Metamaterials are man-made composite structures whose electromagnetic response is tailored to design specifications. To attain such control over the material’s properties, researchers integrate conducting components into these structures to act as resonators. Hundreds of research groups around the world currently work on the study, design, and implementation of metamaterials. Despite such tremendous efforts, however, there are virtually no real-life practical implementations of these artificial structures yet. The main limiting factor in the path toward applications has been that the metallic resonators lose energy owing to radiation and Joule losses. These losses may be reduced by proper arrangement of the resonators in a periodic pattern. There are also other approaches for overcoming losses—for example, compensating energy dissipation by introducing gain into the system, either by using an active medium or utilizing parametric gain.
The approach adopted by Fedotov et. al. in this work is to use high-temperature superconductors instead of metals to suppress the losses of electromagnetic energy to heat, since superconductors have vanishing resistivity below their critical temperature. They created an array of asymmetric resonators operating at millimeter wave frequencies. This structure is known to exhibit a resonance with asymmetric shape, which is called Fano resonance. Such sharp resonance may be useful for applications requiring a narrow passband or steep dispersion characteristics, including slow light and enhanced nonlinear interactions.
The novelty of presented results is manyfold. The authors manufactured the first metamaterial made of high-temperature superconductors, and this should stimulate future work in this direction. The paper also includes the results of the first measurements of large-area superconducting metamaterials in the free-space wave-scattering configuration. Moreover, the change of the resistivity of the YBCO films with temperature allows for a great control over the material response. The authors studied two complementary structures and showed that they both demonstrate significant variation of the transmission properties in a large frequency range and in particular near the Fano resonance frequency.
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