Jing Wang
Here, we predict the tetradymite-type compound MnBi2Te4 and its related materials host topologically nontrivial magnetic states. The magnetic ground state of MnBi2Te4 is an antiferromagetic topological insulator state with a large topologically non-trivial energy gap (0.2 eV). It presents the axion state, which has gapped bulk and surface states, and the quantized topological magnetoelectric effect. It has several advantages over the previous proposals on realizing the topological magnetoelectric effect. The intrinsic magnetic and band inversion further lead to quantum anomalous Hall effect in odd layer MnBi2Te4 thin film with combined inversion and time-reversal symmetry breaking, which has been recently observed in experiments. The high quality intrinsic MnBi2Te4 together with other magnetic/superconducting 2D materials provides fertile ground for exploring exotic topological quantum phenomena.
We further show the Moire superlattice of twisted bilayer MnBi2Te4 exhibits highly tunable Chern bands with Chern number up to 3. We show that a twist angle of 1 degree turns the highest valence band into a flat band with Chern number ±1, that is isolated from all other bands in both ferromagnetic and antiferromagnetic phases. This result provides a promising platform for realizing time-reversal breaking correlated topological phases, such as fractional Chern insulator and p+ip topological superconductor.