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A microscopic theory for ultra-near-field radiation

Using the nonequilibrium Green's function (NEGF) formalism, we propose a microscopic theory for near-field radiative heat transfer between metal plates. Tight-binding models for the electrons are coupled to the electromagnetic field continuum. Our approach differs from the established ones based on fluctuational electrodynamics, in that it describes truly nonequilibrium steady states, and is nonlocal in system's dielectric properties. For a two quantum-dot model a new length scale emerges at which the heat current shows a peak. This length scale is related to the physics of parallel plate capacitors. The three-dimensional model results are consistent with the theory of Polder and van Hove except at very short distances.