On Mon, 30 Aug 2010 14:22:11 -0700, Roy Lewallen
wrote:

The lack of comprehension of fundamental physics on this newsgroup is
astounding, so it's no surprise that a less-known fact has been missed:

A superconductor has zero resistance only at DC. The resistance at RF
depends, among other things, the frequency and the material's
temperature. Because the resistivity of copper drops dramatically at
cryogenic temperatures, it can be difficult to make a superconductor
with resistance as low as copper at the same temperature.

Zero resistance is not strictly a function of direct current. It is
simply the most often reported experimental characteristic in the
popular press. Impracticality of the additional RF characteristic
(which I presume in this forum to be confined to UHF and below) is
unwarranted in materials research at this point, but EHF/IR and above
results are frequently reported in association with other research -
plasmonics and phonon/electron interaction.

The resistivity of copper falls with temperature, true, but we
encounter diminishing returns as we approach absolute zero: the drop
fails to follow through to the expected final zero resistance. This
was an experimental dissappointment decades ago. Silver and gold are
rarely chosen for their electrical properties in the nano-dimension -
chilled or otherwise (although gold is suitable, gold is far more
useful in association with thiols). In fact, what are typically poor
conductors exhibit less low temperature resistance than copper (cold
or warm). I won't go into that list, it is enough to consider that
such "wires" would be confined to thin film depositions on a flexible
tape substrate - pretty exotic.

Going further, it isn't even necessary to drive temperatures to the
basement for improved conduction. Carbon nanotubes are exemplars of
high conductivity (several orders of magnitude better than what we
consider good metals) at room temperature where a carbon macrotube
would be called a resistor. Conductivity and superconductivity
research has long ago left the realm of temperature and has entered
the realm of crystal alignment.

However, even this academic. Carbon Nanotube construction at a scale
to compete with standard copper wire is off by a scale of a million to
billions (of dollars, much less practicability).

73's
Richard Clark, KB7QHC