The Dynamic Structure Factor of LiC6 and KC8 : Inelastic Synchrotron X-Ray Scattering Results

Abstract

Abstract The dynamic structure factor S(q, ω) of electrons in lithium-intercalated graphite (LiC6) and potassium-intercalated graphite (KC8) for momentum transfer q || c-axis has been measured by inelastic synchrotron X-ray scattering. The dielectric function ε(q, ω) was deduced from the data and compared with ε(q, ω) of pristine graphite.The main feature in the different Im [ε(q, ω)]-spectra, a more or less intense peak around 14 eV, can be assigned to maxima of the symmetry-projected joint density of occupied and unoccupied electron states near the Fermi level. Knowing the position of the occupied bands by photoemission experiments, predictions about the unoccupied π and interlayer states can be made.In the case of LiC6 , a shift and broadening of the first Im [ε(q, ω)]-peak was found, which can be explained by a decrease of the energy of the interlayer-band because of the strong hybridization of this graphite-derived band with the Li metal 2s-band.In the case of KC8 , a weakening of the first peak of Im [ε(q, ω)] was observed, which we attribute both to a decreasing overlap of the occupied s-derived state with the empty interlayer state and to a change of symmetry of the occupied π-derived states as well as of the empty rc-derived states.