Evaporation of Metallic Exciton Droplets in Optically Pumped Germanium

High densities of excitons are produced in germanium at liquid-helium temperatures by a pulsed-laser pumping technique. The excitons condense into metallic droplets whose time decay, monitored by a cyclotron resonance method, is nonexponential and displays a cutoff. This is due to surface evaporation, and a measurement of the work function gives a value for the binding energy of the metallic liquid of $16\left(\{+3\mathrm{}\}\{-2\mathrm{}\}\right)$ K which agrees with the value we find from observation of the threshold for the liquid phase.