ZN-DOPING EFFECTS ON THE CHARGE-TRANSPORT IN HIGH-T-C COPPER OXIDES

The experimental results are presented on the in-plane resistivity for Zn-substituted single crystals of YBa2Cu3O7-y and La2-xSrxCuO4. The p rimary effect of the substituted Zn on the charge transport is to act as a strong potential scatterer in the unitarity limit, producing a la rge residual resistivity (rho(0)). There appears a critical change in the Zn-substitution effect as the doped hole density Increases. In the underdoped regime, a superconductor-insulator transition is induced a t rho(0) near the universal value (h/4e(2)), and T-c is depressed with increase of rho(0) following a universal curve, independent of materi al, doped hole density and of species of impurities. By contrast, thes e universal behaviors are not seen in the overdoped superconducting re gime, where the material remains metallic after the superconductivity is suppressed, suggestive of a coexistence of normal and superfluid in this regime.