Disordered Systems and Neural Networks
Fundamental Limits of Stability Inference in High-Dimensional Complex Systems
Michela Costa, Kentaro Hoshisashi, Flaviano Morone et al. (+2 more)
Many complex systems, including ecosystems, neural
circuits, and financial
markets, are inferred to operate close to a threshold of instability, at which a small perturbation can propagate across the entire system. This proximity is often interpreted as functionally advantageous, yet it poses a question common to all these fields: from a finite, noisy recording, how precisely can the distance of a system from that threshold be estimated? Using the multivariate Ornstein-Uhlenbeck process as the canonical linear model of relaxation near a stable fixed point, we show that the attainable precision is governed by three factors: an effective measurement budget, set by the number of samples relative to the system dimension and the sampling interval; the signal-to-noise ratio, given by the magnitude of deterministic interactions relative to
stochastic forcing; and the distance to criticality, which simultaneously sets the system's correlation times and degrades both of the preceding factors. As the slowest dynamical mode softens near the threshold, the
curvature of the log-likelihood flattens along the direction that determines stability, so that the relative uncertainty on the estimated distance diverges as that distance vanishes. Critically, temporal correlations near instability reduce the effective number of independent observations far below the nominal sample count, and inference breaks down when this effective count falls below the system dimension, even when the raw data volume appears sufficient. A direct consequence is the existence of an optimal sampling interval that diverges as the system approaches criticality, with practical implications for experimental design.
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All authors Michela Costa, Kentaro Hoshisashi, Flaviano Morone, Tim Rogers, Paolo Barucca
Soft Condensed Matter
Application of Machine Learning for the Identification of 2D Colloidal Assemblies: A Case Study on Particles of Distinct Shapes
L. T. Khusainova, S. A. Kolegova and K. S. Kolegov
This work addresses the problem of identifying colloidal monolayer assemblies using particles of various shapes (two-dimensional coatings): spheres, ellipsoids, cuboids, and rods. The following classification of assemblies is considered: isolated particles, dimers, chains, clusters, and loops. The YOLO model was chosen as the identification method. Synthetic
datasets were prepared for each of the four particle shapes to train the models. The paper discusses the application of models trained on synthetic data to experimental images. An analysis was carried out on the feasibility of using such models for recognizing configurations in real images. While recognition on artificial images is nearly perfect, tests on experimental images showed a significant deviation. The average error across all particle types was 43.1%, but a considerable spread in values is observed: from 20% for spheres to 58.5% for cuboids, indicating the
algorithm's selective sensitivity to object geometry. The created
datasets and trained models are freely available for use. The corresponding modules have been integrated into the previously developed information system (https://isanm.space/). To further improve prediction results, it is necessary to prepare
datasets based on experimental images.
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Superconductivity
Reentrant superconductivity enabled by spin-orbit coupling: Application to UTe$_2$
Changhee Lee, Nico A. Hackner, Daniel F. Agterberg et al. (+1 more)
Reentrant superconductivity has been understood primarily in terms of the Jaccarino-Peter field-compensation effect or from a change of the strength in the pairing interaction. However, neither mechanism appears able to entirely explain the remarkable phase diagram of UTe$_2$. Here we propose a generic theory of the field-enhancement of opposite-
spin Cooper pairings which does not necessitate the coexistence of magnetism or the vicinity of a
magnetic quantum critical point. Our analytical treatment shows that the reentrance has its origin in the interplay of the sublattice degrees of freedom and
spin-orbit coupling, which can can strikingly enhance opposite-
spin Cooper pairings at strong Zeeman fields. Based on these results, we show that a pairing state with B$_{3u}$
symmetry can reproduce the highly anisotropic phase diagram of the reentrant superconducting state of UTe$_2$.
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All authors Changhee Lee, Nico A. Hackner, Daniel F. Agterberg, P. M. R. Brydon
Materials Science
Two-dimensional stealthy hyperuniform polycrystalline disk packings
Carlo Vanoni, Paul J. Steinhardt and Salvatore Torquato
Polycrystals consist of grains of local crystalline order separated by grain boundaries. Their structure is not hyperuniform, even though perfect
crystals are, because polycrystals consist of randomly sized and oriented grains that generate appreciable long-wavelength density fluctuations. In this paper, we use a collective-coordinate optimization procedure to generate two-dimensional polycrystalline packings composed of identical disks arranged in a pattern that is ultradense, stealthy, and hyperuniform (hereafter named SHU). We compare them with polycrystalline disk packings obtained via a modified Lubachevsky–Stillinger rapid compression
algorithm (hereafter named LS), a molecular dynamics protocol that serves as a standard reference model describing realistic, nonhyperuniform polycrystalline microstructures. We carry out an extensive comparison of polycrystalline SHU and LS packings that includes differences in two-point statistics, grain size, specific surface area,
diffusion spreadability, and optical response as quantified by the imaginary part of the effective dynamic dielectric constant. We find that the polycrystalline SHU packings exhibit a distinctive grain-size distribution, a consequence of long-range correlations between different grains that is absent in the nonhyperuniform case. Within the nonlocal strong-contrast expansion, we confirm that polycrystalline SHU packings made of dielectric material are perfectly transparent to electromagnetic waves at small wave vectors, in contrast to LS packings. Moreover, polycrystalline SHU packings offer enhanced
diffusion spreadability. Although polycrystalline SHU packings are not expected to form spontaneously in nature, they may be created for applications as metamaterials via nanolithography or 3D printing that take advantage of their distinctive optical and transport properties.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.ins-det
Multi-scale reconstruction of single-ion damage tracks in diamond via nitrogen-vacancy centers
Daniel G. Ang, Jiashen Tang, Maximilian Shen et al. (+9 more)
Understanding particle-induced damage tracks in solid-state materials underpins emerging applications in rare-event detection and
quantum defect engineering. Resolving these tracks requires multi-scale readout, from event localization at the millimeter scale to track-morphology reconstruction at the nanoscale. Nitrogen-vacancy (NV) centers in diamond provide such a platform, combining optical localization with
quantum sensing of track morphology. Here, we implant sub-MeV carbon ions into nitrogen-rich diamond and detect individual
recoil events via spatially localized NV formation. We develop a simulation framework that explains the observed NV yield and predicts that directional information is retained in the NV distribution after annealing. Machine learning further recovers much of the information lost to defect
diffusion and limited NV yield, improving head-tail classification to a level comparable to pre-annealed vacancy tracks. Measurements of NV
spin coherence indicate compatibility with nanoscale track reconstruction via NV strain mapping and
magnetic gradient-based techniques. These results identify promising pathways toward NV-diamond directional detectors for rare events, while the track-modeling framework has broader implications for paleodetection and
quantum material synthesis.
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All authors Daniel G. Ang, Jiashen Tang, Maximilian Shen, Michael Titze, Gavishta Liyanage, Jordan Chapman, Chinmay Bharathulwar, Andrew T. Gilpin, Tanguy Terlier, Edward S. Bielejec, Vsevolod Ivanov, Ronald L. Walsworth
Statistical Mechanics
Thermodynamic inference from noisy single-molecule time series
Todd R. Gingrich, Oleg A. Igoshin, Anatoly B. Kolomeisky et al. (+1 more)
Single-molecule or single-particle tracking measurements inherently yield noisy microscopic trajectories, often significantly constrained by the diffraction limit and by the finite rate at which
photons are emitted and counted. Here we study systematically the resulting effects of finite spatial and temporal resolution on one's ability to discern and quantify the arrow of time in microscopic trajectories. Given an experimental time series Y(t) degraded by noise, we consider the problem of estimating the
entropy production associated with the corresponding microscopic variable X(t) using two strategies. The first attempts to infer the statistical properties of X(t) from those of Y(t) before estimating the
entropy production. The second uses the experimental observable as a proxy for the true microscopic observable, with the
entropy production
estimator applied directly to Y(t). We prove that both strategies result in lower bounds on the true
entropy production. Importantly, noise-degraded observables Y(t) undergo non-Markovian dynamics even when X(t) are Markovian, and non-Markovian
entropy production
estimators are advantageous. We further note nontrivial interplay between spatial and temporal resolution: in the presence of detection noise, improving the temporal resolution alone may lead to poorer rather than better
entropy production estimates.
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All authors Todd R. Gingrich, Oleg A. Igoshin, Anatoly B. Kolomeisky, Dmitrii E. Makarov
Materials Science
Data analysis methods for powder x-ray diffraction intensity under laser-driven dynamic compression at Omega and NIF laser facilities
Marius Millot, Federica Coppari, Amy Lazicki et al. (+1 more)
Powder x-ray diffraction (PXRD) under
laser-driven dynamic compression is a powerful tool to investigate material response to extreme pressure, temperature and strain rates. Robust PXRD platforms have been developed at kJ and MJ
laser facilities worldwide including the Powder X-Ray Diffraction Image Plate (PXRDIP) at the Omega
Laser Facility at the Laboratory for
Laser Energetics (LLE) and the TARget Diffraction In Situ (TARDIS) at the National Ignition Facility (NIF). Here we present further developments of data analysis methods focused towards improving the fidelity of the PXRD intensity determination for these platforms. We illustrate these methods by discussing how they can be implemented in a data analysis package and applied to shock compression data on diamond near 1 TPa. We discuss using the XRD signal from the collimating pinhole or a layer of un-compressed material in the sample package as in-situ references for XRD intensity. We detail how to compare data collected with different x-ray sources and how to account for thermal damping of XRD signal when comparing XRD from a shock-compressed, hot material with the reference material at ambient.
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All authors Marius Millot, Federica Coppari, Amy Lazicki, Jon H. Eggert
Mesoscale and Nanoscale Physics
Helical Domain-Wall-Ring Networks Reshape Superconducting Correlations
Yi-Chun Hung and Arun Bansil
Extended domain-wall networks that emerge in moiré materials provide a distinct platform for quasi-one-dimensional electronic states. However, the interaction-driven orders in confined networks remain largely unexplored. Here, we discuss superconducting (SC) correlations in interacting helical domain-wall-ring networks in the closed topological domains formed within the moiré patterns of an underlying twisted
bilayer honeycomb
lattice. We first analyze the system within the framework of an infinite-size theory and show that inter-ring SC-pair tunneling is renormalization-group relevant and thus enhances SC correlations through inter-ring phase locking. To address finite-size effects resulting from the ring-network geometry, we present a self-consistent variational approach. Our analysis shows that even in the regime where the infinite-size theory predicts strongly coupled pair tunneling, the induced phase-locking scale remains strongly suppressed. In contrast, the SC scaling dimension continues to decrease with stronger inter-ring density-density interaction and a decreasing twist angle, while remaining insensitive to the pair-tunneling strength. This discrepancy demonstrates that ring networks do not simply approach their infinite-size counterparts but can exhibit qualitatively distinct collective behavior. Our study highlights how the interplay of confinement effects and ring-network geometry can reshape SC correlations.
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Mesoscale and Nanoscale Physics
Quantum Geometry Driven Finite-Momentum Exciton Fluctuations in Flat-Band Systems
Yi-Chun Hung, Xiaoting Zhou and Arun Bansil
Quantum geometry is instrumental in stabilizing exotic phenomena in systems ranging from topological
insulators to
superconductors. In dispersionless flat bands, where the kinetic energy is quenched, the
quantum metric emerges as the fundamental driver of macroscopic collective phenomena. Here, we theoretically demonstrate that
lattice-geometry-induced flat bands, such as those in kagome and Lieb
lattices, provide a fertile platform for realizing a purely
quantum-geometry-driven excitonic
insulator (EI) phase. By applying an out-of-plane Zeeman field to lift
spin degeneracy without
spin-orbit coupling, we establish a Ginzburg-Landau framework in which the electron-hole wavefunction-overlap directly maps the flat-band
quantum metric onto the macroscopic free energy. This mapping plays a key role in both the EI and the associated superfluid phases, with the coherence length and phase stiffness emerging directly from the
quantum metric. Our analysis reveals that under strong interactions, the
quantum metric induces a negative effective kinetic coefficient for the amplitude mode. Rather than destabilizing the uniform condensate, this softens the amplitude fluctuations at a finite momentum, giving rise to a finite-momentum superfluid density fluctuation (FMSDF) state. This state is observable as a periodically modulated magnitude of in-plane magnetization fluctuations. Our findings establish a rigorous link between flat-band
quantum geometry and dynamic collective excitonic states, with promising pathways for realization in covalent-organic frameworks (COFs).
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Superconductivity
Influence of Harris disorder on quantum-critical superconductivity
Serhii Kryhin, Peter Lunts, Aavishkar A. Patel et al. (+2 more)
In the Hertz theory, a
quantum critical metal is described by the coupling of a
Fermi surface to fluctuations of a Landau-damped bosonic field $\phi$, which may represent either an order parameter or a
Higgs field for a transition without
symmetry breaking. Scattering from $\phi$ produces non-
Fermi-
liquid behavior in the normal state, while the same fluctuations mediate enhanced Cooper pairing. By the Harris criterion,
symmetry-preserving disorder couples most strongly to the coefficient of the $\phi^2$ term, locally tuning the system toward or away from criticality. This random mass (“Harris disorder”) leads to a finite density of localized low-energy $\phi$ modes even when the fermionic states remain extended and continue to provide Landau damping. We study the onset of pairing mediated by these localized overdamped bosonic modes. Starting from a real-space linearized Usadel equation for the two-particle propagator, we show that the localized bosonic wave functions generate both a spatially random pairing vertex and an effective random potential for Cooper pairs. Numerical solution, a self-consistent Born approximation, and Lifshitz-tail analysis reveal two regimes of the pairing instability. At high temperatures, pairing nucleates compact superconducting puddles on the most localized bosonic modes. At lower temperatures, an extended pairing eigenstate appears, but its transition scale and spatial structure remain strongly affected by mesoscopic correlation effects and enhanced probability of returns to favorable regions of the localized bosonic glue. The resulting distribution of local pairing scales has a power-law tail, in contrast to the stretched-exponential tails of disordered BCS
superconductors. This mechanism provides a route to broad gap inhomogeneity and superconducting puddles in
quantum-critical metals, and offers an interpretation of STM measurements of the cuprates.
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All authors Serhii Kryhin, Peter Lunts, Aavishkar A. Patel, Subir Sachdev, Pavel A. Nosov
Materials Science
INCARBench: A Benchmark for Scientific Configuration in VASP INCAR by Large Language Models
Bin Shao, Jixiang Li, Xinyue Zhang et al. (+3 more)
Large
language models (LLMs) are increasingly being integrated into first-principles computational workflows, yet their ability to configure scientific calculations remains poorly understood. Here, we introduce INCARBench, a
benchmark for evaluating LLMs on input configuration for the Vienna Ab initio Simulation Package (VASP) through both configuration generation and repair tasks. Evaluating 19 model configurations reveals substantial capability differences among current frontier models. While several models achieve high semantic and policy accuracy, task-critical correctness remains substantially lower, demonstrating that parameter-level correctness does not necessarily imply scientifically valid configurations. Failure analysis shows that errors concentrate in physically coupled settings involving DFT+$U$, magnetism, and correlated materials, where multiple constraints must be satisfied simultaneously. Repair evaluation further reveals that correcting incorrect settings and preserving already-valid configurations are distinct capabilities, with configuration preservation remaining a major challenge. These findings establish scientific configuration as a measurable capability of large
language models and provide a foundation for developing more reliable AI systems for computational materials science.
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All authors Bin Shao, Jixiang Li, Xinyue Zhang, Baishun Yang, Zhiyang Liu, Weichao Wang
Statistical Mechanics
Skewness tunes the small-drift record rate of random walks and Lévy flights
José Ricardo G. Mendonça
A random walk with small positive drift $\mu$ sets new records at a rate $\lambda(\mu)$ that vanishes as $\mu \to 0$. For Gaussian and strictly stable centered steps whose stable law $Y$ has index $1 < \alpha \leq 2$ and positivity parameter $\rho = \mathbb{P}(Y>0)$, we find $\lambda(\mu) \sim K\mu^{(1-\rho)/\nu}$ as $\mu \to 0$, where $\nu=1-1/\alpha$ and $K$ is explicit. Throughout their domains of attraction, the exponent persists, with a slowly varying factor replacing the constant $K$. The exponent is set by the asymmetry only through $\rho$, sweeping the interval $[1,\,1/(\alpha-1)]$ as the skewness varies. For centered strictly stable steps, $\rho$ also governs the driftless record growth, $\langle R_{N}\rangle \sim N^{\rho}/\Gamma(1+\rho)$, which the small-drift law meets at the crossover where the drift takes over. The formula recovers the Gaussian linear law $\lambda(\mu) \sim \sqrt{2}\mu/\sigma$ and, for symmetric heavy tails, the power $\mu^{\alpha/2(\alpha-1)}$. It follows from one Mellin transform of the harmonic sum in the Spitzer–Baxter identity, which factorizes into a kernel transform carrying the step distribution and a Riemann
zeta function carrying the harmonic weights. Its poles deliver the leading law, its prefactor, and a correction ladder reproducing the known Gaussian and stable series, unifying diffusive, heavy-tailed, and skewed walks. The power law ends at the Cauchy point $\alpha=1$, where $\mu$ is a pure location shift: for the strictly Cauchy family the limiting rate vanishes and records accumulate sublinearly with a shift-dependent exponent.
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Disordered Systems and Neural Networks
Approximating velocity fields with planted point attractors via Neural-ODE for classification purposes
Feliciano Giuseppe Pacifico, Duccio Fanelli, Lorenzo Buffoni et al. (+3 more)
In this work, Neural ODEs equipped with a curated collection of
equilibrium points have been successfully employed for classification tasks. The planted fixed points serve as indicators for the target classes, while the velocity field, leveraging the universal approximation capabilities of the architecture, shapes the dynamical landscape. This process defines the basins of attraction of the trained model, effectively directing each input (provided as an initial condition) toward its corresponding destination target.
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All authors Feliciano Giuseppe Pacifico, Duccio Fanelli, Lorenzo Buffoni, Lorenzo Chicchi, Diego Febbe, Raffaele Marino
Quantum Gases
A dipolar Bose-Bose mixture of Dysprosium isotopes with controllable interspecies interactions
M. Duerbeck, L. Reihs, J.P. Marulanda-Serna et al. (+5 more)
We report on the realization of a
quantum-degenerate Bose-Bose mixture of 162Dy and 164Dy. Owing to the near-identical mass and polarizability of the two isotopes, the mixture thermalizes efficiently, with evaporation trajectories closely following those of the single-isotope case. Using a broad interspecies Feshbach resonance, we explore a miscible-immiscible transition between the two Bose-Einstein condensates. The tunability of the interspecies interaction, combined with the large
magnetic dipole moment of Dy, makes this platform well suited for exploring dipolar effects in ultracold mixtures, including multi-component supersolidity.
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All authors M. Duerbeck, L. Reihs, J.P. Marulanda-Serna, B. Choudhari, J. Seifert, N. Werum, G. Meijer, G. Valtolina
Materials Science
Atomic-scale theory of robust out-of-plane ferroelectricity in ultrathin films
Fengbo Yuan, Yujia Teng, Karin M. Rabe et al. (+1 more)
Ferroelectricity in ultrathin films, characterized by robust switchable out-of-plane polarization, is key to next-generation nanoelectronics. Although the macroscopic theory of ferroelectricity suggests that ferroelectricity is inevitably suppressed as the film thickness decreases, recent studies have demonstrated robust ultra thin-film ferroelectricity, for certain ferroelectric materials, specifically HfO$_2$-based
oxides and bismuth-based
oxides. In this work, we develop an atomic-scale theoretical framework for understanding ferroelectricity in this limiting regime. By considering the work function of the termination layers of the film, we find that robust ferroelectricity arises from “self-polarizing” and “switchable role of the termination layer” effects strongly correlated to the “characteristic structure.” This theory also provides further insights on the importance of top electrodes in stabilizing ferroelectricity for this class of materials in the ultrathin limit. This work aims to develop a comprehensive theoretical framework for thin-film ferroelectricity, providing fundamental insights that can guide the design of next-generation nanoscale devices.
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All authors Fengbo Yuan, Yujia Teng, Karin M. Rabe, Yubo Qi
Materials Science
High-quality single crystals of the kagome metals Ni$_3$In and Ni$_3$Sn grown from Pb flux
Fabian Garmroudi, Jennifer Coulter, Caitlin S.T. Kengle et al. (+4 more)
The
bilayer kagome metal Ni$_3$In has recently attracted
attention due to the presence of a flat band located near the
Fermi level, which has been associated with unconventional thermodynamic and electronic transport properties [Ye et al., Nat. Phys. 20, 610-614 (2024)]. However, further investigation of the intrinsic properties of this system has been hindered by the lack of large, high-quality single
crystals. Here, we report the successful growth of Ni$_3$(In, Sn) single
crystals using a Pb-flux technique. By optimizing the growth conditions, competing binary phases can be effectively suppressed, enabling the synthesis of single
crystals with dimensions reaching several millimeters. We compare the physical properties of our Pb-flux-grown
crystals to previously reported samples prepared by iodine-assisted chemical vapor transport and molecular beam epitaxy as well as to first-principles resistivity calculations. We find a significantly lower electrical resistivity in our
crystals, in excellent agreement with calculations of resistivity from electron-
phonon scattering, a sizeable non-saturating magnetoresistance, and a reduced Sommerfeld coefficient and
magnetic susceptibility compared to previous experimental findings, which are likely related to differences in the
Fermi level position. Our results establish Pb-flux growth as a reliable route for obtaining large single
crystals of the
bilayer kagome metals Ni$_3$(In, Sn) that are suitable for further thermodynamic and spectroscopic investigations of their intrinsic electronic and
magnetic properties.
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All authors Fabian Garmroudi, Jennifer Coulter, Caitlin S.T. Kengle, Joe D. Thompson, Eric D. Bauer, Sean M. Thomas, Priscila F.S. Rosa
Superconductivity
Anomalous charge density wave in a two-dimensional superatomic superconductor
Boqin Song, Shuaishuai Sun, Zhongxu Wei et al. (+12 more)
The spatial modulation of electron density into a wave-like pattern, known as charge density wave (CDW), represents a fundamental
quantum state that often coexists with superconductivity,
quantum Hall states,
axion insulating phases and etc. Conventional CDWs are mediated by longitudinal acoustic
phonons, exhibit picometer-scale
lattice distortions ($10^{-12}$–$10^{-11}$ m), and typically vanish approaching the atomic limit. Here, we report a series of anomalous CDW behaviors in the 2D superatomic
superconductor Au$_6$Te$_{12}$Se$_8$. Remarkably, its CDW is governed by transverse
phonons, accompanied by an extraordinarily high real-space displacement of $\sim 4$ Ångström. Furthermore, we observe an exotic dimensional response persisting up to micrometer-scale thickness, a regime where other materials are already considered as bulk. Through
liquid helium-temperature transmission electron microscopy, ultrafast pump-probe spectroscopy and transport measurements, we demonstrate a dramatic enhancement of the CDW transition temperature ($T_{\text{CDW}}$) from $<2$ K in the bulk to 110 K in approaching the “superatomic limit”. Our findings not only reveal novel facets of both CDW and superatomic materials, but the competition between this anomalous CDW and superconductivity opens avenues for exploring unconventional electron-
phonon interactions.
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All authors Boqin Song, Shuaishuai Sun, Zhongxu Wei, Xinbo Wang, Xiaoping Ma, Kaifa Luo, Lei Wang, Jun Deng, Xu Chen, Tian Qian, Shuya Xing, Zhihai Cheng, Jiangang Guo, Tianping Ying, Xiaolong Chen
Superconductivity
Magnetic-Free Quantum Interference and Universal Josephson Diode Effect Driven by a Supercurrent Gauge Field
Haowei Ye, Wenxue He, Kaixuan Fan et al. (+8 more)
The Josephson effect, a hallmark of superconducting phase coherence, drives modern
quantum technologies. However, Josephson-based
quantum interference has hitherto been tethered to
magnetic fields, despite phase coherence being a quintessential, intrinsic trait of superconductivity. Moreover, the Josephson diode effect (JDE) is typically viewed as an anomalous phenomenon indicative of broken
symmetries in exotic phases of matter. Here, in planar Josephson junctions made with $\mathrm{Bi}_2\mathrm{O}_2\mathrm{Se}$ and
bilayer graphene, we demonstrate that the JDE is a missing universal property of the Josephson effect. Simultaneously, we present an all-electric technology that replaces
magnetic flux for controlling and measuring supercurrent interference. Central to our approach is a supercurrent gauge field (SGF), generated and amplified through high-kinetic-inductance
superconductors and novel device architectures. By establishing the physical equivalence between the SGF and a
magnetic field, we eliminate the reliance on external fields in
quantum interference and reveal a universal, field-free JDE mechanism with broad implications for detecting broken-
symmetry states. Finally, we show that the SGF offers capabilities beyond those of a conventional
magnetic field by experimentally demonstrating a
magnetic-free, phase-sensitive technique to construct and characterize finite-momentum superconductivity, opening new frontiers for exploring novel phases of matter and superconducting
quantum architectures.
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All authors Haowei Ye, Wenxue He, Kaixuan Fan, Yingpeng Zhang, Shijin Li, Yu Pan, Dechao Geng, Fan Yang, Kenji Watanabe, Takashi Taniguchi, Hechen Ren
Strongly Correlated Electrons
Signatures of unconventional magnetism in the layered metallic ferromagnet LaCrSb$_3$ from ferromagnetic resonance spectroscopy
J. J. Abraham, S. Samanta, R. Kolay et al. (+5 more)
LaCrSb$_{3}$ is a metallic ferromagnet with a layered
crystal structure demonstrating intriguing electronic and
magnetic properties, such as large anomalous
Hall effect, strong canting of the
spin lattice, and a peculiar
spin-reorientation transition. Here, we report the results of the temperature-dependent x-ray diffraction, static magnetization, and in particular electron
spin resonance (ESR) and
ferromagnetic resonance (FMR) experiments carried out over a wide range of frequencies,
magnetic fields, and temperatures. Though x-ray data reveals no structural transition down to 15 K, a strong magneto-elastic coupling is detected across the
ferromagnetic transition at $T_{\rm C} \simeq 126$ K. ESR results indicate a presence of the quasi-static short-range correlations extending far above $T_{\rm C}$, which is a typical fingerprint of the low-dimensional magnetism. The frequency-field diagram of the FMR modes mapped below $T_{\rm C}$ strongly suggests presence of two
magnetic sublattices in LaCrSb$_{3}$. A quantitative understanding of the FMR excitations was achieved within a phenomenological model of interacting orthogonal ferro- and
antiferromagnetic sublattices which was earlier proposed to explain unusually strong
spin canting observed by
neutron diffraction [E.~Granado et al., Phys. Rev. Lett. 89, 107204 (2002)]. The FMR results corroborate this scenario and call for the development of the underlying microscopic model of unconventional magnetism in LaCrSb$_{3}$.
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All authors J. J. Abraham, S. Samanta, R. Kolay, V. Singh, R. Nath, B. Büchner, V. Kataev, A. Alfonsov
Quantum Gases
Population eigenstates of the SU(d) spin-exchange model for high-spin fermions in optical lattices
Hubert Dunikowski and Emilia Witkowska
We investigate the $\mathrm{SU}(d)$
spin exchange model describing ultra-cold fermionic atoms with
spin $s\ge 1$ in a one-dimensional optical
lattice. The model emerges from the
Fermi-Hubbard model in the strongly interacting regime with one atom in each
lattice site. The central result of this work is the systematic construction of eigenstates in terms of
magnetic sub-level populations, which we call population eigenstates. Exploiting this framework, we derive effective light-induced
Hamiltonians via a second-order Schrieffer-Wolff transformation projected onto the population eigenstates. The resulting models reveal a qualitative difference between
spin-1/2 and higher-
spin systems: whereas
spin-1/2 dynamics remains confined to the maximal-
spin Dicke
manifold, the extensive $\mathrm{SU}(d)$ degeneracies for $s\ge 1$ allow coherent population transfer across sectors of different collective
spin length, generating unconventional
spin dynamics that cannot be captured by any fixed-
spin-
manifold description. Agreement with exact
Fermi-Hubbard dynamics confirms the framework as a practical foundation for
quantum-enhanced correlations and metrological protocols in high-
spin fermionic systems.
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Statistical Mechanics
Irreversibility Enhances Quantum-Enhanced Markov-Chain Monte Carlo
Kefan Cao, Zidong Cui, Lei Wang et al. (+1 more)
Detailed balance underlies conventional Markov-chain Monte Carlo (MCMC)
algorithms. Yet in classical systems, breaking detailed balance generates irreversible probability currents and can accelerate sampling. Whether irreversibility can similarly enhance
quantum MCMC remains an intriguing question. Here we show that irreversibility provides a new route to improving the recent
quantum-enhanced MCMC (QEMC), which combines
quantum proposals with classical acceptance. By introducing state-dependent proposals that break detailed balance while preserving the target stationary distribution, we develop an irreversible
quantum-enhanced Monte Carlo (IQEMC). Guided by Landau-Zener transitions, IQEMC promotes large energy descents from high-energy states while maintaining stable transitions near low-energy states. On
spin-glass
benchmarks, IQEMC outperforms QEMC without increasing computational complexity and, unlike the annealing baseline, exhibits a spectral gap that increases with system size and annealing speed. These results establish irreversibility as a physically grounded mechanism for enhancing
quantum MCMC.
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All authors Kefan Cao, Zidong Cui, Lei Wang, Ying Tang
Soft Condensed Matter
Dissociation of NaCl in supercritical aqueous fluids of moderate and high concentrations: A molecular dynamics study
Mikhail V. Ivanov and Olga V. Alexandrovich
We report classical molecular dynamics simulations of NaCl association and dissociation in supercritical aqueous fluids over a wide range of salt concentrations, from moderate salinity to highly concentrated H2O-NaCl mixtures attainable at high temperatures. The degree of dissociation a and the corresponding ideal dissociation constant Kd, derived directly from a, were calculated as functions of the stoichiometric NaCl mole fraction at selected pressure-temperature (PT) conditions from 673.15 to 1273.15 K and from 0.1 to 2 GPa. At moderate salinity corresponding to a molality of approximately 1 mol/kg, NaCl remains largely dissociated a = 0.3-0.7 depending on pressure and temperature). In contrast, when the mole fraction of NaCl increases up to xNaCl = 0.333 (27.8 mol/kg), the degree of dissociation tends towards zero, and most ions form Na$^+$Cl$^-$ contact pairs and multi-ion clusters. As a result of these competing trends, the mole fraction of structurally dissociated Na$^+$ and Cl$^-$ ions is a non-monotonic function of the stoichiometric NaCl concentration and typically reaches a maximum at xNaCl = 0.06-0.10. This result shows that increasing salinity does not necessarily increase the abundance of structurally available chloride ions in supercritical aqueous fluids. Additional fixed density simulations at 1 and 7 mol/kg extend the analysis up to 1673.15 K and separate the effects of temperature and density on the associate/dissociate state of the ions. The obtained concentration dependences provide molecular-level constraints for thermodynamic descriptions of concentrated supercritical electrolytes and for evaluating chloride availability in high-temperature aqueous fluids.
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Materials Science · Cross-listed from physics.optics
Hexagonal Boron Nitride Spin Defects for Quantum Photonics: Annealing-Free Generation by Krypton Ion Implantation
Ikshvaku Shyam, Raj Singh, Mangababu Akkanaboina et al. (+11 more)
Controlled, reproducible generation of luminescent defect centres in hBN remains a key challenge for scalable
quantum-photonic technologies. Here, we report Kr$^{+}$ ion implantation as a tunable, annealing-free, and chemically inert route to room-temperature near-infrared luminescent
spin defects in hBN, requiring no pre- or post-implantation annealing. SRIM Monte Carlo simulations were used to optimise the parameters for 40 keV Kr$^{+}$ irradiation of hBN flakes. The implanted samples exhibit a stable near-infrared photoluminescence (PL) band centred at $\sim$830 nm whose intensity increases with implantation fluence over $10^{11}$-$10^{15}$ions/cm$^{2}$. Temperature-dependent PL measurements (20-300 K) reveal a linewidth broadening well described by a $T^{3}$ dependence, consistent with acoustic-
phonon-mediated dephasing. Raman spectra show the characteristic $E_{2g}$ mode of pristine hBN at $\sim$1366 cm$^{-1}$ alongside an implantation-induced defect feature at $\sim$1295 cm$^{-1}$, confirming irradiation-induced
lattice disorder. Electron paramagnetic resonance (EPR) measurements reveal a paramagnetic centre with a $g$-factor of 2.003, and density functional theory (DFT) calculations indicate that a spatially separated $V_{\mathrm{N}}$-$C_{\mathrm{B}}$ donor-acceptor pair complex is a viable origin of the observed optical and
magnetic signatures. Overall, Kr$^{+}$ implantation offers an effective, annealing-free, and scalable platform for generating stable room-temperature luminescent defects, providing a promising route toward
quantum photonics.
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All authors Ikshvaku Shyam, Raj Singh, Mangababu Akkanaboina, A. M. Sonawane, Muthu Satheeshkumar, Amrita Majumder, Ekta, Janhavi Jayawant Khunte, Akash Khaire, Kenji Watanabe, Takashi Taniguchi, Gopalan Rajaraman, S. S. Dahiwale, Anshuman Kumar
Quantum Gases
Degeneracy-governed spin squeezing in high-spin Fermi-Hubbard systems weakly coupled to light
Hubert Dunikowski and Emilia Witkowska
High-
spin alkaline-earth
fermions in optical
lattices are promising platforms for
spin squeezing beyond the
spin-1/2 paradigm. We show that
spin-squeezing dynamics is qualitatively modified by degeneracies inherent to the extended internal
spin structure. We identify these degeneracies as the microscopic origin of the breakdown of the conventional maximal-
spin description and develop an effective population-eigenstate framework that quantitatively reproduces the
spin-squeezing dynamics. Our results establish degeneracy as a generic driver of collective
spin dynamics in high-
spin systems.
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Mesoscale and Nanoscale Physics
Reactive Force Field for P/Sn/I System: Atomistic Insight into the Early Stage of Black Phosphorus and Phosphorene Synthesis Process
Djuric Brice Talonpa Tchoffo, Ismail Benabdallah, Petr Neugebauer et al. (+2 more)
Black phosphorus and its two dimensional counterpart, phosphorene, are typically synthesized through chemical vapor transport using Sn and I2 additives. Chemical vapor deposition synthesis of phosphorene and allotropes is still yet not well understood. Investigating the atomistic mechanisms underlying phosphorus transport and early stage processes is difficult experimentally. In this study, a reactive force field for the PSnI system was developed and applied using ReaxFF based molecular dynamics to explore the early stage phase of the pre nucleation relevant to BP-phosphorene growth. The force field parameters were trained on a comprehensive
quantum mechanical
dataset covering bond dissociation, angle and torsion profiles, and tin condensed phase equation of state and cluster formation energies, showing strong agreement in both gas and condensed phases. We demonstrate that iodine and density together control phosphorus recombination. Under low density, atomic phosphorus dominates with minimal clustering. Adding I2 greatly increases P-P recombination, promotes the formation of PxIy motifs, and transient SnxPyIz compounds. Higher density systems favor the formation of larger Px clusters and support the development of ternary SnxPyIz compounds that grow by capturing transported phosphorus. At the highest density, the system produces condensed, Hittorf like phosphorus structures at the edges of SnxPyIz clusters, along with BP-like hexagons stabilized by iodine that may act as nucleation seeds. These results offer an atomistic view of transport and early stage steps in BP synthesis and provide a practical reactive model for studying growth conditions and additive effects in BP phosphorene vapor synthesis.
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All authors Djuric Brice Talonpa Tchoffo, Ismail Benabdallah, Petr Neugebauer, Anouar Belhboub, Abdelouahad El Fatimy
Other Condensed Matter
Synchronization in coherently and dissipatively coupled spinor polariton time crystals
I. Carraro-Haddad, A. Ramos-Pérez, G. Usaj et al. (+6 more)
The spinor degree of freedom associated to
exciton-polariton condensates can spontaneously self-oscillate breaking time translation
symmetry, thus showing a continuous time-
crystal (CTC) behavior. An open question in such driven-dissipative and non-linear
quantum open systems is what happens when CTCs are brought together to interact. Here we experimentally study polariton condensates in coupled traps, evidencing mutual induction and synchronization of the pseudospin temporal GHz dynamics in the CTC phase. The individual and relative orientation of the (limit cycle) precessing pseudospins can be tuned by the optical excitation power, displaying both ferro and anti-ferro dynamical configurations. We theoretically show that the
exciton reservoir, and both the coherent and long-range dissipative inter-trap coupling, play important roles in the CTC dynamics. The investigation of time-broken
symmetry is thus extended here to more complex non-hermitian systems opening the path to study self-sustained collective dynamics in
lattices of non-linear
quantum condensates.
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All authors I. Carraro-Haddad, A. Ramos-Pérez, G. Usaj, A. Bruchhausen, K. Biermann, P. V. Santos, A. S. Kuznetsov, A. A. Reynoso, A. Fainstein
Superconductivity
Kohn-Luttinger like superconductivity in twisted bilayer graphene at large twist angles
A.O. Sboychakov
We predict that twisted
bilayer graphene with large twist angle and small superlattice
cell can be superconducting. Such a
bilayer graphene can have a gap in the spectrum. This gap appears due to the hybridization of electrons moving in different layers with
Fermi momenta close to the Dirac points which are equivalent to each other in the superlattice Brillouin zone. Small doping of the
bilayer introduces charge carries having large density of states. We show that the screened Coulomb interaction is enough to stabilize superconducting state in the material. The
symmetry of the order parameter is of the $d$-wave type. Application of the bias voltage increases the superconducting transition temperature. For realistic values of the model parameters the transition temperature can be as large as several hundreds of milikelvin.
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Materials Science
Step-Edge Passivation and Quantitative Raman Mapping of Transfer Quality in Aligned Graphene Nanoribbons
Dominik Lüthi, Rimah Darawish, Klaus Müllen et al. (+2 more)
The transfer of aligned
graphene nanoribbons from metallic growth surfaces to device-compatible platforms remains a central bottleneck for nanoribbon electronics. Here, we investigate step-edge passivation of vicinal Au(788) by chevron-GNRs as a strategy to improve the transfer of aligned 9-armchair
graphene nanoribbons. Scanning tunneling microscopy reveals that chevron-GNRs preferentially occupy step-edges, effectively acting as passivators that displace 9-AGNRs toward terrace centers, thereby altering their local growth configuration. To quantify transfer performance, we establish an automated large-area Raman analysis framework that enables pixel-wise classification based on the G mode and the radial breathing-like mode (RBLM). This approach provides a robust and scalable metric for assessing both transfer coverage and local ribbon integrity across macroscopic areas. Raman mapping uncovers strongly inhomogeneous transfer, characterized by extended regions with no detectable GNR signal and pronounced spatial variability in the RBLM-to-G intensity ratio. Transfer quality varies substantially across the sample series, with only a single high-yield outlier and most samples remaining well below 100% transfer yield. These results demonstrate that while chevron passivation locally modifies the growth configuration of 9-AGNRs on Au(788), it does not yet yield reproducible, high-quality transfer of intact aligned ribbons. The presented Raman-based analysis framework establishes a quantitative
benchmark for the systematic optimization of GNR transfer strategies.
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All authors Dominik Lüthi, Rimah Darawish, Klaus Müllen, Roman Fasel, Gabriela Borin Barin
Superconductivity
Harnessing Josephson-Shapiro physics to verify interlayer exciton superfluidity
Filippo Pascucci, Alexander R. Hamilton, Milorad V. Milosevic et al. (+1 more)
Obtaining definitive evidence for zero-
magnetic-field
exciton superfluidity in electron-hole
bilayers remains a longstanding challenge because the condensate is electrically neutral and its phase coherence is difficult to probe directly. We propose a direct test based on Shapiro steps in a Dayem-bridge excitonic Josephson junction. We predict clearly resolvable Shapiro plateaus in experimentally accessible current and voltage regimes for double-
bilayer graphene and, in the low-density regime, double-layer transition-metal dichalcogenides. Moreover, by tuning the density across the BCS-BEC crossover we show that the Shapiro response acquires a distinct nonmonotonic
evolution. This is determined by the nonmonotonic behavior of the healing length in the crossover from bosonic to fermionic excitations. Observation of these signatures would provide direct evidence of
exciton superfluidity and establish
exciton bilayers as a platform for neutral Josephson devices.
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All authors Filippo Pascucci, Alexander R. Hamilton, Milorad V. Milosevic, David Neilson
Strongly Correlated Electrons
Wess-Zumino terms in 0+1 SU(N) superspin systems
J. S. Morales and M. N. Kiselev
These notes present a self-contained introduction to Wess-Zumino (WZ) terms in
quantum systems with $SU(N)$
symmetry, emphasizing the interplay between geometry,
topology, and condensed-matter applications. We begin with the $SU(2)$
spin coherent-state path integral, where the Berry phase appears as a WZ term encoding the
symplectic structure of the Bloch sphere. This example is then used to introduce the
geometric origin of topological terms, their relation to integral
cohomology classes, and the role of Berry
curvature as the first Chern class of the canonical $U(1)$ bundle. We next discuss physical realizations in which such
geometric terms affect dynamics, including adiabatic Berry phases and
geometric quantum noise in
magnetic quantum dots. A substantial part of the notes is devoted to the condensed-matter motivation for higher $SU(N)$
symmetries, covering $SU(N)$ Heisenberg models, $SU(4)$
spin-orbital and
spin-pseudospin systems, multipolar exchange interactions, and higher-
spin multipolar orders. Finally, we develop the 0+1-dimensional $SU(N)$ superspin coherent-state construction, identify the phase space with $CP^{N-1}$, and derive explicit local WZ terms for $SU(3)$ and $SU(4)$. The appendices provide algebraic dictionaries connecting the abstract superspin
language with concrete physical
embeddings, including multipolar generator bases and several useful $SU(4)$ parametrizations.
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