Enhancing the hyperbolic bandwidth in two-dimensional materials via atomic orbital engineering

The emergence of two-dimensional (2D) hyperbolic materials, characterized by opposite-sign optical conductivities along two orthogonal axes within a specific band (known as the hyperbolic region), opens an avenue for optical device engineering. Broadening the hyperbolic region is essential for cutting-edge photonic applications. In this study, based on a correlation between the hyperbolic region and anisotropic electronic structures, we propose a strategic framework for identifying 2D natural hyperbolic materials (NHMs) with broadband hyperbolicity. Using this framework, we engineered a 2D lattice incorporating p and d orbitals, and discovered a series of 2D NHMs, MYZ (M = $\mathrm{Co},\mathrm{Pd},\mathrm{Ru},\mathrm{Rh}$; Y = $\mathrm{S},\mathrm{Se},\mathrm{Te}$; and Z = $\mathrm{Cl},\mathrm{Br},\mathrm{I}$). These materials exhibit broadband hyperbolicity that extends from the near-infrared to the visible-light spectrum. We have confirmed the directional propagation of surface plasmon polaritons on these 2D materials based on Maxwell’s equations. Our findings pave the way for future exploration and practical deployment of 2D NHMs in advanced technological applications.