Impurity effects in d-wave superconductors

Impurity scattering will provide a crucial test for d-wave superconductor in high Tc copper-oxides. Among other things we calculate the static spin susceptibility and find a simple relation between the susceptibility and superfluid density ρs(T)=[λ(0)/λ(T)]2 is broken in the presence of impurity scattering. Also we generalize Lee's universal conductivity at T=0 K. In the presence of a finite concentration of impurity, the order parameter Δ00 in the conductivity has to be replaced by Δ(Γ,0) and Δ(Γ,0) is accessible through the tunneling experiment of the density of states