Two-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 nₛ{}10¹¹ cm^-2 and temperatures T{}1 K in weak or possibly even zero magnetic fields and drives both σₓₓ and σxy 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.