Charge carrier localization in La1-xSrxMnO3 investigated by ac conductivity measurements

We have investigated the complex ac conductivity of La1-xSrxMnO3 for 0 less than or equal to x less than or equal to 0.2, temperatures 15 K less than or equal to T less than or equal to 300 K and frequencies 20 Hz less than or equal to nu less than or equal to 1.8 GHz. In addition, results from de measurements are presented. From the frequency dependence of the complex conductivity we find hopping of Anderson-localized charge carriers as the dominant transport process in certain temperature and composition ranges. We deduce that, while Anderson localization is not the driving mechanism for the metal-insulator transition observed in this compound, it is responsible for the high-resistivity regions observed at low doping levels and low temperatures. The results indicate a polaronic nature of the charge carriers. From the temperature dependence of the ac conductivity and the magnetic permeability, deduced in the skin-effect-dominate regime, various phase transition temperatures have been determined.