  Significant progress has been achieved in fabricating high quality bulk and
thinfilm iron-based superconductors. In particular, artificial layered pnictide
superlattices offer the possibility of tailoring the superconducting properties
and understanding the mechanism of the superconductivity itself. For high field
applications, large critical current densities (Jc) and irreversibility fields
(Hirr) are indispensable along all crystal directions. On the other hand, the
development of superconducting devices such as tunnel junctions requires
multilayered heterostructures. Here we show that artificially engineered
undoped Ba-122 / Co doped Ba-122 compositionally modulated superlattices
produce ab-aligned nanoparticle arrays. These layer and self-assemble along
c-axis aligned defects, and combine to produce very large Jc and Hirr
enhancements over a wide angular range. We also demonstrate a structurally
modulated SrTiO3 (STO) / Co doped Ba-122 superlattice with sharp interfaces.
Success in superlattice fabrication involving pnictides will aid the progress
of heterostructured systems exhibiting novel interfacial phenomena and device
applications.
