Condensed Matter Seminar: Superconducting Dirac point in proximetized graphene

Two-dimensional (2D) materials, composed of single atomic layers, have attracted vast research interest since the breakthrough discovery of graphene. One major benefit of such systems is the simple ability to tune the Fermi level through the charge neutrality point between electron and hole doping. For 2D Superconductors, this means that one may potentially achieve the regime described by Bose Einstein Condensation (BEC) physics of small bosonic tightly bound electron pairs. In my talk I will describe an experiment showing that single layer graphene, in which superconducting pairing is induced by proximity to a low density superconductor, can be tuned from hole to electron superconductivity through an ultra-law carrier density regime. We have studied, both experimentally and theoretically, the vicinity of this "Superconducting Dirac point" and found an unusual situation where reflections at interfaces between normal and superconducting regions within the graphene, suppress the conductance and, at the same time, Andreev reflections maintain a large phase breaking length. In addition, the Fermi level can be adjusted so that the momentum in the normal and superconducting regimes perfectly match giving rise to ideal Andreev reflection processes.