Effective interaction between the interpenetrating Kagome lattices in NaxCoO2 -: art. no. 214414

A multiorbital model for a CoO2 layer in NaxCoO2 is derived. In this model, the kinetic energy for the degenerate t(2g) orbitals is given by indirect hopping over oxygen, leading naturally to the concept of four interpenetrating Kagome lattices. Local Coulomb interaction couples the four lattices and an effective Hamiltonian for the interaction in the top band can be written in terms of fermionic operators with four different flavors. Focusing on charge- and spin-density instabilities, a big variety of possible metallic states with spontaneously broken symmetry are found. These states lead to different charge, orbital, spin, and angular momentum ordering patterns. The strong superstructure formation at x=0.5 is also discussed within this model.