Controlling the transmission line shape of molecular t-stubs and potential thermoelectric applications

TL;DR

This paper introduces a method to analyze and control asymmetric transmission line shapes in molecular junctions, linking molecular structure to quantum interference effects, with implications for thermoelectric device efficiency.

Contribution

The authors develop an analytical approach using simple tight-binding models to understand the structure dependence of interference dips in molecular electron transport.

Findings

Analytical characterization of line shape asymmetry in molecular junctions.

First-principles calculations confirm the model's predictions.

Potential for optimizing thermoelectric performance in molecular devices.

Abstract

Asymmetric line shapes can occur in the transmission function describing electron transport in the vicinity of a minimum caused by quantum interference effects. Such asymmetry can be used to increase the thermoelectric efficiency of molecular junctions. So far, however, asymmetric line shapes have been only empirically found for just a few rather complex organic molecules where the origins of the line shapes relation to molecular structure were not resolved. In the present work we introduce a method to analyze the structure dependence of the asymmetry of interference dips from simple two site tight-binding models, where one site corresponds to a molecular $\pi$ orbital of the wire and the other to an atomic $p_z$ orbital of a side group, which allows us to analytically characterize the peak shape in terms of just two parameters. We assess our scheme with first-principles electron transport calculations for a variety of {\it t-stub} molecules and also address their suitability for thermoelectric applications.