Anisotropy in the electrical, magnetic and optical properties of Pb2Sr2RCu3O8

Measurements of anisotropy in the magnetization, direct current resistivity, and optical properties of Pb2Sr2(Y/Ca) Cu3O8 (PSYCCO) superconductors are presented. The in-plane and c-axis fundamental superconducting parameters of the material were extracted from analysis of the magnetization measurements. The optically derived plasma frequency is considerably smaller while the resistivity is an order of magnitude larger than in both Bi-Sr-Ca and Y-Ba cuprate superconductors. Along with large penetration depth, this suggests that the carrier concentration is unusually small given the high (about 80 K) transition temperature (Tc) and represents a significant deviation from a proposed universal relationship between the level of doping and Tc. The extent of anisotropy in this system is similar to that in YBa2Cu3O(7-x). The doping dependence of the ab-plane optical properties is investigated via the Ca-free Pb2Sr2RCu3O8 series, which exhibits a metal to insulator transition with increasing ionic radius of the rare earth R. In this progression, phonons in the far infrared reflectance of the insulating members become weaker while new phonon modes appear. Examination of several high-Tc superconductors with similar structure leads to the hypothesis that these features are due to the coupling of longitudinal c-axis phonons to the ab-plane mid infrared continuum.