Two-dimensional time-reversal-invariant topological superconductivity in a doped quantum spin-Hall insulator

Time-reversal-invariant topological superconductors have a full paring gap in the bulk and gapless Majorana states at the edge or on the surface. Here, we theoretically propose topological superconductivity in a doped quantum spin-Hall insulator. We study the pairing symmetry of a doped two-dimensional tin film within a two-orbital model, and find that a novel spin-triplet pairing is favored when the interorbital attractive interaction is stronger than the intraorbital interaction. We propose that a doped tin film is a good candidate for a 2d topological superconductor. Edge channels are studied in a tight-binding model numerically. Finally, we discuss the robustness of topological superconductivity in two-dimensional tin films by comparing to 3d superconductivity in bulk tin.