DENSITY-OF-STATES NEAR AN IMPURITY IN AN UNCONVENTIONAL SUPERCONDUCTOR

An impurity in an unconventional superconductor can perturb the order parameter out to a distance of order the coherence length. This can lead to a large change in the density of states near an impurity. We compute the density of states as a function of position and frequency for a two-dimensional d-wave order parameter, while taking into account the effect of impurity scattering both in the Born and unitarity limits. We pay particular attention to the effect of anisotropy of the order parameter on the local density of states.