Franck-Condon blockade in suspended carbon nanotube quantum dots

TL;DR

This paper demonstrates the Franck-Condon blockade in suspended carbon nanotube quantum dots, revealing strong electron-vibron coupling and its implications for quantum transport and nanoelectromechanical systems.

Contribution

It provides the first quantitative analysis of vibron-mediated transport in suspended nanotubes, confirming the Franck-Condon blockade in a highly tunable nanostructure.

Findings

Large electron-vibron coupling observed

Quantitative analysis of vibron-mediated transport

Confirmation of Franck-Condon blockade in nanotubes

Abstract

Understanding the influence of vibrational motion of the atoms on electronic transitions in molecules constitutes a cornerstone of quantum physics, as epitomized by the Franck-Condon principle of spectroscopy. Recent advances in building molecular-electronics devices and nanoelectromechanical systems open a new arena for studying the interaction between mechanical and electronic degrees of freedom in transport at the single-molecule level. The tunneling of electrons through molecules or suspended quantum dots has been shown to excite vibrational modes, or vibrons. Beyond this effect, theory predicts that strong electron-vibron coupling dramatically suppresses the current flow at low biases, a collective behaviour known as Franck-Condon blockade. Here we show measurements on quantum dots formed in suspended single-wall carbon nanotubes revealing a remarkably large electron-vibron coupling and, due to the high quality and unprecedented tunability of our samples, admit a quantitative analysis of vibron-mediated electronic transport in the regime of strong electron-vibron coupling. This allows us to unambiguously demonstrate the Franck-Condon blockade in a suspended nanostructure. The large observed electron-vibron coupling could ultimately be a key ingredient for the detection of quantized mechanical motion. It also emphasizes the unique potential for nanoelectromechanical device applications based on suspended graphene sheets and carbon nanotubes.