All condensed matter systems possess disorder and interaction effects. Still, the qualitative effects of disorder and interactions in quantum systems are poorly understood. This is especially true when it comes to electrical conduction. The standard theory, developed for non-interacting particles over 40 years ago, predicted surprisingly that for the most part, disorder destroys metallic behavior in two-dimensional (2d) systems at zero temperature. For many decades, this "absence of quantum diffusion in 2d" was taken to be scientific law. However, with strong interactions, there is no reason to believe that this dogma survives.
I will review the experiments that have challenged this conventional wisdom, and will describe ongoing theoretical efforts to establish that metallic ground states can occur in 2d due to strong interaction effects.