We report magnetoresistivity measurements of a narrow-barrier double-quantum-well structure which reveal that when two electron subbands are occupied, the positions of the diagonal resistivity maxima originating from these subbands oscillate together in magnetic field as the electron density is changed to give the overall appearance of a single-layer system. By means of Hartree calculations we demonstrate that this narrow-barrier sample is exhibiting a hybrid behavior between that of a single quantum well and a system comprising two independent quantum wells. ͓S0163-1829͑96͒50148-7͔

No abstract

The tunneling current between an electron gas with a periodic potential in two dimensions and a plain two-dimensional electron system (2DES) has been studied. The strength of the periodic potential, the subband energy of the plain 2DES, and an applied in-plane magnetic field were varied, mapping the Fourier transform of the periodic wave function. Periodic peaks were observed and explained by translations in the reciprocal lattice. When the potential was strongly modulated to form an array of antidots, commensurability peaks were seen in lateral transport, but, as expected, not in tunneling.

We have investigated the evolution of quantum Hall states in a GaAs-Al x Ga 1Ϫx As bilayer electron system by low-temperature magnetoresistivity measurements as the system was driven from a balanced to an offbalanced configuration. At low magnetic fields, odd integer filling factor quantum Hall states were observed on balance owing to the symmetric-antisymmetric tunneling gap. However, at high magnetic fields, in the regime of tunneling gap collapse, we observed anomalous quantum Hall states at vϭ2 off balance and vϭ3 on balance. At vϭ2, an energy gap was present all the way from the balanced configuration to far off balance, when only one quantum well was occupied. This is attributed to a transition from a spin-polarized state on balance to a spin-singlet state off balance, either by an abrupt exchange-driven phase transition or a continuous phase transition via a series of interlayer phase coherent states.

No abstract