Unconventional Electronic Structure Evolution with Hole Doping inBi2Sr2CaCu2O8+δ: Angle-Resolved Photoemission Results

Abstract

We report angle-resolved photoemission results on ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{Ca}}_{1-x}{\mathrm{Dy}}_x{\mathrm{Cu}}_2{\mathrm{O}}_{8+\delta }$ and oxygen depleted ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+\delta }$ 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 60–70 K, portions of this Fermi surface are not seen. This change is related to the opening of an energy gap near $(\pi ,0\mathrm{})$ above $T_c$.