Measurements of polarization-dependent soft x-ray absorption reveal that the electronic states determining the low-energy excitations of NaxCoO2 have predominantly a1g symmetry with significant O 2p character. A large transfer of spectral weight observed in O 1s x-ray absorption provides spectral evidence for strong electron correlations in the layered cobaltates. Comparing Co 2p x-ray absorption with calculations based on a cluster model, we conclude that NaxCoO2 exhibits a charge-transfer electronic character rather than a Mott-Hubbard character.
@article{arxiv.cond-mat/0408467,
title = {Orbital Symmetry and Electron Correlation in Na_{x}CoO_2},
author = {W. B. Wu and D. J. Huang and J. Okamoto and A. Tanaka and H. -J. Lin and F. C. Chou and A. Fujimori and C. T. Chen},
journal= {arXiv preprint arXiv:cond-mat/0408467},
year = {2009}
}