Anomaly in the heat capacity of Kondo superconductors

TL;DR

This paper investigates how the interplay between Kondo screening and superconductivity causes anomalous heat capacity features in magnetic impurities, using numerical methods to reveal potential experimental signatures.

Contribution

It introduces a detailed numerical analysis of the thermodynamic behavior of magnetic impurities in superconductors near the Kondo temperature and critical temperature degeneracy.

Findings

Identification of a ln3 peak in impurity entropy at T_K ≈ T_c.

Prediction of an anomalous heat capacity feature linked to entropy increase.

Potential explanation for experimentally observed heat capacity anomalies.

Abstract

Using numerical renormalization group we study thermodynamic properties of a magnetic impurity described by the Anderson impurity model in a superconducting host material described by the BCS Hamiltonian. When the Kondo temperature in the normal state, T_K, is comparable to the critical temperature of the superconducting transition, T_c, the magnetic doublet state may become degenerate with the Kondo singlet state, leading to a ln3 peak in the temperature dependence of the impurity contribution to the entropy. This entropy increase translates into an anomalous feature in the heat capacity which might have already been experimentally observed.