First-principles study for the anisotropy of iron-based superconductors toward power and device applications

Performing the first-principles calculations, we investigate the anisotropy in the superconducting state of iron-based superconductors to gain an insight into their potential applications. The anisotropy ratio γλ of the c-axis penetration depth to the ab-plane one is relatively small in BaFe2As2 and LiFeAs, i.e., γλ-3, indicating that the transport applications are promising in these superconductors. On the other hand, in those having perovskite type blocking layers such as Sr2ScFePO3 we find a very large value, γλ≥200, comparable to that in strongly anisotropic high-Tc cuprate Bi2Sr2CaCu2O8-δ. Thus, the intrinsic Josephson junction stacks are expected to be formed along the c-axis, and novel Josephson effects due to the multi-gap nature are also suggested in these superconductors. (author)