Topological Axion States in the Magnetic Insulator MnBi2Te4 with the Quantized Magnetoelectric Effect

Topological states of quantum matter have attracted great attention in condensed matter physics and materials science. The study of time-reversal-invariant topological states in quantum materials has made tremendous progress. However, the study of magnetic topological states falls much behind due to the complex magnetic structures. Here, we predict the tetradymite-type compound ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$ and its related materials host topologically nontrivial magnetic states. The magnetic ground state of ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$ is an antiferromagetic topological insulator state with a large topologically nontrivial energy gap ($\ensuremath{\sim}0.2\text{ }\text{ }\mathrm{eV}$). It presents the axion state, which has gapped bulk and surface states, and the quantized topological magnetoelectric effect. The ferromagnetic phase of ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$ might lead to a minimal ideal Weyl semimetal.