New Type of Nonlinear Optical Device using Charge-Density-Wave Collective Motion

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(i) Charge density fluctuation and density modulation in ideal 2-dimensional electron systemsResonant light scattering spectra from modulation doped n-type AlGaAs/GaAs single heterojunctions are studied experimentally and theoretically. Based on the light scattering formula due to the charge-density mechanism, the scattering intensities by coupled intersubband plasmon-LO phonon modes are analyzed by taking into account the electron-electron and electron-phonon interactions. Moreover, we carry out a self-consistent calculation of the density modulation of the 2-dimensional electron gas in a lateral surface superlattice.(ii) Charge-density-waves in transition-metal dichalcogenidesSingle crystals of quasi-two-dimensional conductor of TaS_2 have been synthesized by chemical vapor transport technique. Excess sulfur addition at the synthesis suppressed the charge-density-wave transition through a conduction carrier injection; the thermopower measurements revealed that the injected carrier is hole.(iii) Photo-irradiation effect on dynamics of charge-density-wave condensate in quasi-one-dimensional conductorsWe find a new photo-irradiation effect on the current-voltage characteristics of quasi-one-dimensional conductors TaS_3. When the TaS_3 single crystal is irradiated with a weak 488 nm emission from Ar^+ laser, the electrical current is enhanced around the threshold voltage V_t below the Peierls transition temperature T_p. The current enhancement is attributed to the increase of charge-density-wave contribution due to the screened pinning potentials by photo-excited quasi-particles in plastic creep phase of charge-density-wave motion.