Nontrivial interface states confined between two topological insulators

Abstract

By ab initio based tight-binding calculations, we show that nontrivial electronic states exist at an interface of a ${\mathcal{Z}}_{2}$ topological insulator and a topological crystalline insulator. At the exemplary (111) interface between Bi${}_{2}$Te${}_{3}$ and SnTe, the two Dirac surface states at the Brillouin zone center $\overline{\ensuremath{\Gamma}}$ annihilate upon approaching the semi-infinite subsystems but one topologically protected Dirac surface state remains at each time-reversal invariant momentum $\overline{M}$. This leads to a highly conducting spin-momentum-locked channel at the interface but insulating bulk regions. For the Sb${}_{2}$Te${}_{3}$/Bi${}_{2}$Te${}_{3}$ interface, we find complete annihilation of Dirac states because both subsystems belong to the same topology class. Our proof of principle may have impact on planar electric transport in future spintronics devices with topologically protected conducting channels.