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

TL;DR

This paper presents a unified itinerant electron model explaining spin-density-wave order and magnetic excitations in layered Ruddlesden-Popper nickelates, emphasizing the role of mirror symmetry and interband nesting.

Contribution

It introduces a mirror-selective itinerant SDW framework that accounts for magnetic spectra and charge order in multilayer nickelates, highlighting their itinerant magnetic nature.

Findings

Mirror-odd interband nesting drives SDW instability.

The model reproduces experimentally observed spin-wave spectra.

SDW induces secondary charge density waves in La4Ni3O10.

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.