Theoretical study of thermoelectric and Hall effects in the layered cobalt oxides, NaxCoO2

We examine the response of the transport properties to the magnetic field and temperature gradient in the Hubbard model on the kagome lattice within the limit of U → ∞ , using the “retraceable-path” approximation. The layered cobalt oxides, Na x CoO 2 , involve the triangular lattice of the cobalt ions. However, the electron trajectory makes up the kagome lattice due to the orbital degeneracy of t 2 g states. It is shown that this kagome lattice hidden in the CoO 2 layer exhibits the anomalous high-temperature Hall effect recently observed by Wang et al.