The first hints of superconductivity at room temperature -- a goal considered nearly impossible a year ago and a faint hope just a month ago -- are emerging from several laboratories around the world.
None of the labs reports solid evidence of superconductivity that can be reproduced reliably in test after test, but fleeting glimpses of the phenomenon at temperatures ranging between 45 and 79 degrees Fahrenheit suggest that the goal is attainable.
Little is known of the atomic structure of the various materials being tested, but physicists say that as they gain deeper knowledge and can control their manufacturing processes better, room temperature superconductivity should become a proven reality.
Last week's issue of Nature contains a report from India's National Physical Laboratory in New Delhi that the Josephson effect was detected in a synthetic ceramic material at 79 degrees. The effect, which can only occur with superconducting materials, involves electrons that acquire the ability to "tunnel" through a thin film of insulation.
Although this is evidence of superconductivity on at least a microscopic level within the material, tests for a loss of an overall electrical resistance showed no large-scale superconductivity until the material was cooled to 45 degrees below zero Fahrenheit.
Preliminary word of unstable superconductivity at 66 degrees Fahrenheit has come from the laboratory of Alex Zettl and Marvin Cohen at the University of California at Berkeley. When the material was heated to higher temperatures and recooled, however, it lost its superconductivity.
More dramatic evidence from another lab is to be reported in the June 15 issue of Physical Review Letters. Stanford R. Ovshinsky, head of Energy Conversion Devices, Inc., a private research firm in Troy, Mich., will report finding a material in which small regions are superconducting at 9 degrees Fahrenheit. Since submitting his paper, Ovshinsky has found that the same material shows similar superconductivity at 45 degrees Fahrenheit.
In this case, the evidence is not loss of resistance in the bulk material but the appearance of the Meissner effect -- repulsion of a magnetic field, observed only in superconductors.