From Local to Collective Superconductivity in Proximitized Graphene.

Abstract

The superconducting proximity effect induces pairing correlations in metallic systems via Andreev scattering. This effect is particularly intriguing in graphene as it enables two-dimensional superconductivity that is tunable through doping. Understanding how superconducting correlations propagate within the metal is crucial to unveiling the key factors behind this tunability. Here, we employ scanning tunneling microscopy to investigate the energy and length scales of the proximity effect induced by Pb islands on graphene. Using tip-induced manipulation, we assemble S/N/S junctions with tunable N-region spacing and explore the evolution of the proximitized state in the confined normal region. We find that different doping levels can lead to either localized or collective superconducting states. By combining our experimental results with quasiclassical theory, we demonstrate that interface conductance plays a key role in determining the strength and coherence length of pairing correlations and interisland coupling. Our findings provide new insights into the design of novel superconducting states and the control of their properties.