UT-ORNL researchers take step toward understanding superconductivity

December 21, 2007

KNOXVILLE -- A research group at the University of Tennessee and Oak Ridge National Laboratory led by physics professor Pengcheng Dai, along with collaborators at Boston College, has taken a step toward understanding a great physical mystery.

For more than 20 years, scientists have struggled to understand the phenomenon of high-temperature superconductivity. This trait causes materials to move electricity with incredible efficiency -- something that, if fully understood and controlled, could have a major impact on energy use around the world.

Conventional superconductors only possess the property at incredibly cold temperatures -- far too cold for widespread practical use. A class of materials known layered copper oxides shows superconductivity at higher temperatures, but scientists do not yet know what causes them to take on this very useful trait.

"Once you know the mechanism that causes superconductivity," said Pengcheng Dai, a UT-ORNL joint faculty member and leader of the research group, "That opens the door to new directions in research."

Superconductivity occurs in a material when its electrons join together in sets of two called Cooper pairs. Dai and his fellow researchers set out to understand what causes the electrons to pair in a superconducting material known as PLCCO. The specialized material is grown at the University of Tennessee.

The researchers, using a specialized device called a scanning tunneling microscope, determined that a type of particle known as a boson is present when the electrons in the PLCCO pair. According to Dai, the energies of these observed bosons are consistent with magnetism as a possible cause of the pairing, a finding that meshes with previous results.

Dai's previous research had used neutrons to analyze the PLCCO material, which revealed similar causes for the electron pairings so important to superconductivity. By using a different tool to analyze the PLCCO, the researchers were able to find another way to probe and confirm those findings. Their work was published in last week's edition of the journal Nature.

"They say if it looks like a duck and quacks like a duck, then it's probably a duck," said Dai. "These findings add to the understanding that magnetism plays a role in creating these important pairs."

Dai is also quick to note that these finding represent only a step on the way to resolving the many scientific questions about how high-temperature superconductivity works.

"This will not end the debate, but it's another step," said Dai.
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The Nature article is available online at: http://www.nature.com/nature/journal/v450/n7172/abs/nature06430.html.

University of Tennessee at Knoxville

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