Theory of small-polaron band conduction in ultrapure organic crystals

摘要

We present a novel theory of charge-carrier mobilities in organic molecularcrystals of high purity. Our approach is based on Holstein's original conceptof small-polaron bands but generalized with respect to the inclusion ofnonlocal electron-phonon coupling. We derive an explicit expression for themobilities as a function of temperature and, using ab-initio methods to obtainthe material parameters, we demonstrate its predictive power by applying it tonaphthalene. The results show a remarkably good agreement with experiments andprovide new insight into the difference between electron and hole mobilities aswell as their peculiar algebraic and anisotropic temperature dependences.