title: Enhanced antiferromagnetic exchange between magnetic impurities in a superconducting host.
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/r(2) 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.
authors.affiliation: Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: N Y
authors.initials: NY
authors.lastname: Yao
authors.affiliation: Department of Physics, Yale University, New Haven, Connecticut 06520, USA and Department of Applied Physics, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: L I
authors.initials: LI
authors.lastname: Glazman
authors.affiliation: Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: E A
authors.initials: EA
authors.lastname: Demler
authors.affiliation: Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: M D
authors.initials: MD
authors.lastname: Lukin
authors.affiliation: Joint Quantum Institute and Condensed Matter Theory Center, Department of Physics, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: J D
authors.initials: JD
authors.lastname: Sau