Materials Science
A locally ab initio computational framework for arbitrary incommensurate materials interfaces
Drake Niedzielski and Tomás A. Arias
Incommensurate materials interfaces constitute a broad and technologically important class of systems, yet their lack of shared periodicity limits predictive and computationally efficient first-principles electronic-structure methods. Here we introduce a scalable computational framework for constructing locally ab initio electronic
Hamiltonians for arbitrary materials interfaces. Our approach exploits the nearsightedness of Wannier
Hamiltonian matrix elements, enabling their systematic extrapolation and interpolation across interlayer registries. This strategy yields transferable
Hamiltonians that retain first-principles accuracy while bypassing the need for prohibitively large commensurate supercells or Moiré approximations. We validate the framework on quasicrystalline 30{\deg} twisted bilayer
graphene, reproducing experimentally observed spectral features including mirrored Dirac cones and minigaps at avoided crossings arising from generalized interlayer scattering. We further predict quasiperiodic flat-band states in experimentally accessible doping regimes. By enabling predictive electronic-structure calculations across structurally incommensurate interfaces, this framework establishes a practical route to first-principles exploration of emergent interfacial phenomena.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Engineering Giant Thermoelectric Performance through Electrode-Coupling Geometry and Magnetic Flux in Quasiperiodic Su-Schrieffer-Heeger Rings
Sridhar, Souvik Roy and Malay Bandyopadhyay
We investigate coherent thermoelectric transport in
magnetic-flux-threaded quasiperiodic Su-Schrieffer-Heeger (SSH) rings with engineered multi-site electrode couplings using the nonequilibrium Green's function formalism within the Landauer-Büttiker framework. We demonstrate that the electrode-coupling geometry serves as a powerful control parameter for tailoring
quantum interference, thereby reshaping the transmission spectrum and thermoelectric response. In the absence of
magnetic flux, the trivial dimerized phase ($t_1>t_2$) exhibits the highest thermoelectric efficiency, with asymmetric coupling producing a substantially larger figure of merit than the symmetric geometry.
Magnetic flux further reconstructs the transmission spectrum through Aharonov-Bohm interference, driving a crossover of the optimal thermoelectric regime from the trivial to the topological dimerized phase. Under optimal flux conditions, the thermoelectric figure of merit reaches $ZT \approx 12$ for symmetric coupling and is dramatically enhanced to $ZT \approx 90$ for asymmetric coupling through enhanced energy filtering and suppressed electronic thermal transport. We further establish a clear correlation between the enhancement of thermoelectric efficiency and the violation of the Wiedemann-Franz law. Our results demonstrate that the combined interplay of quasiperiodicity,
topology,
magnetic flux, and electrode-coupling geometry provides a versatile strategy for engineering high-performance coherent thermoelectric devices.
Read the full abstract ▾
Materials Science
Generalized Helicity-Dependent Magnetization Switching via Substrate Phonons
F.G.N. Fennema, H. Damas, H. Yoshikawa et al. (+3 more)
Coherent excitation of circularly-polarized substrate
phonons can drive deterministic reversal of magnetization in an adjacent
magnetic layer. However, the extent to which this substrate-mediated mechanism can be generalized across different materials remains unresolved. Here, we measure and compare the spectral dependence of helicity-dependent magnetization reversal in
magnetic GdFeCo layers grown on a diverse set of diamagnetic substrates. Switching is observed for all investigated substrates, spanning six point groups and several infrared-active transverse-optical
phonon symmetries. While the switching spectra broadly overlap with the Reststrahlen bands, their maxima are systematically shifted to wavelengths shorter than the corresponding transverse-optical
phonon resonances. This spectral mismatch shows that substrate absorption alone does not determine the switching efficiency. Transfer-
matrix calculations show that strong absorption concentrates energy deposition near the substrate interface, providing a possible source of local heating that could suppress magnetization reversal. Our results reveal the broad applicability of substrate-mediated phononic switching while showing that its efficiency is governed by the full optical response of the
heterostructure rather than substrate absorption alone.
Read the full abstract ▾
All authors F.G.N. Fennema, H. Damas, H. Yoshikawa, A. Tsukamoto, C.S. Davies, A. Kirilyuk
Materials Science
Influence of dislocation density on the tribological response in oxides: case study on SrTiO3
Chukwudalu Okafor, Oliver Preuß, Thomas Chudoba et al. (+6 more)
Most ceramics suffer from brittle surface damage and cracking when small particles slide across the surface under low load. Microscratching tests are a useful technique to mimic this loading scenario while retaining the material's deformation history; however, the impact of pre-seeded dislocations, which can significantly facilitate plastic deformation, has not been explored in ceramics. Here, the influence of mechanically seeded dislocations on the microscratching response of oxides is investigated using a model perovskite, SrTiO3. First, various dislocation densities over four orders of magnitude are introduced via room-temperature cyclic Brinell indenter scratching. Subsequently, load-ramped microscratching tests are performed within the pristine and dislocation-seeded regions using a nominally 30 {\mu}m spherical diamond tip. On the reference pristine surface, we observe a clear transition from elastic to elasto-plastic deformation, followed by median/radial cracking at higher loads. In contrast, pre-seeded dislocations, accompanied by residual compressive stresses, suppress elastic deformation and lead to median/radial crack shortening and subsequent transition to a partial cone crack. The subsurface cracks are characterized by 3D Nano-CT. The changes in crack geometry, with and without dislocations, were described using the Lawn-Evans-Marshall and Lawn-Wiederhorn-Roberts models. These findings provide direct evidence of dislocation-regulated near-surface damage tolerance, with general applicability to other plastically deformable oxides.
Read the full abstract ▾
All authors Chukwudalu Okafor, Oliver Preuß, Thomas Chudoba, Ujjval Bansal, Daniela Exner, Konrad Priszokovich, Yanfei Gao, Christoph Kirchlechner, Xufei Fang
Statistical Mechanics
Tensor-Network Inference in a Field-Coupled XY Model for Portfolio Allocation
Kartikeya Chowdhry and G Subrahmanya V.R.K. Rao
We apply tensor-network methods to a field-coupled XY model for long-only portfolio construction. Daily return statistics set asset-specific fields and correlation couplings. Correlation distance, four-point Gromov hyperbolicity, and Ward clustering are used to construct a sparse interaction path. A
Fourier-Bessel expansion maps the continuous angular partition function to a finite-current tensor network; bottom-up and top-down contractions then give the one-site marginals and
equilibrium cosine scores. A softmax map converts these scores into positive, fully invested portfolio weights. We study five equity
markets over continuous ranges of inverse temperature beta and concentration gamma, and compare selected parameter pairs with long-only Markowitz frontiers and standard
benchmarks. The same-sample comparisons demonstrate a tractable route from financial time series to network-adjusted allocations; predictive trading performance is outside their scope.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
ANT:UI: An interactive 3D tool for preparing ANT.Gaussian molecular junction geometries
A. Martinez-Garcia, J. J. Palacios and C. Sabater
ANT.UI is a Python graphical interface that automates the construction of molecular-junction geometries for NEGF-DFT
quantum transport calculations. Through a real-time 3D viewer, users interactively position electrodes and molecules and generate complete, ready-to-run input files for Gaussian and ANT.Gaussian without manual scripting. Dedicated Pull, Grid, and Rotation assistants further automate electrode-pulling sequences, surface scans, and step-wise rotation studies, with optional geometry-optimisation chaining across each sequence. By replacing a process that previously demanded days of custom scripting with a point-and-click workflow, ANT.UI accelerates research in theoretical molecular electronics and lowers the barrier to entry for new users. The software also exports all constructed geometries in standard XYZ format, allowing direct reuse in molecular dynamics codes or third-party visualization tools without manual reformatting.
Read the full abstract ▾
Materials Science
Local coordination, structural softening, and polarization-switching energetics in Sc-alloyed GaN
Shailesh Kalal, Gueorgui Kostov Gueorguiev, Martin Magnuson et al. (+8 more)
Sc-alloyed wurtzite nitrides exhibit strongly tunable electromechanical and ferroelectric properties, yet the relationship between their
lattice evolution and local bonding environment remains insufficiently established, particularly in Sc$_x$Ga$_{1-x}$N. Here, we investigate the structural and local bonding
evolution of Sc$_x$Ga$_{1-x}$N across the dilute-to-intermediate composition range by combining X-ray diffraction, Sc K-edge X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS) and first-principles calculations. Sc incorporation produces an anisotropic
lattice expansion and a progressive reduction in the c/a ratio. XANES and EXAFS reveal a concurrent modification of the local environment around Sc, with the effective Sc-N coordination number increasing from 4.1(4) to 4.5(2) and the average Sc-N bond length increasing from 2.045(7) to 2.081(8)Å over x=0.06-0.26. The local response is accompanied by a reduction in the Sc K-edge pre-edge intensity, consistent with a gradual reduction of the local tetrahedral asymmetry. First-principles calculations show that these structural changes are associated with site-selective distortions around Sc and progressive flattening of the structural energy landscape. The calculated intrinsic polarization-switching barrier decreases from 24.2 to 19.0 meV/Å$^3$ with increasing Sc content, while the calculated piezoelectric stress coefficient (e$_{33}$) increases from 0.82 to 1.66~C/m$^2$ and elastic constant (C$_{33}$) decreases from 380 to 227~GPa, resulting in an increase of piezoelectric strain coefficient (d$_{33}$) from 2.99 to 12.46~pC/N. These results show that Sc incorporation progressively modifies the local coordination environment and structural energetics of ScGaN while the long-range wurtzite structure remains preserved over the investigated composition range.
Read the full abstract ▾
All authors Shailesh Kalal, Gueorgui Kostov Gueorguiev, Martin Magnuson, Edward Ferraz de Almeida Junior, Rohini Sanikop, Sagar Jathar, Per Sandström, Ray-Hua Horng, Jens Birch, Per Eklund, Ching-Lien Hsiao
Statistical Mechanics
Anomalous diffusion in porous fractal media
Alexander Iomin and Trifce Sandev
We suggest a model of a diffusive process inside a fractal sponge structure, which is a generalization of the
diffusion processes on a comb and fractal mesh structure. The sponge model is considered as the direct product of Cantor sets. It is shown that the corresponding one-dimensional
diffusion process is governed by a generalized Fokker-Planck equation with a power-law
memory kernel and a position-dependent
diffusion coefficient. That is, the fractal structure of the medium induces
memory effects and heterogeneity in the transport system. The considered model may be of interest to describe anomalous heat transport in porous fractal media.
Read the full abstract ▾
Materials Science · Cross-listed from physics.chem-ph
Operando imaging of intercalation memory in MXenes
Franz Groebmeyer, Mohsen Beladi, Christoph G. Gruber et al. (+6 more)
Ion intercalation enables reversible control of charge, structure and function in layered solids. Yet layered materials contain nanosheets with different thicknesses and stacking, whose intercalation pathways are averaged out in ensemble measurements. This becomes critical under Angstrom-scale confinement, where ion transport couples to solvent reorganization and host deformation, leaving the origins of kinetics, reversibility and activation unresolved. Here we combine operando interferometric scattering and interference reflection microscopy to resolve
proton-driven dynamics in individual single- and multilayer Ti3C2Tx MXene flakes and show that even a few stacked layers introduce a significant kinetic barrier. Cycling then separates nanosheets into three persistent behaviors: reversible monolayers, restacked multilayers with incomplete recovery and delayed deintercalation, and coherently stacked multilayers that self-stabilize through reversible folding. Operando synchrotron X-ray diffraction shows this
memory at electrode scale, where the interlayer structure converges towards a reproducible state. Our findings reveal cycling-induced structural
memory that governs subsequent intercalation in layered MXenes.
Read the full abstract ▾
All authors Franz Groebmeyer, Mohsen Beladi, Christoph G. Gruber, Ruocun Wang, Pol Salles, Nhu Quynh Nguyen, Jakub Drnec, Yury Gogotsi, Emiliano Cortes
Mesoscale and Nanoscale Physics
Bias-field control of the Neel skyrmion nonlinearity in a confined nanostructure
A.V. Valkov, A.A. Matveev, O.Yu. Arkhipova et al. (+3 more)
We study the nonlinear dynamics of a cylindrical skyrmion-based oscillator within the framework of a generalized Thiele model. We demonstrate the influence of an bias
magnetic field applied perpendicular to the plane of the nanocylinder on the oscillation frequency and on the nonlinearity coefficient. It is shown that the field tunes the response frequency, while also producing a substantial change in the nonlinear frequency shift. We find that the nonlinearity coefficient reverses its sign as the field crosses a certain critical value. The variation of the nonlinearity coefficient with the field is clearly illustrated by the observed qualitative changes in nonlinear amplitude-frequency responses. Controlling the nonlinear properties of a skyrmion oscillator by changing the bias
magnetic field opens up prospects for creating tunable computational elements for neuromorphic applications.
Read the full abstract ▾
All authors A.V. Valkov, A.A. Matveev, O.Yu. Arkhipova, R.V. Shcherbakov, A.R. Safin, S.A. Nikitov
Statistical Mechanics
Universal Thermodynamic Law Governing Stochastic Pendulum Clocks
Yuki Izumida
Clocks' performance, especially their precision, is fundamentally limited by thermodynamic laws as they are physical devices. Yet, it is known that the established thermodynamic uncertainty relation (TUR), which imposes an upper bound on the uncertainty product of the precision of oscillations and
entropy production, is violated for underdamped systems such as
stochastic pendulum clocks. Here, we show that for a general class of
stochastic pendulum clocks described as a weakly nonlinear oscillator the uncertainty product of the phase of a pendulum clock and
entropy production takes a universal and simple form that depends solely on the degree of nonlinearity. Its validity and limitations are examined using several representative models of pendulum clocks. Our framework reveals a universal thermodynamic principle governing
stochastic pendulum clocks beyond the conventional TUR and provides a foundation for designing optimal pendulum clocks that operate efficiently in
stochastic environments.
Read the full abstract ▾
Materials Science
Nuclear quantum effects in the thermal conductivity of solid hydrogen
Hengtai Zheng, Zezhu Zeng and David E. Manolopoulos
We use a combination of path integral and
lattice dynamics methods to calculate the thermal conductivity of solid parahydrogen. Path integral molecular dynamics is first used to calculate a centroid potential of mean force at each temperature, on which a harmonic
phonon basis is constructed using the finite displacement method. We then calculate anharmonic force constants on the centroid potential and solve the linearised
phonon Boltzmann transport equation for the thermal conductivity. The resulting renormalised
phonon dispersion curves, heat capacity, and thermal conductivity are all in remarkably good agreement with experimental measurements. We find that the heat transport is dominated by collective relaxon modes at low temperatures and cannot be captured by making the
phonon relaxation time approximation. Indeed, quantitative agreement with the experimental thermal conductivity is only achieved when the nuclear
quantum effects in the centroid potential of mean force,
phonon boundary scattering, and hydrodynamic transport are all explicitly considered. This is also likely to be the case for other
quantum crystals.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Nonreciprocal plasmonic response of drift-biased two-dimensional metals
Gonzalo Álvarez-Pérez and Joel D. Cox
We develop a nonlocal electrodynamic framework for drift-biased two-dimensional electron gases (2DEGs) with Dirac (linear) and parabolic (quadratic) dispersions, deriving closed-form drift-dependent conductivity tensors from the Boltzmann transport equation. We obtain the plasmon dispersion and near-field emission of a point dipole, revealing nonreciprocal propagation in both systems. At equal drift parameter, the parabolic 2DEG exhibits stronger nonreciprocity than the Dirac system, although we find that a larger drift parameter does not by itself produce stronger nonreciprocity: the response is set by the interplay of drift and plasmon nonlocality. As such, the combination of strong nonlocality and experimentally accessible drift velocities of
semiconductor 2DEGs identifies parabolic systems as a promising platform for tunable, nonreciprocal plasmonics.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Cascade spin dynamics of excitons localized in indirect-band-gap (In,Al)As/AlAs quantum dots with type-I band alignment
S. V. Nekrasov, I. V. Kalitukha, A. A. Golovatenko et al. (+5 more)
We investigate the
spin dynamics of
excitons localized in type I (In,Al)As/AlAs
quantum dots with an indirect in momentum space band structure. Polarized selective photoluminescence spectroscopy, i.e. fluorescence line narrowing, under
magnetic fields up to 5 T applied in the Faraday geometry is employed. The experiment reveals a cascade
spin evolution process of
excitons in the indirect band-gap
quantum dots: an initial short term
spin dynamics associated with excited direct
exciton states possessing a large oscillator strength is followed by electron relaxation into the X valley of the Brillouin zone and subsequent long term
spin dynamics of indirect
excitons. The two step mechanism manifests itself in the distinct features of the
magnetic field dependences of photoluminescence: two component recovery of optical orientation, two component linear to circular polarization conversion and the presence of the linear polarization plane rotation. At the same time, suppression of the optical
alignment shows one-component behavior governed by the
spin dynamics of the indirect
exciton states. Within the pseudospin formalism, we derive analytical expressions that quantitatively describe the observed dependences and yield estimates for the anisotropic exchange splitting: 210 {\mu}eV for direct
excitons and 1.3 {\mu}eV for indirect
excitons. Further analysis using the density
matrix formalism agrees well with the pseudospin model calculations and shows that the finite optical orientation at zero
magnetic field is due to comparable magnitudes of the anisotropic splitting of the indirect
exciton states and the splitting of the X-valley electron states caused by the hyperfine interaction with
nuclei.
Read the full abstract ▾
All authors S. V. Nekrasov, I. V. Kalitukha, A. A. Golovatenko, Ya. A. Kuznetsova, N. O. Mikhailenko, M. D. Ragoza, T. S. Shamirzaev, Yu. G. Kusrayev
Superconductivity · Cross-listed from hep-ph
Global Fixed Point Potentials in the Abelian Higgs Model with $N$ flavors
Gergely Fejős and Shunsuke Yabunaka
Existence of charged fixed points in the Abelian
Higgs model with $N$ flavors in $d$ dimensions is studied using the functional renormalization group. We numerically solve the coupled fixed point equations for the scale dependent charge and the non-perturbative effective potential for the scalar field. We show that the $\epsilon=4-d$ expansion, famously successful in theories with $O(N)$
symmetry, fails to produce reliable results when taking the $\epsilon \rightarrow 1$ limit. By determining global fixed point potentials, it is shown that the critical flavor number at which charged fixed points appear, modifies significantly compared to the perturbative treatment. In $d=3$, signs of a richer fixed point structure with presumably multicritical fixed points are also found. Discussions include subtleties of the gauge fixing and the corresponding modified Ward-Takahashi identities, including the possibility of a nonzero dimensionless
photon mass at the infrared fixed point.
Read the full abstract ▾
Soft Condensed Matter
Liquid-liquid phase separation precedes crystallization in supercooled water-glycerol solutions
Iason Andronis, Sharon Berkowicz, Mariia Filianina et al. (+10 more)
Understanding the structural
evolution of supercooled water-glycerol solutions is important for cryopreservation, yet distinguishing
liquid-state transformations from ice crystallization remains challenging. Here, we investigate a deeply supercooled water-glycerol solution by X-ray
photon correlation spectroscopy (XPCS) in ultra-small-angle X-ray scattering (USAXS) geometry, combined with wide-angle X-ray scattering (WAXS). This combination simultaneously captures the structural and dynamical
evolution of the supercooled
liquid upon quenching to cryogenic temperatures (172 K). We observe discontinuous changes in the
liquid structure on molecular length scales and formation of microscale domains. The dynamics slow down during this stage and exhibit hyper-diffusive, ballistic-like relaxation. This transformation precedes ice crystallization, which we identify from the emergence of ice Bragg peaks in WAXS, allowing the two processes to be temporally separated. Phase-field (Cahn-Hilliard) simulations qualitatively reproduce the experimental observations and show that a spinodal-decomposition scenario is consistent with the measured scattering
evolution. These findings are consistent with a
liquid-
liquid phase separation scenario preceding ice crystallization and provide a route to disentangle the two processes in supercooled aqueous systems.
Read the full abstract ▾
All authors Iason Andronis, Sharon Berkowicz, Mariia Filianina, Maddalena Bin, Robin Tyburski, Robert Bauer, Yuriy Chushkin, Federico Zontone, Michael Sprung, Wojciech Roseker, Fabian Westermeier, Felix Lehmkühler, Fivos Perakis
Mesoscale and Nanoscale Physics
Spin-Point-Group Classification of Multipoles for Nonrelativistic Collinear Magnets
Yuuki Ogawa and Satoru Hayami
Multipole moments provide a unified
symmetry language for describing electronic degrees of freedom and their associated physical responses. Although active multipoles have been systematically classified for crystallographic and
magnetic point groups, their classification in
spin point groups, which naturally describe
magnetic systems in the absence of
spin-orbit coupling, has remained unexplored. In this work, we present a complete classification of active orbital and
spin multipoles for all 32 nonmagnetic and 122 collinear
spin point groups. Treating orbital and
spin degrees of freedom independently, we identify the
symmetry-allowed multipoles associated with nonmagnetic and collinear
magnetic orderings and clarify their hierarchy through comparisons among the corresponding
spin point groups. The resulting classification provides a
symmetry-based database that distinguishes structural and
magnetic contributions to active multipoles and directly identifies microscopic order parameters, including those responsible for $d$-, $g$-, and $i$-wave altermagnetism. Furthermore, by classifying response tensors within the same framework, we establish a correspondence between active multipoles and
symmetry-allowed physical responses. This correspondence systematically distinguishes nonrelativistic responses that survive without
spin-orbit coupling from those requiring relativistic effects, providing a unified framework for understanding and predicting
spin-dependent electromagnetic and transport phenomena in
magnetic materials.
Read the full abstract ▾
Soft Condensed Matter
The elasticity of semiflexible polymers with reversible spontaneous curvature in two dimensions
Donghyeon Kim and Panayotis Benetatos
Many semiflexible filaments exhibit structural asymmetries that lead to a curved ground state (
curvature in the absence of thermal fluctuations, external forces, or torques). This property is known as spontaneous
curvature. Many semiflexible
polymers can reversibly develop spontaneous
curvature through internal conformational transitions or through transient interactions with their molecular environment. In this article, we show that such reversible spontaneous
curvature, even in the absence of transitions in the value of the bending stiffness, provides a minimal mechanism for ensemble-dependent elasticity. We formulate an analytically tractable two-state modified wormlike-chain model in two dimensions, in which an uncurved state (without spontaneous
curvature) competes with a curved state (possessing spontaneous
curvature). The transition is controlled by an activation energy. Within the weak-bending approximation, we obtain the Gibbs and Helmholtz partition functions for a stretched filament with reversible constant (uniform along the backbone) or sinusoidal spontaneous
curvature and for a grafted bistable filament driven either by an end torque or a bending force. Stretching or bending induces a crossover from spontaneous-
curvature-dominated to entropic elasticity. We show how the elastic response differs in the two ensembles (Gibbs vs Helmholtz). In addition, we consider the case where the curved state is also characterized by a higher value of the bending stiffness. In that case, a reentrant transition is possible as we stretch the bistable filament.
Read the full abstract ▾
Mesoscale and Nanoscale Physics
Excitation caging in a vertex-frustrated quasiperiodic Einstein artificial spin ice
T. Wang, F. Museur, G. M. Macauley et al. (+5 more)
Naturally occurring bulk quasicrystals are rare, and
magnetic instances are rarer still, with chemical constraints typically permitting the synthesis of approximants rather than true quasicrystalline magnets. Here, we present an artificial
spin ice based on a recently discovered Einstein
lattice, the Hat tiling, which is built from the first known shape - the hat - that tiles the plane only aperiodically. The Einstein artificial
spin ice has long-range structural order with no translational
symmetry, and low-connectivity vertices with well-defined local ground states and excitations. Together, these properties provide a model two-dimensional quasicrystalline magnet, with
magnetic correlations that we probe with
magnetic force microscopy and parallel-tempered Monte Carlo simulations. We identify a two-stage partial ordering process, driven by the competition between two possible positions for
magnetic excitations. This competition is resolved in the ground-state
manifold, where exactly one
magnetic excitation is caged on each antihat, yet the
manifold remains macroscopically degenerate. This yields an unusual type of medium-range order, where the underlying quasiperiodic long-range order is randomly modulated by a strictly constrained disorder. Our findings establish the Einstein artificial
spin ice as a blueprint for understanding quasicrystalline magnetism, demonstrating how quasiperiodic monotile geometries can be exploited to engineer unconventional
magnetic phases with no direct equivalent in periodic systems.
Read the full abstract ▾
All authors T. Wang, F. Museur, G. M. Macauley, J. Colbois, L. Berchialla, F. Flicker, P. M. Derlet, L. J. Heyderman
Materials Science
Multi-task deep-learning optimization of trade-off properties for superior-performance Fe-based soft magnetic alloys
Kang-Yuan Li, Mao-Zhi Li and Wei-Hua Wang
Fe-based amorphous
alloys are promising soft
magnetic materials for developing next-generation devices with high frequency and efficiency. However, optimization of Fe-based
alloys with ultra-high saturation
magnetic flux density (B_s), ultra-low coercivity (H_c), and good glass-forming ability is a notorious problem, owing to the vast composition space and complex trade-offs of these properties. Thus, conventional design methods encounter great challenges. Here we develop a generative multi-task deep learning (GMTDL) to achieve simultaneous optimization of compositions and trade-off properties. The GMTDL can sufficiently exploit and share the knowledge of
datasets across different tasks, despite the limitation and imbalance of these
datasets. Therefore, it exhibits superior performance in prediction of
alloys with multiple targeted properties, outperforming previous machine learning-based design strategies. Moreover, the GMTDL can also tailor compositions, providing an efficient way to regulate properties and generate desired candidates for further experimental processing. The validity and reliability of GMTDL are rigorously tested by benchmarking with Fe-based
alloys reported very recently. Moreover, some new
alloys with ultra-high B_s and ultra-low H_c are predicted. The optimal content windows of key elements and their synergistic effects are also unraveled for practical guidance. Thus, our study establishes an effective and reliable paradigm for simultaneous prediction and optimization of high-performance materials with multiple properties.
Read the full abstract ▾
Superconductivity
On the Stability of the Polar Phase of Superfluid 3He in Nematic Aerogels
E. V. Surovtsev
We study the stability of the solution corresponding to the polar phase of superfluid 3He in nematic aerogels with respect to perturbations induced by
magnetic impurity scattering. We show that when the perturbation simultaneously breaks axial and time-reversal
symmetry, the polar-distorted A phase is realized with the highest transition temperature. Within the proposed model of a p-wave scattering potential, which accounts for the effective
spin-orbit interaction between the orbital angular momentum of a scattering quasiparticle and the
magnetic moment texture of the scatterer, we solve the
eigenvalue and eigenvector problem for the Gor'kov self-consistency equation. Finally, we discuss how our results relate to the available experimental data.
Read the full abstract ▾
Quantum Gases
Spin-Charge Subordination in the Infinite-$U$ $SU(N)$ Hubbard Chain
Cătălin Paşcu Moca, Ovidiu I. Pâţu, Gergely Zaránd et al. (+1 more)
We obtain the exact full counting statistics of charge and flavor transport in the one-dimensional infinite-$U$ $SU(N)$ Hubbard model. The no-passing constraint freezes the ordered flavor sequence while the particle coordinates evolve as free spinless
fermions. Consequently, charge transfer is governed by a free-
fermion determinant, whereas flavor transfer is exactly subordinated to the number of particles crossing the observation cut. For an arbitrary traceless Cartan generator this yields an exact relation between the charge and flavor cumulants. The complete asymptotic flavor distribution is a universal non-Gaussian M-Wright law. Together, these results establish
spin–charge subordination as a kinematic mechanism for anomalously slow internal-state transport in one-dimensional impenetrable
quantum gases.
Read the full abstract ▾
All authors Cătălin Paşcu Moca, Ovidiu I. Pâţu, Gergely Zaránd, Balázs Dóra
Materials Science
Challenges in orbital current-driven domain wall motion in light metal/ferrimagnet heterostructures
Min-Gu Kang, Jaerin Kim, Benjamin J. Jacot et al. (+2 more)
Recent advances in spintronics suggest that orbital Hall currents generated by charge injection in light metals can provide nonequilibrium angular momentum without relying on strong
spin-orbit coupling (SOC). Here, we examine whether such orbital currents can drive domain wall (DW) motion in an amorphous ferrimagnetic
alloy, Gd$_{25}$(Fe$_{9}$Co$_{1}$)$_{75}$ (GFC), where the rare-earth sublattice offers strong SOC for orbital-to-
spin conversion. We compare three representative
heterostructures: Pt/GFC as a
spin Hall reference, light-metal (Mn or Ti)/GFC for direct orbital-current injection, and light-metal/Pt/GFC incorporating an ultrathin Pt layer for orbital-to-
spin conversion. Whereas Pt/GFC exhibits robust and reproducible
spin-orbit-torque-driven DW motion, no current-driven DW motion is detected in Mn/GFC or Ti/GFC. Second-harmonic Hall measurements nevertheless reveal finite damping-like torques in both Mn/GFC and Ti/GFC, demonstrating that angular-momentum transfer into GFC does occur but is far weaker than in Pt/GFC. Inserting a 1-nm-thick Pt conversion layer strongly enhances the damping-like torque and restores DW motion. Thickness-dependent analysis further shows that DW mobility and depinning thresholds correlate with the interfacial Dzyaloshinskii-Moriya interaction and domain-wall width, highlighting weak torque conversion and insufficient interfacial stabilization of chiral DWs as key challenges for orbital-driven DW motion in light-metal/ferrimagnet
heterostructures.
Read the full abstract ▾
All authors Min-Gu Kang, Jaerin Kim, Benjamin J. Jacot, Laura Van Schie, Pietro Gambardella
Materials Science
Field-Driven Coupled Magnon–Phonon–Electron Relaxation in Magnetite Using Steepest-Entropy-Ascent Quantum Thermodynamic Formalism
Deepak Dhariwal, William T. Reynolds, Jr. et al. (+1 more)
A field-driven steepest-
entropy-ascent
quantum thermodynamic (SEAQT) formulation is developed for longitudinal nonequilibrium relaxation in magnetite (Fe$_3$O$_4$) with coupled electron,
phonon, and
magnon populations. Material-specific excitation spectra define the thermodynamic state space, while one relaxation parameter for each population sets its kinetic scale. A longitudinal
magnetic field shifts the dressed
magnon eigenenergies while the occupation basis remains fixed; irreversible redistribution conserves instantaneous energy and electron number while allowing the
magnon population to vary. The formulation yields nonequilibrium subsystem temperatures,
entropy production,
magnetic-work identities, and a coupled small-signal susceptibility incorporating energy-conservation feedback among all three populations; the one-pole Debye response appears only as a limiting case. Numerical results under sinusoidal driving show a transition from nearly quasistatic behavior to frequency-dependent lag, finite-amplitude departure from the linear-response ellipse, and increasing higher-harmonic content. Relaxational work per cycle increases strongly with field amplitude and frequency, while the complex susceptibility is broader and shifted relative to a Debye reference.
Entropy production remains positive, and the electron,
phonon, and
magnon temperatures show distinct excursions followed by secular heating when positive
magnetic work is retained without heat rejection. The calculated work represents longitudinal
magnon quasiparticle relaxation in a homogeneous single-domain model, not the total core loss of a finite ferrite specimen.
Read the full abstract ▾
All authors Deepak Dhariwal, William T. Reynolds, Jr., Michael R. von Spakovsky
Superconductivity
Orientation selection and superconducting properties of epitaxial Al on ferromagnetic semiconductor (In,Fe)As
Hirotaka Hara, Keita Ishihara, Masaaki Tanaka et al. (+1 more)
Superconductor/ferromagnet
heterostructures provide a versatile platform for exploring
spin-dependent superconducting phenomena arising from interfacial proximity effects. In this article, we investigate the structural and superconducting properties of Al thin films grown in situ by molecular beam epitaxy on strained Fe-doped ferromagnetic
semiconductor (FMS) (In,Fe)As layers. X-ray diffraction and transmission electron microscopy reveal the epitaxial growth of single-crystalline Al layers, with the growth orientation changing from (110) to (111) as the in-plane
lattice constant of (In,Fe)As increases. The superconducting critical temperature of Al varies systematically with the film surface morphology and grain size. In addition, the critical
magnetic field of Al exhibits an anomalous decrease below 0.5 K, possibly reflecting
magnetic coupling to the underlying FMS (In,Fe)As layer. These findings provide a guideline for material design of epitaxial Al/(In,Fe)As
heterostructures, which may serve as a promising platform for investigating proximity-induced superconducting and
magnetic phenomena in
semiconductor-based hybrid
quantum devices.
Read the full abstract ▾
All authors Hirotaka Hara, Keita Ishihara, Masaaki Tanaka, Le Duc Anh
Statistical Mechanics
Thermodynamic learning
F. Corberi, S. dello Russo, G. Messuti et al. (+2 more)
We discuss the possibility to train a thermodynamic system, whose micro-variables are fully determined through the
Hamiltonian by the usual statistical mechanical rules, to perform tasks such as memorization and generalization. Training is achieved by the application of suitable external fields, playing the role of data. At variance with conventional machine learning, no other logical or algorithmic rules are introduced. The system is amenable, in principle, to exact analytical calculations. We specialize this general approach to a prototypical Ising system with annealed dichotomous couplings and study its learning ability. Results indicate excellent memorization and good generalization capacity already for small systems, and a tendency to improve with system size.
Read the full abstract ▾
All authors F. Corberi, S. dello Russo, G. Messuti, S. Scarpetta, L. Smaldone
Mesoscale and Nanoscale Physics
Interlayer Exciton Condensate Stiffness Is Non-Monotonic in Quantum Metric
Bo Zou, Yitong Zhang, Siddhartha Sarkar et al. (+3 more)
Identifying the origin of the superfluid stiffness of electron-electron and electron-hole pair condensates is an important issue in flat-band physics. Here, we study the stiffness of bilayer
exciton condensates using exact diagonalization and realistic Coulomb interactions across a wide variety of flat Chern band systems, including Landau levels, mixed Landau levels, and moiré bands. We find that stiffness is non-monotonic in the trace of the
quantum metric and that it develops peaks when the band wavefunctions are engineered to be similar to those of Landau levels. The stiffness predicted by mean-field theory agrees quantitatively with exact diagonalization in these optimal cases, but systematically overestimates it otherwise. Flat bands with identical
quantum geometry tensors can exhibit substantial differences in stiffness. The stiffness of condensates formed between moiré flat bands, which typically have strong variations in Berry
curvature and
quantum metric across their Brillouin zones, tends to be larger when the bands have non-zero Chern numbers and can be larger than that of Landau levels. Our results reveal a behavior that is richer than that suggested by simple
geometric bounds and provide new guiding principles for the design of robust flat-band condensates with large superfluid stiffness.
Read the full abstract ▾
All authors Bo Zou, Yitong Zhang, Siddhartha Sarkar, Shi-Zeng Lin, Allan H. MacDonald, Kai Sun
Statistical Mechanics
Scaling laws and energy dissipation in the dynamics of SLE curve as a 1D turbulence model
Yusuke K. Shibasaki
In this study, we demonstrate the characteristics of the
stochastic Loewner
evolution (SLE) as a one-dimensional (1D)
turbulence model. First, we show that the
diffusion process $x(t)$ obtained by the time coordinate change in the SLE becomes the time dependent
diffusion process that satisfies Richardson's law of
turbulence.Subsequently, we derive the condition on the diffusivity parameter $\kappa$ such that the
diffusion process $x(t)$ satisfies Kolmogorov's 4/5th law, which determines the relation between the mean energy dissipation and velocity in the particles of
turbulence. Further mathematical analysis showed that this condition is seen as the condition on Loewner
entropy $S_{\mathrm{Loew}}$, which includes the white Gaussian noise term $W_{s}$ in the Loewner driving function of the present model. In addition, the numerical simulations were performed to verify the scaling relations of this 1D
turbulence model. These results suggest that the standard SLE becomes a beneficial model of 1D
turbulence by introducing an appropriate time coordinate change and imposing the conditions on $\kappa$ and $S_{\mathrm{Loew}}$.
Read the full abstract ▾
Statistical Mechanics
Mean-field theory for quantum spin chains
Mylène Martirosyan, Astrid Monin-Baroille, Leïla Moueddene et al. (+2 more)
Mean-field theory is a widely used approximation for describing phase transitions, particularly effective above the upper critical dimension. Its origins can be traced back to the van der Waals theory of the
liquid-gas transition and Weiss's molecular field theory of the paramagnetic-ferromagnetic transition. However, it was Lev D. Landau who provided a unifying and general framework applicable to a broad class of physical systems. The mean-field approach typically involves neglecting thermal fluctuations, which is a reasonable assumption in many classical contexts. However, its application to
quantum phase transitions at zero temperature is less common. The aim of this short pedagogical paper is to explore and clarify the use of the mean-field approach in the less familiar domain of
quantum phase transitions. We specifically consider the Ising model and the Blume-Capel model.
Read the full abstract ▾
All authors Mylène Martirosyan, Astrid Monin-Baroille, Leïla Moueddene, Mohammed M. Shabat, Bertrand Berche
Materials Science · Cross-listed from physics.chem-ph
Voltage-embedded equivariant machine learning potential for open system simulations
Yiming Guan, Rongzhi Gao, ChiYung Yam et al. (+2 more)
Modeling electrochemical interfaces under operational non-
equilibrium conditions is vital for energy technologies but remains bottlenecked by the expensive cost of ab initio methods. Current machine learning potentials, largely designed for closed systems under homogeneous electric fields, are limited in open
quantum transport applications. To overcome this, we present an E(3)-equivariant graph neural network that embeds voltage bias for open-system simulations. Our approach decouples the system energy and forces into zero-bias and bias-dependent contributions, assigning distinct vector encodings to electrode and scattering-region atoms to capture non-
equilibrium conditions. Trained on limited discrete bias data, the model achieves high predictive accuracy and robust extrapolation transferability. When applied to a lithium/water interface, our model successfully captures the field-induced dynamic reorientation of water molecules and reproduces asymmetric electrochemical behavior at different electrodes.
Read the full abstract ▾
All authors Yiming Guan, Rongzhi Gao, ChiYung Yam, GuanHua Chen, Ziyang Hu