Temperature Dependence of the Superconducting Gap Anisotropy in Bi2Sr2CaCu2O8+x

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Science  10 Feb 1995:
Vol. 267, Issue 5199, pp. 862-865
DOI: 10.1126/science.267.5199.862


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 Γ-Mand Γ-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 Γ-X direction decreases to values indistinguishable from zero at temperatures for which the gap retains virtually full value along the Γ-M direction. These data rule out the simplest type of d-wave order parameter.