Dielectric function and plasmons in graphene

TL;DR

This paper investigates the dielectric response and plasmon spectrum of graphene using a full band structure approach, revealing dispersion characteristics, damping effects, and anisotropic behaviors as Fermi energy varies.

Contribution

It provides a comprehensive calculation of graphene's dielectric function and plasmon modes based on the full band structure, extending beyond the Dirac approximation.

Findings

Plasmon dispersion similar to Dirac fermion models

Stronger damping due to inter-band absorption

Anisotropic effects with increasing Fermi energy

Abstract

The electromagnetic response of graphene, expressed by the dielectric function, and the spectrum of collective excitations are studied as a function of wave vector and frequency. Our calculation is based on the full band structure, calculated within the tight-binding approximation. As a result, we find plasmons whose dispersion is similar to that obtained in the single-valley approximation by Dirac fermions. In contrast to the latter, however, we find a stronger damping of the plasmon modes due to inter-band absorption. Our calculation also reveals effects due to deviations from the linear Dirac spectrum as we increase the Fermi energy, indicating an anisotropic behavior with respect to the wave vector of the external electromagnetic field.