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

Abstract

By muon spin rotation we studied the depression in condensate density, ${n}_{s}$ by Zn substitution in underdoped, optimal-doped, and overdoped ${\mathrm{Y}}_{0.8}{\mathrm{Ca}}_{0.2}{\mathrm{Ba}}_{2}({\mathrm{Cu}}_{1\ensuremath{-}y}{\mathrm{Zn}}_{y}{)}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$. 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.