Terahertz Funneling-Induced Quantum Tunneling at Angstrom Scale

We demonstrate electron tunneling-induced colossal nonlinear response of vertically oriented angstrom-metallic gaps by irradiation with intense terahertz pulses. We also investigate the sub-picosecond time evolution of the induced tunneling current extracted from the transmission measurement of light passing through the metallic gap. Our technology of angstrom gap lithography enlarges the boundary of quantum plasmonics down to terahertz frequencies, enabling both linear and nonlinear angstrom optics in a broad spectrum domain. Also, our method has a huge potential of merging the knowledge of conventional dc electronic transport measurements and the study of ultrafast dynamics and nonlinear terahertz spectroscopy.