SITE-SPECIFIC UNOCCUPIED ELECTRONIC-STRUCTURE OF ONE-DIMENSIONAL SRCUO2

The unoccupied electronic structure of SrCuO2 single crystals has been studied using x-ray-absorption spectroscopy. By choosing the orientat ion of the single crystals with respect to the polarization vector of the synchrotron radiation, we are able to determine the hole occupatio n of the different O 2p and Cu 3d orbitals. We show that the intrinsic holes in the one-dimensional copper oxide zigzag chains mainly occupy planar Cu 3d(y2-z2) orbitals, which closely resembles the situation i n the undoped parent compounds of the high-temperature superconductors . Additionally, most of the oxygen states that are admired to the uppe r Hubbard band are concentrated in the center of the chains most proba bly as a result of the larger number of nearest neighbors. Our results provide an important check for calculations of one-dimensional correl ated Cu-O systems.