The electronic state in layered cobalt oxides with a hexagonal structure is examined. We find that the electronic structure reflects the nature of the Kagomé lattice hidden in the ${\mathrm{C}\mathrm{o}\mathrm{O}}_2$ layer which consists of stacked triangular lattices of oxygen ions and of cobalt ions. A fundamental model for the electron system is proposed, and the mechanism of the unique transport and magnetic properties of the cobalt oxides are discussed in light of the model.

• Received 27 June 2003

DOI:https://doi.org/10.1103/PhysRevLett.91.257003