SITE-SPECIFIC AND DOPING DEPENDENT ELECTRONIC-STRUCTURE OF YBA2CU3OX PROBED BY O1S AND CU2P X-RAY-ABSORPTION SPECTROSCOPY

The electronic structure of the CuO2 planes and CuO3 chains in single domain crystals of YBa2Cu3Ox has been investigated as a function of ox ygen concentration (6 less than or equal to x less than or equal to 7) using polarization-dependent x-ray absorption spectroscopy at the O1s and Cu2p core absorption edges. The polarization-dependent observatio n of unoccupied states with O2p and with Cu3d orbital character parall el to the crystallographic a, b, and c axes of the crystals allows the determination of hole states near the Fermi level in Cu3d(x2-y2) and O2p(x,y) orbitals in the planes and in Cu3d(y2-z2) and O2p(y,z) orbita ls in the chains. The onset of superconductivity does not significantl y change the hole occupation.