Enhancement of Superconductivity upon reduction of carrier density in proximitized graphene

TL;DR

This study reveals that reducing carrier density in graphene coupled with InO enhances its superconducting transition temperature, contrary to conventional expectations, due to Josephson coupling across electron-hole puddles.

Contribution

It provides both experimental and theoretical evidence that carrier density reduction can increase Tc in proximitized graphene, highlighting the role of inhomogeneous puddles and Josephson effects.

Findings

Tc increases as carrier density decreases.

Maximum Tc occurs near charge neutrality point.

Inhomogeneous puddles facilitate Josephson coupling.

Abstract

The superconducting transition temperature (Tc) of a single layer graphene coupled to an Indium oxide (InO) film, a low carrier-density superconductor, is found to increase with decreasing carrier density and is largest close to the average charge neutrality point in graphene. Such an effect is very surprising in conventional BCS superconductors. We study this phenomenon both experimentally and theoretically. Our analysis suggests that the InO film induces random electron and hole-doped puddles in the graphene. The Josephson effect across these regions of opposite polarity enhances the Josephson coupling between the superconducting clusters in InO, along with the overall Tc of the bilayer heterostructure. This enhancement is most effective when the chemical potential of the system is tuned between the charge neutrality points of the electron and hole-doped regions.