Nonexponential long-range interaction of magnetic impurities in spin-orbit coupled superconductors

A. G. Mal'shukov

doi:10.1103/PhysRevB.98.054504

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Nonexponential long-range interaction of magnetic impurities in spin-orbit coupled superconductors

A. G. Mal'shukov

DOI 10.1103/PhysRevB.98.054504 · Physical Review B

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Abstract

The Ruderman-Kittel-Kasuya-Yosida interaction of magnetic impurities in a superconductor exponentially decreases when the distance r between them is larger than the superconductor's coherence length because this interaction is mediated by quasiparticles, which have a gap in their energy spectra. At the same time, the spin-singlet superconducting condensate was always assumed to stay neutral to magnetic impurities. Due to a spin-orbit coupling (SOC), however, Cooper pairs gain an admixture of spin-triplet correlated states, which provide for a link between impurity spins and an s-wave condensate. It is shown that perturbations of its phase mediate the 1/r2 interaction of these spins in two-dimensional (2D) systems. This effect is considered within two models: of a clean 2D s-wave superconductor with the strong Rashba SOC and of a bilayer system which combines a 2D Rashba coupled electron gas and an s-wave superconducting film. The predicted long-range interaction can have a strong effect on spin orders in superconductor-magnetic impurity systems that are expected to host Majorana fermions.