Probing the Coulomb interaction of PuCoGa5 by phonon spectroscopy

The phonon dispersion curves of the unconventional superconductor PuCoGa5 were studied by inelastic X-ray scattering at room temperature. The experimental data agree well with ab initio   lattice dynamics calculations. An accurate theoretical description of the phonon spectrum is obtained only when a local Coulomb repulsion U≈3U≈3  eV among 5f electrons is taken into account. This implies partial localization of the 5f electrons in this compound. A comparison made with the phonon spectrum of UCoGa5 suggests that the latter compound is better described with a fully itinerant f electrons model.