Superconductivity in undoped BaFe2As2 by tetrahedral geometry design

Significance The results demonstrated here show superconductivity in the antiferromagnetic BaFe2As2 without chemical substitution, by atomic level control of local structure through epitaxial superlattice design. The interfacial interactions modify the FeAs4 tetrahedra via systematic control of tetragonal and orthorhombic structures, inducing superconductivity. This indicates structure and dimensionality play an important role in the superconducting properties in Fe-based superconductors, and opens a path to structural manipulation of superconductivity in ultrathin layers of Fe-based materials. This is likely to play a major role in understanding and developing Fe-based superconductors. Fe-based superconductors exhibit a diverse interplay between charge, orbital, and magnetic ordering. Variations in atomic geometry affect electron hopping between Fe atoms and the Fermi surface topology, influencing magnetic frustration and the pairing strength through changes of orbital overlap and occupancies. Here, we experimentally demonstrate a systematic approach to realize superconductivity without chemical doping in BaFe2As2, employing geometric design within an epitaxial heterostructure. We control both tetragonality and orthorhombicity in BaFe2As2 through superlattice engineering, which we experimentally find to induce superconductivity when the As−Fe−As bond angle approaches that in a regular tetrahedron. This approach to superlattice design could lead to insights into low-dimensional superconductivity in Fe-based superconductors.