Quantum spins and hybridization in artificially-constructed chains of magnetic adatoms on a superconductor

Eva Liebhaber, Lisa M. Rütten, Gaël Reecht, Jacob F. Steiner, Sebastian Rohlf, Kai Rossnagel, Felix Oppen and Katharina J. Franke ()
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Eva Liebhaber: Freie Universität Berlin
Lisa M. Rütten: Freie Universität Berlin
Gaël Reecht: Freie Universität Berlin
Jacob F. Steiner: Freie Universität Berlin
Sebastian Rohlf: Christian-Albrechts-Universität zu Kiel
Kai Rossnagel: Christian-Albrechts-Universität zu Kiel
Felix Oppen: Freie Universität Berlin
Katharina J. Franke: Freie Universität Berlin

Nature Communications, 2022, vol. 13, issue 1, 1-11

Abstract: Abstract Magnetic adatom chains on surfaces constitute fascinating quantum spin systems. Superconducting substrates suppress interactions with bulk electronic excitations but couple the adatom spins to a chain of subgap Yu-Shiba-Rusinov (YSR) quasiparticles. Using a scanning tunneling microscope, we investigate such correlated spin-fermion systems by constructing Fe chains adatom by adatom on superconducting NbSe2. The adatoms couple entirely via the substrate, retaining their quantum spin nature. In dimers, we observe that the deepest YSR state undergoes a quantum phase transition due to Ruderman-Kittel-Kasuya-Yosida interactions, a distinct signature of quantum spins. Chains exhibit coherent hybridization and band formation of the YSR excitations, indicating ferromagnetic coupling. Longer chains develop separate domains due to coexisting charge-density-wave order of NbSe2. Despite the spin-orbit-coupled substrate, we find no signatures of Majoranas, possibly because quantum spins reduce the parameter range for topological superconductivity. We suggest that adatom chains are versatile systems for investigating correlated-electron physics and its interplay with topological superconductivity.

Date: 2022
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DOI: 10.1038/s41467-022-29879-0

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