Ballistic graphene Josephson junctions from the short to the long regime

TL;DR

This study explores how the critical current in ballistic graphene Josephson junctions varies from short to long regimes, revealing temperature-dependent scaling and the influence of cavity level spacing on supercurrent saturation.

Contribution

It demonstrates the crossover behavior in ballistic graphene Josephson junctions and links the critical current scaling to cavity level spacing and mode number.

Findings

Critical current scales exponentially with temperature in long junctions.

Level spacing is independent of carrier density and linked to Fabry-Perot oscillations.

Saturation of critical current at low temperature depends on junction length and mode number.

Abstract

We investigate the critical current, $I_C$, of ballistic Josephson junctions made of encapsulated graphene/boron-nitride heterostructures. We observe a crossover from the short to the long junction regimes as the length of the device increases. In long ballistic junctions, $I_S$ is found to scale as $\propto \exp(-k_bT/\delta E)$. The extracted energies $\delta E$ are independent of the carrier density and proportional to the level spacing of the ballistic cavity, as determined from Fabry-Perot oscillations of the junction normal resistance. As $T\rightarrow 0$ the critical current of a long (or short) junction saturates at a level determined by the product of $\delta E$ (or $\Delta$) and the number of the junction's transversal modes.