Measurement of the Electronic Thermal Conductance Channels and Heat Capacity of Graphene at Low Temperature

The ability to transport energy is a fundamental property of the two-dimensional Dirac fermions in graphene. Electronic thermal transport in this system is relatively unexplored and is expected to show unique fundamental properties and to play an important role in future applications of graphene, including optoelectronics, plasmonics, and ultrasensitive bolometry. Here, we present measurements of bipolar thermal conductances due to electron diffusion and electron-phonon coupling and infer the electronic specific heat, with a minimum value of 10k(B) (10(-22) J/K) per square micron. We test the validity of the Wiedemann-Franz law and find that the Lorenz number equals 1.32 x (pi(2)/3)(k(B)/e)(2). The electron-phonon thermal conductance has a temperature power law T-2 at high doping levels, and the coupling parameter is consistent with recent theory, indicating its enhancement by impurity scattering. We demonstrate control of the thermal conductance by electrical gating and by suppressing the diffusion channel using NbTiN superconducting electrodes, which sets the stage for future graphene-based single-microwave photon detection.