Effects of extended impurity perturbation in d-wave superconductor

Abstract

We describe the effects of electronic perturbation distributed on nearest neighbor sites to the impurity center in a planar \textit{d}-wave superconductor, in approximation of circular Fermi surface. Alike the behavior previously reported for point-like perturbation and square Fermi surface, the quasiparticle density of states $ρ(ε)$ can display a resonance inside the gap (and very weak features from low symmetry representations of non-local perturbation) and asymptotically vanishes at $ε\to 0$ as $ρ\simε/\ln^2ε$. The local suppression of SC order parameter in this model is found to be somewhat weaker than for an equivalent point-like (non-magnetic) perturbation and much weaker than for a spin-dependent (extended) perturbation.