Scanning tunneling microscopy study of the antiferromagnetic topological insulator MnBi2Se4

Topological insulators with intrinsic magnetic ordering such as MnBi2Se4 have been predicted to host many exotic topological phenomena including dissipationless edge states and magnetoelectric effects. Here we use scanning tunneling microscopy to study the surface of MnBi2Se4 epitaxial thin films. Large scale topographic images show steps between van der Waals layers and screw dislocations. While we find the Se-termination predominant on the surface, areas attributed to Bitermination are found at the edges of small islands in as-grown films, or in larger areas upon removal of surface capping. We compare these terminations through an analysis of step heights, atomic resolution images and tunneling spectroscopy. Tunneling spectra on the Se-termination reveals semiconducting behavior, with an apparent bandgap of > 0.18 eV that depends on the tip height. In contrast, tunneling spectra of the Bi-termination appears gapless, which could be an indication of dangling bond states on the surface. In both cases, a hexagonal 3.9 angstrom lattice is observed that is consistent with the expected crystal structure.