Lattice dynamics of mixed-valent SmS

Neutron scattering techniques have been used to measure the phonon dispersion curves for SmS in both the semiconducting and the metallic mixed-valent state. Large softening of the longitudinal acoustic phonon branches was found in the mixed-valent state, particularly for the [111] direction. It is apparent there is a strong coupling between the valence fluctuations and the phonons in the mixed-valent phase of SmS. © 1982 The American Physical Society.