Comparison between the compressibilities of the zero field and composite-fermion metallic states of the two-dimensional electron system

We have studied the capacitance between a two-dimensional electron system and a gate of field-effect transistors, produced from three different wafers with a single remotely doped GaAs/AlxGa1-xAs heterojunction. In the vicinity of the Landau-level filling factor v = 1/2, the increment of the capacitance relative to its zero-magnetic-field value, deltaC(1/2), was found to be insensitive to the carrier density, and close to the value as if the particles are noninteracting. This observation implies that electron-electron interaction affects the compressibility of the zero-field and composite-fermion metallic states in a very similar manner.