Electrochemical Na-intercalation-induced high-temperature superconductivity in FeSe

• Nax(PC)yFe2Se2, with Tc = 43 K has been synthesized
• The co-intercalation of Na and PC into FeSe greatly increases the distance between Se layers, leading to the high Tc
• The electrochemical intercalation method, in which various combinations of metal and solvent are possible, allows for the synthesis of new iron-chalcogenide-based superconductors.

Iron-chalcogenide-based superconductors have attracted much attention due to their relatively high superconducting transition temperatures (Tc) and their simple layered crystal structures. We have performed electrochemical co-intercalation of Na and propylene carbonate (PC) into FeSe, and successfully synthesized a new superconductor, Nax(PC)yFe2Se2, with Tc = 43 K. The type and amount of intercalated metal, and the electrolyte used in the intercalation affected the superconductivity. Our electrochemical intercalation method should be a useful tool for discovering new superconductors by controlling the intercalation conditions.