Scientists probe new class of superconductor

Scientists around the world are scrambling to unlock the secrets behind a new group of materials that act as autobahns for electricity – conducting current with virtually no wasteful resistance.

The discovery establishes a third major group of so-called high-temperature superconductors – a broad category that scientists first uncovered in 1986. Such materials hold the promise of making everything from computers to electric motors far more efficient, as scientists boost the temperature frontiers at which the materials work.

High-temperature is a relative term. The new materials, based on iron and arsenic, so far have reached 55 Kelvin (minus 361 degrees F.) without regaining their resistance to electricity. This has put them on a temperature trajectory similar to the earliest high-temperature superconductors, which scientists have coaxed to work at up to 164 K in the lab.

But these older materials, built around copper oxide, appear to have hit a temperature plateau. So while some recipes for these materials have started to work their way into niche applications and demonstration projects, researchers have not given up the hunt for other high-temperature superconducting candidates.

The new superconductors "are very significant," says David Larbalestier, who heads the Applied Superconductivity Center at Florida State University in Tallahassee. "They are a whole new, very versatile class" of materials.

Their technological promise remains to be seen, Dr. Larbalestier and others say. "But at the very least, this helps us to keep up the faith for the search for new materials with interesting properties," he says.

A relatively high operating temperature is important, researchers say: It cuts the cost of cooling the materials. That's what drives the quest for materials that act as superconductors at ever higher temperatures. But it's only one of three basic properties that a superconductor must exhibit to offer the broadest technological potential. It also must endure high electrical currents and high magnetic fields.

Some experts say they've seen hints suggesting that these new materials should post impressive magnetic-field numbers soon.

The new superconductor, initially a mixture of iron, oxygen, lanthanum, and phosphorous, was discovered two years ago by Japanese scientists at the Tokyo Institute of Technology. The surprise ingredient: iron. It's prone to picking up and retaining magnetic fields, which can shut down superconductivity.

Then, this past February, the team published results showing that by substituting arsenic for phosphorous, it could push the material's "transition" temperature from an initial 4 K to 26 K. The temperature has been rising ever since.

Like its older copper-oxide cousins, the newest materials puzzle scientists: They have yet to figure out why they behave the way they do. "There are at least 15 theoretical models out there, and most of them are pure guesses," says Warren Pickett, a physicist at the University of California at Davis.

Even as researchers chase the latest entry to high-temperature superconductivity, several scientists in the United States chafe at how little money the country invests in the tedious, methodical research that leads to such materials. The biggest spurt in work on the new superconductors has come from China. Among other things, it has the laboratory labor force that can systematically look at ingredients with properties similar to those in the original recipe and try them out.

China and Japan both place high priority on such work because they realize that new materials tend to translate into new technologies, says George Crabtree, a researcher at the Argonne National Laboratory outside Chicago.