Natural Hyperbolicity of Hexagonal Boron Nitride in the Deep Ultraviolet
Abstract
Hyperbolic media enable unique optical phenomena including hyperlensing, negative refraction, enhanced photonic density of states (PDOS), and highly confined polaritons. While most hyperbolic media are artificially engineered metamaterials, certain natural materials with extreme anisotropy can exhibit hyperbolic dispersion. Here, we report the first observation of natural hyperbolic dispersion in hexagonal boron nitride (hBN) in the deep-ultraviolet (DUV) regime, induced by strong, anisotropic exciton resonances. Using imaging spectroscopic ellipsometry (ISE), we characterize the complex dielectric function along in-plane and out-of-plane directions down to 190 nm (6.53 eV), revealing a type-II hyperbolic window in the DUV regime. This hyperbolicity supports hyperbolic exciton polaritons (HEP) with high directionality and slow group velocity. Our findings establish hBN as a promising platform for nanophotonic applications in the technologically significant DUV spectral range.
Keywords
Cite
@article{arxiv.2507.13271,
title = {Natural Hyperbolicity of Hexagonal Boron Nitride in the Deep Ultraviolet},
author = {Bongjun Choi and Jason Lynch and Wangleong Chen and Seong-Joon Jeon and Hyungseob Cho and Kyungmin Yang and Jonghwan Kim and Nader Engheta and Deep Jariwala},
journal= {arXiv preprint arXiv:2507.13271},
year = {2025}
}
Comments
16 pages, 4 figures (main manuscript)