Skyrmions and the nu=1 quantum Hall ferromagnet

Recent experimental and theoretical investigations have resulted in a shift in our understanding of the nu = 1 quantum Hall state. There now exists a wealth of evidence that the excitation gap and the resulting quasiparticle spectrum at nu = 1 are due predominately to the ferromagnetic many-body exchange interaction. A great variety of experimentally observed correlations at nu = 1 cannot be incorporated into a perturbative expansion around the single-particle model, a scheme long thought to describe the integral quantum Hall effect at filling factor 1. Theorists now refer to the nu = 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 nu = 1 quantum Hall regime. The technique of magneto-absorption spectroscopy has proven to be powerful a probe of the occupancy of the lowest Landau level in the regime of 0.7 < nu < 1.3 about the spin gap. Additionally, we have performed simultaneous measurements of the absorption, photoluminescence and photoluminescence excitation spectra of the nu = 1 state in order to elucidate the role of excitonic and relaxation effects in optical spectroscopy in the quantum Hall regime.