Masters Thesis Defense by Zhenzhong Tang

Title: Magnetic Flux-Tunable Superconductivity of Tapered Full-Shell Nanowires

This project investigates the magnetic flux–tunable transport properties of tapered full-shell Al InAs hybrid nanowires.

The full-shell nanowires consist of InAs nanowire segments with dif ferent diameters, connected through a geometrically engineered bottleneck structure and fully surrounded by an epitaxial Al shell. This asymmetric structure can be used for the modulation of superconducting properties by magnetic flux and can serves as a versatile platform to explore geometry-dependent superconductivity.

Differential resistance measurements reveal a flux-periodic modulation of the critical current, forming a pattern consistent with the superposition of Little-Parks effects from the two distinct segments. In addition to the expected periodic structure, several distinct features are observed that cannot be explained by conventional Little-Parks theory, including edge splitting of lobes, localized subgap states, and unexpected modulations near the bottleneck.

These findings demon strate the rich flux-dependent behavior enabled by geometric inhomogeneity and motivate further investigation into the underlying physical mechanisms. These findings highlight the significant impact of nanowire geometry on superconducting phase coherence.

The experimental results show promising potential for future investigations of geomet ric effects, phase transitions, and topological superconductivity in full-shell hybrid nanostructures.

Supervisor: Jesper Nygård