Theory of colossal magnetoresistance in manganites

The recent attempt to account for the existence of several magnetic phases in insulating perovskite manganites in terms of the interplay between the orbital and spin orders produced by the localized e(g) and t(2g) electrons is extended to the metallic state which is obtained on doping. It is shown that the activation energy for electrical conductivity obtained on the basis of the correlated polaron transport depends on the product of the spin and bond order parameters which changes rapidly near the magnetic transition temperature and accounts for the existence of colossal magnetoresistance in this system.