Friday, June 06, 2008

A New Superconductor

Continued from page 1

By Prachi Patel-Predd

The new superconductors could also have another crucial advantage, says David Christen, who leads superconductor research at Oak Ridge National Laboratory. While cuprate power cables have to be fabricated as specially designed flat tapes, it might be easier to make wires from iron arsenide semiconductors. "These materials could be more practical than cuprates if it turns out that they're easier and less expensive to make," Christen says.

Researchers are also hoping that iron arsenides will help unlock the mystery of how high-temperature superconductors work. That will be key for designing materials with even higher critical temperatures. In superconductors that work at very low temperatures, such as niobium and lead, electrons form pairs below the critical temperature. Atoms or defects in the crystal do not have the energy needed to break the pair and deflect the electrons. So the electron pair zips around the material unimpeded, giving rise to superconductivity. But this pairing theory does not hold for high-temperature copper-oxygen materials.

In their Nature paper, Chien and his colleagues show evidence suggesting that the pairing theory might hold for the iron arsenide superconductors. "The pairing of electrons is the soul of the superconductor," Chien says. "If the new materials follow the [pairing] theory, then . . . we will be able to understand the materials a little bit easier."

More evidence from experiments done with many different iron arsenide compounds will be needed to confirm how the superconductors work, says Pengcheng Dai, a physics professor at the University of Tennessee, in Knoxville. The Johns Hopkins work is "just one piece of the puzzle," he says. Indeed, while the pairing mechanism of iron arsenides might be different than that of copper-oxygen compounds, the two materials also have similarities. In a recent online paper, also published in Nature, Dai and Lynn showed that the two materials share key magnetic properties. And both materials also have a similar layered structure.

It might be too early to say just how useful the iron arsenide superconductors will be. For now, Dai says that researchers are excited about having broken the 22-year monopoly of cuprates and about having a new high-temperature superconductor to play with.