Axion Insulator State in a Ferromagnet/Topological Insulator/Antiferromagnet Heterostructure

TL;DR

This paper proposes a new heterostructure design using ferromagnetic and antiferromagnetic insulators with topological insulators to realize the axion insulator state, which is controllable via magnetization and robust against external magnetic fields.

Contribution

It introduces a novel heterostructure approach combining ferromagnetic and antiferromagnetic insulators with topological insulators to realize the axion insulator state.

Findings

Opposite half-quantum Hall conductance on top and bottom surfaces.

Sizable 5.1 meV spin gap in topological surface states.

Proposes a new strategy using van der Waals antiferromagnetic insulators.

Abstract

We propose to use ferromagnetic insulator MnBi2Se4/Bi2Se3/antiferromagnetic insulator Mn2Bi2Se5 heterostructures for the realization of the axion insulator state. Importantly, the axion insulator state in such heterostructures only depends on the magnetization of the ferromagnetic insulator and hence can be observed in a wide range of external magnetic field. Using density functional calculations and model Hamiltonian simulations, we find that the top and bottom surfaces have opposite half-quantum Hall conductance, with a sizable global spin gap of 5.1 meV opened for the topological surface states of Bi2Se3. Our work provides a new strategy for the search of axion insulators by using van der Waals antiferromagnetic insulators along with three-dimensional topological insulators.