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

Topology, magnetism, and two-dimensional materials are among the most actively-pursued fields in physics and material science. Here, we investigate the quantum transport behaviors of exfoliated MnBi₂Te₄, an antiferromagnetic topological insulator that hosts all three properties simultaneously. In the six septuple-layer crystal, we observe robust axion insulator state in zero magnetic field, over a wide field range, and at relatively high temperatures. A moderate magnetic field drives it into the Chern insulator state through a topological quantum phase transition. These results pave the road for realizing the topological magnetoelectric effect and axion electrodynamics in condensed matter systems.