Metal-Insulator Transition in Two Dimensions in a Nearly Periodic   Potential
  A two-dimensional gas of non-interacting quasiparticles in a nearly periodic potential is considered at zero temperature. The potential is a superposition of a periodic potential, induced by the charge density wave of a Wigner crystal, and a weak random potential due to disorder. There is a metal-insulator transition that is controlled by the strength of the periodic potential. The transition is continuous in the presence of randomness. We evaluate the density of states, which is non-zero at the Fermi energy in the metallic phase, and the dc conductivity. The latter changes with decreasing modulation of the periodic potential from 0 to $\sigma\approx2e^2/h$. 
K. Ziegler