DIRECTLY DETECTED NUCLEAR-MAGNETIC-RESONANCE OF OPTICALLY PUMPED GAASQUANTUM-WELLS

Optical pumping strongly enhances nuclear spin polarizations in an n-d oped GaAs/AlGaAs multiple quantum well, allowing NMR signals of the Ga As wells to be investigated by direct, radio-frequency detection in a 7.05 T field. The optically pumped NMR signals exhibit unanticipated d ependences on the pumping wavelength, polarization, and power. The tem perature dependence of the Ga-71 NMR Knight shift is consistent with a g value of -0.49 +/- 0.02 for electrons in the wells, with no exchan ge enhancement. We present evidence that the doped and photoexcited el ectrons do not reach a common spin temperature under optical pumping.