Excitations in a superconducting Coulombic energy gap

Juan Carlos Estrada Saldaña; Alexandros Vekris; Luka Pavešič; Peter Krogstrup; Rok Žitko; Kasper Grove-Rasmussen; Jesper Nygård

doi:10.1038/s41467-022-29634-5

arXiv · 2101.10794

Excitations in a superconducting Coulombic energy gap

Juan Carlos Estrada Saldaña·Alexandros Vekris·Luka Pavešič·Peter Krogstrup·Rok Žitko·Kasper Grove-Rasmussen·Jesper Nygård

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Abstract

Cooper pairing and Coulomb repulsion are antagonists, producing distinct energy gaps in superconductors and Mott insulators. When a superconductor exchanges unpaired electrons with a quantum dot, its gap is populated by a pair of electron-hole symmetric Yu-Shiba-Rusinov excitations between doublet and singlet many-body states. The fate of these excitations in the presence of a strong Coulomb repulsion in the superconductor is unknown, but of importance in applications such as topological superconducting qubits and multi-channel impurity models. Here we couple a quantum dot to a superconducting island with a tunable Coulomb repulsion. We show that a strong Coulomb repulsion changes the singlet many-body state into a two-body state. It also breaks the electron-hole energy symmetry of the excitations, which thereby lose their Yu-Shiba-Rusinov character.

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Juan Carlos Estrada Saldaña, Alexandros Vekris, Luka Pavešič, Peter Krogstrup, Rok Žitko, Kasper Grove-Rasmussen, Jesper Nygård. 2021-01-26. Excitations in a superconducting Coulombic energy gap. https://doi.org/10.1038/s41467-022-29634-5

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