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We have observed very sharp lines in magnetoluminescence spectra of a GaAs-Al Gap As single heterostructure under resonant excitation of 10 -70 meV above the GaAs direct energy gap. More than 14 lines were observed in both o. + and o polarizations, at magnetic fields as low as 0.6 T.The spectral positions of these lines and their dependence on the magnetic field allow us to attribute the strongest lines to optical transitions between electron and light-hole Landau levels with indices from n = 2 to 15. The nonparabolicity of the bands and efFects of the resonant electron-phonon interaction were directly observed in the luminescence spectra. The energies of optical transitions obtained for large Landau indices at low magnetic fields allow an accurate determination of band parameters in the classical limit. The eRective mass and g factors of the light holes are found to be mfa --(0.078 + 0.002)mo and g&'h -30.7 + 0.7 for a magnetic field along the [001] direction.

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A new electromagnetic plasma mode has been discovered in the hybrid system formed by a highly conductive gate strip placed in proximity to the two-dimensional electron system. The new plasmon mode propagates along the gate strip with no potential nodes present in transverse direction. Its unique spectrum combines characteristic features of both gated and ungated 2D plasmons. The new plasma excitation has been found to exhibit anomalously strong interaction with light.