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

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.

Dimensionality of the Superconductivity in the Transition Metal Pnictide WP

“…It is well known indeed that this measurement may be indicative of a superconducting state with 2D or anisotropic 3D character. Within the Tinkham model, the behavior of the H c2 (θ), for a superconductor with 2D character, exhibits the following angular dependence [37,51] H c2 (θ) sin(θ)…”

Effective Magnetic Field Dependence of the Flux Pinning Energy in FeSe0.5Te0.5 Superconductor

“…We find that not all data fall on the same curve. The missing scaling is a signature of the fact that the anisotropy of the material is very weak [37], and this contrasts with the high temperature superconductor's behaviour [38]. In any case, it seems that a partial scaling can be achieved above 20 • , when the crossover field's perpendicular component becomes insensitive to the angular variation of the applied field, as reported in Figure 6b.…”

“…Interestingly, the 30 • value is equivalent to the 60 • value above which Llovo et al observe a deviation of the H c2 (θ) from the ε 2 (θ) scaling [35]. A further step is to test the scaling approach followed by Xiao et al in the case of the layered HTS BiSCCO compound [36], an approach which already has been proven effective to describe the angular dependence of another physical quantity strongly dependent on material pinning properties, which is the Flux Flow Instability critical voltage V* [37]. Thus, we plot the U 0 values at different angles and fields as a function of the perpendicular component µ 0 Hsin(θ) in Figure 6a.…”

Effect of 1.5 MeV Proton Irradiation on Superconductivity in FeSe0.5Te0.5 Thin Films

“…Iron-based and cuprate high-temperature superconductors commonly possess inherent layered structures, consisting of alternating conducting and insulating atomic planes. In general, the strong J c peak for H//ab could be ascribed to the vortex pinning by the intrinsic pinning and planar defects such as intergrowths and stacking faults, parallel to the ab plane [32][33][34][35]. In the iron-chalcogenide Fe(Se,Te) compound, which is composed of only the Fe-Se(Te) layer, J c (θ) has a maximum at H//ab due to intrinsic pinning from the Fe-Se(Te) intralayer and Van der Waals interlayer couplings [29,34,35].…”