Realizing intrinsic magnetic topological insulators with gapped topological surface states in MnBi_2-xSb_xTe₄

The interplay between magnetism and topology of materials could create a variety of exotic topological quantum states, including the quantum anomalous Hall (QAH) effect showing dissipationless chiral edge states, the topological axion states displaying quantized magnetoelectric effects, and Majorana fermions, obeying non-Abelian statistics. All of these quantum states are hopefully realizable in MnBi₂Te₄. However, the Fermi level is usually in the bulk conduction band of the materials, which is not ideal for revealing these topological properties in transport. Here we show that by doping MnBi2Te4 with Sb, the Fermi level can be shifted while the non-trivial topology is maintained. Scanning tunneling microscopy (STM) is utilized to observe electronic band structure by quasi-particle interference, which reveals surface states in the bulk band gap and a surface band gap at the Dirac point. The transport from multiprobe-STM further displays a surface dominant transport. Our results show that the MnBi_2-xSb_xTe₄ is an intrinsic magnetic topological insulator that would offer an ideal platform to observe various exotic topological phenomena.