Plasmons in tunneling coupled bilayer systems with tunable space symmetry studied by far-infrared spectroscopy

Abstract

Tunneling coupled bilayer systems based on ${\mathrm{Al}}_{0.33}{\mathrm{Ga}}_{0.67}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ heterostructures have been investigated with far-infrared spectroscopy (FIR) and magnetotransport measurements. Via a Ti front gate the charge density as well as space symmetry of the bilayer are tuned. Using FIR spectroscopy we observe intrasubband optical plasmon modes and an intersubband plasmon. From magnetotransport measurements we determine the single-particle tunneling gap ${\ensuremath{\Delta}}_{\mathrm{SAS}}$ between the symmetric and antisymmetric subband. By comparing ${\ensuremath{\Delta}}_{\mathrm{SAS}}$ with the resonance energy of the intersubband plasmon, we are able to determine directly from measurement the depolarization shift, i.e., a many-body correction to the intersubband excitation. We study its behavior by changing the space symmetry of the bilayer system.