We report on the transport measurements of two-dimensional holes in GaAs field-effect transistors with record low densities down to $7\times {10}^8{\mathrm{cm}}^{-2}$. Remarkably, such a dilute system (with Fermi wavelength approaching $1\mu \mathrm{m}$) exhibits a nonactivated conductivity that grows with temperature approximately as a power law at sufficiently low temperatures. We contrast it with the activated transport found in more disordered samples and discuss possible transport mechanisms in this strongly interacting regime.

• Received 8 September 2006

DOI:https://doi.org/10.1103/PhysRevB.74.201302