The thermopower properties of interacting systems

TL;DR

This paper explores how various electronic interactions and electron-phonon coupling influence the Seebeck coefficient in thermoelectric materials, revealing enhancements and sign changes linked to Fermi surface topology.

Contribution

It investigates the effects of attractive, nearest-neighbor, and electron-phonon interactions on thermopower, extending understanding beyond on-site Hubbard models.

Findings

Additional interactions can enhance the Seebeck coefficient.

Multiple sign changes occur as a function of doping due to interactions.

Electron-phonon coupling induces Seebeck anomalies without on-site repulsion.

Abstract

The quest for efficient devices has fueled research in thermoelectric materials. In these materials, the goal is to maximize the Figure of Merit $ZT$. One of the components of this quantity is the Seebeck coefficient, which measures the voltage generated in response to a temperature gradient. Recent studies have revealed that strong electronic correlations can enhance the Seebeck coefficient, leading to anomalous behavior near half-filling. However, the impact of interactions beyond the on-site Hubbard remains mostly unexplored. In this work, we investigate the Seebeck coefficient considering attractive interactions, nearest-neighbor interactions, sublattice potentials and electron-phonon coupling. We find that additional interaction scales can enhance the Seebeck coefficient, while also leading to multiple anomalous changes of sign as a function of doping. We also show that the anomalous behavior is connected to a gap opening in the ground state. Moreover, electron-phonon coupling also lead to a Seebeck anomaly, even without on-site repulsion. We connect these changes of sign in the Seebeck coefficient with a restructuring of the Fermi surface and a change in its topology, an effect commonly seen in cuprates.