Pure Carbon Nanotubes Superconduct at 15K

Courtesy:  Electronics Times
April 7, 2001

A Chinese research group from Hong Kong University of Science and Technology has developed individual, highly aligned, single-walled carbon nanotubes that demonstrate superconducting behaviour at around 15K, a much higher temperature than nanotube bundles.

Ping Sheng, a member of the research team, said: "Pure carbon can be superconducting at such elevated temperatures when a carbon sheet is rolled into 4 tubes. "It is the first time that one has observed the signature of one dimensionality on superconductivity. This is very interesting since the 1D world is very different from the 3D world because temperature has a much more significant effect."

Around 40 years ago, two physicists, Mermin and Wagner, published a theorem which prohibited phase transitions in 1 and 2D worlds. Sheng said: "This theorem accurately captures what we see in our nanotubes, which constitutes perhaps the best physical example of one dimensionality. Because of the strong thermal effect, what has been observed is not a sharp transition at 15K but a smoothed transition where behaviour is dictated by the one dimensionality."

Since the discovery of fullerenes, superconductivity has been achieved in alkali metal-doped and hole-doped crystals of C60 (Buckeyballs). Sheng said: "The fact that pure carbon nanotubes can be superconducting at 15K implies that doping may enhance the transition temperature."

NOTE 1: An analog may exist for nanotubes made from silicon, boron-nitride or tungsten-disulfide as well.

NOTE 2: Recent research from the University of Pennsylvania indicates that carbon nanotubes may also be the best heat-conducting material yet discovered. Further, writing in Physical Review Letters (26 March 2002), Alexander Savin and colleagues offer support for a theorem that states that Fourier's law of heat conduction does not generally apply to one-dimensional systems (like nanotubes), where thermal conductivity can be infinite.

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