Unusual critical currents in quasi-one-dimensional superconducting aluminum two-width structures in a magnetic field

TL;DR

This study investigates unusual critical currents in quasi-one-dimensional aluminum superconducting structures under magnetic fields, revealing nonlocal effects and discrepancies with Ginzburg-Landau theory predictions.

Contribution

It reports novel experimental observations of critical currents that challenge existing theories, highlighting nonlocal dependencies and high-field phenomena in aluminum nanostructures.

Findings

Critical currents depend on electron transport in junction areas.

Significant differences between experimental and theoretical switching currents.

Existence of nonzero switching currents at fields above maximum critical field.

Abstract

We measured unusual critical currents as functions of temperature in the zero field and as functions of a magnetic field perpendicular to the substrate surface at a given temperature close to the critical temperature in thin-film long quasi-one-dimensional superconducting aluminum two-width structures consisting of narrow and wide wires with different critical temperatures. It is found that the experimental critical switching current as a function of the field at a given temperature, determined by the appearance of a dc voltage on a short section of the structure, is nonlocal (dependent on electron transport in the area containing the junction line between the narrow and wide wires). When current flows through the narrow and wide wires of the structure, the switching currents, experimental and calculated within the framework of the Ginzburg-Landau theory, differ radically from each other. A nonzero switching current exists in high fields greater than the maximum critical magnetic field in a quasi-one-dimensional superconducting wire. In the aluminum two-width structures studied here, the unusual measured switching current challenges description by known theories.