Massive Dirac surface states in topological insulator/magnetic insulator heterostructures

Abstract

Topological insulators are new states of matter with a bulk gap and robust gapless surface states protected by time-reversal symmetry. When time-reversal symmetry is broken, the surface states are gapped, which induces a topological response of the system to electromagnetic field---the topological magnetoelectric effect. In this paper we study the behavior of topological surface states in heterostructures formed by a topological insulator and a magnetic insulator. Several magnetic insulators with compatible magnetic structure and relatively good lattice matching with topological insulators Bi${}_{2}$Se${}_{3}$, Bi${}_{2}$Te${}_{3}$, Sb${}_{2}$Te${}_{3}$ are identified, and the best candidate material is found to be MnSe, an antiferromagnetic insulator. We perform first-principles calculations in Bi${}_{2}$Se${}_{3}$/MnSe superlattices and obtain the surface state band structure. The magnetic exchange coupling with MnSe induces a gap of $\ensuremath{\sim}$54 meV at the surface states. In addition we tune the distance between Mn ions and the topological insulator surface to study the distance dependence of the exchange coupling.