Effects of strong electronic interactions on the thermopower properties of the repulsive Hubbard model

We obtain the Seebeck coefficient or thermopower $S$, which determines the conversion efficiency from thermal to electrical energy, for the two-dimensional Hubbard model on different geometries (square, triangular, and honeycomb lattices) for different electronic densities and interaction strengths. Using determinantal Quantum Monte Carlo we find the following key results: (a) the bi-partiteness of the lattice affects the doping dependence of $S$; (b) strong electronic correlations can greatly enhance $S$ and produce nontrivial sign changes as a function of doping, especially in the vicinity of the Mott insulating phase; and (c) $S(T)$ near half-filling can show nonmonotonic behavior as a function of temperature. That is, our results show that electronic interactions lead to unexpected behavior for the thermopower for given fillings, even at high temperatures, which may vary depending on the geometry. We emphasize the role of strong interaction effects in engineering better devices for energy storage and applications, as captured by our calculations of the power factor $\text{PF}={S}²\ensuremath{\sigma}$, where $\ensuremath{\sigma}$ is the dc conductivity.