Ballistic Josephson junctions based on CVD graphene

TL;DR

This paper demonstrates the fabrication and characterization of ballistic Josephson junctions using CVD-grown graphene, showing effective superconducting behavior, gate-tunability, and ballistic transport features, advancing scalable graphene-based quantum devices.

Contribution

It introduces CVD-grown graphene as a scalable alternative for Josephson junctions, exhibiting ballistic transport and gate-tunable supercurrent, unlike previous mechanically exfoliated graphene devices.

Findings

Effective Josephson effect with no thermal hysteresis from 1.5 K to 320 mK

Fraunhofer-like interference pattern observed in magnetic field

Normal state resistance oscillates with gate voltage in shortest junctions

Abstract

Josephson junctions with graphene as the weak link between superconductors have been intensely studied in recent years, with respect to both fundamental physics and potential applications. However, most of the previous work was based on mechanically exfoliated graphene, which is not compatible with mass production. Here we present our research using graphene grown by chemical vapour deposition (CVD) as the weak link of Josephson junctions. We demonstrate that CVD-graphene-based Josephson junctions with Nb electrodes can work effectively without any thermal hysteresis from 1.5 K down to a base temperature of 320 mK, and they show an ideal Fraunhofer-like interference pattern in a perpendicular magnetic field. We also show that the critical current of the junction can be tuned by a gate voltage. Furthermore, for our shortest junctions (50 nm in length), we find that the normal state resistance oscillates with the gate voltage, indicating that the junctions are in the ballistic regime, a feature not previously observed in CVD-graphene-based Josephson junctions.