The Boltzmann transport equation based on third-order anharmonic scattering is widely used to predict the thermal conductivity of material lattices, often obtaining results that agree with experimental measurements. 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) [Fig. 1(d)]. 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 m-BAs and bi-BAs with horizontal mirror symmetry after including four-phonon scattering (from 24% to 2% for m-BAs and from 21% to 6% for bi-BAs in AA stacks). At the same time, this phenomenon was not significant in AB stacks lacking horizontal mirror symmetry (from 7% to 4%).
Cuiqian Yu, a doctoral student at Tongji University, is the first author of this paper, and Professor Jie Chen of Tongji University and Professor Dengfeng Li of Chongqing University of Posts and Telecommunications are co-corresponding authors. This work provides physical understanding of the role of mirror symmetry and high-order phonon scattering on the thermal transport in two-dimensional materials.
FIG. 1. Top (upper panel) and side (lower panel) views of optimized structures for (a)m-BAs, (b) bi-BAs-AA, and (c) bi-BAs-AB.(d) κL as a function of temperature for m-BAs, bi-BAs-AA, and bi-Bas-AB. The solid lines represent the calculated κL considering only three-phonon scattering, while the dash-dot lines give the calculated κL considering both three-phonon and four-phonon scatterings
Title: Strong four-phonon scattering in monolayer and hydrogenated bilayer BAs with horizontal mirror symmetry
