Tunable dynamical magnetoelectric effect in antiferromagnetic topological insulator MnBi$_2$Te$_4$ films

TL;DR

This paper demonstrates that the dynamical axion field and tunable magnetoelectric effects can be realized in MnBi$_2$Te$_4$ films by breaking certain symmetries and adjusting parameters like thickness and temperature, advancing axion physics and dark matter research.

Contribution

It reveals the realization and control of dynamical axion fields and magnetoelectric effects in MnBi$_2$Te$_4$ films through symmetry breaking and parameter tuning.

Findings

Dynamical axion field can be induced in MnBi$_2$Te$_4$ films.

Tunable magnetoelectric effects are achieved by adjusting film thickness, temperature, and element substitution.

Symmetry breaking enables the realization of dynamical axion phenomena in antiferromagnetic topological insulators.

Abstract

More than forty years ago, axion was postulated as an elementary particle with a low mass and weak interaction in particle physics to solve the strong $\mathcal{CP}$ (charge conjugation and parity) puzzle. Axions are also considered as a possible component of dark matter of the universe. However, the existence of axions in nature has not been confirmed. Interestingly, axions arise as pseudoscalar fields derived from the Chern-Simons theory in condensed matter physics. In antiferromagnetic insulators, the axion field can become dynamical induced by spin-wave excitations and exhibits rich exotic phenomena, such as, the chiral magnetic effect, axionic polariton and so on. However, the study of the dynamical axion field is rare due to the lack of real materials. Recently, MnBi$_2$Te$_4$ was discovered to be an antiferromagnetic topological insulator with a quantized axion field protected by the inversion symmetry $\mathcal{P}$ and the magnetic-crystalline symmetry $\mathcal{S}$. Here, we studied MnBi$_2$Te$_4$ films in which both the $\mathcal{P}$ and $\mathcal{S}$ symmetries are spontaneously broken and found that the dynamical axion field and largely tunable dynamical magnetoelectric effects can be realized through tuning the thickness of MnBi$_2$Te$_4$ films, the temperature and the element substitution. Our results open a broad avenue to study axion dynamics in antiferromagnetic topological insulator MnBi$_2$Te$_4$ and related materials, and also is hopeful to promote the research of dark matter.