  We demonstrate ultrafast resonance switching of terahertz metamaterials
through optical excitation of radiation damaged silicon placed in the gap of
single split gap ring resonator. We observe the dynamic switching OFF of the
fundamental resonance mode on a time scale of 4 picoseconds (ps) followed by
the switching ON of the same resonance after 20 ps. Electric field
distributions in the metamaterials unit cell derived through numerical
simulations clearly support our experimental observations, showing that the
high electric field at the resonator gaps, responsible for inductive-capacitive
resonance (LC), completely disappears and switches OFF the resonance after
being optically excited. The ultrafast switching of the metamaterial resonance
is attributed to the generation of free carriers in ion-implanted silicon and
their recombination at an ultra-short time scale. Such silicon based active
control of metamaterials can lead to the ultrafast terahertz metadevices.
