New Phenomena in Excitoa Condensation in Germanium

Abstract

We report a sharp optical pumping threshold for the 709-meV luminescence in pure Ge, the simultaneous onset of ${10}^{-11\mathrm{}}$-C charge pulses in Ge junctions, and a pronounced optical hysteresis characteristic of supersaturation. Our results favor the model of exciton condensation into electron-hole droplets over the biexciton model. Our droplet-free exciton coexistence curves yield $\varphi =1.54\mathrm{}\pm 0.25$ meV for the condensation energy.