Nonactivated transport of ultradilute two-dimensional hole systems in GaAs field-effect transistors: Interaction versus disorder

Very strongly interacting high-purity two-dimensional (2D) electron systems at temperatures T -> 0 demonstrate certain nonactivated insulating behaviors that are absent in more disordered systems. By measuring in dark the T dependence of the conductivity of ultrahigh-quality 2D holes with charge densities down to 7 x 10(8) cm(-2), an approximate power-law behavior is identified. Moreover, 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 nonactivated conduction may well be a universal interaction-driven signature of an electron state of strongly correlated (semiquantum) liquid.