NEGATIVE COMPRESSIBILITY OF INTERACTING 2-DIMENSIONAL ELECTRON AND QUASI-PARTICLE GASES

Direct measurements of the compressibility K of the 2D electron gas at both zero magnetic field B and in the high-field extreme quantum limit, nu < 1, are reported. A new method is used to determine both the magnitude and sign of K. At B = 0 we find K-1 changes sign and becomes negative as the 2D density is reduced. At high B, K-1 exhibits negative anomalies near both nu = 0 and 1. Compressibility features near the fractional fillings nu = 1/3 and 2/3 give thermodynamic evidence for dilute interacting quasiparticle gases.