Substitutional disorder and charge localization in manganites.

In the manganites RE(1 - x)AE(x)MnO(3) (RE and AE being rare-earth and alkaline-earth elements, respectively) the random distribution of RE(3 + ) and AE(2 + ) induces random, but correlated, shifts of site energies of charge carriers in the Mn sites. We consider a realistic model of this diagonal disorder, in addition to the double-exchange hopping disorder, and investigate the metal-insulator transition as a function of temperature, across the paramagnetic-ferromagnetic line, and as a function of doping  x. Contrary to previous results, we find that values of parameters, estimated from the electronic structure of the manganites, are not incompatible with the possibility of a disorder-induced metal to insulator transition accompanying the ferromagnetic to paramagnetic transition at intermediate doping (x ∼ 0.2-0.4). These findings indicate clearly that substitutional disorder has to be considered as an important effect when addressing the colossal magnetoresistance properties of manganites.