Study of superconductivity of Li-doped Fe (Se0.5Te0.5) polycrystalline bulk samples

Fe(Se/Te) family compounds are very important among iron-based superconductors. To explore the modification of their physical properties, Li-doped FeSe[Formula: see text]Te[Formula: see text] polycrystalline samples were prepared by using sintering method with metal Li as the dopant. X-ray diffraction (XRD) and Raman scattering indicated that the lattice parameter c and Raman peaks change systematically with increasing Li content, suggesting Li atoms have entered the lattice. Magnetization and electrical transport measurements showed the type-II superconductor behavior. The upper critical field increased with increasing Li doping concentration, while the coherence length decreased with increasing dopant concentration. Li-doping generally improved the superconductivity, including the uniformity of superconducting contents. The thermally activated flux-flow (TAFF) activation energy also increased with increasing dopant concentration. The critical current densities were measured and the flux pinning mechanism and its change with doping were analyzed.