DiraCooper · Interaction of Cooper Pairs and Massless Dirac Fermions in Suspended Superconductor-Graphene Devices

Superconductivity occurs in a metal when the temperature is low enough to favour the appearance of a new ground state comprised of time-reversed pairs of electrons. These composite particles, called Cooper pairs, form a condensate giving rise to the extraordinary phenomena characteristic of superconductivity, including zero electrical resistivity and perfect diamagnetism. Graphene is a two dimensional crystal of carbon atoms which despite being non-superconducting exhibits another type of emergent electronic order. Due to the high symmetry of graphene’s hexagonal lattice its charge carriers are massless Dirac fermions. Unlike in a normal semiconductor or metal, these electronic quasiparticles act like neutrinos, obeying the laws of ""relativistic"" quantum mechanics with an effective speed of light given by the Fermi velocity.This project seeks to study the interaction between these two types of remarkable emergent electronic particles, massless Dirac fermions and Cooper pairs. The conversion of Cooper pairs and massless Dirac fermions, the “relativistic” superconducting proximity effect, can occur in several unique graphene-superconductor (GS) junction devices. It is in the ballistic, short and transparent transport regime that new phenomena, peculiar to the ""relativistic"" nature of massless Dirac fermions, are expected. To obtain GS devices in this so far unattained limit, novel fabrication techniques will be employed, including chemical vapour deposition of graphene on superconducting electrodes, stencil-mask evaporation, multiple-angle deposition, and sample suspension. Low-temperature electronic measurements on these devices should then reveal theoretically-predicted effects such as specular Andreev reflection and gate-dependent multiple Andreev reflection, as well as others yet to be discovered relying on the interaction between Cooper pairs and massless Dirac fermions.""