Understanding resonant charge transport through weakly coupled single-molecule junctions

TL;DR

This paper investigates resonant charge transport in graphene-based molecular junctions, revealing limitations of traditional models and emphasizing the roles of electron-electron and vibrational interactions, with implications for understanding molecular electronics.

Contribution

It introduces a non-adiabatic electron transfer model that accounts for vibrational interactions, challenging the adequacy of Landauer and Marcus theories for resonant transport.

Findings

Non-interacting Landauer theory is inadequate for resonant transport.

Charge transport involves non-adiabatic electron transfers influenced by vibrational interactions.

Transport properties are affected by electron-electron and electron-vibrational couplings.

Abstract

Off-resonant charge transport through molecular junctions has been extensively studied since the advent of single-molecule electronics and it is now well understood within the framework of the non-interacting Landauer approach. Conversely, gaining a qualitative and quantitative understanding of the resonant transport regime has proven more elusive. Here, we study resonant charge transport through graphene-based zinc-porphyrin junctions. We experimentally demonstrate an inadequacy of the non-interacting Landauer theory as well as the conventional single-mode Franck-Condon model. Instead, we model the overall charge transport as a sequence of non-adiabatic electron transfers, the rates of which depend on both outer and inner-sphere vibrational interactions. We show that the transport properties of our molecular junctions are determined by a combination of electron-electron and electron-vibrational coupling, and are sensitive to the interactions with the wider local environment. Furthermore, we assess the importance of nuclear tunnelling and examine the suitability of semi-classical Marcus theory as a description of charge transport in molecular devices.