Effects of extended impurity perturbation in d-wave superconductor

TL;DR

This paper investigates how extended impurity perturbations affect the electronic properties of d-wave superconductors, revealing resonance states and variations in the local suppression of superconductivity.

Contribution

It extends previous models by analyzing the effects of non-local, extended impurities on the quasiparticle density of states in d-wave superconductors.

Findings

Resonance states can appear inside the superconducting gap.

The density of states vanishes as epsilon approaches zero, following a specific logarithmic behavior.

Extended impurities cause weaker suppression of the order parameter compared to point-like or spin-dependent perturbations.

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 $\rho (\epsilon)$ can display a resonance inside the gap (and very weak features from low symmetry representations of non-local perturbation) and asymptotically vanishes at $\epsilon \to 0$ as $\rho\sim\epsilon/\ln^2\epsilon$. 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.