# Fermi Velocity Dependent Critical Current in Ballistic Bilayer Graphene Josephson Junctions

## TL;DR

This study explores how the critical current in bilayer graphene Josephson junctions depends on Fermi velocity and gate voltage, offering new tuning possibilities for these devices.

## Contribution

The paper demonstrates carrier density dependence of δE in bilayer graphene Josephson junctions, a novel feature compared to single-layer systems.

## Key findings

- The critical current IC follows an exponential trend with temperature: exp(−kBT/δE).
- δE increases with gate voltage due to the quadratic dispersion of bilayer graphene.
- BGJJs allow tuning of δE through carrier density, unlike single-layer graphene junctions.

## Abstract

We perform transport measurements on proximitized, ballistic,
bilayer
graphene Josephson junctions (BGJJs) in the intermediate-to-long junction
regime (L > ξ). We measure the device’s
differential resistance as a function of bias current and gate voltage
for a range of different temperatures. The extracted critical current IC follows an exponential trend with temperature:
exp(−kBT/δE). Here δE = ℏνF/2πL: an expected
trend for intermediate-to-long junctions. From δE, we determine the Fermi velocity of the bilayer graphene, which
is found to increase with gate voltage. Simultaneously, we show the
carrier density dependence of δE, which is
attributed to the quadratic dispersion of bilayer graphene. This is
in contrast to single layer graphene Josephson junctions, where δE and the Fermi velocity are independent of the carrier
density. The carrier density dependence in BGJJs allows for additional
tuning parameters in graphene-based Josephson junction devices.