Wiedemann-Franz Law for Molecular Hopping Transport

TL;DR

This paper develops an analog of the Wiedemann-Franz law for molecular hopping systems, revealing a linear temperature dependence replaced by a dependence on nuclear reorganization energy, with implications for molecular device design.

Contribution

It introduces a new Wiedemann-Franz type law for molecular hopping transport, linking thermal and electrical conductance via nuclear reorganization energy.

Findings

Derived an analytical relation between thermal and electrical conductivity in molecular systems.

Confirmed the relation's robustness through molecular junction analysis.

Revealed a linear dependence on nuclear reorganization energy instead of temperature.

Abstract

The Wiedemann-Franz (WF) law is a fundamental result in solid-state physics that relates the thermal and electrical conductivity of a metal. It is derived from the predominant origin of energy conversion in metals: the motion of quasi-free charge-carrying particles. Here, an equivalent WF relationship is developed for molecular systems in which charge carriers are moving not as free particles but instead hop between redox sites. We derive a concise analytical relationship between the electrical and thermal conductivity generated by electron hopping in molecular systems and find that the linear temperature dependence of their ratio as expressed in the standard WF law is replaced by a linear dependence on the nuclear reorganization energy associated with the electron hopping process. The robustness of the molecular WF relation is confirmed by examining the conductance properties of a paradigmatic molecular junction. This result opens a new way to analyze conductivity in molecular systems, with possible applications advancing the design of molecular technologies that derive their function from electrical and/or thermal conductance.