SUPERCONDUCTIVITY IN DISORDERED MATERIALS

The real-space single-particle Green's function formalism is extended to the attractive disordered Hubbard Hamiltonian by matrix Nambu notat ion, thus providing a general approach to the superconductive instabil ity of a disordered system in quantum mean-field approximation. Config urational averages may be performed by a recent method, already employ ed for the repulsive model, thus allowing for spatial fluctuations of the local order parameter. The method is shown to be a natural way of investigating the validity limit of the Anderson theorem. An exact ana lytical solution is provided for a Bethe lattice with no diagonal diso rder and infinitely large connectivity.