X-RAY-ABSORPTION SPECTROSCOPY OF DETWINNED PRXY1-XBA2CU3O7-Y, SINGLE-CRYSTALS - ELECTRONIC-STRUCTURE AND HOLE DISTRIBUTION

Substituting Y in orthorhombic (Y,R)Ba2Cu3O7 by any rare-earth element R has generally little effect on the superconducting properties. For R = Pr, however, superconductivity is completely suppressed, To unders tand this effect we have studied the unoccupied electronic structure o f PrxY1-xBa2Cu3O7-y (x = 0.0, 0.3, 0.8) using polarization-dependent O 1s near-edge x-ray absorption spectroscopy of detwinned single crysta ls. We identify the hole states in the CuO2 planes and the CuO3 chains and give estimates of the relative contributions of the O 2p(x), O 2p (y), and O 2p(z) orbitals to these states, Along with the comparison o f oxygen-rich (y approximate to 0.1) to the oxygen-depleted materials (y approximate to 0.9), this allows a test of the current theoretical explanations for the Pr-induced suppression of superconductivity. Whil e we can rule out models involving hole filling or charge transfer bet ween the planes and the chains, our data are consistent with approache s based on Pr 4f-O 2p(pi) hybridization.