Critical Role Played by Interface Engineering in Weakening Thickness Dependence of Superconducting and Structural Properties of FeSe_0.5Te_0.5-Coated Conductors

Increasing the thickness of a superconducting layer andsimultaneouslyreducing the thickness effect in iron-based superconducting coatedconductors are particularly essential for improving the critical current I (c). Here, for the first time, we have depositedhigh-performance FeSe0.5Te0.5 (FST) superconductingfilms up to 2 mu m on LaMnO3-buffered metal tapes bypulsed laser deposition. An interface engineering strategy, alternatinggrowth of a 10 nm-thick nonsuperconducting FST seed layer and a 400nm-thick FST superconducting layer, was employed to guarantee thecrystalline quality of the films with thicknesses of the order ofmicrometers, resulting in a highly biaxial texture with grain boundarymisorientation angle less than the critical value theta(c) similar to 9 degrees. Moreover, the thickness effect, that the criticalcurrent density (J (c)) shows a clear dependenceon thickness as in cuprates, is reduced by the interface engineering.Also, the maximum J (c) was found for a 400nm-thick film with 1.3 MA/cm(2) in self-field at 4.2 K and0.71 MA/cm(2) (H parallel to ab) and 0.50 MA/cm(2) (H parallel to c) at 9 T. Anisotropic Ginzburg-Landau scaling indicates thatthe major pinning centers vary from correlated to uncorrelated asthe film thickness increases, while the thickness effect is most likelyrelated to the weakening of flux pinning by the fluctuation of charge-carriermean free path (delta l) and strengthening of fluxpinning caused by the variation of superconducting transition temperature(delta T (c)) due to off-stoichiometry withthickness.