1
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Yuan W, Zhou LJ, Yang K, Zhao YF, Zhang R, Yan Z, Zhuo D, Mei R, Wang Y, Yi H, Chan MHW, Kayyalha M, Liu CX, Chang CZ. Electrical switching of the edge current chirality in quantum anomalous Hall insulators. NATURE MATERIALS 2024; 23:58-64. [PMID: 37857889 DOI: 10.1038/s41563-023-01694-y] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/02/2023] [Accepted: 09/18/2023] [Indexed: 10/21/2023]
Abstract
A quantum anomalous Hall (QAH) insulator is a topological phase in which the interior is insulating but electrical current flows along the edges of the sample in either a clockwise or counterclockwise direction, as dictated by the spontaneous magnetization orientation. Such a chiral edge current eliminates any backscattering, giving rise to quantized Hall resistance and zero longitudinal resistance. Here we fabricate mesoscopic QAH sandwich Hall bar devices and succeed in switching the edge current chirality through thermally assisted spin-orbit torque (SOT). The well-quantized QAH states before and after SOT switching with opposite edge current chiralities are demonstrated through four- and three-terminal measurements. We show that the SOT responsible for magnetization switching can be generated by both surface and bulk carriers. Our results further our understanding of the interplay between magnetism and topological states and usher in an easy and instantaneous method to manipulate the QAH state.
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Affiliation(s)
- Wei Yuan
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Ling-Jie Zhou
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Kaijie Yang
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Yi-Fan Zhao
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Ruoxi Zhang
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Zijie Yan
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Deyi Zhuo
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Ruobing Mei
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Yang Wang
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Hemian Yi
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Moses H W Chan
- Department of Physics, The Pennsylvania State University, University Park, PA, USA
| | - Morteza Kayyalha
- Department of Electrical Engineering, The Pennsylvania State University, University Park, PA, USA
| | - Chao-Xing Liu
- Department of Physics, The Pennsylvania State University, University Park, PA, USA.
| | - Cui-Zu Chang
- Department of Physics, The Pennsylvania State University, University Park, PA, USA.
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2
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Zhao YF, Zhang R, Sun ZT, Zhou LJ, Zhuo D, Yan ZJ, Yi H, Wang K, Chan MHW, Liu CX, Law KT, Chang CZ. 3D Quantum Anomalous Hall Effect in Magnetic Topological Insulator Trilayers of Hundred-Nanometer Thickness. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2023:e2310249. [PMID: 38118065 DOI: 10.1002/adma.202310249] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/03/2023] [Revised: 12/07/2023] [Indexed: 12/22/2023]
Abstract
Magnetic topological states refer to a class of exotic phases in magnetic materials with the non-trivial topological property determined by magnetic spin configurations. An example of such states is the quantum anomalous Hall (QAH) state, which is a zero magnetic field manifestation of the quantum Hall effect. Current research in this direction focuses on QAH insulators with a thickness of less than 10 nm. Here, molecular beam epitaxy (MBE) is employed to synthesize magnetic TI trilayers with a thickness of up to ≈106 nm. It is found that these samples exhibit well-quantized Hall resistance and vanishing longitudinal resistance at zero magnetic field. By varying the magnetic dopants, gate voltages, temperature, and external magnetic fields, the properties of these thick QAH insulators are examined and the robustness of the 3D QAH effect is demonstrated. The realization of the well-quantized 3D QAH effect indicates that the nonchiral side surface states of the thick magnetic TI trilayers are gapped and thus do not affect the QAH quantization. The 3D QAH insulators of hundred-nanometer thickness provide a promising platform for the exploration of fundamental physics, including axion physics and image magnetic monopole, and the advancement of electronic and spintronic devices to circumvent Moore's law.
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Affiliation(s)
- Yi-Fan Zhao
- Department of Physics, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Ruoxi Zhang
- Department of Physics, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Zi-Ting Sun
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, 999077, China
| | - Ling-Jie Zhou
- Department of Physics, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Deyi Zhuo
- Department of Physics, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Zi-Jie Yan
- Department of Physics, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Hemian Yi
- Department of Physics, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Ke Wang
- Materials Research Institute, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Moses H W Chan
- Department of Physics, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Chao-Xing Liu
- Department of Physics, The Pennsylvania State University, University Park, PA, 16802, USA
| | - K T Law
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, 999077, China
| | - Cui-Zu Chang
- Department of Physics, The Pennsylvania State University, University Park, PA, 16802, USA
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3
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Andersen MP, Mikheev E, Rosen IT, Tai L, Zhang P, Wang KL, Kastner MA, Goldhaber-Gordon D. Universal Conductance Fluctuations in a MnBi 2Te 4 Thin Film. NANO LETTERS 2023. [PMID: 38029283 DOI: 10.1021/acs.nanolett.3c02932] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/01/2023]
Abstract
Quantum coherence of electrons can produce striking behaviors in mesoscopic conductors. Although magnetic order can also strongly affect transport, the combination of coherence and magnetic order has been largely unexplored. Here, we examine quantum coherence-driven universal conductance fluctuations in the antiferromagnetic, canted antiferromagnetic, and ferromagnetic phases of a thin film of the topological material MnBi2Te4. In each magnetic phase, we extract a charge carrier phase coherence length of about 100 nm. The conductance magnetofingerprint is repeatable when sweeping applied magnetic field within one magnetic phase. Surprisingly, in the antiferromagnetic and canted antiferromagnetic phases, but not in the ferromagnetic phase, the magnetofingerprint depends on the direction of the field sweep. To explain our observations, we suggest that conductance fluctuation measurements are sensitive to the motion and nucleation of magnetic domain walls in MnBi2Te4.
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Affiliation(s)
- Molly P Andersen
- Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
- Department of Physics, University of Cincinnati, Cincinnati, Ohio 45221, United States
| | - Evgeny Mikheev
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
- Department of Physics, Stanford University, Stanford, California 94305, United States
- Department of Physics, University of Cincinnati, Cincinnati, Ohio 45221, United States
| | - Ilan T Rosen
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
- Department of Physics, University of Cincinnati, Cincinnati, Ohio 45221, United States
- Department of Applied Physics, Stanford University, Stanford, California 94305, United States
- Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Lixuan Tai
- Department of Electrical and Computer Engineering, University of California, Los Angeles, Los Angeles, California 90095, United States
| | - Peng Zhang
- Department of Electrical and Computer Engineering, University of California, Los Angeles, Los Angeles, California 90095, United States
| | - Kang L Wang
- Department of Electrical and Computer Engineering, University of California, Los Angeles, Los Angeles, California 90095, United States
| | - Marc A Kastner
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
- Department of Physics, Stanford University, Stanford, California 94305, United States
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - David Goldhaber-Gordon
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
- Department of Physics, Stanford University, Stanford, California 94305, United States
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4
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Qiu G, Yang HY, Chong SK, Cheng Y, Tai L, Wang KL. Manipulating Topological Phases in Magnetic Topological Insulators. NANOMATERIALS (BASEL, SWITZERLAND) 2023; 13:2655. [PMID: 37836296 PMCID: PMC10574534 DOI: 10.3390/nano13192655] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/05/2023] [Revised: 09/21/2023] [Accepted: 09/25/2023] [Indexed: 10/15/2023]
Abstract
Magnetic topological insulators (MTIs) are a group of materials that feature topological band structures with concurrent magnetism, which can offer new opportunities for technological advancements in various applications, such as spintronics and quantum computing. The combination of topology and magnetism introduces a rich spectrum of topological phases in MTIs, which can be controllably manipulated by tuning material parameters such as doping profiles, interfacial proximity effect, or external conditions such as pressure and electric field. In this paper, we first review the mainstream MTI material platforms where the quantum anomalous Hall effect can be achieved, along with other exotic topological phases in MTIs. We then focus on highlighting recent developments in modulating topological properties in MTI with finite-size limit, pressure, electric field, and magnetic proximity effect. The manipulation of topological phases in MTIs provides an exciting avenue for advancing both fundamental research and practical applications. As this field continues to develop, further investigations into the interplay between topology and magnetism in MTIs will undoubtedly pave the way for innovative breakthroughs in the fundamental understanding of topological physics as well as practical applications.
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Affiliation(s)
- Gang Qiu
- Department of Electrical and Computer Engineering, University of California, Los Angeles, CA 90095, USA; (H.-Y.Y.); (S.K.C.); (Y.C.); (L.T.)
- Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN 55455, USA
| | - Hung-Yu Yang
- Department of Electrical and Computer Engineering, University of California, Los Angeles, CA 90095, USA; (H.-Y.Y.); (S.K.C.); (Y.C.); (L.T.)
| | - Su Kong Chong
- Department of Electrical and Computer Engineering, University of California, Los Angeles, CA 90095, USA; (H.-Y.Y.); (S.K.C.); (Y.C.); (L.T.)
- Beijing Academy of Quantum Information Sciences, Beijing 100193, China
| | - Yang Cheng
- Department of Electrical and Computer Engineering, University of California, Los Angeles, CA 90095, USA; (H.-Y.Y.); (S.K.C.); (Y.C.); (L.T.)
| | - Lixuan Tai
- Department of Electrical and Computer Engineering, University of California, Los Angeles, CA 90095, USA; (H.-Y.Y.); (S.K.C.); (Y.C.); (L.T.)
| | - Kang L. Wang
- Department of Electrical and Computer Engineering, University of California, Los Angeles, CA 90095, USA; (H.-Y.Y.); (S.K.C.); (Y.C.); (L.T.)
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5
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Fijalkowski KM, Liu N, Mandal P, Schreyeck S, Brunner K, Gould C, Molenkamp LW. Macroscopic Quantum Tunneling of a Topological Ferromagnet. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2023:e2303165. [PMID: 37314152 PMCID: PMC10401085 DOI: 10.1002/advs.202303165] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2023] [Indexed: 06/15/2023]
Abstract
The recent advent of topological states of matter spawned many significant discoveries. The quantum anomalous Hall (QAH) effect is a prime example due to its potential for applications in quantum metrology, as well as its influence on fundamental research into the underlying topological and magnetic states and into axion electrodynamics. Here, electronic transport studies on a (V,Bi,Sb)2 Te3 ferromagnetic topological insulator nanostructure in the QAH regime are presented. This allows access to the dynamics of an individual ferromagnetic domain. The domain size is estimated to be in the 50-100 nm range. Telegraph noise resulting from the magnetization fluctuations of this domain is observed in the Hall signal. Careful analysis of the influence of temperature and external magnetic field on the domain switching statistics provides evidence for quantum tunneling (QT) of magnetization in a macrospin state. This ferromagnetic macrospin is not only the largest magnetic object in which QT is observed, but also the first observation of the effect in a topological state of matter.
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Affiliation(s)
- Kajetan M Fijalkowski
- Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074, Würzburg, Germany
| | - Nan Liu
- Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074, Würzburg, Germany
| | - Pankaj Mandal
- Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074, Würzburg, Germany
| | - Steffen Schreyeck
- Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074, Würzburg, Germany
| | - Karl Brunner
- Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074, Würzburg, Germany
| | - Charles Gould
- Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074, Würzburg, Germany
| | - Laurens W Molenkamp
- Faculty for Physics and Astronomy (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074, Würzburg, Germany
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6
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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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7
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Rosen IT, Andersen MP, Rodenbach LK, Tai L, Zhang P, Wang KL, Kastner MA, Goldhaber-Gordon D. Measured Potential Profile in a Quantum Anomalous Hall System Suggests Bulk-Dominated Current Flow. PHYSICAL REVIEW LETTERS 2022; 129:246602. [PMID: 36563259 DOI: 10.1103/physrevlett.129.246602] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2022] [Revised: 09/20/2022] [Accepted: 11/04/2022] [Indexed: 06/17/2023]
Abstract
Ideally, quantum anomalous Hall systems should display zero longitudinal resistance. Yet in experimental quantum anomalous Hall systems elevated temperature can make the longitudinal resistance finite, indicating dissipative flow of electrons. Here, we show that the measured potentials at multiple locations within a device at elevated temperature are well described by solution of Laplace's equation, assuming spatially uniform conductivity, suggesting nonequilibrium current flows through the two-dimensional bulk. Extrapolation suggests that at even lower temperatures current may still flow primarily through the bulk rather than, as had been assumed, through edge modes. An argument for bulk current flow previously applied to quantum Hall systems supports this picture.
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Affiliation(s)
- Ilan T Rosen
- Department of Applied Physics, Stanford University, Stanford, California 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
| | - Molly P Andersen
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
- Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, USA
| | - Linsey K Rodenbach
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
- Department of Physics, Stanford University, Stanford, California 94305, USA
| | - Lixuan Tai
- Department of Electrical Engineering, University of California, Los Angeles, California 90095, USA
| | - Peng Zhang
- Department of Electrical Engineering, University of California, Los Angeles, California 90095, USA
| | - Kang L Wang
- Department of Electrical Engineering, University of California, Los Angeles, California 90095, USA
| | - M A Kastner
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
- Department of Physics, Stanford University, Stanford, California 94305, USA
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - David Goldhaber-Gordon
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
- Department of Physics, Stanford University, Stanford, California 94305, USA
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8
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Deng P, Eckberg C, Zhang P, Qiu G, Emmanouilidou E, Yin G, Chong SK, Tai L, Ni N, Wang KL. Probing the mesoscopic size limit of quantum anomalous Hall insulators. Nat Commun 2022; 13:4246. [PMID: 35869045 PMCID: PMC9307791 DOI: 10.1038/s41467-022-31105-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2022] [Accepted: 06/06/2022] [Indexed: 11/09/2022] Open
Abstract
The inelastic scattering length (Ls) is a length scale of fundamental importance in condensed matters due to the relationship between inelastic scattering and quantum dephasing. In quantum anomalous Hall (QAH) materials, the mesoscopic length scale Ls plays an instrumental role in determining transport properties. Here we examine Ls in three regimes of the QAH system with distinct transport behaviors: the QAH, quantum critical, and insulating regimes. Although the resistance changes by five orders of magnitude when tuning between these distinct electronic phases, scaling analyses indicate a universal Ls among all regimes. Finally, mesoscopic scaled devices with sizes on the order of Ls were fabricated, enabling the direct detection of the value of Ls in QAH samples. Our results unveil the fundamental length scale that governs the transport behavior of QAH materials. In quantum anomalous Hall (QAH) materials, the mesoscopic scattering length (Ls) plays an instrumental role in determining transport properties. Here, the authors examine Ls in three regimes (QAH, quantum critical, and insulating) with distinct transport behaviours, and find a universal Ls across all regimes.
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9
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Zhou S, Zhu M, Liu Q, Xiao Y, Cui Z, Guo C. High-Temperature Quantum Hall Effect in Graphite-Gated Graphene Heterostructure Devices with High Carrier Mobility. NANOMATERIALS (BASEL, SWITZERLAND) 2022; 12:3777. [PMID: 36364553 PMCID: PMC9654316 DOI: 10.3390/nano12213777] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/28/2022] [Revised: 10/19/2022] [Accepted: 10/22/2022] [Indexed: 06/16/2023]
Abstract
Since the discovery of the quantum Hall effect in 1980, it has attracted intense interest in condensed matter physics and has led to a new type of metrological standard by utilizing the resistance quantum. Graphene, a true two-dimensional electron gas material, has demonstrated the half-integer quantum Hall effect and composite-fermion fractional quantum Hall effect due to its unique massless Dirac fermions and ultra-high carrier mobility. Here, we use a monolayer graphene encapsulated with hexagonal boron nitride and few-layer graphite to fabricate micrometer-scale graphene Hall devices. The application of a graphite gate electrode significantly screens the phonon scattering from a conventional SiO2/Si substrate, and thus enhances the carrier mobility of graphene. At a low temperature, the carrier mobility of graphene devices can reach 3 × 105 cm2/V·s, and at room temperature, the carrier mobility can still exceed 1 × 105 cm2/V·s, which is very helpful for the development of high-temperature quantum Hall effects under moderate magnetic fields. At a low temperature of 1.6 K, a series of half-integer quantum Hall plateaus are well-observed in graphene with a magnetic field of 1 T. More importantly, the ν = ±2 quantum Hall plateau clearly persists up to 150 K with only a few-tesla magnetic field. These findings show that graphite-gated high-mobility graphene devices hold great potential for high-sensitivity Hall sensors and resistance metrology standards for the new Système International d'unités.
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10
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He QL, Hughes TL, Armitage NP, Tokura Y, Wang KL. Topological spintronics and magnetoelectronics. NATURE MATERIALS 2022; 21:15-23. [PMID: 34949869 DOI: 10.1038/s41563-021-01138-5] [Citation(s) in RCA: 32] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/20/2020] [Accepted: 09/21/2021] [Indexed: 05/08/2023]
Abstract
Topological electronic materials, such as topological insulators, are distinct from trivial materials in the topology of their electronic band structures that lead to robust, unconventional topological states, which could bring revolutionary developments in electronics. This Perspective summarizes developments of topological insulators in various electronic applications including spintronics and magnetoelectronics. We group and analyse several important phenomena in spintronics using topological insulators, including spin-orbit torque, the magnetic proximity effect, interplay between antiferromagnetism and topology, and the formation of topological spin textures. We also outline recent developments in magnetoelectronics such as the axion insulator and the topological magnetoelectric effect observed using different topological insulators.
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Affiliation(s)
- Qing Lin He
- International Center for Quantum Materials, School of Physics, Peking University, Beijing, China.
- Collaborative Innovation Center of Quantum Matter, Beijing, China.
- Interdisciplinary Institute of Light-Element Quantum Materials and Research Center for Light-Element Advanced Materials, Peking University, Beijing, China.
| | - Taylor L Hughes
- Department of Physics and Institute for Condensed Matter Theory, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - N Peter Armitage
- Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD, USA
| | - Yoshinori Tokura
- RIKEN Center for Emergent Matter Science (CEMS), Wako, Japan
- Tokyo College, University of Tokyo, Tokyo, Japan
| | - Kang L Wang
- Department of Electrical and Computer Engineering, University of California, Los Angeles, CA, USA.
- Center of Quantum Sciences and Engineering, University of California, Los Angeles, CA, USA.
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11
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Wimmer S, Sánchez-Barriga J, Küppers P, Ney A, Schierle E, Freyse F, Caha O, Michalička J, Liebmann M, Primetzhofer D, Hoffman M, Ernst A, Otrokov MM, Bihlmayer G, Weschke E, Lake B, Chulkov EV, Morgenstern M, Bauer G, Springholz G, Rader O. Mn-Rich MnSb 2 Te 4 : A Topological Insulator with Magnetic Gap Closing at High Curie Temperatures of 45-50 K. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2021; 33:e2102935. [PMID: 34469013 DOI: 10.1002/adma.202102935] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/18/2021] [Revised: 06/29/2021] [Indexed: 06/13/2023]
Abstract
Ferromagnetic topological insulators exhibit the quantum anomalous Hall effect, which is potentially useful for high-precision metrology, edge channel spintronics, and topological qubits. The stable 2+ state of Mn enables intrinsic magnetic topological insulators. MnBi2 Te4 is, however, antiferromagnetic with 25 K Néel temperature and is strongly n-doped. In this work, p-type MnSb2 Te4 , previously considered topologically trivial, is shown to be a ferromagnetic topological insulator for a few percent Mn excess. i) Ferromagnetic hysteresis with record Curie temperature of 45-50 K, ii) out-of-plane magnetic anisotropy, iii) a 2D Dirac cone with the Dirac point close to the Fermi level, iv) out-of-plane spin polarization as revealed by photoelectron spectroscopy, and v) a magnetically induced bandgap closing at the Curie temperature, demonstrated by scanning tunneling spectroscopy (STS), are shown. Moreover, a critical exponent of the magnetization β ≈ 1 is found, indicating the vicinity of a quantum critical point. Ab initio calculations reveal that Mn-Sb site exchange provides the ferromagnetic interlayer coupling and the slight excess of Mn nearly doubles the Curie temperature. Remaining deviations from the ferromagnetic order open the inverted bulk bandgap and render MnSb2 Te4 a robust topological insulator and new benchmark for magnetic topological insulators.
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Affiliation(s)
- Stefan Wimmer
- Institut für Halbleiter- und Festkörperphysik, Johannes Kepler Universität, Altenberger Straße 69, Linz, 4040, Austria
| | - Jaime Sánchez-Barriga
- Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Straße 15, 12489, Berlin, Germany
| | - Philipp Küppers
- II. Institute of Physics B and JARA-FIT, RWTH Aachen Unversity, 52074, Aachen, Germany
| | - Andreas Ney
- Institut für Halbleiter- und Festkörperphysik, Johannes Kepler Universität, Altenberger Straße 69, Linz, 4040, Austria
| | - Enrico Schierle
- Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Straße 15, 12489, Berlin, Germany
| | - Friedrich Freyse
- Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Straße 15, 12489, Berlin, Germany
- Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Straße 24/25, 14476, Potsdam, Germany
| | - Ondrej Caha
- Department of Condensed Matter Physics, Masaryk University, Kotlářská 267/2, Brno, 61137, Czech Republic
| | - Jan Michalička
- Central European Institute of Technology, Brno University of Technology, Purkyňova 123, Brno, 612 00, Czech Republic
| | - Marcus Liebmann
- II. Institute of Physics B and JARA-FIT, RWTH Aachen Unversity, 52074, Aachen, Germany
| | - Daniel Primetzhofer
- Department of Physics and Astronomy, Universitet Uppsala, Lägerhyddsvägen 1, Uppsala, 75120, Sweden
| | - Martin Hoffman
- Institute for Theoretical Physics, Johannes Kepler Universität, Altenberger Straße 69, Linz, 4040, Austria
| | - Arthur Ernst
- Institute for Theoretical Physics, Johannes Kepler Universität, Altenberger Straße 69, Linz, 4040, Austria
- Max Planck Institute of Microstructure Physics, Weinberg 2, 06120, Halle, Germany
| | - Mikhail M Otrokov
- Centro de Física de Materiales (CFM-MPC), Centro Mixto CSIC-UPV/EHU, San Sebastián/Donostia, 20018, Spain
- IKERBASQUE, Basque Foundation for Science, Bilbao, 48011, Spain
| | - Gustav Bihlmayer
- Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, 52425, Jülich, Germany
| | - Eugen Weschke
- Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Straße 15, 12489, Berlin, Germany
| | - Bella Lake
- Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Straße 15, 12489, Berlin, Germany
| | - Evgueni V Chulkov
- Donostia International Physics Center (DIPC), San Sebastián/Donostia, 20018, Spain
- Departamento de Polímeros y Materiales Avanzados: Física, Química y Tecnología, Facultad de Ciencias Químicas, Universidad del País Vasco UPV/EHU, San Sebastián/Donostia, 20080, Spain
- Saint Petersburg State University, Saint Petersburg, 198504, Russia
- Tomsk State University, Tomsk, 634050, Russia
| | - Markus Morgenstern
- II. Institute of Physics B and JARA-FIT, RWTH Aachen Unversity, 52074, Aachen, Germany
| | - Günther Bauer
- Institut für Halbleiter- und Festkörperphysik, Johannes Kepler Universität, Altenberger Straße 69, Linz, 4040, Austria
| | - Gunther Springholz
- Institut für Halbleiter- und Festkörperphysik, Johannes Kepler Universität, Altenberger Straße 69, Linz, 4040, Austria
| | - Oliver Rader
- Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Straße 15, 12489, Berlin, Germany
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12
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Quantum anomalous Hall edge channels survive up to the Curie temperature. Nat Commun 2021; 12:5599. [PMID: 34552096 PMCID: PMC8458438 DOI: 10.1038/s41467-021-25912-w] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2021] [Accepted: 09/06/2021] [Indexed: 11/09/2022] Open
Abstract
Achieving metrological precision of quantum anomalous Hall resistance quantization at zero magnetic field so far remains limited to temperatures of the order of 20 mK, while the Curie temperature in the involved material is as high as 20 K. The reason for this discrepancy remains one of the biggest open questions surrounding the effect, and is the focus of this article. Here we show, through a careful analysis of the non-local voltages on a multi-terminal Corbino geometry, that the chiral edge channels continue to exist without applied magnetic field up to the Curie temperature of bulk ferromagnetism of the magnetic topological insulator, and that thermally activated bulk conductance is responsible for this quantization breakdown. Our results offer important insights on the nature of the topological protection of these edge channels, provide an encouraging sign for potential applications, and establish the multi-terminal Corbino geometry as a powerful tool for the study of edge channel transport in topological materials. The quantum anomalous Hall effect has so far been limited to temperature of the order of 20 mK. Here, Fijalkowski et al. report the existence of chiral edge channels up to the Curie temperature of bulk ferromagnetism of the magnetic topological insulator with a multi-terminal Corbino geometry.
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13
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Current-induced switching of proximity-induced ferromagnetic surface states in a topological insulator. Nat Commun 2021; 12:1404. [PMID: 33658496 PMCID: PMC7930265 DOI: 10.1038/s41467-021-21672-9] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2020] [Accepted: 02/07/2021] [Indexed: 11/08/2022] Open
Abstract
Electrical manipulation of magnetization could be an essential function for energy-efficient spintronics technology. A magnetic topological insulator, possessing a magnetically gapped surface state with spin-polarized electrons, not only exhibits exotic topological phases relevant to the quantum anomalous Hall state but also enables the electrical control of its magnetic state at the surface. Here, we demonstrate efficient current-induced switching of the surface ferromagnetism in hetero-bilayers consisting of the topological insulator (Bi1-xSbx)2Te3 and the ferromagnetic insulator Cr2Ge2Te6, where the proximity-induced ferromagnetic surface states play two roles: efficient charge-to-spin current conversion and emergence of large anomalous Hall effect. The sign reversal of the surface ferromagnetic states with current injection is clearly observed, accompanying the nearly full magnetization reversal in the adjacent insulating Cr2Ge2Te6 layer of an optimal thickness range. The present results may facilitate an electrical control of dissipationless topological-current circuits. Electrical manipulation of magnetization in devices made of topological materials may be an essential route towards future spintronics technology. Here, Mogi et al. show efficient current-induced switching of surface ferromagnetism in hetero-bilayers of topological insulator (Bi1-xSbx)2Te3 and ferromagnetic insulator Cr2Ge2Te6.
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14
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Chong YX, Liu X, Sharma R, Kostin A, Gu G, Fujita K, Davis JCS, Sprau PO. Severe Dirac Mass Gap Suppression in Sb 2Te 3-Based Quantum Anomalous Hall Materials. NANO LETTERS 2020; 20:8001-8007. [PMID: 32985892 DOI: 10.1021/acs.nanolett.0c02873] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The quantum anomalous Hall (QAH) effect appears in ferromagnetic topological insulators (FMTIs) when a Dirac mass gap opens in the spectrum of the topological surface states (SSs). Unaccountably, although the mean mass gap can exceed 28 meV (or ∼320 K), the QAH effect is frequently only detectable at temperatures below 1 K. Using atomic-resolution Landau level spectroscopic imaging, we compare the electronic structure of the archetypal FMTI Cr0.08(Bi0.1Sb0.9)1.92Te3 to that of its nonmagnetic parent (Bi0.1Sb0.9)2Te3, to explore the cause. In (Bi0.1Sb0.9)2Te3, we find spatially random variations of the Dirac energy. Statistically equivalent Dirac energy variations are detected in Cr0.08(Bi0.1Sb0.9)1.92Te3 with concurrent but uncorrelated Dirac mass gap disorder. These two classes of SS electronic disorder conspire to drastically suppress the minimum mass gap to below 100 μeV for nanoscale regions separated by <1 μm. This fundamentally limits the fully quantized anomalous Hall effect in Sb2Te3-based FMTI materials to very low temperatures.
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Affiliation(s)
- Yi Xue Chong
- LASSP, Department of Physics, Cornell University, Ithaca, New York 14853, United States
- CMPMS Department, Brookhaven National Laboratory, Upton, New York 11973, United States
| | - Xiaolong Liu
- LASSP, Department of Physics, Cornell University, Ithaca, New York 14853, United States
- Kavli Institute at Cornell, Cornell University, Ithaca, New York 14853, United States
| | - Rahul Sharma
- LASSP, Department of Physics, Cornell University, Ithaca, New York 14853, United States
- CMPMS Department, Brookhaven National Laboratory, Upton, New York 11973, United States
| | - Andrey Kostin
- LASSP, Department of Physics, Cornell University, Ithaca, New York 14853, United States
| | - Genda Gu
- CMPMS Department, Brookhaven National Laboratory, Upton, New York 11973, United States
| | - K Fujita
- CMPMS Department, Brookhaven National Laboratory, Upton, New York 11973, United States
| | - J C Séamus Davis
- LASSP, Department of Physics, Cornell University, Ithaca, New York 14853, United States
- Department of Physics, University College Cork, Cork T12R5C, Ireland
- Clarendon Laboratory, University of Oxford, Oxford OX1 3PU, U.K
| | - Peter O Sprau
- LASSP, Department of Physics, Cornell University, Ithaca, New York 14853, United States
- Advanced Development Center, ASML, Wilton, Connecticut 06897, United States
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15
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Wang SW, Xiao D, Dou Z, Cao M, Zhao YF, Samarth N, Chang CZ, Connolly MR, Smith CG. Demonstration of Dissipative Quasihelical Edge Transport in Quantum Anomalous Hall Insulators. PHYSICAL REVIEW LETTERS 2020; 125:126801. [PMID: 33016726 DOI: 10.1103/physrevlett.125.126801] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2020] [Accepted: 08/17/2020] [Indexed: 06/11/2023]
Abstract
Doping a topological insulator (TI) film with transition metal ions can break its time-reversal symmetry and lead to the realization of the quantum anomalous Hall (QAH) effect. Prior studies have shown that the longitudinal resistance of the QAH samples usually does not vanish when the Hall resistance shows a good quantization. This has been interpreted as a result of the presence of possible dissipative conducting channels in magnetic TI samples. By studying the temperature- and magnetic-field-dependence of the magnetoresistance of a magnetic TI sandwich heterostructure device, we demonstrate that the predominant dissipation mechanism in thick QAH insulators can switch between nonchiral edge states and residual bulk states in different magnetic-field regimes. The interactions between bulk states, chiral edge states, and nonchiral edge states are also investigated. Our Letter provides a way to distinguish between the dissipation arising from the residual bulk states and nonchiral edge states, which is crucial for achieving true dissipationless transport in QAH insulators and for providing deeper insights into QAH-related phenomena.
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Affiliation(s)
- Shu-Wei Wang
- Department of Physics, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom
| | - Di Xiao
- Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Ziwei Dou
- Department of Physics, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom
| | - Moda Cao
- Department of Physics, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom
| | - Yi-Fan Zhao
- Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Nitin Samarth
- Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Cui-Zu Chang
- Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Malcolm R Connolly
- Department of Physics, Imperial College London, London SW7 2AZ, United Kingdom
| | - Charles G Smith
- Department of Physics, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom
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16
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Tan A, Labracherie V, Kunchur N, Wolter AUB, Cornejo J, Dufouleur J, Büchner B, Isaeva A, Giraud R. Metamagnetism of Weakly Coupled Antiferromagnetic Topological Insulators. PHYSICAL REVIEW LETTERS 2020; 124:197201. [PMID: 32469595 DOI: 10.1103/physrevlett.124.197201] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/08/2020] [Revised: 02/27/2020] [Accepted: 04/14/2020] [Indexed: 06/11/2023]
Abstract
The magnetic properties of the van der Waals magnetic topological insulators MnBi_{2}Te_{4} and MnBi_{4}Te_{7} are investigated by magnetotransport measurements. We evidence that the relative strength of the interlayer exchange coupling J to the uniaxial anisotropy K controls a transition from an A-type antiferromagnetic order to a ferromagneticlike metamagnetic state. A bilayer Stoner-Wohlfarth model allows us to describe this evolution, as well as the typical angular dependence of specific signatures, such as the spin-flop transition of the uniaxial antiferromagnet and the switching field of the metamagnet.
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Affiliation(s)
- Aoyu Tan
- Université Grenoble Alpes, CNRS, CEA, Spintec, F-38000 Grenoble, France
- Institute for Solid State Physics, Leibniz IFW Dresden, D-01069 Dresden, Germany
| | - Valentin Labracherie
- Université Grenoble Alpes, CNRS, CEA, Spintec, F-38000 Grenoble, France
- Institute for Solid State Physics, Leibniz IFW Dresden, D-01069 Dresden, Germany
| | - Narayan Kunchur
- Institute for Solid State Physics, Leibniz IFW Dresden, D-01069 Dresden, Germany
| | - Anja U B Wolter
- Institute for Solid State Physics, Leibniz IFW Dresden, D-01069 Dresden, Germany
| | - Joaquin Cornejo
- Institute for Solid State Physics, Leibniz IFW Dresden, D-01069 Dresden, Germany
| | - Joseph Dufouleur
- Institute for Solid State Physics, Leibniz IFW Dresden, D-01069 Dresden, Germany
- Center for Transport and Devices, Technische Universität Dresden, D-01069 Dresden, Germany
| | - Bernd Büchner
- Institute for Solid State Physics, Leibniz IFW Dresden, D-01069 Dresden, Germany
- Institut für Festkörperphysik and Würzburg-Dresden Cluster of Excellence ct.qmat, Technische Universität Dresden, 01062 Dresden, Germany
| | - Anna Isaeva
- Institute for Solid State Physics, Leibniz IFW Dresden, D-01069 Dresden, Germany
- Institut für Festkörperphysik and Würzburg-Dresden Cluster of Excellence ct.qmat, Technische Universität Dresden, 01062 Dresden, Germany
| | - Romain Giraud
- Université Grenoble Alpes, CNRS, CEA, Spintec, F-38000 Grenoble, France
- Institute for Solid State Physics, Leibniz IFW Dresden, D-01069 Dresden, Germany
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17
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Davis R, Schlamminger S. Basic Metrology for 2020. IEEE INSTRUMENTATION & MEASUREMENT MAGAZINE 2020; 23:10.1109/MIM.2020.9082793. [PMID: 34248348 PMCID: PMC8268802 DOI: 10.1109/mim.2020.9082793] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Affiliation(s)
- Richard Davis
- International Bureau of Weights and Measures (BIPM) in 1990 following eighteen years at NIST in Gaithersburg, Maryland
| | - Stephan Schlamminger
- Physicist at the National Institute of Standards and Technology in Gaithersburg, Maryland
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18
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Kayyalha M, Xiao D, Zhang R, Shin J, Jiang J, Wang F, Zhao YF, Xiao R, Zhang L, Fijalkowski KM, Mandal P, Winnerlein M, Gould C, Li Q, Molenkamp LW, Chan MHW, Samarth N, Chang CZ. Absence of evidence for chiral Majorana modes in quantum anomalous Hall-superconductor devices. Science 2020; 367:64-67. [DOI: 10.1126/science.aax6361] [Citation(s) in RCA: 70] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2019] [Accepted: 11/07/2019] [Indexed: 11/02/2022]
Affiliation(s)
- Morteza Kayyalha
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Di Xiao
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Ruoxi Zhang
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Jaeho Shin
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Jue Jiang
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Fei Wang
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Yi-Fan Zhao
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Run Xiao
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Ling Zhang
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Kajetan M. Fijalkowski
- Faculty for Physics and Astronomy (EP3), University of Würzburg, Am Hubland, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
| | - Pankaj Mandal
- Faculty for Physics and Astronomy (EP3), University of Würzburg, Am Hubland, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
| | - Martin Winnerlein
- Faculty for Physics and Astronomy (EP3), University of Würzburg, Am Hubland, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
| | - Charles Gould
- Faculty for Physics and Astronomy (EP3), University of Würzburg, Am Hubland, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
| | - Qi Li
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Laurens W. Molenkamp
- Faculty for Physics and Astronomy (EP3), University of Würzburg, Am Hubland, D-97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, D-97074 Würzburg, Germany
| | - Moses H. W. Chan
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Nitin Samarth
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
| | - Cui-Zu Chang
- Department of Physics, Pennsylvania State University, University Park, PA 16802, USA
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19
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Balram AC, Flensberg K, Paaske J, Rudner MS. Current-Induced Gap Opening in Interacting Topological Insulator Surfaces. PHYSICAL REVIEW LETTERS 2019; 123:246803. [PMID: 31922820 DOI: 10.1103/physrevlett.123.246803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2019] [Indexed: 06/10/2023]
Abstract
Two-dimensional topological insulators (TIs) host gapless helical edge states that are predicted to support a quantized two-terminal conductance. Quantization is protected by time-reversal symmetry, which forbids elastic backscattering. Paradoxically, the current-carrying state itself breaks the time-reversal symmetry that protects it. Here we show that the combination of electron-electron interactions and momentum-dependent spin polarization in helical edge states gives rise to feedback through which an applied current opens a gap in the edge state dispersion, thereby breaking the protection against elastic backscattering. Current-induced gap opening is manifested via a nonlinear contribution to the system's I-V characteristic, which persists down to zero temperature. We discuss prospects for realizations in recently discovered large bulk band gap TIs, and an analogous current-induced gap opening mechanism for the surface states of three-dimensional TIs.
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Affiliation(s)
- Ajit C Balram
- Niels Bohr International Academy, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
- Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
- The Institute of Mathematical Sciences, HBNI, CIT Campus, Chennai 600113, India
| | - Karsten Flensberg
- Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
| | - Jens Paaske
- Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
| | - Mark S Rudner
- Niels Bohr International Academy, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
- Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
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20
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Sharpe AL, Fox EJ, Barnard AW, Finney J, Watanabe K, Taniguchi T, Kastner MA, Goldhaber-Gordon D. Emergent ferromagnetism near three-quarters filling in twisted bilayer graphene. Science 2019; 365:605-608. [DOI: 10.1126/science.aaw3780] [Citation(s) in RCA: 724] [Impact Index Per Article: 144.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2018] [Accepted: 07/03/2019] [Indexed: 01/21/2023]
Abstract
When two sheets of graphene are stacked at a small twist angle, the resulting flat superlattice minibands are expected to strongly enhance electron-electron interactions. Here, we present evidence that near three-quarters (34) filling of the conduction miniband, these enhanced interactions drive the twisted bilayer graphene into a ferromagnetic state. In a narrow density range around an apparent insulating state at34, we observe emergent ferromagnetic hysteresis, with a giant anomalous Hall (AH) effect as large as 10.4 kilohms and indications of chiral edge states. Notably, the magnetization of the sample can be reversed by applying a small direct current. Although the AH resistance is not quantized, and dissipation is present, our measurements suggest that the system may be an incipient Chern insulator.
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21
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Rigosi AF, Elmquist RE. The Quantum Hall Effect in the Era of the New SI. SEMICONDUCTOR SCIENCE AND TECHNOLOGY 2019; 34:10.1088/1361-6641/ab37d3. [PMID: 32165778 PMCID: PMC7067285 DOI: 10.1088/1361-6641/ab37d3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The quantum Hall effect (QHE), and devices reliant on it, will continue to serve as the foundation of the ohm while also expanding its territory into other SI derived units. The foundation, evolution, and significance of all of these devices exhibiting some form of the QHE will be described in the context of optimizing future electrical resistance standards. As the world adapts to using the quantum SI, it remains essential that the global metrology community pushes forth and continues to innovate and produce new technologies for disseminating the ohm and other electrical units.
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Affiliation(s)
- Albert F Rigosi
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, United States of America
| | - Randolph E Elmquist
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, United States of America
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22
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Abstract
The chiral Majorana fermion is a massless self-conjugate fermion which can arise as the edge state of certain 2D topological matters. It has been theoretically predicted and experimentally observed in a hybrid device of a quantum anomalous Hall insulator and a conventional superconductor. Its closely related cousin, the Majorana zero mode in the bulk of the corresponding topological matter, is known to be applicable in topological quantum computations. Here we show that the propagation of chiral Majorana fermions leads to the same unitary transformation as that in the braiding of Majorana zero modes and propose a platform to perform quantum computation with chiral Majorana fermions. A Corbino ring junction of the hybrid device can use quantum coherent chiral Majorana fermions to implement the Hadamard gate and the phase gate, and the junction conductance yields a natural readout for the qubit state.
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