Universal T-c suppression by in-plane defects in high-temperature superconductors: Implications for pairing symmetry

The influence of in-plane oxygen defects on the critical temperature, resistivity, and Hall coefficient was studied in YBa2Cu3O6+x (YBCO) films with different oxygen contents (T-c0 ranging from 30 to 93 K) with emphasis on the underdoped ''spin-gap phase.'' A strong T-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 T-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-T-c superconductors. T-c suppression by defects is shown to occur in a universal way which is independent of the T-c0, carrier concentration, and number of CuO2 planes per unit cell. It is shown that, independent of whether the in-plane defects induce localized magnetic moments or not, T-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 T-c suppression in teems of the phase fluctuation theory proposed recently by Emery and Kivelson is also discussed.