Controlled atomic disorder helps researchers understand superconductivity

Ruslan Prozorov and members of his research group.

Ruslan Prozorov’s research group is using disorder in crystal structure to understand the mechanisms of superconductivity — conducting electricity without resistance, in other words, without any loss of energy to heat.

Prozorov, professor in the Department of Physics and Astronomy at Iowa State University and faculty scientist at the U.S. Department of Energy’s (DOE) Ames Laboratory, and his research group study superconductivity and magnetism at low temperatures, in particular, the newest family of unconventional superconductors: iron-based compounds. These materials are “unconventional” due to containing magnetic iron, which is usually an antagonist of superconductivity.

Because these are complex materials with different fractional compositions, there are many variables that control the behavior in the superconducting state, including magnetic field, pressure and composition. Prozorov and his group added another variable: controlled disorder of otherwise perfect arrangement of atoms in a crystal.

"It’s extremely useful to be able to understand and ultimately control disorder," he said. "Instead of fighting it and trying to get rid of it you actually want to study it because in real life things are never perfect, so it’s better to try to use disorder as another “dial” to tune the material’s response."

By bombarding the crystals with energetic electrons moving at nearly the speed of light, his group creates controlled and measurable disorder. Their careful analysis strongly suggests the iron-based compounds exhibit superconductivity due to the magnetic component of the materials. A better understanding of these materials will help scientists to figure out how unconventional superconductivity develops and what other materials might superconduct at even higher temperatures.

Superconductors’ perfect conduction is appealing. Currently, though electrical wires are designed to have very low resistance, those small amounts over long lengths add up creating as much as 60% loss of energy to heat. A superconductor, on the other hand, could theoretically deliver 100% of the electricity generated at power plants.

But in order to enter a superconducting state these materials must be cooled to very low temperatures using liquid helium, which boils above -452F. However, helium is not a readily available, abundant or renewable resource and would be too costly and impractical to use in large quantities for energy-saving applications.

In the search for better superconductors, newer classes have been found which are superconductive at higher temperatures. To date, the compounds found with the highest temperatures, however, are ceramic materials.

"Imagine making wire from clay," Prozorov said. "As soon as it cracks electric current can’t run through it."

Though there has been progress in adapting these brittle materials for wires and cables, he and others continue to search for superconducting materials that will be more practical to use. They hope that by shedding light on the mechanisms of unconventional superconductivity, the knowledge can be used to find more and higher temperature unconventional superconductors.

Read the research group’s published article here.