Graphite-gated graphene junctions: toward fractional quantum Hall Josephson devices

In this thesis, I demonstrate the fabrication and the experimental study of graphite-gated niobium-graphene weak links. This kind of device is fundamental for the development of an experimental platform combining superconductivity and fractional quantum Hall effect, exploitable for the achievement of topological quantum computation. I elaborated and executed fabrication protocols for such devices, producing both standard weak links and other devices implementing a double-gate geometry not experimented before. The effectiveness of the procedures is proven by low-temperature transport measurements. We observed gating action from graphite, ballistic transport of carriers and induced superconductivity. The new double-gate design enabled local control of parallel channels, both in the normal and superconducting regimes. This is a proof of concept for devices with electrostatically defined geometry, a design choice that can bring substantial improvements in terms of quantum coherence, as already demonstrated in the field of edge-state interferometry.