DISORDER EFFECTS IN SUPERCONDUCTORS WITH ANISOTROPIC PAIRING - FROM COOPER PAIRS TO COMPACT BOSONS

In weak coupling BCS-theory normal impurities do not influence superco nducting T-c in case of s-wave pairing. In case of d-wave pairing thes e are strongly pair-breaking. This fact is in rather strong contradict ion with many experiments on disordered high-T-c superconductors. With the growth of electron attraction within the Cooper pair the system s moothly crosses over from BCS-pairs to compact Boson picture of superc onductivity. Significant deviations from universal Abrikosov-Gorkov de pendence of T-c on disorder are expected in this crossover region with superconducting state becoming more stable than in the weak coupling case. As high-T-c superconductors are actually in this intermediate re gion, we can understand the relative stability of their d-wave pairing state under disordering.