Tunneling in suspended carbon nanotubes assisted by longitudinal phonons
  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. 
S. Sapmaz, P. Jarillo-Herrero, Ya.M. Blanter, C. Dekker, and H.S.J.   van der Zant