A three-dimensional graph of three energy bands where evidence of superconducting Cooper pairs of electrons were found in an iron atom. The height of the cylinder shows the energy binding each of those electrons into a Cooper pair, which is different for each band and varies with the direction of travel. Black dots are data points, which were omitted from the inner band for simplicity.
Research at Cornell has for the first time confirmed key theoretical predictions about how iron-based high-temperature superconductors behave.
J.C. Séamus Davis, the James Gilbert White Distinguished Professor in the Physical Sciences at Cornell and director of the Center for Emergent Superconductivity at Brookhaven National Laboratory, and colleagues report in the May 4 online edition of the journal Science that they have identified gaps in the energy levels of electrons in an iron-based superconductor that were predicted by leading theories in this new field. The gaps represent electrons that have paired up with twins from adjacent atoms to form so-called "Cooper pairs" that move through the conductor without interference. The research also confirms a prediction that the energy binding the Cooper pairs varies with the direction they take when leaving an atom.
Studying crystals of a compound of lithium, iron and arsenic, LiFeAs for short, that becomes a superconductor at 15K (Kelvins, or Celsius degrees above absolute zero), the Cornell researchers found three of the five possible electron bands.
"There are two more pairing gaps that we should have been able to detect, and we don’t know yet why not," Davis said. But finding these three along with the directionality is enough to strongly support the theory, he said, and the measurements give the theorists numbers to plug in to refine and extend their predictions.
Superconductivity was first discovered in metals cooled to temperatures very near absolute zero. Recently discovered compounds of iron, arsenic and other elements become superconductors at much higher temperatures, offering a possible new route to room-temperature superconductivity.
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