Potentiality for Low Temperature—High Field Application of Iron Chalcogenide Thin Films

Among the various families of Fe-based superconductors, iron chalcogenides, while presenting a transition temperature not particularly high, show great advantages for potential applications at high fields, albeit at liquid helium temperature. In fact, the critical temperature can be increased by stress up to 21 K in thin films, moreover stress can push the critical field up to more than 50 T, and the irreversibility field up to of 45 T. Also critical current densities higher than 1 MA/cm² can be reached in self field and at 4.2 K, with a very weak dependence on the magnetic field. Interestingly, the J_C anisotropy depends on the mode of growth and substrate used. These high values of J_C can be achieved without appreciable anisotropy. In this work, we present an overview of Fe(Se_0.5Te_0.5) thin film deposition by pulsed laser ablation, and a study of their superconducting properties. STM and TEM techniques have been used to characterise structural and morphological properties and, thus, pinning centres. On different substrates the films grow with different types of defects, hence giving totally different J_C anisotropy. Our preliminary measurements on a Josephson junction show that in Fe(Se,Te), the J_C at the grain boundary is not severely depressed, which makes this material even more interesting from the practical point of view.