Evolution of superconductivity dependence on substrate temperature with thickness of Fe(Se,Te) coated conductors deposited on metal tapes

Abstract

Fe(Se,Te) films of different thicknesses were deposited on metal tapes by pulsed laser deposition at different substrate temperatures. It is found that the substrate temperature dependence of superconductivity changes with the Fe(Se,Te) film thickness. When fabricating thin Fe(Se,Te) films with a thickness of about 150 nm, moderate substrate temperatures are conducive to balancing the influence of texture and stoichiometry on superconductivity, contributing to the obtainment of good superconductivity. When the Fe(Se,Te) films’ thickness is about 300 nm, the optimal substrate temperatures are lowered due to the determination of film superconductivity by the inhomogeneity of longitudinal chalcogen distribution via the cooperation of Te loss in the long-term-ablated target and the attraction of metal ions in the buffer layer. In addition, with a further increase in thickness from 300 to 600 nm, the self-field critical current of thick Fe(Se,Te) films continuously increases, but the critical current density increases first and then decreases, which is thought to be a result of the misoriented grains or non-superconducting phase due to the large deviation between the actual deposition temperature and the set substrate temperature, and the Se excess in the film. In addition, the 450-nm-thick Fe(Se,Te) film exhibits excellent self-field and in-field performances at 4.2 K: 1.308 MA/cm2 at self-field and over 0.5 MA/cm2 at 9 T. Point pinning, which is the local lattice disturbance randomly distributed in the film observed by transmission electron microscopy, dominates over the entire temperature range.