Visualizing the interplay of Dirac mass gap and magnetism at nanoscale in intrinsic magnetic topological insulators

Mengke Liu; Chao Lei; Hyunsue Kim; Yanxing Li; Lisa Frammolino; Jiaqiang Yan; Allan H. Macdonald; Chih Kang Shih

doi:10.1073/pnas.2207681119

Visualizing the interplay of Dirac mass gap and magnetism at nanoscale in intrinsic magnetic topological insulators

Mengke Liu
, Chao Lei
, Hyunsue Kim
, Yanxing Li
, Lisa Frammolino
, Jiaqiang Yan
, Allan H. Macdonald
, Chih Kang Shih

Correlated Electron Materials

Research output: Contribution to journal › Article › peer-review

25 Scopus citations

Abstract

In intrinsic magnetic topological insulators, Dirac surface-state gaps are prerequisites for quantum anomalous Hall and axion insulating states. Unambiguous experimental identification of these gaps has proved to be a challenge, however. Here, we use molecular beam epitaxy to grow intrinsic MnBi₂Te₄ thin films. Using scanning tunneling microscopy/spectroscopy, we directly visualize the Dirac mass gap and its disappearance below and above the magnetic order temperature. We further reveal the interplay of Dirac mass gaps and local magnetic defects. We find that, in high defect regions, the Dirac mass gap collapses. Ab initio and coupled Dirac cone model calculations provide insight into the microscopic origin of the correlation between defect density and spatial gap variations. This work provides unambiguous identification of the Dirac mass gap in MnBi₂Te₄ and, by revealing the microscopic origin of its gap variation, establishes a material design principle for realizing exotic states in intrinsic magnetic topological insulators.

Original language	English
Article number	e2207681119
Journal	Proceedings of the National Academy of Sciences of the United States of America
Volume	119
Issue number	42
DOIs	https://doi.org/10.1073/pnas.2207681119
State	Published - Oct 18 2022

Funding

This work was primarily supported by the NSF through the Center for Dynamics and Control of Materials: an NSF Materials Research Science and Engineering Centers under cooperative agreement no. DMR-1720595 and the US Air Force grant no. FA2386-21-1-4061. Other supports were from NSF grant nos. DMR-1808751, DMR-2219610, and the Welch Foundation F-1672. Work at Oak Ridge National Laboratory was supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. We thank C.Z. Chang and Y.F. Zhao for the helpful discussion on MBE growth. ACKNOWLEDGMENTS. This work was primarily supported by the NSF through the Center for Dynamics and Control of Materials: an NSF Materials Research Science and Engineering Centers under cooperative agreement no. DMR-1720595 and the US Air Force grant no. FA2386-21-1-4061. Other supports were from NSF grant nos. DMR-1808751, DMR-2219610, and the Welch Foundation F-1672. Work at Oak Ridge National Laboratory was supported by the US Department of Energy,

Keywords

Dirac mass gap
STM/STS
magnetic topological insulator
topological phase transition

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10.1073/pnas.2207681119

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title = "Visualizing the interplay of Dirac mass gap and magnetism at nanoscale in intrinsic magnetic topological insulators",

abstract = "In intrinsic magnetic topological insulators, Dirac surface-state gaps are prerequisites for quantum anomalous Hall and axion insulating states. Unambiguous experimental identification of these gaps has proved to be a challenge, however. Here, we use molecular beam epitaxy to grow intrinsic MnBi2Te4 thin films. Using scanning tunneling microscopy/spectroscopy, we directly visualize the Dirac mass gap and its disappearance below and above the magnetic order temperature. We further reveal the interplay of Dirac mass gaps and local magnetic defects. We find that, in high defect regions, the Dirac mass gap collapses. Ab initio and coupled Dirac cone model calculations provide insight into the microscopic origin of the correlation between defect density and spatial gap variations. This work provides unambiguous identification of the Dirac mass gap in MnBi2Te4 and, by revealing the microscopic origin of its gap variation, establishes a material design principle for realizing exotic states in intrinsic magnetic topological insulators.",

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AU - Lei, Chao

AU - Kim, Hyunsue

AU - Li, Yanxing

AU - Frammolino, Lisa

AU - Yan, Jiaqiang

AU - Macdonald, Allan H.

AU - Shih, Chih Kang

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Y1 - 2022/10/18

N2 - In intrinsic magnetic topological insulators, Dirac surface-state gaps are prerequisites for quantum anomalous Hall and axion insulating states. Unambiguous experimental identification of these gaps has proved to be a challenge, however. Here, we use molecular beam epitaxy to grow intrinsic MnBi2Te4 thin films. Using scanning tunneling microscopy/spectroscopy, we directly visualize the Dirac mass gap and its disappearance below and above the magnetic order temperature. We further reveal the interplay of Dirac mass gaps and local magnetic defects. We find that, in high defect regions, the Dirac mass gap collapses. Ab initio and coupled Dirac cone model calculations provide insight into the microscopic origin of the correlation between defect density and spatial gap variations. This work provides unambiguous identification of the Dirac mass gap in MnBi2Te4 and, by revealing the microscopic origin of its gap variation, establishes a material design principle for realizing exotic states in intrinsic magnetic topological insulators.

AB - In intrinsic magnetic topological insulators, Dirac surface-state gaps are prerequisites for quantum anomalous Hall and axion insulating states. Unambiguous experimental identification of these gaps has proved to be a challenge, however. Here, we use molecular beam epitaxy to grow intrinsic MnBi2Te4 thin films. Using scanning tunneling microscopy/spectroscopy, we directly visualize the Dirac mass gap and its disappearance below and above the magnetic order temperature. We further reveal the interplay of Dirac mass gaps and local magnetic defects. We find that, in high defect regions, the Dirac mass gap collapses. Ab initio and coupled Dirac cone model calculations provide insight into the microscopic origin of the correlation between defect density and spatial gap variations. This work provides unambiguous identification of the Dirac mass gap in MnBi2Te4 and, by revealing the microscopic origin of its gap variation, establishes a material design principle for realizing exotic states in intrinsic magnetic topological insulators.

KW - Dirac mass gap

KW - STM/STS

KW - magnetic topological insulator

KW - topological phase transition

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ER -

Visualizing the interplay of Dirac mass gap and magnetism at nanoscale in intrinsic magnetic topological insulators

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