Electronic states in conjugated polymers studied by electron spin resonance

Electron spin resonance (ESR) has been applied to fully-doped conjugated polymers. Two parameters deduced from ESR spectra, integrated intensity and line width, are analysed and we obtained information on the electronic states of various conducting polymers. The former gives us a spin susceptibility and the latter does dynamics of spin carriers through relaxation rates via several interaction paths, such as Elliott and spin diffusion mechanisms. The fully-doped conducting polymers usually show the Pauli-Like, temperature-independent susceptibility with small Curie-one, called Curie-tail. We propose two different origins of the Curie-tail for conducting polymers corresponding to different categories, in terms of disorder. Spin dynamics studies through the ESR line width provide us microscopic transport properties and a suggestion that the polymers in category A, covering such as polyacetylene and polypyrrole, exhibit metallic transport properties down to 2 K. However, the other polymers in category B, such as poly-p-phenylenevinylene-H2SO4 and polyaniline-camphorsulfonicacid, fall into the localized non-metallic states at low temperatures where the Pauli susceptibility disappears.