Degenerate versus semidegenerate transport in a correlated two-dimensional hole system

It has been puzzling that the resistivity of high-mobility two-dimensional (2D) carrier systems in semiconductors with low carrier density often exhibits a large increase followed by a decrease when the temperature T is raised above a characteristic temperature comparable with the Fermi temperature T_F. We find that the metallic 2D hole system in a GaAs quantum well has a linear density- (p-) dependent conductivity σeμ^*(p-p ₀) in both the degenerate (TT_F) and semidegenerate (T~T_F) regimes. The T dependence of σ(p) suggests that the metallic conduction dσ/dT<0 at low T is associated with the increase in μ^*, the effective mobility of itinerant carriers. However, the resistivity decrease in the semidegenerate regime T>T_F originates from the reduced p₀, the density of immobile carriers in a two-phase picture.