Characterization of the Layered Antiferromagnetic Topological Insulator MnBi₂Se₄ Using Scanning Tunneling Microscopy

Magnetic topological insulators (MTIs) have become an area of interest due to the opening of an exchange gap which could allow for the study of topological behavior at elevated temperatures. Additionally, they have been predicted to host several intriguing phenomena such as the quantum anomalous hall effect, magneto-electric effects, and chiral topological edge states. MnBi₂Se₄ (MBS) is a predicted MTI formed of van der Waals separated septuple layers (SL) with a layered anti-ferromagnetic structure. We used scanning tunneling microscopy to study a 20 SL MBS film grown using molecular beam epitaxy and observed two distinct surface terminations, Se and Bi, which we characterized with scanning tunneling spectroscopy (STS) and differential conductance mapping. STS revealed a gap-like local density of states (LDOS) for the Se-termination, and a more metallic LDOS on the Bi-termination. We further investigated the Se-termination by imaging the atomic structure as well as Mn_Bi antisites defects that manifest as threefold symmetric objects in the Se layer. Finally, spatially resolved STS was used to probe the evolution of electronic structure near step edges, and we find in-gap conductance localized to 1SL step edges that could reflect the predicted topological edge states.