  Due to its exceptional electronic and thermal properties, graphene is a key
material for bolometry, calorimetry, and photon detection. However, despite
graphene's relatively simple electronic structure, the physical processes
responsible for the transport of heat from the electrons to the lattice are
experimentally still elusive. Here, we measure the thermal response of
low-disorder graphene encapsulated in hexagonal boron nitride (hBN) by
integrating it within a multi-terminal superconducting device coupled to a
microwave resonator. This technique allows us to simultaneously apply Joule
heat power to the graphene flake while performing calibrated readout of the
electron temperature. We probe the thermalization rates of both electrons and
holes with high precision and observe a thermalization scaling exponent
consistent with cooling dominated by resonant electron-phonon coupling
processes occurring at the interface between graphene and superconducting
leads. The technique utilized here is applicable for wide range of
semiconducting-superconducting interface heterostructures and provides new
insights into the thermalization pathways essential for the next-generation
thermal detectors.
