Occupied electronic states of single-crystal Bi2Ca1+xSr2−xCu2O8+y

Abstract

X-ray photoemission results for ${\mathrm{Bi}}_2{\mathrm{Ca}}_{1+x}{\mathrm{Sr}}_{2-x}{\mathrm{Cu}}_2{\mathrm{O}}_{8+y}$ reveal hybrid valence-band states within ∼8 eV of the Fermi level with a centroid that is shifted ∼1.5 eV to a higher binding energy relative to the independent-particle density of states. Core-level studies reveal a single chemical environment for Bi, inequivalent O sites in the lattice, and Ca-Sr disorder. Comparison with results for Y${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{6.9}$ shows nearly identical valence-band emission with a more pronounced Fermi level cutoff for the Bi compound.