Newly discovered iron-based high-temperature superconductors could pave the way for the development of superconductors that can operate at room temperature.

"If superconductors could exist at room temperatures, the world energy crisis would be solved," said Chia-Ling Chien, a physics professor and director of the Material Research Science and Engineering Center at Johns Hopkins University. He led research that provides insights into why the characteristics of a new family of iron-based superconductors reveal the need for fresh theoretical models. These could improve superconductors for use in industry, medicine, transportation and energy generation, he said.

"It appears to us that the new iron-based superconductors disclose a new physics, contain new mysteries, and may start us along an uncharted pathway to room temperature superconductivity," said Chien, who teamed up on the research with Tingyong Chen and Zlatko Tesanovic, both of Johns Hopkins, and X.H. Chen and R.H. Liu of the Hefei National Laboratory for Physical Science at Microscale and Department of Physics, University of Science and Technology of China in Anhui, China. Their work is the topic of a paper in a recent issue of the journal Nature.

Superconductors are materials that can carry electrical current without friction; as a result, they don't waste electrical energy generating heat. This means an electrical current can flow in a loop of superconducting wire forever without a power source. Today, superconductors are used in hospital MRI machines, as filters in cell phone base stations and in high-speed magnetic levitating trains. Unfortunately, most of today's superconducting materials can only function and operate at extremely low temperatures, which means that they must be paired with expensive supercooling equipment. This presents researchers with a grand challenge: to find superconducting material that can operate at more "normal" temperatures.

Chen said although all metals contain mobile electrons which conduct electricity, a metal becomes a superconductor only when two electrons with opposite "spins" are paired. The superconductor energy "gap," which is the amount of energy that would be needed to break the bond between two electrons forming such a pair to release them from one another, determines the robustness or strength of the superconducting state. This energy gap is highest at low temperatures, but vanishes at the temperatures at which superconductivity ceases to exist.

The team measured this gap and its temperature variation, revealing that the pairing mechanism in iron-based superconductors is different from the one in more traditional, copper-based, high-temperature superconductors. To the researchers' surprise, their results were incompatible with some of the newly proposed theories in this mushrooming field. (See also "SCs Share Magnetism")

"In the face of this discovery, it is clear that we need to reexamine the old and invent some new theoretical models," Tesanovic said. "I predict that these new, iron-based superconductors will keep us physicists busy for a long, long while."

This research was supported by the US National Science Foundation and the Natural Science Foundation of China.

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