Resolving CuO chain and CuO2 plane contributions to the YBa2Cu3O7-d valence band by standing-wave excited hard x-ray photoelectron spectroscopy

We analyzed the valence band (VB) of the 90 K high-temperature superconductor YBa2Cu3O7-d by photoelectron spectroscopy under standing-wave excitation employing hard x rays. Precisely positioning the standing-wave intensity in the unit cell allows selectively probing the VB yield from the CuO chains and CuO2 planes, respectively. Both contribute strongly over the whole VB but the spectral weight of the planes is significantly higher than the chains within about 2 eV from the Fermi level. In the x-ray regime, the major contribution to the VB emission is coming from Cu 3d.