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

Exotic quantum phenomena have been demonstrated in recently discovered intrinsic magnetic topological insulator MnBi2Te4. At its two-dimensional limit, the quantum anomalous Hall (QAH) effect and axion insulator state were observed in odd and even layers of MnBi2Te4, respectively. Here we employ low-temperature scanning tunneling microscopy to study electronic properties of MnBi2Te4. The quasiparticle interference patterns indicate that the electronic structures on the topmost layer of MnBi2Te4 is different from that of the expected out-of-plane A-type antiferromagnetic phase. The topological surface states may be embedded in deeper layers beneath the topmost surface. Such novel electronic structure is presumably related to the modification of crystalline structure during sample cleaving and re-orientation of magnetic moment of Mn atoms near the surface. Mn dopants substituted at the Bi site on the second atomic layer are observed. The electronic structures are fluctuating at atomic scale on the surface, which can affect the magnetism of MnBi2Te4.