Out-of-Equilibrium Dynamics of a Strongly Correlated Electron System in Two Dimensions*

Slow, nonexponential relaxations of conductivity $\sigma (t)$ have been studied in a strongly disordered two-dimensional electron system (2DES) in Si MOSFETs in the vicinity of the metal-insulator transition (MIT). The 2DES is excited far from equilibrium by a rapid change of carrier density $n_s$ at low temperatures $T$. The dramatic and precise dependence of $\sigma(t)$ on $n_s$ and $T$ shows that (a) the equilibration time diverges exponentially as $T\rightarrow 0$, suggesting a glass transition at $T_g=0$, and (b) the Coulomb interactions between 2D electrons play a dominant role in the observed out-of-equilibrium dynamics~[1]. The scaling of $\sigma(t,T)$ is also consistent with $T_g=0$. These results support conclusions based on earlier noise measurements~[2] that, in a 2DES in Si, the glass transition occurs in the metallic phase as a precursor to the MIT.\\ \noindent [1] J. Jaroszy\'nski and D. Popovi\'c, Phys. Rev. Lett. {\bf 96}, 037403 (2006).\\ \noindent [2] S. Bogdanovich and D. Popovi\'c, Phys. Rev. Lett. {\bf 88}, 236401 (2002); J. Jaroszy\'nski, D. Popovi\'c, and T. M. Klapwijk, Phys. Rev. Lett. {\bf 92}, 226403 (2004).