Effect of spin and orbital on thermopower in strongly correlated electron systems

We have studied the thermopower and resistivity based on the Hubbard model with strong on-site Coulomb interaction and orbital degeneracy by using exact diagonalization method. It is shown that the thermopower is strongly enhanced by the spin and orbital degrees of freedom, but the resistivity is significantly less affected. The origin of the large thermopower in NaCo2O4 and a key for the strategy of new thermoelectric materials in transition metal oxides are proposed in the light of the theory