Superconductivity
Electronic Structure and Superconducting Gap of HgBa$_2$Ca$_2$Cu$_3$O$_{8+\delta}$ Revealed by Laser-Based Angle-Resolved Photoemission Spectroscopy
Taimin Miao, Wenshan Hong, Qinghong Wang et al. (+18 more)
The spatially-resolved
laser-based high resolution angle resolved photoemission spectroscopy (ARPES) measurements have been performed on the optimally-doped HgBa$_2$Ca$_2$Cu$_3$O$_{8+\delta}$ (Hg1223)
superconductor with a $T_c$ at 133 K. Two distinct regions are identified on the cleaved surface: the single
Fermi surface region where only one
Fermi surface is observed, and the double
Fermi surface region where two
Fermi surface sheets are resolved coming from both the inner (IP) and outer (OP) CuO$_2$ planes. The electronic structure and superconducting gap are measured on both of these two regions. In both cases, the observed electronic states are mainly concentrated near the nodal region. The momentum dependence of superconducting gap deviates from the standard d-wave form. These results indicate that the surface electronic structure of Hg1223 behaves more like that of underdoped cuprates.
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All authors Taimin Miao, Wenshan Hong, Qinghong Wang, Shanshan Zhang, Bo Liang, Wenpei Zhu, Neng Cai, Mingkai Xu, Shenjin Zhang, Fengfeng Zhang, Feng Yang, Zhimin Wang, Qinjun Peng, Zuyan Xu, Hanqing Mao, Zhihai Zhu, Xintong Li, Guodong Liu, Lin Zhao, Yuan Li, X. J. Zhou
Superconductivity
Raman response of collective modes in multicomponent superconductors
Yuki Yamazaki and Takahiro Morimoto
We formulate a microscopic theory of the Raman response of superconducting collective modes in multicomponent
superconductors. Starting from a general Bogoliubov–de Gennes (BdG)
Hamiltonian with a separable pairing interaction, we derive a gauge-invariant expression for the Raman susceptibility, including a long-range Coulomb interaction. The resulting Raman susceptibility is directly computable for an arbitrary BdG
Hamiltonian, which contains single- and multiband systems,
spin-singlet and triplet order parameters, and time-reversal-symmetric and time-reversal-
symmetry-breaking superconducting states. Based on the microscopic coupling between a Raman source field and collective modes, we derive a
symmetry selection rule for Raman-active collective modes and show a group-theoretical classification for all crystalline point groups. This classification provides a unified framework based on the “higher-order Lifshitz-invariant” to identify Raman-active collective modes such as Leggett mode, Bardasis-Schrieffer (BS) mode, and clapping mode. As an application, we focus on an effective model of the heavy-
fermion superconductor UTe$_2$ with a fully gapped multicomponent odd-parity pairing state. We find sharp in-gap Raman resonances below the quasiparticle continuum, which do not correspond to a conventional Leggett mode but arise from the intraband relative modes between different pairing components.
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Mesoscale and Nanoscale Physics
Direct observation of propagating spin waves in a spin-Hall nano-oscillator
Victor H. González, Frank Schulz, Nilamani Behera et al. (+10 more)
Constriction-based
spin Hall nano-oscillators (SHNOs) show great promise for application as highly tunable microwave sources with straightforward scalability toward large coupled networks. However, details of the magnetization dynamics within SHNOs have thus far not been addressed experimentally, due to the minute time and length scales involved. In this work, we present direct imaging of the magnetization dynamics within a single CoFeB-based SHNO using time-resolved scanning transmission X-ray microscopy (STXM). Our measurements reveal that the
magnon amplitude is the strongest at the two constriction edges, with a pronounced assymetry favoring one edge, and that emitted
spin waves exhibit strongly anisotropic propagation. Micromagnetic simulations suggest that grain boundaries and the Dzyaloshinskii-Moriya interaction (DMI) play a key role in both effects. Furthermore, the magnetodynamics changed during the measurement, indicating that the CoFeB/MgO interface may be more susceptible to X-ray induced modifications than previously recognized, challenging its presumed radiation hardness.
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All authors Victor H. González, Frank Schulz, Nilamani Behera, Martina Ahlberg, Akash Kumar, Andreas Frisk, Felix Groß, Sven Erik Ilse, Steffen Wittrock, Markus Weigand, Gisela Schütz, Johan Åkerman, Sebastian Wintz
Strongly Correlated Electrons
Microscopic origin of an exceptionally large phonon thermal Hall effect from charge puddles in a topological insulator
Rohit Sharma, Yongjian Wang, Yoichi Ando et al. (+2 more)
We present the experimental observation of a drastically enhanced thermal
Hall effect in the topological
insulator material TlBi$_{0.15}$Sb$_{0.85}$Te$_2$. Although heat transport is dominated by
phonons, moderate
magnetic fields generate a thermal
Hall ratio ($\kappa_{xy}/\kappa_{xx}$) above 2%, an unprecedented value for a nonmagnetic material. The transverse thermal conductivity $\kappa_{xy}$ exhibits a pronounced maximum in fields of a few Tesla. This characteristic field dependence allows us to identify the microscopic origin of the thermal
Hall effect in this system. Small densities of charged
impurities induce locally conducting regions, so-called charge puddles, within the bulk insulating
matrix. Via electron-
phonon coupling, these charge puddles imprint a large thermal
Hall effect onto the
phonons accounting for both the magnitude and the
magnetic-field dependence of the observed effect.
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All authors Rohit Sharma, Yongjian Wang, Yoichi Ando, Achim Rosch, Thomas Lorenz
Soft Condensed Matter
Huygens' clocks at the microscale
Yaocheng Li, Ivan Palaia, Jinzi Mac Huang et al. (+2 more)
Weakly coupled oscillators adjust their dynamics to work in unison: they synchronize. This ubiquitous phenomenon is observed for oscillating pendulum, electronic devices, as well as clapping crowds or flashing fireflies. In effect, synchronization constitutes an efficient mean to translate microscopic into large scale dynamics. While broadly studied theoretically, experimental investigations of synchronization of systems at the microscale are limited. Here we devise and study a model system of noisy and "measurably imperfect" colloidal oscillators: autonomous clocks made of an active swimmer revolving around a passive sphere. The distribution of natural frequency of the clock is achieved using passive spheres of various sizes, thus without altering the (phoretic) coupling between clocks. We observe that pairs of oscillators lock phases before slipping and returning to sync, and we characterize the synchronicity of the pair. We rationalize our findings with a
stochastic model, formalizing synchronization as a classical Kramers escape problem in an adequate potential. This provides an analytical expression for the rate of synchronization of a pair set by the ratio between differences of natural frequency and environmental noise, and agrees qualitatively with the experiment. Our results set a blueprint for synchronization with micrometric autonomous systems.
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All authors Yaocheng Li, Ivan Palaia, Jinzi Mac Huang, Antoine Aubret, Jeremie Palacci
Soft Condensed Matter
Probing Anharmonic and Heterogeneous Carrier Dynamics Across Sublattice Melting in a Minimal Model Superionic Conductor
Sucharita Niyogi, Takenobu Nakamura, Genki Kobayashi et al. (+2 more)
Despite decades of research, the microscopic origin of sublattice melting and fast ion transport in superionic conductors remains elusive. Here, we introduce a chemically neutral minimal binary model consisting of a rigid host
lattice stabilized by short-range steric repulsion and a soft carrier sublattice interacting via long-range Wigner-type forces. This contrast naturally produces distinct melting temperatures and an intermediate sublattice-melting phase in which carriers become fluidlike while the host remains crystalline. Molecular dynamics simulations identify three dynamical regimes-crystalline, sublattice-melt, and fully molten-marked by sharp changes in diffusivity, structural correlations, and dynamical heterogeneity. Near sublattice melting, carrier motion is strongly anharmonic and spatially heterogeneous, beyond mean-field hopping descriptions. By tuning the density, we demonstrate that sublattice melting can be continuously controlled, establishing a direct link between
lattice softness, anharmonicity, and collective ion transport. Comparison with conventional long-range Coulombic models confirms that our minimal model reproduces the key dynamical signatures of superionicity, providing a unified microscopic foundation for designing mechanically robust superionic conductors.
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All authors Sucharita Niyogi, Takenobu Nakamura, Genki Kobayashi, Yasunobu Ando, Takeshi Kawasaki
Statistical Mechanics
A Novel Mechanism of Ordering in a Coupled Driven System: Vacancy Induced Phase Separation
Chandradip Khamrai and Sakuntala Chatterjee
We study a coupled driven system where two different species of particles, along with some vacancies or holes, move on a landscape whose shape fluctuates with time. The movement of the particles is guided by the local shape of the landscape, and this shape is also affected by the presence of different particle species. When a particle species push the landscape in the same (opposite) direction of its own motion, it is called an aligned (a reverse) bias. Aligned bias promotes ordering while reverse bias destroys it. In absence of vacancies, the system reduces to previously studied LH model with different kinds of ordered and disordered phases which could be explained as a competition or cooperation between aligned bias and reverse bias. This interplay is expected to remain unaffected even when vacancies are present since vacancies do not impart any kind of bias on the landscape. However, we find presence of vacancies effectively weakens the reverse bias and this significantly changes the outcome of the competition between the two bias types. As a result novel ordered phases emerge which were not seen before. We analytically calculate the new phase boundaries within mean field approximation. We show even when aligned bias is weaker than reverse bias, it is possible to find long range order in the system. We discover two new phases where particle species showing weak aligned bias phase separate and the other species with strong reverse bias stays mixed with the vacancies. We call these phases finite current with partial phase separation (FPPS) and vacancy induced phase separation (VIPS). The landscape beneath the phase separated species takes the form of a macroscopic hill or valley in FPPS phase. But in VIPS phase it has the shape like a plateau whose height scales as square root of system size. The landscape in the remaining part of the system is disordered in both these phases.
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Superconductivity
Higher-Order Topological Superconductivity and Electrically Tunable Majorana Corner Modes in Monolayer MnXPb$_2$ (X=Se, Te)-Pb Heterostructure
Yongting Shi, Qing Wang, Zhen-Guo Fu et al. (+2 more)
Higher-order topological
superconductors host Majorana zero modes localized at corners or hinges, providing a promising route toward scalable and controllable Majorana networks without
vortices or
magnetic flux. Here we propose a
symmetry-enforced higher-order topological superconductivity based on
antiferromagnetic topological
insulators, specifically realized in MnXPb$_2$ (X = Se, Te)-Pb
heterostructure. We show that the intrinsic boundary dichotomy-gapless Dirac states protected by an effective time-reversal
symmetry on
antiferromagnetic edges and
magnetic gaps on
ferromagnetic edges-naturally generates Majorana corner modes as mass domain walls. Superconducting proximity converts the
antiferromagnetic edges into one-dimensional topological
superconductors, and the intersections between superconducting and
magnetic edges bind Majorana zero modes as mass domain walls. Combining first-principles calculations with a calibrated effective boundary theory, we demonstrate robust corner localization and purely electrical control of Majorana fusion and braiding in a triangular geometry. Our results establish MnXPb$_2$ as experimentally promising platform for electrically programmable Majorana networks in two dimensions.
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All authors Yongting Shi, Qing Wang, Zhen-Guo Fu, Ping Zhang, Ning Hao
Statistical Mechanics
Exchange Monte Carlo for continuous-space Path Integral Monte Carlo simulation
Xun Zhao and Synge Todo
We present a novel Exchange Monte Carlo (EMC) method designed for application in continuous-space Path Integral Monte Carlo (PIMC) simulations at finite temperature. Traditional PIMC methods for bosonic systems suffer from long autocorrelation times, particularly when measuring observables affected by particle permutations, such as the winding number. To address this issue, we introduce an exchange update scheme that facilitates replica transitions between different interaction regimes, significantly accelerating Monte Carlo dynamics-especially for global observables sensitive to permutation effects. Furthermore, we incorporate
Stochastic Potential Switching (SPS) to efficiently decompose interactions, substantially enhancing computational efficiency for long-range interatomic pair potentials such as the Lennard-Jones and Aziz potentials.
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Materials Science
Crystallinity Evolution of MOCVD-Grown $\beta$-Ga$_2$O$_3$ Films Probed by In Situ HT-XRD under Different Reactor Heights
Imteaz Rahaman, Botong Li, Bobby G. Duersch et al. (+3 more)
The crystallinity of $\beta$-Ga$_2$O$_3$ thin films grown by metal-organic chemical vapor deposition (MOCVD) is strongly influenced by reactor design and the resulting growth environment. In this work, we investigate the role of reactor height on the crystallinity
evolution of MOCVD-grown $\beta$-Ga$_2$O$_3$ films by directly comparing long- and short-chamber showerhead configurations. Structural
evolution was probed by in situ high-temperature X-ray diffraction (HT-XRD) as the MOCVD-grown films were heated from 25~$^\circ$C to 1100~$^\circ$C. Temperature-dependent XRD reveals a consistent
redshift of the $\beta$-Ga$_2$O$_3$~($-201$) reflection after HT-XRD heating and subsequent cooling to room temperature for both reactor geometries, indicating a similar thermally driven strain response. Quantitative rocking-curve analysis shows a non-monotonic temperature dependence of the ($-201$) full width at half maximum (FWHM), with minimum values of approximately 2.03$^\circ$ and 2.72$^\circ$ for the short- and long-chamber films, respectively, reflecting differences in mosaic
alignment established during growth. Atomic force microscopy further shows that short-chamber-grown films exhibit smoother surfaces, with root-mean-square roughness values of approximately 7.7~nm before and 7.3~nm after HT-XRD heating, compared to 19.3~nm and 12.3~nm, respectively, for long-chamber-grown films. Overall, these results indicate that reactor height influences the initial crystalline and morphological templates of $\beta$-Ga$_2$O$_3$ films and modulates their elevated-temperature structural response, providing practical insights for optimizing MOCVD reactor design for high-quality $\beta$-Ga$_2$O$_3$ growth.
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All authors Imteaz Rahaman, Botong Li, Bobby G. Duersch, Hunter D. Ellis, Kathy Anderson, Kai Fu
Superconductivity
M. Nursagatov, Xiyin Ye, G. A. Bobkov et al. (+2 more)
We predict the formation of ferron-polariton - a hybrid light-matter quasiparticle arising from the coupling between collective ferroelectric excitations (ferrons) and Swihart
photons in a
superconductor/ferroelectric/
superconductor heterostructure. The coupling provides direct evidence for ferrons and reaches the ultrastrong-coupling regime, with a spectral gap in the terahertz range, orders of magnitude larger than those in
magnetic analogues, reflecting the superior strength of electric dipole interactions. Our work establishes
superconductor-ferroelectric
heterostructures as a novel platform for exploring extreme light-matter coupling and for developing high-speed, ferroelectric-based
quantum technologies at terahertz frequencies.
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All authors M. Nursagatov, Xiyin Ye, G. A. Bobkov, Tao Yu, I. V. Bobkova
Statistical Mechanics
Branch-and-Bound Tensor Networks for Exact Ground-State Characterization
Yijia Wang, Xuanzhao Gao, Pan Zhang et al. (+2 more)
Characterizing the ground-state properties of disordered systems, such as
spin glasses and combinatorial optimization problems, is fundamental to science and engineering. However, computing exact ground states and counting their degeneracies are generally NP-hard and #P-hard problems, respectively, posing a formidable challenge for exact
algorithms. Recently, Tensor Networks methods, which utilize high-dimensional linear
algebra and achieve massive hardware parallelization, have emerged as a rapidly developing paradigm for efficiently solving these tasks. Despite their success, these methods are fundamentally constrained by the exponential growth of space complexity, which severely limits their scalability. To address this bottleneck, we introduce the Branch-and-Bound Tensor Network (BBTN) method, which seamlessly integrates the adaptive search framework of branch-and-bound with the efficient contraction of tropical tensor networks, significantly extending the reach of exact
algorithms. We show that BBTN significantly surpasses existing state-of-the-art solvers, setting new
benchmarks for exact computation. It pushes the boundaries of tractability to previously unreachable scales, enabling exact ground-state counting for $\pm J$
spin glasses up to $64 \times 64$ and solving Maximum Independent Set problems on King's subgraphs up to $100 \times 100$. For hard instances, BBTN dramatically reduces the computational cost of standard Tropical Tensor Networks, compressing years of runtime into minutes. Furthermore, it outperforms leading integer-programming solvers by over 30$\times$, establishing a versatile and scalable framework for solving hard problems in statistical physics and combinatorial optimization.
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All authors Yijia Wang, Xuanzhao Gao, Pan Zhang, Feng Pan, Jinguo Liu
Mesoscale and Nanoscale Physics
Compact self-matched gyrators using edge magnetoplasmons
Aldo Tarascio, Yiqi Zhao, Rafael S. Eggli et al. (+5 more)
Edge magnetoplasmons provide a natural platform for
chiral electrodynamics, where broken time-reversal
symmetry enforces unidirectional propagation. When probed at microwave frequencies, they offer a route to compact non-reciprocal devices. So far, implementations have suffered from large losses or required complicated matching networks. Here we show that the circulating modes coupled to capacitive gates give rise to a gyrator response, characterized by directional {\pi} phase difference between forward and reverse transmission. By engineering a three-terminal capacitive geometry, we realize a self-impedance matched gyrator in which the gyration points coincide with transmission maxima, enabling nearly lossless gyration without external matching networks. Our devices are implemented on a GaAs 2D gas, operate from 0.2 to 2 GHz, tuned by
magnetic field, with sub-millimeter footprints and insertion loss as low as 2 dB. This is a factor of 100 smaller and less lossy than commercial and plasmon units, respectively. A dissipative model, in agreement with experiment, provides the fundamental physics and delivers the key materials parameters, leading the way to even less lossy devices approaching ideal operation by materials improvement. The self-impedance matched concept is broadly applicable to a variety of devices, thus providing a foundation for a new generation of high-quality microwave plasmon technology.
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All authors Aldo Tarascio, Yiqi Zhao, Rafael S. Eggli, Taras Patlatiuk, Christian Reichl, Werner Wegscheider, Stefano Bosco, Dominik M. Zumbühl
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Geometric Phases and Holonomy in Structured Optical Fields
Kristina Frizyuk, Evgenii Menshikov and Mauro Spera
Geometric phases are widely used in modern optics, yet their meaning and underlying geometry depend on the actual physical settings, which can substantially differ from one another. This tutorial article introduces
geometric phases in nanophotonic systems, focusing on the interaction of structured light with nanostructures or metaatoms. We compare the present setting with conventional
geometric phases of structured-light optics and show that similar phase laws may correspond to genuinely different underlying geometries. Our aim is to provide a pedagogical bridge between the mathematical
language of
geometric phases and experimentally relevant examples from nanophotonics.
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Materials Science
Ferroelectricity in Atomically Thin Metallic TaNiTe$_5$ with Ultrahigh Carrier Density
Zhihua Liu, Shichong Song, Xunqing Yin et al. (+9 more)
Ferroelectric metals, characterized by the coexistence of ferroelectricity and metallic conductivity, present a fundamental challenge due to the screening effect of free charge carriers on the long-range electric dipole order. Existing strategies to circumvent this obstacle include employing two-dimensional (2D)
crystals, where reduced dimensionality and low carrier densities suppress screening, or designing materials of van der Waals (vdW) superlattice with spatially separated and decoupled conductive and nearly insulating ferroelectric layers. Here, we report an alternative paradigm in TaNiTe5, where an ultrahigh carrier density coexists with an out-of-plane ferroelectric order within the same surface monolayer. Using piezoresponse force microscopy (PFM), we observed robust ferroelectric behavior in TaNiTe5 down to single-unit-
cell thickness (~1.3 nm) at room temperature. Scanning transmission electron microscopy (STEM) gives structural evidence that the ferroelectricity might originate from the vertical displacement of outmost Te atoms on the surface, breaking the inversion
symmetry. Concurrently, electrical transport measurements reveal a metallic state with a carrier density on the order of 10$^{15}$ cm$^{-2}$ (or 10$^{22}$ cm$^{-3}$) – comparable to that of Copper (Cu). Our findings establish a unique platform for exploring the interplay between ferroelectricity and an ultrahigh density of mobile carriers in the 2D limit.
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All authors Zhihua Liu, Shichong Song, Xunqing Yin, Chenhang Xu, Feng Liu, Guohua Wang, Peng Chen, Shengwei Jiang, Chunqiang Xu, Xiaofeng Xu, Weidong Luo, Dong Qian
Materials Science
CatFlow: Co-generation of Slab-Adsorbate Systems via Flow Matching
Minkyu Kim, Nayoung Kim, Honghui Kim et al. (+1 more)
Discovering heterogeneous catalysts tailored for specific reaction intermediates remains a fundamental bottleneck in materials science. While traditional trial-and-error methods and recent generative models have shown promise, they struggle to capture the intrinsic coupling between surface geometry and adsorbate interactions. To address this limitation, we propose CatFlow, a flow matching-based framework for de novo design and structure prediction of heterogeneous catalysts. Our model operates on a primitive
cell-based factorized representation of the slab-adsorbate complex, reducing the number of learnable variables by an average of 9.2x while explicitly encoding the surface orientation of the slab-adsorbate interface. Experiments on the Open Catalyst 2020
dataset demonstrate that CatFlow significantly improves the structural fidelity of generated catalysts compared to autoregressive and sequential baselines. Further experiments show that the generated structures accurately capture the adsorption energy distributions of physically plausible interfaces and lie closer to thermodynamic local minima.
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All authors Minkyu Kim, Nayoung Kim, Honghui Kim, Sungsoo Ahn
Materials Science
Quasi-One-Dimensional Electronic Nature of Ta4SiTe4 Underlying the Giant Thermoelectric Performance
Hironari Isshiki, Ayumu Tabata, Masafumi Horio et al. (+13 more)
Ta4SiTe4 is a one-dimensional van der Waals material that exhibits an exceptionally large thermoelectric power factor below room temperature. However, since this material has been available only in the form of acicular microcrystals, experimental exploration of the electronic properties responsible for its
giant thermoelectric performance has long been challenging. In this study, we quantitatively evaluated the one-dimensional electronic nature of Ta4SiTe4 by combining micro-spot angle-resolved photoemission spectroscopy and transport measurements on focused-ion-beam-processed samples. The angle-resolved photoemission spectroscopy measurements reveal anisotropic band dispersions along and perpendicular to the crystallographic c axis. Consistently, transport measurements demonstrate that the resistivity perpendicular to the c axis is approximately five times larger than that along the c axis at 200 K. These results provide direct experimental evidence for the quasi-one-dimensional electronic character of Ta4SiTe4, which underlies its
giant thermoelectric response reported previously, and offer fundamental insights into the role of electronic dimensionality in enhancing thermoelectric performance.
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All authors Hironari Isshiki, Ayumu Tabata, Masafumi Horio, Motoi Kimata, Youichi Yamakawa, Ryutaro Okuma, Miki Imai, Fumiya Matsunaga, Koshi Takenaka, Kenichi Ozawa, YoshiChika Otani, Fumio Komori, Iwao Matsuda, Masahiro Hara, Yoshihiko Okamoto, Masayuki Hashisaka
Strongly Correlated Electrons
Spectroscopic Evidence of Competing Diagonal Spin Interactions and Spin Disproportionation in the Bilayer Nickelate La$_3$Ni$_2$O$_7$
Dong-Hyeon Gim, Dirk Wulferding, Hengyuan Zhang et al. (+3 more)
A comprehensive spectroscopic map of the electronic,
magnetic, and
lattice excitations is presented for the
bilayer nickelate La$_3$Ni$_2$O$_7$ using Raman scattering at ambient pressure. Upon entering the
spin density wave state below 153 K, the $A_{1g}$ channel exhibits an abrupt electronic spectral gap with a clear isosbestic point. In contrast, the $B_{1g}$ and $B_{2g}$ channels are dominated by pronounced two-
magnon (2M) excitations, representing a signature of incipient Mottness. These 2M signals in both channels constitute evidence for two distinct in-plane
spin exchange interactions along the Ni-O bonding and its diagonal directions. Calculations based on the
spin wave theory further reveal that the 2M mode in the $B_{2g}$ channel arises from the competition between two bond-diagonal
antiferromagnetic interactions mediated by nickel $d_{x^2-y^2}$ orbitals. Furthermore, emergent low-energy 2M excitations below 10 meV are found to originate from distinct, weaker
spin moments, supporting
spin disproportionation. Simultaneously, an anomalous softening of $B_{1g}$
phonons from 280 down to 4.5 K is uncovered, suggesting the presence of an incipient
lattice instability leading to checkerboard-type breathing modulations. Collectively, these findings identify a ground state of the
bilayer nickelate characterized by competing bond-diagonal interactions,
spin disproportionation, and an incipient
lattice instability, establishing key ingredients for understanding the mechanism of nickelate superconductivity.
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All authors Dong-Hyeon Gim, Dirk Wulferding, Hengyuan Zhang, Deyuan Hu, Meng Wang, Kee Hoon Kim
Materials Science
First-principles study of photovoltaic and thermoelectric properties of AgBiSCl2
Sihang Wang, Menghan Chen and Liping Zhang
This work systematically investigates the potential of the hybrid anion
semiconductor AgBiSCl2 for photovoltaic and thermoelectric applications, aiming to provide theoretical guidance for high-performance energy conversion devices. Structural analysis reveals favorable ductility and a relatively low Debye temperature. Analysis of interatomic interactions indicates that Ag-S and Ag-Cl bonds are relatively weak, resulting in local structural softness and enhanced
lattice anharmonicity. These weak bonds facilitate
phonon scattering and give rise to low-frequency localized rattling vibrations primarily associated with Ag atoms, contributing to reduced
lattice thermal conductivity. In contrast, Bi-S bonds exhibit stronger, directional interactions, which help stabilize the overall structure. The coexistence of weak bonding and strong
lattice coupling enables favorable modulation of thermal transport properties.Optically, AgBiSCl2 possesses a high static dielectric constant and exhibits strong absorption in the ultraviolet region. In terms of thermal transport,
phonon spectrum exhibit mode hardening with temperature increasing. The localized Ag vibrations intensify the anharmonicity, reducing
phonon lifetimes and group velocities.For electronic transport, the p-type material maintains a higher Seebeck coefficient than the n-type, while the latter shows greater electrical conductivity. At 700 K, the figure of merit reaches 0.77 for p-type and 0.69 for n-type AgBiSCl2, indicating promising high-temperature thermoelectric performance.In summary, AgBiSCl2 exhibits excellent potential for dual photovoltaic and thermoelectric applications. Its unique bonding features and
lattice response mechanisms offer valuable insights into designing multifunctional energy conversion materials.
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Materials Science
Physics-informed acquisition weighting for stoichiometry-constrained Bayesian optimization of oxide thin-film growth
Yuki K. Wakabayashi, Takuma Otsuka, Yoshiharu Krockenberger et al. (+1 more)
We present a physics-informed
Bayesian optimization (PIBO) with a concise modification to its acquisition function to incorporate the physical prior knowledge. Specifically, this method multiplies the expected improvement (EI) by a weight encoding prior
crystal growth physics. When applied to LaAlO3 molecular-beam epitaxy, the weighting function defines a flat stoichiometric window and penalizes off-window proposals, thereby steering the optimization toward physically plausible regions while maintaining controlled exploration. In a closed-loop optimization, relative to the bare EI, which often proposes off-stoichiometric conditions, the weighted EI constrains the search toward stoichiometric regions while retaining sufficient flexibility to explore neighboring conditions, eventually identifying an optimum slightly beyond the stoichiometric window. Within only 15 growth runs, the
lattice constant of the grown LaAlO3 film converged to the bulk value, evidencing efficient and rapid optimization for the ideal stoichiometric growth. Because physics knowledge is incorporated solely through the weighting function, the approach requires only minimal modification to standard BO workflows and is readily applicable to other material systems, offering a general and practical route to AI-driven materials synthesis.
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All authors Yuki K. Wakabayashi, Takuma Otsuka, Yoshiharu Krockenberger, Yoshitaka Taniyasu
Mesoscale and Nanoscale Physics
Transport signatures of topological commensurate off-diagonal Aubry-André-Harper chain
Arpita Koley
We study the interplay between
quantum transport and
topology in a one-dimensional off-diagonal commensurate Aubry-André-Harper (AAH) chain. The model, formulated within AAH framework, effectively represents a one-dimensional
lattice with two competing commensurate modulations, supporting two distinct types of topological edge modes: zero-energy states in the central gapless region and
quantum Hall (QH) edge states bridging the gapped bulk bands. These edge modes govern the transport behavior and give rise to sharp variations in transmission across the corresponding gap-closing transitions. A pronounced even-odd effect further emerges, where chains with an odd number of sites exhibit nearly perfect zero-energy transmission at the Dirac points, independent of system-lead coupling, system size, or modulation strength; a robust signature of ballistic transport. To capture the influence of environmental decoherence, we also incorporate Büttiker dephasing probes, which enable a phenomenological description of inelastic scattering and reveal how dephasing modifies, and in some regimes enhances, coherent transport.
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Strongly Correlated Electrons
Spin current generation via magnetic skyrmion, bimeron, and meron crystals
Aoi Kajihara, Shun Okumura and Yukitoshi Motome
Spin current offers a promising route toward energy-efficient and high-speed information processing. Developing efficient methods for their generation remains a central challenge in spintronics. Here, we investigate
spin current generation via two-dimensional topological
spin textures: a skyrmion
crystal (SkX) with out-of-plane magnetization, a bimeron
crystal (BmX) with in-plane magnetization, and a meron
crystal (MX) with zero net magnetization. We show that these distinct
spin textures generate
spin currents with characteristic
spin polarization directions. In the absence of
spin–orbit coupling, the SkX and BmX generate
spin currents polarized along their magnetization directions, whereas the MX yields no
spin current. Upon introducing
spin–orbit coupling, while the behavior of the SkX does not qualitatively change, the BmX generates nonzero
spin currents in multiple polarization directions. Notably, the MX, despite its zero net magnetization, exhibits a pronounced
spin current with out-of-plane
spin polarization, driven by an enhanced
spin Berry
curvature associated with characteristic band degeneracy. We further demonstrate that the electronic and
spin transport properties of each texture are governed by their
magnetic symmetries. Our results highlight the topological
spin textures as efficient sources of
spin current even without net magnetization, expanding the design for spintronics devices based on topological
magnetic metals.
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Disordered Systems and Neural Networks
Beyond overcomplication: a linear model suffices to decode hidden structure-property relationships in glasses
Chenyan Wang, Mouyang Cheng and Ji Chen
Establishing reliable and interpretable structure-property relationships in glasses is a longstanding challenge in condensed matter physics. While modern data-driven machine learning techniques have proven highly effective in establishing structure-property correlations, many models are criticized for lacking physical interpretability and being task-specific. In this work, we identify an approximate linear relation between structure profiles and disorder-induced responses of glass properties based on first order perturbation theory. We analytically demonstrate that this relationship holds universally across glassy systems with varying dimensions and distinct interaction types. This robust theoretical relationship motivates the adoption of linear machine learning models, which we show numerically to achieve surprisingly high predictive accuracy for structure-property mapping in a wide variety of glassy materials. We further devise regularization analysis to further enhance the interpretability of our model, bridging the gap between predictive performance and physical insight. Overall, this linear relation establishes a simple yet powerful connection between structural disorder and spectral properties in glasses, opening a new avenue for advancing their studies.
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Materials Science
Multi-wavelength Spin Dynamics of Defects in Hexagonal Boron Nitride
Ivan Zhigulin, Nicholas P. Sloane, Benjamin Whitefield et al. (+3 more)
Optically addressable solid-state
spin defects are essential platforms for
quantum sensing and information processing. Recently, single
spin defects with combined S = 1 and S = 1/2
spin transitions were discovered in hexagonal boron nitride (hBN). In this work we unveil their excitation dynamics. In particular, we study the effects of the excitation wavelength on the
spin-dependent fluorescence and the
spin dynamics of these peculiar
quantum spin defects. We find that changing the excitation wavelength leads to a threefold enhancement in both the optically detected
magnetic resonance (ODMR) contrast and the corresponding
magnetic field sensitivity. In addition, we find that the excitation wavelength has a strong impact on the photodynamics of
spin complex emitters. Our work presents valuable insights to the mechanistic understanding of
spin complex emitters in hBN and highlights the importance of excitation wavelength for optimising their performance in
quantum sensing and
quantum technologies.
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All authors Ivan Zhigulin, Nicholas P. Sloane, Benjamin Whitefield, Jean-Philippe Tetienne, Mehran Kianinia, Igor Aharonovich
Statistical Mechanics · Cross-listed from math-ph
Unified criteria for crystallization in hard-core lattice systems with applications to polyomino fluids and multi-component mixtures
Qidong He
We present a unified extension of two sets of criteria for high-fugacity crystallization in hard-core
lattice systems developed previously by Jauslin, Lebowitz, and the author. Our new criterion is formulated in terms of the existence of a volume allocation rule with desirable optimization and screening properties, in analogy to the scoring function constructed in Hales' proof of the Kepler
conjecture. Notably, our result applies to a large class of polyomino models with discrete rotational degrees of freedom and their
chiral mixtures, as well as multi-component mixtures featuring several geometrically distinct particle shapes. The proof uses a recent systematic extension of Pirogov–Sinai theory to systems with infinite interactions by Mazel–Stuhl–Suhov.
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Strongly Correlated Electrons
lrux: Fast low-rank updates of determinants and Pfaffians in JAX
Ao Chen and Christopher Roth
We present lrux, a JAX-based software package for fast low-rank updates of determinants and Pfaffians, targeting the dominant computational bottleneck in various
quantum Monte Carlo (QMC)
algorithms. The package implements efficient low-rank updates that reduce the cost of successive wavefunction evaluations from $\mathcal{O}(n^3)$ to $\mathcal{O}(n^2k)$ when the update rank $k$ is smaller than the dimension $n$ of
matrices. Both determinant and Pfaffian updates are supported, together with delayed-update strategies that trade floating-point operations for reduced
memory traffic on modern accelerators. lrux natively integrates with JAX transformations such as JIT compilation, vectorization, and automatic differentiation, and supports both real and complex data types.
Benchmarks on GPUs demonstrate up to $1000\times$ speedup at large
matrix sizes. lrux enables scalable, high-performance evaluation of antisymmetric wavefunctions and is designed as a drop-in component for a wide range of QMC workflows. lrux is available at https://github.com/ChenAo-Phys/lrux.
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Materials Science
Substitutional oxygen as the origin of the 3.5 eV luminescence in hexagonal boron nitride
Marek Maciaszek
Although point defects in hexagonal boron nitride exhibiting single-
photon emission attract considerable interest, a broader understanding of defect physics and chemistry in hBN remains limited, potentially hindering further development. Oxygen is among the most common
impurities in hBN, and numerous studies have reported a pronounced photoluminescence band centered near 3.5 eV following oxygen incorporation, yet its microscopic origin has remained unresolved. Here, we demonstrate that this emission originates from hole capture by neutral oxygen substituting for nitrogen (ON). The transition mechanism is non-trivial, involving not only a change in charge state but also a substantial structural reconfiguration: the positive and neutral states exhibit markedly different geometries and
symmetries. In the neutral state the defect adopts a low-
symmetry configuration with out-of-plane displacements of the oxygen and neighboring atoms. The calculated emission energy (3.63 eV) and lineshape are in excellent agreement with experiment.
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Disordered Systems and Neural Networks · Cross-listed from quant-ph
Ryo Watanabe, Joseph Tindall, Shohei Miyakoshi et al. (+1 more)
We propose a tensor-network (TN) approach for solving classical optimization problems that is inspired by spectral filtering and sampling on
quantum states. We first shift and scale an Ising
Hamiltonian of the cost function so that all
eigenvalues become non-negative and the ground states correspond to the the largest
eigenvalues, which are then amplified by power iteration. We represent the transformed
Hamiltonian as a
matrix product operator (MPO) and form an immense power of this object via truncated MPO-MPO contractions,
embedding the resulting operator into a
matrix product state for sampling in the computational basis. In contrast to the density-
matrix renormalization group, our approach provides a straightforward route to systematic improvement by increasing the bond dimension and is better at avoiding local minima. We also study the performance of this power method in the context of a higher-order Ising
Hamiltonian on a heavy-hexagonal
lattice, making a comparison with simulated annealing. These results highlight the potential of
quantum-inspired
algorithms for solving optimization problems and provide a baseline for assessing and developing
quantum algorithms.
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All authors Ryo Watanabe, Joseph Tindall, Shohei Miyakoshi, Hiroshi Ueda
Statistical Mechanics
Mean-field behavior of the finite size Ising model near its critical point
D. Olascoaga-Rodríguez, F. Sastre and V. Romero-Rochín
Universality classes encompass the analogous thermodynamic behavior of unlike physical systems, at different spatial dimensions $d$, in the vicinity of their critical point. Critical exponents define these classes, with the Ising model being the outstanding prototype that elucidates the differences from the mean-field category, believed to be valid above a critical dimension only. Here, in apparent striking contradiction to the Ising universality class, we demonstrate that the critical behavior of a finite Ising system of $N$
spins in $d = 3$ obeys mean-field Landau theory in the vicinity of its critical point, with classical critical exponents. Yet, when expressed in terms of the linear size $L$ of the system, the free energy unveils its proper finite-size scaling form, from which the thermodynamic limit critical temperature $T_c$ and the Ising critical exponents $\nu$, $\gamma$ and $\beta$ can be identified. We find that the larger the size $L$, the smaller the mean-field region, shrinking to zero in the thermodynamic limit. These conclusions are achieved via the use of an alternative approach to collect data from a Monte Carlo simulation of a three-dimensional Ising model that allows for the evaluation of the free energy per
spin $f = f(T,m;L)$ and of the coexistence curve, or spontaneous magnetization at zero
magnetic field, $m_{\rm coex} = m(T;L)$ as functions of temperature $T$ and magnetization per
spin $m = M/N$. Our results suggest a revision of the role of mean-field theory in the elucidation of critical phenomena.
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Disordered Systems and Neural Networks · Cross-listed from hep-th
Towards Worst-Case Guarantees with Scale-Aware Interpretability
Lauren Greenspan, David Berman, Aryeh Brill et al. (+9 more)
Neural networks organize information according to the hierarchical, multi-scale structure of natural data. Methods to interpret model internals should be similarly scale-aware, explicitly tracking how features compose across resolutions and guaranteeing bounds on the influence of fine-grained structure that is discarded as irrelevant noise. We posit that the renormalisation framework from physics can meet this need by offering technical tools that can overcome limitations of current methods. Moreover, relevant work from adjacent fields has now matured to a point where scattered research threads can be synthesized into practical, theory-informed tools. To combine these threads in an AI safety context, we propose a unifying research agenda – scale-aware interpretability – to develop formal machinery and interpretability tools that have robustness and faithfulness properties supported by statistical physics.
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All authors Lauren Greenspan, David Berman, Aryeh Brill, Ro Jefferson, Artemy Kolchinsky, Jennifer Lin, Andrew Mack, Anindita Maiti, Fernando E. Rosas, Alexander Stapleton, Lucas Teixeira, Dmitry Vaintrob