Topological insulators

A new kind of insulator has been proposed recently, which is fully gapped in the bulk but has a metallic edge or surface states that are protected topologically. These electronic materials are dubbed as topological insulators (TIs). Generally speaking, TIs can be divided into two classes. One is the quantum Hall system which was found in the 1980s to show breaking of time reversal symmetry (TRS), and another is the newly discovered type which does not demonstrate TRS breaking and has attracted much attention recently. This article presents a brief review of recent advances in the development of TIs.