Cyclotron-resonance studies of strongly coupled double quantum wells in tilted magnetic fields near the quantum and semiclassical limits

Far-infrared cyclotron-resonance (CR) spectroscopy has been used to study a pair of strongly coupled two-dimensional electron gases (2DEG's) which were formed in two GaAs quantum wells and separated by a thin AlxGa1-xAs barrier. The degree of wave-function hybridization, along with the effect of a magnetic field parallel to the plane of the electron gas, have been investigated near both the quantum and semiclassical limits, corresponding to low and high filling factors, respectively. Near the quantum regime, the CR transitions in the presence of a small parallel field reveal anticrossing between the Landau levels associated with different hybridized subbands. The energies and intensities of these transitions change with front gate bias, yielding information on the bias dependence of the wave-function hybridization and the subband energy splitting. Close to the semiclassical limit and with strong parallel magnetic fields, two CR peaks are observed. The corresponding cyclotron masses are compared to those expected for noncircular Fermi contours created by anticrossing of the parabolic dispersion curves associated with the coupled 2DEG's. Experimental results in both limits are discussed in the light of predictions from self-consistent solutions of Poisson's and Schroedinger's equations.