Tunneling–Coupled Systems

Abstract

The plasmon spectrum of spatially separated two–component plasmas without tunneling has been studied for quite some time (see, e.g., [1]). For finite Coulomb coupling between the layers, the intrasubband charge–density excitation spectrum consists of two modes: The optical plasmon (OP) where both layers oscillate in phase parallel to the layers (see Fig. 7.1a), and, the acoustic plasmon (AP) where the carriers in both layers oscillate out of phase (see Fig. 7.1b). At long wavelengths, the energy of the OP is proportional to √q and the energy of the AP goes linear in q, where q is the wave vector parallel to the layers. It was shown [1] that at large spatial separation of the two layers, the AP can move outside of the continua of possible intraband single–particle transitions. The first experimental observation of coupled– layer plasmons by inelastic light scattering was reported by Fasol et al. [2] on GaAs-AlGaAs samples containing five layers in parallel. In Coulomb–coupled double quantum wells, the observation of AP and OP was reported by Kainth et al. [3].