(Phys.org) —Scientists at the U.S. Department of Energy's Argonne National Laboratory have discovered a previously unknown phase in a class of superconductors called iron arsenides. This sheds light on a debate over the interactions between atoms and electrons that are responsible for their unusual ...
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More research on iron-based superconductors (http://sco.lt/7CfptR), here on doped barium iron arsenide. The electron pairing mechanism is not understood in these unconventional superconductors. To elucidate the mechanism, one issue is to map out the precise phase diagrams.
Here neutron diffraction showed that on lowering the temperature, close to the onset of superconductivity, the structure restores 4-fold symmetry. At higher temperatures the structure has nematic ("thread-like") order with 2-fold symmetry, whereas at room temperature the symmetry is again 4-fold.
The finding appears to support the model that the nematic phase is driven by magnetic interactions and not by iron 3d orbital ordering. And this hints, according to the phys.org article, that it could be magnetism that could be the key to electron pairing.
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The Nature Communications article: