Hall effect inCoO2layers with a hexagonal structure

We examine Hall effect in layered cobalt oxides with hexagonal structure. In the $\mathrm{Co}{\mathrm{O}}_{2}$ layer, the cobalt ions form a triangular lattice. However, the electron trajectory makes up the kagome lattice due to the orbital degeneracy of ${t}_{2g}$ states. It is shown that this kagome lattice hidden in the $\mathrm{Co}{\mathrm{O}}_{2}$ layer exhibits the anomalous high-temperature Hall effect recently observed by Wang et al. (cond-mat/0305455), indicating importance of the electronic lattice different from the crystal.