Topochemical Synthesis and Electronic Structure of High-Crystallinity Infinite-Layer Nickelates on an Orthorhombic Substrate.

Superconductivity in infinite-layer nickelates has stirred much research interest, to which questions regarding the nature of superconductivity remain elusive. A critical leap forward to address these intricate questions is through the growth of high-crystallinity infinite-layer nickelates, including the "parent" phase. Here, we report the synthesis of a high-quality thin-film nickelate, NdNiO. This is achieved through the growth of a perovskite precursor phase (NdNiO) of superior crystallinity on the NdGaO substrate by off-axis RF magnetron sputtering and a low-temperature topochemical reduction using NaH. We observe a nonlinear Hall effect at low temperatures in this "non-doped" phase. We further study the electronic properties using advanced X-ray scattering and first-principles calculations. We observe spectroscopic indications of the enhanced two-dimensionality and a reduced hybridization of Nd 5 and Ni 3 orbitals. These findings unlock new pathways for preparing high-quality infinite-layer nickelates and provide new insights into the intrinsic features of these compounds.