Observation of percolation-induced two-dimensional metal-insulator transition in a Si MOSFET

Abstract

By analyzing the temperature $(T)$ and density $(n)$ dependence of the measured conductivity $(\ensuremath{\sigma})$ of two-dimensional (2D) electrons in the low-density $(\ensuremath{\sim}{10}^{11}\text{ }{\text{cm}}^{\ensuremath{-}2})$ and temperature (0.02--10 K) regimes of high-mobility (1.0 and $1.5\ifmmode\times\else\texttimes\fi{}{10}^{4}\text{ }{\text{cm}}^{2}/\text{Vs}$) Si metal-oxide-semiconductor field-effect transistors, we establish that the putative 2D metal-insulator transition is a density-inhomogeneity-driven percolation transition where the density-dependent conductivity vanishes as $\ensuremath{\sigma}(n)\ensuremath{\propto}{(n\ensuremath{-}{n}_{p})}^{p}$, with the exponent $p\ensuremath{\sim}1.2$ being consistent with a percolation transition. The ``metallic'' behavior of $\ensuremath{\sigma}(T)$ for $n>{n}_{p}$ is shown to be well described by a semiclassical Boltzmann theory, and we observe the standard weak localization-induced negative magnetoresistance behavior, as expected in a normal Fermi liquid, in the metallic phase.