Peer Revenue Equity in science

Papers

Fresh from arXiv, typeset properly. Highlighted words trade on the market.

Physics Condensed Matter

cond-mat Watch Condensed Matter

Saturday 25 July

Materials Science

A DFT and Machine Learning-Assisted Study on the Lattice Thermal Conductivity of LiCdSb for Thermoelectric Applications

R. Zosiamliana, Lalhriat Zuala, N. T. Tien et al. (+3 more)

By using first-principles density functional theory (DFT) and the Boltzmann transport equation, we have calculated the corresponding electronic and thermoelectric properties of LiCdSb. For calculating electron transport properties, accurate band-structure estimation is crucial. Hence, for the precise band gap calculation, we have implemented a hybrid functional HSE06, which is widely known for its high accuracy. To evaluate the thermoelectric performance of a material, the calculation of lattice thermal conductivity (Kl) is a key parameter. However, from a theoretical perspective, the calculation of lattice thermal conductivity is very complex and demands huge computational resources. Therefore, in this work, we have opted for an alternative method of machine-learning interatomic potentials (MLIPs) for the calculation of Kl. Our result of Kl=0.24 Wm^-1K^-1 at room temperature is in qualitative agreement with the available theoretical and experimental data. The figure of merit (ZT) with Kl estimated from Slack+TDEC ZT is 0.18 at 300 K, and machine learning (ML) models ZT is 0.17 at 300K, combining with HSE06-based electronic transport properties agreed well with the available experimentally reported value of ZT is 0.10 at 300K. However, we report the ZT value well above the benchmark value of 1 beyond 600K. The ZT value exceeding 1 at higher temperatures makes LiCdSb a promising material for high-temperature energy conversion.
Read the full abstract

All authors R. Zosiamliana, Lalhriat Zuala, N. T. Tien, Vo Khuong Dien, A. Laref, D. P. Rai

Disordered Systems and Neural Networks

Generalized Bloch-like ground states in distinct electron-site configurations derived from the same quasiperiodic structure

Yuki Yamamoto and Nayuta Takemori

Sutherland-Kalugin-Katz (SKK) states have been proposed as generalized Bloch-like states in quasiperiodic systems where the absence of translational symmetry prevents the application of Bloch's theorem. However, previous studies have largely relied on ansatz-based arguments, and a systematic procedure for constructing the SKK state from a specified Hamiltonian has remained unclear. In this work, we develop a constructive approach based on a generalized Fourier transform of creation operators in tight-binding models. We then apply this framework to vertex and dual models on the Ammann-Beenker (AB) tiling that stem from the same quasiperiodicity but differ in their electron-site configurations. Our construction reproduces the previously reported SKK state in the ground state of the vertex model and reveals a corresponding SKK state in the ground state of the dual model with high fidelity. The structural correspondence between the two SKK states indicates that such states are not tied to a particular choice of electron sites and reflect the underlying quasiperiodicity of the AB tiling.
Read the full abstract

Strongly Correlated Electrons

Field-tuned incommensurate fan phase in an Ising-like triangular antiferromagnet

D. Flavián, R. Okuma, P. Manuel et al. (+3 more)

Using single-crystal neutron diffraction we report the observation of a field-tuned incommensurate phase in a field range just below magnetization saturation in the Ising-like triangular-lattice antiferromagnet Na$_2$BaCo(PO$_4$)$_2$. This phase occurs for magnetic fields applied along the Ising axis and exhibits an in-plane incommensurate propagation vector that moves along the hexagonal Brillouin zone boundary upon varying field, challenging the simple $XXZ$ antiferromagnetic description of the system. Within a semiclassical framework, we successfully identify this pre-saturation phase as a coplanar fan phase and study the role of dipole-dipole interactions and bond-dependent exchange anisotropy in its stabilization mechanism. We additionally present a minimal exchange model including interlayer couplings, which reproduces the complex magnetic phase diagram in field including the observed field-dependence of the incommensurate propagation vector in the fan phase.
Read the full abstract

All authors D. Flavián, R. Okuma, P. Manuel, Q. Huang, H. Zhou, R. Coldea

Mesoscale and Nanoscale Physics

Signatures of Topological Magnon Edge States in THz Spectroscopy and Cavity Response

Ipsika Mohanty, Johannes Knolle and Silvia Viola Kusminskiy

Topological magnon insulators (TMIs) have emerged as promising platforms for low-energy spin-based information processing, due to their non-trivial bulk magnon topology and robust, chiral edge modes that support dissipationless transport. Although theoretical models predict these edge states, direct experimental detection remains challenging due to their limited sensitivity to conventional probes. In this work, we propose an all-optical pathway to detect topological magnon edge modes in ferromagnetic TMIs. Our approach harnesses parametric amplification of edge magnons via resonant electromagnetic driving, enabled by magnetoelectric coupling mechanisms. We concentrate on two-dimensional van der Waals ferromagnetic materials on the honeycomb lattice with magnonic band gaps in the terahertz (THz) range. We show that a spin-dependent effective electric dipole moment, arising from dynamic charge fluctuations and consistent with the lattice symmetry up to next-nearest-neighbor interactions, gives rise to one-photon-two-magnon processes leading to parametric amplification. On this basis, we propose a THz pump-probe spectroscopy protocol in which edge modes are selectively amplified and subsequently detected in absorption. Furthermore, we discuss the possibility of using THz cavities, enabling selective coupling to edge modes while filtering out bulk contributions. These findings establish a route for probing topological magnets and open new avenues for experimental exploration of exotic topological phenomena in magnetic quantum materials.
Read the full abstract

Soft Condensed Matter

Active flows drive anchoring of nematics at rigid walls

Michael Fang, Ioannis Hadjifrangiskou, Sumesh P. Thampi et al. (+2 more)

Although confinement strongly influences flows in active materials, it remains unclear how active particles align at rigid boundaries when no thermodynamic anchoring is imposed. We address this question using continuum simulations of active nematics, together with analytical arguments based on a reduced near-wall description. In the flow-tumbling regime, extensile systems align parallel to the boundary, whereas contractile systems align perpendicular to it, consistent with active anchoring observed at active-passive interfaces. In the flow-aligning regime, the preferred orientation depends on the sign of activity and of the flow aligning parameter: either the shear-like flow generated near the wall selects the Leslie angle, or no unique alignment is established. These results provide a unified framework for activity-induced anchoring at rigid walls, demonstrating that boundary alignment in dense active matter can emerge solely from the interplay between self-generated flows and orientational dynamics.
Read the full abstract

All authors Michael Fang, Ioannis Hadjifrangiskou, Sumesh P. Thampi, Julia M. Yeomans, Jan Rozman

Mesoscale and Nanoscale Physics

Electrical control of the metal-insulator transition in a one dimensional device

J. Craquelin, L. Jarjat, B. Hue et al. (+8 more)

Controlling the low energy spectrum at the nanoscale with an external physical parameter has become an important resource for quantum devices. The emergence of an energy gap is one such key feature, linked to the mitigation of decoherence needed for quantum information processing. Indeed, the detrimental effects of high-energy uncontrolled excitations can only be cured at some specific tuning points in general. Achieving an energy gap is a natural way to extend decoherence countermeasures over a finite region of parameter space. This would be particularly useful in view of the recent efforts to build superconducting topological chains in a top-down approach. In this work, we demonstrate a large energy gap by spatially modulating the local potential of a suspended carbon nanotube, exploiting an analogy with condensed matter systems. This gap is homogeneous on the nanotube and tunable by about two orders of magnitude, bringing the electronic system from an insulating state to a near-metallic state at low temperatures.
Read the full abstract

All authors J. Craquelin, L. Jarjat, B. Hue, A. Théry, C. Fruy, N. Struchkov, D. Stefani, M. M. Desjardins, A. Cottet, M. R. Delbecq, T. Kontos

Statistical Mechanics

Quantum fluctuation-driven transport crossover between two liquid states in distinguishable helium-4

Mika Tanabe, Momoko Tsujimoto and Kenichi Kinugawa

We show the emergence of a quantum fluctuation-driven transport crossover between two liquid states in distinguishable helium-4 obeying Boltzmann statistics, in the absence of atomic exchange. Using path integral centroid molecular dynamics simulations over 0.1-3.3 K and 1-60 bar, we investigate the transport properties of two distinct liquid states: the low quantum-dispersion liquid (LQDL) and the high quantum-dispersion liquid (HQDL). While LQDL exhibits conventional liquid behavior consistent with the Stokes-Einstein (SE) relation, HQDL emerges at lower temperatures and displays anomalous gas-like transport characterized by superdiffusion and ultralow viscosity, accompanied by a breakdown of the SE relation. This counterintuitive emergence of gas-like dynamics upon cooling reflects the dominant role of nuclear quantum fluctuations, in contrast to thermal fluctuations at higher temperatures. Across the LQDL-HQDL boundary, we identify a transport crossover marked by a qualitative change in the velocity autocorrelation function (VAF), a transition in the Prandtl number, and the emergence of transport minima in shear and kinematic viscosities, thermal conductivity, and thermal diffusivity. These minima reflect a crossover from liquid-like to gas-like transport upon cooling in the low-temperature subcritical region, in addition to the universal transport minima observed in the supercritical regime. The transition from oscillatory to monotonic VAF defines a second Frenkel line, distinct from the conventional Frenkel line observed in the supercritical region. LQDL is a heat-transport-dominated dissipative fluid, whereas HQDL is a momentum-dominated inertial fluid. These results demonstrate that nuclear quantum fluctuations alone induce gas-like liquid behavior and provide a unified picture of transport phenomena in distinguishable helium-4 without superfluidity.
Read the full abstract

Mesoscale and Nanoscale Physics

Janus-induced atomic reconstruction amplifies twist-angle modulation of interlayer thermal transport in moiré bilayers

Bin Xu, Rulei Guo, Jie Sun et al. (+8 more)

In two-dimensional moiré bilayers, atomic reconstruction, the spontaneous structural relaxation toward energy-minimizing stacking registries in the near-commensurate regime, can strongly modify local stacking and interlayer coupling, providing a possibility to significantly control phonon-mediated properties. Here we show that the twist-angle dependence of interlayer thermal conductance can be modified by introducing Janus-induced mirror-symmetry breaking into bilayer MoS2. The intrinsic out-of-plane dipole in MoSSe/MoS2 bilayers leads to frictionless interface, and reduces the lattice deformation energy, thereby promoting atomic-reconstruction into locally distorted aperiodic moiré patterns. These features weaken interlayer coupling and suppress phonon transmission across the interface, leading to an anomalously strong twist-angle dependence of thermal conductance, with a pronounced minimum at small twist angles and a reduction rate nearly one order of magnitude larger than that of twisted bilayer MoS2. Our results demonstrate that interlayer thermal transport is modified by atomic reconstruction, highlighting Janus-induced mirror-symmetry breaking as an effective way to promoting phonon engineering in two-dimensional moiré structures.
Read the full abstract

All authors Bin Xu, Rulei Guo, Jie Sun, Hiroo Suzuki, Takuma Yoshida, Ichiro Nakaya, Koki Sawasaki, Yasuhiko Hayashi, Shohei Chiashi, Tomoki Machida, Junichiro Shiomi

Statistical Mechanics · Cross-listed from quant-ph

Digital techniques for the frustrated Ising ring: the role of counter-diabatic terms

Kiran Thengil, Vincenzo Roberto Arezzo and Giuseppe E. Santoro

We investigate the role of local counter-diabatic (CD) terms in enhancing the performance of discrete-time digital protocols for a frustrated Ising ring, a system with an exponentially small spectral gap that acts as a bottleneck for conventional quantum annealing. The techniques investigated range from a digitised version of a fixed-schedule protocol, including lowest-order analytical CD terms, all the way to a full-fledged Quantum Approximate Optimisation Algorithm (QAOA), including variational CD terms (DC-QAOA). By analyzing the resulting residual energy, we show that DC-QAOA combined with Chopped RAndom Basis (CRAB) quantum control techniques for optimizing the circuit parameters, can outperform all the other strategies. By monitoring the ground-state population during the dynamics we learn that DC-QAOA finds effective shortcuts towards the target state through intermediate excited states, a process that is unexpectedly enhanced by the inclusion of local CD unitaries. Our results highlight the importance of flexible variational control of CD dynamics and demonstrate that digital optimization can explore operator dynamics that remain inaccessible to standard analytical CD constructions.
Read the full abstract

Materials Science

Imaging of van der Waals Materials via Standing-Wave Photoemission Microscopy: Depth-Resolved Electronic Structure of WS2

J. R. Paudel, R. Muzzio, M. E. Matzelle et al. (+13 more)

Two-dimensional van der Waals materials promise electronic, optoelectronic, and quantum technologies, yet depth-resolved characterization remains challenging. Here, we demonstrate standing-wave photoemission electron microscopy (SW-PEEM) for Angstrom-scale spectromicroscopy of monolayer WS2 on a W/C multilayer substrate. Tuning the X-ray standing wave through the monolayer yields a chemical depth profile and valence-band modulation with enhanced sensitivity to the top and bottom sulfur layers. X-ray optical modeling determines the structure and field distribution. The measurements reveal an ~0.2 eV shift in sulfur-derived valence-band spectral weight between measurements with enhanced sensitivity to the top and bottom sulfur layers. This shift is unlikely to arise from strong direct substrate hybridization and is instead consistent with sulfur-related surface species, as supported by calculations using a representative elemental-sulfur model. These results establish SW-PEEM as a non-destructive depth-resolved probe, highlighting its potential to probe interfacial coupling, chemical reconstruction, and emergent states in van der Waals and moiré systems.
Read the full abstract

All authors J. R. Paudel, R. Muzzio, M. E. Matzelle, S. Sheikh, A. Fadul, A. Tiwari, F. Salmassi, E. Gullikson, K. M. McCreary, B. T. Jonker, J. Nieminen, C. M. Schneider, F. Kronast, A. Bansil, J. Katoch, A. X. Gray

Superconductivity

Evolution of the electronic and superconducting properties of Re-based quinary high-entropy alloys under chemical and physical pressure

Thiagarajan Maran, Yoshiya Uwatoko, Sathea Suweatha M N et al. (+4 more)

We report a comparative study of chemical- and physical-pressure effects on the electronic and superconducting properties of the Re-based quinary high-entropy alloys (HEAs) [Nb0.67-xRex][TiZrHf]0.33 (x = 0.10, 0.20, and 0.56). Increasing Re concentration suppresses the superconducting transition temperature Tc from 5.4 to 3.9 K while producing positive, composition-dependent cocktail-effect ratios. Field-dependent transport and magnetization establish all three compositions as strongly type-II superconductors and identify x = 0.20 as the most distinctive composition, with the largest upper critical field and Ginzburg-Landau parameter and a Maki parameter close to unity. Most importantly, the pressure coefficient of Tc changes sign across the bcc-hcp structural change: dTc/dP is positive for the bcc x = 0.10 and 0.20 samples, with values of approximately 0.018 and 0.053 K/GPa, respectively, but negative for the hcp x = 0.56 sample, with a value of approximately -0.033 K/GPa. This systematic contrast within a single chemically related alloy series establishes a robust structure-associated superconducting response and identifies crystal structure as a key organizing variable under compression. Metallic transport and superconductivity remain robust up to approximately 8 GPa in all three compositions. These results reveal that chemical substitution and hydrostatic compression are complementary but nonequivalent routes for tuning superconductivity in Re-based HEAs.
Read the full abstract

All authors Thiagarajan Maran, Yoshiya Uwatoko, Sathea Suweatha M N, Sonika Jangid, R.P. Singh, Arumugam Sonachalam, Sathiskumar Mariappan

Materials Science

Hydrogen-Induced Sign Reversal in Magnetic Hysteresis Evolution of CoPd Alloys and Co/Pd Multilayers

S. S. Das and A. Gerber

Hydrogen absorption in magnetic thin film nanostructures can modulate their electronic, magnetic, and transport properties by modifying the electronic structure and lattice strain. However, the influence of composition and nanostructuring on these two competing effects is not well understood. We systematically investigate hydrogen-induced magnetic hysteresis in Co$_x$Pd$_{100-x}$ alloys, [Co(0.1 nm)/Pd(d)]$_{15}$, and [Co(0.2 nm)/Pd(d)]$_{15}$ multilayers, using extraordinary Hall effect characterizations (EHE) in air and 4% H$_2$/N$_2$ mixture. We show that the hydrogen-induced response is not universal, but depends strongly on composition and layer thickness. This reflects competition between Pd-related electronic effects and magnetoelastic anisotropy. In Pd-rich CoPd alloys and Co(0.2 nm)/Pd multilayers, hydrogen initially contracts the hysteresis loops at low Co fractions, followed by loop expansion above x ~ 40%. This contrast results from competition between suppression of Pd-induced magnetization through Pd-4d band filling and hydrogen-driven anisotropic strain that strengthens magnetoelastic anisotropy in Co-rich samples. In contrast, in ultrathin [Co(0.1 nm)/Pd(d)]$_{15}$ multilayers, hydrogen induces a weak, non-monotonic but generally expanding loop behaviour across x = 15-60%, indicating a dominant role of interfacial magnetic connectivity and strain-mediated magnetoelastic anisotropy in the ultrathin limit. Furthermore, we observe a hydrogen-induced reversal of the EHE loop polarity near the crossover regime, reflecting a change in the dominant EHE scattering mechanisms, thus providing an additional degree of magnetic tunability by hydrogen. These results demonstrate that hydrogen can selectively tune the magnetism of CoPd nanostructures via composition-controlled electronic and magnetoelastic effects, offering insights for hydrogen-responsive spintronic and sensing devices.
Read the full abstract

Materials Science

Ferroelastic exciton splitting in hybrid perovskite nanowalls

Afreen, J. Delgado-Alvarez, H. Krishna Mishra et al. (+9 more)

Hybrid metal-halide perovskites are soft semiconductors in which electronic excitations are strongly influenced by lattice distortions and structural phase transitions. An important open question is whether ferroelastic symmetry breaking merely broadens optical resonances or instead modifies excitonic states through exciton-lattice coupling. Here, we address this question using highly aligned MAPbI3 nanowalls fabricated by glancing-angle deposition, enabling symmetry-selective coupling between ferroelastic texture, structural anisotropy, and a well-defined optical axis. Combining temperature-dependent photoluminescence, X-ray diffraction and polarization-resolved ultrafast transient absorption spectroscopy, we observe a polarization-selective excitonic splitting in the orthorhombic phase at 5 K, characterized by orthogonal optical selection rules and a 45 meV energy separation. Near 160 K, where orthorhombic and tetragonal phases coexist, a lower-energy lattice-coupled excitation emerges 58 meV below the centre of the anisotropically split excitonic structure, consistent with coupling between excitonic and lattice-dressed states. At higher temperatures, these excitations progressively acquire lattice-dressed character accompanied by reduced optical anisotropy. A symmetry-guided effective Hamiltonian captures the evolution from anisotropically split excitons to coupled excitonic and lattice-dressed states across the structural transition. Our results show that ferroelastic texture and phase coexistence can modify exciton-lattice coupling, providing a route to symmetry-selective optical responses in soft polar semiconductors.
Read the full abstract

All authors Afreen, J. Delgado-Alvarez, H. Krishna Mishra, J. Castillo-Seoane, Koustav Maiti, Pravrati Taank, A. Borras, A. Barranco, Surajit Saha, Priya Mahadevan, J. R. Sanchez-Valencia, K. V. Adarsh

Materials Science · Cross-listed from cs.IR

VecTree-RAG: An Agentic Retrieval-Augmented Generation Framework Combining Vector and Tree Retrieval for Efficiency and Accuracy

Xinyan Zhong, Yuwei Shi, Yuqi Wei et al. (+3 more)

Scientific question answering requires a retrieval system to solve two distinct problems: identifying which papers are relevant and locating the supporting evidence within those papers. Conventional retrieval-augmented generation typically addresses both through similarity search over fixed-length passages, flattening document structure and separating scientific claims from their methodological and argumentative context. We present VecTree-RAG, an agentic framework that assigns these tasks to complementary retrieval mechanisms. Vector search ranks compact document and section representations across the corpus, whereas reasoning-guided traversal of source-verified section trees localizes evidence within shortlisted papers. Full text is retained in a page store and exposed progressively only after structural localization. We evaluate VecTree-RAG on 300 QASPER questions, an open-access subset of 54 LitQA2 questions, and 49 multi-document MOSAIC questions. Compared with Dense RAG, reranked Dense RAG, RAPTOR, and Search-o1, VecTree-RAG obtained the highest observed answer score on all three benchmarks, reaching 0.800 LLM-judge correctness on QASPER, 0.925 accuracy on LitQA2, and a 0.547 composite score on MOSAIC. On QASPER, its evidence-page precision was 0.274, compared with 0.046–0.071 for the baselines. LitQA2 ablations further showed that the complete vector–tree architecture required fewer inference tokens than variants without tree navigation or corpus-level vector routing. These results indicate that vector retrieval narrows the corpus-level search space and tree navigation concentrates reading on structurally relevant evidence. Although multi-turn inference remains more expensive than single-call retrieval, VecTree-RAG provides a structure-aware and traceable architecture for scientific literature question answering.
Read the full abstract

All authors Xinyan Zhong, Yuwei Shi, Yuqi Wei, Chen Shen, Tianhang Zhou, Zhenghao Wu

Materials Science

Uncertainty-quantified $J$-integral computation for quasicontinuum and finite element methods

Sai Harshith Badi, Stephen M. Whalen, Ronald E. Miller et al. (+1 more)

The $J$-integral is a fundamental concept in fracture mechanics, quantifying the energy release rate that drives crack propagation. While extensively implemented in finite element (FE) codes and adapted for atomistic calculations, its application within multiscale frameworks bridging atomistic and continuum formulations remains unexplored. This work presents a rigorous implementation and validation of the $J$-integral within the three-dimensional quasicontinuum (QC3D) method, computed under plane strain assumptions, using continuum fields (stress, strain energy density) derived from the interatomic potential via the Cauchy-Born rule. The implementation is validated against linear elastic fracture mechanics (LEFM) theory and the virtual crack extension (VCE) method across three regimes: (1) small-strain linear elasticity, with a prescribed anisotropic $K$-field displacement applied throughout; (2) the same field evaluated through the nonlinear Cauchy-Born constitutive relation, without atomic relaxation; and (3) the same relation with atomic relaxation enabled, allowing the crack-tip region to equilibrate. Excellent agreement is shown throughout. We further introduce a Markov chain Monte Carlo framework to statistically quantify the uncertainty of $J$-integral results for a given mesh and integration domain, applicable to conventional FE methods as well. Predictive capability is demonstrated via a QC3D simulation of a three-point bending test of silicon, where the computed critical energy release rate agrees closely with the Griffith criterion. This work establishes a reliable framework for evaluating crack driving forces in multiscale fracture simulations with quantified uncertainty, enabling large-scale fracture simulations while resolving atomistic mechanisms at the crack tip.
Read the full abstract

All authors Sai Harshith Badi, Stephen M. Whalen, Ronald E. Miller, Ellad B. Tadmor

Materials Science

Role of $p$-$d$ Hybridization on Optical Properties of Chalcopyrite Semiconductors

Neunghee Han, Harang Kim, Minjae Kim et al. (+1 more)

Designing quantum materials for coherent optical properties is a central agenda in quantum technology. Semiconductor quantum dots are an emerging approach for controlling coherent optical properties via confinement effects, tunable band gaps, and exciton binding energies, yet their inherent structural and compositional inhomogeneity degrades the coherence of the optical spectra, posing a major obstacle. We show that, for chalcopyrite semiconductors, hybridization between transition-metal $d$ and ligand $p$ electrons in the valence band is key to the coherence of the quantum dot optical spectrum. We demonstrate this using first-principles electronic-structure calculations and optical spectroscopy. The strong $p$-$d$ hybridization in CuInS$_{2}$ induces the Cu($d$) Coulomb scattering channel, giving rise to the incoherent photodoped hole carrier, while the weak $p$-$d$ hybridization in AgInS$_{2}$ induces the delocalized photodoped hole carrier having a predominant S($p$) orbital character. Our experimental results on optical spectra suggest that when the Cu ratio is enhanced in the Ag$_{1-x}$Cu$_{x}$In$_{1-y}$Ga$_{y}$S$_{2}$ quantum dot, Cu atoms at both Ag sites and defect sites experience enhanced $p$-$d$ hybridization, and a coupling begins to develop between the electrons in the quantum dot and the defect electrons at a small Cu ratio. This coupling activates Cu($d$) Coulomb scattering for photodoped holes traversing the defect sites, producing an incoherent optical response that naturally explains the long-standing absence of band-edge spectral signatures in CuIn$_{1-y}$Ga$_y$S$_2$ quantum dots. These results serve as a guideline for designing semiconductor quantum dots. To achieve a coherent optical spectrum, avoid $p$-$d$-hybridized orbital character in the photo-doped carrier.
Read the full abstract

All authors Neunghee Han, Harang Kim, Minjae Kim, Woonhyuk Baek

Statistical Mechanics · Cross-listed from math.PR

Mixing times and spectra of non-equilibrium symmetric exclusion processes on general graphs

Leonard J. Schulman and Alistair Sinclair

The symmetric exclusion process (SEP) is a classical model of interacting particles on a graph, in which multiple particles execute random walks subject to the constraint that no two particles may occupy the same vertex. The version of the process in which the number of particles is fixed, is by now very well understood, through the study of reversible Markov chains. In this paper, we study the non-equilibrium version of the SEP, in which some vertices of the graph interact with external heat baths, held at different temperatures, that mediate transport through the graph. The resulting steady-state distribution is still the stationary distribution of a natural Markov chain, but the chain is no longer reversible. This means that even the steady-state distribution is very hard to describe, and indeed is the subject of a rich literature, which has focused almost exclusively on graphs which are finite subsets of the lattice $Z^d$. Very little is known about other important quantities, notably the mixing time. We derive various quantitative results about the non-equilibrium SEP for arbitrary graphs with arbitrary heat baths. Our main result is a bound on the mixing time in terms of the worst-case hitting time of a single particle to any of the heat baths; this bound is tight up to two logarithmic factors in the size of the graph. We then use this result to derive a simple algorithm, running in time roughly $n^{O(k)}$, that computes the steady-state joint occupation distribution for any set of $k$ vertices; since the steady-state distribution is very elusive, this provides a potentially useful tool to study its $k$-wise correlations for small values of $k$. Finally, we prove that the spectrum of the Markov chain associated with the non-reversible dynamics for the SEP is independent of the heat bath temperatures; thus in particular the spectrum is always real.
Read the full abstract

Statistical Mechanics

Response Morphologies of a Canonical Fluctuation Diagnostic Across Ehrenfest Phase Transitions

Fangfang Wang, Wei Liu, Ying Tang et al. (+1 more)

Microcanonical inflection-point analysis identifies MIPA-type higher-order transition structures from derivatives of the microcanonical entropy. Until recently, however, there was no canonical formulation for probing the corresponding fluctuation-level behavior directly from measurable energy fluctuations without reconstructing the density of states. Previous work addressed this limitation by introducing a canonical fluctuation diagnostic that quantifies energy-fluctuation asymmetry. Here, we investigate how this diagnostic behaves across representative first-, second-, and third-order phase transitions in the Ehrenfest classification. We consider the eight-state Potts model, the two-dimensional Ising model, and ideal three-dimensional Bose–Einstein condensation. The Potts and Ising systems exhibit a robust paired-extremum structure of the diagnostic near their respective transition regions, whereas ideal Bose–Einstein condensation exhibits a discontinuous response at the condensation temperature in the thermodynamic limit. These results show that a single fluctuation-based observable can display qualitatively distinct response morphologies across thermodynamic regimes, reflecting sensitivity to the nature of the underlying phase transition rather than serving as a direct classifier of Ehrenfest order.
Read the full abstract

All authors Fangfang Wang, Wei Liu, Ying Tang, Zengru Di

Mesoscale and Nanoscale Physics

Spectral Topology and Non-Bloch Band Theory for Domain-Wall Systems

Mingtao Xu, Rui Wang, Tian-Shu Deng et al. (+1 more)

We study the spectral topology of one-dimensional non-Hermitian models in a domain-wall configuration, where different domains are arranged in a ring geometry. While eigenstates can localize near an interface under the non-Hermitian skin effect, we show that the localization of an eigenstate originates from the difference in the spectral winding numbers, with respect to the corresponding eigenenergy, between the two adjacent domains. We then obtain the conditions for the generalized Brillouin zone (GBZ) in the complex momentum space, by extending the Ronkin-function formalism to the domain-wall configuration. In addition to the conventional skin modes that correspond to standing waves on individual domains under the open boundary condition, a unique type of traveling-wave-like skin modes emerges, whose construction involves all domains. Besides their difference in the spatial profiles, these two types of modes obey distinct GBZ conditions, making them differentiable on the GBZ. Interestingly, the traveling-wave-like modes further carry a finite flux spectral winding number, indicating their boundary sensitivity.
Read the full abstract

All authors Mingtao Xu, Rui Wang, Tian-Shu Deng, Wei Yi

Materials Science

AEcroscopyWave: Towards Self-Driving Characterization Platforms for Agentic AI

Yongtao Liu, Jawad Chowdhury, Ganesh Narasimha et al. (+8 more)

The characterization of electronic materials has traditionally been stratified into two distinct regimens: industry-scale automated systems to inspect materials for defects and ensure quality (such as in the semiconductor industry), and highly customized, operator-driven systems requiring human experts. The former offers high throughput but limited flexibility, whereas the latter is heavily bandwidth-limited but provides research-grade discovery capabilities. Recent advances in "self-driving" characterization tools offer the potential to bridge the two stratified regimes, by the creation of application program interfaces (APIs) that can control hardware, and the integration of AI methods to incorporate autonomy into the process. Here, we discuss our latest developments in AEcroscopyWave, a custom-built characterization platform for the agentic-AI era, that provides unified control of scanning probe microscopes with programmable peripheral instrumentation, highlighting the design choices that are necessary for maximizing the capability of the system and the ease of use for both human and AI agents. The benefits of making heterogeneous scientific instruments accessible, composable and usable by agents is demonstrated by test cases.
Read the full abstract

All authors Yongtao Liu, Jawad Chowdhury, Ganesh Narasimha, Ralph Bulanadi, Liam Collins, Ruben Millan Solsona, Marti Checa, Asraful Haque, Sumner B. Harris, Stephen Jesse, Rama Vasudevan

Friday 24 July

Statistical Mechanics · Cross-listed from physics.data-an

Data Field Theory: Theory and Applications of the Functional Renormalization Group for Signal Detection

Riccardo Finotello, Vincent Lahoche, Dine Ousmane Samary et al. (+1 more)

We review the renormalization group framework for signal detection in high-dimensional data, tailored to the regime where the signal may be of extensive rank and does not separate from the noise bulk as isolated spikes. The framework provides a conceptually simple criterion for distinguishing signal from noise within a quasi-continuous spectral region near a random-matrix universality class. This scenario lies beyond the reach of standard methods such as the Baik-Ben Arous-Péché threshold, which requires eigenvalues to be cleanly separated from the bulk. The renormalization group approach, by contrast, directly tracks spectral deformations and consistently yields a lower limit of detection without relying on spike separation. We review results that identify the presence of a signal by testing the stability of the Gaussian fixed point of an effective field theory for the collective behaviour of the degrees of freedom in the spectral tail, where the signal resides. We also discuss how the scale dependence of the canonical dimension, induced by the signal, manifests as a dimensional phase transition.
Read the full abstract

All authors Riccardo Finotello, Vincent Lahoche, Dine Ousmane Samary, Parham Radpay

Strongly Correlated Electrons

Single crystal growth, structural and magnetic properties of CeZn$_{2-x}$Ga$_{2+x}$

Danila Sokratov, H. Cein Mandujano, Ram Kumar et al. (+9 more)

The tetragonal BaAl$_4$ ($I4/mmm$) parent structure underpins a diverse family of materials exhibiting novel phenomena, including nematic superconductivity, topological semimetallicity, and heavy fermion behavior. The recent growth of ternary R-Zn-Ga compounds, such as the previously reported CeZn$_2$Ga$_2$, has explored some of the members exhibiting rare-earth magnetism within this family. In this paper, we report on the structural and magnetic properties of single crystals of CeZn$_{2-x}$Ga$_{2+x}$, a Ga-rich analogue of CeZn$_2$Ga$_2$. Our CeZn$_{2-x}$Ga$_{2+x}$ samples exhibit magnetic properties distinct from the paramagnetic behavior previously reported for CeZn$_2$Ga$_2$. We observe a magnetic transition around 4 K, pronounced metamagnetic states at low temperatures, and strong magnetic anisotropy. Though there are batch-to-batch variations that suggest a strong sensitivity to local structural imperfections, we consistently see the presence of magnetic transitions and metamagnetic states in our crystals. To investigate the local structural sensitivity hypothesis, we performed Reverse Monte Carlo analysis of collected powder neutron diffraction data, revealing the presence of significant local crystallographic disorder of the magnetic Ce site. Our findings demonstrate that the positional disorder drives competing ferromagnetic and antiferromagnetic correlations that lead to the observed spin glass behavior and complex anisotropic magnetism. This study illustrates that tuning the local crystallographic disorder enables engineering frustrated magnetic states in BaAl$_4$-type and similar intermetallic structures.
Read the full abstract

All authors Danila Sokratov, H. Cein Mandujano, Ram Kumar, Jared Z. Dans, Phineas Sobel, Nicholas A. Crombie, Alicia Manjón-Sanz, Danielle R. Yahne, Philip Piccoli, Peter Y. Zavalij, Efrain E. Rodriguez, Johnpierre Paglione

Quantum Gases

Emergent integrable dynamics in a non-integrable Rydberg-atom chain

Gianluca Morettini, Luca Capizzi, Leonardo Mazza et al. (+1 more)

We show that integrable and non-integrable dynamics can coexist in the same Rydberg-atom chain, depending on the initial state in which the system is prepared. In the setting we consider, Rydberg atoms mainly experience an effective dipolar interaction and, within the nearest-neighbor approximation, their dynamics can be mapped onto an effective integrable Fermi gas with ballistic transport. The inclusion of longer-range couplings, however, is essential for the theory to be predictive; those terms break the conservation laws associated with integrability, enabling, in particular, the emergence of genuine diffusive transport. We study the dynamics generated by a bipartition protocol and reveal a sharp qualitative change in behavior as the particle density is varied, suggesting the possibility of accessing weaker and stronger integrability breaking dynamics in the same Hamiltonian depending on the relevance of local interactions. We propose a theoretical mechanism that accounts for the differences. Our findings provide clear and concrete evidence that integrability breaking is not solely a property of the Hamiltonian and of the magnitude of the couplings that break integrability, but also of the state in which the system is prepared.
Read the full abstract

All authors Gianluca Morettini, Luca Capizzi, Leonardo Mazza, Maurizio Fagotti

Disordered Systems and Neural Networks · Cross-listed from physics.chem-ph

CP2K: An electronic structure and molecular dynamics software package - Dynamics, Transport, and Spectroscopic Response

Jan Wilhelm, Anna-Sophia Hehn, Hossam Elgabarty et al. (+39 more)

One of the distinguishing aspects of CP2K is its seamless integration of diverse structural and transition-state optimization techniques with advanced sampling approaches including Monte Carlo, molecular dynamics, and metadynamics, enabling the efficient exploration of complex potential- and free-energy landscapes, including rare events. These capabilities are combined with a broad hierarchy of energy and force evaluation methods, ranging from classical and machine-learned interaction potentials and mixed quantum-classical multiscale and semiempirical schemes, to highly accurate quantum-mechanical electronic-structure approaches. At the heart of the latter lies the Gaussian and plane-wave framework, along with its augmented all-electron generalization, which have been described in detail in our previous code review [T. D. Kühne et al., J. Chem. Phys. 152, 194103 (2020)]. Building on this foundation, the present work revisits the methods within CP2K that turn electronic structure into dynamics, transport, and spectroscopic response. Particular emphasis is placed on the coupling between static response calculations and nuclear motion: spectra may be evaluated at optimized structures, averaged over thermally sampled configurations, obtained from time-correlation functions along ab-initio or path integral molecular trajectories, or followed in real time together with electronic and nuclear dynamics. The same modular structure also enables equilibrium and biased transport simulations, from Kubo-type linear response to open-boundary approaches under external potentials, highlighting CP2K's unique capability to unify quantum chemistry with quantum and statistical mechanics within a versatile, holistic simulation environment.
Read the full abstract

All authors Jan Wilhelm, Anna-Sophia Hehn, Hossam Elgabarty, Beliz Sertcan Gökmen, Maximilian Graml, Stepan Marek, Ritaj Tyagi, Frederick Stein, Johann V. Potoschnig, Augustin Bussy, Christian S. Ahart, Zehua Chen, Linnea Andersson, Zdenek Futera, Filip Ivanovic, Margherita Buraschi, Christoph Schran, Remi Pasquier, Leonard Prokisch, Bibek Samal, Jelena Schmitz, Shridhar Sanjay Shanbhag, Harald Forbert, Ole Schütt, Franz Pöschl, Sebastian Ehlert, Stefano Battaglia, Michele Nottoli, Benjamin Stamm, Vamsee Voora, Rustam Z. Khaliullin, Sergey K. Chulkov, Matt B. Watkins, Clotilde S. Cucinotta, Jochen Blumberger, Chao Zhang, Yang Yang, Dominik Marx, Matthias Krack, Jürg Hutter, Marcella Iannuzzi, Thomas D. Kühne

Soft Condensed Matter

From Local Structure to Thermodynamics and Transport of Water with Machine Learning Force Fields

Andreas Kretschmer, Florian Altmann, Nader Nour et al. (+2 more)

We evaluate machine learning force fields derived from different density functional theory exchange correlation functionals using the full six-dimensional pair correlation function of liquid water, three-body structural descriptors, excess entropy, and transport properties. The predicted microscopic structure and dynamics depend strongly on the underlying functional: neglecting dispersion produces pronounced overstructuring, overly negative excess entropy, and suppressed diffusion. Translational and orientational entropy contributions are tightly coupled and together exhibit a clear relationship with the reduced selfdiffusion coefficient. Among the tested models, RPBE-D3 provides the most consistent agreement with experiment across structural, thermodynamic, and transport properties. The classical SPC/E model serves as an additional reference and displays notable similarities to RPBE-D3, consistent with the comparable Born effective and partial charges of the two models.
Read the full abstract

All authors Andreas Kretschmer, Florian Altmann, Nader Nour, Alper T. Celebi, Markus Valtiner

Soft Condensed Matter

Bimodal colloids highlight the structural mirror of rigidity percolation and yielding

Robert A. Campbell, Ziye Zhuang, Ali Mohraz et al. (+1 more)

In metastable particulate gels, it is tempting to believe that the dynamic similarities between the fluid-to-solid non-linear phase transition of rigidity percolation and the solid-to-fluid transition that occurs during yielding represent mirror images of the same continuous process. Even though these behaviors are clearly dynamically similar, their multi-scale nature makes it difficult to determine if they could also follow a unified structural pathway. We know from model monodisperse colloidal gels that both yielding and the elastic modulus seem to be heavily influenced by a small subset of topologically distinct singly-connected bridges linking mesoscale features. Here we use particle simulations to examine the participation of different classes of particle-level bonds and their contributions to the bulk mechanical response. We find that rigidity is disproportionately supported by singly connected intercluster bridges, whereas yielding localizes at bonds with high edge-betweenness centrality (EBC); strikingly, these independently identified populations substantially overlap and perform comparable mechanical roles. Bimodality exposes this correspondence by concentrating large-particle contacts in both populations, thereby providing a compositional label for the common backbone. Thus, rigidity and yielding are opposing mechanical manifestations of the same mesoscale structure: the intercluster bottlenecks that establish rigidity are also the sites at which rigidity is preferentially lost.
Read the full abstract

All authors Robert A. Campbell, Ziye Zhuang, Ali Mohraz, Safa Jamali

Statistical Mechanics · Cross-listed from quant-ph

Universal scaling framework for parameterized quantum evolutions at criticality

Jan T. Schneider, Cristian Tabares, Alejandro González-Tudela et al. (+1 more)

Variational ansätze are a cornerstone of quantum many-body physics, providing compact approximations to complex ground states using finite resources. Recent quantum-technology advances have introduced a new class based on layered parameterized evolutions. Assessing whether they can represent critical ground states is challenging: correlations span all length scales, while finite circuit depth limits how far they extend. Building on finite-resource scaling from tensor networks, we assign each ansatz an emergent correlation length $\xi_D$, the longest range over which it faithfully captures critical correlations. Its growth with refinement parameter $D$, $\xi_D \propto D^\kappa$, defines an exponent $\kappa$ measuring how efficiently an architecture converts resources into long-distance correlations. Applying this framework to the critical transverse-field Ising model, with $D$ the circuit depth of parameterized evolutions, we compare ansätze with nearest-neighbor and long-range generators, and layers where generators act separately or combined. All ansätze are compatible with algebraic growth, but fitted exponents range from $\kappa\simeq1$ to $\kappa\simeq3$. Exponential interactions give the largest exponents, while power-law interactions stay close to nearest-neighbor behavior, showing long-range support alone gives no scaling advantage. Combined-generator layers generally outperform separable ones, so layer organization matters alongside interaction range. Finally, a quasiparticle analysis shows finite depth leaves an unresolved window of width $\xi_D^{-1}$ around the low-energy modes responsible for long-distance correlations. The emergent correlation length thus acts as an infrared resolution scale, providing a benchmark for critical-state preparation and a guide for designing resource-efficient variational architectures.
Read the full abstract

All authors Jan T. Schneider, Cristian Tabares, Alejandro González-Tudela, Luca Tagliacozzo

Mesoscale and Nanoscale Physics

Radiative spin caloritronics in nonreciprocal many-body systems

Philippe Ben-Abdallah

We predict the spin thermal Hall effect in nonreciprocal magneto-optical many-body systems, in which a longitudinal radiative heat current generates a transverse accumulation of the spin angular momentum carried by thermal photons. We show that this effect and the inverse spin thermal Hall effect constitute an Onsager-Casimir reciprocal pair, thereby establishing heat and photon spin as coupled transport channels in nonreciprocal photonic systems. The second law of thermodynamics imposes fundamental bounds on the spin-heat coupling, leading to a thermal-spin figure of merit that quantifies the efficiency of radiative spin-heat conversion. Our results establish a complete thermodynamic framework for photon spin caloritronics and lay the conceptual foundations for spin-controlled thermal radiation and nonreciprocal photonic thermal devices.
Read the full abstract

Strongly Correlated Electrons

New class of exactly flat topological bands - compact localised states protected by local graph topology

Tamaghna Hazra

Strongly correlated quantum matter is fundamentally defined by the tension between non-commuting quantum operators. Hamiltonians exhibiting macroscopic degeneracies are of general interest in this field because they imply an infinite susceptibility to any non-commuting perturbation. In moiré heterostructures, engineering such extensive degeneracies in the kinetic Hamiltonian creates a fertile garden for exotic strongly correlated phases of matter to emerge from the resulting flat bands. Here, we introduce a prescription to construct an infinite family of exact flat band Hamiltonians supported on the faces of arbitrary graphs. We demonstrate this algorithm on the faces of four Bravais lattices. Using a discrete graph generalization of the Atiyah-Singer index theorem, we prove that the extensive degeneracies of such face-graph Hamiltonians are protected by the local topology of the face-graph connectivity. The resulting macroscopic null spaces yield compact localised states that remain localised over time due to frustration in hopping pathways. We discuss the broad implications of such non-dispersing quantum modes in diverse settings, from arrested dynamics in quantum networks and quantum machine learning algorithms to Majorana-free topological quantum computation.
Read the full abstract

Disordered Systems and Neural Networks · Cross-listed from quant-ph

Practical advantage beyond the quadratic speedup limit with fully-quantum walks

Massimiliano Incudini and Guglielmo Mazzola

We introduce a new class of fully-quantum Metropolis walks in which both the proposal and acceptance steps are intrinsically quantum. Unlike standard quantum walks obtained by quantizing classically efficient Markov chains, our algorithm employs Hamiltonian simulation as a quantum-native proposal mechanism, enlarging the class of quantum walks beyond classical counterparts. We target the problem of sampling from the low-temperature Gibbs distribution of classical dense Ising models, within a fixed error in total variation distance. This approach achieves about a cubic polynomial asymptotic advantage over previous quantum-walks, resulting in a total sixth-degree polynomial queries speedup compared to the best classical walk. This shows that speedups beyond the widely assumed quadratic limit are possible within the quantum walk formalism. We perform a complete fault-tolerant compilation of all algorithmic primitives and benchmark against CPU, GPU, and FPGA implementations of the best classical Markov chain. Under identical hardware assumptions, the resulting advantage runtime crossover is reduced from approximately $10^3$ years for conventional quantum walks to less than one day. These results identify fully-quantum Markov chains as a promising route toward practical quantum advantage.
Read the full abstract