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Register a new userNonexponential Relaxations in a Two-Dimensional Electron System in Silicon
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The relaxations of conductivity have been studied in a strongly disordered two-dimensional (2D) electron system in Si after excitation far from equilibrium by a rapid change of carrier density n_s at low temperatures T. The dramatic and precise dependence of the relaxations on n_s and T strongly suggests (a) the transition to a glassy phase as T->0, and (b) the Coulomb interactions between 2D electrons play a dominant role in the observed out-of-equilibrium dynamics.
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The time-dependent fluctuations of conductivity sigma have been studied in a two-dimensional electron system in low-mobility, small-size Si inversion layers. The noise power spectrum is ~1/f^{alpha} with alpha exhibiting a sharp jump at a certain electron density n_s=n_g. An enormous 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.
Studies of low-frequency resistance noise show that the glassy freezing of the two-dimensional electron system (2DES) in Si in the vicinity of the metal-insulator transition (MIT) persists in parallel magnetic fields B of up to 9 T. At low B, both the glass transition density $n_g$ and $n_c$, the critical density for the MIT, increase with B such that the width of the metallic glass phase ($n_c<n_s<n_g$) increases with B. At higher B, where the 2DES is spin polarized, $n_c$ and $n_g$ no longer depend on B. Our results demonstrate that charge, as opposed to spin, degrees of freedom are responsible for glassy ordering of the 2DES near the MIT.
The relaxations of conductivity after a temporary change of carrier density n_s during the waiting time t_w have been studied in a strongly disordered two-dimensional electron system in Si. At low enough n_s < n_g (n_g - the glass transition density), the nonexponential relaxations exhibit aging and memory effects at low temperatures T. The aging properties change abruptly at the critical density for the metal-insulator transition n_c < n_g. The observed complex dynamics of the electronic transport is strikingly similar to that of other systems that are far from equilibrium.
The relaxations of conductivity have been studied in the glassy regime of a strongly disordered two-dimensional electron system in Si after a temporary change of carrier density during the waiting time t_w. Two types of response have been observed: a) monotonic, where relaxations exhibit aging, i.e. dependence on history, determined by t_w and temperature; b) nonmonotonic, where a memory of the sample history is lost. The conditions that separate the two regimes have been also determined.
Large fluctuations of conductivity with time are observed in a low-mobility two-dimensional electron system in silicon at low electron densities $n_s$ and temperatures. A dramatic increase of the noise power ($propto 1/f^{alpha}$) as $n_s$ is reduced below a certain density $n_g$, and a sharp jump of $alpha$ at $n_sapprox n_g$, are attributed to the freezing of the electron glass at $n_s = n_g$. The data strongly suggest that glassy dynamics persists in the metallic phase.
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