Evidence of retribution of the itinerant holes below Tc in Ba2Sr2CaCu2O8 superconductors: A polarized x-ray-absorption study

The microscopic electronic structure of high-quality superconducting Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{ital y}} (Bi2212) single crystals has been investigated in the normal and superconducting states by polarized x-ray-absorption (XAS) measurements. The O {ital K}-edge XAS results led us to conclude the presence of a significant density of {ital p}{sub {ital z}} symmetry orbitals for itinerant holes. We observed a reproducible increase in the number of O 2{ital p}{sub {ital x},}{ital y} itinerant holes accompanied by a decrease of the O {ital K} XAS transition in the upper Hubbard band (covalent holes) while going from the normal to the superconducting state of the system. The increase of O 2{ital p}{sub {ital x},}{ital y} holes was confirmed by an increase in the 3{ital d}{sup 9}{ital L}/3{ital d}{sup 9} ratio estimated from Cu {ital L}{sub 3} XAS measurements. This is in agreement with earlier inverse photoemission measurements and constitutes evidence for the redistribution of the itinerant holes below the transition temperature ({ital T}{sub {ital c}}).