Terahertz Plasmonic Field-Induced Conductivity Modulation in Gold

We report the observation of terahertz (THz) electric field induced conductivity modulation in sub-wavelength gold plasmonic media. Through all-THz pump-probe time-resolved transmission spectroscopy, we demonstrate that the presence of induced surface charges influences near-field mediated light propagation. The phenomenon is ascribed to the enhanced metal conductivity due to enhanced surface density of conduction electrons. The surface induced charge dynamics are revealed via phase-dependent time-resolved signatures. The phenomenon is a prelude to a wide class of ultrafast active THz plasmonic devices and paves the way for plasmonic field effects devices, similar to semiconductor ones.