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 5×10-16J/T at a magnetic field B=10T 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 B>3T. 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.