Speaker: Shinsei Ryu, University of California, Santa Barbara

2/5/08

4:30 p.m., 700 Clark Hall

Recently, a new type of insulators, called Z2 topological insulator, has been discovered. They can be thought of as a close cousin of the integer quantum Hall insulators, but different from the IQHE in many essential ways: Z2 topological insulators exist in systems that respect time reversal symmetry, can be either in 2D or 3D, and are characterized by a Z2 topological number, unlike the integral Hall conductance in the IQHE. Several candidate materials possessing the non-trivial Z2 topological features, such as HgTe quantum wells, and Bismuth-Antimony alloys, have been proposed and tested experimentally. In this talk, we will discuss quantum transport of 2D surface massless Dirac fermion states supported by 3D Z2 topological insulators terminated by a 2D boundary. Although these Dirac fermion states, from the symmetry point of view, belong to the 2D spin-orbit (symplectic) symmetry class of Anderson localization, they inherit the Z2 topological character of the bulk, and exhibit different response to impurities from conventional disorderedconductors with spin-orbit interactions. We also briefly discuss that this surface physics of 3D Z2 topological insulators can be simulated by graphene.