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2013-09-16
Superconductivity in LiFeO2Fe2Se2 with anti-PbO-type Spacer Layers
Superconductivity has been found in the iron-arsenides with different structures by alternative stacking of the conducting Fe2As2 layers and spacer layers including alkali- or alkali-earth metal ions and PbO- or perovskite-type oxides blocks. So far, no spacer layer could be intercalated in between the neutral Fe2Se2 l...
1309.3833v3
2014-01-24
Effect of correlations and doping on the spin susceptibility of iron pnictides: the case of KFe2As2
The temperature dependence of the paramagnetic susceptibility of the iron pnictide superconductor KFe2As2 and its connection with the spectral properties of that material is investigated by a combination of density functional theory (DFT) in the local density approximation and dynamical mean-field theory (DMFT). Unlike...
1401.6291v3
2014-02-12
Electric double-layer transistor using layered iron selenide Mott insulator TlFe1.6Se2
A1-xFe2-ySe2 (A = K, Cs, Rb, Tl) are recently discovered iron-based superconductors with critical temperatures (Tc) ranging up to 32 K. Their parent phases have unique properties when compared with other iron-based superconductors; e.g., their crystal structures include ordered Fe vacancies, their normal states are ant...
1402.2767v2
2014-03-24
Discovery of Enhanced Radiative Recombination Continua of He-like Iron and Calcium from IC 443 and Its Implications
We present deep observations of the Galactic supernova remnant IC 443 with the {\it Suzaku X-ray satellite}. We find prominent K-shell lines from iron and nickel, together with a triangle residual at 8--10~keV, which corresponds to the energy of the radiative recombination continuum (RRC) of He-like iron. In addition, ...
1403.5850v1
2014-04-18
Faint Population III supernovae as the origin of the most iron-poor stars
The most iron-deficient stars in the Milky Way provide important observational constraints on the nature of astrophysical objects that have enriched the primordial gas with heavy elements from which these stars were formed. Among them, the recently discovered iron-deficient star SMSS J031300.36-670839.3 shows a remarka...
1404.4817v3
2014-04-27
Extraordinary quasiparticle scattering and bandwidth-control by dopants in iron-based superconductors
The diversities in crystal structures and ways of doping result in extremely diversified phase diagrams for iron-based superconductors. With angle-resolved photoemission spectroscopy (ARPES), we have systematically studied the effects of chemical substitution on the electronic structure of various series of iron-based ...
1404.6716v1
2014-04-28
Relativistic iron K alpha line detection in the Suzaku spectra of IC 4329A
We present an analysis of five Suzaku observations of the bright Seyfert1 galaxy IC 4329A. The broad energy band and high signal-to-noise ratio of the data give new constraints on the iron K alpha line profile and its relationship with the Compton hump at higher energies. The Fe K bandpass is dominated by a narrow core...
1404.7126v1
2014-05-15
Control and diagnosis of temperature, density, and uniformity in x-ray heated iron/magnesium samples for opacity measurements
Experimental tests are in progress to evaluate the accuracy of the modeled iron opacity at solar interior conditions, in particular to better constrain the solar abundance problem [S. Basu and H.M. Antia, Physics Reports 457, 217 (2008)]. Here we describe measurements addressing three of the key requirements for reliab...
1405.4012v1
2014-07-03
A Clumpy Stellar Wind and Luminosity-Dependent Cyclotron Line Revealed by The First Suzaku Observation of the High-Mass X-ray Binary 4U 1538-522
We present results from the first Suzaku observation of the high-mass X-ray binary 4U 1538-522. The broad-band spectral coverage of Suzaku allows for a detailed spectral analysis, characterizing the cyclotron resonance scattering feature at $23.0 \pm 0.4$ keV and the iron K$\alpha$ line at $6.426 \pm 0.008$ keV, as wel...
1407.1028v1
2014-12-23
Phase diagram of (Li1-xFex)OHFeSe: a bridge between iron selenide and arsenide superconductors
Previous experimental results have shown important differences between iron selenide and arsenide superconductors, which seem to suggest that the high temperature superconductivity in these two subgroups of iron-based family may arise from different electronic ground states. Here, we report the complete phase diagram o...
1412.7236v1
2015-06-12
Observation of universal strong orbital-dependent correlation effects in iron chalcogenides
Establishing the appropriate theoretical framework for unconventional superconductivity in the iron-based materials requires correct understanding of both the electron correlation strength and the role of Fermi surfaces. This fundamental issue becomes especially relevant with the discovery of the iron chalcogenide (FeC...
1506.03888v2
2015-07-22
Mott localization in a pure stripe antiferromagnet Rb$_{1-δ}$Fe$_{1.5-σ}$S$_2$
A combination of neutron diffraction and angle-resolved photoemission spectroscopy measurements on a pure antiferromagnetic stripe Rb$_{1-\delta}$Fe$_{1.5-\sigma}$S$_2$ is reported. A neutron diffraction experiment on a powder sample shows that a 98$\%$ volume fraction of the sample is in the antiferromagnetic stripe p...
1507.06062v2
2015-09-18
A disk wind interpretation of the strong Fe Kα features in 1H 0707-495
1H 0707-495 is the most convincing example of a supermassive black hole with an X-ray spectrum being dominated by extremely smeared, relativistic reflection, with the additional requirement of strongly supersoler iron abundance. However, here we show that the iron features in its 2--10 keV spectrum are rather similar t...
1509.05645v3
2015-09-29
The Impact of Enhanced Iron Opacity on Massive Star Pulsations: Updated Instability Strips
Recently, Bailey et al. (2015) made a direct measurement of the Iron opacity at the physical conditions of the solar tachocline. They found that the wavelength-integrated Iron opacity is roughly 75% higher that what the OP and OPAL models predict. Here, we compute new opacity tables with enhanced Iron and Nickel contri...
1509.08652v1
2015-10-28
Variability of the X-ray Broad Iron Spectral Features in Active Galactic Nuclei and Black-hole Binaries
The "broad iron spectral features" are often seen in X-ray spectra of Active Galactic Nuclei (AGN) and black-hole binaries (BHB). These features may be explained either by the "relativistic disc reflection" scenario or the "partial covering" scenario: It is hardly possible to determine which model is valid from time-av...
1510.08189v1
2015-11-24
Origin of the X-ray Broad Iron Spectral Feature in GRS 1915+105
The X-ray spectrum of GRS 1915+105 is known to have a ``broad iron spectral feature'' in the spectral hard state. Similar spectral features are often observed in Active Galactic Nuclei (AGNs) and other black-hole binaries (BHBs), and several models have been proposed for explaining it. In order to distinguish spectral ...
1511.07630v1
2016-01-11
Investigation of iron emission lines in the eclipsing high mass X-ray binary pulsar OAO 1657-415
We present the results obtained from timing and spectral studies of high mass X-ray binary pulsar OAO 1657-415 using a Suzaku observations in 2011 September. X-ray pulsations were detected in the light curves up to $\sim$70 keV. The continuum spectra during the high- and low-flux regions in light curves were well descr...
1601.02345v1
2016-01-25
Iron Opacity Bump Changes the Stability and Structure of Accretion Disks in Active Galactic Nuclei
Accretion disks around supermassive black holes have regions where the Rosseland mean opacity can be much larger than the electron scattering opacity primarily due to the large number of bound-bound transitions in iron. We study the effects of this iron opacity "bump" on the thermal stability and vertical structure of ...
1601.06836v1
2016-02-09
Quantum states entanglement in hemoglobin molecule active center
An ab initio study of the electronic and spin configuration for the iron ion in the active center of the human hemoglobin molecule is presented. It is well known that the iron ion, being surrounded by the porphyrin ring and the ligands, plays the key role in the realization of the basic oxygen-transport functions of th...
1602.02963v2
2016-03-29
Spin crossover in (Mg,Fe$^{3+}$)(Si,Fe$^{3+}$)O$_3$ bridgmanite: effects of disorder, iron concentration, and temperature
The spin crossover of iron in Fe$^{3+}$-bearing bridgmanite, the most abundant mineral of the Earth's lower mantle, is by now a well-established phenomenon, though several aspects of this crossover remain unclear. Here we investigate effects of disorder, iron concentration, and temperature on this crossover using ab in...
1603.08947v1
2016-04-28
On the evolution of the inner disk radius with flux in the neutron star low-mass X-ray binary Serpens X-1
We analyze the latest \emph{Suzaku} observation of the bright neutron star low-mass X-ray binary Serpens X-1 taken in 2013 October and 2014 April. The observation was taken using the burst mode and only suffered mild pile-up effects. A broad iron line is clearly detected in the X-ray spectrum. We test different models ...
1604.08626v2
2016-06-08
A critical look at the merger scenario to explain multiple populations and rotation in iron-complex globular clusters
Merging has been proposed to explain multiple populations in globular clusters (GCs) where there is a spread in iron abundance (hereafter, iron-complex GCs). By means of N-body simulations, we investigate if merging is consistent with the observations of sub-populations and rotation in iron-complex GCs. The key paramet...
1606.02743v1
2016-07-30
Observation of the anisotropic Dirac cone in the band dispersion of 112-structured iron-based superconductor Ca0.9La0.1FeAs2
CaFeAs2 is a parent compound of recently discovered 112-type iron-based superconductors. It is predicted to be a staggered intercalation compound that naturally integrates both quantum spin Hall insulating and superconducting layers and an ideal system for the realization of Majorana modes. We performed a systematical ...
1608.00072v1
2016-11-23
High-Tc superconductivity in FeSe at high pressure: Dominant hole carriers and enhanced spin fluctuations
The importance of electron-hole interband interactions is widely acknowledged for iron-pnictide superconductors with high transition temperatures (Tc). However, high-Tc superconductivity without hole carriers has been suggested in FeSe single-layer films and intercalated iron-selenides, raising a fundamental question w...
1611.07973v1
2017-03-09
Orbital selective pairing and superconductivity in iron selenides
An important challenge in condensed matter physics is understanding iron-based superconductors. Among these systems, the iron selenides hold the record for highest superconducting transition temperature and pose especially striking puzzles regarding the nature of superconductivity. The pairing state of the alkaline iro...
1703.03170v1
2017-04-18
Unified phase diagram for iron-based superconductors
High-temperature superconductivity is closely adjacent to a long-range antiferromagnet, which is called a parent compound. In cuprates, all parent compounds are alike and carrier doping leads to superconductivity, so a unified phase diagram can be drawn. However, the properties of parent compounds for iron-based superc...
1704.05182v2
2017-07-04
Optical properties of non-stoichiometric amorphous silicates with application to circumstellar dust extinction
Optical constants of non-stoichiometric amorphous magnesium-iron silicates are determined. It is demonstrated that these can well reproduce the observed mid-infrared emission spectra of evolved stars. Stoichiometric and non-stoichiometric amorphous magnesium-iron silicate films are fabricated by pulsed laser deposition...
1707.00903v1
2017-10-05
Whether it is possible to stabilize the 1144-phase pnictides with tri-valence cations?
The 1144 iron arsenide (e.g. CaKFe4As4) has recently been discovered and inspired a tide of search for superconductors. Such far, the discovered compounds are confined to iron arsenides (ABFe4As4), where A and B are either alkali metals or alkaline earth elements. In this work, we propose two directions in searching 11...
1710.01868v2
2018-02-28
The Coulomb problem in iron based superconductors
We discuss the role of strong Coulomb interactions in iron-based superconductors (FeSCs). The presumed $s^{\pm}$ character of these superconductors means that the condensate is not symmetry protected against Coulomb repulsion. Remarkably, the transition temperatures and the excitation gap are quite robust across the la...
1802.10580v3
2018-03-02
Direct observation of multiple topological phases in the iron-based superconductor Li(Fe,Co)As
Topological insulators/semimetals and unconventional iron-based superconductors have attracted major attentions in condensed matter physics in the past 10 years. However, there is little overlap between these two fields, although the combination of topological states and superconducting states will produce more exotic ...
1803.00846v1
2018-06-06
First-principles calculations of iron-hydrogen reactions in silicon
Controlling the contamination of silicon materials by iron, especially dissolved interstitial iron (Fe$_{\mathrm{i}}$), is a longstanding problem with recent developments and several open issues. Among these we have the question whether hydrogen can assist iron diffusion, or if significant amounts of substitutional iro...
1806.02249v2
2018-08-16
Atomic iron and titanium in the atmosphere of the exoplanet KELT-9b
The chemical composition of an exoplanet is a key ingredient in constraining its formation history. Iron is the most abundant transition metal, but has never been directly detected in an exoplanet due to its highly refractory nature. KELT-9b (HD 195689b) is the archetype of the class of ultra-hot Jupiters that straddle...
1808.05653v1
2019-04-15
Using the infrared iron lines to probe solar subsurface convection
Studying the properties of the solar convection using high-resolution spectropolarimetry began in the early 90's with the focus on observations in the visible wavelength regions. Its extension to the infrared (IR) remains largely unexplored. The IR iron lines around 15600\,$\rm{\AA}$, most commonly known for their high...
1904.07306v1
2019-05-21
Impact of the fac/mer isomerism on the excited states dynamics of pyridyl-carbene Fe(II) complexes
The control of photophysical properties of iron complexes and especially of their excited states decay is a great challenge in the search for sustainable alternatives to noble metals in photochemical applications. Herein we report the synthesis and investigations of the photophysics of mer and fac iron complexes bearin...
1905.08858v1
2019-10-03
Decoupling of Lattice and Orbital Degrees of Freedom in an Iron-Pnictide Superconductor
The interplay of structural and electronic phases in iron-based superconductors is a central theme in the search for the superconducting pairing mechanism. While electronic nematicity, defined as the breaking of four-fold symmetry triggered by electronic degrees of freedom, is competing with superconductivity, the effe...
1910.01639v2
2020-02-05
Spin Resonances in Iron-Selenide High-Tc Superconductors by Proximity to Hidden Spin Density Wave
Recent inelastic neutron scattering studies by Pan et al., Nature Communications 8, 123 (2017), find evidence for spin excitations at energies above the quasi-particle gap in an iron-selenide high-Tc superconductor. The momenta of the spin excitations form a diamond around the checkerboard wavevector, Q_AF, that is ass...
2002.01732v2
2020-10-01
A Molecular Dynamics Investigation of Mechanical Properties of Graphene Reinforced Iron Composite and The Effect of Vacancy Defect Distance from the Matrix-Fiber Interface
Graphene is a material of excellent mechanical properties, which make it an ideal fiber for reinforcing metal. Since iron is the most used metal in the world, reinforcing iron with graphene can reduce the overall requirement of material in any application where strength is demanded. However, the effect of graphene rein...
2010.00274v1
2021-06-04
Magnetic states of quasi-one-dimensional iron chalcogenide Ba$_2$FeS$_3$
Quasi-one-dimensional iron-based ladders and chains, with the 3$d$ iron electronic density $n = 6$, are attracting considerable attention. Recently, a new iron chain system Ba$_2$FeS$_3$, also with $n = 6$, was prepared under high-pressure and high-temperature conditions. Here, the magnetic and electronic phase diagram...
2106.02753v2
2021-07-29
Modelling disease progression with multi-level electronic health records data and informative observation times: an application to treating iron deficiency anaemia in primary care of the UK
Modelling disease progression of iron deficiency anaemia (IDA) following oral iron supplement prescriptions is a prerequisite for evaluating the cost-effectiveness of oral iron supplements. Electronic health records (EHRs) from the Clinical Practice Research Datalink (CPRD) provide rich longitudinal data on IDA disease...
2107.13956v1
2021-10-27
Globular Cluster Intrinsic Iron Abundance Spreads: II. Protocluster Metallicities and the Age-Metallicity Relations of Milky Way Progenitors
Intrinsic iron abundance spreads in globular clusters, although usually small, are very common, and are signatures of self enrichment: some stars within the cluster have been enriched by supernova ejecta from other stars within the same cluster. We use the Bailin (2018) self enrichment model to predict the relationship...
2110.14571v1
2021-12-08
Prediction of orbital selective Mott phases and block magnetic states in the quasi-one-dimensional iron chain Ce$_2$O$_2$FeSe$_2$ under hole and electron doping
The recent detailed study of quasi-one-dimensional iron-based ladders, with the $3d$ iron electronic density $n = 6$, has unveiled surprises, such as orbital-selective phases. However, similar studies for $n=6$ iron chains are still rare. Here, a three-orbital electronic Hubbard model was constructed to study the magne...
2112.04049v1
2022-01-07
First-principles study on the solute-induced low diffusion and self-trapping of helium in fcc iron
The addition of alloying elements plays an essential role in helium (He) behaviours produced by transmutation in metal alloys. Effects of solutes (Ni, Cr, Ti, P, Si, C) on the behaviours of He and He-He pair in face-centred cube (fcc) iron have been investigated using first-principles calculations based on density func...
2201.02423v1
2022-02-17
Helium absorption in exoplanet atmospheres is connected to stellar coronal abundances
Transit observations in the helium triplet around 10830 Angstrom are a successful tool to study exoplanetary atmospheres and their mass loss. Forming those lines requires ionisation and recombination of helium in the exoplanetary atmosphere. This ionisation is caused by stellar photons at extreme ultra-violet (EUV) wav...
2202.08838v1
2022-05-24
Iron as a sustainable chemical carrier of renewable energy: Analysis of opportunities and challenges for retrofitting coal-fired power plants
As a result of the 2021 United Nations Climate Change Conference (COP26), several countries committed to phasing down coal electricity as soon as possible, deactivating hundreds of power plants in the near future. CO$_2$-free electricity can be generated in these plants by retrofitting them for iron combustion. Iron ox...
2205.11944v1
2022-11-10
Inferring Type II-P Supernova Progenitor Masses from Plateau Luminosities
Connecting observations of core-collapse supernova explosions to the properties of their massive star progenitors is a long-sought, and challenging, goal of supernova science. Recently, Barker et al. (2022) presented bolometric light curves for a landscape of progenitors from spherically symmetric neutrino-driven core-...
2211.05789v2
2022-12-13
Antiferromagnetic iron based magnetoelectric compounds
The Landau free-energy of a compound that benefits from a linear coupling of an electric field and a magnetic field includes a product of the two fields, one polar and time-even and one axial and time-odd. In ME compounds, expectation values of some atomic magnetic tensors are invariant with respect to anti-inversion. ...
2212.06403v1
2022-12-20
Numerical modeling of pulverized iron flames in a multidimensional hot counterflow burner
Pulverized iron flames stabilized in a multidimensional hot counterflow burner are simulated using a numerical model, which is extended from the state-of-the-art model developed by Hazenberg and van Oijen (PCI, 2021) considering unsteady effects. The results are compared to available experimental data (McRae et al., PC...
2212.10226v1
2023-02-27
Searching for iron nanoparticles with a general-purpose Gaussian approximation potential
We present a general-purpose machine learning Gaussian approximation potential (GAP) for iron that is applicable to all bulk crystal structures found experimentally under diverse thermodynamic conditions, as well as surfaces and nanoparticles (NPs). By studying its phase diagram, we show that our GAP remains stable at ...
2302.13722v2
2023-03-07
The potential of retrofitting existing coal power plants: a case study for operation with green iron
Storing electrical energy for long periods and transporting it over long distances is an essential task of the necessary transition to a CO$_2$-free energy economy. An oxidation-reduction cycle based on iron and its oxides represents a very promising technology in this regard. The present work assesses the potential of...
2303.04000v2
2023-04-14
Performance of TES X-Ray Microcalorimeters Designed for 14.4-keV Solar Axion Search
A 57Fe nucleus in the solar core could emit a 14.4-keV monochromatic axion through the M1 transition if a hypothetical elementary particle, axion, exists to solve the strong CP problem. Transition edge sensor (TES) X-ray microcalorimeters can detect such axions very efficiently if they are again converted into photons ...
2304.07068v2
2023-04-10
Pourable and Destroyable Cosmic Ray Radiation Shield for Spacecraft
Historically, materials such as lead, tungsten, and iron have been used in spacecraft to shield scientific detectors from Cosmic Rays. These materials work well when reentry to Earth is not an issue. The typical strategy is to have a controlled descent of the spacecraft or to have extremely limited shielding, if any, d...
2304.09177v1
2023-04-19
Fabrication of a 64-Pixel TES Microcalorimeter Array with Iron Absorbers Uniquely Designed for 14.4-keV Solar Axion Search
If a hypothetical elementary particle called an axion exists, to solve the strong CP problem, a 57Fe nucleus in the solar core could emit a 14.4-keV monochromatic axion through the M1 transition. If such axions are once more transformed into photons by a 57Fe absorber, a transition edge sensor (TES) X-ray microcalorime...
2304.09539v1
2023-09-22
Decoding 122-Type Iron-Based Superconductors: A Comprehensive Simulation of Phase Diagrams and Transition Temperatures
Iron-based superconductors, a cornerstone of low-temperature physics, have been the subject of numerous theoretical models aimed at deciphering their complex behavior. In this study, we present a comprehensive approach that amalgamates several existing models and incorporates experimental data to simulate the supercond...
2309.12615v1
2023-10-09
Detecting Iron Oxidation States in Liquids with the VOXES Bragg Spectrometer
Determining the oxidation states of metals assumes great importance in various applications because a variation in the oxidation number can drastically influence the material properties. As an example, this becomes evident in edible liquids like wine and oil, where a change in the oxidation states of the contained meta...
2310.06062v1
2024-03-05
Elemental abundances in the diffuse ISM from joint FUV and X-ray spectroscopy: iron, oxygen, carbon and sulfur
In this study, we investigate interstellar absorption lines along the line of sight toward the galactic low-mass X-ray binary Cygnus X-2. We combine absorption line data obtained from high-resolution X-ray spectra collected with Chandra and XMM-Newton satellites, along with Far-UV absorption lines observed by the Hubbl...
2403.02664v1
1999-07-06
Hysteresis properties at zero temperature in the Dipolar-Random Field Ising Model
We present a modified two-dimensional random field Ising model, where a dipolar interaction term is added to the classic random field Hamiltonian. In a similar model it was already verified that the system state can exhibit domains in the form of stripe patterns, typical of thin materials with strong perpendicular anis...
9907074v1
2000-03-21
Field induced ordering in highly frustrated antiferromagnets
We predict that an external field can induce a spin order in highly frustrated classical Heisenberg magnets. We find analytically stabilization of collinear states by thermal fluctuations at a one-third of the saturation field for kagome and garnet lattices and at a half of the saturation field for pyrochlore and frust...
0003343v2
2001-10-10
Modeling Two Dimensional Magnetic Domain Patterns
Two-dimensional magnetic garnets exhibit complex and fascinating magnetic domain structures, like stripes, labyrinths, cells and mixed states of stripes and cells. These patterns do change in a reversible way when the intensity of an externally applied magnetic field is varied. The main objective of this contribution i...
0110208v1
2003-07-28
Low temperature spin fluctuations in geometrically frustrated Yb3Ga5O12
In the garnet structure compound Yb3Ga5O12, the Yb3+ ions (ground state effective spin S' = 1/2) are situated on two interpenetrating corner sharing triangular sublattices such that frustrated magnetic interactions are possible. Previous specific heat measurements evidenced the development of short range magnetic corre...
0307676v1
2006-06-05
Multireference Correlation in Long Molecules with the Quadratic Scaling Density Matrix Renormalization Group
We have devised and implemented a local ab initio Density Matrix Renormalization Group (DMRG) algorithm to describe multireference nondynamic correlations in large systems. For long molecules that are extended in one of their spatial dimensions, this method allows us to obtain an exact characterisation of correlation, ...
0606115v3
2004-05-10
Manifestations of nuclear anapole moments in solid state NMR
We suggest to use insulating garnets doped by rare earth ions for measurements of nuclear anapole moments. A parity violating shift of the NMR frequency arises due to the combined effect of the lattice crystal field and the anapole moment of the rare-earth nucleus. We show that there are two different observable effe...
0405043v1
2006-06-22
Band Edge Effects and Normal Mode Propagation in Waveguide Magnetophotonic Crystals
A study of band edge phenomena in ridge waveguide magnetophotonic crystals is presented. Normal mode analysis is used to examine the near-band edge and Bragg center-wavelength group velocities and their relation to the polarization. Large polarization departures from the input are observed in Bragg gratings patterned b...
0606199v2
1996-02-08
Supersymmetry and the Hartmann Potential of Theoretical Chemistry
The ring-shaped Hartmann potential $ V = \eta \sigma^{2} \epsilon_{0} \left( \frac{2 a_{0}}{r} - \frac{\eta a_{0}^{2}}{r^{2} sin^{2} \theta} \right) $ was introduced in quantum chemistry to describe ring-shaped molecules like benzene. In this article, the supersymmetric features of the Hartmann potential are discussed....
9602005v1
2002-08-01
Entwined Paths, Difference Equations and the Dirac Equation
Entwined space-time paths are bound pairs of trajectories which are traversed in opposite directions with respect to macroscopic time. In this paper we show that ensembles of entwined paths on a discrete space-time lattice are simply described by coupled difference equations which are discrete versions of the Dirac equ...
0208004v2
2007-07-20
The radical character of the acenes: A density matrix renormalization group study
We present a detailed investigation of the acene series using high-level wavefunction theory. Our ab-initio Density Matrix Renormalization Group algorithm has enabled us to carry out Complete Active Space calculations on the acenes from napthalene to dodecacene correlating the full pi-valence space. While we find tha...
0707.3120v1
2007-07-20
Targeted Excited State Algorithms
To overcome the limitations of the traditional state-averaging approaches in excited state calculations, where one solves for and represents all states between the ground state and excited state of interest, we have investigated a number of new excited state algorithms. Building on the work of van der Vorst and Sleijpe...
0707.3121v1
2007-10-23
Structural relaxation around substitutional Cr3+ in pyrope garnet
The structural environment of substitutional Cr3+ ion in a natural pyrope Mg3Al2Si3O12 has been investigated by Cr K-edge Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Absorption Near Edge Structure (XANES) coupled with first-principles computations. The Cr-O distance is close to that in knorringite Mg3Cr2...
0710.4189v1
2007-11-09
An Introduction to the Density Matrix Renormalization Group Ansatz in Quantum Chemistry
The Density Matrix Renormalisation Group (DMRG) is an electronic structure method that has recently been applied to ab-initio quantum chemistry. Even at this early stage, it has enabled the solution of many problems that would previously have been intractable with any other method, in particular, multireference problem...
0711.1398v1
2007-12-14
Orbital Optimization in the Density Matrix Renormalization Group, with applications to polyenes and β-carotene
In previous work we have shown that the Density Matrix Renormalization Group (DMRG) enables near-exact calculations in active spaces much larger than are possible with traditional Complete Active Space algorithms. Here, we implement orbital optimisation with the Density Matrix Renormalization Group to further allow the...
0712.2475v2
2008-06-03
Site symmetry and crystal symmetry: a spherical tensor analysis
The relation between the properties of a specific crystallographic site and the properties of the full crystal is discussed by using spherical tensors. The concept of spherical tensors is introduced and the way it transforms under the symmetry operations of the site and from site to site is described in detail. The law...
0806.0438v1
2009-07-27
Approximating strongly correlated spin and fermion wavefunctions with correlator product states
We explore correlator product states for the approximation of correlated wavefunctions in arbitrary dimensions. We show that they encompass many interesting states including Laughlin's quantum Hall wavefunction, Huse and Elser's frustrated spin states, and Kitaev's toric code. We further establish their relation to com...
0907.4646v3
2010-02-27
Embedding theory for excited states with inclusion of self-consistent environment screening
We present a general embedding theory of electronic excitations of a relatively small, localized system in contact with an extended, chemically complex environment. We demonstrate how to include the screening response of the environment into highly accurate electronic structure calculation of the localized system by me...
1003.0102v1
2010-05-15
Coupling between magnon and ligand-field excitations in magnetoelectric Tb3Fe5O12 garnet
The spectra of far-infrared transmission in Tb3Fe5O12 magnetoelectric single crystals have been studied in the range between 15 and 100 cm-1, in magnetic fields up to 10 T, and for temperatures between 5 and 150 K. We attribute some of the observed infrared-active excitations to electric-dipole transitions between liga...
1005.2705v1
2010-08-29
Tensor factorizations of local second-order Møller Plesset theory
Efficient electronic structure methods can be built around efficient tensor representations of the wavefunction. Here we describe a general view of tensor factorization for the compact representation of electronic wavefunctions. We use these ideas to construct low-complexity representations of the doubles amplitudes in...
1008.4943v1
2010-08-29
Further developments in correlator product states: deterministic optimization and energy evaluation
Correlator product states (CPS) are a class of tensor network wavefunctions applicable to strongly correlated problems in arbitrary dimensions. Here, we present a method for optimizing and evaluating the energy of the CPS wavefunction that is non-variational but entirely deterministic. The fundamental assumption underl...
1008.4945v1
2010-12-16
Dynamical mean-field theory from a quantum chemical perspective
We investigate the dynamical mean-field theory (DMFT) from a quantum chemical perspective. Dynamical mean-field theory offers a formalism to extend quantum chemical methods for finite systems to infinite periodic problems within a local correlation approximation. In addition, quantum chemical techniques can be used to ...
1012.3609v1
2011-01-18
Uniform Peak Optical Conductivity in Single-Walled Carbon Nanotubes
Recent measurements in single-walled carbon nanotubes show that, on resonance, all nanotubes display the same peak optical conductivity of approximately 8 $e^2/h$, independent of radius or chirality [Joh \emph{et al.}, \emph{Nature Nanotechnology} \textbf{6}, 51 (2011)]. We show that this uniform peak conductivity is a...
1101.3546v1
2011-04-22
New Experimental Limit on the Electric Dipole Moment of the Electron in a Paramagnetic Insulator
We report results of an experimental search for the intrinsic Electric Dipole Moment (EDM) of the electron using a solid-state technique. The experiment employs a paramagnetic, insulating gadolinium gallium garnet (GGG) that has a large magnetic response at low temperatures. The presence of the eEDM would lead to a sma...
1104.4391v2
2012-03-30
A correlator product state study of molecular magnetism in the giant Keplerate Mo72Fe30
We have studied the properties of the giant Keplerate molecular magnet Mo72Fe30, as a function of applied magnetic field, using the correlator product state (CPS) tensor network ansatz. The magnet is modeled with an S = 5/2 antiferromagnetic Heisenberg Hamiltonian on the 30-site icosidodecahedron lattice, a model for w...
1203.6883v1
2012-04-12
Analytical modeling for the heat transfer in sheared flows of nanofluids
We developed a model for the enhancement of the heat flux by spherical and elongated nano- particles in sheared laminar flows of nano-fluids. Besides the heat flux carried by the nanoparticles the model accounts for the contribution of their rotation to the heat flux inside and outside the particles. The rotation of th...
1204.2694v1
2012-04-25
Density matrix embedding: A simple alternative to dynamical mean-field theory
We introduce DMET, a new quantum embedding theory for predicting ground-state properties of infinite systems. Like dynamical mean-field theory (DMFT), DMET maps the the bulk interacting system to a simpler impurity model and is exact in the non-interacting and atomic limits. Unlike DMFT, DMET is formulated in terms of ...
1204.5783v2
2012-09-04
Origin of the structural phase transition in Li7La3Zr2O12
Garnet-type Li7La3Zr2O12 (LLZO) is a solid electrolyte material with a low-conductivity tetragonal and a high-conductivity cubic phase. Using density-functional theory and variable cell shape molecular dynamics simulations, we show that the tetragonal phase stability is dependent on a simultaneous ordering of the Li io...
1209.0690v1
2012-10-04
Striped spin liquid crystal ground state instability of kagome antiferromagnets
The Dirac spin liquid ground state of the spin 1/2 Heisenberg kagome antiferromagnet has potential instabilities[1-4]. This has been suggested as the reason why it is not strongly supported in large-scale numerical calculations[5]. However, previous attempts to observe these instabilities have failed. We report on the ...
1210.1585v1
2012-10-05
Excited States, Dynamic Correlation Functions and Spectral Properties from Full Configuration Interaction Quantum Monte Carlo
In this communication, we propose a method for obtaining isolated excited states within the Full Configuration Interaction Quantum Monte Carlo framework. This method allows for stable sampling with respect to collapse to lower energy states and requires no uncontrolled approximations. In contrast with most previous met...
1210.1650v1
2012-11-05
Exact asymptotic behavior of magnetic stripe domain arrays
The classical problem of magnetic stripe domain behavior in films and plates with uniaxial magnetic anisotropy is treated. Exact analytical results are derived for the stripe domain widths as function of applied perpendicular field, $H$, in the regime where the domain period becomes large. The stripe period diverges as...
1211.1366v1
2012-12-12
Density matrix embedding: A strong-coupling quantum embedding theory
We extend our density matrix embedding theory (DMET) [Phys. Rev. Lett. 109 186404 (2012)] from lattice models to the full chemical Hamiltonian. DMET allows the many-body embedding of arbitrary fragments of a quantum system, even when such fragments are open systems and strongly coupled to their environment (e.g., by co...
1212.2679v1
2013-04-15
Off-policy Learning with Eligibility Traces: A Survey
In the framework of Markov Decision Processes, off-policy learning, that is the problem of learning a linear approximation of the value function of some fixed policy from one trajectory possibly generated by some other policy. We briefly review on-policy learning algorithms of the literature (gradient-based and least-s...
1304.3999v1
2013-12-11
Cs2NaAl1-xCrxF6: A family of compounds presenting magnetocaloric effect
In this paper we explore the magnetocaloric effect (MCE) of chromium-doped elpasolite Cs$_2$NaAl$_{1-x}$Cr$_x$F$_6$ (x = 0.01 and 0.62) single crystals. Our magnetization and heat capacity data show the magnetocaloric potentials to be comparable to those of garnets, perovskites and other fluorides, producing magnetic e...
1312.3014v2
2014-05-04
Quasi-three-level laser emission of neodymium doped disordered crystal waveguides
This paper reports on the quasi-three-level continuous wave laser operation based on waveguide structures in neodymium doped calcium niobium gallium garnet disordered crystal. Laser wavelength selection through the waveguide cross section was observed. Waveguide structures with different cross sections were fabricated ...
1405.0704v1
2014-08-21
A flexible multi-reference perturbation theory by minimizing the Hylleraas functional with matrix product states
We describe a formulation of multi-reference perturbation theory that obtains a rigorous upper bound to the second order energy by minimizing the Hylleraas functional in the space of matrix product states (MPS). The first order wavefunctions so obtained can also be used to compute the third order energy with little ove...
1408.5092v1
2014-10-26
Twisted Conjugacy in Houghton's groups
For a fixed $n\ge2$, the Houghton group $H_n$ consists of bijections of $X_n=\{1,\ldots,n\} \times \mathbb{N}$ that are `eventually translations' of each copy of $\mathbb{N}$. The Houghton groups have been shown to have solvable conjugacy problem. In general solvable conjugacy problem does not imply that all finite ext...
1410.7051v6
2014-11-01
A transformed framework for dynamic correlation in multireference problems
We describe how multirefence dynamic correlation theories can be naturally obtained as single-reference correlation theories in a canonically transformed frame. Such canonically transformed correlation theories are very simple and involve identical expressions to their single-reference counterparts. The corresponding e...
1411.0067v4
2015-01-14
Dispersionless spin waves in Gadolinium Gallium Garnet
We report the results of neutron scattering on a powder sample of Gd3Ga5O12 at high magnetic fields. We find that in high fields (B>1.8 T) the system is not fully polarized, but has a small canting of the moments induced by the dipolar interaction. We show that the degree of canting is accurately predicted by the stand...
1501.03493v1
2015-01-28
Interplay of disorder and geometrical frustration in doped Gadolinium Gallium Garnet
The geometrically-frustrated, triangular antiferromagnet GGG exhibits a rich mix of short-range order and isolated quantum states. We investigate the effects of up to 1% Neodymium substitution for Gallium on the ac magnetic response at temperatures below 1 K in both the linear and nonlinear regimes. Substitutional diso...
1501.07229v1
2015-04-02
Search for exotic short-range interactions using paramagnetic insulators
We describe a proposed experimental search for exotic spin-coupled interactions using a solid-state paramagnetic insulator. The experiment is sensitive to the net magnetization induced by the exotic interaction between the unpaired insulator electrons with a dense, non-magnetic mass in close proximity. An existing expe...
1504.00552v2
2015-04-08
Ground-state phase diagram of the square lattice Hubbard model from density matrix embedding theory
We compute the ground-state phase diagram of the Hubbard and frustrated Hubbard models on the square lattice with density matrix embedding theory using clusters of up to 16 sites. We provide an error model to estimate the reliability of the computations and complexity of the physics at different points in the diagram. ...
1504.01784v3
2015-07-07
Fast and rewritable colloidal assembly via field synchronized particle swapping
We report a technique to realize reconfigurable colloidal crystals by using the controlled motion of particle defects above an externally modulated magnetic substrate. The transport of particles is induced by applying a uniform rotating magnetic field to a ferrite garnet film characterized by a periodic lattice of magn...
1507.01964v1
2015-12-14
Spectral Functions of the Uniform Electron Gas via Coupled-Cluster Theory and Comparison to the $GW$ and Related Approximations
We use, for the first time, ab initio coupled-cluster theory to compute the spectral function of the uniform electron gas at a Wigner-Seitz radius of $r_\mathrm{s}=4$. The coupled-cluster approximations we employ go significantly beyond the diagrammatic content of state-of-the-art $GW$ theory. We compare our calculatio...
1512.04556v2
2015-12-26
N-electron valence state perturbation theory based on a density matrix renormalization group reference function, with applications to the chromium dimer and poly-p-phenylene vinylene oligomer
The strongly-contracted variant of second order N -electron valence state perturbation theory (NEVPT2) is an efficient perturbative method to treat dynamic correlation without the problems of intruder states or level shifts, while the density matrix renormalization group (DMRG) provides the capability to tackle static ...
1512.08137v4
2016-03-21
Hybrid graphene/silicon integrated optical isolators with photonic spin-orbit interaction
Optical isolators are an important building block in photonic computation and communication. In traditional optics, isolators are realized with magneto-optical garnets. However, it remains challenging to incorporate such materials on an integrated platform because of the difficulty in material growth and bulky device f...
1603.06332v1