Suspended Graphene Ballistic Josephson Weak Links

TL;DR

This paper reports the fabrication of high-quality suspended graphene-NbN Josephson junctions exhibiting ballistic supercurrents, enabling exploration of intrinsic Dirac Fermion superconductivity and advanced hybrid devices.

Contribution

It introduces a method to create suspended graphene-superconductor junctions with high mobility, revealing ballistic Josephson effects linked to Dirac electron properties.

Findings

Ballistic Josephson current depends linearly on Fermi energy.

Device mobility exceeds 150,000 cm2/Vs.

Supercurrent observed above 2 K.

Abstract

The interplay of graphene and superconductivity has attracted great interest for understanding the two-dimensional Dirac Fermion physics and for superconducting device applications. In previous work, graphene-superconductor junctions fabricated on standard SiO2 substrates were highly disordered. Due to charge carrier scattering and potential fluctuations, the expected intrinsic properties of graphene combined with superconductors remained elusive to experimental observations. We propose suspended graphene-superconductor junctions as an effective solution to the problem. Here, we show the fabrication and characterization of the high-quality suspended monolayer graphene-NbN Josephson junctions that have device mobility greater than 150,000 cm2/Vs, with minimum carrier density below 1e10 cm-2 and a formation of supercurrent at temperature above 2 K.The devices have exhibited a ballistic Josephson current that depend linearly on the Fermi energy of graphene, a manifestation of the ultra-relativistic band structure of Dirac electrons. This work paves the way for future studies of the intrinsic Dirac Fermion superconducting proximity effect and new graphene-superconductor hybrid junctions.