On the Lifshitz tail in the density of states of a superconductor with magnetic impurities

TL;DR

This paper demonstrates that magnetic impurities induce a Lifshitz tail in superconductors, leading to a finite density of states at zero energy due to impurity-induced regions of suppressed superconductivity.

Contribution

It reveals that magnetic impurities cause a gapless state in superconductors through Lifshitz tails, a novel insight into impurity effects on superconducting density of states.

Findings

Finite density of states at zero energy due to impurities

Impurity fluctuations create regions of suppressed superconductivity

Lifshitz tail extends the density of states to zero energy

Abstract

We argue that any superconductor with magnetic impurities is gapless due to a Lifshitz tail in the density of states extending to zero energy. At low energy the density of states $\nu(E \to 0)$ remains finite. We show that fluctuations in the impurity distribution produce regions of suppressed superconductivity, which are responsible for the low energy density of states.