Four phonon-dominated near-field radiation in weakly anharmonic polar materials

TL;DR

This paper predicts that four-phonon scattering significantly enhances near-field radiative heat transfer in boron arsenide and boron antimonide, contrary to its usual role in reducing thermal conductivity, due to activation of numerous heat transfer channels.

Contribution

It reveals that four-phonon scattering dominates NFRHT in specific materials, leading to a substantial increase in heat flux, which is a novel insight compared to prior focus on three-phonon processes.

Findings

Four-phonon scattering increases heat flux by nearly 400 times in BAs films.

Four-phonon processes activate many NFRHT channels, overcoming reduced coupling effects.

Four-phonon scattering can decrease NFRHT in other systems.

Abstract

Inelastic scattering processes typically introduce friction among carriers and reduce the transport properties of photons, phonons, and electrons. However, we predict that in contrast to the role in reducing thermal conductivity, four-phonon scattering dominates near-field radiative heat transfer (NFRHT) in both boron arsenide~(BAs) and boron antimonide. Including four-phonon scattering results in a nearly 400-fold increase in the total heat flux between two BAs thin-films compared to three-phonon scattering alone. This non-intuitive enhancement arises from the large number of NFRHT channels activated by four-phonon scattering outcompete the effect of decreased coupling strength of surface phonon polaritons at the resonance frequency. Additionally, we point out that four-phonon scattering to decrease NFRHT in certain other systems.