Phase diagram of coulomb interactions across the metal-insulator transition in Si:B

Measurements of the single-particle density of states (DOS) near T=0 K in Si:B are used to construct an energy-density phase diagram of Coulomb interactions across the critical density n(c) of the metal-insulator transition. Insulators and metals are found to be distinguishable only below a phase boundary epsilon*(|n/n(c)-1|) determined by the Coulomb energy. Above epsilon* is a mixed state where metals and insulators equidistant from n(c) cannot be distinguished from their DOS structure. The data imply a diverging screening radius at n(c), which may signal an interaction-driven thermodynamic state change.