First order metal-insulator transition in two-dimensional disordered systems

In the absence of magnetic field or spin-orbit coupling the one-parameter s caling theory predicts localization of all states in two-dimensional (2D) d isordered systems, for any amount of disorder. However, a 2D metallic phase has been recently reported in high mobility Si-MOS and GaAs-based material s without magnetic field. We study numerically a recently proposed 2D model which consists of a compactly coupled pure-random plane structure. This al lows to obtain exactly a continuum of one-dimensional ballistic extended st ates which can lead to a marginal metallic phase of finite conductivity sig ma(0) = 2e(2)/h, in a wide energy range whose boundaries define the mobilit y edges of a first-order metal-insulator transition. We present numerical d iagonalization results and the conductivity of the system in perpendicular magnetic field, which verify the above analytical predictions. The model is also discussed in connection to recent experiments.