Fractals Promise Higher-Temperature Superconductors
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more related articles at http://www.stealthskater.com/Science.htm#Fractals note: because important websites are frequently "here today but gone tomorrow", the following was archived http://www.newscientist.com/article/mg20727733.800-fractals-promise- highertemperature-superconductors.html on August 13, 2010. This is NOT an attempt to divert readers from the aforementioned website. Indeed, the reader should only read this back-up copy if it cannot be found at the original author's site. Fractals promise higher-temperature Superconductors by Anil Ananthaswamy New Scientist, August 11, 2010
Superconductors could be made to work at higher temperatures than ever before thanks to the discovery that one such material has an internal structure that behaves like a fractal. Its structure is also similar to the way that the Internet and some social networks are connected up.
With no electrical resistance, superconductors can conduct a large current with no energy lost as heat. This makes them extremely useful for a host of applications from maglev trains to particle accelerators. However, most superconducting materials only work at temperatures close to Absolute Zero though certain compounds containing copper and oxygen work at just over 100 oKelvin.
To better understand these materials, Antonio Bianconi of the Sapienza University of Rome in Italy and colleagues studied different crystalline forms of lanthanum copper oxide. It superconducts at between 16 and 40 oKelvin if it is "doped" with extra oxygen atoms (known as interstitials).
When Bianconi's team used X-ray crystallography to deduce the way the interstitials are arranged in their crystals, a pattern emerged (see picture). The pattern was the same whether the crystal structure was examined at millimeter or micrometer scales. It was behaving like a fractal (Nature, DOI: 10.1038/nature09260). "It's a completely unexpected result," says Bianconi.
This representation of oxygen locations is observed at all scales. (image: Nicola Poccia)
Their analysis also revealed that the superconductor is a "scale-free" network. Meaning that its structure obeys the same mathematics as can be used to describe connections within the Internet and some social networks. "I find it plainly mysterious," says condensed matter physicist Jan Zaanen of Leiden University in the Netherlands. "It is telling us something very deep." 1 The researchers also found that the greater the length scales at which the pattern persisted (or the more complete its "fractality"), the higher the maximum temperature at which the crystal could superconduct. Bianconi speculates that the scale-free distribution of the interstitial oxygen helps preserve the "quantum coherence" of electrons in the crystal. Superconductivity is thought to depend on this property which breaks down as temperature rises.
Engineering superconductors to increase their fractality could yield materials that work at yet higher temperatures, he adds, making it much easier to harness them for practical applications.
Reader Comments
1. Indeed Mysterious by peter / Thu Aug 12, 2010 05:11:26 BST Why is that quantum coherency more stable inside a fractal structure ? I wonder would the quantum world obey a fractal space geometry rules?
If this is so, then fractal effects should be deeply inside particle physics too. Has no one ever observed that?
2. Cool! (no Pun Intended) by allenallen / Thu Aug 12, 2010 18:05:09 BST
"… the greater the length scales at which the pattern persisted (or the more complete its "fractality"), the higher the maximum temperature at which the crystal could superconduct. "
Would be interesting to chart (for the compound they are using) scale/superconductivity loss and see that line. I assume that they can't keep the "fractality" as far up as they want right now. But is there enough to see if there is a predictable ratio? http://www.sciencenews.org/view/generic/id/62006/title/Superconductors_go_fractal Superconductors go Fractal Oxygen atoms arrange themselves in a self-similar pattern by Laura Sanders Science News / August 11, 2010
A new experiment using powerful X-ray beams has found a surprising pattern lurking in a superconductor (a material that conducts electricity without energy-sapping resistance). In a particular kind of superconductor, Oxygen atoms are physically arranged as a fractal showing the same pattern at small and large scales.
Fractals have been spotted in places as diverse as broccoli, England’s coastline, and financial markets. Here, the fractal pattern boosts the efficiency of the superconductor, scientists report August 12 in Nature.
2 The new study is “experimental physics at its best,” says physicist Jan Zaanen of Leiden University in the Netherlands who wrote an accompanying article in the journal. “A new machine comes on line and it produces a surprise nobody expects.”
Though the researchers don’t yet know how the pattern forms or why it enhances superconductivity, they hope the discovery will help in the quest to develop superconductors that work at room temperature says study coauthor Antonio Bianconi of Sapienza University of Rome. Physicists have been pushing to make superconductivity happen at higher temperatures. But the top performers are still stuck about halfway between Absolute Zero and room temperature.
Looking at a copper-oxide superconductor that can perform at approximately -233oCelsius, 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.”
To see whether the fractal pattern was important, the team interfered with it by heating and then quickly cooling the superconductor. Crystals with stronger fractal patterns performed better as a superconductor at higher temperatures than those with weaker fractal patterns. The fractal pattern enhanced the superconductor’s performance, the team concluded.
The finding is “very interesting since it provides a much-welcomed fresh view of the high temperature superconductivity problem,” comments physicist Elbio Dagotto of the University of Tennessee in Knoxville and the Oak Ridge National Laboratory.
Figuring out why the fractal pattern forms in these copper-oxide crystals and how it influences the superconductivity are the next big questions, Bianconi says. Once the details are uncovered, researchers could control the arrangement of Oxygen atoms to design better copper-oxide superconductors. Perhaps even those that operate at room temperature.
Reader Comments
1. by royniles /Aug. 12, 2010 at 2:39pm If fractals are strategic formations that delineate the particular molecular substances involved, perhaps some insight as to the algorithmic nature of those strategies can be derived from analyzing the difference among various observable fractal forms.
3 if on the Internet, press
4