Optical properties of Ba0.6K0.4Fe2As2 thin film prepared by pulsed laser deposition and subsequent post-annealing process

We investigate a unique material system, Ba0.6K0.4Fe2As2 thin film, using the optical spectroscopic technique. The Ba0.6K0.4Fe2As2 thin film was prepared on an Al2O3 (0001) substrate using the pulsed laser deposition (PLD) method and a subsequent post-annealing process. The Ba0.6K0.4Fe2As2 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 Ba0.6K0.4Fe2As2 thin film layer from the measured reflectance spectra of the Ba0.6K0.4Fe2As2/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 Ba0.6K0.4Fe2As2 thin film. Our results indicate that this Ba0.6K0.4Fe2As2 thin film prepared by PLD does retain some of the intrinsic physical properties of single crystal samples.