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

Laëtitia Farinacci, Gelavizh Ahmadi, Gaël Reecht, Michael Ruby, Nils Bogdanoff, Olof Peters, Benjamin W. Heinrich, Felix von Oppen, Katharina J. Franke

DOI 10.1103/PhysRevLett.121.196803 · Physical Review Letters

T1

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Abstract

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.

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FormulaReported Tc (K)Pressure (GPa)Type
Pb

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—Pressure not reportedunknown

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