Interaction-driven versus disorder-driven transport in ultra-dilute GaAs two-dimensional hole systems

It is well-known that the insulating behavior in the two-dimensional metal-to-insulator transition demonstrates a finite temperature conduction via hopping. Recently, however, some very strongly interacting higher purity two-dimensional electron systems at temperatures $T\rightarrow 0$ demonstrate certain nonactivated insulating behaviors that are absent in more disordered systems. Through measuring in dark the $T$-dependence of the conductivity of ultra-high quality 2D holes with charge densities down to $7\times10^{8}$ $cm^{-2}$, an approximate power-law behavior is identified. Moreover, for the lowest charge densities, the exponent exhibits a linearly decreasing density-dependence which suggests an interaction-driven nature. Such an electron state is fragile to even a slight increase of disorder which causes a crossover from nonactivated to activated conduction. The non-activated conduction may well be an universal interaction-driven signature of an electron state of strongly correlated (semiquantum) liquid.