Soft x-ray absorption spectroscopy studies of doped Pr-containing cuprates

Using high-resolution O K-edge x-ray absorption near-edge-structure (XANES) spectroscopy, unoccupied states of the YₓPr_1-xBa₂Cu₃O₇ $(x=0--1)$ thin films and polycrystalline Pr_1-xCaₓBa₂Cu₃O₇ $(x=0--0.3)$ as well as R0.8Pr0.2Ba₂Cu₃O₇ samples (R=Tm, Dy, Gd, and Sm) are investigated. In YₓPr_1-xBa₂Cu₃O₇, hole numbers in the CuO₂ planes decrease significantly with increasing Pr doping level. Hole carriers generated via Ca doping in Pr_1-xCaₓBa₂Cu₃O₇ are directed predominantly into both the Zhang-Rice and Fehrenbacher-Rice (FR) states, while those in the CuO₃ ribbons remain almost unchanged with Ca substitution. In R0.8Pr0.2Ba₂Cu₃O₇, the hole content in the CuO₂ planes decreases monotonically with increasing ionic size of the R³⁺ ions, confirming the hole depletion effect based on the Pr4f--O2p hybridization. We demonstrate the spectroscopic evidence of the existence of the FR states. The present XANES results provide a deeper understanding of the nature of hybridization and the origin of the ionic size effect.