Itinerant Nature of Spin-Density-Wave Order in Ruddlesden-Popper Nickelates

Abstract

The nature of magnetism in layered Ruddlesden-Popper nickelates remains a central open question, particularly in light of recent observations of spin-wave-like magnetic excitations in metallic multilayer compounds. Here, we develop a unified itinerant description of spin-density-wave (SDW) order and magnetic excitations in La${}_3$Ni${}_2$O${}_7$ and La${}_4$Ni${}_3$O${}_{10}$. The essential ingredient is the multilayer mirror structure of the NiO${}_2$ blocks, which organizes the low-energy electronic states into mirror-even and mirror-odd sectors. We show that dominant interband nesting between mirror-opposite bands drives a mirror-selective itinerant SDW instability, whose collective modes naturally reproduce the experimentally observed spin-wave-like spectra. In La${}_4$Ni${}_3$O${}_{10}$, the SDW further induces a secondary mirror-even charge density wave, yielding intertwined spin and charge textures. Our results demonstrate that magnetism in multilayer nickelates is fundamentally itinerant rather than local-moment in origin, and establish mirror-selective interband SDW order as a unifying organizing principle for magnetic correlations in these systems.

6 pages, 4 figures; Supplemental Material: 11 pages, 1 figure