Critical Role Played by Interface Engineering in Weakening Thickness Dependence of Superconducting and Structural Properties of FeSe0.5Te0.5-Coated Conductors

Increasing the thickness of a superconducting layer and simultaneously reducing the thickness effect in iron-based superconducting coated conductors are particularly essential for improving the critical current I_c. Here, for the first time, we have deposited high-performance FeSe_0.5Te_0.5 (FST) superconducting films up to 2 μm on LaMnO₃-buffered metal tapes by pulsed laser deposition. An interface engineering strategy, alternating growth of a 10 nm-thick nonsuperconducting FST seed layer and a 400 nm-thick FST superconducting layer, was employed to guarantee the crystalline quality of the films with thicknesses of the order of micrometers, resulting in a highly biaxial texture with grain boundary misorientation angle less than the critical value θ_c ∼ 9°. Moreover, the thickness effect, that the critical current density (J_c) shows a clear dependence on thickness as in cuprates, is reduced by the interface engineering. Also, the maximum J_c was found for a 400 nm-thick film with 1.3 MA/cm² in self-field at 4.2 K and 0.71 MA/cm² (H∥ab) and 0.50 MA/cm² (H∥c) at 9 T. Anisotropic Ginzburg-Landau scaling indicates that the major pinning centers vary from correlated to uncorrelated as the film thickness increases, while the thickness effect is most likely related to the weakening of flux pinning by the fluctuation of charge-carrier mean free path (δl) and strengthening of flux pinning caused by the variation of superconducting transition temperature (δT_c) due to off-stoichiometry with thickness.