Distinct Terahertz Third-Harmonic Generation of Many-Body Excitonic States

The dynamics of an electron-hole plasma governed by strong Coulomb interaction is a challenging many-body problem. We report on experimental realization of electron-hole many-body states in the picosecond time scale, with tunable densities in a representative semiconductor Cu_{2}O. By using time-resolved optical-pump terahertz third-harmonic-generation spectroscopy, we study the nonlinear terahertz dynamical characteristics of the many-body electron-hole states. We find not only efficient and nonperturbative terahertz third-harmonic yield associated with the excitonic formation but also a nonmonotonic dependence of the excitonic nonlinear response on the electron-hole density, reflecting the exciton dissociation at high charge density. Our results provide an efficient excitonic sensing of the far-from-equilibrium electron-hole many-body states.