Iron in the Mix
Scientists look for the secret behind high-temperature superconductors
Physicist Johnpierre Paglione works in a kitchen of sorts: He precisely blends ingredients, heats his mixtures to just the right temperature and cools them to get the perfect product. But rather than only edible ingredients, his recipes call for toxic chemicals, such as arsenic, and metals — especially iron. His ovens, which line the shelves of his lab at the University of Maryland in College Park, reach 1,700Ë Celsius before he carefully cools his concoctions over days or weeks. When the timer finally dings, out pops a silvery-black pebble with one flat, shiny surface.
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The newly made pebble is a superconductor, a material that shuttles electricity with essentially perfect efficiency, defying the resistance that typically slows electrons down. Because Paglione’s pebble incorporates iron into its molecular structure, it’s a member of a new class of materials known as iron-based superconductors. These materials, discovered in 2008, work at temperatures as high as −218Ë Celsius, or 55 kelvins (degrees above absolute zero). Though that sounds pretty cold, conventional superconductors must be cooled to within a few degrees of absolute zero. Only copper-oxide superconductors work at higher temperatures than the iron-based family, and together the two groups make up what are known as the high-temperature superconductors.
Scientists have been trying to figure out how high-temperature superconductivity works since copper oxides, or cuprates, were found to exhibit resistance-free flow in 1986. Right now, even the most promising cuprate must be cooled to about 138 kelvins. Though liquid nitrogen can get materials that cold fairly easily, the cuprates are hard to form into wires.