Thermoelectric effects in correlated quantum dots and molecules

TL;DR

This paper studies thermoelectric effects in correlated quantum dots and molecules using the Anderson model and numerical renormalization group, revealing sign changes in thermopower linked to Kondo physics and the impact of screening on thermoelectric efficiency.

Contribution

It provides new insights into thermopower behavior and the influence of screening interactions in Kondo and mixed valence regimes of quantum dots and molecules.

Findings

Thermopower exhibits two sign changes in the Kondo regime.

Sign change in thermopower is a signature of strong correlations.

Screening enhances the thermoelectric figure of merit.

Abstract

We investigate thermoelectric properties of correlated quantum dots and molecules, described by a single level Anderson model coupled to conduction electron leads, by using Wilson's numerical renormalization group method. In the Kondo regime, the thermopower, $S(T)$, exhibits two sign changes, at temperatures $T=T_{1}$ and $T=T_{2}>T_{1}$. We find that $T_{2}$ is of order the level width $\Gamma$ and $T_{1}> T_{p}\approx T_{K}$, where $T_{p}$ is the position of the Kondo induced peak in the thermopower and $T_{K}$ is the Kondo scale. No sign change is found outside the Kondo regime, or, for weak correlations, making a sign change in $S(T)$ a particularly sensitive signature of strong correlations and Kondo physics. For molecules, we investigate the effect of screening by conduction electrons on the thermoelectric transport. We find that a large screening interaction enhances the figure of merit in the Kondo and mixed valence regimes.