Impurity bound states in spin-orbit-coupled superconductors

There has recently been much interest in a generalized Anderson's theorem for odd-parity superconducting states in strongly spin-orbit-coupled materials. In this talk we consider a minimal model of such a system based on a bilayer with Rashba spin-orbit coupling. We investigate the spectrum of the bound states around an isolated impurity using numerical self-consistent mean-field theory and an analytic non-self-consistent T-matrix theory. We find excellent agreement between the two methods, which reveals that the main features of the bound state spectrum are fixed by the "fitness" of the pairing state with respect to the impurity potential and the normal-state electronic structure. We generalize our theory to a three-dimensional nodal superconductor and show that the bound state spectrum largely survives as virtual bound states. Our analysis reveals the central role of the superconducting fitness in underpinning the generalized Anderson's theorem.