Dynamical axion state with hidden pseudospin Chern numbers in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>MnBi</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>Te</mml:mi><mml:mn>4</mml:mn></mml:msub></mml:mrow></mml:math>-based heterostructures
Huaiqiang Wang, Dinghui Wang, Zhilong Yang, Minji Shi, Jiawei Ruan, Dingyu Xing, Jing Wang, Haijun Zhang
Abstract
An axion is a hypothetical elementary particle which was initially postulated to solve the charge conjugation-parity problem in particle physics. Interestingly, the axion state has emerged in the effective theory of topological insulators and has attracted extensive attention in condensed matter physics. Time-reversal or inversion symmetry constrains the axion field $\ensuremath{\theta}$ to be quantized. When both the time-reversal and inversion symmetries are broken by, say, an antiferromagnetic order, the axion field $\ensuremath{\theta}$ could become unquantized and dynamical along with magnetic fluctuations, which is termed the dynamical axion field. Here, we reveal that a wide class of topological-insulator-based dynamical axion states could be distinguished from the normal-insulator-based ones by a hidden quantity derived from the pseudospin Chern number. Motivated by recent research on the ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$ family of materials, we further show that such topological-insulator-based dynamical axion states can be hopefully achieved in ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$-based heterostructures, which should greatly facilitate the study of axion electrodynamics in condensed matter physics.