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Physics Condensed Matter

cond-mat Watch Condensed Matter

Saturday 3 October

Materials Science

Band Structure Modulation in Ternary-Based InAs/ AlAs1-xSbx /InAs1-xSbx Superlattices

Arash Dehzangi and Jiakai Li

This study demonstrates an overall view of recent quantum mechanical based modeling effort using empirical tight-binding method to expand the ability of calculation of electronic band structure for strained-layer superlattices composed of ternary InAs/InAs1-xSbx and InAs/InAs1-xSbx/AlAs1-xSbx materials. Using a modified sp3s* empirical tight-binding method and building the superlattice Hamiltonian, we demonstrate that combining the virtual crystal approximation with a bowing parameter for the s-on-site energy accurately predicts ternary superlattice behavior. We provide a comprehensive overview of our numerical simulations, which model diverse superlattice configurations ranging from long wavelength infrared range to wide-bandgap barrier architectures. Notably, the simulated energy levels strongly agree with experimental bandgap measurements of the ternary superlattices and their structural variants.
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Strongly Correlated Electrons

Magneto-transport and electronic structure studies of ternary antimonides, La$T$Sb$_2$ ($T$ = Cu, Ag)

Himanshu Pant, Neeraj Bhatt, Deepali Sharma et al. (+7 more)

We investigate Sb square net-based Dirac semimetallic ternary antimonides La$T$Sb$_2$ ($T$ = Cu, Ag) using magnetotransport and photoelectron spectroscopic studies, complemented by density functional theory (DFT) based ab initio calculations. Our results show that both compounds exhibit a positive temperature coefficient of resistivity, linear magnetoresistance (MR), and a deviation from Fermi liquid behaviour at low temperatures (2-30 K). But only $T$ = Ag compound exhibit signature of charge density wave (CDW) phenomena and the results of its temperature dependent MR data suggest that single-band semiclassical transport is not sufficient to understand the transport behaviour. $\text{DFT}+U$ studies show that in both samples, an on-site Coulomb interaction ($U$) for Cu 3$d$ and Ag 4$d$ electrons, in the presence of spin-orbit coupling (SOC) is required to reproduce experimental valence band spectra. Sb 3$d$, 4$d$ core-level spectra combined with $\text{DFT}+U$ calculations and La 3$d$ spectra confirm the presence and effects of inequivalent Sb sites for both the samples. In contrast to the $T$ = Cu compound, which follows expected temperature-dependent core-level sharpening, the $T$ = Ag compound exhibits an anomalous low-temperature broadening in the CDW phase. The analysis of Sb 3$d$ spectra suggests Sb square nets are linked to CDW phenomena in the $T$ = Ag compound. Temperature-dependent ultraviolet photoemission spectroscopic studies on $T$ = Ag show a small decrement in spectral DOS at the $\epsilon_F$ for the temperature below the CDW transition temperature. These core-level studies provide a valuable spectroscopic benchmark for comparing CDW and non-CDW systems and clarifying the role of local electronic environments in CDW formation.
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All authors Himanshu Pant, Neeraj Bhatt, Deepali Sharma, Asif Ali, A. Thamizhavel, Saurabh Singh, Kentaro Kuga, Tsunehiro Takeuchi, Ravi Shankar Singh, R. Bindu

Materials Science

Materials and Metrology for Out-of-Plane Damping-Like Spin-Orbit Torque

Xiaoxi Huang, Yuhan Liang, Orion Smedley et al. (+1 more)

A new generation of energy-efficient, high-density, and non-volatile memory devices could be enabled if a more efficient mechanism is developed for switching the magnetization orientation of nanoscale magnetic devices possessing perpendicular magnetic anisotropy. A promising strategy under widespread investigation is current-induced damping-like spin-orbit torque with a strong unconventional out-of-plane component, rather than only the conventional in-plane component. In recent years, such torques have been reported in a broad range of materials platforms, arising primarily from three classes of symmetry breaking within the material generating the torque: low crystal symmetry in single-crystalline materials, antiferromagnetic order, and ferromagnetic order. Despite this progress, the field remains fragmented. Measurements using different methods often disagree, artifacts have been misinterpreted, and qualitative observations are sometimes overinterpreted as evidence of technological promise. This Perspective will provide a critical overview of out-of-plane damping-like spin-orbit torques, analyzing the classes of materials which can generate such torques, the experimental methods by which the torques can be quantified, and the progress toward achieving torque efficiencies sufficient for scalable magnetic technologies.
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All authors Xiaoxi Huang, Yuhan Liang, Orion Smedley, Daniel C. Ralph

Statistical Mechanics · Cross-listed from physics.chem-ph

Dielectric Response of Short and Long Range Models of Nonuniform Liquids and Implications for Machine Learned Interatomic Potentials

Atul C. Thakur, Harender S. Dhattarwal and Richard C. Remsing

Dielectric screening of electric fields is modified by interfaces and confinement, and any accurate description of interfacial chemistry necessitates properly modeling the nonuniform dielectric tensor. However, models with short range interactions, such as local machine learned interatomic potentials (MLIPs), are increasingly used in simulations of molecular interfaces without quantitative understanding of their nonuniform dielectric response. To build this understanding, we use the framework provided by local molecular field (LMF) theory to quantify the roles of short and long range electrostatics in confined water. Short and long range models predict the same transverse dielectric profile but short range models predict qualitatively different longitudinal dielectric profiles than their long range counterparts. To understand these differences, we develop a Landau theory that shows that long range interactions stiffen polarization fluctuations by a factor of the bulk dielectric constant and reduce the interfacial polarization correlation length by an order of magnitude. LMF theory, which captures long range interactions with an averaged field, can correct the structure and dielectric response, but the standard fluctuation relation no longer holds. We derive a fluctuation relation and integral equation for LMF theory and demonstrate their accuracy for predicting longitudinal dielectric response. MLIPs that incorporate interfacial configurations in their training essentially learn a static mean field correction at the interface, such that the integral equation can be used to predict their nonuniform dielectric profile from polarization fluctuations. We also show that short range MLIPs can be combined with symmetry preserving mean field (SPMF) theory to provide a linear-scaling alternative for long range interactions and predicting nonuniform dielectric functions.
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Materials Science · Cross-listed from physics.atom-ph

Origin of the inhomogeneous linewidth in a solid state $^{229}$Th:CaF$_2$ nuclear clock

Kai Li, Tian Ooi, Jack F. Doyle et al. (+7 more)

Narrow linewidth (high-Q) quantum discriminators are essential for realizing solid-state $^{229}$Th nuclear clocks, yet the observed transition linewidths remain at the tens-to-hundreds-of-kilohertz level, far exceeding the sub-Hertz linewidth set by the radiative lifetime of the nuclear isomer. Here, we investigate the origin of this broadening in $^{229}$Th:CaF$_2$ through systematic measurements of the linewidth as functions of temperature, thorium concentration, and quadrupole state, accompanied by theoretical analysis and first-principle simulations. We find that the linewidth is independent of temperature, increases linearly with thorium concentration, and depends strongly on the quadrupole state. Data analysis identifies variations of the local electric-field gradient (EFG) as the dominant source of inhomogeneous broadening and reveals that the EFG disorder increases linearly with thorium concentration. The observed Lorentzian line shapes and linewidth linear concentration dependence are explained naturally from the $1/r^3$ scaling of a random distribution of long-range dopant-induced perturbations. Complementary atomistic and ab initio density-functional-theory calculations reproduce these characteristic features and provide insights into the microscopic defect configurations responsible for the broadening. These results establish the dominant broadening mechanism in solid-state $^{229}$Th and provide guidance for engineering nuclear-clock materials with reduced inhomogeneous broadening.
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All authors Kai Li, Tian Ooi, Jack F. Doyle, Konstantin Herb, Emil Pellett, Martin Pimon, Thorsten Schumm, Steven M. Girvin, Leo Radzihovsky, Jun Ye

Statistical Mechanics · Cross-listed from quant-ph

How to distinguish chaos from integrability using OTOC

Alexey Milekhin and Anders Wallberg

The decay of out-of-time-ordered correlators (OTOCs) to a small residual value signals the scrambling of quantum information. This behavior is generic: it occurs in both chaotic and interacting integrable many-body systems, and therefore cannot by itself distinguish between them. In this paper we analytically study the late-time saturation value of a closely related observable, operator purity, and show that its scaling with system size robustly distinguishes chaotic from integrable systems. Our approach is based on the Mazur bound, which provides concrete scaling estimates and makes explicit why the locality of integrable charges matters. We support our findings with numerical simulations of one-dimensional spin chains.
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Materials Science

Molecular Crystal Structure Prediction from Conditional Flow on the Unit Cells

Qiang Zhu and Yihan Weng

A molecular crystal structure is jointly described by its space group symmetry, unit cell, and the molecular alignment within the asymmetric unit. Concurrently predicting all three variables is a daunting task, as it mixes discrete symmetry choices with a high-dimensional search in the continuous space. To address this challenge, we decouple these variables using a three-step generation process. Specifically, we train a flow model to learn the conditional distribution of invariant lattice descriptors (e.g. direct- and reciprocal-lattice successive minima and Selling scalars) from a molecular graph, a Hall setting, and the number of molecules in the asymmetric unit ($Z'$). Using a two sequential quasi-random sampling processes, we first reconstruct the cell parameters that match the predicted lattice invariants and density requirements, and then conduct a molecular packing search within the give symmetry and unit cell constraint. On 84 single-component systems with $Z' \le 1$, our approach reproduces experimental matches for 83 systems; the remaining failure stems from force-field limitations in preserving the experimental structure. These results demonstrate that learned cell proposals can effectively support crystal structure prediction (CSP) for a given Hall setting and $Z'$, which may be extended to fully blind prediction with variable symmetry and $Z'$ settings in the future.
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Materials Science

MOSAIC: Addressing Space for Local, Steerable, and Scalable Atomistic Generation

Ishan Nadkarni, Sebastien Hamel, Flynn Walsh et al. (+1 more)

Generative models are opening new possibilities in molecular discovery and materials science. Realizing this potential, however, requires both local control over atomic placement and the ability to assemble large, heterogeneous structures. We introduce Mosaic, a hybrid mesh-particle representation that partitions space into anchored regions containing atom slots. Each slot encodes occupancy, atomic species, and a continuous displacement from its anchor, providing persistent spatial addresses for local conditioning, hierarchical generation, and scalable assembly. Because Mosaic defines a representation rather than a model, it can be paired with different generative backbones. With the molecular backbone held fixed, its local support and coordinate prior improve molecular connectivity and validity, the resulting model samples efficiently across molecular sizes and enables fine-grained spatial control. At larger material scales, the same representation enables generation of atomistic polycrystals conditioned on coarse spatial layouts. Most notably, locality turns large-scale generation into a bounded assembly problem, enabling structure generation with more than one million atoms. Together, this establishes local spatial addressing as a practical foundation for steerable generation of matter across scales, from individual molecules to large-scale structures of broader engineering significance.
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All authors Ishan Nadkarni, Sebastien Hamel, Flynn Walsh, Fei Zhou

Friday 2 October

Strongly Correlated Electrons

Disorder into Correlation: A Microscopic Mechanism for Sub-McIntyre Avalanche Noise

Shafat Shahnewaz, Hannaneh Karimi, Joe C. Campbell et al. (+1 more)

Avalanche multiplication is intrinsically stochastic, yet experiments reveal excess noise below the minimum predicted by McIntyre's local-field theory. The microscopic origin of this noise suppression remains incompletely understood. We show that polar-optical-phonon emission, confined to a narrow forward cone, competes with elastic alloy scattering that diffuses field-collimated hot carriers out of the cone. Suppressed phonon cooling narrows the ionization path beyond the dead space and synchronizes successive ionizations into a dynamic staircase. This explains the low noise of Sb-based alloys and HgCdTe and makes alloy disorder a design parameter.
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All authors Shafat Shahnewaz, Hannaneh Karimi, Joe C. Campbell, Avik W. Ghosh

Strongly Correlated Electrons

Correlated Low-Energy Model of Monolayer 1H-NbS$_2$: A cRPA+DMFT Study

Karollaine C. Leite, Jorge L. B. de Faria, Luiz Antonio Ribeiro Junior et al. (+3 more)

Monolayer $1\mathrm{H}\text{-}\mathrm{NbS}_2$ hosts a well-separated metallic band of predominant Nb-$d_{z^2}$ character, providing an ideal platform to probe electronic correlations within a single-band setting. In this work, we present a comprehensive study of $1\mathrm{H}\text{-}\mathrm{NbS}_2$ by combining first-principles Wannier interpolation, constrained random-phase approximation (cRPA), and DFT+DMFT. We show that an effective single-band model accurately captures the low-energy electronic structure, reproducing key experimental features from ARPES and STS $dI/dV$ spectra, including a characteristic Van Hove singularity. While static DFT+$U$ fails to describe the correlated metallic nature of the system, DFT+DMFT successfully accounts for the spectral weight redistribution and dynamic correlations. By defining the cRPA target subspace directly within the isolated Nb-$d_{z^2}$ band, we obtain a renormalized local interaction of $U_{\mathrm{cRPA}} = 1.138~\mathrm{eV}$. This interaction stabilizes a strongly correlated metallic state that remains robust upon cooling. Remarkably, this minimal single-band model captures a spectral broadening similar to that previously reported in more elaborate treatments - incorporating larger local interactions ($U \sim 1.8~\mathrm{eV}$, derived from a multiorbital cRPA construction), intersite Coulomb terms ($V$), and electron-phonon coupling - demonstrating that a consistently downfolded local interaction alone can already capture key aspects of the experimentally observed low-energy behavior of monolayer $1\mathrm{H}\text{-}\mathrm{NbS}_2$.
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All authors Karollaine C. Leite, Jorge L. B. de Faria, Luiz Antonio Ribeiro Junior, Alexandre C. Dias, Helena Bragança, Alberto S. de Arruda

Materials Science

Agentic Resource Allocation for Batch Multi-Objective Bayesian Optimization in Autonomous Materials Discovery

Robert Robinson, Shakti Prasad Padhy, Sushant Sinha et al. (+6 more)

The discovery and development of advanced materials is a challenging process constrained by the high time and monetary costs of synthesis, processing, and characterization. The underlying design spaces can be enormous, often with multiple competing objectives. Bayesian optimization (BO) provides a principled approach for efficiently navigating such spaces, but most workflows rely on fixed exploration-exploitation policies that lack the capacity to adapt to shifting constraints in dynamic campaigns typical of self-driving laboratories. In this work, we develop a multi-objective BO framework for alloy design under resource constraints, benchmarking strategies for adaptive policy tuning at each iteration. Our evaluation covers a septenary refractory high-entropy alloy (RHEA) system focused on maximizing melting temperature and minimizing density, and an Fe-Co-Ni-based soft magnetic alloy system targeting saturation magnetization, coercivity, and hardness. We compare an exploitation-focused strategy, a fixed mixed exploratory/exploitative policy, and two distinct LLM-based adaptive strategies with different approaches to batch allocation and campaign signal interpretation, evaluated across baseline and mid-campaign resource event conditions including budget reductions, timeline cuts, and combined disruptions. Our results show that mixed allocation strategies accumulate substantially more mutual information than the exploitation-focused baseline at a proportionally smaller cost to hypervolume and optimization speed, with adaptive strategies outperforming a fixed-mixed allocation policy by adjusting their allocation in response to both evolving campaign statistics and resource constraints. These findings suggest that adaptive resource allocation offers a favorable tradeoff for materials discovery campaigns in reducing predictive uncertainty on Pareto-optimal compositions.
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All authors Robert Robinson, Shakti Prasad Padhy, Sushant Sinha, Sk Md Ahnaf Akif Alvi, Juan Florez Coronel, Brent Vela, Trevor Hastings, Douglas Allaire, Raymundo Arróyave

Materials Science

Distilling universal machine-learning potentials for moiré lattices across one million atoms

Thomas Huang, Yueyao Fan, Kaichen Xie et al. (+7 more)

Atomic reconstruction reshapes moiré materials across multiple scales, from local structure and polarization textures to global electronic topology, yet direct ab initio modeling becomes prohibitive for large superstructures such as marginal-twist-angle moirés and moiré-of-moirés. We develop MoiréMLIP by fine-tuning a universal atomistic model on the density functional theory labeled Moiré Kaleidoscope dataset, which spans transition metal dichalcogenide compositions, symmetries, stackings, and twist angles. MoiréMLIP reproduces ab initio reconstruction with force errors of 6–8\,meV/Å and transfers to smaller twist angles and unseen structures. Knowledge distillation yields MoiréMLIP-mini, which retains this accuracy while extending single-GPU inference to one million atoms. Applied to an alternate-twist MoTe$_2$ trilayer, it reveals a hierarchical polarization network spanning tens of nanometers arising from large moiré-cell distortions sharply localized along the moiré-of-moiré domain walls. These results overcome key accuracy, transferability, and scaling bottlenecks of existing atomistic models and enable predictive simulations across emergent moiré length scales.
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All authors Thomas Huang, Yueyao Fan, Kaichen Xie, Bolun Li, Kaijie Yang, Jenna A. Bilbrey, Eric Bylaska, Peter V. Sushko, Di Xiao, Ting Cao

Mesoscale and Nanoscale Physics

Exchange-controlled quantum beats and entanglement in an exciton–bimodal-cavity system

Cesar E. P. Villegas, Victor P. Brasil, Pedro A. S. Contri et al. (+2 more)

We theoretically demonstrate tunable population transfer and entanglement generation in a two-exciton system coupled to a bimodal optical cavity, including an exciton-exciton exchange interaction. By using dressed-state transformations and Löwdin partitioning, we derive effective Hamiltonians that identify three dynamical time scales: local polaritonic oscillations, long-period dressed-state beats, and direct excitonic exchange. We apply the framework to graphene nanoribbon excitons, using excitonic energies, transition dipoles, and lifetimes obtained from first-principles calculations to parameterize the model. In the small- and moderate-exchange regimes, the dynamics become multiscale, and the beat channel sustains sizable quantum entanglement over long dissipative time windows. In the large-exchange regime, the excitonic Hamiltonian dominates and drives nearly complete population transfer between excitonic states over many coherent cycles. The resulting analytical expressions provide direct design rules connecting the beat period, transfer amplitude, and coherent-cycle number to the exchange interaction, cavity detuning, and light–matter coupling. Our results establish a controllable route for engineering long-lived entanglement and coherent excitonic operations in exciton–bimodal-cavity systems.
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All authors Cesar E. P. Villegas, Victor P. Brasil, Pedro A. S. Contri, Kevin Lizárraga, Jonas Maziero

Statistical Mechanics · Cross-listed from q-bio.PE

Fluctuation theorems and exact multi-allele fixation probabilities

Emil A. Yuzbashyan, Alexander Feigel and Alexandre V. Morozov

A mutant gene that appears in a finite population will, in the long run, either disappear from it or become fixed, so that all members of the population will carry a copy of the mutant gene. Determining the fixation probability of a mutant gene is thus a prerequisite for modeling evolutionary dynamics in finite populations. Within the diffusion theory framework, the mutant's competition with the wild-type genes is described by the closed-form solution of a one-dimensional backward Kolmogorov equation for the mutant fixation probability, derived by Motoo Kimura in 1962. However, in asexual populations the rate of adaptation and the relative importance of alternative evolutionary pathways are shaped by clonal interference - the competition between several lineages arising from distinct beneficial or deleterious mutations. Quantitative descriptions of clonal interference require computing fixation probabilities in populations where multiple alleles are present simultaneously - a formidable mathematical problem which amounts to solving a multi-dimensional backward Kolmogorov equation. Here, we employ fluctuation theorems (a set of exact equalities in non-equilibrium statistical mechanics) in order to re-derive Kimura's fixation probability formula. When extended to multi-allele systems, fluctuation theorems provide a constraint which must be satisfied by any valid set of fixation probabilities. Moreover, we present a recursive analytical solution of the multi-allele fixation probability problem. We use our formalism to study the fate of a novel beneficial mutation in a clonal interference scenario, discovering substantial deviations between our exact treatment and the mean-field approximation in which the target mutation competes with a single effective genotype. Our formalism can be used to replace both explicit simulations and approximate analytical results in models of asexual evolution.
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Materials Science

Studying the evolution of exchange and dipolar interactions and spin correlation in vdW magnet CrCl3 across magnetic phases

Prem B. Karki, Ayodimeji E. Aregbesola, Karishma Prasad et al. (+5 more)

Understanding quantum interactions in van der Waals magnets are critical to realizing their potential for next-generation magnetic, electronic, and spintronic applications. In this study, we investigated the evolution of exchange and dipole-dipole interactions in van der Waals magnet CrCl3 using multifrequency broadband (1-16 GHz) magnetic resonance on a bulk single-crystal CrCl3 sample. We found that the dipolar-broadened low-field resonance linewidth narrows due to exchange narrowing at higher resonance fields. Our findings show that the exchange interaction evolves exponentially as we lower the sample temperature from room temperature to 50 K. However, we found that the dipole-dipole interaction remains constant in the same temperature range. We have also detected the half-field magnetic resonance transition at room temperature, indicating a robust dipole-dipole interaction among spins. The measured inter-spin distance is 2.4(3) A at room temperature. The evolution of dipole interactions, the observation of half-field magnetic resonance, and the strong exchange interaction indicate short-range ordering/correlation in CrCl3 at temperatures far above the magnetic global ordering temperature. This study also demonstrates the significance and sensitivity of the multifrequency electron spin resonance technique for understanding quantum interactions and magnetic correlations in van der Waals magnetic materials.
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All authors Prem B. Karki, Ayodimeji E. Aregbesola, Karishma Prasad, Jonathan Skeels, Avani Inamdar, Pooja Kalal, Jian Wang, Kapildeb Ambal*

Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

Energy-filtered readout preserves gap-enhanced sensing in interacting quantum dots

Shirwan Abdullah

A small excitation gap makes a quantum dot a sensitive probe of a weak electric field, but the charge detector that reads the probe can also excite it. We ask how much of this gap enhancement survives continuous readout, for two interacting electrons tuned through a confinement-driven crossover in a gate-defined quantum dot, using a weak-coupling, stationary two-level model. The answer depends on the energy structure of the detector, not only on its noise. A quantum point contact measures more strongly at higher bias, but once the bias energy exceeds the gap it also excites the probe. When this back-action dominates the probe's own relaxation, the optimised mean-current information rate grows only as the inverse of the gap. A sensor quantum dot with a narrow level instead reaches full measurement strength at a bias below the gap, where, for a non-interacting detector and to second order in the coupling, it cannot excite the probe at zero temperature. This energy-filtered readout keeps the inverse-square gap dependence of the quantum Fisher information, down to a gap set by the detector's level width and the electron temperature. Through such a detector the interacting pair gives about three times the information rate of a single electron with the same gap and detector, compared with 1.6-1.7 in the quantum Fisher information, for both contact and Coulomb-type interactions. These different gap dependences, and the different optimal biases of the two detectors, can be tested by bias and gate sweeps on suitably tuned charge-sensed double dots.
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Statistical Mechanics

Casimir Force, Magnetization, and Susceptibility for \\ Ising Chain with an Impurity Atom in the Presence of an External Field

Daniel Dantchev

The article contains exact results for the behavior of the Casimir force of Ising chain of $N$ atoms containing an impurity atom. The force is considered as a function of $N$ and on both the temperature $T$ and the external magnetic field $h$. The interactions between nearest neighbors within the chain are supposed to be of a ferromagnetic short-ranged type $J>0$. The impurity atom interacts with constants $J_{ia}$ with its nearest neighbors, where $J_{ia}$ can be both of ferromagnetic type, i.e., $J_{ia}>0$, as well as of antiferromagnetic type, i.e., $J_{ia}<0$. It turns out that the Casimir force can be both attractive or repulsive, depending on the sign and the magnitude of the ratio $J_{ia}/J$.
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Strongly Correlated Electrons

ToF-PAX-RIXS: A Time-of-Flight Spectrometer for combined ARPES and RIXS

Chafic Fawaz, Tom Lacmannn, Yaryna Lytvynenko et al. (+24 more)

We present ToF-PAX-RIXS, a compact instrument that combines time-of-flight momentum-microscopy angle-resolved photoemission spectroscopy (ARPES) with resonant inelastic X-ray scattering (RIXS). The latter is based on photoelectron spectrometry for analysis of X-rays (PAX). The two techniques are implemented with a single multimode electron-optical column, allowing measurements to be performed sequentially on the same sample under identical experimental conditions. In ARPES mode, the instrument records the photoemission intensity as a function of kinetic energy and two in-plane momentum components. In PAX-RIXS mode, scattered soft X-ray photons are absorbed in a thin metallic converter, and the generated photoelectrons are analyzed in energy and position of emission on the converter. The electron kinetic energy retains the spectral information of the scattered photons, while the position is related to the scattering angle and therefore to the momentum transfer, enabling simultaneous access to a finite momentum-transfer interval. We describe the mechanical design, converter assembly, scattering geometry, and multimode electron optics of the instrument. Its PAX-RIXS performance is benchmarked at the Cu $L_3$ edge using CaCuO$_2$, with Au, Ag, and Pt converters. The measured spectra reproduce the principal features obtained with a conventional grating RIXS spectrometer, and deconvolution yields an effective reconstructed energy resolution better than $120$~meV under the present conditions. Finally, combined ARPES and PAX-RIXS measurements on the same Ca-doped YBa$_2$Cu$_3$O$_{6.45}$ sample demonstrate the capability of the instrument to correlate electronic structure and collective excitations within a common compact platform.
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All authors Chafic Fawaz, Tom Lacmannn, Yaryna Lytvynenko, Sergii Chernov, Olena Tkach, Siegmar Roth, Jan O. Schunck, Amon Lanz, Jakob Dilling, Lukas Bruckmeier, Markus Scholz, Frank Scholz, Arne Meyer, Dirk Fuchs, Lara Schmieder, Yiran Liu, Matteo Minola, Bernhard Keimer, Dmytro Kutnyakhov, Kai Rossnagel, Olena Fedchenko, Angela Wittmann, Moritz Hoesch, Gerd Schönhense, Matthieu Le Tacon, Hans-Joachim Elmers, Martin Beye

Statistical Mechanics

Transport, Hall Effect, and Collective Dynamics of Driven Particles in Active Chiral Media

C. Reichhardt and C.J.O. Reichhardt

We examine the dc driven transport of particles with Yukawa interactions through an assembly of chiral active particles undergoing circular motion. The driven particles exhibit a jammed phase, a nonlinear disordered or plastic regime where there is a finite Hall effect produced by interactions with the active chiral particles, and a high drive linear regime where the driven and nondriven particles phase separate and the Hall effect nearly disappears. The chiral particles experience strong drag and Hall effects from the driven particles, and these effects vary monotonically with changing thermal fluctuations or chiral motion parameters. The different dynamical phases are correlated with features in the longitudinal and transverse transport curves, and we map out the phases as a function of active orbit size, thermal fluctuations, and particle density.
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Materials Science

Equivariant generative diffusion learns and generalizes the structural ensemble of amorphous oxides

Jun Jiang, Ian Berry, James N. Fry et al. (+1 more)

Amorphous materials are statistical ensembles rather than definitive structures, and conventional density-functional (DFT) and machine-learned-potential simulations sample only a small part of that ensemble. We present an $SE(3)$-equivariant denoising-diffusion model that learns the configurational distribution of amorphous oxides, so the model itself is the structure database. The learning is data efficient. A model trained on $1{,}781$ DFT configurations suffices to reproduce partial radial distribution functions, coordination statistics and bond-angle distributions, and to generate models of over $3\times10^{5}$ atoms at a cost comparable to that of the cheapest classical pair potentials. The trained model can propose amorphous atomic structures for first-principles relaxation to explore the configuration space. For example, it locates an amorphous Zr-Ta-O structure $36$ meV/atom below the previously known minimum. Generation can also extend beyond trained conditions to non-stoichiometric compositions, other mass densities, interfaces, and doping. First-principles verification confirms that generation can be steered to a requested energy, and shows that the denoising training loss does not rank generative quality, because the two measure different things.
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All authors Jun Jiang, Ian Berry, James N. Fry, Hai-Ping Cheng

Disordered Systems and Neural Networks · Cross-listed from cs.LG

Probabilistic Algorithms for Ising Machines from Optimization to Generative AI

Corentin Delacour, Xiuqi Zhang, Abdelrahman S. Abdelrahman et al. (+4 more)

Ising machines have emerged as promising hardware accelerators for intractable optimization and sampling problems, yet their practical impact increasingly hinges on the co-design of algorithms and hardware, where algorithmic demands shape new architectures and new hardware capabilities inspire entirely new algorithms. In this Review, we survey probabilistic algorithms designed for portability across diverse Ising platforms, advocating a top-down perspective that prioritizes principled methods with provable guarantees. We cover foundational methods such as simulated annealing and parallel tempering, including two-dimensional extensions that natively encode hard constraints, and examine approaches that expand the scale of solvable problems from cluster mean-field methods to variational samplers. We highlight the Probabilistic Approximate Optimization Algorithm (PAOA), a classical analog of QAOA that emerged directly from probabilistic hardware development, and explore how generative AI and Ising machines might reinforce each other: learned models propose global moves to accelerate optimization, while probabilistic techniques improve inference in large language models. Much as quantum computing has seen algorithms co-evolve with hardware, probabilistic and Ising computing stand at a similar inflection point. We outline a co-design framework for accelerating the capabilities and adoption of next-generation Ising machines.
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All authors Corentin Delacour, Xiuqi Zhang, Abdelrahman S. Abdelrahman, Saleh Bunaiyan, Kyle Lee, Shuvro Chowdhury, Kerem Y. Camsari

Statistical Mechanics · Cross-listed from math-ph

Branching Gaps, Coexistence, and Boundary Influence for the Ising Model on Spherically Symmetric Trees

Farrukh Mukhamedov and Otabek Khakimov

In this paper, we study the ferromagnetic nearest-neighbor Ising model on rooted spherically symmetric trees with one or \(q\) children per vertex, according to a prescribed sequence of branching levels. Unbounded runs of one-child levels force uniqueness at every nonzero homogeneous field and every finite inverse temperature. We quantify this effect through the locations of sufficiently long nonbranching stretches. Conversely, uniqueness need not entail any uniform rate: for each prescribed vanishing sequence, we construct a density-one tree whose finite-volume boundary influence decays more slowly along a subsequence. The tree retains branching number \(q\), although its nonzero-field coexistence region disappears. For eventually bounded gaps, we prove an optimal uniform comparison with the periodic tree having the largest allowed gap and obtain an explicit interval of coexistence fields. Thus bounded gaps are equivalent, within this family, to coexistence at some finite temperature and nonzero field. For eventually periodic gaps, Gibbs uniqueness is equivalent to fixed-point uniqueness of the full-period return map. A negative Schwarzian derivative yields a complete classification: in the supercritical regime the map has three fixed points inside a closed coexistence interval, two at its endpoints, and one outside. The nonzero endpoints are automatically nondegenerate folds, with square-root splitting of the merging branches.
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Statistical Mechanics

An Absorbing State Model with an Emergent Ising Transition

Shen Ai, Dov Levine and Paul Chaikin

We study a dynamical model of repulsive needles with centers fixed on a square lattice. Needles that overlap are active and receive a repulsive rotation $ \theta \in [0,\epsilon)$; needles with no overlap do not move. This model exhibits an absorbing state transition. Nematic order was observed for long needles. For a range of needle lengths and $\epsilon$, the system self-organizes into a state with checkerboard symmetry. As $\epsilon$ is increased, this phase melts and becomes disordered. Remarkably, we find that this phase boundary exhibits critical exponents identical to those of the equilibrium 2D Ising model.
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Mesoscale and Nanoscale Physics

Escaping the Composite Fermi Sea: An Incompressible State at Half Filling in Graphene's Lowest Landau Level

Domagoj Perkovic, Ziwei Wang and Steven Herbert Simon

Recent experiments in monolayer and trilayer graphene have observed incompressible even-denominator fractional quantum Hall states within narrow regions of parameter space associated with crossings of zeroth Landau levels. This is surprising because at half filling the Coulomb interaction in the zeroth Landau level is expected to favour a compressible composite Fermi liquid. Here we provide the first quantitative energetic study of the candidate incompressible phases and of the microscopic mechanisms that can stabilise them near such Landau-level crossings. Using exact diagonalization and infinite density-matrix renormalisation group, we first study ultra-short-range corrections to the Coulomb interaction arising from finite layer separation, lattice-scale effects, and electron-phonon coupling. We find that a sufficiently strong attractive short-range interaction drives the composite Fermi liquid first into a weakly paired \(d\)-wave pseudospin-singlet state and subsequently into a strongly paired state. However, microscopic estimates of these short-range corrections are far too small to stabilise either incompressible phase. We then incorporate Landau-level mixing through screening within the random-phase approximation. Screening substantially reshapes the effective interaction, suppresses the weak-pairing regime, and strongly enhances the tendency toward strong pairing. For a realistic range of microscopic parameters, the strongly paired phase is stabilised over a substantial fraction of that range. Our results identify the interplay of Landau-level mixing and ultra-short-range interactions as a plausible microscopic mechanism for the experimentally observed incompressible states in monolayer and trilayer graphene and point toward a strongly paired composite-fermion phase as their candidate ground state.
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Strongly Correlated Electrons · Cross-listed from quant-ph

Magic Quantum Code Surgery

Kathleen Chang, Anasuya Lyons, Yuanjie Ren et al. (+5 more)

Non-Clifford operations required for universal quantum computation can be implemented by measuring logical Clifford operators. We present a generalized framework to fault-tolerantly measure transversal Clifford logical operators in quantum low-density parity check (QLDPC) codes. Our protocol takes any QLDPC code and deforms the code across additional ancillary qubits such that a product of stabilizers measures the desired logical Clifford operator. We prove that the deformed, Clifford-stabilized code remains LDPC and that its distance is preserved up to a constant factor independent of the number of physical qubits. We further prove that the Clifford measurement has a fault distance against data qubit and measurement errors that grows linearly with the distance of the original code. We apply our methods to implement logical non-Clifford gates in algorithmically relevant subroutines and to prepare magic states in quantum stabilizer codes.
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All authors Kathleen Chang, Anasuya Lyons, Yuanjie Ren, Harald Putterman, Nathanan Tantivasadakarn, Victor V. Albert, Benjamin J. Brown, Dominic J. Williamson

Statistical Mechanics · Cross-listed from quant-ph

Efficient Quantum Monte Carlo through Cluster Expansions

Jorge Sánchez-Segovia and Álvaro M. Alhambra

The sign problem remains a major obstacle to extending the success of Monte Carlo methods to generic quantum many-body systems. A powerful alternative relies on cluster expansions, which provide convergent representations of free energies and related quantities, with applications ranging from tensor network contractions to quantum dynamics and circuits. Within their convergence regime, these expansions often yield deterministic polynomial-time algorithms. However, such methods require exhaustive enumeration of connected clusters, leading to a computational overhead of $(N\varepsilon^{-1})^{\mathcal{O}(\log\Delta)}$, where $N$ is the system size, $\varepsilon$ the desired precision, and $\Delta$ the interaction-graph degree. This becomes particularly severe in long-range systems, where $\Delta\equiv N$, resulting in quasi-polynomial runtimes. Here, we introduce a Markov chain algorithm that samples cluster expansions directly in the space of connected clusters, replacing deterministic enumeration by Monte Carlo sampling. Because sampling occurs in an abstract cluster space rather than a physical configuration space, the conventional exponential sign problem is absent within the convergence regime. For general polymer models, we establish an FPRAS with runtime $\tilde{\mathcal{O}}(N^4\varepsilon^{-3})$. For quantum partition functions at temperatures $\beta\leq\beta_{\mathrm{sampling}}\equiv\mathcal{O}(1)$, this improves to $\tilde{\mathcal{O}}(N^{3+1/D}\varepsilon^{-3})$, where $D$ is the lattice dimension. The framework directly applies to long-range quantum systems with interactions $\propto1/r^\alpha$, including $2$-local models with $\alpha>2D$.
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Mesoscale and Nanoscale Physics

Integrating spin glass dynamics into nanomechanical resonators

S.Y. Grebenchuk, T.M. Savilov, Y.W. Ho et al. (+15 more)

Spin glasses are non-equilibrium magnetic systems with pronounced slow relaxation, ageing, and chaotic, synaptic-like properties, whose unique history-dependent dynamics have remained difficult to harness in functional devices. Two-dimensional van der Waals spin-glass magnets offer a route to overcome this limitation by allowing controlled coupling between magnetic and mechanical degrees of freedom. Here, we demonstrate the integration of a spin-glass functionality in nanoelectromechanical systems (NEMS) using thin exfoliated NbFeTe$_2$ films, which establishes a robust spin-glass state down to a few tens of nanometer-thick layers. Using cryogenic magnetic force microscopy, we reveal characteristic slow, hour-scale macroscopic magnetic relaxation, associated with glassy reorganisation of its magnetic domain clusters. Incorporation of thin NbFeTe$_2$ into membrane resonators allows the transduction of this glassy magnetic domain relaxation into strain, shifting their mechanical resonance frequency. This provides a functional nanomechanical readout of spin-glass dynamics and establishes a versatile platform for integrating frustrated magnetism into NEMS.
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All authors S.Y. Grebenchuk, T.M. Savilov, Y.W. Ho, A.K. Grebenko, M. Kravtsov, J.M. Wolf, D.A. Litvinov, Z. Yang, P. Cai, S. Ramachandran, R. Duan, L. Zheng, B. Özyilmaz, G. Eda, E.J.G. Santos, M. Koperski, K.S. Novoselov, M. Šiškins

Statistical Mechanics · Cross-listed from quant-ph

Exact Temporal Criticalities of Entanglement and Negativity in Gaussian and Non-Gaussian Dissipative Kitaev Chains

Shrey Chowdhary, Sanket Chirame, Stephan Haas et al. (+1 more)

When the two largest eigenvalues of an entanglement or negativity spectrum meet, the gap of the corresponding entanglement or negativity Hamiltonian closes while entropies stay smooth, an event we call a temporal criticality. We ask when such criticalities occur in open fermionic systems, in which order, and whether they precede the geometric decoherence time, at which the negativity starts to fall. We compare loss and gain, which respect fermion parity only on average (weak symmetry) and keep the state Gaussian, with density dephasing, which respects it in every jump (strong symmetry) and makes the state non-Gaussian. We find that Gaussianity, rather than the symmetry, fixes the criterion for a criticality. In a Gaussian state the entanglement gap of a subsystem closes exactly when its two parity sectors carry equal weight, and the negativity gap closes exactly when this happens for the subsystem or its complement, so the negativity criticality never comes after the entanglement one. Uniform balanced loss and gain only shrink the two parities and leave both criticalities in place at every rate, for any quadratic Hamiltonian. In an open Kitaev chain, weak imbalanced loss and gain shift the criticalities by amounts set by the occupations at the cut, and at strong rates they allow a closing near the relaxation time only when an odd number of neighboring sites pass half filling. For dephasing we solve the non-Gaussian dynamics exactly at the point where the bond terms of the chain commute. Weak dephasing delays both criticalities and, away from the chain ends, moves them ahead of the parity balance, where the parity rules of Gaussian states would place them. As the dephasing rate approaches critical damping, both criticalities recede to infinite time, and at strong dephasing the negativity starts to fall long before either gap begins to shrink.
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All authors Shrey Chowdhary, Sanket Chirame, Stephan Haas, Rishabh Jha

Strongly Correlated Electrons

The ALPS project release 3.0: open source software for strongly correlated systems

F. Alet, T. Chen, A. Feiguin et al. (+16 more)

We present release 3.0 of the ALPS (Algorithms and Libraries for Physics Simulations) project, an open-source software project to develop libraries and application programs for the simulation of strongly correlated quantum lattice models such as quantum magnets, lattice bosons, and strongly correlated fermion systems. As in previous releases, development is centered on common data formats, on libraries to simplify and speed up code development, and on full-featured simulation programs that let non-experts carry out serial or parallel numerical simulations using the important algorithms for quantum lattice models: classical and quantum Monte Carlo (QMC) using non-local updates, extended-ensemble simulations, exact and full diagonalization (ED), the density matrix renormalization group (DMRG), and continuous-time QMC solvers for dynamical mean-field theory (DMFT). Major changes in release 3.0 include distribution of the pyalps binary through the Python Package Index (pip install pyalps) and through Spack for HPC systems; migration of development to GitHub with continuous integration and automated testing; relicensing of the package under the permissive MIT license; a rebuilt documentation and tutorial website, including a set of Jupyter-notebook tutorials and localized content; a broad modernization of the C++ codebase (C++17 compliance, Boost and NumPy 2.0 compatibility, and warning and dead-code cleanup) together with a major DMRG update and associated reliability and build-compatibility fixes; the removal of legacy components (the VisTrails provenance integration and the TEBD, MPS, and directed-worm-algorithm application codes); archival of release 3.0.0 with a Zenodo DOI; and a formal governance and sustainability model developed under the US National Science Foundation (NSF) POSE program. The software is available at https://alps.comp-phys.org.
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All authors F. Alet, T. Chen, A. Feiguin, E. Gull, S. Iskakov, J. P. F. LeBlanc, F. Lin, A. Mirmira, G. Möller, L. Pollet, M. Rosales, V. W. Scarola, H. Shinaoka, H. Terletska, S. Todo, M. Troyer, M. Wallerberger, P. Werner, T. M. R. Wolf

Statistical Mechanics · Cross-listed from quant-ph

On Information Propagation in Krylov Subspaces

Pablo Martinez-Azcona, Maximilian Meyer-Moelleringhof, Adolfo del Campo et al. (+1 more)

Krylov subspace methods provide an efficient tool for modeling any quantum initial value problem as a one dimensional chain. A time ordered path formulation, in which the dynamical generator successively splits probability between paths, yields a speed limit within such dynamical subspaces. For power law growing Lanczos coefficients $b_n \sim n^\delta$ we find super ballistic lightcones, with an exponentially spreading lightcone for maximal growth $\delta = 1$. Causality in the Krylov chain constrains the Lanczos coefficients to grow at most linearly. We illustrate the validity of the above in the $SL(2, R)$ and Heisenberg Weyl algebras, and in a many body skew field Ising model. Moreover, we extend the above bound to the family of $Q$ complexities. Lastly, mapping to a spin chain gives a Lieb Robinson bound analogue and opens the problem to standard condensed matter methods.
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All authors Pablo Martinez-Azcona, Maximilian Meyer-Moelleringhof, Adolfo del Campo, Apollonas S. Matsoukas-Roubeas