Crossover in Electrical Frequency Response through an Insulator-Metal Transition

The insulator-metal transition (IMT) for a model quasi-one-dimensional (quasi-1D) conducting polymer (polyaniline) is probed at room temperature (RT) over an unusually broad frequency range (2 meV--6 eV) and also via T-dependent dc conductivity ( σdc). We determine that the IMT is not monotonic with increasing σdc(RT). The RT far infrared scattering time ( τ) becomes unusually long ( ≥10^-13s) as σdc(RT) increases, even for samples on the insulating side of the IMT. We conclude that the IMT is due to percolation in the presence of inhomogeneous disorder and quasi-1D localization rather than 3D Anderson localization.