Thin film of a topological insulator as a spin Hall insulator

We study the spin conductivity of the surface states in a thin film of a topological insulator within Kubo formalism. Hybridization between the different sides of the film opens a gap at the Dirac point. We found that in the gapped region spin conductivity remains finite. In the gapless region near the band gap, spin conductivity is enhanced. These findings indicate that a thin film of a topological insulator is a promising material for spintronic applications.