Showing 1–50 of 439 results for author: Yang, K

Second-Chern Bounds in Non-Abelian Quantum Geometry

Authors: Junwen Zhao, Zhiming Pan, Kang Yang, Congjun Wu

Abstract: We study the quantum geometry of doubly degenerate energy levels in a four-dimensional parameter space. For degenerate pairs with $SU(2)$ gauge structures, the quantum geometry obeys $\big(\textrm{tr } g\big)^2/16\geq\sqrt{\det g}\geq |\textrm{Tr}(F\wedge F)|/12$. The first inequality characterizes the anisotropy in the metric. The second determinant inequality measures the self-duality of the cur… ▽ More We study the quantum geometry of doubly degenerate energy levels in a four-dimensional parameter space. For degenerate pairs with $SU(2)$ gauge structures, the quantum geometry obeys $\big(\textrm{tr } g\big)^2/16\geq\sqrt{\det g}\geq |\textrm{Tr}(F\wedge F)|/12$. The first inequality characterizes the anisotropy in the metric. The second determinant inequality measures the self-duality of the curvature under Hodge star operation and the inter-level processes that do not close under the three $SU(2)$ rotations of the doubly degenerate levels. The saturation of the determinant bound induces a quaternion Kähler structure on the four-dimensional parameter space, analogous to the complex structure induced by the ideal-band condition in two-dimensional Chern insulators. As examples, four-band Dirac Hamiltonians automatically saturate the determinant bound and possess a topological zero in $\textrm{Tr}(F\wedge F)$. We discuss the comparison to degenerate pairs with $U(2)$ gauge structures. △ Less

Submitted 12 August, 2026; originally announced August 2026.

Comments: 6 pages

Symmetrized Block-Product Periodic Marginals in Infinite Translation-Invariant Quantum Chains

Authors: Xiao Zeng, Kaiyan Yang, Lingxia Zhang, Zizhu Wang

Abstract: We study local marginals in one-dimensional translation-invariant quantum systems that may hide finite-period structure. Given an $n$-site reduced density matrix, we ask whether it can be obtained by repeating a finite $p$-site block state along the chain and averaging over the $p$ lattice translations. This defines a symmetrized block-product periodic marginal problem, which provides a route both… ▽ More We study local marginals in one-dimensional translation-invariant quantum systems that may hide finite-period structure. Given an $n$-site reduced density matrix, we ask whether it can be obtained by repeating a finite $p$-site block state along the chain and averaging over the $p$ lattice translations. This defines a symmetrized block-product periodic marginal problem, which provides a route both to diagnosing hidden periodic order from local data and to upper bounding ground-state energy densities of infinite translation-invariant local Hamiltonians. We develop two complementary methods. The first is a semidefinite-programming relaxation based on block permutation symmetry and positive partial transpose constraints, which outer-approximates the convex hull of such marginals and yields certified infeasibility tests. The second is a symmetrized matrix product state ansatz, which constructs explicit block-product periodic states and gives variational upper bounds. We benchmark the framework on the Majumdar-Ghosh model, transverse-field Ising, XX, XXZ, and contextuality-related spin models. The results show that the method captures the expected finite-period structure in exactly solvable cases and gives systematically improving variational energies as the period and bond dimension increase. We also formulate a periodic-NPA relaxation for translation-invariant contextuality witnesses and recover the known quantum limits in the tested examples. △ Less

Submitted 10 August, 2026; originally announced August 2026.

Comments: 13 pages, 3 figures

Topological Charge-Transfer Excitons

Authors: Huiyuan Zheng, Kaijie Yang, Ting Cao, Di Xiao

Abstract: Excitons possess internal structure absent from single-particle Bloch particles, allowing their band topology to emerge from the bound-state structure rather than being inherited from their constituents. This raises the question of how the internal structure of a bound state can provide a microscopic origin of exciton topology. Here we show that the real-space embedding of charge-transfer excitons… ▽ More Excitons possess internal structure absent from single-particle Bloch particles, allowing their band topology to emerge from the bound-state structure rather than being inherited from their constituents. This raises the question of how the internal structure of a bound state can provide a microscopic origin of exciton topology. Here we show that the real-space embedding of charge-transfer excitons can generate an intrinsic manifold of symmetry-related off-site composite orbitals whose coupling supports topological exciton bands. Lateral electron-hole separation embeds the localized exciton on the bond connecting its constituent sites rather than on either site. We demonstrate this mechanism in a honeycomb lattice, where three bond-centered charge-transfer exciton orbitals form a Kagome lattice. By solving the Bethe-Salpeter equation, we show that this emergent multi-orbital manifold supports a topological exciton flat band upon time-reversal symmetry breaking, even when the electron and hole bands are topologically trivial. The resulting band exhibits nearly uniformly distributed quantum geometry, favorable for interaction-driven bosonic states. Our results establish a general route toward topological bands of localized composite bound states and unconventional strongly correlated bosonic phases. △ Less

Submitted 5 August, 2026; originally announced August 2026.

Comments: 19 pages, 5 figures

Emergence of millimeter-wave resonances in self-assembled ferroelectric metamaterials

Authors: Florian Bergmann, Peter Meisenheimer, Aiden Ross, Marvin Schewe, Fernando Gómez-Ortiz, Kaiwen Yang, Xinyan Li, Thomas J. Lee, Pushpendra Gupta, Liam G. Connolloy, Tzu-Hsuan Hsu, Jack Kramer, Bryan T. Bosworth, Nicholas R. Jungwirth, Eric J. Marksz, Aaron Hagerstrom, Tomasz Karpisz, Arundhati Ghosal, Lane W. Martin, Yimo Han, Angela C. Stelson, Christian J. Long, Ruochen Lu, Lucas Caretta, Javier Junquera , et al. (4 additional authors not shown)

Abstract: Resonators are a key component in modern communications and computing. As demand and technological advances push component requirements into the terahertz regime, there is significant research devoted to the search for resonances at these frequencies. While uniform solid-state materials usually do not intrinsically feature resonances in this frequency range, self-assembled periodic arrays of ferro… ▽ More Resonators are a key component in modern communications and computing. As demand and technological advances push component requirements into the terahertz regime, there is significant research devoted to the search for resonances at these frequencies. While uniform solid-state materials usually do not intrinsically feature resonances in this frequency range, self-assembled periodic arrays of ferroelectric nanodomains may provide an engineering route to design millimeter-wave properties. Here, we utilize prototypical dielectric-ferroelectric SrTiO3/PbTiO3 superlattices to robustly design periodic ferroelectric nano-scale domains. Phase field simulations predict an emergent domain breathing mode in complex polar textures and state-of-the-art millimeter-wave characterization shows evidence for such emergent resonances up to hundreds of GHz. Complex polar textures in these superlattices lead to emergent piezoelectric properties that also result in millimeter-wave resonances, which are predicted by second principles methods and confirmed by direct measurement. The principles investigated in this work suggest a new modality for ferroelectrics in the design of millimeter-wave electronics. △ Less

Submitted 25 June, 2026; originally announced June 2026.

Comments: 40 pages, including 21 main manuscript pages and supplementary

Electrically Programmable Correlated Topology and Magnetism in a Moiré Trilayer

Authors: Christiano Wang Beach, Courtney Baier, Kaijie Yang, Huiyuan Zheng, Yueyao Fan, Weijie Li, Shuai Yuan, Yifan Zhao, Yue Sun, Chaowei Hu, Takashi Taniguchi, Kenji Watanabe, Jiun-haw Chu, Liang Fu, Ting Cao, Satoshi Okamoto, Di Xiao, Xiaodong Xu

Abstract: Strong electron-electron interactions underlie a wide range of quantum many-body phenomena, including magnetism, superconductivity, and charge fractionalization. A central goal is to achieve in situ control over lattice geometry, bandwidth, and band topology within a single platform. Here we realize such an electrically programmable quantum many-body system in an alternating twisted trilayer MoTe… ▽ More Strong electron-electron interactions underlie a wide range of quantum many-body phenomena, including magnetism, superconductivity, and charge fractionalization. A central goal is to achieve in situ control over lattice geometry, bandwidth, and band topology within a single platform. Here we realize such an electrically programmable quantum many-body system in an alternating twisted trilayer MoTe$_2$, where an out-of-plane displacement field continuously modifies the layer polarization, effective lattice, and topology of the moiré bands. At zero displacement field, the system realizes a triangular lattice hosting a correlated insulator at one hole per moiré unit cell ($ν= -1$). Doping this state produces strongly asymmetric magnetic responses: double-exchange-like ferromagnetism for $|ν| > 1$, and signatures of spin polarons and antiferromagnetism for $|ν| < 1$. At large displacement field, interlayer hybridization reconstructs the electronic structure into a honeycomb lattice with a flat Chern band, supporting integer and fractional Chern insulators. Magneto-optical measurements further reveal the signatures of gap closure and Landau-level formation from a spin-polarized Fermi surface near the crossover between the two regimes. These results establish a unified, electrically tunable platform in which correlated magnetism and topological states emerge from a single controllable band structure. △ Less

Submitted 18 June, 2026; originally announced June 2026.

Comments: 23 pages, 4 figures

Switching Chern number by sliding and gating in alternately twisted tetralayer MoTe2

Authors: Xiao-Wei Zhang, Kaijie Yang, Xiaodong Xu, Ting Cao, Di Xiao

Abstract: Switching the bulk Chern number in topological materials is of central importance for the design of topological electronic devices. Motivated by recent observations of integer and fractional quantum anomalous Hall effects in twisted transition metal dichalcogenides (tTMDs), we realize the switching of valley Chern number through sliding and gating in alternately twisted tetralayer (ATT) MoTe… ▽ More Switching the bulk Chern number in topological materials is of central importance for the design of topological electronic devices. Motivated by recent observations of integer and fractional quantum anomalous Hall effects in twisted transition metal dichalcogenides (tTMDs), we realize the switching of valley Chern number through sliding and gating in alternately twisted tetralayer (ATT) MoTe$_{2}$. Using large-scale density functional theory (DFT) calculations, we show that the Chern number of the first $K$-valley moiré band evolves from $+1$ to $-1$ under the interlayer sliding. Furthermore, an applied electric field can switch the valley Chern number from $-1$ to $+1$. Based on the developed continuum model, we reveal that these switching behaviors are caused by the sliding- and gate-dependent intralayer moiré potential distributions across the layers. Our results establish ATT MoTe$_{2}$ as a promising platform for engineering moiré band topologies through the design of moiré potentials with sliding in multilayer moiré systems. △ Less

Submitted 13 June, 2026; originally announced June 2026.

Comments: 6 pages, 4 figures

Complex Temperature-dependent Thermal Conductivity in a Sawtooth Chain Magnet Fe$_\mathrm{2}$SiSe$_\mathrm{4}$

Authors: Kunya Yang, Feihao Pan, Liran Wang, Chenglin Shang, Ying Zhu, Xiancai Hu, Sanjiang He, Xinrun Mi, Long Zhang, Aifeng Wang, Yisheng Chai, Frederic Hardy, Christoph Meingast, Peng Cheng, Mingquan He

Abstract: Geometrically frustrated magnets provide an ideal platform for exploring the interplay between lattice geometry and spin degrees of freedom. Here, we investigate the interactions between lattice and spin via thermal-transport measurements on the triangular sawtooth-lattice olivine magnet Fe$_\mathrm{2}$SiSe$_\mathrm{4}$, which exhibits successive magnetic transitions at $T_1 = 110$ K (antiferromag… ▽ More Geometrically frustrated magnets provide an ideal platform for exploring the interplay between lattice geometry and spin degrees of freedom. Here, we investigate the interactions between lattice and spin via thermal-transport measurements on the triangular sawtooth-lattice olivine magnet Fe$_\mathrm{2}$SiSe$_\mathrm{4}$, which exhibits successive magnetic transitions at $T_1 = 110$ K (antiferromagnetic) and $T_2 = 50$ K (ferrimagnetic). Although phonons dominate the thermal conductivity, its temperature dependence displays a pronounced double-peak structure arising from spin-phonon coupling. In the intermediate temperature range between $T_1$ and $T_2$ , resonant scattering of phonons by magnetic excitations around 5 meV produces a broad maximum around 60 K. Below $T_2$, the resonant spin-phonon scattering is strongly suppressed, leading to a rapid increase in thermal conductivity upon cooling and a pronounced low-temperature peak near 11 K, characteristic of heat transport governed by conventional phonon scattering mechanisms. Notably, this low-temperature peak is enhanced by a factor of $\sim 5$ compared to the broad maximum at higher temperatures. These results demonstrate the strong sensitivity of thermal transport to spin-lattice interactions and highlight spin-phonon scattering as an effective mechanism for tailoring thermal conductivity in geometrically frustrated magnets. △ Less

Submitted 4 June, 2026; originally announced June 2026.

Comments: 10 pages, 3 figures

Journal ref: Phys. Rev. B 113, 174442(2026)

An AI-driven robotic system for two-dimensional hetero-assemblies

Authors: Xiaoxi Li, Jinkun He, Haojie Liu, Xipeng Liu, Zewen Wu, Jing Li, Kai Zhao, Shan Li, Xingdan Sun, Xiaoxue Fan, Zhiren Xiong, Xingguang Wu, Xuanzhe Sha, Zhili Lin, Caixia Yang, Luosha Han, Jie Xu, Woye Pei, Kaining Yang, Jing Zhang, Xiaolong Feng, Tongyao Zhang, Zhu Liang, Kenji Watanabe, Takashi Taniguchi , et al. (6 additional authors not shown)

Abstract: Nanomaterials stacked on-demand, such as rotationally assembled two-dimensional (2D) van der Waals (vdW) layered compounds, provides a versatile platform for quantum simulation and the exploration of exotic electronic phases. Currently, however, such nanoassemblies remain largely confined to inefficiency, manually operated process, limiting their potential for probing emergent physical phenomena.… ▽ More Nanomaterials stacked on-demand, such as rotationally assembled two-dimensional (2D) van der Waals (vdW) layered compounds, provides a versatile platform for quantum simulation and the exploration of exotic electronic phases. Currently, however, such nanoassemblies remain largely confined to inefficiency, manually operated process, limiting their potential for probing emergent physical phenomena. There is a pressing need in the field for high-precision, automated assembling techniques, especially for the scalable fabrication of 2D twistronic heterostructures. Here, we present an intelligent automation system dedicated to the fabrication of van der Waals stacks, following the state-of-the-art protocol for dry transfer of exfoliated 2D materials. The system further employs metadata generated from each automated stacking procedure to perform reinforcement learning, thereby continuously bettering its performances. As a concrete demonstration, we fabricate twisted bilayer graphene (TBLG) -- known for its challenging preparation -- and exhibit its unconventional superconductivity near the magic angle. Our work may pave the way for high-throughput fabrication of low-dimensional nanomaterials including twistronic heterostructures, where integrating data mining and artificial intelligence can accelerate the discovery of novel physical phenomena. △ Less

Submitted 19 May, 2026; originally announced May 2026.

Comments: 18 pages, 11 figures

Nonadiabatic Theory of Phonon Magnetic Moments in Insulators and Metals

Authors: Haoran Chen, Wenqin Chen, Kaijie Yang, Ting Cao, Di Xiao

Abstract: We develop a nonadiabatic theory of phonon magnetic moments applicable to both insulators and metals. By relating the phonon magnetic moment to the force-velocity response of ions in a magnetic field, we derive a gauge-invariant expression using a gauge-covariant Wigner expansion. The formalism naturally separates Fermi-sea and Fermi-surface contributions and captures the full dependence on phonon… ▽ More We develop a nonadiabatic theory of phonon magnetic moments applicable to both insulators and metals. By relating the phonon magnetic moment to the force-velocity response of ions in a magnetic field, we derive a gauge-invariant expression using a gauge-covariant Wigner expansion. The formalism naturally separates Fermi-sea and Fermi-surface contributions and captures the full dependence on phonon frequency. In gapped systems, our theory reduces to previous adiabatic expressions in the low-frequency limit. Beyond this limit, it reveals additional contributions arising from resonant interband processes and the Fermi surface. Applying our theory to Pb$_{1-x}$Sn$_x$Te, we find that the Fermi-surface contribution substantially enhances the phonon magnetic moment, reproducing the same order of magnitude as the experimental observation. Our results provide a unified framework for describing phonon magnetic moments beyond the adiabatic regime. △ Less

Submitted 7 May, 2026; originally announced May 2026.

Comments: 5 pages, 3 figures

Quantum Geometric Quadrupole of Cooper Pairs

Authors: Wenqin Chen, Kaijie Yang, Ting Cao, Shi-Zeng Lin, Jiabin Yu, Di Xiao

Abstract: The size of Cooper pairs defines a fundamental length scale of superconductivity, conventionally set by band dispersion and the superconducting gap. This picture breaks down in flat bands, where quenched dispersion makes quantum geometry essential. Here we develop a general framework based on the Cooper pair quadrupole moment, whose trace gives the pair size. The framework holds for both dispersiv… ▽ More The size of Cooper pairs defines a fundamental length scale of superconductivity, conventionally set by band dispersion and the superconducting gap. This picture breaks down in flat bands, where quenched dispersion makes quantum geometry essential. Here we develop a general framework based on the Cooper pair quadrupole moment, whose trace gives the pair size. The framework holds for both dispersive and flat-band cases, and provides a unified description of the geometric origin of this length scale. In particular, when time-reversal symmetry is broken, Berry curvature enters through the phase structure of the pair wavefunction and gives an essential contribution absent from previous quantum-metric theories. Together, Berry curvature and quantum metric impose a geometric lower bound on the pair size. Applying this framework to rhombohedral graphene, we find that the Berry-curvature-induced contribution can dominate and yields pair sizes comparable to experimentally inferred coherence lengths. These results identify Berry curvature as a central geometric ingredient controlling the microscopic length scale of superconductivity. △ Less

Submitted 4 May, 2026; originally announced May 2026.

Comments: 5 pages, 2 figures

Large language model-enabled automated data extraction for concrete materials informatics

Authors: Zhanzhao Li, Kengran Yang, Qiyao He, Kai Gong

Abstract: The promise of data-driven materials discovery remains constrained by the scarcity of large, high-quality, and accessible experimental datasets. Here, we introduce a generalizable large language model (LLM)-powered pipeline for automated extraction and structuring of materials data from unstructured scientific literature, using concrete materials as a representative and particularly challenging ex… ▽ More The promise of data-driven materials discovery remains constrained by the scarcity of large, high-quality, and accessible experimental datasets. Here, we introduce a generalizable large language model (LLM)-powered pipeline for automated extraction and structuring of materials data from unstructured scientific literature, using concrete materials as a representative and particularly challenging example. The pipeline exhibits robust performance across a broad range of LLMs and achieves an $F_1$ score of up to 0.98 for diverse composition--process--property attributes. Within one hour, it extracts nearly 9,000 high-quality records with over 100 attributes from a corpus screened from more than 27,000 publications, enabling the construction of the largest open laboratory database for blended cement concrete. Machine learning analyses underscore the importance of large, diverse, and information-rich datasets for enhancing both in-distribution accuracy and out-of-distribution generalization to unseen materials. The proposed pipeline is readily adaptable to other materials domains and accelerates the development of scalable data infrastructures for materials informatics. △ Less

Submitted 30 June, 2026; v1 submitted 24 April, 2026; originally announced April 2026.

Comments: 21 pages, 5 figures, 1 table

Giant and Helical Exciton Dipole from Berry Curvature in Flat Chern Bands

Authors: Kaijie Yang, Huiyuan Zheng, Xiaodong Xu, Di Xiao, Ting Cao

Abstract: We show that excitons forming between moiré flat Chern bands possess a substantial electric dipole moment comparable to the moiré lattice parameter times the elementary charge ($\sim10^2$ Debye). At a hole filling factor of one in twisted MoTe$_2$, the dipole moment of the lowest-energy exciton branch develops in-plane helical texture in momentum space from the intrinsic Berry curvature of electro… ▽ More We show that excitons forming between moiré flat Chern bands possess a substantial electric dipole moment comparable to the moiré lattice parameter times the elementary charge ($\sim10^2$ Debye). At a hole filling factor of one in twisted MoTe$_2$, the dipole moment of the lowest-energy exciton branch develops in-plane helical texture in momentum space from the intrinsic Berry curvature of electron and hole. By solving the Bethe-Salpeter equations, we demonstrate that an out-of-plane displacement field induces a Frenkel-to-Wannier exciton transition, accompanied by a reversal of the dipole texture helicity. The resulting attractive exciton dipole-dipole interactions lead to quadrupolar biexcitons that can be probed via two-photon spectroscopy. Our findings establish band topology as a tunable knob to engineer exciton dipole moments and pave the way to manipulate many-body interactions in the terahertz regime. △ Less

Submitted 14 April, 2026; originally announced April 2026.

Chiral skyrmionic superconductivity from doping a Chern Ferromagnet

Authors: Miguel Gonçalves, Kun Yang, Shi-Zeng Lin

Abstract: We show that chiral superconductivity can be stabilized by hole doping a Chern ferromagnet. Performing exact diagonalization and density-matrix-renormalization-group calculations on the repulsive Kane-Mele-Hubbard model at hole doping relative to filling $ν=1$ electron per unit cell, we find that a Cooper pair formed by a magnon (spin-flip excitation) bound to two holes is stabilized at sufficient… ▽ More We show that chiral superconductivity can be stabilized by hole doping a Chern ferromagnet. Performing exact diagonalization and density-matrix-renormalization-group calculations on the repulsive Kane-Mele-Hubbard model at hole doping relative to filling $ν=1$ electron per unit cell, we find that a Cooper pair formed by a magnon (spin-flip excitation) bound to two holes is stabilized at sufficiently strong interactions and sufficiently large Ising spin-orbit coupling (SOC). This Cooper pair exhibits both finite spin chirality -- signaling a noncoplanar skyrmionic spin texture -- and chiral $f$-wave symmetry. The pairing and spin chirality are set by the Chern number/polarization of the parent Chern ferromagnet. We further find that interactions between skyrmion Cooper pairs evolve from repulsive to attractive as the Ising SOC increases, revealing an intermediate-SOC region where chiral superconductivity can emerge from the condensation of hole-skyrmion Cooper pairs. Our findings provide a novel microscopic mechanism for chiral superconductivity and may be relevant for the recent observation of superconductivity in the MoTe$_2$ moiré superlattice. △ Less

Submitted 2 April, 2026; originally announced April 2026.

Towards Computational Microscope of Chemical Order-Disorder via ML-Accelerated Monte Carlo Simulation

Authors: Fanli Zhou, Hao Chen, Pengxiang Xu, Kai Yang, Zongrui Pei, Xianglin Liu

Abstract: Tailoring the performance of next-generation high entropy materials requires a deep understanding of the competition between entropy-driven random solid solution and enthalpy-driven chemical ordering. Investigating such order and disorder complexity demands atomistic simulations that achieve high accuracy, efficiency, and generalizability across vast spatial, temporal, and especially chemical scal… ▽ More Tailoring the performance of next-generation high entropy materials requires a deep understanding of the competition between entropy-driven random solid solution and enthalpy-driven chemical ordering. Investigating such order and disorder complexity demands atomistic simulations that achieve high accuracy, efficiency, and generalizability across vast spatial, temporal, and especially chemical scales. While machine learning (ML) interatomic potentials have transformed molecular dynamics, they remain limited in capturing diffusion-driven chemical evolution over long timescales. The recently introduced SMC-X method brings exciting opportunities. Realizing its full potential requires a comprehensive study, which is the focus of this work. To assess model performance, we systematically benchmark invariant and equivariant architectures using a density functional theory dataset of more than 10,000 configurations spanning seven elements: Fe, Co, Ni, Al, Ti, Ta, and V. To understand the roles of pairwise and higher-order interactions, we decouple their contributions across chemical space using an explainable machine learning approach. We also examine the impact of lattice relaxation by comparing models trained on datasets with and without structural relaxation. Our results clarify how to choose ML surrogate models for Monte Carlo simulations, bridge the gap between theory and experiment, and lay a foundation for establishing ML-accelerated Monte Carlo as a computational microscope for chemical complexity. △ Less

Submitted 22 March, 2026; originally announced March 2026.

A Magnon-Based Electric Field Controlled Magnetoelectric Device for Energy-Efficient Logic-in-Memory

Authors: Rongqing Cong, Sajid Husain, Yumin Su, Sasikanth Manipatruni, Naveed Ahmed, Dmitri E. Nikonov, Ramamoorthy Ramesh, Kaiyuan Yang, Zhi Jackie Yao

Abstract: We demonstrate a non-volatile magnetoelectric magnonic memory (MEMM) that enables fully electrical write/read via direct magnon-driven sensing in an insulating antiferromagnet. A fabricated SrIrO3/La-BiFeO3/SrIrO3 trilayer exhibits sub-100 ps switching, a remnant polarization of 20 uC/cm2, and a readout voltage contrast close to 1mV between high and low-resistance states. To connect device physics… ▽ More We demonstrate a non-volatile magnetoelectric magnonic memory (MEMM) that enables fully electrical write/read via direct magnon-driven sensing in an insulating antiferromagnet. A fabricated SrIrO3/La-BiFeO3/SrIrO3 trilayer exhibits sub-100 ps switching, a remnant polarization of 20 uC/cm2, and a readout voltage contrast close to 1mV between high and low-resistance states. To connect device physics to circuit behavior, we develop and experimentally validate a compact circuit model that captures spin Hall injection and spin transport. Simulations with optimized material parameters predict output voltages > 100mV, enabling cascading without external amplification. Using this framework, we design MEMM-based memory and logic blocks, including a 1T1R array, two inverter implementations (complementary two-device and single-device), and a three-input majority gate, and evaluate deep-pipelined operation. The model projects switching energies down to 1 aJ per operation and logic propagation delays of 30-60 ps, indicating MEMM as a promising platform for energy-constrained, high throughput computing. △ Less

Submitted 21 July, 2026; v1 submitted 15 February, 2026; originally announced February 2026.

Stable boundary modes for fragile topology from spontaneous PT-symmetry breaking

Authors: Kang Yang, Fei Song, Piet W. Brouwer

Abstract: Two-dimensional topological insulators protected by nonlocal symmetries or with fragile topology usually do not admit robust in-gap edge modes due to the incompatibility between the symmetry and the boundary. Here, we show that in a parity-time (PT) symmetric system robust in-gap topological edge modes can be stably induced by non-Hermitian couplings that spontaneously break the PT symmetry of the… ▽ More Two-dimensional topological insulators protected by nonlocal symmetries or with fragile topology usually do not admit robust in-gap edge modes due to the incompatibility between the symmetry and the boundary. Here, we show that in a parity-time (PT) symmetric system robust in-gap topological edge modes can be stably induced by non-Hermitian couplings that spontaneously break the PT symmetry of the eigenstates. The topological edge modes traverse the imaginary spectral gap between a pair of fragile topological bands, which is opened by the presence of the non-Hermitian perturbation. We demonstrate that the net number of resulting in-gap modes is protected by an operator version of anomaly cancellation that extends beyond the Hermitian limit. The results imply that loss and gain can in principle drive fragile topological phenomena to stable topological phenomena. △ Less

Submitted 5 January, 2026; originally announced January 2026.

Comments: 5+6 pages

Anisotropic Photostriction and Strain-modulated Carrier Lifetimes in Orthorhombic Semiconductors

Authors: Jianxin Yu, Kun Yang, Jiawen Li, Sheng Meng, Xinghua Shi, Jin Zhang

Abstract: We demonstrate anisotropic photostriction in two-dimensional orthorhombic semiconductors using time-dependent density functional theory. By tracing the dynamics of photoexcited carriers, we establish a quantitative link between carrier density and lattice deformation in layered black phosphorus and germanium selenides. The structural response exhibits significant anisotropy, featuring lattice expa… ▽ More We demonstrate anisotropic photostriction in two-dimensional orthorhombic semiconductors using time-dependent density functional theory. By tracing the dynamics of photoexcited carriers, we establish a quantitative link between carrier density and lattice deformation in layered black phosphorus and germanium selenides. The structural response exhibits significant anisotropy, featuring lattice expansion along the armchair direction and contraction along the zigzag direction, which is attributed to the interplay between charge redistribution and intrinsic lattice anisotropy. Both the magnitude and orientation of the photostrictive strains can be tuned by photodoping densities, enabling precise control over the photoinduced response. Notably, the photoinduced strains significantly increase carrier recombination lifetimes by suppressing nonradiative recombination, primarily due to the enlarged bandgap and weakened nonadiabatic coupling. These results provide microscopic insight into the origin of anisotropic photostriction in low-dimensional systems and lay the groundwork for light-controllable, directionally sensitive optomechanical devices at the atomic scale. △ Less

Submitted 28 December, 2025; originally announced December 2025.

Kitaev interaction and possible spin liquid state in CoI2 and Co2/3Mg1/3I2

Authors: Yaozhenghang Ma, Ke Yang, Yuxuan Zhou, Hua Wu

Abstract: Kitaev materials are of great interest due to their potential in realizing quantum spin liquid (QSL) states and applications in topological quantum computing. In the pursuit of realizing Kitaev QSL, a Mott insulator with strong bond-dependent frustration and weak geometric frustration is highly desirable. Here we explore Kitaev physics in the van der Waals triangular antiferromagnet (AF) CoI$_2$,… ▽ More Kitaev materials are of great interest due to their potential in realizing quantum spin liquid (QSL) states and applications in topological quantum computing. In the pursuit of realizing Kitaev QSL, a Mott insulator with strong bond-dependent frustration and weak geometric frustration is highly desirable. Here we explore Kitaev physics in the van der Waals triangular antiferromagnet (AF) CoI$_2$, through the spin-orbital states and Wannier function analyses, exact diagonalization and density matrix renormalization group study of the electronic structure and magnetic properties. We find that the high-spin Co$^{2+}$ ion is in the $J_\mathrm{eff}=1/2$ state because of strong spin-orbit coupling, and the weak trigonal elongation and crystal field contribute to the observed weak in-plane magnetic anisotropy. The strong $t_{2g}$-$e_g$ hopping via the strong Co 3$d$-I 5$p$ hybridization gives rise to a strong Kitaev interaction ($K_1$) at the first nearest neighbors (1NN), and the long Co-Co distance and the weak $t_{2g}$-$t_{2g}$ hoppings determine a weak Heisenberg interaction $J_1$. The resultant $|K_1/J_1|$ = 6.63 confirms a strong bond-dependent frustration, while the geometric frustration due to the 3NN Heisenberg interaction $J_3$ gets involved, and they all together result in the experimental helical AF order in CoI$_2$. We then propose to suppress the $J_3$ using a partial Mg substitution for Co, and indeed we find that Co$_{2/3}$Mg$_{1/3}$I$_2$ has the much reduced geometric frustration but hosts the robust bond-dependent frustration, and thus it would be a promising Kitaev material being so far closest to the QSL state. △ Less

Submitted 26 December, 2025; originally announced December 2025.

Journal ref: Phys. Rev. B 112, L220412 (2025)

Layerwise Stratification and Band Reordering in Twisted Multilayer MoTe$_2$

Authors: Yueyao Fan, Xiao-Wei Zhang, Yusen Ye, Xiaoyu Liu, Chong Wang, Kaijie Yang, Di Xiao, Ting Cao

Abstract: We introduce a generalizable, physics informed strategy for generating training data that enables a machine learning force field accurate over a broad range of twist angles and stacking layer numbers in moire systems. Applying this to multilayer twisted MoTe2 (tMoTe2), we identify a structural and electronic stratification: the two moire interface (MI) layers retain substantial lattice reconstruct… ▽ More We introduce a generalizable, physics informed strategy for generating training data that enables a machine learning force field accurate over a broad range of twist angles and stacking layer numbers in moire systems. Applying this to multilayer twisted MoTe2 (tMoTe2), we identify a structural and electronic stratification: the two moire interface (MI) layers retain substantial lattice reconstruction even in thick multilayers, while outer bulk like layers show rapidly attenuated distortions.Surprisingly, this stratification becomes strongest not in the ultra-small twist angle regime (<~1°), where in plane domain formation is well known, but rather at intermediate angles (2-5°). Simultaneously, interlayer hybridization across the MI-bulk boundary is strongly suppressed, leading to electronic isolation. In twisted double bilayer MoTe2, this stratification gives rise to coexisting honeycomb and triangular lattice motifs in the frontier valence bands. We further demonstrate that twist angle and weak gating can create energy shift of bands belonging to the two motifs, producing Chern band reordering and nonlinear electric polarization with modest hole doping. Our approach allows efficient simulation of multilayer moire systems and reveals structural-electronic separation phenomena absent in bilayer systems. △ Less

Submitted 24 November, 2025; originally announced November 2025.

Comments: 7 pages, 4 figures

Transferable potential for molecular dynamics simulations of borosilicate glasses and structural comparison of machine learning optimized parameters

Authors: Kai Yang, Ruoxia Chen, Anders K. R. Christensen, Mathieu Bauchy, N. M. Anoop Krishnan, Morten M. Smedskjaer, Fabian Rosner

Abstract: The simulation of borosilicate glasses is challenging due to the composition and temperature dependent coordination state of boron atoms. Here, we present a newly developed machine learning optimized classical potential for molecular dynamics simulations that achieves transferability across diverse borosilicate glass compositions. Our potential accurately predicts the glass structural variations i… ▽ More The simulation of borosilicate glasses is challenging due to the composition and temperature dependent coordination state of boron atoms. Here, we present a newly developed machine learning optimized classical potential for molecular dynamics simulations that achieves transferability across diverse borosilicate glass compositions. Our potential accurately predicts the glass structural variations in short- and medium-range order in different glass compositions, including validating our potential against experimental X-ray structure factor data. Notably, these data are not included in the optimization framework, which focuses exclusively on density and four-fold coordinated boron fraction. We further investigate the impact of empirical parameters in the force field formulation on the microscopic bond lengths, bond angles and the macroscopic densities, providing new insights into the relationship between interatomic potentials and bulk glass behaviors. △ Less

Submitted 18 November, 2025; originally announced November 2025.

Critical theory of Pomeranchuk transitions via high-dimensional bosonization

Authors: Zhengfei Hu, Jaychandran Padayasi, Oğuz Türker, Kun Yang

Abstract: We use high-dimensional bosonization to derive an effective field theory that describes the Pomeranchuck transition in isotropic two-dimensional Fermi liquids. We find that the transition is triggered by the softening of an eigenmode that leads to spontaneous Fermi surface distortion. The resultant theory in terms of this critical mode has dynamical critical exponent $z = 2$ and the upper critical… ▽ More We use high-dimensional bosonization to derive an effective field theory that describes the Pomeranchuck transition in isotropic two-dimensional Fermi liquids. We find that the transition is triggered by the softening of an eigenmode that leads to spontaneous Fermi surface distortion. The resultant theory in terms of this critical mode has dynamical critical exponent $z = 2$ and the upper critical dimension is $d_c = 4-z= 2$. As a result the system is at the upper critical dimension in 2D, resulting in a Gaussian fixed point with a marginally irrelevant quartic perturbation. △ Less

Submitted 22 June, 2026; v1 submitted 3 November, 2025; originally announced November 2025.

Comments: 8 pages, 2 figures

Journal ref: Phys. Rev. B 113 (2026), L241116

Optimization of Transferable Interatomic Potentials for Glasses toward Experimental Properties

Authors: Ruoxia Chen, Kai Yang, Morten M. Smedskjaer, N. M. Anoop Krishnan, Jaime Marian, Fabian Rosner

Abstract: The accuracy of molecular simulations is fundamentally limited by the interatomic potentials that govern atomic interactions. Traditional potential development, which relies heavily on ab initio calculations, frequently struggles to reproduce the experimentally observed properties that govern real material behavior. To address this challenge, we present a machine learning-driven, active-learning o… ▽ More The accuracy of molecular simulations is fundamentally limited by the interatomic potentials that govern atomic interactions. Traditional potential development, which relies heavily on ab initio calculations, frequently struggles to reproduce the experimentally observed properties that govern real material behavior. To address this challenge, we present a machine learning-driven, active-learning optimization framework for optimizing classical interatomic potentials to reproduce experimental properties. Our method, here showcased on soda-lime borosilicate glasses, targets both global (density) and local (boron coordination) structural features across a wide range of compositions. By combining a surrogate model with iterative active learning, the framework efficiently explores a five-dimensional parameter space using only 400 molecular dynamics simulations over 17 iterations, making it highly data-efficient and eliminating the need for extensive simulation campaigns. Two transferable parameter sets are identified, each demonstrating good agreement with experimental measurements, including glass density, fraction of four-fold boron, and X-ray structure factor. The framework effectively captures and manages inherent trade-offs between structural objectives and compositional regimes, providing insights into the coordination behavior of boron in complex glass networks. The resulting classical force fields are generalizable and do not require reparameterization for individual compositions. Altogether, this work offers a scalable and experimentally grounded approach for developing transferable interatomic potentials suitable for a broad range of materials, including multi-component glass systems, and beyond. △ Less

Submitted 14 October, 2025; originally announced October 2025.

Effects of intertube dipole-dipole interactions in nearly integrable one-dimensional $^{162}$Dy gases

Authors: Yicheng Zhang, Kangning Yang, Benjamin L. Lev, Marcos Rigol

Abstract: We study the effects of the intertube dipole-dipole interactions (DDI) in recent experiments with arrays of nearly integrable one-dimensional (1D) dipolar Bose gases of $^{162}$Dy atoms. An earlier theoretical modeling ignored those interactions, which we include here via a modification of the 1D confining potentials. We investigate the effects of the intertube DDI both during the state preparatio… ▽ More We study the effects of the intertube dipole-dipole interactions (DDI) in recent experiments with arrays of nearly integrable one-dimensional (1D) dipolar Bose gases of $^{162}$Dy atoms. An earlier theoretical modeling ignored those interactions, which we include here via a modification of the 1D confining potentials. We investigate the effects of the intertube DDI both during the state preparation and during the measurements of the rapidity distributions. We explore how the strength of the contact interactions and the magnetic field angles modify the intertube DDI corrections. We find that those corrections slightly change both the properties of the equilibrium state and the rapidity measurements. Remarkably, however, the changes nearly cancel each other, resulting in measured rapidity distributions that are very close to those predicted in the absence of the intertube DDI. △ Less

Submitted 17 February, 2026; v1 submitted 6 October, 2025; originally announced October 2025.

Comments: 10 pages, 11 figures, as published

Journal ref: Phys. Rev. A 113, 023314 (2026)

SMC-X: A Distributed Scalable Monte Carlo Simulation Method for Chemically Complex Alloys

Authors: Xianglin Liu, Kai Yang, Fanli Zhou, Pengxiang Xu

Abstract: To predict the complex chemical evolution in multicomponent alloys, it is highly desirable to have accurate atomistic simulation methods capable of reaching sufficiently large spatial and temporal scales. In this work, we advance the recently proposed SMC-X method through distributed computation on either GPUs or CPUs, pushing both spatial and temporal scales of atomistic simulation of chemically… ▽ More To predict the complex chemical evolution in multicomponent alloys, it is highly desirable to have accurate atomistic simulation methods capable of reaching sufficiently large spatial and temporal scales. In this work, we advance the recently proposed SMC-X method through distributed computation on either GPUs or CPUs, pushing both spatial and temporal scales of atomistic simulation of chemically complex alloys to previously inaccessible scales. This includes a record-breaking 128-billion-atom HEA system extending to the micrometer regime in space, and a 1-billion-atom HEA evolved over more than three million Monte Carlo swap steps, approaching the minute regime in time. We show that such large-scale simulations are essential for bridging the gap between experimental observations and theoretical predictions of the nanoprecipitate sizes in HEAs, based on analysis using the Lifshitz-Slyozov-Wagner (LSW) theory for diffusion-controlled coarsening. This work demonstrates the great potential of SMC-X for simulation-driven exploration of the chemical complexity in high-entropy materials at large spatial and temporal scales. △ Less

Submitted 5 December, 2025; v1 submitted 25 September, 2025; originally announced September 2025.

Morphological and Chemical Changes in Cd-free Colloidal QD-LEDs During Operation

Authors: Ruiqi Zhang, Jamie Geng, Shaun Tan, Shreyas Srinivasan, Taehyung Kim, Mayuran Saravanapavanantham, Kwang-Hee Lim, Mike Dillender, Heejae Chung, Thienan Nguyen, Karen Yang, Yongli Lu, Taegon Kim, Moungi G. Bawendi, Vladimir Bulovic

Abstract: Heavy metal-free quantum-dot light-emitting devices (QD-LEDs) have demonstrated remarkable brightness, saturated color, and high efficiencies across a broad spectral range. However, in contrast to organic LEDs (OLEDs), QD-LED operational lifetimes remain limited, with the underlying degradation mechanisms not fully understood. In the present study, we show that InP/ZnSe/ZnS (red-emitting) and ZnTe… ▽ More Heavy metal-free quantum-dot light-emitting devices (QD-LEDs) have demonstrated remarkable brightness, saturated color, and high efficiencies across a broad spectral range. However, in contrast to organic LEDs (OLEDs), QD-LED operational lifetimes remain limited, with the underlying degradation mechanisms not fully understood. In the present study, we show that InP/ZnSe/ZnS (red-emitting) and ZnTeSe/ZnSe/ZnS (blue-emitting) cadmium-free colloidal QD-LEDs undergo nanoscale morphological changes during operation. Specifically,interparticle coarsening and layer thinning are observed in the electron transport layer (ETL) consisting of ZnMgO nanoparticles (NPs), in the QD emissive layer, and in the organic hole transport layer. This is accompanied by the generation and diffusion of compositional oxygen- and hydrogen-radicals throughout the device, with oxygen accumulating at the electrode/ETL interfance. Moreover, in situ transmission electron microscopy reveals the electron beam exposure, in the presence of hydrogen radicals, accelerates ZnMgO NPs coarsening. To mitigate these degradation pathway, we show that acrylate-based resin-encapsulation treatment stabilize the ETL/QD layers by suppressing the radical formation and halting morphology changes. This approach achieves dramatic stability enhancements, exhibits an 8-fold and 5000-fold lifetime improvement on InP/ZnSe/ZnS and ZnTeSe/ZnSe/ZnS QD-LEDs, respectively. Our findings establish the causal relationships between the morphological degradation, interlayer radical dynamics, and state-of-the-art QD-LEDs instability, providing new insights into a scalable encapsulation treatment that enables efficient and long-lived Cd-free QD-LEDs. △ Less

Submitted 15 September, 2025; originally announced September 2025.

Comments: 34 pages, 5 figures

Symmetry-enforced Moiré Topology

Authors: Yunzhe Liu, Ethan Angerhofer, Kaijie Yang, Chao-Xing Liu, Jiabin Yu

Abstract: Topological flat bands in two-dimensional (2D) moiré materials have emerged as promising platforms for exploring the interplay between topology and correlation effects. However, realistic calculations of moiré band topology using density functional theory (DFT) are computationally inefficient due to the large number of atoms in a single moiré unit cell. In this work, we propose a systematic scheme… ▽ More Topological flat bands in two-dimensional (2D) moiré materials have emerged as promising platforms for exploring the interplay between topology and correlation effects. However, realistic calculations of moiré band topology using density functional theory (DFT) are computationally inefficient due to the large number of atoms in a single moiré unit cell. In this work, we propose a systematic scheme to predict the topology of moiré bands from atomic symmetry data and moiré symmetry group, both of which can be efficiently extracted from DFT. Specifically, for $Γ$-valley electron gases, we find that certain combinations of atomic symmetry data and moiré symmetry groups can enforce nontrivial band topology in the low-energy moiré bands, as long as the moiré band gap is smaller than the atomic band splitting at the moiré Brillouin zone boundary. This symmetry-enforced nontrivial moiré topology, including both topological insulators and topological semimetals, is robust against various material-specific details such as the precise form and strength of the moiré potential or the exact twist angle. By exhaustively scanning all 2D atomic symmetry data and moiré symmetry groups, we identify 197 combinations that can yield symmetry-enforced nontrivial moiré topology, and we verify one such combination using a moiré model with cubic Rashba spin-orbit coupling. By screening the existing 2D material database, we currently identify 92 monolayer materials with (i) the low-energy bands near $Γ$ and (ii) the atomic symmetry data that belong to those combinations. Our approach is generalizable to other valleys and provides a useful guideline for experimental efforts to discover and design new topologically nontrivial moiré materials. △ Less

Submitted 23 November, 2025; v1 submitted 8 September, 2025; originally announced September 2025.

Comments: 44 pages, 10 figures

Orbital Hybridization-Induced Ising-Type Superconductivity in a Confined Gallium Layer

Authors: Hemian Yi, Yunzhe Liu, Chengye Dong, Yiheng Yang, Zi-Jie Yan, Zihao Wang, Lingjie Zhou, Dingsong Wu, Houke Chen, Stephen Paolini, Bing Xia, Bomin Zhang, Xiaoda Liu, Hongtao Rong, Annie G. Wang, Saswata Mandal, Kaijie Yang, Benjamin N. Katz, Lunhui Hu, Jieyi Liu, Tien-Lin Lee, Vincent H. Crespi, Yuanxi Wang, Yulin Chen, Joshua A. Robinson , et al. (2 additional authors not shown)

Abstract: In low-dimensional superconductors, the interplay between quantum confinement and interfacial hybridization effects can reshape Cooper pair wavefunctions and induce novel forms of unconventional superconductivity. In this work, we employ a plasma-free, carbon buffer layer-assisted confinement epitaxy method to synthesize trilayer gallium (Ga) sandwiched between a graphene layer and a 6H-SiC(0001)… ▽ More In low-dimensional superconductors, the interplay between quantum confinement and interfacial hybridization effects can reshape Cooper pair wavefunctions and induce novel forms of unconventional superconductivity. In this work, we employ a plasma-free, carbon buffer layer-assisted confinement epitaxy method to synthesize trilayer gallium (Ga) sandwiched between a graphene layer and a 6H-SiC(0001) substrate, forming an air-stable graphene/trilayer Ga/SiC heterostructure. In this confined light-element Ga layer, we demonstrate interfacial Ising-type superconductivity driven by atomic orbital hybridization between the Ga layer and the SiC substrate. Electrical transport measurements reveal that the in-plane upper critical magnetic field u0Hc2,|| reaches ~21.98T at T=400 mK, approximately 3.38 times the Pauli paramagnetic limit (~6.51T). Angle-resolved photoemission spectroscopy (ARPES) measurements combined with theoretical calculations confirm the presence of split Fermi surfaces with Ising-type spin textures at the K and K' valleys of the confined Ga layer strongly hybridized with SiC. Moreover, by incorporating finite relaxation time induced by impurity scattering into an Ising-type superconductivity model, we reproduce the entire temperature-dependent u0Hc2,|| phase diagram. This work establishes a new strategy to realize unconventional pairing wavefunctions by combining quantum confinement and interfacial hybridization effects in superconducting thin films. It also opens new avenues for designing scalable superconducting quantum electronic and spintronic devices through interfacial engineering. △ Less

Submitted 6 September, 2025; originally announced September 2025.

Comments: 40 pages, 4 figures and 10 extended data figures, comments are welcome

Journal ref: Nature Mater. (2026)

Twist-angle transferable continuum model and second flat Chern band in twisted MoTe2 and WSe2

Authors: Xiao-Wei Zhang, Kaijie Yang, Chong Wang, Xiaoyu Liu, Ting Cao, Di Xiao

Abstract: We develop a twist-angle transferable continuum model for twisted transition metal dichalcogenide (tTMD) homobilayers, using tMoTe2 and tWSe2 as examples. All model parameters are extracted from density functional theory (DFT) calculations at a single twist angle (3.89°) and monolayer data. Our model captures both lattice relaxation effects and the long-range behavior of piezoelectric and ferroele… ▽ More We develop a twist-angle transferable continuum model for twisted transition metal dichalcogenide (tTMD) homobilayers, using tMoTe2 and tWSe2 as examples. All model parameters are extracted from density functional theory (DFT) calculations at a single twist angle (3.89°) and monolayer data. Our model captures both lattice relaxation effects and the long-range behavior of piezoelectric and ferroelectric potentials. Leveraging lattice relaxations obtained via machine learning force fields (MLFFs), the model can be efficiently transferred to other twist angles without requiring additional DFT calculations. It accurately reproduces the DFT band dispersions and quantum geometries across a wide range of twist angles. Furthermore, our model reveals that a second flat Chern band arises near 2° when the interlayer potential difference becomes comparable to the interlayer tunneling. This continuum model provides a clear understanding and starting point for engineering novel electronic phases in moiré TMDs through twist angles and lattice relaxations. △ Less

Submitted 25 August, 2025; originally announced August 2025.

Comments: 8 pages, 5 figures

Revealing Atomic-Scale Switching Pathways in van der Waals Ferroelectrics

Authors: Xinyan Li, Kenna Ashen, Chuqiao Shi, Nannan Mao, Saagar Kolachina, Kaiwen Yang, Tianyi Zhang, Sajid Husain, Ramamoorthy Ramesh, Jing Kong, Xiaofeng Qian, Yimo Han

Abstract: Two-dimensional van der Waals (vdW) materials hold the potential for ultra-scaled ferroelectric (FE) devices due to their silicon compatibility and robust polarization down to atomic scale. However, the inherently weak vdW interactions enable facile sliding between layers, introducing complexities beyond those encountered in conventional ferroelectric materials and presenting significant challenge… ▽ More Two-dimensional van der Waals (vdW) materials hold the potential for ultra-scaled ferroelectric (FE) devices due to their silicon compatibility and robust polarization down to atomic scale. However, the inherently weak vdW interactions enable facile sliding between layers, introducing complexities beyond those encountered in conventional ferroelectric materials and presenting significant challenges in uncovering intricate switching pathways. Here, we combine atomic-resolution imaging under in-situ electrical biasing conditions with first-principles calculations to unravel the atomic-scale switching mechanisms in SnSe, a vdW group-IV monochalcogenide. Our results uncover the coexistence of a consecutive 90 degrees switching pathway and a direct 180 degrees switching pathway from antiferroelectric (AFE) to FE order in this vdW system. Atomic-scale investigations and strain analysis reveal that the switching processes simultaneously induce interlayer sliding and compressive strain, while the lattice remains coherent despite the presence of multidomain structures. These findings elucidate vdW ferroelectric switching dynamics at atomic scale and lay the foundation for the rational design of 2D ferroelectric nanodevices. △ Less

Submitted 28 July, 2025; originally announced July 2025.

Ideal Topological Flat Bands in Two-dimensional Moiré Heterostructures with Type-II Band Alignment

Authors: Yunzhe Liu, Anoj Aryal, Kaijie Yang, Dumitru Calugaru, Zhenyao Fang, Haoyu Hu, Qimin Yan, B. Andrei Bernevig, Chao-xing Liu

Abstract: Topological flat bands play an essential role in inducing exotic interacting physics, ranging from fractional Chern insulators to superconductivity, in moiré materials. In this work, we propose a design principle for realizing topological flat bands with "ideal quantum geometry", namely the trace of Fubini-Study metric equals to the Berry curvature, in a class of two-dimensional moiré heterostruct… ▽ More Topological flat bands play an essential role in inducing exotic interacting physics, ranging from fractional Chern insulators to superconductivity, in moiré materials. In this work, we propose a design principle for realizing topological flat bands with "ideal quantum geometry", namely the trace of Fubini-Study metric equals to the Berry curvature, in a class of two-dimensional moiré heterostructures with type-II band alignment. We first introduce a moiré Chern-band model to describe this system and show that topological flat bands can be realized in this model when the moiré superlattice potential is stronger than the type-II atomic band gap of the heterostructure. Next, we map this model into a topological heavy fermion model that consists of a localized orbital for "f-electron" and a conducting band for "c-electron". We find that both the flatness and quantum geometry of the flat band in the topological heavy fermion model depend on the energy gap between c-electron and f-electron bands at $Γ$ which is experimentally controllable via external gate voltages. This tunability will allow us to realize an ideal topological flat band with zero band-width and ideal quantum geometry. Our design strategy of topological flat bands is insensitive of twist angle. We also discuss possible material candidates for moiré heterostructures with type-II band alignment. △ Less

Submitted 2 February, 2026; v1 submitted 8 July, 2025; originally announced July 2025.

A Generative Diffusion Model for Amorphous Materials

Authors: Kai Yang, Daniel Schwalbe-Koda

Abstract: Generative models show great promise for the inverse design of molecules and inorganic crystals, but remain largely ineffective within more complex structures such as amorphous materials. Here, we present a diffusion model that reliably generates amorphous structures up to 1000 times faster than conventional simulations across processing conditions, compositions, and data sources. Generated struct… ▽ More Generative models show great promise for the inverse design of molecules and inorganic crystals, but remain largely ineffective within more complex structures such as amorphous materials. Here, we present a diffusion model that reliably generates amorphous structures up to 1000 times faster than conventional simulations across processing conditions, compositions, and data sources. Generated structures recovered the short- and medium-range order, sampling diversity, and macroscopic properties of silica glass, as validated by simulations and an information-theoretical strategy. Conditional generation allowed sampling large structures at low cooling rates of 10$^{-2}$ K/ps to uncover a ductile-to-brittle transition and mesoporous silica structures. Extension to metallic glassy systems accurately reproduced local structures and properties from both computational and experimental datasets, demonstrating how synthetic data can be generated from characterization results. Our methods provide a roadmap for the design and simulation of amorphous materials previously inaccessible to computational methods. △ Less

Submitted 7 July, 2025; originally announced July 2025.

Comments: Main: 19 pages, 5 figures; SI: 22 pages, 16 figures

Journal ref: npj Comput. Mater. 12, 29 (2026)

Robustness of real-space topology in moiré systems

Authors: Kryštof Kolář, Kang Yang, Felix von Oppen, Christophe Mora

Abstract: The appearance of fractional Chern insulators in moiré systems can be rationalized by the presence of a fictitious magnetic field associated with the spatial texture of layer-resolved electronic wavefunctions. Here, we present a systematic study of real-space topology and the associated fictitious magnetic fields in moiré systems. We first show that at the level of individual Bloch wavefunctions,… ▽ More The appearance of fractional Chern insulators in moiré systems can be rationalized by the presence of a fictitious magnetic field associated with the spatial texture of layer-resolved electronic wavefunctions. Here, we present a systematic study of real-space topology and the associated fictitious magnetic fields in moiré systems. We first show that at the level of individual Bloch wavefunctions, the real-space Chern number, akin to a Pontryagin index, is a fragile marker. It generically vanishes except for specific limits where the Bloch functions exhibit fine-tuned zeroes within the unit cell, such as the chiral limit of twisted bilayer graphene (TBG) or the adiabatic regime of twisted homobilayer transition metal dichalcogenides (TMD). We then show that these limitations do not apply to textures associated with ensembles of Bloch wavefunctions, such as entire bands or the ensemble of states at a given energy. The Chern number of these textures defines a robust topological index protected by a spectral gap. We find that symmetries constrain it to be nonzero for both twisted TMDs and TBG across all twist angles and levels of corrugation, implying experimental signatures in scanning tunneling microscopy measurements. We also study real-space topology within the topological heavy fermion model of TBG, finding that the real-space topological features are supported only by the light c-electrons. △ Less

Submitted 30 June, 2025; originally announced July 2025.

Electrically tunable quantum interference of atomic spins on surfaces

Authors: Hao Wang, Jing Chen, Peng Fan, Yelko del Castillo, Alejandro Ferrón, Lili Jiang, Zilong Wu, Shijie Li, Hong-Jun Gao, Heng Fan, Joaquín Fernández-Rossier, Kai Yang

Abstract: Controlling quantum interference near avoided energy-level crossings is crucial for fast and reliable coherent manipulation in quantum information processing. However, achieving tunable quantum interference in atomically-precise engineered structures remains challenging. Here, we demonstrate electrical control of quantum interference using atomic spins on an insulating film in a scanning tunneling… ▽ More Controlling quantum interference near avoided energy-level crossings is crucial for fast and reliable coherent manipulation in quantum information processing. However, achieving tunable quantum interference in atomically-precise engineered structures remains challenging. Here, we demonstrate electrical control of quantum interference using atomic spins on an insulating film in a scanning tunneling microscope. Using bias voltages applied across the tunnel junction, we modulate the atomically-confined magnetic interaction between the probe tip and surface atoms with a strong electric field, and drive the spin state rapidly through the energy-level anticrossing. This all-electrical manipulation allows us to achieve Landau-Zener-Stückelberg-Majorana (LZSM) interferometry on both single spins and pairs of interacting spins. The LZSM pattern exhibits multiphoton resonances, and its asymmetry suggests that the spin dynamics is influenced by spin-transfer torque of tunneling electrons. Multi-level LZSM spectra measured on coupled spins with tunable interactions show distinct interference patterns depending on their many-body energy landscapes. These results open new avenues for all-electrical quantum manipulation in spin-based quantum processors in the strongly driven regime. △ Less

Submitted 1 June, 2025; originally announced June 2025.

Journal ref: Nature Communications 16, 8988 (2025)

Photostriction-tunable Polarization and Structural Dynamics in Interlayer Sliding Ferroelectrics

Authors: Kun Yang, Jianxin Yu, Jia Zhang, Sheng Meng, Jin Zhang

Abstract: Two-dimensional ferroelectrics with robust polarization offer promising opportunities for non-volatile memory, field-effect transistors, and optoelectronic devices. However, the impact of lattice deformation on polarization and photoinduced structural response remains poorly understood. Here, we employ first-principles calculations to demonstrate photodoping-induced lattice expansion in rhombohedr… ▽ More Two-dimensional ferroelectrics with robust polarization offer promising opportunities for non-volatile memory, field-effect transistors, and optoelectronic devices. However, the impact of lattice deformation on polarization and photoinduced structural response remains poorly understood. Here, we employ first-principles calculations to demonstrate photodoping-induced lattice expansion in rhombohedrally stacked bilayer MoS2, revealing a strong coupling between photodoping carrier and lattice structure. We identify a pronounced photostrictive response in sliding ferroelectrics, wherein electron-hole excitation leads to substantial in-plane expansion, increased interlayer spacing, and enhanced ferroelectric polarization. This strain-induced modulation drives significant bandgap renormalization. The photostriction-tunable polarization and structural dynamics arise from the strong electromechanical coupling inherent to the non-centrosymmetric rhombohedral stacking. The findings provide critical insights into the nonthermal lattice expansion governing sliding ferroelectrics at atomic-scale timescales, while simultaneously laying the groundwork for next-generation electronic and memory technologies by leveraging lattice-tunable polarization switching. △ Less

Submitted 29 May, 2025; originally announced May 2025.

Comments: 4 figures

In-depth Investigation of Conduction Mechanism on Defect-induced Proton-conducting Electrolytes BaHfO$_3$

Authors: Peng Feng, Hang Ma, Kuan Yang, Yingjie Lv, Ying Liang, Tianxing Ma, Jiajun Linghu, Zhi-Peng Li

Abstract: This study utilizes first-principles computational methods to comprehensively analyze the impact of A-site doping on the proton conduction properties of BaHfO$_3$. The goal is to offer theoretical support for the advancement of electrolyte materials for solid oxide fuel cells. Our research has uncovered that BaHfO$_3$ demonstrates promising potential for proton conduction, with a low proton migrat… ▽ More This study utilizes first-principles computational methods to comprehensively analyze the impact of A-site doping on the proton conduction properties of BaHfO$_3$. The goal is to offer theoretical support for the advancement of electrolyte materials for solid oxide fuel cells. Our research has uncovered that BaHfO$_3$ demonstrates promising potential for proton conduction, with a low proton migration barrier of $0.28$ eV, suggesting efficient proton conduction can be achieved at lower temperatures. Through A-site doping, particularly with low-valence-state ions and the introduction of Ba vacancies, we can effectively decrease the formation energy of oxygen vacancies (\( E_{\text{vac}} \)), leading to an increase in proton concentration. Additionally, our study reveals that the primary mechanism for proton migration in BaHfO$_3$ is the Grotthuss mechanism rather than the vehicle mechanism. Examination of the changes in lattice parameters during proton migration indicates that while doping or vacancy control strategies do not alter the mode of H$^+$ migration, they do influence the migration pathway and barrier. These findings provide valuable insights into optimizing the proton conduction properties of BaHfO$_3$ through A-site doping and lay a solid theoretical foundation for the development of novel, highly efficient solid oxide fuel cell electrolyte materials. △ Less

Submitted 23 June, 2025; v1 submitted 26 May, 2025; originally announced May 2025.

Comments: Published 13 June, 2025

Journal ref: Phys. Rev. B 111, 224110 (2025)

Interlayer Coupling-Induced Quantum Phase Transition in Quantum Anomalous Hall Multilayers

Authors: Ling-Jie Zhou, Deyi Zhuo, Ruobing Mei, Yi-Fan Zhao, Kaijie Yang, Ruoxi Zhang, Zijie Yan, Han Tay, Moses H. W. Chan, Chao-Xing Liu, Cui-Zu Chang

Abstract: A quantum phase transition arises from competition between different ground states and is typically accessed by varying a single physical parameter near absolute zero temperature. The quantum anomalous Hall (QAH) effect with high Chern number C has recently been achieved in magnetic topological insulator (TI) multilayers. In this work, we employ molecular beam epitaxy to synthesize a series of mag… ▽ More A quantum phase transition arises from competition between different ground states and is typically accessed by varying a single physical parameter near absolute zero temperature. The quantum anomalous Hall (QAH) effect with high Chern number C has recently been achieved in magnetic topological insulator (TI) multilayers. In this work, we employ molecular beam epitaxy to synthesize a series of magnetic TI penta-layers by varying the thickness of the middle magnetic TI layer, designated as m quintuple layers. Electrical transport measurements demonstrate a quantum phase transition between C = 1 and C = 2 QAH states. For m 1 and m 2, the sample exhibits the well-quantized C = 1 and C = 2 QAH states, respectively. For 1 m 2, we observe a monotonic decrease in Hall resistance from h/e2 to h/2e2 with increasing m, accompanied by a peak in the longitudinal resistance. The quantum phase transition between C = 1 and C = 2 QAH states is attributed to the weakening of the interlayer coupling between the top and the bottom C = 1 QAH layers. Our findings provide a scalable strategy for engineering QAH devices with a tunable Chern number. This approach enables precise control and enhanced functionality in chiral edge current-based electronic devices. △ Less

Submitted 25 August, 2025; v1 submitted 30 April, 2025; originally announced May 2025.

Comments: 22 pages and 4 figures. Comments are welcome

Journal ref: Phys. Rev. B 111, L201304 (2025)

Response to recent comments on Phys. Rev. B 107, 245423 (2023) and Subsection S4.3 of the Supp. Info. for Nature 638, 651-655 (2025)

Authors: Morteza Aghaee, Zulfi Alam, Mariusz Andrzejczuk, Andrey E. Antipov, Mikhail Astafev, Amin Barzegar, Bela Bauer, Jonathan Becker, Umesh Kumar Bhaskar, Alex Bocharov, Srini Boddapati, David Bohn, Jouri Bommer, Leo Bourdet, Samuel Boutin, Benjamin J. Chapman, Sohail Chatoor, Anna Wulff Christensen, Patrick Codd, William S. Cole, Paul Cooper, Fabiano Corsetti, Ajuan Cui, Andreas Ekefjärd, Saeed Fallahi , et al. (105 additional authors not shown)

Abstract: The topological gap protocol (TGP) is a statistical test designed to identify a topological phase with high confidence and without human bias. It is used to determine a promising parameter regime for operating topological qubits. The protocol's key metric is the probability of incorrectly identifying a trivial region as topological, referred to as the false discovery rate (FDR). Two recent manuscr… ▽ More The topological gap protocol (TGP) is a statistical test designed to identify a topological phase with high confidence and without human bias. It is used to determine a promising parameter regime for operating topological qubits. The protocol's key metric is the probability of incorrectly identifying a trivial region as topological, referred to as the false discovery rate (FDR). Two recent manuscripts [arXiv:2502.19560, arXiv:2503.08944] engage with the topological gap protocol and its use in Phys. Rev. B 107, 245423 (2023) and Subsection S4.3 of the Supplementary Information for Nature 638, 651-655 (2025), although they do not explicitly dispute the main results of either one. We demonstrate that the objections in arXiv:2502.19560 and arXiv:2503.08944 are unfounded, and we uphold the conclusions of Phys. Rev. B 107, 245423 (2023) and Nature 638, 651-655 (2025). Specifically, we show that no flaws have been identified in our estimate of the false discovery rate (FDR). We provide a point-by-point rebuttal of the comments in arXiv:2502.19560 and arXiv:2503.08944. △ Less

Submitted 17 April, 2025; originally announced April 2025.

Comments: Response to arXiv:2502.19560 and arXiv:2503.08944. 11 pages, 5 figures, 2 tables, code for reproduction

Probing Temperature at Nanoscale through Thermal Vibration Characterization using Scanning Precession Electron Diffraction

Authors: Kun Yang, Chao Zhang, Chengwei Wu, Qian Du, Bingzhi Li, Zhen Fang, Liang Li, Jianbo Wu, Tianru Wu, Hui Wang, Tao Deng, Wenpei Gao

Abstract: Accurate, non-contact temperature measurement with high spatial resolution is essential for understanding thermal behavior in integrated nanoscale devices and heterogeneous interfaces. However, existing techniques are often limited by the need for physical contact or insufficient spatial resolution for the measurement of local temperature and mapping its distribution. Here, we showcase the direct… ▽ More Accurate, non-contact temperature measurement with high spatial resolution is essential for understanding thermal behavior in integrated nanoscale devices and heterogeneous interfaces. However, existing techniques are often limited by the need for physical contact or insufficient spatial resolution for the measurement of local temperature and mapping its distribution. Here, we showcase the direct temperature measurement of graphene with nanometer spatial resolution in transmission electron microscopy. In experiments, combining a scanning nanobeam with precession electron diffraction offers the collection of kinemetic diffraction from a local area at the nanometer scale. In analysis, we use a pre-calculated, sample-specific structure-factor-based correction method to enable the linear fitting of the diffraction intensities, allowing the determination of the Debye-Waller factor as a function of temperature at the precision of 10-4Å2/°C. With the high spatial resolution and measurement precision, the temperature and thermal vibration mapping further reveal the influence of graphene lattice parameters and thickness on the Debye-Waller factor, providing valuable insights into the vibrational properties impacted by temperature, lattice structure, and graphene layer thickness. △ Less

Submitted 14 April, 2025; originally announced April 2025.

Comments: 9 pages, 4 figures

Report number: 2026, Vol. 12, No. 7

Journal ref: Science Advances, 2026

Giant Orbital Torque-driven Picosecond Switching in Magnetic Tunnel Junctions

Authors: Yuxuan Yao, Chen Xiao, Xiaobai Ning, Wenlong Cai, Xianzeng Guo, Zongxia Guo, Kailin Yang, Danrong Xiong, Zhengjie Yan, Shiyang Lu, Hongchao Zhang, Siyuan Cheng, Renyou Xu, Dinghao Ma, Chao Wang, Zhaohao Wang, Daoqian Zhu, Kaihua Cao, Hongxi Liu, Aurélien Manchon, Weisheng Zhao

Abstract: Orbital Hall effect was recently discovered as a novel pathway for driving magnetic moment. However, the integration of orbital Hall effect in magnetic memories suffers from low orbital-to-spin conversion efficiency and incompatibility with magnetic tunnel junctions. Here we demonstrate an orbital Hall effect-driven magnetic tunnel junction based on Ru/W bilayer, where the Ru layer possesses a str… ▽ More Orbital Hall effect was recently discovered as a novel pathway for driving magnetic moment. However, the integration of orbital Hall effect in magnetic memories suffers from low orbital-to-spin conversion efficiency and incompatibility with magnetic tunnel junctions. Here we demonstrate an orbital Hall effect-driven magnetic tunnel junction based on Ru/W bilayer, where the Ru layer possesses a strong orbital Hall conductivity and the α-W layer features an orbital-to-spin conversion efficiency exceeding 90% because of the large orbit-spin diffusivity. By harnessing the giant orbital torque, we achieve a 28.7-picosecond switching and a five to eight-fold reduction in driving voltages over conventional spin-orbit torque magnetic memories. Our work bridges the critical gap between orbital effects and magnetic memory applications, significantly advancing the field of spintronics and orbitronics. △ Less

Submitted 11 April, 2025; originally announced April 2025.

Contrasting magnetism in VPS3 and CrI3 monolayers with the common honeycomb S = 3/2 spin lattice

Authors: Ke Yang, Yueyue Ning, Yaozhenghang Ma, Yuxuan Zhou, Hua Wu

Abstract: Two-dimensional (2D) magnetic materials are promising candidates for spintronics and quantum technologies. One extensively studied example is the ferromagnetic (FM) CrI$_3$ monolayer with the honeycomb Cr$^{3+}$ ($t_{2g}^3$, $S$ = 3/2) spin lattice, while VPS$_3$ has a same honeycomb $S$ = 3/2 spin lattice (V$^{2+}$, $t_{2g}^3$) but displays N$\acute{e}$el antiferromagnetism (AFM). In this work, w… ▽ More Two-dimensional (2D) magnetic materials are promising candidates for spintronics and quantum technologies. One extensively studied example is the ferromagnetic (FM) CrI$_3$ monolayer with the honeycomb Cr$^{3+}$ ($t_{2g}^3$, $S$ = 3/2) spin lattice, while VPS$_3$ has a same honeycomb $S$ = 3/2 spin lattice (V$^{2+}$, $t_{2g}^3$) but displays N$\acute{e}$el antiferromagnetism (AFM). In this work, we study the electronic structure and particularly the contrasting magnetism of VPS$_3$ and CrI$_3$ monolayers. We find that VPS$_3$ is a Mott-Hubbard insulator but CrI$_3$ is a charge-transfer insulator, and therefore their magnetic exchange mechanisms are essentially different. The first nearest-neighbor (1NN) direct $d$-$d$ exchange dominates in VPS$_3$, thus leading to a strong antiferromagnetic (AF) coupling. However, the formation of vanadium vacancies, associated with instability of the low-valence V$^{2+}$ ions, suppresses the AF coupling and thus strongly reduces the N$\acute{e}$el temperature ($T_{\text{N}}$) in line with the experimental observation. In contrast, our results reveal that the major 1NN $d$-$p$-$d$ superexchanges in CrI$_3$ via different channels give rise to competing FM and AF couplings, ultimately resulting in a weak FM coupling as observed experimentally. After revisiting several important superexchange channels reported in the literature, based on our MLWFs and tight-binding analyses, we note that some antiphase contributions must be subtly and simultaneously considered, and thus we provide a deeper insight into the FM coupling of CrI$_3$. Moreover, we identify and compare the major contributions to the magnetic anisotropy, i.e., a weak shape anisotropy in VPS$_3$ and a relatively strong exchange anisotropy in CrI$_3$. △ Less

Submitted 8 April, 2025; originally announced April 2025.

Comments: 16 pages, 12 figures, 3 tables

Journal ref: Phys. Rev. B 111, 134421 (2025)

Weyl Semimetals: from Principles, Materials to Applications

Authors: Mengyuan Zhong, Nam Thanh Trung Vu, Wenhao Zhai, Jian Rui Soh, Yuanda Liu, Jing Wu, Ady Suwardi, Huajun Liu, Guoqing Chang, Kian Ping Loh, Weibo Gao, Cheng-Wei Qiu, Joel K. W. Yang, Zhaogang Dong

Abstract: Weyl semimetals have attracted significant interest in condensed matter physics and materials science, due to their unique electronic and topological properties. These characteristics not only deepen our understanding of fundamental quantum phenomena, but also make Weyl semimetals promising candidates for advanced applications in electronics, photonics, and spintronics. This review provides a syst… ▽ More Weyl semimetals have attracted significant interest in condensed matter physics and materials science, due to their unique electronic and topological properties. These characteristics not only deepen our understanding of fundamental quantum phenomena, but also make Weyl semimetals promising candidates for advanced applications in electronics, photonics, and spintronics. This review provides a systematic overview of the field, covering theoretical foundations, material synthesis, engineering strategies, and emerging device applications. We first outline the key theoretical principles and distinctive properties of Weyl semimetals, followed by an examination of recent advancements that enhance their functional versatility. Finally, we discuss the critical challenges hindering their practical implementation and explore future development directions, along with the potential for expanding and enhancing their existing range of applications. By integrating discussions of both opportunities and obstacles, this review offers a balanced perspective on current progress and future directions in Weyl semimetal research. △ Less

Submitted 12 May, 2025; v1 submitted 1 April, 2025; originally announced April 2025.

Spontaneous Chern-Euler Duality Transitions

Authors: Kang Yang, Zhi Li, Peng Xue, Emil J. Bergholtz, Piet W. Brouwer

Abstract: Topological phase transitions are typically characterized by abrupt changes in a quantized invariant. Here we report a contrasting paradigm in non-Hermitian parity-time symmetric systems, where the topological invariant remains conserved, but its nature transitions between the Chern number, characteristic of chiral transport in complex bands, and the Euler number, which characterizes the number of… ▽ More Topological phase transitions are typically characterized by abrupt changes in a quantized invariant. Here we report a contrasting paradigm in non-Hermitian parity-time symmetric systems, where the topological invariant remains conserved, but its nature transitions between the Chern number, characteristic of chiral transport in complex bands, and the Euler number, which characterizes the number of nodal points in pairs of real bands. The transition features qualitative changes in the non-Abelian geometric phases during spontaneous parity-time symmetry breaking, where different quantized components become mutually convertible. Our findings establish a novel topological duality principle governing transitions across symmetry classes and reveal unique non-unitary features intertwining topology, symmetry, and non-Abelian gauge structure. △ Less

Submitted 27 March, 2025; originally announced March 2025.

Comments: 5+12 pages, 3 figures

Revealing Nanostructures in High-Entropy Alloys via Machine-Learning Accelerated Scalable Monte Carlo Simulation

Authors: Xianglin Liu, Kai Yang, Yongxiang Liu, Fanli Zhou, Dengdong Fan, Zongrui Pei, Pengxiang Xu, Yonghong Tian

Abstract: The computational cost of traditional first-principles method quickly becomes prohibitively expensive as the number of atoms increases. This challenge is further amplified by the need to evaluate finite-temperature properties with Monte Carlo (MC) simulations, which is inherently challenging to parallelize due to sequential Markov chain updates. Here, we introduce Scalable Monte Carlo (SMC), an ef… ▽ More The computational cost of traditional first-principles method quickly becomes prohibitively expensive as the number of atoms increases. This challenge is further amplified by the need to evaluate finite-temperature properties with Monte Carlo (MC) simulations, which is inherently challenging to parallelize due to sequential Markov chain updates. Here, we introduce Scalable Monte Carlo (SMC), an efficient MC simulation method that overcomes the parallelization bottlenecks in conventional MC simulation, reducing the computational complexity of a MC sweep from quadratic to linear. We present a GPU implementation of the SMC method, SMC-GPU, which simultaneously harnesses the thousands of processing cores on a GPU to accelerate the computation. By adopting a data-driven workflow that surrogates the computationally expensive density functional theory (DFT) with ML models, we demonstrate that SMC-GPU is capable of simulating systems of more than one-billion atoms, while maintaining the accuracy of first-principles methods. Using this unprecedented capability, we performed billion-atom MC simulations to investigate the nanostructure evolution of two important high-entropy alloys (HEAs), FeCoNiAlTi and MoNbTaW, in which the nanostructures are believed to be responsible for their superb mechanical properties. Our results reveal a rich diversity of nanostructures, including nanoparticles (NP), 3D-connected NP, and disorder protected nanophases. We quantitatively analyze the size, composition, and morphology of the nanostructures, as well as directly simulate the atom-probe-tomography (APT) needle. The results align well with available experimental observations. This work underscores the promising potential of leveraging large-scale MC simulation to explore the largely uncharted territory of nanostructure evolution in HEAs. △ Less

Submitted 12 August, 2025; v1 submitted 16 March, 2025; originally announced March 2025.

Photostriction Facilitates Relaxation of Lattice Distortion in Two-Dimensional Perovskites

Authors: Jin Zhang, Kun Yang, Jianxin Yu, Jia Zhang, Sheng Meng, Xinghua Shi, Wei-Hai Fang

Abstract: The photostriction effect, a light-induced mechanical deformation in materials, originates from the intricate interplay between lattice structure and electronic excitation. In photovoltaic semiconductors, this effect plays a crucial role in shaping non-equilibrium structural responses, yet its fundamental mechanism remains elusive. Here, we uncover lattice expansion and structural reconfiguration… ▽ More The photostriction effect, a light-induced mechanical deformation in materials, originates from the intricate interplay between lattice structure and electronic excitation. In photovoltaic semiconductors, this effect plays a crucial role in shaping non-equilibrium structural responses, yet its fundamental mechanism remains elusive. Here, we uncover lattice expansion and structural reconfiguration in two-dimensional (2D) perovskites driven by photoinduced excitation using first-principles calculations. Our findings reveal that the photoinduced carriers lead to a substantial lattice expansion by about 2%. The expanded lattice facilitates strain relaxation with the amplitude of 20% by increasing interatomic distances and reducing internal stresses, thereby enhancing structural stability. The lattice dynamics can be systematically engineered through photodoping density, unveiling a new pathway to modulate light-matter interactions in 2D perovskites. These insights not only advance the understanding of optically driven structural dynamics but also offer a guiding principle for optimizing next-generation high-efficiency photovoltaic devices and optoelectronics. △ Less

Submitted 15 March, 2025; originally announced March 2025.

Comments: 17 pages, 4 figures

Hydrogen Bond Strength Dictates the Rate-Limiting Steps of Diffusion in Proton-Conducting Perovskites:A Critical Length Perspective

Authors: Hang Ma, Jiajun Linghu, Nannan Han, Peng Feng, Yuling Zhuo, Ying Liang, Kunde Yang, Tianxing Ma, Zhi-Peng Li

Abstract: Identifying the rate-limiting step of proton migration in proton-conducting oxides is essential for assessing and regulating proton conductivity. Proton migration based on the Grotthuss mechanism involves both proton rotation and proton transfer, with the latter typically regarded as the rate-limiting step. However, a universal criterion for identifying the rate-limiting step remains to be establi… ▽ More Identifying the rate-limiting step of proton migration in proton-conducting oxides is essential for assessing and regulating proton conductivity. Proton migration based on the Grotthuss mechanism involves both proton rotation and proton transfer, with the latter typically regarded as the rate-limiting step. However, a universal criterion for identifying the rate-limiting step remains to be established. Here, we perform a quantitative decomposition of the rotation and transfer barriers, revealing that the hydrogen bond to the acceptor oxygen dictates their energy barrier difference via the O$_i$-B-O$_f$ bending mechanism. Based on the energy difference associated with a one-order-of-magnitude variation in residence time, we propose the hydrogen bond length criterion for identifying the rate-limiting step across operating temperatures. Taking the 500 K criterion as an upper limit, when the hydrogen-bond length of systems falls below 2.05~Å, proton rotation becomes competitive with transfer. Applied to a wider range of perovskite materials, this criterion predicts comparable rotation and transfer rates in cubic structures with small lattice constants, low-valent B-site doped systems with moderate ionic radii, and distorted orthorhombic structures. Our findings provide an atomic-scale insight into the proton migration mechanisms in perovskites, and offer practical guidance for optimizing and designing advanced proton-conducting electrolytes. △ Less

Submitted 18 July, 2026; v1 submitted 10 March, 2025; originally announced March 2025.

Comments: 11 Figures with a Supplemental Material

Journal ref: Chem. Mater. 38, 6069(2026)

Exceptional topology on nonorientable manifolds

Authors: J. Lukas K. König, Kang Yang, André Grossi Fonseca, Sachin Vaidya, Marin Soljačić, Emil J. Bergholtz

Abstract: We classify gapped phases and characteristic nodal points of non-Hermitian band structures on two-dimensional nonorientable parameter spaces. Such spaces arise in a wide range of physical systems in the presence of nonsymmorphic parameter space symmetries. For gapped phases, we find that nonorientable spaces provide a natural setting for exploring fundamental structural problems in braid group the… ▽ More We classify gapped phases and characteristic nodal points of non-Hermitian band structures on two-dimensional nonorientable parameter spaces. Such spaces arise in a wide range of physical systems in the presence of nonsymmorphic parameter space symmetries. For gapped phases, we find that nonorientable spaces provide a natural setting for exploring fundamental structural problems in braid group theory, such as torsion and conjugacy. Gapless systems, which host exceptional points (EPs), explicitly violate fermion doubling, even in two-band models. We demonstrate that EPs traversing the nonorientable parameter space exhibit non-Abelian charge inversion. These braided phases and their transitions leave distinct signatures in the form of bulk Fermi arc degeneracies, offering a concrete route toward experimental realization and verification. △ Less

Submitted 27 March, 2026; v1 submitted 6 March, 2025; originally announced March 2025.

Comments: 11+4 pages, 4+1 figures

Journal ref: Phys. Rev. Research 8, 013233 (2026)

Magnetoelectric Control of Helical Light Emission in a Moiré Chern Magnet

Authors: Eric Anderson, Heonjoon Park, Kaijie Yang, Jiaqi Cai, Takashi Taniguchi, Kenji Watanabe, Liang Fu, Ting Cao, Di Xiao, Xiaodong Xu

Abstract: Magnetoelectric effects and their coupling to light helicity are important for both fundamental science and applications in sensing, communication, and data storage. Traditional approaches require complex device architectures, involving separate spin-injection, ferromagnetic, and optically active layers. Recently, the emergence of 2D semiconductor moiré superlattices with flat Chern bands and stro… ▽ More Magnetoelectric effects and their coupling to light helicity are important for both fundamental science and applications in sensing, communication, and data storage. Traditional approaches require complex device architectures, involving separate spin-injection, ferromagnetic, and optically active layers. Recently, the emergence of 2D semiconductor moiré superlattices with flat Chern bands and strong light-matter interactions has established a simple yet powerful platform for exploring the coupling between photon, electron, and spin degrees of freedom. Here, we report efficient current control of spontaneous ferromagnetism and associated helicity of light emission in moiré MoTe2 bilayer - a system which hosts a rich variety of topological phases, including newly discovered zero-field fractional Chern insulators. We show that the current control is effective over a wide range of doping of the first moiré Chern band, implying the uniformity of the Berry curvature distribution over the flat band. By setting the system into the anomalous Hall metal phase, a current as small as 10nA is sufficient to switch the magnetic order, a substantial improvement over both conventional spin torque architectures and other moiré systems. The realized current control of ferromagnetism leads to continuous tuning of trion photoluminescence helicity from left to right circular via spin/valley Hall torque at zero magnetic field. Our results pave the way for topological opto-spintronics based on semiconductors with synthetic flat Chern bands. △ Less

Submitted 4 March, 2025; originally announced March 2025.

Comments: 16 pages, 4 figures, plus supplementary material

Coexistence of topological surface states and superconductivity in Dirac semimetal NiTe$_2$

Authors: Chen He, Jian-Zhou Zhao, Mei Du, Luo-Zhao Zhang, Jia-Ying Zhang, Kuo Yang, Noah F. Q. Yuan, Aleksandr Seliverstov, Ewald Janssens, Jun-Yi Ge, Zhe Li

Abstract: The coexistence of topological bands around the Fermi level ($E_F$) and superconductivity provides a fundamental platform for exploring their interplay. However, few materials inherently display both properties. In this study, we demonstrate the coexistence of topological surface states at the $E_F$ and superconductivity in NiTe$_2$ single crystals, a material hitherto not recognized as supercondu… ▽ More The coexistence of topological bands around the Fermi level ($E_F$) and superconductivity provides a fundamental platform for exploring their interplay. However, few materials inherently display both properties. In this study, we demonstrate the coexistence of topological surface states at the $E_F$ and superconductivity in NiTe$_2$ single crystals, a material hitherto not recognized as superconducting. Quasiparticle interference measurements performed via scanning tunneling microscopy suggest the presence of topological surface states at the $E_F$, which is further corroborated by density functional theory simulations. Experimental evidence for superconductivity is provided via electronic transport measurements and specific heat capacity analyses. Our results suggest that NiTe$_2$ represents a promising platform for investigating the rich interplay between topological states and superconductivity. △ Less

Submitted 3 March, 2025; originally announced March 2025.

A two-dimensional semiconductor-semimetal drag hybrid

Authors: Yingjia Liu, Kaining Yang, Kenji Watanabe, Takashi Taniguchi, Wencai Ren, Zheng Vitto Han, Siwen Zhao

Abstract: Lateral charge transport of a two-dimensional (2D) electronic system can be much influenced by feeding a current into another closely spaced 2D conductor, known as the Coulomb drag phenomenon -- a powerful probe of electron-electron interactions and collective excitations. Yet the materials compatible for such investigations remain limited to date. Especially, gapped 2D semiconductors with inheren… ▽ More Lateral charge transport of a two-dimensional (2D) electronic system can be much influenced by feeding a current into another closely spaced 2D conductor, known as the Coulomb drag phenomenon -- a powerful probe of electron-electron interactions and collective excitations. Yet the materials compatible for such investigations remain limited to date. Especially, gapped 2D semiconductors with inherently large correlations over a broad gate range have been rarely accessible at low temperatures. Here, we show the emergence of a large drag response (drag resistance $R_{\text{drag}}$ at the order of k$Ω$, with a passive-to-active drag ratio up to $\sim$ 0.6) in a semiconductor-semimetal hybrid, realized in a graphene-MoS$_{2}$ heterostructure isolated by an ultrathin 3 nm hexagonal boron nitride (h-BN) dielectric. We observe a crossover of $T$ to $T^{2}$ dependence of $R_{\text{drag}}$, separated by a characteristic temperature $T_{d} \sim E_{F}/k_{F}d$ ($d$ being the interlayer distance), in echo with the presence of a metal-insulator transition in the semiconducting MoS$_{2}$. Interestingly, the current nanostructure allows the decoupling of intralayer interaction-driven drag response by varying density in one layer with that in the other layer kept constant. A large Wigner-Seitz radius $r_{s}$ ($>$ 10 within the density range of 1 to $4 \times 10^{12}~\mathrm{cm}^{-2}$) in the massive Schrödinger carriers in MoS$_{2}$ is thus identified to dominate the quadratic dependence of total carriers in the drag system, while the massless Dirac carriers in graphene induce negligible drag responses as a function of carrier density. Our findings establish semiconductor-semimetal hybrid as a platform for studying unique interaction physics in Coulomb drag systems. △ Less

Submitted 2 March, 2025; originally announced March 2025.

Comments: 14 pages, 8 figures

Photoexcitation-induced Stacking Transition Assisted by Intralayer Reconstruction in Charge-Density-Wave Materials

Authors: Jin Zhang, Yang Yang, Jia Zhang, Mengxue Guan, Jiyu Xu, Kun Yang, Xinghua Shi, Sheng Meng

Abstract: Laser excitation has emerged as an effective tool for probing microscopic interactions and manipulating phases of matter. Among charge density wave (CDW) materials, 1T-TaS2 has garnered significant attention due to its diverse stacking orders and photoexcited responses. However, the mechanisms driving transitions among different stacking orders and the microscopic out-of-equilibrium dynamics remai… ▽ More Laser excitation has emerged as an effective tool for probing microscopic interactions and manipulating phases of matter. Among charge density wave (CDW) materials, 1T-TaS2 has garnered significant attention due to its diverse stacking orders and photoexcited responses. However, the mechanisms driving transitions among different stacking orders and the microscopic out-of-equilibrium dynamics remain unclear. We elucidate that photoexcitation can introduce interlayer stacking order transitions facilitated by laser-induced intralayer reconstruction in 1T-TaS2. Importantly, our finding reveals a novel pathway to introduce different phases through laser excitations, apparently distinct from thermally-induced phase transitions via interlayer sliding. In particular, photoexcitation is able to considerably change potential energy surfaces and evoke collective lattice dynamics. Consequently, the laser-induced intralayer reconstruction plays a crucial role in interlayer stacking-order transition, offering a new method to create exotic stackings and quantum phases. The exploration opens up great opportunities for manipulating CDW phases and electronic properties on the femtosecond timescale. △ Less

Submitted 25 February, 2025; originally announced February 2025.

Comments: 10 pages, 4 figures