When graphene is placed on an atomically flat substrate its charge carrier mobility dramatically increases and therefore its intrinsic properties can be eventually explored. By piling up two-dimensional materials one can design artificial heterostructures which are maintained by van der Waals forces. The case of graphene on hexagonal boron nitride is a striking example. In these systems, conductivity is strongly temperature dependent and charge carrier mobility has been measured up to two orders of magnitude higher than usual graphene on SiO2. We will present some electronic transport experiments where bilayer graphene are sandwiched between two boron nitride multilayers. We studied the effect of a displacement field on the proximity induced superconductivity. We demonstrate that we can tune the system from superconducting to insulating, as well as the effect of a potential barrier on the charge carriers. We will show that the fully encapsulated graphene devices connected solely from the edge provide the best quality devices with ultra-high supercurrent, ultra-low contact resistance, strong multiple Andreev reflection signal, as well as robust Fabry-Pérot interferences directly detected in conductance measurements. We show that the effect on superconductivity is strongly influenced by the presence of a potential barrier.
Karlsruhe Institute of Technology