Metallic behaviour and localisation in 2D GaAs hole systems

We have investigated the apparent “metal”–insulator transition in a variety of high quality 2D GaAs hole systems. Central to the issue of whether such a transition can exist is the question of what happens to the localising quantum corrections to the conductivity predicted by one-parameter scaling theory. We demonstrate that in samples where the phase coherence length is greater than the mean free path, weak localisation corrections are observed in the so-called “metallic” phase. We also observe weak hole–hole interaction corrections close to but on the “metallic” side of the transition. Both these corrections are localising, becoming stronger as T→0. This suggests that despite the strong interactions (rs>10) these 2D GaAs hole systems still behave like Fermi liquids, and there is no true 2D “metallic” state. Instead, we find that conventional temperature dependent screening can account for many aspects of the metallic behaviour.