EFFECT OF IMPURITY SCATTERING ON A (D-WAVE SUPERCONDUCTOR(S))

Recent measurements of the surface impedance in YBa2Cu3O7-delta Single crystals show large in-plane anisotropy which implies that orthorhomb icity due to the Cu-O chains is not small. In addition, the controvers y between the d-wave and the s-wave order parameter persists. In the f ramework of the orthorhombic symmetry an order parameter with (d+s)-wa ve symmetry is considered in an attempt to understand current experime ntal results. We provide a detailed study of the characteristics of su ch an order parameter in the low-temperature behavior of the penetrati on depth, the density of states, and the T-c suppression in the presen ce of nonmagnetic impurity scattering. The results are discussed in co mparison with the d-wave and the anisotropic s-wave cases.