Screening response of valence and core electrons in a metal: Inelastic x-ray scattering study

The screening response of valence and core electrons against a test charge embedded in a metal is investigated. The real space-and-time dynamical response function chi (r, t) is derived from the x-ray inelastic scattering spectra measured over a wide momentum and energy space on elementary Li. Embedding a charge initially induces local screening due to core electrons. This is followed by screening due to valence electrons, which exhibits an oscillatory behavior where the frequency is determined by the plasmon energy. Finally, static screening charges are produced. The static screening charge consists of a local electron cloud surrounding the embedded charge over several angstroms and the oscillatory charge densities have a periodicity twice that of the Fermi wave number in a larger r scale (i.e., the Friedel oscillation). The core electrons also exhibit an oscillatory behavior, where the frequency is determined by the absorption edge energy. This eventually leads to more local screening, further reducing the screening distance.