Enhancement of superconductivity upon reduction of carrier density in proximitized graphene

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