Discussion Topic Posted for the NANOTUBE-99 Workshop:

This appears to be a true mystery in view of the following facts:

• Nanotubes, same as fullerenes, are characterized by the same type of sp² bonding as graphite.
• Graphite, when intercalated, becomes superconducting (albeit at very low tempeartures). Solid C₆₀, when intercalated, is superconducting well above 30 K. Electron-phonon coupling is responsible for superconductivity in these two systems.
• The vibrational spectrum of nanotubes in ropes contains the same high-frequency modes that cause superconductivity in solid C₆₀.
• Same as in graphite, intercalants have been observed to shift the Fermi level towards the Van-Hove singularities, causing a significant increase in the density of states and in the observed conductivity. In solid C₆₀ this increase/onset of conductivity has been accompanied by superconducting behavior.

1.1 "Effects due to the intercalation process"
   by Peter Butzloff, University of North Texas, Department of Materials Science

1.2 "Experimental Evidence for Superconductivity through Single-Walled Carbon Nanotubes"
   by David Tomanek, Michigan State University