Materials Science
Epitaxial growth of WO3 on r-plane sapphire by hot-filament metal-oxide deposition using CO2 as a precursor
Laurent Souqui, Lewis J. Adams, Andreas Tsampanakis et al. (+2 more)
The deposition of epitaxial films of WO3 by hot-filament metal-oxide deposition using CO2 as a precursor was demonstrated. The films were obtained at a low growth rate of 0.25 nm/min. The optical properties of the film were assessed by variable-angle spectroscopic ellipsometry, indicating transparency across the visible spectrum and high absorption above 3 eV.
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All authors Laurent Souqui, Lewis J. Adams, Andreas Tsampanakis, David Rehnlund Maibach, Per Eklund
Materials Science
The role of density in shaping electron trapping in amorphous silicon nitride
Jonathon Cottom and Emilia Olsson
The electronic properties of amorphous silicon nitride vary with processing, which often changes stoichiometry and density together. Separating their contributions is essential to connect film structure with electron trapping. Across 499 stoichiometric configurations spanning 2.86-3.19g cm$^{-3}$, porosity controls the trapping mixture. Lower density increases accessible void fraction from 8.4 to 12.6%, expands internal surface and more than triples the supply of free three-coordinate Si precursors. Capture at pre-existing Si dangling bonds (K centres) rises from 9 to 29%, while induced-K and polaronic trapping decline. A neutral precursor fingerprint predicts the trapping mixture in held-out configurations and reproduces its density dependence. Local compensation controls K-centre activation, electronic competition selects capture, and bond strain predicts polaronic relaxation or induced-K formation. Routes involve distinct network volumes but retain their characteristic depths and relaxation energies across the density range. At fixed stoichiometry, density controls the trapping mixture through porosity and precursor availability.
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Strongly Correlated Electrons · Cross-listed from hep-th
Dielectric constant of holographic insulator from quantum geometry
Debabrata Ghorai, Taewon Yuk and Sang-Jin Sin
We study dielectric properties of holographic
insulators from the
quantum geometry of the ground state. We realize the insulating state by the pseudoscalar interaction of holographic
fermions and calculate the fermionic Green function to extract the effective
hamiltonian. We then derive the
quantum metric and Berry
curvature to compute the transports and finally get the dielectric constant from the imaginary part of conductivity.
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Materials Science
Probing $L_z$ Orbital Angular Momentum via Wavefunction-Interference-Induced Charge Order
Jonas Erhardt, Sven Schemmelmann, Fabian Schöttke et al. (+9 more)
Orbital angular momentum (OAM) characterization is central to understanding
quantum materials such as valley Hall and Rashba systems and, through its connection to Berry
curvature, provides key insight into band
topology. Conventional OAM detection via photoemission dichroism, however, is susceptible to interference artifacts and is largely restricted to occupied states. Here, we demonstrate a real-space approach to map the $L_z$ OAM character using scanning tunneling microscopy in triangular atomic monolayers. Unlike photoemission, this method exploits interference effects arising from the $L_z$ orbital phase and the Bloch phase associated with neighboring atoms. This shifts the local density of states (LDOS) maxima to distinct Wyckoff positions between atoms, encoding $L_z$ information into characteristic real-space LDOS patterns. We exemplify this approach in 2D
quantum materials with contrasting $L_z$ sequences, namely Tl/Si(111) and In/SiC(0001) monolayers, identifying $L_z$-dependent LDOS accumulation associated with distinct topological phases in both systems. Our results establish $L_z$-dependent charge localization as a proxy to atomic obstruction for energetically isolated states in triangular
lattices, including transition-metal dichalcogenides.
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All authors Jonas Erhardt, Sven Schemmelmann, Fabian Schöttke, Cedric Schmitt, Lukas Gehrig, Bing Liu, Domenico Di Sante, Giorgio Sangiovanni, Jörg Schäfer, Peter Krüger, Markus Donath, Ralph Claessen
Materials Science
Achieving room temperature plasticity in TiO2 ceramics by flash processing
Xinghua Su, Zhenyu Li, Xufei Fang et al. (+3 more)
Ceramics are indispensable materials for modern engineering and high-technology applications. However, the intrinsic brittleness at room temperature can cause catastrophic failure and severely limit their widespread applications. Here, we report a flash processing (FP) method based on the coupling of electric and thermal fields to significantly improve the room-temperature plasticity of TiO2 ceramics with a large plastic compressive strain of 15.4% during micropillar compression. This large room-temperature plasticity is attributed to the proliferation of stacking faults and twin boundaries during the loading process, which may be assisted by the high concentration of oxygen vacancies introduced by the FP method. Our findings suggest that FP can be a simple and effective method for achieving improved room-temperature plasticity of ceramic materials through defect engineering.
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All authors Xinghua Su, Zhenyu Li, Xufei Fang, Wenjun Lu, Mengyao Wang, Peng Zhao
Strongly Correlated Electrons
Multipolar fluctuations in localized $4f^2$-electron systems from dynamical mean-field theory: application to $\mathrm{PrCdNi}_4$
Koki Numa and Junya Otsuki
Multipolar-fluctuation analysis based on density functional theory combined with dynamical mean-field theory is extended from $4f^1$- to $4f^2$-electron systems. Two methodological developments are presented. First, many-particle states are constructed within the $j$-$j$ coupling scheme in the $j=5/2$ subspace, so as to reproduce the crystalline-electric-field splitting of the $4f^2$ Hund's-rule ground-state multiplet. Second, multipolar susceptibilities and interactions between $4f^2$ multiplets are derived through a mapping from single-particle to many-particle bases. We apply this framework to PrCdNi$_4$, which has a non-Kramers $\Gamma_3$ doublet ground state, and propose a $(3z^2-r^2)$-type antiferroquadrupolar order at $\boldsymbol{q}=(2\pi,\pi,0)$ driven by the competition between nearest- and fourth-nearest-neighbor interactions. The formalism developed here is applicable to general $4f^n$-electron systems.
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Materials Science
Demonstration of ultrafast coherent sub-picosecond magnon pulses
Peter Kubaščík, Miina Leiviskä, Martin Bušina et al. (+20 more)
Ultrafast magnonics explores routes towards energy-efficient information processing by replacing electrons with pulses of terahertz
magnons. The critical, but so far elusive, requirement on the
magnon pulses is the combination of high-speed and a long-range propagation while maintaining a well-defined narrow waveform of the pulses. Here, we demonstrate the launching of 0.4-picosecond
magnon pulses in the altermagnetic
insulator $\alpha$-Fe$_2$O$_3$ (hematite) using broadband terahertz
spin-orbit torques by an adjacent platinum layer. Phase-resolved terahertz transmission reveals that these sub-picosecond pulses travel ballistically, coherently and non-dispersively at a constant velocity of 23 nm/ps, transport angular momentum and retain their temporal waveform shape over 160 nm, with an inferred relaxation length in hundreds of nanometers or more. Beyond establishing $\alpha$-Fe$_2$O$_3$ as an optimal platform for ultrafast magnonics, our technique introduces a high-resolution, tabletop method to directly extract dispersion relations up to high wavevectors, and explore ultrafast
magnon dynamics in altermagnets and other
magnetic materials with teraherz-range dynamics.
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All authors Peter Kubaščík, Miina Leiviskä, Martin Bušina, Zdenek Kašpar, Katharina Müller, Jonathan Mak, Monika Scheufele, Gal Lemut, Jose Solano, Oliver Franke, Rostislav Matuška, Jiří Jechumtál, Eva Schmorranzerová, Petr Němec, Petr Kužel, Tobias Kampfrath, Piet W. Brouwer, Matthias Opel, Stephan Geprägs, Matthias Althammer, Tomáš Jungwirth, Helena Reichlova, Lukáš Nádvorník
Quantum Gases
Nonlinearity management of matter-wave vector solitons of Bose-Einstein condensates in two dimensions
F. Kh. Abdullaev, J. S. Yuldashev and M. Ögren
The
evolution of matter-wave vector
solitons in two dimensions under nonlinearity management is studied. The averaged over strong and rapid modulations in time of the inter-species interactions vector Gross-Pitaevskii equation is derived. The averaging gives the appearance of the effective nonlinear
quantum pressure depending on the population of the other component. Using this system of equations, the dynamical stabilization of the two-dimensional vector matter-wave
solitons under the management of the mean-field nonlinearity is investigated. It is shown that the nonlinear
quantum pressure arrests the collapse in the averaged system, giving rise to stable vector
solitons. Full numerical simulations of the original, time-dependent system of Gross-Pitaevskii equations confirm that the management strongly prolongs the lifetime of these
solitons compared to the unmanaged case.
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Materials Science · Cross-listed from cs.AI
AtomWorld-Mirror: Macro-Step World Modeling of Critical Evolution Backbones for Materials Dynamics
Ziming Pan, Ruge Zhang, Haozhi Han et al. (+7 more)
Atomistic simulation is a fundamental tool for studying long-term materials
evolution, from
diffusion and defect dynamics to interfacial reactions and fracture. Yet conventional simulators typically advance at microscopic resolution, spending substantial computation on low-impact local updates before reaching structurally consequential states, an evolutionary-resolution bottleneck that limits long-horizon simulation. We propose AtomWorld-Mirror, a time-aware macro-step world model for the critical
evolution backbone of atomic systems. For Step-Wise atomistic simulation, AtomWorld-Mirror distills short micro-event segments into physically reachable transitions between key states, jointly predicting sparse structural edits and accumulated physical time through latent macro-step dynamics. Local reachability, inventory conservation, and continuous-time consistency constrain each transition. By amortizing local atomic physics into a reusable latent macro model and replacing explicit micro-event replay with macro-step inference, this formulation provides a path toward substantially faster prediction of long-term materials
evolution while preserving structural validity and time semantics. Across five atomic systems, spanning Cu-rich RPV steel irradiation aging, Cu-Zr metallic glass, and Li$_3$N-based anti-perovskite solid electrolyte, macro-step inference delivers a speed up of $10^3$ to $10^4$ times over event-by-event simulation.
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All authors Ziming Pan, Ruge Zhang, Haozhi Han, Junkai Zhou, Xingyuan Chen, Yifeng Chen, Yunquan Zhang, Ting Cao, Yunxin Liu, Kun Li
Materials Science
Effects of chlorine substitution on the magneto-optical properties of CrSBr
Z. Śnioch, R. Komar, M. Kuna et al. (+7 more)
We present a systematic study of the effects of chlorine substitution on the magneto-optical properties of the van der Waals layered
semiconductor CrSBr. Our study shows that even at substitution level of $x=56\%$ the $\mathrm{CrSBr_{1-x}Cl_{x}}$ material exhibits qualitatively the same clear magneto-optical coupling that was observed in pure CrSBr
crystals. The values of the relevant parameters are shown to vary smoothly across different substitution levels, thus offering promising tunability for this family of 2D
magnetic materials.
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All authors Z. Śnioch, R. Komar, M. Kuna, M. Raczyński, K. Mosina, A. Söll, Z. Sofer, K. Wohlfeld, P. Kossacki, T. Kazimierczuk
Statistical Mechanics · Cross-listed from quant-ph
Topological Superradiant Universality Classes in Cavity-Mediated Spin Chains
Yunhao Liu, Sheng Yang, Mingyuan Chen et al. (+1 more)
Superradiant phase transitions are fundamental phenomena in light-matter coupled systems. Here, we uncover a novel class of superradiant criticality that is topologically distinct from previously known superradiant transitions. Using cavity-mediated cluster-Ising chains as an illustrative example, we numerically demonstrate that the critical line separating the superradiant phase from the cavity topological phase hosts robust
symmetry-protected edge degeneracies, a feature absent in conventional superradiant transitions. Remarkably, although its local bulk critical properties are indistinguishable from those of the previously identified topologically trivial superradiant transition, the two criticalities cannot be smoothly connected without breaking the protecting
symmetries or passing through a multicritical point. We further show that such topological superradiant criticality is generic, also occurring in cavity-mediated $\mathbb{Z}_{n}^{}$ cluster-qudit chains, as supported by complementary
lattice simulations.
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All authors Yunhao Liu, Sheng Yang, Mingyuan Chen, Xue-Jia Yu
Soft Condensed Matter
Laser fragmentation in liquid - constructing a generic reaction map
Anton Plech, Yogesh Pokhrel, Meike Tack et al. (+2 more)
Excitation of absorbing colloids in
liquid by pulsed
laser irradiation creates highly non-
equilibrium states of matter that relax via defined pathways of thermal and non-thermal dissipation channels. The structural fingerprint of these channels can be probed by ultrafast in situ x-ray scattering methods and classified as a function of temporal delay of excitation excitation density, or specifically
laser fluence. We study the example of photo-excitation of a gold colloid by picosecond
laser pulses at the interband absorption band at 400 nm in water. By quantifying
lattice temperature, crystalline fraction, particle sizes and the structural response of the water around the nanoparticles a reaction map is constructed that allows to pinpoint heating, particle melting, water bubble formation and finally particle fragmentation to form nanoclusters of predominant sizes of < 3 nm for applications in theranostics, photonics or catalysis.
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All authors Anton Plech, Yogesh Pokhrel, Meike Tack, Matteo Levantino, Sven Reichenberger
Superconductivity
From band reconstruction to Bogoliubov dispersion: How dz2-band enhances iron-based superconductivity
Jingming Yan, Shendong Su, Guihao Jia et al. (+6 more)
Conventional understanding of iron-based superconductivity is usually established based on electronic bands at the Fermi level, leaving deeper bands overlooked as potential factor. Here, we expand this view by demonstrating that a deep-lying dz2 band below the Fermi level can be employed to enhance the superconducting paring strength. By using scanning tunneling microscope to mechanically change the
crystal lattice of an iron-based
superconductor, we observe an upward shift of the deep-lying dz2 band related feature, leading to hybridization with the primary superconducting bands at the Fermi level. We visualize the novel evidence of this band hybridization and resulting enhanced superconducting gap through quasiparticle interference imaging, providing conclusive evidence that engineering such correlations between deep and pairing-active bands is a potent mechanism for amplifying the superconducting gap. This work refines the conventional view of pairing-relevant electronic structures and establishes band hybridization as an effective way to optimize superconducting materials.
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All authors Jingming Yan, Shendong Su, Guihao Jia, Yucong Peng, Xuanyu Long, Zheng Liu, Pei Ouyang, Qi-Kun Xue, Wei Li
Materials Science
Generation, Accumulation, and Utilization of Data in the Automatically Controlled End-Station of a Soft X-ray Beamline
Yasunobu Ando, Masashige Miyamamoto, Keita Hiromori et al. (+4 more)
AI is rapidly transforming materials exploration, yet reliable AI-assisted research depends on experimental data that retains their context, provenance, and machine-readable structure. High-throughput synchrotron measurements therefore require more than automated data acquisition: data generation, accumulation, and utilization must be connected within a continuous workflow. Here, we present a data-centric research framework that integrates the PIONEER system, the OMNES, and ML analysis. The PIONEER system automates sample handling,
vacuum transfer, and scanning XAS at the BL08U soft X-ray beamline of NanoTerasu, systematically generating large volumes of spatially resolved spectral data. Measurement and analysis files are stored in the cloud-based ARIM-mdx data system, while OMNES manages metadata describing samples, preparation procedures, measurement conditions, instrument settings, data locations, and analysis histories. Tabular and JavaScript Object Notation formats are used according to the metadata structure, with numerical values stored separately from units to facilitate machine processing. OMNES organizes these records based on causal relationships among experimental and analytical processes, linking samples, measurements, raw data, processed data, and analysis results through a relational data model and visualizing their relationships as a graph. This causality-based organization preserves experimental and analytical provenance and clarifies how each result was derived from the preceding processes and data. The accumulated spectra can subsequently be processed using ML methods, including dimensionality reduction and materials classification, and the resulting data can be registered back into OMNES. Previously reported ML analysis of BN XAS spectra is presented as an example of the analytical workflow that can be applied to data acquired at the beamline.
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All authors Yasunobu Ando, Masashige Miyamamoto, Keita Hiromori, Takeru Nakashima, Masafumi Horio, Masato Kotsugi, Iwao Matsuda
Materials Science · Cross-listed from physics.app-ph
Time-Domain Analysis of Surface Acoustic Wave Magnetoelectric Sensors
Mohsen Samadi, Henrik Wolframm, Felix Weisheit et al. (+4 more)
The transient response of surface acoustic wave sensors is important for understanding their dynamic behavior, propagation delay, and response to time-varying signals. In this work, the time-domain propagation characteristics of a magnetoelectric SAW sensor based on a multilayer Love-wave delay line are investigated using complementary numerical and experimental approaches. Time-domain analysis is employed to determine the delay time and to extract the phase and group velocities, while frequency-domain analysis provides an independent characterization of the wave dispersion. Both numerically and experimentally, the phase and group velocities are found to differ, reflecting the dispersion of the Love wave in the multilayer structure. At the operating frequency of 146 MHz, the simulated group velocity obtained from wave-field tracking agrees within 0.4% with the value determined from the frequency-domain dispersion relation. The simulated delay time and group velocity also show good agreement with experiment, with deviations of 2.7% in delay time and 0.9% in group velocity. These results demonstrate the consistency of the time- and frequency-domain analyses and provide a quantitative characterization of the transient propagation behavior of SAW sensors.
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All authors Mohsen Samadi, Henrik Wolframm, Felix Weisheit, Dirk Meyners, Eckhard Quandt, Michael Höft, Martina Gerken
Materials Science · Cross-listed from physics.ins-det
Autocorrelation-based beam shape optimization in scanning electron microscopy
Rebecca Guan, Andreas Werbrouck, Matthew M. Maschmann et al. (+1 more)
Many automatically focusing
algorithms for scanning electron microscopes exist. Typically, these optimize a single derived metric (such as image sharpness) without considering the intrinsic beam shape. We describe an
algorithm to automatically focus and stigmate scanning electron microscopes based on the autocorrelation of captured images. In the first part of this work, we develop the theoretical basis of using the autocorrelation to approximate the current beam shape. In the second part, we use this to condition the beam shape on various surfaces, using
Bayesian optimization to tune both working distance and, in particular, stigmation. Through a comparison of the full width at half maximum of the autocorrelation arrays before and after optimization and a visual comparison of images taken of the sample surface before and after optimization, we show that the
algorithm is able to successfully optimize the scanning parameters. Overall, our
algorithm can effectively focus on a variety of topographies at different magnifications.
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All authors Rebecca Guan, Andreas Werbrouck, Matthew M. Maschmann, Matthias J Young
Statistical Mechanics
Quantum annealing of the random transverse-field Ising model in one, two, and three dimensions
István A. Kovács, Neil Shah and Róbert Juhász
Quantum annealing must be sufficiently slow to prevent defect formation. We study this problem in the random transverse-field Ising model via the adiabatic
theorem to obtain the limiting rate at which defect formation can be avoided. Our approach based on the strong-disorder renormalization group (SDRG) technique views the annealing process as a gradual aggregation of strongly coupled clusters, giving access to the elementary events of error formation. We present a scaling theory of the statistics of these events in general dimensions and confront it to an extensive numerical analysis carried out in one, two, and three dimensions by an efficient implementation of the SDRG method. This approach is also validated by exact diagonalization in one dimension by means of the free-
fermion technique. Our results consistently show a logarithmically slow decrease of the error density with the annealing time, characterized by the dimension-dependent critical exponents of the corresponding infinite-disorder fixed point of the model. Furthermore, we provide a map of individual events of potential defect formation in the excitation energy - control parameter plane, which may help in the design of optimal annealing paths.
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Mesoscale and Nanoscale Physics
Magnonic cavity-enhanced quantum magnetometry with nitrogen-vacancy centre ensembles
Nikhil Kumar
Nitrogen-vacancy (NV) centre ensembles are leading room-temperature magnetometers, but their sensitivity is usually extracted from a single resonance and relies on external microwave and bias-field hardware. This work proposes a chip-scale NV magnetometer built around a one-dimensional YIG/CoFeB magnonic
crystal, in which a single structural defect forms a passive magnonic cavity and integrated permanent magnets supply the bias field. Micromagnetic simulations show a defect-localised
spin-wave mode at 2.910 GHz inside the 2.5-3.0 GHz magnonic band gap, 40 MHz from the NV zero-field splitting, with a band structure that matches an independent plane-wave calculation. A Tavis-Cummings/Lindblad model in which the microwave reaches the NV ensemble through this mode predicts a hyperfine-resolved optically detected
magnetic resonance spectrum that is strong only within the mode linewidth, and a dispersive homodyne response with one steep edge per $^{14}$N hyperfine line. The master-equation solutions agree with the closed-form homodyne steady state ($R^2 > 0.9999$) and with an approximate analytic ODMR theory (peak positions within 0.012 MHz). For a critically coupled readout with room-temperature electronics, combining the three edges gives a projected sensitivity of 93 pT/$\sqrt{\rm Hz}$, a $\sqrt{3}$-fold gain over the best single edge. Mapping the sensitivity against the NV-
magnon coupling reveals an optimum near $g_{\rm ens}/2\pi \approx 0.2$-$0.4$ MHz, where it reaches 72 pT/$\sqrt{\rm Hz}$ for a 0.64 MHz
spin linewidth and 19 pT/$\sqrt{\rm Hz}$ for 0.17 MHz, with thermal limits of 6.6 and 1.7 pT/$\sqrt{\rm Hz}$. The
antenna-mode coupling, the NV-
magnon coupling and the
spin linewidth are therefore the main design levers.
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Superconductivity
Strain-engineered long-distance supercurrent in an altermagnetic CrSb based-Josephson junction
Yifan Gao, Jin Yan, Junjie Wei et al. (+27 more)
Altermagnetic materials, characterized by vanishing net magnetization and momentum-dependent
spin splitting, provide a unique platform for realizing unconventional superconducting states without the detrimental stray fields. Here, we demonstrate long-distance Josephson supercurrent transport through epitaxial thin films of the strained altermagnet CrSb. We observe a dissipationless supercurrent across a lateral spacer distance of 150 nm in a CrSb-based Josephson junction, exceeding the conventional
spin-singlet coherence length by nearly two orders of magnitude. This supercurrent is further accompanied by a well-defined
magnetic-field-induced
quantum interference pattern, providing direct evidence for genuine Josephson coupling. Our results reveal altermagnets as a promising route toward generating long-distance supercurrents without macroscopic
magnetic stray fields, opening new opportunities for superconducting spintronic applications.
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All authors Yifan Gao, Jin Yan, Junjie Wei, Yifan Zhang, Zhiyuan Zhou, Tong Zou, Ruiyue Chu, Gui Wang, Kaiwen Shen, Zhiwei Zhang, Fang Chen, Yingfen Wei, Hao Jiang, Xumeng Zhang, Ming Wang, Liyang Liao, Jingli Wang, Yijun Yu, Wu Shi, Qi Yao, Xiaobing Chen, Qihang Liu, Yizheng Wu, Yuhang Li, Xufeng Kou, Cheng Song, Xianzhe Chen, Qi Liu, Xincheng Xie, Ming Liu
Materials Science
Data-Driven Variable-Exponent Analysis for Photoemission Yield Spectroscopy: An Autonomous Self-Diagnosing Framework Based on Integrated Residual Metrics
Shinjiro Yagyu, Takahiro Nagata and Yoshiyuki Nakajima
Photoemission yield spectroscopy (PYS) is widely used for evaluating the electronic states of materials. As automated materials discovery advances, unsupervised extraction of physical information from ambient-air PYS data becomes important. Conventional fixed-exponent analyses and logarithmic transformations suffer from heteroscedasticity, which destabilizes estimation in low-signal regions. To address this, we propose a data-driven analysis framework based on the 1/n-Scan method, which operates directly in the original signal space, removing the
geometric bias inherent in log-transform approaches. We further integrate a self-diagnostic quality-evaluation system that quantifies estimation uncertainty with Akaike weights, together with independent residual metrics–the normalized mean absolute error (NMAE), the RMSE-to-MAE ratio (RMR), the Durbin-Watson (DW) statistic, and a macroscopic metric ($\Delta R^2$)–that distinguish hardware-related data degradation from a physical-model mismatch. Applying the framework to differently doped Si and a polycrystalline Au reference in air, we demonstrate autonomous detection, without assumptions on the emission mechanism, of the breakdown of the single-component approximation in heavily doped p-type Si, arising from the overlap of two emission components with different thresholds, as a statistical anomaly–a decrease in DW below its critical value with an auxiliary increase in $\Delta R^2$, despite sound NMAE and RMR–independently confirmed by a two-component fit ($\Delta$AIC $\approx$ 57, DW recovering from 0.8 to 2.0). For heavily doped n-type Si, the gradual surface
evolution was classified as a change within the single-component description. This framework provides a robust, self-diagnosing analysis engine for closed-loop autonomous materials exploration.
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Strongly Correlated Electrons · Cross-listed from hep-th
Fermionic Spectral Functions in a Two-Current Gubser-Rocha Model with Axion Momentum Relaxation
Cai-E Liu and Defu Hou
We investigate fermionic spectral functions in a two-current Gubser-Rocha background with linear-
axion momentum relaxation. Serving as a comparison channel, the dipole coupling $p_1$ is found to produce a soft asymmetric reconstruction without opening a clean hard Mott gap. Our main analysis then focuses on two
axion-dependent non-minimal couplings modulated by current mixing. The $p_2$ tensor channel suppresses the zero-energy Fermi peak and shifts the dominant spectral weight to finite frequencies, resulting in a flat-bottom reconstruction. In contrast, the $p_3$ vector channel creates a strong spectral asymmetry in momentum space, generating open, Fermi-arc-like segments. Varying the momentum-relaxation strength $\beta/\mu$ and the doping parameter $\chi$ reveals a channel-dependent response to the two-current background. Increasing $\beta/\mu$ generally broadens the $p_2$ response, whereas the one-sided $p_3$ feature varies non-monotonically under changes of the background parameters. These results clarify how current mixing,
axion-induced momentum relaxation, and non-minimal
fermion couplings jointly reshape holographic fermionic excitations. These results clarify how current mixing,
axion-induced momentum relaxation, and non-minimal
fermion couplings jointly reshape holographic fermionic excitations.
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Mesoscale and Nanoscale Physics
Displacement-Field-Induced Ionization of Defect States in High-Quality hBN
Ilia Begichev, Daria Belotcerkovtceva, Iakov Reznikov et al. (+10 more)
Encapsulation of two-dimensional (2D) materials with hexagonal boron nitride (hBN) is widely used to fabricate ultraclean van der Waals (vdW)
heterostructures for optoelectronic and
quantum transport studies. These devices are often operated under strong out-of-plane displacement fields that tune the electronic properties of the active 2D material, while the surrounding hBN is typically assumed to remain electronically inert. This assumption, however, neglects defect states that are present even in high-quality hBN
crystals. Here, we probe their response to the applied displacement field using monolayer
graphene encapsulated between hBN
crystals as a sensitive charge sensor. Increasing the displacement field induces notable charge transfer between
graphene and hBN, producing additional electron doping of 10-20x10^9 cm^(-2) even at the moderate displacement field (~0.5 V nm^(-1)), while simultaneously increasing carrier-density inhomogeneity of the
graphene layer. Both effects are consistent with ionization of defect states within the hBN bandgap, with the bulk density ~1-7x10^(-5) nm^(-3) varying across different hBN
crystals. Our results show that displacement-field-induced defect ionization in hBN can modify the electronic response of vdW
heterostructures, with direct implications for device design and interpretation of experiments.
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All authors Ilia Begichev, Daria Belotcerkovtceva, Iakov Reznikov, Sergey Slizovsky, Weijie Lu, Nansi Zhou, Ian Babich, Makars Siskins, Kostya S. Novoselov, Vladimir I. Falko, Kenji Watanabe, Takashi Taniguchi, Alexey I. Berdyugin
Materials Science
Multifunctionality in Janus CrMCN4 (M = Si/Ge) Monolayers: Valleytronic Physics, Piezoelectric Response, and Photocatalytic Potential
Jubair Hossan Abir, M.R.U.S. Shapon, S.S.B. Pallab et al. (+3 more)
Two dimensional Janus
semiconductors integrating
spin-valley coupling, piezoelectricity, and tunable optical responses offer a platform for multifunctional nanodevices. Here, first-principles calculations reveal complementary composition and strain effects in CrSiCN4 and CrGeCN4 monolayers. Both are found to be nonmagnetic direct-gap
semiconductors, with gaps of 1.23 and 1.09 eV using the Perdew-Burke-Ernzerhof functional including
spin-orbit coupling, respectively. HSE06 hybrid-functional calculations retain the direct-gap character, yielding gaps of 1.46 eV for CrSiCN4 and 1.19 eV for CrGeCN4. Opposite out-of-plane
spin character and Berry
curvature emerge at K and K'. Biaxial strain reduces the respective gaps from 1.59 to 0.86 eV and 1.44 to 0.63 eV, drives direct-to-indirect transitions, and
redshifts absorption while preserving valley
spin contrast. CrGeCN4 exhibits larger in-plane piezoelectric response, whereas CrSiCN4 exhibits larger out-of-plane magnitude. Band-edge
alignment satisfies the oxygen
evolution reaction requirement but provides insufficient driving force for the hydrogen
evolution reaction, motivating further strain-induced band-edge modulation toward overall water splitting. These results establish composition and strain as complementary controls for tailoring Cr-based Janus monolayers for valleytronic, optoelectronic, electromechanical, and photocatalytic applications.
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All authors Jubair Hossan Abir, M.R.U.S. Shapon, S.S.B. Pallab, Tanvir Khan, Raihana Shams Islam, Saleh Hasan Naqib
Materials Science
A hinged honeycomb with zero bulk modulus retaining more than four-fifths of its constituent's shear modulus
Chun-Teh Chen
A Poisson's ratio near -1 indicates only that the bulk modulus is small compared with the shear modulus. In solid-void structures, the mechanism that frees the dilation usually weakens the resistance to shear as well, resulting in both moduli becoming small. In two-dimensional linear elasticity, we demonstrate that this loss is not inevitable. We consider a honeycomb of regular hexagonal blocks of a single incompressible isotropic elastic solid, joined along their whole edges by ideal interfaces that allow relative sliding along a direction inclined to the edge normal. Collective infinitesimal block rotations produce an exact dilational mechanism, so the effective bulk modulus vanishes, while sixfold
symmetry ensures isotropy. The interfaces, however, transmit traction along their whole length. In a solid-void realization, each interface is replaced with fine solid plates separated by void, which bend easily yet retain their capacity to transmit axial force. Such dilational materials, which expand or contract freely while resisting every change of shape, could serve as interlayers that accommodate thermal or swelling mismatch while still transmitting shear, and as components in stents and deployable structures that change size without changing shape. An explicit, statically admissible stress field and the complementary energy principle yield a rigorous lower bound on the retained shear modulus, and a limiting argument transfers this bound to the solid-void mixtures. The honeycomb retains more than four-fifths of its constituent's shear modulus at zero bulk modulus: the supremum S of the normalized shear modulus of such mixtures satisfies S > 0.8528 > 4/5, exceeding the value attained by Milton's construction.
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Superconductivity
High-Efficiency and Large Supercurrent Rectification with Superconducting Coil
Takumi Ichikawa, Daisuke Takegami, Gen Nishijima et al. (+8 more)
Superconducting diodes (SDs) are devices that rectify supercurrent through the difference in the superconducting critical current (Ic) between forward and reverse current directions. For bringing such SDs closer to practical superconducting power electronics applications, a combination of both high rectification efficiency ({\eta}) and a large Ic difference ({\Delta}Ic) is required. Here, we propose and demonstrate a coil-shaped superconducting wire device concept to induce a large SD effect, arising from the compensation between an external
magnetic field (Hext) and the field generated by the coil itself. From transport Ic measurements on coil-shaped SDs based on a Sn10-Pb90 solder wire, we achieved a {\eta} of 79% with a {\Delta}Ic of 140 A at Hext = 500 Oe (coil #2) and a {\eta} of 84% with a {\Delta}Ic of 125 A at Hext = 530 Oe (coil #3), confirming high rectification values at large supercurrents. The large-current high-efficiency SDE in the coil-shaped SDs will be highly useful for developing the potential field of supercurrent power electronics.
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All authors Takumi Ichikawa, Daisuke Takegami, Gen Nishijima, Shunsuke Kawakami, Tsutomu Nojima, Yuji Tsuchiya, Satoshi Awaji, Fuyuki Ando, Ken-ichi Uchida, Yuya Hattori, Yoshikazu Mizuguchi
Statistical Mechanics · Cross-listed from cs.LG
Residual spectral instabilities in representation learning
Zhen Li
Learned representations can lose latent degrees of freedom successively, suggesting a cascade of transitions whose underlying stability principle remains unclear. Here we formulate dimension-wise posterior collapse in variational autoencoder (VAE) as a fluctuation theory around partially collapsed states. Interpreting the negative evidence lower bound as an effective free energy, its quadratic expansion defines a Gaussian theory whose Hessian acts as a mass
matrix for latent fluctuations. We show that the collapsed directions form an invariant fluctuation sector and derive its exact mass spectrum in terms of a conditional residual operator. A local reactivation direction lowers the free energy when the decoder variance falls below the residual spectral upper edge, with equality marking marginality. The criterion recovers principal component thresholds in the linear Gaussian VAE limit. Viewed in reverse along continuously connected branches, the reactivation boundary provides a local criterion for successive collapse. Numerical continuation experiments show successive loss of latent dimensions near these spectral marginalities. These results support a spectral cascade interpretation governed by residual information left unexplained by the surviving representation.
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Materials Science
Assessing the Reliability of Foundational Machine Learning Potentials for Evaluating the Veracity of the Crystallography Open Database
Justinas Šlepavičius, Antanas Vaitkus, Andrius Merkys et al. (+2 more)
The Crystallography Open Database (COD) contains over half a million experimentally determined
crystal structures. Validation of crystallographic data proceeds at three hierarchical levels, the third of which assesses the physical plausibility of structures. This level has typically relied on empirical heuristics or expert judgment, which are slow and error-prone given the size of crystallographic databases and the rate at which new structures are deposited. Here we assess whether universal machine-learning interatomic potentials (MLIPs) can automate this level of validation. Of the 522 086 COD entries, 317 457 (60.8%) passed a data-quality filter removing disordered structures, formula mismatches and unmodelled solvent. These structures were relaxed with M3GNet, and 314 153 (99.0%) converged without a large change in
cell volume. For most entries the relaxed and deposited volumes are nearly identical. Convergence and volume change thus provide simple criteria for identifying relaxations that do not confirm the deposited structure. A manual inspection of 327 structures showed that no single descriptor threshold (energy, largest force, or atomic displacement) separates valid from invalid structures. A comparison of M3GNet, CHGNet, PET-MAD and PET-OAM on 524 selected structures revealed model-specific failures: M3GNet distorts cyclopentadienyl and other $\pi$ ligands, and both M3GNet and CHGNet distort thiophene and thiazole rings, whereas the PET models preserve these motifs. All models detected missing hydrogen atoms, and at least some detected spurious hydrogens, incorrectly assigned atom types, and two previously unreported coordinate errors. No single model detected all error types. MLIP relaxation is therefore a useful but model-dependent screening tool, and combining several models is preferable to relying on any single one.
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All authors Justinas Šlepavičius, Antanas Vaitkus, Andrius Merkys, Saulius Gražulis, Linas Vilčiauskas
Mesoscale and Nanoscale Physics
Enhancement of the Topological Hall Effect through Engineering the Skyrmion Size and Shape
Kazuma Murata, Ryunosuke Terasawa and Hiroaki Ishizuka
The topological Hall effect of skyrmions is a promising electrical probe of
magnetic textures, but its small magnitude limits applications. In this work, we theoretically investigate the topological Hall effect induced by sparsely distributed skyrmions in the weak-coupling limit, focusing on how the size and shape of the skyrmion affect the Hall effect. To this end, we used a formalism based on angular-momentum eigenstates, which enables systematic analysis within reasonable computation time. We found that, in clean materials where the electron mean-free path is comparable to or larger than the skyrmion size, the Hall effect depends considerably on the size and shape of the skyrmion. In particular, the Hall effect is largest when $k_F\lambda\sim 1$, and its magnitude can be tuned by the domain-wall width of skyrmions. These findings provide a basis for investigating how the shape and size of skyrmions affect transport properties and demonstrate that the topological Hall effect is controllable by engineering these properties.
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Statistical Mechanics
Markov length can diverge in systems whose universal physics is spatially Markovian
Yu-Hsueh Chen and Tarun Grover
Conditional mutual information (CMI) probes spatial non-Markovianity and plays a central role in a recently developed framework for defining mixed-state phases based on local reversibility. This framework sharply distinguishes exponentially decaying from algebraically decaying CMI, since the latter obstructs equivalence to a state with finite Markov length. Here we show that states that flow to the same renormalization-group (RG) fixed point can nevertheless exhibit qualitatively different CMI. Starting from a critical Gibbs state of a finite-range local classical
Hamiltonian, whose CMI vanishes beyond the interaction range, we show that an RG-irrelevant perturbation that breaks detailed balance generically generates algebraically decaying CMI. Crucially, these power-law tails are cutoff-suppressed: although they lead to an infinite Markov length at every fixed
lattice cutoff, they vanish as a positive power of the cutoff in the continuum limit. We construct solvable models that exhibit this phenomenon and predict that the Ising-symmetric critical point of Toom's cellular automata generically exhibits such behavior. We also find analogous cutoff-suppressed CMI in the high-temperature paramagnetic phase of the long-range Ising paramagnet, in contrast with the genuine power-law CMI at the finite-temperature critical point in this same model that survives the continuum limit. We also derive a general result that in one spatial dimension, CMI decays faster than the inverse square of the buffer length if and only if the long-distance physics is Markovian.
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Strongly Correlated Electrons · Cross-listed from quant-ph
Exact polariton-condensate states via nonlinear Stark coupling
DaKai He and Zhi Song
We study a hybrid system of coupled cavities, with or without two-level atoms doped inside. By employing a building-block construction facilitated by nonlinear Stark coupling, we identify a
manifold of exact many-body eigenstates that remain analytically tractable across arbitrary
lattice geometries and atom distributions. We demonstrate that these exact states exhibit a dual physical nature depending on their spectral positioning: when embedded within the chaotic many-body spectrum, they manifest as
quantum scars that violate the eigenstate thermalization hypothesis and undergo weak ergodicity breaking; conversely, as ground states within fixed-total-excitation sectors, they exhibit off-diagonal long-range order and form polariton condensates. Furthermore, numerical calculations of local excitation-number fluctuations suggest that negative Stark coupling shifts the Mott-
insulator to superfluid transition toward weaker inter-cavity hopping. Our findings provide a versatile framework for engineering both coherent
quantum phases and non-thermalizing states in diverse light-matter architectures.
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