Interfacial charge transfer and its impact on transport properties of LaNiO3/LaFeO3 superlattices

Charge transfer or redistribution at oxide heterointerfaces is a critical phenomenon, often leading to remarkable properties such as two-dimensional electron gas and interfacial ferromagnetism. Despite studies on LaNiO₃/LaFeO₃ superlattices and heterostructures, the direction and magnitude of the charge transfer remain debated, with some suggesting no charge transfer due to the high stability of Fe³⁺ (3d⁵). Here, we synthesized a series of epitaxial LaNiO₃/LaFeO₃ superlattices and demonstrated partial (up to ~0.5 e⁻/interface unit cell) charge transfer from Fe to Ni near the interface, supported by density functional theory simulations and spectroscopic evidence of changes in Ni and Fe oxidation states. The electron transfer from LaFeO₃ to LaNiO₃ and the subsequent rearrangement of the Fe 3d band create an unexpected metallic ground state within the LaFeO₃ layer, strongly influencing the in-plane transport properties across the superlattice. Moreover, we establish a direct correlation between interfacial charge transfer and in-plane electrical transport properties, providing insights for designing functional oxide heterostructures with emerging properties.