Quantum Effects in the Capacitance of Field-Effect Transistors with a Double Quantum Well

The compressibility of electrons in a bilayer electron system implemented in a GaAs double quantum well is investigated. Manifestations of the negative compressibility of a low-density two-dimensional electron system in zero and quantizing magnetic fields are observed. It is found that the magnetic field ranges where incompressible phases at the spin-resolved Landau level filling factors of 2 and 1 exist in the layer with the higher electron density are broadened considerably upon the filling of the other layer. The effect is explained by the stabilization of the quantum Hall effect states owing to the transfer of electrons from the layer with the lower density. The magnitude of jumps in the chemical potential for the corresponding quantum Hall effect states is estimated.