Friday, January 13, 2012

Deconstructing the metal-insulator transition in 2DEGs

There is an interesting preprint, Wigner-Mott scaling of transport near the two-dimensional metal-insulator transition by M. M. Radonjic, D. Tanaskovic, V. Dobrosavljevic, K. Haule, and G. Kotliar.

They argue that the density dependent metal-insulator transition seen in Silicon MOSFETs and other two dimensional electron gases (2DEGs) in semiconductor heterostructures is not driven by disorder (which has been claimed for many years) but rather by electronic correlations. Furthermore, the relevant experimental data can be described by a Dynamical Mean-Field Theory (DMFT) treatment of the Wigner-Mott transition in an extended Hubbard model on a lattice.

This means that the non-monotonic temperature dependence of the resistivity is associated with the crossover from a Fermi liquid at low temperatures to a bad metal at higher temperatures. I think thermopower measurements may be the most effective way to test this claim (see an earlier  post).


  1. Thanks for the kind words Ross. As to thermopower, very recent data by A. Mokashi, S. Li, Bo Wen, S. V. Kravchenko, A. A. Shashkin, V. T. Dolgopolov, M. P. Sarachik, in the preprint entitled "Divergence of the effective mass in a strongly-interacting 2D electron system" (arXiv:1111.7238v1) indeed shows results consistent with what we proposed.

  2. This paper is not published in Phys. Rev. B 85, 085133 (2012).

  3. Today I talked to Kravchenko about measuring the full temperature dependence of the thermopower, to test my claim that it should saturate with a value of order
    k_B/e ~ 40 microvolt/K
    at a temperature of the order of the coherence temperature [which should scale inversely with the effective mass].
    This saturation corresponds to the entropy per electron being of order k_B ln(2), i.e. as expected for a bad metal.

    He said the problem is that his cryostat is a dilution refrigerator and so only works up to one Kelvin. Thus a different apparatus will be needed.
    I still think it is worth the effort.