Thermal and Electronic Transport in Graphene Superconducting Devices

Abstract

This dissertation presents the experimental methods and results of investigations into the nature of thermal and electronic transport at low temperatures in graphene superconducting devices. By coupling graphene to superconductors, we study the nature of complex supercurrent flow in graphene Josephson junctions. Small variations in magnetic fields are used to obtain information about the supercurrent distribution in rectangular two-terminal junctions, and anomalous interference patterns are observed in graphene close to the Dirac point. Extending the number of terminals to a four-terminal device allowed us to study the interplay of various supercurrents in the shared graphene region. Each of the observed supercurrents are identified as specific paths between pairs of terminals and are tracked as a function of charge density in the graphene. Multiple superconducting graphene devices are further studied under high magnetic fields to elucidate the potential transport mechanisms of supercurrent carried by quantum Hall edge states. Finally, we use large-domain graphene to fabricate devices across large length scales in order to study the interdependent heat transfer between electrons and phonons and diffusive electronic processes. With the ability to measure electronic temperature through Universal Conductance Fluctuations we study the heat flow directly as a function of length. Non-uniform thermal gradients are observed and related to equations describing the total heat flux in the graphene device.