Disappearance of the metal-like behavior in GaAs two-dimensional holes below 30mK.

The T-dependence of the resistivity of two-dimensional holes are observed to exhibit two qualitatively different characteristics for a fixed carrier density at temperatures below 100mK. In this putatively metallic regime of the so-called metal-insulator transition, the sign of the derivative of the resistivity with respect to temperature changes from being positive (d$\rho $/dT$>$0) to negative (d$\rho $/dT$<$0) when the temperature is lowered below 30 mK and the resistivity continuously rises with cooling down to 1mK, suggesting a crossover from being metal-like to insulator-like.