In-plane magnetoresistance studies of an extremely coupled double quantum well

We investigate the transport properties of an extremely-coupled AlxGa1-xAs/GaAs double quantum well subject to in-plane magnetic fields B-I. The coupling is sufficiently strong that the symmetric-antisymmetric gap energy Delta(SAS) is larger than the Fermi energy E-F. Thus for all B-I only the lower-energy dispersion branch is occupied. In contrast to systems where Delta(SAS) < E-F, we find: (1) only a single feature in the magnetoresistance, a maximum; (2) a monotonic increase in the cyclotron mass to roughly double the GaAs band mass; and (3) a monotonically increasing Fermi-surface orbit area. These experimental results agree well with our theoretical calculations.