Robust axion insulator and Chern insulator phases in a two-dimensional antiferromagnetic topological insulator

The intricate interplay between non-trivial topology and magnetism in two-dimensional materials can lead to the emergence of interesting phenomena such as the quantum anomalous Hall effect. Here we investigate the quantum transport of both bulk crystal and exfoliated MnBi₂Te₄ flakes in a field-effect transistor geometry. For the six septuple-layer device tuned into the insulating regime, we observe a large longitudinal resistance and zero Hall plateau, which are characteristics of an axion insulator state. The robust axion insulator state occurs in zero magnetic field, over a wide magnetic-field range and at relatively high temperatures. Moreover, a moderate magnetic field drives a quantum phase transition from the axion insulator phase to a Chern insulator phase with zero longitudinal resistance and quantized Hall resistance h/e², where h is Planck's constant and e is electron charge. Our results pave the way for using even-number septuple-layer MnBi₂Te₄ to realize the quantized topological magnetoelectric effect and axion electrodynamics in condensed matter systems.