CHARACTER OF THE PHASE-TRANSITION AT THE 2-DIMENSIONAL ELECTRON LIQUID-TO-SOLID BOUNDARY

Nonlinear threshold electric transport has been studied at T congruent -to 30 mK near the collective insulating transition in a dilute two-di mensional (2D) electron system in high-mobility Si MOSFET's. We found that the threshold electric field becomes steplike at the critical den sity, both when H = 0 and when H not-equal 0. This steplike onset indi cates a weak first-order phase transition at the 2D electron-solid-to- liquid phase boundary.