+present study, we employed time-of-flight inelastic neutron scattering to map
+out the low-temperature spectrum of spin excitations in single-crystalline
+GdPtBi. The observed spectra reveal two spectrally sharp dispersive spin-wave
+modes, which reflects the multi-domain state of the $\mathbf{k} =
+(\frac{1}{2}\frac{1}{2}\frac{1}{2})$ face-centred cubic antiferromagnet in the
+absence of a symmetry-breaking magnetic field. The magnon dispersion reaches an
+energy of $\sim 1.1$~meV and features a gap of $\sim 0.15$~meV. Using linear
+spin-wave theory, we determined the main magnetic microscopic parameters of the
+compound that provide good agreement between the simulated spectra and the
+experimental data. We show that GdPtBi is well within the
+($\frac{1}{2}\frac{1}{2}\frac{1}{2}$) phase and is dominated by second-neighbor
+interactions, thus featuring low frustration.",1910.13845v2
+2020-02-17,Laser-Induced Transient Magnons in Sr3Ir2O7 Throughout the Brillouin Zone,"Although ultrafast manipulation of magnetism holds great promise for new
+physical phenomena and applications, targeting specific states is held back by
+our limited understanding of how magnetic correlations evolve on ultrafast
+timescales. Using ultrafast resonant inelastic x-ray scattering we demonstrate
+that femtosecond laser pulses can excite transient magnons at large wavevectors
+in gapped antiferromagnets, and that they persist for several picoseconds which
+is opposite to what is observed in nearly gapless magnets. Our work suggests
+that materials with isotropic magnetic interactions are preferred to achieve
+rapid manipulation of magnetism.",2002.07301v3
+2020-03-02,Non-Hermitian topology of one-dimensional spin-torque oscillator arrays,"Magnetic systems have been extensively studied both from a fundamental
+physics perspective and as building blocks for a variety of applications. Their
+topological properties, in particular those of excitations, remain relatively
+unexplored due to their inherently dissipative nature. The recent introduction
+of non-Hermitian topological classifications opens up new opportunities for
+engineering topological phases in dissipative systems. Here, we propose a
+magnonic realization of a non-Hermitian topological system. A crucial
+ingredient of our proposal is the injection of spin current into the magnetic
+system, which alters and can even change the sign of terms describing
+dissipation. We show that the magnetic dynamics of an array of spin-torque
+oscillators can be mapped onto a non-Hermitian Su-Schrieffer-Heeger model
+exhibiting topologically protected edge states. Using exact diagonalization of
+the linearized dynamics and numerical solutions of the non-linear equations of
+motion, we find that a topological magnonic phase can be accessed by tuning the
+spin current injected into the array. In the topologically nontrivial regime, a
+single spin-torque oscillator on the edge of the array is driven into
+auto-oscillation and emits a microwave signal, while the bulk oscillators
+remain inactive. Our findings have practical utility for memory devices and
+spintronics neural networks relying on spin-torque oscillators as constituent
+units.",2003.01152v1
+2020-05-20,Controlling the propagation of dipole-exchange spin waves using local inhomogeneity of the anisotropy,"Spin waves are promising candidates to carry, transport, and process
+information. Controlling the propagation characteristics of spin waves in
+magnetic materials is an essential ingredient for designing spin-wave based
+computing architectures. Here, we study the influence of surface
+inhomogeneities on the spin-wave signals transmitted through thin films. We use
+micromagnetic simulations to study the spin-wave dynamics in an in-plane
+magnetized yttrium iron garnet thin film with a thickness in the nanometre
+range in the presence of surface defects in the form of locally introduced
+uniaxial anisotropies. These defects are used to demonstrate that the Backward
+Volume Magnetostatic Spin Waves (BVMSW) are more responsive to backscattering
+in comparison to Magnetostatic Surface Spin Waves (MSSWs). For this particular
+defect type, the reason for this behavior can be quantitatively related to the
+difference in the magnon band structures for the two types of spin waves. To
+demonstrate this, we develop a quasi-analytical theory for the scattering
+process. It shows an excellent agreement with the micromagnetic simulations,
+sheds light on the backscattering processes and provides a new way to analyze
+the spin-wave transmission rates in the presence of surface inhomogeneities in
+sufficiently thin films, for which the role of exchange energy in the spin-wave
+dynamics is significant. Our study paves the way to designing magnonic logic
+devices for data processing which rely on a designed control of the spin-wave
+transmission.",2005.09965v2
+2020-07-17,Coherent coupling between multiple ferrimagnetic spheres and a microwave cavity in the quantum-limit,"The spin resonance of electrons can be coupled to a microwave cavity mode to
+obtain a photon-magnon hybrid system. These quantum systems are widely studied
+for both fundamental physics and technological quantum applications. In this
+article, the behavior of a large number of ferrimagnetic spheres coupled to a
+single cavity is put under test. We use second-quantization modeling of
+harmonic oscillators to theoretically describe our experimental setup and
+understand the influence of several parameters. The magnon-polariton dispersion
+relation is used to characterize the system, with a particular focus on the
+vacuum Rabi mode splitting due to multiple spheres. We combine the results
+obtained with simple hybrid systems to analyze the behavior of a more complex
+one, and show that it can be devised in such a way to minimize the degrees of
+freedom needed to completely describe it. By studying single-sphere coupling
+two possible size-effects related to the sample diameter have been identified,
+while multiple-spheres configurations reveal how to upscale the system. This
+characterization is useful for the implementation of an
+axion-to-electromagnetic field transducer in a ferromagnetic haloscope for dark
+matter searches. Our dedicated setup, consisting in ten 2 mm-diameter YIG
+spheres coupled to a copper microwave cavity, is used for this aim and studied
+at mK temperatures. Moreover, we show that novel applications of
+optimally-controlled hybrid systems can be foreseen for setups embedding a
+large number of samples.",2007.08908v3
+2020-07-27,Magnonic band structure in vertical meander-shaped CoFeB thin films,"The dispersion of spin waves in vertical meander-shaped CoFeB thin films
+consisting of segments located at 90{\deg} angles with respect to each other is
+investigated by Brillouin light scattering spectroscopy. We reveal the periodic
+character of several dispersive branches as well as alternating frequency
+ranges where spin waves are allowed or forbidden to propagate. Noteworthy is
+the presence of the frequency band gaps between each couple of successive modes
+only for wave numbers k=n$\pi$/a, where n is an even integer number and a is
+the size of the meander unit cell, whereas the spectra show propagating modes
+in the orthogonal film segments for the other wavenumbers. The micromagnetic
+simulations and analytical calculations allow us to understand and explain the
+results in terms of the mode spatial localization and symmetry. The obtained
+results demonstrate the wave propagation in three dimensions opening the path
+for multi-level magnonic architectures for signal processing.",2007.13707v2
+2020-08-24,Regge amplitudes in Generalized Fishnet and Chiral Fishnet Theories,"We extend the analysis of \cite{Chowdhury:2019hns} to study the Regge
+trajectories of the Mellin amplitudes of the $0-$ and $1-$ magnon correlators
+of the generalized Fishnet theory in $d$ dimensions and one type of correlators
+of chiral fishnet theory in $4$ dimensions. We develop a systematic procedure
+to perturbatively study the Regge trajectories and subsequently perform the
+spectral integral. Our perturbative method is very generic and in principle can
+be applied to correlators whose perturbative Regge trajectories obey some
+structural conditions which we list down. Our $d$ dimensional results reduce to
+previously known results in $d=4$ for 0-magnon and 1- magnon. As a non trivial
+check, we show that the results for 1-magnon correlator in $d=8$, when
+evaluated using the exact techniques in \cite{Chowdhury:2019hns,
+Korchemsky:2018hnb} are in perfect agreement with our $d$ dimensional
+perturbative results. We also perturbatively compute the Regge trajectories and
+Regge-Mellin amplitudes of the chiral fishnet correlator $\langle{\rm
+Tr}[\phi_1(x_1)\phi_1(x_2)]{\rm
+Tr}[\phi_1^\dagger(x_3)\phi_1^\dagger(x_4)]\rangle$ using the techniques
+developed in this paper. Since this correlator has two couplings $\kappa$ and
+$\omega$, we have obtained closed-form results in the limit $\kappa \to 0,
+\omega \to 0$ with $\kappa/\omega$ held constant. We verify this computation
+with an independent method of computing the same and obtain perfect agreement.",2008.10201v3
+2020-08-26,Theory of three-magnon interaction in a vortex-state magnetic nanodot,"We use vector Hamiltonian formalism (VHF) to study theoretically three-magnon
+parametric interaction (or three-wave splitting) in a magnetic disk existing in
+a magnetic vortex ground state. The three-wave splitting in a disk is found to
+obey two selection rules: (i) conservation of the total azimuthal number of the
+resultant spin-wave modes, and (ii) inequality for the radial numbers of
+interacting modes, if the mode directly excited by the driving field is
+radially symmetric (i.e. if the azimuthal number of the directly excited mode
+is $m = 0$). The selection rule (ii), however, is relaxed in the ""small""
+magnetic disks, due to the influence of the vortex core. We also found, that
+the efficiency of the three-wave interaction of the directly excited mode
+strongly depends on the azimuthal and radial mode numbers of the resultant
+modes, that becomes determinative in the case when several splitting channels
+(several pairs of resultant modes) simultaneously approximately satisfy the
+resonance condition for the splitting. The good agreement of the VHF analytic
+calculations with the experiment and micromagnetic simulations proves the
+capability of the VHF formalism to predict the actual splitting channels and
+the magnitudes of the driving field thresholds for the three-wave splitting.",2008.11812v2
+2020-08-28,Sign structure of thermal Hall conductivity for in-plane-field polarized Kitaev magnets,"The appearance of half-quantized thermal Hall conductivity in
+$\alpha$-RuCl$_3$ in the presence of in-plane magnetic fields has been taken as
+a strong evidence for Kitaev spin liquid. Apart from the quantization, the
+observed sign structure of the thermal Hall conductivity is also consistent
+with predictions from the exact solution of the Kitaev model. Namely, the
+thermal Hall conductivity changes sign when the field direction is reversed
+with respect to the heat current, which is perpendicular to one of the three
+nearest neighbor bonds on the honeycomb lattice. On the other hand, it is
+almost zero when the field is applied along the bond direction. Here, we show
+that such a peculiar sign structure of the thermal Hall conductivity is a
+generic property of the polarized state in the presence of in-plane
+magnetic-fields. In this case, thermal Hall effect arises from topological
+magnons with finite Chern numbers and the sign structure follows from the
+symmetries of the momentum space Berry curvature. Using a realistic spin model
+with bond-dependent interactions, we show that the thermal Hall conductivity
+can have a magnitude comparable to that observed in the experiments. Hence the
+sign structure alone cannot make a strong case for Kitaev spin liquid. The
+quantization at very low temperatures, however, will be a decisive test as the
+magnon contribution vanishes in the zero temperature limit.",2008.12788v1
+2020-10-10,Controlling the anisotropy of a van der Waals antiferromagnet with light,"Magnetic van der Waals materials provide an ideal playground for exploring
+the fundamentals of low-dimensional magnetism and open new opportunities for
+ultrathin spin processing devices. The Mermin-Wagner theorem dictates that as
+in reduced dimensions isotropic spin interactions cannot retain long-range
+correlations; the order is stabilized by magnetic anisotropy. Here, using
+ultrashort pulses of light, we demonstrate all-optical control of magnetic
+anisotropy in the two-dimensional van der Waals antiferromagnet NiPS$_3$.
+Tuning the photon energy in resonance with an orbital transition between
+crystal-field split levels of the nickel ions, we demonstrate the selective
+activation of a sub-THz two-dimensional magnon mode. The pump polarization
+control of the magnon amplitude confirms that the activation is governed by the
+instantaneous magnetic anisotropy axis emergent in response to photoexcitation
+of orbital states with a lowered symmetry. Our results establish pumping of
+orbital resonances as a universal route for manipulating magnetic order in
+low-dimensional (anti)ferromagnets.",2010.05062v1
+2020-11-11,Colossal band renormalization and stoner ferromagnetism induced by electron-antiferromagnetic-magnon coupling,"The interactions between electrons and antiferromagnetic magnons (AFMMs) are
+important for a large class of correlated materials. For example, they are the
+most plausible pairing glues in high-temperature superconductors, such as
+cuprates and iron pnictides. However, unlike electron-phonon interactions
+(EPIs), clear-cut observations regarding how electron-AFMM interactions (EAIs)
+affect the band structure are still lacking. Consequently, critical information
+on the EAIs, such as its strength and doping dependence, remains elusive. Here
+we directly observe that EAIs induces a kink structure in the band dispersion
+in Ba$_{1-x}$K$_x$Mn$_2$As$_2$, and subsequently unveil several key
+characteristics of EAIs. We found that the coupling constant of EAIs can be as
+large as 6, and it shows huge doping dependence and temperature dependence, all
+in stark contrast to the behaviors of EPI and beyond our current understanding
+of EAIs. Such a colossal renormalization of electronic bands by EAIs drives the
+system to the Stoner criteria, giving the intriguing ferromagnetic state in
+Ba$_{1-x}$K$_x$Mn$_2$As$_2$. Our results expand the current knowledge of EAIs,
+which may facilitate the further understanding of many correlated materials
+where EAIs play a critical role, such as high-temperature superconductors.",2011.05683v1
+2020-11-11,Single-quadrature quantum magnetometry in cavity electromagnonics,"A scheme of an ultra-sensitive magnetometer in the cavity quantum
+electromagnonics where the intracavity microwave mode coupled to a magnonic
+mode via magnetic dipole interaction is proposed. It is shown that by driving
+both magnonic and microwave modes with external classical fields and
+controlling the system parameters, one can reduce the added noise of magnetic
+field measurement below the standard quantum limit (SQL). Surprisingly, we show
+that beyond the rotating wave approximation (RWA), not only the added noise can
+be suppressed, but also the output cavity response to the input signal can be
+substantially amplified in order to achieve a precise magnetic-field
+measurement. The estimated theoretical sensitivity of the proposed magnetic
+amplifier-sensor is approximately in the order of $10^{-18}T/\sqrt{Hz}$ which
+is competitive compared to the current state-of-the-art magnetometers like
+superconducting quantum interference devices (SQUIDs) and atomic magnetometers.
+The advantage of the proposed sensor in comparison with the other magnetometers
+is its high sensitivity at room temperature and sensing in a wide range of
+frequency up to MHz as well as its capability to signal-response amplification.",2011.06081v5
+2020-11-27,Perfect Transfer of enhanced entanglement and asymmetric steering in a cavity magnomechanical system,"We propose a hybrid cavity magnomechanical system to realize and transfer the
+bipartite entanglements and Einstein-Podolsky-Rosen (EPR) steerings between
+magnons, photons, and phonons in the regime of stability of the system. As a
+parity-time-symmetric-like structure exhibiting the natural magnetostrictive
+magnon-phonon interaction, our passive-active cavity system can be explored to
+enhance the robust distant quantum entanglement and generate the relatively
+obvious asymmetric (even directional) EPR steering that is useful for the task
+with the highly asymmetric trusts of the bidirectional local measurements
+between two entangled states. It is of great interest that, based on such a
+tunable magnomechanical system, the perfect transfer between near and distant
+entanglements and steerings of different mode pairs is realized by adjusting
+the coupling parameters; in particular, we propose a perfect transfer scheme of
+steerings. These transferring processes suggest indeed an alternative method
+for quantum information storage and manipulation. In addition, the
+entanglements and steerings can also be exchanged between different mode pairs
+by adjusting the detunings between different modes. This work may provide a
+potential platform for distant and asymmetric quantum modulation.",2011.13515v2
+2021-01-14,Laser-induced THz magnetism of antiferromagnetic CoF$_2$,"Excitation, detection and control of coherent THz magnetic excitation in
+antiferromagnets are challenging problems that can be addressed using ever
+shorter laser pulses. We study experimentally excitation of magnetic dynamics
+at THz frequencies in an antiferromagnetic insulator CoF$_2$ by sub-10 fs laser
+pulses. Time-resolved pump-probe polarimetric measurements at different
+temperatures and probe polarizations reveal laser-induced transient circular
+birefringence oscillating at the frequency of 7.45 THz and present below the
+N\'eel temperature. The THz oscillations of circular birefringence are ascribed
+to oscillations of the magnetic moments of Co$^{2+}$ ions induced by the
+laser-driven coherent E$_g$ phonon mode via the THz analogue of the transverse
+piezomagnetic effect. It is also shown that the same pulse launches coherent
+oscillations of the magnetic linear birefringence at the frequency of 3.4 THz
+corresponding to the two-magnon mode. Analysis of the probe polarization
+dependence of the transient magnetic linear birefringence at the frequency of
+the two-magnon mode enables identifying its symmetry.",2101.05622v5
+2021-01-28,Universal field dependence of magnetic resonance near zero frequency,"Magnetic resonance is a widely-established phenomenon that probes magnetic
+properties such as magnetic damping and anisotropy. Even though the typical
+resonance frequency of a magnet ranges from gigahertz to terahertz, experiments
+also report the resonance near zero frequency in a large class of magnets. Here
+we revisit this phenomenon by analyzing the symmetry of the system and find
+that the resonance frequency ($\omega$) follows a universal power law $\omega
+\varpropto |H-H_c|^p$, where $H_c$ is the critical field at which the resonance
+frequency is zero. When the magnet preserves the rotational symmetry around the
+external field ($H$), $p = 1$. Otherwise, $p=1/2$. The magnon excitations are
+gapped above $H_c$, gapless at $H_c$ and gapped again below $H_c$. The zero
+frequency is often accompanied by a reorientation transition in the
+magnetization. For the case that $p=1/2$, this transition is described by a
+Landau theory for second-order phase transitions. We further show that the spin
+current driven by thermal gradient and spin-orbit effects can be significantly
+enhanced when the resonance frequency is close to zero, which can be measured
+electrically by converting the spin current into electric signals. This may
+provide an experimentally accessible way to characterize the critical field.
+Our findings provide a unified understanding of the magnetization dynamics near
+the critical field, and may, furthermore, inspire the study of magnon transport
+near magnetic transitions.",2101.12292v1
+2021-02-27,Curvature-driven homogeneous Dzyaloshinskii-Moriya interaction and emergent weak ferromagnetism in anisotropic antiferromagnetic spin chains,"Chiral antiferromagnets are currently considered for broad range of
+applications in spintronics, spin-orbitronics and magnonics. In contrast to the
+established approach relying on materials screening, the anisotropic and chiral
+responses of low-dimensional antifferromagnets can be tailored relying on the
+geometrical curvature. Here, we consider an achiral, anisotropic
+antiferromagnetic spin chain and demonstrate that these systems possess
+geometry-driven effects stemming not only from the exchange interaction but
+also from the anisotropy. Peculiarly, the anisotropy-driven effects are
+complementary to the curvature effects stemming from the exchange interaction
+and rather strong as they are linear in curvature. These effects are
+responsible for the tilt of the equilibrium direction of vector order
+parameters and the appearance of the homogeneous Dzyaloshinskii-Moriya
+interaction. The latter is a source of the geometry-driven weak ferromagnetism
+emerging in curvilinear antiferromagnetic spin chains. Our findings provide a
+deeper fundamental insight into the physics of curvilinear antiferromagnets
+beyond the $\sigma$-model and offer an additional degree of freedom in the
+design of spintronic and magnonic devices.",2103.00169v1
+2021-03-08,Quantifying the charge carrier interaction in metallic twisted graphene superlattices,"The mechanism of charge carrier interaction in twisted bilayer graphene (TBG)
+remains an unresolved problem, where some researchers proposed the dominance of
+the electron-phonon interaction, while the others showed evidence for
+electron-electron or electron-magnon interactions. Here we propose to resolve
+this problem by generalizing the Bloch-Gr\""uneisen equation and using it for
+the analysis of the temperature dependent resistivity in TBG. It is a
+well-established theoretical result that the Bloch-Gr\""uneisen equation
+power-law exponent, n, exhibits exact integer values for certain mechanisms.
+For instance, n=5 implies the electron-phonon interaction, n=3 is associated
+with electron-magnon interaction and n=2 applies to the electron-electron
+interaction. Here we interpret the linear temperature-dependent resistance,
+widely observed in TBG, as n$\rightarrow$1, which implies the quasielastic
+charge interaction with acoustic phonons. Thus, we fitted TBG resistance curves
+to the Bloch-Gr\""uneisen equation, where we propose that n is a free-fitting
+parameter. We found that TBGs have a smoothly varied n-value (ranging from 1.4
+to 4.4) depending on the Moir\'e superlattice constant, $\lambda$, or the
+charge carrier concentration. This implies that different mechanisms smoothly
+transition from one to another. The proposed generalized Bloch-Gr\""uneisen
+equation is applicable to a wide range of problems, including the Earth
+geology.",2103.04810v1
+2021-03-17,Emergence of a noncollinear magnetic state in twisted bilayer CrI3,"The emergence of two-dimensional (2D) magnetic crystals and moir\'e
+engineering has opened the door for devising new magnetic ground states via
+competing interactions in moir\'e superlattices. Although a suite of
+interesting phenomena, including multi-flavor magnetic states, noncollinear
+magnetic states, moir\'e magnon bands and magnon networks, has been predicted,
+nontrivial magnetic ground states in twisted bilayer magnetic crystals have yet
+to be realized. Here, by utilizing the stacking-dependent interlayer exchange
+interactions in CrI3, we demonstrate in small-twist-angle bilayer CrI3 a
+noncollinear magnetic ground state. It consists of both antiferromagnetic (AF)
+and ferromagnetic (FM) domains and is a result of the competing interlayer AF
+coupling in the monoclinic stacking regions of the moir\'e superlattice and the
+energy cost for forming AF-FM domain walls. Above the critical twist angle of ~
+3{\deg}, the noncollinear state transitions abruptly to a collinear FM ground
+state. We further show that the noncollinear magnetic state can be controlled
+by gating through the doping-dependent interlayer AF interaction. Our results
+demonstrate the possibility of engineering moir\'e magnetism in twisted bilayer
+magnetic crystals, as well as gate-voltage-controllable high-density magnetic
+memory storage.",2103.09850v1
+2021-04-16,Strong magnon-photon coupling with chip-integrated YIG in the zero-temperature limit,"The cross-integration of spin-wave and superconducting technologies is a
+promising method for creating novel hybrid devices for future information
+processing technologies to store, manipulate, or convert data in both classical
+and quantum regimes. Hybrid magnon-polariton systems have been widely studied
+using bulk Yttrium Iron Garnet (Y$_{3}$Fe$_{5}$O$_{12}$, YIG) and
+three-dimensional microwave photon cavities. However, limitations in YIG growth
+have thus far prevented its incorporation into CMOS compatible technology such
+as high quality factor superconducting quantum technology. To overcome this
+impediment, we have used Plasma Focused Ion Beam (PFIB) technology -- taking
+advantage of precision placement down to the micron-scale -- to integrate YIG
+with superconducting microwave devices. Ferromagnetic resonance has been
+measured at millikelvin temperatures on PFIB-processed YIG samples using planar
+microwave circuits. Furthermore, we demonstrate strong coupling between
+superconducting resonator and YIG ferromagnetic resonance modes by maintaining
+reasonably low loss while reducing the system down to the micron scale. This
+achievement of strong coupling on-chip is a crucial step toward fabrication of
+functional hybrid quantum devices that advantage from spin-wave and
+superconducting components.",2104.08068v3
+2021-04-29,The dominance of non-electron-phonon charge carrier interaction in highly-compressed superhydrides,"The primary mechanism governing the emergence of near-room-temperature
+superconductivity in superhydrides is widely accepted to be the electron-phonon
+interaction. If so, the temperature dependent resistance, R(T), in these
+materials should obey the Bloch-Gr\""uneisen equation, where the power-law
+exponent, p, should be equal to the exact integer value of p=5. On the other
+hand, there is a well-established theoretical result that pure electron-magnon
+interaction should be manifested by p=3, and p=2 is the value for pure
+electron-electron interaction. Here we aimed to reveal the type of charge
+carrier interaction in the layered transition metal dichalcogenides PdTe2,
+high-entropy alloy (ScZrNb)0.65[RhPd]0.35, and highly-compressed elemental
+boron and superhydrides H3S, LaHx, PrH9 and BaH12 by fitting the temperature
+dependent resistance of these materials to the Bloch-Gr\""uneisen equation where
+the power-law exponent, p, is a free-fitting parameter. In the result, we
+showed that the high-entropy alloy (ScZrNb)0.65[RhPd]0.35 exhibited pure
+electron-phonon mediated superconductivity with p = 4.9. Unexpectedly we
+revealed that all studied superhydrides exhibit 1.8 < p < 3.2. This implies
+that it is unlikely that the electron-phonon interaction is the primary
+mechanism for the Cooper pairs formation in highly-compressed superhydrides and
+alternative pairing mechanisms, for instance, the electron-magnon, the
+electron-polaron, the electron-electron or other, should be considered as the
+origin for the emergence of near-room-temperature superconductivity in these
+compounds.",2104.14145v3
+2021-05-05,Ni$_{80}$Fe$_{20}$ Nanotubes with Optimized Spintronic Functionalities Prepared by Atomic Layer Deposition,"Permalloy Ni$_{80}$Fe$_{20}$ is one of the key magnetic materials in the
+field of magnonics. Its potential would be further unveiled if it could be
+deposited in three dimensional (3D) architectures of sizes down to the
+nanometer. Atomic Layer Deposition, ALD, is the technique of choice for
+covering arbitrary shapes with homogeneous thin films. Early successes with
+ferromagnetic materials include nickel and cobalt. Still, challenges in
+depositing ferromagnetic alloys reside in the synthesis via decomposing the
+consituent elements at the same temperature and homogeneously. We report
+plasma-enhanced ALD to prepare permalloy Ni$_{80}$Fe$_{20}$ thin films and
+nanotubes using nickelocene and iron(III) tert-butoxide as metal precursors,
+water as the oxidant agent and an in-cycle plasma enhanced reduction step with
+hydrogen. We have optimized the ALD cycle in terms of Ni:Fe atomic ratio and
+functional properties. We obtained a Gilbert damping of 0.013, a resistivity of
+28 $\mu\Omega$cm and an anisotropic magnetoresistance effect of 5.6 $\%$ in the
+planar thin film geometry. We demonstrate that the process also works for
+covering GaAs nanowires, resulting in permalloy nanotubes with high aspect
+ratios and diameters of about 150 nm. Individual nanotubes were investigated in
+terms of crystal phase, composition and spin-dynamic response by microfocused
+Brillouin Light Scattering. Our results enable NiFe-based 3D spintronics and
+magnonic devices in curved and complex topology operated in the GHz frequency
+regime.",2105.01969v1
+2021-05-11,On the connection between magnetic interactions and the spin-wave gap of the insulating phase of NaOsO$_{3}$,"The scenario of a metal-insulator transition driven by the onset of
+antiferromagnetic order in NaOsO$_3$ calls for a trustworthy derivation of the
+underlying effective spin Hamiltonian. To determine the latter we rely on {\it
+ab initio} electronic-structure calculations, linear spin-wave theory, and
+comparison to experimental data of the corresponding magnon spectrum. We arrive
+this way to Heisenberg couplings that are $\lesssim$45\% to$\lesssim$63\%
+smaller than values presently proposed in the literature and
+Dzyaloshinskii-Moriya interactions in the region of 15\% of the Heisenberg
+exchange $J$. These couplings together with the symmetric anisotropic exchange
+interaction and single-ion magnetocrystalline anisotropy successfully reproduce
+the magnon dispersion obtained by resonant inelastic X-ray scattering
+measurements. In particular, the spin-wave gap fully agrees with the measured
+one. We find that the spin-wave gap is defined from a subtle interplay between
+the single-ion anisotropy, the Dzyaloshinskii-Moriya exchange and the symmetric
+anisotropic exchange interactions. The results reported here underpin the
+local-moment description of NaOsO$_3$, when it comes to analyzing the magnetic
+excitation spectra. Interestingly, this comes about from a microscopic theory
+that describes the electron system as Bloch states, adjusted to a mean-field
+solution to Hubbard-like interactions.",2105.04893v2
+2021-05-24,Role of two-dimensional Ising superconductivity in the non-equilibrium quasiparticle spin-to-charge conversion efficiency,"Non-equilibrium studies of two-dimensional (2D) superconductors (SCs) with
+Ising spin-orbit coupling are prerequisite for their successful application to
+equilibrium spin-triplet Cooper pairs and, potentially, Majorana fermions. By
+taking advantage of the recent discoveries of 2D SCs and their compatibility
+with any other materials, we fabricate here non-local magnon devices to examine
+how such 2D Ising superconductivity affects the conversion efficiency of magnon
+spin to quasiparticle charge in superconducting flakes of 2H-NbSe2 transferred
+onto ferrimagnetic insulating Y3Fe5O12. Comparison with a reference device
+based on a conventionally paired superconductor shows that the Y3Fe5O12-induced
+in-plane (IP) exchange spin-splitting in the NbSe2 flake is hindered by its
+inherent out-of-plane (OOP) spin-orbit-field, which, in turn, limits the
+transition-state enhancement of the spin-to-charge conversion efficiency. Our
+out-of-equilibrium study highlights the significance of symmetry matching
+between underlying Cooper pairs and exchange-induced spin-splitting for the
+giant transition-state spin-to-charge conversion and may have implications
+towards proximity-engineered spin-polarized triplet pairing via tuning the
+relative strength of IP exchange and OOP spin-orbit fields in ferromagnetic
+insulator/2D Ising SC bilayers.",2105.11159v4
+2021-06-04,Non-Loudon-Fleury Raman scattering in spin-orbit coupled Mott insulators,"We revisit the theory of magnetic Raman scattering in Mott insulators with
+strong spin-orbit coupling, with a major focus on Kitaev materials. We show
+that Kitaev materials with bond-anisotropic interactions are generally expected
+to show both one- and two-magnon responses. It is further shown that, in order
+to obtain the correct leading contributions to the Raman vertex operator
+$\mc{R}$, one must take into account the precise, photon-assisted microscopic
+hopping processes of the electrons and that, in systems with multiple hopping
+paths, $\mc{R}$ contains terms beyond those appearing in the traditional
+Loudon-Fleury theory. Most saliently, a numerical implementation of the revised
+formalism to the case of the three-dimensional hyperhoneycomb Kitaev material
+$\beta$-Li$_2$IrO$_3$ reveals that the non-Loudon-Fleury scattering terms
+actually dominate the Raman intensity. In addition, they induce a qualitative
+modification of the polarization dependence, including, e.g., the emergence of
+a sharp one-magnon peak at low energies which is not expected in the
+traditional Loudon-Fleury theory. This peak is shown to arise from microscopic
+photon-assisted tunneling processes that are of similar type with the ones
+leading to the symmetric off-diagonal interaction $\Gamma$ (known to be present
+in many Kitaev materials), but take the form of a bond-directional magnetic
+dipole term in the Raman vertex. These results are expected to apply across all
+Kitaev materials and mark a drastic change of paradigm for the understanding of
+Raman scattering in materials with strong spin-orbit coupling and multiple
+exchange paths.",2106.02645v2
+2021-06-08,Quantum Monte Carlo study of honeycomb antiferromagnets under a triaxial strain,"The honeycomb antiferromagnet under a triaxial strain is studied using the
+quantum Monte Carlo simulation. The strain dimerizes the exchange couplings
+near the corners, thus destructs the antiferromagnetic order therein. The
+antiferromagnetic region is continuously reduced by the strain. For the same
+strain strength, the exact numerical results give a much smaller
+antiferromagnetic region than the linear spin-wave theory. We then study the
+strained $XY$ antiferromagnet, where the magnon pseudo-magnetic field behaves
+quite differently. The $0$th Landau level appears in the middle of the
+spectrum, and the quantized energies above (below) it are proportional to
+$n^{\frac{1}{3}} (n^{\frac{2}{3}})$, which is in great contrast to the
+equally-spaced ones in the Heisenberg case. Besides, we find the
+antiferromagnetic order of the $XY$ model is much more robust to the
+dimerization than the Heisenberg one. The local susceptibility of the
+Heisenberg case is extracted by the numerical analytical continuation, and no
+sign of the pseudo-Landau levels is resolved. It is still not sure whether the
+result is due to the intrinsic problem of the numerical analytical
+continuation. Thus the existence of the magnon pseudo-Landau levels in the
+spin-$\frac{1}{2}$ strained Heisenberg Hamiltonian remains an open question.
+Our results are closely related to the two-dimensional van der Waals quantum
+antiferromagnets and may be realized experimentally.",2106.04358v3
+2021-06-15,Dynamical Spin Chains in 4D $\mathcal{N}=2$ SCFTs,"This is the first in a series of papers devoted to the study of spin chains
+capturing the spectral problem of 4d $\mathcal{N}=2$ SCFTs in the planar limit.
+At one loop and in the quantum plane limit, we discover a quasi-Hopf symmetry
+algebra, defined by the $R$-matrix read off from the superpotential. This
+implies that when orbifolding the $\mathcal{N}=4$ symmetry algebra down to the
+$\mathcal{N}=2$ one and then marginaly deforming, the broken generators are not
+lost, but get upgraded to quantum generators. Importantly, we demonstrate that
+these chains are dynamical, in the sense that their Hamiltonian depends on a
+parameter which is dynamically determined along the chain. At one loop we map
+the holomorphic SU(3) scalar sector to a dynamical 15-vertex model, which
+corresponds to an RSOS model, whose adjacency graph can be read off from the
+gauge theory quiver/brane tiling. One scalar SU(2) sub-sector is described by
+an alternating nearest-neighbour Hamiltonian, while another choice of SU(2)
+sub-sector leads to a dynamical dilute Temperley-Lieb model. These sectors have
+a common vacuum state, around which the magnon dispersion relations are
+naturally uniformised by elliptic functions. Concretely, for the $\mathbb{Z}_2$
+quiver theory we study these dynamical chains by solving the one- and
+two-magnon problems with the coordinate Bethe ansatz approach. We confirm our
+analytic results by numerical comparison with the explicit diagonalisation of
+the Hamiltonian for short closed chains.",2106.08449v1
+2021-06-23,Field-Induced Spin Excitations in the Spin-1/2 Triangular-Lattice Antiferromagnet CsYbSe$_2$,"A layered triangular lattice with spin-1/2 ions is an ideal platform to
+explore highly entangled exotic states like quantum spin liquid (QSL). Here, we
+report a systematic in-field neutron scattering study on a perfect
+two-dimensional triangular-lattice antiferromagnet, CsYbSe$_2$, a member of the
+large QSL candidate family rare-earth chalcogenides. The elastic neutron
+scattering measured down to 70 mK shows that there is a short-range
+120$^{\circ}$ magnetic order at zero field. In the field-induced ordered
+states, the spin-spin correlation lengths along the $c$ axis are relatively
+short, although the heat capacity results indicate long-range magnetic orders
+at 3 T $-$ 5 T. The inelastic neutron scattering spectra evolve from highly
+damped continuum-like excitations at zero field to relatively sharp spin wave
+modes at the plateau phase. Our extensive large-cluster density-matrix
+renormalization group calculations with a Heisenberg triangular-lattice
+nearest-neighbor antiferromagnetic model reproduce the essential features of
+the experimental spectra, including continuum-like excitations at zero field,
+series of sharp magnons at the plateau phase as well as two-magnon excitations
+at high energy. This work presents comprehensive experimental and theoretical
+overview of the unconventional field-induced spin dynamics in
+triangular-lattice Heisenberg antiferromagnet and thus provides valuable
+insight into quantum many-body phenomena.",2106.12451v2
+2021-07-09,Excitations and ergodicity of critical quantum spin chains from non-equilibrium classical dynamics,"We study a quantum spin-1/2 chain that is dual to the canonical problem of
+non-equilibrium Kawasaki dynamics of a classical Ising chain coupled to a
+thermal bath. The Hamiltonian is obtained for the general disordered case with
+non-uniform Ising couplings. The quantum spin chain (dubbed Ising-Kawasaki) is
+stoquastic, and depends on the Ising couplings normalized by the bath's
+temperature. We give its exact ground states. Proceeding with uniform
+couplings, we study the one- and two-magnon excitations. Solutions for the
+latter are derived via a Bethe Ansatz scheme. In the antiferromagnetic regime,
+the two-magnon branch states show intricate behavior, especially regarding
+their hybridization with the continuum. We find that that the gapless chain
+hosts multiple dynamics at low energy as seen through the presence of multiple
+dynamical critical exponents. Finally, we analyze the full energy level spacing
+distribution as a function of the Ising coupling. We conclude that the system
+is non-integrable for generic parameters, or equivalently, that the
+corresponding non-equilibrium classical dynamics are ergodic.",2107.04615v3
+2021-07-18,Straintronics: Manipulating the Magnetization of Magnetostrictive Nanomagnets with Strain for Energy-Efficient Applications,"The desire to perform information processing, computation, communication,
+signal generation and related tasks, while dissipating as little energy as
+possible, has inspired many ideas and paradigms. One of the most powerful among
+them is the notion of using magnetostrictive nanomagnets as the primitive units
+of the hardware platforms and manipulating their magnetizations with
+electrically generated static or time varying mechanical strain to elicit
+myriad functionalities. This approach has two advantages. First, information
+can be retained in the devices after powering off since the nanomagnets are
+non-volatile unlike charge-based devices such as transistors. Second, the
+energy expended to perform a given task is exceptionally low since it takes
+very little energy to alter magnetization states with strain. This field is now
+known as ""straintronics"", in analogy with electronics, spintronics,
+valleytronics, etc. We review the recent advances and trends in straintronics,
+including digital information processing (logic), information storage (memory),
+domain wall devices operated with strain, control of skyrmions with strain,
+non-Boolean computing and machine learning with straintronics, signal
+generation (microwave sources) and communication (ultra-miniaturized acoustic
+and electromagnetic antennas) implemented with strained nanomagnets, hybrid
+straintronics-magnonics, and interaction between phonons and magnons in
+straintronic systems. We identify key challenges and opportunities, and lay out
+pathways to advance this field to the point where it might become a mainstream
+technology for energy-efficient systems.",2107.08497v1
+2021-07-20,Spin-wave dispersion measurement by variable-gap propagating spin-wave spectroscopy,"Magnonics is seen nowadays as a candidate technology for energy-efficient
+data processing in classical and quantum systems. Pronounced nonlinearity,
+anisotropy of dispersion relations and phase degree of freedom of spin waves
+require advanced methodology for probing spin waves at room as well as at mK
+temperatures. Yet, the use of the established optical techniques like Brillouin
+light scattering (BLS) or magneto optical Kerr effect (MOKE) at ultra-low
+temperatures is forbiddingly complicated. By contrast, microwave spectroscopy
+can be used at all temperatures but is usually lacking spatial and wavenumber
+resolution. Here, we develop a variable-gap propagating spin-wave spectroscopy
+(VG-PSWS) method for the deduction of the dispersion relation of spin waves in
+wide frequency and wavenumber range. The method is based on the phase-resolved
+analysis of the spin-wave transmission between two antennas with variable
+spacing, in conjunction with theoretical data treatment. We validate the method
+for the in-plane magnetized CoFeB and YIG thin films in $k\perp B$ and
+$k\parallel B$ geometries by deducing the full set of material and spin-wave
+parameters, including spin-wave dispersion, hybridization of the fundamental
+mode with the higher-order perpendicular standing spin-wave modes and surface
+spin pinning. The compatibility of microwaves with low temperatures makes this
+approach attractive for cryogenic magnonics at the nanoscale.",2107.09363v1
+2021-08-30,Bright and dark states of two distant macrospins strongly coupled by phonons,"We study the collective dynamics of two distant magnets coherently coupled by
+acoustic phonons that are transmitted through an intercalated crystal. By
+tuning the ferromagnetic resonances of the two magnets to an acoustic resonance
+of the crystal, we control a coherent three levels system. We show that the
+parity of the phonon mode governs the nature of the indirect coupling between
+the magnets: the resonances with odd / even phonon modes correspond to
+out-of-phase / in-phase lattice displacements at the magnets, leading to bright
+/ dark states in response to uniform microwave magnetic fields, respectively.
+The sample is a tri-layer garnet consisting of two thin magnetic layers
+epitaxially grown on both sides of a half-millimeter thick non-magnetic single
+crystal. In spite of the relatively weak magneto-elastic interaction, the long
+lifetimes of the magnon and phonon modes in the sample are the key to unveil
+this long range strong coupling. This demonstrates that garnets are a great
+platform to study multi-partite hybridization process between magnon and
+phonons at microwave frequencies.",2108.13272v2
+2021-09-23,Dynamics in an exact solvable quantum magnet: benchmark for quantum computer,"Quantum magnets are never short of novel and fascinating dynamics, yet its
+simulation by classical computers requires exponentially-scaled computation
+resources, which renders the research on large-scale many-body dynamics
+fiendishly difficult. In this letter, we explore the dynamic behavior of 2D
+large-scale ferromagnetic J1-J2 Heisenberg model both theoretically and
+experimentally. First, the analytical solution of magnon dynamics is obtained
+to show an obvious ballistic propagation of magnon, which is typical for
+quantum walk. Then, we verify the dynamic behavior of the system through
+numerical approach of exact diagonalization and tensor network method. We also
+calculate out-of-time ordered correlators and butterfly velocities among
+different lattice points, finding that they can well depict the competition
+between different couplings. Finally, a quantum walk experiment is designed and
+conducted on the basis of IBM programmable quantum processors, and the
+experimental results are in consistence with our theoretical predictions. Since
+the analytical results can be used, in principle, to predict the behavior of
+large-scale quantum many-body systems and even those infinitely large, this
+work will help facilitate further research on quantum walk and quantum
+many-body dynamics in large-scale lattice systems, guide future design of
+quantum computers, as well as popularize quantum computers until they are known
+and available to every household in the world.",2109.11371v5
+2021-10-05,Thermal transport of the frustrated spin-chain mineral linarite: Magnetic heat transport and strong spin-phonon scattering,"The mineral linarite (PbCuSO$_4$(OH)$_2$) forms a monoclinic structure where
+a sequence of Cu(OH)$_2$ units forms a spin-$\frac{1}{2}$ chain. Competing
+ferromagnetic nearest-neighbor ($J_1$) and antiferromagnetic
+next-nearest-neighbor interactions ($J_2$) in this quasi-one-dimensional spin
+structure imply magnetic frustration and lead to magnetic ordering below $T_N
+=$2.8 K in a mutliferroic elliptical spin-spiral ground state. Upon the
+application of a magnetic field along the spin-chain direction, distinct
+magnetically ordered phases can be induced. We studied the thermal conductivity
+$\kappa$ in this material across the magnetic phase diagram as well as in the
+paramagnetic regime in the temperature ranges 0.07-1 K and 9-300 K. We found
+that in linarite the heat is carried mainly by phonons but shows a peculiar
+non-monotonic behavior in field. In particular, $\kappa$ is highly suppressed
+at the magnetic phase boundaries, indicative of strong scattering of the
+phonons off critical magnetic fluctuations. Even at temperatures far above the
+magnetically ordered phases, the phononic thermal conductivity is reduced due
+to scattering off magnetic fluctuations. The mean free path due to spin-phonon
+scattering ($l_{\text{spin-phonon}}$) was determined as function of
+temperature. A power law behavior was observed mainly above 0.5 K indicating
+the thermal activation of spin fluctuations. In the critical regime close to
+the saturation field, $l_{\text{spin-phonon}}$ shows a $1/T$ dependence.
+Furthermore, a magnon thermal transport channel was verified in the helical
+magnetic phase. We estimate a magnon mean free path which corresponds to about
+1000 lattice spacings.",2110.01865v1
+2021-12-10,Low-energy excitations and magnetic anisotropy of the layered van der Waals antiferromagnet Ni$_2$P$_2$S$_6$,"The quasi-two-dimensional antiferromagnet Ni$_2$P$_2$S$_6$ belongs to the
+family of magnetic van der Waals compounds that provides a rich material base
+for the realization of fundamental models of quantum magnetism in low
+dimensions. Here, we report high-frequency/high-magnetic field electron spin
+resonance measurements on single crystals of Ni$_2$P$_2$S$_6$. The results
+enable one to reliably determine the positive, ""easy""-plane type of the single
+ion anisotropy of the Ni$^{2+}$ ions with the upper limit of its magnitude
+$\lesssim 0.7$ meV. The resonance response reveals strongly anisotropic spin
+fluctuations setting in shortly above the N\'eel temperature $T_{\rm N} = 158$
+K and extending in the antiferromagnetically ordered state down to low
+temperatures. There, a low-energy magnon excitation gapped from the ground
+state by only $\sim 1$ meV was found. This magnon mode may explain unusual low
+temperature relaxation processes observed in a latest nuclear magnetic
+resonance experiments and together with the estimate of the single ion
+anisotropy they should enable setting up a realistic spin model for an accurate
+description of magnetic properties of Ni$_2$P$_2$S$_6$.",2112.05699v3
+2021-12-11,Optical excitation of electromagnons in hexaferrite,"Understanding ultrafast magnetization dynamics on the microscopic level is of
+strong current interest due to the potential for applications in information
+storage. In recent years, the spin-lattice coupling has been recognized to be
+essential for ultrafast magnetization dynamics. Magnetoelectric multiferroics
+of type II possess intrinsic correlations among magnetic sublattices and
+electric polarization (P) through spin-lattice coupling, enabling fundamentally
+coupled dynamics between spins and lattice. Here we report on ultrafast
+magnetization dynamics in a room-temperature multiferroic hexaferrite
+possessing ferrimagnetic and antiferromagnetic sublattices, revealed by
+time-resolved resonant x-ray diffraction. A femtosecond above-bandgap
+excitation triggers a coherent magnon in which the two magnetic sublattices
+entangle and give rise to a transient modulation of P. A novel microscopic
+mechanism for triggering the coherent magnon in this ferrimagnetic insulator
+based on the spin-lattice coupling is proposed. Our finding opens up a novel
+but general pathway for ultrafast control of magnetism.",2112.05961v1
+2022-01-25,Frustration model and spin excitations in the helimagnet FeP,"The metallic compound FeP belongs to the class of materials that feature a
+complex noncollinear spin order driven by magnetic frustration. While its
+double-helix magnetic structure with a period $\lambda_{\text{s}} \approx 5c$,
+where $c$ is the lattice constant, was previously well determined, the relevant
+spin-spin interactions that lead to that ground state remain unknown. By
+performing extensive inelastic neutron scattering measurements, we obtained the
+spin-excitation spectra in a large part of the momentum-energy space. The
+spectra show that the magnons are gapped with a gap energy of $\sim$5 meV.
+Despite the 3D crystal structure, the magnon modes display strongly anisotropic
+dispersions, revealing a quasi-one-dimensional character of the magnetic
+interactions in FeP. The physics of the material, however, is not determined by
+the dominating exchange, which is ferromagnetic. Instead, the weaker
+two-dimensional antiferromagnetic interactions between the rigid ferromagnetic
+spin chains drive the magnetic frustration. Using linear spin-wave theory, we
+were able to construct an effective Heisenberg Hamiltonian with an anisotropy
+term capable of reproducing the observed spectra. This enabled us to quantify
+the exchange interactions in FeP and determine the mechanism of its magnetic
+frustration.",2201.10358v2
+2022-04-07,Spin dynamics and exchange interaction in orthoferrite TbFeO$_3$ with non-Kramers rare-earth ion,"The low-temperature spin dynamics of the orthorhombic TbFeO$_3$ perovskite
+has been studied. It has been found that the inelastic neutron scattering (INS)
+spectrum contains two modes corresponding to different sublattices in the
+compound. The iron subsystem orders antiferromagnetically at T$_N$ = 632 K and
+exhibits the high-energy magnon dispersion. Magnetic dynamics of this subsystem
+has been described using the linear spin wave theory and our solution yields
+sizable anisotropy between in-plane and out-of-plane exchange interactions.
+This approach was previously used to describe the magnon dispersion in the
+TmFeO$_3$ compound. Three non-dispersive crystal electric field levels
+corresponding to Tb$^{3+}$ ions have been established in the region below 40
+meV at about 17, 26, and 35 meV. Study of diffuse scattering at different
+temperatures has elucidated the behavior of the magnetic correlation length.
+The behavior of the Tb$^{3+}$ ion subsystem has been numerically described in
+the framework of the point charge model. The numerical data agree
+satisfactorily with the experiment and with the general concept of the
+single-ion approximation applied to the rare-earth subsystem of orthorhombic
+perovskites.",2204.03239v1
+2022-04-19,Unravelling the Nature of Spin Excitations Disentangled from Charge Contributions in a Doped Cuprate Superconductor,"The nature of the spin excitations in superconducting cuprates is a key
+question toward a unified understanding of the cuprate physics from long-range
+antiferromagnetism to superconductivity. The intense spin excitations up to the
+over-doped regime revealed by resonant inelastic X-ray scattering bring new
+insights as well as questions like how to understand their persistence or their
+relation to the collective excitations in ordered magnets (magnons). Here, we
+study the evolution of the spin excitations upon hole-doping the
+superconducting cuprate Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ by disentangling the
+spin from the charge excitations in the experimental cross section. We compare
+our experimental results against density matrix renormalization group
+calculations for a $t$-$J$-like model on a square lattice. Our results
+unambiguously confirm the persistence of the spin excitations, which are
+closely connected to the persistence of short-range magnetic correlations up to
+high doping. This suggests that the spin excitations in hole-doped cuprates are
+related to magnons -- albeit short-ranged.",2204.08749v2
+2022-04-22,Controlling magnetism with light in a zero orbital angular momentum antiferromagnet,"Antiferromagnetic materials feature intrinsic ultrafast spin dynamics, making
+them ideal candidates for future magnonic devices operating at THz frequencies.
+A major focus of current research is the investigation of optical methods for
+the efficient generation of coherent magnons in antiferromagnetic insulators.
+In magnetic lattices endowed with orbital angular momentum, spin-orbit coupling
+enables spin dynamics through the resonant excitation of low-energy electric
+dipoles such as phonons and orbital resonances which interact with spins.
+However, in magnetic systems with zero orbital angular momentum, microscopic
+pathways for the resonant and low-energy optical excitation of coherent spin
+dynamics are lacking. Here, we consider experimentally the relative merits of
+electronic and vibrational excitations for the optical control of zero orbital
+angular momentum magnets, focusing on a limit case: the antiferromagnet
+manganese thiophoshate (MnPS3), constituted by orbital singlet Mn2+ ions. We
+study the correlation of spins with two types of excitations within its band
+gap: a bound electron orbital excitation from the singlet orbital ground state
+of Mn2+ into an orbital triplet state, which causes coherent spin precession,
+and a vibrational excitation of the crystal field that causes thermal spin
+disorder. Our findings cast orbital transitions as key targets for magnetic
+control in insulators constituted by magnetic centers of zero orbital angular
+momentum.",2204.10574v1
+2022-06-06,Probing spin dynamics of ultra-thin van der Waals magnets via photon-magnon coupling,"Layered van der Waals (vdW) magnets can maintain a magnetic order even down
+to the single-layer regime and hold promise for integrated spintronic devices.
+While the magnetic ground state of vdW magnets was extensively studied, key
+parameters of spin dynamics, like the Gilbert damping, crucial for designing
+ultra-fast spintronic devices, remains largely unexplored. Despite recent
+studies by optical excitation and detection, achieving spin wave control with
+microwaves is highly desirable, as modern integrated information technologies
+predominantly are operated with these. The intrinsically small numbers of
+spins, however, poses a major challenge to this.
+  Here, we present a hybrid approach to detect spin dynamics mediated by
+photon-magnon coupling between high-Q superconducting resonators and ultra-thin
+flakes of Cr$_2$Ge$_2$Te$_6$ (CGT) as thin as 11\,nm. We test and benchmark our
+technique with 23 individual CGT flakes and extract an upper limit for the
+Gilbert damping parameter. These results are crucial in designing on-chip
+integrated circuits using vdW magnets and offer prospects for probing spin
+dynamics of monolayer vdW magnets.",2206.02460v2
+2022-06-11,Chirality as Generalized Spin-Orbit Interaction in Spintronics,"This review focuses on the chirality observed in the excited states of the
+magnetic order, dielectrics, and conductors that hold transverse spins when
+they are evanescent. Even without any relativistic effect, the transverse spin
+of the evanescent waves are locked to the momentum and the surface normal of
+their propagation plane. This chirality thereby acts as a generalized
+spin-orbit interaction, which leads to the discovery of various chiral
+interactions between magnetic, phononic, electronic, photonic, and plasmonic
+excitations in spintronics that mediate the excitation of quasiparticles into a
+single direction, leading to phenomena such as chiral spin and phonon pumping,
+chiral spin Seebeck, spin skin, magnonic trap, magnon Doppler, and spin diode
+effects. Intriguing analogies with electric counterparts in the nano-optics and
+plasmonics exist. After a brief review of the concepts of chirality that
+characterize the ground state chiral magnetic textures and chirally coupled
+magnets in spintronics, we turn to the chiral phenomena of excited states. We
+present a unified electrodynamic picture for dynamical chirality in spintronics
+in terms of generalized spin-orbit interaction and compare it with that in
+nano-optics and plasmonics. Based on the general theory, we subsequently review
+the theoretical progress and experimental evidence of chiral interaction, as
+well as the near-field transfer of the transverse spins, between various
+excitations in magnetic, photonic, electronic and phononic nanostructures at
+GHz time scales. We provide a perspective for future research before concluding
+this article.",2206.05535v2
+2022-07-30,Excitation Spectra of one-dimensional spin-1/2 Fermi gas with an attraction,"Using exact Bethe ansatz solution, we rigorously study excitation spectra of
+the spin-1/2 Fermi gas (called Yang-Gaudin model) with an attractive
+interaction. Elementary excitations of this model involve particle-hole
+excitations, hole excitations and adding particles in the Fermi seas of pairs
+and unpaired fermions. The gapped magnon excitations in spin sector show a
+ferromagnetic coupling to the Fermi sea of the single fermions. By numerically
+and analytically solving the Bethe ansatz equations and the thermodynamic Bethe
+ansatz equations of this model, we obtain excitation energies for various
+polarizations in the phase of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-like
+state. For a small momentum (long-wavelength limit) and in the strong
+interaction regime, we analytically obtained their linear dispersions with
+curvature corrections, effective masses as well as velocities in particle-hole
+excitations of pairs and unpaired fermions. Such a type of particle-hole
+excitations display a novel separation of collective motions of bosonic modes
+within paired and unpaired fermions. Finally, we also discuss magnon
+excitations in spin sector and the application of the Bragg spectroscopy for
+testing such separated charge excitation modes of pairs and single fermions.",2208.00212v2
+2022-08-17,The importance of the interface for picosecond spin pumping in antiferromagnet-heavy metal heterostructures,"Interfaces between heavy metals (HMs) and antiferromagnetic insulators (AFIs)
+have recently become highly investigated and debated systems in the effort to
+create spintronic devices able to function at terahertz frequencies. Such
+heterostructures have great technological potential because AFIs can generate
+sub-picosecond spin currents which the HMs can convert into charge signals. In
+this work we demonstrate an optically induced picosecond spin transfer at the
+interface between AFIs and Pt using time-resolved THz emission spectroscopy. We
+select two antiferromagnets in the same family of fluoride cubic perovskites,
+KCoF3 and KNiF3, whose magnon frequencies at the centre of the Brillouin zone
+differ by an order of magnitude. By studying their behaviour with temperature
+we correlate changes in the spin transfer efficiency across the interface to
+the opening of a gap in the magnon density of states below the N\'eel
+temperature. Our observations are reproduced in a model based on the spin
+exchange between the localized electrons in the antiferromagnet and the free
+electrons in Pt. These results constitute an important step in the rigorous
+investigation and understanding of the physics of AFIs/HMs interfaces on the
+ultrafast timescale.",2208.08332v1
+2022-09-20,Terahertz spin dynamics in rare-earth orthoferrites,"Recent interest in developing fast spintronic devices and laser-controllable
+magnetic solids has sparked tremendous experimental and theoretical efforts to
+understand and manipulate ultrafast dynamics in materials. Studies of spin
+dynamics in the terahertz (THz) frequency range are particularly important for
+elucidating microscopic pathways toward novel device functionalities. Here, we
+review THz phenomena related to spin dynamics in rare-earth orthoferrites, a
+class of materials promising for antiferromagnetic spintronics. We expand this
+topic into a description of four key elements. (1) We start by describing THz
+spectroscopy of spin excitations for probing magnetic phase transitions in
+thermal equilibrium. While acoustic magnons are useful indicators of spin
+reorientation transitions, electromagnons that arise from dynamic
+magnetoelectric couplings serve as a signature of inversion-symmetry-breaking
+phases at low temperatures. (2) We then review the strong laser driving
+scenario, where the system is excited far from equilibrium and thereby subject
+to modifications to the free energy landscape. Microscopic pathways for
+ultrafast laser manipulation of magnetic order are discussed. (3) Furthermore,
+we review a variety of protocols to manipulate coherent THz magnons in time and
+space, which are useful capabilities for antiferromagnetic spintronic
+applications. (4) Finally, new insights on the connection between dynamic
+magnetic coupling in condensed matter and the Dicke superradiant phase
+transition in quantum optics are provided. By presenting a review on an array
+of THz spin phenomena occurring in a single class of materials, we hope to
+trigger interdisciplinary efforts that actively seek connections between
+subfields of spintronics, which will facilitate the invention of new protocols
+of active spin control and quantum phase engineering.",2209.09468v1
+2022-09-27,Tailoring crosstalk between localized 1D spin-wave nanochannels using focused ion beams,"1D spin-wave conduits are envisioned as nanoscale components of
+magnonics-based logic and computing schemes for future generation electronics.
+`A-la-carte methods of versatile control of the local magnetization dynamics in
+such nanochannels are highly desired for efficient steering of the spin waves
+in magnonic devices. Here, we present a study of localized dynamical modes in
+1-$\mu$m-wide Permalloy conduits probed by microresonator ferromagnetic
+resonance technique. We clearly observe the lowest-energy edge mode in the
+microstrip after its edges were finely trimmed by means of focused Ne$^+$ ion
+irradiation. Furthermore, after milling the microstrip along its long axis by
+focused ion beams, creating consecutively $\sim$50 and $\sim$100 nm gaps,
+additional resonances emerge and are attributed to modes localized at the inner
+edges of the separated strips. To visualize the mode distribution, spatially
+resolved Brillouin light scattering microscopy was used showing an excellent
+agreement with the ferromagnetic resonance data and confirming the mode
+localization at the outer/inner edges of the strips depending on the magnitude
+of the applied magnetic field. Micromagnetic simulations confirm that the
+lowest-energy modes are localized within $\sim$15-nm-wide regions at the edges
+of the strips and their frequencies can be tuned in a wide range (up to 5 GHz)
+by changing the magnetostatic coupling (i.e. spatial separation) between the
+microstrips.",2209.13180v2
+2022-10-11,"Specifics of the Elemental Excitations in ""True One-Dimensional"" MoI$_3$ van der Waals Nanowires","We report on the temperature evolution of the polarization-dependent Raman
+spectrum of exfoliated MoI$_3$, a van der Waals material with a ""true
+one-dimensional"" crystal structure that can be exfoliated to individual atomic
+chains. The temperature evolution of several Raman features reveals anomalous
+behavior suggesting a phase transition of a magnetic origin. Theoretical
+considerations indicate that MoI$_3$ is an easy-plane antiferromagnet with
+alternating spins along the dimerized chains and with inter-chain helical spin
+ordering. The calculated frequencies of the phonons and magnons are consistent
+with the interpretation of the experimental Raman data. The obtained results
+shed light on the specifics of the phononic and magnonic states in MoI$_3$ and
+provide a strong motivation for future study of this unique material with
+potential for spintronic device applications.",2210.05081v1
+2022-10-25,Planar Thermal Hall Effects in Kitaev Spin Liquid Candidate Na2Co2TeO6,"We investigate both the longitudinal thermal conductivity ($\kappa_{xx}$) and
+the planar thermal Hall conductivity ($\kappa_{xy}$) in the Kitaev spin liquid
+candidate of Co-based honeycomb antiferromagnet Na$_2$Co$_2$TeO$_6$ in a
+magnetic field ($B$) applied along the $a$ and $a^*$ axes. A finite
+$\kappa_{xy}$ is resolved for both field directions in the antiferromagnetic
+(AFM) phase below the N\'eel temperature of 27 K. The temperature dependence of
+$\kappa_{xy}/T$ shows the emergence of topological bosonic excitations. In
+addition, the field dependence of $\kappa_{xy}$ shows sign reversals at the
+critical fields in the AFM phase, suggesting the changes in the Chern number
+distribution of the topological magnons. Remarkably, a finite $\kappa_{xy}$ is
+observed in $B \parallel a^*$ between the first-order transition field in the
+AFM phase and the saturation field, which is prohibited in a disordered state
+by the two-fold rotation symmetry around the $a^*$ axis of the honeycomb
+lattice, showing the presence of a magnetically ordered state that breaks the
+two-fold rotation symmetry. Our results demonstrate the presence of topological
+magnons in this compound in the whole field range below the saturation field.",2210.13798v1
+2022-10-29,Micromagnetic frequency-domain simulation methods for magnonic systems,"We present efficient numerical methods for the simulation of small
+magnetization oscillations in three-dimensional micromagnetic systems.
+Magnetization dynamics is described by the Landau-Lifshitz-Gilbert (LLG)
+equation, linearized in the frequency domain around a generic equilibrium
+configuration, and formulated in a special operator form that allows leveraging
+large-scale techniques commonly used to evaluate the effective field in
+time-domain micromagnetic simulations. By using this formulation, we derive
+numerical algorithms to compute the free magnetization oscillations (i.e., spin
+wave eigenmodes) as well as magnetization oscillations driven by ac
+radio-frequency fields for arbitrarily shaped nanomagnets. Moreover,
+semi-analytical perturbation techniques based on the computation of a reduced
+set of eigenmodes are provided for fast evaluation of magnetization frequency
+response and absorption spectra as a function of damping and ac field. We
+present both finite difference and finite element implementations and
+demonstrate their effectiveness on a test case. These techniques open the
+possibility to study generic magnonic systems discretized with several hundred
+thousand (or even millions) of computational cells in a reasonably short time.",2210.16564v3
+2022-11-17,Observation of an unexpected negative magnetoresistance in magnetic Weyl semimetal Co$_3$Sn$_2$S$_2$,"Time-reversal symmetry breaking allows for a rich set of magneto-transport
+properties related to electronic topology. Focusing on the magnetic Weyl
+semimetal Co$_3$Sn$_2$S$_2$, we prepared micro-ribbons and investigated their
+transverse and longitudinal transport properties from 100 K to 180 K in
+magnetic fields $\mu_0 H$ up to 2T. We establish the presence of a
+magnetoresistance (MR) up to 1 % with a strong anisotropy depending the
+projection of $H$ on the easy-axis magnetization, which exceeds all other
+magnetoresistive effects. Based on detailed phenomenological modeling, we
+attribute the observed results with unexpected form of anisotropy to magnon MR
+resulting from magnon-electron coupling. Moreover, a similar angular dependence
+is also found in the transverse resistivity which we show to originate from the
+combination of ordinary Hall and anomalous Hall effects. Thus the interplay of
+magnetic and topological properties governs the magnetotransport features of
+this magnetic Weyl system.",2211.09798v1
+2022-11-30,A proposal for leaky integrate-and-fire neurons by domain walls in antiferromagnetic insulators,"Brain-inspired neuromorphic computing is a promising path towards next
+generation analogue computers that are fundamentally different compared to the
+conventional von Neumann architecture. One model for neuromorphic computing
+that can mimic the human brain behavior are spiking neural networks (SNNs), of
+which one of the most successful is the leaky integrate-and-fire (LIF) model.
+Since conventional complementary metal-oxide-semiconductor (CMOS) devices are
+not meant for modelling neural networks and are energy inefficient in network
+applications, recently the focus shifted towards spintronic-based neural
+networks. In this work, using the advantage of antiferromagnetic insulators, we
+propose a non-volatile magnonic neuron that could be the building block of a
+LIF spiking neuronal network. In our proposal, an antiferromagnetic domain wall
+in the presence of a magnetic anisotropy gradient mimics a biological neuron
+with leaky, integrating, and firing properties. This single neuron is
+controlled by polarized antiferromagnetic magnons, activated by either a
+magnetic field pulse or a spin transfer torque mechanism, and has properties
+similar to biological neurons, namely latency, refraction, bursting and
+inhibition. We argue that this proposed single neuron, based on
+antiferromagnetic domain walls, is faster and has more functionalities compared
+to previously proposed neurons based on ferromagnetic systems.",2211.16845v2
+2022-12-05,Propagating spin-wave spectroscopy in nanometer-thick YIG films at millikelvin temperatures,"Performing propagating spin-wave spectroscopy of thin films at millikelvin
+temperatures is the next step towards the realisation of large-scale integrated
+magnonic circuits for quantum applications. Here we demonstrate spin-wave
+propagation in a $100\,\mathrm{nm}$-thick yttrium-iron-garnet film at the
+temperatures down to $45 \,\mathrm{mK}$, using stripline nanoantennas deposited
+on YIG surface for the electrical excitation and detection. The clear
+transmission characteristics over the distance of $10\,\mu \mathrm{m}$ are
+measured and the subtracted spin-wave group velocity and the YIG saturation
+magnetisation agree well with the theoretical values. We show that the
+gadolinium-gallium-garnet substrate influences the spin-wave propagation
+characteristics only for the applied magnetic fields beyond $75\,\mathrm{mT}$,
+originating from a GGG magnetisation up to $47 \,\mathrm{kA/m}$ at $45
+\,\mathrm{mK}$. Our results show that the developed fabrication and measurement
+methodologies enable the realisation of integrated magnonic quantum
+nanotechnologies at millikelvin temperatures.",2212.02257v3
+2022-12-24,Anatomy of ultrafast quantitative magneto-acoustics in freestanding nickel thin films,"We revisit the quantitative analysis of the ultrafast magneto-acoustic
+experiment in a freestanding nickel thin film by Kim and Bigot [1] by applying
+our recently proposed approach of magnetic and acoustic eigenmodes
+decomposition by Vernik et al. [2]. We show that the application of our
+modeling to the analysis of time-resolved reflectivity measurements allows for
+the determination of amplitudes and lifetimes of standing perpendicular
+acoustic phonon resonances with unprecedented accuracy. The acoustic damping is
+found to scale as $\propto\omega^2$ for frequencies up to 80~GHz and the peak
+amplitudes reach $10^{-3}$. The experimentally measured magnetization dynamics
+for different orientations of an external magnetic field agrees well with
+numerical solutions of magneto-elastically driven magnon harmonic oscillators.
+Symmetry-based selection rules for magnon-phonon interactions predicted by our
+modeling approach allow for the unambiguous discrimination between spatially
+uniform and non-uniform modes, as confirmed by comparing the resonantly
+enhanced magneto-elastic dynamics simultaneously measured on opposite sides of
+the film. Moreover, the separation of time scales for (early) rising and (late)
+decreasing precession amplitudes provide access to magnetic (Gilbert) and
+acoustic damping parameters in a single measurement.",2212.12673v1
+2023-01-10,Magnetic anisotropy and low-energy spin dynamics in the van der Waals compounds Mn$_{2}$P$_{2}$S$_{6}$ and MnNiP$_{2}$S$_{6}$,"We report the detailed high-field and high-frequency electron spin resonance
+(HF-ESR) spectroscopic study of the single-crystalline van der Waals compounds
+Mn$_{2}$P$_{2}$S$_{6}$ and MnNiP$_{2}$S$_{6}$. Analysis of magnetic excitations
+shows that in comparison to Mn$_{2}$P$_{2}$S$_{6}$ increasing the Ni content
+yields a larger magnon gap in the ordered state and a larger g-factor value and
+its anisotropy in the paramagnetic state. The studied compounds are found to be
+strongly anisotropic having each the unique ground state and type of magnetic
+order. Stronger deviation of the g-factor from the free electron value in the
+samples containing Ni suggests that the anisotropy of the exchange is an
+important contributor to the stabilization of a certain type of magnetic order
+with particular anisotropy. At temperatures above the magnetic order, we have
+analyzed the spin-spin correlations resulting in a development of slowly
+fluctuating short-range order. They are much stronger pronounced in
+MnNiP$_{2}$S$_{6}$ compared to Mn$_{2}$P$_{2}$S$_{6}$. The enhanced spin
+fluctuations in MnNiP$_{2}$S$_{6}$ are attributed to the competition of
+different types of magnetic order. Finally, the analysis of the temperature
+dependent critical behavior of the magnon gaps below the ordering temperature
+in Mn$_{2}$P$_{2}$S$_{6}$ suggests that the character of the spin wave
+excitations in this compound undergoes a field induced crossover from a 3D-like
+towards 2D XY regime.",2301.04239v2
+2023-02-10,Traveling Salesman Problem solution using Magnonic Combinatorial Device,"Traveling Salesman Problem (TSP) is a decision-making problem that is
+essential for a number of practical applications. Today, this problem is solved
+on digital computers exploiting Boolean-type architecture by checking one by
+one a number of possible routes. In this work, we describe a special type of
+hardware for the TSP solution. It is a magnonic combinatorial device comprising
+magnetic and electric parts connected in the active ring circuit. There is a
+number of possible propagation routes in the magnetic mesh made of phase
+shifters, frequency filters, and attenuators. The phase shifters mimic cities
+in TSP while the distance between the cities is encoded in the signal
+attenuation. The set of frequency filters makes the waves on different
+frequencies propagate through the different routes. The principle of operation
+is based on the classical wave superposition. There is a number of waves coming
+in all possible routes in parallel accumulating different phase shifts and
+amplitude damping. However, only the wave(s) that accumulates the certain phase
+shift will be amplified by the electric part. The amplification comes first to
+the waves that possess the minimum propagation losses. It makes this type of
+device suitable for TSP solution, where waves are similar to the salesmen
+traveling in all possible routes at a time. We present the results of numerical
+modeling illustrating the TSP solutions for four and six cities. Also, we
+present experimental data for the TSP solution with four cities.",2302.04996v1
+2023-03-29,Stability of superconducting gap symmetries arising from antiferromagnetic magnons,"We consider a planar heterostructure consisting of a normal metal in
+proximity to an antiferromagnetic insulator, with an interlayer exchange
+coupling between the metal and the insulator. The coupling to the two
+sublattices of the antiferromagnetic insulator is allowed to be asymmetric. An
+effective electron-electron interaction in the normal metal, mediated by
+antiferromagnetic magnons in the insulator, is derived to second order in the
+interlayer exchange coupling. Particular emphasis is placed on including
+analytically derived expressions for the effective interactions including
+Umklapp processes in the solutions to the superconducting gap equation. The gap
+equation is first solved at the critical temperature as an eigenvalue problem
+by linearizing the gap equation. The eigenvectors yield information on the
+symmetry of the superconducting gap at the onset of superconductivity, and we
+derive a phase diagram for the order parameter in this case. In the various
+regimes of the phase diagram, we find $p$-wave, $f$-wave, and $d$-wave
+superconductivity, with $p$-wave superconductivity in the dominant part of the
+phase diagram. Umklapp processes, that come into play with increasing size of
+the Fermi surface, yield $f$- and $d$-wave symmetries as the preferred
+symmetries when band filling approaches half filling. To investigate the
+stability of this order parameter symmetry as the temperature is lowered, we
+also consider the nonlinear gap equation at zero temperature. We conclude that
+the phase diagram and the symmetries of the superconducting order parameter
+essentially are left intact as the temperature is lowered to zero temperature.",2303.16916v2
+2023-04-19,Dipole superfluid hydrodynamics,"We construct a theory of hydrodynamic transport for systems with conserved
+dipole moment, U(1) charge, energy, and momentum. These models have been
+considered in the context of fractons, since their elementary and isolated
+charges are immobile by symmetry, and have two known translation-invariant
+gapless phases: a ""p-wave dipole superfluid"" phase where the dipole symmetry is
+spontaneously broken and a ""s-wave dipole superfluid"" phase where both the U(1)
+and dipole symmetries are spontaneously broken. We argue on grounds of symmetry
+and thermodynamics that there is no transitionally-invariant gapless fluid with
+unbroken dipole symmetry. In this work, we primarily focus on the hydrodynamic
+description of p-wave dipole superfluids, including leading dissipative
+corrections. That theory has, in a sense, a dynamical scaling exponent $z=2$,
+and its spectrum of fluctuations includes novel subdiffusive modes $\omega \sim
+-i k^4$ in the shear sector and magnon-like sound mode $\omega\sim \pm k^2 -i
+k^2$. By coupling the fluid to background fields, we find response functions of
+the various symmetry currents. We also present a preliminary generalization of
+our work to s-wave dipole superfluids, which resemble $z=1$ fluids and feature
+sound waves and diffusive shear modes, as in an ordinary fluid. However, the
+spectrum also contains a magnon-like second-sound mode $\omega\sim \pm k^2 \pm
+k^4 -i k^4$ with subdiffusive attenuation.",2304.09852v2
+2023-05-15,Scattering of magnetostatic surface modes of ferromagnetic films by geometric defects,"Magnonics, an emerging field of Magnetism, studies spin waves (SWs) in
+nano-structures, with an aim towards possible applications. As information may
+be eventually transmitted with efficiency stored in the phase and amplitude of
+spin waves, a topic of interest within Magnonics is the propagation of SW
+modes. Thus, understanding mechanisms that may influence SW propagation is of
+interest. Here the effect of localized surface geometric defects on
+magnetostatic surface modes propagation is studied in ferromagnetic films and
+semi-infinite media. Theoretical results are developed that allow to calculate
+the scattering of these surface or Damon-Eshbach (DE) modes. A Green-Extinction
+theorem is used to determine the scattering of incident surface modes, through
+the determination of phase shifts of associated modes that are symmetric and
+anti-symmetric under inversion in the same geometry with geometric defects.
+Choosing localized symmetric depressions as geometric defects, scattering
+transmission coefficients are determined that show perfect transmission at
+specific frequencies or wave-lengths, that we associate with resonances in the
+system. Interestingly the system shows the appearance of localized modes in the
+depression regions, with associated discrete frequencies immersed in the
+continuum spectrum of these surface DE modes. These localized modes have a
+short wave-length content, and appear similarly in semi-infinite surfaces with
+depressions. The latter indicates that these types of scattering effects should
+appear in all surfaces with roughness or more pronounced geometric defects.",2305.08749v1
+2023-06-27,"Three-dimensional spin-wave dynamics, localization and interference in a synthetic antiferromagnet","Spin waves are collective perturbations in the orientation of the magnetic
+moments in magnetically ordered materials. Their rich phenomenology is
+intrinsically three dimensional, from the trajectory of the spin precession
+during their propagation, to the profiles of the spin-wave mode throughout the
+volume of the magnetic system. This gives rise to novel complex phenomena with
+high potential for applications in the field of magnonics. However, the
+three-dimensional imaging of spin waves, key to understanding and harnessing
+these phenomena, has so far not been possible. Here, we image the
+three-dimensional dynamics of spin waves excited in a synthetic
+antiferromagnet, with nanoscale spatial resolution and sub-ns temporal
+resolution, using time-resolved magnetic laminography. In this way, we map the
+distribution of the spin-wave modes throughout the volume of the structure,
+revealing unexpected depth-dependent profiles originating from the interlayer
+dipolar interaction. We experimentally demonstrate the existence of complex
+three-dimensional interference patterns, and analyze them via micromagnetic
+modelling. We find that these patterns are generated by the superposition of
+spin waves with non-uniform amplitude profiles, and that their features can be
+controlled by tuning the composition and structure of the magnetic system. Our
+results open unforeseen possibilities for the study of complex spin-wave modes
+and their interaction within nanostructures, and for the generation and
+manipulation of three-dimensional spin-wave landscapes for the design of novel
+functions in magnonic devices.",2306.15404v1
+2023-07-06,Spin transport from order to disorder,"Schwinger boson mean-field theory (SBMFT) is a non-perturbative approach
+which treats ordered and disordered phases of magnetic systems on equal
+footing. We leverage its versatility to evaluate the spin correlators which
+determine thermally-induced spin transport (the spin Seebeck effect) in
+Heisenberg ferromagnets (FMs) and antiferromagnets (AFs), at arbitrary
+temperatures. In SBMFT, the spin current, $J_s$, is made up of
+particle-hole-like excitations which carry integral spin angular momentum. Well
+below the ordering temperature, $J_s$ is dominated by a magnonic contribution,
+reproducing the behavior of a dilute-magnon gas. Near the transition
+temperature, an additional, paramagnetic-like contribution becomes significant.
+In the AF, the two contributions come with opposite signs, resulting in a
+signature, rapid inversion of the spin Seebeck coefficient as a function of
+temperature. Ultimately, at high temperatures, the low-field behavior of the
+paramagnetic SSE reduces to Curie-Weiss physics. Analysis based on our theory
+confirms that in recent experiments on gadolinium gallium garnet, the low-field
+spin Seebeck coefficient $\mathcal{S}(T) \propto \chi(T)$, the spin
+susceptibility, down to the Curie-Weiss temperature. At lower temperatures in
+the disordered phase, our theory shows a deviation of $\mathcal{S}(T)$ relative
+to $\chi(T)$ in both FMs and AFs, which increases with decreasing temperature
+and arises due to a paramagnetic liquid phase in our theory. These results
+demonstrate that the SSE can be a probe of the short-ranged magnetic
+correlations in disordered correlated spin systems and spin liquids.",2307.02734v1
+2023-07-12,Anisotropic in-plane heat transport of Kitaev magnet Na$_2$Co$_2$TeO$_6$,"We report a study on low-temperature heat transport of Kitaev magnet
+Na$_2$Co$_2$TeO$_6$, with the heat current and magnetic fields along the
+honeycomb spin layer (the $ab$ plane). The zero-field thermal conductivity of
+$\kappa^a_{xx}$ and $\kappa^{a*}_{xx}$ display similar temperature dependence
+and small difference in their magnitudes; whereas, their magnetic field
+(parallel to the heat current) dependence are quite different and are related
+to the field-induced magnetic transitions. The $\kappa^a_{xx}(B)$ data for $B
+\parallel a$ at very low temperatures have an anomaly at 10.25--10.5 T, which
+reveals an unexplored magnetic transition. The planar thermal Hall conductivity
+$\kappa^a_{xy}$ and $\kappa^{a*}_{xy}$ show very weak signals at low fields and
+rather large values with sign change at high fields. This may point to a
+possible magnetic structure transition or the change of the magnon band
+topology that induces a radical change of magnon Berry curvature distribution
+before entering the spin polarized state. These results put clear constraints
+on the high-field phase and the theoretical models for Na$_2$Co$_2$TeO$_6$.",2307.06316v1
+2023-07-14,Magnonic Combinatorial Memory,"In this work, we consider a type of magnetic memory where information is
+encoded into the mutual arrangements of magnets. The device is an active ring
+circuit comprising magnetic and electronic parts connected in series. The
+electric part includes a broad-band amplifier, phase shifters, and attenuators.
+The magnetic part is a mesh of magnonic waveguides with magnets placed on the
+waveguide junctions. There are amplitude and phase conditions for
+auto-oscillations to occur in the active ring circuit. The frequency(s) of the
+auto-oscillation and spin wave propagation route(s) in the magnetic part
+depends on the mutual arrangement of magnets in the mesh. The propagation route
+is detected with a set of power sensors. The correlation between circuit
+parameters and spin wave route is the base of memory operation. The combination
+of input/output switches connecting electric and magnetic parts, and electric
+phase shifters constitute the memory address. The output of power sensors is
+the memory state. We present experimental data on the proof-of-the-concept
+experiments on the prototype with just three magnets placed on top of a
+single-crystal yttrium iron garnet Y3Fe2(FeO4)3 (YIG) film. The results
+demonstrate a robust operation with On/Off ratio for route detection exceeding
+35 dB at room temperature. The number of propagation routes scales factorial
+with the size of the magnetic part. Coding information in propagation routes
+makes it possible to drastically increase the data storage density compared to
+conventional memory devices. MCM with just 25 magnets can store as much as 25!
+(10 Yotta) bits. Physical limits and constraints are also discussed.",2307.07464v1
+2023-07-30,Spin dynamics in ordered phases of anisotropic triangular-lattice antiferromagnet Cs2CoBr4,"We study spin dynamics of ordered phases of Cs2CoBr4 in a magnetic field
+using electron spin resonance (ESR) technique and theoretical analysis. This
+material hosts weakly interacting distorted-triangular-lattice planes of
+spin-3/2 Co(2+) ions which can be viewed as spin chains coupled by frustrating
+interactions. Strong single-ion anisotropy allows to describe the low-energy
+spin dynamics of this system by an effective strongly anisotropic
+pseudospin-1/2 model. Our ESR data show up to seven branches of magnetic
+resonance in four magnetic phases arising due to subtle interplay of
+frustration, low dimensionality and strong anisotropy. In particular, in the
+low-field collinear stripe phase, the field evolution of modes lying below 200
+GHz is described reasonably good by spectra of spin-1 and spin-0 quasiparticles
+which we obtain using the bond-operator technique. These well-defined
+excitations can be treated as conventional magnons and bound states of two
+magnons, respectively. In contrast, numerous excitations lying above 200 GHz
+are not captured by our theory due to pronounced one-dimensional correlations
+inside spin chains which govern the spin dynamics at high enough energies. As
+it was shown before, these modes can be most naturally interpreted as bound
+states of domain walls in individual chains and their sequence resembles the
+so-called ""Zeeman ladder"" in anisotropic Ising-like spin chains. Thus, Cs2CoBr4
+is a system showing spin-dynamics in ordered state characteristic of both
+two-dimensional and one-dimensional magnets.",2307.16251v1
+2023-08-15,Tuning the confinement potential between spinons in the Ising chain CoNb2O6 using longitudinal fields and quantitative determination of the microscopic Hamiltonian,"The Ising chain realizes the fundamental paradigm of spin fractionalization,
+where locally flipping a spin creates two domain walls (spinons) that can
+separate apart at no energy cost. In a quasi-one-dimensional system, the
+mean-field effects of the weak three-dimensional couplings confine the spinons
+into a Zeeman ladder of two-spinon bound states. Here, we experimentally tune
+the confinement potential between spinons in the quasi-one-dimensional Ising
+ferromagnet CoNb2O6 by means of an applied magnetic field with a large
+component along the Ising direction. Using high-resolution single crystal
+inelastic neutron scattering, we directly observe how the spectrum evolves from
+the limit of very weak confinement at low field (with many closely-spaced bound
+states with energies scaling as the field strength to the power 2/3) to very
+strong confinement at high field (where it consists of a magnon and a
+dispersive two-magnon bound state, with a linear field dependence). At
+intermediate fields, we explore how the higher-order bound states disappear
+from the spectrum as they move to higher energies and overlap with the
+two-particle continuum. By performing a global fit to the observed spectrum in
+zero field and high field applied along two orthogonal directions, combined
+with a quantitative parameterization of the interchain couplings, we propose a
+refined single chain and interchain Hamiltonian that quantitatively reproduces
+all observed dispersions and their field dependence.",2308.07699v2
+2023-10-17,Low-energy electronic interactions in ferrimagnetic Sr2CrReO6 thin films,"We reveal in this study the fundamental low-energy landscape in the
+ferrimagnetic Sr2CrReO6 double perovskite and describe the underlying
+mechanisms responsible for the three low-energy excitations below 1.4 eV. Based
+on resonant inelastic x-ray scattering and magnetic dynamics calculations, and
+experiments collected from both Sr2CrReO6 powders and epitaxially strained thin
+films, we reveal a strong competition between spin-orbit coupling, Hund's
+coupling, and the strain-induced tetragonal crystal field. We also demonstrate
+that a spin-flip process is at the origin of the lowest excitation at 200 meV,
+and we bring insights into the predicted presence of orbital ordering in this
+material. We study the nature of the magnons through a combination of ab initio
+and spin-wave theory calculations, and show that two nondegenerate magnon bands
+exist and are dominated either by rhenium or chromium spins. The rhenium band
+is found to be flat at about 200 meV ($\pm$25 meV) through X-L-W-U
+high-symmetry points and is dispersive toward $\Gamma$",2310.11585v1
+2023-11-06,Exploiting polarization dependence in two dimensional coherent spectroscopy: examples of Ce$_2$Zr$_2$O$_7$ and Nd$_2$Zr$_2$O$_7$,"Two dimensional coherent spectroscopy (2DCS) probes the nonlinear optical
+response of correlated systems. An interesting application is the study of
+fractionalized excitations, which are challenging to distinguish unambiguously
+in linear response. Here we demonstrate how the sensitivity of optical matrix
+elements to variations in the photon polarization allows one to probe different
+aspects of low lying excitations in models of the candidate fractionalized
+materials Ce$_2$Zr$_2$O$_7$ and Nd$_2$Zr$_2$O$_7$, which host effective
+one-dimensional spin chains when subjected to a [110] magnetic field. We show
+how both fractionalized spinon excitations or conventional magnons can be
+picked out in the 2DCS response, and how the response from polarized spin
+chains can be used to probe the dipolar-octupolar mixing angle $\theta$ through
+the relative intensity of one- and two-magnon signals. Further, we find that a
+$[001]$ polarization of the probe field is particularly sensitive to lower band
+edge of the spinon continuum and can be used as a measure of the proximity of a
+quantum critical point in Ce$_2$Zr$_2$O$_7$. 2DCS can thus be employed to
+provide invaluable and detailed information both on the constituent degrees of
+freedom of a quantum material and on their collective behaviour.",2311.03200v1
+2023-11-23,Two-dimensional coherent spectrum of high-spin models via a quantum computing approach,"We present and benchmark a quantum computing approach to calculate the
+two-dimensional coherent spectrum (2DCS) of high-spin models. Our approach is
+based on simulating their real-time dynamics in the presence of several
+magnetic field pulses, which are spaced in time. We utilize the adaptive
+variational quantum dynamics simulation (AVQDS) algorithm for the study due to
+its compact circuits, which enables simulations over sufficiently long times to
+achieve the required resolution in frequency space. Specifically, we consider
+an antiferromagnetic quantum spin model that incorporates Dzyaloshinskii-Moriya
+interactions and single-ion anisotropy. The obtained 2DCS spectra exhibit
+distinct peaks at multiples of the magnon frequency, arising from transitions
+between different eigenstates of the unperturbed Hamiltonian. By comparing the
+one-dimensional coherent spectrum with 2DCS, we demonstrate that 2DCS provides
+a higher resolution of the energy spectrum. We further investigate how the
+quantum resources scale with the magnitude of the spin using two different
+binary encodings of the high-spin operators: the standard binary encoding and
+the Gray code. At low magnetic fields both encodings require comparable quantum
+resources, but at larger field strengths the Gray code is advantageous. Lastly,
+we compare the numerical 2DCS with experimental results on a rare-earth
+orthoferrite system. The observed strength of the magnonic high-harmonic
+generation signals in the 2DCS of the quantum high-spin model aligns well with
+the experimental data, showing significant improvement over the corresponding
+mean-field results.",2311.14035v2
+2023-12-14,"Nonlocal damping of spin waves in a magnetic insulator induced by normal, heavy, or altermagnetic metallic overlayer: a Schwinger-Keldysh field theory approach","Understanding spin wave (SW) damping, and how to control it to the point of
+being able to amplify SW-mediated signals, is one of the key requirements to
+bring the envisaged magnonic technologies to fruition. Even widely used
+magnetic insulators with low magnetization damping in their bulk, such as
+yttrium iron garnet, exhibit 100-fold increase in SW damping due to inevitable
+contact with metallic layers in magnonic circuits, as observed in very recent
+experiments [I. Bertelli et al., Adv. Quantum Technol. 4, 2100094 (2021)]
+mapping SW damping in spatially-resolved fashion. Here, we provide microscopic
+and rigorous understanding of wavevector-dependent SW damping using extended
+Landau-Lifshitz-Gilbert equation with nonlocal damping tensor, instead of
+conventional local scalar Gilbert damping, as derived from Schwinger-Keldysh
+nonequilibrium quantum field theory. In this picture, the origin of nonlocal
+magnetization damping and thereby induced wavevector-dependent SW damping is
+interaction of localized magnetic moments of magnetic insulator with conduction
+electrons from the examined three different types of metallic overlayers --
+normal, heavy, and altermagnetic. Due to spin-split energy-momentum dispersion
+of conduction electrons in the latter two cases, the nonlocal damping is
+anisotropic in spin and space, and it can be dramatically reduced by changing
+the relative orientation of the two layers when compared to the usage of normal
+metal overlayer.",2312.09140v1
+2023-12-16,Topological phase transitions and thermal Hall effect in a noncollinear spin texture,"The noncollinear spin textures provide promising avenues to stabilize exotic
+magnetic phases and excitations. They have attracted vast attention owning to
+their nontrivial band topology in the past decades. Distinct from the
+conventional route of involving the Dzyaloshinskii-Moriya interaction in a
+honeycomb magnet, the interplay of bond-dependent Kitaev and $\Gamma$
+interactions, originating from the spin-orbit coupling and octahedra crystal
+field in real materials, has demonstrated to be another source to generate
+noncollinear spin textures with multiple spins in a magnetic unit cell.
+Notably, earlier works have revealed a triple-meron crystal (TmX) consisting of
+eighteen spins in the frustrated Kitaev-$\Gamma$ model. Aligning with previous
+efforts, here we attempt to identity that the TmX hosts several peculiar
+features with the help of the linear spin-wave theory. To begin with, the
+symmetric anisotropic exchanges are beneficial for the existence of
+nonreciprocal magnons, which are stabilized by an external magnetic field.
+Further, within the regime of TmX, successive topological phase transitions
+occur, accompanied by the changes of Chern number in value and thermal Hall
+conductivity in sign. In addition, topological nature of magnons is also
+verified by the onset of chiral edge modes in a nanoribbon geometry. Our
+findings pave the way to study topological phenomena of noncollinear spin
+textures in potential Kitaev materials.",2312.10473v1
+2024-01-12,Scanning spin probe based on magnonic vortex quantum cavities,"Performing nanoscale scanning electron paramagnetic resonance (EPR) requires
+three essential ingredients. First, a static magnetic field together to field
+gradients to Zeeman split the electronic energy levels with spatial resolution.
+Second, a radiofrequency (rf) magnetic field capable of inducing spin
+transitions. Finally, a sensitive detection method to quantify the energy
+absorbed by spins. This is usually achieved by combining externally applied
+magnetic fields with inductive coils or cavities, fluorescent defects or
+scanning probes. Here, we theoretically propose the realization of a EPR
+scanning sensor merging all three characteristics into a single device: the
+vortex core stabilized in ferromagnetic thin-film discs. On one hand, the
+vortex ground state generates a significant static magnetic field and field
+gradients. On the other hand, the precessional motion of the vortex core around
+its equilibrium position produces a circularly polarized oscillating magnetic
+field, which is enough to produce spin transitions. Finally, the spin-magnon
+coupling broadens the vortex gyrotropic frequency, suggesting a direct measure
+of the presence of unpaired electrons. Moreover, the vortex core can be
+displaced by simply using external magnetic fields of a few mT, enabling EPR
+scanning microscopy with large spatial resolution. Our numerical simulations
+show that, by using low damping magnets, it is theoretically possible to detect
+single spins located on the disc's surface. Vortex nanocavities could also
+attain strong coupling to individual spin molecular qubits, with potential
+applications to mediate qubit-qubit interactions or to implement qubit readout
+protocols.",2401.06549v1
+2024-01-25,Thermal and Magnetoelastic Properties of the van der Waals Ferromagnet Fe$_{3-δ}$GeTe$_2$: Anisotropic Spontaneous Magnetostriction and Ferromagnetic Magnon Excitations,"By determining the lattice parameters as a function of temperature of the
+hexagonal van der Waals ferromagnet Fe$_{2.92(1)}$Ge$_{1.02(3)}$Te$_2$ we
+obtain the temperature dependence of the spontaneous in-plane magnetostriction
+in the ferromagnetic and the linear thermal expansion coefficients in the
+paramagnetic state. The spontaneous magnetostriction is clearly seen in the
+temperature dependence of the in-plane lattice parameter $a(T)$, but less well
+pronounced perpendicular to the planes along $c$. Below $T_{\rm C}$ the
+spontaneous magnetostriction follows the square of the magnetization and leads
+to an expansion of the hexagonal layers. Extrapolating to $T\rightarrow$ 0~K we
+obtain a spontaneous in-plane saturation magnetostriction of $\lambda_{{\rm
+sp},a}(T \rightarrow 0) \approx-220 ~\times~10^{-6}$. In the paramagnetic state
+the linear thermal expansion coefficients amount to
+13.9(1)$\times$10$^{-6}$~K$^{-1}$ and to 23.2(2)$\times$10$^{-6}$~K$^{-1}$ for
+the in-plane and out-of-plane direction, respectively, indicating a linear
+volume thermal expansion coefficient of 50.8(4)$\times$10$^{-6}$K$^{-1}$ which
+we use to estimate the volume thermal expansion contribution to the heat
+capacity determined at constant pressure. A Sommerfeld-type linear term in the
+low-temperature heat capacities can be quantitatively ascribed to 2dim
+ferromagnetic magnon excitations.",2401.14050v1
+2024-01-31,Magnetic polarons beyond linear spin-wave theory: Mesons dressed by magnons,"When a mobile hole is doped into an antiferromagnet, its movement will
+distort the surrounding magnetic order and yield a magnetic polaron. The
+resulting complex interplay of spin and charge degrees of freedom gives rise to
+very rich physics and is widely believed to be at the heart of high-temperature
+superconductivity in cuprates. In this paper, we develop a quantitative
+theoretical formalism, based on the phenomenological parton description, to
+describe magnetic polarons in the strong coupling regime. We construct an
+effective Hamiltonian with weak coupling to the spin-wave excitations in the
+background, making the use of standard polaronic methods possible. Our starting
+point is a single hole doped into an AFM described by a 'geometric string'
+capturing the strongly correlated hopping processes of charge and spin degrees
+of freedom, beyond linear spin-wave approximation. Subsequently, we introduce
+magnon excitations through a generalized 1/S expansion and derive an effective
+coupling of these spin-waves to the hole plus the string (the meson) to arrive
+at an effective polaron Hamiltonian with density-density type interactions.
+After making a Born-Oppenheimer-type approximation, this system is solved using
+the self-consistent Born approximation to extract the renormalized polaron
+properties. We apply our formalism (i) to calculate beyond linear spin-wave
+ARPES spectra, (ii) to reveal the interplay of ro-vibrational meson
+excitations, and (ii) to analyze the pseudogap expected at low doping.
+Moreover, our work paves the way for exploring magnetic polarons out-of
+equilibrium or in frustrated systems, where weak-coupling approaches are
+desirable and going beyond linear spin-wave theory becomes necessary.",2402.00130v1
+2024-02-02,Structural and optical characterization of NiO polycrystalline thin films fabricated by spray-pyrolysis,"Nickel (II) oxide, NiO, a wide band gap Mott insulator characterized by
+strong Coulomb repulsion between d-electrons and displaying antiferromagnetic
+order at room temperature, has gained attention in recent years as a very
+promising candidate for applications in a broad set of areas, including
+chemistry and metallurgy to spintronics and energy harvesting. Here, we report
+on the synthesis of polycrystalline NiO fabricated using spray-pyrolysis
+technique, which is a deposition technique able to produce quite uniform films
+of pure and crystalline materials without the need of high vacuum or inert
+atmospheres. We then characterized the composition and structure of our NiO
+thin films using X-ray diffraction, and atomic force and scanning electron
+microscopies, respectively. We completed our study by looking at the phononic
+and magnonic properties of our NiO thin films via Raman spectroscopy, and at
+the ultrafast electron dynamics by using optical pump probe spectroscopy. We
+found that our NiO samples display the same phononic and magnonic dispersion
+expected for single crystal NiO at room temperature, and that electron dynamics
+in our system is similar to those of previously reported NiO mono- and
+poli-crystalline systems synthesized with different techniques. These results
+prove that spray-pyrolysis can be used as affordable and large-scale
+fabrication technique to synthetize strongly correlated materials for a large
+set of applications.",2402.01437v1
+2024-02-29,Resonant generation of propagating second-harmonic spin waves in nano-waveguides,"Generation of second-harmonic waves is one of the universal nonlinear
+phenomena that have found numerous technical applications in many modern
+technologies, in particular, in photonics. This phenomenon also has great
+potential in the field of magnonics, which considers the use of spin waves in
+magnetic nanostructures to implement wave-based signal processing and
+computing. However, due to the strong frequency dependence of the phase
+velocity of spin waves, resonant phase-matched generation of second-harmonic
+spin waves has not yet been achieved in practice. Here, we show experimentally
+that such a process can be realized using a combination of different modes of
+nano-sized spin-wave waveguides based on low-damping magnetic insulators. We
+demonstrate that our approach enables efficient spatially-extended energy
+transfer between interacting waves, which can be controlled by the intensity of
+the initial wave and the static magnetic field. The demonstrated approach can
+be used for the generation of short-wavelength spin waves that are difficult to
+excite directly, as well as for the implementation of novel devices for
+magnonic logic and unconventional computing.",2402.18964v1
+2024-03-15,"Microscopic Modeling, Multi-magnon condensation and Strain effect in chain compound NaVOPO$_4$","Employing first-principles modelling and many-body methods, the magnetic
+properties of spin-1/2 chain compound NaVOPO$_4$ are explored. The extensive
+first-principles calculations establish an intricate three-dimensionally
+coupled model that consists of weakly alternating $J$-$J^{'}$ antiferromagnetic
+chains running along cris-cross directions between two consecutive $ab$ planes,
+connected via two subleading couplings, a ferromagnetic exchange along the $c$
+direction ($J_c$) and a weaker antiferromagnetic exchange ($J_a$) along the
+body diagonal direction. The exact diagonalization and density matrix
+renormalized group study have been carried out on a two-dimensional spin model
+with $J$-$J^{'}$-$J_c$ and effective $J_d$ couplings, constructed based on the
+full model, for numerical ease. The $J_c$-$J_d$ phase diagram is found to host
+a {\it disorder} phase with finite spin gap for comparable values of $J_c$ and
+$J_d$, arising out of the competing nature of these two interactions, other
+than two ordered phases. The predominant manifestation of $J_c$ and $J_d$ in
+the disorder phase happens in stabilisation of a multi-magnon condensed phase,
+upon gap closing by application of an external magnetic field. We further
+explore the effect of tensile uniaxial strain, which is found to drive the
+system from gapful to gapless ground state.",2403.10025v1
+2024-04-03,Discovery of universal phonon thermal Hall effect in crystals,"Thermal Hall effect (THE) in insulator is a remarkable phenomenon that arises
+from the motion of chargeless quasi-particles under a magnetic field. While
+magnons or exotic spin excitations were considered as the origin of THE in some
+magnetic materials, there are more and more evidences suggest that phonons play
+a significant role. However, the mechanism behind phonon THE is still unknown.
+Here we report the observation of THE, including planar THE, in a broad range
+of non-magnetic insulators and semiconductor: SrTiO$_3$, SiO$_2$ (quartz), MgO
+and Si. While the presence of antiferrodistortive domains in SrTiO$_3$ and
+chiral phonons in SiO$_2$ may complicate the interpretation of THE, the
+striking observations of THE in the trivial insulator MgO and high-purity
+intrinsic semiconductor Si demonstrate that phonon THE is a universal property
+of crystals. Without other effects on phonons such as from magnons, this
+universal phonon THE is characterized by a scaling law of |$\kappa_{xy}$|
+$\sim$ $\kappa_{xx}^2$. Our results experimentally discover a fundamental
+physics of phonons in magnetic field, which must come from the direct coupling
+between atom vibrations and the field. Starting from this universal phonon THE
+in crystals, all previous interpretations of THE in magnetic or non-magnetic
+materials need to be reconsidered.",2404.02863v1
+2024-04-06,Non-volatile spin transport in a single domain multiferroic,"Antiferromagnets have attracted significant attention in the field of
+magnonics, as promising candidates for ultralow-energy carriers for information
+transfer for future computing. The role of crystalline orientation distribution
+on magnon transport has received very little attention. In multiferroics such
+as BiFeO$_3$ the coupling between antiferromagnetic and polar order imposes yet
+another boundary condition on spin transport. Thus, understanding the
+fundamentals of spin transport in such systems requires a single domain, a
+single crystal. We show that through Lanthanum(La) substitution, a single
+ferroelectric domain can be engineered with a stable, single-variant spin
+cycloid, controllable by an electric field. The spin transport in such a single
+domain displays a strong anisotropy, arising from the underlying spin cycloid
+lattice. Our work shows a pathway to understand the fundamental origins of spin
+transport in such a single domain multiferroic.",2404.04746v1
+1997-05-06,Resonant Raman Scattering in Antiferromagnets,"Two-magnon Raman scattering provides important information about electronic
+correlations in the insulating parent compounds of high-$T_c$ materials. Recent
+experiments have shown a strong dependence of the Raman signal in $B_{1g}$
+geometry on the frequency of the incoming photon. We present an analytical and
+numerical study of the Raman intensity in the resonant regime. It has been
+previously argued by one of us (A.Ch) and D. Frenkel that the most relevant
+contribution to the Raman vertex at resonance is given by the triple resonance
+diagram. We derive an expression for the Raman intensity in which we
+simultaneously include the enhancement due to the triple resonance and a final
+state interaction. We compute the two-magnon peak height (TMPH) as a function
+of incident frequency and find two maxima at $\omega^{(1)}_{res} \approx
+2\Delta + 3J$ and $\omega^{(2)}_{res} \approx 2\Delta + 8J$. We argue that the
+high-frequency maximum is cut only by a quasiparticle damping, while the
+low-frequency maximum has a finite amplitude even in the absence of damping. We
+also obtain an evolution of the Raman profile from an asymmetric form around
+$\omega^{(1)}_{res}$ to a symmetric form around $\omega^{(2)}_{res}$. We
+further show that the TMPH depends on the fermionic quasiparticle damping, the
+next-nearest neighbor hopping term $t^{\prime}$ and the corrections to the
+interaction vertex between light and the fermionic current. We discuss our
+results in the context of recent experiments by Blumberg et al. on
+$Sr_2CuO_2Cl_2$ and $YBa_2Cu_3O_{6.1}$ and R\""{u}bhausen et al. on
+$PrBa_2Cu_3O_7$ and show that the triple resonance theory yields a qualitative
+and to some extent also quantitative understanding of the experimental data.",9705051v1
+1999-06-03,Optical spectroscopic study of the interplay of spin and charge in NaV2O5,"We investigate the temperature dependent optical properties of NaV2O5, in the
+energy range 4meV-4eV. The symmetry of the system is discussed on the basis of
+infrared phonon spectra. By analyzing the optically allowed phonons at
+temperatures below and above the phase transition, we conclude that a
+second-order change to a larger unit cell takes place below 34 K, with a
+fluctuation regime extending over a broad temperature range. In the high
+temperature undistorted phase, we find good agreement with the recently
+proposed centrosymmetric space group Pmmn. On the other hand, the detailed
+analysis of the electronic excitations detected in the optical conductivity,
+provides direct evidence for a charge disproportionated electronic
+ground-state, at least on a locale scale: A consistent interpretation of both
+structural and optical conductivity data requires an asymmetrical charge
+distribution on each rung, without any long range order. We show that, because
+of the locally broken symmetry, spin-flip excitations carry a finite electric
+dipole moment, which is responsible for the detection of direct two-magnon
+optical absorption processes for E parallel to the a axis. The charged-magnon
+model, developed to interpret the optical conductivity of NaV2O5, is described
+in detail, and its relevance to other strongly correlated electron systems,
+where the interplay of spin and charge plays a crucial role in determining the
+low energy electrodynamics, is discussed.",9906042v2
+2005-10-07,Magnetic and Charge Correlations in La{2-x-y}Nd_ySr_xCuO_4: Raman Scattering Study,"Two aspects in connection with the magnetic properties of
+La_{2-x-y}Nd_ySr_xCuO_4 single crystals are discussed. The first is related to
+long wavelength magnetic excitations in x = 0, 0.01, and 0.03 La_{2-x}Sr_xCuO_4
+detwinned crystals as a function of doping, temperature and magnetic field. Two
+magnetic modes were observed within the AF region of the phase diagram. The one
+at lower energies was identified with the spin-wave gap induced by the
+antisymmetric DM interaction and its anisotropic properties in magnetic field
+could be well explained using a canonical form of the spin Hamiltonian. A new
+finding was a magnetic field induced mode whose dynamics allowed us to discover
+a spin ordered state outside the AF order which was shown to persist in a 9 T
+field as high as 100 K above the N\'eel temperature T_N for x = 0.01. For these
+single magnon excitations we map out the Raman selection rules in magnetic
+fields and demonstrate that their temperature dependent spectral weight is
+peaked at the N\'eel temperature. The second aspect is related to phononic and
+magnetic Raman scattering in La_{2-x-y}Nd_ySr_xCuO_4 with three doping
+concentrations: x = 1/8, y = 0; x = 1/8, y = 0.4; and x = 0.01, y = 0. We
+observed that around 1/8 Sr doping and independent of Nd concentration there
+exists substantial disorder in the tilt pattern of the CuO_6 octahedra in both
+the orthorhombic and tetragonal phases which persist down to 10 K and are
+coupled to bond disorder in the cation layers. The weak magnitude of existing
+charge/spin modulations in the Nd doped structure did not allow us to detect
+specific Raman signatures on lattice dynamics or two-magnon scattering around
+2200 cm-1.",0510191v1
+2005-12-08,High-field Magnetic Torque Measurements in (CH$_3$)$_2$CHNH$_3$CuCl$_3$,"High-field magnetic torque measurements were carried out in the spin gap
+system (CH$_3$)$_2$CHNH$_3$CuCl$_3$. It was observed that the magnitude of the
+magnetic torque $\tau$ is almost zero until the critical field and then
+increases rapidly, which indicates the existence of the magnetic quantum phase
+transition from the spin-gap phase to the field-induced magnetic ordered phase.
+  From the temperature dependence of the magnetic torque $\tau$, the cusp-like
+minimum indicative of the Bose-Einstein condensation (BEC) of magnons was
+observed for $H \perp$ C-plane, while the kink-anomaly was observed for $H
+\perp$ A-plane at the field-induced transition temperature. It was found that
+this different behavior between $H \perp$ A-plane and $H \perp$ C-plane can be
+interpreted as the breaking of the magnon BEC picture due to the rotational
+symmetry breaking. The additional anomaly was also observed in the
+field-induced magnetic ordered phase at the intermediate angle of the applied
+magnetic field in the A-plane and discussed in terms of the spin-flop
+transition, the spin-reorientation transition and the spin-lattice
+correlations. In order to investigate the spin-lattice correlations in
+(CH$_3$)$_2$CHNH$_3$CuCl$_3$, we performed the magnetostriction measurements
+and observed that the magnetostriction appears by vanishing of the spin gap.",0512164v2
+2008-08-25,Low energy theory of the t-t'-t''-U Hubbard Model at half-filling: interaction strengths in cuprate superconductors and an effective spin-only description of La_2CuO_4,"Spin-only descriptions of the half-filled one-band Hubbard model are relevant
+for a wide range of Mott insulators. In addition to the usual Heisenberg
+exchange, many new types of interactions, including ring exchange, appear in
+the effective Hamiltonian in the intermediate coupling regime. In order to
+improve on the quantitative description of magnetic excitations in the
+insulating antiferromagnetic phase of copper-oxide (cuprate) materials, and to
+be consistent with band structure calculations and photoemission experiments on
+these systems, we include second and third neighbor hopping parameters, t' and
+t'', into the Hubbard Hamiltonian. A unitary transformation method is used to
+find systematically the effective Hamiltonian and any operator in the spin-only
+representation. The results include all closed, four hop electronic pathways in
+the canonical transformation. The method generates many ring exchange terms
+that play an important role in the comparison with experiments on La2CuO4.
+Performing a spin wave analysis, we calculate the magnon dispersion as a
+function of U,t,t' and t''. The four parameters are estimated by fitting the
+magnon dispersion to the experimental results of Coldea et al. [Phys. Rev.
+Lett. 86, 5377, {2001}] for La2CuO4. The ring exchange terms are found
+essential, in particular to determine the relative sign of t' and t'', with the
+values found in good agreement with independent theoretical and experimental
+estimates for other members of the cuprate family. The zero temperature
+sublattice magnetization is calculated using these parameters and also found to
+be in good agreement with the experimental value estimated by Lee et al. [Phys.
+Rev. B 60, 3643 (1999)]. We find a value of the interaction strength U~8t
+consistent with Mott insulating behavior.",0808.3167v1
+2009-10-02,"On the room temperature multiferroic BiFeO3: Magnetic, dielectric and thermal properties","Magnetic dc susceptibility between 1.5 and 800 K, ac susceptibility and
+magnetization, thermodynamic properties, temperature dependence of radio and
+audio-wave dielectric constants and conductivity, contact-free dielectric
+constants at mm-wavelengths, as well as ferroelectric polarization are reported
+for single crystalline BiFeO3. A well developed anomaly in the magnetic
+susceptibility signals the onset of antiferromagnetic order close to 635 K.
+Beside this anomaly no further indications of phase or glass transitions are
+indicated in the magnetic dc and ac susceptibilities down to the lowest
+temperatures. The heat capacity has been measured from 2 K up to room
+temperature and significant contributions from magnon excitations have been
+detected. From the low-temperature heat capacity an anisotropy gap of the
+magnon modes of the order of 6 meV has been determined. The dielectric
+constants measured in standard two-point configuration are dominated by
+Maxwell-Wagner like effects for temperatures T > 300 K and frequencies below 1
+MHz. At lower temperatures the temperature dependence of the dielectric
+constant and loss reveals no anomalies outside the experimental errors,
+indicating neither phase transitions nor strong spin phonon coupling. The
+temperature dependence of the dielectric constant was measured contact free at
+microwave frequencies. At room temperature the dielectric constant has an
+intrinsic value of 53. The loss is substantial and strongly frequency dependent
+indicating the predominance of hopping conductivity. Finally, in small thin
+samples we were able to measure the ferroelectric polarization between 10 and
+200 K. The saturation polarization is of the order of 40 microC/cm^2,
+comparable to reports in literature.",0910.0385v2
+2013-10-25,Quantum magnons of the intermediate phase of half-doped manganite oxides,"At half doping, the ground state of three-dimensional manganite perovskite
+oxides like R$_{1-x}$Ca$_x$MnO$_3$, where R is a trivalent ion such as La, Pr,
+etc, is still unclear. Many experimental findings agree better with the
+combined magnetic, charge, and orbital order characteristic of the
+""intermediate phase"", introduced by Efremov et al. in 2004 [Nature Mats. 3,
+853]. This phase consists of spin dimers (thus incorporating aspects of the
+Zener polaron phase (ZP) proposed in 2002 by Daoud-Aladine et al. [Phys. Rev.
+Lett. 89, 097205]), though formed by a pair of parallel Mn spins of different
+magnitude, in principle (thereby allowing for a degree of Mn charge
+disproportionation: not necessarily as large as that of Mn$^{3+}$-Mn$^{4+}$ in
+Goodenough's original CE phase [Phys. Rev. 100, 564 (1955)]). In the
+intermediate phase, consecutive spin dimers localed along the planar zig-zag
+chains are oriented at a constant relative angle $\Phi$ between them. Varying
+Mn-charge disproportionation and $\Phi$, the intermediate phase should allow to
+continuously interpolate between the two limiting cases of the CE phase and the
+dimer phase denoted as ""orthogonal intermediate $\pi/2-$phase"". It is not easy
+to find a microscopic model able to describe the phenomenological intermediate
+phase adequately for the spin, charge, and orbital degrees of freedom
+simultaneously. Here, we study the quantum spin excitations of a planar model
+of interacting localized spins, which we found can stabilize the intermediate
+phase classically. We compare the quantum magnons of the intermediate phase
+with those of the CE and orthogonal $\pi/2$ phases, in the context of recent
+experimental results.",1310.6954v1
+2015-11-30,Generalized isotropic Lipkin-Meshkov-Glick models: ground state entanglement and quantum entropies,"We introduce a new class of generalized isotropic Lipkin-Meshkov-Glick models
+with su$(m+1)$ spin and long-range non-constant interactions, whose
+non-degenerate ground state is a Dicke state of su$(m+1)$ type. We evaluate in
+closed form the reduced density matrix of a block of $L$ spins when the whole
+system is in its ground state, and study the corresponding von Neumann and
+R\'enyi entanglement entropies in the thermodynamic limit. We show that both of
+these entropies scale as $a\log L$ when $L$ tends to infinity, where the
+coefficient $a$ is equal to $(m-k)/2$ in the ground state phase with $k$
+vanishing su$(m+1)$ magnon densities. In particular, our results show that none
+of these generalized Lipkin-Meshkov-Glick models are critical, since when
+$L\to\infty$ their R\'enyi entropy $R_q$ becomes independent of the parameter
+$q$. We have also computed the Tsallis entanglement entropy of the ground state
+of these generalized su$(m+1)$ Lipkin-Meshkov-Glick models, finding that it can
+be made extensive by an appropriate choice of its parameter only when
+$m-k\ge3$. Finally, in the su$(3)$ case we construct in detail the phase
+diagram of the ground state in parameter space, showing that it is determined
+in a simple way by the weights of the fundamental representation of su$(3)$.
+This is also true in the su$(m+1)$ case; for instance, we prove that the region
+for which all the magnon densities are non-vanishing is an $(m+1)$-simplex in
+$\mathbf R^m$ whose vertices are the weights of the fundamental representation
+of su$(m+1)$.",1511.09346v2
+2016-04-28,"Highly-anisotropic exchange interactions of $j_{\rm eff}=1/2$ iridium moments on the fcc lattice in La$_2B$IrO$_6$ ($B$ $=$ Mg, Zn)","We have performed inelastic neutron scattering (INS) experiments to
+investigate the magnetic excitations in the weakly distorted
+face-centered-cubic (fcc) iridate double perovskites La$_2$ZnIrO$_6$ and
+La$_2$MgIrO$_6$, which are characterized by A-type antiferromagnetic ground
+states. The powder inelastic neutron scattering data on these geometrically
+frustrated $j_{\rm eff}=1/2$ Mott insulators provide clear evidence for gapped
+spin wave excitations with very weak dispersion. The INS results and
+thermodynamic data on these materials can be reproduced by conventional
+Heisenberg-Ising models with significant uniaxial Ising anisotropy and sizeable
+second-neighbor ferromagnetic interactions. Such a uniaxial Ising exchange
+interaction is symmetry-forbidden on the ideal fcc lattice, so that it can only
+arise from the weak crystal distortions away from the ideal fcc limit. This may
+suggest that even weak distortions in $j_{\rm eff}=1/2$ Mott insulators might
+lead to strong exchange anisotropies. More tantalizingly, however, we find an
+alternative viable explanation of the INS results in terms of spin models with
+a dominant Kitaev interaction. In contrast to the uniaxial Ising exchange, the
+highly-directional Kitaev interaction is a type of exchange anisotropy which is
+symmetry-allowed even on the ideal fcc lattice. The Kitaev model has a magnon
+gap induced by quantum order-by-disorder, while weak anisotropies of the Kitaev
+couplings generated by the symmetry-lowering due to lattice distortions, can
+pin the order and enhance the magnon gap. Our findings highlight how even
+conventional magnetic orders in heavy transition metal oxides may be driven by
+highly-directional exchange interactions rooted in strong spin-orbit coupling.",1604.08431v1
+2018-02-08,Numerical Algorithm for Exact Finite Temperature Spectra and Its Application to Frustrated Quantum Spin Systems,"A numerical algorithm to calculate exact finite-temperature spectra of
+many-body lattice Hamiltonians is formulated by combining the typicality
+approach and the shifted Krylov subspace method. The combined algorithm, which
+we name finite-temperature shifted Krylov subspace method for simulating
+spectra (FTK$\omega$), efficiently reproduces the canonical-ensemble
+probability distribution at finite temperatures with the computational cost
+proportional to the Fock space dimension. The present FTK$\omega$ enables us to
+exactly calculate finite-temperature spectra of many-body systems whose system
+sizes are twice larger than those handled by the canonical ensemble average and
+allows us to access the frequency domain without sequential real-time evolution
+often used in previous studies. By employing the reweighting method with the
+present algorithm, we obtain significant reduction of the numerical costs for
+temperature sweeps. Application to the Kiteav-Heisenberg model (KHM) on a
+honeycomb lattice demonstrates the capability of the FTK$\omega$. The KHM shows
+quantum phase transitions from the quantum spin liquid (QSL) phase to
+magnetically ordered phases when the finite Heisenberg exchange coupling is
+introduced. We examine temperature dependence of dynamical spin structure
+factors of the KHM in proximity to the QSL. It is clarified that the crossover
+from a spin-excitation continuum, which is a characteristic of the QSL, to a
+damped high-energy magnon mode occurs at temperatures higher than the energy
+scale of the Heisenberg couplings or the spin gap that is a signature of the
+QSL at zero temperature. The crossover and the closeness to the Kitaev's QSL
+are quantitatively measured by the width of the excitation continuum or the
+magnon spectrum. The present results shed new light on analysis of neutron
+scattering and other spectroscopy measurements on QSL candidates.",1802.02854v1
+2018-11-05,Reply to Comment on Optical detection of transverse spin-Seebeck effect in permalloy film using Sagnac interferometer microscopy (arXiv:1810.13220),"In their Comment, Kimling and Kuschel (hereafter the commenters) challenge
+our original interpretation of the magneto-optical Kerr effect (MOKE)
+measurements using ultrasensitive Sagnac interferometer, claiming that the
+transverse spin-Seebeck effect (TSSE) is not the only contribution to the
+measured change in the Kerr rotation angle from a Ni80Fe20 (NiFe) ferromagnetic
+(FM) slab subjected to a lateral temperature gradient in the presence of a
+magnetic field. The authors assert that: (1) the TSSE, in general, has not been
+completely proven so far, and that the existing theories, in particular the
+phonon magnon drag model that we have used in our publication, in fact cannot
+explain the original work of Uchida et al. (2) The commenters based their
+critique on an estimate of the magnitude of the measured effect, arguing that
+to observe the TSSE that we originally claimed, the temperature gradient in our
+measurements should have been much larger than the value we measured. In this
+Reply, firstly, we summarize previous literature reports on the TSSE response
+in FM metallic systems. Secondly, we dispute the estimate of the necessary
+large temperature gradient made by the commenters. Importantly, the Kerr effect
+sensitivity to spin accumulation (via the TSSE response) has not been
+recognized by the commenters, in fact it was mistakenly assumed that the Kerr
+effect sensitivity to the spin accumulation by the TSSE is the same as the Kerr
+sensitivity to the bulk magnetization change due to the temperature change. In
+conclusion, we show that the TSSE is the only viable interpretation of our
+original measurements, and that the phonon-magnon drag model is indeed capable
+of explaining our results.",1811.01877v1
+2014-03-02,Magnons and a two-component spin gap in FeV2O4,"The spinel vanadates have become a model family for exploring orbital order
+on the frustrated pyrochlore lattice, and recent debate has focused on the
+symmetry of local crystal fields at the cation sites. Here, we present neutron
+scattering measurements of the magnetic excitation spectrum in
+$\mathrm{FeV_2O_4}$, a recent example of a ferrimagnetic spinel vanadate which
+is available in single crystal form. We report the existence of two emergent
+magnon modes at low temperatures, which draw strong parallels with the closely
+related material, $\mathrm{MnV_2O_4}$. We were able to reproduce the essential
+elements of both the magnetic ordering pattern and the dispersion of the
+inelastic modes with semi- classical spin wave calculations, using a minimal
+model that implies a sizeable single-ion anisotropy on the vanadium sublattice.
+Taking into account the direction of ordered spins, we associate this
+anisotropy with the large trigonal distortion of $\mathrm{VO_6}$ octahedra,
+previously observed via neutron powder diffraction measurements. We further
+report on the spin gap, which is an order-of-magnitude larger than that
+observed in $\mathrm{MnV_2O_4}$. By looking at the overall temperature
+dependence, we were able to show that the gap magnitude is largely associated
+with the ferro-orbital order known to exist on the iron sublattice, but the
+contribution to the gap from the vanadium sublattice is in fact comparable to
+what is reported in the Mn compound. This reinforces the conclusion that the
+spin canting transition is associated with the ordering of vanadium orbitals in
+this system, and closer analysis indicates closely related physics underlying
+orbital transitions in $\mathrm{FeV_2O_4}$ and $\mathrm{MnV_2O_4}$.",1403.0269v2
+2018-05-22,Frequency linewidth and decay length of spin waves in curved magnetic membranes,"The curvature of a magnetic membrane was presented as a means of inducing
+nonreciprocities in the spin-wave (SW) dispersion relation (see [Ot\'alora et
+al. Phys. Rev. Lett., 2016 117, 227203] and [Ot\'alora et al. Phys. Rev. B.,
+2017 95, 184415]), thereby expanding the toolbox for controlling SWs. In this
+paper, we further complement this toolbox by analytically showing that the
+membrane curvature is also manifested in the absorption of SWs, leading to a
+difference in the frequency linewidth (or lifetime) of counterpropagating
+magnons. Herein, we studied the nanotubular case, predicting changes of
+approximately greater than 10% and up to 20% in the frequency linewidth of
+counterpropagating SWs for a wide range of nanotube radii ranging from 30 nm to
+260 nm and with a thickness of 10 nm. These percentages are comparable to those
+that can be extracted from experiments on heavy metal/magnetic metal
+sandwiches, wherein linewidth asymmetry results from an interfacial
+Dzyaloshinskii-Moriya interaction (DMI). We also show that the interplay
+between the frequency linewidth and group velocity leads to asymmetries in the
+SW decay length, presenting changes between 10\% and 22\% for
+counterpropagating SWs in the frequency range of 2 - 10 GHz. For the case of
+the SW dispersion relation, the predicted effects are identified as the
+classical dipole-dipole interaction, and the analytical expression of the
+frequency linewidth has the same mathematical form as in thin films with the
+DMI. Furthermore, we present limiting cases of a tubular geometry with
+negligible curvature such that our analytical model converges to the case of a
+planar thin film known from the literature. Our findings represent a step
+forward toward the realization of three-dimensional curvilinear magnonic
+devices.",1805.08827v1
+2017-06-30,Comprehensive study of the dynamics of a classical Kitaev spin liquid,"We study the spin-$S$ Kitaev model in the classical ($S \to \infty$) limit
+using Monte Carlo simulations combined with semi-classical spin dynamics. We
+discuss differences and similarities in the dynamical structure factors of the
+spin-$1/2$ and the classical Kitaev liquids. Interestingly, the low-temperature
+and low-energy spectrum of the classical model exhibits a finite energy peak,
+which is the precursor of the one produced by the Majorana modes of the $S=1/2$
+model. The classical peak is spectrally narrowed compared to the quantum result
+and can be explained by magnon excitations within fluctuating one-dimensional
+manifolds (loops). Hence the difference from the classical limit to the quantum
+limit can be understood by the fractionalization of magnons propagating in
+one-dimensional manifolds. Moreover, we show that the momentum space
+distribution of the low-energy spectral weight of the $S=1/2$ model follows the
+momentum space distribution of zero modes of the classical model.",1706.10242v2
+2017-10-17,Spin - Phonon Coupling in Nickel Oxide Determined from Ultraviolet Raman Spectroscopy,"Nickel oxide (NiO) has been studied extensively for various applications
+ranging from electrochemistry to solar cells [1,2]. In recent years, NiO
+attracted much attention as an antiferromagnetic (AF) insulator material for
+spintronic devices [3-10]. Understanding the spin - phonon coupling in NiO is a
+key to its functionalization, and enabling AF spintronics' promise of
+ultra-high-speed and low-power dissipation [11,12]. However, despite its status
+as an exemplary AF insulator and a benchmark material for the study of
+correlated electron systems, little is known about the spin - phonon
+interaction, and the associated energy dissipation channel, in NiO. In
+addition, there is a long-standing controversy over the large discrepancies
+between the experimental and theoretical values for the electron, phonon, and
+magnon energies in NiO [13-23]. This gap in knowledge is explained by NiO
+optical selection rules, high Neel temperature and dominance of the magnon band
+in the visible Raman spectrum, which precludes a conventional approach for
+investigating such interaction. Here we show that by using ultraviolet (UV)
+Raman spectroscopy one can extract the spin - phonon coupling coefficients in
+NiO. We established that unlike in other materials, the spins of Ni atoms
+interact more strongly with the longitudinal optical (LO) phonons than with the
+transverse optical (TO) phonons, and produce opposite effects on the phonon
+energies. The peculiarities of the spin - phonon coupling are consistent with
+the trends given by density functional theory calculations. The obtained
+results shed light on the nature of the spin - phonon coupling in AF insulators
+and may help in developing innovative spintronic devices.",1710.06386v1
+2018-09-06,Spin-current-mediated rapid magnon localisation and coalescence after ultrafast optical pumping of ferrimagnetic alloys,"Sub-picosecond magnetisation manipulation via femtosecond optical pumping has
+attracted wide attention ever since its original discovery in 1996. However,
+the spatial evolution of the magnetisation is not yet well understood, in part
+due to the difficulty in experimentally probing such rapid dynamics. Here, we
+find evidence of rapid magnetic order recovery in materials with perpendicular
+magnetic anisotropy via nonlinear magnon processes. We identify both
+localisation and coalescence regimes, whereby localised magnetic textures
+nucleate and subsequently evolve in accordance with a power law formalism.
+Coalescence is observed for optical excitations both above and below the
+switching threshold. Simulations indicate that the ultrafast generation of
+noncollinear magnetisation via optical pumping establishes exchange-mediated
+spin currents with an equivalent 100% spin polarised charge current density of
+$10^8$ A/cm$^2$. Such large spin currents precipitate rapid recovery of
+magnetic order after optical pumping. These processes suggest an ultrafast
+optical route for the stabilization of desired meta-stable states, e.g.,
+isolated skyrmions.",1809.02076v2
+2015-08-06,Physical properties and electronic structure of Sr$_2$Cr$_3$As$_2$O$_2$ containing CrO$_2$ and Cr$_2$As$_2$ square-planar lattices,"We report the physical properties and electronic structure calculations of a
+layered chromium oxypnictide, Sr$_2$Cr$_3$As$_2$O$_2$, which crystallizes in a
+Sr$_2$Mn$_3$As$_2$O$_2$-type structure containing both CrO$_2$ planes and
+Cr$_2$As$_2$ layers. The newly synthesized material exhibits a metallic
+conduction with a dominant electron-magnon scattering. Magnetic and
+specific-heat measurements indicate at least two intrinsic magnetic transitions
+below room temperature. One is an antiferromagnetic transition at 291 K,
+probably associated with a spin ordering in the Cr$_2$As$_2$ layers. Another
+transition is broad, occurring at around 38 K, and possibly due to a
+short-range spin order in the CrO$_2$ planes. Our first-principles calculations
+indicate predominant two-dimensional antiferromagnetic exchange couplings, and
+suggest a KG-type (i.e. K$_2$NiF$_4$ type for CrO$_2$ planes and G type for
+Cr$_2$As$_2$ layers) magnetic structure, with reduced moments for both Cr
+sublattices. The corresponding electronic states near the Fermi energy are
+mostly contributed from Cr-3$d$ orbitals which weakly (modestly) hybridize with
+the O-2$p$ (As-4$p$) orbitals in the CrO$_2$ (Cr$_2$As$_2$) layers. The bare
+bandstructure density of states at the Fermi level is only $\sim$1/4 of the
+experimental value derived from the low-temperature specific-heat data,
+consistent with the remarkable electron-magnon coupling. The title compound is
+argued to be a possible candidate to host superconductivity.",1508.01371v1
+2016-03-14,Field-driven quantum phase transitions in $S=1/2$ spin chains,"We study the magnetization process of a 1D extended Heisenberg model, the
+$J$-$Q$ model, as a function of an external magnetic field. In this model, $J$
+represents the traditional antiferromagnetic Heisenberg exchange and $Q$ is the
+strength of a competing four-spin interaction. Without external field, this
+system hosts a twofold-degenerate dimerized (valence-bond solid) state above a
+critical value $q_c\approx 0.85$ where $q\equiv Q/J$. The dimer order is
+destroyed and replaced by a partially polarized translationally invariant state
+at a critical field value. We find magnetization jumps (metamagnetism) between
+the partially polarized and fully polarized state for $q>q_{\rm min}$, where we
+have calculated $q_{\rm min}=2/9$ exactly. For $q>q_{\rm min}$ two magnons
+(flipped spins on a fully polarized background) attract and form a bound state.
+Quantum Monte Carlo studies confirm that the bound state corresponds to the
+first step of an instability leading to a finite magnetization jump for
+$q>q_{\rm min}$. Our results show that neither geometric frustration nor
+spin-anisotropy are necessary conditions for metamagnetism. Working in the
+two-magnon subspace, we also find evidence pointing to the existence of
+metamagnetism in the unfrustrated $J_1$-$J_2$ chain ($J_1>0$, $J_2<0$), but
+only if $J_2$ is spin-anisotropic. We also investigate quantum-critical scaling
+near the transition into the fully polarized state for $q\le q_{\rm min}$ at
+$T>0$. While the expected `zero-scale-factor' universality is clearly seen for
+$q=0$ and $q\ll q_{\rm min}$; closer to $q_{\rm min}$ we find that extremely
+low temperatures are required to observe the asymptotic behavior, due to the
+influence of the tricritical point at $q_{\rm min}$, which leads to a
+cross-over at a temperature $T^*(q)$ between logarithmic tricritical scaling
+and zero-scale-factor universality, with $T^*(q)\to 0$ when $q\to q_{\rm min}$.",1603.04359v3
+2020-06-17,Recent Progress on Electrical Excitation and Manipulation of Spin-Waves in Spin Hall Nano-Oscillators,"Spin waves (SWs), the collective precessional motion of spins in a magnetic
+system, have been proposed as a promising alternative system with low-power
+consumption for encoding information. Spin Hall nano-oscillator (SHNO), a
+new-type spintronic nano-device, can electrically excite and control spin waves
+in both nanoscale magnetic metals and insulators with low damping by the spin
+current due to spin Hall effect. Here, we will review recent progress about
+spin-wave excitation and experimental parameters dependent spectrum in SHNOs.
+The nanogap SHNOs based on in-plane magnetization Py/Pt exhibits a nonlinear
+self-localized bullet soliton localized at the center of the gap between the
+electrodes and a secondary high-frequency mode which coexists with the primary
+bullet mode at higher currents. While in the nanogap SHNOs with strong
+perpendicular magnetic anisotropy (PMA), besides both nonlinear bullet soliton
+and propagating spin-wave mode are achieved and controlled by varying the
+external magnetic field and current, the magnetic bubble skyrmion mode also can
+be excited at a low in-plane magnetic field. These SW modes show
+thermal-induced mode hopping behavior at high temperature due to the coupling
+between modes mediated by thermal-magnon-mediated scattering. Moreover, thanks
+to PMA-induced effective field, a single coherent mode also can be achieved
+without applying an external magnetic field. The strong nonlinear effect of
+spin-waves makes SHNOs easy to achieve synchronization with external microwave
+signals or mutual synchronization between multiple oscillators with improving
+the coherence and power of oscillation modes significantly. Spin-waves in SHNOs
+with an external free magnetic layer have a wide range of applications from as
+a nanoscale signal source of low-power consumption magnonic devices to
+spin-based neuromorphic computing systems in the field of artificial
+intelligence.",2006.09737v2
+2021-02-04,Magnon-spinon dichotomy in the Kitaev hyperhoneycomb $β$-Li$_2$IrO$_3$,"The family of edge-sharing tri-coordinated iridates and ruthenates has
+emerged in recent years as a major platform for Kitaev spin liquid physics,
+where spins fractionalize into emergent magnetic fluxes and Majorana fermions
+with Dirac-like dispersions. While such exotic states are usually pre-empted by
+long-range magnetic order at low temperatures, signatures of Majorana fermions
+with long coherent times have been predicted to manifest at intermediate and
+higher energy scales, similar to the observation of spinons in quasi-1D spin
+chains. Here we present a Resonant Inelastic X-ray Scattering study of the
+magnetic excitations of the hyperhoneycomb iridate $\beta$-Li$_2$IrO$_3$ under
+a magnetic field with a record-high-resolution spectrometer. At
+low-temperatures, dispersing spin waves can be resolved around the predicted
+intertwined incommensurate spiral and field-induced zigzag orders, whose
+excitation energy reaches a maximum of 16meV. A 2T magnetic field softens the
+dispersion around ${\bf Q}=0$. The behavior of the spin waves under magnetic
+field is consistent with our semiclassical calculations for the ground state
+and the dynamical spin structure factor, which further predicts that the ensued
+intertwined uniform states remain robust up to very high fields (100 T). Most
+saliently, the low-energy magnon-like mode is superimposed by a broad continuum
+of excitations, centered around 35meV and extending up to 100meV. This
+high-energy continuum survives up to at least 300K -- well above the ordering
+temperature of 38K -- and gives evidence for pairs of long-lived Majorana
+fermions of the proximate Kitaev spin liquid.",2102.02714v2
+2017-04-13,Exact diagonalization and cluster mean-field study of triangular-lattice XXZ antiferromagnets near saturation,"Quantum magnetic phases near the magnetic saturation of triangular-lattice
+antiferromagnets with XXZ anisotropy have been attracting renewed interest
+since it has been suggested that a nontrivial coplanar phase, called the
+$\pi$-coplanar or $\Psi$ phase, could be stabilized by quantum effects in a
+certain range of anisotropy parameter $J/J_z$ besides the well-known 0-coplanar
+(known also as $V$) and umbrella phases. Recently, Sellmann $et$ $al$. [Phys.
+Rev. B {\bf 91}, 081104(R) (2015)] claimed that the $\pi$-coplanar phase is
+absent for $S=1/2$ from an exact-diagonalization analysis in the sector of the
+Hilbert space with only three down-spins (three magnons). We first reconsider
+and improve this analysis by taking into account several low-lying eigenvalues
+and the associated eigenstates as a function of $J/J_z$ and by sensibly
+increasing the system sizes (up to 1296 spins). A careful identification
+analysis shows that the lowest eigenstate is a chirally antisymmetric
+combination of finite-size umbrella states for $J/J_z\gtrsim 2.218$ while it
+corresponds to a coplanar phase for $J/J_z\lesssim 2.218$. However, we
+demonstrate that the distinction between 0-coplanar and $\pi$-coplanar phases
+in the latter region is fundamentally impossible from the symmetry-preserving
+finite-size calculations with fixed magnon number.} Therefore, we also perform
+a cluster mean-field plus scaling analysis for small spins $S\leq 3/2$. The
+obtained results, together with the previous large-$S$ analysis, indicate that
+the $\pi$-coplanar phase exists for any $S$ except for the classical limit
+($S\rightarrow \infty$) and the existence range in $J/J_z$ is largest in the
+most quantum case of $S=1/2$.",1704.04024v2
+2017-04-13,Low energy magnon dynamics and magneto-optics of the skyrmionic Mott insulator Cu$_2$OSeO$_3$,"In this work, we present a comprehensive study of the low energy optical
+magnetic response of the skyrmionic Mott insulator Cu$_2$OSeO$_3$ via high
+resolution time-domain THz spectroscopy. In zero field, a new magnetic
+excitation not predicted by spin-wave theory with frequency $f$ = 2.03 THz is
+observed and shown, with accompanying time-of-flight neutron scattering
+experiments, to be a zone folded magnon from the $\mathrm{R}$ to
+$\mathrm{\Gamma}$ points of the Brillouin zone. Highly sensitive polarimetry
+experiments performed in weak magnetic fields, $\mu_0$H $<$ 200 mT, observe
+Faraday and Kerr rotations which are proportional to the sample magnetization,
+allowing for optical detection of the skyrmion phase and construction of a
+magnetic phase diagram. From these measurements, we extract a critical exponent
+of $\beta$ = 0.35 $\pm$ 0.04, in good agreement with the expected value for the
+3D Heisenberg universality class of $\beta$ = 0.367. In large magnetic fields,
+$\mu_0$H $>$ 5 T, we observe the magnetically active uniform mode of the
+ferrimagnetic field polarized phase whose dynamics as a function of field and
+temperature are studied. In addition to extracting a $g_\text{eff}$ = 2.08
+$\pm$ 0.03, we observe the uniform mode to decay through a non-Gilbert damping
+mechanism and to possesses a finite spontaneous decay rate, $\Gamma_0$
+$\approx$ 25 GHz, in the zero temperature limit. Our observations are
+attributed to Dzyaloshinkii-Moriya interactions, which have been proposed to be
+exceptionally strong in Cu$_2$OSeO$_3$ and are expected to impact the low
+energy magnetic response of such chiral magnets.",1704.04228v1
+2020-01-26,Magnetic field-induced quantum phase transitions in a van der Waals magnet,"Exploring new parameter regimes to realize and control novel phases of matter
+has been a main theme in modern condensed matter physics research. The recent
+discovery of 2D magnetism in nearly freestanding monolayer atomic crystals has
+already led to observations of a number of novel magnetic phenomena absent in
+bulk counterparts. Such intricate interplays between magnetism and crystalline
+structures provide ample opportunities for exploring quantum phase transitions
+in this new 2D parameter regime. Here, using magnetic field and temperature
+dependent circularly polarized Raman spectroscopy of phonons and magnons, we
+map out the phase diagram of CrI3 that has been known to be a layered AFM in
+its 2D films and a FM in its 3D bulk. We, however, reveal a novel mixed state
+of layered AFM and FM in 3D CrI3 bulk crystals where the layered AFM survives
+in the surface layers and the FM appears in deeper bulk layers. We then show
+that the surface layered AFM transits into the FM at a critical magnetic field
+of 2 T, similar to what was found in the few layer case. Interestingly,
+concurrent with this magnetic phase transition, we discover a first-order
+structural phase transition that alters the crystallographic point group from
+C3i to C2h and thus, from a symmetry perspective, this monoclinic structural
+phase belongs to the 3D nematic order universality class. Our result not only
+unveils the complex single magnon behavior in 3D CrI3, but also settles down
+the puzzle of how CrI3 transits from a bulk FM to a thin layered AFM
+semiconductor, despite recent efforts in understanding the origin of layered
+AFM in CrI3 thin layer, and reveals the intimate relationship between the
+layered AFM-to-FM and the crystalline rhombohedral-to-monoclinic phase
+transitions. These findings further open up opportunities for future 2D
+magnet-based magneto-mechanical devices.",2001.09536v1
+2020-05-15,"Thermal generation, manipulation and detection of skyrmions","Recent years have witnessed significant progresses in realizing skyrmions in
+chiral magnets1-4 and asymmetric magnetic multilayers5-13, as well as their
+electrical manipulation2,7,8,10. Equally important, thermal generation,
+manipulation and detection of skyrmions can be exploited for prototypical new
+architecture with integrated computation14 and energy harvesting15. It has yet
+to verify if skyrmions can be purely generated by heating16,17, and if their
+resultant direction of motion driven by temperature gradients follows the
+diffusion or, oppositely, the magnonic spin torque17-21. Here, we address these
+important issues in microstructured devices made of multilayers:
+(Ta_CoFeB_MgO)15, (Pt_CoFeB_MgO_Ta)15 and (Pt_Co_Ta)15 integrated with on-chip
+heaters, by using a full-field soft X-ray microscopy. The thermal generation of
+densely packed skyrmions is attributed to the low energy barrier at the device
+edge, together with the thermally induced morphological transition from stripe
+domains to skyrmions. The unidirectional diffusion of skyrmions from the hot
+region towards the cold region is experimentally observed. It can be
+theoretically explained by the combined contribution from repulsive forces
+between skyrmions, and thermal spin-orbit torques in competing with magnonic
+spin torques17,18,20,21 and entropic forces22. These thermally generated
+skyrmions can be further electrically detected by measuring the accompanied
+anomalous Nernst voltages23. The on-chip thermoelectric generation,
+manipulation and detection of skyrmions could open another exciting avenue for
+enabling skyrmionics, and promote interdisciplinary studies among spin
+caloritronics15, magnonics24 and skyrmionics3,4,12.",2005.07441v1
+2020-08-29,Exploring a quantum-information-relevant magnonic material: Ultralow damping at low temperature in the organic ferrimagnet V[TCNE]x,"Quantum information science and engineering requires novel low-loss magnetic
+materials for magnon-based quantum-coherent operations. The search for low-loss
+magnetic materials, traditionally driven by applications in microwave
+electronics near room-temperature, has gained additional constraints from the
+need to operate at cryogenic temperatures for many applications in quantum
+information science and technology. Whereas yttrium iron garnet (YIG) has been
+the material of choice for decades, the emergence of molecule-based materials
+with robust magnetism and ultra-low damping has opened new avenues for
+exploration. Specifically, thin-films of vanadium tetracyanoethylene (V[TCNE]x)
+can be patterned into the multiple, connected structures needed for hybrid
+quantum elements and have shown room-temperature Gilbert damping ({\alpha} = 4
+\times 10^-5) that rivals the intrinsic (bulk) damping otherwise seen only in
+highly-polished YIG spheres (far more challenging to integrate into arrays).
+Here, we present a comprehensive and systematic study of the low-temperature
+magnetization dynamics for V[TCNE]x thin films, with implications for their
+application in quantum systems. These studies reveal a temperature-driven,
+strain-dependent magnetic anisotropy that compensates the thin-film shape
+anisotropy, and the recovery of a magnetic resonance linewidth at 5 K that is
+comparable to room-temperature values (roughly 2 G at 9.4 GHz). We can account
+for these variations of the V[TCNE]x linewidth within the context of scattering
+from very dilute paramagnetic impurities, and anticipate additional linewidth
+narrowing as the temperature is further reduced.",2008.13061v3
+2021-04-15,Quantum many-body states and Green functions of nonequilibrium electron-magnon systems: Localized spin operators vs. their mapping to Holstein-Primakoff bosons,"The operators of localized spins within a magnetic material commute at
+different sites of its lattice and anticommute on the same site, so they are
+neither fermionic nor bosonic operators. Thus, to construct diagrammatic
+many-body perturbation theory, the spin operators are usually mapped to the
+bosonic ones with Holstein-Primakoff (HP) transformation being the most widely
+used in magnonics and spintronics literature. However, to make calculations
+tractable, the square root of operators in the HP transformation is expanded
+into a Taylor series truncated to some low order. This poses a question on the
+range of validity of truncated HP transformation when describing nonequilibrium
+dynamics of localized spins interacting with each other or with conduction
+electron spins. Here we apply exact diagonalization techniques to Hamiltonian
+of fermions (i.e., electrons) interacting with HP bosons vs. Hamiltonian of
+fermions interacting with the original localized spin operators in order to
+compare their many-body states and one-particle equilibrium or nonequilibrium
+Green functions. The Hamiltonian of fermions interacting with HP bosons gives
+incorrect ground state and electronic spectral function, unless large number of
+terms are retained in truncated HP transformation. Furthermore, tracking
+nonequilibrium dynamics of localized spins over longer time intervals requires
+progressively larger number of terms in truncated HP transformation. Finally,
+we show that recently proposed [M. Vogl et al., Phys. Rev. Research 2, 043243
+(2020); J. K\""{o}nig et al., SciPost Phys. 10, 007 (2021)] resummed HP
+transformation resolves the trouble with truncated HP transformation, while
+allowing us to derive an exact (manifestly Hermitian) Hamiltonian consisting of
+finite and fixed number of boson-boson and electron-boson interacting terms.",2104.07657v2
+2021-04-23,Roadmap of spin-orbit torques,"Spin-orbit torque (SOT) is an emerging technology that enables the efficient
+manipulation of spintronic devices. The initial processes of interest in SOTs
+involved electric fields, spin-orbit coupling, conduction electron spins and
+magnetization. More recently interest has grown to include a variety of other
+processes that include phonons, magnons, or heat. Over the past decade, many
+materials have been explored to achieve a larger SOT efficiency. Recently,
+holistic design to maximize the performance of SOT devices has extended
+material research from a nonmagnetic layer to a magnetic layer. The rapid
+development of SOT has spurred a variety of SOT-based applications. In this
+Roadmap paper, we first review the theories of SOTs by introducing the various
+mechanisms thought to generate or control SOTs, such as the spin Hall effect,
+the Rashba-Edelstein effect, the orbital Hall effect, thermal gradients,
+magnons, and strain effects. Then, we discuss the materials that enable these
+effects, including metals, metallic alloys, topological insulators,
+two-dimensional materials, and complex oxides. We also discuss the important
+roles in SOT devices of different types of magnetic layers. Afterward, we
+discuss device applications utilizing SOTs. We discuss and compare
+three-terminal and two-terminal SOT-magnetoresistive random-access memories
+(MRAMs); we mention various schemes to eliminate the need for an external
+field. We provide technological application considerations for SOT-MRAM and
+give perspectives on SOT-based neuromorphic devices and circuits. In addition
+to SOT-MRAM, we present SOT-based spintronic terahertz generators,
+nano-oscillators, and domain wall and skyrmion racetrack memories. This paper
+aims to achieve a comprehensive review of SOT theory, materials, and
+applications, guiding future SOT development in both the academic and
+industrial sectors.",2104.11459v2
+2021-05-18,Computational Micromagnetics based on Normal Modes: bridging the gap between macrospin and full spatial discretization,"The Landau-Lifshitz equation governing magnetization dynamics is written in
+terms of the amplitudes of normal modes associated with the micromagnetic
+system's appropriate ground state. This results in a system of nonlinear
+ordinary differential equations (ODEs), the right-hand side of which can be
+expressed as the sum of a linear term and nonlinear terms with increasing order
+of nonlinearity (quadratic, cubic, etc.). The application of the method to
+nanostructured magnetic systems demonstrates that the accurate description of
+magnetization dynamics requires a limited number of normal modes, which results
+in a considerable improvement in computational speed. The proposed method can
+be used to obtain a reduced-order dynamical description of magnetic
+nanostructures which allows to adjust the accuracy between low-dimensional
+models, such as macrospin, and micromagnetic models with full spatial
+discretization. This new paradigm for micromagnetic simulations is tested for
+three problems relevant to the areas of spintronics and magnonics: directional
+spin-wave coupling in magnonic waveguides, high power ferromagnetic resonance
+in a magnetic nanodot, and injection-locking in spin-torque nano-oscillators.
+The case studies considered demonstrate the validity of the proposed approach
+to systematically obtain an intermediate order dynamical model based on normal
+modes for the analysis of magnetic nanosystems. The time-consuming calculation
+of the normal modes has to be done only one time for the system. These modes
+can be used to optimize and predict the system response for all possible
+time-varying external excitations (magnetic fields, spin currents). This is of
+utmost importance for applications where fast and accurate system simulations
+are required, such as in electronic circuits including magnetic devices.",2105.08829v2
+2021-06-15,Low-energy spin dynamics in rare-earth perovskite oxides,"We review recent studies of spin dynamics in rare-earth orthorhombic
+perovskite oxides of the type $RM$O$_3$, where $R$ is a rare-earth ion and $M$
+is a transition-metal ion, using single-crystal inelastic neutron scattering
+(INS). After a short introduction to the magnetic INS technique in general, the
+results of INS experiments on both transition-metal and rare-earth subsystems
+for four selected compounds (YbFeO$_3$, TmFeO$_3$, YFeO$_3$, YbAlO$_3$) are
+presented. We show that the spectrum of magnetic excitations consists of two
+types of collective modes that are well separated in energy: gapped magnons
+with a typical bandwidth of $<$70 meV, associated with the
+antiferromagnetically (AFM) ordered transition-metal subsystem, and AFM
+fluctuations of $<$5 meV within the rare-earth subsystem, with no hybridization
+of those modes. We discuss the high-energy conventional magnon excitations of
+the 3$d$ subsystem only briefly, and focus in more detail on the spectacular
+dynamics of the rare-earth sublattice in these materials. We observe that the
+nature of the ground state and the low-energy excitation strongly depends on
+the identity of the rare-earth ion. In the case of non-Kramers ions, the
+low-symmetry crystal field completely eliminates the degeneracy of the
+multiplet state, creating a rich magnetic field-temperature phase diagram. In
+the case of Kramers ions, the resulting ground state is at least a doublet,
+which can be viewed as an effective quantum spin-1/2. Equally important is the
+fact that in Yb-based materials the nearest-neighbor exchange interaction
+dominates in one direction, despite the three-dimensional nature of the
+orthoperovskite crystal structure. The observation of a fractional spinon
+continuum and quantum criticality in YbAlO$_3$ demonstrates that Kramers
+rare-earth based magnets can provide realizations of various aspects of quantum
+low-dimensional physics.",2106.08378v1
+2021-10-09,Imaging the ultrafast coherent control of a skyrmion crystal,"Exotic magnetic textures emerging from the subtle interplay between
+thermodynamic and topological fluctuation have attracted intense interest due
+to their potential applications in spintronic devices. Recent advances in
+electron microscopy have enabled the imaging of random photo-generated
+individual skyrmions. However, their deterministic and dynamical manipulation
+is hampered by the chaotic nature of such fluctuations and the intrinsically
+irreversible switching between different minima in the magnetic energy
+landscape. Here, we demonstrate a method to coherently control the rotation of
+a skyrmion crystal by discrete amounts at speeds which are much faster than
+previously observed. By employing circularly polarized femtosecond laser pulses
+with an energy below the bandgap of the Mott insulator Cu2OSeO3, we excite a
+collective magnon mode via the inverse Faraday effect. This triggers coherent
+magnetic oscillations that directly control the rotation of a skyrmion crystal
+imaged by cryo-Lorentz Transmission Electron Microscopy. The manipulation of
+topological order via ultrafast laser pulses shown here can be used to engineer
+fast spin-based logical devices.",2110.04548v3
+2021-11-26,Enhanced superconductivity and various edge modes in modulated $t$-$J$ chains,"We numerically investigate the ground state of the extended $t$-$J$
+Hamiltonian with periodic local modulations in one dimension by using the
+density-matrix renormalization group method. Examining charge and spin
+excitation gaps, as well as the pair binding energy, with extrapolated results
+to the thermodynamic limit, we obtain a rich ground-state phase diagram
+consisting of the metallic state, the superconducting state, the phase
+separation, and insulating states at commensurate fillings. Compared to the
+homogeneous 1D $t$-$J$ model, the superconductivity is greatly enhanced and
+stabilized by the flat-band structure. This superconducting state in
+quasi-periodic chains shares similar properties with ladder systems:
+significant negative pair binding energy occurs, and the singlet pairing
+correlation function dominates with the algebraic decay while the
+single-particle Green's function and spin correlation function decay
+exponentially. On the other hand, quasi-periodicity leads to nontrivial
+topological nature in insulating states, characterized by different integer
+Chern numbers at different fillings. Due to the interplay among the topology,
+the interaction, and the 1D confinement, gapless edge modes show strong
+spin-charge separation and in different regions can relate to different
+collective modes, which are the charge of a single fermion, the magnon, and the
+singlet-pair. We also find two interaction driven topological transitions: i)
+at particle filling $\rho=1/2$, the low-energy edge excitations change from the
+magnon to singlet-pair, accompanied with pair formation in bulk; and ii) at
+$\rho=3/4$, while the gapless edge mode remains the charge of a single fermion,
+there is a gap-closing point and a $\pi$-phase shift in the quasi-particle
+spectrum.",2111.13718v1
+2022-01-10,Ultrafast manipulation of the NiO antiferromagnetic order via sub-gap optical excitation,"Wide-band-gap insulators such as NiO offer the exciting prospect of
+coherently manipulating electronic correlations with strong optical fields.
+Contrary to metals where rapid dephasing of optical excitation via electronic
+processes occurs, the sub-gap excitation in charge-transfer insulators has been
+shown to couple to low-energy bosonic excitations. However, it is currently
+unknown if the bosonic dressing field is composed of phonons or magnons. Here
+we use the prototypical charge-transfer insulator NiO to demonstrate that 1.5
+eV sub-gap optical excitation leads to a renormalised NiO band-gap in
+combination with a significant reduction of the antiferromagnetic order. We
+employ element-specific X-ray reflectivity at the FLASH free-electron laser to
+demonstrate the reduction of the upper band-edge at the O 1s-2p core-valence
+resonance (K-edge) whereas the antiferromagnetic order is probed via X-ray
+magnetic linear dichroism (XMLD) at the Ni 2p-3d resonance (L2-edge). Comparing
+the transient XMLD spectral line shape to ground-state measurements allows us
+to extract a spin temperature rise of 65 +/- 5 K for time delays longer than
+400 fs while at earlier times a non-equilibrium spin state is formed. We
+identify transient mid-gap states being formed during the first 200 fs
+accompanied by a band-gap reduction lasting at least up to the maximum measured
+time delay of 2.4 ps. Electronic structure calculations indicate that magnon
+excitations significantly contribute to the reduction of the NiO band gap.",2201.03280v1
+2022-04-24,Ground-state phase diagram and thermodynamics of coupled trimer chains,"The density matrix renormalization group and quantum Monte Carlo method are
+used to describe coupled trimer chains in a magnetic field h. The Hamiltonian
+contains exchange terms involving the intra-trimer coupling J1 (taken as the
+unit of energy) and the inter-trimer coupling J2, plus the Zeeman interaction
+for a magnetic field h along the z direction. Results for the magnetization per
+trimer m are calculated in regimes of positive and negative values of the ratio
+J = J2 / J1, from which the rich field-induced ground state phase diagram h vs.
+J is derived, with the presence of Luttinger liquid, the 1/3-plateau (m = 1/2),
+and the one of fully polarized magnetization (m = 3/2). Also, the zero-field
+Lanczos calculation of spin-wave dispersion from the 1/3-plateau for $S^z = 1$
+is shown at the previous regimes of J values. In addition, we also report on
+the decay of correlation functions of trimers along open chains, as well as the
+average two-magnon distribution. The ground state is ferrimagnetic for $0<J\leq
+1$, and is a singlet for $-1\leq J<0$. In the singlet phase, the spin
+correlation functions along the legs present an antiferromagnetic power-law
+decay, similar to the spin-1/2 linear chain, thus suggesting that the ground
+state is made of three coupled antiferromagnetically oriented chains. In the
+singlet phase, the dimensionless thermal magnetic susceptibility per site
+normalized by 1/|J| gets closer to $1/\pi^2$ as the temperature $T\rightarrow
+0$. For the ferrimagnetic phase, we fit the susceptibility to the experimental
+data for the compound Pb$_3$Cu$_3$(PO$_4$)$_4$ and estimate the model exchange
+couplings: J1=74.8 K and J=0.4. These values imply a range of energies for the
+magnon excitations that are in accord with the data from neutron scattering
+experiments on Pb$_3$Cu$_3$(PO$_4$)$_4$ for two excitation modes. The
+1/3-plateau closes only at 1/|J|=0 with J<0.",2204.11186v1
+2022-07-29,Non-linear magnons and exchange Hamiltonians of delafossite proximate quantum spin liquids,"Quantum spin liquids (QSL) are theoretical states of matter with long-range
+entanglement and exotic quasiparticles. However, they generally elude
+quantitative theory, rendering their underlying phases mysterious and hampering
+efforts to identify experimental QSL states. Here we study triangular lattice
+resonating valence bond QSL candidate materials KYbSe$_2$ and NaYbSe$_2$. We
+measure the magnon modes in their 1/3 plateau phase, where quantitative theory
+is tractable, using inelastic neutron scattering and fit them using nonlinear
+spin wave theory. We also fit the KYbSe$_2$ heat capacity using high
+temperature series expansion. Both KYbSe$_2$ fits yield the same magnetic
+Hamiltonian to within uncertainty, confirming previous estimates and showing
+the Heisenberg $J_2/J_1$ to be an accurate model for these materials. Most
+importantly, comparing KYbSe$_2$ and NaYbSe$_2$ shows that smaller $A$-site
+Na$^+$ ion has a larger $J_2/J_1$ ratio. However, hydrostatic pressure applied
+to KYbSe$_2$ increases the ordering temperature (a result consistent with
+density functional theory calculations), indicating that pressure decreases
+$J_2/J_1$. These results show how periodic table and hydrostatic pressure can
+tune the $A$YbSe$_2$ materials in a controlled way.",2207.14785v3
+2023-03-30,Fate of entanglement in magnetism under Lindbladian or non-Markovian dynamics and conditions for their transition to Landau-Lifshitz-Gilbert classical dynamics,"It is commonly assumed in spintronics and magnonics that localized spins
+within antiferromagnets are in the N\'{e}el ground state (GS), as well as that
+such state evolves, when pushed out of equilibrium by current or external
+fields, according to the Landau-Lifshitz-Gilbert (LLG) equation viewing
+localized spins as classical vectors of fixed length. On the other hand, the
+true GS of antiferromagnets is highly entangled, as confirmed by very recent
+neutron scattering experiments witnessing their entanglement. Although GS of
+ferromagnets is always unentangled, their magnonic low-energy excitation are
+superpositions of many-body spin states and, therefore, entangled. In this
+study, we initialize quantum Heisenberg ferro- or antiferromagnetic chains
+hosing localized spins $S=1/2$, $S=1$ or $S=5/2$ into unentangled pure state
+and then evolve them by quantum master equations (QMEs) of Lindblad or
+non-Markovian type, derived by coupling localized spins to a bosonic bath (such
+as due to phonons) or by using additional ``reaction coordinate'' in the latter
+case. The time evolution is initiated by applying an external magnetic field,
+and entanglement of time-evolving {\em mixed} quantum states is monitored by
+computing its logarithmic negativity. We find that non-Markovian dynamics
+maintains some degree of entanglement, which shrinks the length of the vector
+of spin expectation values, thereby making the LLG equation inapplicable.
+Conversely, Lindbladian (i.e., Markovian) dynamics ensures that entanglement
+goes to zero, thereby enabling quantum-to-classical (i.e., to LLG) transition
+in all cases -- $S=1/2$, $S=1$ and $S=5/2$ ferromagnet or $S=5/2$
+antiferromagnet -- {\em except} for $S=1/2$ and $S=1$ antiferromagnet. We also
+investigate the stability of entangled antiferromagnetic GS upon suddenly
+coupling it to the bosonic bath.",2303.17596v3
+2023-08-14,Temperature Evolution of Magnon Propagation Length in Tm$_3$Fe$_5$O$_{12}$ Thin Films: Roles of Magnetic Anisotropy and Gilbert Damping,"The magnon propagation length ($\langle\xi\rangle$) of a ferro/ferrimagnet
+(FM) is one of the key factors that controls the generation and propagation of
+thermally-driven spin current in FM/heavy metal (HM) bilayer based
+spincaloritronic devices. Theory predicts that for the FM layer,
+$\langle\xi\rangle$ is inversely proportional to the Gilbert damping ($\alpha$)
+and the square root of the effective magnetic anisotropy constant ($K_{\rm
+eff}$). However, direct experimental evidence of this relationship is lacking.
+To experimentally confirm this prediction, we employ a combination of
+longitudinal spin Seebeck effect (LSSE), transverse susceptibility, and
+ferromagnetic resonance experiments to investigate the temperature evolution of
+$\langle\xi\rangle$ and establish its correlation with the effective magnetic
+anisotropy field, $H_K^{\rm eff}$ ($\propto K_{\rm eff}$) and $\alpha$ in
+Tm$_3$Fe$_5$O$_{12}$ (TmIG)/Pt bilayers. We observe concurrent drops in the
+LSSE voltage and $\langle\xi\rangle$ below 200$^\circ$K in TmIG/Pt bilayers
+regardless of TmIG film thickness and substrate choice and attribute it to the
+noticeable increases in $H_K^{\rm eff}$ and $\alpha$ that occur within the same
+temperature range. From the TmIG thickness dependence of the LSSE voltage, we
+determined the temperature dependence of $\langle\xi\rangle$ and highlighted
+its correlation with the temperature-dependent $H_K^{\rm eff}$ and $\alpha$ in
+TmIG/Pt bilayers, which will be beneficial for the development of rare-earth
+iron garnet-based efficient spincaloritronic nanodevices.",2308.07236v3
+2023-08-18,Large thermo-spin effects in Heusler alloy based spin-gapless semiconductor thin films,"Recently, Heusler alloys-based spin gapless semiconductors (SGSs) with high
+Curie temperature (TC) and sizeable spin polarization have emerged as potential
+candidates for tunable spintronic applications. We report comprehensive
+investigation of the temperature dependent ANE and intrinsic longitudinal spin
+Seebeck effect (LSSE) in CoFeCrGa thin films grown on MgO substrates. Our
+findings show the anomalous Nernst coefficient for the MgO/CoFeCrGa (95 nm)
+film is $\cong 1.86$ micro V/K at room temperature which is nearly two orders
+of magnitude higher than that of the bulk polycrystalline sample of CoFeCrGa (=
+0.018 micro V/K) but comparable to that of the magnetic Weyl semimetal Co2MnGa
+thin film (2-3 micro V/K). Furthermore, the LSSE coefficient for our
+MgO/CoFeCrGa(95nm)/Pt(5nm) heterostructure is $\cong 20.5$ $\mu$V/K/$\Omega$ at
+room temperature which is twice larger than that of the half-metallic
+ferromagnetic La$_{0.7}$Sr$_{0.3}$MnO$_3$ thin films ($\cong$ 20.5
+$\mu$V/K/$\Omega$). We show that both ANE and LSSE coefficients follow
+identical temperature dependences and exhibit a maximum at $\cong$ 225 K which
+is understood as the combined effects of inelastic magnon scatterings and
+reduced magnon population at low temperatures. Our analyses not only indicate
+that the extrinsic skew scattering is the dominating mechanism for ANE in these
+films but also provide critical insights into the functional form of the
+observed temperature dependent LSSE at low temperatures. Furthermore, by
+employing radio frequency transverse susceptibility and broadband ferromagnetic
+resonance in combination with the LSSE measurements, we establish a correlation
+among the observed LSSE signal, magnetic anisotropy and Gilbert damping of the
+CoFeCrGa thin films, which will be beneficial for fabricating tunable and
+highly efficient Heusler alloys based spincaloritronic nanodevices.",2308.09843v1
+2023-12-02,Interplay of topology and antiferromagnetic order in two-dimensional van der Waals crystals of (NixFe1-x)2P2S6,"Mermin-Wagner theorem forbid spontaneous symmetry breaking of spins in
+one/two-dimensional systems at finite temperature and rules out the
+stabilization of this ordered state. However, it does not apply to all types of
+phase transitions in low dimensions such as topologically ordered phase
+rigorously shown by Berezinskii-Kosterlitz-Thouless (BKT) and experimentally
+realized in very limited systems such as superfluids, superconducting thin
+films. Quasi 2D van der Waals magnets provide an ideal platform to investigate
+the fundamentals of low-dimensional magnetism. We explored the 2D honeycomb
+antiferromagnetic single crystals of (NixFe1-x)2P2S6 with varying spins ( )
+using in depth temperature dependent Raman measurements supported by
+first-principles calculations of the phonon frequencies. As a function of
+doping, a tunable transition from paramagnetic to antiferromagnetic ordering is
+shown via phonons reflected in the strong renormalization of the self-energy
+parameters of the Raman active phonon modes. An anomalously broad magnetic
+continuum attributed to two-magnon excitations is observed and its coupling
+with the phonons is revealed in the observation a Fano line asymmetry.
+Interestingly, the two-magnon continuum is observed only for the finite doping
+understood invoking underlying nature of insulator these materials belongs to,
+i.e. exchange interaction between transition metals via surrounding ligands
+(sulphur) and the resonance involving phonon modes associated with the (P2S6)
+cage. Quite surprisingly, we also observed renormalization of the phonon modes
+much below the long-range magnetic ordered temperature attributed to the
+topological ordered state, namely the BKT phase, which is also found to change
+as a function of doping. The extracted critical exponent of the order-parameter
+evince the signature of topologically active state driven by vortex-antivortex
+excitations.",2312.01098v1
+1993-08-23,The Quartet State of the Two-Dimensional Heisenberg Model with Spin 1/2 on a Square Lattice,"The low-energy properties of the two-dimensional Heisenberg model with
+spin-$\frac{1}{2}$ on a square lattice are investigated on the basis of the
+local dimer order. The lattice is divided into square blocks consisting of the
+quartet of spins. The spin variables and the Heisenberg Hamiltonian are
+expressed in terms of the low-energy quartet variables. On the basis of the
+Dyson-Maleev representation the spin-wave theory of the quartet state is
+developed. The spectrum of the lower magnon excitations consists of three
+degenerate modes with the energy gap $\Delta =0.17J$. The ground state energy
+per spin $E/N =-0.6J$. This preprint repeats in the main the previous one but
+it contains calculations of the basic corrections and therefore has complete
+character.",9308030v1
+1994-07-06,"Exact spectra, spin susceptibilities and order parameter of the quantum Heisenberg antiferromagnet on the triangular lattice","Exact spectra of periodic samples are computed up to $ N=36 $.
+  Evidence of an extensive set of low lying levels, lower than the softest
+magnons, is exhibited.
+  These low lying quantum states are degenerated in the thermodynamic limit;
+their symmetries and dynamics as well as their finite-size scaling are strong
+arguments in favor of N\'eel order.
+  It is shown that the N\'eel order parameter agrees with first-order spin-wave
+calculations. A simple explanation of the low energy dynamics is given as well
+as the numerical determinations of the energies, order parameter and spin
+susceptibilities of the studied samples. It is shown how suitable boundary
+conditions, which do not frustrate N\'eel order, allow the study of samples
+with $ N=3p+1 $ spins.
+  A thorough study of these situations is done in parallel with the more
+conventional case $ N=3p $.",9407028v1
+1994-11-14,$XXZ$ model as effective Hamiltonian for generalized Hubbard models with broken $η$-symmetry,"We consider the limit of strong Coulomb attraction for generalized Hubbard
+models with $\eta$-symmetry. In this limit these models are equivalent to the
+ferromagnetic spin-1/2 Heisenberg quantum spin chain. In order to study the
+behaviour of the superconducting phase in the electronic model under
+perturbations which break the $\eta$-symmetry we investigate the ground state
+of the ferromagnetic non-critical $XXZ$-chain in the sector with fixed
+magnetization. It turns out to be a large bound state of $N$ magnons. We find
+that the perturbations considered here lead to the disappearance of the
+off-diagonal longe-range order.",9411051v2
+1995-08-25,Inverse photoemission in strongly correlated electron systems,"Based on exact results for small clusters of 2D t-J model we demonstrate the
+existence of several distinct `channels' in its inverse photoemission (IPES)
+spectrum. Hole-like quasiparticles can either be annihilated completely, or
+leave behind a variable number of spin excitations, which formed the `dressing
+cloud' of the annihilated hole. In the physical parameter regime the latter
+processes carry the bulk of IPES weight and although the Fermi surface takes
+the form of hole pockets, the distribution of spectal weight including these
+`magnon-bands' in the IPES spectrum is reminiscent of free electrons. The
+emerging scenario for Fermiology and spectral weight distribution is shown to
+be consistent with photoemission, inverse photemission and de Haas--van Alphen
+experiments on cuprate superconductors.",9508114v1
+1995-12-15,The spectral gap of the ferromagnetic XXZ chain,"We prove that the spectral gap of the spin-1/2 ferromagnetic XXZ chain with
+Hamiltonian $H=-\sum_x S^{(1)}_xS^{(1)}_{x+1}+S^{(2)}_xS^{(2)}_{x+1} +\Delta
+S^{(3)}_xS^{(3)}_{x+1}$, is given by $\Delta-1$ for all $\Delta\geq 1$. This is
+the gap in the spectrum of the infinite chain in any of its ground states, the
+translation invariant ones as well as the kink ground states, which contain an
+interface between an {\it up} and a {\it down} region. In particular, this
+shows that the lowest magnon energy is not affected by the presence of a domain
+wall. This surprising fact is a consequence of the $SU_q(2)$ quantum group
+symmetry of the model.",9512120v1
+1996-04-30,Investigation of the Spin-Peierls transition in CuGeO_3 by Raman scattering,"Raman experiments on the spin-Peierls compound CuGeO$_3$ and the substituted
+(Cu$_{1- x}$,Zn$_x$)GeO$_3$ and Cu(Ge$_{1-x}$,Ga$_x$)O$_3$ compounds were
+performed in order to investigate the response of specific magnetic excitations
+of the one-dimensional spin-1/2 chain to spin anisotropies and
+substitution-induced disorder. In pure CuGeO$_3$, in addition to normal phonon
+scattering which is not affected at all by the spin-Peierls transition, four
+types of magnetic scattering features were observed. Below T$_{SP}$=14 K a
+singlet-triplet excitation at 30 cm$^{-1}$, two-magnon scattering from 30 to
+227 cm$^{-1}$ and folded phonon modes at 369 and 819 cm$^{-1}$ were identified.
+They were assigned by their temperature dependence and lineshape. For
+temperatures between the spin-Peierls transition T$_{SP}$ and approximately 100
+K a broad intensity maximum centered at 300 cm$^{-1}$ is observed.",9604181v1
+1996-06-04,On the Bilayer Coupling in the Yttrium-Barium Family of High Temperature Superconductors,"We derive the expressions needed to interpret experiments relating to
+interplane magnetic coupling in YBa$_{2}$Cu$_{3}$O$_{6+x}$ and related
+materials, and use the results to interpret measurements of the optical magnon
+energy in YBa_{2}Cu_{3}O_{6.2} and of the NMR ``cross-relaxation"" rate in
+Y_2Ba_{4}Cu_{7}O_{15}. We estimate $J_{\perp}\sim 14$ meV in both materials,
+and $\chi_{max}/\mu^2_{B} \sim 100$ {states}/{eV}-Cu in Y_2Ba_4Cu_7O_{15} at
+T=100K. We show that there is at present no obvious contradiction between the
+results of a widely-used analysis of NMR experiments and the results of neutron
+scattering experiments in the Y-Ba system. We argue that the 41 meV excitation
+observed in superconducting YBa_{2}Cu_{3}O_{7} is a collective mode pulled down
+below the superconducting gap by interactions, and that the observed
+antisymmetry under interchange of planes follows from the non-negligible value
+of $J_{\perp}$.",9606008v2
+1996-11-04,The J_1-J_2 model revisited : Phenomenology of CuGeO_3,"We present a mean field solution of the antiferromagnetic Heisenberg chain
+with nearest (J_1) and next to nearest neighbor (J_2) interactions. This
+solution provides a way to estimate the effects of frustration. We calculate
+the temperature-dependent spin-wave velocity, v_s(T) and discuss the
+possibility to determine the magnitude of frustration J_2/J_1 present in quasi
+1D compounds from measurements of v_s(T). We compute the thermodynamic
+susceptibility at finite temperatures and compare it with the observed
+susceptibility of the spin-Peierls compound CuGeO_3. We also use the method to
+study the two-magnon Raman continuum observed in CuGeO_3 above the spin-Peierls
+transition.",9611018v1
+1996-11-07,Substitution effects on spin fluctuations in the spin-Peierls compound CuGeO_3,"Using Raman scattering we studied the effect of substitutions on 1D spin
+fluctuations in CuGeO_3 observed as a spinon continuum in frustration induced
+exchange scattering. For temperatures below the spin-Peierls transition
+(T_{SP}=14K) the intensity of this continuum at 120-500 cm^{-1} is
+exponentially suppressed and transferred into a 3D two-magnon density of
+states. Besides a spin-Peierls gap-induced mode at 30 cm^{-1} and additional
+modes at 105 and 370 cm^{-1} are observed. Substitution of Zn on the Cu-site
+and Si on the Ge-site of CuGeO_3 quenches easily the spin-Peierls state.
+Consequently a suppression of the spin-Peierls gap observable below T_{SP}=14K
+as well as a change of the temperature dependence of the spinon continuum are
+observed. These effects are discussed in the context of a dimensional crossover
+of this compound below T_{SP} and strong spin-lattice interaction.",9611053v1
+1996-12-24,Spin polarons in the t-J model in an unconstrained representation,"The report discusses the slave-fermion representations of the t-J model and
+describes another representation, in which fermions and bosons are completely
+commuting and in which the properties of fermions are directly related to the
+properties of physical holes. For a study of the system in the new
+representation at half-filling, interaction of fermions with two magnons is
+treated in mean-field theory. The obtained effective model, in comparison to
+that of the usual slave-fermion representation, has an additional bare hole
+dispersion due to the hole moving by using quantum spin fluctuations present in
+the undoped antiferromagnetic ground state. The single-hole Green's function at
+half-filling is then found numerically using the self-consistent Born
+approximation. For all studied quantities good or excellent agreement with
+numerical data is observed in the entire parameter range, noticeably better
+than in the studies with the slave-fermion representation. Using the same
+effective model, the two-hole problem is also studied by solving numerically
+the Bethe-Salpeter equation with noncrossing diagrams.",9612215v2
+1997-02-19,Electronic structure and magnetism in Ru based perovskites,"The magnetic properties of (Ca,Sr)RuO_3 and Sr_2YRuO_6 are studied within the
+context of band structure based Stoner theory. LSDA calculations without
+recourse to strong correlation effects yield the correct magnetic behavior and
+order in all cases. Insulating character of Sr_2YRuO_6 is reproduced. The
+different magnetic states of SrRuO_3 and CaRuO_3 are shown to be due to the
+different structural distortions. CaRuO_3 is found to be on the verge of a
+ferromagnetic instability. O p states hybridize strongly with Ru d states in
+all three compounds, and O, through this hybridization plays an unusually large
+role in the magnetic properties. Transport properties of CaRuO_3 and SrRuO_3
+are analyzed using the calculated Fermiology. Unusually large magnon and
+paramagnon couplings are found, which are consistent with reported measurements
+of the low temperature specific heat and the resistivity coefficient. We also
+demonstrate how the calculated band structures can be understood in terms of a
+nearest neighbor tight binding model.",9702168v2
+1997-04-02,Dynamical properties of the spin-Peierls compound α'--NaV2O5,"Dynamical properties of the novel inorganic spin-Peierls compound
+\alpha'--NaV2O5 are investigated using a one-dimensional dimerized Heisenberg
+model. By exact diagonalizations of chains with up to 28 sites, supplemented by
+a finite-size scaling analysis, the dimerization parameter \delta is determined
+by requiring that the model reproduces the experimentally observed spin gap
+\Delta. The dynamical and static spin structure factors are calculated. As for
+CuGeO3, the existence of a low energy magnon branch separated from the
+continuum is predicted. The present calculations also suggest that a large
+magnetic Raman scattering intensity should appear above an energy threshold of
+1.9 \Delta. The predicted photoemission spectrum is qualitatively similar to
+results for an undimerized chain due to the presence of sizable short-range
+antiferromagnetic correlations.",9704015v3
+1997-05-05,Dynamical properties of low dimensional CuGeO3 and NaV2O5 systems,"Properties of low-dimensional spin-Peierls systems are described by using a
+one dimensional S=1/2 antiferromagnetic Heisenberg chain linearly coupled to a
+single phonon mode of wave vector pi (whose contribution is expected to be
+dominant). By exact diagonalizations of small rings with up to 24 sites
+supplemented by a finite size scaling analysis, static and dynamical properties
+are investigated. Numerical evidences are given for a spontaneous discrete
+symmetry breaking towards a spin gapped phase with a frozen lattice
+dimerization. Special emphasis is put on the comparative study of the two
+inorganic spin-Peierls compounds CuGeO3 and NaV2O5 and the model parameters are
+determined from a fit of the experimental spin gaps. We predict that the
+spin-phonon coupling is 2 or 3 times larger in NaV2O5 than in CuGeO3. Inelastic
+neutron scattering spectra are calculated and similar results are found in the
+single phonon mode approximation and in the model including a static
+dimerization. In particular, the magnon S=1 branch is clearly separated from
+the continuum of triplet excitations by a finite gap.",9705032v2
+1997-09-27,"Low-temperature electrical transport and double exchange in La(Pb,Ca)MnO","The resistivity in the ferromagnetic state of flux-grown
+La_{2/3}(Pb,Ca)_{1/3}MnO_3 single crystals, measured in magnetic fields up to 7
+T, reveals a strong quadratic temperature dependence at and above 50 K. At
+lower temperatures, this contribution drops precipitously leaving the
+resistivity essentially temperature independent below 20 K. The Seebeck
+coefficient also reflects a change of regime at the same temperature. We
+attribute this behavior to a cut-off of single magnon scattering processes at
+long wavelengths due to the polarized bands of a double-exchange ferromagnet.",9709305v3
+1997-12-19,Domain excitations in spin-Peierls systems,"We study a model of a Spin-Peierls material consisting of a set of
+antiferromagnetic Heisenberg chains coupled with phonons and interacting among
+them via an inter-chain elastic coupling. The excitation spectrum is analyzed
+by bosonization techniques and the self-harmonic approximation. The elementary
+excitation is the creation of a localized domain structure where the dimerized
+order is the opposite to the one of the surroundings. It is a triplet
+excitation whose formation energy is smaller than the magnon gap. Magnetic
+internal excitations of the domain are possible and give the further
+excitations of the system. We discuss these results in the context of recent
+experimental measurements on the inorganic Spin-Peierls compound CuGeO$_3$",9712239v2
+1998-01-28,Exact SO(8) Symmetry in the Weakly-Interacting Two-Leg Ladder,"A perturbative renormalization group analysis of interacting electrons on a
+two-leg ladder reveals that at half-filling any weakly repulsive system scales
+onto an exactly soluble Gross-Neveu model with a hidden SO(8) symmetry. The
+half-filled ground state is a Mott insulator with short-range d-wave pair
+correlations. We extract the exact energies, degeneracies, and quantum numbers
+of *all* the low energy excited multiplets. One energy (mass) m octets contains
+Cooper pair, magnon, and density-wave excitations, two more octets contain
+single-particle excitations, and a mass \sqrt{3}m antisymmetric tensor contains
+28 ""bound states"". Exact single-particle and spin gaps are found for the
+lightly-doped (d-wave paired one-dimension Bose fluid) system. We also
+determine the four other robust phases occuring at half-filling for partially
+attractive interactions. All 5 phases have distinct SO(8) symmetries, but share
+S.C. Zhang's SO(5) as a common subgroup.",9801285v1
+1998-02-27,Quantum spin chains in a magnetic field,"We demonstrate that the ``worm'' algorithm allows very effective and precise
+quantum Monte Carlo (QMC) simulations of spin systems in a magnetic field, and
+its auto-correlation time is rather insensitive to the value of H at low
+temperature. Magnetization curves for the $s=1/2$ and $s=1$ chains are
+presented and compared with existing Bethe ansatz and exact diagonalization
+results. From the Green function analysis we deduce the magnon spectra in the
+s=1 system, and directly establish the ""relativistic"" form E(p)=(\Delta ^2 +v^2
+p^2)^{1/2} of the dispersion law.",9802294v2
+1998-04-19,Impurities and Inelastic Processes in Magnetic Tunnel Junctions,"We have studied tunnel magnetoresistance (TMR) in junctions with 3d
+ferromagnetic electrodes. Previously we predicted that defects in the barrier
+would result in reduced effective polarization P of the impurity assisted
+current. This is confirmed experimentally in the present work: introductions of
+defects into the barrier drastically decreases the TMR. The degradation of
+magnetoresistance with bias has also been studied and shows universal features,
+attributed to effects of tunneling assisted by magnons and phonons, whose
+different role is described. Details of the bias dependence of the TMR depend
+on preparation procedures and well described by the model which includes
+assisted tunneling. Non-linear features, seen at low biases, are related to
+excitation of bulk modes by tunneling electrons. The analysis of factors
+resulting in fall-off of the TMR with bias is presented.",9804208v1
+1998-04-24,Perturbation Theory for Spin Ladders Using Angular-Momentum Coupled Bases,"We compute bulk properties of Heisenberg spin-1/2 ladders using
+Rayleigh-Schr\""odinger perturbation theory in the rung and plaquette bases. We
+formulate a method to extract high-order perturbative coefficients in the bulk
+limit from solutions for relatively small finite clusters. For example, a
+perturbative calculation for an isotropic $2\times 12$ ladder yields an
+eleventh-order estimate of the ground-state energy per site that is within
+0.02% of the density-matrix-renormalization-group (DMRG) value. Moreover, the
+method also enables a reliable estimate of the radius of convergence of the
+perturbative expansion. We find that for the rung basis the radius of
+convergence is $\lambda_c\simeq 0.8$, with $\lambda$ defining the ratio between
+the coupling along the chain relative to the coupling across the chain. In
+contrast, for the plaquette basis we estimate a radius of convergence of
+$\lambda_c\simeq 1.25$. Thus, we conclude that the plaquette basis offers the
+only currently available perturbative approach which can provide a reliable
+treatment of the physically interesting case of isotropic $(\lambda=1)$ spin
+ladders. We illustrate our methods by computing perturbative coefficients for
+the ground-state energy per site, the gap, and the one-magnon dispersion
+relation.",9804261v1
+1998-05-08,Physical properties of the double exchange and its relevance to the specific heat of double perovskite materials,"In response to the experimental discovery of double perovskite Ru- base
+material, The magnetic and electronic properties of the double exchange
+mechanism are studied theoretically. The electron band structure and the spin
+wave spectrum response at zero temperature with the canting background are
+computed from the first principle Hamiltonian. The long range Coulomb
+interaction between charge carriers is found to be crucial in stabilizing the
+canting order. A Monte Carlo simulation is performed on de-Gennes's effective
+magnetic Hamiltonian with classical spin approximation. The peaks of the
+specific heat as a function of temperature, which correspond to FM(AF) and
+canting transitions, and its response to the external magnetic field are
+consistent with the observation. For certain region of parameters, a more
+complex canting order than layer type is found at sufficiently low temperature.
+The effective interaction between carriers via exchanging a magnon wave is
+found to be rather similar to that via exchanging an acoustic phonon. The pros
+and cons to a genuine superconducting order in this system is analyzed.",9805094v1
+1998-05-29,Scaling theory of magnetic ordering in the Kondo lattices with anisotropic exchange interactions,"The lowest-order scaling consideration of the magnetic state formation in the
+Kondo lattices is performed within the $s-f$ model with inclusion of anisotropy
+for both the $f-f$ coupling and $s-f$ exchange interaction. The Kondo
+renormalizations of the effective transverse and longitudinal $s-f$ coupling
+parameters, spin-wave frequency, gap in the magnon spectrum and ordered moment
+are calculated in the case of both ferro- and antiferromagnets. The
+anisotropy-driven change of the scaling behavior (e.g., critical value of $g$
+for entering the strong-coupling region and the corresponding critical
+exponents) is investigated numerically for N=2 and analytically in the large-N
+limit. The dependence of the effective Kondo temperature on the bare $s-f$
+coupling parameter $g$ weakens in the presence of anisotropy. The relative
+anisotropy parameters for both the $s-f$ and $f-f$ coupling are demonstrated to
+decrease during the renormalization process. The role of next-nearest exchange
+interactions for this effect in the antiferromagnet is discussed.",9805390v2
+1998-06-13,Nonanalytic Magnetization Dependence of the Magnon Effective Mass in Itinerant Quantum Ferromagnets,"The spin wave dispersion relation in both clean and disordered itinerant
+quantum ferromagnets is calculated. It is found that effects akin to
+weak-localization physics cause the frequency of the spin-waves to be a
+nonanalytic function of the magnetization m. For low frequencies \Omega, small
+wavevectors k, and small m, the dispersion relation is found to be of the form
+\Omega ~ m^{1-\alpha} k^2, with \alpha = (4-d)/2 (2<d<4) for disordered
+systems, and \alpha = (3-d) (1<d<3) for clean ones. In d=4 (disordered) and d=3
+(clean), \Omega ~ m ln(1/m) k^2. Experiments to test these predictions are
+proposed.",9806168v3
+1998-06-22,Magnetic excitation spectra of $NaV_2O_5$,"We present low temperature Raman spectra of $NaV_2O_5$ single crystal. The
+assignation of the observed modes is done on the basis of Monte Carlo
+calculation of excited states of Heisenberg dimerized Hamiltonian, without
+frustration. We found a good agreement between measured and calculated magnetic
+excitations for $\delta=0.048$ and $J=452 K$. The singlet-triplet,
+singlet-singlet excitations as well as two-magnon mode are observed to be at
+66, 127 and 132 cm^{-1}.",9806258v2
+1998-08-07,Electromagnetic Interactions in the Quantum Hall Ferromagnet,"The $\nu =1$ quantum Hall ground state in samples like GaAs is well known to
+be ferromagnetic. The global SU(2) spin symmetry of the microscopic action is
+broken down to a U(1) symmetry by the ground state. The Goldstone bosons
+corresponding to this spontaneous breaking of symmetry are the ferromagnetic
+magnons which are neutral spin waves. In addition, there are topologically
+nontrivial, electrically charged spin excitations known as spin skyrmions,
+which in these samples are the favoured charge carriers. In this letter, we
+look into the electromagnetic coupling of these spin excitations. The discrete
+symmetries P and T are also broken by the ground state and we find that to the
+leading order, the electromagnetic interaction of the spin waves occurs through
+a nonminimal coupling given by a Chern-Simons like term containing both the
+electromagnetic potentials and the two Euler angles that specify the coset
+SU(2)/U(1) and thereby, the Goldstone bosons.",9808081v1
+1998-10-30,Phase diagram and magnons in quasi-one-dimensional dipolar antiferromagnets,"We investigate antiferromagnetic spin chains, which are coupled by a weak
+antiferromagnetic exchange interaction on a hexagonal lattice. We particulary
+study the role of the dipole-dipole interaction within the framework of a
+Heisenberg model with nearest-neighbor exchange and additional dipolar
+interaction. We find several commensurate and incommensurate phases depending
+on the ratio of dipolar energy to interchain-exchange energy due to their
+competing qualtity. The ground-state analysis is supplemented by a stability
+analysis by means of a linear spin-wave theory. In comparison with experiments
+(CsMnBr_3, RbMnBr_3) we obtain good agreement for the energy gaps. From this we
+conclude, that the dipolar interaction is the most important source of
+anisotropy in these Mn-compounds.",9810402v1
+1998-12-17,Incommensurability in the magnetic excitations of the bilinear-biquadratic spin-1 chain,"We study the magnetic excitation spectrum of the S=1 quantum Heisenberg spin
+chain with Hamiltonian : H = sum_i cos(theta) S_i S_i+1 + sin(theta) (S_i
+S_i+1)^2. We focus on the range -pi/4 < theta < +pi/4 where the spin chain is
+in the gapped Haldane phase. The excitation spectrum and static structure
+factor is studied using direct Lanczos diagonalization of small systems and
+density-matrix renormalization group techniques combined with the single-mode
+approximation. The magnon dispersion has a minimum at q=pi until a critical
+value theta_c = 0.38 is reached at which the curvature (velocity) vanishes.
+Beyond this point, which is distinct from the VBS point and the Lifshitz point,
+the minimum lies at an incommensurate value that goes smoothly to 2pi/3 when
+theta approaches pi/4, the Lai-Sutherland point. The mode remains isolated from
+the other states: there is no evidence of spinon deconfinement before the point
+theta =+pi/4. These findings explain recent observation of the magnetization
+curve M approx (H -H_c)^1/4 for theta =theta_c.",9812296v1
+1998-12-18,"Spinon signatures in the critical phase of the (1,1/2) ferrimagnet in a magnetic field","We propose an effective theory for the critical phase of a quantum
+ferrimagnetic chain with alternating spins 1 and 1/2 in an external magnetic
+field. With the help of the matrix product variational approach, the system is
+mapped to a spin-1/2 XXZ chain in an (effective) magnetic field; as a
+byproduct, we obtain an excellent description of the optical magnon branch in
+the gapped phase. Recent finite-temperature DMRG results for the
+low-temperature part of the specific heat are well described by the present
+approach, and the ``pop-up'' peaks, developing near the critical field values
+and in the middle of the critical phase, are identified with the contributions
+from two different spinon bands of the effective spin-1/2 chain. The effect
+should be as well observable in other spin-gap systems in an external field,
+particularly in spin ladders.",9812326v1
+1999-01-22,The Effective Theory of Hole Doped Spin-1 Chain,"An effective theory for the hole doped spin-1 antiferromagnetic chain is
+proposed in this paper. The two branches of low energy quasipaticle excitation
+is obtained by the diagrammic technique. In the large t limit(in which t is the
+hole hopping term), the lower band is essentially the bound state of one hole
+and one magnon and the other band is the sigle hole state. We find a critical
+value of t, $t_c=0.21\Delta_H$(in which $\Delta_H$ is the Haldane gap).For
+$t>t_c$, with the decrement of t, the mixing of these two bands become stronger
+and stronger, and at the same time the effective band mass becomes larger and
+larger. When $t<t_c$ the minimum of the lower band moves away from zero the
+another point between zero and $\pi/2$. The spin strcture factor is also
+calculated in this paper, and we find that for large t limit the main
+contribution is from the inter-band transition which induce a resonant peak in
+the Haldane gap. While for small t limit the main contribution is from the
+intra-band transition which only cause a diffusion like broad bump in the
+Haldan gap.",9901234v1
+1999-01-28,From Magnons to the Resonance Peak: Spin Dynamics in High-T_C Superconducting Cuprates by Inelastic Neutron Scattering,"The spin dynamics of high temperature superconductors measured by inelastic
+neutron scattering is reviewed. The spin susceptibility evolves a lot with
+increasing doping from the undoped insulating state to the overdoped metallic
+state. In the superconducting state, a strong magnetic resonance peak occurs in
+the spin excitation spectrum whose energy is proportional to the
+superconducting temperature. In underdoped and optimally doped regimes, normal
+state antiferromagnetic fluctuations are observed, proving the existence of
+strong electronic correlations in cuprates. They are characterized by a spin
+pseudo-gap. In contrast, these dynamical spin correlations vanish in overdoped
+samples.",9901333v2
+1999-02-19,Ground State and Excitations of Spin Chain with Orbital Degeneracy,"The one dimensional Heisenberg model in the presence of orbital degeneracy is
+studied at the SU(4) symmetric viewpoint by means of Bethe ansatz. Following
+Sutherland's previous work on an equivalent model, we discuss the ground state
+and the low-lying excitations more extensively in connection to the spin
+systems with orbital degeneracy. We show explicitly that the ground state is a
+SU(4) singlet. We study the degeneracies of the elementary excitations and the
+spectra of the generalized magnons consisting of these excitations. We also
+discuss the complex 2-strings in the context of the Bethe ansatz solutions.",9902269v3
+1999-02-26,The Effect of Ni and Zn Doping in Bi2212 from Tunneling Measurements. The MCS model of the High-Tc Superconductivity in hole-doped cuprates,"We use Ni and Zn impurities doped into Bi2212 to test the MS (Magnetic
+polaron - Spinon) model proposed earlier. We present electron-tunneling
+spectroscopy of pure, Ni- and Zn-doped Bi2212 single crystals below Tc using a
+break-junction technique. We show that the magnetic (Ni) and nonmagnetic (Zn)
+impurities doped into CuO2 planes affect both Tc and the density of states in
+Bi2212 but do it differently. In order to explain the data, we had to modify
+the MS model. Thus, we present a Magnetic Coupling of Stripes (MCS) model. In
+the MCS model, there is only one superconductivity - a spinon superconductivity
+along charged stripes. The coherent state of the spinon superconductivity is
+established by magnons which are excited by motions of charged stripes. So, in
+the MCS model, the superconductivity has two mechanisms: along charged stripes
+and perpendicular to stripes.",9902355v1
+1999-03-10,Functional Schrödinger Representations of Holstein-Primakoff Boson and Slave-Boson Theories for Heisenberg Antiferromagnets,"We present functional Schr\""odinger representations of Holstein-Primakoff
+boson and slave-boson theories for the Heisenberg Hamiltonian and the $t-J$
+Hamiltonian respectively. Based on these representations we obtain the
+dispersion relations of magnons for two dimensional antiferromagnets. By
+applying the functional Schr\""odinger representation of the Holstein-Primakoff
+boson theory to the Heisenberg Hamiltonian, the exchange energy is correctly
+predicted and the self-energy of quasi-hole is obtained. From the use of the
+functional Schr\""odinger representation of the $t-J$ Hamiltonian it is shown
+that at half-filling the dispersion relation obtained from the slave-boson
+theory leads to that obtained from the Holstein-Primakoff boson approach.",9903159v1
+1999-04-06,On the estimate of the spin-gap in quasi-1D Heisenberg antiferromagnets from nuclear spin-lattice relaxation,"We present a careful analysis of the temperature dependence of the nuclear
+spin-lattice relaxation rate $1/T_1$ in gapped quasi-1D Heisenberg
+antiferromagnets. It is found that in order to estimate the value of the gap
+correctly from $1/T_1$ the peculiar features of the dispersion curve for the
+triplet excitations must be taken into account. The temperature dependence of
+$1/T_1$ due to two-magnon processes, is reported for different values of the
+ratio $r=J_{\perp}/J_{\parallel}$ between the superexchange constants in a
+2-leg-ladder. As an illustrative example we compare our results to the
+experimental findings for $^{63}Cu 1/T_1$ in the dimerized chains and
+2-leg-ladders contained in Sr$_{14}Cu_{24}O_{41}$",9904074v1
+1999-06-23,The underscreened Kondo effect in ladder systems,"We introduce a new Kondo ladder model by coupling the well-known
+Takhtajan-Babujan S=1 chain to a half-filled one-dimensional electron gas, and
+we solve it using quantum field theory techniques. Through the so-called
+underscreened Kondo effect, this gives novel insights into low-dimensional spin
+liquid systems. For instance, the optical conductivity reveals only a pseudogap
+at $k=\pi$ despite of the insulating state, a coherent magnon peak in the
+dynamical spin susceptibility coexists with an incoherent spinon background,
+the magnetization yields a fractional-like quantization. More generally, this
+problem belongs to the class of Luttinger liquids in active environments, a
+topic of importance not only to the Kondo physics, but also to striped phases
+or carbon nanotubes. Experimental consequences on heavy-fermion systems are
+also discussed.",9906345v1
+1999-07-13,On the nature of the transition from the spontaneously dimerized to the Neel phase in the two-dimensional J1-J2 model,"We analyze the spectrum of the 2D S=1/2 frustrated Heisenberg model near the
+transition from the spontaneously dimerized spin-liquid phase into the Neel
+ordered phase. Two excitation branches: the triplet magnon, and the collective
+singlet mode, both become gapless at the transition point. However we find that
+the length scales associated with these modes are well separated at the quantum
+transition. While in the quantum disordered phase the singlet excitation has
+finite spectral weight and reflects the existence of spontaneous dimer order,
+near the transition point the size of the singlet bound state grows
+exponentially with the correlation length, and hence the quasiparticle residue
+is exponentially small. Therefore the critical dynamics remains in the O(3)
+universality class in spite of the four gapless modes.",9907178v1
+1999-07-22,Charge carrier density collapse in La_0.67Ca_0.33MnO_3 and La_0.67Sr_0.33MnO_3 epitaxial thin films,"We measured the temperature dependence of the linear high field Hall
+resistivity of La_0.67Ca_0.33MnO_3 (T_C=232K) and La_0.67Sr_0.33MnO_3
+(T_C=345K) thin films in the temperature range from 4K up to 360K in magnetic
+fields up to 20T. At low temperatures we find a charge carrier density of 1.3
+and 1.4 holes per unit cell for the Ca- and Sr-doped compound, respectively. In
+this temperature range electron-magnon scattering contributes to the
+longitudinal resistivity. At the ferromagnetic transition temperature T_C a
+dramatic drop in the number of current carriers $n$ down to 0.6 holes per unit
+cell, accompanied by an increase in unit cell volume, is observed. Corrections
+of the Hall data due to a non saturated magnetic state will lead a more
+pronounced charge carrier density collapse.",9907346v1
+1999-10-18,Three-Dimensional Ordering in Weakly Coupled Antiferromagnetic Ladders and Chains,"A theoretical description is presented for low-temperature magnetic-field
+induced three-dimensional (3D) ordering transitions in strongly anisotropic
+quantum antiferromagnets, consisting of weakly coupled antiferromagnetic
+spin-1/2 chains and ladders. First, effective continuum field theories are
+derived for the one-dimensional subsystems. Then the Luttinger parameters,
+which determine the low-temperature susceptibilities of the chains and ladders,
+are calculated from the Bethe ansatz solution for these effective models. The
+3D ordering transition line is obtained using a random phase approximation for
+the weak inter-chain (inter-ladder) coupling. Finally, considering a Ginzburg
+criterion, the fluctuation corrections to this approach are shown to be small.
+The nature of the 3D ordered phase resembles a Bose condensate of integer-spin
+magnons. It is proposed that for systems with higher spin degrees of freedom,
+e.g. N-leg spin-1/2 ladders, multi-component condensates can occur at high
+magnetic fields.",9910259v1
+1999-11-03,Does the Heisenberg model describe the multimagnon spin dynamics in antiferromagnetic CuO layers ?,"We compute the absorption spectrum for multimagnon excitations assisted by
+phonons in insulating layered cuprates using exact diagonalization in clusters
+of up to 32 sites. The resulting line shape is very sensitive to the underlying
+magnetic Hamiltonian describing the spin dynamics. For the usual Heisenberg
+description of undoped Cu-O planes we find, in accordance with experiment, a
+two-magnon peak followed by high energy side bands. However the relative weight
+of the side bands is too small to reproduce the experiment. An extended
+Heisenberg model including a sizable four-site cyclic exchange term is shown to
+be consistent with the experimental data.",9911037v1
+1999-11-09,Nanoconstriction Microscopy of the Giant Magnetoresistance in Cobalt/Copper Spin Valves,"We use nanometer-sized point contacts to a Co/Cu spin valve to study the
+giant magnetoresistance (GMR) of only a few Co domains. The measured data show
+strong device-to-device differences of the GMR curve, which we attribute to the
+absence of averaging over many domains. The GMR ratio decreases with increasing
+bias current. For one particular device, this is accompanied by the development
+of two distinct GMR plateaus, the plateau level depending on bias polarity and
+sweep direction of the magnetic field. We attribute the observed behavior to
+current-induced changes of the magnetization, involving spin transfer due to
+incoherent emission of magnons and self-field effects.",9911133v1
+1999-11-18,Time-resolved optical observation of spin-wave dynamics,"We have created a nonequilibrium population of antiferromagnetic spin-waves
+in Cr2O3, and characterized its dynamics, using frequency- and time-resolved
+nonlinear optical spectroscopy of the exciton-magnon transition. We observe a
+time-dependent pump-probe line shape, which results from excitation induced
+renormalization of the spin-wave band structure. We present a model that
+reproduces the basic characteristics of the data, in which we postulate the
+optical nonlinearity to be dominated by interactions with long-wavelength
+spin-waves, and the dynamics to be due to spin-wave thermalization.",9911294v1
+1999-11-30,Two-dimensional frustrated Heisenberg model: Variational study,"The stability of the ferromagnetic phase of the 2D quantum spin-1/2 model
+with nearest-neighbor ferro- and next-nearest neighbor antiferromagnetic
+interactions is studied. It turns out that values of exchange integrals at
+which the ferromagnetic state becomes unstable with respect to a creation of
+one and two magnon are different. This difference shows that the classical
+approximation is inapplicable to the study of the transition from the
+ferromagnetic to the singlet state in contrast with 1D case. This problem is
+investigated using a variational function of new type. It is based on the boson
+representation of spin operators which is different from the Holstein-Primakoff
+approximation. This allows us to obtain the accurate estimate of the transition
+point and to study the character of the phase transition.",9911491v1
+2000-01-21,Electron momentum distribution of a single mobile hole in the t-J model,"We investigate the electron momentum distribution function (EMDF) for the
+two-dimensional t-J model. The results are based on the self-consistent Born
+approximation (SCBA) for the self-energy and the wave function. In the Ising
+limit of the model we give the results in a closed form, in the Heisenberg
+limit the results are obtained numerically. An anomalous momentum dependence of
+EMDF is found and the anomaly is in the lowest order in number of magnons
+expressed analitycally. We interpret the anomaly as a fingerprint of an
+emerging large Fermi surface coexisting with hole pockets.",0001306v1
+2000-02-28,Spin stripe dimerization in the t-J model,"In the present work we demonstrate that the spin columnar dimerized phase
+(conducting spin stripe liquid) is stable at doping $x_{c1} < x < x_{c2}$. At
+$x < x_{c1}$ the system undergoes phase transition to the Neel state, and at $x
+> x_{c2}$ it is Normal Fermi liquid. At t/J=3 the critical concentrations are
+$x_{c1}\approx 0.09$ and $x_{c2}\sim 0.36$. To prove stability of the stripe
+phase and to calculate critical concentrations we employ two approaches. The
+first one is more technically involved, and it gives more accurate value of the
+critical concentration. The approach is based on the calculation of the magnon
+Green's function. Imaginary poles in the Green's function indicate transition
+to the Neel state. The second approach consists in direct comparison of ground
+state energies of the Neel state and the columnar dimerized state. Both
+approaches demonstrate stability of the spin stripe phase and give close values
+of the critical concentrations.",0002421v1
+2000-03-02,On the dynamics of coupled S=1/2 antiferromagnetic zig-zag chains,"We investigate the elementary excitations of quasi one-dimensional S=1/2
+systems built up from zig-zag chains with general isotropic exchange constants,
+using exact (Lanczos) diagonalization for 24 spins and series expansions
+starting from the decoupled dimer limit. For the ideal one-dimensional zig-zag
+chain we discuss the systematic variation of the basic (magnon) triplet
+excitation with general exchange parameters and in particular the presence of
+practically flat dispersions in certain regions of phase space. We extend the
+dimer expansion in order to include the effects of 3D interactions on the
+spectra of weakly interacting zig-zag chains. In an application to KCuCl_3 we
+show that this approach allows to determine the exchange interactions between
+individual pairs of spins from the spectra as determined in recent neutron
+scattering experiments.",0003028v2
+2000-03-07,Diagonalization of a bosonic quadratic form using CCM: Application on a system with two interpenetrating square lattice antiferromagnets,"While the diagonalization of a quadratic bosonic form can always be done
+using a Bogoliubov transformation, the practical implementation for systems
+with a large number of different bosons is a tedious analytical task. Here we
+use the coupled cluster method (CCM) to exactly diagonalise such complicated
+quadratic forms. This yields to a straightforward algorithm which can easily be
+implemented using computer algebra even for a large number of different bosons.
+We apply this method on a Heisenberg system with two interpenetrating square
+lattice antiferromagnets, which is a model for the quasi 2D antiferromagnet
+Ba_2Cu_3O_4Cl_2. Using a four-magnon spin wave approximation we get a
+complicated Hamiltonian with four different bosons, which is treated with CCM.
+Results are presented for magnetic ground state correlations.",0003105v1
+2000-04-10,Quantum Impurity in a Nearly Critical Two Dimensional Antiferromagnet,"We describe the spin dynamics of an arbitrary localized impurity in an
+insulating two dimensional antiferromagnet, across the host transition from a
+paramagnet with a spin gap to a Neel state. The impurity spin susceptibility
+has a Curie-like divergence at the quantum-critical coupling, but with a
+universal, effective spin which is neither an integer nor a half-odd-integer.
+In the Neel state, the transverse impurity susceptibility is a universal number
+divided by the host spin stiffness (which determines the energy cost to slow
+twists in the orientation of the Neel order). These, and numerous other results
+for the thermodynamics, Knight shift, and magnon damping have significant
+applications to experiments on layered transition metal oxides.",0004156v1
+2000-05-23,Critical properties of projected SO(5) models at finite temperatures,"We consider the projected SO(5) bosonic model introduced in order to connect
+the SO(5) theory of high-T$_c$ superconductivity with the physics of the
+Mott-insulating gap, and derive the corresponding effective functional
+describing low-energy degrees of freedom. At the
+antiferromagnetic-superconducting transition, SO(5) symmetry-breaking effects
+due to the gap are purely quantum mechanical and become irrelevant in the
+neighborhood of a possible finite-temperature multicritical point separating
+the normal from the antiferromagnetic and the superconducting phases. A
+difference in the magnon and hole-pair mobility always takes the system away
+from the SO(5)-symmetric fixed point towards a region of instability, and the
+phase transition between the normal and the two ordered phases becomes first
+order before merging into the antiferromagnetic-superconducting line. Quantum
+fluctuations at intermediate temperatures, while introducing symmetry-breaking
+terms in the case of equal mobilities, tend to cancel the symmetry-breaking
+effects in the case of different mobilities.",0005385v1
+2000-07-27,Oscillatory Curie temperature of two-dimensional ferromagnets,"The effective exchange interactions of magnetic overlayers Fe/Cu(001) and
+Co/Cu(001) covered by a Cu-cap layer of varying thickness were calculated in
+real space from first principles. The effective two-dimensional Heisenberg
+Hamiltonian was constructed and used to estimate magnon dispersion laws,
+spin-wave stiffness constants, and overlayer Curie temperatures within the
+mean-field and random-phase approximations. Overlayer Curie temperature
+oscillates as a function of the cap-layer thickness in a qualitative agreement
+with a recent experiment.",0007446v3
+2000-08-22,Elementary excitations in one-dimensional spin-orbital models: neutral and charged solitons and their bound states,"We study, both numerically and variationally, the interplay between different
+types of elementary excitations in the model of a spin chain with anisotropic
+spin-orbit coupling, in the vicinity of the ""dimer line"" with an exactly known
+dimerized ground state. Our variational treatment is found to be in a
+qualitative agreement with the exact diagonalization results. Soliton pairs are
+shown to be the lowest excitations only in a very narrow region of the phase
+diagram near the dimer line, and the phase transitions are always governed by
+magnon-type excitations which can be viewed as soliton-antisoliton bound
+states. It is shown that when the anisotropy exceeds certain critical value, a
+new phase boundary appears. In the doped model on the dimer line, the exact
+elementary charge excitation is shown to be a hole bound to a soliton. Bound
+states of those ""charged solitons"" are studied; exact solutions for N-hole
+bound states are presented.",0008321v1
+2000-09-12,Magnetization jump in the XXZ chain with next-nearest-neighbor exchange,"We study the dependence of the magnetization M with magnetic field B at zero
+temperature in the spin-1/2 XXZ chain with nearest-neighbor (NN) J1 and next-NN
+J2 exchange interactions, with anisotropies Delta1 and Delta2 respectively. The
+region of parameters for which a jump in M(B) exists is studied using numerical
+diagonalization, and analytical results for two magnons on a ferromagnetic
+background in the thermodynamic limit. We find a line in the parameter space
+(J2/J1, Delta1/J1, Delta2/J2) (determined by two simple equations) at which the
+ground state is highly degenerate. M(B) has a jump near this line, and at or
+near the isotropic case with ferromagnetic J1 and antiferromagnetic J2, with
+|J2/J1| near 1/4. These results are relevant for some systems containing CuO
+chains with edge-sharing CuO4 units.",0009175v1
+2000-09-27,Projected SO(5) Hamiltonian for Cuprates and Its Applications,"The projected SO(5) (pSO(5)) Hamiltonian incorporates the quantum spin and
+superconducting fluctuations of underdoped cuprates in terms of four bosons
+moving on a coarse grained lattice. A simple mean field approximation can
+explain some key feautures of the experimental phase diagram: (i) The Mott
+transition between antiferromagnet and superconductor, (ii) The increase of T_c
+and superfluid stiffness with hole concentration x and (iii) The increase of
+antiferromagnetic resonance energy as sqrt{x-x_c} in the superconducting phase.
+We apply this theory to explain the ``two gaps'' problem found in underdoped
+cuprate Superconductor-Normal- Superconductor junctions. In particular we
+explain the sharp subgap Andreev peaks of the differential resistance, as
+signatures of the antiferromagnetic resonance (the magnon mass gap). A critical
+test of this theory is proposed. The tunneling charge, as measured by shot
+noise, should change by increments of Delta Q= 2e at the Andreev peaks, rather
+than by Delta Q=e as in conventional superconductors.",0009421v1
+2000-10-11,Magnetic properties of (VO)_2P_2O_7: two-plane structure and spin-phonon interactions,"Detailed experiments on single-crystal (VO)_2P_2O_7 continue to reveal new
+and unexpected features. We show that a model composed of two, independent
+planes of spin chains with frustrated magnetic coupling is consistent with
+nuclear magnetic resonance and inelastic neutron scattering measurements. The
+pivotal role of PO_4 groups in mediating intrachain exchange interactions
+explains both the presence of two chain types and their extreme sensitivity to
+certain lattice vibrations, which results in the strong magnetoelastic coupling
+observed by light scattering. We compute the respective modifications of the
+spin and phonon dynamics due to this coupling, and illustrate their observable
+consequences on the phonon frequencies, magnon dispersions, static
+susceptibility and specific heat.",0010168v1
+2000-10-25,Specific Heat Study of the Field-Induced Magnetic Ordering in the Spin Gap System TlCuCl$_3$,"Specific heat measurements have been performed in the coupled dimer system
+TlCuCl$_3$, which has a singlet ground state with the excitation gap $\Delta
+\simeq 7.5$K. The cusplike anomaly indicative of the 3D magnetic ordering was
+clearly observed in magnetic fields higher than the critical field $H_c$
+corresponding to the gap $\Delta$. The phase boundary determined by the present
+specific heat measurements coincides with that determined by previous
+magnetization measurements. The phase boundary can be described by the power
+law $[ H_{\rm c}(T)-H_{\rm g} ] \propto T^{\phi}$ with $\phi=2.1(1)$. This
+result supports the magnon Bose condensation picture for the field-induced
+magnetic ordering in TlCuCl$_3$ [Nikuni {\it et al}., Phys. Rev. Lett. {\bf 84}
+(2000) 5868].",0010383v2
+2000-10-26,Fingerprints of spin-fermion pairing in cuprates,"We demonstrate that the feedback effect from bosonic excitations on fermions,
+which in the past allowed one to verify the phononic mechanism of a
+conventional, $s-$wave superconductivity, may also allow one to experimentally
+detect the ``fingerprints'' of the pairing mechanism in cuprates. We argue that
+for spin-mediated $d-$wave superconductivity, the fermionic spectral function,
+the density of states, the tunneling conductance through an insulating
+junction, and the optical conductivity are affected by the interaction with
+collective spin excitations, which below $T_c$ are propagating, magnon-like
+quasiparticles with gap $\Delta_s$.
+  We show that the interaction with a propagating spin excitation gives rise to
+singularities at frequencies $\Delta + \Delta_s$ for the spectral function and
+the density of states, and at
+  $2\Delta + \Delta_s$ for tunneling and optical conductivities, where $\Delta$
+is the maximum value of the $d-$wave gap. We further argue that recent optical
+measurements also allow one to detect subleading singularities at $4\Delta$ and
+$2\Delta + 2\Delta_s$. We consider the experimental detection of these
+singularities as a strong evidence in favor of the magnetic scenario for
+superconductivity in cuprates.",0010403v1
+2001-01-10,Soliton dynamics in 3D ferromagnets,"We study the dynamics of solitons in a Landau-Lifshitz equation describing
+the magnetization of a three-dimensional ferromagnet with an easy axis
+anisotropy. We numerically compute the energy dispersion relation and the
+structure of moving solitons, using a constrained minimization algorithm. We
+compare the results with those obtained using an approximate form for the
+moving soliton, valid in the small momentum limit. We also study the
+interaction and scattering of two solitons, through a numerical simulation of
+the (3+1)-dimensional equations of motion. We find that the force between two
+solitons can be either attractive or repulsive depending on their relative
+internal phase and that in a collision two solitons can form an unstable
+oscillating loop of magnons.",0101129v1
+2001-01-18,Observation of Field-Induced Transverse Néel Ordering in the Spin Gap System TlCuCl$_3$,"Neutron elastic scattering experiments have been performed on the spin gap
+system TlCuCl$_3$ in magnetic fields parallel to the $b$-axis. The magnetic
+Bragg peaks which indicate the field-induced N\'{e}el ordering were observed
+for magnetic field higher than the gap field $H_{\rm g}\approx 5.5$ T at $Q=(h,
+0, l)$ with odd $l$ in the $a^*-c^*$ plane. The spin structure in the ordered
+phase was determined. The temperature and field dependence of the Bragg peak
+intensities and the phase boundary obtained were discussed in connection with a
+recent theory which describes the field-induced N\'{e}el ordering as a
+Bose-Einstein condensation of magnons.",0101276v2
+2001-02-12,Quantum effects in the quasiparticle structure of the ferromagnetic Kondo lattice model,"A new ``Dynamical Mean-field theory'' based approach for the Kondo lattice
+model with quantum spins is introduced. The inspection of exactly solvable
+limiting cases and several known approximation methods, namely the second-order
+perturbation theory, the self-consistent CPA and finally a moment-conserving
+decoupling of the equations of motion help in evaluating the new approach. This
+comprehensive investigation gives some certainty to our results: Whereas our
+method is somewhat limited in the investigation of the J<0-model, the results
+for J>0 reveal important aspects of the physics of the model: The energetically
+lowest states are not completely spin-polarized.A band splitting, which occurs
+already for relatively low interaction strengths, can be related to distinct
+elementary excitations, namely magnon emission (absorption) and the formation
+of magnetic polarons. We demonstrate the properties of the ferromagnetic Kondo
+lattice model in terms of spectral densities and quasiparticle densities of
+states.",0102210v1
+2001-03-09,Intermediate phase in the spiral antiferromagnet Ba_2CuGe_2O_7,"The magnetic compound Ba_2CuGe_2O_7 has recently been shown to be an
+essentially two-dimensional spiral antiferromagnet that exhibits an
+incommensurate-to-commensurate phase transition when a magnetic field applied
+along the c-axis exceeds a certain critical value H_c. The T=0 dynamics is
+described here in terms of a continuum field theory in the form of a nonlinear
+sigma model. We are thus in a position to carry out a complete calculation of
+the low-energy magnon spectrum for any strength of the applied field throughout
+the phase transition. In particular, our spin-wave analysis reveals
+field-induced instabilities at two distinct critical fields H_1 and H_2 such
+that H_1 < H_c < H_2. Hence we predict the existence of an intermediate phase
+whose detailed nature is also studied to some extent in the present paper.",0103217v2
+2001-03-21,"Observation of two-magnon bound states in the two-leg ladders of (Ca,La)14Cu24O41","Phonon-assisted 2-magnon absorption is studied at T=4 K in the spin-1/2
+two-leg ladders of Ca_14-x La_x Cu_24 O_41 (x=5 and 4) for polarization of the
+electrical field parallel to the legs and the rungs, respectively. Two peaks at
+about 2140 and 2800 1/cm reflect van-Hove singularities in the density of
+states of the strongly dispersing 2-magnon singlet bound state, and a broad
+peak at about 4000 1/cm is identified with the 2-magnon continuum. Two
+different theoretical approaches (Jordan-Wigner fermions and perturbation
+theory) describe the data very well for J_parallel = 1050 - 1100 1/cm and
+J_parallel / J_perp = 1 - 1.1. A striking similarity of the high-energy
+continuum absorption of the ladders and of the undoped high T_c cuprates is
+observed.",0103438v1
+2001-03-24,Interaction-round-a-face density-matrix renormalization-group method,"A brief review of the interaction-round-a-face (IRF) density-matrix
+renormalization-group (DMRG) method. We have demonstrated the numerical
+superiority of IRF-DMRG method applied to SU(2) invariant quantum spin chains
+over the conventional DMRG. The ground state energy densities and the gap
+energies of both $S = 1$ and $S = 2$ spin chains can be calculated using the
+IRF-DMRG without extensive computations. We have also studied the effect of
+tuning boundary interaction $J_{\rm end}^{~}$ at both ends of the chain from
+the IRF view point. It is clearly observed that the magnon distribution is
+uniform when the best $J_{\rm end}^{~}$ is chosen.",0103508v1
+2001-04-27,Raman scattering study of phonon and spin modes in (TMTSF)2PF6,"We have studied polarized Raman spectra of (TMTSF)2PF6 single crystals in the
+wide spectral and temperature range using different laser energies. We observed
+and assigned 23 Raman active modes. The carbon C=C in-phase and out-of-phase
+stretching modes at 1464 cm-1 and 1602 cm-1 show strong
+electron-molecular-vibration coupling. The mode at about 1565 cm-1 is
+temperature independent below 50 K due to the methyl group motion freezing. For
+(TMTSF)2PF6 in the spin density wave phase for a temperature induced
+dimensionality 1D (quarter filled dimerized linear chain with correlated
+electrons) the spin gapless magnon spectra have been calculated. No evidence of
+spin-lattice coupling or spin-related modes is found in the Raman spectra in
+the spin density wave phase.",0104528v1
+2001-05-03,Zero-field Time Correlation Functions of Four Classical Heisenberg Spins on a Ring,"A model relevant for the study of certain molecular magnets is the ring of
+N=4 classical spins with equal near-neighbor isotropic Heisenberg exchange
+interactions. Assuming classical Heisenberg spin dynamics, we solve explicitly
+for the time evolution of each of the spins. Exact triple integral
+representations are derived for the auto, near-neighbor, and
+next-nearest-neighbor time correlation functions for any temperature. At
+infinite temperature, the correlation functions are reduced to quadrature. We
+then evaluate the Fourier transforms of these functions in closed form, which
+are double integrals. At low temperatures, the Fourier transform functions
+explicitly demonstrate the presence of magnons. Our exact results for the
+infinite temperature correlation functions in the long-time asymptotic limit
+differ qualitatively from those obtained assuming diffusive spin dynamics.
+Whether such explicitly non-hydrodynamic behavior would be maintained for
+large-N rings is discussed.",0105050v1
+2001-08-01,A microscopic model for the structural transition and spin gap formation in alpha'-NaV2O5,"We present a microscopic model for alpha'-NaV2O5. Using an extended Hubbard
+model for the vanadium layers we derive an effective low-energy model
+consisting of pseudospin Ising chains and Heisenberg chains coupled to each
+other. We find a ``spin-Peierls-Ising'' phase transition which causes charge
+ordering on every second ladder and superexchange alternation on the other
+ladders. This transition can be identified with the first transition of the two
+closeby transitions observed in experiment. Due to charge ordering the
+effective coupling between the lattice and the superexchange is enhanced. This
+is demonstrated within a Slater-Koster approximation. It leads to a second
+instability with superexchange alternation on the charge-ordered ladders due to
+an alternating shift of the O sites on the rungs of that ladder. We can explain
+within our model the observed spin gap, the anomalous BCS ratio, and the
+anomalous shift of the critical temperature of the first transition in a
+magnetic field. To test the calculated superstructure we determine the
+low-energy magnon dispersion and find agreement with experiment.",0108008v1
+2001-08-27,Superconductivity and Quantum Phase Transitions in Weak Itinerant Ferromagnets,"It is argued that the phase transition in low-T_c clean itinerant
+ferromagnets is generically of first order, due to correlation effects that
+lead to a nonanalytic term in the free energy. A tricritical point separates
+the line of first order transitions from Heisenberg critical behavior at higher
+temperatures. Sufficiently strong quenched disorder suppresses the first order
+transition via the appearance of a critical endpoint. A semi-quantitative
+discussion is given in terms of recent experiments on MnSi and UGe_2. It is
+then shown that the critical temperature for spin-triplet, p-wave
+superconductivity mediated by spin fluctuations is generically much higher in a
+Heisenberg ferromagnetic phase than in a paramagnetic one, due to the coupling
+of magnons to the longitudinal magnetic susceptibility. This qualitatively
+explains the phase diagram recently observed in UGe_2 and ZrZn_2.",0108443v1
+2001-08-30,Spin dynamics of Sr_14Cu_24O_41 two-leg ladder studied by Raman spectroscopy,"The two-magnon (2M) excitation at 3000 cm-1 in Sr_14Cu_24O_41 two-leg ladder
+is studied by Raman scattering. A slight anisotropy of the superexchange
+coupling J_{\perp}/J_{||} \approx 0.8 with J_{||} = 110 \pm 20 meV is proposed
+from the analysis of the magnetic scattering. The resonant coupling across the
+charge transfer gap increases the 2M intensity by orders of magnitude. The
+anisotropy of Raman scattering is dependent upon the excitation energy. The 2M
+relaxation is found to be correlated with the temperature dependent electronic
+Raman continuum at low frequencies.",0108507v2
+2002-02-07,Carrier induced ferromagnetism in diluted magnetic semi-conductors,"We present a theory for carrier induced ferromagnetism in diluted magnetic
+semi-conductor (DMS). Our approach treats on equal footing quantum fluctuations
+within the RPA approximation and disorder within CPA. This method allows for
+the calculation of $T_c$, magnetization and magnon spectrum as a function of
+hole, impurity concentration and temperature. It is shown that, sufficiently
+close to $T_c$, and within our decoupling scheme (Tyablicov type) the CPA for
+the itinerant electron gas reduces to the Virtual Crystal Approximation. This
+allows, in the low impurity concentration and low density of carriers to
+provide analytical expression for $T_c$. For illustration, we consider the case
+of $Ga_{1-c}Mn_{c}As$ and compare our results with available experimental data.",0202111v1
+2002-02-07,Resistivity extrema in double exchange ferromagnetic nondegenerate semiconductors,"A version of the magnetoimpurity theory of the colossal magnetoresistance
+materials suitable for the double exchange ferromagnetic nondegenerate
+semiconductors is presented. It provides an explanation of the nonmonotonic
+temperature dependence for the charge carrier density in them when it displays
+first a maximum and then a minimum, on increase in temperature. Respectively,
+the resistivity displays first a minimum and then a maximum. The theory is
+based on the relation between the charge carrier activation energy and the
+change in the magnon free energy caused by the ionization of an impurity. This
+is tantamount to the relation between the charge carrier density and the so
+called giant red shift of the optical absorption edge.",0202126v1
+2002-02-09,Ferromagnets and antiferromagnets in the effective Lagrangian perspective,"Nonrelativistic systems exhibiting collective magnetic behavior are analyzed
+within the framework of effective Lagrangians. The method, which formulates the
+dynamics of the system in terms of Goldstone bosons, allows to investigate the
+consequences of spontaneous symmetry breaking from a unified point of view.
+Analogies and differences with respect to the Lorentz-invariant situation
+(chiral perturbation theory) are pointed out. We then consider the
+low-temperature expansion of the partition function both for ferro- and
+antiferromagnets, where the spin waves or magnons represent the Goldstone
+bosons of the spontaneously broken symmetry $O(3) \to O(2)$. In particular, the
+low-temperature series of the staggered magnetization for antiferromagnets and
+the spontaneous magnetization for ferromagnets are compared with the condensed
+matter literature.",0202153v1
+2002-03-14,Random Bond Effect in the Quantum Spin System (Tl$_{1-x}$K$_{x}$)CuCl$_3$,"The effect of exchange bond randomness on the ground state and the
+field-induced magnetic ordering was investigated through magnetization
+measurements in the spin-1/2 mixed quantum spin system
+(Tl$_{1-x}$K$_{x}$)CuCl$_3$ for $x<0.36$. Both parent compounds TlCuCl$_3$ and
+KCuCl$_3$ are coupled spin dimer systems, which have the singlet ground state
+with excitation gaps ${\Delta}/k_{\rm B}=7.7$ K and 31 K, respectively. Due to
+bond randomness, the singlet ground state turns into the magnetic state with
+finite susceptibility, nevertheless, the excitation gap remains. Field-induced
+magnetic ordering, which can be described by the Bose condensation of excited
+triplets, magnons, was observed as in the parent systems. The phase transition
+temperature is suppressed by the bond randomness. This behavior may be
+attributed to the localization effect.",0203293v2
+2002-05-17,Thermodynamic Properties of Weakly Anisotropic Disordered Magnetic Chains in the Large-S Limit,"we investigate the thermodynamic properties of weakly anisotropic disordered
+magnetic chains where the nearest-neighbor Heisenberg exchange coupling is the
+dominant spin-spin interaction. In addition to the exchange interaction, there
+is single-ion anisotropy with the direction of the easy axis being the same for
+all spins. The analysis is carried out in the limit S >> 1, where S denotes the
+ionic spin, and in the temperature range T << JaveS, where Jave is the average
+magnitude of the exchange interaction. It is assumed that the independent boson
+picture is appropriate so that the thermodynamic properties of the chain are
+those of a gas of weakly interacting magnons whose frequencies are obtained
+from linearized equations of motion for the spins. The =+/-J model is studied
+in detail with both random and non-random anisotropy. Particular emphasis is
+placed on the existence",0205372v1
+2002-05-21,Field-Induced Magnetic Ordering in the Quantum Spin System KCuCl$_3$,"KCuCl$_3$ is a three-dimensional coupled spin-dimer system and has a singlet
+ground state with an excitation gap ${\Delta}/k_{\rm B}=31$ K. High-field
+magnetization measurements for KCuCl$_3$ have been performed in static magnetic
+fields of up to 30 T and in pulsed magnetic fields of up to 60 T. The entire
+magnetization curve including the saturation region was obtained at $T=1.3$ K.
+  From the analysis of the magnetization curve, it was found that the exchange
+parameters determined from the dispersion relations of the magnetic excitations
+should be reduced, which suggests the importance of the renormalization effect
+in the magnetic excitations. The field-induced magnetic ordering accompanied by
+the cusplike minimum of the magnetization was observed as in the isomorphous
+compound TlCuCl$_3$. The phase boundary was almost independent of the field
+direction, and is represented by the power law. These results are consistent
+with the magnon Bose-Einstein condensation picture for field-induced magnetic
+ordering.",0205429v1
+2002-05-27,Resistivity and thermoelectric power measurements on CeFe$_2$ and its pseudobinaries,"Resistivity and thermoelectric power (TEP) measurements on CeFe$_2$ and two
+of its pseudo-binaries Ce(Fe, 5% Ir)$_2$ and Ce(Fe, 7% Ru)$_2$ between 78K and
+275K are reported. The resistivity data are analysed in terms of contributions
+from scattering due to phonon, magnon, spin fluctuation and lattice defects,
+and also from interband scattering. Attempts are made to analyze the TEP data
+in terms of these resistivity components. Thermal hysteresis is observed in the
+temperature dependence of TEP in the Ir and Ru doped CeFe$_2$ samples around
+the ferromagnetic to antiferromagnetic transition, indicating the first order
+nature of this transition.",0205539v1
+2002-06-24,"Pressure-Tuned Collapse of the Mott-Like State in Ca_{n+1}Ru_nO_{3n+1} (n=1,2): Raman Spectroscopic Studies","We report a Raman scattering study of the pressure-induced collapse of the
+Mott-like phases of Ca_3Ru_2O_7 (T_N=56 K) and Ca_2RuO_4 (T_N=110 K). The
+pressure-dependence of the phonon and two-magnon excitations in these materials
+indicate: (i) a pressure-induced collapse of the antiferromagnetic (AF)
+insulating phase above P* ~ 55 kbar in Ca_3Ru_2O_7 and P* ~ 5-10 kbar in
+Ca_2RuO_4, reflecting the importance of Ru-O octahedral distortions in
+stabilizing the AF insulating phase; and (ii) evidence for persistent AF
+correlations above the critical pressure of Ca_2RuO_4, suggestive of phase
+separation involving AF insulator and ferromagnetic metal phases.",0206455v2
+2002-07-02,Exchange interactions and Curie temperature in (GaMn)As,"We use supercell and frozen-magnon approaches to study the dependence of the
+magnetic interactions in (Ga,Mn)As on the Mn concentration. We report the
+parameters of the exchange interaction between Mn spins and the estimates of
+the Curie temperature within the mean-field and random-phase approximations. In
+agreement with experiment we obtain a nonmonotonous dependence of the Curie
+temperature on the Mn concentration. We estimate the dependence of the Curie
+temperature on the concentration of the carries in the system and show that the
+decrease of the number of holes in the valence band leads to fast decrease of
+the Curie temperature. We show that the hole states of the valence band are
+more efficient in mediating the exchange interaction between Mn spins than the
+electron states of the conduction band.",0207050v1
+2002-07-30,Microscopic relaxation mechanisms and linear magnetization dynamics,"Linear magnetization dynamics in the presense of a thermal bath is analyzed
+for two general classes of microscopic damping mechanisms. The resulting
+stochastic differential equations are always in the form of a damped harmonic
+oscillator driven by a thermal field. The damping term contains both the
+interaction mechanisms and the symmetry of the magnetic system. Back
+transformation from the oscillator coordinates to the magnetization variables
+results in a macroscopic tensor form of damping that reflects the system
+anisotropy. Scalar Landau-Lifshitz-Gilbert damping term is valid only for
+systems with axial symmetry. Analysis of FMR linewith measurements versus
+frequency, temperature, and film thickness in NiFe films shows good agreement
+with a combination of slow-relaxing impurity and magnon-electron confluence
+processes.",0207721v1
+2002-09-23,Magnetization transport and quantized spin conductance,"We analyze transport of magnetization in insulating systems described by a
+spin Hamiltonian. The magnetization current through a quasi one-dimensional
+magnetic wire of finite length suspended between two bulk magnets is determined
+by the spin conductance which remains finite in the ballistic limit due to
+contact resistance. For ferromagnetic systems, magnetization transport can be
+viewed as transmission of magnons and the spin conductance depends on the
+temperature T. For antiferromagnetic isotropic spin-1/2 chains, the spin
+conductance is quantized in units of order $(g \mu_B)^2/h$ at T=0.
+Magnetization currents produce an electric field and hence can be measured
+directly. For magnetization transport in electric fields phenomena analogous to
+the Hall effect emerge.",0209521v2
+2002-11-26,Spin dynamics of stripes,"The spin dynamics of stripes in high-temperature superconductors and related
+compounds is studied in the framework of a spin-wave theory for a simple
+spin-only model. The magnon dispersion relation and the magnetic structure
+factor are calculated for diagonal and vertical stripes. Acoustical as well as
+optical bands are included in the analysis. The incommensurability and the
+$\pi$ resonance appear as complementary features of the band structure at
+different energy scales. The dependence of spin-wave velocities and resonance
+frequencies on the stripe spacing and coupling is calculated. At low doping,
+the resonance frequency is found to scale roughly inversely proportional to the
+stripe spacing. The favorable comparison of the results with experimental data
+suggests that the spin-only model provides a suitable and simple basis for
+calculating and understanding the spin dynamics of stripes.",0211593v1
+2003-01-10,Quantum Spin Chains with Nonlocally-Correlated Random Exchange Coupling and Random-Mass Dirac Fermions,"S=1/2 quantum spin chains and ladders with random exchange coupling are
+studied by using an effective low-energy field theory and transfer matrix
+methods. Effects of the nonlocal correlations of exchange couplings are
+investigated numerically. In particular we calculate localization length of
+magnons, density of states, correlation functions and multifractal exponents as
+a function of the correlation length of the exchange couplings. As the
+correlation length increases, there occurs a ""phase transition"" and the above
+quantities exhibit different behaviors in two phases. This suggests that the
+strong-randomness fixed point of the random spin chains and random-singlet
+state get unstable by the long-range correlations of the random exchange
+couplings.",0301139v2
+2003-04-15,Ferromagnetic Kondo-Lattice Model,"We present a many-body approach to the electronic and magnetic properties of
+the (multiband) Kondo-lattice model with ferromagnetic interband exchange. The
+coupling between itinerant conduction electrons and localized magnetic moments
+leads, on the one hand, to a distinct temperature-dependence of the electronic
+quasiparticle spectrum and, on the other hand, to magnetic properties, as
+e.~g.the Curie temperature T_C or the magnon dispersion, which are strongly
+influenced by the band electron selfenergy and therewith in particular by the
+carrier density. We present results for the single-band Kondo-lattice model in
+terms of quasiparticle densities of states and quasiparticle band structures
+and demonstrate the density-dependence of the self-consistently derived Curie
+temperature. The transition from weak-coupling (RKKY) to strong-coupling
+(double exchange) behaviour is worked out.
+  The multiband model is combined with a tight-binding-LMTO bandstructure
+calculation to describe real magnetic materials. As an example we present
+results for the archetypal ferromagnetic local-moment systems EuO and EuS. The
+proposed method avoids the double counting of relevant interactions and takes
+into account the correct symmetry of atomic orbitals.",0304338v1
+2003-04-24,Ferromagnetism in a dilute magnetic semiconductor -- Generalized RKKY interaction and spin-wave excitations,"Carrier-mediated ferromagnetism in a dilute magnetic semiconductor has been
+studied using i) a single-impurity based generalized RKKY approach which goes
+beyond linear response theory, and ii) a mean-field-plus-spin-fluctuation
+(MF+SF) approach within a (purely fermionic) Hubbard-model representation of
+the magnetic impurities, which incorporates dynamical effects associated with
+finite frequency spin correlations in the ordered state. Due to a competition
+between the magnitude of the carrier spin polarization and its oscillation
+length scale, the ferromagnetic spin coupling is found to be optimized with
+respect to both hole doping concentration and impurity-carrier spin coupling
+energy $J$ (or equivalently $U$). The ferromagnetic transition temperature
+$T_c$, deteremined within the spin-fluctuation theory, corresponds closely with
+the observed $T_c$ values. Positional disorder of magnetic impurities causes
+significant stiffening of the high-energy magnon modes. We also explicitly
+study the stability/instability of the mean-field ferromagnetic state, which
+highlights the role of competing AF interactions causing spin twisting and
+noncollinear ferromagnetic ordering.",0304557v2
+2003-05-21,Disorder Effect on Spin Excitation in Double Exchange Systems,"Spin excitation spectrum is studied in the double exchange model in the
+presence of disorder. Spin wave approximation is applied in the lowest order of
+1/S expansion. The disorder causes anomalies in the spin excitation spectrum
+such as broadening, branching, anticrossing with gap opening. The origin of the
+anomalies is the Friedel oscillation, in which the perfectly polarized
+electrons form the charge density wave to screen the disorder effect. Near the
+zone center $q = 0$, the linewidth has a $q$ linear component while the
+excitation energy scales to $q^2$, which indicates that the magnon excitation
+is incoherent. As $q$ increases, there appears a crossover from this incoherent
+behavior to the marginally coherent one in which both the linewidth and the
+excitation energy are proportional to $q^2$. The results are compared with
+experimental results in colossal magnetoresistance manganese oxides.
+Quantitative comparison of the linewidth suggests that spatially-correlated or
+mesoscopic-scale disorder is more relevant in real compounds than local or
+atomic-scale disorder. Comparison with other theoretical proposals is also
+discussed. Experimental tests are proposed for the relevance of disorder.",0305488v2
+2003-06-05,Quasiparticle vanishing driven by geometrical frustration,"We investigate the single hole dynamics in the triangular t-J model. We study
+the structure of the hole spectral function, assuming the existence of a 120
+magnetic Neel order. Within the self-consistent Born approximation (SCBA) there
+is a strong momentum and t sign dependence of the spectra, related to the
+underlying magnetic structure and the particle-hole asymmetry of the model. For
+positive t, and in the strong coupling regime, we find that the low energy
+quasiparticle excitations vanish outside the neighbourhood of the magnetic
+Goldstone modes; while for negative t the quasiparticle excitations are always
+well defined. In the latter, we also find resonances of magnetic origin whose
+energies scale as (J/t)^2/3 and can be identified with string excitations. We
+argue that this complex structure of the spectra is due to the subtle interplay
+between magnon-assisted and free hopping mechanisms. Our predictions are
+supported by an excellent agreement between the SCBA and the exact results on
+finite size clusters. We conclude that the conventional quasiparticle picture
+can be broken by the effect of geometrical magnetic frustration.",0306147v3
+2003-07-10,Non-dissipative thermal transport in the massive regimes of the XXZ chain,"We present exact results on the thermal conductivity of the one-dimensional
+spin-1/2 XXZ model in the massive antiferromagnetic and ferromagnetic regimes.
+The thermal Drude weight is calculated by a lattice path integral formulation.
+Numerical results for wide ranges of temperature and anisotropy as well as
+analytical results in the low and high temperature limits are presented. At
+finite temperature, the thermal Drude weight is finite and hence there is
+non-dissipative thermal transport even in the massive regime. At low
+temperature, the thermal Drude weight behaves as $D(T)\sim
+\exp(-\delta/T)/\sqrt{T}$ where $\delta$ is the one-spinon (respectively
+one-magnon) excitation energy for the antiferromagnetic (respectively
+ferromagnetic) regime.",0307227v1
+2003-07-10,Vortex behavior near a spin vacancy in 2D XY-magnets,"The dynamical behavior of anisotropic two dimensional Heisenberg models is
+still a matter of controversy. The existence of a central peak at all
+temperatures and a rich structure of magnon peaks are not yet understood. It
+seems that the central peaks are related, in some way, to structures like
+vortices. In order to contribute to the discussion of the dynamical behavior of
+the model we use Monte Carlo and spin dynamics simulations as well analytical
+calculations to study the behavior of vortices in the presence of nonmagnetic
+impurities. Our simulations show that vortices are attracted and trapped by the
+impurities. Using this result we show that if we suppose that vortices are not
+very much disturbed by the presence of the impurities, then they work as an
+attractive potential to the vortices explaining the observed behavior in our
+simulations.",0307245v1
+2003-07-16,Diffusive energy transport in the S=1 Haldane chain compound AgVP2S6,"We present the results of measurements of the thermal conductivity $\kappa$
+of the spin S=1 chain compound AgVP_2S_6 in the temperature range between 2 and
+300 K and with the heat flow directed either along or perpendicular to the
+chain direction. The analysis of the anisotropy of the heat transport allowed
+for the identification of a small but non-negligible magnon contribution
+$\kappa_m$ along the chains, superimposed on the dominant phonon contribution
+$\kappa_ph$. At temperatures above about 100 K the energy diffusion constant
+D_E(T), calculated from the $\kappa_m(T)$ data, exhibits similar features as
+the spin diffusion constant D_S(T), previously measured by NMR. In this regime,
+the behaviour of both transport parameters is consistent with a diffusion
+process that is caused by interactions inherent to one-dimensional S=1 spin
+systems.",0307383v1
+2003-08-14,Inhomogeneous CuO_{6} Tilt Distribution and Charge/Spin Correlations in La_{2-x-y}Nd_{y}Sr_{x}CuO$_{4} around commensurate hole concentration,"Phononic and magnetic Raman scattering are studied in
+La$_{2-x-y}$Nd$_{y}$Sr$_{x}$CuO$_{4}$ with three doping concentrations: x ~
+1/8, y = 0; x ~ 1/8, y = 0.4; and x = 0.01, y = 0. We observe strong disorder
+in the tilt pattern of the CuO_{6} octahedra in both the orthorhombic and
+tetragonal phases which persist down to 10 K and are coupled to bond disorder
+in the cation layers around 1/8 doping independent of Nd concentration. The
+weak magnitude of existing charge/spin modulations in the Nd doped structure
+does not allow us to detect the specific Raman signatures on lattice dynamics
+or two-magnon scattering around 2200 cm-1.",0308295v1
+2003-08-26,Dynamics of an anisotropic Haldane antiferromagnet in strong magnetic field,"We report the results of elastic and inelastic neutron scattering experiments
+on the Haldane gap quantum antiferromagnet Ni(C5D14N2)2N3(PF6) performed at mK
+temperatures in a wide range of magnetic field applied parallel to the S = 1
+spin chains. Even though this geometry is closest to an ideal axially symmetric
+configuration, the Haldane gap closes at the critical field Hc~4T, but reopens
+again at higher fields. The field dependence of the two lowest magnon modes is
+experimentally studied and the results are compared with the predictions of
+several theoretical models. We conclude that of several existing theories, only
+the recently proposed model [Zheludev et al., cond-mat/0301424 ] is able to
+reproduce all the features observed experimentally for different field
+orientations.",0308545v1
+2003-09-18,Magnetization plateaus in frustrated antiferromagnetic quantum spin models,"Plateaus can be observed in the zero-temperature magnetization curve of
+quantum spin systems at rational values of the magnetization. In one dimension,
+the appearance of a plateau is controlled by a quantization condition for the
+magnetization which involves the length of the local spin and the volume of a
+translational unit cell of the ground state. We discuss examples of
+geometrically frustrated quantum spin systems with large (in general unbounded)
+periodicities of spontaneous breaking of translational symmetry in the ground
+state.
+  In two dimensions, we discuss the square, triangular and Kagome lattices
+using exact diagonalization (ED) for up to N=40 sites. For the spin-1/2 XXZ
+model on the triangular lattice we study the nature and stability region of a
+plateau at one third of the saturation magnetization. The Kagome lattice gives
+rise to particularly rich behaviour with several plateaus in the magnetization
+curve and a jump due to local magnon excitations just below saturation.",0309425v2
+2003-10-09,Exchange interactions in (ZnMn)Se,"One of the remarkable properties of the II-VI diluted magnetic semiconductor
+(ZnMn)Se is the giant spin splitting of the valence band states under
+application of the magnetic field (giant Zeeman splitting). This splitting
+reveals strong exchange interaction between Mn moments and semiconductor
+states. On the other hand, no magnetic phase transition has been observed for
+systems with small Mn content up to very low temperatures. The latter property
+shows weakness of the exchange interaction between Mn moments. In this paper,
+the local density approximation (LDA) and the LDA+U techniques are employed to
+study exchange interactions in (ZnMn)Se. Supercell and frozen-magnon approaches
+applied earlier to III-V diluted magnetic semiconductors are used. It is found
+that both LDA and LDA+U describe successfully the combination of the strong
+Zeeman splitting and weak interatomic exchange. However, the physical pictures
+provided by two techniques differ strongly. A detailed analysis shows that the
+LDA+U method provides the description of the system which is much closer to the
+experimental data.",0310206v1
+2003-10-23,On implementation of ferrite magnetostatic/magnetoelectric particles for quantum computation,"We consider an implementation of quantum gates for quantum computation using
+magnetostatic/magnetoelectric (MS/ME) macroscopically quantized states in small
+ferrite disks. Confinement phenomena for MS oscillations in a normally
+magnetized ferrite disk show typical atomic properties like discrete energy
+levels. Because of discrete energy eigenstates of MS oscillations, the
+oscillating system is described as a collective motion of quasi-particles - the
+light magnons. A macroscopic quantum analysis of MS oscillations underlines the
+physics of quantized ME oscillating spectrums in ferrite disks with surface
+electrodes. We discuss possible technologies for physical realization of new
+logic gates based on MS/ME-particle qubits.",0310558v1
+2003-11-22,Influence of a Uniform Current on Collective Magnetization Dynamics in a Ferromagnetic Metal,"We discuss the influence of a uniform current, $\vec{j} $, on the
+magnetization dynamics of a ferromagnetic metal. We find that the magnon energy
+$\epsilon(\vec{q})$ has a current-induced contribution proportional to
+$\vec{q}\cdot \vec{\cal J}$, where $\vec{\cal J}$ is the spin-current, and
+predict that collective dynamics will be more strongly damped at finite ${\vec
+j}$. We obtain similar results for models with and without local moment
+participation in the magnetic order. For transition metal ferromagnets, we
+estimate that the uniform magnetic state will be destabilized for $j \gtrsim
+10^{9} {\rm A} {\rm cm}^{-2}$. We discuss the relationship of this effect to
+the spin-torque effects that alter magnetization dynamics in inhomogeneous
+magnetic systems.",0311522v1
+2003-11-24,Charge-Density-Wave Formation in the Doped Two-Leg Extended Hubbard Ladder,"We investigate electronic properties of the doped two-leg Hubbard ladder with
+both the onsite and the nearest-neighbor Coulomb repulsions, by using the the
+weak-coupling renormalization-group method. It is shown that, for strong
+nearest-neighbor repulsions, the charge-density-wave state coexisting with the
+p-density-wave state becomes dominant fluctuation where spins form intrachain
+singlets. By increasing doping rate, we have also shown that the effects of the
+nearest-neighbor repulsions are reduced and the system exhibits a quantum phase
+transition into the d-wave-like (or rung-singlet) superconducting state. We
+derive the effective fermion theory which describes the critical properties of
+the transition point with the gapless excitation of magnon. The phase diagram
+of the two-leg ladder compound, Sr_{14-x}Ca_xCu_{24}O_{41}, is discussed.",0311534v2
+2003-12-02,Frustrated antiferromagnets at high fields: the Bose-Einstein condensation in degenerate spectra,"Quantum phase transition at the saturation field is studied for a class of
+frustrated quantum antiferromagnets. The considered models include (i) the
+$J_1$-$J_2$ frustrated square-lattice antiferromagnet with $J_2={1/2}J_1$ and
+(ii) the nearest-neighbor Heisenberg antiferromagnet on a face centered cubic
+lattice. In the fully saturated phase the magnon spectra for the two models
+have lines of degenerate minima. Transition into partially magnetized state is
+treated via a mapping to a dilute gas of hard core bosons and by complementary
+spin-wave calculations. Momentum dependence of the exact four-point boson
+vertex removes the degeneracy of the single-particle excitation spectra and
+selects the ordering wave-vectors at $(\pi,\pi)$ and $(\pi,0,0)$ for the two
+models. The asymptotic behavior of the magnetization curve differs
+significantly from that of conventional antiferromagnet in $d$-spatial
+dimensions. We predict a unique form for the magnetization curve $\Delta
+M=S-M\simeq \mu^{(d-1)/2}(\log\mu)^{(d-1)}$, where $\mu$ is a distance from the
+quantum critical point.",0312076v2
+2003-12-17,Goldstone-Mode Relaxation in a Quantized Hall Ferromagnet in the Presence of Smooth Random Potential,"We discuss the spin relaxation of a strongly correlated two-dimensional (2D)
+electron gas (2DEG) in the quantized Hall regime when the filling factor is
+close to an odd-integer. As the initial state we consider a coherent deviation
+of the spin system from the ${\bf B}$ direction and investigate a break-down of
+this Goldstone-mode state due to the spin-orbit (SO) coupling and smooth
+disorder. The spin relaxation (SR) process is considered in terms of
+annihilation transitions in the system of spin excitons (magnons).",0312427v5
+2003-12-23,Ferromagnetic tunneling junctions at low voltages: elastic versus inelastic scattering at $T=0 K$,"In this paper we analyze different contributions to the magnetoresistance of
+magnetic tunneling junctions at low voltages. A substantial fraction of the
+resistance drop with voltage can be ascribed to variations of the density of
+states and the barrier transmission with the bias. However, we found that the
+anomaly observed at zero bias and the magnetoresistance behavior at very small
+voltages, point to the contribution of inelastic magnon-assisted tunneling. The
+latter is described by a transfer parameter $T^{J}$, which is one or two orders
+of magnitude smaller than $T^{d}$, the direct transmission for elastic
+currents. Our theory is in excellent agreement with experimental data, yielding
+estimated values of $T^{J}$ which are of the order of $T^{d}$ / $T^{J}$ ~ 40.",0312608v1
+2004-04-07,"First-principles calculation of the intersublattice exchange interactions and Curie temperatures of full Heusler alloys Ni2MnX (X=Ga, In, Sn, Sb)","The interatomic exchange interactions and Curie temperatures in Ni-based full
+Heusler alloys Ni2MnX with X=Ga, In, Sn and Sb are studied within the framework
+of the density-functional theory. The calculation of the exchange parameters is
+based on the frozen-magnon approach. Despite closeness of the experimental
+Curie temperatures for all four systems their magnetism appeared to differ
+strongly. This difference involves both the Mn-Mn and Mn-Ni exchange
+interactions. The Curie temperatures, Tc, are calculated within the mean-field
+approximation by solving a matrix equation for a multi-sublattice system. Good
+agreement with experiment for all four systems is obtained. The role of
+different exchange interactions in the formation of Tc of the systems is
+discussed.",0404162v1
+2004-04-08,Finite low-temperature entropy of some strongly frustrated quantum spin lattices in the vicinity of the saturation field,"For a class of highly frustrated antiferromagnetic quantum spin lattices the
+ground state exhibits a huge degeneracy in high magnetic fields due to the
+existence of localized magnon states. For some of these spin lattices (in
+particular, the 1D dimer-plaquette, sawtooth and kagom\'{e}-like chains as well
+as the 2D kagom\'{e} lattice) we calculate rigorously the ground-state entropy
+at the saturation field. We find that the ground-state entropy per site remains
+finite at saturation. This residual ground-state entropy produces a maximum in
+the field dependence of the isothermal entropy at low temperatures. By
+numerical calculation of the field dependence of the low-temperature entropy
+for the sawtooth chain we find that the enhancement of isothermal entropy is
+robust against small deviations in exchange constants. Moreover, the effect is
+most pronounced in the extreme quantum case of spin 1/2.",0404204v1
+2004-05-17,Itinerant Ferromagnetism and Superconductivity,"Superconductivity has again become a challenge following the discovery of
+unconventional superconductivity. Resistance-free currents have been observed
+in heavy-fermion materials, organic conductors and copper oxides. The discovery
+of superconductivity in a single crystal of $UGe_2$, $ZrZn_2$ and $URhGe$
+revived the interest in the coexistence of superconductivity and
+ferromagnetism. The experiments indicate that: i)The superconductivity is
+confined to the ferromagnetic phase. ii)The ferromagnetic order is stable
+within the superconducting phase (neutron scattering experiments). iii) The
+specific heat anomaly associated with the superconductivity in these materials
+appears to be absent. The specific heat depends on the temperature linearly at
+low temperature.
+  I present a review of the recent experimental results and the basic
+theoretical ideas concerning ferromagnetic superconductivity
+(FM-superconductivity) induced by the ferromagnetic spin fluctuations. A
+particular attention is paid to the magnon exchange mechanism of
+FM-superconductivity.",0405371v2
+2004-06-04,Absence of magnetic order for the spin-half Heisenberg antiferromagnet on the star lattice,"We study the ground-state properties of the spin-half Heisenberg
+antiferromagnet on the two-dimensional star lattice by spin-wave theory, exact
+diagonalization and a variational mean-field approach. We find evidence that
+the star lattice is (besides the \kagome lattice) a second candidate among the
+11 uniform Archimedean lattices where quantum fluctuations in combination with
+frustration lead to a quantum paramagnetic ground state. Although the classical
+ground state of the Heisenberg antiferromagnet on the star exhibits a huge
+non-trivial degeneracy like on the \kagome lattice, its quantum ground state is
+most likely dimerized with a gap to all excitations. Finally, we find several
+candidates for plateaux in the magnetization curve as well as a macroscopic
+magnetization jump to saturation due to independent localized magnon states.",0406103v2
+2004-08-02,Disorder in Diluted Spin Systems,"The influence of substitutional disorder on the magnetic properties of
+diluted Heisenberg spin systems is studied with regard to the magnetic
+stability of ferromagnetic diluted semiconductors (DMS). The equation of motion
+for the magnon Green's function within Tyablikov approximation is solved
+numerically for finite systems. The resulting spectral density is then used to
+estimate the magnetization and Curie temperature of an infinite system. This
+method is suitable for any form of a ferromagnetic exchange interaction.
+Besides different lattices and spin magnitude $S$, exchange interactions of
+different range are examined. The results show that, for short-range
+interaction, no magnetic order exists below the critical percolation
+concentration, whereas a linear dependence of the Curie temperature on the
+concentration of spins is found for ferromagnetic long-range interaction.",0408039v1
+2004-08-02,Topological Theory of Electron-Phonon Interactions in High Temperature Superconductors,"There are large isotope effects in the phonon kinks observed in photoemission
+spectra (ARPES) of optimally doped cuprate high temperature superconductors
+(HTSC), but they are quite different (Gweon et al. 2004) from those expected
+for a nearly free electron metal with strong electron-phonon interactions (Tang
+et al. 2003). These differences, together with many other anomalies in infrared
+spectra, seem to suggest that other particles (such as magnons) must be
+contributing to HTSC. Here we use topological (non-Hamiltonian) methods to
+discuss the data, emphasizing nanoscale phase separation and the importance of
+a narrow band of quantum percolative states near the Fermi energy that is
+spatially pinned to a self-organized filamentary dopant array. Topological
+discrete, noncontinuum, nonperturbative methods have previously explained the
+form of HTSC phase diagrams without involving detailed microscopic assumptions,
+and they are especially useful in the presence of strong nanoscale disorder.
+These methods also explain the ``miracle'' of an ideal nearly free electron
+phonon kink in sharply defined nodal quasiparticle states in LSCO at the
+metal-insulator transition. Finally the universality of the kink energy and
+Fermi velocity in different cuprates is the result of the marginally elastic
+nature of these materials, and specifically the isostatic character of the CuO2
+planes.",0408040v1
+2004-09-04,Stochastic dynamic simulations of fast remagnetization processes: recent advances and applications,"Numerical simulations of fast remagnetization processes using the stochastic
+dynamics are widely used to study various magnetic systems. In this paper we
+first address several crucial methodological problems of such simulations: (i)
+the influence of the finite-element discretization on the simulated dynamics,
+(ii) choice between Ito and Stratonovich stochastic calculi by the solution of
+micromagnetic stochastic equations of motion and (iii) non-trivial correlation
+properties of the random (thermal) field. Next we discuss several examples to
+demonstrate the great potential of the Langevin dynamics for studying fast
+remagnetization processes in technically relevant applications: we present
+numerical analysis of equilibrium magnon spectra in patterned structures, study
+thermal noise effects on the magnetization dynamics of nanoelements in pulsed
+fields and show some results for a remagnetization dynamics induced by a
+spin-polarized current.",0409098v1
+2004-09-21,The field-induced magnetic ordering transition in TlCuCl$_3$,"In the first part we investigate in detail if the Bose-Einstein condensation
+scenario for magnons can quantitatively explain the observed field-induced
+magnetic ordering in TlCuCl$_3$. We use a bond-operator approach to map the
+spin system onto hard-core bosons and exactly account for the hard-core
+constraint in the dilute limit. We solve the hard-core model within the
+Hartree-Fock-Popov approximation and discuss its validity and the consequences
+of this approximation for the critical properties. In the second part the
+effects of spin-phonon and spin-orbit coupling are discussed within this
+framework. We show that the experimental magnetization and specific heat data
+are well described if a certain type of anisotropy is included. We also present
+predictions for the quasiparticle gap which might be tested in the future.",0409530v1
+2004-10-01,Magnetic Properties of Cuprate Perovskites,"The magnetic susceptibility of underdoped yttrium and lanthanum cuprates is
+interpreted based on the self-consistent solution of the t-J model of a Cu-O
+plane. The calculations reproduce correctly the frequency dependencies of the
+susceptibility in YBa2Cu3O_{7-y} and La_{2-x}Sr_xCuO4 attributing their
+dissimilarity to the difference in the damping of spin excitations. In
+YBa2Cu3O_{7-y} these excitations are well defined at the antiferromagnetic wave
+vector Q=(\pi,\pi) even in the normal state which manifests itself in a
+pronounced maximum -- the resonance peak -- in the susceptibility. In
+La_{2-x}Sr_xCuO4 the spin excitations are overdamped which leads to a broad
+low-frequency feature in the susceptibility. The low-frequency
+incommensurability in the magnetic response is attributed to a dip in the
+magnon damping at Q. The calculated concentration and temperature dependencies
+of the incommensurability parameter conform with experimental observations.
+Generally the incommensurate magnetic response is not accompanied with an
+inhomogeneity of the carrier density.",0410009v1
+2004-10-07,Quantum Fluctuations and Excitations in Antiferromagnetic Quasicrystals,"We study the effects of quantum fluctuations and the excitation spectrum for
+the antiferromagnetic Heisenberg model on a two-dimensional quasicrystal, by
+numerically solving linear spin-wave theory on finite approximants of the
+octagonal tiling. Previous quantum Monte Carlo results for the distribution of
+local staggered magnetic moments and the static spin structure factor are
+reproduced well within this approximate scheme. Furthermore, the magnetic
+excitation spectrum consists of magnon-like low-energy modes, as well as
+dispersionless high-energy states of multifractal nature. The dynamical spin
+structure factor, accessible to inelastic neutron scattering, exhibits
+linear-soft modes at low energies, self-similar structures with bifurcations
+emerging at intermediate energies, and flat bands in high-energy regions. We
+find that the distribution of local staggered moments stemming from the
+inhomogeneity of the quasiperiodic structure leads to a characteristic energy
+spread in the local dynamical spin susceptibility, implying distinct nuclear
+magnetic resonance spectra, specific for different local environments.",0410180v1
+2004-11-26,The spin-half Heisenberg antiferromagnet on the square-kagomé lattice: Ground state and low-lying excitations,"We discuss the ground state and the low-lying excitations of the spin-half
+Heisenberg antiferromagnet on the two-dimensional square-kagome lattice. This
+magnetic system belongs to the class of highly frustrated spin systems with an
+infinite non-trivial degeneracy of the classical ground state as it is known
+also for the Heisenberg antiferromagnet on the kagome and on the star lattice.
+The quantum ground state of the spin-half system is a quantum paramagnet likely
+with a finite spin gap and with a large number of non-magnetic excitations
+within this gap. The magnetization versus field curve shows plateaux as well as
+a macroscopic magnetization jump to saturation due to independent localized
+magnon states.",0411673v1
+2004-12-02,Interplay between SDW and induced local moments in URu2Si2,"Theoretical model for magnetic ordering in the heavy-fermion metal URu2Si2 is
+suggested. The 17.5K transition in this material is ascribed to formation of a
+spin-density wave, which develops due to a partial nesting between electron and
+hole parts of the Fermi surface and has a negligibly small form-factor.
+Staggered field in the SDW state induces tiny antiferromagnetic order in the
+subsystem of localized singlet-singlet levels. Unlike the other models our
+scenario is based on coexistence of two orderings with the same
+antiferromagnetic dipole symmetry.The topology of the pressure phase diagram
+for such a two order parameter model is studied in the framework of the Landau
+theory. The field dependences of the staggered magnetization and the magnon gap
+are derived from the microscopic theory and found to be in good quantitative
+agreement with experiment.",0412055v2
+2004-12-10,Evidence for very strong electron-phonon coupling in YBa_{2}Cu_{3}O_{6},"From the observed oxygen-isotope shift of the mid-infrared two-magnon
+absorption peak of YBa$_{2}$Cu$_{3}$O$_{6}$, we evaluate the oxygen-isotope
+effect on the in-plane antiferromagnetic exchange energy $J$. The exchange
+energy $J$ in YBa$_{2}$Cu$_{3}$O$_{6}$ is found to decrease by about 0.9% upon
+replacing $^{16}$O by $^{18}$O, which is slightly larger than that (0.6%) in
+La$_{2}$CuO$_{4}$. From the oxygen-isotope effects, we determine the lower
+limit of the polaron binding energy, which is about 1.7 eV for
+YBa$_{2}$Cu$_{3}$O$_{6}$ and 1.5 eV for La$_{2}$CuO$_{4}$, in quantitative
+agreement with angle-resolved photoemission data, optical conductivity data,
+and the parameter-free theoretical estimate. The large polaron binding energies
+in the insulating parent compounds suggest that electron-phonon coupling should
+also be strong in doped superconducting cuprates and may play an essential role
+in high-temperature superconductivity.",0412262v3
+2005-01-03,Magnon and Hole Excitations in the Two-Dimensional Half-filled Hubbard Model,"Spin and hole excitation spectra and spectral weights are calculated for the
+half-filled Hubbard model, as a function of $t/U$. We find that the high energy
+spin spectra are sensitive to charge fluctuations. The energy difference
+$\Delta(\pi,0)- \Delta(\pi/2,\pi/2)$, which is negative for the Heisenberg
+model, changes sign at a fairly small $t/U\approx 0.053(5)$. The hole bandwidth
+is proportional to $J$, and considerably larger than in the t-J models. It has
+a minimum at ($\pi/2,\pi/2$) and a very weak dispersion along the
+antiferromagnetic zone boundary. A good fit to the measured spin spectra in
+La$_2$CuO$_4$ at $T=10K$ is obtained with the parameter values $U=3.1{\rm eV}$,
+$t=0.35{\rm eV}$.",0501029v1
+2005-01-10,Spin excitations under fields in an anisotropic bond-alternating quantum S=1 chain: contrast with Haldane spin chains,"Inelastic neutron scattering experiments on the S=1 quasi-one-dimensional
+bond-alternating antiferromagnet Ni(C9D24N4)(NO2)ClO4 have been performed under
+magnetic fields below and above a critical field Hc at which the energy gap
+closes. Normal field dependece of Zeeman splitting of the excited triplet modes
+below Hc has been observed, but the highest mode is unusually small and smears
+out with increasing field. This can be explained by an interaction with a
+low-lying two magnon continuum at q=pi that is present in dimerized chains but
+absent in uniform ones. Above Hc, we find only one excited mode, in stark
+contrast with three massive excitations previously observed in the structurally
+similar Haldane-gap material NDMAP [A. Zheludev et al., Phys. Rev. B 68, 134438
+(2003)].",0501207v1
+2005-01-20,Magnetically Stabilized Order. II: Critical states and algebraically ordered nematic spin liquids in one-dimensional optical lattices,"We investigate the Zeeman-field-driven quantum phase transitions between
+singlet spin liquids and algebraically ordered O(2) nematic spin liquids of
+spin-one bosons in one-dimensional optical lattices. We find that the critical
+behavior is characterized by condensation of hardcore bosons instead of ideal
+magnons in high dimensional lattices. Critical exponents are strongly
+renormalized by hardcore interactions and critical states are equivalent to the
+free Fermion model up to the Friedal oscillations. We also find that the
+algebraically ordered nematic spin liquids close to critical points are fully
+characterized by the Luttinger liquid dynamics with Luttinger liquid parameters
+magnetically tunable. The Bethe Ansatz solution has been applied to determine
+the critical magnetization and nematic correlations.",0501490v2
+2005-02-01,Can Frustration Preserve a Quasi-Two-Dimensional Spin Fluid?,"Using spin-wave theory, we show that geometric frustration fails to preserve
+a two-dimensional spin fluid. Even though frustration can remove the interlayer
+coupling in the ground-state of a classical anti-ferromagnet, spin layers
+innevitably develop a quantum-mechanical coupling via the mechanism of ``order
+from disorder''. We show how the order from disorder coupling mechanism can be
+viewed as a result of magnon pair tunneling, a process closely analogous to
+pair tunneling in the Josephson effect. In the spin system, the Josephson
+coupling manifests itself as a a biquadratic spin coupling between layers, and
+for quantum spins, these coupling terms are as large as the inplane coupling.
+An alternative mechanism for decoupling spin layers occurs in classical XY
+models in which decoupled ""sliding phases"" of spin fluid can form in certain
+finely tuned conditions. Unfortunately, these finely tuned situations appear
+equally susceptible to the strong-coupling effects of quantum tunneling,
+forcing us to conclude that in general, geometric frustration cannot preserve a
+two-dimensional spin fluid.",0502003v2
+2005-02-11,An ab initio effective Hamiltonian for magnetism including longitudinal spin fluctuations,"We discuss the use of the magnetic force theorem (MFT) using different
+reference states upon which the perturbative approach is based. Using a
+disordered local moment (DLM) state one finds goo d Curie (or Ne\'el)
+temperatures, and good energetics for planar spin spirals in the 3d magnets Fe,
+Co (fcc), Mn, Cr. On the other hand the ferromagnetic reference state provides
+excellent energetics for small $\theta$ spin spirals in Fe, Co and Ni, and by
+extension magnon energies under the assumption of adiabacity. However, planar
+spin spiral energetics and transition temperatures for Ni, Fe, Mn, and Cr show
+worse agreement. The reasons for this, and for the case of fcc Co whe re both
+approaches work very well are discussed. We further provide an extension of the
+mapping of the quantum problem to include longitudinal fluctuations, and
+discuss the role they will play in magnetic phase transitions. This constru
+ction is tested using planar spin spirals where ${\bf q}$ is fixed but the
+moment is allowed to rel ax. It is demonstrated that results from the magnetic
+force theorem approach and directly calculated {\it ab initio} values agree
+very well.",0502291v1
+2005-02-18,Frustrated Quantum Magnets,"A description of different phases of two dimensional magnetic insulators is
+given. The first chapters are devoted to the understanding of the symmetry
+breaking mechanism in the semi-classical Neel phases. Order by disorder
+selection is illustrated. All these phases break SU(2) symmetry and are gapless
+phases with magnon excitations. Different gapful quantum phases exist in two
+dimensions: the Valence Bond Crystal phases (VBC) which have long range order
+in local S=0 objects (either dimers in the usual Valence Bond acception or
+quadrumers..), but also Resonating Valence Bond Spin Liquids (RVBSL), which
+have no long range order in any local order parameter and an absence of
+susceptibility to any local probe. VBC have gapful S = 0, or 1 excitations,
+RVBSL on the contrary have deconfined spin-1/2 excitations. Examples of these
+two kinds of quantum phases are given in chapters 4 and 5. A special class of
+magnets (on the kagome or pyrochlore lattices) has an infinite local degeneracy
+in the classical limit: they give birth in the quantum limit to different
+behaviors which are illustrated and questionned in the last lecture.",0502464v1
+2005-02-18,High-energy Cu spin excitations in PrBa2Cu3O6+x,"This paper describes high-energy neutron inelastic scattering measurements of
+propagating magnetic excitations in PrBa2Cu3O6+x (x approx 0.2 and 0.93). The
+measurements probe the acoustic and optic modes of the
+antiferromagnetically-ordered copper--oxygen bilayers in the energy range
+50-150 meV. The observed magnon dispersion can be described satisfactorily in
+this energy range by a spin wave model including intra- and inter-layer
+nearest-neighbour exchange constants J_parallel and J_perp. We find J_parallel
+= 127 +/- 10 meV and J_perp = 5.5 +/- 0.9 meV. The value of J_parallel is
+virtually the same as that found in YBa2Cu3O6.2, but J_perp is a factor of two
+smaller. To within experimental error the values of J_parallel and J_perp for
+PrBa2Cu3O6+x do not vary with oxygen doping.",0502467v1
+2005-02-21,On the finite temperature Drude weight of the anisotropic Heisenberg chain,"We present a study of the Drude weight $D(T)$ of the spin-1/2 $XXZ$ chain in
+the gapless regime. The thermodynamic Bethe ansatz (TBA) is applied in two
+different ways. In the first application we employ the particle basis of
+magnons and their bound states. In this case we rederive and considerably
+extend earlier work in the literature. However, in the course of our
+investigation we find arguments that cast doubt on the applicability of the TBA
+in this case. In a second application by use of the spinon and anti-spinon
+particle basis we obtain completely different results. Only for anisotropy
+parameter $\Delta$ close to 0 we find that $D(T)$ is a monotonously decaying
+function of temperature. For $\Delta$ close to 1 the behaviour is entirely
+different showing a finite temperature maximum. Also for the isotropic
+antiferromagnetic chain ($\Delta=1$) the results for $D(T)$ are finite for T=0
+as well as for $T>0$ with an infinite positive slope at T=0.",0502516v1
+2005-03-03,Quantum Phase Transitions of Frustrated Heisenberg Antiferromagnets: a Comprehensive Renormalization Approach,"We develop a novel renormalization approach for frustrated quantum
+antiferromagnets. It is designed to consistently treat spin-wave interactions
+all over the magnetic Brillouin zone, including high-energy modes in outer
+regions as well as low energy modes in the center. Focusing on the paradigmatic
+$J_1$-$J_2$ model, we find a unifying description of the second-order
+transition between the N\'eel phase and the paramagnetic phase and the
+first-order transition between the N\'eel phase and the columnar phase. Our
+approach provides explicit results for the renormalized values of the spin
+stiffness and spin-wave velocity characterizing the low-energy magnons in the
+N\'eel phase.",0503076v2
+2005-03-17,Quantum Criticality in an Organic Magnet,"Exchange interactions between $S=\frac{1}{2}$ sites in piperazinium
+hexachlorodicuprate produce a frustrated bilayer magnet with a singlet ground
+state. We have determined the field-temperature phase diagram by high field
+magnetization and neutron scattering experiments. There are two quantum
+critical points: $H_{c1}=7.5$ T separates a quantum paramagnet phase from a
+three dimensional, antiferromagnetically-ordered state while $H_{c2}=37$ T
+marks the onset of a fully polarized state. The ordered phase, which we
+describe as a magnon Bose-Einstein condensate (BEC), is embedded in a quantum
+critical regime with short range correlations. A low temperature anomaly in the
+BEC phase boundary indicates that additional low energy features of the
+material become important near $H_{c1}$.",0503450v2
+2005-03-30,Stability of ferromagnetism in the half-metallic pnictides and similar compounds: A first-principles study,"Based on first-principles electron structure calculations and employing the
+frozen-magnon approximation we study the exchange interactions in a series of
+transition-metal binary alloys crystallizing in the zinc-blende structure and
+calculate the Curie temperature within both the mean-field approximation (MFA)
+and random-phase approximation (RPA). We study two Cr compounds, CrAs and CrSe,
+and four Mn compounds: MnSi, MnGe, MnAs and MnC. MnC, MnSi and MnGe are
+isovalent to CrAs and MnAs is isoelectronic with CrSe. Ferromagnetism is
+particular stable for CrAs, MnSi and MnGe: All three compounds show Curie
+temperatures around 1000 K. On the other hand, CrSe and MnAs show a tendency to
+antiferromagnetism when compressing the lattice. In MnC the half-metallic gap
+is located in the majority-spin channel contrary to the other five compounds.
+The large half-metallic gaps, very high Curie temperatures, the stability of
+the ferromagnetism with respect to the variation of the lattice parameter and a
+coherent growth on semiconductors make MnSi and CrAs most promising candidates
+for the use in spintronics devises.",0503713v1
+2005-03-30,Spintronic transport and Kondo effect in quantum dots,"We investigate the spin-dependent transport properties of quantum-dot based
+structures where Kondo correlations dominate the electronic dynamics. The
+coupling to ferromagnetic leads with parallel magnetizations is known to give
+rise to nontrivial effects in the local density of states of a single quantum
+dot. We show that this influence strongly depends on whether charge
+fluctuations are present or absent in the dot. This result is confirmed with
+numerical renormalization group calculations and perturbation theory in the
+on-site interaction. In the Fermi-liquid fixed point, we determine the
+correlations of the electric current at zero temperature (shot noise) and
+demonstrate that the Fano factor is suppressed below the Poissonian limit for
+the symmetric point of the Anderson Hamiltonian even for nonzero lead
+magnetizations. We discuss possible avenues of future research in this field:
+coupling to the low energy excitations of the ferromagnets (magnons), extension
+to double quantum dot systems with interdot antiferromagnetic interaction and
+effect of spin-polarized currents on higher symmetry Kondo states such as
+SU(4).",0503716v1
+2005-04-26,Pressure dependence of the Curie temperature in Ni2MnSn Heusler alloy: A first-principles study,"The pressure dependence of electronic structure, exchange interactions and
+Curie temperature in ferromagnetic Heusler alloy Ni2MnSn has been studied
+theoretically within the framework of the density-functional theory. The
+calculation of the exchange parameters is based on the frozen--magnon approach.
+The Curie temperature, Tc, is calculated within the mean-field approximation by
+solving the matrix equation for a multi-sublattice system. In agrement with
+experiment the Curie temperature increased from 362K at ambient pressure to 396
+at 12 GPa. Extending the variation of the lattice parameter beyond the range
+studied experimentally we obtained non-monotonous pressure dependence of the
+Curie temperature and metamagnetic transition. We relate the theoretical
+dependence of Tc on the lattice constant to the corresponding dependence
+predicted by the empirical interaction curve. The Mn-Ni atomic interchange
+observed experimentally is simulated to study its influence on the Curie
+temperature.",0504644v1
+2005-04-26,"First-principles study of exchange interactions and Curie temperatures of half-metallic ferrimagnetic full Heusler alloys Mn2VZ (Z=Al, Ge)","We report the parameter-free, density functional theory calculations of
+interatomic exchange interactions and Curie temperatures of half-metallic
+ferrimagnetic full Heusler alloys Mn2VZ (Z=Al, Ge). To calculate the
+interatomic exchange interactions we employ the frozen-magnon approach. The
+Curie temperatures are calculated within the mean-field approximation to the
+classical Heisenberg Hamiltonian by solving a matrix equation for a
+multi-sublattice system. Our calculations show that, although a large magnetic
+moment is carried by Mn atoms, competing ferromagnetic (inter sublattice) and
+antiferromagnetic (intra sublattice) Mn-Mn interactions in Mn2VAl almost cancel
+each other in the mean-field experienced by the Mn atoms. In Mn2VGe the leading
+Mn-Mn exchange interaction is antiferromagnetic. In both compounds the
+ferromagnetism of the Mn subsystem is favored by strong antiferromagnetic Mn-V
+interactions. The obtained value of the Curie temperature of Mn2VAl is in good
+agrement with experiment. For Mn2VGe there is no experimental information
+available and our calculation is a prediction.",0504679v1
+2005-04-27,A generating functional approach to the Hubbard model,"The method of generating functional is generalized to the case of strongly
+correlated systems, and applied to the Hubbard model. For the electronic
+Green's function constructed for Hubbard operators, an equation using
+variational derivatives with respect to the fluctuating fields has been derived
+and its multiplicative form has been determined. Corrections for the electronic
+self-energy are calculated up to the second order with respect to the parameter
+W/U (W width of the band), and a mean field type approximation was formulated,
+including both charge and spin static fluctuations. The equations for the
+Bose-like Green's functions have been derived, describing the collective modes:
+the magnons and doublons. The properties of the poles of the doublon Green's
+functions depend on electronic filling. The investigation of the special case
+n=1 demonstrates that the doublon Green's function has a soft mode at the wave
+vector Q=(pi,pi,...), indicating possible instability of the uniform
+paramagnetic phase relatively to the two sublattices charge ordering. However
+this instability should compete with an instability to antiferromagnetic
+ordering.",0504723v1
+2005-05-11,"Above-room-temperature ferromagnetism in half-metallic Heusler compounds NiCrP, NiCrSe, NiCrTe and NiVAs: A first-principles study","We study the interatomic exchange interactions and Curie temperatures in
+half-metallic semi Heusler compounds NiCrZ (Z=P, Se, Te) and NiVAs. The study
+is performed within the framework of density functional theory. The calculation
+of exchange parameters is based on the frozen-magnon approach. It is shown that
+the exchange interactions in NiCrZ vary strongly depending on the Z
+constituent. The Curie temperature, Tc, is calculated within the mean field and
+random phase approximations. The difference between two estimations is related
+to the properties of the exchange interactions. The predicted Curie
+temperatures of all four systems are considerably higher than room temperature.
+The relation between the half-metallicity and the value of the Curie
+temperature is discussed. The combination of a high spin-polarization of charge
+carriers and a high Curie temperature makes these Heusler alloys interesting
+candidates for spintronics applications.",0505299v1
+2005-06-04,Exact soliton solution of Spin Chain with a external magnetic field in linear wave background,"Employing a simple, straightforward Darboux transformation we construct exact
+N-soliton solution for anisotropic spin chain driven by a external magnetic
+field in linear wave background. As a special case the explicit one- and
+two-soliton solution dressed by the linear wave corresponding to magnon in
+quantum theory is obtained analytically and its property is discussed in
+detail. The dispersion law, effective soliton mass, and the energy of each
+soliton are investigated as well. Our result show that the stability criterion
+of soliton is related with anisotropic parameter and the amplitude of the
+linear wave.",0506104v1
+2005-06-24,Spin dynamics of the quasi two dimensional spin-1/2 quantum magnet Cs_2CuCl_4,"We study dynamical properties of the anisotropic triangular quantum
+antiferromagnet Cs_2CuCl_4. Inelastic neutron scattering measurements have
+established that the dynamical spin correlations cannot be understood within a
+linear spin wave analysis. We go beyond linear spin wave theory by taking
+interactions between magnons into account in a 1/S expansion. We determine the
+dynamical structure factor and carry out extensive comparisons with
+experimental data. We find that compared to linear spin wave theory a
+significant fraction of the scattering intensity is shifted to higher energies
+and strong scattering continua are present. However, the 1/S expansion fails to
+account for the experimentally observed large quantum renormalization of the
+exchange energies.",0506667v1
+2005-07-18,Coupled ferro-antiferromagnetic Heisenberg bilayers investigated by many-body Green's function theory,"A theory of coupled ferro- and antiferromagnetic Heisenberg layers is
+developed within the framework of many-body Green's function theory (GFT) that
+allows non-collinear magnetic arrangements by introducing sublattice
+structures. As an example, the coupled ferro- antiferromagnetic (FM-AFM)
+bilayer is investigated. We compare the results with those of bilayers with
+purely ferromagnetic or antiferromagnetic couplings. In each case we also show
+the corresponding results of mean field theory (MFT), in which magnon
+excitations are completely neglected. There are significant differences between
+GFT and MFT. A remarkable finding is that for the coupled FM-AFM bilayer the
+critical temperature decreases with increasing interlayer coupling strength for
+a simple cubic lattice, whereas the opposite is true for an fcc lattice as well
+as for MFT for both lattice types.",0507408v1
+2005-07-22,Structural instability of two- and three-dimensional pyrochlore spin lattices in high magnetic fields,"We consider the quantum spin-$s$ $XXZ$ Heisenberg antiferromagnet on the two-
+and three-dimensional pyrochlore lattices and examine a spin-Peierls mechanism
+of lowering the total energy by a lattice distortion in a high magnetic field.
+For the exact eigenstates consisting of several independent localized magnons
+in a ferromagnetic environment we show the existence of a spin-Peierls
+instability by rigorous analytical calculations. In addition we report on exact
+diagonalization data for finite two-dimensional pyrochlore lattices up to N=64
+sites. We discuss a scenario of the field-tuned changes in the ground-state
+properties of the frustrated spin lattices due to the coupling between spin and
+lattice degrees of freedom.",0507538v1
+2005-07-28,Exchange interactions and temperature dependence of the magnetization in half--metallic Heusler alloys,"We study the exchange interactions in half-metallic Heusler alloys using
+first-principles calculations in conjunction with the frozen-magnon
+approximation. The Curie temperature is estimated within both mean-field (MF)
+and random-phase-approximation (RPA) approaches. For the half-Heusler alloys
+NiMnSb and CoMnSb the dominant interaction is between the nearest Mn atoms. In
+this case the MF and RPA estimations differ strongly. The RPA approach provides
+better agreement with experiment. The exchange interactions are more complex in
+the case of full-Heusler alloys Co$_2$MnSi and Co$_2$CrAl where the dominant
+effects are the inter-sublattice interactions between the Mn(Cr) and Co atoms
+and between Co atoms at different sublattices. For these compounds we find that
+both MF and RPA give very close values of the Curie temperature slightly
+underestimating experimental quantities. We study the influence of the lattice
+compression on the magnetic properties. The temperature dependence of the
+magnetization is calculated using the RPA method within both quantum mechanical
+and classical approaches.",0507697v2
+2005-09-08,Frustration effects in magnetic molecules,"Besides being a fascinating class of new materials, magnetic molecules
+provide the opportunity to study concepts of condensed matter physics in zero
+dimensions. This contribution will exemplify the impact of molecular magnetism
+on concepts of frustrated spin systems. We will discuss spin rings and the
+unexpected rules that govern their low-energy behavior. Rotational bands, which
+are experimentally observed in various molecular magnets, provide a useful,
+simplified framework for characterizing the energy spectrum, but there are also
+deviations thereof with far-reaching consequences. It will be shown that
+localized independent magnons on certain frustrated spin systems lead to giant
+magnetization jumps, a new macroscopic quantum effect. In addition a
+frustration-induced metamagnetic phase transitions will be discussed, which
+demonstrates that hysteresis can exist without anisotropy. Finally, it is
+demonstrated that frustrated magnetic molecules could give rise to an enhanced
+magnetocaloric effect.",0509204v1
+2005-10-07,Quantum effects in a half-polarized pyrochlore antiferromagnet,"We study quantum effects in a spin-3/2 antiferromagnet on the pyrochlore
+lattice in an external magnetic field, focusing on the vicinity of a plateau in
+the magnetization at half the saturation value, observed in CdCr$_2$O$_4$, and
+HgCr$_2$O$_4$. Our theory, based on quantum fluctuations, predicts the
+existence of a symmetry-broken state on the plateau, even with only
+nearest-neighbor microscopic exchange. This symmetry broken state consists of a
+particular arrangement of spins polarized parallel and antiparallel to the
+field in a 3:1 ratio on each tetrahedron. It quadruples the lattice unit cell,
+and reduces the space group from $Fd\bar{3}m$ to $P4_332$. We also predict that
+for fields just above the plateau, the low temperature phase has transverse
+spin order, describable as a Bose-Einstein condensate of magnons. Other
+comparisons to and suggestions for experiments are discussed.",0510202v1
+2005-10-12,Magnetic susceptibility of the body-centred orthorhombic La$_2$CuO$_4$ system,"A model Hamiltonian representing the Cu spins in La$_2$CuO$_4$ in its
+low-temperature body-centred orthorhombic phase, that includes both spin-orbit
+generated Dzyaloshinskii-Moriya interactions and interplanar exchange, is
+examined within the RPA utilizing a Tyablikov decoupling of various high-order
+Green's functions. The magnetic susceptibility is evaluated as a function of
+temperature and the parameters quantifying these interactions, and compared to
+recently obtained experimental data of Lavrov, Ando and collaborators. An
+effective Hamiltonian corresponding to a simple tetragonal structure is shown
+to reproduce both the magnon spectra and the susceptibility of the more
+complicated body-centred orthorhombic model.",0510328v1
+2005-11-08,Spin-wave interactions in quantum antiferromagnets,"We study spin-wave interactions in quantum antiferromagnets by expressing the
+usual magnon annihilation and creation operators in terms of Hermitian field
+operators representing transverse staggered and ferromagnetic spin
+fluctuations. In this parameterization, which was anticipated by Anderson in
+1952, the two-body interaction vertex between staggered spin fluctuations
+vanishes at long wavelengths. We derive a new effective action for the
+staggered fluctuations only by tracing out the ferromagnetic fluctuations. To
+one loop order, the renormalization group flow agrees with the
+nonlinear-$\sigma$-model approach.",0511199v3
+2005-12-12,Spin-polarized scanning tunneling microscopy of half-metallic ferromagnets: Non-quasiparticle contributions,"The role of the many-body (spin-polaronic) effects in the scanning tunneling
+spectroscopy of half-metallic ferromagnets (HMF) is considered. It is shown
+that the non-quasiparticle (NQP) states exist in the majority or minority spin
+gap in the presence of arbitrary external potential and, in particular, at the
+surfaces and interfaces. Energy dependence of the NQP density of states is
+obtained in various models of HMF, an important role of the hybridization
+nature of the energy gap being demonstrated. The corresponding temperature
+dependence of spin polarization is calculated. It is shown that the NQP states
+result in a sharp bias dependence of the tunneling conductance near zero bias.
+Asymmetry of the NQP states with respect to the Fermi energy provides an
+opportunity to separate phonon and magnon peaks in the inelastic spectroscopy
+by STM.",0512245v1
+2005-12-14,Spin-wave dispersion in orbitally ordered La(0.5)Sr(1.5)MnO(4),"The magnon dispersion in the charge, orbital and spin ordered phase in
+La(0.5)Sr(1.5)MnO(4) has been studied by means of inelastic neutron scattering.
+We find an excellent agreement with a magnetic interaction model basing on the
+CE-type superstructure. The magnetic excitations are dominated by ferromagnetic
+exchange parameters revealing a nearly-one dimensional character at high
+energies. The nearest neighbor ferromagnetic interaction in
+La(0.5)Sr(1.5)MnO(4) is significantly larger than the one in the metallic
+ferromagnetically ordered manganites. The large ferromagnetic interaction in
+the charge/orbital ordered phase appears to be essential for the capability of
+manganites to switch between metallic and insulating phases.",0512305v1
+2005-12-15,Nematic order in square lattice frustrated ferromagnets,"We present a new scenario for the breakdown of ferromagnetic order in a
+two-dimensional quantum magnet with competing ferromagnetic and
+antiferromagnetic interactions. In this, dynamical effects lead to the
+formation of two-magnon bound states, which undergo Bose-Einstein condensation,
+giving rise to bond-centered nematic order. This scenario is explored in some
+detail for an extended Heisenberg model on a square lattice. In particular, we
+present numerical evidence confirming the existence of a state with d-wave
+nematic correlations but no long range magnetic order, lying between the
+saturated ferromagnetic and collinear antiferromagnetic phases of the
+ferromagnetic J1-J2 model. We argue by continuity of spectra that this phase is
+also present in a model with 4-spin cyclic exchange.",0512349v1
+2005-12-16,Evolution of spin-wave excitations in ferromagnetic metallic manganites,"Neutron scattering results are presented for spin-wave excitations of three
+ferromagnetic metallic $A_{1-x}A^{\prime}_{x}$MnO$_3$ manganites (where $A$ and
+$A^\prime$ are rare- and alkaline-earth ions), which when combined with
+previous work elucidate systematics of the interactions as a function of
+carrier concentration $x$, on-site disorder, and strength of the lattice
+distortion. The long wavelength spin dynamics show only a very weak dependence
+across the series. The ratio of fourth to first neighbor exchange ($J_4/J_1$)
+that controls the zone boundary magnon softening changes systematically with
+$x$, but does not depend on the other parameters. None of the prevailing models
+can account for these behaviors.",0512368v1
+2005-12-22,Magnetic properties of a disordered Heisenberg binary spin system with long-range exchange,"The influence of substitutional disorder on the magnetic properties of
+disordered Heisenberg binary spin systems with long-range exchange integrals is
+studied. The equation of motion for the magnon Green's function which is
+decoupled by the Tyablikov approximation is solved in the
+Blackman-Esterling-Berk(BEB) coherent potential approximation(CPA) framework,
+where the environmental disorder term is treated by virtual crystal
+approximation. The long-range exchange integrals include a power-law decaying
+and an oscillating Ruderman-Kittel-Kasuya-Yosida(RKKY) exchange interaction.
+The resulting spectral density, which is calculated by CPA self-consistent
+equation, is then used to estimate the magnetization and Curie temperature. The
+results show, in the case of the three-dimensional simple cubic systems, a
+strong influence of ferromagnetic long-range exchange integrals on the
+magnetization and Curie temperature of the systems, which is obviously
+different from the calculation of short-range interaction.",0512585v1
+2005-12-29,Electron-magnon coupling and nonlinear tunneling transport in magnetic nanoparticles,"We present a theory of single-electron tunneling transport through a
+ferromagnetic nanoparticle in which particle-hole excitations are coupled to
+spin collective modes. The model employed to describe the interaction between
+quasiparticles and collective excitations captures the salient features of a
+recent microscopic study. Our analysis of nonlinear quantum transport in the
+regime of weak coupling to the external electrodes is based on a rate-equation
+formalism for the nonequilibrium occupation probability of the nanoparticle
+many-body states. For strong electron-boson coupling, we find that the
+tunneling conductance as a function of bias voltage is characterized by a large
+and dense set of resonances. Their magnetic field dependence in the large-field
+regime is linear, with slopes of the same sign. Both features are in agreement
+with recent tunneling experiments.",0512697v2
+2006-01-31,Spin-lattice interaction in the quasi one-dimensional helimagnet LiCu_2O_2,"The field dependence of the electron spin resonance in a helimagnet,
+LiCu_2O_2, was investigated for the first time. In the paramagnetic state a
+broad resonance line was observed corresponding to a g-factor of 2.3. In the
+critical regime around the paramagnetic to helimagnetic phase transition the
+resonance broadens and shifts to higher frequencies. A narrow signal is
+recovered at low temperature, corresponding to a spin gap of 1.5 meV in zero
+field. A comprehensive model of the magnons is presented, using exchange
+parameters from neutron scattering (T. Masuda et al,
+  Phys. Rev. B 72, 014405), and the spin anisotropy determined here. The role
+of the quantum fluctuations is discussed.",0601701v1
+2006-02-01,The metal-insulator transition of the ferromagnetic La7/8Sr1/8MnO3 probed by spin waves: a 2D stripe superstructure,"We report a study of spin waves in hole-doped ferromagnetic La7/8Sr1/8MnO3,
+in the metallic state (165K) below TC (181K) and through the puzzling
+metal-insulator transition which occurs at TO'O''=159K. They reveal very
+unusual excitations. Propagating spin waves are observed in the small q-range
+up to q=0.25 (lambda=4a), and, beyond, four dispersionless levels. Both types
+of excitations have a quasi two-dimensional (2D) character. The transition is
+revealed by a folding of the dispersed magnon branch at q=1/8. In the metallic
+state, the dispersionless levels reveal ferromagnetic domains with 4 lattice
+spacings for their size along a and b. They lead to a picture of charge
+segregation with hole-poor domains surrounded with hole-rich paths. Within this
+description, the transition appears as the ordering of domains, which can be
+interpreted in terms of a 2D superstructure of orthogonal stripes.",0602026v1
+2006-02-07,Possible evidence for electromagnons in multiferroic manganites,"Magnetodielectric materials are characterized by a strong coupling of
+magnetic and dielectric properties and in rare cases simultaneously exhibit
+both, magnetic and polar order. Among other multiferroics, TbMnO3 and GdMnO3
+reveal a strong magneto-dielectric (ME) coupling and as a consequence
+fundamentally new spin excitations exist: Electro-active magnons, or
+electromagnons, i. e. spin waves which can be excited by ac electric fields.
+Here we show that these excitations appear in the phase with an incommensurate
+(IC) magnetic structure of the manganese spins. In external magnetic fields
+this IC structure can be suppressed and the electromagnons are wiped out,
+thereby inducing considerable changes in the index of refraction from dc up to
+THz frequencies. Hence, besides adding a new creature to the zoo of fundamental
+excitations, the refraction index can be tuned by moderate magnetic fields,
+which allows the design of a new generation of optical switches and
+optoelectronic devices.",0602173v1
+2006-02-15,Low-energy excitations in the magnetized state of the bond-alternating quantum S=1 chain system NTENP,"High intensity inelastic neutron scattering experiments on the S=1
+quasi-one-dimensional bond-alternating antiferromagnet Ni(C9D24N4)(NO2)ClO4
+(NTENP) are performed in magnetic fields of up to 14.8~T. Excitation in the
+high field magnetized quantum spin solid (ordered) phase are investigated. In
+addition to the previously observed coherent long-lived gap excitation [M.
+Hagiwara et al., Phys. Rev. Lett 94, 177202 (2005)], a broad continuum is
+detected at lower energies. This observation is consistent with recent
+numerical studies, and helps explain the suppression of the lowest-energy gap
+mode in the magnetized state of NTENP. Yet another new feature of the
+excitation spectrum is found at slightly higher energies, and appears to be
+some kind of multi-magnon state.",0602357v1
+2006-03-22,Electronic structure and exchange constants in magnetic semiconductors digital alloys: chemical and band-gap effects,"First-principles simulations have been performed for [001]-ordered Mn/Ge and
+Mn/GaAs ""digital alloys"", focusing on the effects of i) a larger band-gap and
+ii) a different semiconducting host on the electronic structure of the magnetic
+semiconductors of interest. Our results for the exchange constants in Mn/Ge,
+evaluated using a frozen-magnon scheme, show that a larger band-gap tends to
+give a stronger nearest-neighbor ferromagnetic coupling and an overall enhanced
+in-plane ferromagnetic coupling even for longer-ranged coupling constants. As
+for the chemical effects on the exchange constants, we show that Mn/GaAs shows
+a smaller nearest-neighbor ferromagnetic coupling than Mn/Ge, but exchange
+constants for higher Mn-Mn distance show an overall increased ferromagnetic
+behavior in Mn/GaAs. As a result, from the magnetic-coupling point of view, the
+two systems behave on average rather similarly.",0603589v1
+2006-03-23,Condensation of magnons and spinons in a frustrated ladder,"Motivated by the ever-increasing experimental effort devoted to the
+properties of frustrated quantum magnets in a magnetic field, we present a
+careful and detailed theoretical analysis of a one-dimensional version of this
+problem, a frustrated ladder with a magnetization plateau at m=1/2. We show
+that even for purely isotropic Heisenberg interactions, the magnetization curve
+exhibits a rather complex behavior that can be fully accounted for in terms of
+simple elementary excitations. The introduction of anisotropic interactions
+(e.g., Dzyaloshinskii-Moriya interactions) modifies significantly the picture
+and reveals an essential difference between integer and fractional plateaux. In
+particular, anisotropic interactions generically open a gap in the region
+between the plateaux, but we show that this gap closes upon entering fractional
+plateaux. All of these conclusions, based on analytical arguments, are
+supported by extensive Density Matrix Renormalization Group calculations.",0603609v2
+2006-05-05,Bose-Einstein condensation and entanglement in magnetic systems,"We present a study of magnetic field induced quantum phase transitions in
+insulating systems. A generalized scaling theory is used to obtain the
+temperature dependence of several physical quantities along the quantum
+critical trajectory ($H=H_{C}$, $T\to0$) where $H$ is a longitudinal external
+magnetic field and $H_{C}$ the critical value at which the transition occurs.
+We consider transitions from a spin liquid at a critical field $H_{C1}$ and
+from a fully polarized paramagnet, at $H_{C2}$, into phases with long range
+order in the transverse components. The transitions at $H_{C1}$ and $H_{C2}$
+can be viewed as Bose-Einstein condensations of magnons which however belong to
+different universality classes since they have different values of the dynamic
+critical exponent $z$. Finally, we use that the magnetic susceptibility is an
+entanglement witness to discuss how this type of correlation sets in as the
+system approaches the quantum critical point along the critical trajectory,
+$H=H_{C2}$, $T\to0$.",0605148v2
+2006-05-08,Frustrated ferromagnetic spin-1/2 chain in a magnetic field: The phase diagram and thermodynamic properties,"The frustrated ferromagnetic spin-1/2 Heisenberg chain is studied by means of
+a low-energy field theory as well as the density-matrix renormalization group
+and exact diagonalization methods. Firstly, we study the ground-state phase
+diagram in a magnetic field and find an `even-odd' (EO) phase characterized by
+bound pairs of magnons in the region of two weakly coupled antiferromagnetic
+chains. A jump in the magnetization curves signals a first-order transition at
+the boundary of the EO phase, but otherwise the curves are smooth. Secondly, we
+discuss thermodynamic properties at zero field, where we confirm a double-peak
+structure in the specific heat for moderate frustrating next-nearest neighbor
+interactions.",0605204v2
+2006-05-10,Spin-flip processes and ultrafast magnetization dynamics in Co - unifying the microscopic and macroscopic view of femtosecond magnetism,"The femtosecond magnetization dynamics of a thin cobalt film excited with
+ultrashort laser pulses has been studied using two complementary pump-probe
+techniques, namely spin-, energy- and time-resolved photoemission and
+time-resolved magneto-optical Kerr effect. Combining the two methods it is
+possible to identify the microscopic electron spin-flip mechanisms responsible
+for the ultrafast macroscopic magnetization dynamics of the cobalt film. In
+particular, we show that electron-magnon excitation does not affect the overall
+magnetization even though it is an efficient spin-flip channel on the sub-200
+fs timescale. Instead we find experimental evidence for the relevance of
+Elliott-Yafet type spin-flip processes for the ultrafast demagnetization taking
+place on a time scale of 300 fs.",0605272v2
+2006-05-25,Bosonic representation of spin operators in the field-induced critical phase of spin-1 Haldane chains,"A bosonized-field-theory representation of spin operators in the
+uniform-field-induced Tomonaga-Luttinger-liquid (TLL) phase in spin-1 Haldane
+chains is formulated by means of the non-Abelian (Tsvelik's Majorana fermion
+theory) and the Abelian bosonizations and Furusaki-Zhang technique [Phys. Rev.
+B {\bf 60}, 1175 (1999)]. It contains massive magnon fields as well as massless
+boson fields. From it, asymptotic forms of spin correlation functions in the
+TLL phase are completely determined. Applying the formula, we further discuss
+effects of perturbations (bond alternation, single-ion anisotropy terms,
+staggered fields, etc) for the TLL state, and the string order parameter.
+Throughout the paper, we often consider in some detail how the symmetry
+operations of the Haldane chains are translated in the low-energy effective
+theory.",0605636v3
+2006-06-06,Hole dynamics in canted antiferromagnets,"We have analyzed the dynamics of a single hole doped in a canted
+antiferromagnet using the t-J model. Within the self consistent Born
+approximation we have found that the hole propagates at two different energy
+scales along the antiferromagnetic and the ferromagnetic components of the
+canted order, respectively. While the many body quasiparticle excitation has
+its origin in the coherent coupling of the hole with the magnon excitations of
+the antiferromagnetic component, the ferromagnetic component gives rise to a
+free like hole motion at higher energies. We have found a non-trivial behavior
+of the hole spectral function with the canting angle. In particular, in the
+strong coupling regime, the quasiparticle weight strongly depends on the
+momenta, vanishing inside the magnetic Brillouin zone for a canting angle
+greater than 60 degree.",0606157v1
+2006-06-14,Dynamic spin-response function of the high-temperature Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ superconductor form angle resolved photoemission spectra,"We introduce a formalism for calculating dynamic response functions using
+experimental single particle Green's functions derived from angle resolved
+photoemission spectroscopy (ARPES). As an illustration of this procedure we
+estimate the dynamic spin response of the cuprate superconductor
+Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$. We find good agreement with superconducting
+state neutron data, in particular the $(\pi,\pi)$ resonance with its unusual
+`reversed magnon' dispersion. We anticipate our formalism will also be of
+useful in interpreting results from other spectroscopies, such as optical and
+Raman responses.",0606346v2
+2006-07-18,Magentic-Field Induced Quantum Phase Transition and Critical Behavior in a Gapped Spin System TlCuCl$_3$,"Magnetization measurements were performed on TlCuCl$_3$ with gapped ground
+state. The critical density and the magnetic phase diagram were obtained. The
+interacting constant was obtained as $U/k_{\rm B} = 313$ K. The experimental
+phase boundary for $T < 5$ K agrees perfectly with the magnon BEC theory based
+on the Hartree-Fock approximation with realistic dispersion relations and
+$U/k_{\rm B} = 320 $ K. The exponent $\phi$ obtained with all the data points
+for $T < 5$ K is $\phi = 1.99$, which is somewhat larger than theoretical
+exponent $\phi_{\rm BEC} =3/2$. However, it was found that the exponent
+converges at $\phi_{\rm BEC} =3/2$ with decreasing fitting window.",0607439v1
+2006-07-18,Exact spin dynamics of the 1/r^2 supersymmetric t-J model in a magnetic field,"The dynamical spin structure factor S^{zz}(Q,omega) in the small momentum
+region is derived analytically for the one-dimensional supersymmetric t-J model
+with 1/r^2 interaction. Strong spin-charge separation is found in the spin
+dynamics. The structure factor S^{zz}(Q,omega) with a given spin polarization
+does not depend on the electron density in the small momentum region. In the
+thermodynamic limit, only two spinons and one antispinon (magnon) contribute to
+S^{zz}(Q,omega). These results are derived via solution of the SU(2,1)
+Sutherland model in the strong coupling limit.",0607444v1
+2006-07-30,"The Resolution of the Diamond Problem After 200 Years: Phonon, Roton and Magnon Induced Spin-Orbital Dynamics, Subshell Rehybridization and Shell Rotation for the Little Effect","The problem of the physicochemical synthesis of diamond spans more than 200
+years, involving many giants of science. Many technologies have been
+discovered, realized and used to resolve this diamond problem. Here the origin,
+definition and cause of the diamond problem are presented. The Resolution of
+the diamond problem is then discussed on the basis of the Little Effect,
+involving novel roton-phonon driven (antisymmetrical) multi-spin induced
+orbital orientation, subshell rehybridization and valence shell rotation of
+radical complexes in quantum fluids under magnetization across thermal,
+pressure, compositional, and spinor gradients in both space and time. Some
+experimental evidence of this magnetic quantum Resolution is briefly reviewed
+and integrated with this recent fruitful discovery. Furthermore, the
+implications of the Little Effect in comparison to the Woodward-Hoffman Rule
+are considered. The distinction of the Little Effect from the prior radical
+pair effect is clarified. The better compatibility of radicals, dangling bonds
+and magnetism with the diamond lattice relative to the graphitic lattice is
+discussed. Finally, these novel physicochemical phenomena for the Little Effect
+are compared with the natural diamond genesis.",0607793v1
+2006-08-01,Flat spin wave dispersion in a triangular antiferromagnet,"The excitation spectrum of a S=1/2 2D triangular quantum antiferromagnet is
+studied using 1/S expansion. Due to the non-collinearity of the classical
+ground state significant and non-trivial corrections to the spin wave spectrum
+appear already in the first order in 1/S in contrast to the square lattice
+antiferromagnet. The resulting magnon dispersion is almost flat in a
+substantial portion of the Brillouin zone. Our results are in quantitative
+agreement with recent series expansion studies by Zheng, Fjaerestad, Singh,
+McKenzie, and Coldea [PRL 96, 057201 (2006) and cond-mat/0608008].",0608002v2
+2006-08-01,Excitation spectra of the spin-1/2 triangular-lattice Heisenberg antiferromagnet,"We use series expansion methods to calculate the dispersion relation of the
+one-magnon excitations for the spin-1/2 triangular-lattice nearest-neighbor
+Heisenberg antiferromagnet above a three-sublattice ordered ground state.
+Several striking features are observed compared to the classical (large-S)
+spin-wave spectra. Whereas at low energies the dispersion is only weakly
+renormalized by quantum fluctuations, significant anomalies are observed at
+high energies. In particular, we find roton-like minima at special wave-vectors
+and strong downward renormalization in large parts of the Brillouin zone,
+leading to very flat or dispersionless modes. We present detailed comparison of
+our calculated excitation energies in the Brillouin zone with the spin-wave
+dispersion to order 1/S calculated recently by Starykh, Chubukov, and Abanov
+[cond-mat/0608002]. We find many common features but also some quantitative and
+qualitative differences. We show that at temperatures as low as 0.1J the
+thermally excited rotons make a significant contribution to the entropy.
+Consequently, unlike for the square lattice model, a non-linear sigma model
+description of the finite-temperature properties is only applicable at
+extremely low temperatures.",0608008v1
+2006-08-15,Excitations with fractional spin less than 1/2 in frustrated magnetoelastic chains,"We study the magnetic excitations on top of the plateaux states recently
+discovered in spin-Peierls systems in a magnetic field. We show by means of
+extensive density matrix renormalization group (DMRG) computations and an
+analytic approach that one single spin-flip on top of $M=1-\frac2N$
+($N=3,4,...$) plateau decays into $N$ elementary excitations each carrying a
+fraction $\frac1N$ of the spin. This fractionalization goes beyond the
+well-known decay of one magnon into two spinons taking place on top of the M=0
+plateau. Concentrating on the $\frac13$ plateau (N=3) we unravel the
+microscopic structure of the domain walls which carry fractional
+spin-$\frac13$, both from theory and numerics. These excitations are shown to
+be noninteracting and should be observable in x-ray and nuclear magnetic
+resonance experiments.",0608326v2
+2006-08-31,Magnetic phase diagram of the semi-Heusler alloys from first-principles,"The magnetic phase diagram of the Mn-based semi-Heusler alloys is determined
+at T=0 using first-principles calculations in conjunction with the
+frozen-magnon approximation. We show that the magnetism in these systems
+strongly depends on the number of conduction electrons, their spin polarization
+and the position of the unoccupied Mn 3d states with respect to Fermi energy.
+Various magnetic phases are obtained depending on these characteristics. The
+conditions leading to diverse magnetic behavior are identified. We find that in
+the case of a large conduction electron spin polarization and the unoccupied Mn
+3d states lying far above the Fermi level, an RKKY-like ferromagnetic
+interaction is dominating. On the other hand, the antiferromagnetic
+superexchange becomes important in the presence of large peaks of the
+unoccupied Mn 3d states lying close to the Fermi energy. The overall magnetic
+behavior depends on the competition of these two exchange mechanisms. The
+obtained results are in very good agreement with the available experimental
+data.",0609001v1
+2006-09-28,Homogeneous versus Spiral Phases of Hole-doped Antiferromagnets: A Systematic Effective Field Theory Investigation,"Using the low-energy effective field theory for magnons and holes -- the
+condensed matter analog of baryon chiral perturbation theory for pions and
+nucleons in QCD -- we study different phases of doped antiferromagnets. We
+systematically investigate configurations of the staggered magnetization that
+provide a constant background field for doped holes. The most general
+configuration of this type is either constant itself or it represents a spiral
+in the staggered magnetization. Depending on the values of the low-energy
+parameters, a homogeneous phase, a spiral phase, or an inhomogeneous phase is
+energetically favored. The reduction of the staggered magnetization upon doping
+is also investigated.",0609731v1
+2006-09-29,Magnetic Excitation Spectrum of the Square Lattice S=1/2 Heisenberg Antiferromagnet K2V3O8,"We have explored the magnetic excitation spectrum of the S=1/2 square lattice
+Heisenberg antiferromagnet, K2V3O8 using both triple-axis and time-of-flight
+inelastic neutron scattering. The long-wavelength spin waves are consistent
+with the previously determined Hamiltonian for this material. A small energy
+gap of 72+/-9 micro-eV is observed at the antiferromagnetic zone center and the
+near-neighbor exchange constant is determined to be 1.08+/-0.03 meV. A finite
+ferromagnetic interplanar coupling is observed along the crystallographic
+c-axis with a magnitude of Jc=-0.0036+/-0.006 meV. However, upon approaching
+the zone boundary, the observed excitation spectrum deviates significantly from
+the expectation of linear spin wave theory resulting in split modes at the
+(pi/2,pi/2) zone boundary point. The effects of magnon-phonon interaction,
+orbital degrees of freedom, multimagnon scattering, and dilution/site
+randomness are considered in the context of the mode splitting. Unfortunately,
+no fully satisfactory explanation of this phenomenon is found and further
+theoretical and experimental work is needed.",0609775v2
+2006-10-17,Magnetic spin excitations in diluted ferromagnetic systems: the case of $Ga_{1-x}Mn_{x}As$,"We propose a theory which allow to calculate the magnetic excitation spectrum
+in diluted ferromagnetic systems. The approach is rather general and based on
+the Self-Consistent local Random Phase Approximation in which disorder
+(dilution) and thermal fluctuations are properly treated. To illustrate its
+reliability and accuracy we calculate the magnetic excitation in the diluted
+III-V magnetic semiconductor $Ga_{1-x}Mn_{x}As$. It is shown that dilution has
+a drastic effect on the excitation spectrum, indeed well defined magnon
+excitations exist only in a small region of the Brillouin zone centered around
+the $\Gamma$ point. We also calculate the spin stiffness in optimally annealed
+sample as a function of $Mn^{2+}$ concentration. A comparison to available
+measurements is done. We find a very good agreement for both the Curie
+temperature and the spin stiffness measured in well annealed samples and
+provide a plausible explanation for the very small values measured in as grown
+samples.",0610465v2
+2006-11-07,Impurity susceptibility and the fate of spin-flop transitions in lightly-doped La(2)CuO(4),"We investigate the occurrence of a two-step spin-flop transition and spin
+reorientation when a longitudinal magnetic field is applied to lightly
+hole-doped La(2)CuO(4). We find that for large and strongly frustrating
+impurities, such as Sr in La(2-x)Sr(x)CuO(4), the huge enhancement of the
+longitudinal susceptibility suppresses the intermediate flop and the
+reorientation of spins is smooth and continuous. Contrary, for small and weakly
+frustrating impurities, such as O in La(2)CuO(4+y), a discontinuous spin
+reorientation (two-step spin-flop transition) takes place. Furthermore, we show
+that for La(2-x)Sr(x)CuO(4) the field dependence of the magnon gaps differs
+qualitatively from the La(2)CuO(4) case, a prediction to be verified with Raman
+spectroscopy or neutron scattering.",0611183v2
+2007-01-11,Transfer-matrix renormalization group study of the spin ladders with cyclic four-spin interactions,"The temperature dependence of the specific heat and spin susceptibility of
+the spin ladders with cyclic four-spin interactions in the rung-singlet phase
+is explored by making use of the transfer-matrix renormalization group method.
+The values of spin gap are extracted from the specific heat and susceptibility,
+respectively. It is found that for different relative strength between
+interchain and intrachain interactions, the spin gap is approximately linear
+with the cyclic four-spin interaction in the region far away from the critical
+point. Furthermore, we show that the dispersion for the one-triplet magnon
+branch can be obtained by numerically fitting on the partition function.",0701243v1
+2007-02-13,Centipede ladder at quarter filling,"We study the ground state and excitation spectrum of a quasi one-dimensional
+nanostructure consisting of a pole and rungs oriented in the opposite
+directions (""centipede ladder"", CL) at quarter filling. The spin and charge
+excitation spectra are found in the limits of small and large longitudinal
+hopping $t_\|$ compared to the on-rung hopping rate $t_\perp$ and exchange
+coupling $I_\perp$. At small $t_\|$ the system with ferromagnetic on-rung
+exchange demonstrates instability against dimerization. Coherent propagation of
+charge transfer excitons is possible in this limit. At large $t_\|$ CL behaves
+like two-orbital Hubbard chain, but the gap opens in the charge excitation
+spectrum thus reducing the symmetry from SU(4) to SU(2). The spin excitations
+are always gapless and their dispersion changes from quadratic magnon-like for
+ferromagnetic on-rung exchange to linear spinon-like for antiferromagnetic
+on-rung exchange in weak longitudinal hopping limit.",0702307v1
+2007-02-15,Large Magnetoresistance in Co/Ni/Co Ferromagnetic Single Electron Transistors,"We report on magnetotransport investigations of nano-scaled ferromagnetic
+Co/Ni/Co single electron transistors. As a result of reduced size, the devices
+exhibit single electron transistor characteristics at 4.2K. Magnetotransport
+measurements carried out at 1.8K reveal tunneling magnetoresistance (TMR)
+traces with negative coercive fields, which we interpret in terms of a
+switching mechanism driven by the shape anisotropy of the central wire-like Ni
+island. A large TMR of about 18% is observed within a finite source-drain bias
+regime. The TMR decreases rapidly with increasing bias, which we tentatively
+attribute to excitation of magnons in the central island.",0702370v1
+2007-03-09,Infrared-active excitations related to Ho3+ ligand-field splitting at the commensurate-incommensurate magnetic phase transition in HoMn2O5,"Linearly polarized spectra of far-infrared (IR) transmission in HoMn2O5
+multiferroic single crystals have been studied in the frequency range between
+8.5 and 105 cm-1 and for temperatures between 5 K and 300 K. Polarization of
+IR-active excitations depends on the crystallographic directions in HoMn2O5 and
+is sensitive to the magnetic phase transitions. We attribute some of the
+infrared-active excitations to electric-dipole transitions between ligand-field
+split states of Ho3+ ions. For light polarization along crystalline b-axis, the
+oscillator strength of electric dipoles at low frequencies (10.5, 13, and 18
+cm-1) changes significantly at the commensurate-incommensurate
+antiferromagnetic phase transition at T3 = 19 K. This effect shows a strong
+correlation with the pronounced steps of the b-directional static dielectric
+function. We propose that the ligand field (LF) on Ho3+ connects the magnetism
+and dielectric properties of this compound through coupling with the Mn spin
+structure. We comment on the possibility for composite excitations of magnons
+and excited LF states.",0703255v2
+2007-03-16,Distribution of local Lyapunov exponents in spin-glass dynamics,"We investigate the statistical properties of local Lyapunov exponents which
+characterize magnon localization in the $d=1$ Heisenberg-Mattis spin glass
+(HMSG) at zero temperature, by means of a connection to a suitable version of
+the Fokker-Planck (F-P) equation. We consider the local Lyapunov exponents
+(LLE), in particular the case of {\em instantaneous} LLE. We establish a
+connection between the transfer-matrix recursion relation for the problem, and
+an F-P equation governing the evolution of the probability distribution of the
+instantaneous LLE. The closed-form (stationary) solutions to the F-P equation
+are in excellent accord with numerical simulations, for both the unmagnetized
+and magnetized versions of the HMSG. Scaling properties for non-stationary
+conditions are derived from the F-P equation in a special limit (in which
+diffusive effects tend to vanish), and also shown to provide a close
+description to the corresponding numerical-simulation data.",0703444v2
+1994-04-11,The Positivity of Energy for Asymptotically Anti-de Sitter Spacetimes,"We use the formulation of asymptotically anti-de Sitter boundary conditions
+given by Ashtekar and Magnon to obtain a coordinate expression for the general
+asymptotically AdeS metric in a neighbourhood of infinity. From this, we are
+able to compute the time delay of null curves propagating near infinity. If the
+gravitational mass is negative, so will be the time delay (relative to null
+geodesics at infinity) for certain null geodesics in the spacetime. Following
+closely an argument given by Penrose, Sorkin, and Woolgar, who treated the
+asymptotically flat case, we are then able to argue that a negative time delay
+is inconsistent with non-negative matter-energies in spacetimes having good
+causal properties. We thereby obtain a new positive mass theorem for these
+spacetimes. The theorem may be applied even when the matter flux near the
+boundary-at-infinity falls off so slowly that the mass changes, provided the
+theorem is applied in a time-averaged sense. The theorem also applies in
+certain spacetimes having local matter-energy that is sometimes negative, as
+can be the case in semi-classical gravity.",9404019v1
+1995-07-11,Particle Interpretations and Green Functions for a Free Scalar Field,"The formalism of Ashtekar and Magnon \cite{AshtekarMagnon:1975} for the
+definition of particles in quantum field theory in curved spacetime is further
+developed. The relation between basic objects of this formalism (e.g., the
+complex structure) and different Green functions is found. It allows one to
+derive composition laws for Green functions. The relation of two definitions of
+particles is reformulated in the formalism and the base-independent Bogoljubov
+transformation is expressed using quantities which are derivable directly from
+the ``in-out'' Green function.",9507023v2
+1995-10-01,Large enhancement of deuteron polarization with frequency modulated microwaves,"We report a large enhancement of 1.7 in deuteron polarization up to values of
+0.6 due to frequency modulation of the polarizing microwaves in a two liters
+polarized target using the method of dynamic nuclear polarization. This target
+was used during a deep inelastic polarized muon-deuteron scattering experiment
+at CERN. Measurements of the electron paramagnetic resonance absorption spectra
+show that frequency modulation gives rise to additional microwave absorption in
+the spectral wings. Although these results are not understood theoretically,
+they may provide a useful testing ground for the deeper understanding of
+dynamic nuclear polarization.",9509014v1
+2003-08-18,Order from disorder in lattice QCD at high density,"We investigate the properties of the ground state of strong coupling lattice
+QCD at finite density. Our starting point is the effective Hamiltonian for
+color singlet objects, which looks at lowest order as an antiferromagnet, and
+describes meson physics with a fixed baryon number background. We concentrate
+on uniform baryon number backgrounds (with the same baryon number on all
+sites), for which the ground state was extracted in an earlier work, and
+calculate the dispersion relations of the excitations. Two types of Goldstone
+boson emerge. The first, antiferromagnetic spin waves, obey a linear dispersion
+relation. The others, ferromagnetic magnons, have energies that are quadratic
+in their momentum. These energies emerge only when fluctuations around the
+large-N_c ground state are taken into account, along the lines of ``order from
+disorder'' in frustrated magnetic systems. Unlike other spectrum calculations
+in order from disorder, we employ the Euclidean path integral. For comparison,
+we also present a Hamiltonian calculation using a generalized
+Holstein-Primakoff transformation. The latter can only be constructed for a
+subset of the cases we consider.",0308018v4
+1992-07-21,A New Family of Diagonal Ade-Related Scattering Theories,"We propose the factorizable S-matrices of the massive excitations of the
+non-unitary minimal model $M_{2,11}$ perturbed by the operator $\Phi_{1,4}$.
+The massive excitations and the whole set of two particle S-matrices of the
+theory is simply related to the $E_8$ unitary minimal scattering theory. The
+counting argument and the Thermodynamic Bethe Ansatz (TBA) are applied to this
+scattering theory in order to support this interpretation. Generalizing this
+result, we describe a new family of NON UNITARY and DIAGONAL $ADE$-related
+scattering theories. A further generalization suggests the magnonic TBA for a
+large class of non-unitary $\G\otimes\G/\G$ coset models
+($\G=A_{odd},D_n,E_{6,7,8}$) perturbed by $\Phi_{id,id,adj}$, described by
+non-diagonal S-matrices.",9207069v1
+1996-05-07,Ground state and low excitations of an integrable chain with alternating spins,"An anisotropic integrable spin chain, consisting of spins $s=1$ and
+$s=\frac{1}{2}$, is investigated \cite{devega}. It is characterized by two real
+parameters $\bar{c}$ and $\tilde{c}$, the coupling constants of the spin
+interactions. For the case $\bar{c}<0$ and $\tilde{c}<0$ the ground state
+configuration is obtained by means of thermodynamic Bethe ansatz. Furthermore
+the low excitations are calculated. It turns out, that apart from free magnon
+states being the holes in the ground state rapidity distribution, there exist
+bound states given by special string solutions of Bethe ansatz equations (BAE)
+in analogy to \cite{babelon}. The dispersion law of these excitations is
+calculated numerically.",9605040v1
+1997-07-10,Excited states in the twisted XXZ spin chain,"We compute the finite size spectrum for the spin 1/2 XXZ chain with twisted
+boundary conditions, for anisotropy in the regime $0< \gamma <\pi/2$, and
+arbitrary twist $\theta$. The string hypothesis is employed for treating
+complex excitations. The Bethe Ansatz equtions are solved within a coupled
+non-linear integral equation approach, with one equation for each type of
+string. The root-of-unity quantum group invariant periodic chain reduces to the
+XXZ_1/2 chain with a set of twist boundary conditions ($\pi/\gamma\in Z$,
+$\theta$ an integer multiple of $\gamma$). For this model, the restricted
+Hilbert space corresponds to an unitary conformal field theory, and we recover
+all primary states in the Kac table in terms of states with specific twist and
+strings.",9707098v2
+2002-04-24,Positive Mass from Holographic Causality,"For n+1 dimensional asymptotically AdS spacetimes which have holographic
+duals on their n dimensional conformal boundaries, we show that the imposition
+of causality on the boundary theory is sufficient to prove positivity of mass
+for the spacetime when n > 2, without the assumption of any local energy
+condition. We make crucial use of a generalization of the time-delay formula
+calculated in gr-qc/9404019, which relates the time delay of a bulk null curve
+with respect to a boundary null geodesic to the Ashtekar-Magnon mass of the
+spacetime. We also discuss holographic causality for the negative mass AdS
+soliton and its implications for the positive energy conjecture of Horowitz and
+Myers.",0204198v2
+2004-08-30,The First Law of Thermodynamics for Kerr-Anti-de Sitter Black Holes,"We obtain expressions for the mass and angular momenta of rotating black
+holes in anti-de Sitter backgrounds in four, five and higher dimensions. We
+verify explicitly that our expressions satisfy the first law of thermodynamics,
+thus allowing an unambiguous identification of the entropy of these black holes
+with $\ft14$ of the area. We find that the associated thermodynamic potential
+equals the background-subtracted Euclidean action multiplied by the
+temperature. Our expressions differ from many given in the literature. We find
+that in more than four dimensions, only our expressions satisfy the first law
+of thermodynamics. Moreover, in all dimensions we show that our expression for
+the mass coincides with that given by the conformal conserved charge introduced
+by Ashtekar, Magnon and Das. We indicate the relevance of these results to the
+AdS/CFT correspondence.",0408217v3
+2006-06-15,Infinite spin limit of semiclassical string states,"Motivated by recent works of Hofman and Maldacena and Dorey we consider a
+special infinite spin limit of semiclassical spinning string states in AdS5 x
+S5. We discuss examples of known folded and circular 2-spin string solutions
+and demonstrate explicitly that the 1-loop superstring correction to the
+classical expression for the energy vanishes in the limit when one of the spins
+is much larger that the other. We also give a general discussion of this limit
+at the level of integral equations describing finite gap solutions of the
+string sigma model and argue that the corresponding asymptotic form of the
+string and gauge Bethe equations is the same.",0606145v2
+2006-07-25,"BPS Condensates, Matrix Models and Emergent String Theory","A prescription is given for computing anomalous dimensions of single trace
+operators in SYM at strong coupling and large $N$ using a reduced model of
+matrix quantum mechanics. The method involves treating some parts of the
+operators as ""BPS condensates"" which, in certain limit, have a dual description
+as null geodesics on the $S^5$. In the gauge theory, the condensate is similar
+to a representative of the chiral ring and it is described by a background of
+commuting matrices. Excitations around these condensates correspond to
+excitations around this background and take the form of ""string bits"" which are
+dual to the ""giant magnons"" of Hofman and Maldacena. In fact, the matrix model
+approach gives a {\it quantum} description of these string configurations and
+explains why the infinite momentum limit suppresses the quantum effects. This
+method allows, not only to derive part of the classical sigma model Hamiltonian
+of the dual string (in the infinite momentum limit), but also its quantum
+canonical structure. Therefore, it provides an alternative method of testing
+the AdS/CFT correspondence without the need of integrability.",0607204v2
+2006-09-04,A Perspective on Classical Strings from Complex Sine-Gordon Solitons,"We study a family of classical string solutions with large spins on R x S^3
+subspace of AdS_5 x S^5 background, which are related to Complex sine-Gordon
+solitons via Pohlmeyer's reduction. The equations of motion for the classical
+strings are cast into Lame equations and Complex sine-Gordon equations. We
+solve them under periodic boundary conditions, and obtain analytic profiles for
+the closed strings. They interpolate two kinds of known rigid configurations
+with two spins: on one hand, they reduce to folded or circular
+spinning/rotating strings in the limit where a soliton velocity goes to zero,
+while on the other hand, the dyonic giant magnons are reproduced in the limit
+where the period of a kink-array goes to infinity.",0609026v4
+2006-09-06,A Crossing-Symmetric Phase for AdS_5 x S^5 Strings,"We propose an all-order perturbative expression for the dressing phase of the
+AdS_5 x S^5 string S-matrix at strong coupling. Moreover, we are able to sum up
+large parts of this expression. This allows us to start the investigation of
+the analytic structure of the phase at finite coupling revealing a few
+surprising features. The phase obeys all known constraints including the
+crossing relation and it matches with the known physical data at strong
+coupling. In particular, we recover the bound states of giant magnons recently
+found by Hofman and Maldacena as poles of the scattering matrix. At weak
+coupling our proposal seems to differ with gauge theory. A possible solution to
+this disagreement is the inclusion of additional pieces in the phase not
+contributing to crossing, which we also study.",0609044v2
+2007-01-22,Quantum deformed magnon kinematics,"The dispersion relation for planar N=4 supersymmetric Yang-Mills is
+identified with the Casimir of a quantum deformed two-dimensional kinematical
+symmetry, E_q(1,1). The quantum deformed symmetry algebra is generated by the
+momentum, energy and boost, with deformation parameter q=e^{2\pi i/\lambda}.
+Representing the boost as the infinitesimal generator for translations on the
+rapidity space leads to an elliptic uniformization with crossing
+transformations implemented through translations by the elliptic half-periods.
+This quantum deformed algebra can be interpreted as the kinematical symmetry of
+a discrete integrable model with lattice spacing given by the BMN length
+a=2\pi/\sqrt{\lambda}. The interpretation of the boost generator as the corner
+transfer matrix is briefly discussed.",0701200v2
+2007-03-05,Strong coupling limit of Bethe Ansatz equations,"We develop a method to analyze the strong coupling limit of the Bethe ansatz
+equations supposed to give the spectrum of anomalous dimensions of the planar
+${\cal N}=4$ gauge theory. This method is particularly adapted for the three
+rank-one sectors, $su(2)$, $su(1|1)$ and $sl(2)$. We use the elliptic
+parametrization of the Bethe ansatz variables, which degenerates to a
+hyperbolic one in the strong coupling limit. We analyze the equations for the
+highest excited states in the su(2) and $su(1|1)$ sectors and for the state
+corresponding to the twist-two operator in the $sl(2)$ sector, both without and
+with the dressing kernel. In some cases we were able to give analytic
+expressions for the leading order magnon densities. Our method reproduces all
+existing analytical and numerical results for these states at the leading
+order.",0703031v2
+2006-06-27,Periodic structure of spin-transfer current in ferromagnetic multilayers,"We show that the drift-diffusion mechanism in a normal-metal layer in
+combination with the resonance electron-magnon interactions at
+ferromagnet-normal interface of F-N-F heterostucture creates spatial
+instability modes and, out of these modes, a quasi-stable periodic structure of
+spin-transfer d.c. current can arise with certain channel step and
+step-to-radius ratio. The ferromagnetic resonance conditions determine
+spin-transfer current density. Independent nano-oscillators creating
+intersecting arrays of channels can phase-lock on sub-micrometer distance,
+which depends on multilayer geometry and applied fields. By decreasing the
+layer thickness, the number of channels affected by each independent
+d.c.-current source and their radius may be diminished. Phase-locking of
+multiple independent nano-oscillators can be used for enhancement of output
+power.",0606064v1
+2003-10-21,Phonons and Magnetic Excitations in Mott-Insulator LaTiO$_3$,"The polarized Raman spectra of stoichiometric LaTiO$_3$ (T$_N = 150$ K) were
+measured between 6 and 300 K. In contrast to earlier report on half-metallic
+LaTiO$_{3.02}$, neither strong background scattering, nor Fano shape of the
+Raman lines was observed. The high frequency phonon line at 655 cm$^{-1}$
+exhibits anomalous softening below T$_N$: a signature for structural
+rearrangement. The assignment of the Raman lines was done by comparison to the
+calculations of lattice dynamics and the nature of structural changes upon
+magnetic ordering are discussed. The broad Raman band, which appears in the
+antiferromagnetic phase, is assigned to two-magnon scattering. The estimated
+superexchange constant $J = 15.4\pm0.5$ meV is in excellent agreement with the
+result of neutron scattering studies.",0310097v1
+2002-05-22,A switchable controlled-NOT gate in a spin-chain NMR quantum computer,"A method of switching a controlled-NOT gate in a solid-stae NMR quantum
+computer is presented. Qubits of I=1/2 nuclear spins are placed periodically
+along a quantum spin chain (1-D antiferromagnet) having a singlet ground state
+with a finite spin gap to the lowest excited state caused by some quantum
+effect. Irradiation of a microwave tuned to the spin gap energy excites a
+packet of triplet magnons at a specific part of the chain where control and
+target qubits are involved. The packet switches on the Suhl-Nakamura
+interaction between the qubits, which serves as a controlled NOT gate. The
+qubit initialization is achieved by a qubit initializer consisting of
+semiconducting sheets attached to the spin chain, where spin polarizations
+created by the optical pumping method in the semiconductors are transferred to
+the spin chain. The scheme allows us to separate the initialization process
+from the computation, so that one can optimize the computation part without
+being restricted by the initialization scheme, which provides us with a wide
+selection of materials for a quantum computer.",0205135v1
+2002-12-09,Entanglement sharing in one-particle states,"Entanglement sharing among sites of one-particle states is considered using
+the measure of concurrence. These are the simplest in an hierarchy of
+number-specific states of many qubits and corresponds to ``one-magnon'' states
+of spins. We study the effects of onsite potentials that are both integrable
+and nonintegrable. In the integrable case we point to a metal-insulator
+transition that reflects on the way entanglement is shared. In the
+nonintegrable case the average entanglement content increases and saturates
+along with a transition to classical chaos. Such quantum chaotic states are
+shown to have universal concurrence distributions that are modified Bessel
+functions derivable within random matrix theory. Time-reversal breaking and
+time evolving states are shown to possess significantly higher entanglement
+sharing capacity that eigenstates of time-reversal symmetric systems. We use
+the ordinary Harper and kicked Harper Hamiltonians as model systems.",0212049v3
+2003-07-18,Entanglement dynamics and quantum state transport in spin chains,"We study the dynamics of a Heisenberg-XY spin chain with an unknown state
+coded into one qubit or a pair of entangled qubits, with the rest of the spins
+being in a polarized state. The time evolution involves magnon excitations, and
+through them the entanglement is transported across the channel. For a large
+number of qubits, explicit formulae for the concurrences, measures for
+two-qubit entanglements, and the fidelity for recovering the state some
+distance away are calculated as functions of time. Initial states with an
+entangled pair of qubits show better fidelity, which takes its first maximum
+value at earlier times, compared to initial states with no entangled pair. In
+particular initial states with a pair of qubits in an unknown state (alpha
+up-up + beta down-down) are best suited for quantum state transport.",0307135v2
+2004-09-18,Spin wave based quantum storage of electronic spin with a ring array of nuclear spins,"We propose a solid state based protocol to implement the universal quantum
+storage for electronic spin qubit. The quantum memory in this scheme is the
+spin wave excitation in the ring array of nuclei in a quantum dot. We show that
+the quantum information carried by an arbitrary state of the electronic spin
+can be coherently mapped onto the spin wave excitations or the magnon states.
+With an appropriate external control, the stored quantum state in quantum
+memory can be read out reversibly. We also explore in detail the quantum
+decoherence mechanism due to the inhomogeneous couplings between the electronic
+spin and the nuclear spins.",0409120v3
+2006-06-04,Dynamic generation of entangling wave packets in XY spin system with decaying long range couplings,"We study the dynamic generation of spin entanglement between two distant
+sites in an XY model with $1/r^{2}$-decay long range couplings. Due to the
+linear dispersion relation $\epsilon (k)\sim |k|$ of magnons in such model, we
+show that a well-located spin state can be dynamically split into two moving
+entangled local wave packets without changing their shapes. Interestingly, when
+such two wave packets meet at the diametrically opposite site after the fast
+period $\tau =\pi $, the initial well-located state can be recurrent
+completely. Numerical calculation is performed to confirm the analytical result
+even the ring system of sizes $N$ up to several thousands are considered. The
+truncation approximation for the coupling strengths is also studied. Numerical
+simulation shows that the above conclusions still hold even the range of the
+coupling strength is truncated at a relative shorter scale comparing to the
+size of the spin system.",0606029v1
+2006-12-11,Quantum chaos with spin-chains in pulsed magnetic fields,"Recently it was found that the dynamics in a Heisenberg spin-chain subjected
+to a sequence of periodic pulses from an external, parabolic, magnetic field
+can have a close correspondence with the quantum kicked rotor (QKR). The QKR is
+a key paradigm of quantum chaos; it has as its classical limit the well-known
+Standard Map. It was found that a single spin excitation could be converted
+into a pair of non-dispersive, counter-propagating spin coherent states
+equivalent to the accelerator modes of the Standard Map. Here we consider how
+other types of quantum chaotic systems such as a double-kicked quantum rotor or
+a quantum rotor with a double-well potential might be realized with spin
+chains; we discuss the possibilities regarding manipulation of the one-magnon
+spin waves.",0612074v1
+2007-04-23,Neumann and Neumann-Rosochatius integrable systems from membranes on AdS_4xS^7,"It is known that large class of classical string solutions in the type IIB
+AdS_5xS^5 background is related to the Neumann and Neumann-Rosochatius
+integrable systems, including spiky strings and giant magnons. It is also
+interesting if these integrable systems can be associated with some membrane
+configurations in M-theory. We show here that this is indeed the case by
+presenting explicitly several types of membrane embedding in AdS_4xS^7 with the
+searched properties.",0704.3082v4
+2007-05-14,Polaronic features in the optical properties of the Holstein-t-J model,"We derive the exact solution for the optical conductivity $\sigma(\omega)$ of
+one hole in the Holstein-t-J model in the framework of dynamical mean-field
+theory (DMFT). We investigate the magnetic and phonon features associated with
+polaron formation as a function of the exchange coupling $J$, of the
+electron-phonon interaction $\lambda$ and of the temperature. Our solution
+directly relates the features of the optical conductivity to the excitations in
+the single-particle spectral function, revealing two distinct mechanisms of
+closing and filling of the optical pseudogap that take place upon varying the
+microscopic parameters. We show that the optical absorption at the polaron
+crossover is characterized by a coexistence of a magnon peak at low frequency
+and a broad polaronic band at higher frequency. An analytical expression for
+$\sigma(\omega)$ valid in the polaronic regime is presented.",0705.1944v2
+2007-05-17,Single spike solutions for strings on S2 and S3,"We study solutions for rigidly rotating strings on a two sphere. Among them
+we find two limiting cases that have a particular interest, one is the already
+known giant magnon and the other we call the single spike solution. The
+limiting behavior of this last solution is a string infinitely wrapped around
+the equator. It differs from that solution by the existence of a single spike
+of height theta that points toward the north pole.
+  We study its properties and compute its energy E and angular momentum J as a
+function of theta. We further generalize the solution by adding one angular
+momentum to obtain a solution on S3. We find a spin chain interpretations of
+these results in terms of free fermions and the Hubbard model but the exact
+relation with the same models derived from the field theory is not clear.",0705.2429v2
+2007-05-17,Thermodynamics of the Up-Up-Down Phase of the S = 1/2 Triangular-Lattice Antiferromagnet Cs$_2$CuBr$_4$,"Specific heat and the magnetocaloric effect are used to probe the
+field-induced up-up-down phase of Cs2CuBr4, a quasi-two-dimensional spin-1/2
+triangular antiferromagnet with near-maximal frustration. The shape of the
+magnetic phase diagram shows that the phase is stabilized by quantum
+fluctuations, not by thermal fluctuations as in the corresponding phase of
+classical spins. The magnon gaps determined from the specific heat are
+considerably larger than those expected for a Heisenberg antiferromagnet,
+probably due to the presence of a small Dzyaloshinskii-Moriya interaction.",0705.2473v1
+2007-06-21,Quantum and thermal fluctuations in a two-dimensional correlated band ferromagnet -- Goldstone-mode preserving investigation with self-energy and vertex corrections,"Ferromagnetism in the t-t' Hubbard model is investigated on a square lattice.
+Correlation effects in the form of self-energy and vertex corrections are
+systematically incorporated within a spin-rotationally-symmetric scheme which
+explicitly preserves the Goldstone mode and is therefore in accord with the
+Mermin-Wagner theorem. Interplay of band dispersion and correlation effects on
+ferromagnetic-state stability are highlighted with respect to both long- and
+short-wavelength fluctuations, which are shown to have substantially different
+behaviour. Our approach provides a novel understanding of the enhancement of
+ferromagnetism near van Hove filling for t'~0.5 in terms of strongly suppressed
+saddle-point contribution to the destabilizing exchange part of spin stiffness.
+Finite-temperature electron spin dynamics is investigated directly in terms of
+spectral-weight transfer across the Fermi energy due to electron-magnon
+coupling. Relevant in the context of recent magnetization measurements on
+ultrathin films, the role of strong thermal spin fluctuations in low dimensions
+is highlighted, in the anisotropy-stabilized ordered state, by determining the
+thermal decay of magnetization and T_c within a renormalized spin-fluctuation
+theory.",0706.3088v1
+2007-08-03,Strong spin-orbit induced Gilbert damping and g-shift in iron-platinum nanoparticles,"The shape of ferromagnetic resonance spectra of highly dispersed, chemically
+disordered Fe_{0.2}Pt_{0.8} nanospheres is perfectly described by the solution
+of the Landau-Lifshitz-Gilbert (LLG) equation excluding effects by crystalline
+anisotropy and superparamagnetic fluctuations. Upon decreasing temperature, the
+LLG damping $\alpha(T)$ and a negative g-shift, g(T)-g_0, increase proportional
+to the particle magnetic moments determined from the Langevin analysis of the
+magnetization isotherms. These novel features are explained by the scattering
+of the $q \to 0$ magnon from an electron-hole (e/h) pair mediated by the
+spin-orbit coupling, while the sd-exchange can be ruled out. The large
+saturation values, $\alpha(0)=0.76$ and $g(0)/g_0-1=-0.37$, indicate the
+dominance of an overdamped 1 meV e/h-pair which seems to originate from the
+discrete levels of the itinerant electrons in the d_p=3 nm nanoparticles.",0708.0463v1
+2007-08-08,The anomalous Hall Effect and magnetoresistance in the layered ferromagnet Fe_{1/4}TaS_2: the inelastic regime,"The large magnetic anisotropy in the layered ferromagnet Fe_{1/4}TaS_2 leads
+to very sharp reversals of the magnetization $\bf M$ at the coercive field. We
+have exploited this feature to measure the anomalous Hall effect (AHE),
+focussing on the AHE conductivity $\sigma^A_{xy}$ in the inelastic regime. At
+low temperature T (5-50 K), $\sigma^A_{xy}$ is T-independent, consistent with
+the Berry-phase/Karplus-Luttinger theory. Above 50 K, we extract an inelastic
+AHE conductivity $\sigma^{in}_{xy}$ that scales as the square of $\Delta\rho$
+(the T dependent part of the resistivity $\rho$). The term $\sigma^{in}_{xy}$
+clarifies the T dependence and sign-reversal of the AHE coefficient R_s(T). We
+discuss the possible ubiquity of $\sigma^{in}_{xy}$ in ferromagnets, and ideas
+for interpreting its scaling with $(\Delta\rho)^2$. Measurements of the
+magnetoresistance (MR) reveal a rich pattern of behavior vs. T and field
+tilt-angle. We show that the 2 mechanisms, the anisotropic MR effect and
+field-suppression of magnons, account for the intricate MR behavior, including
+the bow-tie features caused by the sharp reversals in $\bf M$.",0708.1143v1
+2007-08-16,Reflecting magnons,"We study the worldsheet reflection matrix of a string attached to a D-brane
+in $AdS_5 \times S^5$. The D-brane corresponds to a maximal giant graviton and
+it wraps an $S^3$ inside $S^5$. In the gauge theory, the open string is
+described by a spin chain with boundaries. We study an open string with a large
+SO(6) charge, which allows us to focus on one boundary at a time and to define
+an asymptotic boundary reflection matrix. We consider two cases corresponding
+to two possible relative orientations for the charges of the giant graviton and
+the open string. Using the symmetries of the problem we compute the boundary
+reflection matrix up to a phase. These matrices obey the boundary Yang Baxter
+equation. A crossing equation is derived for the overall phase. We perform weak
+coupling computations up to two loops and obtain results that are consistent
+with integrability. Finally, we determine the phase factor at strong coupling
+using classical solutions.",0708.2272v2
+2007-10-01,Strongly coupled large N spectrum of two matrices coupled via a Yang-Mills interaction,"We consider the large N spectrum of the quantum mechanical hamiltonian of two
+hermitean matrices coupled via a Yang-Mills interaction. In a framework where
+one of the matrices is treated exactly and the other is treated as a creation
+operator impurity, the difference equation associated with the Yang-Mills
+interaction is derived and solved exactly for two impurities. In this case, the
+full string tension corrected spectrum depends on two momenta. For a specific
+value of one of these momenta, the spectrum has the same structure as that of
+giant magnon bound states. States with general number of impurities are also
+discussed.",0710.0073v2
+2007-09-30,D1-brane in beta-Deformed Background,"We study various configurations of rotating and wound D1-brane in AdS_5\times
+S^5 background and in its beta deformed version. We find giant magnon and spike
+solutions on the world-volume of D1-brane in AdS_5\times S^5 background. We
+also analyse the equations of motion of D1-brane in beta-deformed background.
+We show that in the limit of large electric flux on world-volume of D1-brane
+they reduce to the equations that describe collection of large number of
+fundamental strings. We also construct rotating and wound D1-brane solution
+that has two equal spins on S^5_\gamma.",0710.0148v3
+2007-10-02,Ground-state phase diagram and magnetic properties of a tetramerized spin-1/2 J_1-J_2 model: BEC of bound magnons and absence of the transverse magnetization,"We study the ground state and the magnetization process of a spin-1/2
+$J_1$-$J_2$ model with a plaquette structure by using various methods. For
+small inter-plaquette interaction, this model is expected to have a spin-gap
+and we computed the first- and the second excitation energies. If the gap of
+the lowest excitation closes, the corresponding particle condenses to form
+magnetic orders. By analyzing the quintet gap and magnetic interactions among
+the quintet excitations, we find a spin-nematic phase around $J_1/J_2\sim -2$
+due to the strong frustration and the quantum effect. When high magnetic moment
+is applied, not the spin-1 excitations but the spin-2 ones soften and dictate
+the magnetization process. We apply a mean-field approximation to the effective
+Hamiltonian to find three different types of phases (a conventional BEC phase,
+``striped'' supersolid phases and a 1/2-plateau). Unlike the BEC in spin-dimer
+systems, this BEC phase is not accompanied by transverse magnetization.
+Possible connection to the recently discovered spin-gap compound (CuCl)LaNb2O7
+is discussed.",0710.0463v2
+2007-10-21,From an Antiferromagnet to a Valence Bond Solid: Evidence for a First Order Phase Transition,"Using a loop-cluster algorithm we investigate the spin 1/2 Heisenberg
+antiferromagnet on a square lattice with exchange coupling $J$ and an
+additional four-spin interaction of strength $Q$. We confirm the existence of a
+phase transition separating antiferromagnetism at $J/Q > J_c/Q$ from a valence
+bond solid (VBS) state at $J/Q < J_c/Q$. Although our Monte Carlo data are
+consistent with those of previous studies, we do not confirm the existence of a
+deconfined quantum critical point. Instead, using a flowgram method on lattices
+as large as $80^2$, we find evidence for a weak first order phase transition.
+We also present a detailed study of the antiferromagnetic phase. For $J/Q >
+J_c/Q$ the staggered magnetization, the spin stiffness, and the spinwave
+velocity of the antiferromagnet are determined by fitting Monte Carlo data to
+analytic results from the systematic low-energy effective field theory for
+magnons. Finally, we also investigate the physics of the VBS state at $J/Q <
+J_c/Q$, and we show that long but finite antiferromagnetic correlations are
+still present.",0710.3926v1
+2007-11-06,Half-metallic ferromagnets: From band structure to many-body effects,"A review of new developments in theoretical and experimental electronic
+structure investigations of half-metallic ferromagnets (HMF) is presented.
+Being semiconductors for one spin projection and metals for another ones, these
+substances are promising magnetic materials for applications in spintronics
+(i.e., spin-dependent electronics). Classification of HMF by the peculiarities
+of their electronic structure and chemical bonding is discussed. Effects of
+electron-magnon interaction in HMF and their manifestations in magnetic,
+spectral, thermodynamic, and transport properties are considered. Especial
+attention is paid to appearance of non-quasiparticle states in the energy gap,
+which provide an instructive example of essentially many-body features in the
+electronic structure. State-of-art electronic calculations for correlated
+$d$-systems is discussed, and results for specific HMF (Heusler alloys,
+zinc-blende structure compounds, CrO$_{2},$ Fe$_{3}$O$_{4}$) are reviewed.",0711.0872v1
+2007-11-09,Chirality and $Z_2$ vortices in an Heisenberg spin model on the kagomé lattice,"The phase diagram of the classical \jj model on the \kag lattice is
+investigated using extensive \mc simulations. In a realistic range of
+parameters, this model has a low-temperature chiral-ordered phase without
+long-range spin order. We show that the critical transition marking the
+destruction of chiral order is preempted by the first order proliferation of
+\Zdeux point defects. The core energy of these vortices appears to vanish when
+approaching the T=0 phase boundary, where both \Zdeux defects and gapless
+magnons contribute to disordering the system at very low temperature. This
+situation might be typical of a large class of frustrated magnets. Possible
+relevance for real materials is also discussed.",0711.1497v3
+2007-11-26,Quasi-universal finite-$T$ scaling in gapped one-dimensional quantum magnets,"Temperature dependencies of gap energies and magnon lifetimes are measured in
+the quasi-1-dimensional S=1/2 gapped quantum magnets IPA-CuCl3 and Sul-Cu2Cl4
+using inelastic neutron scattering. The results are compared to those found in
+literature for S=1 Haldane spin chain materials and to theoretical calculations
+for the O(3)- and O(N)- quantum non-linear sigma-models. It is found that when
+the T=0 energy gap Delta is used as the temperature scale, all experimental and
+theoretical curves are identical to within system-dependent but
+temperature-independent scaling factors of the order of unity. This
+quasi-universality extends over a surprising broad T range, at least up to
+kappa T ~ 1.5 Delta.",0711.4094v2
+2007-12-13,Electromagnon excitations in modulated multiferroics,"The phenomenological theory of ferroelectricity in spiral magnets presented
+in [M. Mostovoy, Phys. Rev. Lett. 96, 067601 (2006)] is generalized to describe
+consistently states with both uniform and modulated-in-space ferroelectric
+polarizations. A key point in this description is the symmetric part of the
+magnetoelectric coupling since, although being irrelevant for the uniform
+component, it plays an essential role for the non-uniform part of the
+polarization. We illustrate this importance in generic examples of modulated
+magnetic systems: longitudinal and transverse spin-density wave states and
+planar cycloidal phase. We show that even in the cases with no uniform
+ferroelectricity induced, polarization correlation functions follow to the soft
+magnetic behavior of the system due to the magnetoelectric effect. Our results
+can be easily generalized for more complicated types of magnetic ordering, and
+the applications may concern various natural and artificial systems in
+condensed matter physics (e.g., magnon properties could be extracted from
+dynamic dielectric response measurements).",0712.2138v2
+2007-12-18,Observation of electromagnon excitations in the BiFe0$_3$ spiral magnet,"Recently, oxide multiferroics have attracted much attention due to their
+large magnetoelectric effect which allows the tuning of magnetic properties
+with electric field and vice versa and open new venues for future spintronic
+applications such as multiple-state memory devices with dual magnetic and
+electric control. BiFeO$_3$ (BFO) belongs to this new class of materials and
+shows both ferroelectric and antiferromagnetic orders at room temperature with
+a large electric polarizationassociated with a cycloidal spiral magnetic
+ordering. The incommensurate magnetic order induces magnon zone folding and
+allows investigations by optical probes of unusual spin waves which couples to
+optical phonons, the so called ""`electromagnons""'. Here, we unravel for the
+first time the electromagnon spectra of BFO by means low energy inelastic light
+scattering technique. We show the existence of two species of electromagnons
+corresponding to spin wave excitations in and out of the cycloidal plane. The
+present observations present an unique opportunity to study the interplay
+between ferroelectric and magnetic orders.",0712.3044v1
+2008-01-17,Uncovering a pressure-tuned electronic transition in BiSrYCu2O8 using Raman scattering and x-ray diffraction,"We report pressure tuned Raman and x-ray diffraction data of
+Bi1.98Sr2.06Y0.68Cu2O8 revealing a critical pressure at 21 GPa with anomalies
+in six physical quantities: electronic Raman background, electron-phonon
+coupling, spectral weight transfer from high to low frequency, density
+dependent behaviour of phonon and magnon frequencies, and a compressibility
+change in the c-axis. For the first time in a cuprate, mobile charge carriers,
+lattice, and magnetism all show anomalies at a distinct critical pressure in
+the same experimental setting. Furthermore, the Raman spectral changes are
+similar to that seen traversing the superconducting dome with doping,
+suggesting that the critical pressure at 21 GPa is related to the much
+discussed critical point at optimal doping.",0801.2772v1
+2008-01-17,Bose-Einstein condensation in antiferromagnets close to the saturation field,"At zero temperature and strong applied magnetic fields the ground sate of an
+anisotropic antiferromagnet is a saturated paramagnet with fully aligned spins.
+We study the quantum phase transition as the field is reduced below an upper
+critical $H_{c2}$ and the system enters a XY-antiferromagnetic phase. Using a
+bond operator representation we consider a model spin-1 Heisenberg
+antiferromagnetic with single-ion anisotropy in hyper-cubic lattices under
+strong magnetic fields. We show that the transition at $H_{c2}$ can be
+interpreted as a Bose-Einstein condensation (BEC) of magnons. The theoretical
+results are used to analyze our magnetization versus field data in the organic
+compound $NiCl_2$-$4SC(NH_2)_2$ (DTN) at very low temperatures. This is the
+ideal BEC system to study this transition since $H_{c2}$ is sufficiently low to
+be reached with static magnetic fields (as opposed to pulsed fields). The
+scaling of the magnetization as a function of field and temperature close to
+$H_{c2}$ shows excellent agreement with the theoretical predictions. It allows
+to obtain the quantum critical exponents and confirm the BEC nature of the
+transition at $H_{c2}$.",0801.2795v2
+2008-01-22,Quantum Oscillations of Tunnel Magnetoresistance Induced by Spin-Wave Excitations in Ferromagnet-Ferromagnet-Ferromagnet Double Barrier Tunnel Junctions,"The possibility of quantum oscillations of the tunnel conductance and
+magnetoresistance induced by spin-wave excitations in a
+ferromagnet-ferromagnet-ferromagnet double barrier tunnel junction, when the
+magnetizations of the two side ferromagnets are aligned antiparallel to that of
+the middle ferromagnet, is investigated in a self-consistent manner by means of
+Keldysh nonequilibrium Green function method. It has been found that owing to
+the s-d exchange interactions between conduction electrons and the spin density
+induced by spin accumulation in the middle ferromagnet, the differential
+conductance and the TMR indeed oscillate with the increase of bias voltage,
+being consistent with the phenomenon that is observed recently in experiments.
+The effects of magnon modes, the energy levels of electrons as well as the
+molecular field in the central ferromagnet on the oscillatory transport
+property of the system are also discussed.",0801.3350v1
+2008-03-12,Electron transport and thermoelectric properties of layered perovskite LaBaCo2O5.5,"We have investigated the systematic transport properties of the layered
+112-type cobaltite LaBaCo2O5.5 by means of electrical resistivity,
+magnetoresistance, electroresistance and thermoelectric measurements in various
+conditions. In order to understand the complex conduction mechanism of
+LaBaCo2O5.5, the transport data have been analyzed using different theoretical
+models. The system shows semiconductor-semiconductor like transition (TSC)
+around 326K, corresponding to ferromagnetic transition and in the low
+temperature region resistivity data follows the Motts variable range hopping
+model. Interestingly, near and below the room temperature this compound depicts
+significant change in electro- and magnetoresistance behavior, the latter one
+is noteworthy near the magnetic phase boundary. The temperature dependence of
+thermopower, S(T), exhibits p-type polaronic conductivity in the temperature
+range of 60-320K and reaches a maximum value of 303 uV/K (at 120K). In the low
+temperature AFM region, the unusual S(T) behavior, generally observed for the
+cobaltite series LnBaCo2O5.5 (Ln = Rare Earth), is explained by the electron
+magnon scattering mechanism as previously described for perovskite manganites.",0803.1806v1
+2008-04-07,"Energy equilibriation processes of electrons, magnons and phonons on the femtosecond timescale","By means of time-resolved Kerr spectroscopy experiments we relate the energy
+dissipation processes on the femtosecond (electron-spin relaxation time
+$\tau_{el-sp}$) and nanosecond timescale (Gilbert relaxation $\tau_{\alpha}$)
+and compare the results to the first microscopic model, which was proposed by
+Koopmans. For both energy dissipation processes, Elliot-Yafet scattering is
+proposed as the dominant contributor. We controllably manipulate the energy
+dissipation processes by transition metal doping (Pd) and rare earth doping
+(Dy) of a Permalloy film and find that while a change of $\tau_{\alpha}$ of
+more than a factor two is observed, \tau_{el-sp}$ remains constant, contrary to
+the predictions of the model. We explain the discrepancies by relaxation
+channels not considered in the original microscopic model and identify thereby
+the applicability of the model and possible necessary extensions to the model.",0804.0985v1
+2008-06-19,Magnetoelastic-magnetoelectric phase transitions in multiferroic BiFeO3,"Our measured dielectric constant and mechanical response of multiferroic
+BiFeO3 indicate four phase transitions below room temperature. Features
+correlate with those reported at 50K (from a peak in the zero-field-cooled
+magnetic susceptibility) and 230K (from splitting between field-cooled and
+zero-field-cooled magnetic data[1], and 200K (from magnon light scattering
+cross sections[2]). The primary order parameter is not the polarization in any
+of the low-T transitions. Instead, the transition near 230 K shows strong
+elastic coupling, while that at 50K is fundamentally magnetic, but
+magnetostrictively coupled to the the lattice. The low-T phase transitions
+display glassy behaviour. A further anomaly at 140K interpreted as spin
+reorientation[2,3] shows only weakly in dielectric and mechanical studies,
+indicating that it is predominantly magnetic with little coupling to any of the
+other order parameters.",0806.3241v2
+2008-08-21,High energy spin excitations in BaFe2As2,"We report neutron scattering measurements of cooperative spin excitations in
+antiferromagnetically ordered BaFe2As2, the parent phase of an iron pnictide
+superconductor. The data extend up to ~100meV and show that the spin excitation
+spectrum is sharp and highly dispersive. By fitting the spectrum to a linear
+spin-wave model we estimate the magnon bandwidth to be in the region of 0.17eV.
+The large characteristic spin fluctuation energy suggests that magnetism could
+play a role in the formation of the superconducting state.",0808.2836v2
+2008-09-02,Parametrically-stimulated recovery of a microwave signal using standing spin-wave modes of a magnetic film,"The phenomenon of storage and parametrically-stimulated recovery of a
+microwave signal in a ferrite film has been studied both experimentally and
+theoretically. The microwave signal is stored in the form of standing spin-wave
+modes existing in the film due to its finite thickness. Signal recovery is
+performed by means of frequency-selective amplification of one of these
+standing modes by double- requency parametric pumping process. The time of
+recovery, as well as the duration and magnitude of the recovered signal, depend
+on the timing and amplitudes of both the input and pumping pulses. A mean-field
+theory of the recovery process based on the competitive interaction of the
+signal-induced standing spin-wave mode and thermal magnons with the parametric
+pumping field is developed and compared to the experimental data.",0809.0395v1
+2008-09-29,Systematic Effective Field Theory Investigation of Spiral Phases in Hole-Doped Antiferromagnets on the Honeycomb Lattice,"Motivated by possible applications to the antiferromagnetic precursor of the
+high-temperature superconductor Na$_x$CoO$_2\cdot$yH$_2$O, we use a systematic
+low-energy effective field theory for magnons and holes to study different
+phases of doped antiferromagnets on the honeycomb lattice. The effective action
+contains a leading single-derivative term, similar to the Shraiman-Siggia term
+in the square lattice case, which gives rise to spirals in the staggered
+magnetization. Depending on the values of the low-energy parameters, either a
+homogeneous phase with four or a spiral phase with two filled hole pockets is
+energetically favored. Unlike in the square lattice case, at leading order the
+effective action has an accidental continuous spatial rotation symmetry.
+Consequently, the spiral may point in any direction and is not necessarily
+aligned with a lattice direction.",0809.4998v1
+2008-10-05,Brillouin light scattering study of Co$_{2}$Cr$_{0.6}$Fe$_{0.4}$Al and Co$_{2}$FeAl Heusler compounds,"The thermal magnonic spectra of Co$_{2}$Cr$_{0.6}$Fe$_{0.4}$Al (CCFA) and
+Co$_2$FeAl were investigated using Brillouin light scattering spectroscopy
+(BLS). For CCFA, the exchange constant A (exchange stiffness D) is found to be
+0.48 $\mu$erg/cm (203 meV A$^2$), while for Co$_2$FeAl the corresponding values
+of 1.55 $\mu$erg/cm (370 meV A$^2$) were found. The observed asymmetry in the
+BLS spectra between the Stokes and anti-Stokes frequencies was assigned to an
+interplay between the asymmetrical profiles of hybridized Damon-Esbach and
+perpendicular standing spin-wave modes, combined with the optical sensitivity
+of the BLS signal to the upper side of the CCFA or Co$_2$FeAl film.",0810.0838v2
+2008-10-11,Near Flat Space limit of strings on AdS_4 x CP^3,"The non-linear nature of string theory on non-trivial backgrounds related to
+the AdS/CFT correspondence suggests to look for simplifications. Two such
+simplifications proved to be useful in studying string theory. These are the
+pp-wave limit which describes point-like strings and the so called ""near flat
+space"" limit which connects two different sectors of string theory -- pp-waves
+and ""giant magnons"". Recently another example of AdS/CFT duality emerged -
+$AdS_4/CFT_3$, which suggests duality between $\mathcal N=6$ CS theory and
+superstring theory on $AdS_4\times \cp$. In this paper we study the ""near flat
+space"" limit of strings on the $AdS_4\times \cp$ background and discuss
+possible applications of the reduced theory.",0810.2008v2
+2008-10-13,M2-brane Perspective on N=6 Super Chern-Simons Theory at Level k,"Recently, O. Aharony, O. Bergman, D. L. Jafferis and J. Maldacena (ABJM)
+proposed three-dimensional super Chern-Simons-matter theory, which at level k
+is supposed to describe the low energy limit of N M2-branes. For large N and k,
+but fixed 't Hooft coupling \lambda=N/k, it is dual to type IIA string theory
+on AdS_4 x CP^3. For large N but finite k, it is dual to M theory on AdS_4 x
+S^7/Z_k. In this paper, relying on the second duality, we find exact giant
+magnon and single spike solutions of membrane configurations on AdS_4 x S^7/Z_k
+by reducing the system to the Neumann-Rosochatius integrable model. We derive
+the dispersion relations and their finite-size corrections with explicit
+dependence on the level k.",0810.2171v2
+2008-10-13,Antiferromagnetism in two-dimensional quasicrystals,"Quasiperiodic structures possess long range positional order, but are freed
+of constraints imposed by translational invariance. For spins interacting via
+Heisenberg couplings, one may expect therefore to find novel magnetic
+configurations in such structures. We have studied magnetic properties for
+simple two dimensional models, as a first step towards understanding
+experimentally studied magnetic quasicrystals such as the Zn-Mg-R(rare earth)
+compounds. We analyse properties of the antiferromagnetic ground state and
+magnon excitation modes for bipartite tilings such as the octagonal and Penrose
+tilings. In the absence of frustration, one has an inhomogeneous Neel-ordered
+ground state, with local quantum fluctuations of the local staggered magnetic
+order parameter. We study the spin wave spectrum and wavefunctions of such
+antiferromagnets within the linear spin wave approximation. Some results for
+spin-spin correlations in these systems are discussed.",0810.2312v1
+2008-11-17,Dynamical properties of the one-dimensional spin-1/2 Bose-Hubbard model near Mott-insulator to ferromagnetic liquid transition,"We investigate the dynamics of the one-dimensional strongly repulsive
+spin-1/2 Bose-Hubbard model for filling $\nu\le1.$ While at $\nu=1$ the system
+is a Hubbard-Mott insulator exhibiting dynamical properties of the Heisenberg
+ferromagnet, at $\nu<1$ it is a ferromagnetic liquid with complex spin
+dynamics. We find that close to the insulator-liquid transition the system
+admits for a complete separation of spin and density degrees of freedom valid
+at {\it all} energy and momentum scales within the $t-J$ approximation. This
+allows us to derive the propagator of transverse spin waves and the shape of
+the magnon peak in the dynamic spin structure factor.",0811.2676v2
+2009-01-05,Constraint Effective Potential of the Staggered Magnetization in an Antiferromagnet,"We employ an improved estimator to calculate the constraint effective
+potential of the staggered magnetization in the spin $\tfrac{1}{2}$ quantum
+Heisenberg model using a loop-cluster algorithm. The first and second moment of
+the probability distribution of the staggered magnetization are in excellent
+agreement with the predictions of the systematic low-energy magnon effective
+field theory. We also compare the Monte Carlo data with the universal shape of
+the constraint effective potential of the staggered magnetization and study its
+approach to the convex effective potential in the infinite volume limit. In
+this way the higher-order low-energy parameter $k_0$ is determined from a fit
+to the numerical data.",0901.0445v1
+2009-01-14,Charge and spin transport in strongly correlated one-dimensional quantum systems driven far from equilibrium,"We study the charge conductivity in one-dimensional prototype models of
+interacting particles, such as the Hubbard and the t-V spinless fermion model,
+when coupled to some external baths injecting and extracting particles at the
+boundaries. We show that, if these systems are driven far from equilibrium, a
+negative differential conductivity regime can arise. The above electronic
+models can be mapped into Heisenberg-like spin ladders coupled to two magnetic
+baths, so that charge transport mechanisms are explained in terms of quantum
+spin transport. The negative differential conductivity is due to oppositely
+polarized ferromagnetic domains which arise at the edges of the chain, and
+therefore inhibit spin transport: we propose a qualitative understanding of the
+phenomenon by analyzing the localization of one-magnon excitations created at
+the borders of a ferromagnetic region. We also show that negative differential
+conductivity is stable against breaking of integrability. Numerical simulations
+of non-equilibrium time evolution have been performed by employing a
+Monte-Carlo wave function approach and a matrix product operator formalism.",0901.2032v3
+2009-01-15,Wave function for odd frequency superconductors,"We revisit the question of nature of odd-frequency superconductors, first
+proposed by Berezinskii in 1974. \cite{berezinskii1974} We start with the
+notion that order parameter of odd-frequency superconductors can be thought of
+as a time derivative of the odd-time pairing operator. It leads to the notion
+of the composite boson condensate.\cite{abrahams1995} To elucidate the nature
+of broken symmetry state in odd-frequency superconductors, we consider a wave
+function that properly captures the coherent condensate of composite charge
+$2e$ bosons in an odd-frequency superconductor. We consider the Hamiltonian
+which describes the equal-time composite boson condensation as proposed earlier
+in Phys. Rev. B $\textbf{52}$, 1271 (1995). We propose a BCS-like wave function
+that describes a composite condensate comprised of a spin-0 Cooper pair and a
+spin-1 magnon excitation. We derive the quasiparticle dispersion, the
+self-consistent equation for the order parameter and the density of states. We
+show that the coherent wave function approach recovers all the known
+proposerties of odd-frequency superconductors: the quasi-particle excitations
+are gapless and the superconducting transition requires a critical coupling.",0901.2323v1
+2009-01-16,Evidence of spin-density-wave order in RFeAsO from measurements of thermoelectric power,"Data on the magneto-thermopower and specific heat of three compounds
+belonging to '1111' oxypnictides family are reported. One specimen
+(SmAsFeO0.8F0.2) is a superconductor with Tc = 53 K, while two others (SmAsFeO
+and NdAsFeO) are nonsuperconducting parent compounds. Our results confirm that
+spin density wave (SDW) order is present in SmAsFeO and NdAsFeO. In these two
+samples a strict connection between the thermoelectric power and electronic
+specific heat is found in the vicinity of SDW transition, what indicates that
+the chemical potential of charge carriers strongly depends on temperature in
+this region. Low temperature data suggest presence of significant contribution
+magnon-drag to the thermoelectric power.",0901.2472v2
+2009-01-19,Chiral asymmetry of the spin-wave spectra in ultrathin magnetic films,"We raise the possibility that the chiral degeneracy of the magnons in
+ultrathin films can be lifted due to the presence of Dzyaloshinskii-Moriya
+interactions. By using simple symmetry arguments, we discuss under which
+conditions such a chiral asymmetry occurs. We then perform relativistic first
+principles calculations for an Fe monolayer on W(110) and explicitly reveal the
+asymmetry of the spin-wave spectrum in case of wave-vectors parallel to the
+(001) direction. Furthermore, we quantitatively interpret our results in terms
+of a simplified spin-model by using calculated Dzyaloshinskii-Moriya vectors.
+Our theoretical prediction should inspire experiments to explore the asymmetry
+of spin-waves, with a particular emphasis on the possibility to measure the
+Dzyaloshinskii-Moriya interactions in ultrathin films.",0901.2671v1
+2009-01-30,"Twist-three at five loops, Bethe Ansatz and wrapping","We present a formula for the five-loop anomalous dimension of N=4 SYM
+twist-three operators in the sl(2) sector. We obtain its asymptotic part from
+the Bethe Ansatz and finite volume corrections from the generalized Luescher
+formalism, considering scattering processes of spin chain magnons with virtual
+particles that travel along the cylinder. The complete result respects the
+expected large spin scaling properties and passes non-trivial tests including
+reciprocity constraints. We analyze the pole structure and find agreement with
+a conjectured resummation formula. In analogy with the twist-two anomalous
+dimension at four-loops, wrapping effects are of order log^2 M/M^2 for large
+values of the spin.",0901.4864v2
+2009-02-02,Fermionic spin excitations in two and three-dimensional antiferromagnets,"Spin excitations in an ordered Heisenberg magnet are magnons--bosons with
+spin 1. That may change when frustration and quantum fluctuations suppress the
+order and restore the spin-rotation symmetry. We show that spin excitations in
+the $S=1/2$ Heisenberg antiferromagnet on kagome are spinons--fermions with
+spin 1/2. In the ground state the system can be described as a collection of
+small, heavy pairs of spinons with spin 0. A magnetic excitation of lowest
+energy amounts to breaking up a pair into two spinons at a cost of $0.06 J$.",0902.0378v4
+2009-02-24,Can immobile magnetic vortex nucleate a vortex-antivortex pair?,"It is shown that under the action of rotating magnetic field an immobile
+vortex, contrary to a general belief, can nucleate a vortex-antivortex pair and
+switch its polarity. Two different kinds of OOMMF micromagnetic modeling are
+used: (i) the original vortex is pinned by the highly--anisotropic easy-axes
+impurity at the disk center, (ii) the vortex is pinned by artificially fixing
+the magnetization inside the vortex core in the planar vortex distribution. In
+both types of simulations a dip creation with a consequent vortex-antivortex
+pair nucleation is observed. Polarity switching occurs in the former case only.
+Our analytical approach is based on the transformation to the rotating frame of
+reference, both in the real space and in the magnetization space, and on the
+observation that the physical reason for the dip creation is softening of the
+dipole magnon mode due to magnetic field rotation.",0902.4114v1
+2009-02-27,Monte Carlo Determination of the Low-Energy Constants of a Spin 1/2 Heisenberg Model with Spatial Anisotropy,"Motivated by the possible mechanism for the pinning of the electronic liquid
+crystal direction in YBCO as proposed in \cite{Pardini08}, we use the first
+principles Monte Carlo method to study the spin 1/2 Heisenberg model with
+antiferromagnetic couplings $J_{1}$ and $J_{2}$ on the square lattice. The
+corresponding low-energy constants, namely the spin stiffness $\rho_s$, the
+staggered magnetization density ${\cal M}_s$, the spin wave velocity $c$, as
+well as the ground state energy density $e_0$ are determined by fitting the
+Monte Carlo data to the predictions of magnon chiral perturbation theory. In
+particular, the spin stiffnesses $\rho_{s1}$ and $\rho_{s2}$ are investigated
+as a function of the ratio $J_{2}/J_{1}$ of the couplings. Although we find a
+good agreement between our results with those obtained by the series expansion
+method in the weakly anisotropic regime, for strong anisotropy we observe
+discrepancies.",0902.4861v3
+2009-03-13,"Spin-wave velocities, density of magnetic excitations, and NMR relaxation in ferro-pnictides","We perform an analysis of the experimentally known temperature dependence of
+the staggered magnetization in the antiferromagnetic phase. This analysis
+allows us to put an upper limit on the unknown value of the spin wave velocity
+along the stripes of equal spin direction (spin stripes). The velocity is about
+ten times smaller than the velocity perpendicular to the spin stripes. The
+strongly anisotropic spin-wave dispersion implies a high density of low energy
+magnetic excitations. We demonstrate that this high density strongly enhances
+the $^{75}$As NMR spin-lattice relaxation via the Raman scattering of magnons.
+We derive the polarization dependence of this relaxation channel and find very
+good agreement with experimental data. The high density of low energy magnetic
+excitations deduced from our phenomenological analysis supports the scenario
+that ferro-pnictides are close to a quantum phase transition.",0903.2313v2
+2009-03-17,Microscopic spin-wave theory for yttrium-iron garnet films,"Motivated by recent experiments on thin films of the ferromagnetic insulator
+yttrium-iron garnet (YIG), we have developed an efficient microscopic approach
+to calculate the spin-wave spectra of these systems. We model the
+experimentally relevant magnon band of YIG using an effective quantum
+Heisenberg model on a cubic lattice with ferromagnetic nearest neighbor
+exchange and long-range dipole-dipole interactions. After a bosonization of the
+spin degrees of freedom via a Holstein-Primakoff transformation and a
+truncation at quadratic order in the bosons, we obtain the spin-wave spectra
+for experimentally relevant parameters without further approximation by
+numerical diagonalization, using efficient Ewald summation techniques to carry
+out the dipolar sums. We compare our numerical results with two different
+analytic approximations and with predictions based on the phenomenological
+Landau-Lifshitz equation.",0903.2847v2
+2009-03-24,Nematicity as a route to a magnetic field-induced spin density wave order; application to the high temperature cuprates,"The electronic nematic order characterized by broken rotational symmetry has
+been suggested to play an important role in the phase diagram of the high
+temperature cuprates. We study the interplay between the electronic nematic
+order and a spin density wave order in the presence of a magnetic field. We
+show that a cooperation of the nematicity and the magnetic field induces a
+finite coupling between the spin density wave and spin-triplet staggered flux
+orders. As a consequence of such a coupling, the magnon gap decreases as the
+magnetic field increases, and it eventually condenses beyond a critical
+magnetic field leading to a field-induced spin density wave order. Both
+commensurate and incommensurate orders are studied, and the experimental
+implications of our findings are discussed.",0903.3993v2
+2009-03-30,Universal Holographic Chiral Dynamics in an External Magnetic Field,"In this work we further extend the investigation of holographic gauge
+theories in external magnetic fields, continuing earlier work. We study the
+phenomenon of magnetic catalysis of mass generation in 1+3 and 1+2 dimensions,
+using D3/D7- and D3/D5-brane systems, respectively. We obtain the low energy
+effective actions of the corresponding pseudo Goldstone bosons and study their
+dispersion relations. The D3/D7 system exhibits the usual
+Gell-Mann--Oakes--Renner (GMOR) relation and a relativistic dispersion
+relation, while the D3/D5 system exhibits a quadratic non-relativistic
+dispersion relation and a modified linear GMOR relation. The low energy
+effective action of the D3/D5 system is related to that describing magnon
+excitations in a ferromagnet. We also study properties of general Dp/Dq systems
+in an external magnetic field and verify the universality of the magnetic
+catalysis of dynamical symmetry breaking.",0903.5345v2
+2009-04-14,Electron-lattice interaction and its impact on high Tc superconductivity,"In this Colloquium, the main features of the electron-lattice interaction are
+discussed and high values of the critical temperature up to room temperature
+could be provided. While the issue of the mechanism of superconductivity in the
+high Tc cuprates continues to be controversial, one can state that there have
+been many experimental results demonstrating that the lattice makes a strong
+impact on the pairing of electrons. The polaronic nature of the carriers is
+also a manifestation of strong electron-lattice interaction. One can propose an
+experiment that allows an unambiguous determination of the intermediate boson
+(phonon, magnon, exciton, etc.) which provides the pairing. The
+electron-lattice interaction increases for nanosystems, and this is due to an
+effective increase in the density of states.",0904.2038v1
+2009-04-28,Low-temperature thermal conductivity of BaFe2As2: Parent compound of iron-arsenide superconductors,"We report low-temperature thermal conductivity down to 40 mK of the
+antiferromagnet BaFe$_2$As$_{2}$, which is the parent compound of recently
+discovered iron-based superconductors. In the investigated temperature range
+below 4 K, the thermal conductivity $\kappa$ is well described by the
+expression $\kappa$ = $aT$ + $bT^{2.22}$. We attribute the ``$aT$''-term to an
+electronic contribution which is found to satisfy the Wiedemann-Franz law in
+the $T$ $\to$ 0 K limit, and the remaining thermal conductivity, $\sim$
+$T^{2.22}$, is attributed to phonon conductivity. A small influence on thermal
+conductivity by magnetic fields up to 8 T is well accounted by the observed
+magnetoresistance. The result is consistent with a fully gapped magnon
+spectrum, inferred previously from inelastic neutron scattering measurements.",0904.4470v3
+2009-05-18,Ferro-Orbital Order and Strong Magnetic Anisotropy in the Parent Compounds of Iron-Pnictide Superconductors,"The puzzling nature of magnetic and lattice phase transitions of iron
+pnictides is investigated via a first-principles Wannier function analysis of
+representative parent compound LaOFeAs. A rare ferro-orbital ordering is found
+to give rise to the recently observed highly anisotropic magnetic coupling, and
+drive the phase transitions--without resorting to widely employed frustration
+or nesting picture. The revealed necessity of the additional orbital physics
+leads to a correlated electronic structure fundamentally distinct from that of
+the cuprates. In particular, the strong coupling to the magnons advocates
+active roles of light orbitons in spin dynamics and electron pairing in iron
+pnictides.",0905.2957v2
+2009-05-26,Scattering Theory of Charge-Current Induced Magnetization Dynamics,"In ferromagnets, charge currents can excite magnons via the spin-orbit
+coupling. We develop a novel and general scattering theory of charge current
+induced macrospin magnetization torques in normal metal$|$ferromagnet$|$normal
+metal layers. We apply the formalism to a dirty GaAs$|$(Ga,Mn)As$|$GaAs system.
+By computing the charge current induced magnetization torques and solving the
+Landau-Lifshitz-Gilbert equation, we find magnetization switching for current
+densities as low as $ 5\times 10^{6}$~A/cm$^2$. Our results are in agreement
+with a recent experimental observation of charge-current induced magnetization
+switching in (Ga,Mn)As.",0905.4170v2
+2009-05-28,Resonant Nonlinear Damping of Quantized Spin Waves in Ferromagnetic Nanowires,"We use spin torque ferromagnetic resonance to measure the spectral properties
+of dipole-exchange spin waves in permalloy nanowires. Our measurements reveal
+that geometric confinement has a profound effect on the damping of spin waves
+in the nanowire geometry. The damping parameter of the lowest-energy quantized
+spin wave mode depends on applied magnetic field in a resonant way and exhibits
+a maximum at a field that increases with decreasing nanowire width. This
+enhancement of damping originates from a nonlinear resonant three-magnon
+confluence process allowed at a particular bias field value determined by
+quantization of the spin wave spectrum in the nanowire geometry.",0905.4699v2
+2009-05-29,Ferromagnetic resonance linewidth in ultrathin films with perpendicular magnetic anisotropy,"Transition metal ferromagnetic films with perpendicular magnetic anisotropy
+(PMA) have ferromagnetic resonance (FMR) linewidths that are one order of
+magnitude larger than soft magnetic materials, such as pure iron (Fe) and
+permalloy (NiFe) thin films. A broadband FMR setup has been used to investigate
+the origin of the enhanced linewidth in Ni$|$Co multilayer films with PMA. The
+FMR linewidth depends linearly on frequency for perpendicular applied fields
+and increases significantly when the magnetization is rotated into the film
+plane. Irradiation of the film with Helium ions decreases the PMA and the
+distribution of PMA parameters. This leads to a great reduction of the FMR
+linewidth for in-plane magnetization. These results suggest that fluctuations
+in PMA lead to a large two magnon scattering contribution to the linewidth for
+in-plane magnetization and establish that the Gilbert damping is enhanced in
+such materials ($\alpha \approx 0.04$, compared to $\alpha \approx 0.002$ for
+pure Fe).",0905.4779v2
+2009-06-17,Model for twin electromagnons and magnetically induced oscillatory polarization in multiferroic RMnO$_3$,"We propose a model for the pair of electromagnon excitations observed in the
+class of multiferroic materials {\it R}MnO$_3$ ({\it R} is a rare-earth ion).
+The model is based on a harmonic cycloid ground state interacting with a
+zone-edge magnon and its twin excitation separated in momentum space by two
+times the cycloid wave vector. The pair of electromagnons is activated by cross
+coupling between magnetostriction and spin-orbit interactions. Remarkably, the
+spectral weight of the twin electromagnon is directly related to the presence
+of a magnetically induced oscillatory polarization in the ground state. This
+leads to the surprising prediction that TbMnO$_3$ has an oscillatory
+polarization with amplitude 50 times larger than its uniform polarization.",0906.3059v2
+2009-08-01,Magnetic solitons in frustrated ferromagnetic spin chain,"We study the classical anisotropic ferromagnetic spin chain with frustration.
+The behavior of soliton and kink solutions in the vicinity of the ground state
+phase transition from the ferromagnetic to the spiral phase is studied. The
+dependence of the soliton energy on small anisotropy parameter is established
+using scaling estimates and numerical minimization of the energy functional.
+Conditions of the existence of the solitons are determined. It is shown that
+solitons survive in the spiral phase though with some restrictions on their
+size. A comparison of the energies of the classical solitons and the bound
+magnon complexes in the quantum model shows the functional similarity between
+them. The influence of the finite-size effects on the soliton states is studied
+and it is shown that the localized solitons originate from the uniform state
+when the system size exceeds some critical value depending on the anisotropy.",0908.0068v1
+2009-08-09,Microscopic Model versus Systematic Low-Energy Effective Field Theory for a Doped Quantum Ferromagnet,"We consider a microscopic model for a doped quantum ferromagnet as a test
+case for the systematic low-energy effective field theory for magnons and
+holes, which is constructed in complete analogy to the case of quantum
+antiferromagnets. In contrast to antiferromagnets, for which the effective
+field theory approach can be tested only numerically, in the ferromagnetic case
+both the microscopic and the effective theory can be solved analytically. In
+this way the low-energy parameters of the effective theory are determined
+exactly by matching to the underlying microscopic model. The low-energy
+behavior at half-filling as well as in the single- and two-hole sectors is
+described exactly by the systematic low-energy effective field theory. In
+particular, for weakly bound two-hole states the effective field theory even
+works beyond perturbation theory. This lends strong support to the quantitative
+success of the systematic low-energy effective field theory method not only in
+the ferromagnetic but also in the physically most interesting antiferromagnetic
+case.",0908.1225v1
+2009-08-30,Magnetic-dipolar-mode vortices and microwave subwavelength metamaterials,"There has been a surge of interest in the subwavelength confinement of the
+electromagnetic fields. It is well known that in optics the subwavelength
+confinement can be obtained due to surface plasmon (quasielectrostatic)
+oscillations. In this paper we propose to realize the subwavelength confinement
+in microwaves due to dipolar-mode (quasimagnetostatic) magnon oscillations in
+ferrite particles. Our studies of interactions between microwave
+electromagnetic fields and small ferrite particles with magnetic-dipolar-mode
+(MDM) oscillations show strong localization of electromagnetic energy. MDM
+oscillations in a ferrite disk are origins of topological singularities
+resulting in Poynting-vector vortices and symmetry breakings of the microwave
+near fields. We show that new subwavelength microwave metamaterials can be
+realized based on a system of interacting MDM ferrite disks. The volume- and
+surface-wave propagation of electromagnetic signals in the proposed dense
+metamaterials will be characterized by topological phase variations. The
+MDM-particle-metamaterial concept opens a significantly new area of research.
+In particular, there is a perspective for creation of engineered
+electromagnetic fields with unique symmetry properties.",0908.4383v1
+2009-09-18,Excitations from a chiral magnetized state of a frustrated quantum spin liquid,"We study excitations in weakly interacting pairs of quantum spin ladders
+coupled through geometrically frustrated bonds. The ground state is a
+disordered spin liquid, that at high fields is replaced by an ordered chiral
+helimagnetic phase. The spectra observed by high-field inelastic neutron
+scattering experiments on the prototype compound Sul-Cu2Cl4 are qualitatively
+different from those in the previously studied frustration-free spin liquids.
+Beyond the critical field Hc=3.7 T, the soft mode that drives the quantum phase
+transition spawns two separate excitations: a gapless Goldstone mode and a
+massive magnon. Additional massive quasiparticles are clearly visible below Hc,
+but are destroyed in the ordered phase. In their place one observes a sharply
+bound excitation continuum.",0909.3355v1
+2009-11-03,Evidence for Dynamic Phase Separation and High Energy Spin Dynamics in underdoped La$_{2-x}$Sr$_x$CuO$_4$ from Resonant Inelastic X-Ray Scattering,"We probe the collective magnetic modes of La$_2$CuO$_4$ (LCO) and underdoped
+La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) by momentum resolved Resonant Inelastic X-ray
+Scattering (RIXS) at the Cu $L_3$ edge. In LCO the single magnon dispersion
+measured by RIXS coincides with the one determined by inelastic neutron
+scattering. For LSCO the spin dynamics shows a branch dispersing up to
+$\sim$400 meV coexisting with a branch at lower energy. Only the latter has
+been observed with neutrons so far and is considered a key signature of doped
+cuprates. The presence of the high-energy branch indicates that LSCO is in a
+dynamic inhomogeneous spin state.",0911.0621v1
+2009-11-11,Dilute-Bose-Gas Approach to ground state phases of 3D quantum helimagnets under high magnetic field,"We study high-field phase diagram and low-energy excitations of
+three-dimensional quantum helimagnets. Slightly below the saturation field, the
+emergence of magnetic order may be mathematically viewed as Bose-Einstein
+condensation (BEC) of magnons. The method of dilute Bose gas enables an
+unbiased quantitative analysis of quantum effects in three-dimensional
+helimagnets and thereby three phases are found: cone, coplanar fan and an
+attraction-dominant one. To investigate the last phase, we extend the usual BEC
+approach so that we can handle 2-magnon bound states. In the case of 2-magnon
+BEC, the transverse magnetization vanishes and long-range order occurs in the
+quadrupolar channel (spin-nematic phase). As an application, we map out the
+phase diagram of a 3D helimagnet which consists of frustrated J1-J2 chains
+coupled by an interchain interaction J3.",0911.2186v2
+2009-11-13,Infrared optical absorption spectra of CuO single crystals: Fermion-spinon band and dimensional crossover of the antiferromagnetic order,"We have obtained mid-infrared optical absorption spectra of the S=1/2 quasi
+one-dimensional CuO using polarized transmission measurement and interpreted
+the spectra in terms of phonon assisted magnetic excitations. When the electric
+field is parallel to the main antiferromagnetic direction a Delta shaped peak
+is observed with the maximum at 0.23eV which is attributed to spinons along
+Cu-O chains. At low temperatures in the antiferromagnetic phase another peak
+appears at 0.16eV which is attributed to two-magnon absorption but the spinon
+peak remains. This behavior is interpreted as due to a dimensional crossover
+where the low temperature three-dimensional magnetic phase keeps short range
+characteristics of a one-dimensional magnet.",0911.2573v1
+2009-11-27,Multiple vortex-antivortex pair generation in magnetic nanodots,"The interaction of a magnetic vortex with a rotating magnetic field causes
+the nucleation of a vortex--antivortex pair leading to a vortex polarity
+switching. The key point of this process is the creation of a dip, which can be
+interpreted as a nonlinear resonance in the system of certain magnon modes with
+nonlinear coupling. The usually observed single-dip structure is a particular
+case of a multidip structure. The dynamics of the structure with $n$ dips is
+described as the dynamics of nonlinearly coupled modes with azimuthal numbers
+$m=0,\pm n,\pm 2n$. The multidip structure with arbitrary number of vortex
+antivortex pairs can be obtained in vortex-state nanodisk using a space- and
+time-varying magnetic field. A scheme of a possible experimental setup for
+multidip structure generation is proposed.",0911.5353v2
+2010-01-03,Spin flexoelectricity in multiferroics,"Various phenomena related to inhomogeneous magnetoelectric interaction are
+considered. The interrelation between spatial modulation of order parameter and
+electric polarization, known as flexoelectric effect in liquid crystals, in the
+case of magnetic media appears in a form of electric polarization induced by
+spin modulation and vice versa. This flexomagnetoelectric interaction is also
+related to the influence of ferroelectric domain structure on antiferromagnetic
+vector distribution, and to the magnetoelectric properties of micromagnetic
+structures. The influence of inhomogeneous magnetoelectric interaction on
+dynamic properties of multiferroics, particularly magnon spectra is also
+considered.",1001.0254v2
+2010-01-19,Surface and bulk polaritons in a linear magnetoelectric multiferroic with canted spins: Transverse Electric polarisation,"Some magnetoelectric multiferroics have a canted spin structure that can be
+described by a Dzyaloshinkii-Moriya coupling. We calculate properties and
+features expected for surface and bulk magnon polaritons in such media with a
+linear magnetoelectric interaction for the case of transverse electric
+polarisation. The dielectric polarisation and magnetisation of weak
+ferromagnetism are constrained to lie in the plane parallel to the surface. We
+examine a geometry with the polarisation oriented in the film plane and present
+numerical results for the transverse electric polarisation. Particular
+attention is given to non-reciprocal surface modes, which exist in frequency
+between two bulk bands, and show how these modes can be modified by external
+magnetic field. Results for attenuated total reflection are presented, and
+discussed in relation to nonreciprocity. Example results are calculated for the
+canted antiferromagnet BaMnF4.",1001.3197v1
+2010-02-08,A Triplet Resonance in Superconducting FeSe0.4Te0.6,"From heavy fermions to cuprates and iron pnictides, a spin resonance is a
+staple of nearly magnetic superconductors. Possible explanations include a
+two-particle bound state or loss of magnon damping in the superconductor. While
+both scenarios suggest a central role for magnetic fluctuations, distinguishing
+them is important to identify the right theoretical framework and to guide the
+search for higher temperature superconductors. Using inelastic neutron
+scattering technique, we show that the spin resonance in optimally doped
+Fe(Se,Te) splits into three peaks in a high magnetic field, a signature of a
+two-particle triplet bound state",1002.1617v2
+2010-02-26,Correlation Effects in the Stochastic Landau-Lifshitz-Gilbert Equation,"We analyze the Landau-Lifshitz-Gilbert equation when the precession motion of
+the magnetic moments is additionally subjected to an uniaxial anisotropy and is
+driven by a multiplicative coupled stochastic field with a finite correlation
+time $\tau$. The mean value for the spin wave components offers that the
+spin-wave dispersion relation and its damping is strongly influenced by the
+deterministic Gilbert damping parameter $\alpha$, the strength of the
+stochastic forces $D$ and its temporal range $\tau$. The spin-spin-correlation
+function can be calculated in the low correlation time limit by deriving an
+evolution equation for the joint probability function. The stability analysis
+enables us to find the phase diagram within the $\alpha-D$ plane for different
+values of $\tau$ where damped spin wave solutions are stable. Even for zero
+deterministic Gilbert damping the magnons offer a finite lifetime. We detect a
+parameter range where the deterministic and the stochastic damping mechanism
+are able to compensate each other leading to undamped spin-waves. The onset is
+characterized by a critical value of the correlation time. An enhancement of
+$\tau$ leads to an increase of the oscillations of the correlation function.",1002.4958v1
+2010-03-03,Spin Oscillations in Antiferromagnetic NiO Triggered by Circularly Polarized Light,"Coherent spin oscillations were non-thermally induced by circularly polarized
+pulses in fully compensated antiferromagnetic NiO. This effect is attributed to
+an entirely new mechanism of the action, on the spins, of the effective
+magnetic field generated by an inverse Faraday effect. The novelty of this
+mechanism is that spin oscillations are driven by the time derivative of the
+effective magnetic field acting even on ""pure"" antiferromagnets with zero net
+magnetic moment in the ground state. The measured frequencies (1.07 THz and 140
+GHz) of the spin oscillations correspond to the out-of-plane and in-plane modes
+of antiferromagnetic magnons.",1003.0820v1
+2010-03-13,"Magnetic, thermal and transport properties of Cd doped CeIn$_3$","We have investigated the effect of Cd substitution on the archetypal heavy
+fermion antiferromagnet CeIn$_3$ via magnetic susceptibility, specific heat and
+resistivity measurements. The suppression of the Neel temperature, T$_{N}$,
+with Cd doping is more pronounced than with Sn. Nevertheless, a doping induced
+quantum critical point does not appear to be achievable in this system. The
+magnetic entropy at $T_N$ and the temperature of the maximum in resistivity are
+also systematically suppressed with Cd, while the effective moment and the
+Curie-Weiss temperature in the paramagnetic state are not affected. These
+results suggest that Cd locally disrupts the AFM order on its neighboring Ce
+moments, without affecting the valence of Ce. Moreover, the temperature
+dependence of the specific heat below $T_N$ is not consistent with 3D magnons
+in pure as well as in Cd-doped CeIn$_3$, a point that has been missed in
+previous investigations of CeIn$_3$ and that has bearing on the type of quantum
+criticality in this system.",1003.2723v1
+2010-03-31,Magnonic Crystal with Two-Dimensional Periodicity as a Waveguide for Spin Waves,"We describe a simple method of including dissipation in the spin wave band
+structure of a periodic ferromagnetic composite, by solving the Landau-Lifshitz
+equation for the magnetization with the Gilbert damping term. We use this
+approach to calculate the band structure of square and triangular arrays of Ni
+nanocylinders embedded in an Fe host. The results show that there are certain
+bands and special directions in the Brillouin zone where the spin wave lifetime
+is increased by more than an order of magnitude above its average value. Thus,
+it may be possible to generate spin waves in such composites decay especially
+slowly, and propagate especially large distances, for certain frequencies and
+directions in ${\bf k}$-space.",1003.6092v1
+2010-03-31,Probing Non-Toric Geometry with Rotating Membranes,"Recently Martelli and Sparks presented the first non-toric AdS_4/CFT_3
+duality relation between M-theory on AdS_4 x V_{5,2}/Z_k and a class of
+three-dimensional N=2 quiver Chern-Simons-matter theories. V_{5,2} is a
+seven-dimensional homogeneneous Sasaki-Einstein manifold with isometry group
+SO(5)xU(1)_R, which is in general broken to SU(2)xU(1)xU(1)_R by the orbifold
+projection if k>1. The dual field theory is described by the A_1 quiver, U(N)_k
+x U(N)_{-k} gauge group, four bifundamentals, two adjoint chiral multiplets
+interacting via a cubic superpotential. We explore this proposal by studying
+various classical membrane solutions moving in V_{5,2}. Rotating membrane
+solutions of folded, wrapped, spike, and giant magnon types are presented with
+their dispersion relations. We also discuss their dual operators in the
+Chern-Simons-matter theory.",1003.6111v1
+2010-04-14,Heat capacity uncovers physics of a frustrated spin tube,"We report on refined experimental results concerning the low-temperature
+specific heat of the frustrated spin tube material [(CuCl2tachH)3Cl]Cl2. This
+substance turns out to be an unusually perfect spin tube system which allows to
+study the physics of quasi-one dimensional antiferromagnetic structures in
+rather general terms. An analysis of the specific heat data demonstrates that
+at low enough temperatures the system exhibits a Tomonaga-Luttinger liquid
+behavior corresponding to an effective spin-3/2 antiferromagnetic Heisenberg
+chain with short-range exchange interactions. On the other hand, at somewhat
+elevated temperatures the composite spin structure of the chain is revealed
+through a Schottky-type peak in the specific heat located around 2 K. We argue
+that the dominating contribution to the peak originates from gapped magnon-type
+excitations related to the internal degrees of freedom of the rung spins.",1004.2373v1
+2010-04-21,Thermal Transport Properties of Bechgaard Salts (TMTSF)2PF6 and (TMTSF)2ClO4: Implication of Spin-Charge Separation,"We report thermal transport measurements performed on the
+quasi-one-dimensional Bechgaard salts (TMTSF)2ClO4 and (TMTSF)2PF6 along the
+a-direction. For both salts, magnon-drag effects are found to contribute
+considerably to thermopower above 80 K. These results imply spin-charge
+separation in the metallic state for both salts. Moreover, a linear
+temperature-dependent thermal conductivity is found to be unaffected by anion
+disorder below an anion ordering transition temperature TAO~25 K in
+(TMTSF)2ClO4.",1004.3614v1
+2010-06-11,Quantum Strings and the AdS4/CFT3 Interpolating Function,"The existence of a nontrivial interpolating function h(\lambda) is one of the
+novel features of the new AdS4/CFT3 correspondence involving ABJM theory. At
+strong coupling, most of the investigation of semiclassical effects so far has
+been for strings in the AdS4 sector. Several cutoff prescriptions have been
+proposed, leading to different predictions for the constant term in the
+expansion h(\lambda)=\sqrt{\lambda/2} + c + ... . We calculate quantum
+corrections for giant magnons, using the algebraic curve, and show by comparing
+to the dispersion relation that the same prescriptions lead to the same values
+of c in this CP3 sector. We then turn to finite-J effects, where a comparison
+with the Luescher F-term correction shows a mismatch for one of the three sum
+prescriptions. We also compute some dyonic and higher F-terms for future
+comparisons.",1006.2174v3
+2010-06-21,Vortex core contribution to textural energy in 3He-B below 0.4Tc,"Vortex lines affect the spatial order-parameter distribution in superfluid
+3He-B owing to superflow circulating around vortex cores and due to the
+interaction of the order parameter in the core and in the bulk as a result of
+superfluid coherence over the whole volume. The step-like change of the latter
+contribution at 0.6Tc (at a pressure of 29bar) signifies the transition from
+axisymmetric cores at higher temperatures to broken-symmetry cores at lower
+temperatures. We extended earlier measurements of the core contribution to
+temperatures below 0.2Tc, in particular searching for a possible new core
+transition to lower symmetries. As a measuring tool we track the energy levels
+of magnon condensate states in a trap formed by the order-parameter texture.",1006.4108v1
+2010-06-26,Terahertz Hall Measurements On Optimally Doped Single Crystal Bi-2212,"The infrared Hall angle in optimally doped single crystal $\rm Bi_2 Sr_2 Ca
+Cu_2 O_{8+x}$ was measured from 3.05 to 21.75 meV as a continuous function of
+temperature from 25 to 300\,K. In the normal state, the temperature dependence
+of the real part of the cotangent of the infrared Hall angle obeys the same
+power law as dc measurements. The measured Hall frequency $\rm \omega_H$ is
+significantly larger than the expected value based upon ARPES data analyzed in
+terms of the relaxation time approximation. This discrepancy as well as the
+temperature dependence of $\rm Re(\cot{\theta_H})$ and $\omega_H$ is well
+described by a Fermi liquid theory in which current vertex corrections produced
+by electron-magnon scattering are included.",1006.5106v1
+2010-07-12,Ferromagnetic Excitations in La$_{0.82}$Sr$_{0.18}$CoO$_{3}$ Observed Using Neutron Inelastic Scattering,"Polarized neutron inelastic scattering has been used to measure spin
+excitations in ferromagnetic La$_{0.82}$Sr$_{0.18}$CoO$_{3}$. The magnon
+spectrum of these spin excitations is well defined at low energies but becomes
+heavily damped at higher energies, and can be modeled using a quadratic
+dispersion. We determined a spin wave stiffness constant of $D=94\pm
+3$\,meV\,\AA$^{2}$. Assuming a nearest-neighbor Heisenberg model we find
+reasonable agreement between the exchange determined from D and the bulk Curie
+temperature. Several possible mechanisms to account for the observed spin-wave
+damping are discussed.",1007.1919v1
+2010-07-30,Magnetic excitations in multiferroic LuMnO3 studied by inelastic neutron scattering,"We present data on the magnetic and magneto-elastic coupling in the hexagonal
+multiferroic manganite LuMnO3 from inelastic neutron scattering, magnetization
+and thermal expansion measurements. We measured the magnon dispersion along the
+main symmetry directions and used this data to determine the principal exchange
+parameters from a spin-wave model. An analysis of the magnetic anisotropy in
+terms of the crystal field acting on the Mn is presented. We compare the
+results for LuMnO3 with data on other hexagonal RMnO3 compounds.",1007.5490v2
+2010-09-17,Dynamics of coupled vortices in a pair of ferromagnetic disks,"We here experimentally demonstrate that coupled gyration modes can be
+resonantly excited primarily by the ac current in a pair of ferromagnetic disks
+with varied separating distance. The sole gyrotropic mode clearly splits into a
+higher and a lower frequency modes for different configurations of polarities
+via dipolar interaction. These experimental results indicate that the
+magnetostatically coupled pair of vortices behaves similar to a diatomic
+molecule with bonding and anti-bonding states. These findings lead to the
+possible extension of designing the magnonic band structure in a chain or an
+array of vortices.",1009.3363v3
+2010-09-28,The magnonic limit of domain wall propagation in ferromagnetic nanotubes,"We report a study on the field-driven propagation of vortex-like domain walls
+in ferromagnetic nanotubes. This particular geometry gives rise to a special
+feature of the static wall configuration, which significantly influences its
+dynamics. Unlike domain walls in flat strips, the left-right symmetry of domain
+wall propagation is broken. Furthermore, the domain wall velocity is not
+limited by the Walker breakdown. Under sufficiently large magnetic fields, the
+domain wall velocity reaches the velocity of spin waves (about 1000 m/s) and is
+thereafter connected with a direct emission of spin waves. The moving domain
+wall maintains its main structure but has characteristic spin-wave tails
+attached. The spatial profile of this topological soliton is determined by the
+spin-wave dispersion.",1009.5552v1
+2010-09-30,Magnetic Phase Diagram of Alternating Chain Compound Pb2V3O9,"Pb2V3O9 was found to have antiferromagnetic alternating chains of S=1/2 and
+show the antiferromagnetic long range ordered (AFLRO) state under the magnetic
+field between 4 and 38 T. We succeeded in growing single crystals of Pb2V3O9 by
+floating zone method and determined the asymmetric H-T phase diagram of Pb2V3O9
+from measurements of the magnetization and the heat capacity. Previous reports
+focused on the AFLRO state in the low magnetic field region and that in high
+magnetic field region was not discussed so much. In this paper, we examined the
+AFLRO state in terms of the mean field theory and the picture of Bose-Einstein
+condensation of magnons to discuss the whole phase diagram. Consequently, the
+asymmetry of the phase boundary in Pb2V3O9 is explained by the mixing
+contribution of excited states and by interchain interactions.",1009.6026v1
+2010-10-08,Superspace calculation of the four-loop spectrum in N=6 supersymmetric Chern-Simons theories,"Using N=2 superspace techniques we compute the four-loop spectrum of single
+trace operators in the SU(2) x SU(2) sector of ABJM and ABJ supersymmetric
+Chern-Simons theories. Our computation yields a four-loop contribution to the
+function h^2(\lambda) (and its ABJ generalization) in the magnon dispersion
+relation which has fixed maximum transcendentality and coincides with the
+findings in components given in the revised versions of arXiv:0908.2463 and
+arXiv:0912.3460. We also discuss possible scenarios for an all-loop function
+h^2(\lambda) that interpolates between weak and strong couplings.",1010.1756v2
+2010-10-12,Revealing the degree of magnetic frustration by non-magnetic impurities,"Imaging the magnetic fields around a non-magnetic impurity can provide a
+clear benchmark for quantifying the degree of magnetic frustration. Focusing on
+the strongly frustrated $J_1$-$J_2$ model and the spatially anisotropic
+$J_{1a}$-$J_{1b}$-$J_2$ model, very distinct low energy behaviors reflect
+different levels of magnetic frustration. In the $J_1$-$J_2$ model, bound
+magnons appear trapped near the impurity in the ground state and strongly
+reduce the ordered moments for sites proximal to the impurity. In contrast,
+local moments in the $J_{1a}$-$J_{1b}$-$J_2$ model are enhanced on the impurity
+neighboring sites. These theoretical predictions can be probed by experiments
+such as nuclear magnetic resonance and scanning tunneling microscopy, and the
+results can elucidate the role of frustration in antiferromagnets and help
+narrow the possible models to understand magnetism in the iron pnictdies.",1010.2917v2
+2010-10-18,"Fermionic magnons, non-Abelian spinons, and spin quantum Hall effect from an exactly solvable Kitaev Hamiltonian with SU(2) symmetry","We introduce an exactly solvable SU(2) symmetric Kitaev model with exotic
+spin excitations. With time reversal symmetry (TRS), the ground state is a spin
+liquid with gapless or gapped spin-1 but fermionic excitations. When TRS is
+broken, the resulting spin liquid exhibits deconfined vortex excitations which
+carry spin-1/2 quantum number and obey non-Abelian statistics. We show that
+this SU(2) invariant non-Abelian spin liquid exhibits spin quantum Hall effect
+with quantized spin Hall conductivity \sigma^s_{xy}=\hbar/2\pi, and that the
+spin response is effectively described the SO(3) level-1 Chern-Simons theory at
+low energy. We further propose that a SU(2) level-2 Chern-Simons theory is the
+effective field theory describing the topological structure of the non-Abelian
+SU(2) invariant spin liquid.",1010.3724v2
+2010-10-22,"Single-ion anisotropy, Dzyaloshinskii-Moriya interaction and negative magnetoresistance of the spin-1/2 pyrochlores R2V2O7","The electronic and magnetic properties of spin-1/2 pyrochlores R2V2O7 were
+investigated on the basis of density-functional calculations. Contrary to the
+common belief, the spin-1/2 V4+ ions are found to have a substantial easy-axis
+single-ion anisotropy. The |D/J| ratio deduced from the magnon quantum Hall
+effect of Lu2V2O7, where J is the nearest-neighbor spin exchange and D is the
+Dzyaloshinskii-Moriya parameter, is much greater than the value estimated from
+our calculations (i.e., 0.32 vs. 0.05). We show that this discrepancy is due to
+the neglect of the single-ion anisotropy of the V4+ ions, and the negative
+magnetoresistance observed for R2V2O7 arises from a new mechanism.",1010.4606v1
+2010-10-29,Field-Induced Gap in a Quantum Spin-1/2 Chain in a Strong Magnetic Field,"Magnetic excitations in copper pyrimidine dinitrate, a spin-1/2
+antiferromagnetic chain with alternating $g$-tensor and Dzyaloshinskii-Moriya
+interactions that exhibits a field-induced spin gap, are probed by means of
+pulsed-field electron spin resonance spectroscopy. In particular, we report on
+a minimum of the gap in the vicinity of the saturation field $H_{sat}=48.5$ T
+associated with a transition from the sine-Gordon region (with soliton-breather
+elementary excitations) to a spin-polarized state (with magnon excitations).
+This interpretation is fully confirmed by the quantitative agreement over the
+entire field range of the experimental data with the DMRG investigation of the
+spin-1/2 Heisenberg chain with a staggered transverse field.",1010.6141v1
+2010-11-06,Effect of anisotropy on the field induced quantum critical properties of the three dimensional s=1/2 Heisenberg model,"The field induced quantum critical properties of the three dimensional
+spin-1/2 anisotropic antiferromagnetic Heisenberg model has been studied. We
+have investigated the quantum phase transition between the spiral order and
+field induced ferromagnetic order by means of Bose-Einstein condensation of
+magnons in terms of a bosonic representation. The effect of in-plane anisotropy
+on the critical properties has been studied via the bosonic model by Green's
+function approach. We have found an analytic expression for the gap exponent in
+addition to numerical results for the critical magnetic field in terms of
+anisotropy parameter. The in-plane anisotropy breaks the U(1) symmetry
+explicitly which changes the universal behavior by a drastic change on the gap
+exponent. Moreover, the critical magnetic field depends strongly on the
+in-plane anisotropies. The divergence of the transverse structure factor at the
+antiferromagnetic wave vector confirms the onset of the magnetic order which
+scales with the negative value of gap exponent as the magnetic field approaches
+the critical one. The transverse staggered magnetization as an order parameter
+vanishes with exponent $\beta=0.5$ when the magnetic field reaches its critical
+value in low field region.",1011.1574v1
+2010-11-14,Scattering universality classes of side jump in anomalous Hall effect,"The anomalous Hall conductivity has an important extrinsic contribution known
+as side jump contribution, which is independent of both scattering strength and
+disorder density. Nevertheless, we discover that side jump has strong
+dependence on the spin structure of the scattering potential. We propose three
+universality classes of scattering for the side jump contribution, having the
+characters of being spin-independent, spin-conserving and spin-flip
+respectively. For each individual class, the side jump contribution takes a
+different unique value. When two or more classes of scattering are present, the
+value of side jump is no longer fixed but varies as a function of their
+relative disorder strength. As system control parameter such as temperature
+changes, due to the competition between different classes of disorder
+scattering, the side jump Hall conductivity could flow from one class dominated
+limit to another class dominated limit. Our result indicates that magnon
+scattering plays a role distinct from normal impurity scattering and phonon
+scattering in the anomalous Hall effect because they belong to different
+scattering classes.",1011.3239v1
+2010-11-26,Modes of magnetic resonance of S=1 dimer chain compound NTENP,"The spin dynamics of a quasi one dimensional $S=1$ bond alternating spin-gap
+antiferromagnet Ni(C$_9$H$_{24}$N$_4$)NO$_2$(ClO$_4$) (abbreviated as NTENP) is
+studied by means of electron spin resonance (ESR) technique. Five modes of ESR
+transitions are observed and identified: transitions between singlet ground
+state and excited triplet states, three modes of transitions between spin
+sublevels of collective triplet states and antiferromagnetic resonance
+absorption in the field-induced antiferromagnetically ordered phase.
+Singlet-triplet and intra-triplet modes demonstrate a doublet structure which
+is due to two maxima in the density of magnon states in the low-frequency
+range. A joint analysis of the observed spectra and other experimental results
+allows to test the applicability of the fermionic and bosonic models. We
+conclude that the fermionic approach is more appropriate for the particular
+case of NTENP.",1011.5742v1
+2010-12-01,Persistence of magnons in a site-diluted dimerized frustrated antiferromagnet,"We present inelastic neutron scattering and thermodynamic measurements
+characterizing the magnetic excitations in a disordered non-magnetic
+substituted spin-liquid antiferromagnet. The parent compound Ba3Mn2O8 is a
+dimerized, quasi-two-dimensional geometrically frustrated quantum disordered
+antiferromagnet. We substitute this compound with non-magnetic vanadium for the
+S = 1 manganese atoms, Ba3(Mn1-xVx)2O8, and find that the singlet-triplet
+excitations which dominate the spectrum of the parent compound persist for the
+full range of substitution examined, x = 0.02 to 0.3. We also observe
+additional low-energy magnetic fluctuations which are enhanced at the greatest
+substitution values. These excitations may be a precursor to a low-temperature
+random singlet phase which may exist in Ba3(Mn1-xVx)2O8",1012.0099v1
+2010-12-17,"Review of AdS/CFT Integrability, Chapter IV.3: N=6 Chern-Simons and Strings on AdS4xCP3","We review the duality and integrability of N=6 superconformal Chern-Simons
+theory in three dimensions and IIA superstring theory on the background
+AdS4xCP3. We introduce both of these models and describe how their degrees of
+freedom are mapped to excitations of a long-range integrable spin-chain.
+Finally, we discuss the properties of the Bethe equations, the S-matrix and the
+algebraic curve that are special to this correspondence and differ from the
+case of N=4 SYM theory and strings on AdS5xS5.",1012.3999v5
+2010-12-21,Phase diagram and continuous pair-unbinding transition of the bilinear-biquadratic S=1 Heisenberg chain in a magnetic field,"We investigate the properties of the Heisenberg S=1 chain with bilinear and
+biquadratic interactions in a magnetic field using the Density Matrix
+Renormalization Group, Bethe ansatz and field theoretical considerations. In a
+large region of the parameter space, we identify a magnetized ferroquadrupolar
+Luttinger liquid consisting of a quasi-condensate of bound magnon pairs. This
+liquid undergoes a continuous pair unbinding transition to a more conventional
+Luttinger liquid region obtained by polarizing the system above the Haldane gap
+region. This pair unbinding transition is shown to be in the Ising universality
+class on top of a Luttinger liquid, leading to an effective central charge 3/2.
+We also revisit the nature of the partially polarized Luttinger liquid around
+and above the Uimin-Lai-Sutherland point. Our results confirm that this is a
+two-component liquid and rule out the formation of a single-component vector
+chiral phase.",1012.4518v2
+2011-01-06,Quantum spin ladders of non-Abelian anyons,"Quantum ladder models, consisting of coupled chains, form intriguing systems
+bridging one and two dimensions and have been well studied in the context of
+quantum magnets and fermionic systems. Here we consider ladder systems made of
+more exotic quantum mechanical degrees of freedom, so-called non-Abelian
+anyons, which can be thought of as certain quantum deformations of ordinary
+SU(2) spins. Such non-Abelian anyons occur as quasiparticle excitations in
+topological quantum fluids, including p_x + i p_y superconductors, certain
+fractional quantum Hall states, and rotating Bose-Einstein condensates. Here we
+use a combination of exact diagonalization and conformal field theory to
+determine the phase diagrams of ladders with up to four chains. We discuss how
+phenomena familiar from ordinary SU(2) spin ladders are generalized in their
+anyonic counterparts, such as gapless and gapped phases, odd/even effects with
+the ladder width, and elementary `magnon' excitations. Other features are
+entirely due to the topological nature of the anyonic degrees of freedom.",1101.1186v2
+2011-05-03,Classical integrability in the BTZ black hole,"Using the fact the BTZ black hole is a quotient of AdS_3 we show that
+classical string propagation in the BTZ background is integrable. We construct
+the flat connection and its monodromy matrix which generates the non-local
+charges. From examining the general behaviour of the eigen values of the
+monodromy matrix we determine the set of integral equations which constrain
+them. These equations imply that each classical solution is characterized by a
+density function in the complex plane. For classical solutions which correspond
+to geodesics and winding strings we solve for the eigen values of the monodromy
+matrix explicitly and show that geodesics correspond to zero density in the
+complex plane. We solve the integral equations for BMN and magnon like
+solutions and obtain their dispersion relation. Finally we show that the set of
+integral equations which constrain the eigen values of the monodromy matrix can
+be identified with the continuum limit of the Bethe equations of a twisted
+SL(2, R) spin chain at one loop.",1105.0480v2
+2011-05-10,Longitudinal excitations in quantum antiferromagnets,"By extending our recently proposed magnon-density-waves to low dimensions, we
+investigate, using a microscopic many-body approach, the longitudinal
+excitations of the quasi-one-dimensional (quasi-1d) and quasi-2d Heisenberg
+antiferromagnetic systems on a bipartite lattice with a general spin quantum
+number. We obtain the full energy spectrum of the longitudinal mode as a
+function of the coupling constants in the original lattice Hamiltonian and find
+that it always has a non-zero energy gap if the ground state has a long-range
+order and becomes gapless for the pure isotropic 1d model. The numerical value
+of the minimum gap in our approximation agrees with that of a longitudinal mode
+observed in the quasi-1d antiferromagnetic compound KCuF${}_3$ at low
+temperature. It will be interesting to compare values of the energy spectrum at
+other momenta if their experimental results are available.",1105.1959v3
+2011-05-11,Theory of Raman Scattering in One-Dimensional Quantum Spin-1/2 Antiferromagnets,"We study theoretically the Raman scattering spectra in the one-dimensional
+(1D) quantum spin-1/2 antiferromagnets. The analysis reveals that their
+low-energy dynamics is exquisitely sensitive to various perturbations to the
+Heisenberg chain with nearest-neighbor exchange interactions, such as magnetic
+anisotropy, longer-range exchange interactions, and bond dimerization. These
+weak interactions are mainly responsible for the Raman scattering and give rise
+to different types of spectra as functions of frequency, temperature, and
+external field. In contrast to the Raman spectra in higher dimensions in which
+the two-magnon process is dominant, those in 1D antiferromagnets provide much
+richer information on these perturbations.",1105.2259v2
+2011-05-12,Coupled spin-lattice fluctuations in a compound with orbital degrees of freedom: the Cr based dimer system Sr3Cr2O8,"We report on an extended fluctuation regime in the spin dimer system Sr3Cr2O8
+based on anomalies in Raman active phonons and magnetic scattering. The
+compound has two characteristic temperatures, TS = 275 K, related to a
+Jahn-Teller transition with structural distortions and orbital ordering and a
+second, T*= 150 K, which is due to further changes in the orbital sector. Below
+TS quasielastic scattering marks strong fluctuations and in addition phonon
+anomalies are observed. For temperatures below T* we observe an exponential
+decrease of one phonon linewidth and determine a gap of the orbital
+excitations. At low temperatures the observation of two- and three-magnon
+scattering allows the determination of the spin excitation gap.",1105.2369v1
+2011-05-17,From N=4 gauge theory to N=2 conformal QCD: three-loop mixing of scalar composite operators,"We derive the planar dilatation operator in the closed subsector of scalar
+composite operators of an N=2 superconformal quiver gauge theory to three
+loops. By tuning the ratio of its two gauge couplings we interpolate between a
+Z_2 orbifold of N=4 SYM theory and N=2 superconformal QCD. We find zeta(3)
+contributions at three loops that disappear when the theory is at the orbifold
+point. They are responsible for imaginary contributions to the dispersion
+relation of a single scalar excitation in the spin-chain picture. This points
+towards an interpretation of the individual scalar excitations as effective
+rather than as elementary magnons. We argue that the elementary excitations
+should be associated with certain fermions and covariant derivatives, and that
+integrability in the respective subsectors should persist at least to two
+loops.",1105.3487v1
+2011-05-18,Integrable achiral D5-brane reflections and asymptotic Bethe equations,"We study the reflection of magnons from a D5-brane in the framework of the
+AdS/CFT correspondence. We consider two possible orientations of the D5-brane
+with respect to the reference vacuum state, namely vacuum states aligned along
+""vertical"" and ""horizontal"" directions. We show that the reflections are of the
+achiral type. We also show that the reflection matrices satisfy the boundary
+Yang-Baxter equations for both orientations. In the horizontal case the
+reflection matrix can be interpreted in terms of a bulk S-matrix, S(p, -p), and
+factorizability of boundary scattering therefore follows from that of bulk
+scattering. Finally, we solve the nested coordinate Bethe ansatz for the system
+in the vertical case to find the Bethe equations. In the horizontal case, the
+Bethe equations are of the same form as those for the closed string.",1105.3707v2
+2011-05-23,Scattering of Giant Holes,"We study scalar excitations of high spin operators in N=4 super Yang-Mills
+theory, which are dual to solitons propagating on a long folded string in AdS_3
+x S^1. In the spin chain description of the gauge theory, these are associated
+to holes in the magnon distribution in the sl(2,R) sector. We compute the
+all-loop hole S-matrix from the asymptotic Bethe ansatz, and expand in leading
+orders at weak and strong coupling. The worldsheet S-matrix of solitonic
+excitations on the GKP string is calculated using semiclassical quantization.
+We find an exact agreement between the gauge theory and string theory results.",1105.4596v2
+2011-06-19,Oscillatory Energy Exchange Between Waves Coupled by a Dynamic Artificial Crystal,"We describe a general mechanism of controllable energy exchange between waves
+propagating in a dynamic artificial crystal. We show that if a spatial
+periodicity is temporarily imposed on the transmission properties of a
+wave-carrying medium whilst a wave is inside, this wave is coupled to a
+secondary counter-propagating wave and energy oscillates between the two. The
+oscillation frequency is determined by the width of the spectral band gap
+created by the periodicity and the frequency difference between the coupled
+waves. The effect is demonstrated with spin waves in a dynamic magnonic
+crystal.",1106.3722v1
+2011-07-04,Magnetic field induced dehybridization of the electromagnons in multiferroic TbMnO3,"We have studied the impact of the magnetic field on the electromagnon
+excitations in TbMnO3 crystal. Applying magnetic field along the c axis, we
+show that the electromagnons transform into pure antiferromagnetic modes,
+losing their polar character. Entering in the paraelectric phase, we are able
+to track the spectral weight transfer from the electromagnons to the magnon
+excitations and we discuss the magnetic excitations underlying the
+electromagnons. We also point out the phonons involved in the phase transition
+process. This reveals that the Mn-O distance plays a key role in understanding
+the ferroelectricity and the polar character of the electromagnons. Magnetic
+field measurements along the b axis allow us to detect a new electromagnon
+resonance in agreement with a Heisenberg model.",1107.0593v1
+2011-07-29,"Spin-wave excitations in the ferromagnetic-metallic and in the charge, orbital and spin ordered states in Nd$_{1-x}$Sr$_{x}$MnO$_{3}$ with x$\approx$0.5","Inelastic neutron scattering experiments have been performed on single
+crystals of Nd$_{1-x}$Sr$_{x}$MnO$_{3}$ with x$\approx$0.5. Colossal
+magnetoresistance (CMR) in the manganites arises from the interplay between a
+ferromagnetic metallic and antiferromagnetic charge and orbital ordered
+insulating state. Therefore, it appears important to compare these phases
+concerning their underlying magnetic interaction parameters. Our investigations
+of the spin-wave disperion in the AFM ordered state of
+Nd$_{0.5}$Sr$_{0.5}$MnO$_{3}$ exhibits a strongly anisotropic stiffness. The
+sign of the anisotropy is characteristic for the site-centered model for charge
+and orbital ordering in half-doped manganites. Within this model, linear
+spin-wave theory yields a perfect description of the experimental dispersion.
+Furthermore, magnetic excitations in the ferromagnetic metallic state of
+Nd$_{1-x}$Sr$_{x}$MnO$_{3}$ with x=0.49 and x=0.50 exhibit nearly the same
+magnon dispersion which can be described with a Heisenberg model including
+nearest-neighbor interactions.",1107.5882v1
+2011-08-07,Supergraphs and the cubic Leigh-Strassler model,"We discuss supergraphs and their relation to ""chiral functions"" in N=4 Super
+Yang-Mills. Based on the magnon dispersion relation and an explicit three-loop
+result of Sieg's we make an all loop conjecture for the rational contributions
+of certain classes of supergraphs. We then apply superspace techniques to the
+""cubic"" branch of Leigh-Strassler N=1 superconformal theories. We show that
+there are order 2^L/L single trace operators of length L which have zero
+anomalous dimensions to all loop order in the planar limit. We then compute the
+anomalous dimensions for another class of single trace operators we call
+one-pair states. Using the conjecture we can find a simple expression for the
+rational part of the anomalous dimension which we argue is valid at least up to
+and including five-loop order. Based on an explicit computation we can compute
+the anomalous dimension for these operators to four loops.",1108.1583v2
+2011-08-22,Acoustic spin pumping: Direct generation of spin currents from sound waves in Pt/Y3Fe5O12 hybrid structures,"Using a Pt/Y3Fe5O12 (YIG) hybrid structure attached to a piezoelectric
+actuator, we demonstrate the generation of spin currents from sound waves. This
+""acoustic spin pumping"" (ASP) is caused by the sound wave generated by the
+piezoelectric actuator, which then modulates the distribution function of
+magnons in the YIG layer and results in a pure-spin-current injection into the
+Pt layer across the Pt/YIG interface. In the Pt layer, this injected spin
+current is converted into an electric voltage due to the inverse spin-Hall
+effect (ISHE). The ISHE voltage induced by the ASP is detected by measuring
+voltage in the Pt layer at the piezoelectric resonance frequency of the
+actuator coupled with the Pt/YIG system. The frequency-dependent measurements
+enable us to separate the ASP-induced signals from extrinsic heating effects.
+Our model calculation based on the linear response theory provides us with a
+qualitative and quantitative understanding of the ASP in the Pt/YIG system.",1108.4238v1
+2011-08-27,Localized states on triangular traps and low-temperature properties of the antiferromagnetic Heisenberg and repulsive Hubbard models,"We consider the antiferromagnetic Heisenberg and the repulsive Hubbard model
+on two $N$-site one-dimensional lattices, which support dispersionless
+one-particle states corresponding to localized states on triangular trapping
+cells. We calculate the degeneracy of the ground states in the subspaces with
+$n\le n_{\max}$, $n_{\max}\propto N$ magnons or electrons as well as the
+contribution of these states (independent localized states) to thermodynamic
+quantities. Moreover, we discuss another class of low-lying eigenstates
+(so-called interacting localized states) and calculate their contribution to
+the partition function. We also discuss the effect of extra interactions, which
+lift the degeneracy present due to the chirality of the localized states on
+triangles. The localized states set an extra low-energy scale in the system and
+lead to a nonzero residual ground-state entropy and to one (or more) additional
+low-temperature peak(s) in the specific heat. Low-energy degrees of freedom in
+the presence of perturbations removing degeneracy owing to the chirality can be
+described in terms of an effective (pseudo)spin-1/2 transverse $XX$ chain.",1108.5453v1
+2011-08-30,Quantum criticality of dipolar spin chains,"We show that a chain of Heisenberg spins interacting with long-range dipolar
+forces in a magnetic field h perpendicular to the chain exhibits a quantum
+critical point belonging to the two-dimensional Ising universality class.
+Within linear spin-wave theory the magnon dispersion for small momenta k is
+[Delta^2 + v_k^2 k^2]^{1/2}, where Delta^2 \propto |h - h_c| and v_k^2 \propto
+|ln k|. For fields close to h_c linear spin-wave theory breaks down and we
+investigate the system using density-matrix and functional renormalization
+group methods. The Ginzburg regime where non-Gaussian fluctuations are
+important is found to be rather narrow on the ordered side of the transition,
+and very broad on the disordered side.",1108.6064v3
+2011-09-13,Effects of semiclassical spiral fluctuations on hole dynamics,"We investigate the dynamics of a single hole coupled to the spiral
+fluctuations related to the magnetic ground states of the antiferromagnetic
+J_1-J_2-J_3 Heisenberg model on a square lattice. Using exact diagonalization
+on finite size clusters and the self consistent Born approximation in the
+thermodynamic limit we find, as a general feature, a strong reduction of the
+quasiparticle weight along the spiral phases of the magnetic phase diagram. For
+an important region of the Brillouin Zone the hole spectral functions are
+completely incoherent, whereas at low energies the spectral weight is
+redistributed on several irregular peaks. We find a characteristic value of the
+spiral pitch, Q=(0.7,0.7)\pi, for which the available phase space for hole
+scattering is maximum. We argue that this behavior is due to the non trivial
+interference of the magnon assisted and the free hopping mechanism for hole
+motion, characteristic of a hole coupled to semiclassical spiral fluctuations.",1109.2786v1
+2011-10-03,Weyl problem and Casimir effects in spherical shell geometry,"We compute the generic mode sum that quantifies the effect on the spectrum of
+a harmonic field when a spherical shell is inserted into vacuum. This
+encompasses a variety of problems including the Weyl spectral problem and the
+Casimir effect of quantum electrodynamics. This allows us to resolve several
+long-standing controversies regarding the question of universality of the
+Casimir self-energy; the resolution comes naturally through the connection to
+the Weyl problem. Specifically we demonstrate that in the case of a scalar
+field obeying Dirichlet or Neumann boundary conditions on the shell surface the
+Casimir self-energy is cutoff-dependent while in the case of the
+electromagnetic field perturbed by a conductive shell the Casimir self-energy
+is universal. We additionally show that an analog non-relativistic Casimir
+effect due to zero-point magnons takes place when a non-magnetic spherical
+shell is inserted inside a bulk ferromagnet.",1110.0421v2
+2011-10-06,Spin pumping with coherent elastic waves,"We show that the resonant coupling of phonons and magnons can be exploited to
+generate spin currents at room temperature. Surface acoustic wave (SAW) pulses
+with a frequency of 1.55 GHz and duration of 300 ns provide coherent elastic
+waves in a ferromagnetic thin film/normal metal (Co/Pt) bilayer. We use the
+inverse spin Hall voltage in the Pt as a measure for the spin current and
+record its evolution as a function of time and external magnetic field
+magnitude and orientation. Our experiments show that a spin current is
+generated in the exclusive presence of a resonant elastic excitation. This
+establishes acoustic spin pumping as a resonant analogue to the spin Seebeck
+effect.",1110.1187v2
+2011-10-16,Signatures of asymmetric and inelastic tunneling on the spin torque bias dependence,"The influence of structural asymmetries (barrier height and exchange
+splitting), as well as inelastic scattering (magnons and phonons) on the bias
+dependence of the spin transfer torque in a magnetic tunnel junction is studied
+theoretically using the free electron model. We show that they modify the
+""conventional"" bias dependence of the spin transfer torque, together with the
+bias dependence of the conductance. In particular, both structural asymmetries
+and bulk (inelastic) scattering add {\em antisymmetric} terms to the
+perpendicular torque ($\propto V$ and $\propto j_e|V|$), while the interfacial
+inelastic scattering conserves the junction symmetry and only produces {\em
+symmetric} terms ($\propto |V|^n$, $n\in\mathbb{N}$). The analysis of spin
+torque and conductance measurements displays a signature revealing the origin
+(asymmetry or inelastic scattering) of the discrepancy.",1110.3492v1
+2011-10-18,Anharmonic Phonons and Magnons in BiFeO3,"The phonon density of states (DOS) and magnetic excitation spectrum of
+polycrystalline BiFeO$_3$ were measured for temperatures $200 \leq T \leq
+750\,$K, using inelastic neutron scattering (INS). Our results indicate that
+the magnetic spectrum of BiFeO$_3$ closely resembles that of similar Fe
+perovskites, such as LaFeO$_3$, despite the cycloid modulation in BiFeO$_3$. We
+do not find any evidence for a spin gap. A strong $T$-dependence of the phonon
+DOS was found, with a marked broadening of the whole spectrum, providing
+evidence of strong anharmonicity. This anharmonicity is corroborated by
+large-amplitude motions of Bi and O ions observed with neutron diffraction.
+These results highlight the importance of spin-phonon coupling in this
+material.",1110.3873v3
+2011-10-24,"Synthesis, Characterization and Investigation of Electrical Transport in Metal Nanowires and Nanotubes","This thesis is dedicated to the synthesis, characterization and the study of
+electrical transport through metal nanowires and nanotubes. The metal
+nanowires(Ni, Cu) and nanotubes(Cu) are synthesised by electrochemical
+deposition in nanoporous templates. In the synthesis front, electrochemical
+deposition schemes were developed to achieve single crystallinity and synthesis
+of tubular nanostructures. The nanostructures are characterized using
+structural characterization techniques such as X-ray diffraction, Scanning
+electron microscopy and Transmission electron microscopy. The magnetic
+nanowires are also characterized using VSM and SQUID magnetometers. The
+electrical transport measurements performed in a wide range of temperature
+(3K-700K) to understand the interactions of electrons with phonon, magnon and
+surface when the electron mean free path is limited by the dimension of these
+nanostructures. The measurements were performed in the wide range of
+temperature to encompass and study the ferromagnetic to paramagnetic phase
+transition in case of magnetic nanowires. We observed systematic scaling of
+these interactions and the characteristic temperatures such as the Debye
+temperature(\theta_R) and Curie temperature(T_C) as a function of diameter. We
+also observed how these interactions change as we move from nanowires to
+nanotubes of metals.",1110.5260v1
+2011-10-25,Wilson ratio of a Tomonaga-Luttinger liquid in a spin-1/2 Heisenberg ladder,"Using micromechanical force magnetometry, we have measured the magnetization
+of the strong-leg spin-1/2 ladder compound (C$_7$H$_{10}$N)$_2$CuBr$_2$ at
+temperatures down to 45 mK. Low-temperature magnetic susceptibility as a
+function of field exhibits a maximum near the critical field H_c at which the
+magnon gap vanishes, as expected for a gapped one-dimensional antiferromagnet.
+Above H_c a clear minimum appears in the magnetization as a function of
+temperature as predicted by theory. In this field region, the susceptibility in
+conjunction with our specific heat data yields the Wilson ratio R_W. The result
+supports the relation R_W=4K, where K is the Tomonaga-Luttinger-liquid
+parameter.",1110.5653v2
+2011-10-26,SpinWaves in Ferromagnetic Dots 2D Honeycomb Lattice Stripes,"In this work, the spin wave calculations were carried out using the
+Heisenberg Hamiltonian to study the allowed spin waves of zigzag and armchair
+edged stripes for ferromagnetic nanodots arrayed in a 2D honeycomb lattice
+\cite{Selim2011}. The Hamiltonian is used to construct the $\mathbf{E}$ matrix
+which encodes the exchange flow of magnons in the stripes. It is found that the
+allowed spin wave modes are the eigenvalues of the $\mathbf{E}$ matrix and
+therefore it is used to study the effects of the stripe width, edge exchange,
+the edge uniaxial anisotropy, and impurities on the allowed spin waves of
+stripes. The obtained results almost coincide with the results of graphene
+nanoribbons described by tight binding Hamiltonian for electronic excitations.
+Therefore, we suggest the fabrication of the magnetic counterpart to graphene
+as a new technology in the field of spintronic devices and magnetic
+applications.",1110.5716v1
+2011-12-12,Theory of laser-induced demagnetization at high temperatures,"Laser-induced demagnetization is theoretically studied by explicitly taking
+into account interactions among electrons, spins and lattice. Assuming that the
+demagnetization processes take place during the thermalization of the
+sub-systems, the temperature dynamics is given by the energy transfer between
+the thermalized interacting baths. These energy transfers are accounted for
+explicitly through electron-magnons and electron-phonons interaction, which
+govern the demagnetization time scale. By properly treating the spin system in
+a self-consistent random phase approximation, we derive magnetization dynamic
+equations for a broad range of temperature. The dependence of demagnetization
+on the temperature and pumping laser intensity is calculated in detail. In
+particular, we show several salient features for understanding magnetization
+dynamics near the Curie temperature. While the critical slowdown in dynamics
+occurs, we find that an external magnetic field can restore the fast dynamics.
+We discuss the implication of the fast dynamics in the application of heat
+assisted magnetic recording.",1112.2428v1
+2011-12-12,"Relationship among superconductivity, pseudogap, and high-energy magnetic fluctuations in a model high-Tc superconductor from electronic Raman scattering","We use electronic Raman scattering to study the model single-layer cuprate
+superconductor HgBa2CuO4+d. In an overdoped sample, we observe a pronounced
+amplitude enhancement of a high-energy peak related to two-magnon excitations
+in insulating cuprates upon cooling below the critical temperature Tc. This
+effect is accompanied by the appearance of the superconducting gap and a
+pairing peak above the gap in the Raman spectrum, and it can be understood as a
+consequence of feedback of the Cooper pairing interaction on the high-energy
+magnetic fluctuations. All of these effects occur already above Tc in two
+underdoped samples, demonstrating a related feedback mechanism associated with
+the pseudogap.",1112.2725v1
+2011-12-20,Four-loop anomalous dimensions in Leigh-Strassler deformations,"We determine the scalar part of the four-loop chiral dilatation operator for
+Leigh-Strassler deformations of N=4 super Yang-Mills. This is sufficient to
+find the four-loop anomalous dimensions for operators in closed scalar
+subsectors. This includes the SU(2) subsector of the (complex)
+beta-deformation, where we explicitly compute the anomalous dimension for
+operators with a single impurity. It also includes the ""3-string null""
+operators of the cubic Leigh-Strassler deformation. Our four-loop results show
+that the rational part of the anomalous dimension is consistent with a
+conjecture made in arXiv:1108.1583 based on the three-loop result of
+arXiv:1008.3351 and the N=4 magnon dispersion relation. Here we find additional
+zeta(3) terms.",1112.4787v1
+2012-02-06,High-temperature spin-wave propagation in BiFeO3: relation to the Polomska transition,"In bismuth ferrite thin films the cycloidal spiral spin structure is
+suppressed, and as a result the spin-wave magnon branches of long wavelength
+are reduced from a dozen to one, at \omega = 19.2 cm-1 (T=4K). This spin wave
+has not been measured previously above room temperature, but in the present
+work we show via Raman spectroscopy that it is an underdamped propagating wave
+until 455 K. This has important room-temperature device implications. The data
+show that \omega(T) follows an S=5/2 Brillouin function and hence its Fe+3 ions
+are in the high-spin 5/2 state and not the low-spin S=1/2 state. The spin wave
+cannot be measured as a propagating wave above 455 K. We also suggest that
+since this temperature is coincident with the mysterious ""Polomska transition""
+(M. Polomska et al., Phys. Stat. Sol. A 23, 567, (1974)) at 458+/-5 K, that
+this may be due to overdamping.",1202.1040v1
+2012-02-17,Spin-stretching modes in anisotropic magnets: spin-wave excitations in the multiferroic Ba2CoGe2O7,"We studied spin excitations of the multiferroic Ba2CoGe2O7 in high magnetic
+fields up to 33 T. In the electron spin resonance and far infrared absorption
+spectra we found several spin excitations beyond the two conventional magnon
+modes expected for such a two-sublattice antiferromagnet. We show that a
+multi-boson spin-wave theory can capture these unconventional modes, that
+include spin-stretching modes associated with an oscillating magnetic dipole
+(or only quadrupole) moment. The lack of the inversion symmetry allows these
+modes to become electric dipole active. We expect that the spin-stretching
+modes can be generally observed in inelastic neutron scattering and light
+absorption experiments in a broad class of ordered S > 1/2 spin systems with
+strong single-ion anisotropy and/or non-centrosymmetric lattice structure.",1202.3996v2
+2012-02-23,Tc is insensitive to magnetic interactions in high-Tc superconductors,"A quarter of a century after their discovery the mechanism that pairs
+carriers in the cuprate high-Tc superconductors (HTS) still remains uncertain.
+Despite this the general consensus is that it is probably magnetic in origin
+[1] so that the energy scale for the pairing boson is governed by J, the
+antiferromagnetic exchange interaction. Recent studies using resonant inelastic
+X-ray scattering strongly support these ideas [2]. Here as a further test we
+vary J (as measured by two-magnon Raman scattering) by more than 60% by
+changing ion sizes in the model HTS system LnA2Cu3O7-{\delta} where A=(Ba,Sr)
+and Ln=(La, Nd, Sm, Eu, Gd, Dy, Yb, Lu). Such changes are often referred to as
+""internal"" pressure. Surprisingly, we find Tcmax anticorrelates with J where
+internal pressure is the implicit variable. This is the opposite to the effect
+of external pressure and suggests that J is not the dominant energy scale
+governing Tcmax.",1202.5078v1
+2012-03-08,First principles calculation of the phonons modes in the hexagonal $\rm YMnO_3$ ferroelectric and paraelectric phases,"The lattice dynamics of the $\rm YMnO_3$ magneto-electric compound has been
+investigated using density functional calculations, both in the ferroelectric
+and the paraelectric phases. The coherence between the computed and
+experimental data is very good in the low temperature phase. Using group
+theory, modes continuity and our calculations we were able to show that the
+phonons modes observed by Raman scattering at 1200K are only compatible with
+the ferroelectric $P6_{3} cm$ space group, thus supporting the idea of a
+ferroelectric to paraelectric phase transition at higher temperature. Finally
+we proposed a candidate for the phonon part of the observed electro-magnon.
+This mode, inactive both in Raman scattering and in Infra-Red, was shown to
+strongly couple to the Mn-Mn magnetic interactions.",1203.1752v1
+2012-05-31,Bound States of the q-Deformed AdS5 x S5 Superstring S-matrix,"The investigation of the q deformation of the S-matrix for excitations on the
+string world sheet in AdS5 x S5 is continued. We argue that due to the lack of
+Lorentz invariance the situation is more subtle than in a relativistic theory
+in that the nature of bound states depends on their momentum. At low enough
+momentum |p|<E the bound states transform in the anti-symmetric representation
+of the super-algebra symmetry and become the solitons of the Pohlmeyer reduced
+theory in the relativistic limit. At a critical momentum |p|=E they become
+marginally unstable, and at higher momenta the stable bound states are in the
+symmetric representation and become the familiar magnons in the string limit as
+q->1. This subtlety fixes a problem involving the consistency of crossing
+symmetry with the relativistic limit found in earlier work. With mirror
+kinematics, obtained after a double Wick rotation, the bound state structure is
+simpler and there are no marginally unstable bound states.",1206.0010v1
+2012-05-31,Two-particle response in Cluster Dynamical Mean-Field Theory: Formalism and application to the Raman Response of High-temperature Superconductors,"A method is presented for the unbiased numerical computation of two-particle
+response functions of correlated electron materials via a solution of the
+dynamical mean-field equations in the presence of a perturbing field. The power
+of the method is demonstrated via a computation of the Raman $B_{1g}$ and
+$B_{2g}$ scattering intensities of the two dimensional Hubbard model, in
+parameter regimes believed to be relevant to high-temperature
+superconductivity. The theory reproduces the `two-magnon' peak characteristic
+of the Raman intensity of the insulating parent compounds of high-$T_c$ copper
+oxide superconductors and shows how it evolves to a quasiparticle response as
+carriers are added. The method can be applied in any situation where a solution
+of the equilibrium dynamical mean-field equations is feasible.",1206.0023v1
+2012-07-06,Ferromagnetic Quantum critical behavior in three-dimensional Hubbard model with transverse anisotropy,"One-band Hubbard model with transverse anisotropy is considered at density of
+electrons $n=0.4$. It is shown that when the anisotropy is appropriately
+chosen, the ground state is ferromagnetic with magnetic order perpendicular to
+the anisotropy. The increasing of the ratio $\frac tU$, where $t$ is the
+hopping parameter and $U$ is the Coulomb repulsion, decreases the Curie
+temperature, and the system arrives at the quantum critical point $(T_C=0)$.
+The result is obtained introducing Schwinger bosons and slave Fermions
+representation of the electron operators. Integrating out the spin-singlet
+Fermi fields an effective Heisenberg model with ferromagnetic exchange constant
+is obtained for vectors which identifies the local orientation of the spin of
+the itinerant electrons. The amplitude of the spin vectors is an effective spin
+of the itinerant electrons accounting for the fact that some sites, in the
+ground state, are doubly occupied or empty. Owing to the anisotropy, the magnon
+fluctuations drive the system to quantum criticality and when the effective
+spin is critically small these fluctuations suppress the magnetic order.",1207.1674v1
+2012-07-11,Inner products of Bethe states as partial domain wall partition functions,"We study the inner product of Bethe states in the inhomogeneous periodic XXX
+spin-1/2 chain of length L, which is given by the Slavnov determinant formula.
+We show that the inner product of an on-shell M-magnon state with a generic
+M-magnon state is given by the same expression as the inner product of a
+2M-magnon state with a vacuum descendent. The second inner product is
+proportional to the partition function of the six-vertex model on a rectangular
+Lx2M grid, with partial domain-wall boundary conditions.",1207.2562v3
+2012-07-17,The Free Energy of the Quantum Heisenberg Ferromagnet at Large Spin,"We consider the spin-S ferromagnetic Heisenberg model in three dimensions, in
+the absence of an external field. Spin wave theory suggests that in a suitable
+temperature regime the system behaves effectively as a system of
+non-interacting bosons (magnons). We prove this fact at the level of the
+specific free energy: if $ S \to \infty $ and the inverse temperature $ \beta
+\to 0 $ in such a way that $ \beta S $ stays constant, we rigorously show that
+the free energy per unit volume converges to the one suggested by spin wave
+theory. The proof is based on the localization of the system in small boxes and
+on upper and lower bounds on the local free energy, and it also provides
+explicit error bounds on the remainder.",1207.4050v1
+2012-07-30,Variations on Slavnov's scalar product,"We consider the rational six-vertex model on an L-by-L lattice with domain
+wall boundary conditions and restrict N parallel-line rapidities, N < L/2, to
+satisfy length-L XXX spin-1/2 chain Bethe equations. We show that the partition
+function is an (L-2N)-parameter extension of Slavnov's scalar product of a
+Bethe eigenstate and a generic state, with N magnons each, on a length-L XXX
+spin-1/2 chain.
+  Decoupling the extra parameters, we obtain a third determinant expression for
+the scalar product, where the first is due to Slavnov [1], and the second is
+due to Kostov and Matsuo [2]. We show that the new determinant is a discrete KP
+tau-function in the inhomogeneities, and consequently that tree-level N = 4 SYM
+structure constants that are known to be determinants, remain determinants at
+1-loop level.",1207.6871v1
+2012-08-06,Spin-state Crossover Model for the Magnetism of Iron Pnictides,"We propose a minimal model describing magnetic behavior of Fe-based
+superconductors. The key ingredient of the model is a dynamical mixing of
+quasi-degenerate spin states of Fe2+ ion by intersite electron hoppings,
+resulting in an effective local spin Seff. The moments Seff tend to form
+singlet pairs, and may condense into a spin nematic phase due to the emergent
+biquadratic exchange couplings. The long-range ordered part m of Seff varies
+widely, 0<=m<=Seff, but magnon spectra are universal and scale with Seff,
+resolving the puzzle of large but fluctuating Fe-moments. Unusual temperature
+dependences of a local moment and spin susceptibility are also explained.",1208.1197v3
+2012-08-19,Anderson localization of spinons in a spin-1/2 antiferromagnetic Heisenberg chain,"Anderson localization is a general phenomenon of wave physics, which stems
+from the interference between multiple scattering paths1,2. It was originally
+proposed for electrons in a crystal, but later was also observed for light3-5,
+microwaves6, ultrasound7,8, and ultracold atoms9-12. Actually, in a crystal,
+besides electrons there may exist other quasiparticles such as magnons and
+spinons. However the search for Anderson localization of these magnetic
+excitations is rare so far. Here we report the first observation of spinon
+localization in copper benzoate, an ideal compound of spin-1/2
+antiferromagnetic Heisenberg chain, by ultra-low-temperature specific heat and
+thermal conductivity measurements. We find that while the spinon specific heat
+Cs displays linear temperature dependence down to 50 mK, the spinons thermal
+conductivity ks only manifests the linear temperature dependence down to 300
+mK. Below 300 mK, ks/T decreases rapidly and vanishes at about 100 mK, which is
+a clear evidence for Anderson localization. Our finding opens a new window for
+studying such a fundamental phenomenon in condensed matter physics.",1208.3803v1
+2012-08-30,Quantum-critical spin dynamics in quasi-one-dimensional antiferromagnets,"By means of nuclear spin-lattice relaxation rate 1/T1, we follow the spin
+dynamics as a function of the applied magnetic field in two gapped
+one-dimensional quantum antiferromagnets: the anisotropic spin-chain system
+NiCl2-4SC(NH2)2 and the spin-ladder system (C5H12N)2CuBr4. In both systems,
+spin excitations are confirmed to evolve from magnons in the gapped state to
+spinons in the gapples Tomonaga-Luttinger-liquid state. In between, 1/T1
+exhibits a pronounced, continuous variation, which is shown to scale in
+accordance with quantum criticality. We extract the critical exponent for 1/T1,
+compare it to the theory, and show that this behavior is identical in both
+studied systems, thus demonstrating the universality of quantum critical
+behavior.",1208.6117v1
+2012-09-17,Nonlinear emission of spin-wave caustics from an edge mode of a micro-structured Co2Mn0.6Fe0.4Si waveguide,"Magnetic Heusler materials with very low Gilbert damping are expected to show
+novel magnonic transport phenomena. We report nonlinear generation of higher
+harmonics leading to the emission of caustic spin-wave beams in a low-damping,
+micro-structured Co2Mn0.6Fe0.4Si Heusler waveguide. The source for the higher
+harmonic generation is a localized edge mode formed by the strongly
+inhomogeneous field distribution at the edges of the spin-wave waveguide. The
+radiation characteristics of the propagating caustic waves observed at twice
+and three times the excitation frequency are described by an analytical
+calculation based on the anisotropic dispersion of spin waves in a magnetic
+thin film.",1209.3669v2
+2012-09-20,Anisotropic spin-dynamics in the Kondo semiconductor CeRu2Al10,"Spin dynamics in the new Kondo insulator compound CeRu2Al10 has been studied
+using unpolarized and polarized neutron scattering on single crystals. In the
+unconventional ordered phase forming below T0 = 27.3 K, two excitation branches
+are observed with significant intensities, the lower one of which has a gap of
+4.8 +/- 0.3 meV and a pronounced dispersion up to about 8.5 meV. Comparison
+with RPA magnon calculations assuming crystal-field and anisotropic exchange
+couplings captures major aspects of the data, but leaves unexplained
+discrepancies, pointing to a key role of direction-specific hybridization
+between 4f and conduction band states in this compound.",1209.4613v1
+2012-09-28,Theory of the Spin Seebeck Effect,"The spin Seebeck effect refers to the generation of a spin voltage caused by
+a temperature gradient in a ferromagnet, which enables the thermal injection of
+spin currents from the ferromagnet into an attached nonmagnetic metal over a
+macroscopic scale of several millimeters. The inverse spin Hall effect converts
+the injected spin current into a transverse charge voltage, thereby producing
+electromotive force as in the conventional charge Seebeck device. Recent
+theoretical and experimental efforts have shown that the magnon and phonon
+degrees of freedom play crucial roles in the spin Seebeck effect. In this
+article, we present the theoretical basis for understanding the spin Seebeck
+effect and briefly discuss other thermal spin effects.",1209.6407v2
+2012-10-03,Easy-axis ferromagnetic chain on a metallic surface,"The phases and excitation spectrum of an easy-axis ferromagnetic chain of
+S=1/2 magnetic impurities built on the top of a clean metallic surface are
+studied. As a function of the (Kondo) coupling to the metallic surface and at
+low temperatures, the spin chain exhibits a quantum phase transition from an
+Ising ferromagnetic phase with long-range order to a paramagnetic phase where
+quantum fluctuations destroy the magnetic order. In the paramagnetic phase, the
+system consists of a chain of Kondo-singlets where the impurities are
+completely screened by the metallic host. In the ferromagnetic phase, the
+excitations above the Ising gap are damped magnons, with a finite lifetime
+arising due to the coupling to the substrate. We discuss the experimental
+consequences of our results to spin-polarized electron energy loss spectroscopy
+(SPEELS), and we finally analyze possible extensions to spin chains with S>1/2.",1210.1195v1
+2012-10-22,"Thickness-dependent structural, magnetic and transport properties of epitaxial Co2FeAl Heusler alloy thin films","We report on a systematic study of the structural, magnetic properties and
+the anomalous Hall effect, in the Heusler alloy Co2FeAl (CFA) epitaxial films
+on MgO(001), as a function of film thickness. It was found that the epitaxial
+CFA films show a highly ordered B2 structure with an in-plane uniaxial magnetic
+anisotropy. An analysis of the electrical transport properties reveals that the
+lattice and magnon scattering contributions to the longitudinal resistivity.
+Independent on the thickness of films, the anomalous Hall resistivity of CFA
+films is found to be dominated by skew scattering only. Moreover, the anomalous
+Hall resistivity shows weakly temperature dependent behavior, and its absolute
+value increases as the thickness decreases. We attribute this temperature
+insensitivity in the anomalous Hall resistivity to the weak temperature
+dependent of tunneling spin-polarization in the CFA films, while the thickness
+dependence behavior is likely due to the increasing significance of interface
+or free surface electronic states.",1210.5807v1
+2012-10-26,Ground state in a half-doped manganite distinguished by neutron spectroscopy,"We have measured the spin-wave spectrum of the half-doped bilayer manganite
+Pr(Ca,Sr)2Mn2O7 in its spin, charge, and orbital ordered phase. The
+measurements, which extend throughout the Brillouin zone and cover the entire
+one-magnon spectrum, are compared critically with spin-wave calculations for
+different models of the electronic ground state. The data are described very
+well by the Goodenough model, which has weakly interacting ferromagnetic
+zig-zag chains in the CE-type arrangement. A model that allows ferromagnetic
+dimers to form within the zigzags is inconsistent with the data. The analysis
+conclusively rules out the strongly bound dimer (Zener polaron) model.",1210.7108v2
+2012-10-30,Quantum phases of a frustrated four-leg spin tube,"We study the ground state phase diagram of a frustrated spin-1/2 four-leg
+tube. Using a variety of complementary techniques, namely density matrix
+renormalization group, exact diagonalization, Schwinger boson mean field
+theory, quantum Monte-Carlo and series expansion, we explore the parameter
+space of this model in the regime of all-antiferromagnetic exchange. In
+contrast to unfrustrated four-leg tubes we uncover a rich phase diagram. Apart
+from the Luttinger liquid fixed point in the limit of decoupled legs, this
+comprises several gapped ground states, namely a plaquette, an incommensurate,
+and an antiferromagnetic quasi spin-2 chain phase. The transitions between
+these phases are analyzed in terms of total energy and static structure factor
+calculations and are found to be of (weak) first order. Despite the absence of
+long range order in the quantum case, remarkable similarities to the classical
+phase diagram are uncovered, with the exception of the icommensurate regime,
+which is strongly renormalized by quantum fluctuations. In the limit of large
+leg exchange the tube exhibits a deconfinement cross-over from gapped magnon
+like excitations to spinons.",1210.8199v1
+2012-11-01,On the Integrability of Planar N=2 Superconformal Gauge Theories,"We study the integrability properties of planar N=2 superconformal field
+theories in four dimensions. We show that the spin chain associated to the
+planar dilation operator of N=2 superconformal QCD fails to be integrable at
+two loops. In our analysis we focus on a closed SU(2|1) sector, whose two-loop
+spin chain we fix by symmetry arguments (up to a few undetermined
+coefficients). It turns out that the Yang-Baxter equation for magnon scattering
+is not satisfied in this sector. On the other hand, we suggest that the closed
+SU(2,1|2) sector, which exists in any N=2 superconformal gauge theory, may be
+integrable to all loops.",1211.0271v2
+2012-11-07,Lattice and spin excitations in multiferroic h-YbMnO3,"Lattice and spin excitations have been studied by Raman scattering in
+hexagonal YbMnO3 single crystals. The temperature dependences of the phonon
+modes show that the E2 mode at 256 cm-1 related to the displacement of Mn and O
+ions in a-b plane is coupled to the spin order. The A1 phonon mode at 678 cm-1
+presents a soft mode behavior at the Neel temperature. Connected to the motion
+of the apical oxygen ions along the c direction, this mode controls directly
+the Mn-Mn interactions between adjacent Mn planes and the superexchange path.
+Crystal field and magnon mode excitations have been identified. The temperature
+investigation of the spin excitations shows that the spin structure is strongly
+influence by the Yb-Mn interaction. Under a magnetic field along the c axis, we
+have investigated the magnetic reordering and its impact on the spin
+excitations.",1211.1540v1
+2012-11-11,Electric polarization of magnetic textures: new horizons of micromagnetism,"A common scenario of magnetoelectric coupling in multiferroics is the
+electric polarization induced by spatially modulated spin structures. It is
+shown in this paper that the same mechanism works in magnetic dielectrics with
+inhomogeneous magnetization distribution: the domain walls and magnetic
+vortexes can be the sources of electric polarization. The electric field driven
+magnetic domain wall motion is observed in iron garnet films. The electric
+field induced nucleation of vortex state of magnetic nanodots is theoretically
+predicted and numerically simulated. From the practical point of view the
+electric field control of micromagnetic structures is promising for
+applications in low-power-consumption spintronic and magnonic devices.",1211.2403v1
+2012-11-13,Atomistic spin dynamics of low-dimensional magnets,"We investigate the magnetic properties of a range of low-dimensional
+ferromagnets using a combination of first-principles calculations and atomistic
+spin dynamics simulations. This approach allows us to evaluate the ground state
+and finite temperature properties of experimentally well characterized systems
+such as Co/Cu(111), Co/Cu(001), Fe/Cu(001) and Fe/W(110), for different
+thicknesses of the magnetic layer. We compare our calculated spin wave spectra
+with experimental data available in the literature, and find a good
+quantitative agreement. We also predict magnon spectra for systems for which no
+experimental data exist at the moment, and estimate the role of temperature
+effects.",1211.2964v2
+2012-11-20,Microscopic magnetic structuring of a spin-wave waveguide by ion implantation in a Ni(81)Fe(19) layer,"We investigate the spin-wave excitation in microscopic waveguides fabricated
+by localized Cr+ ion implantation in a ferromagnetic Ni(81)Fe(19) film. We
+demonstrate that spin-wave waveguides can be conveniently made by this
+technique. The magnetic patterning technique yields an increased damping and a
+reduction in saturation magnetization in the implanted regions that can be
+extracted from Brillouin light scattering measurements of the spin-wave
+excitation spectra. Furthermore, the waveguide performance as well as the
+internal field of the waveguide depend on the doping fluence. The results prove
+that localized ion implantation is a powerful tool for the patterning of magnon
+spintronic devices.",1211.4786v1
+2012-11-21,A dynamic su(1|1)^2 S-matrix for AdS3/CFT2,"We derive the S-matrix for the d(2,1;alpha)^2 symmetric spin-chain of
+AdS3/CFT2 by considering the centrally extended su(1|1)^2 algebra acting on the
+spin-chain excitations. The S-matrix is determined uniquely up to four scalar
+factors, which are further constrained by a set of crossing relations. The
+resulting scattering includes non-trivial processes between magnons of
+different masses that were previously overlooked.",1211.5119v3
+2012-11-22,Generating string solutions in BTZ,"Integrability of classical strings in the BTZ black hole enables the
+construction and study of classical string propagation in this background. We
+first apply the dressing method to obtain classical string solutions in the BTZ
+black hole. We dress time like geodesics in the BTZ black hole and obtain open
+string solutions which are pinned on the boundary at a single point and whose
+end points move on time like geodesics. These strings upon regularising their
+charge and spins have a dispersion relation similar to that of giant magnons.
+We then dress space like geodesics which start and end on the boundary of the
+BTZ black hole and obtain minimal surfaces which can penetrate the horizon of
+the black hole while being pinned at the boundary. Finally we embed the giant
+gluon solutions in the BTZ background in two different ways. They can be
+embedded as a spiral which contracts and expands touching the horizon or a
+spike which originates from the boundary and touches the horizon.",1211.5382v1
+2012-11-26,Quantum corrections to spinning superstrings in AdS_3 x S^3 x M^4: determining the dressing phase,"We study the leading quantum string correction to the dressing phase in the
+asymptotic Bethe Ansatz system for superstring in AdS_3 x S^3 x T^4 supported
+by RR flux. We find that the phase should be different from the BES phase
+appearing in the AdS_5 x S^5 case. We use the simplest example of a rigid
+circular string with two equal spins in S^3 and also consider the general
+approach based on the algebraic curve description. We also discuss the case of
+the AdS_3 x S^3 x S^3 x S^1 theory and find the dependence of the 1-loop
+correction to the effective string tension function h(\lambda) (expected to
+enter the magnon dispersion relation) on the parameters alpha related to the
+ratio of the two 3-sphere radii. This correction vanishes in the AdS_3 x S^3 x
+T^4 case.",1211.6090v3
+2012-12-17,The first-principles study of thermodynamical properties of random magnetic overlayers on fcc-Cu(001) substrate,"We present the theoretical study of thermodynamical properties of fcc-Cu(001)
+substrate covered by iron-cobalt monolayer as well as by incomplete iron layer.
+The effective two-dimensional Heisenberg Hamiltonian is constructed from first
+principles and properties of exchange interactions are investigated. The Curie
+temperatures are estimated using the Monte-Carlo (MC) simulations and compared
+with a simplified approach using the random-phase approximation (RPA) in
+connection with the virtual-crystal approach (VCA) to treat randomness in
+exchange integrals. Calculations indicate a weak maximum of the Curie
+temperature as a function of composition of the iron-cobalt overlayer. While a
+good quantitative agreement between RPA-VCA and MC was found for iron-cobalt
+monolayer, the RPA-VCA approach fails quantitatively for low coverage due to
+the magnetic percolation effect. We also present the study of the effect of
+alloy disorder on the shape of magnon spectra of random overlayers.",1212.4057v1
+2013-01-06,Discrete time quantum walk with nitrogen-vacancy centers in diamond coupled to a superconducting flux qubit,"We propose a quantum-electrodynamics scheme for implementing the
+discrete-time, coined quantum walk with the walker corresponding to the phase
+degree of freedom for a quasi-magnon field realized in an ensemble of
+nitrogen-vacancy centres in diamond. The coin is realized as a superconducting
+flux qubit. Our scheme improves on an existing proposal for implementing
+quantum walks in cavity quantum electrodynamics by removing the cumbersome
+requirement of varying drive-pulse durations according to mean quasiparticle
+number. Our improvement is relevant to all indirect-coin-flip cavity
+quantum-electrodynamics realizations of quantum walks. Our numerical analysis
+shows that this scheme can realize a discrete quantum walk under realistic
+conditions.",1301.1050v2
+2013-01-15,Giant gravitons: a collective coordinate approach,"In this paper I describe a collective coordinate approach to the study of
+giant graviton states and their excitations in various field theories. The
+method simplifies considerably the understanding of emergent gauge symmetry of
+these configurations, as well as the calculation of the spectrum of strings
+stretched between the giant gravitons. There is a limit where these results
+reproduce the one loop dispersion relation for giant magnons. I also show that
+this method gives rise to a simple geometric interpretation of a Higgs
+mechanism for the emergent gauge symmetry which parallels the holographic dual
+realization of these sates: the effective Higgs condensate is the geometric
+separation of D-branes in the collective coordinate geometry.",1301.3519v3
+2013-01-17,Excitation spectra of disordered dimer magnets near quantum criticality,"For coupled-dimer magnets with quenched disorder, we introduce a
+generalization of the bond-operator method, appropriate to describe both
+singlet and magnetically ordered phases. This allows for a numerical
+calculation of the magnetic excitations at all energies across the phase
+diagram, including the strongly inhomogeneous Griffiths regime near quantum
+criticality. We apply the method to the bilayer Heisenberg model with bond
+randomness and characterize both the broadening of excitations and the transfer
+of spectral weight induced by disorder. Inside the antiferromagnetic phase this
+model features the remarkable combination of sharp magnetic Bragg peaks and
+broad magnons, the latter arising from the tendency to localization of
+low-energy excitations.",1301.4223v2
+2013-02-03,"Spectral non-uniform temperature, non-local heat transfer, and the spin Seebeck effect","We present a theory of the spin Seebeck effect driven by subthermal non-local
+phonon heat transfer and spectral non-uniform temperature distribution. The
+theory explains the non-local behavior of the effect arising from the fact that
+phonons that store the energy (thermal) and the phonons that transfer it
+(subthermal) are located in different parts of the spectrum and have very
+different kinetics. This gives rise to a spectral phonon distribution function
+that deviates from local equilibrium along the substrate and is sensitive to
+boundary conditions. The theory also predicts a non-magnon origin of the effect
+in ferromagnetic metals in agreement with observations in recent experiments.
+Equilibration of the heat flow out of the substrate to the Pt probe and
+backwards leads to a measurable vertical spin-current produced by the spin
+polarized electrons dragged by the local thermal phonons. We predict specific
+sample length limits and other dependencies that can be probed experimentally,
+and obtain the correct magnitude of the effect.",1302.0499v1
+2013-03-07,THz Magneto-electric atomic rotations in the chiral compound Ba$_3$NbFe$_3$Si$_2$O$_{14}$,"We have determined the terahertz spectrum of the chiral langasite
+Ba$_3$NbFe$_3$Si$_2$O$_{14}$ by means of synchrotron-radiation measurements.
+Two excitations are revealed that are shown to have a different nature. The
+first one, purely magnetic, is observed at low temperature in the magnetically
+ordered phase and is assigned to a magnon. The second one persits far into the
+paramagnetic phase and exhibits both an electric and a magnetic activity at
+slightly different energies. This magnetoelectric excitation is interpreted in
+terms of atomic rotations and requires a helical electric polarization.",1303.1706v2
+2013-03-11,Local quantum criticality out of equilibrium - effective temperatures and scaling in the steady state regime,"We study the out of equilibrium steady state properties of the
+Bose-Fermi-Kondo model, describing a local magnetic moment coupled to two
+ferromagnetic leads that support bosonic (magnons) and fermionic (Stoner
+continuum electrons) low energy excitations. This model describes the
+destruction of the Kondo effect as the coupling to the bosons is increased. Its
+phase diagram comprises three non-trivial fixed points. Using a dynamical
+large-$N$approach on the Keldysh contour, we study two different
+non-equilibrium setups: (a) a finite bias voltage and (b) a finite temperature
+gradient, imposed across the leads. The scaling behavior of the charge and
+energy currents is identified and characterized for all fixed points. We report
+the existence of a fixed-point-dependent effective temperature, defined though
+the fluctuation dissipation relations of the local spin-susceptibility in the
+scaling regime, which permits to recover the equilibrium behavior of both
+dynamical and static spin susceptibilities.",1303.2518v1
+2013-03-11,Measurement of Two Low-Temperature Energy Gaps in the Electronic Structure of Antiferromagnetic USb2 Using Ultrafast Optical Spectroscopy,"Ultrafast optical spectroscopy is used to study the antiferromagnetic
+f-electron system USb2. We observe the opening of two charge gaps at low
+temperatures (<45 K), arising from renormalization of the electronic structure.
+Analysis of our data indicates that one gap is due to hybridization between
+localized f-electron and conduction electron bands, while band renormalization
+involving magnons leads to the emergence of the second gap. These experiments
+thus enable us to shed light on the complex electronic structure emerging at
+the Fermi surface in f-electron systems.",1303.2694v2
+2013-03-16,Dispersive spin excitations in highly overdoped cuprates revealed by resonant inelastic x-ray scattering,"Using resonant inelastic x-ray scattering (RIXS) at the Cu $L$-absorption
+edge, we have observed intense, dispersive spin excitations in highly overdoped
+Tl$_2$Ba$_2$CuO$_{6+\delta}$ (superconducting $T_c =6$ K), a compound whose
+normal-state charge transport and thermodynamic properties have been studied
+extensively and shown to exhibit canonical Fermi-liquid behavior. Complementary
+RIXS experiments on slightly overdoped Tl$_2$Ba$_2$CuO$_{6+\delta}$ ($T_c =89$
+K) and on Y$_{1-x}$Ca$_{x}$Ba$_2$Cu$_3$O$_{6+\delta}$ compounds spanning a wide
+range of doping levels indicate that these excitations exhibit energies and
+energy-integrated spectral weights closely similar to those of
+antiferromagnetic magnons in undoped cuprates. The surprising coexistence of
+Fermi-liquid-like charge excitations and high-energy spin excitations
+reminiscent of antiferromagnetic insulators in highly overdoped compounds poses
+a challenge to current theoretical models of the cuprates.",1303.3947v1
+2013-03-22,Bose-Einstein Condensation of Photons in a Microscopic Optical Resonator: Towards Photonic Lattices and Coupled Cavities,"Bose-Einstein condensation has in the last two decades been observed in cold
+atomic gases and in solid-state physics quasiparticles, exciton-polaritons and
+magnons, respectively. The perhaps most widely known example of a bosonic gas,
+photons in blackbody radiation, however exhibits no Bose-Einstein condensation,
+because the particle number is not conserved and at low temperatures the
+photons disappear in the system's walls instead of massively occupying the
+cavity ground mode. This is not the case in a small optical cavity, with a
+low-frequency cutoff imprinting a spectrum of photon energies restricted to
+values well above the thermal energy. The here reported experiments are based
+on a microscopic optical cavity filled with dye solution at room temperature.
+Recent experiments of our group observing Bose-Einstein condensation of photons
+in such a setup are described. Moreover, we discuss some possible applications
+of photon condensates to realize quantum manybody states in periodic photonic
+lattices and photonic Josephson devices.",1303.5772v1
+2013-04-08,YIG thickness and frequency dependence of the spin-charge current conversion in YIG/Pt systems,"We report the frequency dependence of the spin current emission in a hybrid
+ferrimagnetic insulator/normal metal system as function of the insulating layer
+thickness. The system is based on a yttrium iron garnet (YIG) film [0.2, 1, and
+3 \mu m] grown by liquid-phase-epitaxy coupled with a spin current detector of
+platinum [6 nm]. A strong YIG thickness dependence of the efficiency of the
+spin pumping has been observed. The highest conversion factor \Delta V/P_{abs}
+has been demonstrated for the thinner YIG (1.79 and 0.55 mV/mW^{-1} at 2.5 and
+10 GHz, respectively) which presents an interest for the realisation of
+YIG-based devices. A strong YIG thickness dependence of the efficiency of the
+spin pumping has been also observed and we demonstrate the threshold frequency
+dependence of the three-magnon splitting process.",1304.2190v1
+2013-04-15,Neutron Scattering and Its Application to Strongly Correlated Systems,"Neutron scattering is a powerful probe of strongly correlated systems. It can
+directly detect common phenomena such as magnetic order, and can be used to
+determine the coupling between magnetic moments through measurements of the
+spin-wave dispersions. In the absence of magnetic order, one can detect diffuse
+scattering and dynamic correlations. Neutrons are also sensitive to the
+arrangement of atoms in a solid (crystal structure) and lattice dynamics
+(phonons). In this chapter, we provide an introduction to neutrons and neutron
+sources. The neutron scattering cross section is described and formulas are
+given for nuclear diffraction, phonon scattering, magnetic diffraction, and
+magnon scattering. As an experimental example, we describe measurements of
+antiferromagnetic order, spin dynamics, and their evolution in the
+La(2-x)Ba(x)CuO(4) family of high-temperature superconductors.",1304.4214v1
+2013-04-24,Magnonlike dispersion of spin resonance in Ni-doped BaFe$_2$As$_2$,"Inelastic neutron scattering measurements on
+Ba(Fe$_{0.963}$Ni$_{0.037}$)$_2$As$_2$ manifest a neutron spin resonance in the
+superconducting state with anisotropic dispersion within the Fe layer. Whereas
+the resonance is sharply peaked at Q$_{AFM}$ along the orthorhombic a axis, the
+resonance disperses upwards away from Q$_{AFM}$ along the b axis. In contrast
+to the downward dispersing resonance and hour-glass shape of the spin
+excitations in superconducting cuprates, the resonance in electron-doped
+BaFe$_2$As$_2$ compounds possesses a magnon-like upwards dispersion.",1304.6657v1
+2013-05-01,Predicted Rectification and Negative Differential Spin Seebeck Effect at Magnetic Interfaces,"We study the nonequilibrium Seebeck spin transport across metal-magnetic
+insulator interfaces. The conjugate-converted thermal-spin transport is
+assisted by the exchange interaction at the interface, between conduction
+electrons in the metal lead and localized spins in the insulating magnet lead.
+We predict the rectification and negative differential spin Seebeck effect and
+resolve their microscopic mechanism, as a consequence of the
+strongly-fluctuated electronic density of states in the metal lead. The
+rectification of spin Peltier effect is also discussed. The phenomena predicted
+here are relevant for designing efficient spin/magnon diode and transistor,
+which could play crucial roles in controlling energy and information in
+functional devices.",1305.0301v4
+2013-05-07,Interatomic exchange interactions in non-collinear magnets,"We derive ab inito exchange parameters for general non-collinear magnetic
+configurations, in terms of a multiple scattering formalism. We show that the
+general exchange formula has an anisotropic-like term even in the absence of
+spin-orbit coupling, and that this term is large, for instance for collinear
+configuration in bcc Fe, whereas for fcc Ni it is quite small. We demonstrate
+that keeping this term leads to that one should consider a biquadratic
+effective spin Hamiltonian even in case of collinear arrangement. In
+non-collinear systems this term results in new tensor elements, that are
+important for exchange interactions at finite temperatures but they have less
+importance at low temperature. To illustrate our results in practice, we
+calculate for bcc Fe magnon spectra obtained from configuration dependent
+exchange parameters, where the configurations are determined by finite
+temperature effects. Our theory results in the same quantitative results as the
+finite temperature neutron scattering experiments.",1305.1447v1
+2013-05-14,Electromagnon in ferrimagnetic eps-Fe2O3 nanograin ceramics,"Electromagnons are known from multiferroics as spin waves excited by the
+electric component of electromagnetic radiation. We report the discovery of an
+excitation in the far-infrared spectra of eps-Fe2O3 which we attribute to an
+electromagnon appearing below 110 K, where the ferrimagnetic structure becomes
+incommensurately modulated. Inelastic neutron scattering shows that the
+electromagnon energy corresponds to that of a magnon from the Brillouin zone
+boundary. Dielectric measurements did not reveal any sign of ferroelectricity
+in eps-Fe2O3 down to 10 K, despite its acentric crystal structure. This shows
+that the activation of an electromagnon requires, in addition to the polar
+ferrimagnetic structure, a modulation of the magnetic structure. We demonstrate
+that a combination of inelastic neutron scattering with infrared and / or
+terahertz spectroscopies allows detecting electromagnons in ceramics, where no
+crystal-orientation analysis of THz and infrared spectra is possible.",1305.3064v3
+2013-07-01,Elementary excitations probed by L-edge resonant inelastic x-ray scattering in systems with weak and intermediate electron correlations,"We develop a formalism to calculate the L-edge resonant x-ray scattering
+(RIXS) spectra from transition-metal compounds. Using a multi-orbital
+tight-binding model, we derive useful formulas to calculate the spectra by
+collecting up the ladder diagrams on the basis of the Keldysh scheme, without
+relying on the fast collision approximation. They are feasible in the weak and
+intermediate coupling regimes of itinerant electron systems, where the charge
+and the magnetic excitations are mixed together. We examine the difference
+between the present formulas and those of the fast collision approximation.
+Finally, to demonstrate how our theory works, we employ the formulas to study
+the RIXS spectra on a simple model, the single-orbital Hubbard model on the
+square lattice at half-filling. The intensities originated from the magnon and
+from the continuous states are obtained on the equal footing in the
+antiferromagnetic ground state.",1307.0255v1
+2013-07-01,Doping-Dependent Raman Resonance in the Model High-Temperature Superconductor HgBa2CuO4+d,"We study the model high-temperature superconductor HgBa2CuO4+d with
+electronic Raman scattering and optical ellipsometry over a wide doping range.
+The resonant Raman condition which enhances the scattering cross section of
+""two-magnon"" excitations is found to change strongly with doping, and it
+corresponds to a rearrangement of inter-band optical transitions in the 1-3 eV
+range seen by ellipsometry. This unexpected change of the resonance condition
+allows us to reconcile the apparent discrepancy between Raman and x-ray
+detection of magnetic fluctuations in superconducting cuprates. Intriguingly,
+the strongest variation occurs across the doping level where the antinodal
+superconducting gap reaches its maximum.",1307.0325v1
+2013-07-09,Anisotropic spin fluctuations in the quasi one-dimensional frustrated magnet LiCuVO_4,"We report results of NMR experiments on a single crystal of the quasi
+one-dimensional frustrated magnet LiCuVO_4. The NMR spectra of ^7Li and ^{51}V
+nuclei indicate a helical spin order in a magnetic field of 4 T with the
+helical spin plane perpendicular to the field and a spin-density-wave (SDW)
+order at 10 T with modulation in the magnitude of the moments aligned along the
+field, in agreement with earlier reports. The nuclear spin-lattice relaxation
+rate 1/T_1 at ^{51}V nuclei, which is selectively coupled to the transverse
+spin fluctuations perpendicular to the field, shows a pronounced peak near the
+helical ordering temperature in the field of 4 T applied along the a-axis. In
+the field of 10 T, however, such a peak is absent. Instead 1/T_1 at ^7Li nuclei
+probing longitudinal spin fluctuations shows divergent behavior towards the SDW
+ordering temperature. These results are qualitatively consistent with the
+theoretical description that the SDW correlation is due to bound magnon pairs,
+which produce an energy gap in the transverse spin excitation spectrum.",1307.2346v1
+2013-10-09,Phase Transitions Driven by QuasiParticle Interactions,"Quasiparticles and collective effects may have seemed exotic when first
+proposed in the 1930s, but their status has blossomed with their confirmation
+by todays sophisticated experiment techniques. Evidence has accumulated about
+the interactions of, say, magnons and rotons and with each other and also other
+quasiparticles. We briefly review the conjectures of their existence necessary
+to provide quantitative agreement with experiment which in the early period was
+their only reason for being. Phase transitions in the Anderson model, the Kondo
+effect, roton roton interactions, and highly correlated systems such as
+helium4, the Quantum Hall Effect, and BEC condensates are discussed. Some
+insulator and superconductor theories seem to suggest collective interactions
+of several quasiparticles may be necessary to explain the behavior. We conclude
+with brief discussions of the possibility of using the parameter to detect
+quantum critical points and some background on bound states emerging from the
+continuum. Finally, we present a summary and conclusions and also discuss
+possible future directions.",1310.2522v1
+2013-11-05,Quench Dynamics of the Anisotropic Heisenberg Model,"We develop an analytic approach for the study of the quench dynamics of the
+anisotropic Heisenberg model (XXZ model) on the infinite line. We present the
+exact time-dependent wavefunctions after a quench in an integral form for any
+initial state and for any anisotropy $\Delta$ by means of a generalized Yudson
+contour representation. We calculate the evolution of several observables from
+two particular initial states: starting with a local N\`eel state we calculate
+the time evolution of the antiferromagnetic order parameter--staggered
+magnetization; starting with a state with consecutive flipped spins we
+calculate the propagation of magnons and bound state excitations, and the
+induced spin currents. We also show how the ""string"" solution of Bethe Ansatz
+equations emerge naturally from the contour approach. We confront our results
+with experiments and numerical methods where possible.",1311.1118v1
+2013-11-06,Magnetization dynamics of cobalt grown on graphene,"Ferromagnetic resonance (FMR) spin pumping is a rapidly growing field which
+has demonstrated promising results in a variety of material systems. This
+technique utilizes the resonant precession of magnetization in a ferromagnet to
+inject spin into an adjacent non-magnetic material. Spin pumping into graphene
+is attractive on account of its exceptional spin transport properties. This
+article reports on FMR characterization of cobalt grown on CVD graphene and
+examines the validity of linewidth broadening as an indicator of spin pumping.
+In comparison to cobalt samples without graphene, direct contact
+cobalt-on-graphene exhibits increased FMR linewidth--an often used signature of
+spin pumping. Similar results are obtained in Co/MgO/graphene structures, where
+a 1nm MgO layer acts as a tunnel barrier. However, SQUID, MFM, and Kerr
+microscopy measurements demonstrate increased magnetic disorder in cobalt grown
+on graphene, perhaps due to changes in the growth process and an increase in
+defects. This magnetic disorder may account for the observed linewidth
+enhancement due to effects such as two-magnon scattering or mosaicity. As such,
+it is not possible to conclude successful spin injection into graphene from FMR
+linewidth measurements alone.",1311.1441v1
+2013-11-11,Color Magnetism in Non-Abelian Vortex Matter,"We propose color magnetism as a generalization of the ordinary Heisenberg
+(anti-)ferro magnets on a triangular lattice. Vortex matter consisting of an
+Abrikosov lattice of non-Abelian vortices with color magnetic fluxes shows a
+color ferro or anti-ferro magnetism, depending on the interaction among the
+vortex sites. A prime example is a non-Abelian vortex lattice in rotating dense
+quark matter, showing a color ferromagnetism. We show that the low-energy
+effective theory for the vortex lattice system in the color ferromagnetic phase
+is described by a 3+1 dimensional $CP^{N-1}$ nonlinear sigma model with
+spatially anisotropic couplings. We identify gapless excitations independent
+from Tkachenko modes as color magnons, that is, Nambu-Goldstone modes
+propagating in the vortex lattice with an anisotropic linear dispersion
+relation $\omega_p^2 = c_{xy}^2(p_x^2+p_y^2) + c_z^2 p_z^2$. We calculate the
+transition temperature between the ordered and disordered phases, and apply it
+to dense quark matter. We also identify the order parameter spaces for color
+anti-ferromagnets.",1311.2399v2
+2013-11-21,Mechanism of Ultrafast Relaxation of a Photo-Carrier in Antiferromagnetic Spin Background,"We study the relaxation mechanism of a highly excited carrier propagating in
+the antiferromagnetic background modeled by the $t$-$J$ Hamiltonian on a square
+lattice. We show that the relaxation consists of two distinct stages. The
+initial ultrafast stage with the relaxation time $\tau\sim
+(\hbar/t_0)(J/t_0)^{-2/3}$ (where $t_0$ is the hopping integral and $J$ is the
+exchange interaction) is based on generation of string states in the close
+proximity of the carrier. This unusual scaling of $\tau$ is obtained by means
+of comparison of numerical results with a simplified $t$-$J_z$ model on a Bethe
+lattice. In the subsequent (much slower) stage local spin excitations are
+carried away by magnons. The relaxation time on the two-leg ladder system is an
+order of magnitude longer due to the lack of string excitations. This further
+reinforces the importance of string excitations for the ultrafast relaxation in
+the two-dimensional system.",1311.5574v2
+2013-11-22,Large-Spin Expansions of GKP Strings,"We demonstrate that the large-spin expansion of the energy of
+Gubser-Klebanov-Polyakov (GKP) strings that rotate in RxS2 and AdS3 can be
+expressed in terms of Lambert's W-function. We compute the leading, subleading
+and next-to-subleading series of exponential corrections to the infinite-volume
+dispersion relation of GKP strings that rotate in RxS2. These strings are dual
+to certain long operators of N=4 SYM theory and provide their scaling
+dimensions at strong coupling. We also show that the strings obey a short-long
+(strings) duality. For the folded GKP strings that spin inside AdS3 and are
+dual to twist-2 operators, we confirm the known formulas for the leading and
+next-to-leading coefficients of their anomalous dimensions and derive the
+corresponding expressions for the next-to-next-to-leading coefficients.",1311.5800v3
+2013-11-25,Spin-wave excitation and propagation in microstructured waveguides of yttrium iron garnet (YIG)/Pt bilayers,"We present an experimental study of spin-wave excitation and propagation in
+microstructured waveguides patterned from a 100 nm thick yttrium iron garnet
+(YIG)/platinum (Pt) bilayer. The life time of the spin waves is found to be
+more than an order of magnitude higher than in comparably sized metallic
+structures despite the fact that the Pt capping enhances the Gilbert damping.
+Utilizing microfocus Brillouin light scattering spectroscopy, we reveal the
+spin-wave mode structure for different excitation frequencies. An exponential
+spin-wave amplitude decay length of 31 {\mu}m is observed which is a
+significant step towards low damping, insulator based micro-magnonics.",1311.6305v1
+2013-12-03,Stoner instability revisited: Emergence of local quantum criticality?,"We revisit Stoner instability, an old problem but in a modern point of view.
+An idea is to extract out dynamics of directional fluctuations of spins
+explicitly, resorting to the CP$^{1}$ representation and integrating over their
+amplitude fluctuations. As a result, we derive an effective field theory for
+ferromagnetic quantum phase transitions in terms of bosonic spinons and
+fermionic holons. We show that this effective field theory reproduces
+overdamped spin dynamics in a paramagnetic Fermi liquid and magnon spectrum in
+a ferromagnetic Fermi liquid. An interesting observation is that the velocity
+of spinons becomes zero, approaching the ferromagnetic quantum critical point,
+which implies emergence of local quantum criticality. Based on this scenario,
+we predict the $\omega/T$ scaling behavior near ferromagnetic quantum
+criticality beyond the conventional scenario of the weak-coupling approach.",1312.0807v2
+2013-12-14,Tuning Magnetic Coupling in Sr$_2$IrO$_4$ Thin Films with Epitaxial Strain,"We report x-ray resonant magnetic scattering (XRMS) and resonant inelastic
+x-ray scattering (RIXS) studies of epitaxially-strained $\mathrm{Sr_2IrO_4}$
+thin films. The films were grown on $\mathrm{SrTiO_3}$ and
+$\mathrm{(LaAlO_3)_{0.3}(Sr_2AlTaO_6)_{0.7}}$ substrates, under slight tensile
+and compressive strains, respectively. Although the films develop a magnetic
+structure reminiscent of bulk $\mathrm{Sr_2IrO_4}$, the magnetic correlations
+are extremely anisotropic, with in-plane correlation lengths significantly
+longer than the out-of-plane correlation lengths. In addition, the compressive
+(tensile) strain serves to suppress (enhance) the magnetic ordering temperature
+$\mathrm{T_N}$, while raising (lowering) the energy of the zone boundary
+magnon. Quantum chemical calculations show that the tuning of magnetic energy
+scales can be understood in terms of strain-induced change in bond lengths.",1312.4005v2
+2013-12-17,Superconducting pairing in the spin-density-wave phase of iron pnictides,"Some of the iron pnictides show coexisting superconductivity and
+spin-density-wave order. We study the superconducting pairing instability in
+the spin-density-wave phase. Assuming that the pairing interaction is due to
+spin fluctuations, we calculate the effective pairing interactions in the
+singlet and triplet channels by summing the bubble and ladder diagrams taking
+the reconstructed band structure into account. The leading pairing
+instabilities and the corresponding superconducting gap structures are then
+obtained from the superconducting gap equation. We illustrate this approach for
+a minimal two-band model of the pnictides. Analytical and numerical results
+show that the existence of propagating magnons in the spin-density-wave phase
+strongly enhances the pairing in both the singlet and the spin s_z=0 triplet
+channel. Over a limited parameter range, a spin s_z=0 triplet p_x-wave state is
+the dominant instability. It competes with various singlet states, which have
+mostly s^\pm-type structures. We analyze the effect of various symmetry-allowed
+interactions on the pairing in some detail.",1312.4720v2
+2013-12-18,"Multipolar, magnetic and vibrational lattice dynamics in the low temperature phase of uranium dioxide","We report the results of inelastic neutron scattering experiments performed
+with triple-axis spectrometers to investigate the low-temperature collective
+dynamics in the ordered phase of uranium dioxide. The results are in excellent
+agreement with the predictions of mean-field RPA calculations emphasizing the
+importance of multipolar superexchange interactions. By comparing neutron
+scattering intensities in different polarization channels and at equivalent
+points in different Brillouin zones, we show the mixed
+magneto-vibrational-quadrupolar character of the observed excitations. The high
+energy resolution afforded by the cold triple-axis spectrometer allowed us to
+study in detail the magnon-phonon interaction giving rise to avoided crossings
+along the $[00\xi]$ reciprocal space direction.",1312.5113v1
+2014-01-05,Spin torque building blocks,"The discovery of the spin torque effect has made magnetic nanodevices
+realistic candidates for active elements of memory devices and applications.
+Magnetoresistive effects allow the read-out of increasingly small magnetic
+bits, and the spin torque provides an efficient tool to manipulate - precisely,
+rapidly and at low energy cost - the magnetic state, which is in turn the
+central information medium of spintronic devices. By keeping the same magnetic
+stack, but by tuning a device's shape and bias conditions, the spin torque can
+be engineered to build a variety of advanced magnetic nanodevices. Here we show
+that by assembling these nanodevices as building blocks with different
+functionalities, novel types of computing architectures can be envisisaged. We
+focus in particular on recent concepts such as magnonics and spintronic neural
+networks.",1401.0874v1
+2014-02-14,Spin liquid phase in a spatially anisotropic frustrated antiferromagnet,"We explore the effect of the third nearest-neighbors on the magnetic
+properties of the Heisenberg model on an anisotropic triangular lattice. We
+obtain the phase diagram of the model using Schwinger-boson mean-field theory.
+Competition between N\'eel, spiral and collinear magnetically ordered phases is
+found as we vary the on the ratios of the nearest, J1, next-nearest, J2, and
+third-nearest, J_3, neighbor exchange couplings. A spin liquid phase is
+stabilized between the spiral and collinear ordered states when J2/J1 < 1.8 for
+rather small J3/J1 < 0.1. The lowest energy two-spinon dispersions relevant to
+neutron scattering experiments are analyzed and compared to semiclassical
+magnon dispersions finding significant differences in the spiral and collinear
+phases between the two approaches. The results are discussed in the context of
+the anisotropic triangular materials: Cs2CuCl4 and Cs2CuBr4 and layered organic
+materials, kappa-(BEDT-TTF)2X and Y[Pd(dmit)2]2.",1402.3463v1
+2014-02-24,Spectrally-resolved femtosecond reflectivity relaxation dynamics in undoped SDW 122-structure iron based pnictides,"We systematically investigate temperature- and spectrally-dependent optical
+reflectivity dynamics in AAs$_{2}$Fe$_{2}$, (A=Ba, Sr and Eu), iron-based
+superconductors parent spin-density-wave (SDW) compounds. Two different
+relaxation processes are identified. The behavior of the slower process, which
+is strongly sensitive to the magneto-structural transition, is analyzed in the
+framework of the relaxation-bottleneck model involving magnons. The results are
+compared to recent time resolved angular photoemission results (TR-ARPES) and
+possible alternative assignment of the slower relaxation to the
+magneto-structural order parameter relaxation is discussed.",1402.5811v1
+2014-02-25,Unusual Two-stage Dynamics of the Spin-Lattice Polaron Formation,"We follow the formation of a spin-lattice polaron after a quantum quench that
+simulates absorption of the pump{pulse in the time-resolved experiments. We
+discover a two-stage relaxation where spin and lattice degrees of freedom
+represent an integral part of the relaxation mechanism. In the first stage the
+kinetic energy of the spin-lattice polaron relaxes towards its ground state
+value while relaxation processes via spin and phonon degrees of freedom remain
+roughly independent. In the second, typically much longer stage, a subsequent
+energy transfer between lattice and spin degrees of freedom via the charge
+carrier emerges. The excess local spin energy radiates away via magnon
+excitations.",1402.6104v1
+2014-02-27,Relation between cuprate superconductivity and magnetism: A Raman study of (CaLa)(BaLa)$_{2}$Cu$_{3}$O$_{y}$,"We present an investigation of charge-compensated antiferromagnetic
+(Ca$_{x}$La$_{1-x}$)(Ba$_{1.75-x}$La$_{0.25+x}$)Cu$_{3}$O$_{y}$ single crystals
+using Raman scattering as well as muon spin rotation. In this system the
+parameter $x$ controls the Cu-O-Cu superexchange interaction via bond distances
+and buckling angles. The oxygen content $y$ controls the charge doping. In the
+absence of doping the two-magnon peak position is directly proportional to the
+superexchange strength $J$. We find that both $x$ and $y$ affect the peak
+position considerably. The N\'{e}el temperature determined from muon spin
+rotation on the same samples independently confirms the strong dependence of
+the magnetic interaction on $x$ and $y$. We find a considerable increase in the
+maximum superconducting transition temperature $T_{c}^{max}$ with $J$. This is
+strong evidence of the importance of orbital overlap to superconductivity in
+this family of cuprates.",1402.7053v2
+2014-07-10,Nonsinglet pentagons and NMHV amplitudes,"Scattering amplitudes in maximally supersymmetric gauge theory receive a dual
+description in terms of the expectation value of the super Wilson loop
+stretched on a null polygonal contour. This makes the analysis amenable to
+nonperturbative techniques. Presently, we elaborate on a refined form of the
+operator product expansion in terms of pentagon transitions to compute
+twist-two contributions to NMHV amplitudes. To start with, we provide a novel
+derivation of scattering matrices starting from Baxter equations for flux-tube
+excitations propagating on magnon background. We propose bootstrap equations
+obeyed by pentagon form factors with nonsinglet quantum numbers with respected
+to the R-symmetry group and provide solutions to them to all orders in 't Hooft
+coupling. These are then successfully confronted against available perturbative
+calculations for NMHV amplitudes to three-loop order.",1407.2853v3
+2014-07-14,Electronic excitations and structure of Li2IrO3 thin films grown on ZrO$_{2}$:Y (001) substrates,"Thin films are a prerequisite for application of the emergent exotic ground
+states in iridates that result from the interplay of strong spin-orbit coupling
+and electronic correlations. We report on pulsed laser deposition of
+Li$_{2}$IrO$_{3}$ films on ZrO$_{2}$:Y(001) single crystalline substrates.
+X-ray diffraction confirms preferential (001) and (10-1) out-of-plane
+crystalline orientations with well defined in-plane orientation. Resistivity
+between 35 and 300 K is dominated by a three-dimensional variable range hopping
+mechanism. The dielectric function is determined by means of spectroscopic
+ellipsometry and, complemented by Fourier transform infrared transmission
+spectroscopy, reveals a small optical gap of $\approx$ 300 meV, a splitting of
+the $5d$-$t_{2g}$ manifold, and several in-gap excitations attributed to
+phonons and possibly magnons.",1407.3596v4
+2014-08-04,Excitonic quasiparticles in a spin-orbit Mott insulator,"In condensed matter systems, out of a large number of interacting degrees of
+freedom emerge weakly coupled particles, in terms of which most physical
+properties are described. For example, Landau quasiparticles (QP) determine all
+electronic properties of a normal metal. The lack of identification of such QPs
+is major barrier for understanding myriad exotic properties of correlated
+electrons, such as unconventional superconductivity and non-Fermi liquid
+behaviours. Here, we report the observation of a composite particle in a Mott
+insulator Sr2IrO4---and exciton dressed with magnons---that propagates with the
+canonical characteristics of a QP: a finite QP residue and a lifetime longer
+than the hopping time scale. The dynamics of this charge-neutral bosonic
+excitation mirrors the fundamental process of the analogous one-hole
+propagation in the background of ordered spins, for which a well-defined QP has
+never been observed. The much narrower linewidth of the exciton reveals the
+same intrinsic dynamics that is obscured for the hole and is intimately related
+to the mechanism of high temperature superconductivity.",1408.0804v1
+2014-08-21,Anyonic Liquids in Nearly Saturated Spin Chains,"Most Heisenberg-like spin chains flow to a universal free-fermion fixed point
+near the magnetic-field induced saturation point. Here we show that an exotic
+fixed point, characterized by two species of low-energy excitations with mutual
+anyonic statistics, may also emerge in such spin chains if the dispersion
+relation has two minima. By using bosonization, two-magnon exact calculations,
+and numerical density-matrix-renormalization-group, we demonstrate the
+existence of this anyonic-liquid fixed point in an XXZ spin chain with up to
+second neighbor interactions. We also identify a range of microscopic
+parameters, which support this phase.",1408.5151v2
+2014-09-05,Electric field-induced Skyrmion distortion and giant lattice rotation in the magnetoelectric insulator Cu2OSeO3,"Uniquely in Cu2OSeO3, the Skyrmions, which are topologically protected
+magnetic spin vortex-like objects, display a magnetoelectric coupling and can
+be manipulated by externally applied electric (E) fields. Here, we explore the
+E-field coupling to the magnetoelectric Skyrmion lattice phase, and study the
+response using neutron scattering. Giant E-field induced rotations of the
+Skyrmion lattice are achieved that span a range of $\sim$25$^{\circ}$.
+Supporting calculations show that an E-field-induced Skyrmion distortion lies
+behind the lattice rotation. Overall, we present a new approach to Skyrmion
+control that makes no use of spin-transfer torques due to currents of either
+electrons or magnons.",1409.1756v1
+2014-09-08,Dynamic control of spin wave spectra using spin-polarized currents,"We describe a method of controlling the spin wave spectra dynamically in a
+uniform nanostripe waveguide through spin-polarized currents. A stable periodic
+magnetization structure is observed when the current flows vertically through
+the center of nanostripe waveguide. After being excited, the spin wave is
+transmitted at the sides of the waveguide. Numerical simulations of spin-wave
+transmission and dispersion curves reveal a single, pronounced band gap.
+Moreover, the periodic magnetization structure can be turned on and off by the
+spin-polarized current. The switching process from full rejection to full
+transmission takes place within less than 3ns. Thus, this type magnonic
+waveguide can be utilized for low-dissipation spin wave based filters.",1409.2421v2
+2014-09-15,Frustration and Dzyaloshinsky-Moriya anisotropy in the kagome francisites Cu$_3$Bi(SeO$_3)_2$O$_2$X,"We investigate the antiferromagnetic canting instability of the spin-1/2
+kagome ferromagnet, as realized in the layered cuprates
+Cu$_3$Bi(SeO$_3)_2$O$_2$X (X=Br, Cl, and I). While the local canting can be
+explained in terms of competing exchange interactions, the direction of the
+ferrimagnetic order parameter fluctuates strongly even at short distances on
+account of frustration which gives rise to an infinite ground state degeneracy
+at the classical level. In analogy with the kagome antiferromagnet, the
+accidental degeneracy is fully lifted only by non-linear 1/S corrections,
+rendering the selected uniform canted phase very fragile even for spins-1/2, as
+shown explicitly by coupled-cluster calculations. To account for the observed
+ordering, we show that the minimal description of these systems must include
+the microscopic Dzyaloshinsky-Moriya interactions, which we obtain from
+density-functional band-structure calculations. The model explains all
+qualitative properties of the kagome francisites, including the detailed nature
+of the ground state and the anisotropic response under a magnetic field. The
+predicted magnon excitation spectrum and quantitative features of the
+magnetization process call for further experimental investigations of these
+compounds.",1409.4335v1
+2014-10-03,Neutron Scattering Studies of the Ferroelectric Distortion and Spin Dynamics in the Type-1 Multiferroic Perovskite Sr0.56Ba0.44MnO3,"The magnetic order, spin dynamics, and crystal structure of the multiferroic
+Sr0.56Ba0.44MnO3 have been investigated using neutron and x-ray scattering.
+Ferroelectricity develops at TC=305 K with a polarization of 4.2 microC/cm2
+associated with the displacements of the Mn ions, while the Mn4+ spins order
+below TN = 200 K into a simple G-type commensurate magnetic structure. Below TN
+the ferroelectric order decreases dramatically demonstrating that the two order
+parameters are strongly coupled. The ground state spin dynamics are
+characterized by a spin gap of 4.6(5) meV and the magnon density of states
+peaking at 43 meV. Detailed spin wave simulations with a gap and isotropic
+exchange of J=4.8(2) meV describe the excitation spectrum well. Above TN strong
+spin correlations coexist with robust ferroelectric order.",1410.0922v1
+2014-10-03,On a family of symmetric rational functions,"This paper is about a family of symmetric rational functions that form a
+one-parameter generalization of the classical Hall-Littlewood polynomials. We
+introduce two sets of (skew and non-skew) functions that are akin to P and Q
+Hall-Littlewood polynomials. We establish (a) a combinatorial formula that
+represents our functions as partition functions for certain path ensembles in
+the square grid; (b) symmetrization formulas for non-skew functions; (c)
+identities of Cauchy and Pieri type; (d) explicit formulas for principal
+specializations; (e) two types of orthogonality relations for non-skew
+functions.
+  Our construction is closely related to the half-infinite volume, finite
+magnon sector limit of the higher spin six-vertex (or XXZ) model, with both
+sets of functions representing higher spin six-vertex partition functions
+and/or transfer-matrices for certain domains.",1410.0976v1
+2014-10-24,Non-linear spin-wave excitation at low bias fields,"Non-linear magnetization dynamics is essential for the operation of many
+spintronics devices. For microwave assisted switching of magnetic elements the
+low field regime is of particular interest. In addition a large number of
+experiments uses high amplitude FMR in order to generate d.c. currents via spin
+pumping mechanism. Here we use time resolved X-ray magnetic circular dichroism
+experiments to determine the number density of excited magnons in magnetically
+soft Ni_80Fe_20 thin films at small bias fields and large rf-excitation
+amplitudes. Our data shows that the common model of non-linear ferromagnetic
+resonance is not suitable to describe the low bias field limit. Here we derive
+a new model of parametric spin-wave excitation which correctly predicts
+threshold amplitudes and decay rates also at low bias fields. In fact a new
+series of critical modes with amplitude phase oscillations is found,
+generalizing the theory of parametric spin-wave excitation.",1410.6693v1
+2014-11-04,A micro-sized parametric spin-wave amplifier,"We present the experimental observation of the localized amplification of
+externally excited spin waves in a transversely in-plane magnetized
+Ni$_{81}$Fe$_{19}$ magnonic waveguide by means of parallel pumping. By
+employing microfocussed Brillouin light scattering spectroscopy, we analyze the
+dependency of the amplification on the applied pumping power and on the delay
+between the input spin-wave packet and the pumping pulse. We show that there
+are two different operation regimes: At large pumping powers, the spin-wave
+packet needs to enter the amplifier before the pumping is switched on in order
+to be amplified while at low powers the spin-wave packet can arrive at any time
+during the pumping pulse.",1411.0830v1
+2014-11-12,Electric-Field Control over Spin-Wave and Current Induced Domain Wall Motion and Magnonic Torques in Multiferroics,"We discover that the way spin-waves exert magnetic torques in multiferroic
+materials can cause not only domain wall motion, but also magnetization
+dynamics for homogeneous magnetization textures. Interestingly, the domain wall
+motion can be controlled via purely electrical means with the spin-waves being
+generated by an ac electric field $E$ while the direction of the wall motion
+also is sensitive to an applied dc $E$ field. Moreover, we determine the
+interaction between spin-transfer torque from an electric current and a
+magnetic domain wall in multiferroics and show that the Walker breakdown
+threshold scales with the magnitude of a perpendicular electric field, offering
+a way to control the properties of domain wall propagation via electric gating.",1411.3327v2
+2014-12-11,Non-collinear Magnetic Configurations at Finite Temperature in Thin Films,"The finite-temperature magnetism of a monolayer on a bcc (110) surface was
+examined using a model Hamiltonian containing ferromagnetic or
+antiferromagnetic exchange interactions, Dzyaloshinsky-Moriya interactions and
+easy-axis on-site anisotropy. We examined the competition between the collinear
+ground state parallel to the easy axis and the spin spiral state in the plane
+perpendicular to this axis preferred by the Dzyaloshinsky-Moriya interaction.
+Using approximative methods to calculate the magnon spectrum at finite
+temperatures, it was found that even if the ground state is collinear,
+increasing the Dzyaloshinsky-Moriya interaction strongly decreases the critical
+temperature where this collinear order disappears. Using atomistic spin
+dynamics simulations it was found that at this critical temperature the system
+transforms into the non-collinear state. Including external magnetic field
+helps stabilising the ferromagnetic state. An effect due to the finite size of
+the magnetic monolayer was included in the model by considering a different
+value for the anisotropy at the edges of the monolayer. This effect was shown
+to stabilize the spin spiral state by fixing the phase at the ends of the
+stripe.",1412.3591v1
+2014-12-12,Asymmetric spin-wave dispersion due to Dzyaloshinskii-Moriya interaction in an ultrathin Pt/CoFeB film,"Employing Brillouin spectroscopy, strong interfacial Dzyaloshinskii-Moriya
+interactions have been observed in an ultrathin Pt/CoFeB film. Our
+micromagnetic simulations show that spin-wave nonreciprocity due to asymmetric
+surface pinning is insignificant for the 0.8nmthick CoFeB film studied. The
+observed high asymmetry of the monotonic spin wave dispersion relation is thus
+ascribed to strong Dzyaloshinskii-Moriya interactions present at the Pt/CoFeB
+interface. Our findings should further enhance the significance of CoFeB as an
+important material for magnonic, spintronic and skyrmionic applications.",1412.3907v2
+2014-12-18,Exchange Magnon-Polaritons in Microwave Cavities,"We formulate a scattering theory to study magnetic films in microwave
+cavities beyond the independent-spin and rotating wave approximations of the
+Tavis-Cummings model. We demonstrate that strong coupling can be realized not
+only for the ferromagnetic resonance (FMR) mode, but also for spin wave
+resonances (SWRs); the coupling strengths are mode dependent and decrease with
+increasing mode index. The strong coupling regime can be also accessed
+electrically by spin pumping into a metal contact.",1412.5809v3
+2015-01-08,Fractional excitations in the square-lattice quantum antiferromagnet,"The square-lattice quantum Heisenberg antiferromagnet displays a pronounced
+anomaly of unknown origin in its magnetic excitation spectrum. The anomaly
+manifests itself only for short wavelength excitations propagating along the
+direction connecting nearest neighbors. Using polarized neutron spectroscopy,
+we have fully characterized the magnetic fluctuations in the model
+metal-organic compound CFTD, revealing an isotropic continuum at the anomaly
+indicative of fractional excitations. A theoretical framework based on the
+Gutzwiller projection method is developed to explain the origin of the
+continuum at the anomaly. This indicates that the anomaly arises from
+deconfined fractional spin-1/2 quasiparticle pairs, the 2D analog of 1D
+spinons. Away from the anomaly the conventional spin-wave spectrum is recovered
+as pairs of fractional quasiparticles bind to form spin-1 magnons. Our results
+therefore establish the existence of fractional quasiparticles in the simplest
+model two dimensional antiferromagnet even in the absence of frustration.",1501.01767v1
+2015-01-16,"Spectroscopic Studies of Iron-based Superconductors, Multi-ferroic Oxides and Double-perovskite: Phonons, Electronic and Spin Excitations","Raman spectroscopy is a very powerful probe to study the nature of
+quasi-particle excitations in condensed matter physics. The work presented in
+this thesis is focused on two different families of novel materials, namely the
+iron-based superconductors (FeBS), multiferroic oxides and double perovskite.
+Although the properties of these two systems are quite different, some
+comparison can still be drawn between them. For instance, in both of these
+systems magnetism plays a crucial role and intricate coupling between phononic,
+magnetic and orbital degrees of freedom is crucial to understand their
+underlying physics responsible for their various exotic physical properties.
+Understanding the microscopic origin of quasi-particle excitations, such as
+phonons, magnons, orbitons, plasmons etc., and coupling between them in these
+complex materials, has been an intense field of research because it is believed
+that these excitations hold the key for explaining their rich physics. The
+systems studied in the thesis include (A) FeBS - (i) FeSe0.82 (ii)
+Ce1-zYzFeAsO1-xFx (z = 0, 0.4; x = 0.1, 0.2) (iii) Ca4Al2O5.7Fe2As2 (iv)
+Ca(Fe1-xCox)2As2 (x = 0.03, 0.05). (B) Multiferroic oxides - (i) AlFeO3 (ii)
+TbMnO3 and double perovskite (iii) La2NiMnO6.",1501.04055v1
+2015-01-27,Conformal mass in Einstein-Gauss-Bonnet AdS gravity,"In this paper, we show that the physical information given by conserved
+charges for asymptotically AdS spacetimes in Einstein-Gauss-Bonnet AdS gravity
+is encoded in the electric part of the Weyl tensor. This result generalizes the
+conformal mass definition by Ashtekar-Magnon-Das (AMD) to a gravity theory with
+a Gauss-Bonnet term. This proof makes use of the Noether charges obtained from
+an action renormalized by the addition of counterterms which depend on the
+extrinsic curvature (Kounterterms). If the asymptotic fall-off behaviour of the
+Weyl tensor is same as the one considered in the AMD method, then the
+Kounterterm charges and the AMD charges agree in any dimension.",1501.06861v2
+2015-02-02,Some three-point correlation functions in the eta-deformed AdS_5 x S^5,"We compute some normalized structure constants in the $\eta$-deformed
+$AdS_5\times S^5$ in the framework of the semiclassical approach. This is done
+for the cases when the ""heavy"" string states are finite-size giant magnons
+carrying one angular momentum and for three different choices of the ""light""
+state: primary scalar operators, dilaton operator with nonzero momentum,
+singlet scalar operators on higher string levels. Since the dual field theory
+is still unknown, the results obtained here must be considered as conjectures
+or as predictions from the string theory side.
+  Keywords: Gauge/string duality, Correlation functions
+  PACS:11.25.-w, 11.25.Tq",1502.00610v4
+2015-02-19,The thermal Hall effect of spin excitations in a Kagome magnet,"At low temperatures, the thermal conductivity of spin excitations in a
+magnetic insulator can exceed that of phonons. However, because they are charge
+neutral, the spin waves are not expected to display a thermal Hall effect in a
+magnetic field. Recently, this semiclassical notion has been upended in quantum
+magnets in which the spin texture has a finite chirality. In the Kagome
+lattice, the chiral term generates a Berry curvature. This results in a thermal
+Hall conductivity $\kappa_{xy}$ that is topological in origin. Here we report
+observation of a large $\kappa_{xy}$ in the Kagome magnet Cu(1-3, bdc) which
+orders magnetically at 1.8 K. The observed $\kappa_{xy}$ undergoes a remarkable
+sign-reversal with changes in temperature or magnetic field, associated with
+sign alternation of the Chern flux between magnon bands. We show that thermal
+Hall experiments probe incisively the effect of Berry curvature on heat
+transport.",1502.05688v1
+2015-02-20,Magneto-Plasmonics and Resonant Interaction of Light with Dynamic Magnetisation in Metallic and All-Dielectric Nanostructures (Review),"A significant interest in combining plasmonics and magnetism at the nanoscale
+gains momentum in both photonics and magnetism sectors that are concerned with
+the resonant enhancement of light-magnetic-matter interaction in
+nanostructures. These efforts result in a considerable amount of literature,
+which is difficult to collect and digest in limited time. Furthermore, there is
+insufficient exchange of results between the two research sectors.
+Consequently, the goal of this review paper is to bridge this gap by presenting
+an overview of recent progress in the field of magneto-plasmonics from two
+different points of view: magneto-plasmonics, and magnonics and magnetisation
+dynamics. It is expected that this presentation style will make this review
+paper of particular interest to both general physical audience and specialists
+conducting research on photonics, plasmonics, Brillouin light scattering
+spectroscopy of magnetic nanostructures and magneto-optical Kerr effect
+magnetometry, as well as ultrafast all-optical and THz-wave excitation of spin
+waves. Moreover, readers interested in a new, rapidly emerging field of
+all-dielectric nanophotonics will find a section about all-magneto-dielectric
+nanostructures.",1502.05783v1
+2015-03-05,Casimir effect mechanism of pairing between fermions in the vicinity of a magnetic quantum critical point,"We consider two immobile spin $1/2$ fermions in a two-dimensional magnetic
+system that is close to the $ O(3)$ magnetic quantum critical point (QCP) which
+separates magnetically ordered and disordered phases. Focusing on the
+disordered phase in the vicinity of the QCP, we demonstrate that the
+criticality results in a strong long range attraction between the fermions,
+with potential $V(r) \propto -1/r^{\nu}$, $\nu \approx 0.75$, where $r$ is
+separation between the fermions. The mechanism of the enhanced attraction is
+similar to Casimir effect and corresponds to multi-magnon exchange processes
+between the fermions. While we consider a model system, the problem is
+originally motivated by recent establishment of magnetic QCP in hole doped
+cuprates under the superconducting dome at doping of about 10\%. We suggest the
+mechanism of magnetic critical enhancement of pairing in cuprates.",1503.01554v1
+2015-03-06,Thermal conductivity through the quantum critical point in YbRh2Si2 at very low temperature,"The thermal conductivity of YbRh2Si2 has been measured down to very low
+temperatures under field in the basal plane. An additional channel for heat
+transport appears below 30 mK, both in the antiferromagnetic and paramagnetic
+states, respectively below and above the critical field suppressing the
+magnetic order. This excludes antiferromagnetic magnons as the origin of this
+additional contribution to thermal conductivity. Moreover, this low temperature
+contribution prevails a definite conclusion on the validity or violation of the
+Wiedemann-Franz law at the field-induced quantum critical point. At high
+temperature in the paramagnetic state, the thermal conductivity is sensitive to
+ferromagnetic fluctuations, previously observed by NMR or neutron scattering
+and required for the occurrence of the sharp electronic spin resonance
+fracture.",1503.01991v1
+2015-03-18,Observation of huge thermal spin currents in magnetic multilayers,"Thermal spin pumping constitutes a novel mechanism for generation of spin
+currents; however their weak intensity constitutes a major roadblock for its
+usefulness. We report a phenomenon that produces a huge spin current in the
+central region of a multilayer system, resulting in a giant spin Seebeck effect
+in a structure formed by repetition of ferromagnet/metal bilayers. The result
+is a consequence of the interconversion of magnon and electron spin currents at
+the multiple interfaces. This work opens the possibility to design thin film
+heterostructures that may boost the application of thermal spin currents in
+spintronics.",1503.05594v1
+2015-03-19,Half-Quantum Vortices in an Antiferromagnetic Spinor Bose-Einstein Condensate,"We report on the observation of half-quantum vortices (HQVs) in the
+easy-plane polar phase of an antiferromagnetic spinor Bose-Einstein condensate.
+Using in situ magnetization-sensitive imaging, we observe that pairs of HQVs
+with opposite core magnetization are generated when singly charged quantum
+vortices are injected into the condensate. The dynamics of HQV pair formation
+is characterized by measuring the temporal evolutions of the pair separation
+distance and the core magnetization, which reveals the short-range nature of
+the repulsive interactions between the HQVs. We find that spin fluctuations
+arising from thermal population of axial magnon excitations do not
+significantly affect the HQV pair formation dynamics. Our results demonstrate
+the instability of a singly charged vortex in the antiferromagnetic spinor
+condensate.",1503.05648v3
+2015-04-23,Three-Dimensional Crystallization of Vortex Strings in Frustrated Quantum Magnets,"We demonstrate that frustrated exchange interactions can produce exotic 3D
+crystals of vortex strings near the saturation field (H=Hsat) of body- and
+face-centered cubic Mott insulators. The combination of cubic symmetry and
+frustration leads to a magnon spectrum of the fully polarized spin state
+(H>Hsat) with degenerate minima at multiple noncoplanar Q vectors. This
+spectrum becomes gapless at the quantum critical point H=Hsat and the magnetic
+ordering below Hsat can be formally described as a condensate of a dilute gas
+of bosons. By expanding in the lattice gas parameter, we find that different
+vortex crystals span sizable regions of the phase diagrams for isotropic
+exchange and are further stabilized by symmetric exchange anisotropy.",1504.06270v2
+2015-05-04,Landau-Lifshitz theory of the thermomagnonic torque,"We derive the thermomagnonic torque associated with smooth magnetic textures
+subjected to a temperature gradient, in the framework of the stochastic
+Landau-Lifshitz-Gilbert equation. Our approach captures on equal footing two
+distinct contributions: (1) A local entropic torque that is caused by a
+temperature dependence of the effective exchange field, the existence of which
+had been previously suggested based on numerics and (2) the well-known
+spin-transfer torque induced by thermally-induced magnon flow. The dissipative
+components of two torques have the same structure, following a common
+phenomenology, but opposite signs, with the twice larger entropic torque
+leading to a domain-wall motion toward the hotter region. We compare the
+efficiency of the torque-driven domain-wall motion with the recently proposed
+Brownian thermophoresis.",1505.00818v1
+2015-05-25,Integrable open spin-chains in AdS3/CFT2 correspondences,"We study integrable open boundary conditions for d(2,1;\alpha)^2 and
+psu(1,1|2)^2 spin-chains. Magnon excitations of these open spin-chains are
+mapped to massive excitations of type IIB open superstrings ending on D-branes
+in the AdS_3 x S^3 x S^3 x S^1 and AdS_3 x S^3 x T^4 supergravity geometries
+with pure R-R flux. We derive reflection matrix solutions of the boundary
+Yang-Baxter equation which intertwine representations of a variety of boundary
+coideal subalgebras of the bulk Hopf superalgebra. Many of these integrable
+boundaries are matched to D1- and D5-brane maximal giant gravitons.",1505.06767v3
+2015-06-07,Experimental observation of the interaction of propagating spin waves with Néel domain walls in a Landau domain structure,"The interaction of propagating dipolar spin waves with magnetic domain walls
+is investigated in square-shaped microstructures patterned from the Heusler
+compound Co$_2$Mn$_{0.6}$Fe$_{0.4}$Si. Using magnetic force microscopy, the
+reversible preparation of a Landau state with four magnetic domains separated
+by N\'eel domain walls is confirmed. A local spin-wave excitation using a
+microstructured antenna is realized in one of the domains. It is shown by
+Brillouin light scattering microscopy (BLS) that the domain structure in the
+remanence state has a strong influence on the spin-wave excitation and
+propagation. The domain walls strongly reflect the spin waves and can be used
+as spin-wave reflectors. A comparison with micromagnetic simulations shows that
+the strong reflection is due to the long-range dipolar interaction which has
+important implications for the use of these spin waves for exerting an
+all-magnonic spin-transfer torque.",1506.02303v1
+2015-06-18,Anomalous polarization conversion in arrays of ultrathin ferromagnetic nanowires,"We study optical properties of arrays of ultrathin nanowires by means of the
+Brillouin scattering of light on magnons. We employ the Stokes/anti-Stokes
+scattering asymmetry to probe the circular polarization of a local electric
+field induced inside nanowires by linearly polarized light waves. We observe
+the anomalous polarization conversion of the opposite sign than that in a bulk
+medium or thick nanowires with a great enhancement of the degree of circular
+polarization attributed to an unconventional refraction in the nanowire medium.",1506.05594v1
+2015-06-19,Spin superfluidity and long-range transport in thin-film ferromagnets,"In ferromagnets, magnons may condense into a single quantum state. Analogous
+to superconductors, this quantum state may support transport without
+dissipation. Recent works suggest that longitudinal spin transport through a
+thin-film ferromagnet is an example of spin superfluidity. Although intriguing,
+this tantalizing picture ignores long-range dipole interactions; we demonstrate
+that such interactions dramatically affect spin transport. In single-film
+ferromagnets, ""spin superfluidity"" only exists at length scales (a few hundred
+nanometers in yttrium iron garnet) somewhat larger than the exchange length.
+Over longer distances, dipolar interactions destroy spin superfluidity.
+Nevertheless, we predict re-emergence of spin superfluidity in tri-layer
+ferromagnet--normal metal--ferromagnet films of $\sim 1\, \mu$m in size. Such
+systems also exhibit other types of long-range spin transport in samples
+several micrometers in size.",1506.06029v1
+2015-06-22,Heat transport between antiferromagnetic insulators and normal metals,"Antiferromagnetic insulators can become active spintronics components by
+controlling and detecting their dynamics via spin currents in adjacent metals.
+This cross-talk occurs via spin-transfer and spin-pumping, phenomena that have
+been predicted to be as strong in antiferromagnets as in ferromagnets. Here, we
+demonstrate that a temperature gradient drives a significant heat flow from
+magnons in antiferromagnetic insulators to electrons in adjacent normal metals.
+The same coefficients as in the spin-transfer and spin-pumping processes also
+determine the thermal conductance. However, in contrast to ferromagnets, the
+heat is not transferred via a spin Seebeck effect which is absent in
+antiferromagnetic insulator-normal metal systems. Instead, the heat is
+transferred via a large staggered spin Seebeck effect.",1506.06705v1
+2015-09-02,All-phononic Digital Transistor on the Basis of Gap-Soliton Dynamics in Anharmonic Oscillator Ladder,"A conceptual mechanism of amplification of phonons by phonons on the basis of
+nonlinear band-gap transmission (supratransmission) phenomenon is presented. As
+an example a system of weakly coupled chains of anharmonic oscillators is
+considered. One (source) chain is driven harmonically by boundary with a
+frequency located in the upper band close to the band edge of the ladder
+system. Amplification happens when a second (gate) chain is driven by a small
+signal in the counter phase and with the same frequency as first chain. If the
+total driving of both chains overcomes the band-gap transmission threshold the
+large amplitude band-gap soliton emerges and amplification scenario is
+realized. The mechanism is interpreted as nonlinear superposition of evanescent
+and propagating nonlinear modes manifesting in a single or double soliton
+generation working in band-gap or band-pass regimes, respectively. The results
+could be straightforwardly generalized for all-optical or all-magnonic contexts
+and has all the promises for logic gate operations.",1509.00679v1
+2015-09-11,Thermal generation of spin current in epitaxial CoFe2O4 thin films,"The longitudinal spin Seebeck effect (LSSE) has been investigated in
+high-quality epitaxial CoFe2O4 (CFO) thin films. The thermally excited spin
+currents in the CFO films are electrically detected in adjacent Pt layers due
+to the inverse spin Hall effect (ISHE). The LSSE signal exhibits a linear
+increase with increasing temperature gradient, yielding a LSSE coefficient of
+~100 nV/K at room temperature. The temperature dependence of the LSSE is
+investigated from room temperature down to 30 K, showing a significant
+reduction at low temperatures, revealing that the total amount of thermally
+generated magnons decreases. Furthermore, we demonstrate that the spin Seebeck
+effect is an effective tool to study the magnetic anisotropy induced by
+epitaxial strain, especially in ultrathin films with low magnetic moments.",1509.03601v1
+2015-09-16,Microwave excitation of spin wave beams in thin ferromagnetic films,"We present an approach enabling generation of narrow spin wave beams in thin
+homogeneous ferromagnetic films. The main idea is to match the wave vector of
+the spin wave with that corresponding to the spectral maximum of the exciting
+microwave magnetic field only locally, in the region of space from which the
+beam should be launched. We show that this can be achieved with the aid of a
+properly designed coplanar waveguide transducer generating a nonuniform
+microwave magnetic field. The resulting two-dimensional spin wave beams
+obtained in micromagnetic simulations propagate over distances of several
+micrometers. The proposed approach requires neither inhomogeneity of the
+ferromagnetic film nor nonuniformity of the biasing magnetic field, and it can
+be generalized to yield multiple spin wave beams of different width at the same
+frequency. Other possible excitation scenarios and applications of spin wave
+beam magnonics are also discussed.",1509.05061v2
+2015-09-17,A spin wave diode,"A diode, a device allowing unidirectional signal transmission, is a
+fundamental element of logic structures and lies in the heart of modern
+information systems. Spin wave or magnon, representing a collective
+quasi-particle excitation of the magnetic order in magnetic materials, is a
+promising candidate of information carrier for the next generation
+energy-saving technologies. Here we propose a scalable and reprogrammable pure
+spin wave logic hardware architecture using domain walls and surface anisotropy
+stripes as waveguides on a single magnetic wafer. We demonstrate theoretically
+the design principle of the simplest logic component, a spin wave diode,
+utilizing the chiral bound states in a magnetic domain wall with
+Dzyaloshiskii-Moriya interaction, and confirm its performance through
+micromagnetic simulations. Our findings open a new vista for realizing
+different types of pure spin wave logic components and finally achieving an
+energy-efficient and hardware-reprogrammable spin wave computer.",1509.05095v1
+2015-09-17,Antiferromagnetic Spin Wave Field-Effect Transistor,"In a collinear antiferromagnet with easy-axis anisotropy, symmetry dictates
+that the spin wave modes must be doubly degenerate. Theses two modes,
+distinguished by their opposite polarization and available only in
+antiferromagnets, give rise to a novel degree of freedom to encode and process
+information. We show that the spin wave polarization can be manipulated by an
+electric field induced Dzyaloshinskii-Moriya interaction and magnetic
+anisotropy. We propose a prototype spin wave field-effect transistor which
+realizes a gate-tunable magnonic analog of the Faraday effect, and demonstrate
+its application in THz signal modulation. Our findings open up the exciting
+possibility of digital data processing utilizing antiferromagnetic spin waves
+and enable the direct projection of optical computing concepts onto the
+mesoscopic scale.",1509.05295v3
+2015-09-21,Crystal growth and intrinsic magnetic behavior of Sr$_2$IrO$_4$,"We report on the growth of stoichiometric Sr$_2$IrO$_4$ single crystals,
+which allow us to unveil their intrinsic magnetic properties. The effect of
+different growth conditions has been investigated for crystals grown by the
+flux method. We find that the magnetic response depends very sensitively on the
+details of the growth conditions. We assess the defect concentration based on
+magnetization, X-ray diffraction, Raman scattering, and optical conductivity
+measurements. We find that samples with a low concentration of electronically
+active defects show much reduced in-gap spectral weight in the optical
+conductivity and a pronounced two-magnon peak in the Raman scattering spectrum.
+A prolonged exposure at high temperature during the growth leads to higher
+defect concentration likely due to creation of oxygen vacancies. We further
+demonstrate a systematic intergrowth of Sr$_2$IrO$_4$ and Sr$_3$Ir$_2$O$_7$
+phases by varying the growth temperature. Our results thus emphasize that
+revealing the intrinsic magnetic properties of Sr$_2$IrO$_4$ and related
+materials requires a scrupulous control of the crystal growth process.",1509.06342v2
+2015-09-24,Magnetic behavior of volborthite Cu3V2O7(OH)2(H2O)2 determined by coupled trimers rather than frustrated chains,"Motivated by recent experiments on volborthite single crystals showing a wide
+1/3-magnetization plateau, we perform microscopic modeling by means of density
+functional theory (DFT) with the single-crystal structural data as a starting
+point. Using DFT+U, we find four leading magnetic exchanges: antiferromagnetic
+J and J2, as well as ferromagnetic J' and J1. Simulations of the derived spin
+Hamiltonian show good agreement with the experimental low-field magnetic
+susceptibility and high-field magnetization data. The 1/3-plateau phase
+pertains to polarized magnetic trimers formed by strong J bonds. An effective
+J$\rightarrow\infty$ model shows a tendency towards condensation of magnon
+bound states preceding the plateau phase.",1509.07333v2
+2015-10-07,"Tunable damping, saturation magnetization, and exchange stiffness of half-Heusler NiMnSb thin films","The half-metallic half-Heusler alloy NiMnSb is a promising candidate for
+applications in spintronic devices due to its low magnetic damping and its rich
+anisotropies. Here we use ferromagnetic resonance (FMR) measurements and
+calculations from first principles to investigate how the composition of the
+epitaxially grown NiMnSb influences the magnetodynamic properties of saturation
+magnetization $M_S$, Gilbert damping $\alpha$, and exchange stiffness $A$.
+$M_S$ and $A$ are shown to have a maximum for stoichiometric composition, while
+the Gilbert damping is minimum. We find excellent quantitative agreement
+between theory and experiment for $M_S$ and $\alpha$. The calculated $A$ shows
+the same trend as the experimental data, but has a larger magnitude.
+Additionally to the unique in-plane anisotropy of the material, these
+tunabilities of the magnetodynamic properties can be taken advantage of when
+employing NiMnSb films in magnonic devices.",1510.01894v1
+2015-10-21,Raman study of spin excitations in the tunable quantum spin ladder Cu(Qnx)(Cl$_{1-x}$Br$_x$)$_2$,"Raman spectroscopy is used to study magnetic excitations in the quasi one
+dimensional $S=1/2$ quantum spin systems Cu(Qnx)(Cl$_{1-x}$Br$_x$)$_2$. The low
+energy spectrum is found to be dominated by a two-magnon continuum as expected
+from the numerical calculations for the Heisenberg spin ladder model. The
+continuum shifts to higher energies as more Br is introduced. The cutoff of the
+scattering increases faster than the onset indicating that the increase of
+exchange constant along the leg is the main effect on the magnetic properties.
+The upper and lower continuum thresholds are measured as a function of Br
+content across the entire range and compared to estimates based on previous
+bulk studies. We observe small systematic deviations that are discussed.",1510.06360v2
+2015-10-21,Reconfigurable spin wave band structure of artificial square spin ice,"Artificial square spin ices are structures composed of magnetic elements
+arranged on a geometrically frustrated lattice and located on the sites of a
+two-dimensional square lattice, such that there are four interacting magnetic
+elements at each vertex. Using a semi-analytical approach, we show that square
+spin ices exhibit a rich spin wave band structure that is tunable both by
+external magnetic fields and the configuration of individual elements. Internal
+degrees of freedom can give rise to equilibrium states with bent magnetization
+at the edges leading to characteristic excitations; in the presence of
+magnetostatic interactions these form separate bands analogous to impurity
+bands in semiconductors. Full-scale micromagnetic simulations corroborate our
+semi-analytical approach. Our results show that artificial square spin ices can
+be viewed as reconfigurable and tunable magnonic crystals that can be used as
+metamaterials for spin-wave-based applications at the nanoscale.",1510.06385v2
+2016-01-06,All-electrical detection of spin dynamics in magnetic antidot lattices by the inverse spin Hall effect,"The understanding of spin dynamics in laterally confined structures on
+sub-micron length scales has become a significant aspect of the development of
+novel magnetic storage technologies. Numerous ferromagnetic resonance
+measurements, optical characterization by Kerr microscopy and Brillouin light
+scattering spectroscopy and x-ray studies were carried out to detect the
+dynamics in patterned magnetic antidot lattices. Here, we investigate
+Oersted-field driven spin dynamics in rectangular Ni80Fe20/Pt antidot lattices
+with different lattice parameters by electrical means and compare them to
+micromagnetic simulations. When the system is driven to resonance, a dc voltage
+across the length of the sample is detected that changes its sign upon field
+reversal, which is in agreement with a rectification mechanism based on the
+inverse spin Hall effect. Furthermore, we show that the voltage output scales
+linearly with the applied microwave drive in the investigated range of powers.
+Our findings have direct implications on the development of engineered
+magnonics applications and devices.",1601.01221v1
+2016-01-12,Spin-dependent Bragg spectroscopy of a spinor Bose gas,"We develop a general theory of spin-dependent Bragg spectroscopy for spinor
+Bose-Einstein condensates. This spectroscopy involves using a density and
+spin-coupled optical probe to excite the system. We show that within the linear
+response regime the momentum or energy transferred by the probe is determined
+by a set of density and spin-density dynamic structure factors. We derive a set
+of $f$-sum rules that provide rigorous constraints for the first energy moments
+of these structure factors. As an application we compute the dynamic structure
+factors for cases within all four distinct phases of a spin-1 condensate using
+Bogoliubov theory. Our results demonstrate that spin-dependent Bragg
+spectroscopy can be used to selectively investigate the various phonon and
+magnon excitation branches and will be a useful tool for advancing our
+understanding of spinor condensates.",1601.02716v2
+2016-01-28,Spin-Cherenkov effect in a magnetic nanostrip with interfacial Dzyaloshinskii-Moriya interaction,"Spin-Cherenkov effect enables strong excitations of spin waves (SWs) with
+nonlinear wave dispersions. The Dzyaloshinskii-Moriya interaction (DMI) results
+in anisotropy and nonreciprocity of SWs propagation. In this work, we study the
+effect of the interfacial DMI on SW Cherenkov excitations in permalloy
+thin-film strips within the framework of micromagnetism. By performing
+micromagnetic simulations, it is shown that coherent SWs are excited when the
+velocity of a moving magnetic source exceeds the propagation velocity of the
+SWs. Moreover, the threshold velocity of the moving magnetic source with finite
+DMI can be reduced compared to the case of zero DMI. It thereby provides a
+promising route towards efficient SW generation and propagation, with potential
+applications in spintronic and magnonic devices.",1601.07755v2
+2016-02-04,Investigation of the unidirectional spin heat conveyer effect in a 200nm thin Yttrium Iron Garnet film,"We have investigated the unidirectional spin wave heat conveyer effect in
+sub-micron thick yttrium iron garnet (YIG) films using lock-in thermography
+(LIT). Although the effect is small in thin layers this technique allows us to
+observe asymmetric heat transport by magnons which leads to asymmetric
+temperature profiles differing by several mK on both sides of the exciting
+antenna, respectively. Comparison of Damon-Eshbach and backward volume modes
+shows that the unidirectional heat flow is indeed due to non-reciprocal
+spin-waves. Because of the finite linewidth, small asymmetries can still be
+observed when only the uniform mode of ferromagnetic resonance is excited. The
+latter is of extreme importance for example when measuring the inverse
+spin-Hall effect because the temperature differences can result in
+thermovoltages at the contacts. Because of the non-reciprocity these
+thermovoltages reverse their sign with a reversal of the magnetic field which
+is typically deemed the signature of the inverse spin-Hall voltage.",1602.01662v1
+2016-02-12,Internal dipolar field and soft magnons in periodic nanocomposite magnets,"We study spin wave excitations in a three-dimensional nanocomposite magnet of
+exchange coupled hard (SmCo$_5$) and soft (FeCo) phases. The dipolar
+interaction splits the spin wave energies into the upper and lower branches of
+the spin wave manifold. When the amount of the soft phase is increased the
+energy of low-lying spin excitations is considerably softened due to two
+reasons: (i) the low- lying mode locked into the soft phase region with a spin
+wave gap at ${\bf k}= 0$ which scales approximately proportional to the
+anisotropy constant of the soft phase and (ii) the internal dipolar field which
+comes from magnetic charges forming at hard-soft boundaries with normals
+parallel to the magnetization displaces the spin wave manifold toward the lower
+energies. With adding more soft phase the spin wave gap closes and the system
+moves to another ground state characterized by the magnetization mismatch
+between spins of the hard and soft phases.",1602.04111v1
+2016-02-12,Non-equilibrium itinerant-electron magnetism: a time-dependent mean-field theory,"We study the dynamical magnetic susceptibility of a strongly correlated
+electronic system in the presence of a time-dependent hopping field, deriving a
+generalized Bethe-Salpeter equation which is valid also out of equilibrium.
+Focusing on the single-orbital Hubbard model within the time-dependent
+Hartree-Fock approximation, we solve the equation in the non-equilibrium
+adiabatic regime, obtaining a closed expression for the transverse magnetic
+susceptibility. From this, we provide a rigorous definition of non-equilibrium
+(time-dependent) magnon frequencies and exchange parameters, expressed in terms
+of non-equilibrium single-electron Green functions and self-energies. In the
+particular case of equilibrium, we recover previously known results.",1602.04150v3
+2016-02-17,Fermionic response from fractionalization in an insulating two-dimensional magnet,"Conventionally ordered magnets possess bosonic elementary excitations, called
+magnons. By contrast, no magnetic insulators in more than one dimension are
+known whose excitations are not bosons but fermions. Theoretically, some
+quantum spin liquids (QSLs) -- new topological phases which can occur when
+quantum fluctuations preclude an ordered state -- are known to exhibit Majorana
+fermions as quasiparticles arising from fractionalization of spins. Alas,
+despite much searching, their experimental observation remains elusive. Here,
+we show that fermionic excitations are remarkably directly evident in
+experimental Raman scattering data across a broad energy and temperature range
+in the two-dimensional material $\alpha$-RuCl$_3$. This shows the importance of
+magnetic materials as hosts of Majorana fermions. In turn, this first
+systematic evaluation of the dynamics of a QSL at finite temperature emphasizes
+the role of excited states for detecting such exotic properties associated with
+otherwise hard-to-identify topological QSLs.",1602.05277v1
+2016-02-17,Quantum Rotors on the AB$_2$ Chain with Competing Interactions,"We present the ground state phase diagram of $q = 1/2$ quantum-rotor chains
+with competing interactions (frustration) calculated through cluster
+variational mean field approaches. We consider two interaction patterns, named
+F$_1$ and F$_2$ models, between the quantum-rotor momentum and position
+operators, which follow exchange patterns of known one-dimensional spin-1/2
+systems with a ferrimagnetic state in their phase diagrams. The spin-1/2 F$_1$
+model is known as the diamond chain and is related to the azurite compound,
+while the spin-1/2 F$_2$ model was recently shown to present a
+frustration-induced condensation of magnons. We provide a detailed comparison
+between the quantum-rotor phase diagrams, in single- and multi-site mean-field
+approaches, and known results for the spin-1/2 models, including exact
+diagonalization and density matrix renormalization group data for these
+systems, as well as phase diagrams of the associated classical models.",1602.05383v1
+2016-02-24,Spin Seebeck effect at microwave frequencies,"We experimentally study the transient voltage response of yttrium iron
+garnet/platinum bilayer samples subject to periodic heating up to gigahertz
+frequencies. We observe an intrinsic cutoff frequency of the induced
+thermopower voltage, which characteristically depends on the thickness of the
+yttrium iron garnet film. The cutoff frequency reaches values of up to 350 MHz
+in a 50 nm thick yttrium iron garnet film, but drops to below 1 MHz for
+several-micrometer-thick films. These data corroborate the notion that the
+magnon spectrum responsible for the spin current emission in the spin Seebeck
+effect can be shaped by tuning the thickness of the ferromagnetic layer.",1602.07442v2
+2016-02-24,Super-Poissonian shot noise of squeezed-magnon mediated spin transport,"The magnetization of a ferromagnet (F) driven out of equilibrium injects pure
+spin current into an adjacent conductor (N). Such F$|$N bilayers have become
+basic building blocks in a wide variety of spin based devices. We evaluate the
+shot noise of the spin current traversing the F$|$N interface when F is
+subjected to a coherent microwave drive. We find that the noise spectrum is
+frequency independent up to the drive frequency, and increases linearly with
+frequency thereafter. The low frequency noise indicates super-Poissonian spin
+transfer, which results from quasi-particles with effective spin $\hbar^* =
+\hbar (1 + \delta)$. For typical ferromagnetic thin films, $\delta \sim 1$ is
+related to the dipolar interaction-mediated squeezing of F eigenmodes.",1602.07513v2
+2016-02-25,Magnetic Mass in 4D AdS Gravity,"We provide a fully-covariant expression for the diffeomorphic charge in 4D
+anti-de Sitter gravity, when the Gauss-Bonnet and Pontryagin terms are added to
+the action. The couplings of these topological invariants are such that the
+Weyl tensor and its dual appear in the on-shell variation of the action, and
+such that the action is stationary for asymptotic (anti) self-dual solutions in
+the Weyl tensor. In analogy with Euclidean electromagnetism, whenever the
+self-duality condition is global, both the action and the total charge are
+identically vanishing. Therefore, for such configurations the magnetic mass
+equals the Ashtekhar-Magnon-Das definition.",1602.07975v2
+2016-04-06,Temperature Dependence of Angular Momentum Transport Across Interfaces,"Angular momentum transport in magnetic multilayered structures plays a
+central role in spintronic physics and devices. The angular momentum currents
+or spin currents are carried by either quasi-particles such as electrons and
+magnons, or by macroscopic order parameters such as local magnetization of
+ferromagnets. Based on the generic interface exchange interaction, we develop a
+microscopic theory that describes interfacial spin conductance for various
+interfaces among non-magnetic metals, ferromagnetic and antiferromagnetic
+insulators. Spin conductance and its temperature dependence are obtained for
+different spin batteries including spin pumping, temperature gradient and spin
+Hall effect. As an application of our theory, we calculate the spin current in
+a trilayer made of a ferromagnetic insulator, an antiferromagnetic insulator
+and a non-magnetic heavy metal. The calculated results on the temperature
+dependence of spin conductance quantitatively agree with the existing
+experiments.",1604.01714v2
+2016-04-07,Signatures of strong correlation effects in RIXS on Cuprates,"Recently, spin excitations in doped cuprates are measured using the resonant
+inelastic X-ray scattering (RIXS). The paramagnon dispersions show the large
+hardening effect in the electron-doped systems and seemingly
+doping-independence in the hole-doped systems, with the energy scales
+comparable to that of the antiferromagnetic magnons. This anomalous hardening
+effect was partially explained by using the strong coupling t-J model but with
+a three-site term(Nature communications 5, 3314 (2014)). However we show that
+hardening effect is a signature of strong coupling physics even without
+including this extra term. By considering the t-t'-t""-J model and using the
+Slave-Boson (SB) mean field theory, we obtain, via the spin-spin
+susceptibility, the spin excitations in qualitative agreement with the
+experiments. These anomalies is mainly due to the doping-dependent bandwidth.
+We further discuss the interplay between particle-hole-like and paramagnon-like
+excitations in the RIXS measurements.",1604.01858v3
+2016-04-09,Interaction Corrections to Spin-Wave Theory in the Large-S Limit of the Quantum Heisenberg Ferromagnet,"The Quantum Heisenberg Ferromagnet can be naturally reformulated in terms of
+interacting bosons (called spin waves or magnons) as an expansion in the
+inverse spin size. We calculate the first order interaction correction to the
+free energy, as an upper bound in the limit where the spin size $S \to \infty$
+and $\beta S$ is fixed ($\beta$ being the inverse temperature). Our result is
+valid in two and three spatial dimensions. We extrapolate our result to compare
+with Dyson's low-temperature expansion. While our first-order correction has
+the expected temperature dependance, in higher orders of the perturbation
+theory cancellations are necessary.",1604.02548v2
+2016-04-12,Ab initio determination of spin Hamiltonians with anisotropic exchange interactions: the case of the pyrochlore ferromagnet Lu$_2$V$_2$O$_7$,"We present a general framework for deriving effective spin Hamiltonians of
+correlated magnetic systems based on a combination of relativistic ab initio
+density functional theory calculations (DFT), exact diagonalization of a
+generalized Hubbard Hamiltonian on finite clusters and spin projections onto
+the low-energy subspace. A key motivation is to determine anisotropic bilinear
+exchange couplings in materials of interest. As an example, we apply this
+method to the pyrochlore Lu$_2$V$_2$O$_7$ where the vanadium ions form a
+lattice of corner-sharing spin-1/2 tetrahedra. In this compound, anisotropic
+Dzyaloshinskii-Moriya interactions (DMI) play an essential role in inducing a
+magnon Hall effect. We obtain quantitative estimates of the nearest-neighbor
+Heisenberg exchange, the DMI, and the symmetric part of the anisotropic
+exchange tensor. Finally, we compare our results with experimental ones on the
+Lu$_2$V$_2$O$_7$ compound.",1604.03472v1
+2016-04-21,A novel method for the injection and manipulation of magnetic charge states in nanostructures,"Realising the promise of next-generation magnetic nanotechnologies is
+contingent on the development of novel methods for controlling magnetic states
+at the nanoscale. There is currently demand for simple and flexible techniques
+to access exotic magnetisation states without convoluted fabrication and
+application processes. 360 degree domain walls (metastable twists in
+magnetisation separating two domains with parallel magnetisation) are one such
+state, which is currently of great interest in data storage and magnonics.
+Here, we demonstrate a straightforward and powerful process whereby a moving
+magnetic charge, provided experimentally by a magnetic force microscope tip,
+can write and manipulate magnetic charge states in ferromagnetic nanowires. The
+method is applicable to a wide range of nanowire architectures with
+considerable benefits over existing techniques. We confirm the method's
+efficacy via the injection and spatial manipulation of 360 degree domain walls
+in Py and Co nanowires. Experimental results are supported by micromagnetic
+simulations of the tip-nanowire interaction.",1604.06374v3
+2016-04-21,All-in all-out magnetic order and propagating spin-waves in Sm2Ir2O7,"Using resonant magnetic x-ray scattering we address the unresolved nature of
+the magnetic groundstate and the low-energy effective Hamiltonian of
+Sm$_2$Ir$_2$O$_7$, a prototypical pyrochlore iridate with a finite temperature
+metal-insulator transition. Through a combination of elastic and inelastic
+measurements, we show that the magnetic ground state is an all-in all-out
+(AIAO) antiferromagnet. The magnon dispersion indicates significant electronic
+correlations and can be well-described by a minimal Hamiltonian that includes
+Heisenberg exchange ($J=27.3(6)$ meV) and Dzyaloshinskii-Moriya interaction
+($D=4.9(3)$ meV), which provides a consistent description of the magnetic order
+and excitations. In establishing that Sm$_2$Ir$_2$O$_7$ has the requisite
+inversion symmetry preserving AIAO magnetic groundstate, our results support
+the notion that pyrochlore iridates may host correlated Weyl semimetals.",1604.06401v1
+2016-04-22,Nanoscale control of heat and spin conductance in artificial spin chains,"We describe a mechanism to control energy and magnetisation currents in an
+artificial spin-chain, consisting of an array of Permalloy nano-disks coupled
+through the magneto-dipolar interaction. The chain is kept out of equilibrium
+by two thermal baths with different temperatures connected to its ends, which
+control the current propagation. Transport is enhanced by applying a uniform
+radio frequency pump field resonating with some of the spin-wave modes of the
+chain. Moreover, the two currents can be controlled independently by tuning the
+static field applied on the chain. Thus we describe two effective means for the
+independent control of coupled currents and the enhancement of thermal and
+spin-wave conductivity in a realistic magnonics device, suggesting that similar
+effects could be observed in a large class of nonlinear oscillating systems.",1604.06572v3
+2016-04-24,Coupled Spin-Light dynamics in Cavity Optomagnonics,"Experiments during the past two years have shown strong resonant
+photon-magnon coupling in microwave cavities, while coupling in the optical
+regime was demonstrated very recently for the first time. Unlike with
+microwaves, the coupling in optical cavities is parametric, akin to
+optomechanical systems. This line of research promises to evolve into a new
+field of optomagnonics, aimed at the coherent manipulation of elementary
+magnetic excitations by optical means. In this work we derive the microscopic
+optomagnonic Hamiltonian. In the linear regime the system reduces to the
+well-known optomechanical case, with remarkably large coupling. Going beyond
+that, we study the optically induced nonlinear classical dynamics of a
+macrospin. In the fast cavity regime we obtain an effective equation of motion
+for the spin and show that the light field induces a dissipative term
+reminiscent of Gilbert damping. The induced dissipation coefficient however can
+change sign on the Bloch sphere, giving rise to self-sustained oscillations.
+When the full dynamics of the system is considered, the system can enter a
+chaotic regime by successive period doubling of the oscillations.",1604.07053v3
+2016-06-09,Snell's Law for Spin Waves,"We report the experimental observation of Snell's law for magneto-static spin
+waves in thin ferromagnetic Permalloy films by imaging incident, refracted and
+reflected waves. We use a thickness step as the interface between two media
+with different dispersion relation. Since the dispersion relation for
+magneto-static waves in thin ferromagnetic films is anisotropic, deviations
+from the isotropic Snell's law known in optics are observed for incidence
+angles larger than 25\textdegree{} with respect to the interface normal between
+the two magnetic media. Furthermore, we can show that the thickness step
+modifies the wavelength and the amplitude of the incident waves. Our findings
+open up a new way of spin wave steering for magnonic applications.",1606.02895v1
+2016-06-16,Spin dynamics of counterrotating Kitaev spirals via duality,"Incommensurate spiral order is a common occurrence in frustrated magnetic
+insulators. Typically, all magnetic moments rotate uniformly, through the same
+wavevector. However the honeycomb iridates family Li2IrO3 shows an
+incommensurate order where spirals on neighboring sublattices are
+counter-rotating, giving each moment a different local environment.
+Theoretically describing its spin dynamics has remained a challenge: the Kitaev
+interactions proposed to stabilize this state, which arise from strong
+spin-orbit effects, induce magnon umklapp scattering processes in spin-wave
+theory. Here we propose an approach via a (Klein) duality transformation into a
+conventional spiral of a frustrated Heisenberg model, allowing a direct
+derivation of the dynamical structure factor. We analyze both Kitaev and
+Dzyaloshinskii-Moriya based models, both of which can stabilize counterrotating
+spirals, but with different spin dynamics, and we propose experimental tests to
+identify the origin of counterrotation.",1606.05356v2
+2016-06-28,Nature of Bosonic Excitations revealed by high-energy charge carriers,"We address a long standing problem concerning the origin of bosonic
+excitations that strongly interact with charge carriers. We show that the
+time-resolved pump-probe experiments are capable to distinguish between regular
+bosonic degrees of freedom, e.g. phonons, and the hard-core bosons, e.g.,
+magnons. The ability of phonon degrees of freedom to absorb essentially
+unlimited amount of energy renders relaxation dynamics nearly independent on
+the absorbed energy or the fluence. In contrast, the hard core effects pose
+limits on the density of energy stored in the bosonic subsystems resulting in a
+substantial dependence of the relaxation time on the fluence and/or excitation
+energy. Very similar effects can be observed also in a different setup when the
+system is driven by multiple pulses of equal energy.",1606.08669v1
+2016-07-11,Triple-resonant Brillouin light scattering in magneto-optical cavities,"An enhancement in Brillouin light scattering of optical photons with magnons
+is demonstrated in magneto-optical whispering gallery mode resonators tuned to
+a triple resonance point. This occurs when both the input and output optical
+modes are resonant with those of the whispering gallery resonator, with a
+separation given by the ferromagnetic resonance (FMR) frequency. The
+identification and excitation of specific optical modes allows us to gain a
+clear understanding of the mode-matching conditions. A selection rule due to
+wavevector matching leads to an intrinsic single-sideband excitation. Strong
+suppression of one sideband is essential for one-to-one frequency mapping in
+coherent optical-to-microwave conversion.",1607.02985v2
+2016-07-11,Low loss spin wave resonances in organic-based ferrimagnet vanadium tetracyanoethylene thin films,"We experimentally demonstrate high quality factor spin wave resonances in an
+encapsulated thin film of the organic-based ferrimagnet vanadium
+tetracyanoethylene (V[TCNE]$_\textit{x~2}$) coated on an a-plane sapphire
+substrate by low temperature chemical vapor deposition. The thickness standing
+wave modes are observed in a broad frequency range (1 GHz ~ 5 GHz) with high
+quality factor exceeding 3,200 in ambient air at room temperature, rivaling
+those of inorganic magnetic materials. The exchange constant of
+V[TCNE]$_\textit{x~2}$, a crucial material parameter for future study and
+device design of the V[TCNE]$_\textit{x~2}$, is extracted from the measurement
+with a value of $(4.61\pm 0.35)\times 10^{-16} \mathrm{\: m^{2}}$. Our result
+establishes the feasibility of using organic-based materials for building
+hybrid magnonic devices and circuits.",1607.03041v2
+2016-07-19,Electrical detection of spiral spin structures in Pt|Cu_2OSeO_3 heterostructures,"The interaction between the itinerant spins in metals and localized spins in
+magnetic insulators thus far has only been explored in collinear spin systems,
+such as garnets. Here, we report the spin-Hall magnetoresistance (SMR)
+sensitive to the surface magnetization of the spin-spiral material, Cu_2OSeO_3.
+We experimentally demonstrate that the angular dependence of the SMR changes
+drastically at the transition between the helical spiral and the conical spiral
+phases. Furthermore, the sign and magnitude of the SMR in the conical spiral
+state are controlled by the cone angle. We show that this complex behaviour can
+be qualitatively explained within the SMR theory initially developed for
+collinear magnets. In addition, we studied the spin Seebeck effect (SSE), which
+is sensitive to the bulk magnetization. It originates from the conversion of
+thermally excited low-energy spin waves in the magnet, known as magnons, into
+the spin current in the adjacent metal contact (Pt). The SSE displays
+unconventional behavior where not only the magnitude but also the phase of the
+SSE vary with the applied magnetic field.",1607.05630v1
+2017-02-02,Parameterisation of non-collinear energy landscapes in itinerant magnets,"The magnetic force theorem provides convenient ways to study exchange
+interactions in magnetic systems. However, it is well known that short range
+interactions in itinerant magnetic systems are poorly described with the
+conventional use of the theorem and numerous strategies have been developed
+over the years to overcome this deficiency. In this study, we discuss this
+issue in the context of the frozen magnon method and find that a
+self-consistent approach is in general preferable. Moreover, an extended
+Heisenberg model is suggested in order to better describe finite deviations
+from the magnetic ground state and is shown through cross-validation to give a
+superior description of the interactions in non-collinear magnetic
+configurations compared to the regular Heisenberg model. The present study thus
+supplies a fully self-consistent method for systematic investigations of
+exchange interactions beyond the standard Heisenberg model. This may prove
+relevant to high-throughput computational materials science, e.g., in
+developing high moment materials for the magnetic storage industry.",1702.00599v3
+2017-02-08,Monte Carlo determination of the low-energy constants for a two-dimensional spin-1 Heisenberg model with spatial anisotropy,"The low-energy constants, namely the spin stiffness $\rho_s$, the staggered
+magnetization density ${\cal M}_s$ per area, and the spinwave velocity $c$ of
+the two-dimensional (2D) spin-1 Heisenberg model on the square and rectangular
+lattices are determined using the first principles Monte Carlo method. In
+particular, the studied models have antiferromagnetic couplings $J_1$ and $J_2$
+in the spatial 1- and 2-directions, respectively. For each considered
+$J_2/J_1$, the aspect ratio of the corresponding linear box sizes $L_2/L_1$
+used in the simulations is adjusted so that the squares of the two spatial
+winding numbers take the same values. In addition, the relevant finite-volume
+and -temperature predictions from magnon chiral perturbation theory are
+employed in extracting the numerical values of these low-energy constants. Our
+results of $\rho_{s1}$ are in quantitative agreement with those obtained by the
+series expansion method over a broad range of $J_2/J_1$. This in turn provides
+convincing numerical evidence for the quantitative correctness of our approach.
+The ${\cal M}_s$ and $c$ presented here for the spatially anisotropic models
+are new and can be used as benchmarks for future related studies.",1702.02436v1
+2017-02-13,Kagome-like chains with anisotropic ferromagnetic and antiferromagnetic interactions,"We consider a spin-$\frac{1}{2}$ kagome-like chain with competing ferro- and
+antiferromagnetic anisotropic exchange interactions. The ground state phase
+diagram of this model consists of the ferromagnetic and ferrimagnetic phases.
+We study the ground state and the low-temperature properties on the phase
+boundary between these phases. The ground state on this phase boundary is
+macroscopically degenerate and consists of localized magnon states. We
+calculate the ground state degeneracy and corresponding residual entropy. The
+spontaneous magnetization has a jump on the phase boundary confirming the
+first-order type of the phase transition. In the limit of a strong anisotropy
+the spectrum of the low-energy excitations has multi-scale structure governing
+the peculiar features of the specific heat behavior.",1702.03915v1
+2017-02-20,Parametric pumping of spin waves by acoustic waves,"The linear and nonlinear interactions between spin waves (magnons) and
+acoustic waves (phonons) in magnetostrictive materials provide an exciting
+opportunity for realizing novel microwave signal processing devices and
+spintronic circuits. Here we demonstrate the parametric pumping of spin waves
+by acoustic waves, the possibility of which has long been theoretically
+anticipated but never experimentally realized. Spin waves propagating in a thin
+film of yttrium iron garnet (YIG), a magnetostrictive ferrimagnet with low spin
+and acoustic wave damping, are pumped using an acoustic resonator driven at
+frequencies near twice the spin wave frequency. The observation of a
+counter-propagating idler wave and a distinct pump threshold that increases
+quadratically with frequency non-degeneracy are evidence of a nonlinear
+parametric pumping process consistent with classical theory. This demonstration
+of acoustic parametric pumping lays the groundwork for developing new
+spintronic and microwave signal processing devices based on amplification and
+manipulation of spin waves by efficient, spatially localized acoustic
+transducers.",1702.06038v1
+2017-03-02,On the nonlinear NMR and magnon BEC in antiferromagnetic materials with coupled electron-nuclear spin precession,"We present a new study of nonlinear NMR and Bose-Einstein Condensation (BEC)
+of nuclear spin waves in antiferromagnetic MnCO3 with coupled electron and
+nuclear spins. In particular, we show that the observed behaviour of NMR
+signals strongly contradicts the conventional description of paramagnetic
+ensembles of noninteracting spins based on the phenomenological Bloch
+equations. We present a new theoretical description of the coupled
+electron-nuclear spin precession, which takes into account an indirect
+relaxation of nuclear spins via the electron subsystem. We show that the
+magnitude of the nuclear magnetization is conserved for arbitrary large
+excitation powers, which is drastically different from the conventional heating
+scenario derived from the Bloch equations. This provides strong evidence that
+the coherent precession of macroscopic nuclear magnetization observed
+experimentally can be identified with BEC of nuclear spin waves with k=0.",1703.00614v2
+2017-03-06,"Spindynamics in the antiferromagnetic phases of the Dirac metals $A$MnBi$_2$ ($A=$ Sr, Ca)","The square Bi layers in $A$MnBi$_2$ ($A =$ Sr, Ca) host Dirac fermions which
+coexist with antiferromagnetic order on the Mn sublattice below $T_\mathrm{N} =
+290\,$K (Sr) and $270\,$K (Ca). We have measured the spin-wave dispersion in
+these materials by triple-axis neutron spectroscopy. The spectra show
+pronounced spin gaps of 10.2(2)$\,$meV (Sr) and 8.3(8)$\,$meV (Ca) and extend
+to a maximum energy transfer of 61 - 63$\,$meV. The observed spectra can be
+accurately reproduced by linear spin-wave theory from an Heisenberg effective
+spin Hamiltonian. Detailed global fits of the full magnon dispersion are used
+to determine the in-plane and inter-layer exchange parameters as well as on the
+magnetocrystalline anisotropy constant. To within experimental error we find no
+evidence that the magnetic dynamics are influenced by the Dirac fermions.",1703.01849v1
+2017-03-08,"Interplay of Dirac electrons and magnetism in AMnBi2 (A=Ca, Sr)","Dirac materials exhibit intriguing low-energy carrier dynamics that offer a
+fertile ground for novel physics discovery. Of particular interest is the
+interplay of Dirac carriers with other quantum phenomena, such as magnetism.
+Here we report on a two-magnon Raman scattering study of AMnBi2 (A=Ca, Sr), a
+prototypical magnetic Dirac system comprising alternating Dirac-carrier and
+magnetic layers. We present the first accurate determination of the exchange
+energies in these compounds and, by comparison to the reference compound
+BaMn2Bi2, we show that the Dirac-carrier layers in AMnBi2 significantly enhance
+the exchange coupling between the magnetic layers, which in turn drives a
+charge-gap opening along the Dirac locus. Our findings break new grounds in
+unveiling the fundamental physics of magnetic Dirac materials, which offer a
+novel platform for probing a distinct type of spin-Fermion interaction. The
+outstanding properties of these materials allow a delicate manipulation of the
+interaction between the Dirac carriers and magnetic moments, thus holding great
+promise for applications in magnetic Dirac devices.",1703.02712v1
+2017-03-08,Terahertz sum-frequency excitation of a Raman-active phonon,"In stimulated Raman scattering, two incident optical waves induce a force
+oscillating at the difference of the two light frequencies. This process has
+enabled important applications such as the excitation and coherent control of
+phonons and magnons by femtosecond laser pulses. Here, we experimentally and
+theoretically demonstrate the so far neglected up-conversion counterpart of
+this process: THz sum-frequency excitation of a Raman-active phonon mode, which
+is tantamount to two-photon absorption by an optical transition between two
+adjacent vibrational levels. Coherent control of an optical lattice vibration
+of diamond is achieved by an intense terahertz pulse whose spectrum is centered
+at half the phonon frequency of 40 THz. Remarkably, the carrier-envelope phase
+of the driving pulse is directly imprinted on the lattice vibration. New
+prospects in infrared spectroscopy, light storage schemes and lattice
+trajectory control in the electronic ground state emerge.",1703.02869v1
+2017-03-27,Anisotropic exchange and spin-wave damping in pure and electron-doped Sr$_2$IrO$_4$,"The collective magnetic excitations in the spin-orbit Mott insulator
+(Sr$_{1-x}$La$_x$)$_2$IrO$_4$ ($x=0,\,0.01,\,0.04,\, 0.1$) were investigated by
+means of resonant inelastic x-ray scattering. We report significant magnon
+energy gaps at both the crystallographic and antiferromagnetic zone centers at
+all doping levels, along with a remarkably pronounced momentum-dependent
+lifetime broadening. The spin-wave gap is accounted for by a significant
+anisotropy in the interactions between $J_\text{eff}=1/2$ isospins, thus
+marking the departure of Sr$_2$IrO$_4$ from the essentially isotropic
+Heisenberg model appropriate for the superconducting cuprates.",1703.09051v4
+2017-03-28,Temperature dependent magnetic damping of yttrium iron garnet spheres,"We investigate the temperature dependent microwave absorption spectrum of an
+yttrium iron garnet sphere as a function of temperature (5 K to 300 K) and
+frequency (3 GHz to 43.5 GHz). At temperatures above 100 K, the magnetic
+resonance linewidth increases linearly with temperature and shows a
+Gilbert-like linear frequency dependence. At lower temperatures, the
+temperature dependence of the resonance linewidth at constant external magnetic
+fields exhibits a characteristic peak which coincides with a non-Gilbert-like
+frequency dependence. The complete temperature and frequency evolution of the
+linewidth can be modeled by the phenomenology of slowly relaxing rare-earth
+impurities and either the Kasuya-LeCraw mechanism or the scattering with
+optical magnons. Furthermore, we extract the temperature dependence of the
+saturation magnetization, the magnetic anisotropy and the g-factor.",1703.09444v2
+2017-03-30,Thermal Transport in the Kitaev Model,"In conventional insulating magnets, heat is carried by magnons and phonons.
+In contrast, when the magnets harbor a quantum spin liquid state, emergent
+quasiparticles from the fractionalization of quantum spins can carry heat.
+Here, we investigate unconventional thermal transport yielded by such exotic
+carriers, in both longitudinal and transverse components, for the Kitaev model,
+whose ground state is exactly shown to be a quantum spin liquid with fractional
+excitations described as itinerant Majorana fermions and localized $Z_2$
+fluxes. We find that the longitudinal thermal conductivity exhibits a broad
+peak at very different temperatures between the zero and nonzero frequency
+components, reflecting the spin fractionalization. On the other hand, the
+transverse thermal conductivity induced by the magnetic field shows
+nonmonotonic temperature dependence, due to thermal excitations of the
+localized $Z_2$ fluxes. In the low-temperature limit, the temperature-linear
+coefficient rapidly approaches a quantized value, as expected from the
+topologically nontrivial nature of itinerant Majorana fermions. The
+characteristic behaviors provide experimentally-accessible evidences of
+fractional excitations in the proximity to Kitaev quantum spin liquid.",1703.10395v1
+2017-08-02,Realistic finite temperature simulations of magnetic systems using quantum statistics,"We have performed realistic atomistic simulations at finite temperatures
+using Monte Carlo and atomistic spin dynamics simulations incorporating quantum
+(Bose-Einstein) statistics. The description is much improved at low
+temperatures compared to classical (Boltzmann) statistics normally used in
+these kind of simulations, while at higher temperatures the classical
+statistics are recovered. This corrected low-temperature description is
+reflected in both magnetization and the magnetic specific heat, the latter
+allowing for improved modeling of the magnetic contribution to free energies. A
+central property in the method is the magnon density of states at finite
+temperatures and we have compared several different implementations for
+obtaining it. The method has no restrictions regarding chemical and magnetic
+order of the considered materials. This is demonstrated by applying the method
+to elemental ferromagnetic systems, including Fe and Ni, as well as Fe-Co
+random alloys and the ferrimagnetic system GdFe$_3$ .",1708.00709v1
+2017-08-05,Crystal growth with oxygen partial pressure of the $BaCuSi_2O_6$ and $Ba_{1-x}Sr_xCuSi_2O_6$ spin dimer compounds,"$BaCuSi_2O_6$ is a quasi-two dimensional spin dimer system and a model
+material for studying Bose-Einstein condensation (BEC) of magnons in high
+magnetic fields. The new $Ba_{1-x}Sr_xCuSi_2O_6$ mixed system, which can be
+grown with x < 0.3, and $BaCuSi_2O_6$, both grown by using a crystal growth
+method with enhanced oxygen partial pressure, have the same tetragonal
+structure ($I4_1/acd$) at room temperature. The mixed system shows no
+structural phase transition, so that the tetragonal structure is stable down to
+low temperatures. The oxygen partial pressure acts as control parameter for the
+growth process. A detailed understanding of the crystal structure depending on
+the oxygen content will enable the study of the spin dynamics of field-induced
+order states in this model magnetic compound of high current interest with only
+one type of dimer layers, which shows the same distance between the Cu atoms,
+in the structure.",1708.01739v1
+2017-08-05,Spin Injection and Detection via the Anomalous Spin Hall Effect in a Ferromagnetic Metal,"We report a novel spin injection and detection mechanism via the anomalous
+Hall effect in a ferromagnetic metal. The anomalous spin Hall effect (ASHE)
+refers to the transverse spin current generated within the ferromagnet. We
+utilize the ASHE and its reciprocal effect to electrically inject and detect
+magnons in a magnetic insulator in a non-local geometry. Our experiments reveal
+that permalloy can have a higher spin injection and detection efficiency to
+that of platinum, owing to the ASHE. We also demonstrate the tunability of the
+ASHE via the orientation of the permalloy magnetization, thus creating new
+possibilities for spintronic applications.",1708.01752v1
+2017-08-09,Weak localization of magnons in chiral magnets,"We report on the impact of the Dzyaloshinskii-Moriya interaction on the
+coherent backscattering of spin waves in a disordered magnetic material. This
+interaction breaks the inversion symmetry of the spin-wave dispersion relation,
+such that $\omega_\mathbf{k} = \omega_{2\mathbf{K}^\mathrm{I}-\mathbf{k}} \neq
+\omega_{-\mathbf{k}}$, where $\mathbf{K}^\mathrm{I}$ is related to the
+Dzyaloshinskii-Moriya vectors. As a result of numerical investigations we find
+that the backscattering peak of a wave packet with initial wave vector
+$\mathbf{k}_0$ shifts from $-\mathbf{k}_0$ to
+$2\mathbf{K}^\mathrm{I}-\mathbf{k}_0$, such that the backscattering wave vector
+and the initial wave vector are in general no longer antiparallel. The shifted
+coherence condition is explained by a diagrammatic approach and opens up an
+avenue to measure sign and magnitude of the Dzyaloshinskii-Moriya interaction
+in weakly disordered chiral magnets.",1708.02807v1
+2017-08-11,Goldstone-like phonon modes in a (111)-strained perovskite,"Goldstone modes are massless particles resulting from spontaneous symmetry
+breaking. Although such modes are found in elementary particle physics as well
+as in condensed matter systems like superfluid helium, superconductors and
+magnons - structural Goldstone modes are rare. Epitaxial strain in thin films
+can induce structures and properties not accessible in bulk and has been
+intensively studied for (001)-oriented perovskite oxides. Here we predict
+Goldstone-like phonon modes in (111)-strained SrMnO3 by first-principles
+calculations. Under compressive strain the coupling between two in-plane
+rotational instabilities give rise to a Mexican hat shaped energy surface
+characteristic of a Goldstone mode. Conversely, large tensile strain induces
+in-plane polar instabilities with no directional preference, giving rise to a
+continuous polar ground state. Such phonon modes with U(1) symmetry could
+emulate structural condensed matter Higgs modes. The mass of this Higgs boson,
+given by the shape of the Mexican hat energy surface, can be tuned by strain
+through proper choice of substrate.",1708.03490v1
+2017-08-30,Strain and Magnetic Field Induced Spin-Structure Transitions in Multiferroic BiFeO3,"The magnetic-field-dependent spin ordering of strained BiFeO3 films is
+determined using nuclear resonant scattering and Raman spectroscopy. The
+critical field required to destroy the cycloidal modulation of the Fe spins is
+found to be significantly lower than in the bulk, with appealing implications
+for field-controlled spintronic and magnonic devices.",1708.09183v1
+2018-02-01,Theory of spin and lattice wave dynamics excited by focused laser pulses,"We develop a theory of the spin wave dynamics excited by ultrafast focused
+laser pulses in a magnetic film. We take into account both volume and surface
+spin wave modes in the presence of applied, dipolar and magnetic anisotropy
+fields and include the dependence on laser spot exposure size and magnetic
+damping. We show that the sound waves generated by local heating by an
+ultrafast focused laser pulse can excite a wide spectrum of spin waves (on top
+of a dominant magnon-phonon contribution). Good agreement with recent
+experiments supports the validity of the model.",1802.00178v2
+2018-02-05,Cooper-Pair Spin Current in a Strontium Ruthenate Heterostructure,"It has been recognized that the condensation of spin-triplet Cooper pairs
+requires not only the broken gauge symmetry but also the spin ordering as well.
+One consequence of this is the possibility of the Cooper-pair spin current
+analogous to the magnon spin current in magnetic insulators, the analogy also
+extending to the existence of the Gilbert damping of the collective
+spin-triplet dynamics. The recently fabricated heterostructure of the thin film
+of the itinerant ferromagnet SrRuO3 on the bulk Sr2RuO4, the best-known
+candidate material for the spin-triplet superconductor, offers a promising
+platform for generating such spin current. We will show how such
+heterostructure allows us to not only realize the long-range spin valve but
+also electrically drive the collective spin mode of the spin-triplet order
+parameter. Our proposal represents both a new realization of the spin
+superfluidity and a transport signature of the spin-triplet superconductivity.",1802.01599v1
+2018-02-22,Dirac cones and mass terms in bosonic spectra,"The notion of Dirac cones, wherein two or more bands become degenerate at a
+certain momentum, is the starting point for the study of topological phases.
+Dirac cones have been thoroughly explored in fermionic systems such as
+graphene, Weyl semimetals, etc. The underlying mathematical structure in these
+systems is a Clifford algebra -- a rule for identifying sets of matrices that
+span the Hamiltonian. This structure allows for the identification of suitable
+`mass' terms to open band gaps. In this article, we extend these ideas to
+bosonic systems. Due to the pseudo-orthogonal nature of eigenvectors, the
+algebra of matrices takes a very different form. Taking the honeycomb XY
+ferromagnet as a prototype, we show that a Dirac cone emerges in the magnon
+spectrum. A gap can be opened by a suitable mass term involving next-nearest
+neighbour interactions. We next construct a one-dimensional ladder model with
+triplon excitations. Using the new Clifford algebra, we define winding number
+as a topological invariant. In analogy with the Su-Schrieffer-Heeger model,
+topological transitions occur when the band gap closes, leading to the
+appearance (or disappearance) of protected edge states. Our results suggest a
+new route to studying band touching and band topology in bosonic systems.",1802.08269v1
+2018-04-01,Dynamics of a single hole in the Heisenberg-Kitaev model: a self-consistent Born approximation study,"The magnetic properties of 4d and 5d transition-metal insulating compounds
+with the honeycomb structure are believed to be described by the
+Heisenberg-Kitaev model, which contains both the isotropic Heisenberg
+interaction J and anisotropic Kitaev interaction K. In this paper, to
+investigate the charge dynamics in these materials, we study the single-hole
+propagation of the t-J-K model in various magnetically ordered phases by the
+self-consistent Born approximation. We find that there are low-energy coherent
+quasiparticle (QP) excitations in all of these phases which appear firstly
+around the K point in the Brillouin zone (BZ), but the band-widths of these QPs
+are very small due to the hole-magnon coupling. Interestingly, in the zigzag
+phase relevant to recent experiments, though the QP weights are largely
+suppressed in the physical spectra in the first BZ, we find that they recover
+in the extended BZs. Moreover, our results reveal that the low-energy QP
+spectra are reduced with the increase of K.",1804.00265v1
+2018-04-01,The silver route to cuprate analogs,"The parent compound of high-Tc superconducting cuprates is a unique Mott
+state consisting of layers of spin-1/2 ions arranged on a square lattice and
+with a record high antiferromagnetic coupling within the layers. Compounds with
+similar characteristics have long been searched for. Nickelates and iridates
+had been proposed as cuprate analogs but so far have not reached a satisfactory
+similarity. Here we use a combination of experimental and theoretical tools to
+show that the commercial compound AgF2 is an excellent cuprate analog with
+remarkably similar electronic parameters to La2CuO4 but larger buckling of
+planes. Two-magnon Raman scattering reveals a superexchange constant which
+reaches 70% of that of a typical cuprate. We argue that structures that reduce
+or eliminate the buckling of the AgF2 planes could have an antiferromagnetic
+coupling that matches or surpasses the cuprates.",1804.00329v1
+2018-04-03,Selection rules for cavity-enhanced Brillouin light scattering from magnetostatic modes,"We experimentally identify the magnetostatic modes active for Brillouin light
+scattering in the optical whispering gallery modes of a yttrium iron garnet
+sphere. Each mode is identified by magnetic field dispersion of
+ferromagnetic-resonance spectroscopy and coupling strength to the known field
+distribution of the microwave drive antenna. Our optical measurements confirm
+recent predictions that higher-order magnetostatic modes can also generate
+optical scattering, according to the selection rules derived from the axial
+symmetry. From this we summarize the selection rules for Brillouin light
+scattering. We give experimental evidence that the optomagnonic coupling to
+non-uniform magnons can be higher than that of the uniform Kittel mode.",1804.00965v2
+2018-04-06,Quantum-impurity relaxometry of magnetization dynamics,"Prototypes of quantum impurities (QI), such as NV and SiV centers in diamond,
+have been recently growing in popularity due to their minimally invasive and
+high-resolution magnetic field sensing. Here, we focus on quantum-impurity
+relaxometry as a method to probe collective excitations in magnetic insulators.
+We develop a general framework that relates the experimentally-measurable
+quantum-impurity relaxation rates to the properties of a magnetic system via
+the noise emitted by the latter. We suggest that, when the quantum-impurity
+frequency lies within the spin-wave gap, quantum-impurity relaxometry can be
+effectively deployed to detect signatures of the coherent spin dynamics, such
+as magnon condensation, both in ferromagnetic and antiferromagnetic systems, as
+well as open prospects to nonintrusively probe spin-wave transport regimes in
+magnetic insulators.",1804.02417v1
+2018-04-09,General method for atomistic spin-lattice dynamics with first principles accuracy,"We present a computationally efficient general first-principles based method
+for spin-lattice simulations for solids. Our method is based on a combination
+of atomistic spin dynamics and molecular dynamics, expressed through a
+spin-lattice Hamiltonian where the bilinear magnetic term is expanded to second
+order in displacement, and all parameters are computed using density functional
+theory. The effect of first-order spin-lattice coupling on the magnon and
+phonon dispersion in bcc Fe is reported as an example, and is seen to be in
+good agreement with previous simulations performed with an empirical potential
+approach. In addition, we also illustrate the abilities of our method on a more
+conceptual level, by exploring dissipation-free spin and lattice motion in
+small magnetic clusters (a dimer, trimer and quadmer). Our method opens the
+door for quantitative description and understanding of the microscopic origin
+of many fundamental phenomena of contemporary interest, such as ultrafast
+demagnetization, magnetocalorics, and spincaloritronics.",1804.03119v2
+2018-11-05,Quantum spin liquid at finite temperature: proximate dynamics and persistent typicality,"Quantum spin liquids are long-range entangled states of matter with emergent
+gauge fields and fractionalized excitations. While candidate materials, such as
+the Kitaev honeycomb ruthenate $\alpha$-RuCl$_3$, show magnetic order at low
+temperatures $T$, here we demonstrate numerically a dynamical crossover from
+magnon-like behavior at low $T$ and frequencies $\omega$ to long-lived
+fractionalized fermionic quasiparticles at higher $T$ and $\omega$. This
+crossover is akin to the presence of spinon continua in quasi-1D spin chains.
+It is further shown to go hand in hand with persistent typicality down to very
+low $T$. This aspect, which has also been observed in the spin-1/2 kagome
+Heisenberg antiferromagnet, is a signature of proximate spin liquidity and
+emergent gauge degrees of freedom more generally, and can be the basis for the
+numerical study of many finite-$T$ properties of putative spin liquids.",1811.01671v2
+2010-05-06,A contractor-renormalization study of Hubbard plaquette clusters,"We implement the contractor-renormalization method to study the checkerboard
+Hubbard model on various finite-size clusters as function of the
+inter-plaquette hopping t' and the on-site repulsion U at low hole doping. We
+find that the pair-binding energy and the spin gap exhibit a pronounced maximum
+at intermediate values of t' and U, thus indicating that moderate inhomogeneity
+of the type considered here substantially enhances the formation of hole pairs.
+The rise of the pair-binding energy for t'<t'_max is kinetic-energy driven and
+reflects the strong resonating valence bond correlations in the ground state
+that facilitate the motion of bound pairs as compared to single holes.
+Conversely, as t' is increased beyond t'_max antiferromagnetic magnons
+proliferate and reduce the potential energy of unpaired holes and with it the
+pairing strength. For the periodic clusters that we study the estimated phase
+ordering temperature at t'=t'_max is a factor of 2-7 smaller than the pairing
+temperature.",1005.0978v2
+2010-04-20,Wide-range wavevector selectivity of magnon gases in Brillouin light scattering spectroscopy,"Brillouin light scattering spectroscopy is a powerful technique for the study
+of fast magnetization dynamics with both frequency- and wavevector resolution.
+Here, we report on a distinct improvement of this spectroscopic technique
+towards two-dimensional wide-range wavevector selectivity in a backward
+scattering geometry. Spin-wave wavevectors oriented perpendicular to the bias
+magnetic field are investigated by tilting the sample within the magnet gap.
+Wavevectors which are oriented parallel to the applied magnetic field are
+analyzed by turning the entire setup, including the magnet system. The setup
+features a wide selectivity of wavevectors up to 2.04\cdot 10E5 rad/cm for both
+orientations, and allows selecting and measuring wavevectors of dipole- and
+exchange-dominated spin waves of any orientation to the magnetization
+simultaneously.",1005.5084v1
+2010-05-28,The Kondo-lattice state and non-Fermi-liquid behavior in the presence of Van Hove singularities,"A scaling consideration of the Kondo lattices is performed with account of
+logarithmic Van Hove singularities (VHS) in the electron density of states. The
+scaling trajectories are presented for different magnetic phases. It is
+demonstrated that VHS lead to a considerable increase of the non-Fermi-liquid
+behavior region owing to softening of magnon branches during the
+renormalization process. Although the effective coupling constant remains
+moderate, renormalized magnetic moment and spin-fluctuation frequency can
+decrease by several orders of magnitude. A possible application to f-systems
+and weak itinerant magnets is discussed.",1005.5248v3
+2010-05-30,Quasi-1d quantum helimagnets: The fate of multipolar phases,"Coupled frustrated spin-1/2 chains in high magnetic fields described within
+the ferro- antiferromagnetic J1-J2 Heisenberg model are studied by the DMRG,
+the hard core boson, and the spin wave theory approaches. Multipolar phases
+related to magnon bound states are destroyed (supported) by weak
+antiferromagnetic (ferromagnetic) interchain couplings Jic. We show that
+quantum spin nematics might be found for LiVCuO4 whereas for Li(Na)Cu2O2 it is
+prevented by a sizeable antiferromagnetic Jic. Also for Li2ZrCuO4 with a small
+antiferromagnetic Jic expected triatic or quartic phases are unlikely, too. The
+saturation field is found to be strongly affected even by a relatively small
+Jic.",1005.5500v2
+2013-08-01,Resonant X-ray scattering and the $j_{\mathrm{eff}}=1/2$ electronic ground state in iridate perovskites,"The resonant X-ray scattering (magnetic elastic, RXMS, and inelastic, RIXS)
+of Ir$^{4+}$ at the L$_{2,3}$ edges relevant to spin-orbit Mott insulators
+A$_{n+1}$Ir$_{n}$O$_{3n+1}$ (A=Sr, Ba, etc.) are calculated using a single-ion
+model which treats the spin-orbit and tetragonal crystal-field terms on an
+equal footing. Both RXMS and RIXS in the spin-flip channel are found to display
+a non-trivial dependence on the direction of the magnetic moment,
+$\boldsymbol\mu$. Crucially, we show that for $\boldsymbol\mu$ in the
+\emph{ab}-plane, RXMS at the L$_2$ edge is zero \emph{irrespective} of the
+tetragonal crystal-field; spin-flip RIXS, relevant to measurements of magnons,
+behaves reciprocally being zero at L$_2$ when $\boldsymbol\mu$ is perpendicular
+to the \emph{ab}-plane. Our results provide important insights into the
+interpretation of X-ray data from the iridates, including that a
+$j_{\mathrm{eff}}=1/2$ ground state cannot be assigned on the basis of
+L$_2$/L$_3$ intensity ratio alone.",1308.0128v1
+2013-08-10,Dynamics of an Insulating Skyrmion under a Temperature Gradient,"We study the Skyrmion dynamics in thin films under a temperature gradient.
+Our numerical simulations show that both single and multiple Skyrmions in a
+crystal move towards the high temperature region, which is contrary to particle
+diffusion. Noticing a similar effect in the domain wall motion, we employ a
+theory based on magnon dynamics to explain this counterintuitive phenomenon.
+Unlike the temperature driven domain wall motion, the Skyrmion's topological
+charge plays an important role, and a transverse Skyrmion motion is observed.
+Our theory turns out to be in agreement with numerical simulations, both
+qualitatively and quantitatively. Our calculation indicated that a very
+promising Skyrmion dynamic phenomenon can be observed in experiments.",1308.2343v1
+2013-08-23,Impact of eddy currents on the dispersion relation of surface spin waves in thin conducting magnetic films,"We propose a rigorous solution to a long-standing problem of the impact of
+eddy currents on the dispersion relation of surface spin waves propagating in
+thin conducting magnetic films. Our results confirm the prediction of the
+Almeida-Mill's exchange-free theory that the inclusion of the eddy current
+contribution results in a deviation of the dispersion curve for the fundamental
+mode from the Damon-Eshbach law and a substantial linewidth broadening in a
+large wave vector range. We show that the decrease in the spin wave frequency
+is due to an increase in the in-plane component of the dynamic magnetic field
+within the conducting film. The decrease in the frequency is accompanied by a
+drastic change in the asymmetry of the modal profiles for the waves. This
+effect is not observable in magneto-insulating films and therefore it is
+unambiguously attributed to eddy currents that appear in conducting films only.
+We also show that the wave vector range in which eddy currents affect the
+dispersion curve is strongly correlated with the value of the film
+conductivity. This result holds for conducting films with the thickness 10-100
+nm, which are considered promising for future magnonic and spintronic
+applications.",1308.5040v1
+2013-08-27,Soft confinement in a 3-d spin system,"We consider a 1+3 dimensional spin system. The spin-wave (magnon) field is
+described by the O(3) non-linear sigma model with a symmetry-breaking
+potential. This interacts with a slow spin SU(2) doublet Schrodinger fermion.
+The interaction is described by a generalized nonperturbative Yukawa coupling,
+and the self-consistency condition is solved with the aid of a non-relativistic
+Gribov equation. When the Yukawa coupling is sufficiently strong, the solution
+exhibits supercriticality and soft confinement, in a way that is quite
+analogous to Gribov's light-quark confinement theory.
+  The solution corresponds to a new type of spin polaron, whose condensation
+may lead to exotic superconductivity.",1308.5731v1
+2014-03-04,One dimensional zone center phonons in $O_{h}$ space group,"Motivated by experiments, we performed a systematic study on the one
+dimensional zone center phonons in $O_{h}$ space groups. All the one
+dimensional phonon modes for different Wyckoff positions are tabulated. We show
+that at least four (inequivalent) atoms (in one set of Wyckoff positions) are
+needed to carry a single one dimensional phonon. A general restriction rule on
+the number of atoms and the number of one dimensional phonons is obtained. The
+same restriction applies to phonons of all cubic crystal systems ($T$, $T_{h}$,
+$T_{d}$, $O$, $O_{h}$) and to magnons for crystals whose unitary symmetry
+elements are in ($T$, $T_{h}$, $T_{d}$, $O$, $O_{h}$). Crystals with $A15$
+structure are found to satisfy experimental requirements (to have a
+$\Gamma_{2}^{+}$ phonon) while most crystals of $O_{h}$ space groups do not.
+$A15$ is also used to demonstrate the rules we found regarding the phonon
+structure in $O_{h}$ space groups.",1403.0672v1
+2014-03-07,Symplectic Deformations of Integrable Field Theories and AdS/CFT,"Relativistic integrable field theories like the sine-Gordon equation have an
+infinite set of conserved charges. In a light-front formalism these conserved
+charges are closely related to the integrable modified KdV hierarchy at the
+classical level. The latter hierarchy admits a family of symplectic structures
+which we argue can be viewed as deformations of the relativistic sine-Gordon
+symplectic structure. These deformed theories are integrable but no longer
+relativistic and the basic excitations of the theory, the solitons, have an
+interesting non-relativistic dispersion relation that in a certain limit
+becomes the dispersion relation of dyonic giant magnons of string theory in the
+AdS/CFT correspondence. We argue that the deformed classical theories can be
+lifted to quantum theories when the sine-Gordon theory is embedded in a larger
+theory that describes the string world-sheet sigma model in AdS(5)xS(5).",1403.1899v1
+2014-03-17,Entangled tetrahedron ground state and excitations of the magneto-electric skyrmion material Cu$_2$OSeO$_3$,"The strongly correlated cuprate Cu$_2$OSeO$_3$ has recently been identified
+as the first insulating system exhibiting a skyrmion lattice phase. Using a
+microscopic multi-boson theory for its magnetic ground state and excitations,
+we establish the presence of two distinct types of modes: a low energy manifold
+that includes a gapless Goldstone mode and a set of weakly dispersive
+high-energy magnons. These spectral features are the most direct signatures of
+the fact that the essential magnetic building blocks of Cu$_2$OSeO$_3$ are not
+individual Cu spins, but rather weakly-coupled Cu$_4$ tetrahedra. Several of
+the calculated excitation energies are in nearly perfect agreement with
+reported Raman and far-infrared absorption data, while the magneto-electric
+effect determined within the present quantum-mechanical framework is also fully
+consistent with experiments, giving strong evidence in the entangled Cu$_4$
+tetrahedra picture of Cu$_2$OSeO$_3$. The predicted dispersions along with the
+dynamical dipole and quadrupole spin structure factors call for further
+experimental tests of this picture.",1403.4081v2
+2014-03-18,All-loop worldsheet S matrix for AdS_3 x S^3 x T^4,"We obtain the all-loop worldsheet S matrix for fundamental excitations on
+AdS_3 x S^3 x T^4 by studying the off-shell symmetry algebra of the superspace
+action in lightcone gauge. The massless modes, unaccounted for in earlier
+works, are automatically included in our treatment. Their exact dispersion
+relation is found to be non-relativistic, of giant-magnon form and their
+scattering is naturally well-defined. This opens the way to a complete
+investigation of AdS_3/CFT_2 integrability.",1403.4543v2
+2014-03-24,On the exact spectrum and mirror duality of the (AdS_5 x S^5)_eta superstring,"We discuss the spectrum of a string propagating on eta-deformed AdS_5 x S^5
+by treating its world-sheet theory as an integrable quantum field theory. The
+exact S-matrix of this field theory is given by a q-deformation of the AdS_5 x
+S^5 world-sheet S-matrix with real deformation parameter. By considering mirror
+(double Wick-rotated) versions of these world-sheet theories we give the
+Thermodynamic Bethe Ansatz description of their exact finite size spectra.
+Interestingly, this class of models maps onto itself under the mirror
+transformation. At the level of the string this appears to say that the
+light-cone worldsheet theories of strings on particular pairs of backgrounds
+are related by a double Wick rotation, a feature we call 'mirror duality'. We
+provide a partial check of these statements at the level of the sigma model by
+considering reduced actions and their corresponding (mirror) giant magnon
+solutions.",1403.6104v2
+2016-12-31,First-Principles Study of Exchange Interactions of Yttrium Iron Garnet,"Yttrium Iron Garnet is the ubiquitous magnetic insulator used for studying
+pure spin currents. The exchange constants reported in the literature vary
+considerably between different experiments and fitting procedures. Here we
+calculate them from first-principles. The local Coulomb correction (U - J) of
+density functional theory is chosen such that the parameterized spin model
+reproduces the experimental Curie temperature and a large electronic band gap,
+ensuring an insulating phase. The magnon spectrum calculated with our
+parameters agrees reasonably well with that measured by neutron scattering. A
+residual disagreement about the frequencies of optical modes indicates the
+limits of the present methodology.",1701.00110v1
+2017-01-19,Terahertz Dielectric Analysis and Spin-Phonon Coupling in Multiferroic GeV$_4$S$_8$,"We present an investigation of the multiferroic lacunar spinel compound
+GeV$_4$S$_8$ using time-domain terahertz spectroscopy. We find three
+absorptions which either appear or shift at the antiferromagnetic transition
+temperature, T$_N = 17$ K, as S=1 magnetic moments develop on vanadium
+tetrahedra. Two of these absorptions are coupled to the magnetic state and one
+only appears below the N\'{e}el temperature, and is interpreted as a magnon. We
+also observe isosbestic points in the dielectric constant in both the
+temperature and frequency domains. Further, we perform analysis on the
+isosbestic features to reveal an interesting collapse into a single curve as a
+function of both frequency and temperature, behavior which exists throughout
+the phase transitions. This analysis suggests the importance of spectral
+changes in the terahertz range which are linear in frequency and temperature.",1701.05539v2
+2017-01-25,Stable high-temperature paramagnons in a three-dimensional antiferromagnet near quantum criticality: Application to TlCuCl$_3$,"The complete set of hallmarks of the three-dimensional antiferromagnet near
+the quantum critical point has been recently observed in the spin dimer
+compound TlCuCl$_3$. Nonetheless, the mechanism, responsible for several
+distinct features of the experimental data, has remained a puzzle, namely: (i)
+the paramagnons exhibit remarkable robustness to thermal damping and are stable
+up to high temperatures, where $k_B T$ is comparable with the excitation
+energy, (ii) the width to mass ratios of the high-temperature paramagnons are,
+within the error bars, equal to that of the low-temperature amplitude (or
+Higgs) mode. We propose such a mechanism and identify two principal factors,
+contributing to the scaling between width to mass ratios of the paramagnon and
+the amplitude mode: (i) the emergence of the thermal mass scale reorganizing
+the paramagnon decay processes, and (ii) substantial renormalization of the
+multi-magnon interactions by thermal fluctuations. The study is carried out for
+the general case of a $D= 3 + 1$ quantum antiferromagnet within the framework
+of the $\varphi^4$ model using the hybrid Callan-Symanzik + Wilson thermal
+renormalization group method. Our approach is tested by demonstrating a good
+quantitative agreement with available experimental data across the phase
+diagram of TlCuCl$_3$.",1701.07406v1
+2017-01-30,Quantum transition between magnetically ordered and Mott glass phases,"We discuss a quantum transition from a superfluid to a Mott glass phases in
+disordered Bose-systems by the example of an isotropic spin-$\frac12$
+antiferromagnet with spatial dimension $d\ge2$ and with disorder in tunable
+exchange couplings. Our analytical consideration is based on general properties
+of a system in critical regime, on the assumption that the magnetically order
+part of the system shows fractal properties near the transition, and on a
+hydrodynamic description of long-wavelength magnons in the magnetically ordered
+(""superfluide"") phase. Our results are fully consistent with a scaling theory
+based on an ansatz for the free energy proposed by M.P. Fisher et al. (Phys.
+Rev. B 40, 546 (1989)). We obtain $z=d-\beta/\nu$ for the dynamical critical
+exponent and $\phi = z\nu$, where $\phi$, $\beta$, and $\nu$ are critical
+exponents of the critical temperature, the order parameter, and the correlation
+length, respectively. The density of states of localized excitations (fractons)
+is found to show a superuniversal (i.e., independent of $d$) behavior.",1701.08624v2
+2017-01-27,A unified description of collective magnetic excitations,"In this work, we define a set of analytic tools to describe the dynamic
+response of the magnetization to small perturbations, which can be used on its
+own or in combination with micromagnetic simulations and does not require
+saturation. We present a general analytic description of the ferromagnetic high
+frequency susceptibility tensor to describe angular as well as frequency
+dependent ferromagnetic resonance spectra and account for asymmetries in the
+line shape. Furthermore, we expand this model to reciprocal space and show how
+it describes the magnon dispersion. Finally we suggest a trajectory dependent
+solving tool to describe the equilibrium states of the magnetization.",1701.09078v2
+2018-05-04,Spin wave effects in transport between a ferromagnet and a Weyl semimetal surface,"We experimentally investigate spin-polarized transport between a
+ferromagnetic Ni electrode and a surface of Weyl semimetal, realized in a thick
+WTe$_2$ single crystal. For highly-transparent Ni-WTe$_2$ planar junctions, we
+observe non-Ohmic $dV/dI(I)$ behavior with an overall increase of differential
+resistance $dV/dI$ with current bias, which is accomplished by current-induced
+switchings. This behavior is inconsistent with trivial interface scattering,
+but it is well known for spin-polarized transport with magnon emission. Thus,
+we interpret the experimental results in terms of spin wave excitation in spin
+textures in the WTe$_2$ topological surface states, which is supported by the
+obtained magnetic field and temperature $dV/dI(I)$ dependencies.",1805.01838v2
+2018-04-25,Evolution of the magnetic excitations in NaOsO$_3$ through its metal-insulator transition,"The temperature dependence of the excitation spectrum in NaOsO$_{\text{3}}$
+through its metal-to-insulator transition (MIT) at 410 K has been investigated
+using resonant inelastic X-ray scattering (RIXS) at the Os L$_{\text{3}}$ edge.
+High resolution ($\Delta E \sim$ 56 meV) measurements show that the
+well-defined, low energy magnons in the insulating state weaken and dampen upon
+approaching the metallic state. Concomitantly, a broad continuum of excitations
+develops which is well described by the magnetic fluctuations of a nearly
+antiferromagnetic Fermi liquid. By revealing the continuous evolution of the
+magnetic quasiparticle spectrum as it changes its character from itinerant to
+localized, our results provide unprecedented insight into the nature of the MIT
+in NaOsO$_{\text{3}}$.",1805.03176v1
+2018-05-09,Nature of the Magnetic Interactions in Sr$_3$NiIrO$_6$,"Iridates abound with interesting magnetic behaviours because of their strong
+spin-orbit coupling. Sr$_3$NiIrO$_6$ brings together the spin-orbital
+entanglement of the Ir$^{4+}$ ion with a 3$d$ Ni cation and a one-dimensional
+crystal structure. It has a ferrimagnetic ground state with a 55 T coercive
+field. We perform a theoretical study of the magnetic interactions in this
+compound, and elucidate the role of anisotropic symmetric exchange as the
+source of its strong magnetic anisotropy. Our first-principles calculations
+reproduce the magnon spectra of this compound and predict a signature in the
+cross sections that can differentiate the anisotropic exchange from single-ion
+anisotopy.",1805.03733v2
+2018-05-10,Anomalous spin Hall magnetoresistance in Pt/Co bilayers,"We have studied the spin Hall magnetoresistance (SMR), the magnetoresistance
+within the plane transverse to the current flow, of Pt/Co bilayers. We find
+that the SMR increases with increasing Co thickness: the effective spin Hall
+angle for bilayers with thick Co exceeds the reported values of Pt when a
+conventional drift-diffusion model is used. An extended model including spin
+transport within the Co layer cannot account for the large SMR. To identify its
+origin, contributions from other sources are studied. For most bilayers, the
+SMR increases with decreasing temperature and increasing magnetic field,
+indicating that magnon-related effects in the Co layer play little role.
+Without the Pt layer, we do not observe the large SMR found for the Pt/Co
+bilayers with thick Co. Implementing the effect of the so-called interface
+magnetoresistance and the textured induced anisotropic scattering cannot
+account for the Co thickness dependent SMR. Since the large SMR is present for
+W/Co but its magnitude reduces in W/CoFeB, we infer its origin is associated
+with a particular property of Co.",1805.03843v1
+2018-05-10,New Compact Construction of Eigenstates for Supersymmetric Spin Chains,"The problem of separation of variables (SoV) in supersymmetric spin chains is
+closely related to the calculation of correlation functions in N=4 SYM theory
+which is integrable in the planar limit. To address this question we find a
+compact formula for the spin chain eigenstates, which does not have any sums
+over auxiliary roots one usually gets in the widely adopted nested Bethe
+ansatz. Our construction only involves one application of a simple Bg(u_k)
+operator to the reference state for each of the magnons, in complete analogy
+with the su(2) algebraic Bethe ansatz. This generalizes our SoV based
+construction for su(n) to the supersymmetric su(1|2) case.",1805.03927v2
+2018-05-21,Spin nematics next to spin singlets,"We provide a route to generate nematic order in a spin-1/2 system. Unlike the
+well-known magnon-binding mechanism, our spin nematics requires neigher the
+frustration effect nor a spin polarization in a high field or in the vicinity
+of a ferromagnet, but instead appears next to the spin singlet phase. We start
+from a state consisting of a quantum spin-1/2 singlet dimer placed on each site
+of a triangular lattice, and show that inter-dimer ring exchange interactions
+efficiently dope the SU(2) triplets that itinerate and interact, easily driving
+a stable singlet state to either Bose Einstein condensates or a triplet
+crystal, some hosting a spin nematic order. A variety of roles the ring
+exchange serves include the generation of a bilinear-biquadratic interaction
+between nearby triplets, which is responsible for the emergent nematic order
+separated from the singlet phase by a first order transition.",1805.07910v1
+2018-05-21,Spectral properties of the square-lattice antiferromagnetic J1-J2 Heisenberg model: confinement and deconfinement of spinons,"Based on the mapping between $s=1/2$ spin operators and hard-core bosons, we
+extend the cluster perturbation theory to spin systems and study the whole
+excitation spectrum of the antiferromagnetic $J_{1}$-$J_{2}$ Heisenberg model
+on the square lattice. In the N\'eel phase for $J_{2}\lesssim0.4J_{1}$, in
+addition to the dominant magnon excitation, there is an obvious continuum close
+to $(\pi,0)$ in the Brillouin zone indicating the deconfined spin-1/2 spinon
+excitations. In the stripe phase for $J_{2}\gtrsim0.6J_{1}$, we find similar
+high-energy two-spinon continuums at $(\pi/2,\pi/2)$ and $(\pi/2,\pi)$,
+respectively. The intermediate phase is characterized by a spectrum with
+completely deconfined broad continuum, which is attributed to a $Z_{2}$ quantum
+spin liquid with the aid of a variational-Monte-Carlo analysis.",1805.07915v1
+2018-05-29,Efficient injection and detection of out-of-plane spins via the anomalous spin Hall effect in permalloy nanowires,"We report a novel mechanism for the electrical injection and detection of
+out-of-plane spin accumulation via the anomalous spin Hall effect (ASHE), where
+the direction of the spin accumulation can be controlled by manipulating the
+magnetization of the ferromagnet. This mechanism is distinct from the spin Hall
+effect (SHE), where the spin accumulation is created along a fixed direction
+parallel to an interface. We demonstrate this unique property of the ASHE in
+nanowires made of permalloy (Py), to inject and detect out-of-plane spin
+accumulation in a magnetic insulator, yttrium iron garnet (YIG). We show that
+the efficiency for the injection/detection of out-of-plane spins can be up to
+50% of that of in-plane spins. We further report the possibility to detect spin
+currents parallel to the Py/YIG interface for spins fully oriented in the
+out-of-plane direction, resulting in a sign reversal of the non-local magnon
+spin signal. The new mechanisms that we have demonstrated are highly relevant
+for spin torque devices and applications.",1805.11575v1
+2008-07-03,Finite-size effects of Membranes on AdS_4 x S_7,"We consider semi-classical solution of membranes on the AdS_4 x S^7. This is
+supposed to be dual to the N=6 super Chern-Simons theory with k=1 in a planar
+limit recently proposed by Aharony, Bergmann, Jafferis, and Maldacena (ABJM).
+We have identified giant magnon and single spike states on the membrane by
+reducing them to the Neumamm - Rosochatius integrable system. We also connect
+these to the complex sine-Gordon integrable model. Based on this approach, we
+find finite-size membrane solutions and obtain their images in the complex
+sine-Gordon system along with the leading finite-size corrections to the
+energy-charge relations.",0807.0566v2
+2008-07-11,Dynamical vertex approximation -- an introduction,"We give an elementary introduction to a recent diagrammatic extension of
+dynamical mean field theory (DMFT) coined dynamical vertex approximation
+(D$\Gamma$A). This approach contains the important local correlations of DMFT,
+giving, among others, rise to quasiparticle renormalizations, Mott-Hubbard
+transitions and magnetism, but also non-local correlations beyond. The latter
+are at the very essence of many physical phenomena in strongly correlated
+elecectron systems. As correlations are treated equally on all length scales,
+D$\Gamma$A allows us to describe physical phenomena such as magnons, quantum
+criticality, and the interplay between antiferromagnetism and
+superconductivity. We review results hitherto obtained for the Hubbard model in
+dimensions d=3, 2, and 1.",0807.1860v1
+2008-07-16,Spin currents and spin superfluidity,"The present review analyzes and compares various types of dissipationless
+spin transport: (1) Superfluid transport, when the spin-current state is a
+metastable state (a local but not the absolute minimum in the parameter space).
+(2) Ballistic spin transport, when spin is transported without losses simply
+because sources of dissipation are very weak. (3) Equilibrium spin currents,
+i.e., genuine persistent currents. (4) Spin currents in the spin Hall effect.
+Since superfluidity is frequently connected with Bose condensation, recent
+debates about magnon Bose condensation are also reviewed. For any type of spin
+currents simplest models were chosen for discussion in order to concentrate on
+concepts rather than details of numerous models. The various hurdles on the way
+of using the concept of spin current (absence of the spin-conservation law,
+ambiguity of spin current definition, etc.) were analyzed. The final conclusion
+is that the spin-current concept can be developed in a fully consistent manner,
+and is a useful language for description of various phenomena in spin dynamics.",0807.2524v3
+2008-07-29,Effect of magnesium doping on the orbital and magnetic order in LiNiO2,"In LiNiO2, the Ni3+ ions, with S=1/2 and twofold orbital degeneracy, are
+arranged on a trian- gular lattice. Using muon spin relaxation (MuSR) and
+electron spin resonance (ESR), we show that magnesium doping does not stabilize
+any magnetic or orbital order, despite the absence of interplane Ni2+. A
+disordered, slowly fluctuating state develops below 12 K. In addition, we find
+that magnons are excited on the time scale of the ESR experiment. At the same
+time, a g factor anisotropy is observed, in agreement with $| 3z^{2}-r^{2}>$
+orbital occupancy.",0807.4651v1
+2008-07-30,Efficient precision quantization in AdS/CFT,"Understanding finite-size effects is one of the key open questions in solving
+planar AdS/CFT. In this paper we discuss these effects in the AdS_5xS^5 string
+theory at one-loop in the world-sheet coupling. First we provide a very
+general, efficient way to compute the fluctuation frequencies, which allows to
+determine the energy shift for very general multi-cut solutions. Then we apply
+this to two-cut solutions, in particular the giant magnon and determine the
+finite-size corrections at subleading order. The latter are then compared to
+the finite-size corrections from Luscher-Klassen-Melzer formulas and found to
+be in perfect agreement.",0807.4752v2
+2009-12-08,Bound states in two-dimensional spin systems near the Ising limit: A quantum finite-lattice study,"We analyze the properties of low-energy bound states in the transverse-field
+Ising model and in the XXZ model on the square lattice. To this end, we develop
+an optimized implementation of perturbative continuous unitary transformations.
+The Ising model is studied in the small-field limit which is found to be a
+special case of the toric code model in a magnetic field. To analyze the XXZ
+model, we perform a perturbative expansion about the Ising limit in order to
+discuss the fate of the elementary magnon excitations when approaching the
+Heisenberg point.",0912.1463v2
+2009-12-17,Anomalous dimensions at four loops in N=6 superconformal Chern-Simons theories,"In arXiv:0908.2463 we computed the four-loop correction to a function
+depending on the 't Hooft coupling(s) that appears in the magnon dispersion
+relation of the spin chains derived from single trace operators in N=6
+superconformal Chern-Simons theories. In this paper we give detailed
+descriptions of this calculation and the computation of the four-loop wrapping
+corrections for a length four operator in the 20 of SU(4), the R-symmetry group
+for these theories. Here, we give all relevant Feynman diagrams and loop
+integrals explicitly, and also demonstrate the cancellation of double poles in
+the logarithm of the renormalization constant.",0912.3460v2
+2011-11-08,Analysis of the Collective Behavior of a 10 by 10 Array of Fe3O4 Dots in a Large Micromagnetic Simulation,"We report a full (3D) micromagnetic simulation of a set of 100 ferrite
+(Fe$_3$O$_4$) cylindrical dots, arranged in a 10 by 10 square (planar) array of
+side 3.27 $\mu$m, excited by an external in-plane magnetic field. The resulting
+power spectrum of magnetic excitations and the dynamical magnetization field at
+the resulting resonance modes were investigated. The absorption spectrum
+deviates considerably from that of a single particle reference simulation,
+presenting a mode-shifting and splitting effect. We found an inversion symmetry
+through the center of the array, in the sense that each particle and its
+inversion counterpart share approximately the same magnetization mode behavior.
+Magnonic designs aiming at synchronous or coherent tunings of spin-wave
+excitations at given spatially separated points within a regular square array
+may benefit from the new effects here described.",1111.1866v1
+2011-11-08,Time-dependent spin-wave theory,"We generalize the spin-wave expansion in powers of the inverse spin to
+time-dependent quantum spin models describing rotating magnets or magnets in
+time-dependent external fields. We show that in these cases, the spin operators
+should be projected onto properly defined rotating reference frames before the
+spin components are bosonized using the Holstein-Primakoff transformation. As a
+first application of our approach, we calculate the reorganization of the
+magnetic state due to Bose-Einstein condensation of magnons in the magnetic
+insulator yttrium-iron garnet; we predict a characteristic dip in the
+magnetization which should be measurable in experiments.",1111.2052v2
+2011-11-09,Propagating two-dimensional magnetic droplets,"Propagating, solitary magnetic wave solutions of the Landau-Lifshitz equation
+with uniaxial, easy-axis anisotropy in thin (two-dimensional) magnetic films
+are investigated. These localized, nontopological wave structures, parametrized
+by their precessional frequency and propagation speed, extend the stationary,
+coherently precessing ""magnon droplet"" to the moving frame, a non-trivial
+generalization due to the lack of Galilean invariance. Propagating droplets
+move on a spin wave background with a nonlinear droplet dispersion relation
+that yields a limited range of allowable droplet speeds and frequencies. An
+iterative numerical technique is used to compute the propagating droplet's
+structure and properties. The results agree with previous asymptotic
+calculations in the weakly nonlinear regime. Furthermore, an analytical
+criterion for the droplet's orbital stability is confirmed. Time-dependent
+numerical simulations further verify the propagating droplet's robustness to
+perturbation when its frequency and speed lie within the allowable range.",1111.2310v2
+2011-11-14,Nambu-Goldstone dynamics and generalized coherent-state functional integrals,"The present paper gives a new method of attack on the Nambu-Goldstone
+dynamics in spontaneously broken theories. Since the target space of the
+Nambu-Goldstone fields is a group coset space, their effective quantum dynamics
+can be naturally phrased in terms of generalized coherent-state functional
+integrals. As an explicit example of this line of reasoning we construct a
+low-energy effective Lagrangian for the Heisenberg ferromagnet in broken phase.
+The leading field configuration in the WKB approximation leads to the
+Landau-Lifshitz equation for quantum ferromagnet. The corresponding linearized
+equations allow to identify the Nambu-Goldstone boson with ferromagnetic
+magnon.",1111.3228v2
+2011-12-30,Large magnetic circular dichroism in resonant inelastic x-ray scattering at the Mn L-edge of Mn-Zn ferrite,"We report resonant inelastic x-ray scattering (RIXS) excited by circularly
+polarized x-rays on Mn-Zn ferrite at the Mn L2,3-resonances. We demonstrate
+that crystal field excitations, as expected for localized systems, dominate the
+RIXS spectra and thus their dichroic asymmetry cannot be interpreted in terms
+of spin-resolved partial density of states, which has been the standard
+approach for RIXS dichroism. We observe large dichroic RIXS at the L2-resonance
+which we attribute to the absence of metallic core hole screening in the
+insulating Mn-ferrite. On the other hand, reduced L3-RIXS dichroism is
+interpreted as an effect of longer scattering time that enables spin-lattice
+core hole relaxation via magnons and phonons occurring on a femtosecond time
+scale.",1201.0091v1
+2012-01-02,Localized domain-wall excitations in patterned magnetic dots probed by broadband ferromagnetic resonance,"We investigate the magnetization dynamics in circular Permalloy dots with
+spatially separated magnetic vortices interconnected by domain walls (double
+vortex state). We identify a novel type of quasi one-dimensional (1D) localised
+spin wave modes confined along domain walls, connecting each of two vortex
+cores with two edge half-antivortices. Variation of the mode eigenfrequencies
+with the dot size is in quantitative agreement with the developed model, which
+considers a dipolar origin of the localized 1D spin waves or so-called
+Winter\'s magnons [J.M. Winter, Phys.Rev. 124, 452 (1961)]. These spin waves
+are analogous to the displacement waves of strings, and could be excited in a
+wide class of patterned magnetic nanostructures possessing domain walls, namely
+in triangular, square, circular or elliptic magnetic dots.",1201.0482v1
+2012-01-20,"Vortex Dynamics in Ferromagnetic Superconductors: Vortex Clusters, Domain Walls and Enhanced Viscosity","We demonstrate that there is a long-range vortex-vortex attraction in
+ferromagnetic superconductors due to polarization of the magnetic moments.
+Vortex clusters are then stabilized in the ground state for low vortex
+densities. The motion of vortex clusters driven by the Lorentz force excites
+magnons. This regime becomes unstable at a threshold velocity above which
+domain walls are generated for slow relaxation of the magnetic moments and the
+vortex configuration becomes modulated. This dynamics of vortices and magnetic
+moments can be probed by transport measurements.",1201.4195v3
+2012-01-31,Nonreciprocal Directional Dichroism and Toroidalmagnons in Helical Magnets,"We investigate a dynamical magnetoelectric effect due to a magnetic resonance
+in helical spin structures through the coupling between magnetization and
+electric polarization via a spin current mechanism. We show that the magnon has
+both the dynamical magnetic moment $\Delta M^\omega$ and the electric moment
+$\Delta P^\omega$ ($\perp \Delta M^\omega$), i.e., a dynamical toroidal moment,
+under external magnetic fields, and thus it is named the {\em toroidalmagnon}.
+The toroidalmagnon exists in most conical spin structures owing to the
+generality of the spin current mechanism. In the absorption of electromagnetic
+waves, the toroidalmagnon excitation process generally induces a nonreciprocal
+directional dichroism as a consequence of an interference of the magnetic and
+electric responses.",1201.6458v1
+2012-04-18,On Form Factors in nested Bethe Ansatz systems,"We investigate form factors of local operators in the multi-component Quantum
+Non-linear Schr\""odinger model, a prototype theory solvable by the so-called
+nested Bethe Ansatz. We determine the analytic properties of the infinite
+volume form factors using the coordinate Bethe Ansatz solution and we establish
+a connection with the finite volume matrix elements. In the two-component
+models we derive a set of recursion relations for the ""magnonic form factors"",
+which are the matrix elements on the nested Bethe Ansatz states. In certain
+simple cases (involving states with only one spin-impurity) we obtain explicit
+solutions for the recursion relations.",1204.4037v2
+2012-04-20,Size-dependent electronic-transport mechanism and sign reversal of magnetoresistance in Nd0.5Sr0.5CoO3,"A detailed investigation of electronic-transport properties of Nd0.5Sr0.5CoO3
+has been carried out as a function of grain size ranging from micrometer order
+down to an average size of 28 nm. Interestingly, we observe a size induced
+metal-insulator transition in the lowest grain size sample while the bulk-like
+sample is metallic in the whole measured temperature regime. An analysis of the
+temperature dependent resistivity in the metallic regime reveals that the
+electron-electron interaction is the dominating mechanism while other processes
+like electron-magnon and electron-phonon scatterings are also likely to be
+present. The fascinating observation of enhanced low temperature upturn and
+minimum in resistivity on reduction of grain size is found due to
+electron-electron interaction (quantum interference effect). This effect is
+attributed to enhanced disorder on reduction of grain size. Interestingly, we
+observed a cross over from positive to negative magnetoresistance in the low
+temperature regime as the grain size is reduced. This observed sign reversal is
+attributed to enhanced phase separation on decreasing the grain size of the
+cobaltite.",1204.4572v1
+2012-04-24,Nonlocal feedback in ferromagnetic resonance,"Ferromagnetic resonance in thin films is analyzed under the influence of
+spatiotemporal feedback effects. The equation of motion for the magnetization
+dynamics is nonlocal in both space and time and includes isotropic, anisotropic
+and dipolar energy contributions as well as the conserved Gilbert- and the
+non-conserved Bloch-damping. We derive an analytical expression for the
+peak-to-peak linewidth. It consists of four separate parts originated by
+Gilbert damping, Bloch-damping, a mixed Gilbert-Bloch component and a
+contribution arising from retardation. In an intermediate frequency regime the
+results are comparable with the commonly used Landau-Lifshitz-Gilbert theory
+combined with two-magnon processes. Retardation effects together with Gilbert
+damping lead to a linewidth the frequency dependence of which becomes strongly
+nonlinear. The relevance and the applicability of our approach to ferromagnetic
+resonance experiments is discussed.",1204.5342v1
+2012-04-27,Coupling of spin and lattice modes in the S=1/2 two-dimensional antiferromagnet K$_{2}$V$_{3}$O$_{8}$ with magneto-dielectric couplings,"Lattice dynamics and magnetic excitations are investigated to elucidate the
+origin of magneto-dielectric effects in the S=1/2 two-dimensional quantum spin
+compound K$_2$V$_3$O$_8$. We find evidence for lattice instabilities at 110 K
+and 60 K as optical phonon anomalies and a soft mode at 26 cm$^{-1}$ in A$_1$
+symmetry. Two-magnon excitations in B$_1$ symmetry show an unconventional
+double-peak structure and temperature dependence. This suggests the existence
+of a split mode near the zone boundary caused by a mixing of spin and lattice
+modes.",1204.6210v1
+2012-04-28,"Coupled Phonons, Magnetic Excitations and Ferroelectricity in AlFeO3: Raman and First-principles Studies","We determine the nature of coupled phonons and magnetic excitations in AlFeO3
+using inelastic light scattering from 5 K to 315 K covering a spectral range
+from 100-2200 cm-1 and complementary first-principles density functional
+theory-based calculations. A strong spin-phonon coupling and magnetic ordering
+induced phonon renormalization are evident in (a) anomalous temperature
+dependence of many modes with frequencies below 850 cm-1, particularly near the
+magnetic transition temperature Tc ~ 250 K, (b) distinct changes in band
+positions of high frequency Raman bands between 1100-1800 cm-1, in particular a
+broad mode near 1250 cm-1 appears only below Tc attributed to the two-magnon
+Raman scattering. We also observe weak anomalies in the mode frequencies at ~
+100 K, due to a magnetically driven ferroelectric phase transition.
+Understanding of these experimental observations has been possible on the basis
+of first-principles calculations of phonons spectrum and their coupling with
+spins.",1204.6387v1
+2012-04-30,Chiral gauge field and axial anomaly in a Weyl semi-metal,"Weyl fermions are two-component chiral fermions in (3+1)-dimensions. When
+coupled to a gauge field, the Weyl fermion is known to have an axial anomaly,
+which means the current conservation of the left-handed and right-handed Weyl
+fermions cannot be preserved separately. Recently, Weyl fermions have been
+proposed in condensed matter systems named as ""Weyl semi-metals"". In this paper
+we propose a Weyl semi-metal phase in magnetically doped topological
+insulators, and study the axial anomaly in this system. We propose that the
+magnetic fluctuation in this system plays the role of a ""chiral gauge field""
+which minimally couples to the Weyl fermions with opposite charges for two
+chiralities. We study the anomaly equation of this sytem and discuss its
+physical consequences, including one-dimensional chiral modes in a
+ferromagnetic vortex line, and a novel plasmon-magnon coupling.",1204.6551v1
+2013-09-16,Time resolved spin Seebeck effect experiments,"In this Letter, we present the results of transient thermopower experiments,
+performed at room temperature on yttrium iron garnet/platinum bilayers. Upon
+application of a time-varying thermal gradient, we observe a characteristic
+low-pass frequency response of the ensuing thermopower voltage with cutoff
+frequencies of up to 37 MHz. We interpret our results in terms of the spin
+Seebeck effect, and argue that small wavevector magnons are of minor importance
+for the spin Seebeck effect in our thin film hybrid structures.",1309.3986v2
+2014-05-06,Multifrequency transverse Faraday effect in single magneto-dielectric microspheres,"We propose using a single magneto-dielectric microsphere as a device for
+enhancing the transverse Faraday effect at multiple wavelengths at the same
+time. Although the diameter of the sphere can be $<1$ $\mu$m, the numerically
+predicted strength of its magneto-optical (MO) response can be an order of
+magnitude stronger than in MO devices based on thick magnetic plates. The MO
+response of a microsphere is also comparable with that of subwavelength
+magneto-dielectric gratings which, however, operate at a single wavelength and
+occupy a large area. In contrast to gratings and thick plates, the compact size
+of the microsphere and its capability to support spin-wave excitations make it
+suitable for applications in nanophotonics, imaging systems, and magnonics.",1405.1149v1
+2014-05-09,Magnetic excitations and anomalous spin wave broadening in multiferroic FeV2O4,"We report on the different roles of two orbital-active Fe$^{2+}$ at the A
+site and V$^{3+}$ at the B site in the magnetic excitations and on the
+anomalous spin wave broadening in FeV$_{2}$O$_{4}$. FeV$_{2}$O$_{4}$ exhibits
+three structural transitions and successive paramagnetic (PM)-collinear
+ferrimagnetic (CFI)-noncollinear ferrimagnetic (NCFI) transitions. The
+high-temperature tetragonal/PM -orthorhombic/CFI transition is accompanied by
+the appearance of an energy gap with a high magnitude in the magnetic
+excitations due to strong spin-orbit coupling induced anisotropy at the
+Fe$^{2+}$ site. While there is no measurable increase in the energy gap from
+the orbital ordering of V$^{3+}$ at the orthorhombic/CFI-tetragonal/NCFI
+transition, anomalous spin wave broadening is observed in the orthorhombic/CFI
+state due to V$^{3+}$ spin fluctuations at the B site. The spin wave broadening
+is also observed at the zone boundary without softening, which is discussed in
+terms of magnon-phonon coupling.",1405.2272v2
+2014-05-09,Spin wave spectrum of the quantum ferromagnet on the pyrochlore lattice Lu2V2O7,"Neutron inelastic scattering has been used to probe the spin dynamics of the
+quantum (S=1/2) ferromagnet on the pyrochlore lattice Lu2V2O7. Well-defined
+spin waves are observed at all energies and wavevectors, allowing us to
+determine the parameters of the Hamiltonian of the system. The data are found
+to be in excellent overall agreement with a minimal model that includes a
+nearest- neighbour Heisenberg exchange J = 8:22(2) meV and a
+Dzyaloshinskii-Moriya interaction (DMI) D =1:5(1) meV. The large DMI term
+revealed by our study is broadly consistent with the model developed by Onose
+et al. to explain the magnon Hall effect they observed in Lu2V2O7 [1], although
+our ratio of D=J = 0:18(1) is roughly half of their value and three times
+larger than calculated by ab initio methods [2].",1405.2284v1
+2014-05-23,Magnetic Excitations in Spin-Orbit Coupled $d^4$ Mott Insulator on Square Lattice,"We study the magnetic order and excitations in strong spin-orbit coupled, Van
+Vleck-type, $d^4$ Mott insulators on a square lattice. Extending the previous
+work, we include the tetragonal crystal field splitting and explore its effects
+on magnetic phase diagram and magnon spectra. Two different ordered phases,
+with in-plane and out-of-plane orientation of the staggered moments, are found
+for the higher and lower values of the crystal field splitting, respectively.
+The magnetic excitation spectra for paramagnetic and magnetically ordered
+phases are calculated and discussed in the context of a candidate spin-orbit
+$d^4$ Mott insulator Ca$_2$RuO$_4$.",1405.6062v2
+2014-05-23,Finite-gap equations for strings on AdS_3 x S^3 x T^4 with mixed 3-form flux,"We study superstrings on AdS_3 x S^3 x T^4 supported by a combination of
+Ramond-Ramond and Neveu-Schwarz-Neveu-Schwarz three form fluxes, and construct
+a set of finite-gap equations that describe the classical string spectrum.
+Using the recently proposed all-loop S-matrix we write down the all-loop Bethe
+ansatz equations for the massive sector. In the thermodynamic limit the Bethe
+ansatz reproduces the finite-gap equations. As part of this derivation we
+propose expressions for the leading order dressing phases. These phases differ
+from the well-known Arutyunov-Frolov-Staudacher phase that appears in the pure
+Ramond-Ramond case. We also consider the one-loop quantization of the algebraic
+curve and determine the one-loop corrections to the dressing phases. Finally we
+consider some classical string solutions including finite size giant magnons
+and circular strings.",1405.6087v2
+2014-06-23,"Phonon Anomalies, Orbital-Ordering and Electronic Raman Scattering in iron-pnictide Ca(Fe0.97Co0.03)2As2: Temperature-dependent Raman Study","We report inelastic light scattering studies on Ca(Fe0.97Co0.03)2As2 in a
+wide spectral range of 120-5200 cm-1 from 5K to 300K, covering the tetragonal
+to orthorhombic structural transition as well as magnetic transition at Tsm ~
+160K. The mode frequencies of two first-order Raman modes B1g and Eg, both
+involving displacement of Fe atoms, show sharp increase below Tsm.
+Concomitantly, the linewidths of all the first-order Raman modes show anomalous
+broadening below Tsm, attributed to strong spin-phonon coupling. The high
+frequency modes observed between 400-1200 cm-1 are attributed to the electronic
+Raman scattering involving the crystal field levels of d-orbitals of Fe2+. The
+splitting between xz and yz d-orbital levels is shown to be ~ 25 meV which
+increases as temperature decreases below Tsm. A broad Raman band observed at ~
+3200 cm-1 is assigned to two-magnon excitation of the itinerant Fe 3d
+antiferromagnet.",1406.5844v1
+2014-06-27,Observation of propagating edge spin waves modes,"Broadband magnetization response of equilateral triangular 1000 nm Permalloy
+dots has been studied under an in-plane magnetic field, applied parallel
+(buckle state) and perpendicular (Y state) to the triangles base. Micromagnetic
+simulations identify edge spin waves (E-SWs) in the buckle state as SWs
+propagating along the two adjacent edges. These quasi one-dimensional spin
+waves emitted by the vertex magnetic charges gradually transform from
+propagating to standing due to interference and are weakly affected by dipolar
+interdot interaction and variation of the aspect ratio. Spin waves in the Y
+state have a two dimensional character. These findings open perspectives for
+implementation of the E-SWs in magnonic crystals and thin films.",1406.7186v1
+2016-05-01,Magnetoelectric fields for microwave chirality discrimination in enantiomeric liquids,"Chirality discrimination is of a fundamental interest in biology, chemistry,
+and metamaterial studies. In optics, near-field plasmon-resonance spectroscopy
+with superchiral probing fields is effectively applicable for analyses of large
+biomolecules with chiral properties. We show possibility for microwave
+near-field chirality discrimination analysis based on magnon-resonance
+spectroscopy. Newly developed capabilities in microwave sensing using
+magnetoelectric (ME) probing fields originated from multiresonance
+magnetic-dipolar-mode (MDM) oscillations in quasi-2D yttrium-iron-garnet (YIG)
+disks, provide a potential for unprecedented measurements of chemical and
+biological objects. We report on microwave near-field chirality discrimination
+for aqueous D- and L-glucose solutions. The shown ME-field sensing is addressed
+to microwave biomedical diagnostics and pathogen detection and to deepening our
+understanding of microwave-biosystem interactions. It can be also important for
+an analysis and design of microwave chiral metamaterials.",1605.00212v1
+2016-05-07,Order-by-disorder effects in antiferromagnets on face-centered cubic lattice,"We discuss the role of quantum fluctuations in Heisenberg antiferromagnets on
+face-centered cubic lattice with small dipolar interaction in which the
+next-nearest-neighbor exchange coupling dominates over the nearest-neighbor
+one. It is well known that a collinear magnetic structure which contains (111)
+ferromagnetic planes arranged antiferromagnetically along one of the space
+diagonals of the cube is stabilized in this model via order-by-disorder
+mechanism. On the mean-field level, the dipolar interaction forces spins to lie
+within (111) planes. By considering 1/S - corrections to the ground state
+energy, we demonstrate that quantum fluctuations lead to an anisotropy within
+(111) planes favoring three equivalent directions for the staggered
+magnetization (e.g., $[11\overline{2}]$, $[1\overline{2}1]$, and
+$[\overline{2}11]$ directions for (111) plane). Such in-plane anisotropy was
+obtained experimentally in related materials MnO, $\alpha$-MnS, $\alpha$-MnSe,
+EuTe, and EuSe. We find that the order-by-disorder mechanism can contribute
+significantly to the value of the in-plane anisotropy in EuTe. Magnon spectrum
+is also derived in the first order in 1/S.",1605.02208v2
+2016-05-10,Topological spin-transfer drag driven by skyrmion diffusion,"We study the spin-transfer drag mediated by the Brownian motion of skyrmions.
+The essential idea is illustrated in a two-terminal geometry, in which a thin
+film of a magnetic insulator is placed in between two metallic reservoirs. An
+electric current in one of the terminals pumps topological charge into the
+magnet via a spin-transfer torque. The charge diffuses over the bulk of the
+system as stable skyrmion textures. By Onsager's reciprocity, the topological
+charge leaving the magnet produces an electromotive force in the second
+terminal. The voltage signal decays algebraically with the separation between
+contacts, in contrast to the exponential suppression of the spin drag driven by
+non-protected excitations like magnons. We show how this topological effect can
+be used as a tool to characterize the phase diagram of chiral magnets and thin
+films with interfacial Dzyaloshinskii-Moriya interactions.",1605.02857v2
+2016-05-17,Direct observation of dynamic modes excited in a magnetic insulator by pure spin current,"Excitation of magnetization dynamics by pure spin currents has been recently
+recognized as an enabling mechanism for spintronics and magnonics, which allows
+implementation of spin-torque devices based on low-damping insulating magnetic
+materials. Here we report the first spatially-resolved study of the dynamic
+modes excited by pure spin current in nanometer-thick microscopic insulating
+Yttrium Iron Garnet disks. We show that these modes exhibit nonlinear
+self-broadening preventing the formation of the self-localized magnetic bullet,
+which plays a crucial role in the stabilization of the single-mode
+magnetization oscillations in all-metallic systems. This peculiarity associated
+with the efficient nonlinear mode coupling in low-damping materials can be
+among the main factors governing the interaction of pure spin currents with the
+dynamic magnetization in high-quality magnetic insulators.",1605.05211v1
+2016-05-20,Rewritable Artificial Magnetic Charge Ice,"Artificial ices enable the study of geometrical frustration by design and
+through direct observation. However, it has proven difficult to achieve
+tailored long-range ordering of their diverse configurations, limiting both
+fundamental and applied research directions. We designed an artificial spin
+structure that produces a magnetic charge ice with tunable long-range ordering
+of eight different configurations. We also developed a technique to precisely
+manipulate the local magnetic charge states and demonstrate write-read-erase
+multifunctionality at room temperature. This globally reconfigurable and
+locally writable magnetic charge ice could provide a setting for designing
+magnetic monopole defects, tailoring magnonics, and controlling the properties
+of other two-dimensional materials.",1605.06209v1
+2016-08-02,Picosecond spin Seebeck effect,"We report time-resolved magneto-optic Kerr effect measurements of the
+longitudinal spin Seebeck effect driven by an interfacial temperature
+difference between itinerant electrons and magnons. The measured time-evolution
+of spin accumulation induced by laser-excitation indicates transfer of angular
+momentum across Au/Y$_3$Fe$_5$O$_{12}$ and Cu/Y$_3$Fe$_5$O$_{12}$ interfaces on
+a picosecond time-scale. The product of spin-mixing conductance and interfacial
+spin Seebeck coefficient determined is of the order of $10^8$ A m$^{-2}$
+K$^{-1}$.",1608.00702v1
+2016-08-11,Pumping approximately integrable systems,"Weak perturbations can drive an interacting many-particle system far from its
+initial equilibrium state if one is able to pump into degrees of freedom
+approximately protected by conservation laws. This concept has for example been
+used to realize Bose-Einstein condensates of photons, magnons, and excitons.
+Integrable quantum systems, like the one-dimensional Heisenberg model, are
+characterized by an infinite set of conservation laws. Here we develop a theory
+of weakly driven integrable systems and show that pumping can induce large spin
+or heat currents even in the presence of integrability breaking perturbations,
+since it activates local and quasi-local approximate conserved quantities. The
+resulting steady state is qualitatively captured by a truncated generalized
+Gibbs ensemble with Lagrange parameters that depend on the structure but not on
+the overall amplitude of perturbations nor the initial state. We suggest to use
+spin-chain materials driven by terahertz radiation to realize
+integrability-based spin and heat pumps.",1608.03563v2
+2016-08-16,Giant Spin Gap and Magnon Localization in the Disordered Heisenberg Antiferromagnet Sr2Ir1-xRuxO4,"We study the evolution of magnetic excitations in the disordered
+two-dimensional antiferromagnet Sr2Ir1-xRuxO4. A gigantic magnetic gap greater
+than 40 meV opens at x = 0.27 and increases with Ru concentration, rendering
+the dispersive magnetic excitations in Sr2IrO4 almost momentum independent. Up
+to a Ru concentration of x = 0.77, both experiments and first-principles
+calculations show the Ir Jeff = 1/2 state remains intact. The magnetic gap
+arises from the local interaction anisotropy in the proximity of the Ru
+disorder. Under the coherent potential approximation, we reproduce the
+experimental magnetic excitations using the disordered Heisenberg
+antiferromagnetic model with suppressed next-nearest neighbor ferromagnetic
+coupling.",1608.04640v2
+2016-08-23,Ultrasonic elastic responses in monopole lattice,"The latest experimental advances have extended the scenario of coupling
+mechanical degrees of freedom in chiral magnets (MnSi/MnGe) to the
+topologically nontrivial skyrmion crystal and even monopole lattices. Equipped
+with a spin-wave theory highlighting the topological features, we devise an
+interacting model for acoustic phonons and magnons to explain the experimental
+findings in a monopole lattice with a topological phase transition, i.e.,
+annihilation of monopole-antimonopole pairs. We reproduce the anisotropic
+magnetoelastic modulations of elastic moduli: drastic ultrasonic softening
+around the phase transition and a multi-peak-and-trench fine structure for
+sound waves parallel and orthogonal to the magnetic field, respectively.
+Comparison with experiments indicates that the magnetoelastic coupling induced
+by Dzyaloshinskii-Moriya interaction is comparable to that induced by the
+exchange interaction. Other possibilities such as elastic hardening are also
+predicted. The study implies that the monopole defects and their motion in MnGe
+play a crucial role.",1608.06362v2
+2016-08-25,Temperature-field phase diagram of geometrically frustrated CePdAl,"From the electrical resistivity and ac susceptibility measurements down to
+$T$ = 40 mK, a rich temperature-field phase diagram has been constructed for
+the geometrically frustrated heavy-fermion compound CePdAl. In the limit of
+zero temperature, the field-induced suppression of the antiferromagnetism in
+this compound results in a sequence of phase transitions/corssovers, rather
+than a single critical point, in a critical region of field 3$-$5 T. In the
+lowest temperature region, a power-law description of the temperature-dependent
+resistivity yields $A$$\cdot$$T^n$ with $n$$>$2 for all applied fields.
+However, a quadratic-in-temperature resistivity term can be extracted when
+assuming an additional electron scattering channel from magnon-like
+excitations, with $A$ diverging upon approaching the critical regime. Our
+observations suggest CePdAl to be a new playground for exotic physics arising
+from the competition between Kondo screening and geometrical frustration.",1608.07123v1
+2017-06-06,Observation of spin superfluidity: YIG magnetic films and beyond,"From topology of the order parameter of the magnon condensate observed in
+yttrium-iron-garnet (YIG) magnetic films one must not expect energetic barriers
+making spin supercurrents metastable. But we show that some barriers of
+dynamical origin are possible nevertheless until the gradient of the phase
+(angle of spin precession) does not exceed the critical value (analog of the
+Landau critical velocity in superfluids). On the other hand, recently published
+claims of experimental detection of spin superfluidity in YIG films and
+antiferromagnets are not justified, and spin superfluidity in magnetically
+ordered solids has not yet been experimentally confirmed.",1706.01932v2
+2017-06-08,Penrose limits and spin chains in the GJV/CS-SYM duality,"We examine Penrose limits of the duality proposed by Guarino, Jafferis and
+Varela between a type IIA massive background of the type of a warped, squashed
+$AdS_4\times S^6$, and a 2+1 dimensional IR fixed point of ${\cal N}=8$ super
+Yang-Mills deformed by Chern-Simons terms to ${\cal N}=2$ supersymmetry. One
+type of Penrose limit for closed strings corresponds to a large charge closed
+spin chain, and another, for open strings on giant graviton D-branes,
+corresponds to an open spin chain on sub-determinant operators. For the first
+limit, we find that like in the ABJM case, there are functions $f_a(\lambda)$
+that interpolate between the perturbative and nonperturbative (string) regions
+for the magnon energy. For the second, we are unable to match the gravity
+result with the expected field theory result, making this model more
+interesting than ones with more supersymmetry.",1706.02711v2
+2017-06-09,Structure constants of operators on the Wilson loop from integrability,"We study structure constants of local operators inserted on the Wilson loop
+in ${\cal N}=4$ super Yang-Mills theory. We compute the structure constants in
+the SU(2) sector at tree level using the correspondence between operators on
+the Wilson loop and the open spin chain. The results are interpreted as the
+summation over all possible ways of changing the signs of magnon momenta in the
+hexagon form factors. This is consistent with a holographic description of the
+correlator as the cubic open string vertex, which consists of one hexagonal
+patch and three boundaries. We then conjecture that a similar expression should
+hold also at finite coupling.",1706.02989v3
+2017-06-11,Magnetization spin dynamics in a (LuBi)3Fe5O12 (BLIG) epitaxial film,"Bismuth substituted lutetium iron garnet (BLIG) films exhibit larger Faraday
+rotation, and have a higher Curie temperature than yttrium iron garnet. We have
+observed magnetic stripe domains and measured domain widths of 1.4 {\mu}{\mu}m
+using Fourier domain polarization microscopy, Faraday rotation experiments
+yield a coercive field of 5 Oe. These characterizations form the basis of
+micromagnetic simulations that allow us to estimate and compare spin wave
+excitations in BLIG films. We observed that these films support thermal magnons
+with a precessional frequency of 7 GHz with a line width of 400 MHz. Further,
+we studied the dependence of precessional frequency on the externally applied
+magnetic field. Brillouin light scattering experiments and precession
+frequencies predicted by simulations show similar trend with increasing field.",1706.03340v1
+2017-06-14,Broadband conversion of microwaves into propagating spin waves in patterned magnetic structures,"We have used time-resolved scanning Kerr microscopy (TRSKM) and micromagnetic
+simulations to demonstrate that, when driven by spatially uniform microwave
+field, the edges of patterned magnetic samples represent both efficient and
+highly tunable sources of propagating spin waves. The excitation is due to the
+local enhancement of the resonance frequency induced by the non-uniform dynamic
+demagnetizing field generated by precessing magnetization aligned with the
+edges. Our findings represent a crucial step forward in the design of nanoscale
+spin-wave sources for magnonic architectures, and are also highly relevant to
+the understanding and interpretation of magnetization dynamics driven by
+spatially-uniform magnetic fields in patterned magnetic samples.",1706.04409v2
+2017-06-20,Magnetization process and low-temperature thermodynamics of a spin-1/2 Heisenberg octahedral chain,"Low-temperature magnetization curves and thermodynamics of a spin-1/2
+Heisenberg octahedral chain with the intraplaquette and monomer-plaquette
+interactions are examined within a two-component lattice-gas model of hard-core
+monomers, which takes into account all low-lying energy modes in a highly
+frustrated parameter space involving the monomer-tetramer, localized
+many-magnon and fully polarized ground states. It is shown that the developed
+lattice-gas model satisfactorily describes all pronounced features of the
+low-temperature magnetization process and the magneto-thermodynamics such as
+abrupt changes of the isothermal magnetization curves, a double-peak structure
+of the specific heat or a giant magnetocaloric effect.",1706.06370v1
+2017-06-21,Phase Diagram and Soliton Picture of an Ideal Spin-Peierls Compound D-F$_{5}$PNN,"We investigate magnetic properties of an $S$=1/2 quasi-one dimensional
+organic antiferromagnet, D-F$_{5}$PNN using magnetization measurements taken at
+temperatures as low as 0.5 K. Three distinct phases were observed consisting of
+uniform, dimerized (D), and incommensurate (I) spin structures in the magnetic
+field versus temperature plane, where a significant hysteresis appears between
+D-I transitions in the field scan measurements. A combination of magnon ($S$=1)
+and soliton ($S$=1/2) excitations have successfully reproduced the observed
+magnetic susceptibility. In addition, such excitations provide a reasonable
+interpretation of the temperature dependent electron spin resonance (ESR)
+spectra. By comparison with the theoretical study, we conclude that
+D-F$_{5}$PNN is an ideal compound for investigating the spin-Peierls
+transition.",1706.06797v1
+2017-06-27,Generalized Lipkin-Meshkov-Glick models of Haldane-Shastry type,"We introduce a class of generalized Lipkin-Meshkov-Glick (gLMG) models with
+su$(m)$ interactions of Haldane-Shastry type. We have computed the partition
+function of these models in closed form by exactly evaluating the partition
+function of the restriction of a spin chain Hamiltonian of Haldane-Shastry type
+to subspaces with well-defined magnon numbers. As a byproduct of our analysis,
+we have obtained strong numerical evidence of the Gaussian character of the
+level density of the latter restricted Hamiltonians, and studied the
+distribution of the spacings of consecutive unfolded levels. We have also
+discussed the thermodynamic behavior of a large family of su(2) and su(3) gLMG
+models, showing that it is qualitatively similar to that of a two-level system.",1706.08751v2
+2017-10-10,Lectures on Three-point Functions in N=4 Supersymmetric Yang-Mills Theory,"This is a pedagogical review on the integrability-based approach to the
+three-point function in N=4 supersymmetric Yang-Mills theory. We first discuss
+the computation of the structure constant at weak coupling and show that the
+result can be recast as a sum over partitions of the rapidities of the magnons.
+We then introduce a non-perturbative framework, called the ""hexagon approach"",
+and explain how one can use the symmetries (i.e. superconformal and gauge
+symmetries) and integrability to determine the structure constants. This
+article is based on the lectures given in Les Houches Summer School
+""Integrability: From statistical systems to gauge theory"" in June 2016.",1710.03853v2
+2017-10-15,Itinerant ferromagnetism of the Pd-terminated polar surface of PdCoO$_2$,"We study the electronic structure of the Pd-terminated surface of the
+non-magnetic delafossite oxide metal PdCoO$_2$. Combining angle-resolved
+photoemission spectroscopy and density-functional theory, we show how an
+electronic reconstruction driven by surface polarity mediates a Stoner-like
+magnetic instability towards itinerant surface ferromagnetism. Our results
+reveal how this leads to a rich multi-band surface electronic structure, and
+provide spectroscopic evidence for an intriguing sample-dependent coupling of
+the surface electrons to a bosonic mode which we attribute to electron-magnon
+interactions. Moreover, we find similar surface state dispersions in PdCrO$_2$,
+suggesting surface ferromagnetism persists in this sister compound despite its
+bulk antiferromagnetic order.",1710.05392v1
+2017-10-27,Colour-dressed hexagon tessellations for correlation functions and non-planar corrections,"We continue the study of four-point correlation functions by the hexagon
+tessellation approach initiated in 1611.05436 and 1611.05577. We consider
+planar tree-level correlation functions in $\mathcal{N} = 4$ supersymmetric
+Yang-Mills theory involving two non-protected operators. We find that, in order
+to reproduce the field theory result, it is necessary to include $SU(N)$ colour
+factors in the hexagon formalism; moreover, we find that the hexagon approach
+as it stands is naturally tailored to the single-trace part of correlation
+functions, and does not account for multi-trace admixtures. We discuss how to
+compute correlators involving double-trace operators, as well as more general
+$1/N$ effects; in particular we compute the whole next-to-leading order in the
+large-$N$ expansion of tree-level BMN two-point functions by tessellating a
+torus with punctures. Finally, we turn to the issue of ""wrapping"",
+L\""uscher-like corrections. We show that $SU(N)$ colour-dressing reproduces an
+earlier empirical rule for incorporating single-magnon wrapping, and we provide
+a direct interpretation of such wrapping processes in terms of $\mathcal{N}=2$
+supersymmetric Feynman diagrams.",1710.10212v2
+2017-12-10,Switching of magnons by electric and magnetic fields in multiferroic borates,"Electric manipulation of magnetic properties is a key problem of materials
+research. To fulfil the requirements of modern electronics, these processes
+must be shifted to high frequencies. In multiferroic materials this may be
+achieved by electric and magnetic control of their fundamental excitations.
+Here we identify magnetic vibrations in multiferroic iron-borates which are
+simultaneously sensitive to external electric and magnetic fields. Nearly 100%
+modulation of the terahertz radiation in an external field is demonstrated for
+SmFe3(BO3)4. High sensitivity can be explained by a modification of the spin
+orientation which controls the excitation conditions in multiferroic borates.
+These experiments demonstrate the possibility to alter terahertz magnetic
+properties of materials independently by external electric and magnetic fields.",1712.03501v1
+2017-12-11,Topological Mott Insulator with Bosonic Edge Modes in 1D Fermionic Superlattices,"We investigate topological phase transitions driven by interaction and
+identify a novel topological Mott insulator state in one-dimensional fermionic
+optical superlattices through numerical density matrix renormalization group
+(DMRG) method. Remarkably, the low-energy edge excitations change from spin-1/2
+fermionic single-particle modes to spin-1 bosonic collective modes across the
+phase transition. Due to spin-charge separation, the low-energy theory is
+governed by an effective spin superexchange model, whereas the charge degree of
+freedom is fully gapped out. Such topological Mott state can be characterized
+by a spin Chern number and gapless magnon modes protected by a finite spin gap.
+The proposed experimental setup is simple and may pave the way for the
+experimental observation of exotic topological Mott states.",1712.03671v1
+2017-12-22,Magnetically Ordered Insulators for Advanced Spintronics,"Magnetically ordered, electrically insulating materials pave the way towards
+novel spintronic devices. In these materials the flow of magnetic excitations
+such as magnons results in pure spin currents. These spin currents can be
+driven by gradients of the spin chemical potential and/or temperature such that
+they can play the same role in novel spintronic devices as charge currents in
+traditional electronic circuits. Connecting spin current based and charge
+current based devices requires spin to charge interconversion. This has been
+achieved by the spin Hall effect with an efficiency of several 10%. The recent
+progress in materials development and understanding of pure spin current
+physics opens up a plethora of novel device concepts and opportunities for
+fundamental studies.",1712.08517v1
+2018-09-25,PT-Symmetric magnetic Chaos in cavity magnomechanics,"Here, we research a novel cavity magnomechanical system, where magnon driven
+by a microwave field couples with a phonon mode with a nonlinear
+magneostrictive interaction (radiation pressure-like). Based on this
+interaction, we numerically demonstrate PT-symmetric chaos in this system. With
+only one monochrome driving, the chaotic threshold is lowered to a rather low
+levels, this is due to the dynamical enhancement of nonlinearity in the
+PT-symmetry broken phase. Moreover, by simply manipulating the phase transition
+between PT-symmetry phase and PT-symmetry broken phase, we can switch the
+system between into and out of chaotic regimes. Our work may broaden the cavity
+magnomechanics and provide a promising application for magnetic chaos-related
+security communications.",1809.09309v1
+2019-09-05,The critical nature of the Ni spin state in doped NdNiO$_2$,"Superconductivity with $T_c \approx 15K$ was recently found in doped
+NdNiO$_2$. The Ni$^{1+}$O$_2$ layers are expected to be Mott insulators so hole
+doping should produce Ni$^{2+}$ with $S=1$, incompatible with robust
+superconductivity. We show that the NiO$_2$ layers fall inside a ``critical''
+region where the large $pd$ hybridization favors a singlet $^1\!A_1$ hole-doped
+state like in CuO$_2$. However, we find that the superexchange is about one
+order smaller than in cuprates, thus a magnon ``glue'' is very unlikely and
+another mechanism needs to be found.",1909.02557v3
+2019-09-10,Anisotropic magnetic excitations of a frustrated bilinear-biquadratic spin model -- Implications for spin waves of detwinned iron pnictides,"Elucidating the nature of spin excitations is important to understanding the
+mechanism of superconductivity in the iron pnictides. Motivated by recent
+inelastic neutron scattering measurements in the nearly 100% detwinned
+BaFe$_{2}$As$_{2}$, we study the spin dynamics of an $S=1$ frustrated
+bilinear-biquadratic Heisenberg model in the antiferromagnetic phase with
+wavevector $(\pi,0)$. The biquadratic interactions are treated in a dynamical
+way using a flavor-wave theory in an $SU(3)$ representation. Besides the magnon
+(dipolar) excitations, the biquadratic interactions give rise to quadrupolar
+excitations at high energies. We find that the quadrupolar wave significantly
+influences, in an energy dependent way, the anisotropy between the spin
+excitation spectra along the $(\pi,0)$ and $(0,\pi)$ directions in the wave
+vector space. Our theoretical results capture the essential behavior of the
+spin dynamics measured in the antiferromagnetic phase of the detwinned
+BaFe$_2$As$_2$. More generally, our results underscore the importance of
+electron correlation effects for the microscopic physics of the iron pnictides.",1909.04555v2
+2019-09-11,Spin dynamics of the planar kagome lattice ferromagnet with four-site ring exchange processes,"By means of quantum Monte Carlo simulations, combined with a stochastic
+analytic continuation, we examine the spin dynamics of the spin-1/2 planar (XY)
+ferromagnet on the kagome lattice with additional four-site ring exchange
+terms. Such exchange processes were previously considered to lead into an
+extended $Z_2$ quantum spin liquid phase beyond a quantum critical point from
+the XY-ferromagnet. We examine the dynamical spin structure factor in the
+non-magnetic regime and probe for signatures of spin fractionalization.
+Furthermore, we contrast our findings and the corresponding energy scales of
+the excitation gaps in the ring exchange model to those emerging in a related
+Balents-Fisher-Girvin model with a $Z_2$ quantum spin liquid phase, and monitor
+the softening of the magnon mode upon approaching the quantum critical point
+from the XY-ferromagnetic regime.",1909.04877v1
+2019-09-27,Thermally driven two-magnet nano-oscillator with large spin-charge conversion,"Next-generation spintronic applications require material properties that can
+be hardly met by one material candidate. Here we demonstrate that by combining
+insulating and metallic magnets, enhanced spin-charge conversion and
+energy-efficient thermal spin currents can be realized. We develop a nanowire
+device consisting of an yttrium iron garnet and permalloy bi-layer. An
+interfacial temperature gradient drives the nanowire magnetization into
+auto-oscillations at gigahertz frequencies. Interfacial spin coupling and
+magnetoresistance of the permalloy layer translate spin dynamics into sizable
+microwave signals. The results show prospect for energy-efficient spintronic
+devices and present an experimental realization of magnon condensation in a
+heterogeneous magnetic system.",1909.12445v1
+2019-09-27,Neumann-Rosochatius system for strings in ABJ Model,"Neumann-Rosochatius system is a well known one dimensional integrable system.
+We study the rotating and pulsating string in $AdS_4 \times \mathbb{CP}^3$ with
+a $B_{\rm{NS}}$ holonomy turned on over $\mathbb{CP}^1 \subset \mathbb{CP}^3$,
+or the so called Aharony-Bergman-Jafferis (ABJ) background. We observe that the
+string equations of motion in both cases are integrable and the Lagrangians
+reduce to a form similar to that of deformed Neuman-Rosochatius system. We find
+out the scaling relations among various conserved charges and comment on the
+finite size effect for the dyonic giant magnons on $R_{t}\times
+\mathbb{CP}^{3}$ with two angular momenta. For the pulsating string we derive
+the energy as function of oscillation number and angular momenta along
+$\mathbb{CP}^{3}$.",1909.12632v3
+2020-12-01,Hole in the 2D Ising Antiferromagnet: Origin of the Incoherent Spectrum,"We develop a ""self-avoiding walks"" approximation and use it to calculate the
+spectral function of a single hole introduced into the 2D square lattice Ising
+antiferromagnet. The obtained local spectral function qualitatively agrees with
+the exact diagonalisation result and is largely incoherent. Such a result stays
+in contrast with the spectrum obtained on a Bethe lattice, which consists of
+the well-separated quasiparticle-like peaks and stems from the motion of a hole
+in an effective linear potential. We determine that this onset of the
+incoherent spectrum on a square lattice (i) is not triggered by the so-called
+Trugman loops but (ii) originates in the warping of the linear potential by the
+interactions between magnons created along the tangential paths of the moving
+hole.",2012.00395v2
+2020-12-05,Theory of magnetism in the van der Waals magnet CrI3,"We study the microscopical origin of anisotropic ferromagnetism in the van
+der Waals magnet CrI3. We conclude that the nearest neighbors exchange is well
+described by the Heisenberg-Kitaev-Gamma (HKGamma) model, and we also found a
+nonzero Dzyaloshinskii-Moriya interaction (DMI) on next nearest neighbors. Both
+Kitaev and DMI are known to generate a non-trivial topology of the magnons in
+the honeycomb lattice and have been used separately to describe the low energy
+regime of this material. We discuss that including one or the other leads to
+different signs of the Chern number. Furthermore, the topological gap at
+K-point seems to be mainly produced by DMI, despite it is one order of
+magnitude smaller than Kitaev. Finally, we show that by applying an external
+electric field perpendicular to the crystal plane, it is possible to induce DMI
+on nearest neighbors, and this could have consequences in non-collinear spin
+textures, such as domain walls and skyrmions.",2012.03099v2
+2020-12-11,Compositional effect on auto-oscillation behavior of Ni100-xFex/Pt spin Hall nano-oscillators,"We demonstrate the compositional effect on the magnetodynamic and
+auto-oscillations properties of Ni100-xFex/Pt (x= 10 to 40) nanoconstriction
+based spin Hall nano-oscillators. Using spin-torque ferromagnetic resonance
+(ST-FMR) performed on microstrips, we measure a significant reduction in both
+damping and spin Hall efficiency with increasing Fe content, which lowers the
+spin pumping contribution. The strong compositional effect on spin Hall
+efficiency is primarily attributed to the increased saturation magnetization in
+Fe-rich devices. As a direct consequence, higher current densities are required
+to drive spin-wave auto-oscillations at higher microwave frequencies in Fe-rich
+nano-constriction devices. Our results establish the critical role of the
+compositional effect in engineering the magnetodynamic and auto-oscillation
+properties of spin Hall devices for microwav eand magnonic applications.",2012.06121v2
+2020-12-11,From one- to two-magnon excitations in the S=3/2 magnet $β$-CaCr$_2$O$_4$,"We apply neutron spectroscopy to measure the magnetic dynamics in the S=3/2
+magnet $\beta$-CaCr$_2$O$_4$ (T$_N$=21 K). The low-energy fluctuations, in the
+ordered state, resemble large-S linear spin-waves from the incommensurate
+ground state. However, at higher energy transfers, these semi-classical and
+harmonic dynamics are replaced by an energy and momentum broadened continuum of
+excitations. Applying kinematic constraints required for energy and momentum
+conservation, sum rules of neutron scattering, and comparison against exact
+diagonalization calculations, we show that the dynamics at high-energy
+transfers resemble low-S one-dimensional quantum fluctuations.
+$\beta$-CaCr$_2$O$_4$ represents an example of a magnet at the border between
+classical N\'eel and quantum phases, displaying dual characteristics.",2012.06314v2
+2020-12-12,Magnetization Dynamics of Fibonacci-Distorted Kagome Artificial Spin Ice,"We present results of ferromagnetic resonance (FMR) experiments and
+micromagnetic simulations for a distorted, 2D Kagome artificial spin ice. The
+distorted structure is created by continuously modulating the 2D primitive
+lattice translation vectors of a periodic honeycomb lattice, according to an
+aperiodic Fibonacci sequence used to generate 1D quasicrystals. Experimental
+data and micromagnetic simulations show the Fibonacci distortion causes
+broadening and splitting of FMR modes into multiple branches, which accompany
+the increasing number of segment lengths and orientations that develop with
+increasing distortion. When the applied field is increased in the opposite
+direction to the net magnetization of a segment, spin wave modes appear,
+disappear or suddenly shift, to signal segment magnetization reversal events.
+These results show the complex behavior of reversal events, as well as
+well-defined frequencies and frequency-field slopes of FMR modes, can be
+precisely tuned by varying the severity of the aperiodic lattice distortion.
+This type of distorted structure could therefore provide a new tool for the
+design of complicated magnonic systems.",2012.06837v1
+2020-12-14,Non-collinear ground state from a four-spin chiral exchange in a tetrahedral magnet,"We propose a quartic chiral term $m_x m_y m_z \nabla \cdot \mathbf{m}$ for
+the energy density of a cubic ferromagnet with broken parity symmetry (point
+group $T_d$). We demonstrate that this interaction causes a phase transition
+from a collinear ferromagnetic state to a non-collinear magnetic cone ground
+state provided its strength exceeds the geometric mean of magnetic exchange and
+cubic anisotropy. The corresponding non-collinear ground state may also be
+additionally stabilized by an external magnetic field pointing along certain
+crystallographic directions. The four-spin chiral exchange does also manifest
+itself in peculiar magnon spectra and favors spin waves with the wave vector
+that is perpendicular to the average magnetization direction.",2012.07666v1
+2020-12-17,Geometric magnonics with chiral magnetic domain walls,"Spin wave, the collective excitation of magnetic order, is one of the
+fundamental angular momentum carriers in magnetic systems. Understanding the
+spin wave propagation in magnetic textures lies in the heart of developing pure
+magnetic information processing schemes. Here we show that the spin wave
+propagation across a chiral domain wall follows simple geometric trajectories,
+similar to the geometric optics. And the geometric behaviors are qualitatively
+different in normally magnetized film and tangentially magnetized film. We
+identify the lateral shift, refraction, and total reflection of spin wave
+across a ferromagnetic domain wall. Moreover, these geometric scattering
+phenomena become polarization-dependent in antiferromagnets, indicating the
+emergence of spin wave birefringence inside antiferromagnetic domain wall.",2012.09420v1
+2020-12-18,Breaking Space Inversion-Symmetry to Obtain Asymmetric Spin-Wave Excitation in Systems with Nonuniform Magnetic Exchange,"We report on the consequences of non-uniform exchange in magnetic systems.
+The quantum mechanical exchange interaction between spins is responsible for
+the phenomenon of magnetic order, and is generally considered to be uniform
+across bulk magnetic systems. Partly inspired by the Dzyaloshinskii-Moriya
+interaction--also known as antisymmetric exchange--we use a linearly varying
+exchange interaction along a magnetic strip as a route to spatial inversion
+symmetry-breaking. We find that, in addition to asymmetric modes and
+localization, spatially-varying exchange can be used to design nonreciprocal
+magnetic signal excitation at frequencies that are tunable. Moreover, our work
+predicts nonreciprocity to occur across a vast range of frequencies up to
+hundreds of GHz. Such spin wave engineering is a key area of ongoing research
+in the fields of magnonics and spintronics, which are expected to enable the
+next generation of communication technology. Analogous nonreciprocity is
+expected to occur in other wave systems with gradient properties.",2012.10381v2
+2020-12-21,Effective quantum dynamics induced by a driven two-level-system bath,"We derive a Born-Markov master equation describing the dissipation induced by
+a bath of lossy but coherently driven two-level systems (TLS) coupled to a
+bosonic system via Jaynes-Cummings interaction. We analytically derive all the
+master equation rates. We characterize these rates for the particular case of a
+single-mode system coupled to identical TLS. We study the steady state of the
+system and its exotic properties stemming from the non-thermal stationary state
+of the driven TLS bath. These properties include dissipative amplification,
+bath-induced linear instability, and both coherent and dissipative squeezing.
+The master equation is valid for arbitrarily strong TLS driving, and it can be
+generalized to include multi-level systems or other system-bath interaction
+terms, among others. Our work provides a tool to study and characterize
+TLS-induced decoherence, a key limiting factor in quantum technological devices
+based on, for instance, superconducting circuits, magnonic systems, or quantum
+acoustics.",2012.11235v2
+2020-12-29,Topological to magnetically ordered quantum phase transition in antiferromagnetic spin ladders with long-range interactions,"We study a generalized quantum spin ladder with staggered long range
+interactions that decay as a power-law with exponent $\alpha$. Using large
+scale quantum Monte Carlo (QMC) and density matrix renormalization group (DMRG)
+simulations, we show that this model undergoes a transition from a rung-dimer
+phase characterized by a non-local string order parameter, to a symmetry broken
+N\'eel phase. We find evidence that the transition is second order. In the
+magnetically ordered phase, the spectrum exhibits gapless modes, while
+excitations in the gapped phase are well described in terms of triplons --
+bound states of spinons across the legs. We obtain the momentum resolved spin
+dynamic structure factor numerically and find a well defined triplon band that
+evolves into a gapless magnon dispersion across the transition. We further
+discuss the possibility of deconfined criticality in this model.",2012.14908v5
+2012-05-04,Longitudinal excitations in triangular lattice antiferromagnets,"We study the longitudinal excitations of quantum antiferromagnets on a
+triangular lattice by a recently proposed microscopic many-body approach based
+on magnon-density waves. We calculate the full longitudinal excitation spectra
+of the antiferromagnetic Heisenberg model for a general spin quantum number in
+the isotropic limit. Similar to the square lattice model, we find that, at the
+center of the first hexagonal Brillouin zone $\Gamma(\mathbf q=0)$ and at the
+magnetic ordering wavevectors $\pm[\mathbf Q= (4\pi/3,0)]$, the excitation
+spectra become gapless in the thermodynamic limit, due to the slow, logarithmic
+divergence of the structure factor. However, these longitudinal modes on
+two-dimensional models may be considered as quasi-gapped, as any finite-size
+effect or small anisotropy will induce a large energy gap, when compared with
+the counterpart of the transverse spin-wave excitations. We also discuss a
+possible second longitudinal mode in the triangular lattice model due to the
+noncollinear nature of its magnetic order.",1205.0977v2
+2012-05-16,Softened magnetic excitations in the s = 3/2 distorted triangular antiferromagnet alpha-CaCr2O4,"The spin dynamics and magnetic excitations of the slightly distorted
+triangular s = 3/2 system alpha-CaCr2O4 are investigated by means of Raman
+spectroscopy and electron spin resonance (ESR) to elucidate its peculiar
+magnetic properties. Two-magnon excitations in circular RL symmetry show a
+multi-maximum structure with a dominant spectral weight at low energies. The
+temperature dependence of the ESR linewidth is described by a critical
+broadening DeltaHpp(T) ~ (T - T_N)^{-p} with the exponent p = 0.30(3) - 0.38(5)
+for temperatures above T_N = 42.6 K. The exponent is much smaller than that of
+other s = 3/2 triangular lattices. This is ascribed to soft roton-like modes,
+indicative of the instability of a helical 120{\deg} phase. As an origin we
+discuss a complex spin topology formed by four inequivalent nearest neighbor
+and sizable next-nearest neighbor interactions.",1205.3640v2
+2012-05-16,Symmetry Analysis of Holes Localized on a Skyrmion in a Doped Antiferromagnet,"We use the low-energy effective field theory for holes coupled to the
+staggered magnetization in order to investigate the localization of holes on a
+Skyrmion in a square lattice antiferromagnet. When two holes get localized on
+the same Skyrmion, they form a bound state. The quantum numbers of the bound
+state are determined by the quantization of the collective modes of the
+Skyrmion. Remarkably, for p-wave states the quantum numbers are the same as
+those of a hole-pair bound by one-magnon exchange. Two holes localized on a
+Skyrmion with winding number $n = 1$ or 2 may have s- or d-wave symmetry as
+well. Possible relations with preformed Cooper pairs of high-temperature
+superconductors are discussed.",1205.3677v1
+2012-05-29,Hybrid paramagnon phonon modes at elevated temperatures in EuTiO3,"EuTiO3 (ETO) has recently experienced an enormous revival of interest because
+of its possible multiferroic properties which are currently in the focus of
+research. Unfortunately ETO is an unlikely candidate for enlarged
+multifunctionality since the mode softening - typical for ferroelectrics -
+remains incomplete, and the antiferromagnetic properties appear at 5.5K only.
+However, a strong coupling between lattice and Eu spins exists and leads to the
+appearance of a magnon-phonon-hybrid mode at elevated temperatures as evidenced
+by electron paramagnetic resonance (EPR), muon spin rotation ({\mu}SR)
+experiments and model predictions based on a coupled spin-polarizability
+Hamiltonian. This novel finding supports the notion of strong
+magneto-dielectric (MD) effects being realized in ETO and opens new strategies
+in material design and technological applications.",1205.6287v1
+2017-05-10,Hierarchy of correlations for the Ising model in the Majorana representation,"We study the quantum Ising model in D dimensions with the equation of motion
+technique, in combination with the Majorana representation for spins. The
+decoupling scheme used for the Green's functions is based on the hierarchy of
+correlations in position space. To lowest order this method reproduces the well
+known mean field phase diagram and critical exponents. When correlations
+between spins are included, we show how the appearance of thermal fluctuations
+and magnons strongly affect the physical properties. We demonstrate that in 1D
+and for B=0, thermal fluctuations completely destroy the ordered phase, and
+that near the quantum critical point, the quantum model displays different
+behavior than its classical counterpart. We discuss the connection with the
+Dyson's equation formalism and the explicit form of the self-energies.",1705.03961v2
+2017-05-17,Quantum criticality in the coupled two-leg spin ladder Ba2CuTeO6,"We report on zero-field muon spin rotation, electron spin resonance and
+polarized Raman scattering measurements of the coupled quantum spin ladder
+Ba2CuTeO6. Zero-field muon spin rotation and electron spin resonance probes
+disclose a successive crossover from a paramagnetic through a spin-liquid-like
+into a magnetically ordered state with decreasing temperature. More
+significantly, the two-magnon Raman response obeys a T-linear scaling relation
+in its peak energy, linewidth and intensity. This critical scaling behavior
+presents an experimental signature of proximity to a quantum critical point
+from an ordered side in Ba2CuTeO6.",1705.06035v1
+2017-05-18,Topological quantum paramagnet in a quantum spin ladder,"It has recently been found that bosonic excitations of ordered media, such as
+phonons or spinons, can exhibit topologically nontrivial band structures. Of
+particular interest are magnon and triplon excitations in quantum magnets, as
+they can easily be manipulated by an applied field. Here we study triplon
+excitations in an S=1/2 quantum spin ladder and show that they exhibit
+nontrivial topology, even in the quantum-disordered paramagnetic phase. Our
+analysis reveals that the paramagnetic phase actually consists of two separate
+regions with topologically distinct triplon excitations. We demonstrate that
+the topological transition between these two regions can be tuned by an
+external magnetic field. The winding number that characterizes the topology of
+the triplons is derived and evaluated. By the bulk-boundary correspondence, we
+find that the non-zero winding number implies the presence of localized triplon
+end states. Experimental signatures and possible physical realizations of the
+topological paramagnetic phase are discussed.",1705.06764v3
+2017-05-29,High pressure Raman study of the quantum magnet (C$_4$H$_{12}$N$_2$)Cu$_2$Cl$_6$,"Magnetic and lattice excitations in the quantum antiferromagnet
+(C$_4$H$_{12}$N$_2$)Cu$_2$Cl$_6$ (PHCC) are studied across two pressure-induced
+phase transition at $P_c=4.3~\mathrm{kbar}$ and $P_1=13.4~\mathrm{kbar}$ using
+Raman spectroscopy. It is confirmed that neither transition is a result of a
+structural transformation. Magnetic scattering is detected. It shows a
+pronounced pressure dependence and undergoes substantial changes at both
+transitions. The results are in clear contradiction with previous neutron
+studies, which detected only minor changes of the magnon spectrum at $P_1$. A
+number of phonons show anomalous frequency shifts at low temperatures. This
+effect is pressure dependent and for two of the observed phonons dramatically
+reverses sign at around $P_1$. The anomalous behavior is attributed to strong
+magnetoelastic coupling in PHCC.",1705.10235v3
+2017-05-30,Communication and information processing in magnetic nanostructures with edge spin waves,"Low dissipation data processing with spins is one of the promising directions
+for future information and communication technologies. Despite a signifcant
+progress, the available magnonic devices are not broadband yet and have
+restricted capabilities to redirect spin waves. Here we propose a breakthrough
+approach to the spin wave manipulation in patterned magnetic nanostructures
+with unmatched characteristics, which exploits spin waves analogous to edge
+waves propagating along a water-wall boundary. Using theory, micromagnetic
+simulations and experiment we investigate spin waves propagating along the
+edges in magnetic structures, under an in-plane DC magnetic field inclined with
+respect to the edge. The proposed edge spin waves overcome important challenges
+faced by previous technologies such as the manipulation of the spin wave
+propagation direction, and they substantially improve the capability of
+transmitting information at frequencies exceeding 10 GHz. The concept of the
+edge spin waves allows to design broad range of logic devices such as
+splitters, interferometers, or edge spin wave transistors with unprecedented
+characteristics and potentially strong impact on information technologies.",1705.10536v2
+2017-09-26,Magnetic-field-induced suppression of spin Peltier effect in Pt/${\rm Y_{3}Fe_{5}O_{12}}$ system at room temperature,"We report the observation of magnetic-field-induced suppression of the spin
+Peltier effect (SPE) in a junction of a paramagnetic metal Pt and a
+ferrimagnetic insulator ${\rm Y_{3}Fe_{5}O_{12}}$ (YIG) at room temperature.
+For driving the SPE, spin currents are generated via the spin Hall effect from
+applied charge currents in the Pt layer, and injected into the adjacent thick
+YIG film. The resultant temperature modulation is detected by a commonly-used
+thermocouple attached to the Pt/YIG junction. The output of the thermocouple
+shows sign reversal when the magnetization is reversed and linearly increases
+with the applied current, demonstrating the detection of the SPE signal. We
+found that the SPE signal decreases with the magnetic field. The observed
+suppression rate was found to be comparable to that of the spin Seebeck effect
+(SSE), suggesting the dominant and similar contribution of the low-energy
+magnons in the SPE as in the SSE.",1709.08997v1
+2017-09-29,Non-local Gilbert damping tensor within the torque-torque correlation model,"An essential property of magnetic devices is the relaxation rate in magnetic
+switching which depends strongly on the damping in the magnetisation dynamics.
+It was recently measured that damping depends on the magnetic texture and,
+consequently, is a non-local quantity. The damping enters the
+Landau-Lifshitz-Gilbert equation as the phenomenological Gilbert damping
+parameter $\alpha$, that does not, in a straight forward formulation, account
+for non-locality. Efforts were spent recently to obtain Gilbert damping from
+first principles for magnons of wave vector $\mathbf{q}$. However, to the best
+of our knowledge, there is no report about real space non-local Gilbert damping
+$\alpha_{ij}$. Here, a torque-torque correlation model based on a tight binding
+approach is applied to the bulk elemental itinerant magnets and it predicts
+significant off-site Gilbert damping contributions, that could be also
+negative. Supported by atomistic magnetisation dynamics simulations we reveal
+the importance of the non-local Gilbert damping in atomistic magnetisation
+dynamics. This study gives a deeper understanding of the dynamics of the
+magnetic moments and dissipation processes in real magnetic materials. Ways of
+manipulating non-local damping are explored, either by temperature, material's
+doping or strain.",1709.10365v1
+2018-03-05,Low-Energy Excitations in Quantum Spin-Liquids Identified by Optical Spectroscopy,"The electrodynamic response of organic spin liquids with highly-frustrated
+triangular lattices has been measured in a wide energy range. While the overall
+optical spectra of these Mott insulators are governed by transitions between
+the Hubbard bands, distinct in-gap excitations can be identified at low
+temperatures and frequencies which we attribute to the quantum spin liquid
+state. For the strongly correlated
+$\beta^{\prime}$-EtMe$_3$\-Sb\-[Pd(dmit)$_2$]$_2$, we discover enhanced
+conductivity below $175~{\rm cm}^{-1}$, comparable to the energy of the
+magnetic coupling $J\approx 250$ K. For $\omega\rightarrow 0$ these
+low-frequency excitations vanish faster than the charge-carrier response
+subject to Mott-Hubbard correlations, resulting in a dome-shape band peaked at
+100~\cm. Possible relations to spinons, magnons and disorder are discussed.",1803.01553v2
+2018-03-12,Focused ion beam direct writing of magnetic patterns with controlled structural and magnetic properties,"Focused ion beam irradiation of metastable Fe$_{78}$Ni$_{22}$ thin films
+grown on Cu(100) substrates is used to create ferromagnetic,
+body-centered-cubic patterns embedded into paramagnetic, face-centered-cubic
+surrounding. The structural and magnetic phase transformation can be controlled
+by varying parameters of the transforming gallium ion beam. The focused ion
+beam parameters as ion dose, number of scans, and scanning direction can be
+used not only to control a degree of transformation, but also to change the
+otherwise four-fold in-plane magnetic anisotropy into the uniaxial anisotropy
+along specific crystallographic direction. This change is associated with a
+preferred growth of specific crystallographic domains. The possibility to
+create magnetic patterns with continuous magnetization transitions and at the
+same time to create patterns with periodical changes in magnetic anisotropy
+makes this system an ideal candidate for rapid prototyping of a large variety
+of nanostructured samples. Namely spin-wave waveguides and magnonic crystals
+can be easily combined into complex devices in a single fabrication step.",1803.04348v1
+2018-03-18,Enhancement of photon blockade effect via quantum interference,"We study the photon blockade effect in a coupled cavity system, which is
+formed by a linear cavity coupled to a Kerr-type nonlinear cavity via a
+photon-hopping interaction. We explain the physical phenomenon from the
+viewpoint of the conventional and unconventional photon blockade effects. The
+corresponding physical mechanisms of the two kinds of photon blockade effects
+are based on the anharmonicity in the eigenenergy spectrum and the destructive
+quantum interference between two different transition paths, respectively. In
+particular, we find that the photon blockade via destructive quantum
+interference also exists in the conventional photon blockade regime, and that
+the unconventional photon blockade occurs in both the weak- and strong-Kerr
+nonlinearity cases. The photon blockade effect can be observed by calculating
+the second-order correlation function of the cavity field. This model is
+general and hence it can be implemented in various experimental setups such as
+coupled optical-cavity systems, coupled photon-magnon systems, and coupled
+superconducting-resonator systems. We present some discussions on the
+experimental feasibility.",1803.06642v2
+2018-06-02,Ultra-low damping insulating magnetic thin films get perpendicular,"A magnetic material combining low losses and large Perpendicular Magnetic
+Anisotropy (PMA) is still a missing brick in the magnonic and spintronic
+fields. We report here on the growth of ultrathin Bismuth doped
+Y$_{3}$Fe$_{5}$O$_{12}$ (BiYIG) films on Gd$_{3}$Ga$_{5}$O$_{12}$ (GGG) and
+substituted GGG (sGGG) (111) oriented substrates. A fine tuning of the PMA is
+obtained using both epitaxial strain and growth induced anisotropies. Both
+spontaneously in-plane and out-of-plane magnetized thin films can be
+elaborated. Ferromagnetic Resonance (FMR) measurements demonstrate the high
+dynamic quality of these BiYIG ultrathin films, PMA films with Gilbert damping
+values as low as 3 10$^{-4}$ and FMR linewidth of 0.3 mT at 8 GHz are achieved
+even for films that do not exceed 30 nm in thickness. Moreover, we measure
+Inverse Spin Hall Effect (ISHE) on Pt/BiYIG stacks showing that the magnetic
+insulator$'$s surface is transparent to spin current making it appealing for
+spintronic applications.",1806.00658v1
+2018-06-05,Backscattering immunity of dipole-exchange magnetostatic surface spin waves,"The existence of backscattering-immune spin-wave modes is demonstrated in
+magnetic thin films of nano-scale thickness. Our results reveal that chiral
+Magneto Static Surface Waves (cMSSWs), which propagate perpendicular to the
+magnetization direction in an in-plane magnetized thin film, are robust against
+backscattering from surface defects. cMSSWs are protected against various types
+of surface inhomogeneities and defects as long as their frequency lies inside
+the gap of the volume modes. Our explanation is independent of the topology of
+the modes and predicts that this robustness is a consequence of symmetry
+breaking of the dynamic magnetic fields of cMSSWs due to the off-diagonal part
+of the dipolar interaction tensor, which is present both for long- (dipole
+dominated) and short-wavelength (exchange dominated) spin waves. Micromagnetic
+simulations confirm the robust character of the cMSSWs. Our results open a new
+direction in designing highly efficient magnonic logic elements and devices
+employing cMSSWs in nano-scale thin films.",1806.01554v3
+2018-06-06,Spin liquid fingerprints in the thermal transport of a Kitaev-Heisenberg ladder,"We identify fingerprints of a proximate quantum spin-liquid (QSL), observable
+by finite-temperature dynamical thermal transport within a minimal version of
+the idealized Kitaev model on a two-leg ladder, if subjected to inevitably
+present Heisenberg couplings. Using exact diagonalization and quantum
+typicality, we uncover (i) an insulator-conductor crossover induced by fracton
+recombination at infinitesimal Heisenberg coupling, (ii) low- and high-energy
+signatures of fractons, which survive far off the pure QSL point, and (iii) a
+non-monotonous current life-time versus Heisenberg couplings. Guided by
+perturbation theory, we find (iv) a Kitaev-exchange induced `one-magnon'
+contribution to the dynamical heat transport in the strong Heisenberg rung
+limit.",1806.02344v1
+2018-06-07,On the magnetic and electronic properties of NpPdSn,"We have studied NpPdSn by means of the heat capacity, electrical resistivity,
+Seebeck and Hall effect, $^{237}$Np M\""{o}ssbauer spectroscopy, and neutron
+diffraction measurements in the temperature range 2-300 K and under magnetic
+fields up to 14 T. NpPdSn orders antiferromagnetically below the N\'eel
+temperature $T_N$ = 19 K and shows localized magnetism of Np$^{3+}$ ion with a
+a doubly degenerate ground state. In the magnetic state the electrical
+resistivity and heat capacity are characterized by electron-magnon scattering
+with spin-waves spectrum typical of anisotropic antiferromagnets. An enhanced
+Sommerfeld coefficient and typical behavior of magnetorestistivity, Seebeck and
+Hall coefficients are all characteristic of systems with strong electronic
+correlations. The low temperature antiferromagnetic state of NpPdSn is verified
+by neutron diffraction and $^{237}$Np M\""{o}ssbauer spectroscopy and possible
+magnetic structures are discussed.",1806.02879v1
+2018-06-13,Nature of the spin liquid in underdoped cuprate superconductors,"In the present work we address a long standing problem of the magnetic ground
+state and magnetic excitations in underdoped cuprates. Modelling cuprates by
+the extended $t-J$ model we show that there is a hidden dimensionless parameter
+$\lambda$ which drives magnetic criticality at low doping $x$. Hence we derive
+the zero temperature $\lambda-x$ phase diagram of the model. It is argued that
+all underdoped cuprates are close to the quantum tricritical point $x=0$,
+$\lambda=1$. The three phases ""meet"" at the tricritical point: (i) N\'eel
+antiferromagnet, (ii) spin spiral with antinodal direction of the spiral wave
+vector, (iii) algebraic spin liquid. We argue that underdoped cuprates belong
+either to the spin liquid phase or they are on the borderline between the spin
+liquid and the spin spiral. We calculate the energy position $E_{cross}$ of the
+inelastic neutron scattering response maximum at ${\bm q}=(\pi,\pi)$ and
+compare our results with experiments. We also explain softening of magnons in
+the intermediate regime observed in inelastic neutron scattering.",1806.04855v1
+2018-06-13,Effective Ising model for correlated systems with charge ordering,"Collective electronic fluctuations in correlated materials give rise to
+various important phenomena, such as existence of the charge ordering,
+superconductivity, Mott insulating and magnetic phases, plasmon and magnon
+modes, and other interesting features of such systems. Unfortunately,
+description of these correlation effects requires significant efforts, since
+they almost entirely rely on strong local and nonlocal electron-electron
+interactions. Some collective phenomena, such as magnetism, can be sufficiently
+described by a simple Heisenberg-like models that are formulated in terms of
+bosonic variables. This fact suggests that other many-body excitations can also
+be described by simple bosonic models in spirit of the Heisenberg theory. Here
+we derive an effective bosonic action for charge degrees of freedom for the
+extended Hubbard model and define a physical regime where the obtained action
+reduces to a classical Hamiltonian of an effective Ising model.",1806.04927v3
+2018-06-14,Magnetism of the N=42 kagome lattice antiferromagnet,"For the paradigmatic frustrated spin-half Heisenberg antiferromagnet on the
+kagome lattice we performed large-scale numerical investigation of
+thermodynamic functions by means of the finite-temperature Lanczos method for
+system sizes of up to N=42. We present the dependence of magnetization as well
+as specific heat on temperature and external field and show in particular that
+a finite-size scaling of specific heat supports the appearance of a
+low-temperature shoulder below the major maximum. This seems to be the result
+of a counterintuitive motion of the density of singlet states towards higher
+energies. Other interesting features that we discuss are the asymmetric melting
+of the 1/3 magnetization plateau as well the field dependence of the specific
+heat that exhibits characteristic features caused by the existence of a flat
+one-magnon band. By comparison with the unfrustrated square-lattice
+antiferromagnet the tremendous role of frustration in a wide temperature range
+is illustrated.",1806.05541v1
+2018-06-15,Positivity of hexagon perturbation theory,"The hexagon-form-factor program was proposed as a way to compute three- and
+higher-point correlation functions in $\mathcal{N}=4$ super-symmetric
+Yang-Mills theory and in the dual AdS$_5\times$S$^5$ superstring theory, by
+exploiting the integrability of the theory in the 't Hooft limit. This approach
+is reminiscent of the asymptotic Bethe ansatz in that it applies to a
+large-volume expansion. Finite-volume corrections can be incorporated through
+L\""uscher-like formulae, though the systematics of this expansion is largely
+unexplored so far. Strikingly, finite-volume corrections may feature negative
+powers of the 't Hooft coupling $g$ in the small-$g$ expansion, potentially
+leading to a breakdown of the formalism. In this work we show that the
+finite-volume perturbation theory for the hexagon is positive and thereby
+compatible with the weak-coupling expansion for arbitrary $n$-point functions.",1806.06051v2
+2018-06-18,Cavity optomagnonics with magnetic textures: coupling a magnetic vortex to light,"Optomagnonic systems, where light couples coherently to collective
+excitations in magnetically ordered solids, are currently of high interest due
+to their potential for quantum information processing platforms at the
+nanoscale. Efforts so far, both at the experimental and theoretical level, have
+focused on systems with a homogeneous magnetic background. A unique feature in
+optomagnonics is however the possibility of coupling light to spin excitations
+on top of magnetic textures. We propose a cavity-optomagnonic system with a non
+homogeneous magnetic ground state, namely a vortex in a magnetic microdisk. In
+particular we study the coupling between optical whispering gallery modes to
+magnon modes localized at the vortex. We show that the optomagnonic coupling
+has a rich spatial structure and that it can be tuned by an externally applied
+magnetic field. Our results predict cooperativities at maximum photon density
+of the order of $\mathcal{C}\approx10^{-2}$ by proper engineering of these
+structures.",1806.06727v2
+2018-06-21,Holographic three-point correlators in the Schrodinger/dipole CFT correspondence,"We calculate, for the first time, three-point correlation functions involving
+""heavy"" operators in the Schrodinger/null-dipole CFT correspondence at strong
+coupling. In particular, we focus on the three-point functions of the dilaton
+modes and two ""heavy"" operators. The heavy states are dual to the single spin
+and dyonic magnon, the single spin and dyonic spike solutions or to two novel
+string solutions which do not have an undeformed counterpart. Our results
+provide the leading term of the correlators in the large $\lambda$ expansion
+and are in perfect agreement with the form of the correlator dictated by
+non-relativistic conformal invariance. We also specify the scaling function
+which can not be fixed by using conformal invariance.",1806.08181v1
+2018-07-03,Antiferromagnetism emerging in a ferromagnet with gain,"We present a theoretical mapping to show that a ferromagnet with gain (loss)
+is equivalent to an antiferromagnet with an equal amount of loss (gain). Our
+finding indicates a novel first-order ferromagnet-antiferromagnet phase
+transition by tuning the gain-loss parameter. As an appealing application, we
+demonstrate the realization as well as the manipulation of the
+antiferromagnetic skyrmion, a stable topological quasiparticle not yet observed
+experimentally, in a chiral ferromagnetic thin film with gain. We also consider
+ferromagnetic bilayers with balanced gain and loss, and show that the
+antiferromagnetic skyrmion can be found only in the cases with broken
+parity-time symmetry phase. Our results pave a way for investigating the
+emerging antiferromagnetic spintronics and parity-time symmetric magnonics in
+ferromagnets.",1807.01048v2
+2018-07-08,Hybrid quantum system with nitrogen-vacancy centers in diamond coupled to surface phonon polaritons in piezomagnetic superlattices,"We investigate a hybrid quantum system where an ensemble of nitrogen-vacancy
+(NV) centers in diamond is interfaced with a piezomagnetic superlattice that
+supports surface phonon polaritons (SPhPs). We show that the strong magnetic
+coupling between the collective spin waves in the NV spin ensemble and the
+quantized SPhPs can be realized, thanks to the subwavelength nature of the
+SPhPs and relatively long spin coherence times. The magnon-polariton coupling
+allows different modes of the SPhPs to be mapped and orthogonally stored in
+different spatial modes of excitation in the solid medium. Because of its easy
+implementation and high tunability, the proposed hybrid structure with NV spins
+and piezoactive superlattices could be used for quantum memory and quantum
+computation.",1807.02750v1
+2018-07-16,Magnetic freezing transition in a CoO/Permalloy bilayer revealed by transverse ac susceptibility,"We utilize variable-temperature, variable-frequency magneto-optical
+transverse magnetic susceptibility technique to study the static and dynamical
+magnetic properties of a thin-film CoO/Permalloy bilayer. Our measurements
+demonstrate that in the studied system, the directional asymmetry of the
+hysteresis loop is associated mainly with the difference in the reversal
+mechanisms between the two reversed states of magnetization stabilized by the
+exchange-induced uniaxial anisotropy. The latter is found to be much larger
+than the exchange-induced unidirectional anisotropy of the ferromagnet. We also
+observe an abrupt variation of the frequency-dependent imaginary part of ac
+susceptibility near the exchange bias blocking temperature, consistent with the
+magnetic freezing transition inferred from the previous time-domain studies of
+magnetic aging in similar systems. The developed measurement approach enables
+precise characterization of the dynamical and static characteristics of
+thin-film magnetic heterostructures that can find applications in
+reconfigurable magnonic and neuromorphic circuits.",1807.05990v2
+2018-07-19,Spin-wave amplification and lasing driven by inhomogeneous spin transfer torques,"We show that an inhomogeneity in the spin-transfer torques in a metallic
+ferromagnet under suitable conditions strongly amplifies incoming spin waves.
+Moreover, at nonzero temperatures the incoming thermally occupied spin waves
+will be amplified such that the region with inhomogeneous spin transfer torques
+emits spin waves spontaneously, thus constituting a spin-wave laser. We
+determine the spin-wave scattering amplitudes for a simplified model and
+set-up, and show under which conditions the amplification and lasing occurs.
+Our results are interpreted in terms of a so-called black-hole laser, and could
+facilitate the field of magnonics, that aims to utilize spin waves in logic and
+data-processing devices.",1807.07312v1
+2018-07-25,Left-handed polarized spin waves in ferromagnets induced by spin-transfer torque,"Polarization is a fundamental property of waves that refers to the
+orientation of the oscillations. It has been widely used to encode information
+in photonics and phononics. However, the polarization of spin waves is rarely
+used yet in magnonics. The reason for this is that only the right-handed
+polarized spin waves can be accommodated in ferromagnets. Here, we report that
+stable left-handed polarized spin waves can be introduced into ferromagnets if
+a spin-polarized electrical current is presented. The right-handed and
+left-handed polarized spin waves coexist when the current density is larger
+than a critical value while the system keeps stable. The results are confirmed
+by micromagnetic simulations. This work provides new playgrounds to study spin
+waves and points to new findings for future experimental studies.",1807.09456v2
+2018-07-27,Optimization of Multi-Frequency Magnonic Waveguides with Enhanced Group Velocities by Exchange Coupled Ferrimagnet/Ferromagnet Bilayers,"We report broadband spectroscopy and numerical analysis by which we explore
+propagating spin waves in a magnetic bilayer consisting of a 23 nm thick
+permalloy film deposited on 130 nm thick $Y_{3}Fe_{5}O_{12}$. In the bilayer,
+we observe a characteristic mode that exhibits a considerably larger group
+velocity at small in-plane magnetic field than both the magnetostatic and
+perpendicular standing spin waves. Using the finite element method, we confirm
+the observations by simulating the mode profiles and dispersion relations. They
+illustrate the hybridization of spin wave modes due to exchange coupling at the
+interface. The high-speed propagating mode found in the bilayer can be utilized
+to configure multi-frequency spin wave channels enhancing the performance of
+spin wave based logic devices.",1807.10508v2
+2018-07-30,Topological spin excitations in honeycomb ferromagnet CrI$_3$,"In two dimensional honeycomb ferromagnets, bosonic magnon quasiparticles
+(spin waves) may either behave as massless Dirac fermions or form topologically
+protected edge states. The key ingredient defining their nature is the
+next-nearest neighbor Dzyaloshinskii-Moriya (DM) interaction that breaks the
+inversion symmetry of the lattice and discriminates chirality of the associated
+spin-wave excitations. Using inelastic neutron scattering, we find that spin
+waves of the insulating honeycomb ferromagnet CrI$_3$ ($T_C=61$ K) have two
+distinctive bands of ferromagnetic excitations separated by a $\sim$4 meV gap
+at the Dirac points. These results can only be understood by considering a
+Heisenberg Hamiltonian with DM interaction, thus providing experimental
+evidence that spin waves in CrI$_3$ can have robust topological properties
+useful for dissipationless spintronic applications.",1807.11452v3
+2018-12-04,Optical excitation of single- and multi-mode magnetization precession in Galfenol nanolayers,"We demonstrate a variety of precessional responses of the magnetization to
+ultrafast optical excitation in nanolayers of Galfenol (Fe,Ga), which is a
+ferromagnetic material with large saturation magnetization and enhanced
+magnetostriction. The particular properties of Galfenol, including cubic
+magnetic anisotropy and weak damping, allow us to detect up to 6 magnon modes
+in a 120-nm layer, and a single mode with effective damping ${\alpha}_{eff}$ =
+0.005 and frequency up to 100 GHz in a 4-nm layer. This is the highest
+frequency observed to date in time-resolved experiments with metallic
+ferromagnets. We predict that detection of magnetization precession approaching
+THz frequencies should be possible with Galfenol nanolayers.",1812.01237v1
+2018-12-08,Microwave to optical photon conversion via fully concentrated rare-earth ion crystals,"Most investigations of rare earth ions in solids for quantum information have
+used rare earth ion doped crystals. Here we analyse the conversion of quantum
+information from microwave photons to optical frequencies using crystals where
+the rare earth ions, rather than being dopants, are part of the host crystal.
+The potential of large ion densities and small linewidths makes such systems
+very attractive in this application. We show that, as well as high efficiency,
+large bandwidth conversion is possible. In fact, the collective coupling
+between the rare earth ions and the optical and microwave cavities is large
+enough that the limitation on the bandwidth of the devices will instead be the
+spacing between magnon mode modes in the crystal.",1812.03246v1
+2018-12-14,The Higgs Mode of Planar Coupled Spin-Ladders and its Observation in C$_9$H$_{18}$N$_2$CuBr$_4$,"Polarized inelastic neutron scattering experiments recently identified the
+amplitude (Higgs) mode in C$_9$H$_{18}$N$_2$CuBr$_4$, a two-dimensional
+near-quantum-critical spin-1/2 two-leg ladder compound, which exhibits a weak
+easy-axis exchange anisotropy. Here, we theoretically examine the dynamic spin
+structure factor of such planar coupled spin-ladder systems using large-scale
+quantum Monte Carlo simulations. This allows us to provide a quantitative
+account of the experimental neutron scattering data within a consistent quantum
+spin model. Moreover, we trance the details of the continuous evolution of the
+amplitude mode from a two-particle bound state of coupled ladders in the
+classical Ising limit all the way to the quantum spin-1/2 Heisenberg limit with
+fully restored SU(2) symmetry, where it gets overdamped by the two-magnon
+continuum in neutron scattering.",1812.05853v1
+2018-12-18,Quantum Interface of an Electron and a Nuclear Ensemble,"Coherent excitation of an ensemble of quantum objects underpins quantum
+many-body phenomena, and offers the opportunity to realize a quantum memory to
+store information from a qubit. Thus far, a deterministic and coherent
+interface between a single quantum system, e.g. a qubit, and such an ensemble
+has remained elusive. We first use an electron to cool the mesoscopic
+nuclear-spin ensemble of a semiconductor quantum dot to the nuclear
+sideband-resolved regime. We then implement an all-optical approach to access
+these individual quantized electronic-nuclear spin transitions. Finally, we
+perform coherent optical rotations of a single collective nuclear spin
+excitation corresponding to a spin wave called a nuclear magnon. These results
+constitute the building blocks of a dedicated local memory per quantum-dot spin
+qubit and promise a solid-state platform for quantum-state engineering of
+isolated many-body systems.",1812.07540v1
+2018-12-22,Atomic antiferromagnetic domain wall propagation beyond the relativistic limit,"We theoretically investigate the dynamics of atomic domain walls (DWs) in
+antiferromagnets driven by a spin-orbit field. For a DW with the width of a few
+lattice constants, we identify a Peierls-like pinning effect, with the
+depinning field exponentially decaying with the DW width, so that a spin-orbit
+field moderately larger than the threshold can drive the propagation of an
+atomic DW in a step-wise manner. For a broad DW, the Peierls pinning is
+negligibly small. However, the external spin-orbit field can induce a fast DW
+propagation, accompanied by a significant shrinking of its width down to atomic
+scales. Before stepping into the pinning region, noticeable spin waves are
+emitted at the tail of the DW. The spin-wave emission event not only broadens
+the effective width of the DW, but also pushes the DW velocity over the
+magnonic barrier, which is generally believed to be the relativistic limit of
+the DW speed. While the existing dynamic theory based on the continuum
+approximation fails in the atomic scale, we develop an energy conversion theory
+to interpret the DW dynamics beyond the relativistic limit.",1812.09540v1
+2019-01-07,Simultaneous Optical and Electrical Spin-Torque Magnetometry with Stroboscopic Detection of Spin-Precession Phase,"Spin-based coherent information processing and encoding utilize the
+precession phase of spins in magnetic materials. However, the detection and
+manipulation of spin precession phases remain a major challenge for advanced
+spintronic functionalities. By using simultaneous electrical and optical
+detection, we demonstrate the direct measurement of the precession phase of
+Permalloy ferromagnetic resonance driven by the spin-orbit torques from
+adjacent heavy metals. The spin Hall angle of the heavy metals can be
+independently determined from concurrent electrical and optical signals. The
+stroboscopic optical detection also allows spatially measuring local
+spin-torque parameters and the induced ferromagnetic resonance with
+comprehensive amplitude and phase information. Our study offers a route towards
+future advanced characterizations of spin-torque oscillators, magnonic
+circuits, and tunnelling junctions, where measuring the current-induced spin
+dynamics of individual nanomagnets are required.",1901.01923v1
+2019-01-10,Quantum skyrmions in frustrated ferromagnets,"We develop a quantum theory of magnetic skyrmions and antiskyrmions in a
+spin-1/2 Heisenberg magnet with frustrating next-nearest neighbor interactions.
+Using exact diagonalization we show numerically that a quantum skyrmion exists
+as a stable many-magnon bound state and investigate its quantum numbers. We
+then derive a phenomenological Schr\""odinger equation for the quantum skyrmion
+and its internal degrees of freedom. We find that quantum skyrmions have highly
+unusual properties. Their bandwidth is exponentially small and arises from
+tunneling processes between skyrmion and antiskyrmion. The bandstructure
+changes both qualitatively and quantitatively when a single spin is added or
+removed from the quantum skyrmion, reflecting a locking of angular momentum and
+spin quantum numbers characteristic for skyrmions. Additionally, while for weak
+forces the quantum skyrmion is accelerated parallel to the force, it moves in a
+perpendicular direction for stronger fields.",1901.03343v3
+2019-01-11,"Spin pumping as a generic probe for linear spin fluctuations: demonstration with ferromagnetic and antiferromagnetic orders, metallic and insulating electrical states","We investigated spin injection by spin pumping from a spin-injector(NiFe)
+into a spin-sink to detect spin fluctuations in the spin-sink. By scanning the
+ordering-temperature of several magnetic transitions, we found that enhanced
+spin pumping due to spin fluctuations applies with several ordering states:
+ferromagnetic(Tb) and antiferromagnetic(NiO, NiFeOx, BiFeO3, exchange-biased
+and unbiased IrMn). Results also represent systematic experimental
+investigation supporting that the effect is independent of the metallic and
+insulating nature of the spin-sink, and is observed whether the spin current
+probe involves electronic or magnonic transport, facilitating advances in
+material characterization and engineering for spintronic applications.",1901.03539v1
+2019-01-14,Controllable excitation of quasi-linear and bullet modes in a spin-Hall nano-oscillator,"We experimentally demonstrate that both quasi-linear and nonlinear
+self-localized bullet modes of magnetization auto-oscillation can be excited by
+dc current in the nano-gap spin Hall nano-oscillator, by utilizing the geometry
+with an extended gap. The quasi-linear mode is stable at low driving currents,
+while the bullet mode is additionally excited at larger currents, and becomes
+increasingly dominant with increasing current. Time-resolved measurements show
+that the formation of the bullet mode is delayed relative to the quasi-linear
+mode by up to 100 nanoseconds, demonstrating that the mechanisms of the
+formation of these modes are fundamentally different. We discuss the
+relationship between the observed behaviors and the formation of an unstable
+nonlinear magnon condensate.",1901.04197v1
+2019-01-17,"Influences of interfacial oxidization on surface magnetic energy, magnetic damping and spin-orbit-torques in Pt / ferromagnet / capping structures","We investigate the effect of capping layer (CAP) on the interfacial magnetic
+anisotropy energy density (K_S), magnetic damping ({\alpha}), and spin-orbit
+torques (SOTs) in heavy-metal (Pt) / ferromagnet (Co or Py) / CAP (MgO/Ta,
+HfOx, or TaN). At room temperature (RT) the CAP materials influence the
+effective magnitude of K_S, which is associated with a formation of interfacial
+magnetic oxides. The dynamical dissipation parameters of Co are considerably
+influenced by the CAP (especially MgO) while those of Py are not. This is
+possibly due to an extra magnetic damping via spin-pumping process across the
+Co/CoO interface and incoherent magnon generation (spin fluctuation) in the
+interfacial CoO. It is also observed that both anti-damping and field-like SOT
+efficiencies vary marginally with the CAP in the thickness ranges we examined.
+Our results reveal the crucial role of interfacial oxides on the perpendicular
+magnetic anisotropy, magnetic damping, and SOTs.",1901.05777v1
+2019-02-08,Field-tuned spin excitation spectrum of $kπ$-skyrmion,"We study spin-wave excitation modes of $k\pi$ skyrmion in a magnetic nanodot
+under an external magnetic field along $z$-direction using micromagnetic
+simulations based on Landau-Lifshitz-Gilbert equation. We find that a
+transition of $k\pi$ skyrmion to other skyrmion-like structures appears under
+some critical external field, the corresponding spin-wave spectra are simulated
+for each state in the process of applying magnetic field. For skyrmion, the
+frequencies of excitation modes increases and then decreases with the low
+frequency modes splitting at a critical magnetic field. In addition to the well
+known two in-plane rotational modes and a out-of-plane breathing mode of
+skyrmion, a higher number of excitation modes are found with increasing $k$
+($k=2, 3$). The excitation modes vary as a function of magnetic field, and the
+excitation frequencies for different modes exhibit a rapid or slight change
+depending on the field induced change of magnetization profile. Our study
+indicates the rich spin-wave excitations for $k\pi$ skyrmion and opens a
+possibility in theoretical or experimental investigation of magnonics
+application.",1902.02901v2
+2019-02-12,Thermally assisted Skyrmion drag in a nonuniform electric field,"Magnetic skyrmions are topologically protected excitations of the
+magnetization vector field with promising applications in spintronics and
+spin-caloritronics, particularly due to their high mobility. Skyrmions can be
+steered by a spin-polarized charge current or by exposure to a magnonic spin
+current. Here, we propose a further method for driving skyrmions by applying an
+inhomogeneous electric field and a homogeneous thermal bias. We show that the
+inhomogeneous electric torque leads to an efficient skyrmionic drag which can
+be thermally assisted as to enhance the skyrmion velocity. The calculations and
+analysis are limited to insulating samples; for conducting materials the
+influence of the inhomogeneous electric field on the charge carriers need to be
+taken also into account.",1902.04432v1
+2019-02-11,Onset of spin wave time-domain fractals in a dynamic artificial crystal,"We report on the first observation of an exact fractal pattern in the
+time-domain arising spontaneously from a dynamic artificial crystal (DAC). The
+all-magnon process occurs in a passive, unlithographed magnetic waveguide. The
+DAC was created by a standing spin wave of frequency $f_{\mathrm{DAC}}$ in a
+region of nonlinear waveguide, resulting in a spatio-temporally periodic
+potential. The interaction of travelling spin waves of frequency $f'$ with the
+DAC resulted in a series of new modes appearing in a comb with intervals
+$\Delta f^{(0)} = \mid f_{\mathrm{DAC}}-f'\mid$. As $H$ was increased a 1st
+pre-fractal pattern was observed with frequency interval $\Delta f^{(1)}
+=\Delta f^{(0)}/2$. Finally, the onset of a 2nd pre-fractal was observed with
+frequency interval $\Delta f^{(2)} =\Delta f^{(1)}/2 = \Delta f^{(0)}/4$. The
+magnetic field dependence of the nonlinear signals effect matched that of the
+DAC. The fractal-like behavior was demonstrated for different values of $f'$.",1902.04445v2
+2019-02-12,Ultra-low damping in lift-off structured yttrium iron garnet thin films,"We show that using maskless photolithography and the lift-off technique,
+patterned yttrium iron garnet thin films possessing ultra-low Gilbert damping
+can be accomplished. The films of 70 nm thickness were grown on (001)-oriented
+gadolinium gallium garnet by means of pulsed laser deposition, and they exhibit
+high crystalline quality, low surface roughness, and the effective
+magnetization of 127 emu/cm3. The Gilbert damping parameter is as low as
+5x10-4. The obtained structures have well-defined sharp edges which along with
+good structural and magnetic film properties pave a path in the fabrication of
+high-quality magnonic circuits and oxide-based spintronic devices.",1902.04605v1
+2019-02-14,Quantized ΔS=2 Excitation Spectra by Confinement in an S=1 Spin Chain,"We calculate the dynamical spin-structure factor of the $S=1$ Ising spin
+chain with negative single-ion anisotropy in magnetic fields using the infinite
+time-evolving-block-decimation algorithm. We show that when a transverse
+magnetic field is applied, both the $\Delta S=2$ excitation continuum and
+one-magnon mode appear in the low-lying excitation. When a longitudinal
+magnetic field is further applied, the excitation continuum changes into
+quantized excitation spectra. The quantized $\Delta S=2$ excitation spectra
+originate from the confinement of two domain walls, each of which carries
+$\Delta S=1$. The quantized excitation energies are explained by the negative
+zeros in the Airy function.",1902.05169v3
+2019-02-20,Direct photoluminescence probing of ferromagnetism in monolayer two-dimensional CrBr3,"Atomically thin magnets are the key element to build up spintronics based on
+two-dimensional materials. The surface nature of two-dimensional ferromagnet
+opens up opportunities to improve the device performance efficiently. Here, we
+report the intrinsic ferromagnetism in atomically thin monolayer CrBr3,
+directly probed by polarization resolved magneto-photoluminescence. The
+spontaneous magnetization persists in monolayer CrBr3 with a Curie temperature
+of 34 K. The development of magnons by the thermal excitation is in line with
+the spin-wave theory. We attribute the layer-number dependent hysteresis loops
+in thick layers to the magnetic domain structures. As a stable monolayer
+material in air, CrBr3 provides a convenient platform for fundamental physics
+and pushes the potential applications of the two-dimensional ferromagnetism.",1902.07446v1
+2019-02-25,Nonreciprocal nano-optics with spin-waves in synthetic antiferromagnets,"Integrated optically-inspired wave-based processing is envisioned to
+outperform digital architectures in specific tasks, such as image processing
+and speech recognition. In this view, spin-waves represent a promising route
+due to their nanoscale wavelength in the GHz frequency range and rich
+phenomenology. Here, we realize a versatile optically-inspired platform using
+spin-waves, demonstrating the wavefront engineering, focusing, and robust
+interference of spin-waves with nanoscale wavelength. In particular, we use
+magnonic nanoantennas based on tailored spin-textures for launching spatially
+shaped coherent wavefronts, diffraction-limited spin-wave beams, and generating
+robust multi-beam interference patterns, which spatially extend for several
+times the spin-wave wavelength. Furthermore, we show that intriguing features,
+such as resilience to back-reflection, naturally arise from the spin-wave
+nonreciprocity in synthetic antiferromagnets, preserving the high quality of
+the interference patterns from spurious counterpropagating modes. This work
+represents a fundamental step towards the realization of nanoscale
+optically-inspired devices based on spin-waves.",1902.09420v2
+2019-02-28,Building Magnetic Hysteresis in Holography,"We study the spontaneous magnetization and the magnetic hysteresis using the
+gauge/gravity duality. We first propose a novel and general formula to compute
+the magnetization in a large class of holographic models. By using this
+formula, we compute the spontaneous magnetization in a model like a holographic
+superconductor. Furthermore, we turn on the external magnetic field and build
+the hysteresis curve of magnetization and charge density. To our knowledge,
+this is the first holographic model realizing the hysteresis accompanied with
+spontaneous symmetry breaking. By considering the Landau-Ginzburg type
+effective potential in the symmetry broken phase, we obtain the mass of the
+magnon from the bulk geometry data.",1902.10929v2
+2019-03-03,Dynamical mode coupling and coherence in spin Hall nano-oscillator with perpendicular magnetic anisotropy,"We experimentally study the dynamical modes excited by spin current in Spin
+Hall nano-oscillators based on the Pt/[Co/Ni] multilayers with perpendicular
+magnetic anisotropy. Both propagating spin wave and localized solitonic modes
+of the oscillation are achieved and controlled by varying the applied magnetic
+field and current. At room temperature, the generation linewidth broadening
+associated with mode hopping was observed at currents close to the transition
+between different modes and in the mode coexistence regimes. The mode hopping
+was suppressed at cryogenic temperatures, confirming that the coupling between
+modes is mediated by thermal magnons. We also demonstrate that coherent
+single-mode oscillations with linewidth of 5 MHz can be achieved without
+applying external magnetic field. Our results provide insight into the
+mechanisms controlling the dynamical coherence in nanomagnetic oscillators, and
+guidance for optimizing their applications in spin wave-based electronics.",1903.00822v1
+2019-03-03,Spin wave damping in periodic and quasiperiodic magnonic structures,"We investigated the lifetime of spin wave eigenmodes in periodic and
+quasiperiodic sequences of Py and Co wires. Those materials differ
+significantly in damping coefficients, therefore, the spatial distribution of
+the mode amplitude within the structure is important for the lifetime of
+collective spin wave excitations. Modes of the lower frequencies prefer to
+concentrate in Py wires, because of the lower FMR frequency for this material.
+This inhomogeneous distribution of amplitude of modes (with lower amplitude in
+material of higher damping and with higher amplitude in material of lower
+damping) is preferable for extending the lifetime of the collective excitations
+beyond the volume average of lifetimes for solid materials. We established the
+relation between the profile of the mode and its lifetime for periodic and
+quasiperiodic structures. We performed also the comparative studies in order to
+find the differences resulting from complexity of the structure and enhancement
+of localization in quasiperiodic system on the lifetime of spin waves.",1903.00856v1
+2019-03-06,Honeycomb rare-earth magnets with anisotropic exchange interactions,"We study the rare-earth magnets on a honeycomb lattice, and are particularly
+interested in the experimental consequences of the highly anisotropic spin
+interaction due to the spin-orbit entanglement. We perform a high-temperature
+series expansion using a generic nearest-neighbor Hamiltonian with anisotropic
+interactions, and obtain the heat capacity, the parallel and perpendicular spin
+susceptibilities, and the magnetic torque coefficients. We further examine the
+electron spin resonance linewidth as an important signature of the anisotropic
+spin interactions. Due to the small interaction energy scale of the rare-earth
+moments, it is experimentally feasible to realize the strong-field regime.
+Therefore, we perform the spin-wave analysis and study the possibility of
+topological magnons when a strong field is applied to the system. The
+application and relevance to the rare-earth Kitaev materials are discussed.",1903.02530v3
+2019-03-07,Interplay between spin dynamics and crystal field in multiferroic compound HoMnO$_3$,"In the multiferroic hexagonal manganite HoMnO3, inelastic neutron scattering
+and synchrotron based THz spectroscopy have been used to investigate the spin
+waves associated to the Mn order together with Ho crystal field excitations.
+While the Mn order sets in first below 80 K, a spin reorientation occurs below
+37 K, a rare feature in the rare earth manganites. We show that severalHo
+crystal field excitations are present in the same energy range as the magnons,
+and that they are all affected by the spin reorientation. Moreover, several
+anomalous features are observed in the excitations at low temperature. Our
+analysis and calculations for the Mn spin waves and Ho crystal field
+excitations support Mn-Ho coupling mechanisms as well as coupling to the
+lattice affecting the dynamics.",1903.03009v1
+2019-03-19,Giant localised spin-Peltier effect due to ultrafast domainwalls motion in antiferromagnetic metals,"Spin thermo-electric phenomena have attracted wide attention recently, e.g.
+the Spin Peltier effect (SPE) heat generation by magnonic spin currents. Here
+we find that the Spin Peltier ef-fect also manifests as a heat wave
+accompanying fast moving magnetic textures. High speed andextreme magnetic
+excitation localisation are paramount for efficient transfer of energy from
+thespin-degrees of freedom to electrons and lattice. While satisfying both
+conditions is subject to se-vere restrictions in ferromagnets, we find that
+domain walls in antiferomagnets can overcome theselimitations due to their
+potential ultrahigh mobility and ultra-small widths originating from the
+rel-ativistic contraction. To illustrate our findings, we show that electric
+current driven domain wallmotion in the antiferromagnetic metal Mn2Au can carry
+a localised heat wave with the maximumamplitude up to 1 K . Since domain walls
+are well localised nanoscale magnetic objects, this effecthas the potential for
+nanoscale heating sensing and functionalities.",1903.08034v1
+2019-03-19,Composition dependence of magnetoresistance in Fe$_{1-x}$Ni$_{x}$ alloys,"Resistance of Fe$_{1-x}$Ni$_x$(x=0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 and 0.9)
+has been measured using four probe method from 5K to 300K with and without a
+longitudinal magnetic field of 8T. The zero field resistivity of x=0.1 and 0.9
+alloys, predominant contribution to resistivity above near room temperature is
+due to electron-phonon scattering, whereas for x=05 and 0.7 alloys
+electron-magnon scattering is dominant. Alloys with x=0.1 and 0.9 exhibit
+positive magnetoresistance(MR) from 5K to 300K. For x=0.5 and 0.7 alloys,
+magnetoresistance changes sign from positive to negative with increase in
+temperature. The temperature at which sign changes increase with Ni
+concentration in the alloy. The field dependent magnetoresistance is positive
+for x=0.1, 0.7 and 0.9 alloys whereas it is negative for x=0.5 alloy. MR
+follows linear behaviour with field for x=0.1 alloy. MR of all other alloys
+follow a second order polynomial in field.",1903.08230v3
+2019-03-20,Tracking the ultrafast motion of an antiferromagnetic order parameter,"The unique functionalities of antiferromagnets offer promising routes to
+advance information technology. Their compensated magnetic order leads to spin
+resonances in the THz-regime, which suggest the possibility to coherently
+control antiferromagnetic (AFM) devices orders of magnitude faster than
+traditional electronics. However, the required time resolution, complex
+sublattice interations and the relative inaccessibility of the AFM order
+parameter pose serious challenges to studying AFM spin dynamics. Here, we
+reveal the temporal evolution of an AFM order parameter directly in the time
+domain. We modulate the AFM order in hexagonal YMnO$_\mathrm{3}$ by coherent
+magnon excitation and track the ensuing motion of the AFM order parameter using
+time-resolved optical second-harmonic generation (SHG). The dynamic symmetry
+reduction by the moving order parameter allows us to separate electron dynamics
+from spin dynamics. As transient symmetry reductions are common to coherent
+excitations, we have a general tool for tracking the ultrafast motion of an AFM
+order parameter.",1903.08604v1
+2019-03-22,Exceptional points in classical spin dynamics,"Non-conservative physical systems admit a special kind of spectral
+degeneracy, known as exceptional point (EP), at which eigenvalues and
+eigenvectors of the corresponding non-Hermitian Hamiltonian coalesce. Dynamical
+parametric encircling of the EP can lead to non-adiabatic evolution associated
+with a state flip, a sharp transition between the resonant modes. Physical
+consequences of the dynamical encircling of EPs in open dissipative systems
+have been explored in optics and photonics. Building on the recent progress in
+understanding the parity-time (PT)-symmetric dynamics in spin systems, we use
+topological properties of EPs to implement chiral non-reciprocal transmission
+of a spin through the material with non-uniform magnetization, like helical
+magnet. We consider an exemplary system, spin-torque-driven single spin
+described by the time-dependent non-Hermitian Hamiltonian. We show that
+encircling individual EPs in parameter space results in non-reciprocal spin
+dynamics and find the range of optimal protocol parameters for high-efficiency
+asymmetric spin filter based on this effect. Our findings offer a platform for
+non-reciprocal spin devices for spintronics and magnonics.",1903.09729v2
+2019-03-29,Putative spin-nematic phase in BaCdVO(PO$_{4}$)$_{2}$,"We report neutron scattering and AC magnetic susceptibility measurements of
+the 2D spin-1/2 frustrated magnet BaCdVO(PO$_{4}$)$_{2}$. At temperatures well
+below $T_{\sf N}\approx 1K$, we show that only 34 % of the spin moment orders
+in an up-up-down-down strip structure. Dominant magnetic diffuse scattering and
+comparison to published $\mu$sr measurements indicates that the remaining 66 %
+is fluctuating. This demonstrates the presence of strong frustration,
+associated with competing ferromagnetic and antiferromagnetic interactions, and
+points to a subtle ordering mechanism driven by magnon interactions. On
+applying magnetic field, we find that at $T=0.1$ K the magnetic order vanishes
+at 3.8 T, whereas magnetic saturation is reached only above 4.5 T. We argue
+that the putative high-field phase is a realization of the long-sought
+bond-spin-nematic state.",1903.12462v1
+2019-04-01,Anomalous relaxation and the high-temperature structure factor of XXZ spin chains,"We compute the spin structure factor of XXZ spin chains in the Heisenberg and
+gapped (Ising) regimes in the high-temperature limit for nonzero magnetization,
+within the framework of generalized hydrodynamics including diffusive
+corrections. The structure factor shows a hierarchy of timescales in the gapped
+phase, owing to $s$-spin magnon bound states (`strings') of various sizes.
+Although short strings move ballistically, long strings move primarily
+diffusively as a result of their collisions with short strings. The interplay
+between these effects gives rise to anomalous power-law decay of the spin
+structure factor, with continuously varying exponents, at any fixed separation
+in the late-time limit. We elucidate the crossover to diffusion (in the gapped
+phase) and to superdiffusion (at the isotropic point) in the half-filling
+limit. We verify our results via extensive matrix product operator
+calculations.",1904.01039v1
+2019-04-09,Ferromagnetic Resonance Studies of Strain tuned Bi:YIG Films,"Bismuth-doped Yttrium iron garnet (Bi:YIG) thin films known for large
+Magneto-optical activity with low losses still needs to get probed for its
+magnetization dynamics. We demonstrate a controlled tuning of
+magnetocrystalline anisotropy in Bi-doped Y_3 Fe_5 O_12 (Bi:YIG) films of high
+crystalline quality using growth induced epitaxial strain on [111]-oriented
+Gd_3 Ga_5 O_12 (GGG) substrate. We optimize a growth protocol to get thick
+highly-strained epitaxial films showing large magneto-crystalline anisotropy,
+compare to thin films prepared using a different protocol. Ferromagnetic
+resonance measurements establish a linear dependence of the out-of-plane
+uniaxial anisotropy on the strain induced rhombohedral distortion of Bi:YIG
+lattice. Interestingly, the enhancement in the magnetoelastic constant due to
+an optimum substitution of Bi^(3+) ions with strong spin orbit coupling does
+not strongly affect the precessional damping (~2x10^(-3) ). Large
+magneto-optical activity, reasonably low damping, large magnetocrystalline
+anisotropy and large magnetoelastic coupling in BiYIG are the properties that
+may help BiYIG emerge as a possible material for photo-magnonics and other
+spintronics applications.",1904.04800v2
+2019-04-10,Dynamics of Phase Separated States in the Double Exchange Model,"We present extensive large-scale dynamical simulations of phase-separated
+states in the double exchange model. These inhomogeneous electronic states that
+play a crucial role in the colossal magnetoresistance phenomenon are composed
+of ferromagnetic metallic clusters embedded in an antiferromagnetic insulating
+matrix. We compute the dynamical structure factor of these nanoscale textures
+using an efficient real-space formulation of coupled spin and electron
+dynamics. Dynamical signatures of the various underlying magnetic structures
+are identified. At small hole doping, the structure factor exhibits a
+dominating signal of magnons from the background N\'eel order and localized
+modes from magnetic polarons. A low-energy continuum due to large-size
+ferromagnetic clusters emerges at higher doping levels. Implications for
+experiments on magnetoresistive manganites are discussed.",1904.05252v2
+2019-04-16,Plasmon Soft Mode in an Organic-Inorganic Hybrid Perovskite,"We report inelastic light scattering from underdamped plasmons in azetidinium
+lead bromide (AzPbBr3). The plasmons are very strongly temperature dependent
+and serve as a soft mode for the semiconductor-insulator phase transition near
+TC {\guillemotright} 150 K, demonstrating a continuous decrease in hole
+concentration np(T) by at least a factor of four and implying a nearly
+tricritical transition. The plasmon frequency and linewidth agree with
+independent measurements, and the impedance analysis reveals a frequency
+dependence (modelled by a constant phase element, CPE) that can be identified
+as due to electron-phonon coupling. The dependence of plasmon frequency upon
+(TC-T) is analogous to that for magnons in magnetic insulators or soft
+transverse optical phonons in ferroelectrics and ferroelastics, or for phasons
+in incommensurately modulated insulators.",1904.07573v1
+2019-04-24,Magnetic Susceptibility and Simulated Neutron Signal in the 2D Hubbard Model,"We compute dynamic spin susceptibilities in the two-dimensional Hubbard model
+using the method of Dual Fermions and provide comparison to lattice Monte Carlo
+and cluster dynamical mean field theory. We examine the energy dispersion
+identified by peaks in ${\rm Im}\chi(\omega,q)$ which define spin modes and
+compare the exchange scale and magnon dispersion to neutron experiments on the
+parent La$_2$CuO$_4$ cuprate. We present the evolution of the spin excitations
+as a function of Hubbard interaction strengths and doping and explore the
+particle-hole asymmetry of the spin excitations. We also study the correlation
+lengths and the spin excitation dispersion peak structure and find a `Y'-shaped
+dispersion similar to neutron results on doped HgBa$_2$CuO$_{4+\delta}$.",1904.10782v1
+2019-04-25,Controlled interconversion of quantized spin wave modes via local magnetic fields,"In the emerging field of magnonics, spin waves are considered for information
+processing and transmission at high frequencies. Towards this end, the
+manipulation of propagating spin waves in nanostructured waveguides for novel
+functionality has recently been attracting increasing focus of research.
+Excitations with uniform magnetic fields in such waveguides favors symmetric
+spin wave modes with odd quantization numbers. Interference between multiple
+odd spin wave modes leads to a periodic self-focusing effect of the propagating
+spin waves. Here we demonstrate, how antisymmetric spin wave modes with even
+quantization numbers can be induced by local magnetic fields in a
+well-controlled fashion. The resulting interference patterns are discussed
+within an analytical model and experimentally demonstrated using microfocused
+Brillouin light scattering ({\mu}-BLS).",1904.11613v1
+2019-04-29,Unconventional spin currents in magnetic films,"A spin current - a flow of spin angular momentum - can be carried either by
+spin polarised free electrons or by magnons, the quanta of a moving collective
+oscillation of localised electron spins - a spin wave. Traditionally, it was
+assumed, that a spin wave in a magnetic film with spin-sink-free surfaces can
+transfer energy and angular momentum only along its propagation direction. In
+this work, using Brillouin light scattering spectroscopy in combination with a
+theory of dipole-exchange spin-wave spectra, we show that in obliquely
+magnetized free magnetic films the in-plane propagation of spin waves is
+accompanied by a transverse spin current along the film normal without any
+corresponding transverse transport of energy.",1904.12610v1
+2019-08-06,Spectral properties of spin-orbital polarons as a fingerprint of orbital order,"Transition metal oxides are a rich group of materials with very interesting
+physical properties that arise from the interplay of the charge, spin, orbital,
+and lattice degrees of freedom. One interesting consequence of this,
+encountered in systems with orbital degeneracy, is the coexistence of long
+range magnetic and orbital order, and the coupling between them. In this paper
+we develop and study an effective spin-orbital superexchange model for $e_g^3$
+systems and use it to investigate the spectral properties of a charge (hole)
+injected into the system, which is relevant for photoemission spectroscopy.
+Using an accurate, semi-analytical, magnon expansion method, we gain insight
+into various physical aspects of these systems and demonstrate a number of
+subtle effects, such as orbital to magnetic polaron crossover, the coupling
+between orbital and magnetic order, as well as the orbital order driving the
+system towards one-dimensional quantum spin liquid behavior. Our calculations
+also suggest a potentially simple experimental verification of the character of
+the orbital order in the system, something that is not easily accessible
+through most experimental techniques.",1908.02232v1
+2019-08-06,Goldstone modes in the emergent gauge fields of a frustrated magnet,"We consider magnon excitations in the spin-glass phase of geometrically
+frustrated antiferromagnets with weak exchange disorder, focussing on the
+nearest-neighbour pyrochlore-lattice Heisenberg model at large spin. The
+low-energy degrees of freedom in this system are represented by three copies of
+a U(1) emergent gauge field, related by global spin-rotation symmetry. We show
+that the Goldstone modes associated with spin-glass order are excitations of
+these gauge fields, and that the standard theory of Goldstone modes in
+Heisenberg spin glasses (due to Halperin and Saslow) must be modified in this
+setting.",1908.02271v2
+2019-08-27,Inelastic light scattering in the spin cluster Mott insulator Cu$_{2}$OSeO$_{3}$,"Clusters of single spins form the relevant spin entities in the formation of
+long-range magnetic order in spin cluster Mott insulators. Such type of spin
+order bears resemblance to molecular crystals, and we therefore may expect a
+prototypical spin wave spectrum which can be divided into low-energy external
+and high-energy internal cluster spin wave modes. Here, we study high-energy
+spin cluster excitations in the spin cluster Mott insulator Cu$_{2}$OSeO$_{3}$
+by means of spontaneous Raman scattering. Multiple high-energy optical magnon
+modes are observed, of which the Raman-activity is shown to originate in the
+Elliot-Loudon scattering mechanism. Upon crossing the long-range ordering
+transition temperature the magnetic modes significantly broaden, corresponding
+to scattering from localized spin excitations within the spin clusters.
+Different optical phonon modes show a strong temperature dependence, evidencing
+a strong magnetoelectric coupling between optical phonons and the high-energy
+spin cluster excitations. Our results support the picture that
+Cu$_{2}$OSeO$_{3}$ can be regarded as a solid-state molecular crystal of spin
+nature.",1908.10279v1
+2019-08-28,Raman scattering study of lattice and magnetic excitations in CrAs,"We report on the lattice and spin dynamics in the monopnictide CrAs using
+polarized Raman scattering. This system exhibits a first-order
+magneto-structural phase transition at T_N~ 265 K, below which the magnetic
+moments of Cr form an incommensurate double helical magnetic structure while
+the unit cell volume abruptly expands. Across the transition, the frequencies
+of the fully symmetric Ag phonons strongly renormalize, which along with the
+results of first-principle calculations suggest the presence of a sizeable
+coupling of the phonons to the magnetic degrees of freedom in this compound. In
+addition, we observe two broad modes around 350 and 1700 cm-1 in the magnetic
+phase, which we associate with two-magnon Raman scattering. This work provides
+one of the few examples of magnetic Raman scattering from a non-collinear
+magnet.",1908.10908v2
+2019-11-02,Tuning Non-Gilbert-type damping in FeGa films on MgO(001) via oblique deposition,"The ability to tailor the damping factor is essential for spintronic and
+spin-torque applications. Here, we report an approach to manipulate the damping
+factor of FeGa/MgO(001) films by oblique deposition. Owing to the defects at
+the surface or interface in thin films, two-magnon scattering (TMS) acts as a
+non-Gilbert damping mechanism in magnetization relaxation. In this work, the
+contribution of TMS was characterized by in-plane angular dependent
+ferromagnetic resonance (FMR). It is demonstrated that the intrinsic Gilbert
+damping is isotropic and invariant, while the extrinsic mechanism related to
+TMS is anisotropic and can be tuned by oblique deposition. Furthermore, the two
+and fourfold TMS related to the uniaxial magnetic anisotropy (UMA) and
+magnetocrystalline anisotropy were discussed. Our results open an avenue to
+manipulate magnetization relaxation in spintronic devices.",1911.00728v1
+2019-11-08,Core-level x-ray photoemission and Raman spectroscopy studies on electronic structures in Mott-Hubbard type nickelate oxide NdNiO$_2$,"We perform core-level X-ray photoemission spectroscopy (XPS) and electronic
+Raman scattering studies of electronic structures and spin fluctuations in the
+bulk samples of the nickelate oxide NdNiO$_2$. According to Nd $3d$ and O $1s$
+XPS spectra, we conclude that NdNiO$_2$ has a large transfer energy. From the
+analysis of the main line of the Ni $2p_{3/2}$ XPS, we confirm the NiO$_2$
+planes in NdNiO$_2$ are of Mott-Hubbard type in the Zaanen-Sawatzky-Allen
+scheme. The two-magnon peak in the Raman scattering provides direct evidence
+for the strong spin-fluctuation in NdNiO$_2$. The peak position determines the
+antiferromagnetic exchange $J=25$~meV. Our experimental results agree well with
+our previous theoretical results.",1911.03177v2
+2019-11-12,Parametric generation of propagating spin-waves in ultra thin yttrium iron garnet waveguides,"We present the experimental demonstration of the parallel parametric
+generation of spin-waves in a microscaled yttrium iron garnet waveguide with
+nanoscale thickness. Using Brillouin light scattering microscopy, we observe
+the excitation of the first and second waveguide modes generated by a stripline
+microwave pumping source. Micromagnetic simulations reveal the wave vector of
+the parametrically generated spin-waves. Based on analytical calculations,
+which are in excellent agreement with our experiments and simulations, we prove
+that the spin-wave radiation losses are the determinative term of the
+parametric instability threshold in this miniaturized system. The used method
+enables the direct excitation and amplification of nanometer spin-waves
+dominated by exchange interactions. Our results pave the way for integrated
+magnonics based on insulating nano-magnets.",1911.04926v2
+2019-11-19,Unidirectional Seebeck effect in magnetic topological insulators,"We theoretically investigate the temperature gradient-dependent or
+unidirectional Seebeck effect (USE) in a magnetic/ nonmagnetic topological
+insulator (TI) heterostructure with in-plane magnetization in terms of the
+semiclassical electron dynamics and Fermi golden rule. The USE has a quantum
+origin arising from the magnon asymmetric scattering of surface Dirac electrons
+on TI. We discuss the USE in the heterostructures,
+Cr$_{x}$(Bi$_{1-y}$Sb$_y$)$_{2-x}$Te$_{3}$/ (Bi$_{1-y}$Sb$_{y})_2$Te$_{3}$. The
+USE exhibits $\cos\phi$-dependence (measured from $y$-direction) on the
+orientation of magnetization. It's found that the sign of USE stays unchanged
+when the system is transferred from $p$-doping to $n$-doping. The USE shows on
+inverse-linearly temperature dependent at high temperature.",1911.08122v1
+2019-11-28,First and Second Order Topological Phases on Ferromagnetic Breathing Kagome Lattice,"In this work, topological properties of a ferromagnetic Heisenberg model on a
+breathing kagome lattice are investigated extensively in the presence of
+  Dzyaloshinskii-Moriya interaction. While the kagome ferromagnet hosts only a
+single first order topological phase, the breathing kagome system exhibits
+multiple first and second order topological phases along with their
+coexistence. Magnon dispersion relation is obtained by using linear spin wave
+theory. Flat band and Dirac cones are obtained in the absence of
+  Dzyaloshinskii-Moriya interaction. A topological phase diagram is presented
+where several first and second order phases as well as their overlap are
+identified. Values of thermal Hall conductivity for all the first order phases
+are obtained. Distinct first order phases are characterized by different sets
+of Chern numbers in association with the necessary chiral edge states in
+accordance to the first order bulk-boundary-correspondence rule. Second order
+phase is characterized by polarization along with the emergence of corner
+states. Violation of the second order bulk-corner-correspondence rule has been
+noted in some regions.",1911.12620v2
+2019-11-29,Scaling theory of magnetism in frustrated Kondo lattices,"A scaling theory of the Kondo lattices with frustrated exchange interactions
+is developed, criterium of antiferromagnetic ordering and quantum-disordered
+state being investigated. The calculations taking into account magnon and
+incoherent spin dynamics are performed. Depending on the bare model parameters,
+one or two quantum phase transitions into non-magnetic spin-liquid and Kondo
+Fermi-liquid ground states can occur with increasing the bare coupling
+constant. Whereas the renormalization of the magnetic moment in the ordered
+phase can reach orders of magnitude, spin fluctuation frequency and coupling
+constant are moderately renormalized in the spin-liquid phase. This justifies
+application of the scaling approach. Possibility of a non-Fermi-liquid behavior
+is treated.",1911.13083v1
+2019-12-28,A journey into the tuneable antiferromagnetic spin textures of BiFeO3,"Antiferromagnetic thin films are currently generating considerable excitement
+for low dissipation magnonics and spintronics. However, while tuneable
+antiferromagnetic textures form the backbone of functional devices, they are
+virtually unknown at the submicron scale. Here we image a wide variety of
+antiferromagnetic spin textures in multiferroic BiFeO3 thin films that can be
+tuned by strain and manipulated by electric fields through room temperature
+magnetoelectric coupling. Using piezoresponse force microscopy and scanning NV
+magnetometry in self-organized ferroelectric patterns of BiFeO3, we reveal how
+strain stabilizes different types of non-collinear antiferromagnetic states
+(bulk-like and exotic spin cycloids) as well as collinear antiferromagnetic
+textures. Beyond these local-scale observations, resonant elastic X-ray
+scattering confirms the existence of both types of spin cycloids. Finally, we
+show that electric-field control of the ferroelectric landscape induces
+transitions either between collinear and non-collinear states or between
+different cycloids, offering perspectives for the design of reconfigurable
+antiferromagnetic spin textures on demand.",1912.12470v1
+2019-12-31,Onsager's Scars in Disordered Spin Chains,"We propose a class of non-integrable quantum spin chain models that exhibit
+quantum many-body scars even in the presence of disorder. With the use of the
+so-called Onsager symmetry, we construct such scarred models for arbitrary spin
+quantum number $ S $. There are two types of scar states, namely, coherent
+states associated to an Onsager-algebra element and one-magnon scar states.
+While both of them are highly-excited states, they have area-law entanglement
+and can be written as a matrix product state. Therefore, they explicitly
+violate the eigenstate thermalization hypothesis. We also investigate the
+dynamics of the fidelity and entanglement entropy for several initial states.
+The results clearly show that the scar states are trapped in a perfectly
+periodic orbit in the Hilbert subspace and never thermalize, whereas other
+generic states do rapidly. To our knowledge, our model is the first explicit
+example of disordered quantum many-body scarred model.",1912.13399v3
+2015-08-24,Origin of robust interaction of spin waves with a single skyrmion in perpendicularly magnetized nanostripes,"We studied interactions between propagating spin waves (SWs) and a single
+skyrmion in a perpendicularly magnetized CoFeB nanostripe where the magnetic
+layer is interfaced with W and MgO. Micromagnetic numerical calculations
+revealed that robust interactions between the incident SWs and the skyrmion
+give rise to considerable forward skyrmion motions for specific SW frequencies
+(e.g., here: fsw = 12 - 19 GHz). Additionally, it was found that there exists a
+sufficiently low threshold field amplitude, e.g., 0.1 kOe for the fsw = 15 GHz
+SWs. This frequency-dependent interaction originated from the robust coupling
+of the SWs with the internal modes of the skyrmion, through the SWs' linear
+momentum transfer torque acting on the skyrmion. This work provides for
+all-magnetic control of skyrmion motions without electronic currents, and
+facilitates further understanding of the interactions between magnons and
+topological solitons in constricted geometries.",1508.05682v1
+2015-08-25,Non-local magnetoresistance in YIG/Pt nanostructures,"We study the local and non-local magnetoresistance of thin Pt strips
+deposited onto yttrium iron garnet. The local magnetoresistive response,
+inferred from the voltage drop measured along one given Pt strip upon
+current-biasing it, shows the characteristic magnetization orientation
+dependence of the spin Hall magnetoresistance. We simultaneously also record
+the non-local voltage appearing along a second, electrically isolated, Pt
+strip, separated from the current carrying one by a gap of a few 100 nm. The
+corresponding non-local magnetoresistance exhibits the symmetry expected for a
+magnon spin accumulation-driven process, confirming the results recently put
+forward by Cornelissen et al. [1]. Our magnetotransport data, taken at a series
+of different temperatures as a function of magnetic field orientation, rotating
+the externally applied field in three mutually orthogonal planes, show that the
+mechanisms behind the spin Hall and the non-local magnetoresistance are
+qualitatively different. In particular, the non-local magnetoresistance
+vanishes at liquid Helium temperatures, while the spin Hall magnetoresistance
+prevails.",1508.06130v1
+2016-03-01,Ferromagnetic resonance and magnetic damping in C-doped Mn5Ge3,"Ferromagnetic resonance (FMR) was used to investigate the static and dynamic
+magnetic properties of carbon-doped Mn5Ge3 (C$_{0.1}$ and C$_{0.2}$) thin films
+grown on Ge(111). The temperature dependence of magnetic anisotropy shows an
+increased perpendicular magneto-crystalline contribution at 80K with an
+in-plane easy axis due to the large shape contribution. We find that our
+samples show a small FMR linewidth (corresponding to an intrinsic magnetic
+damping parameter $\alpha$=0.005), which is a measure of the spin relaxation
+and directly related with the magnetic and structural quality of the material.
+In the perpendicular-to-plane geometry, the FMR linewidth shows a minimum at
+around 200K for all the samples, which seems to be not correlated to the
+C-doping. The magnetic relaxation parameters have been determined and indicate
+the two-magnon scattering as the main extrinsic contribution. We observe a
+change in the main contribution from scattering centres in Mn5Ge3C0.2 at low
+temperatures, which could be related to the minimum in linewidth.",1603.00190v1
+2016-03-14,Spin Hall Effect Induced Spin Transfer Through an Insulator,"When charge current passes through a normal metal that exhibits spin Hall
+effect, spin accumulates at the edge of the sample in the transverse direction.
+We predict that this spin accumulation, or spin voltage, enables quantum
+tunneling of spin through an insulator or vacuum to reach a ferromagnet without
+transferring charge. In a normal metal/insulator/ferromagnetic insulator
+trilayer (such as Pt/oxide/YIG), the quantum tunneling explains the
+spin-transfer torque and spin pumping that exponentially decay with the
+thickness of the insulator. In a normal metal/insulator/ferromagnetic metal
+trilayer (such as Pt/oxide/Co), the spin transfer in general does not decay
+monotonically with the thickness of the insulator. Combining with the spin Hall
+magnetoresistance, this tunneling mechanism points to the possibility of a new
+type of tunneling spectroscopy that can probe the magnon density of states of a
+ferromagnetic insulator in an all-electrical and noninvasive manner.",1603.04240v2
+2016-10-11,Semiclassical analysis of a magnetization plateau in a 2D frustrated ferrimagnet,"We use a semiclassical large-$S$ expansion to study a plateau at $1/3$
+saturation in the magnetization curve of a frustrated ferrimagnet on a
+spatially anisotropic kagom\'{e} lattice. The spins have both ferromagnetic and
+antiferromagnetic nearest-neighbor Heisenberg couplings, and a frustrating
+next-nearest-neighbor coupling in one lattice direction. The magnetization
+plateau appears at the classical level for a certain range of couplings, and
+quantum fluctuations significantly broaden it at both ends. Near the region of
+the phase diagram where the classical plateau destabilizes, we find an exotic
+""chiral liquid"" phase that preserves translational and $U(1)$ spin symmetry, in
+which bound pairs of magnons with opposite spins are condensed. We show how
+this state is obtained naturally from a relativistic field theory formulation.
+We comment on the relevance of the model to the material
+$\text{Cu}_3\text{V}_2\text{O}_7\text{(OH)}_2 \cdot 2\text{H}_2\text{O}$
+(volborthite).",1610.03135v3
+2016-10-11,"$SL(2, Z)$ invariant rotating $(m,n)$ strings in $AdS_3\times S^3$ with mixed flux","We study rigidly rotating and pulsating $(m,n)$ strings in $AdS_3 \times S^3$
+with mixed three form flux. The $AdS_3 \times S^3$ background with mixed three
+form flux is obtained in the near horizon limit of $SL(2,Z)$-transformed
+solution, corresponding to the bound state of NS5-branes and fundamental
+strings. We study the probe $(m,n)-$string in this background by solving the
+manifest $SL(2,Z)-$covariant form of the action. We find out the dyonic giant
+magnon and single spike solutions corresponding to the equations of motion of a
+probe string in this background and find out various relationships among the
+conserved charges. We further study a class of pulsating $(m,n)$ string in
+$AdS_3$ with mixed three form flux.",1610.03402v2
+2016-10-13,Spin-wave spectra in periodically surface-modulated ferromagnetic thin films,"This article presents theoretical results for the dynamic response of
+periodically surface-modulated ferromagnetic thin films. For such system, the
+role of the periodic dipolar field induced by the modulation is addressed by
+using the plane-wave method. By controlling the geometry of the modulated
+volumes within the film, the frequency modes and spatial profiles of spin waves
+can be manipulated. The angular dependence of the frequency band-gaps unveils
+the influence of both dynamic and static magnetic charges, which reside in the
+edges of the etching periodic zones, and it is stablished that band-gap widths
+created by static magnetic charges are broader than the one created by dynamic
+magnetic charges. To corroborate the validity of the model, the theoretical
+results are compared with ferromagnetic resonance simulations, where a very
+good agreement is achieved between both methods. The theoretical model allows
+for a detailed understanding of the physics underlying these kind of systems,
+thereby providing an outlook to potential applications associated with magnonic
+crystals-based devices.",1610.04176v1
+2016-10-17,Disorder-induced Revival of the Bose-Einstein Condensation in Ni(Cl$_{1-x}$Br$_x$)$_2$-4SC(NH$_2$)$_2$ at High Magnetic Fields,"Building on recent NMR experiments [Phys. Rev. Lett. 118, 067203], we
+theoretically investigate the high magnetic field regime of the disordered
+quasi-one-dimensional $S=1$ antiferromagnetic material
+Ni(Cl$_{1-x}$Br$_x$)$_2$-4SC(NH$_2$)$_2$. The interplay between disorder,
+chemically controlled by Br-doping, interactions, and the external magnetic
+field, leads to a very rich phase diagram. Beyond the well-known
+antiferromagnetically ordered regime, analog of a Bose condensate of magnons,
+which disappears when $H\ge 12.3$ T, we unveil a resurgence of phase coherence
+at higher field $H\sim 13.6$ T, induced by the doping. Interchain couplings
+stabilize finite temperature long-range order whose extension in the field -
+temperature space is governed by the concentration of impurities $x$. Such a
+""mini-condensation"" contrasts with previously reported Bose-glass physics in
+the same regime, and should be accessible to experiments.",1610.05136v2
+2016-10-21,Spin transport and dynamics in all-oxide perovskite La$_{2/3}$Sr$_{1/3}$MnO$_3$/SrRuO$_3$ bilayers probed by ferromagnetic resonance,"Thin films of perovskite oxides offer the possibility of combining emerging
+concepts of strongly correlated electron phenomena and spin current in magnetic
+devices. However, spin transport and magnetization dynamics in these complex
+oxide materials are not well understood. Here, we experimentally quantify spin
+transport parameters and magnetization damping in epitaxial perovskite
+ferromagnet/paramagnet bilayers of La$_{2/3}$Sr$_{1/3}$MnO$_3$/SrRuO$_3$
+(LSMO/SRO) by broadband ferromagnetic resonance spectroscopy. From the SRO
+thickness dependence of Gilbert damping, we estimate a short spin diffusion
+length of $\lesssim$1 nm in SRO and an interfacial spin-mixing conductance
+comparable to other ferromagnet/paramagnetic-metal bilayers. Moreover, we find
+that anisotropic non-Gilbert damping due to two-magnon scattering also
+increases with the addition of SRO. Our results demonstrate LSMO/SRO as a
+spin-source/spin-sink system that may be a foundation for examining
+spin-current transport in various perovskite heterostructures.",1610.06661v1
+2016-10-22,Giant nonreciprocal emission of spin waves in Ta/Py bilayers,"Spin waves are propagating disturbances in the magnetization of magnetic
+materials. One of their interesting properties is the nonreciprocity,
+exhibiting that their amplitude depends on the magnetization direction.
+Nonreciprocity in spin waves is of great interest in both fundamental science
+and applications, as it offers an extra knob to control the flow of waves for
+the technological fields of logics and switch applications. We show a high
+nonreciprocity in spin waves from Ta/Py bilayer systems with out-of-plane
+magnetic fields. The nonreciprocity depends on the thickness of Ta underlayer
+which is found to induce an interfacial anisotropy. The origin of observed high
+nonreciprocity is twofold; different polarities of the in-plane magnetization
+due to different angles of canted out-of-plane anisotropy and the spin pumping
+effect at the Ta/Py interface. Our findings provide an opportunity to engineer
+highly efficient nonreciprocal spin wave based applications such as
+nonreciprocal microwave devices, magnonic logic gates, and information
+transports.",1610.07023v1
+2016-10-27,On the Semi-Classical Limit of Scalar Products of the XXZ Spin Chain,"We study the scalar products between Bethe states in the XXZ spin chain with
+anisotropy $|\Delta|>1$ in the semi-classical limit where the length of the
+spin chain and the number of magnons tend to infinity with their ratio kept
+finite and fixed. Our method is a natural yet non-trivial generalization of
+similar methods developed for the XXX spin chain. The final result can be
+written in a compact form as a contour integral in terms of Faddeev's quantum
+dilogarithm function, which in the isotropic limit reduces to the classical
+dilogarithm function.",1610.09006v2
+2016-12-06,Increased low-temperature damping in yttrium iron garnet thin films,"We report measurements of the frequency and temperature dependence of
+ferromagnetic resonance (FMR) for a 15-nm-thick yttrium iron garnet (YIG) film
+grown by off-axis sputtering. Although the FMR linewidth is narrow at room
+temperature (corresponding to a damping coefficient $\alpha$ = (9.0 $\pm$ 0.2)
+$\times 10^{-4}$), comparable to previous results for high-quality YIG films of
+similar thickness, the linewidth increases strongly at low temperatures, by a
+factor of almost 30. This increase cannot be explained as due to two-magnon
+scattering from defects at the sample interfaces. We argue that the increased
+low-temperature linewidth is due to impurity relaxation mechanisms that have
+been investigated previously in bulk YIG samples. We suggest that the
+low-temperature linewidth is a useful figure of merit to guide the optimization
+of thin-film growth protocols because it is a particularly sensitive indicator
+of impurities.",1612.01954v1
+2016-12-07,Gilbert damping of magnetostatic modes in a yttrium iron garnet sphere,"The magnetostatic mode (MSM) spectrum of a 300$\mu$m diameter single
+crystalline sphere of yttrium iron garnet is investigated using broadband
+ferromagnetic resonance (FMR). The individual MSMs are identified via their
+characteristic dispersion relations and the corresponding mode number tuples
+$(nmr)$ are assigned. Taking FMR data over a broad frequency and magnetic field
+range allows to analyze both the Gilbert damping parameter~$\alpha$ and the
+inhomogeneous line broadening contribution to the total linewidth of the MSMs
+separately. The linewidth analysis shows that all MSMs share the same Gilbert
+damping parameter $\alpha=2.7(5) \times 10^{-5}$ irrespective of their mode
+index. In contrast, the inhomogeneous line broadening shows a pronounced mode
+dependence. This observation is modeled in terms of two-magnon scattering
+processes of the MSMs into the spin-wave manifold, mediated by surface and
+volume defects.",1612.02360v1
+2016-12-12,Anomalous thermal conductivity and magnetic torque response in the honeycomb magnet $α$-RuCl$_3$,"We report on the unusual behavior of the in-plane thermal conductivity
+($\kappa$) and torque ($\tau$) response in the Kitaev-Heisenberg material
+$\alpha$-RuCl$_3$. $\kappa$ shows a striking enhancement with linear growth
+beyond H = 7 T, where magnetic order disappears, while $\tau$ for both of the
+in-plane symmetry directions shows an anomaly at the same field. The
+temperature- and field-dependence of $\kappa$ are far more complex than
+conventional phonon and magnon contributions, and require us to invoke the
+presence of unconventional spin excitations whose properties are characteristic
+of a field-induced spin-liquid phase related to the enigmatic physics of the
+Kitaev model in an applied magnetic field",1612.03881v3
+2016-12-15,Theory of the Spin Seebeck Effect at a Topological-Insulator/Ferromagnetic-Insulator Interface,"The spin-Seebeck effect refers to voltage signals induced in metals by
+thermally driven spin currents in adjacent magnetic systems. We present a
+theory of the spin-Seebeck signal in the case where the conductor that supports
+the voltage signal is the topologically protected two-dimensional surface-state
+system at the interface between a ferromagnetic insulator (FI) and a
+topological insulator (TI). Our theory uses a Dirac model for the TI
+surface-states and assumes Heisenberg exchange coupling between the TI
+quasiparticles and the FI magnetization. The spin-Seebeck voltage is induced by
+the TI surface states scattering off the nonequilibrium magnon population at
+the surface of the semi-infinite thermally driven FI. Our theory is readily
+generalized to spin-Seebeck voltages in any two-dimensional conductor that is
+exchange-coupled to the surface of a FI. Surface-state
+carrier-density-dependent signal strengths calculated using Bi$_2$Te$_3$ and
+yttrium iron garnet material parameters are consistent with recent experiments.",1612.04916v3
+2016-12-19,Multispin magnons on deformed $ AdS_{3}\times S^{3} $,"In this paper, using the holographic prescription, we study multispin bound
+states and their dispersion relations over the $ \kappa $-deformed $
+AdS_{3}\times S^{3} $ background. In the first part of our analysis,
+considering the conformal gauge conditions (associated with the Polyakov
+action) we explore the dispersion relation associated with spin two bound
+states at strong coupling. We solve corresponding world-sheet fluctuations and
+compute all the conserved quantities associated with the stringy dynamics over
+the deformed background. In the second part of our analysis, we perform similar
+analysis for spin three configurations. In both cases, we observe the emergence
+of non trivial background deformation that vanishes in the limit, $ \kappa
+\rightarrow 0$.",1612.06217v3
+2016-12-19,Dynamical Multiferroicity,"An appealing mechanism for inducing multiferroicity in materials is the
+generation of electric polarization by a spatially varying magnetization that
+is coupled to the lattice through the spin-orbit interaction. Here we describe
+the reciprocal effect, in which a time-dependent electric polarization induces
+magnetization even in materials with no existing spin structure. We develop a
+formalism for this dynamical multiferroic effect in the case for which the
+polarization derives from optical phonons, and compute the strength of the
+phonon Zeeman effect, which is the solid-state equivalent of the
+well-established vibrational Zeeman effect in molecules, using density
+functional theory. We further show that a recently observed behavior -- the
+resonant excitation of a magnon by optically driven phonons -- is described by
+the formalism. Finally, we discuss examples of scenarios that are not driven by
+lattice dynamics and interpret the excitation of Dzyaloshinskii-Moriya-type
+electromagnons and the inverse Faraday effect from the viewpoint of dynamical
+multiferroicity.",1612.06331v2
+2016-12-24,Concomitant enhancement of longitudinal spin Seebeck effect with thermal conductivity,"We report a simultaneous measurement of a longitudinal spin Seebeck effect
+(LSSE) and thermal conductivity in a Pt/${\rm Y_{3}Fe_{5}O_{12}}$ (YIG)/Pt
+system in a temperature range from 10 to 300 K. By directly monitoring the
+temperature difference in the system, we excluded thermal artifacts in the LSSE
+measurements. It is found that both the LSSE signal and the thermal
+conductivity of YIG exhibit sharp peaks at the same temperature, differently
+from previous reports. The maximum LSSE coefficient is found to be
+$S{\rm_{LSSE}}>10\ \mu{\rm V/K}$, one-order-of magnitude greater than the
+previously reported values. The concomitant enhancement of the LSSE and thermal
+conductivity of YIG suggests the strong correlation between magnon and phonon
+transport in the LSSE.",1612.08142v1
+2017-07-03,Heavy-mass magnetic modes in pyrochlore iridates due to dominant Dzyaloshinskii-Moriya interaction,"Materials with strong spin-orbit interactions are presently a main target in
+the search for systems with novel magnetic properties. Magnetic anisotropies
+can be very large in such compounds, ranging from strongly frustrated Kitaev
+exchange in honeycomb iridates and the associated spin-liquid states to robust
+antisymmetric couplings in square-lattice Sr_2IrO_4 . Here we predict from ab
+initio quantum chemistry calculations that another highly unusual regime is
+realized in pyrochlore iridium oxides: the nearest-neighbor Heisenberg
+interaction can vanish whilst the antisymmetric Dzyaloshinskii- Moriya exchange
+reaches values as large as 5 meV, a result which challenges common notions and
+existing phenomenological models of magnetic superexchange. The resulting spin
+excitation spectra reveal a very flat magnon dispersion in the Nd- and Tb-based
+pyrochlore iridates, suggesting the possibility of using these modes to store
+magnetic information. Indeed the magnetization dynamics indicates that these
+modes are unable to propagate out of the excitation region.",1707.00500v1
+2017-07-05,Magnetic Order in Laser-Irradiated Kagome Antiferromagnets,"Dispersionless ""zero energy mode'' is one of the hallmarks of frustrated
+kagome antiferromagnets (KAFMs). It points to extensive classically degenerate
+ground-states. The ""zero energy mode'' can be observed experimentally when
+lifted to a flat mode at finite energy by a strong intrinsic magnetic
+anisotropy. In this letter, we study the effects of irradiation of laser light
+on the KAFMs. We adopt the magnon picture without loss of generality. It is
+shown that circularly or linearly polarized light lifts the ""zero energy
+mode'', stabilizes magnetic order, and induces energy gaps in the KAFMs. We
+find that the circularly polarized light-induced anisotropies have similar
+features as the intrinsic in-plane and out-of-plane Dzyaloshinskii-Moriya
+interaction in KAFMs. The former stabilizes long-range magnetic order and the
+latter induces spin canting out-of-plane with nonzero scalar spin chirality.
+The Floquet thermal Hall effect shows that the synthetic magnetic excitation
+modes in the case of circularly polarized light are topological, whereas those
+of linearly polarized light are not.",1707.01502v3
+2017-07-10,Critical spin superflow in a spinor Bose-Einstein condensate,"We investigate the critical dynamics of spin superflow in an easy-plane
+antiferromagnetic spinor Bose-Einstein condensate. Spin-dipole oscillations are
+induced in a trapped condensate by applying a linear magnetic field gradient
+and we observe that the damping rate increases rapidly as the field gradient
+increases above a certain critical value. The onset of dissipation is found to
+be associated with the generation of dark-bright solitons due to the modulation
+instability of the counterflow of two spin components. Spin turbulence emerges
+as the solitons decay because of their snake instability. We identify another
+critical point for spin superflow, in which transverse magnon excitations are
+dynamically generated via spin-exchanging collisions, which leads to the
+transient formation of axial polar spin domains.",1707.03054v1
+2017-07-17,Indirect K-edge bimagnon resonant inelastic X-ray scattering spectrum of $α$-FeTe,"We calculate the K-edge indirect bimagnon resonant inelastic X-ray scattering
+(RIXS) intensity spectra of the bicollinear antiferromagnetic order known to
+occur in the $\alpha$-FeTe chalcogenide system. Utilizing linear spin wave
+theory for this large-S spin system we find that the bimagnon spectrum contains
+four scattering channels (two intraband and two interband). We find from our
+calculations that for suitable energy-momentum combination the RIXS spectra can
+exhibit a one-, two- or three- peak structure. The number of peaks provides a
+clue on the various bimagnon excitation processes that can be supported both in
+and within the acoustic and optical magnon branches of the bicollinear
+antiferromagnet. Unlike the RIXS response of the antiferromagnetic or the
+collinear antiferromagnetic spin ordering, the RIXS intensity spectrum of the
+bicollinear antiferromagnet does not vanish at the magnetic ordering wave
+vector $(\pi/2,-\pi/2)$. It is also sensitive to next-next nearest neighbor and
+biquadratic coupling interactions. Our predicted RIXS spectrum can be utilized
+to understand the role of multi-channel bimagnon spin excitations present in
+the $\alpha$-FeTe chalcogenide.",1707.05057v1
+2017-07-17,"Ab initio calculation of spin fluctuation spectra using time dependent density functional perturbation theory, planewaves, and pseudopotentials","We present an implementation of time-dependent density functional
+perturbation theory for spin fluctuations, based on planewaves and
+pseudopotentials. We compute the dynamic spin susceptibility self-consistently
+by solving the time-dependent Sternheimer equation, within the adiabatic local
+density approximation to the exchange and correlation kernel. We demonstrate
+our implementation by calculating the spin susceptibility of representative
+elemental transition metals, namely bcc Fe, fcc Ni and bcc Cr. The calculated
+magnon dispersion relations of Fe and Ni are in agreement with previous work.
+The calculated spin susceptibility of Cr exhibits a soft-paramagnon
+instability, indicating the tendency of the Cr spins to condense in a
+incommensurate spin density wave phase, in agreement with experiment.",1707.05219v1
+2017-07-27,Perfect diode in quantum spin chains,"We study the rectification of spin current in $XXZ$ chains segmented in two
+parts, each with a different anisotropy parameter. Using exact diagonalization
+and a matrix product states algorithm we find that a large rectification (of
+the order of $10^4$) is attainable even using a short chain of $N=8$ spins,
+when one half of the chain is gapless while the other has large enough
+anisotropy. We present evidence of diffusive transport when the current is
+driven in one direction and of a transition to an insulating behavior of the
+system when driven in the opposite direction, leading to a perfect diode in the
+thermodynamic limit. The above results are explained in terms of matching of
+spectrum of magnon excitations between the two halves of the chain.",1707.08823v3
+2017-07-31,Spin wave beam propagation in ferromagnetic thin film with graded refractive index: mirage effect and prospective applications,"Using analysis of iso-frequency contours of the spin-wave dispersion
+relation, supported by micromagnetic simulations, we study the propagation of
+spin-wave (SW) beams in thin ferromagnetic films through the areas of the
+inhomogeneous refractive index. We compare the transmission and reflection of
+SWs in areas with gradual and step variation of the SW refractive index. In
+particular, we show the mirage effect for SWs with narrowing SW beam width, and
+an application of the gradual modulation of the SWs refractive index as a
+diverging lens. Furthermore, we study the propagation of SWs in ferromagnetic
+stripe with modulated refractive index. We demonstrate that the system can be
+considered as the graded-index waveguide, which preserves the width of the SW
+beam for a long distance-the property essential for prospective applications of
+magnonics.",1707.09768v4
+2017-11-06,Observation of Intrinsic Half-metallic Behavior of CrO$_2$ (100) Epitaxial Films by Bulk-sensitive Spin-resolved PES,"We have investigated the electronic states and spin polarization of
+half-metallic ferromagnet CrO$_2$ (100) epitaxial films by bulk-sensitive
+spin-resolved photoemission spectroscopy with a focus on non-quasiparticle
+(NQP) states derived from electron-magnon interactions. We found that the
+averaged values of the spin polarization are approximately 100% and 40% at 40 K
+and 300 K, respectively. This is consistent with the previously reported result
+[H. Fujiwara et al., Appl. Phys. Lett. 106, 202404 (2015).]. At 100 K, peculiar
+spin depolarization was observed at the Fermi level ($E_{F}$), which is
+supported by theoretical calculations predicting NQP states. This suggests the
+possible appearance of NQP states in CrO$_2$. We also compare the temperature
+dependence of our spin polarizations with that of the magnetization.",1711.01781v1
+2017-11-17,Ginzburg-Landau-type theory of non-polarized spin superconductivity,"Since the concept of spin superconductor was proposed, all the related
+studies concentrate on spin-polarized case. Here, we generalize the study to
+spin-non-polarized case. The free energy of non-polarized spin superconductor
+is obtained, and the Ginzburg-Landau-type equations are derived by using the
+variational method. These Ginzburg-Landau-type equations can be reduced to the
+spin-polarized case when the spin direction is fixed. Moreover, the expressions
+of super linear and angular spin currents inside the superconductor are
+derived. We demonstrate that the electric field induced by super spin current
+is equal to the one induced by equivalent charge obtained from the second
+Ginzburg-Landau-type equation, which shows self-consistency of our theory. By
+applying these Ginzburg-Landau-type equations, the effect of electric field on
+the superconductor is also studied. These results will help us get a better
+understanding of the spin superconductor and the related topics such as
+Bose-Einstein condensate of magnons and spin superfluidity.",1711.06416v1
+2017-11-26,Brillouin light scattering by magnetic quasi-vortices in cavity optomagnonics,"A ferromagnetic sphere can support \textit{optical vortices} in forms of
+whispering gallery modes and \textit{magnetic quasi-vortices} in forms of
+magnetostatic modes with non-trivial spin textures. These vortices can be
+characterized by their orbital angular momenta. We experimentally investigate
+Brillouin scattering of photons in the whispering gallery modes by magnons in
+the magnetostatic modes, zeroing in on the exchange of the orbital angular
+momenta between the optical vortices and the magnetic quasi-vortices. We find
+that the conservation of the orbital angular momentum results in different
+nonreciprocal behaviors in the Brillouin light scattering. New avenues for
+chiral optics and opto-spintronics can be opened up by taking the orbital
+angular momenta as a new degree of freedom for cavity optomagnonics.",1711.09319v1
+2018-10-01,Hybridization and Decay of Magnetic Excitations in two-dimensional Triangular Lattice Antiferromagnets,"Elementary quasiparticles in solids such as phonons and magnons occasionally
+have nontrivial interactions between them, as well as among themselves. As a
+result, their energy eigenvalues are renormalized, the quasiparticles
+spontaneously decay into a multi-particle continuum state, or they are
+hybridized with each other when their energies are close. As discussed in this
+review, such anomalous features can appear dominantly in quantum magnets but
+are not, a priori, negligible for magnetic systems with larger spin values and
+noncollinear magnetic structures. We review the unconventional magnetic
+excitations in two-dimensional triangular lattice antiferromagnets and discuss
+their implications on related issues.",1810.00498v2
+2018-10-04,Cryogenic Microwave Filter Cavity with a Tunability Greater than 5 GHz,"A wide variety of applications of microwave cavities, such as measurement and
+control of superconducting qubits, magnonic resonators, and phase noise
+filters, would be well served by having a highly tunable microwave resonance.
+Often this tunability is desired in situ at low temperatures, where one can
+take advantage of superconducting cavities. To date, such cryogenic tuning
+while maintaining a high quality factor has been limited to $\sim500$ MHz. Here
+we demonstrate a three-dimensional superconducting microwave cavity that shares
+one wall with a pressurized volume of helium. Upon pressurization of the helium
+chamber the microwave cavity is deformed, which results in in situ tuning of
+its resonant frequency by more than 5 GHz, greater than 60% of the original 8
+GHz resonant frequency. The quality factor of the cavity remains approximately
+constant at $\approx7\times 10^{3}$ over the entire range of tuning. As a
+demonstration of its usefulness, we implement a tunable cryogenic phase noise
+filter, which reduces the phase noise of our source by approximately 10 dB
+above 400 kHz.",1810.02404v1
+2018-10-05,Remagnetization in the array of ferromagnetic nanowires with periodic and quasiperiodic order,"We investigate experimentally and theoretically the magnetization reversal
+process in one-dimensional magnonic structures composed of permalloy nanowires
+of the two different widths and finite length arranged in a periodic and
+quasiperiodic order. The main features of the hysteresis loop are determined by
+different shape anisotropies of the component elements and the dipolar
+interactions between them. We showed, that the dipolar interactions between
+nanowires forming a ribbon can be controlled by change a distance between the
+neighboring ribbons. The quasiperiodic order can influence the hysteresis loop
+by introduction additional tiny switching steps when the dipolar interactions
+are sufficiently strong.",1810.02796v1
+2018-10-08,The role of the rare earth in the lattice and magnetic coupling in multiferroic h-HoMnO3,"We used Raman scattering to study the lattice and magnetic excitations in the
+hexagonal HoMnO3 single crystals. The E2 phonon mode at 237 cm-1 is affected by
+the magnetic order. This mode is related to the displacement of Mn and O ions
+in a-b plane and modulates the Mn-O-Mn bond angles in a-b plane and the
+in-plane Mn-Mn superexchange interaction. The mode at 269 cm-1 associated to
+the displacement of the apical Ho3+ ions along the c direction presents an
+abrupt change of slope at TN showing that the role of the rare earth ions can
+not be neglected in the magnetic transition. We have identified magnon and
+crystal field excitations. The temperature dependence of the magnetic
+excitations has been compared to the Mn and Ho moment and indicates that the
+exchange interaction pattern between Mn and Ho atoms drives the uniaxial
+anisotropy gap above the Mn-spin-rotation transition.",1810.03387v1
+2018-10-15,Localized spin waves in isolated $kπ$ skyrmions,"The localized magnon modes of isolated $k\pi$ skyrmions on a field-polarized
+background are analyzed based on the Landau-Lifshitz-Gilbert equation within
+the terms of an atomistic classical spin model, with system parameters based on
+the Pd/Fe biatomic layer on Ir(111). For increasing skyrmion order $k$ a higher
+number of excitation modes are found, including modes with nodes in the radial
+eigenfunctions. It is shown that at low fields $2\pi$ and $3\pi$ skyrmions are
+destroyed via a burst instability connected to a breathing mode, while $1\pi$
+skyrmions undergo an elliptic instability. At high fields all $k\pi$ skyrmions
+collapse due to the instability of a breathing mode. The effective damping
+parameters of the spin waves are calculated in the low Gilbert damping limit,
+and they are found to diverge in the case of the lowest-lying modes at the
+burst and collapse instabilities, but not at the elliptic instability. It is
+shown that the breathing modes of $k\pi$ skyrmions may become overdamped at
+higher Gilbert damping values.",1810.06471v1
+2018-10-21,Triplon band splitting and topologically protected edge states in the dimerized antiferromagnet,"The search for topological insulators has been actively promoted in the field
+of condensed matter physics for further development in energy-efficient
+information transmission and processing. In this context, recent studies have
+revealed that not only electrons but also bosonic particles such as magnons can
+construct edge states carrying nontrivial topological invariants. Here we
+demonstrate topological triplon bands in the spin-1/2 two-dimensional dimerized
+quantum antiferromagnet Ba$_2$CuSi$_2$O$_6$Cl$_2$, which is closely related to
+a pseudo-one-dimensional variant of the Su-Schrieffer-Heeger (SSH) model,
+through inelastic neutron scattering experiments. The excitation spectrum
+exhibits two triplon bands and a clear band gap between them due to a small
+alternation in interdimer exchange interactions along the $a$-direction, which
+is consistent with the crystal structure. The presence of topologically
+protected edge states is indicated by a bipartite nature of the lattice.",1810.08931v1
+2018-10-24,Strong Coupling of Magnons to Microwave Photons in Three-Dimensional Printed Resonators,"We report on ferromagnetic resonant mode hybridization in re-entrant cavities
+made with a commercial three-dimensional (3D) printer, followed by conventional
+3D metalization with copper and tin. The cavity volume was only 7% that of a
+standard cavity resonating at the same frequency, while maintaining a high
+quality factor. Simulations were in very good agreement. We obtained an
+effective coupling of about 40 MHz in two cavities at room temperature. These
+experimental results demonstrate the utility of tunable filters based on
+complex 3D printed cavities.",1810.10305v3
+2018-10-25,Spin waves near the edge of halogen substitution induced magnetic order in Ni(Cl$_{1-x}$Br$_x$)$_2$$\cdot$4SC(NH$_2$)$_2$,"We report an inelastic neutron scattering study of magnetic excitations in a
+quantum paramagnet driven into a magnetically ordered state by chemical
+substitution, namely Ni(Cl$_{1-x}$Br$_x$)$_2$$\cdot$4SC(NH$_2$)$_2$ with
+$x=0.21(2)$. The measured spectrum is well accounted for by the generalized
+spin wave theory (GSWT) approach [M. Matsumoto and M. Koga, [J. Phys. Soc. Jap.
+76, 073709 (2007)]. This analysis allows us to determine the effective
+Hamiltonian parameters for a direct comparison with those in the previously
+studied parent compound and `underdoped' system. The issue of magnon lifetimes
+due to structural disorder is also addressed.",1810.10912v2
+2018-10-28,Magnetic excitations of the classical spin liquid MgCr2O4,"We report a comprehensive inelastic neutron-scattering study of the
+frustrated pyrochlore antiferromagnet MgCr2O4 in its cooperative paramagnetic
+regime. Theoretical modeling yields a microscopic Heisenberg model with
+exchange interactions up to third-nearest neighbors, which quantitatively
+explains all the details of the dynamic magnetic response. Our work
+demonstrates that the magnetic excitations in paramagnetic MgCr2O4 are
+faithfully represented in the entire Brillouin zone by a theory of magnons
+propagating in a highly-correlated paramagnetic background. Our results also
+suggest that MgCr2O4 is proximate to a spiral spin-liquid phase distinct from
+the Coulomb phase, which has implications for the magneto-structural phase
+transition in MgCr2O4 .",1810.11869v1
+2019-05-02,Anomalous spin Hall angle of a metallic ferromagnet determined by a multiterminal spin injection/detection device,"We report on the determination of the anomalous spin Hall angle in the
+ferromagnetic metal alloy cobalt-iron (Co$_{25}$Fe$_{75}$, CoFe). This is
+accomplished by measuring the spin injection/detection efficiency in a
+multiterminal device with nanowires of platinum (Pt) and CoFe deposited onto
+the magnetic insulator yttrium iron garnet (Y$_3$Fe$_5$O$_{12}$, YIG). Applying
+a spin-resistor model to our multiterminal spin transport data, we determine
+the magnon conductivity in YIG, the spin conductance at the YIG/CoFe interface
+and finally the anomalous spin Hall angle of CoFe as a function of its spin
+diffusion length in a single device. Our experiments clearly reveal a negative
+anomalous spin Hall angle of the ferromagnetic metal CoFe, but a vanishing
+ordinary spin Hall angle. This is in contrast to the results reported for the
+ferromagnetic metals Co and permalloy.",1905.00663v1
+2019-05-05,Effective spin-mixing conductance of heavy-metal-ferromagnet interfaces,"The effective spin-mixing conductance (G_eff) of a heavy metal/ferromagnet
+(HM/FM) interface characterizes the efficiency of the interfacial spin
+transport.Accurately determining G_eff is critical to the quantitative
+understanding of measurements of direct and inverse spin Hall effects. G_eff is
+typically ascertained from the inverse dependence of magnetic damping on the FM
+thickness under the assumption that spin pumping is the dominant mechanism
+affecting this dependence.Here we report that, this assumption fails badly in
+many in-plane magnetized prototypical HM/FM systems in the nm-scale thickness
+regime. Instead, the majority of the damping is from two-magnon scattering at
+the FM interface, while spin-memory-loss scattering at the interface can also
+be significant.If these two effects are neglected, the results will be an
+unphysical ""giant"" apparent G_eff and hence considerable underestimation of
+both the spin Hall ratio and the spin Hall conductivity in inverse/direct spin
+Hall experiments.",1905.01577v2
+2019-05-06,Elementary excitation in the spin-stripe phase in quantum chains,"Elementary excitations in condensed matter capture the complex many-body
+dynamics of interacting basic entities in a simple quasiparticle picture. In
+magnetic systems the most established quasiparticles are magnons, collective
+excitations that reside in ordered spin structures, and spinons, their
+fractional counterparts that emerge in disordered, yet correlated spin states.
+Here we report on the discovery of elementary excitation inherent to
+spin-stripe order that represents a bound state of two phason quasiparticles,
+resulting in a wiggling-like motion of the magnetic moments. We observe these
+excitations, which we dub ""wigglons"", in the frustrated zigzag spin-1/2 chain
+compound $\beta$-TeVO$_4$, where they give rise to unusual low-frequency spin
+dynamics in the spin-stripe phase. This result provides insights into the
+stripe physics of strongly-correlated electron systems.",1905.02079v1
+2019-05-07,Temperature dependence of the Spin Seebeck effect in a mixed valent manganite,"We report on temperature dependent measurements of the Longitudinal Spin
+Seebeck Effect (LSSE) in the mixed valent manganite
+La$_{0.7}$Ca$_{0.3}$MnO$_3$. By disentangling the contribution arising due to
+the Anisotropic Nernst effect, we observe that these two thermally driven
+phenomena vary disparately with temperature. In a narrow low temperature
+regime, the LSSE exhibits a $T^{0.55}$ dependence, which matches well with that
+predicted by the magnon-driven spin current model. Across the double exchange
+driven paramagnetic-ferromagnetic transition, the LSSE exponent is
+significantly higher than the magnetization one. These observations highlights
+the importance of individually ascertaining the temperature evolution of
+different mechanisms which contribute to the measured spin Seebeck signal.",1905.02527v1
+2019-05-08,Nanoscale spin-wave wake-up receiver,"We present the concept of a passive spin-wave device which is able to
+distinguish different radio-frequency pulse trains and validate its
+functionality using micromagnetic simulations. The information is coded in the
+phase of the individual pulses which are transformed into spin-wave packets.
+The device splits every incoming packet into two arms, one of which is coupled
+to a magnonic ring which introduces a well-defined time delay and phase shift.
+Since the time delay is matched to the pulse repetition rate, adjacent packets
+interfere in a combiner which makes it possible to distinguish simple pulse
+train patterns by the read-out of the time-integrated spin-wave intensity in
+the output. Due to its passive construction, this device may serve as an
+energy-efficient wake-up receiver used to activate the main receiver circuit in
+power critical IoT applications.",1905.03006v1
+2019-05-10,Long-wavelength emergent phonons in skyrmion crystals distorted by exchange anisotropy and tilted magnetic fields,"Skyrmion crystals (SkX) are periodic alignment of magnetic skyrmions, i.e., a
+type of topologically protected spin textures. Compared with ordinary crystals,
+they can be drastically deformed under anisotropic effects because they are
+composed of field patterns whose deformation does not cause any bond-breaking.
+This exotic ductility of SkX bring about great tunability of its collective
+excitations called emergent phonons, which are vital for magnonics application.
+The question is how to quantitatively determine the emergent phonons of
+distorted SkX. Here we systematically study the long wavelength emergent
+phonons of SkX distorted by (a) a negative exchange anisotropy, and (b) a
+tilted magnetic field. In both cases, deformation and structural transitions of
+SkX thoroughly influence the frequency, anisotropy of vibrational pattern and
+dispersion relation, and coupling between lattice vibration and in-lattice
+vibration for all modes. Tilted magnetic fields are very effective in tuning
+the emergent phonons, such that all modes except the Goldstone mode can be
+excited by AC magnetic fields when a tilted bias field is presented.",1905.03987v1
+2019-05-26,Mass in Lovelock Unique Vacuum gravity theories,"We derive an expression for conserved charges in Lovelock AdS gravity for
+solutions having $k$-fold degenerate vacua, making manifest a link between the
+degeneracy of a given vacuum and the nonlinearity of the energy formula. We
+show for a black hole solution to the field equations on a branch of
+multiplicity $k$ that its mass comes from an expression that contains the
+product of $k$ Weyl tensors. We prove that all divergent contributions of the
+type (Weyl)$^q$, with $1\le q<k$, are suppressed. Our conserved charge
+definition is a natural generalization of the Conformal Mass by Ashtekar,
+Magnon and Das to the cases when $k>1$. Our results provide insight on the
+holographic properties of degenerate Lovelock theories.",1905.10840v2
+2019-05-27,Spin relaxation in Cs$_2$CuCl$_{4-x}$Br$_x$,"The quantum-spin S = 1=2 chain system Cs$_2$CuCl$_4$ is of high interest due
+to competing anti-ferromagnetic intra-chain J and inter-chain exchange J'
+interactions and represents a paramount example for Bose-Einstein condensation
+of magnons [R. Coldea et al., Phys. Rev. Lett. 88, 137202 (2002)]. Substitution
+of chlorine by bromine allows tuning the competing exchange interactions and
+corresponding magnetic frustration. Here we report on electron spin resonance
+(ESR) in single crystals of Cs$_2$CuCl$_{4-x}$Br$_x$ with the aim to analyze
+the evolution of anisotropic exchange contributions. The main source of the ESR
+linewidth is attributed to the uniform Dzyaloshinskii-Moriya interaction. The
+vector components of the Dzyaloshinskii-Moriya interaction are determined from
+the angular dependence of the ESR spectra using a high-temperature
+approximation. The obtained results support the site selectivity of the Br
+substitution suggested from the evolution of lattice parameters and magnetic
+susceptibility dependent on the Br concentration.",1905.11186v1
+2019-05-27,Magnetic Field Induced Competing Phases in Spin-Orbital Entangled Kitaev Magnets,"There has been a great interest in magnetic field induced quantum spin
+liquids in Kitaev magnets after the discovery of neutron scattering continuum
+and half quantized thermal Hall conductivity in the material $\alpha$-RuCl$_3$.
+In this work, we provide a semiclassical analysis of the relevant theoretical
+models on large system sizes, and compare the results to previous studies on
+quantum models with small system sizes. We find a series of competing magnetic
+orders with fairly large unit cells at intermediate magnetic fields, which are
+most likely missed by previous approaches. We show that quantum fluctuations
+are typically strong in these large unit cell orders, while their magnetic
+excitations may resemble a scattering continuum and give rise to a large
+thermal Hall conductivity. Our work provides an important basis for a thorough
+investigation of emergent spin liquids and competing phases in Kitaev magnets.",1905.11408v2
+2019-05-30,Predicting New Iron Garnet Thin Films with Perpendicular Magnetic Anisotropy,"Perpendicular magnetic anisotropy (PMA) is a necessary condition for many
+spintronic applications like spin-orbit torques switching, logic and memory
+devices. An important class of magnetic insulators with low Gilbert damping at
+room temperature are iron garnets, which only have a few PMA types such as
+terbium and samarium iron garnet. More and stable PMA garnet options are
+necessary for researchers to be able to investigate new spintronic phenomena.
+In this study, we predict 20 new substrate/magnetic iron garnet film pairs with
+stable PMA at room temperature. The effective anisotropy energies of 10
+different garnet films that are lattice-matched to 5 different commercially
+available garnet substrates have been calculated using shape, magnetoelastic
+and magnetocrystalline anisotropy terms. Strain type, tensile or compressive
+depending on substrate choice, as well as the sign and the magnitude of the
+magnetostriction constants of garnets determine if a garnet film may possess
+PMA. We show the conditions in which Samarium, Gadolinium, Terbium, Holmium,
+Dysprosium and Thulium garnets may possess PMA on the investigated garnet
+substrate types. Guidelines for obtaining garnet films with low damping are
+presented. New PMA garnet films with tunable saturation moment and field may
+improve spin-orbit torque memory and compensated magnonic thin film devices.",1905.13042v1
+2020-06-01,Spin-wave spectroscopy of individual ferromagnetic nanodisks,"The increasing demand for ultrahigh data storage densities requires
+development of 3D magnetic nanostructures. In this regard, focused electron
+beam induced deposition (FEBID) is a technique of choice for direct-writing of
+various complex nano-architectures. However, intrinsic properties of
+nanomagnets are often poorly known and can hardly be assessed by local optical
+probe techniques. Here, we demonstrate spatially resolved spin-wave
+spectroscopy of individual circular magnetic elements with radii down to 100
+nm. The key component of the setup is a microwave antenna whose microsized
+central part is placed over a movable substrate with well-separated CoFe-FEBID
+nanodisks. The circular symmetry of the disks gives rise to standing spin-wave
+resonances and allows for the deduction of the saturation magnetization and the
+exchange stiffness of the material using an analytical theory. The presented
+approach is especially valuable for the characterization of direct-write
+elements opening new horizons for 3D nanomagnetism and magnonics.",2006.00763v1
+2020-06-24,Nature of Magnetic Excitations in the High-Field Phase of $α$-RuCl$_3$,"We present comprehensive electron spin resonance (ESR) studies of in-plane
+oriented single crystals of $\alpha$-RuCl$_3$, a quasi-two-dimensional material
+with honeycomb structure, focusing on its high-field spin dynamics. The
+measurements were performed in magnetic fields up to 16 T, applied along the
+[110] and [100] directions. Several ESR modes were detected. Combining our
+findings with recent inelastic neutron- and Raman-scattering data, we identify
+most of the observed excitations. Most importantly, we show that the
+low-temperature ESR response beyond the boundary of the magnetically ordered
+region is dominated by single- and two-particle processes with magnons as
+elementary excitations. The peculiarities of the excitation spectrum in the
+vicinity of the critical field are discussed.",2006.13538v2
+2020-06-30,Negative Gilbert damping in cavity optomagnonics,"Exceptional point (EP) associated with the parity-time (PT) symmetry breaking
+is receiving considerable recent attention by the broad physics community. By
+introducing balanced gain and loss, it has been realized in photonic, acoustic,
+and electronic structures. However, the observation of magnonic EP remains
+elusive. The major challenge is to experimentally generate the negative Gilbert
+damping, which was thought to be highly unlikely but is demanded by the PT
+symmetry. In this work, we study the magneto-optical interaction of
+circularly-polarized lasers with a submicron magnet placed in an optical
+cavity. We show that the off-resonant coupling between the driving laser and
+cavity photon in the far-blue detuning can induce the magnetic gain (or
+negative damping) exactly of the Gilbert type. A hyperbolic-tangent function
+ansatz is found to well describe the time-resolved spin switching as the
+intrinsic magnetization dissipation is overcome. When the optically pumped
+magnet interacts with a purely lossy one, we observe a phase transition from
+the imbalanced to passive PT symmetries by varying the detuning coeffcient. Our
+findings provide a feasible way to manipulate the sign of the magnetic damping
+parameter and to realize the EP in cavity optomagnonics.",2006.16510v1
+2020-09-01,Mapping the stray fields of a nanomagnet using spin qubits in SiC,"We report the use of optically addressable spin qubits in SiC to probe the
+magnetic stray fields generated by a ferromagnetic microstructure
+lithographically patterned on the surface of a SiC crystal. The stray fields
+cause shifts in the resonance frequency of the spin centers. The spin resonance
+is driven by a micrometer-sized microwave antenna patterned adjacent to the
+magnetic element. The patterning of the antenna is done to ensure that the
+driving microwave fields are delivered locally and more efficiently compared to
+conventional, millimeter-sized circuits. A clear difference in the resonance
+frequency of the spin centers in SiC is observed at various distances to the
+magnetic element, for two different magnetic states. Our results offer a
+wafer-scale platform to develop hybrid magnon-quantum applications by deploying
+local microwave fields and the stray field landscape at the micrometer
+lengthscale.",2009.00347v1
+2020-09-06,Exact solution of the Boltzmann equation for low-temperature transport coefficients in metals II: Scattering by ferromagnons,"In a previous paper (Paper I) we developed a technique for exactly solving
+the linearized Boltzmann equation for the electrical and thermal transport
+coefficients in metals in the low-temperature limit. Here we adapt this
+technique to determine the magnon contribution to the electrical and thermal
+conductivities, and to the thermopower, in metallic ferromagnets. For the
+electrical resistivity $\rho$ at asymptotically low temperatures we find $\rho
+\propto \exp{(-T_{\rm min}/T)}$, with $T_{\rm min}$ an energy scale that
+results from the exchange gap and a temperature independent prefactor of the
+exponential. The corresponding result for the heat conductivity is $\sigma_h
+\propto T^3\,\exp{(T_{\rm min}/T)}$, and thermopower is $S \propto T$. All of
+these results are exact, including the prefactors.",2009.02787v1
+2020-09-07,Quantum Sensing of Spin Fluctuations of Magnetic Insulator Films with Perpendicular Anisotropy,"Nitrogen vacancy (NV) centers, optically active atomic defects in diamond,
+have been widely applied to emerging quantum sensing, imaging, and network
+efforts, showing unprecedented field sensitivity and nanoscale spatial
+resolution. Many of these advantages derive from their excellent
+quantum-coherence, controllable entanglement, and high fidelity of operations,
+enabling opportunities to outperform the classical counterpart. Exploiting this
+cutting-edge quantum metrology, we report noninvasive measurement of intrinsic
+spin fluctuations of magnetic insulator thin films with a spontaneous
+out-of-plane magnetization. The measured field dependence of NV relaxation
+rates is well correlated to the variation of magnon density and band structure
+of the magnetic samples, which are challenging to access by the conventional
+magnetometry methods. Our results highlight the significant opportunities
+offered by NV centers in diagnosing the noise environment of functional
+magnetic elements, providing valuable information to design next-generation,
+high-density, and scalable spintronic devices.",2009.02883v1
+2020-09-07,"Exact solution of the Boltzmann equation for low-temperature transport coefficients in metals I: Scattering by phonons, antiferromagnons, and helimagnons","We present a technique for an exact solution of the linearized Boltzmann
+equation for the electrical and thermal transport coefficients in metals in the
+low-temperature limit. This renders unnecessary an uncontrolled approximation
+that has been used in all previous solutions of the integral equations for the
+transport coefficients. Applications include electron-phonon scattering in
+nonmagnetic metals, as well as the magnon contribution to the electrical and
+thermal conductivities, and to the thermopower, in metallic ferromagnets,
+antiferromagnets, and helimagnets. In this paper, the first of a pair, we set
+up the technique and apply it to the scattering of electrons by phonons,
+antiferromagnons, and helimagnons. We show that the Bloch $T^5$ law for the
+electrical resistivity, the $T^2$ law for the thermal resistivity, and the $T$
+law for the thermopower due to phonon and antiferromagnon scattering are exact,
+and determine the prefactors exactly. The corresponding exact results for
+helimagnons are $T^{5/2}$, $T^{1/2}$, and $T$, respectively. In a second paper
+we will consider the scattering by ferromagnons.",2009.03234v1
+2020-09-12,Magnetic ground state and electron doping tuning of Curie temperature in Fe$_3$GeTe$_2$: first-principles studies,"Intrinsic magnetic van der Waals (vdW) materials have attracted much
+attention, especially Fe$_{3}$GeTe$_{2}$ (FGT), which exhibits highly tunable
+properties. However, despite vast efforts, there are still several challenging
+issues to be resolved. Here using a first-principles linear-response approach,
+we carry out comprehensive investigation of both bulk and monolayer FGT. We
+find that although the magnetic exchange interactions in FGT are frustrated,
+our Monte Carlo simulations agree with the total energy calculations,
+confirming that the ground state of bulk FGT is indeed ferromagnetic (FM). A
+tiny electron doping reduces the magnetic frustration, resulting in significant
+increasing of the Curie temperature. We also calculate the spin-wave
+dispersion, and find a small spin gap as well as a nearly flat band in the
+magnon spectra. These features can be used to compare with the future neutron
+scattering measurement and finally clarify the microscopic magnetic mechanism
+in this two-dimensional family materials.",2009.05701v1
+2020-09-27,Dynamical spin susceptibility in La2CuO4 studied by resonant inelastic x-ray scattering,"Resonant inelastic X-ray scattering (RIXS) is a powerful probe of elementary
+excitations in solids. It is now widely applied to study magnetic excitations.
+However, its complex cross-section means that RIXS has been more difficult to
+interpret than inelastic neutron scattering (INS). Here we report
+high-resolution RIXS measurements of magnetic excitations of La2CuO4, the
+antiferromagnetic parent of one system of high-temperature superconductors. At
+high energies (~2 eV), the RIXS spectra show angular-dependent dd orbital
+excitations which are found to be in good agreement with single-site multiplet
+calculations. At lower energies (<0.3 eV), we show that the
+wavevector-dependent RIXS intensities are proportional to the product of the
+single-ion spin-flip cross section and the dynamical susceptibility of the
+spin-wave excitations. When the spin-flip crosssection is dividing out, the
+RIXS magnon intensities show a remarkable resemblance to INS data. Our results
+show that RIXS is a quantitative probe the dynamical spin susceptibility in
+cuprate and therefore should be used for quantitative investigation of other
+correlated electron materials.",2009.12925v1
+2021-02-15,"Angular-Dependent Dynamic Response and Magnetization Reversal in Fibonacci-Distorted, Kagome Artificial Spin Ice","We have measured the angular dependence of ferromagnetic resonance (FMR)
+spectra for Fibonacci-distorted, Kagome artificial spin ice (ASI). The number
+of strong modes in the FMR spectra depend on the orientation of the applied DC
+magnetic field. In addition, discontinuities observed in the FMR
+field-frequency dispersion curves also depend on DC field orientation, and
+signal a multi-step DC magnetization reversal, which is caused by the reduced
+energy degeneracy of Fibonacci-distorted vertices. The results suggest the
+orientation of applied magnetic field and severity of Fibonacci distortion
+constitute control variables for FMR modes and multi-step reversal in future
+magnonic devices and magnetic switching systems.",2102.07532v1
+2021-02-16,Fully Spin-transparent magnetic interfaces enabled by insertion of a paramagnetic NiO layer,"Spin backflow and spin-memory loss have been well established to considerably
+lower the interfacial spin transmissivity of metallic magnetic interfaces and
+thus the energy efficiency of spin-orbit torque technologies. Here we report
+that spin backflow and spin-memory loss at Pt-based heavy metal/ferromagnet
+interfaces can be effectively eliminated by inserting an insulating
+paramagnetic NiO layer of optimum thickness. The latter enables the thermal
+magnon-mediated essentially unity spin-current transmission at room temperature
+due to considerably enhanced effective spin-mixing conductance of the
+interface. As a result, we obtain dampinglike spin-orbit torque efficiency per
+unit current density of up to 0.8 as detected by the standard technology
+ferromagnet FeCoB and others, which reaches the expected upper-limit spin Hall
+ratio of Pt. We establish that Pt/NiO and Pt-Hf/NiO are two energy-efficient,
+integration-friendly, and high-endurance spin-current generators that provide
+>100 times greater energy efficiency than sputter-deposited topological
+insulators BiSb and BiSe. Our finding will benefit spin-orbitronic research and
+advance spin-torque technologies.",2102.08487v1
+2021-02-18,Quantum control of bosonic modes with superconducting circuits,"Bosonic modes have wide applications in various quantum technologies, such as
+optical photons for quantum communication, magnons in spin ensembles for
+quantum information storage and mechanical modes for reversible
+microwave-to-optical quantum transduction. There is emerging interest in
+utilizing bosonic modes for quantum information processing, with circuit
+quantum electrodynamics (circuit QED) as one of the leading architectures.
+Quantum information can be encoded into subspaces of a bosonic superconducting
+cavity mode with long coherence time. However, standard Gaussian operations
+(e.g., beam splitting and two-mode squeezing) are insufficient for universal
+quantum computing. The major challenge is to introduce additional nonlinear
+control beyond Gaussian operations without adding significant bosonic loss or
+decoherence. Here we review recent advances in universal control of a single
+bosonic code with superconducting circuits, including unitary control, quantum
+feedback control, driven-dissipative control and holonomic dissipative control.
+Various approaches to entangling different bosonic modes are also discussed.",2102.09668v2
+2021-02-20,Observation of Coherent Spin Waves in a Three-Dimensional Artificial Spin Ice Structure,"Harnessing high-frequency spin dynamics in three-dimensional (3D)
+nanostructures may lead to paradigm-shifting, next generation devices including
+high density spintronics and neuromorphic systems. Despite remarkable progress
+in fabrication, the measurement and interpretation of spin dynamics in complex
+3D structures remain exceptionally challenging. Here we take a first step and
+measure coherent spin waves within a 3D artificial spin ice (ASI) structure
+using Brillouin light scattering. The 3D-ASI was fabricated by using a
+combination of two-photon lithography and thermal evaporation. Two spin-wave
+modes were observed in the experiment whose frequencies showed a monotonic
+variation with the applied field strength. Numerical simulations qualitatively
+reproduced the observed modes. The simulated mode profiles revealed the
+collective nature of the modes extending throughout the complex network of
+nanowires while showing spatial quantization with varying mode quantization
+numbers. The study shows a well-defined means to explore high-frequency spin
+dynamics in complex 3D spintronic and magnonic structures.",2102.10270v1
+2013-06-08,Systematic Effective Field Theory Analysis of the D=2+1 Quantum XY Model at Low Temperatures,"The low-temperature properties of the (2+1)-dimensional quantum XY model are
+studied within the framework of effective Lagrangians up to three-loop order.
+At zero temperature, the system is characterized by a spontaneously broken spin
+rotation symmetry, O(2) $\to$ 1, where the corresponding Goldstone bosons are
+the spin waves or magnons. Even though there is no spontaneously broken order
+at finite $T$, the low-temperature behavior of the system is still governed by
+the spin waves. The partition function is evaluated and various thermodynamic
+quantities, including the order parameter, are derived in the presence of a
+weak external field. In particular, we show that the spin-wave interaction is
+repulsive at low temperatures, its magnitude depending on the strength of the
+external field. We compare our results with those for the (2+1)-dimensional
+antiferromagnetic Heisenberg model which, at T=0, exhibits the spontaneously
+broken spin rotation symmetry O(3) $\to$ O(2).",1306.1944v1
+2013-06-24,Spinon confinement: dynamics of weakly coupled Hubbard chains,"Using large-scale determinant quantum Monte Carlo simulations in combination
+with the stochastic analytical continuation, we study two-particle dynamical
+correlation functions in the anisotropic square lattice of weakly coupled
+one-dimensional (1D) Hubbard chains at half-filling and in the presence of weak
+frustration. The evolution of the static spin structure factor upon increasing
+the interchain coupling is suggestive of the transition from the power-law
+decay of spin-spin correlations in the 1D limit to long-range antiferromagnetic
+order in the quasi-1D regime and at $T=0$. In the numerically accessible regime
+of interchain couplings, the charge sector remains gapped. The low-energy
+momentum dependence of the spin excitations is well described by the linear
+spin-wave theory with the largest intensity located around the
+antiferromagnetic wave vector. This magnon mode corresponds to a bound state of
+two spinons. At higher energies the spinons deconfine and we observe signatures
+of the two-spinon continuum which progressively fade away as a function of
+interchain hopping.",1306.5775v2
+2015-07-06,Delta chain with anisotropic ferromagnetic and antiferromagnetic interactions,"We consider analytically and numerically an anisotropic spin-$\frac{1}{2}$
+delta-chain (sawtooth chain) with nearest-neighbor ferromagnetic and
+next-nearest-neighbor antiferromagnetic interactions. For certain values of the
+interactions a lowest one-particle band becomes flat and there is a class of
+localized-magnon eigenstates which form a ground state with a macroscopic
+degeneracy. In this case the model depends on a single parameter which can be
+chosen as the anisotropy of the exchange interactions. When this parameter
+changes from zero to infinity the model interpolates between the
+one-dimensional isotropic ferromagnet and the frustrated Ising model on the
+delta-chain. It is shown that the low-temperature thermodynamic properties in
+these limiting cases are governed by the specific structure of the excitation
+spectrum. In particular, the specific heat has one or infinite number of
+low-temperature maxima for the small or the large anisotropy parameter,
+correspondingly. Numerical calculations of finite chains demonstrate that this
+behavior is generic for definite values of the anisotropy parameter.",1507.01389v1
+2015-07-08,Excitations and the tangent space of projected entangled-pair states,"We develop tangent space methods for projected entangled-pair states (PEPS)
+that provide direct access to the low-energy sector of strongly-correlated
+two-dimensional quantum systems. More specifically, we construct a variational
+ansatz for elementary excitations on top of PEPS ground states that allows for
+computing gaps, dispersion relations, and spectral weights directly in the
+thermodynamic limit. Solving the corresponding variational problem requires the
+evaluation of momentum transformed two-point and three-point correlation
+functions on a PEPS background, which we can compute efficiently by using a
+contraction scheme. As an application we study the spectral properties of the
+magnons of the Affleck-Kennedy-Lieb-Tasaki model on the square lattice and the
+anyonic excitations in a perturbed version of Kitaev's toric code.",1507.02151v2
+2015-07-21,Static and Dynamical Properties of the Spin-1/2 Equilateral Triangular-Lattice Antiferromagnet Ba$_3$CoSb$_2$O$_9$,"We present single-crystal neutron scattering measurements of the spin-1/2
+equilateral triangular lattice antiferromagnet Ba$_3$CoSb$_2$O$_9$. Besides
+confirming that the Co$^{2+}$ magnetic moments lie in the ab plane for zero
+magnetic field, we determine all the exchange parameters of the minimal
+quasi-2D spin Hamiltonian, which confirms that Ba$_3$CoSb$_2$O$_9$ is an almost
+perfect realization of the paradigmatic model of frustrated quantum magnetism.
+A comparison with linear and nonlinear spin-wave theory reveals that quantum
+fluctuations induce a strong downward renormalization of the magnon dispersion.",1507.05702v2
+2015-07-26,Antiferromagnetic fluctuations in the quasi-two-dimensional organic superconductor detected by Raman spectroscopy,"Using Raman scattering, the quasi-two dimensional organic superconductor
+k-(BEDT-TTF)2Cu[N(CN)2]Br (T_c=11.8 K) and the related antiferromagnet
+k-(BEDT-TTF)2Cu[N(CN)2]Cl are studied. Raman scattering provides unique
+spectroscopic information about magnetic degrees of freedom that has been
+otherwise unavailable on such organic conductors. Below T=200 K a broad band at
+about 500 cm-1 develops in both compounds. We identify this band with
+two-magnon excitation. The position and the temperature dependence of the
+spectral weight are similar in the antiferromagnet and in the metallic
+Fermi-liquid. We conclude that antiferromagnetic correlations are similarly
+present in the magnetic insulator and the Fermi-liquid state of the
+superconductor.",1507.07178v2
+2015-07-31,Topological spin transport by Brownian diffusion of domain walls,"We propose thermally-populated domain walls (DWs) in an easy-plane
+ferromagnetic insulator as robust spin carriers between two metals. The
+chirality of a DW, which serves as a topological charge, couples to the metal
+spin accumulation via spin-transfer torque and results in the
+chirality-dependent thermal nucleation rates of DWs at the interface. After
+overpopulated DWs of a particular (net) chirality diffuse and leave the
+ferromagnet at the other interface, they reemit the spin current by spin
+pumping. The conservation of the topological charge supports an algebraic decay
+of spin transport as the length of the ferromagnet increases; this is analogous
+to the decaying behavior of superfluid spin transport but contrasts with the
+exponential decay of magnon spin transport. We envision that similar spin
+transport with algebraic decay may be implemented in materials with exotic spin
+phases by exploiting topological characteristics and the associated conserved
+quantities of their excitations.",1507.08767v2
+2015-12-03,Large-$s$ expansions for the low-energy parameters of the honeycomb-lattice Heisenberg antiferromagnet with spin quantum number $s$,"The coupled cluster method (CCM) is employed to very high orders of
+approximation to study the ground-state (GS) properties of the spin-$s$
+Heisenberg antiferromagnet (with isotropic interactions, all of equal strength,
+between nearest-neighbour pairs only) on the honeycomb lattice. We calculate
+with high accuracy the complete set of GS parameters that fully describes the
+low-energy behaviour of the system, in terms of an effective magnon field
+theory, viz., the energy per spin, the magnetic order parameter (i.e., the
+sublattie magnetization), the spin stiffness and the zero-field (uniform,
+transverse) magnetic susceptibility, for all values of the spin quantum number
+$s$ in the range $\frac{1}{2} \leq s \leq \frac{9}{2}$. The CCM data points are
+used to calculate the leading quantum corrections to the classical ($s
+\rightarrow \infty$) values of these low-energy parameters, considered as
+large-$s$ asymptotic expansions.",1512.01063v2
+2015-12-10,Magnetic ordering and non-Fermi-liquid behavior in the multichannel Kondo-lattice model,"Scaling equations for the Kondo lattice in the paramagnetic and magnetically
+ordered phases are derived to two-loop order with account of spin dynamics. The
+results are applied to describe various mechanisms of the non-Fermi-liquid
+(NFL) behavior in the multichannel Kondo-lattice model where a fixed point
+occurs in the weak-coupling region. The corresponding temperature dependences
+of electronic and magnetic properties are discussed. The model describes
+naturally formation of a magnetic state with soft boson mode and small moment
+value. An important role of Van Hove singularities in the magnon spectral
+function is demonstrated. The results are rather sensitive to the type of
+magnetic ordering and space dimensionality, the conditions for NFL behavior
+being more favorable in the antiferromagnetic and 2D cases.",1512.03161v3
+2015-12-24,Collisional Dynamics of Half-Quantum Vortices in a Spinor Bose-Einstein Condensate,"We present an experimental study on the interaction and dynamics of
+half-quantum vortices (HQVs) in an antiferromagnetic spinor Bose-Einstein
+condensate. By exploiting the orbit motion of a vortex dipole in a trapped
+condensate, we perform a collision experiment of two HQV pairs, and observe
+that the scattering motions of the HQVs is consistent with the short-range
+vortex interaction that arises from nonsingular magnetized vortex cores. We
+also investigate the relaxation dynamics of turbulent condensates containing
+many HQVs, and demonstrate that spin wave excitations are generated by the
+collisional motions of the HQVs. The short-range vortex interaction and the
+HQV-magnon coupling represent two characteristics of the HQV dynamics in the
+spinor superfluid.",1512.07696v2
+2016-09-01,Bound states and field-polarized Haldane modes in a quantum spin ladder,"The challenge of one-dimensional systems is to understand their physics
+beyond the level of known elementary excitations. By high-resolution neutron
+spectroscopy in a quantum spin ladder material, we probe the leading
+multiparticle excitation by characterizing the two-magnon bound state at zero
+field. By applying high magnetic fields, we create and select the singlet
+(longitudinal) and triplet (transverse) excitations of the fully spin-polarized
+ladder, which have not been observed previously and are close analogs of the
+modes anticipated in a polarized Haldane chain. Theoretical modelling of the
+dynamical response demonstrates our complete quantitative understanding of
+these states.",1609.00198v1
+2016-09-03,All-phononic Amplification in Coupled Cantilever Arrays based on Gap Soliton Dynamics,"We present a mechanism of amplification of phonons by phonons on the basis of
+nonlinear band-gap transmission phenomenon. As a concept the idea may be
+applied to the various number of systems, however we introduce the specific
+idea of creating amplification scenario in the chain of coupled cantilever
+arrays. One chain is driven at the constant frequency located in the upper band
+of the ladder system, thus no wave enters the system. However the frequency is
+specifically chosen to be very close to the maximum value of frequency
+corresponding to dispersion relation of the system. Amplification scenario
+happens when a counter phase pulse of same frequency with a small amplitude is
+introduced to the second chain. If both signals exceed a threshold amplitude
+for the band-gap transmission a large amplitude soliton enters the system -
+therefore we have an amplifier. Although the concept may be applied in a
+variety of contexts - all optical or all-magnonic systems, we choose the system
+of coupled cantilever arrays and represent a clear example of the application
+of presented conceptual idea. Logical operations is the other probable field,
+where such mechanism could be used, which might significantly broaden the
+horizon of considered applications of band-gap soliton dynamics.",1609.00855v1
+2016-09-14,Post-quench dynamics and suppression of thermalization in an open half-filled Hubbard layer,"We study the time evolution of a half-filled Hubbard layer coupled to a
+magnon bath after a quench of the Hubbard interaction. Qualitatively different
+regimes, regarding the asymptotic long-time dynamics, are identified and
+characterized within the mean-field approximation. In the absence of the bath,
+the dynamics of the closed system is similar to that of a quenched BCS
+condensate. Though the presence of the bath introduces an additional relaxation
+mechanism, our numerical results and analytical arguments show that
+equilibration with the bath is not necessarily attained within the
+approximations used. Instead, nonequilibrium states, similar to the ones
+observed in the closed system, can emerge at long times as a consequence of the
+competition between the intrinsic relaxation mechanism (Landau damping, for
+example), and the bath-induced dissipation.",1609.04151v3
+2016-09-15,Low-damping sub-10-nm thin films of lutetium iron garnet grown by molecular-beam epitaxy,"We analyze the structural and magnetic characteristics of (111)-oriented
+lutetium iron garnet (Lu$_3$Fe$_5$O$_{12}$) films grown by molecular-beam
+epitaxy, for films as thin as 2.8 nm. Thickness-dependent measurements of the
+in- and out-of-plane ferromagnetic resonance allow us to quantify the effects
+of two-magnon scattering, along with the surface anisotropy and the saturation
+magnetization. We achieve effective damping coefficients of $11.1(9) \times
+10^{-4}$ for 5.3 nm films and $32(3) \times 10^{-4}$ for 2.8 nm films, among
+the lowest values reported to date for any insulating ferrimagnetic sample of
+comparable thickness.",1609.04753v1
+2016-11-03,Spin caloritronic nano-oscillator,"Energy loss due to ohmic heating is a major bottleneck limiting down-scaling
+and speed of nano-electronic devices, and harvesting ohmic heat for signal
+processing is a major challenge in modern electronics. Here we demonstrate that
+thermal gradients arising from ohmic heating can be utilized for excitation of
+coherent auto-oscillations of magnetization and for generation of tunable
+microwave signals. The heat-driven dynamics is observed in
+$\mathrm{Y_{3}Fe_{5}O_{12}/Pt}$ bilayer nanowires where ohmic heating of the Pt
+layer results in injection of pure spin current into the
+$\mathrm{Y_{3}Fe_{5}O_{12}}$ layer. This leads to excitation of
+auto-oscillations of the $\mathrm{Y_{3}Fe_{5}O_{12}}$ magnetization and
+generation of coherent microwave radiation. Our work paves the way towards spin
+caloritronic devices for microwave and magnonic applications.",1611.00887v2
+2016-11-03,Scalable synchronization of spin-Hall oscillators in out-of-plane field,"A strategy for a scalable synchronization of an array of spin-Hall
+oscillators (SHOs) is illustrated. In detail, we present micromagnetic
+simulations of two and five SHOs realized by means of couples of triangular
+golden contacts on the top of a Pt/CoFeB/Ta trilayer. Results highlight that
+the synchronization occurs for the whole current region that gives rise to the
+excitation of self-oscillations. This is linked to the role of the
+magnetodipolar coupling, which is the phenomenon driving the synchronization
+when the distance between oscillators is not too large. Synchronization turns
+out to be also robust against geometrical differences of the contacts,
+simulated by considering variable distances between the tips ranging from 100nm
+to 200nm. Besides, it entails an enlargement of the radiation pattern that can
+be useful for the generation of spin-waves in magnonics applications.
+Simulations performed to study the effect of the interfacial
+Dzyaloshinskii-Moriya interaction show nonreciprocity in spatial propagation of
+the synchronized spin-wave. The simplicity of the geometry and the robustness
+of the achieved synchronization make this design of array of SHOs scalable for
+a larger number of synchronized oscillators.",1611.01227v1
+2016-11-21,Coherence and stiffness of spin waves in diluted ferromagnets,"We present results of a numerical analysis of magnon spectra in supercells
+simulating two-dimensional and bulk random diluted ferromagnets with
+long-ranged pair exchange interactions. We show that low-energy spectral
+regions for these strongly disordered systems contain a coherent component
+leading to interference phenomena manifested by a pronounced sensitivity of the
+lowest excitation energies to the adopted boundary conditions. The dependence
+of configuration averages of these excitation energies on the supercell size
+can be used for an efficient determination of the spin-wave stiffness D. The
+developed formalism is applied to the ferromagnetic Mn-doped GaAs semiconductor
+with optional incorporation of phosphorus; the obtained concentration trends of
+D are found in reasonable agreement with recent experiments. Moreover, a
+relation of the spin stiffness to the Curie temperature Tc has been studied for
+Mn-doped GaAs and GaN semiconductors. It is found that the ratio Tc/D exhibits
+qualitatively the same dependence on Mn concentration in both systems.",1611.06691v1
+2016-11-23,Absence of magnetic thermal conductivity in the quantum spin liquid candidate YbMgGaO4,"We present the ultra-low-temperature specific heat and thermal conductivity
+measurements on the single crystals of YbMgGaO$_4$, which was recently argued
+to be a promising candidate for quantum spin liquid (QSL). In the zero magnetic
+field, a large magnetic contribution of specific heat is observed, and exhibits
+a power-law temperature dependence ($C_m \sim T^{0.74}$). On the contrary, we
+do not observed any significant contribution of thermal conductivity from
+magnetic excitations. In magnetic fields $H \ge$ 6 T, the exponential
+$T$-dependence of $C_m$ and the enhanced thermal conductivity indicate a magnon
+gap of the fully-polarized state. The absence of magnetic thermal conductivity
+at the zero field in this QSL candidate puts a strong constraint on the
+theories of its ground state.",1611.07683v1
+2017-04-03,Effects of spatially engineered Dzyaloshinskii-Moriya interaction in ferromagnetic films,"The Dzyaloshinskii-Moriya interaction (DMI) is a chiral interaction that
+favors formation of domain walls. Recent experiments and ab initio calculations
+show that there are multiple ways to modify the strength of the interfacially
+induced DMI in thin ferromagnetic films with perpendicular magnetic anisotropy.
+In this paper we reveal theoretically the effects of spatially varied DMI on
+the magnetic state in thin films. In such heterochiral 2D structures we report
+several emergent phenomena, ranging from the equilibrium spin canting at the
+interface between regions with different DMI, over particularly strong
+confinement of domain walls and skyrmions within high-DMI tracks, to advanced
+applications such as domain tailoring nearly at will, design of magnonic
+waveguides, and much improved skyrmion racetrack memory.",1704.00770v1
+2017-04-12,On the origin of magnetic anisotropy in two dimensional CrI$_3$,"The observation of ferromagnetic order in a monolayer of CrI$_3$ has been
+recently reported, with a Curie temperature of 45 Kelvin and off-plane easy
+axis. Here we study the origin of magnetic anisotropy, a necessary ingredient
+to have magnetic order in two dimensions, combining two levels of modeling,
+density functional calculations and spin model Hamiltonians. We find two
+different contributions to the magnetic anisotropy of the material, both
+favoring off-plane magnetization and contributing to open a gap in the spin
+wave spectrum. First, ferromagnetic super-exchange across the $\simeq $ 90
+degree Cr-I-Cr bonds, are anisotropic, due to the spin orbit interaction of the
+ligand I atoms. Second, a much smaller contribution that comes from the single
+ion anisotropy of the $S=3/2$ Cr atom. Our results permit to establish the XXZ
+Hamiltonian, with a very small single ion anisotropy, as the adequate spin
+model for this system. Using spin wave theory we estimate the Curie temperature
+and we highlight the essential role played by the gap that magnetic anisotropy
+induces on the magnon spectrum.",1704.03849v4
+2017-04-13,Switching of magnetic ground states across the UIr1-xRhxGe alloy system,"We investigated the evolution of magnetism in the UIr1-xRhxGe system by the
+systematic study of high-quality single crystals. Lattice parameters of both
+parent compounds are very similar resulting in almost identical nearest
+interatomic uranium distance close to the Hill limit. We established the x-T
+phase diagram of the UIr1-xRhxGe system and found a discontinuous
+antiferromagnetic/ferromagnetic boundary at xcrit = 0.56 where a local minimum
+in ordering temperature and maximum of the Sommerfeld coefficient 175 mJ/mol K2
+occurs in the UCoGe-URhGe-UIrGe system, signaling an increase in magnetic
+fluctuations. However, a quantum critical point is not realized because of the
+finite ordering temperature at xcrit. A magnon gap on the antiferromagnetic
+side abruptly suppresses magnetic fluctuations. We find a field-induced first
+order transition in the vicinity of the critical magnetic field along the b
+axis in the entire UIr1-xRhxGe system including the ferromagnetic region
+UCo0.6Rh0.4Ge - URhGe.",1704.04013v1
+2017-04-24,Magnetic topological lithography: Gateway to the artificial spin ice manifold,"Nanomagnetic arrays are widespread in data storage and processing. As current
+technologies approach fundamental limits on size and thermal stability,
+extracting additional functionality from arrays is crucial to advancing
+technological progress. One design exploiting the enhanced magnetic
+interactions in dense arrays is the geometrically-frustrated metamaterial
+'artificial spin ice' (ASI). Frustrated systems offer vast untapped potential
+arising from their unique microstate landscapes, presenting intriguing
+opportunities from reconfigurable logic to magnonic devices or hardware neural
+networks. However, progress in such systems is impeded by the inability to
+access more than a fraction of the total microstate space. Here, we present a
+powerful surface-probe lithography technique, magnetic topological lithography,
+providing access to all possible microstates in ASI and related nanomagnetic
+arrays. We demonstrate the creation of two previously elusive states; the
+spin-crystal ground state of dipolar kagome ASI and high-energy, low-entropy
+'monopole-chain' states exhibiting negative effective temperatures.",1704.07439v1
+2017-04-25,Analytical study of the edge states in the bosonic Haldane model,"We investigate the properties of magnon edge states in a ferromagnetic
+honeycomb spin lattice with a Dzyaloshinskii-Moriya interaction (DMI). We
+derive analytical expressions for the energy spectra and wavefunctions of the
+edge states localized on the boundaries. By introducing an external on-site
+potential at the outermost sites, we show that the bosonic band structure is
+similar to that of the fermionic graphene. We investigate the region in the
+momentum space where the bosonic edge states are well defined and we analyze
+the width of the edge state and their dependence with DMI strength. Our
+findings extend the predictions using topological arguments and they allow
+size-dependent confirmation from possible experiments",1704.07746v3
+2017-12-31,Proper dissipative torques in antiferromagnetic dynamics,"There is little doubt that the magnetization dynamics of ferromagnetic
+systems is governed by the Landau-Lifshitz-Gilbert equation or its
+generalization with various spin torques. In contrast, there are several sets
+of dynamic equations for two-sublattice antiferromagnets (AFMs) in literature
+that have different forms of dissipative torques and no proper dynamic
+equations for multi-sublattice AFMs and ferrimagnets in general. Here we
+introduce the general Rayleigh dissipation functional into the Lagrange
+equation and derive the proper form of the dissipative torques in the
+phenomenological equations for the AFMs with multiple sublattices. A new type
+of dissipative torque arising from inter-sublattice drag effect is discovered
+that has important influences on magnon lifetime and domain wall motion. In
+particular, our theory unifies different dynamic equations of AFMs in
+literature.",1801.00217v1
+2018-01-02,Phonon driven Floquet matter,"A resonantly excited coherent phonon leads to a periodic oscillation of the
+atomic lattice in a crystal structure bringing the material into a
+non-equilibrium electronic configuration. Periodically oscillating quantum
+systems can be understood in terms of Floquet theory and we show these concepts
+can be applied to coherent lattice vibrations reflecting the underlying
+coupling mechanism between electrons and bosonic modes. This coupling leads to
+dressed quasi-particles imprinting specific signatures in the spectrum of the
+electronic structure. Taking graphene as a paradigmatic material we show how
+the phonon-dressed states display an intricate sideband structure revealing
+electron-phonon coupling and topological ordering. This work establishes that
+the recently demonstrated concept of light-induced non-equilibrium Floquet
+phases can also be applied when using coherent phonon modes for the dynamical
+control of material properties. The present results are generic for bosonic
+time-dependent perturbations and similar phenomena can be observed for plasmon,
+magnon or exciton driven materials.",1801.00599v1
+2018-01-08,Low frequency spin dynamics in XY quantum spin ice Yb$_2$Pt$_2$O$_7$,"The XY pyrochlore Yb$_2$Ti$_2$O$_7$, with pseudo spin 1/2 at the Yb$^{3+}$
+site, has been celebrated as potential host for the quantum spin ice state. The
+substitution of non-magnetic Ti with Pt gives Yb$_2$Pt$_2$O$_7$, a system with
+remarkably similar magnetic properties. The large nuclear gyromagnetic ratio
+($\gamma_{n}/2 \pi = 9.15$~MHz/T) of $^{195}$Pt makes Yb$_2$Pt$_2$O$_7$ an
+ideal material for NMR investigation of its unconventional magnetic properties.
+Based on the $^{195}$Pt nuclear spin-lattice relaxation rate $1/T_1$ and the
+magnetic specific heat $C_{p}$ measured in a broad range of magnetic field
+$B_{ext}$, we demonstrate that the field-induced magnon gap linearly decreases
+with $B_{ext}$ but additional low energy mode of spin excitations emerge below
+$\sim 0.5$~T.",1801.02724v2
+2018-01-29,Current-induced spin-orbit torques in ferromagnetic and antiferromagnetic systems,"Spin-orbit coupling in inversion-asymmetric magnetic crystals and structures
+has emerged as a powerful tool to generate complex magnetic textures,
+interconvert charge and spin under applied current, and control magnetization
+dynamics. Current-induced spin-orbit torques mediate the transfer of angular
+momentum from the lattice to the spin system, leading to sustained magnetic
+oscillations or switching of ferromagnetic as well as antiferromagnetic
+structures. The manipulation of magnetic order, domain walls and skyrmions by
+spin-orbit torques provides evidence of the microscopic interactions between
+charge and spin in a variety of materials and opens novel strategies to design
+spintronic devices with potentially high impact in data storage, nonvolatile
+logic, and magnonic applications. This paper reviews recent progress in the
+field of spin-orbitronics, focusing on theoretical models, material properties,
+and experimental results obtained on bulk noncentrosymmetric conductors and
+multilayer heterostructures, including metals, semiconductors, and topological
+insulator systems. Relevant aspects for improving the understanding and
+optimizing the efficiency of nonequilibrium spin-orbit phenomena in future
+nanoscale devices are also discussed.",1801.09636v2
+2018-01-26,Probing magnetism in 2D van der Waals crystalline insulators via electron tunneling,"Magnetic insulators are a key resource for next-generation spintronic and
+topological devices. The family of layered metal halides promises ultrathin
+insulating multiferroics, spin liquids, and ferromagnets, but new
+characterization methods are required to unlock their potential. Here, we
+report tunneling through the layered magnetic insulator CrI3 as a function of
+temperature and applied magnetic field. We electrically detect the magnetic
+ground state and inter-layer coupling and observe a field-induced metamagnetic
+transition. The metamagnetic transition results in magnetoresistances of 95%,
+300%, and 550% for bilayer, trilayer, and tetralayer CrI3 barriers,
+respectively. We further measure inelastic tunneling spectra for our junctions,
+unveiling a rich spectrum of collective magnetic excitations (magnons) in CrI3.
+Our results establish vertical tunneling as a versatile probe of magnetism in
+atomically thin insulators.",1801.10075v1
+2018-08-01,The generalized gradient approximation kernel in time-dependent density functional theory,"A complete understanding of a material requires both knowledge of the excited
+states as well as of the ground state. In particular, the low energy
+excitations are of utmost importance while studying the electronic, magnetic,
+dynamical, and thermodynamical properties of the material. Time-Dependent
+Density Functional Theory (TDDFT), within the linear regime, is a successful
+\textit{ab-initio} method to access the electronic charge and spin excitations.
+However, it requires an approximation to the exchange-correlation (XC) kernel
+which encapsulates the effect of electron-electron interactions in the
+many-body system. In this work we derive and implement the spin-polarized XC
+kernel for semi-local approximations such as the adiabatic Generalized Gradient
+Approximation (AGGA). This kernel has a quadratic dependence on the wavevector,
+{\bf q}, of the perturbation, however the impact of this on the electron energy
+loss spectra (EELS) is small. Although the GGA functional is good in predicting
+structural properties, it generality overestimates the exchange spin-splitting.
+This leads to higher magnon energies, as compared to both ALDA and experiment.
+In addition, interaction with the Stoner spin-flip continuum is enhanced by
+AGGA, which strongly suppresses the intensity of spin-waves.",1808.00215v1
+2018-08-02,Impact of the regularization parameter in the Mean Free Path reconstruction method: Nanoscale heat transport and beyond,"The understanding of the mean free path (MFP) distribution of the energy
+carriers in materials (e.g. electrons, phonons, magnons, etc.) is a key
+physical insight into their transport properties. In this context, MFP
+spectroscopy has become an important tool to describe the contribution of
+carriers with different MFP to the total transport phenomenon. In this work, we
+revise the MFP reconstruction technique and present a study on the impact of
+the regularization parameter on the MFP distribution of the energy carriers. By
+using the L-curve criterion, we calculate the optimal mathematical value of the
+regularization parameter. The effect of the change from the optimal value in
+the MFP distribution is analyzed in three case studies of heat transport by
+phonons. These results demonstrate that the choice of the regularization
+parameter has a large impact on the physical information obtained from the
+reconstructed accumulation function, and thus cannot be chosen arbitrarily. The
+approach can be applied to various transport phenomena at the nanoscale
+involving carriers of different physical nature and behavior.",1808.00708v3
+2018-08-06,Spin wave dispersion and intensity correlation in width-modulated nanowire arrays: A Brillouin light scattering study,"Using Brillouin light scattering spectroscopy and dynamical matrix method
+calculations, we study collective spin waves in dense arrays of periodically
+double-side width-modulated Permalloy nanowires. Width modulation is achieved
+by creating a sequence of triangular notches on the two parallel nanowire
+sides, with a periodicity of p=1000 nm, and tunable relative displacement (D)
+of the notches sequence on the two lateral sides. Both symmetric (D=0) and
+asymmetric (D= 250 and 500 nm) width-modulated nanowires were investigated. We
+have found that the detected modes have Bloch-type character and belong to a
+doublet deriving from the splitting of the modes characteristics of the
+nanowire with homogeneous width. Interestingly, the amplitude of the magnonic
+band, the frequency difference of the doublet, as well as their relative
+scattering intensity, can be efficiently controlled by increasing D rather than
+having single- or symmetric (D=0) double-side width-modulation.",1808.01732v1
+2018-08-18,An overview of the NIRSPEC upgrade for the Keck II telescope,"NIRSPEC is a 1-5 micron echelle spectrograph in use on the Keck II Telescope
+since 1999. The spectrograph is capable of both moderate (R~2,000) and high
+(R~25,000) resolution observations and has been a workhorse instrument across
+many astronomical fields, from planetary science to extragalactic observations.
+In the latter half of 2018, we will upgrade NIRSPEC to improve the sensitivity
+and stability of the instrument and increase its lifetime. The major components
+of the upgrade include replacing the spectrometer and slit-viewing camera
+detectors with Teledyne H2RG arrays and replacing all transputer-based
+electronics. We present detailed design, testing, and analysis of the upgraded
+instrument, including the finalized optomechanical design of the new 1-5 micron
+slit-viewing camera, final alignment and assembly of the science array,
+electronics systems, and updated software design.",1808.06024v1
+2018-08-21,Pseudo Jahn-Teller Effect and Magnetoelastic Coupling in Spin-Orbit Mott Insulators,"The consequences of the Jahn-Teller (JT) orbital-lattice coupling for
+magnetism of pseudospin J_{eff}=1/2 and J_{eff}=0 compounds are addressed. In
+the former case, represented by Sr_2IrO_4, this coupling generates, through the
+so-called pseudo-JT effect, orthorhombic deformations of a crystal concomitant
+with magnetic ordering. The orthorhombicity axis is tied to the magnetization
+and rotates with it under magnetic field. The theory resolves a number of
+puzzles in Sr_2IrO_4 such as the origin of in-plane magnetic anisotropy and
+magnon gaps, metamagnetic transition, etc. In J_{eff}=0 systems, the pseudo-JT
+effect leads to spin-nematic transition well above magnetic ordering, which may
+explain the origin of `orbital order' in Ca_2RuO_4",1808.06919v2
+2018-08-23,The infrared imaging spectrograph (IRIS) for TMT: electronics-cable architecture,"The InfraRed Imaging Spectrograph (IRIS) is a first-light instrument for the
+Thirty Meter Telescope (TMT). It combines a diffraction limited imager and an
+integral field spectrograph. This paper focuses on the electrical system of
+IRIS. With an instrument of the size and complexity of IRIS we face several
+electrical challenges. Many of the major controllers must be located directly
+on the cryostat to reduce cable lengths, and others require multiple bulkheads
+and must pass through a large cable wrap. Cooling and vibration due to the
+rotation of the instrument are also major challenges. We will present our
+selection of cables and connectors for both room temperature and cryogenic
+environments, packaging in the various cabinets and enclosures, and techniques
+for complex bulkheads including for large detectors at the cryostat wall.",1808.07853v1
+2018-08-27,Magnetostriction in Antiferromagnets,"We consider magnetostriction in magnetic materials. Starting from a
+microscopic lattice model of the magneto-elastic coupling, we derive the
+continuum magnetostriction Hamiltonian in cubic ferromagnets and
+antiferromagnets. In ferromagnets, our results agree with established results.
+In antiferromagnets, we find a new central contribution which reflects the spin
+ordering. The additional term is essential in certain antiferromagnets where
+magnetic moments order in antiparallel ferromagnetic planes characterized by a
+normal axis. In such antiferromagnets, we predict that the magnetostrictive
+strain depends on the direction of the normal axis. Our findings are relevant
+for materials such as NiO and CoO, where there is a new spin-structure
+dependent strain, but not in RbMnF$_3$. We propose an experimental procedure to
+verify the importance of our findings in NiO that can be readily generalized to
+other materials. We also generalize the theory to include long-wavelength
+magnetoelastic coupling. We expect that the spin-structure dependent term
+critically affects the magnon-phonon coupling.",1808.09013v2
+2018-08-28,An Intrinsic Spin Orbit Torque Nano-Oscillator,"Spin torque and spin Hall effect nanooscillators generate high intensity spin
+wave auto oscillations on the nanoscale enabling novel microwave applications
+in spintronics, magnonics, and neuromorphic computing. For their operation,
+these devices require externally generated spin currents either from an
+additional ferromagnetic layer or a material with a high spin Hall angle. Here
+we demonstrate highly coherent field and current tunable microwave signals from
+nanoconstrictions in single 15 and 20 nm thick permalloy layers. Using a
+combination of spin torque ferromagnetic resonance measurements, scanning
+microBrillouin light scattering microscopy, and micromagnetic simulations, we
+identify the autooscillations as emanating from a localized edge mode of the
+nanoconstriction driven by spin orbit torques. Our results pave the way for
+greatly simplified designs of auto oscillating nanomagnetic systems only
+requiring a single ferromagnetic layer.",1808.09330v1
+2019-06-01,Polarized inelastic neutron scattering of non-reciprocal spin waves in MnSi,"We report spin-polarized inelastic neutron scattering of the dynamical
+structure factor of the conical magnetic helix in the cubic chiral magnet MnSi.
+We find that the spectral weight of spin-flip scattering processes is
+concentrated on single branches for wavevector transfer parallel to the helix
+axis as inferred from well-defined peaks in the neutron spectra. In contrast,
+for wavevector transfers perpendicular to the helix the spectral weight is
+distributed among different branches of the magnon band structure as reflected
+in broader features of the spectra. Taking into account the effects of
+instrumental resolution, our experimental results are in excellent quantitative
+agreement with parameter-free theoretical predictions. Whereas the dispersion
+of the spin waves in MnSi appears to be approximately reciprocal at low
+energies and small applied fields, the associated spin-resolved spectral weight
+displays a pronounced non-reciprocity that implies a distinct non-reciprocal
+response in the limit of vanishing uniform magnetization at zero magnetic
+field.",1906.00221v3
+2019-06-12,Unfolding the complexity of quasi-particle physics in disordered materials,"The concept of quasi-particles forms the theoretical basis of our microscopic
+understanding of emergent phenomena associated with quantum mechanical
+many-body interactions. However, quasi-particle theory in disordered materials
+has proven difficult, resulting in the predominance of mean-field solutions.
+Here we report first-principles phonon calculations and inelastic x-ray and
+neutron scattering measurements on equiatomic alloys (NiCo, NiFe, AgPd, and
+NiFeCo) with force constant dominant disorder - confronting a key 50-year-old
+assumption in the Hamiltonian of all mean-field quasi-particle solutions for
+off-diagonal disorder. Our results have revealed the presence of a large, and
+heretofore unrecognized, impact of local chemical environments on the
+distribution of the species-pair-resolved force constant disorder that can
+dominate phonon scattering. This discovery not only identifies a critical
+analysis issue that has broad implications for other elementary excitations
+such as magnons and skyrmions in magnetic alloys, but also provides an
+important tool for the design of materials with ultra-low thermal conductivity.",1906.04945v1
+2019-06-14,Mechanisms of FMR line broadening in CoFeB-LiNbO$_3$ granular films in the vicinity of metal-insulator transition,"Metal-insulator (CoFeB)$_x$(LiNbO$_3$)$_{100-x}$ nanocomposite films with
+different content of the ferromagnetic (FM) phase $x$ are investigated by
+ferromagnetic resonance (FMR) technique. A strong change of the FMR line shape
+is observed in the vicinity of metal-insulator transition (MIT) of the film,
+where the hopping-type conductivity $\sigma$ modifies to the regime of a strong
+intergranular tunnelling, characterized by a logarithmic dependence $\sigma(T)$
+at high temperatures. It is shown that below MIT, the FMR linewidth is mainly
+determined by the inhomogeneous distribution of the local anisotropy axes in
+the film plane. Above MIT, the contribution of this inhomogeneity to the line
+broadening decreases. At the same time, two-magnon magnetic relaxation
+processes begin to play a significant role in the formation of the linewidth.
+The observed behaviour indicates the critical role of interparticle exchange in
+the tunnelling regime above MIT of the nanocomposite.",1906.06320v2
+2019-06-17,Local Photothermal Control of Phase Transitions for On-demand Room-temperature Rewritable Magnetic Patterning,"The ability to make controlled patterns of magnetic structures within a
+nonmagnetic background is essential for several types of existing and proposed
+technologies. Such patterns provide the foundation of magnetic memory and logic
+devices, allow the creation of artificial spin-ice lattices and enable the
+study of magnon propagation. Here, we report a novel approach for magnetic
+patterning that allows repeated creation and erasure of arbitrary shapes of
+thin-film ferromagnetic structures. This strategy is enabled by epitaxial
+Fe$_{0.52}$Rh$_{0.48}$ thin films designed so that both ferromagnetic and
+antiferromagnetic phases are bistable at room temperature. Starting with the
+film in a uniform antiferromagnetic state, we demonstrate the ability to write
+arbitrary patterns of the ferromagnetic phase by local heating with a focused
+laser. If desired, the results can then be erased by cooling with a
+thermoelectric cooler and the material repeatedly re-patterned.",1906.07239v1
+2019-06-19,Edge localization of spin waves in antidot multilayers with perpendicular magnetic anisotropy,"We study the spin-wave dynamics in nanoscale antidot lattices based on Co/Pd
+multilayers with perpendicular magnetic anisotropy. Using time-resolved
+magneto-optical Kerr effect measurements we demonstrate that the variation of
+the antidot shape introduces significant change in the spin-wave spectra,
+especially in the lower frequency range. By employing micromagnetic simulations
+we show that additional peaks observed in the measured spectra are related to
+narrow shell regions around the antidots, where the magnetic anisotropy is
+reduced due to the Ga+ ion irradiation during the focused ion beam milling
+process of the antidot fabrication. The results point at new possibilities for
+exploitation of localized spin waves in out-of-plane magnetized thin films,
+which are easily tunable and suitable for magnonics applications.",1906.08109v2
+2019-06-24,Octahedral tilting induced isospin reorientation transition in iridate heterostructures,"Iridate heterostructures are gaining interest as their magnetic properties
+are much more sensitive to structural distortion compared to pure spin systems
+due to spin-orbital entanglement induced by strong spin-orbit coupling. While
+bulk monolayer and bilayer iridates show $ab$-plane canted and $c$-axis
+antiferromagnetic (AFM) order, recent experiments on layered iridate
+superlattices (SL) have revealed striking properties, especially in the bilayer
+SL. A spin model is presented including the tilting induced Kitaev type
+interactions, which illustrates the proclivity towards $ab$-plane canted AFM
+order. A realistic Hubbard model including spin-dependent hopping terms arising
+from octahedral rotation and tilting is constructed for the bilayer SL in
+isospin space, and magnetic excitations are investigated in the
+self-consistently determined magnetic state. The Hubbard model analysis
+confirms the spin model results and shows strongly reduced magnon energy gap
+and an isospin reorientation transition from $c$-axis to $ab$-plane canted AFM
+order with increasing tilting.",1906.09879v2
+2019-06-28,Zero-field propagation of spin waves in waveguides prepared by focused ion beam direct writing,"Metastable face-centered-cubic Fe78Ni22 thin films grown on Cu(001)
+substrates are excellent candidates for focused ion beam direct writing of
+magnonic structures due to their favorable magnetic properties after
+ion-beam-induced transformation. The focused ion beam transforms the originally
+nonmagnetic fcc phase into the ferromagnetic bcc phase with additional control
+over the direction of uniaxial magnetic in-plane anisotropy. The
+magnetocrystalline anisotropy in transformed areas is strong enough to
+stabilize the magnetization in transverse direction to the long axis of narrow
+waveguides. Therefore, it is possible to propagate spin waves in these
+waveguides without the presence of an external magnetic field in the favorable
+Demon-Eshbach geometry. Phase-resolved micro-focused Brillouin light scattering
+yields the dispersion relation of these waveguides in zero as well as in
+nonzero external magnetic fields.",1906.12254v2
+2019-07-12,Spin Seebeck effect and phonon energy transfer in heterostructures containing layers of a normal metal and a ferromagnetic insulator,"In the framework of the kinetic approach based on the Boltzmann equation for
+the phonon distribution function, we analyze phonon heat transfer in a
+heterostructure containing a layer of a normal metal ($ N $) and a layer of a
+ferromagnetic insulator ($ F $). Two realistic methods for creating a
+temperature gradient in such a heterostructure are considered: by heating of
+the $N$-layer by an electric current and by placing the $N/F$-bilayer between
+massive dielectrics with different temperatures. The electron temperature $ T_e
+$ in the $ N $-layer and the magnon temperature $ T_m $ in the $ F $-layer are
+calculated. The difference in these temperatures determines the voltage $
+V_{ISHE} $ on the $ N $-layer in the Seebeck spin effect regime. The dependence
+of $ V_{ISHE} $ on the bath temperature and on the thickness of the $ N $ and $
+F $ layers is compared with the available experimental data.",1907.05739v1
+2019-07-16,Polylogarithms from the bound state S-matrix,"Higher-point functions of gauge invariant composite operators in N=4 super
+Yang-Mills theory can be computed via triangulation. The elementary tile in
+this process is the hexagon introduced for the evaluation of structure
+constants. A glueing procedure welding the tiles back together is needed to
+return to the original object.
+  In this note we present work in progress on n-point functions of BPS
+operators. In this case, quantum corrections are entirely carried by the
+glueing procedure. The lowest non-elementary process is the glueing of three
+adjacent tiles by the exchange of two single magnons.
+  This problem has been analysed before. With a view to resolving some
+conceptional questions and to generalising to higher processes we are trying to
+develop an algorithmic approach using the representation of hypergeometric sums
+as integrals over Euler kernels.",1907.07014v1
+2019-07-25,Order out of a Coulomb phase and Higgs transtion: frustrated transverse interactions of Nd2Zr2O7,"The pyrochlore material Nd$_2$Zr$_2$O$_7$ with an ""all-in-all-out"" (AIAO)
+magnetic order shows novel quantum moment fragmentation with gapped flat
+dynamical spin ice modes. The parameterized spin Hamiltonian with a dominant
+frustrated ferromagnetic transverse term reveals a proximity to a U(1) spin
+liquid. Here we study magnetic excitations of Nd$_2$Zr$_2$O$_7$ above the
+ordering temperature ($T_\text{N}$) using high-energy-resolution inelastic
+neutron scattering. We find strong spin ice correlations at zero energy with
+the disappearance of gapped magnon excitations of the AIAO order. It seems that
+the gap to the dynamical spin ice closes above $T_\text{N}$ and the system
+enters a quantum spin ice state competing with and suppressing the AIAO order.
+Classical Monte Carlo, molecular dynamics and quantum boson calculations
+support the existence of a Coulombic phase above $T_\text{N}$. Our findings
+relate the magnetic ordering of Nd$_2$Zr$_2$O$_7$ with the Higgs mechanism and
+provide explanations for several previously reported experimental features.",1907.11056v1
+2019-07-29,A Synthetic Skyrmion Platform with Robust Tunability,"Magnetic skyrmions are topologically non-trivial spin structure, and their
+existence in ferromagnetically coupled multilayers has been reported with
+disordered arrangement. In these multilayers, the heavy metal spacing layers
+provide an interfacial Dzyaloshinskii-Moriya interaction (DMI) for stabilizing
+skyrmions at the expense of interlayer exchanging coupling (IEC). To meet the
+functional requirement of ordered/designable arrangement, in this work, we
+proposed and experimentally demonstrated a scenario of skyrmion nucleation
+using nanostructured synthetic antiferromagnetic (SAF) multilayers. Instead of
+relying on DMI, the antiferromagnetic IEC in the SAF multilayers fulfills the
+role of nucleation and stabilization of skyrmions. The IEC induced skyrmions
+were identified directly imaged with MFM and confirmed by magnetometry and
+magnetoresistance measurements as well as micromagnetic simulation.
+Furthermore, the robustness of the proposed skyrmion nucleation scenario was
+examined against temperature (from 4.5 to 300 K), device size (from 400 to 1200
+nm), and different lattice designs. Hence, our results provide a synthetic
+skyrmion platform meeting the functional needs in magnonic and spintronic
+applications.",1907.12516v1
+2019-10-02,Magnon bound states vs. anyonic Majorana excitations in the Kitaev honeycomb magnet $α$-RuCl$_3$,"The pure Kitaev honeycomb model harbors a quantum spin liquid in zero
+magnetic fields, while applying finite magnetic fields induces a topological
+spin liquid with non-Abelian anyonic excitations. This latter phase has been
+much sought after in Kitaev candidate materials, such as $\alpha$-RuCl$_3$.
+Currently, two competing scenarios exist for the intermediate field phase of
+this compound ($B=7-10$ T), based on experimental as well as theoretical
+results: (i) conventional multiparticle magnetic excitations of integer quantum
+number vs. (ii) Majorana fermionic excitations of possibly non-Abelian nature
+with a fractional quantum number. To discriminate between these scenarios a
+detailed investigation of excitations over a wide field-temperature phase
+diagram is essential. Here we present Raman spectroscopic data revealing
+low-energy quasiparticles emerging out of a continuum of fractionalized
+excitations at intermediate fields, which are contrasted by conventional
+spin-wave excitations. The temperature evolution of these quasiparticles
+suggests the formation of bound states out of fractionalized excitations.",1910.00800v1
+2019-10-07,Spinon confinement and deconfinement in spin-1 chains,"Motivated by the rich phase diagrams recently unveiled in frustrated spin-1
+chains with competing next-nearest neighbour and four-spin interactions, we
+investigate the nature of the elementary excitations of spin-1 chains in the
+vicinity of phase transitions using the matrix-product state (MPS)
+representation of elementary excitations. First, we show that both spinons and
+magnons naturally arise in SU(2) invariant spin chains when describing ground
+states and elementary excitations using MPS. Then we investigate the nature of
+the elementary excitations across the first-oder transition between the Haldane
+phase and the topologically trivial next-nearest neighbor Haldane phase. We
+show explicitly that spinons deconfine at the transition, and we calculate the
+dispersion of these deconfined spinons with MPS. We also show that, immediately
+away from the transition line, spinons confine, forming dispersive
+spinon/anti-spinon bound states on both sides of the transition. Finally, we
+show that deconfined spinons also appear at the transition between the Haldane
+phase and the spontaneously dimerized phase when this transition is first
+order.",1910.03064v2
+2019-10-22,Controlled nonlinear magnetic damping in spin-Hall nano-devices,"Large-amplitude magnetization dynamics is substantially more complex compared
+to the low-amplitude linear regime, due to the inevitable emergence of
+nonlinearities. One of the fundamental nonlinear phenomena is the nonlinear
+damping enhancement, which imposes strict limitations on the operation and
+efficiency of magnetic nanodevices. In particular, nonlinear damping prevents
+excitation of coherent magnetization auto-oscillations driven by the injection
+of spin current into spatially extended magnetic regions. Here, we propose and
+experimentally demonstrate that nonlinear damping can be controlled by the
+ellipticity of magnetization precession. By balancing different contributions
+to anisotropy, we minimize the ellipticity and achieve coherent magnetization
+oscillations driven by spatially extended spin current injection into a
+microscopic magnetic disk. Our results provide a novel route for the
+implementation of efficient active spintronic and magnonic devices driven by
+spin current.",1910.09801v1
+2019-10-26,High-degeneracy points protected by site-permutation symmetries,"Space group symmetries dictate the energy degeneracy of quasiparticles (e.g.,
+electronic, photonic) in crystalline structures. For spinless systems, there
+can only be double or triple degeneracies protected by these symmetries, while
+other degeneracies are usually taken as \textit{accidental}. In this Letter we
+show that it is possible to design higher degeneracies exploring site
+permutation symmetries. These design principles are shown to be satisfied in
+previously studied lattices, and new structures are proposed with three, four
+and five degeneracy points for spinless systems. The results are general and
+apply to different quasiparticle models. Here, we focus on a tight-binding
+approach for the electronic case as a proof of principle. The resulting
+high-degeneracy points are protected by the site-permutation symmetries,
+yielding pseudospin-1 and -2 Dirac fermions. The strategy proposed here can be
+used to design lattices with high-degeneracy points in electronic (e.g.
+metal-organic frameworks), photonic, phononic, magnonic and cold-atom systems.",1910.12144v2
+2019-10-30,Strong coupling-enabled broadband non-reciprocity,"Non-reciprocity of signal transmission enhances capacity of communication
+channels and protects transmission quality against possible signal
+instabilities, thus becoming an important component ensuring coherent
+information processing. However, non-reciprocal transmission requires breaking
+time-reversal symmetry (TRS) which poses challenges of both practical and
+fundamental character hindering the progress. Here we report a new scheme for
+achieving broadband non-reciprocity using a specially engineered hybrid
+microwave cavity. The TRS breaking is realized via strong coherent coupling
+between a selected chiral mode in the microwave cavity and a single collective
+spin excitation (magnon) in a ferromagnetic yttrium iron garnet (YIG) sphere.
+The non-reciprocity in transmission is observed spanning nearly a 0.5 GHz
+frequency band, which outperforms by two orders of magnitude the previously
+achieved bandwidths. Our findings open new directions for robust coherent
+information processing in a broad range of systems in both classical and
+quantum regimes.",1910.14117v2
+2020-01-01,Pseudo-spin rotation symmetry breaking by Coulomb interaction terms in spin-orbit coupled systems,"By transforming from the pure-spin-orbital ($t_{\rm 2g}$) basis to the
+spin-orbital entangled pseudo-spin-orbital basis, the pseudo-spin rotation
+symmetry of the different Coulomb interaction terms is investigated under SU(2)
+transformation in pseudo-spin space. While the Hubbard and density interaction
+terms are invariant, the Hund's coupling and pair-hopping interaction terms
+explicitly break pseudo-spin rotation symmetry systematically. The form of the
+symmetry-breaking terms obtained from the transformation of the Coulomb
+interaction terms accounts for the easy $x$-$y$ plane anisotropy and magnon gap
+for the out-of-plane mode, highlighting the importance of mixing with the
+nominally non-magnetic $J$=3/2 sector, and providing a physically transparent
+approach for investigating magnetic ordering and anisotropy effects in
+perovskite ($\rm Sr_2 Ir O_4$) and other $d^5$ pseudo-spin compounds.",2001.00190v2
+2020-01-15,Yttrium Iron Garnet Thickness Influence on the Spin Pumping in the Bulk Acoustic Wave Resonator,"The features of phonon-magnon interconversion in acoustic resonator determine
+the efficiency of spin pumping from YIG into Pt that may be detected
+electrically through the inverse spin Hall effect (ISHE). Based on the methods
+developed in previous works for calculating resonator structures with a
+piezoelectric (ZnO) and a magnetoelastic layer in contact with the heavy metal
+(YIG/Pt), we present the results of numerical calculations of YIG film
+thickness influence on acoustically driven spin waves. We obtain some YIG film
+thickness regions with various behavior of dc ISHE voltage $U_{ISHE}$. At
+micron and submicron thicknesses, the higher spin wave resonance (SWR) modes
+(both even and odd) can be generated with efficiency comparable and even
+exceeding that of the main mode. The absolute maximum of $U_{ISHE}$ is achieved
+at the thickness about $s_1 \approx 208$ nm under the excitation of the first
+SWR.",2001.05385v1
+2020-01-15,Phonon magnetochiral effect of band-geometric origin in Weyl semimetals,"The phonon magnetochiral effect consists of a nonreciprocity in the velocity
+or attenuation of acoustic waves when they propagate parallel and antiparallel
+to an external magnetic field. The first experimental observation of this
+effect has been reported recently in a chiral magnet and ascribed to the
+hybridization between acoustic phonons and chiral magnons. Here, we predict a
+potentially measurable phonon magnetochiral effect of electronic origin in
+chiral Weyl semimetals. Caused by the Berry curvature and the orbital magnetic
+moment, this effect is enhanced for longitudinal phonons by the chiral anomaly.",2001.05483v3
+2020-01-18,Off-axial focusing of spin-wave lens in the presence of Dzyaloshinskii-Moriya interaction,"We theoretically study the effect of Dzyaloshinskii-Moriya interaction (DMI)
+on the focusing of a spin-wave lens that is constructed by a circular interface
+between two magnetic films. We analytically derive the generalized Snell's law
+in the curved geometry and the position of the focal point which exhibits a
+peculiar off-axial focusing behavior. We uncover a strong dependence of the
+focal point on both the material parameters and the frequency of incident spin
+waves. Full micromagnetic simulations compare well with theoretical
+predictions. Our findings would be helpful to manipulate spin waves in chiral
+magnets and to design functional magnonic devices.",2001.06604v1
+2020-01-21,Nonresonant amplification of coherent spin waves through voltage-induced interface magnetoelectric effect and spin-transfer torque,"We present new mechanism for manipulation of the spin-wave amplitude through
+the use of the dynamic charge-mediated magnetoelectric effect in ultrathin
+multilayers composed of dielectric thin-film capacitors separated by a
+ferromagnetic bilayer. Propagating spin waves can be amplified and attenuated
+with rising and decreasing slopes of the oscillating voltage, respectively,
+locally applied to the sample. The way the spin accumulation is generated makes
+the interaction of the spin-transfer torque with the magnetization dynamics
+mode-selective and restricted to some range of spin-wave frequencies, which is
+in contrary to known types of the spin-transfer torque effects. The interfacial
+nature of spin-dependent screening allows to reduce the thickness of the fixed
+magnetization layer to a few nanometers, thus the proposed effect significantly
+contributes toward realization of the magnonic devices and also miniaturization
+of the spintronic devices.",2001.07474v1
+2020-01-22,On two phases inside the Bose condensation dome of Yb$_2$Si$_2$O$_7$,"Recent experimental data on Bose-Einstein Condensation (BEC) of magnons in
+the spin-gap compound Yb$_2$Si$_2$O$_7$ revealed an asymmetric BEC dome
+arXiv:1810.13096v2. We examine modifications to the Heisenberg model on a
+breathing honeycomb lattice, showing that this physics can be explained by
+competing forms of weak anisotropy. We employ a gamut of analytical and
+numerical techniques to show that the anisotropy yields a field driven phase
+transition from a state with broken Ising symmetry to a phase which breaks no
+symmetries and crosses over to the polarized limit.",2001.08219v2
+2020-01-23,Dephasing-assisted macrospin transport,"Transport phenomena are ubiquitous in physics, and it is generally understood
+that the environmental disorder and noise deteriorates the transfer of
+excitations. There are however cases in which transport can be enhanced by
+fluctuations. In the present work we show, by means of micromagnetics
+simulations, that transport efficiency in a chain of classical macrospins can
+be greatly increased by an optimal level of dephasing noise. We demonstrate
+also the same effect in a simplified model, the dissipative Discrete Nonlinear
+Schr\""odinger equation subject to phase noise. Our results point towards the
+realisation of a large class of magnonics and spintronics devices, where
+disorder and noise can be used to enhance spin-dependent transport efficiency.",2001.08624v2
+2020-01-27,Acoustic ferromagnetic resonance and spin pumping induced by surface acoustic waves,"Voltage induced magnetization dynamics of magnetic thin films is a valuable
+tool to study anisotropic fields, exchange couplings, magnetization damping and
+spin pumping mechanism. A particularly well established technique is the
+ferromagnetic resonance (FMR) generated by the coupling of microwave photons
+and magnetization eigenmodes in the GHz range. Here we review the basic
+concepts of the so-called acoustic ferromagnetic resonance technique (a-FMR)
+induced by the coupling of surface acoustic waves (SAW) and magnetization of
+thin films. Interestingly, additional to the benefits of the microwave excited
+FMR technique, the coupling between SAW and magnetization also offers fertile
+ground to study magnon-phonon and spin rotation couplings. We describe the
+in-plane magnetic field angle dependence of the a-FMR by measuring the
+absorption / transmission of SAW and the attenuation of SAW in the presence of
+rotational motion of the lattice, and show the consequent generation of spin
+current by acoustic spin pumping.",2001.09581v1
+2020-02-09,Walker-like Domain Wall breakdown in layered Antiferromagnets driven by staggered spin-orbit fields,"Within linear continuum theory, no magnetic texture can propagate faster than
+the maximum group velocity of its spin waves. Here we report a transient regime
+due to the appearance of additional antiferromagnetic textures that breaks the
+Lorentz translational invariance of the magnetic system by atomistic spin
+dynamics simulations. This dynamical regime is akin to domain wall
+Walker-breakdown in ferromagnets and involves the nucleation of an
+antiferromagnetic domain wall pair. Subsequently, one of the nucleated
+180$^{\circ}$ domain wall creates with the original domain wall a 360$^{\circ}$
+spin-rotation which remains static even under the action of the spin-orbit
+field. The other 180$^{\circ}$ domain wall becomes accelerated to
+super-magnonic speeds. Under large spin-orbit fields, multiple domain wall
+generation and recombination is obtained which may explain the recently
+experimentally observed current pulse induce shattering of large domain
+structures into small fragmented domains and the subsequent slow recreation of
+large-scale domain formation prior current pulse.",2002.03332v1
+2020-02-11,Sub-micrometer near-field focusing of spin waves in ultrathin YIG films,"We experimentally demonstrate tight focusing of a spin wave beam excited in
+extended nanometer-thick films of Yttrium Iron Garnet by a simple microscopic
+antenna functioning as a single-slit near-field lens. We show that the focal
+distance and the minimum transverse width of the focal spot can be controlled
+in a broad range by varying the frequency/wavelength of spin waves and the
+antenna geometry. The experimental data are in good agreement with the results
+of numerical simulations. Our findings provide a simple solution for
+implementation of magnonic nano-devices requiring local concentration of the
+spin-wave energy.",2002.04284v1
+2020-02-12,Toward room-temperature nanoscale skyrmions in ultrathin films,"Breaking the dilemma between small size and room temperature stability is a
+necessary prerequisite for skyrmion-based information technology. Here we
+demonstrate by means of rate theory and an atomistic spin Hamiltonian that the
+stability of isolated skyrmions in ultrathin ferromagnetic films can be
+enhanced by the concerted variation of magnetic interactions while keeping the
+skyrmion size unchanged. We predict film systems where the lifetime of sub-10
+nm skyrmions can reach years at ambient conditions. The long lifetime of such
+small skyrmions is due to exceptionally large Arrhenius pre-exponential and the
+stabilizing effect of the energy barrier is insignificant at room temperature.
+A dramatic increase in the pre-exponential is achieved thanks to softening of
+magnon modes of the skyrmion, thereby increasing the entropy of the skyrmion
+with respect to the transition state for collapse. Increasing the number of
+skyrmion deformation modes should be a guiding principle for the realization of
+nanoscale, room-temperature stable skyrmions.",2002.05285v2
+2020-02-14,Low energy magnons in the chiral ferrimagnet $\text{Cu}_2\text{OSeO}_3$: a coarse-grained approach,"We report a comprehensive neutron scattering study of low energy magnetic
+excitations in the breathing pyrochlore helimagnetic
+$\text{Cu}_2\text{OSeO}_3$. Fully documenting the four lowest energy magnetic
+modes that leave the ferrimagnetic configuration of the ""strong tetrahedra""
+intact ($|\hbar\omega|<13$ meV), we find gapless quadratic dispersion at the
+$\Gamma$ point for energies above 0.2 meV, two doublets separated by 1.6(2) meV
+at the $R$ point, and a bounded continuum at the $X$ point. Our constrained
+rigid spin cluster model relates these features to Dzyaloshinskii-Moriya (DM)
+interactions and the incommensurate helical ground state. Combining
+conventional spin wave theory with a spin cluster form-factor accurately
+reproduces the measured equal time structure factor through multiple Brillouin
+zones. An effective spin Hamiltonian describing the complex anisotropic
+inter-cluster interactions is obtained.",2002.06283v2
+2020-02-17,Enhancement of magnetization plateaus in low dimensional spin systems,"We study the low-energy properties and, in particular, the magnetization
+process of a spin-1/2 Heisenberg $J_1-J_2$ sawtooth and frustrated chain (also
+known as zig-zag ladder) with a spatially anisotropic $g$-factor. We treat the
+problem both analytically and numerically while keeping the $J_2/J_1$ ratio
+generic. Numerically, we use complete and Lanczos diagonalization as well as
+the infinite time-evolving block decimation (iTEBD) method. Analytically we
+employ (non-)Abelian bosonization. Additionally for the sawtooth chain, we
+provide an analytical description in terms of flat bands and localized magnons.
+By considering a specific pattern for the $g$-factor anisotropy for both
+models, we show that a small anisotropy significantly enhances a magnetization
+plateau at half saturation. For the magnetization of the frustrated chain, we
+show the destruction of the $1/3$ of the full saturation plateau in favor of
+the creation of a plateau at half-saturation. For large anisotropies, the
+existence of an additional plateau at zero magnetization is possible. Here and
+at higher magnetic fields, the system is locked in the half-saturation plateau,
+never reaching full saturation.",2002.07190v1
+2020-02-26,Magnon dispersion and dynamic spin response in three-dimensional spin models for $α$-RuCl$_3$,"In the search for experimental realizations of bond-anisotropic Kitaev
+interactions and resulting spin-liquid phases, the layered magnet
+$\alpha$-RuCl$_3$ is a prime candidate. Its modelling typically involves
+Heisenberg, Kitaev, and symmetric off-diagonal $\Gamma$ interactions on the
+two-dimensional honeycomb lattice. However, recent neutron-scattering
+experiments point towards a sizeable magnetic interlayer coupling. Here we
+study three-dimensional exchange models for $\alpha$-RuCl$_3$, for both
+possible $R\bar{3}$ and $C2/m$ crystal structures. We discuss the symmetry
+constraints on the interlayer couplings, construct minimal models, and use them
+to compute the magnetic mode dispersion and the dynamical spin structure
+factor, in both the zero-field zigzag phase and the paramagnetic high-field
+phase. Our predictions for the interlayer mode dispersion shall guide future
+experiments; they also call for a reevaluation of the quantitative model
+parameters relevant for $\alpha$-RuCl$_3$.",2002.11727v2
+2020-02-27,Ultrafast magnetization dynamics in half-metallic Co$_2$FeAl Heusler alloy,"We report on optically induced, ultrafast magnetization dynamics in the
+Heusler alloy $\mathrm{Co_{2}FeAl}$, probed by time-resolved magneto-optical
+Kerr effect. Experimental results are compared to results from electronic
+structure theory and atomistic spin-dynamics simulations. Experimentally, we
+find that the demagnetization time ($\tau_{M}$) in films of
+$\mathrm{Co_{2}FeAl}$ is almost independent of varying structural order, and
+that it is similar to that in elemental 3d ferromagnets. In contrast, the
+slower process of magnetization recovery, specified by $\tau_{R}$, is found to
+occur on picosecond time scales, and is demonstrated to correlate strongly with
+the Gilbert damping parameter ($\alpha$). Our results show that
+$\mathrm{Co_{2}FeAl}$ is unique, in that it is the first material that clearly
+demonstrates the importance of the damping parameter in the remagnetization
+process. Based on these results we argue that for $\mathrm{Co_{2}FeAl}$ the
+remagnetization process is dominated by magnon dynamics, something which might
+have general applicability.",2002.12255v1
+2020-02-27,Spin Wave Radiation by a Topological Charge Dipole,"The use of spin waves (SWs) as data carriers in spintronic and magnonic logic
+devices offers operation at low power consumption, free of Joule heating.
+Nevertheless, the controlled emission and propagation of SWs in magnetic
+materials remains a significant challenge. Here, we propose that
+skyrmion-antiskyrmion bilayers form topological charge dipoles and act as
+efficient sub-100 nm SW emitters when excited by in-plane ac magnetic fields.
+The propagating SWs have a preferred radiation direction, with clear dipole
+signatures in their radiation pattern, suggesting that the bilayer forms a SW
+antenna. Bilayers with the same topological charge radiate SWs with spiral and
+antispiral spatial profiles, enlarging the class of SW patterns. We demonstrate
+that the characteristics of the emitted SWs are linked to the topology of the
+source, allowing for full control of the SW features, including their
+amplitude, preferred direction of propagation, and wavelength.",2002.12282v1
+2020-03-04,Spin-wave Talbot effect in thin ferromagnetic film,"The Talbot effect has been known in optics since XIX century and found
+various technological applications. In this paper, we demonstrate with the help
+of micromagnetic simulations this self-imaging phenomenon for spin waves
+propagating in a thin ferromagnetic film magnetized out-of-plane. We show that
+the main features of the obtained Talbot carpets for spin waves can be
+described, to a large extent, by the approximate analytical formulas yielded by
+the general analysis of the wave phenomena. Our results indicate a route to a
+feasible experimental realisation of the Talbot effect at low and high
+frequencies and offer interesting effects and possible applications in
+magnonics.",2003.02138v2
+2020-03-09,Colossal quasiparticle radiation in the Lifshitz spin liquid phase of a two-dimensional quantum antiferromagnet,"Strong quantum fluctuations in magnetic systems can create disordered quantum
+spin liquid phases of matter which are not predicted by classical physics. The
+complexity of the exotic phenomena on display in spin liquids has led to a
+great deal of theoretical and experimental interest. However, understanding the
+fundamental nature of the excitations in these systems remains challenging. In
+this work, we consider the Lifshitz quantum critical point in a two-dimensional
+frustrated $XY$ antiferromagnet. At this point, quantum fluctuations destroy
+long range order, leading to the formation of an algebraic Lifshitz spin
+liquid. We demonstrate that the bosonic magnon excitations are long-lived and
+well-defined in the Lifshitz spin liquid phase, though paradoxically, the
+dynamic structure factor has a broad non-Lorentzian frequency distribution with
+no single-particle weight. We resolve this apparent contradiction by showing
+that the Lifshitz spin liquid suffers from an infrared catastrophe: An external
+physical probe always excites an infinite number of arbitrarily low energy
+quasiparticles, which leads to significant radiative broadening of the
+spectrum.",2003.03936v1
+2020-03-11,Spin Seebeck Effect near the Antiferromagnetic Spin-Flop Transition,"We develop a low-temperature, long-wavelength theory for the interfacial spin
+Seebeck effect (SSE) in easy-axis antiferromagnets. The field-induced spin-flop
+(SF) transition of N\'eel order is associated with a qualitative change in SSE
+behavior: Below SF, there are two spin carriers with opposite magnetic moments,
+with the carriers polarized along the field forming a majority magnon band.
+Above SF, the low-energy, ferromagnetic-like mode has magnetic moment opposite
+the field. This results in a sign change of the SSE across SF, which agrees
+with recent measurements on Cr$_2$O$_3$/Pt and Cr$_2$O$_3$/Ta devices [Li
+$\textit{et al.,}$ $\textit{Nature}$ $\textbf{578,}$ 70 (2020)]. In our theory,
+SSE is due to a N\'eel spin current below SF and a magnetic spin current above
+SF. Using the ratio of the associated N\'eel to magnetic spin-mixing
+conductances as a single constant fitting parameter, we reproduce the field
+dependence of the experimental data and partially the temperature dependence of
+the relative SSE jump across SF.",2003.05232v1
+2020-03-17,Odd-parity spin-loop-current order mediated by transverse spin fluctuations in cuprates and related electron systems,"Unconventional symmetry-breaking phenomena due to nontrivial order parameters
+attract increasing attention in strongly correlated electron systems. Here, we
+predict theoretically the occurrence of nanoscale spontaneous spin-current,
+called the spin loop-current (sLC) order, as a promising origin of the
+pseudogap and electronic nematicity in cuprates. We reveal that the sLC is
+driven by the odd-parity electron-hole condensation that are mediated by
+transverse spin fluctuations around the pseudogap temperature $T^*$. At the
+same temperature, odd-parity magnon pair condensation occurs. The sLC order is
+""hidden"" in that neither internal magnetic field nor charge density modulation
+is induced, whereas the predicted sLC with finite wavenumber naturally gives
+the Fermi arc structure. In addition, the fluctuations of sLC order work as
+attractive pairing interaction between adjacent hot spots, which enlarges the
+d-wave superconducting transition temperature $T_c$. The sLC state will be a
+key ingredient in understanding the pseudogap, electronic nematicity as well as
+superconductivity in cuprates and other strongly correlated metals.",2003.07556v3
+2020-03-27,Electrical detection of unconventional transverse spin-currents in obliquely magnetized thin films,"In a typical experiment in magnonics, thin films are magnetized in-plane and
+spin waves only carry angular momentum along their spatial propagation
+direction. Motivated by the experiments of Bozhko et al. [Phys. Rev. Research
+2, 023324 (2020)], we show theoretically that for obliquely magnetized thin
+films, exchange-dipolar spin waves are accompanied by a transverse
+spin-current. We propose an experiment to electrically detect this transverse
+spin-current with Pt strips on top of a YIG film, by comparing the induced
+spin-current for spin waves with opposite momenta. We predict the relative
+difference to be of the order $10^{-4}$, for magnetic fields tilted at least
+$30^{\circ}$ out of plane. This transverse spin-current is the result of the
+long range dipole-dipole interaction and the inversion symmetry breaking of the
+interface.",2003.12520v4
+2020-04-03,Plasma-enhanced atomic layer deposition of nickel nanotubes with low resistivity and coherent magnetization dynamics for 3D spintronics,"We report plasma-enhanced atomic layer deposition (ALD) to prepare conformal
+nickel thin films and nanotubes by using nickelocene as a precursor, water as
+the oxidant agent and an in-cycle plasma enhanced reduction step with hydrogen.
+The optimized ALD pulse sequence, combined with a post-processing annealing
+treatment, allowed us to prepare 30 nm thick metallic Ni layers with a
+resistivity of 8 $\mu\Omega$cm at room temperature and good conformality both
+on the planar substrates and nanotemplates. Thereby we fabricated several
+micrometer-long nickel nanotubes with diameters ranging from 120 to 330 nm. We
+report on the correlation between ALD growth and functional properties of
+individual Ni nanotubes characterized in terms of magneto-transport and the
+confinement of spin wave modes. The findings offer novel perspectives for
+Ni-based spintronics and magnonic devices operated in the GHz frequency regime
+with a 3D device architecture.",2004.01592v2
+2020-04-03,Spin-Phonon Coupling and Thermodynamic Behaviour in YCrO3 and LaCrO3: Inelastic Neutron Scattering and Lattice Dynamics,"We report detailed temperature-dependent inelastic neutron scattering and
+ab-initio lattice dynamics investigation of magnetic perovskites YCrO3 and
+LaCrO3. The magnetic neutron scattering from the Cr ions exhibits significant
+changes with temperature and dominates at low momentum transfer regime.
+Ab-inito calculations performed including magnetic interactions show that the
+effect of magnetic interaction is very signicant on the low- as well as
+high-energy phonon modes. We have also shown that the inelastic neutron
+spectrum of YCrO3 mimics the magnon spectrum from a G-type antiferromagnetic
+system, which is consistent with previously reported magnetic structure in the
+compound. The ab-initio lattice dynamics calculations in both the compounds
+exhibit anisotropic thermal expansion behaviour in the orthorhombic structure
+and predict negative thermal expansion along the crystallographic a-axis at low
+temperatures. We identify the anharmonic phonon modes responsible for this
+anamolous behaviour in LaCrO3 involving low-energy La vibrations and
+distortions of the CrO6 octahedra.",2004.01731v1
+2020-04-11,Quasi-2D magnetic correlations in Ni$_2$P$_2$S$_6$ probed by ${}^{31}$P NMR,"Detailed ${}^{31}$P nuclear magnetic resonance (NMR) measurements are
+presented on well-characterized single crystals of antiferromagnetic van der
+Waals Ni$_2$P$_2$S$_6$. An anomalous breakdown is observed in the
+proportionality of the NMR shift $K$ with the bulk susceptibility $\chi$. This
+so-called $K$$-$$\chi$ anomaly occurs in close proximity to the broad peak in
+$\chi(T)$, thereby implying a connection to quasi-2D magnetic correlations
+known to be responsible for this maximum. Quantum chemistry calculations show
+that crystal field energy level depopulation effects cannot be responsible for
+the $K$$-$$\chi$ anomaly. Appreciable in-plane transferred hyperfine coupling
+is observed, which is consistent with the proposed Ni$-$S$-$Ni super- and
+Ni$-$S$-$S$-$Ni super-super-exchange coupling mechanisms. Magnetization and
+spin$-$lattice relaxation rate ($T_1^{-1}$) measurements indicate little to no
+magnetic field dependence of the N\'eel temperature. Finally, $T_1^{-1}(T)$
+evidences relaxation driven by three-magnon scattering in the antiferromagnetic
+state.",2004.05403v1
+2020-04-21,Interlayer Coupling Induced Quasiparticles,"We present an exact treatment of layered many-body electronic systems in the
+presence of interlayer coupling within the Schwinger functional derivative
+approach on the Keldysh contour. Our transparent approach allows us to clarify
+the definition of interlayer coupling by showing the independent roles
+hybridization and interactions play in generating new electronic and magnetic
+excitations. We find interlayer coupling to induce a variety of plasmons,
+magnons, and excitons, residing within the a layer, traversing between layers,
+or propagating along the interface. Moreover, we predict interfacial
+excitations, including an electron-hole pairing pathway, facilitated by
+previously ignored layer nonconserving interactions. Finally, we briefly
+explore the consequence of interlayer coupling on a bilayer square lattice
+system.",2004.10311v2
+2020-04-22,Magnetic phase diagram of the linear quantum ferro-antiferromagnet Cs$_{2}$Cu$_{2}$Mo$_{3}$O$_{12}$,"A single-crystal sample of the frustrated quasi one-dimensional quantum
+magnet Cs$_{2}$Cu$_{2}$Mo$_{3}$O$_{12}$ is investigated by magnetic and
+thermodynamic measurements.A combination of specific heat and magnetic torque
+measurements maps out the entire $H$-$T$ phase diagram for three
+orientations.Remarkably, a new phase emerges below the saturation field,
+irrespective of the crystal orientation. It is suggested that the presaturation
+phase represents spin-nematic order or other multi-magnon condensate. The phase
+diagrams within the long-range ordered dome are qualitatively different for
+each geometry. In particular, multiple transitions are identified in the field
+along the chain direction.",2004.10636v3
+2020-04-27,Tunneling spectroscopy as a probe of fractionalization in 2D magnetic heterostructures,"In this paper we develop the theory for 2D-to-2D tunneling spectroscopy aided
+by magnetic or quantum-order excitations, and apply it to the description of
+van-der-Waals heterostructures of graphene/ultrathin $\alpha-{\rm RuCl}_3$. We
+study the behavior of both the differential conductance and the inelastic
+electron tunneling spectrum (IETS) of these heterostructures. The IETS in
+particular exhibits features, such as the gap of continuum spinon excitations
+and Majorana bound states, whose energies scale {\it cubicly} with the applied
+magnetic field. Such scaling, which exists for a relatively wide range of
+fields, is at odds with the linear one exhibited by conventional magnons and
+can be used to prove the existence of Kitaev quantum spin liquids.",2004.13036v1
+2020-04-28,Enhancement of acoustic spin pumping by acoustic distributed Bragg reflector cavity,"Surface acoustic waves (SAWs) in the GHz frequency range can inject spin
+currents dynamically into adjacent nonmagnetic layers via spin pumping effect
+associated with ferromagnetic resonance. Here, we demonstrate an enhancement of
+acoustic ferromagnetic resonance and spin current generation by a pair of SAW
+reflector gratings, which form an acoustic analogue of the distributed Bragg
+reflector cavity. In the experiment, we confirmed 2.04 $\pm$ 0.02 times larger
+SAW power absorption in a device with cavity than in case of no acoustic
+cavity. We confirmed up to 2.96 $\pm$ 0.02 times larger spin current generation
+by measuring electric voltages generated by the inverse Edelstein effect (IEE)
+at the interface between Cu and Bi$_2$O$_3$. The results suggest that acoustic
+cavities would be useful to enhance the conversion efficiency in SAW driven
+coupled magnon-phonon dynamics.",2004.13885v3
+2020-04-30,Flat-band physics in the spin-1/2 sawtooth chain,"We consider the strongly anisotropic spin-1/2 $XXZ$ model on the
+sawtooth-chain lattice with ferromagnetic longitudinal interaction
+$J^{zz}=\Delta J$ and aniferromagnetic transversal interaction
+$J^{xx}=J^{yy}=J>0$. At $\Delta=-1/2$ the lowest one-magnon excitation band is
+dispersionless (flat) leading to a massively degenerate set of ground states.
+Interestingly, this model admits a three-coloring representation of the
+ground-state manifold [H.~J.~Changlani et at., Phys. Rev. Lett. {\bf 120},
+117202 (2018)]. We characterize this ground-state manifold and elaborate the
+low-temperature thermodynamics of the system. We illustrate the manifestation
+of the flat-band physics of the anisotropic model by comparison with two
+isotropic flat-band Heisenberg sawtooth chains. Our analytical consideration is
+complemented by exact diagonalization and finite-temperature Lanczos method
+calculations.",2004.14730v1
+2020-05-01,A Narrowband Spintronic Terahertz Emitter based on Magnetoelastic Heterostructures,"Narrowband terahertz (THz) radiation is crucial for high-resolution spectral
+identification, but a narrowband THz source driven by femtosecond (fs) laser
+has remained scarce. Here, it is computationally predicted that a
+metal/dielectric/magnetoelastic heterostructure enables converting a fs laser
+pulse into a multi-cycle THz pulse with a narrow linewidth down to ~1.5 GHz,
+which is in contrast with the single-cycle, broadband THz pulse from the
+existing fs-laser-excited emitters. It is shown that such narrowband THz pulse
+originates from the excitation and long-distance transport of THz spin waves in
+the magnetoelastic film, which can be enabled by a short strain pulse obtained
+from fs laser irradiation of the metal film when the thicknesses of the metal
+and magnetoelastic films both fall into a specific range. These results
+therefore reveal an approach to achieving optical generation of narrowband THz
+pulse based on heterostructure design, which also has implications in the
+design of THz magnonic devices.",2005.00629v3
+2020-05-06,Observation of evanescent spin waves in the magnetic dipole regime,"We observed spin-wave transmission through an air gap that works as a
+prohibited region. The spin waves were excited by circularly polarized pump
+pulses via the inverse Faraday effect, and their spatial propagation was
+detected through the Faraday effect of probe pulses using a pump-probe imaging
+technique. The experimentally observed spin-wave transmission was reproduced
+using numerical calculations with a Green's function method and micromagnetic
+simulation. We found that the amplitude of the spin waves decays exponentially
+in the air gap, which indicates the existence of evanescent spin waves in the
+magnetic dipole regime. This finding will pave the way for controllable
+amplitudes and phases of spin waves propagating through an artificial magnonic
+crystal.",2005.02559v1
+2020-05-07,Low-energy physics of isotropic spin-1 chains in the critical and Haldane phases,"Using a matrix product state algorithm with infinite boundary conditions, we
+compute high-resolution dynamic spin and quadrupolar structure factors in the
+thermodynamic limit to explore the low-energy excitations of isotropic
+bilinear-biquadratic spin-1 chains. Haldane mapped the spin-1 Heisenberg
+antiferromagnet to a continuum field theory, the non-linear sigma model
+(NL$\sigma$M). We find that the NL$\sigma$M fails to capture the influence of
+the biquadratic term and provides only an unsatisfactory description of the
+Haldane phase physics. But several features in the Haldane phase can be
+explained by non-interacting multi-magnon states. The physics at the
+Uimin-Lai-Sutherland point is characterized by multi-soliton continua. Moving
+into the extended critical phase, we find that these excitation continua
+contract, which we explain using a field-theoretic description. New excitations
+emerge at higher energies and, in the vicinity of the purely biquadratic point,
+they show simple cosine dispersions. Using block fidelities, we identify them
+as elementary one-particle excitations and relate them to the integrable
+Temperley-Lieb chain.",2005.03643v2
+2020-05-10,Anisotropic Magnetocaloric Properties of The Ludwigite Single Crystal Cu2MnBO5,"We present the results of a thorough study of the specific heat and
+magnetocaloric properties of a ludwigite crystal Cu2MnBO5 over a temperature
+range of 60 - 350 K and in magnetic fields up to 18 kOe. It is found that at
+temperatures below the Curie temperature (92 K), capacity possesses a linear
+temperature-dependent behavior, which is associated with the predominance of
+two-dimensional antiferromagnetic interactions of magnons. The temperature
+independence of capacity is observed in the temperature range of 95 - 160 K,
+which can be attributed to the excitation of the Wigner glass phase. The
+magnetocaloric effect (i.e. the adiabatic temperature change) was assessed
+through a direct measurement or an indirect method using the capacity data.
+Owing to its strong magnetocrystalline anisotropy, an anisotropic MCE or the
+rotating MCE is observed in Cu2MnBO5. A deep minimum in the rotating MCE near
+the TC is observed and may be associated with the anisotropy of the
+paramagnetic susceptibility.",2005.04572v1
+2020-05-12,Curvilinear one-dimensional antiferromagnets,"Antiferromagnets host exotic quasiparticles, support high frequency
+excitations and are key enablers of the prospective spintronic and
+spin-orbitronic technologies. Here, we propose a concept of a curvilinear
+antiferromagnetism where material responses can be tailored by a geometrical
+curvature without the need to adjust material parameters. We show that an
+intrinsically achiral one-dimensional (1D) curvilinear antiferromagnet behaves
+as a chiral helimagnet with geometrically tunable Dzyaloshinskii--Moriya
+interaction (DMI) and orientation of the N\'{e}el vector. The curvature-induced
+DMI results in the hybridization of spin wave modes and enables a
+geometrically-driven local minimum of the low frequency branch. This positions
+curvilinear 1D antiferromagnets as a novel platform for the realization of
+geometrically tunable chiral antiferromagnets for antiferromagnetic
+spin-orbitronics and fundamental discoveries in the formation of coherent
+magnon condensates in the momentum space.",2005.05835v2
+2020-05-14,"Modelling spin waves in noncollinear antiferromagnets: spin-flop states, spin spirals, skyrmions and antiskyrmions","Spin waves in antiferromagnetic materials have great potential for
+next-generation magnonic technologies. However, their properties and their
+dependence on the type of ground-state antiferromagnetic structure are still
+open questions. Here, we investigate theoretically spin waves in one- and
+two-dimensional model systems with a focus on noncollinear antiferromagnetic
+textures such as spin spirals and skyrmions of opposite topological charges. We
+address in particular the nonreciprocal spin excitations recently measured in
+bulk antiferromagnet $\alpha$--$\text{Cu}_2\text{V}_2\text{O}_7$ utilizing
+inelastic neutron scattering experiments [Phys.\ Rev.\ Lett.\ \textbf{119},
+047201 (2017)], where we help to characterize the nature of the detected
+spin-wave modes. Furthermore, we discuss how the Dzyaloshinskii-Moriya
+interaction can lift the degeneracy of the spin-wave modes in antiferromagnets,
+resembling the electronic Rashba splitting. We consider the spin-wave
+excitations in antiferromagnetic spin-spiral and skyrmion systems and discuss
+the features of their inelastic scattering spectra. We demonstrate that
+antiskyrmions can be obtained with an isotropic Dzyaloshinskii-Moriya
+interaction in certain antiferromagnets.",2005.07250v1
+2020-05-18,Local spin Seebeck imaging with scanning thermal probe,"In this work we present the results of an experiment to locally resolve the
+spin Seebeck effect in a high-quality Pt/YIG sample. We achieve this by
+employing a locally heated scanning thermal probe to generate a highly local
+non-equilibrium spin current. To support our experimental results, we also
+present a model based on the non-equilibrium thermodynamic approach which is in
+a good agreement with experimental findings. To further corroborate our
+results, we index the locally resolved spin Seebeck effect with that of the
+local magnetisation texture by MFM and correlate corresponding regions. We
+hypothesise that this technique allows imaging of magnetisation textures within
+the magnon diffusion length and hence characterisation of spin caloritronic
+materials at the nanoscale.",2005.08539v1
+2020-05-21,Effect of Dzyaloshinskii-Moriya interaction on magnetic vortex switching driven by radial spin waves,"We theoretically investigate the radial-spin-wave induced magnetic vortex
+switching in the presence of Dzyaloshinskii-Moriya interaction (DMI). From
+micromagnetic simulations, we observe a circular-to-radial vortex phase
+transition by increasing the DMI strength. The radial spin-wave excitation
+spectrum for each magnetization configuration is analyzed, showing that the
+frequency of spin-wave mode with a given radial node number monotonically
+increases (decreases) with the DMI parameter of the radial (circular) vortex.
+Interestingly, we find that the DMI can significantly facilitate the polarity
+switching of the circular vortex driven by radial spin waves. Our work provides
+a new insight into the DMI effect on the vortex dynamics and is helpful for
+designing fast all-magnonic memory devices.",2005.10440v1
+2020-05-21,Antiferromagnet-semiconductor van der Waals heterostructures: interlayer interplay of exciton with magnetic ordering,"Van der Waals (vdW) heterostructures have attracted great interest because of
+their rich material combinations.The discovery of two-dimensional magnets has
+provided a new platform for magnetic vdW heterointerfaces; however, research on
+magnetic vdW heterointerfaces has been limited to those with ferromagnetic
+surfaces. Here we report a magnetic vdW heterointerface using layered
+intralayer-antiferromagnetic MPSe3 (M=Mn, Fe) and monolayer transition metal
+dichalcogenides (TMDs). We found an anomalous upshift of the excitonic peak in
+monolayer TMDs below the antiferromagnetic transition temperature in the MPSe3,
+capturing a signature of the interlayer exciton-magnon coupling. This is a
+concept extended from single materials to heterointerfaces. Moreover, this
+coupling strongly depends on the in-plane magnetic structure and stacking
+direction, showing its sensitivity to their magnetic interfaces. Our finding
+offers an opportunity to investigate interactions between elementary
+excitations in different materials across interfaces and to search for new
+functions of magnetic vdW heterointerfaces.",2005.10727v1
+2020-05-25,Evidence for biquadratic exchange in the quasi-two-dimensional antiferromagnet FePS$_3$,"FePS$_3$ is a van der Waals compound with a honeycomb lattice that is a good
+example of a two-dimensional antiferromagnet with Ising-like anisotropy.
+Neutron spectroscopy data from FePS3 were previously analysed using a
+straight-forward Heisenberg Hamiltonian with a single-ion anisotropy. The
+analysis captured most of the elements of the data, however some significant
+discrepancies remained. The discrepancies were most obvious at the Brillouin
+zone boundaries. The data are subsequently reanalysed allowing for unequal
+exchange between nominally equivalent nearest-neighbours, which resolves the
+discrepancies. The source of the unequal exchange is attributed to a
+biquadratic exchange term in the Hamiltonian which most probably arises from a
+strong magnetolattice coupling. The new parameters show that there are features
+consistent with Dirac magnon nodal lines along certain Brillouin zone
+boundaries.",2005.12031v1
+2020-05-25,Dynamical signatures of quasiparticle interactions in quantum spin chains,"We study the transverse dynamical susceptibility of an antiferromagnetic
+spin$-1/2$ chain in presence of a longitudinal Zeeman field. In the low
+magnetization regime in the gapless phase, we show that the marginally
+irrelevant backscattering interaction between the spinons creates a non-zero
+gap between two branches of excitations at small momentum. We further
+demonstrate how this gap varies upon introducing a second neighbor
+antiferromagnetic interaction, vanishing in the limit of a non-interacting
+""spinon gas"". In the high magnetization regime, as the Zeeman field approaches
+the saturation value, we uncover the appearance of two-magnon bound states in
+the transverse susceptibility. This bound state feature generalizes the one
+arising from string states in the Bethe ansatz solution of the integrable case.
+Our results are based on numerically accurate, unbiased matrix-product-state
+techniques as well as analytic approximations.",2005.12399v1
+2020-05-29,Microscopic Theory of the Spin Hall Magnetoresistance,"We consider a microscopic theory for the spin Hall magnetoresistance (SMR).
+We generally formulate a spin conductance at an interface between a normal
+metal and a magnetic insulator in terms of spin susceptibilities. We reveal
+that SMR is composed of static and dynamic parts. The static part, which is
+almost independent of the temperature, originates from spin flip caused by an
+interfacial exchange coupling. However, the dynamic part, which is induced by
+the creation or annihilation of magnons, has an opposite sign from the static
+part. By the spin-wave approximation, we predict that the latter results in a
+nontrivial sign change of the SMR signal at a finite temperature. In addition,
+we derive the Onsager relation between spin conductance and thermal
+spin-current noise.",2005.14494v3
+2020-07-09,Fe3Se4: A Possible Ferrimagnetic Half-Metal?,"Half-metallic ferromagnets show 100% spin-polarization at the Fermi level and
+are ideal candidates for spintronic applications. Despite the extensive
+research in the field, very few materials have been discovered so far. Here we
+present results of electronic band structure calculations based on density
+functional theory and extensive physical-property measurements for Fe3Se4
+revealing signatures of half-metallicity. The spin-polarized electronic band
+structure calculations predict half-metallic ferrimagnetism for Fe3Se4. The
+electrical resistivity follows exponentially suppressed electron-magnon
+scattering mechanism in the low-temperature regime and show a magnetoresistance
+effect that changes the sign from negative to positive with decreasing
+temperature around 100 K. Other intriguing observations include the anomalous
+behavior of Hall resistance below 100 K and an anomalous Hall coefficient that
+roughly follows the \r{ho}2 behavior.",2007.04736v1
+2020-07-10,Fermi Surface Geometry,"Motivated by the famous and pioneering mathematical works by Perelman,
+Hamilton, and Thurston, we introduce the concept of using modern geometrical
+mathematical classifications of multi-dimensional manifolds to characterize
+electronic structures and predict non-trivial electron transport phenomena.
+Here we develop the Fermi Surface Geometry Effect (FSGE), using the concepts of
+tangent bundles and Gaussian curvature as an invariant. We develop an index,
+$\mathbb{H}_F$, for describing the the ""hyperbolicity"" of the Fermi Surface
+(FS) and show a universal correlation (R$^2$ = 0.97) with the experimentally
+measured intrinsic anomalous Hall effect of 16 different compounds spanning a
+wide variety of crystal, chemical, and electronic structure families, including
+where current methods have struggled. This work lays the foundation for
+developing a complete theory of geometrical understanding of electronic (and by
+extension magnonic and phononic) structure manifolds, beginning with Fermi
+surfaces. In analogy to the broad impact of topological physics, the concepts
+begun here will have far reaching consequences and lead to a paradigm shift in
+the understanding of electron transport, moving it to include geometrical
+properties of the E vs k manifold as well as topological properties.",2007.05525v2
+2020-07-23,Nonreciprocal surface magnetoelastic dynamics,"Motivated by recent experiments, we investigate the nonreciprocal
+magnetoelastic interaction between the surface acoustic phonons of dielectric
+non-magnetic substrates and magnons of proximity nanomagnets. The magnetization
+dynamics exerts rotating forces at the edges of the nanomagnet that causes the
+nonreciprocal interaction with surface phonons due to its rotation-momentum
+locking. This coupling induces the nonreciprocity of the surface phonon
+transmission and a nearly complete phonon diode effect by several (tens of)
+magnetic nanowires of high (ordinary) magnetic quality. Phase-sensitive
+microwave transmission is also nonreciprocal that can pick up clear signals of
+the coherent phonons excited by magnetization dynamics. Nonreciprocal pumping
+of phonons by precessing magnetization is predicted using Landauer-B\""uttiker
+formalism.",2007.12240v3
+2020-07-24,Voltage control of magnon spin currents in antiferromagnetic Cr2O3,"Voltage-controlled spintronic devices utilizing the spin degree of freedom
+are desirable for future applications, and may allow energy-efficient
+information processing. Pure spin current can be created by thermal excitations
+in magnetic systems via the spin Seebeck effect (SSE). However, controlling
+such spin currents, only by electrical means, has been a fundamental challenge.
+Here, we investigate voltage control of the SSE in the antiferromagnetic
+insulator Cr2O3. We demonstrate that the SSE response generated in this
+material can be effectively controlled by applying a bias voltage, owing to the
+sensitivity of the SSE to the orientation of the magnetic sublattices as well
+as the existence of magnetoelectric couplings in Cr2O3. Our experimental
+results are explained using a model based on the magnetoelectric effect in
+Cr2O3.",2007.12774v1
+2020-07-28,Electron correlation effects on exchange interactions and spin excitations in 2D van der Waals materials,"Despite serious effort, the nature of the magnetic interactions and the role
+of electron-correlation effects in magnetic two-dimensional (2D) van der Waals
+materials remain elusive. Using CrI$_3$ as a model system, we show that the
+calculated electronic structure including nonlocal electron correlations yields
+spin excitations consistent with inelastic neutron scattering measurements.
+Remarkably, this approach identifies an unreported correlation-enhanced
+interlayer super-superexchange, which rotates the magnon Dirac lines off, and
+introduces a gap along, the high-symmetry $\Gamma$-$K$-$M$ path. This discovery
+provides a different perspective on the gap opening mechanism observed in
+CrI$_3$, which was previously associated with spin-orbit coupling through the
+Dzyaloshinskii-Moriya interaction or Kitaev interaction. Our observation
+elucidates the critical role of electron correlations on the spin ordering and
+spin dynamics in magnetic van der Waals materials and demonstrates the
+necessity of explicit treatment of electron correlations in the broad family of
+2D magnetic materials.",2007.14518v2
+2020-08-02,Magnetic field control of antiferromagnetic domain walls in a thermal gradient,"An antiferromagnetic domain wall in a thermal gradient is found to experience
+a force towards colder regions upon the application of a uniform magnetic field
+along the easy axis. This force increases with the strength of the applied
+field and, for sufficiently high values, it overcomes the entropic force the
+that pushes wall towards the hotter regions. The force is proportional to the
+thermal gradient and it shows a linear dependence with the net magnetic moment
+of the domain wall induced by the field. The origin of this force lies on the
+increase of the domain wall reflectivity due the field-induced sizable break of
+antiferromagnetic order inside it, which turns it into an efficient barrier for
+magnons, which transfer linear momentum to the domain wall when they are
+reflected on it",2008.00533v1
+2020-08-05,Tunneling spectroscopy of quantum spin liquids,"We examine the spectroscopic signatures of tunneling through a Kitaev quantum
+spin liquid (QSL) barrier in a number of experimentally relevant geometries. We
+combine contributions from elastic and inelastic tunneling processes and find
+that spin-flip scattering at the itinerant spinon modes gives rise to a gaped
+contribution to the tunneling conductance spectrum. We address the spectral
+modifications that arise in a magnetic field necessary to drive the candidate
+material $\alpha$-RuCl$_3$ into a QSL phase, and we propose a lateral 1D tunnel
+junction as a viable setup in this regime. The characteristic spin gap is an
+unambiguous signature of the fractionalized QSL excitations, distinguishing it
+from magnons or phonons. The results of our analysis are generically applicable
+to a wide variety of topological QSL systems.",2008.02278v1
+2020-08-10,Finite-temperature dynamics and the role of disorder in nearly critical Ni(Cl$_{1-x}$Br$_x$)$_2$$\cdot$4SC(NH$_2$)$_2$,"Inelastic neutron scattering is used to investigate the temperature
+dependence of spin correlations in the 3-dimensional XY antiferromagnet
+Ni(Cl$_{1-x}$Br$_x$)$_2$$\cdot$4SC(NH$_2$)$_2$, $ x = 0.14(1)$, tuned close to
+the chemical-composition-induced soft-mode transition. The local dynamic
+structure factor shows $\hbar\omega/T$ scaling behavior characteristic of a
+quantum critical point. The deviation of the measured critical exponent from
+spin wave theoretical expectations are attributed to disorder. Another effect
+of disorder is local excitations above the magnon band. Their energy, structure
+factor and temperature dependence are well explained by simple strong-bond
+dimers associated with Br-impurity sites.",2008.04037v2
+2020-08-12,Determination of Niobium Cavity Magnetic Field Screening via a Dispersively Hybridized Magnonic Sensor,"A method for determining the internal DC magnetic field inside a
+superconducting cavity is presented. The method relies on the relationship
+between magnetic field and frequency of the Kittel mode of a ferrimagnetic
+sphere, hybridised in the dispersive regime of the superconducting cavity.
+Results were used to experimentally determine the level of screening a
+superconducting Nb cavity provides as it changes from perfect diamagnetism to
+no screening. Two cavity geometries were tested, a cylinder and single post
+re-entrant cavity. Both demonstrated a consistent value of field that enters
+the cavity, expected to be the superheating critical field. Hysteresis in the
+screened field during ramp up and ramp down of the external magnetic field due
+to trapped vortices was also observed. Some abnormal behaviour was observed in
+the cylindrical cavity in the form of plateaus in the internal field above the
+first critical field, and we discuss the potential origin of this behaviour.
+The measurement approach would be a useful diagnostic for axion dark matter
+searches, which plan on using superconducting materials but need to know
+precisely the internal magnetic field.",2008.05073v2
+2020-08-21,Integration and characterization of micron-sized YIG structures with very low Gilbert damping on arbitrary substrates,"We present a novel process that allows the transfer of monocrystalline
+yttrium-iron-garnet microstructures onto virtually any kind of substrate. The
+process is based on a recently developed method that allows the fabrication of
+freestanding monocrystalline YIG bridges on gadolinium-gallium-garnet. Here the
+bridges' spans are detached from the substrate by a dry etching process and
+immersed in a watery solution. Using drop casting the immersed YIG platelets
+can be transferred onto the substrate of choice, where the structures finally
+can be reattached and thus be integrated into complex devices or experimental
+geometries. Using time resolved scanning Kerr microscopy and inductively
+measured ferromagnetic resonance we can demonstrate that the structures retain
+their excellent magnetic quality. At room temperature we find a ferromagnetic
+resonance linewidth of $\mu_0\Delta H_{HWHM}\approx 195\,\mu T$ and we were
+even able to inductively measure magnon spectra on a single micron-sized
+yttrium-iron-garnet platelet at a temperature of 5 K. The process is flexible
+in terms of substrate material and shape of the structure. In the future this
+approach will allow for new types of spin dynamics experiments up to now
+unthinkable.",2008.09390v1
+2020-10-01,Modeling coupled spin and lattice dynamics,"A unified model of molecular and atomistic spin dynamics is presented
+enabling simulations both in microcanonical and canonical ensembles without the
+necessity of additional phenomenological spin damping. Transfer of energy and
+angular momentum between the lattice and the spin systems is achieved by a
+coupling term based upon the spin-orbit interaction. The characteristic spectra
+of the spin and phonon systems are analyzed for different coupling strength and
+temperatures. The spin spectral density shows magnon modes together with the
+uncorrelated noise induced by the coupling to the lattice. The effective
+damping parameter is investigated showing an increase with both coupling
+strength and temperature. The model paves the way to understanding magnetic
+relaxation processes beyond the phenomenological approach of the Gilbert
+damping and the dynamics of the energy transfer between lattice and spins.",2010.00642v1
+2020-10-05,Open giant magnons on LLM geometries,"We compute sigma model solutions for rigidly rotating open strings suspended
+between giant gravitons in general LLM geometries. These solutions are confined
+to the LLM plane. These all have a dispersion relation for $\Delta-J$ that is
+consistent with saturation of a BPS bound of the centrally extended spin chain.
+For the special case of circularly symmetric LLM geometries, we can further
+evaluate the amount of angular momentum $J$ carried by these strings. This
+quantity diverges for string configurations that try to move between different
+""coloring regions"" in the LLM plane. All of these quantities have a
+perturbative expansion in the t'Hooft coupling. For the strings suspended
+between AdS giants, we can compute in field theory the leading result of $J$
+carried by the string via an analytic continuation of the $SU(2)$ result, with
+the help of the Bethe Ansatz for the $SL(2)$ sector. We thus provide additional
+information on how the radial direction of $AdS$ arises from (open) spin chain
+calculations.",2010.02236v1
+2020-10-14,Semi-classical quantisation of magnetic solitons in the anisotropic Heisenberg quantum chain,"Using the algebro-geometric approach, we study the structure of
+semi-classical eigenstates in a weakly-anisotropic quantum Heisenberg spin
+chain. We outline how classical nonlinear spin waves governed by the
+anisotropic Landau-Lifshitz equation arise as coherent macroscopic low-energy
+fluctuations of the ferromagnetic ground state. Special emphasis is devoted to
+the simplest types of solutions, describing precessional motion and elliptic
+magnetisation waves. The internal magnon structure of classical spin waves is
+resolved by performing the semi-classical quantisation using the
+Riemann-Hilbert problem approach. We present an expression for the overlap of
+two semi-classical eigenstates and discuss how correlation functions at the
+semi-classical level arise from classical phase-space averaging.",2010.07232v6
+2020-10-15,Topological Invariant for Bosonic Bogoliubov-de Gennes Systems with Disorder,"Using the method of noncommutative geometry, we define a topological
+invariant in disordered bosonic Bogoliubov-de Gennes systems, which possess a
+unique mathematical property---non-Hermiticity. To demonstrate the validity of
+the definition, we investigate a disordered artificial spin ice model in two
+dimensions numerically. In the clean limit, we clarify that the topological
+index perfectly coincides with the Chern number. We also show that the
+topological index is robust against disorder. The formula provides the
+topological index $n_{\rm Ch}=1$ in the magnon Hall regime and $n_{\rm Ch}=0$
+in a trivial localized one. We also show by example that our method can be
+extended to other symmetry classes. Our results pave the way for further
+studies on topological bosonic systems with disorder.",2010.07762v1
+2020-10-19,On Choosing a Physically Meaningful Topological Classification for Non-Hermitian Systems and the Issue of Diagonalizability,"The topological classification of hermitian operators is solely determined by
+the presence or absence of certain discrete symmetries. For non-hermitian
+operators we in addition need to specify the type of spectral gap. They come in
+the flavor of a point gap or a line gap. Since the presence of a line gap
+implies the existence of a point gap, there is usually more than one
+mathematical classification applicable to a physical system. That raises the
+question: which of these gap-type classifications is physically meaningful?
+  To decide this question, I propose a simple criterion, namely the choice of
+physically relevant states. This generalizes the notion of Fermi projection
+that plays a crucial role in the topological classification of fermionic
+condensed matter systems, and enters as an auxiliary quantity in the bulk
+classification of photonic and magnonic crystals. After that the classification
+is entirely algorithmic, the system's topology is encoded in (pairs of)
+projections with symmetries and constraints. A crucial point in my
+investigation is the relevance of diagonalizability. Even for existing
+topological classifications of non-hermitian systems diagonalizability needs to
+be assumed to ensure that continuous deformations of the hamiltonian lead to
+continuous deformations of the spectra, projections and unitaries.",2010.09261v1
+2020-10-22,Spin-current version of solar cells in non-centrosymmetric magnetic insulators,"Photovoltaic effect, e.g., solar cells, converts light into DC electric
+current. This phenomenon takes place in various setups such as in
+noncentrosymmetric crystals and semiconductor pn junctions. Recently, we
+proposed a theory for producing DC spin current in magnets using
+electromagnetic waves, i.e., the spin-current counterpart of the solar cells.
+Our calculation shows that the nonlinear conductivity for the spin current is
+nonzero in a variety of noncentrosymmetric magnets, implying that the
+phenomenon is ubiquitous in inversion-asymmetric materials with magnetic
+excitations. Intuitively, this phenomenon is a bulk photovoltaic effect of
+magnetic excitations, where electrons and holes, visible light, and
+inversion-asymmetric semiconductors are replaced with magnons or spinons, THz
+or GHz waves, and asymmetric magnetic insulators, respectively. We also show
+that the photon-driven spin current is shift current type, and as a result, the
+current is stable against impurity scattering. This bulk photovoltaic spin
+current is in sharp contrast to that of well-known spin pumping that takes
+place at the interface between a magnet and a metal.",2010.11795v1
+2020-10-27,Vertex Dependent Dynamic Response of a Connected Kagome Artificial Spin Ice,"We present the dynamic response of a connected Kagome artificial spin ice
+with emphasis on the effect of the vertex magnetization configuration on the
+mode characteristics. We use broadband ferromagnetic resonance (FMR)
+spectroscopy and micromagnetic simulations to identify and characterize
+resonant modes. We find the mode frequencies of elongated, single-domain film
+segments not only depend on the orientation of their easy-axis with respect to
+the applied magnetic field, but also depend on the vertex magnetization
+configuration, which suggests control over the FMR mode can be accomplished by
+altering the vertex magnetization. Moreover, we study differences between the
+vertex center mode (VCM) and the localized domain wall (LDW) mode. We show that
+the LDW mode acts as a signature of the domain wall (DW) nucleation process and
+the DW dynamics active during segment reversal events. The results show the VCM
+and LDW modes can be controlled using a field protocol, which has important
+implications for applications in magnonic and spintronic devices.",2010.13965v1
+2020-10-28,Recent progress in antiferromagnetic dynamics,"Spintronics, since its inception, has mainly focused on ferromagnetic
+materials for manipulating the spin degree of freedom in addition to the charge
+degree of freedom, whereas much less attention has been paid to
+antiferromagnetic materials. Thanks to the advances of micro-nano-fabrication
+techniques and the electrical control of the N\'eel order parameter,
+antiferromagnetic spintronics is booming as a result of abundant room
+temperature materials, robustness against external fields and dipolar coupling,
+and rapid dynamics in the terahertz regime. For the purpose of applications of
+antiferromagnets, it is essential to have a comprehensive understanding of the
+antiferromagnetic dynamics at the microscopic level. Here, we first review the
+general form of equations that govern both antiferromagnetic and ferrimagnetic
+dynamics. This general form unifies the previous theories in the literature. We
+also provide a survey for the recent progress related to antiferromagnetic
+dynamics, including the motion of antiferromagnetic domain walls and skyrmions,
+the spin pumping and quantum antiferromagnetic spintronics. In particular, open
+problems in several topics are outlined. Furthermore, we discuss the
+development of antiferromagnetic quantum magnonics and its potential
+integration with modern information science and technology.",2010.14940v1
+2020-11-02,Spin wave propagation in corrugated waveguides,"Curvature-induced effects allow us to tailor the static and dynamic response
+of a magnetic system with a high degree of freedom. We study corrugated
+magnonic waveguides deposited on a sinusoidally modulated substrate prepared by
+focused electron beam deposition. The surface curvature in films with
+thicknesses comparable to the amplitude of modulation locally modifies the
+contributions of dipolar and exchange energies and results in an effective
+anisotropy term which can be tuned on-demand based on the exact geometry. We
+show, by Brillouin light scattering microscopy, that without the presence of an
+external magnetic field, spin waves propagate over a distance 10$\times$larger
+in the corrugated waveguide than in the planar waveguide. Further, we analyze
+the influence of the modulation amplitude on spin-wave propagation and conclude
+that for moderate modulation amplitudes, the spin-wave decay length is not
+affected. For larger amplitudes, the decay length decreases linearly with
+increasing modulation.",2011.01274v1
+2020-11-04,Level attraction and exceptional points in a resonant spin-orbit torque system,"Level attraction can appear in driven systems where instead of repulsion two
+modes coalesce in a region separated by two exceptional points. This behavior
+was proposed for optomechanical and optomagnonic systems, and recently observed
+for dissipative cavity magnon-polaritons. We demonstrate that such a regime
+exists in a spin-orbit torque system where a magnetic oscillator is resonantly
+coupled to an electron reservoir. An instability mechanism necessary for mode
+attraction can be provided by applying an electric field. The field excites
+interband transitions between spin-orbit split bands leading to an instability
+of the magnetic oscillator. Two exceptional points then appear in the
+oscillator energy spectrum and the region of instability. We discuss conditions
+under which this can occur and estimate the electric field strength necessary
+for reaching the attraction region for a spin-orbit torque oscillator with
+Rashba coupling. A proposal for experimental detection is made using magnetic
+susceptibility measurements.",2011.02520v1
+2020-11-10,Spin-waves in the collinear antiferromagnetic phase of Mn$_\bf{5}$Si$_\bf{3}$,"By combining two independent approaches, inelastic neutron scattering
+measurements and density functional theory calculations, we study the
+spin-waves in the high-temperature collinear antiferromagnetic phase (AFM2) of
+Mn$_5$Si$_3$. We obtain its magnetic ground-state properties and electronic
+structure. This study allowed us to determine the dominant magnetic exchange
+interactions and magnetocrystalline anisotropy in the AFM2 phase of
+Mn$_5$Si$_3$. Moreover, the evolution of the spin excitation spectrum is
+investigated under the influence of an external magnetic field perpendicular to
+the anisotropy easy-axis. The low energy magnon modes show a different magnetic
+field dependence which is a direct consequence of their different precessional
+nature. Finally, possible effects related to the Dzyaloshinskii-Moriya
+interaction are also considered.",2011.05455v3
+2020-11-11,Non-equilibrium heating path for utrafast laser-induced nucleation of skyrmion lattices,"We explore the helicity-independent light-induced nucleation of skyrmion
+lattices in ferromagnetic cobalt-based trilayers with perpendicular magnetic
+anisotropy. Using Atomistic Spin Dynamics simulations, we show that a high
+temperature excitation followed by magnon drops and their non-equilibrium
+relaxation, accessed by an ultrafast laser excitation with specific duration
+and intensity, can lead to the generation of a skyrmion lattice stable at room
+temperature. The nucleation window, the topological density and the skyrmion
+polarity can be additionally manipulated by external magnetic fields. Our
+results provide insight into the non-equilibrium nature of skyrmionic
+excitations at non-zero temperatures and pave additional routes for their use
+in information technologies.",2011.06093v2
+2020-11-18,Field-Tuned Quantum Effects in a Triangular-Lattice Ising Magnet,"We report thermodynamic and neutron scattering measurements of the
+triangular-lattice quantum Ising magnet TmMgGaO 4 in longitudinal magnetic
+fields. Our experiments reveal a quasi-plateau state induced by quantum
+fluctuations. This state exhibits an unconventional non-monotonic field and
+temperature dependence of the magnetic order and excitation gap. In the high
+field regime where the quantum fluctuations are largely suppressed, we observed
+a disordered state with coherent magnon-like excitations despite the
+suppression of the spin excitation intensity. Through detailed semi-classical
+calculations, we are able to understand these behaviors quantitatively from the
+subtle competition between quantum fluctuations and frustrated Ising
+interactions.",2011.09376v3
+2020-11-23,Asymmetric spin wave dispersion due to a saturation magnetization gradient,"We demonstrate using micromagnetic simulations and a theoretical model that a
+gradient in the saturation magnetization ($M_s$) of a perpendicularly
+magnetized ferromagnetic film induces a non-reciprocal spin wave propagation
+and, consequently an asymmetric dispersion relation. The $M_s$ gradient adds a
+linear potential to the spin wave equation of motion consistent with the
+presence of a force. We consider a transformation from an inertial reference
+frame in which the $M_s$ is constant to an accelerated reference frame where
+the resulting inertial force corresponds to the force from the $M_s$ gradient.
+As in the Doppler effect, the frequency shift leads to an asymmetric dispersion
+relation. Additionally, we show that under certain circumstances,
+unidirectional propagation of spin waves can be achieved which is essential for
+the design of magnonic circuits. Our results become more relevant in light of
+recent experimental works in which a suitable thermal landscape is used to
+dynamically modulate the saturation magnetization.",2011.11148v2
+2021-01-12,Double Nuclear Spin Relaxation in Hybrid Quantum Hall Systems,"Recent advances in quantum engineering have given us the ability to design
+hybrid systems with novel properties normally not present in the regime they
+operate in. The coupling of spin ensembles and magnons to microwave resonators
+has for instance lead to a much richer understanding of collective effects in
+these systems and their potential quantum applications. We can also hybridize
+electron and nuclear spin ensembles together in the solid-state regime to
+investigate collective effects normally only observed in the atomic, molecular
+and optical world. Here we explore in the solid state regime the dynamics of a
+double domain nuclear spin ensemble coupled to the Nambu-Goldstone boson in
+GaAs semiconductors and show it exhibits both collective and individual
+relaxation (thermalization) on very different time scales. Further the
+collective relaxation of the nuclear spin ensemble is what one would expect
+from superradiant decay. This opens up the possibility for the exploration of
+novel collective behaviour in solid state systems where the natural energies
+associated with those spins are much less than the thermal energy.",2101.04433v1
+2021-01-21,Effects of the dynamical magnetization state on spin transfer,"We utilize simulations of electron scattering by a chain of dynamical quantum
+spins, to analyze the interplay between the spin transfer effect and the
+magnetization dynamics. We show that the complex interactions between the
+spin-polarized electrons and the dynamical states of the local spins can be
+decomposed into separate processes involving electron reflection and
+transmission, as well as absorption and emission of magnons - the quanta of
+magnetization dynamics. Analysis shows that these processes are substantially
+constrained by the energy and momentum conversation laws, resulting in a
+significant dependence of spin transfer on the electron's energy and the
+dynamical state of the local spins. Our results suggest that exquisite control
+of spin transfer efficiency and of the resulting dynamical magnetization states
+may be achievable by tailoring the spectral characteristics of the conduction
+electrons and of the magnetic systems.",2101.08868v1
+2021-01-26,Enhancing the spin-photon coupling with a micromagnet,"Hybrid quantum systems involving solid-state spins and superconducting
+microwave cavities play a crucial role in quantum science and technology, but
+improving the spin-photon coupling at the single quantum level remains
+challenging in such systems. Here, we propose a simple technique to strongly
+couple a single solid-state spin to the microwave photons in a superconducting
+coplanar waveguide (CPW) cavity via a magnetic microsphere. We show that,
+strong coupling at the single spin level can be realized by virtual magnonic
+excitations of a nearby micromagnet. The spin-photon coupling strength can be
+enhanced up to typically four orders of magnitude larger than that without the
+use of the micromagnet. This work can find applications in quantum information
+processing with strongly coupled solid-state spin-photonic systems.",2101.10600v1
+2021-01-29,Hierarchical excitations from correlated spin tetrahedra on the breathing pyrochlore lattice,"The hierarchy of the coupling strengths in a physical system often engenders
+an effective model at low energies where the decoupled high-energy modes are
+integrated out. Here, using neutron scattering, we show that the spin
+excitations in the breathing pyrochlore lattice compound CuInCr$_4$S$_8$ are
+hierarchical and can be approximated by an effective model of correlated
+tetrahedra at low energies. At higher energies, intra-tetrahedron excitations
+together with strong magnon-phonon couplings are observed, which suggests the
+possible role of the lattice degree of freedom in stabilizing the spin
+tetrahedra. Our work illustrates the spin dynamics in CuInCr$_4$S$_8$ and
+demonstrates a general effective-cluster approach to understand the dynamics on
+the breathing-type lattices.",2101.12363v1
+2021-01-29,Unified First-Principles Study of the Anomalous Hall Effect Based on Exact Muffin-Tin Orbitals,"Based on the exact muffin-tin orbitals (EMTOs), we developed a
+first-principles method to calculate the current operators and investigated the
+anomalous Hall effect in bcc Fe as an example, with which we successfully
+separated the skew scattering contribution from the side jump and intrinsic
+contributions by fitting the scaling law with the introduction of sparse
+impurities. By investigating the temperature dependence of the anomalous Hall
+effect in bulk Fe, we predicted a fluctuated anomalous Hall angle as a function
+of temperature when considering only phonons, which, in the future, can be
+measured in experiments by suppressing magnon excitation, e.g., by applying a
+high external magnetic field.",2101.12474v1
+2021-03-04,X-Ray Scattering from Light-Driven Spin Fluctuations in a Doped Mott Insulator,"Manipulating spin fluctuations with ultrafast laser pulses is a promising
+route to dynamically control collective phenomena in strongly correlated
+materials. However, understanding how photoexcited spin degrees of freedom
+evolve at a microscopic level requires a momentum- and energy-resolved
+characterization of their nonequilibrium dynamics. Here, we study the
+photoinduced dynamics of finite-momentum spin excitations in two-dimensional
+Mott insulators on a square lattice. By calculating the time-resolved resonant
+inelastic x-ray scattering cross-section, we show that an ultrafast pump above
+the Mott gap induces a prompt softening of the spin excitation energy,
+compatible with a transient renormalization of the exchange interaction. While
+spin fluctuations in a hole-doped system (paramagnons) are well described by
+Floquet theory, magnons at half filling are found to deviate from this picture.
+Furthermore, we show that the paramagnon softening is accompanied by an
+ultrafast suppression of $d$-wave pairing correlations, indicating a link
+between the transient spin excitation dynamics and superconducting pairing far
+from equilibrium.",2103.03369v2
+2021-03-07,Phonon Hall Viscosity in Magnetic Insulators,"The Phonon Hall Viscosity is the leading term evincing time-reversal symmetry
+breaking in the low energy description of lattice phonons. It may generate
+phonon Berry curvature, and can be observed experimentally through the acoustic
+Faraday effect and thermal Hall transport. We present a systematic procedure to
+obtain the phonon Hall viscosity induced by phonon-magnon interactions in
+magnetic insulators under an external magnetic field. We obtain a general
+symmetry criterion that leads to non-zero Faraday rotation and Hall
+conductivity, and clarify the interplay between lattice symmetry,
+spin-orbit-coupling, external magnetic field and magnetic ordering. The
+symmetry analysis is verified through a microscopic calculation. By
+constructing the general symmetry-allowed effective action that describes the
+spin dynamics and spin-lattice coupling, and then integrating out the spin
+fluctuations, the leading order time-reversal breaking term in the phonon
+effective action, i.e. the phonon Hall viscosity, can be obtained. The analysis
+of the square lattice antiferromagnet for a cuprate Mott insulator,
+Sr$_2$CuO$_2$Cl$_2$, is presented explicitly, and the procedure described here
+can be readily generalized to other magnetic insulators.",2103.04223v1
+2021-03-12,Temperature dependence of the interface spin Seebeck effect,"We performed temperature-dependent optical pump - THz emission measurements
+in Y3Fe5O12 (YIG)|Pt from 5 K to room temperature in the presence of an
+externally applied magnetic field. We study the temperature dependence of the
+spin Seebeck effect and observe a continuous increase as temperature is
+decreased, opposite to what is observed in electrical measurements where the
+spin Seebeck effect is suppressed as 0K is approached. By quantitatively
+analysing the different contributions we isolate the temperature dependence of
+the spin-mixing conductance and observe features that are correlated to the
+bands of magnon spectrum in YIG.",2103.07307v1
+2021-03-14,Transverse spin dynamics in the anisotropic Heisenberg model realized with ultracold atoms,"In Heisenberg models with exchange anisotropy, transverse spin components are
+not conserved and can decay not only by transport, but also by dephasing. Here
+we utilize ultracold atoms to simulate the dynamics of 1D Heisenberg spin
+chains, and observe fast, local spin decay controlled by the anisotropy.
+Additionally, we directly observe an effective magnetic field created by
+superexchange which causes an inhomogeneous decay mechanism due to variations
+of lattice depth between chains, as well as dephasing within each chain due to
+the twofold reduction of the effective magnetic field at the edges of the
+chains and due to fluctuations of the effective magnetic field in the presence
+of mobile holes. The latter is a new coupling mechanism between holes and
+magnons. All these dephasing mechanisms, corroborated by extensive numerical
+simulations, have not been observed before with ultracold atoms and illustrate
+basic properties of the underlying Hubbard model.",2103.07866v1
+2021-03-23,Low Temperature Suppression of the Spin Nernst Angle in Pt,"We demonstrate the low temperature suppression of the platinum (Pt) spin
+Nernst angle in bilayers consisting of the antiferromagnetic insulator hematite
+($\alpha$-Fe$_2$O$_3$) and Pt upon measuring the transverse spin Nernst
+magnetothermopower (TSNM). We show that the observed signal stems from the
+interplay between the interfacial spin accumulation in Pt originating from the
+spin Nernst effect and the orientation of the N\'eel vector of
+$\alpha$-Fe$_2$O$_3$, rather than its net magnetization. Since the latter is
+negligible in an antiferromagnet, our device is superior to ferromagnetic
+structures, allowing to unambiguously distinguish the TSNM from thermally
+excited magnon transport (TMT), which usually dominates in ferri/ferromagnets
+due to their non-zero magnetization. Evaluating the temperature dependence of
+the effect, we observe a vanishing TSNM below ~100 K. We compare these results
+with theoretical calculations of the temperature dependent spin Nernst
+conductivity and find excellent agreement. This provides evidence for a
+vanishing spin Nernst angle of Pt at low temperatures and the dominance of
+extrinsic contributions to the spin Nernst effect.",2103.12697v1
+2021-03-30,Non-planar universal anomalous dimension of twist-two operators with general Lorentz spin at four loops in N=4 SYM theory,"We compute the non-planar contribution to the universal anomalous dimension
+of twist-two operators in N=4 supersymmetric Yang-Mills theory at four loops
+through Lorentz spin eighteen. Exploiting the results of this and our previous
+calculations along with recent analytic results for the cusp anomalous
+dimension and some expected analytic properties, we reconstruct a general
+expression valid for arbitrary Lorentz spin. We study various properties of
+this general result, such as its large-spin limit, its small-x limit, and
+others. In particular, we present a prediction for the non-planar contribution
+to the anomalous dimension of the single-magnon operator in the beta-deformed
+version of the theory.",2103.16420v1
+2021-04-16,Electronic and magnetic properties of VOCl/FeOCl antiferromagnetic heterobilayers,"We study the electronic properties of the heterobilayer of vanadium and iron
+oxychlorides, VOCl and FeOCl, two layered air stable van der Waals insulating
+oxides with different types of antiferromagnetic order in bulk: VOCl monolayers
+are ferromagnetic (FM) whereas the FeOCl monolayers are antiferromagnetic (AF).
+We use density functional theory (DFT) calculations, with Hubbard correction
+that is found to be needed to describe correctly the insulating nature of these
+compounds. We compute the magnetic anisotropy and propose a spin model
+Hamiltonian. Our calculations show that interlayer coupling in weak and
+ferromagnetic so that magnetic order of the monolayers is preserved in the
+heterobilayers providing thereby a van der Waals heterostructure that combines
+two monolayers with different magnetic order. Interlayer exchange should lead
+both to exchange bias and to the emergence of hybrid collective modes that that
+combine FM and AF magnons. The energy band of the heterobilayer show a type II
+band alignment, and feature spin-splitting of the states of the AF layer due to
+the breaking of the inversion symmetry.",2104.08214v1
+2021-04-22,Spin orbit torque nano-oscillators by dipole field-localized spin wave modes,"We demonstrate a high-quality spin orbit torque nano-oscillator comprised of
+spin wave modes confined by the magnetic field by the strongly inhomogeneous
+dipole field of a nearby micromagnet. This approach enables variable spatial
+confinement and systematic tuning of magnon spectrum and spectral separations
+for studying the impact of multi-mode interactions on auto-oscillations. We
+find these dipole field-localized spin wave modes exhibit good characteristic
+properties as auto-oscillators--narrow linewidth and large amplitude--while
+persisting up to room temperature. We find that the linewidth of the
+lowest-lying localized mode is approximately proportional to temperature in
+good agreement with theoretical analysis of the impact of thermal fluctuations.
+This demonstration of a clean oscillator with tunable properties provides a
+powerful tool for understanding the fundamental limitations and linewidth
+contributions to improve future spin-Hall oscillators.",2104.10838v3
+2021-04-22,Bistable nanomagnet as programmable phase inverter for spin waves,"To realize spin wave logic gates programmable phase inverters are essential.
+We image with phase-resolved Brillouin light scattering microscopy propagating
+spin waves in a one-dimensional magnonic crystal consisting of dipolarly
+coupled magnetic nanostripes. We demonstrate phase shifts upon a single
+nanostripe of opposed magnetization. Using micromagnetic simulations we model
+our experimental finding in a wide parameter space of bias fields and wave
+vectors. We find that low-loss phase inversion is achieved, when the internal
+field of the oppositely magnetized nanostripe is tuned such that the latter
+supports a resonant standing spin wave mode with odd quantization number at the
+given frequency. Our results are key for the realization of phase inverters
+with optimized signal transmission.",2104.11015v1
+2021-04-22,Regular and in-plane skyrmions and antiskyrmions from boundary instabilities,"We formulate a theory of skyrmion and antiskyrmion generation using magnetic
+field and charge current pulses. We show that the topological defect can be
+created at an edge of a system with Dzyaloshinskii-Moriya interaction (DMI) as
+well as at a boundary between regions with different DMI. We consider both
+perpendicular and in-plane (also known as magnetic bimerons) versions of
+skyrmions and antiskyrmions. We show that the magnetization twist in the
+vicinity of an edge or a boundary is described by a kink solution, the presence
+of which can instigate the generation of topological defects. We study the
+collective excitations of magnetization analytically and numerically, and
+demonstrate that under application of magnetic field and charge current pulses
+the magnon modes localized near boundaries can develop instabilities leading to
+the formation of skyrmions or antiskyrmions. Due to the skyrmion and
+antiskyrmion Hall effects, a properly chosen current direction can push the
+topological defects away from the boundary, thus facilitating their generation.",2104.11194v2
+2021-04-23,Collective Excitations in 2D Materials,"Research on 2D materials has been one of the fastest-growing fields in
+condensed matter physics and materials science in the past 10 years. The low
+dimensionality and strong correlations of 2D systems give rise to electronic
+and structural properties, in the form of collective excitations, that do not
+have counterparts in ordinary 3D materials used in modern technology. These 2D
+materials present extraordinary opportunities for new technologies, such as in
+flexible electronics. In this Review, we focus on plasmons, excitons, phonons
+and magnons in 2D materials. We discuss the theoretical formalism of these
+collective excitations and elucidate how they differ from their 3D
+counterparts.",2104.11441v1
+2021-04-30,Control of stripe domain wall magnetization in perpendicular anisotropy multilayers,"We report on the controlled switching of domain wall (DW) magnetization in
+aligned stripe domain structures, stabilized in [Co (0.44 nm)/Pt (0.7 nm)]$_X$
+($X = 48$, 100, 150) multilayers with perpendicular magnetic anisotropy. The
+switching process, induced by an external magnetic field, is monitored by
+measuring the evolution of the in-plane magnetization. % We show that the
+remanent in-plane magnetization originates from the polarization of the
+Bloch-type DWs. With micromagnetic simulations, we reveal that the reversal of
+the DW polarization is the result of the emergence and collapse of horizontal
+Bloch lines within the DWs at particular strengths of the external magnetic
+field, applied opposite to the DW polarization. Our findings are relevant for
+DW-based magnonics and bubble skyrmion applications in magnetic multilayers.",2104.14934v1
+2021-05-18,Spin Spiral and Topological Hall Effect in a Metamagnet Fe$_{3}$Ga$_{4}$,"A new mechanism for Topological Hall Effect (THE) was recently proposed for
+the spiral magnet YMn$_{6}$Sn$_{6},$ which requires transverse conical spiral
+(TCS) magnetism, induced by external magnetic field, combined with thermally
+excite helical spiral magnons. In principle, this mechanism should be
+applicable to other itinerant spiral magnets as well. In this paper, we show
+that another metamagnetic compound, Fe$_{3}$Ga$_{4}$, where THE was observed
+experimentally before, in one of its phases satisfies this condition, and the
+proposed theory of thermal-fluctuation driven THE is quantitatively consistent
+with the experiment. This finding suggests that this mechanism is indeed rather
+universal, and the effect may have been observed in other compounds before, but
+overlooked.",2105.08773v1
+2021-05-23,Multifunctional operation of the double-layer ferromagnetic structure coupled by a rectangular nanoresonator,"The use of spin waves as a signal carrier requires developing the functional
+elements allowing for multiplexing and demultiplexing information coded at
+different wavelengths. For this purpose, we propose a system of thin
+ferromagnetic layers dynamically coupled by a rectangular ferromagnetic
+resonator. We show that a single and double, clockwise and counter-clockwise,
+circulating modes of the resonator offer a wide possibility of control of
+propagating waves. Particularly, at frequency related to the double-clockwise
+circulating spin-wave mode of the resonator, the spin wave excited in one layer
+is transferred to the second one where it propagates in the backward direction.
+Interestingly, the wave excited in the second layer propagates in the forward
+direction only in that layer. This demonstrates add-drop filtering, as well as
+circulator functionality. Thus, the proposed system can become an important
+part of future magnonic technology for signal routing.",2105.10875v1
+2021-06-10,4D Optically Reconfigurable Volumetric Metamaterials,"Metamaterials are artificially created media, which allow introducing
+additional degrees of freedom into electromagnetic design by controlling
+constitutive material parameters. Reconfigurable time-dependent metamaterials
+can further enlarge those capabilities by introducing a temporal variable as an
+additional controllable parameter. Here we demonstrate a first-of-its-kind
+reconfigurable volumetric metamaterial-based scatterer, wherein the
+electromagnetic properties are controlled dynamically with light. In
+particular, hybridized resonances in arrays of split ring resonators give rise
+to a collective mode that presents properties of artificial high-frequency
+magnetism for centimeter waves. Resonant behavior of each individual ring is
+controlled with a photocurrent, which allows the fast tuning of macroscopic
+effective permeability. Thus, the artificial gigahertz magnon resonant
+excitation within a subwavelength spherical scatterer is governed by light
+intensity. Four-dimensional control over electromagnetic scattering in both
+space and time opens new venues for modern applications, including wireless
+communications and automotive radars to name just a few.",2106.05773v1
+2021-06-10,Topological energy release from collision of relativistic antiferromagnetic solitons,"Magnetic solitons offer functionalities as information carriers in multiple
+spintronic and magnonic applications. However, their potential for nanoscale
+energy transport has not been revealed. Here we demonstrate that
+antiferromagnetic solitons, e.g. domain walls, can uptake, transport and
+release energy. The key for this functionality resides in their relativistic
+kinematics; their self-energy increases with velocity due to Lorentz
+contraction of the soliton and their dynamics can be accelerated up to the
+effective speed of light of the magnetic medium. Furthermore, their
+classification in robust topological classes allows to selectively release this
+energy back into the medium by colliding solitons with opposite topology. Our
+work uncovers important energy-related aspects of the physics of
+antiferromagnetic solitons and opens up the attractive possibility for
+spin-based nanoscale and ultra-fast energy transport devices.",2106.05804v1
+2021-06-17,Magnetization process and ordering of the $S=1/2$ pyrochlore magnet in a field,"We study the $S=1/2$ pyrochlore Heisenberg antiferromagnet in a magnetic
+field. Using large scale density-matrix renormalization group (DMRG)
+calculations for clusters up to $128$ spins, we find indications for a finite
+triplet gap, causing a threshold field to nonzero magnetization in the
+magnetization curve. We obtain a robust saturation field consistent with a
+magnon crystal, although the corresponding $5/6$ magnetization plateau is very
+slim and possibly unstable. Most remarkably, there is a pronounced and
+apparently robust $\frac 1 2$ magnetization plateau where the groundstate
+breaks (real-space) rotational symmetry, exhibiting oppositely polarised spins
+on alternating kagome and triangular planes. Reminiscent of the kagome ice
+plateau of the pyrochlore Ising magnet known as spin ice, it arises via a much
+more subtle `quantum order by disorder' mechanism.",2106.09722v2
+2021-06-21,Negative correlation between the linear and the nonlinear conductance in magnetic tunnel junctions,"The current-voltage ($IV$) characteristics beyond the linear response regime
+of magnetic tunnel junction (MTJ) is systematically investigated. We find a
+clear negative correlation between the two coefficients to characterize the
+linear ($I$$\propto$$V$) and the lowest-order nonlinear ($I$$\propto$$V^3$)
+currents, which holds regardless of the temperature and the thickness of the
+tunnel barrier. This observation cannot simply be explained by the standard
+tunneling model such as the Brinkman model, suggesting a mechanism intrinsic to
+MTJ. We propose a phenomenological model based on the Julli\'ere model that
+attributes the observed negative correlation to the spin-flip tunneling
+assisted by a magnon. These results suggest a fundamental law between the
+linear and the nonlinear response of MTJ.",2106.11274v1
+2021-06-21,A low-loss ferrite circulator as a tunable chiral quantum system,"Ferrite microwave circulators allow one to control the directional flow of
+microwave signals and noise, and thus play a crucial role in present-day
+superconducting quantum technology. They are typically viewed as a black-box,
+and their internal structure is not specified, let alone used as a resource. In
+this work, we demonstrate a low-loss waveguide circulator constructed with
+single-crystalline yttrium iron garnet (YIG) in a 3D cavity, and analyze it as
+a multi-mode hybrid quantum system with coupled photonic and magnonic
+excitations. We show the coherent coupling of its chiral internal modes with
+integrated superconducting niobium cavities, and how this enables tunable
+non-reciprocal interactions between the intra-cavity photons. We also probe
+experimentally the effective non-Hermitian dynamics of this system and its
+effective non-reciprocal eigenmodes. The device platform provides a test bed
+for implementing non-reciprocal interactions in open-system circuit QED.",2106.11283v2
+2021-07-05,Identifying intrinsic and extrinsic mechanisms of anisotropic magnetoresistance with terahertz probes,"Identifying the intrinsic and extrinsic origins of magneto-transport in
+spin-orbit coupled systems has long been a central theme in condensed matter
+physics. However, it has been elusive owing to the lack of an appropriate
+experimental tool. In this work, using terahertz time-domain spectroscopy, we
+unambiguously disentangle the intrinsic and extrinsic contributions to the
+anisotropic magnetoresistance (AMR) of a permalloy film. We find that the
+scattering-independent intrinsic contribution to AMR is sizable and is as large
+as the scattering-dependent extrinsic contribution to AMR. Moreover, the
+portion of intrinsic contribution to total AMR increases with increasing
+temperature due to the reduction of extrinsic contribution. Further
+investigation reveals that the reduction of extrinsic contribution is caused by
+the phonon/magnon-induced negative AMR. Our result will stimulate further
+researches on other spin-orbit-interaction-induced phenomena for which
+identifying the intrinsic and extrinsic contributions is important.",2107.01770v1
+2021-07-23,Spin exchange Hamiltonian and topological degeneracies in elemental gadolinium,"We present a comprehensive study of the magnetic exchange Hamiltonian of
+elemental Gadolinium. We use neutron scattering to measure the magnon spectrum
+over the entire Brillouin zone, and fit the excitations to a spin wave model to
+extract the first 26 nearest neighbor magnetic exchange interactions with
+rigorously defined uncertainty. We find these exchange interactions to follow
+RKKY behavior, oscillating from ferromagnetic to antiferromagnetic as a
+function of distance. Finally, we discuss the topological features and
+degeneracies in Gd, and HCP ferromagnets in general. We show theoretically how,
+with asymmetric exchange, topological properties could be tuned with a magnetic
+field.",2107.11370v3
+2021-07-24,Electron-Phonon Scattering governs both Ultrafast and Precessional Magnetization Dynamics in Co-Fe Alloys,"Recent investigations have advanced the understanding of how
+structure-property relationships in ferromagnetic metal alloys affect the
+magnetization dynamics on nanosecond time-scales. A similar understanding for
+magnetization dynamics on femto- to pico-second time-scales does not yet exist.
+To address this, we perform time-resolved magneto optic Kerr effect (TRMOKE)
+measurements of magnetization dynamics in Co-Fe alloys on femto- to nano-second
+regimes. We show that Co-Fe compositions that exhibit low Gilbert damping
+parameters also feature prolonged ultrafast demagnetization upon
+photoexcitation. We analyze our experimental TR-MOKE data with the
+three-temperature-model (3TM) and the Landau-Lifshitz-Gilbert equation. These
+analyses reveal a strong compositional dependence of the dynamics across all
+time-scales on the strength of electron-phonon interactions. Our findings are
+beneficial to the spintronics and magnonics community, and will aid in the
+quest for energy-efficient magnetic storage applications.",2107.11699v1
+2021-08-05,Will Skyrmions Move to the Hot or Cold Region under Temperature Gradients?,"We obtain a dynamic equation at finite temperatures in the thermal bath of
+magnons, electrons, and phonons. We further consider effects of the angular
+momentum, momentum, magneto-crystalline anisotropy gradient, entropy equivalent
+field, dipole field, and diffusion to extend this equation to thermal
+gradients. Our findings are summarized as follows: skyrmions can move towards
+the hot or cold region; the tangential velocity of skyrmions can be reversed;
+two velocity components of skyrmions can have the same or different null
+points; the velocity in the tangential direction can be greater than the heat
+flow direction; the skyrmion Hall angle can be positive and negative; forces
+acting on skyrmions produced by equivalent magnetic fields will decrease with
+temperatures under uniform temperatures. Our results are consistent with
+experiments and beneficial for spintronics.",2108.02621v1
+2021-08-23,Reconfigurable 3D magnonic crystal: tunable and localized spin-wave excitations in CoFeB meander-shaped film,"In this work, we study experimentally by broadband ferromagnetic resonance
+measurements, the dependence of the spin-wave excitation spectra on the
+magnetic applied field in CoFeB meander-shaped films. Two different
+orientations of the external magnetic field were explored, namely parallel or
+perpendicular to the lattice cores. The interpretation of the field dependence
+of the frequency and spatial profiles of major spin-wave modes were obtained by
+micromagnetic simulations. We show that the vertical segments lead to the
+easy-axis type of magnetic anisotropy and support the in-phase and out-of-phase
+spin-wave precession amplitude in the vertical segments. The latter could
+potentially be used for the design of tunable metasurfaces or in magnetic
+memories based on meandering 3D magnetic films.",2108.10232v1
+2021-08-24,Higher-order ferromagnetic resonances in periodic arrays of synthetic-antiferromagnet nanodiscs,"We investigate spin dynamics in nanodisc arrays of synthetic-antiferromagnets
+(SAF) made of Py/NiCu/Py trilayers, where the NiCu spacer undergoes a Curie
+transition at about 200 K. The observed ferromagnetic resonance spectra have
+three distinct resonance modes at room temperature, which are fully recreated
+in our micromagnetic simulations showing also how the intra-SAF asymmetry can
+be used to create and control the higher-order resonances in the structure.
+Below the Curie temperature of the spacer, the system effectively transitions
+into a single-layer nanodisc array with only two resonance modes. Our results
+show how multi-layering of nano-arrays can add tunable GHz functionality
+relevant for such rapidly developing fields as magnetic meta-materials,
+magnonic crystals, arrays of spin-torque oscillators and neuromorphic
+junctions.",2108.10581v1
+2021-08-24,Out-of-plane magnetic anisotropy in bulk ilmenite $\text{CoTiO}_3$,"Structural, electronic and magnetic properties of bulk ilmenite CoTiO$_3$ are
+analyzed in the framework of density functional theory (DFT), using the
+generalized gradient approximation (GGA) and Hubbard-corrected approaches. We
+find that the G-type antiferromagnetic (G-AFM) structure, which consists of
+antiferromagnetically coupled ferromagnetic $ab$ planes, is the ground-state of
+the system, in agreement with experiments. Furthermore, cobalt titanates
+present two critical temperatures related to the breaking of the inter- and
+intra-layer magnetic ordering. This would result in the individual planes
+remaining ferromagnetic even at temperatures above the N\'{e}el temperature.
+When spin-orbit coupling is included in our calculations, we find an
+out-of-plane magnetic anisotropy, which can be converted to an in-plane
+anisotropy with a small doping of electrons corresponding to about 2.5% Ti
+substitution for Co, consistent with experimental expectations. We thus present
+a disorder-dependent study of the magnetic anisotropy in bulk $\text{CoTiO}_3$,
+which will determine its magnon properties, including topological aspects.",2108.10847v2
+2021-09-01,Dynamical properties of the Haldane chain with bond disorder,"By using Lanczos exact diagonalization and quantum Monte Carlo combined with
+stochastic analytic continuation, we study the dynamical properties of the
+$S=1$ antiferromagnetic Heisenberg chain with different strengths of bond
+disorder. In the weak disorder region, we find weakly coupled bonds which can
+induce additional low-energy excitation below the one-magnon mode. As the
+disorder increases, the average Haldane gap closes at $\delta_{\Delta}\sim 0.5$
+with more and more low-energy excitations coming out. After the critical
+disorder strength $\delta_c\sim 1$, the system reaches a random-singlet phase
+with prominent sharp peak at $\omega=0$ and broad continuum at $\omega>0$ of
+the dynamic spin structure factor. In addition, we analyze the distribution of
+random spin domains and numerically find three kinds of domains hosting
+effective spin-1/2 quanta or spin-1 sites in between. These ""spins"" can form
+the weakly coupled long-range singlets due to quantum fluctuation which
+contribute to the sharp peak at $\omega=0$.",2109.00552v1
+2021-09-03,Non-Hermitian skin effect in magnetic systems,"Far from being limited to a trivial generalization of their Hermitian
+counterparts, non-Hermitian topological phases have gained widespread interest
+due to their unique properties. One of the most striking non-Hermitian
+phenomena is the skin effect, i.e., the localization of a macroscopic fraction
+of bulk eigenstates at a boundary, which underlies the breakdown of the
+bulk-edge correspondence. Here we investigate the emergence of the skin effect
+in magnetic insulating systems by developing a phenomenological approach to
+describing magnetic dissipation within a lattice model. Focusing on a
+spin-orbit-coupled van der Waals (vdW) ferromagnet with spin-nonconserving
+magnon-phonon interactions, we find that the magnetic skin effect emerges in an
+appropriate temperature regime. Our results suggest that the interference
+between Dzyaloshinskii-Moriya interaction (DMI) and nonlocal magnetic
+dissipation plays a key role in the accumulation of bulk states at the
+boundaries.",2109.01711v4
+2021-09-30,Observation of the orbital Hall effect in a light metal Ti,"The orbital angular momentum is a core ingredient of orbital magnetism, spin
+Hall effect, giant Rashba spin splitting, orbital Edelstein effect, and
+spin-orbit torque. However, its experimental detection is tricky. In
+particular, direct detection of the orbital Hall effect remains elusive despite
+its importance for electrical control of magnetic nanodevices. Here we report
+the direct observation of the orbital Hall effect in a light metal Ti. The Kerr
+rotation by the accumulated orbital magnetic moment is measured at Ti surfaces,
+whose result agrees with theoretical calculations semiquantitatively and is
+supported by the orbital torque measurement in Ti-based magnetic
+heterostructures. The results confirm the electron orbital angular momentum as
+an essential dynamic degree of freedom, which may provide a novel mechanism for
+the electric control of magnetism. The results may also deepen the
+understanding of spin, valley, phonon, and magnon dynamics coupled with orbital
+dynamics.",2109.14847v1
+2021-09-30,Signatures of quartic asymmetric exchange in a class of two dimensional magnets,"Indirect quartic interaction of spins is suggested to play an important role
+in two dimensional magnets with trigonal prismatic symmetry such as
+Fe$_3$GeTe$_2$ monolayer. The proposed interaction is described by terms in
+micromagnetic energy that are linear in magnetization gradients. Such terms
+enable the stability of non-collinear magnetic textures. We investigate
+signatures of the quartic interaction in magnon spectra in the presence of
+anisotropy and external magnetic field. We also show how magnetic spirals,
+which are induced by the proposed interaction, can be manipulated by external
+field. Our analysis is based on symmetry considerations and can be used to
+quantify the quartic interaction strength in experiments with magnetic
+monolayers.",2109.15297v1
+2021-10-04,Lumped circuit model for inductive antenna spin-wave transducers,"We derive a lumped circuit model for inductive antenna spin-wave transducers
+in the vicinity of a ferromagnetic medium. The model considers the antenna's
+Ohmic resistance, its inductance, as well as the additional inductance due to
+the excitation of ferromagnetic resonance or spin waves in the ferromagnetic
+medium. As an example, the additional inductance is discussed for a wire
+antenna on top of a ferromagnetic waveguide, a structure that is characteristic
+for many magnonic devices and experiments. The model is used to assess the
+scaling properties and the energy efficiency of inductive antennas. Issues
+related to scaling antenna transducers to the nanoscale and possible solutions
+are also addressed.",2110.01318v3
+2021-10-13,Dimensional reduction in quantum spin-1/2 system on a 1/7-depleted triangular lattice,"We study the magnetism of a quantum spin-1/2 antiferromagnet on a maple-leaf
+lattice which is obtained by regularly depleting 1/7 of the sites of a
+triangular lattice. Although the interactions are set to be spatially uniform,
+the ground state shows a stripe Neel order and the temperature dependence of
+magnetic susceptibility follows that of the one-dimensional XXZ model with a
+finite spin gap. We examine the nature of frustration by mapping the low energy
+degenerate manifold of states to the fully packed loop-string model on a dual
+cluster-depleted honeycomb lattice, finding that the order-by-disorder due to
+quantum fluctuation characteristic of highly frustrated magnets is responsible
+for the emergent stripes. The excited magnons split into two spinons and
+propagate in the one-dimensional direction along the stripe which is
+reminiscent of the XXZ or Ising model in one dimension. Unlike most of the
+previously studied dimensional reduction effects, our case is purely
+spontaneous as the interactions of the Hamiltonian retains a spatially
+isotropic two-dimensional structure.",2110.06491v2
+2021-10-17,Understanding and Designing the Spin-Driven Thermoelectrics,"While the thermoelectric materials progress based on the engineering of
+electronic and phononic characteristics is reaching a plateau, adding the spin
+degree of freedom has the potential to open a new landscape for alternative
+thermoelectric materials. Here we present the concepts, current understanding,
+and guidelines for designing spin-driven thermoelectrics. We show that the
+interplay between the spin and heat currents in entropy transport via charge
+carriers can offer a strategic path to enhance the electronic thermopower. The
+classical antiferromagnetic semiconductor manganese telluride (MnTe) is chosen
+as the case study due to its significant spin-mediated thermoelectric
+properties. We show that although the spin-disorder scattering reduces the
+carrier mobility in magnetic materials, spin entropy, magnon, and paramagnon
+carrier drags can dominate over and significantly enhance the thermoelectric
+power factor and hence zT. Finally, several guidelines are drawn based on the
+current understandings for designing high-performance spin-driven
+thermoelectric materials.",2110.08897v1
+2021-10-22,"Magnetic order, disorder, and excitations under pressure in the Mott insulator Sr$_2$IrO$_4$","Protected by the interplay of on-site Coulomb interactions and spin-orbit
+coupling, Sr$_2$IrO$_4$ at high pressure is a rare example of a Mott insulator
+with a paramagnetic ground state. Here, using optical Raman scattering, we
+measure both the phonon and magnon evolution in Sr$_2$IrO$_4$ under pressure,
+and identify three different magnetically-ordered phases, culminating in a
+spin-disordered state beyond 18 GPa. A strong first-order structural phase
+transition drives the magnetic evolution at $\sim$10 GPa with reduced
+structural anisotropy in the IrO$_6$ cages, leading to increasingly isotropic
+exchange interactions between the Heisenberg spins and a spin-flip transition
+to $c$-axis-aligned antiferromagnetic order. In the disordered phase of
+Heisenberg $J_\mathrm{eff}=1/2$ pseudospins, the spin excitations are
+quasi-elastic and continuous to 10 meV, potentially hosting a gapless quantum
+spin liquid in Sr$_2$IrO$_4$.",2110.11588v1
+2021-10-22,Magnetization dynamics fingerprints of an excitonic condensate $t_{2g}^{4}$ magnet,"The competition between spin-orbit coupling $\lambda$ and electron-electron
+interaction $U$ leads to a plethora of novel states of matter, extensively
+studied in the context of $t_{2g}^4$ and $t_{2g}^5$ materials, such as
+ruthenates and iridates. Excitonic magnets -- the antiferromagnetic state of
+bounded electron-hole pairs -- is a prominent example of phenomena driven by
+those competing energy scales. Interestingly, recent theoretical studies
+predicted that excitonic magnets can be found in the ground-state of
+spin-orbit-coupled $t_{2g}^4$ Hubbard models. Here, we present a detailed
+computational study of the magnetic excitations in that excitonic magnet,
+employing one-dimensional chains (via density matrix renormalization group) and
+small two-dimensional clusters (via Lanczos). Specifically, first we show that
+the low-energy spectrum is dominated by a dispersive (acoustic) magnonic mode,
+with extra features arising from the $\lambda=0$ state in the phase diagram.
+Second, and more importantly, we found a novel magnetic excitation forming a
+high-energy optical mode with the highest intensity at wavevector $q\to 0$. In
+the excitonic condensation regime at large $U$, we also have found a novel
+high-energy $\pi$-mode composed solely of orbital excitations. These unique
+fingerprints of the $t_{2g}^4$ excitonic magnet are important in the analysis
+of neutron and RIXS experiments.",2110.11828v1
+2021-10-27,Low temperature competing magnetic energy scales in the topological ferrimagnet TbMn6Sn6,"TbMn6Sn6 is a metallic ferrimagnet displaying signatures of both topological
+electrons and topological magnons arising from ferromagnetism and spin-orbit
+coupling within its Mn kagome layers. Inelastic neutron scattering measurements
+find strong ferromagnetic (FM) interactions within the Mn kagome layer and
+reveal a magnetic bandwidth of ~230 meV. The low-energy magnetic excitations
+are characterized by strong FM Mn-Mn and antiferromagnetic (AFM) Mn-Tb
+interlayer magnetic couplings. We observe weaker, competing long-range FM and
+AFM Mn-Mn interlayer interactions similar to those driving helical magnetism in
+the YMn6Sn6 system. Combined with density-functional theory calculations, we
+find that competing Mn-Mn interlayer magnetic interactions occur in all RMn6Sn6
+compounds with R= Y, Gd-Lu, resulting in magnetic instabilities and tunability
+when Mn-R interactions are weak. In the case of TbMn6Sn6, strong AFM Mn-Tb
+coupling ensures a highly stable three-dimensional ferrimagnetic network.",2110.14713v2
+2021-10-30,Roadmap on Spin-Wave Computing,"Magnonics is a field of science that addresses the physical properties of
+spin waves and utilizes them for data processing. Scalability down to atomic
+dimensions, operations in the GHz-to-THz frequency range, utilization of
+nonlinear and nonreciprocal phenomena, and compatibility with CMOS are just a
+few of many advantages offered by magnons. Although magnonics is still
+primarily positioned in the academic domain, the scientific and technological
+challenges of the field are being extensively investigated, and many
+proof-of-concept prototypes have already been realized in laboratories. This
+roadmap is a product of the collective work of many authors that covers
+versatile spin-wave computing approaches, conceptual building blocks, and
+underlying physical phenomena. In particular, the roadmap discusses the
+computation operations with Boolean digital data, unconventional approaches
+like neuromorphic computing, and the progress towards magnon-based quantum
+computing. The article is organized as a collection of sub-sections grouped
+into seven large thematic sections. Each sub-section is prepared by one or a
+group of authors and concludes with a brief description of the current
+challenges and the outlook of the further development of the research
+directions.",2111.00365v1
+2021-10-31,Thermally induced all-optical ferromagnetic resonance in thin YIG films,"All-optical ferromagnetic resonance (AO-FMR) is a powerful tool for local
+detection of micromagnetic parameters, such as magnetic anisotropy, Gilbert
+damping or spin stiffness. In this work we demonstrate that the AO-FMR method
+can be used in thin films of Yttrium Iron Garnet (YIG) if a metallic capping
+layer (Au, Pt) is deposited on top of the film. Magnetization precession is
+triggered by heating of the metallic layer with femtosecond laser pulses. The
+heating modifies the magneto-crystalline anisotropy of the YIG film and shifts
+the quasi-equilibrium orientation of magnetization, which results in
+precessional magnetization dynamics. The laser-induced magnetization precession
+corresponds to a uniform (Kittel) magnon mode, with the precession frequency
+determined by the magnetic anisotropy of the material as well as the external
+magnetic field, and the damping time set by a Gilbert damping parameter. The
+AO-FMR method thus enables measuring local magnetic properties, with spatial
+resolution given only by the laser spot size.",2111.00586v1
+2021-11-02,Anti-PT-symmetry-enhanced interconversion between microwave and optical fields,"The intrinsic dissipation of systems into a shared reservoir introduces
+coherence between two systems, enabling anti-Parity-Time (anti-PT) symmetry. In
+this paper, we propose an anti-PT symmetric converter, consisting of a
+microwave cavity coupled dissipatively to a ferromagnetic sphere, which
+supports significant improvements in the conversion efficiency when compared to
+coherently coupled setups. In particular, when only the ferrite sample is
+driven, the strong coherence induced by the vacuum of the mediating channel
+leads to much stronger enhancements in the intended conversion. The enhancement
+is an inalienable artifact of the emergence of a long-lived, dark mode
+associated with a quasi-real singularity of the hybrid system. In addition, we
+observe considerable asymmetry in the efficiencies of microwave-to-optical and
+optical-to-microwave conversions, in spite of the symmetrical structure of the
+trilinear optomagnonic coupling stimulating both the transduction phenomena.
+The nonreciprocity stems from the intrinsic asymmetry in the couplings of the
+microwave and optical fields to the cavity-magnon network as well as the phase
+coupling entailed by the spatial separation.",2111.01335v1
+2021-11-03,Efficient geometrical control of spin waves in microscopic YIG waveguides,"We study experimentally and by micromagnetic simulations the propagation of
+spin waves in 100-nm thick YIG waveguides, where the width linearly decreases
+from 2 to 0.5 micrometers over a transition region with varying length between
+2.5 and 10 micrometers. We show that this geometry results in a down-conversion
+of the wavelength, enabling efficient generation of waves with wavelengths down
+to 350 nm. We also find that this geometry leads to a modification of the group
+velocity, allowing for almost-dispersionless propagation of spin-wave pulses.
+Moreover, we demonstrate that the influence of energy concentration outweighs
+that of damping in these YIG waveguides, resulting in an overall increase of
+the spin-wave intensity during propagation in the transition region. These
+findings can be utilized to improve the efficiency and functionality of
+magnonic devices which use spin waves as an information carrier.",2111.02236v1
+2021-11-09,Magnetotransport in ferromagnetic Fe$_2$Ge semimetallic thin films,"Thin films of the ferromagnet Fe$_2$Ge were grown via molecular beam epitaxy,
+and their electrical and magneto-transport properties measured for the first
+time. X-ray diffraction and vibrating sample magnetometry measurements
+confirmed the crystalline ferromagnetic Fe$_2$Ge phase. The observed high
+temperature maximum in the longitudinal resistivity, as well as the observed
+suppression of electron-magnon scattering at low temperatures, point to the
+presence of strong spin polarization in this material. Measurements of the Hall
+resistivity, $\rho_{xy}$, show contributions from both the ordinary Hall effect
+and anomalous Hall effect, $\rho_{xy}^{AH}$, from which we determined the
+charge carrier concentration and mobility. Measurements also show a small
+negative magnetoresistance in both the longitudinal and transverse geometries.
+Fe$_2$Ge holds promise as a useful spintronic material, especially for its
+semiconductor compatibility.",2111.05417v1
+2021-11-17,Large photogalvanic spin current by magnetic resonance in bilayer Cr trihalides,"Magnetic materials show rich optical responses related to the magnetic order.
+These phenomena reflect the nature of their excitations, providing a powerful
+probe for the magnetic states and a way to control them. In recent years, such
+studies were extended to the optical control of spin current using nonlinear
+optical response similar to the photogalvanic effect. However, neither a
+candidate material nor a general formula for calculating the photogalvanic spin
+current is known so far. In this work, we develop a general theory for the
+photogalvanic spin current through a magnetic resonance process. Using the
+nonlinear response formalism, we find the nonlinear conductivity consists of
+two contributions that involve one and two magnon bands; the latter is a
+contribution unknown to date. We argue that the two-band process produces a
+large photogalvanic spin current in the antiferromagnetic phase of bilayer
+CrI$_3$ and CrBr$_3$, whose resonance frequency can be tuned between GHz-THz
+range by an external magnetic field. Our findings open a route to the studies
+on the photogalvanic effect of spin angular momentum in realistic setups.",2111.09007v1
+2021-11-18,Topological to magnetically ordered quantum phase transition in antiferromagnetic spin ladders with long-range interactions,"We study a generalized quantum spin ladder with staggered long range
+interactions that decay as a power-law with exponent $\alpha$. Using large
+scale quantum Monte Carlo (QMC) and the density matrix renormalization group
+(DMRG) simulations, we show that this model undergoes a transition from a
+rung-dimer phase characterized by a non-local string order parameter, to a
+symmetry broken N\'eel phase. We find evidence that the transition is second
+order.In the magnetically ordered phase, the spectrum exhibits gapless modes,
+while excitations in the gapped phase are well described in terms of triplons
+-- bound states of spinons across the legs. We obtain the momentum resolved
+spin dynamic structure factor numerically and find a well defined triplon band
+evolves into a gapless magnon dispersion through the transition. We further
+discuss the possibility of deconfined criticality in this model.",2111.09798v2
+2021-11-21,Antiferromagnetic resonance in the cubic iridium hexahalides (NH$_4$)$_2$IrCl$_6$ and K$_2$IrCl$_6$,"We report on high-field electron spin resonance studies of two iridium
+hexahalide compounds, (NH$_4$)$_2$IrCl$_6$ and K$_2$IrCl$_6$. In the
+paramagnetic state, our measurements reveal isotropic $g$-factors $g = 1.79$(1)
+for the Ir$^{4+}$ ions, in agreement with their cubic symmetries. Most
+importantly, in the magnetically ordered state, we observe two magnon modes
+with zero-field gaps of 11.3 and 14.2 K for (NH$_4$)$_2$IrCl$_6$ and
+K$_2$IrCl$_6$, respectively. Based on that and using linear spin-wave theory,
+we estimate the nearest-neighbor exchange couplings and anisotropic Kitaev
+interactions, $J_1/k_B=10.3$ K, $K/k_B=0.7$ K for (NH$_4$)$_2$IrCl$_6$, and
+$J_1/k_B=13.8$ K, $K/k_B=0.9$ K for K$_2$IrCl$_6$, revealing the
+nearest-neighbor Heisenberg coupling as the leading interaction term, with only
+a weak Kitaev anisotropy.",2111.10884v1
+2021-11-28,Parametrically driven THz magnon-pairs: predictions towards ultimately fast and minimally dissipative switching,"Findings ways to achieve switching between magnetic states at the fastest
+possible time scale that simultaneously dissipates the least amount of energy
+is one of the main challenges in magnetism. Antiferromagnets exhibit intrinsic
+dynamics in the THz regime, the highest among all magnets and are therefore
+ideal candidates to address this energy-time dilemma. Here we study
+theoretically THz-driven parametric excitation of antiferromagnetic
+magnon-pairs at the edge of the Brillouin zone and explore the potential for
+switching between two stable oscillation states. Using a semi-classical theory,
+we predict that switching can occur at the femtosecond time scale with an
+energy dissipation down to a few zepto Joule. This result touches the
+thermodynamical bound of the Landauer principle, and approaches the quantum
+speed limit up to 5 orders of magnitude closer than demonstrated with magnetic
+systems so far.",2111.14202v1
+2021-11-30,Nonreciprocity of spin waves in a double layer ferromagnet with Dzyaloshinskii-Moriya interactions,"In this paper, boundary conditions for Landau-Lifshitz equations at the
+interface between two ferromagnets with different Dzyaloshinskii-Moriya
+interactions are derived. We calculated and verified the analytical expression
+for the energy flux density continuity for the spin-wave propagation through
+the interface between two ferromagnets with/without Dzyaloshinskii-Moriya
+interactions considering the boundary conditions mentioned. Analytical
+expressions for reflection, transmission coefficients and the nonreciprocity
+factor are calculated in the case of spin-wave propagation through a double
+layer ferromagnet with/without Dzyaloshinskii-Moriya interactions in the
+first/second layer. Two principally different types of nonreciprocity effects
+for spin waves are revealed in such a double layer system. The material
+parameters of a double layer ferromagnet with/without Dzyaloshinskii-Moriya
+interactions in the first/second layer are found for which the extremely high
+nonreciprocity factor (>10) is expected according to the results of
+calculations. The results of the paper deepen the knowledge about the spin-wave
+propagation control in magnonic devices.",2111.15244v1
+2021-11-28,Tunable cryogenic THz cavity for strong light-matter coupling in complex materials,"We report here the realization and commissioning of an experiment dedicated
+to the study of the optical properties of light matter hybrids constituted of
+crystalline samples embedded in an optical cavity. The experimental assembly
+developed offers the unique opportunity to study the weak and strong coupling
+regime between a tunable optical cavity in cryogenic environment and low energy
+degrees of freedom such as phonons, magnons or charge fluctuations. We describe
+here the setup developed which allows the positioning of crystalline samples in
+an optical cavity of different quality factor, the tuning of the cavity length
+at cryogenic temperatures and its optical characterization with a broadband
+time domain THz spectrometer (0.2-6 THz). We demonstrate the versatility of the
+setup by studying the vibrational strong coupling in CuGeO3 single crystal at
+cryogenic temperatures.",2112.01560v1
+2021-12-03,Microwave Amplification in a PT -symmetric-like Cavity Magnomechanical System,"We propose a scheme that can generate tunable magnomechanically induced
+amplification in a double-cavity parity-time-(PT -) symmetric-like
+magnomechanical system under a strong control and weak probe field. The system
+consists of a ferromagnetic-material yttrium iron garnet (YIG) sphere placed in
+a passive microwave cavity which is connected with another active cavity. We
+reveal that ideally induced amplification of the microwave probe signal may
+reach the maximum value 1000000 when cavity-cavity, cavity-magnon and
+magnomechanical coupling strengths are nonzero simultaneously. The phenomenon
+might have potential applications in the field of quantum information
+processing and quantum optical devices. Besides, we also find the phenomena of
+slow-light propagation. In this case, group speed delay of the light can
+achieve 0.000035s, which can enhance some nonlinear effect. Moreover, due to
+the relatively flat dispersion curve, the proposal may be applied to sensitive
+optical switches, which plays an important role in storing photons and quantum
+optical chips.",2112.01727v1
+2021-12-06,Charge and spin order dichotomy in NdNiO$_2$ driven by SrTiO$_3$ capping layer,"Superconductivity in infinite-layer nickelates holds exciting analogies with
+that of cuprates, with similar structures and $3d$-electron count. Using
+resonant inelastic x-ray scattering (RIXS) we studied electronic and magnetic
+excitations and charge density correlations in Nd$_{1-x}$Sr$_{x}$NiO$_2$ thin
+films with and without an SrTiO$_3$ capping layer. We observe dispersing
+magnons only in the capped samples, progressively dampened at higher doping. In
+addition, we detect an elastic resonant scattering peak in the uncapped $x=0$
+compound at wave vector (1/3,0), remindful of the charge order signal in hole
+doped cuprates. The peak weakens at $x=0.05$ and disappears in the
+superconducting $x=0.20$ film. The uncapped samples also present a higher
+degree of Ni$3d$-Nd$5d$ hybridization and a smaller anisotropy of the Ni$3d$
+occupation with respect to the capped samples. The role of the capping on the
+possible hydrogen incorporation or on other mechanisms responsible for the
+electronic reconstruction far from the interface remains to be understood.",2112.03341v1
+2021-12-21,Nonreciprocal spin-wave dynamics in Pt/Co/W/Co/Pt multilayers,"We present a detailed study of the spin-wave dynamics in single Pt/Co/W and
+double Pt/Co/W/Co/Pt ferromagnetic layer systems. The dispersion of spin waves
+was measured by wavevector-resolved Brillouin light scattering spectroscopy
+while the in-plane and out-of-plane magnetization curves were measured by
+alternating gradient field magnetometry. The interfacial Dzyaloshinskii-Moriya
+interaction induced nonreciprocal dispersion relation was demonstrated for both
+single and double ferromagnetic layers and explicated by numerical simulations
+and theoretical formulas. The results indicate the crucial role of the order of
+layers deposition on the magnetic parameters. A significant difference between
+the perpendicular magnetic anisotropy constant in double ferromagnetic layer
+systems conduces to the decline of the interlayer interactions and different
+dispersion relations for the spin-wave modes. Our study provides a significant
+contribution to the realization of the multifunctional nonreciprocal magnonic
+devices based on ultrathin ferromagnetic/heavy-metal layer systems.",2112.11206v1
+2021-12-23,NMR evidence against a spin-nematic nature of the presaturation phase in the frustrated magnet SrZnVO(PO4)2,"Using $^{31}$P nuclear magnetic resonance (NMR) we investigate the recently
+discovered presaturation phase in the highly frustrated two-dimensional spin
+system SrZnVO(PO$_4$)$_2$ [F. Landolt et al., Phys. Rev. B 104, 224435 (2021)].
+Our data provide two pieces of evidence against the presumed spin-nematic
+character of this phase: i) NMR spectra reveal that it hosts a dipolar spin
+order and ii) the 1/$T_1$ relaxation rate data recorded above the saturation
+field can be fitted by the sum of a single-magnon term, exponential in the gap,
+and a critical second-order term, exponential in the triple gap, leaving no
+space for a nematic spin dynamics, characterized by a double-gap exponential.
+We explain the unexpectedly broad validity of the simple fit and the related
+critical spin dynamics.",2112.12603v2
+2021-12-24,Skyrmion nucleation on the surface of a topological insulator,"Skyrmion nucleation induced by spin-transfer torques at an interface of a
+topological insulator and a ferromagnetic insulator is investigated. Due to
+strong spin-orbit coupling on a surface of topological insulators, which
+enhances the effect of spin torques, efficient manipulation of skyrmions is
+expected, and therefore, topological insulators could provide the ideal
+platform to achieve high-performance skyrmionic devices. Using micromagnetic
+simulations and energetics, we evaluate properties of the skyrmion nucleation
+on a surface of topological insulators, such as nucleation time, critical
+electric field, and skyrmion numbers. We show that the nucleation time is
+inversely proportional to the applied electric field. We also identify the
+Gilbert damping and temperature dependencies of the critical field.
+Furthermore, we analytically evaluate the effect of the Dzyaloshinskii-Moriya
+interaction and demonstrate that the temperature dependence can be explained by
+the reduction of a magnon excitation gap due to the self-energy corrections.",2112.12967v2
+2021-12-19,Engineering spin wave spectra in thick Ni$_{80}$Fe$_{20}$ rings by using competition between exchange and dipolar fields,"Control of the spin wave dynamics in nanomagnetic elements is very important
+for the realization of a broad range of novel magnonic devices. Here we study
+experimentally the spin wave resonance in thick ferromagnetic rings (100 nm)
+using perpendicular ferromagnetic resonance spectroscopy. Different from what
+was observed for the continuous film of the same thickness, or from ring with
+similar lateral dimensions but with lower thicknesses, the spectra of thick
+patterned rings show a non-monotonic dependence of the mode intensity on the
+resonance field for a fixed frequency. To explain this effect, the theoretical
+approach by considering the dependence of the mode profiles on both the radial
+and axial coordinates was developed. It was demonstrated that such unusual
+behavior is a result of the competition between exchange and dipolar fields
+acting at the spin excitations in the structure under study. The calculations
+are in a good agreement with the experimental results.",2112.13657v1
+2021-12-30,Cavity Quantum Materials,"The emergent field of cavity quantum materials bridges collective many-body
+phenomena in solid-state platforms with strong light-matter coupling in cavity
+quantum electrodynamics (cavity QED). This brief review provides an overview of
+the state of the art of cavity platforms and highlights recent theoretical
+proposals and first experimental demonstrations of cavity control of collective
+phenomena in quantum materials. This encompasses light-matter coupling between
+electrons and cavity modes, cavity superconductivity, cavity phononics and
+ferroelectricity, correlated systems in a cavity, light-magnon coupling, cavity
+topology and the quantum Hall effect, as well as superradiance. An outlook of
+potential future developments is given.",2112.15018v2
+2022-01-07,Control of spin waves by spatially modulated strain,"We suggest using spatially modulated strain for control of a spin wave
+propagating inside a bulk magnet. The modulation with the wave vector $q=2k$,
+by virtue of magnetoelasticity, mixes spin waves with wave vectors near $k$ and
+$-k$. This leads to lifting the degeneracy of the symmetric and antisymmetric
+eigenstate combinations of these waves. The resulting picture reminds one of a
+tunneling particle in a symmetric double-well potential. Here, a moving spin
+wave being subjected to the $2k$-lattice modulation after some time alters its
+propagation direction to the opposite one, and so on. The effect can be
+utilized for the control of the spin-wave propagation that can be useful for
+spintronic and magnonic applications. The control may include a delay line
+element, filtering, and waveguide of the spin waves.",2201.02691v1
+2022-01-19,The planar thermal Hall conductivity in the Kitaev magnet α-RuCl3,"We report detailed measurements of the Onsager-like planar thermal Hall
+conductivity $\kappa_{xy}$ in $\alpha$-RuCl$_3$, a spin-liquid candidate of
+topical interest. With the thermal current ${\bf J}_{\rm Q}$ and magnetic field
+$\bf B\parallel a$ (zigzag axis), the observed $\kappa_{xy}/T$ varies strongly
+with temperature $T$ (1-10 K). The results are well-described by bosonic edge
+excitations which evolve to topological magnons at large $B$. Fits to
+$\kappa_{xy}/T$ yield a Chern number $\sim 1$ and a band energy $\omega_1\sim$1
+meV, in agreement with sharp modes seen in electron spin-resonance experiments.
+The bosonic character is incompatible with half-quantization of
+$\kappa_{xy}/T$.",2201.07873v1
+2022-01-25,Complex vortex-antivortex dynamics in the magnetic superconductor EuFe$_{2}$(As$_{0.7}$P$_{0.3}$)$_{2}$,"We report on the investigation of the magnetic superconductor
+EuFe$_{2}$(As$_{0.7}$P$_{0.3}$)$_{2}$ based on muon-spin spectroscopy and ac
+magnetic susceptibility ($\chi$) measurements. The dependence of the internal
+field at the muon site on temperature is indicative of a ferromagnetic ordering
+of Eu$^{2+}$ magnetic moments and only the conventional magnon scattering
+governs the longitudinal relaxation rate at low temperatures. At the same time,
+we observe a rich phenomenology for the imaginary component of the
+susceptibility $\chi^{\prime\prime}$ by means of both standard ac
+susceptibility and a novel technique based on a microwave coplanar waveguide
+resonator. In particular, we detect activated trends for several features in
+$\chi^{\prime\prime}$ over frequencies spanning ten orders of magnitude. We
+interpret our results in terms of the complex dynamics of vortices and
+antivortices influenced by the underlying structure of magnetic domains.",2201.10216v1
+2022-01-25,Krein-unitary Schrieffer-Wolff transformation and band touchings in bosonic Bogoliubov-de Gennes and other Krein-Hermitian Hamiltonians,"Krein-Hermitian Hamiltonians, i.e., Hamiltonians Hermitian with respect to an
+indefinite inner product, have emerged as an important class of non-Hermitian
+Hamiltonians in physics, encompassing both single-particle bosonic
+Bogoliubov-de Gennes (BdG) Hamiltonians and so-called ""$PT$-symmetric""
+non-Hermitian Hamiltonians. In particular, they have attracted considerable
+scrutiny owing to the recent surge in interest for boson topology. Motivated by
+these developments, we formulate a perturbative Krein-unitary Schrieffer-Wolff
+transformation for finite-size dynamically stable Krein-Hermitian Hamiltonians,
+yielding an effective Hamiltonian for a subspace of interest. The effective
+Hamiltonian is Krein Hermitian and, for sufficiently small perturbations, also
+dynamically stable. As an application, we use this transformation to justify
+codimension-based analyses of band touchings in bosonic BdG Hamiltonians, which
+complement topological characterization. We use this simple approach based on
+symmetry and codimension to revisit known topological magnon band touchings in
+several materials of recent interest.",2201.10580v2
+2022-01-31,Evidence of Two-Spinon Bound States in the Magnetic Spectrum of Ba$_3$CoSb$_2$O$_9$,"Recent inelastic neutron scattering (INS) experiments of the triangular
+antiferromagnet Ba$_3$CoSb$_2$O$_9$ revealed strong deviations from
+semiclassical theories. We demonstrate that key features of the INS data are
+well reproduced by a parton Schwinger boson theory beyond the saddle-point
+approximation. The measured magnon dispersion is well reproduced by the
+dispersion of two-spinon bound states (poles of the emergent gauge fields
+propagator), while the low-energy continuum scattering is reproduced by a
+quasifree two-spinon continuum, suggesting that a free-spinon gas is a good
+initial framework to study magnetically ordered states near a quantum melting
+point.",2201.13369v4
+2022-02-01,Signatures of non-Loudon-Fleury Raman scattering in the Kitaev magnet $β$-Li$_2$IrO$_3$,"We investigate the magnetic excitations of the hyperhoneycomb Kitaev magnet
+$\beta$-$\text{Li}_2\text{IrO}_3$ by means of inelastic Raman scattering. The
+spectra exhibits a coexistence of a broad scattering continuum and two sharp
+low-energy peaks at 2.5 meV and 3 meV, with a distinctive polarization
+dependence. While the continuum is suggestive of fractional quasi-particles
+emerging from a proximate quantum spin liquid phase, the sharp peaks provide
+the first experimental signature of the `non-Loudon-Fleury' one-magnon
+scattering processes proposed recently [Phys. Rev. B 104, 144412 (2021)]. The
+corresponding microscopic mechanism is similar to the one leading to the
+symmetric off-diagonal exchange interaction $\Gamma$ (as it involves a
+combination of both direct and ligand-mediated exchange paths), but is
+otherwise completely unexpected within the traditional Loudon-Fleury theory of
+Raman scattering. The present experimental verification therefore calls for a
+drastic reevaluation of Raman scattering in similar systems with strong spin
+orbit coupling and multiple exchange paths.",2202.00581v1
+2022-02-08,Breakdown of Linear Spin-wave Theory and Existence of Spinon Bound States in the Frustrated Kagome Lattice Antiferromagnet,"Spin dynamics of the spin-1/2 kagome lattice antiferromagnet
+Cs$_2$Cu$_3$SnF$_{12}$ was studied using high-resolution, time-of-flight
+inelastic neutron scattering. The flat mode, a characteristic of the frustrated
+kagome antiferromagnet, and the low-energy dispersive mode, which is dominated
+by magnons, can be well described by the linear spin-wave theory. However, the
+theory fails to describe three weakly dispersive modes between 9 and 14 meV.
+These modes could be attributed to two-spinon bound states, which decay into
+free spinons away from the zone center and at a high temperature, giving rise
+to continuum scattering.",2202.03681v1
+2022-02-10,Composite Spin Approach to the Blockade Effect in Rydberg Atom Arrays,"The Rydberg blockade induces strongly correlated many-body effects in Rydberg
+atom arrays, including rich ground-state phases and many-body scar states in
+the excitation spectrum. In this letter, we propose a composite spin
+representation that can provide a unified description for major features in
+this system. The composite spin combines Rydberg excitation and the auxiliary
+fermions, which are introduced to implement the Rydberg blockade constraint
+automatically. First, we focus on the PXP model describing one-dimensional
+arrays with the Rydberg blocking radius being a lattice spacing. Using
+composite spins, the ground state is simply a ferromagnetic product state of
+composite spins, and the magnon excitations of these composite spins can
+accurately describe the many-body scar states and signal the quantum phase
+transition driven by detuning. Then, we show that Rydberg atom arrays with
+different blocking radii can share a universal description of the composite
+spin representation, and the difference between different blockade radii can be
+absorbed in the formation of composite spins.",2202.04902v1
+2022-02-20,Magneto-optical Spectroscopy with RAMBO: A Table-Top 30 T Magnet,"Optically probing materials in high magnetic fields can provide enlightening
+insight into field-modified electronic states and phases, while optically
+driving materials in high magnetic fields can induce novel nonequilibrium
+many-body dynamics of spin and charge carriers. While there are high-field
+magnets compatible with standard optical spectroscopy methods, they are
+generally bulky and have limited optical access, which prohibit performing
+state-of-the-art ultrafast and/or nonlinear optical experiments. The Rice
+Advanced Magnet with Broadband Optics (RAMBO), a unique 30-T pulsed mini-coil
+magnet system with direct optical access, has enabled previously challenging
+experiments using femtosecond optical pulses, including time-domain terahertz
+spectroscopy, in cutting-edge materials placed in strong magnetic fields. Here,
+we review recent experimental advances made possible by the first-generation
+RAMBO setup. After summarizing technological aspects of combining optical
+spectroscopic techniques with the mini-coil magnet, we describe results of
+magneto-optical studies of a wide variety of materials, providing new insight
+into the states and dynamics of four types of quasiparticles in solids -
+excitons, plasmons, magnons, and phonons - in high magnetic fields.",2202.09732v1
+2022-03-01,turboMagnon -- A code for the simulation of spin-wave spectra using the Liouville-Lanczos approach to time-dependent density-functional perturbation theory,"We introduce turboMagnon, an implementation of the Liouville-Lanczos approach
+to linearized time-dependent density-functional theory, designed to simulate
+spin-wave spectra in solid-state materials. The code is based on the
+noncollinear spin-polarized framework and the self-consistent inclusion of
+spin-orbit coupling that allow to model complex magnetic excitations. The spin
+susceptibility matrix is computed using the Lanczos recursion algorithm that is
+implemented in two flavors - the non-Hermitian and the pseudo-Hermitian one.
+turboMagnon is open-source software distributed under the terms of the GPL as a
+component of Quantum ESPRESSO. As with other components, turboMagnon is
+optimized to run on massively parallel architectures using native mathematical
+libraries (LAPACK and FFTW) and a hierarchy of custom parallelization layers
+built on top of MPI. The effectiveness of the code is showcased by computing
+magnon dispersions for the CrI$_3$ monolayer, and the importance of the
+spin-orbit coupling is discussed.",2203.01120v2
+2022-03-09,Exchange spin waves in thin films with gradient composition,"We report investigation of ferromagnetic resonance phenomenon in
+ferromagnetic thin films with essentially non-uniform composition. Epitaxial
+Pd-Fe thin film with linear distribution of Fe content across the thickness is
+used as the model material. Anomalous perpendicular standing spin waves are
+observed and quantified using the collective dynamic equation. Numerical
+analysis yields the exchange stiffness constant for diluted Pd-Fe alloy
+$D=2A/\mu_0M_s=15$~T$\cdot$nm$^2$ and the ratio of the effective magnetization
+to the saturation magnetization $M_{eff}/M_s=1.16$. It is demonstrated that,
+overall, engineering of thin films with non-uniform composition across the
+thickness can be used for high-frequency or low-field magnonic operations using
+exchange spin waves.",2203.05014v1
+2022-03-10,Dynamics of the collapse of a ferromagnetic skyrmion in a centrosymmetric lattice,"Time dependence of the size and chirality of a ferromagnetic skyrmion in a
+Heisenberg model with the magnetic field on a square lattice has been studied
+analytically and numerically. The lattice and the magnetic field generate
+strong time dependence of the skyrmion chirality. Due to nonlinearity, the
+lattice alone also generates strong intrinsic damping that leads to the
+skyrmion collapse via the emission of spin waves. In the absence of the
+magnetic field the collapse is slow for a large skyrmion but it becomes
+exponentially fast in the presence of the Landau-Lifshitz damping when the
+field is turned on. Magnons emitted by a collapsing skyrmion must have a
+discrete spectrum due to the quantization of the skyrmion magnetic moment.",2203.05342v1
+2022-03-19,Spin wave excitation and directional propagation in presence of magnetic charges in square artificial spin ice,"Artificial spin ice is a special class of engineered lattice of highly shape
+anisotropic single domain magnetic nanostructures which is used as one of the
+model systems to study the spin ice behavior observed in pyrochlore oxides. The
+nanomagnets interact via dipolar interaction which results in correlated
+magnetization dynamics exhibiting macroscopic spin configuration states. Here,
+we exploit the interplay of underlying magnetic state and external bias field
+orientation to study controlled spin wave propagation in square Artificial Spin
+Ice (sASI) by performing detailed micromagnetic simulations. We report that
+careful selection of vertices with local magnetic charges can effectively
+direct the anisotropic spin wave in presence of an external field. Further, we
+explore the influence of local charges due to the excited state in
+even-coordinated vertices as well as uncompensated charges due to
+odd-coordinated vertices on spin wave behavior. Our studies suggest that there
+is no perceptible difference on spin wave dynamical behavior due to the origin
+of local magnetic charge in sASI. Our results of controlled and directional
+spin wave propagation in sASI system may be useful for low-power consumption
+based all magnonic on-chip devices.",2203.10345v1
+2022-03-24,Magnetic Excitations in Square Lattice Iridates: Contrast between Ba$_2$IrO$_4$ and Sr$_2$IrO$_4$,"We report a resonant inelastic x-ray scattering (RIXS) investigation of
+ultra-thin epitaxial films of Ba$_2$IrO$_4$, and compare their low energy
+magnetic and spin-orbit excitations to those of their sister compound
+Sr$_2$IrO$_4$. Due to the 180$^\circ$ Ir-O-Ir bond, the bandwidth of the magnon
+and spin-orbiton is significantly larger in Ba$_2$IrO$_4$, making it difficult
+to describe these two types of excitations as separate well-defined
+quasiparticles. Both types of excitations are found to be quite sensitive to
+the effect of epitaxial strain. In addition, we find that the d-level inversion
+observed in Sr$_2$IrO$_4$ is absent in Ba$_2$IrO$_4$, as predicted in recent
+theoretical studies. Our results illustrate that the magnetic properties of
+Ba$_2$IrO$_4$ are substantially different from those of Sr$_2$IrO$_4$,
+suggesting that these materials need to be examined more carefully with
+electron itinerancy taken into account.",2203.13102v1
+2022-04-07,Domain wall formation and magnon localization in twisted chromium trihalides,"The rise of twistronics has revolutionized the field of condensed matter
+physics, and more specifically the future applications of two-dimensional
+materials. At small twist angles, the microscopic world becomes strongly
+correlated, and unexpected physical phenomena such as superconductivity emerge.
+For magnetic layers, stacking plays a crucial role in the magnetic exchange
+coupling between the layers leading to non-trivial spin configurations and flat
+spin-wave dispersion when twisted. In this work, we give a short overview of
+the most recent theoretical and experimental works reporting the effect of
+twist angles on two-dimensional magnets. Besides, we discuss the effect of the
+twist angle and the local antiferromagnetic interlayer exchange coupling on the
+formation of antiferromagnetic domains in chromium trihalides. Finally, we show
+some preliminary results on the effect of the stacking and the twist angle on
+the spin-wave dispersion of bilayer CrI$_3$",2204.03244v1
+2022-04-13,Ground States and Dynamical Properties of $S>1/2$ Quantum Heisenberg Model on the 1/5-Depleted Square Lattice,"We study the $S>1/2$ antiferromagnetic Heisenberg model on the 1/5-depleted
+square lattice as a function of the ratio of the intra-plaquette coupling to
+the inter-plaquette coupling. Using stochastic series expansion quantum Monte
+Carlo simulations, we numerically identify three quantum phases, including the
+dimer phase, N\'eel phase and plaquette valence bond solid phase. We also
+obtain the accurate quantum critical points that belong to the O(3)
+universality class using the large-scale finite-size scaling. Most importantly,
+we study the dynamic spin structure factors of different phases, which can be
+measured by inelastic neutron scattering experiments. The low-energy
+excitations can be explained as triplons in the dimer phase and plaquette
+valence bond solid phase. While in the N\'eel phase, the more prominent magnon
+mode can be found as the spin magnitude increases. Furthermore, we find a
+broader continuum at smaller $S$, which may be the dynamical signature of
+nearly deconfined spinon excitations.",2204.06573v1
+2022-04-26,"Nonreciprocal electrical transport in multiferroic semiconductor (Ge,Mn)Te","We have investigated the nonreciprocal electrical transport, that is a
+nonlinear resistance effect depending on the current direction, in multiferroic
+Rashba semiconductor (Ge,Mn)Te. Due to coexistence of ferromagnetic and
+ferroelectric orders, (Ge,Mn)Te provides a unique platform for exploring the
+nonreciprocal electrical transport in a bulk form. (Ge,Mn)Te thin films shows a
+large nonreciprocal resistance compared to GeTe, the nonmagnetic counterpart
+with the same crystal structure. The magnetic-field-angle dependence of the
+nonreciprocal resistance is maximized when magnetic field is orthogonal to both
+current and electric polarization, in accord with the symmetry argument. From
+the analysis of temperature and magnetic field dependence, we deduce that
+inelastic scatterings of electrons mediated by magnons dominantly contribute to
+the observed nonreciprocal response. Furthermore, the nonreciprocal resistance
+is significantly enhanced by lowering hole density. The Fermi level dependence
+is attributed to the deformation of the Rashba band in which the spin-momentum
+locked single Fermi surface appears by exchange field from the in-plane
+magnetization. The present study provides a key insight to the mechanisms of
+novel transport phenomena caused by the interplay of ferroelectric and
+ferromagnetic orders in a semiconductor.",2204.12427v1
+2022-04-27,Refining magnetic interactions from the magnetic field dependence of spin-wave excitations in magnetoelectric LiFePO$_4$,"We investigated the spin excitations of magnetoelectric $\text{LiFePO}_4$ by
+THz absorption spectroscopy in magnetic fields up to 33$\,$T. By studying their
+selection rules, we found not only magnetic-dipole, but also electric-dipole
+active (electromagnons) and magnetoelectric resonances. The magnetic field
+dependence of four strong low-energy modes is reproduced well by our
+four-sublattice spin model for fields applied along the three orthorhombic
+axes. From the fit, we refined the exchange couplings, single-ion anisotropies,
+and the Dzyaloshinskii-Moriya interaction parameters. Additional spin
+excitations not described by the mean-field model are observed at higher
+frequencies. Some of them shows a strong shift with magnetic field, up to
+4$\,\text{cm}^{-1}/\text{T}$, when the field is applied along the easy axis.
+Based on this field dependence, we attribute these high frequency resonances to
+excitation of higher spin multipoles and of two magnons, which become
+THz-active due to the low symmetry of the magnetically ordered state.",2204.12967v1
+2022-05-24,Steady entangled-state generation via cross-Kerr effect in a ferrimagnetic crystal,"For solid-state spin systems, the collective spin motion in a single crystal
+embodies multiple magnetostatic modes. Recently, it was found that the
+cross-Kerr interaction between the higher-order magnetostatic mode and the
+Kittel mode introduces a new operable degree of freedom. In this work, we
+propose a scheme to entangle two magnon modes via the cross-Kerr nonlinearity
+when the bias field is inhomogeneous and the system is driven. Quantum
+entanglement persists at the steady state, as demonstrated by numerical results
+using experimentally feasible parameters. Furthermore, we also demonstrate that
+entangled states can survive better in the system where self-Kerr and
+cross-Kerr nonlinearities coexist. Our work provides insights and guidance for
+designing experiments to observe entanglement between different degrees of
+freedom within a single ferrimagnetic crystal. Additionally, it may stimulate
+potential applications in quantum information processing using spintronic
+devices.",2205.11865v1
+2022-05-27,Generation of long-lived $W$ states via reservoir engineering in dissipatively coupled systems,"Very recently, dissipative coupling was discovered, which develops and
+broadens methods for controlling and utilizing light-matter interactions. Here,
+we propose a scheme to generate the tripartite $W$ state in a dissipatively
+coupled system, where one qubit and two resonators simultaneously interact with
+a common reservoir. With appropriate parameters, we find the $W$ state is a
+dark state of the system. By driving the qubit, the dissipatively coupled
+system will evolve from the ground state to the tripartite $W$ state. Because
+the initial state is the ground state of the system and no measurement is
+required, our scheme is easy to implement in experiments. Moreover, the $W$
+state decouples from the common reservoir and thus has a very long lifetime.
+This scheme is applicable to a wide class of dissipatively coupled systems, and
+we specifically illustrate how to prepare the $W$ state in a hybrid
+qubit-photon-magnon system by using this scheme.",2205.13920v2
+2022-06-01,Exceptional spin wave dynamics in an antiferromagnetic honeycomb lattice,"We theoretically investigate possible effects of electric current on the spin
+wave dynamics for the N\'{e}el-type antiferromagnetic order in a honeycomb
+lattice. Based on a general vector decomposition of the spin polarization of
+conduction electrons, we find that there can exist reciprocal and nonreciprocal
+terms in the current-induced torque acting on the local spins in the system.
+Furthermore, we show that the reciprocal terms will cause the spin wave Doppler
+effect, while the nonreciprocal terms can induce rich non-Hermitian topological
+phenomena in the spin wave dynamics, including exceptional points, bulk Fermi
+arc, non-Hermitian skin effect, etc. Our results indicate the capability to
+manipulate non-Hermitian magnons in magnetic materials by electric current,
+which could be important for both fundamental physics and technology
+applications.",2206.00723v1
+2022-06-03,Quasi-2D anomalous Hall Mott insulator of topologically engineered Jeff =1/2 electrons,"We investigate an experimental toy-model system of a pseudospin-half
+square-lattice Hubbard Hamiltonian in [(SrIrO3)1/(CaTiO3)1] to include both
+nontrivial complex hopping and moderate electronic correlation. While the
+former induces electronic Berry phases as anticipated from the weak-coupling
+limit, the later stabilizes an antiferromagnetic (AFM) Mott insulator ground
+state in analogous to the strong-coupling limit. Their combined results in the
+real system are found to be an anomalous Hall effect with a non-monotonic
+temperature dependence due to the self-competition of the electron-hole pairing
+in the Mott state, and an exceptionally large Ising anisotropy that is captured
+as a giant magnon gap beyond the superexchange approach. The unusual phenomena
+highlight the rich interplay of electronic topology and electronic correlation
+in the intermediate-coupling regime that is largely unexplored and challenging
+in theoretical modelling.",2206.01392v1
+2022-06-05,Strain tuning the magnetic and transport properties of Mn$_3$Ge,"The kagome lattice antiferromagnet Mn$_3$Ge has a local hexagonal symmetry
+with a 120$^\circ$ ordered ground state. This non-colinear ground state
+engenders a strong anomalous Hall response. The main goal of this work is to
+understand the effect of strain on this response. We derive an effective model
+for the Hall vector which functions as our order parameter. Using this model we
+show how both intra and inter planar strains can be used to switch the sign of
+the Hall response at a constant magnetic field. Further, we also investigate
+the effect of this strain on the spin wave band gaps and show that strain can
+be used to effectively manipulate them, which can be used to tune the magnon
+responses in this system.",2206.02219v2
+2022-06-17,Melting of magnetization plateaus for kagome and square-kagome lattice antiferromagnets,"Unconventional features of the magnetization curve at zero temperature such
+as plateaus or jumps are a hallmark of frustrated spin systems. Very little is
+known about their behavior at non-zero temperatures. Here we investigate the
+temperature dependence of the magnetization curve of the kagome lattice
+antiferromagnet in particular at 1/3 of the saturation magnetization for large
+lattice sizes of up to N=48 spins. We discuss the phenomenon of asymmetric
+melting and trace it back to a combined effect of unbalanced magnetization
+steps on either side of the investigated plateau as well as on the behavior of
+the density of states across the plateau. We compare our findings to the
+square-kagome lattice that behaves similarly at low temperatures at zero field,
+but as we will demonstrate differently at 1/3 of the saturation magnetization.
+Both systems possess a flat one-magnon band and therefore share with the class
+of flat-band systems the general property that the plateau that precedes the
+jump to saturation melts asymmetrically but now with a minimal susceptibility
+that bends towards lower fields with increasing temperature.",2206.08710v3
+2022-07-01,Texture fluctuations and emergent dynamics in coupled nanomagnets,"We analyse the thermal fluctuations of magnetization textures in two stray
+field coupled elements, forming mesospins. To this end, the energy landscape
+associated with the thermal dynamics of the textures is mapped out and
+asymmetric energy barriers are identified. These barriers are modified by
+changing the gap that separates the mesospins. Moreover, the coupling between
+the edges leads to an anisotropy in the curvature of the energy surface at the
+metastable minima. This yields a dynamic mode splitting of the edge modes and
+affects the attempt switching frequencies. Thus, we elucidate the mechanism
+with which the magnons in the thermal bath generate the stochastic fluctuations
+of the magnetization at the edges.",2207.00395v3
+2022-07-03,Deeply nonlinear excitation of self-normalised exchange spin waves,"Spin waves are ideal candidates for wave-based computing, but the
+construction of magnetic circuits is blocked by a lack of an efficient
+mechanism to excite long-running exchange spin waves with normalised
+amplitudes. Here, we solve the challenge by exploiting the deeply nonlinear
+phenomena of forward-volume spin waves in 200 nm wide nanoscale waveguides and
+validate our concept with microfocused Brillouin light scattering spectroscopy.
+An unprecedented nonlinear frequency shift of >2 GHz is achieved, corresponding
+to a magnetisation precession angle of 55{\deg} and enabling the excitation of
+exchange spin waves with a wavelength of down to ten nanometres with an
+efficiency of >80%. The amplitude of the excited spin waves is constant and
+independent of the input microwave power due to the self-locking nonlinear
+shift, enabling robust adjustment of the spin wave amplitudes in future on-chip
+magnonic integrated circuits.",2207.01121v1
+2022-07-06,Filtering and imaging of frequency-degenerate spin waves using nanopositioning of a single-spin sensor,"Nitrogen-vacancy (NV) magnetometry is a new technique for imaging spin waves
+in magnetic materials. It detects spin waves by their microwave magnetic stray
+fields, which decay evanescently on the scale of the spin-wavelength. Here, we
+use nanoscale control of a single-NV sensor as a wavelength filter to
+characterize frequency-degenerate spin waves excited by a microstrip in a
+thin-film magnetic insulator. With the NV-probe in contact with the magnet, we
+observe an incoherent mixture of thermal and microwave-driven spin waves. By
+retracting the tip, we progressively suppress the small-wavelength modes until
+a single coherent mode emerges from the mixture. In-contact scans at low drive
+power surprisingly show occupation of the entire iso-frequency contour of the
+two-dimensional spin-wave dispersion despite our one-dimensional microstrip
+geometry. Our distance-tunable filter sheds light on the spin-wave band
+occupation under microwave excitation and opens opportunities for imaging
+magnon condensates and other coherent spin-wave modes.",2207.02798v1
+2022-07-12,Multitude of exceptional points in van der Waals magnets,"Several works have recently addressed the emergence of exceptional points
+(EPs), i.e., spectral singularities of non-Hermitian Hamiltonians, in the
+long-wavelength dynamics of coupled magnetic systems. Here, by focusing on the
+driven magnetization dynamics of a van der Waals ferromagnetic bilayer, we show
+that exceptional points can appear over extended portions of the first
+Brillouin zone as well. Furthermore, we demonstrate that the effective
+non-Hermitian magnon Hamiltonian, whose eigenvalues are purely real or come in
+complex-conjugate pairs, respects an unusual wavevector-dependent
+pseudo-Hermiticity. Finally, for both armchair and zigzag nanoribbon
+geometries, we discuss both the complex and purely real spectra of the
+topological edge states and their experimental implications.",2207.05326v3
+2022-08-03,Ultrafast Demagnetization Dynamics Due to Electron-Electron Scattering and Its Relation to Momentum Relaxation in Ferromagnets,"We analyze theoretically the demagnetization dynamics in a ferromagnetic
+model system due to the interplay of spin-orbit coupling and electron-electron
+Coulomb scattering. We compute the $k$-resolved electronic reduced spin-density
+matrix including precessional dynamics around internal spin-orbit and exchange
+fields as well as the electron-electron Coulomb scattering for densities and
+spin coherences. Based on a comparison with numerical solutions of the full
+Boltzmann scattering integrals, we establish that the $k$-resolved reduced
+spin-density matrix dynamics are well described using a simpler generalized
+relaxation-time ansatz for the reduced spin-density matrix. This ansatz allows
+one to relate the complicated scattering dynamics underlying the
+demagnetization dynamics to a physically meaningful momentum relaxation time
+$\tau$. Our approach reproduces the behaviors of the demagnetization time
+$\tau_{m} \propto 1/\tau$ and $\tau_{m} \propto \tau$ for the limits of short
+and long $\tau$, respectively, and is also valid for the intermediate regime.
+The ansatz thus provides a tool to include the correct demagnetization behavior
+in approaches that treat other contributions to the magnetization dynamics such
+as transport or magnon/phonon dynamics.",2208.02356v1
+2022-07-04,"Magnetic levitation within a microwave cavity: characterization, challenges, and possibilities","The low energy losses in the superconducting magnetic levitation make it
+attractive for exciting applications in physics. Recently, superconducting
+magnetic levitation has been realized as novel mechanical transduction for the
+individual spin qubit in the nitrogen-vacancy center [1]. Furthermore, the
+Meissner has been proposed for the study of modified gravitational wave
+detection [2]. Meissner levitation within the microwave cavity could open
+avenues for the novel cavity optomechanical system, readout for quantum object
+such as the transmon, and magnon, gravitational wave detection, and
+magnetomechanics [3]. This work characterized magnetic levitation within a
+microwave. It also discusses possibilities, challenges, and room temperature
+and cryogenic experiments of the cavity-magnet system.",2208.03220v1
+2022-08-11,Magnetic Excitations in Strained Infinite-layer Nickelate PrNiO2,"Strongly correlated materials often respond sensitively to the external
+perturbations. In the recently discovered superconducting infinite-layer
+nickelates, the superconducting transition temperature can be dramatically
+enhanced via only ~1% compressive strain-tuning enabled by substrate design.
+However, the root of such enhancement remains elusive. While the
+superconducting pairing mechanism is still not settled, magnetic Cooper pairing
+- similar to the cuprates has been proposed. Using resonant inelastic x-ray
+scattering, we investigate the magnetic excitations in infinite-layer PrNiO2
+thin films for different strain conditions. The magnon bandwidth of PrNiO2
+shows only marginal response to strain-tuning, in sharp contrast to the
+striking enhancement of the superconducting transition temperature Tc in the
+doped superconducting samples. These results suggest the enhancement of Tc is
+not mediated by spin excitations and thus provide important empirics for the
+understanding of superconductivity in infinite-layer nickelates.",2208.05614v1
+2022-08-15,Tunable Strong Magnetic Anisotropy in Two-Dimensional van der Waals Antiferromagnets,"We show that anisotropic energy of a 2D antiferromagnet is greatly enhanced
+via stacking on a magnetic substrate layer, arising from the
+sublattice-dependent interlayer magnetic interaction that defines an effective
+anisotropic energy. Interestingly, this effective energy couples strongly with
+the interlayer stacking order and the magnetic order of the substrate layer,
+providing unique mechanical and magnetic means to control the antiferromagnetic
+order. These two types of control methods affect distinctly the sublattice
+magnetization dynamics, with a change of the ratio of sublattice precession
+amplitudes in the former and its chirality in the later. In moir\'{e}
+superlattices formed by a relative twist or strain between the layers, the
+coupling with stacking order introduces a landscape of effective anisotropic
+energy across the moir\'{e}, which can be utilized to create nonuniform
+antiferromagnetic textures featuring periodically localized low-energy magnons.",2208.06958v1
+2022-08-17,A Green's function method for the two-dimensional frustrated spin-1/2 Heisenberg magnetic lattice,"The magnon Hedin's equations are derived via the Schwinger functional
+derivative technique, and the resulting self-consistent Green's function method
+is used to calculate ground state spin patterns and magnetic structure factors
+for 2-dimensional magnetic systems with frustrated spin-1/2 Heisenberg exchange
+coupling. Compared to random-phase approximation treatments, the inclusion of a
+self-energy correction improves the accuracy in the case of scalar product
+interactions, as shown by comparisons between our method and exact benchmarks
+in homogeneous and inhomogeneous finite systems. We also find that for
+cross-product interactions (e.g. antisymmetric exchange), the method does not
+perform equally well, and an inclusion of higher corrections is in order. Aside
+from indications for future work, our results clearly indicate that the Green's
+function method in the form proposed here already shows potential advantages in
+the description of systems with a large number of atoms as well as long-range
+interactions.",2208.08359v1
+2022-08-19,The $S=1$ dimer system K$_2$Ni(MoO$_4$)$_2$: a candidate for magnon Bose-Einstein condensation,"Dimerized quantum magnets provide a unique possibility to investigate
+Bose-Einstein condensation of magnetic excitations in crystalline systems at
+low temperature. Here, we model the low-temperature magnetic properties of the
+recently synthesized spin $S=1$ dimer system K${}_2$Ni(MoO${}_4$)$_2$ and
+propose it as a new candidate material for triplon and quintuplon condensation.
+Based on a first principles analysis of its electronic structure, we derive an
+effective spin-dimer model that we first solve within a mean-field
+approximation to refine its parameters in comparison to experiment. Finally,
+the model is solved by employing a numerically exact quantum Monte Carlo
+technique which leads to magnetic properties in good agreement with
+experimental magnetization and thermodynamic results. We discuss the emergent
+spin model of K${}_2$Ni(MoO${}_4$)$_2$ in view of condensation of magnetic
+excitations in a broad parameter regime. Finally, we comment on a geometrical
+peculiarity of the proposed model and discuss how it could host a supersolid
+phase upon structural distortions.",2208.09246v1
+2022-08-29,Determining Kitaev interaction in spin-$S$ honeycomb Mott insulators,"The Kitaev interaction in a honeycomb lattice with higher-spin $S$ has been
+one of the central attractions, as it may offer quantum spin liquids. A
+microscopic theory showed that when the Hund's coupling at the transition metal
+generates $S> \frac{1}{2}$, the spin-orbit coupling at the heavy ligands
+provides a route to the Kitaev interaction. However, there have been debates
+over its strength compared to other symmetry-allowed interactions.
+Investigating the symmetry of the Hamiltonian for general $S$, we show the
+magnon energies at two momentum points related by a broken mirror symmetry
+reflect the Kitaev interaction when a magnetic field is in the mirror plane.
+Applying the symmetry analysis to CrI$_3$ with $S=\frac{3}{2}$ together with
+the available angle-dependent ferromagnetic resonance data, we estimate the
+Kitaev interaction out of the full Hamiltonian and find that it is
+sub-dominant. Our theory can be tested by inelastic neutron scattering on
+candidate materials under the proposed magnetic field direction, which will
+advance the search for general $S$ Kitaev materials.",2208.13807v2
+2022-08-30,Spin-polarized hot electron transport versus spin pumping mediated by local heating,"A `toy model' - aimed at capturing the essential physics - is presented that
+jointly describes spin-polarized hot electron transport and spin pumping driven
+by local heating. These two processes both contribute to spin-current
+generation in laser-excited magnetic heterostructures. The model is used to
+compare the two contributions directly. The spin-polarized hot electron current
+is modeled as one generation of hot electrons with a spin-dependent excitation
+and relaxation scheme. Upon decay, the excess energy of the hot electrons is
+transferred to a thermalized electron bath. The elevated electron temperature
+leads to an increased rate of electron-magnon scattering processes and yields a
+local accumulation of spin. This process is dubbed as spin pumping by local
+heating. The built-up spin accumulation is effectively driven out of the
+ferromagnetic system by (interfacial) electron transport. Within our model, the
+injected spin current is dominated by the contribution resulting from spin
+pumping, while the hot electron spin current remains relatively small. We
+derive that this observation is related to the ratio between the Fermi
+temperature and Curie temperature, and we show what other fundamental
+parameters play a role.",2208.14342v1
+2022-08-31,Frequency splitting of chiral phonons from broken time reversal symmetry in CrI$_3$,"Conventional approaches for lattice dynamics based on static interatomic
+forces do not fully account for the effects of time-reversal-symmetry breaking
+in magnetic systems. Recent approaches to rectify this involve incorporating
+the first-order change in forces with atomic velocities under the assumption of
+adiabatic separation of electronic and nuclear degrees of freedom. In this
+work, we develop a first-principles method to calculate this velocity-force
+coupling in extended solids, and show via the example of ferromagnetic CrI$_3$
+that, due to the slow dynamics of the spins in the system, the assumption of
+adiabatic separation can result in large errors for splittings of zone-center
+chiral modes. We demonstrate that an accurate description of the lattice
+dynamics requires treating magnons and phonons on the same footing.",2208.14593v1
+2022-08-31,Small-angle neutron scattering in fully polarized phase of non-collinear magnets with interfacial-like DMI,"Spin waves in non-collinear magnets with $C_{nv}$ symmetry are discussed in
+the context of inelastic neutron scattering in small-angle scattering geometry.
+In the framework of a minimal model including exchange coupling,
+Dzayloshinskii-Moriya interaction (DMI), and single-ion anisotropy, we consider
+the system properties at moderate external magnetic fields and in the
+high-field fully polarized phase. In the latter case, the magnon spectrum is
+gapped and non-reciprocal due to DMI with the minimum perpendicular to the
+field direction for the in-plane field and is ferromagnetic-like for the field
+along the high-symmetry axis. Inelastic small-angle neutron scattering in the
+fully polarized phase (SWSANS) is considered in four different geometries. It
+is shown that analysis of the field dependence of the SWSANS cutoff feature in
+these geometries allows determining all important parameters of the model. The
+possibility of the proposed method utilization in thin films with interfacial
+DMI is also discussed.",2208.14782v2
+2022-09-07,Dynamical Signatures of Symmetry Broken and Liquid Phases in an $S=1/2$ Heisenberg Antiferromagnet on the Triangular Lattice,"We present the dynamical spin structure factor of the antiferromagnetic
+spin-$\frac{1}{2}$ $J_1-J_2$ Heisenberg model on a triangular lattice obtained
+from large-scale matrix-product state simulations. The high frustration due to
+the combination of antiferromagnetic nearest and next-to-nearest neighbour
+interactions yields a rich phase diagram. We resolve the low-energy excitations
+both in the $120^{\circ}$-ordered phase and in the putative spin liquid phase
+at $J_2/J_1 = 0.125$. In the ordered phase, we observe an avoided decay of the
+lowest magnon-branch, demonstrating the robustness of this phenomenon in the
+presence of gapless excitations. Our findings in the spin-liquid phase chime
+with the field-theoretical predictions for a gapless Dirac spin liquid, in
+particular the picture of low-lying monopole excitations at the corners of the
+Brillouin zone. We comment on possible practical difficulties of distinguishing
+proximate liquid and solid phases based on the dynamical structure factor.",2209.03344v2
+2022-09-09,Control of magnetic states and spin interactions in bilayer CrCl$_{3}$ with strain and electric fields: an ab initio study,"Using ab initio density functional theory (DFT), we demonstrated the
+possibility of controlling the magnetic ground-state properties of bilayer
+CrCl$_{3}$ by means of mechanical strains and electric fields. In principle, we
+investigated the influence of these two fields on parameters describing the
+spin Hamiltonian of the system. The obtained results show that biaxial strains
+change the magnetic ground state between ferromagnetic (FM) and
+antiferromagnetic (AFM) phases. The mechanical strain also affects the
+direction and amplitude of the uniaxial magnetic anisotropy (MAE). Importantly,
+the direction and amplitude of the Dzyaloshinskii-Moriya vectors are also
+highly tunable under external strain and electric fields. The competition
+between nearest neighbor interaction, MAE, and Dzyaloshinskii-Moriya
+interactions can lead to the stabilization of various exotic spin textures and
+novel magnetic excitations. The high tunability of magnetic properties by
+external fields makes bilayer CrCl$_{3}$ a promising candidate for application
+in the emerging field of two-dimensional quantum spintronics and magnonics.",2209.04527v2
+2022-09-12,State Space Geometry of the Spin-1 Antiferromagnetic Heisenberg Chain,"We study the phase diagram of the spin-1 antiferromagnetic Heisenberg chain
+with uniaxial anisotropy and applied magnetic field in terms of the genuine
+multipartite entanglement as witnessed by the mean quantum Fisher information
+density. By generalizing the manifold studied in [1, 2] to the many body case
+for spin 1, we connect the state space curvature in the vicinity of the ground
+state of the Heisenberg chain to the genuine multipartite entanglement. Our
+analysis demonstrates that the quantum critical points and symmetry protected
+topological (SPT) phase exhibit large state space curvature, while the
+separable phases are completely flat, offering insight into the physical
+interpretation of state space curvature. We further show that the entanglement
+in the SPT phase is enhanced by the presence of uniaxial anisotropy, and
+undiminished in the presence of uniform magnetic fields. The magnon condensate
+phase induced by large fields is shown to emanate from the Gaussian critical
+point, and exhibits massive multipartite entanglement over a robust region of
+the parameter space.",2209.05005v4
+2022-09-21,Interactive Entanglement in Hybrid Opto-magno-mechanics System,"We present a novel cavity opto-magno-mechanical hybrid system to generate
+entanglements among multiple quantum carriers, such as magnons, mechanical
+resonators, and cavity photons in both the optical and microwave domains. Two
+Yttrium iron garnet (YIG) spheres are embedded in two separate microwave
+cavities which are joined by a communal mechanical resonator. Because the
+microwave cavities are separate, the ferromagnetic resonate frequencies of two
+YIG spheres can be tuned independently, as well as the cavity frequencies. We
+show that entanglement can be achieved with experimentally reachable
+parameters. The entanglement is robust against environmental thermal noise,
+owing to the mechanical cooling process achieved by the optical cavity. The
+maximum entanglement among different carriers is achieved by optimizing the
+parameters of the system. The individual tunability of the separated cavities
+allows us to independently control the entanglement properties of different
+subsystems and establish quantum channels with different entanglement
+properties in one system. This work could provide promising applications in
+quantum metrology and quantum information tasks.",2209.10120v2
+2022-09-26,Scanning tunneling spectroscopy of Majorana zero modes in a Kitaev spin liquid,"We describe scanning tunneling spectroscopic signatures of Majorana zero
+modes (MZMs) in Kitaev spin liquids. The tunnel conductance is determined by
+the dynamical spin correlations of the spin liquid, which we compute exactly,
+and by spin-anisotropic cotunneling form factors. Near a $\mathbb{Z}_2$ vortex,
+the tunnel conductance has a staircase voltage dependence, where conductance
+steps arise from MZMs and (at higher voltages) from additional vortex
+configurations. By scanning the probe tip position, one can detect the vortex
+locations. Our analysis suggests that topological magnon bound states near
+defects or magnetic impurities generate spectroscopic signatures that are
+qualitatively different from those of MZMs.",2209.12930v2
+2022-09-30,Perspectives on Antiferromagnetic Spintronics,"Although the development of spintronic devices has advanced significantly
+over the past decade with the use of ferromagnetic materials, the extensive
+implementation of such devices has been limited by the notable drawbacks of
+these materials. Antiferromagnets claim to resolve many of these shortcomings
+leading to faster, smaller, more energy-efficient, and more robust electronics.
+Antiferromagnets exhibit many desirable properties including zero net
+magnetization, imperviousness to external magnetic fields, intrinsic
+high-frequency dynamics with a characteristic precession frequency on the order
+of terahertz (THz), and the ability to serve as passive exchange-bias materials
+in multiple magnetoresistance (MR)- based devices. In this Perspective article,
+we will discuss the fundamental physics of magnetic structures in
+antiferromagnets and their interactions with external stimuli such as spin
+current, voltage, and magnons. A discussion on the challenges lying ahead is
+also provided along with an outlook of future research directions of these
+systems.",2209.15187v2
+2022-10-03,Dynamics of mixed quantum-classical spin systems,"Mixed quantum-classical spin systems have been proposed in spin chain theory
+and, more recently, in magnon spintronics. However, current models of
+quantum-classical dynamics beyond mean-field approximations typically suffer
+from long-standing consistency issues, and, in some cases, invalidate
+Heisenberg's uncertainty principle. Here, we present a fully Hamiltonian theory
+of quantum-classical spin dynamics that appears to be the first to ensure an
+entire series of consistency properties, including positivity of both the
+classical and the quantum density, so that Heisenberg's principle is satisfied
+at all times. We show how this theory may connect to recent energy-balance
+considerations in measurement theory and we present its Poisson bracket
+structure explicitly. After focusing on the simpler case of a classical Bloch
+vector interacting with a quantum spin observable, we illustrate the extension
+of the model to systems with several spins, and restore the presence of orbital
+degrees of freedom.",2210.00988v2
+2022-10-12,"Spin Diffusion in Spin Glasses Require Two Magnetic Variables, $\vec{M}$ and $\vec{m}$","Experiment has established that spin-glasses can support a steady-state spin
+current $\vec{j}_{i}$. However, the accepted theory of spin glass dynamics
+permits oscillations but no steady-state spin current. Onsager's irreversible
+thermodynamics implies that the spin current is proportional to the gradient of
+a magnetization. We argue, however, that the magnon distribution function
+associated with the local equilibrium magnetization $\vec{M}$ cannot diffuse
+because it represents $10^{23}$ variables. We therefore invoke the
+non-equilibrium magnetization $\vec{m}$, which in spintronics is called the
+{\it spin accumulation}. Applying the theory of irreversible thermodynamics we
+indeed find that it predicts spin diffusion, and we consider other experimental
+consequences of the theory, including a wavelength-dependent coupling between
+the reactive and the diffusive degrees of freedom.",2210.05865v2
+2022-10-12,Observation of Vector Spin Seebeck Effect in a Noncollinear Antiferromagnet,"Spintronic phenomena to date have been established in magnets with collinear
+moments, where the spin injection through the spin Seebeck effect (SSE) is
+always along the out-of-plane direction. Here, we report the observation of a
+vector SSE in a noncollinear antiferromagnet (AF) LuFeO$_3$, where temperature
+gradient along the out-of-plane and also the in-plane directions can both
+inject a pure spin current and generate a voltage in the heavy metal via the
+inverse spin Hall effect (ISHE). We show that the thermovoltages are due to the
+magnetization from canted spins in LuFeO$_3$. Furthermore, in contrast to the
+challenges of generating, manipulating and detecting spin current in collinear
+AFs, the vector SSE in LuFeO$_3$ is readily viable in zero magnetic field and
+can be controlled by a small magnetic field of about 150 Oe at room
+temperature. The noncollinear AFs expand new realms for exploring spin
+phenomena and provide a new route to low-field antiferromagnetic spin
+caloritronics and magnonics.",2210.06602v1
+2022-10-14,Theory of edge states in graphene-like systems,"Systems that can be described with the same mathematical models that account
+for the properties of electrons in graphene are known as graphene-like systems.
+These include magnons, photons, polaritons, acoustic waves, and electrons in
+honeycomb lattices, either natural or artificial. All of them feature an
+outstanding property, the existence of states localized at the edges. We
+distinguish two classes of edge states depending on whether or not a
+topological band gap is present in the two-dimensional energy bands. We
+introduce the theory of edge states in terms of tight-binding models and
+discuss their properties, with an emphasis on the interplay between their
+one-way character and the topological nature of the bulk phase.",2210.07568v1
+2022-10-21,Optical spin-wave detection beyond the diffraction limit,"Spin waves are proposed as information carriers for next-generation computing
+devices because of their low power consumption. Moreover, their wave-like
+nature allows for novel computing paradigms. Conventional methods to detect
+spin waves are based either on electrical induction, limiting the downscaling
+and efficiency complicating eventual implementation, or on light scattering,
+where the minimum detectable spin-wave wavelength is set by the wavelength of
+the laser. In this Article we demonstrate magneto-optical detection of spin
+waves beyond the diffraction limit using a metallic grating that selectively
+absorbs laser light. Specifically, we demonstrate the detection of propagating
+spin waves with a wavelength of 700 nm using a diffraction-limited laser spot
+with a size of 10 $\mu$m in 20 nm thick Py strips. Additionally, we show that
+this grating is selective to the wavelength of the spin wave, providing
+wavevector-selective spin-wave detection. This should open up new avenues
+towards the integration of the burgeoning fields of photonics and magnonics,
+and aid in the optical detection of spin waves in the short-wavelength exchange
+regime for fundamental research.",2210.12016v1
+2022-11-02,Spin wave excitations in a nanowire spin-torque oscillator with perpendicular magnetic anisotropy,"Spin torque oscillators (STOs) are emerging microwave devices that can
+potentially be used in spin-logic devices and the next-generation high-speed
+computing architecture. Thanks to their non-linear nature, STOs are easily
+tunable by the magnetic field and the dc current. Spin Hall nano-oscillators
+(SHNOs) are promising types of STOs and most of the current studies focus on
+localized modes that can be easily excited. Here, we study using micromagnetic
+simulations, the nature of the spin-torque-induced excitations in nanowire
+devices made of perpendicular magnetic anisotropy (PMA) material. Our results
+showed that upon including PMA the excitation of localized and propagating spin
+wave modes is feasible. We study the nature of the mode excitations as a
+function of the PMA strength (\text{K}$_u$), and the current. Indeed, we
+estimate a critical value of \text{K}$_u$ to allow for the excitation of the
+propagating spin wave. We attribute this mode selectivity between localized and
+propagating modes to a switch in the sign of the nonlinearity of the system
+from negative to positive at a non-zero \text{K}$_u$ which is supported by
+analytical calculations. Our results provide deep insight into engineering
+reconfigurable microwave devices for future magnonic and computational
+applications.",2211.01078v1
+2022-11-09,Topological Superconductivity Mediated by Skyrmionic Magnons,"Topological superconductors are associated with the appearance of Majorana
+bound states, with promising applications in topologically protected quantum
+computing. In this Letter, we study a system where a skyrmion crystal is
+interfaced with a normal metal. Through interfacial exchange coupling, spin
+fluctuations in the skyrmion crystal mediate an effective electron-electron
+interaction in the normal metal. We study superconductivity within a
+weak-coupling approach and solve gap equations both close to the critical
+temperature and at zero temperature. Special features in the effective
+electron-electron interaction due to the noncolinearity of the magnetic ground
+state yield topological superconductivity at the interface.",2211.05129v2
+2022-11-11,Chiral Phonon Mediated High-Temperature Superconductivity,"Breaking down the traditional perception on phonons which are achiral, the
+recent discovery of chiral phonon carrying angular momentum provides possible
+ways to couple electron, photon, spin, magnon and exciton, etc. We
+theoretically proposed an electron-chiral phonon interaction with two-phonon
+process, in contrast to conventional electron-phonon interaction, and a kind of
+effective Hubbard U through exchanging two chiral phonons is proposed. Taking
+two-dimensional diatomic honeycomb lattice as an example, we found this
+repulsive Hubbard U mediated by chiral phonons induces unconventional and
+high-temperature superconductivity. Moreover, the numerical calculations show
+an inverse isotope effect which is consistent with experimental observations in
+high-$T_c$ superconductors. Our finding on electron-chiral phonon and the
+associated Cooper pair provides a path to understand the high-$T_c$
+superconductivity.",2211.06185v1
+2022-11-14,Spin wave diffraction model for perpendicularly magnetized films,"We present a near-field diffraction model for spin waves in perpendicularly
+magnetized films applicable in any geometries of excitation fields. This model
+relies on Kalinikos-Slavin formalism to express the dynamic susceptibility
+tensor in k-space, and calculate the diffraction patterns via inverse
+2D-Fourier transform of the response functions. We show an excellent
+quantitative agreement between our model and MuMax3 micro-magnetic simulations
+on two different geometries of antennas. Our method benchmarks spin wave
+diffraction in perpendicularly magnetized films, and is readily applicable for
+future designs of magnon beamforming and interferometric devices.",2211.07231v2
+2022-11-15,Self-selecting vapor growth of transition metal halide single crystals,"Transition metal halides can host a large variety of novel phenomena, such as
+magnetism in the monolayer limit, quantum spin liquid and spiral spin liquid
+states, and topological magnons and phonons. Sizeable high quality single
+crystals are necessary for investigations of magnetic and lattice excitations
+by, for example, inelastic neutron scattering. In this paper, we review a less
+well-known vapor transport technique, self-selecting vapor growth, and report
+our growths of transition metal halides using this technique. We report the
+growth and characterizations of sizable single crystals of RuCl$_3$, CrCl$_3$,
+Ru$_{1-x}$Cr$_x$Cl$_3$, and CrBr$_3$. In order to expedite the conversion of
+starting powder to single crystals, we modified the technique by cooling the
+growth ampoule through an appropriate temperature range. Our work shows that
+the self-selecting vapor transport technique can provide large single crystals
+of transition metal halides, demonstrating its potential for providing high
+quality single crystals of quantum materials.",2211.07806v1
+2022-11-20,Long-distance propagation of high-velocity antiferromagnetic spin waves,"We report on coherent propagation of antiferromagnetic (AFM) spin waves over
+a long distance ($\sim$10 $\mu$m) at room temperature in a canted AFM
+$\alpha$-Fe$_2$O$_3$ with the Dzyaloshinskii-Moriya interaction (DMI).
+Unprecedented high group velocities (up to 22.5 km/s) are characterized by
+microwave transmission using all-electrical spin wave spectroscopy. We derive
+analytically AFM spin-wave dispersion in the presence of the DMI which accounts
+for our experimental results. The AFM spin waves excited by nanometric coplanar
+waveguides with large wavevectors enter the exchange regime and follow a
+quasi-linear dispersion relation. Fitting of experimental data with our
+theoretical model yields an AFM exchange stiffness length of 1.7 angstrom. Our
+results provide key insights on AFM spin dynamics and demonstrate high-speed
+functionality for AFM magnonics.",2211.10989v1
+2022-11-20,Spin-wave spectra in antidot lattice with inhomogeneous perpendicular magnetocrystalline anisotropy,"Magnonic crystals are structures with periodically varied magnetic properties
+that are used to control collective spin-wave excitations. With micromagnetic
+simulations, we study spin-wave spectra in a 2D antidot lattice based on a
+multilayered thin film with perpendicular magnetic anisotropy (PMA). We show
+that the modification of the PMA near the antidot edges introduces interesting
+modifications to the spin-wave spectra, even in a fully saturated state. In
+particular, the spectra split in two types of excitations, bulk modes with
+amplitude concentrated in a homogeneous part of antidot lattice, and edge modes
+with an amplitude localized in the rims of reduced PMA at the antidot edges.
+Their dependence on the geometrical or material parameters is distinct but at
+resonance conditions fulfilled, we found strong hybridization between bulk and
+radial edge modes. Interestingly, the hybridization between the fundamental
+modes in bulk and rim is of magnetostatic origin but the exchange interactions
+determine the coupling between higher-order radial rim modes and the
+fundamental bulk mode of the antidot lattice.",2211.11002v1
+2022-11-25,Microscopic parameters of the van der Waals CrSBr antiferromagnet from microwave absorption experiments,"Microwave absorption experiments employing a phase-sensitive external
+resistive detection are performed for a topical van der Waals antiferromagnet
+CrSBr. The field dependence of two resonance modes is measured in an applied
+field parallel to the three principal crystallographic directions, revealing
+anisotropies and magnetic transitions in this material. To account for the
+observed results, we formulate a microscopic spin model with a bi-axial
+single-ion anisotropy and inter-plane exchange. Theoretical calculations give
+an excellent description of full magnon spectra enabling us to precisely
+determine microscopic interaction parameters for CrSBr.",2211.14117v1
+2022-11-25,Asymmetric Faraday Effect in a Magnetophotonic Crystal,"It is widely known that the magneto-optical Faraday effect is linear in
+magnetization and therefore the Faraday angles for the states with opposite
+magnetizations are of opposite sign but equal in modulus. Here we
+experimentally study propagation of light through a one-dimensional all-garnet
+magnetophotonic crystal to demonstrate an asymmetric Faraday effect (AFE) for
+which Faraday angles for opposite magnetic states differ not only in sign but
+in the absolute value as well. AFE appears in the vicinity of the cavity
+resonance for an oblique incidence of light which plane of polarization is
+inclined to the incidence plane. Under proper incidence and polarization angles
+the magnitude of AFE could be very large reaching 30% of the absolute value of
+the Faraday effect. The effect originates from the difference in Q-factors for
+p- and s- polarized cavity modes that breaks the symmetry between the two
+opposite directions of polarization rotation. The discovered AFE is of prime
+importance for nanoscale magnonics and optomagnetism.",2211.14355v2
+2022-12-02,Cavity-mediated coupling of antiferromagnetic spin waves,"Coupling of space-separated oscillators is interesting for quantum and
+communication technologies. In this work, it is shown that two
+antiferromagnetic oscillators placed inside an electromagnetic cavity couple
+cooperatively to its terahertz modes and, in effect, hybridized
+magnon-polariton modes are formed. This is supported by a systematic study of
+reflection spectra from two parallel-plane slabs of hematite
+($\alpha$-Fe$_2$O$_3$), measured as a function of their temperatures and
+separation distance, and modeled theoretically. The mediating cavity was formed
+by the crystals themselves and the experiment was performed in a practical
+distance range of a few millimetres and above room temperature. Cavity-mediated
+coupling allows for engineering of complex resonators controlled by their
+geometry and by sharing properties of their components.",2212.01129v1
+2022-12-06,Spin wavepacket propagation in quasi-2D antiferromagnets,"Antiferromagnets are attractive platforms for the propagation of information
+via spin waves, offering advantages over ferromagnets in speed of response and
+immunity to external fields. A recent study of the quasi-2D antiferromagnet
+CrSBr reported that spin wavepackets propagate with group velocities that are
+orders of magnitude higher than expected from the magnon dispersion obtained by
+inelastic neutron scattering [1,2]. Here we show that the anomalous magnitude
+and anisotropy of the group velocity, v_g, are naturally explained by
+considering the long-range magnetic dipole-dipole interaction. We also
+demonstrate that v_g can be tuned over orders of magnitude by applying an
+external magnetic field or varying the sample thickness. Beyond spin wavepacket
+propagation, the dipolar interaction creates the possibility of non-equilibrium
+Bose-Einstein condensation in antiferromagnets, previously thought to be a
+property unique to ferromagnets.",2212.03261v1
+2022-12-13,Non-local correlation effects due to virtual spin-flip processes in itinerant electron ferromagnets,"We present an ab initio method for eletcronic structure calculations, which
+accounts for the interaction of electrons and magnons in ferromagnets. While it
+is based on a many body perturbation theory we approximate numerically complex
+quantities with quantities from time dependent density functional theory. This
+results in a simple and affordable algorithm which allows us to consider more
+complex materials than those usually studied in this context ($3d$
+ferromagnets) while still being able to account for the non-locality of the
+self energy. Furthermore, our approach allows for a relatively simple way to
+incorporate self-consistency. Our results are in a good agreement with
+experimental and theoretical findings for iron and nickel. Especially the
+experimental exchange splitting of nickel is predicted accurately within our
+theory. Additionally, we study the halfmetallic ferromagnet NiMnSb concerning
+its non-qusiparticle states appearing in the bandgap due to spin-flip
+excitations.",2212.06420v3
+2022-12-15,Giant spin ensembles in waveguide magnonics,"The dipole approximation is usually employed to describe light-matter
+interactions under ordinary conditions. With the development of artificial
+atomic systems, `giant atom' physics is possible, where the scale of atoms is
+comparable to or even greater than the wavelength of the light they interact
+with, and the dipole approximation is no longer valid. It reveals interesting
+physics impossible in small atoms and may offer useful applications. Here, we
+experimentally demonstrate the giant spin ensemble (GSE), where a ferromagnetic
+spin ensemble interacts twice with the meandering waveguide, and the coupling
+strength between them can be continuously tuned from finite (coupled) to zero
+(decoupled) by varying the frequency. In the nested configuration, we
+investigate the collective behavior of two GSEs and find extraordinary
+phenomena that cannot be observed in conventional systems. Our experiment
+offers a new platform for `giant atom' physics.",2212.07605v1
+2022-12-24,Directionality between driven-dissipative resonators,"The notion of nonreciprocity, in essence when going forwards is different
+from going backwards, emerges in all branches of physics from cosmology to
+electromagnetism. Intriguingly, the breakdown of reciprocity is typically
+associated with extraordinary phenomena, which may be readily capitalized on in
+the design of (for example) nontrivial electromagnetic devices when Lorentz
+reciprocity is broken. However, in order to enable the exploitation of
+nonreciprocal-like effects in the next generation of quantum technologies,
+basic quantum optical theories are required. Here we present a versatile model
+describing a pair of driven-dissipative quantum resonators, where the relative
+phase difference between the coherent and incoherent couplings induces an
+asymmetry. The interplay between the diverse dissipative landscape - which
+encompasses both intrinsic losses and dissipative couplings - and the coherent
+interactions leads to some remarkable consequences including highly directional
+(or even one-way) energy transport. Our work proffers the tantalizing prospect
+of observing dissipation-induced quantum directionality in areas like photonics
+or cavity magnonics (spin waves), which may aid the design of unconventional
+nanoscopic devices.",2212.12777v1
+2022-12-31,An implementation of the density functional perturbation theory in the PAW framework,"Quantifying materials' dynamical responses to external electromagnetic fields
+is central to understanding their physical properties. Here we present an
+implementation of the density functional perturbation theory for the
+computation of linear susceptibilities using the projector augmented-wave
+method. The Sternheimer equations are solved self-consistently through a nested
+iterative procedure to compute the first-order wavefunctions, from which the
+linear susceptibilities are obtained. As a demonstration, we compute the spin
+wave spectral functions of two magnetic metals. The computed magnon spectra for
+half-metallic CrO$_2$ and a Heusler intermetallic Cu$_2$MnAl show gapless
+Goldstone modes when spin rotation symmetry is preserved and display reasonable
+agreement with available experimental data. The Landau damping is computed to
+be small in CrO$_2$, but significant in Cu$_2$MnAl producing an asymmetric
+Lorentzian spectral lineshape. The access to linear susceptibilities as well as
+first-order wavefunctions offers a range of novel possibilities in quantitative
+understanding of materials' electronic properties from \textit{ab initio}
+methods.",2301.00143v1
+2023-01-03,"Uncovering the role of the light-induced reduction of the inter-atomic exchange in the ultrafast demagnetization of Fe, Co, and Ni","Time resolved measurements of the linear magneto-optical Kerr rotation reveal
+that, in the {\it 3d} ferromagnets Fe, Co and Ni, the amplitude of the
+demagnetization increases linearly with the fluence of the light. We
+rationalize this phenomenon as being linearly driven by the increase in
+temperature, the electron-phonon and electron-magnon scattering, and a
+reduction of the inter-atomic exchange. The amplitude of the latter phenomenon,
+which until the present study has been widely overlooked, is obtained through
+\textit{ab initio} density functional theory calculations, and is argued to be
+the principal source of demagnetization in Ni and Co, while still contributing
+largely in Fe.",2301.01055v3
+2023-01-05,Control of magnetic response in curved stripes by tailoring cross-section,"Curved magnetic architectures are key enablers of the prospective magnetic
+devices with respect to size, functionality and speed. By exploring
+geometry-governed magnetic interactions, curvilinear magnetism offers a number
+of intriguing effects in curved magnetic wires and curved magnetic films. The
+applicability of the current micromagnetic theory requires that the sample has
+constant width and thickness, which does not correspond in many cases to
+specificity of experimental sample preparation. Here, we put forth a
+self-consistent micromagnetic framework of curvilinear magnetism of nanowires
+and narrow stripes with spatially inhomogeneous cross-section. The influence of
+the varying cross-section is exploited and illustrated by an example of the
+simplest topological texture, which is a transversal head-to-head
+(tail-to-tail) domain wall. The cross-section gradient becomes a source of
+domain wall pinning which competes the curvature gradient. Eigenfrequencies of
+the domain wall free oscillations at the pinning potential are determined by
+both curvature and cross-section gradients. Prospects for curvilinear magnonics
+and spintronics are discussed.",2301.02096v2
+2023-01-06,Goldstone bosons and fluctuating hydrodynamics with dipole and momentum conservation,"We develop a Schwinger-Keldysh effective field theory describing the
+hydrodynamics of a fluid with conserved charge and dipole moments, together
+with conserved momentum. The resulting hydrodynamic modes are highly unusual,
+including sound waves with quadratic (magnon-like) dispersion relation and
+subdiffusive decay rate. Hydrodynamics itself is unstable below four spatial
+dimensions. We show that the momentum density is, at leading order, the
+Goldstone boson for a dipole symmetry which appears spontaneously broken at
+finite charge density. Unlike an ordinary fluid, the presence or absence of
+energy conservation qualitatively changes the decay rates of the hydrodynamic
+modes. This effective field theory naturally couples to curved spacetime and
+background gauge fields; in the flat spacetime limit, we reproduce the ""mixed
+rank tensor fields"" previously coupled to fracton matter.",2301.02680v4
+2023-01-16,Role of disorder and strong 5$d$ electron correlation in the electronic structure of Sr2TiIrO6,"Transport and magnetic properties along with high resolution valence band
+photoemission study of disordered double perovskite Sr$_{2}$TiIrO$_{6}$ has
+been investigated. Insulator to insulator transition along with a magnetic
+transition concurrently occurs at 240 K. Comparison of valence band
+photoemission with band structure calculations suggests that the spin orbit
+coupling as well as electron correlation are necessary to capture the line
+shape and width of the Ir 5$d$ band. Room temperature valence band
+photoemission spectra show negligibly small intensity at Fermi energy, $E_{F}$.
+Fermi cut-off is observed at low temperatures employing high resolution. The
+spectral density of states at room temperature exhibits $|E-E_{F}|^{2}$ energy
+dependence signifying the role of electron-electron interaction. This energy
+dependence changes to $|E-E_{F}|^{3/2}$ below the magnetic transition
+evidencing the role of electron-magnon coupling in magnetically ordered state.
+The evolution of pseudogap ($\pm$12 meV) explains the sudden increase in
+resistivity ($\rho$) below 50 K in this disordered system. The temperature
+dependent spectral density of states at $E_{F}$ exhibiting $T^{1/2}$ behaviour
+verifies Altshuler-Aronov theory for correlated disordered systems.",2301.06275v1
+2023-01-18,"Perspectives on high-frequency nanomechanics, nanoacoustics, and nanophononics","Nanomechanics, nanoacoustics, and nanophononics refer to the engineering of
+acoustic phonons and elastic waves at the nanoscale and their interactions with
+other excitations such as magnons, electrons, and photons. This engineering
+enables the manipulation and control of solid-state properties that depend on
+the relative positions of atoms in a lattice. The access to advanced
+nanofabrication and novel characterization techniques enabled a fast
+development of the fields over the last decade. The applications of
+nanophononics include thermal management, ultrafast data processing,
+simulation, sensing, and the development of quantum technologies. In this
+review, we cover some of the milestones and breakthroughs, and identify
+promising pathways of these emerging fields.",2301.07451v1
+2023-01-18,Cavity-controlled magneto-optical properties of a strongly coupled van der Waals magnet,"Controlling the properties of quantum materials with light is of fundamental
+and technological importance. While high-power lasers may achieve this goal,
+more practical strategies aim to exploit the strong coupling of light and
+matter in optical cavities, which has recently been shown to affect elemental
+physical phenomena, like superconductivity, phase transitions, and topological
+protection. Here we report the capacity of strong light-matter coupling to
+modify and control the magneto-optical properties of magnets. Tuning the
+hybridization of magnetic excitons and cavity photons allows us to realize
+distinct optical signatures of external magnetic fields and magnons in the
+archetypal van der Waals magnetic semiconductor CrSBr. These results highlight
+novel directions for cavity-controlled magneto-optics and the manipulation of
+quantum material properties by strong light-matter coupling.",2301.07593v1
+2023-02-02,Designing layered 2D skyrmion lattices in moiré magnetic hetero-structures,"Skyrmions are promising for the next generation of spintronic and magnonic
+devices, but their zero-field stability and controlled nucleation through
+chiral interactions remain challenging. In this theoretical study, we explore
+the potential of moir\'e magnetic heterostructures to generate ordered skyrmion
+lattices from the stacking-dependent magnetism in 2D magnets. We consider
+heterostructures formed by twisting ultrathin CrBr_3 films on top of CrI_3
+substrates, assuming a moderate interfacial Dzyaloshinskii-Moriya interaction.
+At large moir\'e periodicity and appropriate substrate thickness, a moir\'e
+skyrmion lattice emerges in the interfacial CrBr_3 layer due to the weaker
+exchange interactions in CrBr_3 compared to CrI_3. This lattice is then
+projected to the remaining layers of the CrBr_3 film via emergent chiral
+interlayer fields. By varying the pristine stacking configurations within the
+ultrathin CrBr_3 film, we realize layered ferromagnetic and antiferromagnetic
+skyrmion lattices without the need for a permanent magnetic field. Our findings
+suggest the possibility of creating colorful skyrmion lattices in moir\'e
+magnetic heterostructures, enabling further exploration of their fundamental
+properties and technological relevance.",2302.01074v2
+2023-02-04,"Calculating spin-lattice interactions in ferro- and antiferromagnets: the role of symmetry, dimension and frustration","Recently, the interplay between spin and lattice degrees of freedom has
+gained a lot of attention due to its importance for various fundamental
+phenomena as well as for spintronic and magnonic applications. Examples are
+ultrafast angular momentum transfer between the spin and lattice subsystems
+during ultrafast demagnetization, frustration driven by structural distortions
+in transition metal oxides, or in acoustically driven spin-wave resonances. In
+this work, we provide a systematic analysis of spin-lattice interactions for
+ferro- and antiferromagnetic materials and focus on the role of lattice
+symmetries and dimensions, magnetic order, and the relevance of spin-lattice
+interactions for angular momentum transfer as well as magnetic frustration. For
+this purpose, we use a recently developed scheme which allows an efficient
+calculation of spin-lattice interaction tensors from first principles. In
+addition to that, we provide a more accurate and self consistent scheme to
+calculate ab initio spin lattice interactions by using embedded clusters which
+allows to benchmark the performance of the scheme introduced previously.",2302.02066v2
+2023-02-06,Global solutions of the Landau--Lifshitz--Baryakhtar equation,"The Landau--Lifshitz--Baryakhtar (LLBar) equation is a generalisation of the
+Landau--Lifshitz--Gilbert and the Landau--Lifshitz--Bloch equations which takes
+into account contributions from nonlocal damping and is valid at moderate
+temperature below the Curie temperature. Therefore, it is used to explain some
+discrepancies between the experimental observations and the known theories in
+various problems on magnonics and magnetic domain-wall dynamics. In this paper,
+the existence and uniqueness of global weak, strong, and regular solutions to
+LLBar equation are proven. H\""older continuity of the solution is also
+discussed.",2302.02556v3
+2023-02-07,Control of vortex chirality in a symmetric ferromagnetic ring using ferromagnetic nanoelement,"Controlling the vortex chirality in ferromagnetic nanodots and nanorings has
+been a topic of investigation for the last few years. Many control methods have
+been proposed and it has been found that the control is related to the breaking
+of the circular symmetry. In this paper, we present a theoretical study
+demonstrating the control of chirality in ferromagnetic nanoring without
+directly breaking its symmetry, but instead by placing elongated ferromagnetic
+nanoelement inside the ring, Here, the stray magnetostatic field exerted by the
+asymmetrically placed nanoelement determines the movement of the domain walls
+upon remagnetization of the nanoring and the resulting chirality in the
+remanence. This approach allows the chirality of the vortex state to be
+controlled and also promises its control in a dense array of nanorings, thus
+suitable for spintronic and magnonic applications.",2302.03626v1
+2023-02-08,Anisotropic skyrmion mass induced by surrounding conduction electrons: A Schwinger-Keldysh field theory approach,"The current-driven motion of magnetic skyrmions, as topologically protected
+winding vector fields of local magnetization, has attracted considerable
+attention due to both fundamental interest in the dynamics of topological
+solitons, and potential spintronic applications. While widely-used Thiele
+equation with zero skyrmion mass captures its rigid motion under the assumption
+of preserved skyrmion shape, experiments on realistic skyrmions find deviation
+due to inertial mass with numerous attempts to account for it by invoking
+internal skyrmion dynamics, geometry of the nanowire, and interaction with
+magnons or phonons. However, experimentally observed skyrmion mass is often
+much larger than predicted by these theories. In this Letter, we employ
+Schwinger-Keldysh field-theoretical approach to study conduction electrons
+interacting with localized magnetic moments comprising a skyrmion to obtain a
+stochastic differential equation of its motion. By analyzing its time-retarded
+damping kernel, we extract an anisotropic mass governed by conduction electrons
+and demonstrate its substantial effect on the current-driven skyrmion motion,
+even in the absence of any skyrmion deformation.",2302.04220v1
+2023-02-06,Chiral and flat-band magnetic cluster excitations in a ferromagnetic kagome metal,"TbMn6Sn6 is a metallic ferrimagnet that displays signatures of band topology
+arising from a combination of uniaxial ferromagnetism and spin-orbit coupling
+within its Mn kagome layers. Whereas the low energy magnetic excitations can be
+described as collective spin waves using a local moment Heisenberg model,
+sharply defined optical and flat-band collective magnon modes are not observed.
+In their place, we find overdamped chiral and flat-band spin correlations that
+are localized to hexagonal plaquettes within the kagome layer.",2302.04846v1
+2023-02-18,Magnetoresistance signature of two-dimensional electronic states in Co$_3$Sn$_2$S$_2$,"Two-dimensional (2D) Dirac bands and flat bands are characteristics of a
+kagome lattice. However, experimental studies on their electrical transport are
+few, because three-dimensional (3D) bulk bands of kagome materials, consisting
+of stacked 2D kagome layers, dominate the transport. We report a
+magnetoresistance (MR) study of a kagome material, Co$_3$Sn$_2$S$_2$. Based on
+analysis of the temperature, magnetic field, and field angle dependence of the
+resistivity, we obtain a complete anatomy of MR. Besides a magnon MR, a
+chirality-dependent MR, and a chiral-anomaly-induced MR, the most intriguing
+feature is an orbital MR that scales only with the out-of-plane field, which
+strongly indicates its 2D nature. We attribute it to the Dirac band of the
+kagome lattice.",2302.09229v1
+2023-02-21,Amplification and frequency conversion of spin waves using acoustic waves,"We numerically study the acoustic parametric amplification of spin waves
+using surface acoustic waves (SAW) in a magnetic thin film. First, we
+illustrate how the process of parametric spin-wave generation using short-waved
+SAWs with a fixed frequency allows to tune frequencies of the generated spin
+waves by the applied magnetic field. We further present the amplification of
+microwave driven spin waves using this method. The decay length and the
+amplitude of the driven spin waves can be amplified up to approximately 2.5 and
+10 times compared to the reference signal, respectively. More importantly, the
+proposed design can be used as a frequency converter, in which a low (high)
+frequency spin-wave mode stimulates the excitation of a high (low) frequency
+mode. Our results pave the way in designing highly flexible and efficient
+hybrid magnonic device architectures for microwave data transport and
+processing.",2302.10614v1
+2023-02-21,Electron transport and scattering mechanisms in ferromagnetic monolayer Fe$_3$GeTe$_2$,"We study intrinsic charge-carrier scattering mechanisms and determine their
+contribution to the transport properties of the two-dimensional ferromagnet
+Fe$_3$GeTe$_2$. We use state-of-the-art first-principles calculations combined
+with the model approaches to elucidate the role of the electron-phonon and
+electron-magnon interactions in the electronic transport. Our findings show
+that the charge carrier scattering in Fe$_3$GeTe$_2$ is dominated by the
+electron-phonon interaction, while the role of magnetic excitations is
+marginal. At the same time, the magnetic ordering is shown to effect
+essentially on the electron-phonon coupling and its temperature dependence.
+This leads to a sublinear temperature dependence of the electrical resistivity
+near the Curie temperature, which is in line with experimental observations.
+The room temperature resistivity is estimated to be $\sim$35 $\mu \Omega
+\cdot$cm which may be considered as an intrinsic limit for monolayer
+Fe$_3$GeTe$_2$.",2302.10974v1
+2023-02-22,A spin-energy operator inequality for Heisenberg-coupled qubits,"We slightly strengthen an operator inequality identified by Correggi et al.
+that lower bounds the energy of a Heisenberg-coupled graph of $s=1/2$ spins
+using the total spin. In particular, $\Delta H \ge C \Delta\vec{S}^2$ for a
+graph-dependent constant $C$, where $\Delta H$ is the energy above the ground
+state and $\Delta\vec{S}^2$ is the amount by which the square of the total spin
+$\vec{S} = \sum_i \vec{\sigma}_i/2$ falls below its maximum possible value. We
+obtain explicit constants in the special case of a cubic lattice. We briefly
+discuss the interpretation of this bound in terms of low-energy, approximately
+non-interacting magnons in spin wave theory and contrast it with another
+inequality found by B\""arwinkel et al.",2302.11267v1
+2023-03-09,Antiferromagnetic resonances in superconductor-ferromagnet multilayers,"In this work, we study magnetization dynamics in superconductor-ferromagnet
+(S-F) thin-film multilayer. Theoretical considerations supported by the
+broad-band ferromagnetic resonance spectroscopy reveal development of acoustic
+and optic resonance modes in S-F multilayers at significantly higher
+frequencies in comparison to the Kittel mode of individual F-layers. These
+modes are formed due to antiferromagnetic-like interaction between F-layers via
+shared circulating superconducting currents in S-layers. The gap between
+resonance modes is determined by the thickness and superconducting penetration
+depth in S-layers. Overall, rich spectrum of S-F multilayers and its tunability
+opens wide prospects for application of these multialyers in magnonics as well
+as in various superconducting hybrid systems.",2303.05175v2
+2023-03-09,Spin-order-dependent magneto-elastic coupling in two dimensional antiferromagnetic MnPSe$_3$ observed through Raman spectroscopy,"Layered antiferromagnetic materials have emerged as a novel subset of the
+two-dimensional family providing a highly accessible regime with prospects for
+layer-number-dependent magnetism. Furthermore, transition metal phosphorous
+trichalcogenides, MPX3 (M = transition metal; X = chalcogen) provide a platform
+for investigating fundamental interactions between magnetic and lattice degrees
+of freedom providing new insights for developing fields of spintronics and
+magnonics. Here, we use a combination of temperature dependent Raman
+spectroscopy and density functional theory to explore
+magnetic-ordering-dependent interactions between the manganese spin degree of
+freedom and lattice vibrations of the non-magnetic sub-lattice via a
+Kramers-Anderson super-exchange pathway in both bulk, and few-layer, manganese
+phosphorous triselenide (MnPSe$_3$). We observe a nonlinear temperature
+dependent shift of phonon modes predominantly associated with the non-magnetic
+sub-lattice, revealing their non-trivial spin-phonon coupling below the
+N{\'e}el temperature at 74 K, allowing us to extract mode-specific spin-phonon
+coupling constants.",2303.05554v2
+2023-03-10,Dynamic Exchange Coupling between Magnets Mediated by Attenuating Elastic Waves,"Coupling between spatially separated magnets can be mediated by excitations
+such as photons and phonons, which can be characterized as coherent coupling
+and dissipative coupling with real and imaginary coupling rate. We
+theoretically predict the existence of dynamic exchange coupling in a closed
+magneto-elastic system mediated by attenuating elastic waves and whose coupling
+rate is complex in general, leading to alternating repulsive or attractive
+spectrum depending on thickness of the elastic media. The presence of dynamic
+exchange coupling and its competition with coherent coupling are numerically
+verified according to the generalized Hooke's law in magneto-elastic systems.
+The predicted mechanism provides a new strategy to synchronize precessing
+magnets as well as other excitations over long distance and pave the way for
+non-Hermitian engineering of collective modes in hybrid magnonics, phononics
+and photonics.",2303.05778v1
+2023-03-10,Ultrafast magnetization reversal in ferromagnetic spin-valves: an s-d model perspective,"We present an extension to simple s-d models, aiming at simulating ultrafast
+magnetization dynamics and spin transport in metallic heterostructures. In
+particular, we consider an alternative spin dissipation channel due to a finite
+exchange splitting of the s band. From this theory, we show three different
+mechanisms governing the dynamics of spin accumulation. On top of the already
+widely discussed ""-dM/dt"" electron-magnon mechanism, we study the role of a
+dynamic change of exchange splitting (of conduction electrons) as well as the
+rotation of spins reflected at an interface with a ferromagnet. Finally, we use
+the presented theory to explain the recent observation of subpicosecond
+reversal of a ferromagnet in rare-earth free spin-valves. Our conclusion agrees
+with the one of reference [1] favoring magnetization reversal due to the
+rotation of the spin polarization of a reflected spin current.",2303.05907v1
+2023-03-13,Coherent THz Spin Dynamics in Antiferromagnets Beyond the Approximation of the Néel vector,"Controlled generation of coherent spin waves with highest possible
+frequencies and the shortest possible wavelengths is a cornerstone of
+spintronics and magnonics. Here, using the Heisenberg antiferromagnet RbMF$_3$,
+we demonstrate that laser-induced THz spin dynamics corresponding to pairs of
+mutually coherent counter propagating spin waves with the wavevectors up to the
+edge of the Brillouin zone cannot be understood in terms of magnetization and
+antiferromagnetic (N\'eel) vectors, conventionally used to describe spin waves.
+Instead, we propose to model such spin dynamics using the spin correlation
+function. We derive a quantum-mechanical equation of motion for the latter and
+emphasize that, unlike the magnetization and antiferromagnetic vectors the spin
+correlations in antiferromagnets do not exhibit inertia.",2303.06996v4
+2023-03-24,Shannon entropy in quasiparticle states of quantum chains,"In this paper, we investigate the Shannon entropy of the total system and its
+subsystems, as well as the subsystem Shannon mutual information, in
+quasiparticle excited states of free bosonic and fermionic chains and the
+ferromagnetic phase of the spin-1/2 XXX chain. Our focus is on single-particle
+and double-particle states, and we derive various analytical formulas for free
+bosonic and fermionic chains in the scaling limit. These formulas are also
+applicable to magnon excited states in the XXX chain under certain conditions.
+We discover that, unlike entanglement entropy, Shannon entropy does not
+separate when two quasiparticles have a large momentum difference. Moreover, in
+the large momentum difference limit, we obtain universal results for quantum
+spin chains that cannot be explained by a semiclassical picture of
+quasiparticles.",2303.14132v1
+2023-04-03,Spin waves in layered antiferromagnets with honeycomb structure,"We develop a description of spin waves in a $3D$ quantum $XY$ antiferromagnet
+(AFM) in terms of macroscopic variables, magnetization and N\'eel vector
+densities. We consider a layered AFM with spins located on the honeycomb
+lattice. In the discussed system, the spectrum of spin waves consists of four
+modes, all well captured by our macroscopic description. The gapless mode of
+the spin waves, i.e., magnons, is described by a system of equations, which has
+a structure general for the Goldstone mode in AFMs. We demonstrate that the
+parameters in the spin Hamiltonian can be evaluated by fitting the experimental
+data with the results obtained for the four modes using the macroscopic
+variable approach. The description of AFM in terms of macroscopic variables can
+be easily extended to the case when the lattice of the magnetic substance is
+deformed by an external strain or acoustic wave.",2304.00700v1
+2023-04-04,Unidirectional Seebeck effect from Rashba spin-orbit coupling on the subsurface of Ge(111),"A new nonlinear magnetothermal effect, namely unidirectional Seebeck
+effect(USE), has been recently reported in magnetic/nonmagnetic topological
+insulator (TI) heterostructure and is ascribed to the asymmetry magnon
+scattering. Here, we show a new mechanism to generate USE in the Rashba two
+dimensional electron gas (2DEG), in which the magnetism or magnetic order is
+completely absent. It's found that the USE has a quantum origin from the
+spin-momentum locking generated from Rashba spin-orbit coupling. We find that
+the USE exhibits a sine dependence on the orientation of the magnetic field
+with respect to the direction of the temperature gradient and is dominant from
+the states above the Lifshitz point. The USE in the semiconductor Ge(111)
+subsurface states has been theoretically and systematically investigated.",2304.01683v1
+2023-04-04,Geometrical torque on magnetic moments coupled to a correlated antiferromagnet,"The geometrical spin torque mediates an indirect interaction of magnetic
+moments, which are weakly exchange coupled to a system of itinerant electrons.
+It originates from a finite spin-Berry curvature and leads to a non-Hamiltonian
+magnetic-moment dynamics. We demonstrate that there is an unprecedentedly
+strong geometrical spin torque in case of an electron system, where
+correlations cause antiferromagnetic long-range order. The key observation is
+that the anomalous torque is strongly boosted by low-energy magnon modes
+emerging in the two-electron spin-excitation spectrum due to spontaneous
+breaking of SU(2) spin-rotation symmetry. As long as single-electron
+excitations are gapped out, the effect is largely universal, i.e., essentially
+independent of the details of the electronic structure, but decisively
+dependent on the lattice dimension and spatial and spin anisotropies. Analogous
+to the reasoning that leads to the Mermin-Wagner theorem, there is a lower
+critical dimension at and below which the spin-Berry curvature diverges.",2304.02071v1
+2023-04-05,High-energy spin waves in the spin-1 square-lattice antiferromagnet La$_2$NiO$_4$,"Inelastic neutron scattering is used to study the magnetic excitations of the
+$S=1$ square-lattice antiferromagnet La$_2$NiO$_4$. We find that the spin waves
+cannot be described by a simple classical (harmonic) Heisenberg model with only
+nearest-neighbor interactions. The spin-wave dispersion measured along the
+antiferromagnetic Brillouin-zone boundary shows a minimum energy at the
+$(1/2,0)$ position as is observed in some $S=1/2$ square-lattice
+antiferromagnets. Thus, our results suggest that the quantum dispersion
+renormalization effects or longer-range exchange interactions observed in
+cuprates and other $S=1/2$ square-lattice antiferromagnets are also present in
+La$_2$NiO$_4$. We also find that the overall intensity of the spin-wave
+excitations is suppressed relative to linear spin-wave theory indicating that
+covalency is important. Two-magnon scattering is also observed.",2304.02546v2
+2023-04-06,Embedding Integrable Superspin Chain in String Theory,"Using results on topological line defects of 4D Chern-Simons theory and the
+algebra/cycle homology correspondence in complex surfaces $\mathcal{S}$ with
+ADE singularities, we study the graded properties of the $sl(m|n)$ chain and
+its embedding in string theory. Because of the $\mathbb{Z}_{2}$-grading of $
+sl(m|n)$, we show that the $\left( m+n\right) !/m!n!$ varieties of superspin
+chains with underlying super geometries have different cycle homologies. We
+investigate the algebraic and homological features of these integrable quantum
+chains and give a link between graded 2-cycles and genus-g Rieman surfaces
+$\Sigma _{g}$. Moreover, using homology language, we yield the brane
+realisation of the $sl(m|n)$ chain in type IIA string and its uplift to
+M-theory. Other \textrm{aspects} like graded complex surfaces with $sl(m|n)$
+singularity as well as super magnons are also described.",2304.03152v1
+2023-04-12,Machine-Learning Recognition of Dzyaloshinskii-Moriya Interaction from Magnetometry,"The Dzyaloshinskii-Moriya interaction (DMI), which is the antisymmetric part
+of the exchange interaction between neighboring local spins, winds the spin
+manifold and can stabilize non-trivial topological spin textures. Since
+topology is a robust information carrier, characterization techniques that can
+extract the DMI magnitude are important for the discovery and optimization of
+spintronic materials. Existing experimental techniques for quantitative
+determination of DMI, such as high-resolution magnetic imaging of spin textures
+and measurement of magnon or transport properties, are time consuming and
+require specialized instrumentation. Here we show that a convolutional neural
+network can extract the DMI magnitude from minor hysteresis loops, or magnetic
+""fingerprints"" of a material. These hysteresis loops are readily available by
+conventional magnetometry measurements. This provides a convenient tool to
+investigate topological spin textures for next-generation information
+processing.",2304.05905v2
+2023-04-13,Finite Temperature Dynamics of Spin Solitons with Applications in Thermocouples and Refrigerators,"The exploitation of spin Berry phases to generate emergent fields for
+producing miniaturized and high-quality inductors has enjoyed considerable
+popularity among proponents of quantum technologies [Nature 586, 202 (2020)}].
+Inspired by this breakthrough, we extend its mechanism to spin thermoelectrics
+by probing responses of ferrimagnetic domain walls (DWs) to thermal gradients.
+Similarly, voltages here stem from DW-spin collective motion, in contrast to
+normal electron transport phenomena. We further develop finite-temperature
+dynamics to investigate thermoelectric figures of merit and attribute
+corresponding quantum superiority to ultrafast spin evolution of ferrimagnetism
+with tunable non-Abelian phases. We propose a more likely cause of DW motion
+towards hot or cold regions (contrary to conclusions of previous reports) and
+verify existence of efficient magnon-momentum transfers. These findings deepen
+our understanding of heat-driven DW kinetics and suggest profitable new
+directions in an emerging realm of spincaloritronics.",2304.06608v1
+2023-04-26,Rapid-prototyping of microscopic thermal landscapes in Brillouin light scattering spectroscopy,"Since temperature and its spatial and temporal variations affect a wide range
+of physical properties of material systems, they can be used to create
+reconfigurable spatial structures of various types in physical and biological
+objects. This paper presents an experimental optical setup for creating tunable
+two-dimensional temperature patterns on a micrometer scale. As an example of
+its practical application, we have produced temperature-induced magnetization
+landscapes in ferrimagnetic yttrium iron garnet films and investigated them
+using micro-focused Brillouin light scattering spectroscopy. It is shown that,
+due to the temperature dependence of the magnon spectrum, temperature changes
+can be visualized even for microscale thermal patterns.",2304.13658v2
+2023-05-09,On spinning strings in I-brane background,"We revisit semiclassical strings, in particular we focus on rigidly rotating
+strings, in the near horizon geometry of two orthogonal stacks of NS5-branes
+(I-branes) using the string sigma model. We determine the conserved charges for
+the probe string moving in the resulting $\mathbb{R}_t \times
+S^3_{\theta_1}\times S^3_{\theta_2}$ background supported by NS-NS two-forms
+and find a regularized dispersion relation for different values of integration
+constants. Using configurations that move simultaneously on both spheres, we
+obtain the giant magnon like dispersion relation for one particular set of
+parameters, while other consistent set of values gives us a dispersion relation
+reminiscent of the single spike.",2305.05164v3
+2023-05-10,Symmetry and nonlinearity of spin wave resonance excited by focused surface acoustic waves,"The use of a complex ferromagnetic system to manipulate GHz surface acoustic
+waves is a rich current topic under investigation, but the high-power nonlinear
+regime is under-explored. We introduce focused surface acoustic waves, which
+provide a way to access this regime with modest equipment. Symmetry of the
+magneto-acoustic interaction can be tuned by interdigitated transducer design
+which can introduce additional strain components. Here, we compare the impact
+of focused acoustic waves versus standard unidirectional acoustic waves in
+significantly enhancing the magnon-phonon coupling behavior. Analytical
+simulation results based on modified Landau-Lifshitz-Gilbert theory show good
+agreement with experimental findings. We also report nonlinear input power
+dependence of the transmission through the device. This experimental
+observation is supported by the micromagnetic simulation using mumax3 to model
+the nonlinear dependence. These results pave the way for extending the
+understanding and design of acoustic wave devices for exploration of
+acoustically driven spin wave resonance physics.",2305.06259v1
+2023-05-13,Suhl Instabilities in Nanoscopic Spheroids,"We simulate the magnetization dynamics of a permalloy spheroid of nanoscopic
+size in zero external field, such that both dipolar and exchange interactions
+are important. Low excitation power is used to obtain the frequencies and mode
+patterns of many normal modes. At higher power, non-linear three and four mode
+couplings between magnons carrying orbital angular momentum are observed to
+give rise to Suhl instabilities. Suhl's analysis of the selection rules
+governing the allowed processes is extended to initial states other than
+uniform precession. These rules are studied and confirmed by the simulations.
+Both down- and up-conversion are seen as well as three and four-mode processes.
+General trends are inferred for preferred instabilities among those that are
+allowed, although the thresholds for some instabilities appear to be very high.",2305.07986v1
+2023-05-17,Quantum disordered ground state in the spin-orbit coupled Jeff = 1/2 distorted honeycomb magnet BiYbGeO5,"We delineate quantum magnetism in the strongly spin-orbit coupled, distorted
+honeycomb-lattice antiferromagnet BiYbGeO$_{5}$. Our magnetization and heat
+capacity measurements reveal that its low-temperature behavior is well
+described by an effective $J_{\rm eff}=1/2$ Kramers doublet of Yb$^{3+}$. The
+ground state is nonmagnetic with a tiny spin gap. Temperature-dependent
+magnetic susceptibility, magnetization isotherm, and heat capacity could be
+modeled well assuming isolated spin dimers with anisotropic exchange
+interactions $J_{\rm Z} \simeq 2.6$~K and $J_{\rm XY} \simeq 1.3$~K. Heat
+capacity measurements backed by muon spin relaxation suggest the absence of
+magnetic long-range order down to at least 80\,mK both in zero field and in
+applied fields. This sets BiYbGeO$_5$ apart from Yb$_2$Si$_2$O$_7$ with its
+unusual regime of magnon Bose-Einstein condensation and suggests negligible
+interdimer couplings, despite only a weak structural deformation of the
+honeycomb lattice.",2305.10221v1
+2023-05-18,Majorana-fermion origin of the planar thermal Hall effect in the Kitaev magnet $α$-RuCl$_3$,"The field-induced quantum disordered state of layered honeycomb magnet
+$\alpha$-RuCl$_3$ is a prime candidate for Kitaev spin liquids hosting Majorana
+fermions and non-Abelian anyons. Recent observations of anomalous planar
+thermal Hall effect demonstrate a topological edge mode, but whether it
+originates from Majorana fermions or bosonic magnons remains controversial.
+Here we distinguish these origins from low-temperature measurements of
+high-resolution specific heat and thermal Hall conductivity with rotating
+in-plane fields. In the honeycomb bond direction, a distinct closure of the
+low-energy bulk gap is observed concomitantly with the sign reversal of the
+Hall effect. General discussions of topological bands show that this is the
+hallmark of an angle-rotation-induced topological transition of fermions,
+providing conclusive evidence for the Majorana-fermion origin of the thermal
+Hall effect in $\alpha$-RuCl$_3$.",2305.10619v1
+2023-05-21,Quantum estimation of tripartite coupling in Spin-Magnon-Mechanical Hybrid Systems,"Tripartite interactions play a fundamental role in the quantum information
+processing and quantum technology. However, it is generally difficult to
+realize strong tripartite coupling. We investigate the estimation of a
+tripartite coupling strength in a hybrid setup composed of a single
+nitrogen-vacancy (NV) center and a micromagnet. A time-independent parametric
+drive can be utilized to increase the estimation precision of the tripartite
+coupling strength. By calculating the quantum Fisher information (QFI), we can
+obtain the optimal estimation precision by measuring the eigenstate of the
+tripartite system. At the critical position, the QFI is divergent due to that
+the preparation time of the eigenstate is divergent. When the system is
+subjected to a dissipation, the QFI near the critical point of the
+driven-dissipation phase transition is analytically obtained. The direct
+intensity measurement is the optimal measurement near the dissipation phase
+transition point. In addition, we quantify the robustness of an imperfect
+measurement operator by the measurement noise susceptibility based on the error
+propagation formula. We find that the direct intensity measurement is enough
+robust against small measurement disturbance from a coherent drive. But it can
+be disturbed by the nonlinear anti-harmonic measurement noise, especially near
+the critical point.",2305.12435v1
+2023-05-25,Niobium Quantum Interference Microwave Circuits with Monolithic Three-Dimensional (3D) Nanobridge Junctions,"Nonlinear microwave circuits are key elements for many groundbreaking
+research directions and technologies, such as quantum computation and quantum
+sensing. The majority of microwave circuits with Josephson nonlinearities to
+date is based on aluminum thin films, and therefore they are severely
+restricted in their operation range regarding temperatures and external
+magnetic fields. Here, we present the realization of superconducting niobium
+microwave resonators with integrated, three-dimensional (3D) nanobridge-based
+superconducting quantum interference devices. The 3D nanobridges (constriction
+weak links) are monolithically patterned into pre-fabricated microwave LC
+circuits using neon ion beam milling, and the resulting quantum interference
+circuits show frequency tunabilities, flux responsivities and Kerr
+nonlinearities on par with comparable aluminum nanobridge devices, but with the
+perspective of a much larger operation parameter regime. Our results reveal
+great potential for application of these circuits in hybrid systems with e.g.
+magnons and spin ensembles or in flux-mediated optomechanics.",2305.16276v1
+2023-06-07,Gain assisted controllable fast light generation in cavity magnomechanics,"We study the controllable output field generation from a cavity
+magnomechanical resonator system that consists of two coupled microwave
+resonators. The first cavity interacts with a ferromagnetic yttrium iron garnet
+(YIG) sphere providing the magnon-photon coupling. Under passive cavities
+configuration, the system displays high absorption, prohibiting output
+transmission even though the dispersive response is anamolous. We replace the
+second passive cavity with an active one to overcome high absorption, producing
+an effective gain in the system. We show that the deformation of the YIG sphere
+retains the anomalous dispersion. Further, tuning the exchange interaction
+strength between the two resonators leads to the system's effective gain and
+dispersive response. As a result, the advancement associated with the
+amplification of the probe pulse can be controlled in the close vicinity of the
+magnomechanical resonance. Furthermore, we find the existence of an upper bound
+for the intensity amplification and the advancement of the probe pulse that
+comes from the stability condition. These findings may find potential
+applications for controlling light propagation in cavity magnomechanics.",2306.04390v1
+2023-06-24,Synchronization by Magnetostriction,"We show how to utilize magnetostriction to synchronize two mechanical
+vibration modes in a cavity magnomechanical system. The dispersive
+magnetostrictive interaction provides necessary nonlinearity required for
+achieving synchronization. Strong phase correlation between two mechanical
+oscillators can be established, leading to the synchronization robust against
+thermal noise. We develop a theoretical framework to analyze the
+synchronization by solving the constraint conditions of steady-state limit
+cycles. We determine that the strong cavity-magnon linear coupling can enhance
+and regulate the synchronization, which offers a new path to modulate
+synchronization. The work reveals a new mechanism for achieving and modulating
+synchronization and indicates that cavity magnomechanical systems can be an
+ideal platform to explore rich synchronization phenomena.",2306.13942v2
+2023-06-26,Quantum circuits to measure scalar spin chirality,"The scalar spin chirality is a three-body physical observable that plays an
+outstanding role both in classical magnetism, characterizing non-coplanar spin
+textures, and in quantum magnetism, as an order parameter for chiral spin
+liquids. In quantum information, the scalar spin chirality is a witness of
+genuine tripartite entanglement. Here we propose an indirect measurement
+scheme, based on the Hadamard test, to estimate the scalar spin chirality for
+general quantum states. We apply our method to study chirality in two types of
+quantum states: generic one-magnon states of a ferromagnet, and the ground
+state of a model with competing symmetric and antisymmetric exchange. We show a
+single-shot determination of the scalar chirality is possible for chirality
+eigenstates, via quantum phase estimation with a single auxiliary qutrit. Our
+approach provides a unified theory of chirality in classical and quantum
+magnetism.",2306.14804v1
+2023-06-28,Dissipative Spin-wave Diode and Nonreciprocal Magnonic Amplifier,"We propose an experimentally feasible dissipative spin-wave diode comprising
+two magnetic layers coupled via a non-magnetic spacer. We theoretically
+demonstrate that the spacer mediates not only coherent interactions but also
+dissipative coupling. Interestingly, an appropriately engineered dissipation
+engenders a nonreciprocal device response, facilitating the realization of a
+spin-wave diode. This diode permits wave propagation in one direction alone,
+given that the coherent Dzyaloshinskii- Moriya (DM) interaction is balanced
+with the dissipative coupling. The polarity of the diode is determined by the
+sign of the DM interaction. Furthermore, we show that when the magnetic layers
+undergo incoherent pumping, the device operates as a unidirectional spin-wave
+amplifier. The amplifier gain is augmented by cascading multiple magnetic
+bilayers. By extending our model to a one-dimensional ring structure, we
+establish a connection between the physics of spin-wave amplification and
+non-Hermitian topology. Our proposal opens up a new avenue for harnessing
+inherent dissipation in spintronic applications.",2306.15916v1
+2023-07-08,Enhanced Strong Coupling between Spin Ensemble and non-Hermitian Topological Edge States,"Light-matter interaction is crucial to both understanding fundamental
+phenomena and developing versatile applications. Strong coupling, robustness,
+and controllability are the three most important aspects in realizing
+light-matter interactions. Topological and non-Hermitian photonics, have
+provided frameworks for robustness and extensive control freedom, respectively.
+How to engineer the properties of the edge state such as photonic density of
+state, scattering parameters by using non-Hermitian engineering while ensuring
+topological protection has not been fully studied. Here we construct a
+parity-time-symmetric dimerized photonic lattice and generate complex-valued
+edge states via spontaneous PT-symmetry breaking. The enhanced strong coupling
+between the topological photonic edge mode and magnon mode in a ferromagnetic
+spin ensemble is demonstrated. Our research reveals the subtle non-Hermitian
+topological edge states and provides strategies for realizing and engineering
+topological light-matter interactions.",2307.03944v1
+2023-07-12,Microscopic origin of quantum supersonic phenomenon in one dimension,"Using the Bethe ansatz (BA) solution, we rigorously determine non-equilibrium
+dynamics of quantum flutter and revival of an injected impurity with a large
+initial momentum $Q$ into the one-dimensional (1D) interacting bosonic medium.
+We show that two types of BA excited eigenstates drastically dominate the
+oscillation nature of the quantum flutter with a periodicity which is simply
+given by the charge and spin dressed energies $\varepsilon_{\rm c,s}(0)$ at
+zero quasi-momentum $\tau_{\rm QF} = 2\pi/(|\varepsilon_{\rm c}(0)|-
+|\varepsilon_{\rm s}(0)|)$. While we also determine quantum revival dynamics
+with a larger periodicity $\tau_{L} = L/\left(v_{\rm c}(Q-k^*)-v_{\rm
+s}(k^*)\right)$ than $\tau_{\rm QF}$, revealing the quantum reflection of
+excitations induced by the periodic boundary conditions of a finite length $L$.
+Here $v_{\rm c,s}$ are the sound velocities of charge and spin excitations,
+respectively, and $k^*$ is determined by the rapidity of the impurity. Our
+results reveals a microscopic origin of quantum supersonic phenomenon and shed
+light on quantum magnon metrology for a measure of the gravitational force.",2307.05955v1
+2023-07-18,Ultrafast spin-to-charge conversions of antiferromagnetic (111)-oriented $\mathrm{L1_2}$-$\mathrm{Mn_3Ir}$,"Antiferromagnetic $\mathrm{L1_2}$-$\mathrm{Mn_3Ir}$ combines outstanding
+spin-transport properties with magnons in the terahertz (THz) frequency range.
+However, the THz radiation emitted by ultrafast spin-to-charge conversion via
+the inverse spin Hall effect remains unexplored. In this study, we measured the
+THz emission and transmission of a permalloy/(111)-oriented
+$\mathrm{L1_2}$-$\mathrm{Mn_3Ir}$ multilayer by THz time-domain spectroscopy.
+The spin Hall angle was determined to be approximately constant at 0.035 within
+a frequency range of 0.3-2.2 THz, in comparison with the THz spectroscopy of a
+permalloy/Pt multilayer. Our results not only demonstrate the potential of
+$\mathrm{L1_2}$-$\mathrm{Mn_3Ir}$ as a spintronic THz emitter but also provide
+insights into the THz spin transport properties of
+$\mathrm{L1_2}$-$\mathrm{Mn_3Ir}$.",2307.08928v3
+2023-07-20,Robustness and eventual slow decay of bound states of interacting microwave photons in the Google Quantum AI experiment,"Integrable models are characterized by the existence of stable excitations
+that can propagate indefinitely without decaying. This includes multi-magnon
+bound states in the celebrated XXZ spin chain model and its integrable Floquet
+counterpart. A recent Google Quantum AI experiment [A. Morvan et al., Nature
+612, 240 (2022)] realizing the Floquet model demonstrated the persistence of
+such collective excitations even when the integrability is broken: this
+observation is at odds with the expectation of ergodic dynamics in generic
+non-integrable systems. We here study the spectrum of the model realized in the
+experiment using exact diagonalization and physical arguments. We find that
+isolated bands corresponding to the descendants of the exact bound states of
+the integrable model are clearly observable in the spectrum for a large range
+of system sizes. However, our numerical analysis of the localization properties
+of the eigenstates suggests that the bound states become unstable in the
+thermodynamic limit. A perturbative estimate of the decay rate agrees with the
+prediction of an eventual instability for large system sizes.",2307.11164v1
+2023-07-24,Unidirectional spin wave emission by travelling pair of magnetic field profiles,"We demonstrate that the spin wave Cherenkov effect can be used to design the
+unidirectional spin wave emitter with tunable frequency and switchable
+direction of emission. In our numerical studies, we propose to use a pair of
+traveling profiles of the magnetic field which generate the spin waves, for
+sufficiently large velocity of their motion. In the considered system, the spin
+waves of shorter (longer) wavelengths are induced at the front (back) of the
+moving profiles and interfere constructively or destructively, depending on the
+velocity of the profiles. Moreover, we showed that the spin waves can be
+confined between the pair of traveling profiles of the magnetic field. This
+work opens the perspectives for the experimental studies in hybrid
+magnonic-superconducting systems where the magnetic vortices in a
+superconductor can be used as moving sources of the magnetic field driving the
+spin waves in the ferromagnetic subsystem.",2307.12653v2
+2023-07-31,Gating ferromagnetic resonance of magnetic insulators by superconductors via modulating electric-field radiation,"We predict that ferromagnetic resonance in insulating magnetic film with
+inplane magnetization radiates electric fields polarized along the
+magnetization with opposite amplitudes at two sides of the magnetic insulator,
+which can be modulated strongly by adjacent superconductors. With a single
+superconductor adjacent to the magnetic insulator this radiated electric field
+is totally reflected with a $\pi$-phase shift, which thereby vanishes at the
+superconductor side and causes no influence on the ferromagnetic resonance.
+When the magnetic insulator is sandwiched by two superconductors, this
+reflection becomes back and forth, so the electric field exists at both
+superconductors that drives the Meissner supercurrent, which in turn shifts
+efficiently the ferromagnetic resonance. We predict an ultrastrong coupling
+between magnons in the yttrium iron garnet and Cooper pairs in NbN with the
+frequency shift achieving tens of percent of the bare ferromagnetic resonance.",2307.16472v2
+2023-08-04,Experimental analysis of variability in WS$_2$-based devices for hardware security,"This work investigates the variability of tungsten disulfide (WS$_2$)-based
+devices by experimental characterization in view of possible application in the
+field of hardware security. To this aim, a preliminary analysis was performed
+by measurements across voltages and temperatures on a set of seven
+Si/SiO$_2$/WS$_2$ back-gated devices, also considering the effect of different
+stabilization conditions on their conductivity. Obtained results show
+appreciable variability in the conductivity, while also revealing similar
+dependence on bias and temperature across tested devices. Overall, our analysis
+demonstrates that WS$_2$-based devices can be potentially exploited to ensure
+adequate randomness and robustness against environmental variations and then
+used as building blocks for hardware security primitives.",2308.02265v1
+2023-08-21,Photoinduced topological phase transitions in Kitaev-Heisenberg honeycomb ferromagnets with the Dzyaloshinskii-Moriya interaction,"We theoretically study topological properties of Floquet magnon in a
+laser-irradiated Kitaev-Heisenberg honeycomb ferromagnet with the
+Dzyaloshinskii-Moriya interaction by means of the Floquet-Bloch theory. It is
+found that the Kitaev-Heisenberg ferromagnet can reveal two topological phases
+with different Chern numbers when it is irradiated by a circular-polarized
+light laser. Our results show that the topological phase of the system can be
+switched from one topological phase to another one via varying the light
+intensity. The intrinsic DMI plays a crucial role in the occurrence of
+photoinduced topological phase transition. It is shown that the sign reversal
+of the thermal hall conductivity is an important indicator on photoinduced
+topological phase transitions in the Kitaev-Heisenberg honeycomb ferromagnet.",2308.11077v1
+2023-08-24,Quantum interference between non-identical single particles,"Quantum interference between identical single particles reveals the intrinsic
+quantum statistic nature of particles, which could not be interpreted through
+classical physics. Here, we demonstrate quantum interference between
+non-identical bosons using a generalized beam splitter based on a quantum
+memory. The Hong-Ou-Mandel type interference between single photons and single
+magnons with high visibility is demonstrated, and the crossover from the
+bosonic to fermionic quantum statistics is observed by tuning the beam splitter
+to be non-Hermitian. Moreover, multi-particle interference that simulates the
+behavior of three fermions by three input photons is realized. Our work extends
+the understanding of the quantum interference effects and demonstrates a
+versatile experimental platform for studying and engineering quantum statistics
+of particles.",2308.12677v1
+2023-09-05,Signatures and characterization of dominating Kerr nonlinearity between two driven systems with application to a suspended magnetic beam,"We consider a model of two harmonically driven damped harmonic oscillators
+that are coupled linearly and with a cross-Kerr coupling. We show how to
+distinguish this combination of coupling types from the case where a coupling
+of optomechanical type is present. This can be useful for the characterization
+of various nonlinear systems, such as mechanical oscillators, qubits, and
+hybrid systems. We then consider a hybrid system with linear and cross-Kerr
+interactions and a relatively high damping in one of the modes. We derive a
+quantum Hamiltonian of a doubly clamped magnetic beam, showing that the
+cross-Kerr coupling is prominent there. We discuss, in the classical limit,
+measurements of its linear response as well as the specific higher-harmonic
+responses. These frequency-domain measurements can allow estimating the
+magnitude of the cross-Kerr coupling or its magnon population.",2309.02204v2
+2023-09-10,Resonant excitation of vortex gyrotropic mode via surface acoustic waves,"Finding new energy-efficient methods for exciting magnetization dynamics is
+one of the key challenges in magnonics. In this work, we present an approach to
+excite the gyrotropic dynamics of magnetic vortices through the phenomenon of
+inverse magnetostriction, also known as the Villari effect. We develop an
+analytical model based on the Thiele formalism that describes the gyrotropic
+motion of the vortex core including the energy contributions due to inverse
+magnetostriction. Based on this model, we predict excitations of the vortex
+core resonances by surface acoustic waves whose frequency is resonant with the
+frequency of the vortex core. We verify the model's prediction using
+micromagnetic simulations, and show the dependence of the vortex core's
+oscillation radius on the surface acoustic wave amplitude and the static bias
+field. Our study contributes to the advancement of energy-efficient magnetic
+excitations by relying on voltage-induced driven dynamics, which is an
+alternative to conventional current-induced excitations.",2309.04987v1
+2023-09-11,Probing Spin Wave Diffraction Patterns of Curved Antennas,"We report on the dependence of curvilinear shaped coplanar waveguides on the
+near-field diffraction patterns of spin waves propagating in perpendicularly
+magnetized thin films. Implementing the propagating spin waves spectroscopy
+techniques on either concentrically or eccentrically shaped antennas, we show
+how the link budget is directly affected by the spin wave interference, in good
+agreement with near-field diffraction simulations. This work demonstrates the
+feasibility to inductively probe a magnon interference pattern with a
+resolution down to 1$\mu$m$^2$, and provides a methodology for shaping spin
+wave beams from an antenna design. This methodology is successfully implemented
+in the case study of a spin wave Young's interference experiment.",2309.05532v1
+2023-09-12,Probing spatial variation of magnetic order in strained SrMnO$_3$ thin films using Spin Hall Magnetoresistance,"SrMnO$_{3}$ (SMO) is a magnetic insulator and predicted to exhibit a
+multiferroic phase upon straining. Strained films of SMO display a wide range
+of magnetic orders, ranging from G-type to C-and A-type, indicative of
+competing magnetic interactions. The potential of spin Hall magnetoresistance
+(SMR) is exploited as an electrical probe for detecting surface magnetic order,
+to read surface magnetic moments in SMO and its spatial variation, by designing
+and positioning electrodes of different sizes on the film. The findings
+demonstrate antiferromagnetic domains with different magnetocrystalline
+anisotropies along with a ferromagnetic order, where the magnetization arises
+from double exchange mediated ferromagnetic order and canted antiferromagnetic
+moments. Further, from a complete analysis of the SMR, a predominance of
+antiferromagnetic domain sizes of 3.5 $\mu$m$^2$ is extracted. This work
+enhances the applicability of SMR in unraveling the richness of correlation
+effects in complex oxides, as manifested by the detection of coexisting and
+competing ground states and lays the foundation for the study of magnon
+transport for different magnetoelectric based computing applications.",2309.06279v1
+2023-09-14,Exponentially Enhanced non-Hermitian Cooling,"Certain non-Hermitian systems exhibit the skin effect, whereby the
+wavefunctions become exponentially localized at one edge of the system. Such
+exponential amplification of wavefunction has received significant attention
+due to its potential applications in e.g., classical and quantum sensing.
+However, the opposite edge of the system, featured by the exponentially
+suppressed wavefunctions, remains largely unexplored. Leveraging this
+phenomenon, we introduce a non-Hermitian cooling mechanism, which is
+fundamentally distinct from traditional refrigeration or laser cooling
+techniques. Notably, non-Hermiticity will not amplify thermal excitations, but
+rather redistribute them. Hence, thermal excitations can be cooled down at one
+edge of the system, and the cooling effect can be exponentially enhanced by the
+number of auxiliary modes, albeit with a lower bound that depends on the
+dissipative interaction with the environment. Non-Hermitian cooling does not
+rely on intricate properties such as exceptional points or non-trivial
+topology, and it can apply to a wide range of Bosonic modes such as photons,
+phonons, magnons, etc.",2309.07731v2
+2023-09-18,Large Nonreciprocity of Shear-Horizontal Surface Acoustic Waves induced by Magnetoelastic Bilayers,"We report large nonreciprocity in the transmission of shear-horizontal
+surface acoustic waves (SAWs) on LiTaO3 substrate coated with a FeCoSiB/NiFeCu
+magnetoelastic bilayer. The large difference in saturation magnetization of the
+two layers not only brings nonreciprocal spin waves (SWs), but also ensures the
+phonon-magnon (SAWs-SWs) coupling at relatively low wavenumbers. It is found
+that the angle between the magnetization and the wavevector play important
+roles in determining the strength of magnetoelastic coupling and
+nonreciprocity, simultaneously. A large nonreciprocal transmission of SAWs
+about 30 dB (i.e. 60 dB/mm) is demonstrated at 2.33 GHz. In addition, the
+dispersion relation between coupled SH-SAWs and nonreciprocal SWs is developed,
+which provide a good insight into the observed phenomena. Our results offer a
+convenient approach to implement nonreciprocal SAW isolators or circulators.",2309.09521v1
+2023-09-21,Single-crystalline YIG nanoflakes with uniaxial in-plane anisotropy and diverse crystallographic orientations,"We study Y3Fe5O12 (YIG) nanoflakes that we produce via mechanical cleaving
+and exfoliation of YIG single crystals. By characterizing their structural and
+magnetic properties, we find that these YIG nanoflakes have surfaces oriented
+along unusual crystallographic axes and uniaxial in-plane magnetic anisotropy
+due to their shape, both of which are not commonly available in YIG thin films.
+These physical properties, combined with the possibility of picking up the YIG
+nanoflakes and stacking them onto nanoflakes of other van der Waals materials
+or pre-patterned electrodes or waveguides, open unexplored possibilities for
+magnonics and for the realization of novel YIG-based heterostructures and
+devices.",2309.12477v1
+2023-09-22,Electric control of optically-induced magnetization dynamics in a van der Waals ferromagnetic semiconductor,"Electric control of magnetization dynamics in two-dimensional (2D) magnetic
+materials is an essential step for the development of novel spintronic
+nanodevices. Electrostatic gating has been shown to greatly affect the static
+magnetic properties of some van der Waals magnets, but the control over their
+magnetization dynamics is still largely unexplored. Here we show that the
+optically-induced magnetization dynamics in the van der Waals ferromagnet
+Cr$_2$Ge$_2$Te$_6$ can be effectively controlled by electrostatic gates, with a
+one order of magnitude change in the precession amplitude and over 10% change
+in the internal effective field. In contrast to the purely thermally-induced
+mechanisms previously reported for 2D magnets, we find that coherent
+opto-magnetic phenomena play a major role in the excitation of magnetization
+dynamics in Cr$_2$Ge$_2$Te$_6$. Our work sets the first steps towards electric
+control over the magnetization dynamics in 2D ferromagnetic semiconductors,
+demonstrating their potential for applications in ultrafast opto-magnonic
+devices.",2309.12776v1
+2023-09-26,Stable Bosonic Topological Edge Modes in the Presence of Many-Body Interactions,"Many magnetic materials are predicted to exhibit bosonic topological edge
+modes in their excitation spectra, because of the nontrivial topology of their
+magnon, triplon or other quasi-particle band structures. However, there is a
+discrepancy between theory prediction and experimental observation, which
+suggests some underlying mechanism that intrinsically suppresses the expected
+experimental signatures, like the thermal Hall current. Many-body interactions
+that are not accounted for in the non-interacting quasi-particle picture are
+most often identified as the reason for the absence of the topological edge
+modes. Here we report stable bosonic edge modes at the boundaries of a ladder
+quantum paramagnet with gapped triplon excitations in the presence of the full
+many-body interaction. For the first time, we use tensor network methods to
+resolve topological edge modes in the time-dependent spin-spin correlations and
+the dynamical structure factor, which is directly accessible experimentally. We
+further show that these edge modes have anomalously long time coherence,
+discuss the topological phase diagram of the model, demonstrate the
+fractionalization of its low-lying excitations, and propose potential material
+candidates.",2309.15113v1
+2023-09-26,Predictive complexity of quantum subsystems,"We define predictive states and predictive complexity for quantum systems
+composed of distinct subsystems. This complexity is a generalization of
+entanglement entropy. It is inspired by the statistical or forecasting
+complexity of predictive state analysis of stochastic and complex systems
+theory, but is intrinsically quantum. Predictive states of a subsystem are
+formed by equivalence classes of state vectors in the exterior Hilbert space
+that effectively predict the same future behavior of that subsystem for some
+time. As an illustrative example, we present calculations in the dynamics of an
+isotropic Heisenberg model spin chain and show that, in comparison to the
+entanglement entropy, the predictive complexity better signifies dynamically
+important events, such as magnon collisions. We discuss how this quantity may
+usefully characterize a variety of symmetries in quantum systems in an
+information-theoretic way, and comment on possible applications and extensions.",2309.15200v3
+2023-09-27,Goodenough-Kanamori-Anderson high-temperature ferromagnetism in tetragonal transition-metal xenes,"Seminal Goodenough-Kanamori-Anderson (GKA) rules provide the inceptive
+understanding of the superexchange interaction of two magnetic metal ions
+bridged with an anion, and suggest fostered ferromagnetic interaction for
+orthogonal bridging bonds. However, there are no examples of two-dimensional
+(2D) materials with structure that optimizes the GKA arguments towards enhanced
+ferromagnetism and its critical temperature. Here we reveal that an ideally
+planar GKA ferromagnetism is indeed stable in selected tetragonal
+transition-metal xenes (tTMXs), with Curie temperature above 300~K found in CrC
+and MnC. We provide the general orbitally-resolved analysis of magnetic
+interactions that supports the claims and sheds light at the mechanisms
+dominating the magnetic exchange process in these structures. With recent
+advent of epitaxially-grown tetragonal 2D materials, our findings earmark tTMXs
+for facilitated spintronic and magnonic applications, or as a desirable
+magnetic constituent of functional 2D heterostructures.",2309.15445v1
+2023-10-03,Optical excitation of multiple standing spin modes in 3D optomagnonic nanocavities,"We report the first experimental observation of multiple standing spin modes
+in 3D optomagnonic nanocavity formed by nanometer-sized iron-garnet
+nanocylinder. We show that launching of standing spin modes is achieved due to
+a high confinement of the optically generated effective magnetic field caused
+by the localized optical resonance. Quantization and spin-wave mode
+inhomogeneity is achieved in each of the three spatial dimensions. The
+presented approach opens new horizons of 3D optomagnonics by combining
+nanophotonic and magnonic functionalities within a single nanocavity.",2310.01974v1
+2023-10-04,Metadynamics calculations of the effect of thermal spin fluctuations on skyrmion stability,"The stability of magnetic skyrmions has been investigated in the past, but
+mostly in the absence of thermal fluctuations. However, thermal spin
+fluctuations modify the magnetic properties (exchange stiffness,
+Dzyaloshinskii-Moriya interaction (DMI) and anisotropy) that define skyrmion
+stability. Thermal magnons also excite internal skrymion dynamics, deforming
+the skyrmion shape. Entropy has also been shown to modify skyrmion lifetimes in
+experiments, but is absent or approximated in previous studies. Here we use
+metadynamics to calculate the free energy surface of a magnetic thin film in
+terms of the topological charge and magnetization. We identify the free energy
+minima corresponding to different spin textures and the lowest energy paths
+between the ferromagnetic and single skyrmion states. We show that at low
+temperatures the lowest free energy barrier is a skyrmion collapse process.
+However, this energy barrier increases with temperature. An alternative path,
+where a singularity forms on the skrymion edge, has a larger free energy
+barrier at low temperatures but decreases with increasing temperature and
+eventually becomes the lowest energy barrier.",2310.03169v1
+2023-10-20,Multiferroic kinks and spin-flop transition in Ni$_{2}$InSbO$_6$ from first principles,"Magnetoelectric multiferroics are key materials for next-generation devices
+due to their entangled magnetic and ferroelectric properties. Spiral
+multiferroics induce ferroelectric polarization and are particularly promising
+for electric control of magnetism and magnetic control of ferroelectricity. In
+this work, we uncover long-period incommensurate states characterized by unique
+multiferroic kinks in corundum nickelate Ni$_{2}$InSbO$_6$. Utilizing a
+2-orbital $S=1$ model, we derive formulas for Heisenberg and anisotropic
+magnetic exchanges and magnetically-induced polarization, enabling their
+calculations from first principles. Our theory reproduces experimentally
+observed magnetic structures and polarization dependence on the magnetic field
+and predicts a three-step magnetic phase transition (flat spiral $\rightarrow$
+conical spiral $\rightarrow$ spin-flop $\rightarrow$ ferromagnet) under
+external magnetic fields. Kinks in the spiral phases repel each other through a
+Yukawa-like potential arising from exchange of massive magnons. Furthermore,
+our continuum theory predicts that an electric field directed one way
+stabilizes the ferromagnetic state, while the opposite direction stabilizes the
+spiral layer state. Our findings open a new pathway to predictive
+first-principles modelling of multiferroics and may lead to technological
+applications based on multiferroic kinks.",2310.13301v1
+2023-10-20,Surface-symmetry-driven Dzyaloshinskii--Moriya interaction and canted ferrimagnetism in collinear magnetoelectric antiferromagnet Cr$_2$O$_3$,"Antiferromagnets are normally thought of as materials with compensated
+magnetic sublattices. This adds to their technological advantages but
+complicates readout of the antiferromagnetic state. We demonstrate
+theoretically the existence of a Dzyaloshinskii-Moriya interaction (DMI) which
+is determined by the magnetic symmetry classes of Cr$_2$O$_3$ surfaces with an
+in-plane magnetic easy axis. The DMI explains a previously predicted
+out-of-plane magnetization at the nominally compensated surfaces of chromia,
+leading to a surface-localized canted ferrimagnetism. This is in agreement with
+magnetotransport measurements and with density functional theory predictions
+which further allow us to quantify the strength of DMI. The temperature
+dependence of the transversal resistance for these planes shows distinct
+behavior in comparison with that of the Cr$_2$O$_3$ $c$ plane, which we
+attribute to the influence of DMI. Our work provides a framework to analyze
+surface-driven phenomena in antiferromagnets, and motivates the use of
+nominally compensated chromia surfaces for antiferomagnetic spintronics and
+magnonics.",2310.13438v1
+2023-11-08,Quadrupolar Phases and Plateau States In Skewed Ladders,"Exotic quantum phases in low dimensional frustrated quantum magnets emerge
+due to strong quantum fluctuations and competing spin exchanges. Two legged
+skewed spin ladders with periodically missing rung bonds and periodically
+placed slanted rung bonds are particularly interesting from this stand point.
+Here, we study ground state (gs) properties of a spin- 1/2 Heisenberg model on
+3/4, 3/5 and 5/5 skewed ladders in the presence of an axial magnetic field, B,
+using exact diagonalization and the density matrix renormalization group
+method. We note the existence of plateaus at m = 1/3 and 2/3 for 3/4 skewed
+ladder, at m = 1/4, 1/2, and 3/4 for 3/5 skewed ladder, and at m = 0, 1/3, and
+2/3 for 5/5 skewed ladder. The plateau state is always a gapped state and it
+depends on the gap in the system. Surprisingly, the 3/4 and 5/5 skewed ladders
+show interesting quadrupolar or n-type spin nematic phases below the 1/3rd
+plateau, i.e, at very low magnetic fields. These two systems are unique as they
+host both a plateau and a quadrupolar phase at low magnetic fields. The linear
+variation of pitch angle of the spin with magnetization and behavior of binding
+energy of magnon pairs as function of magnetic field are also studied in both
+the systems.",2311.05031v1
+2023-11-10,Relaxation to persistent currents in a Hubbard trimer coupled to fermionic baths,"We consider a ring of fermionic quantum sites, modeled by the Fermi-Hubbard
+Hamiltonian, in which electrons can move and interact strongly via the Coulomb
+repulsion. The system is coupled to fermionic cold baths which by the exchange
+of particles and energy induce relaxation in the system. We eliminate the baths
+and describe the system effectively by the Lindblad master equations in various
+versions valid for different coupling parameter regimes. The early relaxation
+phase proceeds in a universal way, irrespective of the relative couplings and
+approximations. The system settles down to its low-energy sector and is
+consecutively well approximated by the Heisenberg model. In the late
+relaxation, different Lindblad approaches push the system towards different
+final states with opposite, extreme spin orders, from ferromagenetic to
+antiferromagnetic. Due to spin frustration in the trimer (a three site ring),
+degenerate ground states are formed by spin waves (magnons). The system
+described by the global coherent version of the Lindblad operators relaxes
+towards the final states carrying directed persistent spin currents. We
+numerically confirm these predictions.",2311.06331v1
+2023-11-25,Spin pumping in YIG-Pt structures: the role of the van Hove singularities,"Spin pumping by surface and backward volume magnetostatic waves in YIG/Pt
+structures is experimentally studied and analyzed. It is shown that at
+frequencies corresponding to van Hove singularities in the density of states of
+the spin wave spectrum, an increase in the efficiency of electron-magnon
+scattering and spin current generation takes place. The obtained results are
+important for spin wave-based spintronic devices development.",2311.15096v1
+2023-11-27,Gilbert damping in two-dimensional metallic anti-ferromagnets,"A finite spin life-time of conduction electrons may dominate Gilbert damping
+of two-dimensional metallic anti-ferromagnets or anti-ferromagnet/metal
+heterostructures. We investigate the Gilbert damping tensor for a typical
+low-energy model of a metallic anti-ferromagnet system with honeycomb magnetic
+lattice and Rashba spin-orbit coupling for conduction electrons. We distinguish
+three regimes of spin relaxation: exchange-dominated relaxation for weak
+spin-orbit coupling strength, Elliot-Yafet relaxation for moderate spin-orbit
+coupling, and Dyakonov-Perel relaxation for strong spin-orbit coupling. We
+show, however, that the latter regime takes place only for the in-plane Gilbert
+damping component. We also show that anisotropy of Gilbert damping persists for
+any finite spin-orbit interaction strength provided we consider no spatial
+variation of the N\'eel vector. Isotropic Gilbert damping is restored only if
+the electron spin-orbit length is larger than the magnon wavelength. Our theory
+applies to MnPS3 monolayer on Pt or to similar systems.",2311.16268v2
+2023-12-06,Axion and Dark Fermion Electromagnetic Form Factors in Superfluid He-4,"Condensed matter materials have shown great potential in searching for light
+dark matter (DM) via detecting the phonon or magnon signals induced by the
+scattering of DMs off the materials. In this paper, we study the possibility of
+detecting electromagnetic form factors of fermionic DM and axion-like particles
+(ALPs) using superfluid Helium-4. The phonon induced by a sub-GeV fermionic DM
+scattering off the superfluid can be described using the effective field theory
+with the interaction between DM and the bulk ${}^4$He. Signals arising from the
+electromagnetic form factors of light DM in the presence of an external
+electric field are calculated. Projected constraints on the charge radius, the
+anapole moment, and the magnetic moment of the DM are derived with 1
+kg$\cdot$year exposure. The phonon signal induced by the scattering of ALPs off
+the superfluid is also calculated, which can put competitive and the first
+direct detection bounds on ALP-photon-dark photon couplings in the projected
+experiments.",2312.03530v1
+2023-12-12,Bulk Photovoltaic Effects in Helimagnets,"The bulk photovoltaic (BPV) effect that converts light into electric current
+is highly sensitive to the system symmetry and its electronic Bloch
+wavefunction. To create a sizable net electric current, it is necessary to
+break the centrosymmetry P in its host material. Here, we investigate how
+helical spin polarization breaks P that is otherwise kept in its crystalline
+geometry. The magnetic helix widely exists in multiferroics and magnon
+excitation in collinear magnets. We apply symmetry analysis and a tight-binding
+model to show how the symmetry is reduced in helimagnetic platforms under
+various degrees of freedom, namely, different types of spin spiral
+configurations, spin winding angles, magnetic propagation vectors, and spin
+chirality. They offer effective and versatile manipulation of BPV generation in
+helimagnets. Our concept is further illustrated in the monolayer NiI2, a
+typical helimagnetic material. It could host observable direction-dependent BPV
+current, which serves as an opto-electric probe to track the subtle magnetic
+configurations and potential ferroic nature. Our work reveals the fundamental
+mechanism of the multiferroic order and the nonlinear optics process.",2312.06977v1
+2023-12-12,Current-controlled chirality dynamics in a mesoscopic magnetic domain wall,"Chirality as internal degree of freedom of a mesoscopic domain wall inside a
+quasi-one-dimensional fixture can be controlled by spin-polarized current for
+ferro- as well as anti-ferro-magnetic domain walls. We show that the current
+density required for the chirality manipulation can be significantly reduced in
+the low-temperature regime where the chirality dynamics exhibits quantum
+effects. In this quantum regime, weak currents can excite Bloch oscillations of
+the domain wall angular rotation velocity, with the oscillation frequency
+proportional to the current, modulated by a much higher magnon-range frequency.
+In addition to that, the Wannier-Stark localization effects enable controlled
+switching between different chiral states, suppressing inertial effects
+characteristic for the classical regime. We also show that for recently
+discovered novel class of magnetic materials -- altermagnets -- chirality
+switching can be driven by the usual charge current (not spin-polarized).",2312.07487v2
+2023-12-14,Exploration of magnetoelastic deformations in spin-chain compound CuBr$_2$,"We investigate a spin-$\frac{1}{2}$ antiferromagnet, CuBr$_2$, which has
+quasi-one-dimensional structural motifs. The system has previously been
+observed to exhibit unusual Raman modes possibly due to a locally deformed
+crystal structure driven by the low-dimensional magnetism. Using hard X-ray
+scattering and neutron total scattering, here we aim to verify a specific form
+of tetramerized lattice deformation proposed in the previous study. Apart from
+diffuse scattering signals which we can reproduce by performing a thorough
+modeling of the lattice's thermal vibrations, we do not observe evidence for a
+tetramerized lattice structure within our detection sensitivity. As a result,
+it is more likely that the unusual Raman modes in CuBr$_2$ arise from classical
+magnon-phonon hybridization, rather than from quantum spin-singlet-driven
+lattice deformation.",2312.09055v1
+2023-12-18,Doping-control of excitons and magnetism in few-layer CrSBr,"Magnetism in two-dimensional materials reveals phenomena distinct from bulk
+magnetic crystals, with sensitivity to charge doping and electric fields in
+monolayer and bilayer van der Waals magnet CrI3. Within the class of layered
+magnets, semiconducting CrSBr stands out by featuring stability under ambient
+conditions, correlating excitons with magnetic order and thus providing strong
+magnon-exciton coupling, and exhibiting peculiar magneto-optics of
+exciton-polaritons. Here, we demonstrate that both exciton and magnetic
+transitions in bilayer and trilayer CrSBr are sensitive to voltage-controlled
+field-effect charging, exhibiting bound exciton-charge complexes and
+doping-induced metamagnetic transitions. Moreover, we demonstrate how these
+unique properties enable optical probes of local magnetic order, visualizing
+magnetic domains of competing phases across metamagnetic transitions induced by
+magnetic field or electrostatic doping. Our work identifies few-layer CrSBr as
+a rich platform for exploring collaborative effects of charge, optical
+excitations, and magnetism.",2312.11041v1
+2023-12-20,Non-equilibrium criticality at the onset of time-crystalline order in $O(N)$ models,"We explore the phase transitions at the onset of time-crystalline order in
+$O(N)$ models driven out-of-equilibrium. The spontaneous breaking of time
+translation symmetry and its Goldstone mode are captured by an effective
+description with $O(N)\times SO(2)$ symmetry. Using the renormalization group
+and the $\epsilon=4-d$ expansion in a leading two-loop analysis, we identify a
+new non-equilibrium universality class. Strikingly, it controls the
+long-distance physics no matter how small the microscopic breaking of
+equilibrium conditions is. The $O(N=2)\times SO(2)$ symmetry group is realized
+for magnon condensation in pumped yttirum iron garnet (YIG) films and in
+exciton-polariton systems with a polarization degree of freedom.",2312.13372v1
+2023-12-21,Direct evidence from high-field magnetotransport for a dramatic change of quasiparticle character in van der Waals ferromagnet Fe$_{3-x}$GeTe$_2$,"Magnetometry and magnetoresistance (MR) data taken on the van der Waals
+ferromagnet Fe$_{3-x}$GeTe$_2$ (FGT) reveal three distinct contributions to the
+MR: a linear negative component, a contribution from closed Fermi-surface
+orbits, and a $H^2$ enhancement linked to a non-coplanar spin arrangement.
+Contrary to earlier studies on FGT, by accounting for the field dependence of
+the anomalous Hall effect, we find that the ordinary Hall coefficient decreases
+markedly below 80 K, indicating a significant change in character of the
+electrons and holes on the Fermi surface at this temperature. The resulting
+altered ground state eventually causes the Hall coefficient to reverse sign at
+35 K. Our Hall data support the proposal that Kondo-lattice behavior develops
+in this $d$-electron material below 80 K. Additional evidence comes from the
+negative linear component of the MR, which arises from electron-magnon
+scattering with an atypical temperature dependence attributable to the onset of
+Kondo screening.",2312.13894v1
+2023-12-21,Pseudo-spectral Landau-Lifshitz description of magnetization dynamics,"Magnetic materials host a wealth of nonlinear dynamics, textures, and
+topological defects. This is possible due to the competition between strong
+nonlinearity and dispersion that act at the atomic scale as well as long-range
+interactions. However, these features are difficult to analytically and
+numerically study because of the vastly different temporal and spatial scales
+involved. Here, we present a pseudo-spectral approach for the Landau-Lifshitz
+equation that invokes energy and momentum conservation embodied in the magnon
+dispersion relation to accurately describe both atomic and continuum limits.
+Furthermore, this approach enables analytical study at every scale. We show the
+applicability of this model in both the continuum and atomic limit by
+investigating modulational instability and ultrafast evolution of magnetization
+due to transient grating, respectively, in a 1D ferromagnetic chain with
+perpendicular magnetic anisotropy. This model provides the possibility of
+grid-independent multiscale numerical approaches that will enable the
+description of singularities within a single framework.",2312.14068v1
+2023-12-29,Understanding the magnetic interactions of the zig-zag honeycomb lattice: Application to $α$-RuCl$_3$,"This investigation covers the effects of variable exchange interactions on
+the spin dynamics of the zig-zag honeycomb lattice. Using a Holstein-Primakoff
+expansion of the Heisenberg Hamiltonian with easy-axis anisotropy, we
+characterize the effects of multiple nearest-neighbor and next-nearest-neighbor
+interactions with asymmetry within the context of a frustrated and
+non-frustrated zig-zag magnetic configuration. Furthermore, we compare to the
+known inelastic neutron scattering data for the proximate quantum spin liquid
+$\alpha$-RuCl$_3$, and we provide insight into the evolution of the spin
+dynamics, showing that the Heisenberg interaction dominates the majority of the
+spin excitation behavior. By analyzing the frustrated system with multiple
+interactions, direction-dependent Dirac nodes present themselves, and we can
+demonstrate that a standard Heisenberg model can accurately describe the
+observed magnon spectra.",2312.17433v1
+2024-01-03,Synthetically enhanced sensitivity using higher-order exceptional point and coherent perfect absorption,"Sensors play a crucial role in advanced apparatuses and it is persistently
+pursued to improve their sensitivities. Recently, the singularity of a
+non-Hermitian system, known as the exceptional point (EP), has drawn much
+attention for this goal. Response of the eigenfrequency shift to a perturbation
+$\epsilon$ follows the $\epsilon^{1/n}$-dependence at an $n$th-order EP,
+leading to significantly enhanced sensitivity via a high-order EP. However, due
+to the requirement of increasingly complicated systems, great difficulties will
+occur along the path of increasing the EP order to enhance the sensitivity.
+Here we report that by utilizing the spectral anomaly of the coherent perfect
+absorption (CPA), the sensitivity at a third-order EP can be further enhanced
+owing to the cooperative effects of both CPA and EP. We realize this
+synthetically enhanced sensor using a pseudo-Hermitian cavity magnonic system
+composed of two yttrium iron garnet spheres and a microwave cavity. The
+detectable minimum change of the magnetic field reaches $4.2\times10^{-21}$T.
+It opens a new avenue to design novel sensors using hybrid non-Hermitian
+quantum systems.",2401.01613v1
+2024-01-10,Narrowly avoided spin-nematic phase in BaCdVO(PO$_4$)$_2$: NMR evidence,"We present a $^{31}$P nuclear magnetic resonance (NMR) investigation of
+BaCdVO(PO$_4$)$_2$ focusing on the nearly saturated regime between
+$\mu_0H_{c1}$ = 4.05 T and $\mu_0H_{c2}$ = 6.5 T, used to be considered as a
+promising candidate for a spin-nematic phase. NMR spectra establish the absence
+of any dipolar order there, whereas the weak field dependence of the
+magnetization above $H_{c1}$ is accounted for by Dzyaloshinskii-Moriya
+interaction terms. The low-energy spin dynamics (fluctuations), measured by
+nuclear spin-lattice relaxation rate ($T_1^{-1}$), confirms the continuity of
+this phase and the absence of any low-temperature phase transition.
+Unexpectedly, the spin dynamics above $H_{c1}$ is largely dominated by
+two-magnon processes, which is expected above the saturation field of a
+spin-nematic phase, but not inside. This shows that BaCdVO(PO$_4$)$_2$ is
+indeed close to a spin-nematic instability, however, this phase is not
+stabilized. We thus confirm recent theoretical predictions that the
+spin-nematic phase can be stabilized, at most, in an extremely narrow field
+range close to saturation or is rather narrowly avoided [Jiang et al., Phys.
+Rev. Lett. 130, 116701 (2023)].",2401.05269v1
+2024-01-19,Non-Fermi-Liquid/Marginal-Fermi-Liquid Signatures Induced by Van Hove Singularity,"We theoretically study the two-dimensional metal that is coupled to critical
+magnons and features van Hove singularities on the Fermi surface. When there is
+only translationally invariant SYK-liked Yukawa interaction, van Hove points
+suppress the contribution from the part of the Fermi surface away from them,
+dominating and exhibiting non-Fermi-liquid behavior. When introducing
+disordered Yukawa coupling, it leads to a crossover from non-Fermi-liquid to
+marginal-Fermi-liquid, and the marginal-Fermi-liquid region exhibits the $T\ln
+(1/T)$ specific heat and temperature-linear resistivity of strange metal. By
+solving the gap equation, we provide the critical temperature for
+superconductor induced by van Hove singularities and point out the possible
+emergence of pair-density-wave superconductor. Our theory may become a new
+mechanism for understanding non-Fermi-liquid or marginal-Fermi-liquid
+phenomenons.",2401.10707v1
+2024-01-22,Theory of momentum-resolved magnon electron energy loss spectra: The case of Yttrium Iron Garnet,"We explore the inelastic spectra of electrons impinging in a magnetic system.
+The methodology here presented is intended to highlight the charge-dependent
+interaction of the electron beam in a STEM-EELS experiment, and the local
+vector potential generated by the magnetic lattice. This interaction shows an
+intensity $10^{-2}$ smaller than the purely spin interaction, which is taken to
+be functionally the same as in the inelastic neutron experiment. On the other
+hand, it shows a strong scattering vector dependence ($\kappa^{-4}$) and a
+dependence with the relative orientation between the probe wavevector and the
+local magnetic moments of the solid. We present YIG as a case study due to its
+high interest by the community.",2401.12302v2
+2024-01-24,Progress and Prospects in Two-Dimensional Magnetism of van der Waals Materials,"Two-dimensional (2D) magnetism in van der Waals (vdW) atomic crystals and
+moir\'e superlattices has emerged as a topic of tremendous interest in the
+fields of condensed matter physics and materials science within the past
+half-decade since its first experimental discovery in 2016 - 2017. It has not
+only served as a powerful platform for investigating phase transitions in the
+2D limit and exploring new phases of matter, but also provided new
+opportunities for applications in microelectronics, spintronics, magnonics,
+optomagnetics, and so on. Despite the flourishing developments in 2D magnetism
+over this short period of time, further efforts are welcome in multiple
+forefronts of 2D magnetism research for achieving the ultimate goal of
+routinely implementing 2D magnets as quantum electronic components. In this
+review article, we will start with basic concepts and properties of 2D
+magnetism, followed by a brief overview of historical efforts in 2D magnetism
+research and then a comprehensive review of vdW material-based 2D magnetism. We
+will conclude with discussions on potential future research directions for this
+growing field of 2D vdW magnetism.",2401.13781v1
+2024-01-28,Magnetic interactions and excitations in SrMnSb$_2$,"The magnetic interactions in the antiferromagnetic (AFM) Dirac semimetal
+candidate SrMnSb$_2$ are investigated using \textit{ab initio} linear response
+theory and inelastic neutron scattering (INS). Our calculations reveal that the
+first two nearest in-plane couplings ($J_1$ and $J_2$) are both AFM in nature,
+indicating a significant degree of spin frustration, which aligns with
+experimental observations. The orbital resolution of exchange interactions
+shows that $J_1$ and $J_2$ are dominated by direct and superexchange,
+respectively. In a broader context, a rigid-band model suggests that electron
+doping fills the minority spin channel and results in a decrease in the AFM
+coupling strength for both $J_1$ and $J_2$. To better compare with INS
+experiments, we calculate the spin wave spectra within a linear spin wave
+theory framework, utilizing the computed exchange parameters. The calculated
+spin wave spectra exhibit overall good agreement with measurements from INS
+experiments, although with a larger magnon bandwidth. Introducing additional
+electron correlation within the Mn-$3d$ orbitals can promote electron
+localization and reduce the magnetic coupling, further improving the agreement
+with experiments.",2401.15572v1
+2024-01-29,Dipole superfluid hydrodynamics II,"We present a dissipative hydrodynamic theory of ""s-wave dipole superfluids""
+that arise in phases of translation-invariant and dipole-symmetric models in
+which the U(1) symmetry is spontaneously broken. The hydrodynamic description
+is subtle on account of an analogue of dangerously irrelevant operators, which
+requires us to formalize an entirely new derivative counting scheme suitable
+for these fluids. We use our hydrodynamic model to investigate the linearized
+response of such a fluid, characterized by sound modes $\omega \sim \pm k -
+ik^2$, shear modes $\omega\sim-ik^2$, and magnon-like propagating modes $\omega
+\sim \pm k^2 - ik^4$ that are the dipole-invariant version of superfluid
+""second sound"" modes. We find that these fluids can also admit equilibrium
+states with ""dipole superflow"" that resemble a polarized medium. Finally, we
+couple our theory to slowly varying background fields, which allows us to
+compute response functions of hydrodynamic operators and Kubo formulas for
+hydrodynamic transport coefficients.",2401.16385v1
+2024-01-30,"Magneto-synthesis effect on magnetic order, phonons, and magnons in single-crystal Sr$_2$IrO$_4$","It was shown earlier that applying a magnetic field during the growth of
+Sr$_2$IrO$_4$, also known as ""field-alteration"", induces significant changes to
+its structural, magnetic, and transport properties. However, the microscopic
+nature of these changes is enigmatic. In this study, we employed resonant
+elastic and inelastic x-ray scattering, as well as Raman scattering, to
+investigate samples from two batches of Sr$_2$IrO$_4$ grown in magnetic fields
+of different strengths. Our findings reveal that samples grown in a weaker
+magnetic field have similar magnetic order to non-altered samples, whereas
+those grown in a stronger field show a different stacking of weak in-plane
+ferromagnetic moments. Additionally, we observed significant softening and
+broadening of select Raman-active phonons in the field altered samples, with a
+stronger effect in the samples grown in the stronger field. We discuss insights
+that our results provide into the microscopic nature of field-alteration in
+Sr$_2$IrO$_4$.",2401.17407v1
+2024-02-01,Spin wave-driven variable-phase mutual synchronization in spin Hall nano-oscillators,"Spin-orbit torque can drive auto-oscillations of propagating spin wave (PSW)
+modes in nano-constriction spin Hall nano-oscillators (SHNOs). These modes
+allow both long-range coupling and the potential of controlling its phase --
+critical aspect for nano-magnonics, spin wave logic, and Ising machines. Here,
+we demonstrate PSW-driven variable-phase coupling between two nano-constriction
+SHNOs and study how their separation and the PSW wave vector impact their
+mutual synchronization. In addition to ordinary in-phase mutual
+synchronization, we observe, using both electrical measurements and
+phase-resolved $\mu-$Brillouin Light Scattering microscopy, mutual
+synchronization with a phase that can be tuned from 0 to $\pi$ using the drive
+current or the applied field. Micromagnetic simulations corroborate the
+experiments and visualize how the PSW patterns in the bridge connecting the two
+nano-constrictions govern the coupling. These results advance the capabilities
+of mutually synchronized SHNOs and open up new possibilities for applications
+in spin wave logic, unconventional computing, and Ising Machines.",2402.00586v1
+2024-02-09,Resonances involving integer magnons and spin-1/2 excitations in a magnetism modulated two-dimensional electron gas,"We conduct an experimental study of high-mobility two-dimensional electron
+gas (2DEG) in GaAs/AlGaAs quantum wells modulated by strong magnetism at an
+in-plane magnetic field ($B$). The modulated $B$-fields are performed via the
+single stripe and gratings which are made of the heavy rare earth metal Terbium
+(Tb) thin films on the sample surface. The robust ferromagnetic resonances
+(FMRs) persist to the temperature of 50-70 K in both the stripe and grating
+samples, for the ferromagnetism (FM) phase of Tb exists at above 100 K. The
+high-order (with integer numbers of $j \equiv \hbar\omega/g\mu_{B}B = 1,
+2,$...) magnetic resonances can also be observed in the stripe structure via
+the microwave (MW) photovoltaic detection and magnetoresistance under microwave
+irradiation. In addition, the resonance features around $j = 1/2$ are robust in
+the single-stripe modulated sample, which suggests the spinons with spin-1/2
+collective excitations in a 1D Heisenberg model.",2402.06792v1
+2024-03-09,Superconducting Cavity-Based Sensing of Band Gaps in 2D Materials,"The superconducting coplanar waveguide (SCPW) cavity plays an essential role
+in various areas like superconducting qubits, parametric amplifiers, radiation
+detectors, and studying magnon-photon and photon-phonon coupling. Despite its
+wide-ranging applications, the use of SCPW cavities to study various van der
+Waals 2D materials is relatively unexplored. The resonant modes of the SCPW
+cavity exquisitely sense the dielectric environment. In this work, we measure
+the charge compressibility of bilayer graphene coupled to a half-wavelength
+SCPW cavity. Our approach provides a means to detect subtle changes in the
+capacitance of the bilayer graphene heterostructure, which depends on the
+compressibility of bilayer graphene, manifesting as shifts in the resonant
+frequency of the cavity. This method holds promise for exploring a wide class
+of van der Waals 2D materials, including transition metal dichalcogenides
+(TMDs) and their moir\'e where DC transport measurement is challenging.",2403.05867v1
+2024-03-10,Spin Waves and Spin Currents in Magnon-Phonon Composite Resonator Induced by Acoustic Waves of Various Polarizations,"In this work, we present the results of a systematic experimental study of
+linear and parametric spin wave resonant excitation accompanied by spin
+currents (spin pumping) in a multifrequency composite bulk acoustic wave
+resonator with a ZnO-YIG-GGG-YIG/Pt structure. The features of magnetic
+dynamics excitation in YIG films due to magnetoelastic coupling with acoustic
+thickness modes of various polarizations are studied. Acoustic spin waves and
+spin pumping are detected by simultaneous frequency-field mapping of the
+inverse spin Hall effect voltage and the resonant frequencies of thickness
+extensional modes. In the parametric range of frequencies and fields, acoustic
+spin pumping induced by both shear and longitudinal polarization modes was
+observed. Linear acoustic spin waves are excited only by shear thickness
+extensional modes because longitudinal acoustic waves do not couple with the
+magnetic subsystem in linear regime.",2403.06274v1
+2024-03-14,Topological responses from gapped Weyl points in 2D altermagnets,"Altermagnetism combines aspects of both ferromagnetism and
+antiferromagnetism, breaking spin degeneracy while possessing no net
+magnetization. In this work, we study the symmetry requirements for
+topologically protected Weyl points in 2D altermagnets, involving bands with
+the same spin quantum number. We classify all spin-wallpaper groups whose
+symmetries protect 2D Weyl points and show that their nontrivial topology is
+charactrized by a quantized $\pi$-Berry phase. Representative electronic
+tight-binding and magnonic linear spin-wave models are constructed to
+investigate the unusual transport characteristics of these 2D Weyl points.
+Different mass terms, induced for example through strain or via coupling to
+light or a substrate, gap out the Weyl points leading to emerging gapped
+topological phases. Depending on the mass terms, these phases carry finite
+Chern and/or spin Chern numbers and exhibit protected edge states as well as
+anomalous electronic and thermal Hall responses. We calculate these Hall
+currents for the different topological phases.",2403.09520v1
+2024-03-14,Subharmonic lock-in detection and its optimisation for femtosecond noise correlation spectroscopy,"Although often viewed as detrimental, fluctuations carry valuable information
+about the physical system from which they emerge. Femtosecond noise correlation
+spectroscopy (FemNoC) has recently been established to probe the ultrafast
+fluctuation dynamics of thermally populated magnons by measurement of their
+amplitude autocorrelation. Subharmonic lock-in detection is the key technique
+in this method, allowing to extract the pulse-to-pulse polarisation
+fluctuations of two femtosecond optical pulse trains transmitted through a
+magnetic sample. Here, we present a thorough technical description of the
+subharmonic demodulation technique and of the FemNoC measurement system. We
+mathematically model the data acquisition process and identify the essential
+parameters which critically influence the signal-to-noise ratio of the signals.
+Comparing the model calculations to real datasets allows validating the
+predicted parameter dependences and provides a means to optimise FemNoC
+experiments.",2403.09829v1
+2024-03-15,"Structure, control, and dynamics of altermagnetic textures","We present a phenomenological theory of altermagnets, that captures their
+unique magnetization dynamics and allows modelling magnetic textures in this
+new magnetic phase. Focusing on the prototypical d-wave altermagnets, e.g.
+RuO$_2$, we can explain intuitively the characteristic lifted degeneracy of
+their magnon spectra, by the emergence of an effective sublattice-dependent
+anisotropic spin stiffness arising naturally from the phenomenological theory.
+We show that as a consequence the altermagnetic domain walls, in contrast to
+antiferromagnets, have a finite gradient of the magnetization, with its
+strength and gradient direction connected to the altermagnetic anisotropy, even
+for 180$^\circ$ domain walls. This gradient generates a ponderomotive force in
+the domain wall in the presence of a strongly inhomogeneous external magnetic
+field, which may be achieved through magnetic force microscopy techniques. The
+motion of these altermagentic domain walls is also characterized by an
+anisotropic Walker breakdown, with much higher speed limits of propagation than
+ferromagnets but lower than antiferromagnets.",2403.10218v2
+2024-03-18,Uncovering the lowest thickness limit for room-temperature ferromagnetism of Cr$_{1.6}$Te$_{2}$,"Half-metallic ferromagnetic transition metal dichalcogenides have emerged as
+important building blocks for scalable magnonics and memory applications.
+Downscaling such systems to the ultra-thin limit is critical to integrate them
+into technology. Here, we achieved layer-by-layer control over the transition
+metal dichalcogenide Cr$_{1.6}$Te$_{2}$ by using pulsed laser deposition, and
+we uncovered the minimum critical thickness above which room temperature
+magnetic order is maintained. The electronic and magnetic structure is explored
+experimentally and theoretically and it is shown that the films exhibit strong
+in-plane magnetic anisotropy as a consequence of large spin-orbit effects. Our
+study establishes Cr$_{1.6}$Te$_{2}$ as a platform material, viable for
+ferromagnetic nanoscale devices and magnetic-memory architectures.",2403.11977v1
+2024-03-20,Probing Hilbert Space Fragmentation with Strongly Interacting Rydberg Atoms,"Hilbert space fragmentation provides a mechanism to break ergodicity in
+closed many-body systems. Here, we propose a realistic scheme to
+comprehensively explore this exotic paradigm on a Rydberg quantum simulator. We
+show that the Rydberg Ising model in the large detuning regime can be mapped to
+a generalized folded XXZ model featuring a strongly fragmented Hilbert space.
+The emergent Hamiltonian, however, displays distinct time scales for the
+transport of a magnon and a hole excitation. This interesting property
+facilitates a continuous tuning of the Krylov-subspace ergodicity, from the
+integrable regime, to the Krylov-restricted thermal phase, and eventually to
+the statistical bubble localization region. By further introducing nonlocal
+interactions, we find that both the fragmentation behavior and the ergodicity
+of the Krylov subspace can be significantly enriched. We also examine the role
+of atomic position disorders and identify a symmetry-selective many-body
+localization transition. We demonstrate that these phenomena manifest
+themselves in quench dynamics, which can be readily probed in state-of-the-art
+Rydberg array setups.",2403.13790v1
+2024-03-25,Detection of spin pumping free of rectification and thermal artefacts in molecular-based ferromagnetic insulator V[TCNE]x~2,"The molecular-based ferrimagnetic insulator V(TCNE)x has gained recent
+interest for efficient spin-wave excitation due to its low Gilbert damping
+ratio a=4E-5, and narrow ferromagnetic resonance linewidth f=1Oe. Here we
+report a clean spin pumping signal detected on V(TCNE)x/metal bilayer
+structures, free from spin rectification or thermal artifacts. On-chip coupling
+of microwave power is achieved via a coplanar waveguide to measure the in-plane
+angle-dependence of the inverse spin-Hall effect under ferromagnetic resonance
+conditions with respect to a constant external magnetic field. A signature of
+pure spin current from V(TCNE)x is observed in both platinum and permalloy
+metal layers, demonstrating the utility of V(TCNE)x for magnon spintronics
+studies in molecule/solid-state heterostructures.",2403.16429v2
+2024-03-27,Strong-coupling approach to temperature dependence of competing orders of superconductivity: Possible time-reversal symmetry breaking and nontrivial topology,"We use strong-coupling Eliashberg theory to study the competition of separate
+superconducting orders at low temperatures. Specifically, we study
+magnon-mediated superconductivity in a trilayer heterostructure with a thin
+normal metal between two antiferromagnetic insulators. Spin-triplet $p$-wave,
+spin-triplet $f$-wave, and spin-singlet $d$-wave superconducting gaps have been
+predicted to occur close to the critical temperature for the superconducting
+instability. The gap symmetry with the largest critical temperature depends on
+parameters in the model. We confirm that the same gap symmetries appear at any
+temperature below the critical temperature. Furthermore, we show that the
+temperature can affect the competition between the different superconducting
+orders. In addition, we consider time-reversal-symmetry-breaking, complex
+linear combinations of candidate pairings, such as chiral $p$-, $f$-, and
+$d$-wave gaps, as well as $p_x+if_y$-wave gaps. We find indications that some
+of these time-reversal-symmetry-breaking, nodeless gaps offer a greater
+condensation energy than the time-reversal symmetric gaps. This indicates that
+superconducting states with spontaneously broken time-reversal symmetry and
+nontrivial topology may be preferred in this system.",2403.18897v1
+2024-04-02,Probing the band splitting near the Γ point in the van der Waals magnetic semiconductor CrSBr,"This study investigates the electronic band structure of Chromium Sulfur
+Bromide (CrSBr) through comprehensive photoluminescence (PL) characterization.
+We clearly identify low-temperature optical transitions between two closely
+adjacent conduction-band states and two different valence-band states. The
+analysis of the PL data robustly unveils energy splittings, bandgaps and
+excitonic transitions across different thicknesses of CrSBr, ranging from
+monolayer to bulk. Temperature-dependent PL measurements elucidate the
+stability of the band splitting below the N\'eel temperature, suggesting that
+magnons coupled with excitons are responsible for the symmetry breaking and
+brightening of the transitions from the secondary conduction band minimum
+(CBM2) to the global valence band maximum (VBM1). Collectively, these results
+not only reveal band splitting in both the conduction and valence bands, but
+also point to an intricate interplay between the optical, electronic and
+magnetic properties of antiferromagnetic two-dimensional van der Waals
+crystals.",2404.02927v1
+2024-04-04,Temperature-dependent optical and magneto-optical spectra of ferromagnetic BCC Fe,"Optical and magneto-optical properties of magnetic materials have been widely
+exploited to characterize magnetic structures and phenomena, however, their
+temperature dependence is not well understood. This study implements the
+supercell approach with thermal lattice and magnetic disorders to obtain
+optical and magneto-optical spectra at finite temperatures based on
+Williams-Lax theory. Our results show that large optical spectrum signals are
+generated at photon energies below 1 eV, originating from the phonon- and
+magnon-assisted intraband transitions as lattice and magnetic temperatures
+increase. In addition, the prominent peak near 2.7 eV is redshifted
+proportionally to magnetic temperature but depends much less on lattice
+temperature. By analyzing unfolded bands, we show that the reduction of
+exchange splitting due to the thermal demagnetization causes this redshift. Our
+unfolded electronic band structure with magnetic disorder shows band kinks,
+which are characteristic evidence of the coupling between electrons and
+magnetic excitations. First-order magneto-optical spectra at finite temperature
+are also predicted, but due to their small magnitude suffer more from sampling
+errors. We discuss the effect of zero-point vibrations and the connection of
+these simulations to the Drude model for intraband transitions.",2404.03545v1
+2024-04-07,Time-resolved magneto-optical Kerr effect in the altermagnet candidate MnTe,"{\alpha}-MnTe is an antiferromagnetic semiconductor with above room
+temperature TN = 310 K, which is promising for spintronic applications.
+Recently, it was predicted to be an altermagnet, containing bands with
+momentum-dependent spin splitting; time-resolved experimental probes of
+magnetism in MnTe are therefore important both for understanding the magnetic
+structure and potential device applications. We investigate ultrafast spin
+dynamics in epitaxial MnTe(001)/InP(111) thin films using the time-resolved
+magneto-optical Kerr effect. At room temperature, we observe an oscillation
+mode at 55 GHz that does not appear at zero magnetic field. Combining field,
+polarization, and temperature dependence, we identify this mode as an acoustic
+phonon-coupled magnon, likely originating from inverse stimulated Raman
+scattering. Additionally, we observe two optical phonons at 3.6 THz and 4.2
+THz, which broaden and redshift with increasing temperature.",2404.05020v1
+2024-04-11,Mode-resolved micromagnetics study of parametric spin wave excitation in thin-film disks,"We present a computational study of the parametric excitation of spin waves
+in thin film disks with a mode-resolved approach. The method involves
+projecting out the time-dependent magnetization, computed using micromagnetics
+simulations, onto the spatial profile of the eigenmodes that are obtained from
+the linearization of the equations of motion. Unlike spectral analysis in the
+frequency domain, the projection allows for the analysis of transient mode
+dynamics under parametric excitation. We apply this method to parallel pumping
+of quantized spin wave modes in in-plane magnetized thin-film disks, where
+phenomena like frequency pulling, mutual phase locking, and higher-order magnon
+scattering processes are identified.",2404.07561v1
+1993-07-19,Evolution of Magnetic Properties of Lightly Doped Copper Oxides,"We study how doping destroys the AF order in the layered cuprates within the
+framework of the charge--transfer insulator concept. We use the criterion of
+stability of the AF background to show that the stability problem is one of the
+main issues in any correspondence between results for the $t-J$ model and, say,
+the three--band model for the lightly--doped layered oxides. Provided a
+phenomenological conduction band is chosen to satisfy the criterion of
+stability, a detailed picture of how dopants influence the spin wave spectrum
+at $T=0$ is presented. The critical concentration $x_c$ for the destruction of
+the AF long range order is due to the Cherenkov effect when the Fermi velocity
+first exceeds the spin wave velocity. We then discuss the overall spectrum of
+spin excitations and find that the spin wave attenuation for $x < x_c$, $T=0$
+due to Landau damping appears in the range of magnon momenta $k(x) = 2 m^* s
+\pm \alpha \sqrt{x}$. We also argue that in the presence of superconductivity,
+the Cherenkov effect is eliminated due to the gap in the spectrum. This may
+restore the role of the AF fluctuations as the main source of dissipation at
+the lowest temperatures.",9307040v1
+1995-09-30,Integrability and Applications of the Exactly-Solvable Haldane-Shastry One-Dimensional Quantum Spin Chain,"Recently, the one dimensional model of $N$ spins with $S=\frac{1}{2}$ on a
+circle, interacting with an exchange that falls off with the inverse square of
+the separation: $H_{\rm ISE} =\sum_{i\neq j} \frac{1}{[\frac{N}{\pi}
+\sin(\frac{i-j}{N}\pi)]^2}(\svec_i\cdot \svec_j-\frac{1}{4})$, or ISE-model,
+has received ample attention. Its special features include: relatively simple
+eigenfunctions, non-interacting elementary excitations that obey semionic
+statistics (spinons), and a large ``quantum group'' symmetry algebra called the
+Yangian. This model is fully integrable, albeit in a slightly different sense
+than the more traditional nearest neighbor exchange (NNE) Heisenberg chain.
+This thesis comes in 4 chapters. Chapter 1 introduces the model and presents
+the construction of a subset of the eigenfunctions. The other eigenfunctions
+are shown to be generated by the action of the Yangian symmetry algebra of
+$H_{\rm ISE}$. Chapter 2 presents a method to construct the set of constants of
+the motion of the ISE-model. The ISE-model is tractable enough to obtain its
+zero-magnetic-field dynamical structure factors. Chapter 3 attempts to extend
+this to a non-zero magnetic field, where, due to the presence of spinons in the
+groundstate, more complicated excitations contribute: small numbers of magnons
+and spinons. discuss the relation to the more complicated NNE-model. Finally
+chapter 4 illustrates how a recently conjectured new form of Off Diagonal Long
+Range Order in antiferromagnetic spin chains can be reinterpreted as a spinon
+propagator in the ISE-model, and verified numerically. We briefly comment on
+its relevance to stabilizing superconductivity in the layered cuprates.",9509178v1
+1995-12-18,Raman scattering in a two-layer antiferromagnet,"Two--magnon Raman scattering is a useful tool to verify recent suggestions
+concerning the value of the interplanar exchange constant in antiferromagnetic
+two--layer systems, such as $YBa_2Cu_3O_{6+x}$. We present a theory for Raman
+scattering in a two--layer antiferromagnet. We study the spectra for the
+electronic and magnetic excitations across the charge transfer gap within the
+one--band Hubbard model and derive the matrix elements for the Raman scattering
+cross section in a diagrammatic formalism. We analyze the effect of the
+interlayer exchange coupling $J_2$ for the Raman spectra in $A_{1g}$ and
+$B_{1g}$ scattering geometries both in the non--resonant regime (when the
+Loudon--Fleury model is valid), and at resonance. We show that within the
+Loudon--Fleury approximation, a nonzero $J_2$ gives rise to a finite signal in
+$A_{1g}$ scattering geometry. Both, in this approximation and at resonance, the
+intensity in the $A_{1g}$ channel has a peak at {\it small} transferred
+frequency equal to twice the gap in the spin--wave spectrum. We compare our
+results with experiments in $YBa_2Cu_3O_{6.1}$ and $Sr_2CuO_2Cl_2$ compounds
+and argue that the large value of $J_2$ suggested in a number of recent studies
+is incompatible with Raman experiments in $A_{1g}$ geometry.",9512131v1
+1996-09-19,Spectral properties of the t-J model in the presence of hole-phonon interaction,"We examine the effects of electron-phonon interaction on the dynamics of the
+charge carriers doped in two-dimensional (2D) Heisenberg antiferromagnet. The
+$t$-$J$ model Hamiltonian with a Fr\""ohlich term which couples the holes to a
+dispersionless (optical) phonon mode is considered for low doping
+concentration. The evolution of the spectral density function, the density of
+states, and the momentum distribution function of the holes with an increase of
+the hole-phonon coupling constant $g$ is studied numerically. As the coupling
+to a phonon mode increases the quasiparticle spectral weight decreases and a
+``phonon satellite'' feature close to the quasi-particle peak becomes more
+pronounced. Furthermore, strong electron-phonon coupling smears the
+multi-magnon resonances (``string states'') in the incoherent part of the
+spectral function. The jump in the momentum distribution function at the Fermi
+surface is reduced without changing the hole pocket volume, thereby providing a
+numerical verification of Luttinger theorem for this strongly interacting
+system. The vertex corrections due to electron- phonon interaction are
+negligible in spite of the fact that the ratio of the phonon frequency to the
+effective bandwidth is not small.",9609186v1
+1996-10-01,Itinerant Antiferromagnetism in FeGe_2,"FeGe_2, and lightly doped compounds based on it, have a Fermi surface driven
+instability which drive them into an incommensurate spin density wave state.
+Studies of the temperature and magnetic field dependence of the resistivity
+have been used to determine the magnetic phase diagram of the pure material
+which displays an incommensurate phase at high temperatures and a commensurate
+structure below 263 K in zero field. Application of a magnetic field in the
+tetragonal basal plane decreases the range of temperatures over which the
+incommensurate phase is stable. We have used inelastic neutron scattering to
+measure the spin dynamics of FeGe_2. Despite the relatively isotropic transport
+the magnetic dynamics is quasi-one dimensional in nature. Measurements carried
+out on HET at ISIS have been used to map out the spin wave dispersion along the
+c-axis up the 400 meV, more than an order of magnitude higher than the zone
+boundary magnon for wavevectors in the basal plane.",9610009v1
+1997-03-06,Effects of in-chain and off-chain substitutions on spin fluctuations in the spin-Peierls compound CuGeO_3,"The effect of in-chain and off-chain substitutions on 1D spin fluctuations in
+the spin-Peierls compound CuGeO_3 has been studied using Raman scattering in
+order to understand the interplay between defect induced states, enhanced
+spin-spin correlations and the ground state of low dimensional systems.
+In-chain and off-chain substitutions quench the spin-Peierls state and induce
+3D antiferromagnetic order at T\leq 5 K. Consequently a suppression of a 1D
+gap-induced mode as well as a constant intensity of a spinon continuum are
+observed at low temperatures. A 3D two-magnon density of states now gradually
+extends to higher temperatures T\leq 60K compared with pure CuGeO_3. This
+effect is more pronounced in the case of off-chain substitutions (Si) for which
+a N\'eel state occurs over a larger substitution range, starting at very low
+concentrations. Besides, additional low energy excitations are induced. These
+effects, i.e. the shift of a dimensional crossover to higher temperatures are
+due to an enhancement of the spin-spin correlations induced by a small amount
+of substitutions. The results are compared with recent Monte Carlo studies on
+substituted spin ladders, pointing to a similar instability of coupled,
+dimerized spin chains and spin ladders upon substitution.",9703060v1
+1997-03-12,Scaling picture of magnetism formation in the anomalous f-systems: interplay of the Kondo effect and spin dynamics,"Formation of magnetically ordered state in the Kondo lattices is treated
+within the degenerate $s-f$ exchange and Coqblin-Schrieffer models. The Kondo
+renormalizations of the effective coupling parameter, magnetic moment and spin
+excitation frequencies are calculated within perturbation theory. The results
+of one-loop scaling consideration of the magnetic state in Kondo lattices are
+analyzed. The dependence of the critical values of the bare model parameters on
+the type of the magnetic phase and space dimensionality is investigated.
+Renormalization of the effective Kondo temperature by the interatomic exchange
+interactions is calculated. An important role of the character of spin dynamics
+(existence of well-defined magnon excitations, presence of magnetic anisotropy
+etc.) is demonstrated. The regime of strongly suppressed magnetic moments,
+which corresponds to magnetic heavy-fermion system, may occur in a rather
+narrow parameter region only. At the same time, in the magnetically ordered
+phases the renormalized Kondo temperature depends weakly on the bare coupling
+parameter in some interval. The critical behavior, corresponding to the
+magnetic transition with changing the bare $s-f$ coupling parameter, is
+investigated. In the vicinity of the strong coupling regime, the spectrum of
+the Bose excitations becomes softened. Thus on the borderline of magnetic
+instability the Fermi-liquid picture is violated in some temerature interval
+due to scattering of electrons by these bosons. This may explain the fact that
+a non-Fermi-liquid behavior often takes place in the heavy-fermion systems near
+the onset of magnetic ordering.",9703125v1
+1997-08-25,Effects of Phonons and Nuclear Spins on the Tunneling of a Domain Wall,"We consider the quantum dynamics of a magnetic domain wall at low
+temperatures, where dissipative couplings to magnons and electrons are very
+small. The wall motion is then determined by its coupling to phonons and
+nuclear spins, and any pinning potentials. In the absence of nuclear spins
+there is a dominant superOhmic 1-phonon coupling to the wall velocity, plus a
+strongly T-dependent Ohmic coupling to pairs of phonons. There is also a
+T-independent Ohmic coupling between single phonons and the wall chirality,
+which suppresses ``chirality tunneling''. We calculate the effect of these
+couplings on the T-dependent tunneling rate of a wall out of a pinning
+potential. Nuclear spins have a very strong and hitherto unsuspected influence
+on domain wall dynamics, coming from a hyperfine-mediated coupling to the
+domain wall position. For $k_B T \gg \omega_{0}$ this coupling yields a
+spatially random potential, fluctuating at a rate governed by the nuclear
+$T_2$. When $k_B T \ll \omega_{0}$, the hyperfine potential fluctuates around a
+linear binding potential. The wall dynamics is influenced by the fluctuations
+of this potential, ie., by the nuclear spin dynamics. Wall tunneling can occur
+when fluctuations open an occasional ``tunneling window''. This changes the
+crossover to tunneling and also causes a slow ""wandering"", in time, of the
+energy levels associated with domain wall motion inside the pinning potential.
+This effect is fairly weak in $Ni$- and $Fe$- based magnets, and we give an
+approximate treatment of its effect on the tunneling dynamics, as well as a
+discussion of the relationship to recent domain wall tunneling experiments.",9708191v1
+1998-06-30,"Transport, optical and electronic properties of the half metal CrO2","The electronic structure of CrO_2 is critically discussed in terms of the
+relation of existing experimental data and well converged LSDA and GGA
+calculations of the electronic structure and transport properties of this half
+metal magnet, with a particular emphasis on optical properties. We find only
+moderate manifestations of many body effects. Renormalization of the density of
+states is not large and is in the typical for transition metals range. We find
+substantial deviations from Drude behavior in the far-infrared optical
+conductivity. These appear because of the unusually low energy of interband
+optical transitions. The calculated mass renormalization is found to be rather
+sensitive to the exchange-correlation functional used and varies from 10%
+(LSDA) to 90% (GGA), using the latest specific heat data. We also find that
+dressing of the electrons by spin fluctuations, because of their high energy,
+renormalizes the interband optical transition at as high as 4 eV by about 20%.
+Although we find no clear indications of strong correlations of the Hubbard
+type, strong electron-magnon scattering related to the half metallic band
+structure is present and this leads to a nontrivial temperature dependence of
+the resistivity and some renormalization of the electron spectra.",9806378v1
+1998-08-08,Pseudogaps and magnetic properties of the two-dimensional t-J model,"We apply the modified spin-wave theory with the constraint of zero staggered
+magnetization to investigate normal-state spectral and magnetic properties of
+the 2D t-J model in the paramagnetic state. A set of self-energy equations for
+hole and magnon Green's functions is solved numerically in the self-consistent
+Born approximation. The constraint can be fulfilled in the ranges of hole
+concentrations 0.02 < x < 0.17 and temperatures T < 150 K. In this region the
+hole spectrum differs from a conventional metallic spectrum which is manifested
+in the variation with x of the quasiparticle weights of states and in the
+violation of Luttinger's theorem. With decreasing x from x = 0.17 hidden parts
+appear in the hole Fermi surface which can be interpreted as the opening of a
+pseudogap near (pi,0). Obtained size, symmetry and concentration dependence of
+the pseudogap are in agreement with photoemission data in Bi2212. Calculated
+temperature dependencies of the spin correlation length, spin-lattice
+relaxation times at the Cu and O sites, and static susceptibility are typical
+for the quantum disordered regime with a pseudogap in the spectrum of magnetic
+excitations. These quantities are in qualitative and in some cases in
+quantitative agreement with experiment in underdoped YBa2Cu3O(6+y). At x > 0.12
+the considered phase borders the phase of conventional metal.",9808087v1
+1998-12-31,The Heisenberg antiferromagnet on an anisotropic triangular lattice: linear spin-wave theory,"We consider the effect of quantum spin fluctuations on the ground state
+properties of the Heisenberg antiferromagnet on an anisotropic triangular
+lattice using linear spin-wave theory. This model should describe the magnetic
+properties of the insulating phase of the kappa-(BEDT-TTF)_2 X family of
+superconducting molecular crystals. The ground state energy, the staggered
+magnetization, magnon excitation spectra and spin-wave velocities are computed
+as a function of the ratio between the second and first neighbours, J2/J1. We
+find that near J2/J1 = 0.5, i.e., in the region where the classical spin
+configuration changes from a Neel ordered phase to a spiral phase, the
+staggered magnetization vanishes, suggesting the possibility of a quantum
+disordered state. In this region, the quantum correction to the magnetization
+is large but finite. This is in contrast to the frustrated Heisenberg model on
+a square lattice, for which the quantum correction diverges logarithmically at
+the transition from the Neel to the collinear phase. For large J2/J1, the model
+becomes a set of chains with frustrated interchain coupling. For J2 > 4 J1, the
+quantum correction to the magnetization, within LSW, becomes comparable to the
+classical magnetization, suggesting the possibility of a quantum disordered
+state. We show that, in this regime, quantum fluctuations are much larger than
+for a set of weakly coupled chains with non-frustated interchain coupling.",9812429v2
+2000-01-07,Theory of the spin bath,"The quantum dynamics of mesoscopic or macroscopic systems is always
+complicated by their coupling to many ""environmental"" modes.At low T these
+environmental effects are dominated by localised modes, such as nuclear and
+paramagnetic spins, and defects (which also dominate the entropy and specific
+heat). This environment, at low energies, maps onto a ""spin bath"" model. This
+contrasts with ""oscillator bath"" models (originated by Feynman and Vernon)
+which describe {\it delocalised} environmental modes such as electrons,
+phonons, photons, magnons, etc. One cannot in general map a spin bath to an
+oscillator bath (or vice-versa); they constitute distinct ""universality
+classes"" of quantum environment. We show how the mapping to spin bath models is
+made, and then discuss several examples in detail, including moving particles,
+magnetic solitons, nanomagnets, and SQUIDs, coupled to nuclear and paramagnetic
+spin environments. We show how to average over spin bath modes, using an
+operator instanton technique, to find the system dynamics, and give analytic
+results for the correlation functions, under various conditions. We then
+describe the application of this theory to magnetic and superconducting
+systems.Particular attention is given to recent work on tunneling magnetic
+macromolecules, where the role of the nuclear spin bath in controlling the
+tunneling is very clear; we also discuss other magnetic systems in the quantum
+regime, and the influence of nuclear and paramagnetic spins on flux dynamics in
+SQUIDs.",0001080v2
+2000-05-04,Optical Properties of the Spin-Ladder Compound Sr_{14}Cu_{24}O_{41},"We report the measurements of the pseudodielectric function, far-infrared
+reflectivity and Raman scattering spectra in Sr_{14}Cu_{24}O_{41} single
+crystal. We study the lattice and the spin dynamics of the Cu$_2$O$_3$ spin
+ladders and CuO$_2$ chains of this compound. The ellipsometric and the optical
+reflectivity measurements yield the gap values of 1.4 eV, 1.86 eV, 2.34 eV (2.5
+eV) for the ladders (chains) along the {\bf c}-axis and 2.4 eV along the {\bf
+a}-axis. The electronic structure of the Cu$_2$O$_3$ ladders is analyzed using
+tight-binding approach for the correlated electron systems. The correlation gap
+value of 1.4 eV is calculated with the transfer energy (hopping) parameters
+$t=t_{0}$=0.26 eV, along and perpendicular to legs, $t_{xy}$=0.026 eV
+(interladder hopping) and U=2.1 eV, as a Coulomb repulsion. The optical
+parameters of the infrared active phonons and plasmons are obtained by
+oscillator fitting procedure of the reflectivity spectra. Raman scattering
+spectra are measured at different temperatures using different laser line
+energies. The two-magnon peak is observed at about 2880 cm$^{-1}$. At
+temperatures below 150 K the new infrared and Raman modes appear due to the
+charge ordering.",0005096v1
+2001-04-24,Field-induced magnetic transitions in the quasi-two-dimensional heavy-fermion antiferromagnets Ce_{n}RhIn_{3n+2} (n=1 or 2),"We have measured the field-dependent heat capacity in the tetragonal
+antiferromagnets CeRhIn$_{5}$ and Ce$_{2}$RhIn$_{8}$, both of which have an
+enhanced value of the electronic specific heat coefficient $\gamma \sim 400$
+mJ/mol-Ce K$^{2}$ above $T_{N}$. For $T<T_{N},$ the specific heat data at zero
+applied magnetic field are consistent with the existence of an anisotropic
+spin-density wave opening a gap in the Fermi surface for CeRhIn$_{5},$ while
+Ce$_{2}$RhIn$_{8}$ shows behavior consistent with a simple antiferromagnetic
+magnon. From these results, the magnetic structure, in a manner similar to the
+crystal structure, appears more two-dimensional in CeRhIn$_{5}$ than in
+Ce$_{2}$RhIn$_{8}$ where only about 12% of the Fermi surface remains ungapped
+relative to 92% for Ce$_{2}$RhIn$_{8}$. When $B||c,$ both compounds behave in a
+manner expected for heavy fermion systems as both $T_{N}$ and the electronic
+heat capacity decrease as field is applied. When the field is applied in the
+tetragonal basal plane ($B||a$), CeRhIn$_{5}$ and Ce$_{2}$RhIn$_{8}$ have very
+similar phase diagrams which contain both first- and second-order field-induced
+magnetic transitions .",0104446v1
+2002-07-04,"Dynamics, Selection Rules and Dzyaloshinsky-Moriya interactions in Strongly Frustrated Magnets","Anisotropic spin-spin interactions of the symmetry described by Dzyaloshinsky
+and Moriya are generally considered weak, as they depend on the spin-orbit
+couplings. In frustrated spin systems with singlet ground states they can,
+however, have rather strong effects. We discuss recent results related to two
+gapped spin systems: $\rm CuGeO_3$ and $\rm SrCu_2(BO_3)_2$ in particular. In
+the first compound the Dzyaloshinsky-Moriya interactions effectively lower the
+symmetry of the magnetic unit cell and this leads to doubling of the low
+frequency mode. In the second case, the Dzyaloshinsky-Moriya interactions also
+split the lowest magnon mode linearly in the spin-orbit coupling. In addition,
+the relatively weak Dzyaloshinsky-Moriya interactions can dominate the
+dispersion.
+  Consideration of the selection rules for optical transitions show that while
+the Dzyaloshinsky-Moriya interactions can explain much of the dynamics, they do
+not explain the observed transition amplitudes. This leads to a review of
+recent calculations of anisotropic spin-phonon couplings. We discuss how this
+leads to a novel mechanism to explain the ESR intensities in the spin gap
+systems discussed. Selection rules for this novel mechanism involving coupling
+to the electric field of the resonant probe are discussed and relation to
+polarised neutron experiments briefly mentioned.",0207116v1
+2003-01-17,Thermal conductivity of lightly Sr- and Zn-doped La$_2$CuO$_4$ single crystals,"Both ab-plane and c-axis thermal conductivities ($\kappa_{ab}$ and
+$\kappa_c$) of lightly doped La$_{2-x}$Sr$_x$CuO$_4$ and
+La$_2$Cu$_{1-y}$Zn$_y$O$_4$ single crystals ($x$ or $y$ = 0 -- 0.04) are
+measured from 2 to 300 K. It is found that the low-temperature phonon peak (at
+20 -- 25 K) is significantly suppressed upon Sr or Zn doping even at very low
+doping, though its precise doping dependences show interesting differences
+between the Sr and Zn dopants, or between the $ab$ plane and the c axis. Most
+notably, the phonon peak in $\kappa_c$ decreases much more quickly with Sr
+doping than with Zn doping, while the phonon-peak suppression in $\kappa_{ab}$
+shows an opposite trend. It is discussed that the scattering of phonons by
+stripes is playing an important role in the damping of the phonon heat
+transport in lightly doped LSCO, in which static spin stripes has been observed
+by neutron scattering. We also show $\kappa_{ab}$ and $\kappa_c$ data of
+La$_{1.28}$Nd$_{0.6}$Sr$_{0.12}$CuO$_4$ and
+La$_{1.68}$Eu$_{0.2}$Sr$_{0.12}$CuO$_4$ single crystals to compare with the
+data of the lightly doped crystals for the discussion of the role of stripes.
+At high temperature, the magnon peak (i.e., the peak caused by the spin heat
+transport near the N\'{e}el temperature) in $\kappa_{ab}(T)$ is found to be
+rather robust against Zn doping, while it completely disappears with only 1% of
+Sr doping.",0301315v1
+2003-02-25,"Magnon Specific Heat of Single Crystal Borocarbides RNi2B2C (R=Tm, Er, Ho, Dy, Tb, Gd)","Zero-field specific heat of the single crystals RNi2B2C (R= Er, Ho, Dy, Tb,
+Gd) was measured within the temperature range 0.1 K<T<25 K. Linearized spin
+wave analysis was successfully applied to account for and to rationalize the
+thermal evolution of the low--temperature magnetic specific heats of all the
+studied compounds (as well as the one reported for TmNi2B2C) in terms of only
+two parameters, namely an energy gap, delta, and a characteristic temperature,
+theta. The evolution of the gap and theta across the studied compounds
+correlates very well with the known magnetic properties. Theta, as a measure of
+the effective RKKY exchange couplings, scales reasonably well with the de
+Gennes factor. The gap, on the other hand, reflects predominately the
+anisotropic properties: ~2 K for GdNi2B2C, ~6 K for ErNi2B2C, ~7 K for
+TbNi2B2C, and ~8 K for each of HoNi2B2C and DyNi2B2C. The equality in the gap
+of HoNi2B2C and DyNi2B2C, coupled with the similarity in their magnetic
+configurations, indicates that a variation of x in the solid solution
+HoxDy1-xNi2B2C (x<0.8 and Tc<Tn) would not lead to any softening of the gap.
+This supports the hypothesis of Cho et al (PRL 77,163(1996)) concerning the
+influence of the collective magnetic excitations on the superconducting state.
+This work underlines the importance of spin-wave excitations for a valid
+description of low-temperature thermodynamics of borocarbides.",0302526v1
+2003-03-18,On the significance of quantum effects and interactions for the apparent universality of Bloch laws for M_s(T),"The apparent universality of Bloch's T^{3/2}-law for the temperature
+dependence of the spontaneous magnetization, and of generalizations thereof, is
+considered. It is argued that in the derivation one should not only consider
+the exchange interaction between the spins, but also the other interactions
+between them, leading to elliptical spin precession and deviations from the
+parabolic dispersion of magnons. Also interaction effects are important to
+explain the apparent universality of generalized Bloch law exponents e_B,
+defined by M_s(T)= M_s(0)-const. x T^{e_B}, valid in a wide temperature range
+T_1 < T < T_2, and for dimensionalities d = 1, 2, and 3. The above-mentioned
+temperature range, the 'Bloch range', lies above the quantum range, where
+magnetic long-range order (e.g. in d=2 dimensions) is nontrivially enforced by
+the additional interactions, but below the thermal critical region, where
+universal 'anomalous scaling dimensions' apply. In contrast, for the Bloch
+temperature region, the universality is only apparent, i.e. a
+crossover-phenomenon, and simple scaling considerations with 'normal
+dimensions' apply.
+  However, due to interactions, the Bloch exponent e_B depends not only on the
+dimensionality d of the system, but also on the spin quantum number s (mod
+(1/2)) of the system, i.e. for given d the Bloch exponent e_B is different for
+half-integer s and for integer s.",0303357v3
+2003-06-24,First-order transition in the itinerant ferromagnet CoS$_{1.9}$Se$_{0.1}$,"Undoped CoS$_2$ is an isotropic itinerant ferromagnet with a continuous or
+nearly continuous phase transition at $T_{\rm C} = 122$ K. In the doped
+CoS$_{1.9}$Se$_{0.1}$ system, the Curie temperature is lowered to $T_{\rm C} =
+90$ K, and the transition becomes clearly first order in nature. In particular
+we find a discontinuous evolution of the spin dynamics as well as strong time
+relaxation in the ferromagnetic Bragg intensity and small angle neutron
+scattering in vicinity of the ferromagnetic transition. In the ordered state
+the long-wavelength spin excitations were found to be conventional
+ferromagnetic spin-waves with negligible spin-wave gap ($ < 0.04$ meV),
+indicating that this system is also an excellent isotropic (soft) ferromagnet.
+In a wide temperature range up to $0.9T_{\rm C}$, the spin-wave stiffness
+$D(T)$ follows the prediction of the two-magnon interaction theory, $D(T) =
+D(0)(1 - AT^{5/2})$, with $D(0) = 131.7 \pm 2.8$ meV-\AA$^{2}$. The stiffness,
+however, does not collapse as $T \to T_{\rm C}$ from below. Instead a
+quasielastic central peak abruptly develops in the excitation spectrum, quite
+similar to results found in the colossal magnetoresistance oxides such as
+(La-Ca)MnO$_3$.",0306618v1
+2004-03-13,Interplay of structural and electronic phase separation in single crystalline La(2)CuO(4.05) studied by neutron and Raman scattering,"We report a neutron and Raman scattering study of a single-crystal of
+La(2)CuO(4.05) prepared by high temperature electrochemical oxidation. Elastic
+neutron scattering measurements show the presence of two phases, corresponding
+to the two edges of the first miscibility gap, all the way up to 300 K. An
+additional oxygen redistribution, driven by electronic energies, is identified
+at 250 K in Raman scattering (RS) experiments by the simultaneous onset of
+two-phonon and two-magnon scattering, which are fingerprints of the insulating
+phase. Elastic neutron scattering measurements show directly an
+antiferromagnetic ordering below a N\'eel temperature of T_N =210K. The opening
+of the superconducting gap manifests itself as a redistribution of electronic
+Raman scattering below the superconducting transition temperature, T_c = 24K. A
+pronounced temperature-dependent suppression of the intensity of the (100)
+magnetic Bragg peak has been detected below T_c. We ascribe this phenomenon to
+a change of relative volume fraction of superconducting and antiferromagnetic
+phases with decreasing temperature caused by a form of a superconducting
+proximity effect.",0403340v1
+2004-03-28,Fully polarized states and decoherence,"The aim of this review is to show how ``ferromagnetic'' states, that is,
+states having a fully polarization, can produce intrinsic decoherence by
+unitary evolution. This effect can give an understanding of recent experiments
+on mesoscopic devices as quantum point contacts showing the 0.7 conductance
+anomaly and the wide number of data about saturation of dephasing time observed
+at very low temperatures, as a fully polarized two dimensional electron gas.
+But similar effects can be seen in different area of physics as for example the
+Dicke model describing the interaction of two-level systems with a radiation
+mode. In this case one can show that decoherence is intrinsic and remove a
+Schr\""odinger cat state leaving a single coherent state, collapsing the wave
+function in the thermodynamic limit. So, saturation of dephasing time at low
+temperatures in mesoscopic devices can be understood by a fully polarized two
+dimensional electron gas that, by an exchange model, can be reduced to a
+generalized form of the Dicke Hamiltonian and where the quasiparticles are spin
+excitations interacting with magnons. In this way, one can see that several
+experiments on nanowires and quantum dots can be satisfactorily explained. The
+existence of intrinsic decoherence in the thermodynamic limit could have deep
+implications in fundamental problems like quantum measurement and
+irreversibility. Recent experiments with cavities with a large number of
+photons and with nuclear magnetic resonance in organic molecular crystals give
+a first strong support to this view.",0403678v1
+2004-04-19,Néel-Dimer Transition in Antiferromagnetic Heisenberg Model and Deconfinement of Spinons at the Critical Point,"Quantum phase transition from the N\'eel to the dimer states in an
+antiferromagnetic(AF) Heisenberg model on square lattice is studied. We
+introduce a control parameter $\alpha$ for the exchange coupling which connects
+the N\'eel ($\alpha=0$) and the dimer ($\alpha=1$) states. We employ the $CP^1$
+(the Schwinger boson) representation of the $s={1\over 2}$ spin operator and
+integrate out the half of the $CP^1$ variables at odd sites and we obtain a
+$CP^1$ nonlinear $\sigma$ model. The effective coupling constant is a function
+of $\alpha$ and at $\alpha=0$ the $CP^1$ model is in the ordered phase which
+corresponds to the N\'eel state of the AF Heisenberg model. A phase transition
+to the dimer state occurs at a certain critical value of $\alpha_C$ as $\alpha$
+increases. In the N\'eel state, the dynamical composite U(1) gauge field in the
+$CP^1$ model is in a Higgs phase and low-energy excitations are gapless spin
+wave. In the dimer phase, a confinement phase of the gauge theory is realized
+and low-energy excitations are $s=1$ magnons. For the critical point, we argue
+that a deconfinement phase, which is similar to the Coulomb phase in 3 spatial
+dimensions, is realized and $s={1\over 2}$ spinons appear as low-energy
+excitations.",0404427v4
+2004-05-19,Auxiliary-Fermion Approach to Critical Fluctuations in the 2D Quantum AF Heisenberg Model,"The nearest-neighbor quantum-antiferromagnetic (AF) Heisenberg model for spin
+1/2 on a two-dimensional square lattice is studied in the auxiliary-fermion
+representation. Expressing spin operators by canonical fermionic particles
+requires a constraint on the fermion charge Q=1 on each lattice site, which is
+imposed approximately through the thermal average. The resulting interacting
+fermion system is first treated in mean-field theory (MFT), which yields an AF
+ordered ground state and spin waves in quantitative agreement with conventional
+spin-wave theory. At finite temperature a self-consistent approximation beyond
+mean field is required in order to fulfill the Mermin-Wagner theorem. We first
+discuss a fully self-consistent approximation, where fermions are renormalized
+due to fluctuations of their spin density, in close analogy to FLEX. While
+static properties like the correlation length come out correctly, the dynamical
+response lacks the magnon-like peaks which would reflect the appearance of
+short-range order at low T. This drawback, which is caused by overdamping, is
+overcome in a `minimal self-consistent approximation' (MSCA), which we derive
+from the equations of motion. The MSCA features dynamical scaling at small
+energy and temperature and is qualitatively correct both in the regime of
+order-parameter relaxation at long wavelengths and in the short-range-order
+regime. We also discuss the impact of vertex corrections and the problem of
+pseudo-gap formation in the single-particle density of states due to long-range
+fluctuations. Finally we show that the (short-range) magnetic order in MFT and
+MSCA helps to fulfill the constraint on the local fermion occupancy.",0405438v2
+2004-06-02,Asymmetry of the electronic states in hole- and electron-doped cuprates: Exact diagonalization study of the t-t'-t''-J model,"We systematically examine the asymmetry of the electronic states in the hole-
+and electron-doped cuprates by using the t-t'-t''-J model. Numerically exact
+diagonalization method is employed for a 20-site square lattice. We impose
+twisted boundary conditions (BC) instead of standard periodic BC. For static
+and dynamical correlation functions, averaging procedure over the twisted BC is
+used to reduce the finite-size effect. We find that antiferromagnetic spin
+correlation remains strong in electron doping in contrast to the case of hole
+doping, being similar to the case of the periodic BC. This leads to a
+remarkable electron-hole asymmetry in the dynamical spin structure factor and
+two-magnon Raman scattering. By changing the twist, the single-particle
+spectral function is obtained for all momenta in the Brillouin zone. Examining
+the spectral function in detail, we find a gap opening at around the k=(pi,0)
+region for 10% doping of holes (the carrier concentration x=0.1), leading to a
+Fermi arc that is consistent with experiments. In electron doping, however, a
+gap opens at around k=(pi/2,pi/2) and persists up to x=0.2, being correlated
+with the strength of the antiferromagnetic correlation. We find that the
+magnitude of the gaps is sensitive to t' and t''. A pseudogap is also seen in
+the optical conductivity for electron doping, and its magnitude is found to be
+the same as that in the spectral function. We compare calculated quantities
+with corresponding experimental data, and discuss similarities and differences
+between them as well as their implications.",0406041v2
+2005-02-08,Generalized kinetic and evolution equations in the approach of the nonequilibrium statistical operator,"The method of the nonequilibrium statistical operator developed by D. N.
+Zubarev is employed to analyse and derive generalized transport and kinetic
+equations. The degrees of freedom in solids can often be represented as a few
+interacting subsystems (electrons, spins, phonons, nuclear spins, etc.).
+Perturbation of one subsystem may produce a nonequilibrium state which is then
+relaxed to an equilibrium state due to the interaction between particles or
+with a thermal bath. The generalized kinetic equations were derived for a
+system weakly coupled to a thermal bath to elucidate the nature of transport
+and relaxation processes. It was shown that the ""collision term"" had the same
+functional form as for the generalized kinetic equations for the system with
+small interactions among particles. The applicability of the general formalism
+to physically relevant situations is investigated. It is shown that some known
+generalized kinetic equations (e.g. kinetic equation for magnons, Peierls
+equation for phonons) naturally emerges within the NSO formalism. The
+relaxation of a small dynamic subsystem in contact with a thermal bath is
+considered on the basis of the derived equations. The Schrodinger-type equation
+for the average amplitude describing the energy shift and damping of a particle
+in a thermal bath and the coupled kinetic equation describing the dynamic and
+statistical aspects of the motion are derived and analysed. The equations
+derived can help in the understanding of the origin of irreversible behavior in
+quantum phenomena.",0502194v1
+2005-06-07,Effect of local charge fluctuations on spin physics in the Neel state of La$_2$CuO$_4$,"We explore the effect of local charge fluctuations on the spin response of a
+Mott insulator by deriving an effective spin model, and studying it using
+Schwinger boson mean field theory. Applying this to La$_2$CuO$_4$, we show that
+an accurate fit to the magnon dispersion relation, measured by Coldea {\em et
+al.} [Phys. Rev. Lett. {\bf 86}, 5377 (2001)] is obtained with Hubbard model
+parameters $U \approx 2.34 eV$, and $t \approx 360 meV$. These parameters lead
+to estimates of the staggered magnetization ($m_s \approx 0.25$), spin wave
+velocity ($c\approx 800 meV$-\AA), and spin stiffness ($\rho_s \approx 24
+meV$). In particular the staggered moment as well as the effective local moment
+are renormalized to smaller values compared to the Heisenberg model due to
+local charge fluctuations in the Hubbard model. The dynamical structure factor
+shows considerable weight in the continuum along the zone boundary as well as
+secondary peaks that may be observed in high resolution neutron scattering
+experiments.",0506188v2
+2005-10-07,"Collective Spin and Charge Excitations in (Sr,La)_{14-x}Ca_xCu_{24}O_{41} Quantum Spin Ladders","We study magnetic and electronic properties of two-leg ladder materials. We
+observed a two-magnon (2M) resonance which we analyze in terms of symmetry,
+relaxation and resonance properties. Our findings were contrasted to 2M Raman
+measurements in other magnetic crystals. This comparison made us suggest that
+the spin-spin correlations in a self-doped two leg ladder may have a modulated
+component besides the exponential decay characteristic of a spin liquid ground
+state. We found that the 2M intensity resonates at the Mott gap energy.
+Interplane Sr substitution for Ca introduces strong disorder leading to
+inhomogeneous broadening of the 2M resonance. The doped holes in the spin
+liquid ground state further dilute the magnetic correlations, suppressing the
+spectral weight of this excitation. At high Ca concentrations are
+superconducting under pressure and hole pairing was proposed to be a robust
+feature of doped ladders. The measured dielectric response in the microwave
+region, the low energy Raman data, the non-linear transport properties along
+with soft x-ray scattering allowed us to conclude that the ground state for a
+wide range of Ca concentrations (x < 12) is characterized by charge density
+wave correlations. This state seems to be driven not by phonons but by Coulomb
+forces and many-body effects. We highlighted the similarity in the finite
+frequency Raman response as opposed to the very different behavior of the DC
+resistivity between undoped and doped ladders. We found that at high Ca
+concentrations the carrier relaxation is characterized by the same large
+activation energy (~2000 K) as in the self-doped compound. This observation
+prompted us to suggest an unconventional metallic transport driven by
+collective electronic response.",0510193v1
+2006-01-23,Is room-temperature superconductivity with phonons possible?,"By recognizing the vital importance of two-hole Cooper pairs (CPs) in
+addition to the usual two-electron ones in a strongly-interacting many-electron
+system, the concept of CPs was re-examined with striking conclusions. Based on
+this, Bose-Einstein condensation (BEC) theory has been generalized to include
+not boson-boson interactions (also neglected in BCS theory) but rather
+boson-fermion (BF)interaction vertices reminiscent of the Frohlich
+electron-phonon interaction in metals. Unlike BCS theory, the GBEC model is not
+a mean-field theory restricted to weak-coupling as it can be diagonalized
+exactly. In weak coupling it reproduces the BCS condensation energy. Each kind
+of CP is responsible for only half the condensation energy. The GBEC theory
+reduces to all the old known statistical theories as special cases including
+the so-called ""BCS-Bose crossover"" picture which in turn generalizes BCS theory
+by not assuming that the electron chemical potential equals the Fermi energy.
+Indeed, a BCS condensate is precisely the weak-coupling limit of a GBE
+condensate with equal numbers of both types of CPs. With feasible Cooper/BCS
+model interelectonic interaction parameter values, and even without BF
+interactions, the GBEC theory yields transition temperatures [including
+room-temperature superconductivity (RTSC)] substantially higher than the BCS
+ceiling of around 45K, without relying on non-phonon dynamics involving
+excitons, plasmons, magnons or otherwise purely-electronic mechanisms.",0601526v5
+2006-09-26,Competing impurities and reentrant magnetism in La(2-x)Sr(x)Cu(1-z)Zn(z)O(4) revisited. The role of the Dzyaloshinskii-Moriya and XY anisotropies,"We study the order-from-disorder transition and reentrant magnetism in
+La(2-x)Sr(x)Cu(1-z)Zn(z)O(4) within the framework of a long-wavelength
+nonlinear sigma model that properly incorporates the Dzyaloshinskii-Moriya and
+XY anisotropies. Doping with nonmagnetic impurities, such as Zn, is considered
+according to classical percolation theory, whereas the effect of Sr, which
+introduces charge carriers into the CuO(2) planes, is described as a dipolar
+frustration of the antiferromagnetic order. We calculate several magnetic,
+thermodynamic, and spectral properties of the system, such as the
+antiferromagnetic order parameter, the Neel temperature, the spin-stiffness,
+and the anisotropy gaps, as well as their evolution with both Zn and Sr doping.
+We explain the nonmonotonic and reentrant behavior experimentally observed for
+T_N by Hucker et al. in Phys. Rev. B 59, R725 (1999), as resulting from the
+reduction, due to the nonmagnetic impurities, of the dipolar frustration
+induced by the charge carriers (order-from-disorder). Furthermore, we find a
+similar nonmonotonic and reentrant behavior for all the other observables
+studied. Most remarkably, our results show that while for x=2% and z=0 the
+Dzyaloshinskii-Moriya gap \Delta_{DM}=0, for z=15% it is approximately
+\Delta_{DM} = 7.5 cm^(-1). The later is larger than the lowest low-frequency
+cutoff for Raman spectroscopy (~ 5 cm^(-1)), and could thus be observed in
+one-magnon Raman scattering.",0609653v1
+2005-10-11,Mass of Rotating Black Holes in Gauged Supergravities,"The masses of several recently-constructed rotating black holes in gauged
+supergravities, including the general such solution in minimal gauged
+supergravity in five dimensions, have until now been calculated only by
+integrating the first law of thermodynamics. In some respects it is more
+satisfactory to have a calculation of the mass that is based directly upon the
+integration of a conserved quantity derived from a symmetry principal. In this
+paper, we evaluate the masses for the newly-discovered rotating black holes
+using the conformal definition of Ashtekar, Magnon and Das (AMD), and show that
+the results agree with the earlier thermodynamic calculations. We also consider
+the Abbott-Deser (AD) approach, and show that this yields an identical answer
+for the mass of the general rotating black hole in five-dimensional minimal
+gauged supergravity. In other cases we encounter discrepancies when applying
+the AD procedure. We attribute these to ambiguities or pathologies of the
+chosen decomposition into background AdS metric plus deviations when scalar
+fields are present. The AMD approach, involving no decomposition into
+background plus deviation, is not subject to such complications. Finally, we
+also calculate the Euclidean action for the five-dimensional solution in
+minimal gauged supergravity, showing that it is consistent with the quantum
+statistical relation.",0510081v3
+2007-08-24,Disordered Correlated Kondo-lattice model,"We propose a self-consistent approximate solution of the disordered
+Kondo-lattice model (KLM) to get the interconnected electronic and magnetic
+properties of 'local-moment' systems like diluted ferromagnetic semiconductors.
+Aiming at $(A_{1-x}M_x)$ compounds, where magnetic (M) and non-magnetic (A)
+atoms distributed randomly over a crystal lattice, we present a theory which
+treats the subsystems of itinerant charge carriers and localized magnetic
+moments in a homologous manner. The coupling between the localized moments due
+to the itinerant electrons (holes) is treated by a modified RKKY-theory which
+maps the KLM onto an effective Heisenberg model. The exchange integrals turn
+out to be functionals of the electronic selfenergy guaranteeing selfconsistency
+of our theory. The disordered electronic and magnetic moment systems are both
+treated by CPA-type methods.
+  We discuss in detail the dependencies of the key-terms such as the long range
+and oscillating effectice exchange integrals, 'the local-moment' magnetization,
+the electron spin polarization, the Curie temperature as well as the electronic
+and magnonic quasiparticle densities of states on the concentration $x$ of
+magnetic ions, the carrier concentration $n$, the exchange coupling $J$, and
+the temperature. The shape and the effective range of the exchange integrals
+turn out to be strongly $x$-dependent. The disorder causes anomalies in the
+spin spectrum especially in the low-dilution regime, which are not observed in
+the mean field approximation.",0708.3361v1
+2007-12-02,Role of the conduction electrons in mediating exchange interactions in Heusler alloys,"Because of large spatial separation of the Mn atoms in Heusler alloys the Mn
+3d states belonging to different atoms do not overlap considerably. Therefore
+an indirect exchange interaction between Mn atoms should play a crucial role in
+the ferromagnetism of the systems. To study the nature of the ferromagnetism of
+various Mn-based semi- and full-Heusler alloys we perform a systematic
+first-principles calculation of the exchange interactions in these materials.
+The calculation of the exchange parameters is based on the frozen-magnon
+approach. The calculations show that the magnetism of the Mn-based Heusler
+alloys depends strongly on the number of conduction electrons, their spin
+polarization and the position of the unoccupied Mn 3d states with respect to
+the Fermi level. Various magnetic phases are obtained depending on the
+combination of these characteristics. The Anderson's s-d model is used to
+perform a qualitative analysis of the obtained results. The conditions leading
+to diverse magnetic behavior are identified. If the spin polarization of the
+conduction electrons at the Fermi energy is large and the unoccupied Mn 3d
+states lie well above the Fermi level, an RKKY-type ferromagnetic interaction
+is dominating. On the other hand, the contribution of the antiferromagnetic
+superexchange becomes important if unoccupied Mn 3d states lie close to the
+Fermi energy. The resulting magnetic behavior depends on the competition of
+these two exchange mechanisms. The calculational results are in good
+correlation with the conclusions made on the basis of the Anderson s-d model
+which provides useful framework for the analysis of the results of
+first-principles calculations and helps to formulate the conditions for high
+Curie temperature.",0712.0158v1
+2007-12-25,Hierarchies of Geometric Entanglement,"We introduce a class of generalized geometric measures of entanglement. For
+pure quantum states of $N$ elementary subsystems, they are defined as the
+distances from the sets of $K$-separable states ($K=2,...,N$). The entire set
+of generalized geometric measures provides a quantification and hierarchical
+ordering of the different bipartite and multipartite components of the global
+geometric entanglement, and allows to discriminate among the different
+contributions. The extended measures are applied to the study of entanglement
+in different classes of $N$-qubit pure states. These classes include $W$ and
+$GHZ$ states, and their symmetric superpositions; symmetric multi-magnon
+states; cluster states; and, finally, asymmetric generalized $W$-like
+superposition states. We discuss in detail a general method for the explicit
+evaluation of the multipartite components of geometric entanglement, and we
+show that the entire set of geometric measures establishes an ordering among
+the different types of bipartite and multipartite entanglement. In particular,
+it determines a consistent hierarchy between $GHZ$ and $W$ states, clarifying
+the original result of Wei and Goldbart that $W$ states possess a larger global
+entanglement than $GHZ$ states. Furthermore, we show that all multipartite
+components of geometric entanglement in symmetric states obey a property of
+self-similarity and scale invariance with the total number of qubits and the
+number of qubits per party.",0712.4085v3
+2008-02-12,Doping dependence of phonon and quasiparticle heat transport of pure and Dy-doped Bi_2Sr_2CaCu_2O_{8+δ} single crystals,"The temperature and magnetic-field (H) dependences of thermal conductivity
+(\kappa) of Bi_2Sr_2CaCu_2O_{8+\delta} (Bi2212) are systematically measured for
+a broad doping range by using both pure Bi2212 single crystals with tuned
+oxygen contents and Bi_2Sr_2Ca_{1-x}Dy_xCu_2O_{8+\delta} (Dy-Bi2212) single
+crystals with different Dy contents x. In the underdoped samples, the
+quasiparticle (QP) peak below T_c is strongly suppressed, indicating strong QP
+scattering by impurities or oxygen defects, whereas the phonon conductivity is
+enhanced in moderately Dy-doped samples and a phonon peak at 10 K is observed
+for the first time in Bi2212 system, which means Dy^{3+} ions not only
+introduce the impurities or point defects but also stabilize the crystal
+lattice. The subkelvin data show that the QP heat conductivity gradually
+decreases upon lowering the hole doping level. The magnetic-field dependence of
+\kappa at temperature above 5 K is mainly due to the QP scattering off
+vortices. While the underdoped pure Bi2212 show very weak field dependence of
+\kappa, the Dy-doped samples present an additional ""dip""-like term of \kappa(H)
+at low field, which is discussed to be related to the phonon scattering by free
+spins of Dy^{3+} ions. For non-superconducting Dy-Bi2212 samples with x \simeq
+0.50, an interesting ""plateau"" feature shows up in the low-T \kappa(H)
+isotherms with characteristic field at 1 -- 2 T, for which we discuss the
+possible revlevance of magnon excitations.",0802.1559v1
+2008-04-21,Finite-size corrections to the rotating string and the winding state,"We compute higher order finite size corrections to the energies of the
+circular rotating string on AdS_5 x S^5, of its orbifolded generalization on
+AdS_5 x S^5/Z_M and of the winding state which is obtained as the limit of the
+orbifolded circular string solution when J -> infinity and J/M^2 is kept fixed.
+We solve, at the first order in lambda'=lambda/J^2, where lambda is the 't
+Hooft coupling, the Bethe equations that describe the anomalous dimensions of
+the corresponding gauge dual operators in an expansion in m/K, where m is the
+winding number and K is the ""magnon number"", and to all orders in the angular
+momentum J. The solution for the circular rotating string and for the winding
+state can be matched to the energy computed from an effective quantum
+Landau-Lifshitz model beyond the first order correction in 1/J. For the leading
+1/J corrections to the circular rotating string in m^2 and m^4 and for the
+subleading 1/J^2 corrections to the m^2 term, we find agreement. For the
+winding state we match the energy completely up to, and including, the order
+1/J^2 finite-size corrections. The solution of the Bethe equations
+corresponding to the spinning closed string is also provided in an expansion in
+m/K and to all orders in J.",0804.3301v2
+2008-09-24,Quantum spinning strings in AdS_4 x CP^3: testing the Bethe Ansatz proposal,"Recently, an asymptotic Bethe Ansatz that is claimed to describe anomalous
+dimensions of ""long"" operators in the planar N=6 supersymmetric
+three-dimensional Chern-Simons-matter theory dual to quantum superstrings in
+AdS_4 x CP^3 was proposed. It initially passed a few consistency checks but
+subsequent direct comparison to one-loop string-theory computations created
+some controversy. Here we suggest a resolution by pointing out that, contrary
+to the initial assumption based on the algebraic curve considerations, the
+central interpolating function h(\lambda) entering the BMN or magnon dispersion
+relation receives a non-zero one-loop correction in the natural string-theory
+computational scheme. We consider a basic example which has already played a
+key role in the AdS_5 x S^5 case: a rigid circular string stretched in both
+AdS_4 and along an S^1 of CP^3 and carrying two spins. Computing the leading
+one-loop quantum correction to its energy allows us to fix the constant
+one-loop term in h(\lambda) and also to suggest how one may establish a
+correspondence with the Bethe Ansatz proposal, including the non-trivial
+one-loop phase factor. We discuss some problems which remain in trying to match
+a part of world-sheet contributions (sensitive to compactness of the string
+direction) and their Bethe Ansatz counterparts.",0809.4038v2
+2008-10-15,A Large Iron Isotope Effect in SmFeAsO1-xFx and Ba1-xKxFe2As2,"The recent discovery of superconductivity in oxypnictides with the critical
+temperature (TC) higher than McMillan limit of 39 K (the theoretical maximum
+predicted by Bardeen-Cooper-Schrieffer (BCS) theory) has generated great
+excitement. Theoretical calculations indicate that the electron-phonon
+interaction is not strong enough to give rise to such high transition
+temperatures, while strong ferromagnetic/antiferromagnetic fluctuations have
+been proposed to be responsible. However, superconductivity and magnetism in
+pnictide superconductors show a strong sensitivity to the lattice, suggesting a
+possibility of unconventional electron-phonon coupling. Here we report the
+effect of oxygen and iron isotopic mass on Tc and the spin-density wave (SDW)
+transition temperature (TSDW) in SmFeAsO1-xFx and Ba1-xKxFe2As2 systems. The
+results show that oxygen isotope effect on TC and TSDW is very little, while
+the iron isotope exponent alpha=-dlnTc/dlnM is about 0.35, being comparable to
+0.5 for the full isotope effect. Surprisingly, the iron isotope exchange shows
+the same effect on TSDW as TCc These results indicate that electron-phonon
+interaction plays some role in the superconducting mechanism, but simple
+electron-phonon coupling mechanism seems to be rather unlikely because a strong
+magnon-phonon coupling is included. Sorting out the interplay between the
+lattice and magnetic degrees of freedom is a key challenge for understanding
+the mechanism of high-TC superconductivity.",0810.2694v2
+2009-01-21,Instability of the collinear phase in two-dimensional ferromagnet in strong in-plane magnetic field,"It is well-known that in thin ferromagnetic film with a net magnetization
+perpendicular to the film the collinear arrangement of spins is unstable in an
+in-plane field $H$ smaller than its saturation value $H_c$. Existence of a
+stripe phase was proposed with elongated domains of alternating direction of
+magnetization component perpendicular to the film. We consider in the present
+paper the strong-field regime $H<H_c$ and discuss the minimal microscopic model
+describing this phenomenon, two-dimensional Heisenberg ferromagnet with strong
+easy-axis anisotropy and dipolar forces. The noncollinear (stripe) phase is
+discussed using the technique of the Bose-Einstein condensation of magnons.
+Some previously unknown results are observed concerning the stripe phase.
+Evolution is established of the spin arrangement in the noncollinear phase upon
+the field rotation within the plane. We find a rapid decreasing of the period
+of the stripe structure as the field decreases. We demonstrate that spins
+components perpendicular to the film form a sinusoid in the noncollinear phase
+at $H\approx H_c$ that transforms to a step-like profile upon the field
+decreasing so that the domain wall density decreases from unity to a value much
+smaller than unity. The spin-wave spectrum in the noncollinear phase is
+discussed.",0901.3259v2
+2009-05-14,Orbitally induced string formation in the spin-orbital polarons,"We study the spectral function of a single hole doped into the (a,b) plane of
+the Mott insulator LaVO$_3$, with antiferromagnetic (AF) spin order of S=1
+spins accompanied by alternating orbital (AO) order of active
+$\{d_{yz},d_{zx}\}$ orbitals. Starting from the respective t-J model, with
+spin-orbital superexchange and effective three-site hopping terms, we derive
+the polaron Hamiltonian and show that a hole couples simultaneously to the
+collective excitations of the AF/AO phase, magnons and orbitons. Next, we solve
+this polaron problem using the self-consistent Born approximation and find a
+stable quasiparticle solution -- a spin-orbital polaron. We show that the
+spin-orbital polaron resembles the orbital polaron found in $e_g$ systems, as
+e.g. in K$_2$CuF$_4$ or (to some extent) in LaMnO$_3$, and that the hole may be
+seen as confined in a string-like potential. However, the spins also play a
+crucial role in the formation of this polaron -- we explain how the orbital
+degrees of freedom: (i) confine the spin dynamics acting on the hole as the
+classical Ising spins, and (ii) generate the string potential which is of the
+joint spin-orbital character. Finally, we discuss the impact of the results
+presented here on the understanding of the phase diagrams of the lightly doped
+cubic vanadates.",0905.2380v1
+2009-07-31,Effects of Disorder and Interactions in the Quantum Hall Ferromagnet,"This work treats the effects of disorder and interactions in a quantum Hall
+ferromagnet, which is realized in a two-dimensional electron gas (2DEG) in a
+perpendicular magnetic field at Landau level filling factor equal one. We study
+the problem by projecting the original fermionic Hamiltonian into magnon
+states, which behave as bosons in the vicinity of the ferromagnetic ground
+state. The approach permits the reformulation of a strongly interacting model
+into a non-interacting one. The latter is a non-perturbative scheme that
+consists in treating the two-particle neutral excitations of the electron
+system as a bosonic single-particle. Indeed, the employment of bosonization
+facilitates the inclusion of disorder in the study of the system. It has been
+shown previously that disorder may drive a quantum phase transition in the Hall
+ferromagnet. However, such studies have been either carried out in the
+framework of nonlinear sigma model, as an effective low-energy theory, or
+included the long-range Coulomb interaction in a quantum description only up to
+the Hartree-Fock level. Here, we establish the occurrence of a disorder-driven
+quantum phase transition from a ferromagnetic 2DEG to a spin glass phase by
+taking into account interactions between electrons up to the random phase
+approximation level in a fully quantum description.",0907.5513v1
+2009-09-29,New pixelized Micromegas detector for the COMPASS experiment,"New Micromegas (Micro-mesh gaseous detectors) are being developed in view of
+the future physics projects planned by the COMPASS collaboration at CERN.
+Several major upgrades compared to present detectors are being studied:
+detectors standing five times higher luminosity with hadron beams, detection of
+beam particles (flux up to a few hundred of kHz/mm^2, 10 times larger than for
+the present detectors) with pixelized read-out in the central part, light and
+integrated electronics, and improved robustness. Studies were done with the
+present detectors moved in the beam, and two first pixelized prototypes are
+being tested with muon and hadron beams in real conditions at COMPASS. We
+present here this new project and report on two series of tests, with old
+detectors moved into the beam and with pixelized prototypes operated in real
+data taking condition with both muon and hadron beams.",0909.5402v2
+2009-10-24,Determining the Anisotropic Exchange Coupling of CrO_2 via First-Principles Density Functional Theory Calculations,"We report a study of the anisotropic exchange interactions in bulk CrO_2
+calculated from first principles within density functional theory. We determine
+the exchange coupling energies, using both the experimental lattice parameters
+and those obtained within DFT, within a modified Heisenberg model Hamiltonian
+in two ways. We employ a supercell method in which certain spins within a cell
+are rotated and the energy dependence is calculated and a spin-spiral method
+that modifies the periodic boundary conditions of the problem to allow for an
+overall rotation of the spins between unit cells. Using the results from each
+of these methods, we calculate the spin-wave stiffness constant D from the
+exchange energies using the magnon dispersion relation. We employ a Monte Carlo
+method to determine the DFT-predicted Curie temperature from these calculated
+energies and compare with accepted values. Finally, we offer an evaluation of
+the accuracy of the DFT-based methods and suggest implications of the competing
+ferro- and antiferromagnetic interactions.",0910.4671v2
+2010-01-12,Phonon Spectroscopy Near Phase Transition Temperatures in Multferroic BiFeO3 Epitaxial Thin Films,"We report a Raman scattering investigation of multiferroic bismuth ferrite
+BiFeO3 epitaxial (c-axis oriented) thin films from -192 to 1000C. Phonon
+anomalies have been observed in three temperature regions: in the gamma-phase
+from 930C to 950C; at ~370C, Neel temperature (TN), and at ~123C, due to a
+phase transition of unknown type (magnetic or structural). An attempt has been
+made to understand the origin of the weak phonon-magnon coupling and the
+dynamics of the phase sequence. The disappearance of several Raman modes at
+~820C (Tc) is compatible with the known structural phase transition and the
+Pbnm orthoferrite space group assigned by Arnold {\it et al.} \cite{arnold:09}.
+The spectra also revealed a {\it non-cubic} $\beta$-phase from 820-930\dc and
+the same {\it non-cubic} phase extends through the $\gamma$-phase between
+930-950\dc, in agreement with Arnold {\it et al.} \cite{arnold2:09}, and an
+evidence of a cubic $\delta$-phase around 1000\dc in thin films that is not
+stable in powder and bulk. Such a cubic phase has been theoretically predicted
+in \cite{vasquez:prb09}. Micro-Raman scattering and X-ray diffraction showed no
+structural decomposition in thin films during the thermal cycling from
+22-1000\dc.",1001.1997v1
+2010-02-17,Measurement of Gilbert damping parameters in nanoscale CPP-GMR spin-valves,"In-situ, device level measurement of thermal mag-noise spectral linewidths in
+60nm diameter CPP-GMR spin-valve stacks of IrMn/ref/Cu/free, with reference and
+free layer of similar CoFe/CoFeGe alloy, are used to simultaneously determine
+the intrinsic Gilbert damping for both magnetic layers. It is shown that
+careful alignment at a ""magic-angle"" between free and reference layer static
+equilibrium magnetization can allow direct measurement of the broadband
+intrinsic thermal spectra in the virtual absence of spin-torque effects which
+otherwise grossly distort the spectral line shapes and require linewidth
+extrapolations to zero current (which are nonetheless also shown to agree well
+with the direct method). The experimental magic-angle spectra are shown to be
+in good qualitative and quantitative agreement with both macrospin calculations
+and micromagnetic eigenmode analysis. Despite similar composition and
+thickness, it is repeatedly found that the IrMn exchange pinned reference layer
+has ten times larger intrinsic Gilbert damping (alpha ~ 0.1) than that of the
+free-layer (alpha ~ 0.01). It is argued that the large reference layer damping
+results from strong, off -resonant coupling to to lossy modes of an IrMn/ref
+couple, rather than commonly invoked two-magnon processes.",1002.3295v1
+2010-04-14,Measurement of magnetic excitations in the two-dimensional antiferromagnetic Sr2CuO2Cl2 insulator using resonant x-ray scattering:Evidence for extended interactions,"Using high-resolution resonant inelastic x-ray scattering (RIXS), we
+performed a momentum-resolved study of magnetic excitations in the model
+spin-1/2 2D antiferromagnetic insulator Sr_2CuCl_2O_2. We identify both a
+single-spin-wave feature and a multi-magnon continuum, and show that the X-ray
+polarization can be used to distinguish these two contributions in the
+cross-section. The spin-waves display a large (70 meV) dispersion between the
+zone-boundary points ($\pi$,0) and ($\pi$/2,$\pi$/2). Employing an extended
+$t$-$t'$-$t""$-$U$ one-band Hubbard model, we find significant electronic
+hopping beyond nearest-neighbor Cu ions. We conclude that sizeable extended
+magnetic interactions are present in \scoc{} and probably important in all
+undoped cuprates.",1004.2441v3
+2010-04-22,Magnetic excitations in the metallic single-layer Ruthenates Ca(2-x)Sr(x)RuO(4) studied by inelastic neutron scattering,"By inelastic neutron scattering, we have analyzed the magnetic correlations
+in the paramagnetic metallic region of the series Ca(2-x)Sr(x)RuO(4),
+0.2<=x<=0.62. We find different contributions that correspond to 2D
+ferromagnetic fluctuations and to fluctuations at incommensurate wave vectors
+(0.11,0,0), (0.26,0,0) and (0.3,0.3,0). These components constitute the
+measured response as function of the Sr-concentration x, of the magnetic field
+and of the temperature. A generic model is applicable to metallic
+Ca(2-x)Sr(x)RuO(4) close to the Mott transition, in spite of their strongly
+varying physical properties. The amplitude, characteristic energy and width of
+the incommensurate components vary only little as function of x, but the
+ferromagnetic component depends sensitively on concentration, temperature and
+magnetic field. While ferromagnetic fluctuations are very strong in
+Ca1.38Sr0.62RuO4 with a low characteristic energy of 0.2 meV at T=1.5 K, they
+are strongly suppressed in Ca1.8Sr0.2RuO4, but reappear upon the application of
+a magnetic field and form a magnon mode above the metamagnetic transition. The
+inelastic neutron scattering results document how the competition between
+ferromagnetic and incommensurate antiferromagnetic instabilities governs the
+physics of this system.",1004.3957v1
+2010-06-04,"Magnetism and thermodynamics of spin-(1/2,1) decorated Heisenberg chain with spin-1 pendants","The magnetic and thermodynamic properties of a new ferrimagnetic decorated
+spin-(1/2,1) Heisenberg chain with spin-1 pendant spins are investigated for
+three cases: (A) J1,J2>0; (B) J1>0, J2<0; and (C) J1<0, J2>0, where J1 and J2
+are the exchange couplings between spins in the chain and along the rung,
+respectively. The low-lying and magnetic properties are explored jointly by the
+real-space renormalization group, spin wave, and density-matrix renormalization
+group methods, while the transfer-matrix renormalization group method is
+invoked to study the thermodynamics. It is found that the magnon spectra
+consist of a gapless and two gapped branches. Two branches in case (C) have
+intersections. The coupling dependence of low-energy gaps are analyzed. In a
+magnetic field, an m=3/2 (m is the magnetization per unit cell) plateau is
+observed for case (A), while two plateaux at m=1/2 and 3/2 are observed for
+cases (B) and (C). Between the two plateaux in cases (B) and (C), the
+sublattice magnetizations for the spins coupled by ferromagnetic interactions
+have novel decreasing regions with increasing the magnetic field. At finite
+temperature, the zero-field susceptibility temperature product chi*T and
+specific heat exhibit distinct exotic features with varying the couplings and
+temperature for different cases. chi*T is found to converge as T approaches
+zero, which is different from the divergent behavior in the spin-(1/2,1)
+mixed-spin chain without pendants. The observed thermodynamic behaviors are
+also discussed with the help of their low-lying excitations.",1006.0794v1
+2010-06-25,"Comment on ""Two-spinon and four-spinon continuum in a frustrated ferromagnetic spin-1/2 chain"" by M. Enderle et al","We show that LiVCuO4 should be described by strongly ferromagnetically
+coupled Heisenberg antiferromagnetic chains (HAC) in sharp contrast with the
+effective exchange integrals Ji given in Enderle et al., Phys. Rev. Lett. vol.
+104, 237207 (2010), and the main issues of that work, namely, (i) LiVCuO4 is
+well described by two weakly ferromagnetically coupled interpenetrating
+Heisenberg antiferromagnetic spin-1/2 chains, (ii) the extracted exchange
+integrals J1, J2 agree with a previous spin-wave description (Enderle et al.,
+Euphys. Lett. vol. 70, 237 (2005)), (iii) the spectral density of inelastic
+neutron scattering (INS) above 10 meV is ascribed to a 4-spinon continuum.
+Applying exact diagonalization and DMRG methods to fit their INS and
+magnetization M(H) data, supported by two independent microscopic methods
+(5-band Hubbard model and LSDA+U calculations), we demonstrate that LiCuVO4
+exhibits strong inchain frustration with alpha =-J2/J1 < 1, i.e. strong
+coupling of the HAC at odds with (i). An alternative phenomenological set in
+accord with various experimental results is proposed. In view of the recent
+possible discovery of quantum-spin nematics and Bose condensation of two-magnon
+bound states (M. Zhitomirsky et al. arXiv:1003.4096v2 (2010), L. Svistov et al.
+ibid. 1005.5668v2 (2010)) in LiCuVO4 precise knowledge of the main J-values is
+of key importance.",1006.5070v2
+2010-08-05,On three-point correlation functions in the gauge/gravity duality,"We study the effect of marginal and irrelevant deformations on the
+renormalization of operators near a CFT fixed point. New divergences in a given
+operator are determined by its OPE with the operator D that generates the
+deformation. This provides a scheme to compute the couplings a_DAB between the
+operator D and two arbitrary operators O_A and O_B. We exemplify for the case
+of N=4 SYM, considering the simplest case of the exact Lagrangian deformation.
+In this case the deformed anomalous dimension matrix is determined by the
+derivative of the anomalous dimension matrix with respect to the coupling. We
+use integrability techniques to compute the one-loop couplings a_LAB between
+the Lagrangian and two distinct large operators built with Magnons, in the
+SU(2) sector of the theory. Then we consider a_DAA at strong coupling, and show
+how to compute it using the gauge/gravity duality, when D is a chiral operator
+dual to any supergravity field and O_A is dual to a heavy string state. We
+exemplify for the Lagrangian and operators O_A dual to heavy string states,
+showing agreement with the prediction derived from the renormalization group
+arguments.",1008.1070v2
+2010-12-16,Coupled states of electromagnetic fields with magnetic-dipolar-mode vortices: MDM-vortex polaritons,"Under the influence of the material environment, electromagnetic fields in
+the near-field regime exhibit quite different nature from those in the
+far-field free space. A coupled state of an electromagnetic field with an
+electric or magnetic dipole-carrying excitation is well known as a polariton.
+Such a state is the result of the mixing of a photon with an excitation of a
+material. The most discussed types of polaritons are phonon-polaritons,
+exciton-polaritons, and surface plasmon-polaritons. Recently, it was shown that
+in microwaves strong magnon-photon coupling can be achieved due to
+magnetic-dipolar-mode (MDM) vortices in small thin-film ferrite disks. These
+coupled states can be specified as MDM-vortex polaritons. In this paper we
+study properties of MDM-vortex polaritons. We show that MDM-vortex polaritons
+are characterized by helicity behaviors. For the observed frequency splits of
+MDM resonances there are different-type helicities. In the split-resonance
+states one has or localization, or cloaking of electromagnetic fields. We
+analyze numerically a variety of the field topological structures of MDM-vortex
+polaritons and give theoretical insights into the possible origin of such
+topologically distinctive states. The shown properties of MDM-vortex polaritons
+can be useful for realization of novel microwave metamaterial structures and
+near-field sensing applications.",1012.3621v1
+2010-12-29,Criticisms on and Comparison of Experimental Channel Backscattering Extraction Methods,"In this paper we critically review and compare experimental methods, based on
+the Lundstrom model, to extract the channel backscattering ratio in nano
+MOSFETs. Basically two experimental methods are currently used, the most common
+of them is based on the measurement of the saturation drain current at
+different temperatures. We show that this method is affected by very poor
+assumptions and that the extracted backscattering ratio strongly underestimates
+its actual value posing particular attention to the backscattering actually
+extracted in nano devices. The second method is based on the direct measurement
+of the inversion charge by CV characteristics and gets closer to the physics of
+the backscattering model. We show, through measurements in high mobility
+p-germanium devices, how the temperature based method gives the same result of
+the CV based method once that its approximations are removed. Moreover we show
+that the CV based method uses a number of approximations which are partially
+inconsistent with the model. In particular we show, with the aid of 2D quantum
+corrected device simulations, that the value of the barrier lowering obtained
+through the CV based method is totally inconsistent with the barrier lowering
+used to correct the inversion charge and that the extracted saturation
+inversion charge is underestimated.",1012.5981v1
+2011-03-21,Spontaneous Magnetization of an Ideal Ferromagnet: Beyond Dyson's Analysis,"Using the low-energy effective field theory for magnons, we systematically
+evaluate the partition function of the O(3) ferromagnet up to three loops.
+Dyson, in his pioneering microscopic analysis of the Heisenberg model, showed
+that the spin-wave interaction starts manifesting itself in the low-temperature
+expansion of the spontaneous magnetization of an ideal ferromagnet only at
+order $T^4$. Although several authors tried to go beyond Dyson's result, to the
+best of our knowledge, a fully systematic and rigorous investigation of higher
+order terms induced by the spin-wave interaction, has never been achieved. As
+we demonstrate in the present paper, it is straightforward to evaluate the
+partition function of an ideal ferromagnet beyond Dyson's analysis, using
+effective Lagrangian techniques. In particular, we show that the
+next-to-leading contribution to the spontaneous magnetization resulting from
+the spin-wave interaction already sets in at order $T^{9/2}$ -- in contrast to
+all claims that have appeared before in the literature. Remarkably, the
+corresponding coefficient is completely determined by the leading-order
+effective Lagrangian and is thus independent of the anisotropies of the cubic
+lattice. We also consider even higher-order corrections and thereby solve --
+once and for all -- the question of how the spin-wave interaction in an ideal
+ferromagnet manifests itself in the spontaneous magnetization beyond the Dyson
+term.",1103.4110v1
+2011-04-13,The AdS(5)xS(5) Semi-Symmetric Space Sine-Gordon Theory,"The generalized symmetric space sine-Gordon theories are a series of
+1+1-integrable field theories that are classically equivalent to superstrings
+on symmetric space spacetimes F/G. They are formulated in terms of a
+semi-symmetric space as a gauged WZW model with fermions and a potential term
+to deform it away from the conformal fixed point. We consider in particular the
+case of PSU(2,2|4)/Sp(2,2)xSp(4) which corresponds to AdS(5)xS(5). We argue
+that the infinite tower of conserved charges of these theories includes an
+exotic N=(8,8) supersymmetry that is realized in a mildy non-local way at the
+Lagrangian level. The supersymmetry is associated to a double central extension
+of the superalgebra psu(2|2)+psu(2|2) and includes a non-trivial R symmetry
+algebra corresponding to global gauge transformations, as well as 2-dimensional
+spacetime translations. We then explicitly construct soliton solutions and show
+that they carry an internal moduli superspace CP(2|1)xCP(2|1) with both bosonic
+and Grassmann collective coordinates. We show how to semi-classical quantize
+the solitons by writing an effective quantum mechanical system on the moduli
+space which takes the form of a co-adjoint orbit of SU(2|2)xSU(2|2). The
+spectrum consists of a tower of massive states in the short, or atypical,
+symmetric representations, just as the giant magnon states of the string world
+sheet theory, although here the tower is truncated.",1104.2429v2
+2011-06-30,Hole spectral functions in lightly doped quantum antiferromagnets,"We study the hole and magnon spectral functions as a function of hole doping
+in the two-dimensional (2D) t-J and t-t'-t""-J models working within the limits
+of the spin-wave theory, by linearizing the hole-spin-deviation interaction and
+by adapting the non-crossing approximation (NCA). We find that the staggered
+magnetization decreases rather rapidly with doping and it goes to zero at a few
+percent of hole concentration in both t-J and the t-t'-t""-J model. We find that
+with doping, the residue of the quasiparticle peak at G=(pi/2,pi/2) decreases
+rapidly with doping and the spectral function is in agreement with high
+resolution angle-resolved photo-emission spectroscopy (ARPES) studies of the
+copper-oxide superconductors. The observed large shift of the chemical
+potential inside the Mott gap is found to be a result of broadening of the
+quasiparticle peak. We find pockets centered at G, similar to those observed by
+quantum oscillation measurements, (i) with an elliptical shape with large
+eccentricity along the anti-nodal direction in the case of the t-J model, and
+(ii) with an almost circular shape in the case of the t-t'-t""-J model. We also
+find that the spectral intensity distribution in the doped antiferromagnet has
+a waterfall-like patten along the nodal direction of the Brillouin zone, a
+feature that is also seen in ARPES measurements.",1106.6332v1
+2011-07-05,Deformed triangular lattice antiferromagnets in a magnetic field: role of spatial anisotropy and Dzyaloshinskii-Moriya interactions,"Recent experiments on the anisotropic spin-1/2 triangular antiferromagnet
+Cs_2CuBr_4 have revealed a remarkably rich phase diagram in applied magnetic
+fields, consisting of an unexpectedly large number of ordered phases. Motivated
+by this finding, we study the role of spatial anisotropy, Dzyaloshinskii-Moriya
+interactions, and quantum fluctuations on the magnetization process of a
+triangular antiferromagnet, coming from the semiclassical limit. The richness
+of the problem stems from two key facts: 1) the classical isotropic model
+exhibits a large accidental ground state degeneracy, and 2) these three
+ingredients compete with one another and split this degeneracy in opposing
+ways. Using a variety of complementary approaches, including extensive Monte
+Carlo numerics, spin-wave theory, and an analysis of Bose-Einstein condensation
+of magnons at high fields, we find that their interplay gives rise to a complex
+phase diagram consisting of numerous incommensurate and commensurate phases.
+Our results shed light on the observed phase diagram for Cs_2CuBr_4 and suggest
+a number of future theoretical and experimental directions that will be useful
+for obtaining a complete understanding of this material's interesting
+phenomenology.",1107.0772v4
+2011-07-27,Melting of a frustration-induced dimer crystal and incommensurability in the J_1-J_2 two-leg ladder,"The phase diagram of an antiferromagnetic ladder with frustrating
+next-nearest neighbor couplings along the legs is determined using numerical
+methods (exact diagonalization and density-matrix renormalization group)
+supplemented by strong-coupling and mean-field analysis. Interestingly, this
+model displays remarkable features, bridging the physics of the J_1-J_2 chain
+and of the unfrustated ladder. The phase diagram as a function of the
+transverse coupling J_{\perp} and the frustration J_2 exhibits an Ising
+transition between a columnar phase of dimers and the usual rung-singlet phase
+of two-leg ladders. The transition is driven by resonating valence bond
+fluctuations in the singlet sector while the triplet spin gap remains finite
+across the transition. In addition, frustration brings incommensurability in
+the real-space spin correlation functions, the onset of which evolves smoothly
+from the J_1-J_2 chain value to zero in the large-J_{\perp} limit. The onset of
+incommensurability in the spin structure-factor and in the dispersion relation
+is also analyzed. The physics of the frustrated rung-singlet phase is well
+understood using perturbative expansions and mean-field theories in the
+large-J_{\perp} limit. Lastly, we discuss the effect of the non-trivial magnon
+dispersion relation on the thermodynamical properties of the system. The
+relation of this model and its physics to experimental observations on
+compounds which are currently investigated, such as BiCu_2PO_6, is eventually
+addressed.",1107.5498v2
+2011-08-09,Thermal Equilibration and Thermally-Induced Spin Currents in a Thin-Film Ferromagnet on a Substrate,"Recent spin-Seebeck experiments on thin ferromagnetic films apply a
+temperature difference $\Delta T_{x}$ along the length $x$ and measure a
+(transverse) voltage difference $\Delta V_{y}$ along the width $y$. The
+connection between these effects is complex, involving: (1) thermal
+equilibration between sample and substrate; (2) spin currents along the height
+(or thickness) $z$; and (3) the measured voltage difference. The present work
+studies in detail the first of these steps, and outlines the other two steps.
+Thermal equilibration processes between the magnons and phonons in the sample,
+as well as between the sample and the substrate leads to two surface modes,
+with surface lengths $\lambda$, to provide for thermal equilibration.
+Increasing the coupling between the two modes increases the longer mode length
+and decreases the shorter mode length. The applied thermal gradient along $x$
+leads to a thermal gradient along $z$ that varies as $\sinh{(x/\lambda)}$,
+which can in turn produce fluxes of the carriers of up- and down- spins along
+$z$, and gradients of their associated \textit{magnetoelectrochemical
+potentials} $\bar{\mu}_{\uparrow,\downarrow}$, which vary as
+$\sinh{(x/\lambda)}$. By the inverse spin Hall effect, this spin current along
+$z$ can produce a transverse (along $y$) voltage difference $\Delta V_y$, which
+also varies as $\sinh{(x/\lambda)}$.",1108.1872v1
+2011-09-27,Dispersion and damping of zone-boundary magnons in the noncentrosymmetric superconductor CePt3Si,"Inelastic neutron scattering (INS) is employed to study damped spin-wave
+excitations in the noncentrosymmetric heavy-fermion superconductor CePt3Si
+along the antiferromagnetic Brillouin-zone boundary in the low-temperature
+magnetically ordered state. Measurements along the (1/2 1/2 L) and (H H 1/2-H)
+reciprocal-space directions reveal deviations in the spin-wave dispersion from
+the previously reported model. Broad asymmetric shape of the peaks in energy
+signifies strong spin-wave damping by interactions with the particle-hole
+continuum. Their energy width exhibits no evident anomalies as a function of
+momentum along the (1/2 1/2 L) direction, which could be attributed to
+Fermi-surface nesting effects, implying the absence of pronounced commensurate
+nesting vectors at the magnetic zone boundary. In agreement with a previous
+study, we find no signatures of the superconducting transition in the magnetic
+excitation spectrum, such as a magnetic resonant mode or a superconducting spin
+gap, either at the magnetic ordering wavevector (0 0 1/2) or at the zone
+boundary. However, the low superconducting transition temperature in this
+material still leaves the possibility of such features being weak and therefore
+hidden below the incoherent background at energies ~0.1 meV, precluding their
+detection by INS.",1109.5784v1
+2011-10-03,Raman scattering study of delafossite magnetoelectric multiferroic compounds: CuFeO2 and CuCrO2,"Ultrasonic velocity measurements on the magnetoelectric multiferroic compound
+CuFeO2 reveal that the antiferromagnetic transition observed at TN1 = 14 K
+might be induced by an R-3m -> C2/m pseudoproper ferroelastic transition (G.
+Quirion, M. J. Tagore, M. L. Plumer, O. A. Petrenko, Phys. Rev. B 77, 094111
+(2008)). In that case, the group theory states that the order parameter
+associated with the structural transition must belong to a two dimensional
+irreducible representation Eg (x^2 - y^2, xy). Since this type of transition
+can be driven by a Raman Eg mode, we performed Raman scattering measurements on
+CuFeO2 between 5 K and 290 K. Considering that the isostructural multiferroic
+compound CuCrO2 might show similar structural deformations at the
+antiferromagnetic transition TN1 = 24.3 K, Raman measurements have also been
+performed for comparison. At ambient temperature, the Raman modes in CuFeO2 are
+observed at omega_Eg = 352 cm^-1 and omega_Ag = 692 cm^-1, while these modes
+are detected at omega_E_g = 457 cm^-1 and omega_Ag = 709 cm^-1 in CuCrO2. The
+analysis of the temperature dependence of modes shows that the frequency of all
+modes increases down to 5 K. This typical behavior can be attributed to
+anharmonic phonon-phonon interactions. These results clearly indicate that none
+of the Raman active modes observed in CuFeO2 and CuCrO2 drive the pseudoproper
+ferroelastic transition observed at the N\'eel temperature TN1. Finally, a
+broad band at about 550 cm^-1 observed in the magnetoelectric phase of CuCrO2
+below TN2 could be attributed to a magnon mode.",1110.0473v1
+2011-10-10,"Ab-initio calculation of effective exchange interactions, spin waves, and Curie temperature in L2_1- and L1_2-type local moment ferromagnets","Employing first-principles electronic structure calculations in conjunction
+with the frozen-magnon method we study the effective exchange interactions and
+spin waves in local moment ferromagnets. As prototypes we have chosen three
+L2$_1$-type full Heusler alloys Cu$_2$MnAl, Ni$_2$MnSn and Pd$_2$MnSn, and the
+L1$_2$-type XPt$_3$ compounds with X= V, Cr and Mn. We have also included
+CoPt$_3$ which is a usual ferromagnet. In all compounds due to the large
+spatial separation ($\sim 4$ \AA) of the magnetic transition metal atoms, the
+3\textit{d} states belonging to different atoms overlap weakly and as a
+consequence the exchange coupling is indirect, mediated by the \textit{sp}
+electrons. Calculated effective exchange parameters are long range and show
+RKKY-type oscillations. The spin-wave dispersion curves are in reasonable
+agreement with available experimental data. Using the calculated exchange
+parameters we have estimated the Curie temperatures within both the mean-field
+and the random-phase approximations. In local moment ferromagents deviations of
+the estimated Curie temperature with respect to the available experimental data
+occur when the ground-state electronic structure calculations overestimate the
+values of the spin magnetic moments as in VPt$_3$.",1110.2156v1
+2011-12-19,q-Deformation of the AdS5 x S5 Superstring S-matrix and its Relativistic Limit,"A set of four factorizable non-relativistic S-matrices for a multiplet of
+fundamental particles are defined based on the R-matrix of the quantum group
+deformation of the centrally extended superalgebra su(2|2). The S-matrices are
+a function of two independent couplings g and q=exp(i\pi/k). The main result is
+to find the scalar factor, or dressing phase, which ensures that the unitarity
+and crossing equations are satisfied. For generic (g,k), the S-matrices are
+branched functions on a product of rapidity tori. In the limit k->infinity, one
+of them is identified with the S-matrix describing the magnon excitations on
+the string world sheet in AdS5 x S5, while another is the mirror S-matrix that
+is needed for the TBA. In the g->infinity limit, the rapidity torus
+degenerates, the branch points disappear and the S-matrices become meromorphic
+functions, as required by relativistic S-matrix theory. However, it is only the
+mirror S-matrix which satisfies the correct relativistic crossing equation. The
+mirror S-matrix in the relativistic limit is then closely related to that of
+the semi-symmetric space sine-Gordon theory obtained from the string theory by
+the Pohlmeyer reduction, but has anti-symmetric rather than symmetric bound
+states. The interpolating S-matrix realizes at the quantum level the fact that
+at the classical level the two theories correspond to different limits of a
+one-parameter family of symplectic structures of the same integrable system.",1112.4485v1
+2012-02-07,Effect of internal chemical pressure on transport properties and TCR for sensors applications,"In this work, the structural and transport properties of
+(Nd0.7-xLax)Sr0.3MnO3 manganites with x = 0, 0.1 and 0.2 prepared by solid
+state reaction route are studied. These compounds are found to be crystallized
+in orthorhombic structural form. The influence of La substitution in place of
+Nd at A-site shifts the metal to semiconductor/insulator transition temperature
+(TMI) peak towards room temperature with x = 0, 0.1 and 0.2. A composition
+prepared with the value of x = 0.2 in (Nd0.7-xLax)0.7Sr0.3MnO3 manganites (i.e.
+(Nd0.5La0.2)0.7Sr0.3MnO3), TMI was observed at 289 K which is close to room
+temperature. The maximum percentage of TCR values of compounds are increasing
+with average radius <r_A> but %TCR are slightly equal in x = 0.1 and 0.2 as
+compared to the parent compound. The maximum %TCR value is almost independent
+with A-site average radius <r_A> in x = 0.1 and 0.2. The electrical resistivity
+data are explored by different theoretical models and it has been concluded
+that at low temperature (ferromagnetic metallic region) conduction mechanism
+presumably due to the combined effect of electron-electron, electron-phonon and
+electron-magnon scattering, while in paramagnetic semiconducting regime, the
+variation of resistivity with temperature are explained by (1) Mott variable
+range hopping mechanism, (2) Adiabatic small polaron hopping and (3) Thermally
+activated hopping. The polaron hopping and thermal activation energies are
+decreasing with increase of an average A-site ionic radius (<rA>). An
+appropriate enlightenment for the observed behavior is discussed in detail.",1202.1355v1
+2012-07-12,Fingerprints of spin-orbital entanglement in transition metal oxides,"The concept of spin-orbital entanglement on superexchange bonds in transition
+metal oxides is introduced and explained on several examples. It is shown that
+spin-orbital entanglement in superexchange models destabilizes the long-range
+(spin and orbital) order and may lead either to a disordered spin-liquid state
+or to novel phases at low temperature which arise from strongly frustrated
+interactions. Such novel ground states cannot be described within the
+conventionally used mean field theory which separates spin and orbital degrees
+of freedom. Even in cases where the ground states are disentangled,
+spin-orbital entanglement occurs in excited states and may become crucial for a
+correct description of physical properties at finite temperature. As an
+important example of this behaviour we present spin-orbital entanglement in the
+$R$VO$_3$ perovskites, with $R$=La,Pr,...,Yb,Lu, where such finite temperature
+properties of these compounds can be understood only using entangled states:
+($i$) thermal evolution of the optical spectral weights, ($ii$) the dependence
+of transition temperatures for the onset of orbital and magnetic order on the
+ionic radius in the phase diagram of the $R$VO$_3$ perovskites, and ($iii$)
+dimerization observed in the magnon spectra for the $C$-type antiferromagnetic
+phase of YVO$_3$. Finally, it is shown that joint spin-orbital excitations in
+an ordered phase with coexisting antiferromagnetic and alternating orbital
+order introduces topological constraints for the hole propagation and will thus
+radically modify transport properties in doped Mott insulators where hole
+motion implies simultaneous spin and orbital excitations.",1207.3010v1
+2012-07-20,Thermal evolution of the full three-dimensional magnetic excitations in the multiferroic BiFeO3,"The idea of embedding and transmitting information within the fluctuations of
+the magnetic moments of spins (spin waves) has been recently proposed and
+experimentally tested. The coherence of spin waves, which describes how well
+defined these excitations are, is of course vital to this process, and themost
+significant factor that affects the spin-wave coherence is temperature. Here we
+present neutron inelastic scattering measurements of the full threedimensional
+spin-wave dispersion in BiFeO3, which is one of the most promising functional
+multiferroic material, for temperatures from 5K to 700K. Despite the presence
+of strong electromagnetic coupling, the magnetic excitations behave like
+conventional magnons over all parts of the Brillouin zone. At low temperature
+the spin-waves are well-defined coherent modes, described by a classical model
+for a G-type antiferromagnet. A spin-wave velocity softening is already present
+at room temperature, and more pronounced damping occurs as the magnetic
+ordering temperature TN \sim 640K is approached. In addition, a strong
+hybridization of the Fe 3d and O 2p states is found to modify the distribution
+of the spin-wave spectral weight significantly, which implies that the spins
+are not restricted to the Fe atomic sites as previously believed.",1207.5078v1
+2012-09-24,Effective quantum memory Hamiltonian from local two-body interactions,"In [Phys. Rev. A 88, 062313 (2013)] we proposed and studied a model for a
+self-correcting quantum memory in which the energetic cost for introducing a
+defect in the memory grows without bounds as a function of system size. This
+positive behavior is due to attractive long-range interactions mediated by a
+bosonic field to which the memory is coupled. The crucial ingredients for the
+implementation of such a memory are the physical realization of the bosonic
+field as well as local five-body interactions between the stabilizer operators
+of the memory and the bosonic field. Here, we show that both of these
+ingredients appear in a low-energy effective theory of a Hamiltonian that
+involves only two-body interactions between neighboring spins. In particular,
+we consider the low-energy, long-wavelength excitations of an ordered
+Heisenberg ferromagnet (magnons) as a realization of the bosonic field.
+Furthermore, we present perturbative gadgets for generating the required
+five-spin operators. Our Hamiltonian involving only local two-body interactions
+is thus expected to exhibit self-correcting properties as long as the noise
+affecting it is in the regime where the effective low-energy description
+remains valid.",1209.5289v3
+2012-09-26,Classical and quantum integrability in AdS(2)/CFT(1),"We investigate the type IIA string on AdS(2)xS(2)xT(6) supported by RR-flux
+which describes the gravitational side of the AdS(2)/CFT(1) correspondence.
+While the four-dimensional part AdS(2)xS(2) can be realized as a supercoset,
+the full superstring has both coset and non-coset excitations, the latter
+giving rise to massless worldsheet modes, a somewhat novel feature in AdS/CFT.
+The string is nevertheless known to be integrable at the classical level. In
+this paper we perform several computations checking aspects of both classical
+and quantum string integrability. At the classical level we compute energies
+for the near BMN string and successfully match these against Bethe ansatz
+predictions. Furthermore, integrability dictates a magnon dispersion relation
+which we compare with the poles of loop corrected propagators, at both the one
+and two-loop level. At one loop, where only tadpole diagrams contribute, we
+find that the bosonic and fermionic contributions sum up to zero. Under the
+assumption of worldsheet supersymmetry, we then compute the two-loop sunset
+diagram in the near flat space limit. As in AdS(5)xS(5) we find that the result
+fits nicely into the sine-square structure of the dispersion relation.",1209.6062v2
+2012-10-08,Magnetic anisotropy in strained manganite films and bicrystal junctions,"Transport and magnetic properties of LSMO manganite thin films and bicrystal
+junctions were investigated. Manganite films were epitaxially grown on STO,
+LAO, NGO and LSAT substrates and their magnetic anisotropy were determined by
+two techniques of magnetic resonance spectroscopy. Compare with cubic
+substrates a small (about 0.3 persentage), the anisotropy of the orthorhombic
+NGO substrate leads to a uniaxial anisotropy of the magnetic properties of the
+films in the plane of the substrate. Samples with different tilt of
+crystallographic basal planes of manganite as well as bicrystal junctions with
+rotation of the crystallographic axes (RB - junction) and with tilting of basal
+planes (TB - junction) were investigated. It was found that on vicinal NGO
+substrates the value of magnetic anisotropy could be varied by changing the
+substrate inclination angle from 0 to 25 degrees. Measurement of magnetic
+anisotropy of manganite bicrystal junction demonstrated the presence of two
+ferromagnetically ordered spin subsystems for both types of bicrystal
+boundaries RB and TB. The magnitude of the magnetoresistance for TB - junctions
+increased with decreasing temperature and with the misorientation angle even
+misorientation of easy axes in the parts of junction does not change. Analysis
+of the voltage dependencies of bicrystal junction conductivity show that the
+low value of the magnetoresistance for the LSMO bicrystal junctions can be
+caused by two scattering mechanisms with the spin- flip of spin - polarized
+carriers due to the strong electron - electron interactions in a disordered
+layer at the bicrystal boundary at low temperatures and the spin-flip by anti
+ferromagnetic magnons at high temperatures.",1210.2261v1
+2013-02-17,Raman Studies of Anisotropic Magnetic Excitations in Fluctuating Nematic Striped La2-xSrxCuO4 and the Comparison to Uniform Nd2-xCexCuO4,"The mechanism of the high temperature hole-doped superconductivity was
+investigated by Raman scattering. The Raman selection rule is unique, so that
+anisotropic magnetic excitations in a fluctuating spin-charge stripe can be
+detected as if it is static. We use different Raman selection rules for two
+kinds of magnetic Raman scattering processes, two-magnon scattering and
+high-energy electronic scattering. In order to confirm the difference, the
+Raman spectra of striped La2-xSrxCuO4 (LSCO) and non-striped Nd2-xCexCuO4
+(NCCO) were compared. The main results in LSCO are (1) magnetic excitations are
+presented by individual energy dispersions for the k\parallel stripe and the
+k\perp stripe, (2) the charge transfer is allowed only in the direction
+perpendicular to the stripe. The direction is the same as the Burgers vector of
+an edge dislocation. Hence we assume that a charge moves together with the edge
+dislocation of the charge stripe. The superconducting coherence length is close
+to the inter-charge stripe distance at x < 0.2. Therefore we propose a model
+that superconducting pairs are formed in the edge dislocations. The binding
+energy is related to the stripe formation energy.",1302.4060v1
+2013-05-03,"Co2 FeAl thin films grown on MgO substrates: Correlation between static, dynamic and structural properties","Co2FeAl (CFA) thin films with thickness varying from 10 nm to 115 nm have
+been deposited on MgO(001) substrates by magnetron sputtering and then capped
+by Ta or Cr layer. X-rays diffraction (XRD) revealed that the cubic $[001]$ CFA
+axis is normal to the substrate and that all the CFA films exhibit full
+epitaxial growth. The chemical order varies from the $B2$ phase to the $A2$
+phase when decreasing the thickness. Magneto-optical Kerr effect (MOKE) and
+vibrating sample magnetometer measurements show that, depending on the field
+orientation, one or two-step switchings occur. Moreover, the films present a
+quadratic MOKE signal increasing with the CFA thickness, due to the increasing
+chemical order. Ferromagnetic resonance, MOKE transverse bias initial inverse
+susceptibility and torque (TBIIST) measurements reveal that the in-plane
+anisotropy results from the superposition of a uniaxial and of a fourfold
+symmetry term. The fourfold anisotropy is in accord with the crystal structure
+of the samples and is correlated to the biaxial strain and to the chemical
+order present in the films. In addition, a large negative perpendicular
+uniaxial anisotropy is observed. Frequency and angular dependences of the FMR
+linewidth show two magnon scattering and mosaicity contributions, which depend
+on the CFA thickness. A Gilbert damping coefficient as low as 0.0011 is found.",1305.0714v1
+2013-05-10,Open spin chains for giant gravitons and relativity,"We study open spin chains for strings stretched between giant graviton states
+in the N=4 SYM field theory in the collective coordinate approach. We study the
+boundary conditions and the effective Hamiltonian of the corresponding spin
+chain to two loop order.
+  The ground states of the spin chain have energies that match the relativistic
+dispersion relation characteristic of massive W boson particles on the
+worldvolume of the giant graviton configurations, up to second order in the
+limit where the momentum is much larger than the mass. We find evidence for a
+non-renormalization theorem for the ground state wave function of this spin
+chain system. We also conjecture a generalization of this result to all loop
+orders which makes it compatible with a fully relativistic dispersion relation.
+We show that the conjecture follows if one assumes that the spin chain admits a
+central charge extension that is sourced by the giant gravitons, generalizing
+the giant magnon dispersion relation for closed string excitations. This
+provides evidence for ten dimensional local physics mixing AdS directions and
+the five-sphere emerging from an N=4 SYM computation in the presence of a
+non-trivial background (made of D-branes) that break the conformal field theory
+of the system.",1305.2394v2
+2013-05-21,Binding carriers to a non-magnetic impurity in a two-dimensional square Ising antiferromagnet,"A hole in a two-dimensional Ising antiferromagnet was believed to be
+infinitely heavy due to the string of wrongly oriented spins it creates as it
+moves, which should trap it near its original location. Trugman showed that, in
+fact, the hole acquires a finite effective mass due to contributions from
+so-called {\it Trugman loop} processes, where the hole goes nearly twice around
+closed loops, first creating and then removing wrongly-oriented spins, and
+ending up at a different lattice site. This generates effective second- and
+third-nearest-neighbor hopping terms which keep the quasiparticle on the
+sublattice it was created on. Here, we investigate the trapping of the
+quasiparticle near a single attractive non-magnetic impurity placed at one
+lattice site. We consider the two cases with the quasiparticle and impurity
+being on the same versus on different sublattices. The main result is that even
+though the quasiparticle can not see the bare disorder in the latter case, the
+coupling to magnons generates an effective renormalized disorder on its own
+sublattice which is strong enough to lead to bound states, which however have a
+very different spectrum than when the quasiparticle and impurity are on the
+same sublattice.",1305.4691v2
+2013-05-29,Thermodynamic Properties of the Anisotropic Frustrated Spin-chain Compound Linarite PbCuSO$_4$(OH)$_2$,"We present a comprehensive macroscopic thermodynamic study of the
+quasi-one-dimensional (1D) $s = \tfrac{1}{2}$ frustrated spin-chain system
+linarite. Susceptibility, magnetization, specific heat, magnetocaloric effect,
+magnetostriction, and thermal-expansion measurements were performed to
+characterize the magnetic phase diagram. In particular, for magnetic fields
+along the b axis five different magnetic regions have been detected, some of
+them exhibiting short-range-order effects. The experimental magnetic entropy
+and magnetization are compared to a theoretical modelling of these quantities
+using DMRG and TMRG approaches. Within the framework of a purely 1D isotropic
+model Hamiltonian, only a qualitative agreement between theory and the
+experimental data can be achieved. Instead, it is demonstrated that a
+significant symmetric anisotropic exchange of about 10% is necessary to account
+for the basic experimental observations, including the 3D saturation field, and
+which in turn might stabilize a triatic (three-magnon) multipolar phase.",1305.6731v3
+2013-07-02,Electronic excitations in the edge-shared relativistic Mott insulator: Na$_2$IrO$_3$,"We have investigated the excitation spectra of $j_{eff}$=$\frac{1}{2}$ Mott
+insulator Na$_2$IrO$_3$. Taking into account a relativistic multiplet structure
+of Ir ions, we have calculated the optical conductivity $\sigma(\omega)$ and
+resonant inelastic x-ray scattering (RIXS) spectra, which manifest different
+features from those of a canonical $j_{eff}$=$\frac{1}{2}$ system
+Sr$_2$IrO$_4$.Distinctly from the two-peak structure in Sr$_2$IrO$_4$,
+$\sigma(\omega)$ in Na$_2$IrO$_3$ has a broad single peak dominated by
+interband transitions from $j_{eff}$=$\frac{3}{2}$ to $\frac{1}{2}$. RIXS
+spectra exhibit the spin-orbit (SO) exciton that has a two-peak structure
+arising from the crystal-field effect, and the magnon peak at energies much
+lower than in Sr$_2$IrO$_4$. In addition, a small peak near the optical
+absorption edge is found in RIXS spectra, originating from the coupling between
+the electron-hole ($e$-$h$) excitation and the SO exciton. Our findings
+corroborate the validity of the relativistic electronic structure and
+importance of both itinerant and local features in Na$_2$IrO$_3$.",1307.0614v3
+2013-11-29,Controlling magnetic order and quantum disorder in one- and zero-dimensional molecule-based magnets,"We investigate the structural and magnetic properties of two molecule-based
+magnets synthesized from the same starting components. Their different
+structural motifs promote contrasting exchange pathways and consequently lead
+to markedly different magnetic ground states. Through examination of their
+structural and magnetic properties we show that
+[Cu(pyz)(H$_{2}$O)(gly)$_{2}$](ClO$_{4}$)$_{2}$ may be considered a
+quasi-one-dimensional quantum Heisenberg antiferromagnet while the related
+compound [Cu(pyz)(gly)](ClO$_{4}$), which is formed from dimers of
+antiferromagnetically interacting Cu$^{2+}$ spins, remains disordered down to
+at least 0.03 K in zero field, but shows a field-temperature phase diagram
+reminiscent of that seen in materials showing a Bose-Einstein condensation of
+magnons.",1311.7614v1
+2014-01-21,Observation of entanglement propagation in a quantum many-body system,"The key to explaining a wide range of quantum phenomena is understanding how
+entanglement propagates around many-body systems. Furthermore, the controlled
+distribution of entanglement is of fundamental importance for quantum
+communication and computation. In many situations, quasiparticles are the
+carriers of information around a quantum system and are expected to distribute
+entanglement in a fashion determined by the system interactions. Here we report
+on the observation of magnon quasiparticle dynamics in a one-dimensional
+many-body quantum system of trapped ions representing an Ising spin model.
+Using the ability to tune the effective interaction range, and to prepare and
+measure the quantum state at the individual particle level, we observe new
+quasiparticle phenomena. For the first time, we reveal the entanglement
+distributed by quasiparticles around a many-body system. Second, for long-range
+interactions we observe the divergence of quasiparticle velocity and breakdown
+of the light-cone picture that is valid for short-range interactions. Our
+results will allow experimental studies of a wide range of phenomena, such as
+quantum transport, thermalisation, localisation and entanglement growth, and
+represent a first step towards a new quantum-optical regime with on-demand
+quasiparticles with tunable non-linear interactions.",1401.5387v3
+2014-01-27,Direct determination of exchange parameters in Cs2CuBr4 and Cs2CuCl4: high-field ESR studies,"Spin-1/2 Heisenberg antiferromagnets Cs$_2$CuCl$_4$ and Cs$_2$CuBr$_4$ with
+distorted triangular-lattice structures are studied by means of electron spin
+resonance spectroscopy in magnetic fields up to the saturation field and above.
+In the magnetically saturated phase, quantum fluctuations are fully suppressed,
+and the spin dynamics is defined by ordinary magnons. This allows us to
+accurately describe the magnetic excitation spectra in both materials and,
+using the harmonic spin-wave theory, to determine their exchange parameters.
+The viability of the proposed method was proven by applying it to
+Cs$_2$CuCl$_4$, yielding $J/k_B=4.7(2)$ K, $J'/k_B=1.42(7)$ K [$J'/J\simeq
+0.30$] and revealing good agreement with inelastic neutron-scattering results.
+For the isostructural Cs$_2$CuBr$_4$, we obtain $J/k_B=14.9(7)$ K,
+$J'/k_B=6.1(3)$ K, [$J'/J\simeq 0.41$], providing exact and conclusive
+information on the exchange couplings in this frustrated spin system.",1401.6793v2
+2014-02-13,"Fractionalization, entanglement, and separation: understanding the collective excitations in a spin-orbital chain","Using a combined analytical and numerical approach, we study the collective
+spin and orbital excitations in a spin-orbital chain under a crystal field.
+Irrespective of the crystal field strength, these excitations can be
+universally described by fractionalized fermions. The fractionalization
+phenomenon persists and contrasts strikingly with the case of a spin chain,
+where fractionalized spinons cannot be individually observed but confined to
+form magnons in a strong magnetic field. In the spin-orbital chain, each of the
+fractional quasiparticles carries both spin and orbital quantum numbers, and
+the two variables are always entangled in the collective excitations. Our
+result further shows that the recently reported separation phenomenon occurs
+when crystal fields fully polarize the orbital degrees of freedom. In this
+case, however, the spinon and orbiton dynamics are decoupled solely because of
+a redefinition of the spin and orbital quantum numbers.",1402.3255v4
+2014-06-30,Bound states and entanglement in the excited states of quantum spin chains,"We investigate entanglement properties of the excited states of the spin-1/2
+Heisenberg (XXX) chain with isotropic antiferromagnetic interactions, by
+exploiting the Bethe ansatz solution of the model. We consider eigenstates
+obtained from both real and complex solutions (""strings"") of the Bethe
+equations. Physically, the former are states of interacting magnons, whereas
+the latter contain bound states of groups of particles. We first focus on the
+situation with few particles in the chain. Using exact results and
+semiclassical arguments, we derive an upper bound S_MAX for the entanglement
+entropy. This exhibits an intermediate behavior between logarithmic and
+extensive, and it is saturated for highly-entangled states. As a function of
+the eigenstate energy, the entanglement entropy is organized in bands. Their
+number depends on the number of blocks of contiguous Bethe-Takahashi quantum
+numbers. In presence of bound states a significant reduction in the
+entanglement entropy occurs, reflecting that a group of bound particles behaves
+effectively as a single particle. Interestingly, the associated entanglement
+spectrum shows edge-related levels. At finite particle density, the
+semiclassical bound S_MAX becomes inaccurate. For highly-entangled states
+S_A\propto L_c, with L_c the chord length, signaling the crossover to extensive
+entanglement. Finally, we consider eigenstates containing a single pair of
+bound particles. No significant entanglement reduction occurs, in contrast with
+the few-particle case.",1407.0066v2
+2014-08-07,Thermodynamics of AdS Black Holes in Einstein-Scalar Gravity,"We study the thermodynamics of $n$-dimensional static asymptotically AdS
+black holes in Einstein gravity coupled to a scalar field with a potential
+admitting a stationary point with an AdS vacuum. Such black holes with
+non-trivial scalar hair can exist provided that the mass-squared of the scalar
+field is negative, and above the Breitenlohner-Freedman bound. We use the Wald
+procedure to derive the first law of thermodynamics for these black holes,
+showing how the scalar hair (or ""charge"") contributes non-trivially in the
+expression. We show in general that a black hole mass can be deduced by
+isolating an integrable contribution to the (non-integrable) variation of the
+Hamiltonian arising in the Wald construction, and that this is consistent with
+the mass calculated using the renormalised holographic stress tensor and also,
+in those cases where it is defined, with the mass calculated using the
+conformal method of Ashtekar, Magnon and Das. Similar arguments can also be
+given for the smooth solitonic solutions in these theories. Neither the black
+hole nor the soliton solutions can be constructed explicitly, and we carry out
+a numerical analysis to demonstrate their existence and to provide approximate
+checks on some of our thermodynamic results.",1408.1514v2
+2014-08-08,Stable Magnetic Droplet Solitons in Spin Transfer Nanocontacts,"Magnetic thin films with perpendicular magnetic anisotropy (PMA) have
+localized excitations that correspond to reversed dynamically precessing
+magnetic moments, known as magnetic droplet solitons. Fundamentally, these
+excitations are associated with an attractive interaction between elementary
+spin-excitations (i.e., magnons) and were predicted to occur in PMA materials
+in the absence of damping [1,2]. While damping, present in all magnetic
+materials, suppresses these excitations, it is now possible to compensate
+damping by spin transfer torques through electrical current flow in nanometer
+scale contacts to ferromagnetic thin films [3,4]. A theory predicts the
+appearance of magnetic droplet solitons at a threshold current in nanocontacts
+[5] and, recently, experimental signatures of droplet nucleation have been
+reported [6]. However, thus far, they have been observed to be nearly
+reversible excitations, with only partially reversed magnetization and to be
+subject to instabilities that cause them to drift away from the nanocontacts
+(i.e., drift instabilities) [6]. Here we show that magnetic droplet solitons
+can be stabilized in a spin transfer nanocontact. Further, they exhibit a
+strong hysteretic response to fields and currents and a nearly fully reversed
+magnetization in the contact. These observations, in addition to their
+fundamental interest, open up new applications for magnetic droplet solitons as
+multi-state high frequency current and field tunable oscillators.",1408.1902v1
+2014-08-19,Exploring quantum phase transition in Pd_{1-x}Ni_x nanoalloys,"Pd$_{1-x}$Ni$_x$ alloy system is an established ideal transition metal system
+possessing a composition induced paramagnetic to ferromagnetic quantum phase
+transition (QPT) at the critical concentration $x_c \sim$ 0.026 in bulk. A
+low-temperature non-Fermi liquid (NFL) behaviour around $x_c$ usually indicates
+the presence of quantum criticality (QC) in this system. In this work, we
+explore the existence of such a QPT in nanoparticles of this alloy system. We
+synthesized single-phase, polydispersed and 40-50 nm mean diameter crystalline
+nanoparticles of Pd$_{1-x}$Ni$_x$ alloys, with $x$ near $x_c$ and beyond, by a
+chemical reflux method. In addition to the determination of the size,
+composition, phase and crystallinity of the alloys by microscopic and
+spectroscopic techniques, the existence of a possible QPT was explored by
+resistivity and DC magnetization measurements. A dip in the value of the
+exponent $n$ near $x_c$, and a concomitant peak in the constant $A$, of the
+$AT^n$ dependence of the low temperature ($T$) resistivity indicate the
+presence of a quantum-like phase transition in the system. The minimum value of
+$n$, however, remains within the Fermi liquid regime ($n >$ 2). The DC
+magnetization results suggest an anticipatory presence of a superparamagnetic
+to ferromagnetic QPT in the mean-sized nanoparticles. The observation of a
+possible quantum critical NFL behaviour ($n <$ 2) through resistivity is argued
+to be inhibited by the electron-magnon scatterings present in the smaller
+nanoparticles.",1408.4316v1
+2014-09-01,Statistics-dependent quantum co-walking of two particles in one-dimensional lattices with nearest-neighbor interactions,"We investigate continuous-time quantum walks of two indistinguishable
+particles [bosons, fermions or hard-core bosons (HCBs)] in one-dimensional
+lattices with nearest-neighbor interactions. The results for two HCBs are well
+consistent with the recent experimental observation of two-magnon dynamics
+[Nature 502, 76 (2013)]. The two interacting particles can undergo independent-
+and/or co-walking depending on both quantum statistics and interaction
+strength. Two strongly interacting particles may form a bound state and then
+co-walk like a single composite particle with statistics-dependent walk speed.
+Analytical solutions for the scattering and bound states, which appear in the
+two-particle quantum walks, are obtained by solving the eigenvalue problem in
+the two-particle Hilbert space. In the context of degenerate perturbation
+theory, an effective single-particle model for the quantum co-walking is
+analytically derived and the walk seep of bosons is found to be exactly three
+times of the ones of fermions/HCBs. Our result paves the way for experimentally
+exploring quantum statistics via two-particle quantum walks.",1409.0306v3
+2014-09-30,Enhanced gyration-signal propagation speed in one-dimensional vortex-antivortex lattices and its control by perpendicular bias field,"We report on a micromagnetic simulation study of coupled core gyrations in
+one-dimensional (1D) alternating vortex-antivortex (V-AV) lattices formed in
+connected soft-magnetic-disk arrays (round-shaped modulated nanostrips). In the
+V-AV lattices, we found very characteristic standing-wave modes of the coupled
+gyrations as well as efficiently ultrafast gyration-signal propagation between
+vortices through the neighboring antivortices, as originating from their
+combined strong exchange and dipole interactions. Collective core oscillations
+in the V-AV networks are characterized as unique two-branch magnonic bands that
+are affected by the polarization ordering between the neighboring vortex and
+antivortex and controllable by externally applied perpendicular fields each of
+different field strength and direction. The gyration-signal propagation speed
+is much faster than that for 1D disk arrays composed only of vortex states, and
+the propagation speed for the parallel polarization ordering is increased,
+remarkably, to more than 1 km/sec by application of perpendicular static
+fields. This work provides a fundamental understanding of the coupled dynamics
+of topological solitons as well as an additional mechanism for ultrafast
+gyration-signal propagation; moreover, it offers an efficient means of
+significant propagation-speed enhancement that is suitable for information
+carrier applications in continuous nanostrips.",1409.8357v1
+2014-10-14,Symmetry-dependent electron-electron interaction in coherent tunnel junctions resolved by zero bias anomaly measurements,"We provide conclusive experimental evidence that zero bias anomaly in the
+differential resistance of magnetic tunnel junctions (MTJs) is due to
+electron-electron interaction (EEI), clarifying a long standing issue. Magnon
+effect that caused confusion is now excluded by measuring at low temperatures
+down to 0.2 K and with reduced AC measurement voltages down to 0.06 mV. The
+normalized change of conductance is proportional to $\ln{(eV/k_{B}T)}$,
+consistent with the Altshuler-Aronov theory of tunneling that describes the
+reduction of density of states due to EEI, but inconsistent with magnetic
+impurity scattering. The slope of the $\ln{(eV/k_{B}T)}$ dependence is symmetry
+dependent: the slopes for P and AP states are different for coherent tunnel
+junctions with symmetry filtering, while nearly the same for those without
+symmetry filtering (amorphous barriers). This observation may be helpful for
+verifying symmetry preserved filtering in search of new coherent tunneling
+junctions, and for probing and separating electron Bloch states of different
+symmetries in other correlated systems.",1410.3636v2
+2015-02-10,Magnetic-field and doping dependence of low-energy spin fluctuations in the antiferroquadrupolar compound Ce(1-x)La(x)B(6),"CeB(6) is a model compound exhibiting antiferroquadrupolar (AFQ) order, its
+magnetic properties being typically interpreted within localized models. More
+recently, the observation of strong and sharp magnetic exciton modes forming in
+its antiferromagnetic (AFM) state at both ferromagnetic and AFQ wave vectors
+suggested a significant contribution of itinerant electrons to the spin
+dynamics. Here we investigate the evolution of the AFQ excitation upon the
+application of an external magnetic field and the substitution of Ce with
+non-magnetic La, both parameters known to suppress the AFM phase. We find that
+the exciton energy decreases proportionally to T_N upon doping. In field, its
+intensity is suppressed, while its energy remains constant. Its disappearance
+above the critical field of the AFM phase is preceded by the formation of two
+modes, whose energies grow linearly with magnetic field upon entering the AFQ
+phase. These findings suggest a crossover from itinerant to localized spin
+dynamics between the two phases, the coupling to heavy-fermion quasiparticles
+being crucial for a comprehensive description of the magnon spectrum.",1502.03139v2
+2015-03-04,Thermodynamics of quantum systems under dynamical control,"In this review the debated rapport between thermodynamics and quantum
+mechanics is addressed in the framework of the theory of
+periodically-driven/controlled quantum-thermodynamic machines. The basic model
+studied here is that of a two-level system (TLS), whose energy is periodically
+modulated while the system is coupled to thermal baths. When the modulation
+interval is short compared to the bath memory time, the system-bath
+correlations are affected, thereby causing cooling or heating of the TLS,
+depending on the interval. In steady state, a periodically-modulated TLS
+coupled to two distinct baths constitutes the simplest quantum heat machine
+(QHM) that may operate as either an engine or a refrigerator, depending on the
+modulation rate. We find their efficiency and power-output bounds and the
+conditions for attaining these bounds. An extension of this model to multilevel
+systems shows that the QHM power output can be boosted by the multilevel
+degeneracy.
+  These results are used to scrutinize basic thermodynamic principles: (i)
+Externally-driven/modulated QHMs may attain the Carnot efficiency bound, but
+when the driving is done by a quantum device (""piston""), the efficiency
+strongly depends on its initial quantum state. Such dependence has been unknown
+thus far. (ii) The refrigeration rate effected by QHMs does not vanish as the
+temperature approaches absolute zero for certain quantized baths, e.g.,
+magnons, thous challenging Nernst's unattainability principle. (iii)
+System-bath correlations allow more work extraction under periodic control than
+that expected from the Szilard-Landauer principle, provided the period is in
+the non-Markovian domain. Thus, dynamically-controlled QHMs may benefit from
+hitherto unexploited thermodynamic resources.",1503.01195v1
+2015-03-20,Magnetic excitations of perovskite rare-earth nickelates: RNiO$_3$,"The perovskite nickelates RNiO$_3$ (R: rare-earth) have been studied as
+potential multiferroic compounds. A certain degree of charge disproportionation
+in the Ni ions has been confirmed by high resolution synchrotron power
+diffraction: instead of the nominal Ni$^{3+}$ valence, they can have the
+mixed-valence state Ni$^{(3-\delta)+}$ and Ni$^{(3+\delta)+}$, though agreement
+has not been reached on the precise value of $\delta$ (e.g. for NdNiO$_3$,
+$\delta=0.0$ and $\delta=0.29$ were reported). Also, the magnetic ground state
+is not yet clear: collinear and non-collinear Ni-O magnetic structures have
+been proposed to explain neutron diffraction and soft X-ray resonant
+sccattering results in these compounds, and more recently a canted
+antiferromagnetic spin arrangement was proposed on the basis of magnetic
+susceptibility measurements. This scenario is reminiscent of the situation in
+the half-doped manganites.
+  In order to gain insight into the ground state of these compounds, we studied
+the magnetic excitations of some of the different phases proposed, using a
+localized spin model for a simplified spin chain which could describe these
+compounds. We first analize the stability of the collinear, orthogonal, and
+intermediate phases in the classical case. We then explore the quantum ground
+state indirectly, calculating the spin excitations obtained for each phase,
+using the Holstein-Primakoff transformation and the linear spin-wave
+approximation. For the collinear and orthogonal ($\theta=\pi/2$) phases, we
+predict differences in the magnon spectrum which would allow to distinguish
+between them in future inelastic neutron scattering experiments.",1503.06102v1
+2015-03-20,Control of spin current by a magnetic YIG substrate in NiFe/Al nonlocal spin valves,"We study the effect of a magnetic insulator (Yttrium Iron Garnet - YIG)
+substrate on the spin transport properties of Ni$_{80}$Fe$_{20}$/Al nonlocal
+spin valve (NLSV) devices. The NLSV signal on the YIG substrate is about 2 to 3
+times lower than that on a non magnetic SiO$_2$ substrate, indicating that a
+significant fraction of the spin-current is absorbed at the Al/YIG interface.
+By measuring the NLSV signal for varying injector-to-detector distance and
+using a three dimensional spin-transport model that takes spin current
+absorption at the Al/YIG interface into account we obtain an effective
+spin-mixing conductance $G_{\uparrow\downarrow}\simeq 5 - 8\times
+10^{13}~\Omega^{-1}$m$^{-2}$. We also observe a small but clear modulation of
+the NLSV signal when rotating the YIG magnetization direction with respect to
+the fixed spin polarization of the spin accumulation in the Al. Spin relaxation
+due to thermal magnons or roughness of the YIG surface may be responsible for
+the observed small modulation of the NLSV signal.",1503.06108v1
+2015-04-10,MCViNE -- An object oriented Monte Carlo neutron ray tracing simulation package,"MCViNE (Monte-Carlo VIrtual Neutron Experiment) is a versatile Monte Carlo
+(MC) neutron ray-tracing program that provides researchers with tools for
+performing computer modeling and simulations that mirror real neutron
+scattering experiments. By adopting modern software engineering practices such
+as using composite and visitor design patterns for representing and accessing
+neutron scatterers, and using recursive algorithms for multiple scattering,
+MCViNE is flexible enough to handle sophisticated neutron scattering problems
+including, for example, neutron detection by complex detector systems, and
+single and multiple scattering events in a variety of samples and sample
+environments. In addition, MCViNE can take advantage of simulation components
+in linear-chain-based MC ray tracing packages widely used in instrument design
+and optimization, as well as NumPy-based components that make prototypes useful
+and easy to develop. These developments have enabled us to carry out detailed
+simulations of neutron scattering experiments with non-trivial samples in
+time-of-flight inelastic instruments at the Spallation Neutron Source. Examples
+of such simulations for powder and single-crystal samples with various
+scattering kernels, including kernels for phonon and magnon scattering, are
+presented. With simulations that closely reproduce experimental results,
+scattering mechanisms can be turned on and off to determine how they contribute
+to the measured scattering intensities, improving our understanding of the
+underlying physics.",1504.02776v2
+2015-05-14,"First-principles calculations of exchange interactions, spin waves, and temperature dependence of magnetization in inverse-Heusler-based spin gapless semiconductors","Employing first principles electronic structure calculations in conjunction
+with the frozen-magnon method we calculate exchange interactions, spin-wave
+dispersion, and spin-wave stiffness constants in inverse-Heusler-based spin
+gapless semiconductor (SGS) compounds Mn$_2$CoAl, Ti$_2$MnAl, Cr$_2$ZnSi,
+Ti$_2$CoSi and Ti$_2$VAs. We find that their magnetic behavior is similar to
+the half-metallic ferromagnetic full-Heusler alloys, i.e., the intersublattice
+exchange interactions play an essential role in the formation of the magnetic
+ground state and in determining the Curie temperature, $T_\mathrm{c}$. All
+compounds, except Ti$_2$CoSi possess a ferrimagnetic ground state. Due to the
+finite energy gap in one spin channel, the exchange interactions decay sharply
+with the distance, and hence magnetism of these SGSs can be described
+considering only nearest and next-nearest neighbor exchange interactions. The
+calculated spin-wave dispersion curves are typical for ferrimagnets and
+ferromagnets. The spin-wave stiffness constants turn out to be larger than
+those of the elementary 3$d$-ferromagnets. Calculated exchange parameters are
+used as input to determine the temperature dependence of the magnetization and
+$T_\mathrm{c}$ of the SGSs. We find that the $T_\mathrm{c}$ of all compounds is
+much above the room temperature. The calculated magnetization curve for
+Mn$_2$CoAl as well as the Curie temperature are in very good agreement with
+available experimental data. The present study is expected to pave the way for
+a deeper understanding of the magnetic properties of the inverse-Heusler-based
+SGSs and enhance the interest in these materials for application in spintronic
+and magnetoelectronic devices.",1505.03632v1
+2015-10-14,Stability of skyrmion lattices and symmetries of quasi-two-dimensional chiral magnets,"Recently, there has been substantial interest in realizations of skyrmions,
+in particular in 2D systems due to increased stability resulting from reduced
+dimensionality. A stable skyrmion, representing the smallest realizable
+magnetic texture, could be an ideal element for ultra-dense magnetic memories.
+Here, we use the most general form of the 2D free energy with
+Dzyaloshinskii-Moriya interactions constructed from general symmetry
+considerations reflecting the underlying system. We predict that skyrmion phase
+is robust and it is present even when the system lacks the in-plane rotational
+symmetry. In fact, the lowered symmetry leads to increased stability of
+vortex-antivortex lattices with four-fold symmetry and in-plane spirals, in
+some instances even in the absence of an external magnetic field. Our results
+relate different hexagonal and square cell phases to the symmetries of
+materials used for realizations of skyrmions. This will give clear directions
+for experimental realizations of hexagonal and square cell phases, and will
+allow engineering of skyrmions with unusual properties. We also predict
+striking differences in gyro-dynamics induced by spin currents for isolated
+skyrmions and for crystals where spin currents can be induced by charge
+carriers or by thermal magnons. We find that under certain conditions, isolated
+skyrmions can move along the current without a side motion which can have
+implications for realizations of magnetic memories.",1510.04262v3
+2015-10-28,Raman and fluorescence characteristics of resonant inelastic X-ray scattering from doped superconducting cuprates,"Measurements of spin excitations are essential for an understanding of
+spin-mediated pairing for superconductivity; and resonant inelastic X-ray
+scattering (RIXS) provides a considerable opportunity to probe high-energy spin
+excitations. However, whether RIXS correctly measures the collective spin
+excitations of doped superconducting cuprates remains under debate. Here we
+demonstrate distinct Raman- and fluorescence-like RIXS excitations of
+Bi$_{1.5}$Pb$_{0.6}$Sr$_{1.54}$CaCu$_{2}$O$_{8+{\delta}}$ in the mid-infrared
+energy region. Combining photon-energy and momentum dependent RIXS measurements
+with theoretical calculations using exact diagonalization provides conclusive
+evidence that the Raman-like RIXS excitations correspond to collective spin
+excitations, which are magnons in the undoped Mott insulators and evolve into
+paramagnons in doped superconducting compounds. In contrast, the
+fluorescence-like shifts are due primarily to the continuum of particle-hole
+excitations in the charge channel. Our results show that under the proper
+experimental conditions RIXS indeed can be used to probe paramagnons in doped
+high-$T_c$ cuprate superconductors.",1510.08403v1
+2015-10-29,Thermal Conductivity in the Triangular-Lattice Antiferromagnet Ba3CoSb2O9,"We have measured the thermal conductivity in the ab-plane, $\kappa$ab, and
+along the c-axis, $\kappa$c, of single crystals of the S = 1/2
+triangular-lattice antiferromagnet Ba3CoSb2O9 in zero field and magnetic
+fields. In zero field, it has been found that both $\kappa$ab and $\kappa$c
+show a similar broad peak around 40 K, suggesting that the thermal conductivity
+due to phonons is dominant in this compound and that the mean free path of
+phonons is suppressed so much by strong magnetic-fluctuations due to the
+magnetic frustration. It has also been found that both $\kappa$ab and $\kappa$c
+show a kink at the antiferromagnetic transition temperature TN. In magnetic
+fields parallel to the ab-plane up to 14 T, magnetic-field dependences of both
+$\kappa$ab and $\kappa$c at temperatures below and above TN have been found to
+be understood taking into account the phonon-magnon scattering in the so-called
+120${\deg}$ structure phase and the up-up-down (UUD) phase, while the minima of
+$\kappa$ab and $\kappa$c observed in the middle of the UUD phase have not been
+understood. This suggests the occurrence of some change of the magnetic state
+in the middle of the UUD phase.",1510.08635v1
+2016-01-18,"Electromagnons, magnons, and phonons in Eu$_{1-x}$Ho$_x$MnO$_3$","Here we present a detailed study of the THz and FIR response of the mixed
+perovskite manganite system Eu$_{1-x}$Ho$_x$MnO$_3$ for holmium concentrations
+x = 0.1 and 0.3. We compare the magnetic excitations of the four different
+magnetically ordered phases (A-type antiferromagnetic, sinusoidally modulated
+collinear, helical phases with spin planes perpendicular to the
+crystallographic a and c axes). The transition between the two latter phases
+goes hand in hand with a switching of the ferroelectric polarization from P||a
+to P||c. Special emphasis is paid to the temperature dependence of the
+excitations at this transition. We find a significant change of intensity
+indicating that the exchange striction mechanism cannot be the only mechanism
+to induce dipolar weight to spin-wave excitations. We also focus on excitations
+within the incommensurate collinear antiferromagnetic phase and find a so far
+unobserved excitation close to 40 cm$^{-1}$. A detailed analysis of optical
+weight gives a further unexpected result: In the multiferroic phase with P||c
+all the spectral weight of the electromagnons comes from the lowest phonon
+mode. However, for the phase with the polarization P||a additional spectral
+weight must be transferred from higher frequencies.",1601.04486v1
+2016-02-02,Non-Markovian Dynamics in Chiral Quantum Networks with Spins and Photons,"We study the dynamics of chiral quantum networks consisting of nodes coupled
+by unidirectional or asymmetric bidirectional quantum channels. In contrast to
+familiar photonic networks where driven two-level atoms exchange photons via 1D
+photonic nanostructures, we propose and study a setup where interactions
+between the atoms are mediated by spin excitations (magnons) in 1D $XX$ spin
+chains representing spin waveguides. While Markovian quantum network theory
+eliminates quantum channels as structureless reservoirs in a Born-Markov
+approximation to obtain a master equation for the nodes, we are interested in
+non-Markovian dynamics. This arises from the nonlinear character of the
+dispersion with band-edge effects, and from finite spin propagation velocities
+leading to time delays in interactions. To account for the non-Markovian
+dynamics we treat the quantum degrees of freedom of the nodes and connecting
+channels as a composite spin system with the surrounding of the quantum network
+as a Markovian bath, allowing for an efficient solution with time-dependent
+density matrix renormalization group techniques. We illustrate our approach
+showing non-Markovian effects in the driven-dissipative formation of quantum
+dimers, and we present examples for quantum information protocols involving
+quantum state transfer with engineered elements as basic building blocks of
+quantum spintronic circuits.",1602.00926v2
+2016-02-03,Charge dynamics of the antiferromagnetically ordered Mott insulator,"We study the charge dynamics of the half-filled Hubbard model on the square
+lattice at zero temperature. We employ a slave-fermion formulation in which the
+charge degrees of freedom are represented by fermionic holons and doublons and
+the bosonic spin degrees of freedom are assumed to be described by the
+antiferromagnetic Heisenberg model. The ground state has long-ranged magnetic
+(N\'eel) order and its Mott-insulating characteristics are the consequence of
+holon-doublon bound-state formation. Within this framework, we calculate the
+average double occupancy, the electron density of states, and the spectral
+function in the self-consistent Born approximation. The lower and upper Hubbard
+bands are reproduced, there is spectral-weight transfer into a coherent
+quasiparticle band at their lower edges, and the Mott gap, associated with
+holon-doublon binding, is renormalized due to the interactions of the holons
+and doublons with the magnons. We compute the zeros of the Green function at
+the chemical potential to discuss the Luttinger volume and show that the poles
+of the self-energy reflect the underlying quasiparticle dispersion with a
+spin-renormalized hopping parameter. Optical conductivity results relate the
+optical gap to the Mott gap of the insulating system. We conclude that a
+self-consistent treatment of the spin fluctuation effects on the charge degrees
+of freedom captures all the essential physics of the antiferromagnetic
+Mott-Hubbard insulator.",1602.01276v2
+2016-04-20,Magnon Inflation: Slow Roll with Steep Potentials,"We find multi-scalar effective field theories (EFTs) that can achieve a slow
+inflationary roll despite having a scalar potential that does not satisfy the
+usual slow-roll condition (d V)^2 << V^2/Mp^2. They evade the usual slow-roll
+conditions on $V$ because their kinetic energies are dominated by
+single-derivative terms rather than the usual two-derivative terms. Single
+derivatives dominate during slow roll and so do not require a breakdown of the
+usual derivative expansion that underpins calculational control in much of
+cosmology. The presence of such terms requires some sort of UV Lorentz-symmetry
+breaking during inflation (besides the usual cosmological breaking).
+Chromo-natural inflation provides an example of a UV theory that can generate
+the multi-field single-derivative terms we consider, and we argue that the EFT
+we find indeed captures the slow-roll conditions for the background evolution
+for Chromo-natural inflation. We also show that our EFT can be understood as a
+multi-field generalization of the single-field Cuscuton models. The multi-field
+case introduces a new feature, however: the scalar kinetic terms define a
+target-space 2-form, F_{ab}, whose antisymmetry gives new ways for slow roll to
+be achieved.",1604.06048v2
+2016-04-26,First principles studies of the Gilbert damping and exchange interactions for half-metallic Heuslers alloys,"Heusler alloys have been intensively studied due to the wide variety of
+properties that they exhibit. One of these properties is of particular interest
+for technological applications, i.e. the fact that some Heusler alloys are
+half-metallic. In the following, a systematic study of the magnetic properties
+of three different Heusler families $\textrm{Co}_2\textrm{Mn}\textrm{Z}$,
+$\text{Co}_2\text{Fe}\text{Z}$ and $\textrm{Mn}_2\textrm{V}\textrm{Z}$ with
+$\text{Z}=\left(\text{Al, Si, Ga, Ge}\right)$ is performed. A key aspect is the
+determination of the Gilbert damping from first principles calculations, with
+special focus on the role played by different approximations, the effect that
+substitutional disorder and temperature effects. Heisenberg exchange
+interactions and critical temperature for the alloys are also calculated as
+well as magnon dispersion relations for representative systems, the
+ferromagnetic $\textrm{Co}_2\textrm{Fe}\textrm{Si}$ and the ferrimagnetic
+$\textrm{Mn}_2\textrm{V}\textrm{Al}$. Correlations effects beyond standard
+density-functional theory are treated using both the local spin density
+approximation including the Hubbard $U$ and the local spin density
+approximation plus dynamical mean field theory approximation, which allows to
+determine if dynamical self-energy corrections can remedy some of the
+inconsistencies which were previously reported for these alloys.",1604.07552v1
+2016-04-29,Spin Seebeck effect through antiferromagnetic NiO,"We report temperature-dependent spin-Seebeck measurements on Pt/YIG bilayers
+and Pt/NiO/YIG trilayers, where YIG (Yttrium iron garnet, Y$_3$Fe$_5$O$_{12}$)
+is an insulating ferrimagnet and NiO is an antiferromagnet at low temperatures.
+The thickness of the NiO layer is varied from 0 to 10 nm. In the Pt/YIG
+bilayers, the temperature gradient applied to the YIG stimulates dynamic spin
+injection into the Pt, which generates an inverse spin Hall voltage in the Pt.
+The presence of a NiO layer dampens the spin injection exponentially with a
+decay length of $2 \pm 0.6$ nm at 180 K. The decay length increases with
+temperature and shows a maximum of $5.5 \pm 0.8$ nm at 360 K. The temperature
+dependence of the amplitude of the spin-Seebeck signal without NiO shows a
+broad maximum of $6.5 \pm 0.5$ $\mu$V/K at 20 K. In the presence of NiO, the
+maximum shifts sharply to higher temperatures, likely correlated to the
+increase in decay length. This implies that NiO is most transparent to magnon
+propagation near the paramagnet-antiferromagnet transition. We do not see the
+enhancement in spin current driven into Pt reported in other papers when 1-2 nm
+NiO layers are sandwiched between Pt and YIG.",1604.08659v2
+2016-06-30,Correlations of zero-entropy critical states in the XXZ model: integrability and Luttinger theory far from the ground state,"Pumping a finite energy density into a quantum system typically leads to
+`melted' states characterized by exponentially-decaying correlations, as is the
+case for finite-temperature equilibrium situations. An important exception to
+this rule are states which, while being at high energy, maintain a low entropy.
+Such states can interestingly still display features of quantum criticality,
+especially in one dimension. Here, we consider high-energy states in
+anisotropic Heisenberg quantum spin chains obtained by splitting the ground
+state's magnon Fermi sea into separate pieces. Using methods based on
+integrability, we provide a detailed study of static and dynamical spin-spin
+correlations. These carry distinctive signatures of the Fermi sea splittings,
+which would be observable in eventual experimental realizations. Going further,
+we employ a multi-component Tomonaga-Luttinger model in order to predict the
+asymptotics of static correlations. For this effective field theory, we fix all
+universal exponents from energetics, and all non-universal correlation
+prefactors using finite-size scaling of matrix elements. The correlations
+obtained directly from integrability and those emerging from the Luttinger
+field theory description are shown to be in extremely good correspondence, as
+expected, for the large distance asymptotics, but surprisingly also for the
+short distance behavior. Finally, we discuss the description of dynamical
+correlations from a mobile impurity model, and clarify the relation of the
+effective field theory parameters to the Bethe Ansatz solution.",1606.09516v2
+2016-07-04,Hamiltonian truncation approach to quenches in the Ising field theory,"In contrast to lattice systems where powerful numerical techniques such as
+matrix product state based methods are available to study the non-equilibrium
+dynamics, the non-equilibrium behaviour of continuum systems is much harder to
+simulate. We demonstrate here that Hamiltonian truncation methods can be
+efficiently applied to this problem, by studying the quantum quench dynamics of
+the 1+1 dimensional Ising field theory using a truncated free fermionic space
+approach. After benchmarking the method with integrable quenches corresponding
+to changing the mass in a free Majorana fermion field theory, we study the
+effect of an integrability breaking perturbation by the longitudinal magnetic
+field. In both the ferromagnetic and paramagnetic phases of the model we find
+persistent oscillations with frequencies set by the low-lying particle
+excitations not only for small, but even for moderate size quenches. In the
+ferromagnetic phase these particles are the various non-perturbative confined
+bound states of the domain wall excitations, while in the paramagnetic phase
+the single magnon excitation governs the dynamics, allowing us to capture the
+time evolution of the magnetisation using a combination of known results from
+perturbation theory and form factor based methods. We point out that the
+dominance of low lying excitations allows for the numerical or experimental
+determination of the mass spectra through the study of the quench dynamics.",1607.01068v3
+2016-07-12,Thermodynamic transport theory of spin waves in ferromagnetic insulators,"We use the Boltzmann transport theory in the relaxation time approximation to
+describe the thermal transport of spin waves in a ferromagnet. By treating spin
+waves as magnon excitations we are able to compute analytically and numerically
+the coefficients of the constitutive thermo-magnetic transport equations. As a
+main result, we find that the absolute thermo-magnetic power coefficient
+$\epsilon_M$, relating the gradient of the potential of the magnetization
+current and the gradient of the temperature, in the limit of low temperature
+and low field, is a constant $\epsilon_M = -0.6419 \, k_B/\mu_B$. The theory
+correctly describes the low-temperature and magnetic-field dependencies of spin
+Seebeck experiments. Furthermore, the theory predicts that in the limit of very
+low temperatures the spin Peltier coefficient $\Pi_M$, relating the heat and
+the magnetization currents, tends to a finite value which depends on the
+amplitude of the magnetic field. This indicates the possibility to exploit the
+spin Peltier effect as an efficient cooling mechanism in cryogenics.",1607.03301v3
+2016-07-18,Robust Upward Dispersion of the Neutron Spin Resonance in the Heavy Fermion Superconductor Ce$_{1-x}$Yb$_{x}$CoIn$_5$,"The neutron spin resonance is a collective magnetic excitation that appears
+in copper oxide, iron pnictide, and heavy fermion unconventional
+superconductors. Although the resonance is commonly associated with a
+spin-exciton due to the $d$($s^{\pm}$)-wave symmetry of the superconducting
+order parameter, it has also been proposed to be a magnon-like excitation
+appearing in the superconducting state. Here we use inelastic neutron
+scattering to demonstrate that the resonance in the heavy fermion
+superconductor Ce$_{1-x}$Yb$_{x}$CoIn$_5$ with $x=0,0.05,0.3$ has a ring-like
+upward dispersion that is robust against Yb-doping. By comparing our
+experimental data with random phase approximation calculation using the
+electronic structure and the momentum dependence of the $d_{x^2-y^2}$-wave
+superconducting gap determined from scanning tunneling microscopy for
+CeCoIn$_5$, we conclude the robust upward dispersing resonance mode in
+Ce$_{1-x}$Yb$_{x}$CoIn$_5$ is inconsistent with the downward dispersion
+predicted within the spin-exciton scenario.",1607.05326v1
+2016-07-20,Electromagnon in the Z-type hexaferrite $({\rm Ba}_{x}{\rm Sr}_{1-x})_3\rm Co_2Fe_{24}O_{41}$,"We studied experimentally the high-temperature magnetoelectric $({\rm
+Ba}_{x}{\rm Sr}_{1-x})_3\rm Co_2Fe_{24}O_{41}$ prepared as ceramics (x = 0,
+0.2) and a single crystal (x = 0.5) using inelastic neutron scattering, THz
+time-domain, Raman and far-infrared spectroscopies. The spectra, measured with
+varying temperature and magnetic field, reveal rich information about the
+collective spin and lattice excitations. In the ceramics, we observed an
+infrared-active magnon which is absent in $E^{\omega}\perp z$ polarized THz
+spectra of the crystal, and we assume that it is an electromagnon active in
+$E^{\omega} \| z$ polarized spectra. On heating from 7 to 250 K, the frequency
+of this electromagnon drops from 36 to 25 cm$^{-1}$ and its damping gradually
+increases, so it becomes overdamped at room temperature. Applying external
+magnetic field has a similar effect on the damping and frequency of the
+electromagnon, and the mode is no more observable in the THz spectra above 2 T,
+as the transverse-conical magnetic structure transforms into a collinear one.
+Raman spectra reveal another spin excitation with a slightly different
+frequency and much higher damping. Upon applying magnetic field higher than 3
+T, in the low-frequency part of the THz spectra, a narrow excitation appears
+whose frequency linearly increases with magnetic field. We interpret this
+feature as the ferromagnetic resonance.",1607.05878v1
+2016-07-25,Goos-Hanchen shift of a spin-wave beam transmitted through anisotropic interface between two ferromagnets,"The main object of investigation in magnonics, spin waves (SWs) are promising
+information carriers. Presently the most commonly studied are plane wave-like
+SWs and SWs propagating in confined structures, such as waveguides. Here we
+consider a Gaussian SW beam obliquely incident on an ultra-narrow interface
+between two identical ferromagnetic materials. We use an analytical model and
+micromagnetic simulations for an in-depth analysis of the influence of the
+interface properties, in particular the magnetic anisotropy, on the
+transmission of the SW beam. We derive analytical formulas for the reflectance,
+transmittance, phase shift and Goos-Hanchen (GH) shift for beams reflected and
+refracted by an interface between two semi-infinite ferromagnetic media; the
+results for the refracted beam are the first to be reported to date. The GH
+shifts in SW beam reflection and transmission are confirmed by micromagnetic
+simulations in the thin-film geometry. We demonstrate the dependence of the
+characteristic properties on the magnetic anisotropy at the interface, the
+angle of incidence and the frequency of the SWs. We also propose a method for
+the excitation of high-quality SW beams in micromagnetic simulations.",1607.07424v4
+2017-02-16,Scalable Nernst Thermoelectric Power using a Coiled Galfenol Wire,"The Nernst thermopower usually is considered far too weak in most metals for
+waste heat recovery. However, its transverse orientation gives it an advantage
+over the Seebeck effect on non-flat surfaces. Here, we experimentally
+demonstrate the scalable generation of a Nernst voltage in an air-cooled metal
+wire coiled around a hot cylinder. In this geometry, a radial temperature
+gradient generates an azimuthal electric field in the coil. A Galfenol
+(Fe$_{0.85}$Ga$_{0.15}$) wire is wrapped around a cartridge heater, and the
+voltage drop across the wire is measured as a function of axial magnetic field.
+As expected, the Nernst voltage scales linearly with the length of the wire.
+Based on heat conduction and fluid dynamic equations, finite-element method is
+used to calculate the temperature gradient across the Galfenol wire and
+determine the Nernst coefficient. A giant Nernst coefficient of -2.6
+${\mu}$V/KT at room temperature is estimated, in agreement with measurements on
+bulk Galfenol. We expect that the giant Nernst effect in Galfenol arises from
+its magnetostriction, presumably through enhanced magnon-phonon coupling. Our
+results demonstrate the feasibility of a transverse thermoelectric generator
+capable of scalable output power from non-flat heat sources.",1702.04847v3
+2017-02-20,Quantum criticality of spinons,"The free fermion nature of interacting spins in one dimensional (1D) spin
+chains still lacks a rigorous study. In this letter we show that the length-$1$
+spin strings significantly dominate critical properties of spinons, magnons and
+free fermions in the 1D antiferromagnetic spin-1/2 chain. Using the Bethe
+ansatz solution we analytically calculate exact scaling functions of thermal
+and magnetic properties of the model, providing a rigorous understanding of the
+quantum criticality of spinons. It turns out that the double peaks in specific
+heat elegantly mark two crossover temperatures fanning out from the critical
+point, indicating three quantum phases: the Tomonaga-Luttinger liquid (TLL),
+quantum critical and fully polarized ferromagnetic phases. For the TLL phase,
+the Wilson ratio $R_W=4K_s$ remains almost temperature-independent, here $K_s$
+is the Luttinger parameter. Furthermore, applying our results we precisely
+determine the quantum scalings and critical exponents of all magnetic
+properties in the ideal 1D spin-1/2 antiferromagnet
+Cu(C${}_4$H${}_4$N${}_2$)(NO${}_3$)${}_2$ recently studied in Phys. Rev. Lett.
+{\bf 114}, 037202 (2015)]. We further find that the magnetization peak used in
+experiments is not a good quantity to map out the finite temperature TLL phase
+boundary.",1702.05903v2
+2017-03-30,Anisotropy governed competition of magnetic phases in the honeycomb quantum magnet Na$_3$Ni$_2$SbO$_6$ studied by dilatometry and high-frequency ESR,"Thermodynamic properties as well as low-energy magnon excitations of $S=1$
+honeycomb-layered Na$_3$Ni$_2$SbO$_6$ have been investigated by high-resolution
+dilatometry, static magnetisation, and high-frequency electron spin resonance
+studies in magnetic fields up to 16 T. At $T_{\rm N}$ = 16.5 K, there is a
+tricritical point separating two distinct antiferromagnetic phases AF1 and AF2
+from the paramagnetic regime. In addition, our data imply short-range
+antiferromagnetic correlations at least up to $\sim 5\cdot T_{\rm N}$. Well
+below $T_{\rm N}$, the magnetic field $B_{\rm C1}\approx$ 9.5 T is needed to
+stabilize AF2 against AF1. The thermal expansion and magnetostriction anomalies
+at $T_{\rm N}$ and $B_{\rm C1}$ imply significant magnetoelastic coupling, both
+of which associated with a sign change of $\partial L/\partial B$. The
+transition at $B_{\rm C1}$ is associated with softening of the
+antiferromagnetic resonance modes observed in the electron spin resonance
+spectra. The anisotropy gap $\Delta = 360$ GHz implies considerable uniaxial
+anisotropy. We conclude the crucial role of axial anisotropy favoring the AF1
+spin structure over the AF2 one. While the magnetostriction data disprove a
+simple spin-flop scenario at $B_{\rm C1}$, the nature of a second transition at
+$B_{\rm C2}\approx$ 13 T remains unclear. Both the sign of the magnetostriction
+and Gr\""uneisen analysis suggest the short-range correlations at high
+temperatures to be of AF2-type.",1703.10493v1
+2017-08-23,Spin-memory loss due to spin-orbit coupling at ferromagnet/heavy-metal interfaces: Ab initio spin-density matrix approach,"Spin-memory loss (SML) of electrons traversing
+ferromagnetic-metal/heavy-metal (FM/HM), FM/normal-metal (FM/NM) and HM/NM
+interfaces is a fundamental phenomenon that must be invoked to explain
+consistently large number of spintronic experiments. However, its strength
+extracted by fitting experimental data to phenomenological semiclassical
+theory, which replaces each interface by a fictitious bulk diffusive layer, is
+poorly understood from a microscopic quantum framework and/or materials
+properties. Here we describe an ensemble of flowing spin quantum states using
+spin-density matrix, so that SML is measured like any decoherence process by
+the decay of its off-diagonal elements or, equivalently, by the reduction of
+the magnitude of polarization vector. By combining this framework with density
+functional theory (DFT), we examine how all three components of the
+polarization vector change at Co/Ta, Co/Pt, Co/Cu, Pt/Cu and Pt/Au interfaces
+embedded within Cu/FM/HM/Cu vertical heterostructures. In addition, we use ab
+initio Green's functions to compute spectral functions and spin textures over
+FM, HM and NM monolayers around these interfaces which quantify interfacial
+spin-orbit coupling and explain the microscopic origin of SML in long-standing
+puzzles, such as why it is nonzero at Co/Cu interface; why it is very large at
+Pt/Cu interface; and why it occurs even in the absence of disorder, intermixing
+and magnons at the interface.",1708.07105v3
+2018-02-23,Pure spin currents in magnetically ordered insulator/normal metal heterostructures,"Pure spin currents, i.e. the transport of angular momentum without an
+accompanying charge current, represent a new, promising avenue in modern
+spintronics from both a fundamental and an application point of view. Such pure
+spin currents can not only flow in electrical conductors via mobile charge
+carriers, but also in magnetically ordered electrical insulators as a flow of
+spin excitation quanta. Over the course of the last years remarkable results
+have been obtained in heterostructures consisting of magnetically ordered
+insulators interfaced with a normal metal, where a pure spin current flows
+across the interface. This topical review article deals with the fundamental
+principles, experimental findings and recent developments in the field of pure
+spin currents in magnetically ordered insulators. We here put our focus onto
+four different manifestations of pure spin currents in such heterostructures:
+The spin pumping effect, the longitudinal spin Seebeck effect, the spin Hall
+magnetoresistance and the all-electrical detection of magnon transport in
+non-local device concepts. In this article, we utilize a common theoretical
+framework to explain all four effects and explain important material systems
+(especially rare-earth iron garnets) used in the experiments. For each effect
+we introduce basic measurement techniques and detection schemes and discuss
+their application in the experiment. We account for the remarkable progress
+achieved in each field by reporting the recent progress in each field and by
+discussing research highlights obtained in our group. Finally, we conclude the
+review article with an outlook on future challenges and obstacles in the field
+of pure spin currents in magnetically ordered insulator / normal metal
+heterostructures.",1802.08479v1
+2018-04-03,Kinetic frustration induced supersolid in the $S=1/2$ kagome lattice antiferromagnet in a magnetic field,"We examine instabilities of the plateau phases in the spin-1/2 kagome-lattice
+antiferromagnet in an applied field by means of degenerate perturbation theory,
+and find some emergent supersolid phases below the $m=5/9$ plateau. The wave
+functions of the plateau phases in a magnetic field have the particular
+construction based on the building blocks of resonating hexagons and their
+surrounding sites. Magnon excitations on each of these blocks suffer from a
+kinetic frustration effect, namely, they cannot hop easily to the others since
+the hopping amplitudes through the two paths destructively cancel out with each
+other. The itineracy is thus weakened, and the system is driven toward the
+strong coupling regime, which together with the selected paths allowed in real
+space bears a supersolid phase. This mechanism is contrary to that proposed in
+lattice-Bose gases, where the strong competing interactions suppress with each
+other, allowing a small kinetic energy scale to attain the itinerancy.
+Eventually, we find a supersolid state in which the pattern of resonating
+hexagons are preserved from the plateau crystal state and only one-third of the
+originally polarized spins outside the hexagons dominantly join the superfluid
+component, or equivalently, participate in the magnetization process.",1804.00789v3
+2018-04-11,Thermographic measurements of spin-current-induced temperature modulation in metallic bilayers,"Spin-to-heat current conversion effects have been investigated in bilayer
+films consisting of a paramagnetic metal (PM; Pt, W, or Ta) and a ferromagnetic
+metal (FM; CoFeB or permalloy). When a charge current is applied to the PM/FM
+bilayer film, a spin current is generated across the PM/FM interface owing to
+the spin Hall effect in PM. The spin current was found to exhibit cooling and
+heating features depending on the sign of the spin Hall angle of PM, where the
+spin-current-induced contribution is estimated by subtracting the contribution
+of the anomalous Ettingshausen effect in FM monolayer films. We also found that
+the magnitude of the spin-current-induced temperature modulation in the
+Pt/CoFeB film is greater than but comparable to that in the Pt/permalloy film,
+although the spin dependence of the Peltier coefficient for CoFeB is expected
+to be greater than that for permalloy. We discuss the origin of the observed
+behaviors with the aid of model calculations; the signals in the PM/FM films
+may contain the contributions not only from the electron-driven spin-dependent
+Peltier effect but also from the magnon-driven spin Peltier effect.",1804.04068v1
+2018-04-13,Ni$_2$Mo$_3$O$_8$: zig-zag antiferromagnetic order an integer spin non-centrosymmetric honeycomb lattice,"Theoretical studies have predicted the existence of topological magnons in
+honeycomb compounds with zig-zag antiferromagnetic (AFM) order. Here we report
+the discovery of zig-zag AFM order in the layered and non-centrosymmetric
+honeycomb nickelate Ni$_2$Mo$_3$O$_8$ through a combination of magnetization,
+specific heat, x-ray and neutron diffraction and electron paramagnetic
+resonance measurements. It is the first example of such order in an
+integer-spin non-centrosymmetric structure ($P$$_6$3$mc$). Further, each of the
+two distinct sites of the bipartite honeycomb lattice has a unique crystal
+field environment, octahedral and tetrahedral Ni$^{2+}$ respectively, enabling
+independent substitution on each sublattice. Replacement of Ni by Mg on the
+octahedral site suppresses the long range magnetic order and results in a
+weakly ferromagnetic state. Conversely, substitution of Fe for Ni enhances the
+AFM ordering temperature. Thus Ni$_2$Mo$_3$O$_8$ provides a platform on which
+to explore the rich physics of $S = 1$ on the honeycomb in the presence of
+competing magnetic interactions with a non-centrosymmetric, formally
+piezeo-polar, crystal structure.",1804.04776v1
+2018-04-16,Magnetic interactions in PdCrO$_2$ and their effects on its magnetic structure,"We report a neutron scattering study of the metallic triangular lattice
+antiferromagnet PdCrO$_2$. Powder neutron diffraction measurements confirm that
+the crystalline space group symmetry remains $R\bar{3}m$ below $T_N$. This
+implies that magnetic interactions consistent with the crystal symmetry do not
+stabilise the non-coplanar magnetic structure which was one of two structures
+previously proposed on the basis of single crystal neutron diffraction
+measurements. Inelastic neutron scattering measurements find two gaps at low
+energies which can be explained as arising from a dipolar-type exchange
+interaction. This symmetric anisotropic interaction also stabilises a magnetic
+structure very similar to the coplanar magnetic structure which was also
+suggested by the single crystal diffraction study. The higher energy magnon
+dispersion can be modelled by linear spin wave theory with exchange
+interactions up to sixth nearest-neighbors, but discrepancies remain which hint
+at additional effects unexplained by the linear theory.",1804.05573v1
+2018-11-27,Hybrid magneto-dynamical modes in a single magnetostrictive nanomagnet on a piezoelectric substrate arising from magneto-elastic modulation of precessional dynamics,"Magneto-elastic (or ""straintronic"") switching has emerged as an extremely
+energy-efficient mechanism for switching the magnetization of magnetostrictive
+nanomagnets in magnetic memory, logic and non-Boolean circuits. Here, we
+investigate the ultrafast magneto-dynamics associated with straintronic
+switching in a single quasi-elliptical magnetostrictive Co nanomagnet deposited
+on a piezoelectric PMN-PT substrate using time-resolved magneto-optical Kerr
+effect (TR-MOKE) measurements. The pulsed laser pump beam in the TR-MOKE plays
+a dual role: it causes precession of the nanomagnet's magnetization about an
+applied bias magnetic field and it also generates surface acoustic waves (SAWs)
+in the piezoelectric substrate that produce periodic strains in the
+magnetostrictive nanomagnet and modulate the precessional dynamics. This
+modulation gives rise to intriguing hybrid magneto-dynamical modes in the
+nanomagnet, with rich spin wave texture. The characteristic frequencies of
+these modes are 5-15 GHz, indicating that strain can affect magnetization in a
+magnetostrictive nanomagnet in time scales much smaller than 1 ns (~100 ps).
+This can enable ~10 GHz-range magneto-elastic nano-oscillators that are
+actuated by strain instead of a spin-polarized current, as well as ultrafast
+magneto-electric generation of spin waves for magnonic logic circuits,
+holograms, etc.",1811.11297v1
+2018-11-29,"High Saturation Magnetization, Low Coercivity and Fine YIG Nanoparticles Prepared by Modifying Co-Precipitation Method","Nanoparticles with their specific properties newly have drawn a great deal of
+attention of researchers [1-3]Yttrium iron Garnet magnetic nanoparticles
+(YIG-NPs) are promising materials with novel applications in microwave,
+spintronics, magnonics, and magneto-optical devices. However, achieving stable
+and remarkable magnetic YIG-NPs has been remaining as a great challenge. In
+this paper, synthesized YIG-NPs by modifying co-precipitation (MCP) method is
+reported. Structural and magnetic properties of final products are compared to
+those of the materials prepared by citrate-nitrate (CN) method. Smaller
+crystals and particle size have been found by MCP method comparing to that of
+synthesized by CN method. Using a relatively low annealing temperatures for
+both sets of samples (~700 {\deg}C), the final YIG samples prepared by MCP
+method show more structural purity than those made by CN method. Higher
+saturation magnetization (Ms) and lower coercivity (Hc) are observed in MCP YIG
+sample (23.23 emu/g 36 and 30.1 Oe) than the CN prepared YIG sample (16.43
+emu/g and 44.95 Oe). The Curie temperature is measured to be 569 {\deg}C for
+the MCP YIG sample determined from set of Ms measurement at different
+temperatures ranging from 80-600 K. These findings lead to significant
+improvement in quality of synthesized (synthetic methods) of YIG-NPs.",1811.12511v1
+2013-08-01,Magnetostatic wave analog of integer quantum Hall state in patterned magnetic films,"A magnetostatic spin wave analog of integer quantum Hall (IQH) state is
+proposed in realistic patterned ferromagnetic thin films. Due to magnetic shape
+anisotropy, magnetic moments in a thin film lie within the plane, while all
+spin-wave excitations are fully gapped. Under an out-of-plane magnetic field,
+the film acquires a finite magnetization, where some of the gapped magnons
+become significantly softened near a saturation field. It is shown that, owing
+to a spin-orbit locking nature of the magnetic dipolar interaction, these soft
+spin-wave volume-mode bands become chiral volume-mode bands with finite
+topological Chern integers. A bulk-edge correspondence in IQH physics suggests
+that such volume-mode bands are accompanied by a chiral magnetostatic spin-wave
+edge mode. The existence of the edge mode is justified both by micromagnetic
+simulations and by band calculations based on a linearized Landau-Lifshitz
+equation. Employing intuitive physical arguments, we introduce proper
+tight-binding models for these soft volume-mode bands. Based on the
+tight-binding models, we further discuss possible applications to other systems
+such as magnetic ultrathin films with perpendicular magnetic anisotropy (PMA).",1308.0199v3
+2013-08-17,Thickness and power dependence of the spin-pumping effect in Y3Fe5O12/Pt heterostructures measured by the inverse spin Hall effect,"The dependence of the spin-pumping effect on the yttrium iron garnet
+(Y3Fe5O12, YIG) thickness detected by the inverse spin Hall effect (ISHE) has
+been investigated quantitatively. Due to the spin-pumping effect driven by the
+magnetization precession in the ferrimagnetic insulator YIG film a
+spin-polarized electron current is injected into the Pt layer. This spin
+current is transformed into electrical charge current by means of the ISHE. An
+increase of the ISHE-voltage with increasing film thickness is observed and
+compared to the theoretically expected behavior. The effective damping
+parameter of the YIG/Pt samples is found to be enhanced with decreasing YIG
+film thickness. The investigated samples exhibit a spin mixing conductance of
+g=(7.43 \pm 0.36) \times 10^{18} m^{-2} and a spin Hall angle of theta_{ISHE} =
+0.009 \pm 0.0008. Furthermore, the influence of nonlinear effects on the
+generated voltage and on the Gilbert damping parameter at high excitation
+powers are revealed. It is shown that for small YIG film thicknesses a
+broadening of the linewidth due to nonlinear effects at high excitation powers
+is suppressed because of a lack of nonlinear multi-magnon scattering channels.
+We have found that the variation of the spin-pumping efficiency for thick YIG
+samples exhibiting pronounced nonlinear effects is much smaller than the
+nonlinear enhancement of the damping.",1308.3787v1
+2013-08-21,Intense low-energy ferromagnetic fluctuations in the antiferromagnetic heavy-fermion metal CeB6,"Heavy-fermion metals exhibit a plethora of low-temperature ordering
+phenomena, among them the so-called hidden-order phases that in contrast to
+conventional magnetic order are invisible to standard neutron diffraction. One
+of the oldest and structurally simplest hidden-order compounds, CeB6, became
+famous for an elusive phase that was attributed to the antiferroquadrupolar
+ordering of cerium-4f moments. In its ground state, CeB6 also develops a more
+usual antiferromagnetic (AFM) order. Hence, its essential low-temperature
+physics was always considered to be solely governed by AFM interactions between
+the dipolar and multipolar Ce moments. Here we overturn this established
+perspective by uncovering an intense ferromagnetic (FM) low-energy collective
+mode that dominates the magnetic excitation spectrum of CeB6. Our inelastic
+neutron-scattering data reveal that the intensity of this FM excitation by far
+exceeds that of conventional spin-wave magnons emanating from the AFM wave
+vectors, thus placing CeB6 much closer to a FM instability than could be
+anticipated. This propensity of CeB6 to ferromagnetism may account for much of
+its unexplained behavior, such as the existence of a pronounced electron spin
+resonance, and should lead to a substantial revision of existing theories that
+have so far largely neglected the role of FM interactions.",1308.4491v1
+2014-03-17,Non-relativistic Nambu-Goldstone modes propagating along a skyrmion line,"We study Nambu-Goldstone (NG) modes or gapless modes propagating along a
+skyrmion (lump) line in a relativistic and non-relativistic O(3) sigma model,
+the latter of which describes isotropic Heisenberg ferromagnets. We show for
+the non-relativistic case that there appear two coupled gapless modes with a
+quadratic dispersion. In addition to the well-known Kelvin mode consisting of
+two translational zero modes transverse to the skyrmion line, we show that the
+other consists of a magnon and dilaton, that is, a NG mode for a spontaneously
+broken internal U(1) symmetry and a quasi-NG mode for a spontaneously broken
+scale symmetry of the equation of motion. We find that the commutation
+relations of Noether charges admit a central extension between the dilatation
+and phase rotation, in addition to the one between two translations found
+recently. The counting rule is consistent with the Nielsen-Chadha and
+Watanabe-Brauner relations only when we take into account quasi-NG modes.",1403.4031v4
+2017-01-09,Spin-Wave versus Joule Heating in Spin-Hall-Effect/Spin-Transfer-Torque Driven Cr/Heusler/Pt Waveguides,"We present a time-resolved study of the DC-current driven magnetization
+dynamics in a microstructured Cr/Heusler/Pt waveguide by means of Brillouin
+light scattering. A reduction of the effective spin-wave damping via the
+spin-transfer-torque effect leads to a strong increase in the magnon density.
+This is accompanied by a decrease of the spin-wave frequencies. By evaluating
+the time scales of these effects, the origin of this frequency shift can be
+identified. However, recently, we found that the experimental setup partially
+influences the decay of the spin-wave intensity after the current pulse is
+switched off. Thus, further investigations on the presented effect are needed
+to allow for a more detailed analysis. For this reason, we need to withdraw the
+manuscript at this point and might publish an updated version later.",1701.02094v2
+2017-01-27,The nature of spin excitations in the one-third magnetization plateau phase of Ba$_3$CoSb$_2$O$_9$,"Magnetization plateaus in quantum magnets---where bosonic quasiparticles
+crystallize into emergent spin superlattices---are spectacular yet simple
+examples of collective quantum phenomena escaping classical description. While
+magnetization plateaus have been observed in a number of spin-1/2
+antiferromagnets, the description of their magnetic excitations remains an open
+theoretical and experimental challenge. Here, we investigate the dynamical
+properties of the triangular-lattice spin-1/2 antiferromagnet
+Ba$_3$CoSb$_2$O$_9$ in its one-third magnetization plateau phase using a
+combination of nonlinear spin-wave theory and neutron scattering measurements.
+The agreement between our theoretical treatment and the experimental data
+demonstrates that magnons behave semiclassically in the plateau in spite of the
+purely quantum origin of the underlying magnetic structure. This allows for a
+quantitative determination of Ba$_3$CoSb$_2$O$_9$ exchange parameters. We
+discuss the implication of our results to the deviations from semiclassical
+behavior observed in zero-field spin dynamics of the same material and conclude
+they must have an intrinsic origin.",1701.07971v4
+2018-05-09,Dynamic spin-lattice coupling and nematic fluctuations in NaFeAs,"We use inelastic neutron scattering to study acoustic phonons and spin
+excitations in single crystals of NaFeAs, a parent compound of iron pnictide
+superconductors. NaFeAs exhibits a tetragonal-to-orthorhombic structural
+transition at $T_s\approx 58$ K and a collinear antiferromagnetic (AF) order at
+$T_N\approx 45$ K. While longitudinal and out-of-plane transverse acoustic
+phonons behave as expected, the in-plane transverse acoustic phonons reveal
+considerable softening on cooling to $T_s$, and then harden on approaching
+$T_N$ before saturating below $T_N$. In addition, we find that spin-spin
+correlation lengths of low-energy magnetic excitations within the FeAs layer
+and along the $c$-axis increase dramatically below $T_s$, and show weak anomaly
+across $T_N$. These results suggest that the electronic nematic phase present
+in the paramagnetic tetragonal phase is closely associated with dynamic
+spin-lattice coupling, possibly arising from the one-phonon-two-magnon
+mechanism.",1805.03493v1
+2018-05-10,"Magnetic excitations in bulk multiferroic two-dimensional triangular lattice antiferromagnet (Lu,Sc)FeO$_3$","Non-collinear two-dimensional triangular lattice antiferromagnets (2D TLAF)
+are currently an area of very active research due to their unique magnetic
+properties, which lead to non-trivial quantum effects that experimentally
+manifest themselves in the spin excitation spectra. Recent examples of such
+insulating 2D TLAF include (Y,Lu)MnO$_3$, LiCrO$_2$, and CuCrO$_2$. Hexagonal
+LuFeO3 is a recently synthesized 2D TLAF which exhibits properties of an ideal
+multiferroic material, partially because of the high spin ($S=5/2$) and strong
+magnetic super-exchange interactions. We report the full range of spin dynamics
+in a bulk single crystal of (Lu$_{0.6}$Sc$_{0.4}$)FeO$_3$ (Sc doping to
+stabilize the hexagonal structure) measured via time-of-flight inelastic
+neutron scattering. Modeling with linear spin wave theory yields a nearest
+neighbor exchange coupling of $J$ = 4.0(2) meV (DFT calculations for
+$h$-LuFeO$_3$ predicted a value of 6.31 meV) and anisotropy values of $K_D$ =
+0.17(1) meV (easy plane) and $K_A$~=~-0.05(1)~meV (local easy axis). It is
+observed that the magnon bandwidth of the spin wave spectra is twice as large
+for $h$-(Lu,Sc)FeO$_3$ as it is for $h$-LuMnO$_3$.",1805.03912v2
+2018-05-13,Giant peak of the Inverse Faraday effect in the band gap of magnetophotonic crystal,"Optical impact on the spin system in a magnetically ordered medium provides a
+unique possibility for local manipulation of magnetization at subpicosecond
+time scales that is very promising for magnetic data processing and other
+magnonics applications. One of the mechanisms of the optical manipulation is
+related to the inverse Faraday effect (IFE). Usually the IFE is observed in
+crystals and magnetic films on a substrate. Here we demonstrate the IFE induced
+by fs-laser pulses in the magnetic film inside the magnetophotonic crystal.
+Spectral dependence of the IFE on the laser pulse wavelength in the band gap of
+the magnetophotonic crystal has a sharp peak leading to a significant
+enhancement of the IFE. This phenomenon is explained by strong confinement of
+the electromagnetic energy and angular momentum within the magnetic film.
+Calculated near field distribution of the IFE effective magnetic field
+indicates its subwavelength localization within 30 nm along the film thickness.
+These excited volumes can be shifted along the sample depth via e.g. changing
+frequency of the laser pulses. The obtained results open a way for the new
+applications in the areas of ultrafast spintronics and quantum information
+processing.",1805.04862v1
+2018-05-18,Quantum theory of spin waves for Helical ground states in Hollandite lattice,"We perform spin wave analysis of classical ground states of a model
+Hamiltonian proposed earlier(Phys. Rev. B {\bf 90}, 104420(2014)) for
+$\alpha-MnO_2$ compounds. It is known that the phase diagram of the Hollandite
+lattice (lattice of $\alpha-MnO_2$ compounds) consists of four different
+Helical phases(FH, A2H, C2H, CH phase) in the space of model parameters
+$J_1,~J_2,~J_3$. The spin wave dispersion shows presence of gapless mode which
+interpolates between quadratic to linear depending on phases and values of
+$J_i$'s. In most cases, the 2nd lowest mode shows the existence of a roton
+minima mainly from $X$ to $M$ and $M$ to $Z$ path. Few higher modes also show
+roton minima. Each helical phase has its characteristic traits which can be
+used to determine the phases itself. The analytical expressions of eigenmodes
+at high symmetry points are obtained which can be utilized to extract the
+values of $J_i$'s. Density of states, specific heat and susceptibilities at low
+temperature has been studied within spin wave approximation. The specific heat
+shows departure from $T^{1.5(3)}$ dependence found in three dimensional
+unfrustrated ferromagnetic(anti-ferromagnetic) system which seems to be the
+signature of incommensurate helical phase. The parallel susceptibility is
+maximum for FH phase and minimum for CH phase at low temperature. The
+perpendicular susceptibility is found to be independent of temperature at very
+low temperature. Our study can be used to compare experimental results on
+magnon spectrum, elastic neutron scattering, and finite temperature properties
+mentioned above for clean $\alpha-MnO_2$ system",1805.07156v1
+2018-05-23,Elliptic String Solutions on RxS^2 and Their Pohlmeyer Reduction,"We study classical string solutions on RxS^2 that correspond to elliptic
+solutions of the sine-Gordon equation. In this work, these solutions are
+systematically derived inverting Pohlmeyer reduction and classified with
+respect to their Pohlmeyer counterparts. These solutions include the spiky
+strings and other well-known solutions, such as the BMN particle, the GKP
+string or the giant magnons, which arise as special limits, and reveal many
+interesting features of the AdS/CFT correspondence. A mapping of the physical
+properties of the string solutions to those of their Pohlmeyer counterparts is
+established. An interesting element of this mapping is the correspondence of
+the number of spikes of the string to the topological charge in the sine-Gordon
+theory. In the context of the sine-Gordon/Thirring duality, the latter is
+mapped to the Thirring model fermion number, leading to a natural
+classification of the solutions to fermionic objects and bosonic condensates.
+Finally, the convenient parametrization of the solutions, enforced by the
+inversion of the Pohlmeyer reduction, facilitates the study of the string
+dispersion relation. This leads to the identification of an infinite set of
+trajectories in the moduli space of solutions, where the dispersion relation
+can be expressed in a closed form by means of some algebraic operations,
+arbitrarily far from the infinite size limit.",1805.09301v1
+2011-11-17,Resonant magnetic exciton mode in the heavy-fermion antiferromagnet CeB6,"Resonant magnetic excitations are widely recognized as hallmarks of
+unconventional superconductivity in copper oxides, iron pnictides, and
+heavy-fermion compounds. Numerous model calculations have related these modes
+to the microscopic properties of the pair wave function, but the mechanisms
+underlying their formation are still debated. Here we report the discovery of a
+similar resonant mode in the non-superconducting, antiferromagnetically ordered
+heavy-fermion metal CeB6. Unlike conventional magnons, the mode is
+non-dispersive, and its intensity is sharply concentrated around a wave vector
+separate from those characterizing the antiferromagnetic order. The magnetic
+intensity distribution rather suggests that the mode is associated with a
+coexisting order parameter of the unusual antiferro-quadrupolar phase of CeB6,
+which has long remained ""hidden"" to the neutron-scattering probes. The mode
+energy increases continuously below the onset temperature for
+antiferromagnetism, in parallel to the opening of a nearly isotropic spin gap
+throughout the Brillouin zone. These attributes bear strong similarity to those
+of the resonant modes observed in unconventional superconductors below their
+critical temperatures. This unexpected commonality between the two disparate
+ground states indicates the dominance of itinerant spin dynamics in the ordered
+low-temperature phases of CeB6 and throws new light on the interplay between
+antiferromagnetism, superconductivity, and ""hidden"" order parameters in
+correlated-electron materials.",1111.4151v1
+2012-04-13,Low temperature thermodynamic properties near the field-induced quantum critical point in DTN,"We present a comprehensive experimental and theoretical investigation of the
+thermodynamic properties: specific heat, magnetization and thermal expansion in
+the vicinity of the field-induced quantum critical point (QCP) around the lower
+critical field $H_{c1} \approx 2$\,T in DTN . A $T^{3/2}$ behavior in the
+specific heat and magnetization is observed at very low temperatures at
+$H=H_{c1}$ that is consistent with the universality class of Bose-Einstein
+condensation of magnons. The temperature dependence of the thermal expansion
+coefficient at $H_{c1}$ shows minor deviations from the expected $T^{1/2}$
+behavior. Our experimental study is complemented by analytical calculations and
+Quantum Monte Carlo simulations, which reproduce nicely the measured
+quantities. We analyze the thermal and the magnetic Gr\""{u}neisen parameters
+that are ideal quantities to identify QCPs. Both parameters diverge at $H_{c1}$
+with the expected $T^{-1}$ power law. By using the Ehrenfest relations at the
+second order phase transition, we are able to estimate the pressure
+dependencies of the characteristic temperature and field scales.",1204.3064v1
+2013-09-07,On the broken time translation symmetry in macroscopic systems: precessing states and off-diagonal long-range order,"The broken symmetry state with off-diagonal long-range order (ODLRO), which
+is characterized by the vacuum expectation value of the operator of creation of
+the conserved quantum number Q, has the time-dependent order parameter.
+However, the breaking of the time reversal symmetry is observable only if the
+charge Q is not strictly conserved and may decay. This dihotomy is resolved in
+systems with quasi-ODLRO. These systems have two well separated relaxation
+times: the relaxation time \tau_Q of the charge Q and the energy relaxation
+time \tau_E. If \tau_Q >> \tau_E, the perturbed system relaxes first to the
+state with the ODLRO, which persists for a long time \tau_Q and finally relaxes
+to the full equilibrium static state. In the limit \tau_Q -> \infty, but not in
+the strict limit case when the charge Q is conserved, the intermediate ODLRO
+state can be considered as the ground state of the system at fixed Q with the
+observable spontaneously broken time reversal symmetry. Examples of systems
+with quasi-ODLRO are provided by superfluid phase of liquid 4He, Bose-Einstein
+condensation of magnons (phase coherent spin precession) and precessing
+vortices.",1309.1845v2
+2013-09-20,Internal modes of a skyrmion in the ferromagnetic background in chiral magnets,"A spin texture called skyrmion has been recently observed in certain chiral
+magnets without inversion symmetry. The observed skyrmions are extended objects
+with typical linear sizes of 10 nm to 100 nm that contain $10^3$ to $10^5$
+spins and can be deformed in response to external perturbations. Weak
+deformations are characterized by the internal modes which are localized around
+the skyrmion center. Knowledge of internal modes is crucial to assess the
+stability and rigidity of these topological textures. Here we compute the
+internal modes of a skyrmion in the ferromagnetic background state by numerical
+diagonalization of the dynamical matrix. We find several internal modes below
+the magnon continuum, such as the mode corresponding to the translational
+motion, and different kinds of breathing modes. The number of internal modes is
+larger for lower magnetic fields. Indeed, several modes become gapless in the
+low field region indicating that the single skyrmion solution becomes unstable,
+although a skyrmion lattice is thermodynamically stable. On the other hand, at
+high fields only three internal modes exist and the skyrmion is stable even at
+higher fields when the ferromagnetic state is thermodynamically stable. We also
+show that the presence of out-of-plane easy-axis anisotropy stabilizes the
+single skyrmion solution. Finally, we discuss the effects of damping and
+possible experimental observations of these internal modes.",1309.5168v2
+2014-05-20,Origin of the spin Seebeck effect probed by temperature dependent measurements in Gd$_{3}$Fe$_{5}$O$_{12}$,"We probe the spin Seebeck effect in Gd$_{3}$Fe$_{5}$O$_{12}$/Pt hybrid
+structures as a function of temperature and observe two sign changes of the
+spin Seebeck signal with decreasing temperature. A first sign change occurs at
+a temperature close to the Gd$_{3}$Fe$_{5}$O$_{12}$ magnetic compensation point
+at around 280 K. There the spin Seebeck signal changes sign abruptly with
+unaltered amplitude, indicating that the spin current is mainly caused by the
+magnetic Fe sub-lattices, which reorient their directions at this temperature.
+A second, more gradual sign change takes place around the ordering temperature
+of the Gd sub-lattice in the range of 65-85 K, showing that the Gd magnetic
+sub-lattice dominates the thermally driven spin current at lower temperatures.
+These sign changes together with the non-monotonous dependence of the spin
+Seebeck signal on the temperature demonstrate that the magnonic spin current is
+not simply replicating the effective magnetization of Gd$_{3}$Fe$_{5}$O$_{12}$.
+Rather, the thermally generated net spin current results from a complex
+interplay of the three magnetic sub-lattices involved.",1405.4971v1
+2016-05-22,Low Gilbert damping in Co2FeSi and Fe2CoSi films,"Thin highly textured Fe$_{\mathrm{1+x}}$Co$_{\mathrm{2-x}}$Si ($0 \leq$ x
+$\leq 1$) films were prepared on MgO (001) substrates by magnetron
+co-sputtering. The magneto-optic Kerr effect (MOKE) and ferromagnetic resonance
+(FMR) measurements were used to investigate the composition dependence of the
+magnetization, the magnetic anisotropy, the gyromagnetic ratio and the
+relaxation of the films. The effective magnetization for the thin
+Fe$_{\mathrm{1+x}}$Co$_{\mathrm{2-x}}$Si films, determined by FMR measurements,
+are consistent with the Slater Pauling prediction. Both MOKE and FMR
+measurements reveal a pronounced fourfold anisotropy distribution for all
+films. In addition we found a strong influence of the stoichiometry on the
+anisotropy as the cubic anisotropy strongly increases with increasing Fe
+concentration. The gyromagnetic ratio is only weakly dependent on the
+composition. We find low Gilbert damping parameters for all films with values
+down to $0.0012\pm0.00012$ for Fe$_{1.75}$Co$_{1.25}$Si. The effective damping
+parameter for Co$_2$FeSi is found to be $0.0018\pm 0.0004$. We also find a
+pronounced anisotropic relaxation, which indicates significant contributions of
+two-magnon scattering processes that is strongest along the easy axes of the
+films. This makes thin Fe$_{\mathrm{1+x}}$Co$_{\mathrm{2-x}}$Si films ideal
+materials for the application in STT-MRAM devices.",1605.06797v1
+2016-05-31,The mechanical back-action of a spin-wave resonance in a magnetoelastic thin film on a surface acoustic wave,"Surface acoustic waves (SAWs) traveling on the surface of a piezoelectric
+crystal can, through the magnetoelastic interaction, excite traveling spin-wave
+resonance in a magnetic film deposited on the substrate. This spin-wave
+resonance in the magnetic film creates a time dynamic surface stress of
+magnetoelastic origin that acts back on the surface of the piezoelectric and
+modifies the SAW propagation. Unlike previous analyses that treat the
+excitation as a magnon-phonon polariton, here the magnetoelastic film is
+treated as a perturbation modifying boundary conditions on the SAW. We use
+acoustical perturbation theory to find closed form expressions for the
+back-action surface stress and strain fields and the resultant SAW velocity
+shifts and attenuation. We demonstrate that the shear stress fields associated
+with this spin-wave back-action also generate effective surface currents on the
+piezoelectric both in-phase and out-of-phase with the driving SAW potential.
+Characterization of these surface currents and their applications in
+determination of the magnetoelastic coupling are discussed. The perturbative
+calculation is carried out explicitly to first order (a regime corresponding to
+many experimental situations of current interest) and we provide a sketch of
+the implications of the theory at higher order.",1605.09475v2
+2016-08-22,Doping Evolution of Magnetic Order and Magnetic Excitations in (Sr$_{1-x}$La$_x$)$_3$Ir$_2$O$_7$,"We use resonant elastic and inelastic X-ray scattering at the Ir-$L_3$ edge
+to study the doping-dependent magnetic order, magnetic excitations and
+spin-orbit excitons in the electron-doped bilayer iridate
+(Sr$_{1-x}$La$_{x}$)$_3$Ir$_2$O$_7$ ($0 \leq x \leq 0.065$). With increasing
+doping $x$, the three-dimensional long range antiferromagnetic order is
+gradually suppressed and evolves into a three-dimensional short range order
+from $x = 0$ to $0.05$, followed by a transition to two-dimensional short range
+order between $x = 0.05$ and $0.065$. Following the evolution of the
+antiferromagnetic order, the magnetic excitations undergo damping, anisotropic
+softening and gap collapse, accompanied by weakly doping-dependent spin-orbit
+excitons. Therefore, we conclude that electron doping suppresses the magnetic
+anisotropy and interlayer couplings and drives
+(Sr$_{1-x}$La$_x$)$_3$Ir$_2$O$_7$ into a correlated metallic state hosting
+two-dimensional short range antiferromagnetic order and strong
+antiferromagnetic fluctuations of $J_{\text{eff}} = \frac{1}{2}$ moments, with
+the magnon gap strongly suppressed.",1608.06268v2
+2017-06-05,Bose-Einstein Condensation in a Plasmonic Lattice,"Bose-Einstein condensation is a remarkable manifestation of quantum
+statistics and macroscopic quantum coherence. Superconductivity and
+superfluidity have their origin in Bose-Einstein condensation. Ultracold
+quantum gases have provided condensates close to the original ideas of Bose and
+Einstein, while condensation of polaritons and magnons have introduced novel
+concepts of non-equilibrium condensation. Here, we demonstrate a Bose-Einstein
+condensate (BEC) of surface plasmon polaritons in lattice modes of a metal
+nanoparticle array. Interaction of the nanoscale-confined surface plasmons with
+a room-temperature bath of dye molecules enables thermalization and
+condensation in picoseconds. The ultrafast thermalization and condensation
+dynamics are revealed by an experiment that exploits thermalization under
+propagation and the open cavity character of the system. A crossover from BEC
+to usual lasing is realized by tailoring the band structure. This new
+condensate of surface plasmon lattice excitations has promise for future
+technologies due to its ultrafast, room-temperature and on-chip nature.",1706.01528v3
+2017-06-07,Evaluation of the operatorial Q-system for non-compact super spin chains,"We present an approach to evaluate the full operatorial Q-system of all
+$\mathfrak{u}(p,q|r+s)$-invariant spin chains with representations of
+Jordan-Schwinger type. In particular, this includes the super spin chain of
+planar $\mathcal{N}=4$ super Yang-Mills theory at one loop in the presence of a
+diagonal twist. Our method is based on the oscillator construction of
+Q-operators. The Q-operators are built as traces over Lax operators which are
+degenerate solutions of the Yang-Baxter equation. For non-compact
+representations these Lax operators may contain multiple infinite sums that
+conceal the form of the resulting functions. We determine these infinite sums
+and calculate the matrix elements of the lowest level Q-operators. Transforming
+the Lax operators corresponding to the Q-operators into a representation
+involving only finite sums allows us to take the supertrace and to obtain the
+explicit form of the Q-operators in terms of finite matrices for a given magnon
+sector. Imposing the functional relations, we then bootstrap the other
+Q-operators from those of the lowest level. We exemplify this approach for
+non-compact spin $-s$ spin chains and apply it to $\mathcal{N}=4$ SYM at the
+one-loop level using the BMN vacuum as an example.",1706.02320v3
+2017-06-29,Reconfigurable topological spin wave beamsplitters and interferometers,"Conventional magnonic devices use three classes of magnetostatic waves that
+require detailed manipulation of magnetization structure that makes the design
+and the device/circuitry scalability difficult tasks. Here, we demonstrate that
+devices based on topological exchange spin waves do not suffer from the problem
+with additional nice features of nano-scale wavelength and high frequency. Two
+results are reported. 1) A perpendicular ferromagnet on a honeycomb lattice is
+generically a topological magnetic material in the sense that topologically
+protected chiral edge spin waves exist in the band gap as long as spin-orbit
+induced nearest-neighbor pseudodipolar interaction (and/or next-nearest
+neighbor Dzyaloshinskii-Moriya interaction) is present. 2) As a proof of
+concept, spin wave beamsplitters and spin wave interferometers are designed by
+using domain walls to manipulate the propagation of topologically protected
+chiral spin waves. Since magnetic domain walls can be controlled by magnetic
+fields or electric current/fields, one can essentially draw, erase and redraw
+different spin wave devices and circuitry on the same magnetic plate so that
+the proposed devices are reconfigurable and tunable. Devices made from magnetic
+topological materials are robust against both internal and external
+perturbations such as the spin wave frequency variation and device geometry as
+well as defects.",1706.09548v2
+2017-10-02,Signatures of low-energy fractionalized excitations in $α$-RuCl$_3$ from field-dependent microwave absorption,"Topologically ordered states of matter are generically characterized by
+excitations with quantum number fractionalization. A prime example is the spin
+liquid realized in Kitaev's honeycomb-lattice compass model where spin-flip
+excitations fractionalize into Majorana fermions and Ising gauge fluxes. While
+numerous compounds have been proposed to be proximate to such a spin-liquid
+phase, clear-cut evidence for fractionalized excitations is lacking. Here we
+employ microwave absorption measurements to study the low-energy excitations in
+$\alpha$-RuCl$_3$ over a wide range of frequencies, magnetic fields, and
+temperatures, covering in particular the vicinity of the field-driven quantum
+phase transition where long-range magnetic order disappears. In addition to
+conventional gapped magnon modes we find a highly unusual broad continuum
+characteristic of fractionalization which -- most remarkably -- extends to
+energies below the lowest sharp mode and to temperatures significantly higher
+than the ordering temperature, and develops a gap of a nontrivial origin in
+strong magnetic fields. Our results unravel the signatures of fractionalized
+excitations in $\alpha$-RuCl$_3$ and pave the way to a more complete
+understanding of the Kitaev spin liquid and its instabilities.",1710.00670v3
+2017-12-02,Coherent excitation of heterosymmetric spin waves with ultrashort wavelengths,"In the emerging field of magnonics, spin waves are foreseen as signal
+carriers for future spintronic information processing and communication
+devices, owing to both the very low power losses and a high device
+miniaturisation potential predicted for short-wavelength spin waves. Yet, the
+efficient excitation and controlled propagation of nanoscale spin waves remains
+a severe challenge. Here, we report the observation of high-amplitude,
+ultrashort dipole-exchange spin waves (down to 80 nm wavelength at 10 GHz
+frequency) in a ferromagnetic single layer system, coherently excited by the
+driven dynamics of a spin vortex core. We used time-resolved x-ray microscopy
+to directly image such propagating spin waves and their excitation over a wide
+range of frequencies. By further analysis, we found that these waves exhibit a
+heterosymmetric mode profile, involving regions with anti-Larmor precession
+sense and purely linear magnetic oscillation. In particular, this mode profile
+consists of dynamic vortices with laterally alternating helicity, leading to a
+partial magnetic flux closure over the film thickness, which is explained by a
+strong and unexpected mode hybridisation. This spin-wave phenomenon observed is
+a general effect inherent to the dynamics of sufficiently thick ferromagnetic
+single layer films, independent of the specific excitation method employed.",1712.00681v3
+2017-12-05,Peculiarities of the electronic transport in half-metallic Co-based Heusler alloys,"Electrical, magnetic and galvanomagnetic properties of half-metallic Heusler
+alloys of Co$_2$YZ (Y = Ti, V, Cr, Mn, Fe, Ni, and Z = Al, Si, Ga, Ge, In, Sn,
+Sb) were studied in the temperature range 4.2--900 K and in magnetic fields of
+up to 100 kOe. It was found that varying Y in affects strongly the electric
+resistivity and its temperature dependence $\rho(T)$, while this effect is not
+observed upon changing Z. When Y is varied, extrema (maximum or minimum) are
+observed in $\rho(T)$ near the Curie temperature $T_C$. At $T < T_C$, the
+$\rho(T)$ behavior can be ascribed to a change in electronic energy spectrum
+near the Fermi level. The coefficients of the normal and anomalous Hall effect
+were determined. It was shown that the latter coefficient, $R_S$, is related to
+the residual resistivity $\rho_0$ by a power law $R_S \sim \rho_0^k/M_S$ with
+$M_S$ the spontaneous magnetization. The exponent $k$ was found to be 1.8 for
+Co$_2$FeZ alloys, which is typical for asymmetric scattering mechanisms, and
+2.9 for Co$_2$YAl alloys, which indicates an additional contribution to the
+anomalous Hall effect. The temperature dependence of resistivity at low
+temperatures is analyzed and discussed in the framework of the two-magnon
+scattering theory.",1712.01584v1
+2017-12-19,Dispersive Magnetic and Electronic Excitations in Iridate Perovskites Probed with Oxygen $K$-Edge Resonant Inelastic X-ray Scattering,"Resonant inelastic X-ray scattering (RIXS) experiments performed at the
+oxygen-$K$ edge on the iridate perovskites {\SIOS} and {\SION} reveal a
+sequence of well-defined dispersive modes over the energy range up to $\sim
+0.8$ eV. The momentum dependence of these modes and their variation with the
+experimental geometry allows us to assign each of them to specific collective
+magnetic and/or electronic excitation processes, including single and
+bi-magnons, and spin-orbit and electron-hole excitons. We thus demonstrated
+that dispersive magnetic and electronic excitations are observable at the O-$K$
+edge in the presence of the strong spin-orbit coupling in the $5d$ shell of
+iridium and strong hybridization between Ir $5d$ and O $2p$ orbitals, which
+confirm and expand theoretical expectations. More generally, our results
+establish the utility of O-$K$ edge RIXS for studying the collective
+excitations in a range of $5d$ materials that are attracting increasing
+attention due to their novel magnetic and electronic properties. Especially,
+the strong RIXS response at O-$K$ edge opens up the opportunity for
+investigating collective excitations in thin films and heterostructures
+fabricated from these materials.",1712.06895v1
+2017-12-21,Exchange-torque-induced excitation of perpendicular standing spin waves in nanometer-thick YIG films,"Spin waves in ferrimagnetic yttrium iron garnet (YIG) films with ultralow
+magnetic damping are relevant for magnon-based spintronics and low-power
+wave-like computing. The excitation frequency of spin waves in YIG is rather
+low in weak external magnetic fields because of its small saturation
+magnetization, which limits the potential of YIG films for high-frequency
+applications. Here, we demonstrate how exchange-coupling to a CoFeB film
+enables efficient excitation of high-frequency perpendicular standing spin
+waves (PSSWs) in nanometer-thick (80 nm and 295 nm) YIG films using uniform
+microwave magnetic fields. In the 295-nm-thick YIG film, we measure intense
+PSSW modes up to 10th order. Strong hybridization between the PSSW modes and
+the ferromagnetic resonance mode of CoFeB leads to characteristic anti-crossing
+behavior in broadband spin-wave spectra. A dynamic exchange torque at the
+YIG/CoFeB interface explains the excitation of PSSWs. The localized torque
+originates from exchange coupling between two dissimilar magnetization
+precessions in the YIG and CoFeB layers. As a consequence, spin waves are
+emitted from the YIG/CoFeB interface and PSSWs form when their wave vector
+matches the perpendicular confinement condition. PSSWs are not excited when the
+exchange coupling between YIG and CoFeB is suppressed by a Ta spacer layer.
+Micromagnetic simulations confirm the exchange-torque mechanism.",1712.08204v1
+2018-09-11,Detecting Crystallographic Lattice Chirality using Resonant Inelastic X-ray Scattering,"The control and detection of crystallographic chirality is an important and
+challenging scientific problem. Chirality has wide ranging implications from
+medical physics to cosmology including an intimate but subtle connection in
+magnetic systems, for example Mn$_{1-x}$Fe$_{x}$Si. X-ray diffraction
+techniques with resonant or polarized variations of the experimental setup are
+currently utilized to characterize lattice chirality. We demonstrate using
+theoretical calculations the feasibility of indirect $K$ -edge bimagnon
+resonant inelastic X-ray scattering (RIXS) spectrum as a viable experimental
+technique to distinguish crystallographic handedness. We apply spin wave theory
+to the recently discovered $\sqrt {5}\times\sqrt {5}$ vacancy ordered
+chalcogenide Rb$_{0.89}$Fe$_{1.58}$Se$_{2}$ for realistic X-ray experimental
+set up parameters (incoming energy, polarization, and Bragg angle) to show that
+the computed RIXS spectrum is sensitive to the underlying handedness (right or
+left) of the lattice. A Flack parameter definition that incorporates the right-
+and left- chiral lattice RIXS response is introduced. It is shown that the RIXS
+response of the multiband magnon system RbFeSe arises both from inter- and
+intra- band scattering processes. The extinction or survival of these RIXS
+peaks are sensitive to the underlying chiral lattice orientation. This in turn
+allows for the identification of the two chiral lattice orientations.",1809.04148v2
+2018-09-13,Single-layer antiferromagnetic semiconductor CoS2 with the pentagonal structure,"Structure-property relationships have always been guiding principles in
+discovering new materials. Here we explore the relationships to discover novel
+two-dimensional (2D) materials with the goal of identifying 2D magnetic
+semiconductors for spintronics applications. In particular, we report a density
+functional theory + $U$ study of single-layer antiferromagnetic (AFM)
+semiconductor CoS$_2$ with the pentagonal structure forming the so-called Cairo
+Tessellation. We find that this single-layer magnet exhibits an indirect
+bandgap of 1.06 eV with light electron and hole effective masses of 0.03 and
+0.10 $m_0$, respectively, which may lead to high carrier mobilities. The hybrid
+density functional theory calculations correct the bandgap to 2.24 eV. We also
+compute the magnetocrystalline anisotropy energy (MAE), showing that the easy
+axis of the AFM ordering is out of plane with a sizable MAE of 153 $\mu$eV per
+Co ion. We further calculate the magnon frequencies at different spin-spiral
+vectors, based on which we estimate the N$\acute{e}$el temperatures to be 20.4
+and 13.3 K using the mean field and random phase approximations, respectively.
+We then apply biaxial strains to tune the bandgap of single-layer pentagonal
+CoS$_2$. We find that the energy difference between the ferromagnetic and AFM
+structures strongly depends on the biaxial strain, but the ground state remains
+the AFM ordering. Although the low critical temperature prohibits the magnetic
+applications of single-layer pentagonal CoS$_2$ at room temperature, the
+excellent electrical properties may find this novel single-layer semiconductor
+applications in optoelectronic nanodevices.",1809.05055v1
+2018-09-28,Isotropic non-local Gilbert damping driven by spin currents in epitaxial Pd/Fe/MgO(001) films,"Although both theoretical predications and experimental observations
+demonstrated that the damping factor is anisotropic at
+ferromagnet/semiconductor interface with robust interfacial spin-orbit
+coupling, it is not well understood whether non-local Gilbert damping driven by
+spin currents in heavy metal/ferromagnetic metal (HM/FM) bilayers is
+anisotropic or not. Here, we investigated the in-plane angular- and frequency-
+dependence of magnetic relaxation of epitaxial Fe/MgO(001) films with different
+capping layers of Pd and Cu. After disentangling the parasitic contributions,
+such as two-magnon scattering (TMS), mosaicity, and field-dragging effect, we
+unambiguously observed that both local and non-local Gilbert damping are
+isotropic in Fe(001) plane, suggesting that the pure spin currents absorption
+is independent of Fe magnetization orientation in the epitaxial Pd/Fe
+heterostructure. First principles calculation reveals that the effective spin
+mixing conductance of Pd/Fe interface is nearly invariant for different
+magnetization directions in good agreement with the experimental observations.
+These results offer a valuable insight into the transmission and absorption of
+pure spin currents, and facilitate us to utilize next-generation spintronic
+devices.",1809.11020v1
+2019-09-05,Extraction of Dzyaloshinksii-Moriya interaction from propagating spin waves validated,"The interfacial Dzyaloshinksii-Moriya interaction (iDMI) is of great interest
+in thin-film magnetism because of its ability to stabilize chiral spin
+textures. It can be quantified by investigating the frequency non-reciprocity
+of oppositely propagating spin waves. However, as the iDMI is an interface
+interaction the relative effect reduces when the films become thicker making
+quantification more difficult. Here, we utilize all-electrical Propagating Spin
+Wave Spectroscopy (PSWS) to disentangle multiple contributions to spin wave
+frequency non-reciprocity to determine the iDMI. This is done by investigating
+non-reciprocities across a wide range of magnetic layer thicknesses (from 4 to
+26 nm) in Pt/Co/Ir, Pt/Co/Pt, and Ir/Co/Pt stacks. We find the expected sign
+change in the iDMI when inverting the stack order, and a negligible iDMI for
+the symmetric Pt/Co/Pt. We additionally extract a difference in surface
+anisotropies and find a large contribution due to the formation of different
+crystalline phases of the Co, which is corroborated using nuclear magnetic
+resonance and high-resolution transmission-electron-microscopy measurements.
+These insights will open up new avenues to investigate, quantify and
+disentangle the fundamental mechanisms governing the iDMI, and pave a way
+towards engineered large spin-wave non-reciprocities for magnonic applications.",1909.02467v1
+2019-09-09,Intrinsic quantum Ising model on a triangular lattice magnet TmMgGaO$_{4}$ and beyond,"The rare-earth magnet TmMgGaO$_{4}$ is proposed to be an intrinsic quantum
+Ising magnet described by the antiferromagnetic transverse field Ising model
+(TFIM) on a triangular lattice, where the relevant degrees of freedom are the
+non-degenerate dipole-multipole doublets of the Tm$^{3+}$ ions and the
+transverse field has an intrinsic origin from the weak splitting of the
+doublet. We compare this special doublet of Tm$^{3+}$ with the dipole-octupole
+Kramers doublet. We study the proposed effective model for the Tm-based
+triangular lattice and consider the effects of external magnetic fields and
+finite temperatures. From the ""orthogonal operator approach"", we show that the
+TFIM with the three-sublattice intertwined ordered state agrees with the
+experiments and further clarify the discrepancy in the nubmers of the magnetic
+sublattices and the measured magnon branches. We make specific predictions for
+the evolution of the magnetic properties with the external magnetic field.
+Furthermore, we demonstrate that an emergent U(1) symmetry emerges in thermal
+melting of the underlying orders and at the criticality, and summarize the
+previously known signatures related to the finite-temperature
+Berezinskii-Kosterlitz-Thouless (BKT) physics. We discuss the broad relevance
+of intrinsic quantum Ising magnets to many other systems, especially the
+Tm-based materials.",1909.03608v3
+2019-09-10,"Twisting and tweezing the spin wave: on vortices, skyrmions, helical waves, and the magnonic spiral phase plate","Spin waves are the low-energy excitations of magnetically ordered materials.
+They are key elements in the stability analysis of the ordered phase and have a
+wealth of technological applications. Recently, we showed that spin waves of a
+magnetic nanowire may carry a definite amount of orbital angular momentum
+components along the propagation direction. This helical, in addition to the
+chiral, character of the spin waves is related to the spatial modulations of
+the spin wave phase across the wire. It, however, remains a challenge to
+generate and control such modes with conventional magnetic fields. Here, we
+make the first proposal for a \textit{magnetic} spiral phase plate by
+appropriately synthesizing two magnetic materials that have different speeds of
+spin waves. It is demonstrated with full-numerical micromagnetic simulations
+that despite the complicated structure of demagnetization fields, a homogeneous
+spin wave passing through the spiral phase plate attains the required twist and
+propagates further with the desired orbital angular momentum. While excitations
+from the ordered phase may have a twist, the magnetization itself can be
+twisted due to internal fields and forms what is known as a magnetic vortex. We
+point out the differences between both types of magnetic phenomena and discuss
+their possible interaction.",1909.04457v2
+2019-09-10,Real-space imaging of confined magnetic skyrmion tubes,"Magnetic skyrmions are topologically nontrivial particles with a potential
+application as information elements in future spintronic device architectures.
+While they are commonly portrayed as two dimensional objects, in reality
+magnetic skyrmions are thought to exist as elongated, tube-like objects
+extending through the thickness of the sample. Study of this skyrmion tube
+(SkT) state is highly relevant for investigating skyrmion metastability and for
+implementation in recently proposed magnonic computing. However, direct
+experimental imaging of skyrmion tubes has yet to be reported. Here, we
+demonstrate the first real-space observation of skyrmion tubes in a lamella of
+FeGe using resonant magnetic x-ray imaging and comparative micromagnetic
+simulations, confirming their extended structure. The formation of these
+structures at the edge of the sample highlights the importance of confinement
+and edge effects in the stabilisation of the SkT state, opening the door to
+further investigations into this unexplored dimension of the skyrmion spin
+texture.",1909.04528v2
+2019-09-11,Giant pressure-enhancement of multiferroicity in CuBr2,"Type-II multiferroic materials, in which ferroelectric polarization is
+induced by inversion non-symmetric magnetic order, promise new and highly
+efficient multifunctional applications based on the mutual control of magnetic
+and electric properties. Although this phenomenon has to date been limited to
+low temperatures, here we report a giant pressure-dependence of the
+multiferroic critical temperature in CuBr$_2$. At 4.5 GPa, $T_\mathrm{C}$ is
+enhanced from 73.5 to 162 K, to our knowledge the highest value yet reported
+for a non-oxide type-II multiferroic. This growth shows no sign of saturating
+and the dielectric loss remains small under these high pressures. We establish
+the structure under pressure and demonstrate a 60\% increase in the two-magnon
+Raman energy scale up to 3.6 GPa. First-principles structural and magnetic
+energy calculations provide a quantitative explanation in terms of dramatically
+pressure-enhanced interactions between CuBr$_2$ chains. These large,
+pressure-tuned magnetic interactions motivate structural control in cuprous
+halides as a route to applied high-temperature multiferroicity.",1909.04989v2
+2019-09-24,Unconventional Hund Metal in a Weak Itinerant Ferromagnet,"The physics of weak itinerant ferromagnets is challenging due to their small
+magnetic moments and the ambiguous role of local interactions governing their
+electronic properties, many of which violate Fermi liquid theory. While
+magnetic fluctuations play an important role in the materials' unusual
+electronic states, the nature of these fluctuations and the paradigms through
+which they arise remain debated. Here we use inelastic neutron scattering to
+study magnetic fluctuations in the canonical weak itinerant ferromagnet MnSi.
+Data reveal that short-wavelength magnons continue to propagate until a mode
+crossing predicted for strongly interacting quasiparticles is reached, and the
+local susceptibility peaks at a coherence energy predicted for a correlated
+Hund metal by first-principles many-body theory. Scattering between electrons
+and orbital and spin fluctuations in MnSi can be understood at the local level
+to generate non-Fermi liquid character. These results provide crucial insight
+into the role of interorbital Hund's exchange within the broader class of
+enigmatic multiband itinerant, weak ferromagnets.",1909.11195v2
+2020-12-07,Double-Exchange Enhanced Magnetic Blue-Shift of Mott Gaps,"A substantial energy gap of charge excitations induced by strong correlations
+is the characteristic feature of Mott insulators. We study how the Mott gap is
+affected by long-range antiferromagnetic order. Our key finding is that the
+Mott gap is increased by the magnetic ordering: a magnetic blue-shift (MBS)
+occurs. Thus, the effect is proportional to the exchange coupling in the
+leading order in the Hubbard model. In systems with additional localized spins
+the double-exchange mechanism induces an additional contribution to the MBS
+which is proportional to the hopping in the leading order. The coupling between
+spin and charge degrees of freedom bears the potential to enable spin-to-charge
+conversion in Mott systems on extreme time scales determined by hopping and
+exchange only, since a spin-orbit mediated transfer of angular momentum is not
+involved in the process. In view of spintronic and magnonic applications, it is
+highly promising to observe that several entire classes of compounds show
+exchange and double-exchange effects. Exemplarily, we show that the magnetic
+contribution to the band-gap blue-shift observed in the optical conductivity of
+$\alpha$-MnTe is correctly interpreted as the MBS of a Mott gap.",2012.04018v2
+2020-12-21,Development of short and long-range magnetic order in the double perovskite based frustrated triangular lattice antiferromagnet Ba2MnTeO6,"Oxide double perovskites wherein octahedra formed by both 3d elements and
+sp-based heavy elements give rise to unconventional magnetic ordering and
+correlated quantum phenomena crucial for futuristic applications. Here, by
+carrying out experimental and first principles investigations, we present the
+electronic structure and magnetic phases of Ba2MnTeO6, where Mn^2+ ions with S
+= 5/2 spins constitute a perfect triangular lattice. The magnetic
+susceptibility reveals a large Curie- Weiss temperature -152 K suggesting the
+presence of strong antiferromagnetic interactions between Mn^2+ moments in the
+spin lattice. A phase transition at 20 K is revealed by magnetic susceptibility
+and specific heat which is attributed to the presence of a sizeable inter-plane
+interactions. Below the transition temperature, the specific heat data show
+antiferromagnetic magnon excitations with a gap of 1.4 K. Furthermore, muon
+spin-relaxation reveals the presence of static internal fields in the ordered
+state and provides strong evidence of short-range spin correlations for T > TN.
+The DFT+U calculations and spin-dimer analysis infer that Heisenberg
+interactions govern the inter and intra-layer spin-frustrations in this
+perovskite. The inter and intra-layer exchange interactions are of comparable
+strengths (J1 = 4.6 K, J2 = 0.92 J1). However, a weak third nearest-neighbor
+ferromagnetic inter-layer interaction exists (J3=-0.04 J1) due to
+double-exchange interaction via the linear path Mn-O-Te-O-Mn. The combined
+effect of J2 and J3 interactions stabilizes a three dimensional long-range
+magnetic ordering in this frustrated magnet.",2012.11292v1
+2020-12-23,Monolayer CrCl$_3$ as an ideal Test Bed for the Universality Classes of 2D Magnetism,"The monolayer halides CrX$_3$ (X=Cl, Br, I) attract significant attention for
+realizing 2D magnets with genuine long-range order (LRO), challenging the
+Mermin-Wagner theorem. Here, we show that monolayer CrCl$_3$ has the unique
+benefit of exhibiting tunable magnetic anisotropy upon applying a compressive
+strain. This opens the possibility to use CrCl$_3$ for producing and studying
+both ferromagnetic and antiferromagnetic 2D Ising-type LRO as well as the
+Berezinskii-Kosterlitz-Thouless (BKT) regime of 2D magnetism with quasi-LRO.
+Using state-of-the-art density functional theory, we explain how realistic
+compressive strain could be used to tune the monolayer's magnetic properties so
+that it could exhibit any of these phases. Building on large-scale quantum
+Monte Carlo simulations, we compute the phase diagram of strained CrCl$_3$, as
+well as the magnon spectrum with spin-wave theory. Our results highlight the
+eminent suitability of monolayer CrCl$_3$ to achieve very high BKT transition
+temperatures, around 50 K, due to their singular dependence on the weak
+easy-plane anisotropy of the material.",2012.12801v2
+2000-06-22,"Magnetic ordering and fluctuation in kagome lattice antiferromagnets, Fe and Cr jarosites","Jarosite family compounds, KFe_3(OH)_6(SO_4)_2, (abbreviate Fe jarosite), and
+KCr_3(OH)_6(SO_4)_2, (Cr jarosite), are typical examples of the Heisenberg
+antiferromagnet on the kagome lattice and have been investigated by means of
+magnetization and NMR experiments. The susceptibility of Cr jarosite deviates
+from Curie-Weiss law due to the short-range spin correlation below about 150 K
+and shows the magnetic transition at 4.2 K, while Fe jarosite has the
+transition at 65 K. The susceptibility data fit well with the calculated one on
+the high temperature expansion for the Heisenberg antiferromagnet on the kagome
+lattice. The values of exchange interaction of Cr jarosite and Fe jarosite are
+derived to be J_Cr = 4.9 K and J_Fe = 23 K, respectively. The 1H-NMR spectra of
+Fe jarosite suggest that the ordered spin structure is the q = 0 type with
+positive chirality of the 120 degrees configuration. The transition is caused
+by a weak single-ion type anisotropy. The spin-lattice relaxation rate, 1/T_1,
+of Fe jarosite in the ordered phase decreases sharply with lowering the
+temperature and can be well explained by the two-magnon process of spin wave
+with the anisotropy.",0006343v1
+2017-05-03,Linearly polarized GHz magnetization dynamics of spin helix modes in the ferrimagnetic insulator Cu$_{2}$OSeO$_{3}$,"Linear dichroism -- the polarization dependent absorption of electromagnetic
+waves -- is routinely exploited in applications as diverse as structure
+determination of DNA or polarization filters in optical technologies. Here
+filamentary absorbers with a large length-to-width ratio are a prerequisite.
+For magnetization dynamics in the few GHz frequency regime strictly linear
+dichroism was not observed for more than eight decades. Here, we show that the
+bulk chiral magnet Cu$_{2}$OSeO$_{3}$ exhibits linearly polarized magnetization
+dynamics at an unexpectedly small frequency of about 2 GHz. Unlike optical
+filters that are assembled from filamentary absorbers, the magnet provides
+linear polarization as a bulk material for an extremely wide range of
+length-to-width ratios. In addition, the polarization plane of a given mode can
+be switched by 90$^\circ$ via a tiny variation in width. Our findings shed a
+new light on magnetization dynamics in that ferrimagnetic ordering combined
+with anisotropic exchange interaction offers strictly linear polarization and
+cross-polarized modes for a broad spectrum of sample shapes. The discovery
+allows for novel design rules and optimization of microwave-to-magnon
+transduction in emerging microwave technologies.",1705.01582v1
+2017-05-12,Switching dynamics of the spin density wave in superconducting CeCoIn5,"The ordering wave vector $\mathbf{Q}$ of a spin density wave (SDW),
+stabilized within the superconducting state of $\mathrm{CeCoIn_5}$ in a high
+magnetic field, has been shown to be hypersensitive to the direction of the
+field. $\mathbf{Q}$ can be switched from a nodal direction of the $d$-wave
+superconducting order parameter to a perpendicular node by rotating the
+in-plane magnetic field through the antinodal direction within a fraction of a
+degree. Here, we address the dynamics of the switching of $\mathbf{Q}$. We use
+a free energy functional based on the magnetization density, which describes
+the condensation of magnetic fluctuations of nodal quasiparticles, and show
+that the switching process includes closing of the SDW gap at one $\mathbf{Q}$
+and then reopening the SDW gap at another $\mathbf{Q}$ perpendicular to the
+first one. The magnetic field couples to $\mathbf{Q}$ through the spin-orbit
+interaction. Our calculations show that the width of the hysteretic region of
+switching depends linearly on the deviation of magnetic field from the critical
+field associated with the SDW transition, consistent with our thermal
+conductivity measurements. The agreement between theory and experiment supports
+our scenario of the hypersensitivity of the $Q$ phase on the direction of
+magnetic field, as well as the magnon condensation as the origin of the SDW
+phase in $\mathrm{CeCoIn_5}$.",1705.04655v1
+2017-05-19,Impurity-induced magnetic droplet in unconventional superconductors near magnetic instability: Application to Nd doped $\mathbf{CeCoIn_5}$,"Beside the spin density wave (SDW) order inside the superconducting phase in
+$\mathrm{CeCoIn_5}$ at high magnetic fields, recent neutron scattering
+measurements have found Bragg peaks in $5\%$ Nd doped $\mathrm{CeCoIn_5}$ at
+low fields. The intensity of Bragg peaks in low fields is suppressed by
+increasing field. Based on the phenomenological and microscopic modeling, we
+show that for the Pauli limited $d$-wave superconductors in the vicinity of SDW
+instability relevant for $\mathrm{CeCoIn_5}$, magnetic impurities locally
+induce droplets of SDW order. Because of the strong anisotropy in the momentum
+space in the spin fluctuations guaranteed by the $d$-wave pairing symmetry,
+sharp peaks in spin structure factor at $\mathbf{Q}$s are produced by the
+impurities, even when the droplets of SDW do not order. At zero field, the Nd
+impurity spins are along the $c$ axis due to the coupling to the conduction
+electrons with an easy $c$ axis, besides their own crystal field effect. The
+in-plane magnetic field cants the impurity moments toward the $ab$ plane, which
+suppress the droplets of SDW order. At high fields, the long-range SDW inside
+the superconducting phase is stabilized as a consequence of magnon
+condensation. Our results are consistent with the recent neutron scattering and
+thermal conductivity measurements.",1705.07174v1
+2017-09-03,Femtosecond formation dynamics of the spin Seebeck effect revealed by terahertz spectroscopy,"Understanding the transfer of spin angular momentum is essential in modern
+magnetism research. A model case is the generation of magnons in magnetic
+insulators by heating an adjacent metal film. Here, we reveal the initial steps
+of this spin Seebeck effect with <27fs time resolution using terahertz
+spectroscopy on bilayers of ferrimagnetic yttrium-iron garnet and platinum.
+Upon exciting the metal with an infrared laser pulse, a spin Seebeck current
+$j_\textrm{s}$ arises on the same ~100fs time scale on which the metal
+electrons thermalize. This observation highlights that efficient spin transfer
+critically relies on carrier multiplication and is driven by conduction
+electrons scattering off the metal-insulator interface. Analytical modeling
+shows that the electrons' dynamics are almost instantaneously imprinted onto
+$j_\textrm{s}$ because their spins have a correlation time of only ~4fs and
+deflect the ferrimagnetic moments without inertia. Applications in material
+characterization, interface probing, spin-noise spectroscopy and terahertz spin
+pumping emerge.",1709.00768v5
+2017-08-29,Novel magnetoelectric effects via penta-linear interactions,"Magnetoelectric multiferroic materials, particularly with the perovskite
+structure, are receiving a lot of attention because of their inherent coupling
+between electrical polarization and magnetic ordering. However, very few types
+of direct coupling between polarization and magnetization are known, and it is
+unclear whether they can be useful to the design of novel spintronic devices
+exploiting the control of magnetization by electric fields. For instance, the
+typical bi-quadratic coupling only allows to change the magnitude of the
+magnetization by an electric field, but it does not permit an
+electric-field-induced switching of the magnetization. Similarly, the so-called
+Lifshitz invariants allow an electric-field control of complicated magnetic
+orderings, but not of the magnetization. Here, we report the discovery of novel
+direct couplings between polarization and magnetization in epitaxial perovskite
+films, via the use of first-principles methods and the development of an
+original Landau-type phenomenological theory. Our results feature penta-linear
+interactions involving the ferromagnetic and anti-ferromagnetic vectors as well
+as the polar distortions and oxygen octahedral tilting, and permit a number of
+striking effects. Examples include a continuous electric-field control of the
+magnetization magnitude and sign, and the discrete switching of the
+magnetization magnitude. Thus, the high-order, penta-linear couplings
+demonstrated in this work may open new paths towards novel magneto-electric
+effects, as well as, spintronic and magnonic devices.",1709.01789v1
+2017-09-08,Quartz-based flat-crystal resonant inelastic x-ray scattering spectrometer with sub-10 meV energy resolution,"Continued improvement of the energy resolution of resonant inelastic x-ray
+scattering (RIXS) spectrometers is crucial for fulfilling the potential of this
+technique in the study of electron dynamics in materials of fundamental and
+technological importance. In particular, RIXS is the only alternative tool to
+inelastic neutron scattering capable of providing fully momentum resolved
+information on dynamic spin structures of magnetic materials, but is limited to
+systems whose magnetic excitation energy scales are comparable to the energy
+resolution. The state-of-the-art spherical diced crystal analyzer optics
+provides energy resolution as good as 25 meV but has already reached its
+theoretical limit. Here, we demonstrate a novel sub-10meV RIXS spectrometer
+based on flat-crystal optics at the Ir-L$_3$ absorption edge (11.215$\sim$ keV)
+that achieves an analyzer energy resolution of 3.9$\sim$meV, very close to the
+theoretical value of 3.7$\sim$meV. In addition, the new spectrometer allows
+efficient polarization analysis without loss of energy resolution. The
+performance of the instrument is demonstrated using longitudinal acoustical and
+optical phonons in diamond, and magnon in Sr$_3$Ir$_2$O$_7$. The novel
+sub-10$\sim$meV RIXS spectrometer thus provides a window into magnetic
+materials with small energy scales.",1709.02777v1
+2018-03-15,Diffuson contribution to anomalous Hall effect in disordered Co2FeSi thin films,"A wide variation in the disorder strength, as inferred from an order of
+magnitude variation in the longitudinal resistivity of Co2FeSi (CFS) Huesler
+alloy thin films of fixed (50 nm) thickness, has been achieved by growing these
+films on Si(111) substrates at substrate temperatures ranging from room
+temperature (RT) to 600 C. An in-depth study of the influence of disorder on
+anomalous Hall resistivity,longitudinal resistivity(LR) and magnetoresistance,
+enabled by this approach, reveals the following. The side-jump mechanism gives
+a dominant contribution to anomalous Hall resistivity (AHR) in the CFS thin
+films, regardless of the degree of disorder present. A new and novel
+contribution to both LR and AHR characterized by the logarithmic temperature
+dependence at temperatures below the minimum, exclusive to the amorphous CFS
+films, originates from the scattering of conduction electrons from the
+diffusive hydrodynamic modes associated with the longitudinal component of
+magnetization, called diffusons. In these amorphous CFS films, the
+electron-diffuson, e d, scattering and weak localization (WL) mechanisms
+compete with that arising from the inelastic electron magnon, e m, scattering
+to produce the minimum in longitudinal resistivity, whereas the minimum in AHR
+is caused by the competing contributions from the e d and e m scattering, as WL
+does not make any contribution to AHR. In sharp contrast, in crystalline films,
+enhanced electron electron Coulomb interaction (EEI), which is basically
+responsible for the resistivity minimum, makes no contribution to AHR with the
+result that AHR does not exhibit a minimum.",1803.05590v1
+2018-06-25,"Boundary twists, instabilities, and creation of skyrmions and antiskyrmions","We formulate and study the general boundary conditions dictating the
+magnetization profile in the vicinity of an interface between magnets with
+dissimilar properties. Boundary twists in the vicinity of an edge due to
+Dzyaloshinskii-Moriya interactions have been first discussed in [Wilson et al.,
+Phys. Rev. B 88, 214420 (2013)] and in [Rohart and Thiaville, Phys. Rev. B 88,
+184422 (2013)]. We show that in general case the boundary conditions lead to
+the magnetization profile corresponding to the N\'eel, Bloch, or intermediate
+twist. We explore how such twists can be utilized for creation of skyrmions and
+antiskyrmions, e.g., in a view of magnetic memory applications. To this end, we
+study various scenarios how skyrmions and antiskyrmions can be created from
+interface magnetization twists due to local instabilities. We also show that a
+judicious choice of Dzyaloshinskii-Moriya tensor (hence a carefully designed
+material) can lead to local instabilities generating certain types of skyrmions
+or antiskyrmions. The local instabilities are shown to appear in solutions of
+the Bogoliubov-de-Gennes equations describing ellipticity of magnon modes bound
+to interfaces. In one considered scenario, a skyrmion-antiskyrmion pair can be
+created due to instabilities at an interface between materials with properly
+engineered Dzyaloshinskii-Moriya interactions. We use micromagnetics
+simulations to confirm our analytical predictions.",1806.09546v3
+2018-07-02,A tunable time-resolved spontaneous Raman spectroscopy setup for probing ultrafast collective excitation and quasiparticle dynamics in quantum materials,"We present a flexible and efficient ultrafast time-resolved spontaneous Raman
+spectroscopy setup to study collective excitation and quasi-particle dynamics
+in quantum matter. The setup has a broad energy tuning range extending from the
+visible to near infrared spectral regions for both the pump excitation and
+Raman probe pulses. Additionally, the balance between energy and
+time-resolution can be controlled. A high light collecting efficiency is
+realized by high numerical aperture collection optics and a high-throughput
+flexible spectrometer. We demonstrate the functionality of the setup with a
+study of the zone-center longitudinal optical phonon and hole continuum
+dynamics in silicon, and discuss the role of the Raman tensor in time-resolved
+Raman scattering. In addition, we show evidence for unequal phonon softening
+rates at different high symmetry points in the Brillouin zone of silicon by
+means of detecting pump-induced changes in the two-phonon overtone spectrum.
+Demagnetization dynamics in the helimagnet Cu2OSeO3 is studied by observing
+softening and broadening of a magnon after photo-excitation, underlining the
+unique power of measuring transient dynamics in the frequency domain, and the
+feasibility to study phase transitions in quantum matter.",1807.00525v1
+2018-07-20,Ising versus Potts criticality in a low-temperature magnetothermodynamics of a frustrated spin-1/2 Heisenberg triangular bilayer,"Low-temperature magnetization curves and thermodynamics of a frustrated
+spin-1/2 Heisenberg triangular bilayer with the antiferromagnetic intradimer
+interaction and either ferromagnetic or antiferromagnetic interdimer
+interaction are investigated in a highly frustrated parameter region, where
+localized many-magnon eigenstates provide the most dominant contribution to
+magnetothermodynamics. Low-energy states of the highly frustrated spin-1/2
+Heisenberg triangular bilayer can be accordingly found from a mapping
+correspondence with an effective triangular-lattice spin-1/2 Ising model in a
+field. A description based on the effective Ising model implies that the
+frustrated Heisenberg triangular bilayer with the ferromagnetic interdimer
+coupling displays in a zero-temperature magnetization curve discontinuous
+magnetization jump, which is reduced upon increasing of temperature until a
+continuous field-driven phase transition from the Ising universality class is
+reached at a certain critical temperature. The frustrated Heisenberg triangular
+bilayer with the antiferromagnetic interdimer coupling contrarily exhibits
+multistep magnetization curve with intermediate plateaus at one-third and
+two-thirds of the saturation magnetization, whereas discontinuous magnetization
+jumps observable at zero temperature change to continuous field-driven phase
+transitions from the universality class of three-state Potts model at
+sufficiently low temperatures. Exact results and Monte Carlo simulations of the
+effective Ising model are confronted with full exact diagonalization data for
+the Heisenberg triangular bilayer in order to corroborate these findings.",1807.08042v2
+2018-07-26,"Quantum Magnetism, Spin Waves, and Light","Both magnetic materials and light have always played a predominant role in
+information technologies, and continue to do so as we move into the realm of
+quantum technologies. In this course we review the basics of magnetism and
+quantum mechanics, before going into more advanced subjects. Magnetism is
+intrinsically quantum mechanical in nature, and magnetic ordering can only be
+explained by use of quantum theory. We will go over the interactions and the
+resulting Hamiltonian that governs magnetic phenomena, and discuss its
+elementary excitations, denominated magnons. After that we will study
+magneto-optical effects and derive the classical Faraday effect. We will then
+move on to the quantization of the electric field and the basics of optical
+cavities. This will allow us to understand a topic of current research
+denominated Cavity Optomagnonics. These notes were written as the accompanying
+material to the course I taught in the Summer Semester 2018 at the
+Friedrich-Alexander University in Erlangen. The course is intended for Master
+or advanced Bachelor students. Basic knowledge of quantum mechanics,
+electromagnetism, and solid state at the Bachelor level is assumed. Each
+section is followed by a couple of simple exercises which should serve as to
+""fill in the blanks"" of what has been derived, plus specific references to
+bibliography, and a couple of check-points for the main concepts developed. The
+figures are pictures of the blackboard taken during the lecture.",1807.10626v2
+2018-12-06,Interplay between non-Hermiticity and non-Abelian gauge potential in topological photonics,"Topological phases in spinless non-Hermitian models have been widely studied
+both theoretically and experimentally in some artificial materials using
+photonics, phononics and magnon. In this work, we investigate the interplay
+between non-Hermitian loss and gain and non-Abelian gauge potential realized in
+a two-component superconducting circuit. In our model, the non-Hermiticity
+along only gives rise to trivial gain and loss to the states; while the
+non-Abelian gauge along gives rise to flying butterfly spectra and associated
+edge modes, which in photonics can be directly measured by the intensity of
+photons at the boundaries. These two terms do not commute, and their interplay
+can give rise to several intriguing non-Hermitian phases, including the fully
+gapped quantum spin Hall (QSH) phase, gapless QSH phase, trivial gapped phase
+and gapless metallic phase. The bulk-edge correspondence is absent and we find
+that during the closing of energy gap in the gapped QSH phase, the system
+enters the gapless QSH phase regime which still supports two
+counter-propagating edge modes. We have also unveiled the intriguing role of
+non-Hermiticity on the chiral symmetry and time-reversal symmetry of the
+Hermitian models, which can be applied to other physical models.",1812.02610v2
+2018-12-13,EDRIXS: An open source toolkit for simulating spectra of resonant inelastic x-ray scattering,"Resonant inelastic x-ray scattering (RIXS) has become a very powerful
+experimental technique to probe a broad range of intrinsic elementary
+excitations, for example, from low energy phonons and (bi-)magnons to high
+energy $d$-$d$, charge-transfer and plasmons excitations in strongly correlated
+electronic systems. Due to the complexity of the RIXS cross-section and strong
+core-hole effects, theoretical simulation of the experimental RIXS spectra is
+still a difficult task which hampers the understanding of RIXS spectra and the
+development of the RIXS technique. In this paper, we present an open source
+toolkit (dubbed EDRIXS) to facilitate the simulations of RIXS spectra of
+strongly correlated materials based on exact diagonalization (ED) of certain
+model Hamiltonians. The model Hamiltonian can be from a single atom, small
+cluster or Anderson impurity model, with model parameters from density
+functional theory plus Wannier90 or dynamical mean-field theory calculations.
+The spectra of x-ray absorption spectroscopy (XAS) and RIXS are then calculated
+using Krylov subspace techniques. This toolkit contains highly efficient ED,
+XAS and RIXS solvers written in modern Fortran 90 language and a convenient
+Python library used to prepare inputs and set up calculations. We first give a
+short introduction to RIXS spectroscopy, and then we discuss the implementation
+details of this toolkit. Finally, we show three examples to demonstrate its
+usage.",1812.05735v2
+2018-12-18,Thermal gradient driven domain wall dynamics,"The issue of whether a thermal gradient acts like a magnetic field or an
+electric current in the domain wall (DW) dynamics is investigated. Broadly
+speaking, magnetization control knobs can be classified as energy-driving or
+angular-momentum driving forces. DW propagation driven by a static magnetic
+field is the best-known example of the former in which the DW speed is
+proportional to the energy dissipation rate, and the current-driven DW motion
+is an example of the latter. Here we show that DW propagation speed driven by a
+thermal gradient can be fully explained as the angular momentum transfer
+between thermally generated spin current and DW. We found DW-plane rotation
+speed increases as DW width decreases. Both DW propagation speed along the wire
+and DW-plane rotation speed around the wire decrease with the Gilbert damping.
+These facts are consistent with the angular momentum transfer mechanism, but
+are distinct from the energy dissipation mechanism. We further show that
+magnonic spin-transfer torque (STT) generated by a thermal gradient has both
+damping-like and field-like components. By analyzing DW propagation speed and
+DW-plane rotation speed, the coefficient ( \b{eta}) of the field-like STT
+arising from the non-adiabatic process, is obtained. It is found that \b{eta}
+does not depend on the thermal gradient; increases with uniaxial anisotropy
+K_(||) (thinner DW); and decreases with the damping, in agreement with the
+physical picture that a larger damping or a thicker DW leads to a better
+alignment between the spin-current polarization and the local magnetization, or
+a better adiabaticity.",1812.07244v2
+2019-01-03,Colossal electromagnon excitation in the non-cycloidal phase of TbMnO3 under pressure,"The magnetoelectric coupling, i.e., cross-correlation between electric and
+magnetic orders, is a very desirable property to combine functionalities of
+materials for next-generation switchable devices. Multiferroics with
+spin-driven ferroelectricity presents such a mutual interaction concomitant
+with magneto- and electro-active excitations called electromagnons. TbMnO3 is a
+paradigmatic material in which two electromagnons have been observed in the
+cycloidal magnetic phase. However, their observation in TbMnO3 is restricted to
+the cycloidal spin phase and magnetic ground states that can support the
+electromagnon excitation are still under debate. Here, we show by performing
+Raman spectroscopy measurements under pressure that the lower-energy
+electromagnon (4 meV) disappears when the ground state enters from a cycloidal
+phase to an antiferromagnetic phase (E-type). On the contrary, the
+magnetoelectric activity of the higher-energy electromagnon (8 meV) increases
+in intensity by one order of magnitude. Using microscopic model calculations,
+we demonstrate that the lowerenergy electromagnon, observed in the cycloidal
+phase, originates from a higher harmonic of the magnetic cycloid, and we
+determine that the symmetric exchange-striction mechanism is at the origin of
+the higher-energy electromagnon which survives even in the E-type phase. The
+colossal enhancement of the electromagnon activity in TbMnO3 paves the way to
+use multiferroics more efficiently for generation, conversion and control of
+spin waves in magnonic devices.",1901.00919v1
+2019-01-09,"The magnetic phase diagram of the frustrated spin chain compound linarite, PbCuSO$_4$(OH)$_2$, as seen by neutron diffraction and $^1$H-NMR","We report on a detailed neutron diffraction and $^1$H-NMR study on the
+frustrated spin-1/2 chain material linarite, PbCuSO$_4$(OH)$_2$, where
+competing ferromagnetic nearest neighbor and antiferromagnetic next-nearest
+neighbor interactions lead to frustration. From the magnetic Bragg peak
+intensity studied down to 60 mK, the magnetic moment per Cu atom is obtained
+within the whole magnetic phase diagram for $H \parallel b$ axis. Further, we
+establish the detailed configurations of the shift of the SDW propagation
+vector in phase V with field and temperature. Finally, combining our neutron
+diffraction results with those from a low-temperature/high-field NMR study we
+find an even more complex phase diagram close to the quasi-saturation field
+suggesting that bound two-magnon excitations are the lowest energy excitations
+close to and in the quasi-saturation regime. Qualitatively and
+semi-quantitatively, we relate such behavior to $XYZ$ exchange anisotropy and
+contributions from the Dzyaloshinsky-Moriya interaction to affect the magnetic
+properties of linarite.",1901.02842v1
+2019-01-10,Giant thermal Hall conductivity from neutral excitations in the pseudogap phase of cuprates,"The nature of the pseudogap phase of cuprates remains a major puzzle.
+Although there are indications that this phase breaks various symmetries, there
+is no consensus on its fundamental nature. Although Fermi-surface, transport
+and thermodynamic signatures of the pseudogap phase are reminiscent of a
+transition into a phase with antiferromagnetic order, there is no evidence for
+an associated long-range magnetic order. Here we report measurements of the
+thermal Hall conductivity $\kappa_{\rm xy}$ in the normal state of four
+different cuprates (Nd-LSCO, Eu-LSCO, LSCO, and Bi2201) and show that a large
+negative $\kappa_{\rm xy}$ signal is a property of the pseudogap phase,
+appearing with the onset of that phase at the critical doping $p^*$. Since it
+is not due to charge carriers -- as it persists when the material becomes an
+insulator, at low doping -- or magnons -- as it exists in the absence of
+magnetic order -- or phonons -- since skew scattering is very weak, we
+attribute this $\kappa_{\rm xy}$ signal to exotic neutral excitations,
+presumably with spin chirality. The thermal Hall conductivity in the pseudogap
+phase of cuprates is reminiscent of that found in insulators with spin-liquid
+states. In the Mott insulator LCO, it attains the highest known magnitude of
+any insulator.",1901.03104v1
+2019-01-19,Resolving the nature of electronic excitations in resonant inelastic x-ray scattering,"The study of elementary bosonic excitations is essential toward a complete
+description of quantum electronic solids. In this context, resonant inelastic
+X-ray scattering (RIXS) has recently risen to becoming a versatile probe of
+electronic excitations in strongly correlated electron systems. The nature of
+the radiation-matter interaction endows RIXS with the ability to resolve the
+charge, spin and orbital nature of individual excitations. However, this
+capability has been only marginally explored to date. Here, we demonstrate a
+systematic method for the extraction of the character of excitations as
+imprinted in the azimuthal dependence of the RIXS signal. Using this novel
+approach, we resolve the charge, spin, and orbital nature of elastic
+scattering, (para-)magnon/bimagnon modes, and higher energy dd excitations in
+magnetically-ordered and superconducting copper-oxide perovskites (Nd2CuO4 and
+YBa2Cu3O6.75). Our method derives from a direct application of scattering
+theory, enabling us to deconstruct the complex scattering tensor as a function
+of energy loss. In particular, we use the characteristic tensorial nature of
+each excitation to precisely and reliably disentangle the charge and spin
+contributions to the low energy RIXS spectrum. This procedure enables to
+separately track the evolution of spin and charge spectral distributions in
+cuprates with doping. Our results demonstrate a new capability that can be
+integrated into the RIXS toolset, and that promises to be widely applicable to
+materials with intertwined spin, orbital, and charge excitations.",1901.06583v1
+2019-01-20,Terahertz Strong-Field Physics without a Strong External Terahertz Field,"Traditionally, strong-field physics explores phenomena in matter (atoms,
+molecules, and solids) driven by an extremely strong laser field
+nonperturbatively. However, even in the complete absence of an external
+electromagnetic field, strong-field phenomena can arise when matter strongly
+couples with the zero-point field of the quantum vacuum state, i.e.,
+fluctuating electromagnetic waves whose expectation value is zero. Some of the
+most striking examples of this occur in a cavity setting, in which an ensemble
+of two-level atoms resonantly interacts with a single photonic mode of vacuum
+fields, producing vacuum Rabi splitting. In particular, the nature of the
+matter-vacuum-field coupled system fundamentally changes when the coupling rate
+(equal to one half of the vacuum Rabi splitting) becomes comparable to, or
+larger than, the resonance frequency. In this so-called ultrastrong coupling
+regime, a non-negligible number of photons exist in the ground state of the
+coupled system. Furthermore, the coupling rate can be cooperatively enhanced
+(via so-called Dicke cooperativity) when the matter is comprised of a large
+number of identical two-level particles, and a quantum phase transition is
+predicted to occur as the coupling rate reaches a critical value. Low-energy
+electronic or magnetic transitions in many-body condensed matter systems with
+large dipole moments are ideally suited for searching for these predicted
+phenomena. Here, we discuss two condensed matter systems that have shown
+cooperative ultrastrong interactions in the terahertz frequency range: a
+Landau-quantized two-dimensional electron gas interacting with
+high-quality-factor cavity photons, and an Er$^{3+}$ spin ensemble interacting
+with Fe$^{3+}$ magnons in ErFeO$_3$.",1901.06749v1
+2019-01-26,All optical detection of picosecond spin-wave dynamics in two-dimensional annular antidot lattice,"Novel magnetic structures with precisely controlled dimensions and shapes at
+the nanoscale have potential applications in spin logic, spintronics and other
+spin-based communication devices. We report the fabrication of two-dimensional
+bi-structure magnonic crystal in the form of embedded nanodots in a periodic
+Ni80Fe20 antidot lattice structure (annular antidot) by focused ion-beam
+lithography. The spin-wave spectra of the annular antidot sample,studied for
+the first time by a time-resolved magneto-optic Kerr effect microscopy show a
+remarkable variation with bias field, which is important for the above device
+applications. The optically induced spin-wave spectra show multiple modes in
+the frequency range 14.7 GHz to 3.5 GHz due to collective interactions between
+the dots and antidots as well as the annular elements within the whole array.
+Numerical simulations qualitatively reproduce the experimental results, and
+simulated mode profiles reveal the spatial distribution of the spin wave modes
+and internal magnetic fields responsible for these observations. It is observed
+that the internal field strength increases by about 200 Oe inside each dot
+embedded within the hole of annular antidot lattice as compared to pure antidot
+lattice and pure dot lattice. The stray field for the annular antidot lattice
+is found to be significant (0.8kOe) as opposed to the negligible values of the
+same for the pure dot lattice and pure antidot lattice. Our findings open up
+new possibilities for development of novel artificial crystals.",1901.09152v1
+2019-01-31,Fundamental Spin Interactions Underlying the Magnetic Anisotropy in the Kitaev Ferromagnet CrI$_3$,"We lay the foundation for determining the microscopic spin interactions in
+two-dimensional (2D) ferromagnets by combining angle-dependent ferromagnetic
+resonance (FMR) experiments on high quality CrI$_3$ single crystals with
+theoretical modeling based on symmetries. We discover that the Kitaev
+interaction is the strongest in this material with $K \sim -5.2$ meV, 25 times
+larger than the Heisenberg exchange $J \sim -0.2$ meV, and responsible for
+opening the $\sim$5 meV gap at the Dirac points in the spin-wave dispersion.
+Furthermore, we find that the symmetric off-diagonal anisotropy $\Gamma \sim
+-67.5$ $\mu$eV, though small, is crucial for opening a $\sim$0.3 meV gap in the
+magnon spectrum at the zone center and stabilizing ferromagnetism in the 2D
+limit. The high resolution of the FMR data further reveals a $\mu$eV-scale
+quadrupolar contribution to the $S=3/2$ magnetism. Our identification of the
+underlying exchange anisotropies opens paths toward 2D ferromagnets with higher
+$T_\text{C}$ as well as magnetically frustrated quantum spin liquids based on
+Kitaev physics.",1902.00077v2
+2019-02-14,Polarization resolved Cu $L_3$-edge resonant inelastic x-ray scattering of orbital and spin excitations in NdBa$_{2}$Cu$_{3}$O$_{7-δ}$,"High resolution resonant inelastic x-ray scattering (RIXS) has proven
+particularly effective in the determination of crystal field and spin
+excitations in cuprates. Its strength lies in the large Cu $L_{3}$ resonance
+and in the fact that the scattering cross section follows quite closely the
+single-ion model predictions, both in the insulating parent compounds and in
+the superconducting doped materials. However, the spectra become increasingly
+broader with (hole) doping, hence resolving and assigning spectral features has
+proven challenging even with the highest energy resolution experimentally
+achievable. Here we have overcome this limitation by measuring the complete
+polarization dependence of the RIXS spectra as function of momentum transfer
+and doping in thin films of NdBa$_{2}$Cu$_{3}$O$_{7-\delta}$. Besides
+confirming the previous assignment of $dd$ and spin excitations (magnon,
+bimagnon) in the antiferromagnetic insulating parent compound, we unequivocally
+single out the actual spin-flip contribution at all dopings. We also
+demonstrate that the softening of $dd$ excitations is mainly attributed to the
+shift of the $xy$ peak to lower energy loss. These results provide a definitive
+assessment of the RIXS spectra of cuprates and demonstrate that RIXS
+measurements with full polarization control are practically feasible and highly
+informative.",1902.05471v1
+2019-02-20,Spin-charge conversion in NiMnSb Heusler alloy films,"Half-metallic Heusler alloys are attracting considerable attention because of
+their unique half-metallic band structures which exhibit high spin polarization
+and yield huge magnetoresistance ratios. Besides serving as ferromagnetic
+electrodes, Heusler alloys also have the potential to host spin-charge
+conversion which has been recently demonstrated in other ferromagnetic metals.
+Here, we report on the spin-charge conversion effect in the prototypical
+Heusler alloy NiMnSb. Spin currents were injected from Y3Fe5O12 into NiMnSb
+films by spin pumping, and then the spin currents were converted to charge
+currents via spin-orbit interactions. Interestingly, an unusual charge signal
+was observed with a sign change at low temperature, which can be manipulated by
+film thickness and ordering structure. It is found that the spin-charge
+conversion has two contributions. First, the interfacial contribution causes a
+negative voltage signal, which is almost constant versus temperature. The
+second contribution is temperature dependent because it is dominated by
+minority states due to thermally excited magnons in the bulk part of the film.
+This work provides a pathway for the manipulation of spin-charge conversion in
+ferromagnetic metals by interface-bulk engineering for spintronic devices.",1902.07406v1
+2019-02-21,Asymmetric Ferromagnetic Criticality in Pyrochlore Ferromagnet Lu$_2$V$_2$O$_7$,"Critical phenomenon at the phase transition reveals the universal and
+long-distance properties of the criticality. We study the ferromagnetic
+criticality of the pyrochlore magnet Lu$_2$V$_2$O$_7$ at the ferromagnetic
+transition ${T_\text{c}\approx 70\, \text{K}}$ from the isotherms of
+magnetization $M(H)$ via an iteration process and the Kouvel-Fisher method. The
+critical exponents associated with the transition are determined as ${\beta =
+0.32(1)}$, ${\gamma = 1.41(1)}$, and ${\delta = 5.38}$. The validity of these
+critical exponents is further verified by scaling all the $M(H)$ data in the
+vicinity of $T_\text{c}$ onto two universal curves in the plot of
+$M/|\varepsilon|^\beta$ versus $H/|\varepsilon|^{\beta+\gamma}$, where
+${\varepsilon = T/T_\text{c} -1}$. The obtained $\beta$ and $\gamma$ values
+show asymmetric behaviors on the ${T < T_\text{c}}$ and the ${T > T_\text{c}}$
+sides, and are consistent with the predicted values of 3D Ising and cubic
+universality classes, respectively. This makes Lu$_2$V$_2$O$_7$ a rare example
+in which the critical behaviors associated with a ferromagnetic transition
+belong to different universality classes. We describe the observed criticality
+from the Ginzburg-Landau theory with the quartic cubic anisotropy that
+microscopically originates from the anti-symmetric Dzyaloshinskii-Moriya
+interaction as revealed by recent magnon thermal Hall effect and theoretical
+investigations.",1902.07924v1
+2019-03-04,Evolution of interlayer and intralayer magnetism in three atomically thin chromium trihalides,"We conduct a comprehensive study of three different magnetic semiconductors,
+CrI$_3$, CrBr$_3$, and CrCl$_3$, by incorporating both few- and bi-layer
+samples in van der Waals tunnel junctions. We find that the interlayer magnetic
+ordering, exchange gap, magnetic anisotropy, as well as magnon excitations
+evolve systematically with changing halogen atom. By fitting to a spin wave
+theory that accounts for nearest neighbor exchange interactions, we are able to
+further determine a simple spin Hamiltonian describing all three systems. These
+results extend the 2D magnetism platform to Ising, Heisenberg, and XY spin
+classes in a single material family. Using magneto-optical measurements, we
+additionally demonstrate that ferromagnetism can be stabilized down to
+monolayer in more isotropic CrBr$_3$, with transition temperature still close
+to that of the bulk.",1903.01409v2
+2019-03-28,High spin-polarization in the low Curie temperature complex itinerant ferromagnet EuTi$_{1-x}$Nb$_x$O$_3$,"The physical systems with ferromagnetism and ""bad"" metallicity hosting
+unusual transport properties are playgrounds of novel quantum phenomena.
+Recently EuTi$_{1-x}$Nb$_x$O$_3$ emerged as a ferromagnetic system where
+non-trivial temperature dependent transport properties are observed due to
+coexistence and competition of various magnetic and non-magnetic scattering
+processes. In the ferromagnetic state, the resistivity shows a $T^2$
+temperature dependence possibly due to electron-magnon scattering and above the
+Curie temperature $T_c$, the dependence changes to $T^{3/2}$ behaviour
+indicating a correlation between transport and magnetic properties. In this
+paper, we show that the transport spin-polarization in EuTi$_{1-x}$Nb$_x$O$_3$,
+a low Curie temperature ferromagnet, is as high ($\sim 40\%$) as that in some
+of the metallic ferromagnets with high Curie temperatures. In addition, owing
+to the low Curie temperature of EuTi$_{1-x}$Nb$_x$O$_3$, the temperature ($T$)
+dependence of $P_t$ could be measured systematically up to $T_c$ which revealed
+a proportionate relationship with magnetization $M_s$ vs. $T$. This indicates
+that such proportionality is far more universally valid than the ferromagnets
+with ideal parabolic bands. Furthermore, our band structure calculations not
+only helped understand the origin of such high spin polarization in
+EuTi$_{1-x}$Nb$_x$O$_3$ but also provided a route to estimate the Hubbard $U$
+parameter in complex metallic ferromagnets in general using experimental
+inputs.",1903.12022v1
+2019-04-10,Optical excitation of propagating magnetostatic waves in an epitaxial Galfenol film by an ultrafast magnetic anisotropy change,"Using a time-resolved optically-pumped scanning optical microscopy technique
+we demonstrate the laser-driven excitation and propagation of spin waves in a
+20-nm film of a ferromagnetic metallic alloy Galfenol epitaxially grown on a
+GaAs substrate. In contrast to previous all-optical studies of spin waves we
+employ laser-induced thermal changes of magnetocrystalline anisotropy as an
+excitation mechanism. A tightly focused 70-fs laser pulse excites packets of
+magnetostatic surface waves with a $e^{-1}$ propagation length of 3.4 $\mu$m,
+which is comparable with that of permalloy. As a result, laser-driven
+magnetostatic spin waves are clearly detectable at distances up to 10 $\mu$m,
+which promotes epitaxial Galfenol films to the limited family of materials
+suitable for magnonic devices. A pronounced in-plane magnetocrystalline
+anisotropy of the Galfenol film offers an additional degree of freedom for
+manipulating the spin waves' parameters. Reorientation of an in-plane external
+magnetic field relative to the crystallographic axes of the sample tunes the
+frequency, amplitude and propagation length of the excited waves.",1904.05171v2
+2019-04-11,Spin dynamics of the antiferromagnetic Heisenberg model on a kagome bilayer,"We study the spin dynamics of classical Heisenberg antiferromagnet with
+nearest neighbor interactions on a quasi-two-dimensional kagome bilayer. This
+geometrically frustrated lattice consists of two kagome layers connected by a
+triangular-lattice linking layer. By combining Monte Carlo with precessional
+spin dynamics simulations, we compute the dynamical structure factor of the
+classical spin liquid in kagome bilayer and investigate the thermal and
+dilution effects. While the low frequency and long wavelength dynamics of the
+cooperative paramagnetic phase is dominated by spin diffusion, weak magnon
+excitations persist at higher energies, giving rise the half moon pattern in
+the dynamical structure factor. In the presence of spin vacancies, the
+dynamical properties of the diluted system can be understood within the two
+population picture. The spin diffusion of the ""correlated"" spin clusters is
+mainly driven by the zero-energy weather-van modes, giving rise to an
+autocorrelation function that decays exponentially with time. On the other
+hand, the diffusive dynamics of the quasi-free ""orphan"" spins leads to a
+distinctive longer time power-law tail in the autocorrelation function. We
+discuss the implications of our work for the glassy behaviors observed in the
+archetypal frustrated magnet SrCr$_{9p}$Ga$_{12-9p}$O$_{19}$ (SCGO).",1904.05863v3
+2019-04-15,Topological Hall effect at above room temperature in heterostructures composed of a magnetic insulator and a heavy metal,"Non-volatile memory and computing technology rely on efficient read and write
+of ultra-tiny information carriers that do not wear out. Magnetic skyrmions are
+emerging as a potential carrier since they are topologically robust nanoscale
+spin textures that can be manipulated with ultralow current density. To date,
+most of skyrmions are reported in metallic films, which suffer from additional
+Ohmic loss and thus high energy dissipation. Therefore, skyrmions in magnetic
+insulators are of technological importance for low-power information processing
+applications due to their low damping and the absence of Ohmic loss. Moreover,
+they attract fundamental interest in studying various magnon-skyrmion
+interactions11. Skyrmions have been observed in one insulating material
+Cu2OSeO3 at cryogenic temperatures, where they are stabilized by bulk
+Dzyaloshinskii-Moriya interaction. Here, we report the observation of magnetic
+skyrmions that survive above room temperature in magnetic insulator/heavy metal
+heterostructures, i.e., thulium iron garnet/platinum. The presence of these
+skyrmions results from the Dzyaloshinskii-Moriya interaction at the interface
+and is identified by the emergent topological Hall effect. Through tuning the
+magnetic anisotropy via varying temperature, we observe skyrmions in a large
+window of external magnetic field and enhanced stability of skyrmions in the
+easy-plane anisotropy regime. Our results will help create a new platform for
+insulating skyrmion-based room temperature low dissipation spintronic
+applications.",1904.07107v1
+2019-04-15,Signatures of a Deconfined Phase Transition on the Shastry-Sutherland Lattice: Applications to Quantum Critical SrCu$_2$(BO$_3$)$_2$,"We study a possible deconfined quantum phase transition in a realistic model
+of a two-dimensional Shastry-Sutherland quantum magnet, using both numerical
+and field theoretic techniques. Using the infinite density matrix
+renormalization group (iDMRG) method, we verify the existence of an
+intermediate plaquette valence bond solid (pVBS) order, with two fold
+degeneracy, between the dimer and N\'eel ordered phases. We argue that the
+quantum phase transition between the N\'eel and pVBS orders may be described by
+a deconfined quantum critical point (DQCP) with an emergent O(4) symmetry. By
+analyzing the correlation length spectrum obtained from iDMRG, we provide
+evidence for the DQCP and emergent O(4) symmetry in the lattice model. Such a
+phase transition has been reported in the recent pressure tuned experiments in
+the Shastry-Sutherland lattice material $\mathrm{SrCu_2 (BO_3)_2}$. The
+non-symmorphic lattice structure of the Shastry-Sutherland compound leads to
+extinction points in the scattering, where we predict sharp signatures of a
+DQCP in both the phonon and magnon spectra associated with the spinon
+continuum. The effect of weak interlayer couplings present in the three
+dimensional material is also discussed. Our results should help guide the
+experimental study of DQCP in quantum magnets.",1904.07266v3
+2019-08-21,Half-metallic ferromagnetism and Ru-induced localization in quaternary Heusler alloy CoRuMnSi,"We report a combined theoretical and experimental investigation of
+half-metallic ferromagnetism in equiatomic quaternary Heusler alloy CoRuMnSi.
+Room temperature XRD analysis reveals that the alloy crystallizes in L21
+disorder instead of pristine Y-type structure due to 50% swap disorder between
+the tetrahedral sites, i.e., Co and Ru atoms. Magnetization measurements reveal
+a net magnetization of 4 $\mu_B$ with Curie temperature of ~780 K. Resistivity
+measurement reveals the presence of localization effect below 35 K while above
+100 K, a linear dependence is observed. Resistivity behavior indicates the
+absence of single magnon scattering, which indirectly supports the
+half-metallic nature. The majority spin band near the Fermi level clearly
+indicates the overlap of flat eg bands with sharply varying conduction bands
+that are responsible for the localization. In-depth analysis of the projected
+atomic d-orbital character of band structure reveals unusual bonding, giving
+rise to the flat eg bands purely arising out of Ru ions. Co-Ru swap disorder
+calculations indicate the robustness of half-metallic nature, even when the
+structure changes from Y-type to L21-type, with no major change in the net
+magnetization of the system. Thus, robust half-metallic nature, stable
+structure, and high Curie temperature make this alloy quite a promising
+candidate to be used as a source of highly spin-polarized currents in
+spintronic applications.",1908.07804v1
+2019-08-26,Amplitude and frequency sensing of microwave fields with a superconducting transmon qudit,"Experiments with superconducting circuits require careful calibration of the
+applied pulses and fields over a large frequency range. This remains an ongoing
+challenge as commercial semiconductor electronics are not able to probe signals
+arriving at the chip due to its cryogenic environment. Here, we demonstrate how
+the on-chip amplitude and frequency of a microwave signal can be inferred from
+the ac Stark shifts of higher transmon levels. In our time-resolved
+measurements we employ Ramsey fringes, allowing us to detect the amplitude of
+the systems transfer function over a range of several hundreds of MHz with an
+energy sensitivity on the order of $10^{-4}$. Combined with similar
+measurements for the phase of the transfer function, our sensing method can
+facilitate pulse correction for high fidelity quantum gates in superconducting
+circuits. Additionally, the potential to characterize arbitrary microwave
+fields promotes applications in related areas of research, such as quantum
+optics or hybrid microwave systems including photonic, mechanical or magnonic
+subsystems.",1908.09556v3
+2019-08-30,"High-Field Quantum Disordered State in $α$-RuCl3: Spin Flips, Bound States, and a Multi-Particle Continuum","Layered $\alpha$-RuCl3 has been discussed as a proximate Kitaev spin liquid
+compound. Raman and THz spectroscopy of magnetic excitations confirm that the
+low-temperature antiferromagnetic ordered phase features a broad Raman
+continuum, together with two magnon-like excitations at 2.7 and 3.6 meV,
+respectively. The continuum strength is maximized as long-range order is
+suppressed by an external magnetic field. The state above the field-induced
+quantum phase transition around 7.5 T is characterized by a gapped
+multi-particle continuum out of which a two-particle bound state emerges,
+together with a well-defined single-particle excitation at lower energy. Exact
+diagonalization calculations demonstrate that Kitaev and off-diagonal exchange
+terms in the Fleury-Loudon operator are crucial for the occurrence of these
+features in the Raman spectra. Our study firmly establishes the
+partially-polarized quantum disordered character of the high-field phase.",1908.11617v1
+2019-12-19,Dynamical properties of Néel and valence-bond phases in the $J_1-J_2$ model on the honeycomb lattice,"By using a variational Monte Carlo technique based upon Gutzwiller-projected
+fermionic states, we investigate the dynamical structure factor of the
+antiferromagnetic $S=1/2$ Heisenberg model on the honeycomb lattice, in
+presence of first-neighbor ($J_1$) and second-neighbor ($J_2$) couplings, for
+${J_2 < 0.5 J_1}$. The ground state of the system shows long-range
+antiferromagnetic order for ${J_2/J_1 \lesssim 0.23}$, plaquette valence-bond
+order for ${0.23 \lesssim J_2/J_1 \lesssim 0.36}$, and columnar dimer order for
+${J_2/J_1 \gtrsim 0.36}$. Within the antiferromagnetic state, a well-defined
+magnon mode is observed, whose dispersion is in relatively good agreement with
+linear spin-wave approximation for $J_2=0$. When a nonzero second-neighbor
+super-exchange is included, a roton-like mode develops around the $K$ point
+(i.e., the corner of the Brillouin zone). This mode softens when $J_2/J_1$ is
+increased and becomes gapless at the transition point, $J_2/J_1 \approx 0.23$.
+Here, a broad continuum of states is clearly visible in the dynamical spectrum,
+suggesting that nearly-deconfined spinon excitations could exist, at least at
+relatively high energies. For larger values of $J_2/J_1$, valence-bond order is
+detected and the spectrum of the system becomes clearly gapped, with a triplon
+mode at low energies. This is particularly evident for the spectrum of the
+dimer valence-bond phase, in which the triplon mode is rather well separated
+from the continuum of excitations that appears at higher energies.",1912.09310v1
+2015-08-12,Localization of Fe d-states in Ni-Fe-Cu alloys and implications for ultrafast demagnetization,"Ni$_{80}$Fe$_{20}$ (Py) and Py-Cu exhibit intriguing ultrafast
+demagnetization behavior, where the Ni magnetic moment shows a delayed response
+relative to the Fe [S. Mathias et al., PNAS {\bf 109}, 4792 (2012)]. To unravel
+the mechanism responsible for this behavior, we have studied Py-Cu alloys for a
+wide range of Cu concentrations using X-ray magnetic circular dichroism (XMCD).
+The magnetic moments of Fe and Ni are found to respond very differently to Cu
+alloying: Fe becomes a strong ferromagnet in Py, with the magnetic moment
+largely unaffected by Cu alloying. In contrast, the Ni magnetic moment
+decreases continuously with increasing Cu concentration. Our results are
+corroborated by ab-initio calculations of the electronic structure, which we
+discuss in the framework of virtual bound states (VBSs). For high Cu
+concentrations, Ni exhibits VBSs below the Fermi level, which are likely
+responsible for an increased orbital/spin magnetic ratio at high Cu
+concentrations. Fe exhibits VBSs in the minority band, approximately 1 eV above
+the Fermi level in pure Py, that move closer to the Fermi level upon Cu
+alloying. A strong interaction between the VBSs and excited electrons above the
+Fermi level enhances the formation of localized magnons at Fe sites, which
+explains the different behavior between Fe and Ni during ultrafast
+demagnetization.",1508.03015v1
+2016-03-01,Magnetic field dependence of the neutron spin resonance in CeB6,"In zero magnetic field, the famous neutron spin resonance in the f-electron
+superconductor CeCoIn5 is similar to the recently discovered exciton peak in
+the non-superconducting CeB6. Magnetic field splits the resonance in CeCoIn5
+into two components, indicating that it is a doublet. Here we employ inelastic
+neutron scattering (INS) to scrutinize the field dependence of spin
+fluctuations in CeB6. The exciton shows a markedly different behavior without
+any field splitting. Instead, we observe a second field-induced magnon whose
+energy increases with field. At the ferromagnetic zone center, however, we find
+only a single mode with a non-monotonic field dependence. At low fields, it is
+initially suppressed to zero together with the antiferromagnetic order
+parameter, but then reappears at higher fields inside the hidden-order phase,
+following the energy of an electron spin resonance (ESR). This is a unique
+example of a ferromagnetic resonance in a heavy-fermion metal seen by both ESR
+and INS consistently over a broad range of magnetic fields.",1603.00383v2
+2016-10-17,"Structural, magnetic, electric, dielectric, and thermodynamic properties of multiferroic GeV4S8","The lacunar spinel GeV4S8 undergoes orbital and ferroelectric ordering at the
+Jahn-Teller transition around 30 K and exhibits antiferromagnetic order below
+about 14 K. In addition to this orbitally driven ferroelectricity, lacunar
+spinels are an interesting material class, as the vanadium ions form V4
+clusters representing stable molecular entities with a common electron
+distribution and a well-defined level scheme of molecular states resulting in a
+unique spin state per V4 molecule. Here we report detailed x-ray, magnetic
+susceptibility, electrical resistivity, heat capacity, thermal expansion, and
+dielectric results to characterize the structural, electric, dielectric,
+magnetic, and thermodynamic properties of this interesting material, which also
+exhibits strong electronic correlations. From the magnetic susceptibility, we
+determine a negative Curie-Weiss temperature, indicative for antiferromagnetic
+exchange and a paramagnetic moment close to a spin S = 1 of the V4 molecular
+clusters. The low-temperature heat capacity provides experimental evidence for
+gapped magnon excitations. From the entropy release, we conclude about strong
+correlations between magnetic order and lattice distortions. In addition, the
+observed anomalies at the phase transitions also indicate strong coupling
+between structural and electronic degrees of freedom. Utilizing dielectric
+spectroscopy, we find the onset of significant dispersion effects at the polar
+Jahn-Teller transition. The dispersion becomes fully suppressed again with the
+onset of spin order. In addition, the temperature dependencies of dielectric
+constant and specific heat possibly indicate a sequential appearance of orbital
+and polar order.",1610.05244v1
+2016-10-28,Insulating nanomagnets driven by spin torque,"Magnetic insulators, such as yttrium iron garnet (Y$_3$Fe$_5$O$_{12}$), are
+ideal materials for ultra-low power spintronics applications due to their low
+energy dissipation and efficient spin current generation and transmission.
+Recently, it has been realized that spin dynamics can be driven very
+effectively in micrometer-sized Y$_3$Fe$_5$O$_{12}$/Pt heterostructures by
+spin-Hall effects. We demonstrate here the excitation and detection of spin
+dynamics in Y$_3$Fe$_5$O$_{12}$/Pt nanowires by spin-torque ferromagnetic
+resonance. The nanowires defined via electron-beam lithography are fabricated
+by conventional room temperature sputtering deposition on Gd$_3$Ga$_5$O$_{12 }$
+substrates and lift-off. We observe field-like and anti-damping-like torques
+acting on the magnetization precession, which are due to simultaneous
+excitation by Oersted fields and spin-Hall torques. The Y$_3$Fe$_5$O$_{12}$/Pt
+nanowires are thoroughly examined over a wide frequency and power range. We
+observe a large change in the resonance field at high microwave powers, which
+is attributed to a decreasing effective magnetization due to microwave
+absorption. These heating effects are much more pronounced in the investigated
+nanostructures than in comparable micron-sized samples. By comparing different
+nanowire widths, the importance of geometrical confinements for magnetization
+dynamics becomes evident: quantized spin-wave modes across the width of the
+wires are observed in the spectra. Our results are the first stepping stones
+toward the realization of integrated magnonic logic devices based on
+insulators, where nanomagnets play an essential role.",1610.09360v1
+2016-12-11,Phase Structure of XX0 Spin Chain and Nonintersecting Brownian Motion,"We study finite size and temperature XX0 Heisenberg spin chain in weak and
+strong coupling regimes. By using an elegant connection of the model to
+integrable combinatorics and probability, we explore and interpret a possible
+phase structure of the model in asymptotic limit: the limit of large inverse
+temperature and size. First, partition function and free energy of the model
+are derived by using techniques and results from random matrix models and
+nonintersecting Brownian motion. We show that, in the asymptotic limit,
+partition function of the model, written in terms of matrix integral, is
+governed by the Tracy-Widom distribution. Second, the exact analytic results
+for the free energy, which is obtained by the asymptotic analysis of the
+Tracy-Widom distribution, indicate a completely new and sophisticated phase
+structure of the model. This phase structure consists of second- and
+third-order phase transitions. Finally, to shed light on our new results, we
+provide a possible interpretation of the phase structure in terms of dynamical
+behavior of magnons in the spin chain. We demonstrate distinct features of the
+phases with schematic spin configurations which have definite features in each
+region of the phase diagram.",1612.03463v2
+2016-12-18,Chiral limit of N = 4 SYM and ABJM and integrable Feynman graphs,"We consider a special double scaling limit, recently introduced by two of the
+authors, combining weak coupling and large imaginary twist, for the
+$\gamma$-twisted $\mathcal{N}=4$ SYM theory. We also establish the analogous
+limit for ABJM theory. The resulting non-gauge chiral 4D and 3D theories of
+interacting scalars and fermions are integrable in the planar limit. In spite
+of the breakdown of conformality by double-trace interactions, most of the
+correlators for local operators of these theories are conformal, with
+non-trivial anomalous dimensions defined by specific, integrable Feynman
+diagrams. We discuss the details of this diagrammatics. We construct the
+doubly-scaled asymptotic Bethe ansatz (ABA) equations for multi-magnon states
+in these theories. Each entry of the mixing matrix of local conformal operators
+in the simplest of these theories - the bi-scalar model in 4D and tri-scalar
+model in 3D - is given by a single Feynman diagram at any given loop order. The
+related diagrams are in principle computable, up to a few scheme dependent
+constants, by integrability methods (quantum spectral curve or ABA). These
+constants should be fixed from direct computations of a few simplest graphs.
+This integrability-based method is advocated to be able to provide information
+about some high loop order graphs which are hardly computable by other known
+methods. We exemplify our approach with specific five-loop graphs.",1612.05895v3
+2016-12-20,Doping Dependence of Collective Spin and Orbital Excitations in Spin 1 Quantum Antiferromagnet La$_{2-x}$Sr$_x$NiO$_4$ Observed by X-rays,"We report the first empirical demonstration that resonant inelastic x-ray
+scattering (RIXS) is sensitive to \emph{collective} magnetic excitations in
+$S=1$ systems by probing the Ni $L_3$-edge of La$_{2-x}$Sr$_x$NiO$_4$ ($x = 0,
+0.33, 0.45$). The magnetic excitation peak is asymmetric, indicating the
+presence of single and multi spin-flip excitations. As the hole doping level is
+increased, the zone boundary magnon energy is suppressed at a much larger rate
+than that in hole doped cuprates. Based on the analysis of the orbital and
+charge excitations observed by RIXS, we argue that this difference is related
+to the orbital character of the doped holes in these two families. This work
+establishes RIXS as a probe of fundamental magnetic interactions in nickelates
+opening the way towards studies of heterostructures and ultra-fast pump-probe
+experiments.",1612.06903v2
+2016-12-22,Bismuth iron garnet Bi3Fe5O12: a room temperature magnetoelectric material,"The possibility to control the magnetic properties of a material with an
+electric field at room temperature is highly desirable for modern applications.
+Moreover, a coupling between magnetic and electric orders within a single
+material presenting a wide range of exceptional physical properties, such as
+bismuth iron garnet (BIG), may lead to great advances in the field of
+spintronic applications. In particular, the combination of the magnetoelectric
+(ME) coupling with the low damping of spin waves in BIG can allow the control
+and manipulation of spin waves by an electric field in magnonic devices. Here
+we report the unambiguous observation of linear magnetoelectric coupling above
+300 K in BIG using ferromagnetic resonance technique with electric field
+modulation. The measured coupling value is comparable with that observed for
+prototypal magnetoelectric Cr2O3. On the basis of our experimental results, the
+strength of this linear ME coupling is directly linked to the presence of
+bismuth ions inducing strong spin orbit coupling and to the appearance of local
+magnetic inhomogeneities related to the magnetic domain structure. The
+unprecedented combination of magnetic, optical and magnetoelectrical properties
+in BIG is expected to trigger significant interest for technological
+applications as well as for theoretical studies.",1612.07531v3
+2017-07-18,Crossover from itinerant to localized magnetic excitations through the metal-insulator transition in NaOsO$_{\text{3}}$,"NaOsO$_{\text{3}}$ undergoes a metal-insulator transition (MIT) at 410 K,
+concomitant with the onset of antiferromagnetic order. The excitation spectra
+have been investigated through the MIT by resonant inelastic x-ray scattering
+(RIXS) at the Os L$_{\text{3}}$ edge. Low resolution ($\Delta E \sim$ 300 meV)
+measurements over a wide range of energies reveal that local electronic
+excitations do not change appreciably through the MIT. This is consistent with
+a picture in which structural distortions do not drive the MIT. In contrast,
+high resolution ($\Delta E \sim $ 56 meV) measurements show that the
+well-defined, low energy magnons in the insulating state weaken and dampen upon
+approaching the metallic state. Concomitantly, a broad continuum of excitations
+develops which is well described by the magnetic fluctuations of a nearly
+antiferromagnetic Fermi liquid. By revealing the continuous evolution of the
+magnetic quasiparticle spectrum as it changes its character from itinerant to
+localized, our results provide unprecedented insight into the nature of the MIT
+in \naoso. In particular, the presence of weak correlations in the paramagnetic
+phase implies a degree of departure from the ideal Slater limit.",1707.05551v2
+2017-07-27,Magnetism in artificial Ruddlesden-Popper iridates leveraged by structural distortions,"We report on the tuning of magnetic interactions in superlattices composed of
+single and bilayer SrIrO$_3$ inter-spaced with SrTiO$_3$. Magnetic scattering
+shows predominately $c$-axis antiferromagnetic orientation of the magnetic
+moments for the bilayer justifying these systems as viable artificial analogues
+of the bulk Ruddlesden-Popper series iridates. Magnon gaps are observed in both
+superlattices, with the magnitude of the gap in the bilayer being reduced to
+nearly half that in its bulk structural analogue, Sr$_3$Ir$_2$O$_7$. We assign
+this to modifications in the anisotropic exchange driven by bending of the
+$c$-axis Ir-O-Ir bond and subsequent local environment changes, as detected by
+x-ray diffraction and modeled using spin wave theory. These findings explain
+how even subtle structural modulations driven by heterostructuring in iridates
+are leveraged by spin orbit coupling to drive large changes in the magnetic
+interactions.",1707.08910v1
+2017-11-19,SU($N$) spin-wave theory: Application to spin-orbital Mott insulators,"We present the application of the SU($N$) ($N>2$) spin-wave theory to
+spin-orbital Mott insulators whose ground states exhibit magnetic orders. When
+taking both the spin and orbital degrees of freedom into account rather than
+projecting onto the Kramers doublet, the lowest spin-orbital locking energy
+levels, due to the inevitable spin-orbital multipole exchange interactions, the
+SU($N$) spin-wave theory should take the place of the SU($2$) one. To implement
+the application, we introduce an efficient general local mean field approach
+which involves all the local fluctuations into the SU($N$) linear spin-wave
+theory. Our approach is tested firstly by calculating the multipolar spin-wave
+spectra of the SU($4$) antiferromagnetic model. Then we apply it to
+spin-orbital Mott insulators. It is revealed that the Hund's coupling would
+influence the effectiveness of the isospin-$1/2$ representation when the spin
+orbital coupling is not large enough. Besides, we also calculate the spin-wave
+spectra based on the first principle calculations for two concrete materials,
+$\alpha$-RuCl$_3$ and Sr$_2$IrO$_4$. The SU($N$) spin-wave theory appropriately
+depicts the low-energy magnons and the spin-orbital excitations qualitatively.",1711.07041v1
+2017-11-28,Unconventional transport properties of an itinerant ferromagnet: EuTi$_{1-x}$Nb$_{x}$O$_3$ ($x$=0.10$-$0.20),"We report the temperature and magnetic field dependence of resistivity
+($\rho$) for single-crystalline EuTi$_{1-x}$Nb$_{x}$O$_3$ ($x$=0.10$-$0.20), an
+itinerant ferromagnetic system with very low Curie temperature ($T_C$). The
+detailed analysis reveals that the charge conduction in
+EuTi$_{1-x}$Nb$_{x}$O$_3$ is extremely sensitive to Nb concentration and
+dominated by several scattering mechanisms. Well below the $T_C$, where the
+spontaneous magnetization follows the Bloch's $T^{3/2}$ law, $\rho$ exhibits
+$T^2$ dependence with a large coefficient $\sim$10$^{-8}$ $\Omega$ cm K$^{-2}$
+due to the electron-magnon scattering. Remarkably, all the studied samples
+exhibit a unique resistivity minimum at $T$$=$$T_{\rm min}$ below which $\rho$
+shows logarithmic increment with $T$ (for $T_{\rm C}$$<$$T$$<$$T_{\rm min}$)
+due to the Kondo scattering of Nb 4$d^1$ itinerant electrons by the localized
+4$f$ moments of Eu$^{2+}$ ions which suppresses strongly with applied magnetic
+field. In the paramagnetic state, $T^{2}$ and $T^{3/2}$ dependence of the
+resistivity have been observed, suggesting an unusual crossover from a
+Fermi-liquid to a non-Fermi-liquid behavior with increasing $T$. The observed
+temperature and magnetic field dependence of resistivity has been analysed
+using different theoretical models.",1711.10140v1
+2019-05-10,Magnetic tunnel junctions with a B2-ordered CoFeCrAl equiatomic Heusler alloy,"The equiatomic quaternary Heusler alloy CoFeCrAl is a candidate material for
+spin-gapless semiconductors (SGSs). However, to date, there have been no
+experimental attempts at fabricating a junction device. This paper reports a
+fully epitaxial (001)-oriented MgO barrier magnetic tunnel junction (MTJ) with
+CoFeCrAl electrodes grown on a Cr buffer. X-ray and electron diffraction
+measurements show that the (001) CoFeCrAl electrode films with atomically flat
+surfaces have a $B2$-ordered phase. The saturation magnetization is 380
+emu/cm$^3$, almost the same as the value given by the Slater--Pauling--like
+rule, and the maximum tunnel magnetoresistance ratios at 300 K and 10 K are 87%
+and 165%, respectively. Cross-sectional electron diffraction analysis shows
+that the MTJs have MgO interfaces with fewer dislocations. The temperature- and
+bias-voltage-dependence of the transport measurements indicates magnon-induced
+inelastic electron tunneling overlapping with the coherent electron tunneling.
+X-ray magnetic circular dichroism (XMCD) measurements show a ferromagnetic
+arrangement of the Co and Fe magnetic moments of $B2$-ordered CoFeCrAl, in
+contrast to the ferrimagnetic arrangement predicted for the $Y$-ordered state
+possessing SGS characteristics. Ab-initio calculations taking account of the
+Cr-Fe swap disorder qualitatively explain the XMCD results. Finally, the effect
+of the Cr-Fe swap disorder on the ability for electronic states to allow
+coherent electron tunneling is discussed.",1905.04070v1
+2019-05-17,High-efficiency triple-resonant inelastic light scattering in planar optomagnonic cavities,"Optomagnonic cavities have recently been emerging as promising candidates for
+implementing coherent microwave-to-optical conversion, quantum memories and
+devices, and next generation quantum networks. A key challenge in the design of
+such cavities is the attainment of high efficiencies, which could, e.g., be
+exploited for efficient optical interfacing of superconducting qubits, as well
+as the practicality of the final designs, which ideally should be planar and
+amenable to on-chip integration. Here, on the basis of a novel time Floquet
+scattering-matrix approach, we report on the design and optimization of a
+planar, multilayer optomagnonic cavity, incorporating a Ce:YIG thin film,
+magnetized in-plane, operating in the triple-resonant inelastic light
+scattering regime. This architecture allows for conversion efficiencies of
+about 5%, under realistic conditions, which is orders of magnitude higher than
+alternative designs. Our results suggest a viable way forward for realizing
+practical information inter-conversion between microwave photons and optical
+photons, mediated by magnons, with efficiencies intrinsically greater than
+those achieved in optomechanics and alternative related technologies, as well
+as a platform for fundamental studies of classical and quantum dynamics in
+magnetic solids, and implementation of futuristic quantum devices.",1905.07278v1
+2019-05-23,Lattice frustration in spin-orbit Mott insulator Sr3Ir2O7 at high pressure,"The intertwined charge, spin, orbital, and lattice degrees of freedom could
+endow 5d compounds with exotic properties. Current interest is focused on
+electromagnetic interactions in these materials, whereas the important role of
+lattice geometry remains to be fully recognized. For this sake, we investigate
+pressure-induced phase transitions in the spin-orbit Mott insulator Sr3Ir2O7
+with Raman, electrical resistance, and x-ray diffraction measurements. We
+reveal an interesting magnetic transition coinciding with a structural
+transition at 14.4 GPa, but without a concurrent insulator-metal transition.
+The conventional correlation between magnetic and Mott insulating states is
+thereby absent. The observed softening of the one-magnon mode can be explained
+by a reduced tetragonal distortion, while the actual magnetic transition is
+associated with tilting of the IrO6 octahedra. This work highlights the
+critical role of lattice frustration in determining the high-pressure phases of
+Sr3Ir2O7. The ability to control electromagnetic properties via manipulating
+the crystal structure with pressure promises a new way to explore new quantum
+states in spin-orbit Mott insulators.",1905.09637v1
+2019-05-29,Thermal Tensor Network Simulations of the Heisenberg Model on the Bethe Lattice,"We have extended the canonical tree tensor network (TTN) method, which was
+initially introduced to simulate the zero-temperature properties of quantum
+lattice models on the Bethe lattice, to finite temperature simulations. By
+representing the thermal density matrix with a canonicalized tree tensor
+product operator, we optimize the TTN and accurately evaluate the thermodynamic
+quantities, including the internal energy, specific heat, and the spontaneous
+magnetization, etc, at various temperatures. By varying the anisotropic
+coupling constant $\Delta$, we obtain the phase diagram of the spin-1/2
+Heisenberg XXZ model on the Bethe lattice, where three kinds of magnetic
+ordered phases, namely the ferromagnetic, XY and antiferromagnetic ordered
+phases, are found in low temperatures and separated from the high-$T$
+paramagnetic phase by a continuous thermal phase transition at $T_c$. The XY
+phase is separated from the other two phases by two first-order phase
+transition lines at the symmetric coupling points $ \Delta=\pm 1$. We have also
+carried out a linear spin wave calculation on the Bethe lattice, showing that
+the low-energy magnetic excitations are always gapped, and find the obtained
+magnon gaps in very good agreement with those estimated from the TTN
+simulations. Despite the gapped excitation spectrum, Goldstone-like transverse
+fluctuation modes, as a manifestation of spontaneous continuous symmetry
+breaking, are observed in the ordered magnetic phases with $|\Delta|\le 1$. One
+remarkable feature there is that the prominent transverse correlation length
+reaches $\xi_c=1/\ln{(z-1)}$ for $T\leq T_c$, the maximal value allowed on a
+$z$-coordinated Bethe lattice.",1905.12478v1
+2019-05-29,Coherent long-range transfer of angular momentum between magnon Kittel modes by phonons,"We report ferromagnetic resonance in the normal configuration of an
+electrically insulating magnetic bilayer consisting of two yttrium iron garnet
+(YIG) films epitaxially grown on both sides of a 0.5-mm-thick nonmagnetic
+gadolinium gallium garnet (GGG) slab. An interference pattern is observed and
+it is explained as the strong coupling of the magnetization dynamics of the two
+YIG layers either in phase or out of phase by the standing transverse sound
+waves, which are excited through a magnetoelastic interaction. This coherent
+mediation of angular momentum by circularly polarized phonons through a
+nonmagnetic material over macroscopic distances can be useful for future
+information technologies.",1905.12523v3
+2019-05-31,Fingerprints of Kitaev physics in the magnetic excitations of honeycomb iridates,"In the quest for realizations of quantum spin liquids, the exploration of
+Kitaev materials - spin-orbit entangled Mott insulators with strong
+bond-directional exchanges - has taken center stage. However, in these
+materials the local spin-orbital j=1/2 moments typically show long-range
+magnetic order at low temperature, thus defying the formation of a spin-liquid
+ground state. Using resonant inelastic x-ray scattering (RIXS), we here report
+on a proximate spin liquid regime with clear fingerprints of Kitaev physics in
+the magnetic excitations of the honeycomb iridates alpha-Li2IrO3 and Na2IrO3.
+We observe a broad continuum of magnetic excitations that persists up to at
+least 300K, more than an order of magnitude larger than the magnetic ordering
+temperatures. We prove the magnetic character of this continuum by an analysis
+of the resonance behavior. RIXS measurements of the dynamical structure factor
+for energies within the continuum show that dynamical spin-spin correlations
+are restricted to nearest neighbors. Notably, these spectroscopic observations
+are also present in the magnetically ordered state for excitation energies
+above the conventional magnon excitations. Phenomenologically, our data agree
+with inelastic neutron scattering results on the related honeycomb compound
+RuCl3, establishing a common ground for a proximate Kitaev spin-liquid regime
+in these materials.",1905.13590v1
+2020-05-30,Magnetization dynamics in proximity-coupled superconductor/ferromagnet/superconductor multilayers,"In this work, magnetization dynamics is studied in
+superconductor/ferromagnet/superconductor three-layered films in a wide
+frequency, field, and temperature ranges using the broad-band ferromagnetic
+resonance measurement technique. It is shown that in presence of both
+superconducting layers and of superconducting proximity at both
+superconductor/ferromagnet interfaces a massive shift of the ferromagnetic
+resonance to higher frequencies emerges. The phenomenon is robust and
+essentially long-range: it has been observed for a set of samples with the
+thickness of ferromagnetic layer in the range from tens up to hundreds of
+nanometers. The resonance frequency shift is characterized by proximity-induced
+magnetic anisotropies: by the positive in-plane uniaxial anisotropy and by the
+drop of magnetization. The shift and the corresponding uniaxial anisotropy grow
+with the thickness of the ferromagnetic layer. For instance, the anisotropy
+reaches 0.27~T in experiment for a sample with 350~nm thick ferromagnetic
+layer, and about 0.4~T in predictions, which makes it a ferromagnetic film
+structure with the highest anisotropy and the highest natural resonance
+frequency ever reported. Various scenarios for the superconductivity-induced
+magnetic anisotropy are discussed. As a result, the origin of the phenomenon
+remains unclear. Application of the proximity-induced anisotropies in
+superconducting magnonics is proposed as a way for manipulations with a
+spin-wave spectrum.",2006.00348v1
+2020-06-05,2D ferromagnetism at finite temperatures under quantum scrutiny,"Recent years have seen a tremendous rise of two-dimensional (2D) magnetic
+materials, several of which verified experimentally. However, most of the
+theoretical predictions to date rely on ab-initio methods, at zero temperature
+and fluctuations-free, while one certainly expects detrimental quantum
+fluctuations at finite temperatures. Here we present the solution of the
+quantum Heisenberg model for honeycomb/hexagonal lattices with anisotropic
+exchange interaction up to third nearest neighbors and in an applied field in
+arbitrary direction, that answers the question whether long-range magnetization
+can indeed survive in the ultrathin limit of materials, up to which
+temperature, and what the characteristic excitation (magnon) frequencies are,
+all essential to envisaged applications of magnetic 2D materials. We find that
+long-range magnetic order persists at finite temperature for materials with
+overall easy-axis anisotropy. We validate the calculations on the examples of
+monolayer CrI3, CrBr3 and MnSe2. Moreover, we provide an easy-to-use tool to
+calculate Curie temperatures of new 2D computational materials.",2006.03287v2
+2020-06-08,Higher-order exchange interactions in two-dimensional magnets,"Magnetism in recently discovered van der Waals materials has opened new
+avenues in the study of fundamental spin interactions in truly two-dimensions.
+A paramount question is what effect higher-order interactions beyond bilinear
+Heisenberg exchange have on the magnetic properties of few-atom thick
+compounds. Here we demonstrate that biquadratic exchange interactions, which is
+the simplest and most natural form of non-Heisenberg coupling, assume a key
+role in the magnetic properties of layered magnets. Using a combination of
+nonperturbative analytical techniques, non-collinear first-principles methods
+and classical Monte Carlo calculations that incorporate higher-order exchange,
+we show that several quantities including magnetic anisotropies, spin-wave gaps
+and topological spin-excitations are intrinsically renormalized leading to
+further thermal stability of the layers. We develop a spin Hamiltonian that
+also contains antisymmetric exchanges (e.g. Dzyaloshinskii-Moriya interactions)
+to successfully rationalize numerous observations currently under debate, such
+as the non-Ising character of several compounds despite a strong magnetic
+anisotropy, peculiarities of the magnon spectrum of 2D magnets, and the
+discrepancy between measured and calculated Curie temperatures. Our results lay
+the foundation of a universal higher-order exchange theory for novel 2D
+magnetic design strategies.",2006.04891v1
+2020-08-31,Electronic properties in itinerant ferromagnet SrRu$_{1-x}$Ti$_x$O$_3$,"Here, we study the electrical transport and specific heat in 4$d$ based
+ferromagnetic material SrRuO$_3$ and its Ti substituted SrRu$_{1-x}$Ti$_x$O$_3$
+series ($x$ $\le$ 0.7). The SrRuO$_3$ is a metal and shows itinerant
+ferromagnetism with transition temperature $T_c$ $\sim$ 160 K. The nonmagnetic
+Ti$^{4+}$ (3$d^0$) substitution would not only weaken the active Ru-O-Ru
+channel but is also expected to tune the electronic density and electron
+correlation effect. A metal to insulator transition has been observed around
+$x$ $\sim$ 0.4. The nature of charge transport in paramagnetic-metallic state
+($x$ $\leq$ 0.4) and in insulating state ($x$ $>$ 0.4) follows modified Mott's
+variable range hopping model. In ferromagnetic-metallic state, resistivity
+shows a $T^2$ dependence below $T_c$ which though modifies to $T^{3/2}$
+dependence at low temperature. In Ti substituted samples, temperature range for
+$T^{3/2}$ dependence extends to higher temperature. Interestingly, this
+$T^{3/2}$ dependence dominates in whole ferromagnetic regime in presence of
+magnetic field. This evolution of electronic transport behavior can be
+explained within the framework of Fermi liquid theory and electron-magnon
+scattering mechanism. The negative magnetoresistance exhibits a hysteresis and
+a crossover between negative and positive value with magnetic field which is
+connected with magnetic behavior in series. The decreasing electronic
+coefficient of specific heat with $x$ supports the increasing insulating
+behavior in present series. We calculate a high Kadowaki-Woods ratio ($x$
+$\leq$ 0.3) for SrRuO$_3$ which increases with substitution concentration. This
+signifies an increasing electronic correlation effect with substitution
+concentration.",2009.00076v1
+2020-09-01,Spin coherence on the ferromagnetic spherical surface,"Spintronics on flat surfaces has been studied over the years, and the
+scenario is relatively well-known; however, there is a lack of information when
+we consider non-flat surfaces. In this paper, we are concerned about the spin
+dynamics of the ferromagnetic model on the spherical surface. We use the
+Schwinger bosonic formalism for describing the thermodynamics of spin operators
+in terms of spinon operators. Opposite to the flat two-dimensional model, which
+is disordered at finite temperature, the curvature of the spherical surface
+provides non-zero critical temperature for Schwinger boson condensation, which
+characterizes order at finite temperature even in the absence of external
+magnetic fields. The thermodynamics is then analyzed in the low-temperature
+regime. In addition, we consider the presence of both static and oscillating
+magnetic fields, the necessary condition for inducing the ferromagnetic
+resonance, and we show systematically that the studied model is well-described
+by $SU(2)$ coherent states, which provides the correct dynamics of the
+magnetization. The archived results can be applied for describing a diversity
+of experiments such as spin superfluidity, angular momentum injection by spin
+pumping and spin-transfer torque in non-conventional junctions, magnon
+dissipation, and magnetoelectronics on the spherical surface.",2009.00636v2
+2020-09-04,Experimental observation of the curvature-induced asymmetric spin-wave dispersion in hexagonal nanotubes,"Theoretical and numerical studies on curved magnetic nano-objects predict
+numerous exciting effects that can be referred to as magneto-chiral effects,
+which do not originate from the intrinsic Dzyaloshinskii-Moriya interaction or
+surface-induced anisotropies. The origin of these chiral effects is the
+isotropic exchange or the dipole-dipole interaction present in all magnetic
+materials but renormalized by the curvature. Here, we demonstrate
+experimentally that curvature induced effects originating from the
+dipole-dipole interaction are directly observable by measuring spin-wave
+propagation in magnetic nanotubes with hexagonal cross section using time
+resolved scanning transmission X-ray microscopy. We show that the dispersion
+relation is asymmetric upon reversal of the wave vector when the propagation
+direction is perpendicular to the static magnetization. Therefore
+counter-propagating spin waves of the same frequency exhibit different
+wavelenghts. Hexagonal nanotubes have a complex dispersion, resulting from
+spin-wave modes localised to the flat facets or to the extremely curved regions
+between the facets. The dispersion relations obtained experimentally and from
+micromagnetic simulations are in good agreement. %The asymmetric spin-wave
+transport is present for all modes, promoting hexagonal nanotubes for magnonic
+applications. These results show that spin-wave transport is possible in 3D,
+and that the dipole-dipole induced magneto-chiral effects are significant.",2009.02238v1
+2020-09-29,Structural Phase Dependent Giant Interfacial Spin Transparency in W/CoFeB Thin Film Heterostructure,"Pure spin current has transfigured the energy-efficient spintronic devices
+and it has the salient characteristic of transport of the spin angular
+momentum. Spin pumping is a potent method to generate pure spin current and for
+its increased efficiency high effective spin-mixing conductance (Geff) and
+interfacial spin transparency (T) are essential. Here, a giant T is reported in
+Sub/W(t)/Co20Fe60B20(d)/SiO2(2 nm) heterostructures in \beta-tungsten (\beta-W)
+phase by employing all-optical time-resolved magneto-optical Kerr effect
+technique. From the variation of Gilbert damping with W and CoFeB thicknesses,
+the spin diffusion length of W and spin-mixing conductances are extracted.
+Subsequently, T is derived as 0.81 \pm 0.03 for the \beta-W/CoFeB interface. A
+sharp variation of Geff and T with W thickness is observed in consonance with
+the thickness-dependent structural phase transition and resistivity of W. The
+spin memory loss and two-magnon scattering effects are found to have negligible
+contributions to damping modulation as opposed to spin pumping effect which is
+reconfirmed from the invariance of damping with Cu spacer layer thickness
+inserted between W and CoFeB. The observation of giant interfacial spin
+transparency and its strong dependence on crystal structures of W will be
+important for pure spin current based spin-orbitronic devices.",2009.14143v1
+2021-02-14,Unusual exchange couplings and intermediate temperature Weyl state in Co3Sn2S2,"Understanding the magnetism and its possible correlations to the topological
+properties has emerged as a forefront and difficult topic in studying magnetic
+Weyl semimetals. Co$_{3}$Sn$_{2}$S$_{2}$ is a newly discovered magnetic Weyl
+semimetal with a kagome lattice of cobalt ions and has triggered intense
+interest for rich fantastic phenomena. Here, we report the magnetic exchange
+couplings of Co$_{3}$Sn$_{2}$S$_{2}$ using inelastic neutron scattering and two
+density functional theory (DFT) based methods: constrained magnetism and
+multiple-scattering Green's function methods. Co$_{3}$Sn$_{2}$S$_{2}$ exhibits
+highly anisotropic magnon dispersions and linewidths below $T_{C}$, and
+paramagnetic excitations above $T_{C}$. The spin-wave spectra in the
+ferromagnetic ground state is well described by the dominant third-neighbor
+""across-hexagon"" $J_{d}$ model. Our density functional theory calculations
+reveal that both the symmetry-allowed 120$^\circ$ antiferromagnetic orders
+support Weyl points in the intermediate temperature region, with distinct
+numbers and the locations of Weyl points. Our study highlights the important
+role Co$_{3}$Sn$_{2}$S$_{2}$ can play in advancing our understanding of kagome
+physics and exploring the interplay between magnetism and band topology.",2102.07050v2
+2013-06-11,Bethe ansatz description of edge-localization in the open-boundary XXZ spin chain,"At large values of the anisotropy \Delta, the open-boundary Heisenberg
+spin-1/2 chain has eigenstates displaying localization at the edges. We present
+a Bethe ansatz description of this `edge-locking' phenomenon in the entire
+\Delta>1 region. We focus on the simplest spin sectors, namely the highly
+polarized sectors with only one or two overturned spins, i.e., one-particle and
+two-particle sectors. Edge-locking is associated with pure imaginary solutions
+of the Bethe equations, which are not commonly encountered in periodic chains.
+In the one-particle case, at large anisotropies there are two eigenstates with
+imaginary Bethe momenta, related to localization at the two edges. For any
+finite chain size, one of the two solutions become real as the anisotropy is
+lowered below a certain value. For two particles, a richer scenario is
+observed, with eigenstates having the possibility of both particles locked on
+the same or different edge, one locked and the other free, and both free either
+as single magnons or as bound composites corresponding to `string' solutions.
+For finite chains, some of the edge-locked spins get delocalized at certain
+values of the anisotropy (`exceptional points'), corresponding to imaginary
+solutions becoming real. We characterize these phenomena thoroughly by
+providing analytic expansions of the Bethe momenta for large chains, large
+anisotropy, and near the exceptional points. In the large-chain limit all the
+exceptional points coalesce at the isotropic point (\Delta=1) and edge-locking
+becomes stable in the whole \Delta>1 region.",1306.2666v3
+2015-07-04,Spiral magnets with Dzyaloshinskii-Moriya interaction containing defect bonds,"We present a theory describing spiral magnets with Dzyaloshinskii-Moriya
+interaction (DMI) subject to bond disorder at small concentration $c$ of
+defects. It is assumed that both DMI and exchange coupling are changed on
+imperfect bonds. Qualitatively the same physical picture is obtained in two
+models which are considered in detail: B20 cubic helimagnets and layered
+magnets in which DMI leads to a long-period spiral ordering perpendicular to
+layers. We find that the distortion of the spiral magnetic ordering around a
+single imperfect bond is long-range: values of additional turns of spins decay
+with the distance $r$ to the defect as $1/r^2$ being governed by the Poisson's
+equation for electric dipole. At finite concentration of randomly distributed
+imperfect bonds, we calculate correction to the spiral vector. We show that
+this correction can change the sign of spin chirality even at $c\ll1$ if
+defects are strong enough. It is demonstrated that impurities lead to a diffuse
+elastic neutron scattering which has power-law singularities at magnetic Bragg
+peaks positions. Then, each Bragg peak acquires power-law decaying tails.
+Corrections are calculated to the magnon energy and to its damping caused by
+scattering on impurities.",1507.01139v2
+2015-07-27,Physical and mathematical justification of the numerical Brillouin zone integration of the Boltzmann rate equation by Gaussian smearing,"Scatterings of electrons at quasiparticles or photons are very important for
+many topics in solid state physics, e.g., spintronics, magnonics or photonics,
+and therefore a correct numerical treatment of these scatterings is very
+important. For a quantum-mechanical description of these scatterings Fermi's
+golden rule is used in order to calculate the transition rate from an initial
+state to a final state in a first-order time-dependent perturbation theory. One
+can calculate the total transition rate from all initial states to all final
+states with Boltzmann rate equations involving Brillouin zone integrations. The
+numerical treatment of these integrations on a finite grid is often done via a
+replacement of the Dirac delta distribution by a Gaussian. The Dirac delta
+distribution appears in Fermi's golden rule where it describes the energy
+conservation among the interacting particles. Since the Dirac delta
+distribution is a not a function it is not clear from a mathematical point of
+view that this procedure is justified. We show with physical and mathematical
+arguments that this numerical procedure is in general correct, and we comment
+on critical points.",1507.07420v1
+2015-12-11,Ultra-low magnetic damping of a metallic ferromagnet,"The phenomenology of magnetic damping is of critical importance for devices
+that seek to exploit the electronic spin degree of freedom since damping
+strongly affects the energy required and speed at which a device can operate.
+However, theory has struggled to quantitatively predict the damping, even in
+common ferromagnetic materials. This presents a challenge for a broad range of
+applications in spintronics and spin-orbitronics that depend on materials and
+structures with ultra-low damping. Such systems enable many experimental
+investigations that further our theoretical understanding of numerous magnetic
+phenomena such as damping and spin-transport mediated by chirality and the
+Rashba effect. Despite this requirement, it is believed that achieving
+ultra-low damping in metallic ferromagnets is limited due to the scattering of
+magnons by the conduction electrons. However, we report on a binary alloy of Co
+and Fe that overcomes this obstacle and exhibits a damping parameter
+approaching 0.0001, which is comparable to values reported only for
+ferrimagnetic insulators. We explain this phenomenon by a unique feature of the
+bandstructure in this system: The density of states exhibits a sharp minimum at
+the Fermi level at the same alloy concentration at which the minimum in the
+magnetic damping is found. This discovery provides both a significant
+fundamental understanding of damping mechanisms as well as a test of
+theoretical predictions.",1512.03610v1
+2016-09-17,Influence of apical oxygen on the extent of in-plane exchange interaction in cuprate superconductors,"In high Tc superconductors the magnetic and electronic properties are
+determined by the probability that valence electrons virtually jump from site
+to site in the CuO2 planes, a mechanism opposed by on-site Coulomb repulsion
+and favored by hopping integrals. The spatial extent of the latter is related
+to transport properties, including superconductivity, and to the dispersion
+relation of spin excitations (magnons). Here, for three antiferromagnetic
+parent compounds (single-layer Bi2Sr0.99La1.1CuO6+delta, double-layer
+Nd1.2Ba1.8Cu3O6 and infinite-layer CaCuO2) differing by the number of apical
+atoms, we compare the magnetic spectra measured by resonant inelastic x-ray
+scattering over a significant portion of the reciprocal space and with
+unprecedented accuracy. We observe that the absence of apical oxygens increases
+the in-plane hopping range and, in CaCuO2, it leads to a genuine 3D
+exchange-bond network. These results establish a corresponding relation between
+the exchange interactions and the crystal structure, and provide fresh insight
+into the materials dependence of the superconducting transition temperature.",1609.05405v1
+2016-09-20,Magnetic anisotropy and the phase diagram of chiral MnSb2O6,"The magnetic phase diagram and low-energy magnon excitations of structurally
+and magnetically chiral MnSb2O6 are reported. The specific heat and the static
+magnetization are investigated in magnetic fields up to 9 and 30 T,
+respectively, while the dynamicmagnetic properties are probed by X-band as well
+as tunable high-frequency electron spin-resonance spectroscopy. Below TN = 11.5
+K, we observe antiferromagnetic resonance modes which imply small but finite
+planar anisotropy showing up in a zero-field splitting of 20 GHz. The data are
+well described by means of an easy-plane two-sublattice model with the
+anisotropy field BA = 0.02 T. The exchange field BE = 13 T is obtained from the
+saturation field derived from the pulsed-field magnetization. A crucial role of
+the small anisotropy for the spin structure is reflected by competing
+antiferromagnetic phases appearing, at T = 2 K, in small magnetic fields at BC1
+$\approx$ 0.5 T and BC2 = 0.9 T. We discuss the results in terms of spin
+reorientation and of small magnetic fields favoring helical spin structure over
+the cycloidal ground state which, at B = 0, is stabilized by the planar
+anisotropy. Above TN, short-range magnetic correlations up to >=60 K and
+magnetic entropy changes well above TN reflect the frustrated triangular
+arrangement of Mn2+ ions in MnSb2O6.",1609.06105v1
+2016-09-22,Magnetization oscillations and waves driven by pure spin currents,"Recent advances in the studies of pure spin currents - flows of angular
+momentum (spin) not accompanied by the electric currents - have opened new
+horizons for the emerging technologies based on the electron's spin degree of
+freedom, such as spintronics and magnonics. The main advantage of pure spin
+current, as compared to the spin-polarized electric current, is the possibility
+to exert spin transfer torque on the magnetization in thin magnetic films
+without electrical current flow through the material. In addition to minimizing
+Joule heating and electromigration effects, this characteristic enables the
+implementation of spin torque devices based on the low-loss insulating magnetic
+materials, and offers an unprecedented geometric flexibility. Here we review
+the recent experimental achievements in investigations of magnetization
+oscillations excited by pure spin currents in different magnetic nanosystems
+based on metallic and insulating magnetic materials. We discuss the spectral
+properties of spin-current nano-oscillators, and relate them to the spatial
+characteristics of the excited dynamic magnetic modes determined by the
+spatially-resolved measurements. We also show that these systems support
+locking of the oscillations to external microwave signals, as well as their
+mutual synchronization, and can be used as efficient nanoscale sources of
+propagating spin waves.",1609.06899v1
+2016-11-10,Magnetism and ultra-fast magnetization dynamics of Co and CoMn alloys at finite temperature,"Temperature-dependent magnetic experiments like pump-probe measurements
+generated by a pulsed laser have become a crucial technique for switching the
+magnetization in the picosecond time scale. Apart from having practical
+implications on the magnetic storage technology, the research field of
+ultrafast magnetization poses also fundamental physical questions. To correctly
+describe the time evolution of the atomic magnetic moments under the influence
+of a temperature-dependent laser pulse, it remains crucial to know if the
+magnetic material under investigation has magnetic excitation spectrum that is
+more or less dependent on the magnetic configuration, e.g. as reflected by the
+temperature dependence of the exchange interactions. In this article, we
+demonstrate from first-principles theory that the magnetic excitation spectra
+in Co with fcc, bcc and hcp structures are nearly identical in a wide range of
+non-collinear magnetic configurations. This is a curious result of a balance
+between the size of the magnetic moments and the strength of the Heisenberg
+exchange interactions, that in themselves vary with configuration, but put
+together in an effective spin Hamiltonian results in a configuration
+independent effective model. We have used such a Hamiltonian, together with
+ab-initio calculated damping parameters, to investigate the magnon dispersion
+relationship as well as the ultrafast magnetisation dynamics of Co and Co-rich
+CoMn alloys.",1611.03541v2
+2017-04-10,Tunable mode coupling in nano-contact spin torque oscillators,"Recent experiments on spin torque oscillators have revealed interactions
+between multiple magnetodynamic modes, including mode-coexistence,
+mode-hopping, and temperature-driven cross-over between modes. Initial
+multimode theory has indicated that a linear coupling between several dominant
+modes, arising from the interaction of the subdynamic system with a magnon
+bath, plays an essential role in the generation of various multimode behaviors,
+such as mode hopping and mode coexistence. In this work, we derive a set of
+rate equations to describe the dynamics of coupled magnetodynamic modes in a
+nano-contact spin torque oscillator. Expressions for both linear and nonlinear
+coupling terms are obtained, which allow us to analyze the dependence of the
+coupled dynamic behaviors of modes on external experimental conditions as well
+as intrinsic magnetic properties. For a minimal two-mode system, we further map
+the energy and phase difference of the two modes onto a two-dimensional phase
+space, and demonstrate in the phase portraits, how the manifolds of periodic
+orbits and fixed points vary with external magnetic field as well as with
+temperature.",1704.03076v2
+2017-04-20,Coupled mode theory for the acoustic wave and spin wave interaction in the magphonic crystals: Propagating magnetoelastic waves,"We have investigated co-directional and contra-directional couplings between
+spin wave and acoustic wave in one-dimensional periodic structure (magphonic
+crystal). The system consists of two ferromagnetic layers alternating in space.
+We have taken into consideration materials commonly used in magnonics: yttrium
+iron garnet, CoFeB, permalloy, and cobalt. The coupled mode theory (CMT)
+formalism have been successfully implemented to describe magnetoelastic
+interaction as a periodic perturbation in the magphonic crystal. The results of
+CMT calculations have been verified by more rigorous simulations by
+frequency-domain plane wave method and time-domain finite element method. The
+presented resonant coupling in the magphonic crystal is an active in-space
+mechanism which spatially transfers energy between propagating spin and
+acoustic modes, thus creating propagating magnetoelastic wave. We have shown,
+that CMT analysis of the magnetoelastic coupling is an useful tool to optimize
+and design a spin wave - acoustic wave transducer based on a magphonic
+crystals. The effect of spin wave damping has been included to the model to
+discuss the efficiency of such a device. Our model shows that it is possible to
+obtain forward conversion of the acoustic wave to the spin wave in case of
+co-directional coupling and backward conversion in case of contra-directional
+coupling.",1704.06118v1
+2017-04-24,Antiferromagnetic resonance and terahertz continuum in $α-$RuCl$_3$,"We report measurements of optical absorption in the zig-zag antiferromagnet
+$\alpha$-RuCl$_3$ as a function of temperature, $T$, magnetic field, $B$, and
+photon energy, $\hbar\omega$ in the range $\sim$ 0.3 to 8.3 meV, using
+time-domain terahertz spectroscopy. Polarized measurements show that 3-fold
+rotational symmetry is broken in the honeycomb plane from 2 K to 300 K. We find
+a sharp absorption peak at 2.56 meV upon cooling below the N\'eel temperature
+of 7 K at $B=0$ that we identify as magnetic-dipole excitation of a
+zero-wavevector magnon, or antiferromagnetic resonance (AFMR). With application
+of $B$, the AFMR broadens and shifts to lower frequency as long-range magnetic
+order is lost in a manner consistent with transitioning to a spin-disordered
+phase. From direct, internally calibrated measurement of the AFMR spectral
+weight, we place an upper bound on the contribution to the $dc$ susceptibility
+from a magnetic excitation continuum.",1704.07357v3
+2018-01-03,Magnetic structure and excitation spectrum of the hyperhoneycomb Kitaev magnet $β$-Li$_2$IrO$_3$,"We present a theoretical study of the static and dynamical properties of the
+Kitaev magnet $\beta$-Li$_2$IrO$_3$ based on the minimal $J$-$K$-$\Gamma$
+model. We argue that the incommensurate magnetic order of $\beta$-Li$_2$IrO$_3$
+can be qualitatively understood in terms of a long-wavelength twisting of a
+nearby commensurate, period-3 state, that shares the same symmetry, propagation
+vector, counter-rotation of the two spin sublattices, and non-coplanarity. This
+period-3 state shows very different structure when either the Kitaev
+interaction $K$ or the off-diagonal exchange anisotropy $\Gamma$ is dominant,
+featuring in particular ferromagnetic or antiferromagnetic spin dimers,
+respectively. We compute the magnon excitation spectra and the dynamical spin
+structure factor for both structures. The results for the momentum and energy
+dependence of the neutron-scattering intensity provide distinctive qualitative
+and quantitative fingerprints of the $K$-dominant or $\Gamma$-dominant states
+and thus gives additional information on the relative strength of these
+interactions in $\beta$-Li$_2$IrO$_3$.",1801.00874v3
+2018-01-13,Lattice-Mediated Magnetic Order Melting in TbMnO3,"Recent ultrafast magnetic-sensitive measurements [Phys. Rev. B 92, 184429
+(2015) and Phys. Rev. B 96, 184414 (2017)] have revealed a delayed melting of
+the long-range cycloid spin-order in TbMnO$_3$ following photoexcitation across
+the fundamental Mott-Hubbard gap. The microscopic mechanism behind this slow
+transfer of energy from the photoexcited carriers to the spin degrees of
+freedom is still elusive and not understood. Here, we address this problem by
+combining spectroscopic ellipsometry, ultrafast broadband optical spectroscopy
+and ab initio calculations. Upon photoexcitation, we observe the emergence of a
+complex collective response, which is due to high-energy coherent optical
+phonons coupled to the out-of-equilibrium charge density. This response
+precedes the magnetic order melting and is interpreted as the fingerprint of
+the formation of anti-Jahn Teller polarons. We propose that the charge
+localization in a long-lived self-trapped state hinders the emission of magnons
+and other spin-flip mechanisms, causing the energy transfer from the charge to
+the spin system to be mediated by the reorganization of the lattice.
+Furthermore, we provide evidence for the coherent excitation of a phonon mode
+associated with the ferroelectric phase transition.",1801.04368v1
+2018-01-16,Spin-orbit-torque and magnetic damping in tailored ferromagnetic bilayers,"We study spin-orbit-torque-driven ferromagnetic resonance (FMR) in
+ferromagnetic (FM) bilayers, consisting of Co and permalloy (Py), sandwiched
+between Pt and MgO layers. We find that the FM layer in contact with the Pt
+layers dominantly determines that spin Hall angle, which is consistent with the
+spin-transparency model. By contrast, the FMR linewidths are considerably
+influenced not only by the spin-pumping effect across the Pt|FM in terface but
+also by the spin relaxation such as two-magnon scattering at the FMMgO
+interface.The CoMgO interface leads to notably increased FMR linewidths, while
+the Py|MgO interface has less effect. This different contribution of each
+interface to the spin Hall angel and dissipation parameter suggests that the
+stack configuration of Pt|Co|Py|MgO requires less writing energy than
+Pt|Py|Co|MgO in spin-orbit-torque-driven magnetic switching. Our approach
+offers a promising method to optimize material parameters by engineering either
+interfaces in contact with the heavy-metal or the oxide layer.",1801.05131v2
+2018-08-04,The magnetic exchange parameters and anisotropy of the quasi-two dimensional antiferromagnet NiPS$_3$,"Neutron inelastic scattering has been used to measure the magnetic
+excitations in powdered NiPS$_3$, a quasi-two dimensional antiferromagnet with
+spin $S = 1$ on a honeycomb lattice. The spectra show clear, dispersive magnons
+with a $\sim 7$ meV gap at the Brillouin zone center. The data were fitted
+using a Heisenberg Hamiltonian with a single-ion anisotropy assuming no
+magnetic exchange between the honeycomb planes. Magnetic exchange interactions
+up to the third intraplanar nearest-neighbour were required. The fits show
+robustly that NiPS$_3$ has an easy axis anisotropy with $\Delta = 0.3$ meV and
+that the third nearest-neighbour has a strong antiferromagnetic exchange of
+$J_3 = -6.90$ meV. The data can be fitted reasonably well with either $J_1 < 0$
+or $J_1 > 0$, however the best quantitative agreement with high-resolution data
+indicate that the nearest-neighbour interaction is ferromagnetic with $J_1 =
+1.9$ meV and that the second nearest-neighbour exchange is small and
+antiferromagnetic with $J_2 = -0.1$ meV. The dispersion has a minimum in the
+Brillouin zone corner that is slightly larger than that at the Brillouin zone
+center, indicating that the magnetic structure of NiPS$_3$ is close to being
+unstable.",1808.01480v1
+2018-08-05,"Dispersion, damping, and intensity of spin excitations in the single-layer (Bi,Pb)$_{2}$(Sr,La)$_{2}$CuO$_{6+δ}$ cuprate superconductor family","Using Cu-$L_3$ edge resonant inelastic x-ray scattering (RIXS) we measured
+the dispersion and damping of spin excitations (magnons and paramagnons) in the
+high-$T_\mathrm{c}$ superconductor (Bi,Pb)$_{2}$(Sr,La)$_{2}$CuO$_{6+\delta}$
+(Bi2201), for a large doping range across the phase diagram ($0.03\lesssim
+p\lesssim0.21$). Selected measurements with full polarization analysis
+unambiguously demonstrate the spin-flip character of these excitations, even in
+the overdoped sample. We find that the undamped frequencies increase slightly
+with doping for all accessible momenta, while the damping grows rapidly, faster
+in the (0,0)$\rightarrow$(0.5,0.5) nodal direction than in the
+(0,0)$\rightarrow$(0.5,0) antinodal direction. We compare the experimental
+results to numerically exact determinant quantum Monte Carlo (DQMC)
+calculations that provide the spin dynamical structure factor
+$S(\textbf{Q},\omega)$ of the three-band Hubbard model. The theory reproduces
+well the momentum and doping dependence of the dispersions and spectral weights
+of magnetic excitations. These results provide compelling evidence that
+paramagnons, although increasingly damped, persist across the superconducting
+dome of the cuprate phase diagram; this implies that long range
+antiferromagnetic correlations are quickly washed away, while short range
+magnetic interactions are little affected by doping.",1808.01682v1
+2018-08-13,Single crystal investigation of proposed type-II Weyl semimetal CeAlGe,"We present details of materials synthesis, crystal structure, and anisotropic
+magnetic properties of single crystals of CeAlGe, a proposed type-II Weyl
+semimetal. Single-crystal x-ray diffraction confirms that CeAlGe forms in
+noncentrosymmetric I4$_1$md space group, in line with predictions of
+non-trivial topology. Magnetization, specific heat and electrical transport
+measurements were used to confirm antiferromagnetic order below 5 K, with an
+estimated magnon excitation gap of $\Delta$ = 9.11 K from heat capacity and
+hole-like carrier density of 1.44 $\times$ 10$^{20}$ cm$^{-3}$ from Hall effect
+measurements. The easy magnetic axis is along the [100] crystallographic
+direction, indicating that the moment lies in the tetragonal $\it{ab}$-plane
+below 7 K. A spin-flop transition to less than 1 $\mu_B$/Ce is observed to
+occur below 30 kOe at 1.8 K in the $M(H)$ ($\bf{H}\|\bf{a}$) data. Small
+magnetic fields of 3 kOe and 30 kOe are sufficient to suppress magnetic order
+when applied along the $\it{a}$- and $\it{c}$-axes, respectively, resulting in
+a complex $\it{T-H}$ phase diagram for $\bf{H}\|\bf{a}$ and a simpler one for
+$\bf{H}\|\bf{c}$.",1808.04434v1
+2019-06-14,Tunneling Magnetoresistance and Spin-Dependent Diode Performance in Fully Epitaxial Magnetic Tunnel Junctions with Rock-salt Type ZnO/MgO,"We fabricate fully epitaxial Fe/ZnO/MgO/Fe magnetic tunnel junctions (MTJs)
+with a bilayer tunnel barrier, in which ZnO has a metastable rock-salt crystal
+structure. We observe a high magnetoresistance ratio up to 96% at room
+temperature (RT) and find that these MTJs have asymmetric current-voltage
+characteristics, and their rectifying performances are largely dependent on the
+magnetization alignments of the Fe electrodes. Diode responsibilities at a
+zero-bias voltage ($\beta_{0}$), which is an important performance index for
+harvesting applications, are observed up to 1.3 A/W at RT in the antiparallel
+alignment of the magnetizations while maintaining rather low resistance-area
+(RA) products (a few tens of k${\Omega\mu}$m$^2$). Even with the same top and
+bottom electrodes (Fe), the obtained $\beta_{0}$ values are comparable to those
+of reported high-performance tunnel diodes consisting of amorphous bilayer
+tunnel barriers with polycrystalline dissimilar electrodes. This strongly
+suggests that the epitaxial ZnO/MgO bilayer tunnel barrier is effective for
+enhancing the $\beta_{0}$ without significant increase in the RA. In addition,
+we demonstrate that a zero-bias anomaly in thetunnel conductance, which
+originates from the magnon excitations at the Fe/barrier interfaces, plays a
+crucial role in observed spin-dependent diode performance. The results indicate
+that a fully epitaxial MTJ with a bilayer tunnel barrier is a promising
+candidate to establish a high-performance high-frequency rectifying system.",1906.05981v1
+2019-06-18,Dynamical and thermal magnetic properties of the Kitaev spin liquid candidate $α$-RuCl$_3$,"What is the correct low-energy spin Hamiltonian description of
+$\alpha$-RuCl$_3$? The material is a promising Kitaev spin liquid candidate,
+but is also known to order magnetically, the description of which necessitates
+additional interaction terms. The nature of these interactions, their
+magnitudes and even signs, remain an open question. In this work we
+systematically investigate dynamical and thermodynamic magnetic properties of
+proposed effective Hamiltonians. We calculate zero-temperature inelastic
+neutron scattering (INS) intensities using exact diagonalization, and magnetic
+specific heat using a thermal pure quantum states method. We find that no
+single current model satisfactorily explains all observed phenomena of
+$\alpha$-RuCl$_3$. In particular, we find that Hamiltonians derived from first
+principles can capture the experimentally observed high-temperature peak in the
+magnetic specific heat, while overestimating the magnon energy at the zone
+center. In contrast, other models reproduce important features of the INS data,
+but do not adequately describe the magnetic specific heat. To address this
+discrepancy we propose a modified ab initio model that is consistent with both
+magnetic specific heat and low-energy features of INS data.",1906.07579v3
+2019-06-28,Lattice and magnetic dynamics in polar chiral incommensurate antiferromagnet Ni$_2$InSbO$_6$,"Complex systems with coexisting polarity, chirality and incommensurate
+magnetism are of great interest because they open new degrees of freedom in
+interaction between different subsystems and therefore they host a plethora of
+intriguing physical properties. Here we report on optical properties and
+lattice and spin dynamics of Ni$_2$InSbO$_6$ single crystals studied with the
+use of polarized optical microscopy and micro-Raman spectroscopy in the
+temperature range 10-300 K. Ni$_2$InSbO$_6$ crystallizes in a polar structure
+described by the noncentrosymmetric space group R3 and two types of structural
+domains were visualized due to natural optical activity of opposite chirality.
+Raman tensor elements of most A and E phonons along with their symmetry were
+determined. The manifestation of LO-TO splitting was observed for the A modes.
+By tracking the temperature dependencies of phonon frequencies the well
+pronounced spin-phonon interaction was observed for several modes below and
+above the N\'eel transition temperature TN = 76 K. In antiferromagnetic phase a
+wide excitation centred at 247 cm-1 was detected and assigned to the two-magnon
+mode and this value was used for estimating exchange parameters through linear
+spin-wave theory calculations.",1906.12327v1
+2019-07-05,Propagation length of antiferromagnetic magnons governed by domain configurations,"The compensated magnetic order and characteristic, terahertz frequencies of
+antiferromagnetic materials makes them promising candidates to develop a new
+class of robust, ultra-fast spintronic devices. The manipulation of
+antiferromagnetic spin-waves in thin films is anticipated to lead to new exotic
+phenomena such as spin-superfluidity, requiring an efficient propagation of
+spin-waves in thin films. However, the reported decay length in thin films has
+so far been limited to a few nanometers. In this work, we achieve efficient
+spin-wave propagation, over micrometer distances, in thin films of the
+insulating antiferromagnet hematite with large magnetic domains whilst
+evidencing much shorter attenuation lengths in multidomain thin films. Through
+transport and magnetic imaging, we conclude on the role of the magnetic domain
+structure and spin-wave scattering at domain walls to govern the transport. We
+manipulate the spin transport by tailoring the domain configuration through
+field cycle training. For the appropriate crystalline orientation, zero-field
+spin-transport is achieved across micrometers, as required for device
+integration.",1907.02751v2
+2019-10-07,Chiral spin-wave velocities induced by all-garnet interfacial Dzyaloshinskii-Moriya interaction in ultrathin yttrium iron garnet films,"Spin waves can probe the Dzyaloshinskii-Moriya interaction (DMI) which gives
+rise to topological spin textures, such as skyrmions. However, the DMI has not
+yet been reported in yttrium iron garnet (YIG) with arguably the lowest damping
+for spin waves. In this work, we experimentally evidence the interfacial DMI in
+a 7~nm-thick YIG film by measuring the nonreciprocal spin wave propagation in
+terms of frequency, amplitude and most importantly group velocities using all
+electrical spin-wave spectroscopy. The velocities of propagating spin waves
+show chirality among three vectors, i.e. the film normal direction, applied
+field and spin-wave wavevector. By measuring the asymmetric group velocities,
+we extract a DMI constant of 16~$\mu$J/m$^{2}$ which we independently confirm
+by Brillouin light scattering. Thickness-dependent measurements reveal that the
+DMI originates from the oxide interface between the YIG and garnet substrate.
+The interfacial DMI discovered in the ultrathin YIG films is of key importance
+for functional chiral magnonics as ultra-low spin-wave damping can be achieved.",1910.02599v2
+2019-10-29,Origin of the Magnetic Spin Hall Effect: Spin Current Vorticity in the Fermi Sea,"The interplay of spin-orbit coupling (SOC) and magnetism gives rise to a
+plethora of charge-to-spin conversion phenomena that harbor great potential for
+spintronics applications. In addition to the spin Hall effect, magnets may
+exhibit a magnetic spin Hall effect (MSHE), as was recently discovered [Kimata
+\textit{et al.}, Nature \textbf{565}, 627-630 (2019)]. To date, the MSHE is
+still awaiting its intuitive explanation. Here we relate the MSHE to the
+vorticity of spin currents in the Fermi sea, which explains pictorially the
+origin of the MSHE. For all magnetic Laue groups that allow for nonzero spin
+current vorticities the related tensor elements of the MSH conductivity are
+given. Minimal requirements for the occurrence of a MSHE are compatibility with
+either a magnetization or a magnetic toroidal quadrupole. This finding implies
+in particular that the MSHE is expected in all ferromagnets with sufficiently
+large SOC. To substantiate our symmetry analysis, we present various models, in
+particular a two-dimensional magnetized Rashba electron gas, that corroborate
+an interpretation by means of spin current vortices. Considering thermally
+induced spin transport and the magnetic spin Nernst effect in magnetic
+insulators, which are brought about by magnons, our findings for electron
+transport can be carried over to the realm of spincaloritronics, heat-to-spin
+conversion, and energy harvesting.",1910.13375v1
+2020-01-15,Analog spacetimes from nonrelativistic Goldstone modes in spinor condensates,"It is well established that linear dispersive modes in a flowing quantum
+fluid behave as though they are coupled to an Einstein-Hilbert metric and
+exhibit a host of phenomena coming from quantum field theory in curved space,
+including Hawking radiation. We extend this analogy to any nonrelativistic
+Goldstone mode in a flowing spinor Bose-Einstein condensate. In addition to
+showing the linear dispersive result for all such modes, we show that the
+quadratically dispersive modes couple to a special nonrelativistic spacetime
+called a Newton-Cartan geometry. The kind of spacetime (Einstein-Hilbert or
+Newton-Cartan) is intimately linked to the mean-field phase of the condensate.
+To illustrate the general result, we further provide the specific theory in the
+context of a pseudo-spin-1/2 condensate where we can tune between relativistic
+and nonrelativistic geometries. We uncover the fate of Hawking radiation upon
+such a transition: it vanishes and remains absent in the Newton-Cartan geometry
+despite the fact that any fluid flow creates a horizon for certain wave
+numbers. Finally, we use the coupling to different spacetimes to compute and
+relate various energy and momentum currents in these analog systems. While this
+result is general, present day experiments can realize these different
+spacetimes including the magnon modes for spin-1 condensates such as $^{87}$Rb,
+$^{7}$Li, $^{41}$K (Newton-Cartan), and $^{23}$Na (Einstein-Hilbert).",2001.05496v2
+2020-01-24,Axion search with a quantum-limited ferromagnetic haloscope,"A ferromagnetic axion haloscope searches for Dark Matter in the form of
+axions by exploiting their interaction with electronic spins. It is composed of
+an axion-to-electromagnetic field transducer coupled to a sensitive rf
+detector. The former is a photon-magnon hybrid system, and the latter is based
+on a quantum-limited Josephson parametric amplifier. The hybrid system consists
+of ten 2.1 mm diameter YIG spheres coupled to a single microwave cavity mode by
+means of a static magnetic field. Our setup is the most sensitive rf
+spin-magnetometer ever realized. The minimum detectable field is
+$5.5\times10^{-19}\,$T with 9 h integration time, corresponding to a limit on
+the axion-electron coupling constant $g_{aee}\le1.7\times10^{-11}$ at 95% CL.
+The scientific run of our haloscope resulted in the best limit on DM-axions to
+electron coupling constant in a frequency span of about 120 MHz, corresponding
+to the axion mass range $42.4$-$43.1\,\mu$eV. This is also the first apparatus
+to perform an axion mass scanning by changing the static magnetic field.",2001.08940v1
+2020-02-25,Strain-Tuned Magnetic Anisotropy in Sputtered Thulium Iron Garnet Ultrathin Films and TIG/Au/TIG Valve Structures,"Defining the magnetic anisotropy for in-plane or out-of-plane easy axis in
+ferrimagnetic insulators films by controlling the strain, while maintaining
+high-quality surfaces, is desirable for spintronic and magnonic applications.
+We investigate ways to tune the anisotropy of amorphous sputtered ultrathin
+thulium iron garnet (TIG) films, and thus tailor their magnetic properties by
+the thickness (7.5 to 60 nm), substrate choice (GGG and SGGG), and
+crystallization process. We correlate morphological and structural properties
+with the magnetic anisotropy of post-growth annealed films. 30 nm thick films
+annealed at 600 {\deg}C show compressive strain favoring an in-plane magnetic
+anisotropy (IPMA), whereas films annealed above 800 {\deg}C are under a tensile
+strain leading to a perpendicular magnetic anisotropy (PMA). Air-annealed films
+present a high degree of crystallinity and magnetization saturation close to
+the bulk value. These results lead to successful fabrication of trilayers
+TIG/Au/TIG, with coupling between the TIG layers depending on Au thickness.
+These results will facilitate the use of TIG to create various in situ clean
+hybrid structures for fundamental interface exchange studies, and towards the
+development of complex devices. Moreover, the sputtering technique is
+advantageous as it can be easily scaled up for industrial applications.",2002.10608v2
+2020-02-26,Exceeding the Landau superflow speed limit with topological Bogoliubov Fermi surfaces,"A common property of topological systems is the appearance of topologically
+protected zero-energy excitations. In a superconductor or superfluid such
+states set the critical velocity of dissipationless flow $v_{\mathrm{cL}}$,
+proposed by Landau, to zero. We check experimentally whether stable superflow
+is nevertheless possible in the polar phase of p-wave superfluid $^3$He, which
+features a Dirac node line in the energy spectrum of Bogoliubov quasiparticles.
+The fluid is driven by rotation of the whole cryostat, and superflow breakdown
+is seen as the appearance of single- or half-quantum vortices. Vortices are
+detected using the relaxation rate of a Bose-Einstein condensate of magnons,
+created within the fluid. The superflow in the polar phase is found to be
+stable up to a finite critical velocity $v_{\rm c}\approx 0.2\,$cm/s, despite
+the zero value of the Landau critical velocity. We suggest that the stability
+of the superflow above $v_{\mathrm{cL}}$ but below $v_{\rm c}$ is provided by
+the accumulation of the flow-induced quasiparticles into pockets in the
+momentum space, bounded by Bogoliubov Fermi surfaces. In the polar phase this
+surface has non-trivial topology which includes two pseudo-Weyl points.
+Vortices forming above the critical velocity are strongly pinned in the
+confining matrix, used to stabilize the polar phase, and hence stable
+macroscopic superflow can be maintained even when the external drive is brought
+to zero.",2002.11492v2
+2020-03-17,Electrical generation and detection of terahertz signal based on spin-wave emission from ferrimagnets,"Terahertz (THz) signals, mainly generated by photonic or electronic
+approaches, are being sought for various applications, whereas the development
+of magnetic source might be a necessary step to harness the magnetic nature of
+electromagnetic radiation. We show that the relativistic effect on the
+current-driven domain-wall motion induces THz spin-wave emission in
+ferrimagnets. The required current density increases dramatically in materials
+with strong exchange interaction and rapidly exceeds 1012 A m-2, leading to the
+device breakdown and thus the lack of experimental evidence. By translating the
+collective magnetization oscillations into voltage signals, we propose a
+three-terminal device for the electrical detection of THz spin wave. Through
+material engineering, wide frequency range from 264 GHz to 1.1 THz and uniform
+continuous signals with improved output power can be obtained. As a reverse
+effect, the spin wave generated in this system is able to move ferrimagnetic
+domain wall. Our work provides guidelines for the experimental verification of
+THz spin wave, and could stimulate the design of THz spintronic oscillators for
+wideband applications as well as the all-magnon spintronic devices.",2003.07750v1
+2020-04-12,Hybridized quadrupolar excitations in the spin-anisotropic frustrated magnet FeI2,"Magnetic order is usually associated with well-defined magnon excitations.
+Exotic magnetic fluctuations with fractional, topological or multipolar
+character, have been proposed for radically different forms of magnetic matter
+such as spin-liquids. As a result, considerable efforts have searched for, and
+uncovered, low-spin materials with suppressed dipolar order at low
+temperatures. Here, we report neutron-scattering experiments and quantitative
+theoretical modeling of an exceptional spin-1 system -- the uniaxial triangular
+magnet FeI2 -- where a bright and dispersive band of mixed dipolar-quadrupolar
+fluctuations emerges just above a dipolar ordered ground-state. This excitation
+arises from anisotropic exchange interactions that hybridize overlapping modes
+carrying fundamentally different quantum numbers. Remarkably, a generalization
+of spin-wave theory to local SU(3) degrees of freedom accounts for all details
+of the low-energy dynamical response of FeI2 without going beyond quadratic
+order. Our work highlights that quantum excitations without classical
+counterparts can be realized even in presence of fully developed magnetic
+order.",2004.05623v1
+2020-04-22,Rethinking $α$-RuCl$_3$,"We argue that several empirical constraints strongly restrict parameters of
+the effective microscopic spin model describing $\alpha$-RuCl$_3$. In
+particular, such constraints dictate a substantial \emph{positive} off-diagonal
+anisotropic coupling, $\Gamma^\prime\!>\!0$, not anticipated previously. The
+renormalization by quantum fluctuations allows to reconcile larger values of
+the advocated bare parameters with their earlier assessments and provides a
+consistent description of the field evolution of spin excitations in the
+paramagnetic phase. We assert that large anisotropic terms inevitably result in
+strong anharmonic coupling of magnons, necessarily leading to broad features in
+their spectra due to decays, in accord with the observations in
+$\alpha$-RuCl$_3$. Using duality transformations, we explain the origin of the
+pseudo-Goldstone mode that is ubiquitous to the studied parameter space and is
+present in $\alpha$-RuCl$_3$. Our analysis offers a description of
+$\alpha$-RuCl$_3$ as an easy-plane ferromagnet with antiferromagnetic
+further-neighbor and strong off-diagonal couplings, which is in a fluctuating
+zigzag ground state proximate to an incommensurate phase that is continuously
+connected to a ferromagnetic one.",2004.10753v4
+2020-05-05,Dimensional crossover in spin Hall oscillators,"Auto-oscillations of magnetization driven by direct spin current have been
+previously observed in multiple quasi-zero-dimensional (0D) ferromagnetic
+systems such as nanomagnets and nanocontacts. Recently, it was shown that pure
+spin Hall current can excite coherent auto-oscillatory dynamics in
+quasi-one-dimensional (1D) ferromagnetic nanowires but not in
+quasi-two-dimensional (2D) ferromagnetic films. Here we study the 1D to 2D
+dimensional crossover of current-driven magnetization dynamics in wire-based
+Pt/$\mathrm{Ni}_{80}\mathrm{Fe}_{20}$ bilayer spin Hall oscillators via varying
+the wire width. We find that increasing the wire width results in an increase
+of the number of excited auto-oscillatory modes accompanied by a decrease of
+the amplitude and coherence of each mode. We also observe a crossover from a
+hard to a soft onset of the auto-oscillations with increasing the wire width.
+The amplitude of auto-oscillations rapidly decreases with increasing
+temperature suggesting that interactions of the phase-coherent auto-oscillatory
+modes with incoherent thermal magnons plays an important role in suppression of
+the auto-oscillatory dynamics. Our measurements set the upper limit on the
+dimensions of an individual spin Hall oscillator and elucidate the mechanisms
+leading to suppression of coherent auto-oscillations with increasing oscillator
+size.",2005.01925v2
+2020-05-07,Spin caloritronics in a CrBr$_3$-based magnetic van der Waals heterostructure,"The recently reported magnetic ordering in insulating two-dimensional (2D)
+materials, such as chromium triiodide (CrI$_3$) and chromium tribromide
+(CrBr$_3$), opens new possibilities for the fabrication of magneto-electronic
+devices based on 2D systems. Inevitably, the magnetization and spin dynamics in
+2D magnets are strongly linked to Joule heating. Therefore, understanding the
+coupling between spin, charge and heat, i.e. spin caloritronic effects, is
+crucial. However, spin caloritronics in 2D ferromagnets remains mostly
+unexplored, due to their instability in air. Here we develop a fabrication
+method that integrates spin-active contacts with 2D magnets through hBN
+encapsulation, allowing us to explore the spin caloritronic effects in these
+materials. The angular dependence of the thermal spin signal of the CrBr$_3$/Pt
+system is studied, for different conditions of magnetic field and heating
+current. We highlight the presence of a significant magnetic proximity effect
+from CrBr$_3$ on Pt revealed by an anomalous Nernst effect in Pt, and suggest
+the contribution of the spin Seebeck effect from CrBr$_3$. These results pave
+the way for future magnonic devices using air-sensitive 2D magnetic insulators.",2005.03561v1
+2020-05-08,Sublattice magnetizations of ultrathin ferrimagnetic lamellar nanostructures between cobalt leads,"In this work we model the salient magnetic properties of the alloy lamellar
+ferrimagnetic nanostructures
+$[Co_{1-c}Gd_c]_{\ell^{\prime}}[Co]_\ell[Co_{1-c}Gd_c]_{\ell^{\prime}}$ between
+$Co$ semi-infinite leads. We have employed the Ising spin effective field
+theory (EFT) to compute the reliable magnetic exchange constants for the pure
+cobalt $J_{Co-Co}$ and gadolinium $J_{Gd-Gd}$ materials, in complete agreement
+with their experimental data. The sublattice magnetizations of the $Co$ and
+$Gd$ sites on the individual hcp atomic (0001) planes of the $Co-Gd$ layered
+nanostructures are computed for each plane and corresponding sites, by using
+the combined EFT and mean field theory (MFT) spin methods. The sublattice
+magnetizations, effective site magnetic moments, and ferrimagnetic compensation
+characteristics for the individual hcp atomic planes of the embedded
+nanostructures, are computed as a function of temperature, and for various
+stable eutectic concentrations in the range $c\leq$ 0.5. The theoretical
+results for the sublattice magnetizations and the local magnetic variables of
+these ultrathin ferrimagnetic lamellar nanostructured systems, between cobalt
+leads, are necessary for the study of their magnonic transport properties, and
+eventually their spintronic dynamic computations. The method developed in this
+work is general and can be applied to comparable magnetic systems
+nanostructured with other materials.",2005.03965v3
+2020-05-18,Nature of the spin resonance mode in CeCoIn$_5$,"Spin-fluctuation-mediated unconventional superconductivity can emerge at the
+border of magnetism, featuring a superconducting order parameter that changes
+sign in momentum space. Detection of such a sign-change is experimentally
+challenging, since most probes are not phase-sensitive. The observation of a
+spin resonance mode (SRM) from inelastic neutron scattering is often seen as
+strong phase-sensitive evidence for a sign-changing superconducting order
+parameter, by assuming the SRM is a spin-excitonic bound state. Here, we show
+that for the heavy fermion superconductor CeCoIn$_5$, its SRM defies
+expectations for a spin-excitonic bound state, and is not a manifestation of
+sign-changing superconductivity. Instead, the SRM in CeCoIn$_5$ likely arises
+from a reduction of damping to a magnon-like mode in the superconducting state,
+due to its proximity to magnetic quantum criticality. Our findings emphasize
+the need for more stringent tests of whether SRMs are spin-excitonic, when
+using their presence to evidence sign-changing superconductivity.",2005.08441v2
+2020-05-28,Anomalous planar Hall effect in a kagome ferromagnet,"The macroscopic signature for Weyl nodes so far has been the negative
+longitudinal magnetoresistance arising from the chiral anomaly. However,
+negative longitudinal magnetoresistance is not unique to chiral anomaly and can
+arise due to completely different mechanisms such as current jetting or in
+ferromagnetic systems due to the suppression of scattering with magnons.
+Therefore, a macroscopic effect that can be uniquely attributed to the presence
+of Weyl nodes is desirable. Here we show that the planar Hall effect could be a
+hallmark for Weyl nodes. We investigated the anisotropic magnetoresistance and
+planar Hall effect in Fe$_3$Sn$_2$, which has a kagome lattice and has been
+predicted to be a type II Weyl metal. We discover that the planar Hall effect
+contains a field antisymmetric contribution in addition to the ordinary field
+symmetric contribution. The field antisymmetric planar Hall effect has a 3-fold
+rotational symmetry, distinctively different from the symmetric planar Hall
+effect, but consistent with the 3-fold rotational degeneracy of the
+magnetization in Fe$_3$Sn$_2$. The temperature and field dependence of the
+antisymmetric planar Hall effect rules out an interpretation based on
+contribution from the anomalous Hall effect and is different from the symmetric
+planar Hall effect, pointing to a different origin. We attribute the
+antisymmetric planar Hall effect to the topological nature of Fe$_3$Sn$_2$ due
+to the presence of Weyl II nodes. Our finding offers a promising route for
+macroscopically probing Weyl systems.",2005.14237v1
+2020-07-02,Disorder-Free Localization and Many-Body Quantum Scars from Magnetic Frustration,"The concept of geometrical frustration has led to rich insights into
+condensed matter physics, especially as a mechansim to produce exotic low
+energy states of matter. Here we show that frustration provides a natural
+vehicle to generate models exhibiting anomalous thermalization of various types
+within high energy states. We consider three classes of non-integrable
+frustrated spin models: (I) systems with local conserved quantities where the
+number of symmetry sectors grows exponentially with the system size but more
+slowly than the Hilbert space dimension, (II) systems with exact eigenstates
+that are singlet coverings, and (III) flat band systems hosting magnon
+crystals. We argue that several 1D and 2D models from class (I) exhibit
+disorder-free localization in high energy states so that information
+propagation is dynamically inhibited on length scales greater than a few
+lattice spacings. We further show that models of class (II) and (III) exhibit
+quantum many-body scars -- eigenstates of non-integrable Hamiltonians with
+finite energy density and anomalously low entanglement entropy. Our results
+demonstrate that magnetic frustration supplies a means to systematically
+construct classes of non-integrable models exhibiting anomalous thermalization
+in mid-spectrum states.",2007.01311v2
+2020-07-08,Order-by-Disorder from Bond-Dependent Exchange and Intensity Signature of Nodal Quasiparticles in a Honeycomb Cobaltate,"Recent theoretical proposals have argued that cobaltates with edge-sharing
+octahedral coordination can have significant bond-dependent exchange couplings
+thus offering a platform in 3$d$ ions for such physics beyond the much-explored
+realizations in 4$d$ and 5$d$ materials. Here we present high-resolution
+inelastic neutron scattering data within the magnetically ordered phase of the
+stacked honeycomb magnet CoTiO$_3$ revealing the presence of a finite energy
+gap and demonstrate that this implies the presence of bond-dependent
+anisotropic couplings. We also show through an extensive theoretical analysis
+that the gap further implies the existence of a quantum order-by-disorder
+mechanism that, in this material, crucially involves virtual crystal field
+fluctuations. Our data also provide an experimental observation of a universal
+winding of the scattering intensity in angular scans around linear
+band-touching points for both magnons and dispersive spin-orbit excitons, which
+is directly related to the non-trivial topology of the quasiparticle
+wavefunction in momentum space near nodal points.",2007.04199v2
+2020-07-23,Spin-waves in 2D honeycomb lattice $XXZ$-type van der Waals antiferromagnet CoPS$_3$,"The magnetic excitations in CoPS$_3$, a two-dimensional van der Waals (vdW)
+antiferromagnet with spin $S=3/2$ on a honeycomb lattice, has been measured
+using powder inelastic neutron scattering. Clear dispersive spin waves are
+observed with a large spin gap of ~13 meV. The magnon spectra were fitted using
+an $XXZ$-type $J_1-J_2-J_3$ Heisenberg Hamiltonian with a single-ion anisotropy
+assuming no magnetic exchange between the honeycomb layers. The best-fit
+parameters show ferromagnetic exchange $J_1=-2.08$ meV and $J_2=-0.26$ meV for
+the nearest and second-nearest neighbors and a sizeable antiferromagnetic
+exchange $J_3=4.21$ meV for the third-nearest neighbor with the strong
+easy-axis anisotropy $K=-2.06$ meV. The suitable fitting could only be achieved
+by the anisotropic $XXZ$-type Hamiltonian, in which the exchange interaction
+for the out-of-plane component is smaller than that for the in-plane one by a
+ratio $\alpha=J_z/J_x=0.6$. Moreover, the absence of spin-orbit exciton around
+30 meV indicates that Co$^{2+}$ ions in CoPS$_3$ have a $S=3/2$ state rather
+than a spin-orbital entangled $J_\rm{eff}=1/2$ ground state. Our result
+directly shows that CoPS$_3$ is an experimental realization of the $XXZ$ model
+with a honeycomb lattice in 2D vdW magnets.",2007.11791v1
+2020-08-11,Enhanced spin correlations in the Bose-Einstein condensate compound Sr3Cr2O8,"Combined experimental and modeling studies of the magnetocaloric effect,
+ultrasound, and magnetostriction were performed on single-crystal samples of
+the spin-dimer system Sr$_3$Cr$_2$O$_8$ in large magnetic fields, to probe the
+spin-correlated regime in the proximity of the field-induced XY-type
+antiferromagnetic order also referred to as a Bose-Einstein condensate of
+magnons. The magnetocaloric effect, measured under adiabatic conditions,
+reveals details of the field-temperature ($H,T$) phase diagram, a dome
+characterized by critical magnetic fields $H_{c1}$ = 30.4 T, $H_{c2}$ = 62 T,
+and a single maximum ordering temperature $T_{{\rm max}}(45~$T$)\simeq$8 K. The
+sample temperature was observed to drop significantly as the magnetic field is
+increased, even for initial temperatures above $T_{{\rm max}}$, indicating a
+significant magnetic entropy associated to the field-induced closure of the
+spin gap. The ultrasound and magnetostriction experiments probe the coupling
+between the lattice degrees of freedom and the magnetism in Sr$_3$Cr$_2$O$_8$.
+Our experimental results are qualitatively reproduced by a minimalistic
+phenomenological model of the exchange-striction by which sound waves
+renormalize the effective exchange couplings.",2008.04547v1
+2020-08-19,Strong Superexchange in a $d^{9-δ}$ Nickelate Revealed by Resonant Inelastic X-Ray Scattering,"The discovery of superconductivity in a $d^{9-{\delta}}$ nickelate has
+inspired disparate theoretical perspectives regarding the essential physics of
+this class of materials. A key issue is the magnitude of the magnetic
+superexchange, which relates to whether cuprate-like high-temperature nickelate
+superconductivity could be realized. We address this question using Ni L-edge
+and O K-edge spectroscopy of the reduced trilayer nickelate $d^{9-1/3}$
+La4Ni3O8 and associated theoretical modeling. A magnon energy scale of ~80 meV
+resulting from a nearest-neighbor magnetic exchange of $J = 69(4)4$ meV is
+observed, proving that $d^{9-{\delta}}$ nickelates can host a large
+superexchange. This value, along with that of the Ni-O hybridization estimated
+from our O K-edge data, implies that trilayer nickelates represent an
+intermediate case between the infinite-layer nickelates and the cuprates, and
+suggests that they represent a promising route towards higher-temperature
+nickelate superconductivity.",2008.08209v2
+2020-08-20,Magnetic Two-Dimensional Chromium Trihalides: A Theoretical Perspective,"The discovery of ferromagnetic order in monolayer 2D crystals has opened a
+new venue in the field of two dimensional (2D) materials. 2D magnets are not
+only interesting on their own, but their integration in van der Waals
+heterostructures allows for the observation of new and exotic effects in the
+ultrathin limit. The family of Chromium trihalides, CrI$_3$, CrBr$_3$ and
+CrCl$_3$, is, so far, the most studied among magnetic 2D crystals. In this
+mini-review, we provide a perspective of the state of the art of the
+theoretical understanding of magnetic 2D trihalides, most of which will also be
+relevant for other 2D magnets, such as vanadium trihalides. We discuss both the
+well-established facts, such as the origin of the magnetic moment and magnetic
+anisotropy and address as well open issues such as the nature of the
+anisotropic spin couplings and the magnitude of the magnon gap. Recent
+theoretical predictions on Moir\' e magnets and magnetic skyrmions are also
+discussed. Finally, we give some prospects about the future interest of these
+materials and possible device applications.",2008.08855v2
+2020-08-23,Multispinon excitations in the spin S=1/2 antiferromagnetic Heisenberg model,"With the commutation relations of the spin operators, we first write out the
+equations of motion of the spin susceptibility and related correlation
+functions that have a hierarchical structure, then under the ""soft cut-off""
+approximation, we give a set of equations of motion of spin susceptibilities
+for a spin S=1/2 antiferromagnetic Heisenberg model, that is independent of
+whether or not the system has a long range order in the low energy/temperature
+limit. Applying for a chain, a square lattice and a honeycomb lattice,
+respectively, we obtain the upper and the lowest boundaries of the low-lying
+excitations by solving this set of equations. For a chain, the upper and the
+lowest boundaries of the low-lying excitations are the same as that of the
+exact ones obtained by the Bethe ansatz, where the elementary excitations are
+the spinon pairs. For a square lattice, the spin wave excitation (magnons)
+resides in the region close to the lowest boundary of the low-lying
+excitations, and the multispinon excitations take place in the high energy
+region close to the upper boundary of the low-lying excitations. For a
+honeycomb lattice, we have one kind of ""mode"" of the low-lying excitation. The
+present results obey the Lieb-Schultz-Mattis theorem, and they are also
+consistent with recent neutron scattering observations and numerical
+simulations for a square lattice.",2008.09974v1
+2020-10-15,Dynamic fingerprint of fractionalized excitations in single-crystalline Cu$_3$Zn(OH)$_6$FBr,"Quantum spin liquid (QSL) represents a new class of condensed matter states
+characterized by the long-range many-body entanglement of topological orders.
+The most prominent feature of the elusive QSL state is the existence of
+fractionalized spin excitations. Subject to the strong quantum fluctuations,
+the spin-1/2 antiferromagnetic system on a kagome lattice is the promising
+candidate for hosting a QSL ground state, but the structurally ideal
+realization is rare. Here, we report Raman scattering on the single crystalline
+Cu$_3$Zn(OH)$_6$FBr, and confirm that the ideal kagome structure remains down
+to low temperatures without any lattice distortion by the angle-resolved
+polarized Raman responses and second-harmonic-generation measurements.
+Furthermore, at low temperatures the Raman scattering reveals a continuum of
+the spin excitations in Cu$_3$Zn(OH)$_6$FBr, in contrast to the sharp magnon
+peak in the ordered kagome antiferromagnet EuCu$_3$(OH)$_6$Cl$_3$. Such
+magnetic Raman continuum, in particular, the substantial low-energy one-pair
+spinon excitation serves as strong evidence for fractionalized spin excitations
+in Cu$_3$Zn(OH)$_6$FBr.",2010.07900v1
+2020-10-17,Tuning spin excitations in magnetic films by confinement,"Spin excitations of magnetic thin films are the founding element for novel
+transport concepts in spintronics, magnonics, and magnetic devices in general.
+While spin dynamics have been extensively studied in bulk materials, their
+behaviour in mesoscopic films is less known due to experimental limitations.
+Here, we employ Resonant Inelastic X-Ray Scattering to investigate the spin
+excitation spectrum in mesoscopic Fe films, from bulk-like down to 3 unit cells
+thick. In bulk-like samples, we find isotropic, dispersive ferromagnons
+consistent with the dispersion observed by neutron scattering in bulk single
+crystals. As the thickness is reduced, these ferromagnons survive and evolve
+anisotropically: renormalising to lower energies along the out-of-plane
+direction while retaining their dispersion in the in-plane direction. This
+thickness dependence is captured by simple Heisenberg model calculations
+accounting for the confinement in the out-of-plane direction through the loss
+of Fe bonds. Our findings highlight the effects of mesoscopic scaling on spin
+dynamics and identify thickness as a knob for fine-tuning and controlling
+magnetic properties in films.",2010.08745v1
+2020-10-21,Chiral switching and dynamic barrier reductions in artificial square ice,"Collective dynamics in lithographically-defined artificial spin ices offer
+profound insights into emergent correlations and phase transitions of
+geometrically-frustrated Ising spin systems. Their temporal and spatial
+evolution are often simulated using kinetic Monte Carlo simulations, which rely
+on the precise knowledge of the switching barriers to obtain predictive results
+in agreement with experimental observations. In many cases, however, the
+barriers are derived from simplified assumptions only, and do not take into
+account the full physical picture of nanomagnetic switching. Here we describe
+how the immediate magnetic environment of a nanomagnet reversing via
+quasi-coherent rotation can induce clockwise and counter-clockwise switching
+channels with different barrier energies. This barrier splitting for chiral
+reversal channels can be sizeable and, as string-method micromagnetic
+simulations show, is relevant for artificial spin ice systems made of both
+exchange -- as well as magnetostatically --dominated units. Due to the barrier
+splitting (and further reductions due to non-uniform reversal) transition rates
+can be exponentially enhanced by several orders of magnitude compared to
+mean-field predictions, especially in the limit of rare switching events where
+thermal excitation is less likely. This leads to significantly faster
+relaxation time scales and modified spatial correlations. Our findings are thus
+of integral importance to achieve realistic kinetic Monte Carlo simulations of
+emergent correlations in artificial spin systems, magnonic crystals, or the
+evolution of nanomagnetic logic circuits.",2010.11291v1
+2020-10-26,Spin Insulatronics,"Spin insulatronics covers efforts to generate, detect, control, and utilize
+high-fidelity pure spin currents and excitations inside magnetic insulators.
+Ultimately, the new findings may open doors for pure spin-based information and
+communication technologies. The aim is to replace moving charges with dynamical
+entities that utilize low-dissipation coherent and incoherent spin excitations
+in antiferromagnetic and ferromagnetic insulators. The ambition is that the new
+pure spin-based system will suffer reduced energy losses and operate at high
+frequencies. In magnetic insulators, there are no mobile charge carriers that
+can dissipate energy. Integration with conventional electronics is possible via
+interface exchange interactions and spin-orbit couplings. In this way, the free
+electrons in the metals couple to the localized spins in the magnetic
+insulators. In turn, these links facilitate spin-transfer torques and
+spin-orbit torques across metal-insulator interfaces and the associated
+phenomena of spin-pumping and charge-pumping. The interface couplings also
+connect the electron motion inside the metals with the spin fluctuations inside
+the magnetic insulators. These features imply that the system can enable
+unprecedented control of correlations resulting from the electron-magnon
+interactions. We review recent developments to realize electric and thermal
+generation, manipulation, detection, and control of pure spin information in
+insulators.",2010.13512v1
+2020-10-30,High-field thermal transport properties of the Kitaev quantum magnet alpha-RuCl3: evidence for low-energy excitations beyond the critical field,"We investigate the phononic in-plane longitudinal low-temperature thermal
+conductivity kappa_ab of the Kitaev quantum magnet alpha-RuCl3 for large
+in-plane magnetic fields up to 33 T. Our data reveal for fields larger than the
+critical field Bc ~ 8 T, at which the magnetic order is suppressed, a dramatic
+increase of kappa_ab at all temperatures investigated. The analysis of our data
+shows that the phonons are not only strongly scattered by a magnetic mode at
+relatively large energy which scales roughly linearly with the magnetic field,
+but also by a small-energy mode which emerges near Bc with a square-root-like
+field dependence. While the former is in striking agreement with recent spin
+wave theory (SWT) results of the magnetic excitation spectrum at the Gamma
+point, the energy of the latter is too small to be compatible with the
+SWT-expected magnon gap at the M point, despite the matching field dependence.
+Therefore, an alternative scenario based on phonon scattering off the thermal
+excitation of random-singlet states is proposed.",2010.16282v1
+2020-11-04,Spin Matrix Theory String Backgrounds and Penrose Limits of AdS/CFT,"Spin Matrix theory (SMT) limits provide a way to capture the dynamics of the
+AdS/CFT correspondence near BPS bounds. On the string theory side, these limits
+result in non-relativistic sigma models that can be interpreted as novel
+non-relativistic strings. This SMT string theory couples to non-relativistic
+$U(1)$-Galilean background geometries. In this paper, we explore the relation
+between pp-wave backgrounds obtained from Penrose limits of AdS${}_5 \times
+S^5$, and a new type of $U(1)$-Galilean backgrounds that we call flat-fluxed
+(FF) backgrounds. These FF backgrounds are the simplest possible SMT string
+backgrounds and correspond to free magnons from the spin chain perspective. We
+provide a catalogue of the $U(1)$-Galilean backgrounds one obtains from SMT
+limits of string theory on AdS${}_5 \times S^5$ and subsequently study large
+charge limits of these geometries from which the FF backgrounds emerge. We show
+that these limits are analogous to Penrose limits of AdS${}_5 \times S^5$ and
+demonstrate that the large charge/Penrose limits commute with the SMT limits.
+Finally, we point out that $U(1)$-Galilean backgrounds prescribe a symplectic
+manifold for the transverse SMT string embedding fields. This is illustrated
+with a Hamiltonian derivation for the SMT limit of a particle.",2011.02539v1
+2020-11-05,Tailoring Dzyaloshinskii-Moriya interaction in a transition metal dichalcogenide by dual-intercalation,"Dzyaloshinskii-Moriya interaction (DMI) is vital to form various chiral spin
+textures, novel behaviors of magnons and permits their potential applications
+in energy-efficient spintronic devices. Here, we realize a sizable bulk DMI in
+a transition metal dichalcogenide (TMD) 2H-TaS2 by intercalating Fe atoms,
+which form the chiral supercells with broken spatial inversion symmetry and
+also act as the source of magnetic orderings. Using a newly developed protonic
+gate technology, gate-controlled protons intercalation could further change the
+carrier density and intensely tune DMI via the Ruderman-Kittel-Kasuya-Yosida
+mechanism. The resultant giant topological Hall resistivity of 1.4 uohm.cm at
+-5.2V (about 460% of the zero-bias value) is larger than most of the known
+magnetic materials. Theoretical analysis indicates that such a large
+topological Hall effect originates from the two-dimensional Bloch-type chiral
+spin textures stabilized by DMI, while the large anomalous Hall effect comes
+from the gapped Dirac nodal lines by spin-orbit interaction. Dual-intercalation
+in 2HTaS2 provides a model system to reveal the nature of DMI in the large
+family of TMDs and a promising way of gate tuning of DMI, which further enables
+an electrical control of the chiral spin textures and related electromagnetic
+phenomena.",2011.02642v2
+2020-11-09,Classical many-body chaos with and without quasiparticles,"We study correlations, transport and chaos in a Heisenberg magnet as a
+classical model many-body system. By varying temperature and dimensionality, we
+can tune between settings with and without symmetry breaking and accompanying
+collective modes or quasiparticles. We analyse both conventional and
+out-of-time-ordered spin correlators (`decorrelators') to track the spreading
+of a spatiotemporally localised perturbation -- the wingbeat of the butterfly
+-- as well as transport coefficients and Lyapunov exponents. We identify a
+number of qualitatively different regimes. Trivially, at $T=0$, there is no
+dynamics at all. In the limit of low temperature, $T=0^+$, integrability
+emerges, with infinitely long-lived magnons; here the wavepacket created by the
+perturbation propagates ballistically, yielding a lightcone at the spin wave
+velocity which thus subsumes the butterfly velocity; inside the lightcone, a
+pattern characteristic of the free spin wave spectrum is visible at short
+times. On top of this, residual interactionslead to spin wave lifetimes which,
+while divergent in this limit, remain finite at any nonzero $T$. At the longest
+times, this leads to a `standard' chaotic regime; for this regime, we show that
+the Lyapunov exponent is simply proportional to the inverse spin-wave lifetime.
+Visibly strikingly, between this and the `short-time' integrable regimes, a
+scarred regime emerges: here, the decorrelator is spatiotemporally highly
+non-uniform, being dominated by rare and random scattering events seeding
+secondary lightcones. As the spin correlation length decreases with increasing
+$T$, the distinction between these regimes disappears and at high temperature
+the previously studied chaotic paramagnetic regime emerges. For this, we
+elucidate how, somewhat counterintuitively, the ballistic butterfly velocity
+arises from a diffusive spin dynamics.",2011.04700v1
+2020-11-10,Nonlinear level attraction of cavity axion polariton in antiferromagnetic topological insulator,"Strong coupling between cavity photons and various excitations in condensed
+matters boosts the field of light-matter interaction and generates several
+exciting sub-fields, such as cavity optomechanics and cavity magnon polariton.
+Axion quasiparticles, emerging in topological insulators, were predicted to
+strongly couple with the light and generate the so-called axion polariton.
+Here, we demonstrate that there arises a gapless level attraction in cavity
+axion polariton of antiferromagnetic topological insulators, which originates
+from a nonlinear interaction between axion and the odd-order resonance of
+cavity. Such a novel level attraction is essentially different from
+conventional level attractions with the mechanism of either a linear coupling
+or a dissipation-mediated interaction, and also different from the level
+repulsion induced by the strong coupling in common polaritons. Our results
+reveal a new mechanism of level attractions, and open up new roads for
+exploring the axion polariton with cavity technologies. They have potential
+applications for quantum information and dark matter research.",2011.04916v3
+2020-11-18,Non-planar geometrical effects on the magnetoelectrical signal in a three-dimensional nanomagnetic circuit,"Expanding nanomagnetism and spintronics into three dimensions (3D) offers
+great opportunities for both fundamental and technological studies. However,
+probing the influence of complex 3D geometries on magnetoelectrical phenomena
+poses important experimental and theoretical challenges. In this work, we
+investigate the magnetoelectrical signals of a ferromagnetic 3D nanodevice
+integrated into a microelectronic circuit using direct-write nanofabrication.
+Due to the 3D vectorial nature of both electrical current and magnetisation, a
+complex superposition of several magnetoelectrical effects takes place. By
+performing electrical measurements under the application of 3D magnetic fields,
+in combination with macrospin simulations and finite element modelling, we
+disentangle the superimposed effects, finding how a 3D geometry leads to
+unusual angular dependences of well-known magnetotransport effects such as the
+anomalous Hall effect. Crucially, our analysis also reveals a strong role of
+the noncollinear demagnetising fields intrinsic to 3D nanostructures, which
+results in an angular dependent magnon magnetoresistance contributing strongly
+to the total magnetoelectrical signal. These findings are key to the
+understanding of 3D spintronic systems and underpin further fundamental and
+device-based studies.",2011.09199v1
+2021-01-20,Protected Long-Distance Guiding of Hypersound Underneath a Nano-Corrugated Surface,"Within a new paradigm for communications on the nanoscale, high-frequency
+surface acoustic waves are becoming effective data carrier and encoder. On-chip
+communications require acoustic wave propagation along nano-corrugated surfaces
+which strongly scatter traditional Rayleigh waves. Here we propose the delivery
+of information using subsurface acoustic waves with hypersound frequencies ~20
+GHz, which is a nanoscale analogue of subsurface sound waves in the ocean. A
+bunch of subsurface hypersound modes is generated by pulsed optical excitation
+in a multilayer semiconductor structure with a metallic nanograting on top. The
+guided hypersound modes propagate coherently beneath the nanograting, retaining
+the surface imprinted information, on a distance of more than 50 {\mu}m which
+essentially exceeds the propagation length of Rayleigh waves. The concept is
+suitable for interfacing single photon emitters, such as buried quantum dots,
+carrying coherent spin excitations in magnonic devices, and encoding the
+signals for optical communications at the nanoscale.",2101.08189v1
+2021-01-29,Dynamically stable negative-energy states induced by spin-transfer torques,"We investigate instabilities of the magnetic ground state in ferromagnetic
+metals that are induced by uniform electrical currents, and, in particular, go
+beyond previous analyses by including dipolar interactions. These instabilities
+arise from spin-transfer torques that lead to Doppler shifted spin waves. For
+sufficiently large electrical currents, spin-wave excitations have negative
+energy with respect to the uniform magnetic ground state, while remaining
+dynamically stable due to dissipative spin-transfer torques. Hence, the uniform
+magnetic ground state is energetically unstable, but is not able to dynamically
+reach the new ground state. We estimate this to happen for current densities $
+j\gtrsim (1-D/D_c)10^{13} \mathrm{A/m^2} $ in typical thin film experiments,
+with $ D $ the Dzyaloshinskii-Moriya interaction constant, and $ D_c $ the
+Dzyaloshinskii-Moriya interaction that is required for spontaneous formation of
+spirals or skyrmions. These current densities can be made arbitrarily small for
+ultrathin film thicknesses at the order of nanometers, due to surface- and
+interlayer effects. From an analogue gravity perspective, the stable negative
+energy states are an essential ingredient to implement event horizons for
+magnons -- the quanta of spin waves -- giving rise to e.g. Hawking radiation
+and can be used to significantly amplify spin waves in a so-called black-hole
+laser.",2101.12544v1
+2021-02-26,Gapless Spin Wave Transport through a Quantum Canted-Antiferromagnet,"In the Landau levels of a two-dimensional electron system or when flat bands
+are present, e.g. in twisted van der Waals bilayers, strong electron-electron
+interaction gives rise to quantum Hall ferromagnetism with spontaneously broken
+symmetries in the spin and isospin sectors. Quantum Hall ferromagnets support a
+rich variety of low-energy collective excitations that are instrumental to
+understand the nature of the magnetic ground states and are also potentially
+useful as carriers of quantum information. Probing such collective excitations,
+especially their dispersion {\omega}(k), has been experimentally challenging
+due to small sample size and measurement constraints. In this work, we
+demonstrate an all-electrical approach that integrates a Fabry-P\'erot cavity
+with non-equilibrium transport to achieve the excitation, wave vector selection
+and detection of spin waves in graphene heterostructures. Our experiments
+reveal gapless, linearly dispersed spin wave excitations in the E = 0 Landau
+level of bilayer graphene, thus providing direct experimental evidence for a
+predicted canted antiferromagnetic order. We show that the gapless spin wave
+mode propagates with a high group velocity of several tens of km/s and
+maintains phase coherence over a distance of many micrometers. Its dependence
+on the magnetic field and temperature agree well with the hydrodynamic theory
+of spin waves. These results lay the foundation for the quest of spin
+superfluidity in this high-quality material. The resonant cavity technique we
+developed offers a powerful and timely method to explore the collective
+excitation of many spin and isospin-ordered many-body ground states in van der
+Waals heterostructures and open the possibility of engineering magnonic
+devices.",2103.00018v1
+2021-03-05,Why the Schwinger Boson mean field theory fails to describe the spin dynamics of the triangular lattice antiferromagnetic Heisenberg model?,"We find that the Schwinger Boson mean field theory(SBMFT) supplemented with
+Gutzwiller projection provides an exceedingly accurate description for the
+ground state of the spin-$\frac{1}{2}$ triangular lattice antiferromagnetic
+Heisenberg model(spin-$\frac{1}{2}$ TLHAF). However, we find the SBMFT fails
+even qualitatively in the description of the dynamical behavior of the system.
+In particular, the SBMFT fails to predict the Goldstone mode in the magnetic
+ordered phase. We show that the coherent peak in the two-spinon continuum in
+the presence of spinon condensate should not be interpreted as a magnon mode.
+The SBMFT also predicts incorrectly a gapless longitudinal spin fluctuation
+mode in the magnetic ordered phase. We show that these failures are related to
+the following facts: (1)Spinon condensation fails to provide a consistent
+description of the order parameter manifold of the 120 degree ordered phase.
+(2)There lacks in the SBMFT the coupling between the uncondensed spinon and the
+spinon condensate, which breaks both the spin rotational and the translational
+symmetry. (3)There lacks in the SBMFT the rigidity that is related to the no
+double occupancy constraint on the spinon system. We show that such failures of
+the SBMFT is neither restricted to the spin-$\frac{1}{2}$ TLHAF nor to the
+magnetic ordered phase. We proposed a generalized SBMFT to resolve the first
+two issues and a new formalism to address the third issue.",2103.03484v2
+2021-03-08,Environmental Screening and Ligand-Field Effects to Magnetism in CrI$_3$ Monolayer,"We present a detailed study on the microscopic origin of magnetism in
+suspended and dielectrically embedded CrI$_3$ monolayer. To this end, we
+down-fold two distinct minimal generalized Hubbard models with different
+orbital basis sets from \emph{ab initio} calculations using the constrained
+random phase approximation. Within mean-field approximation, we show that these
+models are capable of describing the formation of localized magnetic moments in
+CrI$_3$ and of reproducing electronic properties of full \emph{ab initio}
+calculations. We utilize the magnetic force theorem to study microscopic
+magnetic exchange channels between the different orbital manifolds. We find a
+multi-orbital super-exchange mechanism as the origin of magnetism in CrI$_3$
+resulting from a detailed interplay between effective ferro- and
+anti-ferromagnetic Cr-Cr $d$ coupling channels, which is decisively affected by
+the ligand (I) $p$ orbitals. We show how environmental screening such as
+resulting from encapsulation with hexagonal boron nitride (hBN) of the CrI$_3$
+monolayer affects the Coulomb interaction in the film and how this successively
+controls its magnetic properties. Driven by a non-monotonic interplay between
+nearest and next-nearest neighbour exchange interactions we find the magnon
+dispersion and the Curie temperature to be non-trivially affected by the
+environmental dielectric screening.",2103.04686v1
+2021-03-10,"Spin texture induced by non-magnetic doping and spin dynamics in 2D triangular lattice antiferromagnet h-Y(Mn,Al)O3","Novel effects induced by nonmagnetic impurities in frustrated magnets and
+quantum spin liquid represent a highly nontrivial and interesting problem. A
+theoretical proposal of extended modulated spin structures induced by doping of
+such magnets, distinct from the well-known skyrmions has attracted significant
+interest. Here, we demonstrate that nonmagnetic impurities can produce such
+extended spin structures in h-YMnO3, a triangular antiferromagnet with
+noncollinear magnetic order. Using inelastic neutron scattering (INS), we
+measured the full dynamical structure factor in Al-doped h-YMnO3 and confirmed
+the presence of magnon damping with a clear momentum dependence. Our
+theoretical calculations can reproduce the key features of the INS data,
+supporting the formation of the proposed spin textures. As such, our study
+provides the first experimental confirmation of the impurity-induced spin
+textures. It offers new insights and understanding of the impurity effects in a
+broad class of noncollinear magnetic systems.",2103.05936v2
+2021-03-15,Electron-plasmon interaction induced plasmonic-polaron band replication in epitaxial perovskite SrIrO$_3$ films,"Electron-boson interaction is fundamental to a thorough understanding of
+various exotic properties emerging in many-body physics. In photoemission
+spectroscopy, photoelectron emission due to photon absorption would trigger
+diverse collective excitations in solids, including the emergence of phonons,
+magnons, electron-hole pairs, and plasmons, which naturally provides a reliable
+pathway to study electron-boson couplings. While fingerprints of
+electron-phonon/-magnon interactions in this state-of-the-art technique have
+been well investigated, much less is known about electron-plasmon coupling, and
+direct observation of the band renormalization solely due to electron-plasmon
+interactions is extremely challenging. Here by utilizing integrated oxide
+molecular-beam epitaxy and angle-resolved photoemission spectroscopy, we
+discover the long sought-after pure electron-plasmon coupling-induced low-lying
+plasmonic-polaron replica bands in epitaxial semimetallic SrIrO$_3$ films, in
+which the characteristic low carrier concentration and narrow bandwidth combine
+to provide a unique platform where the electron-plasmon interaction can be
+investigated kinematically in photoemission spectroscopy. This finding enriches
+the forms of electron band normalization on collective modes in solids and
+demonstrates that, to obtain a complete understanding of the quasiparticle
+dynamics in 5d electron systems, the electron-plasmon interaction should be
+considered on equal footing with the acknowledged electron-electron interaction
+and spin-orbit coupling.",2103.08192v1
+2021-03-26,Microwave resonances of magnetic skyrmions in thin film multilayers,"Non-collinear magnets exhibit a rich array of dynamic properties at microwave
+frequencies. They can host nanometre-scale topological textures known as
+skyrmions, whose spin resonances are expected to be highly sensitive to their
+local magnetic environment. Here, we report a magnetic resonance study of an
+[Ir/Fe/Co/Pt] multilayer hosting N\'eel skyrmions at room temperature.
+Experiments reveal two distinct resonances of the skyrmion phase during
+in-plane ac excitation, with frequencies between 6-12 GHz. Complementary
+micromagnetic simulations indicate that the net magnetic dipole moment rotates
+counterclockwise (CCW) during both resonances. The magnon probability
+distribution for the lower-frequency resonance is localised within isolated
+skyrmions, unlike the higher-frequency mode which principally originates from
+areas between skyrmions. However, the properties of both modes depend
+sensitively on the out-of-plane dipolar coupling, which is controlled via the
+ferromagnetic layer spacing in our heterostructures. The gyrations of stable
+isolated skyrmions reported in this room temperature study encourage the
+development of new material platforms and applications based on skyrmion
+resonances. Moreover, our material architecture enables the resonance spectra
+to be tuned, thus extending the functionality of such applications over a
+broadband frequency range.",2103.14524v1
+2021-04-16,Implementing a magnonic time-delay reservoir computer model,"Recently we demonstrated experimentally that microwave oscillators based on
+the time delay feedback provided by traveling spin waves could operate as
+reservoir computers. In the present paper, we extend this concept by adding the
+feature of time multiplexing made available by the large propagation
+times/distances of traveling spin waves. The system utilizes the nonlinear
+behavior of propagating magnetostatic surface spin waves in a yttrium-iron
+garnet thin film and the time delay inherent in the active ring configuration
+to process time dependent data streams. Higher reservoir dimensionality is
+obtained through the time-multiplexing method, emulating ""virtual"" neurons as
+temporally separated spin-wave pulses circulating in the active ring below the
+auto-oscillation threshold. To demonstrate the efficacy of the concept, the
+active ring reservoir computer is evaluated on the short-term memory and parity
+check benchmark tasks, and the physical system parameters are tuned to optimize
+performance. By incorporating a reference line to mix the input signal directly
+onto the active ring output, both the amplitude and phase nonlinearity of the
+spin waves can be exploited, resulting in significant improvement on the
+nonlinear parity check task. We also find that the fading memory capacity of
+the system can be easily tuned by controlling the active ring gain. Finally, we
+show that the addition of a second spin-wave delay line configured to transmit
+backward volume spin waves can partly compensate dispersive pulse broadening
+and enhance the fading memory capacity of the active ring.",2104.07879v1
+2021-04-20,Exceptional Point and Cross-Relaxation Effect in a Hybrid Quantum System,"Exceptional points (EPs) are exotic degeneracies of non-Hermitian systems,
+where the eigenvalues and the corresponding eigenvectors simultaneously
+coalesce in parameter space, and these degeneracies are sensitive to tiny
+perturbations on the system. Here we report an experimental observation of the
+EP in a hybrid quantum system consisting of dense nitrogen (P1) centers in
+diamond coupled to a coplanar-waveguide resonator. These P1 centers can be
+divided into three subensembles of spins, and cross relaxation occurs among
+them. As a new method to demonstrate this EP, we pump a given spin subensemble
+with a drive field to tune the magnon-photon coupling in a wide range. We
+observe the EP in the middle spin subensemble coupled to the resonator mode,
+irrespective of which spin subensemble is actually driven. This robustness of
+the EP against pumping reveals the key role of the cross relaxation in P1
+centers. It offers a novel way to convincingly prove the existence of the
+cross-relaxation effect via the EP.",2104.09811v1
+2021-05-03,Relaxation of a single defect spin by the low-frequency gyrotropic mode of a magnetic vortex,"We excite the gyrotropic mode of a magnetic vortex and observe the resulting
+effect on the spin state of a nearby nitrogen-vacancy (NV) defect in diamond.
+Thin permalloy disks fabricated on a diamond sample are magnetized in a vortex
+state in which the magnetization curls around a central core. The magnetization
+dynamics of this configuration are described by a discrete spectrum of confined
+magnon modes, as well as a low-frequency gyrotropic mode in which the vortex
+core precesses about its equilibrium position. Despite the spin transition
+frequencies being far-detuned from the modes of the ferromagnet, we observe
+enhanced relaxation of the NV spin when driving the gyrotropic mode. Moreover,
+we map the spatial dependence of the interaction between the vortex and the
+spin by translating the vortex core within the disk with an applied magnetic
+field, resulting in steplike motion as the vortex is pinned and de-pinned. The
+strong spin relaxation is observed when the vortex core is within approximately
+250 nm of the NV center defect. We attribute this effect to the higher
+frequencies in the spectrum of the magnetic fringe field arising from the
+soliton-like nature of the gyrotropic mode when driven with sufficiently large
+amplitude.",2105.00927v1
+2021-05-10,Parameterization of magnetic vector potentials and fields for efficient multislice calculations of elastic electron scattering,"The multislice method, which simulates the propagation of the incident
+electron wavefunction through a crystal, is a well-established method for
+analyzing the multiple scattering effects that an electron beam may undergo.
+The inclusion of magnetic effects into this method proves crucial towards
+simulating magnetic differential phase contrast images at atomic resolution,
+enhanced magnetic interaction of vortex beams with magnetic materials,
+calculating magnetic Bragg spots, or searching for magnon signatures, to name a
+few examples. Inclusion of magnetism poses novel challenges to the efficiency
+of the multislice method for larger systems, especially regarding the
+consistent computation of magnetic vector potentials and magnetic fields over
+large supercells. We present in this work a tabulation of parameterized
+magnetic values for the first three rows of transition metal elements computed
+from atomic density functional theory calculations, allowing for the efficient
+computation of approximate magnetic vector fields across large crystals using
+only structural and magnetic moment size and direction information.
+Ferromagnetic bcc Fe and tetragonal FePt are chosen as examples in this work to
+showcase the performance of the parameterization versus directly obtaining
+magnetic vector fields from the unit cell spin density by density functional
+theory calculations, both for the quantities themselves and the resulting
+magnetic signal from their respective use in multislice calculations.",2105.04195v1
+2021-05-10,Switchable Magnetic Frustration in Buckyball Nanoarchitectures,"Recent progress in nanofabrication has led to the emergence of
+three-dimensional magnetic nanostructures as a vibrant field of research. This
+includes the study of three-dimensional arrays of interconnected magnetic
+nanowires with tunable artificial spin-ice properties. Prominent examples of
+such structures are magnetic buckyball nanoarchitectures, which consist of
+ferromagnetic nanowires connected at vertex positions corresponding to those of
+a C60 molecule. These structures can be regarded as prototypes for the study of
+the transition from two- to three-dimensional spin-ice lattices. In spite of
+their significance for three-dimensional nanomagnetism, little is known about
+the micromagnetic properties of buckyball nanostructures. By means of
+finite-element micromagnetic simulations, we investigate the magnetization
+structures and the hysteretic properties of several sub-micron-sized magnetic
+buckyballs. Similar to ordinary artificial spin ice lattices, the array can be
+magnetized in a variety of zero-field states with vertices exhibiting different
+degrees of magnetic frustration. Remarkably, and unlike planar geometries,
+magnetically frustrated states can be reversibly created and dissolved by
+applying an external magnetic field. This easiness to insert and remove
+defect-like magnetic charges, made possible by the angle-selectivity of the
+field-induced switching of individual nanowires, demonstrates a potentially
+significant advantage of three-dimensional nanomagnetism compared to planar
+geometries. The control provided by the ability to switch between ice-rule
+obeying and magnetically frustrated structures could be an important feature of
+future applications, including magnonic devices exploiting differences in the
+fundamental frequencies of these configurations.",2105.04509v1
+2021-05-17,Fluctuation-induced ferrimagnetism in sublattice-imbalanced antiferromagnets with application to SrCu$_2$(BO$_3$)$_2$ under pressure,"We show that a collinear Heisenberg antiferromagnet, whose sublattice
+symmetry is broken at the Hamiltonian level, becomes a fluctuation-induced
+ferrimagnet at any finite temperature $T$ below the N\'eel temperature $T_{\rm
+N}$. We demonstrate this using a layered variant of a square-lattice
+$J_1$-$J_2$ model. Linear spin-wave theory is used to determine the
+low-temperature behavior of the uniform magnetization, and non-linear
+corrections are argued to yield a temperature-induced qualitative change of the
+magnon spectrum. We then consider a layered Shastry-Sutherland model,
+describing a frustrated arrangement of orthogonal dimers. This model displays
+an antiferromagnetic phase for large intra-dimer couplings. A lattice
+distortion which breaks the glide symmetry between the two types of dimers
+corresponds to broken sublattice symmetry and hence gives rise to
+ferrimagnetism. Given indications that such a distortion is present in the
+material SrCu$_2$(BO$_3$)$_2$ under hydrostatic pressure, we suggest the
+existence of a fluctuation-induced ferrimagnetic phase in pressurized
+SrCu$_2$(BO$_3$)$_2$. We predict a non-monotonic behavior of the uniform
+magnetization as function of temperature.",2105.08088v2
+2021-06-15,Exciton-driven antiferromagnetic metal in a correlated van der Waals insulator,"Collective excitations of bound electron-hole pairs -- known as excitons --
+are ubiquitous in condensed matter, emerging in systems as diverse as band
+semiconductors, molecular crystals, and proteins. Recently, their existence in
+strongly correlated electron materials has attracted increasing interest due to
+the excitons' unique coupling to spin and orbital degrees of freedom. The
+non-equilibrium driving of such dressed quasiparticles offers a promising
+platform for realizing unconventional many-body phenomena and phases beyond
+thermodynamic equilibrium. Here, we achieve this in the van der Waals
+correlated insulator NiPS$_3$ by photoexciting its newly discovered
+spin-orbit-entangled excitons that arise from Zhang-Rice states. By monitoring
+the time evolution of the terahertz conductivity, we observe the coexistence of
+itinerant carriers produced by exciton dissociation and the long-wavelength
+antiferromagnetic magnon that coherently precesses in time. These results
+demonstrate the emergence of a transient metallic state that preserves
+long-range antiferromagnetism, a phase that cannot be reached by simply tuning
+the temperature. More broadly, our findings open an avenue toward the
+exciton-mediated optical manipulation of magnetism.",2106.08355v1
+2021-06-30,Classifying charge carrier interaction in highly-compressed elements and silane,"Since pivotal experimental discovery of the near-room-temperature
+superconductivity (NRTS) in highly-compressed sulphur hydride by Drozdov et al
+(2015 Nature 525 73-76), more than a dozen of binary and of ternary
+hydrogen-rich phases exhibited superconducting transition above 100 K have been
+discovered to date. There is a widely accepted theoretical point of view that
+primary mechanism governing the emergence of superconductivity in hydrogen-rich
+phases is the electron-phonon pairing. However, our recent analysis of
+experimental temperature dependent resistance in $H_{3}S$, $LaH_{x}$, $PrH_{9}$
+and $BaH_{12}$ (arXiv: 2104.14145) showed that these compounds exhibit the
+dominance of non-electron-phonon charge carrier interaction and, thus, it is
+unlikely that the electron-phonon pairing is the primary mechanism for the
+emergence of superconductivity in these materials. Here we use the same
+approach to reveal charge carrier interaction in highly-compressed lithium,
+black phosphorous, sulfur, and silane. We found that all these superconductors
+exhibit the dominance of non-electron-phonon charge carrier interaction. This
+explains the failure of high-Tc values predicted for these materials by the
+first-principles calculations which utilized the electron-phonon pairing as the
+mechanism for the emergence of superconductivity in these materials. Our result
+implies that alternative pairing mechanisms (i.e., electron-magnon,
+electron-polaron, electron-electron, etc.) should be tested within
+first-principles calculations approach as possible mechanisms for the emergence
+of superconductivity in highly-compressed superconductors.",2106.15873v1
+2021-07-09,Electric field driven flat bands: Enhanced magnetoelectric and electrocaloric effects in frustrated quantum magnets,"The $J_1$-$J_2$ quantum spin sawtooth chain is a paradigmatic one-dimensional
+frustrated quantum spin system exhibiting unconventional ground-state and
+finite-temperature properties. In particular, it exhibits a flat energy band of
+one-magnon excitations accompanied by an enhanced magnetocaloric effect for two
+singular ratios of the basal interactions $J_1$ and the zigzag interactions
+$J_2$. In our paper, we demonstrate that one can drive the spin system into a
+flat-band scenario by applying an appropriate electric field, thus overcoming
+the restriction of fine-tuned exchange couplings $J_1$ and $J_2$ and allowing
+one to tune more materials towards flat-band physics, that is to show a
+macroscopic magnetization jump when crossing the magnetic saturation field, a
+residual entropy at zero temperature as well as an enhanced magnetocaloric
+effect. While the magnetic field acts on the spin system via the ordinary
+Zeeman term, the coupling of an applied electric field with the spins is given
+by the sophisticated Katsura-Nagaosa-Balatsky (KNB) mechanism, where the
+electric field effectively acts as a Dzyaloshinskii-Moriya spin-spin
+interaction. The resulting novel features are corresponding reciprocal effects:
+We find a magnetization jump driven by the electric field as well as a jump of
+the electric polarization driven by the magnetic field, i.e.\ the system
+exhibits an extraordinarily strong magnetoelectric effect. Moreover, in analogy
+to the enhanced magnetocaloric effect the system shows an enhanced
+electrocaloric effect.",2107.04371v2
+2021-07-16,Large Unidirectional Magnetoresistance in Metallic Heterostructures in the Spin Transfer Torque Regime,"A large unidirectional magnetoresistance (UMR) ratio of UMR/$R_{xx}\sim$
+$0.36\%$ is found in W/CoFeB metallic bilayer heterostructures at room
+temperature. Three different regimes in terms of the current dependence of UMR
+ratio are identified: A spin-dependent-scattering mechanism regime at small
+current densities $J \sim$ $10$$^{9}$A/m$^{2}$ (UMR ratio $\propto$ $J$), a
+spin-magnon-interaction mechanism regime at intermediate $J \sim$
+$10$$^{10}$A/m$^{2}$ (UMR ratio $\propto$ $J$$^{3}$), and a spin-transfer
+torque (STT) regime at $J \sim$ $10$$^{11}$A/m$^{2}$ (UMR ratio independent of
+$J$). We verify the direct correlation between this large UMR and the transfer
+of spin angular momentum from the W layer to the CoFeB layer by both
+field-dependent and current-dependent UMR characterizations. Numerical
+simulations further confirm that the large STT-UMR stems from the tilting of
+the magnetization affected by the spin Hall effect-induced spin-transfer
+torques. An alternative approach to estimate damping-like spin-torque
+efficiencies from magnetic heterostructures is also proposed.",2107.07780v1
+2021-07-19,MoP$_3$SiO$_{11}$: a $4d^3$ honeycomb antiferromagnet with disconnected octahedra,"We report the crystal structure and magnetic behavior of the $4d^3$
+spin-$\frac32$ silicophosphate MoP$_3$SiO$_{11}$ studied by high-resolution
+synchrotron x-ray diffraction, neutron diffraction, thermodynamic measurements,
+and ab initio band-structure calculations. Our data revise the crystallographic
+symmetry of this compound and establish its rhombohedral space group ($R\bar
+3c$) along with the geometrically perfect honeycomb lattice of the Mo$^{3+}$
+ions residing in disconnected MoO$_6$ octahedra. Long-range antiferromagnetic
+order with the propagation vector $\mathbf k=0$ observed below $T_N=6.8$ K is a
+combined effect of the nearest-neighbor in-plane exchange coupling $J\simeq
+2.6$ K, easy-plane single-ion anisotropy $D\simeq 2.2 $ K, and a weak
+interlayer coupling $J_c\simeq 0.8$ K. The 12% reduction in the ordered
+magnetic moment of the Mo$^{3+}$ ions and the magnon gap of $\Delta\simeq 7$ K
+induced by the single-ion anisotropy further illustrate the impact of
+spin-orbit coupling on the magnetism. Our analysis puts forward single-ion
+anisotropy as an important ingredient of $4d^3$ honeycomb antiferromagnets
+despite their nominally quenched orbital moment.",2107.08618v2
+2021-07-19,Reconfigurable Training and Reservoir Computing in an Artificial Spin-Vortex Ice via Spin-Wave Fingerprinting,"Strongly-interacting artificial spin systems are moving beyond mimicking
+naturally-occurring materials to emerge as versatile functional platforms, from
+reconfigurable magnonics to neuromorphic computing. Typically artificial spin
+systems comprise nanomagnets with a single magnetisation texture: collinear
+macrospins or chiral vortices. By tuning nanoarray dimensions we achieve
+macrospin/vortex bistability and demonstrate a four-state metamaterial
+spin-system 'Artificial Spin-Vortex Ice' (ASVI). ASVI can host Ising-like
+macrospins with strong ice-like vertex interactions, and weakly-coupled
+vortices with low stray dipolar-field. Vortices and macrospins exhibit
+starkly-differing spin-wave spectra with analogue-style mode-amplitude control
+and mode-frequency shifts of df = 3.8 GHz.
+  The enhanced bi-textural microstate space gives rise to emergent physical
+memory phenomena, with ratchet-like vortex training and history-dependent
+nonlinear fading memory when driven through global field cycles. We employ
+spin-wave microstate fingerprinting for rapid, scaleable readout of vortex and
+macrospin populations and leverage this for spin-wave reservoir computation.
+ASVI performs linear and non-linear mapping transformations of diverse input
+signals as well as chaotic time-series forecasting. Energy costs of machine
+learning are spiralling unsustainably, developing low-energy neuromorphic
+computation hardware such as ASVI is crucial to achieving a zero-carbon
+computational future.",2107.08941v3
+2021-08-03,Possibility to detect the bound state of the Heisenberg ferromagnetic chain at intermediate temperature,"Motivated by the lack of direct evidence with inelastic neutron scattering of
+the well documented bound state of Heisenberg ferromagnets, we use the
+time-dependent Thermal Density Matrix Renormalization Group algorithm to study
+the temperature dependence of the dynamical spin structure factor of Heisenberg
+ferromagnetic spin chains. For spin-1/2, we show that the bound state appears
+as a well defined excitation with significant spectral weight in the
+temperature range $J/12 \lesssim T \lesssim J/3$, pointing to the possibility
+of detecting it with inelastic neutron scattering near $k=\pi$ provided the
+temperature is neither too low nor too high - at low temperature, the spectral
+weight only grows as $T^{3/2}$, and at high temperature the bound state peak
+merges with the two-magnon continuum. For spin-1, the situation is more subtle
+because the bound state with two neighboring spin flips competes with an
+anti-bound state with two spin-flips on the same site. As a consequence, the
+relative spectral weight of the bound state is smaller than for spin-1/2, and a
+weak resonance due to the anti-bound state appears in the continuum. A clearer
+signature of the bound state (resp. anti-bound state) can be obtained if a
+negative (resp. positive) biquadratic interaction is present.",2108.01401v3
+2021-08-11,Instabilities of spin-1 Kitaev spin liquid phase in presence of single-ion anisotropies,"We study the spin-one Kitaev model on the honeycomb lattice in the presence
+of single-ion anisotropies. We consider two types of single ion anisotropies: A
+$D_{111}$ anisotropy which preserves the symmetry between $X$, $Y$, and $Z$
+bonds but violates flux conservation and a $D_{100}$ anisotropy that breaks the
+symmetry between $X$, $Y$, and $Z$ bonds but preserves flux conservation. We
+use series expansion methods, degenerate perturbation theory, and exact
+diagonalization to study these systems. Large positive $D_{111}$ anisotropy
+leads to a simple product ground state with conventional magnon-like
+excitations, while large negative $D_{111}$ leads to a broken symmetry and
+degenerate ground states. For both signs there is a phase transition at a small
+$|D_{111}| \approx 0.12$ separating the more conventional phases from the
+Kitaev spin liquid phase. With large $D_{100}$ anisotropy, the ground state is
+a simple product state, but the model lacks conventional dispersive excitations
+due to the large number of conservation laws. Large negative $D_{100}$ leads to
+decoupled one-dimensional systems and many degenerate ground states. No
+evidence of a phase transition is seen in our numerical studies at any finite
+$D_{100}$. Convergence of the series expansion extrapolations all the way to
+$D_{100}=0$ suggests that the nontrivial Kitaev spin liquid is a singular limit
+of this type of single-ion anisotropy going to zero, which also restores
+symmetry between the $X$, $Y$, and $Z$ bonds.",2108.05040v2
+2021-08-18,Dispersionless propagation of ultra-short spin-wave pulses in ultrathin yttrium iron garnet waveguides,"We study experimentally the propagation of nanosecond spin-wave pulses in
+microscopic waveguides made of nanometer-thick yttrium iron garnet films. For
+these studies, we use micro-focus Brillouin light scattering spectroscopy,
+which provides the possibility to observe propagation of the pulses with high
+spatial and temporal resolution. We show that, for most spin-wave frequencies,
+dispersion leads to broadening of the pulse by several times at propagation
+distances of 10 micrometers. However, for certain frequency interval, the
+dispersion broadening is suppressed almost completely resulting in a
+dispersionless pulse propagation. We show that the formation of the
+dispersion-free region is caused by the competing effects of the dipolar and
+the exchange interaction, which can be controlled by the variation of the
+waveguide geometry. These conclusions are supported by micromagnetic
+simulations and analytical calculations. Our findings provide a simple solution
+for the implementation of high-speed magnonic systems that require undisturbed
+propagation of short information-carrying spin-wave pulses.",2108.08054v1
+2021-09-08,Room-Temperature Intrinsic and Extrinsic Damping in Polycrystalline Fe Thin Films,"We examine room-temperature magnetic relaxation in polycrystalline Fe films.
+Out-of-plane ferromagnetic resonance (FMR) measurements reveal Gilbert damping
+parameters of $\approx$ 0.0024 for Fe films with thicknesses of 4-25 nm,
+regardless of their microstructural properties. The remarkable invariance with
+film microstructure strongly suggests that intrinsic Gilbert damping in
+polycrystalline metals at room temperature is a local property of nanoscale
+crystal grains, with limited impact from grain boundaries and film roughness.
+By contrast, the in-plane FMR linewidths of the Fe films exhibit distinct
+nonlinear frequency dependences, indicating the presence of strong extrinsic
+damping. To fit our in-plane FMR data, we have used a grain-to-grain two-magnon
+scattering model with two types of correlation functions aimed at describing
+the spatial distribution of inhomogeneities in the film. However, neither of
+the two correlation functions is able to reproduce the experimental data
+quantitatively with physically reasonable parameters. Our findings advance the
+fundamental understanding of intrinsic Gilbert damping in structurally
+disordered films, while demonstrating the need for a deeper examination of how
+microstructural disorder governs extrinsic damping.",2109.03684v2
+2021-09-08,Schwinger boson theory of ordered magnets,"The Schwinger boson theory provides a natural path for treating quantum spin
+systems with large quantum fluctuations. In contrast to semi-classical
+treatments, this theory allows us to describe a continuous transition between
+magnetically ordered and spin liquid states, as well as the continuous
+evolution of the corresponding excitation spectrum. The square lattice
+Heisenberg antiferromagnet is one of the first models that was approached with
+the Schwinger boson theory. Here we revisit this problem to reveal several
+subtle points that were omitted in previous treatments and that are crucial to
+further develop this formalism. These points include the freedom for the choice
+of the saddle point (Hubbard-Stratonovich decoupling and choice of the
+condensate) and the $1/N$ expansion in the presence of a condensate. A key
+observation is that the spinon condensate leads to Feynman diagrams that
+include contributions of different order in $1/N$, which must be accounted to
+get a qualitatively correct excitation spectrum. We demonstrate that a proper
+treatment of these contributions leads to an exact cancellation of the
+single-spinon poles of the dynamical spin structure factor, as expected for a
+magnetically ordered state. The only surviving poles are the ones arising from
+the magnons (two-spinon bound states), which are the true collective modes of
+an ordered magnet.",2109.03964v2
+2021-09-15,Spin-Current Instability at a Magnetic Domain Wall in a Ferromagnetic Superfluid: a Generation Mechanism of Eccentric Fractional Skyrmions,"Spinful superfluids of ultracold atoms are ideal for investigating the
+intrinsic properties of spin current and texture because they are realized in
+an isolated, nondissipative system free from impurities, dislocations, and
+thermal fluctuations. This study theoretically reveals the impact of spin
+current on a magnetic domain wall in spinful superfluids. An exact wall
+solution is obtained in the ferromagnetic phase of a spin-1 Bose--Einstein
+condensate with easy-axis anisotropy at zero temperature. The
+bosonic-quasiparticle mechanics analytically show that the spin current along
+the wall becomes unstable if the velocity exceeds the critical spin-current
+velocities, leading to complicated situations because of the competition
+between transverse magnons and ripplons. Our direct numerical simulation
+reveals that this system has a mechanism to generate an eccentric fractional
+skyrmion, which has a fractional topological charge, but its texture is not
+similar to that of a meron. This mechanism is in contrast to the generation of
+conventional skyrmions in easy-axis magnets. The theoretical findings can be
+examined in the same situation as in a recent experiment on ultracold atoms. In
+terms of the universality of spontaneous symmetry breaking, unexplored similar
+phenomena are expected in different physical systems with the same broken
+symmetry.",2109.07144v2
+2021-09-16,Thermoelectric films and periodic structures and spin Seebeck effect systems: Facets of performance optimization,"The growing market for sensors, internet of things, and wearable devices is
+fueling the development of low-cost energy-harvesting materials and systems.
+Film based thermoelectric (TE) devices offer the ability to address the energy
+requirements by using ubiquitously available waste-heat. This review narrates
+recent advancements in fabricating high-performance TE films and superlattice
+structures, from the aspects of microstructure control, doping, defects,
+composition, surface roughness, substrate effect, interface control,
+nanocompositing, and crystal preferred orientation realized by regulating
+various deposition parameters and subsequent heat treatment. The review begins
+with a brief account of heat conduction mechanism, quantum confinement effect
+in periodic layers, film deposition processes, thin film configurations and
+design consideration for TE in-plane devices, and characterization techniques.
+It then proceeds to alayzing the latest findingd on the TE properties of
+Bi2(Te,Se)3 and (Bi,Sb)2Te3, PbTe, GeTe, SnSe, SnTe, Cu2-xSe, and skutterudite
+films, including superlattices and the performance of TE generators, sensors,
+and cooling devices. Thickness dependent microstructure evolution and TE
+characteristics of films in relation to temperature are also analyzed. In the
+context of spin Seebeck effect (SSE) based systems, SSE mechanism analysis,
+developments in enhancing the spin Seebeck signal since its first observation,
+and recent developments are covered from the facets of new system design,
+signal collection, magnetic manipulation, interface conditions,
+thickness-dependent longitudinal spin Seebeck signal, and length scale of
+phonon and magnon transport in longitudinal SSE (LSSE) in different bi-layer
+systems. At the end, possible strategies for further enhancing zT of TE films
+and spin Seebeck signals of many systems are addressed.",2109.08179v1
+2021-09-17,Towards Exotic Layered Materials: 2D Cuprous Iodide,"Heterostructures composed of two-dimensional (2D) materials are already
+opening many new possibilities in such fields of technology as electronics and
+magnonics, but far more could be achieved if the number and diversity of 2D
+materials is increased. So far, only a few dozen 2D crystals have been
+extracted from materials that exhibit a layered phase in ambient conditions,
+omitting entirely the large number of layered materials that may exist in other
+temperatures and pressures. Here, we demonstrate how these structures can be
+stabilized in 2D van der Waals stacks under room temperature via growing them
+directly in graphene encapsulation by using graphene oxide as the template
+material. Specifically, we produce an ambient stable 2D structure of copper and
+iodine, a material that normally only occurs in layered form at elevated
+temperatures between 645 and 675 K. Our results establish a route to the
+production of more exotic phases of materials that would otherwise be difficult
+or impossible to stabilize for experiments in ambient.",2109.08456v2
+2021-09-17,Visualizing band selective enhancement of quasiparticle lifetime in a metallic ferromagnet,"Electrons navigate more easily in a background of ordered magnetic moments
+than around randomly oriented ones. This fundamental quantum mechanical
+principle is due to their Bloch wave nature and also underlies ballistic
+electronic motion in a perfect crystal. As a result, a paramagnetic metal that
+develops ferromagnetic order often experiences a sharp drop in the resistivity.
+Despite the universality of this phenomenon, a direct observation of the impact
+of ferromagnetic order on the electronic quasiparticles in a magnetic metal is
+still lacking. Here we demonstrate that quasiparticles experience a significant
+enhancement of their lifetime in the ferromagnetic state of the low-density
+magnetic semimetal EuCd2As2, but this occurs only in selected bands and
+specific energy ranges. This is a direct consequence of the magnetically
+induced band splitting and the multi-orbital nature of the material. Our
+detailed study allows to disentangle different electronic scattering mechanisms
+due to non-magnetic disorder and magnon exchange. Such high momentum and energy
+dependence quasiparticle lifetime enhancement can lead to spin selective
+transport and potential spintronic applications.",2109.08538v1
+2021-09-22,Bulk and edge dynamics of a 2D Affleck-Kennedy-Lieb-Tasaki model,"We study the dynamical properties of both bulk and edge spins of a
+two-dimensional Affleck-Kennedy-Lieb-Tasaki (AKLT) model mainly by using the
+stochastic series expansion quantum Monte Carlo method with stochastic analytic
+continuation. In the deep AKLT phase, we obtain a spin spectrum with flat band,
+which is a strong evidence for a localized state. Through the spectrum
+analysis, we see a clear continuous phase transition from the AKLT phase to the
+N\'eel phase in the model, and the energy gap becomes closed at the
+corresponding momentum point. In comparison with linear spin-wave theory, the
+differences show that there are strong interactions among magnons at high
+energies. With open boundary condition, the gap of edge spins in the AKLT phase
+closes at both the $\Gamma$ point and the $\pi$ point interestingly to emerge
+into a flat-band-like Luttinger liquid phase, which can be explained by
+symmetry and perturbation approximation. This paper helps us to better
+understand the completely different dynamical behaviors of bulk and edge spins
+in the symmetry protected topological phase.",2109.10901v2
+2021-09-22,Optically- and thermally-driven huge lattice orbital and spin angular momenta from spinning fullerenes,"Lattice vibration in solids may carry angular momentum. But unlike the
+intrinsic spin of electrons, the lattice vibration is rarely rotational. To
+induce angular momentum, one needs to find a material that can accommodate a
+twisted normal mode, two orthogonal modes or excitation of magnons. If
+excitation is too strong, one may exceed the Lindemann limit, so the material
+melts. Therefore these methods are not ideal. Here, we theoretically propose a
+new route to phonon angular momentum in a molecular crystal $\rm C_{60}$. We
+find that a single laser pulse is able to inject a significant amount of
+angular momentum to $\rm C_{60}$, and the momentum transfer is
+helicity-dependent. Changing from right-circularly polarized light to
+left-circularly polarized light switches the direction of phonon angular
+momentum. On the ultrafast time scale, the orbital angular momentum change
+closely resembles the displacive excitation of coherent phonons, with a
+cosine-function dependence on time, different from the spin counterpart. Atomic
+displacements, even under strong laser excitation, remain far below the
+Lindemann criterion. Under thermal excitation, spinning $\rm C_{60}$ even at
+room temperature generates a huge angular momentum close to several hundred
+$\hbar$. Our finding opens the door to a large group of fullerenes, from $\rm
+C_{60}$, C$_{70}$ to their endohedral derivatives, where angular momentum can
+be generated through light or temperature. This paves the way to the phononic
+control electronic spin and harvesting thermal energy through phonon angular
+momentum.",2109.11055v1
+2021-10-01,Spin liquid in twisted homobilayers group-VI gichalcogenides,"Twisted transition metal dichalcogenide (TMD) homobilayers have recently
+emerged as a powerful platform for studying correlated insulating states. In
+the strongly correlated limit, we construct an effective spin Hamiltonian on a
+honeycomb lattice that includes the Heisenberg interaction and nonsymmetric
+interactions such as a Dzyaloshinskii-Moriya interaction and a Kane-Mele
+coupling for the Mott-insulating phase at half-filling. For the twisted TMD
+homobilayers, the spin-orbit coupling in the Hubbard model, which is expected
+to induce the antisymmetric exchange couplings in the effective spin
+Hamiltonian, is a highly tunable and experimentally accessible quantity that
+can be tuned by an applied electric field. In this study, we investigate
+classical and quantum phase diagrams of the effective spin Hamiltonian using
+analytical and numerical methods. We show that the model exhibits a rich
+classical phase diagram including an antiferromagnetic (AFM) phase, a planar
+spiral ordered phase with high classical degeneracy, a $z$-AFM phase, a
+noncoplanar phase, a noncollinear phase, and a 120$^{\circ}$-AFM phase. In the
+quantum treatment, we calculate low-energy magnon excitation spectrum, ground
+state energy, and static spin structure factor using linear spin-wave theory
+and density matrix renormalization group methods to compose the quantum phase
+diagram of the effective spin Hamiltonian. Beyond the Heisenberg interaction,
+we find that the existence of these antisymmetric couplings is responsible for
+the quantum spin liquid, $z$-AFM, noncoplanar, and 120$^{\circ}$ phases.
+Twisted TMD homobilayers, therefore, offer rich platforms for realizing rich
+phases of matter such as quantum spin liquid, noncoplanar, and 120$^{\circ}$,
+resulting from the spin-orbit coupling.",2110.00536v1
+2021-10-19,"Duality,Hidden Symmetry and Dynamic Isomerism in 2D Hinge Structures","Recently, a new type of duality was reported in some deformable mechanical
+networks which exhibit Kramers-like degeneracy in phononic spectrum at the
+self-dual point. In this work, we clarify the origin of this duality and
+propose a design principle of 2D self-dual structures with arbitrary
+complexity. We find that this duality originates from the (PCI) symmetry of the
+hinge, which belongs to a more general end-fixed scaling transformation. This
+symmetry gives the structure an extra degree of freedom without modifying its
+dynamics. This results in , i.e., dissimilar 2D mechanical structures, either
+periodic or aperiodic, having identical dynamic modes, based on which we
+demonstrate a new type of wave-guide without reflection or loss. Moreover, the
+PCI symmetry allows us to design various 2D periodic isostatic networks with
+hinge duality. At last, by further studying a 2D non-mechanical magnonic
+system, we show that the duality and the associated hidden symmetry should
+exist in a broad range of Hamiltonian systems.",2110.09999v3
+2021-11-01,Spectrum evolution and chirping of laser-induced spin wave packets in thin iron films,"We present the experimental study of ultrafast optical excitation of
+magnetostatic surface spin wave (MSSW) packets and their spectral properties in
+thin films of pure iron. As the packets leave the excitation area and propagate
+in space, their spectra evolve non-trivially. Particularly, low or high
+frequency components are suppressed at the border of the excitation area
+depending on the orientation of the external magnetic field with respect to the
+magnetocrystolline anisotropy axes of the film. The effect is ascribed to the
+ultrafast local heating of the film. Further, the time resolution of the
+implemented all-optical technique allows us to extract the chirp of the MSSW
+packet in the time domain via wavelet analysis. The chirp is a result of the
+group velocity dispersion of the MSSW and, thus, is controlled by the film
+magnetic parameters, magnetization and anisotropy, and external field
+orientation. The demonstrated tunable modulation of MSSW wave packets with
+femtosecond laser pulses may find application in future magnonic-photonic
+hybrid devices for wave-based data processing.",2111.00983v2
+2021-11-02,Ultrafast coherent THz lattice dynamics coupled to spins in a van der Waals antiferromagnetic flake,"A coherent THz optical lattice mode is triggered by femtosecond laser pulses
+in the antiferromagnetic van der Waals semiconductor FePS$_3$. The 380 nm thick
+exfoliated flake was placed on a substrate and laser-driven lattice and spin
+dynamics were investigated as a function of the excitation photon energy and
+sample temperature. The pump-probe spectroscopic measurements reveal that the
+photo-induced phonon is generated by a displacive mechanism. The amplitude of
+the phononic signal decreases as the sample is heated up to the N\'eel
+temperature and vanishes as the phase transition to the paramagnetic phase
+occurs. This evidence confirms that the excited lattice mode is intimately
+connected to the long-range magnetic order. Therefore our work discloses a
+pathway towards a femtosecond coherent manipulation of the magneto-crystalline
+anisotropy in a van der Waals antiferromagnet. In fact, it is reported that by
+applying a magnetic field the induced phonon mode hybridizes via the
+Kittel-mechanism with zone-centre magnons.",2111.01464v1
+2021-11-05,Quadrupolar magnetic excitations in an isotropic spin-1 antiferromagnet,"The microscopic origins of emergent behaviours in condensed matter systems
+are encoded in their excitations. In ordinary magnetic materials, single
+spin-flips give rise to collective dipolar magnetic excitations called magnons.
+Likewise, multiple spin-flips can give rise to multipolar magnetic excitations
+in magnetic materials with spin $\mathbf{S} \boldsymbol{\ge} \mathbf{1}$.
+Unfortunately, since most experimental probes are governed by dipolar selection
+rules, collective multipolar excitations have generally remained elusive. For
+instance, only dipolar magnetic excitations have been observed in isotropic
+$\mathbf{S}\boldsymbol{=}\mathbf{1}$ Haldane spin systems. Here, we unveil a
+hidden quadrupolar constituent of the spin dynamics in antiferromagnetic
+$\mathbf{S}\boldsymbol{=}\mathbf{1}$ Haldane chain material
+Y$_\mathbf{2}$BaNiO$_\mathbf{5}$ using Ni $\mathbf{L_3}$-edge resonant
+inelastic x-ray scattering. Our results demonstrate that pure quadrupolar
+magnetic excitations can be probed without direct interactions with dipolar
+excitations or anisotropic perturbations. Originating from on-site double
+spin-flip processes, the quadrupolar magnetic excitations in
+Y$_\mathbf{2}$BaNiO$_\mathbf{5}$ show a remarkable dual nature of collective
+dispersion. While one component propagates as non-interacting entities, the
+other behaves as a bound quadrupolar magnetic wave. This result highlights the
+rich and largely unexplored physics of higher-order magnetic excitations.",2111.03625v1
+2021-11-05,Ultrafast optical excitation of magnetic dynamics in van der Waals magnets: Coherent magnons and BKT dynamics in NiPS$_3$,"Optical pump-probe experiments carried out in the time domain reveal both the
+intrinsic low energy dynamics and its connections to higher energy excitations
+in correlated electron systems. In this work, we propose two microscopic
+mechanisms for the optical generation of coherent magnetic modes in van der
+Waals magnets, and derive the corresponding effective light-spin interactions:
+either through pumping atomic orbital excitations resonantly or via a
+light-induced Floquet spin Hamiltonian, the ground state of the system is
+driven out of equilibrium. The subsequent long-time relaxational dynamics can
+then be probed using, e.g. the magneto-optical Kerr effect or transient grating
+spectroscopy. As an example, we apply our framework to NiPS$_3$, which is
+magnetically ordered in the bulk, and is conjectured to realize the XY model in
+the monolayer limit. Our theory makes explicit how the material's low-energy
+response depends sensitively on the microscopic details of the light-spin
+coupling as well as pump fluence, frequency and polarization. For the case of
+bulk NiPS$_3$, we find quantitative agreement with recent experiments by
+Afanasiev et al. [Science Advances 7, abf3096 (2021)]. We further propose
+pump-probe experiments for monolayer NiPS$_3$ and detail how anomalous
+relaxational behaviour may reveal excitations of a (proximate) BKT phase in a
+proposed effective XY model.",2111.03674v2
+2021-11-08,Magnetic properties of a capped kagome molecule with 60 quantum spins,"We compute ground-state properties of the isotropic, antiferromagnetic
+Heisenberg model on the sodalite cage geometry. This is a 60-spin spherical
+molecule with 24 vertex-sharing tetrahedra which can be regarded as a molecular
+analogue of a capped kagome lattice and which has been synthesized with
+high-spin rare-earth atoms. Here, we focus on the $S=1/2$ case where quantum
+effects are strongest. We employ the SU(2)-symmetric density-matrix
+renormalization group (DMRG).
+  We find a threefold degenerate ground state that breaks the spatial symmetry
+and that splits up the molecule into three large parts which are almost
+decoupled from each other. This stands in sharp contrast to the behaviour of
+most known spherical molecules. On a methodological level, the disconnection
+leads to ""glassy dynamics"" within the DMRG that cannot be targeted via standard
+techniques.
+  In the presence of finite magnetic fields, we find broad magnetization
+plateaus at 4/5, 3/5, and 1/5 of the saturation, which one can understand in
+terms of localized magnons, singlets, and doublets which are again nearly
+decoupled from each other. At the saturation field, the zero-point entropy is
+$S=\ln(182)\approx 5.2$ in units of the Boltzmann constant.",2111.04549v4
+2021-11-09,Spin-lattice couplings in two-dimensional CrI$_3$ from first-principles study,"Since thermal fluctuations become more important as dimensions shrink, it is
+expected that low-dimensional magnets are more sensitive to lattice distortions
+and phonons than bulk systems are. Here we present a fully relativistic
+first-principles study on the spin-lattice coupling, i.e. how the magnetic
+interactions depend on local lattice distortions, of the prototypical
+two-dimensional ferromagnet CrI$_3$. We extract an effective measure of the
+spin-lattice coupling in CrI$_3$ which is up to ten times larger than what is
+found for bcc Fe. The magnetic exchange interactions, including Heisenberg and
+relativistic Dzyaloshinskii-Moriya interactions, are sensitive both to the
+in-plane motion of Cr atoms and out-of-plane motion of ligand atoms. We find
+that significant magnetic pair interactions change sign from ferromagnetic (FM)
+to anti-ferromagnetic (AFM) for atomic displacements larger than 0.16 {\AA}. We
+explain the observed strong spin-lattice coupling by analyzing the orbital
+decomposition of isotropic exchange interactions, involving different
+crystal-field-split Cr$-3d$ orbitals. The competition between the AFM t$_{2g}$
+- t$_{2g}$ and FM t$_{2g}$ - e$_{g}$ contributions depends on the bond angle
+formed by Cr and I atoms as well as Cr-Cr distance. In particular, if a Cr atom
+is displaced, the FM-AFM sign change when the I-Cr-I bond angle approaches
+90$^\circ$. The obtained spin-lattice coupling constants, along with the
+microscopic orbital analysis can act as a guiding principle for further studies
+of the thermodynamic properties and combined magnon-phonon excitations in
+two-dimensional magnets.",2111.05382v1
+2021-11-15,Relating spin-polarized STM imaging and inelastic neutron scattering in the van-der-Waals ferromagnet Fe3GeTe2,"Van-der-Waals (vdW) ferromagnets have enabled the development of
+heterostructures assembled from exfoliated monolayers with spintronics
+functionalities, making it important to understand and ultimately tune their
+magnetic properties at the microscopic level. Information about the magnetic
+properties of these systems comes so far largely from macroscopic techniques,
+with little being known about the microscopic magnetic properties. Here, we
+combine spin-polarized scanning tunneling microscopy and quasi-particle
+interference imaging with neutron scattering to establish the magnetic and
+electronic properties of the metallic vdW ferromagnet Fe3GeTe2. By imaging
+domain walls at the atomic scale, we can relate the domain wall width to the
+exchange interaction and magnetic anisotropy extracted from the magnon
+dispersion as measured in inelastic neutron scattering, with excellent
+agreement between the two techniques. From comparison with Density Functional
+Theory calculations we can assign the quasi-particle interference to be
+dominated by spin-majority bands. We find a dimensional dichotomy of the bands
+at the Fermi energy: bands of minority character are predominantly
+two-dimensional in character, whereas the bands of majority character are
+three-dimensional. We expect that this will enable new design principles for
+spintronics devices.",2111.08013v1
+2021-11-29,Magnetic anisotropy and magnetic ordering of transition-metal phosphorus trisulfides,"Here, a magnetic model with an unprecedentedly large number of parameters was
+determined from first-principles calculations for transition-metal phosphorus
+trisulfides (TMPS$_3$'s), which reproduced the measured magnetic ground states
+of bulk TMPS$_3$'s. Our Monte Carlo simulations for the critical temperature,
+magnetic susceptibility, and specific heat of bulk and few-layer TMPS$_3$'s
+agree well with available experimental data and show that the antiferromagnetic
+order of FePS$_3$ and NiPS$_3$ persists down to monolayers. Remarkably, the
+orbital polarization, which was neglected in recent first-principles studies,
+dramatically enhances the magnetic anisotropy of FePS$_3$ by almost two orders
+of magnitude. A recent Raman study [K. Kim et al., Nat. Commun. 10, 345 (2019)]
+claimed that magnetic ordering is absent in monolayer NiPS$_3$ but
+simultaneously reported a strong two-magnon continuum; we show that the
+criterion used to judge magnetic ordering there is invalid in monolayer
+NiPS$_3$, thus providing an understanding of the two seemingly contradictory
+experimental results. The rich predictions on the magnetic susceptibility and
+specific heat of few-layer FePS$_3$ and NiPS$_3$ await immediate experimental
+verifications.",2111.14869v1
+2021-11-30,Comparison of spin-wave transmission in parallel and antiparallel magnetic configurations,"Parallel (P) and antiparallel (AP) configurations are widely applied in
+magnetic heterostructures and have significant impacts on the spin-wave
+transmission in magnonic devices. In the present study, a theoretical
+investigation was conducted into the transmission of exchange-dominated spin
+waves with nanoscale wavelengths in a type of heterostructure including two
+magnetic media, of which the magnetization state can be set to the P (AP)
+configuration by ferromagnetic (antiferromagnetic) interfacial exchange
+coupling (IEC). The boundary conditions in P and AP cases were derived, by
+which the transmission and reflection coefficients of spin waves were
+analytically given and numerically calculated. In the P configuration, a
+critical angle $\theta_{\textrm{c}}$ always exists and has a significant
+influence on the transmission. Spin waves are refracted and reflected when the
+incident angle $\theta_{\textrm{i}}$ is smaller than the critical angle
+($\theta_{\textrm{i}} < \theta_{\textrm{c}}$), while total reflection occurs as
+$\theta_{\textrm{i}} \geq \theta_{\textrm{c}}$. In the AP configuration, the
+spin-wave polarizations of medium 1 and 2 are inverse, that is, right-handed
+(RH) and left-handed (LH), leading to the total reflection being independent of
+$\theta_{\textrm{i}}$. As demonstrated by the difference in spin-wave
+transmission properties between the P ($\theta_{\textrm{i}} <
+\theta_{\textrm{c}}$) and AP cases, there is a polarization-dependent
+scattering. However, as $\theta_{\textrm{i}}$ exceeds $\theta_{\textrm{c}}$,
+the P ($\theta_{\textrm{i}} > \theta_{\textrm{c}}$) case exhibits similarities
+with the AP case, where the transmitted waves are found to be evanescent in
+medium 2 and their decay lengths are investigated.",2111.15091v2
+2021-12-01,Low power continuous-wave all-optical magnetic switching in ferromagnetic nanoarrays,"All-optical magnetic switching promises ultrafast, high-resolution
+magnetisation control with the technological attraction of requiring no
+magnetic field. Existing all-optical switching schemes are driven by ultrafast
+transient effects, typically requiring power-hungry femtosecond-pulsed lasers
+and complex magnetic materials. Here, we demonstrate deterministic, all-optical
+magnetic switching in simple ferromagnetic nanomagnets (Ni$_{81}$Fe$_{19}$,
+Ni$_{50}$Fe$_{50}$) with sub-diffraction limit dimensions using a focused
+low-power, linearly-polarised continuous-wave laser. Isolated nanomagnets are
+switched across a range of dimensions, laser wavelengths and powers. All
+square-geometry artificial spin ice vertex configurations are written,
+including ground-state and energetically-unfavourable `monopole-like' states at
+powers as low as 2.74 mW. Usually, magnetic switching with linearly polarised
+light is symmetry-forbidden; however, here the laser spot has a similar size to
+the nanomagnets, producing an absorption distribution dependent on the relative
+nanoisland-spot displacement. We attribute the observed deterministic switching
+to the transient dynamics of this asymmetric absorption. No switching is
+observed in Co samples, suggesting the multi-species nature of NiFe alloys
+plays a role in reversal. The results presented here usher in cheap, low-power
+optically-controlled devices with impact across data storage, neuromorphic
+computation and reconfigurable magnonics.",2112.00697v2
+2021-12-06,Complex magnetic structure and spin waves of the noncollinear antiferromagnet Mn5Si3,"The investigations of the interconnection between micro- and macroscopic
+properties of materials hosting noncollinear antiferromagnetic ground states
+are challenging. These forefront studies are crucial for unraveling the
+underlying mechanisms at play, which may prove beneficial in designing cutting
+edge multifunctional materials for future applications. In this context, Mn5Si3
+has regained scientific interest since it displays an unusual and complex
+ground state, which is considered to be the origin of the anomalous transport
+and thermodynamic properties that it exhibits. Here, we report the magnetic
+exchange couplings of the noncollinear antiferromagnetic phase of Mn5Si3 using
+inelastic neutron scattering measurements and density functional theory
+calculations. We determine the ground-state spin configuration and compute its
+magnon dispersion relations which are in good agreement with the ones obtained
+experimentally. Furthermore, we investigate the evolution of the spin texture
+under the application of an external magnetic field to demonstrate
+theoretically the multiple field-induced phase transitions that Mn5Si3
+undergoes. Finally, we model the stability of some of the material's magnetic
+moments under a magnetic field and we find that very susceptible magnetic
+moments in a frustrated arrangement can be tuned by the field.",2112.03368v1
+2021-12-14,Enhanced valley polarization in WS$_2$/LaMnO$_3$ heterostructure,"Monolayer transition metal dichalcogenides have attracted great attentions
+for potential applications in valleytronics. However, the valley polarization
+degree is usually not high because of the intervalley scattering. Here, we
+demonstrate a largely enhanced valley polarization up to 80\% in monolayer
+WS$_2$ under non-resonant excitation at 4.2 K using WS$_2$/LaMnO$_3$ thin film
+heterostructure, which is much higher than that for monolayer WS$_2$ on
+SiO$_2$/Si substrate with a valley polarization of 15\%. Furthermore, the
+greatly enhanced valley polarization can be maintained to a high temperature of
+about 160 K with a valley polarization of 53\%. The temperature dependence of
+valley polarization is strongly correlated with the thermomagnetic curve of
+LaMnO$_3$, indicating an exciton-magnon coupling between WS$_2$ and LaMnO$_3$.
+A simple model is introduced to illustrate the underlying mechanisms. The
+coupling of WS$_2$ and LaMnO$_3$ is further confirmed with an observation of
+two interlayer excitons with opposite valley polarizations in the
+heterostructure, resulting from the spin-orbit coupling induced splitting of
+the conduction bands in monolayer transition metal dichalcogenides. Our results
+provide a pathway to control the valleytronic properties of transition metal
+dichalcogenides by means of ferromagnetic van der Waals engineering, paving a
+way to practical valleytronic applications.",2112.07321v1
+2021-12-20,On the nature of valence charge and spin excitations via multi-orbital Hubbard models for infinite-layer nickelates,"Building upon the recent progress on the intriguing underlying physics for
+the newly discovered infinite-layer nickelates, in this article we review an
+examination of valence charge and spin excitations via multi-orbital Hubbard
+models as way to determine the fundamental building blocks for Hamiltonians
+that can describe the low energy properties of infinite-layer nickelates. We
+summarize key results from density-functional approaches, and apply them to the
+study of x-ray absorption to determine the valence ground states of
+infinite-layer nickelates in their parent form, and show that a fundamental
+$d^9$ configuration as in the cuprates is incompatible with a self-doped ground
+state having holes in both $d_{x^2-y^2}$ and a rare-earth-derived axial
+orbital. When doped, we determine that the rare-earth-derived orbitals empty
+and additional holes form low spin $(S=0)$ $d^8$ Ni states, which can be
+well-described as a doped single-band Hubbard model. Using exact
+diagonalization for a 2-orbital model involving Ni and rare earth orbitals, we
+find clear magnons at 1/2 filling that persist when doped, albeit with larger
+damping, and with a dependence on the precise orbital energy separation between
+the Ni- and rare-earth-derived orbitals. Taken together, a full two-band model
+for infinite-layer nickelates can well describe the valence charge and spin
+excitations observed experimentally.",2112.10758v1
+2021-12-21,Fast long-wavelength exchange spin waves in partially-compensated Ga:YIG,"Spin waves in yttrium iron garnet (YIG) nano-structures attract increasing
+attention from the perspective of novel magnon-based data processing
+applications. For short wavelengths needed in small-scale devices, the group
+velocity is directly proportional to the spin-wave exchange stiffness constant
+$\lambda_\mathrm{ex}$. Using wave vector resolved Brillouin Light Scattering
+(BLS) spectroscopy, we directly measure $\lambda_\mathrm{ex}$ in Ga-substituted
+YIG thin films and show that it is about three times larger than for pure YIG.
+Consequently, the spin-wave group velocity overcomes the one in pure YIG for
+wavenumbers $k > 4$ rad/$\mu$m, and the ratio between the velocities reaches a
+constant value of around 3.4 for all $k > 20$ rad/$\mu$m. As revealed by
+vibrating-sample magnetometry (VSM) and ferromagnetic resonance (FMR)
+spectroscopy, Ga:YIG films with thicknesses down to 59 nm have a low Gilbert
+damping ($\alpha < 10^{-3}$), a decreased saturation magnetization $\mu_0
+M_\mathrm{S}~\approx~20~$mT and a pronounced out-of-plane uniaxial anisotropy
+of about $\mu_0 H_{\textrm{u1}} \approx 95 $ mT which leads to an out-of-plane
+easy axis. Thus, Ga:YIG opens access to fast and isotropic spin-wave transport
+for all wavelengths in nano-scale systems independently of dipolar effects.",2112.11348v1
+2021-12-25,Lattice and magnetic dynamics in YVO$_{3}$ Mott insulator studied by neutron scattering and first-principles calculations,"The Mott insulator YVO$_{3}$ with $T_{N}$ = 118 K is revisited to explore the
+role of spin, lattice and orbital correlations across the multiple structural
+and magnetic transitions observed as a function of temperature. Upon cooling,
+the crystal structure changes from orthorhombic to monoclinic at 200 K, and
+back to orthorhombic at 77 K, followed by magnetic transitions. From the
+paramagnetic high temperature phase, C-type ordering is first observed at 118
+K, followed by a G-type spin re-orientation transition at 77 K. The dynamics of
+the transitions were investigated via inelastic neutron scattering and first
+principles calculations. An overall good agreement between the neutron data and
+calculated spectra was observed. From the magnon density of states, the
+magnetic exchange constants were deduced to be $J_{ab}$ = $J_{c}$ = -5.8 meV in
+the G-type spin phase, and $J_{ab}$ = -3.8 meV, $J_{c}$ = 7.6 meV at 80 K and
+$J_{ab}$ = -3.0 meV, $J_{c}$ = 6.0 meV at 100 K in the C-type spin phase.
+Paramagnetic scattering was observed in the spin ordered phases, well below the
+C-type transition temperature, that continuously increased above the
+transition. Fluctuations in the temperature dependence of the phonon density of
+states were observed between 50 and 80 K as well, coinciding with the G-type to
+C-type transition. These fluctuations are attributed to optical oxygen modes
+above 40 meV, from first principles calculations. In contrast, little change in
+the phonon spectra is observed across $T_{N}$.",2112.13172v1
+2022-01-12,Asymmetric modulation of Majorana excitation spectra and nonreciprocal thermal transport in the Kitaev spin liquid under a staggered magnetic field,"We present the theoretical results for the Majorana band structure and
+thermal transport properties in the Kitaev honeycomb model under a staggered
+magnetic field in addition to a uniform one. The Majorana band structure is
+asymmetrically modulated in momentum space, and the valley degree of freedom is
+activated and controlled by the magnitudes and directions of the uniform and
+staggered magnetic fields; as a result, the Majorana excitation is either
+gapped or gapless, the latter of which in general has Majorana Fermi surfaces,
+in contrast to the point nodes in the absence of the fields. We show that the
+asymmetric deformation of the Majorana band induces a nonlinear (nonreciprocal)
+thermal transport, in addition to the linear one. The field dependence of the
+linear thermal current is correlated with the magnitude of the Majorana gap,
+while that of the nonlinear thermal current is associated with the asymmetry of
+the Majorana excitation spectra. We show the estimates of the thermal currents
+and discuss that the linear response is experimentally measurable, whereas
+future improvement is required for the observation of the nonlinear one. We
+also discuss how the thermal currents are modulated by other additional effects
+of the magnetic field and contributions from conventional magnons, latter of
+which are expected in heterostructures to realize an internal staggered
+magnetic field.",2201.04274v2
+2022-01-28,Spin Excitation Spectra of Anisotropic Spin-$1/2$ Triangular Lattice Heisenberg Antiferromagnets,"Investigation of dynamical excitations is difficult but crucial to the
+understanding of many exotic quantum phenomena discovered in quantum materials.
+This is particularly true for highly frustrated quantum antiferromagnets whose
+dynamical properties deviate strongly from theoretical predictions made based
+on the spin-wave or other approximations. Here we present a large-scale
+numerical calculation on the dynamical correlation functions of spin-$1/2$
+triangular Heisenberg model using a state-of-the-art tensor network
+renormalization group method. The calculated results allow us to gain for the
+first time a comprehensive picture on the nature of spin excitation spectra in
+this highly frustrated quantum system. It provides a quantitative account for
+all the key features of the dynamical spectra disclosed by inelastic neutron
+scattering measurements for $\rm Ba_3CoSb_2O_9$, revealing the importance of
+the interplay between low- and high-energy excitations and its renormalization
+effect to the low-energy magnon bands and high-energy continuums. We identify
+the longitudinal Higgs modes in the intermediate-energy scale and predict the
+energy and momentum dependence of spectral functions along the three principal
+axes that can be verified by polarized neutron scattering experiments.
+Furthermore, we find that the spin excitation spectra weakly depend on the
+anisotropic ratio of the antiferromagnetic interaction.",2201.12121v2
+2022-02-09,Nonreciprocal transport in a bilayer of MnBi2Te4 and Pt,"MnBi2Te4 (MBT) is the first intrinsic magnetic topological insulator with the
+interaction of spin-momentum locked surface electrons and intrinsic magnetism,
+and it exhibits novel magnetic and topological phenomena. Recent studies
+suggested that the interaction of electrons and magnetism can be affected by
+the Mn-doped Bi2Te3 phase at the surface due to inevitable structural defects.
+Here we report an observation of nonreciprocal transport, i.e.
+current-direction-dependent resistance, in a bilayer composed of
+antiferromagnetic MBT and nonmagnetic Pt. The emergence of the nonreciprocal
+response below the N\'eel temperature confirms a correlation between
+nonreciprocity and intrinsic magnetism in the surface state of MBT. The angular
+dependence of the nonreciprocal transport indicates that nonreciprocal response
+originates from the asymmetry scattering of electrons at the surface of MBT
+mediated by magnon. Our work provides an insight into nonreciprocity arising
+from the correlation between magnetism and Dirac surface electrons in intrinsic
+magnetic topological insulators.",2202.05398v1
+2022-02-21,Thermal Conductivity and Theory of Inelastic Scattering of Phonons by Collective Fluctuations,"We study the intrinsic scattering of phonons by a general quantum degree of
+freedom, i.e. a fluctuating ""field"" $Q$, which may have completely general
+correlations, restricted only by unitarity and translational invariance. From
+the induced scattering rates, we obtain the consequences on the thermal
+conductivity tensor of the phonons. We find that the lowest-order diagonal
+scattering rate, which determines the longitudinal conductivity, is controlled
+by two-point correlation functions of the $Q$ field, while the off-diagonal
+scattering rates involve a minimum of three to four point correlation
+functions. We obtain general and explicit forms for these correlations which
+isolate the contributions to the Hall conductivity, and provide a general
+discussion of the implications of symmetry and equilibrium. We evaluate these
+two- and four-point correlation functions and hence the thermal transport for
+the illustrative example of an ordered two dimensional antiferromagnet. In this
+case the $Q$ field is a composite of magnon operators arising from spin-lattice
+coupling. A numerical evaluation of the required integrals demonstrates that
+the results satisfy all the necessary symmetry restrictions but otherwise lead
+to non-vanishing scattering and Hall effects, and in particular that this
+mechanism leads to comparable thermal Hall conductivity for thermal currents
+within and normal to the plane of the antiferromagnetism.",2202.10366v3
+2022-03-04,Exchange interactions and spin dynamics in the layered honeycomb ferromagnet CrI$_3$,"We derive the microscopic spin Hamiltonian for rhombohedral CrI$_3$ using
+extensive first-principles density functional theory (DFT) calculations which
+incorporate spin-orbit coupling and Hubbard U. Our calculations indicate a
+dominant nearest-neighbor ferromagnetic Heisenberg exchange with weaker
+further-neighbor Heisenberg terms. In addition, we find a Dzyaloshinskii-Moriya
+interaction which primarily drives a topological gap in the spin-wave spectrum
+at the Dirac point, and uncover a non-negligible antiferromagnetic Kitaev
+coupling between the S=3/2 Cr moments. The out-of-plane magnetic moment is
+stabilized by weak symmetric bond-dependent terms and a local single-ion
+anisotropy. Using linear spin wave theory, we find that our exchange parameters
+are in reasonably good agreement with inelastic neutron scattering (INS)
+experiments. Employing classical Monte Carlo simulations, we study the magnetic
+phase transition temperature $T_c$ and its evolution with an applied in-plane
+magnetic field. We further demonstrate how future high-resolution INS
+experiments on the magnon dispersion of single crystals in an in-plane magnetic
+field may be used to quantitatively extract the strength of the
+antiferromagnetic Kitaev exchange coupling.",2203.02567v1
+2022-03-17,Tilings and Twist at 1/N^4,"We re-consider operator mixing in the so-called $SU(2)$ sector of ${\cal N}
+\, = \, 4$ super Yang-Mills theory with gauge group $SU(N)$. Where possible,
+single-trace operators of moderate length are completed by higher-trace
+admixtures so as to yield large $N$ tree level eigenstates.
+  We are particularly interested in parity pairs with three excitations. Since
+parity is respected in the mixing, the odd single-trace operators at low length
+cannot receive too many admixtures. We reproduce the tree-level norms of a set
+of large $N$ eigenstates up to order $1/N^4$ by integrability methods. This
+involves evaluating two-point functions on the sphere, the torus, and the
+double-torus. A perfect match is found as long as descendents are absent from
+the mixing.
+  Using twist to make the descendents appear in the integrability picture
+immediately leads to the question how to modify the entangled states occurring
+in the hexagon tessellations. We take a closer look at the double-trace
+admixtures to the parity even three-excitation operator at length seven, which
+are both products of a primary state and a descendent. Their two-point
+functions are sensitive to the twist introduced into the Bethe equations. For
+transverse scalar excitations we succeed in recovering the corresponding field
+theory results. For longitudinal magnons our methods fail, pointing at a
+potential weakness of the formalism.",2203.09399v1
+2022-03-21,Scattering of spin waves by a Bloch domain wall: effect of the dipolar interaction,"It is known that a Bloch domain wall in an anisotropic ferromagnet is
+transparent to spin waves. This result is derived by approximating the dipolar
+interaction between magnetic moments by an effective anisotropy interaction. In
+this paper we study the the scattering of spin waves by a domain wall taking
+into account the full complexity of the dipolar interaction, treating it
+perturbatively in the distorted wave Born approximation. Due to the
+peculiarities of the dipolar interaction, the implementation of this
+approximation is not straightforward. The difficulties are circumvented here by
+realizing that the contribution of the dipolar interaction to the spin wave
+operator can be split into two terms: i) an operator that commutes with the
+spin wave operator in absence of dipolar interaction, and ii) a local operator
+suitable to be treated as a perturbation in the distorted wave Born
+approximaton. We analyze the scattering parameters obtained within this
+approach. It turns out that the reflection coefficient does not vanish in
+general, and that the transmitted waves suffer a lateral shift even at normal
+incidence. This lateral shift can be greatlty enhanced by making the spin wave
+go through an array of well separated domain walls. The outgoing spin wave will
+no be attenuated by the scattering at the domain walls since the reflection
+coefficient vanishes at normal incidence. This effect may be very useful to
+control the spin waves in magnonic devices.",2203.11140v1
+2022-03-29,"Coupled frustrated ferromagnetic and antiferromagnetic quantum spin chains in the quasi-one-dimensional mineral antlerite, Cu$_3$SO$_4$(OH)$_4$","Magnetic frustration, the competition among exchange interactions, often
+leads to novel magnetic ground states with unique physical properties which can
+hinge on details of interactions that are otherwise difficult to observe. Such
+states are particularly interesting when it is possible to tune the balance
+among the interactions to access multiple types of magnetic order. We present
+antlerite, Cu$_3$SO$_4$(OH)$_4$, as a potential platform for tuning
+frustration. Contrary to previous reports, the low-temperature magnetic state
+of its three-leg zigzag ladders is a quasi-one-dimensional analog of the
+magnetic state recently proposed to exhibit spinon-magnon mixing in
+botallackite. Density functional theory calculations indicate that antlerite's
+magnetic ground state is exquisitely sensitive to fine details of the atomic
+positions, with each chain independently on the cusp of a phase transition,
+indicating an excellent potential for tunability.",2203.15343v2
+2022-04-08,Probing the spin dimensionality in single-layer CrSBr van der Waals heterostructures by magneto-transport measurements,"Two-dimensional (2D) magnetic materials offer unprecedented opportunities for
+fundamental physics and applied research in spintronics and magnonics. Beyond
+the pioneering studies on 2D CrI3 and Cr2Ge2Te6, this emerging field has
+expanded to 2D antiferromagnets exhibiting different spin anisotropies and
+textures. Of particular interest is the layered metamagnet CrSBr, a relatively
+air-stable semiconductor formed by antiferromagnetically-coupled ferromagnetic
+layers (Tc~150 K) that can be exfoliated down to the single-layer. It presents
+a complex magnetic behavior with a dynamic magnetic crossover leading to a
+low-temperature hidden order below T*~40 K. Here, we inspect the
+magneto-transport properties of CrSBr vertical heterostructures in the 2D
+limit. Our results demonstrate the marked low-dimensional character of the
+ferromagnetic monolayer, with short-range correlations above Tc and an
+Ising-type in-plane anisotropy, being the spins spontaneously aligned along the
+easy-axis b below Tc. By applying moderate magnetic fields along a and c axes,
+a spin reorientation occurs, leading to a magnetoresistance enhancement below
+T*. In multilayers, a spin-valve behavior is observed, with negative
+magnetoresistance strongly enhanced along the three directions below T*. These
+results show that CrSBr monolayer/bilayer provides an ideal platform for
+studying and controlling field-induced phenomena in two-dimensions, offering
+new insights regarding 2D magnets and their integration into vertical
+spintronic devices.",2204.04095v2
+2022-05-08,Spin interaction and magnetism in cobaltate Kitaev candidate materials: an $ab$ $initio$ and model Hamiltonian approach,"In the quest for materials hosting Kitaev spin liquids, much of the efforts
+have been focused on the fourth- and fifth-row transition metal compounds,
+which are spin-orbit coupling assisted Mott insulators. Here, we study the
+structural and magnetic properties of 3$d$ transition metal oxides,
+Na$_2$Co$_2$TeO$_6$ and Na$_3$Co$_2$SbO$_6$. The partial occupancy of sodium in
+former compound is addressed using a cluster expansion, and a honeycomb lattice
+of sodiums is found to be energetically favored. Starting from the \textit{ab
+initio} band structures, a many-body second order perturbation theory leads to
+a pseudospin-$\frac{1}{2}$ Hamiltonian with estimated magnetic interactions. We
+show that the experimentally observed zigzag magnetic state is stabilized only
+when the first neighbor Kitaev coupling dominates over the Heisenberg term,
+both of which are highly suppressed due to presence of $e_g$ orbitals. A third
+neighbor Heisenberg interaction is found dominant in both these compounds. We
+also present a phase diagram for Na$_2$Co$_2$TeO$_6$ by varying the
+electron-electron and spin-orbit interactions. The computed spin excitation
+spectra are found to capture essential features of recent experimental magnon
+spectrum, lending support to our results.",2205.03836v2
+2022-05-16,Phase diagram and magnetic excitations of $J_1$-$J_3$ Heisenberg model on the square lattice,"We study the phase diagram and the dynamical spin structure factor of the
+spin-1/2 J1-J3 Heisenberg model on the square lattice using density matrix
+renormalization group, exact diagonalization (ED), and cluster perturbation
+theory (CPT). By extrapolating the order parameters and studying the level
+crossings of the low-lying energy and entanglement spectra, we obtain the phase
+diagram of this model and identify a narrow region of quantum spin liquid (QSL)
+phase followed by a plaquette valence-bond solid (PVBS) state in the
+intermediate region, whose nature has been controversial for many years. More
+importantly, we use CPT and ED to study the dynamical spin structure factor in
+the QSL and the PVBS phase. In the QSL phase, the high-energy magnon mode
+completely turns into some dispersive weak excitations around the X and M
+points. For the PVBS phase, the low-energy spectrum is characterized by a
+gapped triplet excitation, and at the high energy, we find another branch of
+dispersive excitation with broad continua, which is unlike the plaquette phase
+in the 2x2 checkerboard model. In the latter case, the second branch of
+excitation is nearly flat due to the weak effective interactions between the
+local excitations of the plaquettes. And in the J1-J3 Heisenberg model, the
+uniform interactions and the spontaneously translational symmetry breaking of
+the PVBS phase make the difference in the excitation spectra.",2205.07910v2
+2022-05-25,Spin dynamics and continuum spectra of the honeycomb J1-J2 antiferromagnetic Heisenberg model,"We employ the spin cluster perturbation theory to investigate the dynamical
+properties of the antiferromagnetic $J_{1}$-$J_{2}$ Heisenberg model on the
+honeycomb lattice. We obtain the excitation spectra for all possible phases in
+the phase diagram, including the N\'{e}el phase, plaquette valence-bond-solid
+phase, dimer valence-bond-solid phase and stripe antiferromagnetic phase. In
+the N\'{e}el phase, besides the obvious renormalization of the magnon
+dispersion, we find that the spectrum exhibits a dome-shaped broad continuum
+around the second Brillouin zone (BZ) and the additional strong continuum close
+to the corner of the BZ. In the valence-bond-solid phases, the spectra are
+dominated by a strong broad continuum all the way down to below $J_1$
+coexisting with the lowest-energy triplon modes characterizing the plaquette
+and dimer phases. We ascribe this strong broad continuum and the additional
+continuum close to the BZ corner in the N\'{e}el phase to the contributions of
+fractionalized spinon excitations. In the stripe phase, a clear difference from
+the linear spin wave approximation is that the spectrum is gapped at the $M$
+point while that obtained by the latter is gapless due to the strong quantum
+fluctuations. We point out that the features observed in the N\'{e}el phase are
+consistent with the recent neutron scattering experiments on YbCl$_{3}$ and
+YbBr$_{3}$.",2205.12822v1
+2022-05-26,Enhanced collisionless laser absorption in strongly magnetized plasmas,"Strongly magnetizing a plasma adds a range of waves that do not exist in
+unmagnetized plasmas and enlarges the laser-plasma interaction (LPI) landscape.
+In this paper, we use particle-in-cell (PIC) simulations to investigate
+strongly magnetized LPI in one dimension under conditions relevant for
+magneto-inertial fusion experiments, focusing on a regime where the
+electron-cyclotron frequency is greater than the plasma frequency and the
+magnetic field is at an oblique angle with respect to the wave vectors. We show
+that when electron-cyclotron-like hybrid wave frequency is about half the laser
+frequency, the laser light resonantly decays to magnetized plasma waves via
+primary and secondary instabilities with large growth rates. These distinct
+magnetic-field-controlled instabilities, which we collectively call two-magnon
+decays, are analogous to two-plasmon decays in unmagnetized plasmas. Since
+additional phase mixing mechanisms are introduced by the oblique magnetic
+field, collisionless damping of large-amplitude magnetized waves substantially
+broadens the electron distribution function, especially along the direction of
+the magnetic field. During this process, energy is transferred efficiently from
+the laser to plasma waves and then to electrons, leading to a large overall
+absorptivity when strong resonances are present. The enhanced laser energy
+absorption may explain hotter-than-expected temperatures observed in magnetized
+laser implosion experiments and may also be exploited to develop more efficient
+laser-driven x-ray sources.",2205.13478v2
+2022-05-30,Geometrical frustration versus Kitaev interactions in BaCo$_2$(AsO$_4$)$_2$,"Recently, Co-based honeycomb magnets have been proposed as promising
+candidate materials to host the Kitaev spin liquid state. One of the
+front-runners is BaCo$_2$(AsO$_4$)$_2$ (BCAO), where it was suggested that the
+exchange processes between Co$^{2+}$ ions via the surrounding edge-sharing
+oxygen octahedra could give rise to bond-dependent Kitaev interactions. In this
+work, we present and analyze comprehensive inelastic neutron scattering studies
+of BCAO with fields in the honeycomb plane. Combining the constraints from the
+magnon excitations in the high-field polarized state and the inelastic spin
+structure factor measured in zero magnetic field, we examine two leading
+theoretical models: the Kitaev-type \JKG model and the \XXZ model. We show that
+the existing experimental data can be consistently accounted for by the \XXZ
+model but not by the \JKG model, and we discuss the implications of these
+results for the realization of a spin liquid phase in BCAO and more generally
+for the realization of the Kitaev model in cobaltates.",2205.15262v1
+2022-06-06,Quantitative theory of magnetic interactions in solids,"In this report we review the method of explicit calculations of interatomic
+exchange interactions of magnetic materials. This involves exchange mechanisms
+normally referred to as Heisenberg exchange, Dzyaloshinskii-Moriya interaction
+and anisotropic symmetric exchange. The connection between microscopic theories
+of the electronic structure, such as density functional theory or dynamical
+mean field theory, and interatomic exchange, is given in detail. The different
+aspects of extracting information for an effective spin Hamiltonian that
+involves thousands of atoms, from electronic structure calculations considering
+significantly fewer atoms (1-50) is highlighted. Examples of exchange
+interactions of a large group of materials is presented, which involves heavy
+elements of the 3d period, alloys between transition metals, Heusler compounds,
+multilayer systems as well as overlayers and adatoms on a substrate, transition
+metal oxides, 4f elements, magnetic materials in two dimensions and molecular
+magnets. Where possible, a comparison to experimental data is made, that
+naturally becomes focused on the magnon dispersion. The influence of relativity
+is reviewed for a few cases, as is the importance of dynamical correlations.
+Development to theories that handle out of equilibrium conditions is also
+described here. The review ends with a short description of extensions of the
+theories behind explicit calculations of interatomic exchange, to non-magnetic
+situations, e.g. that describe chemical (charge) order and superconductivity.",2206.02415v2
+2022-06-07,Non-volatile electric control of spin-orbit torques in an oxide two-dimensional electron gas,"Spin-orbit torques (SOTs) have opened a novel way to manipulate the
+magnetization using in-plane current, with a great potential for the
+development of fast and low power information technologies. It has been
+recently shown that two-dimensional electron gases (2DEGs) appearing at oxide
+interfaces provide a highly efficient spin-to-charge current interconversion.
+The ability to manipulate 2DEGs using gate voltages could offer a degree of
+freedom lacking in the classical ferromagnetic/spin Hall effect bilayers for
+spin-orbitronics, in which the sign and amplitude of SOTs at a given current
+are fixed by the stack structure. Here, we report the non-volatile
+electric-field control of SOTs in an oxide-based Rashba-Edelstein 2DEG. We
+demonstrate that the 2DEG is controlled using a back-gate electric-field,
+providing two remanent and switchable states, with a large resistance contrast
+of 1064%. The SOTs can then be controlled electrically in a non-volatile way,
+both in amplitude and in sign. This achievement in a 2DEG-CoFeB/MgO
+heterostructures with large perpendicular magnetization further validates the
+compatibility of oxide 2DEGs for magnetic tunnel junction integration, paving
+the way to the advent of electrically reconfigurable SOT MRAMS circuits, SOT
+oscillators, skyrmion and domain-wall-based devices, and magnonic circuits.",2206.03068v1
+2022-06-24,"Symmetry Resolved Entanglement of Excited States in Quantum Field Theory II: Numerics, Interacting Theories and Higher Dimensions","In a recent paper we studied the entanglement content of zero-density excited
+states in complex free quantum field theories, focusing on the symmetry
+resolved entanglement entropy (SREE). By zero-density states we mean states
+consisting of a fixed, finite number of excitations above the ground state in
+an infinite-volume system. The SREE is defined for theories that possess an
+internal symmetry and provides a measure of the contribution to the total
+entanglement of each symmetry sector. In our work, we showed that the ratio of
+Fourier-transforms of the SREEs (i.e. the ratio of charged moments) takes a
+very simple and universal form for these states, which depends only on the
+number, statistics and symmetry charge of the excitations as well as the
+relative size of the entanglement region with respect to the whole system's
+size. In this paper we provide numerical evidence for our formulae by computing
+functions of the charged moments in two free lattice theories: a 1D Fermi gas
+and a complex harmonic chain. We also extend our results in two directions: by
+showing that they apply also to excited states of interacting theories (i.e.
+magnon states) and by developing a higher dimensional generalisation of the
+branch point twist field picture, leading to results in (interacting)
+higher-dimensional models.",2206.12223v2
+2022-07-13,Marginally deformed Schrödinger/dipole CFT correspondence,"We construct and thoroughly study a new integrable example of the AdS/CFT
+correspondence with Schr\""{o}dinger symmetry. On the gravity side, the
+supergravity solution depends on two parameters and is obtained by marginally
+deforming the internal space of the Schr\""{o}dinger background through a series
+of TsT transformations. On the field theory side, we identify the dual field
+theory which also depends on two parameters. We find a point-like string
+solution and derive its dispersion relation. A non-trivial test of the
+correspondence is provided by using the Landau-Lifshitz coherent state approach
+to reproduce the leading, in the deformation parameters, terms of that
+relation. Then, we calculate the Wilson loop, describing the quark/anti-quark
+potential at strong coupling. It exhibits confining behaviour when the
+separation length is much less than the Schr\""{o}dinger parameter. When the
+separation length is much greater than the Schr\""{o}dinger parameter the
+behaviour is that of a conformal theory. Subsequently, we take the Penrose
+limit along a certain null geodesic of the constructed background and calculate
+the bosonic spectrum. Based on that spectrum, we make an educated guess for the
+exact, in the 't Hooft coupling, dispersion relation of the magnon excitations
+in the original doubly deformed background. This provides us with an exact
+prediction for the dimensions of the dual field theory operators.",2207.06092v1
+2022-07-19,Static and dynamical signatures of Dzyaloshinskii-Moriya interactions in the Heisenberg model on the kagome lattice,"Motivated by recent experiments on Cs$_2$Cu$_3$SnF$_{12}$ and
+YCu$_{3}$(OH)$_{6}$Cl$_{3}$, we consider the ${S=1/2}$ Heisenberg model on the
+kagome lattice with nearest-neighbor super-exchange $J$ and (out-of-plane)
+Dzyaloshinskii-Moriya interaction $J_D$, which favors (in-plane) ${\bf
+Q}=(0,0)$ magnetic order. By using both variational Monte Carlo (based upon
+Gutzwiller-projected fermionic wave functions) and tensor-network approaches
+(built from infinite projected-entangled pair/simplex states), we show that the
+ground state develops a finite magnetization for $J_D/J \gtrsim 0.03 - 0.04$,
+while the gapless spin liquid remains stable for smaller values of the
+Dzyaloshinskii-Moriya interaction. The relatively small value of $J_D/J$ for
+which magnetic order sets in is particularly relevant for the interpretation of
+low-temperature behaviors of kagome antiferromagnets, including
+ZnCu$_{3}$(OH)$_{6}$Cl$_{2}$. In addition, we assess the spin dynamical
+structure factors and the corresponding low-energy spectrum, by using the
+variational Monte Carlo technique. The existence of a continuum of excitations
+above the magnon modes is reported within the magnetically ordered phase,
+similarly to what has been detected by inelastic neutron scattering on
+Cs$_{2}$Cu$_{3}$SnF$_{12}$.",2207.09274v3
+2022-07-19,"Supersymmetry on the lattice: Geometry, Topology, and Spin Liquids","In quantum mechanics, supersymmetry (SUSY) posits an equivalence between two
+elementary degrees of freedom, bosons and fermions. Here we show how this
+fundamental concept can be applied to connect bosonic and fermionic lattice
+models in the realm of condensed matter physics, e.g., to identify a variety of
+(bosonic) phonon and magnon lattice models which admit topologically nontrivial
+free fermion models as superpartners. At the single-particle level, the bosonic
+and the fermionic models that are generated by the SUSY are isospectral except
+for zero modes, such as flat bands, whose existence is undergirded by the
+Witten index of the SUSY theory. We develop a unifying framework to formulate
+these SUSY connections in terms of general lattice graph correspondences and
+discuss further ramifications such as the definition of supersymmetric
+topological invariants for generic bosonic systems. Notably, a Hermitian form
+of the supercharge operator, the generator of the SUSY, can itself be
+interpreted as a hopping Hamiltonian on a bipartite lattice. This allows us to
+identify a wide class of interconnected lattices whose tight-binding
+Hamiltonians are superpartners of one another or can be derived via squaring or
+square-rooting their energy spectra all the while preserving band topology
+features. We introduce a five-fold way symmetry classification scheme of these
+SUSY lattice correspondences, including cases with a non-zero Witten index,
+based on a topological classification of the underlying Hermitian supercharge
+operator. These concepts are illustrated for various explicit examples
+including frustrated magnets, Kitaev spin liquids, and topological
+superconductors.",2207.09475v1
+2022-07-26,Dynamics of spin-1/2 $J_1$-$J_2$ model on the triangular lattice,"We discuss spin-$\frac12$ $J_1$--$J_2$ model on the triangular lattice using
+recently proposed bond-operator theory (BOT). In agreement with previous
+discussions of this system, we obtain four phases upon $J_2$ increasing: the
+phase with $120^\circ$ ordering of three sublattices, the spin-liquid phase,
+the state with the collinear stripe order, and the spiral phase. The
+$120^\circ$ and the stripe phases are discussed in detail. All calculated
+static characteristics of the model are in good agreement with previous
+numerical findings. In the $120^\circ$ phase, we observe the evolution of
+quasiparticles spectra and dynamical structure factors (DSFs) upon approaching
+the spin-liquid phase. Some of the considered elementary excitations were
+introduced first in our recent study of this system at $J_2=0$ using the BOT.
+In the stripe phase, we observe that the doubly degenerate magnon spectrum
+known from the spin-wave theory (SWT) is split by quantum fluctuations which
+are taken into account more accurately in the BOT. As compared with other known
+findings of the SWT in the stripe state, we observe additional spin-1 and
+spin-0 quasiparticles which give visible anomalies in the transverse and
+longitudinal DSFs. We obtain also a special spin-0 quasiparticle named singlon
+who produces a peak only in four-spin correlator and who is invisible in the
+longitudinal DSF. We show that the singlon spectrum lies below energies of all
+spin-0 and spin-1 excitations in some parts of the Brillouin zone. Singlon
+spectrum at zero momentum can be probed by the Raman scattering.",2207.12708v3
+2022-08-09,Hybrid spin Hall nano-oscillators based on ferromagnetic metal/ferrimagnetic insulator heterostructures,"Spin-Hall nano-oscillators (SHNOs) are promising spintronic devices to
+realize current controlled GHz frequency signals in nanoscale devices for
+neuromorphic computing and creating Ising systems. However, traditional SHNOs
+-- devices based on transition metals -- have high auto-oscillation threshold
+currents as well as low quality factors and output powers. Here we demonstrate
+a new type of hybrid SHNO based on a permalloy (Py) ferromagnetic-metal
+nanowire and low-damping ferrimagnetic insulator, in the form of epitaxial
+lithium aluminum ferrite (LAFO) thin films. The superior characteristics of
+such SHNOs are associated with the excitation of larger spin-precession angles
+and volumes. We further find that the presence of the ferrimagnetic insulator
+enhances the auto-oscillation amplitude of spin-wave edge modes, consistent
+with our micromagnetic modeling. This hybrid SHNO expands spintronic
+applications, including providing new means of coupling multiple SHNOs for
+neuromorphic computing and advancing magnonics.",2208.04539v2
+2022-08-10,Forward volume magnetoacoustic spin wave excitation with micron-scale spatial resolution,"The interaction between surface acoustic waves (SAWs) and spin waves (SWs) in
+a piezoelectric-magnetic thin film heterostructure yields potential for the
+realization of novel microwave devices and applications in magnonics. In the
+present work, we characterize magnetoacoustic waves in three adjacent magnetic
+micro-stripes made from CoFe+Ga, CoFe, and CoFe+Pt with a single pair of
+tapered interdigital transducers (TIDTs). The magnetic micro-stripes were
+deposited by focused electron beam-induced deposition (FEBID) and focused ion
+beam-induced deposition (FIBID) direct-writing techniques. The transmission
+characteristics of the TIDTs are leveraged to selectively address the
+individual micro-stripes. Here, the external magnetic field is continuously
+rotated out of the plane of the magnetic thin film and the forward volume SW
+geometry is probed with the external magnetic field along the film normal. Our
+experimental findings are well explained by an extended phenomenological model
+based on a modified Landau-Lifshitz-Gilbert approach that considers SWs with
+nonzero wave vectors. Magnetoelastic excitation of forward volume SWs is
+possible because of the vertical shear strain $\varepsilon_{xz}$ of the
+Rayleigh-type SAW.",2208.05205v1
+2022-08-16,Easy-plane anisotropic-exchange magnets on a honeycomb lattice: quantum effects and dealing with them,"We provide analytical and numerical insights into the phase diagram and other
+properties of the extended Kitaev-Heisenberg model on the honeycomb lattice in
+the {\it easy-plane} limit, in which interactions are only between spin
+components that belong to the plane of magnetic ions. This parameter subspace
+allows for a much-needed systematic {\it quantitative} investigation of spin
+excitations in the ordered phases and of their generic features. Specifically,
+we demonstrate that in this limit one can consistently take into account magnon
+interactions in both zero-field zigzag and field-polarized phases. For the
+nominally polarized phase, we propose a regularization of the unphysical
+divergences that occur at the critical field and are plaguing the
+$1/S$-approximation in this class of models. For the explored parameter
+subspace, all symmetry-allowed terms of the standard parametrization of the
+extended Kitaev-Heisenberg model, such as $K$, $J$, and $\Gamma$, are
+significant, making the offered consideration relevant to a much wider
+parameter space. The dynamical structure factor near paramagnetic critical
+point illustrates this relevance by showing features that are reminiscent of
+the ones observed in $\alpha$-RuCl$_3$, underscoring that they are not unique
+and should be common to a wide range of parameters of the model and, by an
+extension, to other materials.",2208.07617v3
+2022-08-16,Liger at Keck Observatory: Design of Imager Optical Assembly and Spectrograph Re-Imaging Optics,"Liger is an adaptive optics (AO) fed imager and integral field spectrograph
+(IFS) designed to take advantage of the Keck All-sky Precision Adaptive-optics
+(KAPA) upgrade for the W.M. Keck Observatory. We present the design and
+analysis of the imager optical assembly including the spectrograph Re-Imaging
+Optics (RIO) which transfers the beam path from the imager focal plane to the
+IFS slicer module and lenslet array. Each imager component and the first two
+RIO mechanisms are assembled and individually aligned on the same optical
+plate. Baffling suppresses background radiation and scattered light, and a
+pupil viewing camera allows the imager detector to focus on an image of the
+telescope pupil. The optical plate mounts on an adapter frame for alignment of
+the overall system. The imager and RIO will be characterized in a cryogenic
+test chamber before installation in the final science cryostat.",2208.07936v1
+2022-09-06,Dynamic coupling and spin-wave dispersions in a magnetic hybrid system made of an artificial spin-ice structure and an extended NiFe underlayer,"We present a combined experimental and numerical study of the spin-wave
+dispersion in NiFe artificial spin-ice (ASI) system consisting of an array of
+stadium-shaped nanoislands deposited on the top of a continuous NiFe film with
+nonmagnetic spacer layers of varying thickness. The spin-wave dispersion,
+measured by wavevector resolved Brillouin light scattering spectroscopy in the
+Damon-Eshbach configuration, consists of a rich number of modes, with either
+stationary or propagating character. We find that the lowest frequency mode
+displays a bandwidth of approximately 0.5 GHz, which is independent of the
+presence of the film underneath. On the contrary, the BLS intensity of some of
+the detected modes strongly depends on the presence of the extended thin-film
+underlayer. Micromagnetic simulations unveil the details of the dynamic
+coupling between ASI lattice and film underlayer. Interestingly, the ASI
+lattice facilitates dynamics of the film either specific wavelengths or
+intensity modulation peculiar to the modes of the ASI elements imprinted in the
+film. Our results demonstrate that propagating spin waves can be modulated at
+the nanometer length scale by harnessing the dynamic mode coupling in the
+vertical, i.e., the out-of-plane direction of suitably designed magnonic
+structures.",2209.02783v1
+2022-09-16,Unveiling new quantum phases in the Shastry-Sutherland compound SrCu2(BO3)2up to the saturation magnetic field,"Under magnetic fields, quantum magnets often undergo exotic phase transitions
+with various kinds of order. The discovery of a sequence of fractional
+magnetization plateaus in the Shastry-Sutherland compound SrCu2(BO3)2 has
+played a central role in the high-field research on quantum materials, but so
+far this system could only be probed up to half the saturation value of the
+magnetization. Here, we report the first experimental and theoretical
+investigation of this compound up to the saturation magnetic field of 140 T and
+beyond. Using ultrasound and magnetostriction techniques combined with
+extensive tensor-network calculations (iPEPS), several spin-supersolid phases
+are revealed between the 1/2 plateau and saturation (1/1 plateau). Quite
+remarkably, the sound velocity of the 1/2 plateau exhibits a drastic decrease
+of -50%, related to the tetragonal-to-orthorhombic instability of the
+checkerboard-type magnon crystal. The unveiled nature of this paradigmatic
+quantum system is a new milestone for exploring exotic quantum states of matter
+emerging in extreme conditions.",2209.07652v2
+2022-09-21,Spin current driven by ultrafast magnetization of FeRh,"Laser-induced ultrafast demagnetization is an important phenomenon that
+probes arguably ultimate limits of the angular momentum dynamics in solid.
+Unfortunately, many aspects of the dynamics remain unclear except that the
+demagnetization transfers the angular momentum eventually to the lattice. In
+particular, roles of electron-carried spin current are debated. Here we
+experimentally probe the spin current in the opposite phenomenon, i.e.,
+laser-induced ultrafast magnetization of FeRh, where the laser pump pulse
+initiates the angular momentum build-up rather than its dissipation. Using the
+time-resolved magneto-optical Kerr effect, we directly measure the
+ultrafast-magnetization-driven spin current in a FeRh/Cu heterostructure.
+Strong correlation between the spin current and the net magnetization change
+rate of FeRh is found even though the spin filter effect is negligible in this
+opposite process. This result implies that the angular momentum build-up is
+achieved by an angular momentum transfer from the electron bath (supplier) to
+the magnon bath (receiver) and followed by the spatial transport of angular
+momentum (spin current) and dissipation of angular momentum to the phonon bath
+(spin relaxation).",2209.10290v1
+2022-10-06,All hourglass bosonic excitations in the 1651 magnetic space groups and 528 magnetic layer groups,"The band connectivity as imposed by the compatibility relations between the
+irreducible representations of little groups can give rise to the exotic
+hourglass-like shape composed of four branches of bands and five band crossings
+(BCs). Such an hourglass band connectivity could enforce the emergence of
+nontrivial excitations like Weyl fermion, Dirac fermion or even beyond them. On
+the other hand, the bosons, like phonons, magnons, and photons, were also shown
+to possess nontrivial topology and a comprehensive symmetry classification of
+the hourglass bosonic excitations would be of great significance to both
+materials design and device applications. Here we firstly list all concrete
+positions and representations of little groups in the Brillouin zone (BZ)
+related with the hourglass bosonic excitations in all the 1651 magnetic space
+groups and 528 magnetic layer groups, applicable to three dimensional (3D) and
+two dimensional (2D) systems, respectively. 255 (42) MSGs (MLGs) are found to
+essentially host such hourglass BCs: Here ``essentially'' means that the
+bosonic hourglass BC exists definitely as long as the studied system is
+crystallized in the corresponding MSG/MLG. We also perform first-principles
+calculations on hundreds of 3D nonmagnetic materials essentially hosting
+hourglass phonons and propose that the 2D material AlI can host hourglass
+phonons. We choose AuX (X=Br and I) as illustrative examples to demonstrate
+that two essential hourglass band structures can coexist in the phonon spectra
+for both materials while for AuBr, an accidental band crossing sticking two
+hourglasses is found interestingly. Our results of symmetry conditions for
+hourglass bosonic excitations can provide a useful guide of designing
+artificial structures with hourglass bosonic excitations.",2210.02954v1
+2022-10-10,Complete field-induced spectral response of the spin-1/2 triangular-lattice antiferromagnet CsYbSe$_2$,"Fifty years after Anderson's resonating valence-bond proposal, the spin-1/2
+triangular-lattice Heisenberg antiferromagnet (TLHAF) remains the ultimate
+platform to explore highly entangled quantum spin states in proximity to
+magnetic order. Yb-based delafossites are ideal candidate TLHAF materials,
+which allow experimental access to the full range of applied in-plane magnetic
+fields. We perform a systematic neutron scattering study of CsYbSe$_2$, first
+proving the Heisenberg character of the interactions and quantifying the
+second-neighbour coupling. We then measure the complex evolution of the
+excitation spectrum, finding extensive continuum features near the
+120$^{\circ}$-ordered state, throughout the 1/3-magnetization plateau and
+beyond this up to saturation. We perform cylinder matrix-product-state (MPS)
+calculations to obtain an unbiased numerical benchmark for the TLHAF and
+spectacular agreement with the experimental spectra. The measured and
+calculated longitudinal spectral functions reflect the role of multi-magnon
+bound and scattering states. These results provide valuable insight into
+unconventional field-induced spin excitations in frustrated quantum materials.",2210.04928v3
+2022-10-11,Magnetic anisotropy reversal driven by structural symmetry-breaking in monolayer α-RuCl3,"Layered {\alpha}-RuCl3 is a promising material to potentially realize the
+long-sought Kitaev quantum spin liquid with fractionalized excitations. While
+evidence of this exotic state has been reported under a modest in-plane
+magnetic field, such behavior is largely inconsistent with theoretical
+expectations of Kitaev phases emerging only in out-of-plane fields. These
+predicted field-induced states have been mostly out of reach due to the strong
+easy-plane anisotropy of bulk crystals, however. We use a combination of
+tunneling spectroscopy, magnetotransport, electron diffraction, and ab initio
+calculations to study the layer-dependent magnons, anisotropy, structure, and
+exchange coupling in atomically thin samples. Due to structural distortions,
+the sign of the average off-diagonal exchange changes in monolayer
+{\alpha}-RuCl3, leading to a reversal of magnetic anisotropy to easy-axis. Our
+work provides a new avenue to tune the magnetic interactions in {\alpha}-RuCl3
+and allows theoretically predicted quantum spin liquid phases for out-of-plane
+fields to be more experimentally accessible.",2210.05733v1
+2022-11-09,Magnetization reversal through an antiferromagnetic state,"Magnetization reversal in ferro- and ferrimagnets is a well-known archetype
+of non-equilibrium processes, where the volume fractions of the oppositely
+magnetized domains vary and perfectly compensate each other at the coercive
+magnetic field. Here, we report on a fundamentally new pathway for
+magnetization reversal that is mediated by an antiferromagnetic state.
+Consequently, an atomic-scale compensation of the magnetization is realized at
+the coercive field, instead of the mesoscopic or macroscopic domain
+cancellation in canonical reversal processes. We demonstrate this unusual
+magnetization reversal on the Zn-doped polar magnet Fe$_2$Mo$_3$O$_8$. Hidden
+behind the conventional ferrimagnetic hysteresis loop, the surprising emergence
+of the antiferromagnetic phase at the coercive fields is disclosed by a sharp
+peak in the field-dependence of the electric polarization. In addition, at the
+magnetization reversal our THz spectroscopy studies reveal the reappearance of
+the magnon mode that is only present in the pristine antiferromagnetic state.
+According to our microscopic calculations, this unusual process is governed by
+the dominant intralayer coupling, strong easy-axis anisotropy and spin
+fluctuations, which result in a complex interplay between the ferrimagnetic and
+antiferromagnetic phases. Such antiferro-state-mediated reversal processes
+offer novel concepts for magnetization control, and may also emerge for other
+ferroic orders.",2211.05028v1
+2022-11-10,Static and dynamic magnetic properties of the spin-5/2 triangle lattice antiferromagnet Na3Fe(PO4)2 studied by 31P NMR,"$^{31}$P nuclear magnetic resonance (NMR) measurements have been carried out
+to investigate the magnetic properties and spin dynamics of Fe$^{3+}$ ($S$ =
+5/2) spins in the two-dimensional triangular lattice (TL) compound
+Na$_3$Fe(PO$_4$)$_2$. The temperature ($T$) dependence of nuclear spin-lattice
+relaxation rates ($1/T_1$) shows a clear peak around N\'eel temperature,
+$T_{\rm N} = 10.9$~K, corresponding to an antiferromagnetic (AFM) transition.
+From the temparature dependence of NMR shift ($K$) above $T_{\rm N}$, an
+exchange coupling between Fe$^{3+}$ spins was estimated to be $J/k_{\rm
+B}\simeq 1.9$~K using the spin-5/2 Heisenberg isotropic-TL model. The
+temperature dependence of $1/T_1T$ divided by the magnetic susceptibility
+($\chi$), $1/T_1T\chi$, above $T_{\rm N}$ proves the AFM nature of spin
+fluctuations below $\sim$ 50 K in the paramagnetic state. In the magnetically
+ordered state below $T_{\rm N}$, the characteristic rectangular shape of the
+NMR spectra is observed, indicative of a commensurate AFM state in its ground
+state. The strong temperature dependence of 1/$T_1$ in the AFM state is well
+explained by the two-magnon (Raman) process of the spin waves in a 3D
+antiferromagnet with a spin-anisotropy energy gap of 5.7 K. The temperature
+dependence of sublattice magnetization is also well reproduced by the spin
+waves. Those results indicate that the magnetically ordered state of
+Na$_3$Fe(PO$_4$)$_2$ is a conventional 3D AFM state, and no obvious spin
+frustration effects were detected in its ground state.",2211.05921v1
+2022-11-23,Raman scattering signatures of the strong spin-phonon coupling in the bulk magnetic van der Waals material CrSBr,"Magnetic excitations in layered magnetic materials that can be thinned down
+the two-dimensional (2D) monolayer limit are of high interest from a
+fundamental point of view and for applications perspectives. Raman scattering
+has played a crucial role in exploring the properties of magnetic layered
+materials and, even-though it is essentially a probe of lattice vibrations, it
+can reflect magnetic ordering in solids through the spin-phonon interaction or
+through the observation of magnon excitations. In bulk CrSBr, a layered A type
+antiferromagnet (AF), we show that the magnetic ordering can be directly
+observed in the temperature dependence of the Raman scattering response i)
+through the variations of the scattered intensities, ii) through the activation
+of new phonon lines reflecting the change of symmetry with the appearance of
+the additional magnetic periodicity, and iii) through the observation, below
+the Neel temperature (TN) of second order Raman scattering processes. We
+additionally show that the three different magnetic phases encountered in
+CrSBr, including the recently identified low temperature phase, have a
+particular Raman scattering signature. This work demonstrates that magnetic
+ordering can be observed directly in the Raman scattering response of bulk
+CrSBr with in-plane magnetization, and that it can provide a unique insight
+into the magnetic phases encountered in magnetic layered materials.",2211.12939v1
+2022-12-06,Giant gate-tunable renormalization of spin-correlated flat-band states and bandgap in a 2D magnetic insulator,"Emergent quantum phenomena in two-dimensional van der Waal (vdW) magnets are
+largely governed by the interplay between the exchange and Coulomb
+interactions. The ability to tune the Coulomb interaction in such strongly
+correlated materials enables the precise control of spin-correlated flat-band
+states, bandgap (Eg) and unconventional magnetism, all of which are crucial for
+next-generation spintronics and magnonics applications. Here, we demonstrate a
+giant gate-tunable renormalization of spin-correlated flat-band states and
+bandgap in magnetic chromium tribromide (CrBr3) monolayers grown on graphene.
+Our gate-dependent scanning tunneling spectroscopy (STS) studies reveal that
+the inter-flat-band spacing and bandgap of CrBr3 can be continuously tuned by
+120 meV and 240 meV respectively via electrostatic injection of carriers into
+the hybrid CrBr3/graphene system, equivalent to the modulation of the Cr
+on-site Coulomb repulsion energy by 500 meV. This can be attributed to the
+self-screening of CrBr3 arising from the gate-induced carriers injected into
+CrBr3, which dominates over the opposite trend from the remote screening of the
+graphene substrate. Precise tuning of the spin-correlated flat-band states and
+bandgap in 2D magnets via electrostatic modulation of Coulomb interactions not
+only provides new strategies for optimizing the spin transport channels but
+also may exert a crucial influence on the exchange energy and spin-wave gap,
+which could raise the critical temperature for magnetic order.",2212.02772v1
+2022-12-16,Spin excitations in the kagome-lattice metallic antiferromagnet Fe$_{0.89}$Co$_{0.11}$Sn,"Kagome-lattice materials have attracted tremendous interest due to the broad
+prospect for seeking superconductivity, quantum spin liquid states, and
+topological electronic structures. Among them, the transition-metal kagome
+lattices are high-profile objects for the combination of topological
+properties, rich magnetism, and multiple-orbital physics. Here we report an
+inelastic neutron scattering study on the spin dynamics of a kagome-lattice
+antiferromagnetic metal Fe$_{0.89}$Co$_{0.11}$Sn. Although the magnetic
+excitations can be observed up to $\sim$250 meV, well-defined spin waves are
+only identified below $\sim$90 meV and can be modeled using Heisenberg exchange
+with ferromagnetic in-plane nearest-neighbor coupling $J_1$, in-plane
+next-nearest-neighbor coupling $J_2$, and antiferromagnetic (AFM) interlayer
+coupling $J_c$ under linear spin-wave theory. Above $\sim$90 meV, the spin
+waves enter the itinerant Stoner continuum and become highly damped
+particle-hole excitations. At the K point of the Brillouin zone, we reveal a
+possible band crossing of the spin wave, which indicates a potential Dirac
+magnon. Our results uncover the evolution of the spin excitations from the
+planar AFM state to the axial AFM state in Fe$_{0.89}$Co$_{0.11}$Sn, solve the
+magnetic Hamiltonian for both states, and confirm the significant influence of
+the itinerant magnetism on the spin excitations.",2212.08590v2
+2022-12-19,Machine learning assisted derivation of effective low energy models for metallic magnets,"We consider the problem of extracting an effective low-energy spin model from
+a Kondo Lattice Model (KLM) with classical localized moments. The non-analytic
+dependence of the effective spin-spin interactions on the Kondo exchange $J$
+excludes the possibility of using perturbation theory beyond the second order
+Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction at zero temperature. Here we
+introduce a Machine Learning (ML) assisted protocol to extract effective two-
+and four-spin interactions by integrating out the conduction electrons of the
+original KLM. The resulting effective spin model reproduces the phase diagram
+obtained with the original KLM as a function of magnetic field and easy-axis
+anisotropy and reveals the effective four-spin interactions that are
+responsible for the field induced skyrmion crystal phase. Moreover, this
+minimal spin model enables an efficient computation of static and dynamical
+properties with a much lower numerical cost relative to the original KLM. A
+comparison of the dynamical spin structure factor in the fully polarized phase
+computed with the effective model and the original KLM reveals a good agreement
+for the magnon dispersion despite the fact that this information was not
+included in the training data set.",2212.09796v2
+2022-12-22,Nonreciprocal magnetoacoustic waves in synthetic antiferromagnets with Dzyaloshinskii-Moriya interaction,"The interaction between surface acoustic waves (SAWs) and spin waves (SWs) in
+a piezoelectric/magnetic thin film heterostructure yields potential for the
+realization of novel microwave devices and applications in magnonics. In the
+present work, we investigate the SAW-SW interaction in a Pt/Co(2 nm)/Ru(0.85
+nm)/Co(4 nm)/Pt synthetic antiferromagnet (SAF) composed of two ferromagnetic
+layers with different thicknesses separated by a thin nonmagnetic Ru spacer
+layer. Because of the combined presence of interfacial Dzyaloshinskii--Moriya
+interaction (iDMI) and interlayer dipolar coupling fields, the optical SW mode
+shows a large nondegenerate dispersion relation for oppositely propagating SWs.
+Due to SAW-SW interaction, we observe nonreciprocal SAW transmission in the
+piezoelectric/SAF hybrid device. The equilibrium magnetization directions of
+both Co layers are manipulated by an external magnetic field to set a
+ferromagnetic, canted, or antiferromagnetic configuration. This has a strong
+impact on the SW dispersion, its nonreciprocity, and SAW-SW interaction. The
+experimental results are in agreement with a phenomenological SAW-SW
+interaction model, which considers the interlayer exchange coupling, iDMI, and
+interlayer dipolar coupling fields of the SWs.",2212.11838v1
+2022-12-30,Selection rules for ultrafast laser excitation and detection of spin correlations dynamics in a cubic antiferromagnet,"Exchange interactions determine the correlations between microscopic spins in
+magnetic materials. Probing the dynamics of these spin correlations on
+ultrashort length and time scales is, however rather challenging, since it
+requires simultaneously high spatial and high temporal resolution. Recent
+experimental demonstrations of laser-driven two-magnon modes - zone-edge
+excitations in antiferromagnets governed by exchange coupling - posed questions
+about the microscopic nature of the observed spin dynamics, the mechanism
+underlying its excitation, and their macroscopic manifestation enabling
+detection. Here, on the basis of a simple microscopic model, we derive the
+selection rules for cubic systems that describe the polarization of pump and
+probe pulses required to excite and detect dynamics of nearest-neighbor spin
+correlations, and can be employed to isolate such dynamics from other magnetic
+excitations and magneto-optical effects. We show that laser-driven spin
+correlations contribute to optical anisotropy of the antiferromagnet even in
+the absence of spin-orbit coupling. In addition, we highlight the role of
+subleading anisotropy in the spin system and demonstrate that the dynamics of
+the antiferromagnetic order parameter occurs only in next-to-leading order,
+determined by the smallness of the magnetic anisotropy as compared to the
+isotropic exchange interactions in the system. We expect that our results will
+stimulate and support further studies of magnetic correlations on the shortest
+length and time scale.",2212.14698v2
+2023-01-02,Dynamical properties of quantum many-body systems with long range interactions,"Employing large-scale quantum Monte Carlo simulations, we systematically
+compute the energy spectra of the 2D spin-1/2 Heisenberg model with long-range
+interactions. With the $1/r^{\alpha}$ ferromagnetic and staggered
+antiferromagnetic interactions, we find the explicit range in $\alpha$ for
+{\color{black} the short-range Goldstone-type (gapless), anomalous
+Goldstone-type (gapless) and Higgs-type (gapped) spectra. Accompanied by the
+spin wave analysis, our numerical results vividly reveal how the long-range
+interactions alter the usual linear and quadratic magnon dispersions in 2D
+quantum magnets and give rise to anomalous dynamical exponents. Moreover, we
+find explicit case where the gapped excitation exists even when the Hamiltonian
+is extensive. This work provides the first set of unbiased dynamical data} of
+long-range quantum many-body systems and suggests that many universally
+accepted low-energy customs for short-range systems need to be substantially
+modified for long-range ones which are of immediate relevance to the ongoing
+experimental efforts from quantum simulators to 2D quantum moir\'e materials.",2301.00829v3
+2023-01-15,Exact solution of a non-Hermitian $\mathscr{PT}$-symmetric Heisenberg spin chain,"We construct the exact solution of a non-Hermitian $\mathscr{PT}$-symmetric
+isotropic Heisenberg spin chain with integrable boundary fields. We find that
+the system exhibits two types of phases we refer to as $A$ and $B$ phases. In
+the $B$ type phase, the $\mathscr{PT}$- symmetry remains unbroken and it
+consists of eigenstates with only real energies, whereas the $A$ type phase
+contains a $\mathscr{PT}$-symmetry broken sector comprised of eigenstates with
+only complex energies and a sector of unbroken $\mathscr{PT}$-symmetry with
+eigenstates of real energies. The $\mathscr{PT}$-symmetry broken sector
+consists of pairs of eigenstates whose energies are complex conjugates of each
+other. The existence of two sectors in the $A$ type phase is associated with
+the exponentially localized bound states at the edges with complex energies
+which are described by boundary strings. We find that both $A$ and $B$ type
+phases can be further divided into sub-phases which exhibit different ground
+states. We also compute the bound state wavefunction in one magnon sector and
+find that as the imaginary value of the boundary parameter is increased, the
+exponentially localized wavefunction broadens thereby protruding more into the
+bulk, which indicates that exponentially localized bound states may not be
+stabilized for large imaginary values of the boundary parameter.",2301.06004v1
+2023-02-01,A Brillouin light scattering study of the spin-wave magnetic field dependence in a magnetic hybrid system made of an artificial spin-ice structure and a film underlayer,"We present a combined Brillouin light scattering and micromagnetic simulation
+investigation of the magnetic-field dependent spin-wave spectra in a hybrid
+structure made of permalloy (NiFe) artificial spin-ice (ASI) systems, composed
+of stadium-shaped nanoislands, deposited on the top of an unpatterned permalloy
+film with a nonmagnetic spacer layer. The thermal spin-wave spectra were
+recorded by Brillouin light scattering (BLS) as a function of the magnetic
+field applied along the symmetry direction of the ASI sample. Magneto-optic
+Kerr effect magnetometry was used to measure the hysteresis loops in the same
+orientation as the BLS measurements. The frequency and intensity of several
+spin-wave modes detected by BLS were measured as a function of the applied
+magnetic field. Micromagnetic simulations enabled us to identify the modes in
+terms of their frequency and spatial symmetry and to extract information about
+the existence and strength of the dynamic coupling, relevant only to a few
+modes of a given hybrid system. Using this approach, we suggest a way to
+understand if dynamic coupling between ASI and film modes is present or not,
+with interesting implications for the development of future three-dimensional
+magnonic applications and devices.",2302.00483v1
+2023-02-01,Temperature-independent ferromagnetic resonance shift in Bi-doped YIG garnets through magnetic anisotropy tuning,"Thin garnet films are becoming central for magnon-spintronics and
+spin-orbitronics devices as they show versatile magnetic properties together
+with low magnetic losses. These fields would benefit from materials in which
+heat does not affect the magnetization dynamics, an effect known as the
+non-linear thermal frequency shift. In this study, low damping Bi substituted
+Iron garnet (Bi:YIG) ultra-thin films have been grown using Pulsed Laser
+Deposition. Through a fine tuning of the growth parameters, the precise control
+of the perpendicular magnetic anisotropy allows to achieve a full compensation
+of the dipolar magnetic anisotropy. Strikingly, once the growth conditions are
+optimized, varying the growth temperature from 405 {\deg}C to 475 {\deg}C as
+the only tuning parameter induces the easy-axis to go from out-of-plane to
+in-plane. For films that are close to the dipolar compensation, Ferromagnetic
+Resonance measurements yield an effective magnetization $\mu _{0}M_{eff} (T)$
+that has almost no temperature dependence over a large temperature range (260 K
+to 400 K) resulting in an anisotropy temperature exponent of 2. These findings
+put Bi:YIG system among the very few materials in which the temperature
+dependence of the magnetic anisotropy varies at the same rate than the
+saturation magnetization. This interesting behavior is ascribed
+phenomenologically to the sizable orbital moment of $Bi^{3+}$.",2302.00585v1
+2023-02-09,Structural changes induced by electric currents in a single crystal of Pr$_2$CuO$_4$,"We demonstrate a novel approach to the structural and electronic property
+modification of perovskites, focusing on Pr$_2$CuO$_4$, an undoped parent
+compound of a class of electron-doped copper-oxide superconductors. Currents
+were passed parallel or perpendicular to the copper-oxygen layers with the
+voltage ramped up until a rapid drop in the resistivity was achieved, a process
+referred to as ""flash"". The current was then further increased tenfold in
+current-control mode. This state was quenched by immersion into liquid
+nitrogen. Flash can drive many compounds into different atomic structures with
+new properties, whereas the quench freezes them into a long-lived state.
+Single-crystal neutron diffraction of as-grown and modified Pr$_2$CuO$_4$
+revealed a $\sqrt{10}$x$\sqrt{10}$ superlattice due to oxygen-vacancy order.
+The diffraction peak intensities of the superlattice of the modified sample
+were significantly enhanced relative to the pristine sample. Raman-active
+phonons in the modified sample were considerably sharper. Measurements of
+electrical resistivity, magnetization and two-magnon Raman scattering indicate
+that the modification affected only the Pr-O layers, but not the Cu-O planes.
+These results point to enhanced oxygen-vacancy order in the modified samples
+well beyond what can be achieved without passing electrical current. Our work
+opens a new avenue toward electric field/quench control of structure and
+properties of layered perovskite oxides.",2302.04385v2
+2023-02-12,Quantum Simulation of an Extended Dicke Model with a Magnetic Solid,"The Dicke model describes the cooperative interaction of an ensemble of
+two-level atoms with a single-mode photonic field and exhibits a quantum phase
+transition as a function of light--matter coupling strength. Extending this
+model by incorporating short-range atom--atom interactions makes the problem
+intractable but is expected to produce new phases. Here, we simulate such an
+extended Dicke model using a crystal of ErFeO$_3$, where the role of atoms
+(photons) is played by Er$^{3+}$ spins (Fe$^{3+}$ magnons). Through
+magnetocaloric effect and terahertz magnetospectroscopy measurements, we
+demonstrated the existence of a novel atomically ordered phase in addition to
+the superradiant and normal phases that are expected from the standard Dicke
+model. Further, we elucidated the nature of the phase boundaries in the
+temperature--magnetic-field phase diagram, identifying both first-order and
+second-order phase transitions. These results lay the foundation for studying
+multiatomic quantum optics models using well-characterized many-body condensed
+matter systems.",2302.06028v2
+2023-02-14,Magnetic excitations in the topological semimetal $\mathrm{YbMnSb}_2$,"We report neutron scattering measurements on YbMnSb$_2$ which shed new light
+on the nature of the magnetic moments and their interaction with Dirac
+fermions. Using half-polarized neutron diffraction we measured the
+field-induced magnetization distribution in the paramagnetic phase and found
+that the magnetic moments are well localised on the Mn atoms. Using triple-axis
+neutron scattering we measured the magnon spectrum throughout the Brillouin
+zone in the antiferromagnetically ordered phase, and we determined the dominant
+exchange interactions from linear spin-wave theory. The analysis shows that the
+interlayer exchange is five times larger than in several related compounds
+containing Bi instead of Sb. We argue that the coupling between the Mn local
+magnetic moments and the topological band states is more important in
+YbMnSb$_2$ than in the Bi compounds.",2302.07007v1
+2023-02-15,Magnetically-dressed CrSBr exciton-polaritons in ultrastrong coupling regime,"The strong coupling between photons and matter excitations such as excitons,
+phonons, and magnons is of central importance in the study of light-matter
+interactions. Bridging the flying and stationary quantum states, the strong
+light-matter coupling enables the coherent transmission, storage, and
+processing of quantum information, which is essential for building photonic
+quantum networks. Over the past few decades, exciton-polaritons have attracted
+substantial research interest due to their half-light-half-matter bosonic
+nature. Coupling exciton-polaritons with magnetic orders grants access to rich
+many-body phenomena, but has been limited by the availability of material
+systems that exhibit simultaneous exciton resonances and magnetic ordering.
+Here we report magnetically-dressed microcavity exciton-polaritons in the van
+der Waals antiferromagnetic (AFM) semiconductor CrSBr coupled to a Tamm plasmon
+microcavity. Angle-resolved spectroscopy reveals an exceptionally high
+exciton-polariton coupling strength attaining 169 meV, demonstrating
+ultrastrong coupling that persists up to room temperature.
+Temperature-dependent exciton-polariton spectroscopy senses the magnetic order
+change from AFM to paramagnetism in CrSBr, confirming its magnetic nature. By
+applying an out-of-plane magnetic field, an effective tuning of the polariton
+energy is further achieved while maintaining the ultrastrong exciton-photon
+coupling strength, which is attributed to the spin canting process that
+modulates the interlayer exciton interaction. Our work proposes a hybrid
+quantum platform enabled by robust opto-electronic-magnetic coupling, promising
+for quantum interconnects and transducers.",2302.07616v1
+2023-03-06,Phononic-magnetic dichotomy of the thermal Hall effect in the Kitaev-Heisenberg candidate material Na$_2$Co$_2$TeO$_6$,"Majorana fermions as emergent excitations of the Kitaev quantum spin liquid
+ground state constitute a promising concept in fault tolerant quantum
+computation. Experimentally, the recently reported topological half-quantized
+thermal Hall effect in the Kitaev material $\alpha$-RuCl$_3$ seems to confirm
+the Majorana nature of the material's magnetic excitations. It has been argued,
+however, that the thermal Hall signal in $\alpha$-RuCl$_3$ rather stems from
+phonons or topological magnons than from Majorana fermions. Here we investigate
+the thermal Hall effect of the closely related Kitaev quantum material
+Na$_2$Co$_2$TeO$_6$, and we show that the thermal Hall signal emerges from at
+least two components, phonons and magnetic excitations. This dichotomy results
+from our discovery that the transversal heat conductivity $\kappa_{xy}$ carries
+clear signatures of the phononic $\kappa_{xx}$, but changes sign upon entering
+the low-temperature, magnetically ordered phase. We systematically resolve the
+two components by considering the detailed temperature and field dependence of
+both $\kappa_{xy}$ and $\kappa_{xx}$. Our results demonstrate that uncovering a
+genuinely quantized magnetic thermal Hall effect in a Kitaev topological
+quantum spin liquid requires to disentangle phonon vs. magnetic contributions
+where the latter include potentially fractionalized excitations such as the
+expected Majorana fermions.",2303.03067v1
+2023-03-15,Magnetization Dynamics and Peierls Instability in Topological Josephson Structures,"We study a long topological Josephson junction with a ferromagnetic strip
+between two superconductors. The low-energy theory exhibits a non-local in time
+and space interaction between chiral Majorana fermions, mediated by the
+magnonic excitations in the ferromagnet. While short ranged interactions turn
+out to be irrelevant by power counting, we show that sufficiently strong and
+long-ranged interactions may induce a $\mathbb{Z}_2$-symmetry breaking. This
+spontaneous breaking leads to a tilting of the magnetization perpendicular to
+the Majorana propagation direction and the opening of a fermionic gap (Majorana
+mass). It is analogous to the Peierls instability in the commensurate
+Fr\""ohlich model and reflects the nontrivial interplay between Majorana modes
+and magnetization dynamics. Within a Gaussian fluctuation analysis, we estimate
+critical values for the temporal and spatial non-locality of the interaction,
+beyond which the symmetry breaking is stable at zero temperature -- despite the
+effective one-dimensionality of the model. We conclude that non-locality, i.e.,
+the stiffness of the magnetization in space and time, stabilizes the symmetry
+breaking. In the stabilized regime, we expect the current-phase relation to
+exhibit an experimentally accessible discontinuous jump. At nonzero
+temperatures, as usual in the 1D Ising model, the long-range order is destroyed
+by solitonic excitations, which in our case carry each a Majorana zero mode. In
+order to estimate the correlation length, we investigate the solitons within a
+self-consistent mean-field approach.",2303.08321v1
+2023-03-16,Antiferromagnet-mediated interlayer exchange: hybridization versus proximity effect,"We investigate the interlayer coupling between two thin ferromagnetic (F)
+films mediated by an antiferromagnetic (AF) spacer in F*/AF/F trilayers and
+show how it transitions between different regimes on changing the AF thickness.
+Employing layer-selective Kerr magnetometry and ferromagnetic-resonance
+techniques in a complementary manner enables us to distinguish between three
+functionally distinct regimes of such ferromagnetic interlayer coupling. The F
+layers are found to be individually and independently exchange-biased for thick
+FeMn spacers - the first regime of no interlayer F-F* coupling. F-F* coupling
+appears on decreasing the FeMn thickness below 9 nm. In this second regime
+found in structures with 6.0-9.0 nm thick FeMn spacers, the interlayer coupling
+exists only in a finite temperature interval just below the effective N\'eel
+temperature of the spacer, which is due to magnon-mediated exchange through the
+thermally softened antiferromagnetic spacer, vanishing at lower temperatures.
+The third regime, with FeMn thinner than 4 nm, is characterized by a much
+stronger interlayer coupling in the entire temperature interval, which is
+attributed to a magnetic-proximity induced ferromagnetic exchange. These
+experimental results, spanning the key geometrical parameters and thermal
+regimes of the F*/AF/F nanostructure, complemented by a comprehensive
+theoretical analysis, should broaden the understanding of the interlayer
+exchange in magnetic multilayers and potentially be useful for applications in
+spin-thermionics.",2303.09301v2
+2023-04-04,Collective nature of orbital excitations in layered cuprates in the absence of apical oxygens,"We have investigated the 3d orbital excitations in CaCuO2 (CCO), Nd2CuO4
+(NCO), and La2CuO4 (LCO) using high-resolution resonant inelastic x-ray
+scattering. In LCO they behave as well-localized excitations, similarly to
+several other cuprates. On the contrary, in CCO and NCO the dxy orbital clearly
+disperse, pointing to a collective character of this excitation (orbiton) in
+compounds without apical oxygen. We ascribe the origin of the dispersion as
+stemming from a substantial next-nearest-neighbor (NNN) orbital superexchange.
+Such an exchange leads to the liberation of orbiton from its coupling to
+magnons, which is associated with the orbiton hopping between nearest neighbor
+copper sites. We show that the exceptionally large NNN orbital superexchange
+can be traced back to the absence of apical oxygens suppressing the charge
+transfer energy.",2304.02115v3
+2023-04-22,Lattice effect on the superexchange interaction in antiferromagnetic Bi$_2$Sr$_2$CaCu$_2$O$_8$,"The in-plane superexchange interaction $J$ of cuprate superconductors has
+long been suggested to be an important parameter for exploring their
+high-temperature superconductivity. The bilayer
+Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ is the most studied system with high-quality
+single crystals in the wide doping range with the the same structure and phase.
+So far, the lattice parameter dependence of $J$ in its antiferromagnetic parent
+compound Bi$_2$Sr$_2$CaCu$_2$O$_{8}$ has not been established. By combining
+Raman scattering and x-ray diffraction techniques on the same sample in the
+same pressure environment, we obtain the evolution of both the two-magnon
+spectrum and the structural parameters with pressure up to nearly 30 GPa, The
+relationship between pressure or the in-plane lattice parameter and $J$ is thus
+established for Bi$_2$Sr$_2$CaCu$_2$O$_{8}$. Over the studied pressure range,
+superconductivity does not appear in this parent compound based on a sensitive
+magnetic measurement technique. The effects of pressure and chemical doping on
+the superexchange interaction and structure and their implications for
+superconductivity are discussed from the comparison of the obtained
+experimental data with the existing experiments. The results and findings
+provide valuable information for the understanding of superconductivity and the
+future theory developments for superconductivity in cuprates.",2304.11311v1
+2023-04-28,"Noncollinear magnetic order, in-plane anisotropy, and magnetoelectric coupling in a pyroelectric honeycomb antiferromagnet Ni$_{2}$Mo$_{3}$O$_{8}$","Ni$_{2}$Mo$_{3}$O$_{8}$ is a pyroelectric honeycomb antiferromagnet
+exhibiting peculiar changes of its electric polarization at magnetic
+transitions. Ni$_{2}$Mo$_{3}$O$_{8}$ stands out from the isostructural magnetic
+compounds, showing an anomalously low magnetic transition temperature and
+unique magnetic anisotropy. We determine the magnetic structure of
+Ni$_{2}$Mo$_{3}$O$_{8}$ utilizing high-resolution powder and single-crystal
+neutron diffraction. A noncollinear stripy antiferromagnetic order is found in
+the honeycomb planes. The magnetic space group is \textit{P$_C$na}2$_1$. The
+in-plane magnetic connection is of the stripy type both for the $ab$-plane and
+the $c$-axis spin components. This is a simpler connection than the one
+proposed previously. The ferromagnetic interlayer order of the $c$-axis spin
+components in our model is also distinct. The magnetic anisotropy of
+Ni$_{2}$Mo$_{3}$O$_{8}$ is characterized by orientation-dependent magnetic
+susceptibility measurements on a single crystal, consistent with neutron
+diffraction analysis. The local magnetoelectric tensor analysis using our
+magnetic models provides new insights into its magnetoelectric coupling and
+polarization. Thus, our results deliver essential information for understanding
+both the unusual magnetoelectric properties of Ni$_{2}$Mo$_{3}$O$_{8}$ and the
+prospects for observation of exotic nonreciprocal, Hall, and magnonic effects
+characteristic to this compound family.",2304.14641v2
+2023-04-28,Persistent dynamic magnetic state in artificial honeycomb spin ice,"Topological magnetic charges, arising due to the non-vanishing magnetic flux
+on spin ice vertices, serve as the origin of magnetic monopoles that traverse
+the underlying lattice effortlessly. Unlike spin ice materials of atomic
+origin, the dynamic state in artificial honeycomb spin ice is conventionally
+described in terms of finite size domain wall kinetics that require magnetic
+field or current application. Contrary to this common understanding, here we
+show that thermally tunable artificial permalloy honeycomb lattice manifests a
+perpetual dynamic state due to self-propelled magnetic charge defect relaxation
+in the absence of any external tuning agent. Quantitative investigation of
+magnetic charge defect dynamics using neutron spin echo spectroscopy reveals
+sub-ns relaxation times that are comparable to monopole's relaxation in bulk
+spin ices. Most importantly, the kinetic process remains unabated at low
+temperature where thermal fluctuation is negligible. This suggests that dynamic
+phenomena in honeycomb spin ice are mediated by quasi-particle type entities,
+also confirmed by quantum Monte-Carlo simulations that replicate the kinetic
+behavior. Our research unveils a new `macroscopic' magnetic particle that
+shares many known traits of quantum particles, namely magnetic monopole and
+magnon.",2305.00093v1
+2023-05-05,Nonlinear terahertz Néel spin-orbit torques in antiferromagnetic Mn$_2$Au,"Antiferromagnets have large potential for ultrafast coherent switching of
+magnetic order with minimum heat dissipation. In novel materials such as
+Mn$_2$Au and CuMnAs, electric rather than magnetic fields may control
+antiferromagnetic order by N\'eel spin-orbit torques (NSOTs), which have,
+however, not been observed on ultrafast time scales yet. Here, we excite
+Mn$_2$Au thin films with phase-locked single-cycle terahertz electromagnetic
+pulses and monitor the spin response with femtosecond magneto-optic probes. We
+observe signals whose symmetry, dynamics, terahertz-field scaling and
+dependence on sample structure are fully consistent with a uniform in-plane
+antiferromagnetic magnon driven by field-like terahertz NSOTs with a torkance
+of (150$\pm$50) cm$^2$/A s. At incident terahertz electric fields above 500
+kV/cm, we find pronounced nonlinear dynamics with massive N\'eel-vector
+deflections by as much as 30{\deg}. Our data are in excellent agreement with a
+micromagnetic model which indicates that fully coherent N\'eel-vector switching
+by 90{\deg} within 1 ps is within close reach.",2305.03368v1
+2023-05-08,Thermal Hall effects in quantum magnets,"In the recent years, the thermal Hall transport has risen as an important
+diagnosis of the physical properties of the elementary excitations in various
+quantum materials, especially among the Mott insulating systems where the
+electronic transports are often featureless. Here we review the recent
+development of thermal Hall effects in quantum magnets where all the relevant
+excitations are charge-neutral. In addition to summarizing the existing
+experiments, we pay a special attention to the underlying mechanisms of the
+thermal Hall effects in various magnetic systems, and clarify the connection
+between the microscopic physical variables and the emergent degrees of freedom
+in different quantum phases. The external magnetic field is shown to modify the
+intrinsic Berry curvature properties of various emergent and/or exotic
+quasiparticle excitations in distinct fashions for different quantum systems
+and quantum phases, contributing to the thermal Hall transports. These include,
+for example, the conventional ones like the magnons in ordered magnets, the
+triplons in dimerized magnets, the exotic and fractionalized quasparticles such
+as the spinons and the magnetic monopoles in quantum spin liquids. We review
+their contribution and discuss their presence in the thermal Hall conductivity
+in different physical contexts. We expect this review to provide a useful
+guidance for the physical mechanism of the thermal Hall transports in quantum
+magnets.",2305.04830v1
+2023-06-09,Strain-Tuned Magnetic Frustration in a Square Lattice $J_1$-$J_2$ Material,"Magnetic frustration is a route that can lead to the emergence of novel
+ground states, including spin liquids and spin ices. Such frustration can be
+introduced through either the geometry of lattice structures or by incompatible
+exchange interactions. Identifying suitable strategies to control the degree of
+magnetic frustration in real systems is an active field of research. In this
+study, we devise a design principle for the tuning of frustrated magnetism on
+the square lattice through the manipulation of nearest (NN) and next-nearest
+neighbor (NNN) antiferromagnetic (AF) exchange interactions. By studying the
+magnon excitations in epitaxially-strained La$_2$NiO$_4$ films using resonant
+inelastic x-ray scattering (RIXS) we show that, in contrast to the cuprates,
+the dispersion peaks at the AF zone boundary. This indicates the presence of an
+AF-NNN spin interaction. Using first principles simulations and an effective
+spin-model, we demonstrate the AF-NNN coupling to be a consequence of the
+two-orbital nature of La$_2$NiO$_4$. Our results demonstrate that compressive
+strain can enhance this coupling, providing a design principle for the
+tunability of frustrated magnetism on a square lattice.",2306.05828v1
+2023-06-29,Phonon thermal transport shaped by strong spin-phonon scattering in a Kitaev material Na$_2$Co$_2$TeO$_6$,"The recent report of a half-quantized thermal Hall effect in the Kitaev
+material $\alpha$-RuCl$_3$ has sparked a strong debate on whether it is
+generated by Majorana fermion edge currents or whether other more conventional
+mechanisms involving magnons or phonons are at its origin. A more direct
+evidence for Majorana fermions which could be expected to arise from a
+contribution to the longitudinal heat conductivity $\kappa_{xx}$ at
+$T\rightarrow0$ is elusive due to a very complex magnetic field dependence of
+$\kappa_{xx}$. Here, we report very low temperature (below 1~K) thermal
+conductivity ($\kappa$) of another candidate Kitaev material,
+Na$_2$Co$_2$TeO$_6$. The application of a magnetic field along different
+principal axes of the crystal reveals a strong directional-dependent
+magnetic-field ($\bf B$) impact on $\kappa$. We show that no evidence for
+mobile quasiparticles except phonons can be concluded at any field from 0~T to
+the field polarized state. In particular, severely scattered phonon transport
+is observed across the $B-T$ phase diagram, which is attributed to prominent
+magnetic fluctuations. Cascades of phase transitions are uncovered for all $\bf
+B$ directions by probing the strength of magnetic fluctuations via a precise
+record of $\kappa$($B$). Our results thus rule out recent proposals for
+itinerant magnetic excitations in Na$_2$Co$_2$TeO$_6$, and emphasise the
+importance of discriminating true spin liquid transport properties from
+scattered phonons in candidate materials.",2306.16963v1
+2023-07-04,Dynamic paramagnon-polarons in altermagnets,"The combined rotational and time-reversal symmetry breakings that define an
+altermagnet lead to an unusual d-wave (or g-wave) magnetization order
+parameter, which in turn can be modeled in terms of multipolar magnetic
+moments. Here, we show that such an altermagnetic order parameter couples to
+the dynamics of the lattice even in the absence of an external magnetic field.
+This coupling is analogous to the non-dissipative Hall viscosity and describes
+the stress generated by a time-varying strain under broken time-reversal
+symmetry. We demonstrate that this effect generates a hybridized
+paramagnon-polaron mode, which allows one to assess altermagnetic excitations
+directly from the phonon spectrum. Using a scaling analysis, we also
+demonstrate that the dynamic strain coupling strongly affects the altermagnetic
+phase boundary, but in different ways in the thermal and quantum regimes. In
+the ground state for both 2D and 3D systems, we find that a hardening of the
+altermagnon mode leads to an extended altermagnetic ordered regime, whereas for
+non-zero temperatures in 2D, the softening of the phonon modes leads to
+increased fluctuations that lower the altermagnetic transition temperature. In
+3D even at finite temperatures the dominant effect is the suppression of
+quantum fluctuations. We also discuss the application of these results to
+standard ferromagnetic systems.",2307.01855v3
+2023-07-11,Adiabatic dynamics of coupled spins and phonons in magnetic insulators,"In conventional \textit{ab initio} methodologies, phonons are calculated by
+solving equations of motion involving static interatomic force constants and
+atomic masses. The Born-Oppenheimer approximation, where all electronic degrees
+of freedom are assumed to adiabatically follow the nuclear dynamics, is also
+adopted. This approach does not fully account for the effects of broken
+time-reversal symmetry in systems with magnetic order. Recent attempts to
+rectify this involve the inclusion of the velocity dependence of the
+interatomic forces in the equations of motion, which accounts for time-reversal
+symmetry breaking, and can result in chiral phonon modes with non-zero angular
+momentum even at the zone center. However, since the energy ranges of phonons
+and magnons typically overlap, the spins cannot be treated as adiabatically
+following the lattice degrees of freedom. Instead, phonon and spins must be
+treated on a similar footing. Focusing on zone-center modes, we propose a
+method involving Hessian matrices and Berry curvature tensors in terms of both
+phonon and spin degrees of freedom, and describe a first-principles methodology
+for calculating these. We then solve Lagrange's equations of motion to
+determine the energies and characters of the mixed excitations, allowing us to
+quantify, for example, the energy splittings between chiral pairs of phonons in
+some cases, and the degree of magnetically induced mixing between infrared and
+Raman modes in others. The approach is general, and can be applied to determine
+the adiabatic dynamics of any mixed set of slow variables.",2307.05668v2
+2023-07-14,Dark matter detection using nuclear magnetization in magnet with hyperfine interaction,"We consider the possibility to detect cosmic light dark matter (DM), i.e.,
+axions and dark photons, of mass $\sim 10^{-6}$ eV and $\sim 10^{-4}$ eV, by
+magnetic excitation in a magnet with strong hyperfine interaction. In
+particular, we consider a canted anti-ferromagnet, MnCO$_3$, as a concrete
+candidate material. With spin transfer between nuclear and electron spins
+allowed by the hyperfine interaction, nuclear spins become naturally highly
+polarized due to an effective (electron-spin-induced) magnetic field, and have
+long-range interactions with each other. The collective precession of nuclear
+spins, i.e., a nuclear magnon, can be generated by the DM field through the
+nucleon-DM interaction, while they are also sensitive to the electron-DM
+interaction through the electron-nuclear spin mixing. Compared with
+conventional nuclear-spin precession experiments, this system as a DM sensor is
+sensitive to higher frequency needing only a small static magnetic field
+applied. The system also has collective precession of electron spins, mixed
+with nuclear spins, as the additional channels that can be used for DM probes.
+We estimate the sensitivity under appropriate readout setups such as an
+inductive pick-up loop associated with an LC resonant circuit, or a photon
+cavity with a photon counting device. We show that this method covers an
+unexplored parameter region of light bosonic DM.",2307.08577v2
+2023-07-24,Evidence of Charge-Phonon coupling in Van der Waals materials Ni1-xZnxPS3,"NiPS3 is a Van der Waals antiferromagnet that has been found to display
+spin-charge and spin-phonon coupling in its antiferromagnetically ordered state
+below TN = 155 K. Here, we study high-quality crystals of site-diluted
+Ni1-xZnxPS3 (0 < x < 0.2) using temperature-dependent specific heat and Raman
+spectroscopy probes. The site dilution suppresses the antiferromagnetic
+ordering in accordance with the mean-field prediction. In NiPS3, we show that
+the phonon mode P2 (176 cm-1) associated with Ni vibrations show a distinct
+asymmetry due to the Fano resonance, which persists only in the paramagnetic
+phase, disappearing below T_N = 155 K. This was further supported by
+temperature-dependent Raman data on an 8% Zn-doped crystal (T_N = 135 K) where
+Fano resonance similarly van in the magnetically ordered phase. This is
+contrary to the behaviour of the Raman mode P9 (570 cm-1), which shows a Fano
+resonance at low temperatures below T_N due to its coupling with the two-magnon
+continuum. We show that the Fano resonance of P2 arises from its coupling with
+an electronic continuum that weakens considerably upon cooling to low
+temperatures. In the doped crystals, the Fano coupling is found to enhance with
+Zn-doping. These observations suggest the presence of strong electron-phonon
+coupling in the paramagnetic phase of NiPS3 due to charge density fluctuations
+associated with the negative charge transfer state of Ni.",2307.12733v2
+2023-07-24,The Spin Point Groups and their Representations,"The spin point groups are finite groups whose elements act on both real space
+and spin space. Among these groups are the magnetic point groups in the case
+where the real and spin space operations are locked to one another. The
+magnetic point groups are central to magnetic crystallography for strong
+spin-orbit coupled systems and the spin point groups generalize these to the
+intermediate and weak spin-orbit coupled cases. The spin point groups were
+introduced in the 1960's and enumerated shortly thereafter. In this paper, we
+complete the theory of spin point groups by presenting an account of these
+groups and their representation theory. Our main findings are that the
+so-called nontrivial spin point groups (numbering 598 groups) have co-irreps
+corresponding exactly to the (co-)irreps of regular or black and white groups
+and we tabulate this correspondence for each nontrivial group. However a total
+spin group, comprising the product of a nontrivial group and a spin-only group,
+has new co-irreps in cases where there is continuous rotational freedom. We
+provide explicit co-irrep tables for all these instances. We also discuss new
+forms of spin-only group extending the Litvin-Opechowski classes. To exhibit
+the usefulness of these groups to physically relevant problems we discuss a
+number of examples from electronic band structures of altermagnets to magnons.",2307.12784v2
+2023-06-25,Antiferromagnetic $α$-MnTe: Molten-Salt-Assisted Chemical Vapor Deposition Growth and Magneto-Transport Properties,"Antiferromagnetic (AF) materials are attracting increasing interest of
+research in magnetic physics and spintronics. Here, we report controllable
+synthesis of room-temperature AF $\alpha$-MnTe nanocrystals (N\'eel temperature
+~ 307 K) via molten-salt-assisted chemical vapor deposition method. The growth
+kinetics are investigated regarding the dependence of flake dimension and
+macroscopic shape on growth time and temperature. The high crystalline quality
+and atomic structure are confirmed by various crystallographic characterization
+means. Cryogenic magneto-transport measurements reveal anisotropic
+magnetoresistance (MR) response and a complicated dependence of MR on
+temperature, owing to the subtle competition among multiple scattering
+mechanisms of thermally excited magnetic disorders (magnon drag), magnetic
+transition and thermally populated lattice phonons. Overall positive MR
+behavior with twice transitions in magnitude is observed when out-of-plane
+external magnetic field ($B$) is applied, while a transition from negative to
+positive MR response is recorded when in-plane $B$ is applied. The rich
+magnetic transport properties render $\alpha$-MnTe a promising material for
+exploiting functional components in magnetic devices.",2307.13615v1
+2023-08-03,Flavor-wave theory with quasiparticle damping at finite temperatures: Application to chiral edge modes in the Kitaev model,"We propose a theoretical framework to investigate elementary excitations at
+finite temperatures within a localized electron model that describes the
+interactions between multiple degrees of freedom, such as quantum spin models
+and Kugel-Khomskii models. Thus far, their excitation structures have been
+mainly examined using the linear flavor-wave theory, an SU($N$) generalization
+of the linear spin-wave theory. These techniques introduce noninteracting
+bosonic quasiparticles as elementary excitations from the ground state, thereby
+elucidating numerous physical phenomena, including excitation spectra and
+transport properties characterized by topologically nontrivial band structures.
+Nevertheless, the interactions between quasiparticles cannot be ignored in
+systems exemplified by $S=1/2$ quantum spin models, where strong quantum
+fluctuations are present. Recent studies have investigated the effects of
+quasiparticle damping at zero temperature in such models. In our study,
+extending this approach to the flavor-wave theory for general localized
+electron models, we construct a comprehensive method to calculate excitation
+spectra with the quasiparticle damping at finite temperatures. We apply our
+method to the Kitaev model under magnetic fields, a typical example of models
+with topologically nontrivial magnon bands. Our calculations reveal that chiral
+edge modes undergo significant damping in weak magnetic fields, amplifying the
+damping rate by the temperature increase. This effect is caused by collisions
+with thermally excited quasiparticles. Since our approach starts from a general
+Hamiltonian, it will be widely applicable to other localized systems, such as
+spin-orbital coupled systems derived from multi-orbital Hubbard models in the
+strong correlation limit.",2308.01711v1
+2023-08-21,Rotating Curved Spacetime Signatures from a Giant Quantum Vortex,"Gravity simulators are laboratory systems where small excitations like sound
+or surface waves behave as fields propagating on a curved spacetime geometry.
+The analogy between gravity and fluids requires vanishing viscosity, a feature
+naturally realised in superfluids like liquid helium or cold atomic clouds.
+Such systems have been successful in verifying key predictions of quantum field
+theory in curved spacetime. In particular, quantum simulations of rotating
+curved spacetimes indicative of astrophysical black holes require the
+realisation of an extensive vortex flow in superfluid systems. Here we
+demonstrate that despite the inherent instability of multiply quantised
+vortices, a stationary giant quantum vortex can be stabilised in superfluid
+$^4$He. Its compact core carries thousands of circulation quanta, prevailing
+over current limitations in other physical systems such as magnons, atomic
+clouds and polaritons. We introduce a minimally invasive way to characterise
+the vortex flow by exploiting the interaction of micrometre-scale waves on the
+superfluid interface with the background velocity field. Intricate wave-vortex
+interactions, including the detection of bound states and distinctive analogue
+black hole ringdown signatures, have been observed. These results open new
+avenues to explore quantum-to-classical vortex transitions and utilise
+superfluid helium as a finite temperature quantum field theory simulator for
+rotating curved spacetimes.",2308.10773v4
+2023-09-07,Coherent spin dynamics between electron and nucleus within a single atom,"The nuclear spin, being much more isolated from the environment than its
+electronic counterpart, enables quantum experiments with prolonged coherence
+times and presents a gateway towards uncovering the intricate dynamics within
+an atom. These qualities have been demonstrated in a variety of nuclear spin
+qubit architectures, albeit with limited control over the direct environment of
+the nuclei. As a contrasting approach, the combination of electron spin
+resonance (ESR) and scanning tunnelling microscopy (STM) provides a bottom-up
+platform to study the fundamental properties of nuclear spins of single atoms
+on a surface. However, access to the time evolution of these nuclear spins, as
+was recently demonstrated for electron spins, remained a challenge. Here, we
+present an experiment resolving the nanosecond coherent dynamics of a
+hyperfine-driven flip-flop interaction between the spin of an individual
+nucleus and that of an orbiting electron. We use the unique local
+controllability of the magnetic field emanating from the STM probe tip to bring
+the electron and nuclear spins in tune, as evidenced by a set of avoided level
+crossings in ESR-STM. Subsequently, we polarize both spins through scattering
+of tunnelling electrons and measure the resulting free evolution of the coupled
+spin system using a DC pump-probe scheme. The latter reveals a complex pattern
+of multiple interfering coherent oscillations, providing unique insight into
+the atom's hyperfine physics. The ability to trace the coherent hyperfine
+dynamics with atomic-scale structural control adds a new dimension to the study
+of on-surface spins, offering a pathway towards dynamic quantum simulation of
+low-dimensional magnonics.",2309.03749v1
+2023-09-11,Singularity theory of Weyl-point creation and annihilation,"Weyl points (WP) are robust spectral degeneracies, which can not be split by
+small perturbations, as they are protected by their non-zero topological
+charge. For larger perturbations, WPs can disappear via pairwise annihilation,
+where two oppositely charged WPs merge, and the resulting neutral degeneracy
+disappears. The neutral degeneracy is unstable, meaning that it requires the
+fine-tuning of the perturbation. Fine-tuning of more than one parameter can
+lead to more exotic WP mergers. In this work, we reveal and analyze a
+fundamental connection of the WP mergers and singularity theory: phase boundary
+points of Weyl phase diagrams, i.e., control parameter values where Weyl point
+mergers happen, can be classified according to singularity classes of maps
+between manifolds of equal dimension. We demonstrate this connection on a
+Weyl--Josephson circuit where the merger of 4 WPs draw a swallowtail
+singularity, and in a random BdG Hamiltonian which reveal a rich pattern of
+fold lines and cusp points. Our results predict universal geometrical features
+of Weyl phase diagrams, and generalize naturally to creation and annihilation
+of Weyl points in electronic (phononic, magnonic, photonic, etc) band-structure
+models, where Weyl phase transitions can be triggered by control parameters
+such as mechanical strain.",2309.05506v1
+2023-09-20,Magnetic imaging and domain nucleation in CrSBr down to the 2D limit,"Recent advancements in 2D materials have revealed the potential of van der
+Waals magnets, and specifically of their magnetic anisotropy that allows
+applications down to the 2D limit. Among these materials, CrSBr has emerged as
+a promising candidate, because its intriguing magnetic and electronic
+properties have appeal for both fundamental and applied research in spintronics
+or magnonics. Here, nano SQUID-on-tip (SOT) microscopy is used to obtain direct
+magnetic imaging of CrSBr flakes with thicknesses ranging from monolayer (N=1)
+to few-layer (N=5). The ferromagnetic order is preserved down to the monolayer,
+while the antiferromagnetic coupling of the layers starts from the bilayer
+case. For odd layers, at zero applied magnetic field, the stray field resulting
+from the uncompensated layer is directly imaged. The progressive spin
+reorientation along the out-of-plane direction (hard axis) is also measured
+with a finite applied magnetic field, allowing to evaluate the anisotropy
+constant, which remains stable down to the monolayer and is close to the bulk
+value. Finally, by selecting the applied magnetic field protocol, the formation
+of N\'eel magnetic domain walls is observed down to the single layer limit.",2309.11550v1
+2023-09-25,Domain wall dynamics driven by a transient laser-induced magnetisation,"One of the fundamental effects of the laser-matter interaction is the
+appearance of an induced transient magnetisation. While the underlying
+phenomena differ in their microscopic origin and cover a diverse array of
+materials, here we address a fundamental question about the possibility to
+drive domain-wall dynamics on the femtosecond timescale of the exchange
+interactions solely by longitudinal changes of the magnetic moments. We verify
+the viability of this hypothesis in the case of a generic ferromagnetic system
+described in the framework of the high-temperature micromagnetic model based on
+the Landau-Lifshitz-Bloch equation. The effect is investigated in a 1D model at
+constant temperature as well as in a full micromagnetic framework considering
+realistic laser-induced heating. Our results demonstrate that domain-wall
+deformation in a femtosecond timeframe leads to the displacement of the wall on
+a larger timescale up to nanoseconds accompanied by a release of excess energy
+in the form of spin waves. The domain wall deformation leads to the appearance
+of a magnetisation gradient across the wall which promotes the motion towards
+the region consisting of spins with decreased magnetisation length. The total
+displacement is enhanced at larger temperatures and smaller damping due to an
+increase of the longitudinal relaxation time which ensures the longer presence
+of the induced magnetisation gradient. We also demonstrate an enhanced domain
+wall motion in the presence of the Dzyaloshinskii-Moriya interaction attributed
+to augmented magnonic torques. Our results are important towards the
+understanding of ultrafast magnetism phenomena on the sub-picosecond timescale.",2309.14287v1
+2023-09-29,Planar thermal Hall effect from phonons in a Kitaev candidate material,"Kitaev materials are a promising platform for the realization of quantum spin
+liquid states. The thermal Hall effect has emerged as a potential probe of
+exotic excitations within such states. In the Kitaev candidate material
+$\alpha$-RuCl$_{3}$, however, the thermal Hall conductivity $\kappa_{xy}$ has
+been attributed not only to exotic Majorana fermions or chiral magnons, but
+also to phonons. It has been shown theoretically that the former two types of
+heat carriers can generate a ""planar"" thermal Hall effect, whereby the magnetic
+field is parallel to the heat current, as observed experimentally, but it is
+unknown whether phonons also could. Here we show that a planar thermal Hall
+effect is present in another Kitaev candidate material,
+Na$_{2}$Co$_{2}$TeO$_{6}$. On the basis of a striking similarity between the
+temperature and field dependence of $\kappa_{xy}$ and that of the
+phonon-dominated thermal conductivity $\kappa_{xx}$, we argue that the planar
+thermal Hall effect in Na$_{2}$Co$_{2}$TeO$_{6}$ is generated by phonons. The
+phonon contributed planar $\kappa_{xy}$ also shows a strong sample dependence,
+which indicates an extrinsic origin of the mechanism. By conducting a complete
+study with different in-plane configurations of heat current $J$ and magnetic
+field $H$, $i.e.$ $H$ $\|$ $J$ and $H$ $\bot$ $J$, we observe a large
+difference in $\kappa_{xy}$ between these two configurations, which reveals
+that the direction of the heat current $J$ may play an important role in
+determining the planar thermal Hall effect. Our observation calls for a
+re-evaluation of the planar thermal Hall effect observed in
+$\alpha$-RuCl$_{3}$.",2309.17231v2
+2023-10-01,Effect of Spin Fluctuations on Magnetoresistance and Anomalous Hall Effect in the Chiral Magnet Co8Zn8Mn4,"The beta Mn type Co-Zn-Mn alloys have seized significant attention due to
+their ability to host skyrmions at room temperature. Here we analyse the
+unconventional magneto-transport properties of Co8Zn8Mn4 single crystals with a
+Curie temperature of 275 K. A negative magnetoresistance is obtained over a
+wide temperature range of 50K to 300K. The deviation of the isothermal
+magnetoresistance (MR) curves from linearity to non-linearity as one approaches
+higher temperatures points towards the transition from the dominance of magnons
+to spin fluctuations. In the paramagnetic phase, the change in the shape of the
+MR curve has been explained using the Khosla and Fischer model. The
+relationship between the anomalous Hall effect (AHE) and longitudinal
+resistivity reveals the dominance of the skew-scattering mechanism, which is
+inexplicable based on the theories of semi-classical magneto-transport. We
+experimentally determine that the spin fluctuation is the source of the
+skew-scattering mechanism in Co8Zn8Mn4. In general skew-scattering mechanisms
+predominate in compounds with high conductivity, but our findings demonstrate
+that this is not always the case and that other aspects also require equal
+consideration. Our work throws new light on the predominant scattering
+mechanism in chiral magnets with skyrmionics phase at low conductivity.",2310.00739v1
+2023-10-11,Planar thermal Hall effect from phonons in cuprates,"A surprising ""planar"" thermal Hall effect, whereby the field is parallel to
+the current, has recently been observed in a few magnetic insulators, and this
+has been attributed to exotic excitations such as Majorana fermions or chiral
+magnons. Here we investigate the possibility of a planar thermal Hall effect in
+three different cuprate materials, in which the conventional thermal Hall
+conductivity $\kappa_{\rm {xy}}$ (with an out-of-plane field perpendicular to
+the current) is dominated by either electrons or phonons. Our measurements show
+that the planar $\kappa_{\rm {xy}}$ from electrons in cuprates is zero, as
+expected from the absence of a Lorentz force in the planar configuration. By
+contrast, we observe a sizable planar $\kappa_{\rm {xy}}$ in those samples
+where the thermal Hall response is due to phonons, even though it should in
+principle be forbidden by the high crystal symmetry. Our findings call for a
+careful re-examination of the mechanisms responsible for the phonon thermal
+Hall effect in insulators.",2310.07696v2
+2023-10-16,Implementation of a laser-neutron pump-probe capability at HYSPEC,"Exciting new fundamental scientific questions are currently being raised
+regarding nonequilibrium dynamics in spin systems, as this directly relates to
+low power and low loss energy transport for spintronics. Inelastic neutron
+scattering (INS) is an indispensable tool to study spin excitations in complex
+magnetic materials. However, conventional INS spectrometers currently only
+perform steady-state measurements and probe averaged properties over many
+collision events between spin excitations in thermodynamic equilibrium, while
+the exact picture of re-equilibration of these excitations remains unknown. In
+this work, we designed and implemented a time-resolved laser-neutron pump-probe
+capability at HYSPEC (Hybrid Spectrometer, beamline 14-B) at the Spallation
+Neutron Source (SNS) at Oak Ridge National Laboratory. This capability allows
+us to excite out-of-equilibrium magnons with a nanosecond pulsed laser source
+and probe the resulting dynamics using INS. Here, we discussed technical
+aspects to implement such a capability in a neutron beamline, including choices
+of suitable neutron instrumentation and material systems, laser excitation
+scheme, experimental configurations, and relevant firmware and software
+development to allow for time-synchronized pump-probe measurements. We
+demonstrated that the laser-induced nonequilibrium structural factor is able to
+be resolved by INS in a quantum magnet. The method developed in this work will
+provide SNS with advanced capabilities for performing out-of-equilibrium
+measurements, opening up an entirely new research direction to study
+out-of-equilibrium phenomena using neutrons.",2310.10540v1
+2023-10-27,Effect of interfacial Dzyaloshinskii-Moriya interaction in spin dynamics of an Antiferromagnet coupled Ferromagnetic double-barrier Magnetic Tunnel Junction,"In this work, we have studied the spin dynamics of a synthethic
+Antiferromagnet (SAFM)$|$Heavy Metal (HM)$|$Ferromagnet (FM) double barrier
+magnetic tunnel junction (MTJ) in presence of Ruderman-Kittel-Kasuya-Yoside
+interaction (RKKYI), interfacial Dzyaloshinskii-Moriya interaction (iDMI),
+N\'eel field and Spin-Orbit Coupling (SOC) with different Spin Transfer Torque
+(STT). We employ Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation to
+investigate the AFM dynamics of the proposed system. We found that the system
+exhibits a transition from regular to damped oscillations with the increase in
+strength of STT for systems with weaker iDMI than RKKYI while display sustained
+oscillatons for system having same order of iDMI and RKKYI. On the other hand
+the iDMI dominating system exhibits self-similar but aperiodic patterns in
+absence of N\'eel field. In the presence of N\'eel field, the RKKYI dominating
+systems exhibit chaotic oscillations for low STT but display sustained
+oscillation under moderate STT. Our results suggest that the decay time of
+oscillations can be controlled via SOC. The system can works as an oscillator
+for low SOC but display nonlinear characteristics with the rise in SOC for
+systems having weaker iDMI than RKKYI while an opposite characteristic are
+noticed for iDMI dominating systems. We found periodic oscillations under low
+external magnetic field in RKKYI dominating systems while moderate field are
+necessary for sustained oscillation in iDMI dominating systems. Moreover, the
+system exhibits saddle-node bifurcation and chaos under moderate N\'eel field
+and SOC with suitable iDMI and RKKYI. In addition, our results indicate that
+the magnon lifetime can be enhanced by increasing the strength of iDMI for both
+optical and acoustic modes.",2310.18175v1
+2023-11-09,Bose-Einstein condensation in systems with flux equilibrium,"We consider flux equilibrium in dissipative nonlinear wave systems subject to
+external energy pumping. In such systems, the elementary excitations, or
+quasiparticles, can create a Bose-Einstein condensate. We develop a theory on
+the Bose-Einstein condensation of quasiparticles for various regimes of
+external excitation, ranging from weak and stationary to ultra-strong pumping,
+enabling us to determine the number of quasiparticles near the bottom of the
+energy spectrum and their distribution along wave vectors. We identify physical
+phenomena leading to condensation in each of the regimes. For weak stationary
+pumping, where the distribution of quasiparticles deviates only slightly from
+thermodynamic equilibrium, we define a range of pumping parameters where the
+condensation occurs and estimate the density of the condensate and the fraction
+of the condensed quasiparticles. As the pumping amplitude increases, a powerful
+influx of injected quasiparticles is created by the Kolmogorov-Zakharov
+scattering cascade, leading to their Bose-Einstein condensation. With even
+stronger pumping, kinetic instability may occur, resulting in a direct transfer
+of injected quasiparticles to the bottom of the spectrum. For the case of
+ultra-strong parametric pumping, we have developed a stationary nonlinear
+theory of kinetic instability. The theory agrees qualitatively with
+experimental data obtained using Brillouin light scattering spectroscopy during
+parametric pumping of magnons in room-temperature films of yttrium-iron garnet.",2311.05315v1
+2023-11-13,Multiple topological phase transitions in magnetic systems: role of anisotropic Dzyaloshinskii-Moriya interaction,"In this work we study the topological properties of magnons in both
+ferromagnetically and antiferromagnetically ordered systems on a
+two-dimensional square lattice. While topological features emerge owing to the
+violation of time reversal symmetry induced by the Dzyaloshinskii-Moriya
+interaction (DMI), here we consider an anisotropic DMI and ascertain the role
+of the anisotropy parameter on the topological phase transitions. In
+particular, our phase plot for the ferromagnetic case demonstrates multiple
+topological phase transitions, that is, from a topological phase to another
+topological phase, and as well, from a topological phase to a trivial phase. In
+the former, the topological invariant, namely the Chern number, discontinuously
+changes from one finite value to another ($-1 \rightarrow +1$), while it
+vanishes ($1 \rightarrow 0$) in the latter. Further, an extended trivial region
+is observed where the DMI is non-zero, which is surprising since DMI is the
+origin of the topological gap. The nature of the phases and the phase
+transitions, therein are characterized by their band structure, presence (or
+absence) of the chiral edge modes, computation of the topological Hall effect,
+etc. In contrast, the antiferromagnetic case presents a more predictable
+scenario, in the sense, it behaves as a trivial insulator in the absence of
+DMI, although demonstrate a topological to trivial phase transition.",2311.07201v1
+2023-11-17,Calibration Unit Design for High-Resolution Infrared Spectrograph for Exoplanet Characterization (HISPEC),"The latest generation of high-resolution spectrograph instruments on
+10m-class telescopes continue to pursue challenging science cases.
+Consequently, ever more precise calibration methods are necessary to enable
+trail-blazing science methodology. We present the High-resolution Infrared
+SPectrograph for Exoplanet Characterization (HISPEC) Calibration Unit (CAL),
+designed to facilitate challenging science cases such as Doppler imaging of
+exoplanet atmospheres, precision radial velocity, and high-contrast
+high-resolution spectroscopy of nearby exoplanets. CAL builds upon the heritage
+from the pathfinder instrument Keck Planet Imager and Characterizer (KPIC) and
+utilizes four near-infrared (NIR) light sources encoded with wavelength
+information that are coupled into single-mode fibers. They can be used
+synchronously during science observations or asynchronously during daytime
+calibrations. A hollow cathode lamp (HCL) and a series of gas absorption cells
+provide absolute calibration from 0.98 {\mu}m to 2.5 {\mu}m. A laser frequency
+comb (LFC) provides stable, time-independent wavelength information during
+observation and CAL implements a lower finesse astro-etalon as a backup for the
+LFC. Design lessons from instrumentation like HISPEC will serve to inform the
+requirements for similar instruments for the ELTs in the future.",2311.10239v1
+2023-11-20,Thermal Hall effects due to topological spin fluctuations in YMnO$_3$,"The thermal Hall effect in magnetic insulators has been considered a powerful
+method for examining the topological nature of charge-neutral quasiparticles
+such as magnons. Yet, unlike the kagome system, the triangular lattice has
+received less attention for studying the thermal Hall effect because the scalar
+spin chirality cancels out between adjacent triangles. However, such
+cancellation cannot be perfect if the triangular lattice is distorted, which
+could open the possibility of a non-zero thermal Hall effect. Here, we report
+that the trimerized triangular lattice of multiferroic hexagonal manganite
+YMnO$_3$ produces a highly unusual thermal Hall effect due to topological spin
+fluctuations with the additional intricacy of a Dzyaloshinskii-Moriya
+interaction under an applied magnetic field. We conclude the thermal Hall
+conductivity arises from the system's topological nature of spin fluctuations.
+Our theoretical calculations demonstrate that the thermal Hall conductivity is
+also related in this material to the splitting of the otherwise degenerate two
+chiralities, left and right, of its 120$^{\circ}$ magnetic structure. Our
+result is one of the most unusual cases of topological physics due to this
+broken $Z_2$ symmetry of the chirality in the supposedly paramagnetic state of
+YMnO$_3$, with strong topological spin fluctuations. These new mechanisms in
+this important class of materials are crucial in exploring new thermal Hall
+physics and exotic excitations.",2311.11527v1
+2023-12-20,An effective field theory of damped ferromagnetic systems,"Using the in-in formalism, we generalize the recently constructed
+magnetoelastic EFT arXiv:2112.13873 [hep-th] to describe the damping dynamics
+of ferromagnetic systems at long wavelengths. We find that the standard Gilbert
+damping term naturally arises as the simplest leading-order symmetry-consistent
+non-conservative contribution within the in-in framework. The EFT is easily
+generalized to scenarios with anisotropy and inhomogeneity. In particular, we
+find the classic Landau-Lifshitz damping term emerges when isotropy is broken
+by a constant external background field. This provides a first principle
+explanation for distinguishing the two types of damping dynamics that were
+originally constructed phenomenologically. Furthermore, the EFT framework could
+also incorporate intrinsic anisotropy of the material in a straightforward way
+using the spurion method. For systems with inhomogeneity such as nontrivial
+spin textures, we find that the leading order derivative correction yields the
+generalized Gilbert damping equations that were found in condensed matter
+literature. This shows that the EFT approach enables us to derive the form of
+higher-derivative-order corrections in a systematic way. Lastly, using the
+phonon-magnon coupling deduced in the magnetoelastic EFT, we are able to make a
+prediction for the generic form of the phononic contribution to the damping
+equation.",2312.13093v1
+2024-01-05,Solutions to the Landau-Lifshitz-Gilbert equation in the frequency space: Discretization schemes for the dynamic-matrix approach,"The dynamic matrix method addresses the Landau-Lifshitz-Gilbert (LLG)
+equation in the frequency domain by transforming it into an eigenproblem.
+Subsequent numerical solutions are derived from the eigenvalues and
+eigenvectors of the dynamic matrix. In this work we explore discretization
+methods needed to obtain a matrix representation of the dynamic operator, a
+fundamental counterpart of the dynamic matrix. Our approach opens a new set of
+linear algebra tools for the dynamic matrix method and expose the
+approximations and limitations intrinsic to it. Moreover, our discretization
+algorithms can be applied to various discretization schemes, extending beyond
+micromagnetism problems. We present some application examples, including a
+technique to obtain the dynamic matrix directly from the magnetic free energy
+function of an ensemble of macrospins, and an algorithmic method to calculate
+numerical micromagnetic kernels, including plane wave kernels. We also show how
+to exploit symmetries and reduce the numerical size of micromagnetic
+dynamic-matrix problems by a change of basis. This procedure significantly
+reduces the size of the dynamic matrix by several orders of magnitude while
+maintaining high numerical precision. Additionally, we calculate analytical
+approximations for the dispersion relations in magnonic crystals. This work
+contributes to the understanding of the current magnetization dynamics methods,
+and could help the development and formulations of novel analytical and
+numerical methods for solving the LLG equation within the frequency domain.",2401.02933v2
+2024-01-05,Dark Matter Candidates of a Very Low Mass,"We review dark matter (DM) candidates of a very low mass, appearing in the
+window below the traditional weakly-interacting massive particle $m_\chi
+\lesssim 10$ GeV and extending down to $m_\chi \gtrsim 1$ meV, somewhat below
+the mass limit where DM becomes wavelike. Such candidates are motivated by
+hidden sectors such as Hidden Valleys, which feature hidden forces and rich
+dynamics, but have evaded traditional collider searches looking for New Physics
+because of their relatively weak coupling to the Standard Model. Such sectors
+can still be detected through dedicated low-energy colliders which, through
+their intense beams, can have sensitivity to smaller couplings, or through
+astrophysical observations of the evolution of DM halos and stellar structures
+which, through the Universe's epochs, can be sensitive to small DM
+interactions. We also consider mechanisms where the DM abundance is fixed
+through the interaction with the SM, which directly motivates the search for
+light DM in terrestrial experiments. The bulk of this review is dedicated to
+the new ideas that have been proposed for directly detecting such DM candidates
+of a low mass, through nuclear recoils, electronic excitations, or collective
+modes such as phonons and magnons. The rich tapestry of materials and modes in
+the Condensed Matter landscape is reviewed, along with specific prospects for
+detection.",2401.03025v1
+2024-01-09,Microwave magnetic excitations in U-type hexaferrite Sr$_4$CoZnFe$_{36}$O$_{60}$ ceramics,"Microwave (MW) spectra of ferrimagnetic U-hexaferrite
+Sr$_4$CoZnFe$_{36}$O$_{60}$ ceramics were studied using several experimental
+techniques from 100 MHz to 50 GHz at temperatures between 10 and 390 K. They
+revealed 9 excitations, which exhibit remarkable temperature dependences near
+the magnetic phase transitions at 145 K and 305 K. Some of them also change
+under the application of a weak bias magnetic field at room temperature. Three
+lowest-frequency modes seen between 200 MHz and 3 GHz were assigned to the
+dynamics of the magnetic domains. The mode attributed to the natural
+ferromagnetic resonance exhibits a dramatic critical slowing-down from 25 GHz
+at 390 K to 5 GHz near the 305 K phase transition, and again a hardening to ~11
+GHz on further cooling. The higher-frequency excitations are most likely spin
+wave (magnon) modes arising from the complex ferrimagnetic structure of
+Sr$_4$CoZnFe$_{36}$O$_{60}$. The high sensitivity of the MW spectra to the weak
+magnetic bias field $H$ < 700 Oe at room temperature is shown to be caused by
+the transformation of the polydomain magnetic structure in randomly oriented
+ceramic grains to a monodomain one. The MW response measured above 2 GHz using
+coplanar and microstrip lines with different electromagnetic field distribution
+and sample coupling revealed the same excitations with similar temperature and
+bias field dependences. It confirms the reliability of the results and proves
+the effectiveness of the used MW techniques.",2401.04678v1
+2024-01-12,Superorders and acoustic modes folding in BiFeO$_3$/LaFeO$_3$ superlattices,"Superlattices are materials created by the alternating growth of two
+chemically different materials. The direct consequence of creating a
+superlattice is the folding of the Brillouin zone which gives rise to
+additional electronic bands and phonon modes. This has been successfully
+exploited to achieve new transport and optical properties in semiconductor
+superlattices, for example. Here, we show that multiferroic BiFeO$_3$/LaFeO$_3$
+superlattices are more than just periodic chemical stacking. Using transmission
+electron microscopy, X-ray diffraction and first-principles calculations, we
+demonstrate the existence of a new order of FeO$_6$ octahedra, with a period
+along the growth direction about twice that of the chemical supercell, i.e. a
+superorder. The effect of this new structural order on the lattice dynamics is
+studied with ultrafast optical pump-probe experiments. While a mode at 1.2 THz
+is attributed solely to the chemical modulation of the superlattice, the
+existence of another 0.7 THz mode seems to be explained only by a double
+Brillouin zone folding in agreement with the structural description. Our work
+shows that multiferroic BiFeO$_3$/LaFeO$_3$ superlattices can be used to tune
+the spectrum of coherent THz phonons, and potentially that of magnons or
+electromagnons.",2401.06647v1
+2024-01-21,Exploring Intrinsic Magnetic Topological Insulators: The Case of EuIn$_2$As$_2$,"In this study, ultrafast optical spectroscopy was employed to elucidate the
+intricate topological features of EuIn$_2$As$_2$, a promising candidate for a
+magnetic topological-crystalline axion insulator. Our investigation, focusing
+on the real-time evolution of topological states, unveiled a narrow surface
+magnetic gap (2$\Delta_0$ $\simeq$ 8.2 meV)) emerging at the antiferromagnetic
+transition temperature ($T_N$ $\approx$ 16 K). Below $T_N$, two extremely
+low-energy collective modes, $\omega_1$ and $\omega_2$, with frequencies of
+$\sim$9.9 and 21.6 GHz at $T$ = 4 K, respectively, were observed, exhibiting
+strong temperature dependence. $\omega_1$ correlates with an acoustic phonon,
+while $\omega_2$ is associated with a magnon. The results suggest that
+EuIn$_2$As$_2$ has the potential to manifest a magnetic topological-crystalline
+axion insulator, presenting a small magnetic energy gap on the (001) surface.
+The findings further our understanding of the interplay between magnetism and
+topology in this material, showcasing its potential for applications in quantum
+information processing and spintronics.",2401.11386v1
+2024-02-02,Skyrmions: A review on materials perspective for future electronic devices,"Recent years have witnessed an enormous rise in research interest in magnetic
+skyrmions owing to their capability to improve over contemporary spintronic
+devices. An overview of the various magnetic interactions responsible for the
+formation of skyrmion together with distinct noncentrosymmetric and
+centrosymmetric skyrmion candidates is given in this review article. The
+magnetic interactions known as Dzyaloshinskii-Moriya interactions (DMI) have
+been extensively studied over the years to better understand the mechanism of
+skyrmions in chiral magnets that have larger skyrmion sizes. Because of their
+low skyrmion size, the centrosymmetric frustrated magnets are dwelling to
+skyrmions controlled by long-range interactions such as the
+Ruderman-Kittel-Kasuya-Yosida interaction (RKKY), which may be useful in the
+development of high-density memory devices. To lay a solid foundation for the
+magnetic interactions involved in skyrmion formations and many other special
+physical properties, more research in the field of centrosymmetric skyrmions is
+required. Apart from studying candidates with low skyrmion sizes, one of the
+main goals for the future is to better understand the dynamics of skyrmion
+using polarized magnons, which has the potential to be extremely beneficial for
+spintronic applications.",2402.01503v3
+2024-02-05,Tracing d-d transitions in FePS$_{3}$ on ultrafast time scales,"Excitations between localized 3d states of transition metal ions within
+crystalline solids, commonly known as d-d transitions, play a pivotal role in
+diverse phenomena across solid state physics, materials science, and chemistry.
+These transitions contribute to the coloration in transition metal oxides,
+catalytic processes on oxide surfaces, and high-temperature superconductivity.
+They also couple optical excitation to quantized collective phenomena such as
+phonons and magnons in magnetic systems. Until now, an experimental method to
+unravel the complex quasiparticle dynamics associated with d-d transitions has
+remained elusive. We bridge this gap by demonstrating that d-d transitions can
+be distinctly traced in momentum space and time using time- and angle-resolved
+photoelectron spectroscopy (trARPES). Through this approach, we can assign
+specific momentum-dependent characteristics and elucidate the decay mechanisms
+of specific d-d transitions in FePS$_{3}$, a two-dimensional van der Waals
+antiferromagnet with a rich array of quantum phenomena stemming from d-d
+transitions. This study pioneers the use of ARPES in probing the dynamics of
+d-d transitions across a wide spectrum of solid-state systems.",2402.03018v1
+2024-03-06,"Crystal, ferromagnetism, and magnetoresistance with sign reversal in a EuAgP semiconductor","We synthesized the ferromagnetic EuAgP semiconductor and conducted a
+comprehensive study of its crystalline, magnetic, heat capacity, band gap, and
+magnetoresistance properties. Our investigation utilized a combination of X-ray
+diffraction, optical, and PPMS DynaCool measurements. EuAgP adopts a hexagonal
+structure with the $P6_3/mmc$ space group. As the temperature decreases, it
+undergoes a magnetic phase transition from high-temperature paramagnetism to
+low-temperature ferromagnetism. We determined the ferromagnetic transition
+temperature to be $T_{\textrm{C}} =$ 16.45(1) K by fitting the measured
+magnetic susceptibility using a Curie-Weiss law. Heat capacity analysis of
+EuAgP considered contributions from electrons, phonons, and magnons, revealing
+$\eta$ = 0.03 J/mol/$\textrm{K}^\textrm{2}$, indicative of semiconducting
+behavior. Additionally, we calculated a band gap of $\sim$ 1.324(4) eV based on
+absorption spectrum measurements. The resistivity versus temperature of EuAgP
+measured in the absence of an applied magnetic field shows a pronounced peak
+around $T_{\textrm{C}}$, which diminishes rapidly with increasing applied
+magnetic fields, ranging from 1 to 14 T. An intriguing phenomenon emerges in
+the form of a distinct magnetoresistance transition, shifting from positive
+(e.g., 1.95\% at 300 K and 14 T) to negative (e.g., -30.73\% at 14.25 K and 14
+T) as the temperature decreases. This behavior could be attributed to
+spin-disordered scattering.",2403.03650v1
+2024-03-12,Crystal design of altermagnetism,"Symmetry plays a fundamental role in condensed matter. The unique
+entanglement between magnetic sublattices and alternating crystal environment
+in altermagnets provides a unique opportunity for designing magnetic space
+symmetry. There have been extensive experimental efforts concentrated on tuning
+the Neel vector to reconstruct altermagnetic symmetry. However, it remains
+challenging to modulate the altermagnetic symmetry through the crystal aspect.
+Here, the crystal design of altermagnetism is successfully realized, by
+breaking glide mirrors and magnetic mirrors of the (0001) crystallographic
+plane in CrSb films via crystal distortion. We establish a locking relationship
+between altermagnetic symmetry and the emergent Dzyaloshinskii-Moriya (DM)
+vectors in different CrSb films, realizing unprecedentedly room-temperature
+spontaneous anomalous Hall effect in an altermagnetic metal. The concept of
+exchange-coupling torques is broadened to include both antiferromagnetic
+exchange-coupling torque and DM torque. Their relationship is designable,
+determining electrical manipulation modes, e.g., field-assisted switching for
+CrSb(1-100)/Pt and field-free switching for W/CrSb(11-20). Particularly, the
+unprecedentedly field-free 100-percent switching of Neel vectors is realized by
+making these two torques parallel or antiparallel, dependent on Neel vector
+orientation. Besides unravelling the rich mechanisms for electrical
+manipulation of altermagnetism rooted in broadened concept of exchange-coupling
+torques, we list other material candidates and propose that crystal design of
+altermagnetism would bring rich designability to magnonics, topology, etc.",2403.07396v1
+2024-03-12,A compact approach to higher-resolution resonant inelastic X-ray scattering detection using photoelectrons,"The detection of inelastically scattered soft X-rays with high energy
+resolution usually requires large grating spectrometers. Recently,
+photoelectron spectrometry for analysis of X-rays (PAX) has been rediscovered
+for modern spectroscopy experiments at synchrotron light sources. By converting
+scattered photons to electrons and using an electron energy analyser, the
+energy resolution for resonant inelastic X-ray scattering (RIXS) becomes
+decoupled from the X-ray spot size and instrument length. In this work, we
+develop PAX towards high energy resolution using a modern photoemission
+spectroscopy setup studying Ba2Cu3O4Cl2 at the Cu L3-edge. We measure a
+momentum transfer range of 24% of the first Brillouin zone simultaneously. Our
+results hint at the observation of a magnon excitation below 100 meV energy
+transfer and show intensity variations related to the dispersion of
+dd-excitations. With dedicated setups, PAX can become an alternative to the
+best and largest RIXS instruments, while at the same time opening new
+opportunities to acquire RIXS at a range of momentum transfers simultaneously
+and combine it with angle-resolved photoemission spectroscopy in a single
+instrument.",2403.07452v1
+2024-03-17,Merons and magnetoelectric switching in centrosymmetric spiral magnets,"Spiral multiferroics exhibit a strong coupling between magnetic and
+ferroelectric orders, allowing cross-control. Since the seminal work of Kimura
+et al. in 2003, these materials have attracted great interest galvanized by the
+prospect of new high-efficiency memory devices, where magnetic (electric) bits
+are switched via an external electric (magnetic) field. Nevertheless, the
+mechanism underlying such a switching process - the electric field-driven
+dynamics of domain walls (DWs) - is still poorly understood. We address this
+problem for meron DWs, which represent one of the main DW types in spiral
+multiferroics and consist of an array of meron (half-skyrmion) strings. Minimum
+energy walls feature merons with alternating topological charges and move as
+relativistic massive particles, with the limiting velocity set by magnon speed.
+Low-energy defects in this alternating charge sequence, which appear during
+domain nucleation, can lead to DWs with net topological charge. This induces a
+peculiar non-local dynamics where all the spins in the system rotate, merons
+translate within the wall, and the DW mobility is suppressed. The topological
+charge of the wall and the meron helicity can be easily modified via an
+external magnetic and electric field, respectively, offering fine control over
+DW dynamics. Defects within the meron strings, analogous to Bloch points, have
+hedgehog-like spin texture and are strongly pinned to the lattice. The
+fascinating interplay between domain wall motion, translation of merons within
+the wall, and precession of spins in the entire domains opens a new playground
+for the electric manipulation of topological spin textures.",2403.11195v1
+2024-03-25,Giant tunability of magnetoelasticity in Fe$_4$N system: Platform for unveiling correlation between magnetostriction and magnetic damping,"Flexible spintronics has opened new avenue to promising devices and
+applications in the field of wearable electronics. Particularly, miniaturized
+strain sensors exploiting the spintronic function have attracted considerable
+attention, in which the magnetoelasticity linking magnetism and lattice
+distortion is a vital property for high-sensitive detection of strain. This
+paper reports the demonstration that the magnetoelastic properties of Fe$_4$N
+can be significantly varied by partially replacing Fe with Co or Mn. The high
+quality Fe$_4$N film exhibits large negative magnetostriction along the [100]
+direction ($\lambda_{100}$) of -121 ppm while Fe$_{3.2}$Co$_{0.8}$N shows
+$\lambda_{100}$ of +46 ppm. This wide-range tunability of $\lambda_{100}$ from
+-121 to +46 across 0 allows us to thoroughly examine the correlation between
+the magnetoelasticity and other magnetic properties. The strong correlation
+between $\lambda_{100}$ and magnetic damping ($\alpha$) is found. The enhanced
+extrinsic term of $\alpha$ is attributable to the large two magnon scattering
+coming from the large magnetostriction. In addition, the density of states at
+the Fermi level plays a primal role to determine both $\lambda_{100}$ and the
+intrinsic term of $\alpha$. Thanks to the giant tunability and the bipolarity
+of magnetoelasticity, magnetic nitrides are candidate materials for
+high-sensitive spintronic strain sensors.",2403.16679v1
+2024-04-04,Waveguide QED at the onset of spin-spin correlations,"We experimentally explore the competition between light-mediated and direct
+matter-matter interactions in waveguide quantum electrodynamics. For this, we
+couple a superconducting line to a model magnetic material, made of organic
+free radical DPPH molecules with a spin $S=1/2$ and a $g_{S}$ factor very close
+to that of a free electron. The microwave transmission has been measured in a
+wide range of temperatures ($0.013$ K $\leq T \leq 2$ K), magnetic fields
+($0\leq B \leq 0.5$ T) and frequencies ($0 \leq \omega/2 \pi \leq 14$ GHz). We
+find that molecules belonging to the crystal sublattice B form one-dimensional
+spin chains. Temperature then controls intrinsic spin correlations along the
+chain in a continuous and monotonic way. In the paramagnetic region ($T > 0.7$
+K), the microwave transmission shows evidences for the collective coupling of
+quasi-identical spins to the propagating photons, with coupling strengths that
+reach values close to the dissipation rates. As $T$ decreases, the growth of
+intrinsic spin correlations, combined with the anisotropy in the spin-spin
+exchange constants, break down the collective spin-photon coupling. In this
+regime, the temperature dependence of the spin resonance visibility reflects
+the change in the nature of the dominant spin excitations, from single spin
+flips to bosonic magnons, which is brought about by the magnetic correlation
+growth.",2404.03727v1
+2000-01-11,Magnetic Susceptibilities of Spin-1/2 Antiferromagnetic Heisenberg Ladders and Applications to Ladder Oxide Compounds,"A comprehensive theoretical and experimental study is presented of the
+magnetic susceptibility versus temperature \chi(T) of spin S = 1/2 two- and
+three-leg Heisenberg ladders and ladder oxide compounds. Extensive quantum
+Monte Carlo simulations of \chi(T) were carried out for both isolated and
+coupled two-leg ladders with spatially anisotropic intraladder exchange.
+Accurate fits to these and related literature QMC data were obtained. We have
+also calculated the one- and two-magnon dispersion relations and the dynamical
+spin structure factor for anisotropic isolated 2 x 12 ladders. The exchange
+constants in the two-leg ladder compound SrCu2O3 are estimated from LDA+U
+calculations. We report the detailed crystal structure of SrCu2O3 and of the
+three-leg ladder compound Sr2Cu3O5. New experimental \chi(T) data are reported
+for the two-leg ladder cuprates SrCu2O3 and LaCuO_{2.5}, and for the
+(nominally) two-leg ladder vanadates CaV2O5 and MgV2O5. The new and literature
+\chi(T) data for these compounds and for Sr2Cu3O5 are modeled using our QMC
+\chi(T) simulation fits, and the exchange coupling constants between the
+spins-1/2 are thereby estimated for each material. The surpisingly strong
+spatial anisotropy of the bilinear intraladder exchange constants in the
+cuprate compounds is discussed together with the results of other experiments
+sensitive to this anisotropy. Recent theoretical predictions are discussed
+including those which indicate that a four-spin cyclic exchange interaction
+within a Cu4 plaquette is important to determining the magnetic properties and
+which can significantly influence the exchange interactions estimated from
+\chi(T) data assuming the presence of only bilinear exchange.",0001147v1
+2000-01-13,Extensive infrared spectroscopic study of CuO: signatures of strong spin-phonon interaction and structural distortion,"Optical properties of single-crystal monoclinic CuO in the range 70 - 6000
+\cm were studied at temperatures from 7 to 300 K. Normal reflection spectra
+were obtained from the (001) and (010) crystal faces thus giving for the first
+time separate data for the $A_{u}$ and $B_{u}$ phonon modes excited in the
+purely transverse way (TO modes). Mode parameters, including polarizations of
+the $B_{u}$ modes not determined by the crystal symmetry, were extracted by the
+dispersion analysis of reflectivity curves as a function of temperature.
+Spectra of all the components of the optical conductivity tensor were obtained
+using the Kramers-Kronig method recently extended to the case of the
+low-symmetry crystals. The number of strong phonon modes is in agreement with
+the factor-group analysis for the crystal structure, currently accepted for the
+CuO. However, several ""extra"" modes of minor intensity are detected. Comparison
+of frequencies of ""extra"" modes with the available phonon dispersion curves
+points to possible ""diagonal"" doubling of the unit cell \{{\bf a}, {\bf b},
+{\bf c}\} $\to$ \{{\bf a}+{\bf c}, {\bf b}, {\bf a}-{\bf c}\} and formation of
+the superlattice. The previously reported softening of the $A^{3}_{u}$ mode
+($\sim$ 400 \cm) with cooling at $T_{N}$ is found to be $\sim$ 10 % for the TO
+mode. The mode is very broad at high temperatures and strongly narrows in the
+AFM phase. We attribute this effect to strong resonance coupling of this mode
+to optical or acoustic bi-magnons and reconstruction of the magnetic
+excitations spectrum at the N\'eel point. A significant anisotropy of
+$\epsilon^{\infty}$ is observed: it was found to be 5.9 along the {\bf b}-axis,
+6.2 along the {[}101{]} chains and 7.8 the {[}10$\bar{1}${]} chains. The
+""transverse"" effective charge is value is about 2 electrons.",0001176v2
+2001-01-08,Influence of s-d interfacial scattering on the magnetoresistance of magnetic tunnel junctions,"We propose the two-band s-d model to describe theoretically a diffuse regime
+of the spin-dependent electron transport in magnetic tunnel junctions (MTJ's)
+of the form F/O/F where F's are 3d transition metal ferromagnetic layers and O
+is the insulating spacer. We aim to explain the strong interface sensitivity of
+the tunneling properties of MTJ's and investigate the influence of electron
+scattering at the nonideal interfaces on the degradation of the TMR magnitude.
+The generalized Kubo formalism and the Green's functions method were used to
+calculate the conductance of the system. The vertex corrections to the
+conductivity were found with the use of ""ladder"" approximation combined with
+the coherent-potential approximation (CPA) that allowed to consider the case of
+strong electron scattering. It is shown that the Ward identity is satisfied in
+the framework of this approximation that provides the necessary condition for a
+conservation of a tunneling current. Based on the known results of ab-initio
+calculations of the TMR for ballistic junctions, we assume that exchange split
+quasi-free s-like electrons with the density of states being greater for the
+majority spin sub-band give the main contribution to the TMR effect. We show
+that, due to interfacial inter-band scattering, the TMR can be substantially
+reduced even down to zero value. This is related to the fact that delocalized
+quasi-free electrons can scatter into the strongly localized d sub-band with
+the density of states at the Fermi energy being larger for minority spins
+compared to majority spins. It is also shown that spin-flip electron scattering
+on the surface magnons within the interface leads to a further decrease of the
+TMR at finite temperature.",0101090v2
+2001-10-26,(Sr/Ca)_{14}Cu_{24}O_{41} spin ladders studied by NMR under pressure,"(63)Cu-NMR measurements have been performed on two-leg hole-doped spin
+ladders Sr_{14-x}Ca_{x}Cu_{24}O_{41} single crystals (0-x-12) at several
+pressures up to the pressure domain where the stabilization of a
+superconducting ground state can be achieved. The data reveal marked decrease
+of the spin gap derived from Knight shift measurements upon Ca substitution and
+also under pressure and confirm the onset of low lying spin excitations around
+P_{c} as previously reported. The spin gap in Sr_{2}Ca_{12}Cu_{24}O_{41} is
+strongly reduced above 20 kbar. However, the data of an experiment performed at
+P=36 kbar where superconductivity has been detected at 6.7K by an inductive
+technique have shown that a significant amount of spin excitations remains
+gapped at 80K when superconductivity sets in. The standard relaxation model
+with two and three-magnon modes explains fairly well the activated relaxation
+data in the intermediate temperature regime corresponding to gapped spin
+excitations using the spin gap data derived from Knight shift experiments.The
+data of Gaussian relaxation rates of heavily doped samples support the
+limitation of the coherence lenght at low temperature by the average distance
+between doped holes. We discuss the interplay between superconductivity and the
+spin gap and suggest that these new results support the exciting prospect of
+superconductivity induced by the interladder tunnelling of preformed pairs as
+long as the pressure remains lower than the pressure corresponding to the
+maximum of the superconducting critical temperature.",0110559v1
+2004-10-04,Dissipative dynamics of topological defects in frustrated Heisenberg spin systems,"We study the dynamics of topological defects of a frustrated spin system
+displaying spiral order. As a starting point we consider the SO(3) nonlinear
+sigma model to describe long-wavelength fluctuations around the noncollinear
+spiral state. Besides the usual spin-wave magnetic excitations, the model
+allows for topologically non-trivial static solutions of the equations of
+motion, associated with the change of chirality (clockwise or counterclockwise)
+of the spiral. We consider two types of these topological defects, single
+vortices and vortex-antivortex pairs, and quantize the corresponding solutions
+by generalizing the semiclassical approach to a non-Abelian field theory. The
+use of the collective coordinates allows us to represent the defect as a
+particle coupled to a bath of harmonic oscillators, which can be integrated out
+employing the Feynman-Vernon path-integral formalism. The resulting effective
+action for the defect indicates that its motion is damped due to the scattering
+by the magnons. We derive a general expression for the damping coefficient of
+the defect, and evaluate its temperature dependence in both cases, for a single
+vortex and for a vortex-antivortex pair. Finally, we consider an application of
+the model for cuprates, where a spiral state has been argued to be realized in
+the spin-glass regime. By assuming that the defect motion contributes to the
+dissipative dynamics of the charges, we can compare our results with the
+measured inverse mobility in a wide range of temperature. The relatively good
+agreement between our calculations and the experiments confirms the possible
+relevance of an incommensurate spiral order for lightly doped cuprates.",0410082v3
+2005-05-14,"Magnetic, electronic and Shubnikov-de Haas investigation of the dense Kondo system CeAgSb2","Of the dense Kondo materials in the class CeTSb2 (where T = Au, Ag, Ni, Cu,
+or Pd), CeAgSb2 is special due to its complex magnetic ground state, which
+exhibits both ferro- and anti-ferromagnetic character below an ordering
+temperature TO ~ 9.8 K. To further elucidate a description this magnetic ground
+state, we have carried out a systematic study of single crystalline CeAgSb2 by
+magnetic, electrical magneto-transport, and Shubnikov-de Haas (SdH) studies
+over a broad range of temperature and magnetic field. We have constructed the
+magnetic phase diagram based solely on magnetoresistance data. Here, depending
+on the orientation of the magnetic field H, either ferromagnetic or
+antiferromagnetic ordering occurs below TO. The resistivity of this compound
+below TO does not follow a simple Fermi liquid behavior, but requires an
+additional contribution from conduction electron scattering from boson
+excitations with an energy gap, D. At zero field the temperature dependent
+resistivity below TO is most consistent with antiferromagnetic order, based on
+the transport theory which includes magnon scattering. Crystal field effect
+theory applied to the susceptibility data yields splitting energies from the
+ground state to the first and second excited states of 53 K and 137 K,
+respectively. Although there is some uncertainty in the Kondo temperature
+determination, we estimate TK ~ 23 K from our analysis. In the Fermi surface
+studies, the measurements show very small Fermi surface sections, not predicted
+by band structure calculations, and the SdH amplitudes are very sensitive to
+field direction. Only by considering lens orbits between the main Fermi surface
+cylinders can the SdH results be reconciled with the Fermi surface topology
+predicted from band structure.",0505362v1
+1998-09-16,Slow Magnetic Monopole: Interaction with Matter and New Possibility of Their Detection,"The possibility of existence of a magnetic monopole has been surveyed by P.
+Dirac even in 1931, and then from the point of view of the modern theory by
+A.M. Polyakov and G.~ 'tHooft in 1974. Numerous and unsuccessful attempts of
+experimental search for monopole in cosmic rays and on accelerators in high
+energy particle collisions have been done. Also the searches have been carried
+out in mica for monopole tracks as well as for relict monopoles, entrapped by
+ferromagnetic inclusions in iron-ores, moon rock and meteorites. These
+entrapped monopoles, when released, would have the lowest velocities
+$\beta<10^{-6}$ and do not yield ionization at all, and are hard to detect.
+Therefore it is necessary to examine thoroughly the mechanisms of slow heavy
+monopole interaction with matter and their scale of energy loss.
+  We discuss here the interaction of a massive slow magnetic monopole with
+magnetically ordered matter, with conductors, superconductors and with
+condensed matter in general. Our results indicate that the energy loss of a
+slow supermassive monopole reach $10^{8} eV/cm$ and more if we take into
+consideration the Cherenkov radiation of magnons or phonons and conductivity of
+the media. A new method of search for cosmic and relict monopoles by
+magnetically ordered film is considered too. This approach resembles the
+traditional method of nuclear emulsion chamber. Apparently the proposed method
+is particularly attractive for detection of relict monopoles, released from
+melting iron ore.",9809420v3
+2002-04-09,"On the Geometry and Mass of Static, Asymptotically AdS Spacetimes, and the Uniqueness of the AdS Soliton","We prove two theorems, announced in hep-th/0108170, for static spacetimes
+that solve Einstein's equation with negative cosmological constant. The first
+is a general structure theorem for spacetimes obeying a certain convexity
+condition near infinity, analogous to the structure theorems of Cheeger and
+Gromoll for manifolds of non-negative Ricci curvature. For spacetimes with
+Ricci-flat conformal boundary, the convexity condition is associated with
+negative mass. The second theorem is a uniqueness theorem for the negative mass
+AdS soliton spacetime. This result lends support to the new positive mass
+conjecture due to Horowitz and Myers which states that the unique lowest mass
+solution which asymptotes to the AdS soliton is the soliton itself. This
+conjecture was motivated by a nonsupersymmetric version of the AdS/CFT
+correspondence. Our results add to the growing body of rigorous mathematical
+results inspired by the AdS/CFT correspondence conjecture. Our techniques
+exploit a special geometric feature which the universal cover of the soliton
+spacetime shares with familiar ``ground state'' spacetimes such as Minkowski
+spacetime, namely, the presence of a null line, or complete achronal null
+geodesic, and the totally geodesic null hypersurface that it determines. En
+route, we provide an analysis of the boundary data at conformal infinity for
+the Lorentzian signature static Einstein equations, in the spirit of the
+Fefferman-Graham analysis for the Riemannian signature case. This leads us to
+generalize to arbitrary dimension a mass definition for static asymptotically
+AdS spacetimes given by Chru\'sciel and Simon. We prove equivalence of this
+mass definition with those of Ashtekar-Magnon and Hawking-Horowitz.",0204081v4
+2007-11-20,Highly Frustrated Magnetic Clusters: The kagome on a sphere,"We present a detailed study of the low-energy excitations of two existing
+finite-size realizations of the planar kagome Heisenberg antiferromagnet on the
+sphere, the cuboctahedron and the icosidodecahedron. After highlighting a
+number of special spectral features (such as the presence of low-lying singlets
+below the first triplet and the existence of localized magnons) we focus on two
+major issues. The first concerns the nature of the excitations above the
+plateau phase at 1/3 of the saturation magnetization Ms. Our exact
+diagonalizations for the s=1/2 icosidodecahedron reveal that the low-lying
+plateau states are adiabatically connected to the degenerate collinear
+``up-up-down'' ground states of the Ising point, at the same time being well
+isolated from higher excitations. A complementary physical picture emerges from
+the derivation of an effective quantum dimer model which reveals the central
+role of the topology and the intrinsic spin s. We also give a prediction for
+the low energy excitations and thermodynamic properties of the spin s=5/2
+icosidodecahedron Mo72Fe30. In the second part we focus on the low-energy
+spectra of the s>1/2 Heisenberg model in view of interpreting the broad
+inelastic neutron scattering response reported for Mo72Fe30. To this end we
+demonstrate the simultaneous presence of several broadened low-energy ``towers
+of states'' or ``rotational bands'' which arise from the large discrete spatial
+degeneracy of the classical ground states, a generic feature of highly
+frustrated clusters. This semiclassical interpretation is further corroborated
+by their striking symmetry pattern which is shown, by an independent group
+theoretical analysis, to be a characteristic fingerprint of the classical
+coplanar ground states.",0711.3231v2
+2008-02-07,Spin-wave interaction in two-dimensional ferromagnets with dipolar forces,"We discuss the spin-wave interaction in two-dimensional (2D) Heisenberg
+ferromagnet (FM) with dipolar forces at $T_C\gg T\ge0$ using 1/S expansion. A
+comprehensive analysis is carried out of the first 1/S corrections to the
+spin-wave spectrum. In particular, similar to 3D FM discussed in our previous
+paper A.V. Syromyatnikov, PRB {\bf 74}, 014435 (2006), we obtain that the
+spin-wave interaction leads to the {\it gap} in the spectrum $\epsilon_{\bf k}$
+renormalizing greatly the bare gapless spectrum at small momenta $k$.
+Expressions for the spin-wave damping $\Gamma_{\bf k}$ are derived
+self-consistently and it is concluded that magnons are well-defined
+quasi-particles in both quantum and classical 2D FMs at small $T$. We observe
+thermal enhancement of both $\Gamma_{\bf k}$ and $\Gamma_{\bf k}/\epsilon_{\bf
+k}$ at small momenta. In particular, a peak appears in $\Gamma_{\bf k}$ and
+$\Gamma_{\bf k}/\epsilon_{\bf k}$ at small $k$ and at any given direction of
+$\bf k$. If $S\sim1$ the height of the peak in $\Gamma_{\bf k}/\epsilon_{\bf
+k}$ is not larger than a value proportional to $T/D\ll1$, where $D$ is the
+spin-wave stiffness. In the case of large spins $S\gg1$ the peak in
+$\Gamma_{\bf k}/\epsilon_{\bf k}$ cannot be greater than that of the classical
+2D FM found at $k=0$ which height is small only {\it numerically}: $\Gamma_{\bf
+0}/\epsilon_{\bf 0}\approx0.16$ for the simple square lattice. Frustrating
+next-nearest-neighbor exchange coupling increases $\Gamma_{\bf 0}/\epsilon_{\bf
+0}$ in classical 2D FM only slightly. We find expressions for spin Green's
+functions and the magnetization. The latter differs from the well-known result
+by S.V. Maleev, Sov. Phys. JETP {\bf 43}, 1240 (1976). The effect of the
+exchange anisotropy is also discussed briefly.",0802.0958v1
+2009-02-03,Pattern recognition and PID for COMPASS RICH-1,"A package for pattern recognition and PID by COMPASS RICH-1 has been
+developed and used for the analysis of COMPASS data collected in the years 2002
+to 2004, and 2006-2007 with the upgraded RICH-1 photon detectors. It has
+allowed the full characterization of the detector in the starting version and
+in the upgraded one, as well as the PID for physics results. We report about
+the package structure and algorithms, and the detector characterization and PID
+results.",0902.0444v1
+2010-10-29,Revisiting the Phase Transition of Spin-1/2 Heisenberg Model with a Spatially Staggered Anisotropy on the Square Lattice,"Puzzled by the indication of a new critical theory for the spin-1/2
+Heisenberg model with a spatially staggered anisotropy on the square lattice as
+suggested in \cite{Wenzel08}, we re-investigate the phase transition of this
+model induced by dimerization using first principle Monte Carlo simulations. We
+focus on studying the finite-size scaling of $\rho_{s1} L$ and $\rho_{s2} L$,
+where $L$ stands for the spatial box size used in the simulations and
+$\rho_{si}$ with $i \in \{1,2\}$ is the spin-stiffness in $i$-direction. From
+our Monte Carlo data, we find that $\rho_{s2} L$ suffers a much less severe
+correction compared to that of $\rho_{s1} L$. Therefore $\rho_{s2} L$ is a
+better quantity than $\rho_{s1} L$ for finite-size scaling analysis concerning
+the limitation of the availability of large volumes data in our study. Further,
+motivated by the so-called cubical regime in magnon chiral perturbation theory,
+we additionally perform a finite-size scaling analysis on our Monte Carlo data
+with the assumption that the ratio of spatial winding numbers squared is fixed
+through all simulations. As a result, the physical shape of the system remains
+fixed in our calculations. The validity of this new idea is confirmed by
+studying the phase transition driven by spatial anisotropy for the ladder
+anisotropic Heisenberg model. With this new strategy, even from $\rho_{s1} L$
+which receives the most serious correction among the observables considered in
+this study, we arrive at a value for the critical exponent $\nu$ which is
+consistent with the expected $O(3)$ value by using only up to $L = 64$ data
+points.",1010.6267v1
+2011-06-14,Intense paramagnon excitations in a large family of high-temperature superconductors,"In the search for the mechanism of high-temperature superconductivity,
+intense research has been focused on the evolution of the spin excitation
+spectrum upon doping from the antiferromagnetic insulating to the
+superconducting states of the cuprates. Because of technical limitations, the
+experimental investigation of doped cuprates has been largely focused on
+low-energy excitations in a small range of momentum space. Here we use resonant
+inelastic x-ray scattering to show that a large family of superconductors,
+encompassing underdoped YBa$_2$Cu$_4$O$_8$ and overdoped YBa$_2$Cu$_3$O$_{7}$,
+exhibits damped spin excitations (paramagnons) with dispersions and spectral
+weights closely similar to those of magnons in undoped cuprates. %The results
+are in excellent agreement with the spin excitations obtained by exact
+diagonalization of the $\bf t-J$ Hamiltonian on finite-sized clusters. The
+comprehensive experimental description of this surprisingly simple spectrum
+permits quantitative tests of magnetic Cooper pairing models. A numerical
+solution of the Eliashberg equations for the magnetic spectrum of
+YBa$_2$Cu$_3$O$_{7}$ reproduces its superconducting transition temperature
+within a factor of two, a level of agreement comparable to Eliashberg theories
+of conventional superconductors.",1106.2641v1
+2011-09-25,Spiky strings and the AdS/CFT correspondence,"We first focus on the finite-gap formalism for type IIB strings in AdS_3 x
+S^1, which allows to encode the semiclassical spectrum of a very large family
+of string solutions in a Riemann surface, the spectral curve. Then, we show
+that, in the large angular momentum limit, it separates into two distinct
+surfaces, allowing the derivation of an explicit expression for the spectrum,
+which is correspondingly characterised by two separate branches. The latter may
+be interpreted in terms of two kinds of spikes appearing on the strings:
+""large"" spikes, yielding an infinite contribution to the energy and angular
+momentum of the string, and ""small"" spikes, representing finite excitations
+over the background of the ""large"" spikes.
+  On the other side of the AdS/CFT correspondence, we consider the sl(2) sector
+of N=4 super Yang-Mills theory. The corresponding 1-loop spectrum, in the large
+conformal spin limit, is also encoded in a spectral curve and characterised in
+terms of the so-called holes. We show that, with the appropriate
+identifications and with the usual extrapolation from weak to strong 't Hooft
+coupling described by the cusp anomalous dimension, the large-S spectra of
+gauge theory and of string theory coincide. Furthermore, we explain how ""small""
+and ""large"" holes may be identified with ""small"" and ""large"" spikes.
+  Finally, we discuss several explicit spiky string solutions in AdS_3 which
+display the finite-gap spectrum. We compute their spectral curves in the large
+S limit, finding that they correspond to specific regions of the moduli space
+of the finite-gap curves. We also explain how ""large"" spikes may be used in
+order to extract a discrete system of degrees of freedom from string theory,
+which can then be matched with the degrees of freedom of the dual gauge theory
+operators, and how ""small"" spikes are in fact very similar to the Giant Magnons
+living in R x S^2.",1109.5401v1
+2012-07-20,"Ferromagnetic Ordering in CeIr2B2: Transport, magnetization, specific heat and NMR studies","We present a complete characterization of ferromagnetic system CeIr2B2 using
+powder x-ray diffraction XRD, magnetic susceptibility chi(T), isothermal
+magnetization M(H), specific heat C(T), electrical resistivity rho(T,H), and
+thermoelectric power S(T) measurements. Furthermore 11B NMR study was performed
+to probe the magnetism on a microscopic scale. The chi(T), C(T) and rho(T) data
+confirm bulk ferromagnetic ordering with Tc = 5.1 K. Ce ions in CeIr2B2 are in
+stable trivalent state. Our low-temperature C(T) data measured down to 0.4 K
+yield Sommerfeld coefficient gamma = 73(4) mJ/molK2 which is much smaller than
+the previously reported value of gamma = 180 mJ/molK2 deduced from the specific
+heat measurement down to 2.5 K. For LaIr2B2 gamma = 6(1) mJ/molK2 which implies
+the density of states at the Fermi level D(EF) = 2.54 states/(eV f.u.) for both
+spin directions. The renormalization factor for quasi-particle density of
+states and hence for quasi-particle mass due to 4f correlations in CeIr2B2 is
+12. The Kondo temperature TK ~ 4 K is estimated from the jump in specific heat
+of CeIr2B2 at Tc. Both C(T) and rho(T) data exhibit gapped-magnon behavior in
+magnetically ordered state with an energy gap Eg ~ 3.5 K. The rho data as a
+function of magnetic field H indicate a large negative magnetoresistance (MR)
+which is highest for T = 5 K.While at 5 K the negative MR keeps on increasing
+up to 10 T, at 2 K an upturn is observed near H = 3.5 T. On the other hand, the
+thermoelectric power data have small absolute values (S ~ 7 {\mu}V/K)
+indicating a weak Kondo interaction. A shoulder in S(T) at about 30 K followed
+by a minimum at ~ 10 K is attributed to crystal electric field (CEF) effects
+and the onset of magnetic ordering. 11B NMR line broadening provides strong
+evidence of ferromagnetic correlations below 40 K.",1207.5061v1
+2013-02-26,Superconducting pairing and the pseudogap in nematic striped La2-xSrxCuO4,"The individual k\parallel and k\perp stripe excitations in fluctuating
+spin-charge stripes have not been observed yet. In Raman scattering if we set,
+for example, incident and scattered light polarizations to two possible stripe
+directions, we can observe the fluctuating stripe as if it is static. Using the
+different symmetry selection rule between the B1g two-magnon scattering and the
+B1g and B2g isotropic electronic scattering, we succeeded to obtain the
+k\parallel and k\perp strip magnetic excitations separately in La2-xSrxCuO4.
+Only the k\perp stripe excitations appear in the wide-energy isotropic
+electronic Raman scattering, indicating that the charge transfer is restricted
+to the direction perpendicular to the stripe. This is the same as the Burgers
+vector of an edge dislocation which easily slides perpendicularly to the
+stripe. Hence charges at the edge dislocation move together with the
+dislocation perpendicularly to the stripe, while other charges are localized. A
+looped edge dislocation has lower energy than a single edge dislocation. The
+superconducting coherence length is close to the inter-charge stripe distance
+at x \le 0.2. Therefore we conclude that Cooper pairs are formed at looped edge
+dislocations. The restricted charge transfer direction naturally explains the
+opening of a pseudogap around (0, {\pi}) for the stripe parallel to the b axis
+and the reconstruction of the Fermi surface to have a flat plane near (0,
+{\pi}). They break the four-fold rotational symmetry. Furthermore the
+systematic experiments revealed the carrier density dependence of the isotropic
+and anisotropic electronic excitations, the spin density wave and/or charge
+density wave gap near ({\pi}/2, {\pi}/2), and the strong coupling between the
+electronic states near ({\pi}/2, {\pi}/2) and the zone boundary phonons at
+({\pi}, {\pi}).",1302.6917v1
+2014-10-01,Search for a spin-nematic phase in the quasi-one-dimensional frustrated magnet LiCuVO$_4$,"We have performed NMR experiments on the quasi one-dimensional frustrated
+spin-1/2 system LiCuVO$_4$ in magnetic fields $H$ applied along the c-axis up
+to field values near the saturation field $H_{\rm sat}$. For the field range
+$H_{\rm c2}<H<H_{\rm c3}$ ($\mu_0H_{\rm c2}\approx 7.5$T and $\mu_0H_{\rm c3} =
+[40.5 \pm 0.2]$T) the $^{51}$V NMR spectra at $T$ = 380mK exhibit a
+characteristic double-horn pattern, as expected for a spin-modulated phase in
+which the magnetic moments of Cu$^{2+}$ ions are aligned parallel to the
+applied field $H$ and their magnitudes change sinusoidally along the magnetic
+chains. For higher fields, the $^{51}$V NMR spectral shape changes from the
+double-horn pattern into a single Lorentzian line. For this Lorentzian line,
+the internal field at the $^{51}$V nuclei stays constant for $\mu_0 H > 41.4$T,
+indicating that the majority of magnetic moments in LiCuVO$_4$ are already
+saturated in this field range. This result is inconsistent with the previously
+observed linear field dependence of the magnetization $M(H)$ for $H_{\rm
+c3}<H<H_{\rm sat}$ with $\mu_0H_{\rm sat}=45$T [L. E. Svistov {\it et al}.,
+JETP Letters {\bf 93}, 21 (2011)]. We argue that the discrepancy is due to
+non-magnetic defects in the samples. The results of the spin-lattice relaxation
+rate of $^7$Li nuclei indicate an energy gap which grows with field twice as
+fast as the Zeeman energy of a single spin, therefore, suggesting that the
+two-magnon bound state is the lowest energy excitation. The energy gap tends to
+close at $\mu_0H \approx 41$T. Our results suggest that the theoretically
+predicted spin-nematic phase, if it exists in LiCuVO$_4$, can be established
+only within the narrow field range $40.5 < \mu_0 H < 41.4$T .",1410.0160v1
+2014-10-23,The 2014 Magnetism Roadmap,"Magnetism is a very fascinating and dynamic field. Especially in the last 30
+years it has experienced many major advances in the full range from novel
+fundamental phenomena to new products. Applications such as hard disk drives
+and magnetic sensors are part of our daily life, and new applications, such as
+in non-volatile computer random access memory, are expected to surface shortly.
+Thus it is timely for describing the current status, and current and future
+challenges in the form of a Roadmap article. This 2014 Magnetism Roadmap
+provides a view on several selected, currently very active innovative
+developments. It consists of 12 sections, each written by an expert in the
+field and addressing a specific subject, with strong emphasize on future
+potential. This Roadmap cannot cover the entire field. We have selected several
+highly relevant areas without attempting to provide a full review - a future
+update will have room for more topics. The scope covers mostly nano-magnetic
+phenomena and applications, where surfaces and interfaces provide additional
+functionality. New developments in fundamental topics such as interacting
+nano-elements, novel magnon-based spintronics concepts, spin-orbit torques and
+spin-caloric phenomena are addressed. New materials, such as organic magnetic
+materials and permanent magnets are covered. New applications are presented
+such as nano-magnetic logic, non-local and domain-wall based devices,
+heat-assisted magnetic recording, magnetic random access memory, and
+applications in biotechnology. May the Roadmap serve as a guideline for future
+emerging research directions in modern magnetism.",1410.6404v1
+2015-04-07,Generation of coherent spin-wave modes in Yttrium Iron Garnet microdiscs by spin-orbit torque,"Spin-orbit effects [1-4] have the potential of radically changing the field
+of spintronics by allowing transfer of spin angular momentum to a whole new
+class of materials. In a seminal letter to Nature [5], Kajiwara et al. showed
+that by depositing Platinum (Pt, a normal metal) on top of a 1.3 $\mu$m thick
+Yttrium Iron Garnet (YIG, a magnetic insulator), one could effectively transfer
+spin angular momentum through the interface between these two different
+materials. The outstanding feature was the detection of auto-oscillation of the
+YIG when enough dc current was passed in the Pt. This finding has created a
+great excitement in the community for two reasons: first, one could control
+electronically the damping of insulators, which can offer improved properties
+compared to metals, and here YIG has the lowest damping known in nature;
+second, the damping compensation could be achieved on very large objects, a
+particularly relevant point for the field of magnonics [6,7] whose aim is to
+use spin-waves as carriers of information. However, the degree of coherence of
+the observed auto-oscillations has not been addressed in ref. [5]. In this
+work, we emphasize the key role of quasi-degenerate spin-wave modes, which
+increase the threshold current. This requires to reduce both the thickness and
+lateral size in order to reach full damping compensation [8] , and we show
+clear evidence of coherent spin-orbit torque induced auto-oscillation in
+micron-sized YIG discs of thickness 20 nm.",1504.01512v1
+2015-06-16,Evidence of quantum dimer excitations in Sr$_3$Ir$_2$O$_7$,"The magnetic excitation spectrum in the bilayer iridate Sr$_3$Ir$_2$O$_7$ has
+been investigated using high-resolution resonant inelastic x-ray scattering
+(RIXS) performed at the iridium L$_3$ edge and theoretical techniques. A study
+of the systematic dependence of the RIXS spectrum on the orientation of the
+wavevector transfer, $\mathbf{Q}$, with respect to the iridium-oxide bilayer
+has revealed that the magnon dispersion is comprised of two branches well
+separated in energy and gapped across the entire Brillouin zone. Our results
+contrast with those of an earlier study which reported the existence of a
+single dominant branch. While these earlier results were interpreted as two
+overlapping modes within a spin-wave model of weakly coupled iridium-oxide
+planes, our results are more reminiscent of those expected for a system of
+weakly coupled dimers. In this latter approach the lower and higher energy
+modes find a natural explanation as those corresponding to transverse and
+longitudinal fluctuations, respectively. We have therefore developed a
+bond-operator theory which describes the magnetic dispersion in
+Sr$_3$Ir$_2$O$_7$ in terms of quantum dimer excitations. In our model
+dimerisation is produced by the leading Heisenberg exchange, $J_c$, which
+couples iridium ions in adjacent planes of the bilayer. The Hamiltonian also
+includes in plane exchange, $J$, as well as further neighbour couplings and
+relevant anisotropies. The bond-operator theory provides an excellent account
+of the dispersion of both modes, while the measured $\mathbf{Q}$ dependence of
+the RIXS intensities is in reasonable qualitative accord with the spin-spin
+correlation function calculated from the theory. We discuss our results in the
+context of the quantum criticality of bilayer dimer systems in the presence of
+anisotropic interactions derived from strong spin-orbit coupling.",1506.04877v1
+2015-06-23,Semi-phenomenological analysis of neutron scattering results for quasi-two dimensional quantum anti-ferromagnet,"The available results from the inelastic neutron scattering experiment
+performed on the quasi-two dimensional spin $\frac{1}{2}$ anti-ferromagnetic
+material $La_2 Cu O_4$ have been analysed theoretically. The formalism of ours
+is based on a semi-classical like treatment involving a model of an ideal gas
+of mobile vortices and anti-vortices built on the background of the
+N$\acute{e}$el state, using the bipartite classical spin configuration
+corresponding to an XY- anisotropic Heisenberg anti-ferromagnet on a square
+lattice. The results for the integrated intensities for our spin $\frac{1}{2}$
+model corresponding to different temperatures, show occurrence of vigorous
+unphysical oscillations, when convoluted with a realistic spectral window
+function. These results indicate failure of the conventional semi-classical
+theoretical model of ideal vortex/anti-vortex gas arising in the
+Berezinskii-Kosterlitz-Thouless theory for the low spin magnetic systems. A
+full fledged quantum mechanical formalism and calculations seem crucial for the
+understanding of topological excitations in such low spin systems. Furthermore,
+a severe disagreement is found to occur at finite values of energy transfer
+between the integrated intensities obtained theoretically from the conventional
+formalism and those obtained experimentally. This further suggests strongly
+that the full quantum treatment should also incorporate the interaction between
+the fragile-magnons and the topological excitations. This is quite plausible in
+view of the recent work establishing such a process in XXZ quantum ferromagnet
+on 2D lattice. The high spin XXZ quasi-two dimensional antiferromagnet like
+$MnPS_3$ however follows the conventional theory quite well",1506.06856v3
+2016-02-28,"Effective field theory and the scattering process for magnons in the ferromagnet, antiferromagnet, and ferrimagnet","We discuss that a low-energy effective Lagrangian relying on SO(3)
+$\rightarrow$ SO(2) is applicable for a ferrimagnet as well as a ferromagnet
+and an antiferromagnet. The analysis of the particle states shows that there
+exist not only massless modes with the dispersion relations $\omega \propto
+|\bm{k}|,\, |\bm{k}|^2$, i.e., the so-called type-I and type-II Nambu-Goldstone
+modes, respectively, but also gapped modes with $\omega \propto
+m^2+|\bm{k}|^2$. We clarify how the coefficients of the terms with one time
+derivative and those with two time derivatives in the effective Lagrangian
+determine the order parameters specifying whether the system is in a
+ferromagnetic, antiferromagnetic or ferrimagnetic state; we stress that the
+gapped mode related to the spontaneous symmetry breaking appears only in the
+ferrimagnetic system and not in the ferromagnetic and antiferromagnetic
+systems. We also establish the power counting scheme and calculate the
+scattering amplitudes and thereby the scattering lengths between the two
+Nambu-Goldstone bosons. We show that the scattering length of the gapped mode
+is finite and proportional to the gap. This characteristic property of the
+gapped NG mode can be used to discriminate it from gapped excitations which
+originate in other mechanisms. Finally, we study the effects of the explicit
+symmetry breaking that are given by an external magnetic field and a single-ion
+anisotropy, and show that the external magnetic fields do not have any effects
+on the scattering amplitudes in all the spin systems as was known for the
+ferromagnet system. In contrast, the anisotropy does affect the scattering
+amplitudes, the phase shift, and the scattering length except for spin 1/2
+systems. This result supports the possibility of the Efimov effect in spin
+systems discussed in previous studies.",1602.08692v2
+2018-11-26,Supersymmetric $t$-$J$ models with long-range interactions: partition function and spectrum,"We study the spectrum of the long-range supersymmetric su$(m)$ $t$-$J$ model
+of Kuramoto and Yokoyama in the presence of an external magnetic field and a
+charge chemical potential. To this end, we first establish the precise
+equivalence of a large class of models of this type to a family of su$(1|m)$
+spin chains with long-range exchange interactions and a suitable chemical
+potential term. We exploit this equivalence to compute in closed form the
+partition function of the long-range $t$-$J$ model, which we then relate to
+that of an inhomogeneous vertex model with simple interactions. From the
+structure of this partition function we are able to deduce an exact formula for
+the restricted partition function of the long-range $t$-$J$ model in subspaces
+with well-defined magnon content in terms of its analogue for the equivalent
+vertex model. This yields a complete analytical description of the spectrum in
+the latter subspaces, including the precise degeneracy of each level, by means
+of the supersymmetric version of Haldane's motifs and their related skew Young
+tableaux. As an application, we determine the structure of the motifs
+associated with the ground state of the spin $1/2$ model in the thermodynamic
+limit in terms of the magnetic field strength and the charge chemical
+potential. This leads to a complete characterization of the distinct ground
+state phases, determined by their spin content, in terms of the magnetic field
+strength and the charge chemical potential.",1811.10297v2
+2011-11-14,New pixelized Micromegas detector with low discharge rate for the COMPASS experiment,"New Micromegas (Micro-mesh gaseous detectors) are being developed in view of
+the future physics projects planned by the COMPASS collaboration at CERN.
+Several major upgrades compared to present detectors are being studied:
+detectors standing five times higher luminosity with hadron beams, detection of
+beam particles (flux up to a few hundred of kHz/mm^{2}, 10 times larger than
+for the present Micromegas detectors) with pixelized read-out in the central
+part, light and integrated electronics, and improved robustness. Two solutions
+of reduction of discharge impact have been studied, with Micromegas detectors
+using resistive layers and using an additional GEM foil. Performance of such
+detectors has also been measured. A large size prototypes with nominal active
+area and pixelized read-out has been produced and installed at COMPASS in 2010.
+In 2011 prototypes featuring an additional GEM foil, as well as an resistive
+prototype, are installed at COMPASS and preliminary results from those
+detectors presented very good performance. We present here the project and
+report on its status, in particular the performance of large size prototypes
+with an additional GEM foil.",1111.3337v4
+2014-05-28,Anomalous dimensions from rotating open strings in AdS/CFT,"We propose a new entry within the dictionary of the AdS/CFT duality at strong
+coupling: in the limit of a large spin or a large R-charge, the anomalous
+dimension of the gauge theory operator dual to a semiclassical rotating string
+is proportional to the string proper length. This conjecture is motivated by a
+generalization to strings of the rule for computing anomalous dimensions of
+massive particles and supergravity fields in the anti-de Sitter space. We show
+that this proportionality holds for a rotating closed string in global AdS
+space, representing a high spin operator made of fields in the adjoint
+representation. It is also valid for closed strings rotating in $S^5$
+(representing operators with large R-charge), for closed strings with multiple
+AdS spin, and for giant magnons. Based on this conjecture, we calculate the
+anomalous dimension $\delta$ of operators made of fields in the fundamental
+representation, associated with high spin mesons, and which are represented by
+rotating open strings attached to probe D7-branes. The result is a logarithmic
+dependence upon the spin, $\delta\sim \sqrt{\lambda}\ln S$, similar to the
+closed string case. We show that the operator properties --- anomalous
+dimension and spin --- are obtained from measurements made by a local observer
+in the anti-de Sitter space. For the open string case, this ensures that these
+quantities are independent of the mass scale introduced by the D7-branes (the
+quark mass), as expected on physical grounds. In contrast, properties of the
+gauge theory states, like the energy, correspond to measurements by a gauge
+theory observer and depend upon the mass scale --- once again, as expected.",1405.7388v2
+2014-06-17,Phonons and Hybrid Modes in the High and Low Temperature Far Infrared Dynamics of Hexagonal TmMnO3,"We report on TmMnO3 far infrared emissivity and reflectivity spectra from
+1910 K to 4 K. At the highest temperature the number of infrared bands is lower
+than that predicted for centrosymmetric P63/mmc (D6h4) (Z=2) space group due
+high temperature anharmonicity and possible defect induced bitetrahedra
+misalignments. On cooling, at ~1600 K TmMnO3 goes from non-polar to an
+antiferroelectric-ferroelectric polar phase reaching the ferroelectric onset at
+the ~700 K. The 300 K reflectivity is fitted using 19 oscillators and this
+number of phonons is maintained down to 4 K. A weak phonon anomaly in the band
+profile at 217 cm-1 (4 K) suggests subtle Rare Earth magnetoelectric couplings
+at ~TN and below. A low energy collective excitation is identified as a THz
+instability associated with room temperature eg electrons in a d-orbital
+fluctuating environment. It condenses into two modes that emerge pinned to the
+E-type antiferromagmetic order hardening simultaneously down to 4 K. They obey
+power laws with TN as the critical temperature and match known zone center
+magnons. The one peaking at 26 cm-1, with critical exponent \b{eta}=0.42 as for
+antiferromagnetic order in a hexagonal lattice, is dependent on the Rare Earth.
+The band at ~50 cm-1, with \b{eta}=0.25, splits at ~TN into two peaks. The
+weaker band of the two is assimilated to the upper branch of gap opening in the
+transverse acoustical (TA) phonon branch crossing the magnetic dispersion found
+in YMnO3. (Petit et al, 2007 PRL 99, 266604). The stronger second at ~36 cm-1
+corresponds to the lower branch of the TA gap. We assign both excitations as
+zone center magnetoelectric hybrid quasiparticles concluding that in NdMnO3
+perovskite the equivalent picture corresponds to an instability which may be
+driven by an external field to transform NdMnO3 into a multiferroic compound by
+perturbation enhancing the TA phonon-magnetic correlation.",1406.4382v1
+2020-12-10,Magnetic order and magneto-transport in half-metallic ferrimagnetic Mn$_y$Ru$_x$Ga thin films,"The ruthenium content of half-metallic Mn$_2$Ru$_x$Ga thin films, with a
+biaxially-strained inverse Heusler structure, controls the ferrimagnetism that
+determines their magnetic and electronic properties. An extensive study of
+Mn$_y$Ru$_x$Ga films on MgO (100) substrates with $1.8 \leq y \leq 2.6$ and $x
+= 0.5$, 0.7 or 0.9, including crystallographic, magnetic order,
+magneto-transport and spin polarisation is undertaken to map specific
+composition-dependent properties in this versatile ternary system. A comparison
+of experimental densities obtained from X-ray reflectivity with calculated
+densities indicates full site occupancy for all compositions, which implies
+chemical disorder. All moments lie on the Slater-Pauling plot with slope 1 and
+all except $x = 0.5$, $y = 2.2$ exhibit magnetic compensation at \tcmp~below
+500~K. The coercivity near \tcmp~exceeds 10~T. Increasing the Mn or Ru content
+raises \tcmp, but increasing Ru also decreases the spin polarisation determined
+by point contact Andreev reflection. Molecular field theory is used to model
+the temperature dependence of the net ferrimagnetic moment and three principal
+exchange coefficients are deduced. Marked differences in the shape of anomalous
+Hall and net magnetisation hysteresis loops are explained by substantial
+canting of the small net moment by up to \SI{40}{\degree} relative to the
+$c$-axis in zero field, which is a result of slight non-collinearity of the
+Mn$^{4c}$ sublattice moments due to competing intra-sublattice exchange
+interactions arising from antisite disorder and excess Mn in the unit cell.
+Consequences are reduced spin polarisation and an enhanced intrinsic
+contribution to the anomalous Hall effect. The systematic investigation of the
+physical properties as a function of $x$ and $y$ will guide the selection of
+compositions to meet the requirements for magnonic and spintronic MRG-based
+devices.",2012.05736v5
+2020-12-11,Antiferromagnetic Kitaev interaction in $J_\rm{eff}=1/2$ cobalt honeycomb materials Na$_3$Co$_2$SbO$_6$ and Na$_2$Co$_2$TeO$_6$,"Finding new materials with antiferromagnetic (AFM) Kitaev interaction is an
+urgent issue to broaden and enrich the quantum magnetism research
+significantly. By carrying out inelastic neutron scattering experiments and
+subsequent analysis, we conclude that Na$_3$Co$_2$SbO$_6$ and
+Na$_2$Co$_2$TeO$_6$ are new honeycomb cobalt-based AFM Kitaev systems. The
+spin-orbit excitons at 20-28~meV in both compounds strongly supports the idea
+that Co$^{2+}$ ions of both compounds have a spin-orbital entangled
+$J_\rm{eff}=1/2$ state. Furthermore, we found that a generalized
+Kitaev-Heisenberg Hamiltonian can well describe the spin-wave excitations of
+both compounds with additional 3rd nearest-neighbor interaction. Our best-fit
+parameters show large AFM Kitaev terms and off-diagonal symmetric anisotropy
+terms of a similar magnitude in both compounds. We should stress that our
+parameters' optimized magnetic structures are consistent with the magnetic
+structures reported from neutron diffraction studies. Moreover, there is also
+the magnon-damping effect at the higher energy part of the spin waves, as
+usually observed in other Kitaev magnets. We demonstrate that
+Na$_3$Co$_2$SbO$_6$ and Na$_2$Co$_2$TeO$_6$ are the first experimental
+realization of AFM Kitaev magnets based on the systematic studies of the spin
+waves and analysis.",2012.06167v3
+2020-12-22,Fragility of $\mathcal{Z}_2$ topological invariant characterizing triplet excitations in a bilayer kagome magnet,"The discovery by Kane and Mele of a model of spinful electrons characterized
+by a $\mathcal{Z}_2$ topological invariant had a lasting effect on the study of
+electronic band structures. Given this, it is natural to ask whether similar
+topology can be found in the band-like excitations of magnetic insulators, and
+recently models supporting $\mathcal{Z}_2$ topological invariants have been
+proposed for both magnon [Kondo et al. Phys. Rev. B 99, 041110(R) (2019)] and
+triplet [D. G. Joshi and A. P. Schnyder, Phys. Rev. B 100, 020407 (2019)]
+excitations. In both cases, magnetic excitations form time--reversal (TR)
+partners, which mimic the Kramers pairs of electrons in the Kane-Mele model but
+do not enjoy the same type of symmetry protection. In this paper, we revisit
+this problem in the context of the triplet excitations of a spin model on the
+bilayer kagome lattice. Here the triplet excitations provide a faithful analog
+of the Kane-Mele model as long as the Hamiltonian preserves the TR$\times$U(1)
+symmetry. We find that exchange anisotropies, allowed by the point group and
+typical in realistic models, break the required TR$\times$U(1) symmetry and
+instantly destroy the $\mathcal{Z}_2$ band topology. We further consider the
+effects of TR breaking by an applied magnetic field. In this case, the lifting
+of spin-degeneracy leads to a triplet Chern insulator, which is stable against
+the breaking of TR$\times$U(1) symmetry. Kagome bands realize both a quadratic
+and a linear band touching, and we provide a thorough characterization of the
+Berry curvature associated with both cases. We also calculate the
+triplet-mediated spin Nernst and thermal Hall signals which could be measured
+in experiments. These results suggest that the $\mathcal{Z}_2$ topology of
+band-like excitations in magnets may be intrinsically fragile compared to their
+electronic counterparts.",2012.11765v3
+2018-07-11,Probing the Dzyaloshinskii-Moriya interaction via the propagation of spin waves in ferromagnetic thin films,"The Dzyaloshinskii-Moriya interaction (DMI) has attracted considerable recent
+attention owing to the intriguing physics behind and the fundamental role it
+played in stabilizing magnetic solitons, such as magnetic skyrmions and chiral
+domain walls. A number of experimental efforts have been devoted to probe the
+DMI, among which the most popular method is the Brillouin light scattering
+spectroscopy (BLS) to measure the frequency difference of spin waves with
+opposite wave vectors $\pm\mathbf{k}$ perpendicular to the in-plane
+magnetization $\mathbf{m}$. Such a technique, however, is not applicable for
+the cases of $\mathbf{k}\parallel\mathbf{m}$, since the spin-wave reciprocity
+is recovered then. For a narrow magnetic strip, it is also difficult to measure
+the DMI strength using BLS because of the spatial resolution limit of lights.
+To fill these gaps, we propose to probe the DMI via the propagation of spin
+waves in ferromagnetic films. We show that the DMI can cause the
+non-collinearity of the group velocities of spin waves with
+$\pm\mathbf{k}\parallel\mathbf{m}$. In heterogeneous magnetic thin films with
+different DMIs, negative refractions of spin waves emerge at the interface
+under proper conditions. These findings enable us to quantify the DMI strength
+by measuring the angle between the two spin-wave beams with
+$\pm\mathbf{k}\parallel\mathbf{m}$ in homogeneous film and by measuring the
+incident and negative refraction angles in heterogeneous films. For a narrow
+magnetic strip, we propose a nonlocal scheme to determine the DMI strength via
+nonlinear three-magnon processes. We implement theoretical calculations and
+micromagnetic simulations to verify our ideas. The results presented here are
+helpful for future measurement of the DMI and for designing novel spin-wave
+spintronic devices.",1807.04025v2
+2018-12-03,Magnetoelastic hybrid excitations in CeAuAl$_3$,"The interactions between elementary excitations such as phonons, plasmons,
+magnons, or particle-hole pairs, drive emergent functionalities and electronic
+instabilities such as multiferroic behaviour, anomalous thermoelectric
+properties, polar order, or superconductivity. Whereas various hybrid
+excitations have been studied extensively, the feed-back of prototypical
+elementary excitations on the crystal electric fields (CEF), defining the
+environment in which the elementary excitations arise, has been explored for
+very strong coupling only. We report high-resolution neutron spectroscopy and
+ab-initio phonon calculations of {\ceaual}, an archetypal fluctuating valence
+compound. The high resolution of our data allows us to quantify the energy
+scales of three coupling mechanisms between phonons, CEF-split localized 4f
+electron states, and conduction electrons. Although these interactions do not
+appear to be atypically strong for this class of materials, we resolve, for the
+first time, a profound renormalization of low-energy quasiparticle excitations
+on all levels. The key anomalies of the spectrum we observe comprise (1) the
+formation of a CEF-phonon bound state with a comparatively low density of
+acoustic phonons reminiscent of vibronic modes observed in other materials,
+where they require a pronounced abundance of optical phonons, (2) an
+anti-crossing of CEF states and acoustic phonons, and (3) a strong broadening
+of CEF states due to the hybridization with more itinerant excitations. The
+fact that all of these features are well resolved in CeAuAl$_3$ suggests that
+similar hybrid excitations should also be dominant in a large family of related
+materials. This promises a predictive understanding towards the discovery of
+new magneto-elastic functionalities and instabilities.",1812.01020v1
+2018-12-23,Voltage control of the long-range p-d exchange coupling in a ferromagnet-semiconductor quantum well hybrid structure,"Voltage control of ferromagnetism on the nanometer scale is highly appealing
+for the development of novel electronic devices. Here a key challenge is to
+implement and combine low power consumption, high operation speed, reliable
+reversibility and compatibility with semiconductor technology. Hybrid
+structures based on the assembly of ferromagnetic and semiconducting building
+blocks are attractive candidates in that respect as such systems bring together
+the properties of the isolated constituents: They are expected to show magnetic
+order as a ferromagnet and to be electrically tunable as a semiconductor. Here
+we demonstrate the electrical control of the exchange coupling in a hybrid
+consisting of a ferromagnetic Co layer and a semiconductor CdTe quantum well,
+separated by a thin non-magnetic (Cd,Mg)Te barrier. The effective magnetic
+field of the exchange interaction reaches up to 2.5 Tesla and can be turned on
+and off by application of 1 V bias across the heterostructure. The mechanism of
+this electric field control is essentially different from the conventional
+concept, in which wavefunctions are spatially redistributed to vary the
+exchange interaction, requiring high field strengths. Here we address instead
+control of the novel exchange mechanism that is mediated by elliptically
+polarized phonons emitted from the ferromagnet, i.e. the phononic ac Stark
+effect. An essential parameter of this coupling is the splitting between heavy
+and light hole states in the quantum well which can be varied by the electric
+field induced band bending. Thereby the splitting can be tuned with respect to
+the magnon-phonon resonance energy in the ferromagnet, leading to maximum
+coupling for flat band conditions. Our results demonstrate the feasibility of
+electrically controlled exchange coupling in hybrid semiconductor
+nanostructures at quite moderate electric field strengths.",1812.09680v1
+2019-02-01,Summary Report of Physics Beyond Colliders at CERN,"Physics Beyond Colliders is an exploratory study aimed at exploiting the full
+scientific potential of CERN's accelerator complex and its scientific
+infrastructure in the next two decades through projects complementary to the
+LHC, HL-LHC and other possible future colliders. These projects should target
+fundamental physics questions that are similar in spirit to those addressed by
+high-energy colliders, but that require different types of beams and
+experiments. A kick-off workshop held in September 2016 identified a number of
+areas of interest and working groups have been set-up to study and develop
+these directions. All projects currently under consideration are presented
+including physics motivation, a brief outline of the experimental set-up and
+the status of the corresponding beam and detector technological studies. The
+proposals are also put in context of the worldwide landscape and their
+implementation issues are discussed.",1902.00260v1
+2019-02-12,Ultrafast X-Ray Induced Changes of the Electronic and Magnetic Response of Solids Due to Valence Electron Redistribution,"We report a novel mechanism, consisting of redistribution of valence
+electrons near the Fermi level, during interactions of intense femtosecond
+X-ray pulses with a Co/Pd multilayer. The changes in Co 3d valence shell
+occupation were directly revealed by fluence-dependent changes of the Co L$_3$
+X-ray absorption and magnetic circular dichroism spectra near the excitation
+threshold. The valence shell redistribution arises from inelastic scattering of
+high energy Auger electrons and photoelectrons that lead to transient holes
+below and electrons above the Fermi level on the femtosecond time scale. The
+valence electron reshuffling effect scales with the energy deposited by X-rays
+and within 17 fs extends to valence states within 2 eV of the Fermi level. As a
+consequence the sample demagnetizes by more than twenty percent due to magnon
+generation.",1902.04611v1
+2019-08-02,Giant magnetoelastic coupling in Love acoustic waveguide based on uniaxial multilayered TbCo2/FeCo nanostructured thin film on Quartz ST-cut,"Coupling between dynamic strain and magnetization in ferromagnetic thin films
+has attracted special consideration as it presents both intriguing fundamental
+physics problems and technological importance for potential multi-functional
+devices and information handling. The dynamic strain can be generated by
+acoustic waves including bulk, surface or guided waves. In this work, we
+propose the theoretical and experimental investigation of the interaction of
+pure shear horizontal (SH) wave with a uniaxial multilayered TbCo2/FeCo thin
+film in a delay line configuration fabricated on Quartz ST-90X cut. We evaluate
+theoretically the evolution of phase velocity as a function of magnetic field
+and experimentally the variation of the transmission coefficient. A
+piezomagnetic model was developed allowing us to calculate the elastic
+stiffness constants of the multilayer as a function of the applied magnetic
+field. The model was also implemented for acoustic waves dispersion curves
+calculation. We show that the evolution of phase velocity is dominated by the
+C66 elastic stiffness constant variation as expected for the case of shear
+horizontal surface wave. The fabricated device let us exciting both fundamental
+and third harmonic shear mode at 410 MHz and 1.2 GHz, respectively. For both
+modes, the theoretical results corroborate very well the experimental ones. At
+1.2 GHz the mode exhibits a maximum phase velocity shift close to 2.5% and an
+attenuation reaching 500 dB/cm, for a sensitivity as high as 250 ppm/Oe. The
+reported theoretical model and experimental results are of tremendous interest
+for the development of advanced devices for magnetic field sensing applications
+as well as investigating magnon-phonon interaction at a fundamental level.",1908.10443v2
+2019-08-29,Pushing down the lateral dimension of single and coupled magnetic dots to the nanometric scale: characteristics and evolution of the spin-wave eigenmodes,"Planar magnetic nanoelements, either single- or multi-layered, are exploited
+in a variety of current or forthcoming spintronic and/or ICT devices, such as
+read heads, magnetic memory cells, spin-torque nano-oscillators, nanomagnetic
+logic circuits, magnonic crystals and artificial spin-ices. The lateral
+dimensions of the elemental magnetic components have been squeezed down during
+the last decade to a few tens of nanometers, but they are still an order of
+magnitude larger that the exchange correlation length of the constituent
+materials. This means that the spectrum of spin-wave eigenmodes, occurring in
+the GHz range, is relatively complex and cannot be described within a simple
+macrospin approximation. On the other hand, a detailed knowledge of the
+dynamical spectrum is needed to understand or to predict crucial
+characteristics of the devices. With this focused review we aim at the analysis
+and the rationalization of the characteristics of the eigenmodes spectrum of
+magnetic nanodots, paying special attention to the following key points: (i)
+Consider and compare the case of in-plane and out of-plane orientation of the
+magnetization, as well as of single- and multi-layered dots, putting in
+evidence similarities and diversities, and proposing a unifying nomenclature
+and labelling scheme; (ii) Underline the evolution of the spectrum when the
+lateral size of magnetic dots is squeezed down from hundreds to tens of
+nanometers, as in current devices, with emphasis given to the occurrence of
+soft modes and to the change of spatial localization of the fundamental mode
+for in-plane magnetized dots; (iii) Extend the analysis from isolated elements
+to twins of dots, as well as to dense arrays of dipolarly interacting dots,
+showing how the discretized eigenmodes distinctive of the single element
+transform in finite-width frequency bands of spin waves propagating through the
+array.",1908.11098v1
+2019-11-26,Free-standing and positionable microwave antenna device for magneto-optical spectroscopy experiments,"Modern spectroscopic techniques for the investigation of magnetization
+dynamics in micro- and nano- structures or thin films use typically microwave
+antennas which are directly fabricated on top of the sample by means of
+electron-beam-lithography (EBL). Following this approach, every magnetic
+structure on the sample needs its own antenna, resulting in additional EBL
+steps and layer deposition processes. We demonstrate a new approach for
+magnetization excitation that is suitable for optical and non-optical
+spectroscopy techniques. By patterning the antenna on a separated flexible
+glass cantilever and insulating it electrically, we solved the before mentioned
+issues. Since we use flexible transparent glass as a substrate, optical
+spectroscopy techniques like Brillouin-light-scattering microscopy ({\mu}BLS),
+time resolved magneto-optical Kerr effect measurements (TRMOKE) or optical
+detected magnetic resonance (ODMR) measurements can be carried out at visible
+laser wavelengths. As the antenna is detached from the sample it can be freely
+positioned in all three dimensions to adress only the desired magnetic sample
+structures and to achieve effective excitation. We demonstrate the
+functionality of these antennas using {\mu}BLS and compare coherently and
+thermally excited magnon spectra to show the enhancement of the signal by a
+factor of about 400 due to the excitation by the antenna. Moreover, we succeed
+to characterize yttrium iron garnet thin films with spatial resolution using
+optical ferromagnetic resonance (FMR) experiments. We analyse the spatial
+excitation profile of the antenna by measuring the magnetization dynamics in
+two dimensions. The technique is furthermore applied to investigate
+injection-locking of spin Hall nano-oscillators.",1911.11517v1
+2019-12-03,"Temperature dependence of the $(π,0)$ anomaly in the excitation spectrum of the 2D quantum Heisenberg antiferromagnet","It is well established that in the low-temperature limit, the two-dimensional
+quantum Heisenberg antiferromagnet on a square lattice (2DQHAFSL) exhibits an
+anomaly in its spectrum at short-wavelengths on the zone-boundary. In the
+vicinity of the $(\pi,0)$ point the pole in the one-magnon response exhibits a
+downward dispersion, is heavily damped and attenuated, giving way to an
+isotropic continuum of excitations extending to high energies. The origin of
+the anomaly and the presence of the continuum are of current theoretical
+interest, with suggestions focused around the idea that the latter evidences
+the existence of spinons in a two-dimensional system. Here we present the
+results of neutron inelastic scattering experiments and Quantum Monte Carlo
+calculations on the metallo-organic compound Cu(DCOO)$_2\cdot 4$D$_2$O (CFTD),
+an excellent physical realisation of the 2DQHAFSL, designed to investigate how
+the anomaly at $(\pi,0)$ evolves up to finite temperatures $T/J\sim2/3$. Our
+data reveal that on warming the anomaly survives the loss of long-range,
+three-dimensional order, and is thus a robust feature of the two-dimensional
+system. With further increase of temperature the zone-boundary response
+gradually softens and broadens, washing out the $(\pi,0)$ anomaly. This is
+confirmed by a comparison of our data with the results of finite-temperature
+Quantum Monte Carlo simulations where the two are found to be in good accord.
+At lower energies, in the vicinity of the antiferromagnetic zone centre, there
+was no significant softening of the magnetic excitations over the range of
+temperatures investigated.",1912.01364v1
+2019-12-28,Non-Equilibrium Heat Transport in Pt and Ru Probed by an Ultrathin Co Thermometer,"Non-equilibrium of electrons, phonons, and magnons in metals is a fundamental
+phenomenon in condensed matter physics and serves as an important driver in the
+field of ultrafast magnetism. In this work, we demonstrate that the
+magnetization of a sub-nm-thick Co layer with perpendicular magnetic anisotropy
+can effectively serve as a thermometer to monitor non-equilibrium dynamics in
+adjacent metals, Pt and Ru, via time-resolved magneto-optic Kerr effect. The
+temperature evolutions of the Co thermometer embedded in Pt layers of different
+thicknesses, 6-46 nm, are adequately described by a phenomenological three
+temperature model with a consistent set of materials parameters. We do not
+observe any systematic deviations between the model and the data that can be
+caused by a non-thermal distribution of electronic excitations. We attribute
+the consistently good agreement between the model and the data to strong
+electron-electron interaction in Pt. By using Pt/Co/Pt and Pt/Co/Pt/Ru
+structures, we determine the electron-phonon coupling parameters of Pt and Ru,
+g_ep(Pt)=(6+/-1)x10^17 W m-3 K-1 and g_ep(Ru)=(9+/-2)x10^17 W m-3 K-1. We also
+find that the length scales of non-equilibrium between electrons and phonons
+are l_ep=({\Lambda}_e/g_ep)^1/2 =9 nm for Pt and 7 nm for Ru, shorter than
+their optical absorption depths, 11 and 13 nm, respectively. Therefore, the
+optically thick Pt and Ru layers show two steps of temperature rise: The
+initial jump of electron temperature that occurs within 1 ps is caused by
+direct optical excitation and electronic heat transport within a distance l_ep
+for the Co layer. The second temperature rise is caused by heat transport by
+electrons and phonons that are near thermal equilibrium. We contrast
+two-temperature modeling of heat transport in Pt an Ru films to calculations
+for Cu, which has a much longer non-equilibrium length scale, l_ep=63 nm.",1912.12425v1
+2016-10-27,Hybridization gap in the heavy-fermion compound UPd$_2$Al$_3$ via quasiparticle scattering spectroscopy,"We present results from point-contact spectroscopy of the antiferromagnetic
+heavy-fermion superconductor UPd$_2$Al$_3$: conductance spectra are taken from
+single crystals with two major surface orientations as a function of
+temperature and magnetic field, and analyzed using a theory of co-tunneling
+into an Anderson lattice. Spectroscopic signatures are clearly identified
+including the distinct asymmetric double-peak structure arising from the
+opening of a hybridization gap when a coherent heavy Fermi liquid is formed.
+Both the hybridization gap, found to be 7.2 $\pm$ 0.3 meV at 4 K, and the
+conductance enhancement above a flat background decrease upon increasing
+temperature. While the hybridization gap is extrapolated to remain finite up to
+$\sim$28 K, close to the temperature around which the magnetic susceptibility
+displays a broad peak, the conductance enhancement vanishes at $\sim$18 K,
+slightly above the antiferromagnetic transition temperature ($T_\textrm{N}$
+$\approx$ 14 K). This rapid decrease of the conductance enhancement is
+understood as a consequence of the junction drifting away from the ballistic
+regime due to increased scattering off magnons associated with the localized U
+5$f$ electrons. This shows that while the hybridization gap opening is not
+directly associated with the antiferromagnetic ordering, its visibility in the
+conductance is greatly affected by the temperature-dependent magnetic
+excitations. Our findings are not only consistent with the 5$f$ dual-nature
+picture in the literature but also shed new light on the interplay between the
+itinerant and localized electrons in UPd$_2$Al$_3$.",1610.08601v3
+2020-06-18,Spin Wave Normalization Towards all Magnonic Circuits,"The key enabling factor for Spin Wave (SW) technology utilization for
+building ultra low power circuits is the ability to energy efficiently cascade
+SW basic computation blocks. SW Majority gates, which constitute a universal
+gate set for this paradigm, operating on phase encoded data are not input
+output coherent in terms of SW amplitude, and as such, their cascading requires
+information representation conversion from SW to voltage and back, which is by
+no means energy effective. In this paper, a novel conversion free SW gate
+cascading scheme is proposed that achieves SW amplitude normalization by means
+of a directional coupler. After introducing the normalization concept, we
+utilize it in the implementation of three simple circuits and, to demonstrate
+its bigger scale potential, of a 2-bit inputs SW multiplier. The proposed
+structures are validated by means of the Object Oriented Micromagnetic
+Framework (OOMMF) and GPU-accelerated Micromagnetics (MuMax3). Furthermore, we
+assess the normalization induced energy overhead and demonstrate that the
+proposed approach consumes 20% to 33% less energy when compared with the
+transducers based conventional counterpart. Finally, we introduce a
+normalization based SW 2-bit inputs multiplier design and compare it with
+functionally equivalent SW transducer based and 16nm CMOS designs. Our
+evaluation indicate that the proposed approach provided 26% and 6.25x energy
+reductions when compared with the conventional approach and 16nm CMOS
+counterpart, respectively, which demonstrates that our proposal is energy
+effective and opens the road towards the full utilization of the SW paradigm
+potential and the development of SW only circuits.",2006.10432v3
+2020-09-12,Anomalous thermodynamics of a quantum spin system with large residual entropy,"In contrast to strongly frustrated classical systems, their quantum
+counterparts typically have a non-degenerate ground state. A counterexample is
+the celebrated Heisenberg sawtooth spin chain with ferromagnetic zigzag bonds
+$J_1$ and competing antiferromagnetic basal bonds $J_2$. At a quantum phase
+transition point $|J_2/J_1|=1/2$, this model exhibits a flat one-magnon
+excitation band leading to a massively degenerate ground-state manifold which
+results in a large residual entropy. Thus, for the spin-half model, the
+residual entropy amounts to exactly one half of its maximum value
+$\lim_{T\to\infty} S(T)/N = \ln2$. In the present paper we study in detail the
+role of the spin quantum number $s$ and the magnetic field $H$ in the parameter
+region around the transition (flat-band) point. For that we use full exact
+diagonalization up to $N=20$ lattice sites and the finite-temperature Lanczos
+method up to $N=36$ sites to calculate the density of states as well as the
+temperature dependence of the specific heat, the entropy and the
+susceptibility. The study of chain lengths up to $N=36$ allows a careful
+finite-size analysis. At the flat-band point we find extremely small
+finite-size effects for spin $s=1/2$, i.e., the numerical data virtually
+correspond to the thermodynamic limit. In all other cases the finite-size
+effects are still small and become visible at very low temperatures. In a
+sizeable parameter region around the flat-band point the former massively
+degenerate ground-state manifold acts as a large manifold of low-lying
+excitations leading to extraordinary thermodynamic properties at the transition
+point as well as in its vicinity such as an additional low-temperature maximum
+in the specific heat. Moreover, there is a very strong influence of the
+magnetic field on the low-temperature thermodynamics including an enhanced
+magnetocaloric effect.",2009.05809v2
+2020-09-29,"Twisted Bilayer Graphene V: Exact Analytic Many-Body Excitations in Twisted Bilayer Graphene Coulomb Hamiltonians: Charge Gap, Goldstone Modes and Absence of Cooper Pairing","We find exact analytic expressions for the energies and wavefunctions of the
+charged and neutral excitations above the exact ground states (at rational
+filling per unit cell) of projected Coulomb Hamiltonians in twisted bilayer
+graphene. Our exact expressions are valid for any form of the Coulomb
+interaction and any form of $AA$ and $AB/BA$ tunneling. The single charge
+excitation energy is a convolution of the Coulomb potential with a quantum
+geometric tensor of the TBG bands. The neutral excitations are (high-symmetry
+group) magnons, and their dispersion is analytically calculated in terms of the
+form factors of the active bands in TBG. The two-charge excitation energy and
+wavefunctions are also obtained, and a sufficient condition on the graphene
+eigenstates for obtaining a Cooper-pair from Coulomb interactions is obtained.
+For the actual TBG bands at the first magic angle, we can analytically show
+that the Cooper pair binding energy is zero in all such projected Coulomb
+models, implying that either phonons and/or non-zero kinetic energy are needed
+for superconductivity. Since the [Phys. Rev. Lett. 122, 246401] showed that the
+kinetic energy bounds on the superexchange energy are less $10^{-3}$ in Coulomb
+units, the phonon mechanism becomes then very likely. If nonetheless the
+superconductivity is due to kinetic terms which render the bands non-flat, one
+prediction of our theory is that the highest $T_c$ would not occur at the
+highest DOS.",2009.14200v4
+2020-09-30,How coordinate Bethe ansatz works for Inozemtsev model,"Three decades ago, Inozemtsev found an isotropic long-range spin chain with
+elliptic pair potential that interpolates between the Heisenberg and
+Haldane-Shastry (HS) spin chains while admitting an exact solution throughout,
+based on a connection with the elliptic quantum Calogero-Sutherland model.
+Though Inozemtsev's spin chain is widely believed to be quantum integrable, the
+underlying algebraic reason for its exact solvability is not yet well
+understood. As a step in this direction we refine Inozemtsev's `extended
+coordinate Bethe ansatz' and clarify various aspects of the model's exact
+spectrum and its limits.
+  We identify quasimomenta in terms of which the $M$-particle energy is close
+to being (functionally) additive, as one would expect from the limiting models;
+our expression is additive iff the energy of the elliptic Calogero-Sutherland
+system is so. This enables us to rewrite the energy and Bethe-ansatz equations
+on the elliptic curve, turning the spectral problem into a rational problem as
+might be expected for an isotropic spin chain.
+  We treat the $M=2$ particle sector and its limits in detail. We identify an
+$S$-matrix that is independent of positions. We show that the Bethe-ansatz
+equations reduce to those of Heisenberg in one limit and give rise to the
+`motifs' of HS in the other limit. We show that, as the interpolation parameter
+changes, the `scattering states' from Heisenberg become Yangian highest-weight
+states for HS, while bound states become ($\mathfrak{sl}_2$-highest weight
+versions of) affine descendants of the magnons from $M=1$. For bound states we
+find a generalisation of the known equation for the `critical length' for the
+Heisenberg spin chain. We discuss completeness for $M=2$ by passing to the
+elliptic curve.
+  Our review of the two-particle sectors of the Heisenberg and HS spin chains
+may be of independent interest.",2009.14513v3
+2015-07-23,Ultrafast Laser-Induced Melting of Long-Range Magnetic Order in Multiferroic TbMnO3,"We performed ultrafast time-resolved near-infrared pump, resonant soft X-ray
+diffraction probe measurements to investigate the coupling between the
+photoexcited electronic system and the spin cycloid magnetic order in
+multiferroic TbMnO3 at low temperatures. We observe melting of the long range
+antiferromagnetic order at low excitation fluences with a decay time constant
+of 22.3 +- 1.1 ps, which is much slower than the ~1 ps melting times previously
+observed in other systems. To explain the data we propose a simple model of the
+melting process where the pump laser pulse directly excites the electronic
+system, which then leads to an increase in the effective temperature of the
+spin system via a slower relaxation mechanism. Despite this apparent increase
+in the effective spin temperature, we do not observe changes in the wavevector
+q of the antiferromagnetic spin order that would typically correlate with an
+increase in temperature under equilibrium conditions. We suggest that this
+behavior results from the extremely low magnon group velocity that hinders a
+change in the spin-spiral wavevector on these time scales.",1507.06628v1
+2015-12-09,"Standard model of the rare-earths, analyzed from the Hubbard I approximation","In this work we examine critically the electronic structure of the rare-earth
+elements by use of the so-called Hubbard I approximation. From the theoretical
+side all measured features of both occupied and unoccupied states are
+reproduced, without significant deviations between observations and theory. We
+also examine cohesive properties like the equilibrium volume and bulk modulus,
+where we find, in general, a good agreement between theory and measurements. In
+addition we have reproduced the spin and orbital moments of these elements, as
+they are reflected from measurements of the saturation moment. We have also
+employed the Hubbard I approximation to extract the interatomic exchange
+parameters of an effective spin Hamiltonian for the heavy rare earths. We show
+that the Hubbard I approximation gives results which are consistent with
+calculations where $4f$ electrons are treated as core states for Gd. The latter
+approach was also used to address the series of the heavy/late rare-earths. Via
+Monte Carlo simulations we obtained ordering temperatures which reproduce
+measurements within about $20\%$. We have further illustrated the accuracy of
+these exchange parameters by comparing measured and calculated magnetic
+configurations for the heavy rare earths and the magnon dispersion for Gd. The
+Hubbard I approximation is compared to other theories of the electronic
+structure, and we argue that it is superior. We discuss the relevance of our
+results in general, and how this makes it possible to treat the electronic
+structure of materials containing rare-earth elements, such as permanent
+magnets, magnetostrictive compounds, photovoltaics, optical fibers, topological
+insulators, and molecular magnets.",1512.02848v2
+2016-11-17,Holographic Dynamics from Multiscale Entanglement Renormalization Ansatz,"The Multiscale Entanglement Renormalization Ansatz (MERA) is a tensor network
+based variational ansatz that is capable of capturing many of the key physical
+properties of strongly correlated ground states such as criticality and
+topological order. MERA also shares many deep relationships with the AdS/CFT
+(gauge-gravity) correspondence by realizing a UV complete holographic duality
+within the tensor networks framework. Motivated by this, we have re-purposed
+the MERA tensor network as an analysis tool to study the real-time evolution of
+the 1D transverse Ising model in its low energy excited state sector. We
+performed this analysis by allowing the ancilla qubits of the MERA tensor
+network to acquire quantum fluctuations, which yields a unitary transform
+between the physical (boundary) and ancilla qubit (bulk) Hilbert spaces. This
+then defines a reversible quantum circuit which is used as a `holographic
+transform' to study excited states and their real-time dynamics from the point
+of the bulk ancillae. In the gapped paramagnetic phase of the transverse field
+Ising model, we demonstrate the holographic duality between excited states
+induced by single spin-flips (Ising `magnons') acting on the ground state and
+single ancilla qubit spin-flips. The single ancillae qubit excitation is shown
+to be stable in the bulk under real-time evolution and hence defines a stable
+holographic quasiparticle which we have named the `hologron'. The `dictionary'
+between the bulk and boundary is determined and realizes many features of the
+holographic correspondence in a non-CFT limit of the boundary theory. As an
+added spin-off, this dictionary together with the extension to multi-hologron
+sectors gives us a systematic way to construct quantitatively accurate low
+energy effective Hamiltonians.",1611.05877v1
+2018-08-26,Resonating quantum three-coloring wavefunctions for the kagome quantum antiferromagnet,"Motivated by the recent discovery of a macroscopically degenerate exactly
+solvable point of the spin-$1/2$ $XXZ$ model for $J_z/J=-1/2$ on the kagome
+lattice [H. J. Changlani et al. Phys. Rev. Lett 120, 117202 (2018)] -- a result
+that holds for arbitrary magnetization -- we develop an exact mapping between
+its exact quantum three-coloring wavefunctions and the characteristic localized
+and topological magnons. This map, involving resonating two-color loops, is
+developed to represent exact many-body ground state wavefunctions for special
+high magnetizations. Using this map we show that these exact ground state
+solutions are valid for any $J_z/J \geq -1/2$. This demonstrates the
+equivalence of the ground-state wavefunction of the Ising, Heisenberg and $XY$
+regimes all the way to the $J_z/J=-1/2$ point for these high magnetization
+sectors. In the hardcore bosonic language, this means that a certain class of
+exact many-body solutions, previously argued to hold for purely repulsive
+interactions ($J_z \geq 0$), actually hold for attractive interactions as well,
+up to a critical interaction strength. For the case of zero magnetization,
+where the ground state is not exactly known, we perform density matrix
+renormalization group calculations. Based on the calculation of the ground
+state energy and measurement of order parameters, we provide evidence for a
+lack of any qualitative change in the ground state on finite clusters in the
+Ising ($J_z \gg J$), Heisenberg ($J_z=J$) and $XY$ ($J_z=0$) regimes,
+continuing adiabatically to the vicinity of the macroscopically degenerate
+$J_z/J=-1/2$ point. These findings offer a framework for recent results in the
+literature, and also suggest that the $J_z/J=-1/2$ point is an unconventional
+quantum critical point whose vicinity may contain the key to resolving the
+spin-$1/2$ kagome problem.",1808.08633v1
+2019-07-17,Topical Review on Skyrmions and Hall Transport,"We review recent progresses towards an understanding of the Skyrmion Hall
+transport in insulating as well as conducting materials. First, we consider a
+theoretical breakthrough based on the quantum field theory Ward identity, a
+first principle analysis, relying on symmetries and conservation laws. Broken
+parity (inversion) symmetry plays a crucial role in Skyrmion Hall transport. In
+addition to the well known thermal and electric Hall conductivities, our
+analysis has led us to the discovery of a new and unforeseen physical quantity,
+Hall viscosity - an anti-symmetric part of the viscosity tensor. We propose a
+simple way to confirm the existence of Hall viscosity in the measurements of
+Hall conductivity as a function of momentum. We provide various background
+materials to assist the readers to understand the quantum field theory Ward
+identity.
+  In the second part, we review recent theoretical and experimental
+advancements of the Skyrmion Hall effects and the topological (Magnon) Hall
+effects for conducting (insulting) magnets. For this purpose, we consider two
+enveloping themes: spin torque and thermo-electromagnetic effect. First, we
+overview various spin torques, such as spin transfer torque, spin-orbit torque,
+and spin Hall torque, and generalized Landau-Lifshitz-Gilbert equations and
+Thiele equations using a phenomenological approach. Second, we consider
+irreversible thermodynamics to survey possible thermo-electromagnetic effects,
+such as Seebeck, Peltier and Thompson effects in the presence of the electric
+currents, along with the Hall effects in the presence of a background magnetic
+field. Recently developed spin Seebeck effects are also a significant part of
+the survey. We also accommodate extensive background materials to make this
+review self-contained. Finally, we revisit the Skyrmion Hall transport from the
+Ward identity view point.",1907.07696v1
+2019-10-11,"Low-Damping Ferromagnetic Resonance in Electron-Beam Patterned, High-$Q$ Vanadium Tetracyanoethylene Magnon Cavities","Integrating patterned, low-loss magnetic materials into microwave devices and
+circuits presents many challenges due to the specific conditions that are
+required to grow ferrite materials, driving the need for flip-chip and other
+indirect fabrication techniques. The low-loss ($\alpha = 3.98 \pm 0.22 \times
+10^{-5}$), room-temperature ferrimagnetic coordination compound vanadium
+tetracyanoethylene ($\mathrm{V[TCNE]}_x$) is a promising new material for these
+applications that is potentially compatible with semiconductor processing. Here
+we present the deposition, patterning, and characterization of
+$\mathrm{V[TCNE]}_x$ thin films with lateral dimensions ranging from 1 micron
+to several millimeters. We employ electron-beam lithography and liftoff using
+an aluminum encapsulated poly(methyl methacrylate), poly(methyl
+methacrylate-methacrylic acid) copolymer bilayer (PMMA/P(MMA-MAA)) on sapphire
+and silicon. This process can be trivially extended to other common
+semiconductor substrates. Films patterned via this method maintain low-loss
+characteristics down to 25 microns with only a factor of 2 increase down to 5
+microns. A rich structure of thickness and radially confined spin-wave modes
+reveals the quality of the patterned films. Further fitting, simulation, and
+analytic analysis provides an exchange stiffness, $A_{ex} = 2.2 \pm 0.5 \times
+10^{-10}$ erg/cm, as well as insights into the mode character and surface spin
+pinning. Below a micron, the deposition is non-conformal, which leads to
+interesting and potentially useful changes in morphology. This work establishes
+the versatility of $\mathrm{V[TCNE]}_x$ for applications requiring highly
+coherent magnetic excitations ranging from microwave communication to quantum
+information.",1910.05325v1
+2020-01-17,Temporal and spectral fingerprints of ultrafast all-coherent spin switching,"Future information technology demands ultimately fast, low-loss quantum
+control. Intense light fields have facilitated important milestones, such as
+inducing novel states of matter, accelerating electrons ballistically, or
+coherently flipping the valley pseudospin. These dynamics leave unique
+signatures, such as characteristic bandgaps or high-order harmonic radiation.
+The fastest and least dissipative way of switching the technologically most
+important quantum attribute - the spin - between two states separated by a
+potential barrier is to trigger an all-coherent precession. Pioneering
+experiments and theory with picosecond electric and magnetic fields have
+suggested this possibility, yet observing the actual dynamics has remained out
+of reach. Here, we show that terahertz (1 THz = 10$^{12}$ Hz) electromagnetic
+pulses allow coherent navigation of spins over a potential barrier and we
+reveal the corresponding temporal and spectral fingerprints. This goal is
+achieved by coupling spins in antiferromagnetic TmFeO$_{3}$ with the locally
+enhanced THz electric field of custom-tailored antennas. Within their duration
+of 1 ps, the intense THz pulses abruptly change the magnetic anisotropy and
+trigger a large-amplitude ballistic spin motion. A characteristic phase flip,
+an asymmetric splitting of the magnon resonance, and a long-lived offset of the
+Faraday signal are hallmarks of coherent spin switching into adjacent potential
+minima, in agreement with a numerical simulation. The switchable spin states
+can be selected by an external magnetic bias. The low dissipation and the
+antenna's sub-wavelength spatial definition could facilitate scalable spin
+devices operating at THz rates.",2001.06255v1
+2020-01-29,Magnetic Fluctuations and the Spin-Orbit Interaction in Mott Insulating CoO,"Motivated by the presence of an unquenched orbital angular momentum in CoO, a
+team at Chalk River, including a recently hired research officer Roger Cowley,
+performed the first inelastic neutron scattering experiments on the classic
+Mott insulator [Sakurai $\textit{et al.}$ 1968 Phys. Rev. $\mathbf{167}$ 510].
+Despite identifying magnon modes at the zone boundary, the team was unable to
+parameterise the low energy magnetic excitation spectrum below $T\rm{_{N}}$
+using conventional pseudo-bosonic approaches. It would not be for another 40
+years that Roger, now at Oxford and motivated by the discovery of the
+high-$T_{c}$ cuprate superconductors [Bednorz & Muller 1986 Z. Phys. B
+$\mathbf{64}$ 189], would make another attempt at the parameterisation of the
+magnetic excitation spectrum that had previously alluded him. Upon his return
+to CoO, Roger found a system embroiled in controversy, with some of its most
+fundamental parameters still remaining undetermined. Faced with such a
+formidable task, Roger performed a series of inelastic neutron scattering
+experiments in the early 2010's on both CoO and a magnetically dilute
+structural analogue MgO. These experiments would prove instrumental in the
+determination of both single-ion [Cowley $\textit{et al.}$ 2013 Phys. Rev. B
+$\mathbf{88}$ 205117] and cooperative magnetic parameters [Sarte $\textit{et
+al.}$ 2018 Phys. Rev. B $\mathbf{98}$ 024415] for CoO. Both these sets of
+parameters would eventually be used in a spin-orbit exciton model [Sarte
+$\textit{et al.}$ 2019 Phys. Rev. B $\mathbf{100}$ 075143], developed by his
+longtime friend and collaborator Bill Buyers, to successfully parameterise the
+complex spectrum that both measured at Chalk River almost 50 years prior. The
+story of CoO is of one that has come full circle, one filled with both
+spectacular failures and intermittent, yet profound, little victories.",2001.10923v1
+2020-04-24,Skyrmionic order and magnetically induced polarization change in lacunar spinel compounds GaV$_{4}$S$_{8}$ and GaMo$_{4}$S$_{8}$: comparative theoretical study,"We show how low-energy electronic models derived from the first-principles
+electronic structure calculations can help to rationalize the magnetic
+properties of two lacunar spinel compounds GaM4S8 with light (M=V) and heavy
+(M=Mo) transition-metal elements, which are responsible for different
+spin-orbit interaction strength. In the model, each magnetic lattice point was
+associated with the M4S4 molecule, and the model itself was formulated in the
+basis of molecular Wannier functions constructed for three magnetic t2 bands.
+The effects of rhombohedral distortion, spin-orbit interaction, band filling,
+and the screening of Coulomb interactions in the t2 bands are discussed in
+details. The electronic model is further treated in the superexchange
+approximation, which allows us to derive an effective spin model for the energy
+and electric polarization ($P$) depending on the relative orientation of spins
+in the bonds, and study the properties of this model by means of classical
+Monte Carlo simulations with the emphasis on the possible formation of the
+skyrmionic phase. While isotropic exchange interactions clearly dominate in
+GaV4S8, all types of interactions -- isotropic, antisymmetric, and symmetric
+anisotropic -- are comparable in the case of GaMo4S8. Particularly, large
+uniaxial exchange anisotropy has a profound effect on the properties of
+GaMo4S8. On the one hand, it raises the Curie temperature by opening a gap in
+the spectrum of magnon excitations. On the other hand, it strongly affects the
+skyrmionic phase by playing the role of a molecular field, which facilitates
+the formation of skyrmions, but makes them relatively insensitive to the
+external magnetic field in the large part of the phase diagram. We predict
+reversal of the magnetic dependence of $P$ in the case of GaMo4S8 caused by the
+reversal of direction of the rhombohedral distortion.",2004.11548v1
+2020-05-28,"Dirac-type nodal spin liquid revealed by refined quantum many-body solver using neural-network wave function, correlation ratio, and level spectroscopy","Pursuing fractionalized particles that do not bear properties of conventional
+measurable objects, exemplified by bare particles in the vacuum such as
+electrons and elementary excitations such as magnons, is a challenge in
+physics. Here we show that a machine-learning method for quantum many-body
+systems that has achieved state-of-the-art accuracy reveals the existence of a
+quantum spin liquid (QSL) phase in the region $0.49\lesssim
+J_2/J_1\lesssim0.54$ convincingly in spin-1/2 frustrated Heisenberg model with
+the nearest and next-nearest neighbor exchanges, $J_1$ and $J_2$, respectively,
+on the square lattice. This is achieved by combining with the cutting-edge
+computational schemes known as the correlation ratio and level spectroscopy
+methods to mitigate the finite-size effects. The quantitative one-to-one
+correspondence between the correlations in the ground state and the excitation
+spectra enables the reliable identification and estimation of the QSL and its
+nature. The spin excitation spectra containing both singlet and triplet gapless
+Dirac-like dispersions signal the emergence of gapless fractionalized spin-1/2
+Dirac-type spinons in the distinctive QSL phase. Unexplored critical behavior
+with coexisting and dual power-law decays of N\'{e}el antiferromagnetic and
+dimer correlations is revealed. The power-law decay exponents of the two
+correlations differently vary with $J_2/J_1$ in the QSL phase and thus have
+different values except for a single point satisfying the symmetry of the two
+correlations. The isomorph of excitations with the cuprate $d$-wave
+superconductors implies a tight connection between the present QSL and
+superconductivity. This achievement demonstrates that the quantum-state
+representation using machine learning techniques, which had mostly been limited
+to benchmarks, is a promising tool for investigating grand challenges in
+quantum many-body physics.",2005.14142v6
+2020-07-22,An Electromagnetic Approach to Cavity Spintronics,"The fields of cavity quantum electrodynamics and magnetism have recently
+merged into \textit{`cavity spintronics'}, investigating a quasiparticle that
+emerges from the strong coupling between standing electromagnetic waves
+confined in a microwave cavity resonator and the quanta of spin waves, magnons.
+This phenomenon is now expected to be employed in a variety of devices for
+applications ranging from quantum communication to dark matter detection. To be
+successful, most of these applications require a vast control of the coupling
+strength, resulting in intensive efforts to understanding coupling by a variety
+of different approaches. Here, the electromagnetic properties of both resonator
+and magnetic samples are investigated to provide a comprehensive understanding
+of the coupling between these two systems. Because the coupling is a
+consequence of the excitation vector fields, which directly interact with
+magnetisation dynamics, a highly-accurate electromagnetic perturbation theory
+is employed which allows for predicting the resonant hybrid mode frequencies
+for any field configuration within the cavity resonator, without any fitting
+parameters. The coupling is shown to be strongly dependent not only on the
+excitation vector fields and sample's magnetic properties but also on the
+sample's shape. These findings are illustrated by applying the theoretical
+framework to two distinct experiments: a magnetic sphere placed in a
+three-dimensional resonator, and a rectangular, magnetic prism placed on a
+two-dimensional resonator. The theory provides comprehensive understanding of
+the overall behaviour of strongly coupled systems and it can be easily modified
+for a variety of other systems.",2007.11483v2
+2020-08-21,"Macroscopic, layered onion shell like magnetic domain structure generated in YIG film using ultrashort, megagauss magnetic pulses","Study of the formation and evolution of large scale, ordered structures is an
+enduring theme in science. The generation, evolution and control of large sized
+magnetic domains are intriguing and challenging tasks, given the complex nature
+of competing interactions present in any magnetic system. Here, we demonstrate
+large scale non-coplanar ordering of spins, driven by picosecond, megagauss
+magnetic pulses derived from a high intensity, femtosecond laser. Our studies
+on a specially designed Yttrium Iron Garnet (YIG)/dielectric/metal film
+sandwich target, show the creation of complex, large, concentric, elliptical
+shaped magnetic domains which resemble the layered shell structure of an onion.
+The largest shell has a major axis of over hundreds of micrometers, in stark
+contrast to conventional sub micrometer scale polygonal, striped or bubble
+shaped magnetic domains found in magnetic materials, or the large dumbbell
+shaped domains produced in magnetic films irradiated with accelerator based
+relativistic electron beams. Through micromagnetic simulations, we show that
+the giant magnetic field pulses create ultrafast terahertz (THz) spin waves. A
+snapshot of these fast propagating spin waves is stored as the layered onion
+shell shaped domains in the YIG film. Typically, information transport via spin
+waves in magnonic devices occurs in the gigahertz (GHz) regime, where the
+devices are susceptible to thermal disturbances at room temperature. Our
+intense laser light pulse - YIG sandwich target combination, paves the way for
+room temperature table-top THz spin wave devices, which operate just above or
+in the range of the thermal noise floor. This dissipation-less device offers
+ultrafast control of spin information over distances of few hundreds of
+microns.",2008.09473v1
+2020-11-23,2-input 4-output Programmable Spin Wave Logic Gate,"To bring Spin Wave (SW) based computing paradigm into practice and develop
+ultra low power Magnonic circuits and computation platforms, one needs basic
+logic gates that operate and can be cascaded within the SW domain without
+requiring back and forth conversion between the SW and voltage domains. To
+achieve this, SW gates have to possess intrinsic fanout capabilities, be
+input-output data representation coherent, and reconfigurable. In this paper,
+we address the first and the last requirements and propose a novel 4-output
+programmable SW logic. First, we introduce the gate structure and demonstrate
+that, by adjusting the gate output detection method, it can parallelly evaluate
+any 4-element subset of the 2-input Boolean function set AND, NAND, OR, NOR,
+XOR, and XNOR. Furthermore, we adjust the structure such that all its 4 outputs
+produce SWs with the same energy and demonstrate that it can evaluate Boolean
+function sets while providing fanout capabilities ranging from 1 to 4. We
+validate our approach by instantiating and simulating different gate
+configurations such as 4-output AND/OR, 4-output XOR/XNOR, output energy
+balanced 4-output AND/OR, and output energy balanced 4-output XOR/XNOR by means
+of Object Oriented Micromagnetic Framework (OOMMF) simulations. Finally, we
+evaluate the performance of our proposal in terms of delay and energy
+consumption and compare it against existing state-of-the-art SW and 16nm CMOS
+counterparts. The results indicate that for the same functionality, our
+approach provides 3x and 16x energy reduction, when compared with conventional
+SW and 16nm CMOS implementations, respectively.",2011.11316v2
+2021-03-25,Twist engineering of the two-dimensional magnetism in double bilayer chromium triiodide homostructures,"Twist engineering, or the alignment of two-dimensional (2D) crystalline
+layers with desired orientations, has led to tremendous success in modulating
+the charge degree of freedom in hetero- and homo-structures, in particular, in
+achieving novel correlated and topological electronic phases in moir\'e
+electronic crystals. However, although pioneering theoretical efforts have
+predicted nontrivial magnetism and magnons out of twisting 2D magnets,
+experimental realization of twist engineering spin degree of freedom remains
+elusive. Here, we leverage the archetypal 2D Ising magnet chromium triiodide
+(CrI3) to fabricate twisted double bilayer homostructures with tunable twist
+angles and demonstrate the successful twist engineering of 2D magnetism in
+them. Using linear and circular polarization-resolved Raman spectroscopy, we
+identify magneto-Raman signatures of a new magnetic ground state that is
+sharply distinct from those in natural bilayer (2L) and four-layer (4L) CrI3.
+With careful magnetic field and twist angle dependence, we reveal that, for a
+very small twist angle (~ 0.5 degree), this emergent magnetism can be
+well-approximated by a weighted linear superposition of those of 2L and 4L CI3
+whereas, for a relatively large twist angle (~ 5 degree), it mostly resembles
+that of isolated 2L CrI3. Remarkably, at an intermediate twist angle (~ 1.1
+degree), its magnetism cannot be simply inferred from the 2L and 4L cases,
+because it lacks sharp spin-flip transitions that are present in 2L and 4L CrI3
+and features a dramatic Raman circular dichroism that is absent in natural 2L
+and 4L ones. Our results demonstrate the possibility of designing and
+controlling the spin degree of freedom in 2D magnets using twist engineering.",2103.13537v2
+2021-03-28,Magnetic field-induced softening of spin waves and hard-axis order in Kondo-lattice ferromagnet CeAgSb$_{2}$,"A significant number of Kondo-lattice ferromagnets order perpendicular to the
+easy magnetization axis dictated by the crystalline electric field. The nature
+of this phenomenon has attracted considerable attention, but remains poorly
+understood. In the present paper we use inelastic neutron scattering supported
+by magnetization and specific heat measurements to study the spin dynamics in
+the hard-axis ferromagnet CeAgSb2. In the zero field state we observed two
+sharp magnon modes, which are associated with Ce ordering and extended up to
+$\approx 3 meV with a considerable spin gap of 0.6 meV. Application of a
+magnetic field perpendicular to the moment direction reduces the spectral
+intensity and suppresses the gap and significantly enhances the low-temperature
+specific heat at a critical field of Bc ~ 2.8 T via a mean-field-like
+transition. Above the transition, in the field polarized state, the gap
+eventually reopens due to the Zeeman effect. We modeled the observed dispersion
+using linear spin-wave theory (LSWT) taking into account the ground state Gamma
+6 doublet and exchange anisotropy. Our model correctly captures the essential
+features of the spin dynamics including magnetic dispersion, distribution of
+the spectral intensity as well as the field-induced behavior, although several
+minor features remain obscure. The observed spectra do not show significant
+broadening due to the finite lifetime of the quasiparticles. Along with a
+moderate electronic specific heat coefficient gamma = 46 mJ/mol K2 this
+indicates that the Kondo coupling is relatively weak and the Ce moments are
+well localized. Altogether, our results provide profound insight into the spin
+dynamics of the hard-axis ferromagnet CeAgSb2 and can be used as solid ground
+for studying magnetic interactions in isostructural compounds including
+CeAuSb2, which exhibits nematicity and unusual mesoscale magnetic textures.",2103.15137v2
+2021-04-21,Atomic Layer Deposition of Yttrium Iron Garnet Thin Films for 3D Magnetic Structures,"A wide variety of new phenomena such as novel magnetization configurations
+have been predicted to occur in three dimensional magnetic nanostructures.
+However, the fabrication of such structures is often challenging due to the
+specific shapes required, such as magnetic tubes and spirals. Furthermore, the
+materials currently used to assemble these structures are predominantly
+magnetic metals that do not allow to study the magnetic response of the system
+separately from the electronic one. In the field of spintronics, the
+prototypical material used for such experiments is the ferrimagnetic insulator
+yttrium iron garnet (Y$_3$Fe$_5$O$_{12}$, YIG). YIG is one of the best
+materials especially for magnonic studies due to its low Gilbert damping. Here,
+we report the first successful fabrication of YIG thin films via atomic layer
+deposition. To that end we utilize a supercycle approach based on the
+combination of sub-nanometer thin layers of the binary systems Fe$_2$O$_3$ and
+Y$_2$O$_3$ in the correct atomic ratio on Y$_3$Al$_5$O$_{12}$ substrates with a
+subsequent annealing step. Our process is robust against typical growth-related
+deviations, ensuring a good reproducibility. The ALD-YIG thin films exhibit a
+good crystalline quality as well as magnetic properties comparable to other
+deposition techniques. One of the outstanding characteristics of atomic layer
+deposition is its ability to conformally coat arbitrarily-shaped substrates.
+ALD hence is the ideal deposition technique to grant an extensive freedom in
+choosing the shape of the magnetic system. The atomic layer deposition of YIG
+enables the fabrication of novel three dimensional magnetic nanostructures,
+which in turn can be utilized for experimentally investigating the phenomena
+predicted in those structures.",2104.10293v2
+2021-06-14,One-dimensional ghost imaging with an electron microscope: a route towards ghost imaging with inelastically scattered electrons,"In quantum mechanics, entanglement and correlations are not just a mere
+sporadic curiosity, but rather common phenomena at the basis of an interacting
+quantum system. In electron microscopy, such concepts have not been extensively
+explored yet in all their implications; in particular, inelastic scattering can
+be reanalyzed in terms of correlation between the electron beam and the sample.
+While classical inelastic scattering simply implies loss of coherence in the
+electron beam, performing a joint measurement on the electron beam and the
+sample excitation could restore the coherence and the lost information. Here,
+we propose to exploit joint measurement in electron microscopy for a surprising
+and counter-intuitive application of the concept of ghost imaging. Ghost
+imaging, first proposed in quantum photonics, can be applied partially in
+electron microscopy by performing joint measurement between the portion of the
+transmitted electron beam and a photon emitted from the sample reaching a
+bucket detector. This would permit us to form a one-dimensional virtual image
+of an object that even has not interacted with the electron beam directly. This
+technique is extremely promising for low-dose imaging that requires the
+minimization of radiation exposure for electron-sensitive materials, because
+the object interacts with other form of waves, e.g., photons/surface plasmon
+polaritons, and not the electron beam. We demonstrate this concept
+theoretically for any inelastic electron-sample interaction in which the
+electron excites a single quantum of a collective mode, such as a photon,
+plasmon, phonon, magnon, or any optical polariton.",2106.08955v1
+2021-06-22,"XY magnetism, Kitaev exchange, and long-range frustration in the $J_{\rm eff}=1/2$ honeycomb cobaltates","The quest for Kitaev quantum spin liquids has led to great interest in
+honeycomb quantum magnets with strong spin-orbit coupling. It has been recently
+proposed that even Mott insulators with $3d$ transition metal ions, having
+nominally weak spin-orbit coupling, can realize such exotic physics. Motivated
+by this, we study the rhombohedral honeycomb cobaltates CoTiO$_3$,
+BaCo$_2$(PO$_4$)$_2$, and BaCo$_2$(AsO$_4$)$_2$, using $\textit{ab initio}$
+density functional theory, which takes into account realistic crystal field
+distortions and chemical information, in conjunction with exact diagonalization
+numerics. We show that these Co$^{2+}$ magnets host $j_\text{eff}=1/2$ local
+moments with highly anisotropic $g$-factors, and we extract their full spin
+Hamiltonians including longer-range and anisotropic exchange couplings. For
+CoTiO$_3$, we find a nearest-neighbor easy-plane ferromagnetic $XXZ$ model with
+additional bond-dependent anisotropies and interlayer exchange, which supports
+three-dimensional (3D) Dirac nodal line magnons. In contrast, for
+BaCo$_2$(PO$_4$)$_2$ and BaCo$_2$(AsO$_4$)$_2$, we find a strongly suppressed
+interlayer coupling, and significant frustration from additional third-neighbor
+antiferromagnetic exchange mediated by P/As. Such bond-anisotropic $J_1$-$J_3$
+spin models can support collinear zig-zag or coplanar spiral ground states; we
+discuss their dynamical spin correlations which reveal a gapped Goldstone mode,
+and argue that the effective parameters of these pseudospin-$1/2$ models may be
+strongly renormalized by coupling to a low energy spin-exciton. Our results
+call for re-examining proposals for realizing Kitaev spin liquids in the
+honeycomb cobaltates.",2106.11982v3
+2021-07-22,When can localized spins interacting with conduction electrons in ferro- or antiferromagnets be described classically via the Landau-Lifshitz equation: Transition from quantum many-body entangled to quantum-classical nonequilibrium states,"Experiments in spintronics and magnonics operate with macroscopically large
+number of localized spins within ferromagnetic (F) or antiferromagnetic (AF)
+materials, so that their nonequilibrium dynamics is standardly described by the
+Landau-Lifshitz (LL) equation treating localized spins as classical vectors of
+fixed length. However, spin is a genuine quantum degree of freedom, and even
+though quantum effects become progressively less important for spin value
+$S>1$, they exist for all $S < \infty$. While this has motivated exploration of
+limitations/breakdown of the LL equation, by using examples of F insulators,
+analogous comparison of fully quantum many-body vs. quantum (for
+electrons)-classical (for localized spins) dynamics in systems where
+nonequilibrium conduction electrons are present is lacking. Here we employ
+quantum Heisenberg F or AF chains of $N=4$ sites, whose localized spins
+interact with conduction electrons via $sd$ exchange interaction, to perform
+such comparison by starting from unentangled pure (at zero temperature) or
+mixed (at finite temperature) quantum state of localized spins as the initial
+condition. This reveals that quantum-classical dynamics can faithfully
+reproduce fully quantum dynamics in the F metallic case, but only when spin
+$S$, Heisenberg exchange between localized spins and $sd$ exchange are
+sufficiently small. Increasing any of these three parameters can lead to
+substantial deviations, which are explained by the dynamical buildup of
+entanglement between localized spins and/or between them and electrons. In the
+AF metallic case, substantial deviations appear even at early times, despite
+starting from unentangled N\'{e}el state, which therefore poses a challenge on
+how to rigorously justify wide usage of the LL equation in phenomenological
+modeling of antiferromagnetic spintronics experiments.",2107.10776v3
+2021-07-22,Spin-orbit torque control of spin waves in a ferromagnetic waveguide,"Spin-orbit torque (SOT) created by a spin current injected into a ferromagnet
+by an adjacent heavy metal represents an efficient tool for the excitation and
+manipulation of spin waves. Here we report the micromagnetic simulations
+describing the influence of SOT on the propagation of spin waves in the
+$\mathrm{W}/\mathrm{CoFeB}/\mathrm{MgO}$ nanostructure having
+voltage-controlled magnetic anisotropy (VCMA). The simulations show that two
+spin waves travelling in the opposite directions can be generated in the center
+of the $\mathrm{CoFeB}$ waveguide via the modulation of VCMA induced by a
+microwave voltage locally applied to the $\mathrm{MgO}$ nanolayer. The
+amplitudes of these waves exponentially decrease with the propagation distance
+with similar decay lengths of about 2.5 $\mu$m. In the presence of a direct
+electric current injected into the $\mathrm{W}$ film beneath the waveguide
+center, the decay lengths of two spin waves change in the opposite way owing to
+different directions of the electric currents flowing in the underlying halves
+of the $\mathrm{W}$ layer. Remarkably, above the critical current density
+$J_\mathrm{W} \approx 2 \times 10^{10}$ A m$^{-2}$, SOT provides the
+amplification of the spin wave propagating in one half of the waveguide and
+strongly accelerates the attenuation of the wave travelling in the other half.
+As a result, a long-distance spin-wave propagation takes place in a half of the
+$\mathrm{CoFeB}$ waveguide only. Furthermore, by reversing the polarity of the
+dc voltage applied to the heavy-metal layer one can change the propagation area
+and switch the travel direction of the spin wave in the ferromagnetic
+waveguide. Thus, the $\mathrm{W}/\mathrm{CoFeB}/\mathrm{MgO}$ nanostructure can
+be employed as an electrically controlled magnonic device converting the
+electrical input signal into a spin signal, which can be transmitted to one of
+two outputs of the device.",2107.10795v2
+2021-07-27,The Keck Planet Imager and Characterizer: A dedicated single-mode fiber injection unit for high resolution exoplanet spectroscopy,"The Keck Planet Imager and Characterizer (KPIC) is a purpose-built instrument
+to demonstrate new technological and instrumental concepts initially developed
+for the exoplanet direct imaging field. Located downstream of the current Keck
+II adaptive optic system, KPIC contains a fiber injection unit (FIU) capable of
+combining the high-contrast imaging capability of the adaptive optics system
+with the high dispersion spectroscopy capability of the current Keck high
+resolution infrared spectrograph (NIRSPEC). Deployed at Keck in September 2018,
+this instrument has already been used to acquire high resolution spectra ($R >
+30,000$) of multiple targets of interest. In the near term, it will be used to
+spectrally characterize known directly imaged exoplanets and low-mass brown
+dwarf companions visible in the northern hemisphere with a spectral resolution
+high enough to enable spin and planetary radial velocity measurements as well
+as Doppler imaging of atmospheric weather phenomena. Here we present the design
+of the FIU, the unique calibration procedures needed to operate a single-mode
+fiber instrument and the system performance.",2107.12556v1
+2021-08-16,Symmetry- and curvature effects on spin waves in vortex-state hexagonal nanotubes,"Analytic and numerical studies on curved magnetic nano-objects predict
+numerous exciting effects that can be referred to as magneto-chiral effects,
+which do not originate from intrinsic Dzyaloshinskii-Moriya interaction or
+interface-induced anisotropies. In constrast, these chiral effects stem from
+isotropic exchange or dipole-dipole interaction, present in all magnetic
+materials, which acquire asymmetric contributions in case of curved geometry of
+the specimen. As a result, for example, the spin-wave dispersion in round
+magnetic nanotubes becomes asymmetric, namely spin waves of the same frequency
+propagating in opposite directions along the nanotube exhibit different
+wavelenghts. Here, using time-resolved scanning transmission X-ray microscopy
+experiments, standard micromagntic simulations and a dynamic-matrix approach,
+we show that the spin-wave spectrum undergoes additional drastic changes when
+transitioning from a continuous to a discrete rotational symmetry, i.e. from
+round to hexagonal nanotubes, which are much easier to fabricate. The polygonal
+shape introduces localization of the modes both to the sharp, highly curved
+corners and flat edges. Moreover, due to the discrete rotational symmetry, the
+degenerate nature of the modes with azimuthal wave vectors known from round
+tubes is partly lifted, resulting in singlet and duplet modes. For comparison
+with our experiments, we calculate the microwave absorption from the
+numerically obtained mode profiles which shows that a dedicated antenna design
+is paramount for magnonic applications in 3D nano-structures. To our knowledge
+these are the first experiments directly showing real space spin-wave
+propagation in 3D nano objects.",2108.07103v1
+2021-10-11,Transition of laser-induced terahertz spin currents from torque- to conduction-electron-mediated transport,"Spin transport is crucial for future spintronic devices operating at
+bandwidths up to the terahertz (THz) range. In F|N thin-film stacks made of a
+ferro/ferrimagnetic layer F and a normal-metal layer N, spin transport is
+mediated by (1) spin-polarized conduction electrons and/or (2) torque between
+electron spins. To identify a cross-over from (1) to (2), we study laser-driven
+spin currents in F|Pt stacks where F consists of model materials with different
+degrees of electrical conductivity. For the magnetic insulators YIG, GIG and
+maghemite, identical dynamics is observed. It arises from the THz interfacial
+spin Seebeck effect (SSE), is fully determined by the relaxation of the
+electrons in the metal layer and provides an estimate of the spin-mixing
+conductance of the GIG/Pt interface. Remarkably, in the half-metallic
+ferrimagnet Fe3O4 (magnetite), our measurements reveal two spin-current
+components with opposite direction. The slower, positive component exhibits SSE
+dynamics and is assigned to torque-type magnon excitation of the A- and B-spin
+sublattices of Fe3O4. The faster, negative component arises from the
+pyro-spintronic effect and can consistently be assigned to ultrafast
+demagnetization of e-sublattice minority-spin hopping electrons. This
+observation supports the magneto-electronic model of Fe3O4. In general, our
+results provide a new route to the contact-free separation of torque- and
+conduction-electron-mediated spin currents.",2110.05462v2
+2021-10-13,"A Combined First Principles Study of the Structural, Magnetic, and Phonon Properties of Monolayer CrI$_{3}$","The first magnetic 2D material discovered, monolayer (ML) CrI$_3$, is
+particularly fascinating due to its ground state ferromagnetism. Yet, because
+monolayer materials are difficult to probe experimentally, much remains
+unresolved about ML CrI$_{3}$'s structural, electronic, and magnetic
+properties. Here, we leverage Density Functional Theory (DFT) and high-accuracy
+Diffusion Monte Carlo (DMC) simulations to predict lattice parameters, magnetic
+moments, and spin-phonon and spin-lattice coupling of ML CrI$_{3}$. We exploit
+a recently developed surrogate Hessian DMC line search technique to determine
+CrI$_{3}$'s monolayer geometry with DMC accuracy, yielding lattice parameters
+in good agreement with recently-published STM measurements - an accomplishment
+given the $\sim 10$% variability in previous DFT-derived estimates depending
+upon the functional. Strikingly, we find previous DFT predictions of ML
+CrI$_3$'s magnetic spin moments are correct on average across a unit cell, but
+miss critical local spatial fluctuations in the spin density revealed by more
+accurate DMC. DMC predicts magnetic moments in ML CrI$_3$ are 3.62 $\mu_B$ per
+chromium and -0.145 $\mu_B$ per iodine; both larger than previous DFT
+predictions. The large disparate moments together with the large spin-orbit
+coupling of CrI$_3$'s I-$\textit{p}$ orbital suggests a ligand
+superexchange-dominated magnetic anisotropy in ML CrI$_3$, corroborating recent
+observations of magnons in its 2D limit. We also find ML CrI$_3$ exhibits a
+substantial spin-phonon coupling of $\sim$3.32 cm$^{-1}$. Our work thus
+establishes many of ML CrI$_{3}$'s key properties, while also continuing to
+demonstrate the pivotal role DMC can assume in the study of magnetic and other
+2D materials.",2110.06731v1
+2021-10-25,Germanium monosulfide as a natural platform for highly anisotropic THz polaritons,"Terahertz (THz) electromagnetic radiation is key to optically access
+collective excitations such as magnons (spins), plasmons (electrons), or
+phonons (atomic vibrations), thus bridging between optics and solid-state
+physics. Confinement of THz light to the nanometer length scale is desirable
+for local probing of such excitations in low dimensional systems, thereby
+inherently circumventing the large footprint and low spectral density of
+far-field THz optics. For that purpose, phonon polaritons (PhPs, i.e., light
+coupled to lattice vibrations in polar crystals) in anisotropic van der Waals
+(vdW) materials have recently emerged as a promising platform for THz
+nanooptics; yet the amount of explored, viable materials is still exiguous.
+Hence, there is a demand for the exploration of novel materials that feature
+not only THz PhPs at different spectral regimes, but also exhibit unique
+anisotropic (directional) electrical, thermoelectric, and vibronic properties.
+To that end, we introduce here the semiconducting alpha-germanium(II) sulfide
+(GeS) as an intriguing candidate. By employing THz nano-spectroscopy supported
+by theoretical analysis, we provide a thorough characterization of the
+different in-plane hyperbolic and elliptical PhP modes in GeS. We find not only
+PhPs with long life times ($\tau$ > 2 ps) and excellent THz light confinement
+($\lambda_0/\lambda$ > 45), but also an intrinsic, phonon-induced anomalous
+dispersion as well as signatures of naturally occurring PhP canalization within
+one single GeS slab.",2110.13295v2
+2021-12-02,Structures of magnetic excitations in the spin-1/2 kagome-lattice antiferromagnets Cs$_2$Cu$_3$SnF$_{12}$ and Rb$_2$Cu$_3$SnF$_{12}$,"We show the structures of magnetic excitations in spin-1/2 kagome-lattice
+antiferromagnets Cs$_2$Cu$_3$SnF$_{12}$ and Rb$_2$Cu$_3$SnF$_{12}$ investigated
+by inelastic neutron scattering in wide energy and momentum ranges. For
+Cs$_2$Cu$_3$SnF$_{12}$, four single-magnon excitation modes were observed.
+Low-energy three modes are assigned to be transverse modes and the high-energy
+fourth mode is suggested to be an amplitude mode. It was found that the broad
+excitation continuum without a marked structure spreads in a wide energy range
+from $0.15J$ to approximately $2.5J$ in contrast to the clearly structured
+excitation continuum observed in the spin-1/2 triangular-lattice Heisenberg
+antiferromagnet. These findings strongly suggest spinon excitations as
+elementary excitations in Cs$_2$Cu$_3$SnF$_{12}$. In Rb$_2$Cu$_3$SnF$_{12}$,
+singlet-triplet excitations from the pinwheel VBS state and their ghost modes
+caused by the enlargement of the chemical unit cell were clearly confirmed. It
+was found that the excitation continuum is structured in the low-energy region
+approximately below $J_{\mathrm{avg}}$ and the almost structureless high-energy
+excitation continuum extends to approximately $2.6J_{\mathrm{avg}}$. The
+characteristics of the high-energy excitation continuum are common to both
+Cs$_2$Cu$_3$SnF$_{12}$ and Rb$_2$Cu$_3$SnF$_{12}$, irrespective of their ground
+states. The experimental results strongly suggest that the spin liquid
+component remains in the ground state as quantum fluctuations in
+Cs$_2$Cu$_3$SnF$_{12}$ and Rb$_2$Cu$_3$SnF$_{12}$.",2112.00934v2
+2022-02-15,Thermodynamics of the spin-half square-kagome lattice antiferromagnet,"Over the last decade, the interest in the spin-$1/2$ Heisenberg
+antiferromagnet (HAF) on the square-kagome (also called shuriken) lattice has
+been growing as a model system of quantum magnetism with a quantum paramagnetic
+ground state, flat-band physics near the saturation field, and quantum scars.
+Here, we present large-scale numerical investigations of the specific heat
+$C(T)$, the entropy $S(T)$ as well as the susceptibility $\chi(T)$ by means of
+the finite-temperature Lanczos method for system sizes of
+$N=18,24,30,36,42,48$, and $N=54$. We find that the specific heat exhibits a
+low-temperature shoulder below the major maximum which can be attributed to
+low-lying singlet excitations filling the singlet-triplet gap, which is
+significantly larger than the singlet-singlet gap. This observation is further
+supported by the behavior of the entropy $S(T)$, where a change in the
+curvature is present just at about $T/J=0.2$, the same temperature where the
+shoulder in $C$ sets in. For the susceptibility the low-lying singlet
+excitations are irrelevant, and the singlet-triplet gap leads to an
+exponentially activated low-temperature behavior. The maximum in $\chi(T)$ is
+found at a pretty low temperature $T_{\rm max}/J=0.146$ (for $N=42$) compared
+to $T_{\rm max}/J=0.935$ for the unfrustrated square-lattice HAF signaling the
+crucial role of frustration also for the susceptibility. We find a striking
+similarity of our square-kagome data with the corresponding ones for the kagome
+HAF down to very low $T$. The magnetization process featuring plateaus and
+jumps and the field dependence of the specific heat that exhibits
+characteristic peculiarities attributed to the existence of a flat one-magnon
+band are as well discussed.",2202.07357v2
+2022-04-11,Curvilinear spin-wave dynamics beyond the thin-shell approximation: Magnetic nanotubes as a case study,"Surface curvature of magnetic systems can lead to many static and dynamic
+effects which are not present in flat systems of the same material. These
+emergent magnetochiral effects can lead to frequency nonreciprocity of spin
+waves, which has been shown to be a bulk effect of dipolar origin and is
+related to a curvature-induced symmetry breaking in the magnetic volume
+charges. So far, such effects have been investigated theoretically mostly for
+thin shells, where the spatial profiles of the spin waves can be assumed to be
+homogeneous along the thickness. Here, using a finite-element dynamic-matrix
+approach, we investigate the transition of the spin-wave spectrum from thin to
+thick curvilinear shells, at the example of magnetic nanotubes in the vortex
+state. With increasing thickness, we observe the appearance of higher-order
+radial modes which are strongly hybridized and resemble the
+perpendicular-standing-waves (PSSWs) in flat films. Along with an increasing
+dispersion asymmetry, we uncover the curvature-induced non-reciprocity of the
+mode profiles. This is explained in a very simple picture general for thick
+curvilinear shells, considering the inhomogeneity of the emergent geometric
+volume charges along the thickness of the shell. Such curvature-induced
+mode-profile asymmetry also leads to non-reciprocal hybridization which can
+facilitate unidirectional spin-wave propagation. With that, we also show how
+curvature allows for nonlinear three-wave splitting of a higher-order radial
+mode into secondary modes which can also propagate unidirectionally. We believe
+that our study provides a significant contribution to the understanding of the
+spin-wave dynamics in curvilinear magnetic systems, but also advertises these
+for novel magnonic applications.",2204.05065v1
+2022-04-22,Would Magnonic Circuits Outperform CMOS Counterparts?,"In the early stages of a novel technology development, it is difficult to
+provide a comprehensive assessment of its potential capabilities and impact.
+Nevertheless, some preliminary estimates can be drawn and are certainly of
+great interest and in this paper we follow this line of reasoning within the
+framework of the Spin Wave (SW) computing paradigm. In particular, we are
+interested in assessing the technological development horizon that needs to be
+reached in order to unleash the full SW paradigm potential such that SW
+circuits can outperform CMOS counterparts in terms of energy consumption. In
+view of the zero power SWs propagation through ferromagnetic waveguides, the
+overall SW circuit power consumption is determined by the one associated to SWs
+generation and sensing by means of transducers. While current antenna based
+transducers are clearly power hungry recent developments indicate that
+magneto-electric (ME) cells have a great potential for ultra-low power SW
+generation and sensing. Given that MEs have been only proposed at the
+conceptual level and no actual experimental demonstration has been reported we
+cannot evaluate the impact of their utilization on the SW circuit energy
+consumption. However, we can perform a reverse engineering alike analysis to
+determine ME delay and power consumption upper bounds that can place SW
+circuits in the leading position. To this end, we utilize a 32-bit Brent-Kung
+Adder (BKA) as discussion vehicle and compute the maximum ME delay and power
+consumption that could potentially enable a SW implementation able to
+outperform its 7nm CMOS counterpart. We evaluate different BKA SW
+implementations that rely on conversion or normalization gate cascading and
+consider continuous or pulsed SW generation scenarios. 31nW is the maximum
+transducer power consumption for which a 32-bit BKA SW implementation can
+outperform its 7nm CMOS counterpart.",2204.10732v1
+2022-05-23,"Highly tunable spin Hall magnetoresistance in room-temperature magnetoelectric multiferroic, $\text{Sr}_{3}\text{Co}_{2}\text{Fe}_{24}\text{O}_{41}|$Pt hybrids","We present spin transport studies on a low-field, room-temperature
+magnetoelectric multiferroic polycrystalline
+$\text{Sr}_{3}\text{Co}_{2}\text{Fe}_{24}\text{O}_{41}$ (SCFO)|Pt
+heterostructure wherein a highly tunable transverse conical magnetic phase is
+responsible for static and dynamic magnetoelectric coupling. We measured
+angular dependence of spin Hall magnetoresistance (SMR) at constant magnetic
+fields ($H$) in the range of 50 to 100 kOe. Application of field below the
+critical value (2.5 kOe), yielded negative SMR and the $H$-evolution of
+normalized SMR exhibited a negative gradient. Further, an increase in the $H$
+resulted in the positive slope of normalized SMR Vs. $H$ and later at higher
+$H$ around 14 kOe, a crossover from negative to positive SMR was observed. We
+employed a simple model for estimating the equilibrium magnetic configuration
+and computed the SMR modulation at various values of $H$. We argue that the
+tilting of the cone is dominant and in turn responsible for the observed nature
+of SMR below 2.5 kOe while, the closing of the cone-angle is pronounced at
+higher fields causing a reversal in sign of the SMR from negative to positive.
+Importantly, SMR experiments revealed that a change in the helicity with a
+reversal of the magnetic field has no influence on the observed SMR.
+Longitudinal spin Seebeck effect (LSSE) signal was measured to be 500 nV at 280
+K, under application of thermal gradient, $\Delta T = 23$ K and field, 60 kOe.
+The observed LSSE signal, originating from pure magnon spin current, showed a
+similar $H$-dependent behavior as that of the magnetization of SCFO. Our
+detailed spin transport studies on polycrystalline SCFO|Pt heterostructure
+demonstrate high tunability of the amplitude and the sign of the SMR,
+highlighting its potential for novel spintronic devices such as SMR-based spin
+valves and voltage-controlled spin transport devices.",2205.11539v1
+2022-08-16,Liger at Keck Observatory: Design of the Data Reduction System and Software Interfaces,"Liger is a second generation near-infrared imager and integral field
+spectrograph (IFS) for the W. M. Keck Observatory that will utilize the
+capabilities of the Keck All-sky Precision Adaptive-optics (KAPA) system. Liger
+operates at a wavelength range of 0.81 {\mu}m - 2.45 {\mu}m and utilizes a
+slicer and a lenslet array IFS with varying spatial plate scales and fields of
+view resulting in hundreds of modes available to the astronomer. Because of the
+high level of complexity in the raw data formats for the slicer and lenslet IFS
+modes, Liger must be designed in conjunction with a Data Reduction System (DRS)
+which will reduce data from the instrument in real-time and deliver
+science-ready data products to the observer. The DRS will reduce raw imager and
+IFS frames from the readout system and provide 2D and 3D data products via
+custom quick-look visualization tools suited to the presentation of IFS data.
+The DRS will provide the reduced data to the Keck Observatory Archive (KOA) and
+will be available to astronomers for offline post-processing of observer data.
+We present an initial design for the DRS and define the interfaces between
+observatory and instrument software systems.",2208.07937v1
+2022-08-16,Liger at Keck Observatory: Imager Detector and IFS Pick-off Mirror Assembly,"Liger is a next-generation near-infrared imager and integral field
+spectrograph (IFS) planned for the W.M. Keck Observatory. Liger is designed to
+take advantage of improved adaptive optics (AO) from the Keck All-Sky Precision
+Adaptive Optics (KAPA) upgrade currently underway. Liger operates at 0.84-2.45
+$\mu$m with spectral resolving powers of R$\sim$4,000-10,000. Liger makes use
+of a sequential imager and spectrograph design allowing for simultaneous
+observations. There are two spectrograph modes: a lenslet with high spatial
+sampling of 14 and 31 mas, and a slicer with 75 and 150 mas sampling with an
+expanded field of view. Two pick-off mirrors near the imager detector direct
+light to these two IFS channels. We present the design and structural analysis
+for the imager detector and IFS pick-off mirror mounting assembly that will be
+used to align and maintain stability throughout its operation. A piezoelectric
+actuator will be used to step through $\rm3\,mm$ of travel during alignment of
+the instrument to determine the optimal focus for both the detector and
+pick-off mirrors which will be locked in place during normal operation. We will
+demonstrate that the design can withstand the required gravitational and
+shipping loads and can be aligned within the positioning tolerances for the
+optics.",2208.07938v1
+2022-08-23,Design of SCALES: A 2-5 Micron Coronagraphic Integral Field Spectrograph for Keck Observatory,"We present the design of SCALES (Slicer Combined with Array of Lenslets for
+Exoplanet Spectroscopy) a new 2-5 micron coronagraphic integral field
+spectrograph under construction for Keck Observatory. SCALES enables
+low-resolution (R~50) spectroscopy, as well as medium-resolution (R~4,000)
+spectroscopy with the goal of discovering and characterizing cold exoplanets
+that are brightest in the thermal infrared. Additionally, SCALES has a 12x12""
+field-of-view imager that will be used for general adaptive optics science at
+Keck. We present SCALES's specifications, its science case, its overall design,
+and simulations of its expected performance. Additionally, we present progress
+on procuring, fabricating and testing long lead-time components.",2208.10721v1
+2022-09-06,Enhancement of spin-orbit torque efficiency by tailoring interfacial spin-orbit coupling in Pt-based magnetic multilayers,"We study inserting Co layer thickness-dependent spin transport and spin-orbit
+torques (SOTs) in the Pt/Co/Py trilayers by spin-torque ferromagnetic
+resonance. The interfacial perpendicular magnetic anisotropy energy density
+($K_s = 2.7~erg/cm^2$), which is dominated by interfacial spin-orbit coupling
+(ISOC) in the Pt/Co interface, total effective spin-mixing conductance
+($G_{eff,tot} = 0.42 {\times} 10^{15}~{\Omega}^{-1} m^{-2}$) and two-magnon
+scattering (${\beta}_{TMS} = 0.46~nm^2$) are first characterized, and the
+damping-like torque (${\xi}_{DL}$ = 0.103) and field-like torque (${\xi}_{FL}$
+= -0.017) efficiencies are also calculated quantitatively by varying the
+thickness of the inserting Co layer. The significant enhancement of
+${\xi}_{DL}$ and ${\xi}_{FL}$ in Pt/Co/Py than Pt/Py bilayer system originates
+from the interfacial Rashba-Edelstein effect due to the strong ISOC between
+Co-3d and Pt-5d orbitals at the Pt/Co interface. Additionally, we find a
+considerable out-of-plane spin polarization SOT, which is ascribed to the spin
+anomalous Hall effect and possible spin precession effect due to IPMA-induced
+perpendicular magnetization at the Pt/Co interface. Our results demonstrate
+that the ISOC of the Pt/Co interface plays a vital role in spin transport and
+SOTs-generation. Our finds offer an alternative approach to improve the
+conventional SOTs efficiencies and generate unconventional SOTs with
+out-of-plane spin polarization to develop low power Pt-based spintronic via
+tailoring the Pt/FM interface.",2209.02282v1
+2022-10-20,Ultrafast behavior of induced and intrinsic magnetic moments in CoFeB/Pt bilayers probed by element-specific measurements in the extreme ultraviolet spectral range,"The ultrafast and element-specific response of magnetic systems containing
+ferromagnetic 3d transition metals and 4d/5d heavy metals is of interest both
+from a fundamental as well as an applied research perspective. However, to date
+no consensus about the main microscopic processes describing the interplay
+between intrinsic 3d and induced 4d/5d magnetic moments upon femtosecond laser
+excitation exist. In this work, we study the ultrafast response of CoFeB/Pt
+bilayers by probing element-specific, core-to-valence band transitions in the
+extreme ultraviolet spectral range using high harmonic radiation. We show that
+the combination of magnetic scattering simulations and analysis of the energy-
+and time-dependent magnetic asymmetries allows to accurately disentangle the
+element-specific response in spite of overlapping Co and Fe M$_{2,3}$ as well
+as Pt O$_{2,3}$ and N$_7$ resonances. We find a considerably smaller
+demagnetization time constant as well as much larger demagnetization amplitudes
+of the induced moment of Pt compared to the intrinsic moment of CoFeB. Our
+results are in agreement with enhanced spin-flip probabilities due to the high
+spin-orbit coupling localized at the heavy metal Pt, as well as with the
+recently formulated hypothesis that a laser generated, incoherent magnon
+population within the ferromagnetic film leads to an overproportional reduction
+of the induced magnetic moment of Pt.",2210.11390v3
+2022-10-25,Nuclear and magnetic spin structure of the antiferromagnetic triangular lattice compound LiCrTe$_2$ investigated by $μ^+$SR as well as neutron and X-ray diffraction,"Two$-$dimensional (2D) triangular lattices antiferromagnets (2D$-$TLA) often
+manifest intriguing physical and technological properties, due to the strong
+interplay between lattice geometry and electronic properties. The recently
+synthesized 2$-$dimensional transition metal dichalcogenide LiCrTe$_2$, being a
+2D$-$TLA, enriched the range of materials which can present such properties. In
+this work, muon spin rotation ($\mu^+$SR) and neutron powder diffraction (NPD)
+have been utilized to reveal the true magnetic nature and ground state of
+LiCrTe$_2$. From high$-$resolution NPD the magnetic spin order at
+base$-$temperature is not, as previously suggested, helical, but rather
+collinear antiferromagnetic (AFM) with ferromagnetic (FM) spin coupling within
+the $ab-$plane and AFM coupling along the $c-$axis. The ordered magnetic Cr
+moment is established as $\mu_{\rm Cr}=$ 2.36 $\mu_{\rm B}$. From detailed
+$\mu^+$SR measurements we observe an AFM ordering temperature $T_{\rm
+N}\approx$ 125 K. This value is remarkably higher than the one previously
+reported by magnetic bulk measurements. From $\mu^+$SR we are able to extract
+the magnetic order parameter, whose critical exponent allows us to categorize
+LiCrTe$_2$ in the 3D Heisenberg AFM universality class. Finally, by combining
+our magnetic studies with high$-$resolution synchrotron X$-$ray diffraction
+(XRD), we find a clear coupling between the nuclear and magnetic spin lattices.
+This suggests the possibility for a strong magnon$-$phonon coupling, similar to
+what has been previously observed in the closely related compound LiCrO$_2$.",2210.14079v1
+2022-11-03,Skyrmion Jellyfish in Driven Chiral Magnets,"Chiral magnets can host topological particles known as skyrmions, which carry
+an exactly quantised topological charge $Q=-1$. In the presence of an
+oscillating magnetic field ${\bf B}_1(t)$, a single skyrmion embedded in a
+ferromagnetic background will start to move with constant velocity ${\bf
+v}_{\text{trans}}$. The mechanism behind this motion is similar to the one used
+by a jellyfish when it swims through water. We show that the skyrmion's motion
+is a universal phenomenon, arising in any magnetic system with translational
+modes. By projecting the equation of motion onto the skyrmion's translational
+modes and going to quadratic order in ${\bf B}_1(t)$, we obtain an analytical
+expression for ${\bf v}_{\text{trans}}$ as a function of the system's linear
+response. The linear response and consequently ${\bf v}_{\text{trans}}$ are
+influenced by the skyrmion's internal modes and scattering states, as well as
+by the ferromagnetic background's Kittel mode. The direction and speed of ${\bf
+v}_{\text{trans}}$ can be controlled by changing the polarisation, frequency
+and phase of the driving field ${\bf B}_1(t)$. For systems with small Gilbert
+damping parameter $\alpha$, we identify two distinct physical mechanisms used
+by the skyrmion to move. At low driving frequencies, the skyrmion's motion is
+driven by friction, and $v_{\text{trans}}\sim\alpha$, whereas at higher
+frequencies above the ferromagnetic gap, the skyrmion moves by magnon emission,
+and $v_{\text{trans}}$ becomes independent of $\alpha$.",2211.01714v5
+2022-12-14,Method of difference-differential equations for some Bethe ansatz solvable models,"In studies of one-dimensional Bethe ansatz solvable models, a Fredholm
+integral equation of the second kind with a difference kernel on a finite
+interval often appears. This equation does not generally admit a closed-form
+solution and hence its analysis is quite complicated. Here we study a family of
+such equations concentrating on their moments. We find exact relations between
+the moments in the form of difference-differential equations. The latter
+results significantly advance the analysis, enabling one to practically
+determine all the moments from the explicit knowledge of the lowest one. As
+applications, first we study the moments of the quasimomentum distribution in
+the Lieb-Liniger model and find explicit analytical results. The latter moments
+determine several basic quantities, e.g., the $N$-body local correlation
+functions. We prove the equivalence between different expressions found in the
+literature for the three-body local correlation functions and find an exact
+result for the four-body local correlation function in terms of the moments of
+the quasimomentum distributions. We eventually find the analytical results for
+the three- and four-body correlation functions in the form of asymptotic series
+in the regimes of weak and strong interactions. Next, we study the exact form
+of the low-energy spectrum of a magnon (a polaron) excitation in the
+two-component Bose gas described by the Yang-Gaudin model. We find its explicit
+form, which depends on the moments of the quasimomentum distributions of the
+Lieb-Liniger model. Then, we address a seemingly unrelated problem of
+capacitance of a circular capacitor and express the exact result for the
+capacitance in the parametric form. In the most interesting case of short plate
+separations, the parametric form has a single logarithmic term. This should be
+contrasted with the explicit result that has a complicated structure of
+logarithms.",2212.07480v1
+2023-02-28,Quantifying interaction mechanism in infinite layer nickelate superconductors,"The relationship between the long-range antiferromagnetic order in cuprates
+and the high-temperature superconductivity in these compounds represents
+unresolved, nearly four-decades long scientific problem. Because recently
+discovered nickelate superconductors are crystallographical counterparts of
+cuprates, many properties and difficulties into describing these compounds are
+common to both families. Recently, Fowlie et al (2022 Nature Physics 18 1043)
+aimed to detect the antiferromagnetic order in $R_{1-x}Sr_{x}NiO_{2}$ (R = Nd,
+Pr, La, x ~ 0.2) films by using the muon spin rotation (muSR) technique. This
+research group reported on the existence of short-range antiferromagnetic order
+in all studied nickelates. Here, we aimed to reveal the existence of this
+interaction in the same nickelate films by analyzing the temperature dependent
+resistivity, $\rho(T)$, reported by the same research group. Global $\rho(T)$
+data fits to the advanced Bloch-Gr\""uneisen model showed that each of
+R1-xSrxNiO2 compounds can be characterized by a unique power-law exponent, p
+(where p=2 for the electron-electron scattering, p=3 for the electron-magnon
+scattering, and p=5 for the electron-phonon scattering), and global
+characteristic temperature, $T_{\omega}$ (which has the meaning of the Debye
+temperature at p=5). We found that p=2.0 in Nd- and Pr-based compounds, and
+p=1.3 for La-based compound. The latter value does not have any interpretation
+within established theoretical models. We also analyzed $\rho(T)$ data for
+$Nd_{1-x}Sr_{x}NiO_{2}$ (0.125 < x < 0.325) reported by Lee et al (2022
+arXiv2203.02580). Because our analysis showed that p-values in nickelates are
+remarkably different from p=3, we call for the developent of a new theoretical
+model to describe $\rho(T)$ in materials exhibiting a short-range
+antiferromagnetic order.",2302.14729v3
+2023-03-13,Unusual magnetotransport and anomalous Hall effect in quasi-two-dimensional van der Waals ferromagnet Fe$_4$GeTe$_2$,"Fe$_4$GeTe$_2$, an itinerant vdW ferromagnet (FM) having Curie temperature
+(T$_C$) close to room temperature ($\sim 270$ K), exhibits another transition
+(T$_{SR}$ $\sim$ 120 K) where the easy axis of magnetization changes from
+in-plane to the out-of-plane direction in addition to T$_C$. Here, we have
+studied the magnetotransport in a multilayer Hall bar device fabricated on 300
+nm Si/SiO$_2$ substrate. Interestingly, the zero field resistivity shows a
+negligible change in resistivity near T$_C$ unlike the typical metallic FM,
+whereas, it exhibits a dramatic fall below T$_{SR}$. Also, the resistivity
+shows a weak anomaly at T $ \sim $ 38 K (T$_Q$), below which the resistivity
+shows a quadratic temperature dependence according to the Fermi liquid
+behavior. Temperature-dependent Hall data exhibits important consequences. The
+ordinary Hall coefficient changes sign near T$_{SR}$ indicating the change in
+majority carriers. In a similar manner, the magnetoresistance (MR) data shows
+significantly large negative MR near T$_{SR}$ and becomes positive below T$_Q$.
+The observations of anomaly in the resistivity, sign-change of the ordinary
+Hall coefficient and maximum negative MR near T$_{SR}$, together suggest a
+possible Fermi surface reconstruction associated with the spin reorientation
+transition. Furthermore, analysis of the Hall data reveals a significant
+anomalous Hall conductivity (AHC) from $\sim 123 \Omega^{-1}$ cm$^{-1}$ (at T
+$\approx$ 5 K) to the maximum value of $\sim 366 \Omega^{-1}$ cm$^{-1}$ near
+T$_{SR}$. While the low-temperature part may originate due to the intrinsic KL
+mechanism, our analysis indicates that the temperature-dependent AHC is
+primarily appearing due to the side-jump mechanism as a result of the spin-flip
+electron-magnon scattering. Our study demonstrates an interplay between
+magnetism and band topology and its consequence on electron transport in
+Fe$_4$GeTe$_2$.",2303.07440v1
+2023-05-05,Spin-phonon scattering-induced low thermal conductivity in a van der Waals layered ferromagnet Cr$_2$Si$_2$Te$_6$,"Layered van der Waals (vdW) magnets are prominent playgrounds for developing
+magnetoelectric, magneto-optic and spintronic devices. In spintronics,
+particularly in spincaloritronic applications, low thermal conductivity
+($\kappa$) is highly desired. Here, by combining thermal transport measurements
+with density functional theory calculations, we demonstrate low $\kappa$ down
+to 1 W m$^{-1}$ K$^{-1}$ in a typical vdW ferromagnet Cr$_2$Si$_2$Te$_6$. In
+the paramagnetic state, development of magnetic fluctuations way above
+$T_\mathrm{c}=$ 33 K strongly reduces $\kappa$ via spin-phonon scattering,
+leading to low $\kappa \sim$ 1 W m$^{-1}$ K$^{-1}$ over a wide temperature
+range, in comparable to that of amorphous silica. In the magnetically ordered
+state, emergence of resonant magnon-phonon scattering limits $\kappa$ below
+$\sim$ 2 W m$^{-1}$ K$^{-1}$, which would be three times larger if magnetic
+scatterings were absent. Application of magnetic fields strongly suppresses the
+spin-phonon scattering, giving rise to large enhancements of $\kappa$. Our
+calculations well capture these complex behaviours of $\kappa$ by taking the
+temperature- and magnetic-field-dependent spin-phonon scattering into account.
+Realization of low $\kappa$ which is easily tunable by magnetic fields in
+Cr$_2$Si$_2$Te$_6$, may further promote spincaloritronic applications of vdW
+magnets. Our theoretical approach may also provide a generic understanding of
+spin-phonon scattering, which appears to play important roles in various
+systems.",2305.13268v1
+2023-06-01,Large Charge 't Hooft Limit of $\mathcal{N}=4$ Super-Yang-Mills,"The planar integrability of $\mathcal{N}=4$ super-Yang-Mills (SYM) is the
+cornerstone for numerous exact observables. We show that the large charge
+sector of the ${\rm SU}(2)$ $\mathcal{N}=4$ SYM provides another interesting
+solvable corner which exhibits striking similarities despite being far from the
+planar limit. We study non-BPS operators obtained by small deformations of
+half-BPS operators with $R$-charge $J$ in the limit $J\to\infty$ with
+$\lambda_{J}\equiv g_{\rm YM}^2 J/2$ fixed. The dynamics in this {\it large
+charge 't Hooft limit} is constrained by a centrally-extended
+$\mathfrak{psu}(2|2)^2$ symmetry that played a crucial role for the planar
+integrability. To the leading order in $1/J$, the spectrum is fully fixed by
+this symmetry, manifesting the magnon dispersion relation familiar from the
+planar limit, while it is constrained up to a few constants at the next order.
+We also determine the structure constant of two large charge operators and the
+Konishi operator, revealing a rich structure interpolating between the
+perturbative series at weak coupling and the worldline instantons at strong
+coupling. In addition we compute heavy-heavy-light-light (HHLL) four-point
+functions of half-BPS operators in terms of resummed conformal integrals and
+recast them into an integral form reminiscent of the hexagon formalism in the
+planar limit. For general ${\rm SU}(N)$ gauge groups, we study integrated HHLL
+correlators by supersymmetric localization and identify a dual matrix model of
+size $J/2$ that reproduces our large charge result at $N=2$. Finally we discuss
+a relation to the physics on the Coulomb branch and explain how the dilaton
+Ward identity emerges from a limit of the conformal block expansion. We comment
+on generalizations including the large spin 't Hooft limit, the combined large
+$N$-large $J$ limits, and applications to general $\mathcal{N}=2$
+superconformal field theories.",2306.00929v1
+2023-06-09,Coexistence of symmetry-protected topological order and Neel order in the spin-1/2 ladder antiferromagnet C9H18N2CuBr4,"Topological phases of matter are beyond the paradigm of Landau's symmetry
+breaking and have challenged our understanding of condensed matter systems.
+Here we report a new type of symmetry-protected topological phase of matter in
+the spin-1/2 coupled two-leg ladder antiferromagnet C9H18N2CuBr4, DLCB for
+short. In this two-sublattice antiferromagnet with a weak easy-axis anisotropy,
+we find no evidence of a conventional spin-flop transition in the magnetization
+with the magnetic field applied parallel to the easy axis at T=0.4 K, well
+below TN=2.0 K. Moreover, the temperature dependence of the gapped transverse
+excitations across TN indicates that they are not the conventional S=1 magnons
+associated with explicit symmetry breaking. Instead, the thermal
+renormalization of the gap energy shows a remarkable agreement with a
+calculation for the three-dimensional O(3) nonlinear sigma model. Accordingly,
+the spin gap in DLCB is not due to the spin anisotropy but to the separation
+between a spin singlet state and a triplet excited state. Since an
+antiferromagnetic spin-1/2 ladder systems can be mapped onto the spin-1 chain,
+the notion of the Haldane gap is proposed to explain the opening of the spin
+gap in DLCB. Therefore, the ground state of DLCB is best described as a quantum
+superposition of a Haldane phase and a Neel-ordered phase, which resembles the
+quantum state of a qubit in quantum computing. Our results indicate the
+presence of a symmetry-protected topological order coexisting with an
+antiferromagnetic order in this material.",2306.06021v3
+2023-06-22,"Gilbert damping in metallic ferromagnets from Schwinger-Keldysh field theory: Intrinsically nonlocal and nonuniform, and made anisotropic by spin-orbit coupling","Understanding the origin of damping mechanisms in magnetization dynamics of
+metallic ferromagnets is a fundamental problem for nonequilibrium many-body
+physics of systems where quantum conduction electrons interact with localized
+spins assumed to be governed by the classical Landau-Lifshitz-Gilbert (LLG)
+equation. It is also of critical importance for applications, as damping
+affects energy consumption and speed of spintronic and magnonic devices. Since
+the 1970s, a variety of linear-response and scattering theory approaches have
+been developed to produce widely used formulas for computation of
+spatially-independent Gilbert scalar parameter as the magnitude of the Gilbert
+damping term in the LLG equation. The largely unexploited for this purpose
+Schwinger-Keldysh field theory (SKFT) offers additional possibilities, such as
+to rigorously derive an extended LLG equation by integrating quantum electrons
+out. Here we derive such equation whose Gilbert damping for metallic
+ferromagnets is nonlocal, i.e., dependent on all localized spins at a given
+time, and nonuniform, even if all localized spins are collinear and spin-orbit
+coupling (SOC) is absent. This is in sharp contrast to standard lore, where
+nonlocal damping is considered to emerge only if localized spins are
+noncollinear; for such situations, direct comparison on the example of magnetic
+domain wall shows that SKFT-derived nonlocal damping is an order of magnitude
+larger than the previously considered one. Switching on SOC makes such nonlocal
+damping anisotropic, in contrast to standard lore where SOC is usually
+necessary to obtain nonzero Gilbert damping scalar parameter. Our analytical
+formulas, with their nonlocality being more prominent in low spatial
+dimensions, are fully corroborated by numerically exact quantum-classical
+simulations.",2306.13013v4
+2023-10-02,Quantum spin nematic phase in a square-lattice iridate,"Spin nematic (SN) is a magnetic analog of classical liquid crystals, a fourth
+state of matter exhibiting characteristics of both liquid and solid.
+Particularly intriguing is a valence-bond SN, in which spins are quantum
+entangled to form a multi-polar order without breaking time-reversal symmetry,
+but its unambiguous experimental realization remains elusive. Here, we
+establish a SN phase in the square-lattice iridate Sr$_2$IrO$_4$, which
+approximately realizes a pseudospin one-half Heisenberg antiferromagnet (AF) in
+the strong spin-orbit coupling limit. Upon cooling, the transition into the SN
+phase at T$_C$ $\approx$ 263 K is marked by a divergence in the static spin
+quadrupole susceptibility extracted from our Raman spectra, and concomitant
+emergence of a collective mode associated with the spontaneous breaking of
+rotational symmetries. The quadrupolar order persists in the antiferromagnetic
+(AF) phase below T$_N$ $\approx$ 230 K, and becomes directly observable through
+its interference with the AF order in resonant x-ray diffraction, which allows
+us to uniquely determine its spatial structure. Further, we find using resonant
+inelastic x-ray scattering a complete breakdown of coherent magnon excitations
+at short-wavelength scales, suggesting a resonating-valence-bond-like quantum
+entanglement in the AF state. Taken together, our results reveal a quantum
+order underlying the N\'eel AF that is widely believed to be intimately
+connected to the mechanism of high temperature superconductivity (HTSC).",2310.00886v2
+2023-11-20,Electrical control of magnetism by electric field and current-induced torques,"While early magnetic memory designs relied on magnetization switching by
+locally generated magnetic fields, key insights in condensed matter physics
+later suggested the possibility to do it electrically. In the 1990s,
+Slonczewzki and Berger formulated the concept of current-induced spin torques
+in magnetic multilayers through which a spin-polarized current may switch the
+magnetization of a ferromagnet. This discovery drove the development of
+spin-transfer-torque magnetic random-access memories (STT-MRAMs). More recent
+research unveiled spin-orbit-torques (SOTs) and will lead to a new generation
+of devices including SOT-MRAMs. Parallel to these advances, multiferroics and
+their magnetoelectric coupling experienced a renaissance, leading to novel
+device concepts for information and communication technology such as the MESO
+transistor. The story of the electrical control of magnetization is that of a
+dance between fundamental research (in spintronics, condensed matter physics,
+and materials science) and technology (MRAMs, MESO, microwave emitters,
+spin-diodes, skyrmion-based devices, components for neuromorphics, etc). This
+pas de deux led to major breakthroughs over the last decades (pure spin
+currents, magnetic skyrmions, spin-charge interconversion, etc). As a result,
+this field has propelled MRAMs into consumer electronics products but also
+fueled discoveries in adjacent research areas such as ferroelectrics or
+magnonics. Here, we cover recent advances in the control of magnetism by
+electric fields and by current-induced torques. We first review fundamental
+concepts in these two directions, then discuss their combination, and finally
+present various families of devices harnessing the electrical control of
+magnetic properties for various application fields. We conclude by giving
+perspectives in terms of both emerging fundamental physics concepts and new
+directions in materials science.",2311.11724v1
+2023-12-18,"Moiré Fractional Chern Insulators III: Hartree-Fock Phase Diagram, Magic Angle Regime for Chern Insulator States, the Role of the Moiré Potential and Goldstone Gaps in Rhombohedral Graphene Superlattices","We investigate in detail the $\nu=+1$ displacement-field-tuned interacting
+phase diagram of $L=3,4,5,6,7$ layer rhombohedral graphene aligned to hBN
+(R$L$G/hBN). Our calculations account for the 3D nature of the Coulomb
+interaction, the inequivalent stacking orientations $\xi=0,1$, the effects of
+the filled valence bands, and the choice of `interaction scheme' for specifying
+the many-body Hamiltonian. We show that the latter has a dramatic impact on the
+Hartree-Fock phase boundaries and the properties of the phases, including for
+pentalayers (R5G/hBN) with large displacement field $D$ where recent
+experiments observed a Chern insulator at $\nu=+1$ and fractional Chern
+insulators for $\nu<1$. In this large $D$ regime, the low-energy conduction
+bands are polarized away from the aligned hBN layer, and are hence
+well-described by the folded bands of moir\'eless rhombohedral graphene at the
+non-interacting level. Despite this, the filled valence bands develop
+moir\'e-periodic charge density variations which can generate an effective
+moir\'e potential, thereby explicitly breaking the approximate continuous
+translation symmetry in the conduction bands, and leading to contrasting
+electronic topology in the ground state for the two stacking arrangements.
+Within time-dependent Hartree-Fock theory, we further characterize the strength
+of the moir\'e pinning potential in the Chern insulator phase by computing the
+low-energy $\mathbf{q}=0$ collective mode spectrum, where we identify competing
+gapped pseudophonon and valley magnon excitations. Our results emphasize the
+importance of careful examination of both the single-particle and interaction
+model for a proper understanding of the correlated phases in R$L$G/hBN.",2312.11617v1
+2023-12-18,"Twisted van der Waals Quantum Materials: Fundamentals, Tunability and Applications","Twisted vdW quantum materials have emerged as a rapidly developing field of
+2D semiconductors. These materials establish a new central research area and
+provide a promising platform for studying quantum phenomena and investigating
+the engineering of novel optoelectronic properties such as single-photon
+emission, non-linear optical response, magnon physics, and topological
+superconductivity. These captivating electronic and optical properties result
+from, and can be tailored by, the interlayer coupling using moir\'e patterns
+formed by vertically stacking atomic layers with controlled angle
+misorientation or lattice mismatch. Their outstanding properties and the high
+degree of tunability position them as compelling building blocks for both
+compact quantum-enabled devices and classical optoelectronics. This article
+offers a comprehensive review of recent advancements in the understanding and
+manipulation of twisted van der Waals structures and presents a survey of the
+state-of-the-art research on moir\'e superlattices, encompassing
+interdisciplinary interests. It delves into fundamental theories, synthesis and
+fabrication, and visualization techniques, and the wide range of novel physical
+phenomena exhibited by these structures, with a focus on their potential for
+practical device integration in applications ranging from quantum information
+to biosensors, and including classical optoelectronics such as modulators,
+light emitting diodes (LEDs), lasers, and photodetectors. It highlights the
+unique ability of moir\'e superlattices to connect multiple disciplines,
+covering chemistry, electronics, optics, photonics, magnetism, topological and
+quantum physics. This comprehensive review provides a valuable resource for
+researchers interested in moir\'e superlattices, shedding light on their
+fundamental characteristics and their potential for transformative applications
+in various fields.",2312.11757v1
+2024-03-01,Emergence of interfacial magnetism in strongly-correlated nickelate-titanate superlattices,"Strongly-correlated transition-metal oxides are widely known for their
+various exotic phenomena. This is exemplified by rare-earth nickelates such as
+LaNiO$_{3}$, which possess intimate interconnections between their electronic,
+spin, and lattice degrees of freedom. Their properties can be further enhanced
+by pairing them in hybrid heterostructures, which can lead to hidden phases and
+emergent phenomena. An important example is the LaNiO$_{3}$/LaTiO$_{3}$
+superlattice, where an interlayer electron transfer has been observed from
+LaTiO$_{3}$ into LaNiO$_{3}$ and is predicted to result in a high-spin state.
+However, macroscopic emergence of magnetic order has so far not been observed.
+Here, by using muon spin rotation, x-ray absorption, and resonant inelastic
+x-ray scattering, we present direct evidence of an emergent antiferromagnetic
+order with high magnon energy and exchange interactions at the
+LaNiO$_{3}$/LaTiO$_{3}$ interface. As the magnetism is purely interfacial, a
+single LaNiO$_{3}$/LaTiO$_{3}$ interface can essentially behave as an
+atomically thin quasi-two-dimensional antiferromagnet, potentially allowing its
+technological utilisation in advanced spintronic devices. Furthermore, its
+strong quasi-two-dimensional magnetic correlations and orbitally-polarized
+planar ligand holes make its electronic and magnetic configurations resemble
+the precursor states of superconducting cuprates and nickelates, but with an S
+$\rightarrow$ 1 spin state instead.",2403.00728v1
+2024-04-03,Unraveling the Mn $L_3$-edge RIXS spectrum of lightly manganese doped Sr$_{3}$Ru$_{2}$O$_{7}$,"Resonant inelastic x-ray scattering (RIXS) experiment was performed at the Mn
+$L_3$ edge. A 10 $\%$ Mn-doped Sr$_{3}$Ru$_{2}$O$_{7}$ compound, where the
+Mn$^{3+}$ ions are in the 3$d^4$ state, were probed for $dd$ excitations. The
+dilute doping concentration allows one to treat the dopant Mn$^{3+}$ ions as
+effectively free in the host ruthenium compound. The local nature of $dd$ RIXS
+spectroscopy permits one to use a single-site model to simulate the
+experimental spectra. The simulated spectra reproduces the in-plane [100]
+experimental RIXS spectrum. We also predict the intensity for the in-plane
+[110] direction and the out-of-plane spin orientation configuration [001].
+Based on our single-ion model we were able to fit the experimental data to
+obtain the crystal field parameters, the 10Dq value, and the intra-orbital
+spin-flip energy 2$\mathcal{J}$(or $3J_{H}$, where $J_{H}$ is the Hund's
+energy) of the Mn$^{3+}$ ion. Utilizing our computed RIXS quantum transition
+amplitudes between the various $d$ orbitals of the Mn$^{3+}$ ion, the
+expression for the Kramers-Heisenberg cross section, and a self-consistent
+fitting procedure we also identify the energy boundaries of the non-spin-flip
+and spin-flip $dd$ excitations present in the experimental data. From our
+fitting procedure we obtain $2\mathcal{J} (3J_{H})=2.06$ eV, a value which is
+in excellent agreement with that computed from the free ion Racah parameters.
+We also identified the charge transfer boundary. In addition to predicting the
+microscopic parameters, we find a quantum spin-flip transition in the non-cross
+($\sigma_{in}-\sigma_{out}$, $\pi_{in}-\pi_{out}$) x-ray polarization channels
+of the $dd$ RIXS spectra. A similar transition, was previously predicted to
+occur in the $\pi-\pi$ channel of the magnon spectrum in the non-collinear
+non-coplanar Kagome compound composed of Cu$^{2+}$ 3d$^{9}$ ion.",2404.02963v1
+2014-07-09,The Integral Field Spectrograph for the Gemini Planet Imager,"The Gemini Planet Imager (GPI) is a complex optical system designed to
+directly detect the self-emission of young planets within two arcseconds of
+their host stars. After suppressing the starlight with an advanced AO system
+and apodized coronagraph, the dominant residual contamination in the focal
+plane are speckles from the atmosphere and optical surfaces. Since speckles are
+diffractive in nature their positions in the field are strongly wavelength
+dependent, while an actual companion planet will remain at fixed separation. By
+comparing multiple images at different wavelengths taken simultaneously, we can
+freeze the speckle pattern and extract the planet light adding an order of
+magnitude of contrast. To achieve a bandpass of 20%, sufficient to perform
+speckle suppression, and to observe the entire two arcsecond field of view at
+diffraction limited sampling, we designed and built an integral field
+spectrograph with extremely low wavefront error and almost no chromatic
+aberration. The spectrograph is fully cryogenic and operates in the wavelength
+range 1 to 2.4 microns with five selectable filters. A prism is used to produce
+a spectral resolution of 45 in the primary detection band and maintain high
+throughput. Based on the OSIRIS spectrograph at Keck, we selected to use a
+lenslet-based spectrograph to achieve an rms wavefront error of approximately
+25 nm. Over 36,000 spectra are taken simultaneously and reassembled into image
+cubes that have roughly 192x192 spatial elements and contain between 11 and 20
+spectral channels. The primary dispersion prism can be replaced with a
+Wollaston prism for dual polarization measurements. The spectrograph also has a
+pupil-viewing mode for alignment and calibration.",1407.2314v1
+2023-09-20,The development of HISPEC for Keck and MODHIS for TMT: science cases and predicted sensitivities,"HISPEC is a new, high-resolution near-infrared spectrograph being designed
+for the W.M. Keck II telescope. By offering single-shot, R=100,000 between 0.98
+- 2.5 um, HISPEC will enable spectroscopy of transiting and non-transiting
+exoplanets in close orbits, direct high-contrast detection and spectroscopy of
+spatially separated substellar companions, and exoplanet dynamical mass and
+orbit measurements using precision radial velocity monitoring calibrated with a
+suite of state-of-the-art absolute and relative wavelength references. MODHIS
+is the counterpart to HISPEC for the Thirty Meter Telescope and is being
+developed in parallel with similar scientific goals. In this proceeding, we
+provide a brief overview of the current design of both instruments, and the
+requirements for the two spectrographs as guided by the scientific goals for
+each. We then outline the current science case for HISPEC and MODHIS, with
+focuses on the science enabled for exoplanet discovery and characterization. We
+also provide updated sensitivity curves for both instruments, in terms of both
+signal-to-noise ratio and predicted radial velocity precision.",2309.11050v1
+2012-02-18,Leading order determination of the gluon polarisation from DIS events with high-p_T hadron pairs,"We present a determination of the gluon polarisation Delta g/g in the
+nucleon, based on the longitudinal double-spin asymmetry of DIS events with a
+pair of large transverse-momentum hadrons in the final state. The data were
+obtained by the COMPASS experiment at CERN using a 160 GeV/c polarised muon
+beam scattering off a polarised ^6LiD target. The gluon polarisation is
+evaluated by a Neural Network approach for three intervals of the gluon
+momentum fraction x_g covering the range 0.04 < x_g < 0.27. The values obtained
+at leading order in QCD do not show any significant dependence on x_g. Their
+average is Delta g/g = 0.125 +/- 0.060 (stat.) +/- 0.063 (syst.) at x_g=0.09
+and a scale of mu^2 = 3 (GeV/c)^2.",1202.4064v1
+2012-02-28,Transverse spin effects in hadron-pair production from semi-inclusive deep inelastic scattering,"First measurements of azimuthal asymmetries in hadron-pair production in
+deep-inelastic scattering of muons on transversely polarised ^6LiD (deuteron)
+and NH_3 (proton) targets are presented. The data were taken in the years
+2002-2004 and 2007 with the COMPASS spectrometer using a muon beam of 160 GeV/c
+at the CERN SPS. The asymmetries provide access to the transversity
+distribution functions, without involving the Collins effect as in single
+hadron production. The sizeable asymmetries measured on the NH_ target indicate
+non-vanishing u-quark transversity and two-hadron interference fragmentation
+functions. The small asymmetries measured on the ^6LiD target can be
+interpreted as indication for a cancellation of u- and d-quark transversities.",1202.6150v2
+2012-07-09,Measurement of the Cross Section for High-p_T Hadron Production in Scattering of 160 GeV/c Muons off Nucleons,"The differential cross section for production of charged hadrons with high
+transverse momenta in scattering of 160\,GeV/$c$ muons off nucleons at low
+photon virtualities has been measured at the COMPASS experiment at CERN. The
+results, which cover transverse momenta from 1.1\,GeV/$c$ to 3.6\,GeV/$c$, are
+compared to a perturbative Quantum Chromodynamics (pQCD) calculation, in order
+to evaluate the applicability of pQCD to this process in the kinematic domain
+of the experiment. The shape of the calculated differential cross section as a
+function of transverse momentum is found to be in good agreement with the
+experimental data, but the absolute scale is underestimated by next-to-leading
+order (NLO) pQCD. The inclusion of all-order resummation of large logarithmic
+threshold corrections reduces the discrepancy from a factor of three to four to
+a factor of two. The dependence of the cross section on the pseudo-rapidity and
+on virtual photon energy fraction is investigated. Finally the dependence on
+the charge of the hadrons is discussed.",1207.2022v2
+2012-07-18,Exclusive rho^0 muoproduction on transversely polarised protons and deuterons,"The transverse target spin azimuthal asymmetry A_UT in hard exclusive
+production of rho^0 mesons was measured at COMPASS by scattering 160 GeV/c
+muons off transversely polarised protons and deuterons. The measured asymmetry
+is sensitive to the nucleon helicity-flip generalised parton distributions E^q,
+which are related to the orbital angular momentum of quarks in the nucleon. The
+Q^2, x_B and p_t^2 dependence of A_UT is presented in a wide kinematic range.
+Results for deuterons are obtained for the first time. The measured asymmetry
+is small in the whole kinematic range for both protons and deuterons, which is
+consistent with the theoretical interpretation that contributions from GPDs E^u
+and E^d approximately cancel.",1207.4301v2
+2012-11-07,D* and D Meson Production in Muon Nucleon Interactions at 160 GeV/c,"The production of D* and D mesons in inelastic scattering of 160 GeV/c muons
+off a ^6LiD target has been investigated with the COMPASS spectrometer at CERN
+for 0.003 (GeV/c)^2 < Q^2 < 10 (GeV/c)^2 and 3x10^-5< x_Bj < 0.1. The study is
+based on 8100 events where a D^0 or anti D^0 is detected subsequently to a D*+
+or D*- decay, and on 34000 events, where only a D^0 or anti D^0 is detected.
+Kinematic distributions of D*, D and K*_2 are given as a function of their
+energy E, transverse momentum p_T, energy fraction z, and of the virtual photon
+variables nu, Q^2 and x_Bj. Semi-inclusive differential D* production
+cross-sections are compared with theoretical predictions for D* production via
+photon-gluon fusion into open charm. The total observed production
+cross-section for D*+/- mesons with laboratory energies between 22 and 86 GeV
+is 1.9 nb. Significant cross-section asymmetries are observed between D*+ and
+D*- production for nu<40 GeV and z>0.6.",1211.1575v2
+2012-11-29,Leading and Next-to-Leading Order Gluon Polarisation in the Nucleon and Longitudinal Double Spin Asymmetries from Open Charm Muoproduction,"The gluon polarisation in the nucleon was measured using open charm
+production by scattering 160 GeV/c polarised muons off longitudinally polarised
+protons or deuterons. The data were taken by the COMPASS collaboration between
+2002 and 2007. A detailed account is given of the analysis method that includes
+the application of neural networks. Several decay channels of D^0 mesons are
+investigated. Longitudinal spin asymmetries of the D meson production
+cross-sections are extracted in bins of D^0 transverse momentum and energy. At
+leading order QCD accuracy the average gluon polarisation is determined as
+(Delta g/G)^LO=-0.06 +/- 0.21 (stat.) +/- 0.08 (syst.) at the scale <mu^2> ~13
+(GeV/c)^2 and an average gluon momentum fraction <x>~ 0.11. For the first time,
+the average gluon polarisation is also obtained at next-to-leading order QCD
+accuracy as (Delta g/G)^NLO = -0.13 +/- 0.15 (stat.) +/- 0.15 (syst.) at the
+scale <mu^2> ~ 13 (\GeV/c)^2 and <x> ~ 0.20.",1211.6849v2
+2013-04-03,Study of Σ(1385) and Ξ(1321) hyperon and antihyperon production in deep inelastic muon scattering,"Large samples of \Lambda, \Sigma(1385) and \Xi(1321) hyperons produced in
+deep-inelastic muon scattering off a ^6LiD target were collected with the
+COMPASS experimental setup at CERN. The relative yields of \Sigma(1385)^+,
+\Sigma(1385)^-, \bar{\Sigma}(1385)^-, \bar{\Sigma}(1385)^+, \Xi(1321)^-, and
+\bar{\Xi}(1321)^+ hyperons decaying into \Lambda(\bar{\Lambda})\pi were
+measured. The heavy hyperon to \Lambda and heavy antihyperon to \bar{\Lambda}
+yield ratios were found to be in the range 3.8% to 5.6% with a relative
+uncertainty of about 10%. They were used to tune the parameters relevant for
+strange particle production of the LEPTO Monte Carlo generator.",1304.0952v2
+2013-05-31,Hadron Transverse Momentum Distributions in Muon Deep Inelastic Scattering at 160 GeV/$c$,"Multiplicities of charged hadrons produced in deep inelastic muon scattering
+off a $^6$LiD target have been measured as a function of the DIS variables
+$x_{Bj}$, $Q^2$, $W^2$ and the final state hadron variables $p_T$ and $z$. The
+$p_T^2$ distributions are fitted with a single exponential function at low
+values of $p_T^2$ to determine the dependence of $\langle p_T^2 \rangle$ on
+$x_{Bj}$, $Q^2$, $W^2$ and $z$. The $z$-dependence of $\langle p_T^2 \rangle$
+is shown to be a potential tool to extract the average intrinsic transverse
+momentum squared of partons, $\langle k_{\perp}^2 \rangle$, as a function of
+$x_{Bj}$ and $Q^2$ in a leading order QCD parton model.",1305.7317v1
+2013-10-05,Transverse target spin asymmetries in exclusive $ρ^0$ muoproduction,"Exclusive production of $\rho^0$ mesons was studied at the COMPASS experiment
+by scattering 160 GeV/$c$ muons off transversely polarised protons. Five
+single-spin and three double-spin azimuthal asymmetries were measured as a
+function of $Q^2$, $x_{Bj}$, or $p_{T}^{2}$. The $\sin \phi_S$ asymmetry is
+found to be $-0.019 \pm 0.008(stat.) \pm 0.003(syst.)$. All other asymmetries
+are also found to be of small magnitude and consistent with zero within
+experimental uncertainties. Very recent calculations using a GPD-based model
+agree well with the present results. The data is interpreted as evidence for
+the existence of chiral-odd, transverse generalized parton distributions.",1310.1454v2
+2014-01-24,Measurement of azimuthal hadron asymmetries in semi-inclusive deep inelastic scattering off unpolarised nucleons,"Spin-averaged asymmetries in the azimuthal distributions of positive and
+negative hadrons produced in deep inelastic scattering were measured using the
+CERN SPS muon beam at $160$ GeV/c and a $^6$LiD target. The amplitudes of the
+three azimuthal modulations $\cos\phi_h$, $\cos2\phi_h$ and $\sin\phi_h$ were
+obtained binning the data separately in each of the relevant kinematic
+variables $x$, $z$ or $p_T^{\,h}$ and binning in a three-dimensional grid of
+these three variables. The amplitudes of the $\cos \phi_h$ and $\cos 2\phi_h$
+modulations show strong kinematic dependencies both for positive and negative
+hadrons.",1401.6284v1
+2014-01-30,A high-statistics measurement of transverse spin effects in dihadron production from muon-proton semi-inclusive deep-inelastic scattering,"A measurement of the azimuthal asymmetry in dihadron production in
+deep-inelastic scattering of muons on transversely polarised proton (NH$_{3}$)
+targets are presented. They provide independent access to the transversity
+distribution functions through the measurement of the Collins asymmetry in
+single hadron production. The data were taken in the year $2010$ with the
+COMPASS spectrometer using a $160\,\mbox{GeV}/c$ muon beam of the CERN SPS,
+increasing by a factor of about three the available statistics of the
+previously published data taken in the year $2007$. The measured sizeable
+asymmetry is in good agreement with the published data. An approximate equality
+of the Collins asymmetry and the dihadron asymmetry is observed, suggesting a
+common physical mechanism in the underlying fragmentation.",1401.7873v1
+2014-07-23,Search for exclusive photoproduction of Z$_c^{\pm}$(3900) at COMPASS,"A search for the exclusive production of the $Z_c^{\pm}(3900)$ hadron by
+virtual photons has been performed in the channel $Z_c^{\pm}(3900)\rightarrow
+J/\psi \pi^{\pm}$. The data cover the range from 7 GeV to 19 GeV in the
+centre-of-mass energy of the photon-nucleon system. The full set of the COMPASS
+data set collected with a muon beam between 2002 and 2011 has been used. An
+upper limit for the ratio $BR(Z_c^{\pm}(3900)\rightarrow J/\psi \pi^{\pm}
+)\times \sigma_{
+  \gamma~N \rightarrow Z_c^{\pm}(3900)~ N} /\sigma_{\gamma~N \rightarrow
+  J/\psi~ N}$ of $3.7\times10^{-3}$ has been established at the confidence
+level of 90%.",1407.6186v1
+2014-08-19,"Odd and Even Partial Waves of $ηπ^-$ and $η'π^-$ in $π^-p\toη^{(\prime)}π^-p$ at $191\,\textrm{GeV}/c$","Exclusive production of $\eta\pi^-$ and $\eta'\pi^-$ has been studied with a
+$191\,\textrm{GeV}/c$ $\pi^-$ beam impinging on a hydrogen target at COMPASS
+(CERN). Partial-wave analyses reveal different odd/even angular momentum ($L$)
+characteristics in the inspected invariant mass range up to
+$3\,\textrm{GeV}/c^2$. A striking similarity between the two systems is
+observed for the $L=2,4,6$ intensities (scaled by kinematical factors) and the
+relative phases. The known resonances $a_2(1320)$ and $a_4(2040)$ are in line
+with this similarity. In contrast, a strong enhancement of $\eta'\pi^-$ over
+$\eta\pi^-$ is found for the $L=1,3,5$ waves, which carry non-$q\bar q$ quantum
+numbers. The $L=1$ intensity peaks at $1.7\,\textrm{GeV}/c^2$ in $\eta'\pi^-$
+and at $1.4\,\textrm{GeV}/c^2$ in $\eta\pi^-$, the corresponding phase motions
+with respect to $L=2$ are different.",1408.4286v1
+2014-08-19,Collins and Sivers asymmetries in muonproduction of pions and kaons off transversely polarised proton,"Measurements of the Collins and Sivers asymmetries for charged pions and
+charged and neutral kaons produced in semi-inclusive deep-inelastic scattering
+of high energy muons off transversely polarised protons are presented. The
+results were obtained using all the available COMPASS proton data, which were
+taken in the years 2007 and 2010. The Collins asymmetries exhibit in the
+valence region a non-zero signal for pions and there are hints of non-zero
+signal also for kaons. The Sivers asymmetries are found to be positive for
+positive pions and kaons and compatible with zero otherwise.",1408.4405v1
+2014-10-07,The COMPASS Setup for Physics with Hadron Beams,"The main characteristics of the COMPASS experimental setup for physics with
+hadron beams are described. This setup was designed to perform exclusive
+measurements of processes with several charged and/or neutral particles in the
+final state. Making use of a large part of the apparatus that was previously
+built for spin structure studies with a muon beam, it also features a new
+target system as well as new or upgraded detectors. The hadron setup is able to
+operate at the high incident hadron flux available at CERN. It is characterised
+by large angular and momentum coverages, large and nearly flat acceptances, and
+good two and three-particle mass resolutions. In 2008 and 2009 it was
+successfully used with positive and negative hadron beams and with liquid
+hydrogen and solid nuclear targets. This article describes the new and upgraded
+detectors and auxiliary equipment, outlines the reconstruction procedures used,
+and summarises the general performance of the setup.",1410.1797v1
+2015-01-23,Observation of a new narrow axial-vector meson $a_1(1420)$,"The COMPASS collaboration at CERN has measured diffractive dissociation of
+190 GeV/$c$ pions into the $\pi^-\pi^-\pi^+$ final state using a stationary
+hydrogen target. A partial-wave analysis (PWA) was performed in bins of $3\pi$
+mass and four-momentum transfer using the isobar model and the so far largest
+PWA model consisting of 88 waves. A narrow $J^{PC} = 1^{++}$ signal is observed
+in the $f_0(980)\,\pi$ channel. We present a resonance-model study of a subset
+of the spin-density matrix selecting $3\pi$ states with $J^{PC} = 2^{++}$ and
+$4^{++}$ decaying into $\rho(770)\,\pi$ and with $J^{PC} = 1^{++}$ decaying
+into $f_0(980)\,\pi$. We identify a new $a_1$ meson with mass
+$(1414^{+15}_{-13})$ MeV/$c^2$ and width $(153^{+8}_{-23})$ MeV/$c^2$. Within
+the final states investigated in our analysis, we observe the new $a_1(1420)$
+decaying only into $f_0(980)\,\pi$, suggesting its exotic nature.",1501.05732v3
+2015-03-31,The Spin Structure Function $g_1^{\rm p}$ of the Proton and a Test of the Bjorken Sum Rule,"New results for the double spin asymmetry $A_1^{\rm p}$ and the proton
+longitudinal spin structure function $g_1^{\rm p}$ are presented. They were
+obtained by the COMPASS collaboration using polarised 200 GeV muons scattered
+off a longitudinally polarised NH$_3$ target. The data were collected in 2011
+and complement those recorded in 2007 at 160\,GeV, in particular at lower
+values of $x$. They improve the statistical precision of $g_1^{\rm p}(x)$ by
+about a factor of two in the region $x\lesssim 0.02$. A next-to-leading order
+QCD fit to the $g_1$ world data is performed. It leads to a new determination
+of the quark spin contribution to the nucleon spin, $\Delta \Sigma$ ranging
+from 0.26 to 0.36, and to a re-evaluation of the first moment of $g_1^{\rm p}$.
+The uncertainty of $\Delta \Sigma$ is mostly due to the large uncertainty in
+the present determinations of the gluon helicity distribution. A new evaluation
+of the Bjorken sum rule based on the COMPASS results for the non-singlet
+structure function $g_1^{\rm NS}(x,Q^2)$ yields as ratio of the axial and
+vector coupling constants $|g_{\rm A}/g_{\rm V}| = 1.22 \pm 0.05~({\rm stat.})
+\pm 0.10~({\rm syst.})$, which validates the sum rule to an accuracy of about
+9\%.",1503.08935v1
+2015-09-11,Longitudinal double spin asymmetries in single hadron quasi-real photoproduction at high $p_T$,"We measured the longitudinal double spin asymmetries $A_{LL}$ for single
+hadron muo-production off protons and deuterons at photon virtuality $Q^2$ <
+1(GeV/$\it c$)$^2$ for transverse hadron momenta $p_T$ in the range 0.7
+GeV/$\it c$ to 4 GeV/$\it c$ . They were determined using COMPASS data taken
+with a polarised muon beam of 160 GeV/$\it c$ or 200 GeV/$\it c$ impinging on
+polarised $\mathrm{{}^6LiD}$ or $\mathrm{NH_3}$ targets. The experimental
+asymmetries are compared to next-to-leading order pQCD calculations, and are
+sensitive to the gluon polarisation $\Delta G$ inside the nucleon in the range
+of the nucleon momentum fraction carried by gluons $0.05 < x_g < 0.2$.",1509.03526v2
+2016-04-10,Multiplicities of charged pions and unidentified charged hadrons from deep-inelastic scattering of muons off an isoscalar target,"Multiplicities of charged pions and unidentified hadrons produced in
+deep-inelastic scattering were measured in bins of the Bjorken scaling variable
+$x$, the relative virtual-photon energy $y$ and the relative hadron energy $z$.
+Data were obtained by the COMPASS Collaboration using a 160 GeV muon beam and
+an isoscalar target ($^6$LiD). They cover the kinematic domain in the photon
+virtuality $Q^2$ > 1(GeV/c$)^2$, $0.004 < x < 0.4$, $0.2 < z < 0.85$ and $0.1 <
+y < 0.7$. In addition, a leading-order pQCD analysis was performed using the
+pion multiplicity results to extract quark fragmentation functions.",1604.02695v2
+2016-06-12,Exclusive $ω$ meson muoproduction on transversely polarised protons,"Exclusive production of $\omega$ mesons was studied at the COMPASS experiment
+by scattering $160~\mathrm{GeV}/\mathit{c}$ muons off transversely polarised
+protons. Five single-spin and three double-spin azimuthal asymmetries were
+measured in the range of photon virtuality $1~(\mathrm{GeV}/\mathit{c})^2 < Q^2
+< 10~(\mathrm{GeV}/\mathit{c})^2$, Bjorken scaling variable $0.003 <
+x_{\mathit{Bj}} < 0.3$ and transverse momentum squared of the $\omega$ meson
+$0.05~(\mathrm{GeV}/\mathit{c})^2 < p_{T}^{2} <
+0.5~(\mathrm{GeV}/\mathit{c})^2$. The measured asymmetries are sensitive to the
+nucleon helicity-flip Generalised Parton Distributions (GPD) $E$ that are
+related to the orbital angular momentum of quarks, the chiral-odd GPDs $H_{T}$
+that are related to the transversity Parton Distribution Functions, and the
+sign of the $\pi\omega$ transition form factor. The results are compared to
+recent calculations of a GPD-based model.",1606.03725v2
+2014-03-11,Measurement of radiative widths of $a_2(1320)$ and $π_2(1670)$,"The COMPASS Collaboration at CERN has investigated the reaction $\pi^- \gamma
+\rightarrow \pi^-\pi^-\pi^+$ embedded in the Primakoff reaction of
+$190~\textrm{GeV}$ pions scattering in the Coulomb field of a lead target,
+$\pi^- \text{Pb} \rightarrow \pi^-\pi^-\pi^+ \text{Pb}$. Exchange of quasi-real
+photons is selected by isolating the sharp Coulomb peak observed at momentum
+transfer below $0.001~(\text{GeV}/c)^2$. Using a partial-wave analysis the
+amplitudes and relative phases of the $a_2(1320)$ and $\pi_2(1670)$ mesons have
+been extracted, and the Coulomb and the diffractive contributions have been
+disentangled. Measuring absolute production cross sections we have determined
+the radiative width of the $a_2(1320)$ to be $\Gamma_0(a_2(1320) \rightarrow
+\pi\gamma) = (358 \pm 6_{\textrm{stat}} \pm 42_{\textrm{syst}})~\textrm{keV}$.
+As the first measurement, $\Gamma_0(\pi_2(1670) \rightarrow \pi\gamma) = (181
+\pm 11_{\textrm{stat}} \pm 27_{\textrm{syst}})~\textrm{keV} \cdot
+(\textrm{BR}^{\textrm{PDG}}_{f_2 \pi}/\textrm{BR}_{f_2 \pi})$ is obtained for
+the radiative width of the $\pi_2(1670)$, where in this analysis the branching
+ratio $\textrm{BR}^{\textrm{PDG}}_{f_2 \pi}=0.56$ has been used. We compare
+these values to previous measurements and theoretical predictions.",1403.2644v1
+2011-11-25,First Measurement of Chiral Dynamics in π^- γ-> π^- π^- π^+,"The COMPASS collaboration at CERN has investigated the \pi^- \gamma -> \pi^-
+\pi^- \pi^+ reaction at center-of-momentum energy below five pion masses,
+sqrt(s) < 5 m(\pi), embedded in the Primakoff reaction of 190 GeV pions
+impinging on a lead target. Exchange of quasi-real photons is selected by
+isolating the sharp Coulomb peak observed at smallest momentum transfers, t' <
+0.001 (GeV/c)^2. Using partial-wave analysis techniques, the scattering
+intensity of Coulomb production described in terms of chiral dynamics and its
+dependence on the 3\pi-invariant mass m(3\pi) = sqrt(s) were extracted. The
+absolute cross section was determined in seven bins of $\sqrt{s}$ with an
+overall precision of 20%. At leading order, the result is found to be in good
+agreement with the prediction of chiral perturbation theory over the whole
+energy range investigated.",1111.5954v2
+2014-05-25,Spin alignment and violation of the OZI rule in exclusive $ω$ and $φ$ production in pp collisions,"Exclusive production of the isoscalar vector mesons $\omega$ and $\phi$ is
+measured with a 190 GeV$/c$ proton beam impinging on a liquid hydrogen target.
+Cross section ratios are determined in three intervals of the Feynman variable
+$x_{F}$ of the fast proton. A significant violation of the OZI rule is found,
+confirming earlier findings. Its kinematic dependence on $x_{F}$ and on the
+invariant mass $M_{p\mathrm{V}}$ of the system formed by fast proton
+$p_\mathrm{fast}$ and vector meson $V$ is discussed in terms of diffractive
+production of $p_\mathrm{fast}V$ resonances in competition with central
+production. The measurement of the spin density matrix element $\rho_{00}$ of
+the vector mesons in different selected reference frames provides another
+handle to distinguish the contributions of these two major reaction types.
+Again, dependences of the alignment on $x_{F}$ and on $M_{p\mathrm{V}}$ are
+found. Most of the observations can be traced back to the existence of several
+excited baryon states contributing to $\omega$ production which are absent in
+the case of the $\phi$ meson. Removing the low-mass $M_{p\mathrm{V}}$ resonant
+region, the OZI rule is found to be violated by a factor of eight,
+independently of $x_\mathrm{F}$.",1405.6376v1
+2014-05-25,Measurement of the charged-pion polarisability,"The COMPASS collaboration at CERN has investigated pion Compton scattering,
+$\pi^-\gamma\rightarrow \pi^-\gamma$, at centre-of-mass energy below 3.5 pion
+masses. The process is embedded in the reaction
+$\pi^-\mathrm{Ni}\rightarrow\pi^-\gamma\;\mathrm{Ni}$, which is initiated by
+190\,GeV pions impinging on a nickel target. The exchange of quasi-real photons
+is selected by isolating the sharp Coulomb peak observed at smallest momentum
+transfers, $Q^2<0.0015$\,(GeV/$c$)$^2$. From a sample of 63\,000 events the
+pion electric polarisability is determined to be $\alpha_\pi\ =\ (\,2.0\ \pm\
+0.6_{\mbox{\scriptsize stat}}\ \pm\ 0.7_{\mbox{\scriptsize syst}}\,) \times
+10^{-4}\,\mbox{fm}^3$ under the assumption $\alpha_\pi=-\beta_\pi$, which
+relates the electric and magnetic dipole polarisabilities. It is the most
+precise measurement of this fundamental low-energy parameter of strong
+interaction, that has been addressed since long by various methods with
+conflicting outcomes. While this result is in tension with previous dedicated
+measurements, it is found in agreement with the expectation from chiral
+perturbation theory. An additional measurement replacing pions by muons, for
+which the cross-section behavior is unambigiously known, was performed for an
+independent estimate of the systematic uncertainty.",1405.6377v2
+2016-08-24,Multiplicities of charged kaons from deep-inelastic muon scattering off an isoscalar target,"Precise measurements of charged-kaon multiplicities in deep inelastic
+scattering were performed. The results are presented in three-dimensional bins
+of the Bjorken scaling variable x, the relative virtual-photon energy y, and
+the fraction z of the virtual-photon energy carried by the produced hadron. The
+data were obtained by the COMPASS Collaboration by scattering 160 GeV muons off
+an isoscalar 6 LiD target. They cover the kinematic domain 1 (GeV/c)2 < Q2 < 60
+(GeV/c)^2 in the photon virtuality, 0.004 < x < 0.4, 0.1 < y < 0.7, 0.20 < z <
+0.85, and W > 5 GeV/c^2 in the invariant mass of the hadronic system. The
+results from the sum of the z-integrated K+ and K- multiplicities at high x
+point to a value of the non-strange quark fragmentation function larger than
+obtained by the earlier DSS fit.",1608.06760v1
+2017-10-03,Longitudinal double-spin asymmetry $A_1^{\rm p}$ and spin-dependent structure function $g_1^{\rm p}$ of the proton at small values of $x$ and $Q^2$,"We present a precise measurement of the proton longitudinal double-spin
+asymmetry $A_1^{\rm p}$ and the proton spin-dependent structure function
+$g_1^{\rm p}$ at photon virtualities $0.006~({\rm GeV}/c)^2<Q^2 < 1~({\rm
+GeV}/c)^2$ in the Bjorken $x$ range of $4 \times 10^{-5} < x < 4 \times
+10^{-2}$. The results are based on data collected by the COMPASS Collaboration
+at CERN using muon beam energies of $160~{\rm GeV}$ and $200~{\rm GeV}$. The
+statistical precision is more than tenfold better than that of the previous
+measurement in this region. In the whole range of $x$, the measured values of
+$A_1^{\rm p}$ and $g_1^{\rm p}$ are found to be positive. It is for the first
+time that spin effects are found at such low values of $x$.",1710.01014v1
+2018-09-09,Measurement of $P_T$-weighted Sivers asymmetries in leptoproduction of hadrons,"The transverse spin asymmetries measured in semi-inclusive leptoproduction of
+hadrons, when weighted with the hadron transverse momentum $P_T$, allow for the
+extraction of important transverse-momentum-dependent distribution functions.
+In particular, the weighted Sivers asymmetries provide direct information on
+the Sivers function, which is a leading-twist distribution that arises from a
+correlation between the transverse momentum of an unpolarised quark in a
+transversely polarised nucleon and the spin of the nucleon. Using the
+high-statistics data collected by the COMPASS Collaboration in 2010 with a
+transversely polarised proton target, we have evaluated two types of
+$P_T$-weighted Sivers asymmetries, which are both proportional to the product
+of the firsttransverse moment of the Sivers function and of the fragmentation
+function. The results are compared to the standard unweighted Sivers
+asymmetries and used to extract the first transverse moments of the Sivers
+distributions for $u$ and $d$ quarks.",1809.02936v1
+2012-05-23,Experimental investigation of transverse spin asymmetries in muon-p SIDIS processes: Collins asymmetries,"The COMPASS Collaboration at CERN has measured the transverse spin azimuthal
+asymmetry of charged hadrons produced in semi-inclusive deep inelastic
+scattering using a 160 GeV positive muon beam and a transversely polarised NH_3
+target. The Collins asymmetry of the proton was extracted in the Bjorken x
+range 0.003<x<0.7. These new measurements confirm with higher accuracy previous
+measurements from the COMPASS and HERMES collaborations, which exhibit a
+definite effect in the valence quark region. The asymmetries for negative and
+positive hadrons are similar in magnitude and opposite in sign. They are
+compatible with model calculations in which the u-quark transversity is
+opposite in sign and somewhat larger than the d-quark transversity distribution
+function. The asymmetry is extracted as a function of Bjorken $x$, the relative
+hadron energy $z$ and the hadron transverse momentum p_T^h. The high statistics
+and quality of the data also allow for more detailed investigations of the
+dependence on the kinematic variables. These studies confirm the leading-twist
+nature of the Collins asymmetry.",1205.5121v1
+2012-05-23,Experimental investigation of transverse spin asymmetries in muon-p SIDIS processes: Sivers asymmetries,"The COMPASS Collaboration at CERN has measured the transverse spin azimuthal
+asymmetry of charged hadrons produced in semi-inclusive deep inelastic
+scattering using a 160 GeV positive muon beam and a transversely polarised NH_3
+target. The Sivers asymmetry of the proton has been extracted in the Bjorken x
+range 0.003<x<0.7. The new measurements have small statistical and systematic
+uncertainties of a few percent and confirm with considerably better accuracy
+the previous COMPASS measurement. The Sivers asymmetry is found to be
+compatible with zero for negative hadrons and positive for positive hadrons, a
+clear indication of a spin-orbit coupling of quarks in a transversely polarised
+proton. As compared to measurements at lower energy, a smaller Sivers asymmetry
+for positive hadrons is found in the region x > 0.03. The asymmetry is
+different from zero and positive also in the low x region, where sea-quarks
+dominate. The kinematic dependence of the asymmetry has also been investigated
+and results are given for various intervals of hadron and virtual photon
+fractional energy. In contrast to the case of the Collins asymmetry, the
+results on the Sivers asymmetry suggest a strong dependence on the
+four-momentum transfer to the nucleon, in agreement with the most recent
+calculations.",1205.5122v1
+2019-03-28,Measurement of the cross section for hard exclusive $π^0$ leptoproduction,"We report on a measurement of hard exclusive $\pi^0$ muoproduction on the
+proton by COMPASS using 160 GeV/$c$ polarised $\mu^+$ and $\mu^-$ beams of the
+CERN SPS impinging on a liquid hydrogen target. From the average of the
+measured $\mu^+$ and $\mu^-$ cross sections, the virtual-photon proton cross
+section is determined as a function of the squared four-momentum transfer
+between initial and final proton in the range $0.08\,(\text{GeV/}c)^2 < |t| <
+0.64\,(\text{GeV/}c)^2$. The average kinematics of the measurement are $\langle
+Q^2 \rangle =2.0\; {(\text{GeV}/c)^2}$, $\langle \nu \rangle = 12.8\;
+{\text{GeV}}$, $\langle x_{Bj} \rangle = 0.093 $ and $\langle -t \rangle =
+0.256\; {(\text{GeV}/c)^2} $. Fitting the azimuthal dependence reveals a
+combined contribution by transversely and longitudinally polarised photons of
+$(8.1 \ \pm \ 0.9_{\text{stat}}{}_{- \ 1.0}^{+ \
+1.1}\big\rvert_{\text{sys}})\,{\text{nb}}/{(\text{GeV}/c)^{2}}$, as well as
+transverse-transverse and longitudinal-transverse interference contributions of
+$(-6.0 \pm 1.3_{\text{stat}}{}_{- \ 0.7}^{+ \
+0.7}\big\rvert_{\text{sys}})\,{\text{nb}}/{(\text{GeV}/c)^{2}}$ and $(1.4 \pm
+0.5_{\text{stat}}{}_{- \ 0.2}^{+ \
+0.3}\big\rvert_{\text{sys}})\,{\text{nb}}/{(\text{GeV}/c)^{2}}$, respectively.
+Our results provide important input for modelling Generalised Parton
+Distributions. In the context of the phenomenological Goloskokov-Kroll model,
+the statistically significant transverse-transverse interference contribution
+constitutes clear experimental evidence for the chiral-odd GPD
+$\overline{E}_T$.",1903.12030v1
+2019-08-02,AEDGE: Atomic Experiment for Dark Matter and Gravity Exploration in Space,"We propose in this White Paper a concept for a space experiment using cold
+atoms to search for ultra-light dark matter, and to detect gravitational waves
+in the frequency range between the most sensitive ranges of LISA and the
+terrestrial LIGO/Virgo/KAGRA/INDIGO experiments. This interdisciplinary
+experiment, called Atomic Experiment for Dark Matter and Gravity Exploration
+(AEDGE), will also complement other planned searches for dark matter, and
+exploit synergies with other gravitational wave detectors. We give examples of
+the extended range of sensitivity to ultra-light dark matter offered by AEDGE,
+and how its gravitational-wave measurements could explore the assembly of
+super-massive black holes, first-order phase transitions in the early universe
+and cosmic strings. AEDGE will be based upon technologies now being developed
+for terrestrial experiments using cold atoms, and will benefit from the space
+experience obtained with, e.g., LISA and cold atom experiments in microgravity.
+  This paper is based on a submission (v1) in response to the Call for White
+Papers for the Voyage 2050 long-term plan in the ESA Science Programme. ESA
+limited the number of White Paper authors to 30. However, in this version (v2)
+we have welcomed as supporting authors participants in the Workshop on Atomic
+Experiments for Dark Matter and Gravity Exploration held at CERN: ({\tt
+https://indico.cern.ch/event/830432/}), as well as other interested scientists,
+and have incorporated additional material.",1908.00802v2
+2019-12-21,Contribution of exclusive diffractive processes to the measured azimuthal asymmetries in SIDIS,"Hadron leptoproduction in Semi-Inclusive measurements of Deep-Inelastic
+Scattering (SIDIS) on unpolarised nucleons allows one to get information on the
+intrinsic transverse momentum of quarks in a nucleon and on the Boer-Mulders
+function through the measurement of azimuthal modulations in the cross section.
+These modulations were recently measured by the HERMES experiment at DESY on
+proton and deuteron targets, and by the COMPASS experiment using the CERN SPS
+muon beam and a $^6$LiD target. In both cases, the amplitudes of the
+$\cos\phi_h$ and $\cos 2\phi_h$ modulations show strong kinematic dependences
+for both positive and negative hadrons. It has been known since some time that
+the measured final-state hadrons in those SIDIS experiments receive a
+contribution from exclusive diffractive production of vector mesons,
+particularly important at large values of $z$, the fraction of the virtual
+photon energy carried by the hadron. In previous measurements of azimuthal
+asymmetries this contribution was not taken into account, because it was not
+known that it could distort the azimuthal modulations. Presently, a method to
+evaluate the contribution of the exclusive reactions to the azimuthal
+asymmetries measured by COMPASS has been developed. The subtraction of this
+contribution results in a better understanding of the kinematic effects, and
+the remaining non-zero $\cos 2\phi_h$ modulation gives indication for a
+non-zero Boer-Mulders effect.",1912.10322v1
+2017-07-10,New analysis of $ηπ$ tensor resonances measured at the COMPASS experiment,"We present a new amplitude analysis of the $\eta\pi$ $D$-wave in $\pi^- p\to
+\eta\pi^- p$ measured by COMPASS. Employing an analytical model based on the
+principles of the relativistic $S$-matrix, we find two resonances that can be
+identified with the $a_2(1320)$ and the excited $a_2^\prime(1700)$, and perform
+a comprehensive analysis of their pole positions. For the mass and width of the
+$a_2$ we find $M=(1307 \pm 1 \pm 6)$~MeV and $\Gamma=(112 \pm 1 \pm 8)$~MeV,
+and for the excited state $a_2^\prime$ we obtain $M=(1720 \pm 10 \pm 60)$~MeV
+and $\Gamma=(280\pm 10 \pm 70)$~MeV, respectively.",1707.02848v1
+2020-06-09,Triangle Singularity as the Origin of the $a_1(1420)$,"The COMPASS experiment recently discovered a new isovector resonance-like
+signal with axial-vector quantum numbers, the $a_1(1420)$, decaying to
+$f_0(980)\pi$. With a mass too close to and a width smaller than the
+axial-vector ground state $a_1(1260)$, it was immediately interpreted as a new
+light exotic meson, similar to the $X$, $Y$, $Z$ states in the hidden-charm
+sector. We show that a resonance-like signal fully matching the experimental
+data is produced by the decay of the $a_1(1260)$ resonance into $K^\ast(\to
+K\pi)\bar{K}$ and subsequent rescattering through a triangle singularity into
+the coupled $f_0(980)\pi$ channel. The amplitude for this process is calculated
+using a new approach based on dispersion relations. The triangle-singularity
+model is fitted to the partial-wave data of the COMPASS experiment. Despite
+having less parameters, this fit shows a slightly better quality than the one
+using a resonance hypothesis and thus eliminates the need for an additional
+resonance in order to describe the data. We thereby demonstrate for the first
+time in the light-meson sector that a resonance-like structure in the
+experimental data can be described by rescattering through a triangle
+singularity, providing evidence for a genuine three-body effect.",2006.05342v3
+2020-09-07,Spin Density Matrix Elements in Exclusive $ω$ Meson Muoproduction $^*$,"We report on a measurement of Spin Density Matrix Elements (SDMEs) in hard
+exclusive $\omega$ meson muoproduction on the proton at COMPASS using 160
+GeV/$c$ polarised $ \mu ^{+}$ and $ \mu ^{-}$ beams impinging on a liquid
+hydrogen target. The measurement covers the range 5.0 GeV/$c^2$ $< W <$ 17.0
+GeV/$c^2$, with the average kinematics $\langle Q^{2} \rangle=$ 2.1
+(GeV/$c$)$^2$, $\langle W \rangle= 7.6$ GeV/$c^2$, and $\langle p^{2}_{\rm T}
+\rangle = 0.16$ (GeV/$c$)$^2$. Here, $Q^2$ denotes the virtuality of the
+exchanged photon, $W$ the mass of the final hadronic system and $p_T$ the
+transverse momentum of the $\omega$ meson with respect to the virtual-photon
+direction. The measured non-zero SDMEs for the transitions of transversely
+polarised virtual photons to longitudinally polarised vector mesons
+($\gamma^*_T \to V_L$) indicate a violation of $s$-channel helicity
+conservation. Additionally, we observe a sizeable contribution of
+unnatural-parity-exchange (UPE) transitions that decreases with increasing $W$.
+The results provide important input for modelling Generalised Parton
+Distributions (GPDs). In particular, they may allow to evaluate in a
+model-dependent way the contribution of UPE transitions and assess the role of
+parton helicity-flip GPDs in exclusive $\omega$ production.",2009.03271v3
+2015-07-27,Interplay among transversity induced asymmetries in hadron leptoproduction,"In the fragmentation of a transversely polarized quark several left-right
+asymmetries are possible for the hadrons in the jet. When only one unpolarized
+hadron is selected, it exhibits an azimuthal modulation known as Collins
+effect. When a pair of oppositely charged hadrons is observed, three
+asymmetries can be considered, a di-hadron asymmetry and two single hadron
+asymmetries. In lepton deep inelastic scattering on transversely polarized
+nucleons all these asymmetries are coupled with the transversity distribution.
+From the high statistics COMPASS data on oppositely charged hadron-pair
+production we have investigated for the first time the dependence of these
+three asymmetries on the difference of the azimuthal angles of the two hadrons.
+The similarity of transversity induced single and di-hadron asymmetries is
+discussed. A new analysis of the data allows to establish quantitative
+relationships among them, providing for the first time strong experimental
+indication that the underlying fragmentation mechanisms are all driven by a
+common physical process.",1507.07593v2
+2016-09-23,Sivers asymmetry extracted in SIDIS at the hard scale of the Drell-Yan process at COMPASS,"Proton transverse-spin azimuthal asymmetries are extracted from the COMPASS
+2010 semi-inclusive hadron measurements in deep inelastic muon-nucleon
+scattering in those four regions of the photon virtuality $Q^2$, which
+correspond to the four regions of the di-muon mass $\sqrt{Q^2}$ used in the
+ongoing analysis of the COMPASS Drell-Yan measurements. This allows for a
+future direct comparison of the nucleon transverse-momentum-dependent parton
+distribution functions extracted from these two alternative measurements.
+Various two-dimensional kinematic dependences are presented for the azimuthal
+asymmetries induced by the Sivers transverse-momentum-dependent parton
+distribution function. The integrated Sivers asymmetries are found to be
+positive with an accuracy that appears to be sufficient to test the sign change
+of the Sivers function predicted by Quantum Chromodynamics.",1609.07374v2
+2017-04-03,First measurement of transverse-spin-dependent azimuthal asymmetries in the Drell-Yan process,"The first measurement of transverse-spin-dependent azimuthal asymmetries in
+the pion-induced Drell-Yan (DY) process is reported. We use the CERN SPS 190
+GeV/$c$, $\pi^{-}$ beam and a transversely polarized ammonia target. Three
+azimuthal asymmetries giving access to different transverse-momentum-dependent
+(TMD) parton distribution functions (PDFs) are extracted using dimuon events
+with invariant mass between 4.3 GeV/$c^2$ and 8.5 GeV/$c^2$. The observed sign
+of the Sivers asymmetry is found to be consistent with the fundamental
+prediction of Quantum Chromodynamics (QCD) that the Sivers TMD PDFs extracted
+from DY have a sign opposite to the one extracted from semi-inclusive
+deep-inelastic scattering (SIDIS) data. We present two other asymmetries
+originating from the pion Boer-Mulders TMD PDFs convoluted with either the
+nucleon transversity or pretzelosity TMD PDFs. These DY results are obtained at
+a hard scale comparable to that of a recent COMPASS SIDIS measurement and hence
+allow unique tests of fundamental QCD universality predictions.",1704.00488v1
+2020-03-26,Antiproton over proton and K$^-$ over K$^+$ multiplicity ratios at high $z$ in DIS,"The $\bar{\rm p} $ over p multiplicity ratio is measured in deep-inelastic
+scattering for the first time using (anti-) protons carrying a large fraction
+of the virtual-photon energy, $z>0.5$. The data were obtained by the COMPASS
+Collaboration using a 160 GeV muon beam impinging on an isoscalar $^6$LiD
+target. The regime of deep-inelastic scattering is ensured by requiring $Q^2$ >
+1 (GeV/$c$)$^2$ for the photon virtuality and $W > 5$ GeV/$c^2$ for the
+invariant mass of the produced hadronic system. The range in Bjorken-$x$ is
+restricted to $0.01 < x < 0.40$. Protons and antiprotons are identified in the
+momentum range $20 \div 60$ GeV/$c$. In the whole studied $z$-region, the
+$\bar{\rm p}$ over p multiplicity ratio is found to be below the lower limit
+expected from calculations based on leading-order perturbative Quantum
+Chromodynamics (pQCD). Extending our earlier analysis of the K$^-$ over K$^+$
+multiplicity ratio by including now events with larger virtual-photon energies,
+this ratio becomes closer to the expectation of next-to-leading order pQCD. The
+results of both analyses strengthen our earlier conclusion that the phase space
+available for hadronisation should be taken into account in the pQCD formalism.",2003.11791v1
+2021-04-28,Probing transversity by measuring $Λ$ polarisation in SIDIS,"Based on the observation of sizeable target-transverse-spin asymmetries in
+single-hadron and hadron-pair production in Semi-Inclusive measurements of Deep
+Inelastic Scattering (SIDIS), the chiral-odd transversity quark distribution
+functions $h_1^q$ are nowadays well established. Several possible channels to
+access these functions were originally proposed. One candidate is the
+measurement of the polarisation of $\Lambda$ hyperons produced in SIDIS off
+transversely polarised nucleons, where the transverse polarisation of the
+struck quark might be transferred to the final-state hyperon. In this article,
+we present the COMPASS results on the transversity-induced polarisation of
+$\Lambda$ and $\bar{\Lambda}$ hyperons produced in SIDIS off transversely
+polarised protons. Within the experimental uncertainties, no significant
+deviation from zero was observed. The results are discussed in the context of
+different models taking into account previous experimental results on $h_1^u$
+and $h_1^d$.",2104.13585v2
+2021-08-03,The exotic meson $π_1(1600)$ with $J^{PC} = 1^{-+}$ and its decay into $ρ(770)π$,"We study the spin-exotic $J^{PC} = 1^{-+}$ amplitude in single-diffractive
+dissociation of 190 GeV$/c$ pions into $\pi^-\pi^-\pi^+$ using a hydrogen
+target and confirm the $\pi_1(1600) \to \rho(770) \pi$ amplitude, which
+interferes with a nonresonant $1^{-+}$ amplitude. We demonstrate that
+conflicting conclusions from previous studies on these amplitudes can be
+attributed to different analysis models and different treatment of the
+dependence of the amplitudes on the squared four-momentum transfer and we thus
+reconcile their experimental findings. We study the nonresonant contributions
+to the $\pi^-\pi^-\pi^+$ final state using pseudo-data generated on the basis
+of a Deck model. Subjecting pseudo-data and real data to the same partial-wave
+analysis, we find good agreement concerning the spectral shape and its
+dependence on the squared four-momentum transfer for the $J^{PC} = 1^{-+}$
+amplitude and also for amplitudes with other $J^{PC}$ quantum numbers. We
+investigate for the first time the amplitude of the $\pi^-\pi^+$ subsystem with
+$J^{PC} = 1^{--}$ in the $3\pi$ amplitude with $J^{PC} = 1^{-+}$ employing the
+novel freed-isobar analysis scheme. We reveal this $\pi^-\pi^+$ amplitude to be
+dominated by the $\rho(770)$ for both the $\pi_1(1600)$ and the nonresonant
+contribution. We determine the $\rho(770)$ resonance parameters within the
+three-pion final state. These findings largely confirm the underlying
+assumptions for the isobar model used in all previous partial-wave analyses
+addressing the $J^{PC} = 1^{-+}$ amplitude.",2108.01744v2
+2022-04-04,Double $J/ψ$ production in pion-nucleon scattering at COMPASS,"We present the study of the production of double $J/\psi$ mesons using
+COMPASS data collected with a 190 GeV/$c$ $\pi^-$ beam scattering off NH$_{3}$,
+Al and W targets. Kinematic distributions of the collected double $J/\psi$
+events are analysed, and the double $J/\psi$ production cross section is
+estimated for each of the COMPASS targets. The results are compared to
+predictions from single- and double-parton scattering models as well as the
+pion intrinsic charm and the tetraquark exotic resonance hypotheses. It is
+demonstrated that the single parton scattering production mechanism gives the
+dominant contribution that is sufficient to describe the data. An upper limit
+on the double intrinsic charm content of pion is evaluated. No significant
+signatures that could be associated with exotic tetraquarks are found in the
+double $J/\psi$ mass spectrum.",2204.01817v1
+2022-10-30,Spin Density Matrix Elements in Exclusive $ρ^0$ Meson Muoproduction,"We report on a measurement of Spin Density Matrix Elements (SDMEs) in hard
+exclusive $\rho ^0$ meson muoproduction at COMPASS using 160~GeV/$c$ polarised
+$ \mu ^{+}$ and $ \mu ^{-}$ beams impinging on a liquid hydrogen target. The
+measurement covers the kinematic range 5.0~GeV/$c^2$ $< W <$ 17.0~GeV/$c^2$,
+1.0 (GeV/$c$)$^2$ $< Q^2 <$ 10.0 (GeV/$c$)$^2$ and 0.01 (GeV/$c$)$^2$ $<
+p_{\rm{T}}^2 <$ 0.5 (GeV/$c$)$^2$. Here, $W$ denotes the mass of the final
+hadronic system, $Q^2$ the virtuality of the exchanged photon, and $p_{\rm{T}}$
+the transverse momentum of the $\rho ^0$ meson with respect to the
+virtual-photon direction. The measured non-zero SDMEs for the transitions of
+transversely polarised virtual photons to longitudinally polarised vector
+mesons ($\gamma^*_T \to V^{ }_L$) indicate a violation of $s$-channel helicity
+conservation. Additionally, we observe a dominant contribution of
+natural-parity-exchange transitions and a very small contribution of
+unnatural-parity-exchange transitions, which is compatible with zero within
+experimental uncertainties. The results provide important input for modelling
+Generalised Parton Distributions (GPDs). In particular, they may allow one to
+evaluate in a model-dependent way the role of parton helicity-flip GPDs in
+exclusive $\rho ^0$ production.",2210.16932v2
+2022-10-31,Collins and Sivers transverse-spin asymmetries in inclusive muoproduction of $ρ^0$ mesons,"The production of vector mesons in deep inelastic scattering is an
+interesting yet scarsely explored channel to study the transverse spin
+structure of the nucleon and the related phenomena. The COMPASS collaboration
+has performed the first measurement of the Collins and Sivers asymmetries for
+inclusively produced $\rho^0$ mesons. The analysis is based on the data set
+collected in deep inelastic scattering in $2010$ using a $160\,\,\rm{GeV}/c$
+$\mu^+$ beam impinging on a transversely polarized $\rm{NH}_3$ target. The
+$\rho^{0}$ mesons are selected from oppositely charged hadron pairs, and the
+asymmetries are extracted as a function of the Bjorken-$x$ variable, the
+transverse momentum of the pair and the fraction of the energy $z$ carried by
+the pair. Indications for positive Collins and Sivers asymmetries are observed.",2211.00093v2
+2023-12-28,Final COMPASS results on the transverse-spin-dependent azimuthal asymmetries in the pion-induced Drell-Yan process,"The COMPASS Collaboration performed measurements of the Drell-Yan process in
+2015 and 2018 using a 190 GeV/c $\pi^{-}$ beam impinging on a transversely
+polarised ammonia target. Combining the data of both years, we present final
+results on the amplitudes of the five azimuthal modulations in the dimuon
+production cross section. Three of these transverse-spin-dependent azimuthal
+asymmetries (TSAs) probe the nucleon leading-twist Sivers, transversity, and
+pretzelosity transverse-momentum dependent (TMD) parton distribution functions
+(PDFs). The other two are induced by subleading effects. These TSAs provide
+unique new inputs for the study of the nucleon TMD PDFs and their universality
+properties. In particular, the Sivers TSA observed in this measurement is
+consistent with the fundamental QCD prediction of a sign change of naive
+time-reversal-odd TMD PDFs when comparing the Drell-Yan process with
+semi-inclusive measurements of deep inelastic scattering. Also, within the
+context of model predictions, the observed transversity TSA is consistent with
+the expectation of a sign change for the Boer-Mulders function.",2312.17379v1
+2023-12-30,High-statistics measurement of Collins and Sivers asymmetries for transversely polarised deuterons,"New results are presented on a high-statistics measurement of Collins and
+Sivers asymmetries of charged hadrons produced in deep inelastic scattering of
+muons on a transversely polarised $^6$LiD target. The data were taken in 2022
+with the COMPASS spectrometer using the 160 \gevv\ muon beam at CERN, balancing
+the existing data on transversely polarised proton targets. The first results
+from about two-thirds of the new data have total uncertainties smaller by up to
+a factor of three compared to the previous deuteron measurements. Using all the
+COMPASS proton and deuteron results, both the transversity and the Sivers
+distribution functions of the $u$ and $d$ quark, as well as the tensor charge
+in the measured $x$-range are extracted. In particular, the accuracy of the $d$
+quark results is significantly improved.",2401.00309v1
+2008-02-15,Collins and Sivers asymmetries for pions and kaons in muon-deuteron DIS,"The measurements of the Collins and Sivers asymmetries of identified hadrons
+produced in deep-inelastic scattering of 160 GeV/c muons on a transversely
+polarised 6LiD target at COMPASS are presented. The results for charged pions
+and charged and neutral kaons correspond to all data available, which were
+collected from 2002 to 2004. For all final state particles both the Collins and
+Sivers asymmetries turn out to be small, compatible with zero within the
+statistical errors, in line with the previously published results for not
+identified charged hadrons, and with the expected cancellation between the u-
+and d-quark contributions.",0802.2160v2
+2015-09-03,Resonance Production and $ππ$ S-wave in $π^- + p \rightarrow π^- π^- π^+ + p_{recoil}$ at 190 GeV/c,"The COMPASS collaboration has collected the currently largest data set on
+diffractively produced $\pi^-\pi^-\pi^+$ final states using a negative pion
+beam of 190 GeV/c momentum impinging on a stationary proton target. This data
+set allows for a systematic partial-wave analysis in 100 bins of three-pion
+mass, $0.5 < m_{3\pi} < 2.5$ GeV/c$^2$ , and in 11 bins of the reduced
+four-momentum transfer squared, $0.1 < t < 1.0$ (GeV/c)$^2$ . This
+two-dimensional analysis offers sensitivity to genuine one-step resonance
+production, i.e. the production of a state followed by its decay, as well as to
+more complex dynamical effects in nonresonant $3\pi$ production. In this paper,
+we present detailed studies on selected $3\pi$ partial waves with $J^{PC} =
+0^{-+}$, $1^{++}$, $2^{-+}$, $2^{++}$, and $4^{++}$. In these waves, we observe
+the well-known ground-state mesons as well as a new narrow axial-vector meson
+$a_1(1420)$ decaying into $f_0(980) \pi$. In addition, we present the results
+of a novel method to extract the amplitude of the $\pi^-\pi^+$ subsystem with
+$I^{G}J^{PC} = 0^+ 0^{++}$ in various partial waves from the $\pi^-\pi^-\pi^+$
+data. Evidence is found for correlation of the $f_0(980)$ and $f_0(1500)$
+appearing as intermediate $\pi^- \pi^+$ isobars in the decay of the known
+$\pi(1800)$ and $\pi_2(1880)$.",1509.00992v2
+2018-02-02,K$^{-}$ over K$^{+}$ multiplicity ratio for kaons produced in DIS with a large fraction of the virtual-photon energy,"The K$^{-}$ over K$^{+}$ multiplicity ratio is measured in deep-inelastic
+scattering, for the first time for kaons carrying a large fraction $z$ of the
+virtual-photon energy. The data were obtained by the COMPASS collaboration
+using a 160 GeV muon beam and an isoscalar $^6$LiD target. The regime of
+deep-inelastic scattering is ensured by requiring $Q^2>1$ (GeV/$c)^2$ for the
+photon virtuality and $W>5$ GeV/$c^2$ for the invariant mass of the produced
+hadronic system. Kaons are identified in the momentum range from 12 GeV/$c$ to
+40 GeV/$c$, thereby restricting the range in Bjorken-$x$ to $0.01<x<0.40$. The
+$z$-dependence of the multiplicity ratio is studied for $z>0.75$. For very
+large values of $z$, $i.e.$ $z>0.8$, we observe the kaon multiplicity ratio to
+fall below the lower limits expected from calculations based on leading and
+next-to-leading order perturbative quantum chromodynamics. Also, the kaon
+multiplicity ratio shows a strong dependence on the missing mass of the
+single-kaon production process. This suggests that within the perturbative
+quantum chromodynamics formalism an additional correction may be required,
+which takes into account the phase space available for hadronisation.",1802.00584v2
+2018-02-08,Transverse Extension of Partons in the Proton probed by Deeply Virtual Compton Scattering,"We report on the first measurement of exclusive single-photon muoproduction
+on the proton by COMPASS using 160 GeV/$c$ polarized $\mu^+$ and $\mu^-$ beams
+of the CERN SPS impinging on a liquid hydrogen target. We determine the
+dependence of the average of the measured $\mu^+$ and $\mu^-$ cross sections
+for deeply virtual Compton scattering on the squared four-momentum transfer $t$
+from the initial to the final final proton. The slope $B$ of the $t$-dependence
+is fitted with a single exponential function, which yields $B=(4.3 \ \pm \
+0.6_{\text{stat}}\_{- \ 0.3}^{+ \ 0.1}\big\rvert_{\text{sys}})
+(\text{GeV}/c)^{-2}$. This result can be converted into an average transverse
+extension of partons in the proton, $\sqrt{\langle r_{\perp}^2 \rangle} = (0.58
+\ \pm \ 0.04_{\text{stat}}\_{- \ 0.02}^{+ \
+0.01}\big\rvert_{\text{sys}})\text{fm}$. For this measurement, the average
+virtuality of the photon mediating the interaction is $\langle Q^2 \rangle =
+1.8\,(\text{GeV/}c)^2$ and the average value of the Bjorken variable is
+$\langle x_{\text{Bj}} \rangle = 0.056$.",1802.02739v2
+2018-02-16,Light isovector resonances in $π^- p \to π^-π^-π^+ p$ at 190 GeV/${\it c}$,"We have performed the most comprehensive resonance-model fit of
+$\pi^-\pi^-\pi^+$ states using the results of our previously published
+partial-wave analysis (PWA) of a large data set of diffractive-dissociation
+events from the reaction $\pi^- + p \to \pi^-\pi^-\pi^+ + p_\text{recoil}$ with
+a 190 GeV/$c$ pion beam. The PWA results, which were obtained in 100 bins of
+three-pion mass, $0.5 < m_{3\pi} < 2.5$ GeV/$c^2$, and simultaneously in 11
+bins of the reduced four-momentum transfer squared, $0.1 < t' < 1.0$
+$($GeV$/c)^2$, are subjected to a resonance-model fit using Breit-Wigner
+amplitudes to simultaneously describe a subset of 14 selected waves using 11
+isovector light-meson states with $J^{PC} = 0^{-+}$, $1^{++}$, $2^{++}$,
+$2^{-+}$, $4^{++}$, and spin-exotic $1^{-+}$ quantum numbers. The model
+contains the well-known resonances $\pi(1800)$, $a_1(1260)$, $a_2(1320)$,
+$\pi_2(1670)$, $\pi_2(1880)$, and $a_4(2040)$. In addition, it includes the
+disputed $\pi_1(1600)$, the excited states $a_1(1640)$, $a_2(1700)$, and
+$\pi_2(2005)$, as well as the resonancelike $a_1(1420)$. We measure the
+resonance parameters mass and width of these objects by combining the
+information from the PWA results obtained in the 11 $t'$ bins. We extract the
+relative branching fractions of the $\rho(770) \pi$ and $f_2(1270) \pi$ decays
+of $a_2(1320)$ and $a_4(2040)$, where the former one is measured for the first
+time. In a novel approach, we extract the $t'$ dependence of the intensity of
+the resonances and of their phases. The $t'$ dependence of the intensities of
+most resonances differs distinctly from the $t'$ dependence of the nonresonant
+components. For the first time, we determine the $t'$ dependence of the phases
+of the production amplitudes and confirm that the production mechanism of the
+Pomeron exchange is common to all resonances.",1802.05913v2
+2017-01-10,First measurement of the Sivers asymmetry for gluons from SIDIS data,"The Sivers function describes the correlation between the transverse spin of
+a nucleon and the transverse motion of its partons. It was extracted from
+measurements of the azimuthal asymmetry of hadrons produced in semi-inclusive
+deep inelastic scattering of leptons off transversely polarised nucleon
+targets, and it turned out to be non-zero for quarks. In this letter the
+evaluation of the Sivers asymmetry for gluons in the same process is presented.
+The analysis method is based on a Monte Carlo simulation that includes three
+hard processes: photon-gluon fusion, QCD Compton scattering and leading-order
+virtual-photon absorption process. The Sivers asymmetries of the three
+processes are simultaneously extracted using the LEPTO event generator and a
+neural network approach. The method is applied to samples of events containing
+at least two hadrons with large transverse momentum from the COMPASS data taken
+with a 160 GeV/$c$ muon beam scattered off transversely polarised deuterons and
+protons. With a significance of more than two standard deviations a negative
+value is obtained for the gluon Sivers asymmetry. The result of a similar
+analysis for a Collins-like asymmetry for gluons is consistent with zero.",1701.02453v1
+2017-09-21,Transverse-momentum-dependent Multiplicities of Charged Hadrons in Muon-Deuteron Deep Inelastic Scattering,"A semi-inclusive measurement of charged hadron multiplicities in deep
+inelastic muon scattering off an isoscalar target was performed using data
+collected by the COMPASS Collaboration at CERN. The following kinematic domain
+is covered by the data: photon virtuality $Q^{2}>1$ (GeV/$c$)$^2$, invariant
+mass of the hadronic system $W > 5$ GeV/$c^2$, Bjorken scaling variable in the
+range $0.003 < x < 0.4$, fraction of the virtual photon energy carried by the
+hadron in the range $0.2 < z < 0.8$, square of the hadron transverse momentum
+with respect to the virtual photon direction in the range 0.02 (GeV/$c)^2 <
+P_{\rm{hT}}^{2} < 3$ (GeV/$c$)$^2$. The multiplicities are presented as a
+function of $P_{\rm{hT}}^{2}$ in three-dimensional bins of $x$, $Q^2$, $z$ and
+compared to previous semi-inclusive measurements. We explore the
+small-$P_{\rm{hT}}^{2}$ region, i.e. $P_{\rm{hT}}^{2} < 1$ (GeV/$c$)$^2$, where
+hadron transverse momenta are expected to arise from non-perturbative effects,
+and also the domain of larger $P_{\rm{hT}}^{2}$, where contributions from
+higher-order perturbative QCD are expected to dominate. The multiplicities are
+fitted using a single-exponential function at small $P_{\rm{hT}}^{2}$ to study
+the dependence of the average transverse momentum $\langle
+P_{\rm{hT}}^{2}\rangle$ on $x$, $Q^2$ and $z$. The power-law behaviour of the
+multiplicities at large $P_{\rm{hT}}^{2}$ is investigated using various
+functional forms. The fits describe the data reasonably well over the full
+measured range.",1709.07374v1
+2016-12-02,Final COMPASS results on the deuteron spin-dependent structure function $g_1^{\rm d}$ and the Bjorken sum rule,"Final results are presented from the inclusive measurement of deep-inelastic
+polarised-muon scattering on longitudinally polarised deuterons using a $^6$LiD
+target. The data were taken at $160~{\rm GeV}$ beam energy and the results are
+shown for the kinematic range $1~({\rm GeV}/c)^2 < Q^2 < 100~({\rm GeV}/c)^2$
+in photon virtuality, $0.004<x<0.7$ in the Bjorken scaling variable and $W >
+4~{\rm GeV}/c^2$ in the mass of the hadronic final state. The deuteron
+double-spin asymmetry $A_1^{\rm d}$ and the deuteron longitudinal-spin
+structure function $g_1^{\rm d}$ are presented in bins of $x$ and $Q^2$.
+Towards lowest accessible values of $x$, $g_1^{\rm d}$ decreases and becomes
+consistent with zero within uncertainties. The presented final $g_1^{\rm d}$
+values together with the recently published final $g_1^{\rm p}$ values of
+COMPASS are used to again evaluate the Bjorken sum rule and perform the QCD fit
+to the $g_1$ world data at next-to-leading order of the strong coupling
+constant. In both cases, changes in central values of the resulting numbers are
+well within statistical uncertainties. The flavour-singlet axial charge $a_0$,
+{which is identified in the $\overline{\rm MS}$ renormalisation scheme with the
+total contribution of quark helicities to the nucleon spin}, is extracted from
+only the COMPASS deuteron data with negligible extrapolation uncertainty: $a_0
+(Q^2 = 3~({\rm GeV}/c)^2) = 0.32 \pm 0.02_{\rm stat} \pm0.04_{\rm syst} \pm
+0.05_{\rm evol}$. Together with the recent results on the proton spin structure
+function $g_1^{\rm p}$, the results on $g_1^{\rm d}$ constitute the COMPASS
+legacy on the measurements of $g_1$ through inclusive spin-dependent deep
+inelastic scattering.",1612.00620v1
+2017-07-06,Search for muoproduction of $X(3872)$ at COMPASS and indication of a new state $\widetilde{X}(3872)$,"We have searched for exclusive production of exotic charmonia in the reaction
+$\mu^+~N \rightarrow \mu^+ (J\!/\!\psi\pi^+\pi^-)\pi^{\pm}~N'$ using COMPASS
+data collected with incoming muons of 160 GeV/$c$ and 200 GeV/$c$ momentum. In
+the $J\!/\!\psi\pi^+\pi^-$ mass distribution we observe a signal with a
+statistical significance of 4.1 $\sigma$. Its mass and width are consistent
+with those of the $X(3872)$. The shape of the $\pi^+\pi^-$ mass distribution
+from the observed decay into $J\!/\!\psi\pi^+\pi^-$ shows disagreement with
+previous observations for $X(3872)$. The observed signal may be interpreted as
+a possible evidence of a new charmonium state. It could be associated with a
+neutral partner of $X(3872)$ with $C = -1$ predicted by a tetraquark model. The
+product of cross section and branching fraction of the decay of the observed
+state into $J\!/\!\psi\pi^+\pi^-$ is determined to be
+71$\pm$28(stat)$\pm$39(syst) pb.",1707.01796v2
+2015-12-16,Leading-order determination of the gluon polarisation from semi-inclusive deep inelastic scattering data,"Using a novel analysis technique, the gluon polarisation in the nucleon is
+re-evaluated using the longitudinal double-spin asymmetry measured in the cross
+section of semi-inclusive single-hadron muoproduction with photon virtuality
+$Q^2>1~({\rm GeV}/c)^2$. The data were obtained by the COMPASS experiment at
+CERN using a 160 GeV/$c$ polarised muon beam impinging on a polarised $^6$LiD
+target. By analysing the full range in hadron transverse momentum $p_{\rm T}$,
+the different $p_{\rm T}$-dependences of the underlying processes are separated
+using a neural-network approach. In the absence of pQCD calculations at
+next-to-leading order in the selected kinematic domain, the gluon polarisation
+$\Delta g/g$ is evaluated at leading order in pQCD at a hard scale of $\mu^2=
+\langle Q^2 \rangle = 3 ({\rm GeV}/c)^2$. It is determined in three intervals
+of the nucleon momentum fraction carried by gluons, $x_{\rm g}$, covering the
+range $0.04 \!<\! x_{ \rm g}\! <\! 0.28$~ and does not exhibit a significant
+dependence on $x_{\rm g}$. The average over the three intervals, $\langle
+\Delta g/g \rangle = 0.113 \pm 0.038_{\rm (stat.)}\pm 0.036_{\rm (syst.)}$ at
+$\langle x_{\rm g} \rangle \approx 0.10$, suggests that the gluon polarisation
+is positive in the measured $x_{\rm g}$ range.",1512.05053v2
+2016-09-20,Azimuthal asymmetries of charged hadrons produced in high-energy muon scattering off longitudinally polarised deuterons,"Single hadron azimuthal asymmetries of positive and negative hadrons produced
+in muon semi-inclusive deep inelastic scattering off longitudinally polarised
+deuterons are determined using the 2006 COMPASS data and also combined all
+deuteron COMPASS data. For each hadron charge, the dependence of the azimuthal
+asymmetry on the hadron azimuthal angle $\phi$ is obtained by means of a
+five-parameter fitting function that besides a $\phi$-independent term includes
+four modulations predicted by theory: $\sin\phi$, $\sin 2 \phi$, $\sin 3\phi$
+and $\cos\phi$. The amplitudes of the five terms have been extracted, first,
+for the hadrons in the whole available kinematic region. In further fits,
+performed for hadrons from a restricted kinematic region, the $\phi$-dependence
+is determined as a function of one of three variables (Bjorken-$x$, fractional
+energy of virtual photon taken by the outgoing hadron and hadron transverse
+momentum), while disregarding the others. Except the $\phi$-independent term,
+all the modulation amplitudes are very small, and no clear kinematic dependence
+could be observed within experimental uncertainties.",1609.06062v2
+2018-08-02,Letter of Intent: A New QCD facility at the M2 beam line of the CERN SPS (COMPASS++/AMBER),"A New QCD facility at the M2 beam line of the CERN SPS
+  COMPASS++/AMBER",1808.00848v6