Enhancement of the Na$_x$CoO$_2$ thermopower due to electronic correlations

TL;DR

This paper demonstrates how electronic correlations significantly enhance the thermopower of Na$_{0.7}$CoO$_2$ by 200%, revealing a new mechanism involving asymmetric shifts of electrons and holes from the Fermi level, which could improve thermoelectric performance.

Contribution

It introduces a novel correlation-driven mechanism that increases thermopower in Na$_{0.7}$CoO$_2$, combining local density approximation with dynamical mean field theory.

Findings

Thermopower of Na$_{0.7}$CoO$_2$ increases by 200% due to correlations.

Asymmetric shifts of electrons and holes from the Fermi level are responsible.

Potential for enhanced thermoelectric efficiency through bandstructure and correlation engineering.

Abstract

Using the merger of local density approximation and dynamical mean field theory, we show how electronic correlations increase the thermopower of Na$_{0.7}$CoO$_2$ by 200%. The newly revealed mechanism is an asymmetric shift of (quasi) electrons and holes away from the Fermi level, concurrent with an asymmetry of the respective (group) velocities. Exploiting this effect in bandstructure and correlation engineering may lead to a substantial increase of the thermoelectric figure of merit.