Synopsis: Success without pressure

Superconductivity in the iron selenide KxFe2Se2 (0≤x≤1.0)

Jiangang Guo, Shifeng Jin, Gang Wang, Shunchong Wang, Kaixing Zhu, Tingting Zhou, Meng He, and Xiaolong Chen

Published November 29, 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 $AFe2As2$ (). 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