Interplay between Cation and Charge Ordering in La1/3Sr2/3FeO3 Superlattices

The electronic properties of digital superlattices are reported, which are cation-ordered analogs of the perovskite La1/3Sr2/3FeO3, a material that undergoes a charge-ordering transition. Superlattices of LaFeO3 (LFO), an antiferromagnetic insulator, and SrFeO3 (SFO), a conductor with a helical magnetic ground state, are fabricated via oxide molecular beam epitaxy. Three isocompositional superlattices with repeat structures of SSLSSL (S2), SSSLSL (S3), and SSSSLL (S4) (S = SFO, L = LFO) are studied with cation orderings along the [001] and [111] directions for experimental and computational work, respectively. The experimental superlattice structures are confirmed via synchrotron X-ray diffraction and corresponding simulations of (00L) crystal truncation rods. The S2 and S3 superlattices are found to undergo an electronic phase transition as measured by a discontinuity in the temperature-dependent resistivity similar to the random alloy, indicating that the superlattices do not behave as a simple combination of LFO and SFO. The charge-ordering transition is not observed in the S4 sample. The electronic structure calculations using density functional theory, confirming the energetic favorability of charge ordering in the S2 and S3 structures compared to the S4 structure, are consistent with experimental trends.