Spin in the quantum Hall effect: OPNMR studies of skyrmions and composite fermions

In this thesis we report optically pumped nuclear magnetic resonance (OPNMR) measurements of the 71Ga spectra and the nuclear spin-lattice relaxation rate 1/T1, carried out in n-doped GaAs/Al 0.1Ga0.9As multiple quantum well (MQW) samples.; As we lower the temperature down to T ≈ 0.3 K, a "tilted plateau" emerges in the Knight shift data near the integer quantum Hall ground state nu = 1. This "tilted plateau" is a novel experimental signature of quasiparticle localization. The dependence of the spectra on both T and nu suggests that the localization is a collective process. The frozen limit spectra appear to rule out a 2D lattice of conventional Skyrmions.; Our OPNMR measurements of the Knight shift and the nuclear spin-lattice relaxation rate 1/T1 at Landau level filling factor nu = 1/2 provide new constraints on the theoretical description of the nu = 1/2 state. We compare the data with predictions of a weakly-interacting composite fermion model and the extended Hamiltonian theory.; The last chapter has a different focus: unexpected NMR phenomena observed in a dilute dipolar solid. We report 29Si NMR measurements of Carr-Purcell-MeiboomGill (CPMG) spin echoes obtained in doped silicon powders. The CPMG echoes have several unusual differences from ordinary Hahn echoes, including even-odd echo asymmetry, effects evoking spin-locking and stimulated echoes, and longer "coherence" times. The surprising phenomena appear to be consequences of the homonuclear dipolar coupling, and are therefore relevant to physical implementations of quantum computation.