Enhanced Antiferromagnetic Exchange between Magnetic Impurities in a Superconducting Host

N. Y. Yao; L. I. Glazman; E. A. Demler; M. D. Lukin; J. D. Sau

doi:10.1103/PhysRevLett.113.087202

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Enhanced Antiferromagnetic Exchange between Magnetic Impurities in a Superconducting Host

N. Y. Yao, L. I. Glazman, E. A. Demler, M. D. Lukin, J. D. Sau

DOI 10.1103/PhysRevLett.113.087202 · Physical Review Letters

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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 the superconducting coherence length (r≲ξ), this exchange is thought to be dominated by Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions, identical to the those in a normal metallic host. This perception is based on a perturbative treatment of the exchange interaction. Here, we provide a nonperturbative analysis and demonstrate that the presence of Yu-Shiba-Rusinov bound states induces a strong 1/r2 antiferromagnetic interaction that can dominate over conventional RKKY even at distances significantly smaller than the coherence length (r≪ξ). Experimental signatures, implications, and applications are discussed.