Nanoscale engineering of electronic and magnetic modulations in gradient functional oxide heterostructures

Advanced interface engineering provides a way to control the ground state of correlated oxide heterostructures, which enables the shaping of future electronic and magnetic nanodevices with enhanced performance. An especially promising and rather new avenue is to find and explore low-dimensional phases of structural, ferroic and superconducting origin. In this multimodal study, we present a novel dynamic growth control method that enables the synthesis of compositionally graded superlattices (SLs) of (LaMnO₃)₁₀/(SrMnO₃)₁₀ (LMO/SMO), in which the layers gradually change their composition between LMO and SMO with gradient G values ranging from 0 to 100%. This leads to strong modulations in the material's electronic properties and of the two-phase ferromagnetic (FM) behavior. In particular, we observe that G surprisingly has almost no impact on the emergent high-temperature FM phase; in contrast, the low-temperature volume-like FM phase increases drastically with higher G-factors and thus can serve as a precise marker for chemical composition on a nanoscale. Focusing on the interfacial charge transfer found at sharp SMO/LMO interfaces (G = 0), we observe that for higher G-factors a long-range charge modulation develops, which is accompanied by an insulator-to-metal transition. These findings showcase G as a crucial control parameter that can shape a superlattice's intrinsic properties and provide a perspective for designing functional oxide heterostructures with artificially disordered interfaces.