See Inside August 2009

An Iron Key to High-Temperature Superconductivity?

The discovery that compounds known as iron pnictides can superconduct at 50 degrees above absolute zero has reignited physicists' quest for better high-temperature superconductors, and may offer clues to unlocking a 20-year mystery


Hideo Hosono's research group at the Tokyo Institute of Technology was not looking for a superconductor in 2006. Rather the team was trying to create new kinds of transparent semiconductors for flat-panel displays. But when the researchers characterized the electronic properties of their new substance—a combination of lanthanum, oxygen, iron and phosphorus—they found that below four kelvins, or –269 degrees Celsius, it lost all resistance to carrying an electric current; that is, it superconducted.

Although 4 K is far below the current laboratory record of 138 K (let alone the holy grail of “room temperature,” or about 300 K), experimentalists with a new superconductor are like yachtsmen with a new boat design. The sailors want to know how fast they can make it go; the physicists, how hot any variant of the material can superconduct. Superconductors’ uses in industry are hobbled by the need for expensive, complicated, space-hogging cooling systems. Any increase in operating temperature could ease those drawbacks for existing devices and make completely fresh applications technically and economically viable. Engineers envisage, for instance, lossless power cables carrying huge currents and compact superstrong magnets—for magnetic resonance imaging, levitated trains, particle accelerators and other wonders—all without the exorbitant expense and trouble of the liquid-helium cooling systems required by the old, cold, conventional super­conductors.

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