Infrared spectroscopy of quantum crossbars

Infrared (IR) spectroscopy can be used as an important and effective tool for probing periodic networks of quantum wires or nanotubes (quantum crossbars, QCBs) at frequencies far from the Luttinger liquid fixed point. Plasmon excitations in QCB may be involved in resonance diffraction of incident electromagnetic waves and in optical absorption in the IR part of the spectrum. Direct absorption of external electric field in QCBs strongly depends on the direction of the wave vector q. This results in two types of ID→2D dimensional crossover with varying angle of an incident wave or its frequency. In the case of QCBs interacting with semiconductor substrate, capacitive contact between them does not destroy the Luttinger liquid character of the long wave QCB excitations. However, the dielectric losses on a substrate surface are significantly changed due to appearance of additional Landau damping. The latter is initiated by diffraction processes on a QCB super-lattice and manifests itself as strong but narrow absorption peaks lying below the damping region of an isolated substrate.