Universal Tc suppression by in-plane defects in high-temperature superconductors: Implications for pairing symmetry.

Abstract

The influence of in-plane oxygen defects on the critical temperature, resistivity, and Hall coefficient was studied in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6+\mathit{x}}$ (YBCO) films with different oxygen contents (${\mathit{T}}_{\mathit{c}0}$ ranging from 30 to 93 K) with emphasis on the underdoped ``spin-gap phase.'' A strong ${\mathit{T}}_{\mathit{c}}$ suppression was observed, but no influence of the defects on ``spin-gap'' features in the transport properties was found. A comparison is made with ${\mathit{T}}_{\mathit{c}}$ suppression by other in-plane defects such as Zn substitutions for Cu, Pr substitutions for Y in YBCO, and radiation defects in Bi-2201 and Bi-2212 high-${\mathit{T}}_{\mathit{c}}$ superconductors. ${\mathit{T}}_{\mathit{c}}$ suppression by defects is shown to occur in a universal way which is independent of the ${\mathit{T}}_{\mathit{c}0}$, carrier concentration, and number of ${\mathrm{CuO}}_{2}$ planes per unit cell. It is shown that, independent of whether the in-plane defects induce localized magnetic moments or not, ${\mathit{T}}_{\mathit{c}}$ is a universal function of the impurity scattering rate, which can be described by the pair-breaking theory for potential scatterers in d-wave superconductors, but requires that the pair-breaking rate be a factor of 3 smaller than that suggested by the transport data. An alternative description of the ${\mathit{T}}_{\mathit{c}}$ suppression in terms of the phase fluctuation theory proposed recently by Emery and Kivelson is also discussed. \textcopyright{} 1996 The American Physical Society.