Thickness effect on the evolution of superconducting properties in FeSe_0.4Te_0.6 thin films

Abstract A series of high-quality FeSe 0.4 Te 0.6 epitaxial thin films with different thicknesses were fabricated on CaF 2 substrates by pulsed laser deposition. With increasing the film thickness, the superconducting transition temperature is enhanced rapidly but deteriorates gradually in over thick films. The superconducting transition occurs in all films including the 5 nm one, and T c above 21 K persists in the films with thicknesses from 45 to 180 nm. We find that T c and the c -axis lattice constant show a nearly linear correlation, suggesting a strong interdependence between T c and the lattice strain characteristics. The upper critical field, anisotropy and effective pinning energy are studied in detail for the 15, 60, 90 and 180 nm films. These observations provide key insights in understanding the thickness effect on the superconductivity of the FeSe 0.4 Te 0.6 films.