Anisotropy and Interplane Interactions in the Dielectric Response of Graphite

Abstract

We determined the anisotropic dielectric response of graphite by means of time-dependent density-functional theory and high-resolution valence electron energy-loss spectroscopy. The calculated loss function was in very good agreement with the experiment for a wide range of momentum-transfer orientations with respect to the graphitic basal planes, provided that local-field effects were included in the response. The calculations also showed strong effects of the interlayer Coulomb interaction on the total pi+sigma plasmon. This finding must be taken into account for the explanation of recent loss spectra of carbon nanotube materials.

Ultrafast Multiphoton Thermionic Photoemission from Graphite

“…Therefore, the minimum in the density of states (DOS) of graphene and graphite at the Fermi level makes the screening weak and prone to modification by carrier doping through photonic, electrical, or chemical stimulation [29,34]. Another feature owing to the 2D character of graphene and graphite is that Coulomb interaction with small momentum transfers is unscreened [25,35,36]. When photoexcitation and subsequent carrier multiplication suddenly raise the free carrier density above the unperturbed value, a new regime of screening with three-dimensional (3D) character can come about in graphite on a time scale of the inverse frequency of the photoexcited plasma [37,38].…”

“…Moreover, strong modulation of the carrier density through ultrafast optical excitation and the ensuing hot carrier multiplication drives the electron and hole distributions to different chemical potentials, enabling applications in energy harvesting, ultrafast electronics, and coherent optics [1,3,[16][17][18][19][20]. These novel properties derive from graphene's Dirac fermion band structure, weak screening, and strong, moleculelike electron correlation [21][22][23][24][25][26][27][28][29][30][31], which distinguish it from conventional metals and semiconductors [22,32,33].…”

“…Immediately following the excitation, ineffective screening causes the primary distribution to undergo rapid energy and momentum redistribution through e-e and e-p scattering [21,25,61,62]. Electron energy relaxation occurs through Coulomb interaction where two electrons scatter into two unoccupied hole states in a process that conserves both energy and momentum [22,[63][64][65].…”

High-energy collective electronic excitations in layered transition-metal dichalcogenides

“…The only collective excitation involving solely π states in TMD is hence the intraband plasmon originating from the Nb d z orbital [20]. The anisotropy in the dielectric function is also clearly visible when LFE are taken into account [41] since the induced charge is specially more homogeneous in the plane of the layers than in the direction perpendicular to them. In fact, we find that LFE are almost negligible for in-plane 2 , where the π -σ * peak is strongly suppressed and blueshifted towards the plasmon energy.…”

“…7(a)] the first peak is suppressed and the oscillator strength is transferred to higher-energy interband transitions between 4.7 and 5.5 eV, which involve mainly π and σ * bands. Thus, like in graphite [41], π -π * and σ -σ * transitions dominate the optical spectrum for in-plane Q, while for out-ofplane Q the main contribution comes from π -σ * transitions. The main difference with graphite is that in this case, since π and σ bands overlap between them, σ -σ * and π -σ * transitions are not completely separated and are very close to the π -π * ones.…”