Landau Level Anticrossing Manifestations in the Phase Diagram Topology   of a Two Subband System
  In a two-subband GaAs/AlGaAs two-dimensional electron system, the phase diagram of longitudinal resistivity \rho_xx in density and magnetic field plane exhibits an intriguing structure centered at filling factor \nu = 4 which is strikingly different from the ring-like structures at lower magnetic fields. Thermal activation measurements reveal an anticrossing gap on each boundary of the structure where intersubband Landau Levels with parallel or antiparallel spin are brought into degeneracy. While the physics of the anticrossing can be ascribed to the pseudospin quantum Hall ferromagnetism, as reported earlier by Muraki et al, the mapping and modeling of the phase diagram topology allow us to establish a more complete picture of the consequences of real spin / pseudo-spin interactions for the two subband system. 
X. C. Zhang, I. Martin, and H. W. Jiang