Synthesis and electronic properties of Ndn +1NinO3 n +1 Ruddlesden-Popper nickelate thin films

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_nO_{3 n +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 3 d⁸ to 3 d⁷ as we move across the series from n =1 to ∞ . The n =3 −5 compounds exhibit weakly hysteretic metal-to-insulator transitions with transition temperatures that depress with increasing order toward NdNiO₃ (n =∞ ) .