Angular dependence of vortex instability in a layered superconductor: the case study of Fe(Se,Te) material.

Anisotropy effects on flux pinning and flux flow are strongly effective in cuprate as well as iron-based superconductors due to their intrinsically layered crystallographic structure. However $\textrm{Fe(Se,Te)}$ thin films grown on $\textrm{CaF}_2$ substrate result less anisotropic with respect to all the other iron based superconductors. We present the first study on the angular dependence of the flux flow instability, which occurs in the flux flow regime as a current driven transition to the normal state at the instability point ($I^*$,$V^*$) in the current-voltage characteristics. The voltage jumps are systematically investigated as a function of the temperature, the external magnetic field, and the angle between the field and the $\textrm{Fe(Se,Te)}$ film. The scaling procedure based on the anisotropic Ginzburg-Landau approach is successfully applied to the observed angular dependence of the critical voltage $V^*$. Anyway, we find out that $\textrm{Fe(Se,Te)}$ represents the case study of a layered material characterized by a weak anisotropy of its static superconducting properties, but with an increased anisotropy in its vortex dynamics due to the predominant perpendicular component of the external applied magnetic field. Indeed, $I^*$ shows less sensitivity to angle variations, thus being promising for high field applications.