We used angle-resolved photoemission spectroscopy (ARPES) and density functional theory calculations to study the electronic properties of ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$, 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 $E_B=-280\mathrm{meV}$. 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, ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ provides a unique platform for studying the interplay between magnetic ordering and topology.

• Received 24 July 2019
• Accepted 2 March 2020

DOI:https://doi.org/10.1103/PhysRevB.101.161109