Landau level anticrossing manifestations in the phase-diagram topology of a two-subband system

Abstract

In a two-subband $\mathrm{Ga}\mathrm{As}∕\mathrm{Al}\mathrm{Ga}\mathrm{As}$ two-dimensional electron system, the phase diagram of longitudinal resistivity ${\ensuremath{\rho}}_{xx}$ in density and magnetic field plane exhibits an intriguing structure centered at filling factor $\ensuremath{\nu}=4$ which is strikingly different from the ringlike 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/pseudospin interactions for the two-subband system.