Tuning the Coupling of an Individual Magnetic Impurity to a Superconductor: Quantum Phase Transition and Transport

The exchange scattering at magnetic adsorbates on superconductors gives rise to Yu-Shiba-Rusinov (YSR) bound states. Depending on the strength of the exchange coupling, the magnetic moment perturbs the Cooper pair condensate only weakly, resulting in a free-spin ground state, or binds a quasiparticl...

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Bibliographic Details
Published in:Physical review letters 2018-11, Vol.121 (19), p.196803-196803, Article 196803
Main Authors: Farinacci, Laëtitia, Ahmadi, Gelavizh, Reecht, Gaël, Ruby, Michael, Bogdanoff, Nils, Peters, Olof, Heinrich, Benjamin W, von Oppen, Felix, Franke, Katharina J
Format: Article
Language:English
Subjects:
Adsorbates
Coupling
Coupling (molecular)
Electron tunneling
Exchanging
Ground state
Magnetic moments
Phase transitions
Transport processes
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Summary:The exchange scattering at magnetic adsorbates on superconductors gives rise to Yu-Shiba-Rusinov (YSR) bound states. Depending on the strength of the exchange coupling, the magnetic moment perturbs the Cooper pair condensate only weakly, resulting in a free-spin ground state, or binds a quasiparticle in its vicinity, leading to a (partially) screened spin state. Here, we use the flexibility of Fe-porphin (FeP) molecules adsorbed on a Pb(111) surface to reversibly and continuously tune between these distinct ground states. We find that the FeP moment is screened in the pristine adsorption state. Approaching the tip of a scanning tunneling microscope, we exert a sufficiently strong attractive force to tune the molecule through the quantum phase transition into the free-spin state. We ascertain and characterize the transition by investigating the transport processes as function of tip-molecule distance, exciting the YSR states by single-electron tunneling as well as (multiple) Andreev reflections.
ISSN:0031-9007
1079-7114
DOI:10.1103/physrevlett.121.196803