Spin gap behavior and electronic phase separation in doped polyacetylene

In ClO4−-doped ν-polyacetylene with the dopant concentration of 2–6%, the ESR susceptibility was found to decrease below 200 K. Meanwhile, the thermoelectric power did not exhibit the corresponding anomaly, although the resistivity showed a change suggesting a variation in the carrier dynamics. The ESR line-shape analysis revealed that a phase separation due to droplet nucleation undergoes in a mixed phase of a soliton state associated with spin-charge separation and a polaron state. For the 2.6% doped, the spin-charge separated state appeared with negligible content of the metallic phase, suggesting that the upper bound for a homogeneous soliton state is ∼3% in the dopant concentration. The superconductivity by frustration mechanism is considered to be pre-empted by the soliton phase.