Being an antiferromagnetic topological insulator (AFM-TI), MnBi2Te4 offers an ideal platform to study the interplay between magnetism and topological order. We combine both transport and scanning microwave impedance microscopy (sMIM) to examine such interplay in atomically thin MnBi2Te4 with even-layer thickness. Transport measurement shows a quantized Hall resistivity under a magnetic field above 6 T signaling a Chern insulator phase, and a zero Hall plateau at low fields consistent with axion insulator phase. With sMIM, we directly visualize a magnetic-field-driven insulator-to-metal (IMT) transition of the bulk resulting from a quantum phase transition from a Chern insulator to axion insulator phase. Strikingly, sMIM reveals a persistent edge state across the transition. The observed edge state at low fields, in particular at zero field, calls for careful considerations for the topological nature of its bulk state. We discuss the possibility of having edge states in the context of axion insulator and beyond such a context. Our finding signifies the richness of topological phases in MnB2Te4 that has yet to be fully explored.
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