Unusual doping-dependent sign changes of the Seebeck coefficient in strongly correlated systems

The thermoelectric performance of a material is determined by its Seebeck coefficient, or the thermopower which may be enhanced, among other sources, by strong electronic correlations. In view of this, we investigate the Seebeck coefficient for the two-dimensional repulsive Fermi Hubbard model on different geometries (square, triangular, and honeycomb lattices). We employ Determinant Quantum Monte Carlo as an unbiased numerical technique to investigate the behavior of the Seebeck coefficient as a function of particle doping. Our analysis is conducted in weak to strong interaction regimes, that includes the critical point for onset of Mott physics. The DQMC simulation is performed at high enough temperatures to alleviate the sign problem and preclude spontaneous symmetry breaking. We interpret the DQMC data from a mean-field perspective, employing a Hartree Fock mean-field for the weak coupling regime and Parton mean-field theory for the strong coupling regime. Our analysis indicates that the non-trivial sign change and the singularities in the Seebeck coefficient (compared to the noninteracting case) can be attributed to the charge physics brought by the onset of the "Mottness" of the system.