Substitutional disorder and charge localization in manganites

Abstract

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 ($x\sim0.2-0.4$). These findings indicate clearly that substitutional disorder has to be considered as an important effect when addressing the colossal magnetoresistance properties of manganites.