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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.
cond-mat/9805383
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