A terahertz metamaterial with unnaturally high refractive index

• Published in: Nature (London) 2011-02, Vol.470 (7334), p.369-373
• Main Authors: Choi, Muhan, Lee, Seung Hoon, Kim, Yushin, Kang, Seung Beom, Shin, Jonghwa, Kwak, Min Hwan, Kang, Kwang-Young, Lee, Yong-Hee, Park, Namkyoo, Min, Bumki
• Format: Article
• Language: English
• Subjects: 639/301/1019/1015; 639/766/400/561; Behavior; Comparative analysis; Etching; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Humanities and Social Sciences; letter; Magnetic fields; Materials; Measurement; Methods; multidisciplinary; Optical materials; Optical properties; Optics; Permeability; Photonic bandgap materials; Physics; R&D; Refractive index; Research & development; Science; Science (multidisciplinary); Strontium; Sulfides
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature09776

Refractive index of 30-plus in new metamaterial Metamaterials, artificially designed composites with electromagnetic properties unobtainable in the natural world, are providing new opportunities for fundamental research as well as for useful applications. So far, the search for materials with a negative refractive index has been a priority, but to extend the scope for novel 'transformation optics' applications, materials with an unnaturally high refractive index would be similarly useful. Bumki Min and colleagues have now produced a broadband, flexible terahertz metamaterial with an unprecedentedly high refractive index of 38.6. Based on layered arrays of I-shaped thin gold building blocks, the new metamaterial provides a starting point for work on small-footprint cloaking devices, wide-angle lenses and slow-light devices. In the area of metamaterials it is shown that electromagnetic properties can be achieved that are not attainable with natural materials. The main research efforts have been directed towards experimentally realizing materials with negative refractive index, but to extend the potential and design flexibility for novel 'transformation optics' applications, it is of considerable interest to produce a material with unnaturally high refractive index. A broadband, flexible terahertz metamaterial with unprecedented high refractive index, reaching a value of 38.6, is now demonstrated. 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 metamaterials 1 , 2 , 3 . The range of various structured artificial ‘atoms’ has promised a vast variety of otherwise unexpected physical phenomena 3 , 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 optics 9 , 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 frequencies 18 . Previous approaches using metamaterials were not successful in realizing broadband high refractive i