A microscopic theory for ultra-near-field radiation

TL;DR

This paper develops a microscopic nonequilibrium Green's function approach to model ultra-near-field radiative heat transfer between metal plates, capturing nonlocal effects and new length scales.

Contribution

It introduces a microscopic NEGF-based theory for near-field radiation, differing from fluctuational electrodynamics by describing true nonequilibrium steady states and nonlocal dielectric properties.

Findings

Identification of a new length scale where heat current peaks

Consistency with Polder and van Hove theory at larger distances

Discovery of a peak in heat transfer at nanoscale distances

Abstract

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.