Momentum Dependence of the superconducting gap of Bi_2Sr_2CaCu_2O_8.

We show detailed measurement of the superconducting gap along the Fermi surface of Bi_2Sr_2CaCu_2O₈ by high resolution angle-resolved photoemission spectroscopy (ARPES). It is found that umklapp bands due to the incommensurate superlattice in this material may obscure the intrinsic momentum dependence of the gap. By taking these into consideration, we find a d-wave-like gap function. We also show some results on the controlled introduction of point scattering centers on the gap function and the spectral function.