Effects of Annealing under Tellurium Vapor for Fe1.03Te0.8Se0.2 Single Crystals

In this study, the effects of annealing under tellurium vapor have been investigated for Fe 1.03 Te 0.8 Se 0.2 single crystals. The as-grown crystal is not superconducting. After annealing it at 400 °C for 250 h in tellurium (Te) vapor, it shows metallic resistivity temperature dependence below 150 K and a sharp superconducting transition at 13 K. The sample also shows a full magnetic shielding effect at low temperatures. The improvement in superconductivity has been attributed to the removal of excess Fe, which is inevitably incorporated in the as-grown crystals, by the annealing.