ZWG817/Abstract · Datasets at Hugging Face

publicationDate stringlengths 1 2.79k	title stringlengths 1 36.5k ⌀	abstract stringlengths 1 37.3k ⌀	id stringlengths 9 47
2002-12-30	Dark propagation modes in optical lattices	We examine the stimulated light scattering onto the propagation modes of a dissipative optical lattice. We show that two different pump-probe configurations may lead to the excitation, via different mechanisms, of the same mode. We found that in one configuration the scattering on the propagation mode results in a resonance in the probe transmission spectrum while in the other configuration no modification of the scattering spectrum occurs, i.e. the mode is dark. A theoretical explanation of this behaviour is provided.	0212157v1
2003-09-29	Phase-control of directed diffusion in a symmetric optical lattice	We demonstrate the phenomenon of directed diffusion in a symmetric periodic potential. This has been realized with cold atoms in a one-dimensional dissipative optical lattice. The stochastic process of optical pumping leads to a diffusive dynamics of the atoms through the periodic structure, while a zero-mean force which breaks the temporal symmetry of the system is applied by phase-modulating one of the lattice beams. The atoms are set into directed motion as a result of the breaking of the temporal symmetry of the system.	0309208v1
2003-09-29	Synchronization of Hamiltonian motion and dissipative effects in optical lattices: Evidence for a stochastic resonance	We theoretically study the influence of the noise strength on the excitation of the Brillouin propagation modes in a dissipative optical lattice. We show that the excitation has a resonant behavior for a specific amount of noise corresponding to the precise synchronization of the Hamiltonian motion on the optical potential surfaces and the dissipative effects associated with optical pumping in the lattice. This corresponds to the phenomenon of stochastic resonance. Our results are obtained by numerical simulations and correspond to the analysis of microscopic quantities (atomic spatial distributions) as well as macroscopic quantities (enhancement of spatial diffusion and pump-probe spectra). We also present a simple analytical model in excellent agreement with the simulations.	0309210v1
2006-06-23	Playing Quantum Physics Jeopardy with zero-energy eigenstates	We describe an example of an exact, quantitative Jeopardy-type quantum mechanics problem. This problem type is based on the conditions in one-dimensional quantum systems that allow an energy eigenstate for the infinite square well to have zero curvature and zero energy when suitable Dirac delta functions are added. This condition and its solution are not often discussed in quantum mechanics texts and have interesting pedagogical consequences.	0606196v1
2006-10-18	Subsystem Codes	We investigate various aspects of operator quantum error-correcting codes or, as we prefer to call them, subsystem codes. We give various methods to derive subsystem codes from classical codes. We give a proof for the existence of subsystem codes using a counting argument similar to the quantum Gilbert-Varshamov bound. We derive linear programming bounds and other upper bounds. We answer the question whether or not there exist [[n,n-2d+2,r>0,d]]<sub>q</sub> subsystem codes. Finally, we compare stabilizer and subsystem codes with respect to the required number of syndrome qudits.	0610153v1
2007-05-14	The dynamical response to the node defect in thermally activated remagnetization of magnetic dot array	The influence of nonmagnetic central node defect on dynamical properties of regular square-shaped 5 x 5 segment of magnetic dot array under the thermal activation is investigated via computer simulations. Using stochastic Landau-Lifshitz-Gilbert equation we simulate hysteresis and relaxation processes. The remarkable quantitative and qualitative differences between magnetic dot arrays with nonmagnetic central node defect and magnetic dot arrays without defects have been found.	0705.1889v1
2007-05-18	Steady-state conduction in self-similar billiards	The self-similar Lorentz billiard channel is a spatially extended deterministic dynamical system which consists of an infinite one-dimensional sequence of cells whose sizes increase monotonically according to their indices. This special geometry induces a nonequilibrium stationary state with particles flowing steadily from the small to the large scales. The corresponding invariant measure has fractal properties reflected by the phase-space contraction rate of the dynamics restricted to a single cell with appropriate boundary conditions. In the near-equilibrium limit, we find numerical agreement between this quantity and the entropy production rate as specified by thermodynamics.	0705.2758v1
2007-06-04	Generation of microwave radiation in planar spin-transfer devices	Current induced precession states in spin-transfer devices are studied in the case of large easy plane anisotropy (present in most experimental setups). It is shown that the effective one-dimensional planar description provides a simple qualitative understanding of the emergence and evolution of such states. Switching boundaries are found analytically for the collinear device and the spin-flip transistor. The latter can generate microwave oscillations at zero external magnetic field without either special functional form of spin-transfer torque, or ``field-like'' terms, if Gilbert constant corresponds to the overdamped planar regime.	0706.0529v1
2007-12-26	Mass and angular-momentum inequalities for axi-symmetric initial data sets. II. Angular-momentum	We extend the validity of Dain's angular-momentum inequality to maximal, asymptotically flat, initial data sets on a simply connected manifold with several asymptotically flat ends which are invariant under a U(1) action and which admit a twist potential.	0712.4064v2
2008-01-28	TER: A Robot for Remote Ultrasonic Examination: Experimental Evaluations	This chapter: o Motivates the clinical use of robotic tele-echography o Introduces the TER system o Describes technical and clinical evaluations performed with TER	0801.4355v1
2008-03-14	Spin-torque shot noise in magnetic tunnel junctions	Spin polarized current may transfer angular momentum to a ferromagnet, resulting in a spin-torque phenomenon. At the same time the shot noise, associated with the current, leads to a non-equilibrium stochastic force acting on the ferromagnet. We derive stochastic version of Landau-Lifshitz-Gilbert equation for a magnetization of a ''free'' ferromagnetic layer in contact with a ''fixed'' ferromagnet. We solve the corresponding Fokker-Planck equation and show that the non-equilibrium noise yields to a non-monotonous dependence of the precession spectrum linewidth on the current.	0803.2101v1
2008-04-07	Paired Orbitals for Different Spins equations	Eigenvalue-type equations for Lowdin-Amos-Hall spin-paired (corresponding) orbitals are developed to provide an alternative to the standard spin-polarized Hartree-Fock or Kohn-Sham equations. Obtained equations are non-canonical unrestricted Hartree-Fock-type equations in which non-canonical orbitals are fixed to be biorthogonal spin-paired orbitals. To derive paired orbitals for different spins (PODS) equations there has been applied Adams-Gilbert localizing operator approach. PODS equations are especially useful for treatment of the broken-symmetry solutions for antiferromagnetic materials.	0804.0967v1
2008-04-26	Spin-torque oscillator based on tilted magnetization of the fixed layer	The spin torque oscillator (STO), where the magnetization of the fixed layer is tilted out of the film plane, is capable of strong microwave signal generation in zero magnetic field. Through numerical simulations of the Landau-Lifshitz-Gilbert-Slonczewski equations, within a macro-spin approximation, we study the microwave signal generation as a function of drive current for two realistic tilt angles. The tilt magnetization of the fixed layer can be achieved by using a material with high out-of-plane magnetocrystalline anisotropy, such as L10 FePt.	0804.4213v1
2008-07-11	Superconductivity up to 29 K in SrFe2As2 and BaFe2As2 at high pressures	We report the discovery of superconductivity at high pressure in SrFe2As2 and BaFe2As2. The superconducting transition temperatures are up to 27 K in SrFe2As2 and 29 K in BaFe2As2, making these the highest pressure-induced superconducting materials discovered thus far.	0807.1896v2
2008-07-14	An Adaptive Entanglement Distillation Scheme Using Quantum Low Density Parity Check Codes	Quantum low density parity check (QLDPC) codes are useful primitives for quantum information processing because they can be encoded and decoded efficiently. Besides, the error correcting capability of a few QLDPC codes exceeds the quantum Gilbert-Varshamov bound. Here, we report a numerical performance analysis of an adaptive entanglement distillation scheme using QLDPC codes. In particular, we find that the expected yield of our adaptive distillation scheme to combat depolarization errors exceed that of Leung and Shor whenever the error probability is less than about 0.07 or greater than about 0.28. This finding illustrates the effectiveness of using QLDPC codes in entanglement distillation.	0807.2122v1
2008-07-16	Analytical solution of the equation of motion for a rigid domain wall in a magnetic material with perpendicular anisotropy	This paper reports the solution of the equation of motion for a domain wall in a magnetic material which exhibits high magneto-crystalline anisotropy. Starting from the Landau-Lifschitz-Gilbert equation for field-induced motion, we solve the equation to give an analytical expression, which specifies the domain wall position as a function of time. Taking parameters from a Co/Pt multilayer system, we find good quantitative agreement between calculated and experimentally determined wall velocities, and show that high field uniform wall motion occurs when wall rigidity is assumed.	0807.2604v3
2008-07-16	A graphical extension for the Windows version of the Parallel Finite Element Micromagnetics Package (MagParExt)	In the current paper we present a graphical user interface useful for settings input parameter of the Windows precompiled binaries for the Parallel Finite Element Micromagnetics Package (MagPar). The Package is used for magnetization dynamics analysis on a base of the Landau-Lifshitz-Gilbert (LLG) equation. In an available version of the MagPar package there are several text files which control simulations. Presented here graphical extension (MagParExt) enables easy preparation of input and output data, stored in text files, and additionally, direct and fast creation of figures obtained from dependencies between simulated physical quantities.	0807.2655v1
2008-08-17	Attempt frequency of magnetization in nanomagnets with thin-film geometry	Solving the stochastic Landau-Lifshitz-Gilbert equation numerically, we investigate the effect of the potential landscape on the attempt frequency of magnetization in nanomagnets with the thin-film geometry. Numerical estimates of the attempt frequency are analyzed in comparison with theoretical predictions from the Fokker-Planck equation for the Neel-Brown model. It is found that for a nanomagnet with the thin-film geometry, theoretically predicted values for the universal case are in excellent agreement with numerical estimates.	0808.2281v1
2008-08-30	Path integral study of the role of correlation in exchange coupling of spins in double quantum dots and optical lattices	We explore exchange coupling of a pair of spins in a double dot and in an optical lattice. Our algorithm uses the frequency of exchanges in a bosonic path integral, evaluated with Monte Carlo. This algorithm is simple enough to be a "black box" calculator, yet gives insights into the role of correlation through two-particle probability densities, visualization of instantons, and pair correlation functions. We map the problem to Hubbard model and see that exchange and correlation renormalize the effective parameters, dramatically lowering U at larger separations.	0809.0038v1
2008-09-16	Stochastic dynamics of magnetization in a ferromagnetic nanoparticle out of equilibrium	We consider a small metallic particle (quantum dot) where ferromagnetism arises as a consequence of Stoner instability. When the particle is connected to electrodes, exchange of electrons between the particle and the electrodes leads to a temperature- and bias-driven Brownian motion of the direction of the particle magnetization. Under certain conditions this Brownian motion is described by the stochastic Landau-Lifshitz-Gilbert equation. As an example of its application, we calculate the frequency-dependent magnetic susceptibility of the particle in a constant external magnetic field, which is relevant for ferromagnetic resonance measurements.	0809.2611v1
2008-12-09	On densest packings of equal balls of $\rb^{n}$ and Marcinkiewicz spaces	We investigate, by "a la Marcinkiewicz" techniques applied to the (asymptotic) density function, how dense systems of equal spheres of $\rb^{n}, n \geq 1,$ can be partitioned at infinity in order to allow the computation of their density as a true limit and not a limsup. The density of a packing of equal balls is the norm 1 of the characteristic function of the systems of balls in the sense of Marcinkiewicz. Existence Theorems for densest sphere packings and completely saturated sphere packings of maximal density are given new direct proofs.	0812.1720v1
2009-01-26	Bioprotectant glassforming solutions confined in porous silicon nanocapillaries	Glycerol and trehalose-glycerol binary solutions are glass-forming liquids with remarkable bioprotectant properties. In this paper, we address the effects of confining of these solutions in straight channels of diameter D=8 nm formed by porous silicon. Neutron diffraction and incoherent quasielastic neutron scattering are used to reveal the different effects of nanoconfinement and addition of trehalose on the intermolecular structure and molecular dynamics of the liquid and glassy phases, on a nanosecond timescale.	0901.3994v1
2009-02-12	Computing equations for residually free groups	We show that there is no algorithm deciding whether the maximal residually free quotient of a given finitely presented group is finitely presentable or not. Given a finitely generated subgroup G of a finite product of limit groups, we discuss the possibility of finding an explicit set of defining equations (i.e. of expressing G as the maximal residually free quotient of an explicit finitely presented group).	0902.2119v2
2009-03-06	Simulation of current-induced microwave oscillation in geometrically confined domain wall	We studied magnetization dynamics of a geometrically confined domain wall under dc current by solving simultaneously the Landau-Lifshitz-Gilbert equation and diffusion equation for spin accumulation. We showed that the oscillation motion of the domain wall is driven by the spin-transfer torque and the dc current is converted to the ac voltage signal. The results means that the geometrically confined domain wall is applicable as a source of microwave oscillator.	0903.1151v1
2009-04-05	Projective Space Codes for the Injection Metric	In the context of error control in random linear network coding, it is useful to construct codes that comprise well-separated collections of subspaces of a vector space over a finite field. In this paper, the metric used is the so-called "injection distance", introduced by Silva and Kschischang. A Gilbert-Varshamov bound for such codes is derived. Using the code-construction framework of Etzion and Silberstein, new non-constant-dimension codes are constructed; these codes contain more codewords than comparable codes designed for the subspace metric.	0904.0813v2
2009-05-28	Hamilton cycles in random geometric graphs	We prove that, in the Gilbert model for a random geometric graph, almost every graph becomes Hamiltonian exactly when it first becomes 2-connected. This answers a question of Penrose. We also show that in the k-nearest neighbor model, there is a constant \kappa\ such that almost every \kappa-connected graph has a Hamilton cycle.	0905.4650v2
2009-06-25	Nonlinear Schroedinger-Poisson Theory for Quantum-Dot Helium	We use a nonlinear Schroedinger-Poisson equation to describe two interacting electrons with opposite spins confined in a parabolic potential, a quantum dot. We propose an effective form of the Poisson equation taking into account the dimensional mismatch of the two-dimensional electronic system and the three-dimensional electrostatics. The results agree with earlier numerical calculations performed in a large basis of two-body states and provide a simple model for continuous quantum-classical transition with increasing nonlinearity. Specific intriguing properties due to eigenstate non-orthogonality are emphasized.	0906.4650v1
2009-06-29	Performance of Magnetic Quantum Cellular Automata and Limitations due to Thermal Noise	Operation parameters of magnetic quantum cellular automata are evaluated for the purposes of reliable logic operation. The dynamics of the nanomagnets is simulated via the Landau-Lifshitz-Gilbert equations with a stochastic magnetic field corresponding to thermal fluctuations. It is found that in the macrospin approximation the switching speed does not change under scaling of both size and distances between nanomagnets. Thermal fluctuations put a limitation on the size of nanomagnets, since the gate error rate becomes excessive for nanomagnets smaller than 200nm at room temperature.	0906.5172v1
2009-09-15	Critical current density for spin transfer torque switching with composite free layer structure	Critical current density of composite free layer (CFL) in magnetic tunneling junction is investigated. CFL consists of two exchange coupled ferromagnetic layers, where the coupling is parallel or anti-parallel. Instability condition of the CFL under the spin transfer torque, which is related with critical current density, is obtained by analytic spin wave excitation model and confirmed by macro-spin Landau-Lifshitz-Gilbert equation. The critical current densities for the coupled two identical layers are investigated with various coupling strengths, and spin transfer torque efficiencies.	0909.2711v1
2009-09-25	Tunable steady-state domain wall oscillator with perpendicular magnetic anisotropy	We theoretically study domain wall oscillations upon the injection of a dc current through a geometrically constrained wire with perpendicular magnetic anisotropy. The oscillation frequency spectrum can be tuned by the injected current density, but additionally by the application of an external magnetic field independent of the power. The results of analytical calculations are supported by micromagnetic simulations based on the Landau-Lifshitz-Gilbert equation. The simple concept of our localized steady-state oscillator might prove useful as a nanoscale microwave generator with possible applications in telecommunication or for rf-assisted writing in magnetic hard drives.	0909.4733v1
2009-10-13	Dipolar field effect on microwave oscillation in a domain wall spin-valve	We examined dipolar field effects on the microwave generation in the domain wall spin-valve by solving simultaneously the Landau-Lifshitz-Gilbert and Zhang-Levy-Fert diffusion equations. By numerically analyzing dipolar field dependence, we showed that the microwave generation needs the dipole-dipole interaction for a 180$^\circ$ domain wall and the amplitude of the microwave voltage signal depends strongly on the exchange length. In order to design a microwave generator using the domain wall spin-valve with high efficiency, we propose that the materials with short exchange length are preferred.	0910.2280v1
2009-10-30	Dissipative dynamics of magnetic solitons in metals	Soliton dynamics in spin-textured metals generate electrical currents, which produce backaction through spin torques. We modify the Landau-Lifshitz-Gilbert equation and the corresponding solitonic equations of motion to include such higher-order texture effects. We also find a quasistatic equation for the induced electrochemical potential, which needs to be solved for self-consistently, in the incompressible limit. As an example, we consider the orbital motion of a vortex in a point-contact spin valve, and discuss modifications of orbit radius, frequency, and dissipation power.	0910.5912v2
2009-11-16	JSJ decompositions: definitions, existence, uniqueness. I: The JSJ deformation space	This paper and its companion arXiv:1002.4564 have been replaced by arXiv:1602.05139. We give a general simple definition of JSJ decompositions by means of a universal maximality property. The JSJ decomposition should not be viewed as a tree (which is not uniquely defined) but as a canonical deformation space of trees. We prove that JSJ decompositions of finitely presented groups always exist, without any assumption on edge groups. Many examples are given.	0911.3173v3
2010-02-15	Domain wall motion in ferromagnetic nanowires driven by arbitrary time-dependent fields: An exact result	We address the dynamics of magnetic domain walls in ferromagnetic nanowires under the influence of external time-dependent magnetic fields. We report a new exact spatiotemporal solution of the Landau-Lifshitz-Gilbert equation for the case of soft ferromagnetic wires and nanostructures with uniaxial anisotropy. The solution holds for applied fields with arbitrary strength and time dependence. We further extend this solution to applied fields slowly varying in space and to multiple domain walls.	1002.2913v1
2010-05-24	SN2010U -- a Luminous Nova in NGC 4214	The luminosity, light curve, post--maximum spectrum, and lack of a progenitor on deep pre-outburst images suggest that SN 2010U was a luminous, fast nova. Its outburst magnitude is consistent with that for a fast nova using the Maximum Magnitude-Rate of Decline relationship for classical novae.	1005.4356v1
2010-06-11	Highly Parallel Sparse Matrix-Matrix Multiplication	Generalized sparse matrix-matrix multiplication is a key primitive for many high performance graph algorithms as well as some linear solvers such as multigrid. We present the first parallel algorithms that achieve increasing speedups for an unbounded number of processors. Our algorithms are based on two-dimensional block distribution of sparse matrices where serial sections use a novel hypersparse kernel for scalability. We give a state-of-the-art MPI implementation of one of our algorithms. Our experiments show scaling up to thousands of processors on a variety of test scenarios.	1006.2183v1
2010-06-24	Boundary regularity for minimizers of the micromagnetic energy functional	Motivated by the construction of time-periodic solutions for the three-dimensional Landau-Lifshitz-Gilbert equation in the case of soft and small ferromagnetic particles, we investigate the regularity properties of minimizers of the micromagnetic energy functional at the boundary. In particular, we show that minimizers are regular provided the volume of the particle is sufficiently small. The approach uses a reflection construction at the boundary and an adaption of the well-known regularity theory for minimizing harmonic maps into spheres.	1006.4766v1
2010-06-24	Time-periodic Néel wall motions	In thin ferromagnetic films, the predominance of the magnetic shape anisotropy leads to in-plane magnetizations. The simplest domain wall in this geometry is the one-dimensional Neel wall that connects two magnetizations of opposite sign by a planar 180 degree rotation. In this paper, we perturb the static Neel wall profile in order to construct time-periodic Neel wall motions governed by to the Landau-Lifshitz-Gilbert equation. Our construction works within a certain parameter regime and requires the restriction to external magnetic fields with small amplitudes and suitable time averages.	1006.4768v1
2010-06-30	Supercurrent-Induced Magnetization Dynamics	We investigate supercurrent-induced magnetization dynamics in a Josephson junction with two misaligned ferromagnetic layers, and demonstrate a variety of effects by solving numerically the Landau-Lifshitz-Gilbert equation. In particular, we demonstrate the possibility to obtain supercurrent-induced magnetization switching for an experimentally feasible set of parameters, and clarify the favorable condition for the realization of magnetization reversal. These results constitute a superconducting analogue to conventional current-induced magnetization dynamics and indicate how spin-triplet supercurrents may be utilized for practical purposes in spintronics.	1007.0004v1
2010-07-09	Polarization and magnetization dynamics of a field-driven multiferroic structure	We consider a multiferroic chain with a linear magnetoelectric coupling induced by the electrostatic screening at the ferroelectric/ferromagnet interface. We study theoretically the dynamic ferroelectric and magnetic response to external magnetic and electric fields by utilizing an approach based on coupled Landau- Khalatnikov and finite-temperature Landau-Lifshitz-Gilbert equations. Additionally, we compare with Monte Carlo calculations. It is demonstrated that for material parameters corresponding to BaTiO3/Fe the polarization and the magnetization are controllable by external magnetic and electric fields respectively.	1007.1543v1
2010-07-11	Factorization of banded permutations	We consider the factorization of permutations into bandwidth 1 permutations, which are products of mutually nonadjacent simple transpositions. We exhibit an upper bound on the minimal number of such factors and thus prove a conjecture of Gilbert Strang: a banded permutation of bandwidth $w$ can be represented as the product of at most $2w-1$ permutations of bandwidth 1. An analogous result holds also for infinite and cyclically banded permutations.	1007.1760v2
2010-07-14	Nonlinear interference in a mean-field quantum model	Using similar nonlinear stationary mean-field models for Bose-Einstein Condensation of cold atoms and interacting electrons in a Quantum Dot, we propose to describe the original many-particle ground state as a one-particle statistical mixed state of the nonlinear eigenstates whose weights are provided by the eigenstate non-orthogonality. We search for physical grounds in the interpretation of our two main results, namely, quantum-classical nonlinear transition and interference between nonlinear eigenstates.	1007.2408v1
2011-01-17	Steiner Ratio for Manifolds	The Steiner ratio characterizes the greatest possible deviation of the length of a minimal spanning tree from the length of the minimal Steiner tree. In this paper, estimates of the Steiner ratio on Riemannian manifolds are obtained. As a corollary, the Steiner ratio for flat tori, flat Klein bottles, and projective plane of constant positive curvature are computed. Steiner ratio - Steiner problem - Gilbert--Pollack conjecture - surfaces of constant curvature	1101.3144v1
2011-02-04	Current-induced dynamics of composite free layer with antiferromagnetic interlayer exchange coupling	Current-induced dynamics in spin valves including composite free layer with antiferromagnetic interlayer exchange coupling is studied theoretically within the diffusive transport regime. We show that current-induced dynamics of a synthetic antiferromagnet is significantly different from dynamics of a synthetic ferrimagnet. From macrospin simulations we obtain conditions for switching the composite free layer, as well as for appearance of various self-sustained dynamical modes. Numerical simulations are compared with simple analytical models of critical current based on linearized Landau-Lifshitz-Gilbert equation.	1102.1028v2
2011-04-01	Spin waves cause non-linear friction	Energy dissipation is studied for a hard magnetic tip that scans a soft magnetic substrate. The dynamics of the atomic moments are simulated by solving the Landau-Lifshitz-Gilbert (LLG) equation numerically. The local energy currents are analysed for the case of a Heisenberg spin chain taken as substrate. This leads to an explanation for the velocity dependence of the friction force: The non-linear contribution for high velocities can be attributed to a spin wave front pushed by the tip along the substrate.	1104.0197v2
2011-05-31	Upper and Lower Bounds on the Minimum Distance of Expander Codes	The minimum distance of expander codes over GF(q) is studied. A new upper bound on the minimum distance of expander codes is derived. The bound is shown to lie under the Varshamov-Gilbert (VG) bound while q >= 32. Lower bounds on the minimum distance of some families of expander codes are obtained. A lower bound on the minimum distance of low-density parity-check (LDPC) codes with a Reed--Solomon constituent code over GF(q) is obtained. The bound is shown to be very close to the VG bound and to lie above the upper bound for expander codes.	1105.6224v1
2011-06-28	Stability of precessing domain walls in ferromagnetic nanowires	We show that recently reported precessing solution of Landau-Lifshitz-Gilbert equations in ferromagnetic nanowires is stable under small perturbations of initial data, applied field and anisotropy constant. Linear stability is established analytically, while nonlinear stability is verified numerically.	1106.5808v2
2011-07-01	Current induced magnetization reversal on the surface of a topological insulator	We study dynamics of the magnetization coupled to the surface Dirac fermions of a three di- mensional topological insulator. By solving the Landau-Lifshitz-Gilbert equation in the presence of charge current, we find current induced magnetization dynamics and discuss the possibility of mag- netization reversal. The torque from the current injection depends on the transmission probability through the ferromagnet and shows nontrivial dependence on the exchange coupling. The mag- netization dynamics is a direct manifestation of the inverse spin-galvanic effect and hence another ferromagnet is unnecessary to induce spin transfer torque in contrast to the conventional setup.	1107.0116v1
2011-08-05	Thermoelectric detection of ferromagnetic resonance of a nanoscale ferromagnet	We present thermoelectric measurements of the heat dissipated due to ferromagnetic resonance of a Permalloy strip. A microwave magnetic field, produced by an on-chip coplanar strip waveguide, is used to drive the magnetization precession. The generated heat is detected via Seebeck measurements on a thermocouple connected to the ferromagnet. The observed resonance peak shape is in agreement with the Landau-Lifshitz-Gilbert equation and is compared with thermoelectric finite element modeling. Unlike other methods, this technique is not restricted to electrically conductive media and is therefore also applicable to for instance ferromagnetic insulators.	1108.1286v1
2011-08-31	Effects of Fermion Flavor on Exciton Condensation in Double Layer Systems	We use fermionic path integral quantum Monte Carlo to study the effects of fermion flavor on the physical properties of dipolar exciton condensates in double layer systems. We find that by including spin in the system weakens the effective interlayer interaction strength, yet this has very little effect on the Kosterlitz-Thouless transition temperature. We further find that, to obtain the correct description of screening, it is necessary to account for correlation in both the interlayer and intralayer interactions. We show that while the excitonic binding cannot completely surpress screening by additional fermion flavors, their screening effectiveness is reduced leading to a much higher transition temperatures than predicted with large-N analysis.	1108.6107v1
2011-09-30	An ultrafast image recovery and recognition system implemented with nanomagnets possessing biaxial magnetocrystalline anisotropy	A circular magnetic disk with biaxial magnetocrystalline anisotropy has four stable magnetization states which can be used to encode a pixel's shade in a black/gray/white image. By solving the Landau-Lifshitz- Gilbert equation, we show that if moderate noise deflects the magnetization slightly from a stable state, it always returns to the original state, thereby automatically de-noising the corrupted image. The same system can compare a noisy input image with a stored image and make a matching decision using magneto-tunneling junctions. These tasks are executed at ultrahigh speeds (~2 ns for a 512\times512 pixel image).	1109.6932v1
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
2011-11-29	Supercurrent induced domain wall motion	We study the dynamics of a magnetic domain wall, inserted in, or juxtaposed to, a conventional superconductor, via the passage of a spin polarized current through a FSF junction. Solving the Landau-Lifshitz-Gilbert equation of motion for the magnetic moments we calculate the velocity of the domain wall and compare it with the case of a FNF junction. We find that in several regimes the domain wall velocity is larger when it is driven by a supercurrent.	1111.6751v1
2011-12-02	The Main Diagonal of a Permutation Matrix	By counting 1's in the "right half" of $2w$ consecutive rows, we locate the main diagonal of any doubly infinite permutation matrix with bandwidth $w$. Then the matrix can be correctly centered and factored into block-diagonal permutation matrices. Part II of the paper discusses the same questions for the much larger class of band-dominated matrices. The main diagonal is determined by the Fredholm index of a singly infinite submatrix. Thus the main diagonal is determined "at infinity" in general, but from only $2w$ rows for banded permutations.	1112.0582v2
2011-12-11	Stability of the Greedy Algorithm on the Circle	We consider a single-server system with service stations in each point of the circle. Customers arrive after exponential times at uniformly-distributed locations. The server moves at finite speed and adopts a greedy routing mechanism. It was conjectured by Coffman and Gilbert in~1987 that the service rate exceeding the arrival rate is a sufficient condition for the system to be positive recurrent, for any value of the speed. In this paper we show that the conjecture holds true.	1112.2389v3
2011-12-12	Riffle shuffles with biased cuts	The well-known Gilbert-Shannon-Reeds model for riffle shuffles assumes that the cards are initially cut 'about in half' and then riffled together. We analyze a natural variant where the initial cut is biased. Extending results of Fulman (1998), we show a sharp cutoff in separation and L-infinity distances. This analysis is possible due to the close connection between shuffling and quasisymmetric functions along with some complex analysis of a generating function.	1112.2650v1
2011-12-15	Solutions of the Fully Compressible Semi-Geostrophic System	The fully compressible semi-geostrophic system is widely used in the modelling of large-scale atmospheric flows. In this paper, we prove rigorously the existence of weak Lagrangian solutions of this system, formulated in the original physical coordinates. In addition, we provide an alternative proof of the earlier result on the existence of weak solutions of this system expressed in the so-called geostrophic, or dual, coordinates. The proofs are based on the optimal transport formulation of the problem and on recent general results concerning transport problems posed in the Wasserstein space of probability measures.	1112.3553v2
2012-01-23	Micromagnetic Simulations for Spin Transfer Torque in Magnetic Multilayers	We investigate the spin transfer torque (STT) in the magnetic multilayer structures with micromagnetic simulations. We implement the STT contribution for the magnetic multilayer structures in addition to the Landau-Lifshitz-Gilbert (LLG) micromagnetic simulators. Not only the Sloncewski STT term, the zero, first, and second order field- like terms are also considered, and the effects of the Oersted field by the current are addressed. We determine the switching current densities of the free layer with the exchange biased synthetic ferrimagnetic reference layers for various cases.	1201.4707v1
2012-01-26	Pseudospin Transfer Torques in Semiconductor Electron Bilayers	We use self-consistent quantum transport theory to investigate the influence of electron-electron interactions on interlayer transport in semiconductor electron bilayers in the absence of an external magnetic field. We conclude that, even though spontaneous pseudospin order does not occur at zero field, interaction-enhanced quasiparticle tunneling amplitudes and pseudospin transfer torques do alter tunneling I-V characteristics, and can lead to time-dependent response to a dc bias voltage.	1201.5569v2
2012-03-03	Skyrmion Generation by Current	Skyrmions, once a hypothesized field-theoretical object believed to describe the nature of elementary particles, became common sightings in recent years among several non-centrosymmetric metallic ferromagnets. For more practical applications of Skyrmionic matter as carriers of information, thus realizing the prospect of "Skyrmionics", it is necessary to have the means to create and manipulate Skyrmions individually. We show through extensive simulation of the Landau-Lifshitz-Gilbert equation that a circulating current imparted to the metallic chiral ferromagnetic system can create isolated Skyrmionic spin texture without the aid of external magnetic field.	1203.0638v1
2012-04-25	Numerical Study on Spin Torque Switching in Thermally Activated Region	We studied the spin torque switching of the single free layer in the thermally activated region by numerically solving the Landau-Lifshitz-Gilbert equation. We found that the temperature dependence of the switching time of the in-plane magnetized system is nonlinear, which means $b \neq 1$. Here, $b$ is the exponent of the current term in the switching rate formula and has been widely assumed to be unity. This result enables us to evaluate the thermal stability of spintronics devices.	1204.5596v2
2012-07-13	Theory of current-driven motion of Skyrmions and spirals in helical magnets	We study theoretically the dynamics of the spin textures, i.e., Skyrmion crystal (SkX) and spiral structure (SS), in two-dimensional helical magnets under external current. By numerically solving the Landau-Lifshitz-Gilbert equation, it is found that (i) the critical current density of the motion is much lower for SkX compared with SS in agreement with the recent experiment, (ii) there is no intrinsic pinning effect for SkX and the deformation of the internal structure of Skyrmion reduces the pinning effect dramatically, (iii) the Bragg intensity of SkX shows strong time-dependence as can be observed by neutron scattering experiment.	1207.3224v1
2012-07-19	Solar Orbiter: Exploring the Sun-heliosphere connection	The heliosphere represents a uniquely accessible domain of space, where fundamental physical processes common to solar, astrophysical and laboratory plasmas can be studied under conditions impossible to reproduce on Earth and unfeasible to observe from astronomical distances. Solar Orbiter, the first mission of ESA's Cosmic Vision 2015-2025 programme, will address the central question of heliophysics: How does the Sun create and control the heliosphere? In this paper, we present the scientific goals of the mission and provide an overview of the mission implementation.	1207.4579v2
2012-07-19	Harnessing the modulation instability spectrum in optical fibers with a periodic dispersion landscape	We report the experimental demonstration of modulation instability process assisted by a dispersion grating in an optical fiber. A simple analytical model is developed to further analyze and explain the complex dynamics of this process, showing that each of the multiple spectral components grows thanks to a quasi phase-matching mechanism inherent to the periodicity of the waveguide parameters. This model is confirmed by numerical simulations and it is successfully used to tailor the multi-peak modulation instability spectrum shape. These theoretical predictions are confirmed by experiments.	1207.4667v1
2012-08-11	Lexicodes over Rings	In this paper, we consider the construction of linear lexicodes over finite chain rings by using a $B$-ordering over these rings and a selection criterion. % and a greedy Algorithm. As examples we give lexicodes over $\mathbb{Z}_4$ and $\mathbb{F}_2+u\mathbb{F}_2$. %First, greedy algorithms are presented to construct %lexicodes using a multiplicative property. Then, greedy algorithms %are given for the case when the selection criteria is not %multiplicative such as the minimum distance constraint. It is shown that this construction produces many optimal codes over rings and also good binary codes. Some of these codes meet the Gilbert bound. We also obtain optimal self-dual codes, in particular the octacode.	1208.2361v2
2012-09-07	Self-sustained current oscillations in spin-blockaded quantum dots	Self-sustained current oscillation observed in spin-blockaded double quantum dots is explained as a consequence of periodic motion of dynamically polarized nuclear spins (along a limit cycle) in the spin-blockaded regime under an external magnetic field and a spin-transfer torque. It is shown, based on the Landau-Lifshtz-Gilbert equation, that a sequence of semistable limit cycle, Hopf and homoclinic bifurcations occurs as the external field is tuned. The divergent period near the homoclinic bifurcation explains well why the period in the experiment is so long and varies by many orders of magnitudes.	1209.1548v1
2012-10-04	All Spin Nano-magnetic State Elements	We propose an all spin state element to enable all spin state machines using spin currents and nanomagnets. We demonstrate via numerical simulations the operation of a state element a critical building block for synchronous, sequential logic computation. The numerical models encompass Landau-Lifshitz-Gilbert (LLG) nanomagnet dynamics with stochastic models and vector spin-transport in metallic magnetic and non-magnetic channels. Combined with all spin combinatorial logic, the state elements can enable synchronous and asynchronous computing elements.	1210.1613v1
2012-11-02	Effect of Spin Torque on Magnetization Switching Speed Having Nonuniform Spin Distribution	We study the influence of the spin torque, which depends on the space and time derivative of magnetization, on magnetization reversal time in a ferromagnetic fine particle. The spin torque operates to dissipate the angular momentum of the magnetization precession, and the torque increases in a spin vortex structure. We calculate the magnetization reversal time under a DC magnetic field using the Landau-Lifshitz-Gilbert equation containing a spin torque term. We found that the spin torque changes the magnetization switching speed significantly during the reversal process by maintaining a spin vortex in an intermediate state.	1211.0360v1
2013-01-14	magnum.fe: A micromagnetic finite-element simulation code based on FEniCS	We have developed a finite-element micromagnetic simulation code based on the FEniCS package called magnum.fe. Here we describe the numerical methods that are applied as well as their implementation with FEniCS. We apply a transformation method for the solution of the demagnetization-field problem. A semi-implicit weak formulation is used for the integration of the Landau-Lifshitz-Gilbert equation. Numerical experiments show the validity of simulation results. magnum.fe is open source and well documented. The broad feature range of the FEniCS package makes magnum.fe a good choice for the implementation of novel micromagnetic finite-element algorithms.	1301.3061v2
2013-02-04	Control of dissipation in superconducting films by magnetic stray fields	Hybrid superconducting/magnetic nanostructures on Si substrates have been built with identical physical dimensions but different magnetic configurations. By constructing arrays based on Co-dots with in-plane, out-of-plane, and vortex state magnetic configurations, the stray fields are systematically tuned. Dissipation in the mixed state of superconductors can be decreased (increased) by several orders of magnitude by decreasing (increasing) the stray magnetic fields. Furthermore, ordering of the stray fields over the entire array helps to suppress dissipation and enhance commensurability effects increasing the number of dissipation minima.	1302.0680v1
2013-02-09	Lower bounds on the minimum distance of long codes in the Lee metric	The Gilbert type bound for codes in the title is reviewed, both for small and large alphabets. Constructive lower bounds better than these existential bounds are derived from geometric codes, either over Fp or Fp2 ; or over even degree extensions of Fp: In the latter case the approach is concatena- tion with a good code for the Hamming metric as outer code and a short code for the Lee metric as an inner code. In the former case lower bounds on the minimum Lee distance are derived by algebraic geometric arguments inspired by results of Wu, Kuijper, Udaya (2007).	1302.2246v1
2013-03-04	Mansuripur's Paradox	A recent article claims that the Lorentz force law is incompatible with special relativity. We discuss the "paradox" on which this claim is based. The resolution depends on whether one assumes a "Gilbert" model for the magnetic dipole (separated monopoles) or the standard "Ampere" model (current loop). The former was presented in these pages many years ago; the latter requires the inclusion of "hidden momentum."	1303.0732v2
2013-04-09	Instability of Walker Propagating Domain Wall in Magnetic Nanowires	Stability of the well-known Walker propagating domain wall (DW) solution of the Landau-Lifshitz-Gilbert equation is analytically investigated. Surprisingly, the Walker's rigid body propagating DW mode is not stable against the spin wave/wavepacket emission. In the low field region only stern spin waves are emitted while both stern and bow waves are generated under high fields. In a high enough field, but below the Walker breakdown field, the Walker solution could be convective/absolute unstable if the transverse magnetic anisotropy is larger than a critical value, corresponding to a significant modification of the DW profile and DW propagating speed.	1304.2439v1
2013-04-26	Maximizing Spin Torque Diode Voltage by Optimizing Magnetization Alignment	The optimum condition of the magnetization alignment to maximize the spin torque diode voltage is derived by solving the Landau-Lifshitz-Gilbert equation. We show that the optimized diode voltage can be one order of magnitude larger than that of the conventional alignment where the easy axes of the free and the pinned layers are parallel. These analytical predictions are confirmed by numerical simulations.	1304.7079v1
2013-05-23	Residual properties of automorphism groups of (relatively) hyperbolic groups	We show that Out(G) is residually finite if G is a one-ended group that is hyperbolic relative to virtually polycyclic subgroups. More generally, if G is one-ended and hyperbolic relative to proper residually finite subgroups, the group of outer automorphisms preserving the peripheral structure is residually finite. We also show that Out(G) is virtually p-residually finite for every prime p if G is one-ended and toral relatively hyperbolic, or infinitely-ended and virtually p-residually finite.	1305.5403v3
2013-05-25	Thermally-Assisted Spin-Transfer Torque Dynamics in Energy Space	We consider the general Landau-Lifshitz-Gilbert theory underlying the magnetization dynamics of a macrospin magnet subject to spin-torque effects and thermal fluctuations. Thermally activated dynamical properties are analyzed by averaging the full magnetization equations over constant- energy orbits. After averaging, all the relevant dynamical scenarios are a function of the ratio between hard and easy axis anisotropies. We derive analytically the range of currents for which limit cycles exist and discuss the regimes in which the constant energy orbit averaging technique is applicable.	1305.5945v2
2013-06-10	Imperfect Construction of Microclusters	Microclusters are the basic building blocks used to construct cluster states capable of supporting fault-tolerant quantum computation. In this paper, we explore the consequences of errors on microcluster construction using two error models. To quantify the effect of the errors we calculate the fidelity of the constructed microclusters and the fidelity with which two such microclusters can be fused together. Such simulations are vital for gauging the capability of an experimental system to achieve fault tolerance.	1306.2202v1
2013-06-19	Weyl Phases in Point-Group Symmetric Superconductors	We study superconductivity in a Weyl semimetal with broken time-reversal symmetry and stabilized by a point-group symmetry. The resulting superconducting phase is characterized by topologically protected bulk nodes and surface states with Fermi arcs. The topological invariant governing the system is calculated using changes in eigenvalues of the point-group operator along high-symmetry momentum lines. We show that this invariant is determined by the Fermi surface topology of the Weyl semimetal. We discuss the effect of surface orientation and $C_4$-breaking strain as possible experimental consequences.	1306.4696v1
2013-06-21	The Polarization Signature of Local Bulk Flows	A large peculiar velocity of the intergalactic medium produces a Doppler shift of the cosmic microwave background with a frequency-dependent quadrupole term. This quadrupole will act as a source for polarization of the cosmic microwave background, creating a large-scale polarization anisotropy if the bulk flow is local and coherent on large scales. In the case where we are near the center of the moving region, the polarization signal is a pure quadrupole. We show that the signal is small, but detectable with future experiments for bulk flows as large as some recent reports.	1306.5248v3
2013-07-21	Rigidity in the Positive Mass Theorem with Charge	In this paper we show how a natural coupling of the Dirac equation with the generalized Jang equation, leads to a proof of the rigidity statement in the positive mass theorem with charge, without the maximal slicing condition, provided a solution to the coupled system exists.	1307.5499v4
2014-01-08	Tri-Dirac Surface Modes in Topological Superconductors	We propose a new type of topological surface modes having cubic dispersion in three-dimensional topological superconductors. Lower order dispersions are prohibited by the threefold rotational symmetry and time-reversal symmetry. Cooper pairing in the bulk changes sign under improper rotations, akin to$^{3}$He-B. The surface manifestations are a divergent surface density of states at the Fermi level and isospins that rotate three times as they circle the origin in momentum space. We propose that Heusler alloys with band inversion are candidate materials to harbor the novel topological superconductivity.	1401.1823v1
2014-01-09	Automated Code Generation for Lattice Quantum Chromodynamics and beyond	We present here our ongoing work on a Domain Specific Language which aims to simplify Monte-Carlo simulations and measurements in the domain of Lattice Quantum Chromodynamics. The tool-chain, called Qiral, is used to produce high-performance OpenMP C code from LaTeX sources. We discuss conceptual issues and details of implementation and optimization. The comparison of the performance of the generated code to the well-established simulation software is also made.	1401.2039v1
2014-01-13	Effect of Dzyaloshinskii Moriya interaction on magnetic vortex	The effect of the Dzyaloshinskii Moriya interaction on the vortex in magnetic microdisk was investigated by micro magnetic simulation based on the Landau Lifshitz Gilbert equation. Our results show that the DM interaction modifies the size of the vortex core, and also induces an out of plane magnetization component at the edge and inside the disk. The DM interaction can destabilizes one vortex handedness, generate a bias field to the vortex core and couple the vortex polarity and chirality. This DM-interaction-induced coupling can therefore provide a new way to control vortex polarity and chirality.	1401.3292v1
2014-01-31	Self-Oscillation in Spin Torque Oscillator Stabilized by Field-like Torque	The self-oscillation of the magnetization in a spin torque oscillator (STO) with a perpendicularly magnetized free layer and an in-plane magnetized pinned layer in the absence of an applied magnetic field was studied by numerically solving the Landau-Lifshitz-Gilbert equation. It was pointed out that field-like torque was necessary to realize stable self-oscillation in this type of STO at zero field. The numerical simulation at finite temperature showed that the presence of the field-like torque led to a high power with a relatively high oscillation frequency.	1401.8088v2
2014-02-05	Spin-polarized transport in ferromagnetic multilayers: An unconditionally convergent FEM integrator	We propose and analyze a decoupled time-marching scheme for the coupling of the Landau-Lifshitz-Gilbert equation with a quasilinear diffusion equation for the spin accumulation. This model describes the interplay of magnetization and electron spin accumulation in magnetic and non-magnetic multilayer structures. Despite the strong nonlinearity of the overall PDE system, the proposed integrator requires only the solution of two linear systems per time-step. Unconditional convergence of the integrator towards weak solutions is proved.	1402.0983v2
2014-02-12	An efficient algorithm for the entropy rate of a hidden Markov model with unambiguous symbols	We demonstrate an efficient formula to compute the entropy rate $H(\mu)$ of a hidden Markov process with $q$ output symbols where at least one symbol is unambiguously received. Using an approximation to $H(\mu)$ to the first $N$ terms we give a $O(Nq^3$) algorithm to compute the entropy rate of the hidden Markov model. We use the algorithm to estimate the entropy rate when the parameters of the hidden Markov model are unknown.In the case of $q =2$ the process is the output of the Z-channel and we use this fact to give bounds on the capacity of the Gilbert channel.	1402.2733v2
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
2014-04-18	Sparse Approximation, List Decoding, and Uncertainty Principles	We consider list versions of sparse approximation problems, where unlike the existing results in sparse approximation that consider situations with unique solutions, we are interested in multiple solutions. We introduce these problems and present the first combinatorial results on the output list size. These generalize and enhance some of the existing results on threshold phenomenon and uncertainty principles in sparse approximations. Our definitions and results are inspired by similar results in list decoding. We also present lower bound examples that bolster our results and show they are of the appropriate size.	1404.5190v2
2014-04-25	Linewidth of Power Spectrum Originated from Thermal Noise in Spin Torque Oscillator	A theoretical formula of the linewidth caused by the thermal activation in a spin torque oscillator with a perpendicularly magnetized free layer and an in-plane magnetized pinned layer was developed by solving the stochastic Landau-Lifshitz-Gilbert equation in the energy-phase representation. It is shown that the linewidth can be suppressed down to 0.1 MHz by applying a large current (10 mA for typical material parameters). A quality factor larger than 10^{4} is predicted in the large current limit, which is two orders of magnitude larger than the recently observed experimental value.	1404.6558v1
2014-08-11	An optimal irrigation network with infinitely many branching points	The Gilbert-Steiner problem is a mass transportation problem, where the cost of the transportation depends on the network used to move the mass and it is proportional to a certain power of the "flow". In this paper, we introduce a new formulation of the problem, which turns it into the minimization of a convex functional in a class of currents with coefficients in a group. This framework allows us to define calibrations, which can be used to prove the optimality of concrete configurations. We apply this technique to prove the optimality of a certain irrigation network, having the topological property mentioned in the title.	1408.2406v1
2014-09-04	Integer Generalized Splines on Cycles	Let G be a graph whose edges are labeled by positive integers. Label each vertex with an integer and suppose if two vertices are joined by an edge, the vertex labels are congruent to each other modulo the edge label. The set of vertex labels satisfying this condition is called a generalized spline. Gilbert, Polster, and Tymoczko recently defined generalized splines based on work on polynomial splines by Billera, Rose, Haas, Goresky-Kottwitz-Machperson, and many others. We focus on generalized splines on $n$-cycles. We construct a particularly nice basis for the module of splines on $n$-cycles. As an application, we construct generalized splines on star graphs, wheel graphs, and complete graphs.	1409.1481v1
2014-09-10	Proof of the Riemannian Penrose Inequality with Charge for Multiple Black Holes	We present a proof of the Riemannian Penrose inequality with charge in the context of asymptotically flat initial data sets for the Einstein-Maxwell equations, having possibly multiple black holes with no charged matter outside the horizon, and satisfying the relevant dominant energy condition. The proof is based on a generalization of Hubert Bray's conformal flow of metrics adapted to this setting.	1409.3271v2
2014-09-15	Enhanced synchronization in an array of spin torque nano oscillators in the presence of oscillating external magnetic field	We demonstrate that the synchronization of an array of electrically coupled spin torque nano-oscillators (STNO) modelled by Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation can be enhanced appreciably in the presence of a common external microwave magnetic field. The applied microwave magnetic field stabilizes and enhances the regions of synchronization in the parameter space of our analysis, where the oscillators are exhibiting synchronized oscillations thereby emitting improved microwave power. To characterize the synchronized oscillations we have calculated the locking range in the domain of external source frequency.	1409.4384v2
2014-10-19	Extensions of the Charged Riemannian Penrose Inequality	In this paper we investigate the extension of the charged Riemannian Penrose inequality to the case where charges are present outside the horizon. We prove a positive result when the charge densities are compactly supported, and present a counterexample when the charges extend to infinity. We also discuss additional extensions to other matter models.	1410.5027v2
2014-10-23	Quantum spin dynamics	The classical Landau-Lifshitz equation has been derived from quantum mechanics. Starting point is the assumption of a non-Hermitian Hamilton operator to take the energy dissipation into account. The corresponding quantum mechanical time dependent Schr\"odinger, Liouville and Heisenberg equation have been described and the similarities and differences between classical and quantum mechanical spin dynamics have been discussed. Furthermore, a time dependent Schr\"odinger equation corresponding to the classical Landau-Lifshitz-Gilbert equation and two ways to include temperature into the quantum mechanical spin dynamics have been proposed.	1410.6383v1
2014-12-04	Role of Magnetic Field in Self-Oscillation of Nanomagnet Excited by Spin Torque	The critical current of the self-oscillation of spin torque oscillator (STO) consisting of a perpendicularly magnetized free layer and an in-plane magnetized pinned layer was studied by solving the Landau-Lifshitz-Gilbert (LLG) equation. We found that the critical current diverged at certain field directions, indicating that the self-oscillation does not occur at these directions. It was also found that the sign of the critical current changed depending on the applied field direction.	1412.1532v1
2015-01-30	Memory functions of magnetic skyrmions	Magnetic skyrmion, a swirling spin texture, in chiral magnets is characterized by (i) nano-scale size ($\sim$1nm -- 100nm), (ii) topological stability, and (iii) gyro-dynamics. These features are shown to be advantageous for (a) high-density data-storage, (b) nonvolatile memory, and (c) ultra-low current and energy cost manipulation, respectively. By the numerical simulations of Landau-Lifshitz-Gilbert equation, the elementary functions of skyrmions are demonstrated aiming at the design principles of skyrmionic memory devices.	1501.07650v1
2015-02-14	Energy dissipation in single-domain ferromagnetic nanoparticles: Dynamical approach	We study, both analytically and numerically, the phenomenon of energy dissipation in single-domain ferromagnetic nanoparticles driven by an alternating magnetic field. Our interest is focused on the power loss resulting from the Landau-Lifshitz-Gilbert equation, which describes the precessional motion of the nanoparticle magnetic moment. We determine the power loss as a function of the field amplitude and frequency and analyze its dependence on different regimes of forced precession induced by circularly and linearly polarized magnetic fields. The conditions to maximize the nanoparticle heating are also analyzed.	1502.04222v1
2015-02-23	The Positive Mass Theorem for Multiple Rotating Charged Black Holes	In this paper a lower bound for the ADM mass is given in terms of the angular momenta and charges of black holes present in axisymmetric initial data sets for the Einstein-Maxwell equations. This generalizes the mass-angular momentum-charge inequality obtained by Chrusciel and Costa to the case of multiple black holes. We also weaken the hypotheses used in the proof of this result for single black holes, and establish the associated rigidity statement.	1502.06290v2
2015-02-24	An Upper Bound on the Minimum Distance of LDPC Codes over GF(q)	In [1] a syndrome counting based upper bound on the minimum distance of regular binary LDPC codes is given. In this paper we extend the bound to the case of irregular and generalized LDPC codes over GF(q). The comparison to the lower bound for LDPC codes over GF(q) and to the upper bound for non-binary codes is done. The new bound is shown to lie under the Gilbert-Varshamov bound at high rates.	1502.06874v1

2002-12-30

Dark propagation modes in optical lattices

We examine the stimulated light scattering onto the propagation modes of a dissipative optical lattice. We show that two different pump-probe configurations may lead to the excitation, via different mechanisms, of the same mode. We found that in one configuration the scattering on the propagation mode results in a resonance in the probe transmission spectrum while in the other configuration no modification of the scattering spectrum occurs, i.e. the mode is dark. A theoretical explanation of this behaviour is provided.

0212157v1

2003-09-29

Phase-control of directed diffusion in a symmetric optical lattice

We demonstrate the phenomenon of directed diffusion in a symmetric periodic potential. This has been realized with cold atoms in a one-dimensional dissipative optical lattice. The stochastic process of optical pumping leads to a diffusive dynamics of the atoms through the periodic structure, while a zero-mean force which breaks the temporal symmetry of the system is applied by phase-modulating one of the lattice beams. The atoms are set into directed motion as a result of the breaking of the temporal symmetry of the system.

0309208v1

2003-09-29

Synchronization of Hamiltonian motion and dissipative effects in optical lattices: Evidence for a stochastic resonance

We theoretically study the influence of the noise strength on the excitation of the Brillouin propagation modes in a dissipative optical lattice. We show that the excitation has a resonant behavior for a specific amount of noise corresponding to the precise synchronization of the Hamiltonian motion on the optical potential surfaces and the dissipative effects associated with optical pumping in the lattice. This corresponds to the phenomenon of stochastic resonance. Our results are obtained by numerical simulations and correspond to the analysis of microscopic quantities (atomic spatial distributions) as well as macroscopic quantities (enhancement of spatial diffusion and pump-probe spectra). We also present a simple analytical model in excellent agreement with the simulations.

0309210v1

2006-06-23

Playing Quantum Physics Jeopardy with zero-energy eigenstates

We describe an example of an exact, quantitative Jeopardy-type quantum mechanics problem. This problem type is based on the conditions in one-dimensional quantum systems that allow an energy eigenstate for the infinite square well to have zero curvature and zero energy when suitable Dirac delta functions are added. This condition and its solution are not often discussed in quantum mechanics texts and have interesting pedagogical consequences.

0606196v1

2006-10-18

Subsystem Codes

We investigate various aspects of operator quantum error-correcting codes or, as we prefer to call them, subsystem codes. We give various methods to derive subsystem codes from classical codes. We give a proof for the existence of subsystem codes using a counting argument similar to the quantum Gilbert-Varshamov bound. We derive linear programming bounds and other upper bounds. We answer the question whether or not there exist [[n,n-2d+2,r>0,d]]<sub>q</sub> subsystem codes. Finally, we compare stabilizer and subsystem codes with respect to the required number of syndrome qudits.

0610153v1

2007-05-14

The dynamical response to the node defect in thermally activated remagnetization of magnetic dot array

The influence of nonmagnetic central node defect on dynamical properties of regular square-shaped 5 x 5 segment of magnetic dot array under the thermal activation is investigated via computer simulations. Using stochastic Landau-Lifshitz-Gilbert equation we simulate hysteresis and relaxation processes. The remarkable quantitative and qualitative differences between magnetic dot arrays with nonmagnetic central node defect and magnetic dot arrays without defects have been found.

0705.1889v1

2007-05-18

Steady-state conduction in self-similar billiards

The self-similar Lorentz billiard channel is a spatially extended deterministic dynamical system which consists of an infinite one-dimensional sequence of cells whose sizes increase monotonically according to their indices. This special geometry induces a nonequilibrium stationary state with particles flowing steadily from the small to the large scales. The corresponding invariant measure has fractal properties reflected by the phase-space contraction rate of the dynamics restricted to a single cell with appropriate boundary conditions. In the near-equilibrium limit, we find numerical agreement between this quantity and the entropy production rate as specified by thermodynamics.

0705.2758v1

2007-06-04

Generation of microwave radiation in planar spin-transfer devices

Current induced precession states in spin-transfer devices are studied in the case of large easy plane anisotropy (present in most experimental setups). It is shown that the effective one-dimensional planar description provides a simple qualitative understanding of the emergence and evolution of such states. Switching boundaries are found analytically for the collinear device and the spin-flip transistor. The latter can generate microwave oscillations at zero external magnetic field without either special functional form of spin-transfer torque, or ``field-like'' terms, if Gilbert constant corresponds to the overdamped planar regime.

0706.0529v1

2007-12-26

Mass and angular-momentum inequalities for axi-symmetric initial data sets. II. Angular-momentum

We extend the validity of Dain's angular-momentum inequality to maximal, asymptotically flat, initial data sets on a simply connected manifold with several asymptotically flat ends which are invariant under a U(1) action and which admit a twist potential.

0712.4064v2

2008-01-28

TER: A Robot for Remote Ultrasonic Examination: Experimental Evaluations

This chapter: o Motivates the clinical use of robotic tele-echography o Introduces the TER system o Describes technical and clinical evaluations performed with TER

0801.4355v1

2008-03-14

Spin-torque shot noise in magnetic tunnel junctions

Spin polarized current may transfer angular momentum to a ferromagnet, resulting in a spin-torque phenomenon. At the same time the shot noise, associated with the current, leads to a non-equilibrium stochastic force acting on the ferromagnet. We derive stochastic version of Landau-Lifshitz-Gilbert equation for a magnetization of a ''free'' ferromagnetic layer in contact with a ''fixed'' ferromagnet. We solve the corresponding Fokker-Planck equation and show that the non-equilibrium noise yields to a non-monotonous dependence of the precession spectrum linewidth on the current.

0803.2101v1

2008-04-07

Paired Orbitals for Different Spins equations

Eigenvalue-type equations for Lowdin-Amos-Hall spin-paired (corresponding) orbitals are developed to provide an alternative to the standard spin-polarized Hartree-Fock or Kohn-Sham equations. Obtained equations are non-canonical unrestricted Hartree-Fock-type equations in which non-canonical orbitals are fixed to be biorthogonal spin-paired orbitals. To derive paired orbitals for different spins (PODS) equations there has been applied Adams-Gilbert localizing operator approach. PODS equations are especially useful for treatment of the broken-symmetry solutions for antiferromagnetic materials.

0804.0967v1

2008-04-26

Spin-torque oscillator based on tilted magnetization of the fixed layer

The spin torque oscillator (STO), where the magnetization of the fixed layer is tilted out of the film plane, is capable of strong microwave signal generation in zero magnetic field. Through numerical simulations of the Landau-Lifshitz-Gilbert-Slonczewski equations, within a macro-spin approximation, we study the microwave signal generation as a function of drive current for two realistic tilt angles. The tilt magnetization of the fixed layer can be achieved by using a material with high out-of-plane magnetocrystalline anisotropy, such as L10 FePt.

0804.4213v1

2008-07-11

Superconductivity up to 29 K in SrFe2As2 and BaFe2As2 at high pressures

We report the discovery of superconductivity at high pressure in SrFe2As2 and BaFe2As2. The superconducting transition temperatures are up to 27 K in SrFe2As2 and 29 K in BaFe2As2, making these the highest pressure-induced superconducting materials discovered thus far.

0807.1896v2

2008-07-14

An Adaptive Entanglement Distillation Scheme Using Quantum Low Density Parity Check Codes

Quantum low density parity check (QLDPC) codes are useful primitives for quantum information processing because they can be encoded and decoded efficiently. Besides, the error correcting capability of a few QLDPC codes exceeds the quantum Gilbert-Varshamov bound. Here, we report a numerical performance analysis of an adaptive entanglement distillation scheme using QLDPC codes. In particular, we find that the expected yield of our adaptive distillation scheme to combat depolarization errors exceed that of Leung and Shor whenever the error probability is less than about 0.07 or greater than about 0.28. This finding illustrates the effectiveness of using QLDPC codes in entanglement distillation.

0807.2122v1

2008-07-16

Analytical solution of the equation of motion for a rigid domain wall in a magnetic material with perpendicular anisotropy

This paper reports the solution of the equation of motion for a domain wall in a magnetic material which exhibits high magneto-crystalline anisotropy. Starting from the Landau-Lifschitz-Gilbert equation for field-induced motion, we solve the equation to give an analytical expression, which specifies the domain wall position as a function of time. Taking parameters from a Co/Pt multilayer system, we find good quantitative agreement between calculated and experimentally determined wall velocities, and show that high field uniform wall motion occurs when wall rigidity is assumed.

0807.2604v3

2008-07-16

A graphical extension for the Windows version of the Parallel Finite Element Micromagnetics Package (MagParExt)

In the current paper we present a graphical user interface useful for settings input parameter of the Windows precompiled binaries for the Parallel Finite Element Micromagnetics Package (MagPar). The Package is used for magnetization dynamics analysis on a base of the Landau-Lifshitz-Gilbert (LLG) equation. In an available version of the MagPar package there are several text files which control simulations. Presented here graphical extension (MagParExt) enables easy preparation of input and output data, stored in text files, and additionally, direct and fast creation of figures obtained from dependencies between simulated physical quantities.

0807.2655v1

2008-08-17

Attempt frequency of magnetization in nanomagnets with thin-film geometry

Solving the stochastic Landau-Lifshitz-Gilbert equation numerically, we investigate the effect of the potential landscape on the attempt frequency of magnetization in nanomagnets with the thin-film geometry. Numerical estimates of the attempt frequency are analyzed in comparison with theoretical predictions from the Fokker-Planck equation for the Neel-Brown model. It is found that for a nanomagnet with the thin-film geometry, theoretically predicted values for the universal case are in excellent agreement with numerical estimates.

0808.2281v1

2008-08-30

Path integral study of the role of correlation in exchange coupling of spins in double quantum dots and optical lattices

We explore exchange coupling of a pair of spins in a double dot and in an optical lattice. Our algorithm uses the frequency of exchanges in a bosonic path integral, evaluated with Monte Carlo. This algorithm is simple enough to be a "black box" calculator, yet gives insights into the role of correlation through two-particle probability densities, visualization of instantons, and pair correlation functions. We map the problem to Hubbard model and see that exchange and correlation renormalize the effective parameters, dramatically lowering U at larger separations.

0809.0038v1

2008-09-16

Stochastic dynamics of magnetization in a ferromagnetic nanoparticle out of equilibrium

We consider a small metallic particle (quantum dot) where ferromagnetism arises as a consequence of Stoner instability. When the particle is connected to electrodes, exchange of electrons between the particle and the electrodes leads to a temperature- and bias-driven Brownian motion of the direction of the particle magnetization. Under certain conditions this Brownian motion is described by the stochastic Landau-Lifshitz-Gilbert equation. As an example of its application, we calculate the frequency-dependent magnetic susceptibility of the particle in a constant external magnetic field, which is relevant for ferromagnetic resonance measurements.

0809.2611v1

2008-12-09

On densest packings of equal balls of $\rb^{n}$ and Marcinkiewicz spaces

We investigate, by "a la Marcinkiewicz" techniques applied to the (asymptotic) density function, how dense systems of equal spheres of $\rb^{n}, n \geq 1,$ can be partitioned at infinity in order to allow the computation of their density as a true limit and not a limsup. The density of a packing of equal balls is the norm 1 of the characteristic function of the systems of balls in the sense of Marcinkiewicz. Existence Theorems for densest sphere packings and completely saturated sphere packings of maximal density are given new direct proofs.

0812.1720v1

2009-01-26

Bioprotectant glassforming solutions confined in porous silicon nanocapillaries

Glycerol and trehalose-glycerol binary solutions are glass-forming liquids with remarkable bioprotectant properties. In this paper, we address the effects of confining of these solutions in straight channels of diameter D=8 nm formed by porous silicon. Neutron diffraction and incoherent quasielastic neutron scattering are used to reveal the different effects of nanoconfinement and addition of trehalose on the intermolecular structure and molecular dynamics of the liquid and glassy phases, on a nanosecond timescale.

0901.3994v1

2009-02-12

Computing equations for residually free groups

We show that there is no algorithm deciding whether the maximal residually free quotient of a given finitely presented group is finitely presentable or not. Given a finitely generated subgroup G of a finite product of limit groups, we discuss the possibility of finding an explicit set of defining equations (i.e. of expressing G as the maximal residually free quotient of an explicit finitely presented group).

0902.2119v2

2009-03-06

Simulation of current-induced microwave oscillation in geometrically confined domain wall

We studied magnetization dynamics of a geometrically confined domain wall under dc current by solving simultaneously the Landau-Lifshitz-Gilbert equation and diffusion equation for spin accumulation. We showed that the oscillation motion of the domain wall is driven by the spin-transfer torque and the dc current is converted to the ac voltage signal. The results means that the geometrically confined domain wall is applicable as a source of microwave oscillator.

0903.1151v1

2009-04-05

Projective Space Codes for the Injection Metric

In the context of error control in random linear network coding, it is useful to construct codes that comprise well-separated collections of subspaces of a vector space over a finite field. In this paper, the metric used is the so-called "injection distance", introduced by Silva and Kschischang. A Gilbert-Varshamov bound for such codes is derived. Using the code-construction framework of Etzion and Silberstein, new non-constant-dimension codes are constructed; these codes contain more codewords than comparable codes designed for the subspace metric.

0904.0813v2

2009-05-28

Hamilton cycles in random geometric graphs

We prove that, in the Gilbert model for a random geometric graph, almost every graph becomes Hamiltonian exactly when it first becomes 2-connected. This answers a question of Penrose. We also show that in the k-nearest neighbor model, there is a constant \kappa\ such that almost every \kappa-connected graph has a Hamilton cycle.

0905.4650v2

2009-06-25

Nonlinear Schroedinger-Poisson Theory for Quantum-Dot Helium

We use a nonlinear Schroedinger-Poisson equation to describe two interacting electrons with opposite spins confined in a parabolic potential, a quantum dot. We propose an effective form of the Poisson equation taking into account the dimensional mismatch of the two-dimensional electronic system and the three-dimensional electrostatics. The results agree with earlier numerical calculations performed in a large basis of two-body states and provide a simple model for continuous quantum-classical transition with increasing nonlinearity. Specific intriguing properties due to eigenstate non-orthogonality are emphasized.

0906.4650v1

2009-06-29

Performance of Magnetic Quantum Cellular Automata and Limitations due to Thermal Noise

Operation parameters of magnetic quantum cellular automata are evaluated for the purposes of reliable logic operation. The dynamics of the nanomagnets is simulated via the Landau-Lifshitz-Gilbert equations with a stochastic magnetic field corresponding to thermal fluctuations. It is found that in the macrospin approximation the switching speed does not change under scaling of both size and distances between nanomagnets. Thermal fluctuations put a limitation on the size of nanomagnets, since the gate error rate becomes excessive for nanomagnets smaller than 200nm at room temperature.

0906.5172v1

2009-09-15

Critical current density for spin transfer torque switching with composite free layer structure

Critical current density of composite free layer (CFL) in magnetic tunneling junction is investigated. CFL consists of two exchange coupled ferromagnetic layers, where the coupling is parallel or anti-parallel. Instability condition of the CFL under the spin transfer torque, which is related with critical current density, is obtained by analytic spin wave excitation model and confirmed by macro-spin Landau-Lifshitz-Gilbert equation. The critical current densities for the coupled two identical layers are investigated with various coupling strengths, and spin transfer torque efficiencies.

0909.2711v1

2009-09-25

Tunable steady-state domain wall oscillator with perpendicular magnetic anisotropy

We theoretically study domain wall oscillations upon the injection of a dc current through a geometrically constrained wire with perpendicular magnetic anisotropy. The oscillation frequency spectrum can be tuned by the injected current density, but additionally by the application of an external magnetic field independent of the power. The results of analytical calculations are supported by micromagnetic simulations based on the Landau-Lifshitz-Gilbert equation. The simple concept of our localized steady-state oscillator might prove useful as a nanoscale microwave generator with possible applications in telecommunication or for rf-assisted writing in magnetic hard drives.

0909.4733v1

2009-10-13

Dipolar field effect on microwave oscillation in a domain wall spin-valve

We examined dipolar field effects on the microwave generation in the domain wall spin-valve by solving simultaneously the Landau-Lifshitz-Gilbert and Zhang-Levy-Fert diffusion equations. By numerically analyzing dipolar field dependence, we showed that the microwave generation needs the dipole-dipole interaction for a 180$^\circ$ domain wall and the amplitude of the microwave voltage signal depends strongly on the exchange length. In order to design a microwave generator using the domain wall spin-valve with high efficiency, we propose that the materials with short exchange length are preferred.

0910.2280v1

2009-10-30

Dissipative dynamics of magnetic solitons in metals

Soliton dynamics in spin-textured metals generate electrical currents, which produce backaction through spin torques. We modify the Landau-Lifshitz-Gilbert equation and the corresponding solitonic equations of motion to include such higher-order texture effects. We also find a quasistatic equation for the induced electrochemical potential, which needs to be solved for self-consistently, in the incompressible limit. As an example, we consider the orbital motion of a vortex in a point-contact spin valve, and discuss modifications of orbit radius, frequency, and dissipation power.

0910.5912v2

2009-11-16

JSJ decompositions: definitions, existence, uniqueness. I: The JSJ deformation space

This paper and its companion arXiv:1002.4564 have been replaced by arXiv:1602.05139. We give a general simple definition of JSJ decompositions by means of a universal maximality property. The JSJ decomposition should not be viewed as a tree (which is not uniquely defined) but as a canonical deformation space of trees. We prove that JSJ decompositions of finitely presented groups always exist, without any assumption on edge groups. Many examples are given.

0911.3173v3

2010-02-15

Domain wall motion in ferromagnetic nanowires driven by arbitrary time-dependent fields: An exact result

We address the dynamics of magnetic domain walls in ferromagnetic nanowires under the influence of external time-dependent magnetic fields. We report a new exact spatiotemporal solution of the Landau-Lifshitz-Gilbert equation for the case of soft ferromagnetic wires and nanostructures with uniaxial anisotropy. The solution holds for applied fields with arbitrary strength and time dependence. We further extend this solution to applied fields slowly varying in space and to multiple domain walls.

1002.2913v1

2010-05-24

SN2010U -- a Luminous Nova in NGC 4214

The luminosity, light curve, post--maximum spectrum, and lack of a progenitor on deep pre-outburst images suggest that SN 2010U was a luminous, fast nova. Its outburst magnitude is consistent with that for a fast nova using the Maximum Magnitude-Rate of Decline relationship for classical novae.

1005.4356v1

2010-06-11

Highly Parallel Sparse Matrix-Matrix Multiplication

Generalized sparse matrix-matrix multiplication is a key primitive for many high performance graph algorithms as well as some linear solvers such as multigrid. We present the first parallel algorithms that achieve increasing speedups for an unbounded number of processors. Our algorithms are based on two-dimensional block distribution of sparse matrices where serial sections use a novel hypersparse kernel for scalability. We give a state-of-the-art MPI implementation of one of our algorithms. Our experiments show scaling up to thousands of processors on a variety of test scenarios.

1006.2183v1

2010-06-24

Boundary regularity for minimizers of the micromagnetic energy functional

Motivated by the construction of time-periodic solutions for the three-dimensional Landau-Lifshitz-Gilbert equation in the case of soft and small ferromagnetic particles, we investigate the regularity properties of minimizers of the micromagnetic energy functional at the boundary. In particular, we show that minimizers are regular provided the volume of the particle is sufficiently small. The approach uses a reflection construction at the boundary and an adaption of the well-known regularity theory for minimizing harmonic maps into spheres.

1006.4766v1

2010-06-24

Time-periodic Néel wall motions

In thin ferromagnetic films, the predominance of the magnetic shape anisotropy leads to in-plane magnetizations. The simplest domain wall in this geometry is the one-dimensional Neel wall that connects two magnetizations of opposite sign by a planar 180 degree rotation. In this paper, we perturb the static Neel wall profile in order to construct time-periodic Neel wall motions governed by to the Landau-Lifshitz-Gilbert equation. Our construction works within a certain parameter regime and requires the restriction to external magnetic fields with small amplitudes and suitable time averages.

1006.4768v1

2010-06-30

Supercurrent-Induced Magnetization Dynamics

We investigate supercurrent-induced magnetization dynamics in a Josephson junction with two misaligned ferromagnetic layers, and demonstrate a variety of effects by solving numerically the Landau-Lifshitz-Gilbert equation. In particular, we demonstrate the possibility to obtain supercurrent-induced magnetization switching for an experimentally feasible set of parameters, and clarify the favorable condition for the realization of magnetization reversal. These results constitute a superconducting analogue to conventional current-induced magnetization dynamics and indicate how spin-triplet supercurrents may be utilized for practical purposes in spintronics.

1007.0004v1

2010-07-09

Polarization and magnetization dynamics of a field-driven multiferroic structure

We consider a multiferroic chain with a linear magnetoelectric coupling induced by the electrostatic screening at the ferroelectric/ferromagnet interface. We study theoretically the dynamic ferroelectric and magnetic response to external magnetic and electric fields by utilizing an approach based on coupled Landau- Khalatnikov and finite-temperature Landau-Lifshitz-Gilbert equations. Additionally, we compare with Monte Carlo calculations. It is demonstrated that for material parameters corresponding to BaTiO3/Fe the polarization and the magnetization are controllable by external magnetic and electric fields respectively.

1007.1543v1

2010-07-11

Factorization of banded permutations

We consider the factorization of permutations into bandwidth 1 permutations, which are products of mutually nonadjacent simple transpositions. We exhibit an upper bound on the minimal number of such factors and thus prove a conjecture of Gilbert Strang: a banded permutation of bandwidth $w$ can be represented as the product of at most $2w-1$ permutations of bandwidth 1. An analogous result holds also for infinite and cyclically banded permutations.

1007.1760v2

2010-07-14

Nonlinear interference in a mean-field quantum model

Using similar nonlinear stationary mean-field models for Bose-Einstein Condensation of cold atoms and interacting electrons in a Quantum Dot, we propose to describe the original many-particle ground state as a one-particle statistical mixed state of the nonlinear eigenstates whose weights are provided by the eigenstate non-orthogonality. We search for physical grounds in the interpretation of our two main results, namely, quantum-classical nonlinear transition and interference between nonlinear eigenstates.

1007.2408v1

2011-01-17

Steiner Ratio for Manifolds

The Steiner ratio characterizes the greatest possible deviation of the length of a minimal spanning tree from the length of the minimal Steiner tree. In this paper, estimates of the Steiner ratio on Riemannian manifolds are obtained. As a corollary, the Steiner ratio for flat tori, flat Klein bottles, and projective plane of constant positive curvature are computed. Steiner ratio - Steiner problem - Gilbert--Pollack conjecture - surfaces of constant curvature

1101.3144v1

2011-02-04

Current-induced dynamics of composite free layer with antiferromagnetic interlayer exchange coupling

Current-induced dynamics in spin valves including composite free layer with antiferromagnetic interlayer exchange coupling is studied theoretically within the diffusive transport regime. We show that current-induced dynamics of a synthetic antiferromagnet is significantly different from dynamics of a synthetic ferrimagnet. From macrospin simulations we obtain conditions for switching the composite free layer, as well as for appearance of various self-sustained dynamical modes. Numerical simulations are compared with simple analytical models of critical current based on linearized Landau-Lifshitz-Gilbert equation.

1102.1028v2

2011-04-01

Spin waves cause non-linear friction

Energy dissipation is studied for a hard magnetic tip that scans a soft magnetic substrate. The dynamics of the atomic moments are simulated by solving the Landau-Lifshitz-Gilbert (LLG) equation numerically. The local energy currents are analysed for the case of a Heisenberg spin chain taken as substrate. This leads to an explanation for the velocity dependence of the friction force: The non-linear contribution for high velocities can be attributed to a spin wave front pushed by the tip along the substrate.

1104.0197v2

2011-05-31

Upper and Lower Bounds on the Minimum Distance of Expander Codes

The minimum distance of expander codes over GF(q) is studied. A new upper bound on the minimum distance of expander codes is derived. The bound is shown to lie under the Varshamov-Gilbert (VG) bound while q >= 32. Lower bounds on the minimum distance of some families of expander codes are obtained. A lower bound on the minimum distance of low-density parity-check (LDPC) codes with a Reed--Solomon constituent code over GF(q) is obtained. The bound is shown to be very close to the VG bound and to lie above the upper bound for expander codes.

1105.6224v1

2011-06-28

Stability of precessing domain walls in ferromagnetic nanowires

We show that recently reported precessing solution of Landau-Lifshitz-Gilbert equations in ferromagnetic nanowires is stable under small perturbations of initial data, applied field and anisotropy constant. Linear stability is established analytically, while nonlinear stability is verified numerically.

1106.5808v2

2011-07-01

Current induced magnetization reversal on the surface of a topological insulator

We study dynamics of the magnetization coupled to the surface Dirac fermions of a three di- mensional topological insulator. By solving the Landau-Lifshitz-Gilbert equation in the presence of charge current, we find current induced magnetization dynamics and discuss the possibility of mag- netization reversal. The torque from the current injection depends on the transmission probability through the ferromagnet and shows nontrivial dependence on the exchange coupling. The mag- netization dynamics is a direct manifestation of the inverse spin-galvanic effect and hence another ferromagnet is unnecessary to induce spin transfer torque in contrast to the conventional setup.

1107.0116v1

2011-08-05

Thermoelectric detection of ferromagnetic resonance of a nanoscale ferromagnet

We present thermoelectric measurements of the heat dissipated due to ferromagnetic resonance of a Permalloy strip. A microwave magnetic field, produced by an on-chip coplanar strip waveguide, is used to drive the magnetization precession. The generated heat is detected via Seebeck measurements on a thermocouple connected to the ferromagnet. The observed resonance peak shape is in agreement with the Landau-Lifshitz-Gilbert equation and is compared with thermoelectric finite element modeling. Unlike other methods, this technique is not restricted to electrically conductive media and is therefore also applicable to for instance ferromagnetic insulators.

1108.1286v1

2011-08-31

Effects of Fermion Flavor on Exciton Condensation in Double Layer Systems

We use fermionic path integral quantum Monte Carlo to study the effects of fermion flavor on the physical properties of dipolar exciton condensates in double layer systems. We find that by including spin in the system weakens the effective interlayer interaction strength, yet this has very little effect on the Kosterlitz-Thouless transition temperature. We further find that, to obtain the correct description of screening, it is necessary to account for correlation in both the interlayer and intralayer interactions. We show that while the excitonic binding cannot completely surpress screening by additional fermion flavors, their screening effectiveness is reduced leading to a much higher transition temperatures than predicted with large-N analysis.

1108.6107v1

2011-09-30

An ultrafast image recovery and recognition system implemented with nanomagnets possessing biaxial magnetocrystalline anisotropy

A circular magnetic disk with biaxial magnetocrystalline anisotropy has four stable magnetization states which can be used to encode a pixel's shade in a black/gray/white image. By solving the Landau-Lifshitz- Gilbert equation, we show that if moderate noise deflects the magnetization slightly from a stable state, it always returns to the original state, thereby automatically de-noising the corrupted image. The same system can compare a noisy input image with a stored image and make a matching decision using magneto-tunneling junctions. These tasks are executed at ultrahigh speeds (~2 ns for a 512\times512 pixel image).

1109.6932v1

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

2011-11-29

Supercurrent induced domain wall motion

We study the dynamics of a magnetic domain wall, inserted in, or juxtaposed to, a conventional superconductor, via the passage of a spin polarized current through a FSF junction. Solving the Landau-Lifshitz-Gilbert equation of motion for the magnetic moments we calculate the velocity of the domain wall and compare it with the case of a FNF junction. We find that in several regimes the domain wall velocity is larger when it is driven by a supercurrent.

1111.6751v1

2011-12-02

The Main Diagonal of a Permutation Matrix

By counting 1's in the "right half" of $2w$ consecutive rows, we locate the main diagonal of any doubly infinite permutation matrix with bandwidth $w$. Then the matrix can be correctly centered and factored into block-diagonal permutation matrices. Part II of the paper discusses the same questions for the much larger class of band-dominated matrices. The main diagonal is determined by the Fredholm index of a singly infinite submatrix. Thus the main diagonal is determined "at infinity" in general, but from only $2w$ rows for banded permutations.

1112.0582v2

2011-12-11

Stability of the Greedy Algorithm on the Circle

We consider a single-server system with service stations in each point of the circle. Customers arrive after exponential times at uniformly-distributed locations. The server moves at finite speed and adopts a greedy routing mechanism. It was conjectured by Coffman and Gilbert in~1987 that the service rate exceeding the arrival rate is a sufficient condition for the system to be positive recurrent, for any value of the speed. In this paper we show that the conjecture holds true.

1112.2389v3

2011-12-12

Riffle shuffles with biased cuts

The well-known Gilbert-Shannon-Reeds model for riffle shuffles assumes that the cards are initially cut 'about in half' and then riffled together. We analyze a natural variant where the initial cut is biased. Extending results of Fulman (1998), we show a sharp cutoff in separation and L-infinity distances. This analysis is possible due to the close connection between shuffling and quasisymmetric functions along with some complex analysis of a generating function.

1112.2650v1

2011-12-15

Solutions of the Fully Compressible Semi-Geostrophic System

The fully compressible semi-geostrophic system is widely used in the modelling of large-scale atmospheric flows. In this paper, we prove rigorously the existence of weak Lagrangian solutions of this system, formulated in the original physical coordinates. In addition, we provide an alternative proof of the earlier result on the existence of weak solutions of this system expressed in the so-called geostrophic, or dual, coordinates. The proofs are based on the optimal transport formulation of the problem and on recent general results concerning transport problems posed in the Wasserstein space of probability measures.

1112.3553v2

2012-01-23

Micromagnetic Simulations for Spin Transfer Torque in Magnetic Multilayers

We investigate the spin transfer torque (STT) in the magnetic multilayer structures with micromagnetic simulations. We implement the STT contribution for the magnetic multilayer structures in addition to the Landau-Lifshitz-Gilbert (LLG) micromagnetic simulators. Not only the Sloncewski STT term, the zero, first, and second order field- like terms are also considered, and the effects of the Oersted field by the current are addressed. We determine the switching current densities of the free layer with the exchange biased synthetic ferrimagnetic reference layers for various cases.

1201.4707v1

2012-01-26

Pseudospin Transfer Torques in Semiconductor Electron Bilayers

We use self-consistent quantum transport theory to investigate the influence of electron-electron interactions on interlayer transport in semiconductor electron bilayers in the absence of an external magnetic field. We conclude that, even though spontaneous pseudospin order does not occur at zero field, interaction-enhanced quasiparticle tunneling amplitudes and pseudospin transfer torques do alter tunneling I-V characteristics, and can lead to time-dependent response to a dc bias voltage.

1201.5569v2

2012-03-03

Skyrmion Generation by Current

Skyrmions, once a hypothesized field-theoretical object believed to describe the nature of elementary particles, became common sightings in recent years among several non-centrosymmetric metallic ferromagnets. For more practical applications of Skyrmionic matter as carriers of information, thus realizing the prospect of "Skyrmionics", it is necessary to have the means to create and manipulate Skyrmions individually. We show through extensive simulation of the Landau-Lifshitz-Gilbert equation that a circulating current imparted to the metallic chiral ferromagnetic system can create isolated Skyrmionic spin texture without the aid of external magnetic field.

1203.0638v1

2012-04-25

Numerical Study on Spin Torque Switching in Thermally Activated Region

We studied the spin torque switching of the single free layer in the thermally activated region by numerically solving the Landau-Lifshitz-Gilbert equation. We found that the temperature dependence of the switching time of the in-plane magnetized system is nonlinear, which means $b \neq 1$. Here, $b$ is the exponent of the current term in the switching rate formula and has been widely assumed to be unity. This result enables us to evaluate the thermal stability of spintronics devices.

1204.5596v2

2012-07-13

Theory of current-driven motion of Skyrmions and spirals in helical magnets

We study theoretically the dynamics of the spin textures, i.e., Skyrmion crystal (SkX) and spiral structure (SS), in two-dimensional helical magnets under external current. By numerically solving the Landau-Lifshitz-Gilbert equation, it is found that (i) the critical current density of the motion is much lower for SkX compared with SS in agreement with the recent experiment, (ii) there is no intrinsic pinning effect for SkX and the deformation of the internal structure of Skyrmion reduces the pinning effect dramatically, (iii) the Bragg intensity of SkX shows strong time-dependence as can be observed by neutron scattering experiment.

1207.3224v1

2012-07-19

Solar Orbiter: Exploring the Sun-heliosphere connection

The heliosphere represents a uniquely accessible domain of space, where fundamental physical processes common to solar, astrophysical and laboratory plasmas can be studied under conditions impossible to reproduce on Earth and unfeasible to observe from astronomical distances. Solar Orbiter, the first mission of ESA's Cosmic Vision 2015-2025 programme, will address the central question of heliophysics: How does the Sun create and control the heliosphere? In this paper, we present the scientific goals of the mission and provide an overview of the mission implementation.

1207.4579v2

2012-07-19

Harnessing the modulation instability spectrum in optical fibers with a periodic dispersion landscape

We report the experimental demonstration of modulation instability process assisted by a dispersion grating in an optical fiber. A simple analytical model is developed to further analyze and explain the complex dynamics of this process, showing that each of the multiple spectral components grows thanks to a quasi phase-matching mechanism inherent to the periodicity of the waveguide parameters. This model is confirmed by numerical simulations and it is successfully used to tailor the multi-peak modulation instability spectrum shape. These theoretical predictions are confirmed by experiments.

1207.4667v1

2012-08-11

Lexicodes over Rings

In this paper, we consider the construction of linear lexicodes over finite chain rings by using a $B$-ordering over these rings and a selection criterion. % and a greedy Algorithm. As examples we give lexicodes over $\mathbb{Z}_4$ and $\mathbb{F}_2+u\mathbb{F}_2$. %First, greedy algorithms are presented to construct %lexicodes using a multiplicative property. Then, greedy algorithms %are given for the case when the selection criteria is not %multiplicative such as the minimum distance constraint. It is shown that this construction produces many optimal codes over rings and also good binary codes. Some of these codes meet the Gilbert bound. We also obtain optimal self-dual codes, in particular the octacode.

1208.2361v2

2012-09-07

Self-sustained current oscillations in spin-blockaded quantum dots

Self-sustained current oscillation observed in spin-blockaded double quantum dots is explained as a consequence of periodic motion of dynamically polarized nuclear spins (along a limit cycle) in the spin-blockaded regime under an external magnetic field and a spin-transfer torque. It is shown, based on the Landau-Lifshtz-Gilbert equation, that a sequence of semistable limit cycle, Hopf and homoclinic bifurcations occurs as the external field is tuned. The divergent period near the homoclinic bifurcation explains well why the period in the experiment is so long and varies by many orders of magnitudes.

1209.1548v1

2012-10-04

All Spin Nano-magnetic State Elements

We propose an all spin state element to enable all spin state machines using spin currents and nanomagnets. We demonstrate via numerical simulations the operation of a state element a critical building block for synchronous, sequential logic computation. The numerical models encompass Landau-Lifshitz-Gilbert (LLG) nanomagnet dynamics with stochastic models and vector spin-transport in metallic magnetic and non-magnetic channels. Combined with all spin combinatorial logic, the state elements can enable synchronous and asynchronous computing elements.

1210.1613v1

2012-11-02

Effect of Spin Torque on Magnetization Switching Speed Having Nonuniform Spin Distribution

We study the influence of the spin torque, which depends on the space and time derivative of magnetization, on magnetization reversal time in a ferromagnetic fine particle. The spin torque operates to dissipate the angular momentum of the magnetization precession, and the torque increases in a spin vortex structure. We calculate the magnetization reversal time under a DC magnetic field using the Landau-Lifshitz-Gilbert equation containing a spin torque term. We found that the spin torque changes the magnetization switching speed significantly during the reversal process by maintaining a spin vortex in an intermediate state.

1211.0360v1

2013-01-14

magnum.fe: A micromagnetic finite-element simulation code based on FEniCS

We have developed a finite-element micromagnetic simulation code based on the FEniCS package called magnum.fe. Here we describe the numerical methods that are applied as well as their implementation with FEniCS. We apply a transformation method for the solution of the demagnetization-field problem. A semi-implicit weak formulation is used for the integration of the Landau-Lifshitz-Gilbert equation. Numerical experiments show the validity of simulation results. magnum.fe is open source and well documented. The broad feature range of the FEniCS package makes magnum.fe a good choice for the implementation of novel micromagnetic finite-element algorithms.

1301.3061v2

2013-02-04

Control of dissipation in superconducting films by magnetic stray fields

Hybrid superconducting/magnetic nanostructures on Si substrates have been built with identical physical dimensions but different magnetic configurations. By constructing arrays based on Co-dots with in-plane, out-of-plane, and vortex state magnetic configurations, the stray fields are systematically tuned. Dissipation in the mixed state of superconductors can be decreased (increased) by several orders of magnitude by decreasing (increasing) the stray magnetic fields. Furthermore, ordering of the stray fields over the entire array helps to suppress dissipation and enhance commensurability effects increasing the number of dissipation minima.

1302.0680v1

2013-02-09

Lower bounds on the minimum distance of long codes in the Lee metric

The Gilbert type bound for codes in the title is reviewed, both for small and large alphabets. Constructive lower bounds better than these existential bounds are derived from geometric codes, either over Fp or Fp2 ; or over even degree extensions of Fp: In the latter case the approach is concatena- tion with a good code for the Hamming metric as outer code and a short code for the Lee metric as an inner code. In the former case lower bounds on the minimum Lee distance are derived by algebraic geometric arguments inspired by results of Wu, Kuijper, Udaya (2007).

1302.2246v1

2013-03-04

Mansuripur's Paradox

A recent article claims that the Lorentz force law is incompatible with special relativity. We discuss the "paradox" on which this claim is based. The resolution depends on whether one assumes a "Gilbert" model for the magnetic dipole (separated monopoles) or the standard "Ampere" model (current loop). The former was presented in these pages many years ago; the latter requires the inclusion of "hidden momentum."

1303.0732v2

2013-04-09

Instability of Walker Propagating Domain Wall in Magnetic Nanowires

Stability of the well-known Walker propagating domain wall (DW) solution of the Landau-Lifshitz-Gilbert equation is analytically investigated. Surprisingly, the Walker's rigid body propagating DW mode is not stable against the spin wave/wavepacket emission. In the low field region only stern spin waves are emitted while both stern and bow waves are generated under high fields. In a high enough field, but below the Walker breakdown field, the Walker solution could be convective/absolute unstable if the transverse magnetic anisotropy is larger than a critical value, corresponding to a significant modification of the DW profile and DW propagating speed.

1304.2439v1

2013-04-26

Maximizing Spin Torque Diode Voltage by Optimizing Magnetization Alignment

The optimum condition of the magnetization alignment to maximize the spin torque diode voltage is derived by solving the Landau-Lifshitz-Gilbert equation. We show that the optimized diode voltage can be one order of magnitude larger than that of the conventional alignment where the easy axes of the free and the pinned layers are parallel. These analytical predictions are confirmed by numerical simulations.

1304.7079v1

2013-05-23

Residual properties of automorphism groups of (relatively) hyperbolic groups

We show that Out(G) is residually finite if G is a one-ended group that is hyperbolic relative to virtually polycyclic subgroups. More generally, if G is one-ended and hyperbolic relative to proper residually finite subgroups, the group of outer automorphisms preserving the peripheral structure is residually finite. We also show that Out(G) is virtually p-residually finite for every prime p if G is one-ended and toral relatively hyperbolic, or infinitely-ended and virtually p-residually finite.

1305.5403v3

2013-05-25

Thermally-Assisted Spin-Transfer Torque Dynamics in Energy Space

We consider the general Landau-Lifshitz-Gilbert theory underlying the magnetization dynamics of a macrospin magnet subject to spin-torque effects and thermal fluctuations. Thermally activated dynamical properties are analyzed by averaging the full magnetization equations over constant- energy orbits. After averaging, all the relevant dynamical scenarios are a function of the ratio between hard and easy axis anisotropies. We derive analytically the range of currents for which limit cycles exist and discuss the regimes in which the constant energy orbit averaging technique is applicable.

1305.5945v2

2013-06-10

Imperfect Construction of Microclusters

Microclusters are the basic building blocks used to construct cluster states capable of supporting fault-tolerant quantum computation. In this paper, we explore the consequences of errors on microcluster construction using two error models. To quantify the effect of the errors we calculate the fidelity of the constructed microclusters and the fidelity with which two such microclusters can be fused together. Such simulations are vital for gauging the capability of an experimental system to achieve fault tolerance.

1306.2202v1

2013-06-19

Weyl Phases in Point-Group Symmetric Superconductors

We study superconductivity in a Weyl semimetal with broken time-reversal symmetry and stabilized by a point-group symmetry. The resulting superconducting phase is characterized by topologically protected bulk nodes and surface states with Fermi arcs. The topological invariant governing the system is calculated using changes in eigenvalues of the point-group operator along high-symmetry momentum lines. We show that this invariant is determined by the Fermi surface topology of the Weyl semimetal. We discuss the effect of surface orientation and $C_4$-breaking strain as possible experimental consequences.

1306.4696v1

2013-06-21

The Polarization Signature of Local Bulk Flows

A large peculiar velocity of the intergalactic medium produces a Doppler shift of the cosmic microwave background with a frequency-dependent quadrupole term. This quadrupole will act as a source for polarization of the cosmic microwave background, creating a large-scale polarization anisotropy if the bulk flow is local and coherent on large scales. In the case where we are near the center of the moving region, the polarization signal is a pure quadrupole. We show that the signal is small, but detectable with future experiments for bulk flows as large as some recent reports.

1306.5248v3

2013-07-21

Rigidity in the Positive Mass Theorem with Charge

In this paper we show how a natural coupling of the Dirac equation with the generalized Jang equation, leads to a proof of the rigidity statement in the positive mass theorem with charge, without the maximal slicing condition, provided a solution to the coupled system exists.

1307.5499v4

2014-01-08

Tri-Dirac Surface Modes in Topological Superconductors

We propose a new type of topological surface modes having cubic dispersion in three-dimensional topological superconductors. Lower order dispersions are prohibited by the threefold rotational symmetry and time-reversal symmetry. Cooper pairing in the bulk changes sign under improper rotations, akin to$^{3}$He-B. The surface manifestations are a divergent surface density of states at the Fermi level and isospins that rotate three times as they circle the origin in momentum space. We propose that Heusler alloys with band inversion are candidate materials to harbor the novel topological superconductivity.

1401.1823v1

2014-01-09

Automated Code Generation for Lattice Quantum Chromodynamics and beyond

We present here our ongoing work on a Domain Specific Language which aims to simplify Monte-Carlo simulations and measurements in the domain of Lattice Quantum Chromodynamics. The tool-chain, called Qiral, is used to produce high-performance OpenMP C code from LaTeX sources. We discuss conceptual issues and details of implementation and optimization. The comparison of the performance of the generated code to the well-established simulation software is also made.

1401.2039v1

2014-01-13

Effect of Dzyaloshinskii Moriya interaction on magnetic vortex

The effect of the Dzyaloshinskii Moriya interaction on the vortex in magnetic microdisk was investigated by micro magnetic simulation based on the Landau Lifshitz Gilbert equation. Our results show that the DM interaction modifies the size of the vortex core, and also induces an out of plane magnetization component at the edge and inside the disk. The DM interaction can destabilizes one vortex handedness, generate a bias field to the vortex core and couple the vortex polarity and chirality. This DM-interaction-induced coupling can therefore provide a new way to control vortex polarity and chirality.

1401.3292v1

2014-01-31

Self-Oscillation in Spin Torque Oscillator Stabilized by Field-like Torque

The self-oscillation of the magnetization in a spin torque oscillator (STO) with a perpendicularly magnetized free layer and an in-plane magnetized pinned layer in the absence of an applied magnetic field was studied by numerically solving the Landau-Lifshitz-Gilbert equation. It was pointed out that field-like torque was necessary to realize stable self-oscillation in this type of STO at zero field. The numerical simulation at finite temperature showed that the presence of the field-like torque led to a high power with a relatively high oscillation frequency.

1401.8088v2

2014-02-05

Spin-polarized transport in ferromagnetic multilayers: An unconditionally convergent FEM integrator

We propose and analyze a decoupled time-marching scheme for the coupling of the Landau-Lifshitz-Gilbert equation with a quasilinear diffusion equation for the spin accumulation. This model describes the interplay of magnetization and electron spin accumulation in magnetic and non-magnetic multilayer structures. Despite the strong nonlinearity of the overall PDE system, the proposed integrator requires only the solution of two linear systems per time-step. Unconditional convergence of the integrator towards weak solutions is proved.

1402.0983v2

2014-02-12

An efficient algorithm for the entropy rate of a hidden Markov model with unambiguous symbols

We demonstrate an efficient formula to compute the entropy rate $H(\mu)$ of a hidden Markov process with $q$ output symbols where at least one symbol is unambiguously received. Using an approximation to $H(\mu)$ to the first $N$ terms we give a $O(Nq^3$) algorithm to compute the entropy rate of the hidden Markov model. We use the algorithm to estimate the entropy rate when the parameters of the hidden Markov model are unknown.In the case of $q =2$ the process is the output of the Z-channel and we use this fact to give bounds on the capacity of the Gilbert channel.

1402.2733v2

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

2014-04-18

Sparse Approximation, List Decoding, and Uncertainty Principles

We consider list versions of sparse approximation problems, where unlike the existing results in sparse approximation that consider situations with unique solutions, we are interested in multiple solutions. We introduce these problems and present the first combinatorial results on the output list size. These generalize and enhance some of the existing results on threshold phenomenon and uncertainty principles in sparse approximations. Our definitions and results are inspired by similar results in list decoding. We also present lower bound examples that bolster our results and show they are of the appropriate size.

1404.5190v2

2014-04-25

Linewidth of Power Spectrum Originated from Thermal Noise in Spin Torque Oscillator

A theoretical formula of the linewidth caused by the thermal activation in a spin torque oscillator with a perpendicularly magnetized free layer and an in-plane magnetized pinned layer was developed by solving the stochastic Landau-Lifshitz-Gilbert equation in the energy-phase representation. It is shown that the linewidth can be suppressed down to 0.1 MHz by applying a large current (10 mA for typical material parameters). A quality factor larger than 10^{4} is predicted in the large current limit, which is two orders of magnitude larger than the recently observed experimental value.

1404.6558v1

2014-08-11

An optimal irrigation network with infinitely many branching points

The Gilbert-Steiner problem is a mass transportation problem, where the cost of the transportation depends on the network used to move the mass and it is proportional to a certain power of the "flow". In this paper, we introduce a new formulation of the problem, which turns it into the minimization of a convex functional in a class of currents with coefficients in a group. This framework allows us to define calibrations, which can be used to prove the optimality of concrete configurations. We apply this technique to prove the optimality of a certain irrigation network, having the topological property mentioned in the title.

1408.2406v1

2014-09-04

Integer Generalized Splines on Cycles

Let G be a graph whose edges are labeled by positive integers. Label each vertex with an integer and suppose if two vertices are joined by an edge, the vertex labels are congruent to each other modulo the edge label. The set of vertex labels satisfying this condition is called a generalized spline. Gilbert, Polster, and Tymoczko recently defined generalized splines based on work on polynomial splines by Billera, Rose, Haas, Goresky-Kottwitz-Machperson, and many others. We focus on generalized splines on $n$-cycles. We construct a particularly nice basis for the module of splines on $n$-cycles. As an application, we construct generalized splines on star graphs, wheel graphs, and complete graphs.

1409.1481v1

2014-09-10

Proof of the Riemannian Penrose Inequality with Charge for Multiple Black Holes

We present a proof of the Riemannian Penrose inequality with charge in the context of asymptotically flat initial data sets for the Einstein-Maxwell equations, having possibly multiple black holes with no charged matter outside the horizon, and satisfying the relevant dominant energy condition. The proof is based on a generalization of Hubert Bray's conformal flow of metrics adapted to this setting.

1409.3271v2

2014-09-15

Enhanced synchronization in an array of spin torque nano oscillators in the presence of oscillating external magnetic field

We demonstrate that the synchronization of an array of electrically coupled spin torque nano-oscillators (STNO) modelled by Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation can be enhanced appreciably in the presence of a common external microwave magnetic field. The applied microwave magnetic field stabilizes and enhances the regions of synchronization in the parameter space of our analysis, where the oscillators are exhibiting synchronized oscillations thereby emitting improved microwave power. To characterize the synchronized oscillations we have calculated the locking range in the domain of external source frequency.

1409.4384v2

2014-10-19

Extensions of the Charged Riemannian Penrose Inequality

In this paper we investigate the extension of the charged Riemannian Penrose inequality to the case where charges are present outside the horizon. We prove a positive result when the charge densities are compactly supported, and present a counterexample when the charges extend to infinity. We also discuss additional extensions to other matter models.

1410.5027v2

2014-10-23

Quantum spin dynamics

The classical Landau-Lifshitz equation has been derived from quantum mechanics. Starting point is the assumption of a non-Hermitian Hamilton operator to take the energy dissipation into account. The corresponding quantum mechanical time dependent Schr\"odinger, Liouville and Heisenberg equation have been described and the similarities and differences between classical and quantum mechanical spin dynamics have been discussed. Furthermore, a time dependent Schr\"odinger equation corresponding to the classical Landau-Lifshitz-Gilbert equation and two ways to include temperature into the quantum mechanical spin dynamics have been proposed.

1410.6383v1

2014-12-04

Role of Magnetic Field in Self-Oscillation of Nanomagnet Excited by Spin Torque

The critical current of the self-oscillation of spin torque oscillator (STO) consisting of a perpendicularly magnetized free layer and an in-plane magnetized pinned layer was studied by solving the Landau-Lifshitz-Gilbert (LLG) equation. We found that the critical current diverged at certain field directions, indicating that the self-oscillation does not occur at these directions. It was also found that the sign of the critical current changed depending on the applied field direction.

1412.1532v1

2015-01-30

Memory functions of magnetic skyrmions

Magnetic skyrmion, a swirling spin texture, in chiral magnets is characterized by (i) nano-scale size ($\sim$1nm -- 100nm), (ii) topological stability, and (iii) gyro-dynamics. These features are shown to be advantageous for (a) high-density data-storage, (b) nonvolatile memory, and (c) ultra-low current and energy cost manipulation, respectively. By the numerical simulations of Landau-Lifshitz-Gilbert equation, the elementary functions of skyrmions are demonstrated aiming at the design principles of skyrmionic memory devices.

1501.07650v1

2015-02-14

Energy dissipation in single-domain ferromagnetic nanoparticles: Dynamical approach

We study, both analytically and numerically, the phenomenon of energy dissipation in single-domain ferromagnetic nanoparticles driven by an alternating magnetic field. Our interest is focused on the power loss resulting from the Landau-Lifshitz-Gilbert equation, which describes the precessional motion of the nanoparticle magnetic moment. We determine the power loss as a function of the field amplitude and frequency and analyze its dependence on different regimes of forced precession induced by circularly and linearly polarized magnetic fields. The conditions to maximize the nanoparticle heating are also analyzed.

1502.04222v1

2015-02-23

The Positive Mass Theorem for Multiple Rotating Charged Black Holes

In this paper a lower bound for the ADM mass is given in terms of the angular momenta and charges of black holes present in axisymmetric initial data sets for the Einstein-Maxwell equations. This generalizes the mass-angular momentum-charge inequality obtained by Chrusciel and Costa to the case of multiple black holes. We also weaken the hypotheses used in the proof of this result for single black holes, and establish the associated rigidity statement.

1502.06290v2

2015-02-24

An Upper Bound on the Minimum Distance of LDPC Codes over GF(q)

In [1] a syndrome counting based upper bound on the minimum distance of regular binary LDPC codes is given. In this paper we extend the bound to the case of irregular and generalized LDPC codes over GF(q). The comparison to the lower bound for LDPC codes over GF(q) and to the upper bound for non-binary codes is done. The new bound is shown to lie under the Gilbert-Varshamov bound at high rates.

1502.06874v1