Orbital Engineering in Trigonal CrVO₃ Superlattices

Complex oxides form a fertile ground for a rich variety of functional phenomena that can be controlled upon doping, strain, interfacial charge transfer, confinement, and many others. Tuning these parameters often involves complex architectures such as heterostructures, superlattices or nanocomposites, with the ultimate aim to bring these quantum phenomena towards device applications. Moreover, many of the explored complex oxides are perovskites ABO₃ hosting the common high-temperature cubic structure, while materials with trigonal and hexagonal symmetry have remained largely unexplored.<br/><br/>In this work, we study corundum CrVO₃ (V₂O₃/Cr₂O₃) superlattices with symmetric periodicities ranging from 1 to 14 monolayers (ML) grown by oxide molecular beam epitaxy (MBE). By means of transport and optical spectroscopy, it is shown how the strong electron correlations in V₂O₃ are suppressed by quantum confinement. While infrared and Raman spectroscopy prove that this is accompanied by the absence of the monoclinic ground state at low temperature. By combining density functional theory (DFT) and Raman spectroscopy, it is shown that this dimensional crossover can be largely explained by a change in the orbital states dictating the phase diagram of V₂O₃.<br/><br/>In a second part, we focus on the 1ML limit of superlattices, which can be considered as a new ordered ilmenite structure (R-3) and is predicted to be a ferromagnetic insulator by DFT methods. Furthermore, the capability to grow these corundum materials in a monolayer fashion unlocks a complete new set of ABO₃materials with a trigonal symmetry (R3, R-3, R3c) where both A and B are transition metals. Finally, we also propose a way to grow these materials in the polar ordered (R3c) structure where the existence of two magnetic sublattices promises new high-temperature multiferroicity, motivating the search for novel ordered trigonal materials.