Dynamic response of parabolically confined electron systems

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Abstract
The far-infrared response of electron systems confined in a parabolic potential is investigated experimentally. We present recent studies on cyclotron resonance, intersubband resonance and hybrid modes using various experimental techniques and geometries and compare our experimental findings with theoretical results based on a generalization of Kohn's theorem. We also focus on the far-infrared spectrum of so-called imperfect parabolic wells with intentionally induced deviations from ideal parabolicity. Here, new symmetry-forbidden resonances are observed which yield a sensitive test for a theoretical description. At finite wavevector, intrasubband plasmonic excitations are also possible. We study their dispersion and investigate their interaction with the intersubband modes. If subjected to an in-plane magnetic field, the intrasubband plasmon exhibits a strongly anisotropic dispersion which can be directly related to so-called one-dimensional plasmons. Due to the simplicity of the confining potentials, most of our experimental results can be explained in straightforward ways. Many of our results as well as the theoretical descriptions directly apply to recent investigations of lateral nanostructures and thus may also serve for a better understanding of this rapidly developing field.