LOCALIZED ANISOTROPIC SUPERCONDUCTORS

We address the question of whether an anisotropic gap of d(x2-y2) symm etry is compatible with localized states in the normal phase. The issu e is important for high-T-c superconductors for which a superconductor -to-insulator transition is observed, together with a number of experi ments that support d-wave pairing. We prove that d-wave superconductiv ity is compatible with a localized normal state. When the coherence le ngth is of the order of the lattice constant, the effects of localizat ion are important. We find a re-entrant behaviour of superconductivity in the strongly disordered phase.