Tail states in clean superconductors with magnetic impurities

TL;DR

This paper investigates how weak magnetic impurities affect the density of states in clean s-wave superconductors, revealing a finite density of states within the gap and anisotropic optimal fluctuations.

Contribution

It introduces a self-consistent analysis of the density of states in superconductors with magnetic impurities, highlighting the anisotropic nature of optimal fluctuations in the clean limit.

Findings

Density of states is finite throughout the superconducting gap.

Near the gap edge, the density of states varies logarithmically with energy.

Optimal fluctuations are strongly anisotropic in the studied regime.

Abstract

We analyse the behavior of the density of states in a singlet s-wave superconductor with weak magnetic impurities in the clean limit. By using the method of optimal fluctuation and treating the order parameter self-consistently we show that the density of states is finite everywhere in the superconducting gap, and that it varies as $\ln N(E)\propto -|E-\Delta_0|^{(7-d)/4}$ near the mean field gap edge $\Delta_0$ in a d-dimensional superconductor. In contrast to most studied cases the optimal fluctuation is strongly anisotropic.