The so-called two dimensional metal-insulator transition
  We provide a critical perspective on the collection of low-temperature transport phenomena in low-density two-dimensional semiconductor systems often referred to as the 2D metal-insulator transition. We discuss the physical mechanisms underlying the anomalous behavior of the two-dimensional effective metallic phase and the metal-insulator transition itself. We argue that a key feature of the 2D MIT physics is the long-range bare Coulombic disorder arising from the random distribution of charged impurities in the low-density 2D semiconductor structures. 
S. Das Sarma and E. H. Hwang