Mapping electronic phase coexistence in nickelate superlattices by STEM-EELS

To study the electronic couplings, and their characteristic length-scales, that are established at the coherent interfaces of epitaxial heterostructures, novel characterization techniques capable of mapping electronic phase coexistence at the atomic-scale level are required. Here, we show that scanning transmission electron microscopy in combination with electron energy-loss spectroscopy (STEM-EELS) can be used to map electronic phase coexistence in rare-earth nickelate materials.
The feasibility of the experiment is demonstrated by using two NdNiO₃/SmNiO₃ superlattices (SLs) whose constituent SmNiO₃ layers are either insulating or metallic at room temperature depending on their corresponding layer thickness. [1] By tracing the evolution of specific fingerprints present in the EELS fine structures, we are able to map the metallic and insulating regions in both SLs, and to further estimate the width associated to the metallic/insulating boundaries.

[1] C. Domínguez et al., Nat. Mater. 19, 1182 (2020)