Plasmon electron-hole resonance in epitaxial graphene.

The quasiparticle dynamics of the sheet plasmons in epitaxially grown graphene layers on SiC(0001) has been studied systematically as a function of temperature, intrinsic defects, influence of multilayers and carrier density using electron energy loss spectroscopy with high energy and momentum resolution. The opening of an inter-band decay channel appears as an anomalous kink in the plasmon dispersion which we describe as a resonance effect in the formation of electron-hole pairs. Due to the inevitable strong coupling of plasmons with single particle excitations in reduced dimensions, such signatures are generally expected.