Van Hove singularity and superconductivity in a disordered Hubbard model

We apply the Coherent Potential Approximation (CPA) to a simple extended Hubbard model with a nearest and next nearest neighbour hopping for disordered superconductors with s-, d- and p-wave pairing. We show how the Van Hove singularities in the electron density of states enhance the transition temperature T-c for exotic superconductors in a clean and weakly disordered system. The Anderson theorem and the pair-breaking effects in presence of the Van Hove singularity caused by non-magnetic disorder are also discussed.