Studying charge transfer phenomena in (SrCoO_3-x)­_n/(SrIrO₃)_n superlattices and heterostructures grown by molecular beam epitaxy (MBE)

Interfacial charge transfer in complex oxide films induces emergent electronic and magnetic properties in interfaces making them promising avenues for the study of quantum materials. To study DFT predictions [1] of charge transfer in ABO₃/AB’O₃ interfaces, we grew a series of (SrCoO_3-x)_n /(SrIrO₃)_n superlattices, where Ir is expected to donate charge to Co, using molecular beam epitaxy (MBE) on two different substrates: La_0.3Sr_0.7Al_0.65Ta_0.35O₃ (LSAT), and SrTiO₃ (STO). Good crystallinity of the superlattice was observed during growth using in-situ reflection high-energy electron diffraction (RHEED), followed by ex-situ X-ray diffraction (XRD). The epitaxial nature was further confirmed using scanning transmission electron microscopy (STEM) along with energy dispersive X-ray (EDX) spectroscopy. From temperature dependent transport measurements, we observed a metallic nature in the superlattice, with an increase in resistivity with increasing strain and a decrease in resistivity with shorter superlattice unit cell period, n. The chemical state of the superlattices was studied first using in-vacuo X-ray photoelectron spectroscopy (XPS), and interfacial charge transfer was confirmed using X-ray absorption spectroscopy (XAS). Our study provides a scope to explore charge transfer induced emergent properties in metastable oxide perovskites in superlattice or double-perovskite structures.