Magneto-quantum-resistance oscillations in tunnel-coupled double quantum wells in tilted magnetic fields: Variable Landau biladders

We present a linear-response theory of magneto-quantum-resistance oscillations of the in-plane resistances Rₓₓ and Ryy in two coupled quasi-two-dimensional electron layers in tilted magnetic fields B=(B_∥,B_⊥), and explain recent data from GaAs/AlₓGa_1-xAs double quantum wells. In this system, the electrons are in the two tunnel-split ground sublevels. The cyclotron masses of the two orbits on the Fermi surface have opposite dependences on the in-plane field B_∥: one increases monotonically, while the other decreases as a function of B_∥ in the regime of interest. As a result, the rungs of one Landau ladder sweep up through the Fermi level, while those of the other Landau ladder sweep down when B_∥ is increased at a fixed perpendicular field B_⊥. Ridges are obtained in the three-dimensional plots of both Rₓₓ and Ryy and the density of states versus (B_∥,B_⊥) due to Fermi-level crossing by the rungs of the Landau ladders. Giant peaks are obtained when two ridges intersect each other. The (B_∥,B_⊥) dependence of Rₓₓ as well as theoretical evidence of magnetic breakdown yields good agreement with recent data from GaAs/AlₓGa_1-xAs double quantum wells.