Brillouin scattering on intermediate valent Sm _{1 − x} Tm _x S

Abstract

On Tm doped cubic SmS crystals surface acoustic waves have been measured using inelastic light scattering (Brillouin scattering). The angular dispersion of the velocity of the surface acoustic phonons in the (100)-oriented plane allowed to calculate the whole tensor elastic constants and Poisson's ratio. Depending on the doping concentration C12 and the Poisson's ratio turn out to become negative, which is a typical intermediate valent behaviour and can be explained by the special electronic structure of these compounds.