Bethe ansatz approach to thermodynamics of superconducting magnetic alloys

TL;DR

This paper develops thermodynamic Bethe ansatz equations for a model of magnetic impurities in superconductors, revealing how impurities can both suppress and enhance superconductivity depending on the regime, with analytical solutions at zero temperature.

Contribution

It introduces an analytical Bethe ansatz framework for understanding impurity effects on superconductivity in a novel model, including zero-temperature solutions.

Findings

Impurities suppress superconductivity in the Kondo limit.

At T=0, the system remains superconducting regardless of impurity concentration.

In the mixed-valence regime, impurities can enhance superconductivity.

Abstract

We derive thermodynamic Bethe ansatz equations for a model describing an $U\to\infty$ Anderson impurity embedded in a BCS superconductor. The equations are solved analytically in the zero-temperature limit, T=0. It is shown that the impurities depress superconductivity in the Kondo limit, however at T=0 the system remains in the superconducting state for any impurity concentration. In the mixed-valence regime, an impurity contribution to the density of states of the system near the Fermi level overcompensates a Cooper pairs weakening, and superconductivity is enhanced.