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We present two representations of the order-parameter ͑OP͒ eigenfunctions for tetragonal cuprate superconductors, and for orthorhombic YBa 2 Cu 3 O 7Ϫ␦ and Bi 2 Sr 2 CaCu 2 O 8ϩ␦ ͑BSCCO͒. Recent BSCCO c-axis twist Josephson junction experiments of Li et al. demonstrate that the tunneling is strongly incoherent, and that the OP contains an isotropic s-wave component, but not any d x 2 Ϫy 2-wave component. We propose a c-axis twist tetracrystal ring experiment. J c J (45°) at tϭ0.7. 14 Moreover, since BSCCO is highly anisotropic, 2,3 we have recalculated J c J ( 0 )/J c J (0) for d ϭ d Јϭ0.1,0.001, and plotted the results for tϭ0.5,0.9,0.99 in Fig. 1. For d ϭ0.1, these effects are small but clearly visible. For d ϭ0.001, the suppression of the dominant d x 2 Ϫy 2-wave OP component would be noticeable only very close to T c . For T below the fluctuation regime, J c J ( 0 )/J c J (0)Ϸ͉cos(2 0 )͉. Clearly, J ( 0 )/J c J (0)ϭ1, consistent with the data. 1 The other pure l-wave states have some 0 * at which J c J ( 0 *)ϭ0. For lϭ2, 0 *ϭ45°, and for lϭ4, 0 * ϭ22.5°,67.5°. Including higher l compatible components will not change these qualitative results. As shown in Fig. 2, an A 2 state always has some 0 * at which J c J ( 0 *)ϭ0. If the isotropic component of an A 1 state were nearly negligible, then J c J ( 0 )/J c J (0) could also be highly anisotropic. Otherwise, an A 1 state gives the least anisotropic J c J ( 0 ) behavior. Thus, the observation J c J ( 0 )/J c S ϭ1 at and below T c in BSCCO is prima facie evidence that the dominant OP is ͉s ϩd xy ͘, with an isotropic component. 1 In addition, if the tunneling across the twist and intrinsic junctions were equal and purely incoherent, ( f l0 →0 for l 0), then the ͉d x 2 Ϫy 2ϩ g xy(x 2 Ϫy 2 ) ͘ state would have J c J ( 0 )ϭJ c S ϭ0᭙ 0 , and the ͉sϩd xy ͘ state would have J c J ( 0 )/J c S ϭ1, as observed, provided that it had an isotropic s-wave component. 1 An example of an OP consistent with many experiments is the ''extended s-wave'' OP, FIG. 2. Plots of ͉Aϩcos(2 0 )ϩBcos(4 0 )͉/͉1ϩAϩB͉, along with the A,B values, of the lowest l contributions to J c J ( 0 )/J c J (0) in Eq. ͑4͒. Upper two curves: A 1 states. Lower three curves: A 2 states. PRB 61 5915 BRIEF REPORTS

A nested Fermi surface with nearly parallel orbit segments is found to yield a singlet d-wave superconducting state at high temperatures for a restricted range of the on-site Coulomb repulsion that avoids the competing spin density wave instability. The computed superconducting transition temperature drops dramatically as the nesting vector is decreased, in accord with recent photo-emission data on the Bi2212 and Bi2201 cuprates.