Robust hyperbolic plasmons in a graphene allotrope with dual anisotropic Dirac cones

Graphene has significantly influenced advanced photonics, due to its exceptional ability to confine light at atomic scales. However, the presence of isotropic Dirac cones (DCs) in graphene restricts its capability to support hyperbolic surface plasmon polaritons (SPPs) propagation without specific patterning treatments. Additionally, the plasmon frequency in graphene is highly sensitive to the Fermi level, making it unstable under external perturbations. In this study, we present a dual anisotropic Dirac cone (DADC) model that addresses these limitations. We demonstrate that this DADC exhibits highly in-plane anisotropic plasmons and extensive hyperbolic regions capable of supporting hyperbolic SPPs. By maintaining the Fermi level between the Dirac points of the two DCs, we ensure that the plasmon frequency remains independent of Fermi level. Furthermore, we identify \ensuremath{\omega}-graphene, a graphene allotrope, as a potential material for this model. Our first-principles calculations revealed that \ensuremath{\omega}-graphene exhibits significantly anisotropic plasmons, with a maximal frequency of 1.68 eV along the $x$ direction and 0.128 eV along the $y$ direction, accompanied by a low-loss hyperbolic region spanning from 0.48 to 1.16 eV. Notably, the plasmon frequency remains stable despite variations in Fermi energy within an experimentally attainable region. The highly directional propagation of SPPs in the hyperbolic regions was also confirmed using Maxwell's equations. These findings introduce a compelling candidate for SPPs devices and open exotic avenues for designing and investigating natural hyperbolic surfaces.