Low-loss hyperbolic dispersion and anisotropic plasmonic excitation in nodal-line semimetallic yttrium nitride

Hyperbolic isofrequency of materials (referred to as hyperbolic materials) renders an unusual electromagnetic response and has potential applications, such as all-angle negative refraction, sub-diffraction imaging and nano-sensing. Compared with artificially structured hyperbolic metamaterials, natural hyperbolic materials have many obvious advantages. However, present natural hyperbolic materials are facing the limitations of narrow operating frequency intervals and high loss stemming from electron-hole excitations. Using first-principles calculations, we demonstrated that the recently-discovered nodal-line semimetallic yttrium nitride (YN) can be tuned to a type-I natural hyperbolic material with a broad frequency window from near-IR (∼1.4 μm) to the visible regime (∼769 nm) along with ultra-low energy loss, owning to the unique electronic band structure near the Fermi level. The unusual optical properties of YN, such as all-angle negative refraction and anisotropic light propagation were verified. The tunable hyperbolic dispersion can be interpreted in terms of the linear relation between critical frequency and plasma frequency. A branch of plasmon dispersion with strong anisotropy in the low-energy region was also revealed in the electron-doped YN. This work is expected to offer a promising strategy for exploring high-performance hyperbolic materials and regulating plasmon properties.