Superconductivity in layered iron Selenide induced by cobalt- and   sodium-doping
  Superconductivity with zero resistance transition temperature (Tc) up to 8.4 K and 8.3 K can be obtained by doping cobalt and sodium in alfa-FeSe with the nominal composition of Fe0.92Co0.08Se and Na0.1FeSe, respectively. The electrical resistivity and AC magnetic susceptibility of the prepared samples, measured with physical property measurement system (PPMS), unambiguously consistent with each other to indicate that the samples are superconductive. The respective doping mechanisms for cobalt and sodium into the parent alfa-FeSe are the Fe-site substitution and the interlayer insertion. It is the first time that alfa-FeSe can be induced to be a superconductor with Na+ intercalated into the interlayers. 
Zhanqiang Liu, Aihua Fang, Fuqiang Huang, Mianheng Jiang