One-step synthesis of KxFe2−ySe2 single crystal for high critical current density

We have established a simple process that allows for the one-step synthesis of KxFe2−ySe2 single crystals, which exhibit high critical current density Jc. The post annealing and quenching technique has improved the homogeneity of as-grown crystals, resulting in full shielding of the external magnetic field. The quenched crystals show a superconducting transition at Tconset=32.9 K and Tczero=32.1 K. The upper critical fields μ 0 H02 (0) for H∥ab and H∥c are estimated to be ∼206 and ∼50 T, respectively. The critical current densities Jc for H∥ab and H∥c reach as high as 1.0×105 and 3.4×104 A/cm2 at 5 K. Furthermore, Jc exhibits a high field performance and a significantly weak temperature dependence up to 5 T, suggesting strong pinning. These results demonstrate that KxFe2−ySe2 would be a promising candidate material for practical applications.