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Very high field measurements unveil the puzzling behaviour of Fe(Se,Te).
Leo A., Mizzi C.A., Maiorov B.A., Khan M.R., Putti M., Braccini V., Scuderi M., Polichetti M., Galluzzi A., Pace S., Nigro A., Grimaldi G.
Fe(Se,Te) is one of the most promising materials to realize devices for high field and high power applications. Anyway, the fundamental nature of superconductivity, as well as some peculiar pinning properties of this material are still puzzling. Here we will present a comprehensive analysis of electrical transport measurements on Fe(Se,Te) thin films grown on $CaF_2$. We determine the upper critical field and irreversibility field dependence on temperature by angular-dependent magnetoresistance measurements carried out up to 60 T, and down to 1.2 K. A clear crossover between the curves obtained with field applied perpendicular and parallel to the sample $a-b$ plane has been found. The existence of this anisotropy crossover has two main consequences. From the point of view of applications, we can identify a temperature range of almost perfectly isotropic superconductivity and pinning. Regarding the fundamental properties of Fe(Se,Te) thin films, the crossover in upper critical field is clear evidence of multiband effects, while the crossover in irreversibility field enlighten the crucial role played by material complex pinning landscape.