Origin of plasmon damping in pristine graphene

The physical origin and the fundamental limits of plasmonic losses in graphene is a problem that attracted much attention. Recent near-field experiments have provided a key input for solving it, namely, the temperature dependence of the losses. We identify electron-phonon coupling through pseudomagnetic field as the dominant mechanism that limits the frequency-dependent transport scattering rate of Dirac electrons and therefore plasmon damping. We calculate scattering rate due to two types of phonons, the acoustic and the A^′₁ zone-boundary ones. The former induces intravalley scattering. It dominates at low temperatures and has a weak frequency dependence. The latter causes intervalley scattering of Dirac electrons. It has an activated dependence on temperature, an exponential dependence on plasmon frequency, and it becomes dominant at room temperature. We also consider additional small contributions from electron-electron scattering. Previously studied electron-phonon coupling due to deformation potential is shown to be negligible. Our theoretical results are in quantitative agreement with the experiments.