Orbital symmetry and electron correlation in NaxCoO2

Abstract

We present measurements of polarization-dependent soft X-ray absorption on NaxCoO2. The results reveal that the electronic states determining the low-energy excitations of NaxCoO2 have predominantly a(1g) 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 NaxCoO2 with the Na doping higher than half. For the Na concentration less than half, our measurements of O 1s absorption suggest that Na2CoO2 exhibits band-like electronic character. (c) 2006 Published by Elsevier B.V.