Unraveling P-type and N-type interfaces in superconducting infinite-layer nickelate thin films

After decades of research, superconductivity is finally found in nickel-based analogs of superconducting cuprates, with infinite-layer (IL) structure. These results are so far restricted to thin films in the case of IL-nickelates. Therefore, the nature of the interface with the substrate, and how it couples with the thin film properties is still an open question. Here, using scanning transmission electron microscopy (STEM)- electron energy loss spectroscopy (EELS), a novel p-type interface defined by SrO termination with the SrTiO${}_3$ substrate is observed in superconducting (SC) IL-praseodymium nickelate samples. Its interfacial charge and polarity are compared with the previously reported n-type interface characterized by TiO${}_2$ termination. In combination with ab-initio calculations, it is found that the influence of the interface on the electronic structure is local and does not extend beyond 2-3 unit cells into the thin film. This decouples the direct influence of the interface in driving the superconductivity, and indicates that the IL-nickelate thin films do not have a universal interface model. Insights into the spatial hole-distribution in SC samples, provided by monochromated EELS and total reflection-hard X-ray photoemission spectroscopy, suggest that this particular distribution might be directly influencing superconductivity. (© 2024 The Author(s). Advanced Materials published by Wiley‐VCH GmbH)