1
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Chong SK, Lei C, Cheng Y, Lee SH, Mao Z, MacDonald AH, Wang KL. Exchange-Driven Chern States in High-Mobility Intrinsic Magnetic Topological Insulators. PHYSICAL REVIEW LETTERS 2024; 132:146601. [PMID: 38640375 DOI: 10.1103/physrevlett.132.146601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2023] [Revised: 01/25/2024] [Accepted: 03/12/2024] [Indexed: 04/21/2024]
Abstract
The layer-dependent Chern number (C) in MnBi_{2}Te_{4} is characterized by the presence of a Weyl semimetal state in the ferromagnetic coupling. However, the influence of a key factor, namely, the exchange coupling, remains unexplored. This study focuses on characterizing the C=2 state in MnBi_{2}Te_{4}, which is classified as a higher C state resulting from the anomalous n=0 Landau levels (LLs). Our findings demonstrate that the exchange coupling parameter strongly influences the formation of this Chern state, leading to a competition between the C=1 and 2 states. Moreover, the emergence of odd-even LL sequences, resulting from the breaking of LL degeneracy, provides compelling evidence for the strong exchange coupling strength. These findings highlight the significance of the exchange coupling in understanding the behavior of Chern states and LLs in magnetic quantum systems.
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Affiliation(s)
- Su Kong Chong
- Department of Electrical and Computer Engineering, University of California, Los Angeles, California 90095, USA
| | - Chao Lei
- Department of Physics, The University of Texas at Austin, Austin, Texas 78712, USA
| | - Yang Cheng
- Department of Electrical and Computer Engineering, University of California, Los Angeles, California 90095, USA
| | - Seng Huat Lee
- 2D Crystal Consortium, Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
- Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Zhiqiang Mao
- 2D Crystal Consortium, Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
- Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Allan H MacDonald
- Department of Physics, The University of Texas at Austin, Austin, Texas 78712, USA
| | - Kang L Wang
- Department of Electrical and Computer Engineering, University of California, Los Angeles, California 90095, USA
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2
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Li S, Liu T, Liu C, Wang Y, Lu HZ, Xie XC. Progress on the antiferromagnetic topological insulator MnBi 2Te 4. Natl Sci Rev 2024; 11:nwac296. [PMID: 38213528 PMCID: PMC10776361 DOI: 10.1093/nsr/nwac296] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2022] [Revised: 10/18/2022] [Accepted: 11/09/2022] [Indexed: 01/13/2024] Open
Abstract
Topological materials, which feature robust surface and/or edge states, have now been a research focus in condensed matter 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 orders. In 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 MnBi2Te4 from 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 MnBi2Te4 thin 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.
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Affiliation(s)
- Shuai Li
- Department of Physics, Harbin Institute of Technology, Harbin 150001, China
- Shenzhen Institute for Quantum Science and Engineering and Department of Physics, Southern University of Science and Technology (SUSTech), Shenzhen 518055, China
- Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area (Guangdong), Shenzhen 518045, China
- Shenzhen Key Laboratory of Quantum Science and Engineering, Shenzhen 518055, China
- International Quantum Academy, Shenzhen 518048, China
| | - Tianyu Liu
- Shenzhen Institute for Quantum Science and Engineering and Department of Physics, Southern University of Science and Technology (SUSTech), Shenzhen 518055, China
- Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area (Guangdong), Shenzhen 518045, China
- Shenzhen Key Laboratory of Quantum Science and Engineering, Shenzhen 518055, China
- International Quantum Academy, Shenzhen 518048, China
| | - Chang Liu
- Beijing Academy of Quantum Information Sciences, Beijing 100193, China
- Beijing Key Laboratory of Optoelectronic Functional Materials & Micro-Nano Devices, Department of Physics, Renmin University of China, Beijing 100872, China
| | - Yayu Wang
- State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
- Frontier Science Center for Quantum Information, Beijing 100084, China
- Hefei National Laboratory, Hefei 230088, China
| | - Hai-Zhou Lu
- Shenzhen Institute for Quantum Science and Engineering and Department of Physics, Southern University of Science and Technology (SUSTech), Shenzhen 518055, China
- Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area (Guangdong), Shenzhen 518045, China
- Shenzhen Key Laboratory of Quantum Science and Engineering, Shenzhen 518055, China
- International Quantum Academy, Shenzhen 518048, China
| | - X C Xie
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
- Institute for Nanoelectronic Devices and Quantum Computing, Fudan University, Shanghai 200433, China
- Hefei National Laboratory, Hefei 230088, China
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3
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Tan H, Yan B. Distinct Magnetic Gaps between Antiferromagnetic and Ferromagnetic Orders Driven by Surface Defects in the Topological Magnet MnBi_{2}Te_{4}. PHYSICAL REVIEW LETTERS 2023; 130:126702. [PMID: 37027867 DOI: 10.1103/physrevlett.130.126702] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2022] [Accepted: 03/03/2023] [Indexed: 06/09/2023]
Abstract
Many experiments observed a metallic behavior at zero magnetic fields (antiferromagnetic phase, AFM) in MnBi_{2}Te_{4} thin film transport, which coincides with gapless surface states observed by angle-resolved photoemission spectroscopy, while it can become a Chern insulator at field larger than 6 T (ferromagnetic phase, FM). Thus, the zero-field surface magnetism was once speculated to be different from the bulk AFM phase. However, recent magnetic force microscopy refutes this assumption by detecting persistent AFM order on the surface. In this Letter, we propose a mechanism related to surface defects that can rationalize these contradicting observations in different experiments. We find that co-antisites (exchanging Mn and Bi atoms in the surface van der Waals layer) can strongly suppress the magnetic gap down to several meV in the AFM phase without violating the magnetic order but preserve the magnetic gap in the FM phase. The different gap sizes between AFM and FM phases are caused by the exchange interaction cancellation or collaboration of the top two van der Waals layers manifested by defect-induced surface charge redistribution among the top two van der Waals layers. This theory can be validated by the position- and field-dependent gap in future surface spectroscopy measurements. Our work suggests suppressing related defects in samples to realize the quantum anomalous Hall insulator or axion insulator at zero fields.
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Affiliation(s)
- Hengxin Tan
- Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Binghai Yan
- Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 7610001, Israel
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4
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Zhou LJ, Mei R, Zhao YF, Zhang R, Zhuo D, Yan ZJ, Yuan W, Kayyalha M, Chan MHW, Liu CX, Chang CZ. Confinement-Induced Chiral Edge Channel Interaction in Quantum Anomalous Hall Insulators. PHYSICAL REVIEW LETTERS 2023; 130:086201. [PMID: 36898119 DOI: 10.1103/physrevlett.130.086201] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2022] [Revised: 01/20/2023] [Accepted: 01/23/2023] [Indexed: 06/18/2023]
Abstract
In quantum anomalous Hall (QAH) insulators, the interior is insulating but electrons can travel with zero resistance along one-dimensional (1D) conducting paths known as chiral edge channels (CECs). These CECs have been predicted to be confined to the 1D edges and exponentially decay in the two-dimensional (2D) bulk. In this Letter, we present the results of a systematic study of QAH devices fashioned in a Hall bar geometry of different widths under gate voltages. At the charge neutral point, the QAH effect persists in a Hall bar device with a width of only ∼72 nm, implying the intrinsic decaying length of CECs is less than ∼36 nm. In the electron-doped regime, we find that the Hall resistance deviates quickly from the quantized value when the sample width is less than 1 μm. Our theoretical calculations suggest that the wave function of CEC first decays exponentially and then shows a long tail due to disorder-induced bulk states. Therefore, the deviation from the quantized Hall resistance in narrow QAH samples originates from the interaction between two opposite CECs mediated by disorder-induced bulk states in QAH insulators, consistent with our experimental observations.
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Affiliation(s)
- Ling-Jie Zhou
- Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Ruobing Mei
- Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Yi-Fan Zhao
- Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Ruoxi Zhang
- Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Deyi Zhuo
- Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Zi-Jie Yan
- Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Wei Yuan
- Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Morteza Kayyalha
- Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802, USA
- Department of Electrical Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Moses H W Chan
- Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Chao-Xing Liu
- Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Cui-Zu Chang
- Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802, USA
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5
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Lei Y, Zhang T, Lin YC, Granzier-Nakajima T, Bepete G, Kowalczyk DA, Lin Z, Zhou D, Schranghamer TF, Dodda A, Sebastian A, Chen Y, Liu Y, Pourtois G, Kempa TJ, Schuler B, Edmonds MT, Quek SY, Wurstbauer U, Wu SM, Glavin NR, Das S, Dash SP, Redwing JM, Robinson JA, Terrones M. Graphene and Beyond: Recent Advances in Two-Dimensional Materials Synthesis, Properties, and Devices. ACS NANOSCIENCE AU 2022; 2:450-485. [PMID: 36573124 PMCID: PMC9782807 DOI: 10.1021/acsnanoscienceau.2c00017] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/04/2022] [Revised: 08/22/2022] [Accepted: 08/23/2022] [Indexed: 12/30/2022]
Abstract
Since the isolation of graphene in 2004, two-dimensional (2D) materials research has rapidly evolved into an entire subdiscipline in the physical sciences with a wide range of emergent applications. The unique 2D structure offers an open canvas to tailor and functionalize 2D materials through layer number, defects, morphology, moiré pattern, strain, and other control knobs. Through this review, we aim to highlight the most recent discoveries in the following topics: theory-guided synthesis for enhanced control of 2D morphologies, quality, yield, as well as insights toward novel 2D materials; defect engineering to control and understand the role of various defects, including in situ and ex situ methods; and properties and applications that are related to moiré engineering, strain engineering, and artificial intelligence. Finally, we also provide our perspective on the challenges and opportunities in this fascinating field.
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Affiliation(s)
- Yu Lei
- Department
of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, United States,Center
for Atomically Thin Multifunctional Coatings, The Pennsylvania State University, University Park, Pennsylvania 16802, United States,Institute
of Materials Research, Tsinghua Shenzhen
International Graduate School, Shenzhen, Guangdong 518055, China,Center
for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Tianyi Zhang
- Center
for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802, United States,Department
of Material Science and Engineering, The
Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Yu-Chuan Lin
- Center
for Atomically Thin Multifunctional Coatings, The Pennsylvania State University, University Park, Pennsylvania 16802, United States,Center
for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802, United States,Department
of Material Science and Engineering, The
Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Tomotaroh Granzier-Nakajima
- Department
of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, United States,Center
for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - George Bepete
- Department
of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, United States,Center
for Atomically Thin Multifunctional Coatings, The Pennsylvania State University, University Park, Pennsylvania 16802, United States,Center
for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802, United States,Department
of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Dorota A. Kowalczyk
- Department
of Solid State Physics, Faculty of Physics and Applied Informatics, University of Lodz, Pomorska 149/153, Lodz 90-236, Poland
| | - Zhong Lin
- Department
of Physics, University of Washington, Seattle, Washington 98195, United States
| | - Da Zhou
- Department
of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, United States,Center
for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Thomas F. Schranghamer
- Department
of Engineering Science and Mechanics, Pennsylvania
State University, University Park, Pennsylvania 16802, United States
| | - Akhil Dodda
- Department
of Engineering Science and Mechanics, Pennsylvania
State University, University Park, Pennsylvania 16802, United States
| | - Amritanand Sebastian
- Department
of Engineering Science and Mechanics, Pennsylvania
State University, University Park, Pennsylvania 16802, United States
| | - Yifeng Chen
- Department
of Materials Science and Engineering, National
University of Singapore, 9 Engineering Drive, Singapore 117456, Singapore
| | - Yuanyue Liu
- Texas
Materials Institute and Department of Mechanical Engineering, The University of Texas at Austin, Austin, Texas 78712, United States
| | | | - Thomas J. Kempa
- Department
of Chemistry, Johns Hopkins University, Baltimore, Maryland 21287, United States
| | - Bruno Schuler
- nanotech@surfaces
Laboratory, Empa − Swiss Federal
Laboratories for Materials Science and Technology, Dübendorf 8600, Switzerland
| | - Mark T. Edmonds
- School
of Physics and Astronomy, Monash University, Clayton, Victoria 3800, Australia
| | - Su Ying Quek
- Department
of Materials Science and Engineering, National
University of Singapore, 9 Engineering Drive, Singapore 117456, Singapore
| | - Ursula Wurstbauer
- Institute
of Physics, University of Münster, Wilhelm-Klemm-Str. 10, Münster 48149, Germany
| | - Stephen M. Wu
- Department
of Electrical and Computer Engineering & Department of Physics
and Astronomy, University of Rochester, Rochester, New York 14627, United States
| | - Nicholas R. Glavin
- Air
Force
Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson AFB, Dayton, Ohio 45433, United States
| | - Saptarshi Das
- Center
for Atomically Thin Multifunctional Coatings, The Pennsylvania State University, University Park, Pennsylvania 16802, United States,Center
for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802, United States,Department
of Material Science and Engineering, The
Pennsylvania State University, University Park, Pennsylvania 16802, United States,Department
of Engineering Science and Mechanics, Pennsylvania
State University, University Park, Pennsylvania 16802, United States
| | - Saroj Prasad Dash
- Department
of Microtechnology and Nanoscience, Chalmers
University of Technology, Göteborg SE-412 96, Sweden
| | - Joan M. Redwing
- Center
for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802, United States,Department
of Material Science and Engineering, The
Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Joshua A. Robinson
- Center
for Atomically Thin Multifunctional Coatings, The Pennsylvania State University, University Park, Pennsylvania 16802, United States,Center
for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802, United States,Department
of Material Science and Engineering, The
Pennsylvania State University, University Park, Pennsylvania 16802, United States,
| | - Mauricio Terrones
- Department
of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, United States,Center
for Atomically Thin Multifunctional Coatings, The Pennsylvania State University, University Park, Pennsylvania 16802, United States,Center
for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802, United States,Department
of Material Science and Engineering, The
Pennsylvania State University, University Park, Pennsylvania 16802, United States,Department
of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, United States,Research
Initiative for Supra-Materials and Global Aqua Innovation Center, Shinshu University, 4-17-1Wakasato, Nagano 380-8553, Japan,
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6
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Lin W, Feng Y, Wang Y, Zhu J, Lian Z, Zhang H, Li H, Wu Y, Liu C, Wang Y, Zhang J, Wang Y, Chen CZ, Zhou X, Shen J. Direct visualization of edge state in even-layer MnBi 2Te 4 at zero magnetic field. Nat Commun 2022; 13:7714. [PMID: 36513662 DOI: 10.1038/s41467-022-35482-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2021] [Accepted: 12/06/2022] [Indexed: 12/15/2022] Open
Abstract
Being the first intrinsic antiferromagnetic (AFM) topological insulator (TI), MnBi2Te4 is argued to be a topological axion state in its even-layer form due to the antiparallel magnetization between the top and bottom layers. Here we combine both transport and scanning microwave impedance microscopy (sMIM) to investigate such axion state in atomically thin MnBi2Te4 with even-layer thickness at zero magnetic field. While transport measurements show a zero Hall plateau signaturing the axion state, sMIM uncovers an unexpected edge state raising questions regarding the nature of the "axion state". Based on our model calculation, we propose that the edge state of even-layer MnBi2Te4 at zero field is derived from gapped helical edge states of the quantum spin Hall effect with time-reversal-symmetry breaking, when a crossover from a three-dimensional TI MnBi2Te4 to a two-dimensional TI occurs. Our finding thus signifies the richness of topological phases in MnB2Te4 that has yet to be fully explored.
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Affiliation(s)
- Weiyan Lin
- State Key Laboratory of Surface Physics and Institute for Nanoelectronic Devices and Quantum Computing, Fudan University, Shanghai, China
| | - Yang Feng
- Department of Physics, Fudan University, Shanghai, China
| | - Yongchao Wang
- State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing, China.,Beijing Innovation Center for Future Chips, Tsinghua University, Beijing, China
| | - Jinjiang Zhu
- Department of Physics, Fudan University, Shanghai, China
| | - Zichen Lian
- State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing, China
| | - Huanyu Zhang
- Department of Physics, Fudan University, Shanghai, China
| | - Hao Li
- School of Materials Science and Engineering, Tsinghua University, Beijing, China.,Tsinghua-Foxconn Nanotechnology Research Center, Department of Physics, Tsinghua University, Beijing, China
| | - Yang Wu
- Tsinghua-Foxconn Nanotechnology Research Center, Department of Physics, Tsinghua University, Beijing, China.,Department of Mechanical Engineering, Tsinghua University, Beijing, China
| | - Chang Liu
- State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing, China.,Beijing Academy of Quantum Information Science, Beijing, China
| | - Yihua Wang
- Department of Physics, Fudan University, Shanghai, China.,Shanghai Research Center for Quantum Sciences, Shanghai, China
| | - Jinsong Zhang
- State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing, China.,Frontier Science Center for Quantum Information, Beijing, China
| | - Yayu Wang
- State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing, China.,Frontier Science Center for Quantum Information, Beijing, China
| | - Chui-Zhen Chen
- School of Physical Science and Technology, Soochow University, Suzhou, China.,Institute for Advanced Study, Soochow University, Suzhou, China
| | - Xiaodong Zhou
- State Key Laboratory of Surface Physics and Institute for Nanoelectronic Devices and Quantum Computing, Fudan University, Shanghai, China. .,Zhangjiang Fudan International Innovation Center, Fudan University, Shanghai, China. .,Shanghai Qi Zhi Institute, Shanghai, China.
| | - Jian Shen
- State Key Laboratory of Surface Physics and Institute for Nanoelectronic Devices and Quantum Computing, Fudan University, Shanghai, China. .,Department of Physics, Fudan University, Shanghai, China. .,Zhangjiang Fudan International Innovation Center, Fudan University, Shanghai, China. .,Shanghai Qi Zhi Institute, Shanghai, China. .,Collaborative Innovation Center of Advanced Microstructures, Nanjing, China.
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7
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Lujan D, Choe J, Rodriguez-Vega M, Ye Z, Leonardo A, Nunley TN, Chang LJ, Lee SF, Yan J, Fiete GA, He R, Li X. Magnons and magnetic fluctuations in atomically thin MnBi2Te4. Nat Commun 2022; 13:2527. [PMID: 35534477 PMCID: PMC9085848 DOI: 10.1038/s41467-022-29996-w] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2021] [Accepted: 04/11/2022] [Indexed: 11/24/2022] Open
Abstract
Electron band topology is combined with intrinsic magnetic orders in MnBi2Te4, leading to novel quantum phases. Here we investigate collective spin excitations (i.e. magnons) and spin fluctuations in atomically thin MnBi2Te4 flakes using Raman spectroscopy. In a two-septuple layer with non-trivial topology, magnon characteristics evolve as an external magnetic field tunes the ground state through three ordered phases: antiferromagnet, canted antiferromagnet, and ferromagnet. The Raman selection rules are determined by both the crystal symmetry and magnetic order while the magnon energy is determined by different interaction terms. Using non-interacting spin-wave theory, we extract the spin-wave gap at zero magnetic field, an anisotropy energy, and interlayer exchange in bilayers. We also find magnetic fluctuations increase with reduced thickness, which may contribute to a less robust magnetic order in single layers. MnBi2Te4, referred to as MBT, is a van der Waals material combining topological electron bands with magnetic order. Here, Lujan et al study collective spin excitations in MBT, and show that magnetic fluctuations increase as samples reduce in thickness, implying less robust magnetic order.
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8
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Cai J, Ovchinnikov D, Fei Z, He M, Song T, Lin Z, Wang C, Cobden D, Chu JH, Cui YT, Chang CZ, Xiao D, Yan J, Xu X. Electric control of a canted-antiferromagnetic Chern insulator. Nat Commun 2022; 13:1668. [PMID: 35351900 PMCID: PMC8964814 DOI: 10.1038/s41467-022-29259-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2021] [Accepted: 03/07/2022] [Indexed: 11/17/2022] Open
Abstract
The interplay between band topology and magnetism can give rise to exotic states of matter. For example, magnetically doped topological insulators can realize a Chern insulator that exhibits quantized Hall resistance at zero magnetic field. While prior works have focused on ferromagnetic systems, little is known about band topology and its manipulation in antiferromagnets. Here, we report that MnBi2Te4 is a rare platform for realizing a canted-antiferromagnetic (cAFM) Chern insulator with electrical control. We show that the Chern insulator state with Chern number C = 1 appears as the AFM to canted-AFM phase transition happens. The Chern insulator state is further confirmed by observing the unusual transition of the C = 1 state in the cAFM phase to the C = 2 orbital quantum Hall states in the magnetic field induced ferromagnetic phase. Near the cAFM-AFM phase boundary, we show that the dissipationless chiral edge transport can be toggled on and off by applying an electric field alone. We attribute this switching effect to the electrical field tuning of the exchange gap alignment between the top and bottom surfaces. Our work paves the way for future studies on topological cAFM spintronics and facilitates the development of proof-of-concept Chern insulator devices. Exotic states emerge from the interplay between band topology and ferromagnetism, but it remains less known in canted-antiferromagnetic phase. Here, the authors realize a canted-antiferromagnetic Chern insulator in atomically-thin MnBi2Te4 with electrical control of chiral-edge state transport.
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