Dispersive line shape in the vicinity of the ν = 1 quantum Hall state: Coexistence of Knight shifted and unshifted resistively detected NMR responses

The frequency splitting between the dip and the peak of the resistively detected nuclear magnetic resonance (RDNMR) dispersive line shape (DLS) has been measured in the quantum Hall effect regime as a function of filling factor, carrier density and nuclear isotope. The splitting increases as the filling factor tends to ν = 1 and is proportional to the hyperfine coupling, similar to the usual Knight shift versus ν-dependence. The peak frequency shifts linearly with magnetic field throughout the studied filling factor range and matches the unshifted substrate signal, detected by classical NMR. Thus, the evolution of the splitting is entirely due to the changing Knight shift of the dip feature. The nuclear spin relaxation time, T1, is extremely long (hours) at precisely the peak frequency. These results are consistent with the local formation of a ν = 2 phase due to the existence of spin singlet D$^-$ complexes.