Gyrotropy and magneto-spatial dispersion effects at intersubband transitions in quantum wells

Gyrotropic properties of multiple quantum well structures are studied theoretically. Symmetry analysis is performed yielding the gyrotropy tensor components for structures grown along [001], [110] and [311] crystallographic directions. Angular dependences of circular dichroism and natural optical activity signals are established. Phenomenological model and microscopic theory based on spin-orbit splitting of size-quantized subbands are developed for photon energies close to the energy of the intersubband optical transition. Magneto-spatial dispersion effects arising from the diamagnetic shift of the intersubband energy gap linear in the electron momentum are also considered. It is demonstrated that the spectral dependence of the gyrotropy and magneto-spatial dispersion constants represents an asymmetrical peak with a degree of asymmetry governed by the mean electron energy. The estimates show that the considered effects are detectable in experiments.