Increasing experimental evidence is building which indicates that signatures of strong correlations are present in the Na rich region of NaxCoO2 (ie. x≈0.7) and absent in the Na poor region (ie. x≈0.3). This is unexpected given that NaCoO2 is a band insulator and CoO2 has an integer filled open shell making it a candidate for strong correlations. We explain these experimental observations by presenting a minimal low-energy Hamiltonian for the cobaltates and solving it within LDA+DMFT. The Na potential is shown to be a key element in understanding correlations in this material. Furthermore, LDA calculations for the realistic Na ordering predict a \emph{binary} perturbation of the Co sites which correlates with the Na1 sites (ie. Na sites above/below Co sites).
@article{arxiv.cond-mat/0605177,
title = {Na Induced Correlations in Na$_x$CoO$_2$},
author = {C. A. Marianetti and G. Kotliar},
journal= {arXiv preprint arXiv:cond-mat/0605177},
year = {2009}
}