Evidence for Interlayer Band Shifts upon Lithium Intercalation in Graphite from Inelastic X-Ray Scattering

The dielectric function $\epsilon (\mathbf{q},\omega )$ of Li-intercalated graphite (Li${\mathrm{C}}_6$) with $\mathbf{q}\parallel c$ axis was deduced from inelastic x-ray scattering data and compared with $\epsilon (\mathbf{q},\omega )$ of pristine graphite. A displacement and broadening of the first peak of $\mathrm{Im}\epsilon (\mathbf{q},\omega )$ upon intercalation was found, which we attribute to a 2-eV shift of the "metal" $\sigma$ state of Li${\mathrm{C}}_6$ to lower energies relative to the $\sigma$-type interlayer state of graphite.