Nonlinear magnetic field dependence of spin polarization in high-density two-dimensional electron systems

The spin polarization (P) of high-density InSb two-dimensional electron systems (2DESs) has been measured using both parallel and tilted magnetic fields. P is found to exhibit a superlinear increase with the total field B. This P-B nonlinearity results in a difference in spin susceptibility between its real value Χ_s and Χ_gm ∝ m ^*g^* (m^* and g ^* are the effective mass and g factor, respectively) as routinely used in experiments. We demonstrate that such a P-B nonlinearity originates from the linearly P-dependent g^* due to the exchange coupling of electrons rather than from the electron correlation as predicted for the low-density 2DES.