Metal–Insulator Transition Unexpectedly Appears in a Two‐Dimensional Electron System

For roughly the last two decades, it has generally been believed among those interested in two‐dimensional disordered electron systems that, in zero magnetic field, such systems do not undergo a metal‐insulator transition at 0 K. In an influential 1979 paper, Elihu Abrahams, Philip Anderson, Donald Licciardello and T. V. Ramakrishnan, who became known as the Gang of Four, had used scaling arguments, assumed there were no electron‐electron interactions and found that an electron in a two‐dimensional random potential at 0 K would not diffuse. So, if the temperature were lowered toward 0 K, no transition from insulator to metal would occur in a disordered system. Even if the twodimensional electron systems were conducting at high temperatures, the disorder and the two‐dimensionality would be sufficient to localize the electrons, preventing metallic behavior at $T = 0.$