Crossover from 2D Ferromagnetic Insulator to Wide Band Gap Quantum Anomalous Hall Insulator in Ultrathin MnBi2Te4

Chi Xuan Trang, Qile Li, Yuefeng Yin, Jinwoong Hwang, Golrokh Akhgar, Iolanda Di Bernardo, Antonija Grubišić-Čabo, Anton Tadich, Michael S. Fuhrer, Sung Kwan Mo, Nikhil V. Medhekar, Mark T. Edmonds*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

40 Citations (Scopus)

Abstract

Intrinsic magnetic topological insulators offer low disorder and large magnetic band gaps for robust magnetic topological phases operating at higher temperatures. By controlling the layer thickness, emergent phenomena such as the quantum anomalous Hall (QAH) effect and axion insulator phases have been realized. These observations occur at temperatures significantly lower than the Néel temperature of bulk MnBi2Te4, and measurement of the magnetic energy gap at the Dirac point in ultrathin MnBi2Te4 has yet to be achieved. Critical to achieving the promise of this system is a direct measurement of the layer-dependent energy gap and verification of a temperature-dependent topological phase transition from a large band gap QAH insulator to a gapless TI paramagnetic phase. Here we utilize temperature-dependent angle-resolved photoemission spectroscopy to study epitaxial ultrathin MnBi2Te4. We directly observe a layer-dependent crossover from a 2D ferromagnetic insulator with a band gap greater than 780 meV in one septuple layer (1 SL) to a QAH insulator with a large energy gap (>70 meV) at 8 K in 3 and 5 SL MnBi2Te4. The QAH gap is confirmed to be magnetic in origin, as it becomes gapless with increasing temperature above 8 K.

Original languageEnglish
Pages (from-to)13444-13452
Number of pages9
JournalAcs Nano
Volume15
Issue number8
DOIs
Publication statusPublished - 24-Aug-2021
Externally publishedYes

Keywords

  • angle-resolved photoemission spectroscopy
  • ferromagnetic insulator
  • magnetic topological insulator
  • MnBiTe
  • quantum anomalous Hall insulator
  • thin film

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