Emergent Phases at Oxide Interfaces in LaCoO₃-based Heterostructures

The interplay of orbital, spin, and charge states in transition metal oxides creates a rich phase space, displaying a wide range of novel phenomena, from magnetism to superconductivity. Incorporating TMOs into epitaxial heterostructures expands the space of new phenomena possible due to dimensional confinement and interfacial coupling. For cobaltates, orbital filling and spin configuration can display a number of different patterns based on an interplay between crystal field, exchange, and Hund’s energies. These energies can be tuned by combining the perovskite cobaltate LaCoO₃ with other oxide perovskites, such as LaTiO₃, in (LaCoO₃)_n/(LaTiO₃)_n heterostructures grown by molecular beam epitaxy. Interfacial charge transfer from Ti to Co in the heterostructure leads to significant modifications of the cobaltate unit cell structure, which allows the tuning of orbital polarization in the cobaltates. We investigate the varying degree of charge transfer and orbital polarization in these superlattices by controlling layer thickness, n, and by using x-ray absorption spectroscopy(XAS) and resonant inelastic x-ray scattering(RIXS) to characterize electronic properties. This study demonstrates an approach to systematically tune the orbital and charge states in LaCoO₃-based heterostructures.