Quantum phase transition from axion insulator to Chern insulator in MnBi2Te4

Chang Liu, Yongchao Wang, Hao Li, Yang Wu, Yaoxin Li, Jiaheng Li, Ke He, Yong Xu, Jinsong Zhang, Yayu Wang

Published 2019-05-02Version 1

Finding novel topological quantum matter and topological phase transitions has been a central theme in modern physics. An outstanding example is the Chern insulator, first conceived as a theoretical model for the quantum Hall effect without Landau levels, which was realized experimentally in magnetically doped topological insulator (TI) at zero magnetic field, known as the quantum anomalous Hall (QAH) effect. The axion insulator is another distinct topological phase that has vanishing Chern number but a finite topological Chern-Simon term. It was proposed to be a promising platform for exploring quantized topological magnetoelectric coupling and axion electrodynamics in condensed matter. Previous attempts to construct the axion insulator phase involve heterostructures of two QAH layers with different coercive fields, which require complex epitaxial growth and ultralow temperature measurement in finite magnetic field. Here we report the realization of an intrinsic axion insulator phase in MnBi2Te4, which has been predicted to be a TI with interlayer antiferromagnetic (AFM) order. We found that when the crystal is exfoliated down to 6 septuple layers (SLs) and tuned into the insulating regime, the axion insulator phase is observed at zero magnetic field when the top and bottom surfaces are subjected to opposite magnetization. More interestingly, a moderate magnetic field drives a transition from the axion insulator phase, characterized by large longitudinal resistance and zero Hall resistance, to a Chern insulator with zero longitudinal resistance and quantized Hall resistance h/e2 (h is the Plank constant and e is the elemental charge). The robust and tunable axion insulator and Chern insulator phases hosted by one stoichiometric crystal at relatively high temperature makes it a versatile system for investigating exotic topological phases and phase transitions.