09 May 2011
from NatureAsia Website



A new metamaterial breaks new ground with the highest refractive index of any known substance.

Illustration of the metamaterial

consisting of ‘I’-shaped metal wires

When a light beam crosses from one medium to another, it’s path is altered by refraction according the refractive indices of the two mediums and the wavelength of light.


The refractive indices of common materials like glass and water are in the range of 1.3 to 1.5, and the values for natural materials seldom exceed 8-10.


Researchers from the Korea Advanced Institute of Science and Technology have now developed an artificial ‘metamaterial’ with a peak refractive index of more than 38 - higher than for any substance known.1

“Our work shows for the first time that such an extremely high positive index is indeed possible,” says Bumki Min, who led the research team.

Metamaterials are artificial constructs consisting of microstructures designed to interact with light in some very unusual ways.


By their nature and specificity of design, however, these microstructures are generally able to interact only with light in specific and narrow wavelength bands, and the development of metamaterials with high refractive index over a broad wavelength range remains a challenge.


The metamaterial developed by Min and his team consists of thin ‘I’-shaped metal wires separated by narrow gaps (see image above), resulting in a broadband refractive index of more than 20. More remarkably, the refractive index peaks at 38.6 at the resonance frequency of close to 0.5 THz.

Materials with such extraordinarily high refractive index could be particularly useful for imaging applications, where a higher refractive index provides better resolution.

“With this advance,” says Min, “it might be possible to build lenses that provide resolution even smaller than the wavelength of light.”

This new development expands the realm of what is achievable with regard to the refractive properties of metamaterials, which have previously been shown to be capable of negative refractive indices - an unnatural property that could lead to the development of perfect lenses and even invisibility or cloaking devices.


The latter are complex designs based on the concept of ‘transformation optics’ and typically combine a range of refractive indices in a single device design.

“If this high-index metamaterial is combined with transformation optics, the broadened index spectrum will provide more design freedom in the control of light,”



  1. Choi, M.1, Lee, S. H.1, Kim, Y.1, Kang, S. B.2, Shin, J.3, Kwak, M. H.2, Kang, K.-Y.2, Lee, Y.-H.3, Park, N.4 & Min, B.1 A terahertz metamaterial with unnaturally high refractive index. Nature 470, 369–373 (2011). | article


Author affiliation

  1. Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-751, Korea

  2. Convergence Components and Materials Research Laboratory, Electronics and Telecommunications Research Institute (ETRI), Daejeon 305-700, Korea

  3. Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-751, Korea

  4. School of Electrical Engineering and Computer Science, Seoul National University, Seoul 151-744, Korea