  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 chemical
potential by back-gating, in-principle enabling to vary the Fermi level through
the charge neutrality point, thus tuning between electron and hole doping. For
2D Superconductors, this means that one may potentially achieve the
strongly-coupled superconducting regime described by Bose Einstein Condensation
physics of small bosonic tightly bound electron pairs. Furthermore, it should
be possible to access both electron and hole based superconductivity in a
single system. However, in most 2D materials, an insulating gap opens up around
the charge neutrality point, thus preventing approach to this regime. Graphene
is unique in this sense since it is a true semi-metal in which the un-gapped
Dirac point is protected by the symmetries. In this work we show that single
layer graphene, in which superconducting pairing is induced by proximity to
regions of a low density superconductor, can be tuned from hole to electron
superconductivity through the strong coupling regime. We study, both
experimentally and theoretically, the vicinity of this "Superconducting Dirac
point" and find 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.
