Temperature Dependence of the Superconducting Gap Anisotropy in Bi2Sr2CaCu2O8+x

Science. 1995 Feb 10;267(5199):862-5. doi: 10.1126/science.267.5199.862.

Abstract

Detailed data on the momentum-resolved temperature dependence of the superconducting gap of Bi(2)Sr(2)CaCu(2)O(8+x) are presented, complemented by similar data on the intensity of the photoemission superconducting condensate spectral area. The gap anisotropy between the Gamma-Mand 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 direction. These data rule out the simplest type of d-wave order parameter.