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 nu = 2/3 as a probe. Temporarily tuning nu to a different value, nu(temp) , with a gate demonstrates that the R-xx peak regenerates even after complete depletion (nu(temp) = 0 ), while it rapidly relaxes on either side of nu(temp) = 1 . This indicates that the nu = 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 nu = 1/2 and 3/2 suggests a Fermi sea of partially polarized composite fermions.