Asymmetric Franck-Condon factors in suspended carbon nanotube quantum dots

TL;DR

This paper investigates how spatial variations in electronic density within suspended carbon nanotube quantum dots influence vibrational coupling, revealing asymmetric Franck-Condon factors that significantly affect electronic transport properties.

Contribution

It introduces a model incorporating space-dependent Franck-Condon factors, extending beyond the conventional Anderson-Holstein framework for quantum dot vibrational coupling.

Findings

Space-dependent Franck-Condon factors cause asymmetric vibrational effects.

Transport measurements align with the predicted effects of spatial fluctuations.

The model is applicable to various nano-electromechanical systems.

Abstract

Electronic states and vibrons in carbon nanotube quantum dots have in general different location and size. As a consequence, the conventional Anderson-Holstein model, coupling vibrons to the dot total charge only, may no longer be appropriated in general. Here we explicitly address the role of the spatial fluctuations of the electronic density, yielding space-dependent Franck-Condon factors. We discuss the consequent marked effects on transport which are compatible with recent measurements. This picture can be relevant for tunneling experiments in generic nano-electromechanical systems.