EFFECT OF IMPURITY SCATTERING ON A D- LOW-TEMPERATURE BEHAVIOR OF PENETRATION DEPTH(S WAVE SUPERCONDUCTOR )

Currently there exist several experimental reports on high-T-c oxides which favor d-wave order parameter symmetry. However, several others w ould support an s-wave gap. Recent measurements of the penetration dep th in YBa2Cu3O7-delta single crystals show large differences in a and b directions in the basal plane, which implies that orthorhombicity du e to the chains is not small. As an attempt to understand current expe rimental results we consider an order parameter with d + s wave symmet ry, which can arise naturally as a deviation from d-wave due to the pr esence of orthorhombicity. We provide a detailed study of the characte ristics of such an order parameter in the low temperature behavior of the penetration depth in the presence of non-magnetic impurity scatter ing. The results are discussed in comparison with d-wave and anisotrop ic s-wave cases.