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SCIENCE FILE

It's Electric, Exciting--and Elusive

Ten years after breakthroughs in superconductivity were announced, scientists still don't understand how it all works.

July 11, 1996|K.C. COLE | TIMES SCIENCE WRITER

HOUSTON — An understated article in an obscure German physics journal 10 years ago set off an avalanche of discoveries that culminated at a happening that came to be known as the "Woodstock of Physics."

During a meeting of the American Physical Society several months after the article appeared, scientists by the thousands crammed into the New York Hilton to hear about miraculous new materials that openly flouted the laws of nature, promising to provide the ultimate free lunch: electricity that flowed eternally without resistance.

Earlier this year, scientists at a 10-year anniversary workshop in Houston gathered to reflect on how these so-called high-temperature superconductors perform the impossible--conduct electric currents in perpetual motion with no loss of energy.

Their consensus is that after a decade of study, they remain essentially clueless. The new materials "are having a lot of fun hiding how they do that," said Alex Muller, the IBM Zurich researcher who won a Nobel Prize for his discovery.

When Muller and George Bednorz announced they had found a ceramic material that conducted electricity perfectly at the relatively balmy temperature of 77 degrees above "absolute zero" (459 degrees Fahrenheit below zero), it was as unexpected as the sudden appearance of an ice cube in a pot of boiling soup. "It proves that the unexpected in science can still happen--and in a big way," said physicist Robert Cava of AT&T Bell Labs.

Until 1986, superconductivity had only been seen at extremely cold temperatures, a few dozen degrees above the absolute zero mark. As a technology, that rendered it practically useless because of the enormous expense required to cool something to those frigid depths.

The discovery of these comparatively high-temperature superconductors opened up the possibility of unlimited power, magnetically levitated trains and colossal magnets for medical applications such as magnetic resonance imagining.

Few of these futuristic technologies were on display at the Houston meeting, however. The closest thing to a magnetically levitating train was a toy car that raced around on a small superconducting track set up by the Texas Center for Superconductivity. The Electric Power Research Institute showed off a 160-foot-long flexible superconducting cable--the longest ever made, although still far short of what would be needed for practical uses.

The truth is, turning the dream of friction-free electricity into reality has been a lot more difficult than anyone predicted. There is progress, but it's been painfully slow. The materials are complicated, easily contaminated and brittle. Trying to make a wire out them, says the institute's Paul Grant, is like trying to make a wire out of a dinner plate.

Superconductivity was discovered in 1911 in the metal mercury--a far more likely candidate for a conductor of electricity than ceramics. And until 1986, all new superconductors were metals. They all became superconducting at very low temperatures barely above absolute zero.

Supercold and superconducting go hand in hand because superconductivity is a state of matter that's frozen beyond solid. Take a familiar substance, like H2O, or water. Hot water molecules careen around in steamy disarray; cooler water gets organized enough to flow, or stay put in a glass; really cold water can freeze rock solid. The atoms in superconductors line up in an even more ordered array--so well ordered, in fact, that they all behave like a single atom. When electricity flows through this super-crystalline arrangement, it doesn't collide with atoms in the metal, scattering its energy this way and that, as normal currents do. It doesn't waste its energy as heat. So the current loses none of its punch.

But just as ice won't freeze above 32 degrees Fahrenheit, materials won't superconduct above their "transition temperature," which is different for each material. Like a freezing point, it's the temperature at which the transformation from solid to superconducting takes place.

Traditional (pre-1986) superconductors all had transition temperatures below about 40 degrees above absolute zero. The only way to get something that cold is to surround it with liquid helium, the coldest liquid that can be created on Earth. But liquid helium is so expensive that any efficiency savings from superconductivity are quickly eaten up in cooling costs.

The miracle of 1986 was twofold: First, the new materials were ceramics, and no one could figure out how a ceramic could carry electricity at all--much less without resistance. Second, the materials became superconducting at temperatures "warm" enough to be cooled with liquid hydrogen, which the physicists point out is cheaper than beer.

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