Direct visualization of edge state in even-layer MnBi2Te4 at zero magnetic field

TL;DR

This study combines transport and microwave impedance microscopy to visualize edge states in even-layer MnBi2Te4 at zero magnetic field, revealing unexpected topological phenomena and proposing a crossover from 3D to 2D topological insulator behavior.

Contribution

It provides the first direct visualization of edge states in even-layer MnBi2Te4 at zero field and introduces a model linking these states to gapped helical edge states of quantum spin Hall effect.

Findings

Transport shows zero Hall plateau indicating axion state.

sMIM uncovers an unexpected edge state.

Proposes edge state arises from crossover from 3D to 2D topological insulator.

Abstract

Being the first intrinsic antiferromagnetic(AFM) topological insulator(TI), MnBi2Te4 is argued to be a topological axion state in its even-layer form due to the antiparallel magnetization between the top and bottom layers. Here we combine both transport and scanning microwave impedance microscopy(sMIM) to investigate such axion state in atomically thin MnBi2Te4 with even-layer thickness at zero magnetic field. While transport measurements show a zero Hall plateau signaturing the axion state, sMIM uncovers an unexpected edge state raising questions regarding the nature of the 'axion state'. Based on our model calculation, we propose that the edge state of even-layer MnBi2Te4 at zero field is derived from gapped helical edge states of the quantum spin Hall effect with time-reversal-symmetry breaking, when a crossover from a three-dimensional TI MnBi2Te4 to a two-dimensional TI occurs. Our finding thus signifies the richness of topological phases in MnB2Te4 that has yet to be fully explored.