Fig. 4
From: Hyperbolic metamaterials: fusing artificial structures to natural 2D materials
a Adapted with permission from ref. [27], copyright 2019, NPG. b Adapted with permission from ref. [26], copyright 2008, AAAS. c, d Adapted with permission from ref. [109], copyright 2013, AIP. e, f Adapted with permission from ref. [61], copyright 2015, NPG. g, h Adapted with permission from ref. [110], copyright 2012, NAS. i Adapted with permission from ref. [111], copyright 2007, NPG
Negative refraction using HMMs. a 2D isofrequency contours of HMM (blue) and air (red). Yellow arrows represent the wave vectors in air (\(\text {A}_{{1}}\)) and HMM (\(\text {B}_{{1}}\)), and green arrows represent Poynting vectors in air (\(\text {A}_{{2}}\)) and HMM (\(\text {B}_{{2}}\)). b Negative refraction in bulk HMMs composed of Ag NW structures at visible frequencies. c Real part of the mode index of a HMS composed of Ag gratings at wavelengths of 500 nm, 543 nm and 633 nm. d Negative refraction of surface plasmons at \(\lambda \) = 458 nm. The surface plasmons propagate from a flat Ag-air interface to a HMS. e Angle of refraction according to the wavelength at a flat Ag/HMS interface. Blue-shaded areas indicate the hyperbolic dispersion. f Measured refraction of SPPs at the interface; dashed lines denote the location of the HMSs. g Real and imaginary parts of the effective permittivity of a HMM composed of aluminum-doped zinc oxide (AZO) and zinc oxide (ZnO) films in the plane parallel and perpendicular to the layers. h Observation of negative refraction by the measurement of relative transmittance. i Negative refraction using multilayers of semiconductors in the far-infrared region.