Disorder-induced stabilization of the quantum Hall ferromagnet

TL;DR

This study measures the spin polarization of the $ u=1$ quantum Hall state, revealing that disorder can stabilize the ferromagnetic phase by inducing a transition to a Skyrmion glass, highlighting the role of disorder in quantum Hall ferromagnetism.

Contribution

It provides the first absolute measurements of spin polarization near $ u=1$ and demonstrates how disorder can stabilize the quantum Hall ferromagnet through a transition to a Skyrmion glass phase.

Findings

Complete polarization at low magnetic fields near $ u=1$

Depolarization with increased magnetic field or density

Disorder stabilizes ferromagnetism via Skyrmion glass transition

Abstract

We report on an absolute measurement of the electronic spin polarization of the $\nu=1$ integer quantum Hall state. The spin polarization is extracted in the vicinity of $\nu=1$ (including at exactly $\nu=1$) via resistive NMR experiments performed at different magnetic fields (electron densities), and Zeeman energy configurations. At the lowest magnetic fields, the polarization is found to be complete in a narrow region around $\nu=1$. Increasing the magnetic field (electron density) induces a significant depolarization of the system, which we attribute to a transition between the quantum Hall ferromagnet and the Skyrmion glass phase theoretically expected as the ratio between Coulomb interactions and disorder is increased. These observations account for the fragility of the polarization previously observed in high mobility 2D electron gas, and experimentally demonstrate the existence of an optimal amount of disorder to stabilize the ferromagnetic state.