Electrically tunable quantum spin Hall state in topological crystalline insulator thin films

Based on electronic structure calculations and theoretical analysis, we predict the (111) thin films of the SnTe class of three-dimensional (3D) topological crystalline insulators (TCIs) realize the quantum spin Hall phase in a wide range of thicknesses. The nontrivial topology originates from the intersurface coupling of the topological surface states of TCIs in the 3D limit. The intersurface coupling changes sign and gives rise to topological phase transitions as a function of film thickness. Furthermore, this coupling can be strongly affected by an external electric field, hence the quantum spin Hall phase can be effectively tuned under the experimentally accessible electric field.