Charge and spin textures of Ising quantum Hall ferromagnet domain walls

TL;DR

This paper analytically and numerically studies charge and spin textures in Ising quantum Hall ferromagnet domain walls, revealing universal charge dipoles and complex spin structures relevant for nuclear resonance phenomena.

Contribution

It provides explicit formulas for charge and spin densities linked to pseudospin textures and uncovers universal charge dipoles and complex spin multipolar structures in domain walls.

Findings

Universal quantized charge dipole density proportional to Landau level difference

Localized excess charge can occur at domain walls due to non-uniformities

Complex multipolar spin structures emerge in domain walls

Abstract

We investigate the charge and spin structures associated with arbitrary smooth polarization textures in Ising (integer) quantum Hall ferromagnets. We consider the case where the two polarizations (denoted "pseudospin" up and down) correspond to states with opposite physical spin and different Landau level indices, $n\uparrow$ and $m\downarrow$. We derive analytic expressions for the charge and spin densities, as functions of the underlying pseudospin texture, and use these results to investigate different types of linear domain walls, both analytically and numerically. We find that any smooth domain wall between two oppositely polarized domains carries a universal quantized charge dipole density proportional to the difference of Landau level indices, $n-m$. Additionally, non-uniformities in the domain wall may give rise to excess net charge localized at the domain wall. Interestingly, the physical spin density associated with the domain wall generally exhibits a much more complex multipolar structure than that of the pseudospin texture. These results should for example help to elucidate the mechanisms underlying nuclear electric resonance and nuclear polarization oscillations in Ising quantum Hall systems.