Effects of extended impurity perturbation in a d-wave superconductor -: art. no. 014516

We describe the effects of electronic perturbation distributed on nearest-neighbor sites to the impurity center in a planar d-wave superconductor, in approximation of circular Fermi surface. The behavior previously reported for pointlike perturbation and square Fermi surface, the quasiparticle density of states rho(epsilon) can display a resonance inside the gap and asymptotically vanishes at epsilon-->0 as rhosimilar toepsilon/ln(2) epsilon. Unique features are weak antiresonances from low-symmetry representations of nonlocal perturbation. The local suppression of superconducting (SC) order parameters in this model is found to be somewhat weaker than for an equivalent pointlike (nonmagnetic) perturbation and much weaker than for a spin-dependent (extended) perturbation. The developed approach can be used for a wide class of nonlocal impurity perturbations in superconductors.