ESR study of Li-doped polyacenic semiconductor (PAS) materials

The electronic states of Li-doped polyacenic semiconductor (PAS) materials have been examined based on electron spin resonance (ESR) observations. It has been found that Li doping causes not only metallic transition but increase in the peak-to-peak linewidth (ΔHpp) of the ESR lineshape, probably due to enhancement of the spin-orbit interactions occurring in conduction electrons on the Li atoms. Increase in ΔHpp has been observed up to the C2Li stage without any sign of liberation of Li clusters. The temperature dependence of ΔH pp suggests a certain hopping process for conduction electrons to migrate onto Li atoms. The PAS samples doped beyond the C2Li stage have shown a two-phase ESR spectrum, which consists of a broader component coming from the original carbon π-radicals and a narrow spike from the liberated Li clusters.