Filling-factor–dependent oscillations of the coupled intersubband plasmon-LO phonon mode in a tunneling coupled-bilayer system

Abstract

We have investigated an ${\mathrm{Al}}_{0.33}{\mathrm{Ga}}_{0.67}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ tunneling coupled-bilayer heterostructure with magnetotransport and far-infrared spectroscopy. With a front gate the charge density could be tuned. A grating coupler was prepared to investigate the collective excitations. We observed an intersubband plasmon which is coupled to the GaAs LO phonon. In a magnetic field applied perpendicular to the two-dimensional electron gas plane, the mode exhibits a strong filling-factor--dependent oscillation of the resonance energy.