Topology of the Pseudogap and Shadow Bands inBi2Sr2CaCu2O8+δat Optimum Doping

We report topology of the Fermi surface of ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+\delta }$ superconducting system at the optimum doping determined by sequential angle-scanning photoemission combined with high intensity of synchrotron radiation. The Fermi surface at the optimum doping has a pseudogap around $(\pi ,0\mathrm{})$ as in underdoped samples, showing missing segments near the $M$ points, and shadow bands around $(0.5\pi ,0.5\mathrm{}\pi )$ and equivalent locations. The $k$ dependence of the pseudogap shows a particular asymmetric topology that imposes a strong constraint on its theoretical explanation.