Electron states in liquid metals: especially optical and magnetic properties

Abstract

The theory of optical absorption of the simple liquid metals (e.g. the alkalis) is outlined. At not too large frequencies, the Drude theory is regained. The relaxation time is that given by the weak scattering (Ziman) theory of electrical resistivity. For high frequencies, the relaxation time, however, becomes frequency dependent. Appreciable structure enters the theory, arising from collective excitations. The relation to recent ellipsometric measurements on liquid Na is briefly discussed. The optical conductivity and density of states in the divalent metals Hg and Be is then discussed, followed by the relation between photoemission and soft X-ray experiments and current electron theory. Specific attention is given to the evidence for a pseudo-gap in the divalent metals and to changes in the electron states which occur on melting the noble metals.The second major area treated is concerned with the magnetic properties of liquid metals. The theory of orbital and spin magnetism in simple liquid metals is reviewed and confronted with experiment. It is clear that the electron–electron enhancement effects have a dominant influence on the trend of the spin susceptibility of simple liquid metals as a function of density. However, electron–ion interactions must be introduced as corrections to the interacting electron gas values and in a metal like Li the nearly free electron theory fails to do this adequately. Knight shift results are summarized, and some attention is given to a recent experiment on the Knight shift of expanded fluid Hg. Difficulties for the theory in relation to transport and the pseudo-gap are pointed out. Finally, new theoretical calculations are reported on the relation between the magnetic properties of the liquid rare earth metals and their electrical conductivity. Mathiessen's rule is shown to break down because of very strong potential scattering. A recent theory of this by Parrinello et al. shows that in the strong scattering limit the magnitude of the localized spin carried by the rare earth ion drops out of the transport theory, as required by the experiments of Güntherodt et al.