Physical mechanism of negative differential conductance in substrateless metallic carbon nanotubes

The existence of pronounced negative differential conductance at room temperature in suspended metallic carbon nanotubes was recently proven. We investigate here the physical nature of this phenomenon, which is of considerable importance for high-frequency devices, such as oscillators working up to few hundreds of GHz. Besides previous explanations, we find a new physical mechanism that explains the negative differential conductivity at room temperature. The entire suspended metallic carbon nanotube behaves as a very large quantum well, the negative differential conductance occurring due to the depletion of carriers on high-energy resonant levels.