• superconductivity
• graphene
• junction thermodynamics
• solid state refrigerator

The advent of normal metal-insulator-superconductor (NIS) junction is considered a milestone in electronic cooling: it has been demonstrated that when a NIS junction is biased with a proper voltage, the superconducting gap can act as energy filter, allowing only high energy electrons to be removed from the metal electrode. The heat thus is extracted from the electron in N part and is transported into the S part.
The phonons of the metal are typically well thermalized with the substrate, so that the electron-phonon coupling acts as a thermal leakage from the phonon environment to the refrigerated electron system. Furthermore, the heat extracted from the metal heats up the superconducting leads, with subsequent decrease of the superconductive gap and deterioration of the energy filtering.

Recently a SI-Graphene-IS device has been proposed as refrigerator. The graphene, due to its dimensionality, has a weaker electron-phonon coupling; it may thus potentially reach lower temperatures with respect to a SINIS device and overcome the problem of the heat current pumped into the superconducting lead.

The aim of this thesis is to fabricate a refrigerator based on hybrid superconductor-graphene tunnel junctions.
As preliminary stage for the fabrication of the genuine SIGIS device, we want to demonstrate the thermal transport and cooling properties of graphene in a SIGIS-like device.
In particular in this thesis I have calculated some alternative geometries and via numerical calculations I have predicted their base temperature. Afterwards, one of the numerically simulated device has been selected and fabricated. Data collection, involving thermometry and electrical characterization of the device, was performed in the NEST laboratory in Pisa. Finally, the results have been analysed demonstrating the heating transport and also the cooling effects in graphene.