A simple noninteracting-electron model, combining local quantum tunneling and global classical percolation (due to a finite dephasing time at low temperatures), is introduced to describe a metal-insulator transition in two dimensions. It is shown that many features of the experiments, such as the exponential dependence of the resistance on temperature in the metallic phase, the linear dependence of the exponent on density, the $e^2/h$ scale of the critical resistance, the quenching of the metallic phase by a parallel magnetic field, and the nonmonotonic dependence of the critical density on a perpendicular magnetic field, can be explained by the model.

• Received 27 April 1999

DOI:https://doi.org/10.1103/PhysRevLett.83.3506