New experimental results on the transport behavior of electrons in dense helium gas at liquid-helium temperatures are presented. These include accurate measurements of the initial deviation of the mobility from the classical Boltzmann behavior as the density is increased and a complete characterization of the hotelectron behavior through the localization transition. The initial deviations at these temperatures are found to be of the same form as those observed in previous high-temperature studies, and a universal relationship is proposed. Contrary to an assumption that has often been made, there appears to be no reason to consider the initial deviation and the localization transition as distinct phenomena. A comparison with the percolation model of Eggarter and Cohen yields surprisingly good agreement over the whole range of densities and temperature. The role played by the helium-gas problem in the field of disordered materials is discussed, and possibilities for further theoretical progress are pointed out.

• Received 20 July 1979

DOI:https://doi.org/10.1103/PhysRevB.21.5125