Phonon renormalization and four-phonon scattering in semiconductors and insulators*

In semiconductors and insulators, heat is carried by phonons. Conventional ab initio methods for thermal conductivity (k) of materials assume that the lowest order theory of 3-phonon scattering sufficiently describes thermal transport. Here we show that this is not the case for several materials where higher-order 4-phonon scattering can significantly affect k. Furthermore, we show that for many naturally occurring materials, phonon scattering is so strong that not only is 4-phonon scattering important, but the underlying phonon quasiparticle picture itself can break down. To address this issue, we present a novel ab initio method that features an anharmonic many-body renormalization scheme to create well-defined phonon quasiparticles with weakened interactions, and includes both 3-phonon and 4-phonon scattering to obtain k [1]. We demonstrate the method’s success by comparing with experimental data of k for many common semiconductors and insulators. Our work presents a unified ab initio framework to accurately predict the thermal properties of solids with varying bond strengths.

[1] N. K. Ravichandran and D. Broido, Phys. Rev. B. 98, 085205, 2018.