Robustness of a Topologically Protected Surface State in a Sb 2 Te 2 Se Single Crystal

A topological insulator (TI) is a quantum material in a new class with attractive properties for physical and technological applications. Here we derive the electronic structure of highly crystalline Sb 2 Te 2 Se single crystals studied with angle-resolved photoemission spectra. The result of band mapping reveals that the Sb 2 Te 2 Se compound behaves as a p -type semiconductor and has an isolated Dirac cone of a topological surface state, which is highly favored for spintronic and thermoelectric devices because of the dissipation-less surface state and the decreased scattering from bulk bands. More importantly, the topological surface state and doping level in Sb 2 Te 2 Se are difficult to alter for a cleaved surface exposed to air; the robustness of the topological surface state defined in our data indicates that this Sb 2 Te 2 Se compound has a great potential for future atmospheric applications.