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.
Bibliographical noteFunding Information:
We would like to thank Peter Orth and Robert McQueeney for very insightful discussions. Research at Ames Laboratory and ORNL was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Science and Engineering. P.S. and Y.W. were supported by the Center for the Advancement of Topological Semimetals, an Energy Frontier Research Center funded by the US DOE, Office of Basic Energy Sciences. Ames Laboratory is operated for the US Department of Energy by Iowa State University under Contract No. DE-AC02-07CH11358. B.S. was supported by CEM, a NSF MRSEC, under Grant No. DMR-1420451.
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