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

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${}_2$. 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${}_2$. 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.

References in corpus (18)

• Observation of Majorana Fermions in Ferromagnetic Atomic Chains on a Superconductor
• Topological Superconductivity induced by Ferromagnetic Metal Chains
• Strong localization of Majorana end states in chains of magnetic adatoms
• Protection of excited spin states by a superconducting energy gap
• Orbital Picture of Yu-Shiba-Rusinov Multiplets
• Evidence of topological Shiba bands in artificial spin chains on superconductors
• Intrinsic atomic scale modulations of the superconducting gap of 2H-NbSe2
• Spin-orbit coupling induced splitting of Yu-Shiba-Rusinov states in antiferromagnetic dimers
• Magnetic anisotropy effects on quantum impurities in superconducting host
• Spiral magnetic order and topological superconductivity in a chain of magnetic adatoms on a two-dimensional superconductor
• Majorana Fermions in Magnetic Chains
• Phase diagram and excitations of a Shiba molecule
• Tuning interactions between spins in a superconductor
• Yu-Shiba-Rusinov states in real metals
• Non-Majorana modes in diluted spin chains proximitized to a superconductor
• Long range and highly tunable interaction between local spins coupled to a superconducting condensate
• Atomic Manipulation of In-gap States on the $\beta$-Bi${}_2$Pd Superconductor
• Quantum magnetism and topological superconductivity in Yu-Shiba-Rusinov chains

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