MOMENTUM DEPENDENCE OF THE SUPERCONDUCTING GAP IN BI2SR2CACU2O8

We measure the momentm dependence of the superconducting gap along the Fermi surface of Bi2Sr2CaCu2O8 by high resolution angle-resolved photoemission spectroscopy. The gap is large in the vicinity of the M̄ point (where γ- M̄ is along the Cu-O bond), and small along the γ- X and γ- Y (π,π) directions. However, the gap is not zero along these directions, but, within our accuracy, becomes zero about 10 on either side of the (π,π) directions. We discuss the implications of these results for the symmetry of the order parameter. © 1995 The American Physical Society.