Linear high-field magnetoconductivity of doped polyacetylene up to 30 tesla

We have studied the high-field (up to H=30 T) magnetoconductivity (Δσ(H)/σ(0)=[σ(H)-σ(0)]/ σ(0)) of highly conducting polyacetylene films heavily doped with Cl₄^-, FeCl₄^-, and iodine at the temperature range 0.6-1.4 K. At relatively low fields, their field dependence is different from each other according to the specific properties of the dopant with which the spin state of conduction electrons are coupled. In the high-field region, however, the magnetoconductivity is linearly dependent on the magnetic field irrespective of the type of dopants. The change from the low field Δσ(H)/σ(0)∝H^1/2 to the high field Δσ-(H)/σ-(0)∝H as well as the effect of dopants is attributed to the competition between the magnetic length L_H and the dopant-specific length scales, both of which are relevant to the delocalization under the magnetic field. The origin of linear dependence of magnetoconductivity at high fields is also discussed.