Direct Observation of Low-Energy Sm Phonon in SmRu₄P₁₂

Abstract

Measurements of S ( Q ,ω) of the filled skutterudite SmRu 4 P 12 using inelastic x-ray scattering show a dispersionless mode at 9 meV. Meanwhile, the Sm partial phonon density of states measured by nuclear resonant inelastic scattering shows a strong peak at the same energy. The temperature dependence of the Sm phonon energy suggests that the Sm modes are anharmonic. The comparison of the experimental results in SmRu 4 P 12 with the calculated ones in LaRu 4 P 12 indicates the absence of any significant lattice instability due to 4f electrons.