Microscopic dynamics in liquid metals: The experimental point of view

The experimental results relevant for the understanding of the microscopic dynamics in liquid metals are reviewed, with special regard to the ones achieved in the last two decades. Inelastic neutron scattering played a major role since the development of neutron facilities in the 1960s. The last ten years, however, saw the development of third generation radiation sources, which opened the possibility of performing inelastic scattering with x rays, thus disclosing previously unaccessible energy-momentum regions. The purely coherent response of x rays, moreover, combined with the mixed coherent or incoherent response typical of neutron scattering, provides enormous potentialities to disentangle aspects related to the collectivity of motion from the single-particle dynamics. If the last 20 years saw major experimental developments, on the theoretical side fresh ideas came up to the side of the most traditional and established theories. Beside the raw experimental results therefore models and theoretical approaches are reviewed for the description of microscopic dynamics over different length scales, from the hydrodynamic region down to the single-particle regime, walking the perilous and sometimes uncharted path of the generalized hydrodynamics extension. Approaches peculiar of conductive systems, based on the ionic plasma theory, are also considered, as well as kinetic and mode coupling theory applied to hard-sphere systems, which turn out to mimic with remarkable detail the atomic dynamics of liquid metals. Finally, cutting edge issues and open problems, such as the ultimate origin of the anomalous acoustic dispersion or the relevance of transport properties of a conductive system in ruling the ionic dynamic structure factor, are discussed.