Effect of Disorder Outside theCuO2Planes onTcof Copper Oxide Superconductors

Abstract

The effect of disorder on the superconducting transition temperature $T_c$ of cuprate superconductors is examined. Disorder is introduced into the cation sites in the plane adjacent to the ${\mathrm{CuO}}_2$ planes of two single-layer systems, ${\mathrm{Bi}}_{2.0}{\mathrm{Sr}}_{1.6}{\mathrm{Ln}}_{0.4}{\mathrm{CuO}}_{6+\delta }$ and ${\mathrm{La}}_{1.85-y}{\mathrm{Nd}}_y{\mathrm{Sr}}_{0.15}{\mathrm{CuO}}_4$. Disorder is controlled by changing rare earth (Ln) ions with a different ionic radius in the former, and by varying the Nd content in the latter with the doped carrier density kept constant. We show that this type of disorder works as weak scatterers in contrast to the in-plane disorder produced by Zn, but remarkably reduces $T_c$, suggesting novel effects of disorder on high-$T_c$ superconductivity.