Studies of Charge Ordering and Superconductivity in the Parent Infinite Layer Nickelates

One of the key issues regarding the infinite-layer nickelate superconductors are their similarities and differences with their cuprate cousins. In this talk, we contrast some of the defining characteristics of the cuprates, such as the presence of charge or spin density wave ordering and an insulating parent state, with those of the nickelates. Using a new approach using atomic hydrogen reduction, we synthesize infinite layer nickelates with excellent crystallinity and low residual resistivities. We perform x-ray scattering and spectroscopy measurements on a series of NdNiO₂ samples, which reveal that charge density wave order is absent in fully reduced, single-phase NdNiO₂ and LaNiO₂. We find that excess apical oxygens in partially reduced samples form ordered rows with three-unit-cell periodicity, with signatures that can resemble charge ordering. In addition, we report evidence for superconductivity in samples of the nominally undoped parent compound, NdNiO₂. We propose that superconductivity could be intrinsic to the undoped infinite-layer nickelates but could be suppressed by disorder due to its nodal order parameter.