Homes scaling and BCS

TL;DR

This paper demonstrates that the BCS theory explains the universal scaling of the zero-temperature penetration depth with conductivity and critical temperature across a broad range of scattering conditions in superconductors.

Contribution

It shows that the scaling law for penetration depth is valid beyond the extreme dirty limit, providing a theoretical basis within BCS theory.

Findings

Scaling law holds for a wide range of scattering parameters.

BCS theory naturally explains the universal scaling.

Supports the idea of a universal property of superconductors.

Abstract

It is argued on the basis of the BCS theory that the zero-$T$ penetration depth satisfies $ \lambda^{-2}(0)\propto\sigma T_c $ ($\sigma$ is the normal state dc conductivity) not only in the extreme dirty limit $\xi_0/\ell \gg 1$, but in a broad range of scattering parameters down to $\xi_0/\ell \sim 1$ ($\xi_0$ is the zero-$T$ BCS coherence length and $\ell$ is the mean-free path). Hence, the scaling $ \lambda^{-2}(0)\propto\sigma T_c $, suggested as a new universal property of superconductors,\cite{Homes} finds a natural explanation within the BCS theory.