Polarization-independent metamaterial with broad ultrahigh refractive index in Terahertz region

In this article, we report a broadband, isotropic threedimensional metamaterial design with extremely high refractive index in the terahertz region. Two peaks of refractive index, 67.9 at 2.14 THz and 66.9 at 2.16 THz, are observed under TE and TM mode polarizations, respectively. The high refractive index metamaterial maintains low loss with figure of merit as high as 15 under both polarizations. Moreover, the refractive index does not decrease sharply at higher frequencies, and shows a very broadband behavior with a fullwidth at half-maximum (FWHM) of 2 THz.