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→0 as
ρ∼ϵ/ln2ϵ. 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.Comment: 7 pages, 5 figures, some minor typos and the curves in Fig. 5
correcte