SUPERCONDUCTING GAP AND ORDER-PARAMETER IN BI2SR2CACU2O8+X

Using angle-resolved photoemission, we observed a nonzero superconduct ing gap and the presence of a superconducting condensate along all thr ee major symmetry directions. We find that the gap is highly anisotrop ic, with a gap as small as 1-2 meV along GAMMA-Y, 4-8 meV along GAMMA- X, and 14-20 meV along GAMMA-M. We argue that our data imply either an anisotropic s-wave order parameter or an unconventional, two-componen t order parameter, and that measuring the size of the gap does not by itself distinguish between the two possibilities. We propose a phenome nological unconventional order parameter, and note the quantitative ag reement between theory and experiment.