Topological insulators in Bi 2 Se 3, Bi 2 Te 3 and Sb 2 Te 3 with a single Dirac cone on the surface

Topological insulators are new states of quantum matter in which surface states residing in the bulk insulating gap of such systems are protected by time-reversal symmetry. The study of such states was originally inspired by the robustness to scattering of conducting edge states in quantum Hall systems. Recently, such analogies have resulted in the discovery of topologically protected states in two-dimensional and three-dimensional band insulators with large spin-orbit coupling. So far, the only known three-dimensional topological insulator is Bi x Sb 1x, which is an alloy with complex surface states. Here, we present the results of first-principles electronic structure calculations of the layered, stoichiometric crystals Sb 2 Te 3, Sb 2 Se 3, Bi 2 Te 3 and Bi 2 Se 3. Our calculations predict that Sb 2 Te 3, Bi 2 Te 3 and Bi 2 Se 3 are topological insulators, whereas Sb 2 Se 3 is not. These topological insulators have robust and simple surface states consisting of a single Dirac cone at the point. In addition, we predict that Bi 2 Se 3 has a topologically non-trivial energy gap of 0.3 eV, which is larger than the energy scale of room temperature. We further present a simple and unified continuum model that captures the salient topological features of this class of materials.