Coulomb correlations and the Wigner-Mott transition

Strong correlation effects, such as a marked increase in the effective mass of the carriers of electricity, recently observed in the low-density electron gas(1) have provided spectacular support for the existence of a sharp metal-insulator transition in dilute two-dimensional electron gases(2). Here, we show that strong correlations, normally expected only for narrow integer-filled bands, can be effectively enhanced even far away from integer-filling, owing to incipient charge ordering driven by non-local Coulomb interactions. This general mechanism is illustrated by solving an extended Hubbard model using dynamical mean-field theory(3). Our findings account for the key aspects of the experimental phase diagram, and reconcile the early viewpoints of Wigner and Mott. The interplay of short-range charge order and local correlations should result in a three-peak structure in the electron spectral function, which can be observed in tunnelling and optical spectroscopy. These experiments will discriminate between the Wigner-Mott scenario and the alternative perspective that views disorder as the main driving force for the two-dimensional metal-insulator transition(4).