OPTICAL ANISOTROPY IN THE PB2SR2(Y, CA)CU3O8+DELTA SUPERCONDUCTOR

We present ellipsometric and reflectance measurements of the polarization dependence of the optical response of Pb2Sr2(Y, Ca)Cu3O8+delta for light polarized parallel and perpendicular to the Cu2O planes on a single crystal. A plasma edge can only be observed in the a-direction, indicating a carrier concentration of 0.28 holes per unit cell which is comparable to the carrier concentration in YBa2Cu3O6.3. In the region between 1.7 and 5 eV several structures are present in the optical spectra and can be analyzed in terms of a band structure calculation by Mattheiss et al. Most noteworthy in this energy region is the absence of a sharp excitation at 4.1 eV suggesting that the Ba-admixture to the final state is important for the appearance of this transition in YBa2Cu3O6.