Optical and electrical conductivity of La0.8Sr0.2MnO3 thin films deposited by laser ablation

La0.8Sr0.2MnO3 thin films have been grown by pulsed laser deposition on a SrTiO3 (1 0 0) single crystal substrate. The ‘metal’ (low-temperature)–‘insulator’ (high-temperature) phase transition manifests itself by a jump of resistivity near room temperature. A possible dependence of these properties upon the film thickness is investigated. The optical conductivity is deduced from the best fit to reflectivity spectra of a ‘double-damping Drude’ model, itself derived from the factorized form of the dielectric function. The model allows in particular to discriminate the contributions to the optical conductivity of trapped charges (polarons) and mobile charge carriers.