Synopsis: Success without pressure

Iron selenide is transformed into an ambient high-temperature superconductor by a purely chemical method, substituting extremely high pressure.
Synopsis figure
Credit: J. Guo et al., Phys. Rev. B (2010)

In the last two years, many distinct families of pnictide and chalcogenide superconductors have been discovered as a result of concerted efforts in this field. In almost all cases, an “ordinary” parent compound is turned into a superconductor either by chemical doping, or by application of pressure. One of the structurally simpler materials available is iron selenide, which has as basic building blocks layers of FeSe4 tetrahedra. Application of extremely high pressure has yielded a superconducting critical temperature Tc above 30K, approximately half of the highest reported Tc of 55K in oxygen-deficient SmFeAsO.

Now, in a Rapid Communication appearing in Physical Review B, Jiangang Guo and collaborators from the Chinese Academy of Sciences in Beijing, report the synthesis of KxFe2Se2, a superconducting compound with a critical temperature Tc slightly above 30K at ambient pressure. That value sets a new record for the highest critical temperature at ambient pressure for this family of compounds. Structurally, these materials are related to the pnictide 122 compounds AFe2As2 (A=K, Sr, Ba). In this case, the potassium is intercalated between the FeSe layers, and the authors claim that the enhancement of Tc is due to the optimization of the carrier density in the FeSe layers and also due to the Fe-Se tetrahedra achieving a shape close to the ideal. – Alexios Klironomos


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