# On anomalously large nano-scale heat transfer between metals

## TL;DR

This paper investigates unexpectedly large heat transfer between metals at nanometer distances, proposing a model that explains experimental data and suggests phonon-surface polarization coupling as a key mechanism.

## Contribution

It introduces a simple model for nanometer-scale heat transfer between metals, aligning with experimental results and highlighting phonon-surface polarization interactions as significant.

## Key findings

- Heat transfer exceeds classical predictions at nanoscales.
- A model matches experimental distance dependence data.
- Phonon-surface polarization coupling likely influences heat transfer.

## 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.