Universal Superconductor-Insulator Transition andTcDepression in Zn-Substituted High-TcCuprates in the Underdoped Regime

The experimental results are presented on the in-plane resistivity for Zn-substituted single crystals of ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-y}$ and ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ with various hole densities. The primary effect of Zn is to produce a large residual resistivity ( ${\rho }_0$) as a potential scatterer in the unitarity limit. In the underdoped regime, due also to low carrier density in the ${\mathrm{CuO}}_2$ plane, only a few percent Zn is sufficient for ${\rho }_0$ to reach the critical value near the universal two-dimensional resistance $h/{4e}^2$ and to induce a superconductor-insulator transition. By contrast, the universal behavior is not seen in the highly doped regime, suggestive of a radical change in the electronic state.