Showing 1–50 of 124 results for author: Gao, M

Entanglement spectrum ordering and flavor polarization in the two-flavor Schwinger model at vacuum angle $θ= π$

Authors: Boliang Yu, Ruixin Zhou, Meisen Gao

Abstract: Entanglement spectra in gauge theories can encode both symmetry breaking and the organization of gauge sectors. In the two-flavor Schwinger model at vacuum angle $θ=π$, we find that the joint Schmidt distribution $p_{Q_A,F_A}$, labeled by the subsystem gauge charge $Q_A$ and flavor imbalance $F_A$, reveals a cut-dependent gauge-sector hierarchy and a mass-induced flavor asymmetry: changing the sta… ▽ More Entanglement spectra in gauge theories can encode both symmetry breaking and the organization of gauge sectors. In the two-flavor Schwinger model at vacuum angle $θ=π$, we find that the joint Schmidt distribution $p_{Q_A,F_A}$, labeled by the subsystem gauge charge $Q_A$ and flavor imbalance $F_A$, reveals a cut-dependent gauge-sector hierarchy and a mass-induced flavor asymmetry: changing the staggered cut reorganizes the gauge-charge distribution $p_{Q_A}$, while mass imbalance breaks the $F_A\leftrightarrow-F_A$ symmetry of the conditional flavor distribution $p_{F_A|Q_A}$. Defining the combined weight $W_F^{(q)}=p_{q,+1}+p_{q,-1}$ and conditional polarization $\mathcal P_F^{(q)}=(p_{q,+1}-p_{q,-1})/W_F^{(q)}$, we find that changing the cut reverses the weight hierarchy, $W_F^{(-1)}>W_F^{(+1)}$ at unit-cell boundaries but $W_F^{(+1)}>W_F^{(-1)}$ at intra-cell cuts, while mass imbalance drives $\mathcal P_F^{(q)}$ away from zero with a $q$-dependent cut response. Symmetry resolution therefore separates gauge-sector ordering, sector weight, and flavor polarization that are mixed in the globally ordered entanglement spectrum. △ Less

Submitted 16 August, 2026; v1 submitted 14 August, 2026; originally announced August 2026.

Comments: 21 pages, 6 figures. Submitted to $\textit{Chinese Physics C}$

Screening phonon-mediated superconductors from static orbital Hamiltonians

Authors: Jian-Feng Zhang, Ze-Feng Gao, Xiao-Qi Han, Dingshun Lv, Miao Gao, Kai Liu, Xinguo Ren, Zhong-Yi Lu, Tao Xiang

Abstract: The first-principles search for superconductors is severely limited by the high cost of electron-phonon coupling (EPC) calculations. Here we develop a low-cost, physically transparent framework that identifies strong-EPC materials directly from static orbital-based Hamiltonians without explicit phonon perturbation calculations. Verification using density functional perturbation theory (DFPT) for r… ▽ More The first-principles search for superconductors is severely limited by the high cost of electron-phonon coupling (EPC) calculations. Here we develop a low-cost, physically transparent framework that identifies strong-EPC materials directly from static orbital-based Hamiltonians without explicit phonon perturbation calculations. Verification using density functional perturbation theory (DFPT) for representative superconductors shows that the framework captures semi-quantitatively the EPC scale at substantially lower computational cost. Applied to more than 36,000 compounds in the MattKeyBond database, it identifies 34 dynamically stable superconducting candidates with calculated $T_c > 10$ K after DFPT verification. These candidates reveal two distinct routes to relatively high-$T_c$ superconductivity: a metallized covalent $σ$-bond route that is more favorable for achieving high-$T_c$ superconductors, and a Fermi-level density-of-states accumulation route that can enhance $T_c$ but usually to a more limited extent. △ Less

Submitted 3 August, 2026; originally announced August 2026.

Comments: 12 pages, 5 figures, 2 tables

Hybrid-order nonlinear topological phases

Authors: Yu-Peng Ma, Ming-Jian Gao, Jun-Hong An

Abstract: The bulk-boundary correspondence (BBC), which relates topological invariants to boundary modes, is well understood for linear systems but remains an open question in the presence of nonlinearity, where multigap topologies make the BBC obscure and the topological description troublesome. We address this by developing an auxiliary-system formalism that enables topological classification of nonlinear… ▽ More The bulk-boundary correspondence (BBC), which relates topological invariants to boundary modes, is well understood for linear systems but remains an open question in the presence of nonlinearity, where multigap topologies make the BBC obscure and the topological description troublesome. We address this by developing an auxiliary-system formalism that enables topological classification of nonlinear-eigenvalue systems. In the two-dimension (2D) case, we show that two fixed eigenvalues can harbor first-order gapless boundary modes and second-order corner modes. Stacking this 2D system along the third dimension (3D) reveals distinct hybrid-order realizations. Under uniform stacking, the corner states in the $xy$ plane transform into hinge states along the $z$ axis, yielding a 3D second-order phase, while the gapless boundary states become side-surface states, yielding a 3D first-order phase. For dimerized stacking, these states are further confined to the two ends of the $z$ axis, yielding a 3D third-order phase, and localized at the hinges, yielding a 3D second-order phase. Our results establish a multiband bulk-boundary correspondence and identify stacking engineering as a versatile platform for exploring hybrid-order topological phases in nonlinear systems. △ Less

Submitted 3 July, 2026; originally announced July 2026.

Probing Quantum Geometric Phases via Scanning Tunneling Microscopy

Authors: Chao Yan, Mu-Wei Gao, Yue Zhao, Jia-Xin Yin

Abstract: The quantum geometric phase intrinsically dictates the geometry, topology, and many-body correlations of electronic wave functions. While quantum geometric phases are conventionally inferred through momentum-space probes or macroscopic transport measurements, their direct visualization and quantification in real space have historically been restricted by the spatial averaging of bulk techniques. S… ▽ More The quantum geometric phase intrinsically dictates the geometry, topology, and many-body correlations of electronic wave functions. While quantum geometric phases are conventionally inferred through momentum-space probes or macroscopic transport measurements, their direct visualization and quantification in real space have historically been restricted by the spatial averaging of bulk techniques. Scanning tunneling microscopy and spectroscopy (STM/STS) circumvent this limitation, leveraging atomic-scale spatial resolution and high energy sensitivity to resolve local electronic phase profiles directly. This review highlights recent progress across four representative methodologies: probing the Aharonov-Bohm (AB) geometric phase via nanoscale real space interferometry; extracting the Berry phase from defect-induced quasiparticle interference and wavefront dislocations; reconstructing the complex phase structure in symmetric systems, such as magic-angle graphene, using order parameter decomposition; and mapping the phase textures and topological defects of pair density wave (PDW) and charge density wave (CDW) in unconventional superconductors utilizing the numerical 2D lock-in technique. Together, these developments show how quantum phases can be translated onto real space and locally resolvable observables. Phase-resolved STM imaging provides stringent constraints on topological states of matter, symmetry-breaking patterns, and strong electronic correlations, outlining a robust framework for in situ phase engineering in quantum materials. △ Less

Submitted 5 July, 2026; v1 submitted 28 June, 2026; originally announced June 2026.

Journal ref: Acta Physica Sinica. 2026, 75(12): 120701

Speculative Sampling For Faster Molecular Dynamics

Authors: Arthur Kosmala, Stephan Günnemann, Meng Gao, Brandon Wood

Abstract: Molecular dynamics (MD) is a key tool for simulating the dynamical behavior of atomic systems. However, MD is inherently serial, which makes it difficult to increase single-system throughput with concurrent compute. To address this, we introduce Langevin Speculative Dynamics (LSD), a distributed and model-agnostic speculative sampler for accelerating MD without adding relative error. Inspired by s… ▽ More Molecular dynamics (MD) is a key tool for simulating the dynamical behavior of atomic systems. However, MD is inherently serial, which makes it difficult to increase single-system throughput with concurrent compute. To address this, we introduce Langevin Speculative Dynamics (LSD), a distributed and model-agnostic speculative sampler for accelerating MD without adding relative error. Inspired by speculative methods in language and diffusion modeling, LSD uses a draft model to propose fast simulation steps and verifies them in parallel with a slower target model, applying a transport map from the draft to the target distribution. We extend speculative sampling to second-order Langevin dynamics, derive the achievable speedup as a function of physical parameters, show that LSD generalizes across different systems and draft-target combinations with a 3-9x speedup, and confirm theoretically and empirically that LSD samples trajectories from its target model distribution. △ Less

Submitted 1 June, 2026; originally announced June 2026.

Comments: Forty-Third International Conference on Machine Learning (ICML 2026). 32 pages, 14 figures, 8 tables

Josephson spectroscopy study of kagome superconductors toward the deep point-contact regime

Authors: Hailang Qin, Xiao-Yu Yan, Hanbin Deng, Mu-Wei Gao, Guowei Liu, Yuanyuan Zhao, Jia-Xin Yin

Abstract: Josephson scanning tunneling microscopy (JSTM) has emerged as an important technique for probing the superconducting order parameter at the atomic scale. However, the Josephson current in JSTM may behave quite differently when the coupling strength varies. Here, we push the junction to the deep point-contact regime, reaching a normal-state junction resistance of only 0.15… ▽ More Josephson scanning tunneling microscopy (JSTM) has emerged as an important technique for probing the superconducting order parameter at the atomic scale. However, the Josephson current in JSTM may behave quite differently when the coupling strength varies. Here, we push the junction to the deep point-contact regime, reaching a normal-state junction resistance of only 0.15 $h/2e^2 \simeq 2~{\rm k}Ω$. We demonstrate, using kagome superconductors, that the zero-bias conductance, a key characteristic of the Josephson current, deviates strongly from the quadratic dependence on the normal-state conductance upon entering the deep point-contact regime. Furthermore, we observe a striking saturation of the zero-bias conductance, which we show arises from the series resistance in the circuit. This also serves as a cautious reminder when interpreting zero-bias conductance saturation or quantization in studies of exotic physics such as that of Majorana zero modes if the tip-sample junction resistance is extremely small. Finally, we identify an optimum regime where JSTM can be used as an atomic-scale probe for studying pair-density wave states in materials with low superconducting transition temperature, such as AV3Sb5 kagome superconductors. △ Less

Submitted 7 May, 2026; originally announced May 2026.

Comments: 13 Pages, 4 figures

Journal ref: Phys. Rev. B 113, 174502 (2026)

Building a physics-aware AI ecosystem for solid-state hydrogen storage materials

Authors: Seong-Hoon Jang, Yiwen Yao, Chuanyu Liu, Linda Zhang, Di Zhang, Xue Jia, Hung Ba Tran, Eric Jianfeng Cheng, Ryuhei Sato, Yusuke Ohashi, Toyoto Sato, Yusuke Hashimoto, Mark Allendorf, Nongnuch Artrith, Marcello Baricco, Andreas Borgschulte, Darren P. Broom, Ang Cao, Benjamin W. J. Chen, Lixin Chen, Ping Chen, Eun Seon Cho, Stefano Deledda, Zhao Ding, Martin Dornheim , et al. (44 additional authors not shown)

Abstract: Hydrogen storage remains a central bottleneck for scalable hydrogen energy systems due to the multiscale and coupled nature of the thermodynamics, kinetics, and microstructural evolution of hydrogen storage materials (HSMs). Although artificial intelligence (AI) has accelerated materials discovery, current approaches remain constrained by fragmented data, limited physical consistency, and weak int… ▽ More Hydrogen storage remains a central bottleneck for scalable hydrogen energy systems due to the multiscale and coupled nature of the thermodynamics, kinetics, and microstructural evolution of hydrogen storage materials (HSMs). Although artificial intelligence (AI) has accelerated materials discovery, current approaches remain constrained by fragmented data, limited physical consistency, and weak integration with experimental validation. Here, we propose a unified framework that integrates coherent data infrastructure, physics-grounded modeling, and AI-driven inverse design within a closed-loop discovery paradigm. By embedding physical constraints and experimental feedback, this approach enables adaptive, physically consistent optimization, thereby establishing a pathway toward autonomous, digital-twin-enabled discovery of HSMs. △ Less

Submitted 19 May, 2026; v1 submitted 4 May, 2026; originally announced May 2026.

Bridging Crystal Structure and Material Properties via Bond-Centric Descriptors

Authors: Jian-Feng Zhang, Ze-Feng Gao, Xiao-Qi Han, Bo Zhan, Dingshun Lv, Miao Gao, Kai Liu, Xinguo Ren, Zhong-Yi Lu, Tao Xiang

Abstract: Although chemical bonding is the fundamental mechanistic bridge connecting atomic structure to macroscopic material properties, current data-driven materials science largely treats it as an implicit "black box". Existing machine learning (ML) models rely predominantly on geometric coordinates, forcing them to implicitly relearn complex quantum mechanics from scratch. This lack of intermediate phys… ▽ More Although chemical bonding is the fundamental mechanistic bridge connecting atomic structure to macroscopic material properties, current data-driven materials science largely treats it as an implicit "black box". Existing machine learning (ML) models rely predominantly on geometric coordinates, forcing them to implicitly relearn complex quantum mechanics from scratch. This lack of intermediate physical features limits model interpretability and generalizability, particularly when training data is scarce. To solve this problem, we introduce MattKeyBond, a bond-centric materials database that explicitly maps the local electronic landscape and bonding interactions of materials. Building on this, we propose Bonding Attractivity (BA), a novel element-specific descriptor that quantifies the intrinsic capability of atoms to form covalent networks. By providing pre-calculated, energy-dimensional bonding descriptors, MattKeyBond transforms the implicit "black box" into physically interpretable features. This strategy relieves ML models from the burden of deducing physical laws from pure geometry, enabling accurate predictions even with limited data and seamlessly integrating electronic structure theory into modern AI workflows. △ Less

Submitted 27 July, 2026; v1 submitted 19 March, 2026; originally announced March 2026.

Comments: 17 pages, 10 figures

$σ$ bands driven high-temperature superconductivity in hydrogenated hexagonal BC$_3$ monolayer

Authors: Guo Chen, Ru Zheng, Jin-Hua Sun, Fengjie Ma, Xun-Wang Yan, Miao Gao, Tian Cui, Zhong-Yi Lu

Abstract: Material with metallic $σ$-bonding bands is expected to be a high-temperature superconductor, due to the sensitivity of $σ$ electrons to lattice vibration. Based on the first-principles calculations, electronic structures of hydrogenated BC$_3$ monolayers (H$_n$-B$_2$C$_6$ with $n$=1-8) are systematically investigated. At high coverage of hydrogen, the monolayer stabilizes in chair-like $sp^3$-hyb… ▽ More Material with metallic $σ$-bonding bands is expected to be a high-temperature superconductor, due to the sensitivity of $σ$ electrons to lattice vibration. Based on the first-principles calculations, electronic structures of hydrogenated BC$_3$ monolayers (H$_n$-B$_2$C$_6$ with $n$=1-8) are systematically investigated. At high coverage of hydrogen, the monolayer stabilizes in chair-like $sp^3$-hybridized configurations, leading to the metallization of $σ$ bands, especially in H$_7$-B$_2$C$_6$ and H$_8$-B$_2$C$_6$. This metallicity originates from the electron deficiency of boron, compared with insulating graphane. Utilizing Wannier interpolation, the electron-phonon coupling strengths for metallic phases of H$_n$-B$_2$C$_6$ are determined. As expected, strong couplings are identified between the conducting $σ$ electrons and low-frequency phonon modes. By solving the anisotropic Eliashberg equations, we confirm that H$_7$-B$_2$C$_6$ and H$_8$-B$_2$C$_6$ are single-gap superconductors with critical temperature being 87 K, exceeding the boiling point of liquid nitrogen. Considering that monolayer BC$_3$ has been synthesized in experiment, our results demonstrate that hydrogenation of two-dimensional BC$_3$ provides a viable pathway to achieve high-temperature superconductivity at ambient pressure. △ Less

Submitted 28 February, 2026; originally announced March 2026.

Comments: 6 pages, 6 figures

Journal ref: Chin. Phys. Lett. 43, 060709 (2026)

Strain-triggered high-temperature superconducting transition in two-dimensional carbon allotrope

Authors: Tian Yan, Ru Zheng, Jin-Hua Sun, Fengjie Ma, Xun-Wang Yan, Miao Gao, Tian Cui, Zhong-Yi Lu

Abstract: Driving non-superconducting materials into a superconducting state through specific modulation is a key focus in the field of superconductivity. Pressure is a powerful method that can switch a three-dimensional (3D) material between non-superconducting and superconducting states. In the two-dimensional (2D) case, strain engineering plays a similar role to pressure. However, purely strain-induced s… ▽ More Driving non-superconducting materials into a superconducting state through specific modulation is a key focus in the field of superconductivity. Pressure is a powerful method that can switch a three-dimensional (3D) material between non-superconducting and superconducting states. In the two-dimensional (2D) case, strain engineering plays a similar role to pressure. However, purely strain-induced superconductivity in 2D systems remains exceedingly scarce. Using first-principles calculations, we demonstrate that a superconducting transition can be induced solely by applying biaxial tensile strain in a 2D carbon allotrope, THO-graphene, which is composed of triangles, hexagons, and octagons. Free-standing THO-graphene is non-superconducting. Surprisingly, the electron-phonon coupling in strained THO-graphene is enhanced strong enough to pair electrons and realize superconductivity, with the highest superconducting transition temperature reaching 45 K. This work not only provides a notable example of controlling metal-superconductor transition in 2D system just via strain, but also sets a new record of superconducting transition temperature for 2D elemental superconductors. △ Less

Submitted 3 January, 2026; originally announced January 2026.

Comments: 7 pages, 5 figures

Journal ref: Front. Phys. 21, 125205 (2026)

Topological Phases in Non-Hermitian Nonlinear-Eigenvalue Systems

Authors: Yu-Peng Ma, Ming-Jian Gao, Jun-Hong An

Abstract: The discovery of topological phases has ushered in a new era of condensed matter physics and revealed a variety of natural and artificial materials. They obey the bulk-boundary correspondence (BBC), which guarantees the emergence of boundary states with nonzero topological invariants in the bulk. Widespread attention has been paid to extending topological phases to nonlinear and non-Hermitian syst… ▽ More The discovery of topological phases has ushered in a new era of condensed matter physics and revealed a variety of natural and artificial materials. They obey the bulk-boundary correspondence (BBC), which guarantees the emergence of boundary states with nonzero topological invariants in the bulk. Widespread attention has been paid to extending topological phases to nonlinear and non-Hermitian systems. However, the BBC and topological invariants of non-Hermitian nonlinear systems remain largely unexplored. Here, we establish a complete BBC and topological characterization of the topological phases in a class of non-Hermitian nonlinear-eigenvalue systems by introducing an auxiliary system. We restore the BBC broken by non-Hermiticity via employing the generalized Brillouin zone on the auxiliary system. Remarkably, we discover that the interplay between non-Hermiticity and nonlinearity creates an exotic complex-band topological phase that coexists with the real-band topological phase. Our results enrich the family of nonlinear topological phases and lay a foundation for exploring novel topological physics in metamaterial systems. △ Less

Submitted 5 March, 2026; v1 submitted 17 November, 2025; originally announced November 2025.

Journal ref: Phys. Rev. B 113, L121401 (2026)

Distortion-Driven Carrier Decoupling in Doped LiMgPO4

Authors: Zhihua Zheng, Xiaolong Yao, Cailian Yu, Menghao Gao, Fangping Ouyang, Shiwu Gao

Abstract: The interplay between lattice distortions and charge carriers governs the properties of many functional oxides. In alkali-doped LiMgPO4, a significant enhancement in dosimetric response is observed, but its microscopic origin is not understood. Using non-adiabatic molecular dynamics, we reveal a fundamental mechanism of carrier decoupling driven by a hierarchy of lattice distortions. We show that… ▽ More The interplay between lattice distortions and charge carriers governs the properties of many functional oxides. In alkali-doped LiMgPO4, a significant enhancement in dosimetric response is observed, but its microscopic origin is not understood. Using non-adiabatic molecular dynamics, we reveal a fundamental mechanism of carrier decoupling driven by a hierarchy of lattice distortions. We show that electrons localize into stable small polarons on an ultrafast timescale, trapped by the strong local potential induced by the dopant, while holes form more delocalized polarons that migrate efficiently through a lattice smoothed by global strain. The stark contrast between the dynamics of trapped electrons and mobile holes explains the suppressed recombination and enhanced energy storage. These results present a clear physical picture of how multiscale lattice distortions can independently control electron and hole transport, offering new insights into the physics of polarons in complex materials. △ Less

Submitted 1 December, 2025; v1 submitted 16 November, 2025; originally announced November 2025.

Electron-phonon coupling of one-dimensional (3,0) carbon nanotube

Authors: Zhenfeng Ouyang, Jing Jiang, Jian-Feng Zhang, Miao Gao, Kai Liu, Zhong-Yi Lu

Abstract: A very recent report claims that ambient-pressure high-temperature ($T_c$) superconductivity was found in boron-doped three-dimensional networks of carbon nanotubes (CNTs). Here, we systematically study the electron-phonon coupling (EPC) of one-dimensional (1D) (3,0) CNT under ambient pressure. Our results show that the EPC constant $λ$ of the undoped 1D (3,0) CNT is 0.70, and reduces to 0.44 afte… ▽ More A very recent report claims that ambient-pressure high-temperature ($T_c$) superconductivity was found in boron-doped three-dimensional networks of carbon nanotubes (CNTs). Here, we systematically study the electron-phonon coupling (EPC) of one-dimensional (1D) (3,0) CNT under ambient pressure. Our results show that the EPC constant $λ$ of the undoped 1D (3,0) CNT is 0.70, and reduces to 0.44 after 1.3 holes/cell doping. Further calculations show that the undoped (3,0) CNT is a two-gap superconductor with a superconducting $T_c$ $\sim$ 33 K under ambient pressure. Additionally, we identify three characteristic phonon modes with strong EPC, establishing that the pristine (3,0) CNT is a high-$T_c$ superconducting unit, and further suggest that searching for those superconducting units with strong EPC phonon mode would be an effective way to discover high-$T_c$ phonon-mediated superconductors. Our study not only provide a crucial and timely theoretical reference for the recent report regarding superconducting CNTs, but also uncover that the pristine (3,0) CNT hosts the highest record of superconducting $T_c$ among the elemental superconductors under ambient pressure. △ Less

Submitted 5 November, 2025; originally announced November 2025.

Comments: 6 pages, 5 figures, 1 table

COFAP: A Universal Framework for COFs Adsorption Prediction through Designed Multi-Modal Extraction and Cross-Modal Synergy

Authors: Zihan Li, Mingyang Wan, Mingyu Gao, Xishi Tai, Zhongshan Chen, Xiangke Wang, Feifan Zhang

Abstract: Covalent organic frameworks (COFs) are promising adsorbents for gas adsorption and separation, while identifying the optimal structures among their vast design space requires efficient high-throughput screening. Conventional machine-learning predictors rely heavily on specific gas-related features. However, these features are time-consuming and limit scalability, leading to inefficiency and labor-… ▽ More Covalent organic frameworks (COFs) are promising adsorbents for gas adsorption and separation, while identifying the optimal structures among their vast design space requires efficient high-throughput screening. Conventional machine-learning predictors rely heavily on specific gas-related features. However, these features are time-consuming and limit scalability, leading to inefficiency and labor-intensive processes. Herein, a universal COFs adsorption prediction framework (COFAP) is proposed, which can extract multi-modal structural and chemical features through deep learning, and fuse these complementary features via cross-modal attention mechanism. Without relying on explicit gas-specific thermodynamic descriptors, COFAP achieves state-of-the-art prediction performance on the hypoCOFs dataset under the conditions investigated in this study, outperforming existing approaches. Based on COFAP, we also found that high-performing COFs for gas separation concentrate within a narrow range of pore size and surface area. A weight-adjustable prioritization scheme is also developed to enable flexible, application-specific ranking of candidate COFs for researchers. Superior efficiency and accuracy render COFAP directly deployable in crystalline porous materials. △ Less

Submitted 23 March, 2026; v1 submitted 3 November, 2025; originally announced November 2025.

Switchable chiral 2x2 pair density wave in pure CsV3Sb5

Authors: Wei Song, Xiao-Yu Yan, Xin Yu, Desheng Wu, Deng Hu, Hailang Qin, Guowei Liu, Hanbin Deng, Chao Yan. Muwei Gao, Zhiwei Wang, Rui Wu, Jia-Xin Yin

Abstract: We investigate electron pairing in a super clean kagome superconductor CsV3Sb5 with a residual resistivity ratio (RRR) of 290. By using the dilution-refrigerator-based scanning tunneling microscopy (STM) at the Synergetic Extreme Condition User Facility (SECUF), we find that the pairing gap exhibits chiral 2x2 modulations, and their chirality can be controlled by magnetic field training. We introd… ▽ More We investigate electron pairing in a super clean kagome superconductor CsV3Sb5 with a residual resistivity ratio (RRR) of 290. By using the dilution-refrigerator-based scanning tunneling microscopy (STM) at the Synergetic Extreme Condition User Facility (SECUF), we find that the pairing gap exhibits chiral 2x2 modulations, and their chirality can be controlled by magnetic field training. We introduce nonmagnetic impurities to observe the complete suppression of 2x2 pairing modulations in presence of persistent 2x2 charge order. This nonmagnetic pair-breaking effect provides phase-sensitive evidence for pair-density-wave (PDW) induced pairing modulations. Our results support switchable chiral 2x2 PDW in this super clean kagome superconductor. △ Less

Submitted 20 March, 2026; v1 submitted 14 October, 2025; originally announced October 2025.

Journal ref: Physical Review B113,125127(2026)

Phase-sensitive evidence for pair density waves in a kagome superconductor

Authors: Xiao-Yu Yan, Guowei Liu, Hanbin Deng, Xitong Xu, Haiyang Ma, Hailang Qin, Junyi Zhang, Yuanyuan Zhao, Xiuhao Fan, Wei Song, Muwei Gao, Haitian Zhao, Zhe Qu, Yigui Zhong, Kozo Okazaki, Xiquan Zheng, Yingying Peng, Zurab Guguchia, Xianxin Wu, Da Wang, Qiang-Hua Wang, Hendrik Hohmann, Matteo Dürrnagel, Ronny Thomale, Jia-Xin Yin

Abstract: Pair density wave (PDW) exhibits periodic amplitude and sign modulations of the superconducting order parameter. Such a pairing state has long been proposed to be highly sensitive to nonmagnetic scattering, but its experimental realization remains elusive. Here we discover a nonmagnetic PDW-breaking effect in a kagome superconductor, using designer atomic nonmagnetic impurities and high-precision… ▽ More Pair density wave (PDW) exhibits periodic amplitude and sign modulations of the superconducting order parameter. Such a pairing state has long been proposed to be highly sensitive to nonmagnetic scattering, but its experimental realization remains elusive. Here we discover a nonmagnetic PDW-breaking effect in a kagome superconductor, using designer atomic nonmagnetic impurities and high-precision scanning tunneling microscopy (STM) at a base temperature of 30mK. We detect 2x2 pair density modulations by Josephson STM with a superconducting tip and 2x2 pairing gap modulations by normal STM. We find that the pairing modulations in both cases are substantially suppressed upon doping the kagome lattice with dilute isovalent nonmagnetic impurities, whereas the charge order and uniform superconductivity remain robust. We further identify the correlation between atomic dopants and the local suppression of PDW. We attribute these findings to a nonmagnetic pair-breaking effect, arising from the phase modulation of PDW in the kagome d-orbital. Taken together with its signatures in other state-of-the-art spectroscopy and transport measurements linked by theory, our findings support the ground state of the kagome superconductor as a correlated topological phase with superconducting loop currents. △ Less

Submitted 29 June, 2026; v1 submitted 12 October, 2025; originally announced October 2025.

Comments: 15 pages, 5 figures; Supplementary Material included; updated to match the published version

Journal ref: Proc. Natl. Acad. Sci. U.S.A. 123, e2604142123 (2026)

Learning from the electronic structure of molecules across the periodic table

Authors: Manasa Kaniselvan, Benjamin Kurt Miller, Meng Gao, Juno Nam, Daniel S. Levine

Abstract: Machine-Learned Interatomic Potentials (MLIPs) require vast amounts of atomic structure data to learn forces and energies, and their performance continues to improve with training set size. Meanwhile, the even greater quantities of accompanying data in the Hamiltonian matrix H behind these datasets has so far gone unused for this purpose. Here, we provide a recipe for integrating the orbital inter… ▽ More Machine-Learned Interatomic Potentials (MLIPs) require vast amounts of atomic structure data to learn forces and energies, and their performance continues to improve with training set size. Meanwhile, the even greater quantities of accompanying data in the Hamiltonian matrix H behind these datasets has so far gone unused for this purpose. Here, we provide a recipe for integrating the orbital interaction data within H towards training pipelines for atomic-level properties. We first introduce HELM ("Hamiltonian-trained Electronic-structure Learning for Molecules"), a state-of-the-art Hamiltonian prediction model which bridges the gap between Hamiltonian prediction and universal MLIPs by scaling to H of structures with 100+ atoms, high elemental diversity, and large basis sets including diffuse functions. To accompany HELM, we release a curated Hamiltonian matrix dataset, 'OMol_CSH_58k', with unprecedented elemental diversity (58 elements), molecular size (up to 150 atoms), and basis set (def2-TZVPD). Finally, we introduce 'Hamiltonian pretraining' as a method to extract meaningful descriptors of atomic environments even from a limited number atomic structures, and repurpose this shared embedding space to improve performance on energy-prediction in low-data regimes. Our results highlight the use of electronic interactions as a rich and transferable data source for representing chemical space. △ Less

Submitted 7 December, 2025; v1 submitted 30 September, 2025; originally announced October 2025.

Breakdown of the symmetry constraint in a Floquet topological insulator

Authors: Ming-Jian Gao, Jun-Hong An

Abstract: A topological insulator is regarded as an ideal candidate for information storage and high-speed lossless electrical transmission devices due to robust topological protected boundary modes. Previous studies revealed that symmetry exerts an unbreakable constraint on the existence, classes, and orders of its boundary modes. It severely limits the controllability and application of a topological insu… ▽ More A topological insulator is regarded as an ideal candidate for information storage and high-speed lossless electrical transmission devices due to robust topological protected boundary modes. Previous studies revealed that symmetry exerts an unbreakable constraint on the existence, classes, and orders of its boundary modes. It severely limits the controllability and application of a topological insulator. Here, we propose a Floquet-engineering method to break this symmetry-imposed constraint on a topological insulator. By applying periodic driving on a system belonging to a symmetry class that prohibits the existence of first-order topological phases, we find that rich first-order boundary modes are created. Interestingly, exotic hybrid-order topological insulators with coexisting first-order helical boundary modes and second-order corner modes not only in two different quasienergy gaps but also in one single gap are generated easily by periodic driving. Refreshing the prevailing understanding of symmetry constraint on topological phases, our result opens an avenue for the creation of exotic topological insulators without altering symmetries. It greatly expands the scope of the fabricated materials that host topological insulators. △ Less

Submitted 3 January, 2026; v1 submitted 24 September, 2025; originally announced September 2025.

Journal ref: Phys. Rev. B 113, L041103 (2026)

Quantum anomalous Hall effect with high Chern number in two dimensional ferromagnets Ti2TeSO

Authors: Panjun Feng, Miao Gao, Xun-Wang Yan, Fengjie Ma

Abstract: Two-dimensional Chern insulators have emerged as crucial platforms for the realization of the quantum anomalous Hall effect, and as such have attracted significant interest in spintronics and topological quantum physics due to their unique coexistence of spontaneous magnetization and nontrivial topological characteristics. Nonetheless, substantial challenges persist in such systems, encompassing s… ▽ More Two-dimensional Chern insulators have emerged as crucial platforms for the realization of the quantum anomalous Hall effect, and as such have attracted significant interest in spintronics and topological quantum physics due to their unique coexistence of spontaneous magnetization and nontrivial topological characteristics. Nonetheless, substantial challenges persist in such systems, encompassing spin entanglement and the possession of only one edge state (Chern number C=1), which significantly hinder their practical applications. Herein, we propose a novel two-dimensional ferromagnetic half-semi-Weyl-metal, monolayer Ti2TeSO, that exhibits exceptional electronic properties. Its majority spin channel possesses only a pair of symmetry-protected Weyl points at the Fermi level, while the states of minority one locate far away from the Fermi level. When spin-orbit coupling is included, a substantial band gap of ~ 92.8 meV is induced at the Weyl points. Remarkably, the emergence of dual dissipationless chiral edge channels and a quantized Hall conductivity plateau at 2e2/h collectively establish monolayer Ti2TeSO as a high-Chern-number insulator with C=2. Furthermore, it is demonstrated that valley polarization can be achieved and controlled through the application of strain and the manipulation of the direction of magnetization. The first-principles calculations, in conjunction with Monte Carlo simulations, yield a Curie temperature of 161 K for monolayer Ti2TeSO, thereby indicating the plausibility of coexistence of valley polarization and topological states at elevated temperatures. These findings could provide a foundation for the development of multi-channels dissipationless transport devices and nonvolatile multistate memory architectures. △ Less

Submitted 2 September, 2025; originally announced September 2025.

Journal ref: Materials Today Physics 62 (2026) 102050

Violation of Luttinger's theorem in one-dimensional interacting fermions

Authors: Meng Gao, Yin Zhong

Abstract: Using the density matrix renormalization group method, we systematically investigate the evolution of the Luttinger integral in the one-dimensional generalized $t$-$V$ model as a function of filling and interaction strength, and identify three representative phases. In the weak-coupling regime, the zero-frequency Green's function exhibits a branch-cut structure at the Fermi momentum, and the Lutti… ▽ More Using the density matrix renormalization group method, we systematically investigate the evolution of the Luttinger integral in the one-dimensional generalized $t$-$V$ model as a function of filling and interaction strength, and identify three representative phases. In the weak-coupling regime, the zero-frequency Green's function exhibits a branch-cut structure at the Fermi momentum, and the Luttinger integral accurately reflects the particle density, indicating that the Luttinger theorem holds. As the interaction increases, the spectral weight near the Fermi momentum is gradually suppressed. Interestingly, in the strong coupling regime near half-filling, this singularity is progressively destroyed, accompanied by the emergence of momentum-space zeros in the real part of the Green's function, leading to a novel non-Fermi liquid metallic phase beyond the classic Luttinger liquid paradigm, where the Luttinger surface is no longer defined by a single singularity. While finite spectral weight remains at the original Fermi momentum, the singularity gradually diminishes. Meanwhile, zeros with negligible spectral weight appear away from this momentum, significantly affecting the integral. At exact half-filling, a single-particle gap opens, and the Green's function becomes nearly vanishing across the entire momentum space, indicating the complete suppression of low-energy electronic states consistent with the nature of an insulating charge-density-wave phase. These results suggest that the breakdown of the Luttinger theorem is not triggered by a single mechanism, but rather results from the interplay between interaction-driven evolution of excitation modes and the breaking of particle-hole symmetry, ultimately leading to a continuous reconstruction of the generalized Fermi surface from topologically protected to correlation-driven. △ Less

Submitted 12 September, 2025; v1 submitted 4 June, 2025; originally announced June 2025.

Comments: 11 pages, 8 figures; Accepted for publication in Phys. Rev. B (2025)

Report number: BF15117

Converting $PT$-Symmetric Topological Classes by Floquet Engineering

Authors: Ming-Jian Gao, Jun-Hong An

Abstract: Going beyond the conventional classification rule of Altland-Zirnbauer symmetry classes, $PT$ symmetric topological phases are classified by $(PT)^2=1$ or $-1$. The interconversion between the two $PT$-symmetric topological classes is generally difficult due to the constraint of $(PT)^2$. Here, we propose a scheme to control and interconvert the $PT$-symmetric topological classes by Floquet engine… ▽ More Going beyond the conventional classification rule of Altland-Zirnbauer symmetry classes, $PT$ symmetric topological phases are classified by $(PT)^2=1$ or $-1$. The interconversion between the two $PT$-symmetric topological classes is generally difficult due to the constraint of $(PT)^2$. Here, we propose a scheme to control and interconvert the $PT$-symmetric topological classes by Floquet engineering. We find that it is the breakdown of the $\mathbb{Z}_2$ gauge, induced by the $π$ phase difference between different hopping rates, by the periodic driving that leads to such an interconversion. Relaxing the system from the constraint of $(PT)^2$, rich exotic topological phases, e.g., the coexisting $PT$-symmetric first-order real Chern insulator and second-order topological insulators not only in different quasienergy gaps, but also in one single gap, are generated. In contrast to conventional Floquet topological phases, our result provides a way to realize exotic topological phases without changing symmetries. It enriches the family of topological phases and gives an insightful guidance for the development of multifunctional quantum devices. △ Less

Submitted 20 April, 2025; originally announced April 2025.

Comments: 7 pages and 4 figures

Multiple topological corner states in the continuum of extended kagome lattice

Authors: Shun-Peng Zhang, Ming-Jian Gao, Wei Jia, Jun-Hong An

Abstract: The kagome lattice is renowned for its exotic electronic properties, such as flat bands, Dirac points, and Van Hove singularities. These features have provided a fertile ground for exploring exotic quantum phenomena. Here, we discover that a breathing kagome lattice with long-range hoppings can host multiple zero-energy corner states, which emerge as topologically protected bound states in the con… ▽ More The kagome lattice is renowned for its exotic electronic properties, such as flat bands, Dirac points, and Van Hove singularities. These features have provided a fertile ground for exploring exotic quantum phenomena. Here, we discover that a breathing kagome lattice with long-range hoppings can host multiple zero-energy corner states, which emerge as topologically protected bound states in the continuum (BICs). This result demonstrates that additional hopping control can induce further non-trivial physics of the kagome lattice. Since the zero-energy corner states in the continuum are intertwined with a substantial number of zero-energy bulk states, we also develop a momentum-space topological characterization theory to precisely quantify the number of corner states, revealing a general bulk-corner correspondence. Furthermore, we uncover three distinct types of topological phase transitions (TPTs) for the BICs driven by shifts in the spatial localization of zero-energy bulk and/or edge states. These TPTs are exactly captured by our characterization theory. This work provides deep insights into the topological physics of the kagome lattice and broadens the understanding of its electronic properties △ Less

Submitted 18 September, 2025; v1 submitted 1 April, 2025; originally announced April 2025.

Comments: 8+6 pages,4+1 figures

Journal ref: Phys. Rev. B 112, L121106 (2025)

Type-II quantum spin Hall insulator

Authors: Panjun Feng, Chao-Yang Tan, Miao Gao, Xun-Wang Yan, Zheng-Xin Liu, Peng-Jie Guo, Fengjie Ma, Zhong-Yi Lu

Abstract: Quantum spin Hall effect is usually realized in two-dimensional materials with time-reversal symmetry, but whether it can be realized without symmetry protection remains unexplored. Here, we propose type-II quantum spin Hall insulator with quantized spin Hall conductivity, whose edge states with opposite chirality and polarization, distributed in different Brillouin zone regions, connect the condu… ▽ More Quantum spin Hall effect is usually realized in two-dimensional materials with time-reversal symmetry, but whether it can be realized without symmetry protection remains unexplored. Here, we propose type-II quantum spin Hall insulator with quantized spin Hall conductivity, whose edge states with opposite chirality and polarization, distributed in different Brillouin zone regions, connect the conduction and valence bands at the boundary. Thus, the type-II quantum spin Hall insulator does not require any symmetry protection other than translational symmetry. Then, based on symmetry analysis and the first-principles electronic structure calculations, we demonstrate that type-II quantum spin Hall insulator can be realized in both altermagnetic materials and Luttinger compensated magnetic materials. Furthermore, based on lattice model, we find that as long as $U(1)$ symmetry exists, type-II quantum spin Hall insulator phase can always exist stably. However, if $U(1)$ symmetry is broken, type-II quantum spin Hall insulator phase transforms into an obstructed atomic insulator phase as spin-orbit coupling effect is enhanced. Therefore, our work not only proposes a new mechanism for realizing the quantum spin Hall effect, but also enriches the types of unconventional magnetic topological phases. △ Less

Submitted 31 March, 2025; v1 submitted 17 March, 2025; originally announced March 2025.

Comments: 6pages, 4 figures

Prediction of two-dimensional ferromagnetic VO$_2$ layers in the hexagonal and tetragonal phases

Authors: Lihui Han, Lujia Tian, Bing-Xin Liu, Zong-liang Li, Miao Gao, Fengjie Ma, Xun-Wang Yan

Abstract: Ferromagnetism in the two-dimensional materials is of great significance and has become an emerging topic. The ferromagnetic VS$_2$ and VSe$_2$ monolayers have been experimentally synthesized, and O element belongs to the same group as S and Se elements. Thus, whether there exists the ferromagnetic VO$_2$ monolayer is a necessary and urgent question. Using first-principles methods within the frame… ▽ More Ferromagnetism in the two-dimensional materials is of great significance and has become an emerging topic. The ferromagnetic VS$_2$ and VSe$_2$ monolayers have been experimentally synthesized, and O element belongs to the same group as S and Se elements. Thus, whether there exists the ferromagnetic VO$_2$ monolayer is a necessary and urgent question. Using first-principles methods within the framework of density functional theory, we predict two kinds of VO$_2$ monolayers with the hexagonal and tetragonal phases and investigate their structural stability, electronic and magnetic properties, and ferromagnetic phase transition. The computational results demonstrate that the two two-dimensional structural phases are stable and possess the ferromagnetic ground states, and they are half-metal with large energy gap. In addition, by solving the Heisenberg model with the Monte Carlo simulation methods, the ferromagnetic phase transition at 270 K in the hexagonal phase is determined. These findings not only predict a new type of intrinsic half-metallic ferromagnet with a high Curie temperature but also fill in an important gap that are lacking in the series of studies from VO$_2$, VS$_2$, VSe$_2$, to VTe$_2$. △ Less

Submitted 13 March, 2025; originally announced March 2025.

Huge Stress-induced Adiabatic Temperature Change in a High-Toughness All-d-metal Heusler Alloy

Authors: Rui Cai, Zhiyang Wei, Hongjie Ren, Hanyang Qian, Xinyu Zhang, Yao Liu, Xiang Lu, Wen Sun, Meng Gao, Enke Liu, Jian Liu, Guowei Li

Abstract: The elastocaloric effect (eCE), referring to the thermal effect triggered by a uniaxial stress, provides a promising and versatile routine for green and high efficient thermal management. However, current eCE materials generally suffer from relatively low eCE and poor mechanical properties, hindering their practical applications. Here, we report a exceptionally huge eCE with a directly measured ad… ▽ More The elastocaloric effect (eCE), referring to the thermal effect triggered by a uniaxial stress, provides a promising and versatile routine for green and high efficient thermal management. However, current eCE materials generally suffer from relatively low eCE and poor mechanical properties, hindering their practical applications. Here, we report a exceptionally huge eCE with a directly measured adiabatic temperature change of up to 57.2 K in a dual-phase all-d-metal Heusler Mn50Ni37.5Ti12.5 polycrystalline alloy, revealing an extra contribution to the latent heat during the stress-induced martensitic transformation from B2 to L10, and breaking the record of adiabatic temperature change for elastocaloric alloys. Moreover, thanks to the combined strengthening effect of d-d hybridization and well-dispersed secondary cubic γ phase, the alloy can endure a uniaxial stress up to 1760 MPa. Such an abnormal huge eCE is attributed to the combination of the enhanced entropy change associated with a stress-induced B2 to L10 martensitic transformation under higher stress, in contrast with the thermally induced B2 to 5-layer modulated structure one, and the high transformation fraction due to the multi-point nucleation facilitated by the γ phase dispersed in the main phase. This work provides insight into making full use of the transformation heat to enhance the caloric effect for high-efficient thermal management systems. △ Less

Submitted 3 March, 2025; originally announced March 2025.

Bright hybrid excitons in molecularly tunable bilayer crystals

Authors: Tomojit Chowdhury, Aurélie Champagne, Patrick Knüppel, Zehra Naqvi, Ariana Ray, Mengyu Gao, David A. Muller, Nathan Guisinger, Kin Fai Mak, Jeffrey B. Neaton, Jiwoong Park

Abstract: Bilayer crystals, built by stacking crystalline monolayers, generate interlayer potentials that govern excitonic phenomena but are constrained by fixed covalent lattices and orientations. Replacing one layer with an atomically thin molecular crystal overcomes this limitation, as diverse functional groups enable tunable molecular lattices and interlayer potentials, tailoring a wide range of exciton… ▽ More Bilayer crystals, built by stacking crystalline monolayers, generate interlayer potentials that govern excitonic phenomena but are constrained by fixed covalent lattices and orientations. Replacing one layer with an atomically thin molecular crystal overcomes this limitation, as diverse functional groups enable tunable molecular lattices and interlayer potentials, tailoring a wide range of excitonic properties. Here, we report hybrid excitons in four-atom-thick hybrid bilayer crystals (HBCs), directly synthesized with single-crystalline perylene diimide (PDI) molecular crystal atop WS2 monolayers. These excitons arise from a hybridized bilayer band structure, revealed by lattice-scale first-principles calculations, inheriting properties from both monolayers. They exhibit bright photoluminescence with near-unity polarization above and below the WS2 bandgap, along with spectral signatures of exciton delocalization, supported by theory, while their energies and intensities are tuned by modifying the HBC composition by synthesis. Our work introduces a molecule-based 2D quantum materials platform for bottom-up design and control of optoelectronic properties. △ Less

Submitted 19 February, 2025; originally announced February 2025.

Comments: arXiv admin note: text overlap with arXiv:2412.12027

Liquid crystalline structures formed by sphere-rod amphiphilic molecules in solvents

Authors: Nilanthi P. Haputhanthrige, Yifan Zhou, Jingfan Wei, Min Gao, Tianbo Liu, Oleg D. Lavrentovich

Abstract: Self-assembly of amphiphilic molecules is an important phenomenon attracting a broad range of research. In this work, we study the self-assembly of KTOF4 sphere-rod amphiphilic molecules in mixed water-dioxane solvents. The molecules are of a T-shaped geometry, comprised of a hydrophilic spherical Keggin-type cluster attached by a flexible bridge to the center of a hydrophobic rod-like oligodialky… ▽ More Self-assembly of amphiphilic molecules is an important phenomenon attracting a broad range of research. In this work, we study the self-assembly of KTOF4 sphere-rod amphiphilic molecules in mixed water-dioxane solvents. The molecules are of a T-shaped geometry, comprised of a hydrophilic spherical Keggin-type cluster attached by a flexible bridge to the center of a hydrophobic rod-like oligodialkylfluorene (OF), which consists of four OF units. Transmission electron microscopy (TEM) uncovers self-assembled spherical structures of KTOF4 in dilute solutions. These spheres are filled with smectic-like layers of KTOF4 separated by layers of the solution. There are two types of layer packings: (i) concentric spheres and (ii) flat layers. The concentric spheres form when the dioxane volume fraction in the solution is 35-50 vol%. The flat layers are formed when the dioxane volume fraction is either below (20 and 30 vol%.) or above (55 and 60 vol%.) the indicated range. The layered structures show no in-plane orientational order and thus resemble thermotropic smectic A liquid crystals and their lyotropic analogs. The layered packings reveal edge and screw dislocations. Evaporation of the solvent produces a bulk birefringent liquid crystal phase with textures resembling the ones of uniaxial nematic liquid crystals. These findings demonstrate that sphere-rod molecules produce a variety of self-assembled structures that are controlled by the solvent properties. △ Less

Submitted 10 February, 2025; originally announced February 2025.

Comments: This article has 21 pages, 7 figures and one Table

MSC Class: 00 ACM Class: E.1

Topological semimetal with coexisting nodal points and nodal lines

Authors: Bing-Bing Luo, Ming-Jian Gao, Jun-Hong An

Abstract: Featuring exotic quantum transport and surface states, topological semimetals can be classified into nodal-point, nodal-line, and nodal-surface semimetals according to the degeneracy and dimensionality of their nodes. However, a topological semimetal that possesses both nodal points and nodal lines is rarely reported. Here, we propose a scheme to construct this type of topological semimetal, which… ▽ More Featuring exotic quantum transport and surface states, topological semimetals can be classified into nodal-point, nodal-line, and nodal-surface semimetals according to the degeneracy and dimensionality of their nodes. However, a topological semimetal that possesses both nodal points and nodal lines is rarely reported. Here, we propose a scheme to construct this type of topological semimetal, which simultaneously exhibits hinge Fermi arcs and drumhead surface states. Then, by applying periodic driving on the system, we find a hybrid-order topological semimetal with nodal points and rich nodal-line structures and its conversion into a first-order topological semimetal, which are absent in a static system. Our results enrich the family of topological semimetals, and establish a foundation for further exploration of their potential applications. △ Less

Submitted 16 July, 2025; v1 submitted 23 January, 2025; originally announced January 2025.

Journal ref: Phys. Rev. B 112, 045126 (2025)

The critical role of entropy in glass transition kinetics

Authors: Lijian Song, Meng Gao, Juntao Huo, Li-Min Wang, Yuanzheng Yue, Jun-Qiang Wang

Abstract: Glass transition is a reversible transition that occurs in most amorphous materials. However, the nature of glass transition remains far from being clarified. A key to understand the glass transition is to clarify what determines the glass transition temperature (Tg) and liquid fragility (m). Here the glass transition thermodynamics for 150 different glass-forming systems are studied statistically… ▽ More Glass transition is a reversible transition that occurs in most amorphous materials. However, the nature of glass transition remains far from being clarified. A key to understand the glass transition is to clarify what determines the glass transition temperature (Tg) and liquid fragility (m). Here the glass transition thermodynamics for 150 different glass-forming systems are studied statistically. It is found that the activation characters in the energy landscape are crucial to precisely portray the glass transition and, in particular, both the activation free energy (G*) and the activation entropy (S*) play critical roles. G* determines Tg, Tg=G*/290+25.5, while S* determines m, m=S*/Rln10+15 with R is gas constant. Based on the Boltzmann definition of entropy, the fragility is an indication of the number of the degeneracy of the evolution paths. This explains why the nano-confined, low-dimension or high-pressured glasses exhibit stronger characteristics, which has been a puzzling phenomenon for a long time. △ Less

Submitted 24 June, 2026; v1 submitted 20 January, 2025; originally announced January 2025.

Comments: 7 pages, 4 figures

Journal ref: Sci. China Phys. Mech. Astron., 68, 296162 (2025)

Machine Learning Relationships between Nanoporous Structures and Electrochemical Performance in MOF Supercapacitors

Authors: Zhenxiang Wang, Taizheng Wu, Liang Zeng, Jiaxing Peng, Ding Yu, Ming Gao, Guang Feng

Abstract: The development of supercapacitors is impeded by the unclear relationships between nanoporous electrode structures and electrochemical performance, primarily due to challenges in decoupling the complex interdependencies of various structural descriptors. While machine learning (ML) techniques offer a promising solution, their application is hindered by the lack of large, unified databases. Herein,… ▽ More The development of supercapacitors is impeded by the unclear relationships between nanoporous electrode structures and electrochemical performance, primarily due to challenges in decoupling the complex interdependencies of various structural descriptors. While machine learning (ML) techniques offer a promising solution, their application is hindered by the lack of large, unified databases. Herein, we use constant-potential molecular simulation to construct a unified supercapacitor database with hundreds of metal-organic framework (MOF) electrodes. Leveraging this database, well-trained decision-tree-based ML models achieve fast, accurate, and interpretable predictions of capacitance and charging rate, experimentally validated by a representative case. SHAP analyses reveal that specific surface area (SSA) governs gravimetric capacitance while pore size effects are minimal, attributed to the strong dependence of electrode-ion coordination on SSA rather than pore size. SSA and porosity, respectively, dominate volumetric capacitance in 1D-pore and 3D-pore MOFs, pinnacling the indispensable effects of pore dimensionality. Meanwhile, porosity is found to be the most decisive factor in the charging rate for both 1D-pore and 3D-pore MOFs. Especially for 3D-pore MOFs, an exponential increase with porosity is observed in both ionic conductance and in-pore ion diffusion coefficient, ascribed to loosened ion packing. These findings provide profound insights for the design of high-performance supercapacitor electrodes. △ Less

Submitted 15 January, 2025; originally announced January 2025.

Molecular tuning of excitons in four-atom-thick hybrid bilayer crystals

Authors: Tomojit Chowdhury, Aurélie Champagne, Patrick Knüppel, Zehra Naqvi, Mengyu Gao, Nathan Guisinger, Kin Fai Mak, Jeffrey B. Neaton, Jiwoong Park

Abstract: Bilayer crystals, formed by stacking monolayers of two-dimensional (2D) crystals, create interlayer potentials that govern excitonic phenomena but are constrained by their fixed covalent lattices. Replacing one layer with an atomically thin molecular crystal overcomes this limitation, as precise control of functional groups enables tunable 2D molecular lattices and, consequently, electronic struct… ▽ More Bilayer crystals, formed by stacking monolayers of two-dimensional (2D) crystals, create interlayer potentials that govern excitonic phenomena but are constrained by their fixed covalent lattices. Replacing one layer with an atomically thin molecular crystal overcomes this limitation, as precise control of functional groups enables tunable 2D molecular lattices and, consequently, electronic structures. Here, we report molecular tuning of lattices and excitons in four-atom-thick hybrid bilayer crystals (HBCs), synthesized as monolayers of perylene-based molecular and transition metal dichalcogenide (TMD) single crystals. In HBCs, we observe an anisotropic photoluminescence signal exhibiting characteristics of both molecular and TMD excitons, directly tuned by molecular geometry and HBC composition. Ab initio calculations reveal that this anisotropic emission arises from hybrid excitons, which inherit properties from both layers through a hybridized bilayer band structure. Our work establishes a synthetically derived, molecule-based 2D quantum materials platform with the potential for engineering interlayer potentials. △ Less

Submitted 8 February, 2025; v1 submitted 16 December, 2024; originally announced December 2024.

Comments: This revised version of the paper has undergone substantial modifications, and a portion of these changes has been submitted as a separate work under the ID arXiv:2502.01629

Discovery of an Antiferromagnetic Topological Nodal-line Kondo Semimetal

Authors: D. F. Liu, Y. F. Xu, H. Y. Hu, J. Y. Liu, T. P. Ying, Y. Y. Lv, Y. Jiang, C. Chen, Y. H. Yang, D. Pei, D. Prabhakaran, M. H. Gao, J. J. Wang, Q. H. Zhang, F. Q. Meng, B. Thiagarajan, C. Polley, M. Hashimoto, D. H. Lu, N. B. M. Schröter, V. N. Strocov, A. Louat, C. Cacho, D. Biswas, T. -L. Lee , et al. (12 additional authors not shown)

Abstract: The symbiosis of strong interactions, flat bands, topology and symmetry has led to the discovery of exotic phases of matter, including fractional Chern insulators, correlated moiré topological superconductors, and Dirac and Weyl semimetals. Correlated metals, such as those present in Kondo lattices, rely on the screening of local moments by a sea of non-magnetic conduction electrons. Here, we repo… ▽ More The symbiosis of strong interactions, flat bands, topology and symmetry has led to the discovery of exotic phases of matter, including fractional Chern insulators, correlated moiré topological superconductors, and Dirac and Weyl semimetals. Correlated metals, such as those present in Kondo lattices, rely on the screening of local moments by a sea of non-magnetic conduction electrons. Here, we report on a unique topological Kondo lattice compound, CeCo2P2, where the Kondo effect - whose existence under the magnetic Co phase is protected by PT symmetry - coexists with antiferromagnetic order emerging from the flat bands associated with the Co atoms. Remarkably, this is the only known Kondo lattice compound where magnetic order occurs in non-heavy electrons, and puzzlingly, at a temperature significantly higher than that of the Kondo effect. Furthermore, at low temperatures, the emergence of the Kondo effect, in conjunction with a glide-mirror-z symmetry, results in a nodal line protected by bulk topology near the Fermi energy. These unusual properties, arising from the interplay between itinerant and correlated electrons from different constituent elements, lead to novel quantum phases beyond the celebrated topological Kondo insulators and Weyl Kondo semimetals. CeCo2P2 thus provides an ideal platform for investigating narrow bands, topology, magnetism, and the Kondo effect in strongly correlated electron systems. △ Less

Submitted 21 November, 2024; originally announced November 2024.

Comments: 17pages,4 figures

Open Materials 2024 (OMat24) Inorganic Materials Dataset and Models

Authors: Luis Barroso-Luque, Muhammed Shuaibi, Xiang Fu, Brandon M. Wood, Misko Dzamba, Meng Gao, Ammar Rizvi, C. Lawrence Zitnick, Zachary W. Ulissi

Abstract: The ability to discover new materials with desirable properties is critical for numerous applications from helping mitigate climate change to advances in next generation computing hardware. AI has the potential to accelerate materials discovery and design by more effectively exploring the chemical space compared to other computational methods or by trial-and-error. While substantial progress has b… ▽ More The ability to discover new materials with desirable properties is critical for numerous applications from helping mitigate climate change to advances in next generation computing hardware. AI has the potential to accelerate materials discovery and design by more effectively exploring the chemical space compared to other computational methods or by trial-and-error. While substantial progress has been made on AI for materials data, benchmarks, and models, a barrier that has emerged is the lack of publicly available training data and open pre-trained models. To address this, we present a Meta FAIR release of the Open Materials 2024 (OMat24) large-scale open dataset and an accompanying set of pre-trained models. OMat24 contains over 110 million density functional theory (DFT) calculations focused on structural and compositional diversity. Our EquiformerV2 models achieve state-of-the-art performance on the Matbench Discovery leaderboard and are capable of predicting ground-state stability and formation energies to an F1 score above 0.9 and an accuracy of 20 meV/atom, respectively. We explore the impact of model size, auxiliary denoising objectives, and fine-tuning on performance across a range of datasets including OMat24, MPtraj, and Alexandria. The open release of the OMat24 dataset and models enables the research community to build upon our efforts and drive further advancements in AI-assisted materials science. △ Less

Submitted 19 May, 2026; v1 submitted 16 October, 2024; originally announced October 2024.

Comments: 19 pages

A quasi-ohmic back contact achieved by inserting single-crystal graphene in flexible Kesterite solar cells

Authors: Yixiong Ji, Wentong Yang, Di Yan, Wei Luo, Jialu Li, Shi Tang, Jintao Fu, James Bullock, Mei Gao, Xin Li, Zhancheng Li, Jun Yang, Xingzhan Wei, Haofei Shi, Fangyang Liu, Paul Mulvaney

Abstract: Flexible photovoltaics with a lightweight and adaptable nature that allows for deployment on curved surfaces and in building facades have always been a goal vigorously pursued by researchers in thin-film solar cell technology. The recent strides made in improving the sunlight-to-electricity conversion efficiency of kesterite Cu$_{2}$ZnSn(S, Se)$_{4}$ (CZTSSe) suggest it to be a perfect candidate.… ▽ More Flexible photovoltaics with a lightweight and adaptable nature that allows for deployment on curved surfaces and in building facades have always been a goal vigorously pursued by researchers in thin-film solar cell technology. The recent strides made in improving the sunlight-to-electricity conversion efficiency of kesterite Cu$_{2}$ZnSn(S, Se)$_{4}$ (CZTSSe) suggest it to be a perfect candidate. However, making use of rare Mo foil in CZTSSe solar cells causes severe problems in thermal expansion matching, uneven grain growth, and severe problems at the back contact of the devices. Herein, a strategy utilizing single-crystal graphene to modify the back interface of flexible CZTSSe solar cells is proposed. It will be shown that the insertion of graphene at the Mo foil/CZTSSe interface provides strong physical support for the subsequent deposition of the CZTSSe absorber layer, improving the adhesion between the absorber layer and the Mo foil substrate. Additionally, the graphene passivates the rough sites on the surface of the Mo foil, enhancing the chemical homogeneity of the substrate, and resulting in a more crystalline and homogeneous CZTSSe absorber layer on the Mo foil substrate. The detrimental reaction between Mo and CZTSSe has also been eliminated. Through an analysis of the electrical properties, it is found that the introduction of graphene at the back interface promotes the formation of a quasi-ohmic contact at the back contact, decreasing the back contact barrier of the solar cell, and leading to efficient collection of charges at the back interface. This investigation demonstrates that solution-based CZTSSe photovoltaic devices could form the basis of cheap and flexible solar cells. △ Less

Submitted 28 August, 2024; originally announced August 2024.

Screening of half-Heuslers with temperature-induced band convergence and enhanced thermoelectric properties

Authors: Jinyang Xi, Zirui Dong, Menghan Gao, Jun Luo, Jiong Yang

Abstract: Enhancing band convergence is an effective way to optimize the thermoelectric (TE) properties of materials. However, the temperature-induced band renormalization is commonly ignored. By employing the recently-developed electron-phonon renormalization (EPR) method, the nature of band renormalization in half-Heusler (HH) compounds TiCoSb and NbFeSb is revealed, and the key factors for temperature-in… ▽ More Enhancing band convergence is an effective way to optimize the thermoelectric (TE) properties of materials. However, the temperature-induced band renormalization is commonly ignored. By employing the recently-developed electron-phonon renormalization (EPR) method, the nature of band renormalization in half-Heusler (HH) compounds TiCoSb and NbFeSb is revealed, and the key factors for temperature-induced conduction band convergence in HH are found out. Using these as the screening criteria, 3 out of 274 HHs (TiRhBi, TiPtSn, NbPtTl) are then stood out from our MatHub-3d database. Taking TiPtSn as the example, it shows the conduction band convergence at mid-high temperature, and further resulting in enhanced Seebeck coefficient S: e.g., at 600 K with electron concentration 10^20 cm^-3, the predicted S with and without renormalized band is 352.83 uV/K and 289.52 uV/K, respectively. Herein, the former is closer to our measurement value of 338.79 uV/K. Besides, the effective masses obtained from calculation and experiment are both enlarged with temperature, indicating the existence of band convergence. Our work demonstrates for the first time the significance of adding the temperature effect on electronic structure in the design of potential high-performance TE materials. △ Less

Submitted 29 June, 2024; originally announced July 2024.

Revisiting first-principles thermodynamics by quasiharmonic approach: Application to study thermal expansion of additively-manufactured Inconel 625

Authors: Shun-Li Shang, Rushi Gong, Michael C. Gao, Darren C. Pagan, Zi-Kui Liu

Abstract: An innovative method is developed for accurate determination of thermodynamic properties as a function of temperature by revisiting the density functional theory (DFT) based quasiharmonic approach (QHA). The present methodology individually evaluates the contributions from static total energy, phonon, and thermal electron to free energy for increased efficiency and accuracy. The Akaike information… ▽ More An innovative method is developed for accurate determination of thermodynamic properties as a function of temperature by revisiting the density functional theory (DFT) based quasiharmonic approach (QHA). The present methodology individually evaluates the contributions from static total energy, phonon, and thermal electron to free energy for increased efficiency and accuracy. The Akaike information criterion with a correction (AICc) is used to select models and model parameters for fitting each contribution as a function of volume. Using the additively manufactured Inconel alloy 625 (IN625) as an example, predicted temperature-dependent linear coefficient of thermal expansion (CTE) agrees well with dilatometer measurements and values in the literature. Sensitivity and uncertainty are also analyzed for the predicted IN625 CTE due to different structural configurations used by DFT, and hence different equilibrium properties determined. △ Less

Submitted 15 May, 2024; originally announced May 2024.

Comments: This manuscript includes both the main text and the supplementary material, but without the supplementary Excel file

Unveiling Higher-Order Topology via Polarized Topological Charges

Authors: Wei Jia, Bao-Zong Wang, Ming-Jian Gao, Jun-Hong An

Abstract: Higher-order topological phases (HOTPs) host exotic topological states that go beyond the traditional bulk-boundary correspondence. Up to now, there is still a lack of experimentally measurable momentum-space topological characterization for the HOTPs, which is not conducive to revealing the essential properties of these topological states and also restricts their detection in quantum simulation s… ▽ More Higher-order topological phases (HOTPs) host exotic topological states that go beyond the traditional bulk-boundary correspondence. Up to now, there is still a lack of experimentally measurable momentum-space topological characterization for the HOTPs, which is not conducive to revealing the essential properties of these topological states and also restricts their detection in quantum simulation systems. Here, we propose a concept of polarized topological charges to characterize chiral-symmetric HOTPs in momentum space, which further facilitates a feasible experimental scheme to detect the HOTPs in $^{87}$Rb cold atomic system. Remarkably, our characterization theory not only shows that the second-order (third-order) topological phases are determined by a quarter (negative eighth) of the total polarized topological charges, but also reveals that the higher-order topological phase transitions are identified by the creation or annihilation of polarized topological charges. Particularly, these polarized topological charges can be measured by pseudospin structures of the systems. Due to theoretical simplicity and observational intuitiveness, this work shall advance the broad studies of the HOTPs in both theory and experiment. △ Less

Submitted 3 December, 2024; v1 submitted 8 May, 2024; originally announced May 2024.

Comments: 8+9 pages, 4+3 figures. References are updated.Typos are corrected

Journal ref: Phys. Rev. B 110, L201117 (2024)

A method for quantifying the generalization capabilities of generative models for solving Ising models

Authors: Qunlong Ma, Zhi Ma, Ming Gao

Abstract: For Ising models with complex energy landscapes, whether the ground state can be found by neural networks depends heavily on the Hamming distance between the training datasets and the ground state. Despite the fact that various recently proposed generative models have shown good performance in solving Ising models, there is no adequate discussion on how to quantify their generalization capabilitie… ▽ More For Ising models with complex energy landscapes, whether the ground state can be found by neural networks depends heavily on the Hamming distance between the training datasets and the ground state. Despite the fact that various recently proposed generative models have shown good performance in solving Ising models, there is no adequate discussion on how to quantify their generalization capabilities. Here we design a Hamming distance regularizer in the framework of a class of generative models, variational autoregressive networks (VAN), to quantify the generalization capabilities of various network architectures combined with VAN. The regularizer can control the size of the overlaps between the ground state and the training datasets generated by networks, which, together with the success rates of finding the ground state, form a quantitative metric to quantify their generalization capabilities. We conduct numerical experiments on several prototypical network architectures combined with VAN, including feed-forward neural networks, recurrent neural networks, and graph neural networks, to quantify their generalization capabilities when solving Ising models. Moreover, considering the fact that the quantification of the generalization capabilities of networks on small-scale problems can be used to predict their relative performance on large-scale problems, our method is of great significance for assisting in the Neural Architecture Search field of searching for the optimal network architectures when solving large-scale Ising models. △ Less

Submitted 6 May, 2024; originally announced May 2024.

Comments: 10 pages, 7 figures

Journal ref: Mach. Learn.: Sci. Technol. 5 (2024) 025011

Message Passing Variational Autoregressive Network for Solving Intractable Ising Models

Authors: Qunlong Ma, Zhi Ma, Jinlong Xu, Hairui Zhang, Ming Gao

Abstract: Many deep neural networks have been used to solve Ising models, including autoregressive neural networks, convolutional neural networks, recurrent neural networks, and graph neural networks. Learning a probability distribution of energy configuration or finding the ground states of a disordered, fully connected Ising model is essential for statistical mechanics and NP-hard problems. Despite tremen… ▽ More Many deep neural networks have been used to solve Ising models, including autoregressive neural networks, convolutional neural networks, recurrent neural networks, and graph neural networks. Learning a probability distribution of energy configuration or finding the ground states of a disordered, fully connected Ising model is essential for statistical mechanics and NP-hard problems. Despite tremendous efforts, a neural network architecture with the ability to high-accurately solve these fully connected and extremely intractable problems on larger systems is still lacking. Here we propose a variational autoregressive architecture with a message passing mechanism, which can effectively utilize the interactions between spin variables. The new network trained under an annealing framework outperforms existing methods in solving several prototypical Ising spin Hamiltonians, especially for larger spin systems at low temperatures. The advantages also come from the great mitigation of mode collapse during the training process of deep neural networks. Considering these extremely difficult problems to be solved, our method extends the current computational limits of unsupervised neural networks to solve combinatorial optimization problems. △ Less

Submitted 9 April, 2024; originally announced April 2024.

Comments: 18 pages, 14 figures

Journal ref: Communications Physics 7, 236 (2024)

Absence of phonon-mediated superconductivity in La$_3$Ni$_2$O$_7$ under pressure

Authors: Zhenfeng Ouyang, Miao Gao, Zhong-Yi Lu

Abstract: A recent experimental study announced the emergence of superconductivity in La$_3$Ni$_2$O$_7$ under pressure, with the highest observed superconducting transition temperature ($T_c$) reaching approximately 80 K beyond 14 GPa. While extensive studies have been devoted to the electronic correlations and potential superconducting pairing mechanisms, there lack investigations into the phonon propertie… ▽ More A recent experimental study announced the emergence of superconductivity in La$_3$Ni$_2$O$_7$ under pressure, with the highest observed superconducting transition temperature ($T_c$) reaching approximately 80 K beyond 14 GPa. While extensive studies have been devoted to the electronic correlations and potential superconducting pairing mechanisms, there lack investigations into the phonon properties and electron phonon coupling. Using density functional theory in conjunction with Wannier interpolation techniques, we study the phonon properties and electron phonon interactions in La$_3$Ni$_2$O$_7$ under 29.5 GPa. Our findings reveal that the electron phonon coupling is insufficient to solely explain the observed high superconducting $T_c$ $\sim$ 80 K in La$_3$Ni$_2$O$_7$. And the calculated strong Fermi surface nesting may explain the experimental observed charge density wave transition in La$_3$Ni$_2$O$_7$. Our calculations substantiate La$_3$Ni$_2$O$_7$ is an unconventional superconductor. △ Less

Submitted 21 March, 2024; originally announced March 2024.

Comments: 5 pages, 4 figures

Journal ref: npj Quantum Mater. 9, 80 (2024)

Two-dimensional Kagome-in-Honeycomb materials (MN$_4$)$_3$C$_{32}$ (M=Pt or Mn)

Authors: Jingping Dong, Miao Gao, Xun-Wang Yan, Fengjie Ma, Zhong-Yi Lu

Abstract: We propose two novel two-dimensional (2D) topological materials, (PtN$_4$)$_3$C$_{32}$ and (MnN$_4$)$_3$C$_{32}$, with a special geometry that we named as kagome-in-honeycomb (KIH) lattice structure, to illustrate the coexistence of the paradigmatic states of kagome physics, Dirac fermions and flat bands, that are difficult to be simultaneously observed in three-dimensional realistic systems. In s… ▽ More We propose two novel two-dimensional (2D) topological materials, (PtN$_4$)$_3$C$_{32}$ and (MnN$_4$)$_3$C$_{32}$, with a special geometry that we named as kagome-in-honeycomb (KIH) lattice structure, to illustrate the coexistence of the paradigmatic states of kagome physics, Dirac fermions and flat bands, that are difficult to be simultaneously observed in three-dimensional realistic systems. In such system, MN$_4$(M=Pt or Mn) moieties are embedded in honeycomb graphene sheet according to kagome lattice structure, thereby resulting in a KIH lattice. Using the first-principles calculations, we have systemically studied the structural, electronic, and topological properties of these two materials. In the absence of spin-orbit coupling (SOC), they both exhibit the coexistence of Dirac/quadratic-crossing cone and flat band near the Fermi level. When SOC is included, a sizable topological gap is opened at the Dirac/quadratic-crossing nodal point. For nonmagnetic (PtN$_4$)$_3$C$_{32}$, the system is converted into a $\mathbb{Z}_2$ topological quantum spin Hall insulator defined on a curved Fermi level, while for ferromagnetic (MnN$_4$)$_3$C$_{32}$, the material is changed from a half-semi-metal to a quantum anomalous Hall insulator with nonzero Chern number and nontrivial chiral edge states. Our findings not only predict a new family of 2D quantum materials, but also provide an experimentally feasible platform to explore the emergent kagome physics, topological quantum Hall physics, strongly correlated phenomena, and theirs fascinating applications. △ Less

Submitted 5 March, 2024; originally announced March 2024.

Comments: 6 figures. arXiv admin note: text overlap with arXiv:2207.03703

Majorana modes in trapped-ion system and their Floquet engineering

Authors: Ming-Jian Gao, Yu-Peng Ma, Jun-Hong An

Abstract: Obeying non-Abelian statistics, Majorana fermions holds a promise to implement fault-tolerant quantum computing. It was found that Majorana fermions can be simulated by the zero-energy excitation in a nanowire with strong spin-orbit coupling interacting with an $s$-wave superconductor under a magnetic field. However, the signal of Majorana fermion in that system is obscured by the disorder in the… ▽ More Obeying non-Abelian statistics, Majorana fermions holds a promise to implement fault-tolerant quantum computing. It was found that Majorana fermions can be simulated by the zero-energy excitation in a nanowire with strong spin-orbit coupling interacting with an $s$-wave superconductor under a magnetic field. However, the signal of Majorana fermion in that system is obscured by the disorder in the nanowire and the confinement potential at the wire end. Thus, more controllable platforms are desired to simulate Majorana fermions. We here propose an alternative scheme to simulate the Majorana fermions in a trapped-ion system. Our dimerized-ion configuration permits us to generate the Majorana modes not only at zero energy but also at the nonzero ones, which enlarge the family of Majorana modes and supply another qubit carrier for quantum computing. We also investigate the controllability of the Majorana modes by Floquet engineering. It is found that a widely tunable number of Majorana modes are created on demand by applying a periodic driving on the trapped-ion system. Enriching the platforms for simulating Majorana fermions, our result would open another avenue for realizing fault-tolerant quantum computing. △ Less

Submitted 22 May, 2024; v1 submitted 21 January, 2024; originally announced January 2024.

Journal ref: Phys. Rev. B 109, 184518 (2024)

Twisted van der Waals Quantum Materials: Fundamentals, Tunability and Applications

Authors: Xueqian Sun, Manuka Suriyage, Ahmed Khan, Mingyuan Gao, Jie Zhao, Boqing Liu, Mehedi Hasan, Sharidya Rahman, Ruosi Chen, Ping Koy Lam, Yuerui Lu

Abstract: Twisted vdW quantum materials have emerged as a rapidly developing field of 2D semiconductors. These materials establish a new central research area and provide a promising platform for studying quantum phenomena and investigating the engineering of novel optoelectronic properties such as single-photon emission, non-linear optical response, magnon physics, and topological superconductivity. These… ▽ More Twisted vdW quantum materials have emerged as a rapidly developing field of 2D semiconductors. These materials establish a new central research area and provide a promising platform for studying quantum phenomena and investigating the engineering of novel optoelectronic properties such as single-photon emission, non-linear optical response, magnon physics, and topological superconductivity. These captivating electronic and optical properties result from, and can be tailored by, the interlayer coupling using moiré patterns formed by vertically stacking atomic layers with controlled angle misorientation or lattice mismatch. Their outstanding properties and the high degree of tunability position them as compelling building blocks for both compact quantum-enabled devices and classical optoelectronics. This article offers a comprehensive review of recent advancements in the understanding and manipulation of twisted van der Waals structures and presents a survey of the state-of-the-art research on moiré superlattices, encompassing interdisciplinary interests. It delves into fundamental theories, synthesis and fabrication, and visualization techniques, and the wide range of novel physical phenomena exhibited by these structures, with a focus on their potential for practical device integration in applications ranging from quantum information to biosensors, and including classical optoelectronics such as modulators, light emitting diodes (LEDs), lasers, and photodetectors. It highlights the unique ability of moiré superlattices to connect multiple disciplines, covering chemistry, electronics, optics, photonics, magnetism, topological and quantum physics. This comprehensive review provides a valuable resource for researchers interested in moiré superlattices, shedding light on their fundamental characteristics and their potential for transformative applications in various fields. △ Less

Submitted 18 December, 2023; originally announced December 2023.

Comments: 179 pages, 42 figures, Chemical Reviews

MSC Class: 85-06 ACM Class: J.2

Ab-initio tensile tests applied to BCC refractory alloys

Authors: Vishnu Raghuraman, Saro San, Michael C. Gao, Michael Widom

Abstract: Refractory metals exhibit high strength at high temperature, but often lack ductility. Multiprinciple element alloys such as high entropy alloys offer the potential to improve ductility while maintaining strength, but we don't know $a-priori$ what compositions will be suitable. A number of measures have been proposed to predict the ductility of metals, notably the Pugh ratio, the Rice-Thomson D-pa… ▽ More Refractory metals exhibit high strength at high temperature, but often lack ductility. Multiprinciple element alloys such as high entropy alloys offer the potential to improve ductility while maintaining strength, but we don't know $a-priori$ what compositions will be suitable. A number of measures have been proposed to predict the ductility of metals, notably the Pugh ratio, the Rice-Thomson D-parameter, among others. Here we examine direct $ab-initio$ simulation of deformation under tensile strain, and we apply this to a variety of Nb- and Mo-based binary alloys and to several quaternary alloy systems. Our results exhibit peak stresses for elastic deformation, beyond which defects such as lattice slip, stacking faults, transformation, and twinning, relieve the stress. The peak stress grows strongly with increasing valence electron count. Correlations are examined among several physical properties, including the above-mentioned ductility parameters. △ Less

Submitted 5 December, 2023; v1 submitted 29 November, 2023; originally announced November 2023.

Comments: 22 pages, 13 figures, accepted for publication in Physical Review Materials

Engineering rich two-dimensional higher-order topological phases by flux and periodic driving

Authors: Ming-Jian Gao, Jun-Hong An

Abstract: Nodal-line semimetals are commonly believed to exist in $\mathcal{PT}$ symmetric or mirror-rotation symmetric systems. Here, we find a flux-induced parameter-dimensional second-order nodal-line semimetal (SONLS) in a two-dimensional system without $\mathcal{PT}$ and mirror-rotation symmetries. It has coexisting hinge Fermi arcs and drumhead surface states. Meanwhile, we discover a flux-induced sec… ▽ More Nodal-line semimetals are commonly believed to exist in $\mathcal{PT}$ symmetric or mirror-rotation symmetric systems. Here, we find a flux-induced parameter-dimensional second-order nodal-line semimetal (SONLS) in a two-dimensional system without $\mathcal{PT}$ and mirror-rotation symmetries. It has coexisting hinge Fermi arcs and drumhead surface states. Meanwhile, we discover a flux-induced second-order topological insulator (SOTI). We then propose a Floquet engineering scheme to create exotic parameter-dimensional hybrid-order nodal-line semimetals with abundant nodal-line structures and widely tunable numbers of corner states in a SONLS and SOTI, respectively. Our results break the perception of SONLSs and supply a convenient way to artificially synthesize exotic topological phases by periodic driving. △ Less

Submitted 8 December, 2023; v1 submitted 4 September, 2023; originally announced September 2023.

Journal ref: Phys. Rev. B 108, L241402 (2023)

Predictions and correlation analyses of Ellingham diagrams in binary oxides

Authors: Shun-Li Shang, Shuang Lin, Michael C. Gao, Darrell G. Schlom, Zi-Kui Liu

Abstract: Knowing oxide-forming ability is vital to gain desired or avoid deleterious oxides formation through tuning oxidizing environment and materials chemistry. Here, we have conducted a comprehensive thermodynamic analysis of 137 binary oxides using the presently predicted Ellingham diagrams. It is found that the active elements to form oxides easily are the f-block elements (lanthanides and actinides)… ▽ More Knowing oxide-forming ability is vital to gain desired or avoid deleterious oxides formation through tuning oxidizing environment and materials chemistry. Here, we have conducted a comprehensive thermodynamic analysis of 137 binary oxides using the presently predicted Ellingham diagrams. It is found that the active elements to form oxides easily are the f-block elements (lanthanides and actinides), elements in the groups II, III, and IV (alkaline earth, Sc, Y, Ti, Zr, and Hf), and Al and Li; while the noble elements with their oxides nonstable and easily reduced are coinage metals (Cu, Ag, and especially Au), Pt-group elements, and Hg and Se. Machine learning based sequential feature selection indicates that oxide-forming ability can be represented by electronic structures of pure elements, for example, their d- and s-valence electrons, Mendeleev numbers, and the groups, making the periodic table a useful tool to tailor oxide-forming ability. The other key elemental features to correlate oxide-forming ability are thermochemical properties such as melting points and standard entropy at 298 K of pure elements. It further shows that the present Ellingham diagrams enable qualitatively understanding and even predicting oxides formed in multicomponent materials, such as the Fe-20Cr-20Ni alloy (in wt.%) and the equimolar high entropy alloy of AlCoCrFeNi, which are in accordance with thermodynamic calculations using the CALPHAD approach and experimental observations in the literature. △ Less

Submitted 10 August, 2023; originally announced August 2023.

Structural, electronic, magnetic properties of Cu-doped lead-apatite Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O

Authors: Jianfeng Zhang, Huazhen Li, Ming Yan, Miao Gao, Fengjie Ma, Xun-Wang Yan, Z. Y. Xie

Abstract: The recent report of superconductivity in the Cu-doped PbPO compound stimulates the extensive researches on its physical properties. Herein, the detailed atomic and electronic structures of this compound are investigated, which are the necessary information to explain the physical properties, including possible superconductivity. By the first-principles electronic structure calculations, we find t… ▽ More The recent report of superconductivity in the Cu-doped PbPO compound stimulates the extensive researches on its physical properties. Herein, the detailed atomic and electronic structures of this compound are investigated, which are the necessary information to explain the physical properties, including possible superconductivity. By the first-principles electronic structure calculations, we find that the partial replacement of Pb at $4f$ site by Cu atom, instead of Pb at $6h$ site, plays a crucial role in dominating the electronic state at Fermi energy. The $3d$ electronic orbitals of Cu atom emerge near the Fermi energy and exhibit strong spin-polarization, resulting in the local moment around the doped Cu atom. Particularly, the ground state of Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O (x = 1) is determined to be a semiconducting phase, in good agreement with the experimental measurements. △ Less

Submitted 8 August, 2023; originally announced August 2023.

Superconductivity at ambient pressure in hole-doped LuH$_3$

Authors: Zhenfeng Ouyang, Miao Gao, Zhong-Yi Lu

Abstract: Very recently, a report on possible room-temperature superconductivity in N-doped lutetium hydrides near 1 GPa pressure has drawn lots of attentions. To date, the superconductivity is not confirmed under relatively low pressure in subsequent studies. Based on the density functional theory first-principles calculations, we extensively investigate the influence of charge doping on the stability and… ▽ More Very recently, a report on possible room-temperature superconductivity in N-doped lutetium hydrides near 1 GPa pressure has drawn lots of attentions. To date, the superconductivity is not confirmed under relatively low pressure in subsequent studies. Based on the density functional theory first-principles calculations, we extensively investigate the influence of charge doping on the stability and superconductivity of LuH$_3$ at ambient pressure. Although electron doping can not stabilize LuH$_3$, we find that the room-pressure stability of LuH$_3$ can be achieved by doping holes with concentrations in between 0.15-0.30 holes/cell. Moreover, our calculations reveal a positive dependence of superconducting transition temperature on the number of doped holes, with the highest value close to 54 K. These findings suggest that realizing superconductivity in hole-doped LuH$_3$ at ambient pressure is not impossible, although the transition temperature is still far away from the room temperature. △ Less

Submitted 24 June, 2023; originally announced June 2023.

Comments: 6 pages, 6 figures

Microscopic resolution of superconducting electrons in ultrahigh-pressed hydrogen sulfide

Authors: Jian-Feng Zhang, Bo Zhan, Miao Gao, Kai Liu, Xinguo Ren, Zhong-Yi Lu, Tao Xiang

Abstract: We investigate the electronic and phonon properties of hydrogen sulfide (SH$_3$) under ultrahigh pressure to elucidate the origin of its high-T$_c$ superconductivity. Contrary to the prevailing belief that the metalized S-H $σ$ bond is responsible, our analysis, based on the anisotropic Migdal-Eliashberg equation and the crystal orbital Hamilton population (COHP) calculation, reveals that the H-H… ▽ More We investigate the electronic and phonon properties of hydrogen sulfide (SH$_3$) under ultrahigh pressure to elucidate the origin of its high-T$_c$ superconductivity. Contrary to the prevailing belief that the metalized S-H $σ$ bond is responsible, our analysis, based on the anisotropic Migdal-Eliashberg equation and the crystal orbital Hamilton population (COHP) calculation, reveals that the H-H $σ$-antibonding states play a dominant role in the large electron-phonon coupling that leads to the superconducting pairing in SH$_3$. Furthermore, by partially restricting the vibration of S atoms, we demonstrate that the S-H bonds provide subsidiary contributions to the pairing interaction. These findings shed light on the importance of the previously overlooked H-H $σ^*$ bonds in driving high-T$_c$ superconductivity in SH$_3$ and offer insights into the relationship between metallic H-H covalent antibonding and high-T$_c$ superconductivity in other hydrogen-rich materials under high pressure. △ Less

Submitted 6 June, 2023; originally announced June 2023.

Comments: 11 pages, 9 figures, 59 references

Single-shot spatial instability and electric control of polariton condensates at room temperature

Authors: Ying Gao, Xuekai Ma, Xiaokun Zhai, Chunzi Xing, Meini Gao, Haitao Dai, Hao Wu, Tong Liu, Yuan Ren, Xiao Wang, Anlian Pan, Wei Hu, Stefan Schumacher, Tingge Gao

Abstract: In planar microcavities, the transverse-electric and transverse-magnetic (TE-TM) mode splitting of cavity photons arises due to their different penetration into the Bragg mirrors and can result in optical spin-orbit coupling (SOC). In this work, we find that in a liquid crystal (LC) microcavity filled with perovskite microplates, the pronounced TE-TM splitting gives rise to a strong SOC that leads… ▽ More In planar microcavities, the transverse-electric and transverse-magnetic (TE-TM) mode splitting of cavity photons arises due to their different penetration into the Bragg mirrors and can result in optical spin-orbit coupling (SOC). In this work, we find that in a liquid crystal (LC) microcavity filled with perovskite microplates, the pronounced TE-TM splitting gives rise to a strong SOC that leads to the spatial instability of microcavity polariton condensates under single-shot excitation. Spatially varying hole burning and mode competition occurs between polarization components leading to different condensate profiles from shot to shot. The single-shot polariton condensates become stable when the SOC vanishes as the TE and TM modes are spectrally well separated from each other, which can be achieved by application of an electric field to our LC microcavity with electrically tunable anisotropy. Our findings are well reproduced and traced back to their physical origin by our detailed numerical simulations. With the electrical manipulation our work reveals how the shot-to-shot spatial instability of spatial polariton profiles can be engineered in anisotropic microcavities at room temperature, which will benefit the development of stable polariton-based optoeletronic and light-emitting devices. △ Less

Submitted 2 May, 2023; originally announced May 2023.