Coexistence of Chern Band and Landau Quantization in Intrinsic Magnetic Topological Insulator*

The intrinsic magnetic topological insulators MnBi₂Te₄ family exhibits rich topological quantum states and magnetic phases. By introducing the Sb substitution, the fermi level of the bulk band can be effectively controlled and thus allows access to the exotic topological bulk and surface states. Here, we fabricated Mn(Bi,Sb)₂Te₄ devices with different flake thicknesses and studied their quantum transport properties at the optimal Sb concentrations. In higher electron mobility devices, we observe the development of quantum Hall (ν=-3, -5, etc.) states in addition to the Chern insulating state (C=-1) when the magnetic moment is aligned into the ferromagnetic phase by a magnetic field. The Landau level spectrum of the Mn(Bi,Sb)₂Te₄ behaves very differently from the bulk-insulating three-dimensional topological insulators. In the relatively thick Mn(Bi,Sb)₂Te₄ flake, the dual-gating feature for the quantum Hall plateaus remains a stripe-like pattern at odd integer Landau level degeneracy, indicating an intrinsic bulk-surface state coupling effect. The results suggest that the Mn(Bi,Sb)₂Te₄ is a promising candidate for the exploration of the unique quantization in a coupled topological surface and Weyl states in magnetic topological insulators.