NMR study of the electron spin polarization in the fractional quantum Hall effect of a single quantum well: Spectroscopic evidence for domain formation

The authors have developed a technique to determine the electron spin polarization in a single GaAs quantum well by combining resistance-detected (RD) nuclear magnetic resonance (NMR) with conventional NMR. We use this method to study the unpolarized-polarized spin transition at filling factor nu=2/3 for small and large currents. The formation of domains with these two polarizations at the transition was observed spectroscopically. Domains with full, partial, or no polarization were also uncovered at nu=3/5 and 4/7. An anomalous NMR line shape around filling factor nu=1/3, 1, and 2/3 was measured. This pecularity of the NMR line is probably not due to skyrmions, as previously reported for nu=1.