Recent Advances in Weyl Semimetal (MnBi2Se4) and Axion Insulator (MnBi2Te4)

Extensive research is currently focused on 2D and 3D magnetic topological insulators (MTIs), as their many novel properties make them excellent candidates for applications in spintronics and quantum computing. Practical MTIs require a combination of strong spin–orbit coupling (SOC) and magnetic ordering. SOC induces band inversion, while magnetic order breaks time-reversal symmetry (TRS), with the consequent opening of a gap in the 2D Dirac surface states of a TRS invariant topological insulator. Most importantly, MTIs with broken TRS and strong SOC can display quantized Hall conductance, σ xy = C e 2 2 h , where C , the Chern number, is a topologically invariant integer. Recently, the scientific community has pursued several different strategies to synthesize and tune MTIs, such as (i) chemical doping of TRS invariant topological insulators with magnetic atoms, (ii) modification of magnetic materials with strain or doping, and (iii) heterostructure engineering. This review will discuss the recent theoretical and experimental advances related to MTIs like MnBi 2 Se 4 (Weyl insulator), MnBi 2 Te 4 (Axion insulator), where the topological classification depends on inversion symmetry rather than time-reversal symmetry.