Abstract
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 Fe(Se,Te) thin films grown on CaF2 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 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 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.
Highlights
The angular dependence of the critical current density Jc, the upper critical magnetic field Hc2 and the irreversibility field Hirr as a function of the orientation of the external applied field has been far and wide investigated in High Temperature Superconductors (HTS)[1]
We focus on the angular dependence of the flux flow instability, in particular of the critical parameters that are the quenching current I* and the critical voltage V*, which identifies the upper limits of the flux flow regime, that suddenly is driven into the normal resistive state[23]
The flux flow instability consists in a quenching of the superconducting state, which abruptly drives the system from the dynamic non-linear flux flow resistive state into the normal resistance branch
Summary
The angular dependence of the critical current density Jc, the upper critical magnetic field Hc2 and the irreversibility field Hirr as a function of the orientation of the external applied field has been far and wide investigated in High Temperature Superconductors (HTS)[1]. In the search for high-performance high-field superconductors, a good candidate can be the Fe(Se,Te) grown on CaF2 substrate[15], which shows the lowest anisotropy[16], a very robust Jc(H) dependence[17], and a sufficient stability against quench under relatively high bias currents[18,19] In this compound the study of vortex dynamics has been recently performed at subcritical current values and in self magnetic fields[20]. In the presence of an external applied magnetic field and at high vortex velocities, we have established the intrinsic nature of a quenching mechanism of the superconducting state, known as flux flow instability, occurring above Jc in the current driven transition to the normal state[18]. Experimental data analysis emphasizes a fundamental aspect of the Fe(Se,Te) material similar to some HTS such as BSCCO26, but it demonstrates a relevant difference on the quenching current of the Fe(Se,Te) compound, which provides more efficient, robust and field independent electric current transport on the orientation of the magnetic field
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