Inward dispersion of the spin excitation spectrum of stripe-ordered La2NiO4+d

TL;DR

This study investigates the spin excitation spectrum in stripe-ordered La2NiO4+d using neutron scattering, revealing an anomalous inward spectral weight shift at low energies that challenges existing spin-wave models.

Contribution

It provides new experimental insights into the spin dynamics of stripe-ordered La2NiO4+d, highlighting discrepancies with current theoretical models of spin-wave dispersion.

Findings

Magnetic spectral weight shifts anomalously towards the antiferromagnetic wave vector at low energies.

Observed inward dispersion cannot be explained by conventional spin-wave models.

Discussion of potential extensions to existing models to account for findings.

Abstract

Polarized- and unpolarized-neutron scattering measurements of the spin excitation spectrum in the stripe-ordered phase of La2NiO4+d (d = 0.11) are presented. At low energies, the magnetic spectral weight is found to shift anomalously towards the two-dimensional antiferromagnetic wave vector, similar to the low-energy dispersions observed in cuprate superconductors. While spin-wave spectra in stripe phases can exhibit an apparent inward dispersion, we find that the peak shifts measured here cannot be accounted for by this effect. Possible extensions of the model are discussed.