title: Proximity-Induced Shiba States in a Molecular Junction.
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.
authors.affiliation: Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, Netherlands.
authors.forename: Joshua O
authors.initials: JO
authors.lastname: Island
authors.affiliation: Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, Netherlands.
authors.forename: Rocco
authors.initials: R
authors.lastname: Gaudenzi
authors.affiliation: Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, Netherlands.
authors.forename: Joeri
authors.initials: J
authors.lastname: de Bruijckere
authors.affiliation: Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, Netherlands.
authors.forename: Enrique
authors.initials: E
authors.lastname: Burzurí
authors.affiliation: Institut de Ciéncia de Materials de Barcelona (ICMAB-CSIC) and CIBER-BBN, Campus de la UAB, 08193 Bellaterra, Spain.
authors.forename: Carlos
authors.initials: C
authors.lastname: Franco
authors.affiliation: Institut de Ciéncia de Materials de Barcelona (ICMAB-CSIC) and CIBER-BBN, Campus de la UAB, 08193 Bellaterra, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Mas-Torrent
authors.affiliation: Institut de Ciéncia de Materials de Barcelona (ICMAB-CSIC) and CIBER-BBN, Campus de la UAB, 08193 Bellaterra, Spain.
authors.forename: Concepció
authors.initials: C
authors.lastname: Rovira
authors.affiliation: Institut de Ciéncia de Materials de Barcelona (ICMAB-CSIC) and CIBER-BBN, Campus de la UAB, 08193 Bellaterra, Spain.
authors.forename: Jaume
authors.initials: J
authors.lastname: Veciana
authors.affiliation: Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, Netherlands.|Physics Department, Moscow State Pedagogical University, Moscow 119991, Russia.
authors.forename: Teun M
authors.initials: TM
authors.lastname: Klapwijk
authors.affiliation: Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas (ICMM-CSIC), Sor Juana Inés de la Cruz 3, 28049 Madrid, Spain.
authors.forename: Ramón
authors.initials: R
authors.lastname: Aguado
authors.affiliation: Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, Netherlands.
authors.forename: Herre S J
authors.initials: HS
authors.lastname: van der Zant