Colossal Terahertz Nonlinearity in Angstrom- and Nanometer-Sized Gaps

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• 作者：Sanghoon Han ; Joon-Yeon Kim ; Taehee Kang ; Young-Mi Bahk ; Jiyeah Rhie ; Bong Joo Kang ; Yong Seung Kim ; Joohyun Park ; Won Tae Kim ; Hyeongtag Jeon ; Fabian Rotermund ; Dai-Sik Kim
• 刊名：ACS Photonics
• 出版年：2016
• 出版时间：August 17, 2016
• 年：2016
• 卷：3
• 期：8
• 页码：1440-1445
• 全文大小：495K
• 年卷期：0
• ISSN：2330-4022

文摘

We investigated optical nonlinearity induced by electron tunneling through an insulating vertical gap between metals, both at terahertz frequency and at near-infrared frequency. We adopted graphene and alumina layers as gap materials to form gap widths of 3 Å and 1.5 nm, respectively. Transmission measurements show that tunneling-induced transmittance changes from strong fields at the gaps can be observed with relatively weak incident fields at terahertz frequency due to high field enhancement, whereas nonlinearity at the near-infrared frequency is restricted by laser-induced metal damages. Even when the same level of tunneling currents occurs at both frequencies, transmittance in the terahertz regime decreases much faster than that in the near-infrared regime. An equivalent circuit model regarding the tunneling as a resistance component reveals that strong terahertz nonlinearity is due to much smaller displacement currents relative to tunneling currents, also explaining small nonlinearity of the near-infrared regime with orders of magnitude larger displacement currents.