TEMPERATURE-DEPENDENCE OF THE SUPERCONDUCTING GAP ANISOTROPY IN BI2SR2CACU2O8+X

Detailed data on the momentum-resolved temperature dependence of the superconducting gap of Bi2Sr2CaCu2O8+x are presented, complemented by similar data on the intensity of the photoemission superconducting condensate spectral area. The gap anisotropy between the Gamma-(M) over bar and Gamma-X directions increases markedly with increasing temperature, contrary to what happens for conventional anisotropic-gap superconductors, such as lead. Specifically, the size of the superconducting gap along the Gamma-X direction decreases to values indistinguishable from zero at temperatures for which the gap retains virtually full value along the Gamma-(M) over bar direction. These data rule out the simplest type of d-wave order parameter.