Wednesday, August 11, 2010

Superconductors Go Fractal - Science News

Superconductors Go Fractal - Science News: "Looking at a copper-oxide superconductor that can perform at approximately -233 degrees Celsius, Bianconi and his team developed a new technique to determine the detailed structure of its atoms. They bombarded the superconductor with powerful X-rays generated at the European Synchrotron Radiation Facility in Grenoble, France. The resulting diffraction pattern revealed atoms’ locations.

The team knew the material was made like a layered cake, with layers of superconducting copper oxide alternating with spacer layers. At higher temperatures, oxygen atoms tend to roam around in the spacer layer. But when temperatures drop, they settle down. These oxygen atoms — and the electrons they bring to what would otherwise be vacancies — are thought to contribute to the drop in resistance that accompanies superconductivity. But until now, no one had been able to see the structure with high resolution.

Bianconi and his team got a shock when they realized the pattern formed by the once-roaming oxygen atoms was fractal. The pattern looked the same at the 1-micrometer scale as it did at the 400-micrometer scale.

This self-similarity was completely unexpected in superconductors, Bianconi says. “We were very astonished. We couldn’t believe our eyes,” he says. “This is not an area where we expected to see a fractal pattern.”"

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