INFRARED PROPERTIES OF YBA2CU3O7 AND BI2SR2CAN-1CUNO2N-FILMS(4 THIN)

We report room-temperature optical reflectivity and transmission measu rements on a variety of YBa2Cu3O7 and Bi2Sr2Can-1CunO2n+4 thin films i n the 500-25000 cm-1 frequency range. Reflectivity data when not biase d by the substrate are used to compute the optical conductivity. A com parison of our results with published reflectivity data on single-doma in YBa2Cu3O7 crystals suggests an overwhelming contribution of the CuO 2 planes (with respect to the chains) to the optical conductivity. The data can be analyzed In terms of a Drude low-frequency contribution a nd a so-called midinfrared band. However, the anomalous infrared respo nse appears to be uniquely described by a generalized Drude response: for all the samples investigated, the relaxation rate (which increases linearly with frequency) and the effective mass are found to be the s ame as a function of frequency.