  According to the scaling theory of localization, all quantum electronic
states are localized in two-dimensional (2D) systems. One consequence of the
theory is that there is no quantum percolation transition in 2D. However, in a
real system at a finite temperature, electron phase coherent length is finite
and the system is between quantum and classical. We find, in such a 2D system,
a metal-insulator transition (MIT) caused by a novel type of percolation,
meta-percolation. The relevance to recently observed 2D MIT is also discussed.

Disordered Systems and Neural Networks;Mesoscale and Nanoscale Physics