Superconductivity Possible at 250 Kelvins

By Lipkin, R. | Science News, December 18, 1993 | Go to article overview

Superconductivity Possible at 250 Kelvins


Lipkin, R., Science News


"If it's true, it would be fantastic," says Miles V. Klein, a physicist at the University of Illinois at Urbana-Champaign. "250 degrees kelvin is almost room temperature in Siberia."

Klein was referring to the report this week by a French team that it had attained superconductivity at 250 kelvins (-23 degrees C) in a thin film. Albeit a fleeting phenomenon in tiny samples, superconductivity at this temperature is the highest officially reported so far, nearly 100 kelvins above what other groups have published (SN: 10/2/93, p. 214).

Reporting in the Dec. 17 SCIENCE, Michel Lagues, a physicist at a Centre National de la Recherche Scientifique (CNRS) facility in Paris, and his colleagues describe a method for making a finicky, thin film of copper oxide. The film contains eight layers of copper and oxygen molecules sandwiched between other layers of bismuth, strontium, calcium, and oxygen. The scientists built the thin film painstakingly atom by atom, using a method called sequentially imposed layer epitaxy.

The material itself - a type of cuprate compound belonging to a well-known family of materials denoted BiSrCaCuO is not fundamentally new.

"The basic architecture of this material is well known," Lagues says. "What's new here is the way we grew these materials, layer by layer. It's not hard to make a sequence of layers - copper, calcium, copper, calcium - many times. But it's very difficult to get the structure just right, with the right conditions. So what we've done is made the material well enough to obtain superconductivity at this temperature."

Subjecting the material to standard tests for superconductivity, the researchers watched its electrical resistance drop by a factor of 100,000 as the sample cooled from 280 to 250 kelvins. At 235 kelvins, its resistance fell below detection levels. …

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