Dynamic Structure Factor of Electrons in Li by Inelastic Synchrotron X-Ray Scattering

The dynamic structure factor, $S(\overrightarrow{\mathrm{q}},\omega )$, of single-crystal Li exhibits a strong anisotropy of peak position and peak dispersion. For $q>\mathrm{}{q}_c$ ($q_c$ is the plasmon cutoff vector), at least the anisotropy of one peak position in $S(\overrightarrow{\mathrm{q}},\omega )$ can be attributed to zone-boundary collective states within the limits of a one-reciprocal-lattice-vector model. Therefore, the double-peak structure of $S(\overrightarrow{\mathrm{q}},\omega )$ for $q>\mathrm{}{q}_c$ seems not to be a universal property of the strongly correlated electron gas.