Polarization-resolved electron spin resonance in a two-dimensional electron system

Abstract

We report on polarization-resolved electron spin resonance (ESR) in a two-dimensional electron system in AlAs quantum wells. The transmission spectra in the subterahertz frequency range reveals unusual behavior as a function of the light polarization and of experimental geometry. In the Faraday geometry, the excitation conditions for spin resonance are reversed compared with the cyclotron resonance, while in the Voigt geometry the absorption exhibits a twofold dependence on the azimuthal angle of an in-plane static magnetic field. These results contradict a pure magnetic nature of ESR in AlAs quantum wells, revealing a dominating Dresselhaus spin-orbit coupling as a microscopic mechanism of the electric-dipole absorption. A theoretical model that includes an inversion asymmetry and the spin-orbit coupling successfully explains the experimental observations.