Theory of Vibrationally Inelastic Electron Transport through Molecular Bridges

TL;DR

This paper develops a theoretical framework to analyze vibrationally inelastic electron transport through molecular junctions, examining the effects of vibrational motion and approximations on electron transmission and current.

Contribution

It introduces a generic model and numerical methods for exact transmittance evaluation, exploring vibrational effects and the validity of common approximations in molecular electron transport.

Findings

Vibrational motion significantly influences electron transmission.

Exact transmittance calculations reveal limitations of common approximations.

Strong and weak coupling regimes show distinct transport characteristics.

Abstract

Vibrationally inelastic electron transport through a molecular bridge that is connected to two leads is investigated. The study is based on a generic model of vibrational excitation in resonant transmission of electrons through a molecular junction. Employing methods from electron-molecule scattering theory, the transmittance through the molecular bridge can be evaluated numerically exactly. The current through the junction is obtained approximately using a Landauer-type formula. Considering different parameter regimes, which include both the case of a molecular bridge that is weakly coupled to the leads, resulting in narrow resonance structures, and the opposite case of a broad resonance caused by strong interaction with the leads, we investigate the characteristic effects of coherent and dissipative vibrational motion on the electron transport. Furthermore, the validity of widely used approximations such as the wide-band approximation and the restriction to elastic transport mechanisms is investigated in some detail.