On the theory of charge transport and entropic effects in solvated molecular junctions

TL;DR

This paper extends a unified charge transport theory for molecular junctions to include entropic effects, analyzing temperature dependence and proposing experimental detection criteria, with implications for understanding solvated systems.

Contribution

It introduces an extension of the unified Landauer-Marcus theory to incorporate entropic effects and nuclear tunneling, providing a comprehensive framework for charge transport analysis.

Findings

Entropic effects significantly influence charge transport in solvated junctions.

The extended theory accurately predicts temperature-dependent current behavior.

Experimental criteria are proposed for detecting entropic contributions.

Abstract

Experimental studies on single-molecule junctions are typically in need of a simple theoretical approach that can reproduce or be fitted to experimentally measured transport data. In this context, the single-level variant of the Landauer approach is most commonly used but methods based on Marcus theory are also gaining in popularity. Recently, a generalized theory unifying these two approaches has also been developed. In the present work, we extend this theory so that it includes entropic effects (which can be important when polar solvents are involved, but are likely minor for solid-state systems). We investigate the temperature-dependence of the electric current and compare it to the behavior predicted by the Landauer and the conventional Marcus theory. We argue that this generalized theory provides a simple yet effective framework for understanding charge transport through molecular junctions. Furthermore, we explore the role of the entropic effects in different transport regimes and suggest experimental criteria for detecting them in solvated molecular junctions. Lastly, in order to account for nuclear tunnelling effects, we also demonstrate how lifetime broadening can be introduced into the Marcus-Levich-Dogonadze-Jortner-type description of electron transport.