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Superconductivity challenges
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17/11/2008
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In two papers discussing a recently discovered class of high temperature superconductors, researchers at the US National Institute of Standards and Technology (NIST) report the relationship between magnetism and superconductivity may be more involved than previously thought. In fact, the researchers suggest a whole new mechanism may drive some types of superconductors.
When temperatures approach 0K, many materials become superconductors, but magnetism shatters their superconductive state. In 1986, scientists discovered ‘high temperature’ (HTc) superconductors capable of operating at temperatures in excess of the previous limit of 30K. Current copper oxide materials, for example, are superconductive in liquid nitrogen at 77K.
However, says NIST, no one really understands how HTc superconductivity works, although scientists have long suspected that in this case, magnetism boosts rather than suppresses the effect.
Early in 2008, Japanese researchers announced the discovery of a new class of iron based HTc superconductors. In addition to being easier to shape into wires than copper oxides, such materials provide scientists fresh new subjects with which to develop and test theories about HTc superconductivity’s origins.
NIST scientists, along with researchers from the University of Tennessee at Knoxville, Oak Ridge National Laboratory, the University of Maryland, Ames Laboratory and Iowa State University, used neutron beams to examine a superconductor’s atomic structure. They found iron based superconductors to be similar to copper oxide materials in how ‘doping’ influences their magnetic properties and superconductivity.
The team then tested the iron based material without doping it. Under moderate pressure, the volume of the material’s crystal structure compressed by 5%. Intriguingly, it also became superconductive without a hint of magnetism.
This behaviour under pressure may suggest that an entirely different mechanism lies behind the iron material’s superconductivity than found with copper oxide materials.
Understanding the origin of the superconductivity, says NIST, will help engineers tailor materials to specific applications, guide materials scientists in the search for new materials with improved properties and, scientists hope, usher in higher temperature superconductors.
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Author
Graham Pitcher
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