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 osci llations of the in-plane resistances R-xx and R-yy in two coupled quas i-two-dimensional electron layers in tilted magnetic fields B=(B-paral lel to, B-perpendicular to), and explain recent data from GaAs/Al(x)Ga l(1-x)As double quantum wells. In this system, the electrons are in th e two tunnel-split ground sublevels. The cyclotron masses of the two o rbits on the Fermi surface have opposite dependences on the in-plane f ield B-parallel to: one increases monotonically, while the other decre ases as a function of B-parallel to, in the regime of interest. As a r esult, the rungs of one Landau ladder sweep up through the Fermi level , while those of the other Landau ladder sweep down when B-parallel to is increased at a fixed perpendicular field B-perpendicular to. Ridge s are obtained in the three-dimensional plots of both R-xx and R-yy an d the density of states versus (B-parallel to, B-perpendicular to) due to Fermi-level crossing by the rungs of the Landau ladders. Giant pea ks are obtained when two ridges intersect each other. The (B-parallel to, B-perpendicular to) dependence of R-xx as well as theoretical evid ence of magnetic breakdown yields good agreement with recent data from GaAs/AlxGa1-xAs double quantum wells. [S0163-1829(98)05027-9].