Impurity-induced gap modification in anisotropic superconductors: mixed-state specific heat of La2-xSrx(Cu1-yZny)O-4 and Y(Ni1-xPtx)(2)B2C

We have examined the effect of nonmagnetic impurity on the superconducting gap of La2-xSr3(Cu1-yZny)O-4 and Y(Ni1-xPtx)(2)B2C from the mixed-state spe cific heat C(T,H). In La2-xSrxCuO4, impurity scattering leads to an appeara nce of a finite density of states (DOS) at the Fermi level, consistent with d-wave pairing state with nonmagnetic impurity scattering. In contrast, no nmagnetic impurity scattering in YNi2B2C leads to a smearing of the gap ani sotropy and the opening of a gap in the DOS over the whole Fermi surface, t hough C(T,H) for pure compound suggests the presence of anisotropic gap. Th is indicates YNi2B2C is a highly anisotropic s-wave superconductor. (C) 200 1 Elsevier Science B.V. All rights reserved.