Enhancement of the thermoelectric power by electronic correlations in bad metals: a study of the Kelvin formula

TL;DR

This study demonstrates that electronic correlations in a Hubbard model on an anisotropic triangular lattice significantly enhance thermoelectric power and cause non-monotonic temperature dependence, aligning semi-quantitatively with experimental observations.

Contribution

It shows how electronic correlations influence thermopower in bad metals using the Kelvin formula within a Hubbard model framework.

Findings

Electronic correlations enhance thermopower magnitude.

Thermopower exhibits non-monotonic temperature dependence.

Crossover from Fermi liquid to bad metal with increasing temperature.

Abstract

In many strongly correlated electron metals the thermoelectric power has a non-monotonic temperature dependence and values that are orders of magnitude larger than for elemental metals. Kelvin proposed a particularly simple expression for the thermopower in terms of the temperature dependence of the chemical potential. We consider a Hubbard model on an anisotropic triangular lattice at half filling, a minimal effective Hamiltonian for several classes of organic charge transfer salts. The finite temperature Lanczos method is used to calculate the temperature dependence of the thermopower using the Kelvin formula. We find that electronic correlations significantly enhance the magnitude of the thermopower and lead to a non-monotonic temperature dependence. The latter reflects a crossover with increasing temperature from a Fermi liquid to a bad metal. Although, the Kelvin formula gives a semi-quantitative description of some experimental results it cannot describe the directional dependence of the sign of the thermopower in some materials.