Proximity-Induced Shiba States in a Molecular Junction
J.O. Island (TU Delft - QN/van der Zant Lab, Kavli institute of nanoscience Delft)
R. Gaudenzi (Kavli institute of nanoscience Delft, TU Delft - QN/van der Zant Lab)
J. de Bruijckere (Kavli institute of nanoscience Delft, TU Delft - QN/van der Zant Lab)
E. Burzuri Linares (Kavli institute of nanoscience Delft, TU Delft - QN/van der Zant Lab)
Carlos Franco (Biomaterials and Nanomedicine (CIBER-BBN))
Marta Mas-Torrent (Biomaterials and Nanomedicine (CIBER-BBN))
Concepcio Rovira (Biomaterials and Nanomedicine (CIBER-BBN))
Jaume Veciana (Biomaterials and Nanomedicine (CIBER-BBN))
T.M. Klapwijk (Kavli institute of nanoscience Delft, TU Delft - QN/Klapwijk Lab, Moscow State Pedagogical University)
Ramón Aguado (Instituto de Ciencia de Materiales de Madrid (ICMM))
H.S.J. van der Zant (TU Delft - QN/van der Zant Lab, Kavli institute of nanoscience Delft)
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Abstract
Superconductors containing magnetic impurities exhibit intriguing phenomena derived from the competition between Cooper pairing and Kondo screening. At the heart of this competition are the Yu-Shiba-Rusinov (Shiba) states which arise from the pair breaking effects a magnetic impurity has on a superconducting host. Hybrid superconductor-molecular junctions offer unique access to these states but the added complexity in fabricating such devices has kept their exploration to a minimum. Here, we report on the successful integration of a model spin 1/2 impurity, in the form of a neutral and stable all organic radical molecule, in proximity-induced superconducting break junctions. Our measurements reveal excitations which are characteristic of a spin-induced Shiba state due to the radical's unpaired spin strongly coupled to a superconductor. By virtue of a variable molecule-electrode coupling, we access both the singlet and doublet ground states of the hybrid system which give rise to the doublet and singlet Shiba excited states, respectively. Our results show that Shiba states are a robust feature of the interaction between a paramagnetic impurity and a proximity-induced superconductor where the excited state is mediated by correlated electron-hole (Andreev) pairs instead of Cooper pairs.
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