Structurally and magnetically self-organized MnBi2Te4/(Bi2Te3)n: magnetic topological insulator

A platform where magnetism meets topology opens up wide possibilities for implementation of new ideas, such as the quantum anomalous Hall effect, the magnetoelectric effect, the axion insulator state. Among magnetic topological insulators, the MnBi2Te4/(Bi2Te3)n family has recently attracted a special interest. Here, the classic Bi2Te3 topological insulator is combined with a compatible magnetic MnBi2Te4. Interestingly, the MnBi2Te4/(Bi2Te3)n superlattices with different spacing (n) between the MnBi2Te4 septuplet layers self-organize both structurally and magnetically during standard (e.g. Bridgman) crystal growth. Mn in MnBi2Te4 is oriented planarly, forming a 2D ferromagnet with the out-of-plane easy axis. The interplay between magnetism of this highly-ordered layer and the topology of Bi2Te3 is manifested in the high-temperature quantum anomalous Hall effect (Nature Physics (2020), DOI: 10.1038/s41567-020-0998-2) due to breaking down the time-reversal symmetry. In this communication I will discuss the influence of the MnBi2Te4 septuplet layer on the electronic structure of topological surface states, which is very broad due to possible different surface terminations of MnBi2Te4/(Bi2Te3)n superlattice. This problem is currently controversial due to many, often contradictory literature reports, and the assignment of the bands is still under discussion. Next, I will present the complex magnetism of MnBi2Te4/(Bi2Te3)n, which consists of both intra-layer interactions between Mn spins in MnBi2Te4 and inter-layer interactions between individual septuplet layers. Understanding magnetism and its effect on surface states is critical to applying the material to new phenomena. We would like to acknowledge NCN (Poland) grant no 2016/21/B/ST3/02565.