Electrodynamics of superconducting pnictide superlattices

It was recently shown that superlattices where layers of the 8% Co-doped BaFe₂As₂ superconducting pnictide are intercalated with non superconducting ultrathin layers of either SrTiO₃ or of oxygen-rich BaFe₂As₂, can be used to control flux pinning, thereby increasing critical fields and currents, without significantly affecting the critical temperature of the pristine superconducting material. However, little is known about the electron properties of these systems. Here, we investigate the electrodynamics of these superconducting pnictide superlattices in the normal and superconducting state by using infrared reflectivity, from THz to visible range. We find that multigap structure of these superlattices is preserved, whereas some significant changes are observed in their electronic structure with respect to those of the original pnictide. Our results suggest that possible attempts to further increase the flux pinning may lead to a breakdown of the pnictide superconducting properties.