Huge longitudinal resistance maxima at fractional filling factors

Very large resistance maxima can be observed in the longitudinal magnetoresistance of a narrow single quantum well. They exist only at certain fractional filling factors and are clearly related to the coupling of the electron to the nuclear spin system. In resistively detected NMR experiments, which are possible in this system, a very unusual fine structure of the resonance lines is observed, which hints towards an unusual coupling between the electron and nuclear system.