  We study two dimensional electron systems confined in wide quantum wells
whose subband separation is comparable with the Zeeman energy. Two N = 0 Landau
levels from different subbands and with opposite spins are pinned in energy
when they cross each other and electrons can freely transfer between them. When
the disorder is strong, we observe clear hysteresis in our data corresponding
to instability of the electron distribution in the two crossing levels. When
the intra-layer interaction dominates, multiple minima appear when a Landau
level is 1/3 or 2/3 filled and fractional quantum hall effect can be
stabilized.
