Negative refraction of ultra-squeezed in-plane hyperbolic designer polaritons
Qiaolu Chen, Yihao Yang, Li Zhang, Jialin Chen, Min Li, Xiao Lin, Rujiang Li, Zuojia Wang, Baile Zhang, Hongsheng Chen
Abstract
The in-plane negative refraction of high-momentum (i.e., high- <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m1"> <mml:mrow> <mml:mi>k</mml:mi> </mml:mrow> </mml:math> ) photonic modes could enable many applications such as imaging, focusing, and waveguiding in a planar platform at deep-subwavelength scales. However, its practical implementation in experiments remains elusive so far. Here we propose a class of hyperbolic metasurfaces, which is characterized by an anisotropic magnetic sheet conductivity and can support the in-plane ultra-high- <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m2"> <mml:mrow> <mml:mi>k</mml:mi> </mml:mrow> </mml:math> magnetic designer polaritons. Based on such metasurfaces, we report the experimental observation of the all-angle negative refraction of designer polaritons at extremely deep-subwavelength scales. Moreover, we directly visualize the designer polaritons with hyperbolic dispersions. Importantly, for these hyperbolic polaritons, we find that their squeezing factor is ultra-large. To be specific, it can be up to 129 in the experiments, an ultra-high value exceeding those in naturally hyperbolic materials. This work may pave a way toward exploring the extremely high confinement and unusual propagation of magnetic designer polaritons over monolayer or twisted bilayer hyperbolic metasurfaces.