Characterization of superconductivity in FeTe_0.61Se _0.39 single crystal with T_c ∼ 14 K

We report resistivity, magnetization, critical current density, and the upper critical field of the single crystalline FeTe_0.61Se _0.39 with T_c ∼ 14 K synthesized via slow-furnace cooling followed by low-temperature annealing. Magneto-optical observation confirms the uniformity of current flow in the crystal and the critical current density is estimated to exceed 1 × 10⁵ A/cm² below 5 K under zero field. Weak fish-tail effect is identified at lower temperatures. Upper critical field along ab-plane at T = 0 K estimated from WHH theory exceeds 1000 kOe, which is much higher than that in Ba(Fe_0.9Co _0.1)₂As₂.