Prof. Yshai Avishai (Department of Physics, Ben-Gurion University, Israel)
"Disorder in Quantum Spin Hall Systems"

The quantum spin Hall phase is a novel state of matter with topological properties. It might be realized in graphene and probably also in type III semiconductors quantum wells. Most recent theoretical treatments of this phase discuss its occurrence in clean systems with perfect crystal symmetry. In this seminar I will report on a recent work (in collaboration with N. Nagaosa and M. Onoda) on disordered quantum spin Hall systems. Following a brief introduction and background I will discuss the persistence of topological terms also in disordered systems (following a recent work of Sheng and Haldane) and then present our results on the localization problem in two dimensional systems. Due to spin-orbit interaction, there is a metallic phase as is well known for the symplectic ensemble. Together with the existence of a topological term it leads to some surprising results regarding the scaling theory of localization.