HIGH-FIELD MAGNETOCONDUCTANCE IN ANDERSON INSULATORS

We report on high-held magnetoconductance measurements made on indium- oxide films as a function of temperature and static disorder. Special emphasis is given to the strong-localization regime when the magnetoco nductance reveals a negative contribution associated with a spin-align ment mechanism in addition to the positive contribution associated wit h orbital, quantum-coherence effects. While the overall features of th e theoretically expected effects are observed in our experiments, they depart in certain ways from the detailed predictions. We discuss the merits and shortcomings of current models to describe them, in particu lar, as they apply to the regime where the localized wave functions be come larger than the Bohr radius. The main results of this paper are b oth quantum interference and spin effects contribute to the magnetocon ductance throughout the entire range studied. In the limit of very str ong disorder, the quantum interference effects are faithfully describe d by the Nguyen et al. model. The spin effects, on the other hand, sho w only qualitative agreement with current models which are unable to a ccount for the saturation field being insensitive to changes in disord er.