Negative compressibility of interacting two-dimensional electron and quasiparticle gases

Abstract

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, \ensuremath{\nu}1, are reported. A new method is used to determine both the magnitude and IsignR of K. At B=0 we find ${\mathit{K}}^{\mathrm{\ensuremath{-}}1}$ changes sign and becomes negative as the 2D density is reduced. At high B, ${\mathit{K}}^{\mathrm{\ensuremath{-}}1}$ exhibits negative anomalies near both \ensuremath{\nu}=0 and 1. Compressibility features near the fractional fillings \ensuremath{\nu}=1/3 and 2/3 give thermodynamic evidence for dilute interacting quasiparticle gases.