Superconducting materials are able to carry electricity without shedding energy loss only below a specific material’s critical temperature (TC), which is, for all the superconductors discovered to date, far away from ambient conditions. Further, the physical mechanism under the superconductivity is still poorly understood. Thus, the researchers are continuously in search of new superconducting materials. In 2019, a new family of superconductors was discovered in layered nickelate compounds, a structure called “infinite-layer”, with TC≈10-15K. This ground-breaking discovery has given rise to an entirely new realm of research whose progress has been impeded by the complicated synthesis process of the materials. The two-step synthesis requires to start from a high-quality parent phase and then perform a chemical reduction to selectively remove one third of the oxygen atoms of the structure. In this work, we shed light on the key ingredients to attain superconducting thin films and the importance of the combined optimization of both steps of the synthesis. Our results will contribute to improve the synthesis of these compounds and will hopefully encourage more research groups to synthesize superconducting films, scarce to date, pushing forward the experimental research in this nascent field.

“Towards reliable synthesis of superconducting infinite layer nickelate thin films by topochemical reduction”, A. Gutiérrez-Llorente et al., Advanced Science, 2309092 (2024)

Superconducting nickelates

On the left, scanning transmission electron microscopy (STEM) image of the structure studied in this work composed by an SrTiO3 (STO) substrate, a Pr0.8Sr0.2NiO2 (PSNO2) thin film and a capping layer of STO. In the center, atomic resolution TEM image of the interface highlighted in the left panel as a dashed orange rectangle, and 4D-STEM image revealing the absence of apical oxygen atoms, therefore confirming the infinite-layer structure of the nickelate thin film. On the right panel, temperature dependence of the resistivity ρ (T) of the infinite-layer sample, showing the superconducting transition with a TC ⁓ 8 K.