[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Active modulation of electromagnetically induced transparency analogue in terahertz hybrid metal-graphene metamaterials

In this paper, a dual-band perfect absorber, composed of a periodically patterned elliptical nanodisk graphene structure and a metal ground plane spaced by a thin SiO(2) dielectric layer, is proposed and investigated. Numerical results reveal that the absorption spectrum of the graphene-based structure displays two perfect absorption peaks in the terahertz band, corresponding to the absorption value of 99% at 35μm and 97%at 59μm, respectively. And the resonance frequency of the absorber can be tunned by controlling the Fermi level of graphene layer. Further more, it is insensitive to the polarization and remains very high over a wide angular range of incidence around ±60(0). Compared with the previous graphene dual-band perfect absorption, our absorber only has one shape which can greatly simplify the manufacturing process.

Dual-band tunable perfect metamaterial absorber in the THz range

We have produced ultrathin epitaxial graphite films which show remarkable 2D electron gas (2DEG) behavior. The films, composed of typically 3 graphene sheets, were grown by thermal decomposition on the (0001) surface of 6H-SiC, and characterized by surface-science techniques. The low-temperature conductance spans a range of localization regimes according to the structural state (square resistance 1.5 kOhm to 225 kOhm at 4 K, with positive magnetoconductance). Low resistance samples show characteristics of weak-localization in two dimensions, from which we estimate elastic and inelastic mean free paths. At low field, the Hall resistance is linear up to 4.5 T, which is well-explained by n-type carriers of density 10^{12} cm^{-2} per graphene sheet. The most highly-ordered sample exhibits Shubnikov - de Haas oscillations which correspond to nonlinearities observed in the Hall resistance, indicating a potential new quantum Hall system. We show that the high-mobility films can be patterned via conventional lithographic techniques, and we demonstrate modulation of the film conductance using a top-gate electrode. These key elements suggest electronic device applications based on nano-patterned epitaxial graphene (NPEG), with the potential for large-scale integration.

Ultrathin epitaxial graphite: 2D electron gas properties and a route toward graphene-based nanoelectronics

Metasurfaces, two-dimensional equivalents of metamaterials, are engineered surfaces consisting of deep subwavelength features that have full control of the electromagnetic waves. Metasurfaces are not only being applied to the current devices throughout the electromagnetic spectrum from microwave to optics but also inspiring many new thrilling applications such as programmable on-demand optics and photonics in future. In order to overcome the limits imposed by passive metasurfaces, extensive researches have been put on utilizing different materials and mechanisms to design active metasurfaces. In this paper, we review the recent progress in tunable and reconfigurable metasurfaces and metadevices through the different active materials deployed together with the different control mechanisms including electrical, thermal, optical, mechanical, and magnetic, and provide the perspective for their future development for applications.

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Tunable and reconfigurable metasurfaces and metadevices

A broadband absorber, which is composed of graphene analog of electromagnetically induced transparency (EIT) and a metal ground plane spaced by a thin SiO 2 dielectric layer, is proposed and investigated. Numerical results reveal that the working bandwidth can be dynamically tuned between broadband absorption and narrowband absorption by varying the Fermi level of graphene through controlling of the electrostatic gating. Furthermore, absorption behaviors can be tuned to the state of off when the electric polarized is rotated to another axis. It is also found that the coupling strength between the radiative element and dark element is tuned by the distance between the disconnected vertical graphene strip and horizontal graphene strip. In addition, this type of graphene-based absorber is very sensitive to the incident angles.

Dynamically Electrically Tunable Broadband Absorber Based on Graphene Analog of Electromagnetically Induced Transparency

Design of a tunable multiband terahertz waves absorber

Active control of graphene plasmon-induced transparency (GPIT) metamaterial structures, composed of periodically patterned monopolar graphene and dipolar graphene, are presented and investigated. Numerical results reveal that the resonant frequency of GPIT structures can be dynamically tuned by varying the Fermi level of the T-shape graphene strip through controlling the voltage of the electrostatic gating. Coupled Lorentz oscillator model is applied to explore the physical mechanism of the frequency tunable GPIT. Furthermore, the group index of terahertz light can be controlled to exceed 350 in the THz region. It is also found that the interaction strength between the dipolar graphene and the monopolar graphene can be tuned by changing the distance between the radiative mode and the dark mode as well as the degree of the symmetry breaking. These tunable features of the GPIT devices are significant and may offer new opportunity to design active devices in the THz region, such as ultrasensitive sensors, slow light devices, and spectral filters.

Dynamically Tunable Graphene Plasmon-Induced Transparency in the Terahertz Region

Active control of terahertz waves is critical to the development of terahertz devices. Two-dimensional materials with excellent optical properties provide more choices for opto-electrical devices due to the advancement in their preparation technology. We proposed a hybrid structure of a metamaterial/monolayer MoS2/Si and investigated its optical properties in the terahertz range. The plasmon-induced transparency (PIT) effect was observed in the transmission spectra, resulting from the near-field coupling of two bright modes. According to the simulated results, this phenomenon confirmed its dependency on the length of the cutwire and the distance between DSSRs. Furthermore, an external optical field supported by a 1064 nm laser could exert a switch effect on the sample. The resonances of the PIT metamaterial disappeared when the optical power was further increased, as the excited carriers in the MoS2/Si substrate blocked the coupling effect. In addition, the experimental results indicated that the PIT metamaterial enhanced the interaction of infrared light with the monolayer MoS2/Si substrate.

Furi Ling

Papers

Dual-band tunable perfect metamaterial absorber in the THz range

Dynamically Electrically Tunable Broadband Absorber Based on Graphene Analog of Electromagnetically Induced Transparency

Design of a tunable multiband terahertz waves absorber

Dynamically Tunable Graphene Plasmon-Induced Transparency in the Terahertz Region

Active control of terahertz plasmon-induced transparency in the hybrid metamaterial/monolayer MoS2/Si structure.