Anisotropy of the electronic structure and superconducting gap in Bi2Sr2CaCu2O8

Existence of a large anisotropy of the superconducting energy gap in Bi2Sr2CaCu2O8 was confirmed by angle-resolved photoemission. The gap size, Δ (the full superconducting energy gap being 2Δ), is 0-4 meV for the ΓX and ΓY directions while that of the ΓM̄ direction, 45°away from the former two, is 17-19 meV. Comparison with previous reports was made with regard to the symmetry of the superconducting order parameter. It was also found that the electronic structure of the normal state in the ΓY direction is considerably modified by the incommensurate superstructure in the BiO plane. In contrast, the size of superconducting gap is identical within the present accuracy for both ΓX and ΓY directions, suggesting that the superstructure has a negligible effect on the size of the superconducting energy gap.