Chalcogen (O2, S, Se, Te) atmosphere annealing induced bulk superconductivity in Fe1+yTe1−xSex single crystal

• Bulk superconductivity is induced in Fe1+yTe1−xSex by annealing in the atmosphere of chalcogens (O2, S, Se, Te).
• Annealed crystals show large value of Jc ∼ 2–4 × 105 A/cm2.
• Magneto-optical images reveal a homogeneous and isotropic Jc in the annealed crystals.

We reported a detailed study of Fe1+yTe0.6Se0.4 single crystals annealed in the atmosphere of chalcogens (O2, S, Se, Te). After annealing with appropriate amount of chalcogens, Fe1+yTe0.6Se0.4 single crystals show Tc higher than 14 K with a sharp transition width ∼1 K. Critical current density Jc for the annealed crystals reach a very high value ∼2–4 × 105 A/cm2 under zero field, and is also robust under applied field at low temperatures. Magneto-optical imaging reveal that the Jc is homogeneously distributed in the annealed crystals and isotropic in the ab-plane. Our results show that annealing in the atmosphere of chalcogens can successfully induce bulk superconductivity in Fe1+yTe0.6Se0.4.