Low-temperature magnetoresistance in fully-doped polyacetylene with disorder

Summary form only given. The electrical conductivity of the doped polyacetylene has been improved dramatically by recent synthesis [1]. It is worthwhile to revisit the physical properties with this new polyacetylene. We have taken up fully I/sub 2/-doped and FeCl/sub 3/-doped polyacetylene to get metallic conduction even at low temperature. We found, however, that the highly conductive fully doped polyacetylene changed from metallic to nonmetallic by room-temperature aging due to Anderson localization. For this change, low temperature magnetoresistance changed from negative to positive on crossing the transition. The field dependences of the resistance are qualitatively different for the I/sub 2/-doped and the FeCl/sub 3/-doped. The results are successfully explained in terms of the magnetic field effect to the hopping conduction among Anderson-localized states with Coulomb correlation. The difference by the dopant species is ascribed to the depth of the Fermi energy from the mobility edge. The temperature and magnetic field dependences found in the fully doped case are distinguished from lightly doped case characterized by the Coulomb gap.