Showing 1–50 of 289 results for author: Lin, X

Morphology-Guided Deterministic Fabrication of Low-Noise High-Temperature Superconducting Quantum Interference Devices

Authors: Bingke Xiang, Wanjuan Tang, Shiqun Liu, Lingtong Hou, Geming Zhang, Yibo Wang, Ruonan Wang, Zhiqiang Cao, Jiaqi Wei, Xueshen Wang, Xueying Zhang, Xiaoyang Lin

Abstract: Reproducible bicrystal high-temperature superconducting quantum interference devices remain limited by local variability along the grain boundaries that form the Josephson junctions. Here, we develop a site-selective fabrication workflow in which atomic force microscopy maps the intended junction region before lithography, quantifies an apparent grain-boundary width, rejects pore-rich segments, an… ▽ More Reproducible bicrystal high-temperature superconducting quantum interference devices remain limited by local variability along the grain boundaries that form the Josephson junctions. Here, we develop a site-selective fabrication workflow in which atomic force microscopy maps the intended junction region before lithography, quantifies an apparent grain-boundary width, rejects pore-rich segments, and writes a nearby registration mark for site-specific pattern alignment. The apparent grain-boundary width provides a practical morphology metric, with narrower regions consistently yielding larger critical currents and characteristic voltages. Iterative optimization within this workflow further improves junction and device performance, reaching a liquid-nitrogen-temperature field-noise level of 40 fT Hz^(-1/2). This strategy turns local grain-boundary heterogeneity from an uncontrolled source of variability into a basis for site-selective fabrication, providing a route towards scalable manufacturing of low-noise HTS SQUIDs with high uniformity. △ Less

Submitted 16 August, 2026; originally announced August 2026.

Comments: 12 pages, 4 figures

Pressure induced magnetic-field-free superconducting diode effect in NbSe2 flake

Authors: Shihao Zhu, Tian Le, Cuiying Pei, Changhua Li, Yi Liao, Yi Zhao, Lingxiao Zhao, Qi Wang, Juefei Wu, Qilian Zhang, Yueshen Wu, Tonghuan Fu, Xujie Lü, Wenge Yang, Jie Shen, Jun Li, Yulin Chen, Xiao Lin, Wen-Yu He, Yanpeng Qi

Abstract: The superconducting diode effect (SDE) is a fascinating nonreciprocal phenomenon where the critical current is different for opposite current directions. It is widely believed that realizing SDE requires breaking both inversion symmetry (IS) and time-reversal symmetry (TRS), which are usually achieved via heterostructure engineering and applying external magnetic fields. Here, we report a pressure… ▽ More The superconducting diode effect (SDE) is a fascinating nonreciprocal phenomenon where the critical current is different for opposite current directions. It is widely believed that realizing SDE requires breaking both inversion symmetry (IS) and time-reversal symmetry (TRS), which are usually achieved via heterostructure engineering and applying external magnetic fields. Here, we report a pressure-induced magnetic-field-free SDE in NbSe2 flakes without any heterostructures. We show that pressure alone breaks the IS, as confirmed by the second harmonic generation. Crucially, upon applying an out-of-plane magnetic field (B), the SDE exhibits even-in-B behavior, implying the absence of explicit TRS breaking. This finding challenges the prevailing theoretical paradigm and demonstrates that a magnetic-field-free SDE can emerge without explicitly breaking TRS. Thereby, our work establishes pressure engineering as a powerful tool for inducing nonreciprocal superconductivity and designing versatile, magnetic-field-free superconducting devices. △ Less

Submitted 3 August, 2026; originally announced August 2026.

Comments: 10 pages,4 figues

Journal ref: Phys. Rev. Lett. 137, 076003 (2026)

Ultracold atomic lattice systems for simulating topological phases: A review

Authors: Bei-Bei Wang, Xiao-Dong Lin, Jinyi Zhang, Long Zhang

Abstract: Owing to rapid recent progress, ultracold atomic lattice systems for simulating topological phases are now at a pivotal stage, evolving from established paradigms into increasingly versatile and programmable quantum simulators. In this review, we survey recent experimental advances across four major classes of platforms: optical lattices, including optical lattices with laser-assisted tunneling an… ▽ More Owing to rapid recent progress, ultracold atomic lattice systems for simulating topological phases are now at a pivotal stage, evolving from established paradigms into increasingly versatile and programmable quantum simulators. In this review, we survey recent experimental advances across four major classes of platforms: optical lattices, including optical lattices with laser-assisted tunneling and optical Raman lattices; synthetic lattices in momentum or internal-state space; Floquet-engineered lattices; and optical tweezer arrays, all of which offer distinct capabilities for realizing and probing topological matter. For each class, we highlight representative experimental breakthroughs, the topological models that have been realized, and the advanced detection and characterization techniques employed, emphasizing how these complementary approaches collectively expand the frontier of quantum simulation. We also discuss emerging directions in strongly correlated and nonequilibrium topological phases, and conclude with an outlook on future prospects. △ Less

Submitted 17 June, 2026; v1 submitted 15 June, 2026; originally announced June 2026.

Comments: 22 pages, 8 figure, 1 table, submitted to Quantum Review Letters. A slightly revised version

Journal ref: Quantum Review Letters 2, 117-134 (2026)

Curvature-driven revival of charge density waves in non-Euclidean space

Authors: Zhipeng Song, Zeyu Liu, Junde Liu, Yi Biao, Anning Yang, Qian Fang, Mojun Pan, Chen Liu, Jiaou Wang, Tian Qian, Chenmin shen, Hongliang Lu, Wei Ji, Hong-Jun Gao, Xiao Lin

Abstract: Strongly correlated quantum states, such as charge density waves (CDWs), are exquisitely sensitive to Fermi surface topology and lattice symmetry, and are typically quenched by heavy carrier doping. In two-dimensional (2D) systems, however, macroscopic geometric curvature emerges as a novel structural degree of freedom to modulate microscopic quantum coherence. This raises a compelling physical qu… ▽ More Strongly correlated quantum states, such as charge density waves (CDWs), are exquisitely sensitive to Fermi surface topology and lattice symmetry, and are typically quenched by heavy carrier doping. In two-dimensional (2D) systems, however, macroscopic geometric curvature emerges as a novel structural degree of freedom to modulate microscopic quantum coherence. This raises a compelling physical question: can non-Euclidean geometric deformations compete with extreme electronic perturbations to reshape, or even revive, a quenched macroscopic quantum order? Here, by constructing monolayer TiSe$_2$-NbSe$_2$ heterostructure on a BLG/SiC substrate for the first time, we report the curvature-driven revival of a frustrated charge order in a non-Euclidean space. Low-temperature angle-resolved photoemission spectroscopy (ARPES) reveals a massive interfacial charge transfer, which destroys the global Fermi surface nesting and completely suppresses the long-range CDW order in Euclidean flat regions. Strikingly, high-resolution scanning tunneling microscopy (STM) reveals that a novel, non-linear CDW state miraculously survives, remaining strictly localized within morphologically distorted, non-Euclidean nanoscale curved regions. Atomistic simulations unravel the structural origin of this phenomenon, demonstrating that interfacial twist and lattice mismatch spontaneously generate a corrugated superlattice. △ Less

Submitted 3 June, 2026; originally announced June 2026.

Three- and four-boson systems expanded around the unitarity limit: Application to $^4$He

Authors: Feng Wu, Xincheng Lin, Ubirajara van Kolck, Sebastian König

Abstract: The three- and four-boson systems with a large scattering length and a short effective range in the two-body sector are studied in the framework of Short-Range Effective Field Theory. The starting point (leading order) of the EFT is taken to be the universal unitarity limit, where the two-body sector is parameter-free and only one three-body parameter enters. In this limit, physical systems manife… ▽ More The three- and four-boson systems with a large scattering length and a short effective range in the two-body sector are studied in the framework of Short-Range Effective Field Theory. The starting point (leading order) of the EFT is taken to be the universal unitarity limit, where the two-body sector is parameter-free and only one three-body parameter enters. In this limit, physical systems manifests discrete scale invariance. Deviations from universality arising from finite scattering-length and effective-range corrections, as well as a four-body force required by renormalization, are included perturbatively at next-to-leading order. The three-body ground state and its associated four-body ground and first-excited states are studied using the Faddeev-Yakubovsky formalism and a complementary diagrammatic approach. By employing techniques to remove contributions from deep trimers in tetramer calculations, we extend our analysis to larger cutoffs than previously accessible within the FY approach. Our results for binding energies and radii of $^4$He three- and four-atom systems converge well to results obtained with sophisticated phenomenological potentials. These successes suggest that the physics of $^4$He atomic clusters is governed by only small deviations from discrete scale invariance. △ Less

Submitted 30 May, 2026; originally announced June 2026.

Comments: 29 pages, 20 figures

Zero-Field Thermal Hall Effect in Insulator

Authors: Zhe Cui, Haoran Fan, Wenjiang Zhou, Xianghong Jin, Yuchen Gu, Da Ma, Cong Xiao, Hua Jiang, Xincheng Xie, Bai Song, Yuan Li, Xi Lin

Abstract: Fourier's law dictates that heat flow is usually parallel to the applied temperature gradient. However, under a high magnetic field, heat flow carried by both electrons in conductors and phonons in insulators can be deflected, a phenomenon known as thermal Hall effect. Intriguingly, we observe at zero field a spontaneous thermal Hall effect in an antiferromagnetic insulator. Despite a vanishingly… ▽ More Fourier's law dictates that heat flow is usually parallel to the applied temperature gradient. However, under a high magnetic field, heat flow carried by both electrons in conductors and phonons in insulators can be deflected, a phenomenon known as thermal Hall effect. Intriguingly, we observe at zero field a spontaneous thermal Hall effect in an antiferromagnetic insulator. Despite a vanishingly small uncompensated magnetization, the magnitude of this effect is surprisingly large, comparable to typical responses induced by several teslas of external field. This zero-field behavior indicates that charge-neutral heat carriers can be governed by an intrinsic effective field arising from the unique spin arrangement. Our discovery challenges the centuries-old preconception of heat conduction and open up new avenues for exploring non-trivial topological responses in quantum materials. △ Less

Submitted 27 May, 2026; originally announced May 2026.

Momentum-Resolved Tunneling Modulation Induced Giant Multistate Resistance in Antiferroelectric Multiferroic Junction

Authors: Wei Yang, Yibo Xu, Shen Li, Jiangchao Han, Jiayou Chen, Juan-Carlos Rojas-Sánchez, Stéphane Mangin, Xiaoyang Lin, Weisheng Zhao

Abstract: Multiferroic tunnel junctions (MFTJs), integrating ferroelectric and ferromagnetic functionalities within a single nanoscale device, hold significant promise for non-volatile, multi-state memory and innovative computing paradigms. In conventional MFTJs, tunneling resistance modulation relies primarily on ferroelectric (FE) polarization switching, which alters interfacial electric fields and shifts… ▽ More Multiferroic tunnel junctions (MFTJs), integrating ferroelectric and ferromagnetic functionalities within a single nanoscale device, hold significant promise for non-volatile, multi-state memory and innovative computing paradigms. In conventional MFTJs, tunneling resistance modulation relies primarily on ferroelectric (FE) polarization switching, which alters interfacial electric fields and shifts the Fermi level of adjacent ferromagnetic electrodes. However, achieving high tunnelelectroresistance (TER) through this approach demands strong built-in electric fields, which simultaneously hinder FE polarization switching, creating an intrinsic trade-off between reliable data reading and efficient writing. Here, we propose a dual mechanism that combines antiferroelectric (AFE) phase-transition modulation of the evanescent decay states with interfacial spin filtering based on $Fe_3GaTe_2$/bilayer-$In_2Se_3$/$Fe_3GaTe_2$ heterostructure. Beyond altering the electrostatic potential as in AFE-FE switching, the transitions between head-type and tail-type AFE states preserve the centrosymmetric potential profile yet fundamentally modulate the momentum-resolved distribution of evanescent decay rates across the Brillouin zone. When integrated with perfect spin filtering at the $Fe_3GaTe_2$/$α$-$In_2Se_3$ interface, this mechanism yields a giant TER (~$7.6\times10^3\%$), over 4 times that of conventional FE-based MFTJs, and a TMR exceeding $6.8\times10^5\%$, enhanced by two orders of magnitude over typical MFTJs. These mechanisms resolve the performance trade-off in MFTJs, enabling six distinct non-volatile resistance states at room temperature. △ Less

Submitted 22 May, 2026; originally announced May 2026.

Comments: 26 pages, 5 figures

Journal ref: ACS Nano 19 (2025) 38573-38582

Discovery of a nonsymmorphic superconductor with spontaneous rotational symmetry breaking and nontrivial zero modes

Authors: Hui Guo, Zhixuan Li, Senhao Lv, Tianqi Gao, Zihao Huang, Kuanrong Hao, Lizhi Zhang, Ke Zhu, Siyu Li, Xianghe Han, Xiao Lin, Shengshan Qin, Wu Zhou, Haitao Yang, Hui Chen, Hong-Jun Gao

Abstract: Topological superconductivity has attracted great interest due to its fundamental significance for realizing Majorana quasiparticles and fault-tolerant quantum computation. Nonsymmorphic superconductors, with symmetry-protected nontrivial electronic structures, offer a promising route to exotic topological superconducting states, yet experimental realizations remain scarce. Here we identify nonsym… ▽ More Topological superconductivity has attracted great interest due to its fundamental significance for realizing Majorana quasiparticles and fault-tolerant quantum computation. Nonsymmorphic superconductors, with symmetry-protected nontrivial electronic structures, offer a promising route to exotic topological superconducting states, yet experimental realizations remain scarce. Here we identify nonsymmorphic compound PtPb4 as a robust platform hosting superconductivity with spontaneous rotational symmetry breaking and nontrivial zero-energy modes. PtPb4 crystallizes in a frustrated Shastry-Sutherland lattice and exhibits nontrivial band topology. By combining in-plane and out-of-plane resistivity measurements, pronounced twofold anisotropy is observed in both the superconducting state and the upper critical field, evidencing spontaneous rotational symmetry breaking. Scanning tunneling microscopy/spectroscopy further reveal twofold-symmetric magnetic vortices, providing direct real-space evidence for the symmetry-broken superconducting state. Notably, a robust zero-energy vortex bound state emerges and persists without spatial splitting over extended distances, consistent with the characteristics expected for Majorana bound state. These findings uncover an exotic superconducting state in PtPb4 and establish a promising platform for exploring topological superconductivity and superconducting quantum devices. △ Less

Submitted 11 May, 2026; originally announced May 2026.

Comments: 18 pages, 5 figures

Cascade of fractional quantum Hall states in 2D system

Authors: Zhimou Chen, Jiaojie Yan, Yuxuan Zhu, Zhe Cui, Loren N. Pfeiffer, Kenneth W. West, Kirk W. Baldwin, Adbhut Gupta, Yang Liu, Wei Zhu, Wenchen Luo, Ying-Hai Wu, Shuai Yuan, Xi Lin

Abstract: The observation of the fractional quantum Hall (FQH) effect in 2D electron gases ushered in investigations of topological phases driven by strong electron correlations. Their remarkable features include fractionalized elementary excitations, gapless boundary states, and non-trivial quantum entanglement patterns. Thanks to persistent efforts in the building of new platforms and making higher-qualit… ▽ More The observation of the fractional quantum Hall (FQH) effect in 2D electron gases ushered in investigations of topological phases driven by strong electron correlations. Their remarkable features include fractionalized elementary excitations, gapless boundary states, and non-trivial quantum entanglement patterns. Thanks to persistent efforts in the building of new platforms and making higher-quality samples, a diverse plethora of FQH states have been unveiled in experiments. We report a systematic study of ultrahigh-quality GaAs/AlGaAs quantum wells with mobility up to 3.7*10^7 cm^2/V/s using quantum transport measurements in nuclear adiabatic demagnetization and dilution refrigerators down to 1 mK. In addition to many FQH states that have already been identified in previous work, new longitudinal resistance dips are observed at filling factors 17/33 and 15/31. The application of an in-plane magnetic field causes disparate variations of the FQH states. The theoretical foundation of these states is discussed in the framework of composite fermion theory. While most fractions can be explained as non-interacting composite fermions forming integer quantum Hall states, a few states correspond to FQH states of composite fermions that arise from residual interaction between them. We summarize the observed fractions in the range of 0 < ν < 2 and propose a pattern to account for their experimental appearance that provides an intuitive picture about the relative strengths of different FQH states. △ Less

Submitted 11 May, 2026; originally announced May 2026.

Comments: 15 pages, 4 figures and 1 table in manuscript; 5 pages and 4 figures in supplemental material

Journal ref: National Science Review 13(8): nwag079, 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.

Discovery of parity-violating chiral polar-nematic charge density wave and superconductivity in kagome metals

Authors: Xingwei Shi, Geng Li, Zhan Wang, Chuqi Zhang, Ke Zhu, Keyu Zeng, Zikun Tang, Li Huang, Zhen Zhao, Jianping Sun, Xiao Liu, Jin-Guang Cheng, Chengmin Shen, Shu Ping Lau, Kian Ping Loh, Haitao Yang, Xiao Lin, Ziqiang Wang, Hong-Jun Gao

Abstract: Nonmagnetic kagome metals and superconductors AV3Sb5 (A = K, Rb, Cs) host unconventional charge density wave (CDW) and superconducting (SC) phases accompanied by multiple electronic symmetry breaking. Due to the centrosymmetric crystal structure, inversion symmetry has generally been assumed to hold. Here, using scanning tunneling microscopy complemented by atomic force microscopy and optical seco… ▽ More Nonmagnetic kagome metals and superconductors AV3Sb5 (A = K, Rb, Cs) host unconventional charge density wave (CDW) and superconducting (SC) phases accompanied by multiple electronic symmetry breaking. Due to the centrosymmetric crystal structure, inversion symmetry has generally been assumed to hold. Here, using scanning tunneling microscopy complemented by atomic force microscopy and optical second-harmonic generation, we directly reveal that inversion symmetry in the kagome plane is spontaneously broken in the CDW state. The mixed-parity CDW state exhibits ferroelectric dipolar and nematic quadrupolar ordered moments. The coexistence and coupling between the dipole and quadrupole favor noncollinear ferro-polar and nematic alignment that breaks all mirror symmetries and gives rise to robust electronic chirality in the 3Q CDW. The multipolar coupling to in-plane electric field enables electric field control and manipulation of the chiral polar-nematic CDW state, including its chirality. Below the SC transition, we observe parity-violating pair density modulations at both the original and the CDW lattice wavevectors. Our findings of parity-violating electronic chiral multipolar order provide microscopic insights into the magnetoelectric and nonreciprocal transport, loop current order, pairing density waves, and unconventional superconductivity in kagome metals and related quantum materials. △ Less

Submitted 22 April, 2026; originally announced April 2026.

Enhanced Anomalous Nernst Effect in the Ferromagnetic Kondo Lattice CeCo2As2

Authors: Shuyue Guan, Weian Guo, Pengyu Zheng, Xinxuan Lin, Yuqing Huang, Jiawei Li, Xiao-Bin Qiang, Longfei Li, Weiwei Xie, Hai-Zhou Lu, Zhiping Yin, Shuang Jia

Abstract: The anomalous Nernst effect (ANE), generating a voltage perpendicular to a temperature gradient due to magnetization, is closely linked to the Berry curvature (BC) near the Fermi energy in topological magnets. We report an enhanced spontaneous ANE in the ferromagnetic Kondo lattice CeCo2As2, which features Kondo-screened cerium-based 4f moments embedded in a ferromagnetic d-electron framework. The… ▽ More The anomalous Nernst effect (ANE), generating a voltage perpendicular to a temperature gradient due to magnetization, is closely linked to the Berry curvature (BC) near the Fermi energy in topological magnets. We report an enhanced spontaneous ANE in the ferromagnetic Kondo lattice CeCo2As2, which features Kondo-screened cerium-based 4f moments embedded in a ferromagnetic d-electron framework. The observed large anomalous Nernst coefficient, greater than the Seebeck coefficient, is attributed to the strong BC present in the f-orbital-dominated flat bands. The enhanced ANE in CeCo2As2 serves as a signature of the Fermi energy pinning within the topological flat band, highlighting the correlation-driven topology in the Kondo lattice. △ Less

Submitted 20 April, 2026; originally announced April 2026.

Journal ref: Phys. Rev. Lett. 136, 036505 (2026)

Strain-Induced Curvature in Monolayer Graphene: Effects on Electronic Structure, Phonon Dynamics, and Lattice Thermal Conductivity

Authors: M. C. Santos, E. Lora da Silva, D. S. Baptista, T. Santos, M. Molinari, F. J. Manjón, Yin Cui, Xidong Lin, Tao Yang

Abstract: We present a comprehensive set of calculations to investigate the effect of strain-induced x-y topological perturbation in the monolayer graphene sheet. We show that the induced curvature with the defined strain constraint, energetically stabilizes the systems. The electronic properties are modified when the amplitude of the curvature of the sheet increases, which induces Van Hove singularities of… ▽ More We present a comprehensive set of calculations to investigate the effect of strain-induced x-y topological perturbation in the monolayer graphene sheet. We show that the induced curvature with the defined strain constraint, energetically stabilizes the systems. The electronic properties are modified when the amplitude of the curvature of the sheet increases, which induces Van Hove singularities of the electronic Density of States to approach the Fermi energy. The highly curved system exhibits coexisting flat and linear dispersions close to the Fermi level, which is a promising feature for thermoelectric applications. We also demonstrate, through the phonon dispersion curves, that respective systems are dynamically stable within the studied range of strains/curvatures. Moreover, the flexural acoustic mode transitions from quadratic to linear dispersion under strain, mimicking the 3D behavior and enhancing phonon scattering. The increase of phonon scattering will therefore decrease the value of the lattice thermal conductivity, $κ_L$. Such results allows us to conclude that it is possible to tune $κ_L$ by applying x-y strain to the monolayer sheet, and inducing different topological curvatures. △ Less

Submitted 13 April, 2026; originally announced April 2026.

Comments: 14 pages, 8 main figures and 3 supplementary figures

LLM-Driven Discovery of High-Entropy Catalysts via Retrieval-Augmented Generation

Authors: AI Scientists, Xinyi Lin, Danqing Yin, Ying Guo

Abstract: CO2 reduction requires efficient catalysts, yet materials discovery remains bottlenecked by 10-20 year development cycles requiring deep domain expertise. This paper demonstrates how large language models can assist the catalyst discovery process by helping researchers explore chemical spaces and interpret results when augmented with retrieval-based grounding. We introduce a retrieval-augmented ge… ▽ More CO2 reduction requires efficient catalysts, yet materials discovery remains bottlenecked by 10-20 year development cycles requiring deep domain expertise. This paper demonstrates how large language models can assist the catalyst discovery process by helping researchers explore chemical spaces and interpret results when augmented with retrieval-based grounding. We introduce a retrieval-augmented generation framework that enables GPT-4 to navigate chemical space by accessing a database of 50,000+ known materials, adapting general-purpose language understanding for high-throughput materials design. Our approach generated over 250 catalyst candidates with an 82% thermodynamic stability rate while addressing multi-objective constraints: 68% achieved <$100/kg cost with metallic conductivity (band gap<0.1eV) and mechanical stability (B/G>1.75). The best-performing Fe0.2Co0.2Ni0.2Ir0.1Ru0.3 achieves 0.285V limiting potential (25% improvement over IrO2), while Cr0.2Fe0.2Co0.3Ni0.2Mo0.1 optimally balances performance-cost trade-offs at $18/kg. Volcano plot analysis confirms that 78% of LLM-generated catalysts cluster near the theoretical activity optimum, while our system achieves 200x computational efficiency compared to traditional high-throughput screening. By demonstrating that retrieval-augmented generation can ground AI creativity in physical constraints without sacrificing exploration, this work demonstrates an approach where natural language interfaces can streamline materials discovery workflows, enabling researchers to explore chemical spaces more efficiently while the LLM assists in result interpretation and hypothesis generation. △ Less

Submitted 16 March, 2026; originally announced March 2026.

Journal ref: Open Conference of AI Agents for Science 2025

Melting of quantum Hall Wigner and bubble crystals

Authors: H. Xia, Qianhui Xu, Jiasen Niu, Jian Sun, Yang Liu, L. N. Pfeiffer, K. W. West, Pengjie Wang, Bo Yang, Xi Lin

Abstract: A two-dimensional crystal melts via the proliferation and unbinding of topological defects, yet quantitatively predicting the melting temperature $T_m$ in real systems is challenging. Here we resolve this discrepancy in quantum Hall electron bubble phases by combining Corbino-geometry transport experiment in an ultraclean GaAs/AlGaAs quantum well for Landau levels 2 to 5 with Hartree--Fock elastic… ▽ More A two-dimensional crystal melts via the proliferation and unbinding of topological defects, yet quantitatively predicting the melting temperature $T_m$ in real systems is challenging. Here we resolve this discrepancy in quantum Hall electron bubble phases by combining Corbino-geometry transport experiment in an ultraclean GaAs/AlGaAs quantum well for Landau levels 2 to 5 with Hartree--Fock elasticity and the full Kosterlitz--Thouless--Halperin--Nelson--Young melting criterion including the finite-temperature renormalization-group calculation. The theoretically obtained $T_m$ quantitatively captures the measured solid-liquid phase transition boundaries across all probed ranges, validating the bubble-crystal interpretation and establishing defect--mediated melting as a predictive framework for strongly interacting electronic solids. This agreement further supports using bulk transport to probe the energetics of topological defects and screening in quantum Hall physics, and the approach is readily extendable to other electronic crystals, including the generalized Wigner crystal in moiré Chern bands. △ Less

Submitted 6 March, 2026; v1 submitted 12 February, 2026; originally announced February 2026.

Comments: 16 pages, 5 figures

Proposal for realizing unpaired Weyl points in a three-dimensional periodically driven optical Raman lattice

Authors: Xiao-Dong Lin, Jinyi Zhang, Long Zhang

Abstract: In static lattice systems, the Nielsen-Ninomiya theorem enforces the pairing of Weyl points with opposite chiralities, which precludes the chiral magnetic effect (CME) in equilibrium. Periodic driving provides a viable route to circumvent this no-go constraint. Here, we propose a scheme to realize and control unpaired Weyl points using ultracold atoms in a three-dimensional (3D) optical Raman latt… ▽ More In static lattice systems, the Nielsen-Ninomiya theorem enforces the pairing of Weyl points with opposite chiralities, which precludes the chiral magnetic effect (CME) in equilibrium. Periodic driving provides a viable route to circumvent this no-go constraint. Here, we propose a scheme to realize and control unpaired Weyl points using ultracold atoms in a three-dimensional (3D) optical Raman lattice under continuous periodic driving. By engineering distinct relative symmetries between the lattice and multiple Raman potentials, the configuration generates an effective 3D spin-orbit coupling and yields a tunable topological-insulator phase. Through adiabatic periodic modulation of this system, we show that eight Weyl points emerge in the quasienergy spectrum of the low-energy sector, whose net chirality can be precisely tuned. A nonzero total chirality directly corresponds to the formation of unpaired Weyl points. Furthermore, by implementing a synthetic magnetic field via laser-assisted tunneling in this setup, we demonstrate that the chirality imbalance drives a quantized charge current in the weak-field regime, providing a direct signature of the CME. We verify that the adiabatic condition of the driving protocol, as well as the proposed experimental preparation and detection techniques, are within reach of current ultracold-atom experiments. This work establishes a realistic and controllable platform for exploring chiral-anomaly physics and nonequilibrium topological phenomena linked to Weyl fermions. △ Less

Submitted 28 May, 2026; v1 submitted 12 February, 2026; originally announced February 2026.

Comments: 14 pages, 5 figures, to appear in PRA

Journal ref: Phys. Rev. A 113, 063303 (2026)

Nonvolatile electric switching of critical current in cross-bar superconducting junctions

Authors: Jiajun Ma, Jingyi He, Qiong Qin, Tian Le, Zhiwei Wang, Jie Wu, Congjun Wu, Xiao Lin

Abstract: Superconducting (SC) diodes are key passive building blocks for future SC electronics. However, realizing their active counterparts is essential for functional logic. Here, we demonstrate deterministic nonvolatile electrical switching of the critical current ($I_\text{c}$) in overlap crossbar SC junctions. By applying a minimal perpendicular magnetic field ($H_\text{z}$), $I_\text{c}$ is modulated… ▽ More Superconducting (SC) diodes are key passive building blocks for future SC electronics. However, realizing their active counterparts is essential for functional logic. Here, we demonstrate deterministic nonvolatile electrical switching of the critical current ($I_\text{c}$) in overlap crossbar SC junctions. By applying a minimal perpendicular magnetic field ($H_\text{z}$), $I_\text{c}$ is modulated by a factor of four with a large switching efficiency of 60\%, achieved at a significantly reduced excitation current density of $5\times10^5$~A/cm$^2$. We also uncover anomalous behaviors: an electrically switchable critical temperature and a non-monotonic $I_\text{c}$-$H_\textit{z}$ response. These observations are interpreted in terms of unique asymmetry involving isolated vortex injection, configuration and repulsion inherent to the junction geometry. Our device provides a scalable, low-power alternative to complex SQUID-based architectures, paving the way for high-density SC integrated circuits. △ Less

Submitted 23 January, 2026; originally announced January 2026.

Comments: 7 pages, 4 figures

Laughlin pumping assisted by surface acoustic waves

Authors: Renfei Wang, Xiao Liu, Adbhut Gupta, Kirk W. Baldwin, Loren Pfeiffer, Wenfeng Zhang, Rui-Rui Du, Mansour Shayegan, Xi Lin, Ying-Hai Wu, Yang Liu

Abstract: The quantum Hall effect is a fascinating electrical transport phenomenon signified by precise quantization of Hall conductivity $σ_\mathrm{xy}$ and vanishing longitudinal conductivity $σ_\mathrm{xx}$. Laughlin proposed an elegant explanation in which adiabatic insertion of a flux tube pumps charge through the system. This analysis unveils the fundamental role of gauge invariance and provides a com… ▽ More The quantum Hall effect is a fascinating electrical transport phenomenon signified by precise quantization of Hall conductivity $σ_\mathrm{xy}$ and vanishing longitudinal conductivity $σ_\mathrm{xx}$. Laughlin proposed an elegant explanation in which adiabatic insertion of a flux tube pumps charge through the system. This analysis unveils the fundamental role of gauge invariance and provides a compelling argument about the fractional charge of fractional quantum Hall states. While it has been used extensively as a theoretical tool, a quantitative experimental investigation is lacking despite multiple attempts. Here we report successful realizations of Laughlin pumping in several integer and fractional quantum Hall states. One essential technical innovation is using surface acoustic waves to periodically clear the charges accumulated during the pumping process. Magnetic fluxes are inserted at a constant rate so there is no need to perform complicated data fitting. Furthermore, our setting can reliably extract $σ_\mathrm{xx}$ that is several orders of magnitude lower than the limit of conventional techniques. Effective energy gaps can be deduced from the temperature dependence of $σ_\mathrm{xx}$, which are drastically different from those provided by conventional transport data. This work not only brings a famous gedanken experiment to reality but also serves as a portal for many future investigations. △ Less

Submitted 17 January, 2026; originally announced January 2026.

Comments: 23 pages, 14 figures

Growth of Large Crystals of Janus Phase RhSeCl Using Self-Selecting Vapour Growth

Authors: Anastasiia Lukovkina, Maria A. Herz, Xiaohanwen Lin, Volodymyr Multian, Alberto Morpurgo, Enrico Giannini, Fabian O. von Rohr

Abstract: In recent years, interest in 2D Janus materials has grown exponentially, particularly with regard to their applications in spintronics and optoelectronic devices. The defining feature of Janus materials is the ordered arrangement of different layer terminations - creating chemically distinct surfaces and an inherent out-of-plane polarity. Among the few known Janus materials, RhSeCl is particularly… ▽ More In recent years, interest in 2D Janus materials has grown exponentially, particularly with regard to their applications in spintronics and optoelectronic devices. The defining feature of Janus materials is the ordered arrangement of different layer terminations - creating chemically distinct surfaces and an inherent out-of-plane polarity. Among the few known Janus materials, RhSeCl is particularly intriguing as a rare example of an intrinsic Janus compound. Owing to its exceptional chemical stability, RhSeCl offers a promising platform for exploring the physics related to the Janus-structure. However, synthesising large, high-quality crystals of this compound remains a significant challenge. Here, we report a novel synthetic pathway for growing crystals up to 6 mm in lateral size via a two-step self-selecting vapour growth reaction. We further present a comprehensive comparison of newly developed synthesis routes with all previously reported methods for RhSeCl. During these investigations, we identified a previously unreported impurity that forms in specific growth pathways and demonstrate how it can be avoided to obtain phase-pure few- and monolayer flakes. We showcase the reproducibility of the process to obtain high-quality, large single-crystals and flakes. △ Less

Submitted 16 January, 2026; originally announced January 2026.

Journal ref: CrystEngComm, 2026

Emergence of unconventional magnetic order in strain-engineered RuO2/TiO2 superlattices

Authors: Seung Gyo Jeong, Seungjun Lee, Jin Young Oh, Bonnie Y. X. Lin, Anand Santhosh, James M. LeBeau, Alexander J. Grutter, Woo Seok Choi, Tony Low, Valeria Lauter, Bharat Jalan

Abstract: The spin ordering in RuO2 remains a highly debated topic, owing to its elusive nature, with reports ranging from a nonmagnetic ground state to signatures of unconventional magnetic order. Here we provide the first unambiguous, and direct evidence of unconventional magnetism in epitaxial, fully strained RuO2/TiO2 superlattices on TiO2 (110) substrate grown by hybrid molecular beam epitaxy. Polarize… ▽ More The spin ordering in RuO2 remains a highly debated topic, owing to its elusive nature, with reports ranging from a nonmagnetic ground state to signatures of unconventional magnetic order. Here we provide the first unambiguous, and direct evidence of unconventional magnetism in epitaxial, fully strained RuO2/TiO2 superlattices on TiO2 (110) substrate grown by hybrid molecular beam epitaxy. Polarized neutron reflectometry reveals a finite magnetic moment localized within the compressively strained RuO2 layers, consistent with predictions obtained from first-principles calculations. Complementary density functional theory and X-ray photoemission spectroscopy show that epitaxial strain drives the Ru 4d states toward the Fermi level, triggering a Stoner-type instability that stabilizes non-compensated magnetic order. These unique results reveal that RuO2 exhibits unconventional magnetic states under epitaxial strain, which are not accessible in bulk and establish strain engineering as a powerful route to uncover and control magnetic phases in RuO2 and related oxides. △ Less

Submitted 15 January, 2026; originally announced January 2026.

Comments: 23 pages, 3 figures

Magnetic-Field-Driven Insulator-Superconductor Transition in Rhombohedral Graphene

Authors: Jian Xie, Zihao Huo, Zhimou Chen, Zaizhe Zhang, Kenji Watanabe, Takashi Taniguchi, Xi Lin, Xiaobo Lu

Abstract: Recent studies of rhombohedral multilayer graphene (RMG) have revealed a variety of superconducting states that can be induced or enhanced by magnetic fields, reinforcing RMG as a powerful platform for investigating novel superconductivity. Here we report an insulator-superconductor transition driven by in-plane magnetic fields B|| in rhombohedral hexalayer graphene. The upper critical in-plane fi… ▽ More Recent studies of rhombohedral multilayer graphene (RMG) have revealed a variety of superconducting states that can be induced or enhanced by magnetic fields, reinforcing RMG as a powerful platform for investigating novel superconductivity. Here we report an insulator-superconductor transition driven by in-plane magnetic fields B|| in rhombohedral hexalayer graphene. The upper critical in-plane field of 2T violates the Pauli limit, and an analysis based on isospin symmetry breaking supports a spin-polarized superconductor. At in-plane B = 0, such spin-polarized superconductor transitions into an insulator, exhibiting a thermally activated gap of 0.1 meV. In addition, we observe four superconducting states in the hole-doped regime, as well as phases with orbital multiferroicity near charge neutrality point. These findings substantially enrich the phase diagram of rhombohedral graphene and provide new insight into the microscopic mechanisms of superconductivity △ Less

Submitted 30 December, 2025; originally announced December 2025.

The Three-Body Limit Cycle: Universal Form for General Regulators

Authors: Langxuan Chen, Feng Wu, Xincheng Lin, Sebastian König, Ubirajara van Kolck, Pengfei Zhang

Abstract: The Efimov effect, a remarkable realization of discrete scale invariance, emerges in the three-body problem with short-range interactions and is understood as a renormalization group (RG) limit cycle within Short-Range Effective Field Theory (SREFT). While the analytic form of the three-body renormalization relation has been established for a sharp cutoff regulator, its universality for other regu… ▽ More The Efimov effect, a remarkable realization of discrete scale invariance, emerges in the three-body problem with short-range interactions and is understood as a renormalization group (RG) limit cycle within Short-Range Effective Field Theory (SREFT). While the analytic form of the three-body renormalization relation has been established for a sharp cutoff regulator, its universality for other regulators remains underexplored. In this work, we derive the universal functional form of the three-body renormalization relation for general separable regulators through a detailed analysis of the Skorniakov-Ter-Martirosian and Faddeev equations. We find that the relation follows from a real Möbius transformation characterized by three parameters. This universality is verified numerically for various regulators. Although the functional form remains the same, the parameters characterizing the limit cycle exhibit regulator dependence. These findings broaden the class of RG limit cycles in SREFT and offer a more complete understanding of three-body renormalization. △ Less

Submitted 29 January, 2026; v1 submitted 4 September, 2025; originally announced September 2025.

Comments: 10 pages, 4 figures

Journal ref: Phys. Rev. A 113, 013314 (2026)

Unilateral Criticality and Phase Transition in the Cavity-Ising Model

Authors: Zeyu Rao, Xiaoshui Lin, Xiwang Luo, Guangcan Guo, Han Pu, Ming Gong

Abstract: Superradiant phase transitions from cavity light-matter coupling have been widely explored across platforms. Here, we report a unilateral critical endpoint (UCEP) and a tricritical point (TCP) in the phase diagram of the cavity-coupled transverse Ising model with $\mathbb{Z}_2$ symmetry. At zero temperature, we demonstrate that this model hosts three phases separated by two second-order and one fi… ▽ More Superradiant phase transitions from cavity light-matter coupling have been widely explored across platforms. Here, we report a unilateral critical endpoint (UCEP) and a tricritical point (TCP) in the phase diagram of the cavity-coupled transverse Ising model with $\mathbb{Z}_2$ symmetry. At zero temperature, we demonstrate that this model hosts three phases separated by two second-order and one first-order transitions. These lines intersect at a TCP and a UCEP, the latter not captured by existing phase-transition paradigms. The UCEP displays one-sided criticality: approaching the point from one side, the system behaves as a second-order transition, while from the other side it is first-order. Correspondingly, two order parameters, respectively, undergo the first- and the second-order phase transitions at the same point. We construct a minimal description of UCEP with the density of the free energy $f = c_{1}(\tildeα^{2}+c_{2})+(\tildeα^{2}+c_{2})^{2}\ln{\vert\tildeα^{2}+c_{2}\vert}$, with the UCEP at $(c_{1},c_{2})=(1/e,0)$ and $\tildeα$ being the order parameter. We further map the finite-temperature phase diagram and perform a symmetry analysis. By unifying first- and second-order signatures in a single, direction-dependent endpoint, the UCEP introduces a qualitatively new class of phase transition and may have applications in fields such as quantum measurement and quantum sensing. This work also provides an intriguing platform for exploring novel critical phenomena in cavity-coupled many-body systems with or without dissipation. △ Less

Submitted 5 September, 2025; v1 submitted 4 September, 2025; originally announced September 2025.

Comments: 9 pages, 4 figures. Supplementary Material provided as ancillary file (supp.pdf, 15 pages)

Thermomodulated intrinsic Josephson effect in Kagome CsV3Sb5

Authors: Tian Le, Zhuokai Xu, Jinjin Liu, Ruiya Zhan, Zhiwei Wang, Xiao Lin

Abstract: Superconducting chiral domains associated with a time-reversal symmetry-breaking order parameter have garnered significant attention in Kagome systems. In this work, we demonstrate both the intrinsic direct-current and alternating-current Josephson effects in the nanoplates of the vanadium-based Kagome material CsV3Sb5, as evidenced by Fraunhofer-like patterns and Shapiro steps. Moreover, both the… ▽ More Superconducting chiral domains associated with a time-reversal symmetry-breaking order parameter have garnered significant attention in Kagome systems. In this work, we demonstrate both the intrinsic direct-current and alternating-current Josephson effects in the nanoplates of the vanadium-based Kagome material CsV3Sb5, as evidenced by Fraunhofer-like patterns and Shapiro steps. Moreover, both the Fraunhofer-like patterns and Shapiro steps are modulated by thermal cycling, suggesting that the Josephson effects arise from dynamic superconducting domains. These findings may provide new insights into chiral superconductivity in CsV3Sb5 and highlight the potential of these intrinsic Josephson junctions for applications in chiral superconductor based quantum devices. △ Less

Submitted 22 August, 2025; originally announced August 2025.

Comments: 13 pages, 5 figures, Physical Review Letter in press

Microstructural and preliminary optical and microwave characterization of erbium doped CaMoO$_4$ thin films

Authors: Ignas Masiulionis, Bonnie Y. X. Lin, Sagar Kumar Seth, Gregory D. Grant, Wanda L. Lindquist, Sungjoon Kim, Junghwa Kim, Angel Yanguas-Gil, Jeffrey W. Elam, Jiefei Zhang, James M. LeBeau, David D. Awschalom, Supratik Guha

Abstract: This work explores erbium-doped calcium molybdate (CaMoO$_4$) thin films grown on silicon and yttria stabilized zirconia (YSZ) substrates, as a potential solid state system for C-band (utilizing the $\sim$1.5 $μ$m Er$^{3+}$ 4f-4f transition) quantum emitters for quantum network applications. Through molecular beam epitaxial growth experiments and electron microscopy, X-ray diffraction and reflecti… ▽ More This work explores erbium-doped calcium molybdate (CaMoO$_4$) thin films grown on silicon and yttria stabilized zirconia (YSZ) substrates, as a potential solid state system for C-band (utilizing the $\sim$1.5 $μ$m Er$^{3+}$ 4f-4f transition) quantum emitters for quantum network applications. Through molecular beam epitaxial growth experiments and electron microscopy, X-ray diffraction and reflection electron diffraction studies, we identify an incorporation limited deposition regime that enables a 1:1 Ca:Mo ratio in the growing film leading to single phase CaMoO$_4$ formation that can be in-situ doped with Er (typically 2-100 ppm). We further show that growth on silicon substrates is single phase but polycrystalline in morphology; while growth on YSZ substrates leads to high-quality epitaxial single crystalline CaMoO$_4$ films. We perform preliminary optical and microwave characterization on the suspected $Y_1 - Z_1$ transition of 2 ppm, 200 nm epitaxial CaMoO$_4$ annealed thin films and extract an optical inhomogeneous linewidth of 9.1(1) GHz, an optical excited state lifetime of 6.7(2) ms, a spectral diffusion-limited homogeneous linewidth of 6.7(4) MHz, and an EPR linewidth of 1.10(2) GHz. △ Less

Submitted 20 August, 2025; originally announced August 2025.

Comments: 8 pages, 4 figures

Orbital-selective charge transfer drives two-step negative thermal expansion structural transitions in PbTa2Se4

Authors: Peng Li, Xiaohui Yang, Wenhua Song, Zhefeng Lou, Tongrui Li, Zhengtai Liu, Zhu'an Xu, Zhuoyu Chen, Xiao Lin, Yang Liu

Abstract: The negative thermal expansion (NTE) effect has been found generally combined with structural phase transitions. However, the charge and orbital freedoms of the NTE has not been well studied. This study employs angle-resolved photoemission spectroscopy and first-principles calculations to elucidate the charge and orbital kinetics of the anomalous two-step negative thermal expansion structural phas… ▽ More The negative thermal expansion (NTE) effect has been found generally combined with structural phase transitions. However, the charge and orbital freedoms of the NTE has not been well studied. This study employs angle-resolved photoemission spectroscopy and first-principles calculations to elucidate the charge and orbital kinetics of the anomalous two-step negative thermal expansion structural phase transitions in PbTa2Se4. As the temperature decreases, each transition undergoes a similar block-layer sliding, although the charge transfer behaviors differ significantly. During the first transition, charge is mainly transferred from the Pb 6pz orbital to an M-shaped band below the Fermi level, barely altering the Fermi surface. In contrast, the second transition involves modifications to both the Fermi surface and charge-transfer orbitals, with charge selectively transferred from Pb 6px/py orbitals to Ta 5dz2 orbitals and a decrease of the Fermi pockets formed by Pb 6px/py orbitals. Furthermore, a small pressure can easily tune the base structure phase among the three phases and the corresponding superconductivity. Therefore, our findings reveal that the orbital-selective charge transfer drives the unusual structure transition in PbTa2Se4, offering new insights into the NTE mechanisms and providing a unique window to study the pressure-tuned superconductivity in this metal-intercalated transition chalcogenides. △ Less

Submitted 29 July, 2025; originally announced July 2025.

Comments: 4 figures

Strain-Stabilized Interfacial Polarization Tunes Work Function Over 1 eV in RuO2/TiO2 Heterostructures

Authors: Seung Gyo Jeong, Bonnie Y. X. Lin, Mengru Jin, In Hyeok Choi, Seungjun Lee, Zhifei Yang, Sreejith Nair, Rashmi Choudhary, Juhi Parikh, Anand Santhosh, Matthew Neurock, Kelsey A. Stoerzinger, Jong Seok Lee, Tony Low, Qing Tu, James M. LeBeau, Bharat Jalan

Abstract: Interfacial polarization-charge accumulation at the heterointerface-is a well-established tool in semiconductors, but its influence in metals remains unexplored. Here, we demonstrate that interfacial polarization can robustly modulate surface work function in metallic rutile RuO2 layers in epitaxial RuO2/TiO2 heterostructures grown by hybrid molecular beam epitaxy. Using multislice electron ptycho… ▽ More Interfacial polarization-charge accumulation at the heterointerface-is a well-established tool in semiconductors, but its influence in metals remains unexplored. Here, we demonstrate that interfacial polarization can robustly modulate surface work function in metallic rutile RuO2 layers in epitaxial RuO2/TiO2 heterostructures grown by hybrid molecular beam epitaxy. Using multislice electron ptychography, we directly visualize polar displacements of transition metal ions relative to oxygen octahedra near the interface, despite the conductive nature of RuO2. This interfacial polarization enables over 1 eV modulation of the RuO2 work function, controlled by small thickness variation (2-4 nm) as measured by Kelvin probe probe microscopy, with a critical thickness of 4 nm - corresponding to the transition from fully strained to relaxed film. These results establish interfacial polarization as a powerful route to control electronic properties in metals and have implications for designing tunable electronic, catalytic, and quantum devices through interfacial control in polar metallic systems. △ Less

Submitted 10 July, 2025; originally announced July 2025.

Comments: 25 pages, 4 figures

Soliton and traveling wave solutions in coupled one-dimensional condensates

Authors: Zeyu Rao, Xiaoshui Lin, Jingsong He, Guangcan Guo, Ming Gong

Abstract: Ultracold condensates provide a unique platform for exploring soliton physics. Motivated by the recent experiments realizing the sine-Gordon model in a split one-dimensional (1D) BEC, we demonstrate that this system naturally supports various density and phase solitons. We explore the physics using the bosonization technique, in which the phase and density are conjugate pairs, and determine its ef… ▽ More Ultracold condensates provide a unique platform for exploring soliton physics. Motivated by the recent experiments realizing the sine-Gordon model in a split one-dimensional (1D) BEC, we demonstrate that this system naturally supports various density and phase solitons. We explore the physics using the bosonization technique, in which the phase and density are conjugate pairs, and determine its effective Language equation and the associated equation of motion. We show that in the presence of asymmetry between the two condensates, new solutions beyond those in the sine-Gordon model emerge. We calculate the traveling wave solutions and soliton solutions in this model and determine their corresponding energy densities analytically. Finally, we discuss the relevance of these solutions to the experiments and discuss their observations. This theory does not rely on the mechanism of quasi-particle excitation, which yields the Lee-Huang-Yang correction in higher dimensions, and is thus much more suitable to describe the physics in 1D systems. Since the physical models have already been realized in experiments, this work opens a new frontier for the realization of various soliton and periodic solutions using two coupled condensates. △ Less

Submitted 9 July, 2025; originally announced July 2025.

Microscopic mechanisms of Strong Electron Scattering and Giant Anomalous Hall Effect in high-Curie-temperature Fe3GaTe2 van der Waals Films

Authors: Zhengxiao Li, Xin Lin, Yu Zou, Fanjie Tan, Wenliang Zhu, Lijun Zhu

Abstract: Van der Waals ferromagnet Fe3GaTe2 with room-temperature perpendicular magnetic anisotropy and strong anomalous Hall effect has attracted considerable interest for their potential in spintronics. However, the microscopic mechanisms and manipulation of the electron scattering and the anomalous Hall effect of Fe3GaTe2 have remained unsettled. Here, we demonstrate strong tuning of the electron scatte… ▽ More Van der Waals ferromagnet Fe3GaTe2 with room-temperature perpendicular magnetic anisotropy and strong anomalous Hall effect has attracted considerable interest for their potential in spintronics. However, the microscopic mechanisms and manipulation of the electron scattering and the anomalous Hall effect of Fe3GaTe2 have remained unsettled. Here, we demonstrate strong tuning of the electron scattering and anomalous Hall effect of pattern-defined Fe3GaTe2 Hall-bar devices with perpendicular magnetic anisotropy, high Curie temperature (340 K, as high as that of Fe3GaTe2 bulk), and giant anomalous Hall effect by varying the layer thickness and temperature. Temperature-dependent resistivity experiments reveal that the electron scattering of the high-quality Fe3GaTe2 is dominated by impurity scattering and phonon scattering, regardless of the thickness. Combined temperature- and thickness-dependent scaling analyses of the anomalous Hall resistivity reveal that the anomalous Hall effect of the Fe3GaTe2 is predominantly from the positive, temperature-independent skew-scattering contribution that competes with negative temperature-independent, side-jump contribution, and negative, temperature-dependent intrinsic Berry-curvature contribution. The intrinsic anomalous Hall conductivity decreases rapidly with increasing impurity scattering, which is consistent with the characteristic variation of intrinsic Hall conductivities in the dirty-metal regime. These findings advance the understanding of electron scattering and the anomalous Hall effect in van der Waals magnets and would benefit the application of the Fe3GaTe2 in spintronics. △ Less

Submitted 2 June, 2025; originally announced June 2025.

Journal ref: Advanced Functional Materials 35, e12048 (2025)

Measuring topological invariants of even-dimensional line-gapped non-Hermitian systems through quench dynamics

Authors: Xiao-Dong Lin, Long Zhang

Abstract: The accurate determination of non-Hermitian (NH) topological invariants plays a central role in the study of NH topological phases. In this work, we propose a general framework for directly measuring NH topological invariants in even-dimensional systems with real line gaps through quench dynamics. Our approach hinges on constructing an auxiliary Hermitian matrix topologically equivalent to the ori… ▽ More The accurate determination of non-Hermitian (NH) topological invariants plays a central role in the study of NH topological phases. In this work, we propose a general framework for directly measuring NH topological invariants in even-dimensional systems with real line gaps through quench dynamics. Our approach hinges on constructing an auxiliary Hermitian matrix topologically equivalent to the original NH Hamiltonian, enabling topological characterization via reduced-dimensional momentum subspaces called band-inversion surfaces (BISs). A key insight lies in the emergence of chiral symmetry in the NH Hamiltonian specifically on BISs -- a critical property that allows extension of the dynamical characterization scheme previously developed for odd-dimensional NH systems with chiral or sublattice symmetry [Lin et al., Phys. Rev. Res. 7, L012060 (2025)]. We show that NH topological invariants can be extracted from the winding patterns of a dynamical field constructed from post-quench spin textures on BISs. We demonstrate our approach through a detailed analysis of NH Chern insulators and then extend the framework to higher even-dimensional systems by introducing second-order BISs for characterization. The framework is also generalized to imaginary line-gapped topological phases. This work establishes an experimentally accessible protocol for detecting NH topological invariants in quantum platforms. △ Less

Submitted 3 September, 2025; v1 submitted 29 May, 2025; originally announced May 2025.

Comments: 12 pages, 5 figures; complementary to arXiv: 2410.13241; to appear in PRB

Journal ref: Phys. Rev. B 112, 125133 (2025)

Pseudo-Goldstone Modes at Finite Temperature

Authors: Xiyue Lin, Tao Shi

Abstract: Goldstone's theorem and its extension to pseudo-Goldstone (PG) modes have profound implications across diverse areas of physics, from quantum chromodynamics to quantum magnetism. PG modes emerge from accidental degeneracies lifted by quantum and thermal fluctuations, leading to a finite gap--a phenomenon known as "order by disorder." In this paper, we derive a general curvature formula for the PG… ▽ More Goldstone's theorem and its extension to pseudo-Goldstone (PG) modes have profound implications across diverse areas of physics, from quantum chromodynamics to quantum magnetism. PG modes emerge from accidental degeneracies lifted by quantum and thermal fluctuations, leading to a finite gap--a phenomenon known as "order by disorder." In this paper, we derive a general curvature formula for the PG gap at finite temperature, applicable to both collinear (e.g., ferromagnets and anti-ferromagnets) and noncollinear magnetic orders (e.g., coplanar orders in frustrated magnetic systems). After validating our formula against known models, we apply it to the XXZ model on the triangular lattice, which hosts coplanar magnetic orders in equilibrium and is relevant to materials such as Na2BaCo(PO4)2 and K2Co(SeO3)2, known for their supersolid phases and giant magnetocaloric effects. Our results reveal a distinct scaling behavior: a linear decrease of the PG gap with temperature, driven by entropy effects from magnon scattering across multiple bands. This stands in stark contrast to the high-temperature scaling recently proposed for systems with a single magnon band. This work establishes a general framework for investigating PG modes at finite temperatures and opens an avenue to explore rich quantum phases and dynamics in frustrated systems with noncollinear magnetic orders. △ Less

Submitted 12 May, 2025; originally announced May 2025.

Normal mode analysis within relativistic massive transport

Authors: Xin Lin, Qiu-Ze Sun, Xin-Hui Wu, Jin Hu

Abstract: In this paper, we address the normal mode analysis on the linearized Boltzmann equation for massive particles in the relaxation time approximation. One intriguing feature of massive transport is the coupling of the secular equations between the sound and heat channels. This coupling vanishes as the mass approaches zero. By utilizing the argument principle in complex analysis, we determine the exis… ▽ More In this paper, we address the normal mode analysis on the linearized Boltzmann equation for massive particles in the relaxation time approximation. One intriguing feature of massive transport is the coupling of the secular equations between the sound and heat channels. This coupling vanishes as the mass approaches zero. By utilizing the argument principle in complex analysis, we determine the existence condition for collective modes and find the onset transition behavior of collective modes previously observed in massless systems. We numerically determine the critical wavenumber for the existence of each mode under various values of the scaled mass. Within the range of scaled masses considered, the critical wavenumbers for the heat and shear channels decrease with increasing scaled mass, while that of the sound channel exhibits a non-monotonic dependence on the scaled mass. In addition, we analytically derive the dispersion relations for these collective modes in the long-wavelength limit. Notably, kinetic theory also incorporates collisionless dissipation effects, known as Landau damping. We find that the branch cut structure responsible for Landau damping differs significantly from the massless case: whereas the massless system features only two branch points, the massive system exhibits an infinite number of such points forming a continuous branch cut. △ Less

Submitted 12 April, 2026; v1 submitted 7 May, 2025; originally announced May 2025.

Comments: Match the vesrion of PRD. Add comparison with other related studies. 17 pages, 5 figures, any questions, comments are welcome!

Journal ref: Phys. Rev. D 113, 076010, 2026

Dimensionality Enhanced Out-of-Plane Spin Currents in NbIrTe$_4$ for Efficient Field-Free Switching of Perpendicular Magnetization

Authors: Wei Yang, Xinhe Wang, Jianing Liu, Daming Zhou, Xiaoyang Lin, Ke Zhang, Heloise Damas, Xinyue Wang, Xianyang Lu, Haozhe Yang, Stephane Mangin, Sebastien Petit-Watelot, Michel Hehn, Albert Fert, Juan-Carlos Rojas-Sanchez, Weisheng Zhao

Abstract: Efficient generation of out-of-plane (OOP) spin currents is crucial for advanced spintronic memory applications. However, the theoretical understanding and experimental implementation of robust OOP spin currents for high-density and low-power magnetization switching remain significant challenges of spintronics. Here, we demonstrate that transitioning NbIrTe$_4$ from a two-dimensional quantum spin… ▽ More Efficient generation of out-of-plane (OOP) spin currents is crucial for advanced spintronic memory applications. However, the theoretical understanding and experimental implementation of robust OOP spin currents for high-density and low-power magnetization switching remain significant challenges of spintronics. Here, we demonstrate that transitioning NbIrTe$_4$ from a two-dimensional quantum spin Hall insulator to a three-dimensional type-II Weyl semimetal markedly enhances OOP spin current generation. The bulk topological Weyl semimetal nature of NbIrTe$_4$, characterized by its Weyl cone, significantly enhances the OOP spin Berry curvature, enabling an unprecedented OOP spin Hall conductivity exceeding $10^5\hbar/2e$ $Ω^{-1}m^{-1} $. This enhancement, surpassing the in-plane component by more than fourfold, enables efficient and field-free spin-orbit torque (SOT) switching of perpendicular magnetization with a low current density of 1.4 MA/cm$^2$. The improved spin Hall conductivity reduces the overall power consumption by more than two orders of magnitude compared to existing systems, such as heavy metals. Our findings highlight the pivotal role of dimensionality in harnessing robust OOP spin currents in topological Weyl semimetals, paving the way for the development of high-density, low-power spintronic memory technologies. △ Less

Submitted 7 April, 2025; originally announced April 2025.

Comments: 25 pages, 5 figures en the main text plus 27 pages including 9 Notes, 17 supplementary figures and 1 supplementary table

Switching on and off the spin polarization of the conduction band in antiferromagnetic bilayer transistors

Authors: Fengrui Yao, Menghan Liao, Marco Gibertini, Cheol-Yeon Cheon, Xiaohanwen Lin, Fan Wu, Kenji Watanabe, Takashi Taniguchi, Ignacio Gutiérrez-Lezama, Alberto F. Morpurgo

Abstract: Antiferromagnetic conductors with suitably broken spatial symmetries host spin-polarized bands, which lead to transport phenomena commonly observed in metallic ferromagnets. In bulk materials, it is the given crystalline structure that determines whether symmetries are broken and spin-polarized bands are present. Here we demonstrate experimentally that double-gate transistors realized on bilayers… ▽ More Antiferromagnetic conductors with suitably broken spatial symmetries host spin-polarized bands, which lead to transport phenomena commonly observed in metallic ferromagnets. In bulk materials, it is the given crystalline structure that determines whether symmetries are broken and spin-polarized bands are present. Here we demonstrate experimentally that double-gate transistors realized on bilayers of van der Waals antiferromagnetic semiconductor CrPS4 allow the relevant symmetry to be controlled by a perpendicular electric displacement field. Such a level of control enables the spin-polarization of the conduction band to be switched on and off. Because conduction band states with opposite spin-polarizations are hosted in the different layers and are spatially separated, these devices also give control over the magnetization of the electrons that are accumulated electrostatically. Our experiments show that double-gated CrPS4 transistors provide a viable platform to create gate-induced conductors with near unity spin polarization at the Fermi level, as well as devices with a full electrostatic control of the total magnetization of the system. △ Less

Submitted 17 March, 2025; originally announced March 2025.

Rapid morphology characterization of two-dimensional TMDs and lateral heterostructures based on deep learning

Authors: Junqi He, Yujie Zhang, Jialu Wang, Tao Wang, Pan Zhang, Chengjie Cai, Jinxing Yang, Xiao Lin, Xiaohui Yang

Abstract: Two-dimensional (2D) materials and heterostructures exhibit unique physical properties, necessitating efficient and accurate characterization methods. Leveraging advancements in artificial intelligence, we introduce a deep learning-based method for efficiently characterizing heterostructures and 2D materials, specifically MoS2-MoSe2 lateral heterostructures and MoS2 flakes with varying shapes and… ▽ More Two-dimensional (2D) materials and heterostructures exhibit unique physical properties, necessitating efficient and accurate characterization methods. Leveraging advancements in artificial intelligence, we introduce a deep learning-based method for efficiently characterizing heterostructures and 2D materials, specifically MoS2-MoSe2 lateral heterostructures and MoS2 flakes with varying shapes and thicknesses. By utilizing YOLO models, we achieve an accuracy rate of over 94.67% in identifying these materials. Additionally, we explore the application of transfer learning across different materials, which further enhances model performance. This model exhibits robust generalization and anti-interference ability, ensuring reliable results in diverse scenarios. To facilitate practical use, we have developed an application that enables real-time analysis directly from optical microscope images, making the process significantly faster and more cost-effective than traditional methods. This deep learning-driven approach represents a promising tool for the rapid and accurate characterization of 2D materials, opening new avenues for research and development in material science. △ Less

Submitted 1 March, 2025; originally announced March 2025.

Optimal neutralization of negative space charges in photon-enhanced thermionic emission devices under bidirectional discharge

Authors: Xinqiao Lin, Zhiqiang Fan, Shunjie Zhang, Xiaohang Chen, Zhimin Yang, Jincan Chen, Shanhe Su

Abstract: In this study, we innovatively modeled photon-enhanced thermionic emission (PETE) devices, incorporating positive ion injection and bidirectional discharge's effects on the space charge barrier simultaneously. Compared to previous models, our model allows the positive ion distribution function to be compatible with scenarios in which the anode motive is either higher or lower than the cathode moti… ▽ More In this study, we innovatively modeled photon-enhanced thermionic emission (PETE) devices, incorporating positive ion injection and bidirectional discharge's effects on the space charge barrier simultaneously. Compared to previous models, our model allows the positive ion distribution function to be compatible with scenarios in which the anode motive is either higher or lower than the cathode motive, and also adapts to significant anode discharge. Through numerical simulations and parametric analyses, we found that: (1) As the ratio of the positive ion increases, the capability for space charge neutralization becomes stronger. (2) The lower the electron affinity is, the smaller the ratio of positive ions are required. (3) When the anode temperature is higher or the anode work function is lower, the impact of reverse discharge on the net current density is more pronounced. Conversely, when the anode temperature is higher or the anode work function is greater, the ratio of positive ions required to achieve complete space charge neutralization increases. This study further elucidates the mechanisms and characteristics of space charge neutralization effects in PETE devices, providing a theoretical foundation for optimizing their design. Additionally, the accompanying theory and algorithm possess the potential to spark innovative research across diverse fields. △ Less

Submitted 25 February, 2025; originally announced February 2025.

Exact mobility edges in quasiperiodic network models with slowly varying potentials

Authors: Hai-Tao Hu, Yang Chen, Xiaoshui Lin, Ai-Min Guo, Zijing Lin, Ming Gong

Abstract: Quasiperiodic models are important physical platforms to explore Anderson transitions in low dimensional systems, yet the exact mobility edges (MEs) are generally hard to be determined analytically. To date, the MEs in only a few models can be determined exactly. In this manuscript, we propose a new class of network models characterized by quasiperiodic slowly varying potentials and the absence of… ▽ More Quasiperiodic models are important physical platforms to explore Anderson transitions in low dimensional systems, yet the exact mobility edges (MEs) are generally hard to be determined analytically. To date, the MEs in only a few models can be determined exactly. In this manuscript, we propose a new class of network models characterized by quasiperiodic slowly varying potentials and the absence of hidden self-duality, and exactly determine their MEs. We take the mosaic models with slowly varying potentials as examples to illustrate this result and derive its MEs from the effective Hamiltonian. In this method, we can integrate out the periodic sites to obtain an effective Hamiltonian with energy-dependent potentials $g(E)V$ and effective eigenenergy $f(E)$, which directly yields the MEs at $f(E) = \pm(2t^κ\pm g(E)V)$, where $κ\in \mathbb{Z}^+$. With this idea in hand, we then generalize our method to more quasiperiodic network models, including those with much more complicated geometries and non-Hermitian features. Finally, we propose the realization of these models using optical waveguides and show that the Anderson transition can be observed even in small physical systems (with lattice sites about $L = 50 - 100$). Our results provide some key insights into the understanding and realization of exact MEs in experiments. △ Less

Submitted 25 December, 2025; v1 submitted 25 February, 2025; originally announced February 2025.

Comments: 13 pages, 10 figures

Journal ref: Phys. Rev. B 112, 054201 (2025)

AV$_3$Sb$_5$ kagome superconductors: a review with transport measurements

Authors: Zhuokai Xu, Tian Le, Xiao Lin

Abstract: Kagome systems have garnered considerable attention due to the unique features of the sublattice structure and band topology. The recently discovered kagome metals AV$_3$Sb$_5$ (where A = K, Rb, Cs) host a rich array of symmetry-breaking phases, including exotic charge density waves (CDW), electronic nematicity, pair density waves (PDW) and superconductivity. Despite extensive experimental and the… ▽ More Kagome systems have garnered considerable attention due to the unique features of the sublattice structure and band topology. The recently discovered kagome metals AV$_3$Sb$_5$ (where A = K, Rb, Cs) host a rich array of symmetry-breaking phases, including exotic charge density waves (CDW), electronic nematicity, pair density waves (PDW) and superconductivity. Despite extensive experimental and theoretical investigations into the diverse phases, several key issues remain contentious, such as a solid clarification of the time-reversal symmetry breaking (TRS-breaking) in the CDW order and its implications for the nature of superconducting (SC) pairing symmetry. This review aims to shed light on the transport properties of these intertwined phases, emphasizing the pivotal role that transport measurements play in uncovering the non-trivial quantum states of matter. △ Less

Submitted 20 February, 2025; v1 submitted 19 February, 2025; originally announced February 2025.

Comments: Chin. Phys. Lett

Superconducting Diode Effects: Mechanisms, Materials and Applications

Authors: Jiajun Ma, Ruiya Zhan, Xiao Lin

Abstract: Superconducting diode effects (SDEs) generally emerge in superconducting systems where both time-reversal and inversion symmetries are broken, showing nonreciprocal current characteristics: nondissipative in one direction and ohmic in the opposite. Since the discovery of the SDEs by Ando et al. in the noncentrosymmetric superconductor [Nb/V/Ta]n in 2020, notable progress has been achieved on both… ▽ More Superconducting diode effects (SDEs) generally emerge in superconducting systems where both time-reversal and inversion symmetries are broken, showing nonreciprocal current characteristics: nondissipative in one direction and ohmic in the opposite. Since the discovery of the SDEs by Ando et al. in the noncentrosymmetric superconductor [Nb/V/Ta]n in 2020, notable progress has been achieved on both the theoretical and experimental fronts. It has been proposed that intrinsic SDEs are closely linked to various exotic superconducting states, such as the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, topological superconductivity, and chiral superconductivity. Recently, SDEs have emerged as important experimental tools for detecting symmetry breaking in exotic superconducting states. This advancement not only enhances our understanding of the fundamental nature of SDEs but also opens new possibilities for their applications in superconducting physics and related fields. This review focuses on the recent experimental progress in the observation of the SDEs and discusses their primary mechanisms from the perspective of material properties and symmetry breaking. Finally, we summarize the observed rectification efficiency of SDE devices and discuss future research directions in this rapidly developing field. △ Less

Submitted 17 February, 2025; originally announced February 2025.

Comments: 17 pages, 8 figures, published to Adv. Phys. Res

Journal ref: Advanced Ahysics Research,2400180 (2025)

Quantum Geometric Origin of Strain-Tunable Giant Second-Harmonic Generation in Bi$_2$O$_2$X (X=S, Se, Te)

Authors: Zhefeng Lou, Zhihao Gong, Ziye Zhu, Wenbin Li, Xiao Lin, Hua Wang

Abstract: Two-dimensional (2D) materials with giant nonlinear optical (NLO) responses are essential for the development of advanced on-chip NLO devices. Using first-principles calculations, we predict a remarkable strain-induced enhancement of second-harmonic generation (SHG) in the high-performance 2D semiconductors Bi$_2$O$_2$X (X = S, Se, Te). The SHG susceptibilities of Bi$_2$O$_2$X under strain are on… ▽ More Two-dimensional (2D) materials with giant nonlinear optical (NLO) responses are essential for the development of advanced on-chip NLO devices. Using first-principles calculations, we predict a remarkable strain-induced enhancement of second-harmonic generation (SHG) in the high-performance 2D semiconductors Bi$_2$O$_2$X (X = S, Se, Te). The SHG susceptibilities of Bi$_2$O$_2$X under strain are on the order of 1~nm/V, rivalling the highest values reported among 2D materials. This giant SHG response originates from gauge-invariant geometric quantities, including the quantum metric, shift vector, and triple phase product. The strain also induces a bandgap variation in Bi$_2$O$_2$X. Intriguingly, in Bi$_2$O$_2$Te, strain-induced bandgap tuning drives a transition from a semiconductor to a half-metal, and ultimately to a polar metal. Our findings present a unique platform that combines strain-tunable bandgap engineering with exceptional NLO properties, while also highlighting the crucial role of quantum geometry in enhancing SHG. △ Less

Submitted 28 January, 2025; originally announced January 2025.

Comments: 8 pages, 4 figures

Linear Enhancement of Spin-Orbit Torques and Absence of Bulk Rashba-Type Spin Splitting in Perpendicularly Magnetized [Pt/Co/W]n Superlattices

Authors: Zhihao Yan, Zhengxiao Li, Lujun Zhu, Xin Lin, Lijun Zhu

Abstract: The development of magnetic heterostructures with strong spin-orbit torques (SOTs), low impedance, strong perpendicular magnetic anisotropy (PMA), and good integration compatibility at the same time is central for high-performance spintronic memory and computing applications. Here, we report the development of the symmetry-broken spin-orbit superlattice [Pt/Co/W]n that can be sputtered-deposited o… ▽ More The development of magnetic heterostructures with strong spin-orbit torques (SOTs), low impedance, strong perpendicular magnetic anisotropy (PMA), and good integration compatibility at the same time is central for high-performance spintronic memory and computing applications. Here, we report the development of the symmetry-broken spin-orbit superlattice [Pt/Co/W]n that can be sputtered-deposited on commercial oxidized silicon substrates and have giant SOTs, strong uniaxial PMA of 9.2 Merg/cm3. The dampinglike and fieldlike SOTs of the [Pt/Co/W]n superlattices exhibit a linear increase with the repeat number n and reach the giant values of 225% and -33% (two orders of magnitude greater than that in clean-limit Pt) at n = 12, respectively. The dampinglike SOT is also of the opposite sign and much greater in magnitude than the fieldlike SOT, regardless of the number of n. These results clarify that the spin current that generates SOTs in the [Pt/Co/W]n superlattices arises predominantly from the spin Hall effect rather than bulk Rashba-type spin splitting, providing a unified understanding of the SOTs in the superlattices. We also demonstrate deterministic switching in thicker-than-50-nm PMA [Pt/Co/W]12 superlattices at a low current density. This work establishes the [Pt/Co/W]n superlattice as a compelling material candidate for ultra-fast, low-power, long-retention nonvolatile spintronic memory and computing technologies. △ Less

Submitted 24 December, 2024; originally announced December 2024.

Journal ref: Chinese Physics Letters 42, 090701 (2025)

Highly Polarizable Semiconductors and Universal Origin of Ferroelectricity in Materials with a Litharge-Type Structural Unit

Authors: Ziye Zhu, Jiaming Hu, Yubo Yuan, Hua Wang, Xiao Lin, Wenbin Li

Abstract: We discover that a large family of [Pb$_2$F$_2$]- and [Bi$_2$O$_2$]-based mixed-anion materials with a litharge-type structural unit are highly polarizable layered semiconductors on the edge of ferroelectricity. First-principles calculations demonstrate that in this family of materials, compounds as diverse as PbFBr, BiOCl, BiCuOSe, Bi$_2$OS$_2$, and Bi$_5$O$_4$S$_3$Cl exhibit static dielectric co… ▽ More We discover that a large family of [Pb$_2$F$_2$]- and [Bi$_2$O$_2$]-based mixed-anion materials with a litharge-type structural unit are highly polarizable layered semiconductors on the edge of ferroelectricity. First-principles calculations demonstrate that in this family of materials, compounds as diverse as PbFBr, BiOCl, BiCuOSe, Bi$_2$OS$_2$, and Bi$_5$O$_4$S$_3$Cl exhibit static dielectric constants an order of magnitude higher than typical semiconductors. Additionally, they undergo a ferroelectric transition when subjected to a few percent of tensile strain. The ferroelectric transitions of these materials are found to have a universal origin in the strong cross-bandgap hybridization of the cation $p$ orbitals, enabled by the cation 6s$^2$ lone-pair electrons and the litharge-type structure of the [Pb$_2$F$_2$] and [Bi$_2$O$_2$] layers, as demonstrated by the strain-induced ferroelectric transition in the archetypal litharge $α$-PbO. These results establish materials with a litharge-type structural unit as a large and versatile family of highly polarizable layered semiconductors in proximity to ferroelectricity, offering vast opportunities for multifunctional materials design. △ Less

Submitted 16 December, 2024; originally announced December 2024.

Comments: 7 pages, 3 figures

Journal ref: Nano Lett. 25, 4093-4100 (2025)

Homogeneous Linewidth Behaviour of Narrow Optical Emitters at Sub-kelvin Temperatures

Authors: X Lin, M T Hartman, P Goldner, B Fang, Y Le Coq, S Seidelin

Abstract: We explore the properties of ultra-narrow spectral holes in ensembles of solid-state emitters in crystals over a range of sub-kelvin temperatures, with a focus on their potential application in frequency stabilization schemes as an alternative to ultrastable cavities. We investigate how the parameters used to burn the spectral hole impact its shape, and how these factors determine the minimum achi… ▽ More We explore the properties of ultra-narrow spectral holes in ensembles of solid-state emitters in crystals over a range of sub-kelvin temperatures, with a focus on their potential application in frequency stabilization schemes as an alternative to ultrastable cavities. We investigate how the parameters used to burn the spectral hole impact its shape, and how these factors determine the minimum achievable linewidth. In addition to the stability of the hole's center frequency, the linewidth and contrast play a crucial role in frequency locking. At sub-kelvin temperatures, the temperaturedependent T^7 broadening from two-phonon Raman scattering is expected to be negligible, and the spectral hole's linewidth should therefore remain constant in this interval. We observe however a linear broadening with increasing temperature, highlighting the need for further investigation into the mechanisms governing the linewidth at ultra-low temperatures. △ Less

Submitted 6 December, 2024; originally announced December 2024.

Journal ref: Appl. Phys. Lett. 126, 054101 (2025)

Hidden self-duality and exact mobility edges in quasiperiodic network models

Authors: Hai-Tao Hu, Xiaoshui Lin, Ai-Min Guo, Guangcan Guo, Zijin Lin, Ming Gong

Abstract: In one-dimensional quasiperiodic systems, only a few models with exact mobility edges (MEs) have been constructed using generalized self-duality theory, Avila's global theory, or the renormalization group method. This raises an intriguing question that whether we can realize more physical models with exact solvable MEs. In this work, we uncover the hidden self-duality within a class of quasiperiod… ▽ More In one-dimensional quasiperiodic systems, only a few models with exact mobility edges (MEs) have been constructed using generalized self-duality theory, Avila's global theory, or the renormalization group method. This raises an intriguing question that whether we can realize more physical models with exact solvable MEs. In this work, we uncover the hidden self-duality within a class of quasiperiodic network models constituted by periodic and quasiperiodic sites. Although the original Hamiltonians appear to lack self-duality, their effective Hamiltonians obtained by integrating out the periodic sites exhibit self-duality, which yield MEs. The well-studied mosaic model, which is the simplest case of quasiperiodic network models, was previously thought to exhibit MEs due to the absence of self-duality, but we show that they actually arise from the hidden self-duality. Using the effective Hamiltonian, we further introduce the concept of resonant states to understand the shape of MEs. Finally, we present in detail how to determine the MEs in various network models, including some non-Hermitian models, based on the hidden self-duality. These predictions can be experimentally realized using optical and acoustic waveguide arrays. Our work can greatly advance our understanding of MEs in Anderson transition. △ Less

Submitted 25 December, 2025; v1 submitted 11 November, 2024; originally announced November 2024.

Comments: Published in Phys. Rev. Lett.; 19 pages, 11 figures

Journal ref: Phys. Rev. Lett. 134, 246301 (2025)

Positive oscillating magnetoresistance in a van der Waals antiferromagnetic semiconductor

Authors: Xiaohanwen Lin, Fan WU, Nicolas Ubrig, Menghan Liao, Fengrui Yao, Ignacio Gutiérrez-Lezama, Alberto F. Morpurgo

Abstract: In all van der Waals layered antiferromagnetic semiconductors investigated so far a negative magnetoresistance has been observed in vertical transport measurements, with characteristic trends that do not depend on applied bias. Here we report vertical transport measurements on layered antiferromagnetic semiconductor CrPS$_4$ that exhibit a drastically different behavior, namely a strongly bias dep… ▽ More In all van der Waals layered antiferromagnetic semiconductors investigated so far a negative magnetoresistance has been observed in vertical transport measurements, with characteristic trends that do not depend on applied bias. Here we report vertical transport measurements on layered antiferromagnetic semiconductor CrPS$_4$ that exhibit a drastically different behavior, namely a strongly bias dependent, positive magnetoresistance that is accompanied by pronounced oscillations for devices whose thickness is smaller than 10 nm. We establish that this unexpected behavior originates from transport being space-charge limited, and not injection limited as for layered antiferromagetic semiconductors studid earlier. Our analysis indicates that the positive magnetoresistance and the oscillations only occur when electrons are injected into in-gap defect states, whereas when electrons are injected into the conduction band the magnetoresistance vanishes. We propose a microscopic explanation for the observed phenomena that combines concepts typical of transport through disordered semiconductors with known properties of the CrPS$_4$ magnetic state, which captures all basic experimental observations. Our results illustrate the need to understand in detail the nature of transport through vdW magnets, to extract information about the nature of the order magnetic states and its microscopic properties. △ Less

Submitted 23 October, 2024; originally announced October 2024.

Comments: 10pages, 7 figures, under evaluation

Measuring Non-Hermitian Topological Invariants Directly from Quench Dynamics

Authors: Xiao-Dong Lin, Long Zhang

Abstract: While non-Hermitian (NH) topological phases and phenomena have been observed across various quantum systems, directly measuring NH topological invariants remains a significant challenge. In this study, we present a generic and unified framework for the direct measurement of various NH topological invariants in odd-dimensional systems through quench dynamics. We demonstrate that in one-dimensional… ▽ More While non-Hermitian (NH) topological phases and phenomena have been observed across various quantum systems, directly measuring NH topological invariants remains a significant challenge. In this study, we present a generic and unified framework for the direct measurement of various NH topological invariants in odd-dimensional systems through quench dynamics. We demonstrate that in one-dimensional (1D) NH systems with sublattice symmetry, the line-gap winding number and point-gap braiding degree can be extracted from the winding patterns of a dynamically constructed field based on post-quench spin textures. Specifically, line-gap topology is characterized by integer-valued winding, whereas point-gap complex-band braiding is revealed by half-integer or integer winding with abrupt jumps. We also extend our approach to higher-dimensional winding numbers and non-Bloch topological invariants under open-boundary conditions. Additionally, we propose a practical cold-atom setup to realize and detect 1D NH topological phases, showing that our dynamical measurement scheme is feasible in current experimental settings. This work paves the way for the direct measurement of NH topological invariants in quantum systems. △ Less

Submitted 27 February, 2025; v1 submitted 17 October, 2024; originally announced October 2024.

Comments: 8+13 pages, 4+5 figures. To appear in Physical Review Research as a Letter

Journal ref: Phys. Rev. Research 7, L012060 (2025)

Observation of Transient Trion Induced by Ultrafast Charge Transfer in Graphene/MoS2 Heterostructure

Authors: Chen Wang, Yu Chen, Qiushi Ma, Peng Suo, Kaiwen Sun, Yifan Cheng, Xian Lin, Weimin Liu, Guohong Ma

Abstract: Van der Waals (Vdw) heterostructures constructed from TMDCs provide an ideal platform for exploring various quasiparticle behaviors, with trion-composed of neutral exciton and charged carrier-being a notable example. There are typically three methods to generate trion: electrical doping, chemical doping, and direct optical doping. The first two methods generate static trion, while the last gives r… ▽ More Van der Waals (Vdw) heterostructures constructed from TMDCs provide an ideal platform for exploring various quasiparticle behaviors, with trion-composed of neutral exciton and charged carrier-being a notable example. There are typically three methods to generate trion: electrical doping, chemical doping, and direct optical doping. The first two methods generate static trion, while the last gives rise to transient trion. Here, we present an indirect optical doping approach to generate transient trion via ultrafast charge transfer (CT) and achieve control over the trion-to-exciton ratio by adjusting CT in Gr/MoS2 heterostructure. Furthermore, we demonstrated that dynamics of the transient trion generated with this method, which shows slightly longer lifetime than that of exciton accounted for the Coulomb interactions between trion and charged defect. This study provides fresh perspectives on the construction of new quasiparticles, dynamical characterization and the control of the many-body interaction in two-dimensional structure. △ Less

Submitted 26 September, 2024; originally announced September 2024.

Comments: 16 pages, 4 figures

Efficient generation of out-of-plane polarized spin current in polycrystalline heavy metal devices with broken electric symmetries

Authors: Qianbiao Liu, Xin Lin, Ariel Shaked, Zhuyang Nie, Guoqiang Yu, Lijun Zhu

Abstract: Spin currents of perpendicularly polarized spins (z spins) by an in-plane charge current have received blooming interest for the potential in energy-efficient spin-orbit torque switching of perpendicular magnetization in the absence of a magnetic field. However, generation of z spins is limited mainly to magnetically or crystallographically low-symmetry single crystals (such as non-colinear antife… ▽ More Spin currents of perpendicularly polarized spins (z spins) by an in-plane charge current have received blooming interest for the potential in energy-efficient spin-orbit torque switching of perpendicular magnetization in the absence of a magnetic field. However, generation of z spins is limited mainly to magnetically or crystallographically low-symmetry single crystals (such as non-colinear antiferromagnets) that are hardly compatible with the integration to semiconductor circuits. Here, we report efficient generation of z spins in sputter-deposited polycrystalline heavy metal devices via a new mechanism of broken electric symmetries in both the transverse and perpendicular directions. Both the dampinglike and fieldlike spin-orbit torques of z spins can be tuned significantly by varying the degree of the electric asymmetries via the length, width, and thickness of devices as well as by varying the type of the heavy metals. We also show that the presence of z spins enables deterministic, nearly-full, external-magnetic-field-free switching of a uniform perpendicularly magnetized FeCoB layer, the core structure of magnetic tunnel junctions, with high coercivity at a low current density. These results establish the first universal, energy-efficient, integration-friendly approach to generate z-spin current by electric asymmetry design for dense and low-power spin-torque memory and computing technologies and will stimulate investigation of z-spin currents in various polycrystalline materials. △ Less

Submitted 10 August, 2024; originally announced August 2024.

Journal ref: Advanced Materials (2024)

Building spin-1/2 antiferromagnetic Heisenberg chains with diaza-nanographenes

Authors: Xiaoshuai Fu, Li Huang, Kun Liu, João C. G. Henriques, Yixuan Gao, Xianghe Han, Hui Chen, Yan Wang, Carlos-Andres Palma, Zhihai Cheng, Xiao Lin, Shixuan Du, Ji Ma, Joaquín Fernández-Rossier, Xinliang Feng, Hong-Jun Gao

Abstract: Understanding and engineering the coupling of spins in nanomaterials is of central importance for designing novel devices. Graphene nanostructures with π-magnetism offer a chemically tunable platform to explore quantum magnetic interactions. However, realizing spin chains bearing controlled odd-even effects with suitable nanographene systems is challenging. Here, we demonstrate the successful on-s… ▽ More Understanding and engineering the coupling of spins in nanomaterials is of central importance for designing novel devices. Graphene nanostructures with π-magnetism offer a chemically tunable platform to explore quantum magnetic interactions. However, realizing spin chains bearing controlled odd-even effects with suitable nanographene systems is challenging. Here, we demonstrate the successful on-surface synthesis of spin-1/2 antiferromagnetic Heisenberg chains with parity-dependent magnetization based on antiaromatic diaza-hexa-peri-hexabenzocoronene (diaza-HBC) units. Using distinct synthetic strategies, two types of spin chains with different terminals were synthesized, both exhibiting a robust odd-even effect on the spin coupling along the chain. Combined investigations using scanning tunneling microscopy, non-contact atomic force microscopy, density functional theory calculations, and quantum spin models confirmed the structures of the diaza-HBC chains and revealed their magnetic properties, which has an S = 1/2 spin per unit through electron donation from the diaza-HBC core to the Au(111) substrate. Gapped excitations were observed in even-numbered chains, while enhanced Kondo resonance emerged in odd-numbered units of odd-numbered chains due to the redistribution of the unpaired spin along the chain. Our findings provide an effective strategy to construct nanographene spin chains and unveil the odd-even effect in their magnetic properties, offering potential applications in nanoscale spintronics. △ Less

Submitted 29 July, 2024; originally announced July 2024.

Journal ref: Nature Synthesis (2025)

Unraveling the role of Ta in the phase transition of Pb(Ta1+xSe2)2 using low-temperature Raman spectroscopy

Authors: Yu Ma, Chi Sin Tang, Xiaohui Yang, Yi Wei Ho, Jun Zhou, Wenjun Wu, Shuo Sun, Jin-Ke Bao, Dingguan Wang, Xiao Lin, Magdalena Grzeszczyk, Shijie Wang, Mark B H Breese, Chuanbing Cai, Andrew T. S. Wee, Maciej Koperski, Zhu-An Xu, Xinmao Yin

Abstract: Phase engineering strategies in two-dimensional transition metal dichalcogenides (2D-TMDs) have garnered significant attention due to their potential applications in electronics, optoelectronics, and energy storage. Various methods, including direct synthesis, pressure control, and chemical doping, have been employed to manipulate structural transitions in 2D-TMDs. Metal intercalation emerges as a… ▽ More Phase engineering strategies in two-dimensional transition metal dichalcogenides (2D-TMDs) have garnered significant attention due to their potential applications in electronics, optoelectronics, and energy storage. Various methods, including direct synthesis, pressure control, and chemical doping, have been employed to manipulate structural transitions in 2D-TMDs. Metal intercalation emerges as an effective technique to modulate phase transition dynamics by inserting external atoms or ions between the layers of 2D-TMDs, altering their electronic structure and physical properties. Here, we investigate the significant structural phase transitions in Pb(Ta1+xSe2)2 single crystals induced by Ta intercalation using a combination of Raman spectroscopy and first-principles calculations. The results highlight the pivotal role of Ta atoms in driving these transitions and elucidate the interplay between intercalation, phase transitions, and resulting electronic and vibrational properties in 2D-TMDs. By focusing on Pb(Ta1+xSe2)2 as an ideal case study and investigating like metal intercalation, this study advances understanding in the field and paves the way for the development of novel applications for 2D-TMDs, offering insights into the potential of these materials for future technological advancements. △ Less

Submitted 8 August, 2024; v1 submitted 28 July, 2024; originally announced July 2024.