Scientists trace superconductivity anomalies to a single point

Dec 8, 2013

Superconducting materials that function at room temperature make electrons behave unpredictably. The electrons sometimes arrange themselves in lines or around atoms in an asymmetrical arrangement. This is one reason superconductors have not proliferated into everyday use -- an advance that would render everything from power lines to personal computers far, far more efficient. But two scientists now say they have discovered the cause of those anomalies in zero-resistance systems and are now working on a practical way to get rid of them.

The scientists say they can now predict the behavior of electrons in copper- and iron-based and "heavy fermion" superconducting materials at high temperatures. Here, "high temperatures" means about 150 Kelvin, or about 150 degrees Celsius above absolute zero. It's at that kind of temperatures that electrons behave erratically.

The electrons in question form stripes and lines -- "intertwined ordered phases" (shown in the grey area of the image above) -- caused by the electrons' varying energy levels. The phenomenon is explained as a mathematical expression called the "Fermi surface." By injecting or "doping" a superconducting material with new materials and thus changing the surface, engineers can produce a material that reduces or eliminates intertwined ordered phases.

A formula for that material combination is the so-called "holy grail" the scientists are after. By honing in on the point at which "Cooper pairs" of electrons bond and shake apart, they can find out which materials are best suited to resistance-free conductivity at room temperature. That property --zero resistance -- is the very essence of a superconductor.

The discovery was made after ten years of research using scanning tunneling microscopes insulated from vibration. The microscopes were able to scan in layers thinner than an atom to measure the energy levels of electrons. The scientists conducting the research were J.C. Séamus Davis for Cornell and the Center for Emergent Superconductivity at Brookhaven National Laboratory, and Dung-Hai Lee for UCLA-Berkeley and Lawrence Berkeley National Laboratory. Their new theory appeared in Proceedings of the National Academy of Sciences.


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