The elusive quantum anomalous Hall effect in MnBi2Te4: a materials perspective
Observation of the quantum anomalous Hall effect (QAHE) in MnBi$_2$Te$_4$ flakes is one of the most exciting results in the study of the intrinsic magnetic topological insulator MnBi$_2$Te$_4$ and related compounds. This fascinating result is yet to be reproduced two years after its first report. The quality of starting MnBi$_2$Te$_4$ single crystals is believed to be the key factor. An interesting and important question to address is what is the right quality to enable the QAHE. In this perspective, we present possible approaches to tuning the magnetic and topological properties of MnBi$_2$Te$_4$ by using lattice imperfections, strain, stacking sequence, and interactions between the substrate and flakes/films. It is of critical importance to eventually identify the factor(s) responsible for the realization of QAHE.