Using magnetocapacitance data, we directly determine the chemical potential jump at low temperatures of about 25 mK when the filling factor traverses the spin gap at $\nu =1\mathrm{}$ and the cyclotron gap at $\nu =2\mathrm{}$. The chemical potential jump for the cyclotron gap is found to increase proportionally to the magnetic field with a slope that is determined by an effective mass ${0.071m}_0$. The data yield a spin gap that also increases proportionally with magnetic field and is described by an enhanced Landé factor $g\approx 5.2$. This result has not been explained by existing theoretical models.

• Received 24 February 1997

DOI:https://doi.org/10.1103/PhysRevLett.79.729