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

Abstract

An effective experimental method for compensation of Zeeman energy of two-dimensional (2D) electrons based on optical pumping of nuclear spins is proposed 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 nuclei along (or against) the direction of the external magnetic field and that the energy of the hyperfine contact interaction between 2D electrons and optically oriented nuclear spins can be comparable to the electronic Zeeman energy. It is shown that a compensation of the Zeeman energy by the hyperfine interaction at fixed magnetic field results in an enhancement of skyrmionic excitations and the dependence of the skyrmionic radius as a function of the ratio between Zeeman and Coulomb energies is measured. A strong increase of the skyrmion radius is observed for ${E}_{Z}{/E}_{C}<0.005,$ and the quenching of the skyrmion at ${E}_{Z}{/E}_{C}=0.011\ifmmode\pm\else\textpm\fi{}0.001$ is established. Strong electron-nuclear coupling was used for optical detection of the nuclear magnetic resonance from the variation of the polarized luminescence intensity.