Anisotropic impurities in anisotropic superconductors

TL;DR

This paper investigates how anisotropic impurity scattering affects the physical properties of anisotropic superconductors, revealing deviations from the traditional universal pair-breaking effects predicted by isotropic models.

Contribution

It introduces corrections for anisotropic impurity scattering, showing both quantitative and qualitative deviations from the standard isotropic s-wave impurity scattering theory.

Findings

Anisotropic scattering leads to non-universal pair-breaking effects.

Transition temperature and density of states are affected by anisotropic impurities.

Impurity-induced quasiparticle states and flux pinning are influenced by anisotropy.

Abstract

Physical properties of anisotropic superconductors like the critical temperature and others depend sensitively on the electron mean free path. The sensitivity to impurity scattering and the resulting anomalies are considered a characteristic feature of strongly anisotropic pairing. These anomalies are usually analyzed in terms of s-wave impurity scattering which leads to universal pair breaking effects depending on only two scattering parameters, the mean free path and the impurity cross section. We investigate here corrections coming from anisotropies in the scattering cross section, and find not only quantitative but also qualitative deviations from universal s-wave isotropic pairbreaking. The properties we study are the transition temperature, the density of states, quasiparticle bound states at impurities, and pinning of flux lines by impurities.