Current-voltage characteristics of suspended single-wall carbon nanotube quantum dots show a series of steps equally spaced in voltage. The energy scale of this harmonic, low-energy excitation spectrum is consistent with that of the longitudinal low-k phonon mode (stretching mode) in the nanotube. Agreement is found with a Franck-Condon-based model in which the phonon-assisted tunneling process is modeled as a coupling of electronic levels to underdamped quantum harmonic oscillators. Comparison with this model indicates a rather strong electron-phonon coupling factor of order unity.
@article{arxiv.cond-mat/0508270,
title = {Tunneling in suspended carbon nanotubes assisted by longitudinal phonons},
author = {S. Sapmaz and P. Jarillo-Herrero and Ya. M. Blanter and C. Dekker and H. S. J. van der Zant},
journal= {arXiv preprint arXiv:cond-mat/0508270},
year = {2007}
}