Metal–insulator transitions in pressed pellets of BF−4doped poly(3-methylthiophene)

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Abstract
From Electron Spin Resonance (ESR) data in pressed pellets of BF− 4 doped Poly (3–methylthiophene) (P3MT) we obtained simultaneously the paramagnetic susceptibility and the microwave conductivity. We observed a transition from a high-temperature insulator state to a room-temperature metallic state. Around 240 K evidence of a Peierls transition is observed, but if the sample is slowly cooled, this transition is partially suppressed. DC conductivity data taken with the sample quenched to 79 K show a non-linear I-V response for very small electric fields, suggesting depinning of Charge-Density Wave (CDW). The data for heating and cooling the system above room temperature, indicate the formation of bipolarons.