Unraveling P‐Type and N‐Type Interfaces in Superconducting Infinite‐Layer Nickelate Thin Films

Abstract

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 SrTiO3 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 TiO2 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.