The magnetic field dependence of the chemical potential of a two-dimensional electron system (2DES), realized in a GaAs/Al0.33Ga0.67As heterostructure, is measured by using a metallic single-electron transistor (SET) on top of the 2DES. At low magnetic fields, the Landau level depopulation with increasing magnetic field is observed. At high magnetic fields, charge fluctuations are detected within the quantum-Hall regime. The insulator-like behavior of the 2DES in the quantum-Hall regime is demonstrated by controlling the SET by a metal-gate electrode underneath the 2DES. (C) 1998 Elsevier Science B.V. All rights reserved. [References: 12]
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