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Lemberger

Research Could Explain Behavior in Unusual Superconductors

Since their discovery in 1986, the crystalline ceramic materials known as cuprates have puzzled scientists for their high-temperature superconductivity.

Efforts to understand cuprates have generated a great deal of debate, in part because the materials seem to demonstrate a split personality. In some experiments, their superconducting electrons exhibit d-wave behavior, meaning they appear to orbit each other in an a formation resembling a four leaf clover; other times they exhibit s-wave behavior, in which the electrons appear to follow spherical paths, but in opposite directions.

In Ohio State's Department of Physics, Professor Thomas Lemberger is confronting this controversy head-on. In tests with thin films of cuprates, he and his colleagues may have found a transition in which the material switches from d-wave behavior to s-wave. This work, which was done in collaboration with NTT Basic Research Laboratories in Japan, might explain the varied research results other teams have found in the past.

"It seems that the mechanisms for d-wave and s-wave behavior are always present in the material," Lemberger said, "so if you could suppress the d-wave behavior, a cuprate would automatically switch to s-wave."

S-wave behavior has some technical advantages over d-wave. Buckyballs, Lemberger pointed out, demonstrate high-temperature s-wave-type superconductivity at 40 Kelvin. Scientists have speculated that cuprates could sustain s-wave superconductivity at a temperature as high as 90 Kelvin.

"The question now is, how high can we push s-wave superconductivity?" Lemberger said.

Finding the answer will be a very complex task. And along the way, Lemberger and graduate student John Skinta have discovered something else surprising about cuprates.

Working with physicists at Pennsylvania State University, Lemberger and Skinta measured thermal fluctuations in a thin film cuprate. "The fluctuations are not nearly as strong as they should be," Lemberger said. "It's as if the layers of the material are much more strongly coupled than other measurements have led us to expect."

At the moment, the implications of these findings are unclear, but Lemberger and his collaborators have written two articles detailing their work, both of which have been accepted for publication in Physical Review Letters.





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