Materials Science
ATLAS: A Foundation Neural Sampler for Amorphous Materials
Mouyang Cheng, Denis Blessing, Botao Yu et al. (+4 more)
Amorphous materials exhibit exceptional mechanical and functional properties, yet their rugged energy landscapes are notoriously difficult to sample. Below the glass-transition temperature, conventional molecular dynamics and Monte Carlo become inefficient because equilibration relies on rare barrier-crossing events, while data-driven generative models are constrained by scarce and biased reference ensembles. Here, we introduce ATLAS, an efficient sampler that learns a
diffusion process to generate Boltzmann-distributed amorphous structures directly from a target energy function. Parameterized by an equivariant graph neural network, ATLAS generalizes across system size, temperature, and composition. By exploiting the time reversal of the
diffusion process, it enables efficient estimation of thermodynamic quantities and steering toward target observables. In two-dimensional Kob-Andersen systems, ATLAS reproduces parallel tempering Markov chain Monte Carlo structural distributions, free energies and
entropies, achieving below 0.2% free energy error in the low-temperature glass regime with over 500-fold fewer energy evaluations. In Cu-Zr and Cr-Co-Ni metallic glasses, ATLAS recovers experimentally observed short-range-order trends and steers structures toward prescribed order parameters and optimized bulk
moduli. Moreover, composition-amortized pretraining outperforms composition-specific training from scratch, reduces inverse-design costs by several hundred-fold, and enables sampling with expensive universal machine learning interatomic potentials. Coupled to a large
language model
agent, ATLAS searches an eight-element space for high-
entropy metallic glasses balancing stiffness and ductility, identifying a converged Pareto frontier within 480 oracle evaluations. Together, these results establish ATLAS as a foundation model for sampling, steering and designing amorphous materials.
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All authors Mouyang Cheng, Denis Blessing, Botao Yu, Gerhard Neumann, Mingda Li, Carles Domingo-Enrich, Yuanqi Du
Disordered Systems and Neural Networks
Free energy landscape of Dense Associative Memory
Sumedha and Abhishek Singh
Using large deviations theory, we solve and obtain a general expression for the free energy functional for a broad class of associative
memories, including dense associative
memories. We illustrate the method by reproducing classical results for the Hopfield model. For a finite number of patterns, we derive the temperature-dependent free energy functional for dense associative
memories featuring
polynomial interactions and Log-Sum-Exponential (LSE) activation. We also evaluate the disorder-averaged ground-state energy of these systems in the extensive limit. Our analytical framework reveals how
memory retrieval depends on the initial state in higher-order dense networks, and gives the exact full-
retrieval threshold for the LSE model. This method provides a systematic procedure for analyzing diverse, complex architectures in associative
memory.
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Soft Condensed Matter
One geometric barrier unifies melting, vitrification and jamming of hard spheres in all dimensions
Sujin B Babu
The Lindemann criterion that a solid loses stability once atomic vibrations reach roughly a tenth of the interparticle spacing, has remained an empirical rule for over a century. The numerical value was reproduced by mode-coupling and replica theories but never isolated as the consequence of a simple, verifiable argument. Here we show that for hard spheres in $d$ dimensions the rule follows from three exact
geometric ingredients. The contact
theorem fixing the coordination number from the equation of state, an isotropy identity fixing how non touching neighbors project onto an escape direction, and a first-passage argument which is derived, in which the elementary hop spans one interparticle spacing rather than one particle diameter. The resulting parameter-free master equation locates the kinetic glass transition, random close packing, the Kauzmann point, glass close packing, and
equilibrium crystal melting in $d=3$–$12$, each to within a few per cent of reported independent simulation and replica-theory values, and places all five on a single barrier surface. The theory makes two predictions that are verifiable, the Lindemann constant, $\c_L(3)=0.13$ per neighbor spacing in $3$ dimensions derived from the theory, which must fall systematically with increasing dimensions. The other being in two dimensions, the current theory predicts the arrest in the volume fraction $\eta_g=0.781$, the jamming at $\eta=0.832$, and both steps of the two-stage melting scenario, all of which are already corroborated by independent simulations and experiments.
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Statistical Mechanics
Boundary quenches in (1+1)-dimensional conformal field theory
Michele Fossati, Colin Rylands, Eytan Grosfeld et al. (+2 more)
We investigate a class of local
quantum quenches in which the conformal boundary condition of a (1+1)-dimensional conformal field theory is abruptly changed. We derive a remarkably simple and universal expression for the time
evolution of one-point functions on the half-line. This result provides a direct description of the propagation of the disturbance generated by the quench and, in turn, allows us to determine the dynamics of bipartite
entanglement for subsystems adjacent to the boundary. We show that, once the subsystem becomes fully causally connected to the quench event, the
entanglement entropy undergoes a sharp finite jump whose magnitude is universally given by the logarithm of the ratio of the boundary g-factors associated with the initial and final boundary conditions. We
benchmark these analytical predictions against
Matrix Product State simulations of the critical Ising
spin chain, finding excellent agreement. The numerical analysis further allows us to investigate the time
evolution of the
spin-flip
entanglement asymmetry, revealing how the
symmetry-breaking perturbation emitted from the boundary propagates through the system. Our results uncover universal dynamical signatures of boundary quenches and establish a direct connection between nonequilibrium
entanglement dynamics and boundary critical phenomena.
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All authors Michele Fossati, Colin Rylands, Eytan Grosfeld, Eran Sela, Pasquale Calabrese
Mesoscale and Nanoscale Physics
Magnonic crystalline properties of stripe textures in thin ferromagnetic films
Joo-Von Kim, Victor Leroy and Titiksha Srivastava
Ordered stripe domains in
ferromagnetic thin films form a natural one-dimensional
crystal for propagating
spin waves. Their spatial periodicity can be tuned readily with an applied
magnetic field, making these systems an attractive platform for exploring how
magnon band structures evolve as a function of the
lattice constant $a$, a tuning that is difficult to achieve in physically patterned materials. In this work we employ micromagnetic simulations to calculate the
spin-wave spectra of a model iron-garnet film, focusing on the influence of the external field and of cubic anisotropy. We find that band gaps at the Brillouin-zone center ($k = 0$) and at the zone boundary ($k = \pm \pi/a$) respond differently to the applied field, appearing over a broad range of frequencies and wave vectors. When a perpendicular
magnetic field or cubic anisotropy is present, additional gaps can appear at the middle of the reduced Brillouin zone ($k = \pm \pi/2a$). This behavior is interpreted as a Peierls-type distortion of the domain-wall
lattice, wherein “up” and “down” domains alternately expand and contract under the influence of the effective perpendicular field.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Direct Spatiotemporal Imaging of Charge Carrier Dynamics in Operative Semiconductor Devices
Adriano Cola, Antonio Valletta, Isabella Farella et al. (+2 more)
Understanding charge carrier dynamics within electronic devices is crucial, as it governs both the internal
evolution of signals and the externally measurable current. Yet, direct imaging of these dynamics remains elusive: existing approaches are often indirect or inherently perturbative. Here, we introduce Carrier Dynamics by Pockels Imaging (CDPI), a sensitive, quantitative, and non-invasive method that enables direct access to internal charge dynamics. By probing the local electric field, CDPI visualizes photogenerated electron clouds in real space while simultaneously correlating their
evolution with both conduction and displacement currents, thereby establishing a unified picture of carrier transport. The technique provides direct insight into fundamental mechanisms \textemdash including drift,
diffusion, carrier-carrier interactions, trapping and detrapping \textemdash as well as the spatiotemporal
evolution of carrier cloud morphology. Demonstrated in CdTe radiation detectors with micrometre-scale spatial resolution and nanosecond temporal resolution, CDPI is broadly applicable to systems exhibiting appreciable electro-optic responses. Beyond conventional
semiconductors, the approach extends to organic, perovskite, and two-dimensional optoelectronic materials, offering a new paradigm for directly linking internal carrier dynamics to device-level functionality.
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All authors Adriano Cola, Antonio Valletta, Isabella Farella, Vaclav Dědič, Lorenzo Dominici
Statistical Mechanics · Cross-listed from quant-ph
Dimension Reduction for Quantum Adaptive Agents
Rishi Sundar and Thomas J. Elliott
Adaptive
agents realise complex reactive behaviours by using a
memory of past input stimuli and output actions to guide structured future responses.
Quantum adaptive
agents can operate while storing less information in
memory than optimal classical counterparts; yet, this does not necessarily translate into a reduced dimension of the
memory that must be physically realised. We introduce a route-truncate-repair procedure that can convert entropic
quantum memory advantages into reductions in
memory dimension. Routing a reference input process through an
agent yields a temporal
matrix product state representation whose canonical bond is identified with the joint reference–
agent memory. Truncating the
agent's share of this bond and locally repairing the resulting dynamics produces a smaller, physically-valid
agent that remains capable of responding to arbitrary input sequences. A fidelity-divergence certificate quantifies the resulting trade-off between accuracy and
memory dimension.
Benchmark adaptive processes exhibit substantial dimension reduction whilst preserving the underlying behaviour with high fidelity. The construction extends to feedback and coherent
quantum interactions, with accuracy guarantees under arbitrary adaptive interrogation for a class of
agents. For a resettable clock, four
quantum memory dimensions attain an input–output fidelity divergence rate first matched with eleven states in our search over classical reduced models. These results establish a route from entropic
memory advantages to practical, dimension-reduced adaptive
quantum agents.
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Statistical Mechanics · Cross-listed from quant-ph
Irreversibility, equilibrium and measurement in quantum mechanics
Christopher J. N. Coveney and Peter V. Coveney
Quantum mechanics is widely recognised as being incomplete. It is not consistent with the second law of thermodynamics and does not provide a scientifically credible physical account of the measurement process, the means by which coherence is broken and classically observable states are recorded. This has led to many ad hoc assumptions being used to account for various properties of
quantum systems, among which is the coherence time of
quantum devices that determines their ability to perform computations. Here, we show that all these properties can be accommodated naturally and consistently in the context of mixing
quantum systems which exhibit continuous spectra, as arises in the thermodynamic limit in
quantum statistical mechanics and
quantum gravity. In particular, for isolated systems we show that the time-reversal
symmetry associated with
unitary time
evolution of the
quantum state gives rise to time-
symmetry breaking and a semi-group
evolution which attains thermodynamic
equilibrium at long times. Moreover, the emergence of this non-
unitary time-asymmetry leads to microcanonical
equilibrium states in which all
quantum coherence is lost and is accompanied by the transformation of pure states into mixtures, leading in turn to an increase in
entropy. Inclusion of a macroscopic measurement apparatus shows how the outcome of a measurement corresponds to the von Neumann projection postulate, arising with probabilities in conformance with the Born rule. The mathematical structure of the theory which applies to
quantum systems with continuous spectra is closely analogous to the classical ergodic theory of dynamical systems and the conditions under which they attain
equilibrium states.
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Soft Condensed Matter
Auxetic behaviour in crystals of hard polyhedra
Rinske M. Alkemade, Silvana A. Caipa Cure, Alptuğ Ulugöl et al. (+8 more)
Auxetic materials - systems that, when subjected to a compression in one direction, also compress in one or more perpendicular directions - have intrigued researchers for decades due to their counterintuitive mechanical properties. Their unique behaviour gives auxetic materials potential for a wide range of applications such as shock absorbers, and electrodes in piezoelectric sensors. Most known auxetic materials are realized by connecting rigid, anisotropic units in a hinging manner, which are systems that often are hard to realize experimentally on the microscopic scale. Here, we explore the elastic behaviour of six
crystals composed of discrete space-filling hard polygons or polyhedra. We show that some of these systems show partial auxetic behaviour, emerging from the interplay of
entropy and geometry alone. To demonstrate the feasibility and robustness of this phenomenon, we create two experimental realizations of square-shaped particles, spanning both colloidal particles driven by Brownian motion and granular particles driven by external vibrations, and confirm the emergence of auxeticity in both cases.
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All authors Rinske M. Alkemade, Silvana A. Caipa Cure, Alptuğ Ulugöl, Andrea Plati, Vera Belde, Haadi Naqvi, Felix Verbiest, Giuseppe Foffi, Daniela Kraft, Frank Smallenburg, Laura Filion
Materials Science
Thermal and electrical conductivity of a refractory high-entropy alloy after high-pressure torsion: Electron versus phonon contributions
Jacqueline Hidalgo-Jimenez, Payam Edalati, Md Amirul Islam et al. (+3 more)
The equiatomic refractory high-
entropy alloy TiZrHfNbTa was processed by high-pressure torsion (HPT) to investigate the effect of nanostructuring and defect engineering on thermal and electrical transport properties. Severe plastic deformation (SPD) via the HPT treatment induces substantial accumulation of dislocations, grain refinement to the nanometer level (average: 40 nm), and partial transformation from the BCC phase to the omega phase. While hardness increases to a steady state with processing, the specific heat capacity exhibits a non-monotonic behavior: it decreases at low strains due to the suppression of low-frequency vibrational modes by dislocations, then partially recovers at high strains due to anharmonic vibrations at newly formed high-angle grain boundaries. Thermal conductivity decreases at low strains but shows a slight recovery at high strains, whereas electrical conductivity decreases monotonically to a steady state without recovery. Analysis using the Wiedemann-Franz law reveals that the electronic contribution dominates thermal transport, while the phononic contribution (limited by the scattering of
phonons on defects) is only 11 to 23%, depending on the degree of straining. The contrasting
evolution of thermal and electrical conductivity is ascribed to the transition from dislocation-dominated vibrations at low strains to grain boundary-dominated vibrations at high strains, which affects
phonons and electrons with different efficiencies.
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All authors Jacqueline Hidalgo-Jimenez, Payam Edalati, Md Amirul Islam, Makoto Arita, Bidyut Baran Saha, Kaveh Edalati
Quantum Gases
Programmable Spin Conversion in Gradient Quantum Matter
Mamoru Matsuo, Yuta Sekino and Hiroyuki Tajima
We propose programmable
spin conversion in ultracold gases as gradient
quantum matter, whose
spin-dependent self-energy varies in space.
Quantum kinetic theory shows that a dissipative self-energy
curvature turns a force-driven scalar anisotropy into a
spin source with mixed longitudinal-transverse momentum parity.
Spin-resolved time-of-flight imaging can reveal a transverse
spin texture that changes sign when either the drive or programmed
curvature is reversed. Ultracold gases thereby offer a controllable
spin source for gradient
quantum matter.
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Materials Science
Doping tunable charge density waves in misfit layer compounds
Hugo Le Du, Ludovica Zullo, Justine Cordiez et al. (+14 more)
The ability to tune charge density waves (CDWs) through external control knobs, such as doping, pressure or strain is crucial for exploring the phase diagram of two dimensional (2D) or quasi-2D materials. Yet, controlling CDWs critical temperature and ordering vector remains a challenge for current experimental techniques. In this work, we establish misfit layer compound
heterostructures as a reliable platform to manipulate CDWs in transition metal dichalcogenides. By combining ab initio calculations with low-temperature scanning tunneling microscopy, we show how to achieve doping tunable control over NbSe2 CDW by chemically alloying in the rocksalt subunit. Crucially, we prove that tuning the La Pb ratio in the misfit family (LaxPb1xSe)1.14(NbSe2)2 enables stabilization of different CDW orders, such as 2x2 or 3x3 patterns, and even coexisting phases. This work paves the way for engineering transition metal dichalcogenides with tailored charge density waves within misfit
heterostructures.
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All authors Hugo Le Du, Ludovica Zullo, Justine Cordiez, Robin Salvatore, Daniel Schmieg, Arindam Mukherjee, Giovanni Marini, Dominik Volavka, Francois Debontridder, Marie Herve, Tomas Samuely, Shunsuke Sasaki, Florent Pawula, Etienne Janod, Matteo Calandra, Laurent Cario, Tristan Cren
Statistical Mechanics · Cross-listed from nlin.CD
Quasi-stationary and quasi-ergodic distributions in the Pelikan random map
Samuel Brevitt and Rainer Klages
In this paper we present a concrete example of a substochastic discrete-time Markov chain on a countable state space producing a spectrum of infinitely many quasi-stationary distributions (QSDs) for generic parameter values, with each QSD supporting a distinct escape rate. Our system is motivated by an open variant of the Pelikan dynamical system, a random map introduced in the 1980s. These QSDs, and their stability to perturbative random noise, are tested in numerical simulations. The existence of unique QEDs is also established for some parameter values.
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Strongly Correlated Electrons · Cross-listed from quant-ph
Lower Bounds on Spectral Gaps of Parent Hamiltonians via Tensor Networks
Milán Ádám Rozmán, András Molnár and Norbert Schuch
Proving spectral gaps above the ground space is a central problem in
quantum many-body physics. Yet, finding lower bounds on the gap is notoriously difficult. We revisit the martingale method, originally developed by Fannes, Nachtergaele, and Werner [Fannes '92, Nachtergaele '96] to prove the existence of spectral gaps of parent
Hamiltonians of
Matrix Product States (MPS), and provide improvements to the different steps of the method. Most importantly, we devise a new technique which allows to compute the key quantity in the martingale method – the overlap of local ground spaces – exactly and efficiently. This enables a clear improvement of the method, allowing it to outperform other existing techniques to lower bound gaps, which we demonstrate by benchmarking on several models. Remarkably, our – numerically motivated – approach at the same time also yields a significantly simplified proof of the fact that parent
Hamiltonians of any (well-behaved) MPS are always gapped.
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Soft Condensed Matter · Cross-listed from cs.LG
Deep learning-based prediction of time-resolved adhesive forces in viscoelastic Hertzian contacts
Ali Maghami, Merten Stender, Michele Ciavarella et al. (+1 more)
Fast prediction of the response of adhesive soft viscoelastic contacts represents a current challenge in soft robotics and for gripping and manipulation tasks. Determining the complete time-resolved force trajectory requires full numerical simulations, whose computational cost is strongly parameter-dependent, making them impractical for real-time application or design-optimization loops. In this work, we overcome this limitation by training a scalar-conditioned, stateful, sequence-to-sequence deep learning model to predict the full force
evolution from a prescribed displacement history for both short- and long-range adhesion regimes. The data set spans four orders of magnitude in loading and unloading rates and includes varied dwell times, with the Tabor parameter ranging from $0.2$ to $3.2$. To enable learning across these heterogeneous time scales, we introduce a fixed-measurement-step (FMS) representation that converts variable-length trajectories into fixed-length sequences while preserving their physical-time information. Different architectures were trained, including long short-term
memory (LSTM) networks, temporal convolutional neural (TCN) networks, and time-distributed dense layers with three different Tabor-conditioning mechanisms. The models were compared using global waveform and error metrics. We found that the best-performing model has an LSTM architecture with concatenated conditioning, which achieves a held-out mean-squared error of $5.0\times10^{-4}$, a median pull-off-force error of $\approx2.2\%$, and a median hysteresis error of $\approx1.1\%$. For the held-out protocols, the model predicts a complete force trajectory with a median inference time of $0.16$ s. The model is tested across unseen parameter combinations and against analytical limiting cases, providing a rapid surrogate for repeated numerical evaluations with potential use in control-oriented applications.
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All authors Ali Maghami, Merten Stender, Michele Ciavarella, Antonio Papangelo
Mesoscale and Nanoscale Physics
Electrostatic Control Enables Robust Helical Edge Channel Transport in III-V Quantum Spin Hall Insulators
Manuel Meyer, Tobias Fähndrich, Sebastian Schmid et al. (+12 more)
Quantum spin Hall transport in InAs/GaInSb-based two-dimensional topological
insulators can be limited by parasitic bulk and edge contributions. We demonstrate that these limitations are effectively mitigated through electrostatic control in dual-gated InAs/GaInSb/InAs trilayer
quantum wells grown on AlSb quasi-substrates. In macroscopic
Hall bars exceeding the phase coherence length, a multi-probe analysis reveals an insulating bulk and a constant edge resistance over a wide electric-field range. In microscopic devices with edge lengths below the phase coherence lengths, the edge resistance remains robust and quantized across a broad field range, revealing the intrinsic resilience of helical edge channels to electric-field perturbations. Only beyond a threshold value, parasitic edge contributions emerge. These results establish dual gating as a reliable strategy to suppress parasitic conduction while stabilizing helical edge transport, providing a versatile and reproducible platform for tunable topological transport in III-V
quantum spin Hall systems.
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All authors Manuel Meyer, Tobias Fähndrich, Sebastian Schmid, Justus Walter, Martin Kamp, Adriana Wolf, Sergey Krishtopenko, Guillaume Sigu, Jean-Baptiste Rodriguez, Eric Tournie, Gerald Bastard, Frederic Teppe, Fabian Hartmann, Sven Höfling, Benoit Jouault
Soft Condensed Matter
Activity and Competing Length Scales in an Anomalous Core-Softened Fluid
Davi Felipe Kray Silva, Thiago Puccinelli, Walas Silva-Oliveira et al. (+2 more)
The interplay between activity and competing interaction length scales remains largely unexplored, despite its relevance to many soft and biological systems. Here, we study Active Brownian Particles interacting through a ramp-like core-softened potential that exhibits water-like anomalies in
equilibrium. By varying the activity over a broad range of densities along two representative isotherms, one within the anomalous region and the other above it, we examine how self-propulsion modifies the structure and dynamics of the fluid. To gain microscopic insight into these changes, we construct effective interactions from the steady-state pair correlations using iterative Boltzmann inversion. We find that activity progressively suppresses the anomalies of the passive fluid, although signatures of the underlying structural crossover remain visible in normalized quantities. The effective interactions reveal that self-propulsion lowers the distinction between the local environments and facilitates population transfer between the two characteristic length scales. These results indicate that activity primarily acts by facilitating population transfer between the two local environments, thereby reducing the structural competition responsible for the anomalous response.
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All authors Davi Felipe Kray Silva, Thiago Puccinelli, Walas Silva-Oliveira, Leandro B. Krott, José Rafael Bordin
Mesoscale and Nanoscale Physics
Pure Spin Bulk Photovoltaic Effect in an Altermagnetic Higher-Order Topological Insulator
Sibgat Ulah, Ankan Bhattacharyya and Manisha Thakurathi
We investigate the bulk photovoltaic effect (BPVE) in a $PT$-symmetric two-dimensional
heterostructure consisting of a topological
insulator coupled to a $d$-wave altermagnet. To describe the
symmetry-enforced degenerate bands of this system, we develop a non-Abelian formulation of the
spin BPVE, extending the conventional theory from isolated nondegenerate bands to $PT$-degenerate
manifolds. We show that the orientation of the Néel vector controls both the topological phase and the character of the nonlinear optical response. When the Néel vector lies in the $xy$-plane, the
heterostructure realizes a second-order topological
insulator (SOTI) protected by $C_{4z}T$
symmetry. The system also retains $C_{2z}$
symmetry, which completely suppresses second-order charge photocurrents while allowing finite
spin photocurrents. As a result, the BPVE becomes an intrinsically pure
spin photovoltaic effect, generating a dc
spin current without an accompanying charge current. We find that linearly polarized light drives a
spin shift current, whereas circularly polarized light generates a
spin injection current. Both responses undergo a sign reversal whenever the local Dirac mass changes sign. As the Néel vector is rotated toward the $z$-axis, the SOTI phase transforms into a first-order topological insulating phase, leading to the coexistence of charge and
spin photocurrents. Our results establish $PT$-symmetric altermagnetic topological-
insulator heterostructures as a versatile platform for generating and controlling pure
spin photocurrents and reveal nonlinear
spin transport as a sensitive probe of
topology and
magnetic symmetry.
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Materials Science
Deciphering Mechanoluminescence: How the Nature of Mechanical Stress and Structural Dimensionality Shape Mechanisms and Responses
Alexis Duval, Xavier Rocquefelte, Yann Gueguen et al. (+2 more)
Mechanoluminescent materials exhibit a broad spectrum of controllable light-emission responses to mechanical stimuli of varying types and magnitudes. Yet progress toward high-performance systems remains constrained by an incomplete and often contradictory mechanistic understanding. Here, density functional theory (DFT) calculations optimized for the quantitative treatment of point defects are used to systematically investigate the interplay between stress type (hydrostatic vs. shear) and active-phase dimensionality (1D vs. 3D), using $SrAl_2O_4:Eu^{2+}, Dy^{3+}$ and $Ba_4Si_6O_{16}:Eu^{2+}, Ho^{3+}$ as representative model systems. Two distinct emission-driving mechanisms are identified: a piezoelectric contribution, and a second, apparently universal, mechanism arising from stress-induced structural reorganization at point defects sites. These results establish a design framework for mechanoluminescent materials in which
crystal dimensionality, stress type and stress-sensitive point defects are deliberately matched to tune emission behavior and overall performance.
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All authors Alexis Duval, Xavier Rocquefelte, Yann Gueguen, Patrick Houizot, Tanguy Rouxel
Superconductivity
Annealing-enhanced spin-orbit effects in non-centrosymmetric superconducting NbRe films
Zahra Makhdoumi Kakhaki, Yuriy Yerin, Francesco Avitabile et al. (+5 more)
$\text{Nb}_{0.18}\text{Re}_{0.82}$ (NbRe) is a non-centrosymmetric
superconductor with a transition temperature $T_\mathrm{c}$ reaching $9\text{ K}$ in bulk form. While bulk and single-crystalline NbRe exhibit signatures of multigap superconductivity, thin films generally display a single-gap superconducting state due to structural disorder and reduced crystallite dimensions. Here, we investigate the impact of thermal annealing on the superconducting and normal-state magnetotransport properties of NbRe films. The temperature dependence of the upper critical field, $B_{\mathrm{c2}}(T)$, is analyzed within the microscopic Werthamer–Helfand–Hohenberg (WHH) framework, while the normal-state magnetoconductivity is described using the three-dimensional Kawabata weak-localization/weak-anti-localization model. Annealing drives a pronounced change in the electronic response, manifested by a strong weak anti-localization behavior in the normal state and an upper critical field that surpasses both the conventional orbital-limiting field and the Pauli paramagnetic limit. The microscopic analysis reveals a strong intrinsic increase in the relative
spin–orbit scattering strength, with the annealed film showing a significantly enhanced
spin–orbit-to-dephasing field ratio. These findings provide direct, independent evidence that thermal modification of the NbRe microstructure successfully amplifies
spin–orbit-mediated
quantum transport, which acts as the key mechanism protecting the non-centrosymmetric superconducting state against paramagnetic pair-breaking well beyond conventional theoretical boundaries.
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All authors Zahra Makhdoumi Kakhaki, Yuriy Yerin, Francesco Avitabile, Abhishek Kumar, Francesco Colangelo, Carla Cirillo, Oleksandr V. Dobrovolskiy, Carmine Attanasio
Materials Science
Mag4: An Automated First-Principles Workflow to Extract Magnetic Interactions, from Pair Couplings to Four-Spin Ring Exchange
Xavier Rocquefelte and Peter Blaha
Chemists design
magnetic materials through structure-property relationships built on pairwise exchange couplings $J$, now extracted routinely from first principles by energy-mapping. But wherever four
magnetic centers close a loop—as in cuprate CuO$_2$ planes or infinite-layer square nets—a four-
spin ring exchange $J_{\rm ring}$ can arise, reshaping ground states and corrupting the $J$ values used for design. Missing has been a direct, local way to obtain it, as the four-state method gives for $J$. We supply it by generalizing that method to a sixteen-state ($2^4$) scheme, automated in the open Mag4 package—the first automatic implementation of the four-state family. From one cif file, Mag4 proposes the supercell that isolates the couplings, generates DFT inputs in the user's chosen functional, extracts $J$ and $J_{\rm ring}$ with band-gap and local-moment diagnostics, and predicts the
magnetic order, propagation vector, and critical temperature.
Symmetry reduces the sixteen configurations to six or eight inequivalent energies, so the cost is modest. The derivation shows the conventional four-state $J$ is itself ring-renormalized by $\mp 2 J_{\rm ring} S^2$, the sign set by the reference state. T-La$_2$CuO$_4$ confirms this: three routes agree on $J_{\rm ring}$ to $0.2\%$, giving $J_{\rm ring}/J_1=0.25$, and a four-state $J_1$ quoted without its reference is wrong by $12\%$. The sixteen-state value is itself reference-dependent—Néel and
ferromagnetic baths bracket it—a fourth-order fingerprint of interactions beyond the pair-plus-ring model, resolved by further baths into a bare $J_{\rm ring}$ and a converging tower of six- and eight-
spin loop couplings. SrFeO$_2$ ($S=2$), same plaquette yet $J_{\rm ring}/J=0.006$, is the negative control: a plaquette is necessary for ring exchange but far from sufficient—a structure-property criterion for screening new multi-
spin magnets.
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Disordered Systems and Neural Networks · Cross-listed from physics.soc-ph
Single-Snapshot Inference of Network Couplings from Universal Dynamics at Relative Equilibrium
Moritz Lampert, Dominic Grün and Ingo Scholtes
Many real-world systems can be modelled as complex networks whose collective behaviour is governed by hidden interactions between nodes. Existing methods for inferring these interactions typically require controlled perturbations, time-resolved observations or multiple independent snapshots, all of which are often unavailable in practice. Here we show that class-based coupling strengths can be inferred from a single snapshot of node states when the system is observed close to a relative
equilibrium. In this regime, all nodes share a common velocity, which can be absorbed into an effective class bias, transforming the inverse problem into a homogeneous linear system. The coefficients of this linear system are determined entirely by the observed local neighbourhoods and their coupling mechanism, enabling the application to arbitrary known coupling functions. We validate the approach on three different linear and nonlinear dynamical systems, recovering relative class-based couplings and, in special cases, absolute couplings. These results show that spatial heterogeneity can substitute for temporal sampling, enabling single-snapshot inference of hidden coupling strengths in networked dynamical systems.
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Statistical Mechanics
Discrete distributions and statistical mechanics of small systems
Lev B. Klebanov and Michal Šumbera
We study connections between discrete probability distributions and the statistical mechanics of small systems. Using probability generating functions, we develop the theory of power series, infinitely divisible, and scalable distributions of non-negative integer-valued random variables, and introduce the class of Markovian distributions that arise naturally in stationary solutions of birth-death processes and in scalable infinitely divisible distributions. These results are applied to the grand canonical ensemble description in statistical mechanics: the infinite divisibility leads to a quasiparticle picture of an interacting gas, and the virial expansion is linked to the combinants of the distribution. A kinetic model of the
liquid-vapor phase transition is presented, in which the particle-number distribution at the critical point converges to the Discrete Stable distribution - the fixed point of a renormalization semi-group transformation. We also show that the scalability of the particle-number distribution is preserved in Tsallis non-extensive thermodynamics, even though infinite divisibility fails. Moreover, deformed discrete distributions, including the negative binomial as a q-deformation of the Poisson, arise naturally in this setting.
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Materials Science
Stereochemical Vacuum Gap Explains Out-of-Plane Thermal Insulation in MXenes
O. Mateos-Lopez, J. G. Vilhena, Isaac Armstrong et al. (+3 more)
Two-dimensional MXenes are promising materials for thermal management and spectral camouflage, combining low out-of-plane thermal conductivity with low infrared emissivity and mechanical robustness. Yet the near-order-of-magnitude spread in experimental out-of-plane thermal conductivity measurements (0.14-0.8 W/mK) and the systematic overestimation by simulations point to a fundamental gap in our understanding of heat transport in these materials. Here, we argue these differences originate in the overlooked role of heterogeneous surface terminations. Using Non-
Equilibrium Molecular Dynamics simulations of Ti3C2Tx, we show that this discrepancy arises from a stereochemically induced
vacuum gap between adjacent layers, formed when surface terminations of different sizes coexist. Even minor deviations from homogeneous terminations drastically suppress out-of-plane thermal conductivity, bringing simulated values into quantitative agreement with experiment. We also show that thermal conductivity scales strongly with the atomic density, and that introducing bulky surface terminations, including residual water, reduces the thermal conductivity to 0.3 W/mK, an order of magnitude below homogeneous termination values and below the minimum thermal conductivity limit predicted for disordered solids. Thus, we propose a chemistry-driven route to engineer thermal transport in MXenes.
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All authors O. Mateos-Lopez, J. G. Vilhena, Isaac Armstrong, Hendrik Heinz, Miguel Muñoz Rojo, Juan Carlos Cuevas
Statistical Mechanics · Cross-listed from math-ph
Integrable multi-species SSEP with reactive particle species
Mathieu Dabrowski, Loïc Poulain d'Andecy and Eric Ragoucy
We investigate integrable exclusion Markov processes constructed from set-theoretical solutions of the Yang-Baxter Equation (YBE) that generalise the multi-species Symmetric Simple Exclusion Process (SSEP). We first introduce the process called the $ (p,1) $-SSEP that is analogous to the multi-species SSEP but with an extra particle species qualified as reactive. Reactive species are able to evaporate and condense by pairs or to transform by pairs depending on the interpretation. We provide a full combinatorial study of the sectors in the periodic case. We prove the integrability of the process in the periodic case and in the open case for two types of boundaries that we introduce using Baxterisations of solutions of the reflection equation. Next we move on to the process called $ (p,q) $-SSEP, i.e. the multi-species SSEP with an arbitrary number of reactive particle species. We prove its integrability in the periodic case and, for the open case, we introduce integrable boundaries generalising the ones considered for the $ (p,1) $-SSEP. Finally, we define physical quantities relevant to the models and we compute them in the non-
equilibrium stationary state of the open $ (p,q) $-SSEP for one type of integrable boundaries.
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Soft Condensed Matter
Isosbestic points in time resolved SAXS: from spectroscopic analogy to model free structural markers during colloidal gelation
Alain Gibaud, Wilbert J. Smit, Safa Jamali et al. (+1 more)
Gelation is the transition from a fluid state into a system-spanning, out of equilibrim soft-solid network through a hierarchical process that couples local particle interactions to mesoscopic clustering and global connectivity. In time-resolved small-angle X-ray scattering (SAXS), isosbestic points – scattering wavevectors where scattering intensity remains invariant – emerge during this transformation, yet their physical meaning has remained unclear. Here, we show that two isosbestic points, $q_1$ and $q_2$, observed during salt-induced gelation of Ludox colloids, reflect fundamental structural constraints rather than a two-species interconversion. The high-$q$ point $q_2$ is a universal
geometric marker, determined by particle contact distances, while the low-$q$ point $q_1$ arises from Porod invariant conservation and separates rapidly arrested local clusters from the growing mesoscopic network. By decomposing the Porod invariant across the reciprocal-space regions defined by these points, we define a dimensionless parameter, $\Phi(t/t_g)$, whose sigmoidal
evolution provides a simple, model-free, scale-resolved fingerprint of gelation. Together with the combined
evolution of $S(q_{\min},t)$ and $S(q \rightarrow 0,t)$, these results establish a quantitative model free framework linking local structuring, global connectivity, and scattering signatures, clarifying the role of isosbestic points in soft-matter transformations.
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All authors Alain Gibaud, Wilbert J. Smit, Safa Jamali, Thomas Gibaud
Quantum Gases
Bose-Einstein Condensates in Time Dependent Traps
Yvan Castin and Ralph Dum
We present analytical results for the macroscopic wave function of a Bose-Einstein condensate in a time dependent harmonic potential. The
evolution of the spatial density is a dilatation, characterized by three scaling factors which allow a classical interpretation of the dynamics. This approach is an efficient tool for the analysis of recent experimental results on the expansion and collective excitation of a condensate.
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Materials Science
Phase equilibria in MnSb2Te4-GeSb2Te4 system and magnetic properties of Mn1-xGexSb2Te4 solid solutions
Fuad Safarov, Dunya Babanly, Jerome Robert et al. (+4 more)
As a sister compound of the
antiferromagnetic topological
insulator MnBi2Te4, MnSb2Te4 is also a candidate for exotic
magnetic topological phases. On the other hand, the structurally analogous but nonmagnetic phase-change material GeSb2Te4 is also known to exhibit nontrivial band
topology. Motivated by their shared
crystal structure, the similar ionic radii of Mn2+ and Ge2+, and the opportunity to explore the interplay between magnetism and
topology, here we investigate the effects of Ge substitution at Mn sites in MnSb2Te4. The Mn1-xGexSb2Te4 solid solutions were synthesized via high-temperature solid-state reaction and characterized for composition, structure, phase behavior, and magnetism using SEM-EDS, PXRD, DTA, and SQUID. Ge substitution was successful across the full composition range, producing homogeneous, single-phase samples that melt via peritectic reactions, as confirmed by the MnSb2Te4GeS-b2Te4 phase diagram. Ge substitution strengthens the sample's paramagnetism, but with ferrimagnetic ordering up to x = 0.75, with both effective moment and saturation magnetization decreasing with increasing Ge content. Two distinct
magnetic transitions - high-temperature paramagnetic to ferrimagnetic and low-temperature ferrimagnetic to
ferromagnetic - were identified, with a dome-like shape dependence of the low-temperature
magnetic transition on Ge substitution. A negative magnetization was observed in the pristine MnSb2Te4 and x = 0.12 substituted samples, while two distinct
spin-flop transitions appeared in the samples with x = 0.32 and x = 0.55 Ge substitutions as a result of competing
magnetic orderings. These findings facilitate future selective single-
crystal growth of homogeneous,
magnetic phases, paving the way for magneto-transport and topological surface states investigations.
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All authors Fuad Safarov, Dunya Babanly, Jerome Robert, Elnur Orujlu, Elvin Ahmadov, Martin Bowen, Bohdan Kundys
Mesoscale and Nanoscale Physics
Bridging distributed quantum materials via multi-hotspot vacuum: remote Cooper pairing and Andreev teleportation
Zuzhang Lin, Zhijian Song, Chengxin Xiao et al. (+1 more)
We introduce an architecture where mesoscopic
quantum matter distributed over spatially separated nodes can be correlated in
equilibrium, creating an unprecedented form of many-body
quantum system. Central to the design is a multi-gap split-ring resonator (SRR) where the cavity
photon has multiple hot spots – each with deep-subwavelength volume at a split gap and separated by millimeter-scale distances. The cavity's
vacuum fluctuations can then mediate a many-body interaction that bridges the distributed
quantum materials embedded in the multiple gaps, coupling them into a single correlated mesoscopic system in
equilibrium. As an example, we consider a THz SRR with two split gaps, each proximitized to a metallic moiré superlattice, where virtual exchange of a
photon in the cavity
vacuum mediates a current-current interaction across the gaps. The inherent attractive interaction channels lead to remote Cooper pairing reminiscent of mesoscopic superconductivity, demonstrated with density
matrix renormalization group and exact diagonalization calculations. With the two constituents of a Cooper pair now paired across a millimeter-scale separation, a hole incident at one split gap can be converted into an outgoing electron at the remote gap, a process we term Andreev teleportation. The
entanglement entropy between the two mesoscopic superlattices is shown to scale linearly with the area (total number of sites) of the mesoscopic
lattice. Our results suggest an intriguing paradigm for
equilibrium quantum networks of mesoscopic matter that enable emergent nonlocal functionalities and distributed
quantum resources.
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All authors Zuzhang Lin, Zhijian Song, Chengxin Xiao, Wang Yao
Statistical Mechanics
Energy Conversion, Fluctuation Suppression, and Information Transfer in the Thermodynamic Performance of Kinesin
Riku Kato, Takayuki Ariga and Tomohiro Tanogami
Kinesin is a molecular motor that transports intracellular cargoes along microtubules. Recent studies have quantified kinesin performance using various efficiencies within the framework of
stochastic thermodynamics; however, quantitative comparisons remain difficult because different models and assumptions have been employed. As a result, it remains unclear which aspect of kinesin performance, if any, is thermodynamically optimized. Here, we systematically compare multiple thermodynamic efficiencies within a single kinesin-cargo model. To this end, we construct a thermodynamically consistent two-state kinesin-cargo model that retains both the discrete stepping of kinesin and its coupling to the cargo. Assuming a separation of time scales between the motor and the cargo, we derive analytical expressions for the thermodynamic efficiency, the information-thermodynamic efficiency, the thermodynamic uncertainty relation (TUR) efficiency, and the bipartite TUR efficiency, and compare them with numerical simulation results. We find that these efficiencies generally remain low, suggesting that kinesin is not optimized for maximizing the thermodynamic efficiencies considered here. Our results suggest that thermodynamic efficiencies alone may not fully characterize kinesin performance and motivate further investigation of complementary kinetic perspectives for assessing molecular motor function.
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