Metallic temperature dependence of resistivity in polypyrrole and poly(3-methylthiophene) at low temperatures with and without pressure

The temperature dependence of resistivity (TDR) has been studied in PF6− doped poly(3-methylthiophene) (PMeT(PF6−) and AsF6− doped polypyrrole (PPy(AsF6−)). For several samples of PMeT(PF6−) metallic TDR was observed below 8K similar to that in PPy(PF6−). For PPyCAsF6−), application of a pressure of 13.5 Kbar induced the metallic TDR below 9K, despite of the semiconducting TDR at ambient pressure throughout the whole temperatures. We have also observed a clear transition from semiconducting to metallic TDR in PMeT(PF6−) with increasing pressure. From our observations, it is indicated that the metallic TDR is not an exceptional phenomenon only in the PPy(PF6−).