THE METAL-INSULATOR TRANSITION AND SUPERCONDUCTIVITY IN AMORPHOUS MOLYBDENUM-GERMANIUM ALLOYS (LOCALIZATION, ELECTRON INTERACTION, SCALING THEORY, SPUTTERING, RANDOM POTENTIAL)

The electrical and thermodynamic properties of amorphous molybdenum-germanium alloys in three dimensions have been studied as a function of composition as well as temperature. Homogeneous amorphous molybdenum-germanium films have been synthesized over a wide compositional range by co-sputtering from pure molybdenum (Mo) and pure germanium (Ge) targets. The physical properties of the films have been investigated by electrical conductivity, tunneling, magnetoresistance, low-temperature specific heat measurements, and superconductivity. Experimental results have been analyzed by the recent theories of localization and electron interaction.; The results from the electrical conductivity extrapolate to a metal-insulator (M-I) transition near 10 atomic percent (at%) Mo. The extrapolated zero temperature conductivity is a continuous function of concentration on the metallic side.; The tunneling conductance shows an anomalous behavior in the single-particle density of states near the Fermi level due to the electron interaction near the M-I transition.; The specific heat measurements show that the thermodynamic density of states is continuous and finite at the M-I transition, in direct contrast to the single-particle density of states which goes to zero at the M-I transition. Since the thermodynamic density of states, which is a relevant parameter in the electrical conductivity, is finite, it is shown experimentally that the M-I transition is driven by a vanishing electron diffusion constant.; Magnetoresistance (MR) increases at larger Ge concentrations and at lower temperatures. The positive and H(' 1/2)-dependent MR of metallic samples at high fields is consistent with electron interaction theory. However, the MR behaviors of insulating samples are not well explained by current theories.; The behavior of superconducting transition temperature T(,c) as a function of concentration can be correlated with the structural results of Kortright. The upper critical fields H(,c2) in the Mo-rich region show the enhancement of H(,c2) above the Werthamer-Helfand-Hohenberg-Maki (WHHM) theory, which is predicted by the renormalization of the Coulomb interaction due to effects of weak localization. However, H(,c2) near the M-I transition shows a behavior below the WHHM fit, which has not been predicted by strong localization theories.