EXCITONIC CLUSTERS AND THE PHASE TRANSITIONS IN FLUID MERCURY.

A review is presented of the metal-nonmetal transition in expanded liquid mercury and the dielectric transition in dense mercury vapor. Previous explanations for these transitions are found to be deficient. The authors propose that the high-temperature, high-pressure fluid is an excitonic insulator phase. The condensation instability of the Frenkel excitons is shown to result from improved coordination within the fluid. The phase diagram for the excitonic insulator naturally explains both the metal-nonmetal and the dielectric transitions.