Electron Cooling with Graphene-Insulator-Superconductor Tunnel Junctions and Applications to Fast Bolometry

Electronic cooling in hybrid normal-metal-insulator-superconductor junctions is a promising technology for the manipulation of thermal loads in solid-state nanosystems. One of the main bottlenecks for efficient electronic cooling is the electron-phonon coupling, as it represents a thermal leakage channel to the phonon bath. Graphene is a two-dimensional material that exhibits a weaker electron-phonon coupling compared to standard metals. For this reason, we study the electron cooling in graphene-based systems consisting of a graphene sheet contacted by two insulator-superconductor junctions. We show that, by properly biasing the graphene, its electronic temperature can reach base values lower than those achieved in similar systems based on metallic ultrathin films. Moreover, the lower electron-phonon coupling is mirrored in a lower heat power pumped into the superconducting leads, thus avoiding their overheating and preserving the cooling mechanisms. Finally, we analyze the possible application of cooled graphene as a bolometric radiation sensor. We study its main figures of merit, i.e., responsivity, noise equivalent power, and response time. In particular, we show that the built-in electron refrigeration allows reaching a responsivity of the order of 50nA/pW and a noise equivalent power of order of 10-18WHz-1/2 while the response speed is about 10 ns corresponding to a thermal bandwidth in the order of 20 MHz.