Inelastic X-ray scattering study of the collective dynamics in simple liquid metals

The collective dynamics of the so-called `simple' liquids (in particular, liquid metals) are a good paradigm to illustrate the capabilities of inelastic X-ray scattering (IXS). In particular, it is shown how the present accuracy of the data can be exploited to provide not only a precise determination of the main spectral features (dispersion relations), but also a clue for the physical assessment of the microscopic relaxation mechanisms underlying the dynamics of the liquid state. Starting from new IXS data on liquid sodium as an example, we apply a generalized hydrodynamic framework in order to describe the details of the experimental lineshapes. A comparison with recent data on liquid lithium and aluminium is also reported: although quantitative differences indicate that the principle of corresponding states seems not to be applicable, in all these systems a simple viscoelastic approach turns out to be inadequate to reproduce the experimental data.