Critical Behavior and Universal Signature of an Axion Insulator State

TL;DR

This paper explores the disorder-induced phase transition in axion insulators within 3D topological insulators, revealing a universal signature akin to quantum Hall transitions, and proposes a new experimental detection method.

Contribution

It introduces a phenomenological theory linking the axion insulator state to the Chalker-Coddington network model and suggests a practical way to detect axion insulators experimentally.

Findings

Identifies a 2D disorder-induced phase transition with quantum Hall universality.

Maps the axion insulator state to the Chalker-Coddington network model.

Proposes an experimental routine to probe the axion insulator state.

Abstract

Recently, the search for an axion insulator state in the ferromagnet-3D topological insulator (TI) heterostructure and $\mathrm{MnBi_2Te_4}$ has attracted intensive interest. However, its detection remains difficult in experiments. We systematically investigate the disorder-induced phase transition of the axion insulator state in a 3D TI with antiparallel magnetization alignment surfaces. It is found that there exists a 2D disorder-induced phase transition which shares the same universality class with the quantum Hall plateau to plateau transition. Then, we provide a phenomenological theory which maps the random mass Dirac Hamiltonian of the axion insulator state into the Chalker-Coddington network model. Therefore, we propose to probe the axion insulator state by investigating the universal signature of such a phase transition in the ferromagnet-3D TI heterostructure and $\mathrm{MnBi_2Te_4}$. Our findings not only show a global phase diagram of the axion insulator state, but also provide a new experimental routine to probe it.