ETD

• graphene
• Josephson junctions
• superconducting pockets

In this Master thesis work we present and discuss the optimization of the fabrication protocol for hexagonal Boron Nitride - encapsulated graphene Josephson Junctions, followed by a complete characterization of the optimized devices. We also illustrate the study and characterization of superconducting pockets in the intermediate magnetic field regime, below the onset of quantum Hall states.
The fabrication protocol was optimized by performing low temperature magneto-transport measurements on nine distinct devices fabricated according to different protocols. This allowed to determine how materials choice, device dimensions and specific fabrication steps influence performance and characteristics. Our optimized devices show unprecedented supercurrent density values up to 4.2 A/m and remarkably transparent interfaces.
Differently from previous examples reported in literature, superconducting pockets were observed not only in the n-type doping regime, where they survive up to more than 1 T, but also for p-type doping. In this regime we observed pockets in fields as high as 0.5 T. In connection with differences observed in the current density distributions (extracted from quantum interference patterns), we suggest that local sample-dependent properties may play an important role in the determination of superconducting features at high magnetic fields.