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Physics Condensed Matter

cond-mat Watch Condensed Matter

Friday 3 July

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

Community structure of the pseudofractal web

Alexei Vazquez

The Ramsey community number $r_\kappa$ is the smallest network size at which a graph is better described by a partition into communities than by no partition, under a prescribed detection rule. On a scale-free graph this question is confounded: a block model can split the network merely to absorb its degree distribution. I compute $r_\kappa$ analytically for the deterministic pseudofractal scale-free web of Dorogovtsev, Goltsev, and Mendes, separating genuine community structure from degree heterogeneity with two closed-form detection rules. Under a plain Bernoulli stochastic block model, the web's natural recursive bipartition is unpreferred while small and breaks at $r_\kappa=1095$ nodes, with a log-evidence growing as $(\ln 3-\tfrac{2}{3}\ln 2)n$. Under a degree-corrected model tested against the configuration-model null, the same partition survives, breaking far earlier at $r_\kappa=42$, with a log-evidence growing as $(2\ln 3-\tfrac{4}{3}\ln 2)n$ – exactly twice the plain slope, and independent of the prior. Degree correction reverses the ordering of the candidate cuts, demoting the hub-leaf split and elevating the recursive one. Because the web is self-similar, the best description is not two communities but a nested hierarchy: the degree-corrected evidence keeps rising as the partition is refined, and is maximised at of order $\sqrt{n}$ communities of $\sim\sqrt{n}$ nodes. A purely local recursive rule thus builds true hierarchical community structure, over and above the scale-free degree sequence it also produces, in an exactly solvable setting.
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Mesoscale and Nanoscale Physics

Hall Shift Current and Nonlinear Anomalous Hall Effect in Gapped Dirac Fermion Systems

Toshihito Osada

We discuss a new mechanism for the nonlinear anomalous Hall effect in tilted two-dimensional gapped Dirac fermion systems. This mechanism originates from a side-jump displacement associated with Landau-Zener tunneling across the mass gap. In lightly doped tilted Dirac systems with a small gap, this interband mechanism can contribute to the nonlinear anomalous Hall effect in addition to the conventional intraband mechanism arising from the Berry curvature dipole. It provides a possible explanation for the nonlinear Hall effect accompanied by nonlinear longitudinal transport observed in the organic Dirac fermion system {\alpha}-(ET)2I3 with an extremely small gap.
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Materials Science · Cross-listed from cs.CV

MatPhaseBench: A Semantics-Guided Benchmark for Materials Phase Diagrams Understanding

Hanwen Wang, Sihan Liang, Zhiwei Liu et al. (+4 more)

Materials phase diagrams are a core knowledge representation in materials science, encoding temperature,composition, phase stability, and phase transformation pathways, with their full understanding requiring thermodynamic mechanism analysis and scientific reasoning. Although VLMs have shown promise in scientific image understanding, their systematic evaluation on such logically complex images demanding deep mechanistic interpretation remains limited, and phase diagrams provide a challenging testbed for this purpose. We introduce MatPhaseBench, a high-quality, high-reliability benchmark for complex scientific image understanding, focused on materials phase diagrams. MatPhaseBench is constructed from 3681 papers in classical materials science journals, from which 200 high-quality diagram-text pairs were selected, covering 189 material systems and 70 elements. The benchmark has three key features: (1)targeting complex scientific image understanding-it moves beyond simple objective tests to open-ended tasks requiring deep comprehension; (2)comprehensive image-text alignment-semantic information associated with images is fully preserved during literature mining and matching; (3) high-quality human-supervised text acquisition-all descriptions undergo strict manual validation. Experimental results show that current VLMs remain substantially behind expert-level understanding: they are largely limited to surface visual perception, lack deep reasoning grounded in thermodynamic mechanisms, have limited domain awareness and expert analytical experience, and perform poorly in distinguishing fine-grained differences in composite or multi-diagram settings. Overall, MatPhaseBench constitutes a challenging research-grade benchmark, providing a foundational platform for complex scientific image understanding, phase diagram analysis, and trustworthy multi-modal AI in science.
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All authors Hanwen Wang, Sihan Liang, Zhiwei Liu, Yangang Wang, Wei Yan, Yuqin Liu, Zongguo Wang

Materials Science

Thermophysical and mechanical properties of UFe$_2$ fabricated by spark plasma sintering

Yifan Sun, Hironobu Nakamura, Daisuke Okada et al. (+3 more)

Following the accident at the Fukushima Daiichi Nuclear Power Plant in 2011, core meltdown produced fuel debris whose safe retrieval and management require reliable thermophysical and mechanical property data. Among the metallic phases identified in the debris, the U-Fe system is particularly important because of the abundant iron originating from in-vessel stainless steel structures. However, within this system, the high-temperature thermophysical properties of UFe$_2$ have received relatively little attention, with most prior studies focusing on its magnetic and electronic properties. To fill this data gap in the literature, we fabricated dense, nearly single-phase polycrystalline UFe$_2$ by arc melting followed by spark plasma sintering, and characterized its thermal and mechanical properties from room temperature to 1073 K. Results show that the thermal conductivity of UFe$_2$ increased monotonically from 10 Wm$^{-1}$K$^{-1}$ at 306 K to 25 Wm$^{-1}$K$^{-1}$ at 1073 K, surpassing those of the iron intermetallics Fe$_2$Zr and Fe$_2$B at high temperatures. In addition, UFe$_2$ is mechanically more compliant, displaying a Young's modulus $E$ of 69 GPa, a shear modulus $G$ of 24 GPa, and a Vickers hardness $H_{\mathrm{V}}$ of 5.6 GPa, all well below those of both Fe intermetallics. Consequently, during decommissioning, thermal-management and structural evaluations should take into account the comparatively high-conductivity and mechanically compliant nature of UFe$_2$ within the heterogeneous fuel debris.
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All authors Yifan Sun, Hironobu Nakamura, Daisuke Okada, Hiroaki Muta, Yuji Ohishi, Ken Kurosaki

Mesoscale and Nanoscale Physics

Electrically tunable interfacial thermal conduction via electronic structure engineering in ${Au}$/$Bi_{1-x}$$Sb_{x}$ topological insulators

Min Young Kim, Joon Sang Kang, Jangwoo Ha et al. (+8 more)

This work provides direct experimental evidence for the role of topological interface states in thermal conduction across a metal/topological insulator junction. It also shows that this conduction can be reversibly modulated by electrical current injection, offering a new approach toward active control of heat flow at solid-state interfaces. Specifically, the interfacial thermal conductance of ${Au}$/$Bi_{89}$$Sb_{11}$ and ${Au}$/$Bi_{87}$$Sb_{13}$ junctions demonstrates distinct temperature- and bias-dependent behavior. Both responses are attributed to carrier redistribution between topological interface and bulk band states, driven thermally by Fermi-Dirac broadening and electrically by quasi-Fermi-level shifts and WKB tunneling into nearby bulk bands. Control experiments using trivial semimetals and insulating interlayers further confirm the topological specificity of the effect. Such electrically tunable interfacial heat conduction positions interface electronic structure engineering as a promising route for active thermal management. In doing so, it lays the groundwork for a mechanically robust alternative to conventional structure-driven thermal control compatible with increasingly dense, high-power solid-state devices.
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All authors Min Young Kim, Joon Sang Kang, Jangwoo Ha, Hyungyu Jin, Sandy A. Ekahana, Pratik Saud, Chris Jozwiak, Eli Rotenberg, Aaron Bostwick, Jyoti Katoch, Joseph P. Heremans

Strongly Correlated Electrons · Cross-listed from hep-th

Learning Effective Bulk Fields from Fermionic Spectra: Application to an Extended Power-Law Liquid Model for Cuprate Strange Metals

Hong-Zhi Xiao, Zhan-Zhi He, Zhuo-Yu Xian et al. (+1 more)

We develop a Neural-ODE framework to infer effective bulk metric functions and the charge-weighted gauge potential from boundary fermionic spectra within a static, planar black-hole ansatz. Controlled benchmarks recover the known bulk profiles of the Einstein–Maxwell and Gubser–Rocha models. We then use normalized interaction self-energy targets generated from an extended power-law liquid model with parameters calibrated by angle-resolved photoemission measurements to test the proposed geometric explanation of cuprate strange-metal spectra in a semi-holographic setting. For this application, we use a massless probe in backgrounds with conformal-to-$\mathrm{AdS}_2\times\mathbb{R}^2$ asymptotics and derive a spectral extraction formula from the conserved radial Dirac flux. We identify coordinate/Weyl redundancy and a degeneracy in the scaled Hawking temperature of the normalized inverse problem. The conformal factor remains undetermined, so bulk entropy and the associated contribution to electronic specific heat require independent input. Low-temperature targets are fitted accurately across the studied doping range. In the high-temperature test, however, the present ansatz and optimization search have not yielded a refined geometry that accurately reproduces the thermal spectral shape while preserving frequency symmetry. These results may guide the further development of semi-holographic models for cuprates, and the framework may also find applications in other strongly correlated electron systems.
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All authors Hong-Zhi Xiao, Zhan-Zhi He, Zhuo-Yu Xian, Shao-Feng Wu

Materials Science · Cross-listed from physics.optics

Electron-beam Writing of Spectrally Uniform Green Single-photon Emitters in Hexagonal Boron Nitride

Qingsong Tao, Fuyi Zhou, Zhijie Li et al. (+16 more)

Scalable quantum photonic technologies require single-photon emitters whose positions and emission energies can be engineered simultaneously. Hexagonal boron nitride (hBN) is an attractive room-temperature host, but deterministic creation of spectrally reproducible emitters remains challenging. Here, we use a standard scanning electron microscope as a direct-writing tool to activate bright green single-photon emitters in hBN at predefined sites, without ion implantation or post-fabrication thermal annealing. The written emitters exhibit reproducible zero-phonon-line emission centered near 536 nm, room-temperature antibunching with g(2)(0) as low as 0.08, high brightness, strong linear polarization, and stable emission. Thickness-dependent activation, stacking experiments, cathodoluminescence spectroscopy, and first-principles calculations support a carbon-related defect complex as the most plausible origin of the emission. As a proof of nanophotonic compatibility, we further activate emitters in a nanoparticle-on-mirror plasmonic nanocavity and observe photoluminescence enhancement accompanied by shortened emission lifetimes. These results establish electron-beam direct writing as a practical route to site-selective, spectrally uniform green quantum emitters in hBN, offering a promising basis for integrated room-temperature quantum photonic architectures.
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All authors Qingsong Tao, Fuyi Zhou, Zhijie Li, Yihao Yan, Shuangyue Li, Yuelan Gao, Zijing Wu, Yizhou Liu, Tao Liang, Shuai Yuan, Dakun Wu, Hongzhi Zhou, Qi Zhang, Zhenyi Ni, Chunlei Yu, Pan Wang, Fei Yu, Lili Hu, Ning Zhou

Materials Science

Crystal structure and basic properties of dirhenate quantum materials

Danrui Ni, Xianghan Xu, Stephen Zhang et al. (+3 more)

The anhydrous divalent 3d-metal dirhenate quantum materials, M(ReO$_4$)$_2$,were synthesized using solid-state methods for M = Mn through Zn. Previously unreported Mg(ReO4)2 is also described. Their layered crystal structures, which feature an in-plane triangular lattice of M$^{2+}$, were refined using single crystal X-ray diffraction, and their optical absorption and several other physical properties were characterized. Their magnetism and heat capacity reveal long-range magnetic order at low temperatures in many of the M(ReO$_4$)$_2$ phases. Notably, many of these ordered states are sensitive to applied magnetic fields and can be readily suppressed by relatively small fields, suggesting competing magnetic interactions in a low-dimensional framework, which appear worthy of further study.
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All authors Danrui Ni, Xianghan Xu, Stephen Zhang, N.P. Ong, Sanfeng Wu, R. J. Cava

Thursday 2 July

Mesoscale and Nanoscale Physics

Universality and Dynamical Inequivalence in Isospectral Non-Hermitian Anderson Transitions

Aziz Hasan, Anant Vijay Varma, Namit Anand et al. (+1 more)

The Hatano Nelson paradigm establishes that extensive bulk nonreciprocity can destabilize Anderson localization via an imaginary gauge flux. Here, we demonstrate that extensive nonreciprocity is not a necessary ingredient: a single non-Hermitian boundary bond in a disordered one-dimensional ring suffices to drive the localization-delocalization transition. More generally, we construct an exactly isospectral family of non-Hermitian Hamiltonians that continuously interpolates between the uniform Hatano Nelson model and the single-bond limit. We show that the universal critical behavior encompassing spectral, eigenstate, and topological diagnostics is gauge invariant and governed solely by the total imaginary gauge flux, regardless of its spatial distribution. Remarkably, despite sharing identical spectra and critical exponents, different configurations within this isospectral family exhibit qualitatively distinct quantum dynamics, establishing a fundamental separation between static and dynamical universality in non-Hermitian systems. Specifically, the single boundary realization features rapid operator scrambling, oscillatory wavepacket acceleration, and a double re-entrant steady state entanglement transition. Finally, we propose an experimentally feasible realization based on multi-terminal topological transport, providing a realistic route toward observing boundary induced non Hermitian criticality and its unconventional dynamical signatures.
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All authors Aziz Hasan, Anant Vijay Varma, Namit Anand, Sourin Das

Soft Condensed Matter

Folding-Driven Auxetic Weft Knit Textiles with Integrated Capacitive Sensing

Kausalya Mahadevan, Helen E. Read, Anya X. Zhang et al. (+3 more)

Machine knitting provides a scalable platform for manufacturing multifunctional textiles in which geometry, mechanics, and embedded functionality can be programmed at the stitch level. However, predictive design tools capable of linking knit architecture to large-deformation mechanical response remain limited. Here, we develop a reduced-order spring-network model that captures the relaxation, unfolding, and deformation of knitted fabrics composed of checkerboard arrangements of rib and garter patches. The model accurately predicts the corrugated relaxed configuration of the knits and the evolution of local deformations under tensile loading using only linear extensional and torsional springs. Combining simulations with experiments, we show that the programmed unfolding of the corrugations generates tunable auxetic behavior, with both the magnitude of the negative Poisson's ratio and the strain at which it occurs governed by the unit-cell geometry. We further integrate capacitive strain sensing directly during fabrication through partial plating of conductive yarns, eliminating post-processing. The resulting knitted capacitors exhibit programmable tradeoffs between strain sensitivity and sensing range, enabling either highly sensitive sensors over narrow deformation windows or lower-sensitivity sensors capable of measuring larger strains. Together, our modeling framework and fabrication strategy provide a route toward the rational design of mechanically programmable, sensorized knits with tailored shape-morphing and sensing functionalities.
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All authors Kausalya Mahadevan, Helen E. Read, Anya X. Zhang, Louis-Justin Tallot, Michelle C. Yuen, Katia Bertoldi

Materials Science

Twist-configured moire-moire reconstruction governs diverse commensurate double-moire phases in twisted bilayer graphene on h-BN

Yuta Seo, Naoto Nakatsuji, Jimpei Kawase et al. (+6 more)

The coexistence of multiple moire lattices in van der Waals heterostructures raises a fundamental question: how do distinct moire patterns interact and reconstruct? Here, we investigate twisted bilayer graphene (tBG) on hexagonal boron nitride (h-BN), where tBG and graphene/h-BN moire structures coexist, using conductive atomic force microscopy combined with continuum-model simulations. We show that reconstruction between these moire lattices-moire-moire reconstruction-manifests across multiple length scales, giving rise to diverse commensurate double-moire phases. Locally, the stacking registry between the two moire lattices is uniquely selected by the global twist configuration (helical or alternate), mediated by rotational relaxation of the shared graphene layer. This registry, together with twist angle and strain, governs commensurate domains from C3z-symmetric to strained symmetry-modified structures. These results establish moire-moire reconstruction as a general framework for engineering structural and electronic order – including theoretically predicted topological flat bands below the magic angle – in multilayer moire materials.
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All authors Yuta Seo, Naoto Nakatsuji, Jimpei Kawase, Naoto Hishida, Kenji Watanabe, Takashi Taniguchi, Takuto Kawakami, Mikito Koshino, Tomoki Machida

Quantum Gases · Cross-listed from physics.atom-ph

Reconfigurable Bitter-Type Electromagnet for Zeeman Slowing

Emma G. Hataway, Emma K. Falk, Kaia E. O'Neill et al. (+2 more)

Many Zeeman slower magnets are geometrically captured by a vacuum chamber, preventing modification or repair without breaking vacuum. We describe a Bitter-type electromagnet coil design that can be easily disassembled, reconfigured, repaired, and replaced without disturbing the vacuum system. This coil, designed to slow lithium atoms, produces a near-ideal field profile with a single DC power supply. With a resistance of 5.7(9) m$\Omega$, an inductance of 8.8(2) $\mu$H, and switching times as low as $\sim100$ $\mu$s, the coil compares favorably to other designs, and can be disassembled, modified, and reassembled repeatedly without loss of performance. With forced-air cooling, the coil experiences moderate heating. This coil design offers greater flexibility than traditional electromagnet designs, and it can retrofitted onto existing UHV chambers.
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All authors Emma G. Hataway, Emma K. Falk, Kaia E. O'Neill, Morgan P. Berghof, Ben A. Olsen

Superconductivity

Theoretical investigation of power absorbed by superconductors with Rashba spin-orbit coupling in the presence external time-dependent perturbation

Reza Afzali, Bahman Takrim and Amir Hossein Asghari

The absorbed power in superconductors driven by a time-dependent external perturbation is investigated through transitions between Bogoliubov quasiparticle states. The transition matrix element contains the superconducting coherence factor, which determines the role of the gap, excitation spectrum, and external frequency in the absorption process. The formulation is applied to a Hubbard-model superconductor including correlated hopping and Rashba spin-orbit coupling. In this model, numerical calculations are used to obtain the quasiparticle energies, density of states, chemical potential, and temperature-dependent superconducting gap. The normalized absorbed power is then evaluated for different values of temperature, interaction strength, correlated hopping parameter, and spin-orbit coupling strength. The results show that the absorption response is strongly affected by the superconducting gap and by changes in the quasiparticle spectrum. Rashba spin-orbit coupling changes the density of states and therefore modifies the absorption. These results show that hopping processes, interaction strength, and spin-orbit coupling play important roles in the ultrasonic and electromagnetic absorption of superconducting systems.
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Materials Science

First principles study of chalcogen vacancy effect on the optoelectronic and photocatalytic properties of transition metal dichalcogenides monolayers

Tahir Wahab, Antonio Cammarata and Tomas Polcar

In working conditions, chalcogen vacancies spontaneously occur in two-dimensional transition metal dichalcogenides (TMDCs) monolayers, affecting their optoelectronic and photocatalytic properties. To study how chalcogen vacancies affect such properties, we use quantum mechanical calculations considering prototypical MX$_2$ (M = Mo, W, X = S and Se) TMDCs monolayers. Structural optimisations show that M-X bond lengths about a vacancy are different compared to the bond lengths in the pristine structure. Band structure calculations reveal that the introduction of vacancies produce electronic states about the Fermi level, hence resulting in the reduction of the band gap. Work function and electrostatic potential calculations show that the introduction of vacancies induce an asymmetry in the electrostatic potential facilitating the charge separation; such feature is absent in a pristine monolayer. All the considered defective structures are capable of performing hydrogen evolution reaction, while co-catalyst is required to perform oxygen evolution reaction when used for water splitting. WS$_2$ and WSe$_2$ defective monolayers can serve as an efficient photocatalytic material for reducing CO$_2$ into useful chemical products. The presented results show that vacancy-containing TMDCs monolayers own photocatalytic capabilities compared to the pristine counterparts, thus showing that defective TMD monolayers have prospective applications and should not be regarded as flawed products to be discarded. Finally, the results might constitute guidelines for the experimental synthesis of vacancy-engineered MX$_2$ monolayers for optoelectronic devices and photocatalytic applications.
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Soft Condensed Matter

Shear and crystallization in deformable granular packings: why don't auxetics order?

Joel T. Clemmer, Nicholas W. Hackney and Gary S. Grest

Shear of three-dimensional, highly compressed granular packings is simulated using a bonded particle approach that explicitly resolves elastic deformation. Varying Poisson's ratio $\nu$ produces significant changes in rheology, packing structure, and grain morphology. During flow, conventional systems ($\nu > 0$) readily crystallize while auxetics ($\nu < 0$) resist ordering. This duality reflects the fact that conventional grains develop polyhedral-like facets but conserve volume while auxetics behave oppositely, demonstrating an unexpected interaction between elasticity, geometry, and crystallization.
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Materials Science

Magnetic ordering in VI3: a van der Waals material combining vastly different magnetic anisotropies

K. K. Pokhrel, S. Ray, N. Machavcova et al. (+2 more)

Among magnetic van der Waals materials, the vanadium trihalide family exhibits unique features. In particular, VI3 contains V atoms of two different types, as two energetically close electronic occupations can coexist in real samples. These types show strikingly different magnetic anisotropy, predicted to differ by more than an order of magnitude. The combination forms a distinctive magnetic system. VI3 also displays an unusual thickness dependence: the monolayer Curie temperature (TC) is higher than that of the bulk, contrary to the expectation that interlayer coupling reinforces magnetic order. Using atomistic spin-dynamics simulations informed by first-principles calculations, we investigate the critical temperature behavior from the combined perspective of single-ion anisotropy and exchange interactions. The strong anisotropy contrast significantly affects thermal stability: increasing the fraction of high-anisotropy sites raises the energy cost of transverse spin fluctuations and increases the ordering temperature. Furthermore, V-atom inhomogeneity makes the interlayer super-superexchange network spatially nonuniform, creating competing exchange pathways. This weakens coherent interlayer order while preserving robust intralayer ferromagnetic correlations, thus modifying the bulk-monolayer TC relation. Our model reproduces experimental TC values when the ratio of the two V types is close to 1:1, in agreement with two experimental methods. This supports the coexistence of two V configurations in VI3. The monolayer TC is reproduced with a slightly modified ratio, possibly linked to polaron concentration. The sensitivity of TC to this ratio suggests that the ordering temperature of VI3 can in principle be tuned over a broad range by controlling the relative occupation of the two vanadium configurations.
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All authors K. K. Pokhrel, S. Ray, N. Machavcova, A. Koliogiorgos, K. Carva

Mesoscale and Nanoscale Physics

Anisotropic magnetoresistance of two-dimensional Rashba systems with in-plane Zeeman field and point-like disorder

Igor Gornyi and Alexander Khaetskii

We study the dc conductivity of a two-dimensional Rashba system with an in-plane Zeeman field and delta-correlated scalar disorder. We show that, although the field deforms the two helicity Fermi contours and rotates the spin texture, it does not produce anisotropic magnetoresistance in the leading quasiclassical conductivity. The result follows from a geometric identity for the total area occupied by the two helicity sheets. A density Ward identity fixes the spin-vector part of the Born self-energy to the derivative of the total particle density with respect to the field. This derivative vanishes, because the total area enclosed by the two Rashba-Zeeman sheets is independent of the in-plane field. The Born self-energy is therefore scalar and field independent, and the quasiparticle lifetime stays isotropic. The same occupied-area identity controls transport: the leading impurity ladder reduces the current vertex to the parabolic velocity, and the diagonal intraband Kubo conductivity collapses onto the two-sheet occupied area and is field independent as well. Thus, point-like nonmagnetic impurities produce neither angular anisotropy nor field-magnitude dependence in the leading diagonal two-sheet quasiclassical conductivity. Any residual AMR from delta-correlated disorder must originate from corrections outside this sector.
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Strongly Correlated Electrons

Correlation-Induced Topological Reconstruction in a Periodically Driven Kagome Mott Insulator

Rahul Ghosh, Subhajyoti Pal and Ganesh C Paul

We study the interplay between electronic correlations and circularly polarized periodic driving in the Hubbard model on a Kagome lattice. Using Brillouin-Wigner perturbation theory, we derive an effective Floquet Hamiltonian in which the drive renormalizes the bare hopping and generates chiral nearest- and next-nearest-neighbor terms, producing repeated topological transitions and a flat band whose position is continuously tunable across the spectrum. Within slave-rotor mean-field theory, we show that the resulting Mott transition is strongly non-monotonic in the drive amplitude, yielding repeated metal-insulator transitions, and that the spinon excitations inside the Mott phase acquire a band topology distinct from that of the non-interacting Floquet bands. This correlation-driven topological reconstruction produces emergent flat-band spinon insulators inaccessible to either driving or interactions alone. Our results establish periodically driven Kagome systems as a platform for engineering correlated topological flat-band physics out of equilibrium, with proposed realizations in ultracold atomic lattices.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.optics

Nonlinear Self-Action across Temporal Regimes in Resonant Dielectric Metasurfaces

Alfonso Nardi, Sonia Freddi, Michael Scalora et al. (+8 more)

Quasi-bound states in the continuum (qBICs) enable exceptional field confinement, strongly reducing the pump intensity threshold for nonlinear light-matter interaction in dielectric metasurfaces. As a result, nonlinear self-action effects, often elusive in bulk nonlinear media, emerge at moderate excitation intensities. Here, nonlinear self-action in resonantly enhanced third-harmonic (TH) generation from a dielectric metasurface supporting a qBIC resonance is investigated across distinct temporal excitation regimes. These regimes establish different coupling conditions between the excitation and the resonant mode, causing the same nonlinear self-action to emerge through complementary intensity-dependent signatures. Under spectrally narrow picosecond excitation, resonance-enhanced TH generation shows pronounced deviations from cubic scaling at high intensities. In contrast, broadband femtosecond excitation transiently drives the resonance, encoding the nonlinear response in the spectral reshaping and broadening of the TH signal. Simulations reproduce both regimes: continuous-wave modeling captures picosecond power scaling and the role of higher-order nonlinear susceptibilities, while time-domain simulations resolve femtosecond dynamics. These results clarify how pulse duration, bandwidth, and resonant coupling determine the observable signatures of nonlinear self-action in resonant dielectric metasurfaces, linking field confinement to conversion efficiency, power-law scaling, and ultrafast spectral dynamics.
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All authors Alfonso Nardi, Sonia Freddi, Michael Scalora, Agostino Di Francescantonio, Johann Osmond, Sofia Martins, Attilio Zilli, Marco Finazzi, Michele Celebrano, Monica Bollani, Maria Antonietta Vincenti

Strongly Correlated Electrons · Cross-listed from quant-ph

Quench Spectroscopy of Magnetic Excitations on a Superconducting Quantum Processor

D. A. Millar, G. W. Pennington, N. T. M. Siow et al. (+5 more)

The elementary excitation spectrum of a many-body quantum system encodes many key properties, including phenomena as diverse as transport, thermalisation and ground state structure. Excitation spectra of strongly correlated systems are typically encoded in dynamical structure factors, which are demanding to measure experimentally and challenging to compute classically. Here we use quench spectroscopy on a superconducting quantum processor to extract excitation spectra of spin chains of $L=101$ spins. By tailoring the combination of quench protocol and observable, we selectively access distinct excitation sectors across several phases of the spin-$1/2$ XXZ chain, resolving free magnons, multi-magnon bound states, and two-spinon continua. Notably, we demonstrate that the protocol does not rely on ground state preparation: in the classically challenging gapless regime, we extract spectra directly from the quench dynamics of easily prepared product states, a procedure that is natural and straightforward on quantum hardware. Our work establishes quench spectroscopy as a fast and flexible probe of many-body excitation spectra on digital quantum hardware, introduces a novel quench protocol that does not require costly state preparation routines, and provides a scalable route towards regimes where classical simulation may become intractable.
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All authors D. A. Millar, G. W. Pennington, N. T. M. Siow, S. Brandhofer, J. Crain, F. H. L. Essler, A. G. Green, S. J. Thomson

Statistical Mechanics

Non-equilibrium phase transition in the Brownian Ising Model: field theory, renormalization group, and exact results

Mattia Scandolo and Luca Di Carlo

We present a complete field-theoretical renormalization-group (RG) analysis of the Brownian Ising Model (BIM), in which a $\mathbb{Z}_2$ order parameter is coupled to a passive conserved density, breaking detailed balance. Using the Martin-Siggia-Rose formalism and an $\epsilon=4-d$ expansion, we show that this density-order parameter coupling is RG-relevant below four dimensions and drives the system to a new non-equilibrium fixed point, distinct from the Ising universality class. Critical exponents are computed at lowest nontrivial order, some of which require a dedicated two-loop analysis. At large scales, the density acts as an effective noise that is white in time but long-range in space, enhancing order-parameter fluctuations and producing a negative anomalous dimension $\eta$. A defining feature of the new class is that the correlation and response functions acquire different anomalous dimensions, $\eta \neq 2 - \gamma / \nu$ - a direct, observable signature of fluctuation-dissipation-theorem violation at large scales that cannot occur in equilibrium. We also find a small correction-to-scaling exponent, implying large preasymptotic corrections that must be accounted for in numerical and experimental tests. We further derive a set of relations among renormalization factors that hold to all orders in perturbation theory, following from the linearity of the density dynamics and an emergent shift symmetry. These yield an exact scaling relation $\nu = 2/(d+z-2)$ at the BIM fixed point and establish that the Ising universality class, as well as that of quenched diluted-Ising, is unstable in $d=3$. This establishes the BIM fixed point as the unique infrared attractor for any nonzero diffusion constant.
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Statistical Mechanics

Non-equilibrium coupling to a diffusing density breaks Ising universality

Mattia Scandolo, Johannes Pausch, Michael E. Cates et al. (+1 more)

The Ising universality class is remarkably robust to non-equilibrium perturbations, which generically flow to zero under renormalization. We show that this robustness fails when an order parameter is coupled nonreciprocally to a conserved diffusive density. Below $d_c=4$, the renormalization group flows to a fast-diffusion fixed point at which the density acts as a long-range multiplicative noise, producing a novel universality class. The non-equilibrium nature of the fixed point is manifest in the large-scale violation of the fluctuation-dissipation relations, reflected in a splitting of the scaling exponents of the two-point correlation and response functions–a measurable hallmark of non-equilibrium critical fluctuations. A two-loop calculation establishes the stability of this fixed point but yields a small correction-to-scaling exponent $\omega\approx0.020$ in $d=3$, implying strong finite-size corrections. An all-orders modified Harris criterion $\nu>2/(d+z-2)$ confirms that the BIM fixed point governs criticality in $d=3$, with Ising universality recovered only at $d=2$.
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All authors Mattia Scandolo, Johannes Pausch, Michael E. Cates, Luca Di Carlo

Statistical Mechanics · Cross-listed from hep-th

Time-Dependent Integrability from Gauge Theory, I

Shota Komatsu, Jun-ichi Sakamoto, Anders Wallberg et al. (+1 more)

Solvable time-dependent systems provide important settings for studying non-equilibrium physics, where exact results are rare. They are also useful for benchmarking quantum simulations, which can directly probe real-time dynamics beyond the reach of conventional numerical approaches. In this paper, we show that the four-dimensional Chern-Simons theory offers a natural and unifying framework for constructing such systems. Focusing on classically integrable field theories, we consider a generalization of the four-dimensional Chern-Simons theory in which the usual holomorphic one-form is replaced by a more general, spacetime-dependent one-form. This yields a systematic procedure for generating time-dependent integrable field theories and establishes a universal relation: for every theory obtained in this way, the allowed time dependence coincides with the one-loop renormalization group flow. Despite the explicit time dependence, these theories retain Lax integrability and remain solvable by inverse scattering methods. Our construction applies to both ultralocal and non-ultralocal theories and extends previously known time-dependent sigma models to a much broader class of integrable systems. It also admits rewriting as dilaton gravity coupled to matter, producing a large family of classically integrable dilaton gravity theories in two dimensions. We also comment on connections to time-dependent integrable models studied recently in condensed matter physics and non-autonomous integrable systems arising from dimensionally-reduced Einstein gravity.
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All authors Shota Komatsu, Jun-ichi Sakamoto, Anders Wallberg, Masahito Yamazaki

Materials Science

High-Entropy Nitride Photocatalysts for Visible-Light Antibiotic Degradation: Structural Stability, In Situ Interfacial Visualization, and Molecular-Level Mechanistic Insights

Zahoor Manzoor, Shamik Chowdhury, Raphael Benjamim de Oliveira et al. (+5 more)

High-entropy nitrides (HENs) have emerged as a promising class of advanced materials with tunable electronic structures, high stability, and abundant active sites. The incorporation of nitrogen enhances visible-light absorption, promotes efficient charge separation, and improves structural robustness, making these materials highly suitable for photocatalytic applications. In this study, (MnFeCoNiCu)N-based HEN nanoparticles (NPs) were synthesized as visible-light-assisted photocatalysts for the degradation of antibiotics, including sulfamethoxazole (SME) and tetracycline (TCL). The catalyst exhibited excellent performance, achieving 96% degradation of SME and 94% removal of TCL within 2 h of visible-light irradiation. The photocatalytic activity was systematically evaluated under varying operational parameters, including solution pH, catalyst dosage, pollutant concentration, and the presence of coexisting ions. Notably, the catalyst maintained high efficiency in real water matrices, demonstrating its practical applicability. The entropy-stabilized nitride framework exhibited negligible metal leaching, excellent thermal and structural stability as confirmed by temperature-dependent synchrotron angle-dispersive X-ray diffraction, and stable performance over multiple reuse cycles. Furthermore, in situ liquid-cell transmission electron microscopy provided real-time insight into catalyst-pollutant interactions, while complementary molecular simulations revealed the structural stability of the HEN NPs during molecular adsorption and the distinct interaction modes of the two antibiotics. Phytotoxicity tests using Vigna radiata confirmed the effective detoxification of treated solutions. Overall, this work establishes (MnFeCoNiCu)N HENs as efficient and durable visible-light-driven photocatalysts for the removal of antibiotics from complex aqueous environments.
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All authors Zahoor Manzoor, Shamik Chowdhury, Raphael Benjamim de Oliveira, Marcelo Lopes Pereira Junior, Guilherme da Silva Lopes Fabris, Prikshat Dadhwal, Douglas S. Galvao, Chandra Sekhar Tiwary

Statistical Mechanics

On the emergence of quantum many-body chaos for tunably-broken integrability

Sounak Biswas, Sthitadhi Roy and Roderich Moessner

We develop a quantitative theory for the emergence of quantum many-body chaos as integrability is broken via a tunable parameter. In a circuit model of free fermions, 'doped' with a tunable density of integrability-breaking gates, we uncover the microscopic mechanisms underpinning the crossover from early-time integrable behaviour to late-time chaos through the lens of the out-of-time-ordered correlators (OTOCs). The integrability-breaking gates act as local, in spacetime, hotspots which locally amplify the OTOCs such that an accumulation of them eventually leads to fully-developed chaos. We identify the explicit characteristic time and length scales governing this crossover, as well as the dependence of the chaotic OTOC characteristics – such as the butterfly velocity and front broadening – on the integrability-breaking parameter.
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Statistical Mechanics · Cross-listed from quant-ph

Quantum mutual information as a robust probe of integrability in open quantum systems

Nirupam Sen, Keshav Das Agarwal and Aditi Sen De

The dynamics of a quantum system encode signatures of whether the underlying Hamiltonian is integrable or chaotic, giving rise to the concept of quantum information scrambling through the properties of the resulting dynamical states or operators. We introduce an information-theoretic framework based on the Haar-averaged sum of total correlations (aSTC), together with average genuine multipartite entanglement generated dynamically from initially fully separable states, as robust probes of quantum information scrambling. Using the long-range quantum XYZ spin model in transverse and longitudinal magnetic fields, whose integrable limit is the nearest-neighbor transverse XY model, we demonstrate that the long-time average and, more importantly, the temporal fluctuations of the aSTC provide a faithful and system-size-independent signature of integrable and chaotic dynamics, similar to the conventional measure of scrambling, out-of-time-ordered correlator (OTOC). When the system is in contact with the thermal reservoir and system-bath coupling follows Markovianity, we find that the fluctuations of the aSTC and OTOC continue to distinguish integrable and chaotic dynamics only at intermediate times. However, we observe that in the non-Markovian domain, information backflow restores the scrambling dynamics, enabling the aSTC to retain its distinguishing power even at long times. Interestingly, we exhibit that, under Markovian amplitude damping and non-Markovian dephasing noise, the temporal fluctuations of the aSTC can discriminate between integrability and non-integrability in the weak Markovian regime, even when OTOC fails to do so.
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Strongly Correlated Electrons

Anomalous thermopower from the drag of overdamped collective modes

G. Mirarchi, G. Seibold, M. Grilli et al. (+1 more)

Inspired by the observation of a Seebeck coefficient ratio that exhibits a seemingly logarithmic divergence at low temperature in high-temperature superconducting cuprates, we show that a mechanisms similar to the standard phonon drag can give rise to anomalies in the thermopower of a metal, if the dragged collective mode is overdamped, with a damping coefficient that increases with lowering the temperature. Our finding adds a piece to the puzzle of the strange-metal behavior observed in many different systems and supports our proposal that overdamped charge density fluctuations can be responsible of such a behavior in high-temperature superconducting cuprates.
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All authors G. Mirarchi, G. Seibold, M. Grilli, S. Caprara

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

On a Rosenzweig-Porter-type model

Giorgio Cipolloni, László Erdős and Joscha Henheik

We consider a very general Rosenzweig-Porter-type model, $H=H_0+\lambda W$, where $H_0$ is an arbitrary Hermitian matrix and $W$ is a standard Wigner matrix. We precisely trace the localization properties of the eigenvectors and the eigenstate thermalisation hypothesis (ETH) as the coupling constant $\lambda$ interpolates between the trivial $\lambda=0$ case and the fully mean field regime of large $\lambda$. Our results hold uniformly in $H_0$ and $\lambda$, substantially generalising all previous local laws on deformed Wigner matrices even in the mean field regime. Our proof precisely captures the deterministic approximation to the resolvent which exhibits a strongly inhomogeneous structure. As a byproduct, we conclude the emergence of a mobility edge and study the phenomenon of re-entrant localization.
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Soft Condensed Matter

Curvature-induced host-mediated polarization of active particles

Giulia Janzen and D. A. Matoz-Fernandez

Polar collective motion commonly arises from alignment interactions, particle anisotropy, or an imposed directional bias. Here we identify a distinct route to polar order that does not rely on alignment interactions between the active particles. We show that non-aligning active Brownian particles embedded in a dense passive medium can develop polar coherence when confined to a compact curved surface. Persistent active motion redistributes stress through the host and creates passive-depleted regions. When the stress-spreading length becomes comparable to the sphere radius, these regions merge into elongated scars that channel active motion and, through feedback with the active flux, promote a common direction of motion. Removing the passive host suppresses polar coherence even though the active particles continue to cluster on the same sphere. Our results establish an environment-mediated route to collective polarity in which symmetry breaking emerges from the coupling between active motion, passive stress redistribution, and compact geometry.
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Disordered Systems and Neural Networks

Complex dynamics in the Sherrington-Kirkpatrick game

Desmond Chan and Tobias Galla

We study the outcome of adaptive learning of a large number of players engaging in sets of two-strategy two-player games. We are interested in typical games, and generate the payoff matrices at random at the beginning. The payoff matrices then remain fixed during the learning process. This provides a game theoretic foundation for the Sherrington-Kirkpatrick (SK) game, recently introduced by Garnier-Brun, Benzaquen and Bouchaud. The original model by these authors is a special case, with no bias towards any strategy. We here determine stability of learning for SK games with general random bias, and find that the nature of the stable state is affected by random fields. We also introduce a grand-canonical version of the SK game, in which players can choose to abstain. We determine the stability of learning for this game. Our analysis confirms that complex situations involving many players are frequently unlearnable, even if each player only chooses between two different actions. The rate with which players lose memory of past payoffs and the competitiveness of the game emerge as key parameters determining whether learning converges to a unique fixed point, whether there are many fixed points, or if the dynamics remains persistently volatile.
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