Plasmon-Fano resonance inside the particle-hole excitation spectrum of simple metals and semiconductors

It is shown that local-field effects in simple metals and semiconductors couple the plasmon into the large-wave-vector q particle-hole excitation spectrum, leading to a plasmon antiresonance (plasmon-Fano resonance). The resulting structure is observed in inelastic X-ray scattering spectroscopy (IXSS) of single-crystal Si for scattering vectors q along the < 111 > direction. The inclusion of exchange and correlation effects is important to obtain good agreement between theory and experiment. Previously unexplained structures in the IXSS of single-crystal Li for q along the < 110 > direction and of single-crystal beryllium for q along < 100 > and < 001 > are also identified as plasmon-Fano resonances.