Transport Measurements on 2D Systems at Low-Filling Factors: Evidence for Wigner Crystal

Abstract

A review of recent transport measurements on low disorder, two-dimensional (2D) electron and hole systems at semiconductor interfaces in the regime of low Landau-level filling factor (v) is given. This is the regime where transition(s) from liquid/gas to (Wigner) solid has been long expected. The presentation will highlight and contrast the experimental results reported by different groups. None of these results provide direct and conclusive evidence for the transition to a Wigner crystal. However, in 2D electron systems at the GaAs/AlGaAs interface, the observation of an insulating phase reentrant around the v=1/5 fractional liquid state, and the nonlinear IV, noise, and the temperature characteristics of the insulating phase are consistent with the formation of a pinned Wigner crystal. The recent results for dilute 2D hole systems which show strikingly similar behavior at a much larger v=1/3 provide additional evidence for the Wigner crystal interpretation.