DENSITY BISTABILITY IN AN INTERACTING ELECTRON-HOLE SYSTEM IN COHERENTLY EXCITED SEMICONDUCTORS

An electron-hole system in a direct-gap semiconductor that is coherently excited by a high-intensity laser is investigated. The stationary state of the system in the presence of laser field is described by Bogolyubov quasiparticles. Using a mean-field approximation, we derive a set of basic equations including electron-electron, hole-hole, and electron-hole screened Coulomb interactions. The screening effects are incorporated self-consistently on the basis of a quasistatic random-phase approximation. The stationary state has a fixed chemical potential and is controlled by the frequency of the laser field. By numerical analysis of the basic equations, we show that a resonatorless bistability occurs; that is, an electron-hole pair-density bistability with respect to the excitation energy is shown to be caused by many-body effects via the screened Coulomb interaction. We clarify how the stationary state changes its entity depending on the frequency and intensity of the laser field, and how such a characteristic behavior is observed in optical spectra of probe light.