Local-field effects and anisotropic plasmon dispersion in diamond

We have measured the plasmon dispersion of diamond along the high-symmetry directions using electron energy-loss spectroscopy in transmission. We found the plasmon dispersion to be considerably anisotropic. A comparison of the experimental results to ab initio calculations that take local-field effects into account demonstrates the importance of local-field effects for the dielectric response of systems with strongly inhomogeneous electron distributions.