IMPURITY EFFECT IN HIGH-T(C) SUPERCONDUCTORS - A CONSISTENT ANALYSIS BY D-WAVE SUPERCONDUCTING MODEL

The contrast between Zn- and Ni-impurity effects in YBa2Cu3O7 and the imperfection-induced gapless superconductivity in Bi2Sr2CaCu2O8 reported previously are quantitatively analyzed based on the d-wave superconducting model. By taking account of the fact that the Zn impurity which caused the gapless superconductivity acts as a unitarity or strong scatterer, it is demonstrated that the Ni impurity does not give rise to the gapless superconductivity, although it is not so weak as to be treated in terms of Born scattering. The d-wave model can explain the characteristic feature such that even though T(c) is moderately reduced by impurity scattering, the superconductivity changes into the gapless type with a finite density of states at the Fermi level.