Ballistic Phonon Thermal Transport in Multi-Walled Carbon Nanotubes

We report electrical transport experiments using the phenomenon of electrical breakdown to perform thermometry that probe the thermal properties of individual multi-walled nanotubes. Our results show that nanotubes can readily conduct heat by ballistic phonon propagation, reaching a quantum-mechanical limit to thermal conductance. We determine the thermal conductance quantum, the ultimate limit to thermal conductance for a single phonon channel, and find good agreement with theoretical calculations. Moreover, our results suggest a breakdown mechanism of thermally activated C-C bond breaking coupled with the electrical stress of carrying ~10^12 A/m^2. We also demonstrate a current-driven self-heating technique to improve the conductance of nanotube devices dramatically.