Coherent transport and electron interference in cuprate superconductor/graphene junctions

Proximity-induced superconductivity is particularly interesting in graphene. Among other reasons, because that effect can be externally controlled by tuning the Fermi energy (and vector) via electrical gating. For example, using high-temperature superconducting YBa₂Cu₃O₇/graphene planar junctions, we recently demonstrated [1] gate-controlled superconducting electron interferences that allow modulating the Andreev reflection at the superconductor/graphene interface via Klein tunneling of electron/hole pairs. Here we will discuss new experiments in the same type of junctions, in which a different type of interferences –this time controlled by the bias voltage– are observed which are due to geometrical resonances and coherent propagation of electron/hole pairs across a graphene channel. This is substantiated by the relationship of the oscillations period and the graphene channel length (up to hundreds on nm), as well as by numerical simulations of the device conductance -which reproduce both the observed resonances and the background conductance. [1] D. Perconte et al. Nature Physics 14, 25 (2018)