Extreme Optical Anisotropy in the Type-II Dirac Semimetal NiTe₂ for Applications to Nanophotonics

Compared to artificial metamaterials, where nano-fabrication complexities and finite-size inclusions can hamper the desired electromagnetic response, several natural materials like van der Waals crystals hold great promise for designing efficient nanophotonic devices in optical range. Here, we investigate unusual response of NiTe$_2$, a crystal type-II Dirac semimetal hosting Lorentz-violating fermions. By {\it ab~initio~} density functional theory modeling, show that NiTe$_2$ harbors multiple topological photonic regimes evanescent waves (such as surface plasmons) across near-infrared electron energy-loss experiments, identify plasmon resonances near transition points at epsilon-near-zero (ENZ) frequencies $\approx 0.79$, $1.64$, $2.22$ eV. Driven by extreme anisotropy presence fermions, experimental evidence ENZ confirm non-trivial electronic topology NiTe$_2$. Our study paves way realizing light manipulation deep-subwavelength scales based on physics nanophotonics, optoelectronics, imaging, biosensing applications.