ZERO-MAGNETIC-FIELD COLLECTIVE INSULATOR PHASE IN A DILUTE 2D ELECTRON-SYSTEM

We report on a collective low temperature metal-insulator transition which develops in a dilute 2D electron system in Si at zero magnetic field, below a critical carrier density n(sc) almost-equal-to 10(11) cm-2. In the insulator phase, the dc conduction is thermally activated and exhibits a sharp threshold as a function of electric field. The collective insulator state at zero field shows many of the features attributed to the pinned Wigner solid. We have also observed a trend from a collective to a single-particle insulator state with decreasing electron density and/or increasing disorder.