Multi-orbital Effects on Thermoelectric Properties of Strongly Correlated Materials

TL;DR

This study investigates how electronic correlations and orbital degeneracy influence thermoelectric properties in multi-orbital Hubbard models, revealing non-monotonic Seebeck behavior and enhanced thermopower in strongly correlated regimes.

Contribution

It demonstrates the impact of multi-orbital effects on thermoelectric performance, highlighting the role of strong correlations and orbital degeneracy in enhancing thermopower.

Findings

Seebeck coefficient shows non-monotonic temperature dependence with strong correlations.

Strongly correlated systems exhibit increased thermopower and figure of merit.

Multi-orbital models produce larger thermopower than single orbital models.

Abstract

The effects of electronic correlations and orbital degeneracy on thermoelectric properties are studied within the context of multi-orbital Hubbard models on different lattices. We use dynamical mean field theory with iterative perturbation theory as a solver to calculate the self-energy of the models in wide range of interaction strengths. The Seebeck coefficient, which measures the voltage drop in response to a temperature gradient across the system, shows a non-monotonic behavior with temperatures 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. 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 band width, 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 multi-orbital systems will typically yield larger thermopower compared to single orbital models.