CURRENT EXPERIMENTAL STATUS OF DYNAMICS IN SOLIDS

We review the experimental status of the study of dynamics of atoms an d molecules in solids, focussing mainly on the interplay between neutr on inelastic scattering experiments and theoretical models for the dyn amics of complex crystals. Particular references are made to studies o n C60 and the high temperature superconductors. Besides the investigat ions of phonon dispersion relation using neutron reactors, we also cit e examples of recent efforts using pulse neutron sources and X-rays fr om synchrotrons. While single crystals are needed for the determinatio n of dispersion relation, powder samples are used to obtain the phonon density of states. Partial density of states corresponding to specifi c atoms is obtained by their isotopic substitution. We briefly touch u pon dynamical phenomena other than that described by phonons, such as diffusion of molecular reorientation, which may be studied by techniqu es such as computer experiments or neutron quasielastic scattering.