Evidence for mixed phases and percolation at the metal-insulator transition in two dimensions

The in-plane magnetoconductance of the strongly interacting two-dimensional electron system in a silicon MOSFET (metal-oxide-semiconductor-field-effect transistor) exhibits an unmistakeable kink at a well-defined electron density, $n_k$. The kink at $n_k$ is near, but not at the critical density $n_c$ determined from resistivity measurements, and the density at which $n_k$ occurs varies with temperature. These features are inconsistent with expectations for a quantum phase transition. We suggest instead that this is a percolation transition and present a detailed model based on the formation of a mixed insulating and metallic phase within which a metal-insulator transition takes place by percolation.