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Roller coaster superconductivity discovered

• PHYSORG.com
Superconductors are more than 150 times more efficient at carrying electricity than copper wires. However, to attain the superconducting state, these materials have to be cooled below an extremely low, so-called transition temperature, at which point normal electrical resistance disappears. Developing superconductors with higher transition temperatures is one of physics' greatest quests. 
 

Until now, copper-laden materials called cuprates have been the only superconductors whose transition temperatures are higher than the liquid nitrogen boiling point at -321F (77 K). Whether researchers can make transition temperatures higher in such materials remains a challenge.

Now, researchers at the Carnegie Institution's Geophysical Laboratory, with colleagues, have unexpectedly found that the transition temperature can be induced under two different intense pressures in a three-layered bismuth oxide crystal referred to as "Bi2223." The higher produces the higher transition temperature. They believe this unusual two-step phenomena comes from competition of electronic behavior in different kinds of copper-oxygen layers in the crystal. The work is published in the August 19, 2010, issue of Nature.

"Bi2223 is like a layered cake," explained lead author Xiao-Jia Chen at Carnegie. "On the top and bottom there are insulating bismuth-oxide layers. On the inside of those, come layers of strontium oxide. Next, are layers of , then calcium, and finally the middle is another copper-oxide layer. Interestingly, the outermost and inner layers of copper oxide have different physical properties resulting in an imbalance of electric charge between the layers."

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