Enhanced resonant coupling between one- and two-dimensional energy states in quantum wires

250-nm narrow quantum wires have been prepared by deep-mesa etching of modulation-doped ${\mathrm{Ga}}_{\mathit{x}}$${\mathrm{In}}_{1\mathrm{-}\mathit{x}}$As heterostructures. The far-infrared response of these quantum wires is strongly governed by collective excitations. In tilted magnetic fields B we observe a resonant coupling of these collective wire modes to ‘‘two-dimensional’’ (2D) energy states, i.e., states that arise from the confinement in the original 2D system. We can qualitatively explain this coupling, in particular the observed anisotropy with respect to the tilt directions, within a one-particle model. Quantitatively, however, the coupling appears drastically enhanced in the 1D quantum wires as compared to the coupling in 2D systems.