Electronic states and magnetic response of MnBi₂Te₄ surface by scanning tunneling microscopy and spectroscopy

The newly discovered intrinsic magnetic topological insulator, MnBi₂Te₄, has demonstrated novel quantum phenomena. Quantized Hall conductance and topological axion state have been realized in its thin flakes. However, the measured band structures show deviations from calculation results and the reason is still in debate. In our studies, low-temperature scanning tunneling microscopy experiment is carried out to investigate its surface states and magnetic response. Unexpected electronic structures are obtained from quasiparticle interference patterns on the topmost layer, which show deviations from the prediction of out-of-plane A-type antiferromagnetic structure. Such differences presumably originate from the re-orientation of magnetic moments near the surface. Moreover, 5% of Mn substitutions at Bi sites are observed. They not only give rise to fluctuating electronic structures, but also affect the magnetism of the material. Our findings shed new lights on the magnetic property of MnBi₂Te₄ and the design of magnetic topological insulators.