Sharp metal-insulator transition in a random solid

Zero-temperature metallic conductivities have been measured above and below Mott's minimum value min in bulk crystals of P-doped Si. Conductivities below min increase by over 103 as the density is raised by less than 1%, and do not rule out a discontinuous transition. However, over a wider density range the data can be fitted with a scaling form with a characteristic length that tends to diverge with the same exponent in the metal and insulator.