Optical study of an untwinned (Bi1.57Pb0.43)Sr2CaCu2O8+delta single crystal: ab-plane anisotropy

We report on the ab-plane polarized reflectance of an untwinned (Bi1.57Pb0. 43)Sr2CaCu2O8+delta single crystal over the frequency range from 80 to 32 0 00 cm(-1) (10 meV-4 eV) at temperatures between 10 and 300 K. We find a cle ar anisotropy in the ab-plane optical conductivity above and below T-c, whi ch is very similar to that formerly published data of Bi2Sr2CaCu2O8 (M.A. Q uijada et al., Z. Phys. B 94, 255 (1994)). We employ both the one-component and two-component analyses to the optical data, which suggest that the nor mal-state infrared anisotropy of (Bi1.57Pb0.43)Sr2CaCu2O8+delta originates not only from the mass anisotropy, but also from the scattering rate anisot ropy. Our results provide evidence that the electronic structures within th e CuO2 plane are anisotropic. In the superconducting state: there is a defi nite ab-plane anisotropy to the far-infrared absorption. This anisotropy co uld be due either to anisotropy of the superconducting gap or to anisotropy of the mid-infrared component to the conductivity. We also observe the sup erconducting condensate is anisotropic. The value of the superconducting pe netration depth in the a-direction is slightly smaller than that along the b-axis.