Dynamical magnetoelectric coupling in axion insulator thin films

TL;DR

This paper demonstrates that dynamical magnetoelectric coupling in axion insulator thin films produces a measurable polarization current, providing a potential experimental signature to identify axion insulators more effectively than traditional methods.

Contribution

It introduces a new mechanism of dynamical magnetoelectric coupling induced by surface magnetization dynamics in axion insulator thin films, offering a stronger experimental signature.

Findings

Dynamical magnetoelectric current increases as film thickness decreases.

Current at magnetic resonance is at least ten times larger than TME.

The effect provides a more detectable signature for axion insulators.

Abstract

Axion insulator is an exotic magnetic topological insulator with zero Chern number but a nonzero quantized Chern-Simons magnetoelectric coupling. A conclusive experimental evidence for axion insulators is still lacking due to the small signal of topological magnetoelectric effect (TME). Here we show that the dynamical magnetoelectric coupling can be induced by the \emph{out-of-plane} surface magnetization dynamics in axion insulator thin films, which further generates a polarization current in the presence of an external magnetic field in the same direction. Such a current is finite in the bulk and increases as the film thickness $d$ decreases, in opposite to TME current which decreases as $d$ decreases. Remarkably, the current in thin films at magnetic resonance is at least ten times larger than that of TME, and thus may serve as a smoking gun signature for axion insulators.