Competing Incommensurate Spin Fluctuations and Magnetic Excitations in Infinite-Layer Nickelate Superconductors*

The recently discovered infinite-layer nickelates show great promise in helping to disentangle the various cooperative mechanisms responsible for high-T_c superconductivity. However, lack of antiferromagnetic order in the pristine nickelates presents a challenge for connecting the physics of the cuprates and nickelates. Here, by using a quantum many-body Green's function-based approach to treat the electronic and magnetic structures, we unveil the presence of many two- and three-dimensional magnetic stripe instabilities that are shown to persist across the phase diagram of LaNiO₂. Our analysis indicates that the magnetic properties of the infinite-layer nickelates are closer to those of the doped cuprates which hosts a fluctuating ground state rather than the undoped cuprates. The theoretically obtained magnon dispersion in LaNiO₂ is found to contain an admixture of contributions from localized and itinerant carriers, in accord with corresponding RIXS experiments. Our study gives insight into the origin of inhomogeneity in the infinite-layer nickelates and their relationship with the cuprates.