Plasmon Bands and Gaps in Metal Crystals

Abstract
We consider the influence of a periodic lattice upon the plasmon energy in a metal, by means of the equation of motion proposed by March and Tosi. The solution, within the random-phase approximation and for a weak periodic potential, shows the existence of two plasmon bands separated by a complex energy gap near the Brillouin zone border. This gap, due to plasmon Bragg diffraction, is rapidly quenched in presence of damping in simple metals. Group-IV metals and semiconductors should offer better chances for the observation of these "nearly-free-plasmon" bands near the Brillouin zone border.