Bulk Superconductivity in Fe1+yTe0.6Se0.4 Induced by Removal of Excess   Fe
  Experimental evidences from transport, magnetic, and magneto-optical (MO) image measurements confirmed that arsenic (As) vapor annealing was another effective way to induce bulk superconductivity with isotropic, large, and homogenous superconducting critical current density (Jc) in Fe1+yTe0.6Se0.4 single crystal. Since As is an exotic and easily detectable heavy element to Fe1+yTe0.6Se0.4 single crystal, As vapor annealing is very advantageous for the study of annealing mechanism. Detailed micro-structural and elemental analyses exclude the possibility that intercalating or doping effect may happen in the other post-annealing methods, proving that Fe reacts with As on the surface of the crystal and the reaction itself acts as a driving force to drag excess Fe out. The removal of excess Fe results in the good superconductivity performance. 
Wei Zhou, Yue Sun, Shuo Zhang, Jincheng Zhuang, Feifei Yuan, Xiong Li,   Zhixiang Shi, Tatsuhiro Yamada, Yuji Tsuchiya, and ...
cond-mat.supr-con