Recent scattering-type scanning near-field optical spectroscopy (s-SNOM) experiments on single-layer graphene have reported Dirac plasmon lifetimes that are substantially shorter than the dc transport scattering time ${\tau }_{\mathrm{tr}}$. We argue that this discrepancy arises from the fact that the plasmon lifetime is fundamentally different from ${\tau }_{\mathrm{tr}}$ since it is controlled by the imaginary part of the current-current linear response function at finite momentum and frequency. Taking this into account, we show that a minimal theory of the extrinsic lifetime of Dirac plasmons due to scattering against charged impurities yields a plasmon damping rate which is in good agreement with s-SNOM experimental results.

• Received 31 July 2013

DOI:https://doi.org/10.1103/PhysRevB.88.121405