Energy Gap Modulation in Proximitized Superconducting Puddles of Graphene

Abstract: We investigated proximity-induced superconductivity in a graphene-insulating InO bilayer system through gate-controlled transport measurements. Distinct oscillations in the differential conductance are observed across both the electron and hole doping regimes, with oscillation amplitudes increasing as the chemical potential moves away from the Dirac point. These findings are explained using a theoretical model of a normal-superconductor-normal (NSN) junction, which addresses reflection and transmission probabilities at normal incidence. From this model, we extract key parameters for the proximitized graphene, including the superconducting energy gap Delta and the effective length scale Ls of the superconducting regions. Near the Dirac point, we observe a minimal Ls and a maximal Delta, aligning with the theory that the gap in strongly disordered superconductors increases as the coherence length of localized pairs decreases. This suggests that spatial confinement in a low-density superconductor leads to an effective increase in the superconducting gap.