Effect of metal permittivity on resonant properties of terahertz metamaterials

School of Electrical and Computer Engineering, Oklahoma State University, Stillwater, Oklahoma 74078, USA.
Optics Letters (Impact Factor: 3.29). 08/2008; 33(13):1506-8. DOI: 10.1364/OL.33.001506
Source: PubMed


We investigate the effect of metal permittivity on resonant transmission of metamaterials by terahertz time-domain spectroscopy. Our experimental results on double split-ring resonators made from different metals confirm the recent numerical simulations [Phys. Rev. E 65, 036622 (2002)] that metamaterials exhibit permittivity-dependent resonant properties. In the terahertz regime, the measured inductive-capacitive resonance is found to strengthen with a higher ratio of the real to the imaginary parts of metal permittivity, and this remains consistent at various metal thicknesses. Furthermore, we found that metamaterials made even from a generally poor metal become highly resonant owing to a drastic increase in the value of the permittivity at terahertz frequencies.

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    • "It has been shown that metal conductivity as well as thickness can affect metamaterial resonance [25] [26], though such tunability is through design and fabrication. Noble metals are still the choice for fabricating metamaterial structures because of their high conductivity, which, however, makes the resonance tuning rely on the integration of additional materials able to respond to external stimuli. "
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    ABSTRACT: Through the integration of semiconductors or complex oxides into metal resonators, tunable metamaterials have been achieved by a change of environment using an external stimulus. Metals provide high conductivity to realize a strong resonant response in metamaterials; however, they contribute very little to the tunability. The complex conductivity in high-temperature superconducting films is highly sensitive to external perturbations, which provides new opportunities in achieving tunable metamaterials resulting directly from the resonant elements. Here we demonstrate ultrafast dynamical tuning of resonance in the terahertz (THz) frequency range in YBa_2Cu_3O_7-\delta (YBCO) split-ring resonator arrays excited by near-infrared femtosecond laser pulses. The photoexcitation breaks the superconducting Cooper pairs to create the quasiparticle state. This dramatically modifies the imaginary part of the complex conductivity and consequently the metamaterial resonance in an ultrafast timescale. We observed resonance switching accompanied with a wide range frequency tuning as a function of photoexcitation fluence, which also strongly depend on the nano-scale thickness of the superconducting films. All of our experimental results are well reproduced through calculations using an analytical model, which takes into account the SRR resistance and kinetic inductance contributed from the complex conductivity of YBCO films. The theoretical calculations reveal that the increasing SRR resistance upon increasing photoexcitation fluence is responsible for the reduction of resonance strength, and both the resistance and kinetic inductance contribute to the tuning of resonance frequency.
    11/2011; 1(1). DOI:10.1515/nanoph-2012-0007
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    • "The incident angle is fixed at . The Drude permittivity of metals at terahertz frequencies can be approximated by [10], where is the dc conductivity, is the damping rate and is the vacuum permittivity. Here we have assumed S/m and s , which are typical values for silver [11]. "
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    ABSTRACT: Enhanced transmission through metallic gratings with narrow slits is a well-known phenomenon for TM polarized waves at optical and microwave frequencies. A similar though fundamentally different phenomenon, i.e., enhanced reflection at terahertz frequencies, is reported here for the geometrical complement of the structure with narrow slits. The latter phenom- enon cannot be related to the former by Babinet's principle, as their origin is quite different, and both are observed for the same polarization. This phenomenon is explored by studying the field profiles within the grating, and is attributed to the presence of TM cavity modes at specific frequencies. A simple formula is given to anticipate the frequencies at which the anomalies appear. The accuracy of this formula is verified by using a rigorous numerical approach. Index Terms—Metallic grating, enhanced reflection, enhanced transmission.
    IEEE Transactions on Terahertz Science and Technology 11/2011; 1(2):435-440. DOI:10.1109/TTHZ.2011.2162898 · 2.18 Impact Factor
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    ABSTRACT: As the variation of temperature alters the intrinsic carrier density in a semiconductor, numerical simulations indicate that the consequent variation of the relative permittivity in the terahertz regime provides a way to realize thermally tunable split-ring resonators. Electromagnetic metasurfaces and metamaterials that are thermally tunable in the terahertz regime can thus be implemented. Comment: 9 pages
    Journal of Modern Optics 08/2008; 56(4). DOI:10.1080/09500340802621785 · 1.01 Impact Factor
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