Dimensional crossover and metal-insulator transition in quasi-two-dimensional disordered conductors

We study the metal-insulator transition (MIT) in weakly coupled disordered planes on the basis of a Non-Linear Sigma Model (NL$\sigma$M). Using two different methods, a renormalization group (RG) approach and an auxiliary field method, we calculate the crossover length between a 2D regime at small length scales and a 3D regime at larger length scales. The 3D regime is described by an anisotropic 3D NL$\sigma$M with renormalized coupling constants. We obtain the critical value of the single particle interplane hopping which separates the metallic and insulating phases. We also show that a strong parallel magnetic field favors the localized phase and derive the phase diagram.