Inelastic neutron scattering study of the infinite layer nickelate Nd_0.8Sr_0.2NiO₂

Infinite layer nickelates with spin-1/2 Ni¹⁺ ions in square coordination in NiO₂ planes exhibit similar electronic properties as the cuprates. The observation of superconductivity up to 15K in thin films of the infinite layer nickelates thus opened the question whether superconductivity in these compounds has the same underlying pairing mechanism as the cuprates. While much theoretical and experimental efforts have been devoted to these systems, the difficulty to synthesize infinite layer compounds in particular in bulk form, leaves many open questions regarding their properties, Here we report inelastic neutron scattering investigations performed on a bulk sample of Nd_0.8Sr_0.2NiO₂, the same nominal composition for which superconductivity was observed in thin film form grown on a SrTiO₃ substrate. These measurements provide the phonon density of states, which can give provide insight on possible superconducting mechanisms, and provides direct information regarding the Nd³⁺ crystal field states.