Synthesis and electronic properties of Nd${}_{n+1}$Ni${}_n$O${}_{3n+1}$ Ruddlesden-Popper nickelate thin films

Abstract

The rare-earth nickelates possess a diverse set of collective phenomena including metal-to-insulator transitions, magnetic phase transitions, and, upon chemical reduction, superconductivity. Here, we demonstrate epitaxial stabilization of layered nickelates in the Ruddlesden-Popper form, Nd${}_{n+1}$Ni${}_n$O${}_{3n+1}$, using molecular beam epitaxy. By optimizing the stoichiometry of the parent perovskite NdNiO${}_3$, we can reproducibly synthesize the $n=1-5$ member compounds. X-ray absorption spectroscopy at the O $K$ and Ni $L$ edges indicate systematic changes in both the nickel-oxygen hybridization level and nominal nickel filling from 3$d^8$ to 3$d^7$ as we move across the series from $n=1$ to $n=\infty$. The $n=3-5$ compounds exhibit weakly hysteretic metal-to-insulator transitions with transition temperatures that depress with increasing order toward NdNiO${}_3$ ($n=\infty )$.

11 pages, 4 figures with Supplemental Information

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