Middle-IR optical response and composition of Bi-based (2212)-type high-T_c superconductors

The optical response in the middle- and near-IR region has been examined in a sequence of Bi-based single crystals with various doping levels and phase compositions. The features in the optical spectra, which have been considered in the pseudodielectric function approximation, are used to characterize the free-carrier system in high-T_c compounds. A correlation between the chemical and phase composition, on the one hand, and the optical characteristics, on the other hand, has been analysed in Bi-based (2212)-type single crystals doped by Y(RE) ions.