Far-infrared response of one-dimensional electronic systems in single- and two-layered quantum wires.

The far-infrared (FIR) response of arrays of periodic single- and two-layered quantum wires has been investigated. The wire structures have been prepared by ultrafine deep-mesa etching of modulation-doped $\frac{{\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}}{\mathrm{GaAs}}$ heterostructures and two-layered quantum-well systems. Due to narrow geometrical dimensions (500 nm), quantum confinement arises and leads to the formation of one-dimensional electronic subbands with a typical energy separation of 1-3 meV. The FIR transmission spectra of the single- and two-layered quantum wire structures show one and two resonances, respectively. The resonance frequencies are observed at significantly higher energies compared to the one-dimensional subband separation. This implies that collective interactions have a strong influence on the excited transitions and leads to the conclusion that the FIR resonances in the one-dimensional electronic systems have predominantly the character of layer-coupled local plasmon modes.