Synopsis: Superconductivity can be sensitive

Small changes in stoichiometry can destroy superconductivity in FeSe.
Synopsis figure
Illustration: Alan Stonebraker

Following the explosion of interest in the iron-based (pnictide) superconductors, many compounds belonging to the same family of materials have been discovered. FeSe is a recent new addition, composed of Fe2Se2 layers analogous to the Fe2As2 layers of the prototypical pnictide LaFeAsO, but with an overall simpler structure [1]. However, the robustness of this material’s physical properties with respect to changes in stoichiometry is not established.

In Physical Review B, Robert Cava and Nai Phuan Ong of Princeton University, and collaborators in the USA and Europe, report a variety of techniques to grow and characterize FeSe that contains an excess of iron. They find that Fe1.03Se compared to Fe1.01Se, destroys seemingly robust superconductivity, which they believe most likely results from disorder in the crystal structure caused by the additional iron. Moreover, while stoichiometric FeSe exhibits magnetic order at temperatures above the superconductivity transition, the magnetism apparently disappears in Fe1.03Se.

These results point to the role of deviations from stoichiometry and pose intriguing theoretical questions regarding the interplay of magnetism and superconductivity, with implications for the entire family of iron-based superconductors. – Alexios Klironomos

[1] Michelle Johannes, Physics 1, 28 (2008).


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