Long- to short-junction crossover and field-reentrant critical current in Al/Ag-nanowires/Al Josephson junctions

TL;DR

This study investigates the superconducting proximity effect in Al/Ag nanowire/Al Josephson junctions, revealing a crossover from long to short junction behavior and a reentrant critical current under magnetic fields, with deviations from theoretical predictions.

Contribution

It provides experimental insights into the length and magnetic field dependence of critical current in high-quality Ag nanowire Josephson junctions, including novel field effects with aluminum contacts.

Findings

Critical current amplitude is smaller than theoretical predictions.

Critical current decays quasi-Gaussian with magnetic field in most contacts.

Non-monotonous critical current behavior observed with aluminum contacts.

Abstract

We have probed the superconducting proximity effect through long high-quality monocrystalline Ag nanowires, by realizing Josephson junctions of different lengths, with different superconducting materials. Thanks to the high number of junctions probed, both the contact resistance and electron diffusion constant could be determined, enabling a comparison of the measured critical current to theoretical expectation, over the entire regime from short to long diffusive junction. Although the length dependence of the critical current is as expected, the amplitude of the $R_{N}I_c$ product is smaller than predicted by theory. We also address the magnetic field dependence of the critical current. The quasi-gaussian decay of the critical current with field expected of a long narrow junction is observed for all superconducting contacts we used except for aluminum. We present the striking non-monotonous effect of field on the critical current of junctions with aluminum contacts, and analyze it in terms of improved quasiparticle thermalization by a magnetic field.