Plasma excitations of dressed Dirac electrons in graphene layers

Abstract

Collective plasma excitations of optically dressed Dirac electrons in single and double graphene layers are calculated in the RPA. The presence of circularly polarized light gives rise to an energy gap Eg between the conduction and valence energy bands. Its value may be adjusted by varying the frequency and intensity of the light, and may reach values of the gap reported for epitaxially grown graphene and far exceeding that caused by spin-orbit coupling. We report plasmon dispersion relations for various energy gaps and separations between graphene layers. For a single graphene sheet, we find that plasmon modes may be excited for larger wave vector and frequency when subjected to light. For double layers, we obtained an optical and phononlike mode and found that the optical mode is not as sensitive as the phononlike mode in the long wavelength limit when the layer separation is varied, for a chosen Eg. The dressed electron plasma—although massive—still has Dirac origin, giving rise to anomalous plasmon behavior upon crossing the ω=ℏνFq cone.