Highly Directional and Carrier Density-Independent Plasmons in Quasi-One-Dimensional Electron Gas Systems

Abstract Hyperbolic materials (HMs) have garnered significant attention for their distinct electromagnetic response characteristics. Recent advancements in developing meta hyperbolic surfaces through intricate substrate patterning have enabled the realization of highly-directional hyperbolic surface plasmons, which play a crucial role in optoelectronic devices. In this study, we expand the possibility of natural two-dimensional (2D) materials in achieving exceptional electromagnetic scenarios akin to those observed in meta hyperbolic surfaces. Notably, natural hyperbolic 2D materials provide inherent advantages in terms of simplicity, predictability, and lower losses compared to meta-surfaces. By employing first-principles calculations, we unveil the possibility of achieving this mechanism in a realistic 2D material, specifically the RuOCl2 monolayer. Our results demonstrate that the RuOCl2 monolayer sustains carrier-density-independent and broadband low-loss hyperbolic responses across the terahertz to ultraviolet spectral range, owning to the highly-anisotropic electronic band structures characterized by quasi-one-dimensional electron gas (Q1DEG). These findings shed light on the integration of hyperbolicity in natural 2D materials, opening new avenues for the design and development of novel optoelectronic devices and nanoscale imaging systems.