Inequivalent effect of Dirac valleys on low‐energy plasmons in heavily doped graphene

Abstract

Using an empirical atomistic approach associated with the method of random‐phase approximation, we investigated the behaviors of plasmons in heavily doped graphene. We show that, in the range of low energy and of long wavelength, a novel plasmon mode may appear below the conventional Dirac plasmon. The novel mode is strongly anisotropic and only appears in a finite range of the transfer wave number. It is found that the appearance of the novel plasmon stems from the anisotropy of the energy surfaces forming the Dirac cones and the inequivalance of the two Dirac valleys in the Brillouin zone. Interestingly, we demonstrate that these two unique electronic features of graphene act, respectively, as the necessary and sufficient factors in governing the formation of the novel plasmon mode.