Enhanced anti-ferromagnetic exchange between magnetic impurities in a superconducting host

TL;DR

This paper reveals that Yu-Shiba-Rusinov bound states significantly enhance anti-ferromagnetic interactions between magnetic impurities in superconductors, surpassing traditional RKKY interactions at short distances, with implications for quantum materials.

Contribution

It provides a non-perturbative analysis showing Yu-Shiba-Rusinov states induce a strong 1/r^2 anti-ferromagnetic interaction, a novel insight beyond previous perturbative approaches.

Findings

Yu-Shiba-Rusinov states induce a 1/r^2 anti-ferromagnetic interaction

This interaction can dominate over RKKY at distances smaller than the coherence length

Implications for designing magnetic interactions in superconducting materials

Abstract

It is generally believed that superconductivity only weakly affects the indirect exchange between magnetic impurities. If the distance r between impurities is smaller than than the superconducting coherence length (r < \xi), this exchange is thought to be dominated by RKKY interactions, identical to the those in a normal metallic host. This perception is based upon a perturbative treatment of the exchange interaction. Here, we provide a non-perturbative analysis and demonstrate that the presence of Yu-Shiba-Rusinov bound states induces a strong 1/r^2 anti-ferromagnetic interaction that can dominate over conventional RKKY even at distances significantly smaller than the coherence length. Experimental signatures, implications and applications are discussed.