Inelastic neutron scattering from intermediate-valence compounds in the quasiparticle approximation

We investigate the dynamic structure factor characterizing inelastic neutron scattering from intermediate-valence compounds. Starting with the ionic model of Jefferson and Stevens, we formulate a quasiparticle theory for the high-frequency scattering. At low temperatures the scattering at the center of the zone arises from three processes: excitation across the hybridization gap, excitation from gap modes, which do not hybridize with the conduction electrons to the upper hybrid mode, and excitation from the lower hybrid mode to the gap modes. We calculate the structure factor at $q=0\mathrm{}$, neglecting crystal-field splittings. The qualitative features of the temperature and wave-vector dependence of the scattering are discussed. An alternative approach based on a decoupled-mode approximation is proposed for the high-temperature regime. We comment on the relation of the theory to recent theoretical and experimental studies.