Unusually Strong Four-Phonon Scattering Effects on Low-Temperature Thermal Conductivity in Two-Dimensional Materials

TL;DR

This study reveals that four-phonon scattering significantly impacts low-temperature thermal conductivity in two-dimensional materials, especially due to out-of-plane acoustic phonons, and can be tuned via strain engineering.

Contribution

It uncovers unusually strong four-phonon processes at low temperatures in 2D materials and demonstrates their manipulation through strain engineering.

Findings

Strong four-phonon processes affect low-temperature thermal conductivity.

Out-of-plane acoustic phonons (ZA mode) are key to these effects.

Strain engineering can modulate four-phonon scattering and thermal conductivity.

Abstract

First principles-based predictions of lattice thermal conductivity (TC) from perturbation theory have achieved significant success. Usually, it only included three-phonon (3ph) scattering processes, only recently four-phonon (4ph) scattering processes were found to have a comparable impact as 3ph scattering at medium and high temperatures in various materials. While the influence of 4ph scattering on TC at low temperatures was generally believed to be insignificant. By combining the first-principles calculations, machine learning techniques, and Boltzmann transport equation (BTE), we find that there are unusually strong 4ph processes even in the low-frequency range of two-dimensional (2D) materials such as h-XN (X = B, Al, Ga), which have a remarkable influence on the low-temperature TC. Such strong 4ph processes originated from the out-of-plane acoustic (ZA) phonon mode of 2D materials. Furthermore, we find that the intensity of 4ph scattering and thus TC can be effectively manipulated by changing the dispersion of ZA phonon mode, which can be easily achieved through strain engineering. The present study provides new insights into low-temperature phonon transport and its manipulation in 2D materials.