LOW-TEMPERATURE MAGNETORESISTANCE OF IODINE-DOPED POLYACETYLENE IN METAL-NONMETAL TRANSITION REGION

Highly conductive heavily iodine-doped polyacetylene changes from meta llic to nonmetallic by room-temperature aging. For this change, thermo electric power varies little, suggesting that the transition is not as cribed to change in carrier concentration but to increase of the degre es of disorder. Corresponding to the transition, low temperature magne toresistance changes from negative to positive on crossing the transit ion. The magnetoresistance in the metallic region is interpreted in te rms of weak localization, while that in the nonmetallic state is expla ined by field effect to variable range hopping conduction among Anders on localization states. The transition to the nonmetallic state procee ds inhomogeneously.