Robustness of states at the interface between topological insulators of opposite spin Chern number

We study the nature of the states at the interface between two time-reversal symmetric topological insulators characterized by opposite spin Chern numbers. We show using a multi-orbital model that interface states are usually present in the common topological gaps of the materials. The transport in these states is robust against disorder scattering only when the two spin sectors are uncoupled (no Rashba spin-orbit coupling). Otherwise, the topological protection associated with the spin Chern number is lost and back-scattering is allowed, even in the absence of disorder, due to the coupling between states flowing in opposite directions and originating from the two sides of the interface. Conditions that minimize this effect can be found but the interface states remain sensitive to disorder. Copyright (C) EPLA, 2017