Spin-orbit splitting of the cyclotron resonance in GaAs

We have studied the relevance of spin-orbit coupling to the splitting of the cyclotron resonance of electron space-charge layers in GaAs recently observed by Manger [Phys. Rev. B 63, 121203R (2001)]. We show that the spin-orbit interaction couples density and spin-density excitations in the long-wavelength limit and is able to explain all the features observed in the experiment.