An ARPES view of topological insulator surfaces

Topological insulators (TIs) are a recently discovered form of quantum matter characterized by a bulk band inversion driven by strong spin-orbit coupling. They maintain a band gap in the bulk, but unusually possess unconventional surface states which are guaranteed to be metallic. Angle-resolved photoemission (ARPES) is an ideal tool to study the detailed electronic structure of these surface Dirac fermions. I will present our recent ARPES measurements of the Bi-chalcogenide family of TIs. While several of these compounds suffer from degenerate n-type self-doping, we show that Te-rich ternary compounds can have an insulating bulk. Thus, these are model examples of true topological insulators, where only a single topological surface state intersects the chemical potential. By adsorbing n-type dopants at the surface of several TIs, we mimic the effects of an externally-applied gate voltage, of the form desirable for electronic applications. We create a two-dimensional electron gas (2DEG) that co-exists with the topological surface state and can be driven to develop a large Rashba spin-splitting, suggesting potential for its application in advanced spintronic devices such as the spin-transistor. The tuneable surface band bending also provides a novel opportunity to probe the interplay of quantization and topological order.