Dynamical Coulomb Blockade in Superconducting Single-Electron Transistors

• Applicant: Professorin Dr. Elke Scheer
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 553541898

This project deals with the interplay between charging effects and superconducting multiparticle transport in mesoscopic electronic circuits. The goal is to better understand the phenomenon of dynamical Coulomb blockade (DCB) in the superconducting state. DCB is an electronic interaction effect that occurs at very low temperatures in mesoscopic conductors. It is well understood in the normal conducting state where it depends on the electromagnetic properties of the embedding circuit of the conductor and manifests itself as a reduced zero bias conductance, while it is not well studied in the superconducting state. DCB can also be also considered as a remainder of Coulomb blockade (CB) which is in principle a classical that occurs as a result of charging effects and becomes apparent in small, electrically isolated conductors. Practically CB is studied by weakly coupling the conductor to an environment (electrodes) as well, similar to devices for studying DCB. The main difference between DCB and CB is that ion the case of CB the small conductor is regarded as a separate entity, while in DCB it is not. This means the research question addressed in this project can also be phrased as: what are the conditions under which a conductor is sufficiently isolated from its environment to be considered a separate entity. While this question is answered in the normal conducting state, it is not in the superconducting state where different kinds of charge carriers (individual quasiparticles, Cooper pairs, combinations of Cooper pairs and quasiparticles, nicknamed Andreev clusters) carry the charge transport. Preliminary studies have shown that the same device might be in the DCB regime in its normal state and in the CB regime in its superconducting state. These questions will be addressed from the experimental side, by studying devices with an in-situ tunable junction to the small conductor, and by simulations using the master equation approach that is well established for studying CB. We want to explore how far it can also be applied to describe the transition between CB and DCB both in the normal conducting and in the superconducting state.

• DFG Programme: Research Grants