Supercurrent in Nb/InAs-Nanowire/Nb Josephson junctions

TL;DR

This study fabricates and characterizes Nb/InAs nanowire Josephson junctions, demonstrating tunable supercurrents, magnetic field effects, and enhanced conductance fluctuations due to Andreev reflection, advancing understanding of mesoscopic superconducting devices.

Contribution

It introduces Nb/InAs nanowire Josephson junctions with tunable properties and analyzes their behavior under various conditions, including magnetic field and gate voltage, with detailed conductance fluctuation studies.

Findings

Supercurrents up to 100 nA observed in high-doping junctions.

Josephson coupling persists up to 4K due to Nb superconductors.

Conductance fluctuations are significantly enhanced in superconducting contacts.

Abstract

We report on the fabrication and measurements of planar mesoscopic Josephson junctions formed by InAs nanowires coupled to superconducting Nb terminals. The use of Si-doped InAs-nanowires with different bulk carrier concentrations allowed to tune the properties of the junctions. We have studied the junction characteristics as a function of temperature, gate voltage, and magnetic field. In junctions with high doping concentrations in the nanowire Josephson supercurrent values up to 100\,nA are found. Owing to the use of Nb as superconductor the Josephson coupling persists at temperatures up to 4K. In all junctions the critical current monotonously decreased with the magnetic field, which can be explained by a recently developed theoretical model for the proximity effect in ultra-small Josephson junctions. For the low-doped Josephson junctions a control of the critical current by varying the gate voltage has been demonstrated. We have studied conductance fluctuations in nanowires coupled to superconducting and normal metal terminals. The conductance fluctuation amplitude is found to be about 6 times larger in superconducting contacted nanowires. The enhancement of the conductance fluctuations is attributed to phase-coherent Andreev reflection as well as to the large number of phase-coherent channels due to the large superconducting gap of the Nb electrodes.