Superconductivity Heats Up

By MICHAEL D. LEMONICK

At the University of Alabama in Huntsville, physicists last month placed a chip of a green, brittle compound inside a thermos-like container, doused it with frigid liquid nitrogen and sent an electric current through it. As the temperature dropped, they took careful measurements of the compound's electrical resistance -- its opposition to the passage of current.*

Suddenly, at 93 Kelvin (-292 degrees F), the resistance dropped precipitously. The substance had become a superconductor, able to transmit current with virtually no loss of energy. "We were so excited and so nervous that our hands were shaking," says Physicist Maw-kuen Wu. "At first we were suspicious that it was an error."

Not so. Wu's group, under the direction of University of Houston Physicist Paul C.W. Chu, had achieved the phenomenon of superconductivity at a higher temperature than ever before. And the National Science Foundation announced last week that Chu's Houston lab had pushed that temperature 5 degrees higher -- to 98 K. Under such conditions -- far less extreme than those required only a few years ago -- superconducting technology might eventually become inexpensive and even commonplace. Possible applications: superconducting cables that could transmit electricity from a power plant to a distant city with essentially no energy loss; practical versions of trains that "fly" ) just above their tracks at hundreds of miles an hour, cushioned on magnetic fields; more widespread use of magnetic resonance imaging machines, which take sharp pictures of the soft tissues of the body. Says Northwestern University Physicist Arthur Freeman: "A barrier has been broken. It's exciting for the physics community and for mankind as a whole."

Superconductivity was discovered in 1911, when Dutch Physicist Heike Onnes cooled the element mercury to near absolute zero (0 Kelvin, or -460 degrees F) and discovered that it had lost its resistance to electric current. Since then more than two dozen chemical elements and hundreds of compounds have been found to be superconductors near that temperature extreme. The only practical way to make something that cold is to bathe it in liquid helium, which exists only at temperatures below 4 K. But helium is rare, and expensive to liquefy. Even so, the efficiency of electromagnets wound with superconducting wires is so great that in certain situations the expense is justified.

For example, giant particle accelerators require extremely powerful magnets to keep the particles confined to a circular track as they move at nearly the speed of light. At Fermilab, near Chicago, the world's most powerful accelerator, known as Tevatron, uses more than 1,000 superconducting magnets cooled with liquid helium at a cost of $5 million a year. But the efficiency of the magnets saves Fermilab an estimated $185 million annually in electric energy costs. The superconducting super collider, a mammoth accelerator 52 miles in circumference, endorsed last month by President Reagan for completion in the 1990s at a projected cost of between $4 billion and $6 billion, will use 10,000 superconducting magnets and save nearly $600 million annually.

In most uses, however, the cost of liquid helium outweighs the benefits of superconducting technology. For that reason, scientists have long searched for a compound that would become a superconductor at less extreme temperatures -- particularly above 77 K (-320 degrees F), the point at which nitrogen gas liquefies. Reason: nitrogen is a common gas and costs no more than a tenth as much in liquid form as helium. In fact, says Iowa State University Physicist Douglas Finnemore, liquid nitrogen, priced as low as a nickel a liter, is a "heck of a lot cheaper than beer."

The much sought-after goal proved to be elusive. In the early 1970s scientists found an alloy of niobium and germanium that lost all resistance at 23 K. Then, last April, a group at the IBM Zurich Research Laboratory in Switzerland announced development of a compound of barium, lanthanum, copper and oxygen that appeared to begin the transition to superconductivity at 35 K.

In October the Zurichers confirmed their result, which other researchers duplicated and then tried to beat. A slow-moving branch of physics became a horse race as laboratories around the world attempted to push temperatures higher. Last week's announcement does not end the competition. Says Paul Fleury, director of AT&T Bell Laboratories' Physical Research Laboratory: "It took physicists 75 years to raise superconductivity temperatures by 19 degrees. We have more than doubled that in the last 75 days. We're now dealing with new science, and we don't know what the upper limits are."

Chu foresees a balmy 120 K within a few months, and does not rule out superconductors that could operate at 300 K (room temperature). University of Illinois Physicist John Bardeen, who shared the Nobel Prize in 1972 for his part in explaining the quantum-mechanical basis of superconductivity, agrees that there is no theoretical reason precluding higher temperature superconductors. But, he says, "finding materials with the right combination of properties is tricky." Admits Chu: "There was a bit of serendipity involved."

Chu will describe the new material and details of how it was developed in an upcoming issue of Physical Review Letters, but the University of Houston has already applied for a patent on both product and process. If it is granted, Chu stands to share in the profits, which could be large. "It's phenomenal -- we're excited," says Robert Jake of American Magnetics, a manufacturer of superconducting magnets. "But it will take several years of research and development to make it feasible for commercial application." When such applications come, says Chu, they will make clear the significance of his discovery: "I think it could almost be like the discovery of electricity."

FOOTNOTE: *It is resistance that converts electric energy into heat, as in the coils of an electric heater.

With reporting by J. Madeleine Nash/Chicago and Richard Woodbury/Houston