  The quasiparticle dynamics of the sheet plasmons in epitaxially grown
graphene layers on SiC(0001) have been studied systematically as a function of
temperature, intrinsic defects, influence of multilayers and carrier density.
The opening of the inter-band loss channel appears as a characteristic upward
shift in the plasmon dispersion and a dip in the width of the loss peak, which
is explained as a resonance effect in the formation of electron-hole pairs.
Despite the existence of strong electronic correlations, the plasmon dispersion
can be quantitatively described within the framework of a nearly free electron
gas.
