Intrinsic Plasmons In Two-Dimensional Dirac Materials

We consider theoretically, using the random phase approximation (RPA), low-energy intrinsic plasmons for two-dimensional (2D) systems obeying Dirac-like linear chiral dispersion with the chemical potential set precisely at the charge neutral Dirac point. The "intrinsic Dirac plasmon" energy has the characteristic root q dispersion in the 2D wave vector q, but vanishes as root T in temperature for both monolayer and bilayer graphene. The intrinsic plasmon becomes overdamped for a fixed q as T -> 0 since the level broadening (i.e., the decay of the plasmon into electron-hole pairs due to Landau damping) increases as 1/root T as temperature decreases, however, the plasmon mode remains well defined at any fixed T (no matter how small) as q -> 0. We find the intrinsic plasmon to be well defined as long as q < k(B)T/e(2). We give analytical results for low and high temperatures, and numerical RPA results for arbitrary temperatures, and consider both single- and double-layer intrinsic Dirac plasmons. We provide extensive comparison and contrast between intrinsic and extrinsic graphene plasmons, and critically discuss the prospects for experimentally observing intrinsic Dirac point graphene plasmons.