PhD defense: Alexandros Vekris

Title: Exploring quantum phenomena in hydrid double nanowire devices

Abstract:

This thesis investigates quantum phenomena in superconductor-semiconductor junctions fabricated in a new material platform of in-situ grown parallel nanowires motivated by theoretical proposals describing quantum states such as coupled hybrid states and topological effects in such devices. Even though these two phenomena were not observed in these 1st generation devices, a systematic study of novel double-nanowire platforms was performed in various geometries. Initially, supercurrent was studied through a parallel double quantum dot system which was formed in a double nanowire Josephson junction.  Minimal inter-dot coupling was found. Driven by the flux-induced studies in full shell nanowires, a first study of Little-Parks oscillations in double nanowires was performed, showing that an ellipsoid cross section, such one of double nanowires, can be fitted with good agreement using a simple model. The final study of double nanowires shown in this thesis involves multi-probe measurements of superconducting islands. Temperature analysis of the island resonances is well understood using a thermodynamic model, and the behavior of the resonances points towards a common sub-gap state extending across the device. Finally, insight on thephysics of a superconducting island in close proximity to a tunable quantum dot is investigated in a single nanowire, where Coulomb-aided Yu-Shiba-Rusinov states are studied in various regimes.