Abstract
Controlling the electromagnetic properties of materials, going beyond the limit that is attainable with naturally existing substances, has become a reality with the advent of metamaterials1,2,3. The range of various structured artificial ‘atoms’ has promised a vast variety of otherwise unexpected physical phenomena3,4,5,6,7,8,9,10,11,12,13,14,15,16,17, among which the experimental realization of a negative refractive index has been one of the main foci thus far. Expanding the refractive index into a high positive regime will complete the spectrum of achievable refractive index and provide more design flexibility for transformation optics9,10,11,12,13,14. Naturally existing transparent materials possess small positive indices of refraction, except for a few semiconductors and insulators, such as lead sulphide or strontium titanate, that exhibit a rather high peak refractive index at mid- and far-infrared frequencies18. Previous approaches using metamaterials were not successful in realizing broadband high refractive indices19,20,21. A broadband high-refractive-index metamaterial structure was theoretically investigated only recently22, but the proposed structure does not lend itself to easy implementation. Here we demonstrate that a broadband, extremely high index of refraction can be realized from large-area, free-standing, flexible terahertz metamaterials composed of strongly coupled unit cells. By drastically increasing the effective permittivity through strong capacitive coupling and decreasing the diamagnetic response with a thin metallic structure in the unit cell, a peak refractive index of 38.6 along with a low-frequency quasi-static value of over 20 were experimentally realized for a single-layer terahertz metamaterial, while maintaining low losses. As a natural extension of these single-layer metamaterials, we fabricated quasi-three-dimensional high-refractive-index metamaterials, and obtained a maximum bulk refractive index of 33.2 along with a value of around 8 at the quasi-static limit.
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References
Veselago, V. G. The electrodynamics of substances with simultaneously negative values of ε and μ. Sov. Phys. Usp. 10, 509–514 (1968)
Pendry, J. B., Holden, A. J., Robbins, D. J. & Stewart, W. J. Magnetism from conductors and enhanced nonlinear phenomena. IEEE Trans. Microwave Theory Tech. 47, 2075–2084 (1999)
Smith, D. R., Padilla, J. W., Vier, D. C., Nemat-Nasser, S. C. & Schultz, S. Composite medium with simultaneously negative permeability and permittivity. Phys. Rev. Lett. 84, 4184–4187 (2000)
Shelby, R. A., Smith, D. R. & Schultz, S. Experimental verification of a negative index of refraction. Science 292, 77–79 (2001)
Eleftheriades, G. V., Iyer, A. K. & Kremer, P. C. Planar negative refractive index media using periodically L–C loaded transmission lines. IEEE Trans. Microwave Theory Tech. 50, 2702–2712 (2002)
Xiao, S. et al. Loss-free and active optical negative-index metamaterials. Nature 466, 735–738 (2010)
Valentine, J. et al. Three-dimensional optical metamaterial with a negative refractive index. Nature 455, 376–379 (2008)
Zhang, S. et al. Negative refractive index in chiral metamaterials. Phys. Rev. Lett. 102, 023901 (2009)
Pendry, J. B., Schrurig, D. E. & Smith, D. R. Controlling electromagnetic fields. Science 312, 1780–1782 (2006)
Schurig, D. et al. Metamaterial electromagnetic cloak at microwave frequencies. Science 314, 977–980 (2006)
Cai, W. S., Chettiar, U. K., Kildishev, A. V. & Shalaev, V. M. Optical cloaking with metamaterials. Nature Photon. 1, 224–227 (2007)
Liu, R. et al. Broadband ground-plane cloak. Science 323, 366–369 (2009)
Valentine, J., Li, J. S., Zentgraf, T., Bartal, G. & Zhang, X. An optical cloak made of dielectrics. Nature Mater. 8, 568–571 (2009)
Gabrielli, L. H., Cardenas, J., Poitras, C. B. & Lipson, M. Silicon nanostructure cloak operating at optical frequencies. Nature Photon. 3, 461–463 (2009)
Pendry, J. B. Negative refraction makes a perfect lens. Phys. Rev. Lett. 85, 3966–3969 (2000)
Liu, Z., Lee, H., Xiong, Y., Sun, C. & Zhang, X. Far-field optical hyperlens magnifying sub-diffraction-limited objects. Science 315, 1686 (2007)
Smolyaninov, I. I., Hung, Y. J. & Davis, C. C. Magnifying superlens in the visible frequency range. Science 315, 1699–1701 (2007)
Palik, E. D. Handbook of Optical Constants of Solids (Academic, 1998)
Enkrich, C. et al. Magnetic metamaterials at telecommunication and visible frequencies. Phys. Rev. Lett. 95, 203901 (2005)
Sievenpiper, D. F. et al. 3D metallo-dielectric photonic crystals with strong capacitive coupling between metallic islands. Phys. Rev. Lett. 80, 2829–2832 (1998)
Shen, J. T., Catrysse, P. B. & Fan, S. Mechanism for designing metallic metamaterials with a high index of refraction. Phys. Rev. Lett. 94, 197401 (2005)
Shin, J., Shen, J. T. & Fan, S. Three-dimensional metamaterials with an ultrahigh effective refractive index over a broad bandwidth. Phys. Rev. Lett. 102, 093903 (2009)
Smith, D. R., Vier, D. C., Koschny & Soukoulis, C. M. Electromagnetic parameter retrieval from inhomogeneous metamaterials. Phys. Rev. E 71, 036617 (2005)
Tao, H. et al. Terahertz metamaterials on free-standing highly-flexible polyimide substrates. J. Phys. D Appl. Phys. 41, 232004 (2008)
Liu, R., Cui, T. J., Huang, D., Zhao, B. & Smith, D. R. Description and explanation of electromagnetic behaviors in artificial metamaterials based on effective medium theory. Phys. Rev. E 76, 026606 (2007)
Ferguson, B. & Zhang, X. C. Materials for terahertz science and technology. Nature Mater. 1, 26–33 (2002)
Duvillaret, L., Garet, F. & Coutaz, J. L. A reliable method for extraction of material parameters in terahertz time-domain spectroscopy. IEEE J. Sel. Top. Quantum Electron. 2, 739–746 (1996)
Liu, N. & Giessen, H. Three-dimensional optical metamaterials as model systems for longitudinal and transverse magnetic coupling. Opt. Express 16, 21233–21238 (2008)
Papasimakis, N. et al. Metamaterial analog of electromagnetically induced transparency. Phys. Rev. Lett. 101, 253903 (2008)
Seo, M. A. et al. Terahertz field enhancement by a metallic nano slit operating beyond the skin-depth limit. Nature Photon. 3, 152–156 (2009)
Chen, X., Grzegorczyk, T. M., Wu, B.-I., Pacheco, J. & Kong, J. A. Robust method to retrieve the constitutive effective parameters of metamaterials. Phys. Rev. E 70, 016608 (2004)
Acknowledgements
We thank B. Kang for help in the fabrication of micrometre-gap metamaterials, J. S. Chang for proofreading the manuscript before submission, and D. S. Kim for discussions. This work was supported by National Research Foundation of Korea grants funded by the Korean government (numbers 2009-0069459, 2008-0062235 and 2010-0012058). K.-Y.K. acknowledges support by the IT Research and Development programme of MKE/KEIT (number 2006-S-005-04). Y.-H.L. acknowledges support from the National Research Foundation of Korea (number 2007-0093863) and N.P. acknowledges support from National Research Foundation (numbers GRL K20815000003 and 2010-0001859), funded by the Korean government.
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M.C. and Y.K. performed the numerical simulations. S.H.L. fabricated micro/nano-gap metamaterial samples. S.B.K., M.H.K. and K.-Y.K. conducted THz-TDs experiments. M.C., S.H.L., Y.K., J.S. and B.M. analysed numerical and experimental data. M.C., S.H.L., Y.K., J.S., Y.-H.L., N.P. and B.M. discussed the results. M.C., J.S., Y.-H.L., N.P. and B.M. wrote the manuscript. B.M. led the overall direction of the project.
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The file contains Supplementary Text and Data 1-8, Supplementary Figures 1-8 with legends and additional references. (PDF 1815 kb)
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Choi, M., Lee, S., Kim, Y. et al. A terahertz metamaterial with unnaturally high refractive index. Nature 470, 369–373 (2011). https://doi.org/10.1038/nature09776
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DOI: https://doi.org/10.1038/nature09776
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