FAR-INFRARED SPECTROSCOPY OF ONE-DIMENSIONAL AND ZERO-DIMENSIONAL ELECTRONIC SYSTEMS

We review the far infrared (FIR) response of one- and zero-dimensional electronic systems (0DES and 1DES), quantum wires and quantum dots, respectively, which have been realized by ultrafine mesa etching of modulation-doped AlGaAs/GaAs heterostructures. From dc magnetotransport measurements on quantum wires the formation of 1D subbands with typical energy separations of 1 to 3 meV was found in electron channels of 400 to 150nm width. However, in the far infrared (FIR) response resonances at significantly higher frequencies were observed as compared to the single particle energy level separation. We will discuss that the optical response exhibits a very complex behaviour which is dominated by collective effects. In the case of a purely parabolic external potential the FIR response can be easily understood as the excitation of a rigid oscillation of the whole electron distribution. Especially in our quantum dot structures we are able to resolve additional excitation modes and a resonant anticrossing, probing the internal motion of the electrons within a single dot. We will discuss these excitations starting from two different models, namely from a classical one, which is based on plasmonic excitations in 2DES of finite size, and, in more details, from a quantum mechanical model, which treats atom-like systems with discrete energy levels including collective corrections. © 1991.