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Emergent Z2 topological invariant and robust helical edge states in two-dimensional topological metals

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Science china(Physics,Mechanics & Astronomy) 2020年第10期63卷 105-110页

作者： chui-Zhen chen Hua Jiang Dong-Hui xu x.c.xie Institute for Advanced Study and School of Physical Science and Technology Soochow UniversitySuzhou 215006China Department of Physics Hubei UniversityWuhan 430062China International center for Quantum Materials School of PhysicsPeking UniversityBeijing 100871China cAS center for Excellence in Topological Quantum computation University of Chinese Academy of SciencesBeijing 100190China Beijing Academy of Quantum Information Sciences Beijing 100193China

In this work,we study the effects of disorder on topological metals that support a pair of helical edge modes deeply embedded inside the gapless bulk ***,we predict that a quantum spin Hall(QSH)phase can be obtained from such topological metals without opening a global band *** be specific,disorder can lead to a pair of robust helical edge states which is protected by an emergent Z2 topological invariant,giving rise to a quantized conductance plateau in transport *** results are instructive for solving puzzles in various transport experiments on QSH materials that are intrinsically *** work also will inspire experimental realization of the QSH effect in disordered topological metals.

关键词： topological metal disorder Z2 topological invariant

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Dephasing eflfects in topological insulators

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Frontiers of physics 2019年第4期14卷 47-61页

作者： Junjie Qi Haiwen Liu Hua Jiang x.c.xie International center for Quantum Materials and School of Physics Peking University Beijing 100871 China collaborative Innovation center of Quantum Matter Beijing China center for Advanced Quantum Studies Department of Physics Beijing Normal University Beijing 100875China School of Physical Science and Technology Soochow University Suzhou 215006 China Institute for Advanced Study Soochow University Suzhou 215006 China

Topological insulators,a class of typical topological materials in both two dimensions and three dimensions,are insulating in bulk and metallic at *** spin-momentum locked surface states and peculiar transport properties exhibit promising potential applications on quantum devices,which generate extensive interest in the last *** is the process of the loss of phase coherence,which inevitably exists in a realistic *** this review,we focus on recent progress in dephasing effects on the topological *** general,there are two types of dephasing processes:normal dephasing and spin *** two-dimensional topological insulators,the phenomenologically numerical investigation shows that the longitudinal resistance plateaus is robust against normal dephasing but fragile with spin *** microscopic mechanisms of spin dephasing are then *** three-dimensional topological insulators,the helical surface states exhibit a helical spin texture due to the spin-momentum locking ***,normal dephasing has close connection to spin dephasing in this case,and gives rise to anomalous "gap-like" *** effects on properties of helical surface states are investigated.

关键词： dephasing effects topological insulators backscattering

The preface: Interplay of topological and magnetic orders in the Mn-Bi-Te family

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National Science Review 2024年第2期11卷 6-7页

作者： Fu-chun Zhang Hai-Zhou Lu x.c.xie Kavli Institute for Theoretical Sciences University of Chinese Academy of Sciences Department of Physics Southern University of Science and Technology (SUSTech) International center for Quantum Materials School of Physics Peking University

The discovery and synthesis of MnBi2Te4in 2013 initially garnered little attention [1]. Yet, the revelation of its topological properties in 2019 [2–6] sparked a surge of research into the MnBiTe family. These extensive studies are primarily driven by two objectives:the realization of a high-temperature quantum anomalous Hall effect （QAHE） and the exploration of exotic phases born from the interplay of topological and magnetic orders,

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Quantum to classical crossover under dephasing effects in a two-dimensional percolation model

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Science china(Physics,Mechanics & Astronomy) 2020年第2期63卷 130-134页

作者： Junjie Qi Haiwen Liu chui-Zhen chen Hua Jiang x.c.xie International center for Quantum Materials and School of Physics Peking UniversityBeijing 100871China collaborative Innovation center of Quantum Matter Beijing 100871China center for Advanced Quantum Studies Department of PhysicsBeijing Normal UniversityBeijing 100875China Institute for Advanced Study and School of Physical Science and Technology Soochow UniversitySuzhou 215006China

Scaling theory predicts complete localization in d = 2 in quantum systems belonging to the orthogonal class(i.e., with timereversal symmetry and spin-rotation symmetry). The conductance g behaves as g^exp(-L/l) with system size L and localization length l in the strong disorder limit. However, classical systems can always have metallic states in which Ohm’s law shows a constant g in d=2. We study a two-dimensional quantum percolation model by controlling dephasing effects. The numerical investigation of g aims at simulating a quantum-to-classical percolation evolution. An unexpected metallic phase, where g increases with L, generates immense interest before the system becomes completely classical. Furthermore, the analysis of the scaling plot of g indicates a metal-insulator crossover.

关键词： quantum percolation model dephasing effects metal-insulator crossover

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Recent experimental progress of fractional quantum Hall effect: 5/2 illing state and graphene

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National Science Review 2014年第4期1卷 564-579页

作者： x.Lin R.R.Du x.c.xie International center for Quantum Materials Peking University

The phenomenon of fractional quantum Hall efect(FQHE)was irst experimentally observed 33 years *** involves strong coulomb interactions and correlations among the electrons,which leads to quasiparticles with fractional elementary *** decades later,the ield of FQHE is still active with new discoveries and new technical developments.A signiicant portion of atention in FQHE has been dedicated to illing factor 5/2 state,for its unusual even denominator and possible application in topological quantum ***,FQHE has been observed in high-mobility Ga As heterostructure,but new materials such as graphene also open up a new area for *** review focuses on recent progress of FQHE at 5/2 state and FQHE in graphene.

关键词： fractional quantum Hall efect experimental progress 5/2 state graphene

Progress on the antiferromagnetic topological insulator MnBi2Te4

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National Science Review 2024年第2期11卷 33-49页

作者： Shuai Li Tianyu Liu chang Liu Yayu Wang Hai-Zhou Lu x.c.xie Department of Physics Harbin Institute of Technology Shenzhen Institute for Quantum Science and Engineering and Department of Physics Southern University of Science and Technology(SUSTech) Quantum Science center of Guangdong-Hong Kong-Macao Greater Bay Area(Guangdong) Shenzhen Key Laboratory of Quantum Science and Engineering International Quantum Academy Beijing Academy of Quantum Information Sciences Beijing Key Laboratory of Optoelectronic Functional Materials&Micro-Nano Devices Department of Physics Renmin University of China State Key Laboratory of Low Dimensional Quantum Physics Department of PhysicsTsinghua University Frontier Science center for Quantum Information Hefei National Laboratory International center for Quantum Materials School of Physics Peking University Institute for Nanoelectronic Devices and Quantum computing Fudan University

Topological materials, which feature robust surface and/or edge states, have now been a research focus in condensed maTher physics. They represent a new class of materials exhibiting nontrivial topological phases,and provide a platform for exploring exotic transport phenomena, such as the quantum anomalous Hall effect and the quantum spin Hall effect. Recently, magnetic topological materials have attracted considerable interests due to the possibility to study the interplay between topological and magnetic *** particular, the quantum anomalous Hall and axion insulator phases can be realized in topological insulators with magnetic order. MnBi2Te4, as the first intrinsic antiferromagnetic topological insulator discovered, allows the examination of existing theoretical predictions; it has been extensively studied, and many new discoveries have been made. Here we review the progress made on MnBi2Te4from both experimental and theoretical aspects. The bulk crystal and magnetic structures are surveyed first, followed by a review of theoretical calculations and experimental probes on the band structure and surface states, and a discussion of various exotic phases that can be realized in MnBi2Te4. The properties of MnBi2Te4thin films and the corresponding transport studies are then reviewed, with an emphasis on the edge state transport. Possible future research directions in this field are also discussed.

关键词： MnBi2Te4 magnetic topological insulator antiferromagnetic quantum anomalous Hall effect axion insulator

Layer Hall effect induced by hidden Berry curvature in antiferromagnetic insulators

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National Science Review 2024年第2期11卷 15-23页

作者： Rui chen Hai-Peng Sun Mingqiang Gu chun-Bo Hua Qihang Liu Hai-Zhou Lu x.c.xie Shenzhen Institute for Quantum Science and Engineering and Department of Physics Southern University of Science and Technology(SUSTech) International Quantum Academy Institute for Theoretical Physics and Astrophysics University of Würzburg School of Electronic and Information Engineering Hubei University of Science and Technology Guangdong Provincial Key Laboratory of computational Science and Material Design Southern University of Science and Technology Shenzhen Key Laboratory of Quantum Science and Engineering International center for Quantum Materials School of PhysicsPeking University collaborative Innovation center of Quantum Matter cAS center for Excellence in Topological Quantum computation University of Chinese Academy of Sciences

The layer Hall effect describes electrons spontaneously deflected to opposite sides at different layers, which has been experimentally reported in the MnBi2Te4thin films under perpendicular electric fields. Here, we reveal a universal origin of the layer Hall effect in terms of the so-called hidden Berry curvature, as well as material design principles. Hence, it gives rise to zero Berry curvature in momentum space but non-zero layer-locked hidden Berry curvature in real space. We show that, compared to that of a trivial insulator, the layer Hall effect is significantly enhanced in antiferromagnetic topological insulators. Our universal picture provides a paradigm for revealing the hidden physics as a result of the interplay between the global and local symmetries, and can be generalized in various scenarios.

关键词： layerHall effect hidden Berry curvature antiferromagnetic insulator axion insulator, quantum transport

Unconventional Hall effect induced by Berry curvature

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National Science Review 2020年第12期7卷 1879-1885页

作者： Jun Ge Da Ma Yanzhao Liu Huichao Wang Yanan Li Jiawei Luo Tianchuang Luo Ying xing Jiaqiang Yan David Mandrus Haiwen Liu x.c.xie Jian Wang International center for Quantum Materials School of PhysicsPeking University Department of Applied Physics The Hong Kong Polytechnic University Department of Physics Pennsylvania State UniversityUniversity Park Department of Materials Science and Engineering School of New Energy and MaterialsChina University of Petroleum Department of Materials Science and Engineering University of Tennessee Materials Science and Technology Division Oak Ridge National Laboratory center for Advanced Quantum Studies Department of PhysicsBeijing Normal University cAS center for Excellence in Topological Quantum computation University of Chinese Academy of Sciences Beijing Academy of Quantum Information Sciences collaborative Innovation center of Quantum Matter

Berry phase and Berry curvature play a key role in the development of topology in physics and do contribute to the transport properties in solid state *** this paper,we report the finding of novel nonzero Hall effect in topological material Zr Te5 flakes when the in-plane magnetic field is parallel and perpendicular to the ***,both symmetric and antisymmetric components with respect to magnetic field are detected in the in-plane Hall *** theoretical analysis suggests that the magnetotransport properties originate from the anomalous velocity induced by Berry curvature in a tilted Weyl *** work not only enriches the Hall family but also provides new insights into the Berry phase effect in topological materials.

关键词： Berry curvature topological material Hall effect tilted Weyl semimetal Berry phase effect

Magnetoresistance Oscillations of Ultrathin Pb Bridges

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Nano Research 2009年第9期2卷 671-677页

作者： Jian Wang xucun Ma Shuaihua Ji Yun Qi Yingshuang Fu Aizi Jin Li Lu changzhi Gu x.c.xie Mingliang Tian Jinfeng Jia Qikun xue Institute of Physics Chinese Academy of SciencesBeijing 100190China The center for Nanoscale Science and Department of Physics The Pennsylvania State UniversityUniversity ParkPennsylvania 16802-6300USA Department of Physics Oklahoma State UniversityStillwaterOK 74078USA Department of Physics Tsinghua UniversityBeijing 100084China

Pb nanobridges with a thickness of less than 10 nm and a width of several hundred nm have been fabricated from single-crystalline Pb fi lms using low-temperature molecular beam epitaxy and focus ion beam microfabrication *** observed novel magnetoresistance oscillations below the superconducting transition temperature(Tc)of the *** oscillations which were not seen in the crystalline Pb fi lmsmay originate from the inhomogeneity of superconductivity induced by the applied magnetic fi elds on approaching the normal state,or the degradation of fi lm quality by thermal evolution.

关键词： Pb nanobridge magnetoresistance superconductivity molecular beam epitaxy scanning tunneling microscope focus ion beam