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-toinsulator transitions, magnetic phase transitions, and, upon chemical reduction, superconductivity. Here, we demonstrate epitaxial stabilization of layered nickelates in the Ruddlesden-Popper form, Ndn+1NinO3n+1, using molecular beam epitaxy. By optimizing the stoichiometry of the parent perovskite NdNiO3, 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 3d 8 to 3d 7 as we move across the series from n = 1 to n = ∞. The n = 3 − 5 compounds exhibit weakly hysteretic metal-to-insulator transitions with transition temperatures that depress with increasing order toward NdNiO3 (n = ∞).