Quantum plasmons with optical-range frequencies in doped few-layer graphene

Abstract

Although plasmon modes exist in doped graphene, the limited range of doping achieved by gating restricts the plasmon frequencies to a range that does not include the visible and infrared. Here we show, through the use of first-principles calculations, that the high levels of doping achieved by lithium intercalation in bilayer and trilayer graphene shift the plasmon frequencies into the visible range. To obtain physically meaningful results, we introduce a correction of the effect of plasmon interaction across the vacuum separating periodic images of the doped graphene layers, consisting of transparent boundary conditions in the direction perpendicular to the layers; this represents a significant improvement over the exact Coulomb cutoff technique employed in earlier works. The resulting plasmon modes are due to local field effects and the nonlocal response of the material to external electromagnetic fields, requiring a fully quantum mechanical treatment. We describe the features of these quantum plasmons, including the dispersion relation, losses, and field localization. Our findings point to a strategy for fine-tuning the plasmon frequencies in graphene and other two-dimensional materials.

Dynamics and Spin-Valley Locking Effects in Monolayer Transition Metal Dichalcogenides

“…Finally, we investigate the energy distributions of carriers that are excited upon optical absorption in these materials, accounting for both direct and phonon-assisted transitions using our previously established first-principles methodology. [40][41][42][43][44][45][46][47] Fig. 5 show that direct transitions dominate carrier generation in all these materials, as expected for direct gap semiconductors where the band gap and optical gap are equal so that direct transitions are always allowed.…”

Universal behavior of a dispersive Dirac cone in gradient-index plasmonic metamaterials

“…In particular, graphene is a rather special 2D plasmonic material exhibiting ultrasubwavelength plasmons, and a high density of free carriers which is controllable by chemical doping or bias voltage 21,[23][24][25] . An important finding is that the ENZ behavior introduced by subwavelength plasmons is characterized by the presence of dispersive Dirac cones in wavenumber space [2][3][4][5] .…”

Graphene epsilon-near-zero plasmonic crystals

“…where E F is the Fermi level associating with the density of electric carriers and corresponding to the electronic doping; the E F can be dynamically tuned by an external gate field or can be fixed by chemical deposition or intercalation [5,20,25]. The electron charge is denoted by e, ℏ is the reduced Planck constant, and τ is electronic relation time accounting for optical losses with a typically value of τ = 0.5 ps.…”

“…Graphene is a quite interesting material because it allows control of electronic and, in turn, plasmonic properties by changing the density of the free charge carriers through an external gate field, chemical deposition, or intercalation [5,20,25]. It has been shown that graphene plasmonic crystals can serve as an ingredient in a tunable metamaterial [15,17,23].…”