Magnetoresistance and cyclotron mass in extremely-coupled double quantum wells under in-plane magnetic fields

We experimentally investigate the transport properties of an extremely-coupled AlGaAs/GaAs double quantum well, subject to in-plane magnetic fields (B_||). The coupling of the double quantum well is sufficiently strong that the symmetric-antisymmetric energy gap (Δ_SAS) is larger than the Fermi energy (E_F). Thus for all B_|| only the lower energy branch of the dispersion curve is occupied. In contrast to systems with weaker coupling such that Δ_SAS<E_F we find: (1) only a single feature, a maximum, in the in-plane magnetoresistance, (2) a monotonic increase with B_|| in the cyclotron mass up to 2.2 times the bulk GaAs mass, and (3) an increasing Fermi surface orbit area with B_||, in good agreement with theoretical predictions