Study of vortex glass-liquid transition in superconducting Fe(Te, Se) thin films on LaAlO3 substrates

Abstract

Superconducting thin films of two different thicknesses have been fabricated on (100) LaAlO3 substrates using a polycrystalline target of composition Fe1.05Te0.50Se0.50 by the pulsed laser deposition technique. The onset of superconducting transition temperatures (TConset) at 0 T magnetic field of the grown thin films of thickness of ∼74 nm and ∼185 nm are ∼12.65 and 13.15 K, respectively. The upper critical field BC2(0) values have been calculated by the Ginzburg–Landau theory as well as by the Werthamer–Helfand–Hohenberg model, and the corresponding coherence lengths have been estimated. In the present work, the thermally activated energy (TAE) has been obtained using the conventional Arrhenius law as well as by a modified thermally activated flux flow (TAFF) theory. For both models, the TAEs of vortices show a crossover at a magnetic field of ∼2 T corresponding to the transition from the single vortex pinning regime to the collective vortex pinning regime. Based on the analysis of the field dependence of TAE, the planer/point defect dominating magnetic field regions have been identified. The analysis of the magnetotransport data with the modified TAFF model reveals the dominating three dimensional behavior of vortices for both thin films. Moreover, in the vortex phase diagram, a narrow vortex melting region and a vortex glass-liquid phase transition below BC2 have been observed for both of the grown thin films. Furthermore, the X-ray photoelectron spectroscopy results show that Fe is present in Fe2+ and Fe3+ chemical states in both thin films.