Capping Effects on Spin and Charge Excitations in Parent and Superconducting Nd_{1-x}Sr_{x}NiO_{2}

Superconductivity in infinite layer nickelates Nd_{1-x}Sr_{x}NiO_{2} has so far been achieved only in thin films, raising questions on the role of substrates and interfaces. Given the challenges associated with their synthesis it is imperative to identify their intrinsic properties. We use resonant inelastic x-ray scattering to investigate the influence of the SrTiO_{3} capping layer on the excitations of Nd_{1-x}Sr_{x}NiO_{2} (x=0 and 0.2). Spin excitations are observed in parent and 20% doped Nd_{1-x}Sr_{x}NiO_{2} regardless of capping, proving that magnetism is intrinsic to infinite-layer nickelates and appears in a significant fraction of their phase diagram. In parent and superconducting Nd_{1-x}Sr_{x}NiO_{2}, the spin excitations are slightly hardened in capped samples compared to the noncapped ones. Additionally, a weaker Ni-Nd charge transfer peak at ∼0.6  eV suggests that the hybridization between Ni 3d and Nd 5d orbitals is reduced in capped samples. From our data, capping induces only minimal differences in Nd_{1-x}Sr_{x}NiO_{2} and we phenomenologically discuss these differences based on the reconstruction of the SrTiO_{3}-NdNiO_{2} interface and other mechanisms such as crystalline disorder.