MAGNETIC-FIELD-INDUCED METAL-INSULATOR TRANSITIONS IN GRAPHITE AND DILUTED MAGNETIC SEMICONDUCTORS

Two topical subjects related with the effect of magnetic held on elect rical conduction and the metal-insulator transition are discussed. The first topic is an electronic phase transition in graphite, which is i nterpreted as a manifestation of a nesting-type instability inherent t o a one-dimensional narrow Landau sub-band. The second topic is spin-d ependent tranport in III-V based diluted magnetic semiconductors; in p articular, a large negative magnetoresistance observed in the vicinity of metal-nonmetal transition.