Onset of metallic behavior in strained (LaNiO₃)_n/(SrMnO₃)₂ superlattices

(LaNiO₃)_n/(SrMnO₃)₂ superlattices were grown using ozone-assisted molecular beam epitaxy. In situ reflection high-energy electron diffraction and x-ray scattering has been used to characterize the structural properties of the superlattices, which are strained to the SrTiO₃ substrates. The superlattices exhibit excellent crystallinity and interfacial roughness of less than 1 unit cell. A metal-insulator transition is observed as n is decreased from 4 to 1. Analysis of the transport data suggests an evolution from gapped insulator (n=1) to hopping conductor (n=2) to metal (n=4) with increasing LaNiO₃ concentration.