  Exotic quantum phenomena have been demonstrated in recently discovered
intrinsic magnetic topological insulator MnBi2Te4. At its two-dimensional
limit, quantum anomalous Hall (QAH) effect and axion insulator state are
observed in odd and even layers of MnBi2Te4, respectively. The measured band
structures exhibit intriguing and complex properties. Here we employ
low-temperature scanning tunneling microscopy to study its surface states and
magnetic response. 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 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 ratio of Mn/Bi substitutions is 5%.
The electronic structures are fluctuating at atomic scale on the surface, which
can affect the magnetism of MnBi2Te4. Our findings shed new lights on the
magnetic property of MnBi2Te4 and thus the design of magnetic topological
insulators.
