AsF5-Doped Polyparaphenylene: Evidence for Polaron and Bipolaron Formation

Both elastic and inelastic electron scattering have been used to characterize and investigate the electronic properties of As${\mathrm{F}}_5$-doped polyparaphenylene. Evidence is presented for the existence of a polaron state slightly above the top of the valence band at low doping levels. An increase in the doping level first leads to the formation of bipolaron states which broaden and finally form a band in the gap in agreement with recent theoretical predictions.