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Dilute electron gas near the metal-insulator transition in two dimensions

In recent years systematic experimental studies of the temperature dependence of the resistivity in a variety of dilute, ultra clean two dimensional electron/hole systems have revived the fundamental question of localization or, alternatively, the existence of a metal-insulator transition in the presence of strong electron-electron interactions in two dimensions. We argue that under the extreme conditions of ultra clean systems not only is the electron-electron interaction very strong but the role of other system specific properties are also enhanced. In particular, we emphasize the role of valleys in determining the transport properties of the dilute electron gas in silicon inversion layers (Si-MOSFETs). It is shown that for a high quality sample the temperature behavior of the resistivity in the region close to the critical region of the metal-insulator transition is well described by a renormalization group analysis of the interplay of interaction and disorder if the electron band is assumed to have two distinct valleys. The decrease in the resistivity up to five times has been captured in the correct temperature interval by this analysis, without involving any adjustable parameters. The considerable variance in the data obtained from different Si-MOSFET samples is attributed to the sample dependent scattering rate across the two valleys, presenting thereby with a possible explanation for the absence of universal behavior in Si-MOSFET samples of different quality.