We compare experimental resistivity data on Ga1-xMnxAs films with theoretical calculations using a scaling theory for strongly disordered ferromagnets. The characteristic features of the temperature dependent resistivity can be quantitatively understood through this approach as originating from the close vicinity of the metal-insulator transition. However, accounting for thermal fluctuations is crucial for a quantitative description of the magnetic field induced changes in resistance. While the noninteracting scaling theory is in reasonable agreement with the data, we find clear evidence for interaction effects at low temperatures.

Scanning tunneling microscopy (STM) has recently been used in the study of bulk arsenic antisite defects in GaAs. In this work, we report extensive theoretical calculations of such defects in the vicinity of a GaAs(110) surface, which provide essential information for the interpretation of experiments. Defects display remarkably distinct properties depending on whether they are fourfold or threefold coordinated. The nature of “satellite peaks” observed in experiment is elucidated. We predict the conditions under which STM-measured properties will be faithful to the properties of the bulk defect.

Recent advances in our understanding of electronic conduction have pointed up deficiencies in traditional thinking. For a metal at a sufficiently low temperature, it is known both theoretically and experimentally that the conventional picture in terms of the Boltzmann theory breaks down. Improved understanding of both electron localization and the effects of electron-electron interactions in a disordered medium has led to experimentally verifiable predictions. These effects have an important influence on the nature of the metal-insulator transition.

Interaction effects in disordered Fermi systems are considered in the metallic regime. In two dimensions, logarithmic corrections are obtained for conductivity, density of states, specific heat, and Hall constant. These results are compared with a recent theory of localization as well as some experiments.

Arguments are presented that the T=0 conductance G of a disordered electronic system depends on its length scale L in a universal manner. Asymptotic forms are obtained for the scaling function β(G)=dlnG / dlnL, valid for both G≪Gc≃e2 / ℏ and G≫Gc. In three dimensions, Gc is an unstable fixed point. In two dimensions, there is no true metallic behavior; the conductance crosses over smoothly from logarithmic or slower to exponential decrease with L.