Abstract-Ultimate terahertz field enhancement of single nanoslits

Young-Mi Bahk, Sanghoon Han, Jiyeah Rhie, Joohyun Park, Hyeongtag Jeon, Namkyoo Park, and Dai-Sik Kim

Phys. Rev. B 95, 075424

http://journals.aps.org/prb/abstract/10.1103/PhysRevB.95.075424

A single metallic slit is the simplest plasmonic structure for basic physical understanding of electromagnetic field confinement. By reducing the gap size, the field enhancement is expected to first go up and then go down when the gap width becomes subnanometer because of the quantum tunneling effects. A fundamental question is whether we reach the classical limit of field enhancement before entering the quantum regime, i.e., whether the quantum effects undercut the highest field enhancement classically possible. Here, by performing terahertz time domain spectroscopy on single slits of widths varying from 1.5 nm to 50 µm, we show that ultimate field enhancement determined by the wavelength of light and film thickness can be reached before we hit the quantum regime. Our paper paves way toward designing a quantum plasmonic system with maximum control yet without sacrificing the classical field enhancements.

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Abstract-Terahertz field enhancement in asymmetric and tapered nano-gaps

Sanghoon Han, Young-Mi Bahk, Namkyoo Park, and Dai-Sik Kim
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-3-2065

We investigate field enhancement inside metal-insulator-metal gaps with asymmetric thicknesses and tapered shapes in the terahertz regime. Finite-difference time-domain simulations were conducted for calculation of field enhancement factor. The calculation indicates that for asymmetric sample, field enhancement increases proportionally with the decrease of the thinner of the two metal film thicknesses surrounding the gap. Concomitantly, angle variation has little effect on the field enhancement if the thickness of the narrowest gap region is fixed. A model based on the capacitor concept is proposed for intuitive understanding of the phenomena.

© 2016 Optical Society of America

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Abstract-Electromagnetic Saturation of Angstrom-Sized Quantum Barriers at Terahertz Frequencies

Young-Mi Bahk, Bong Joo Kang, Yong Seung Kim, Joon-Yeon Kim, Won Tae Kim, Tae Yun Kim, Taehee Kang, Jiyeah Rhie, Sanghoon Han, Cheol-Hwan Park, Fabian Rotermund, and Dai-Sik Kim

Phys. Rev. Lett. 115, 125501 – Published 16 September 2015

http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.115.125501

Metal-graphene-metal hybrid structures allow angstrom-scale van der Waals gaps, across which electron tunneling occurs. We squeeze terahertz electromagnetic waves through these λ/10 000 000 gaps, accompanied by giant field enhancements. Unprecedented transmission reduction of 97% is achieved with the transient voltage across the gap saturating at 5 V. Electron tunneling facilitated by the transient electric field strongly modifies the gap index, starting a self-limiting process related to the barrier height. Our work enables greater interplay between classical optics and quantum tunneling, and provides optical indices to the van der Waals gaps.

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Abstract-Terahertz-triggered phase transition and hysteresis narrowing in a nanoantenna patterned vanadium dioxide film

ZACHARY J. THOMPSON, Andrew J. Stickel, YOUNG-GYUN JEONG, SANGHOON HAN, BYUNG HEE SON, MICHAEL J. PAUL, BYOUNGHWAK LEE, ALI MOUSAVIAN, GIWAN SEO, Hyun-Tak Kim, Yun-Shik Lee, and Dai-Sik Kim

Nano Lett., Just Accepted Manuscript

DOI: 10.1021/acs.nanolett.5b01970

Publication Date (Web): August 24, 2015

Copyright © 2015 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/acs.nanolett.5b01970

We demonstrate that high-field THz pulses trigger transient insulator-to-metal transition in a nanoantenna patterned vanadium dioxide thin film. THz transmission of vanadium dioxide instantaneously decreases in the presence of strong THz fields. The transient THz absorption indicates that strong THz fields induce electronic insulator-to-metal transition without causing a structural transformation. The transient phase transition is activated on the sub-cycle time scale during which the THz pulse drives the electron distribution of vanadium dioxide far from equilibrium and disturb the electron correlation. The strong THz fields lower the activation energy in the insulating phase. The THz-triggered insulator-to-metal transition gives rise to hysteresis loop narrowing, while lowering the transition temperature both for heating and cooling sequences. THz nanoantennas enhance the field-induced phase transition by intensifying the field strength and improve the detection sensitivity via antenna resonance. The experimental results demonstrate a potential that plasmonic nanostructures incorporating vanadium dioxide can be the basis for ultrafast, energy-efficient electronic and photonic devices.