New perspectives onto the metal-to-non-metal transition in expanded liquid metals

The collective dynamics of liquid rubidium was measured by inelastic neutron scattering from melting up to 1673K and 6.4MPa to explore an electron gas instability, forecasted by theory at sufficient expansion. Pronounced variations are observed when the predicted conditions are approached. They comply with a scenario for the density-driven metal-to-non-metal transition suggested for fluid mercury where the liquid metal decomposes into a nanoemulsion of metallic and non-metallic domains and the metallic domains constantly disappear with ongoing expansion. Collective modes appear as an unambiguous signature of the metallic phase allowing to directly observe this process.