Optical absorption measurements are used to probe the spin polarization in the integer and fractional quantum Hall effect regimes. The system is fully spin polarized only at filling factor ν=1 and at very low temperatures(∼40 mK). A small change in filling factor (δν≈±0.01) leads to a significant depolarization. This suggests that the itinerant quantum Hall ferromagnet at ν=1 is surprisingly fragile against increasing temperature, or against small changes in filling factor.
@article{arxiv.0901.3959,
title = {Optical absorption to probe the quantum Hall ferromagnet at filling factor $\nu=1$},
author = {P. Plochocka and J. M. Schneider and D. K. Maude and M. Potemski and M. Rappaport and V. Umansky and I. Bar-Joseph and J. G. Groshaus and Y. Gallais and A. Pinczuk},
journal= {arXiv preprint arXiv:0901.3959},
year = {2009}
}