The effects of electronic correlations and orbital degeneracy on thermoelectric properties are studied within the context of multiorbital Hubbard models on different lattices. We use dynamical mean field theory with a modified version of iterative perturbation theory as a solver to calculate the self-energy of the models in a wide range of interaction strengths. The Seebeck coefficient, which measures the voltage drop in response to a temperature gradient across the system, shows a nonmonotonic behavior with temperature in the presence of strong correlations. This anomalous behavior is associated with a crossover from a Fermi liquid metal at low temperatures to a bad metal with incoherent excitations at high temperatures, and is qualitatively captured by the Kelvin formula but not quantitatively. We find that for interactions comparable to the bandwidth, the Seebeck coefficient acquires large values at low temperatures. Moreover, for strongly correlated cases, where the interaction is larger than the bandwidth, the figure of merit is enhanced over a wide range of temperatures because of decreasing electronic contributions to the thermal conductivity. We also find that multiorbital systems will typically yield larger thermopower and figure of merit compared to single-orbital models over a temperature range possibly relevant to applications.

• Received 16 August 2013

DOI:https://doi.org/10.1103/PhysRevB.88.205141