Axion was postulated as an elementary particle with a low mass and weak interaction in particle physics to solve the strong CP (charge conjugation and parity) puzzle, and later axion was also considered to be a possible component of dark matter in the universe. However, the existence of axions in nature has not been confirmed. Interestingly, axions arise out of pseudoscalar fields derived from the Chern-Simons theory in condensed matter physics. In antiferromagnetic insulators, the axion field can become dynamical due to spin-wave excitations and exhibits rich exotic phenomena, such as the chiral magnetic effect and axion polariton. However, antiferromagnetic dynamical axion insulator has yet been experimentally identified in realistic materi- als. Very recently, MnBi2Te4 was discovered to be an antiferromagnetic topological insulator with a quantized static axion field protected by inversion symmetry P and magnetic-crystalline symmetry S. In this talk, we will show that both the P and S symmetries in MnBi2Te4 films are spontaneously broken and that substantially enhanced dynamical magnetoelectric effects could be realized through tuning the film thickness, temperature or element substitutions. Our results show that antiferromagnetic topological insulator films of MnBi2Te4 and related compounds could provide a promising material platform to experimentally study axion electrodynamics.

Referee:

arxiv 2010.05424 (2020)

arxiv 2011.04916 (2020)

PRL 122, 206401 (2019)

PRB 101, 081109 (R) (2020)

CPL (express) 37, 077304 (2020)