On the role of chalcogen vapor annealing in inducing bulk superconductivity in Fe_(1+y)Te_(1-x)Se_(x)

Recent investigations have shown that Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ can be made superconducting by annealing it in Se and O vapors. The current lore is that these chalcogen vapors induce superconductivity by removing the magnetic excess Fe atoms. To investigate this phenomenon we performed a combination of magnetic susceptibility, specific heat and transport measurements together with scanning tunneling microscopy and spectroscopy and density functional theory calculations on Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ treated with Te vapor. We conclude that the main role of the Te vapor is to quench the magnetic moments of the excess Fe atoms by forming FeTe$_{m}$ (m $\geq$ 1) complexes. We show that the remaining FeTe$_{m}$ complexes are still damaging to the superconductivity and therefore that their removal potentially could further improve superconductive properties in these compounds.