We study a delocalization transition in a system of noninteracting quasiparticles moving in two dimensions, which belongs to a new symmetry class C. This symmetry class can be realized in a dirty, gapless superconductor in which time-reversal symmetry for orbital motion is broken, but spin-rotation symmetry is intact. In this class spin current is transferred by electron-hole pairs. Further, we consider a three-dimensional realization of class C. In the last part of the talk, we discuss application of the generalized Chalker-Coddington network model to the quantum spin Hall effect in graphene, which differs significantly from class C. In particular, spin current is transferred by electrons with opposite spins moving in the opposite directions.
Informal seminar: "Spin quantum Hall effect in class C superconductors and quantum spin Hall effect in graphene"
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