Heat dissipation and its relation to thermopower in single-molecule junctions

TL;DR

This paper provides a theoretical analysis of Joule heating in single-molecule junctions, revealing how heat dissipation varies with electronic structure and bias polarity, and its relation to thermopower.

Contribution

It combines Landauer transport theory with ab initio calculations to link heat dissipation asymmetries to thermopower in molecular junctions.

Findings

Heat dissipation is asymmetric and depends on bias polarity.

Heat dissipation correlates with thermopower in molecular junctions.

Strategies are proposed to explore thermoelectric effects in molecular electronics.

Abstract

Motivated by recent experiments [Lee et al. Nature 498, 209 (2013)], we present here a detailed theoretical analysis of the Joule heating in current-carrying single-molecule junctions. By combining the Landauer approach for quantum transport with ab initio calculations, we show how the heating in the electrodes of a molecular junction is determined by its electronic structure. In particular, we show that in general the heat is not equally dissipated in both electrodes of the junction and it depends on the bias polarity (or equivalently on the current direction). These heating asymmetries are intimately related to the thermopower of the junction as both these quantities are governed by very similar principles. We illustrate these ideas by analyzing single-molecule junctions based on benzene derivatives with different anchoring groups. The close relation between heat dissipation and thermopower provides general strategies for exploring fundamental phenomena such as the Peltier effect or the impact of quantum interference effects on the Joule heating of molecular transport junctions.