Quantum features of angular dependent magnetoresistance oscillations in quasi-two-dimensional conductors near high magnetic field quantum limit

We report novel features of angular dependent magnetoresistance oscillations (AMROs) observed in strong magnetic fields where only a few Landau levels are occupied. In order to realize this "near-quantum-limit" in real Q2D systems, we have chosen GaAs/AlGaAs semiconductor superlattices for AMRO experiments. Near the quantum limit, the peak position of AMRO slightly depends on field strength, and it jumps synchronizing Shubnikov-de Haas peaks. AMRO disappears when the parallel field component exceeds a certain value which gives a broad local minimum of interlayer resistance. The observed features are hardly expected from the conventional picture based on the semiclassical Fermi surface topological effect ignoring Landau quantization. We have successfully explained these new features by the quantum mechanical picture which evaluates interlayer conductivity from magnetic eigen states using the Kubo formula. This quantum picture gives the most general and complete description of AMRO in Q2D conductors.