Conductance fluctuations in graphene devices with superconducting contacts in different charge density regimes

TL;DR

This study investigates conductance fluctuations in graphene with superconducting contacts, revealing enhancement due to superconductivity, weak dependence on charge density, and the influence of series resistance on fluctuation magnitude.

Contribution

It provides new insights into how superconductivity affects conductance fluctuations in graphene and emphasizes the importance of series resistance correction.

Findings

Superconductivity enhances conductance fluctuations by a factor of 1.4 to 2.

Phase coherence length is at least half the device length.

Conductance fluctuations show weak dependence on charge density.

Abstract

Conductions fluctuations (CF) are studied in single layer graphene devices with superconducting source and drain contacts made from aluminium. The CF are found to be enhanced by superconductivity by a factor of 1.4 to 2. This (near) doubling of the CF indicates that the phase coherence length is l_phi >= L/2. As compared to previous work, we find a relatively weak dependence of the CF on the gate voltage, and hence on the carrier density. We also demonstrate that whether the CF are larger or smaller at the charge neutrality point can be strongly dependent on the series resistance R_C, which needs to be subtracted.