Small polaron transport and colossal magnetoresistance in $La2/3Ca1/3MnO3$

Despite numerous attempts to explain the phenomenon of transport and magnetoresistance in manganites based on Jahn–Teller phonon coupling and double exchange mechanisms, satisfactory results could not be reached. The small polaron transport mechanism, based on the valence exchange arising from Madelung energy, is shown to account for the resistivity and magnetoresistance of the doped manganite $La2/3Ca1/3MnO3$ in the ferromagnetic range. The transport equation for the correlated polaron based on the Holstein Hamiltonian shows the well known transition from the low temperature band to the localized polaron hopping conductivity at high temperature in agreement with experiment. The present attempt is to demonstrate that the complexity of the problem that involves the interplay between the spin and charge order on one hand and itinerant and localized behavior on the other for a simple ferromagnetic metal system of manganites is best described by the correlated small polaron model leaving the more complicated systems for future studies.