Bound states 2023

Yu-Shiba-Rusinov states in proximitized quantum dots

Jens Paaske

Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark

In this tutorial, I will discuss the Andreev bound states, which are induced by Coulomb blockaded quantum dots contacted by superconducting leads. With normal metallic leads, the paradigmatic Coulomb diamonds demarcate regions of suppressed conductance except for pronounced zero-bias Kondo resonances for odd-occupied, spinful ground states. Correspondingly, with superconducting leads, the quantum dot states are gapped by proximity effect, except for pronounced Yu-Shiba-Rusinov (YSR) sub-gap states for odd-parity, spinful ground states. In both cases, the hybridization between dot and leads serves to screen the local magnetic moment by means of dynamical singlet formation. This compromise between Kondo screening and induced Cooper pairing will be illustrated in terms of simple effective models and a selection of exemplary experiments.