Possibility of acoustic plasmons in mixed-valence metals and their interaction with phonons

Abstract

Mixed-valence metals are characterized by the presence of both the very heavy $f$ and the light $s-d$ electrons near the Fermi surface. These conditions are propitious for the existence of the plasmon branch with acoustic character. We derive the dispersion relation for such modes and consider their interaction with the phonons of the lattice. The longitudinal sound velocity is shown to be strongly reduced by the interaction, as is experimentally observed. We propose that ultrasonic experiments be used to directly observe the acoustic plasmons.