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 (LaAlO
₃
), strontium titanate (SrTiO
₃
), and calcium fluoride (CaF
₂
). 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 SrTiO
₃
exhibits a higher critical current when the field is perpendicular to the film surface, opposite to what happens in the sample grown on LaAlO
₃
due to the presence of extrinsic pinning along the
c
-axis, while we observe almost no anisotropy on the thin film grown on CaF
₂
.