Superconducting order parameters with sign changes: The density of states and impurity scattering

Abstract

We compute Ns(E) for a family of superconducting order parameters with sign changes at the Fermi surface, and find surprising results. We consider all Δ(k^) such that Δ(k^)=+Δ0 on part of the Fermi surface, and Δ(k^)=-Δ0 on the rest, yielding an average of 〈Δ(k^)〉=rΔ0, where 0≤r≤1. For 0<r<1, as the impurity concentration increases, the number of low-lying states increases, and the superconductor becomes gapless. As the impurity concentration is further increased, the gap in the spectrum is restored, and Ns(E) approaches the pure limit BCS form, with a renormalized gap. © 1996 The American Physical Society.

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