Comparison of Superconducting Properties of $\hbox {FeSe}_{0.5}\hbox {Te}_{0.5}$ Thin Films Grown on Different Substrates

We have shown that the superconducting properties of FeSe_0.5 Te_0.5 thin films are strongly dependent on the growth conditions and, in particular, the in-plane lattice constant of the substrate influences the crystallographic lattice parameters of the films, affecting the strain and is responsible for strong enhancements of the critical temperature T_c and for the introduction of different pinning mechanisms. Here we compare the structural, electrical and transport properties of superconducting Fe(Se_0.5, Te_0.5) epitaxial films deposited through pulsed laser ablation on three different substrates namely lanthanum aluminate (LaAlO₃), strontium titanate (SrTiO₃), and calcium fluoride (CaF₂). We analyze in particular the critical current density J_c as a function of the temperature and magnetic field, and its anisotropy, which is related to the different pinning mechanisms in play. The film grown on SrTiO₃ exhibits a higher critical current when the field is perpendicular to the film surface, opposite to what happens in the sample grown on LaAlO₃ due to the presence of extrinsic pinning along the c-axis, while we observe almost no anisotropy on the thin film grown on CaF₂.