Zero-sound-like modes in simple liquid metals

Onset of transverse (shear) waves in strongly-coupled Yukawa fluids

A simple practical approach to describe transverse (shear) waves in strongly-coupled Yukawa fluids is presented. Theoretical dispersion curves, based on hydrodynamic consideration, are shown to compare favorably with existing numerical results for plasma-related systems in the long-wavelength regime. The existence of a minimum wave number below which shear waves cannot propagate and its magnitude are properly accounted in the approach. The relevance of the approach beyond plasma-related Yukawa fluids is demonstrated by using experimental data on transverse excitations in liquid metals Fe, Cu, and Zn, obtained from inelastic x-ray scattering. Some potentially important relations, scalings, and quasi-universalities are discussed. The results should be interesting for a broad community in chemical physics, materials physics, physics of fluids and glassy state, complex (dusty) plasmas, and soft matter.

State dependent particle dynamics in liquid alkali metals

This paper gives a survey of the particle dynamics in the liquid alkali metals observed with inelastic x-ray and neutron scattering experiments. Liquid rubidium and sodium are chosen as model fluids to represent the behaviour of this group of fluids. In the dense metallic monatomic melt the microscopic dynamics is characterized by collective excitations similar to those in the corresponding solids. The collective particle behaviour is appropriately described using a memory function formalism with two relaxation channels for the density correlation. A similar behaviour is found for the single particle motion where again two relaxation mechanisms are needed to accurately reproduce the experimental findings. Special emphasis is given to the density dependence of the particle dynamics. An interesting issue in liquid metals is the metal to non-metal transition, which is observed if the fluid is sufficiently expanded with increasing temperature and pressure. This causes distinct variations in the interparticle interactions, which feed back onto the motional behaviour. The associated variations in structure and dynamics are reflected in the shape of the scattering laws. The experimentally observed features are discussed and compared with simple models and with the results from computer simulations.

Collective dynamics in liquid lead: generalized propagating excitations

A microscopic approach to the investigation of generalized collective excitations, developed recently for pure liquids, is applied to the study of the spectrum of collective excitations in a liquid metal. The calculations are performed for liquid lead at two temperatures (above the melting point and in high-temperature region) and the results are compared. From the analysis of spectra, obtained for different basis sets of dynamical variables, we conclude that there exist three branches of propagating collective excitations, which correspond to sound and heat (high- and low-frequency) waves in the liquid. It is shown that the branch of low-frequency heat waves contains a propagation gap in the hydrodynamic region. An analytical expression for the width of the propagation gap for low-frequency heat waves is derived.