Metal-insulator transition in expanded alkali-metal fluids and alkali-metal—rare-gas films

Abstract

We have developed a theoretical model for expanded alkali metals and alkali-metal---rare-gas films that is based on a physically realistic picture of the atomic-scale structure of these materials. It emphasizes the disorder in the systems, in particular the random atomic coordination number. Using this model we have calculated the density- and the energy-dependent conductivity as a function of the mean alkali-metal atomic coordination number. Although the theory contains only two parameters, both of which are fixed by the properties of pure materials at normal temperatures, we have been able to explain results measured over a temprature range from 4.2 to >2000 K in a variety of different alkali-metal systems. Conductivity and magnetic-susceptibility measurements, in particular, have been considered in some detail. In addition, the theory provides insight into the nature and location of the metal-insulator transition, the nature of the critical point for the alkali metals, and the thermal instability of the alkali-metal---rare-gas films.