Enhanced shot noise at bilayer graphene -- superconductor junction

TL;DR

This study investigates shot noise in bilayer graphene-Niobium superconductor junctions, revealing enhanced charge transport and Fano factor variations across different regimes, advancing understanding of graphene-superconductor interfaces.

Contribution

It provides the first detailed shot noise measurements in bilayer graphene-superconductor junctions, highlighting the persistent enhancement of shot noise within the superconducting gap.

Findings

Fano factor ~ 1/3 above the gap at Dirac point

Fano factor increases to ~ 0.5 below the gap

Enhanced shot noise observed in quantum Hall regime

Abstract

Transport properties of graphene - superconductor junction has been studied extensively to understand the interplay of the relativistic Dirac quasiparticles and superconductivity. Though shot noise measurements in graphene has been performed to realize many theoretical predictions, both at zero magnetic field as well as quantum Hall (QH) regime, its junction with superconductor remain unexplored. Here, we have carried out the shot noise measurements in an edge contacted bilayer graphene - Niobium superconductor junction at zero magnetic field as well as QH regime. At the Dirac point we have observed a Fano factor ~ 1/3 above the superconducting gap and a transition to an enhanced Fano factor ~ 0.5 below the superconducting gap. By changing the carrier density we have found a continuous reduction of Fano factor for both types of carriers, however the enhancement of Fano factor within the superconducting gap by a factor of ~ 1.5 is always preserved. The enhancement of shot noise is also observed in the QH regime, where the current is carried by the edge state, below the critical magnetic field and within the superconducting gap. These observations clearly demonstrate the enhanced charge transport at the graphene-superconductor interface.