Anomalous lattice dynamics of ruthenium

The lattice dynamics of the transition metal ruthenium is investigated both by inelastic neutron-scattering experiments and by first-principles densit y-functional perturbation calculations. There is excellent agreement betwee n experiment and theory. We observe many phonon anomalies, in particular in the vicinity of the M point at the Brillouin-zone boundary, which are uniq ue among the class of elements with hexagonal structure. Theoretical analys is provides evidence that they are not due to nesting effects but arise fro m a significant momentum dependence of the electron-phonon coupling matrix elements.