Onset of Glassy Dynamics in a Two-Dimensional Electron System in Silicon

The fluctuations of conductivity $\sigma$ with time have been studied in a two-dimensional electron system in low-mobility Si inversion layers. The noise power spectrum is $\sim {1/f}^{\alpha }$ with $\alpha$ exhibiting a sharp jump at an electron density $n_s{=n}_g$. A huge increase in the relative variance of $\sigma$ is observed as $n_s$ is reduced below $n_g$, reflecting a dramatic slowing down of the electron dynamics. This is attributed to the freezing of the electron glass. The data strongly suggest that glassy dynamics persists in the metallic phase.