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 Y_xPr_1-xBa₂Cu₃O₇ (x=0-1) thin films and polycrystalline Pr_1-xCa_xBa₂Cu₃O₇ (x=0-0.3) as well as R_0.8Pr_0.2Ba₂Cu₃O₇ samples (R=Tm, Dy, Gd, and Sm) are investigated. In Y_xPr_1-xBa₂Cu₃O₇, hole numbers in the CuO₂ planes decrease significantly with increasing Pr doping level. Hole carriers generated via Ca doping in Pr_1-xCa_xBa₂Cu₃O₇ 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 R_0.8Pr_0.2Ba₂Cu₃O₇, 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 Pr 4f-O 2p 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.