Coherent potential approximation for d-wave superconductivity in disordered systems

A coherent-potential approximation CPA is developed for s-wave and d-wave s uperconductivity in disordered systems. We show that the CPA formalism repr oduces the standard pair breaking formula, the self-consistent Born approxi mation and the self-consistent T-matrix approximation in the appropriate li mits. We implement the theory and compute T-c for s-wave and d-wave pairing using an attractive nearest-neighbor Hubbard model featuring both binary-a lloy disorder and a uniform distribution of scattering site potentials. We determine the density of states and examine its consequences for low-temper ature heat capacity. [S0163-1829(99)02034-2].