Supercurrent diode effect in thin film Nb tracks

TL;DR

This study demonstrates a supercurrent diode effect in Nb thin films, showing nonreciprocal critical currents influenced by track width, temperature, and magnetic field, with potential applications in superconducting computing.

Contribution

First demonstration of supercurrent diode effect in Nb thin films with detailed analysis of width dependence and a proposed model explaining the phenomenon.

Findings

Maximum diode efficiency of ~30% at 4 μm width tracks.

Diode effect diminishes or disappears in tracks wider than 4 μm.

Effect varies with temperature and magnetic field.

Abstract

We demonstrate nonreciprocal critical current in 65 nm thick polycrystalline and epitaxial Nb thin films patterned into tracks. The nonreciprocal behavior gives a supercurrent diode effect, where the current passed in one direction is a supercurrent and the other direction is a normal state (resistive) current. We attribute fabrication artefacts to creating the supercurrent diode effect in our tracks. We study the variation of the diode effect with temperature and magnetic field, and find a dependence with the width of the Nb tracks from 2-10 $\mu$m. For both polycrystalline and epitaxial samples, we find that tracks of width 4 $\mu$m provides the largest supercurrent diode efficiency of up to $\approx$30$\%$, with the effect reducing or disappearing in the widest tracks of 10 $\mu$m. We propose a model based on the limiting contributions to the critical current density to explain the track width dependence of the induced supercurrent diode effect. It is anticipated that the supercurrent diode will become a ubiquitous component of the superconducting computer.