DOPING-INDUCED CHANGE OF SUPERCONDUCTING GAP ANISOTROPY IN BI2SR2CA1CU2O8+DELTA

High-resolution angle-resolved photoemission measurements were perform ed on single crystals of Bi2Sr2Ca1Cu2O8+delta with different oxygen st oichiometries. The data establish that the gap anisotropy (ratio of th e gap along T-M to the gap along T-X) can be reversibly changed from s imilar to 20:1 (optimal or underdoped) to similar to 2:1 (overdoped). Differences in sample doping explain the conflicting reports on gap an isotropy in the literature. Possible effects of this change in gap ani sotropy on the symmetry of the order parameter are discussed. There re mains some ambiguity as to the relation between the order parameter an d doping.