Extreme Metaphotonics with Ultra High-Index Topological Insulators

We experimentally measure the complex dielectric constant of Bi
2
Se
3
and Bi
2
Te
3
topological insulators, revealing record high refractive index values peaking at n≈11. We further demonstrate deep-subwavelength metasurfaces with unit cell sizes smaller than λ/10, that simultaneously support large magnetic and electric field enhancements.