We derive an effective Hamiltonian for highly correlated $t_{2g}$ states centered at the Co sites of ${\mathrm{Na}}_x{\mathrm{CoO}}_2$. The essential ingredients of the model are an O mediated hopping, a trigonal crystal-field splitting, and on-site effective interactions derived from the exact solution of a multiorbital model in a ${\mathrm{CoO}}_6$ cluster, with parameters determined previously. The effective model is solved by dynamical mean field theory. We obtain a Fermi surface and electronic dispersion that agrees well with angle-resolved photoemission spectra. Our results also elucidate the origin of the “sinking pockets” in different doping regimes.

• Received 22 October 2008

DOI:https://doi.org/10.1103/PhysRevLett.102.066402