Tuning the resonance in high-temperature superconducting terahertz metamaterials.
ABSTRACT In this Letter, we present resonance properties in terahertz metamaterials consisting of a split-ring resonator array made from high-temperature superconducting films. By varying the temperature, we observe efficient metamaterial resonance switching and frequency tuning. The results are well reproduced by numerical simulations of metamaterial resonance using the experimentally measured complex conductivity of the superconducting film. We develop a theoretical model that explains the tuning features, which takes into account the resistive resonance damping and additional split-ring inductance contributed from both the real and imaginary parts of the temperature-dependent complex conductivity. The theoretical model further predicts more efficient resonance tuning in metamaterials consisting of a thinner superconducting split-ring resonator array, which are also verified in subsequent experiments.
Full-textDOI: · Available from: Quanxi Jia, Dec 20, 2013
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ABSTRACT: We present a complementary THz metasurface realised with Niobium thin film which displays a quality factor Q = 54 and a fully switchable behaviour as a function of the temperature. The switching behaviour and the high quality factor are due to a careful design of the metasurface aimed at maximising the ohmic losses when the Nb is above the critical temperature and minimising the radiative coupling. The superconductor allows the operation of the cavity with high Q and the use of inductive elements with a high aspect ratio. Comparison with three dimensional finite element simulations highlights the crucial role of the inductive elements and of the kinetic inductance of the Cooper pairs in achieving the high quality factor and the high field enhancement. (C) 2014 AIP Publishing LLC.Applied Physics Letters 11/2014; 105(26). DOI:10.1063/1.4905199 · 3.52 Impact Factor
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ABSTRACT: We demonstrate an all-optical terahertz modulator based on single-layer graphene on germanium (GOG), which can be driven by a 1.55 μm CW laser with a low-level photodoping power. Both the static and dynamic THz transmission modulation experiments were carried out. A spectrally wide-band modulation of the THz transmission is obtained in a frequency range from 0.25 to 1 THz, and a modulation depth of 94% can be achieved if proper pump power is applied. The modulation speed of the modulator was measured to be ~200 KHz using a 340 GHz carrier. A theoretical model is proposed for the modulator and the calculation results indicate that the enhanced THz modulation is mainly due to the third order nonlinear effect in the optical conductivity of the graphene monolayer.Scientific Reports 12/2014; 4:7409. DOI:10.1038/srep07409 · 5.08 Impact Factor
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ABSTRACT: In this paper, a point has been proposed that coupling current exist in terahertz devices, especially some typical structures, such as split ring resonators. Gaps are no longer treated as capacitances are not exact. By varying the width of gap, a kind of relationship between coupling ratio and gap's width has been made. And it has been testified to be approximately suitable in some other structures. Equivalent electrical length has been brought in to explain how the currents with the same orient cause resonance, of which fabricate a frequency band, via S parameter. Our work may open another method to explain electromagnetic wave resonating in metal structure.2013 IEEE International Conference on Applied Superconductivity and Electromagnetic Devices (ASEMD); 10/2013