Gapless Dirac surface states in the antiferromagnetic topological insulator MnBi2 Te4

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2020-04-15
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Swatek, Przemyslaw
Wu, Yun
Wang, Lin-Lin
Lee, Kyungchan
Schrunk, Benjamin
Yan, Jiaqiang
Kaminski, Adam
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Physics and Astronomy
Physics and astronomy are basic natural sciences which attempt to describe and provide an understanding of both our world and our universe. Physics serves as the underpinning of many different disciplines including the other natural sciences and technological areas.
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Ames National LaboratoryPhysics and Astronomy
Abstract

We used angle-resolved photoemission spectroscopy (ARPES) and density functional theory calculations to study the electronic properties of MnBi2Te4, a material that was predicted to be an intrinsic antiferromagnetic (AFM) topological insulator. In striking contrast to earlier literature showing a full gap opening between two surface band manifolds on the (0001) surface, we observed a gapless Dirac surface state with a Dirac point sitting at EB=−280meV. Furthermore, our ARPES data revealed the existence of a second Dirac cone sitting closer to the Fermi level. Surprisingly, these surface states remain intact across the AFM transition. The presence of gapless Dirac states in this material may be caused by different ordering at the surface from the bulk or weaker magnetic coupling between the bulk and surface. Whereas the surface Dirac cones seem to be remarkably insensitive to the AFM ordering most likely due to weak coupling to magnetism, we did observe a splitting of the bulk band accompanying the AFM transition. With a moderately high ordering temperature and interesting gapless Dirac surface states, MnBi2Te4 provides a unique platform for studying the interplay between magnetic ordering and topology.

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