Temperature dependence of thermopower in strongly correlated multiorbital systems

多軌道強相関電子系における熱起電力の温度依存性

森 道康  ; 関野 まり*; 岡本 敏史*; 小椎八重 航*; 前川 禎通

Mori, Michiyasu; Sekino, Mari*; Okamoto, Satoshi*; Koshibae, Wataru*; Maekawa, Sadamichi

The thermopower in strongly correlated electron systems attracts much attention. The thermopower is the entropy flow by the electric current, so that the spin and orbital degrees of freedom are of importance to enhance the thermopower. For the strongly correlated systems, the thermopower was shown to exhibit the non-monotonic temperature dependence. Furthermore, in the multiorbital correlated system, the electronic state reflects the crystal field splitting and the Hund coupling. It is worth examining the effect of the crystal field splitting and the Hund coupling on the temperature dependence of the thermopower in multiorbital correlated systems. We study temperature dependence of the thermopower in the two- and three-orbital Hubbard models by using the dynamical mean-field theory with the non-crossing approximation as impurity solver. It is clarified how the Hund coupling, the crystal field splitting and the Coulomb interaction produce the non-monotonic temperature behavior of the thermopower. It is also found that the sign of thermopower is changed by temperature and electron density. The entropy consideration at high temperatures, i.e., Heikes formula, consistently explains the effect of the crystal field splitting and the Hund coupling on the thermopower. Several materials are discussed in the light of our theory.