ZN-SUBSTITUTION EFFECTS ON THE OPTICAL CONDUCTIVITY IN YBA2CU3O7-DELTA CRYSTALS - STRONG PAIR-BREAKING AND REDUCTION OF INPLANE ANISOTROPY

Zn substitution effects on the a-, b-, and c-axis optical conductivity spectra have been investigated for optimally annealed YBa2Cu3O7-delta crystals. It was revealed that a very small amount of Zn seriously af fects the low-energy charge dynamics in both normal and superconductin g states. In addition to the increase of scattering rates, Zn substitu tion introduces additional features in the conductivity spectra and re duces the in-plane anisotropy by suppressing the plasma frequency in t he b direction in the normal state. In the superconducting state, a ve ry strong anisotropic pair-breaking effect was found.