Unconventional electronic structure evolution with hole doping in Bi2Sr2CaCu2O8+ delta : Angle-resolved photoemission results.

We report angle-resolved photoemission results on ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{Ca}}_{1\ensuremath{-}x}{\mathrm{Dy}}_{x}{\mathrm{Cu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ and oxygen depleted ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ investigating the electronic structure changes above ${T}_{c}$ in materials with hole doping levels ranging from insulating to slightly overdoped. Near optimal hole doping, the Fermi surface is large and consistent with band calculations. In underdoped samples with ${T}_{c}$ of 60\char21{}70 K, portions of this Fermi surface are not seen. This change is related to the opening of an energy gap near $(\ensuremath{\pi},0)$ above ${T}_{c}$.