2-DIMENSIONAL ELECTRON SOLID FORMATION IN SI INVERSION-LAYERS

We have studied experimentally the nature of the giant resistance peaks previously observed in two-dimensional (2D) low-density electron layers on a Si surface at low temperatures and magnetic fields. The measurements of the low-frequency impedance of the metal-oxide-semiconductor structure indicate that this effect takes place homogeneously over the "2D bulk" and measurements of the Hall resistance show that the development of the giant resistance peaks is not related to a diminution in the concentration of delocalized electrons. Both diagonal and Hall conductivities were found to reach their minima near half-integer filling of Landau levels, where the single-particle density of states should be at its maximum value. These results evidently contradict the single-particle localization picture. At the same time, the experimental results are well consistent with the formation of an electron solid. This solid forms at low electron densities n(s) approximately less-than 10(11) cm-2 and temperatures T approximately less-than 1 K in weak or possibly even zero magnetic fields and drives both sigma-xx and sigma-xy to zero with decreasing temperature. In the vicinity of integer filling factors 1 and 2, the solid melts, thus providing well-defined quantized-Hall-resistance states.