Abstract-Tunnelling current-voltage characteristics of Angstrom gaps measured with terahertz time-domain spectroscopy.

Kim JY1, Kang BJ2, Bahk YM1, Kim YS3, Park J4, Kim WT2, Rhie J1, Han S1, Jeon H4,5, Park CH6, Rotermund F2, Kim DS1.

• 1Department of Physics and Astronomy and Center for Atom Scale Electromagnetism, Seoul National University, Seoul 08826, Korea.
• 2Department of Physics and Department of Energy Systems Research, Ajou University, Suwon 16499, Korea.
• 3Graphene Research Institute and Department of Physics, Sejong University, Seoul 05006, Korea.
• 4Department of Nanoscale Semiconductor Engineering and Hanyang University, Seoul 04763, Korea.
• 5Division of Materials Science and Engineering, Hanyang University, Seoul 04763, Korea.
• 6Department of Physics and Astronomy and Center for Theoretical Physics, Seoul National University, Seoul 08826, Korea.
• http://www.ncbi.nlm.nih.gov/pubmed/27357346

Quantum tunnelling becomes inevitable as gap dimensions in metal structures approach the atomic length scale, and light passing through these gaps can be used to examine the quantum processes at optical frequencies. Here, we report on the measurement of the tunnelling current through a 3-Å-wide metal-graphene-metal gap using terahertz time-domain spectroscopy. By analysing the waveforms of the incident and transmitted terahertz pulses, we obtain the tunnelling resistivity and the time evolution of the induced current and electric fields in the gap and show that the ratio of the applied voltage to the tunnelling current is constant, i.e., the gap shows ohmic behaviour for the strength of the incident electric field up to 30 kV/cm. We further show that our method can be extended and applied to different types of nanogap tunnel junctions using suitable equivalent RLC circuits for the corresponding structures by taking an array of ring-shaped nanoslots as an example.