Superconductivity​—What’s All the Excitement About?

INSIDE what looks like the bottom half of a Styrofoam coffee cup is a pellet of some black material the size of a small button. On top of the pellet sits a still smaller chip of metal. Cautiously, the young student pours a fuming liquid into the cup, a little at a time. Everyone around the table watches with keen anticipation.

At first the liquid fizzles violently when it hits the cup. Soon things quiet down and the air becomes still. Then, the small metal chip begins to jitter as in a little dance. All of a sudden, it lifts itself off the pellet and floats in thin air! The student takes a wire loop and slips it past the chip. No tricks, no gimmicks​—the chip is levitating!

That was an experiment on superconductivity performed by a group of students in a California high school. Only a year or two ago, such an experiment could only be performed in advanced research laboratories with sophisticated equipment and substantial funding. The fact that high school students are doing it today is an indication of the rapid pace of developments in this field.

Time magazine ran a cover story last May entitled “Superconductors!​—The startling breakthrough that could change our world.” Newsweek called it “A New Electrical Revolution.” Life magazine titled its coverage “Fast-Food Physics,” hinting at how quickly things are moving along in this area. So, what is superconductivity? And what is all the excitement about?

A Long-Sought Ideal

Conductivity, by definition, is the measure of a substance’s ability to carry an electric current. Most of us know that materials such as glass and porcelain do not conduct electricity. On the other hand, metals like copper, gold, and platinum are good conductors because they offer relatively little resistance to the current passing through them. Superconductivity, then, is the absence of all electrical resistance in a substance​—that ideal state in which electricity flows unimpeded and with no loss.

Scientists have long envisioned the vast potential that such an ideal material​—a superconductor—​would hold. For example, power transmission lines made of superconductors would eliminate not only the enormous energy loss due to resistance in conventional wires but also the unsightly and costly power lines that crisscross the countryside. Use of superconductors would make it possible to build densely packed supercomputers that operate at speeds hitherto unattainable. The unusual magnetic properties of superconductors could lead to a new generation of powerful electromagnets that could make practical such experimental devices as medical scanners, levitating high-speed trains, giant particle accelerators, and even fusion energy.

Fascinating as all of that is, however, there is one catch. For more than 75 years, scientists have known that certain metals do exhibit superconductivity but only when cooled to extremely low temperatures, hundreds of degrees below freezing. It was in 1911 that a Dutch scientist, Heike Kamerlingh Onnes, first stumbled upon the path of superconductors. Having just worked out a technique for liquefying the gas helium, for which he was awarded the Nobel prize in 1913, he was investigating the effect of low temperatures on various metals. Unexpectedly, he found that mercury loses all electrical resistance at about -452° F. [-269° C.], or 4 K, four degrees above what scientists call absolute zero on the Kelvin scale.a

Although superconductivity was discovered quite by accident, its value was soon recognized. However, the extremely low temperature, called the transition, or critical, temperature, at which the material became superconducting was a severe handicap. The high cost and complexity of working at such low temperatures limited its practical value. In the following decades, scientists experimented with other materials in hopes of finding something that would become superconducting at higher temperatures. But progress was slow in coming.

Over the years, however, other properties of superconductors came to light. One of the most important, discovered in 1933, was that when a superconductor is placed in a magnetic field, it would not allow any of the magnetic flux to pass through it, but it will repel or be repelled by the flux. This phenomenon, called the Meissner effect, is the cause of levitation, as demonstrated in the high school experiment. Its discovery led to renewed efforts in the search for higher-temperature superconductors. Still, progress was at a snail’s pace. As recently as 1973, the best that had been found was a certain metallic alloy that became superconducting at 23 K, or -418° F. [-250° C.], still an impractically low temperature. And for the next dozen years or so, things remained more or less at a standstill.

Temperature Rising!

A new twist of events began when two scientists in the IBM research laboratory in Zurich, Switzerland, came up with the idea that perhaps the reason other researchers were not having much success was that they were looking at the wrong kind of material. Up to that time, most of the research was done with metals and alloys. “I became convinced that you could not make any more progress along those lines,” said Alex Müller, one of the two scientists.

Müller and his partner, Georg Bednorz, started experimenting with metallic oxides in 1983. By early 1986 they had achieved the first major advance in years, superconductivity at 35 K, or -396° F. [-238° C.], using a compound consisting of barium, lanthanum, copper, and oxygen. When the news was eventually published in September 1986, the scientific community was taken by surprise. The material used by the scientists in the Swiss laboratory, a family of ceramics, was normally an insulator, and no one would suspect that this was where the biggest breakthrough in decades was to come.

In quick succession, one new record was replaced by another. By February 1987, a team led by C. W. Chu of the University of Houston discovered superconductivity in a material at a record high of 93 K, or -292° F. [-180° C.], by replacing the lanthanum in Müller’s mixture with yttrium, another of the so-called rare earth elements.

This achievement opened up a new chapter in high-temperature superconductivity. Up to that point, liquid helium had to be used to bring the materials under study to the low temperature required​—a very expensive and complicated process. With the new discovery, the cooling could now be done with liquid nitrogen, which liquefies at 77 K, or -321° F [-196° C.]. Liquid nitrogen is readily available, costs only about as much as milk, and can be handled without elaborate equipment. This, along with the fact that the oxide material is also easy to make and inexpensive, played a major role in giving research in superconductivity an added boost.

The ultimate goal, of course, would be a superconductor at room temperature, eliminating any need for cooling, and scientists all over the world are in hot pursuit of this goal. As a matter of fact, reports of “fleeting traces” of room-temperature superconductivity have begun to appear.

By the end of May 1987, Chu and his group had bettered their own record. They found a small portion of a specimen turned superconducting at 225 K, or -54° F. [-48° C.], but only intermittently. “You can observe it once,” said Pei-Heng Hor, one member of the team, “then after a while it disappears, but you can see it again.” Another group, at the University of California at Berkeley, reported the appearance of superconductivity at 292 K, or 66° F. [19° C.], in a material they were working on, but they were not able to repeat the result.

Golden Age Just Ahead?

All the exciting news about superconductors has given many people the impression that we are now at the threshold of a new era, a technological golden age. Our life is about to change, they say, the way it did with inventions of the past, such as the electric light and the transistor. Are all the wonderful things that superconductors are supposed to make possible really just around the corner?

To begin with, “a much fuller basic scientific understanding will have to be obtained before we will be able to put superconductivity to widespread use,” observed Erich Bloch, director of the U.S. National Science Foundation. Scientists have not as yet been able to come up with definite answers as to why the man-made ceramic materials work the way they do.

Because of this, many experts feel it will likely be years before superconductors will leave the laboratories and be put to practical use. “The potential of these materials is great, but the timetable that’s been set up by the press is wrong,” says a researcher at the National Bureau of Standards. “It will be five years before we see them in thin films in computers, and up to twenty years before we see them in bulk applications.”

One obstacle lies in the fact that the high-temperature superconductor materials are not malleable or workable as are metals. Nor can these brittle materials be flexed easily, as anyone knows who has ever dropped a ceramic or china dinner plate. Yet, for the superconductors to be used in practical applications, they must be fabricated into wires and films. In computers and integrated electronic circuits, for example, they would have to be made into films only fractions of a micron thick. Motors and magnets require thin, flexible wires in their windings, and power transmission lines must be strong and flexible.

To complicate matters further, scientists are not sure if the superconducting materials are capable of carrying the large electric currents or magnetic fields that many applications call for. All superconductors have a threshold above which they will lose their superconductivity. At present, that threshold is relatively low. Perhaps all these problems can be solved​—but not by tomorrow.

There is, however, a more ominous side to it. Already there is talk of using superconductors in particle or directed-energy weapons in space warfare! Will superconductivity turn out to be the blessing that everyone is predicting and hoping for, or will it turn out the way other revolutionary inventions of the past​—as gunpowder and nuclear fission—​did? That is a question apparently no one is prepared to answer.

[Footnotes]

[Box on page 21]

The Potential of Superconductors

“Practical nitrogen-cooled superconductors could save the utilities billions​—and save enough energy to put 50 or more power plants in mothballs,” says Business Week. Superconducting generators and power lines could also mean more powerful generating plants farther away from cities, which could cut pollution, cost, and danger.

Maglevs​—magnetically-levitated trains—​with speeds up to 300 miles an hour [480 km/​h] may be made practicable by lightweight superconducting magnets. Electric cars powered by efficient superconducting motors could cut down urban air pollution. Even ships can be operated by such motors.

Superconducting microchip devices that are a thousand times faster than silicon transistors are already being developed. Using such chips, not only will future computers be faster but, by greatly reducing the heat produced, they will also be smaller. Desktop computers will be as powerful as today’s mainframes.

NMRs (nuclear magnetic resonance scanners) and SQUIDs (superconducting quantum interference devices) are machines that can peer into the human body and detect brain waves. The reduction in cost and complexity when superconductors are used can bring these machines within the reach of ordinary hospitals and clinics.

The potential for superconductors is great. How much of it will be realized?

[Picture Credit Line on page 19]

IBM Research