Observation of the Band-Hopping Transition for Electrons in Naphthalene

Transient photoconductivity has been used to measure the electron drift mobility in the $c^{\prime }$ direction of single-crystal naphtalene from 54 to 324 K. Below 100 K the mobility rises exponentially with decreasing temperature, an effect which we attribute to the onset of band-type motion limited by optical-phonon scattering. This observation allows the identification of the approximately constant mobility at higher temperatures ($T>\mathrm{}100\mathrm{}$ K) with the hopping of localized charge carriers.