  Superconductivity can be induced in a normal material via the leakage of
superconducting pairs of charge carriers from an adjacent superconductor. This
so-called proximity effect is markedly influenced by graphene unique electronic
structure, both in fundamental and technologically relevant ways. These include
an unconventional form of the leakage mechanism the Andreev reflection and the
potential of supercurrent modulation through electrical gating. Despite the
interest of high-temperature superconductors in that context, realizations have
been exclusively based on low-temperature ones. Here we demonstrate
gate-tunable, high-temperature superconducting proximity effect in graphene.
Notably, gating effects result from the perfect transmission of superconducting
pairs across an energy barrier -a form of Klein tunneling, up to now observed
only for non-superconducting carriers- and quantum interferences controlled by
graphene doping. Interestingly, we find that this type of interferences become
dominant without the need of ultra-clean graphene, in stark contrast to the
case of low-temperature superconductors. These results pave the way to a new
class of tunable, high-temperature Josephson devices based on large-scale
graphene.
