Poster presentation

Cooper Pair Excitation Mediated by a Molecular Quantum Spin on a Superconducting Proximitized Gold Film
Stefano Trivini^1,3, Jon Ortuzar², Katerina Vaxevani¹, Jingchen Li¹, M. Cazadilla^3,4, S. Bergeret², J. I. Pascual^1,4

1 CIC nanoGUNE, San Sebastian (Spain)
2 Centro de Física de Materiales, San Sebastian (Spain)
3 Donostia International Physics Center, San Sebastian (Spain)
4 Ikerbasque, Basque Foundation for Science, 48013 Bilbao, Spain

Breaking a correlated pair in a superconductor requires an even number of fermions providing at least twice the pairing energy Δ. Here, we show that a single tunneling electron can also excite a pair breaking excitation in a proximitized gold film in the presence of magnetic impurities. Combining scanning tunneling spectroscopy with theoretical modelling, we map the excitation spectrum of an Fe-porphyrin molecule on the Au/V(100)proximitized surface into a manifold of entangled Yu-Shiba-Rusinov and spin excitations. Pair excitations emerge in the tunneling spectra as peaks outside the spectral gap only in the strong coupling regime, where the presence of a bound quasiparticle in the ground state ensures the even fermion parity of the excitation. Our results unravel the quantum nature of magnetic impurities on superconductors and demonstrate that pair excitations unequivocally reveal the parity of the ground state.