Tail states in superconductors with weak magnetic impurities

TL;DR

This paper investigates how weak magnetic impurities affect the density of states in s-wave superconductors, revealing a specific energy dependence near the gap edge and highlighting the anisotropic nature of optimal fluctuations.

Contribution

It introduces a novel analysis of the density of states near the gap edge using the optimal fluctuation method, emphasizing anisotropy in higher dimensions.

Findings

Density of states varies as $ ext{ln} N(E) o -|E- riangle_0|^{(7-d)/4}$ near the gap edge.

Optimal fluctuations are strongly anisotropic in dimensions greater than one.

Comparison with other approaches validates the results.

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. We show that the density of states 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. The optimal fluctuation in d>1 is strongly anisotropic. We compare the density of states with that obtained in other recent approaches.