Enhancement of the skyrmionic excitations due to the suppression of Zeemanenergy by optical orientation of nuclear spins

An effective experimental method for compensation of Zeeman energy of two-d imensional (2D) electrons based on optical pumping of nuclear spins is prop osed and used to enhance skyrmionic excitations under conditions of integer and fractional quantum Hall effect. We demonstrate that photoexcitation by circularly polarized light can result in a strong spin orientation of nucl ei along (or against) the direction of the external magnetic field and that the energy of the hyperfine contact interaction between 2D electrons and o ptically oriented nuclear spins can be comparable to the electronic Zeeman energy. It is shown that a compensation of the Zeeman energy by the hyperfi ne interaction at fixed magnetic field results in an enhancement of skyrmio nic excitations and the dependence of the skyrmionic radius as a function o f the ratio between Zeeman and Coulomb energies is measured. A strong incre ase of the skyrmion radius is observed for E-Z/E-C<0.005, and the quenching of the skyrmion at E-Z/E-C = 0.011 +/- 0.001 is established. Strong electr on-nuclear coupling was used for optical detection of the nuclear magnetic resonance from the variation of the polarized luminescence intensity. [S016 3-1829(99)12527-X].