Nonresonant contributions to energy transfer through micron-size gaps between neighboring nanostructures

Current theoretical approaches to the analysis of radiative heat exchange at the nanoscale are based on Rytov's stochastic electrodynamics. However, this approach falls short in the description of microscale energy transfer since it overlooks non-resonant contributions arising from the coupling between different modes of relaxation in the material. We show that the phonon density of states given through a log-normal distribution accounts for such mode-coupling and leads to a general expression for the heat transfer coefficient which includes non-resonant contributions. This expression fits the existing experimental results with remarkable accuracy. Thus, our theory goes beyond stochastic electrodynamics and offers an overall explanation of energy transfer through micrometric gaps regardless of geometrical configurations.