Magnetic field–induced metal–insulator transitions in graphite and diluted magnetic semiconductors

Two topical subjects related with the effect of magnetic field on electrical conduction and the metal–insulator transition are discussed. The first topic is an electronic phase transition in graphite, which is interpreted as a manifestation of a nesting–type instability inherent to a one–dimensional narrow Landau sub–band. The second topic is spin–dependent tranport in III–V based diluted magnetic semiconductors; in particular, a large negative magnetoresistance observed in the vicinity of metal–non–metal transition.