High-sensitive superconducting magnetometry on a two-dimensional electron gas up to 10 Tesla

We report on new magnetization studies on a two-dimensional electron system (2DES) revealing spin splitting of the Landau levels. For this, we have built a high-sensitive susceptometer consisting of a low-noise thin-film de superconducting quantum interference device (SQUID) with a multiturn input coil and a wire-wound first-order gradiometer. The system noise level is only 40 X 10(-6)phi(0)/root(Hz) down to a frequency of a few Hz in unshielded environment. In background fields up to 10 T, the system exhibits significant low-frequency noise. At frequencies above 1 kHz, however, the SQUID sensitivity is barely affected and we have reached a value of about 10(-14) J/T at 1 T and better than 10(-13) J/T at 10 T. With this, we have studied the de Haas-van Alphen effect for a tunable 2DES starting from zero carrier density. (C) 1997 American institute of Physics.