Using a magnetocapacitance technique, we determine the magnetic field of the spin transition, $B^{*}$, at filling factor $\nu =2/3$ in the two-dimensional electron system in GaAs/AlGaAs heterojunctions. The field $B^{*}$ is found to decrease appreciably as the wave function extent controlled by back gate voltage is increased. Our calculations show that the contributions to the shift of $B^{*}$ from the change of the Coulomb energy and the $g$ factor change due to nonparabolicity are approximately the same. The observed relative shift of $B^{*}$ is described with no fitting parameters.

• Received 1 October 2012

DOI:https://doi.org/10.1103/PhysRevB.87.081306