Critical current scaling in long diffusive graphene-based Josephson junctions

TL;DR

This study investigates how the critical current in long diffusive graphene-based Josephson junctions scales with the Thouless energy, revealing a linear relationship but a smaller than expected IcRn/ETh ratio.

Contribution

It provides experimental validation of the linear scaling of IcRn with ETh and highlights deviations from theoretical predictions in the ratio for graphene junctions.

Findings

IcRn scales linearly with ETh in the studied junctions.

The ratio IcRn /ETh is significantly smaller than theoretical predictions.

Critical current varies from a few nA to over 5 μA depending on carrier density.

Abstract

We present transport measurements on long diffusive graphene-based Josephson junctions. Several junctions are made on a single-domain crystal of CVD graphene and feature the same contact width of ~9$\mu$m but vary in length from 400 to 1000 nm. As the carrier density is tuned with the gate voltage, the critical current in the these junctions spans a range from a few nA up to more than $5\mu$A, while the Thouless energy, ETh, covers almost two orders of magnitude. Over much of this range, the product of the critical current and the normal resistance IcRn is found to scale linearly with ETh, as expected from theory. However, the ratio IcRn /ETh is found to be 0.1-0.2: much smaller than the predicted ~10 for long diffusive SNS junctions.