Electrons in fluids: the role of disorder

Abstract

I review the present status of the theory of those aspects of the theory of disordered materials which are particularly relevant to the physics of electrons in fluids. First, however, I describe a general theory of the movement of slow electrons in fluids of arbitrary complexity in which the fluid is treated as a fluctuating medium. Coupling to the fluctuations is via a set of generalized deformation potentials. It is shown that this concept permits a way out of the impasse that has been reached in understanding the mobility of slow electrons in liquid argon via Lekner's theory. Assuming that molecular motion can be neglected on the electronic time scale permits taking over various relevant results from the theory of electrons in disordered solids, which is briefly reviewed. The effect of molecular motion is studied next. It is shown that strict localization does not occur and that the quasi-localized electrons diffuse with a characteristic correlation frequency depending on electron–molecule coupling and upon the characteristic frequencies of molecular motion as well as with a correlation length related to the localization length in static problems. Under easily reached conditions, this diffusion process is faster than that giving rise to the Stokes law mobility. Finally, a discussion is given of mobility transitions in which localization by disorder is distinguished from self-trapping.