Gate-induced superconductivity in a solution-processed organic polymer film

The electrical and optical properties of conjugated polymers have received considerable attention in the context of potentially low-cost replacements for conventional metals and inorganic semiconductors. Charge transport in t hese organic materials has been characterized in both the doped-metallic an d the semiconducting state(1-4), but superconductivity has not hitherto bee n observed in these polymers. Here we report a distinct metal-insulator tra nsition and metallic levels of conductivity in a polymer field-effect trans istor. The active material is solution-cast regioregular poly(3-hexylthioph ene), which forms relatively well ordered films owing to self-organization, and which yields a high charge carrier mobility (0.05-0.1 cm(2) V-1 s(-1)) at room temperature. At temperatures below similar to2.35 K with sheet car rier densities exceeding 2.5 x 10(14) cm(-2), the polythiophene film become s superconducting. The appearance of superconductivity seems to be closely related to the self-assembly properties of the polymer, as the introduction of additional disorder is found to suppress superconductivity. Our finding s therefore demonstrate the feasibility of tuning the electrical properties of conjugated polymers over the largest range possible-from insulating to superconducting.