The electronic structure of the doped one-dimensional transition metal oxide Y_(2-x)Ca_xBaNiO_5 studied using X-ray absorption

摘要

A strong anisotropic distribution of the holes in Ni 3d and O 2p orbitals is observed in the polarization dependent O 1s and Ni 2p_(3/2) X-ray absorption spectroscopy of the linear-chain nickelate Y_(2-x)Ca_xBaNiO_5 (x = 0, 0.05, 0.1, 0.2), which demonstrates the one-dimensional nature of the electronic state in these compounds. The holes introduced by Ca-doping occupy both O 2p and Ni 3d orbitals along the NiO_5 chains. By comparing the experimental Ni 2p_(3/2) absorption spectra of Y_(2-x)Ca_xBaNiO_5 to those from charge transfer multiplet calculations we can derive the orbital character of the additional holes to be of ～60% O2p and ～40% Ni 3d.