Atomic-scale structure and composition mapping in nickelate heterostructures

Strongly correlated electronic systems display a wide range of interesting properties, including ferroelectricity, superconductivity, metal-insulator transitions, and novel magnetic phenomena. The electrical and magnetic properties of thin film heterostructures based on these systems are directly linked to their atomic scale structure and composition. This link is important for the rare earth nickelates, which exhibit first-order metal-insulator transitions, antiferromagnetism, and charge ordering. At the interfaces present in these systems, structural coupling can lead to new effects. We use a synchrotron-based resonant anomalous x-ray scattering method to elucidate the physical and electronic structure at complex oxide heterointerfaces of nickelates grown using molecular beam epitaxy. Temperature dependent resonant x-ray studies in doped 8 unit-cell thick NdNiO$_3$ films reveal subtle changes in atomic structure and Ni charge disproportionation at the metal-insulator transition.