High-temperature superconductors

You’ve probably heard of “The Spy Who Came in from the Cold.” More than a decade ago, there was a lot of hoopla about something else coming in out of the cold: superconductivity. Newsmagazines did cover stories on the new high-temperature superconductors, and promised they would soon change our lives. After that…nothing.

A new technological development, though, means that the hype was not necessarily unwarranted, merely premature.

First, some background. Superconductivity was discovered 80 years ago at the University of Leiden, Holland, by Heike Kamerlingh Onnes, who was experimenting with cryogenics (extremely low temperatures). In 1908 he succeeded in liquifying helium, which has a boiling point just a little over -269 C. That’s just four degrees above absolute zero, the lowest temperature possible (because it’s the temperature at which all molecular motion stops), and is usually referred as 4 Kelvin. (The Kelvin temperature scale starts at absolute zero and uses Celsius-sized degrees. Reducing the vapor pressure can drop the temperature of liquid helium all the way to 1 K.

In 1911, Kamerlingh Onnes noticed that electrical resistance in mercury and other metals virtually disappeared below 4.15 K, allowing an electrical current to flow for hours or even days with no additional input. They had become superconductors.

For the next seven decades, all experiments with superconductors required cooling metals with expensive, hard-to-work-with liquid helium. Then, in 1986, two IBM researchers in Zurich, Georg Bednorz and Alex Muller, stumbled on a ceramic made from lanthanum, copper, barium and oxygen that became super-conducting at 35 K. U.S. scientists then discovered a ceramic which became superconducting at 98 K–high enough that it could be cooled with cheap, easy-to-work-with liquid nitrogen, which has a boiling point of 77 K. The current record, achieved in 1994, is 138 K.

These high-temperature superconductors (HTS) are what triggered the media frenzy more than a decade ago. The rosy predictions of a cheap-superconductor future didn’t pan out, though, for one very simple reason: ceramics, being hard and brittle, are very hard to make into wire. The best attempt so far has produced a wire that’s five to 10 times as expensive as copper wire, while being only two or three times as conductive. (Even so, some power utilities have been experimenting with it.)

But now, the NASA-funded Texas Centre for Superconductivity and Advanced Materials at the University of Houston, along with Metal Oxide Technologies, Inc., also based in Houston, have discovered, thanks to experiments carried out on the space shuttle, how to make HTS wire that costs about the same as copper wire to produce, but lives up to its potential of being 100 times as conductive. The wire is made by growing a thin film of a HTS only a few thousandths of a millimeter thick onto a flexible foundation.

Affordable HTS offer many exciting possibilities. Today, about seven percent of the electricity generated in North America is lost on its way to consumers, due to the natural resistance of copper wire. HTS power lines and electrical circuits would drastically reduce energy consumption, making electricity cheaper and reducing greenhouse emissions and pollution.

HTS could revolutionize transportation. Superconductors repel magnetic fields—and can also be used to make super-powerful magnets. This is the basis for magnetic levitation, or maglev, trains. Superconductors in the special track repel superconductor-based magnets in the train, making the train actually float above the surface of the track. Efficient, fast, and quiet, maglev trains could replace noisy, polluting airplanes on many routes—if they were more affordable. Today’s experimental maglevs require expensive low-temperature superconductors. Tomorrow’s could be much cheaper thanks to HTS.

HTS has applications in space, as well The gyroscopes that keep satellites oriented could be made with frictionless bearings making use of superconducting magnets, keeping the satellites more precisely oriented, reducing fuel requirements and extending their life. Electric motors, widely used on spacecraft, could be reduced to one quarter of their current size—or less—with superconducting components.

At home, medical scanners could become cheaper and smaller; imagine a tabletop MRI scanner using HTS instead of today’s low-temperature superconductors.

In 1962 Brian D. Josephson of England predicted that if two superconductors were brought close toegther but not allowed to touch, electrons could jump the gap and current could flow as if the two conductors were touching. His prediction proved accurate. Because the current across the “Josephson junction” is very sensitive to electric and magnetic fields, it can be used as a very accurate sensor or as an incredibly tiny and incredibly fast electronic on-off switch. HTS could thus point the way to next-generation supercomputers.


The hype may have long since faded away, but the potential of high-temperature superconductors to improve our lives is very real—and closer to being realized than you might think.

Permanent link to this article: https://edwardwillett.com/2003/03/high-temperature-superconductors/

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