AC transport and full-counting statistics of molecular junctions in the weak electron-vibration coupling regime

TL;DR

This paper theoretically investigates electron-vibration interactions in molecular junctions under weak coupling, analyzing current fluctuations, vibrational mode distributions, and responses to ac fields using nonequilibrium Green's functions.

Contribution

It provides a detailed analysis of full-counting statistics and vibrational dynamics in molecular junctions with weak electron-vibration coupling, including effects of ac fields.

Findings

Electron-vibration interaction influences current fluctuation statistics.

Vibrational mode populations deviate from equilibrium under bias.

The response to ac fields reveals additional transport features.

Abstract

The coupling of the charge carriers passing through a molecule bridging two bulky conductors with local vibrational modes of the molecule, gives rise to distinct features in the electronic transport properties on one hand, and to nonequilibrium features in the vibrations' properties, e.g., their population, on the other. Here we explore theoretically a generic model for a molecular junction biased by an arbitrary dc voltage in the weak-coupling regime. We analyze the signature of the electron-vibration interaction on the full-counting statistics of the current fluctuations (i.e., the cumulant generating-function of the current correlations), we give a detailed account of the response to an ac field exerted on the junction (on top of the dc bias voltage), we study the nonequilibrium distribution of the vibrational modes and the fluctuations they cause in the displacement of the molecule center of mass. The calculations use the technique of nonequilibrium Green's functions, and treat the electron-vibration coupling in perturbation theory, within the random-phase approximation when required.