Renormalization approach to the superconducting Kondo model

TL;DR

This paper introduces a renormalization approach using unitary transformations to analyze bound states in superconducting systems, effectively reproducing known results and enabling exploration of topological properties in magnetic impurity chains.

Contribution

The paper presents a novel renormalization method based on unitary transformations for studying bound states in superconductors, extending the analysis to topological properties and complex impurity arrangements.

Findings

Reproduces results from t-matrix and numerical studies

Provides a unified view of YSR and Kondo states

Enables study of topological properties in impurity chains

Abstract

An approach to bound states based on unitary transformations of Hamiltonians is presented. The method is applied to study the interaction between electrons in a BCS $s$-wave superconductor and a quantum spin. It is shown that known results from the t-matrix method and numerical studies are reproduced by this new method. As a main advantage, the method can straightforwardly be extended to study the topological properties of combined bound states in chains of many magnetic impurities. It also provides a uniform picture of the interplay between the Yu-Shiba-Rusinov (YSR) bound states and the Kondo singlet state.