On anomalously large nano-scale heat transfer between metals

Abstract

The non-contact heat transfer between two bodies is more efficient than the Stefan-Boltzmann law, when the distances are on the nanometer scale (shorter than Wien's wavelength), due to contributions of thermally excited near fields. This is usually described in terms of the fluctuation electrodynamics due to Rytov, Levin, and co-workers. Recent experiments in the tip-plane geometry have reported "giant" heat currents between metallic (gold) objects, exceeding even the expectations of Rytov theory. We discuss a simple model that describes the distance dependence of the data and permits to compare to a plate-plate geometry, as in the proximity (or Derjaguin) approximation. We extract an area density of active channels which is of the same order for the experiments performed by the groups of Kittel (Oldenburg) and Reddy (Ann Arbor). It is argued that mechanisms that couple phonons to an oscillating surface polarisation are likely to play a role.

Contribution of the acoustic waves to near-field heat transfer

“…However, this contribution is unlikely (see discussion in Ref. 24,37 ). According to the experimental dada 24,25 for the distances above 1nm the tunnelling current is negligible.…”

“…In the extreme near field the electron tunnelling can also contribute to the heat transfer. However, this contribution is unlikely (see discussion in [24,37]). According to the experimental dada [24,25] for the distances above 1nm the tunnelling current is negligible.…”

“…These discrepancies stimulate the search of the alternative channels of the heat transfer that can be activated in an extreme near-field. One of the obvious channel is related with phonon tunneling which stimulated active research of the phonon heat transfer in this region [27][28][29][30][31][32][33][34][35][36][37][38] . Most papers consider phonon tunneling mediated by the van der Waals interaction.…”