| The recently discovered "topological insulators" are three-dimensional nonmagnetic materials in which spin-orbit coupling generates an insulating phase characterized by topologically protected surface states. These surface states, analogous to the edge states of the quantum Hall effect in one lower dimension, have recently been observed in BiSb alloys and Bi2Se3. We review this rapidly developing field and explain how investigation of the origin of this phase leads to a Berry-phase picture of magnetoelectric polarizability in three-dimensional solids, closely analogous to the Berry-phase theory of polarization in insulators. In closing we discuss how topological insulators, which are essentially independent-electron materials, can nevertheless be used to create new correlated phases. |
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