Collective Yu-Shiba-Rusinov states in magnetic clusters at superconducting surfaces

Simon Körber; Björn Trauzettel; Oleksiy Kashuba

doi:10.1103/PhysRevB.97.184503

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Collective Yu-Shiba-Rusinov states in magnetic clusters at superconducting surfaces

Simon Körber, Björn Trauzettel, Oleksiy Kashuba

DOI 10.1103/PhysRevB.97.184503 · Physical Review B

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Abstract

We study the properties of collective Yu-Shiba-Rusinov (YSR) states generated by multiple magnetic adatoms (clusters) placed on the surface of a superconductor. For magnetic clusters with equal distances between their constituents, we demonstrate the formation of effectively spin-unpolarized YSR states with subgap energies independent of the spin configuration of the magnetic impurities. We solve the problem analytically for arbitrary spin structure and analyze both spin-polarized (dispersive energy levels) and spin-unpolarized (pinned energy levels) solutions. While the energies of the spin-polarized solutions can be characterized solely by the net magnetic moment of the cluster, the wave functions of the spin-unpolarized solutions effectively decouple from it. This decoupling makes them stable against thermal fluctuation and detectable in scanning tunneling microscopy experiments.