Self-doping instability of the Wigner-Mott insulator

We present a theory describing the mechanism for the two-dimensional (2D) metal-insulator transition (MIT) in the absence of disorder. A two-band Hubbard model is introduced, describing vacancy-interstitial pair excitations within the Wigner crystal. Kinetic energy gained by delocalizing such excitations is found to lead to an instability of the insulator to self-doping above a critical carrier concentration n=n_c, mapping the problem to a density-driven Mott MIT. This mechanism provides a natural explanation of several puzzling experimental features, including the large effective mass enhancement, the large resistivity drop, and the large positive magnetoresistance on the metallic side of the transition. We also present a global phase diagram for the clean 2D electron gas as a function of n and parallel magnetic field B_∥, which agrees well with experimental findings in ultraclean samples.