Dielectric function and plasmon structure of stage-1 intercalated graphite

Abstract

In this paper, we carefully study the dielectric function of stage-1, acceptor-type graphite intercalated compounds (GIC’s). We model the system by a superlattice of an infinite number of graphite layers, each of which has the band structure described by the two-dimensional calculation of Blinowski et al. Tunneling between graphite layers is neglected, and so are effects due to intercalants except that of determining the Fermi level. However, we have retained a Coulomb term that describes the interaction between electrons on different layers. With this model, we are able to express the result in analytical form, and our treatment is essentially exact. Because of the Coulomb interaction along the c axis, the excitation spectrum has a plasmon band in the (q,ω) plane, where q is the in-plane momentum transfer and ω the energy transfer. This plasmon band is typical for the superlattice structure and contains a three-dimensional mode. We find that, despite the presence of a complicated band structure in GIC’s, the three-dimensional characteristics of the plasmons still dominate. A quantitative comparison of plasmon structure between our theory and electron scattering experiments is made in this work. We obtain reasonable agreements between our theory and the measurement, concerning the plasmon energy, the plasmon width, and the plasmon intensity. The agreement suggests that our dielectric function is reliable in describing the dynamic screening mechanism for GIC’s.