Metal-insulator transition in two dimensions: Effects of disorder and magnetic field

The behavior indicative of a metal-insulator transition in a two-dimensional electron system in silicon has been studied. By applying substrate bias, we have reduced the disorder and increased the mobility of our samples and observed the emergence of the metallic behavior when the mobility was high enough in the regime of electron densities where Coulomb interaction energy is much larger than the Fermi energy. In a perpendicular magnetic field, the magnetoconductance is positive in the vicinity of the transition but negative elsewhere. Our experiment suggests that such behavior results from a decrease of the spin-dependent part of the interaction in the vicinity of the transition.