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.