Scale-dependent heat transport in dissipative media via electromagnetic fluctuations

TL;DR

This paper presents a comprehensive theory for electromagnetic heat transport in media, revealing how electromagnetic fluctuations influence thermal conductivity in various regimes, especially at interfaces and in dilute or nanoscale systems.

Contribution

It introduces a spatially nonlocal thermal conductivity tensor based on electromagnetic Green's functions, applicable to diverse media and interface configurations.

Findings

Electromagnetic heat transport can dominate in dilute media.

Nanosheets exhibit unique conductivity behaviors, including absence of Fourier regime.

Electromagnetic contributions are significant even in dense media with interfaces.

Abstract

We develop a theory for heat transport via electromagnetic waves inside media, and use it to derive a spatially nonlocal thermal conductivity tensor, in terms of the electromagnetic Green's function and potential, for any given system. While typically negligible for optically dense bulk media, the electromagnetic component of conductivity can be significant for optically dilute media, and shows regimes of Fourier transport as well as unhindered transport. Moreover, the electromagnetic contribution is relevant even for dense media, when in presence of interfaces, as exemplified for the in-plane conductivity of a nanosheet, which shows a variety of phenomena, including absence of a Fourier regime.