Spin-wave dispersion in half-doped LaSrNiO

TL;DR

This paper investigates the spin-wave dispersion in half-doped LaSrNiO, explaining magnetic excitations and the optical mode through stripe twinning and symmetry considerations, advancing understanding of magnetic properties in nickelates.

Contribution

It introduces a model accounting for stripe twinning and symmetry to explain previously unaccounted optical modes in LaSrNiO.

Findings

Optical mode explained by stripe twinning

Magnetic coupling structure has two-fold symmetry

Spin-wave dispersion consistent with experimental data

Abstract

Recent neutron scattering measurements reveal spin and charge ordering in the half-doped nickelate, La$_{3/2}$ Sr$_{1/2}$ NiO$_4$. Many of the features of the magnetic excitations have been explained in terms of the spin waves of diagonal stripes with weak single-ion anisotropy. However, an optical mode dispersing away from the (\pi,\pi) point was not captured by this theory. We show here that this apparent optical mode is a natural consequence of stripe twinning in a diagonal stripe pattern with a magnetic coupling structure which is two-fold symmetric, i.e. one possessing the same spatial rotational symmetry as the ground state.