Electrical generation and absorption of phonons in carbon nanotubes

We have performed low temperature scanning tunneling spectroscopy on individual single-wall carbon nanotubes freely suspended over trenches. Spatially resolved spectroscopy shows a Coulomb-staircase behavior superimposed on the local density of states. In addition to the Coulomb peaks from the addition of electrons, side peaks appear due to phonon-assisted tunneling. Electrons inelastically tunneling into the nanotube cause a non-equilibrium phonon occupation, leading to both emission and absorption of phonons by successive tunneling electrons. The addition of a gate electrode into our STM configuration allows further validation of this interpretation. These observations represent a new class of electrical transport phenomena, namely a current induced non-equilibrium phonon distribution and its influence on transport through a molecule.