Effects of Iodine Annealing on Fe1+yTe0.6Se0.4

Effects of iodine annealing to induce bulk superconductivity in Fe1+yTe0.6Se0.4 have been systematically studied by changing the molar ratio of iodine to the sample and annealing temperature. The optimal condition to induce bulk superconductivity with Tc ~14.5 K and self-field Jc(2 K) ~ 5x10^5 A/cm2 is found to be a molar ratio of iodine of 5-7 % at the annealing temperature of 400 C. Furthermore, the fact that no compounds containing iodine are detected in the crystal and a significant amount of FeTe2 is produced after the iodine annealing strongly indicate that the excess iron is consumed to form FeTe2 and iodine works as a catalyst in this process.