We have measured compressibility of a two-dimensional hole gas in p-GaAs/AlxGa1-xAs heterostructure, grown on a (100) surface, in the presence of a tilted magnetic field. It turns out that the parallel component of magnetic field affects neither the spin splitting nor the density of states. We conclude that (a) g factor in the parallel magnetic field is nearly zero in this system, and (b) the level of the disorder potential is not sensitive to the parallel component of the magnetic field.

We have used a field-penetration method to measure thermodynamic compressibility of a moderately interacting two-dimensional electron system ($r_{s}$ $\approx$ 0.5-3) in a three terminal GaAs/AlGaAs device, fabricated with an epitaxial lift-off technique. We found that the density and temperature dependencies of the compressibility are qualitatively different from that observed in earlier studies of the 2D hole system, where interaction energies are considerably stronger. We show that the observed characteristics can be described by the recently developed formalism for compressibility of the droplet state.

By tracking the delocalized states of the two-dimensional hole gas in a p-type GaAs/AlGaAs heterostructure as a function of magnetic field, we mapped out a phase diagram in the density-magnetic-field plane. We found that the energy of the delocalized state from the lowest Landau level flattens out as the magnetic field tends toward zero. This finding is different from that for the two-dimensional electron system in an n-type GaAs/AlGaAs heterostructure where delocalized states diverge in energy as B goes to zero indicating the presence of only localized states below the Fermi energy. The possible connection of this finding to the recently observed metal-insulator transition at B = 0 in the two-dimensional hole gas systems is discussed.