Soft inter-Landau-level spin-flip magnetoexciton as a precursor of ferromagnetic instability
Abstract
We investigate the impact of Coulomb correlations on the low-energy collective excitations in two-dimensional electron systems in the quantum Hall state ν =2 . The collective excitations are studied using inelastic light scattering in the set of MgZnO/ZnO heterostructures with high-mobility two-dimensional electrons. The study focuses on the lowest-energy collective excitations in the paramagnetic state ν =2 , the cyclotron spin-flip magnetoexcitons (CSFMs), which are associated with inter-Landau-level transitions with a simultaneous spin flip. The Coulomb contribution to the CSFM energy is measured independently of the Zeeman term as a function of electron density. It is established that in the range of electron concentrations corresponding to the Wigner-Seitz parameter rs∼5 -7 , the combination of the Coulomb and Zeeman contributions leads to a softening of the CSFM. This softening accompanies spontaneous switching of the spin configuration in the ν =2 quantum Hall system from paramagnetic to ferromagnetic. Theoretical estimates are given for the correlation energy terms of the CSFM responsible for its softening and a concomitant ferromagnetic transition.
- Publication:
-
Physical Review B
- Pub Date:
- September 2018
- DOI:
- 10.1103/PhysRevB.98.121412
- Bibcode:
- 2018PhRvB..98l1412V