Optical properties of Ba_0.6K_0.4Fe₂As₂ thin film prepared by pulsed laser deposition and subsequent post-annealing process

We investigate a unique material system, Ba_0.6K_0.4Fe₂As₂ thin film, using the optical spectroscopic technique. The Ba_0.6K_0.4Fe₂As₂ thin film was prepared on an Al₂O₃ (0001) substrate using the pulsed laser deposition (PLD) method and a subsequent post-annealing process. The Ba_0.6K_0.4Fe₂As₂ thin film sample shows a much larger residual resistivity as compared to that of a single crystal of the same compound. We applied the well-known multilayer thin film analysis to obtain optical constants of Ba_0.6K_0.4Fe₂As₂ thin film layer from the measured reflectance spectra of the Ba_0.6K_0.4Fe₂As₂/Al₂O₃ sample. The overall temperature-dependent optical properties were found to be similar to those of a corresponding single crystal. From our analysis, we also roughly estimated the superfluid density of 3860 cm⁻¹ and the corresponding London penetration depth of 412 nm of the Ba_0.6K_0.4Fe₂As₂ thin film. Our results indicate that this Ba_0.6K_0.4Fe₂As₂ thin film prepared by PLD does retain some of the intrinsic physical properties of single crystal samples.