Statistical Mechanics · Cross-listed from quant-ph
Thermal screening and critical scaling of quantum energy teleportation in a harmonic chain
Taisanul Haque
We develop a finite-temperature Gaussian-state formulation of
quantum energy teleportation in the one-dimensional harmonic chain. For Gibbs states, the optimized measurement-feedback protocol reduces to thermal two-point functions. In the single-site protocol, the extracted energy is governed by a single correlator, which makes the thermodynamic and near-critical limits analytically tractable. At fixed finite temperature, the extracted energy is exponentially screened with distance and is controlled by a thermal correlation length for both critical and non-critical $\alpha$. In the zero-temperature critical limit taken after the thermodynamic limit, we derive the exact asymptotic law $E_{\mathrm{ext}}\sim d^{-4}$. Numerical results confirm both regimes and resolve the crossover responsible for the apparent drift of the effective decay exponent at intermediate distances. We also analyze squeezed Gaussian measurements and show that they modify the extraction prefactor: $p-$squeezing enhances the extracted energy, whereas $q-$squeezing suppresses it, without changing the large-distance scaling.
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Mesoscale and Nanoscale Physics
Francesco Buonemani, Massimo Balmelli and Olesia Dmytruk
We theoretically study a hybrid
superconductor-
semiconductor platform hosting Majorana bound states coupled to a single mode photonic cavity. Starting with a one-dimensional wire coupled to a bulk $s$-wave
superconductor embedded in a photonic cavity, we derive an effective light-matter
Hamiltonian for such a platform. Assuming that the photonic vector potential is aligned along the tunneling between a wire and a
superconductor, we find that the cavity coupling enters only in the effective superconducting pairing term. By solving the coupled electron-
photon Hamiltonian using different approaches, such as exact diagonalization in case of zero or large number of
photons, high-frequency expansion, and mean-field decoupling, we find that the phase boundary between the topological trivial phases is shifted to smaller values of the Zeeman energy compared to the uncoupled case. Cavity
embedding has the strongest effect on the phase diagram in the semiclassical regime, corresponding to a large number of
photons. In all cases, we find that at large values of the light-matter coupling strength the effective superconducting pairing is suppressed, driving the system into the gapless phase. We demonstrate that even small light-matter coupling strength allows for entering the topological phase at values of the Zeeman energy compared to the uncoupled platform.
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Materials Science
Element priors and target support shape chemical transfer in materials graph networks
Ran Zhao and Kangming Li
Materials graph neural networks must often transfer to chemical regions weakly represented in training data. Such transfer can rely on predefined relations among elements or supervised evidence from target-containing structures, but these pathways are usually entangled. Here, held-out-element splits and incremental target support separate their roles. Without target-containing training structures, formation-energy errors depend strongly on the element representation, particularly for H, O and F. Matched perturbations show that representation-induced sharing matters beyond input dimension or numerical form, while a label-free similarity-graph prior reduces selected zero-shot errors. Adding a few target-containing structures sharply lowers errors and contracts differences among one-hot, k-hot and continuous inputs across ALIGNN and CGCNN. Calibration explains only part of this recovery, and freezing the initial element projection preserves most gains in five of six ALIGNN splits. Target support therefore shifts chemical transfer from reliance on static element relations toward learning from target-containing environments.
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Statistical Mechanics · Cross-listed from nlin.AO
Synchronization Pathways and Resilience in Power Grids
Cook Hyun Kim, Jihye Kim, Sangjoon Park et al. (+1 more)
Ensuring a sustainable energy supply requires maintaining power-grid stability. Rotor dynamics are governed by the swing equation, which takes the form of a second-order Kuramoto model with a correlation between power and total coupling strength. Yet the microscopic mechanisms that nucleate and propagate synchronized clusters remain poorly understood. Using a minimal model motivated by empirical grid data and the \Adhoc potential method, we reveal two distinct seed cluster types and propagation pathways: a population-driven seed cluster at the center of the power distribution propagating to its tails by rotor
accretion, and, for a symmetric distribution, coupling-driven seed clusters at its tails propagating inward to the center by cluster merger. These differences generate distinct order-parameter patterns, while inertia controls whether the seed clusters persist with distinct angular velocities. The same propagation pathways also govern recovery following external disturbances. We further confirm that the same selection–persistence rule holds in data-derived annealed representations of European power grids. Therefore, our results can inform strategies for sustaining stable power-grid operation. More generally, our pathway-based framework reframes synchronization by emphasizing the dynamics of cluster formation and recovery rather than relying solely on static criteria.
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All authors Cook Hyun Kim, Jihye Kim, Sangjoon Park, B. Kahng
Materials Science
Fourier Neural Operators for Composition-Driven Crystal Structure Discovery
Zhijie Yu, Jingyu Li, Yang Huang et al. (+1 more)
Crystalline materials discovery is essential for energy, electronics, and catalysis, but the vast chemical and structural space makes exhaustive screening infeasible. Existing voxel-based methods are limited by the local receptive fields of three-dimensional convolutional neural networks and the posterior collapse of high-dimensional variational autoencoders. Here, we develop a
Fourier Neural Operator (FNO)-based
crystal-field solver that maps a prescribed chemical formula and
lattice parameters to periodic number-density and electron-density fields. By operating on global
Fourier modes, the solver captures long-range correlations in periodic
crystal fields beyond conventional local convolutions. Building on this solver, we construct a coupled generation-solving framework in which a conditional variational autoencoder generates diverse candidate
lattice parameters in a low-dimensional basis-coefficient space, followed by density-field prediction and atomic reconstruction through peak detection, position optimization, and weight optimization. The reconstructed structures are further screened using voxel-level filtering, machine-learning interatomic-potential relaxation, and first-principle calculations. The framework generates novel structures across 104 chemical formulas with competitive reconstruction accuracy, demonstrating high generative diversity and structural validity. By extending
Fourier neural operators to periodic
crystal fields and coupling them with composition-conditioned
lattice generation, our approach provides a scalable route to
crystal structure discovery from prescribed chemical compositions.
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All authors Zhijie Yu, Jingyu Li, Yang Huang, Jingrun Chen
Materials Science
Large Exchange Magnetostriction in a Kagome Antiferromagnet at Room Temperature
Jie Du, Liang Yao, Hang Li et al. (+5 more)
The pursuit of high-performance magnetostrictive materials is crucial for advancing technologies in sensing, actuation, and microelectromechanical systems. Although pronounced magnetostrictive effects have been observed in a few ferromagnets, a systematic exploration of magnetostriction across a broader range of antiferromagnets remains limited. Here, we report the observation of large magnetostriction in the kagome antiferromagnet YMn6Sn6. Under a
magnetic field, the system undergoes a field-induced
evolution from a helical
magnetic ground state toward a collinear field-polarized state, accompanied by a large anisotropic
lattice strain and a substantial volume magnetostriction exceeding 400 ppm at room temperature. Remarkably, the magnetostrictive response remains nearly fully reversible up to 9 T with nearly hysteresis-free behavior, effectively minimizing the energy dissipation commonly associated with domain-wall pinning. Combined experimental measurements and theoretical calculations reveal that the large, nearly hysteresis-free magnetostriction originates from the competition between intralayer ferromagnetic and interlayer exchange interactions. This exchange-driven magnetoelastic coupling further gives rise to a strongly direction-dependent
lattice distortion pathway. This work establishes kagome helimagnets as a tunable platform for low-dissipation magnetoelastic functionalities and responsive magnetomechanical applications.
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All authors Jie Du, Liang Yao, Hang Li, Xiaodong Zhou, Yuan Yao, Xuekui Xi, Yong-Chang Lau, Wenhong Wang
Materials Science
Independent Tuning of Surface Acoustic-Waves and Spin-Waves via Buffer-Layer Engineering in Co2FeGe Heusler Thin Films
A. V. Achuthan, A. Vovk, S. Bunyaev et al. (+7 more)
Understanding and controlling acoustic and
spin-wave excitations in
magnetic thin films is critical for the development of magnonic and
spin-acoustic devices. We report on the use of Cr and W buffer layers to independently modify the acoustic and
magnetic excitations in Co2FeGe full-Heusler thin films grown on MgO(001). Using Brillouin light scattering (BLS) spectroscopy and ferromagnetic resonance (FMR), we probed Rayleigh and Sezawa surface acoustic waves (SAWs) alongside Damon-Eshbach and perpendicular standing
spin-wave (PSSW) modes. Our results show that acoustic dispersion depends strongly on the buffer material; W-buffered films exhibit a pronounced 16% reduction in Rayleigh SAW frequency compared to buffer-free films, primarily due to mass loading and acoustic impedance shifts. While the buffer layers significantly shift acoustic frequencies, they simultaneously modify the dynamic
magnetic response (increasing
spin-wave group velocity by ~34%) through different physical mechanisms. Finite-element simulations show excellent agreement with the experimental acoustic data. These findings demonstrate that buffer-layer engineering is an effective strategy for the independent tailoring of elastic and
magnetic excitations, providing a versatile platform for hybrid
spin-acoustic technologies.
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All authors A. V. Achuthan, A. Vovk, S. Bunyaev, B. Postolnyi, P. Štrichovanec, P. A. Algarabel, K. Załęski, J. P. Araujo, G. N. Kakazei, A. Trzaskowska
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Spatio-temporal coherent molding and retrieval of pulsed signals in optical waveguides
Nika Durishvili, Ramaz Khomeriki, Vakhtang Jandieri et al. (+3 more)
Optical waveguides are key elements for high fidelity, long distance optical communications. Coupled waveguide arrays allow for higher information density, steerting the propagation direction, and for encoding information. However, due to the mixing of relative phases for short pulses containing multiple waveguide-mode frequencies, a process for retrieving an encoded input state once these signals undergo coherent propagation remains elusive. A concept is presented to extract with high fidelity the phase-encrypted input signal from spatio-temporal propagated states. As a realization, an array of coupled waveguides is suggested with the
retrieval mechanism being realized by local phase shifts that comply with the identified
retrieval concept. Three dimensional full-wave electromagnetic simulations for broadband optical signals in coupled dielectric waveguides confirm the validity of the scheme and the high fidelity of information
retrieval pointing to potential applications, for instance in ultrafast coherent coding and decoding of information imprinted on pulse sequences.
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All authors Nika Durishvili, Ramaz Khomeriki, Vakhtang Jandieri, Douglas H. Werner, Daniel Erni, Jamal Berakdar
Soft Condensed Matter
Optimizing diffusion-limited transport, with applications to electrochemical systems
Manu Mannattil and L. Mahadevan
Transport in certain systems fails when
diffusion cannot replenish or remove material from a boundary rapidly enough, causing the boundary concentration to reach a critical minimum or maximum. Motivated by experiments in electrochemical systems that demonstrate this
diffusion-limited failure of charge transport, we determine dynamic current protocols that maximize charge transfer subject to a prescribed concentration constraint. The optimal protocol has a "bang-ride" structure: the maximum feasible current is used until the boundary concentration reaches its critical value, after which the current is progressively reduced to maintain that value. For semi-infinite domains, we derive the optimal currents analytically and obtain system-independent upper bounds on their improvement over constant-current operation. We also extend the framework to finite and multilayer domains and show that the same formulation applies to both charging and discharging.
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Materials Science
Metastable defects in III-Nitrides
A.E.Belyaev
Metastable states in III-nitrides (AlN, GaN, InN and their
alloys) are an important topic across materials science, device physics, and epitaxial growth because these compounds exhibit multiple competing
crystal structures, defect configurations, and phase behaviors that strongly affect optical, electrical, and mechanical properties. The paper is a concise, structured review-style summary covering the main concepts, mechanisms, experimental signatures, theoretical approaches, and device implications. Actions that should be proposed to avoid effect of metastable defects in III-Nitride based devices are discussed. Avoiding metastable defect effects in III nitride devices requires preventing their formation (through growth and doping control), stabilizing their electronic configuration (by annealing or optical activation), and designing device architectures that minimize field- or temperature induced transitions. These combined actions ensure consistent carrier density, higher mobility, and superior optical and electrical reliability in GaN , AlGaN , and InGaN based devices.
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Materials Science
Shangfei Wu, Laur Peedu, Zhihao Wang et al. (+12 more)
Point defects have been successfully utilized in various
quantum technologies, serving as
quantum qubits for
quantum computation, single-
photon emitters for
quantum communication, and nanoscale sensors for
quantum metrology. However, their further development faces key challenges, particularly in discovering and exploring suitable defect-host systems that meet the necessary criteria for
quantum applications. Here, using polarization-resolved Raman spectroscopy and terahertz absorption spectroscopy, we discover three distinct chromium-vacancy-induced excitations in the uniaxial antiferromagnetic
insulator, Cr$_2$O$_3$. These vacancy-induced excitations have an energy scale of a few tens of millielectronvolts and are twofold degenerate, and the lowest one at 64 $cm^{-1}$ is sharp and sensitive to the external
magnetic field along the easy-axis direction, particularly close to the
spin-flop regime around 6T, where the mode softens from 64 to 27$cm^{-1}$. Based on the defect supercell first-principles calculations, we interpret the mode at 64 $cm^{-1}$ as a local
magnetic excitation of the local moment within the chromium vacancy state. Our results establish that the
magnetic defect states in Cr$_2$O$_3$ have potential for
quantum applications.
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All authors Shangfei Wu, Laur Peedu, Zhihao Wang, Xuecong Wang, Xianghan Xu, Kai Du, Sang-Wook Cheong, Aleksei Boldin, Joosep Link, Ivo Heinmaa, Raivo Stern, Sai Mu, Urmas Nagel, Toomas Rõõm, Girsh Blumberg
Materials Science
Agentic programs: an emerging form of scientific software in computational materials science
Yunsung Lim, Haekwan Jeon, Jaesun Kim et al. (+2 more)
Computational materials science has traditionally delegated algorithmic tasks to computers while leaving scientific judgments to humans. We argue that recent LLM-based
agent harnesses enable an emerging form of scientific software, agentic programs, that combine deterministic
algorithms with bounded LLM-based judgment, task-specific verification, episodic maturation, and complete delegation in production. We illustrate this concept with DeMARS, an agentic program for constructing atomistic models from experimentally measured disordered
crystal structures.
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All authors Yunsung Lim, Haekwan Jeon, Jaesun Kim, Jisu Kim, Seungwu Han
Mesoscale and Nanoscale Physics
Anti-higher-order Weyl semimetal
Cheng-Ming Miao, Yu-Hao Wan and Qing-Feng Sun
Higher-order
topology extends the bulk-boundary correspondence by enabling corner or hinge localized states. Here we identify an anti-higher-order Weyl semimetal, a three dimensional topological phase in which the conventional boundary hierarchy is reversed. Unlike conventional higher-order Weyl semimetals where bulk
topology enforces hinge Fermi arcs, this phase hosts anti-hinge states, meaning the bulk
topology forces states to vanish at specific hinge orientations. Using a minimal two-band model, we show how Weyl points separate the Brillouin zone into
quantum anomalous Hall and anti-higher-order topological insulating regions, with the latter characterized by a band-inversion surface enclosing two distinct high-
symmetry points carrying opposite topological charges. Analytical solutions for Weyl points, Berry
curvature monopoles, and slice Chern numbers are derived, with numerical simulations confirming the resulting anti-hinge behavior. Our work establishes anti-higher-order
topology as a dual counterpart to conventional higher-order phenomena, further extending the exploration of topological phases.
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Mesoscale and Nanoscale Physics
Anti-higher-order topological insulators
Cheng-Ming Miao, Yu-Hao Wan, Ying-Tao Zhang et al. (+1 more)
Duality is a fundamental concept in physics that connects complementary opposites like particles and holes. Similarly, while topological states in topological
insulators localize at boundaries, the existence and nature of their dual counterparts remain unexplored. Here, we introduce anti-topological states as the dual of topological states, exemplified by anti-higher-order topological
insulators. Unlike higher-order topological
insulators, where states localize at corners, anti-higher-order topological
insulators host states along edges but absent at corners, realizing an inverted distribution of states. We demonstrate this phenomenon in a bilayer Chern
insulator with opposite Chern numbers, where the band inversion surfaces enclose distinct high-
symmetry points. The topological invariant distinguishing these phases is given by the topological charges enclosed by band inversion surfaces. This work establishes anti-
topology as a new paradigm, opening a chapter in topological research.
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All authors Cheng-Ming Miao, Yu-Hao Wan, Ying-Tao Zhang, Qing-Feng Sun
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Superconducting Flux Memory for Cryogenic Applications
Gregory R. Boyd, Jeremy Clark, Mark Covington et al. (+15 more)
We report the development of flux
memory for use with superconducting
circuits. This technology stores persistent currents in superconducting loops on-chip to be used to provide flux biasing for superconducting
circuits, like
qubits. We developed three types of flux
memory and draw comparisons among them for
circuit design. We demonstrate the utility of flux
memory by using an in-situ flux detector and characterize each approach and further demonstrate that once flux is set in a
memory cell, benchtop DC control sources can be powered off, leaving the on-chip flux bias in place. We propose that flux
memory can be arranged in a two-dimensional configuration to multiplex control signals and reduce how line counts scale (N^2 devices -> 2N control lines), and our experimental results pave the path to the proposed scalability. We demonstrate the use of flux
memory to flux bias a transmon
qubit and show the tunability of the
qubit state to a target frequency which remained stable on-chip for 20 hours.
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All authors Gregory R. Boyd, Jeremy Clark, Mark Covington, David G. Ferguson, Aref Fouladi, Keith D. Hillaire, Moe Khalil, John McFarland, Aaron Pesetski, Anthony J. Przybysz, John X. Przybysz, Sambarta Rakshit, Aruna N. Ramanayaka, Brian Sears, Robert Smith, Colin Stack, Robert M. Young, Tony X. Zhou
Mesoscale and Nanoscale Physics
Classifying coherent peaks in nanoelectronic devices by the presence or absence of spin exchange
Jongbae Hong
Coherent peaks appearing in the differential conductance of
quantum-dot single-electron transistors (QDSETs) and
quantum point contact (QPC) devices are classified into two categories according to the scaling function onto which the temperature-scaled differential-conductance maxima collapse and the underlying
spin dynamics. The zero-bias peaks (ZBPs) observed in QPCs and in the triplet state of the even-particle sector of QDSETs belong to the same category, whereas the ZBP in the odd-particle sector of a QDSET belongs to a different category together with all finite-bias coherent peaks observed in QPCs and in the even-particle sector of QDSETs. The
spin dynamics of the former category involve
spin exchange, a hallmark of Kondo dynamics, whereas those of the latter category involve only cotunneling of an up–down
spin pair. Furthermore, for the former type of ZBP, the scaling temperature coincides with one-half of the full width at half maximum (FWHM), which corresponds to the Kondo temperature. In contrast, for the latter type, the scaling temperature does not coincide with the (1/2)FWHM-derived energy scale. To support these findings, the gate-voltage-dependent differential-conductance line shapes measured in the odd-particle sector of a QDSET are theoretically reproduced. The results demonstrate that the observed ZBP is a merging of two coherent side peaks generated solely by the cotunneling of up–down
spin pairs.
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Disordered Systems and Neural Networks · Cross-listed from q-bio.QM
Efficiently classifying shocks in complex systems requires dormant reporters
David A. Brewster and Philippe Cluzel
Many natural and engineered systems are large complex networks of interacting components, and external perturbations drive them along different dynamical paths. Identifying which perturbation occurred matters for diagnosis, control, and prediction. Yet often times only a few components can be jointly monitored. Which components should be monitored? Experimental practice usually favors placing reporters at the most sensitive sites, where perturbations produce the largest effects. Using a simple dynamical model for complex systems with heterogeneous connectivity, we ask how sparse reporter panels should be chosen to classify shocks from partial trajectories when repeated trials only approximately reproduce an ideal initial condition. Once that reproduction is imperfect, sensitivity ranked panels fall far short of optimal, and the shortfall grows with the noise. We find that the best panels mix two kinds of reporters. A promiscuous reporter responds to most shocks, so it separates them mainly by degree, and degree fluctuates from trial to trial. A dormant reporter responds to only a few shocks but strongly, and its answers do not scatter as much between trials. As noise grows, the cost of losing a dormant reporter rises to meet the cost of losing a promiscuous one. Panels of either kind alone classify worse than the mixture, and no property of the members collected individually explains the ordering. Most of all, we find that only a minuscule number of reporters are needed on a panel to accurately identify which shock hit the system. We implement an efficient
algorithm to assemble such a panel. Together these results provide a low cost practical design principle for monitoring large complex dynamical systems.
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Materials Science
Phase Switchable Photocatalytic Water Splitting via a Paraelectric-Ferroelectric Transition in Zr2Ge2S6 Monolayer: A Comprehensive Theoretical Insights
Jubair Hossan Abir, Tauhidur Rahman, Md. Tanvir Khan et al. (+3 more)
Photocatalytic water splitting (PWS) is a promising technology for addressing the global energy crisis and producing renewable and clean hydrogen fuel. Although numerous 2D materials have recently been proposed as potential photocatalysts, effective strategies for regulating photocatalytic reactions and improving energy conversion efficiency remain limited due to performance regulation challenges. Here, using first-principles calculations, we demonstrate that the photocatalytic activity and energy conversion efficiency of a Zr2Ge2S6 monolayer can be effectively tuned through a paraelectric-ferroelectric phase transition. The Zr2Ge2S6 monolayer exhibits excellent structural stability, favorable mechanical properties, a suitable band gap, optimal band edge positions, and broad-spectrum light absorption. Moreover, the Zr2Ge2S6 monolayer exhibits a higher oxidation potential and a stronger driving force for photogenerated holes to promote oxygen
evolution reaction (OER) in the ferroelectric phase. In contrast, the paraelectric phase provides photogenerated electrons with a greater reduction potential and driving force for hydrogen
evolution reaction (HER). The solar-to-hydrogen conversion efficiency is also strongly influenced by the phase transition, increasing from 7.71% in the paraelectric phase to 15.31% in the ferroelectric phase because of the improved carrier utilization. Our theoretical investigation not only highlights the crucial role of ferroelectric polarization in photocatalytic water splitting but also provides an effective strategy for tuning the photocatalytic properties of 2D ferroelectric materials through ferroelectric switching.
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All authors Jubair Hossan Abir, Tauhidur Rahman, Md. Tanvir Khan, S.S.B. Pallab, Raihana Shams Islam, Saleh Hasan Naqib
Mesoscale and Nanoscale Physics
Process-Technology Co-optimization for 2D-FETs
Shao-Heng Yang, Jainil Dharmil Shah, Mayukh Das et al. (+15 more)
We present the first experimental machine learning (ML)-enabled Process-Technology Co-Optimization (PTCO) framework for optimizing 2D transition metal dichalcogenide (TMD) FET fabrication directly from statistically meaningful experimental data rather than pure simulation data. We first introduce a transition voltage metric, VTrans, to quantify the gate voltage required for off-to-on switching and reveal its direct correlation with subthreshold swing (SS), highlighting an overlooked switching characteristic that governs both off-state and on-state performance. By integrating automated metric extraction, multi-objective recipe ranking, and predictive modeling, our framework uncovers hidden process-performance correlations and predicts the performance of unexplored fabrication recipes from limited experimental data. Experimental validation shows close agreement with ML predictions, thus demonstrating the framework's ability to efficiently guide gate stack optimization through iterative experimental feedback.
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All authors Shao-Heng Yang, Jainil Dharmil Shah, Mayukh Das, Yuanqiu Tan, Hao-Yu Lan, Hsing-Chien Chien, Himani Jawa, Shalini Tripathi, Marco Antonio Villena, Xiangyu Wu, Daire Cott, Kaustav Banerjee, Pierre Morin, César Javier Lockhart de la Rosa, Gaurav Thareja, Dennis Lin, Joerg Appenzeller, Zhihong Chen
Statistical Mechanics
BKT-like Correlation Scaling and Twist Responses in a One-Dimensional Fractional $U(1)$ Ginzburg–Landau Model
Hitomi Endo and Michikazu Kobayashi
We study a one-dimensional fractional $U(1)$ Ginzburg–Landau model whose quadratic part has
Fourier multiplier $|k|^\sigma$, focusing on the marginal case $\sigma=1$. This dispersion yields logarithmic
spin-wave fluctuations, suggesting BKT-like behavior despite the one-dimensional setting. We sample the
equilibrium Gibbs measure using
stochastic Gross–Pitaevskii dynamics and analyze correlation functions, dimensionless ratios, effective exponents, and twist responses. The correlation function shows a low-temperature algebraic branch with a temperature-dependent exponent, while the high-temperature regime exhibits a nonlocal-kernel-induced tail consistent with $C(r)\sim r^{-2}$. The correlation and Binder ratios are nearly size independent at low temperature and collapse with the BKT-type variable $(T-T_{\rm BKT})(\log L)^2$; finite-size effects set in around $T\simeq0.35\text{--}0.4$, consistent with $T_{\rm BKT}\simeq0.35$. Unlike the two-dimensional XY model, twist responses do not yield a finite helicity modulus: the ordinary linear-response quantity grows with system size, whereas the cusp twist response scales as $L^{-\eta(T)}$, like the squared zero-mode order parameter. Thus, the transition is BKT-like in correlation scaling, but lacks a universal helicity-modulus jump.
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Strongly Correlated Electrons
Correlation-Driven Nonlinear Magnetoelectric Response in an Altermagnet: A Dynamical Mean-Field Study
Robert Peters and Jun Ōiké
We investigate the optical nonlinear magnetoelectric effect (NMEE) in a strongly correlated altermagnet using dynamical mean-field theory. Unlike effective band descriptions with an imposed
spin splitting, our approach determines the altermagnetic order, electronic spectrum, and optical nonlinear response self-consistently. We find that the NMEE is finite in the altermagnetic phase and vanishes in the paramagnetic phase. Its frequency dependence reflects the
spin-resolved spectral structure and provides an estimate of the characteristic altermagnetic
spin-splitting scale. Interaction and temperature tuning produce qualitatively different behavior: at low temperature, reducing the interaction strength toward the interaction-driven
magnetic phase boundary enhances the response, whereas increasing the temperature suppresses it and drives it to zero above the critical temperature. These results establish the optical NMEE as a probe of correlated altermagnetic order and suggest that tuning parameters such as pressure, strain, or chemical substitution toward an interaction-driven phase boundary may provide a promising route to maximizing the response.
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Mesoscale and Nanoscale Physics
Narrow-Sense Type-III Dirac Cones and Additional Flat Lines on a Honeycomb Lattice with Anisotropic Next-Nearest-Neighbor Hoppings
Keita Kishigi and Yasumasa Hasegawa
Critically tilted Dirac cones have attracted considerable
attention because of their unconventional electronic properties in two-dimensional massless Dirac-
fermion systems. Among them, the narrow-sense type-III Dirac cone is characterized by a flat dispersion along the direction connecting the two Dirac points. Using a tight-binding model on a single-orbital honeycomb
lattice, we demonstrate that narrow-sense type-III Dirac cones can be realized by tuning anisotropic next-nearest-neighbor hoppings. Type-I and type-II Dirac cones emerge on either side of the critical point, enabling a systematic investigation of the electronic properties across the type-I, narrow-sense type-III, and type-II regimes. We further find that the present model exhibits additional flat lines in momentum space whose energy coincides with the Dirac-point energy at the narrow-sense type-III critical point. This band structure produces a pronounced enhancement of the density of states at the Fermi energy and, consequently, a substantial enhancement of the electronic specific heat compared with that expected for an ideal narrow-sense type-III Dirac cone. Our results show that the honeycomb
lattice with anisotropic next-nearest-neighbor hoppings provides a simple platform for exploring unconventional thermodynamic properties arising from the energy coincidence of narrow-sense type-III Dirac cones and additional flat lines at the Fermi energy.
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Materials Science · Cross-listed from cs.CV
Separating perception from reasoning in vision-language models: a model-free render ceiling for crystal structures
Can Polat, Mustafa Kurban, Erchin Serpedin et al. (+1 more)
Multimodal evaluations cannot say whether a
vision-
language model misread an image or misreasoned about it, because every existing method for separating the two places a second model in the loop. We introduce the render ceiling, a model-free reference for
benchmarks built by rendering known objects: inverting the frozen cameras and re-solving cross-view correspondence recovers exactly the answer the images support. We prove the ceiling fails only through an enumerable set of projection coincidences and certify that set empty on 2,160 rendered
crystal structures, so every point of a model's deficit belongs to the model. Across fourteen
vision-
language models, supplying exact geometry as text lifts every model yet closes under half the gap for thirteen, while a supervised
vision model with no
language component reads the same images at 0.8952, above every
vision-
language model. The instrument exposes extraction-stage fabrication that downstream accuracy would misattribute to
reasoning, yields camera-placement rules for
benchmark builders, and transfers to any
benchmark with an invertible forward rendering.
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All authors Can Polat, Mustafa Kurban, Erchin Serpedin, Hasan Kurban
Statistical Mechanics
Strengthened second law for periodic processes
Jake Schaefer, Ben Ansbacher, Jan Korbel et al. (+1 more)
We derive a lower bound on the
entropy production of any physical system that evolves as a periodic process. Crucially, this lower bound is completely independent of the physical mechanism implementing the periodic dynamics; it follows purely from the definition of
entropy production and the fact that whatever the physical mechanism is, it repeats in each period. In particular, the lower bound holds in both Markovian and non-Markovian systems, in systems that obey or violate (local) detailed balance, and even if the underlying physical mechanism uses currently unknown laws of physics. Moreover, the bound is strictly positive whenever the dynamics is not logically invertible. In this breadth of applicability, our bound is a strict strengthening of the second law. We illustrate our bound for
spins coupled to two heat reservoirs and for finite automata.
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All authors Jake Schaefer, Ben Ansbacher, Jan Korbel, David H. Wolpert
Soft Condensed Matter
A deviatoric-stress closure for constitutive modeling of viscoelastic dynamics
Souta Miyamoto, Shotaro Moro, Takeshi Sato et al. (+4 more)
Standard rheological measurements yield only selected stress components; thus, inferring tensorial constitutive equations from experimentally accessible observables is complicated. We propose a constitutive formulation written in terms of a deviatoric stress tensor, whose trace is zero, rather than the extra stress tensor. From rheometric data including shear stress, first and second normal stress differences under shear, and elongational stress under uniaxial elongation, we can construct a deviatoric stress state without the indeterminate isotropic stress. The deviatoric-stress dynamics is represented by a closure inferred through symbolic regression, constrained to satisfy material objectivity and a given linear Maxwell response. To demonstrate the proposed formulation, two closures inferred from stress responses of the Giesekus and Larson models successfully captured untrained transient-flow responses under planar elongation and mixed shear/uniaxial elongations at deformation rates around an inverse relaxation time. Steady rheological functions of the closures agreed with the original models in the linear-response regime and over a deformation-rate range connected to the training data, whereas deviations and divergent responses appeared at larger deformation rates outside the training regime. These results demonstrate that the proposed deviatoric-stress formulation provides a practical route for constitutive modeling of observable linear and nonlinear viscoelastic dynamics, while clarifying its range of validity under strong deformation.
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All authors Souta Miyamoto, Shotaro Moro, Takeshi Sato, Shota Kato, Katsuaki Tanabe, John J. Molina, Takashi Taniguchi
Mesoscale and Nanoscale Physics
Floquet scattering and Fano resonances in nodal-ring and multi-Weyl semimetals: Role of propagating and evanescent modes
Sandip Bera and Ipsita Mandal
We develop a comprehensive Floquet scattering theory for
quantum transport in periodically driven nodal-ring semimetals (NRSs) and multi-Weyl semimetals (mWSMs), extending our earlier study reported in Annalen der Physik 535, 2200460 (2023), in which evanescent modes were neglected, to a complete formalism that includes both propagating and evanescent channels. By solving the full boundary-value problem, we obtain the complete set of scattering states and show that, although evanescent modes are indispensable for satisfying the matching conditions at the potential interfaces, they carry zero net probability current and do not contribute to any observable transport quantity. We identify a previously unexplored transport regime in NRSs in which two propagating channels coexist and participate in coherent scattering, producing multi-channel
quantum interference and Floquet-induced Fano resonances. The transmission, reflection, pumped shot noise, and the associated Fano resonance features are determined entirely by the propagating channels, and the resonance energies coincide with those of the corresponding quasi-bound states of the static potential well. Our results establish a unified framework for Floquet transport in anisotropic topological semimetals, and confirm that the approximation of neglecting evanescent modes in our earlier work is justified for all measurable transport properties.
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Materials Science
Overcoming the Efficiency-Stability Trade-off in Spin-Orbit Torque Devices with Thermally Robust BCC NiW Alloys
Yu-Ming Pan, Chen-Yi Wei, Yi-Cheng Tsou et al. (+3 more)
The development of high-performance
spin-orbit torque (SOT)
magnetic memories is fundamentally constrained by a persistent trade-off between
spin Hall efficiency, thermal structural stability, and perpendicular
magnetic anisotropy in conventional heavy metals. Here, we overcome this limitation by engineering body-centered-cubic (BCC) Ni-doped W
alloys as highly efficient and thermally robust
spin-current sources. Ni$_{30}$W$_{70}$/CoFeB
heterostructures achieve deterministic out-of-plane magnetization switching at an ultra-low critical current density of 1.78 MA/cm$^2$, nearly threefold lower than that of $\beta$-W, while maintaining a high anisotropy field of 8,500 Oe and a thermal stability factor of 57.9. The BCC Ni$_{30}$W$_{70}$
alloy preserves its structural integrity and the perpendicular
magnetic anisotropy of the adjacent CoFeB layer after annealing at 450 $^\circ$C, demonstrating robustness under the stringent thermal processing conditions relevant to back-end-of-line integration. Harmonic Hall and ferromagnetic resonance measurements reveal a large
spin Hall angle of -0.39 and a high interfacial
spin transparency of 0.75, demonstrating efficient
spin-current generation and interfacial transmission. First-principles calculations further reveal enhanced intrinsic
spin Hall conductivity in W-rich BCC NiW
alloys, associated with the Fermi level lying within a
spin-orbit-coupling-induced band gap. These findings establish BCC NiW
alloys as a scalable and thermally resilient material platform for energy-efficient SOT-MRAM.
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All authors Yu-Ming Pan, Chen-Yi Wei, Yi-Cheng Tsou, Tsung-Yu Pan, Guang-Yu Guo, Chih-Huang Lai
Statistical Mechanics
Feedback-Enhanced Quantum Metrology and Clock Precision under Thermodynamic Uncertainty
Jincheng Lu and Chen Wang
Feedback can convert continuously monitored
quantum jumps into a thermodynamic resource. We formulate full counting statistics for open
quantum systems under unital jump feedback by incorporating the feedback maps into the tilted generator. The resulting trajectory ensemble determines both current fluctuations and the Fisher information of the measurement record. We show that feedback can enhance reservoir-parameter estimation and clock precision without necessarily changing average thermodynamic currents. This enhanced precision is not bounded by reservoir
entropy production alone. By
embedding the reduced dynamics in an enlarged measurement-feedback process, we derive a feedback-modified thermodynamic uncertainty relation in which the information
entropy production of the feedback apparatus supplies the missing cost. A charge-monitored double
quantum dot illustrates the framework: jump-conditioned feedback improves thermometry and chemical-potential sensing, and stabilizes a
quantum clock defined by output-current ticks.
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Materials Science
GW and Bethe-Salpeter Theory for Molecular Polaritons, Quasiparticles, and Excitons
Soohaeng Yoo Willow, Gi Beom Sim, Tae Hyeon Park et al. (+6 more)
The electron self-energy is central to quasiparticle theory, yet how an optical cavity enters it remains unclear. We address this question for a molecule in a single-mode cavity using the dipole-gauge Pauli-Fierz
Hamiltonian and a coherent-state QED Hartree-Fock reference. The cavity enters through three channels: the static dipole self-energy (DSE) shift of reference orbital energies, direct DSE augmentation of the screened interaction, and the polariton pole carrying the bilinear electron-
photon coupling. We
benchmark QED-$GW$ ionization potentials (IPs) and electron affinities (EAs) against a cavity $\Delta$-method ladder from QED-HF to correlated wave-function methods, whose cavity-induced shifts agree within 1 meV where directly comparable. For closed-shell molecules with unbound anions, $GW$ systematically overestimates cavity-induced IP
redshifts, whereas EA shifts are reproduced nearly quantitatively, although this does not imply comparable accuracy for absolute EAs. For ionic molecules with bound anions, this ordering reverses, consistent with published QED coupled-cluster results. Coupling and detuning scans show that the error is predominantly quadratic in $\lambda$ and DSE-driven rather than resonant. The spectral function develops a polariton-replica photoemission sideband with weight scaling as $\lambda^2$. In the static screened interaction used in the Bethe-Salpeter equation, bare-
photon exchange cancels the matching DSE contribution to the direct interaction, while exchange and polariton-screening corrections remain. Their net effect on the lowest excitation is appreciable only for ammonia in the molecules studied.
Exciton-binding energies involving unbound anions are strongly basis-dependent and should therefore be viewed as diagnostics of electron-hole interactions rather than basis-converged molecular quantities.
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All authors Soohaeng Yoo Willow, Gi Beom Sim, Tae Hyeon Park, Tae In Kim, D. ChangMo Yang, Mikuláš Matoušek, Jiří Brabec, Libor Veis, Chang Woo Myung
Soft Condensed Matter
Bond-number-controlled durability of cohesive granular materials under repeated vibration
Hikari Yokota and Rei Kurita
Cohesive granular materials derive their mechanical stability not only from the strength of individual interparticle bonds but also from the number of bonds forming the load-bearing network. However, these two effects are difficult to separate experimentally because conventional control parameters, such as
liquid content, generally alter both simultaneously. Here, we use a mixed granular system composed of cohesive and noncohesive grains to control the cohesive bond number while keeping the bond strength approximately unchanged. We investigate the failure lifetime under repeated vibration and find that the number of cycles to failure, $N_f$, depends strongly on the mixing ratio $\alpha$. In a mean-field picture of random mixing, the fraction of cohesive contacts scales as $\alpha^2$, and $N_f$ increases approximately exponentially with $\alpha^2$. By contrast, although the lifetime tends to decrease with increasing vibration intensity $G$, its dependence on $G$ is comparatively weak over the present experimental range. Remarkably, although the Young's modulus is nearly independent of $\alpha$ above the rigidity threshold, the lifetime continues to increase strongly with $\alpha$. This demonstrates that mechanical rigidity and durability against repeated perturbations exhibit distinct dependences on the cohesive network. These results identify bond number as a key control parameter for the durability of cohesive granular materials.
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