Further Evidence for a Collapse of the Exchange-Enhanced Spin Splitting in Two Dimensional Systems

The collapse of spin splitting in the integer quantum Hall effect is investigated for a series of AlxGa1-xAs/GaAs heterojunctions and quantum wells. Magnetoresistance measurements are performed at mK temperature, and a simple model is developed to simulate spin splitting. As expected a single-electron picture cannot reproduce the observed spin splitting, whereas a phenomenological enhanced-spin gap taking into account exchange interactions between electrons provides a good description. The phenomenological spin gap, which is linear in B at high magnetic field, collapses when the spin splitting collapses. This is consistent with previously proposed disorder-driven destruction of exchange interactions with decreasing magnetic field.