Unraveling p-type and n-type interfaces in Superconducting Infinite-Layer Nickelate thin films

TL;DR

This study investigates the nature of p-type and n-type interfaces in superconducting infinite-layer nickelate thin films, revealing that interface effects are local and do not universally drive superconductivity, with implications for understanding their electronic structure.

Contribution

The paper provides the first detailed comparison of p-type and n-type interfaces in IL-nickelate thin films using advanced microscopy and spectroscopy, challenging the idea of a universal interface model for superconductivity.

Findings

P-type interface is chemically sharp and highly polar.

Interface influence on electronic structure is limited to 2-3 unit cells.

Spatial hole-distribution may directly affect superconductivity.

Abstract

After decades of research, superconductivity was 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) and four-dimensional (4D)-STEM, a novel chemically sharp p-type interface is observed in a series of superconducting IL-praseodymium nickelate samples, and a comparative study is carried out with the previously reported n-type interface obtained in other samples. Both interfaces have strong differences, with the p-type interface being highly polar. In combination with ab-initio calculations, we find 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.