Low temperature singularity of the electrical conductivity in potassium doped polyacetylene

We present the temperature dependence of the electrical conductivity of highly potassium doped polyacetylene. While the conductivity σ of these systems usually decreases when T decreases, we show that it is possible to observe an increase of a for decreasing temperatures when T < 7 K. The Sheng model is able to explain the behaviour of the conductivity for T > 10 K but it diverges from our data for T < 10 K. Highly potassium doped polyacetylene behaves like a metal for 4.2 K < T < 10 K and we demonstrate that a model of disordered metal correctly fits our results. This study gives an interpretation for the electrical conductivity behaviour in the whole temperature range 4.2 K – 300 K and shows the importance of the intrinsic disorder of the polymer in the observation of the singularity at low temperature.