Fig. 5. Phonon lifetimes due to anharmonic phonon–phonon scattering for bulk and monolayer systems.

Phonon lifetimes through the Brillouin zones for all polarizations and propagation directions at room temperature in a MoS₂ and b h-BN. For h-BN, phonon lifetimes are truncated at 15 THz. Lifetimes over the entire frequency range are shown in Supplementary Fig. 16. Low-frequency plot (log-log) showing temperature dependences of lifetimes for cross-plane LA phonons in c MoS₂ and d h-BN from anharmonic scattering (dashed curves, η = 0) and from the sum of anharmonic scattering and surface losses (solid curves, η = 0.13). η is the root mean square variation of the surface height (i.e., rms roughness in nanometers).