A second group of French researchers has claimed to have achieved superconductivity
at the relatively high temperature of 250 kelvin, or about the temperature
of a cold night in Siberia. J. L. Tholence of the National Centre for Scientific
Research (CNRS) in Grenoble observed 鈥榓 partial or total drop of the resistivity鈥�
near 250 K in mercury-barium-calcium-copper oxide.
Last month, Michel Lagues of the College of Industrial Physics and
Chemistry in Paris reported superconductivity at the same temperature in
a material made of bismuth-strontium-calcium-copper oxide.
The big question is whether superconductors that conduct at such high
temperatures can be produced reliably. In a recent issue of Nature, Paul
Grant of the Electric Power Research Institute in Palo Alto, California,
recalled 鈥榤any sightings of Unidentified Superconducting Objects鈥�, which
could never be verified. They could be experimental artefacts, or unstable
phases present only in small quantities and for short times. If the French
results cannot be replicated, they will add to the ranks of USOs, he says.
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