Distinguishing d-wave from highly anisotropic s-wave superconductors

TL;DR

This paper proposes impurity doping as a method to distinguish between d-wave and anisotropic s-wave superconductors by analyzing impurity effects on the energy gap and related observable properties.

Contribution

It demonstrates how impurity scattering influences the energy gap in anisotropic s-wave superconductors, providing criteria to differentiate from d-wave superconductors.

Findings

Potential scattering increases gap minima in s-wave states.

Impurity effects lead to activated temperature behavior in observables.

Magnetic scattering can cause gapless behavior or nonmonotonic gap dependence.

Abstract

Systematic impurity doping in the Cu-O plane of the hole-doped cuprate superconductors may allow one to decide between unconvention al ("d-wave") and anisotropic conventional ("s-wave") states as possible candidates for the order parameter in these materials. We show that potential scattering of any strength always increases the gap minima of such s-wave states, leading to activated behavior in temperature with characteristic impurity concentration dependence in observable quantities such as the penetration depth. A magnetic component to the scattering may destroy the energy gap and give rise to conventional gapless behavior, or lead to a nonmonotonic dependence of the gap on impurity concentration. We discuss how experiments constrain this analysis.