Charge carrier localization in investigated by ac conductivity measurements

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Abstract
We have investigated the complex ac conductivity of for , temperatures and frequencies . In addition, results from dc 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-dominated regime, various phase transition temperatures have been determined.