25 research outputs found
Plane-wave scattering by self-complementary metasurfaces in terms of electromagnetic duality and Babinet's principle
We investigate theoretically electromagnetic plane-wave scattering by
self-complementary metasurfaces. By using Babinet's principle extended to
metasurfaces with resistive elements, we show that the frequency-independent
transmission and reflection are realized for normal incidence of a circularly
polarized plane wave onto a self-complementary metasurface, even if there is
diffraction. Next, we consider two special classes of self-complementary
metasurfaces. We show that self-complementary metasurfaces with rotational
symmetry can act as coherent perfect absorbers, and those with translational
symmetry compatible with their self-complementarity can split the incident
power equally, even for oblique incidences
Frequency-Independent Response of Self-Complementary Checkerboard Screens
This research resolves a long-standing problem on the electromagnetic
response of self-complementary metallic screens with checkerboardlike geometry.
Although Babinet's principle implies that they show a frequency-independent
response, this unusual characteristic has not been observed yet due to the
singularities of the metallic point contacts in the checkerboard geometry. We
overcome this difficulty by replacing the point contacts with resistive sheets.
The proposed structure is prepared and characterized by terahertz time-domain
spectroscopy. It is experimentally confirmed that the resistive checkerboard
structures exhibit a flat transmission spectrum over 0.1--1.1 THz. It is also
demonstrated that self-complementarity can eliminate even the
frequency-dependent transmission characteristics of resonant metamaterials.Comment: 6 pages, 5 figures + Supplemental Material (6 pages, 7 figures
Broadband and energy-concentrating terahertz coherent perfect absorber based on a self-complementary metasurface
We demonstrate that a self-complementary checkerboard-like metasurface works
as a broadband coherent perfect absorber (CPA) when symmetrically illuminated
by two counter-propagating incident waves. A theoretical analysis based on wave
interference and results of numerical simulations of the proposed metasurface
are provided. In addition, we experimentally demonstrate the proposed CPA in
the terahertz regime by using a time-domain spectroscopy technique. We observe
that the metasurface can work as a CPA below its lowest diffraction frequency.
The size of the absorptive areas of the proposed CPA can be much smaller than
the incident wavelength. Unlike conventional CPAs, the presented one
simultaneously achieves the broadband operation and energy concentration of
electromagnetic waves at the deep-subwavelength scale.Comment: 5 pages, 4 figure
Dynamic inversion of planar-chiral response of terahertz metasurface based on critical transition of checkerboard structures
Dynamic inversion of the planar-chiral responses of a metasurface is experimentally demonstrated in the terahertz regime. To realize this inversion, the critical transition of the checkerboard-like metallic structures is used. Resonant structures with planar chirality and their complementary enantiomeric patterns are embedded in the checkerboard. Using vanadium dioxide as a variable resistance, the metasurface is implemented in the terahertz regime. The responses of the metasurface to circularly polarized waves are then characterized by terahertz time-domain spectroscopy. Further, the sign of the circular conversion dichroism, which is closely related to the handedness of the planar chirality of the metasurface, is observed to be inverted at 0.64 THz by varying the temperature. Such invertible planar-chiral responses can be applied practically to the handedness-invertible chiral mirrors
Microwave characterization of tantalum superconducting resonators on silicon substrate with niobium buffer layer
Tantalum thin films sputtered on unheated silicon substrates are
characterized with microwaves at around 10 GHz in a 10 mK environment. We show
that the phase of tantalum with a body-centered cubic lattice (-Ta) can
be grown selectively by depositing a niobium buffer layer prior to a tantalum
film. The physical properties of the films, such as superconducting transition
temperature and crystallinity, change markedly with the addition of the buffer
layer. Coplanar waveguide resonators based on the composite film exhibit
significantly enhanced internal quality factors compared with a film without
the buffer layer. The internal quality factor approaches at a
large-photon-number limit. While the quality factor decreases at the
single-photon level owing to two-level system (TLS) loss, we have identified
the primary cause of TLS loss to be the amorphous silicon layer at the
film-substrate interface, which originates from the substrate cleaning before
the film deposition rather than the film itself. The temperature dependence of
the internal quality factors shows a marked rise below 200 mK, suggesting the
presence of TLS-TLS interactions. The present low-loss tantalum films can be
deposited without substrate heating and thus have various potential
applications in superconducting quantum electronics.Comment: 6 pages, 4 figures + Supplementary Material (7 pages, 5 figures