Quantum Spins and Hybridization in Artificially-constructed Chains of Magnetic Adatoms on a Superconductor

Overview

Journal Nat Commun

Specialty Biology

Date 2022 Apr 21

PMID 35443753

Authors

Eva Liebhaber

Lisa M Rutten

Gael Reecht

Jacob F Steiner

Sebastian Rohlf

Kai Rossnagel

Felix von Oppen

Katharina J Franke

Affiliations

Soon will be listed here.

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 NbSe. 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 NbSe. 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.

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