Dynamic nuclear spin polarization of ν = 2/3 fractional quantum Hall states in multiply-connected Corbino geometry

We studied spatially resolved measurements of dynamic nuclear spin polarization (DNP) in the fractional quantum Hall state. To avoid the influence of quantum Hall edge effects and to perform spatially resolved measurements of bulk DNP alone, we fabricated a device with a multiply connected Corbino geometry from a high-mobility GaAs/AlGaAs two-dimensional electron system wafer. We simultaneously measured six sets of resistances to track their time evolution during the depolarization, DNP, and relaxation processes. DNP was induced using both large alternating and direct currents, and the polarization was carried out in the polarized phase. Under AC-DNP, only monotonic changes in resistance were observed during the DNP process, whereas under DC-DNP, non-monotonic behavior was detected, such as resistance switching from increase to decrease or from decrease to increase. This result is consistent with our previous measurements performed using a Hall bar. In terms of spatial resolution, some electrode pairs exhibited the expected behavior, while others showed anomalous characteristics.