Correlation effects on the small-polaron hopping conductivity

Abstract

On the basis of a spinless fermion model, which takes into account the intersite Coulomb interaction and the formation of small polarons (SP) due to the interaction with phonons, the correlation effects (due to the SP-SP interaction) on the electrical SP hopping conductivity are investigated. The particle transfer is treated in lowest nonvanishing order of perturbation theory, and the case of non-adiabatic SP hopping is considered. The polaronic short-range order (SRO) results in an additional activation of the dc conductivity due to hopping processes without and with changes of the Coulombic configurational energy. For sufficiently low SRO the dc conductivity is enhanced relative to its magnitude in the case of non-interacting SP. The SRO leads to an additional optical absorption and a positive shift of the absorption spectrum. The theory maybe relevant for the description of inhomogeneous mixed-valence compounds and superionic conductors.