Heat transfer statistics in extreme-near-field radiation

We investigate the full counting statistics of extreme-near-field radiative heat transfer using nonequilibrium Green's function formalism. In the extreme near field, the electron-electron interactions between two metallic bodies dominate the heat transfer process. We start from a general tight-binding electron Hamiltonian and obtain a Levitov-Lesovik-like scaled cumulant-generating function (SCGF) using random-phase approximation to deal with electron-electron interaction. The expressions of heat current and its fluctuation (second cumulant) are obtained from the SCGF. The fluctuation symmetry relation of the SCGF is verified. In the linear response limit (small-temperature gradient), we express the heat current cumulant by a linear combination of lower-order cumulants. The heat current fluctuation is $2{k}_B{T}²$ times the thermal conductance with $T$ being the average temperature in the linear response limit, and this provides an evaluation of heat current fluctuation by measuring the thermal conductance in extreme-near-field radiative heat transfer.