Scanning tunneling microscopy study of the antiferromagnetic topological insulator MnBi2Se4

Abstract

Topological insulators with intrinsic magnetic ordering such as MnBi 2 Se 4 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 MnBi 2 Se 4 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 Bi-termination 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 Å lattice is observed that is consistent with the expected crystal structure. • First STM study of MnBi 2 Se 4 surface. • Atomic resolution imaging confirms predominance of Se termination and antisite defects. • Large areas of Bi termination correlated with Se cap removal. • Tunneling spectroscopy reveals termination-dependent density of states. • Se termination exhibits ∼0.2 eV semiconducting gap.