Hyeong-Ryeol Park

Unusual performances of metamaterials such as negative index of refraction, memory effect, and cloaking originate from the resonance features of the metallic composite atom(1-6). Indeed, control of metamaterial properties by changing dielectric environments of thin films below the metallic resonators has been demonstrated(7-11). However, the dynamic control ranges are still limited to less than a factor of 10,(7-11) with the applicable bandwidth defined by the sharp resonance features. Here, we

Molecules have extremely small absorption cross sections in the terahertz range even under resonant conditions, which severely limit their detectability, often requiring tens of milligrams. We demonstrate that nanoantennas tailored for the terahertz range resolves the small molecular cross section problem. The extremely asymmetric electromagnetic environment inside the slot antenna, which finds the electric field being enhanced by thousand times with the magnetic field changed little, forces the

Abstract The terahertz (THz) spectrum is the focus of basic research in solid‐state physics, chemistry, and materials science as well as applications in next‐generation communications, far‐infrared bolometer, bio/chemical‐sensing, and medical imaging. This wavelength range is at the intersection between photonics and electronics, presenting tremendous opportunities to boost fundamental light–matter interactions enabled by plasmonic nanostructures, metamaterials, and inherent molecular vibrationa

Utilizing highly oriented multiwalled carbon nanotube aerogel sheets, we fabricated micrometer-thick freestanding carbon nanotube (CNT) polarizers. Simple winding of nanotube sheets on a U-shaped polyethylene reel enabled rapid and reliable polarizer fabrication, bypassing lithography or chemical etching processes. With the remarkable extinction ratio reaching ∼37 dB in the broad spectral range from 0.1 to 2.0 THz, combined with the extraordinary gravimetric mechanical strength of CNTs, and the

We experimentally show that terahertz (THz) waves confined in sub-10 nm metallic gaps can detect refractive index changes caused by only a 1 nm thick (∼λ/10 6 ) dielectric overlayer. We use atomic layer lithography to fabricate a wafer-scale array of annular nanogaps. Using THz time-domain spectroscopy in conjunction with atomic layer deposition, we measure spectral shifts of a THz resonance peak with increasing Al 2 O 3 film thickness in 1 nm intervals. Because of the enormous mismatch in lengt

Abstract Although numerous natural materials exhibit chiral optical phenomena, they are typically very weak. Chiral nanophotonic structures can significantly enhance the chiroptical responses and provide unprecedented design flexibility. However, achieving extreme chirality that approaches the ultimate theoretical limit remains challenging. Here, chiral quasibound states in the continuum are realized in the visible range, and maximally chiral emission from a perovskite metasurface is demonstrate

. Large-area high-density 20 nm-gap rectangular loop structures, containing a resonant frequency in the terahertz range, were fabricated on a 4-inch wafer using atomic layer lithography. When target viruses with a 60 nm diameter were located on the nanogaps, we observed a significant redshift of the resonant peak already with an average number of about 100 viruses per unit loop due to the strong field confinement and enhancement near the gap. Furthermore, when the virus was tightly attached to a

Nanoscale metallic barriers embedded in terahertz (THz) slot antennas are shown to provide unprecedented control of the transition state arising at the crossover between the full- and half-wavelength resonant modes of such antennas. We demonstrate strong near-field coupling between two paired THz slot antennas separated by a 5 nm wide nanobarrier, almost fully inducing the shift to the resonance of the double-length slot antenna. This increases by a factor of 50 the length-scale needed to observ

High carrier mobility and tunability in graphene enable fundamental studies for plasmonics and various applications. Despite its versatility, however, single‐layer graphene (SLG) suffers from poor coupling efficiency to electromagnetic waves, presenting a major challenge for photonic applications. Compared with visible or infrared radiation, terahertz (THz) waves exhibit higher absorption in SLG due to Drude‐like intraband transitions, but the wavelength‐to‐SLG size mismatch becomes even more dr

Abstract Recent technological advances in fabrication methods have allowed researchers to manipulate light–matter interactions in the subwavelength region and develop a wide variety of innovative optical applications from the visible to the microwave region. Metal patterning at a subwavelength scale plays a crucial role in realizing these optical applications. Various standard lithography techniques including laser beam machining, focused ion beam, photolithography, and electron‐beam lithography

Nanoconfined waters exhibit low static permittivity mainly due to interfacial effects that span about one nanometer. The characteristic length scale may be much longer in the terahertz (THz) regime where long-range collective dynamics occur; however, the THz dynamics have been largely unexplored because of the lack of a robust platform. Here, we use metallic loop nanogaps to sharply enhance light-matter interactions and precisely measure real and imaginary THz refractive indices of nanoconfined

A pinch harmonic (or guitar harmonic) is a musical note produced by lightly pressing the thumb of the picking hand upon the string immediately after it is picked [J. Chem. Educ. 84, 1287 (2007)]. This technique turns off the fundamental and all overtones except those with a node at that location. Here we present a terahertz analogue of pinch harmonics, whereby a metallic nano rod placed at a harmonic node on a terahertz nanoresonator suppresses the fundamental mode, making the higher harmonics d

The rapid development of 6G communications using terahertz (THz) electromagnetic waves has created a demand for highly sensitive THz nanoresonators capable of detecting these waves. Among the potential candidates, THz nanogap loop arrays show promising characteristics but require significant computational resources for accurate simulation. This requirement arises because their unit cells are 10 times smaller than millimeter wavelengths, with nanogap regions that are 1 000 000 times smaller. To a

We have investigated the extraordinary optical transmission of terahertz waves through an array of nanogaps with varying dimensions and periodicities, and used this platform to demonstrate terahertz sensing of a thin film of single-walled carbon nanotubes. We have used atomic layer lithography to fabricate periodic arrays of nanogap loops that have a gap size of 2 nm and a loop length of 100 μm (aspect ratio of 50,000). These sub-mm-scale loops of nanogaps can sustain terahertz electromagnetic r