One-step synthesis of K _xFe _2-ySe ₂ single crystal for high critical current density

We have established a simple process that allows for the one-step synthesis of K _xFe _2-ySe ₂ single crystals, which exhibit high critical current density J _c. 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 T _c ^onset=32.9 K and T _c ^zero=32.1 K. The upper critical fields _{μ 0} H ₀₂ (0) for Hab and Hc are estimated to be ∼206 and ∼50 T, respectively. The critical current densities J _c for Hab and Hc reach as high as 1.0×10 ⁵ and 3.4×10 ⁴ A/cm ² at 5 K. Furthermore, J _c exhibits a high field performance and a significantly weak temperature dependence up to 5 T, suggesting strong pinning. These results demonstrate that K _xFe _2-ySe ₂ would be a promising candidate material for practical applications.