The Metal-insulator Transition through the Wigner Glass
S. Chakravarty, UCLA
Recent experiments on the two dimensional electron gas in various semiconductor devices have revealed an unexpected metal-insulator transition and have challenged the previously held assumption that there is no such transition in two dimensions. While the experiments are still at the stage of rapid development, it is becoming evident that they cannot be understood from the conventional perspective of weak interactions. In the present paper, we propose the following. (1) The low-density insulating state is the Wigner Glass, a phase with quasi-long-range translational order and competing ferromagnetic and antiferromagnetic spin-exchange interactions. (2) The transition is the melting of this Wigner Glass, disorder being the agent allowing the transition to be second order. (3) Within the Wigner Glass phase, there are at least two, distinct magnetic ground-states, a ferromagnetic state at very low electron density and a spin-liquid state with a spin pseudo-gap at higher densities. (4) The metallic side of the transition is a non-Fermi liquid.

These conclusions are encapsulated in the the proposed phase diagram as a function of disorder strength and density; we also suggest experimental signatures of the various phases and transitions. A specific prediction is that the compressibility approaching the transition from the conducting side should vanish as $(r_s^c-r_s)^{\nu}$, where $r_s$ is the interaction parameter and $r_s^c$ its critical value; $\nu$ is the correlation length exponent. The experimental value of $\nu$ appears to be 1.5, obtained from a combination of temperature and electric field scaling [S. V. Kravchenko et al., Phys. Rev. Lett. 77, 4938 (1996)]. This critical behavior of the compressibility is consistent with the data shown by H. -W. Jiang at this conference.

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