Topological insulator

This is a very intersting topic, in many ways. Topological insulator is a new quantum phase of matter, recently proposed theoretically. It is required to be a bulk insulator and a topologically protected surface metal. ARPES data have been crucial in ascertaining the topological insulator nature of various materials, now accepted as topological insulators, even though the bulk crystal of many of these materials have remnant charge carriers and thus is not an insulator. The protected surface state has a strong similarity to the electronic structure of graphene, whose Dirac-cone electronic structure was measured by ARPES for the first time by G.-H. Gweon and others.