Metal-insulator transition below the Curie temperature in layered manganites

Abstract

In contrast to the traditional viewpoint that a metal-insulator transition (MIT) occurs just at the resistivity peak temperature ${T}_{p},$ we propose that in perovskite manganites with temperature-dependent disorder, ${T}_{\mathrm{MI}}$ at which the MIT occurs may be well below the Curie temperature ${T}_{C}(\ensuremath{\simeq}{T}_{p}).$ At temperatures between ${T}_{\mathrm{MI}}$ and ${T}_{C},$ due to a decrease in localization length upon heating, the resistivity of the localized electrons behaves with metallic temperature dependence. Only above ${T}_{C}$ does the resistivity exhibit semiconductorlike temperature behavior. Such an idea that the MIT occurs below ${T}_{C}$ can account for the anomalous resistivity behavior in the layered manganite crystal ${\mathrm{La}}_{2\ensuremath{-}2x}{\mathrm{Sr}}_{1+2x}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$ with $x=0.3.$