Robustness of states at topological insulator interfaces (Vol. 48, No. 5-6)

Topological phases of matter are characterized by invariant numbers. In two-dimensional time-reversal symmetric electronic systems, a Z₂ valued (0 or 1) invariant distinguishes trivial insulators from non-trivial ones. Interfaces between trivial and non-trivial topological insulators are known to host conductive channels protected against disorder. The protection of these states originates from the necessity of a gap closure in order to change topology. However, if the two regions are of the same topological phase, there is no such requirement.

Using a multi-orbital model, it is shown in this study that conductive states can also emerge at the interface between two non-trivial topological insulators characterized by opposite spin Chern numbers, another invariant. In general, these states are sensitive to disorder. However, it is possible under some conditions to reduce the effect of disorder, or even to cancel it. These conditions are clarified. Since analogues of topological insulators can be presently made with polaritons, ultracold atomic gases, phononic or photonic materials, these conclusions should motivate experimental studies in many directions.

A. Tadjine and Ch. Delerue, Robustness of states at the interface between topological insulators of opposite spin Chern number, EPL 118, 67003 (2017)
[Abstract]