Inelastic x-ray scattering study of collective electron excitations inMgB2

Abstract

We report an experimental inelastic x-ray scattering study of the collective electron excitations in $\mathrm{Mg}{\mathrm{B}}_{2}$. Single-crystal and polycrystalline samples were used to study the free-electron-like $(\ensuremath{\sim}20\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ plasmon and the recently theoretically predicted low energy $(\ensuremath{\sim}3\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ plasmon mode. We present the energy-loss spectra for several momentum transfer values and find that the excitations exhibit a strong directional dependence. We discuss the dispersion of collective excitations and find a good agreement between the experimental results and the published theoretical calculations. Some discrepancies between the experimental data and the calculations were observed, namely slightly differing excitation energies and momentum-transfer dependence. However, these discrepancies are the same order of magnitude as the uncertainties within the various computational methods.