Showing 1–50 of 477 results for author: Hu, X

Crystallization in the Fractional Quantum Hall Regime with Disorder-Aware Neural Quantum States

Authors: Jihang Zhu, Yi Huang, Xiaodong Hu, Di Xiao, Ting Cao

Abstract: We present the first microscopic demonstration of a disorder-pinned hole Wigner crystal (WC), providing a natural explanation for the reentrant integer quantum Hall effect observed near $ν=2/3$, as well as its analogs in fractional Chern insulators. We further identify a novel crossover regime above filling $ν=2/3$ that connects this hole WC to an electron WC, characterized by a network-like elect… ▽ More We present the first microscopic demonstration of a disorder-pinned hole Wigner crystal (WC), providing a natural explanation for the reentrant integer quantum Hall effect observed near $ν=2/3$, as well as its analogs in fractional Chern insulators. We further identify a novel crossover regime above filling $ν=2/3$ that connects this hole WC to an electron WC, characterized by a network-like electron density structure. To uncover these phenomena, we use neural-network variational Monte Carlo (NNVMC) with a disorder-aware self-attention neural quantum state that describes both fractional quantum Hall (FQH) liquids and Wigner crystals within a single unbiased variational framework. More broadly, our method establishes a unified phase diagram that exposes a fundamental asymmetry in crystallization across half-filling: near $ν=1/3$, increasing LL mixing and disorder both stabilize an electron WC, whereas near $ν=2/3$, the hole WC dominates at weak LL mixing and ultimately gives way to the electron WC at strong LL mixing. △ Less

Submitted 7 April, 2026; originally announced April 2026.

Comments: 10 pages, 4 figures

Nonlinearity-Induced Thouless Pumping in Quasiperiodic Lattices

Authors: Xiao-Xiao Hu, Dun Zhao, Hong-Gang Luo

Abstract: Nonlinear Thouless pumping has been established in periodic lattices; its counterpart in quasiperiodic lattices remains unexplored. Here, we show a nonlinear topological pumping of gap solitons in quasiperiodic lattices where the local nonlinear self-consistent potentials lead to a lattice potential reconstruction; as a result, an emergent topological structure induced by this local reconstruction… ▽ More Nonlinear Thouless pumping has been established in periodic lattices; its counterpart in quasiperiodic lattices remains unexplored. Here, we show a nonlinear topological pumping of gap solitons in quasiperiodic lattices where the local nonlinear self-consistent potentials lead to a lattice potential reconstruction; as a result, an emergent topological structure induced by this local reconstruction governs the dynamics of the gap solitons. This enables solitons to adiabatically occupy a single topological band, realizing quasi-quantized Thouless pumping. In addition, the intrinsic lattice perturbations disrupt this band occupation, which drives solitons into a non-quantized drifting regime. However, even in this regime, we also find that the soliton transport is constrained by the topological properties of a critical rational approximant. Tuning nonlinearity or lattice scaling reveals a controllable switching among topological pumping, drifting, and localization. Our work uncovers a mechanism for nonlinearity-induced topological behavior in complex lattice potentials. △ Less

Submitted 1 April, 2026; originally announced April 2026.

Two-electron spectrum of a silicon quantum dot

Authors: Bilal Tariq, Xuedong Hu

Abstract: The energy spectrum and wave functions of electrons in a single silicon quantum dot provide valuable insights into the capabilities and limitations of such a system in quantum information processing. Here we investigate the low-lying singlet and triplet configurations and spectra in a two-electron silicon quantum dot. To build toward a comprehensive understanding, we first examine the competition… ▽ More The energy spectrum and wave functions of electrons in a single silicon quantum dot provide valuable insights into the capabilities and limitations of such a system in quantum information processing. Here we investigate the low-lying singlet and triplet configurations and spectra in a two-electron silicon quantum dot. To build toward a comprehensive understanding, we first examine the competition between Coulomb interaction and electron kinetic and confinement energy in the absence of valley-orbit coupling, as well as consequences of valley blockade in the presence of an ideal smooth interface. For realistic interfaces the variations in the magnitude and phase of valley-orbit coupling lead to inter-valley leakage, particularly when orbital splittings approach the valley splitting. In our study we particularly focus on the impact on the compositions of low-lying singlets and triplets. We find that for experimentally relevant parameter regimes the ground singlet and triplet states usually contain multiple configurations with significant weights as a result of a complicated competition among valley-orbit coupling, confinement potential, and Coulomb interaction. We further analyze the effects of an out-of-plane magnetic field on these the two-electron spectra. Our findings could have important implications for spin qubits in Si quantum dot in various contexts, such as qubit encoding and spin measurement. △ Less

Submitted 25 March, 2026; originally announced March 2026.

Exotic Pressure-Driven Band Gap Widening in Carbon Chain-Filled KFI Zeolite and Its Pathway to High-Pressure Semiconducting Electronics and High-Temperature Superconductivity

Authors: C. T. Wat, K. C. Lam, W. Y. Chan, C. P. Chau, S. P. Ng, W. K. Loh, L. Y. F. Lam, X. Hu, C. H. Wong

Abstract: Semiconducting devices face persistent challenges in operating at high pressure, as the band theory predicts that materials transition to a more metallic state under compression. However, our findings with carbon chains in KFI substrates reveal a conditional deviation from this norm. We not only witness the transition from polyyne (semiconductor) to cumulene (metal) at medium pressure, but we also… ▽ More Semiconducting devices face persistent challenges in operating at high pressure, as the band theory predicts that materials transition to a more metallic state under compression. However, our findings with carbon chains in KFI substrates reveal a conditional deviation from this norm. We not only witness the transition from polyyne (semiconductor) to cumulene (metal) at medium pressure, but we also observe an unexpected re-entrance of the polyyne at high pressures, where the band gap in the polyyne increases with pressure. In addition, the synthesis of long cumulene chains has posed a longstanding challenge in the quest for high-temperature organic superconductivity. We have identified critical conditions for synthesizing extended cumulene chains within zeolite frameworks, highlighting the interplay between unconventional charge density waves and significant torsions. The KFI zeolite facilitates the formation of carbon chains exceeding 5,000 atoms, in stark contrast to around 100 other zeolites that are limited to ~10 atoms. The cumulene@KFI system demonstrates a superconducting transition temperature reaching ~62 K, surpassing the highest reported values for bulk iron-based superconductors. This interplay between carbon structures and superconductivity not only advances our understanding of charge density waves but also heralds a new era in the study of novel applications △ Less

Submitted 6 March, 2026; originally announced March 2026.

Competing magnetic states in a non-coplanar Kagome magnet

Authors: Xiaodong Hu, Amar Fakhredine, Roger Guzman, Martin Frentrup, Jinan Shi, Giulio I. Lampronti, Sami El-Khatib, Waichuen Tse, Laura Gorzawski, Angelo Di Bernardo, Nadia Stelmashenko, Wu Zhou, Mehmet Egilmez, Danfeng Li, Grzegorz P. Mazur, Mario Cuoco, Carmine Autieri, Jason W. A. Robinson

Abstract: Non-collinear Kagome antiferromagnets (AFMs) Mn3X (X = Sn, Ga, Ge, Ir, Pt) can generate an anomalous Hall effect (AHE) despite vanishing net magnetization, enabled by broken time-reversal and inversion symmetries. However, strong in-plane anisotropy has limited studies of the AFM-AHE and electronic applications to coplanar spin configurations. Non-coplanar spin textures in these systems have been… ▽ More Non-collinear Kagome antiferromagnets (AFMs) Mn3X (X = Sn, Ga, Ge, Ir, Pt) can generate an anomalous Hall effect (AHE) despite vanishing net magnetization, enabled by broken time-reversal and inversion symmetries. However, strong in-plane anisotropy has limited studies of the AFM-AHE and electronic applications to coplanar spin configurations. Non-coplanar spin textures in these systems have been realized only in low temperature spin-glass states or at interfaces with heavy metals. Here, we report an intrinsic non-coplanar spin configuration persisting up to 400 K in cubic-phase Mn3Ge, originating from coexisting symmetric and antisymmetric exchange interactions. Competing magnetic states associated with this non-coplanar spin configuration give rise to an unconventional AHE with a magnetic-field-induced sign reversal and a hump-like feature. Our findings establish a platform for non-coplanar magnetism in AFM spintronics. △ Less

Submitted 10 February, 2026; originally announced February 2026.

Probing valley quantum oscillations via the spin Seebeck effect in transition metal dichalcogenide/ferromagnet hybrids

Authors: Xin Hu, Yuya Ominato, Mamoru Matsuo

Abstract: We theoretically investigate spin-valley-locked tunneling transport in a transition-metal dichalcogenide/ferromagnetic-insulator heterostructure under a perpendicular magnetic field, driven by the spin Seebeck effect. We demonstrate that spin-valley coupling together with the magnetic-field-induced valley-asymmetric Landau-level structure enables the generation of a valley-polarized spin current f… ▽ More We theoretically investigate spin-valley-locked tunneling transport in a transition-metal dichalcogenide/ferromagnetic-insulator heterostructure under a perpendicular magnetic field, driven by the spin Seebeck effect. We demonstrate that spin-valley coupling together with the magnetic-field-induced valley-asymmetric Landau-level structure enables the generation of a valley-polarized spin current from valley-selective spin excitation. We compare the spin current and the valley-polarized spin current in the conduction and valence bands and clarify their distinct microscopic origins. We predict pronounced quantum oscillations of the valley-polarized spin current, providing a clear experimental signature of quantized valley states. △ Less

Submitted 6 February, 2026; originally announced February 2026.

Comments: 10 pages, 7 figures

Mechanics of hierarchical twisted and coiled polymer artificial muscles: Decoupling force from kinematic limits

Authors: Ye Xiao, Zhao Luo, Falin Tian, Xinghao Hu, Dabiao Liu, Chun Li

Abstract: Thermally actuated twisted and coiled polymer (TCP) artificial muscles exhibit exceptional specific work capacities but are limited by an inherent competition between load-bearing capacity and actuation stroke. To address this limitation, we investigate a hierarchical helical structure designed to decouple force generation from kinematic limits. We propose a coupled thermo-mechanical model incorpo… ▽ More Thermally actuated twisted and coiled polymer (TCP) artificial muscles exhibit exceptional specific work capacities but are limited by an inherent competition between load-bearing capacity and actuation stroke. To address this limitation, we investigate a hierarchical helical structure designed to decouple force generation from kinematic limits. We propose a coupled thermo-mechanical model incorporating inter-filamentary contact mechanics and geometric nonlinearities to predict the assembly's equilibrium response. The results indicate that this hierarchical topology significantly amplifies isometric actuation stress compared to monofilament baselines, while maintaining a biological-like contraction stroke of approximately 22%. A critical topological threshold governed by the balance between cooperative load-sharing and geometric confinement is identified. Beyond an optimal bundle complexity, the geometric jamming dominates, as excessive inter-filamentary friction hinders actuation. Furthermore, we elucidate a stiffness-stroke synergy in homochiral configurations, where high helical angles amplify the thermal untwisting torque to overcome increased structural rigidity. Crucially, the volumetric energy density exhibits scale invariance regarding the hierarchical radius, implying that absolute force output can be linearly scaled through geometric upsizing without compromising efficiency. These findings provide a mechanics-based rationale for the structural programming, demonstrating that soft actuator performance limits are dictated by topological order rather than intrinsic material properties. △ Less

Submitted 1 February, 2026; originally announced February 2026.

Deriving Reliable Nucleation Rates from Metadynamics Simulations: Application to Yukawa Fluids

Authors: B. Arnold, J. Daligault, D. Saumon, S. X. Hu

Abstract: In order to solidify the usefulness of metadynamics in studying nucleation of crystals from supercooled liquids, we provide a specific procedure to calculate nucleation free energy barriers. After a pedagogical review of the important elements of classical nucleation theory and how metadynamics is used to find nucleation free energy barriers, we explain the benefits of local collective variables o… ▽ More In order to solidify the usefulness of metadynamics in studying nucleation of crystals from supercooled liquids, we provide a specific procedure to calculate nucleation free energy barriers. After a pedagogical review of the important elements of classical nucleation theory and how metadynamics is used to find nucleation free energy barriers, we explain the benefits of local collective variables over more common global collective variables. We show how a metadynamics free energy barrier must be carefully postprocessed so that classical nucleation theory can be applied to calculate nucleation rates. We apply our procedure to a Yukawa plasma and show that a particular physically-motivated fit to metadynamics data reproduces low-temperature reference data, justifying the usefulness of metadynamics to predict nucleation rates and the nucleation critical temperature. △ Less

Submitted 30 January, 2026; originally announced February 2026.

Comments: 20 pages including supplementary material, 10 figures

Inhibiting Conduction by He Mixing in Interiors of Jupiter and Saturn

Authors: Valentin V. Karasiev, S. X. Hu, Joshua P. Hinz, R. M. N. Goshadze, Shuai Zhang, Armin Bergermann, Ronald Redmer

Abstract: Accurate knowledge of the electrical and thermal conductivities and structural properties of hydrogen-helium mixtures under thermodynamic conditions within and beyond the immiscibility range is very important to predict the thermal evolution and internal structure of gas giant planets like Jupiter and Saturn. Here, we propose a novel method to determine the immiscibility boundary accurately withou… ▽ More Accurate knowledge of the electrical and thermal conductivities and structural properties of hydrogen-helium mixtures under thermodynamic conditions within and beyond the immiscibility range is very important to predict the thermal evolution and internal structure of gas giant planets like Jupiter and Saturn. Here, we propose a novel method to determine the immiscibility boundary accurately without the need for free energy calculations, while providing consistent insights into structural and transport properties of mixtures. We show with direct large-scale ab initio simulations that the insulator-metal transition (IMT) of the hydrogen subsystem is strongly affected by an admixture with a small fraction of helium and occurs at temperatures significantly higher than those of pure hydrogen. At pressures below 150 GPa, the IMT boundary is not related anymore to the H2 subsystem dissociation, the system remains insulating even after the full dissociation of H2 molecules and its transition to an H-He mixture. The offset of the IMT in the H-He mixture relative to the dissociation region in the hydrogen subsystem and the significant reduction of static electrical and thermal conductivity by a factor between two and a few thousand relative to pure hydrogen found in mixtures have consequences for Jupiter and Saturn's thermal evolution, internal structure, and dynamo action, affecting a large fraction of the interior of both planets. △ Less

Submitted 30 January, 2026; originally announced January 2026.

RKKY-like interactions between two magnetic skyrmions

Authors: Xuchong Hu, Huaiyang Yuan, Xiangrong Wang

Abstract: Understanding skyrmion-skyrmion interactions is crucial for effectively manipulating the motion of multiple skyrmions in racetrack and logic devices. However, the fundamental nature and microscopic origins of these interactions remain poorly understood. In this study, we investigate skyrmion-skyrmion interactions in chiral magnetic films and reveal that they possess intrinsic, anisotropic, and osc… ▽ More Understanding skyrmion-skyrmion interactions is crucial for effectively manipulating the motion of multiple skyrmions in racetrack and logic devices. However, the fundamental nature and microscopic origins of these interactions remain poorly understood. In this study, we investigate skyrmion-skyrmion interactions in chiral magnetic films and reveal that they possess intrinsic, anisotropic, and oscillatory characteristics. Specifically, we demonstrate that the attractive and repulsive forces between skyrmions oscillate with a well-defined period, akin to the Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling observed between two magnetic moments in metals. Our analysis uncovers the essential physics behind a previously unrecognized universal wavy tail in the skyrmion spin texture. Notably, the resulting RKKY-like interaction between skyrmions is universal for all tilted skyrmions, irrespective of whether the titled easy-axis is from an external field or a crystalline magnetic anisotropy. These findings introduce a novel physical principle for the design of skyrmion molecules or skyrmion superstructures, which hold significant potential for applications in skyrmion-based spintronics and neuromorphic computing. △ Less

Submitted 25 January, 2026; originally announced January 2026.

Comments: 6 pages, 4 figures

Magnetic switching of exciton lifetime in CrSBr

Authors: Ina V. Kalitukha, Ilya A. Akimov, Mikhail O. Nestoklon, Torsten Geirsson, Alejandro Molina-Sánchez, Eyüp Yalcin, Claudia Ruppert, Daniel A. Mayoh, Geetha Balakrishnan, Muthumalai Karuppasamy, Zdeněk Sofer, Yadong Wang, Daniel J. Gillard, Xuerong Hu, Alexander I. Tartakovskii, Manfred Bayer

Abstract: Exciton dynamics in layered magnetic semiconductors provide a sensitive probe of the interplay between spin order and light-matter interaction. Here, we study thin CrSBr layers using time-resolved photoluminescence spectroscopy in an external magnetic field, revealing a step-like reduction in the exciton lifetime from 11 to 7 ps, during the magnetization flip from the antiferromagnetic to the ferr… ▽ More Exciton dynamics in layered magnetic semiconductors provide a sensitive probe of the interplay between spin order and light-matter interaction. Here, we study thin CrSBr layers using time-resolved photoluminescence spectroscopy in an external magnetic field, revealing a step-like reduction in the exciton lifetime from 11 to 7 ps, during the magnetization flip from the antiferromagnetic to the ferromagnetic phase. The reduction of the exciton lifetime in the ferromagnetic phase persists below the Néel temperature, as evidenced by its strong magnetic-field dependence that disappears in the paramagnetic phase. Ab initio calculations reveal a one-dimensional nature of free excitons accompanied by a pronounced change in the oscillator strength across the magnetic phase transition predicting a shorter radiative lifetime of free excitons in the antiferromagnetic phase of CrSBr contradicting the experimental observations. This discrepancy is explained by strong localization of excitons at low tempature. We show both experimentally and theoretically that the observed magnetic switching of the exciton lifetime is attributed to a larger exciton localization volume leading to a larger oscillator strength in the ferromagnetic phase. The results show that disorder-induced localization effects play a key role in exciton dynamics in CrSBr. △ Less

Submitted 8 January, 2026; originally announced January 2026.

Concentration-Dependent Tungsten Effects on Short-Range Order and Deformation Behavior in Ni-W alloys

Authors: Shaozun Liu, Zehao Li, Hantong Chen, Xingyuan San, Bi-Cheng Zhou, Dieter Isheim, Tiejun Wang, Hong Gao, Nie Zhao, Yu Liu, Yong Gan, Xiaobing Hu

Abstract: Ni-W based medium heavy alloys offer a promising pathway to bridge the density-strength gap between tungsten heavy alloys and ultrahigh-strength steels. In this study, the effects of W concentration on short-range order (SRO), deformation behavior, and grain boundary chemistry of Ni-xW alloys in the range x = 0 to 38 wt% were systematically investigated using a suite of advanced characterization a… ▽ More Ni-W based medium heavy alloys offer a promising pathway to bridge the density-strength gap between tungsten heavy alloys and ultrahigh-strength steels. In this study, the effects of W concentration on short-range order (SRO), deformation behavior, and grain boundary chemistry of Ni-xW alloys in the range x = 0 to 38 wt% were systematically investigated using a suite of advanced characterization and modeling techniques, including synchrotron X-ray diffraction, transmission electron microscopy, atom probe tomography, and first-principles thermodynamic simulations. Our study reveals that strong SRO emerges when W content exceeds about 30 wt%, producing distinct diffuse scattering and significantly enhancing strain-hardening capacity. During deformation, the presence of SRO promotes planar slip and twin formation, leading to strong dislocation interactions and elevated flow stress. Hall-Petch analysis demonstrates an exceptionally high grain boundary strengthening coefficient (ky about 1100 MPa micrometer^(1/2)) in Ni-38W, underscoring the intrinsic strengthening effect associated with SRO. First-principles cluster expansion coupled with Monte Carlo simulations reveals that increasing W content enhances SRO tendency through the stabilization of Ni4W-type local configurations. These findings establish a mechanistic link between W concentration, SRO evolution, and mechanical response, providing new insights for designing high-density, high-strength Ni-W based alloys with optimized performance. △ Less

Submitted 25 December, 2025; originally announced December 2025.

Novel coupling between charge order and time-reversal-symmetry-breaking superconductivity

Authors: Quanxin Hu, Lingfeng Zhang, Yu Zheng, Yongwei Li, Qiheng Wang, Xinyu Liang, Baiqing Lv, Chi-Ming Yim, Takuto Kawakami, Vadim Grinenko, Xiao Hu, Hong Ding

Abstract: The interplay between charge-density waves (CDWs), which break translational symmetry, and spatially homogeneous superconductivity, which breaks global U(1) gauge symmetry, can give rise to an intriguing phenomenon: the pair-density wave, characterized by a spatial modulation of the superconducting order parameter. Yet how CDWs couple to unconventional superconducting states-particularly those wit… ▽ More The interplay between charge-density waves (CDWs), which break translational symmetry, and spatially homogeneous superconductivity, which breaks global U(1) gauge symmetry, can give rise to an intriguing phenomenon: the pair-density wave, characterized by a spatial modulation of the superconducting order parameter. Yet how CDWs couple to unconventional superconducting states-particularly those with time-reversal symmetry breaking (TRSB)-remains largely unexplored. Here, using scanning tunneling microscopy on heavily hole-doped Ba$_{1-x}$K$_x$Fe$_2$As$_2$, which hosts an s $\pm$ is superconducting state, we reveal a previously unobserved coupling between a surface CDW and TRSB superconductivity. Experimentally, the TRSB superconductivity imparts "chirality" to the CDW, which manifests as commensurate domains separated by domain walls with $π$-phase slips-forming what we term a bipolar CDW. The domain walls delineate TRSB domains of opposite chirality, consistent with spontaneous breaking of U(1) $\times$ Z2. Supported by theoretical modelling, we construct a framework in which a hidden interfacial pair-density modulation (PDM) mediates a linear coupling between the surface CDW and interband Josephson currents of TRSB superconductivity. Crucially, the theory shows that realizing this linear coupling requires a controlled global phase difference $δ$ $φ$ = $π$/2 between the PDM and CDW states. Our results uncover a previously overlooked connection between charge ordering and TRSB superconductivity, opening a pathway to explore intertwined quantum orders in iron-based superconductors and other strongly correlated systems. △ Less

Submitted 8 December, 2025; originally announced December 2025.

Comments: 34 pages, 14 figures

Evidence of a two-dimensional nitrogen crystalline structure on silver surfaces

Authors: Xuegao Hu, Haijun Cao, Zhicheng Gao, Hui Zhou, Daiyu Geng, Dong Li, Jisong Gao, Qiaoxiao Zhao, Zhihao Cai, Peng Cheng, Lan Chen, Sheng Meng, Kehui Wu, Baojie Feng

Abstract: Nitrogen, the most abundant element in Earth's atmosphere, exists as a diatomic gas under standard temperature and pressure. In the two-dimensional (2D) limit, atomically thin nitrogen, termed nitrogene, has been theoretically predicted to form crystalline materials with various polymorphic configurations, exhibiting diverse chemical and physical properties. However, the synthesis of nitrogene has… ▽ More Nitrogen, the most abundant element in Earth's atmosphere, exists as a diatomic gas under standard temperature and pressure. In the two-dimensional (2D) limit, atomically thin nitrogen, termed nitrogene, has been theoretically predicted to form crystalline materials with various polymorphic configurations, exhibiting diverse chemical and physical properties. However, the synthesis of nitrogene has remained elusive due to the strong nitrogen-nitrogen triple bonds. Here, we report experimental evidence of the formation of nitrogen-based crystalline structures compatible with nitrogene on silver surfaces via ion-beam-assisted epitaxy. Through a combination of scanning tunneling microscopy, angle-resolved photoemission spectroscopy, and first-principles calculations, we demonstrate that the nitrogene-like structure adopts a puckered honeycomb lattice. Notably, our calculations predict a nitrogene band gap of up to 7.5 eV, positioning it as a promising candidate for ultraviolet optoelectronic devices and high-k dielectric applications. △ Less

Submitted 3 December, 2025; originally announced December 2025.

Comments: Nature Communications; In Press

Journal ref: Nat. Commun. 17, 846 (2026)

CycleChemist: A Dual-Pronged Machine Learning Framework for Organic Photovoltaic Discovery

Authors: Hou Hei Lam, Jiangjie Qiu, Xiuyuan Hu, Wentao Li, Fankun Zeng, Siwei Fu, Hao Zhang, Xiaonan Wang

Abstract: Organic photovoltaic (OPV) materials offer a promising path toward sustainable energy generation, but their development is limited by the difficulty of identifying high performance donor and acceptor pairs with strong power conversion efficiencies (PCEs). Existing design strategies typically focus on either the donor or the acceptor alone, rather than using a unified approach capable of modeling b… ▽ More Organic photovoltaic (OPV) materials offer a promising path toward sustainable energy generation, but their development is limited by the difficulty of identifying high performance donor and acceptor pairs with strong power conversion efficiencies (PCEs). Existing design strategies typically focus on either the donor or the acceptor alone, rather than using a unified approach capable of modeling both components. In this work, we introduce a dual machine learning framework for OPV discovery that combines predictive modeling with generative molecular design. We present the Organic Photovoltaic Donor Acceptor Dataset (OPV2D), the largest curated dataset of its kind, containing 2000 experimentally characterized donor acceptor pairs. Using this dataset, we develop the Organic Photovoltaic Classifier (OPVC) to predict whether a material exhibits OPV behavior, and a hierarchical graph neural network that incorporates multi task learning and donor acceptor interaction modeling. This framework includes the Molecular Orbital Energy Estimator (MOE2) for predicting HOMO and LUMO energy levels, and the Photovoltaic Performance Predictor (P3) for estimating PCE. In addition, we introduce the Material Generative Pretrained Transformer (MatGPT) to produce synthetically accessible organic semiconductors, guided by a reinforcement learning strategy with three objective policy optimization. By linking molecular representation learning with performance prediction, our framework advances data driven discovery of high performance OPV materials. △ Less

Submitted 5 March, 2026; v1 submitted 23 November, 2025; originally announced November 2025.

Scalable data-driven modeling of microstructure evolution by learning local dependency and spatiotemporal translation invariance rules in phase field simulation

Authors: Zishuo Lan, Qionghuan Zeng, Weilong Ma, Xiangju Liang, Yue Li, Yu Chen, Yiming Chen, Xiaobing Hu, Junjie Li, Lei Wang, Jing Zhang, Zhijun Wang, Jincheng Wang

Abstract: Phase-field (PF) simulation provides a powerful framework for predicting microstructural evolution but suffers from prohibitive computational costs that severely limit accessible spatiotemporal scales in practical applications. While data-driven methods have emerged as promising approaches for accelerating PF simulations, existing methods require extensive training data from numerous evolution tra… ▽ More Phase-field (PF) simulation provides a powerful framework for predicting microstructural evolution but suffers from prohibitive computational costs that severely limit accessible spatiotemporal scales in practical applications. While data-driven methods have emerged as promising approaches for accelerating PF simulations, existing methods require extensive training data from numerous evolution trajectories, and their inherent black-box nature raises concerns about long-term prediction reliability. This work demonstrates, through examples of grain growth and spinodal decomposition, that a minimalist Convolutional Neural Network (CNN) trained with a remarkably small dataset even from a single small-scale simulation can achieve seamless scalability to larger systems and reliable long-term predictions far beyond the temporal range of the training data. The key insight of this work lies in revealing that the success of CNN-based models stems from the alignment between their inductive biases and the physical priors of phase-field simulations specifically, locality and spatiotemporal translation invariance. Through effective receptive field analysis, we verify that the model captures these essential properties during training. Therefore, from a reductionist perspective, the surrogate model essentially establishes a spatiotemporally invariant regression mapping between a grid point's local environment and its subsequent state. Further analysis of the model's feature space demonstrates that microstructural evolution effectively represents a continuous redistribution of a finite set of local environments. When the model has already encountered nearly all possible local environments in the early-stage training data, it can reliably generalize to much longer evolution timescales, regardless of the dramatic changes in global microstructural morphology. △ Less

Submitted 13 November, 2025; originally announced November 2025.

Magnetism and Peierls distortion in Dirac semimetal CaMnBi$_2$

Authors: Aashish Sapkota, Niraj Aryal, Xiao Hu, Masaaki Matsuda, Yan Wu, Guangyong Xu, John M. Wilde, Andreas Kreyssig, Paul C. Canfield, Cedomir Petrovic, John M. Tranquada, Igor A. Zaliznyak

Abstract: Dirac semimetals of the form $A$Mn$X_2$ ($A =$ alkaline-earth or divalent rare earth; $X =$ Bi, Sb) host conducting square-net Dirac-electron layers of $X$ atoms interleaved with antiferromagnetic Mn$X$ layers. In these materials, canted antiferromagnetism can break time-reversal symmetry (TRS) and produce a Weyl semimetallic state. CaMnBi$_2$ was proposed to realize this behavior below… ▽ More Dirac semimetals of the form $A$Mn$X_2$ ($A =$ alkaline-earth or divalent rare earth; $X =$ Bi, Sb) host conducting square-net Dirac-electron layers of $X$ atoms interleaved with antiferromagnetic Mn$X$ layers. In these materials, canted antiferromagnetism can break time-reversal symmetry (TRS) and produce a Weyl semimetallic state. CaMnBi$_2$ was proposed to realize this behavior below $T^{*}\sim 50$ K, where anomalies in resistivity and optical conductivity were reported. We investigate single-crystal CaMnBi$_{2}$ using polarized and unpolarized neutron diffraction, x-ray diffraction, and density functional theory (DFT) calculations to elucidate the underlying crystal and magnetic structures. The results show that the observed anomalies do not originate from spin canting or weak ferromagnetism; no measurable uniform Mn spin canting is detected. Instead, CaMnBi$_2$ undergoes a coupled structural and magnetic symmetry-lowering transition at $T^{*} = 46(2)$ K, from a tetragonal lattice with C-type antiferromagnetism to an orthorhombic phase with unit-cell doubling along the $c$ axis and minimal impact on magnetism. Analysis of superlattice peak intensities and lattice distortion reveals a continuous second-order transition governed by a single order parameter. The refined atomic displacements correspond to a zigzag bond-order-wave (BOW) modulation of Bi-Bi bonds, consistent with an electronically driven Peierls-type instability in the Dirac-electron Bi layer, long anticipated by Hoffmann and co-workers [W.~Tremel and R.~Hoffmann, \textit{J. Am. Chem. Soc.} \textbf{109}, 124 (1987); G.~A.~Papoian and R.~Hoffmann, \textit{Angew. Chem. Int. Ed.} \textbf{39}, 2408 (2000)]. %\textcite{TremelHoffman_JACS1987} [JACS {\bf 109}, 124 (1987)]. △ Less

Submitted 5 November, 2025; originally announced November 2025.

Comments: 25 pages with 19 figures including appendices; 15 pages, 11 figs main text

Laser-Induced Commensurate-Incommensurate Transition of Charge Order in a Hubbard Superlattice

Authors: Hua Chai, Zhenyu Cheng, Qinxin Hu, Zhongbing Huang, Xiang Hu, Xuedong Tian, Liang Du

Abstract: We investigate the nonequilibrium dynamics of charge density waves in a pumped one-dimensional Hubbard superlattice with staggered onsite Coulomb interactions at half-filling, using time-dependent exact diagonalization. In equilibrium, the system exhibits commensurate charge correlations consistent with the superlattice periodicity. Under laser excitation, the charge correlation function exhibits… ▽ More We investigate the nonequilibrium dynamics of charge density waves in a pumped one-dimensional Hubbard superlattice with staggered onsite Coulomb interactions at half-filling, using time-dependent exact diagonalization. In equilibrium, the system exhibits commensurate charge correlations consistent with the superlattice periodicity. Under laser excitation, the charge correlation function exhibits distinct behaviors across four representative frequencies, spanning both linear and nonlinear optical regimes. Notably, we observe a laser-induced commensurate-to-incommensurate transition in the charge order, manifested by a shift in the peak wavevector of the charge structure factor. This transition is driven by sublattice-selective doublon-holon dynamics, where the laser frequency and intensity determine whether excitations predominantly destabilize the charge order on the weakly or strongly interacting sublattice. Our analysis of the excitation spectrum and site-resolved correlation dynamics reveals the underlying mechanisms of this transition. These results suggest a promising optical strategy for controlling charge order in superlattice-based quantum materials. △ Less

Submitted 30 October, 2025; originally announced October 2025.

Comments: 8 pages, 4 figures

Development of a 10.8-eV Tabletop Femtosecond Laser with Tunable Polarization for High-Resolution Angle-Resolved Photoemission Spectroscopy

Authors: Jisong Gao, Qiaoxiao Zhao, Wenbo Liu, Dong Li, Zhicheng Gao, Yudian Zhou, Xuegao Hu, Zhihao Cai, Zhilin Li, Youguo Shi, Peng Cheng, Zhaojun Liu, Lan Chen, Kehui Wu, Zhigang Zhao, Baojie Feng

Abstract: The development of extreme ultraviolet sources is critical for advancing angleresolved photoemission spectroscopy (ARPES), a powerful technique for probing the electronic structure of materials. Here, we report the construction of a tabletop 10.8-eV femtosecond laser through cascaded third-harmonic generation, which operates at a repetition rate of 1 MHz and delivers a photon flux of approximately… ▽ More The development of extreme ultraviolet sources is critical for advancing angleresolved photoemission spectroscopy (ARPES), a powerful technique for probing the electronic structure of materials. Here, we report the construction of a tabletop 10.8-eV femtosecond laser through cascaded third-harmonic generation, which operates at a repetition rate of 1 MHz and delivers a photon flux of approximately 1012 photons/s. The system achieves a high energy resolution of approximately 11.8 meV and tunable polarization. This flexibility enables detailed studies of orbitaland (pseudo)spin characteristics in quantum materials. We demonstrate the capabilities of this laser-ARPES system by investigating several prototypical materials, showcasing its potential for elucidating complex phenomena in quantum materials. △ Less

Submitted 28 October, 2025; originally announced October 2025.

Journal ref: Rev. Sci. Instrum. 96, 093004 (2025)

Anisotropic linear magnetoresistance in nanoflakes of Dirac semimetal NiTe2

Authors: Ding Bang Zhou, Kuang Hong Gao, Tie Lin, Yang Yang, Meng Fan Zhao, Zhi Yan Jia, Xiao Xia Hu, Qian Jin Guo, Zhi Qing Li

Abstract: This work investigates the magneto-transport properties of exfoliated NiTe2 nano-flakes with varying thicknesses and disorder levels, unveiling two distinct physical mechanisms governing the observed anisotropic linear magnetoresistance (MR). For the perpendicular magnetic field configuration, the well-defined linear MR in high fields is unambiguously attributed to a classical origin. This conclus… ▽ More This work investigates the magneto-transport properties of exfoliated NiTe2 nano-flakes with varying thicknesses and disorder levels, unveiling two distinct physical mechanisms governing the observed anisotropic linear magnetoresistance (MR). For the perpendicular magnetic field configuration, the well-defined linear MR in high fields is unambiguously attributed to a classical origin. This conclusion is supported by the proportionality between the MR slope and the carrier mobility, and between the crossover field and the inverse of mobility. In stark contrast, the linear MR under parallel magnetic fields exhibits a non-classical character. It shows a pronounced enhancement with decreasing flake thickness, which correlates with an increasing hole-to-electron concentration ratio. This distinctive thickness dependence suggests an origin in the nonlinear band effects near the Dirac point, likely driven by the shift of the Fermi level. Furthermore, the strengthening of MR anisotropic with enhanced inter-layer transport contradicts the prediction of the guiding-center diffusion model for three-dimensional systems. Our findings highlight the critical roles of band topology and structural dimensional in the anomalous magneto-transport of Dirac semi-metals. △ Less

Submitted 6 December, 2025; v1 submitted 1 October, 2025; originally announced October 2025.

Spontaneous elongation of 3D gastruloids from local cell polarity alignment

Authors: Richard D. J. G. Ho, Endre J. L. Mossige, Sergei Ponomartcev, Natalia Smirnova, Xian Hu, Keqing Sunny Dai, Stefan Krauss, Dag Kristian Dysthe, Luiza Angheluta

Abstract: Gastruloids are 3D stem cell aggregate models for early embryogenesis that provide a unique platform to study how collective cell dynamics drive tissue symmetry breaking and axial elongation. Using 3D light sheet imaging, we show that a pulse of Chiron, a Wnt activator, induces coherent alignment of cell polarity during elongation. While nuclear elongation occurs with or without treatment, only Ch… ▽ More Gastruloids are 3D stem cell aggregate models for early embryogenesis that provide a unique platform to study how collective cell dynamics drive tissue symmetry breaking and axial elongation. Using 3D light sheet imaging, we show that a pulse of Chiron, a Wnt activator, induces coherent alignment of cell polarity during elongation. While nuclear elongation occurs with or without treatment, only Chiron-treated gastruloids exhibit quasi-long-range alignment of nuclear axes, linking cell polarity coherence to tissue-scale remodeling. A minimal physical model of polarized cells, incorporating alignment-dependent torques and polarity-mediated adhesion, reproduces symmetry breaking and elongation, demonstrating that local cell polarity alignment alone can drive tissue-scale convergence-extension flows. △ Less

Submitted 10 September, 2025; originally announced September 2025.

Polarization- and time-resolved nonlinear multi-photon spectroscopy for confocal microscopy of semiconductor nanostructures

Authors: Nikita V. Siverin, Andreas Farenbruch, Dmitri R. Yakovlev, Daniel J. Gillard, Xuerong Hu, Alexander I. Tartakovskii, Manfred Bayer

Abstract: We present a versatile confocal microscopy setup for optical second harmonic generation (SHG) and multi-photon spectroscopy that enables polarization-resolved studies of semiconductor bulk crystals and low-dimensional structures. The system offers full polarization control in both excitation and detection, spatial scanning with micrometer resolution, and spectrally tunable excitation over a broad… ▽ More We present a versatile confocal microscopy setup for optical second harmonic generation (SHG) and multi-photon spectroscopy that enables polarization-resolved studies of semiconductor bulk crystals and low-dimensional structures. The system offers full polarization control in both excitation and detection, spatial scanning with micrometer resolution, and spectrally tunable excitation over a broad energy range from 0.5 to 4.0 eV, using femtosecond and picosecond laser pulses. Samples are mounted in a helium-flow cryostat, allowing temperature control from 4 to 300 K. Magnetic fields up to 0.625 T can be applied in the Voigt geometry via an electromagnet. The nonlinear optical signals are analyzed using a high-resolution spectrometer with a spectral resolution of 60 $μ$eV. We demonstrate the potential of the setup by means of SHG polarization tomography measurements on a Cu$_2$O crystal as well as through a SHG spectral scan of a ZnSe crystal over a wide energy range from 1.4 to 3.1 eV. Polarization-resolved confocal SHG mapping of various twisted mono- and bilayer MoS$_2$ structures is also presented. In addition, time-resolved two-color pump-probe experiments are shown for a Cs$_2$AgBiBr$_6$ crystal, illustrating the potential of the system for investigating coherent exciton and phonon dynamics. △ Less

Submitted 25 August, 2025; originally announced August 2025.

Metallic Contact Contributions in Thermal Hall Conductivity Measurements

Authors: Hongyu Ma, Xuesong Hu, Junren Shi

Abstract: We investigate the influence of metallic contacts on thermal Hall measurements. By analyzing typical measurement setups, we show that heat currents bypassing through metallic contacts could generate non-negligible thermal Hall signals. We find that contributions from metallic contacts with thicknesses on the order of 10$^{-2}$ of sample widths can approximately replicate experimental observations… ▽ More We investigate the influence of metallic contacts on thermal Hall measurements. By analyzing typical measurement setups, we show that heat currents bypassing through metallic contacts could generate non-negligible thermal Hall signals. We find that contributions from metallic contacts with thicknesses on the order of 10$^{-2}$ of sample widths can approximately replicate experimental observations across different materials in both temperature dependence and magnitude, assuming silver contacts with a conductivity of $10^{8}~\mathrm{S/m}$. Our analysis underscores the need to minimize metallic contact effects in thermal Hall measurements, which can be achieved by optimizing measurement configurations. △ Less

Submitted 23 December, 2025; v1 submitted 15 August, 2025; originally announced August 2025.

Composite Fermion Theory of Fractional Chern Insulator Stability

Authors: Xiaodong Hu, Ying Ran, Di Xiao

Abstract: We develop a mean-field theory of the stability of fractional Chern insulators based on the dipole picture of composite fermions (CFs). We construct CFs by binding vortices to Bloch electrons and derive a CF single-particle Hamiltonian that describes a Hofstadter problem in the enlarged CF Hilbert space, with the trace-condition term emerging naturally in the small-$q$ limit as part of the CF Hami… ▽ More We develop a mean-field theory of the stability of fractional Chern insulators based on the dipole picture of composite fermions (CFs). We construct CFs by binding vortices to Bloch electrons and derive a CF single-particle Hamiltonian that describes a Hofstadter problem in the enlarged CF Hilbert space, with the trace-condition term emerging naturally in the small-$q$ limit as part of the CF Hamiltonian. Going beyond the small-$q$ limit, we apply our theory to twisted MoTe$_2$ and calculate its CF band structures. The resulting CF phase diagram matches closely with that from exact diagonalization, and the projected many-body wavefunctions achieve exceptionally high overlaps with the latter. Our theory provides both a microscopic understanding and a computationally efficient tool for identifying fractional Chern insulators. △ Less

Submitted 9 January, 2026; v1 submitted 5 August, 2025; originally announced August 2025.

Quantum oscillations of valley current driven by microwave irradiation in transition-metal dichalcogenide/ferromagnet hybrids

Authors: Xin Hu, Yuya Ominato, Mamoru Matsuo

Abstract: We theoretically study spin and valley transport in a transition-metal dichalcogenide(TMDC)/ferromagnet heterostructure under a perpendicular magnetic field. We find that microwave-driven spin pumping induces a valley-selective spin excitation, a direct consequence of the valley-asymmetric Landau levels in the TMDC conduction band. This process generates a pure valley current which, as our central… ▽ More We theoretically study spin and valley transport in a transition-metal dichalcogenide(TMDC)/ferromagnet heterostructure under a perpendicular magnetic field. We find that microwave-driven spin pumping induces a valley-selective spin excitation, a direct consequence of the valley-asymmetric Landau levels in the TMDC conduction band. This process generates a pure valley current which, as our central finding, exhibits pronounced quantum oscillations as a function of chemical potential. These oscillations provide a definitive experimental signature of the quantized valley states and establish another pathway to interface spintronics and valleytronics. △ Less

Submitted 30 December, 2025; v1 submitted 16 July, 2025; originally announced July 2025.

Comments: 7 pages, 3 figures, one table

Journal ref: Phys. Rev. B 112, L220414(2025)

First-principles analysis of the effect of magnetic states on the oxygen vacancy formation energy in doped La$_{0.5}$Sr$_{0.5}$CoO$_3$ perovskite

Authors: Wei Wei, Florian Fuchs, Andreas Zienert, Xiao Hu, Jörg Schuster

Abstract: Oxygen vacancies are critical for determining the electrochemical performance of fast oxygen ion conductors. The perovskite La$_{0.5}$Sr$_{0.5}$CoO$_3$, known for its excellent mixed ionic-electronic conduction, has attracted significant attention due to its favorable vacancy characteristics. In this study, we employ first-principles calculations to systematically investigate the impact of 3$d$ tr… ▽ More Oxygen vacancies are critical for determining the electrochemical performance of fast oxygen ion conductors. The perovskite La$_{0.5}$Sr$_{0.5}$CoO$_3$, known for its excellent mixed ionic-electronic conduction, has attracted significant attention due to its favorable vacancy characteristics. In this study, we employ first-principles calculations to systematically investigate the impact of 3$d$ transition-metal doping on the oxygen vacancy formation energies in the perovskite. Two magnetic states, namely the ferromagnetic and paramagnetic states, are considered in our models to capture the influence of magnetic effects on oxygen vacancy energetics. Our results reveal that the oxygen vacancy formation energies are strongly dependent on both the dopant species and the magnetic state. Notably, the magnetic states alter the vacancy formation energy in a dopant-specific manner due to double exchange interactions, indicating that relying solely on the ferromagnetic ground state may result in misleading trends in doping behavior. These findings emphasise the importance of accounting for magnetic effects when investigating oxygen vacancy properties in perovskite oxides. △ Less

Submitted 10 July, 2025; originally announced July 2025.

Pairing symmetry and superconductivity in La$_3$Ni$_2$O$_7$ thin films

Authors: Wenyuan Qiu, Zhihui Luo, Xunwu Hu, Dao-Xin Yao

Abstract: The recent discovery of superconductivity with a transition temperature $T_c$ over 40 K in La$_3$Ni$_2$O$_7$ and (La,Pr)$_{3}$Ni$_2$O$_7$ thin films at ambient pressure marks an important step in the field of nickelate superconductors. Here, we perform a renormalized mean-field theory study of the superconductivity in $\mathrm{La_3Ni_2O_7}$ thin films, using a bilayer two-orbital $t-J$ model. Our… ▽ More The recent discovery of superconductivity with a transition temperature $T_c$ over 40 K in La$_3$Ni$_2$O$_7$ and (La,Pr)$_{3}$Ni$_2$O$_7$ thin films at ambient pressure marks an important step in the field of nickelate superconductors. Here, we perform a renormalized mean-field theory study of the superconductivity in $\mathrm{La_3Ni_2O_7}$ thin films, using a bilayer two-orbital $t-J$ model. Our result reveals an $s_\pm$-wave pairing symmetry driven by the strong interlayer superexchange coupling of $d_{z^2}$ orbital, resembling the pressurized bulk case. Also, we roughly reproduce the experimentally observed nodeless shape of the superconducting gap at the $β$ pocket and the superconducting $T_c$. In addition, by analysing the orbital-resolved pairing configurations and their projections onto Fermi surface, we find that the nodeless feature of $β$ pocket is related to the interlayer pairing within both $d_{z^2}$ and $d_{x^2-y^2}$ orbitals. Moreover, we identify a formation of the inplane inter-orbital $d$-wave pairing between $d_{z^2}$ and $d_{x^2-y^2}$ orbitals, which can even enhance the dominated interlayer $s_\pm$-wave. △ Less

Submitted 9 July, 2025; v1 submitted 25 June, 2025; originally announced June 2025.

Comments: 7 pages, 6 figures

Topological Jackiw-Rebbi States in Photonic Van der Waals Heterostructures

Authors: Sam A. Randerson, Paul Bouteyre, Xuerong Hu, Oscar J. Palma-Chaundler, Alexander J. Knight, Helgi Sigurðsson, Casey K. Cheung, Yue Wang, Kenji Watanabe, Takashi Taniguchi, Roman Gorbachev, Alexander I. Tartakovskii

Abstract: Topological phenomena, first studied in solid state physics, have seen increased interest for applications in nanophotonics owing to highly controllable light confinement with inherent robustness to defects. Photonic crystals can be designed to host topologically protected interface states for directional light transport, localization and robust lasing via tuning of the bulk topological invariant.… ▽ More Topological phenomena, first studied in solid state physics, have seen increased interest for applications in nanophotonics owing to highly controllable light confinement with inherent robustness to defects. Photonic crystals can be designed to host topologically protected interface states for directional light transport, localization and robust lasing via tuning of the bulk topological invariant. At the same time, van der Waals (vdW) materials, in both their monolayer and quasi-bulk forms, are emerging as exciting additions to the field of nanophotonics, with a range of unique optoelectronic properties and intrinsic adherence to any type of host material, allowing fabrication of complex multi-layer structures. We present here a 1D topological photonic platform made from stacked nanostructured and planar layers of quasi-bulk WS$_2$ to achieve Jackiw-Rebbi (JR) interface states between two topologically distinct gratings in the near-infrared range around 750 nm. Such states are measured in the far-field with angle-resolved reflectance contrast measurements, exhibiting linewidth of 10 meV and highly directional emission with an angular bandwidth of 8.0$^\circ$. Subsequent local mapping of the structure via sub-wavelength resolution scattering-type scanning near-field optical microscopy (s-SNOM) reveals strong spatial confinement of the JR state to the grating interface region. Finally, we couple in the JR state the photoluminescence of monolayer WSe$_2$ incorporated in a five-layer vdW grating heterostructure, giving rise to directional enhancement of the excitonic emission of up to 22 times that of uncoupled monolayer, thus demonstrating the potential of the topological interface states for highly directional light emission in addition to light scattering. △ Less

Submitted 4 June, 2025; originally announced June 2025.

Comments: 13 pages main text, 6 figures, 9 pages supplementary information, 6 supplementary notes

Pressure tuning of competing interactions on a honeycomb lattice

Authors: Piyush Sakrikar, Bin Shen, Eduardo H. T. Poldi, Faranak Bahrami, Xiaodong Hu, Eric M. Kenney, Qiaochu Wang, Kyle W. Fruhling, Chennan Wang, Ritu Gupta, Rustem Khasanov, Hubertus Luetkens, Stuart A. Calder, Adam A. Aczel, Gilberto Fabbris, Russell J. Hemley, Kemp W. Plumb, Ying Ran, Philipp Gegenwart, Alexander A. Tsirlin, Daniel Haskel, Michael J. Graf, Fazel Tafti

Abstract: Magnetic exchange interactions are mediated via orbital overlaps across chemical bonds. Thus, modifying the bond angles by physical pressure or strain can tune the relative strength of competing interactions. Here we present a remarkable case of such tuning between the Heisenberg (J) and Kitaev (K) exchange, which respectively establish magnetically ordered and spin liquid phases on a honeycomb la… ▽ More Magnetic exchange interactions are mediated via orbital overlaps across chemical bonds. Thus, modifying the bond angles by physical pressure or strain can tune the relative strength of competing interactions. Here we present a remarkable case of such tuning between the Heisenberg (J) and Kitaev (K) exchange, which respectively establish magnetically ordered and spin liquid phases on a honeycomb lattice. We observe a rapid suppression of the Neel temperature (TN) with pressure in Ag3LiRh2O6, a spin-1/2 honeycomb lattice with both J and K couplings. Using a combined analysis of x-ray data and first-principles calculations, we find that pressure modifies the bond angles in a way that increases the |K/J| ratio and thereby suppresses TN. Consistent with this picture, we observe a spontaneous onset of muon spin relaxation (muSR) oscillations below TN at low pressure, whereas in the high-pressure phase, oscillations appear only when T < TN/2. Unlike other candidate Kitaev materials, Ag3LiRh2O6 is tuned toward a quantum critical point by pressure while avoiding a structural dimerization in the relevant pressure range. △ Less

Submitted 23 May, 2025; originally announced May 2025.

Comments: 1 pdf, 3 figures, 1 table, published

Journal ref: Nature Communications 16, 4712 (2025)

Polarization Vortices in a Ferromagnetic Metal via Twistronics

Authors: Yingzhuo Lun, Xinxin Hu, Qi Ren, Umair Saeed, Kapil Gupta, Bernat Mundet, Ivan Pinto-Huguet, Jose Santiso, Jessica Padilla-Pantoja, Jose Manuel Caicedo Roque, Yunpeng Ma, Qian Li, Gang Tang, David Pesquera, Xueyun Wang, Jiawang Hong, Jordi Arbiol, Gustau Catalan

Abstract: Recent advances in moire engineering provide new pathways for manipulating lattice distortions and electronic properties in low-dimensional materials. Here, we demonstrate that twisted stacking can induce dipolar vortices in metallic SrRuO3 membranes, despite the presence of free charges that would normally screen depolarizing fields and dipole-dipole interactions. These polarization vortices are… ▽ More Recent advances in moire engineering provide new pathways for manipulating lattice distortions and electronic properties in low-dimensional materials. Here, we demonstrate that twisted stacking can induce dipolar vortices in metallic SrRuO3 membranes, despite the presence of free charges that would normally screen depolarizing fields and dipole-dipole interactions. These polarization vortices are correlated with moire-periodic flexoelectricity induced by shear strain gradients, and exhibit a pronounced dependence on the twist angle. In addition, multiferroic behavior emerges below the ferromagnetic Curie temperature of the films, whereby polarization and ferromagnetism coexist and compete, showing opposite twist-angle dependencies of their respective magnitudes. Density functional theory calculations provide insights into the microscopic origin of these observations. Our findings extend the scope of polarization topology design beyond dielectric materials and into metals. △ Less

Submitted 23 May, 2025; originally announced May 2025.

Comments: Manuscript(14 pages, 4 figures)+Supplementary Information

Size-Dependent Tensile Behavior and Dislocation Dynamics in Cu and Ag Nanowires: A Molecular Dynamics Study

Authors: Xiaorui Hu, Jiawei Xiong

Abstract: By using molecular dynamics simulations, the research examine how copper and silver nanowires respond to tensile loading in order to clarify their nanoscale deformation mechanisms. The results demonstrate that these two metal nanowires follow notably different stress - strain trends, with silver wires exhibiting greater elastic stiffness and higher yield points at equivalent diameters - an effect… ▽ More By using molecular dynamics simulations, the research examine how copper and silver nanowires respond to tensile loading in order to clarify their nanoscale deformation mechanisms. The results demonstrate that these two metal nanowires follow notably different stress - strain trends, with silver wires exhibiting greater elastic stiffness and higher yield points at equivalent diameters - an effect likely rooted in silver's stronger atomic bonding and more stable microstructure. A pronounced size effect is observed: as the wire diameter diminishes, both the yield strength and ultimate tensile strength increase substantially, a behavior driven by the higher proportion of surface atoms that enhance dislocation nucleation and mobility. Atomistic analyses further underscore the dominant role of dislocations during plastic deformation, and in particular reveal that surface - initiated dislocations in thinner wires critically affect their fracture behavior. △ Less

Submitted 1 May, 2025; originally announced May 2025.

Valley Polarization and Anomalous Valley Hall Effect in Altermagnet Ti2Se2S with Multipiezo Properties

Authors: Xin Hu, Weihang Zhao, Wenjun Xia, Hanbo Sun, Chao Wu, Yin-Zhong Wu, Ping Li

Abstract: Recently, altermagnets demonstrate numerous newfangle physical phenomena due to their inherent antiferromagnetic coupling and spontaneous spin splitting, that are anticipated to enable innovative spintronic devices. However, the rare two-dimensional altermagnets have been reported, making it difficult to meet the requirements for high-performance spintronic devices on account of the growth big dat… ▽ More Recently, altermagnets demonstrate numerous newfangle physical phenomena due to their inherent antiferromagnetic coupling and spontaneous spin splitting, that are anticipated to enable innovative spintronic devices. However, the rare two-dimensional altermagnets have been reported, making it difficult to meet the requirements for high-performance spintronic devices on account of the growth big data. Here, we predict a stable monolayer Ti2Se2S with out-of-plane altermagnetic ground state and giant valley splitting. The electronic properties of altermagnet Ti2Se2S are highly dependent on the onsite electron correlation. Through symmetry analysis, we find that the valleys of X and Y points are protected by the mirror Mxy symmetry rather than the time-reversal symmetry. Therefore, the multipiezo effect, including piezovalley and piezomagnetism, can be induced by the uniaxial strain. The total valley splitting of monolayer Ti2Se2S can be as high as ~500 meV. Most interestingly, the direction of valley polarization can be effectively tuned by the uniaxial strain, based on this, we have defined logical "0", "+1", and "-1" states for data transmission and storage. In addition, we have designed a schematic diagram for observing the anomalous Hall effect in experimentally. Our findings have enriched the candidate materials of two-dimensional altermagnet for the ultra-fast and low power consumption device applications. △ Less

Submitted 25 April, 2025; originally announced April 2025.

Comments: 7 pages, 6 figures

Zero-shot Autonomous Microscopy for Scalable and Intelligent Characterization of 2D Materials

Authors: Jingyun Yang, Ruoyan Avery Yin, Chi Jiang, Yuepeng Hu, Xiaokai Zhu, Xingjian Hu, Sutharsika Kumar, Xiao Wang, Xiaohua Zhai, Keran Rong, Yunyue Zhu, Tianyi Zhang, Zongyou Yin, Jing Kong, Neil Zhenqiang Gong, Zhichu Ren, Haozhe Wang

Abstract: Characterization of atomic-scale materials traditionally requires human experts with months to years of specialized training. Even for trained human operators, accurate and reliable characterization remains challenging when examining newly discovered materials such as two-dimensional (2D) structures. This bottleneck drives demand for fully autonomous experimentation systems capable of comprehendin… ▽ More Characterization of atomic-scale materials traditionally requires human experts with months to years of specialized training. Even for trained human operators, accurate and reliable characterization remains challenging when examining newly discovered materials such as two-dimensional (2D) structures. This bottleneck drives demand for fully autonomous experimentation systems capable of comprehending research objectives without requiring large training datasets. In this work, we present ATOMIC (Autonomous Technology for Optical Microscopy & Intelligent Characterization), an end-to-end framework that integrates foundation models to enable fully autonomous, zero-shot characterization of 2D materials. Our system integrates the vision foundation model (i.e., Segment Anything Model), large language models (i.e., ChatGPT), unsupervised clustering, and topological analysis to automate microscope control, sample scanning, image segmentation, and intelligent analysis through prompt engineering, eliminating the need for additional training. When analyzing typical MoS2 samples, our approach achieves 99.7% segmentation accuracy for single layer identification, which is equivalent to that of human experts. In addition, the integrated model is able to detect grain boundary slits that are challenging to identify with human eyes. Furthermore, the system retains robust accuracy despite variable conditions including defocus, color temperature fluctuations, and exposure variations. It is applicable to a broad spectrum of common 2D materials-including graphene, MoS2, WSe2, SnSe-regardless of whether they were fabricated via chemical vapor deposition or mechanical exfoliation. This work represents the implementation of foundation models to achieve autonomous analysis, establishing a scalable and data-efficient characterization paradigm that fundamentally transforms the approach to nanoscale materials research. △ Less

Submitted 14 April, 2025; originally announced April 2025.

Comments: 13 pages, 4 figures

Tuning Charge Density Wave in the Transition from Magnetically Frustrated Conductor to Ferrimagnetic Insulator in Carbon Nanowire within Boron Nitride Nanotube

Authors: Chi Ho Wong, Zong Liang Guo, King Cheong Lam, Chun Pong Chau, Wing Yu Chan, Chak-yin Tang, Yuen Hong Tsang, Leung Yuk Frank Lam, Xijun Hu

Abstract: The emergence of exotic charge density wave (CDW) alongside ferrimagnetism materials opens exciting new possibilities for quantum switching, particularly in field-tuning CDW electronics. However, these two phenomena often compete and rely heavily on strong electronic correlations. While carbon nanowire arrays have been experimentally shown to exhibit ferromagnetism above 400 K, our research shows… ▽ More The emergence of exotic charge density wave (CDW) alongside ferrimagnetism materials opens exciting new possibilities for quantum switching, particularly in field-tuning CDW electronics. However, these two phenomena often compete and rely heavily on strong electronic correlations. While carbon nanowire arrays have been experimentally shown to exhibit ferromagnetism above 400 K, our research shows that encapsulating a linear carbon chain (LCC) within zigzag boron nitride nanotubes (BNT) induces a short-range CDW state under a competing effect of ferrimagnetism and magnetic frustrations. However, for this exotic feature to occur, the LCC needs to break the symmetry along the circular plane of the BNT. Then we utilize a Monte Carlo model to identify the optimal length of LCC@BNT to tackle its size effect, while also comparing the stability of chains provided by carbon nanotubes. The shorter LCC@BNT displays a more prominent long-range CDW pattern with a tunneling barrier of 2.3 eV on the Fermi surface, transitioning into an unconventional insulator. Meanwhile, magnetic frustrations disappear, and ferrimagnetism remains stable up to 280 K. Our discovery of ferrimagnetic CDW carbyne insulators, which function without conventional periodic lattice distortion, spin-orbit coupling, or complex d and f hybridization represents a groundbreaking shift in thinking, which demonstrates that such exotic properties are not exclusive to transition metal elements. We anticipate that spin fluctuations in LCC@BNT could enable fine-tuning of the CDW pattern, and applying an electric excitation of 2.3 eV triggers an abrupt insulator-to-conductor transition for quantum switching applications. △ Less

Submitted 10 April, 2025; originally announced April 2025.

Superior electrochemical performance of zinc-ion batteries with fine-grained and textured zinc anode produced by high-pressure torsion

Authors: Xinxin Hu, Shivam Dangwal, Xucheng Wang, Fan Zhang, Haijuan Kong, Jun Li, Kaveh Edalati

Abstract: Zinc-ion batteries are promising alternatives to lithium-ion batteries, offering advantages in safety, cost, and environmental impact. However, their performance is often limited by the functioning of the zinc anode. This study employs severe plastic deformation via the high-pressure torsion (HPT) method to enhance the electrochemical performance of zinc anodes. HPT reduced the grain size from >10… ▽ More Zinc-ion batteries are promising alternatives to lithium-ion batteries, offering advantages in safety, cost, and environmental impact. However, their performance is often limited by the functioning of the zinc anode. This study employs severe plastic deformation via the high-pressure torsion (HPT) method to enhance the electrochemical performance of zinc anodes. HPT reduced the grain size from >1000 μm to 20 μm and introduced a (002) basal texture. The battery assembled with HPT-processed zinc demonstrated improved cycling stability, rate performance, and specific discharge capacity (>500 mAh/g at 0.5 A/g after 50 cycles), particularly at high current densities. This performance enhancement was attributed to grain-boundary and texture effects on improved ion transfer (confirmed by electrochemical impedance spectroscopy), fast redox reaction kinetics (confirmed by cyclic voltammetry), and reduced corrosion (confirmed by microscopy and potentiodynamic polarization test). This study highlights the potential of severely deformed materials with textured fine grains for advanced rechargeable battery technologies. △ Less

Submitted 27 March, 2025; originally announced March 2025.

Electronic structures and multi-orbital models of La$_3$Ni$_2$O$_7$ thin films at ambient pressure

Authors: Xunwu Hu, Wenyuan Qiu, Cun-Qun Chen, Zhihui Luo, Dao-Xin Yao

Abstract: The recent discovery of superconductivity with a transition temperature $T_c$ exceeding 40 K in La$_3$Ni$_2$O$_7$ and (La,Pr)$_{3}$Ni$_2$O$_7$ thin films at ambient pressure marks a significant breakthrough in the field of nickelate superconductors. Using density functional theory (DFT), we propose a double-stacked two-orbital effective model for La$_3$Ni$_2$O$_7$ thin film based on the Ni$-e_g$ o… ▽ More The recent discovery of superconductivity with a transition temperature $T_c$ exceeding 40 K in La$_3$Ni$_2$O$_7$ and (La,Pr)$_{3}$Ni$_2$O$_7$ thin films at ambient pressure marks a significant breakthrough in the field of nickelate superconductors. Using density functional theory (DFT), we propose a double-stacked two-orbital effective model for La$_3$Ni$_2$O$_7$ thin film based on the Ni$-e_g$ orbitals. Our analysis of the Fermi surface reveals three electron pockets ($α,α^{\prime},β$) and two hole pockets ($γ,γ^{\prime}$), where the additional $α^{\prime}$ and $γ^{\prime}$ pockets arise from inter-stack interactions. Furthermore, we introduce a high-energy model that incorporates O$-p$ orbitals to facilitate future studies. Calculations of spin susceptibility within the random phase approximation (RPA) indicate that magnetic correlations are enhanced by nesting of the $γ$ pocket, which is predominantly derived from the Ni$-d_{z^2}$ orbital. Our results provide a theoretical foundation for understanding the electronic and magnetic properties of La$_3$Ni$_2$O$_7$ thin films. △ Less

Submitted 5 January, 2026; v1 submitted 21 March, 2025; originally announced March 2025.

Journal ref: Commun Phys 8, 506 (2025)

Ferromagnetism in LaFeO3/LaNiO3 Superlattices with High Curie Temperature

Authors: Tianlin Zhou, Fei Gao, Qinghua Zhang, Yuansha Chen, Xinzhe Hu, Yuzhou He, Yuchen Zhao, Jianjie Li, Minghang Li, Shaojin Qi, Fengxia Hu, Jirong Sun, Yunzhong Chen, Baogen Shen

Abstract: Interfacing complex oxides in atomically engineered layered structures can give rise to a wealth of exceptional electronic and magnetic properties that surpass those of the individual building blocks. Herein, we demonstrate a ferromagnetic spin order with a high Curie temperature of 608 K in superlattices consisting of otherwise paramagnetic perovskite LaNiO3 (LNO) and antiferromagnetic LaFeO3 (LF… ▽ More Interfacing complex oxides in atomically engineered layered structures can give rise to a wealth of exceptional electronic and magnetic properties that surpass those of the individual building blocks. Herein, we demonstrate a ferromagnetic spin order with a high Curie temperature of 608 K in superlattices consisting of otherwise paramagnetic perovskite LaNiO3 (LNO) and antiferromagnetic LaFeO3 (LFO). The extraordinary ferromagnetism likely results from the covalent exchange due to interfacial charge transfer from Fe to Ni cations. By deliberately controlling the thickness of the LNO sublayers thus the amount of charge transfer, a robust ferromagnetism of 4 uB is realized for a stacking periodicity consisting of one single unit cell of both LNO and LFO, an emergent double perovskite phase of La2FeNiO6 with B-site layered ordering configurations. The ferromagnetic LFO/LNO superlattices offer great potential for the search of emergent magnetodielectric and/or multiferroic properties as well as applications in spintronics and electrocatalysts. △ Less

Submitted 17 March, 2025; originally announced March 2025.

Comments: 4 figures, 1 table.to be appear in Nat. Commun.2025

Hole spin splitting in a Ge quantum dot with finite barriers

Authors: Jiawei Wang, Xuedong Hu, Herbert F Fotso

Abstract: We study the low-energy spectrum of a single hole confined in a planar Ge quantum dot (QD) within the effective-mass formalism. The QD is sandwiched between two GeSi barriers of finite potential height grown along the [001] direction. To treat this finite barrier problem, we adopt an independent-band approach in dealing with boundary conditions. The effects of different system parameters are inves… ▽ More We study the low-energy spectrum of a single hole confined in a planar Ge quantum dot (QD) within the effective-mass formalism. The QD is sandwiched between two GeSi barriers of finite potential height grown along the [001] direction. To treat this finite barrier problem, we adopt an independent-band approach in dealing with boundary conditions. The effects of different system parameters are investigated, including the width of the out-of-plane confining well, the size of the dot, and silicon concentration in the confining layers. The more accurate finite-barrier model results in the non-negligible dependence of the anisotropic $g$-factor on the choice of boundary conditions and on the silicon concentration in the barrier. Furthermore, while the ideal model of a planar dot with a square-well heterostructure already has an intrinsic spin-orbit coupling, realistic effects arising from the experimental setup may give rise to additional contributions. We investigate the impact from the top-gate electric field and the residual tensile strain on the qubit states. The results indicate that these effects are important contributions to the total spin-orbit coupling which enables fast electric control. △ Less

Submitted 26 September, 2025; v1 submitted 14 March, 2025; originally announced March 2025.

Journal ref: Phys. Rev. B 112, 115309 (2025)

Beyond the Boltzmann equation for weakly coupled quantum fields

Authors: Xu-Yao Hu, Vladimir Rosenhaus

Abstract: We study the kinetic theory of a weakly interacting quantum field. Assuming a state that is close to homogeneous and stationary, we derive a closed kinetic equation for the rate of change of the occupation numbers, perturbatively in the coupling. For a dilute gas, this reproduces the quantum Boltzmann equation, which only accounts for two-to-two scattering processes. Our expression goes beyond thi… ▽ More We study the kinetic theory of a weakly interacting quantum field. Assuming a state that is close to homogeneous and stationary, we derive a closed kinetic equation for the rate of change of the occupation numbers, perturbatively in the coupling. For a dilute gas, this reproduces the quantum Boltzmann equation, which only accounts for two-to-two scattering processes. Our expression goes beyond this, with terms accounting for multi-particle scattering processes, which are higher order in the density. △ Less

Submitted 1 September, 2025; v1 submitted 12 March, 2025; originally announced March 2025.

Comments: 19 pages, v2: typos fixed, references added

UniGenX: a unified generative foundation model that couples sequence, structure and function to accelerate scientific design across proteins, molecules and materials

Authors: Gongbo Zhang, Yanting Li, Renqian Luo, Pipi Hu, Yang Yang, Zeru Zhao, Lingbo Li, Guoqing Liu, Zun Wang, Ran Bi, Kaiyuan Gao, Liya Guo, Yu Xie, Chang Liu, Jia Zhang, Tian Xie, Robert Pinsler, Claudio Zeni, Ziheng Lu, Hongxia Hao, Yingce Xia, Marwin Segler, Maik Riechert, Wei Yang, Hao Jiang , et al. (9 additional authors not shown)

Abstract: Function in natural systems arises from one-dimensional sequences forming three-dimensional structures with specific properties. However, current generative models suffer from critical limitations: training objectives seldom target function directly, discrete sequences and continuous coordinates are optimized in isolation, and conformational ensembles are under-modeled. We present UniGenX, a unifi… ▽ More Function in natural systems arises from one-dimensional sequences forming three-dimensional structures with specific properties. However, current generative models suffer from critical limitations: training objectives seldom target function directly, discrete sequences and continuous coordinates are optimized in isolation, and conformational ensembles are under-modeled. We present UniGenX, a unified generative foundation model that addresses these gaps by co-generating sequences and coordinates under direct functional and property objectives across proteins, molecules, and materials. UniGenX represents heterogeneous inputs as a mixed stream of symbolic and numeric tokens, where a decoder-only autoregressive transformer provides global context and a conditional diffusion head generates numeric fields steered by task-specific tokens. Besides the new high SOTAs on structure prediction tasks, the model demonstrates state-of-the-art or competitive performance for the function-aware generation across domains: in materials, it achieves "conflicted" multi-property conditional generation, yielding 436 crystal candidates meeting triple constraints, including 11 with novel compositions; in chemistry, it sets new benchmarks on five property targets and conformer ensemble generation on GEOM; and in biology, it improves success in modeling protein induced fit (RMSD < 2 Å) by over 23-fold and enhances EC-conditioned enzyme design. Ablation studies and cross-domain transfer substantiate the benefits of joint discrete-continuous training, establishing UniGenX as a significant advance from prediction to controllable, function-aware generation. △ Less

Submitted 26 August, 2025; v1 submitted 9 March, 2025; originally announced March 2025.

Crystal nucleation rates in one-component Yukawa systems

Authors: B. Arnold, J. Daligault, D. Saumon, Antoine Bédard, S. X. Hu

Abstract: Nucleation in the supercooled Yukawa system is relevant for addressing current challenges in understanding a range of crystallizing systems including white dwarf (WD) stars. We use both brute force and seeded molecular dynamics simulations to study homogeneous nucleation of crystals from supercooled Yukawa liquids. With our improved approach to seeded simulations, we obtain quantitative prediction… ▽ More Nucleation in the supercooled Yukawa system is relevant for addressing current challenges in understanding a range of crystallizing systems including white dwarf (WD) stars. We use both brute force and seeded molecular dynamics simulations to study homogeneous nucleation of crystals from supercooled Yukawa liquids. With our improved approach to seeded simulations, we obtain quantitative predictions of the crystal nucleation rate and cluster size distributions as a function of temperature and screening length. These quantitative results show trends towards fast nucleation with short-ranged potentials. They also indicate that for temperatures $T > 0.9T_m$, where $T_m$ is the melt temperature, classical homogeneous nucleation is too slow to initiate crystallization but transient clusters of around 100 particles should be common. We apply these general results to a typical WD model and obtain a delay of approximately 0.6 Gyr in the onset of crystallization that may be observable. △ Less

Submitted 7 March, 2025; originally announced March 2025.

Comments: 17 pages, 14 figures

Report number: LA-UR-24-30554

Journal ref: Phys. Rev. E 111, 025206, Published 21 February, 2025

Flat bands and temperature-driven phase transition in quasi-one-dimensional zigzag chains

Authors: Jisong Gao, Haijun Cao, Xuegao Hu, Hui Zhou, Zhihao Cai, Qiaoxiao Zhao, Dong Li, Zhicheng Gao, Shin-ichiro Ideta, Kenya Shimada, Peng Cheng, Lan Chen, Kehui Wu, Sheng Meng, Baojie Feng

Abstract: Flat-band materials have garnered extensive attention due to their captivating properties associated with strong correlation effects. While flat bands have been discovered in several types of 2D materials, their existence in 1D systems remains elusive. Here, we propose a 1D frustrated lattice, specifically the 1D zigzag lattice, as a platform for hosting flat bands. This lattice can be experimenta… ▽ More Flat-band materials have garnered extensive attention due to their captivating properties associated with strong correlation effects. While flat bands have been discovered in several types of 2D materials, their existence in 1D systems remains elusive. Here, we propose a 1D frustrated lattice, specifically the 1D zigzag lattice, as a platform for hosting flat bands. This lattice can be experimentally realized by growing CuTe chains on Cu(111). The presence of flat bands was confirmed by tight-binding model analysis, first-principles calculations, and angle-resolved photoemission spectroscopy measurements. In addition, we discovered a temperature-driven phase transition at approximately 250 K. Detailed analyses demonstrate that the system has a Tomonaga-Luttinger liquid behavior, accompanied by spin-charge separation effects. Our work unveils new prospects for investigating strongly correlated electron behaviors and topological properties in the 1D limit. △ Less

Submitted 3 March, 2025; originally announced March 2025.

Journal ref: Physical Review Letters 134, 086202 (2025)

Hidden States and Dynamics of Fractional Fillings in tMoTe2 Moiré Superlattices

Authors: Yiping Wang, Jeongheon Choe, Eric Anderson, Weijie Li, Julian Ingham, Eric A. Arsenault, Yiliu Li, Xiaodong Hu, Takashi Taniguchi, Kenji Watanabe, Xavier Roy, Dmitri Basov, Di Xiao, Raquel Queiroz, James C. Hone, Xiaodong Xu, X. -Y. Zhu

Abstract: The fractional quantum anomalous Hall (FQAH) effect was recently discovered in twisted MoTe2 bilayers (tMoTe2). Experiments to date have revealed Chern insulators from hole doping at v = -1, -2/3, -3/5, and -4/7 (per moiré unit cell). In parallel, theories predict that, between v = -1 and -3, there exist exotic quantum phases, such as the coveted fractional topological insulators (FTI), fractional… ▽ More The fractional quantum anomalous Hall (FQAH) effect was recently discovered in twisted MoTe2 bilayers (tMoTe2). Experiments to date have revealed Chern insulators from hole doping at v = -1, -2/3, -3/5, and -4/7 (per moiré unit cell). In parallel, theories predict that, between v = -1 and -3, there exist exotic quantum phases, such as the coveted fractional topological insulators (FTI), fractional quantum spin Hall (FQSH) states, and non-abelian fractional states. Here we employ transient optical spectroscopy on tMoTe2 to reveal nearly 20 hidden states at fractional fillings that are absent in static optical sensing or transport measurements. A pump pulse selectively excites charge across the correlated or pseudo gaps, leading to the disordering (melting) of correlated states. A probe pulse detects the subsequent melting and recovery dynamics via exciton and trion sensing. Besides the known states, we observe additional fractional fillings between v = 0 and -1 and a large number of states on the electron doping side (v > 0). Most importantly, we observe new states at fractional fillings of the Chern bands at v = -4/3, -3/2, -5/3, -7/3, -5/2, and -8/3. These states are potential candidates for the predicted exotic topological phases. Moreover, we show that melting of correlated states occurs on two distinct time scales, 2-4 ps and 180-270 ps, attributed to electronic and phonon mechanisms, respectively. We discuss the differing dynamics of the electron and hole doped states from the distinct moiré conduction and valence bands. △ Less

Submitted 28 February, 2025; originally announced February 2025.

Comments: 19 pages, 4 figures, 13 extended figures

Effect of disorder and strain on the operation of planar Ge hole spin qubits

Authors: Abhikbrata Sarkar, Pratik Chowdhury, Xuedong Hu, Andre Saraiva, A. S. Dzurak, A. R. Hamilton, Rajib Rahman, Dimitrie Culcer

Abstract: Germanium quantum dots in strained $\text{Ge}/\text{Si}_{1-x}\text{Ge}_{x}$ heterostructures exhibit fast and coherent hole qubit control in experiments. In this work, we theoretically and numerically address the effects of random alloy disorder and gate-induced strain on the operation of planar Ge hole spin qubits. Electrical operation of hole quantum dot spin qubits is enabled by the strong Rash… ▽ More Germanium quantum dots in strained $\text{Ge}/\text{Si}_{1-x}\text{Ge}_{x}$ heterostructures exhibit fast and coherent hole qubit control in experiments. In this work, we theoretically and numerically address the effects of random alloy disorder and gate-induced strain on the operation of planar Ge hole spin qubits. Electrical operation of hole quantum dot spin qubits is enabled by the strong Rashba spin-orbit coupling (SOC) originating from the intrinsic SOC in the Ge valence band as well as from the structural inversion asymmetry inherent in the underlying 2D hole gas. We use the atomistic valence force field (VFF) method to compute the strain due to random alloy disorder, and thermal expansion models in COMSOL Multiphysics to obtain the strain from a realistic gate-stack of planar hole quantum dot confinement. Recently, spin-orbit coupling terms $\propto k$ have been shown to be induced by strain inhomogeneity. Our hybrid approach to realistic device modeling suggests that strain inhomogeneity due to both random alloy disorder and gate-induced strain make a strong contribution to the linear-$k$ Dresselhaus spin-orbit coupling, which eventually dominates hole spin EDSR; and there exist specific in-plane orientations of the global magnetic field $\mathbf{B}$ and the microwave drive $\mathbf{\tilde{E}}_{\text{ac}}$ for maximum EDSR Rabi frequency of the hole spin qubit. The current model including strain inhomogeneity accurately predicts the EDSR Rabi frequency to be $\!\sim\!100$ MHz for typical electric and magnetic fields in experiments, which represents at least an order of magnitude improvement in accuracy over phenomenological models assuming uniform uniaxial strain. State-of-the-art atomistic tight binding calculations via nano-electronic modeling (NEMO3D) are in agreement with the $\mathbf{k}{\cdot}\mathbf{p}$ description. △ Less

Submitted 29 April, 2025; v1 submitted 10 February, 2025; originally announced February 2025.

Journal ref: npj Quantum Information 11, 185 (2025)

Two- and many-body physics of ultracold molecules dressed by dual microwave fields

Authors: Fulin Deng, Xinyuan Hu, Wei-Jian Jin, Su Yi, Tao Shi

Abstract: We investigate the two- and many-body physics of the ultracold polar molecules dressed by dual microwaves with distinct polarizations. Using Floquet theory and multichannel scattering calculations, we identify a regime with the largest elastic-to-inelastic scattering ratio which is favorable for performing evaporative cooling. Furthermore, we derive and, subsequently, validate an effective interac… ▽ More We investigate the two- and many-body physics of the ultracold polar molecules dressed by dual microwaves with distinct polarizations. Using Floquet theory and multichannel scattering calculations, we identify a regime with the largest elastic-to-inelastic scattering ratio which is favorable for performing evaporative cooling. Furthermore, we derive and, subsequently, validate an effective interaction potential that accurately captures the dynamics of microwave-shielded polar molecules (MSPMs). We also explore the ground-state properties of the ultracold gases of MSPMs by computing physical quantities such as gas density, condensate fraction, momentum distribution, and second-order correlation. It is shown that the system supports a weakly correlated expanding gas state and a strongly correlated self-bound gas state. Since the dual-microwave scheme introduces addition control knob and is essential for creating ultracold Bose gases of polar molecules, our work pave the way for studying two- and many-body physics of the ultracold polar molecules dressed by dual microwaves. △ Less

Submitted 15 January, 2025; v1 submitted 9 January, 2025; originally announced January 2025.

Intrinsic thermal Hall effect of optical phonons enhanced by discrete rotational symmetry

Authors: Xuesong Hu, Junren Shi

Abstract: We investigate the intrinsic thermal Hall conductivity contributed by optical phonons in a cubic system. The discrete rotational symmetry of the system splits the degeneracy of transverse modes across most regions of wave-vector space, except along a few high-symmetry lines. Consequently, in the presence of an external magnetic field, phonon Berry curvatures become sharply peaked near these high-s… ▽ More We investigate the intrinsic thermal Hall conductivity contributed by optical phonons in a cubic system. The discrete rotational symmetry of the system splits the degeneracy of transverse modes across most regions of wave-vector space, except along a few high-symmetry lines. Consequently, in the presence of an external magnetic field, phonon Berry curvatures become sharply peaked near these high-symmetry lines. We find that the singular distribution of the Berry curvature induces an intrinsic thermal Hall conductivity that is significantly enhanced compared to an isotropic system. It exhibits a nonlinear $B\ln B$ dependence on the magnetic field $B$ and a non-monotonic temperature dependence. At elevated temperatures, it reverses sign and approaches a non-vanishing value asymptotically. Our analysis indicates that the behavior results from competition between contributions from Berry curvatures near different high-symmetry lines. △ Less

Submitted 28 April, 2025; v1 submitted 5 January, 2025; originally announced January 2025.

Comments: 9 pages,6 figures

Large upper critical fields and strong coupling superconductivity in the medium-entropy alloy (Ti1/3Hf1/3Ta1/3)1-xNbx

Authors: Longfu Li, Hongyan Tian, Xunwu Hu, Lingyong Zeng, Kuan Li, Peifeng Yu, Kangwang Wang, Rui Chen, Zaichen Xiang, Dao-Xin Yao, Huixia Luo

Abstract: Since the discovery of high-entropy superconductors in 2014, superconductivity has remained a focal point of interest in medium- and high-entropy alloys (MEAs-HEAs). Here, we report a series of (Ti0.33Hf0.33Ta0.33)1-xNbx MEA superconductors crystallized in the BCC structure, whose superconductivity was characterized by resistivity, magnetization, and specific heat measurements. The study found tha… ▽ More Since the discovery of high-entropy superconductors in 2014, superconductivity has remained a focal point of interest in medium- and high-entropy alloys (MEAs-HEAs). Here, we report a series of (Ti0.33Hf0.33Ta0.33)1-xNbx MEA superconductors crystallized in the BCC structure, whose superconductivity was characterized by resistivity, magnetization, and specific heat measurements. The study found that the (Ti0.33Hf0.33Ta0.33)1-xNbx MEAs exhibit bulk superconductivity. With the doping of Nb, the superconducting transition temperature (Tc) increases from 5.31 K to 9.11 K, and the normalized Cel jumps at Tc, and the logarithmically averaged characteristic phonon frequency exhibit dome-shaped curves. Results from specific heat measurements indicate that the superconductivity is of a strongly coupled s-wave type observed. Furthermore, at low Nb content, the upper critical field of the samples is larger than the Pauli paramagnetic limit. The strongly coupling behavior and large upper critical field in s-wave type (Ti0.33Hf0.33Ta0.33)1-xNbx MEA superconductors are unusual, as they typically occur in other unconventional superconductors. Thus, (Ti0.33Hf0.33Ta0.33)1-xNbx may have significant potential in the research and understanding of physical mechanisms. △ Less

Submitted 5 January, 2025; originally announced January 2025.

Comments: 20 pages, 5 figures

Journal ref: Superconductor Science and Technology,2025

Architected Dual-Network Solvent-free Adhesives for Stretchable Fabrics

Authors: Gabriela Moreira Lana, Cornelia Meissner, Siddhant Iyer, Xin Hu, Perin Jhaveri, Skylar Tibbits, Alfred J. Crosby

Abstract: Natural systems, such as tendons and spider silk, demonstrate how the combination of strength and stretchability can be effectively achieved by integrating stiff and flexible network structures. Inspired by these systems, we developed a novel, solvent-free dual-network adhesive based on a self-assembling ABA triblock copolymer, poly(methyl methacrylate)-poly(n-butyl acrylate)-poly(methyl methacryl… ▽ More Natural systems, such as tendons and spider silk, demonstrate how the combination of strength and stretchability can be effectively achieved by integrating stiff and flexible network structures. Inspired by these systems, we developed a novel, solvent-free dual-network adhesive based on a self-assembling ABA triblock copolymer, poly(methyl methacrylate)-poly(n-butyl acrylate)-poly(methyl methacrylate) (PMMA-b-PnBA-b-PMMA), designed for applications requiring both high strength and stretchability. The triblock copolymer forms a physically crosslinked network through microdomains of PMMA end-blocks that provide structural integrity, while the PnBA mid-block forms a soft, stretchable matrix. To further enhance mechanical performance, a second poly(n-butyl acrylate) (PnBA) network is polymerized in situ, locking the PMMA microdomains in place and creating a load-bearing system. By varying the crosslinking density of the secondary network, we tailor the adhesive's mechanical properties (Young's modulus: 0.17 - 1.18 MPa) to suit different substrates, creating a mechanically transparent seam. The resulting dual-network system combines different strategies to achieve high strength and stretchability, with adhesive performance comparable to industrial methods such as sewing, particularly in bonding neoprene fabric composites and sealing the joints. Our solvent-free approach also eliminates the need for lengthy solvent evaporation steps, offering an eco-friendly and more efficient alternative for flexible adhesive applications in fields such as soft robotics, flexible electronics, and sports apparel. △ Less

Submitted 2 January, 2025; originally announced January 2025.

Comments: 28 pages, 5 figures, supplemental included at the end

Thermal Induced Structural Competitiveness and Metastability of Body-centered Cubic Iron under Non-Equilibrium Conditions

Authors: Shuai Zhang, Aliza Panjwani, Penghao Xiao, Maitrayee Ghosh, Tadashi Ogitsu, Yuan Ping, S. X. Hu

Abstract: The structure and stability of iron near melting at multi-megabar pressures are of significant interest in high pressure physics and earth and planetary sciences. While the body-centered cubic (BCC) phase is generally recognized as unstable at lower temperatures, its stability relative to the hexagonal close-packed (HCP) phase at high temperatures (approximately 0.5 eV) in the Earth's inner core (… ▽ More The structure and stability of iron near melting at multi-megabar pressures are of significant interest in high pressure physics and earth and planetary sciences. While the body-centered cubic (BCC) phase is generally recognized as unstable at lower temperatures, its stability relative to the hexagonal close-packed (HCP) phase at high temperatures (approximately 0.5 eV) in the Earth's inner core (IC) remains a topic of ongoing theoretical and experimental debate. Our ab initio calculations show a significant drop in energy, the emergence of a plateau and a local minimum in the potential energy surface, and stabilization of all phonon modes at elevated electron temperatures (>1-1.5 eV). These effects increase the competition among the BCC, HCP, and the face-centered cubic (FCC) phases and lead to the metastability of the BCC structure. Furthermore, the thermodynamic stability of BCC iron is enhanced by its substantial lattice vibration entropy. This thermally induced structural competitiveness and metastability under non-equilibrium conditions provide a clear theoretical framework for understanding iron phase relations and solidification processes, both experimentally and in the IC. △ Less

Submitted 31 December, 2024; originally announced January 2025.

Comments: 5 pages, 4 figures

Journal ref: Phys. Rev. B 111, 224106 (2025)

Experimental discovery of Sarma state in atomically thick superconducting FeSe films under high magnetic fields

Authors: Wantong Huang, Yuguo Yin, Haicheng Lin, Wei Chen, Yaowu Liu, Lichen Ji, Zichun Zhang, Xinyu Zhou, Xusheng Wang, Xiaopeng Hu, Yong Xu, Lianyi He, Xi Chen, Qi-Kun Xue, Shuai-Hua Ji

Abstract: Many-body ground states of imbalanced Fermi gas have been studied both theoretically and experimentally for several decades because of their fundamental significance in condensed matter physics, cold atom physics and nuclear physics. The Sarma state, a gapless spin-polarized superfluid, is one of those long sought-after exotic ground states of spin imbalanced Fermi gas. Yet, an unambiguous experim… ▽ More Many-body ground states of imbalanced Fermi gas have been studied both theoretically and experimentally for several decades because of their fundamental significance in condensed matter physics, cold atom physics and nuclear physics. The Sarma state, a gapless spin-polarized superfluid, is one of those long sought-after exotic ground states of spin imbalanced Fermi gas. Yet, an unambiguous experimental evidence of Sarma superfluid state has not been found. Here, we report the experimental discovery of the Sarma state in atomically thick FeSe films by a dilution-refrigerator scanning tunneling microscope under high magnetic fields. In the bilayer or trilayer FeSe films, we directly observe the key evidence of the entrance of the Sarma state: the inner Zeeman splitting coherence peaks cross the Fermi level under high in-plane magnetic fields. The angle dependent critical in-plane magnetic field of coherence peak crossing shows a two-fold symmetry due to the anisotropy of the in-plane g-factor of FeSe films. Moreover, in a superconducting FeSe monolayer of a lateral size of several hundred nanometers, the Sarma state can also be induced by strong out-of-plane magnetic fields. Our findings pave the way to explore the unusual physical properties and potential applications in superconducting spintronics of the spin-polarized Sarma superfluid state. △ Less

Submitted 20 December, 2024; originally announced December 2024.