Energy gap measurement of nanostructured thin aluminium films for use in single Cooper-pair devices

TL;DR

This study investigates how the superconducting energy gap in nanostructured aluminium films varies with film thickness and grain size, and demonstrates the application of engineered gaps in single Cooper-pair transistors.

Contribution

It provides new insights into the relationship between film thickness, grain size, and superconducting gap, and applies this knowledge to optimize single Cooper-pair device performance.

Findings

Superconducting gap increases as aluminium film thickness decreases.

Grain size in films ≥10 nm does not significantly affect the energy gap.

Engineered gap profiles modify transport processes in Cooper-pair transistors.

Abstract

Within the context of superconducting gap engineering, Al-\alox-Al tunnel junctions have been used to study the variation in superconducting gap, $\Delta$, with film thickness. Films of thickness 5, 7, 10 and 30 nm were used to form the small area superconductor-insulator-superconductor (SIS) tunnel junctions. In agreement with previous measurements we have observed an increase in the superconducting energy gap of aluminium with a decrease in film thickness. In addition, we find grain size in small area films with thickness \textbf{$\geq$} 10 nm has no appreciable effect on energy gap. Finally, we utilize 7 and 30 nm films in a single Cooper-pair transistor, and observe the modification of the finite bias transport processes due to the engineered gap profile.