Looking for magnetic clues
Thin films of the neodymium nickelate NdNiO2 doped with strontium have recently been found to be superconducting. This materials class bears structural and electronic similarities to the famed cuprate superconductors, but how far the analogy goes remains unclear. Lu et al. used resonant inelastic x-ray scattering to look for magnetism, which exists in the cuprates, in Nd1-xSrxNiO2 films (see the Perspective by Benckiser). The authors observed magnetic modes in the undoped compound that had a doping evolution consistent with the behavior of a doped Mott insulator.
The discovery of superconductivity in infinite-layer nickelates brings us tantalizingly close to a material class that mirrors the cuprate superconductors. We measured the magnetic excitations in these nickelates using resonant inelastic x-ray scattering at the Ni L3-edge. Undoped NdNiO2 possesses a branch of dispersive excitations with a bandwidth of approximately 200 milli–electron volts, which is reminiscent of the spin wave of strongly coupled, antiferromagnetically aligned spins on a square lattice. The substantial damping of these modes indicates the importance of coupling to rare-earth itinerant electrons. Upon doping, the spectral weight and energy decrease slightly, whereas the modes become overdamped. Our results highlight the role of Mottness in infinite-layer nickelates.