Gate-controlled de Haas–van Alphen effect in an interacting two-dimensional electron system

We have measured the de Haas–van Alphen (dHvA) oscillations of a gated two-dimensional electron system formed in a modulation-doped AlGaAs/GaAs heterojunction by means of a novel and highly sensitive cantilever magnetometer. We achieve a sensitivity of at a magnetic field by detecting the deflection of the cantilever using a fiber optic interferometer. The dHvA oscillation at ν=1 yields a thermodynamic energy gap that scales linearly with the applied magnetic field for . The slope corresponds to an exchange enhanced g factor g^*=3.5±0.3 originating from electron–electron interaction in the spin-polarized state of the 2DES.