Electrical transport and reflectance studies on polypyrrole- CF3SO3- in the vicinity of metal-insulator transition

We discuss the disorder induced metal-insulator transition in polypyrrole d oped with CF3SO3- in an attempt to understand the electrical transport in t he vicinity of the transition. With the temperature dependence of conductiv ity and magnetotransport measurements performed over a wide temperature ran ge spanning from 1.5K to 300K, we have been able to separate out various re gimes of transport. The temperature dependence of conductivity changes from a sigma (T) = sigma (0) + mT(1/2) + BTp/2 behaviour reminiscent of conduct ion in a disordered metal to a sigma (T) similar to T-beta dependence at th e critical regime and then to a variable range hopping dependence as the MI transition is traversed. Together with the magnetotransport, it is evident that the electron-electron interaction plays a crucial role in determining the conduction near the transition. The dominant dephasing mechanism that determines the temperature dependence of incipient-localization has been ac counted for the inelastic scattering of electrons by phonons. Reflectance i n the metallic regime has been studied over a wide spectral range from 0.02 eV to 6eV. Spectral features like plasma resonance and high reflectivity in the IR, which are unique to a metal, are seen. Localization-modified Drude model has been found to be adequate in describing the energy dependence of the optical conductivity.