Effects of Te- and Fe-doping on the superconducting properties in FeySe1-xTex thin films

High quality Fe y Se 1− x Te x epitaxial thin films have been fabricated on TiO 2 -buffered SrTiO 3 substrates by pulsed laser deposition technology. There is a significant composition deviation between the nominal target and the thin film. Te doping can affect the Se/Te ratio and Fe content in chemical composition. The superconducting transition temperature T c is closely related to the chemical composition. Fe vacancies are beneficial for the Fe y Se 1− x Te x films to exhibit the higher T c . A 3D phase diagram is given that the optimize range is x  = 0.13 − 0.15 and y  = 0.73 − 0.78 for Fe y Se 1− x Te x films. The anisotropic, effective pining energy and critical current density for the Fe 0.72 Se 0.94 Te 0.06 , Fe 0.76 Se 0.87 Te 0.13 and Fe 0.91 Se 0.77 Te 0.23 samples were studied in detail. The scanning transmission electron microscopy images display a regular pattern without obviously scale defects at the interfacial structure.