  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.
