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 density-functional perturbation calculations. There is excellent agreement between experiment and theory. We observe many phonon anomalies, in particular in the vicinity of the M point at the Brillouin-zone boundary, which are unique among the class of elements with hexagonal structure. Theoretical analysis provides evidence that they are not due to nesting effects but arise from a significant momentum dependence of the electron-phonon coupling matrix elements.