Metallic states of PF6-doped polypyrroles at low temperature

The electrical resistivity of conducting PF6-doped polypyrroles exhibiting resistance maximum near 15 K was measured down to 1 mK. The thermoelectric power was almost proportional to temperature, while ESR measurements exhibited temperature-independent paramagnetic spin concentration of the order of 1.1×1021 per mole of pyrrole rings. We propose a conduction model in relation to the spin concentration. The resistance maximum may be ascribed to crossover from hopping conduction to coherent motion. The logarithmic temperature dependence below 1 K is ascribed to scattering of conduction carriers by centers with internal degrees of freedom as in amorphous metal alloys.