Wavefunction Topology of Two-dimensional Time-Reversal Symmetric Superconductors
We discuss the topology of the wavefunctions of two-dimensional time-reversal symmetric superconductors. We consider (a) the planar state, (b) a system with broken up-down reflection symmetry, and (c) a system with general spin-orbit interaction. We show explicitly how the relative sign of the order parameter on the two Fermi surfaces determines this topology, and clarify the meaning of the Z2 classification for these topological states.