Effect of K-doping on the superconducting properties of FeSe0.5Te0.5 single crystals

Fe1-xKxSe0.5Te0.5 ( x = 0, 0.025, 0.05, 0.075 and 0.1) single crystals were grown by self-flux method. The effects of K-doping on the length of c-axis, critical temperature, anisotropy and critical current density were investigated. With the increase of K-doping content x, the length of c-axis increases, the critical temperature rises at first and then falls, and the anisotropy decreases. The critical current density displays a significant increase at x = 0.075. Subsequently, the superconducting properties of Fe(0.925)K(0.075)Se(0.5)Te(0.5 )were thoroughly studied. The field-dependent pinning energy U(H) and the temperature-dependent upper critical field H-c2(T) were given. Additionally, the Dew-Hughes model was used to scale the flux pinning force, and the result suggests that the superconductor had a temperature-induced pinning mechanism from normal point pinning to normal surface pinning, in which twins play an important role. We also discussed the temperature-dependent critical current density J(c)(T)=J(c)(0)(1-T/T-1)(n) and found that the n-value depends on different flux pinning regimes, including single flux pinning, strong collective pinning associated with twins and weak collective pinning associated with point defects. (C) 2022 Published by Elsevier B.V.

Automated summary

Fe1-xKxSe0.5Te0.5 (x = 0, 0.025, 0.05, 0.075, and 0.1) single crystals were grown by self-flux method. The effects of K-doping on various properties were investigated, including the length of c-axis, critical temperature, anisotropy, and critical current density. It was found that with the increase of K-doping content, the length of c-axis increased, the critical temperature initially rose and then fell, and the anisotropy decreased. At x = 0.075, a significant increase in critical current density was observed. The superconducting properties of Fe(0.925)K(0.075)Se(0.5)Te(0.5) were also thoroughly studied, including field-dependent pinning energy and temperature-dependent upper critical field. The results suggested a temperature-induced pinning mechanism from normal point pinning to normal surface pinning, with the involvement of twins. The temperature-dependent critical current density J(c)(T)=J(c)(0)(1-T/T-1)(n) was discussed, and the n-value was found to depend on different flux pinning regimes.