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) between 30 and 117K. Sheng
said: "The fact that pure carbon nanotubes can be
superconducting at 15K implies that doping may enhance
the transition temperature."
NOTE: 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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http://superconductors.org/15K.htm
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