Broadband Negative Refraction of Highly Squeezed Hyperbolic Polaritons in 2D Materials
All-angle negative refraction of highly squeezed polaritons supported by hyperbolic metasurfaces. (a) Structural schematic. The hyperbolic metasurfaces can be created by anisotropic 2D materials (such as black phosphorous) or nanostructured 2D materials (such as graphene nanoribbon array here). (b) Isofrequency contours of hyperbolic graphene plasmons, supported by metasurfaces in left/right regions in (a). The dashed grey line represents the condition for conservation of wave vectors parallel to the boundary. The arrows represent the directions of group velocity, indicating that for polaritons in the left region incident with arbitrary angle, negative refraction can happen at the boundary. (c) Distribution of electric field excited by a dipole source. The red dashed line represents the boundary between left/right regions. Here, and in Figures 2 and 3, the nanostructured graphene has a conservative electron mobility of 10000 cm2V−1s−1, a pitch of nm, and a width of nm. The chemical potential of graphene is 0.1 eV. The working frequency is 15 THz.