Presence of an Incipient Wigner Electron Lattice in Solid-State Electron Gases

In x-ray studies of the dynamic structure factor $S(k, \omega )$ in Be, graphite, and Al a new type of excitation spectrum is observed for momentum transfers $k$ between $k_{\mathrm{F}}$ and $2k_{\mathrm{F}}$. The similarity of the observed spectra in these systems, when scaled according to electron-gas parameters, strongly indicates that the new excitation is a property of a solid-state electron gas and not a one-electron band-structure effect.