The Non-Adiabatic Polaron Model Revisited

• DOI: 10.1007/s13538-014-0208-8
• Publication Date: 2014-05-14T12:49:32Z
• Authors: Fabian E. N. Ramirez; José Antonio Souza
• Keywords: Manganite

We revisit Holstein's polaron model to derive an extension of the expression for the thermal dependence of the electrical resistivity in the non-adiabatic small-polaron regime. Our analysis relaxes Holstein's assumption that the vibrational-mode energies ωk are much smaller than the thermal energy kBT and substitutes a fifth-order expansion in powers of ωk/kB T for the linear approximation in the expression for the quasiparticle hopping probability in the original treatment. The resulting expression for the electri- cal resistivity has the form ρ(T ) = ρ0T 3/2 exp(Ea/kB T − C/T 3 + D/T 5 ) ,w hereC and D are constants related to the molecule-electron interaction energy, or alternatively to the polaron binding energy, and the dispersion relation of the vibrational normal modes. We show that experimen- tal data for the La1−xCaxMnO3 (x = 0.30, 0.34, 0.40, and 0.45) manganite system, which are poorly fitted by the conventional non-adiabatic model, are remarkably well described by the more accurate expression. Our results sug- gest that, under conditions favoring high resistivity, the higher-order terms associated with the constants C and D in the above expression should taken into account in compar- isons between theoretical and experimental results for the temperature-dependent transport properties of transition- metal oxides.