Abstract-Terahertz rectification in ring-shaped quantum barriers

Taehee Kang, R. H. Joon-Yeon Kim, Geunchang Choi, Jaiu Lee, Hyunwoo Park, Hyeongtag Jeon, Cheol-Hwan Park, Dai-Sik Kim, 

https://www.nature.com/articles/s41467-018-07365-w

Tunneling is the most fundamental quantum mechanical phenomenon with wide-ranging applications. Matter waves such as electrons in solids can tunnel through a one-dimensional potential barrier, e.g. an insulating layer sandwiched between conductors. A general approach to control tunneling currents is to apply voltage across the barrier. Here, we form closed loops of tunneling barriers exposed to external optical control to manipulate ultrafast tunneling electrons. Eddy currents induced by incoming electromagnetic pulses project upon the ring, spatiotemporally changing the local potential. The total tunneling current which is determined by the sum of contributions from all the parts along the perimeter is critically dependent upon the symmetry of the loop and the polarization of the incident fields, enabling full-wave rectification of terahertz pulses. By introducing global geometry and local operation to current-driven circuitry, our work provides a novel platform for ultrafast optoelectronics, macroscopic quantum phenomena, energy harvesting, and multi-functional quantum devices.

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.

• 
• 
• 
•