Colossal magnetoresistance and quenched disorder in manganese oxides

We give an overview on several recent topics of colossal magnetoresistive manganites in both experiments and theories, focusing on the effect of quenched disorder. The disorder is intrinsically involved since the compounds are solid solutions, and its importance has been pointed out in several experiments of transport and magnetic properties. Recent progress in the experimental control of the strength of disorder is also reviewed. Theoretically, the effect of the disorder has been explored within the framework of the double-exchange mechanism. Several efforts to understand the phase diagram and the electronic properties are reviewed. We also briefly discuss a recent topic on the effect of disorder on competing phases and the origin of colossal magnetoresistance.