Optical determination of the spin polarization of a quantum Hall ferromagnet

Recent experimental and theoretical investigations have resulted in a shift in our understanding of the ν = 1 quantum Hall state. There now exists a wealth of evidence that the excitation gap and the resulting quasi-particle spectrum at ν = 1 are due predominately to the ferromagnetic many-body exchange interaction. A great variety of experimentally observed correlations at ν = 1 cannot be incorporated into a perturbative expansion around the single-particle model, a scheme long thought to describe the integral quantum Hall effect (IQHE) at filling factor 1. Theorists now refer to the ν = 1 state as the quantum Hall ferromagnet. In this paper, we review recent theoretical and experimental progress and detail our own optical investigations of the ν = 1 quantum Hall regime.