WHY IS D-WAVE PAIRING IN HTS ROBUST IN THE PRESENCE OF IMPURITIES

In the recent theory of strong correlations by [1] - [3] it was shown that by lowering doping concentration a forward peak is developed in t he charge scattering channel. Physically, this means that short-range impurity scattering potential is transformed into long-range one. Acco rdingly, near the optimal doping the nonmagnetic scattering is pronoun ced in the d-channel and d-wave pairing is robust against defects and impurities. It is reflected in a decrease of the slope of the critical temperature T-c(T-s) at Gamma(s) --> 0 by factor (1 - beta), where be ta is the scattering anisotropy parameter and Gamma(s) is an average s cattering rate. For large doping, beta is small [1], [2] and d-wave pa iring loses its robustness. The theory is generally formulated for the bi-layer model by including: (1) intra-and inter-plane pairing; (2) i ntra-and inter-plane impurities. (C) 1997 Elsevier Science Ltd.