Strong four-phonon scattering in monolayer and hydrogenated bilayer BAs with horizontal mirror symmetry

Recently, the important role of high-order anharmonic phonon–phonon interactions has been revealed in several materials, such as cubic boron arsenide (BAs), in which the wide phononic energy gap is found to be a critical factor causing the importance of four-phonon scattering. In this work, by solving the Boltzmann transport equation, we show that the four-phonon scattering has a significant impact on the thermal transport in honeycomb structured monolayer BAs (m-BAs) and its hydrogenated bilayer counterparts (bi-BAs). The lattice thermal conductivity (κL) values of all these structures are reduced after considering four-phonon scattering. Particularly, a huge drop in κL as large as 80% is observed for m-BAs compared to the case without four-phonon scattering, which is mainly caused by the suppression of phonon lifetimes. More interestingly, as opposed to the case of graphene, κL of m-BAs is abnormally lower than its bi-BAs counterparts, which is attributed to the much larger phonon scattering rate in m-BAs compared to that in bi-BAs. By further comparing BAs sheets with and without horizontal mirror symmetry, it is found that the contribution of flexural acoustic phonon exhibits most significant reduction in both mi-BAs and bi-BAs with horizontal mirror symmetry after including four-phonon scattering. This work provides physical understanding of the role of mirror symmetry and high-order phonon scattering on the thermal transport in two-dimensional materials.