We take advantage of the recent advances in terahertz-nano technology to study quantum scale light-matter interaction. Terahertz waves can be squeezed down to extreme aspect ratio nanogaps which are composed of metal-insulator-metal barriers. Noble metals such as gold or silver can serve as good conductors at this terahertz frequencies, and the electric field intensity inside the metallic nanogaps can be orders of magnitudes larger than the incident one. Cross sections of molecules can be hugely enhanced and the probing depth decrease dramatically. As the gap size decreases down to the nanometer regime, quantum mechanical effects such as electron tunneling across the nanogaps are almost inevitable, rendering different dielectric constants to the gap material than that without tunneling. These efforts originated from the nearly perfect transmission through terahertz slot antennas with tens of microns of feature sizes, together with its nanometer-sized counterparts.
In this work, we will discuss our recent results of extreme terahertz phenomena on plasmonic nanoantenna structures. On the one hand, we demonstrate ultrafast control of tunneling currents using macroscopic loops of terahertz antenna. Light-field induced surface currents projects upon the barrier loops fabricated on a metallic film, spatiotemporally changing the local electric potentials. The total tunneling currents flowing through the loops are critically affected by the symmetry of the loop, enabling ultrafast full-wave rectification of electromagnetic waves in sub-picosecond scale. On the other hand, we demonstrate our terahertz nanoresonator can support nearly up to 70 % absorption of incident terahertz radiation by direct Ohmic loss in metal at this long wavelength limit, breaking the good conductor approximation which is generally considered in terahertz frequency.