Interfacial Heat Transport via Evanescent Radiation by Hot Electrons

We predict an additional thermal transport pathway across metal-nonmetal interfaces with large electron-phonon nonequilibrium via evanescent radiative heat transfer. In such systems, electron scattering processes vary drastically and can be leveraged to guide heat across interfaces via radiative heat transport without engaging the lattice directly. We employ the formalism of fluctuational electrodynamics to simulate the spectral radiative heat flux across the interface of a metal film and a nonmetal substrate. We find that the radiative conductance can exceed 300 MW m^{-2} K^{-1} at an electron temperature of 5000 K for an emitting tungsten film on a hexagonal boron nitride substrate, becoming comparable to its conductive counterpart. This allows for a more holistic approach to the heat flow across interfaces, accounting for electron-phonon nonequilibrium and ultrafast near-field phonon-polariton coupling.