TOPOLOGY OF THE PSEUDOGAP AND SHADOW BANDS IN BI2SR2CACU2O8+DELTA AT OPTIMUM DOPING

We report topology of the Fermi surface of Bi2Sr2CaCu2O8+delta superco nducting system at the optimum doping determined by sequential angle-s canning photoemission combined with high intensity of synchrotron radi ation. The Fermi surface at the optimum doping has a pseudogap around (pi, 0) as in underdoped samples, showing missing segments near the M points, and shadow bands around (0.5 pi, 0.5 pi) and equivalent locati ons. The k dependence of the pseudogap shows a particular asymmetric t opology that imposes a strong constraint on its theoretical explanatio n.