Disordering of the Electronic Structure of YBaCuO Amorphous Films upon Incorporation of Crystalline Clusters Formed in Laser-Induced Plasma into Their Composition

The effect of crystalline clusters formed in a laser-induced plasma on the optical properties of YBa2Cu3O6+x amorphous films prepared by pulsed laser deposition has been investigated. It has been demonstrated that an increase in the number of clusters leads to a gradual disappearance of interference fringes inherent in optically homogeneous media. Simultaneously, the incorporation of metallic and insulating clusters into the amorphous medium results in a decrease in the optical band gap E-0 of the YBaCuO amorphous matrix from 1.28 to 1.06 eV and a considerable decrease in the probability of interband optical transitions with charge transfer O 2p --> Cu 3d due to the loosening of the structure and generation of local stresses. It has been revealed that there is an additional band gap E-1, which decreases from 0.25-0.30 eV to zero values with a decrease in the optical band gap E-0. The additional gap has been interpreted as an energy gap between localized states that belong to the valence and conduction bands. A decrease in the density of electronic states in the narrow 3d band leads to the overlap of tails of the density of states, so that the band gap E-1 becomes negative.