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Sophia E. Hayes

Washington University in St. Louis
Laser-enhanced NMR: New tools for the study of semiconductors
Abstract: Laser-enhanced NMR? combines nuclear magnetic resonance (NMR) with optical excitation in semiconductors to polarize populations of spins. Enhanced signals can then be observed through direct radio-frequency detection (?optically-polarized NMR,? OPNMR) and through the optical detection of luminescence polarization (?optically-detected NMR,? ODNMR). The purpose of this presentation is to provide information on these two emerging techniques: the background theory, their application to GaAs in both bulk and quantum well form, and prospects for further application to additional materials and devices. Recent developments have combined NMR with optical excitation in semiconductors to boost the sensitivity by enhancing the number of polarized spins. Irradiation of III-V semiconductors with circularly polarized light results in the polarization of conduction electrons. Laser light is used to excite spin-polarized electron-hole pairs by transferring angular momentum from a circularly polarized photon to the electrons and subsequently to the nuclear spins. The observable in the experiments depend on the polarization (electron or nuclear). Signal enhancements of orders of magnitude have been achieved, making systems of rare nuclear spins amenable to NMR analyses.
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