Science
Breakdown of Fluctuational Electrodynamics in the Extreme Near Field
Key Points
Announce Type: cross Abstract: Fluctuational electrodynamics relies on the assumption that thermal fluctuations in distinct bodies are statistically independent. We show that this approximation breaks down in the extreme near-field regime, where overlapping evanescent surface fields hybridize optical phonons across nanometric vacuum gaps and generate fluctuating-current cross correlations between opposite interfaces.
arXiv:2606.05845v1 Announce Type: cross
Abstract: Fluctuational electrodynamics relies on the assumption that thermal fluctuations in distinct bodies are statistically independent. We show that this approximation breaks down in the extreme near-field regime, where overlapping evanescent surface fields hybridize optical phonons across nanometric vacuum gaps and generate fluctuating-current cross correlations between opposite interfaces. Using a microscopic coupled-oscillator model combined with a Green-tensor formulation of the Poynting vector, we derive the resulting correlation-induced correction to the radiative heat flux. For polar materials supporting surface phonon-polaritons, these correlations become significant when the hybridization energy is comparable to the intrinsic damping rate and can substantially modify conventional fluctuational-electrodynamics predictions at subnanometric separations. Our results establish a microscopic framework for correlated thermal fluctuations in the extreme near-field regime and quantify their impact on radiative heat transfer.