Quantum Hall spin textures far beyond the skyrmion limit

Abstract

In strongly correlated quantum Hall ferromagnets with noninteger filling factors between $\ensuremath{\nu}=1$ and $\ensuremath{\nu}=3/2$, evidence of offbeat spin textures is obtained. The platforms for the study are two-dimensional electron systems based on MgZnO/ZnO heterostructures, in which the parameters of Zeeman and exchange energies are inconsistent with ordinary skyrmions. Experimental probing of magnetic order is fulfilled via exploration of the spectra of collective spin excitations by means of inelastic light scattering. In addition to the ferromagnetic spin exciton, a low-energy spin mode is observed, bearing witness to broken spin-rotational symmetry in the ground state. The two spin modes exhibit a pronounced anticrossing behavior, depending on the two-dimensional momentum, electron concentration, filling factor, and magnetic field tilt. The properties of the electron system are simulated using the exact diagonalization technique, showing that Landau level mixing and crossing play a key role in the nontrivial spin configuration. The corresponding spin textures emerging between $\ensuremath{\nu}=1$ and $\ensuremath{\nu}=3/2$ involve the orbital degree of freedom and are qualitatively different from skyrmions. Experiments at elevated temperatures show the destruction of this orbital spin texture phase with critical temperature far below the Zeeman energy. On the other side of $\ensuremath{\nu}=1$ the textures are absent.