Local density of states near an impurity in unconventional superconductors

A nonmagnetic impurity can break Cooper pairs in unconventional superconductors and perturb the density of states out to the distance of order the coherence length. We compute the density of states as a function of position for the d-wave, p-wave and anisotropic s-wave order parameters which have often been considered in the high temperature superconductors. We find that the local density of states near an impurity oscillates with the Tomasch wavelength which depends strongly on the frequency and the symmetry of order parameters. This is, in principle, detectable perhaps through the scanning tunneling microscopy and could provide a crucial information on the symmetry of the underlying order parameters.