Muon Spin Relaxation Studies of Zn-Substitution Effects in High-TcCuprate Superconductors

We have performed transverse-field muon spin relaxation measurements of the Zn-substituted cuprate high- $T_c$ superconductors: ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x\left({\mathrm{Cu}}_{1-y}{\mathrm{Zn}}_y\right){\mathrm{O}}_4$ and ${\mathrm{YBa}}_2({\mathrm{Cu}}_{1-y}{\mathrm{Zn}}_y{)}_3{\mathrm{O}}_{6.63}$. The superconducting carrier density/effective mass $n_s/m^{*}$ ratio at $T\to 0$ decreases with increasing Zn concentration, in a manner consistent with our “swiss cheese” model in which charge carriers within an area $\pi {\xi }_{\mathrm{ab}}^2$ around each Zn are excluded from the superfluid. We discuss this result in the context of Bose condensation, pair localization, and pair breaking.