Phonon Linewidth in Twisted Bilayer Graphene

In a perfect crystal, the phonon linewidth is primarily determined by electron-phonon and phonon-phonon interactions. We have computed phonon lifetimes in twisted bilayer graphene as a function of twist angle, doping and temperature. Phonon modes are calculated using classical force fields and the electronic band structure using an atomistic tight-binding model. We use mode projected velocity autocorrelation functions for calculating the phonon-phonon contribution to the linewidth. This approach includes three, four and higher phonon-phonon interactions (up to all orders). The electron-phonon contribution to the phonon linewidth is calculated within the Migdal approximation. We provide estimates of the phonon linewidths that can be observed under experimental conditions in these systems.