ULTRASLOW ELECTRON-SPIN DYNAMICS IN GAAS QUANTUM-WELLS PROBED BY OPTICALLY PUMPED NMR

Optically pumped nuclear magnetic resonance (OPNMR) measurements were performed in two different electron-doped multiple quantum Well sample s near the fractional quantum Hall effect ground state nu = 1/3 Below 0.5 kelvin, the spectra provide evidence that spin-reversed charged ex citations of the nu = 1/3 ground state are Localized over the NMR time scale of about 40 microseconds. Furthermore, by varying NMR pulse par ameters, the electron spin temperature (as measured by the Knight shif t) could be driven above the Lattice temperature, which shows that the value of the electron spin-lattice relaxation time tau(1s) is between 100 microseconds and 500 milliseconds at nu = 1/3.