Spin gap in the two-dimensional electron system ofGaAs∕AlxGa1−xAssingle heterojunctions in weak magnetic fields

We study the interaction-enhanced spin gaps in the two-dimensional electron gas confined in $\mathrm{Ga}\mathrm{As}∕\mathrm{Al}\mathrm{Ga}\mathrm{As}$ single heterojunctions subjected to weak magnetic fields. The values are obtained from the chemical potential jumps measured by magnetocapacitance. The gap increase with parallel magnetic field indicates that the lowest-lying charged excitations are accompanied with a single spin flip at the odd-integer filling factor $\ensuremath{\nu}=1$ and $\ensuremath{\nu}=3$, in disagreement with the concept of skyrmions.