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 YBa2Cu3O6+x (YBCO) films with different oxygen contents (Tc0 ranging from 30 to 93 K) with emphasis on the underdoped ‘‘spin-gap phase.’’ A strong Tc suppression was observed, but no influence of the defects on ‘‘spin-gap’’ features in the transport properties was found. A comparison is made with Tc 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-Tc superconductors. Tc suppression by defects is shown to occur in a universal way which is independent of the Tc0, 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, Tc 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 Tc suppression in terms of the phase fluctuation theory proposed recently by Emery and Kivelson is also discussed. © 1996 The American Physical Society.

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