摘要
We present measurements of polarization-dependent soft X-ray absorption on Na x CoO 2 . The results reveal that the electronic states determining the low-energy excitations of Na x CoO 2 have predominantly a 1 g 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 Na x CoO 2 with the Na doping higher than half. For the Na concentration less than half, our measurements of O 1s absorption suggest that Na x CoO 2 exhibits band-like electronic character. © 2006.