  A terahertz metamaterial consisting of radiative slot antennas and subradiant
complementary split-ring resonators exhibits plasmon induced opacity in a
narrow spectral range due to the destructive interference between the bright
and dark modes of the coupled oscillators. Femtosecond optical excitations
instantly quench the mode coupling and plasmon oscillations, injecting
photocarriers into the metamaterial. The plasmon resonances in the coupled
metamaterial are transiently restored by intense terahertz pulses. The strong
terahertz fields induce intervalley scattering and interband tunneling of the
photocarries, and achieve significant reduction of the photocarrier mobility.
The ultrafast dynamics of the nonlinear THz interactions reveals intricate
interplay between photocarriers and plasmon oscillations. The high-field THz
control of the plasmon oscillations implies potential applications to
ultrahigh-speed plasmonics.
