Suppression of the Superconducting Condensate in the High-TcCuprates by Zn Substitution and Overdoping: Evidence for an Unconventional Pairing State

By muon spin rotation we studied the depression in condensate density, $n_s$ by Zn substitution in underdoped, optimal-doped, and overdoped ${\mathrm{Y}}_{0.8}{\mathrm{Ca}}_{0.2}{\mathrm{Ba}}_2({\mathrm{Cu}}_{1-y}{\mathrm{Zn}}_y{)}_3{\mathrm{O}}_{7-\delta }$. The rapid initial decrease of $n_s$ is inconsistent with $s$-wave pairing and magnetic scattering but points towards a $d$-wave pairing state with nonmagnetic scattering in the unitarity limit irrespective of the doping state. A similar conclusion is inferred from the depression of $T_c$ and $n_s$ with overdoping in the pure compounds where pair breaking appears to be associated with increasing three dimensionality.