Electrically Controlled Nuclear Spin Polarization and Relaxation by Quantum-Hall States

We study interactions between electrons and nuclear spins by using the resistance ( R_xx) peak which develops near the Landau-level filling factor ν = 2/3 as a probe. Temporarily tuning ν to a different value, ν_temp, with a gate demonstrates that the R_xx peak regenerates even after complete depletion ( ν_temp = 0), while it rapidly relaxes on either side of ν_temp = 1. This indicates that the ν = 2/3 domain morphology is memorized by the nuclear spins which can be rapidly depolarized by Skyrmions. An additional enhancement in the nuclear spin relaxation around ν = 1/2 and 3/2 suggests a Fermi sea of partially polarized composite fermions.