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

## TL;DR

This study demonstrates the realization of robust axion insulator and Chern insulator phases in a 2D antiferromagnetic topological insulator, MnBi2Te4, through quantum transport experiments, highlighting potential for topological magnetoelectric effects.

## Contribution

It provides experimental evidence of axion and Chern insulator phases in MnBi2Te4, a stoichiometric 2D magnetic topological insulator, under various magnetic fields and temperatures.

## Key findings

- Observation of axion insulator state with zero Hall plateau
- Magnetic field induces transition to a Chern insulator with quantized Hall resistance
- Axion insulator state is stable over wide temperature and magnetic field ranges

## Abstract

The intricate interplay between nontrivial topology and magnetism in two-dimensional (2D) materials has led to the emergence of many novel phenomena and functionalities. An outstanding example is the quantum anomalous Hall (QAH) effect, which was realized in magnetically doped topological insulators (TIs) in the absence of magnetic field. Recently, the layered van der Waals compound MnBi2Te4 has been theoretically predicted and experimentally verified to be a TI with interlayer antiferromagnetic (AFM) order. It is a rare stoichiometric material with coexisting topology and magnetism, thus represents a perfect building block for complex topological-magnetic structures. Here we investigate the quantum transport behaviors of both bulk crystal and exfoliated MnBi2Te4 flakes in a field effect transistor geometry. In the 6 septuple layers (SLs) device tuned into the insulating regime, we observe a large longitudinal resistance and zero Hall plateau, which are characteristic of the 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 (h is the Plank constant and e is the elemental charge). These results pave the road for using even-number-SL MnBi2Te4 to realize the quantized topological magnetoelectric effect and axion electrodynamics in condensed matter systems.

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Source: https://tomesphere.com/paper/1905.00715