UNIVERSAL T-C SUPPRESSION BY INPLANE 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) fi lms with different oxygen contents (T-c0 ranging from 30 to 93 K) with emphasis on the underdoped ''spin-gap phase.'' A strong T-c suppressi on was observed, but no influence of the defects on ''spin-gap'' featu res 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 a nd Bi-2212 high-T-c superconductors. T-c suppression by defects is sho wn to occur in a universal way which is independent of the T-c0, carri er concentration, and number of CuO2 planes per unit cell. It is shown that, independent of whether the in-plane defects induce localized ma gnetic moments or not, T-c is a universal function of the impurity sca ttering rate, which can be described by the pair-breaking theory for p otential scatterers in d-wave superconductors, but requires that the p air-breaking rate be a factor of 3 smaller than that suggested by the transport data. An alternative description of the T-c suppression in t eems of the phase fluctuation theory proposed recently by Emery and Ki velson is also discussed.