Microscopic quantum point contact formation as the electromigration mechanism in granular superconductor nanowires

TL;DR

This study combines experimental and computational methods to demonstrate that electromigration in granular aluminium nanowires is driven by the formation of quantum point contacts between grains, affecting their electrical properties.

Contribution

It introduces a model linking grain morphology to electromigration behavior and validates it through experiments on nanowires of varying lengths.

Findings

Electromigration is driven by quantum point contact formation between grains.

The model predicts resistance dependence on grain size and distribution.

Experimental results confirm the role of quantum contacts in electromigration.

Abstract

Granular aluminium is a high kinetic inductance thin film superconductor which, when formed into nanowires can undergo an intrinsic electromigration process. We use a combination of experimental and computational approaches to investigate the role of grain morphology and distribution in granular aluminium thin films, when formed into nanowire constrictions. Treating the granular aluminium film as a network of randomly distributed resistors with parameters motivated by the film microstructure allows us to model the electrical characteristics of the nanowires. This model provides estimates of the dependence of sheet resistance on grain size and distribution, and the resulting device to device variation for superconducting nanowires. By fabricating a series of different length nanowires, we study the electromigration process as a function of applied current, and then compare directly to the results of our computational model. In doing so we show that the electromigration is driven by the formation of quantum point contacts between metallic aluminium grains.