Evidence of the charge-density wave state in polypyrrole nanotubes

Abstract

We present a detailed investigation of the low-frequency dielectric and conductivity properties of conducting polymer nanowires. Our results, obtained by connecting $\ensuremath{\sim}{10}^{7}$ nanowires in parallel, show that these polypyrrole nanowires behave like conventional charge-density wave (CDW) materials, in their nonlinear and dynamic response, together with scaling of relaxation time and conductivity. The observed Arrhenius law for both these quantities gives a CDW gap of 3.5 meV in the regime of temperature $(\ensuremath{\sim}40$ K) in which the CDW state survives. We find good agreement with a theory of weakly pinned CDW, screened by thermally excited carriers across the CDW gap. The identification of polymer nanowires as CDW provides us a model system to investigate charge ordering owing to electrostatic interaction, relevant to a variety of systems from dusty plasma to molecular biology.