COLLAPSE OF QUANTIZED HALL PLATEAUS IN ASYMMETRIC DOUBLE-QUANTUM-WELLSYSTEMS

The integer quantum Hall effect in asymmetric double-quantum-well stru ctures is investigated for electron concentrations which are varied up to around the population threshold of the excited subband. The scatte ring time of electrons in the system is shown to be governed by the in terface roughness. The ratio between the transport and single-particle scattering times is used to evaluate the fluctuations in the interfac e. We map out a phase diagram of spin-polarized and spin-unpolarized s tates. When the Fermi energy is raised to the bottom of the second sub band, the resistance peak for the Landau level filling factor nu betwe en 2 and 3 broadens and the nu = 3 Hall plateau collapses. The couplin g of the Landau levels in the two quantum wells leads to an enhancemen t of the dissipative conductivity. The anomalous peak is found to exhi bit nonlinear current-voltage characteristics.